THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA LOS ANGELES THE SCIENCE AND PRACTICE OF DENTAL SURGERY PUBLISHED BY THE JOINT COMMITTEE OF HENRY FROWDE and HODDER & STOUGHTON AT THE OXFORD PRESS WAREHOUSE, FALCON SQUARE LONDON, E.C. THE SCIENCE AND PRACTICE OF DENTAL SURGERY F.DITFl) BY NORMAN G. BENNETT M.A., M.B., B.C. (Cantab.), L.D.S. (Eng.) ,.>,, ynv T,. sr (KORCE'S HOSPH \1. AND IHH KnV.M, DENTAL HOSPITAL. LONDON ; MEMBER OK THE """• "i'^rr^AM^^^N DENIAL SVR.ERV. ROVAL COLLECT OE S.R.EO.S OE EN.LANO WITH AN APPENDIX ON DENT./^L JURISPRUDENCE P. B. HENDERSON, B.A. (Oxon.) >i„lidtor of Ibr Siipifrnt Court iriTH MNE HiWDKED AND MSETY-THREE lEllSTRATinSS NEW YORK WILLIAM WOOD AND COMPANY M D C C C 1" X 1 \' g^wMMj wu PKEFACE ^ In sul)mitting this work to my colleagues in the Dental Profession, I feel that a few intro- ductory remarks may not be out of place. Dental Surgery has advanced so rapidly within recent years, both in the many branches of science on which it is based and in the intricacies of manipu- lative procedure, that the production of a new comprehensive work by a single WTiter has become almost an impossibility. Certain defects are usually associated with, if not necessarily inherent in, a work by many writers, and one object that I have had in mind, from the commencement of the long period during which the work has been as continuously in hand as the demands of other duties permitted, has been to eliminate these defects as far as jiossible. I have endeavoured to impart unity of conception and style to the whole, and to prevent overlappino- except where it seemed permissible that a particular subject .should be presented from different points of view- Cross-references have been liberally inserted. Another object that I have had in view has been to combine the scientific with the practical, for neither is of much value to the practitioner without the other, and in a work of this kind it is desirable that their nnitual interdependence should be brought prominently before the reader. The work does not represent any particular school of thought ; the contributors belong not only to the United Kingdom but to the most distant parts of the Dominions beyond the Seas, and an effort has been made to include everytliinw in pathology or practice, from whatever country or source, that might be of value to the modern practitioner. Obsolete theories in pathology or abandoned metliods of treatment have been omitted, or only briefly referred to where their historical interest is great. In all these objects I have been well supported by my contriljutors, and I wish to take this opportunity of thanking them most sincerely for the careful way in which they have considered the principles laid down, and written their chapters in conformity with the scheme that I outlined- and also for allowing me so much freedom in making such alterations as I thought necessary in the interest of uniformity. I venture to think that they have produced excellent woik, and managed to combine "eneral knowledge derived from the work of others with the subtle touch of individual experience without which discussion on problems of aetiology and descriptions of manipulative procedure have little value. The Appendix on Dental Jurisprudence will perhaps afford my colleagues useful information on matters of importance in their relations with the State, the public, and their fellows. It is hoped that the bracketed numbers in the text referring to the Biljliographies at the ends of the chapters will be useful to those desiring fuller information on any particular aspects of a subject than is po.ssible in the available space of a text-book. The illustrations must be allowed to speak for themselves, but I may say that they have been inserted solely with a view to the elucida- tion of the text, or as a better alternative to more lengthy descriptive writing, and not for mere decorative effect. The chapters on Abnormalities of Position have been written by Mr. Harold Chapman and myself, and although we are each responsible for our own f)arts — he for tlie practical details of treatment, and I for the jiroljlems of aetiology and classification and the broad principles of treatment — nevertheless the two parts have been wTitten in close collaboration, even to the extent of transferring portions of text already wTitten from one part to the other when it seemed desirable. In the part dealing with the Mechanics of Tooth Movement I have approached the subject from the purely scientific side, instead of dealing with it merely from an empirical standpoint. The movements of teeth due to the application of forces are subject to the same creneral laws as govern the movements of other bodies, and a consideration of mechanical problems is necessary for a proper understanding of them. My own knowledge of mathematics would have been insufticient to ensure lucidity or correctness, but I have had the great advantage of the assistance of mv brother Mr. G. T. Bennett, M.A., F.R.S., Fellow and Mathematical Lecturer of Emmanuel College' Cambridge. We have endeavoured to write this part in such a way as not to assume more than an elementary knowledge of mechanics on the part of the reader, and we hope that it will be found intelligible. It is perhaps unfortunate that the subject is necessarily a mathematical one, if treated vi PREFACE iu a scientific manner; and although this point of view may seem somewhat remote from the practical details of application, I wish to emphasize the fact that the successful adoption of the latter is more dependent on theoretical knowledge than is generally believed to be the case. I may at least state with confidence that the truth of the laws enunciated is indisputable. The matter of terminology has been a source of some difficulty. Many dental \\ ords in common use are incorrect etymologically or in their strict meaning, and it is much to be desired that an authoritative Committee on Dental Nomenclature should consider the whole subject. Until this has been done it seems unmse to make many changes. However, such accepted alterations in anatomical nomenclature as occur in comiection with dental science have been adopted, and certain terms employed in the chapters on Orthodontics need explanation. Among the former the more important are the following : — Ectoderm . . . instead of Epiblast. Mesoderm . . . ,, Mesoblast. Entoderm . . . ,, Hypoblast Spinal Medulla . . ,, Spinal Cord. Stomatodaeum . . ,, Stomodaeum Mandible . . . . ,, Inferior Maxilla Mandibular Fossa . . ,, Glenoid Fossa Lymph Vessel . . . ,, Lymphatic Lymph Gland . . . ,, Lymphatic Gland Inferior Alveolar Canal . ,, Inferior Dental Canal Inferior Alveolar Nerve . ,, Inferior Dental Nerve Mandibular Foramen . ,, Mental Foramen Inter -articular Meniscus ,, Inter-articular Cartilage Maxillary Sinus . . ,, Antrum Mandibular Articulation ,, Temporo-mandibular Articulation Medial .... ,, Mesial Auditory Tube . . ,, Eustachian Tube Some of these are in current use. The one that occurs most frequently is '' medial " for " mesial ". " Mesial " and " proximal " are used in different senses in contradistinction from " distal ". '■ Proximal " and " distal " are words of Latin origin, whereas " mesial " is Greek, and it is obvious that the Latin form " medial " is the more correct. We still have the other Latin form " median ", meaning at the centre, as distinguished from " medial ", toimrds the centre. To indicate the surfaces of teeth normally in contact, the word " approximal " has been generally used and the words " interstitial " and " proximal " avoided. The objections to the former are oljvious, and the use of the latter invites confusion with the meaning of the word when used in contradistinction from '' distal ". It has seemed necessary to modify some of the terms used in Orthodontics or the meanings of them, and in some cases to coin new ones. " Protrusion " and " retrusion " are used with their usual significance to indicate a forward or backward position of the teeth, especially the anterior teeth. But it is now well understood that such forward or backward position may involve the whole tooth, or only the crown ; in other words tlie tootli may be completely out of place or only tilted. For the latter I have used the terms " proclinatio7i " and " retrochnation ", suggested by Dr. Sim Wallace, on the analogy of inclination, and for the former I have ventured to coin the terms " pre- placement " and " postplacement " on the analogy of " displacement ". For forward and backward positions of the jaws themselves the anthropological terms " prognathism " and " retrognathism " are used. It may be undesirable to use these with a pathological or semi-pathological significance, but it is convenient in distinguishing between malpo.sition of the teeth alone and abnormalities involving the bones themselves. "Imbrication" is used to indicate overlapping, especially of the lower incisors, due to insufficient space. My use of the term " occlusion " and its congeners I have endeavoured to explain and justify in the text itself. The words '" open bite " and " close bite " have been deliberately retained. Tliey may be colloquial, but they are not on that account the less scientific or clear in their meaning, and I do not consider that any of the terms that have been proposed as substitutes have any advantage over them on either of those grounds. " Pre-normal occlusion " and " post-normal occlusion " are used with their generally accepted meaning, which is perfectly clear. I regret, however, that they have the defect of being not merely descriptive terms but of connoting a diagnostic conclusion. It is always necessary in using them to say which jaw is referred to. For example, the condition in which the medial two-thirds of the first lower molar occludes with the upper, instead of the distal two-thirds of the lower occluding with PREFACE vii the upper, as normally, is perfectly well kno\\7i. This condition obviously may be due to mal- position of either tooth, i.e. it may be post-normal lower or pre-normal upper. It is much to be desired that a term should be invented to indicate simply the relationship, without further diagnostic conclusion. The word "bow" has been used throughout instead of wire "arch". The latter term is obviously likely to lead to confusion with " dental arch ", and moreover is incorrect, because the appliance is not used to support anji:hing. The term " bow " simply indicates a curved piece of wire adapted to the " dental arch ". " Ligature "has been used generally for all forms of attachment — whether wire, silk, or otherwise — of the teeth to the bow. In a work of this kind many minds are employed, and I have pleasure in expressing my indebted- ness to many kind helpers besides my contributors. Mr. F. G. H. Armin rendered valuable assist- ance in the early stages by bibUographical researches, which assisted the contributors in their wTiting and formed the basis of the Bibliographies at the ends of the chapters. Mr. E. L. Fickhng is respon- sible for the Contents pages and Index, and has given me great help by his careful reading of the proof-sheets. Mr. J. F. Gow has kindly performed a similar oflSce with many of the final proofs. The illustrations in the chapter on Abnormalities of Size, Form, and Structure are from drawings by Mr. W. H. Dye, formerly House Surgeon at the Royal Dental Hospital. I am obliged to Dr. Harold Austen for looking over the various prescriptions occurring tliroughout the book to ensure correctness and uniformity of style. Li connection with my chapters on Orthodontics I have pleasure in recording the assistance given me by friends whose names appear under the figures of models, etc., that they have kindly lent, particularly Mr. J. H. Badcock, Mr. Harold Chapman, Mi-. George Northcroft, and Mr. J. E. Spiller. The figures under which my name appears are from photographs taken by Mr. George Payne of patients under my care, or of material prepared by myself, and I am indebted to successive House Surgeons in the Children's Department of the Royal Dental Hospital for their help in this matter, namely, Mr. G. T. Yonge, Mr. H. D. Stephens, Mr. T. C. Kidner.Mr. A. Lawrey, and Mr. A. L. Packham. I wish to express my thanks to the Royal Society of Medicine, Sir W. Ai-buthnot Lane, Dr. E. H. Angle, Dr. C. S. Case ; the Editorial Committee and Editors of the British Dental Jourrial ; Mr. Ai'thur Underwood, the Editor, and Messrs. Segg & Co., the publishers, of the British Journal of Dental Science; Dr. G. V. Black and the Medico-Dental Pubhshing Co., Chicago, the pubhshers of his work on Operative Dentistry : Messrs. Appleton & Co. , of New York, the publishers of Kingsley 's Oral Deformities ;• and to Messrs. Rauhe, for permission to reproduce illustrations. To Mr. W. Rushton, the Editor of the Dental Record, and to the Dental Manufacturing Company, I am obliged for the free use of blocks from that journal and from the Company's catalogue. To Messrs. Claudius Ash, Sons & Co., I am likewise indebted for blocks from Aslts Quarterly (now AsVs Monthly) and from their Catalogue. To Messrs. John Wright & Sons, Ltd., of Bri.stol, I am indebted for the loan of a block from an article of my own in Pye's Surgical Handicraft ; to Messrs. Plucknett, Mayer & Meltzer, and W. Watson & Sons, for the use of blocks or electros from their catalogues ; and to Mr. Frederick Rose for an electro. I wish to express my thanks to Dr. E. C. Kirk for his cordial co-operation in obtaining for me electros from the Dental Cosmos, and the Text-hook of Operative Dentistry, and in getting permission for me to use them from the various writers whose names appear under these figures ; to the S. S. \\'hite Dental Manufacturing Company for the supply of these electros and others from their Cata- logue ; and to Mr. Henry Kimpton, the English publisher of the Text-hook of Operative Dentistry, for permission to reproduce. My thanks are due to Dr. Ottolengui, the Editor of Items of Interest, and to the Consolidated Dental Manufacturing Company, the publishers, for the supply of electros from this journal, and to the wTiters whose names appear beneath the figures for permission to use them ; and also to Messrs. Adlard & Co., Bale, Sons & Danielsson, J. & A. Churchill & Co., and H. K. Lewis, for the supply of electros. I am greatly obliged to Prof. Arthur Keith, Curator of the Museum of the Royal College of Surgeons of England, for allowing me to reproduce illustrations from his works, and especially for permission to photograph specimens in the Museum. Mr. Garrett and Mr. Cray, the librarians of Messrs. Ash's Library, and Mr. Yarrow of the Dental Manufacturing Company have given me every possible assistance in the verification of references and other matters. The artists employed on the work, Mr. Sydney A. Sewell and Miss Ethel Wright, have been successful in carrying out the wishes of myself and my contributors, and Mr. Frank Butterworth has rendered valuable assistance in photograpliing specimens and preparing photographs for reproduction. viii PREFACE To tlie publishers, Messrs. Fro%\de and Hodder & Stoughton, and to their Medical Editor, Mr. J. Keogli Murphy, I am greatly indebted for much sympathetic treatment, and especially for the consideration they gave to my opinions on various questions as the work progressed. Certain details of orthography, syntax, and punctuation to be found in this book are perhaps somewliat unusual : my authorities are cliiefly The Concise Oxford Dictionary , The Kind's English, and Rules for Compositors and Readers at the University Press, Oxford, by Horace Hart ; and my thanks are due to Messrs. Richard Clay & Sons, the printers, for carefully carrying out my instructions. Last, but by no means least, I wsli to say that the pubUcation of this work \\ould scarcely have been possible without the wilhng help of my secretary. Miss E. Messer. In addition to much other onerous work, she has been largely responsible for the correctness of the Bibliographies and references in the text, lias proved a most careful and efficient proof-reader, and has in every way and at all times done all that was possible to reheve my work as Editor and Contributor. NoKMAN G. Bennett. London, IF. March 1914. TABLE OF CONTENTS CHAPTER I Development of the Jaws and Teeth before Birth Development of the Visceral Arches Development of the Teeth .... Ossification and Growth of tlie Jaws Development of the Jaws .\nd Teeth after Birth First Dentition. — Eruption of the Teetli Theories .... Dates .... Diseases associated Development of the Jaws and Teetli Absorption of the Teeth Second Dentition. — Eruption of the Teeth Development of the Jaws and Teeth CHAPTER II Affections assocl\ted w- ith the Third Mandibular Molar Anatomical Relations ...... The State of Eruption of tlie Tootli Mode and Sjinptoms of Infection .... Treatment ....... PAGE 1 1 U 12 15 15 15 18 19 23 27 . 28 29 33 33 34 34 37 CHAPTER III Abnormalities of Size, Number, Form, and Structure Abnormalities of the Permanent Teeth Size Number Absence Excess . Form . Maxillary Teeth Mandibular Teeth Abnormalities of the Deciduous Teeth Size .... Number Form Gemination Abnormalities of Structure . Hypoplasia of Malnutrition Hypoplasia of Local Origin Hypoplasia, Congenital 38 38 38 38 39 40 40 41 42 43 43 43 45 45 46 47 48 49 CHAPTER IV ABNORM-ALrriES OF POSITION OF THE TEETH AND ABNORMAL DEVELOPMENT OF THE ASSOCIATED PaRTS Occlusion (Jrowth of the .Jaws Aetiological FacU)rs Heredity Environment Pathological Influences 52 52 55 68 68 75 75 X CONTENTS CHAPTER V PAQE Abnobmautdes of Position (continued) ............ 82 Classification ...............82 Consideration of Different Types ............ 84 Causation. Principles of Treatment. Deciduous Dentition Abnormalities . . . . . . . . ■ . .135 CHAPTER VI ABNORMAiiTiES OF POSITION (continued) ............ 143 Diagnosis ..........•..••• 143 General Objects of Treatment ............ 145 Estimation of Arch ..........■■•■ 145 Extraction and Mechanical Treatment ........... 147 Complications caused by Caries . . . . . • • • • • • .148 Age for Mechanical Treatment ............ 149 Principles of Retention . . . . . . • • • • • .150 Mechanics and Physiology of Tooth Movement . . . . ■ • ■ • .150 Anchorage .,..,......••■■ 154 Reciprocal Action .............. 156 Preliminaries of Treatment ............. 159 Care of the Mouth and Appliances . . . . . . . • . . ■ .160 Surgical Treatment .............. 161 CHAPTER VII Abnobmauties OF Position — Treatment . 167 Treatment by Means of Appliances . . . . . . . . . • .167 Tooth Movement ...,......,,.. 181 Major Tooth Movements ............ 183 CHAPTER VIII Abnormaiities of Position — Treatment (continued) ......... 204 Individual Tooth Movements ............ 204 Treatment by Appliances. CHAPTER Abnormalities of Position — Treatment (continued) The Head-gear and Traction Bar . The Movement of the Roots of Teeth Force as Regards the Movement of Teeth Technique of Orthodontics The Construction of Appliances IX 216 216 217 221 222 225 CHAPTER Abnobmauties of Position — Treatment (continued) Retention ....... The Treatment of Particular Cases 227 227 239 CHAPTER XI Saliva and CALCtTLus ............... 247 Constitution of the Saliva in Health and Disease ......... 248 Chemiotaxis ............... 249 Calculus or Tartar .............. 250 Calculus in Salivary Ducts and Glands ........... 253 Discolorations of Teeth due to External Deposit ......... 254 CONTENTS CHAPTER XII Thk Bacteria of the JIouth Cocci BacUli Spirilla Streptothricao Blastomyces Leptothricae XI PAGE 256 269 266 273 277 278 280 CHAPTER XIII The Aetiology of Dental Caries .........•■•• 282 Chemistry ..........•••-•■ 282 Diet 285 Civilization ........■••■•••■ 287 Race ........■■■•■■■■ 288 The Chemical Constitution of the Teeth .......•■■ 289 The Influence of the Saliva 291 Susceptibility and Immunity ........•■■• 292 Relative Liability of Diiferent Teeth to Caries .......•■• 293 CHAPTER XIV The Pathology of Dental Caries ............ 295 Microscopical Phenomena .........••• 296 Micro-organisms ........•••■•■■ 299 "Arrested" Caries ...........•■• 302 Caries in Unusual Situations ............ 303 CHAPTER XV The Pathology of Erosion, Attrition, and Abrasion 304 CHAPTER XVI Diseases of the Dental Pulp .............. 306 Aetiology ................ 306 Hyperaemia . . . . . . . . . . • • .312 Inflammation ...........••■• 313 Retrogressive Changes in the Pulp . . . • • • • • • • • .316 The Degenerations ,..........•• 317 Calcification or Calcareous Infiltration .......... 318 Necrosis and Putrefaction ............ 320 CHAPTER XVII The Dental Operating Room . Its Appointments and Hygiene 322 322 CHAPTER XVIII Oral Hygiene and Prev'entive Treatment of Dental Caries Natural Means of Cleansing ..... Artificial Moans of Cleansing ..... Periodical Cleansing ...... Treatment ........ 328 329 330 333 334 Xll CONTENTS CHAPTER XIX Treatment of Cavities in the Teeth by Filung Examination of the Mouth and Teeth Exclusion of SaKva .... Separation ...... General Principles of Cavity Preparation . Sensitive Dentine and the Avoidance of Pain Objects and Intentions of Tooth Restoration Filling Materials Gold Tin Amalgams Cements Inlays . Gutta-percha The Appropriate Filling in Cavities of Various Degrees in Different Teeth at Different Ages PAGE 336 336 337 343 344 346 348 356 356 357 357 359 360 360 361 CHAPTER XX Antiseptic Technique in Dental Surgery Dressings and Temporary Fillings . 363 368 CHAPTER XXI The Manipulation of Gold 370 CHAPTER XXII Filling with Foil ...... Suitable Cavities ..... Unsuitable Cavities .... Special Requirements in the Form of Cavities Hints on working Gold 374 374 375 375 380 CHAPTER XXIII Plastic Fillings . . . Dental Amalgams Osteo-plastic Cements Gutta-percha Compoimds 386 386 397 401 CHAPTER XXIV PoRCEL.iiN Inlays Cavity Preparation Making of Inlays . Making of a Fused Inlay Retention Fixing of the Inlay 404 405 408 414 419 420 CHAPTER XXV Gold Inlays ........... 422 Suitable Cavities ........ 424 Obtaining the Wax Model ....... 430 Methods of Casting under Pressui'e ...... 432 Retention .......... 433 Insertion and Cementation ....... 433 CONTENTS CHAPTER XXVI DiAONOSIS OF THE CaUSE OF PaIN Odontalgia and Neuralgia Aids to Diagnosis Head's Areas XIU PAGE 435 436 443 444 CHAPTER XXVII Treatment of the Dental Pulp ......... Management wlien almost exposed ....... Devitalization ........... Conditions requiring Devitalization of the Dental Pulp .... Removal of Pulps .......... Management of Root-canals of Teeth having Dead Pulps .... Devitalization and Management of Pulp and Root-canals of Deciduous Teetli Filling Root-canals . ......... Selection of Materials ......... 451 451 454 461 465 471 474 474 478 CHAPTER XXVIII The Treatment of Children and Chtldren's Teeth Prevention of Dental Disease . Treatment ...... 483 483 484 CHAPTER XXIX Diseases of the Periodontal Membrane Anatomy Acute Local Periodontitis Chronic Local Periodontitis Productive Periodontitis Anchylosis Rarefying Periodontitis Necrosis of Teeth General Periodontitis 487 487 488 491 492 495 497 499 500 CHAPTER XXX Diseases of the Periodontal Membrane (continued) Chronic Suppurative Periodontitis . 502 502 CHAPTER XXXI Dental Electro-therapeutics Apparatus Cataphoresis Ionic Medication . Treatment 514 514 519 519 520 CHAPTER XXXII Injuries of the Teeth due to Violence Concussion . . . . . Dislocation . . . . . Fracture . . . . . 524 524 524 526 XIV CONTENTS CHAPTER XXXIII PAGE The Mechanical Stresses of Mastication ........... 529 In Normal Arches and under Normal Conditions ......... 529 Under Abnormal Conditions ............. 531 In Relation to Bridge-work ............. 534 CHAPTERS XXXIV to XXXVI Artificial Crowns ...... General Considerations .... Roots suitable for Crowns Principles of Crowning .... Various Types of Crowns considered in Detail Replacing Porcelain Facings . Partial Crowns ..... Fixing Crowns ..... 537 537 539 540 559 590 596 597 CHAPTERS XXXVII to XXXIX Bbidqe-work ....... Selection of Cases and General Considerations Impressions ....... Description of Making a Fixed Bridge Descrip'^ion of Making a Removable Bridge Abutments for Removable Bridges Saddle Bridges Pressure- Casting . Cementing of Bridges Repairing Bridges Porcelain Bridges . Cast Sectional Bridges 602 602 606 608 617 620 623 625 626 626 628 631 CHAPTER XL Extraction of Teeth ........ 640 General Principles ....... 641 The Operation ........ 642 Difficulties ......... 655 Accidents ......... 657 Sequels ......... 658 CHAPTER XLI Local Anaesthesia 664 CHAPTER XLII Alveolar Abscess ...... Course and Pathology .... Clinical Course and Signs of Acute Abscess Clinical Course and Signs of Chronic Abscess Rarer Forms of Chronic Abscess Treatment ...... Sequelae ...... 671 671 672 673 674 674 676 CONTENTS CHAPTER XLIII XV PAQB Empyema of the Maxillary Sinus ....... 678 Dental Causes 678 Traumatic Causes . 679 Acute Inflammation 680 Clironic Empyema . 682 CHAPTER XLIV Necrosis of the Jaw ............... 687 Causes ................ 687 Treatment 689 CHAPTER XLV Fractures of the Jaws Mandible Causes Signs and Symptoms Displacement Complications Treatment Maxilla Dislocation of the Mandible 690 690 690 691 691 692 692 698 699 CHAPTER XLVI Oral Sepsis ................. 701 Diseases associated with Chronic Septic Processes in the Mouth ....... 702 CHAPTER XLVII Dental Radiography ............... 712 Film Radiograplis in the Mouth . . . . . . . . .'. . .713 Stereoscopes . . . . . . . . . . . . . . .714 Diagnosis by means of X-rays . . . . . . . . . . . .716 CHAPTER XLVIII Reflex Affections Due to Diseased Teeth ........... 727 CHAPTER XLIX Diseases of the Mucous Membrane of the Mouth — Immobility of the Mandible 736 CHAPTER L Odontomes ................. 740 Classification ............... 741 Diagnosis ................ 762 CHAPTER LI Actinomycosis or Streptothricosis ...........'.. 767 Course, Pathology, and Symptoms ........... 767 Treatment ................ 770 APPENDIX Dental Jurisprudence .... The Dentist and the State The Dentist and the Lay Public . The Dentist and his Fellow Practitioners Index ........ 771 771 777 782 787 CONTEIBUTORS A. W. W. BAKER, A.B., M.D., M.Ch. Dub., F.R.C.S.I., L.D.S.I., M.Dent. Sc. Dub. (hon. causa) ; Consulting Dentist, Royal Victoria Eye and Ear Hospital; Dentist, Incorporated Dental Hospital, Ireland ; University Examiner in Dental Surgery, Trinity College, Dublin ; late Examiner in Dental Surgery, R. C.S.I. Diagnosis of the Cause of Pain Chapter XXVI, pp. 435-50 H. BALDWIN, M.R.C.S., L.D.S. Eng. ; late Assistant Dental Surgeon, Royal Dental Hospital, London. Artificial Crowns Chapters XXXIV— XXXVI, pp. 537-601 NORMAN G. BENNETT, M.A., M.B., B.C. Cantab., L.D.S. Eng. ; Dental Surgeon, St. George's Hospital and Royal Dental Hospital, London ; Member of the Board of Examiners in Dental Surgery, R.C.S. Eng. ; late External Examiner in Dentistry, University of Birmingham. Abnormalities of Position of the Teeth, and Abnormal Development of the Associated Parts Chapters IV— VI, pp. 52-166 Fractures and Dislocation of the Jaws Chapter XLV, pp. 690-700 G. G. CAMPION, L.D.S. Eng. ; Dental Surgeon, Dental Hospital of Manchester; Lecturer on Orthoilontics, ^'l(•toria L^niversitv of Manchester. The Mechanical Stresses of Mastication, jointly with C. H. PRESTON {see below) Chapter XXXIII, pp. 529-36 HAROLD CHAPMAN, L.D.S. Eng., D.D.S. Penn. ; Dental Surgeon, London Hospital, and Lecturer on Udunto-prosupic Orthopaedics, London Hospital Dental School. Treatment of Abnormalities of Position of the Teeth . . . Chapters VII — X, pp. 167-246 C. A. CLARK, L.D.S.I. ; Radiographer, Royal Dental Hospital, and National Dental Hospital, London. Dental Radiography Chapter XL VI, pp. 712-26 FRANK COLEMAN, L.R.C.P. Lond., M.R.C.S., L.D.S. Eng. ; Assistant Dental Surgeon, St. l)arthol(jnie\v's llos])ital and Royal Dental Hospital, London. The Development of the Jaws and Teeth ....... Chapter I, pp. 1 — 32 STANLEY COLYER, M.D., M.R.C.P. Lond. Oral Sepsis Chapter XL VI, pp. 701-11 E. B. DOWSETT, L.R.C.P. Lond., M.R.C.S., L.D.S. Eng. ; Assistant Dental Surgeon, Guy's lliis|iitai. and Demonstrator of Dental Histology, Guy's Hospital Dental School. Oral Hygiene and Preventive Treatment of Dental Caries . . . Chapter XVIII, pp. 328-35 DOUGLAS P. GABELL, L.R.C.P. Lond., M.R.C.S., L.D.S. Eng. ; Dental Sui'geon and Lecturer on Dnital .Mechanics, Royal Dental Hospital, London: late External Examiner in Dentistry, Victoria University of Manchester, Abnormalities of Size, Number, Form, and Structure of the Teeth, jointly with A. LANDON WHITEHOUSE {see ielow) Chapter III, pp. 38-51 xviii CONTRIBUTORS KENNETH W. GOADBY, L.R.C.P. Lond., M.R.C.S., L.D.S. Eng., D.P.H. Cantab. ; Pathologist and Lecturer on Bacteriology, National Dental Hospital ; Dental Surgeon, Seamen's Hospital Society, and Lecturer on Oral Hygiene, London School of Tropical Medicine; John Tomes Prizeman, Erasmus Wilson Lecturer, and Hunterian Professor, R.C.S. Eng. The Bacteria of the Mouth Chapter XII, pp. 256-81 W. C. GOWAN, D.D.S. Chicago, L.D.S. Ontario. Filling with Foil Chapter XXII, pp. 374-85 Gold Inlays Chapter XXV, pp. 422-34 WILLIAM GUY, L.R.C.P., F.R.C.S., L.D.S. Edin., F.R.S.E. ; Consulting Dental Surgeon, Royal Infirmary, Edinburgh ; Dean, and Lecturer on Dental Anatomy and Physiology and Dental Histology, Edinburgh Dental Hospital ; Examiner in Dentistry, R.C.S. Edin. Extraction of Teeth Chapter XL, pp. 640-63 P. B. HENDERSON, B.A. Oxon ; Solicitor of the Supreme Court. Dental Jurisprudence Appendix, pp. 771-86 W. ARCHER HODGSON, L.D.S. Eng. ; Demonstrator of Practical Dentistry, Guy's Ho.spital Dental School. Diseases of the Periodontal Membrane (Chronic Suppurative Periodontitis) Chapter XXX, pp. 502-13 A. HOPEWELL-SMITH, L.R.C.P. Lend., M.R.C.S., L.D.S. Eng. ; Dental Surgeon and Lecturer on Dental Anatomy and Physiology, Royal Dental Hospital, London ; John Tomes Prize- man, R.C.S. Eng. ; External Examiner in Dentistry, Universities of Leeds and Liverpool ; late External Examiner in Dentistry, University of Birmingham. The Pathology of Dental Caries Chapter XIV, pp. 295-303 The Pathology of Erosion, Abrasion and Attrition .... Chapter XV, pp. 304-5 Diseases of the Dental Pulp Chapter XVI, pp. 306-21 MONTAGU F. HOPSON, L.D.S. Eng. ; Dental Surgeon, Guy's Hospital, and Lecturer on Dental Anatomy and Physiology, Guy's Hospital Dental Scliool ; Member of the Board of Ex- aminers in Dental Surgery, R.C.S. Eng. ; External Examiner in Dentistry, University of Birmingham. Plastic Fillings Chapter XXIII, pp. 386^03 Injuries of the Teeth due to Violence ...... Chapter XXXII, pp. 524-8 EDWIN HOUGHTON, L.D.S.I. Cast Sectional Bridge-work Chapter XXXIX, pp. 631-9 W. WARWICK JAMES, L.R.C.P. Lond., F.R.C.S., L.D.S. Eng. ; Assistant Dental Surgeon, Middle- sex Hospital ; Assistant Dental Surgeon and Lecturer on Operative Dental Surgery, Royal Dental Hospital, London. Serious Affections Associated with the Third Mandibular Molar . . . Chapter II, pp. 33-7 Odontomes Chapter L, pp. 740-66 Actinomycosis Chapter LI, pp. 767-70 GEORGE NORTHCROFT, L.D.S. Eng., D.D.S. Mich. ; Dental Surgeon, London Hospital, and Lecturer uu Ojn.Tative Dental Surgery, London Hospital Dental School. The Treatment of Children and Children's Teeth .... Chapter XXVIII, pp. 483-6 CONTRIBUTORS xix J. B. PARFITT, L.R.C.P. Lond., M.R.C.S., L.D.S. Eng. ; Dental Surgeon, Guy's Hospital, and Lecturer on Operative Dental Surgery, Guy's Hospital Dental School. The Denial Operating Room, Its Appointments and Hygiene . Chapter XVII, pp. 322-7 The Manipulation of Gold Chapter XXI, pp. 370-3 Porcelain Inlays Chapter XXIV, pp. 404-21 J. LEWIN PAYNE, L.R.C.P. Lend., IM.R.C.S., L.D.S. Eng. ; Assistant Dental Surgeon, Guy's Hospital, and Lecturer on Dental Mechanics, Guy's Hospital Dental School. Diseases of the Periodontal Membrane Chapter XXIX, pp. 487-501 FRANK J. PEARCE, L.D.S. Eng.. D.D.S. Penn. ; Assistant Dental Surgeon, Guy's Hospital, and Demonstrator of Practical Dental Metallurgy, Guy's Hospital Dental School. Local Anaesthesia .......... Chapter XLI, pp. 664-70 H. PERCY PICKERILL, M.D., B.Ch., M.D.S. Birm., L.D.S. Eng. ; Professor of Dentistry and Director of Dental School, University of Otago ; Hon. Stomatologist, Dunedin Hospital ; Cartwright Prizeman, R.C.S. Eng. ; Examiner in Dental Surgery, LTniversity of New Zealand. Antiseptic Technique in Dental Surgery — Dressings and Temporary Fillings Chapter XX, pp. 363-9 Reflex Affections due to Diseased Teeth Chapter XLVIII, pp. 727-35 G. PATON POLLITT, L.D.S. Eng., D.D.S. Penn. ; Dental Surgeon, London Hospital, and Lecturer on Operative Dental Prosthesis, London Hospital Dental School. Bridge-work Chapters XXXVII and XXXVIII, pp. 602^0 C. H. PRESTON, M.D., B.S. Lond., B.Sc. Vict., L.R.C.P. Lond., F.R.C.S., L.D.S. Eng. ; Surgeon aud Tutor, Victoria Dental Hospital, Manchester; Lecturer on Dental Anatomy, Victoria University of Manchester. Saliva and Calculus Chapter XI, pp. 247-55 The Mechanical Stresses of Mastication, jointly with G. G. CAMPION (see above) Chapter XXXIII, pp. 529-36 W. G. T. STORY, M.B., B.A.O., B.Ch., D.P.H. Dub., L.D.S.I. ; Dental Surgeon, Dental Hospital of Ireland; Examiner in Dental Surgery, R.C.S. I. Treatment of Cavities in the Teeth by Filling Chapter XIX, pp. 348-62 ERNEST STURRIDGE, L.D.S. Eng., D.D.S. N.Y. Dental Electro-Therapeutics Chapter XXXI, pp. 514-23 HERBERT TILLEY, M.D., B.S. Lond., F.R.C.S. Eng. ; Surgeon, Ear and Throat Department, University College Hospital; Lecturer on the Diseases of the Ear, Nose, and Throat, Royal Army iledical College ; Larjiigologist, Radium Institute. Empyema of the Maxillary Sinus Chapter XLIII, pp. 678-86 J. G. TURNER, L.R.C.P. Lond., F.R.C.S., L.D.S. Eng. ; Dental Surgeon and Lecturer on Dental Surgery, Royal Dental Hospital, London. Alveolar Abscess Chapter XLII, pp. 671-7 Necrosis of the Jaws Chapter XLIV, pp. 687-9 Diseases of the Mucous Membrane of the Mouth — Immobility of the Mandible Chapter XLIX, pp. 736-9 J. SIM WALLACE, M.D., CM., D.Sc, Glas., L.D.S. Eng. ; Dental Surgeon, West End Hospital for Nervous Diseases. The Aetiology of Dental Caries Chapter XIII, pp. 282-94 XX CONTRIBUTORS A. E. WEBSTER, M.D., D.D.S. Chicago, L.D.S. Ontario; Professor of Operative Dentistry in the School of the Royal College of Dental Surgeons of Ontario. Treatment of the Dental Pulp Chapter XXVII, pp. 451-82 A. LANDON WHITEHOUSE, L.R.C.P. Lond., M.R.C.S., L.D.S. Eng. ; Dental Surgeon, Royal Waterloo Hospital for Women and Children ; Assistant Dental Surgeon, Royal Dental Hospital, London. Abnormalities of Size, Number, Form and Structure of the Teeth, jointly with DOUGLAS P. GABELL {see above) Chapter III, pji. 38-51 J. A. WOODS, M.D.S. Liver., L.D.S. Eng. ; Hon. Dental Surgeon, Dental Hospital, Liverpool ; Lecturer on Dental Anatomy and Physiology and Demonstrator of Dental Histology, and Internal Examiner, University of Liverpool; External Examiner in Dentistry, Victoria University of Manchester. Treatment of Cavities in the Teeth by Filling Chapter XIX, pp. 336-48 CHAPTER I THE DEVELOPMENT OF THE JAWS AND TEETH A. DEVELOPMENT OF THE JAWS AND TEETH BEFORE BIRTH 1. Development of the Visceral Arches. — The period of human crestatioii has been arbitrarily divided into three stages — (1) Tlie pre-embryo- nic, or stage of the zygote, comprising the fii'st two weeks of develop- ment. (2) The stage of tlie embryo, ex- tending from the end of tlie second week to the end of tlie second month, during Mhicli During the third period, or stage of the foetus, the earliest indications of tooth formation appear ; while during the second period the earliest indications of a mouth can be detected, together with the subsequent changes that lead to the formation of the jaws. The first Fig. -Showing segmentation of the fertiUzed oviun or zygote in the rabbit (from Cunningham). time the zygote ^' Division into two segments; B, Division into four segments; C, Division into •'S . severalsegments (morula) ; P, Polar bodies (minute portions of the egg substance, begins to assume definite human characteristics V VM- Nll Fig. 1. — Tlie ovimi with its coverings partly shown (from Cunningham). (Diagrammatic.) C, Corona radiata ; G, Granular layer ; Z, Oolemma (Zona pellucida); VJI, Vitelline membrane; V, Vitellus or yolk ; NM, Nuclear membrane ; GV Nucleus (Germinal vesicle) ; GS, Nucleolus (Germinal spot). (3) The stage of the foetus, which includes the remainder of the term of intra-uterine existence. 1 containing nucleus and yolk, budded off from the zygote). period, or stage of the zygote, is not directly concerned in tooth or jaw formation, but only in the preparation for such, by a laying down of the '■ ground-work "' and differentiation of the ceUs into ectodermic, mesodermic, and entodermic, from which are evolved the axial and ajipendicular skeleton with the contained viscera. The development of the teeth camiot be rendered intelligible unless it is preceded by an outline of the development of the jaws as a whole. The earliest indication of a mouth can be detected at the twelfth day of intra- uterine life ; before this the zygote has passed through the stage of the ovum (see Fig. 1) with its fertilization and segmentation followed by its morula and vesicular forms (see Figs. 2, 3), the development of the embryonic area (see Pig. 4), and the commencement of differentiation of its cells into ectoderm, mesoderm, and entoderm (see Figs. 5, 6, 7). The primitive mouth or stomatodaeuni, as it is then termed, consists of superimposed layers of ectoderm and entoderm (oral plate), situated in a depression (oral pit) bounded by two prominences. The prominence in front of the oral plate is produced by an enlarge- ment of the cephalic or head end of the neural tube to form the cerebral vesicles, and the prominence behind the oral plate arises from the development of the visceral arches (see Fig. 8). The oral pit, stomatodaeum, or future mouth, becomes deejDened by the growth of these prominences and by the downward folding of the anterior prominence or fore-brain vesicle ; so that the stomatodaeum comes to occupy a its floor is formed by the oral plate, or meeting of the surface ectoderm with the entoderm of the primitive fore-gut (see Figs. 5, 8). The oral plate, whicli is later known as the bucco- pharyngeal membrane, forms a partition between the primitive oral cavity, or stomatodaeum, and the fore-gut, and disappears about the third week, thus bringing the mouth into A Trophoblast. B Trophobla&t. Amniotic ectoderm. -j^ — Ectomesoderm, -lA Embryonic entoderm. .Extra-embryo- nic entoderm. Primary mesoderm. Amnion cavity. Primitive alimentary canal Extra-embryonic coelom. D plasmodial trophoblast. Cellular trophoblast. Amniotic ectoderm. Embryonic ectomesoderm Embryonic entoderm. Extra-embryonic entoderm. Primary mesoderm. Plasmodial trophoblast. Cellular trophoblast. Amniotic ectoderm. Embryonic ectomesoderm. i;inbryonic entoderm .Extra-embryonic entoderm. Primary mesoderm. Fig. 3. — Differentiation of the morula and the formation of the amnion, yolk, and coelomic cavities (after Cunningham). A, Showing outer layer of cells (trophoblast), and inner mass of cells, which have now separ- ated into three groups, viz. ectoderm, ento- derm, and primary mesoderm. The darker shaded cells of the inner mass are those i^' - - from which the embryo will be formed. In some mammals a cavity (segmentation cavity) replaces the space occupied by the cells of the primary mesoderm. B, Showing further differentiation of the cells of the inner mass. The primary mesoderm has proliferated still further, and now separates the cells of the inner mass from the outer layer of cells (trophoblast) except in the embryonic region of the zygote. C, Showing the ectomesodermal and entodermal portions of the inner mass assuming the form of hoUow vesicles owing to the formation of cavities in their substance. The darker shaded cells of the vesicles where they he in apposition indicate the situation at which the embryo will be formed. D.'Showing enlargement of the vesicles to form respectively the amnion cavity and the yolk sac, from the latter of which the aUiuentary canal is separated off. The appearance of the extra-embryonic coelom in the primary mesoderm around the embryonic area is indicated. The coelomic cavity increases in size at the expense of the primary mesoderm until the latter merely forms a thin layer lining the trophoblast and covering the extra-embryonic portions of the ectomesodermal and entodermal vesicles. In the human subject a small portion of primary mesoderm surroimds both vesicles. position in front of, and below, the bhnd end of the primitive fore-gut (see Figs. 5, 9). The prominence behind the oral pit is further increased by the development of the heart, on the ventral side of the fore-gut (see Figs. 5, 8). Thus the oral pit is at first bounded in front (cephalad) by the prominence of the fore-brain vesicle, and beliind (caudad) by the prominence formed by the heart and the visceral arches, and communication with the upper end of the alimen- tary canal (fore-gut), and with the respiratory passage, which develops as an ofishoot from the fore-gut (see Fig. 8). The position of the bucco -pharyngeal membrane may be repre- sented in the adult by an oblique plane extending from the roof of the pharynx to the front of the tongue (see Figs. 9, 24). During the third week, the naso -frontal or median nasal process appears as a thickening on the ventral wall of the fore-brain vesicle (see Fig. 11, I and II); growing downwards and Fig. 4. — Shuwiug upper pole (i. e. embryonic region) of the blastodermic vesicle in a ferret (from Cunningham). {Diagrammatic.) A, Surface view. B and C, Transverse sections through the blastoderm in the region of lines b and c respectively. E, Embryonic area ; P, Primitive streak ; N, Neural groove ; M, Mesoderm ; NO, Notochord ; EP, Ectoderm ; H, Entoderm. forwards from either side of this central pro- minence are the lateral nasal processes. The median and lateral nasal processes together now form the upper boundary of the oral jjit, the fissure between these prominences forming the nasal pit, or future anterior iiarLs. The oral ^lu pit is bounded below by the mandibular pro- cesses and laterally by the maxillary processes, both of which arise from the first visceral arch. The fissure be- tween the maxiOary and mandibular processes forms the future mouth, and that between the maxillary and lateral nasal processes the naso- orbital sulcus, or future lacrimal duct. During the fifth week the mandibular pro- cesses unite ventrally to form the mandibular arch, and a week later process are formed the central portions of the pre-maxillae (endognathia), or that portion carrying the central incisor teeth, a correspond- ing portion of the upper lip, and the septum and bridge of the nose. From each lateral nasal process are formed tlie lateral por- tion of the pre-maxilla (mesognathion), or that por- tion carrying the lateral incisor tooth, a correspond- ing portion of the upper lip (except its free margin), and the ala of the nose. These processes, with the naso-frontal process, form the OS incisivum (Albrecht) and complete the anterior nares. The incisive bone, according to Kolliker, is formed entirely from the naso-frontal process. The greater portion of the maxiUa, containing the remaining teeth (exognathion), results from a metamorphosis of the maxillary process. The maxillary process likewise forms the zygomatic and palatine bones, a corresponding portion of SpC -.EC BP SpM Soli Fig. 5. — Longitudinal section of a developing ovum about the end of the second week (from Cunningham). The folding off of the embryo has commenced, and the downward bend of the head fold has invaginated the amniotic area. The tail fold is partly formed, and the primitive alimentary canal, closed in front by the bucco-pharyngeal membrane and behind by the cloacal membrane, is distinguishable ; it communicates freely with the yolk sac by a wide umbilical aperture, ^t,";^!, "+.ri.ra -^hZc."~\^^ C, Coelom; EN, Entoderm; SoM, Somatic mesoderm; EC, Ectoderm; M, Moso- umon takes piace oe- derm ; SpM, Splanchnic mesoderm ; BP, Buoco-pharyngeal membrane ; PA. tween the naso-frontal, ~ ■ ■ ' .r, .__:_.■_ r_ij . ^»t, t,:j u..„:„. c„,. c.,:.,„i — j.,ii~ . lateral nasal, and maxil- lary processes, but in such a way that the lateral nasal processes fall share in the formation of Placental area; AF, Amniotic fold; MB, ilid-brain; SpC, Spinal medulla; N, Notochord ; RS, Rhomboidal sinus ; PS, Primitive streak ; CM, Cloacal membrane ; H, Heart. short and take no the free margin of the lips (see Fig. 12). From the naso-frontal the lips and cheek, and by means of its internal or lateral prominence the future palate (except that formed by the pre-maxiUa), thus closing off the mouth from the nose (see Fig. 13). The mandibular processes form the mandible, the lower lip, and the chin. The fusion of the internal prominences of Fig. 6. — Transverse section of the embryonic area of the oviun of a sheep at the end of the second week (after Bonnet). pcj. Primitive groove ; ps. Primitive streali ; e. Ectoderm ; m. Mesoderm ; pm. Parietal mesoderm; c, C'oelom or primitive body cavity; vm. Visceral mesoderm ; h, Entoderm ; am. Amnion fold. the maxillary processes commences anteriorly at the eighth week and is completed at the eleventh week. Failure of union of the internal maxillary prominences results in a cleft palate, varying in extent from a bifid uvula to a cleft extending to the anterior palatine foramen, or junction of the maxiUae and pre- niaxillae. If the naso-frontal process on tlie medial aspect and the lateral nasal and maxillary processes on the lateral aspect also fail to coalesce, the cleft will extend forwards to one or other side of the median plane, be- tween tlie segments of the pre-maxilla (?'. e. meso- and endo-gnathion), and thus open into the nostril. The alveolar portion of the cleft will pass between the central and lateral incisor teeth, as these are developed in the endognathion and mesogna- thion respectively (see Fig. 14). The discrepancy in opinion that has arisen with respect to the position of the alveolar cleft may be explained by the occa.sional development of a supenuimerary tooth in the endognathion seg- ment and the absence of tooth formation in the mesognathion segment (see Fig. 15), so tltat the supernumerary tooth is mistaken for the lateral incisor and the cleft is consequently stated to pass between the lateral incisor and canine. Now if in addition to the supernumerary tooth a lateral incisor is formed in the lateral nasal process, the latter tooth is then ingeni- ously called a pre-canine, to avoid designating both teeth as lateral incisors. In other words, it is the development of the teeth that is subject to variation and rarely the position of the cleft, so that when the teeth are normally developed the alveolar cleft passes between the central and lateral incisors. A simple or incomplete hare-lip results from failure of union of the naso-frontal and maxillary processes. If this failure of union extends to the lateral nasal process, the cleft will then involve the alveolus and open into the nostril — a condition known as an alveolar or complete hare-lip and usually asso- ciated with a cleft palate. ■'"!/. Fio. 7. — Transverse section of a sheep-embryo between the second and third weeks (after Bonnet). Medullary or primitive groove ; m. Mesoderm ; h. Entoderm ; pm. Parietal mesoderm ; vm. Visceral mesoderm ; pe. Primitive endocardium ; hp. Heart plates ; ppc, Pleuro-pericardial cavity ; pp. Pericardial plates ; c, C'oelom ; am. Amnion. The Notochord is formed from tlie entoderm in the region of the medullary groove. Coalescence of the palatine portions of the naso- frontal, lateral nasal, and maxillary processes commences at the anterior palatine foramen and extends both forwards and backwards from this point, the lip and tlie uvnla being the last parts to unite ; so that a cleft lip or cleft uvula may exist without the involvement of the jaw, whereas the reverse condition would be im- possible for developmental reasons. Failure of union of the naso-frontal and lateral nasal processes medially \\ith the maxillary process laterally gives rise to what is known as an oblique facial cleft (naso-orbital). This cleft commences below at the usual situation of a hare-lip, but extends upwards around the base of the nose to the iimer canthus of the eye, and frontal process, and the same condition of the lower lip from non-union of the mandil)ular proces.ses (see Fig. 11, II). The lower jaw results from a metamorphosis of the mandibular processes, which fuse in the middle line at about the thirty-fifth day. At this period the oral margin of (lie jaw ])rescnts two parallel ridges, the outer and larger ridge Fig. 8. — Showing tlio stomatodaeum and primltivo pliaryiix of a third week embryo in sagittal section (after His). FB, Fore-brain ; NF, Naso-frontal process ; MX. Maxil- lary process ; MD, Jlandibiilar process ; H, Heart ; A, Aorta; 1, 2, 3, 4, Upper four visceral arches; VC, Visceral clefts (second and third) ; P. Pharynx ; S, Stomatodaeum; OP, Oral plate; DS, Dorsum sellae ; 0, Oesophagus ; L, Lung bud ; PB-, Buccal portion of hypophysis cerebri ; SP, Sessel's pouch. wiU involve the soft tissues alone, or in addition the bone, according to the extent of non-union. Deficient or excessive union between the maxil- lary and mandibidar processes produces the conditions known as macro- and micro-stoma respectively. A median cleft of the upper or lower lip may occur, and may or may not involve the subjacent bone according to the extent of non-union. Clefts of the upper or lower lip in the median line are rare deformities, more especially the latter. A median cleft of the upper lip would arise through non-union of the globular or lateral tubercles on the naso- cu Fig. 9. — -Vertical section through the head of a rat embryo (from Cunningham). Ectoderm is repre- sented in black, mesoderm stippled, and entoderm striated. T, Tongue ; H, Heart ; N, Nasal Cavity ; CH, Cerebral hemisphere ; TH, Thalamenccphalon ; P, Pineal body; MB, Mid-brain; HB, Hind-brain; PBS Cerebral part of hypophysis cerebri; PB'-, Buccal part of hypophysis cerebri; AT, Atlas; EP, Epi- stropheus; SG, Spinal ganglion; BCA, Basi-cranial axis; FG, Fore-gut; A, Amnion; BP, Bucco- pharyngeal membrane; NF, Naso-frontal process; MD, Mandibular process; S, Stomatodaeum. developing into the future lip, while tlie inner and smaller forms the gum (see Fig. 13). Incomplete separation of the oral margin of the primitive jaw to form the lips and gums gives rise to the condition known as atresia of the lips and gums, a rare malformation except in its slight forms, in which it occurs in association with a complete hare-lip. A thick fraenum labii is a less marked degree of this condition. The mandible at an early period consists entirely of Meckel's cartilage, embedded in embryonic tissue; at an earher .stage it con- sisted of mesoderm enclosed between the snrface ectoderm and the entoderm of the fore-gut. the entire structure being known as a visceral arch (see Fig. 1(5). Growing into each of the five visceral arches is an artery (visceral arch 6 vessel) arising from the truncus arteriosus of the primitive heart (see Fig. 10). The visceral arch vessel supplying the first and second arches is derived from the external carotid artery. The nerve of supply to the first visceral arch {i. e. the mandibular nerve) is derived from the first cephalic ganghon,a segment of the neural Fig. 10. — Hiiman embryo of about three weeks, showing the visceral arclies and clefts (after Quain). S, StomatodEieum ; O, Olfactory depression ; CV, Cerebral vesicles ; H, Heart ; TA, Truncus arteri- osus ; A^, Aortic branch of first visceral arch ; VC, Visceral cleft (first) ; OV, Otic vesicle ; JV, Jugular vein ; CV, Cardinal vein ; DC, Duct of Cuvier ; W, Vitelline vein ; UV, tj mbUical vein ; UA, Umbilical artery; All, Allantois; P, Placenta; PS, Primitive mesodermal somite ; nf, Naso-frontal process ; »i. Maxillary process ; md, Mandibular process. crest or ectodermic tliickening of the medullary groove, the earliest representative of a central nervous system in the embryo (see Figs. 6, 7). The mcsodermic tissue of the visceral arches becomes differentiated into connective tissue, and this constitutes the membranous stage of the Jaw, the remaining mesoderroic tissue forming the muscular and connective tissues around the jaw (see Fig. 17). Cartilage develops in each of the visceral arches ; the cartilaginous bar of MX Fig. 11. — I. Lateral aspect of the head of a human embryo about a month old, showing the olfactory pit and the visceral arches and clefts (from His). Olfactory pit; E, Eye; MX, Maxillary process; MX), Mandibular process ; H, Hyoid arch ; OV, Otic vesicle ; P, Prosencephalon ; T, Thalamen- cephalon ; M, Mesencephalon. OP, II. Front aspect of the head of hiunan embryo about five weeks old, showing the globular pro- cesses arising from the naso-frontal process, the olfactory pit between the naso-frontal (globular process) and lateral nasal process, the naso-lacrimal sulcus between the lateral nasal and maxil- lary process. The approximation of the naso- frontal, lateral nasal and maxillary processes is indicated and the lateral nasal process failing to share in the formation of the free margin of the lip. (from His). NF, Naso-frontal process ; G, Globular process ; LN, Lateral nasal process ; MX, Maxillary process ; MD, Mandibular process ; HA, Hyoid arch ; H, Heart ; E, Eye ; P, Prosencephalon or fore-brain ; OP, Olfactory pit. the first visceral arch (mandibular) being known as Meckel's cartilage, and that of the second visceral arch (stylo-hyoid) as Reichert's cartilage. The second visceral arch is represented by the stapes, stylo-hyoid process, stylo-hyoid ligament, and the lesser cornua of the liyoid bone. The third arch (thyreo- hyoid) is represented by the body of the hyoid bone and its greater cornua. The fourth and fifth arches fuse, and to- gether form a por- tion of the larynx (see Fig. 18). The intermediate tissues of the neck are formed from meso- dermic tissue invad- ing between the vis- ceral arches. The tongue de- FiG. 12.— Head of a hunian velops from the walls embryo about two months of the pharynx, its old, showing fusion of the anterior portion from naso-frontal process (glo- a central tubercle bular) with the lateral nasal and maxillary pro- cesses to form tlie anterior nares and the upper hp (from His). AN, Anterior nares ; NF, Naso-frontal process (glo- bular) ; MX, Maxillary pro- cess ; MD, Mandibular process. MX UD (tuberculum impar) arising between the first and second vis- ceral arches, and from two lateral tubercles arising from the ventral extremi- ties of the mandibular arches ; its posterior portion from the copula or united ventral ends of the hyoid arches (see Pig. 16). The V-shaped AN' the foramen caecum representing the apex of their junction. The buccal portion of the tongue contains the papillae (including the vallate) and is concerned vnth mastication ; the pharyngeal portion contains glandular and lymph tissue and is concerned with deglutition. The salivary glands develop as ingrowths from the oral ecto- derm between the sixth and eighth weeks. Fig. 14. — Diagram showing the position of the alveolar and palatine clefts in hare-lip and cleft palate (after Rose and Carless). »', i-, c, m', m'. Deciduous teeth ; eg, Endognathion ; mg, Mesognatliion (represented too extensive) ; exg, Exognathion. The centre bone behind the endognathion is the vomer. The four visceral, or branchial, clefts form deep transverse depressions partly encirchng the front part of the fore-gut. These clefts probably never exist as pervious channels in man, but only as ectodermic and entodermic evaginations from the surface ectoderm and pharyngeal EV entoderm MX LD respectively. At the bottom of these clefts the two membranes are in contact and consti- tute what is known as the closing membrane (see Fig. 16). In the lower vertebrates the closing membrane dis- appears (see Fig. 19), and the margins of the clefts become vascular- ized for respiratory purposes (gill slits). The visceral clefts (except Fig. 13. — I. Head of liuman embryo about two and a half months old (from His), the first) become ob- The labio-dental groove is weU-formed and the line of the common tooth-band is visible literatcd by a nieso- on tlie alveolar prominence. The palatal plates of the naso-frontal, lateral nasal (Jpj-jjjjc invasion be- and maxillary processes are commencing to grow inwards to close off the nasal +1 I ,.0 f tUa from the buccal cavity. tween tue la> ers 01 tue AN, Anterior Nares; E, Eye; NF, Nasofrontal process; MX, Maxillary process; closing membrane (i.e. PP, Palatal process or palate ; PD, Hypophysial depression. ectoderm and entO- II. Transverse section of an embryo after the fusion of the palatine processes with derm). This invading each other and with the nasal septum (ethrao-vomerine plate) to close off the nasal mesoderm is merely from the oral cavity. ^ represented in the first M, Mouth ; T, Tongue ; LD, Labio-dental sulcus ; DG, Dental germ ; MC, Meckel's YJggprf^I cleft bv the cartilage; J, Jacobson's organ ; NC, Nasal cavity ; EV, Ethmo-vomrrine plate. V. . ' c t.u ^ ' ' b • > J . . t- connective tissue 01 the line of union of the two main portions is indi- I tympanum (substantia propria) ; and but for this cated in the adult organ by the vallate papillae, 1 connective tissue and its enclosing membranes 8 the cleft would be pervious. Should this meso- dermic invasion fail to take place, a branchial fistula results, which may be rendered pervious if the closing membrane subsequently ruirtures, or be blind externally or internally, accorcUng to the stage of niesodermic development. Fig. 15. — Diagram showing the relation of the teeth to tlie oral clefts. The left side of the diagram represents the normal arrangement of the teeth and the right side, a condition frequently present in complete hare-lip. nf, Naso-frontal process; In, Lateral nasal process; mx. Maxillary process; md. Mandibular process; 1^, 1-, C, P', V', M', M^, M^, the Permanent teeth ; S,' Supernumerary tooth. Note absence of lateral incisor on right side of diagram. The visceral clefts are botnided above and below by the rounded bars of tissue known as the vnsceral arches (Fig. 16). The first visceral or branchial cleft normally EP L Fig. 16. — Showing the front wall or floor of pharynx in a human embryo at the fourth week {after Hist. ) 1, 2, 3, 4, 5, The five visceral arches ; MD, Mandibular or first arch ; HA, Hyoid or second arch ; T, Region of trimk; CM, Cleft membrane (first); E, Ectoderm; H, Entoderm; TI, Tubercuhuii impar, which forms part of the anterior portion of tongue ; LT, Lateral tubercles ; FC, Foramen caecvun ; PT, Posterior or pharyngeal portion > f tongue (copula); EP, Epiglottis; L, Larynx; SP, Sinus praecervicalis (formed by a sinking in of the lower arches and clefts and the more rapid growth of the second arch), the sinus or fossa is subsequently obliterated by the coalescence of its margins (HA and T). persists, and is represented by the external ear, the middle ear, and the auditory tube ; the ex- ternal ear representing tlie ectodermic evagina- tion of this cleft, and the auditory tube and the middle ear representing the entodermic evagination. This explains why the external ear (ectodermic development) is lined by skin, and the auditory tube and middle ear (ento- dermic development) by mucous membrane. The remaining visceral clefts disappear, except small portions of their imier parts, which form respectively the fossa of Rosenmiiller (a recess Fig. 17. — Schematic section of a visceral arch (after Keith). CM, Cleft membrane; E, Ectoderm; H, Entoderm; N, A, V, Nervous, arterial, and venous supply of a visceral arch ; M, Muscle ; C, Cartilage. The remainder of the mesoderm develops into the connective tissues. behind the auditory tube), the piriform fossa, and rudiments of the thymus and thyreoid glands. During the fourth week the membranous cranium undergoes a cartilaginous stage, \\hich 1, Fig. 18. — Showing the destination of the cartilaginous visceral arches (after Keith). 2, 3, 4, 5, The five visceral arches; MC, Meckel's Cartilage; M, Malleus; In., Incus; S, Stapes (tympano-hyal); SP, Stylo-hyoid process (stylo- hyal) ; SHL, Stylo-hyoid ligament (epi-hyal) ; LCH, Lesser cornu of hyoid bone (cerato-hyalj ; B, and GCH, Body and greater cornu of hyoid Ijone (thyreo-hyal) ; Th., Thyreoid cartilage formed by the fourth and fifth arches; T, Tongue; TR, Tym- panic ring. is imperfect in the head of the skeleton of man and the higher vertebrates. Cartilaginous cover- ings are provided for the organs of smell, sight, and hearing (see Fig. 20), and a cartilaginous visceral skeleton delineates the mandible, the bones of the middle ear, the styloid process, and the hyoid bone (see Figs. 21, 22). An imperfect cartilaginous capside is formed around the base of the brain, but the vault remains membranous (see Fig. 23). The cartilages of the nose are derived from the septal and ethmoidal cartilages, themselves derivatives of the trabeculae cranii (see Fig. 20). The pterygo -palatine cartilage, which forms the primitive support of the maxillary process. A, AAO Fig. 19. — Showing tlie position of the lieart and tlie relation of tlie aortic arclies to the visceral or gill-clefts in a tish (after Gegenbaur). Auricle ; V, Ventricle ; BA, Bulbus arteriosus ; VA, Ventral aorta ; DA, Dorsal aorta ; C, Carotid artery; AA^, Artery of first or mandibular arch; AA=^, Artery of fifth arch; AA«, Artery of sixth arch; GC, Gill-cleft; E, Eye; NP, Nasal pit. The sixth arch shown hi the diagram does not become differentiated from the body wall. I SHL GH Fig. 20. — Showing the cartilaginous eranivun at an early stage of development (after Wiedersheim). Diagram I. — N, Notochord ; P.cti, Parachordal cartilages; Tr., Trabeculae cranii; p, Hypothysis cerebri; 0,V, A, Situations of olfactory, visual, and auditory organs. Diagram II (a few- days later). — b. Basilar cartilage ; na. Nasal septum ; Eth, Ethmoidal cartilage surrounding (O) olfactory organ; o.n.. Foramina for olfactory nerve fibres. The commencement of formation of the lens by a dipping in of the ectoderm is showii and the cupping of the optic stalk (retina) to receive this invagination. 1* Fig. 21. — Head and neck of a luunan foetus four and a half months old showing the visceral skeleton exposed (after KSlliker). Md, Mandible; MG, Meckel's Cartilage; M, Malleus; I, Incus; S, Stapes; TR, Tympanic ring; SP, Styloid process; SGM, Stylo -glossus muscle; SHL, Stylo-hyoid ligament; LH, Lesser comu of hyoid bone ; GH, CJreater cornu of hyoid bone ; MH, Mylo-hyoid muscle; SMM, Stemo-mastoid muscle. extends to the proximal end of Meckel's cartilage; at this situation it undergoes ossification in birds and reptiles, forming the quadrate bone. The destination of the quadrate bone in mammals is uncertain ; Gadow believes that it becomes the tympanic ring (see Fig. 22). Chondrification commences in the visceral arches during the fourth week and is visible up to the seventh month ; at this period Meckers cartilage disappears, ex- cept its distal extremity \\'hich ossifies and forms a small portion of tlie mandible near the symphysis. Small pendulous tags of skin con- taining a nodule of cartilage are not infrequently seen below and in front of the ear; these represent small portions of persisting cartilage from the first visceral arcii, and are known as accessor^' auricles. Similar tags may occur in the neck associated witli the branchial clefts and are then known as cervical auricles. 10 The proximal extremity of Meckel's cartilage persists as the malleus and, possibly, the incus ; there is, however, some doubt as to whether the SHP Fig. 22. — Sho%viiig the parts formed from tlie cartilages of the maxillary and mandibular processes in the human skull (after Keith). mx, Maxilla; md, Mandible; MC, Meckel's Cartilage; C, Condyle of jaw; SML, Spheno-mandibular ligament ; AO, Auditory ossicles ; TR, Tympanic ring (? quadrate bone) : SHP, Stylo-hyoid process ; P, Palate ; IP, Internal pterygoid. incus may not belong to the second arch or to both arclies (see Figs. 21, 22). The spheno- mandibular ligament of the mandible probably AF (23). Portions of the condyle, coronoid process, and symphysis of the mandible, are formed from cartilage, but are ossified from the surrounding LL DL EBD MD Flo. 23. — The cranium at birth, showmg the bones that are formed in membrane and those formed in cartilage (stippled). F, Frontal ; P, Parietal ; O, Occipital (showing inter- parietal portion formed in membrane) ; T, Temporal (petro-mastoid portion formed in cartilage) ; TR, Tympanic ring ; S, Sphenoid ; MD, Mandible (symphysis developed in cartilage) ; AF, Anterior fontanelle ; PF, Posterior fontanelle ; W, Wormian bone developed in membrane in region of a-sterion ; there is a similar ossific develop- ment shown in the pterion region (epipteric bone). represents the fibrous sheath of the intermediate portion of Meckel's cartilage, and the inter- articular meniscus of the mandibular joint is believed to be also a remnant of this structure Fig. 24. — Section through the lip and mandible of a third month foetus, showing the downgrowth of oral epitheliiun to form the dental lamina (diagrammatic). LL, Lower lip ; LD, Labio-dental groove ; T, Tongue ; E, Ectoderm ; BP, Position of bucco-pharyngeal membrane ; DL, Dental lamina ; EBD, Enamel- bud of a deciduous tooth ; EBP, Enamel-bud of a permanent tooth ; EC, Enamel-cells ; DP, Dental papilla ; DS, Dental sac ; B, Bone of jaw; MC, Meckel's cartilage. membrane bone. Thus the mandible develops eliiefly from intra-membranous ossification. The maxillary process continues as a mem- branous structure ^ until the seventh or eighth week, when ossification commences from an uncertain number of centres. The pre-maxil- lary segments result from an ossification in membrane of jDart of the naso-frontal and lateral nasal processes, the remaining portion of these processes entering into the formation of the upper lip and nose, as previously mentioned. This brief outline of the development of the visceral arches extends to the period at which the first indication of tooth formation appears. The origin and development of the visceral arches is so much involved in the morphology of the body as a whole that there is some difficulty in abstracting those portions oidy which liave a direct bearing on the development of the jaws. Tlie reader is referred to Keith's Human Embryology and Morphology, or the section on ' A cartilaginous bar (the palato-pterygoid) is present in the maxillary process of some of the lower animals. 11 cmbryoloiiv in Cumiingham's Text-book of Anatomi/. ior more general information. 2. Development of the Teeth. — During the sixth week of intra -uterine life an ingro\\ th of ectoderm into the substance of the first visceral arch takes place in a situation corresponding to the futiu'e alveolar border of the ja«' (see Fig. 24). This ectodermic ingrowth {tooth-band or zahn- leiste) forms a continuous lamina and becomes specialized in certain parts, where teeth are to be formed ; and in these positions the lamina LL REG MV Fig. 25. — Section through tho lip and mandible of a six months foetus, to show the stage of tooth development in the incisor region. (Diagram- matic.) LL, Lower lip ; A, Alveolar ridge ; LD, Labio-dental groove; E, Ectoderm; T, Tongue; DL, Dental lamina ; DS, Dental sac (showing its two layers) enclosing the deciduous tooth-germ ; EEC, External enamel-celLs ; REO, Reticuliun of enamel- organ ; lEC, Internal enamel-celLs (araeloblasts) ; E, Enamel; D, Dentine; O, Odontoblasts; DP, Dental papilla ; B, Bone of jaw ; ME, Muscle fibres ; MN, Mandibular nerve ; MA, Mandibular artery ; MV, Mandibular veins (venae comites) ; MC, Meckel's cartilage. thickens, so as to appear on section club-shaped, and later flask-shaped, the neck of the " flask " retaining its comiection with the epithelial lamina. This ectodermic thickening in the region of tooth formation is known as the enamel- organ, and is invariably formed on the outer or labial aspect of the tooth-band. Persistence j of portions of this ectodermic lamina, either in the region of tooth formation or elsewhere, is believai to be the origin of multUocular cystic epithelial tumours, dental and dentigerous cysts, and possibly in some cases of epitheliomata. About the same period, or a week or two later, the mesodermie tissue m the neighbourhood of the enamel-organ rises up in a papilla-like form and invagmates the enamel-organ, so that the latter a.ssumes the shape of a bell. This special- ization of the mesoderm, known as the dental papilla, takes the shape of the tooth it represents. The base or periphery of the dental papilla expands and encircles the tooth-germ, giving rise to its follicle (see Fig. 25). Tomes (32), APF PM X MUMX PPF Fig. 26. — Showing the hard palate at about the ago of six (modified from Keith). i', i', c, m^, in'-. The deciduoiui teeth ; E, Endognathion ; M, Mesognathion ; PMX, Palatine process of maxilla; PP, Palatine process of palate; APF, Anterior palatine fossa (line indicates position of foramina of Stenson) ; SF, Foramina of Scarpa lying in median suture ; PPF, Posterior palatine foramen ; OF, Gubeniacular foramen (showing a lateral incisor in its crypt) ; M'MX, Crypt for first permanent molar. however, believes that the portion of mesoderm forming the tooth-follicle ma}' be a spontaneous specialization of cells, and not an extension from the mesoderm forming the dental papilla. An aperture exists in the bone covering the foUicle for the passage of the giibeniaculum, a fibrous structure comiecting the tooth-sac with the overlying gum tissue and at one time believed to play an important part in the eruption of the teeth. The foramina seen in the dried skull behind the upper deciduous incisor teeth are supposed to rej)resent the persistence of these apertures after ossification has set in (see Fig. 26). Successional teeth are formed about the fifth month of intra-uterine life; the enamel- organ from specialization of cells arising from the continued growth of tiie free end of the tooth-band, and the dentine papilla, as before, from the mesoderm in the neighbourhood of the enamel-organ. An exception occurs in the case of the permanent molars, all of which arise 12 from a continuation of the same tooth -band as that which gave rise to the second deciduous molar ; the lateral end of this tooth -band grows more deeply into the mesoderm of the ja\\% thus losing its continuity with the surface ectoderm. The origin of supernumerary teeth can be explained by an adventitious formation of an enamel-organ from the tooth-band; and the reason for their more common appearance in the region of the clefts may be the fact that the tissues are apt to be disturbed in these regions, and foreign epithelium may be included, which takes on an aberrant growth (e. g. the mid-line and cleft dermoids). ;5f yea~ 6 morithh , Birth... ythmth {before birth iti-mt\[bi>lore birth year qIK year I i'^ year f^^vQar Fig. 27. — Showmg the amount of calcification the deciduous and permanent teeth have undergone at various ages. The deciduous teeth are represented in the upper part of the iUustration. Theories as to the development of the per- manent teeth-germs are — (1) Tomes (32) beheves that the permanent teeth grow from the tooth-band near the neck of the enamel-organ of the deciduous teeth. (2) Baume is of the opinion that the per- manent teeth develop from the remains of the primitive inflection, without having any direct connection with the deciduous teeth- germs. (3) Rose takes the view that the deciduous and permanent teeth-germs originate from a common tooth-band (zahnleiste), but ari.se independently of one another, the mesoderm invaginating the ectodermic tooth-band and so receiving its cap of enamel. The enamel, or adamant, is formed from the enamel-organ, and chiefly from that part of it which is applied to the dental papilla (internal enamel-cells), deposition taking place from within outwards. The dentine, or ivory, is formed from those cells which line the periphery of the papilla (odontoblasts), but probably not by their direct calcification, deposition proceeding from without inwards. The dental sac, or follicle, is divisible into two layers; by calcification of its inner or looser layer the cementum, or substantia ossia, is formed, while from its outer layer, together with the surrounding mesoderm, arises the periosteum of the tooth-socket (periodontal membrane). Calcification («. e. of enamel and dentine) of the deciduous incisors commences about the seventeenth week of intra-uterine life, and of the deciduous molars a few days later (see Fig. 27). Calcification of the cementum is comparable to membranous ossification of bone ; it occurs later than that of the enamel and dentine, the cementum not being formed until those tissues are completed, and often not being itself completed for a year or more after the tooth has erupted. At birth, calcification ~-, has involved the crowns of the deciduous incisors and the cusps of the canines and molars. Models showing the formation of the tooth-germ and the relation of its ectodermic and mesodermic elements can be prepared by em- ploying Born's (26) method, which is briefly as follows — Serial sections of the tissue are cut with an automatic microtome, and every fifth section or so is photographed and magnified to the extent required. The outline of the enlarged photograph is transferred to wa.x sheets bearing a defimte relation in thickness to that of the section, and the object carved out. The cut out wax sheets are placed serially in position and fixed together by melting tlie wax with a hot spatula, thus producing a wax model of the original object photographed. The model may then be coloured, so that the different parts are clearly shown. 3. Ossification and Growth of the Jaws. — It has already been briefly explained liow the jaws, first consisting of mesoderm, rapidly pass through a membranous and a cartilaginous stage. It has also been mentioned that in the mandible the cartilaginous bar, known as Meckel's carti- lage, disappears, except its anterior end, which undergoes direct ossification to form part of the symphysis of the jaw. The remaining portion of Meckel's cartilage is absorbed and replaced by membrane, in which one or more centres of ossification appear. The pterygo-palatine cartilaginous bar of the maxillary process serves merely as scaffolding around which the ossific centres develop, and it is entirely absorbed. The maxilla develops from one centre, appearing m the region of the canine tooth- germ during the second month of intra-uterine life. An infra- vomerine centre is described by Ramband and Renault between the incisive and palatine portions of the maxilla. Albrecht 13 > 38 15 50 )» 46 21 55 j> 47 26 56 52 30 70 ,, 54 40 At birth . 15 months 2| years . 9 „ . 12 „ . 15 „ . Adult " In the accompanying table certain dimen- sions of the upper jaw of man at various stages of growth are given. The measurements refer to three dimensions of the jaw ; in column A the length of the upper jaw, measured from the fronto-maxiUary suture to the edge of the central incisor crown ; under column B, the length of the alveolar margin, measured in a straight line ; under C, the depth of the posterior border of the jaw, measured from tlie floor of the orbit to the alveolar margin. These measure- ments refer indirectly to the maxillary sinus. Its growtli in each direction is most rapid during the eruption of the permanent molar teeth. The alveolus occupies practically the whole depth of the posterior margin of the jaw at birtli. While the posterior border of the jaw quadruples its extent from birth to maturity, tlie facial border becomes little more than double, and the alveolar margin increases in even a smaller degree. Growth adds to the depth of the posterior part of the jaw much more than to any other dimension, and this addition is entirely due to tlie growth of the maxillary suture. "' The rapid growth of the jaw along its posterior border, caused b}' the extension into it of the maxillary sinus, not only leads to the forward rotatory movement already mentioned, but also necessarily leads to marked changes in the growth of the lower jaw. At birth the ramus of the lower jaw is very short, and the angle at which it joins the body of the jaw is open. The do«iiward growth of the maxillary sinus leads to an elongation of tlie ramus of the mandible. Growtli in the maxillary sinus and ramus proceeds — must necessarily proceed — at a corresponding rate and be closely correlated, but probably that of the sinus is the primary and determining factor. It is tlie downward growth of the maxillary sinus that leads to the accentuation of the angle of the Jaw; were the angle not accentuated, only the molar teeth would come in contact. " The development of the sinus during the eruption of the milk teeth — at about the 15th month — is shown in Fig. 94. The sinus is spreading backwards over the sac of the first (XmSh. s.m.t: Fig. 94. — The development of the maxillary sinus in a child of fifteen months and the relationship to it of the dental sacs of the second milk molar and first permanent molar. Antr., maxillary sinus; Op., Opening of sinus ; S. M. F., Spheno-maxillary fossa; Pt. pr., External pterygoid process. *C'ancellous bones into which the sinus is spreading. (Nat. size.) (Keith : Brit. Journ. of Dent. Sci.) permanent molar to reach that of the second. Over the sac of this molar tooth, the bone is markedly cancellous, a porosity of the bone always preceding the extension of the sinus into it. This is seen in the specimens represented in Fig. 94. " Whenever the dental sac of a permanent or milk molar is formed, an extension of the maxillary sinus over it rapidly takes place. Thus a study of the maxillary sinus shows how closely it is connected in its origin and develop- ment with the appearance and eruption of the molar teeth." Keith further states that in tlie higher apes the size of the maxillary sinus varies inversely with the size of the inferior meatus, and that this same relationship may be observed in different instances in man. The average measurements of the deciduous 60 and permanent teeth are given by G. V. Black (26), and phenomena of growth correlated with the differences in size between the teeth of the two dentitions are well discussed by Simms (141). Fig. 95. — Delicinit growth of luaiidibk' iii [jutient aged 12 years, the result of destruction of the joint at the age of eighteen months. (iSiR \V. Arbuthnot Lane : Tranx. Odont. Soc.) Fig. 9U. — Deficient growth of mandible, the result of anchylosis due presumably to injury at birth. (VV. J. PvOE : Dental Cosmos.) ■Wliile there is httle doubt that the mere presence of the developing permanent teeth in their crypts is a stimulus to bony development, it is certain that a further incentive is needed, and it is highly probable that the theories promulgated by Sim Wallace (162) are correct, and that lack of functional activity from an early age is the main cause of interference with the normal process. If the coronal surface of a molar be taken as roughly twice the area of a premolar or deciduous molar, the masticating surface of an adult, including the third molars, is about three and a half times that of a child of three to five years of age. The weight of a boy of three is about 2J stone, and that of a man about IH stone, on an average, or more than four times as much, so that a child of three Fig. 97. — Deficient growtli of mandible, the result of anchylosis due to injiu'y at four years of age. (\V. J. Roe : Dental Cosmos.) is equipped with a more efficient masticating apparatus in proportion to body weight than an adult. It stands to reason that these teeth should be vigorously used in the mastication of solid substances. Function is the best stimulus to growth, whether by reflex stimula- tion of trophic nerves, or by increasing vascu- larity, or both, and there can be no doubt that insufficient mastication is responsible for much imperfect development of the jaws. Lawrence W. Baker (18) made experiments on young rabbits by grinding down the teeth on one side ; he found marked differences in development of the bones of the skull between the two sides. Sir W. Arbuthnot Lane (8) has recorded two cases of deficient development of the mandible con- sequent on early temporo-mandibularanchylosis. In one case the joint was affected at the age of eighteen months, and the effect on the growth 61 of the mandible was profound (see Fig. 95). Other cases have been recorded by W. J. Roe e pre- vails. It should be remem- bered that only about thirtj'^ or forty generations separate the Englishman of to-day from the several races from whose fusion he derives his inheritance, and it would l)e surprising if uniformity of type had become evolved ill so short a time. It is, then, necessary to recognize the fact of somewhat wide diversity of form and feature in the skull and face, and the shape of the arch within limits that may fairly be called normal is not the least 65 variable factor. Excellent profile photographs showing normal and abnormal variations and types are given in Lischer's monograph (105). (e) The character of the face bears a dis- tinct relation to the character of the body. Fig. 107. — Bushman. The arelies are small compared with others sliown, but the Bushmen are a small race. (Half natural size.) (Museum of the Royal College of Surgeons of England.) The operator who ventures so to mould his jDatient's jaws and features as to conform to his own or a theoretical ideal is exceeding the limitations of his profession and courting failure. This is not to say that vast improvements in ap- pearance may not be gained by judicious treatment of the teeth and alveolus. So true is this that caution is the more necessary, in order to avoid providing a patient with a " dento-facial " area out of harmony ^^•itll the type of which he or she happens to be an example. The principles of art that should guide the orthodontist have been clearly enunciated by Henry Read (136) in a short but illuminating article. His conclusions are — (ft) There is no absolute standard of human beauty. (b) A relative standard can be found in the aver- age or composite. (c) Such average or composite must be con- fined to a group. (d) Race, sex, and so-called temperament, indicate the meaning of a group. 3 Fig. 108.- Side view of same. Note the vertical forehead and the prognathous jaws. (Half natural size.) (/) Function may be the ultimate test of beauty, but tliere are practical obstacles to any effective application of the test. 66 Fig. 109. — Tasmanian. Note the well-developed but nearly parallel-sided arches. (Half natural size.) {Museum of the Royal College of Surgeons of England.) Fig. 110. — Side view of same. Note the prognathous jaws. (Half natural size. Fig. 111. — A Sandwich Islander. Note the well-developed arches. (Half natiu'al size.) College of Surgeons of England.) {Museum of the Hoyal Much di.scussion ha.s centred round the problem whether Nature ever pro- vides teeth of a .size too large for the jaw and face, and whether, therefore, ex- traction is ever justifiable. Even if perfect osseous de- velopment be assumed, it is doubtful «'hether in more or less recently mixed races the blending of parts is so complete as never to justify extraction for improvement. In the breeding of animals remarkably inharmonious results may be obtained by certain kinds of crossing. The question is discussed from the comparative stand- lioint by William Bebb (24). Undoubtedly cases occur in Avhich very small teeth widely separated are found in large jaws, and the as- sumption is that large teeth occur in small jaws and small faces. Cryer (60) be- lieves that both phenomena frequently occur (see Figs. 113, 114, 115, 116, 117). Just as in striving for an artificial ideal caution is necessary, so it is in determining whether the teeth are really too large for the individual or not. This question is di.scussed more fully in Fig. 112.- Side view of same. Dolichocephalic and i'l-ognathuus. (Half natural size.) connection with hereditary aetiological factors. (See pp. 68, and 71 et seq.) However, the real point of the controversy 68 lies outside the realms of blending of races and genetic variation ; the problem is concerned mainly with environment and pliysical develop- ment, and consists in the question whether the -Small teeth in large well-developed arch. (G. XORTHCROFT.) teeth are ever too large for the jaws as they exist, and whether the mechanical restoration of an approximately normal arch in patients of feeble osseous development \rill be compen- sated for by subsequent bony growth. It is undoubtedly very difficult to estimate the probable development of of a child who, for instance, at the age of eight exhibits marked insufficiency in the incisor region, and caution is necessary with regard to early extrac- tion : but in the opinion of the writer bone formation is and remains in many cases, especially those associated with nasal stenosis, quite insufficient to pro- vide space for teeth that by inheritance are of a certain fixed size, and restora- tion of a normal arcli with the full com- plement of teeth can only result in an unpleasing appearance. Angle (6) has published cases to show how, after treatment of a case in which bony growth is deficient, by means of the stimulus of function, alveolar develop- ment occurs, so that even the apices of the roots are thereby moved. How- ever, he describes a "working" retainer to bring force to bear upon the roots in a labial direction, thus indicating that natural processes are not always sufficient, or at least very slow. A. H. Ketcham (96) has also published cases intended to show that extraction is never justifiable and that expansion is always compensated for by subsequent •■ bone-gro\rth ", but the illustrations do not altogether show ideal results. Cr\-er (60) has shown a good case in which a condition of anterior open bite was caused during the eruption of the posterior teeth (that the anterior teeth had been in occlusion was shown by the ground-off edges). The case is clearly one in which there is not sufficient bone- space' for the teeth, in spite of the lingual position of the second upper premolars, and in which correction without extraction would but in- tensify the evil. This sub- ject is dealt with in detail lutder the classification and treatment of different types of alinormality. Part II Aetiological Factors It will presently be shown that many com- paratively simple abnor- malities of position are due to more or less obvious local causes ; but the origin of the more complex conditions associ- ated with defective formation of the jaws and abnormal relation of the mandible to the 3i years. Fig. ll-l. — Small teeth in large arch. Note the spacing, and the position of the premolars. No teeth have been removed. (XoRMAX G. Bennett.) maxiUa must be sought for in the influence of pathological conditions of adjacent parts, in the environment and liabits of the individual during the period of development, and in the factor of inheritance. Heredity. — If the skulls of prehistoric man, 69 palaeolithic and neolithic, are compared vdth the skulls of the modem Englishman, striking differences may be noticed. One of the most Fig. 115. — Small teeth in large arches. (.J. E. Sp tttf r ) William Wright (174) in a short but interesting communication gives measurements of the jaws of skulls found in the East Riding of Yorkshire. Some belonged to the Xeohthic and Bronze ages, and others to the early Iron age. He states : ■' All the measurements are greater in the jaws of the Stone and Bronze periods than in those of the Iron period, and tills is specially true of the bicondyloid width and the Avidth of the ramus. Tlie indices show obvious is the smaller size of the maxilla and | that the earlier race was more orthognathic, and mandible, especially the latter, in relation to that they had relatively wider pafates and a the rest of the skuU in the recent tvpes. It must be at once stated that in many well-developed modem skulls this difference does not exist to any appreciable extent, but it can scarcely be denied that the counterpart of the average mandible of to-day is not to be found among pre- historic and early British re- mains. Valuable comparative measurements of the width of the arch and height of the palate in various ancient and modern races are given by Talbot (149. pp. 49 and 81). Xot only is the modem mandible and, perhaps to a less extent, the maxilla also. of smaller size, but their form is much more variable, even within limits that exclude the srrosslv abnormal (see Figs. 118. 119).' It is interesting to find that an ancient, highly civilized, and to some extent degenerate com- munity — the Incas and Aymaras of Peru — exhibited many of the abnormalities of position of the teeth common in the European of to-day. tliough not to so pro- nounced a degree. Alton H. Thompson (150) has described these carefully, but it is not evident to what extent the dental defects were due to reduc- tion in size of the jaws. Some of those referred to, however, seem to be obviously ascribable to this cause. Fig 110. — Large teeth iii small arch. Space tor upper canmes (.mierupted) obhterated. Probably forward movement of upper molars. (Xorma>" G. Benxett.) smaller basio-nasal length . explaining the liigher palatal index and the equal molar index, although the molar lengths are absolutely greater." 70 The question at once arises, Is this difference an inlierited character, the result of gradual change through successive generations, or is it solely the result of the influence of external conditions, diet and such like, operating during the lifetime of the individual? The problems of heredity have been attacked in recent years from \\idely different standpoints. The great generalizations of Darwin, founded upon a study of the facts of variation, ofiened up large fields of investigation as to the extent of resemblance between parents and children (22) (106), the material basis of inheritance, and the reasons for the differences between an organism and its progenitors ; and the re- discovery of Mendel's experiments in breeding has stimulated a large number of workers to investigate on the same lines and accumulate further evidence in support of his laws of Fig. 117. — Two maxillae, showing a large amount of t jaw, A, and mucli less in the larger jaw, B. (Matthew descent. It is, of course, impossible to discuss these various metiiods in detail, but it will be necessary to refer to such results as have been obtained bearing upon the form and size of the jaws in man. The apjalication of Mendelian metiiods and arguments to man is but in its infancy. They are primarily experimental, and the conclusions are based on the numeri- cal results of first crosses and fertilization of like forms in succeeding generations (23) (72). The classical experiments were made with tall and dwarf jjeas, in which a first cross between tall and short always produced tall peas, but fertilization of tall by tall in the next genera- tion produced botli tall and short, and subse- quent union of short and short produced only short. The quality of tallness is said to be dominant to the quality of shortness, which is called therefore recessive ; and inasmuch as there is no blending, with production of peas of intermediate height, but rather transmission of sliortness througli a tall generation, the two qualities are said to "segregate". The subject is far too complex to enter into at all fully, but references must be made to such investigations as have been carried out concerning human inheritance. Analysis of certain families with regard to particular pairs of qualities, or the presence of a quality and the absence of it, has shown that the inheritance proceeds according to Mendel's laws. Hurst (72, p. 102) has investigated the problem of eye-colour, and finds that complete absence of pigment in the front of the iris is recessive to the presence of pigment. That is to say, two blue-eyed parents will have only blue- eyed children, but two parents with pigmented eyes may have blue-eyed children in addition to children with pigmented eyes. The two characters of pigmented and non-f)igmented are said to " segregate ", and not to produce intermediate forms that breed pure. Similar investigations have been made with regard to " brachydactyly ", night- blindness, congenital cataract, and other char- acters, and an explanation of the want of blending of particular characters in mixed races like the Eng- lish and American may perhaps be found in the Mendelian theory ; it is possible that the applica- tion of this method of analysis to characters of jaw-form may one day afford important results. The biometricians. Gal- ton, Pearson, and others (72, p. 41 ), work on differ- ent lines, and analyse the statistical results derived from the examination of a large number of individuals with regard to a particular quality, to show the varying amount of diverg- ence from an average, and the intensity of inheritance. Galton formulated a physiological "law of ancestral heredity", by which a child obtained on an average half its heritage from its parents, a quarter from its grandparents, an eighth from its great-grandparents, etc., the sum of the series being equal to one. The prepotencies or subpotencies of particular ancestors are eliminated by a law that deals only with average contributions. There is a constant tendency tow ards an average ; as Galton puts it, society moves as a vast fraternity, and the law of filial regression constantly neutralizes the effects of inheritance from abnormal parents. Pearson has found from statistical examination that the heritage from the parents is greater, and that from the ancestors less, than by Galton's law, but it remains a useful indication of the average expectation. It might certainly be expected ooth tissue in the smaller Cbyer : Dental Cosmos.) 71 that the statistical method applied to dimen- sions of the jaws would lead to the discovery acquired characters is now pretty generally discredited hy biologists. Weismann (169) has Fig. 118. — Ancient Egyptian (female), prc-clynastio (4000-(3UOlt n.c.) Note the well-developed arches, and the marked attrition of the teeth. (Half natural size.) {Museum of the Royal College of Stirgeons of EiuiUind.) of useful facts, as soon as means have been devised for accurate measurement. The immediate jiroblem to be considered is : As- suming for the sake of argument that the com- paratively small size of the jaws at the present day is an inlierited quality, in what way can the diminu- tion be explained ? Mucli disctission has centred round the question of the possibility of the inherit- ance of acquired charac- ters, that is to say, of a character acquired as the result of external influence during the lifetime of the individual. Much of this discussion has been in relation to the inheritance of disease, be- cause it is difficult to understand in many cases how a useless or harmful character, which is appar- ently inherited, should be perpetuated, except as the result of external influ- ences. It is impossible to discuss this question at length, but the Lamarckian hypothesis of the inheritance of Fig. US). — Side view of same. Brachyeeplialie and On liogiiathoiis. Note the attrition of the teeth. (Half natural size.) propounded and elaborated the theory that influences affecting the " soma " cannot produce a heritable result on the germ-cells from which the next generation is derived ; but it should be clearly understood that this means only that a condition correspondincj to any acquired modification of a particular part, as the result, for instance, of use or disuse, cannot be inherited. Weismann fully admits the effect of external conditions, such as temperature, on the germ-cells, and discusses very fully such results in the case of certain butterflies. In fact, Weismann considers that nutrition (using the word in a wide sense) of the germ-cells is the prime origin of the variations made use of in natural selection, and that similar minute fluctuations in a large number of the elements of the germ-plasm are or may be accumulated in the next generation by the i)rocess of " amphi- mixis " — the conjugation of unicellular and the sexual reproduction of multicellular organisms, — an essential condition for the production of variations. It is sometimes assumed that if the trans- mission of a small jaw, the result of comparative disuse, is impossible, no alternative exists to regarding every small jaw as being produced de novo in each generation in an individual potentially capable of having developed a normal one. Such, however, is not the case. Weismann writes : " The fact, however, that we deny the transmission of the effects is of no importance ; and I have already attempted to show in former essays that both use and disuse may lead indirectly to variations — the latter in all cases in which an organ is no longer of any importance in the preservation of the species, and in which, so far as the disused organ is concerned, " panmixia " occurs — in my former essays sufficient proof is given to show that the gradual degeneration of organs which are no longer of use does not require the assumption of the transmission of somatogenic variations." Again, " the transformation of a species as well as the preservation of its constancy are based upon natural selection, and this is constantly at work, never ceasing for a moment." " Every species is under the uninterrupted control of natural selection, as is clearly shown by the degeneration of parts ^\hich have become useless. And since the old hypotliesis of the transmission of somatic variations must, it appears to me, be definitely rejected, this process of degeneration can only be explained as the result of panmixia, i. e. the cessation of the control of natural selection over that part which is no longer of use. Examples of such effects are the rudimentary nature of the wings of the Khvi. a New Zealand bird, which has gradually adopted the habit of living on the ground among the short under- growth ; the acquired blindness of crustaceans living in caves, and of deep-sea organisms ; and the loss of protective colouring in domestic animals." This cjuestion of the indirect im- portance of accjuired modifications is discussed l)y J. Arthur Thomson (151, p. 242). Now although the jaws and teeth of civihzed man can scarcely be described as no longer of use, yet there can be no doubt that the demands made upon them for mastication are very much less tlian in the case of primitive man. The reduc- tion in size is less marked in the teeth than in the jaws, except in the case of the third molars and possibly the lateral incisors. J. T. Carter (42), in a valuable essay on the growth of the jaws, states that the teeth and tooth-bearing parts change least in the phylogeny of a race, and the parts to which muscles are attached undergo the greatest change ; and that in the progress of civilization the size of the mandible has become reduced out of jiroportion to reduc- tion in the size of the teeth. It is probable that the jaws and third molars are chiefly affected in each individual by diminished nutrition and blood-supply, correlated with lack of functional activity (146). Such modi- fication is a somatic variation and therefore not directly inheritable, but it can scarcely be argued that some of tlie very aberrant forms of third molar are solely the result of external influences during their growth, and it seem.s reasonable to suppose that the degenerative adaptation in each generation serves in the way described by Weismann as the cover, as it were, for a gradual blastogenic variation leading to reduction. Russel Wallace gives the human jaw as an example of regression due to non- continuance of selection. This explanation is probably far nearer the truth than anything founded on the principle of "reversion". Incomplete reversion to a comparatively recent ancestor is occasionally observed in man, but should produce a well-formed jaw rather than a diminished one ; reversion to remotely ancestral types is common only in the production of hybrids in plants and animals, but occasionally occurs in man — for instance, in the form of superiuimerary nipples. Weismann remarks : " It is well known that organs which have lost their value in the preservation of the species become rudimentary in the course of genera- tions ; they diminish in size, become stunted and ultimately disappear altogether." The re- duction and disappearance of parts by atrophy is in fact an essential part of evolutionary processes (29) (68). Such organs occasionally reappear by reversion ; if this ever takes place in tlie case of the jaws it should be in the form of increased rather than diminished size. But quite apart from diminished size, there exists considerable diversity in the form of the jaws in modern man within the limits of the normal. It has already been pointed out that to expect aU ja«s and arches to conform to an 73 ideal or canonical contour is not logical. Marked differences exist in the shape of the parts of the body, especially of the skull and bones of the face, and there is no more reason to label a retrousse nose as abnormal than an aquiline one. It is almost certain that such variation in the form of the ja\\s and arches is of blasto- genic origin, and often very definitely inherited from generation to generation. It would, indeed, be strange if this were not so. When striking resemblances are found to exist between parent and child in the colour of a moustache, the curve of an eyebrow, and even passing expression the result of transient emotion, tricks of manner, and habits of thought, it would surely be very remarkable if the form of so variable a part as the ja\\s were not inherited. Perhaps the most extreme examples within normal limits are some of the moderately well- defined laterally contracted arches in \\hich occlusion is normal ; but other slight peculiarities are frequently inherited, and no doubt forms clearly abnormal also are. The c£uestion arises, to what extent inherit- ance may be from one parent or both or from grandparents and so on, with regard to parti- cular characters. As Weismann says : "Three principal kinds of combination have to be considered in any attempt to explain the blending of parental characters in the child. These are: (1) the characters of the child are intermediate between those of the parents ; (2) the child exclusively or principally resembles one parent ; and (3) the child resembles the father as regards some characters and the mother in respect of others." These kinds of inheritance have been termed respectively blended, exclusive, and particulate (151, p. 106). It is the third that bears upon the question of jaw-formation. The fact that a child often resembles one parent very markedly in certain characters, and the other parent in other characters, is familiar to every one ; it is necessary to consider whether this is true only on broad lines, or whether it may be fairly applied even to small details. One of the reasons sometimes given for the condition in which the jaws do not appear to be large enough to jDermit normal alignment and occlu- sion of the teeth, is that small jaws may be inherited from one parent and large teeth from the other. This argument is treated with scorn by several writers, but curiously enough neither the propounders nor opponents of the view give very adequate reasons for their belief. It is said by the latter that it would be as reasonable to expect a child to inherit a large hand from one parent and a small hand from the other. But as Weismann points out, in the bilaterally symmetrical human being paired organs are nearly always similar ; the 3* method of development makes this probable, and any argument drawn from observation of symmetrical parts and apphed to unpaired organs is fallacious. Even paired organs are not always alike. Weismann writes : " One brown and one blue eye sometimes occur in dogs, especially in boar-hounds, and I know of a similar instance in the human subject : the father, a brewer in a small suburban town, has blue eyes, and the mother brown eyes, while a daughter of twelve years of age has one blue and one brown one." As a matter of fact the particulate inheritance from the two parents extends to characters of almost minute detail. The jjoint is import- ant, and so well discussed by Weismann that the writer ventures to quote at some length — " A child may closely resemljle its mother as regards the arms and hands, and nevertheless may take after its father in respect of the legs and feet. The form of the skull may resemble that of the father and the face that of the mother ; or the form of the entire head and face may be like the mother, while the eyes may be similar to the father's in every detail. The son may, like his father, po.ssess a dimple on the chin, although he takes much more closely after his mother as regards the shape of the face and nose. That the combination of parental characteristics may even extend into far greater details is shown especially by the remarkable amalgamation of the mental qualities of the parents which often occurs. The intellect and practical talent may be inherited from the mother, and .strength of will and unselfishness from the father : and all these qualities may be contained in one skull, the form of which essentially resembles that of one of the parents only. " It must, of course, be admitted that there is a very close correlation in growth between the teeth and the jaws, which should tend to oblite- rate any want of adaptability derived from particulate inheritance ; but in view of the statement above, of which the truth may be substantiated by the careful observation of any one, it is obvious that the theory of the large teeth in the small jaw must not be con- temptuously swept aside without more cogent proof of it's absurdity. The writer does not, however, wish to suggest that it is at all a frequent phenomenon. It is probable that a more reasonable explanation of many cases is to be found in the view previously suggested of retrogression of the jaws, from imnmixia, more ra])icl than retrogression of the teeth ; and it is still more probable that in most cases the factor of lack of function and nutrition during growth is the most important of all. This will presently 74 be considered. J. Lowe Young (177) states that bony insufficiency, and consequent abnormality in position of individual deciduous teeth, are rare, and he deduces from this that inheritance plays a small jjart in the production of abnor- malities of the permanent dentition. The argument is, however, fallacious, as inherited characteristics often appear only at certain stages of development, and inherited reduction in the size of the jaws would not be expected to show itself in quite early years. [See J. E. Spiller (143).] It has been sometimes observed that certain some^^hat abnormal forms of jaw, such as an arch slightly contracted laterally, is transmitted through several generations, although only through one parent in each. Historical in- stances of this, sometimes cited (93) (151, p. 112) (169, p. 290), are the high forehead and widely separated eyes of the Caesars, the hooked nose of the Bourbons, and the inferior protrusion of the reigning dynasty of Spain. Such indi- vidual prepotency is a familiar phenomenon to breeders of stock, who have often found that certain individual animals have a remarkable power of transmitting their characteristics to a majority of their progeny. It is one that must distinctly be taken into account in considering the heredity of various jaw-forms. Explanations of diminished size of the jaw expressed in general terms, such as civilization, crossing of races, and sexual selection, are not of much value unless the exact method by which gradual changes may have been brought about are discussed. That the jaws are reduced in most civilized races is an undoubted fact, and the direct effect in each generation of modern environment and methods vaW presently be considered. But if the reduction has been gradual it is not necessary to have recourse to " use inheritance " for an explanation, or to try to show that civilized races have actually benefited in the struggle for life by a slight decrease. It should not be forgotten that in the processes of evolution progressiv'e atrophy plays a part almost as important as increase, in successive generations. There is competition between organs as well as between individuals and between species, and the balance between the nutrition of different organs may be con- ceived of as correlated with their degrees of usefulness, without implying the direct inherit- ance of small size from diminished use from one generation to the next. Sim Wallace (162, p. 159) refers to the fact that the American negro has in a few generations become more or less orthognathous, and considers that restora- tion to original surroundings would at once produce a new generation of the original form. However this may be, it is pretty clear that some blastogenic variation of a retrogressive kind I has taken place, because if the effect were the outcome of external influences acting de novo in each generation, there is no reason why it should not have been brought about in a single generation instead of a jew. The question of the influence of the crossing of races has already been referred to in connec- tion with " reversion ". There is, as Sim Wallace points out, no reason to think that the crossing of diverse types would result in reduced jaws, but rather the other way. On the other hand, a recently mixed race like that of the United States and, to a less extent, of Great Britain, may be expected to have blended less completely than an older race, and the various phenomena of " particulate " inlieritance from the two parents are likely to be more frequent and more pronounced. This question cannot be set aside by a general condemnation of the large teeth and small jaw theory. The question of sexual selection need not be more than referred to, for there is no evidence that imperfectly develoj)ed jaws in the "oval face", and abnormal alignment of teeth, are regarded by a majority as features of beauty. Talbot (148) (149) has investigated in remark- able detail the question of the relation between various forms of mental and physical degeneracy and abnormal or defective formation of the maxillae and other bones of the face. While it may be admitted that he gives a large number of cases that show some such deformities, it cannot be said that he has at all proved that such deformities as a laterally contracted arch, for instance, are really pathognomonic of con- stitutional degeneracy. It is not unnatural that defective development should manifest itself in the jaws as well as in other parts or organs of an individual of a degenerate type ; but in the opinion of the writer, Talbot, regard- ing such phenomena from an hereditary stand- point, gravely underestimates the effects of lack of function in mastication during growth, and pathological conditions such as adenoids, both presently to be considered. It is important to remember that defective bone-formation is not a disease, and considera- tion bearing upon the question of direct inherit- ance of predisposition to certain diseases, such as tuberculosis and cancer, do not apply. Furthermore, whatever may be the inherited variations in the direction of defect of any kind, it is, after all, the normal that constantly tends most strongly to be reproduced. This point is well brought out by J. Howell Evans (69, p. 98). In the course of the foregoing brief arguments the writings of Weismann have been frequently quoted, firstly, because, although his views have not been by any means accepted in their entirety, they have exercised a profound 75 influence on the trend of thought in biology, and secondly, because his main contentions have sometimes been misapplied in connection with the problem of abnormal jaw-formation and dental alignment. Environment. — Whatever may be the extent of the influence of heredity, there can be no doubt that the effect of environment, in its widest sense, during the growth of the individual is of vast imfiortance. The growth of the jaws is dependent, as other parts are, on general nutrition and con- stitutional conditions of vitality or depression, and it can hardly be expected that an ill- nourished child will have jaws anything like as '\\ell developed as they might have been under happier circumstances. When assimila- tion and metabolic activity are sub-normal the vital organs absorb most of the supplies, and the bones and other relatively less important connective tissues suffer. Whether the teeth share in this defect is uncertain ; temporary malnutrition associated with a period of acute iUness causes hypoplasia of enamel, but it is not very probable that normally formed teeth are developed on a reduced scale as the result of general malnutrition. In any case they are mostly calcified long before the completion of the period during which deficient nutrition in childhood occurs, and it is extremely likely that many children with normal teeth are stunted in growth, and have jaws not large enough to permit of normal alignment and occlusion. Those who beheve that correlative growth of the jaws will always bring this about, with or without the aid of mechanical means, are expecting too much from the jaws of a stunted child. But the local effect of lack of function is more important than the results of general mal- nutrition. Function stimulates growth ; this is particularly true of muscle, and also of bone, in so far as it is the means of muscular attach- ment. The length of a long bone will not be increased by excessive use, although it should be remarked that after such a disease as infantile paralysis normal length is not usually attained ; but the size, density, and form, of such bones as the maxilla and mandible vary according to the e.xtent to which they are used during the period of growth. The dependence of the structural formation of the inner as well as superficial parts of the mandible upon muscular tension has been demonstrated by Walkhoff (146). Sim Wallace points out that in such races as the negro and aboriginal Australian, not only are the jaws wide and well developed, but the malar bones are pronounced and broad, and in the latter race the squamous portion of the temporal bones is so much enlarged that it articulates with the frontal bone. In those races who use the jaws adequately the maxilla and arch of the teeth (and, of course, the mandible also) are usually brought more forward during development than in other races. The backward position of the arches in ortho- gnathous tyi^es has been w ell described by Cryer (58) (146). But it must not be supposed that prognathism is necessarily associated with function, for, as Harry Campbell (40) remarks, certain hill tribes of North-East India have jaws that are comparatively short antero- posteriorly. These quaHties are, of course, racial characteristics and are inherited (not necessarily as the cUrect result of use-modifica- tion), but it can hardly be doubted that jaws of diminished size in civilized man are frequently the chrect result of lack of function in childhood. The exact nature of the process is uncertain, but probably diminished vascularity and com- parative stagnation of lymph are chiefly respon- sible, and possibly want of stimulus of trophic nerves. The question is well discussed by Harry Campbell (40). Sim Wallace, who has given much attention to this subject, considers that the chief result of deficient mastication is imperfect dev^elopment of the tongue, and that the tongue is an important factor in ensuring normal develoj)ment and expansion of the jaws. Muscle tissue, it is true, probaljly responds to exercise to a greater extent than any other tissue, and there is much to be said for Sim WaOace's contention ; he has himself adduced many arguments in support of his theory, though it should be remarked that fibrous food requiring much mastication is not necessarily the kind of diet that gives most exercise to the tongue ; soft sticky foods like suet pudding require much activity on the part of the tongue. The facts, so far as they are at present known, hardly endorse the idea that the tongue is the aU-important factor; for the reasons already given, it is probable that the effect of the stress of mastication on the growth of the jaws themselves is very considerable. It is no uncommon experience to find that children from two to six years of age and later are fed almost entirely on soft foods, paps, and puddings, which discourage all use of the teeth, and un- fortunately this erroneous method of feeding is advocated in many otherwise excellent medical works. Such methods are productive of many evils, among which one of the chief is the prevalence of dental caries ; the subject is fully discussed in the chapter on its aetiology, and has been referred to in connection with the development of the jaws in the first section of this chapter, and need not therefore be more fully dealt with here. Pathological Influences. — In a subsequent chapter, the various types of abnormahty of position of the teeth associated with abnormal 76 development of bone will be described in detail. Many of these cases are associated with mouth- breathing, and it will be convenient to discuss briefly at this point the general effects of nasal obstruction on the growth of bone and the con- formation of the dental arches. The relation- ship between mouth-breathing and dental disease and deformity of the jaws was recognized many years ago, and a paper by Scanes Spicer (142) on the subject pubhshed in 1890 is well worth reading at the present day. Mouth- breathing is sometimes spoken of as a habit, but it is almost certain that the habit is in nearly every case a compulsory one, and arises from inability to inliale a sufficient quantity of air through the nasal passages on account of obstruction at one part or another. The most usual source of obstruction consists in hypertrophy of Luschka's tonsil situated in the naso-pharynx, commonly known as " adenoids ". This is usually associated with hypertrophy of the faucial tonsils, which, although not of itself likely to impede nasal breathing, probably assists in obliterating the pharyngeal air-way. Nasal obstruction may also be caused by devia- tion of the septum, but as simple deviation, while reducing the calibre of the passage on one side, must enlarge it on the other, it is probable that the defective development of bone asso- ciated with, or the cause of, deviation of the septum is the more important factor. Spurs or crests are sometimes found associated with a deflected septum. Chronic congestion of the mu- cous membrane of the inferior turbinate bones is sometimes given as a form of obstruction sufficient to induce habitual mouth-breathing, but according to Tilley (1.52) this condition is generally dependent on the presence of adenoids. The cause of adenoids does not properly come within the scope of this chapter, but it is generally believed that clamp, and chronic catarrh, are mainly responsible, and Tflley con- siders that improper feeding on soft food is also to Ijlame. Other writers, such as Marfan (114) and Korner (102), consider that rickets is the real cause and acts by inducing glandular hypertrophy and sclerosis of bone ; Marfan holds the opinion that the deformed upper arch frequently associated with adenoids is directly caused by rickets. The evidence is, however, not altogether satisfactory. Adenoids have been included among the many indications of degeneracy (100), but if this is an exi^lanation at all it is but a very vague one. Adenoids develop usually between the ages of about one and seven years ; at a later period, after several harmful consequences have accrued, they may become reduced in size, and may almost disappear about the time of puberty. The cardinal symptoms are open mouth during sleep, snormg, some degree of deafness, and a liability to repeated " colds ". In course of time a typical adenoid facies develops, with narrow- flattened nose, dropped chin, thickened everted lips, pallid complexion, and generally dull appearance (see Fig. 120). Other signs and symptoms belong to the more remote effects of adenoids on the growth of other parts of the body, such as a flattened chest and impaired nutrition (see Fig. 121). The view has been advanced by Sajous and elabor- ated by Parke Lewis (133). that nutrition is Fig. 12U. — Adenoid faeies. (Sir \V. AuiiUT.iNdT Lane : Trans. Odont. Soc.) controlled by the pituitary body, and that adenoids may obstruct the foramen lacerum medium, and so interfere with the nervous connection of this organ, which lies in close proximity. Other authorities claim that deficiency of thy- reoid secretion is responsible alike for the growth of adenoids and the softness and plasticity of bone, because the thyreoid glancl stimulates activity of w hite blood corpuscles and controls fixing of lime salts. W. R. H. RoUinson Wliitaker (171) supports this view, and Prof. Keith says : "I am sure there is a relation 77 more than a mechanical one between face development and adenoids, more likely through the pituitary body than through tiie thyreoid, but probably both." H. Ewan Waller (166) gives an excellent account of the physiology of the thyreoid secretion, especially in its rela- tion to dentistry. He believes that contracted arches are due to muscular action on bones ^ Fig. 121. — Adenoid thorax aji.l atinudr. (Sii! W. Arbuthnot L.\ne: Trans. Udont. .'^oc.) deficient in lime salts on account of thyreoid inactivity, and he thus eliminates nasal ob- struction as a causative factor. The causes of deflected septum have not been definitely established, but injury in early years is generally accepted as one of the most frequent, and Mosher (118) has propounded the view, also accepted by Pfaff (128), that the defect is commonly associated with irregularity in the period of eruption of the permanent central incisors. He has investigated the question with much care and in a large number of cases, and has studied in detail the form and growth of the pre-maxilla. His views are as foUoN^s : The pre-maxilla, in the course of development, should shrink in size and turn down ; failure to do so i^roduces the negro type of dentition, and this failure is caused by irregular eruption of the permanent incisors or by uijury. Delayed eruption of one incisor causes hypertrophy of the pre-maxillary wing above it ; this disturbs the retaining groove of tlie wmgs in wliich the tip of the vomer rests. The cartilaginous septum slips from its bed in the groove made by the two leaves of the vomer, and the groove spreads out, one side disappearing ; so that a spur is formed along its upper edge. The lower edge of the cartilage curls upward and outward and a compensating convexity occurs above the enlarged pre-maxillary \\ing and forms a short basal spur. Whatever may be the exact cause, the deviation of the septum does not usually develop till about seven years of age, at \^hich the central incisors erupt, and it may possibly be regarded as a direct consequence of nasal insufficiency due to adenoids, for if the vertical development of the air-passage with a high-arched palatal vault is sub-normal, the septum may be forced to adopt a sinuous form for want of accom- modation. The liarmful effects of nasal obstruction by adenoids or deflected septum vary considerably in individuals of dift'erent type. The size of the naso-pharynx exhibits a large range in different people (155, p. 337), and in the so- called leptoprosopic or narrow face obstruction is easily caused by a comparatively slight amount of adenoid hypertrophy, said to be more frequent in such people, or by a trivial deflection of the septum (49) ; whereas, m the opposite type of chamaeprosopic face adenoids of moderate size produce little ill-effect, and a deflected septum is of slight consequence (112) (128) (175). The narrow face occurs most frequently in doli- chocephalic people, so that the occurrence of mouth-breathing is to some extent a racial char- acteristic (84). It is rather curious that most of the gross forms of abnormal occlusion — superior and inferior protrusion and retrusion — may be associated with nasal obstruction and mouth- breathing, although it should be recognized, on the one hand, that these forms of mal- occlusion may occur independently of mouth - breathing, and on the other hand, that mouth- breathing is not al\\ ays follow ed by any obvious deformity of the maxilla or mandible or dental arches (175). The usual tyiae of maxUla in these cases shows a laterally contracted arch with high -vaulted palate and anterior teeth prominent and mclined forward; it does not 78 usually become evident tiU about six years of age (100). In some cases, the central incisors are rotated, so that the lingual surfaces approxi- mate, the laterals are rotated and displaced lingually, and the general form of the arch is V-shaped (see Fig. 122). In others the arch is more U-shaped, and the incisors, though pro- minent, are not rotated. In the V-shaped arch the want of space in the incisor and canine region is very apparent, the latter tooth often being incompletely erupted, whereas in the U-shaped arch there is often spacing, and the canine sliares to some extent in the prominence and obliquity Fio. 122. — Adenoid arches. The maxilla is very characteristic : note the V-shaped arch and the rotation and displacement of the incisors. (Norman G. Bennett.) of the incisors. Brady (35) draws a sharp distinction between these two forms, but it is doubtful whether this can be upheld. Turner (155, p. 337) appears to ascribe want of proper spacing of the deciduous teeth at about five years of age, and failure in vertical development of the anterior portions of the maxilla, leading later to "open bite", both to adenoids ; but in the opinion of the writer the former phenomenon, at lea.st, occurs quite frequently with normal breathing, and is refer- able to want of development from other causes. ThLs is discussed more fully later. It is a moot point whether the summit of the palatal vault is really higher than normal or not (130) (175), or whether it only appears to be so by reason of the buccal teeth and alveolus being more vertical than is normally the case, and more closely approximated ; but it is probable that owing to nasal insufficiency a proper downward growth of the palate ha.s not been mduced. Brady points out that protrusion is favoured by shortness of the upper lip occasioned by faulty nasal development, and Turner (155, p. 337) also emphasizes the influence of the length of the upper lip in determining whether the anterior teetli shall protrude or be deflected back- wards, and thereby augment irregularity in position of the buccal teeth. It is generally agreed that the form of the lower arch is not directly affected by adenoids, but Kohler (100) considers that the rate of alteration in the angle is diminished ; and in cases of post-normal occlusion of the lower teeth there must almost of necessity be a failure in backward growth, and probably a correlated change in the ascending ramus and articula- tion. Although the deformities of tlte dental arches associated with mouth-breathing are so generally recognized, there is a remarkable divergence of opinion as to the exact manner in which the changes are brought about. Perhaps the most commonly accepted view is that the open condition of mouth produces tension in the muscular tissue of the cheeks, and a slight approximation of the two sides, and that thereby pressure is brought to bear on the buccal surfaces of the upper arch. Distinction is drawn by different writers between tissue tension and muscle tension, the former being simply a passive stretching, and the latter involving the' active use of the muscles. Confirmation of the latter view is to be found.^ the description of a case by Lambert Lack^n wliich facial paralysis had occurred at two years of age ; as a result of adenoids, and mouth-breathing contraction of the arch occurred only on the healthy side. Kohler (100) attaches special importance to the action of the muscles in mastication. Asso- ciated with this increased pressure from with- out, there mu.st be a diminished pressure from within by the tongue; in normal nasal breathing, 79 with the mouth closed, the tongue is firmly pressed against the palate ; but even a slightly open mouth reduces this pressure or removes the tongue from the palate entirely (84) (112) (152) (155, p. 337). The influence of the normal tongue in expand- ing the arches finds some corroboration in the peculiar formation associated with hypertrophy of the tongue. In the case of cretins the tongue is usually much enlarged, and the dental arches are also large and widely spread. Increase m size of the tongue from other diseases, such as new growtlis, if of sufficient duration usually causes modification of the dental arches. The question of the relationship between diminished size of the tongue and contracted arches has already been referred to and A\ill be further considered. Other writers reject the cheek theory, and believe that the explanation is to be found in alterations in atmospheric pressure above and below the vault of the palate. This view finds different methods of expression by various authors, but the effects described are not very difl^erent. Mayo Collier (50) found, by intro- ducing a manometer into the nose, that the air-pressure was increased at each respiration, and he cites the experiments of Ziem on animals, in which blocking of one nostril caused defective development, not only of the maxilla on that side, but also of most of the other bones of the face and anterior part of the cranium. Sir W. Arbuthnot Lane (7) takes the same view, and further points out that the lack of intra- nasal pressure is antedated by a dimmished vital capacity of the lungs, whereby the effect is augmented. Metzger (178) has pomted out that the mouth can be kept closed for long periods without fatigue, but that the muscles soon tire if it is slightly open. He concludes that muscular equilibrium is not the sole means by which the mouth Ls kept easily closed, but that the mandible is really slung to the palate by suction, the tongue completely closing the oral cavity ; that is to say, atmospheric pressure from \sithout partly supports the mandible. Donders (178) corroborated this view by introducing a small manometer, and demonstrating the existence of a small suetion- ciiamber between the centre of the dorsum of the tongue and the junction of the hard and soft palates, and another anteriorly between the lower surface of the tongue and the floor of the mouth and lips ; the latter, he says, is only produced when the tongue is drawii backwards or downwards. It Ls clear that in mouth-breathuig the downward pull on the vault of the palate would be absent. This theory, briefly stated, sounds somewhat fan- tastic, but it is probable that something of the kind really exists, and may be an important factor in the downward growth of the palate. Donders well points out that a very powerful suction is recognized as retaining the head of the femur in the acetabulum of the hip-joint. Emil Herbst (89) has experimented on similar lines. He corroborates the findings of Metzger in the main, but disagrees with Donders in his dis- crimination between an anterior and a posterior space. He believes that the action of the tongue in producing them is supplemented by move- ment of the mandible. He goes so far as to ascribe the development of polypi of the gum or pulp, and lengthening of unopposed teeth, and enlargement of the maxillary sums under suni- lar conditions, to "suction"". Herbst"s paper contams references to most of the publications by German writers on this subject. Some writers (1) (84) content themselves with pointmg out that the palate fafls to develop and expand because the proper air-passages within are not used, on the general prmciple that function is necessary for growth. It may be that this is no real explanation at all, but although it offers no clue as to the exact mechanism, it emphasizes the important biological principle that deficiency is to be expected from disuse, and that it is not essential to seek explanation i in adventitious external forces. One other possible factor must be remembered. Under normal conditions the occlusion of the teeth probably affords considerable stimulus to growth, and tends to retain a proper degree of shallowness of the vault of the palate. When the mouth is kejrt constantly open, the upper buccal teeth tend to grow dowiiwards and inw-ards, and so produce depth of vault and parallelism of the sides of the arch (100) (175). The question arises, to what extent me- chanical expansion of the maxillary arch will affect parts other than the alveolus, and bring about a widening of the nasal passages. In the case of patients whose adenoids have not been removed, but have become reduced in size in course of years, the more recently formed portions of the arch are more nearly of the normal width — the second permanent molars erupt in a wider arch than that of the other buccal teeth. It is obvious, therefore, that removal of adenoids is imperatively required at an early age to allow of subsequent develop- ment proceeding on normal lines ; to what extent improvement takes place in the parts already formed is not certain, but probably it is very little in the absence of mechanical treatment. According to Turner (155, p. 337) the power of increase of size in the anterior portion of the arch is lost after about twelve years of age. It must be remembered that after removal of adenoids the acquired habit of mouth - , breathing is sometimes retained, and further- 80 more that want of development of the nasal passages, with or without deviation of the septum, may be such as to offer very little inducement for normal breathing. In these Fig. 123. — Characteristic deciduous children. Left, child aged 4i aged 5 years. (G. Noethcroft ; Dental Review.) ai-clu'S in bottle-fed years ; right, cliild Dental Record : from eases there is very little doubt that mechanical expansion widens the nasal air-way ; accord- mg to Pfaff (128) there is actually a lowering of the vault of the palate if the operation is conducted suflficiently slo\\ly, but Feder.spiel (73) in a recent article denies this. Mosher ( HB) and Black (27) affirm the efficacy of such means for the treatment of deflected septum. In an interesting article, C. A. Hawley (86) illustrates cases to show that there is, as a rule, little or no natural expansion of the arch after removal of adenoids, but that artificial ex- pansion produces a profound effect on the general development of the face. The question of «hat really happens under mechanical treatment for maxillary expansion — whether the alveolus only is bent outwards (or absorbed and redeposited), or whether there is actually separation follo\\ed by deposit at the median suture — i.s discussed under '■ Physiology of Tooth Movement " ; but if, as seems often to be the case, nasal inefficiency is remedied, the latter process must apparently occur, and it is probable that the effect produced depends largely on the method employed. The effects of artificial feeding of infants on jaw-formation has been much discussed. It has been pointed out that the ordinary rubl)er teat dift'ers so much from the natural organ that unnatural methods of taking in the milk are engendered in the infant. In natural feeding the whole of the nipple and part of the breast are firmly grasped by the infant, and the milk is mainly obtained by alternate acts of com- pression and release, in a manner analogous to that adopted in cow-milking ; it is said that suction plays little or no part in the process. The rubber teat, on the other hand, is smaller and much less solid and more compressible, and the infant has to a great extent to suck the milk out of the bottle ; in this ■\\'ay the cheek muscles are brought into play and pressure is broutrht to bear on the maxilla. It is urged that lateral compression and anterior prolongation are induced in this manner, and that the effect is exhibited ev^en in the permanent dentition. G. Northcroft (122), who has studied with much care the development of the jaws in early years, finds a remarkable similarity in the type of deciduous arch (with in-standing laterals and centrals in malalignment) in many bottle- fed children (see Figs. 123. 124). f. Pedley (127) is a strong advocate for thi.s view, and Colyer (55) has published diagrams showing the association of abnormal forms of palate with bottle-feeding. The cases cited by Pedley are, however, exceptional, inasmuch as artificial feeding with the rubber teat was continued for prolonged periods up to two and three years of age. In the ordinary course bottle-feeding is, or should be, abated con- siderably at nine to twelve months and aban- doned altogether as soon after as possible. Fig. 124. — The same in occlusion. Upper figure corresponds with the left-hand figure of 123; lower figure with right-hand figure. Note the occlusion — normal in the upper figure, post- normal in the lower. (CJ. Northcroft : Dental Record ; from Dental Review.) Harm jirobably results when artificial adminis- tration of milk is badly managed and unduly prolonged, especially if imperfect apparatus is employed ; much importance attaches to the size of the orifice in the teat, and the regula- 81 tion of the flow by providing for ingress of air at the opposite end of tiie bottle. If these are so adjusted that the infant takes its meal in about the same time, twenty minutes, as it would in a natural way, the risks are minimized. Within recent years rubber teats liave been introduced to resemble the human breast. In the opinion of the writer the evils of artificial feeding have been greatly exagger- ated, and he believes that if proper care is taken no evil effects on maxillary development need accrue. McKenzie (112) (113) is of opinion that the more gross deformities of the maxillae cannot be produced in this way. The constant u.se of the " baby comforter", whether solid or perforated, is quite a different matter. This is used for an unnatural purpose for prolonged periods, and should be con- demned ; the desire for it by the infant is very much a matter of habit, and acquiescence by the mother or nurse is an indication of lazi- ness. Its only merit is that it jjractically com- pels nasal breathing, which, however, is not an acquired art, but a natural instinct on the part of a healthy infant free from malformation and disease. J. F. CoJyer is of opinion that serious defects of development are to be ascribed to the use of the '■ baby comforter ". He considers that the arches are flattened, and that the upper arch is drawn forward, and that the type of superior protrusion described on p. 128 [Class III (2) (c)] is so produced. Colyer includes in this class many of the cases described as Inferior Retru- sion by the writer. Injuries, such as fracture of the bones, or cicatrices from burns, will of course produce abnormalities in the position of the teeth. J. F. Colyer has described t«o marked examples of post-normal mandible that he considers were due to injury at birth during prolonged face presentation {Dental Record, Feb. 1914, p. 100). One other jJathological condition must be mentioned. Cryer (60) believes that excessive calcification of bone occurs sometimes in patients of a gouty or rheumatic diathesis, and that under certain condition.s this may cause the contained teeth to adopt abnormal posi- tions, or may prevent normal eruption. In another paper Cryer (61) discusses some other minor pathological causes. CHAPTER V ABNORMALITIES OF POSITION (continued) Part III Classification of Abnormalities, Consideration of the Different Types, their Causation, and the Principles of their Treatment Classification of abnormalities may be based on a consideration of the tooth or teeth affected, and the bones involved, and the nature of the deviation from the normal — that is to say, on pathology — or on the aetiology of the various conditions. Great difficulties at once present themselves in either case ; the diversity among abnormalities is considerable, and the nature of them is as a rule very complex, only a small number consisting of a simple deviation arismg from a direct and obvious cause, so that even though well -recognized type-forms only are selected, it is difficult to classify them on any useful basis by which the relation of one form to another may be shown, and it is still more difficult to relegate the more complex forms, exhibiting a combination of different kinds of abnormality, to their appointed place. Of the simple forms the immediate cause is usually recognized and known, but as regards the more complex forms, especially those clearly involving some error of bony development, causation is for the most part imperfectly unr^rurtood ; the immediate origin of some of them I'ect be fairly obvious, but the real first origo ; is far to seek. On the one hand, the saic^pensin cause operating in different individuals^y exporoduce quite different results, probably >it out«unt of differences in the adventitious or «libuting causes ; and on the other hand, •! biases that appear to be identical or nearly so'; may be and often are due to quite different causes, and are indeed inherently and pathologically different, and require treatment on different principles. For example the kinds of deformity that used to be known generally as superior protrusion are now more fully understood, and it has become clear that at least four types totally different in their aetiology and pathology were included under that title ; in the classification shortly to be outlined these types will be dis- tinguished from one another. It is probable ., that in tlie development of the lower part of ^Ahe face, the nasal cavities, the jaws and teeth, hiore complex and subtle changes occur in j Towth from infancy to adolescence than in any other part of the body ; and furthermore these changes or their results are often the vehicle of hereditary transmission as to form and structure, and are very markedly the play- thing of influences of environment, such as diet. It is therefore not to be wondered at that when so many possibilities of error in development exist, diversity of form should be so great, and that whereas hi the normal process so many influences contribute to a perfect result, a small deviation in one particular may throw the whole sequence out of gear and originate a deformity of a magnitude out of all proportion to the original cause. It may be said, then, that the processes of growth and development of the teeth and the associated parts are subject to much variation, and are particularly susceptible to external stimulus in the form of modified function of the mouth and nose, and that they are intimately connected with, and mutually dependent upon, one another. Defects in the process lead to such diversified forms of abnor- mal development that not only is it difficult to trace the exact causes, but even the precise diagnosis of the exact conditions is in many cases far from easy. Study of the aetiology and pathology is, how- ever, only useful in so far as it indicates rational lines for preventive and remedial treatment. Surgical or mechanical interference depends for its success on a knowledge of causation, and until investigation has provided a more perfect equipment of that kind treatment must remain largely empirical. Ingenuity of con- trivance cannot compensate for lack of know- ledge, and to this fact must be attributed the» want of uniformity of success with different cases, even in the hands of the most skilful operators. It should be recognized that the liability l'"^ a deformity that has apparently been fulP^^wrected to recur, even after time has been allowed for deposit of new bone around the ro i|r of translated teeth, depends upon one of t j' things : either the correction is apparent rather than real and is incomplete in itself, or the causes that produced the deformity continue to operate. Such causes may or may not be remediable, but further acquisition of knowledge will certainly show what are the possibUities of permanent improvement, and also establish the principles of prevention and early treatment. 82 / 83 On these grounds it has seemed best to attempt ] of individual teeth, whether of one or more, to classify abnormalities of position primarily in which the cause of the displacement acts on an aetiological basis into three classes, and directly, or nearly directly, on the teeth them- then to discuss the several forms occurring ! selves, and any bony abnormality that there under these heads, and to define the pathological condition, and the immediate and remote may be is secondary : in the second and third classes, on tlie other hand, the imme- causes, and the consequent principles of treat- i diate cause of dental malposition is defective ment, as far as the present state of knowledge | bony development, wliich is itself the outcome permits. It may at once be said that the first j of more remote causes, whether genetic or class is mainly concerned with malposition | environmental. CLASSIFICATION I. — Abnormal position of one or more teeth due to local causes. (1) Retained deciduous teeth. (2) Teeth of abnormal form. (3) Supernumeraries. (4) Absent teeth. (5) Abnormal fraenum labii. (G) Position of crypt, and total displacement. (7) Thumb or finger sucking — Superior proclination. Inferior retroclination. Open bite. (8) Premature loss of deciduous or permanent teeth. Deciduous incLsors. Deciduous canines. First deciduous molars. Second deciduous molars — forward translation or inclination of first permanent molars. Buccal or lingual inclination of canines. Buccal or lingual inclination of premolars. Rotation of upper incisors. Imbrication of lower incisors. First permanent molars. Close bite and secondary superior proclination, or secondary inferior retro- clination. Backward translation or inclination of premolars. Deviation of centre. Other permanent teeth. II. — Abnormal formation of a part or the whole of either arch due to developmental defects of bone. (1) Conditions first showing themselves while deciduous molars are still in place. Rotation or postplacement of upper incisors. Imbrication or " fanning "' of lower mcLsors. (2) Conditions arising or further developing after loss of deciduous molars. Buccal or lingual inclination of canines. Buccal or lingual inclination of premolars. Accentuation of rotation of upper incisors, or of imbrication of lower incisors. (Lingual incHnation of posterior teeth.) III. — ^Abnormal relationship between the upper and lower arches, and between either arch and the facial contour, and correlated abnormal formation of either arch, due to developmental defects of bone. (1) Vertical. (o) Open bite. (6) Close bite. Secondary superior proclination. 84 (2) Antero-posterior (pre-normal or post-normal occlusion of upper or lower arch). (a) Normal or sub-normal. (b) Inferior retrusion. Inferior retrognathism. Secondary superior proclination. Secondary superior retroclination. (c) Superior protrusion. Superior dental preplacement or proclination. Superior prognathism. ((/) Inferior protrusion. Inferior prognathism. (e) Superior retrusion. Superior retrognathism. (/) Double protrusion. Superior and inferior dental preplacement or proclination. Superior and inferior prognathism. (g) Double retrusion. Superior and inferior dental postplacement or retroclination. Superior and inferior retrognathism. (3) Lateral. Labial or lingual occlusion of upper or lower posterior teeth on one side or both. CLASS I. — Abnormal Position of One or More Teeth due to Local Causes 1. Retained Deciduous Teeth. — In some cases the absorption of the roots and the shedding of the crowns of the deciduous teeth are delayed beyond the normal periods, possibly because of the tardy development of the permanent suc- cessors. If, however, the process of shedding, even though delayed, follows an orderly course, no irregularity of the kind under consideration is likely to ensue. It is where single teeth are retained tliat tlie ultimate position of the per- FiG. 125. — Retained right deciduou.s central, inierupted permanent central, rotated permanent lateral, and flattened arch.' (Norman G. Bennett.) nianent successor is affected, and the offending tooth or root is nearly always one in which death of the pulp has supervened on caries or injury. The normal process of absorption is interfered with, if not inhibited, under these circumstances, and even a single root of a molar will retain its hold sometimes for a con- siderable time. Less frequently, the absorption of the roots of a deciduous tooth is imperfect ^ A radiograph has shown the presence of an un- erupted snpernnmerarj- tooth impeding the eruption of the permanent central incisor. because of a slight deviation from the normal in the Ime of eruption, or the position of the crypt, of the succeeding permanent tooth ; in such cases only the portion of the root or roots directly impinged upon will be absorbed by the intervening osteoclasts. The commonest example of this is .seen in the upper molars, where a somewhat widely divergent palatine root may be only hollowed out on its buccal aspect and serve to retain the crown in position. It is remarkable to what extent a tooth may be deflected from its course during eruption by a small piece of loose root, the direction of the deflection being usually, but not always, determined by the normal j)ositioii of the crypts and line of approach. For example, the upper incisors erupt on the buccal aspect and the lower on the lingual ; ia the case of an upper tooth the evil may be increased by interposition of the lower lip. If the deciduous tooth is shed or removed sufficiently soon, before the adjacent permanent teeth are fully erupted, natural forces, namely the pressure of the lips and tongue, will probably correct the , but if it is retained beyond that period, the adjacent teeth will move into contact with the relatively small deciduous tooth and encroach on the space that should have been filled by the permanent successor, and thereby prevent correction by natural force. An upper tooth outside the lower lip or in lingual occlusion with the lower, and a lower tooth in labial or buccal occlusion, will not be corrected naturallv (155, p. 337). (See Figs. 125, 126, 127, 128, 201.) Treatment in either event consists in removal of the offending tooth or root, and if necessarj' deformity 85 n the restoration of space by correcting the position of the adjacent teeth, and the transla- tion of the misplaced tooth. Treatment should be undertaken at once, because the tooth is more easily moved while the root is incomplete, and consequent misplacement of other teeth is avoided. Retention for two or three months is usually sufficient. It should be remem- bered, however, that delayed sheddini; of a sound deciduous tooth is prima facie evidence of possible abnormality in the jjosition of the erupting successor. In some cases [see I (6)] this abnormality is of such a character that eruption in a normal direction is impossible even with artificial assist- the best indication as to the correct treatment to be pursued. Fig. 121). — Retained deciduous canines, left per- manent canine lingual to arch. (Norman G. Bennett.) Fig. 127. — Retained left Imver deciduous canine, permanent canine distal to it. (Ger.\ld H.\rborovv.) ance, and the deciduous tooth if allowed to remain will retain its place with the permanent teeth for many years. A radiograph affords Flu. 12S. — Retained crown of first left lower deciduous molar, premolar displaced buccally and in buccal occlusion with iijjper premolar. (Norm,\n G. Bennett.) In cases where a retained deciduous tooth has prevented the eruption of its successor, rather than deflected the latter from its course, «hile the adjacent teeth have encroached on the normal space, the permanent tooth may, after the loss of the deciduous tooth, And its way into normal alignment, but with some degree of axial rotation. That is to say. the tooth becomes turned so that a smaller diameter may intervene bet\\een the adjacent teeth in the restricted sjmce. This may occur with incisors or canines. Treatment should be undertaken at once, the space restored, and the abnormality corrected . 2. Teeth of Abnormal Form. — An abnor- mally shaped tooth may give rise to deformity in various ways. If it is of excessive size it may fail to erupt com- pletely or in normal alignment, or if it does completely erupt may usurp an undue amount of simce. If, on the other hand, it is small, it will permit movement of the adjacent teeth and interfere with perfect occlusion, and possibly cause lateral deviation of the central incisors from the median plane. 86 Treatment. — In the case of slight abnormality the tooth should be brought into position. Fig. 129. — Displacement, of left upper central incisor by supernumerary. (Norm.^n G. Bennett.) When the crown of the tooth is grossly mal- formed, but the root (as sho\ni by a radiograph) is normal or nearly normal, the tooth .should be brought into position, and after a period of quiescence an arti- ficial crown should be fixed. When both crown and root are grossly malformed the tooth should be extracted, and the space allowed to close or an artificial substi- tute (fixed or removable) inserted. 3. Supernumeraries. Supernumerary or supple- mental teeth (see Chapter III) sometimes erupt ex- ternal or internal to the arch, and sometimes in alignment with the other teeth in the arch. In the former case extraction is, of course, the only treatment required. In the latter case one or more of the other teeth must have been displaced ; they may be in normal alignment, but rotated or separated by the intrusive tooth, or be alto- gether prevented from taking their place in the arch. Supernumerary teeth most frequently occur in the upper incisor region, and probably the commonest site is be- tween the central incisors (see Figs. 129, 130). Treatment. — Supernume- rary and supplemental teeth should be extracted, and in some cases natural forces will I)rin2 the other teeth into correct position ; in other cases these must be corrected l)y artificial means. Doubt \\ill sometimes arise in diagnosing between a supernumerary tooth and a lateral incisor, but a radiograph w ill usually solve the difficulty. 4. Absent Teeth. — Absence of teeth, such as the lateral incisors or the premolars, usually induces dimimition of the size of the arch and abnormality of occlusion (see Figs. 131. 132, 133, 134). Treatment is not usually desirable or bene- ficial beyond such correction of occlusion as may be possible. Some writers recommend that the space proper to the absent tooth be preserved or restored, and an artificial sub- stitute inserted. In the case of the lateral incisors the deformity is not usually sufficiently serious, or the effect on occlusion great enough to justify this course. 5. Abnormal Fraenum Labii. — The fraenum of the upper lip is usually attached to, and blends with, the gum on the labial side of the teeth. Fig. 130. — Displacement of left upper central and lateral incisors, two unerupted supernumeraries behind centrals. (Harold Chapman.) but in a few cases it passes between the central incisors and blends w ith the gum of the palate. The necessary result is separation, usually accompanied with slight rotation of the central incisors (see Fig. 135). Treatment. — It is some- times recommended that the portion of the fraenum pass- ing between the teeth should be excised, but it is usually sufficient to divide it. A very narrow scalpel should be used, and it is essential that the division should be complete between the two teeth and carried down to the alveolus ; some operators use the electro-cautery either instead of, or in addition to, the scalpel. The movement of the lip will generally pre- vent reunion. When the be corrected before the eruption of the laterals ; and in all cases treated late mechanical assistance is also necessary. The writer has experience Flu. 131. — Absence of lateral incisors, retained decidu- ous canines, lingual displacement of right permanent canine. (N. H. Ketti.kwell.) Fig. 132. — Absence of left lateral incisor, lingual displacement of permanent canine, forward move- ment of posterior teeth. (G. Northcroft.) separation is slight, and the fraenum is divided before the eruption of the canmes, mechanical treatment is usually unnecessary, because the erupting canuies force the incisors together ; but if the separation is wide the teeth should tin. 133. — Retained deciduous canines, absence of right permanent lateral incisor. Left-liand figure shows right deciduous lateral still in position ; right-liand figure shows a later condition with permanent canine erupting against central. {G. Northcroft.) of a case in which, after thorough division of the fraenum, wide separation of the central incisors was reduced by natural means before the eruption of the canines, \\hich, however, were partially impacted. G. Northcroft (123), in a recent article, de- scribes an operation m which he dissects away the fraenum, and fixes, by means of bands on the central incisors, a horseshoe-shajjed w ire convex upwards and not quite touching the gum, to keep the lip away and prevent reunion. 6. Position of Crypt and Total Displacement. Teeth occasionally erupt in positions quite remote from their normal situation and in an abnormal direction. This happens most fre- quently in the case of the upper canine, which may appear in a nearly horizontal direction high up on the buccal side of the arch, or in the palate. A central incisor may be similarly misplaced, and when it appears in the palate may be rotated through a quarter of a circle about its ape.v. The probable cause is some congenital aberration of the crypt, or of the direction of the axis of the crown in the crypt. An extreme degree of this condition may prevent the tooth erupting at all, even in cases where there is no marked encroachment by the other teeth on the space that it should occupy, at any rate until a period considerably later than that of its normal eruption. This occurs most often in the case of one or both upper canines (see Figs. 136, 137, 138, 139). ^ It may be objected that the cause of this form of abnormality is not strictly a local one, but rather developmental. However, the effects are local ; and the origin, although ob.scure, is not connected with gross defects of growth of bone, such as wiU be considered in Classes II and III. 1 Excellent examples, including premolars and molars, of abnormalities of this class, in dried speci- mens, are illustrated by J. F. Colyer (Dental Record, Feb. 1914, p. 87). 88 Treatment. — The question of treatment for all these gross abnormalities is difficult. A radio- graph should always be taken, in order to ascertain the character and direction of the root. If this is not curved or bent or dilacerated, a partially erupted tooth may by mechanical Fig. 134. — Absence of riglit lateral incisor, small size and abnormal form of left lateral, separation of centrals due to suj^erfluous space. (S. Merkill Weeks : Dental Cosmos.) means be moved to its normal position, after space has been made for it when this has been encroached upon. In other cases, where the tooth is grossly misplaced or malformed, extrac- tion is the only treatment possible. In the case of an unerupted tooth, the possibilities of bringing it into position depend chiefly upon the direction of the axis of the tooth. If space is obtained by movement of the adjacent teeth, or in the case of a canine by the extraction of a first premolar, which is sometimes justifiable, the tooth may be induced to erujit by the temporary use of a denture, but it is wise not to extract another tooth unless there is every probability of ultimate eruption of the aberrant tooth . Success has followed the operation of cutting clown uijon a misplaced canine, fixing into it an iridio-plati- num pin, and applying a rubber ligature. 7. The habit of thumb, fmger, toe, lip, or tongue sucking is very common in infancy or early childhood, but is usually abandoned before any harm results to the teeth or jaws. The thumb and finger are by far the most frecpient agents, and the kind of deformity produced depends uf)on the manner in which one or other of these is used. In the case of the thumb, the crowns of the upper central incisors are pushed forwards, and to a less degree those of the lower incisors backwards (see Fig. 140). If tlie extended fingers are used in a similar manner w ith the extremities pushed up against the palate, a greater amount of space is taken up and marked proclination of all the upper incisors will result ; the condition may be exaggerated by the intrusion of the lower lip. This deformity may be seen sometimes with the deciduous teeth (see Fig. 226), but the cases that usually come under notice are those of deformity of the permanent teeth when the habit has been long continued. It is possible that the deformity may occur as the result of earlier finger-sucking, even though the habit has been aban- doned before the eruption of the permanent teeth, o\\'ing to displace- ment of the deciduous teeth and the alveolus and the crypts of the per- manent teeth. A similar deformity is produced by lip-sucking. It is important to distinguish this condition from other cases of real and apparent protrusion due to other more remote and deep-seated causes to be described later. There is not usually any abnormality of position or occlusion of the other teeth, but Guilford (82) and Colyer have pointed out that by means of the separation of the jaws and the muscular action of the cheeks in pro- ducing suction, a lingual inclination of the premolars and molars is sometimes l^roduced. The condition is a purely local one due to a local cause, and is not associ- ated with any errors in bony development of the body or ramus of the mandible, or contrac- tion of the maxilla. Fig. 135. — Separation of upper central incisors by abnormal traenum labii. (H.\rolu C'H.iPMAN.) If the fingers are inserted horizontally or hooked over the lower teeth, a quite different deformity will result. The upper incisors, and possiUy canines, will be forced upwards and slightly forwards, and the lowers downwards and forwards, so that a species of open bite is 89 produced. Here again the condition must be Treatment. — The treatment of these conditions carefully distinguished from the cases of open is easy; the habit must be cured by moral or bite associated with errors of occlusion and bony ' mechanical means, and the teeth reduced to development. Fig. l',m. — Left upjjer central incisor erupting tlirough lip in patient aged ',i6. For some years previously a hard swelling had been noticeable in the region where this tooth subsequently presented. About three years ago the patient received a blow on the face, which was followed by considerable inflammation and swelling, and the tooth shortly afterwards appeared through the lip and gradually came lower to its present position (January 1912). On examination inside the mouth there seemed no indication that the tooth had ever erupted high up in the sulcus. (G. G. Campion.) In both these deformities the condition is plainly due to an evenly distributed pressure, and can generally be easily diagnosed from cases Fig. 137. — Transposition of left canine and first premolar (G. NORTHCKOFT.) of misplacement caused by other local influences. An interesting case of buccal occlusion of the right lo«er premolars and molars caused by tongue-sucking is recorded by J. H. Badcock {11M14). 1 their normal position. Retention will only be necessary for a short period, when the cause has been removed. 8. Premature Loss of Deciduous or Permanent Teeth. — The premature loss of deciduous teeth is a frecjuent cau.se of misplacement of the permanent teeth. It may happen that in a particular case other causes leading to diminu- tion of the size of the arch or alteration in its shape may contribute to tlie same result ; but in the study of abnormal positions of the teeth, consideration of the effects of definite causes is more instructive than the description of a series of cases more or less alike but associated with entirely different aetiological factors, \\^len the effects of definite causes are clearly understood, it liecomes not very diiWcult to picture the beginnings of more complex forms. For the jiurpose of this group, tlien, it will be assumed that bony development is normal or nearly so, and that the character of the dental arch is normal, except in so far as loss of teeth may have caused contraction. Deciduous Incisors. — The premature loss of deciduous incLsors does not generally conduce to any very great deformity. It is probable 90 that tlie consequent loss of function may to some extent inliibit the growth of bone in the pre-maxilla and anterior portion of tlie mandible, but definite information on this point is wanting. Fig. ]:JS. — Prominence on right side in.li.at.s an uncTupted permanent tooth grossly misplared. (G. NOHTHCROFT.) It has l)een pointed out by G. Northcroft (119) (120), however, that premature eruption of the permanent incisors before the first permanent molars are fully erupted and in occlusion is a source of serious abnormality, and this premature eruption is probably encour- aged, if not directly brought about, by premature loss of tlie deciduous incisors". Deciduous Canines.— It does not often happen that the deciduous canines are lost prematurely unless they are extracted; but, in the case of the mandible especially, these teeth are sometimes removed to make room for the lateral incisors. It ynl\ often be found that when the growth of the jaw has not kept pace with the eruption of the anterior teeth— a question that will he considered more fully later — the lower lateral incisors erupt "lingually and slightly overlap the permanent centrals and deciduous canines, because the space formerly occupied by the deciduous laterals is not sufficient for their accommodation (see Figs. 141, 142). The extraction of the deciduous canines is not usually correct or justifiable, except where the subsequent removal of the erupted or unerupted first premolars is contemplated — a question that will also be discussed later. The proper treatment is to advance the centrals, which are really posterior to their normal position, and move the canines in an antero-buccal direction, and then reduce the laterals to their correct places ; in this way the growth of bone will be stimulated, and the upper incisors will not be allowed to fall back to the position of the lower. A similar condition does not so often arise in the ujjper jaw; the laterals usually find their way into position, perhaps somewhat rotated. The effect of extraction of the deciduous canines is twofold. The lateral incisors encroach on the space that ought to be occupied later by the permanent canines, and the deciduous molars (or the premolars at a later stage) move forward under the influence of the pressure of the re- cently erupted first permanent molars and the developing bone in their vicinity and the soft parts behind them. The latter result is par- ticularly likely to happen ui the mandible. When it is remembered that the deciduous canine is considerably smaller than the per- manent canine, and that in the normal course space for the latter is only obtained by the buccal translation and spacing of the anterior deciduous teeth and the buccal movement of the deciduous molars, it will become obvious that the almost certain result of further dimi- nution of sjjace will be buccal eruption of the permanent canines. Treatment. — The correct treatment of the ultimate condition depends upon whether the reduction of space has been caused mainly by the anterior or the posterior teeth, or, in other words, whether the incisors are placed too far Fig. 139. — Kailm^raph of case shown in Fig. 138. lingually or not. In the former case, the correct course to pursue is to expand the anterior por- tion of one or both arches, as may be required. In the latter case, and Avith normal occlusion of the posterior teeth, a premolar on each side of both jaws should be removed. As a general 91 rule, the first premolars should be chosen j The ideal treatment, recommended by some because mechanical treatment is tlien usually unnecessary; but if the amount of space required is small, say less than half the width operators, would be to move back all the posterior teetli. t)ut when all the evils attendant upon extensive tooth-movements are considered, the advantages do not seem sufficient to justify the treatment. Ho\\ ever, if adopted early, before the eruption of the premolars, backward movement of the first permanent molars may be under- taken. The question of extraction of upper laterals, or of a lower central, does not usually arise in the case of deformity due to pre- mature loss of deciduous canines ; it wiU be discussed m connection with defective development of the anterior portion of the mouth. First Deciduous Molars. — The premature loss of these teeth, unless very early, does not usually Fig. 140. — Proclination of upper incisors and retro- clination of lower incisors due to thumb-sucking. (.J. E. Spiller.) Fig. 142. — Lateral deviation of lower incisors duo to premature loss of right deciduous canine. (G. NORTHCROFT.) of a premolar, or if tlie second premolars are lead to much deformity. If a single molar is carious, then those teetli should be preferred , lost the occlusion of the remaining teeth is for extraction, liecause tlie first premolars can i generally sufficient to prevent forward move- ment of the posterior teetli, and even ^\here upper and lower on one side are lost, the for\\ard movement is often but slight ; the first premolars generally erupt prematurely in such cases and fill tlie sjiace, even as early as the eighth year. Turner (155, ]). 193) states that if a first upper deciduous molar is lost at about seven years, the arcli tends to become flat and to carry the lower with it, and tliat tliere will thus be insufficient space for the permanent teeth, so Fig. 141.— Rotation and postplacement of upper lateral incisors and that the canme or a premolar cannot buccal displacement of canines, due to deficient anterior develop- reach proper alignment, and even the ment and probably premature loss of deciduous canines. (Norm.\n incisoi'S may be pushed in a lingual ^""""~" ' direction. But, as he also remarks, G. Bennett.) easily be moved backwards to allow the canines to erupt into normal alicnment, and the re- mainder of the space gained will be closed naturally by forward movement of the molars. a well-formed lower deciduous arch and the inter-digitation of cusps may be enough to prevent this, and it is probable that in most instances such is the case. 92 Second Deciduous Molars. — The premature loss of tlie second deciduous molars is a frequent cause of misplacement of the permanent teeth ; the loss of upper and lower on one side before the second premolars are ready to erupt removes Fig. 143. — Forward jiim\ im.iil "f lirsl upper per- manent molar duo to preniatiiro loss of second deciduous molar ; early treatment. Lower figure shows results of treatment. (G. Northcrofx : Trans. B.S.S.O. ; Dental Record.) every obstacle to a for\\'ard movement of the first permanent molars. It should not be imagined that there is in these teeth any in- herent power of translation ; they simply move in the direction in which they are pushed, or in which resistance is least or absent. About this period the growth of bone around the erupting or recently erupted first permanent molars and about the angle of the mandible and posterior border of the maxilla is very consider- able. It is probable that the developing second permanent molars still enclosed in their crypts afford a stimulus to this backward growth of both jaws. The jjurpose of this growth is clearly to afford room for these first and second molars, and it would seem that a deposit of bone around teeth ^^ould not produce any force likely to propel them in any direction. How- ever, the eruption of these molars at different periods takes place in a confined space ; in the mandible this is most marked, and the tooth is pushed through between the ascending ramus behind and the tooth in front ; in the maxilla the tooth develops high up near the pterygo- maxillary fissure and travels down\\'ards and rotates forwards in consequence of the growth and expansion of the maxillary sinus (95). (See p. 30.) Whatever may be the actual force that causes teeth to erupt, it is obvious that it must be considerable to overcome the resistance encountered, and in the case of the first lower permanent molar, if the second deciduous molar has been lost, the confined space is relieved in that direction, and the elastic resistance of the soft tissues behmd will suffice to push the erupting tooth forward. The slight back- ward curve of most lo^er molar roots (especially the third molars) is evidence of a forward movement durmg normal eruption. J. F. Colyer (53) considers that forward movement of the first permanent molars " occurs mainly in mouths where the growth of jaws is inter- fered with by want of function, either due to insufficient mastication or lack of nasal breathing." He is inclined to think that if, by removal of the deciduous molars, tlie perma- nent molars are rendered functional. " the growth of the jaw wUl be stimulated and room made for the development of the second and third molars, with no forward pressure from those teeth, and, with the first molars occluding correctly, there will be little, if any, forward movement." For the rea.sons given, however, and from clinical experience, the writer does not think this view can be maintained. In the case of the upper molar the reasons for forward movement are not cjuite so clear, but in the normal process there is, as has been explained, a downward and forward ^■ispace ■ 7?t J^i^^^^^^^^B H- ^^^^^^^^^1 ^B^^tTTT " . i\ nonn.ll ^ ^^H ^V>M ^^B Fici. 144. — Similar to 143. (G. Northcroft : Trans. B.S.S.O. ; Dental Record.) movement, which brings the tooth into close apposition with the tooth anterior to it, and if the latter is absent it is not remarkable that the forward movement should be ex- cessive. Exact measurements have not yet been made to show how far the upper first 93 permanent molar moves forward in the normal process of eruption and afterwards. It has been pomted out that its relationship to the malar process does not afford sufficient evidence, because this portion of bone is itself added to posteriorly and absorbed anteriorly during the process of growth. Edward H. Angle (4) has shown that variability in position of the first upper molar is much less extensive than in the case of the lower. He correlates .such variability as does occur with variation of type in different races and different hidi- viduals, and even goes so far as to say that when an upper molar moves forward in consequence of loss of the second deciduous molar, such movement is even hardly greater than would have occurred naturally a few years later. Angle is probably correct in regarding the first upper permanent molar as a tooth that varies but little in position, but clinical experience hardly supports his extreme contention. L. S. Lourie (108) shows convincing examples of considerable forward movement of first upper molars following loss of deciduous teeth. See also E. A. Bogue (32) (34). The natural occlusion of the first permanent molars, ichen they are fully erupted, usually prevents a forward movement of one tooth only. molar occludes with it and is thereby locked. The loss of the lower deciduous tooth is there- fore relatively less important, and it may be said that the second upper deciduous molar is the most important tooth of its set in relation Fig. 145. — Flattening of arch, backward movement of left lower canine and first premolar, and lingual displacement of second prenaolar, due to premature loss of second deciduous molar. (The permanent molar appears to have moved forwards, but this is not so ; the occlusion was normal.) (J. G. Turner: Brit. Dent. Jour.) If the second U2:)per deciduous molar alone has been lost there may be some forward movement of the first upper molar, but it is jjrobable that the retention of the second upper deciduous molar only is sufficient as a mle to prevent forw-ard movement of either permanent tooth, for the reason that the first lower permanent Fig. 146. — Flattening of arch and impaction of second right premolar (indicated by small triangle) due to premature loss of second deciduous molar. (B. Frank Gr.\y : Dental Cosmos.) to the permanent dentition. Its premature loss is more conducive of evil than that of any other deciduous tooth (see Figs. 143, 144). The effects of this forward movement of the first permanent molars in both upper and lower jaws, where the arches are of normal size and shape, Ls obviously to reduce the space available for the premolars and canhies ; there may also be, as J. G. Turner (155, p. 241) has shown by excellent illustrations (see Fig. 145), a flattening of the arch due to backward and lingual movement of the first deciduous molars and teeth anterior to them (see Fig. 146). The actual de- formity produced depends upon two factors namely, the amount of movement and the order of eruption, and possibly also on the density of the bone around the roots of the anterior teeth. If the forward movement has been considerable, the last tooth to erupt will be prevented from coming into alignment. This may be either the second premolar or the canine ; in the former case lingual deviation is the most frequent, and in the latter buccal eruption (see Figs. 110, 147, 148, 149). In an early stage of eruption of the upper canhies, pressure on the roots of the lateral incisors may cause rotation, and proclination of the crowns ; the un- erupted lower canine may conduce to a fan-shaped disposition of the lo«er uicisors by pressure on the roots. It should be remem- bered, however, that the second deciduous molar is larger than the second premolar. It is possible that this little extra space may be made use of for the benefit of the permanent canine, which is considerably larger than its predecessor ; it is more probable, however, 94 that the space required by the eanme is normally found by its translation into a larger arcli tlian that occupied primarily by the Fig. 14"- — Buccal displacement of right canine due to premature loss of deciduous molars and forward movement of first permanent molar. (.J. E. Spiller.) deciduous teeth, and that the little extra space provided by the large second deciduous molar affords some latitude for \\ hat should properly be the last of these teeth to erupt, namely, the second pre- molar, and that it is closed by a slight forward movement of the molar. The character of the abnormality produced, of course, varies greatly with other con- tributory causes, beyond the actual amount of space avail- able, and may be to some extent corrected or increased by the occlusal relations with the oppos- ing teeth that become established. Where the forward movement of the molars has been slight, the subsequently erupting teeth are not prevented from coming into alignment, but only impeded in their progress ; that is to say, the force producing eruption has more to contend with than usual, but may be sufficient to push aside the obstructing teeth. When the second premolar erupts after the canine, the result may be only a slight abnormality of occlusal relationship, or a slight pressure brought to bear on the front teeth. It is, however, where the canine erupts last that any effects on the front teeth may more often be noticed. Such results may be, in the maxUla, a slight rotation of the lateral incLsors and lapping of them over the centrals, a slight rotation of the centrals, or a slight proclination of the incisors generally, and they are more likely to occur when there is some slight tendency to these forms of deformity. It is very doubtful whether any marked degree of proclination or other deformity is ever pro- duced by the erupting canines when the incisor teeth are firmly implanted in a normal manner ; it is probable that the typical V-shaped arch is never produced in this way. In the case of the mandible the only result likely to happen is an exaggeration of any slight degree of imbrication or " fanning " of the incisors already present. Treatment. — Treatment, in the case of slight forward movement and slight deformity, should consist in backward movement of the molars and correction of any misplaced teeth. It is not, however, wise to adopt this method where the movement has been at all considerable, or after the eruption of the second permanent molars. Extraction is then the best remedy, for expansion is inadmissible in an arch of normal character and size, and extensive back- ward movement does not offer advantages commensurate with the extent and difficulties of the proce.ss. Cryer (60) considers that successful backward movement of a first lower Fig [ormal occlusion of upper molars and preinolars and buc- cal displacement of canines, due to forward movement of molars. (J. E. Spiller.) ntolar half its width after eruption of the second molars is impossible. The selection of the particular tooth, or teeth, to be extracted depends upon varying circumstances, such as the character of the deformity, and condition 95 as to caries ; and it is impossible to lay down definite rules. It may be said that the molars should be preserved unless carious to an extent that renders permanent filling impossible ; that for deformities produced by the process inider discussion extraction of the laterals is scarcely ever justifiable ; and that an aberrant premolar and the corresponding tooth in the opposite jaw, or a pair of premolars (right and left) to make room for canmes, are the teeth usually to be chosen. It is generally best to extract symmetrically on both sides of the mouth ; otherw ise a deviation of the central incisors to one side of tiie median line w ill almost certainly follow. Some amount of such deviation is usually associated with buccal eruption of one upper canme, and will be increased by extraction on one side only. Fig. 149. — Lingual disijhiceinent of second left upper premolar, due to forward movement of first molar. (J. E. Spiller.) In the mandible, the extraction of a single incisor (central for choice) may be good treat- ment, when there is some degree of imbrication or " fanning ", to make room for a canine. The most misplaced tooth should not necessarily be selected, but preference should be given to a tooth labially misplaced rather than lingually, as the latter is more likely to be reduced by natural forces. Mechanical treatment is not often required, but any tooth locked by false occlusion will always need correction, and some application of artificial force may be necessary in other cases. Premature Loss of Most or All of the Deciduous Teeth. — The elTects of extraction of most or all of the deciduous teeth (including second molars) before the age of six is not definitely known. It is almost certain that there is a forward transla- tion of the first permanent molars in course of eruption, but ^^•hether there is any tendency to prevent these teeth eruj)ting to their full extent, and thereby cause an undue approximation of the jaws and secondary proclination of the upper mcisors, is not known. It is at least probable that the growth of bone of the jaws depends upon the presence and function of the deciduous teeth, as well as upon the stimulus of the development of their successors, and it is unlikely that such a gross interference with natural routine can be unproductive of harmful results. It should, however, be clearly under- stood that such treatment may be imperatively demanded on grounds of hygiene exceeding in importance the risk of deformities to follow; although it may be borne in mind that where some teeth can be preserved the second molars and the canines are the most valuable. The method has been largely practised by J. F. Colyer at the Royal Dental Hospital of London in the case of children \xith septic mouths. He has kept careful records and seen many of the patients years after, and does not believe that deficiency of bony growth necessarily follows (53) (54). First Permanent 3Iolars.— The ill effects of loss of one or more first permanent molars depend upon the age at which they are removed. They are m themselves by far the most useful masticating teeth in the mouth, and should receive careful and frequent attention from the time of their eruption. But the j^resent discus- sion is concerned chiefly ^\ith the effects of their loss on the shape of the arch and the position of the other teeth ; the artificially created space influences development anteriorly and posteriorly in different ways. Early Loss. — It will be well first to consider the evils arising from extraction prior to the full eruption of the premolars. The loss of both upper teeth, or both lowers, or all four, \\ill throw the force of mastication entirely on the deciduous molars if these are still in ijlace, or in their absence on the anterior teeth. In the former case, if the transition from the deciduous to the permanent dentition proceeds normally, the first premolars will erupt and occlude before the second deciduous molars are shed, but there is great probability that during this process the forces of masti- cation will be thrown at one time or another on the incisor teeth. It is in fact one of the chief functions of the first permanent molars to take up the forces of mastication during a variable period between the eighth and the twelfth years, while the premolarsand canines are taking their places in the arch ; that is to say, in the orderly but delicate process of transition, their duty is, as it were, to hold the fort while the reserves are being mobilized. The effect of mastication on the incisor teeth is a proclination of the uppers and to a less extent a retroclination of the lowers, associated with undue approximation of the jaws. This altered relationship of the jaws is, as it were, accejjted by the subsequently eruptmg teeth, 96 which do not erupt to their normal extent ; and the deformity is thus perpetuated. The kind of protrusion produced is as a rule not only different m origin, but also in character, from those forms to be described later whose causa- tion is more recondite, and it differs in important respects from that caused by thumb and finger Flo. 150. — Pronouncod overbite of incisors due to loss of first permanent molars. (E. E. Hall : Items of Interest.) sucking. The ends of the roots are unaffected, but the teeth are inclined forwards and some- what separated ; in other words, they are not translated forwards but spread. The lower teeth occlude with the cmgula high up, or with the gum behind the cingula (see Figs. 211, 212). The appearance of the teeth of each jaw considered separately may be similar to that produced by thumb or finger sucking, but in the undue approximation of the jaws the condition resembles those forms to be considered later that are associated with, if not caused by, abnormal bony development. In other cases excessive overbite occurs with- out proclination (see Fig. 150). \\^iere all four molars have been lost, there will probably be later on some movement back- wards and spacing of the premolars ; in some cases this is caused by the interaction of the inclined planes of the coronal surfaces, but in others " travelling " of the premolars occurs while they are still unerupted (see Figs. 151, 152). The greater part of the space, however, will be taken up by the second permanent molars, which do not usually become tilted when the first per- manent molars are lost so early. There will also probably be some lateral contraction of the arches, as J. G. Turner (155, p. 241) has demonstrated by illustrative models, but this does not necessarily follow, and the factor that perhaps determines the result is the size and development of the tongue. In those cases where the upper teeth only, or the lower only, are lost, the opposing second molars usually move forward nearly completely (one unit) during eruption, so as almost exactly to take up the positions of the lost teeth. Where a pair of teeth on one side of the mouth only are lost, the resultant deformities will be limited to the effects on the premolars of that side, together with a slight lateral deviation of the incisors. Treatment. — The treatment of the type of protrusion described above consists m raising the bite sufficiently to allow of the upper in- cisors being drawn back and the lowers drawn forward into normal occlusion, and in retaining the teeth in their positions until the complete eruption and normal occlusion of the premolars. There is, as a rule, no great difficulty in this because the undue approximation of the jaws is not due to abnormal jaw formation. If the premolars have moved back, they must be brought forward and retained until the second permanent molars have come into contact with them, and into normal occlusion witli their opponents. Where there is contraction of the arch or arches, in spite of the loss of teeth expansion must be resorted to, normal position and occlusion of the premolars restored, and the teeth retained until complete eruption and forward movement of the second permanent molars has taken place. Excellent results ensue from tliis treatment. Deformities limited to one side require similar treatment as regards the premolars. Fig. 151. — Backward movement of premolars on both sides, due to early loss of first permanent molars. Early erup- tion of third molars. (J. F. Govv.) Late Loss. — Loss of all' four first permanent molars after the complete eruption of the jyremolars has no effect on the incisor teeth. The effect on the premolars and second permanent molars depends very definitely on the age at which the extraction has taken place. If the latter teeth are already erupted or just about to erupt, there will be a subsequent forward movement and forward tilting of the lower molars, and some backward 97 movement of the premolars. If, on the other hand, the loss lias occurred before about the eleventh year, then tlie molars will come forward with little or no tilting, but more time will have been given for the backward movement of the premolars (see Figs. 153, 154). J. G. Turner (154) states that in the maxilla the second molar moves forward very readily, but that in the mandible movement is chiefly confined to the premolars, which travel back- wards (155, p. 241). No doubt this is true of many cases, but it is difficult to see how, with the inter-digitation of cusps in a normal occlu- sion, the lower premolars can move backwards unless the upper do likewise. The state of eruption of the premolars at the time of extrac- tion of the molars is probably a determining factor. Treatment. — Treatment consists in correction of the premolars, and drawing forward the second permanent molars when necessary. Loss of One Molar on Either Side. — When only a single molar on either side has been lost, movement of the premolars is prevented, except to a very slight extent. If the first lower molar has been lost and the second per- manent molar is already erupted or nearly so, the second lower permanent molar will be locked by occlusion, and become tilted, so that nearly all the space remains (.see Fig. 122). tilting, and the second premolar backwards. The occlusion is, of course, very imperfect. An earlier loss of one first molar permits almost complete forward movement of the Fig. 153. — Good dccIush.h first permanent molars. Cosmos.) after extraction of foiir (Matthew Ckyer : Dental Fig. 152.- -Radiograph of case shown in Fig. 151, taken before the second right molar was removed. In the case of the loss of the first upper molar the evil is not quite so great, as the locking is less complete, and the second upper molar usually moves forward to some extent without second molar with little or no tilting (see Fig. 155). Treatment. — Treatment after eruption of the second molars should usually consist in extrac- tion of the opposing fir.st molar, especially when this is the upper. The second molars will then move for- ward together and tilting of the lower be largely pre- vented ; if this has already taken place it can be remedied to a great extent by force acting in a forward direction and applied as near the roots as possible. After the tooth is in contact with the second premolar this will have the effect of drawing the roots forward. Importance of First Perma- nent Molars. — It is clear that the effects of loss of the first permanent molars are varied and extensive, and, as has been stated, their treatment and preservation from the time of eruption is of cardinal importance. It may be said that the worst results follo«' very early loss and the next worst happen with late loss, the least evil result- ing from extraction during an intermediate period (about the tenth and eleventh years). The various ill effects caused by unjustifiable 98 extraction are well shown by E. Forberg (77) in an excellent series of models, and the question Fig. 154. — Good occlusion after extraction of four first permanent molars when cusps of second molars first appeared. (Matthew C'ryer : Dental Cosmos.) is well discussed and illustrated by A. C. Lockett (107), who sums up the ill results of injudicious extraction as follows — (1) Complete rum of a perfect masticating surface. (2) Movement of pre- molars and second molars. (3) Tilting of second molars. (4) Straightening of the curve of occlusion. (5) Spacing. ((5) Elongation of unop- posed teeth. (7) Overwork of anterior teeth. AU of these ills occur at one time or another in differ- ent cases, but, as has been shown above, the particular effect depends very mucli upon concomitant condi- tions, of which one of tlie most important is the date of extraction (or period of complete destruction by caries). Unfortunately it often happens that when a case comes under ol)servation one (or more) of these teeth is beyond preservation. It is important to remember that according to the princi{)les discus.sed it may be necessary sometimes to extract all four, and in other cases the uppers or lowers only. It is often possible to preserve them temporarily so as to extract at the most javourahle moment. When a pair of molars on one side only are removed, movement of premolars and deviation of anterior teeth must be prevented until complete eruption of the second permanent molars, as already described. Other Permanent Teeth. — The effect of the loss of other permanent teeth is usually limited to the adjacent teeth. In the case of a central incisor it is sometimes recommended to allow the space to close, or to close it by mechanical means, but the result is very imperfect and ugly. On the whole it would appear to be better to preserve tlie space and supply the tooth by means of a small bridge or dummy tooth attached to the adjacent central. Loss of a lateral is less obvious and may in some cases be left untreated ; but where there is any dis- placement of the other lateral, and it appears that the spaces can be closed without unduly diminishing the size of the arch, it is better to extract that also. Loss of a canine is verv Fig. 155. — Normal occlusion on right side. Good forward movement of second lower molar on left side, some backward movement of premolars ; fair occlusion after removal of first molar at about eight years of age. (Norman G. Bennett.) rare. Early loss of a premolar allows move- ment of the adjacent teeth and entirely prevents 99 normal occlusion being established (see Fig. 156). Late loss affects the occlusion of the adopt positions which are consistent with their eruption in an arch smaller than that for which their size adapts them ; that is to say, they must exhibit some form of individual rotation or over- FiG. 15(i. — Forward movement of first loft upper molar due to loss of second premolar. (H.\ROLn Ch.\pman.) adjacent teeth to some extent ; it is sometimes well to extract the opposing tooth, and prevent deviation of the incisors pending for- ward movement of the posterior teeth. In other cases a dummy tooth may be carried on an adjacent tooth by means of a C'armichael or staple ci'own ; or it may be left untreated. Loss of a second permanent molar before the eruption of the third molars is usually followed by complete for- ward movement of the third molars into the space ; loss after eruption of the third molars causes tilting in a manner similar to that already dis- cussed in connection with the first and second molars. Fig. 157. — Rotation of i-mlral and lateral incisors due to deficient anterior development (aged nine). (N'orm.\n G. Bennett.) lapping. Perhaps the most usual type shows a rotation forwards of the medial surfaces of the central incisors (see Figs. 157, 158, 193). In that case the laterals may find room to Fia. 158. — Rotation of upper central and lateral incisors and dis- placement of left lower canine, due to deficient anterior development. (Harold Chapman.) _^ CLASS II.— Abnormal Formation of a Part or the Whole of either Arch due to Developmental Defects of Bone The development of the jaws in con- nection with the eruption of the teeth, the causes of imperfect bony develop- ment, and the parts of the jaws likely to be affected, have been already described. It is clear that the effects of this imper- fect development upon the positions of the permanent teeth must be profound, and it will be convenient to consider them under two aL'e-L'Voujjs. 1. Conditions first showing themselves while the deciduous molars are still in place. In the ]irc-Hiaxilla the |icrrnaiieHt mci.sors usually erupt on the lal)ial side of the arch of their deciduous predeces- sors ; if. therefore, insufhcient space has been erupt in normal relation with the centrals, though really placed lingually to their proper position. This condition is the commence- ment of the typical laterally contracted or V-shaped arch, as will be seen shortly. The Fig 159. — Rotation of upp.!- lateral iiu-isors and indirication of lo%ver incisors, duo to dolioiont anterior dovolopmont. (Norman G. Bennett.) crowns of the teeth are anterior to the apices provided for thek accommodation, they must | to an abnormal extent and give the appearance 100 of protrusion. It should be understood, how- ever, that the apices of the teeth are really more misplaced than the crowns ; the con- rotation, so that the lingual surface of the lateral overlies the labial surface of the central (see Figs. 159, 160, 161). In such cases there may be sliglit rotation of the cen- trals in either direction, with approximation of their labial or Ungual surfaces (see Figs. 162,163). In the former vari- ety, wlien the rotation of the centrals is at all considerable, the laterals are often placed on a posterior plane, so that the lingual surface of each central overlies the labial surface of the adjacent laterals. In other cases the laterals are on a plane anterior to the centrals, and have their distal surfaces rotated forwards (see Fig. 164). When the degree of lingual malposition (postplacement) is extreme, all four incisors may occlude behind the lower incisors. It is probable that this is most likely to occur when the deciduous upper incisors and canines are all lost prematurely, so that in the limited space afforded by im- perfect bony development, the incisors are able to encroach freely on the portion proper Fig. 100. — Rotation of upper lateral inci-sors and Ungual displacement of to the permanent Canines, and lower lateral incisors, due to deficient anterior development. (Haroi.d are not forced to take up a V- CHAPM-iN. ) shaped alignment or to overlap dition is one of proclination, rather than of! one another (see Figs. 165, 166, 167, 168, 169). undue advancement of the whole tooth. ' Of course modifications of these conditions In other cases the central incisors take up arise, but most cases approach more or less Fig. 161. — Typical case of rotation of lateral incisors and overlapping of centrals by laterals, due to slightly deficient anterior development in other- wise well-formed arch. (Harold Chapman.) a nearly normal position relatively to one another, but are really placed too far lingually and encroach on the space for the laterals. When these erupt the crowns wiU be deflected forwards and there will be a certain amount of Fig. 162. — " Reverse " rotation of central incisors due to deficient anterior development. (Norman G. Bennett. ) closely to these type forms. The position finally taken up by the upper incisors is, of course, partly controlled by the development of the mandible and the position of the lower incisors. 101 In tlie mandible the conditions of develop- ment are different. The permanent teeth erupt usually on the lingual aspect of the deciduous arch, and are translated forwards (probably by the action of the tongue). If the growth of bone has pro- vided insufftcient space for the centrals, and the de- ciduous laterals are still in position, this forward move- ment will be prevented (see Fig. 170). The laterals will then probably erupt later labially to the centrals and will overlap them. If, on the other hand, the centrals are able to move forward, lap and override the deciduous canines, but the apices remaui in the contracted space occasioned by insufficient bony development and the typical Fig. 103. — Slight •■ reverse " rotation of central incisors. (Harold Chapman.) on account of loss of the deciduous laterals, as often happens, then they take up a nearly normal ])osition. except that they may be Fig. 1(J4. — Postplacemcnt of the upper central incisors and all lower incisors and slight " reverse " rotation of upper laterals, due to deficient anterior develop- ment. (G. NORTHCROFT.) placed somewhat too far lingually and their apices are too close together. The crowns of the laterals as they erupt will then be forced lingually (see Figs. 176, 223) ; or they may over- FlG. J 65. — Slight postplacement of upper central incisors (normal occlusion of molars). (Harold Chapman.) fan-shaped condition is produced. It should be noted that this fan-shaped arrangement does not at all necessarily involve any excessive degree of eruption and occlusion behind the cingula of the uppers, which is a distinct phenomenon. A some- what similar appearance is occasionally seen in the upper incisors. The ulti- mate position of both iipjjer and lower teeth is influenced by the oc- clusion, and the abnor- malities in each jaw react on the position of the teeth in the other. It may be said that in the mandible rotation is far less frequently adopted by the erupting teeth under the pressure of external forces than in the pre-maxilla, because in the lower incisors the labio-lingual diameter more nearly approaches the medio-distalthan in 102 the upper. The shape of the lower incisors favours overlapping of two or more teeth sufficient to remedy the cause of the evU, and it is of prime importance that growth of bone should be stimulated by attention to general health, physical exercises, and rational methods of feed- ing. In the cases of lingual malocclusion of the four upper incisors, premolar and molar occlusion bemg normal, a forward move- ment of the roots will not usually be necessary if the position of the crowns has been corrected at a fairly early age — before twelve according to Case ; when necessary it may perhaps best be accomplished by means of the contouring apparatus of Case, to be referred to again subse- quently. Some authors (52, p. 81) (54) recommend tliat iii cases of this kind the anterior teeth should not be translated labially but only corrected as regards their alignment, and that ^ in order to prevent the Fig. 166.— Postplacement of upper incisors (lingual occlusion), and secondary subsequent development inferior protrusion. For details of treatment of this case and figure showing O'- ^"^ kmd 01 aunormall- results see p. 244; Figs. 374, 375, 376, 377. (Norman G. Bennett.) ties shortly to be described, (imbrication), and more or less complete labial or luigual displacement, or spreading of the crowns and overlapping of the deciduous canines by the permanent laterals (see Figs. 171, 159. 160). ^ Treatment. — The treatment of these conditions should be commenced at once. The crowns of the misplaced teeth should be reduced by mechanical means to their proper positions, so that sufficient space will be provided for the eventual eruption of the permanent canines. The effect of this movement of the crowns will be to produce an appearance of protrusion, really proclination (especially of the upper teeth), because the roots remain in an abnorm- ally lingual position. If, however, development proceeds subsequently on normal lines this error wiU to a large extent be corrected by growth, which may be supplemented bj' mechanical means. But it should be under- stood that mechanical treatment is not alone ' J. F. Colyer has illustrated excellent examples of dried specimens showing, as the result of defective bony growth, abnormal positions of the teeth in their crypts, (-u_ f„„„ „„„„... i j i i ii i such as would naturally develop into the forms of Y"^ /°?'' unerupted premolars should be ex- abnormalitydescribed above (Zienta/ i?e,corrf, Feb. 1914, tracted. It LS possible that in Some CaseS P- 112). where there is disproportion between the size 103 of the teeth and the individual physique, or , an age. If extraction proves necessary later, where it is improbable that later physical i the results need not be inferior to those pro- development will compensate for early mal- j duced by extraction of the unerupted premolars, nutrition, this method may be the correct 2. Conditions arising or further developing after loss of the deciduous molars. It is obvious that if the space proper to the permanent canine has been encroached upon by the iiicisors, and if the deciduous canine has not been translated forwards and outwards by interstitial bony growth, the space necessary for the teeth intervening between the in- cisors and first molars wUl be insufficient. Therefore, deformities similar in appearance to tliose pro- duced by premature loss of the deciduous molars and forward translation of the permanent molars will be produced. It is impor- FlG. 168. — Postplacement of upper incisors, unerupted canines, normal occlusion of molars, lingual occlusion of second upper premolars. (Norman G. Bennett.) Fig. 170. — Lingual displacement of right central incisor, deciduous laterals still in position, due to deficient anterior development. (J. H. Badtock.) Portrait of case shown in Fiji one to pursue ; but in the opinion of the ^^•riter sucli cases are not very frequent, and at all events considerable judgement is necessary on the part of the operator to determine the pro- bable course of future development at so early Fig. 171. — Imbrication of lower incisors, lingual displacement of left lateral, right lateral over- lapping deciduous canine, due to deficient anterior development. (Norman G. Bennett.) tant, however, to bear in mind the cardinal diSer- ences between apparently similar cases, and to distinguish between the abnormality of position of a canine or premolar that is, on the one hand, due to posterior encroachment, and on the 104 other liand, to anterior encroachment caused by imperfect bony development. The two are fundamentally different, and the treatment is also different in principle and detail.^ Fig. 172. — Buccal cli.splaceineiit of upper canines due to deficient anterior development. (H.^rold Chapm.4N.) The first premolar is not usually much mis- placed, because sufficient space is retained for it by its equally large deciduous predecessor, but it is probable that the transverse dimension between the two first premolars is less than normal, and the arch somewhat contracted in the premolar region. The tooth most frequently afl^ected must obviously be the canine, which, in such cases, in the maxilla usually erupts high up on the buccal side of the alveolus (less often lingually), and never attains proper alignment with the other teeth, although the conditions may im- prove in tlie natural course of growth (.see Figs. 172, 173, 174, 175, 141); in "the mandible it may also erupt on tjie buccal or Imgual aspect, more frequently the former (see Fig. 158). ^ It should be pointed out, however, that a form of posterior encroachment due to deficient development may occiu". If backward growth of the maxilla is deficient, the erupting first permanent molar may cause absorption of the distal surface of the second deciduous molar, and eventually take up a position too far forward and reduce the space available for the premolars. Such deficiency of growth is usually correlated with deficient anterior development and malalignment of the incisors already described. It should be remembered that the apparently erring tooth is often really le.ss out of position than its neighbours. The order of eruption has less influence on the character of the deform- ity than in the cases pre- viously described as being due to forward translation of molars. If the second premolars erupt before the canine the malposition of the canine will the more certainly be produced. If the canine erupts first the deformity produced will de- pend to some extent on the amount of space available for it. Where this is quite insufficient the effect will be as just described, but \\here the encroachment has been but small, the force of eruption of the canine may be sufficient to move the adjacent teeth. In tliis way, by a slight backward movement of the first premolar, the second premolar may be prevented from coming into normal alignment and normal occlu- sion with its opponent, and nnist erupt on the Fig. 173. — Buccal displacomenl of right canine due to deficient anterior development. {Norman G. Bennett.) buccal or lingual aspect, more usually the latter. Malposition of a premolar from this cause is, however, probably far less common than the same abnormality associated with forward translation of molars (see Fig. 176). The teeth more frequently influenced by the 105 enipting canine are the incisors. In the case of the upper teeth tlie two typical conditions previously described, namely, rotated centrals, or rotated laterals overlapping the centrals, are often accentuated. But it is very doubt- ful whether a typical laterally contracted or V- shaped arch is ever produced at this period unless there has previously been a small defor- mity of the kind (see Figs. 177, 178, 179). The question of the relative influences of inheritance and environment in contributing to this and other conditions has already been discussed, and although it seems clear that the active causes are largely dependent on conditions of environment in each generation, it is never- theless probable tliat inherited genetic varia- tions form an important factor, and at the least j)redispose the individual to the influence of such external agencies. It will be unclerstood that the displacement of the canine is chiefly towards the median line (although the tooth shows a buccal inclination), so tliat the distance between the two canines is diminished ; the premolars are not greatly affected, except that they come into line between the canine and first molar, and thus in extreme cases the arcli of the teeth from the central the incisors will usually be increased by the erup- tion of the canine, and narrowness of the anterior Fig. 174. — Postplacement and rotation of upper incisors due to very deficient anterior development. Post-normal occlusion of lower molars and mandible, probably secondary to maxillary development. (Norman G. Bennett.) mcisors to the second molars is reduced very nearly to a straight line. In a similar manner in the case of the lower teeth, imbrication of 4* Portrait of case shown in Fig. portion of the lower jaw produced in this way is often associated with a contracted upper arch ; a fan-sliaf)ed condition of the lower incisors may be somewhat accentuated by the same cause. The deformities described may be connected with (or in the later stages of their develop- ment be increased by) obstruc- tion to nasal breathing from adenoids, or other nasal diseases or deformity ; but it is probable that such cases are almost always associated with abnor- mal occlusion and relationship of the two jaws, and constitute the various forms of protrusion and retrusion to be presently considered. The typical V- shaped arch, so-called, is not necessarily or usually associated with malocclusion of the molars and premolars. There remain to be con- sidered those cases m which the anterior teeth are normally, or nearly normally, arranged, but in which the laosterior teeth are lingually inclined, and the upper arch exhibits a U -shape «ith the sides nearly parallel, and the lower shows a corre- sponding deformity. It is pro- bable that defective bony development is not as a rule the cause of the evil. Although there is a transverse narrowness of the arch, the reduction lOG is rather of the distance between the crowns than the roots, and differs in this respect from the contracted palate associated with nasal stenosis, in which tlie vault is both high and narrow. It is possible that the prime cause is smaU- ness and imperfect development of the tongue, which allows the nniscles of the cheek to force the crowns of the teeth towards the median line during eruption. Fio. 17G. — Lingual dis|jlacement of upper second premolars and lingual displace- ment of lower lateral incisors, due to deficient development. (G. Northcroft.) Treatment. — The treatment of cases of this large class is difficult, and requires careful consideration of the causes that have been, and are, operative. It should be remembered that the defect is anterior to the first molars and theoretically the correct treatment is to expand the anterior portion of the arch or arches and reduce each tooth to correct alignment and occlusion. In simple cases this should obviously be undertaken ; but in cases where, for example, the canines are almost com- pletely excluded from the arch, and where the bony development in the incisor region is deficient in rela- tion to the teeth, but not markedly so m relation to the facial contour, so that the incisors although really placed too far lingually do not appear so (by reason of their proclination), treat- ment by expansion on ideal lines may result in a pro- gnathous appearance, be- cause the roots of the incisors must be translated labiaUy as well as the crowns. Cases of this kind not infrequently present themselves in ill- nourished children, in whom there is but little hope of subsequent development making up the arrears of stagnation, and providing the child with face and jaws in harmony with the teeth, which are of a normal size and have calcified too early to have been subject to the same depressing influence. It then becomes necessary to extract, and the general rule may be laid down that the canines should scarcely ever, if ever, be removed ; that the laterals should be removed only m a small minor- ity of instances ; that the first premolars should usually be selected ; and that extraction should Ije symmetrical. In deciding between the laterals and the first premolars in tlie case of outstanding canines, attention should be given to the direc- tion and incluiation of the canines, because movement of the crowns is compara- tively easy, and of the roots exceedmgly difficult. Where only a small additional space is required the second pre- molars should be selected in J (reference to the first ; the first premolars can easily Ix- moved back sufficiently to allow the canines to reach normal alignment. In those cases in which the aberrant tooth (or teeth) is a second premolar, it should usually be preferred to the first. It has been pointed out that cases of this class are not necessarily associated with abnormal occlusion of tlie molars and pre- molars, and it is for this reason that extraction should usually be symmetrical ; but if the lower teeth are in post-normal occlusion with the upper, and the lower incisors are imbricated, it is often good treatment to remove two upper -Proclination upper incisors increased by eruption of canines. (O. Northcroft.) first premolars and a lower incisor, not neces- sarily selecting the one most misplaced, but preferring an incisor misplaced labially to one misplaced lingually, because the latter is more easily reduced by nature and art. In some cases where extraction is rightly practised, natural forces will in due time correct the deformity, but in the greater number mechanical assistance should be pro- vided. In all cases the operator should have 107 regard to the state of the teeth in respect to caries, and select carious teeth for extraction whenever other considerations permit. It may sometimes be advisable not to extract opposing teeth but to choose, for example, a first pre- molar in one jaw and a second ua the other, and move the teeth into occlusion mechanically ; or in other cases to extract two first premolars on one side and two second premolars on the other. Cases frequently occur in which, if all the teeth were sound, the first premolars would be Fig. its. Fig. 179. Fig. 178 from casts at 10 to 11 years of age ; Fig. 179 at 13 to 14 years of age. Note the change in the form of the arches produced by pressiu'e diu'ing the eruption of the canines and second premolars. In Fig. 178 the left upper lateral is in lingual occlusion. In Fig. 179 the left upper premolars are in lingual occlusion, and also the first molar, which was normal before. The arch has become narrowed ^'/j of an inch. (F. A. Gocgh : Dental Cosmos.) chosen for extraction, but in which some or all of the first molars are extensively carious or even abscessed. The only treatment then possible is to extract the molars and move back the premolars, but a certam amount of backA\ard inclination of the premolars usually remains, and is difficult to remedy. It is clear tliat where so many factors requu'e consideration, nice judgement is needful in determining the best course of treatment, and it is impossible to do more than lay down the general principles by which the operator should be guided. [ CLASS III.— Abnormal Relationship between the j Upper and Lower Arches and between either Arch and the Facial Contour, and Correlated j Abnormal Formation of either Arch, due to [ Developmental Defects of Bone The particular types of abnormal position of the teeth so far considered have been those hi \^hich the relationship of the two arches is not necessarily involved. The abnormalities may occur in one or both arches and errors of occlusion may in consequence often exist, but the malocclusion is as a rule local and limited to the particular portion of the arch in which the teeth are misplaced. In the cases now to be considered there is an abnormal relationship between the arches involving the whole arch, or at least a large part of it, and the malocclusion is not the result of misplacement of individual teeth, but rather of more deep-seated causes of a developmental kind. In fact the question of occlusion becomes of fundamental importance in connection with cases of this class, and credit is due to Angle for his insistence on its value as a diagnostic factor. In the opinion of the writer, Angle goes too far m making it almost the sole basis of classi- fication of malposition of the teeth, and Case is right m emphasizing the need to consider not only the relationship of the two arches but also the relationship of each arch to the facial contour. It Ls clear that abnormality of the relationship of the arches may be of three kinds : (1) Vertical, (2) Antero-posterior, and (3) Lateral. 1.— VERTICAL When the teeth occlude normally the upper and lower mcisors overlap, so that about one-third of the lower incisors is concealed by the uppers, and the edges of the lowers occlude with that portion of the upj)er incisors that is commencing to thicken to form the cingulum. Variation in the amount of this overlap may occur in either direction, and the question at once arises, whether the abnormality exists m that part of the arch where it is most apparent, namely, the anterior portion, or whe- ther the posterior region is also mvolved. It is probable that in a few cases the defect occurs in connection with, and is reaUy limited to, the incLsor region only ; but undoubtedly in most cases the bony development of the ascendmg ranius or angle of the mandible or posterior por- tion of the maxilla is at fault, and the anterior defect is a necessary consequence. Li some of the latter it is clear that secondary changes occur later in the development of the incisor region, and produce conditions that simulate cases of malformation due to difi'erent causes. («) Open Bite. — The extent to which the teeth fail to occlude may vary between a small lOS separation of the incLsors and a which only the second molars condition in occlude. In Fig. 180. — Open bite. Tlie only teath that occlude are the second left molars. On the right side the second molars have moved forward, especially tlie upper. For the interesting result of treatment of this case, and figures, seep. 244; Figs. 371, 372, 373. (Norman G. Bennett.) a typical case abnormal development of the mandible is very apparent ; the ascending ramus is short and the angle unduly oblique. It is easy to understand that if the depth of the mandible and height of the molar teeth in both jaws are normal, the effect of a short ascending ramus nuist be to produce an open condition anteriorly, and the obliquity of the angle is a necessary concomitant. Curiously enough the anterior portion of the mandible presents in different cases exactly opposite conditions. Sometimes there is deficient development, and sometimes excessive growth of chin together with an apparent bending at the anterior border of the insertion of the masseter muscle ^ (see Figs. 180, 181, 182). Deficient development occurs also in the anterior portion of the maxilla and in the pre- maxilla, and in either jaw is not very difficult 1 Rushton considers tliat this difference is associated with antero-posterior malocclusion, and depends upon whether the mandible is retruded or protruded. In the former case tliere would be deficient anterior develop - ment, and in the latter excessive growth. to understand, because failure to occlude involves loss of function, or at least diminished function ; that is to say, the an- terior defect is probably secon- dary to the posterior. It might be expected that the incisor teeth would continue to erupt on account of the failure to occlude, but it is probable that the belief in this tendency of teeth to be raised in their sockets until they meet their fellows has little foundation in fact. It is extremely difficult to produce this result, at any rate permanently, when desu'ed, in the case of molars, as wiU presently be seen, and it is probable that the extni- sive force of eruption ceases after complete formation of the roots of teeth. The eleva- tion from its socket of a tooth that has no oi3j)osing teeth in later life is of a different char- acter ; it is associated with alveolar absorption rather than with the deposit of bone that accompanies normal eruiJtion. It is doubtful whether cases of open bite caused by de- fective anterior development in otherwise normal jaws ever occur. Such apparent examples are usually due to external conditions — e. g. thumb-suck- ing — and should not be con- fused with cases of the type now under con- sideration. The excessive growth of the mental Fig. 181. — Portrait of case shown in Fig. 180. portion of the mandible and the apparent bend- ing is difficult to understand ; an excellent ex- ample is figured in Tomes and Nowell (153). It 109 is indeed doubtful whether the anterior growth is excessive absohitely, or only relatively to deficient posterior growth. It has been suggested that the bending takes place as the result of muscular action, the anterior portion being pulled down by the depressor muscles of the chin ; there is no evidence to show whether this occurs, but it is possible that in the course of development, if the anterior teeth fail to occlude, the depressor nuiscles will naturally become accommodated to the condi- tion and retain the anterior jJortion of bone in that position, whOe the powerful masseter muscle will be constantly acting in an opposite direction in endeavouring to produce complete closure, and will induce deposits of boiie about its insertion. It should be remembered that the function of the bone of the mandible is to support the teeth and afford insertion for muscle. It is probable that some explanation of the kind is not very far from the truth, but it should be distinctly understood that the condition requires further elucidation. Many if not most cases of open bite mal- occlusion are associated with adenoids and mouth-breathing, and in them the palate is narrow and has a high vault (56). The prime 183). It is not altogether easy to see how a highly vaulted palate will produce open bite, because the increased height is upwards in the centre rather than down\^ards at the sides, and is due r^'x / Fig. 182. — Open bite with nearly normal arches. (B. E. Lischer : Dental Cosmos.) cause of the open bite seems then to reside in the maxilla rather than the mandible, which may be normal or nearly so, but is usually naiTOw with lingually inclined molars and premolars (see Fig. Fig. 183. — Open bite with imiihv arches. (A. P. Rogers : Dental Cosmos.) to defective nasal expansion. But the narrow- ness is probably associated with increased depth in the molar region ; it should be remembered that the upper molars have nor- maUy a buccal inclination, whereas in the narrowed arch the axes of the molars of the two sides approach parallel- ism. The effect of this must be in- creased depth, which nuist have the same result in producing lack of occlusion of the anterior teeth as shortness of the ascending ramus of the mandible. Defective de- velopment around the upper incisor teeth is very fre- (juently associ- ated with these cases, probably more often than in the cases where the mandible is chiefly at fault. The cause may be found in loss of function, but it has been noticed that examples associated with narrow palate and W^ :/ ■^ 110 nasal stenosis often exhibit hypoplasia of enamel, and the inference is obvious that early mal- nutrition lias been the origin of several defective conditions of de- velopment whose interaction results in phenomena not easily traced in every detail (see Figs. 184, 185, 186, 187). It is possible that the constant this uifluence, while the anterior portion of the mandible is kept depressed by the hyo-mandi- bular muscles, the posterior portion is constantly forced upwards by the masseter and internal pterygoid muscles, and so the obliquity of angle associated M'ith the early years of life is maintained. It will be perceived Fig. 184. -Open bite associated with liypoplasia, anterior gingivitis, adenoids and small pharynx. Normal molar occUision. (Norman G. Bennett.) 185. — Portraits of case shown in Fig. 184. habit of mouth-breathing consequent on nasal I that^ this explanation is practically the same stenosis may be the initial cause of open bite. I in its method of action as that offered above esaC, in 1894, advanced the view that under | for the bending of the mandible. At present Ill it is impossible to say whether the obliquity of angle and shortness of ascending ramus are consequent on mouth-breathing and muscular action ; or whether deformation of the horizontal ramus is secondary to shortness of ascending ramus or increased depth of maxilla or both, and mouth-breathing only the natural con- comitant of the nasal stenosLs that causes the narrow and deep maxilla. J. Sim Wallace (162) advances the view that the obliquity of angle is caused by insufficient use of the masseter and internal pterygoid muscles m mastication, associ- ated with an abnormally posterior position of both arches due to insufficient use and develojD- ment of the tongue in mastication. He points out that in a well-developed jaw the mandible is widened and everted by deposition of bone around the insertion of the masseter at the angle, and along the lower and outer border, and that where function is deficient the obliquity normal to infancy is maintamed ; in that case the second lower molar erupting behind the already retruded arch must find room for its eruption by a raising of the alveolus, and anterior open bite is the necessary result. Sim Wallace states that the condition usually develops rapidly at the time of eruption of period, consequent on discomfort attendant on eruption of the molars. He believes that rapid Fio. 186. — Open bite associated with hypoplasia. Molar occlusion lower post-normal half a unit. (Gorman G. Bennett.) the second molars, and he associates this with a rapid development of the tongue, occasioned by its excessive use in mastication at this Fig. 187. — Portrait of case shown in Fig. 186. growth of the tongue may produce open bite apart from other conditions. It may be said that part of Sim Wallace's explanation appears to be rather far-fetched, because as a rule the eruption of the second molars gives rise to little or no incon- venience, and that his explanation involves a rather curious alternation of deficient and excessive masticating function at different periods ; but there is probably much truth in his view as to the obliquity of the angle being primarily dependent on diminished function. An interesting and plausible theory of the cause of open bite has been put forward by Van Broadus Dalton (65). He ascribes the condition to undue retention of the deciduous molars. He ];oints out very rightly that the height of the bite is normally fixed and con- trolled by the first permanent molars during the period when the premolars are erupting, and shows by examples that when a deciduous molar is retained it is often forced in an occlusal direction by the premolar erupting vertically l)eneath. In this way the bite is propped open and the permanent molars con- tinue to erupt as far as the level abnormally created. The cases illus- trated by Dalton are very convincing as far as they go ; but much diversity of form exists in open bite, and although this is probably one cause, it can scarcely be held accountable for all or even a majority of examples (see Figs. 188, 189). 112 It must be admitted tliat tlie question of the aetiology of open bite is at present ^vTapped in obscurity. Some excellent ex - amples of open bite are figured by Alfred P. Rogers (138), but, ill the opinion of tlie wTiter, it would be better not to class together cases due to ex- ternal causes, such as thumb-sucking, with conditions caused by de- velopmental de- fects of tongue or teeth. Open bite is not necessarily asso- ciated with any abnormal antero- posterior relation of the jaws, but as a matter of fact a pre-normal position of the lower molars in re- lation to the upper is very coinmon. An example is described by Hedley Visick (160). Case offers the ex- planation that deficient maxillary development occasions a posterior position of the upper molars, and that mouth-breathing, by causing the mouth to be kept habitually slightly open, carries the mandible forwards, and that if the effect of these two factors is to cause the cusps of the lower molars to occlude a little in front of their normal cusps. In other examples open bite is associated with post-normal occlusion of the lower molars. Fig. 189. — Open bite produced by undue reten- tion of second upper deciduous molars. (Vau Broadus D.4XTON : Items of Interest.) Fig. 1S8. — Open bite produced by undue retention of second upper deciduous molar. (V.4N Bkoadus Dalton : Items of Interest.) inter-digitation, the condition will be increased and then maintained by the interaction of the A curious ex- ample of open bite developing at the age of about 22 has been descril^ed by J. H. Bad- cock (16). It appeared to be due to elonga- tion of the pos- terior lower teeth c o 11 s e - quent on ten- derness and disease. Treatme7it. The treatment of open bite is usually difficult, and in many eases amelioration rather than cure is all that may be expected. The object to be attained is to restore the occlusion of the anterior teeth, and it is obvious that this may be effected by extrusion of the anterior teeth, or by intrusion or reduction in height of the posterior teeth. The former method should as a rule only be relied upon in cases where the deformity is not excessive ; it is accomplished by means of elastic ^^■ire bows around the upper and lower teeth connected togetlier by rubber ligatures. The force applied to tlie lower front teeth may be assisted by occipital force. Occipital force applied by means of skull- and chin-caps, the direction of the force being arranged as vertically as possible, is also useful in cases of slight deformity, or in com- bination with other methods of treatment ; it \\-as successfully used in a pronounced case by 113 F. Heiickeroth (92) as long ago as 1892. It is especially ajjplicable when the lower teeth are in pre-normal occlusion with the upper, but should not generally be used when the lower teeth are in post-normal occlusion. The effect is probably to drive the molars into the bone and they are very apt to rise again unless treatment is maintained for a ' period. long grnidmg down affords no prospect of cure it may be necessary to extract the second molars. In many cases, however, the second molars are sound and the first molars extensively carious. The best treatment then is usually to extract the first molars; the second molars will then move forwards (or may be moved) to a crreat extent into the position of the first molars, wliere there is more vertical space for their accoinmoda- Fio. 190. — Close bite, pronounced overbite ut nicisors, and retroclinatiuu uf uppers. Jlaudible post-normal. The daughter of tliis patient is shown in Figs. 234, 235. (Xorman G. Bennett.) In all severe cases it is advisable to reduce the height of the second, and if necessary the first molars, by grinding down the cusps. Only a little should be removed at a time. If the dentine is reached, silver nitrate should be applied after the operation, and an interval of three or four weeks should elapse between the visits, during which the patient should apply spirits of wine twice a day to the dried surfaces of the teeth. In this way the pain- fulness of the process is minimized and the deposition of secondary dentine is encouraged. If necessary the upper molars should be devital- ized. If the degree of openness is so great that tion, and a certain amount of grinding down at a later date will probablv effect a cure. (See p. 244, and Figs. 371, 372, 374.) It has been said above that many cases of open bite are associated with adenoids, enlarged tonsils, and nasal stenosis. These conditions of course demand treatment ; and the expansion of the upper arch, and, if necessary, the lower arch sufficiently to produce normal occlusion, \^ill improve the bite, because buccal movement of the upper molars effects a relative shortening. It has also been remarked above that in some ca.ses a proclination of the upper incisors supervenes on the lack of occlusion ; this can 114 often be remedied by mechanical means, and where the teeth are not markedly short the Fio. I'.M. ('lipHii liilci (uul HcH'dMilary prdi'liiial inn of u|i|ii'r iiicisorH, duo to di'licicnl' |)(isU'niE : Dental Orthopedia.) tllOUgU not normal, _LS irom a practical point of view suinci- correct alignment and occlusion, but in whicli the degree of closure is excessive, so that the appearance of the cheeks and lips has some resemblance to that of an edentulous patient. An excellent example of this is de- scribed and figured by Case (43, p. 322 ; see Fig. 194). Treatment should be on similar lines, the bite being tem- porarily raised on the first permanent molars, and the other teeth being slowly extruded by means of inter- maxillary force, after which the molars should be raised by the same means. 2.— ANTERO-POSTERIOR Li the cases now to be considered either arch may be in abnormal relationship with the other, that is to say, the upper may be too far back or forward m relation to the lo^^•er, or the lower may be too far back or forward in relation to the upper. Furthermore, either arch, whether in normal relationship with the other or not, may be too far forward or back in relation to the facial contour — the upper or lower lip may be pushed forward or allowed to fall too far back by variations in the positions of the anterior upper teeth; or the mandible ently perfect. In coming to a decision between these two issues the question of the complexity of the procedure and the likelihood of perman- ence merits much consideration. A. Upper Apical Zone B. Upper Coronal Zone C. Lower Coronal Zone D. Lower Apical Zone Fig. 195. — (C. S. Case : Dental Orthopedia.) The part of the face that is involved in deformities of the jaws and teeth includes the alae and tip of the nose, the upper and lower lips, and the dim, but from the point of view of artificial modification some distinction must be drawn between these several parts. It is 117 clear that the position of the chin in relation to the nose and upper part of the face is less susceptible of alteration than the lips. Such a change can only be effected in the compara- tively rare instances of successful back^\ard movement by occipital force, and for\\ard movement by inter-maxillary force ; these methods Mill be dLscussed in connection Avith the examples to which they may be applicable. Case (43, p. 176) defines the " dento-facial area ", which it is possible to modify by move- ment of teeth, as being " formed by the upper and lo^^■er lips, and lower ijortion of the nose, bounded laterally by the nasolabial folds and It is undeniably true that form one of the chief and the most expressive and that the position of the subjacent teeth and bone affects to a con- siderable degree the contour of the lips in repose and the potentiality of expression of the lips in movement. It is remarkable to what extent the facial harmony and beauty of the individual may be modified by a comparatively slight movement of the croons or roots of the anterior teeth. Case (43, p. 177) shows clearly the below by the chui " the mouth and lips features of the face of transient emotion ; Fig. 196. — Normal type, showing points of measure- ment (in tlie same plane). Mandibular angle, 115°; profile angle, 75°. Note that the facial line is almost parallel with the ramus. Contrast this with Figs. 198, 199, and 200, in which the corre- sponding lines converge in descent. (W. Rushton : Trans. B.S.S.O. ; Dental Record.) parts affected by different kinds of movement by dividing the dento-facial area into four zones, the upper apical and coronal, and the lower coronal and apical, the two former being modifiable by movement of the roots and crowns of the u]iper teeth respectively, and the two latter by similar movements of the lower teeth (see Fig."l!l.5). Careful observation and judgement are re(juu-ed in determining the ex- tent to which an unperfect facial contour is Fig. 197. — Boy just under ten. Normal type. Tonsils removed at the age of six. (W. Rushton : Trans. B.S.S.O. : D'-nlal Record.) dependent on dental malf)osition ; and in con- sidering the possibility of modifying it beneficially by tooth movement, or on the other hand, the risk of magnifying the imperfection by a method of treatment based only on considerations of occlusion. The matter «ill be dealt with further under " Diagnosis ". This question of the extent to which de- formities of the mandible are associated ^^ith errors of occlusion has been carefuUy investi- gated by W. Rushton (139), who has made a large number of measurements of skulls and living subjects — adults and children. He writes : " I had been struck by ob.serving that the angle formed by the ascending ramus with the body of the mandible varied in different people. It is an equally true observation that the chief feature of facial abnormality is caused by the position of the mandible being anterior or posterior to its proper position. My object was to try and estimate and correlate these two j)henomena. To estimate the former I took a point just in front of the antihelix of the ear (corresjjonding with the mandibular fossa), the point where the ramus joins the mandible and a point in the same plane corresponding to the point of the chin. This is called the mandibular angle. To estimate the latter I chose the 118 same point in front of the ear, a point in the same plane corresponding to the base of the nose (these being probably fairly stable cranial points), and measured the angle formed by these with a line drawn from the base of the be noted particularly that according to his investigations protrusion of the mandible, as judged by the mandibular and profile angles, sometimes exists without labial occlusion of the mandibular incisors. He believes that mouth-breathmg is by far the most frequent cause of these deformities (see Figs. 198, 199, 200). Rushton's measurements are — Normal. Length Length Total length Length of of of of ramus, body. mandible. face. Mandi- bular angle. Pro- file angle Children Adults . 11 3i 4J (130:100) 2J 3| 5| (126:100) Retruded Mandible. 3i 12r 120° 74° 73° Children Adults . If 2J 4i (120:100) 2\ 3 54(107:100) Protruded Mandible 3i 4| 129° 134° 66° 65° Children Adults . lYi 3,V, 5 (119-5:100) 2,V 3^ 51(110:100) 4A 132° 137° 74° 76° He remarks in comiection with them : " The chief points to be noted in the above tables are Fig. 198. — Youth aged 17. Had adenoids and tonsils removed a year ago, but still a mouth- breather. Long narrow face; large mandibular angle, 128°; small profile angle, 63°. Observe the downward and backward drag of the muscles shown by depressed alae of the nose, short upper hp, and retracted mandible ; general aspect of the face convex. Upper incisors crowded but not pro- truding. Narrow arches. The facial Une and ramus are shown to converge slightly as they descend. (W. Rushton : Trans. B.S.S.O.; Dental Record.) nose to the most prominent point of the chin. This I called the auriculo-facial or profile angle." Rushton found that the mandibular and profile angles both for European skulls and Greek and Roman statuary were about 115° and 73° respectively, and that the mandi- bular angle is a very constant one for people of all races — even the Negro, in whom the prognathous appearance is due not to obtuse- ness of the mandibular angle, but to " the profile angle being large, owing to the length of the body of the mandible, the large teeth set forward in the jaws, the forward inclination of the incisor, the thick lips and flat nose " (see Figs. 196, 197). Rushton found further that in cases of both inferior retrusion and inferior protrusion the mandibular angle was always more obtuse than normal ; and that the profile angle was larger or smaller according to the position of the mandible, whether normal, protruded, or re- truded; and also that protrusion was a more common abnormality than retrusion. It should Fig. 199. — Youth aged 19. Mouth- breather and has large tonsils. Long narrow face (100: 100); mandibular angle large, 128°, but profile angle good and facial contour not unpleasing. Both arches narrow ; teeth crowded ; cross bite. Note everted lower lip, wliich belongs to the protruded and not to the retracted mandible ; upper lip not short nor alae nasi depressed. (W. Rushton: Trans. B.S.S.O.; Dental Record.) tliat in those cases chosen as approaching the normal the total length of the mandible is considerably greater than the length of the face ; in the t\\'o other classes the mandible 119 is proportionately shorter and the face longer. In the normal the proportions between the children's and adults' measurements remain very stable ; in the abnormal classes the ab- normality is worse in the adult than in the child, that is to say, the angle has stUl further in- creased and the face lengthened." The writer has quoted rather fully from Rushton's paper because he considers that the work is an attempt (as in the case of the pro- sopometer of Sim Wallace and Northcroft) to Fig. 200. — Girl aged 11. Mouth- breather ; has large tonsils. Maxillary arch narrow, mandibular well developed. Mandibular angle very large, 145° ; profile angle also large, 76°. Note everted lower lip ; no " down drag ". Converging lines of ramus and facial Unes very marked. Medial occlusion to the extent of half an inch. Facial aspect concave. (W. Rushton : T'rans. B.S.S.O.; Dental Record.) obtain information as definite as possible con- cerning variations in bony development ; and that the method may be helpful in clinical investigation of uidividual cases. Rushton expressly states that his measurements are not mathematically accurate ; but the errors probably do not approach the considerable variations shown. The paper merits study. In a later paper Rushton (140) repeats his previous conclusions, and also discusses the apparently hereditary character of the Habsburg jaw. He says : " I stiU believe that the main factor in abnormalities of the jaws and teeth is slight continuous muscular action caused by the open mouth, the result of hypertrophied tonsils and adenoids ; that this hypertrophy is possibly caused by affections of the pituitary or thjTeoid, or botli, and possibly that softness of the bone arising from these causes allows it to be more easily acted on by muscular strain ; that probably the condition is in many cases hereditary; but whether primarily, or as a result of mouth-breathing, I could not say." Theoretical Considerations.- — Before proceeding to discuss the different varieties of antero- posterior malocclusion that actually occur, it wiU be well to consider what combinations are possible by abnormal forward and backward positions of the mandible, i.e. of either arch in relation to the other and to the unchangeable upper part of the face. It will jiresently be seen that this theoretical consideration accords remarkably with clinical observations, and is of material assistance in formulating a scientific classification of antero-posterior malpositions. For this purpose it wUl be sufficient to deal with comparatively small relative malpositions ; even within narrow limits the number of combinations is considerable, and the main object is to define the kind of deformity rather than the degree. The mter-digitation of the cusps usually causes the error of occlusion between upjjcr and lower teeth to be the width of a premolar. It is true that an intermediate position occurs m which corresponding teeth occlude solely with one another instead of inter-digitatuig, the outer cusps of tlie lower premolars occluding with the fissure between the outer and inner cusps of their fellows in the maxilla, and the first permanent molars occludhig in a somewhat similar manner ; but the xtnit of error may be defined as the width of a premolar, and the test tooth may be taken to be the first permanent molar, whose position in an arch of uninterrupted curvature (whether narrow or not ij not the point) prescribes the position of the other teeth. The upper arch may be too far forward or back in relation to the face to a considerable extent, and so may the lower arch, but it is probable that m very few cases does the error exceed the width of a premolar, or one unit, and for the present purpose errors of not more than one unit wiU suffice. Agaui, the mandilile as a whole may be forward (and the cliin very prominent) or too far back, but not usually to the extent of more than one unit. Of course it must be remembered that tlie mental promin- ence itself may be developed to a greater or less degree, and judgement is required to dis- tinguish between this and malposition of the whole mandible. This is a practical point, but does not affect a classification including cases in which the whole mandible is misplaced or badly developed. It is possible that the posi- tion of the maxilla as a whole may vary, but at the present time no means exist of estimating such variation, and for practical purpcses it is sufficient to consider the antero-posterior variation of the maxillary arch. This view is supported by SpiUer (143). It should be clearly 120 understood that to restrict the consideration of displacements to those of one unit in each variable — mandible, upper arch, and lower arch ■ — in relation to the unchangeable area of the face does not affect the theoretical classification of such cases (the majority) as are included ; those that are excluded must be only variations in degree but not in kind. It \\ill be convenient to make use of symbols for the sake of brevity. Let F represent the fixed base with reference to which the three variables occupy different positions in different cases. It is not any definite point, but repre- sents the forehead, bridge of the nose, and malar bones, as the most prominent parts of the unchangeable upper part of the face. Of course these various portions of the upper part of the face vary in relation to one another, but the sum-total of these features forms a fixed base, which, for practical purposes, camiot be modified ; and the existence of individuals with great mandibular and maxillary development and poor frontal development does not affect the present investigation. Let M represent the first permanent upper molar and m the first permanent lo«er molar. Let C represent the mandible as shown mainly by the chin, normal mental development being assumed. The bear- ing of abnormal mental development on the treatment of individual cases will be discussed later. Then let F M m C represent normal relationship of the three variables to the fixed base. By moving each of these variables separately one "unit in each duection, and excluding all combinations in which any two variables are separated from one another more than one unit, the following combinations are obtained — A little consideration will show that each of these classes exhibits a well-recognized clinical type of deformity. Class (a) may' be regarded as including only slight variations from the normal. The teeth are in correct occlusion and the arches are normally disposed ; in the one case, the mandible is some"what retruded, and in the other pro- truded, but the imperfect or excessive develop- ment has not been sufficient to produce a pre- or post-normal occlusion of the lower arch. Class (6) exhibits two varieties of ^^hat is correctly described as Inferior Retrusion. This is a very common deformity and probably provides the greatest number of the cases that were formerly all classed together as Superior Protrusion. As a matter of fact in many cases the upper incisors are, as will presently be seen, retruded. In each variety the lower molars (and premolars) are in post-normal relationship with the upper, but in the one case the mandible is plainly retruded, and in the other is about normally disposed in relation to the unchange- able area of the face. The distinction is not only a very real one clinically, but affords indications for different lines of treatment. (a) Sub-normal. C P M m m M m F M C F m C M C m C {b) Inf. Retrusion. m C M (c) Sup. Protrusion. F m C M (d) Inf. Protrusion. F M C m F M (e) Sup. Retrusion. M C F m M F m C M m C (/) Double Protrusion. F C M m 1 F (U) Double Retrusion. M m C F M m F C Class (c) consists of true Superior Protrusion, in reality a somewhat rare condition. The upper arch is too far forward and is in pre- normal relationship with the lower, which is normally disposed in relation to the face. In the one variety the mandible also is normal and in the other the mandible is promment ; the former is the usual condition. Class (d) exhibits two varieties of the ordinary forms of Inferior Protrusion, in which the upper arch is normal, but the lower arch is in pre- normal relationship with the upper. In the one variety the protrusion is mainly of the teeth, the mandible bemg normally disposed, and in the other, the more common form, the mandible shares in the protrusion. 121 Class (e) exhibits the deformity correctly termed Superior Retrusion. These cases were formerly grouped under the head of Inferior Protrusion or " underhung bite ", but in reality they are fundamentally different. The upper molars are in post-normal relationship with the lowers, and the whole upper arch is as a rule plainly too far back in relation to the face and upper lip. Any false relationship of the mandible is quite an unusual, although possible, complication. Class (/) exhibits the form generally known as prognathism, but this term should be re- stricted to conditions in which prominence of the teeth is due to excessive bony grow th anteriorly, such as occurs normally in the Negro. The teeth are in normal occlusion, but prominent in both jaws ; in the one case the mandible shares in the deformity, while in the other it does not — a distinc- tion that is clinically very im- portant. Class ((/) exliibits the somewhat though not very rare condition of Double Retrusion, in which the teeth are in normal occlusion, but the arches are plainly retruded in relation to the face and lips. The mandible usually seems promin- ent, but this appearance is often connected with the backward position of the anterior teeth, allowing the lips to fall in. It will have been seen that the main basis of classification Is con- cerned with the occlusion of the arches, and to a somewhat less extent with the relationship of each arch to the face, and tiiat the relationship of the mandible to the face provides, clinically, minor variations, which only now and then assume importance. It should be clearly recognized that insistence by Angle upon the importance of occlusion as a basis of classification and treatment has done much to advance this branch of the subject ; it is not perhaps unnatural that its very value should to some extent have overshadowed other important factors. The writer believes that the method here propounded of considering all possible combinations does something still further to restore order out of chaos. Of course it will be understood that all cases do not definitely conform to a clear-cut type, and that combinations— for example, of Classes (b) and (c),or {d) and (e) — constantly occur; but it will be found that even the most bizarre example of antero-posterior abnormality is but a modi- fication of degree and not of kind, and nuist of necessity find a place in one class or another, or in more than one. A classification of cases of antero-posterior malocclusion somewhat simi- lar to that herein adopted has been eminciated by Sim Wallace (165). It will now be necessary to consider each of these classes in detail. Class (a), Normal or Sub-normal. — Cases in this group do not usually come withhi the scope of treatment. They are normal in all respects, save the prominence and development of the mandible, but where the occlusion is not Fiu. 201. — lul'orior rotrusiou (lialf a unit on loft siilo), and procliiiation of upper central incisors, associated with very abnormal jaw forma- tion and dental hypoplasia. Retained deciduous canines. Not« the lingual inclination of lower premolars and complete lingual occlusion of those teetli on the left side. (Norman ti. Bennett.) affected the defective or excessive development can be but slight, and mechanical interference is neither requisite nor desirable. Class (b). Inferior Retrusion. — The essential features of cases of this group are that the antero-posterior relationship of the upper arch to the upper part of the face is normal and that the lower arch is in post -normal occlusion with the upper arch. In the one type the mandible and lower teeth arc both too far back ; and in the other only the teeth, the mandible appearing to be in normal relationship with the face, and the chin not markedly receding,, as it is in the first type, which is by far the more common. Clinically the differences between the two types are of varj-ing degrees; it is' but rarely that the 122 mandible does not participate to some extent in the posterior position of the teeth, but the measure of the recession presents much diversity. The position of the upper incisor teeth is Fig. 202. — Typical oaso of inferuir retrusiun (one unit), and .sucundary pruclina- tion of upper incisors. (J. H. Badcock.) nearly always abnormal and is of two distinct types. In the more common form the crowns are markedly jyro- tr tided (procliaation) ; the lower incisors occkide with the gum just behind the cingula of the upper, and are often arranged in a fan- shaped manner ; and the lower lip intervenes between the lower teeth and the edges of the upper (see Figs. 201, 202, 203). This protru- sion is, however, a secondary characteristic, and in most instances probably a second- ary development. Cases must not be confused with those due solely to closeness of bite (antero-posterior occlusal relationship being normal), or to thumb-suck- ing ; or ^^ itli the cases of true superior protrusion (with lower teeth and jaw- normal) shortly to be con- sidered. In tlie less common form the crowns of the upper incisor teeth are relruded (retroclination) , especially the centrals, the laterals often slightly overlappmg the centrals on the labial aspect (see Figs. 204, 205). Angle has emphasized in the two divisions of his Class II the essential connection between these two apparently dissimilar forms dependent on a post-normal position of the lower teeth. The contour of the arches is not necessarily abnormal, but many cases exhibit a narrowing of the upper arch associated usually with nasal stenosis (see Fig. 206) ; and in some the arch is laterally contracted in the canine regions, and the incisors are rotated so as to exhibit a V-shaped for- mation of the kind already described (see Fig. 207). But this formation, although an expression of defective bony development, or contraction of the anterior portion of the arch, is far from being a characteristic of thLs type of so-called superior protru- sion, of which the essential feature is the post-normal relationship of the first lower molars and the premolars, the proclination and spread- Fio. 2U3. — Inferior retrusion (lialf a unit), and secondary proclination of upper incisors, less marked than in Fig. 202. The narrow upper arch is probably responsible. (H.\r<)ld Chapman.) ing of the upper incisors being secondary (see Figs. 208, 209, 210). The form of the mandible is often far removed from the normal, the angle being unduly oblique and feebly developed, and 123 the ascending ramus apparently short. There is, in fact, paradoxical as it seems, a certain resemblance in general conformation to that seen in cases of " open bite ", but the horizontal ramus is usually of more slender development, and the depth from the crown of the first molar to the lower border of the jaw less than normal. There is also not infrequently some degree of closeness of bite, which, as has already been shown, is itself a cause of secondary superior proclination (see Figs. 211 and 212). Associated with these abnormalities in form, and perhaps dependent on them, will usually be found some variation from the normal curve of occlusion. The defect usually consists mainly in an elonga- tion of the lower incisors, but this is often accompanied by want of depth in the molar region. The causation of these forms has been, and is still, the subject of much discussion, and remains debatable. There can be little doubt that the condition itself, or at any rate pre- disposition to it, is often inherited, as indeed cases undoubtedly occur in children who are of somewhat feeble physique, and by whom b IG. 204. — Typical case of inferior retrusion, and secondary retrocliiiation of upper central incisors. The occlusion of tlio molars is normal, but this is caused by loss or non-eruption of the second tower premolars and forward movement of lower molars. The whole mandible is post- normal (retrognatliism). (Norman G. Bennett.) IS the case in most gross abnormalities involving the jaws themselves. This view is endorsed by J. H. Badcock (12). On the other hand, most Fio. 2().">. — inferior retrusion (one unit), and secondary retrochnation of upper central incisors, less marked than in case shown in Fig. 204. (Harold Chapman.) mastication has been imperfectly performed. Unfortunately it is just these delicate children who are often improperly fed on a soft dietary, and in whom development of the tongue and jaws is the more inhibited. The importance of malnutrition in the production of this type of abnor- mality is emphasized by Rodri- gues Ottolengui. It is probable that the condition really com- mences to develop during the period of the deciduous dentition or bef(^re ; and as the first per- manent lower molars are normally moved forward durmg eruption in a well-developed and developing jaw, it is not very difficult to understand tliat when growth is defective the erupting teeth wiU remain too far back and come into post-normal occlusion %\itli tlie upper molars, and thus remain locked. If it were possible to trace cases back to early years, it would almost certainly be found that many of them followed of necessity a post -normal occlusion of the lower deciduous molars, occurring not always as a gradual development, but even from the period of eruption. Such cases are clearly congenital. (See Part IV "Deciduous Dentition", p.l35.) Then there is the important factor of the frequent narrowness of the maxillary arcli, perhaps associated with nasal stenosis, or merely with defective growth of the tongue. The molars and premolars, when meeting their fellows 124 dviring eruption, are guided into position by the interaction of the cusps ; tliis applies not only as regards the antero-posterior relation- corresponding lower teeth must occlude buc- cally : or the corresponding lower teeth must be tilted lingually, contracting tlie lower arch ; or non-corresponding teeth placed in a more forward, and therefore narro\^•er, part of the lower arch must occlude. As a matter of clinical observation the first scarcely ever happens, the second does occasionally, and the third is the most usual occurrence. It is certainly a fact that a fairly expanded lower arch is often associated with a contracted upper arch in these cases, and it is at least pos.sible that the initial tendency to post-normal occlu- sion , by allowing the second lower premolars to occlude with the ujjper molars, also permits of an apparently normal-shaped arch in a too backward position. This explanation is upheld and ^^ell described by Brady (35). The point is associated with the practical question of the possibility of altering the occlu- sion one unit. Some authors deny the possi- bility of this lieing done, or at any rate of the esult being permanent a.s regards the position of the mandible as a whole; but, on the other hand, .several practitioners have advanced very convincing examples to prove the possibility. Federspiel (73) believes that success is possible if the attempt is made early enough — during the development of the mandibular fossa. There can be little doubt that many of these cases exhibit considerable mobility of the mandible and even an alternative bite, and in the experience of the writer and many others, the treatment is not only possible but effective in quite young subjects w hen associated m ith early expansion or other necessary correction of the upper arch. It is the latter factor that not only frees the held-back mandible, but renders normal occlusion the easiest position for the patient. An interesting example of successful treatment on these lines of a patient fifteen years old is recorded by J. G. Turner (156). The rising of the lower incisors and the spreading of the upper are the natural result of the anterior malocclu- sion, and are most marked when close- Fici. 20(j.— Typical c-use of iiifenor retrusion (one uuit) ussoeiated „ess of bite is a concomitant feature, witli narrow upper arch. Considerable rotation of upper rr'i i ■. • c ^.i, ■ „•, ,.„ ;„ incisors. Proclnlation not very marked because of short.iess The malposition of the upper inClSors IS and postplacement of upper incisors in arch deficiently further intensified by the action ot developed. On the left side the lower molars have moved the lower lip in getting between the forward. Adenoids removed at about 15 years of age. upper and lower teeth. Indeed, the (XoRMAN G. Bennett.) r a- i ii i i ^ ' formation of the upper and lower ship, but also as regards the bucco-lingual. lips may be the chief factor in determining Now if the width of the upper arch is unduly | whether the upper incisors shall be inclined narrow one of three things must happen; the | forwards or liaokwards — -a short upper lip 125 Fig. permits proclination, a long upper lip almost pre- vents it. Cases of this class do not necessarily involve pre-normal malposition of the upper buccal teeth, such as will be considered in the next class ; but it should be clearl\' under- stood that any kind of combination of the two classes may, and often does, occur between the two extremes of pro- nounced mandibular retro- gnathism associated with slight secondary proclina- tion of the upper incisors, on the one hand, and marked superior protru- sion on the other hand, associated with abnormal antero- posterior relation- ship of the premolars and molars, in which the upper arch is markedly too far forward and the mandible and lower teeth but little, or not at all, too far back. Treatment. — The first essential is to expand the upper arch, if necessary, and in some cases the lower. The next requirement is to correct the curve of occlusion. The form of the curve of occlusion and its relationship to the mandibular articulation has not often been .sufficiently taken into consideration. For this pur- pose Snow's face-bow and an anatomical articulator must be used; the models can then be adjusted in the articu- lator in their natural position, as in prosthetic work. The application of these appliances to orthodontic treatment has been referred to by R. D. McBride (110) and is 'fully dis- cussed bv Leuman M. Waugh (167). The latter writer points out that methods of treat- ment that ignore the preserva- tion or production of a correct relationship between the curve of occlusion and the mandibular articulation are liable to permit of reversion. 207. — Inferior retrusion (one unit), and secondary jjrotilination of upjier incisors. Rotation of upper incisors and postplacement due to deficient anterior development. The upper arch is very narrow, and tlie upper molars are all in lingual occlusion. This narrowness is probably responsible for the post-normal position of the mandible (retrognathism), which is otherwise well developed. (.J. H. Badcock.) Fig. 208. — Inferior retrusion (half a unit), and secondary proclination of upper incisors, associated with wide arches. (Norman G. Bennett.) 126 However, information appears to be wanting with regard to normal conditions at different Fig. 209. — Inferior retrusion, and secondary proclina- tion of upper incisors, associated with fairly wide upper arch. Tlie main defect here is in tlie small size of the mandible. The first lower molars have been able to move forward into normal occlusion •with the upper molars owing to premature loss of the second lower deciduous molars. (J. E. Spiller.) distinguish between a forward movement of the whole mandible (associated presumably with modifications of the condyle), and forward translation of all the lower teeth. The former only may correctly be described by this term, and according to many operators can be success- fully accomplished. A case in point is recorded by Ottolengui (126). In a useful paper by S. Merrill Weeks (168), bearing upon this problem, the relation- ship between the formation of the mandibular articulation and abnormal occlusion and jaw for- mation is discussed. Weeks con- siders that the variation of facial contour in the class of cases under consideration, and in others, can only be accounted for by a false relation of the mandible as a whole, and that movement of teeth alone cannot produce correction. Mat- thew Cryer gives illustrations of a large number of specimens, in opening a discussion on Weeks's paper. R. D. McBride (110) discusses very fully the physiological changes involved in " jumping the bite ". He considers that no permanent change takes place when a bite-plate with inclined plate behind the upper incisors Is used, because although the habit may be acquired of biting hi normal occlusion the mandible drops back in a position of rest. Before the intro- duction of inter-maxillary force he used bite- bars attached to molar crowns in association with a bite-plate, so that a post-normal position of the mandible was at all times impossible to ages, and until this has been obtained any estimate of the degree of abnormality in particular cases is impossible. Thec|ues- tion of the correction of the occlusion de- pends upon the extent to which the mandible as a whole shares in the post-normal re- lationship of the lower teeth. Where this is marked an attempt should be made, in young subjects at least, to bring forward the mandible ; it will probably be necessary also to raise the bite and depress the lower incisors. Case considers that to "jump the bite", and it , 210. — Portraits of case shown in Fig. 209 before and after treatment. it is impossible 1 the patient, and in this way considered that he is necessary to | obtained permanent results by causing modifica- 127 tions of the eminentia articularis, and the formation of a new site of articulation. In a later paper McBride (111) shows some excellent results achieved by the use of inter-maxillary force, and in recent years many other operators have published similar cases. It should be stated, however, that some operators do not believe in the permanency of the result. They con- sider that although the teeth remain in normal occlusion the mandible drops back to its old posi- tion, i.e. the teeth move forward in the bone. If treatment so far has been successful, the correction of protruded upper incisor crowns will then be the least difficult part of the process and can be accom- plished by occipital force, or traction from within the mouth. In cases of retro- clination of the upper incisors the position of the crowns will have been partially corrected during expansion, before altera- tion of occlusion, and can be completed afterwards. \\'lien it is impossible, or unwise to attempt, to change the occlusion and advance the mandible, the lower buccal teeth should not be disturbed. If they are moved forward, even though it be into what is really a normal position and normal occlusion, the effect will be to produce the appearance of a markedly receding chin. The better treatment of cases char acterized liy procluiation of the upper incisors is to raise the bite and depress the lower incisors, and to extract the first upper pre- molars and draw back the upper incisors. This plan, however, is usually inadvisaljle in cases of retro- clination of the incisors, for it is difficult to move back the roots sufficiently to close the space formed by extraction and produce good alignment of the incisors. Those cases in which the post-normal relation- ship is limited to the lower teeth require a different plan of treatment. Advancement of the mandible is clearly out of the question, and extraction of the first upper premolars would produce a laxity and depression of both lips, and an appearance somewhat resembling that of edentulous old age. The proper treatment is to dra«- forward the lower teeth by means of inter-maxillary force, to treat the closeness of bite when necessary, and correct the upper Fi(i. 211. — Extreme case of interior retru.siori, and secondary proclinatioii of upper incisors, combined with closeness of bite. There is no occlusion of posterior teeth ; and premature loss of the deciduous teeth associated with the post-normal position of tlie mandible has allowed the lower incisors to tilt the upper incisors forward. (Xorman G. BENNErr.) incisors. This, of course, involves a somewhat extensive movement of teeth, but will probably produce the best result if carried out slowly. In estimating the relative positions of the mandible and arches the methods of measure- ment suggested by Rushton (see pp. 118 and 119) should be found very useful. The same observation applies to the other classes in this group presently to be discussed. 128 In all these cases retention is necessary for a considerable period after treatment — at least a year and often more, — and permanency of result will depend upon the extent to which later bony development compensates for early Fig 212. — Portrait of case shown in Fig. 211. the well-marked inferior retrognathism. Note defect. Treatment to be successful must take into accoiuit physical characteristics, and oper- ate in conjunction with natural gro\rth and not in opposition to it. The question of general treatment liaving reference to functions of the jaws and tongue is dealt with in another section. Class (c), Superior Protru- sion. — In this class the lo\^er teeth are in correct relationsliip \\ ith the upper part of the face, but the upper teeth are in pre- normal occlusion with the lower, that is to say, the whole upper arch is too far forward, ^'ariations occur in the relationship of the mandible to the face, but do not usually exceed the range that may be con- sidered to be embraced within normal limits. Pro- minence of the upper in- cisors and upper lip will often cause the chin to appear recessive when such is not really the case. In estimating the abnor- mality of the parts of the facial profile below the nose each portion should be considered in relation to the unchangeable area of the upper part of the face. The protrusion of the upper incisors conse- quent on pre-normal occlusion of the upper molars and premolars to the extent of one unit may take various forms, and exhibit minor modifications of true superior protrusion. The usual form is that in which the crow ns alone are protruded and spread (proclination), the apices of the roots being normally situated. In other cases the roots also are unduly prominent (pre- placement). In rare examples this prominence of the roots is excessive, so that the cro\\iis, although really too far forward, do not appear to be protruded. On the other hand, in cases of marked protrusion of the crowns the apices of the roots may even be somewhat re traded. To what extent excessive bony growth (pro- gnathism) is concerned m these types of deformity is uncertain. The cause of true superior protrusion is un- known. It is difficult to see how errors in development due to conditions of environment and function can bring it about, unless it be supposed that such cases are in the first place post-normal occlusion of the lower teeth, and that subsequent growth has compensated for the early deficiency and carried forward the teeth of both jaws. It is probable that congenital variation is responsible for most of these cases. It should be remembered, however, that the type is a comparatively rare one, and that most cases of superior protrusion are associated with some degree of inferior retrusion.' It has already been pointed out tliat between the two extremes of classes (6) and (c), considered .separately for Fig. 213.- Inferior protrusion. Edge to edge bite, in pre-normal occhision (half a unit). lower molars and premolars (G. NORTHCKOFT.) the sake of lucidity, an infinite variety of com- binations may, and does, occur. • As has already been stated (p. 81), J. F. Colyer ascribes many cases of both classes to the use of the "baby comforter." 129 Rodrigues Ottolengui (125) appears to deny the existence of this class of eases, for in dis- cussing abnormal antero-posterior occlusion, he states that where the relationship is such that tlie anterior two-thirds of the lower molar occludes with the posterior two-thu-ds of the upper molar, the fault always lies with the lower molar, or mandible as a \\ hole. That Ls to say, the lower molar is in post-normal occlusion, not tlie upper in pre-normal occlusion, and the condition is inferior retrusion and not superior protrusion. In a similar way he argues that in the converse state of affairs the lower arch is always in pre-normal occlusion, and the upper never in post-normal occlusion, and that inferior protrusion, therefore, is what must be dealt with, and never superior retrusion. N. S. Hofi in discussing the paper dissents from these views, and in the opinion of the writer clinical experience shows Ottolengui's view to be untenable. The paper is illustrated with ad- mirable examples of hiferior retrusion. E. H. Angle (4) also regards the first upper molar as a tooth whose position is almost invariable, except as regards diversity in racial type, and he appears to deny the existence of a true superior protrusion. It is not easy, however, to draw a hard-and-fast line between racial or individual premature loss of deciduous molars already described, the upper first molars have moved forward to a very considerable extent. The ^vriter has knowledge of an adult in whom a B^IG. Note Fig. 214. — Inferior protrusion associated with well-formed arches. Lower molars and premolars in pre-normal occlusion (one unit). The mandible itself is too far forward (prognathism). (B. E. Lischer : Dental Cosinos.) variation, within normal limits, and abnormal variation ; and, furthermore, most practitioners are familiar with cases in which, as a result of 5 215. — Portrait of case sliown iu Fig. 214. the well-marked inferior prognathism. first permanent upper molar is in contact \\ith the canine. If such movement is possible under any conditions, it seems unwise to deny its occurrence even apart from any question of loss of teeth anterior to the molar. TrealmetU.—The principles of treat- ment are in all cases the same. If the upper teeth are too far forward extraction is neces- sary, and the first upper premolars should usually be chosen. Where the first upper molars are extensively carious these should be extracted and the premolars moved back. The mcisors may be corrected by means of a movable or fixed apparatus within the mouth, or by occipital force, or by both. Some \\ riters advise the back- ward movement of all the upper teeth, but it is difficult to see any great advantages in this plan 130 of treatment, and the disadvantages are very obvious. Cryer (60) gives good examples to Fig. 216. — Superior retrusion, combined with inferior to some extent. The cliief defect lies in the ■ developed maxilla (retrognatliisna) and upper arch. The mandible is not very much too far forward, but appears so by contrast with the depressed upper lip (see next figure). The con- formation of the mandible is abnormal; note the very obtuse angle, the pointed chin, and great anterior depth. This form of mandible is not infrequently associated with this type of abnormal occlusion. In closing, the lower teeth pass entirely outside the upper arch. The retro- clination of the lower incisors is caused by pressure of the lower lip. (Norman G. Bennett.) show the inadvisability of backward movement of molars m certain conditions. Movement of the roots either forward or backward is possible by means of the " contour- ing apparatus " designed by Case. Li some cases it may be necessary to raise the bite, or depress the lower incisors, in order to reduce the upper incisor crowns to a normal position. Combinations of Classes (b) and (c). — Treat- ment ua these cases will naturally include the methods applicable to each of the pure types. Considerable judgement will be required to decide to what extent the upper or lower teeth contrary movement of upper and lower teeth is usually required, the treatment is to some extent simplified, and it is to cases of this type that inter-maxillary force is particularly applicable. Class (d), Inferior Protrusion. — All cases in this class are characterized by pre-normal occlusion of the lower molars and premolars, and labial, or edge to edge, malposition of the canines and incisors (see Figs. 213, 166, 167). In some the protrusion Ls limited to the teeth, and in others the mandible shares in, or is even the most con- spicuous feature of, the deformity. Pure examples of these types are perhajis some^A'hat rare, the cases being complicated by retrusion of the upper teeth, but for the sake of clear- ness the latter vvUl be considered separ- ately. The class includes examples of remarkable deformity, and the exact cause is not understood. Obviously there exists an over-development of the mandible (prognathism) in many cases, or at least evidence of an irregularity of development (see Figs. 214, 215). In those cases where the teeth are cliiefly at fault it is reason- able to suppose that the original cause of the pre-normal occlusion has been an excessive gro^vth of bone about the angle of the mandible at a compara- tively early age. On the other hand, protrusion '* i® probably true that prominence of rery badly the mandible itself generally occurs as Fig. 217. — Portrait of case shown in Fig. 216. the features there referred to. Note the result of abnormal development during the (and mandible) are at fault ; but, inasmuch as a I later periods of adolescence, and cases have been 131 described in which the error of occlusion and the protrusion of the mandible commenced con- temporaneously with the eruption of the third Fig. 2 is. — Inferior protrusion (prognathism) combined with superior retrusion (retrognathisni). Tlie lower arch is well developed, but not abnormally large ; the posterior teeth are all tilted lingually. The maxilla and upper arch are badly developed. The lower molars and premolars are in pre-normal occlusion (one unit) and also in buccal occlusion. The retroclination of the lower incisors and canines is caused by pressure of the lower lip. (N'orman G. Bennett.) molars. But the real cause of excessive develop- ment of bone of one kind or another is for the present quite obscure. There is undoubted evidence of uilierited tendency in many cases. Li other cases habit seems to play an important part in the development of this deformity, and according to Henry A. Baker (17) the condyle then adopts an abnormally anterior position ; he believes that it is only in such examples that the deformity may be reduced by a backward movement of the whole mandible. Treatment. — Whenever it is thought that the deformity is prirnarily one of habit an attempt should be made to reduce the mandible with the skull- and chin-cap. Where this is impossible, the first necessity of treatment is to extract the two first lower premolars ; the anterior teeth can then be retruded by means of inter-maxillary force associated with the application of occipital force. Where the deformity concerns chiefly the teeth this wiU usually effect a successful result, but in cases where the mandible is pro- truded, this prominence will be somewhat accentuated, and it is justifiable to move forward the upper incisors to some extent rather than retrude the lowers so far as would be necessarj' to cause them to occlude lingually with the uppers. A move- ment of the crowTis alone -of the lower anterior teeth will not as a rule suffice to correct the deformity, and the "contouring appliance" of Case is probably the best method of retruding the roots also. It must be agreed that cases of this class are among the most difficult to treat with permanently good results ; but successful results with the skull- and chin -cap were re- corded by F. Heuckeroth (90) (91) as long ago as 1892. Abnormal development continued, as it often is, until a late age defies treat- ment by mechanical means, and even in the simpler cases retention appliances are neces- sary for a prolonged period. The somewhat severe operation of double resection of the mandible was probably first recommended by Fig. 219. — Portrait of case shown in Fig. 218. Note the depressed upper lip, and the prominent mandible with very obtuse angle. Angle. The first case that the \vriter can find is recorded by J. Wiipple (170), and the opera- tion was performed by Blair. After removal 132 of a piece of bone on each side the bones were wired. Tlie wires failed to hold, and Wliipple continued the treatment with fracture bands and traction screws with a considerable measure Fig. 220. — Double protrusion with well-formed arches and normal occlusion. The right- hand figures show the result of treatment by extraction of four first premolars and drawing back the anterior teeth. (C. L. Goddard ; Trans. Amer. Soc. of Ortho- dontists; Items of Interest.) of success. Angle (5) considers that a better result ^^ould have been obtained if a metal or vulcanite splint, made to a corrected model and cemented to the teeth, according to the method adopted in case of fracture, had been employed, instead of wiring the bones. Operations on other cases have been carried out with appa- rently satisfactory results by Arbuthnot-Lane (ft) in England, and others in America (19) (28) (147) ; and recently by H. P. Pickerill (129) in Xew Zealand. The methods are fully discussed by W. Wayne Babcock (10). Class (e), Superior Retrusion. — In this class the lower teeth are in normal relationship with the upper part of the face. There is an appear- ance of inferior protrusion, ■\\hich is really due to the whole upper arch being placed too far back. In many cases the upper arch seems to be entirely too small for the lower and there is not only ' post-normal occlusion of the upper molars and premolars, but lingual malocclusion as well. Variations may occur in the position of the mandilile in relation to the lower teeth and to the facial contour, but in pure examples of superior retrusion these small variations are only of academic mterest, and do not affect the salient features of the deformity (see Figs. 216, 217). The cause of this medial misplacement and contraction of the entue upper arch is obscure. In many cases it is clearly connected with nasal stenosis and consequent imper- fect expansion and growth of the maxilla (retrogna- thism), and in fact a condition of open bite due to the same cause is often combined with the other deformity. Turner (155, p. 337) well remarks : "If the difficulty of breathing, even of mouth - breathing, be very great owing to adenoids, en- larged tonsils, or enlarged lingual tonsUs, the child \\ill not merely drop the jaw inter- mittently, but will constantly hold the mandible down- wards and forwards Thus the mandibular arch by muscular action entirely escapes from the containing maxillary arch, and a maxilla of stimted growth and Fifi -INji'ti'aits ui cii.se shown in Fig. 22l.) ; treatment ; B, after treatment. tore compressed by mouth -breathing is opposed by a full-grown mandible whose horizontal ramus may have been compressed by excessive muscular action (mylo-hyoids) and by excessive lateral pressure. All this means inferior protrusion. 133 The appearance of protrusion is accentuated on closing the teeth, as in edentulous old people." Case attributes the evil to extraction of the first permanent molars. No doubt this is a fruitful cause of maxillary contraction, but it is difficult to see how upper incisors that have fully erupted in normal labial occlusion with the lower will be induced to fall back as the result of such interference. In eases of deficient anterior development when the upper incisors are already in lingual occlusion with the lower, extraction of the first permanent molars will, of course, intensify the evil and produce an ex- tremely contracted upper arch. However, the only cases properly included in this class are those in which all the teeth are present, or at any rate those in which extraction has been an incident rather than a cause of evil ; among such many ex- amples of the deformity under discussion occur. Treatment. — Treatment is difficult and unsatis- factory, for the reason that no application of mechanical force will com- pensate for defective bony growth. For the sake of appearance it is often good treatment to restore the anterior teeth to normal occlusion by mov- ing forward both cro\TOs and roots, and to insert artificial substitutes pos- teriorly. Where the maxiLIarjf deformity is not excessive it may be per- missible to accept the evU, such as it is and reduce the lower arch m the way already described. Combinations of Inferior Protrusion and Superior Retrusion. — It should be clearly understood that just as inferior retrusion and superior protrusion occur commonly in combination, so also do inferior protrusion and superior retrusion (see Figs. 21S, 219). The treatment necessary will then involve both arches, and in fact may be the simpler for that reason, because not only is a smaller movement of the teeth of each arch required, but the use of inter-maxillary force is the more applicable. Class (f), Double Protrusion. — In this class the relationshij) between the upper and lower teeth is normal, but both arches arc placed too far forward in relation to the upper part of the face and lips, and possibly an overgrowth of bone produces a share in the deformity. The condition is not very common, but the pre- placement or proclination is very prejudicial to appearance. The mandible as a whole shares m the prominence of the teeth to a vary- ing extent, but as a general rule the deformity involves the teeth alone or chiefly. The align- ment of the teeth is generally regular, and the prominence of the upper incisors often includes the roots and superjacent l)one as much as the crowns. A good example of the condition is figured and described by C. L. Goddard (78), Fig. 222. — Left-hand figures show double protrusion «itli nonual ocehision. Middle figiu-es show normal molar occlusion and normal profile. Right-hand figures show double retrusion (the lower arch is in post-normal occlusion). The face casts are very good examples of these types of profile. (C. S. Case : Dental Orthopedia.) who extracted the four first premolars as part of the method of treatment (see Figs. 220, 221). In the discussion on the pajier. by E. H. Anglo and others, rather contradictory views were expressed. Angle regards such cases as extreme rarities, and as belonging to a special type of face. He considers Goddard's treat- ment incorrect, and that widening the arches and reduction of the incisors would have produced a more satisfactory result. Other speakers considered the original condition more in harmony with the type of face than the condition produced by Goddard's treatment. In the clinical experience of the writer, such 134 cases, although not common, are not ex- tremely rare, and in his opinion the best results cannot often be obtained without the aid of extraction. In a study of the question from the comparative standpoint, E. C. Kirk (99) speaks of irregularities of position of the dental arches, even though the occlusion is perfect. The cause of the condition is not known. Beyond the fact that there is excessive bony gro^^i:li (prognathism), approaching almost to the condition usually characterized as hyper- trophy, little more can be said. It is diiiScult to connect the deformity with conditions of Fig. 223. — Lingual occlusiuu uf second right lower molar. Lingual displacement of lower lateral incisors. (G. Northcroft.) environment, and although it is probable that the potentiality must exist as a genetic varia- tion, there is not sufficient evidence of its direct transmissibility as an inherited characteristic. Treatment. — Treatment depends upon the extent of the deformity. As has just been said, in many cases good results can be achieved by expansion of the arches and lingual movement of incisors. In others four first premolars, or posterior teeth when extensively carious, must be removed prior to reduction of incisors. It will often be necessary to draw back the roots j^i well as the crowns of the upper teeth, but jjjs form of treatment is less efficacious, and j^g '^nately less often necessary, in the case of of thf^^'" incisors and canines. and to(S)' Double Retrusion. — This is an unusual of supp'^' ^^^ ^^ *^'^^ opposite of the last ; the arches are in normal occlusion, but are post-nor- mally placed. The amount of retrognathism of the mandible itself is variable, but is not usually very obvious. In fact the diminished support to the lips, and the accentuation of the normal folds of the lips, cause the chin to appear rela- tively prominent, and produce an appearance somewhat similar to tliat caused by a close-bite malocclusion. The incisors often have a lingual inclination (retroclination) (see Fig. 222). The cause 'of the condition, beyond the fact that bony development is uniformly deficient (retrognathism), is unknown.^ Treatment. — Treatment at the best is unsatisfactory; any general movement of all the teeth is out of the ques- tion. The lingual inclination may be corrected with bene- ficial results, but otherwise cases of only moderate de- formity are best left alone. It is sometimes recommended to advance the anterior teeth and supply artificial substi- tutes for the spaces thereby created, but the wisdom of this course is doubtful. 3.— LATERAL. Reference has already been made to the fact that in cases of ill-developed upper arches the upper buccal teeth occlude with the lower in such a way that the outer cusps of the upper are lingual to the outer cusps of the lower. A remarkable example of the reverse condition in which the lower teeth are completely lingual to the upper, and in fact do not occlude at all, is described by J. H. Badcock (13). Lateral malocclusion of a single upper or lower premolar or molar is not at all uncommon (see Figs. 223, 201, 207). A condition in which on one side the occlusion is apparently normal, and on the other the upper teeth are in lingual malocclusion, sometimes occurs, and is often known as " cross-bite ". The mandible usually exhibits lateral deviation, as shown by the relation of the inter-space between the central incisors in the upper and lower arches, and at the point of crossing there may be an edge to edge occlusion, or an inter- locking facilitated by rotation of an upper in- cisor. In these cases the real error is often mainly on the apparently normal side, and expansion of the upper arch on that side is necessary to permit the correction of the deviation of the mandible. As a secondary result of the faulty ' It is, of course, here assiuned that the normal number of teeth are present. The condition is a natural result of absence of some of the teeth. The writer has experi- ence of such a case. See also J. L. Courrier, Dental Cosmos, July 1911. 135 occlusion on the other side there is usually some displacement of the upper canine or other individual teeth. The deformity sometimes commences in the deciduous dentition, and an example is figured in the next section from the ^vriter"s practice, in which the first cause was factitious, and the condition the outcome of habit. Li other cases it is probable that misplacement of one or two individual teeth and consequent malocclusion may cause deviation of the mandible, and that contraction of the upper arch on the side from which the mandible deviates follows as the result of interaction of the cusps and the pressure of the cheek. Contraction of the mandible on the opposite side is also likely. Treatment. — The treatment of almost all cases of this class affecting several teeth resolves itself into expansion, either of the whole upper arch, or of one side of the upper or lower. The deviation of the mandible can then be easily of a removable plate. Retention is only neces- sary for a short period, as the normal interac- tion of the cusps when once restored prevents recurrence. Fig. 224. — Separation of deciduous central incisors by abnormal fraenimr labii. (Xorman G. Bennett.) corrected by means of suitably arranged inclined planes and flanges as fixtures to the upper buccal teeth on one or both sides, or by means Fig. 225. — Proclination of upper deciduous incisors and retrocliuation of lower deciduous incisors due to thumb-sucking. (G. Northcrojt.) Part IV Deciduous Dentition It has seemed best to consider briefly ab- normalities in the deciduous dentition after those of the permanent dentition. This may at first sight appear to be a reversal of the logical order of procedure, but examples of the latter are more frequent and more varied, and afford a better opportunity of taking a comprehensive survey of the subject. Further- more, in discussmg the subject from the aetio- logical standpoint, the causation of many deformities in the second dentition has been found in defective development while the first teeth are still in place ; and it becomes easier to try and go back a little further, and find the relation between such defective development and the concrete effects of it manifested at so early a period as from the third to the sixth years or earlier. Misplacements due to local causes are un- common, but supernumeraries and malformed teeth have been recorded. Abnormal fraenum labii causes separation of the deciduous in- CLSors (see Fig. 224), and the condition should receive treatment in order that the permanent incisors may have an opportunity to erupt normally. The iiabit of finger- and thumb-suckuig of course affects the deciduous incisors in a maimer similar to that in which it influences the position of the permanent incisors when the habit is continued (see Figs. 225, 226). To what extent misplacement of the deciduous teeth from this cause wUl produce a similar deformity afterwards if the habit has ceased is uncertain. In any case 136 the habit should be cured as soon as possible, but it is probably best to a^^ait the eruption of the permanent meisors and then apply treatment if necessary. Caries of approximal surfaces, especially of molars, allows movement of adjacent teeth and the development of a faulty occlusion, which becomes more pronounced with the eruption of the first permanent molars and later teeth. Preventive treatment consists in fillmg, with restoration of contour. Malpositions of mdividual teeth, such as slight rotation of one or more uicisors from want of space, are occasionally seen (see Figs. 227, 228). These are probably due to defective bony de- velopment dating from infancy. Examples are given by W. M. Dailey (64). The wTiter refers elsewhere (see pp. 114, 137 ; Figs. 190, 234, 235) to a case of apparent inlieritance of abnormal alignment and ex- cessive overbite m the incisor region. North- croft (122) has shown several examples of excessive overbite among twenty-five children find a defuiite post-normal occlusion to the extent of one unit, though examination of a large number of children would probably dis- FiG. 22G. — Protrusion of upper deciduous incisors in patient aged 3i years, due to thumb-sucking. The figuTe.s on the left (tliree months later) show the result of treatment. (W. W. James : Trans. B.S.S.O. ; Dental Record.) from two and a quarter to six and a half years of age (see Fig. 241). By far the most important defect noticeable in the deciduous dentition (apart from the ^^•ant of spacing m the anterior region, which is a certain forerunner of later deformity) is a com- mencing faulty occlusion in the molar region, in which the lower molars are posterior to the normal position. It is perhaps more rare to Fig. 227. — Overlapping upper deciduous central incisors. (G. Northcroft.) ^ _r cover a good many cases (see Figs. 229, 2S0, 231). The successfid treatment by inter-maxillary force of such a case due to adenoids is recorded by Guilhermena P. Mendell (116) (see Figs. 232, 233) ; the subsequent development of this case (117) was not so satisfactory as might have been expected ; but, as G. P. Mendell remarks, this was very likely due to the adenoids having been allowed to remain because they were small in amount. The usual feature is a gradual development of a condition in which each molar occludes whoUy and solely with the corresponding tooth in the ujjper jaw. It is natural to correlate this defect "ith the insufficient anterior spacing, and it seems obvious that insufficient growth takes jDlace at the condyle and angle of the mandible as well as in other parts of both ja«s. There may also be insuificient transverse development of the upjjer arch, which, as has been said, should normally increase in width during the period Fig. 228. — Rotation and Ungual displacement of right lower lateral deciduous incisor. (G. Northcroft.) of the deciduous dentition, and it is probable that the factor of mouth-breathing and nasal stenosis enters thus early into many of these cases. In considering this gradualdevelopraent \_ 137 of faulty molar occlusion it must be remembered that the crowns of the deciduous molars have flatter surfaces and smaller cusps than the permanent teeth, and that interlocking scarcely exists, especially after wear of the cusps. Credit is due to G. Northcroft (119) for emi^hasizing the import- ance of seeking the commencement of what will be a post-normal occlusion of the permanent teeth in faulty occlusion of the decidu- ous molars. Among twenty cases of abnormality in the deciduous dentition before the eruption of the first permanent molars, he found six cases showing post- normal occlusion. He further points out that the average medio- distal width of the lower decidu- ous molars is r4 mm. greater than that of the upper, and that therefore any great discrepancy between these, or any diminution of space in the upper arch caused by caries, will facilitate the production of an occlusion in which the lower teeth are posterior to normal or the upper are anterior to normal. This argument, drawn result of the deciduous upper centrals erupting before the lower, as sometimes happens. The writer has observed a very instructive case (referred to on pp. 114, 136, as an example of excessive overlap in the incisor region) in which Fig. 229. — Inferior retrusion. Post-normal occlusion (one unit) of deciduous arch in very young patient. (Harold Chapman.) from a consideration of the teeth themselves, is interesting as affording an additional explana- tion to that derived from insufficient mandi- bular development about the angle and condyle. Northcroft has also drawn attention to the possibility of faulty occlusion occurring as a 5 * Fig. 230. — Inferior retrusion and secondary proclination of upper incisors. Lower deciduous arch post-normal (one unit), molars also lingual. (Harold Chapman.) the upper mcisors erupted first and exhibited an abnormal alignment, almost certainly inherited with the edges directed unduly backwards, instead of vertically. A post-normal occlusion of the entire lower arch followed almost of necessity from thLs condition (see Figs. 234,235). The proper treatment for such a case is plainly to correct the deciduous upper incisors before the age of six, and at least afford an opportunity, with the wear of the molar cusps, for the lower jaw to move forward and allow the first permanent molars to achieve a normal occlusion (see Fig. 236). Harold Chapman (46), in an excellent study of the decidu- ous dentition, expresses his belief that the discrepancy between the medio-distal width of the upper and lower molars is greater than 14 mm., and that the distal margin of the second lower is but little if at all anterior to the distal margin of the second upper molar. He deduces from this that the first lower permanent molar must move forward more than the upper molar to produce normal occlusion. However, it is probable that such examples cannot be regarded as normal, and that in any case the downward and forward rotatory movement of the first upper permanent molar during eruption will generally ensure locking of the cusps with the lower. It should be remembered that the lower lowt 138 usually, though not always, erupts first. The early development of post-normal occlusion in connection with tlie differences m size between for treatment for such young children, when so much depends upon the character of the mdividual. An attempt should usually be made to remedy as soon as possible such gross deformities as those just described. Improved knowledge of the aetiology of abnormalities of occlusion tends to show with increasing force the importance of early treat- ment. Only a few years ago arguments were directed to show that treatment should not Fig. 231. — Skull sliowing post-normal occlusion of lower deciduous molars. (Harold Chapman : Trans. B.S.S.O. ; Denial Record.) the deciduous and permanent teeth is discussed by Simms (141). As regards other gross deformities Paton Pollitt (131) has recorded a very rare case of pre-normal occlusion (see Fig. 237). Cases of buccal and lingual malocclusion are occasionally seen. An interesting example in a boy of five occurred in the writer's ex- perience ; the lower arch was deflected to the left, and the left side was in buccal occlusion with the upper, and the "crossing" occurred at the region of the left lateral (see Fig. 238). The real defect consisted in narrow- ness of the upper arch, which needed expansion on the right side, after which reduction of the Fig. 232. — Inferior retrusion and secondary proclination of upper incisors in patient aged 3} 5 years. Lower molars in post-normal occlusion (one unit). (G. P. Mendell : Denial Cosmos.) mandible and correction of occlusion were easily effected. Somewhat similar cases are recorded by C. R. Fitch (75) and G. Northcroft (121) (see Figs. 239, 240, 241, 230). Treatment. — It is diflBcult to lay down rules Fig. 233.- I'oriiait ..f L;isr sIm.hii ni Fig. 232. (Dental Cofaa n\ xix. \ Vaa n\ iv. Olei Gaultheriae Olei Cassiae . Sp. Vin. Rect. Tinct. Capsici Aq. Destillatam M. ft. collutorium. Sig.- — One teaspoonful in lialf a glass of hot water. 6 [Sia. gr. xxx. ad. 3 The question of iU effects produced by the use in the mouth of noble metals and German silver has been carefully investigated by Clarence J. Grieves (79) (80). He finds that the latter wastes considerably and produces a profound modification in the character of the saliva, to such an extent as probably to uihibit the digestion of starches by ptyalin. He therefore recommends that noble metals oiJy should be used in the mouth, although there is greater likelihood of enamel decalcification, which, however, can be largely prevented by prophy- lactic measures. Grieves discourages the use of ligatures without cemented bands, and such appliances as afford lodgement for food particles, and speaks of tlie advantages of removable appliances. It is interesting to find that it is possible for propliylaxis to be too perfect and promote caries by, as he considers, removal of mucus. He advocates silver nitrate treatment for coagulation of mucus. Part IX Surgical Treatment Before describing the various more or less complicated appliances by which teeth may be brought into correct alignment and occlu- sion, it will be well to describe the method of surgical treatment ; its application is very limited m scope, but within those limits "immediate regu- lation ", as it is usually called, is distinctly useful. There are two methods of treatment, of which the simpler wfll be first described. It consists in forcibly reducing a tooth to its proper position by means of a special pair of forceps designed by Grevers, of which one blade resembles those of an ordinary pair of straight forceps and the other is square m section and has fitted to it a T-piecc. consistmg of a slightly curved metal plate covered with thick rubber tubing, to rest on tlie gums above the roots of the tooth to be moved and tlie adjacent teeth (see Fig. 269). The particular form of abnor- mality to which the treatment is best suited, if not limited, is lingually placed upper in- cisors and canines occluding lingually with the correspondmg lower teeth. It is necessary that the normal space of the misplaced tooth should not have been encroached upon to any serious extent, although it is not necessary that the Fig. 269. — Grovers' forceps. 162 space should be ample, as the adjacent teeth can be forcibly separated a little during the operation. Tlie patient should preferably be anaesthetized, the plain blade is applied to the cuiguluni of the tooth, and the rubber-covered plate to the gum above the apex on the labial aspect, and steady forward pressure is made. On account of the elasticity of the alveolus a considerable amomit of movement of the tooth takes place without fracture of the anterior plate of alveolus, but pressure should be main- tained until fracture occurs with a sudden snap, and the tooth forced into a position slightly in advance of normal. When the alignment of the lower teeth is normal no further treatment is requu'ed, as the occlusion will be sufficient for retention, but ui some cases a swaged or cast- metal splmt, or bands, should be cemented to the tooth and adjacent teeth as soon as anj^ slight bleeding has ceased. 8uch a splint should of course have been made beforehand to a corrected model. The teeth to which the method is particularly adapted are upper lateral incisors, and if the operation is performed at an age before the complete calcification of the apex, no doubts need be entertauied as to the survival of the pulp. In fact, it may be done with toler- able safety at later ages, and Sidney Spokes (144), who has had considerable experience of the method, considers that there is no risk of death of the puljj after calcification of the apex. The operation is hi the experience of the wTiter one that can be carried out easily and successfully. The more elaborate operation, used and described by Bryan (38), and Cumiingham (62) (63), consists in dividing both plates of alveolus on each side of the misplaced tooth bet^^een it and the adjacent teeth by means of a circular saw, and then forcibly reducuig the tooth, together with the portion of alveolus attached, by means of a special pair of forceps. A vulcanite plate is used to fit over the jaw, teeth, and gums, to protect the parts during the operation of sawmg. A groove is cut in this plate exposmg the tooth to be moved, and a brace of steel or brass is embedded in the vulcanite over the apex of the root, to act as a supjiort for one beak of the forceps. The tooth can be retained in the new position until bony reunion has taken place by means of silk thread attached to it and its neighbours. There is thus no separation from the lingual plate as m the other metliod, but as this alveolus is in any ca.se soon re-formed tliere does not appear to be any great advantage therehi. Death of the pulp frequently ensues, and it must be removed before staining occurs. This method of " alveolotomy " has been u.sed by W. H. Dolamore (71), who has related a large number of cases. Instead of a circular saw he used in some instances a modified Hey's saw, or a special fret-saw. He employed Bryan's forceps, and retained the tooth m its new position by means of a metal cap cemented in position and covermg the adjacent teeth. Possibly the more elaborate method is applicable to more grossly misplaced teeth than the one first described, but, on the other hand, it is at least doubtful whether in such circumstances gradual methods would not be preferable. N. G. B. (1) 2 3 4 BIBLIOGRAPHY Allen, J. H. Obstructed Nasal Respiration and its Relation to Dental Deformities. Dental Cosmos, 1008, Vol. L, pp. 453-8. Angle, E. H. Malocclusion of the Teeth. Angle, E. H. Art in Relation to Orthodontia. Trans. Anier. Soc. of Orthodontists, 1902, p. 151. Item^ of Interest, 1903, p. 646. Angle, E. H. The Upper First Molar as a Basis of Diagnosis in Orthodontia. Trans. Amer. Soc. of Orthodontists, 1905, p. 1. Items of Interest, 1906, p. 421. Angle, E. H. Double Resection of the Lower Maxilla. Dental Cosmos, Aug. 1898, Vol. XL, p. 635. Angle, E. H. Bone-growing. 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(77) FoRBERG, E. Is the Symmetrical Extraction of the First Permanent Molar justifiable ? Srit. Dent. Jour., 1902, Vol. XXIII, p. 65. (78) GoDDABD, C. L.' Influence of the Premolar on the Profile. Trans. Amer. Soc. of Orthodontists, 1903-4, p. 144. Items of Interest, 1904, p. 421. (79) Grieves, Clarence J. Base Metal versus Noble Metal Appliances in Orthodontia. Trans. Amer. Soc. of Orthodontists, 1908, p. 45. Items of Interest, 1909, p. 326. Discussion, p. 440. (80) Grievi:s, Clarence, J. Report of Work on " Base versus Noble Metals in the Mouth." Trans. Amer. Soc. of Orthodontists, 1909. Items of Interest, 1910, p. 90. (81) Groth, Joh. An Apparatus for Discovering the Inharmonious Lines and Abnormal Traits in Maxillary Deformity. Ash's Monthly, May 1911, p. 332. (82) Guilford, S. H. Orthodontia. (83) Hall, E. E. Malocclusion from the Dentist's Standpoint. Trans. Amer. Soc. of Ortho- dontists, 1909. Items of Interest, 1910, p. 337. (Si) Hartz, Henry J. The Influence of Nasal Ob- struction and Mouth-breathing upon the Development of the Face, Palate, Teeth and Chest. Trans. Amer. Soc. of Orthodontists, 190 7, p. 57. Items of Interest, 1908, p. 344. Discussion, p. 357. (85) Hawley, C. a. Determination of the Normal Arch. Dental Cosmos, 1905, Vol. XLVII, pp. 541-52. (86) Hawley, C. A. The Function of the Teeth in the Development of the Face. Dental Cosmos, 1910, Vol. LII, p. 1053. (87) Hawley, C. A. An Accurate Method in Ortho- dontia. Trans. Amer. Soc. of Orthodontists, 1905, p. 174. Items of Interest, 1906, p. 895. (88) H.awley, C. a. a Study of Maxillary Move- ments. Items of Interest, June, 1912, p. ■126. (89) Herbst, Emil. On Appearances in the Buccal Cavity, consequent upon the External Air Pressure. (Trans, from " Deutschen Zahnarzt- lichen Wochenschrift "). Ash's Quarterly, March 1904, p. 1. (90) Hettckeroth, F. Protrusion of Lower Jaw in a Female Patient Aged Eleven. Ash's Quarterly, June 1892, p. 89. (91) Heuckeroth, F. Abnormal Size of the Lower Jaw in Proportion to the Entire Skull in a Female aged Seventeen. Ash's Quarterly, Sept. 1892, p. 183. (92) Heuckeroth, F. Open Bite in a Female aged Fifteen. Ash's Quarterly, Dec. 1892, p. 281. (93) Hopson, Montagu F. Heredity. Trans. B.S.S.O., November 1909. Dental Record, 1910, Vol. XXX, p. 1. Discussion, p. 43. (94) Johnson, H. H. Forcing Eruption of Canines. Dental Cosmos, 1907, Vol. XLIX, p. 266. (95) Keith, Arthur. The Expansion of the Maxillary Antrum. Brit. Jour, of Dent. Sci., June 16, 1902, p. 529. (96) Ketcham, a. H. Are the " New School Ortho- dontists " practising Excessive Expansion ? Dental Cosmos, 1910, Vol. LII, p. 949. (97) Ketcham, A. H. Treatment by the Orthodontist Supplementing that by the Hhinologist. Dental Cosmos, Dec. 1912, Vol. LIV, p. 1312. (98) Ketcham, A. H. The Radiograph in Ortho- dontia. Items of Interest, 1911, p. 281. (99) Kirk, E. C. A Comparative Study of Mandibular Protrusion. Trans. Amer. Soc. of Orthodontists, 1902, p. 48. Items of Interest, 1903, p. 270. (100) KoHLER, C. H. The Deformities of the Superior Maxilla from the Standpoint of the Rhinologist. Trans. Amer. Soc. of Orthodontists, 1902, p. 28. Iterns of Interest, 1903, p. 180. Discussion, p. 195. (101) KoRBTTZ, Alfred. The Geometrical Deter- mination of the Orthodontic (Expansion) Arch. Brit. Dent. Jour., 1911, Vol. XXXII, p. 1129. (102) KoRNEB, E. M. Rickets, Adenoids, and Palatal Deformities. Brit. Dent. Jour., 1907, Vol. XXVIII, p. 303. ( 103) Landsberger, Richard. The Widening of the Floor of the Nose by Means of Maxillary Expansion. (Trans, from " Correspondenz Blatt fiir Zahnarzte "). Ash's Quarterly, July 1909, p. 385. (104) Landsberger, Richard. Anatomical Altera- tions in the Osseous Tissue of the Palate during Maxillary Orthopaedic Treatment. Ash's Quarterly, July 1909, p. 395. (105) LiscHER, B. E. Principles and Methods of Orthodontics. (106) Lock, R. H. Variation, Heredity, and Evolu- tion. (107) Lockett, a. C. The Results of Extraction. Trans. B.S.S.O., Jan. 1909. Dental Record, 1909, Vol. XXIX, p. 331. (108) LouRiE, Llovd S. Distal Movement of Molars and Bicuspids. Trans. Amer. Soc. of Ortho- dontists, 1902, p. 101. Items of Interest, 1903, p. 433. (109) LouRiE, Lloyd S. The Necessity for Early Treatment in Orthodontia. Dental Review, 1904, p. 427. (110) McBride, R. D. Jimaping the Bite. Dental Review, 1901, p. 841. (111) MoBbide, R. D. Modern Developments in Orthodontia. Dental Review, 1904, p. 1029. (112) McKenzie, Dan. The Relation of Dentistry and Oto-Laryngology. Trans. B.S.S.O., Oct. 1909. Dental Record, 1909, Vol. XXIX, p. 713. (113) McKenzie, Dan. Adenoids, Deformities of the Palate, and Artificial Infant Feeding. An Analysis of Two Hundred and Twenty-two Cases. Brit. Dent. Jour., 1909, Vol. XXX, p. 159. (114) Marfan. Rickets in Relation to Arched Palate and Adenoids. Brit. Dent. Jour., 1908, Vol. XXIX, p. 247. (115) Mass.art, Jean. Evolution by Atrophy. (116) Mendell, GtfiLHERMENA P. Corrected Case of Malocclusion of Temporary Teeth. Dental Cosmos, 1907, Vol. XLIX, p.' 820. (117) Mendell, Gotlhermena P. A Corrected Case of Pronounced Malocclusion of the Deciduous Teeth — Continued. Dental Cosmos, 1911, Vol. LIll,p. 530. (118) MosHER, Harris Peyton. The Influence of the Pre-maxillae upon the Form of the Hard Palate and upon the Septum. Trans. Amer. Soc. of Orthodontists, 1908, p. 88. Items of Interest, 1909, p. 481. (119) Nobthcroft, G. Orthodontia. Brit. Dent. Jour., 1908, Vol. XXIX, p. 11. (120) Nobthcroft, G. Trans. B.S.S.O., Jan. to April 1908. Dental Record, 1908, Vol. XXVIII, p. 214. (121) Northcroft, G. Lateral Malocclusion in Deciduous Dentition. Trans. B.S.S.O., Dec. 1909. Dental Record, 1910, Vol. XXX, p. 105. (122) Northcboft, G. A Few Observations on the Mouths of 25 Children from Two and a Quarter to Six and a Half Years of Age. Dental Record, Feb. 1910, Vol. XXX, p. 116 (from Dental Review). 165 An Operation on the Fraenum B.S.S.O., 1912. Dental Record, (123) NORTHCROFT, G. Labii. Trans. p. 874. (124) NoYES, Frederick B. A Study of the Peri- dental Membrane from the Orthodontist's Standpoint. Trans. Ainer. Soc. of Ortho- dontists, 1903—4, p. 144. Items of Interest, 1904, p. 795. (125) Ottolengui, Rodrigues. A Contribution to tlie Knowledge of the Aetiology and Treat- ment of Cases in Class II. Trans. Amer. Soc. of Orthodontists, 1907, p. 85. Items of Interest, 1908, p. 495. Discussion, p. 510. (126) Ottolengui, RoDRiorE-;. Discussion on Early Treatment of Malocclusion. [J. Lowe Yoting (176).] Dental Cosmos, 1909, Vol. LI, p. 580. (127) Pedley, T. F. Rubber Teat and Deformities of the Jaws. Brit. Dent. Jour., 1907, Vol. XXVIII, p. 249. (128) Pfaff, W. Stenosis of Nasal Cavity — Abnormal Position of Teeth. Dental Cosmos, 1905, Vol. XLVII, p. 570. (129) PuKERiLL, H. P. Double Resection of the Mandible. Dental Cosmos, Nov. 1912, Vol. LIV, p. 1114. (130) Plumley, A. G. Adenoids in Relation to Mouth-breathing. Brit. Dent. Jour., 1906, Vol. XXVII, p. 1011. (131) PoLLiTT, G. Paton. Inferior Protrusion in Deciduous Dentition. Trans. B.S.S.O., Feb. 1910. Dental Record, 1910, Vol. XXX, p. 242. (132) PuLLEN, H. A. Johnson s Operative Dentistry. (133) PuLLEN, H. A. Mouth-breathing. Dental Cos- mos, 1906, Vol. XLVIII, pp. 998-1014. (134) PuLLEN, H. A. Expansion of the Dental Arch and Opening the Maxillary Suture, in Relation to the Development of the Internal and External Face. Dental Cosmos, May 1912, Vol. LIV, p; 509. (135) PuLLEN, R. N. Early Corrective Treatment of Malocclusion. Items of Interest, 1909, p. 908. (136) Read, Henry. Facial Expression from the Point of View of the Artist. Items of Interest, 1911, p. 328. (137) Rogers, Alfred P. Art in Model-making. Trans. Amer. Soc. of Orthodontists, 1905, p. 79. Items of Interest, 1906, p. 060. (138) Rogers, Alfred P. A Consideration of Infra- occlusion. Trans. Amer. Soc. of Orthodontists, 1908, p. 27. Items of Interest, 1909, p. 248. (,139) RusHTON, William. Mouth-breathing and Facial Contour; with a Suggested Classifica- tion. Trans. B.S.S.O., Jan. 1911. Dental Record, 1911, Vol. XXXI, p. 131. (140) RusHTON, William. The Effects of Mouth- treathing on Facial Contour. Brit. Dent. Jour., 1911, Vol. XXXII, p. 1132. (141) SIMMS, W. The Eruption of the Teeth con- sidered especially with Reference to Cases of Superior Protrusion. Brit. Dent. Jour., 1909, Vol. XXX, p. 1238. (142) Spicer, Sc.\nes. On Nasal Obstruction and Mouth-1 reathing as Factors in the Aetiology of Caries of the Teeth, and in the Development of the Vaulted Palate. Trans. Odont. Soc, 1889-90, Vol. XXII, p. 75. (143) Spiller, J. E. A Classification of Dento-facial Irregularities based on the Mechanical Factors of Causation. Trans. B.S.S.O. Dental Re- cord, March 1911, Vol. XXXI, p. 259. (144) Spokes, Sidney. The Forcible Advancement of Ingrowing Teeth. Trans. Odont. Soc, 1894-5, Vol. XXVII, p. 180. (145) Str.vng, R. H. W. Preventive Orthodontia. Dental Cosmos, 1908, Vol. L, p. 797. 146) 147) 148) 149) 160) 1.^1) 152) 153) 154) 155) 156) 157) 158) 159) 160) 161) 162) 103) 164) 165) 166) 167) 168)"^' 169) 170) 171) 172) SuMMA, Richard. A Few Thoughts Concern- ing the Teetli and their Osseous Base. Trans. Amer. Soc. of Orthodontists, 1905, p. 41. Items of Interest, 1906, p. 493. Talbot, W. O. A Case of Double Resection of I he Mandible. Trans. Amer. Soc of Ortho- dontists, 1906, p. 94. Items of Interest, 1907, p. 631. Aetiology of Face, Nose and Jaw Dental Cosmos, 1909, Vol. LI, Talbot, E. S. Deformities. p. 754. Talbot, E. S. Thompson, A. The Irregularities of the Teeth. H. Malocclusion of the Teeth iimongthe Ancient Peruvians. Dental Record, 1903. Vol. XXIII, p. 390, from Items of Interest. Thomson, J. Arthur. Heredity. TiLLEY, Herbert. The Relationship of Nasal Obstruction in Children to Defective Develop- ment of the Jaw. Trans. B.S.S.O., Jan. to April 1908. Dental Record, 1908, Vol. XXVIII, p. 297. Tomes & Nowell. A System of Dental Surgery. Turner, J. G. Influence of the Growth of Bone on the Positions of tlio Teeth. Brit. Dent. Jour., 1905, Vol. XXVI, pp. 329, 379. Turner, J. G. Aetiology and Prevention of Deformities of Dental Arches. Brit. Dent. Jour., 1907, Vol. XXVIII, pp. 193, 241, 337. Turner, J. G. Trans. B.S.S.O., Oct. 1908 Dental Record, 1908, Vol. XXVIII, p. 656. Turner, J. G. Report on Phenomena found in Post-normal Occlusion. Trans. B.S.S.O. Dental Record, 1910, Vol. XXX, p. 298. Vandervelde, Emile. Evolution by Atrophy. VowLES, F. Tension Springs in Orthodontia. Brit. Dent. Jour., 1907, Vol. XXVIII, p. 669. VisiCK, Hedley C. a Case of Open Bite. Trans. B.S.S.O., July 1909. Dental Record, 1909, Vol. XXIX, p. 655. VisicK, Hedley C. The Northcroft Plaster- plane. Trans. Amer. Soc. of Orthodontists. 1909. Items of Interest, 1910, p. 124. Wallace, J. Sim. Irregularities of the Teeth. Wallace, J. Sim. Trans. B.S.S.O., Jan. to April 1908. Dental Record, 1908, Vol. XXVIII, p. 173. Wallace, J. Sim. Trans. B.S.S.O., Feb. 1911. Dental Record, 1911, Vol. XXXI. p. 216. Wallace, J. Sim. A Classification of Dento- facial Irregularities. Proc Roy. Soc. of Med. (Odont. Sec), Vol. I, p. 140. Waller, H. Ewan. The Relationship of the Thyroid Gland to Dentistry. Brit. Dent. Jour., 1912, Vol. XXXIIL p. 4. Waugh, Leuman M. The Laws of Antagoniza- tion of the Teeth in Orthodontia. Trans. Amer. Soc of Orthodontists, 1909. Items of Interest, 1910, p. 192. Discussion, p. 257. Weeks, S. Merrill. Consideration of the Temporo-mandibular Region. Trans. Amer. Soc. of Orthodontists, 1908, p. 157. Items of Interest, 1909, p. 583. Weismann, A. The Germ Plasm — A Theory of Heredity. Whipple, J. Double Resection of the Inferior Maxilla for Protruding Lower Jaw. Dental Cosmos, July 1898, Vol. XL, p. 552. Whitaker, W. R. H. Rollinson. The Relation- ship of Nasal Obstruction to Contracted Arches luid Dental Irregularities. Brit. Dent. Jour., .June 1, 1911, Vol. XXXII, p. 537. Willis, F. M. Rapid Separation of the Superior Maxillary Bones to relieve Defieeted Nasal Septum and Contracted Nares. Dental Cosmos. 1911, Vol. LIII, p. 784. 166 (173) Wright, Geo. H. Deformities of the Nasal Respiratory Tract. Dental Cosmos, Mar. 1912, Vol. LI V. p. 261. (174) Wright, William. The Teeth and Jaws of a Series of Prehistoric Skulls. Brit. Dent. Jour., 1903, Vol. XXIV, p. 57. (175) YoNGE, E. S. Abnormalities in Relation to Disease of Upper Air Passages. Dental Record, 1908, Vol. XXVIII, p. 14. (176) yoTJNG, J. Lowe. Early Treatment of Mal- occlusion. Denial Cosmos, 1909, Vol. LI, p. 397. Discussion, p. 665. (177) Young, J. Lowe. Deficient Development of the Arches of the Deciduous Teeth and the Necessity of Early Treatment. Dental Cosmos, 1910, Vol. LII, p. 1185. (178) Zeliska, Franz. The Influence of the Atmo- spheric Pressure upon the Moulding of the Dental Arch. Dental Cosmos, 1905, Vol. XL VII, p. 583. CHAPTER VIT ABNORMALITIES OF POSITION— TREATMENT BY MEANS OF APPLIANCES The purpose of this chapter is to deal with the treatment of orthodontical cases ; with the movement of the teetli and associated struc- tures ; and with the retention of these move- ments till the teeth have become fixed in their new positions, and the tendency to relapse has been overcome by natural means, i. e. by the establishment of physiological equilibrium between all the tissues involved. The previous chapters dealt with orthodontics from the aetiological and pathological stand- points, so that the object of this will not be to treat of the subject from the point of view of different classes, but according to the tooth movements that are to be performed. The reasons for, and directions of, these movements have been decided upon before this aspect of the subject has been taken up. Tooth movement \\ ill be considered in two classes — I. — The major movements, i. e. the move- ment of several teeth in the same direction without special attention to particularities of individual teeth ; II. — The minor movements, i. e. the move- ment of individual teeth ; so that the operator may select and plan out the course of treatment by reference to the following paragraphs, which deal with all the movements he is likely to be called upon to effect. The object here is to treat of principles rather than of particular cases, because if the principles of moving teeth, collectively and individually, in all directions, are thoroughly grasped, the orthodontist will have no difficulty m apj^ly- ing them in their various combinations, whereas it would be impracticable and require need- less repetition to deal with the treatment of numerous actual cases covering all possi- bilities. Therefore, the operator, having de- cided what tooth movements he wishes to accomplish in any given case, and having mastered the general principles mvolved m all cases, such as anchorage, adjustment of appli- ances, the use of certain accessories common to all cases, etc., must refer to the sections deal- ing with such movements in order to learn how they are to be brought about, and not expect to find an exhaustive exposition of the treatment of an identical case, though a description of several typical ones will conclude this subject. (See pp. 239-240.) The problems that present themselves in any case are five — A. Wliat irregularities are present ? B. What condition is it desired to create ? C. \Vliat movements, major and minor, are necessary to brmg this about ? D. How shall these movements be accom- plished ? — i. e. treatment. E. How, and for how long, are these move- ments to be artificially retained ? — i. e. retention. Problems A, B, and C are dealt with in Chapters IV, V, and VI, but as they are questions that are vitally connected with treatment it will not be out of place to refer to them again, but entirely from the point of view of treatment. A. What irregularities are present ? These must not be considered from the point of view of an obvious dental irregularity, but from the standpoint of teeth, jaws, and face — the tout ensemble of which is concerned in the irregularity ; the malocclusion is not a purely dental defect — generally speaking — but an error in bony development of which the misjalaced teeth are an expression. If regard is paid to only one very obvious deformity, such as lin- guaUy placed laterals, and that alone treated, the grosser deformities that are rarely insepar- able from this being disregarded, it would be found later that the case was little if any better than at first. Each dental arch must be considered — (1) per se ; (2) m relation to its fellow ; (3) in relation to the face. It is, therefore, of the utmost importance to decide upon all the deviations from normal in every case. 1 B. Wliat condition is it desu-ed to create ? 1 Having decided what irregularities are present, the next point to decide is w:hat condition — what positions of the teeth and jaws — shall be the goal ? 167 168 (1) Shall it be normal occlusion ? This implies the normal relation of — (a) The teeth of either jaw to one other ; (b) The teeth of one jaw to the teeth of the other jaw ; (c) The jaws to each other ; (d) The jaws to the remainder of the face. If normal occlusion is desired and to be sought, then the way is clear when once the irregularities have been diagnosed. (2) Shall it be some de\aation from that ideal (normal occlusion), which topical exigencies may necessitate ? These exigencies include — • (a) Absence of teeth — congenital or due to operative procedure. (b) The time and opportunity to undergo treatment sufficiently prolonged to establish normal occlusion may not be available. If there must be any departure from the ideal of normal occlusion the following points deserve careful consideration in arriving at a decision — (a) Whether it is possible to establish good approximal contact between all adja- cent teeth — avoiding aU spacing. (6) Whether it is possible to establish an occlusion that is perfect for the teeth that remain ; with thLs is included the tnter-digitation of cusps both medio- distally and bucco-lingually. (c) Whetlier it is possible to produce an aesthetic result. C. What movements, major and minor, are necessary to bring this about ? The previous chapters, supplemented by the preceding paragraph, fuUy answer this question, which includes the direction of movement of every tooth ; and the greatest factor in deciding this is the aesthetic one, normal occlusion of course beuig coupled with it. If it is decided that any particular tooth is in its absolutely correct position, such as an upper central or fir.st permanent molar, it is not difficult to build up a dental arcli from such fixed point, and so decide the movement each tooth must undergo. D. How sliall these movements be accom- plished (treatment) ? E. How, and for ho\\- long, are these move- ments to be artificially retained (retention) ? (See Chapter X.) The answ er to these two ([uestions demands a consideration of the subject of appliances, and to this problem considerable space must be devoted — in fact, the remaining pages allotted to this subject, — as it bears on the practical aspect of the practice of orthodontics. Before passing to it. however, the writer wishes to direct attention again for a moment to question (B) and its answer, but in another form, as he is of ophiion that therein lies the secret of failure or success. One not infrequently sees cases under treatment, of \\hich the operator has formed no clear opinion of the ultimate result he \\-ishes to produce. It is superfluous to emphasize the futility of such a proceeding. The' operator must have an object in view ; he must aim for that object and strive to the very utmost to attain it. The latter is not the greatest difficulty in orthodontics ; often it is a greater difficulty to decide \\hat tlie object shaU be, but as this must be done before the treatment of any case is undertaken, the orthodontist has set himself a task ; and having accomplished it — having attained his object — has reached the greatest difficulty, the mainten- ance of the new conditions. But now there is no reason to believe that he mUI allow the result of his labours to be rumed by neglecting this of wliicli he may be proud; he will grapple -with the problem with greater pertinacity in order that the prize may not be lost. Tlie problem is not merely to work, but to work with an object. The object has been set before the orthodontist, but probably no branch of dentis- try requires greater perseverance, concentration, and continuity, that it shall not be beyond his reach. D. How shall these movements be brought about ? Treatment. — This division of the subject deals with the actual movement of teetli, and demands a consideration of appliances and their choice. An orthodontical appliance, whatever its nature, is a macliine constructed to do certain work for which a liigh standard of efficiency is necessary. Efficiency is the one essential property that aU must possess (apart from their otlier advantages or disadvantages) ; without this they are worse than useless. But it must be constantly borne in mind that efficiency does not depend solely on the appliance, but to a much greater extent on its application and use ; that is to say, whatever form of appliance is used, the way in which it is to do its work must be thoroughly grasped, and it must be applied with sucli care and thought tliat it will not fail to jiroduce the desired results. The importance of tliis statement cannot be impressed too forcibly, and as a practical example it need only bo remembered that, by means of tlie wire bow, any tooth movement, and almost any combination of tooth movements, at one and the same time, are possible ; it is obvious, tlien, that it is of the greatest importance that whatever appliance is used, should be arranged 169 for those, and only those, movements that are to which various attachments are soldered (see intended — neither more nor less. p. 217). These are intended to APPUANCES (2) VuLCAMTE Appliances Appliances may be conveniently divided into (a) Plates not designed for expansion (see two classes— " Figs. 303, 308, 291). ~ A. Fixed, B. Removable, according as it is impossible or not for the patient to remove them from the mouth without difficulty. The Nature of the Variocs Appliances A. Fixed. — All fixed appliances are on the same principle ; they consist essentially of a wire bow, and bands to which it is attached (see Fig. 287). The wire bow passes across the Fig. 271. — Schelliugs moditication of a Coflki plate. In this instance the spring is designed to obtain the greatest amount of expansion in the canine region. 17 7 Fig. 270. — Vulcanite expansion plate of the Coffin- spring type. There are two spurs in one half of the plate fitting two tubes in the other half, wliieh keep the two halves ia correct relation to one another. WTien the spring is altered there is a tendency for the relation of the halves to one another to be disturbed. If guide-wires are not used there are clasps of platinized gold on the deciduous canines and first permanent molars to hold the plate in situ. buccal surfaces of the teeth and fits into tubes soldered to the bands, which have been at- tached to one of the back teeth (deciduous molar, premolar, or permanent molar). By means of ligatures and various attachments every tooth may be brought under control. As devised by Angle they are simple, practical, and efficient ; they can be used to deal with simple and complex cases equally well. B. Removable. — (1) Metal appliances; (2) Vulcanite appliances. (1) Metal Appliances (a) Plates similar to vulcanite plates, the description of which will apply to these also. (b) Jackson Appliances, consisting of a base of pure tin fitted to the necks of some of the teeth, 6* Fig. 272. — Badcoek screw. 1. The middle of the screw is in the form of a square boss, whereby the screw is turned; one end of the screw is smooth and rotates in the tube, 2. from wliich it cannot be removed. 3. The other end of the screw; it is threaded to correspond with the thread on the tube. 4. of the design shown to hold it in the \iilcanite. 5. A plain wire soldered to (4) and shaped as shown, the free end entering the tube, 6. which is roughened to hold it in the vulcanite ; this accessory is to prevent the two halves of the plate rotating on one another. 7. A wire tag, which holds the screw in the flask for packing. It is removed after viilcaniza- tion. 8. A metal tag on (2) to hold it in the vulcanite and prevent its rotation. To obtain a definite degree of expansion, measure the amount on the screw, coimt the niunber of threads exposed, and direct the patient to tiun the boss completely round that number of times. A quarter of a turn everj' other day is a convenient rate at wliich to proceed. This repre- sents nearly one complete turn per week. produce movement of individual teeth imder separate control, or simple collective move- ments of several teeth. Springs and the elas- ticity of rubber are the forces most generally employed. 170 {b) Plates designed for ex'pansion of the dental arches (they may in addition f)rodiice other necessary movements). There are numerous forms of these, the important ones being — ■•; (i) Coffin Plate, operated by piano-wii-e spring (see Figs. 270, 271, 301). Fig. 27.3. — Highton device. A. The device complete. B. The halves of the device, the back and front having been removed. C. The inner side of the back of the device with parallel ribs to prevent its rotation. D. The inner side of the front of the device on which is the raised spiral cam. E. The back of the device which, with the screw, clamps all the parts together. 1. The outer and exposed portion of D with a groove for turning with a screw-driver. 2. Flanges for holding the device in the vxilcanite. 3. The sides of the expanding portion of the device, through which movement is transmitted to the vulcanite. 4. Lateral flanges lying between the ribs on C. 5. Central flanges which lie in the central groove of C. These flanges have raised ends, which engage the spiral cam on D, the turning of which forces these two flanges apart. The two lateral holes on E enable the parts of the appliance to be kept clamped together. (ii) Reed Screw, operated by a screw in a threaded tube; a jack-screw may be used in the same way. (iii) Badcock Plate, operated by a screw in a threaded tube, the screw not being du'ectly attached to the vulcanite as in the Reed screw (see Figs. 272, 274). (iv) Highton Device, operated by a spiral cam (see Figs. 273, 275). Cast metal, such as gold, tm, Gartrell's metal. or Brophy's metal, may be used to replace the vulcanite in these. Advantages and Disadvantages of Fixed Appliances Advantages. The greatest effici- ency of any appliance. Give individual control of every tooth. Every tooth movement pos- sible. Not under con- trol of tlie patient and must be worn. Least liability to displace- ment. Least inter- ference with speecli and the other func- tions of the mouth. Least discomfort and bulk of any appliance. Must operate constant- ly if properly adjusted. Infrequent necessity to change the appliance. May act as a retaining appliance. Disadvantages. In many cases re- quire skilled attention once a week. The length of time required for adjust- ment. Some few patients will not trouble to exercise the necessary cleanliness. More of the opera- tor's time required to maintain the efficiency of the appliance, but this is more than com- pensated for by in- creased efficiency. Advantages and Disadvantages of Eemovable Appliances Advantages. In simple cases one appliance will satis- factorily perform the work; these eases are few. Cleanliness has been urged, but some patients do not keep the mouth clean Mith these. Controlled by pa- tient (not always an advantage), if screws or rubber is used. If scre\\'s only are used to exert force, the appliance may be used passively as a retainer. May be inconspicuous. Disadvantages. Liability not to be worn. New appliances more frequently neces- sary, as the various movements capable of beuig produced are limited, and adjust- ment beyond a certain pomt is impossible. Greater bidk. Liability to be dis- placed. Individual control of every tooth impos- sible. In some cases patient may lisp temporarily. (1) Metal Appliances. (a) Plates. Advantages. Disadvantages. Strength. Time and expense necessary for construc- tion may be out of pro- portion to the work to be performed. 171 (b) Jackson Appliances. Advantages. Disadvantages. Can be made to per- Complicated if many form a large number of individual tooth move- tooth movements at ments have to be per- one time. Low cost of formed. Adjustment material used in its of the various springs manufacture. Does difficult, not entirely cover the mucous membrane of the palate. (2) Vulcanite Appliances. (a) Plates not designed for Expansion of the Dental Arches. Advantages. Disadvantages. Ease of construction Efficiency limited to and manipulation, re- few tooth movements quiring little time to at one time, adjust. (b) Plates designed for E.xpansion of the Dental Arches. General. Advantages. Disadvantages. Expansive force ex- May be worn or erted directly on to bone not, according to the as well as on to teeth, patient's mclination. Appliance can be made and fitted at much less No individual con- cost of time to patient trol of all the teeth. and operator tlian in the case of fixed ap- paratus. (i) Coffin Plate. Advantages. Disadvantages. Rapidity of action. Adjustment easily Very low cost. Force upset. Not applica- can be applied at any Ijle in lower jaw. An- dcsired point to a chorage not satisfac- limited degree. tory when the teeth have short crowns. Not under the patient's control. (ii) Reed Screw. Advantages. Disadvantages. Ease and simplicity The two halves of of construction. the plate revolve on one another. Conse- quent loss of rigidity and impairment of adaptability. A com- plete turn of the screw must be made — the screw havmg a high pitch ; this may give too much expansion at one time. (iii) Badcock Plate. Advantages. Disadvantages. One of the best forms It must be seen that of expansion plate ; the back pressure, due operated by a single to the tendency of the nut ; amount of expan- teeth to relapse, does sion can be exactly as not cause the screw to desired. The two halves rotate backwards. The Fig. 274. — Vulcanite Badcock plate in position to expand molars, premolars, and canines ; in this case it will also move the laterals distally. The vulcanite point between tlie centrals should be cut off so as not to carry the left central distally. Platinized gold wire clasps for the first molars and first premolars are shown holding the plate in position. The surface of the plate is thickened and inclined forwards and upwards to open the bite and bring the lower jaw forward. of the plate do not re- end of the threaded volve on one another, tube should be closed Good rigidity for a a little with pliers to divided plate, and con- prevent this, sequently it may be made to perform ac- cessory movements. Crib clasps may be used to increase its j stability. Applicable to either jaw. In order j that its position may be maintamed in the lower jaw cleats should engage the lingual sul- cus of the first molar ; and in order that the lingual halves may ex- pand satisfactorily they should have their rigidity increased by metal inserted in the vulcanite. 172 (iv) Highton Device. Advantages. May be used in very Darrow jaws ; it is made in two sizes, the smal- ler of \\hich can be employed iii the smal- lest mouth. No lia- bility for screw to turn back due to inward pressure of expanded jaws. The patient con- trols the expansion, which may be little or much, as desired. Wlien expanded to its full extent this device can be re-fitted and used again. Disadvantages. Range of move- ment with the smaller device very slight ; therefore change should be made to the larger device at first opportu- nity. Not as strong as Badcock plate. ?5R? Fig. 275. — Highton device in position in a very narrow lower dental arch. There are cleats on the second deciduous molars to prevent the plate sinking into the soft tissues. To obtain the best results from removable appUances, the casts used to make these should always be from plaster impressions, in order that they may fit perfectly ; their stability, and with it the anchorage, is increased thereby. Wire clasps, or other wires that have to pass between the t\\o teeth near their contact point, should usually be strengthened, as they not only have to maintain the plate in position but the bite of the opposite jaw often comes on them. They may be strengthened and made to fit very accurately by burnishmg platinum into the space over which the wire will pass ; the clasp wire is then fitted and the two are united with solder. The fit, rigidity, and strength of the clasp is thus improved whilst its power to retain the plate in position is not interfered with. As it frequently happens that patients can only be seen at long intervals, the details regarding the accomplishment of any tooth movement with removable appliances will be dealt with. (A) Fixed Appliances To justify their name these must possess the power to remain on the teeth — in spite of any interference on the part of the patient and any force applied to the teeth through them — -which is obtained by the use of — (1) Clamp-bands, and (2) Oxy-phosphate cements. When these are used in combination the cement is only to prevent the access of fluids to tooth surface that cannot be cleansed, and so prevent decalcification of the enamel, though it often does actually increase the fixity of the band. Fixed appliances include essentially — 1. Bands — Qamp (see Figs. 277, 278) Plain (see Fig. 337) For the attach- ment of acces- sories, such as tubes and spurs. 2. Bows- Plain (see Figs. 280. 285) 1 Develop force Ribbed (see Fig. 281) 'r for tooth Divided (see Fig. 282) J movement. Wliereby teeth and bows are con- nected with one another, and teeth moved. 3. Ligatures — Wke (see Fig. 287) SUk (see Fig. 331) Rubber 4. Accessories — Buccal Tubes (see Figs. 277, 276, 283) Nuts (see Figs. 281, 270, 271, 280c), 1. Bands Clamp-Bands. — These are necessary for — (1) Anatomical reasons ; (2) Mechanical reasons. (1) Atiatomical Reasons. — The circumference of a tooth at the neck being less than at the occlusal surface, it is unpossible to adjust satisfactorily a soldered band to a molar tooth (except possibly in the case of teeth where the disproportion is least pronounced) ; hence the anatomical necessity for a clamp-band ; so that it may be passed over the greatest diameter of the tooth, and the ends di'awn together to embrace clo.sely every portion of the tooth. (2) Mechanical Reasons. — If a soldered band can be placed on a tooth without adjustment it can similarly be removed from the tooth ; that is to say, its attachment to the tooth depends solely on cementation (except in so far as burnishing may be able to adjust the band to 173 the neck ; but on this procedure little reliance is to be placed). In the case of a clamp-band, however, it is impossible to remove the band (if properly fitted) intact from a tooth without loosening the nut. These bands are the basis of security of fixed (D ^ a of band material is suitable. These bands should always be' cemented on, to prevent the ingress of the oral fluids between the band and the tooth. The width of clamp-bands is such as to correspond approximately with the depth of enamel on a tooth — -it is not greater than this ; and as enamel has no attachments to its outer surface it is unnecessary, except in rare instances, Fig. 276. — The part.s of a clamp-band. 1. The band proper. 2. Threaded wire soldered to the band material on whicli the nut, 3. runs to engage 5. a short length of tube, soldered at the oppo- site end (but not at the edge) of the band proper, through which the tlireaded wire passes. 6. Kound buccal tube in plan, the end that is to be distal being bevelled. 7. Round buccal tube in section. 4. Solder flowed on the centre of the band preparatory to attacliing the buccal tube. appliances. They support the bows, so that it is vital to successful manipulation that they shall be securely held on the teeth. This object is attained by the proper adjustment of the component parts (see Fig. 276) : 1 . The band proper— a, straight piece of band material of suitable length. 2. The clamping mechanism — it consists of — 5. A short length of tube soldered a short distance from one extreme edge of the band. 2. A length of threaded wire on which runs a nut to engage the tube (5). Fig. 2 1 7. — All-closing clamp-band with oval tube. 1, 2, 3, and 5, as in Fig. 276. 6. Oval buccal tube. 7. Oval buccal tube in section. Xotice that when the band is closed its ends overlap. The tube (5) is placed so far from the end of the band that when it is tightened up the tooth will be completely encircled by the band proper, not leaving any intermediate tooth surface exposed to the oral fluids ; a band so con.structed may be fitted to any tooth, provided the length Fio. 278. — Luken's band. 1. The band proper. 2. The buccal tube, which is also the clamping mechanism ; it is threaded externally, and cut square at one end to serve as a nut. 3. Plain tube on the end of the band nearer the nut (or square end). 4. Tube threaded internally in which the buccal tube tiu-ns. (a) Cross-section of buccal tube. to cut the band at all narrower ( deciduous molars excepted, as these are shorter teeth). This is obviously an unwise procedure as the surface area of material is reduced, and so the attachment to the tooth is reduced, and the stability of the baud thereon is affected — it has already been stated that the clamp-band is the basis of fixity of fixed appliances. Fig. 279. — Clamp-band for a premolar, where the tube has to be placed more distally than for a molar, or else the threaded portion of the bow might not be long enough. The tube is held away from direct contact with the band material by an intervening piece of wire ; this is necessary in those cases in which the adjacent teeth prevent the tube assimiing its correct position. To the lingual aspect of the band an extension spur is soldered to engage the first molar, so that it may be included with the premolar as it expands buccally. A tube soldered to the buccal surface of the clamp-band is the medium whereby the bow and band are connected. Another form of clamp-band, the Luken's (see Fig. 278), is that in which the tube and clamping arrangement are combmed, leaving one surface free of attachments. The bolt or threaded wire portion is hollow, and thus becomes the tube ; one end is cut square and serves as the nut ; the other passes through a short plain tube on one extremitv of the baud and then engages 174 a tube, threaded internally, which is soldered at the other end of the band, and is the means whereby the band can be closed, the square end of the bolt engaging the plam tube. The ordinary clanip-band permits the adjust- ment of the buccal tube in any position ; the type just described cannot have its tube placed in any du'ection ; this will be better appreciated when the fitting of clamp-bands is described. Clamp-bands are used both on molars and premolars (see Fig. 279) ; they are to be had in different sizes with or w ithout buccal tubes. Plain Bands are made for individual teeth and have a soldered jomt ; the metals most frequently used for their construction are — (a) Iridio-platinum (10-30 per cent) ; (b) Platmized gold ; (c) German silver. Of the first two, iridio-platinum is to be preferred on account of its greater toughness when very thin material is needed ; y uVir inch is a suitable thickness, although for bands on incisors, which have not to withstand much strain, they may be even thinner. On account of its harshness iridio-platinum is not as easily worked as platinized gold. 2. Bows These are lengths of wiie, in which " spring " may be developed, and in other ways eSect the movement of teeth ; each end is threaded and furnished with a nut ; the length of the Fig. 2S0. — Plain bow. (a) and (b). Sections of bows of different gauges in the unthreaded portion, but of the same gauge in the threaded portions. (c) Split nut, whose edges may be brought closer together, so that it will turn on the bow by means of a wrench only. bow is such as to embrace the dental arch on its buccal surface from the first molar on one side to the first molar on the other side, when the teeth have been brought into normal occlusion; as the wire bow must not project through the distal ends of the buccal tubes, it may not be possible, when starting treatment, to use one that will be sufficiently long to complete the operation. The bow is threaded sufficiently from either end to accom- modate the buccal tube and nut, whether the tube is on a molar or premolar band. A plain bow (see Fig. 280) is one as described above. Fig. 281. — Angle's ribbed bow. A. The bow in plan. B. The bow and rib in section. C. The nut and tube m section. 1. The rib. 2. The bow proper. 3 and 4. The nut. 3. The square end of tlie nut. 4. The circular extension of the nut to fit in the sleeve (6), which forms the front portion of the buccal tube. 5 and 6. The buccal tube. 5. The main portion of the tube which the bow fits exactly. 6. The front of the tube enlarged to receive the circular extension (4) on the distal end of the nut, which it fits acciurately. A ribbed bow (see Fig. 281) is one that has on its outer surface a flat piece of metal extending about f of an inch on either side of its centre. Its special function is to facOitate medial and distal movements of the incisor teeth. A divided how (see Fig. 282) is one that is composed of three pieces ; that is to say, a plain bow is divided in the centre, the two new ends thus formed are threaded, and nuts run on them ; they then pass mto a tube, about half an inch in length (one at each end) the extremities of which are engaged by the nuts. 3. Ligatures Brass wii'e is usually used for ligatures ; two sizes, 26 and 28 American gauge (Browii and Sharp), are most frequently employed. Silk is also used, that form kno\TO as Japanese grass line being the most suitable. It con- tracts considerably when moistened. It is to be obtained in several sizes. Rubber ligatures, or rather rubber rmgs, are made by cutting short sections, varying in width, of black rubber tubing. Tubing of several different diaineters is desirable. 175 The bow is attached to the clamp-bands tlirough the medium of 4. Accessories Buccal Tubes. — Tliese are usually round (see Figs. 276, 278, 279, 281, 288, a), and then, whatever the vertical position of the anchor tooth due to movement, the bow will always engage them ; ui other words, the relationship of the long axis of the tooth with the vertical may vary \\'ithout affecting the adjustment (see Fig. 286). Other tubes have been designed to keep this relationship constant. A method of doing this is to replace the round tube by a square buccal tube. A special attachment is soldered to the end of the bow, which accurately fits this tube. The nut must be put on before the special threaded square tube is soldered to the bow. Another method is by means of an Otto- lengui tube ; in this case a flange is soldered to the bow where it enters the tube, which is split to accommodate it. The simplest method is to use an oval tube (see Figs. 277, 288, b), and a bow whose threaded ends are flat and accurately fit the buccal tube (see Fig. 280, a and 6). Tliese devices are used when it is desired to increase the resistance of the banded tooth to movement, as with them translational movement only is possible (see Fig. 286). Nuts. — The nuts on the bow are subject to considerable friction from the cheeks, which is Fig. 282. — Divided bow. (a) Lateral portions ; each medial end is flattened and threaded to receive a nut, in addition to the losual thread on this part of the bow. (b) Central portion, an oval tube, into which the anterior ends of the lateral portions fit accurately ; a nut engages each end of the tube to permit of great expansion in the canine region. often sufficient to turn them ; this is very un- desirable. The best means of obviating this is by an extension of the nut (see Fig. 281, 4), which fits mto the front of the buccal tube, which has been counter-sunk for this purpose. The idea is a patent of Angle's, and so not to be had on any appliance except those sold under his name. Other devices have been used with varying success ; an efficient one is a split nut (see Fig. 280, c), whose edges may be brought closer together when occasion demands it. Materials used in the Construction of Bands and Bows The clamp-bands and bows are usually made of — (1) Platinized gold, or (2) German silver. The former are more easily worked, and more easily cleaned and kept clean ; bows of this -"^ Fig. 283. — Ottolengui tube. 1. Threaded tube with flange (a) into which tlie bow passes and to whicli it is soldered so tliat (a) engages the split portion of the buccal tube (6) seen in 2 and 3, which show tlie split tube, engaged by the flange (a) in two positions. 4. Shows the bow (c) passing into the threaded tube which carries the flange. Bow and tube are soldered to one another so that their relation may not be variable. material are more efficient, and do not greatly deteriorate in appearance with use. German silver is cheaper. The metal de- teriorates in the mouth, and in the case of bows these consequently lose their springiness in time, and a new bow may have to be employed. German silver appliances are, there- fore, less efficient ; it is more difficult to preserve their good appearance (and later, impossible), and they are more liable to need renewal. C. J. Grieves (3) has conducted a number of very valuable ex|)eriments as to the merits and demerits of the various metals and alloys used in the mouth for orthodontical appliances. His conclusions are that every band should be cemented to the tooth, as in this way only can the enamel be protected against decalcification ; and that, from the point of view of decalcifi- cation, German silver, unplated, is the least 176 harmful material that can be used when un- cemented, but that it is to be rigidly condemned because it corrodes so readily, and becomes dirty even on the exposed surfaces that can usually be kept clean. The alloys of the precious metals, the preference being given to platinized gold, are the most desirable materials with which to make aiipliances : they practically never corrode, though prophylactic treatment is essen- tial every t^\'o weeks or so to cleanse surfaces exposed to metal but not jirotected by cement. Any discoloration of these appliances is due to deposit of sulphides and not to corrosion, unless zinc is in the alloy. Removable ap- pliances do less harm than fixed ones; they should not fit the teeth too accurately, but only touch them at a sufficient number of points to give stability. Where there is no contact between tooth and metal the space should be large enough for the easy passage of saliva, which dilutes the decalcifying acids. Grieves fovuid that wherever food retention centres occurred, the enamel was frequently de- calcified ; deposits of dark salts were formed on the roughened enamel, but the stain caused was removed by buffing. In conclusion, wherever cleanliness was not possible, in that situation there was a potential source of injury to tooth structure. The explanation of these phenomena is that electrolysis is set \vp between the metal and tooth ; when the metal is one easily attacked by acids, then the effect is seen there ; but when the metal is one less easily affected than tooth structure, then the latter is the sufferer. In the same paper the composition and properties of various alloys used in orthodontics is discussed. Fitting of Clamp-bands Separation on each side of the tooth to be banded often facilitates the operation, though not essential in all cases. Tliis can be done by means of ligature silk around which a little cotton-wool has been wrapped, passed through the inter-proximal space and then tied round the contact point of the two teeth. Lowe Young recommends the use of heavy ligature wire in the same way, but without any cotton-wool. He also uses ligature silk ; he passes a double strand through the inter-proximal space by means of floss silk; a double strand of this is passed between the two teeth, and the ligature silk made to engage the looped end ; the ligature sUk can then be drawn tlirough the space by the floss silk, which is now removed ; one free end of the ligature silk is made to engage tlie looped end, the two ends are pulled tight, and securely tied. The shrinkage of the silk wlien wet (it should be applied dry) is sufficient to give the required separation, which need only be slight. If it were greater the liability to periodontitis would be increased, and the fitting of the band \\ould have to be post- poned till this had subsided. Both bands and bows need preparation before they can be fitted in the mouth. A band of suitable lengtli must be chosen — such that when it is properly fitted the ends overlap, and the portions of the band to which the clamping parts are attached are almost in contact ; it must then be shaped to tlie outline of the tooth ; for this purpose Peeso pliers (see Fig. 689 ; one beak is flat and the other rounded and a trifle shorter ; both are smooth) serve admirably. The shapmg shoidd be done so that the nut will coincide with the inter- proximal space between the tooth fitted and the adjacent one (see Fig. 288) ; this is to enable the nut to be turned without difficulty. It is, therefore, important to decide first the medio- lingual angle of the band ; this having been done, the other angles and surfaces are fixed according to the jjarticular requirements of the tooth being operated upon. The cervical edge of the band must not be cut, but drawn in, so that when the band is clamped it will accurately fit the neck of the tooth ; in the case of an upper molar this contouring is approximately the same all the way round the tooth, but with a lower molar the contouring is only necessary medially, distally, and lingually ; buccally the tooth pre- sents a very convex surface right down to its neck, and it is often advantageous to stretch the cervical edge of the band in this region (the Peeso stretching pliers (see Fig. 697) may be used for this purpose). It is also well to contour the occlusal edge of the band, in order that the burn- ishing that must be done here to adapt it perfectly to the tooth may be facilitated ; the degree to which this is done is determined by the form of tlie individual tooth, the buccal surface of a lower molar requiring the greatest amount of " puUmg in "', and this is another reason why it is advisable to stretch the cervical edge of this part of the band for a lower molar. The tooth having been perfectly cleaned on all its surfaces, and the band havmg been shaped and the two edges suitably prepared, it is ready to be fitted to the tooth (always in the mouth, never on tlie model) ; it shovild be well opened so that the constricted cervical jDortion may easily pass the greatest diameter of the tooth at the contact points on both sides simul- taneously up to the gum margin ; the band may now be closed slightly to allow it to pass between gum and tooth without ])ain or injury, and then pressed on till the occlusal edge of the band coincides with the occlusal surface of the tooth. A flattened piece of wood or bone of the size of a small handle of a tooth-brush, or the short flat end of a metal spatula, is well adapted for this purpose ; if the resistance is too great for want of separation, the Peeso pliers may be used to force the band past the 177 contact points. On the distal surface it should not be carried quite as far as on the medial, thus leaving a small piece of the band to be burnished on to the occlusal surface, which removes any liability there might be for the band to slide toA\ards the root of the tooth, and also gives the front end of the tube an inclination towards the gum. The latter object is desirable as it facilitates the adjust- ment of the bow. The band should now be burnished to conform accurately to the tooth, startijig in the centre of the buccal surface, and gradually \\orking round to the lingual, and tightenmg the band at intervals as its conformation is improved. A large egg-shaped burn- isher should be used on the buccal and lingual surfaces ; on the medial and distal surfaces a strong, short, flat instrument is more suit- able, being supjjlemented by the former. The j)ro- cedure is the same « liether the buccal tube Ls already attached to the band or not, though the latter is simpler and better, the ' tube beuig ultimately sol- dered exactly where it is needed. The band having been firmly clamjjed on the tooth, the surjilus end of the threaded -wiie should not be cut off, as a general rule, but bent to lie close against the Imgual surface of the adjacent tooth, just above the gingival margin Fio. 284.— Iiistriunenfc (see Fig. 288). de\ased by G. North- Position of the Buccal croft. One end is to Tube.— When the band is augn buccal tubes , , , ■/ 1 . i . i and the other is a bought with the tube wrench. already attached they are united at their centres ; as the t%\o are parallel this permits of such bands being used for any tooth — right or left, upper or lower, — and as the attachment extends over a very small area the direction of the tube may be adjusted to a slight extent, for individual teeth, by insertmg into it an instrument which fits it accurately, such as that designed by G. Northcroft (see Fig. 284), and then givmg the tube the desired direction by the necessary movement of the instrument. (1) Medio-dislal Position. — The buccal tube i should be soldered to the band so that when the nut on the bow is m contact with its medial end it wUl be opposite the inter-proximal space between the banded tooth and the one in front. In the case of molar bands, the centre of the tube is soldered to the centre of the buccal side of the band (see Figs. 276, 277) ; in the ease of premolar bands a portion nearer the medial end of the tube must be attached to the band (see Fig. 279). (2) Occlmo-cervical Position. — The tube should be at the centre of the band (see Fig. 276), or nearer the cervical edge «hen practicable. This is often essential in the lo\\er jaw in order that the tube may be free from the buccal cusj)s of the corresponding upper teeth when the teeth are in occlusion. (3) Distance from the Buccal Surface of tJie Tooth. — If the banded tooth is lingually placed in relation to the tooth in front of it, it may be necessary to bring the tube further out buccally than would be the case if the tube were soldered direct to the band. In such a case the band should be thickened by suitable pieces of metal, or a short length of thick platinum wire (see Fig. 279) should be soldered to its buccal surface at right angles, where the tube is usually at- tached ; the tube is soldered to whichever of these additions has been employed. The latter has the advantage that the direction of the tube can be easily altered by means of a suitable instrument — one that accurately fits the tube. Direction of the Buccal Tube. — The vertical direction should be such that when the bow is placed m the tube it \\ill pass across the necks of the mcLsor teeth (or other desired position) without the necessity of bending the bow. (See p. 178.) The horizontal direction should be such that the tubes of the two sides are parallel, so that the bow may be adjusted to them without sharj) bends bemg requued. A compromise bet\\een these two requuements will probably have to be made in most cases. (See Fig. 288.) The tubes must approximate parallelism with the buccal surfaces of the teeth ; otherwise one end wiU project buccally and probably not be tolerated by the cheek. The distal ends of the tubes should always be bevelled, and m some cases it may be advisable to cut away so much of the tube on its buccal aspect that the lumen is exposed. Having fitted the bands, without tubes, to the teeth, some ojierators now take an im- pression, remove the bands from the teeth, and set them in place in the impression. A cast is made, and the tubes are soldered to the bands, wHle on this ; when this has been done the bow is also fitted to the cast before the bands are taken off. Cementation of the Bands. — The tooth should 178 be thoroughly cleansed by meaiLS of powder and brushes or tape on every surface, and wiped over with hj^drogen peroxide and well syringed, so as to remove every trace of debris and mucus. The field of operation should now be protected from moisture by the use of fibre lint buccally and a cotton-wool roll Imgually, assisted by the saliva ejector; the tooth should be dried thoroughly and wiped with chloroform, which removes any remauiing traces of mucus. A hydraulic oxj'-jjhosphate cement should be used to cement the band, as it is not always possible to ensure absolute dryness of the tooth ; havmg been thmly mixed a sufficient quantity is placed on the inner surface of the band — first j applied at the cervical edge, wlience it will flow to the other edge. The band is now f)laced over the tooth, and its cervical edge carried completely home by a thumb or finger pressed over its occlusal edge ; this procedure will ensure the cement being carried clown on the tooth to its cervical edge along with the band, which is now clamped on the tooth by tightening the nut. When it is no longer possible to keep the field of operation dry, the patient is instructed to rinse with hot water to hasten the setting. When hard the surplus cement is removed, special care being taken to clean the cervical margm. Lo^\e Young recommends the use of Evans' Orthodontical Gutta-percha ; the tooth need not be dry and there is no fear of the material being washed out. The Adjustment of the Bow. — The next step in the preparation for active treatment is the proper adjustment of the wii-e bow, known also as the expansion bow, alignment bow, etc. This cannot be undertaken till the position of the buccal tubes has been definitely fixed. It must be clearly recognized that the wire bow is the frame that is to serve as the mould on which to re-form the irregular dental arch ; the irregular teeth are to be made to conform to its outline, and when this has been accomplished a normal dental arch should be the result. It is, therefore, of the utmost importance that this wire bow should be adjusted with the greatest care, for it is not too much to say that it is possible by its use to perform any combina- tion of tooth movements, but that in order to bring about any given combination of move- ments it must be manipulated with skill and forethought. The first step, then, in the operation is the correct adjustment of the wire bow m the buccal tubes and the correct shaping of the bow throughout the remainder of its length. The bow is fitted by first securhig a basis from which to work ; this is done by placing only one end of the bow in its buccal tube and turning the corresponding nut to engage the medial end of that tube ; the position of the nut should be such that the threaded fiortions of the bow shall terminate at corresponding pomts of the dental arch on both sides. If the end of the bow projects a considerable distance beyond the end of the tube, it should be shortened so as to project oidy one-eighth of an inch ; this is to permit of subsequent adjust- ment if such should be found necessary, and ultimate shortenmg so that its end shall coincide ■with the end of the tube. The cut end should then be rounded so as not to present sharp edges m case it should come in contact with the tissues. On one side the end of the bow should be notched with a thin stone so that the right and left sides may be recognized without trial ; this should always be done on the same side. Considerations Affecting the Shape of the Wire Bow. — As has already been stated, the wu-e bow is the frame to \\hicli the normal dental arch is to be built ; it must, therefore, be given the shape of the normal dental arch. Except in a few cases, this is impracticable at the com- mencement of treatment, because the wire bow would be so far away from the dental arch that — • (a) it could not be tolerated by the lips and cheeks ; and (h) its efficiency would be considerably impaired. Its form, then, must be a compromise between the normal and the actual ; it must be close to the teeth, so that the ligatures may be used to the greatest advantage, and the comfort of the soft tissues not disturbed. Durmg the course of treatment it may be necessary to re-bend the bow as the teeth move out to it, causing it to assume the outline of the normal arch by stages. The bow in use is adjustable m its relation to the distance — (1) between the incisors and molars; (2) between the molars and second premolars of the two sides. But as regards the first premolars and canines the transverse distance between these is deter- mined by their relation to the bow ; that is to say, buccal movement of these teeth can only be obtamed by having bent the bow to a suitable form before \\ iring the teeth to it."^ Wliercas the relationship of the wire bow to the incisors, and to the molars and second jsremolars, can be adjusted by means of the nuts on the threaded portion of the bow, and by means of the spring, respectively, without any re-bending; the re- lation of the bow to the canines and first pre- molars, on the other hand, can only be varied by re-bendmg the wire bow. Therefore, if ' Except when a divided bow is used. 179 these teeth need buccal movement to the same extent as the remaming teeth, it is advisable to allow tlie bow to stand furtlier away from them tlian from the remainder. It will be observed that the position of the bow as regards its distance from the teetli is now being con- sidered. The proper alignment of the buccal j tubes should have given it the correct position, across the necks of the teeth and close to I the gum ; if the bow were nearer the mcisal edges the hgatures would not remain on the ; teeth ; if it w ere nearer the roots of the teetli injury would be done to the soft tissues and pain caused. If this needs correction it should be done now by changing the direction of the tubes with a suitable instrument, or by bending the bow, or by both. Supposing the irregular dental arch to be composed of small teeth in alignment, which Fig. 285. — Plaiii bow. Adjusted in the buccal tubes for expansion of the molar region. (o) Incorrect method of giving spring to the bow; it causes rotation of the molar. (6) Correct method of giving spring to tlie bow by bending its extremity lingually just in front of the nut. (c) Shows effect of (b) on direction of movement of molar (directly outwards without rotation) as compared with the effects of (a). are to be placed in a larger concentric arch, the wire bow should be bent to rest across tlie necks of the teeth, almost in contact with the second premolar, further from the first pre- molar, and slightly further from the canine on its distal surface ; but should begui to approach tlie median line of the mouth as it nears the medial surface of the canuie, and then come almost in contact with the lateral and central if these teeth are to be moved forward (buccally). Any individual irregularity must be dealt with as it occurs, such as bending the bow round an outstanding tooth, and then makmg it only approximate to the position suggested above. The bow having been adjusted by repeated trials to all the teeth, as outlined, it is ready to be bent to enter the other buccal tube, and the position that this end of the wire bow must assume before being placed therein is one of parallelism ui both the horizontal and vertical planes with the corresponding tube (the other end already conforms to this demand). This having been done, the bow is removed and made to enter the two tubes simultaneously, when the position of the nuts may be made exact, and the ends of the bow made to coincide with the ends of the tubes. The bow is now a passive instrument, and ready to be converted into a positive force to brmg about any tooth movement or combination of tooth movements. For the anchor tooth and that immediately medial to it, this is accomplished by giving spring to the bow, that is, by separating the extremities. This having been done, and the bow replaced in the tubes, the distal end of the wire bow M'ill move through the arc of a larger circle than the part just in front of the buccal tube, as the connection between the wire bow and the anchor molar tooth is more or less rigid ; the result is to rotate the molar, a movement to be avoided as a rule. This is accomplished by bending the bow on each side, just in front of the nuts, so that the termuial portions approach more nearly to parallelism (see Fig. 285). As the molars ex- pand this adjustment may be repeated ; it ensures the molars moving buccally without any rotation. ANCHORAGE. The successful practice of orthodontics depends entirely on what is known as anchorage, and on its use to the greatest advantage. Pullen defines it as "the resistance selected as a base from which force is to be delivered for the movement of teeth ", and as " a study of comparative resistance values in the teeth and dental arches " (8). So-called anchorage, for orthodontical pur- poses, is obtained from teeth and bone, directly from the former, mdirectly from the latter, and then only m the case of removable appliances. To facilitate the description it is accepted that each tooth has a certain resistance value, this value varying m the different teeth. Resistance value depends on — (1) Size of tooth, i. e. size of the root of the tooth ; (2) Length and number of roots ; (3) Position in the bone and arrangement of surrounding alveolus ; (4) Age of patient ; (5) The adjacent teeth (if any) and their relation to the tooth under considera- tion ; (6) The direction of movement ; (7) Occlusion. 180 For example — • ' (1) A lateral will offer less resistance than a premolar ; a central less than a molar. The canine when fuUy developed probably offers more resistance than any other tooth. (2) Three united roots will offer greater resistance than a single or double root, all being of equal size ; one long root, e. g. the upper canine, probably offers more resist- ance than a first upper molar ; a lower molar certauily cannot be relied on in moving a lo\\er canine without bemg disjjlaced itself. (See p. 155.) (3) A lower molar usually offers greater re- sistance to buccal movement than an upper A. Simple — the resistance of the anchorage to the foi-ce of reaction is so much greater than the resistance of the tooth to be moved that little movement of the anchor tooth (or teeth) occurs. Reciprocal — the resistance to action and reaction is less unequal, and movement occurs and is desired at both points. Stationary — the point of resistance to the force of reaction is fixed (the only real anchorage). B C. Movement by inclination. Line akowing direction of movement Movement by translation. i-ine ahourinff dircction of" rnoircment ■ . Plain band on left upper central. " at which the second premolar has ''• ^"''^'V "" ^'''"" "^ ^' '" T'''"'' ""^ "PP'''' ^"^ """^^^ ^° ^^''^'^ re ■ ii i 1 4. 1 1 u -ti displacement towards the mcisal edge by the pull of the sufficiently erupted to be dealt ^^•ltll ^..^ber band, or cervically on acount of the slope of the often closely approaches that at winch central incisors, the second upper molar erupts, and the D. Distal Movement (i) First Molars and Second Premolars. On both sides. 21. Fixed Appliances. — Anchorage : Simple. Distal movement of the first upper molar and second premolar to- treatment \\ould then involve the distal move- ment of that tooth also ; but while the second deciduous molar is still present the condition is one to respond favourably. In patients under ten years of age tlie second deciduous molar should be used as anchorage, if it is still sufficiently firm in the jaw ; otherw ise the first permanent molar should be used and the case treated as one of individual tooth move- ment (see pp. 205 and 210); inter-maxiUaiy force can then lie dispensed with, but it should be remembered that this force can give very valuable aid. In the treatment of a case of this nature with- out inter-maxillary force, most of the remain- ing teeth must be in situ and sufficiently firm to offer some resistance. The bows having been fitted with the clamp-ljands on the second deciduous molars, spurs, directed medially, are soldered to the bow opposite the medial aspect moving molars, and the distal end of the buccal tube of the opposite jaw, must be resorted to immediately, and if it happen that this does not suffice the head-gear must be made use of. With the head-gear all other anchorage may be discarded or ignored except in the intervals when it is not worn. It w ould be unsafe to rely on the available anchorage (the remainmg teeth in the upper jaw, and the lower jaw itself) in patients over ten years of age, unless supplemented by occipital anchorage, when this movement could certainly be undertaken. The second molar (if it has to be included in the movement) will be forced distally by the first molar with which it is hi contact ; it is necessary to ligature the premolar to the molar so that they shall move together. (a) Anchor Clamp-band on First Permanent Molar. — The screw of the band should be directed distally ; if the second molar is un- erupted the surplus should be cut off ; this 190 position of the band will necessitate a reversal of the buccal tube. On the buccal and lingual surfaces of the band smaU hooks directed back- wards should be soldered ; they should be large enough to engage a small rubber band if neces- sary. The distal end of the buccal tube may be used as one spur, and the clamp-wire as the other when it is directed distally (see Fig. 298). A plain band is cemented to the second pre- molar, bearing hooks on the buccal and lingual surfaces, directed forwards, and large enough to hold rubber ligature bands. The two teeth to be moved are now coupled together by rubber bands if they are not in contact, and by wire ligatures, if they are already in contact ; the latter are to be substituted for the former when the premolar touches the molar. Wire could be used from the beginning, but its rene^\al as the tooth moves is more difficult. Fig. 298. — Arrangement of bands and spurs for coupling a premolar and molar together for distal move- ment of these teeth. They are held together by wire ligatures ; if they are not in contact rubber bands are first used to accomplish this. (h) Anchor Clamp-band 07i Second Premolar. If the conditions are such that the premolar can be relied on to push back the molar (the second molar being unerupted or not about to erupt), then the clamp-band should be fitted to the premolar, the lingual screw being again directed distally ; as already indicated the buc- cal tube is set back on jiremolar bands ; then the tube buccally and the screw lingually will keep the molar in its bucco-lingual position. The bow is now adjusted, the nuts engaging the medial ends of the buccal tubes, and being so situated on the bow that the latter is not in contact with the incisors. The case is then ready for the application of occipital traction in order that the teeth may be moved. As it is unlikely that the patient will wear the head- gear continuously, arrangements must be made to hold the movement obtained in the intervals when it is not worn. This is done by using inter-maxillary force in the usual way, the bow, etc., being applied in the lower jaw. 22. Removable Appliances. — In reading this paragraph it should be borne in mind that the second deciduous molar or second premolar may be absent. (a) Patients under Ten Years of Age : Anchor- age : Simple. — Anterior teeth and bone to resist force applied to move posterior teeth. If there is a space in front of the second pre- molar or second deciduous molar, or first permanent molar in the absence of these (and it is not very likely that cases of this kind wiU have arisen without sucli a space), a well-fitting plate is made from a plaster impression to embrace the teeth accurately, having clasps from behind forward for the most distal of the anterior teeth. It should carry powerful coil springs of platuiized gold or pianoforte wire to impuige on the medial surface of the f)remolar or cleciduous molar, or permanent molar should it stand alone. If the anterior teeth are not further forward than they should be, the anchorage «ill be sufficient to carry the posterior teeth distally, as it is obtained directly from bone and teeth ; but if the in- cisors are already mclined forward, fixed appliances should be used with mter-maxillary force. If the plate is designed to expand, as with the Badcock screw, this movement may be combmed with what is the primary movement so far as this paragraph is concerned. The edge of the plate engaging the lingual surfaces of the posterior teeth should be straight. (b) Patients over Ten Years of Age. — Fixed appliances, with the greater possibilities of satisfactory anchorage, should be used, unless forward movement of the anterior teeth is desired ; for with a removable appliance this \\ould almost certainly occur at this age, unless the second premolar is inierupted, when the plate can be made more stable. ' Another method, applicable in (a) and (b) where circumstances permit, is to vulcanize in the plate a small screw occupying the space of the second deciduous molar on both sides, its distal end being free and reaching to the medial surface of the first molar. A nut engages the free end of the screw. By turning the nut the posterior teeth will be forced distally. A suitable screw can be made from the end of a bow, with a nut as long as can be fitted into the space ; the nut engages the medial surface of the anterior of the two teeth to be moved. This device may be employed without a plate ; in that case the threaded wire on which the nut runs is soldered to the medial surface of a band on the molar in order that the small appliance may be secure (see p. 234, and Fig. 299). The iuit, in this instance, operates against the distal surface of the tooth immediately in front of the space. To increase the area of contact of the nut an oblong piece of plate may be soldered to its medial end ; this would also .serve as a 191 guide in turning the nut a given amount. In treating a ease in this way everything has to be exceedingly small, but the short nut necessary at the start may be replaced by longer ones as the space, resulting from tooth move- ment, increases. It must be observed that the anchorage Ls sufficient to ensure the molar moving and not the other teeth. Tliis method may be used as an auxiliary to the other methods described. See also paragraph 24. In the lower jaw this appliance can be successfully used on both sides. On one side only. 2.3. Fixed Appliances. Anchorage : Keinjorced Simple. Auxiliary Anchorage : The opposing jaw (intcr-maxillary force). The bow is applied as wlien this move- FlG. 299. — Retention and enlargement of a space between two teetli. It is not necessary tliat the bow should be used at the same time. ment has to be performed on both sides. The anchorage, however, can be better secured, as all the remaming teeth are available to move one tooth. The bow Ls arranged as in the other case, except that all tlie spurs are in the same direction, the bow is considered as a straiglit wire, and the nut on the side on which the teeth have not to be moved kept forward, so as not to touch the front of the tube. All the available teeth are ligatured to tlio bow in such a way, by means of the spurs, that they oppose the distal movement of the molar as the nut is tm'ued against the front of the buccal tube on the misplaced tooth (see Fig. 300). The anchorage described should be ample, but if for any reason it is desh-ed to augment it, this may be done by means of inter -maxillary force. 24. Removable. — This operation is precisely the same as No. 22, except that the movement is required on one side only, and so the same appliance adapted to do this may be used. But, in place of the coil sprmgs or jack-screws, a spring of the Coffin type may be employed (see Fig. 301). the plate being divided in front of the more medial tooth to be moved. The Fio. 300. — Wire bow arranged to move the first right lower molar distally ; this tooth has moved medially, probably on account of the early removal of the second deciduous molar. All "the teeth from the first right premolar to the left lateral are tied to the bow ; in each ligature a spur on the bow is included, so that the total resistance of each ligatured tooth may be opposed against the molar when the nut in the front of the buccal tube is turned against it. This resistance will suffice to move the molar distally; inter-maxillary force may be used to increase the resistance of the anterior teeth. saw cut should extend to the posterior edge in the case of an upper plate, and in the case of a lower, as shown in Fig. 301. In order to maintaui stability and accurate relation- ship between the two portions of the plate, a wire fixed into one piece of the plate should Fig. .301. — -Vulcanite plate with modified Coffin sprmgs to increase the space between the canines and first molars, where the plato is split on each side. Four clasps hold the plate in position. (After Balding.) engage a tube in the other piece (the wire fitting the tube accurately ami being parallel with the desired Une of movement of tlie tooth or teeth) ; one of these attachments should be near each extremity of the plate. They were suggested to the writer by F. L. Aubrey. 192 (ii) First Premolars and Canines. On both sides. 25. Fixed Appliances. — Anchorage : (a) Opposing jaw (inter-maxillary force). The teeth in the opposing jaw are station- ary or moved reciprocally as desired. (6) Recijarocal by movement of the corre- sponding first molar forward. (c) Reciprocal by movement of the incisors forward. (d) Reciprocal by movement of the premolars for^^ ard on the same side of the opposmg jaw. Apparatus. — Clamp-bands on the first per- manent molars, and bows. (a) The most satisfactory method is by anchor- age obtained from the opposite jaw. (See also (d) below.) Spurs are soldered to the bow distal to the teeth to be moved, and at any convenient point a hook, for an intcr-maxi]lary ligature, is also soldered to the bow. The premolar and canine are ligatured to the arch as shown in Fig. 292, 1), the ligatures engaging the spurs, which are dhected distally. The effect of this is to puU the bow forward out of its buccal tubes, but the mter-maxUlary ligature, which should now be applied, prevents this, and indeed pulls back the bow and with it the teeth whose ligatures engage the spurs on the bow, which must not be in contact with the mcisors. In such a case as this the nuts should be turned forward or entirely removed, so that as the teeth and bow are pulled back the latter wUl slide in the tube. The bow on the opposing jaw should be wired to all the teeth. (b) Reciprocal anchorage by forward move- ment of the corresponding first permanent molars. The same apparatus is used except that it need only be applied to the jaw being operated on. The spurs on the bow are to be arranged as before, that is, ju.st behind the teeth to be moved and sloping distally. The hook for a rubber ligature is also arranged simOarly, but instead of passing to the distal aspect of the corresponduig buccal tube in the opposite jaw, it passes to this point on the clamped molar of the same side of the same jaw (see Fig. 292). The teeth should be moved one at a time ; if the canine offers great resistance occipital anchorage or inter-maxillary force must be resorted to. In (a) and (b) the spurs may have to be moved to more distal positions as the teeth travel back. (c) Reciprocal anchorage by forward move- ment of the incisors, the action being similar to that when molars give the anchorage, except that in this case the premolars are to move as well as the incisors. The clamp-bands may be attached to the first molars or first premolars of the same jaw. In the first instance the first premolars and canines are ligatured to spurs on the bow as previously described; the incisors are also ligatured to the bow, and it is the force necessary to displace these that moves the premolars and canines distally ; each tooth should he dealt with separately to avoid strain- ing the anchorage — the premolars first, and then the canines. The nuts may be turned as deshed, to accommodate the incisors as they move, but not till after that has been done should the ligatures on the canines and pre- molars be tigiitened. \Vlien the first premolars are used as anchorage, pressure is brought to bear directly on these teeth, the anterior teeth providing the resistance necessary to move first the premolar and then the canme. The nuts must be kept turned well up against the front of the tubes. The canme is moved by a spur on the bow directed distally, or it may be ligatured either by wire or rubber to the premolar itself. The four anterior teeth would probably not be able to give simple anchorage for the movements under considera- tion ; for this reason any attempt to move both the premolar and canine distally at the same time should not be made. {d) Probably the best method of all by which to accomplish this procedure is as an individual tooth movement. Plain bands with spurs directed forward are cemented to the teeth to be pulled back, the necessary anchorage being derived from the opposite jaw, reciprocally if any teeth (which should have similar attachments) are to be moved forwards (see Fig. 302, b), or by simple mter- maxUlary traction from the molar tube (the wire bow beuig in position and wired to several teeth) if a reciprocal movement is not requhed (see Fig. 302, a). The former method is particularly desiiable when the pre- molars are to be elongated ; if the elongation needed is only slight, the anchorage should be from the molar tube, not directly from the teeth, as the direction of force is then more nearly vertical. In the case of the canine band, an elongated spur, extendmg beyond the tip of the tooth, and bent so as to hold a rubber band, increases the leverage, and so the resistance offered to movement is more easily overcome. These several methods of movmg canines and premolars may be used m combuiation ; it will probably be found that this is the most desirable plan ; for instance, when the four incisors are used to move the premolar directly by means of a clamp-band and bow, the anchorage of the one jaw may be considerably augmented by inter-maxillary anchorage. 193 2G. Removable. First Premolars. — By means of coil springs as descrilx'd for second premolars and molars under paragraph 22. If necessary make room for the sprbig between the canine and first premolar by separatuig these two teeth (see Fig. 303). Canines. — By means of a Coffin-t>'pe spring in the buccal sulcus, its medial end engaging the medial surface of the canine from the buccal aspect, and its other end attached to the plate j)alatally and passing to the buccal vestibule eitiier in front of or behind the first molar. Anotlier method is to cement to the canine a plain band with buccal and lingual spurs, both directed medially ; into tlie plate a wire is fixed to pass along the distal surface of the first molar, and is bent into a liook directed backwards at the disto-buccal corner of the tooth ; on the palatal surface of the plate, opposite and near the first molar, a hook directed dlstally is vulcanized. Two rubber bands are stretched from the canine to the attachments on the plate near the corresponding molar, one being buccal and the other palatal to the teeth. The spurs on tlic canine band should be towards the distal aspect of that tooth. The jJate should accu- rately fit the medial surface of the first molar if that surface is exposed. On one side. 27. Fixed Appliances. — As in paragraph 25, the apparatus being arranged to operate on one side only. 28. Removable Appliances. — As in para- graph 26, the apparatus being arranged to operate on one side only. is, when the abnormal position of the lower jaw and teeth have given rise to inferior protrusion. The treatment is the reverse of that adopted in cases of inferior retrusion. Upper and lower bows are applied, tlie latter having a hook for the application of intcr-maxillary force about opposite the canine ; at its other end the rubber bow must Fio. 302. — Tlie left-hand figure, A, shows movement of the first upper premolar distally by means of inter-maxillary force applied from the lower jaw (simple anchorage). The right-hand figure, B, shows movement of the upper canine distally and of the lower first premolar medially (reciprocal anchorage). The rubber bands are attached to spurs or plain bands, except in the case of the molar, when the distal end of the buccal tube is used. (iii) The Lower Jaw. 29. Fixed Appliances. (Removable ajipliances are not applicable.) Anchorage: The opposing jaw {inter-maxillary force). Distal movement of the lower molars and ])rem(ilars and canine is only necessary when the lowei- jaw itself has to be moved distally, that Fig. 303.- \ uk.Liuu pl.Lli \\ii\i two cuil -springs; one to move the right first premolar distally, and the other to move the right central and lateral labially. Clasp wires on the first molars retain the plate in position. band exerting the inter-maxUlary force is caught on the distal end of the buccal tube of the clamp- band m the upper jaw. The type of anchorage obtauied from the upper jaw depends on the movement desired there. If the upper dental arch is to remain stationary, then the wire be .suitably bent, and all the teeth ligatured to it. If it is desired to pull the upper molar forward, then it is necessaiy to have the nuts turned forward so that the force shall be exerted on those teeth only. If the first permanent upper molar is to remain in its iJosition but the upper incisors are to go forward, then the force used to pull back the lower jaw is applied, recipro- cally, to do this ; it cannot be directly applied, but acts through the medium of the upper molar, which serves as a connecting Imk or passiv'e agent in the two move- ments — the molar itself does not move. This molar has pressure acting on it in a medial direction from the lower jaw, and in a distal direction from the up^Jcr incisors ; so long as the two forces are appro.ximately equal the molar will not move. If it is desired to move the upper incisors forward without the use of the first molars as a connecting link, tlien the rubber band must be attached in the 194 upper jaw to a hook soldered on the upper bow just in front of the nut, which would not be serving any special purpose. If the teeth liave to be moved, apart from tlie movement of the lower jaw distally, it is accomplished as descrilied in parasfraphs 21, 25, 38, and 40. E. Depression Tliis movement, 30-33, is one of tlie most difficult, and one that is rarely needed. It might be attempted by making a vulcanite plate to cover the occlusal surfaces of those teeth to be depressed. The writer recalls a case \\here this inadvertently happened owing to such treatment. It would be well to note whether the teeth ojiposing the covered teeth were also depressed. Grinding of the occlusal surfaces of the teeth will probably have to be resorted to. The treatment of these cases will be again referred to under individual movement. F. Elongation of Molars, Premolars and Canines (i) In both Jaws simultaneously This movement is usually needed for the lower jaw more than for the upper. 34. Fixed Appliances. — Anchorage: Inter- maxillary, Reci'procal. — The princijJe to be adopted is that of inter-maxUlary force acting reciprocally to bring the opposing teeth of the two jaws closer together, so that the bones them- selves are further apart, when the teeth are in the position of occlusion, than was originally the case. A suitable hook directed rootwards Ls soldered to the buccal surface of the lower molar band at the medio-buccal corner, and from this a rubber band is stretched to engage the distal end of the buccal tube on the upper molar (or a special hook as for the lower) and the usual inter-maxillary hook on the upper bow (see Fig. 304), or it may engage hooks on bands on the premolars. The attachment to the upper bow is only used when the lower jaw has to be moved forward.' Another band should be stretched from the lower molar to the lower premolars (or a hook on the bow in this region) and first upper premolar. The manner of application of these rubber ligatures may be varied considerably. Wlien they pass over hooks on the bow instead of directly to the teeth, the latter must be securely ligatured to the bow. 35. Removable Appliances. — This move- ment is obtained by allowing the teeth to elongate in their sockets, and tliLs happens when the position of occlusion is made impos- sible. All that is necessary to prevent the teeth coming into occlusion is to place in the upper jaw a vulcanite plate — a bite-plate — that has been made sufficiently thick behind the incisors to compel the lower incisors to strike this thickened portion of vulcanite before the posterior teeth of the two jaws meet one another, and thereby keep them from coming into contact at any time (see Fig. 355). The plate must be worn constantly, even during meals, and it will be found that the teeth move towards one anotlier, and ultimately meet again. The time necessary varies from one or two months to four or five times as long. If the movement requu'ed is considerable the vulcanite should be thickened from time to time, instead of being made the requisite thickness at first, as the discomfort caused would probably be sufficient to be noticed and mastication would be unduly interfered \\ith. This is a movement that is very frequently called for ; it is necessary in all cases in which the upper centrals overlap the lower centrals Fig. 304. — Shows the application of inter-maxillary force to elongate the two molars, as well as to move the lower jaw medially. (1) Anchor clamp-band. (2) Buccal tube. (3) Upper bow. (4) Lower bow. (5) Hook, soldered to bo%v, for attachment of the rubber band to the upper bow. (6) Spurs on the buccal tubes for attachment of the rubber bands to the molars. by more than one-third of their height ; such an arrangement precludes the possibOity of normal occlusion, and in many instances it is impossible to pull back upper incisors tUl thLs condition has been corrected (see Fig. 305) ; in treatment these points are frequently neglected. Usually other movements are necessary in these cases. They may be done simultaneously, or the plate may be used before or after the other treatment. During the period of movement of teeth the bite is usually opened somewhat by the teeth being unable to inter-digitate correctly, and even after normal occlusion has been established there may be some permanent raismg of the bite. When the overbite is only a little in excess of normal this opening due to general tooth movement may suffice. (ii) In one Jazv only 36. Fixed Appliances. — Anchorage : Inter- maxillary, Simple.— Exactly as in 34, but with the 195 appliances arranged to move the teetli in one Jaw only, by arrangintr tlie inter-maxillary force so that it is clelivertd from a simple reinforced anchorage instead of acting reciprocally. 37. Removable Appliances. — Anchorage : Simple. — If the lower teeth only are to elongate, the upper plate should have cleats attached to it ; these cleats should engage the occlusal surfaces of the molars and premolars — m the former by a simple wire engaging the lingual sulcus, and in the latter by two pieces of wire passing from the medio-lingual and dLsto-lingiial aspects of the tooth towards the centre of the crown. If the upper teeth are to elongate and not the lower, a lower plate is constructed w ith cleats to engage the occlusal surfaces of the molars and premolars as just described. The plate should not cover the lingual surfaces of the incisor Fig. 305. — Shows the relation of the upper and lower incisors to one another in cases of excessive overbite (post-normal occlusion frequently accom- panies this condition). The overbite must be corrected if it is desired to bring about normal occlusion of the incisors. teeth and gum margin, but consist m this region of an oval wire, which passes either just above or just below the necks of the teeth (see Fig. 343). If the.se movements are reciuu'ed on one side only, the apparatus can be arranged accordingly. (See also references to elongation under " Indi- vidual Tooth Movement ", pp. 205, 210, 213.) G. Rotation Only possible as an individual tooth move- ment . n— INCISORS A. Labial Movement : Upper and Lower 38. Fixed Appliances. Anchorage : Simple. — Upper and lower bows are adjusted as usual ; hooks for inter-maxUlary elastics should be attached to the bows if it is thought that inter-maxillary force will be needed. The bow is bent to pass across the necks of the teetli, so as just to escape touching the soft tis.sues, even though in actual contact with the teeth. It should project one to two milli- metres beyond the teeth, but it is preferable to let the patient wear the bow in contact with them for a few days and, when he is accus- tomed to it, to move it forward by means of the nuts before applying ligatures. It should be borne in mind that it is better to turn the nuts forward only once in two weeks or so, and to move the teeth out to the bow in this position (one or two millimetres beyond the teeth) by means of the ligatures, tightenmg and renewing them as necessary. Ligatures, W'U'e or silk, are now applied to the teeth to be moved, and made sufficiently taut just to avoid causing the patient pain — whether it be immediate or otherwise. In addition to the amount of immediate tooth move- ment thus obtained — dependent on the force applied as the ligature is tied, the spring of the bow, and its distance from the labial surface of the teeth — the spring of the bow is constantly operating to carry the teeth forward; for its anterior portion will have been pulled hi, and this causes the side portions to bulge out (see Fig. 334), the nuts being hard against the anterior ends of the buccal tubes ; the tendency of the bow to resume its origuial shape re- sults in the forward movement of the incisors. The ligatures should be tightened or renewed once or twice a week ; the latter is prefer- able as then the operator has better control of the apparatus, and its cleansing can be more satisfactorily supervised ; when teeth are moving cjuickly ligatures are likely to be very loose at the end of a week. As the teeth move forward and come in contact with the bow, the nuts should then be turned, and then only, so as to bring the bow one or two milli- metres in advance of the teeth agam, and the process of ligaturing continued ; bj' repetition of these operations teeth may be moved as far forward as desired. If this movement is con- siderable, it may be that in time the length of the bow will not suffice for its support in the buccal tubes of the anchor bands ; m such a case a new bow must be substituted. If, at the same time, much increase in width of the arch of teeth in the canine region is needed, a re- bending of the bow wOl probably be necessary in the course of treatment, so that it shall serve as an accurate mould for the new positions of the teeth, and yet never be in a position of in- efficiency as regards its work, or discomfort as regards the patient. 39. Removable Appliances. — Anchorage: Simple. — Springs of platinized gold wire are 196 the most suitable devices for developing the necessary force. They should be the usual coil spring arranged to exert its force by uncoiling ; the force should be delivered as near the neck of the tooth as possible. The spring for the right central, or right central and lateral, should come from the left side of the plate and vice versa. Rubber or wooden wedges are also used to move incLsors forward ; the plate is made thick opposite the tooth (or teeth) to be moved, and an inverted wedge-shaped piece is cut out, and mto the slot so formed is tightly fitted a piece of orange wood or rubber. The latter moves the tooth by its inherent po\ier of elas- ticity ; the former s\\ells, when moistened, and so moves the tooth. Small screws passing through the vulcanite to impinge on the palatal surface of an upper incisor are also used. They may be vulcanized in the plate, or fixed in the Fig. 306. — The two bows are identical as regards their length and the position of the nuts. The interrupted lines show the original shape of the wire bow ; the uninterrupted lines show that the bow becomes sliorter as it widens if the nuts remain in their original position in contact with the medial ends of the buccal tubes. front part of the plate (which has been thickened) after it has been made. The end of the screw should be cut square so that it may be readily turned. Por this purj)ose a watch key is well adapted. A small nut may be vulcanized in the plate to take the screw, which can then be readily renewed when desired (see Fig. 291, a and c). B. Lingual Movement of Incisors 40. Fixed Appliances. — Anchorage: Becipro- cal ; Inter-inaxillury, simple or reciprocal ; Occipital. (a) By the spring of the bow, in conjunction with expansion m the molar region. As the wire bow widens it necessarily becomes shorter (see Fig. 306), its position in relation to the buccal tubes remainmg the same ; it will, therefore, exert pressure on the mcisors and move them in a palatal or Imgual direction. In order that this movement may be increased, the nuts are turned forward on the bow and kej)t free from the buccal tubes, or they are removed altogether ; then as the upper incisors move, the bow slides I back in the tubes of the clamp-bands, and permits of more shortening of the dental arch than would be possible whilst the nuts engaged the tubes. (6) By mter-maxillary force. Hooks are soldered m the canme region to the I bow of that jaw whose uicisors are to be pulled back ; to these, mter-maxillary ligatures are attached, and stretched so as to engage the distal end of the buccal tube of the clamp-band m the opposite jaw, to which a bow must be fitted and a sufficient number of teeth ligatured to it to afford the necessary anchorage. The nuts are kept quite free of the tubes, as regards the bow that is moving the mcisors back. The full force exerted by the rubber bands is thus brought to bear on the incisors. In cases of this kind, the bows should not rest at the necks of the teeth but at the centre of the labial surfaces (the greater power thus obtained necessitates the use of less force to obtain the same amount of movement). It wiU usually be found that teeth recjuhing this move- ment have their long axes slopmg downward and forward in the case of the upper incisors ; this slope prevents the bow restmg at the desired spot on the labial surface of the tooth, so m order to achieve this object, a plam band, with the seam on the labial surface and a notch cut in the seam, is made for one or both central in- cisors, and in this notch the bow rests (see Figs. 337 (a) and 297). This may have the effect of shortenmg the banded tooth. In such a case both incisors should be similarly treated. Some operators prefer to solder lugs to the bow, which will engage the incisal edges of the centrals, and so prevent the displacement of the bow to the neck of the teeth. The writer prefers the former method, as it is neater, more efficient (preventmg movement in both direc- tions), and does not interfere with the bite as lugs engagmg the mcisal edges may do. Precautions to hold the bow in situ are less necessary when inter-maxillary force is bemg used, as the tendency for it to slip to the neck of the tooth is counteracted by the pull of the rubber band in the opposite direction. (c) By occijjital anchorage. The appliances are arranged as they would be for (a) and (b), with the addition that a knob is soldered in the centre of the bow that is to carry the teeth inwards. This engages a de- pression in the centre of the cross-bar of the head-gear, to the extremities of which suitable elastic bands are attached, the other ends of the bands being fixed to the skull-cap (see Fig. 328). 197 It will be noticed that in the methods de- scribed for lingual movements of incisors there is no tendency for the molars and premolars of the same jaw to move forward, ;". e. medially. If it is wished to move tliese medially as w ell as the incisors lingually, rubber bands should be stretched from the hook for inter-maxillary force to the distal end of the buccal tube of the same side of the same jaw. Movement obtained by means of occipital ancliorage may be retained by light rubber bands used in the way just described for moving the molars medially ; they must not be so strong as to exert more pressure than is necessary for retention, or they will move the molars, as just referred to — a movement which in all but rare instances has to be carefully guarded against. The question of overbite enters largely into consideration when upper incLsors have to be moved lingually, because in many instances this movement cannot be fully accomplished until the overbite has been corrected, or prepara- tion, by means of a bite-plate for instance, has been made to do it. 41. Removable Appliances. — Tlie methods that have been described to perform this move- ment are numerous. The followuig may be regarded as among the more efficient. (a) A platinized gold wire is fixed in a vulcanite plate and brought round tlie front of the incisors, passing from the palatal to the buccal surface between the canine and first premolar, or between the first and second pre- molars (see Fig. 307). [Read deciduous molars [ instead of premolars when necessary.] Opposite the canine one or two U -loops are made in the wire, whicli should be carefully fitted to the in- cisors, so as to come in contact with, them at the junction of their middle and incisal thirds ; the same means as \\ere adopted in tlie case of fixed appliances may be used to keep the wire in situ. (Paragraph 40 (b).) Care must be taken in bending the wire not to allow its more distal portions to impinge on the soft tissues. Move- ment is obtained by gradually closing the U- ! springs on both sides, and thus bringing pressure I on the teeth. AVlieii the plate is being inserted, the wire should be placed over the teeth first, and the plate then carried into position. If this method is used in combination with an ex- pansion plate the effect is increased, because the buccal w ire shortens as it widens. (6) Instead of a complete buccal wire with U-springs in its course a plain piece of wire may be used. These incisors are often much in- clined, and then the wire should be held in position on the tooth by means of a spur or notch on a band on one of the centrals (see Fig. 315). When the patient is accustomed to the appliance, the wire is divided in the centre, and bent so as to exert s]iring pressure on as many of the incisors as are to be moved. If the plate is an expansion one it is not essential to divide the wire when only slight hngual movement of the centrals is reijuired. More power is obtained by having a separate wire on each side, the left one reaching to the right central and the right one to tlie left central. These plates may be held in position by crib clasp-wires when desirable ; these may be on molar, pre- molar, or deciduous canine, or on any tW'O, on one side or both. (c) The wire, having passed between the teeth, may be cut off short, and bent into a Fig. 307. — Badcock plate with buccal wire, having U -loops, passing from canine to canine. As the plate is widened the wire is drawn tight on the labial surface of the incisors ; the pressure thus exerted may be increased by closing the loops of the U. The plate is cut away behind the incisors, or else their lingual movement would be impeded ; it is thickened in front to open the bite and shaped as an inclined plane to bring the lower jaw forward. hook on each side, so that a rubber band may be stretched from one to the other passing over the labial surfaces of the anterior teeth. As it becomes necessary a smaller and smaller rubber band may be used ; it is often desirable to have plaui bands with spurs on one or two incisors, ^^•hich \\ill resist any tendency of the band to slip on to the gum or off the teeth. This apparatus is unsiglitly, but efficient, and the patient can maniiwlate it. Rnbber-dam with the necessary holes punched in it may be used in place of rubber bands. (f/) A fixed appliance is attached to the incLsors, arranged so that tension exerted from a suitable point will be transferred to all the incisors ; for instance, a band may be cemented 198 to one of the centrals, with a labial wire extend- ing on each side to engage the remaining in- cisors. To the palatal surface of the band a spur is soldered, which will support a rubber Fig. 308. — Vulcanite plate and fi.xed attaclxment on the right central incisors to move the two centrals lingually. Palatal view of the upper dental arch and plate in position ; buccal view of the two incisors and sectional view of the former are shown. 1, Plain band, on the right central, with 2, a spur directed incisally for the attachment of 3, a rubber band, which is also attached to 4, a spur directed backwards in 6, the vulcanite plate which is held in place by 5, the wire clasps. band stretched from it to a similar spur or hook in the centre of the palatal portion of the plate (see Fig. 308). .Shorter bands are sub- stituted as the teeth move. The plate is held in place as already described under (b). If the rubber bands exert too powerful a pull the plate will be displaced. Ill all four methods the plate should be cut well back from the palatal surface of the incisors, and its edge carefully rounded and bevelled from the surface in contact with the soft tissues. In this way the "' heaping up " of gum between the teeth and plate may be avoided. A zinc chloride mouth-wash will assist in controlling this condition, should it arise. C. and D. Medial and Distal Movement of Incisors 42. Fixed Appliances. — Anchorage : Simple or Reciprocal; either may be Inter-maxillary. These two movements are taken together, as they both indicate movement along the line of tlie dental arch, the one towards and the other away from the median line. Simple ligaturing of a tooth to the bow is insufficient to effect these movements ; it is necessary to obtain a fixed point on the bow (see Fig. 309), preferably for each tooth, to which the tooth may lie moved by simply including in one liga- ture the tootli and fixed point. This alone is sufficient to effect the desired movement, which, however, may be increased by means of the nuts engaging the buccal tubes ; the nut away from wliich tooth movement is desired Ls turned at intervals, so that the action of the ligatures may be increased by means of the spring of the bow, which is now also working as a jack-screw. The fixed points on the bow are obtained either by filing notches m the rib of a ribbed bow, or by soldering spurs to the bow as described on p. 225. Any number of teeth may be moved in this way, so long as the anchorage (simple at the molar) is sufficient. As an auxiliary in assisting this movement, inter-maxillary force may be made available by stretching a rubber band from the pomt where the greatest force is desired to a suitable point in the opposite jaw, where all the teeth should be liga- tured to the bow in order tliat the necessary an- chorage may be obtained (see Fig. 309). 43. Removable Appliances. — Anchorage: Simple ; teeth and hone via plate. Where several teeth have to be moved medially by Fig. 309. — Medial and distal movement of incisors. 1. Upper bow. 2. Lower bow. 3. Spur on (1) for attachment of (8), a rubber band to exert force laterally on the upper bow, and through it on the teeth. 4. Spur for attachment of rubber band on (2). 5. Spurs on upper bow for attachment of ligatures (fi) to exert lateral force directly on to the teeth. Wire ligatures attaching teeth to upper bow. Wire ligatures attaching teeth to lower bow. Dotted line to show position of median line of mouth, with which the space between the two upper centrals should coincide. 9 means of a removable appliance, a fixed point must be obtained on one of them and on the plate. From the latter a platinized gold wire passes to the buccal sulcus near the point to 199 uhich the teeth are to be brought, yet the two points must be sufficiently far from one another that a rubber band stretched between tlie two will exert tension (see Fig. 310). The wire is bent towards the necks of the teeth and then into a hook, which is directed away from the teeth to be moved ; this hook is to carry the rubber ligature. For the tooth most distant (of those to be moved) from this hook, a plain band is made, which will also carry a rubber ligature by means of a spur near the neck of the tooth ; this spur is directed away from the hook. A rubber band is now stretched from the hook to the spur. This pulls the teeth towards the anchorage obtained from the plate ; it also tends to move the intervening teeth palatally, but this is avoided by having the vulcanite plate fit close up to them. The edge of the vulcanite plate sliould be well rounded and present an unl)roken line, so that it guides the teeth ; they then move along it without difficulty. Incisors can also be moved medially or distally by means of ordinary coil springs arranged to engage the appro.ximal surfaces of the teeth, as may be necessary. The application of such an appliance is limited by the number of teeth to which the necessary force can be efficiently applied. E. (i) Depression in both Jaws simultaneously 44. Fixed Appliances. Anchorage : (a) Simple from the molars. (6) Reciprocal. (a) Wlien the bow is being fitted, it is bent to rest over the alveolar process rather than over the necks of the teeth (see Fig. 311). Ligatures are then applied to all the incisors, care being taken that in so doing the bow is pulled as low down as possible, i.e. the bow is sprung from its position of rest, and the teeth are holding it in its new- position, but, being movable, they cannot hold it there permanently ; the spring of the bow grad- ually overcomes the resistance of the tissues, and then the bow slowly regains its old position, carrying the teeth with it, that is, the teeth are depressed in their sockets (see Fig. 287 (/) and {g) ). It will be noticed that the position of the ligature on the tooth must remain constant, ai:d it is probaljle that the bow will drag the ligature over the cingulum and neck of the tooth, rather than depress the tooth in its socket. To obviate this, the teeth to be depressed are banded, and spurs directed towards the incisal edge are soldered to their lingual surfaces ; as the ligature passes round tlie tooth it is caught beneath the spur, so that the spring of the bow is now definitely brought to bear on the teeth. Any tendency for the molars to be elongated nnist be combated by increasing the anchorage, which is done by putting spurred bands on the premolars and arranging that if there is any elongation of the molars it would be shared by the premolars, -v^' Fig. 310. — A vulcanite plate and fixed attachments on the incisors to move them laterally, those on the right medially and those on the left distally. On the right lateral and left central are plain bands with spurs, from which rubber bands — providing the force to move the teeth — are stretched to the hook that passes from the plate between the left premolars. The right lateral will also move the right central and the left central the left lateral. The plate is left in contact with tlio lingual surfaces of the incisors, so that they will not be moved lingually by the pressure of the rubber bands ; but the edge of the plate must present an even line so that the teeth will pass along it. the bow engaging the spurs direct or tlirough the medium of ligatures. If it isnot necessary to have the teeth under separate control, spurs projecting at right angles KiG. 311. — Shows the wire bow and plain bands, with notch, on the central arranged to depress the incisor in its socket. The dotted line shows the bow at rest, and to make it an active force it is pulled down to rest in the notch on the plain band. from the labial surface of the bands on the incisors are arranged so as to engage the bow when it is sprung towards the incLsal edges of the teeth : agahi the force is transferred direct from the bow to tlie teeth. Instead of soldering 200 spurs to the labial surface of the bands, the seam of the band may be made on the most prominent part of tlie labial surface of the tooth and left projecting ; a notch is then cut in the seam into ^\hich the bovv will just fit (see Fig. 315, reversed); the upper arm of the notch takes the place of the spur and con- FiG. 312. — Bows and accessories to depress the upper and lower incisors in their sockets. Plain bands on all incisors ; to one a labial wire is soldered engaging spurs incisally on the other three bands ; to this labial wire spurs are soldered for the attachment of rubber bands to exert inter-maxillary force, the upper and lower bows intervening, as shown. Rubber bands may also be used to effect medial or distal move- ment of any of the incisors, as shown, and this movement may be assisted by turning that nut against the buccal tube away from which the tooth lias to move. Spurs on the buccal wire or bands at its extremities may be employed to prevent any lateral movement ; spin's may also be used to include another tooth in the medial or distal movement — one to which the rubber band is not directly attached. sequently should be left longer ; it is then better able to support the springy bow. (b) Reciprocal Anchorage. Clamp-bands on first molars. The bow, not less than gauge 16 (B and S), is bent to pass across the alveolar process in both jaws, and the premolars and canines are firmly ligatured to it. All four incisors must be banded, and attachments soldered to them whereby all the teeth wUl move equally, although force is applied at only one or two points. The manner in which the band attachments are arranged may be as follows, though equally efficient modifications will suggest themselves to the thoughtful operator. To the band on one of the centrals a labial wire is soldered so as to pass across the labial surfaces of the remaining incisors ; in doing so it should engage spurs on bands on the remaining incisors just long enough to receive the force transmitted through the labial wire ; if there is any tendency for the laterals to move distally, it may be counteracted by giving the wire an inclination towards the gingival margin. or a rectangular bend may be given to it (see Fig. 312). Similar appliances are made for both jaws, and then rubber bands are stretched from the labial wii-e at points between the upper laterals and centrals to corresponding points on the appliance on the lower teeth. The rubber bands may be slipped over the ends of the horizontal or buccal wire and past any spurs, by stretching it, to the desired point ; it is attached m both jaws in the same manner, the two wire bows intervening ; another method of attachment of the rubber bands is by looping it at one end on to one buccal wire and at the other catching it on a special spur (see Fig. 312) directed towards the incisal edges of the teeth. If it is desired to move any of the teeth medially or distally at the same time,, it can be done by rubber bands passing from the spurs on the teeth to the bow (simple anchorage), or to other teeth — incisors or premolars — ,when the anchorage would be simple or reciprocal, according to the arrangement of rubber bands adopted. The band to which the labial wire is soldered should, for preference, be on a tooth that has not to move medially or distally. A rubber band from one lateral to another would move each equally (reciprocal anchorage), un- less one were in contact with a central, when the anchorage would be reinforced, the latter tooth taking little or no part in the movement ; if it w ere necessary to make this anchorage more Fig. 313. — A variation of the appliance shown in Fig. 312, to depress teeth in their sockets. (a) Plain band on left central to which is soldered (6) a labial wire terminating at (c) as hooks to engage the incisal edges of the incisors, (d!) An extension soldered to (6) to engage the right central just as (c), (o) engage the laterals, (e) Spur on (6) for the attachment of (g) a rubber band to exert inter-maxillary force. In passing to be attached on the lower bow it passes over (/) the upper wire bow. secure, it could be done by soldering vertical spurs to the labial wire in such a way that they engage the spurs on the bands, and thus prevent the movement laterally of individual teeth (see Fig. 312). Instead of soldering spurs to the bands, the seam, placed labially, can be left long, and cut so as to act as the spur. 201 If the bite permits a wire or similar attach- ment to engage tlie incisal edge of any of the teeth, a band may be dispensed with on tliat tootli (the appliance cannot be constructed without one band). To secure this the labial \x ire iis brought half-way across the tooth and then given a rectangular bend, so as to pass to its incLsal edge ; it is bent sharply on itself so as to engage the incLsal edge of the tooth (see Fig. 313); both ends of the wire are similarly arranged ; if an intervening tooth Ls to be dealt with in this May, a piece of wire is soldered to the labial wire so as to extend to the incisal edge of the tooth and then engage it. 45. Removable Appliances. — Anchorage : Simple. {Teeth and bone via plate.) The in- cisors may be depressed in their sockets by a platinized gold wire passing across the labial surfaces of the incisors ; it is attached in the palate of the vulcanite plate, and passes to the buccal aspect either between the pre- molars, or first premolars and canines. The wire must exert pressure on the crown of the tooth in tlie direction of the root, and for this purpose lugs should be soldered to it, which will engage the incisal edges of the teeth to be depressed (see Fig. 357) ; they may be made of wire or plate. As an alternative to the lugs, which might be impracticable in the case of a very close bite, ])lain bands should be made for and cemented to the teeth to be depressed, bearing on their labial aspect spurs, which the labial wire will engage on their incisal aspect when it is at rest. Tliat tlie plate may be absolutely stable it should be made on a model from a plaster impression, and be held in situ by four w ire crib-clasps on the fii'st permanent molars and first premolars. Tlie labial wire at rest now engages the spurs on the bands on the teeth ; the plate is removed from the mouth, and the wire is bent towards the roots of the teeth, and the plate replaced, so that the wii'e occupies the same relation to the teeth as previously, but now exerts pressure on those teeth through the spurs to depress them. The pressure is increased from time to time until the desired movement has taken place. E. (ii) Depression in one Jaw only 46. Fixed Appliances. — Anchorage: Simple. Tliis movement is obtained as described in paragraph 44. The arrangement described at the end of paragraph 44 (6) may also be used, the bow engagmg a spur on the one band that is fitted. 47. Removable Appliances. — Exactly as in paragraph 45. F. (i) Elongation in both Jaws simultaneously 48. Fixed Appliances. — Anchorage : Simple of depression, which has just been described, and is accomplished in a similar but reverse mamier. Li this case the bow is bent to rest at or beyond the incisal edge of the incisors. The latter are then securely ligatured to the bow, which at the same time is pulled up so as to rest on a level with the necks of the teeth (see Figs. 314, 287 {(l) and (e)). The spring of the bow, which is tending to return to its original position, causes the movement of the teeth. Fig. 314. — Cross-section of an incisor with wire bow in position to elongate it. (a) Cross-section of incisor. (6) Cross-section of wire bow at rest. (c) Cross-section of wire bow pulled up into position at the neck of the tooth by [d) the wire ligature. The arrow indicates tlie direction of movement of the tooth due to the effort of the bow to return to its position of rest. It will be observed that the ligatures may not be held securely at the neck of tlie teeth, and these should, therefore, have plain bands, with spurs at tlie cervical edge directed root- wards, cemented to them. The ligatures are then passed round the tooth, being held in position on the cervical aspect of the spur. By this method the operator has, in addition, and Reciprocal. 7* This movement is the reverse Fig. 315. (a) Plain band for an incisor. (b) Seam of the band. (c) Notch cut in the seam to support (d) bow or labial wire, which is to exert force towards (6). control of both labial and lingual movements of individual teeth. If this additional control is unnecessary, or not desired, the teeth to be elongated are banded as before, but, instead of spurs being soldered to the lingual aspect of the bands, the seam — which lias been made on the labial surface — should be cut so as to form a sjjur, on the gingival aspect of wliich the bow may rest (sjc Fig. 315). Lingual movement of the incisors is pos.sible at the 202 same time as elongation when the appliances are adjusted in this way. This movement (elongation) may be increased by the reciprocal action of inter-maxillary force, one or tv o rubber bands being used between the two jaws. To attach these, spurs are soldered to the bows, opposite the approximal surfaces of the centrals and laterals ^^•hen two rubber Fig. 316. — Fixed appliance arranged to elongate incisors. (a) Tlie wire bow to which is soldered (b) a spur for the attachment of (g) rubber bands to exert inter-maxillary force, attached also to (/)■ a spur on (e) the lower bow. (c) Plain bands with (d) spurs to be engaged on the gingival aspect by (a), whence the force is transmitted to the teeth. bands are to be used, and between the U\o centrals when only one is needed (see Fig. 316). These spurs slioidd be straight lengths of wire attached to the bow at right angles and pro- jecting into the labial sulcus ; their length need only be sufficient to prevent a rubber band jumping off. The rubber bands should be worn continuously except during meals ; when they are stretched from the canine to the molar region, there is no need to remove them except for cleansing the teeth and renewal. It is possible to apply force to an incisor to elongate it without the intervention of a cemented band, though not with very satis- factory results. A wire ligature, gauge 24 or 26, is tied tightly round the neck of the tooth to be elongated, being made as secure as possible. Then the free ends are used to ligature the tooth to the bow, -which, in so doing, is pulled up to the necks of the teeth from the incisal edges. The spring of the bow causes it to exert force to return to its original position ; this force is transmitted through the wire ligature to the tooth, which is thus pulled downwards in the upper jaw and upwards in the lower. 49. Removable Appliances. — As in the case of fixed appliances, accessories must be securely fixed to the teeth to be moved, whereby the force may be transmitted to them. Force in a vertical direction camiot be applied direct to the teeth them.selves (when removable appli- ances are used) ; the simplest method to adopt is that already described in paragraph 48 — bands cemented to all the incisors to be moved, such bands having labial seams cut to form a spur, which may be engaged by a buccal wire. If it is desired to solder a spur to the band, this may be done ; in that case the seam may be placed lingually. The spur should be a straight piece of wire soldered at right angles, or with a slight inclination gingivally, to the labial surface of the band, and just long enough to be engaged by the bow attached to the plate without the possibility of the wire bow slipping past it. All these free ends of wire should be care- fully rounded and smoothed to obviate any irritation of the soft tissues due to movement over them. The removable appliance itself consists of a vulcanite plate to which a buccal wire is at- tached ; this wire issues from the palatal surface of the plate between the two premolars ; from its attachment to just beyond the first bend as it turns to pass over the buccal surfaces of the teeth it should be considerably strengthened ; this may be done by burnishing thin platinum foil on to the teeth just where the wire passes across them and uniting the two with solder. To increase the spring of the wire it should be looped in the neighbourhood of the canine, the loops being parallel A\ith the general direction of the wire as shown in Fig. 317. This labial Fig. 317. — Removable appliance to elongate incisors, (a) Vulcanite plate passing from which, between the premolars, is (6) a spring to exert force incisally on the central, througli (tl) a spur on (c) a plain band. A cross-section of the central with band and spring in position is also shown. wire is adjusted to rest on the gingival aspect of the spurs on the labial surface of the bands on the incisors; this having been done, the wire, by means of its looped portion, is bent in the direction of the cutting edges of the teeth, so that it rests beyond them ; great care must be taken, in making this bend, not to disturb the wire in the least behind the loop, or its accurate fit in the premolar region will be .203 disturbed. Movement of the teeth is now controlled entirely by the amount of spring given to the buccal wire. Clasps are neces- sary to retain the plate, as the spring of the buccal wire tends to displace it. On a low er plate cleats should be arranged to engage the lingual sulcus of the first permanent molar to jjrevent the plate being forced dow n into the soft tissues. F. (ii) Elongation in one Jaw only 50. Fixed Appliances. — This movement is brought about in exactly the same way as described in paragraph 48, when it is produced in both jaws simultaneously, except that when inter-maxillary force is used the anchorage, instead of being reciprocal, must be simple, i. e. the teeth of one jaw are used as anchorage to move the four incisors of the opposite jaw. 51. Removable Appliances. — Paragraph 49 describes this movement for each jaw separately, and it applies exactly to this movement. G. Rotation 52. Fixed Appliances. — E. H. Angle de- scribes a method of rotating simultaneously two approximal incisors whose inwardly turned corners are contiguous. A section of wire, gauge 15 (B. & S.), and in length aboiit one- third the combined width of the teeth to be rotated, is soft-soldered to a brass wire ligature. The wire is placed on the lingual surface of tlie teeth to be rotated and the ligature passed through the inter-proximal space, one end being above and the other below the bow ; the ligature is then tightly tied, and the in- standing comers are gradually pulled out. The rapidity of movement may be hastened by stretching a strip of rubber between the bow and the outstanding corners. It is believed that rotation of the teeth individually will be found to be more satis- factory for these reasons : (1) the wire, in order to be effectual, nuist rest against the flattened and wider portion of the incisor teeth, i. e. nearer the incisal edge than the cervical, where the bow rests ; tlie tendency then is for the bow to be displaced from its position of greatest efficiency w hen the ligature is tied ; (2) if the wire is placed near the neck of the tooth so that the ligature will not dis- place the bow, then the efficiency of the wire is much impaired, because it bears against a narrower and rounded part of the tooth. (For description of another appliance for rotating incisors see p. 158). 53. Removable Appliances. — Removable appliances are not well adapted for the rotation of teeth, but they will bring about this move- ment in suitable cases. Such a one is that in which the distal corners of two centrals are outstanding ; a labial w ire constantly exei-ting pressure on these corners, behind which the plate has been cut away, whilst the medial corners are held in position by the vulcanite against the lingual surfaces, will slowly rotate the two teeth. It must be remembered that a rotated tooth occupies less space in the arch than one in normal alignment ; it is, there- fore, essential that room be made for the tooth when normally placed before the operation of rotation is undertaken, or at least that room be made as the tooth rotates. With some forms of appliance the two movements assist one another. As an in- stance of this one may refer to the case of an upper jaw that is too narrow, especially in the canine region, and in which the incisors protrude, the centrals being rotated so that their distal corners are outstanding, and all the teeth being in contact with one another. Such a case may be treated by widening the upper teeth — from canine to molar included ; as the canine moves outward the laterals will go with it — so that the laterals become more separated, in this way making room for the centrals, which are being rotated by a labial wire. This wire passes from the palatal surface of the plate between premolars, or first pre- molar and canine, on one side, to be similarly attached on the other ; it may have loops in its course opposite the canines whereby the amount of pressure on the centrals can be con- trolled ; this is not essential, as the widening of the plate has the eflFect of shortening the wire, and if this did not suffice, the course of the wire, instead of being allowed to remain straight or direct, may be made sinuous or indirect by bending with pliers. By one of these methods pressure is exerted on the outstanding comers of the centrals ; the plate is made as described at the beginning of this paragraph (53) . The widening movement of the laterals may in some cases be assisted by the pressure of the distal corner of the central on their medio-buccal corners, which are prevented from moving inwards by the vulcanite liehind them. CHAPTEE VIII ABNORMALITIES OF POSITION— TREATMENT [continued) INDIVIDUAL TOOTH MOVEMENTS Molars. II. Premolars. III. Canines. IV. Incisors. I A. Buccal. B. Lingual. C. Medial. D. Distal. E. Depression. F. Elongation. G. Rotation. Appliances. (1) Fixed. (2) Remov- able I MOLARS A. Buccal Movement (1) Fixed Appliances. — (a) With the damp- hands on the molars. This is done by means of simple anchorage. The buccal tube (permitting tilting movement) on the band on the tooth to be moved should be a round one, and the lingual clamping wire shoidd not be allo\\ed to come in contact with the lingual surface of any of the teeth. On the opposite side, the buccal tube should be one that permits of translational movement in preference to one that admits of a tilting movement of the molar ; tlie clamping wire should be in contact with the lingual sur- face of the approximal tooth, and all the teeth on this side, in front of these two, should be ligatured to the bow after it has been bent to fit closely to them. Before the bow is fuially put in tlie tubes and the teeth are ligatured to it, spring, sufficient to accomplish the desired tooth movement, is given to the bow by pulling its ends apart. In this ^^•ay six or seven teetli on one side are used as anchorage to move one tooth on the other side. (6) With the clamp-bands on the second pre- molars. The clamping ^\ ire should be directed backwards, and arranged by adjustment, and bending if necessary, to lie against the neck of the molar tooth to be moved ; but for its attachment to the secand premolars, the bow is arranged exactly as in (a), except that the pre- molars and canines on both sides are ligatured to it, and it lias no spring. A piece of rubber is now stretched between the clamping ^^•ire and molar to be moved. (If the same arrange- ment of the clamp-band is adopted on the other side it should be in contact \\ith the tooth.) The effect of the rubber is to move the molar buccally, the premolars and canine remaining stationary, because their combined resistance is greater than that of the molar. Simple anchorage is now used in another form to move the molar buccally, it being this time the total of the resistance of the first and second pre- molars and canine to lingual movement, in addition to the resistance that the bow offers to its extremities being made to approximate one another. (c) Buccal movement of molars may also be brought about by inter-maxillary force ; a rubber band is fixed to the lingual surface of the clamp-band through the medium of a spur cervically inclined, and is stretched thence to the buccal surface of the corresponding tooth in the opposite jaw (s3e Fig. 290). With appliances so arranged, tooth movement would be recipro- cal, so a buccal wii'e or bow mugt be arranged to augment the resistance of the tooth not to be moved ; the buccal wire or bow should be bent to touch the two premolars and canines, to which it may be ligatured to give it greater stability. If the second molar has erupted the buccal wire should be extended to engage this tooth also. It must be remembered that there is a tendency for the molars to elongate by this method. Methods («) and (c) may be combined. (2) Re.movable Appliances. — A powerful coil sj)ring acting on the lingual surface of an upper molar will move it buccally ; on account of the convexity and slope of the surface on which it is to act, there is every probability that the spring will not exert its force just where it is needed ; to overcome this difficulty means should be adopted to make this surface vertical, or to give it such a slope as will prevent the spring slipping off. This is done by means of a band, which is thickened by the addition of solder to give it the necessary shape ; or a spur may be soldered to the lingual surface of the band so as to retain the active arm of the spring in the desired position. The band must, of course, be cemented to the tooth ; a plain soldered band serves the purpose well ; the size of the tooth may be obtained by means of Herbst's bands used for measuring roots tha ' are to be crowned. Three or four clasps she ■'''® be used to hold the plate in position, or r po^\erful spring will dislodge it. The same method may be adopt case of a lower molar, except that a necessary to hold the arm of .it in teeth, , .tre must to disturb looji, or its position, but more clasps are region will be 204 205 the plate securely. Two at least are essential on the same side as the Sf)ring ; they must em- brace the buccal surfaces of the teeth well, so that the spring does not displace the plate lingually. Another method is by means of a jack-screw, ' one end of which acts directly on the tooth to be mo\-ed, ^^■hilst the force at the other end of the screw is received by several teeth, whose combined resistance affords the simple anchorage for the movement of the one molar. Either fixed appliances or a \ailcanite plate may afford the support for the jack-screw, whose force should be delivered to the tooth indirectly, i. e. through the medium of a band arranged to ensure that the force shall be delivered in such a way. that it will do the required \\ork. A screw in a vulcanite plate, as shown in Fig. 291, may also be employed. B. Lingual Movement of Molars (1) Fixed Appliances. — This is exactly as described in paragraph 11, Chapter VII. Inter- maxillary force may be used as an auxiliary, : in the reverse way just described for buccal movement under (1) (c). (2) Removable Appliances. — This has already been described in paragraph 12, Chapter VII. C. Medial Movement of Molars j (1) Fixed Appliances. — This opportunity will be taken to jioint out that when a nut is used on a bow it always engages the medial end of a buccal tube. It is never intended to be put on the bow after the latter has passed through the tube ; this would always be difficult — at times impossible. There are simpler methods of obtaining the same result as would i be achieved by that means. Molars are moved medially by means of force from an elastic band caught on the distal end of the buccal tube behind, and in front to a hook opposite the canine in either jaw, according to the needs of the case. If the elastic band operates on one jaw only the operator must be j prepared for the incisors to move distally or lingually, as it is unlikely that they can give the necessary anchorage ; the buccal tube and bow permit of translatirnal movement only, if the bow is held in a fixed ]x«ition on the incisors. If the clamp-band is on a premolar, the molar may also be banded, and carry buccal and 1 igual spurs, with rubber bands from each of e to some anterior point on either the bow '^anded tooth. Tilting movement is pos- w, and less force will be required to molar. i " Distal Movement of Molars — 1 ^es ", p. 205. I -I Appliances. — A soldered band, having two spurs both directed di.stally, one on the buccal aspect and the other on the lingual, is cemented to the tooth to be moved. A vulcanite plate is made with buccal and lingual attachments, each of which is to hold a rubber band. The attachment on the lingual surface of the plate is fixed as far forward as possible and as nearly directly in front of the molar as can be arranged. The buccal attach- ment is a platinized gold wire, vulcanized to the plate on its lingual surface, passing thence to the buccal aspect of the teeth between the lateral and canine or canine and first premolar, bent up towards the gingival margin, and terminating in a hook, which will support a rubber band stretched from the buccal spur on the molar band. A rubber band is similarly attached on the lingual surface to the corresponding spurs. The plate must be firmly held by clasps, one on the side of the moving tooth, and two on the other side. A buccal wire on the incisors would increase the resistance and stability of the plate. D. Distal (1) Fixed Appliances. (Exactly as in para- giaph 23, Chapter VII.) — Another methcd is to use inter-maxillary force applied direct to the tooth to move it distally. The anchorage, simple or reciprocal as may be desired, is obtained from the opposite ja\\-, the corresponding tooth being employed when a lower molar has to be moved, and one more distal, if possible, when the upper molar has to be moved. The spurs to which the rubber bands are attached should be well forward on the distally moving tooth and far back on the medially moving tooth, so as to make the rubber bands as efficient as possible, though this position of the spurs tends to tilting of the molars. When rcciiirocal anchorage is used the oppos- ing molar moves mtdially. This principle also applies to premolars. (2) Removable Appliances. — Exactly as in paragraj)h 24, Chapter VII. E. Depression (1) Fixed Appliances. (2) Removable Appli.ances. This is a movement seldom called for, but it could be done by such an ap])aratus as shown in Fig. 318 (Fixed), and Fig. 319 (Removable). F. Elongation (1) Fixed Appliances. — This is best done by inter-maxillary force applied to the tooth by means of buccal and lingual rubber ligatures attached to sjjurs on a plain band. The resist- ance is obtained from the ojiposite jaw through the medium of the bow, to whicli suitable spurs 206 have been soldered ; the bow must be fixed to a number of teeth. (2) Removable Appliances. — A plate should be made with buccal and lingual wire springs to engage hooks on the corresponding surfaces of a band on the tooth to be moved. The plate must be very securely held in place by crib- clasps, and the pressure on the tooth be as Fig. 318. — A fixed appliance to depress a molar, (a) A rigid wire bow in the usual position in the incisor region, but shomi at (6) in the molar region to have been bent to rest high up in the buccal sulcus, (c) Plain or clamp-bands; to those on the premolars are soldered ((i) spurs to support the bow; there is also a spur on the molar band for the attachment of (f) book for attachment of rubber band. (/) A rubber band, passing over the rigid bow to be attached on the lower jaw, so that it may exert force to depress the upper molar. moderate as is consistent with obtaining move- ment, because the direction of the force tends to displace the plate. The attachment of the buccal spring must be made very rigid, not only to the plate, but also in its passage to assume the horizontal position, which it takes up to get to the molar ; the spring should pass from the lingual surface Fig. 319. — Cross-section of part of a removable appliance to depress an upper molar, (a) Plain band to which is soldered (6) a spur directed occlusally, which is engaged by (o) a coil spring fi-xed in a vulcanite plate and exerting force in the direction shown by the arrows. between canine and first premolar and be made of platinized gold wire. On the lingual surface a coil spring is used, attached as far forward on the plate as possible. G. Rotation (1) Fixed Appliances. — The method de- scribed by E. H. Angle is to give the extremity of the bow a bend, so as to a.ssume a position parallel with the direction that the buccal sur- face of the molar should occupy when normally placed, and in tlie same plane, instead of allowing it to remain parallel with the direc- tion of the buccal surface of the tooth in its abnormal position. To rotate the distal corner of the tooth outwards is comparatively easy (see Fig. 320), for this takes place as the result of expansion force applied to a molar through the medium of a buccal tube and bow, because the distal end of the tube ^^•ill move through a larger arc of a concentric circle than the medial end. This movement may usually be expected \\ hen using a bow unless care is taken to prevent it. The movement may be increased by Ijending out^\■ards the extremity of the bow. Slight rotation in the opposite direction may be produced by giving the extremity of the bow a bend inwards just in front of the nut (see Fig. 321). Lowe Young (12, p. 245) describes a method of rotating a molar when the medio-buccal corner has to be moved buccally or outwards. B Fig. 320. — The heavy lines show the original position of the anchor tooth and buccal tube, on the clamp- band. The light linos show the position of the same after expansion of the molar if the ends of the bow were parallel with the tubes originally, and no further adjustment has been made. (See also Fig. 285.) The clamp-band is fitted with the screw directed distally ; the buccal tube having been removed, a shorter tube is soldered to the band at the medio-buccal corner and parallel with the long axis of the tooth. To the medial end of the original buccal tube a short length of wire, which accurately fits the new buccal tube on the band, is soldered at or near its extremity and at right angles to its length, so that when it is inserted in the short tube, the original buccal tube will be in correct position to accom- modate the bow, the spring of which exerts an outward movement on the medio-buccal corner of the tooth. The disto-lingual corner is pulled inwards, i. e. in the opposite direction, by a rubber band stretched from a spur on the lingual surface of the band, distally, to a spur on the bow, if there is no second deciduous molar or first premolar. This spur is to be so situated that the rubber band will not exert pressure on any tooth except the molar. If there is no space, then a length of spring-wire is soldered to the disto-lingual corner of the band and arranged to extend forwards, but directed across the palate, so that it is not in 207 contact witli the premolars; it is then pulled up close to the premolars by a ligature, \\ liieh passes between the canine and lateral and engages the bow and the spring-wire. Tilting of Molars. — This movement has not been referred to in the classification of tooth movement, though molars are frequently seen to be leaning forward as the result of loss of the medial tooth. The movement is ef- fected by a method similar to that for rotation described first, except that the plane in which the parallelism of tube and bow extremity varies is the vertical one, w hereas in the previous case it was the horizontal one. In the present instance either the tube or bow extremity may assume the variable position, a I, nnr^ \ Fig. 321. — Rotation of the distal corner of a molar inwards, (a) Extremity of bow as bent to lie parallel with the buccal tube. (6) Extremity of bow as bent to obtain lingual move- ment of the molar without any rotation, (c) Extremity of bow as bent to oljtain rotation inwards of the distal corner of the molar. SO neither will interfere with the comfort of the soft tissues, whereas in the previous case, if the direction of the tube varied much from the general direction of the buccal surface of the molar, it would be a source of irritation to the soft tissues by its projecting corner. As tilt- ing of molars is usually in a forward direction, due to loss of the tooth m front, the correc- tion of that position will be described. The simpler way is as follows : The clamp-band is adjusted as usual, and as if the tooth stood vertically in its socket ; the tube is directed with its medial end downwards, if on a lower tooth ; the bow is bent as usual, but instead of this extremity being made parallel \\ith the tube, it is left in the position it would oc- cupy if the tooth were normally placed. The bow is now inserted in the tubes, and its effect on the malposed molar is to elevate the medial aspect of the tooth in its socket and to depress the other; the latter being the nmch more difficult movement to produce, the former may be expected to happen. There will also be a tendency to tilt down the medial end of the normal molar, which for the reasons just given may be disregarded. Wlien a molar on each side has to be tilted, the bow at rest will be over the gum instead of across the necks of the incisor teeth. In order that it may exert the necessary force on the molars, it must be pulled up to the teeth and securely ligatured to them ; the tendency of this is to depress the inci.sors in their .sockets, but as depression is more difficult than elevation, upward movement of the medial aspect of the molar may be expected, rather than depression of its distal end, and of the incisors. If the direction of the buccal tubes on the clamp-bands is changed, so as to correspond with the usual bow alignment, then the extremity (or extremities) of the bow must be bent just in front of the nuts, so as to secure an arrange- ment similar in effect to that already described. II— PREMOLARS (with which Deciduous Molars are to be included) A. Buccal Movement (1) Fixed Appliances. — If the clamp-band is on this tooth, then it is moved buccally by the direct action of the spring of the bow. If the clamp-band is on a posterior tooth, then the premolar is moved buccally by ligaturing it to the bow and tightening or renewing the ligature as may be necessary. The marked convexity of the lingual surface of premolars is frequently a cause of the ligature sliding far down on the tooth to^^■ards the root, so that it may be quite covered by the gum ; thus an irritation of the soft tissues is set up, which may render the parts quite sore. To prevent this a crib is soldered to the ligature ; this crib consists of a piece of ligature wire soldered to the ligature itself at both ends and in such a position that it will occupy the medio-distal sulcus of the tooth when the ligature is in posit ion. Silver solder may be used for soldering in this instance. The same disadvantage applies to ligatures on deciduous molars. Pullen (10, p. 595) advo- cates another form of crib for dealing \\ith these ; an extra piece of ligature wire is soldered to the centre of the ligature; this wire passes from the centre of the lingual surface of the tooth across the occlusal surface, and is included ^\■ith the two ends of the ligature as it is tied (see Fig. :i22). Second premolars may be moved buccally, when the threaded wire of a clamp-band passes across the lingual surface, by stretching be- tween the two a piece of separating rubber ; it 208 must not be forgotten that the rubber exerts the same amount of force to move the clamped or banded tooth lingually, and slightly to rotate it, as to move the premolar outwards. The tendency of the molar to move lingually may be opposed by the spring of the bow. The buccal movement of any tooth may usually be made more rapid by placing a piece of separating rubber on the lingual surface of the tooth and including both rubber and tooth in the ligature. It is presumed that in all these cases the operator has arranged the bow either to afford the necessary anchorage or to move other teeth as desired. (2) Removable Appliances. — To move a premolar buccally ^\ith these appliances, a spring, a small jack-screw, rubber, or the expan- sion of wood, may be used. The use of springs in such situations has already been referred to (Chapter VII, para- graphs 4 and 8). Rubber is used by cutting a dovetailed slot in the plate edge, which should be thickened Fig. 322. — Crib ligature for a deciduous molar. The central strand of wire is soldered to the wire encircling the tooth and included with it when the ligature is tied. (After Pullen.) for the purpose, opposite the tooth to be moved ; in this slot a piece of rubber is placed ; the dove- tailing holds the rubber, which should be a piece sufficiently large for the plate to need forcing into position, when the effort of the rubber to resume its original shape moves the tooth outwards. In using wood the plate is again given a thickened edge opposite the tooth to be moved. In the edge a cylindrical hole is cut, and a piece of compressed hickory wood is forced into it from the surface that is in contact with the tooth ; the wood should project just so far that a little effort is necessary to press the plate into position. The moisture of the mouth causes the wood to swell, and so the tooth is moved. B. Lingual Movement (1) Fixed Appliances. — («) By stretching separating rubber between the bow and buccal surface of the tooth to be moved — the elasticity of the rubber moves the tooth inwards. It usually happens that if one premolar has to be moved lingually there are other teeth to be moved buccally, and then the use of rubber contributes to reciprocal tooth movement (see Fig. 323, A). If simple anchorage has to be used, the resist- ance must be carefully thought out before rubber is employed, or else the desired result may not be obtained. (b) Inter-maxillary force may also be used to move a premolar lingually by stretching a rubber band from the buccal surface of the tooth to the lingual surface of an opposing tooth, or teeth, according to the amount of resistance required, which again depends on whether simple or reciprocal movement is desired. The rubber bands are attached to the teeth through the medium of bands carrying suitable spurs. (c) If no other movement is desired, a rubber band may be stretched from one side of the mouth to the other, and by making use of simple anchorage one tooth is moved lingually by means of the resistance of three or four teeth on the other side ; this resistance is obtained by banding one tooth and soldering a buccal wire to it that shall be in contact with two or three of the approximal teeth. The rubber bands are attached to spurs on the lingual surfaces of the soldered bands. The method is applicable only in the upper jaw. {(l) Bands are attached to two teeth, one on either side of the tooth (or teeth) to be moved, and coiuiected by a buccal wire. Separating rubber is stretched between the teeth and the wire ; if the resistance is insufficient lingual wires may lie added to the bands to increase the resistance of the banded teeth by adding thereto the resistance of the approximal teeth. As the premolar moves the wire should be bent to remain in contact with it. If the resistance of the canine and premolar is insufficient that of the lateral incisor and molar should lie added by means of lingual wires. (e) The plan described in (a) may be re- versed. As before two teeth are banded and united by a lingual wire. Three modes of arrangement of the wires are shown in the cUagram (see Fig. 323, B, C, and D). The wire may be soldered directly to the bands, or may fit in tubes soldered to the bands. (/) By a Siegfried spring on the lingual sur- face of the tooth to be moved (see p. 217, and paragraph III a (1) c.) (2) Removable Appliances. — (a) By stretching rubber between a buccal wire fixed ! to a plate — this has the great disadvantage of difficult renewal, which would be necessary every time the plate is removed from the mouth. (b) By a rubber band stretched from the tootli to the palatal surface of the plate, where it is attached on a spur, or to the opposite corresponding tooth, the plate being cut away 209 lingually to the tooth to be moved. The rubber bands are attached to the teeth through the medium of bands carrying spurs. (c) By a spring on the palatal surface of tiie plate, which engages a hook on the lingual surface of a band on the tooth to be moved. of the premolar. The spring should be made to engage the distal surface of the premolar well , and (1) C. Medial Movement Fixed Appliances. — (a) Clamp- band on the first permanent molar. A ligature engages the tooth, and a spur is placed on the bow anterior to the tooth. The nut on the bow must closely engage the medial end of the buccal tube, as it is the molar that offers the resistance whereby the premolar is moved. (6) Clamp-band on the premolar that is being moved medially. The nut on the bow is turned considerably forward so that it is quite away from the buccal tube, or it may be removed entirely. A hook to engage a rubber band is soldered well forward on the lower bow on the same side. This rubber band is stretched from the liook on the lower bow to the distal end of the buccal tube of the tooth to be moved ; the lower teeth, through their bow, afford the resistance necessary for moving the premolar forward. (c) A plain band with spur is made for the premolar that is to be moved medially ; a band is stretched from this spur to a suitable fixed point in the loA\er ja\\', which may be a single tooth, more than one tooth, or the bow itself, according to the resistance required. (rf) If the first upper premolar has to be moved forward, and there is a space between it and the first permanent molar, which is to be occupied by the second premolar later, a tiny jack-screw may be fitted between the two teeth ; the premolar will move, ceteris paribus, as it offers the less resistance. The jack- screw may be attached to a plain band on the premolar. To this band is soldered a piece of threaded \\ire, which ^^ ill just occupy the space between it and the molar. A nut is put on this threaded wire, and left just short enough to enable the band to be cemented in position. Then the nut is turned against the molar, and the space enlarged in this way. Methods (a) and (c) may be used in conjunction with this one. (2) Removable Appliances. — -Coil- springs on a vulcanite plate offer the most suit- able means of bringing about medial movement Fig. 323. — Lingual movement of a premolar by fixed appliances. A. Wire bow in position ; second premolar and canine requiring buccal movement. (a) Wire bow. (b) Ligatures for buccal movement of canine and second premolar. (c) Rubber wedge between bow and first premolar to bring about lingual movement of the latter. Notice that the clamp-band {licable to the (onstruotion of retaining appliances. It may happen that a retaining appliance has to be repaired hurriedly ; for instance, a band to which a buccal or lingual retaining wire is 226 soldered, has broken and has to be made anew. The wire, with any bands that may be attached to it, is removed from the mouth ; the broken band is detached from the rest of the appliance and a new one made to replace the broken one. The retaining wire is replaced in the mouth, ligatures being used to support it against the teeth if necessary. A sand-and-plaster impres- sion is now taken so that the parts to be united are accurately held in it, but no impression material is allowed to come in contact with those parts that are to be soldered together ; if it does this must be removed, and soldering proceeded ■n-itli at once. In this ^\'ay a repair may be done whUe the patient is in the chair. All edges of bands or wire should be smoothed and rounded with stones or discs before the appliance is cemented in the mouth. SIZES OF MATERIALS USED IN ORTHODONTICS Clamp-bands Band Material. Length. Tliickness. Width. Permanent Molars and Premolars. Deciduous Molars. Platinized gold . . 27, 30, 33, and 36 mm. ■18 mm. 5 mm. 4-5 mm. German silver 30 mm. and two other sizes •18 mm. 5 mm. 45 mm. Tubes. — The size of the tubes should be such that the bows fit them accurately. This is essential for the efficiency of the apparatus. One firm manufactures all its bows, of which there are five sizes, so that the threaded ijortion is the same size in all, only the intermediate portion of the bow being variable. Li this way only one size of tube is necessary. These same bows have the threaded portion flattened, so that it accurately fits the oval or round tube (see Fig. 280). Buccal tubes are -J inch in length. The Clamping Mechanism. — Gauge 16 wire is used to make the threaded wire ; the nut and tube are of a size to correspond. Plain Bands. — The length of these is such that they fit the tooth accurately and yet not absolutely tightly, or else there will be no room for the cement on which their retention on the tooth depends as well as on their fit. Material. Thickness. Width for Incisors. Permanent Molars. Deciduous Molars. Iridio- platinum . •08 mm. •14 mm. 3^6 mm. 4-0 mm. suitable for any tooth Platinized gold . . •18 mm. •10 mm. 5'0 mm. 4-0 mm. 4 mm. German silver ' . . C F H •10 mm. •14 mm. •14 mm. 4-0 mm. 4^0 mm. 5^0 mm. As regards the use of precious metals for plain bands, platinized gold is to be preferred for molars and premolars when they are to be used as anchorage for moving teeth ; it is softer than iridio-platinum, and is therefore more satisfactorily worked and burnished. This point is of practical imf)ortance because molar and premolar bands for anchorage purposes must be thicker and stronger than for retention or holding ligatures, and must be more or less burnished to fit the tooth. In the case of plain bands for incisors and premolars (when not for anchorage), these may be thinner and narrower ; for this reason they should be made of iridio-platinum, which is tougher than platinized gold, and in these circumstances can be satisfactorily burnished, if they do not already fit the tooth accurately by the simple tightening of the material round it with pliers. Ligatures. — Ligatures are of brass wire, gauges 26, 28, and 30 (B. & S.) ; 26 gauge is the one most used when the patients are not more than ten years old. Above that age, and when bows, gauge 16, are being used, gauge 28 wire is indi- cated ; the 30 gauge wire is seldom needed. Silk ligatures are discussed elsewhere. Tliree sizes should be kept ready for use. (See p. 218.) The use of rubber bands of various sizes for inter-maxillary force is discussed by Pullen (9). 1 The letters refer to the material sold by the S. S. White Company. CHAPTEE X ABNORMALITIES OF POSITION— TREATIMENT {continued) RETENTION E. How, and for how long, are these move- ments to be artificially retained (retention) ? General Principles. — If possible the retention of teeth in their new positions is of greater importance than the moving of teeth, on account of the very great tendency they exhibit to return to their former positions. The object of retention is to combat this tendency. The necessity for retention, natural or artificial, exists in every case ; it occasionally happens that natural retention ■\\ill suffice, but it may be taken for granted that these cases are so few in number as to be negligible, and that the operator errs on the right side in retaining unnecessarily. It has been pointed out that the two dental arches, whether normal or abnormal, tend to harmonize in size ; if there has been coiLsiderable movement of the upper and lower teeth, the tendency of both to relapse is more or less equal. Before treatment these dental arches harmonize in size, and at the conclusion thereof they have been made to harmonize again in size, and so, if both are not carefully and efficiently retained, they, the new arches, will show a strong ten- dency to collapse together, and again exliibit those features which most marked the original irregularity. Especially is it necessary for one arch to be absolutely retained, \\hen any ten- dency to relapse shown by the other arch may be combated, if even for a time only, by the one that is securely held. This leads up to those cases in wliich only one arch has been treated, the other remaining exactly as it presented. This untreated arch may, therefore, be regarded as a stable unit and one that will materially a.ssist, passively of course, in the retention of the other — i. e. it will offer natural retention ; but artificial retention is also neces- sary, because a relapse would most certainly occur unless the teeth had very prominent cusps correctly occluding with those of the opposite jaw in which there had been no move- ment, and unless equilibrium had been estab- lislied between all the tis.sues involved. Retention must be maintained until equi- librium has been established; this does not take place till all the tissues — bone and soft tissues — ^have developed and accommodated themselves to correspond \\ith the new positions of the teeth. The teeth have been moved to occupy the positions they would have occupied had the jaws developed normally ; these move- ments are carried out nuich more rapidly than bone and muscle can develop their normal form and function, and until this takes place natural retention is not to be ex]5ccted. ^\'hen it does result, permanent and natural retention may be said to have been established, and it will be readily understood that the younger the patient the more quickly will it take place ; at six to eight years of age it may be expected to occur in six months or so, whereas at sixteen years of age a less satisfactory state will obtam after three years of artificial retention. (The extent and direction of tooth movement also have a bearing on this point.) Until natural retention has been established there mil be a tendency — more or less great according to the extent to which artificial retention lias been successfully carried out — for the bone and adjacent soft tissues to resume their former state, and in so doing the teeth ■^^■ill be carried with them to occupy their former malpositions. It is the function of retention to combat this tendency. Retention is the holding of teeth in their new positions until the surrounding tissues have accommodated themselves perfectly to the teeth in those positions. Mechanical resistance in the form of apj)lianccs, usually passive but occasionally active, is employed to retain teeth much in the way that force was used to move the teeth. This resistance must be sufficient, or else there will be a greater or less relapse according to the amount of the insufficiency of the resistance. Natural retention is the result of inter- digitation of cusps, both medio-distally and bucco-lingually, as well as of the normal function of the lips and cheeks buccally and the tongue lingually. Anchorage deals with the resistance of teeth to movement ; retention also deals \rith the resistance of teeth to movement. In the former it was resistance to obtain movement that was dealt '.\ith ; in the latter it is resistance to prevent movement that has to be considered. 227 228 Retention may be considered under the same headings as Anchorage. ((«) Simplest. -(b) Reinforced. [(c) Resistance to transla- tion. 1(a) Simplest. \(h) Reinforced. ( Imjjracticable as a force t for retention. A. Simple B. Reciprocal C. Stationary Any of those included in A and B may also be inter-maxillary, i. e. may act between the two jaws. Fio. 339. — Retention — simplest reciprocal ancliorage. Two upper central incisors misplaced in opposite directions, one labially and the other lingually. A. Before treatment. B. and C. After treatment with retainers in position. B. Plain band on the lingually misplaced central with labial spur to the other central to hold the latter lingually, which is reciprocally holding the former labially. C. Plain band on the labially misplaced central with lingual spur to the other central to hold the latter labially, which is reciprocally holding the former lingually. In addition to these purely artificial methods of retention, natural retention may be active to some extent as soon as the tooth-moving appliances are removed. A. Simple. — (a) The Simplest Retention is that in which a larger and stronger tooth will resist the tendency of a smaller one to return to its former position, e. g. a molar will be sufficient resistance to prevent a premolar relapsing. As the force required to retain a tooth is less than that required to move it, a tooth of low resistance value will frequently suffice to retain one of greater resistance value (see Fig. 360). (b) Reinforced Retention is similar to (a), but two or more teeth are employed instead of one ; e. g. a central and lateral wUl retain an inter- vening central. (c) Resistance to Translation. — A molar that can only move by translational movement will be of greater retaining value than if it were capable of movement by inclination. B. Reciprocal. — (a) Simplest. Two incisors that have been moved in opposite directions will retain one another if suitably opposed (see Fig. 339). (b) Reinforced is that form of retention in which several teeth that have been moved are employed to retain teeth that have been moved in the opposite direction, e. g. buccal movement of the molar series on opposite sides of the same jaw. C. Stationary Retention is that derived from the occiput and associated bones. Retaining Appliances Having to exert passive force only, re- taining appliances should be much simpler, in design than appliances for moving teeth. They must, however, be strong and well constructed, as they are to be worn a considerable time, during \\ hich they must be efficient without the need of constant attention. Their strength as regards retain- ing the teeth has only to be sufficient to ensure that they will not be overcome by the tendency of the teeth to relapse, so that the younger the patient the lighter may be the appliance ; just as a weaker or lighter appliance will move the teeth of a young patient than would be required for an older one. It must be remembered, however, that retaining appliances are often constructed to engage the lingual surfaces of the teeth (whereas tooth-moving apphances are more frequently on their buccal sin-faces) where the effects of masti- cation will be more severe on them than on the other class of apiiliances, and they must be designed with this fact in mind. Following the course adopted with tooth- moving appliances, devices to retain teeth in their new positions may be classified as — ■ A. Fixed. B. Removable. A. Fixed. — Fixed appliances are to be pre- ferred, because they may be simple and con- structed to exliibit the highest degree of efficiency. They are not apt to damage the soft tissues, as is always likely to occur with vulcanite plates. Above all, they are out of the patient's control and must be worn, whereas a removable appliance is likely to be forgotten 229 or even lost; the result of this would, in all probability, be disastrous. These appliances should be constructed so that, as far as possible, the various parts are separate from one another, and thus allow the repair or renewal of any one jiart without dis- mantling the entire appliance. They must receive support from attachments fixed to teeth, which are placed at closer intervals than is necessary in the case of appliances to move the teeth, ^hen two clamp-bands, one on each first molar, are sufficient to hold and firmly support a wire bow, because they are supplemented by ligatures. Ligatures are undesirable in comiection ^\ith retaining appliances, so definite additional support from a band on an intervening tooth must be given to a retaining bo^\ that is attached to two first molars or even two second premolars. As has been already men- tioned, a lingual wire is also nuicli more exposed to stresses that result from mastication than a buccal arch ; this is another reason why extra support is necessary. Li the case of retaimng ap- pliances a free end of wire may extend beyond the actual attachment, but it must be rigid and shoidd not include more than one tooth, as the free end is likely to be bent, if at all prolonged, by the repeated stress put upon it (see Fig. 341). Fixed Appliances consist of — 1. Bands, plain or clam]), with spurs soldered to them (see Figs. 3-41, 344, 360). 2. \Mre bo^\s, complete or partial, at- tached to (1) (see Figs. 344, 356). Plain bands are more commonly em- ployed, as they are simpler and their attachment to the teeth by cement usually suffices. The bands in one jaw are united by wire attachments so arranged that they will resist the tendency of the teeth to return to their former jjositions (see Figs. 344, 356). Wire used for retention, \\hether it includes one tooth or a number of teeth, and whether removable or fixed, should only touch the teeth at their most prominent i^oints unless othenA'ise necessary for special reasons ; it is not good practice to fit these \\ires accurately round the exposed surfaces of the teeth. The following tj'pes of attachment may be used to unite bands and wires — (i) The main retaining wire is soldered direct to a band (see Fig. 356 (2) ). (ii) The wire bow engages a loop on the band, both being arranged and situated so as to be a source of strength to the appliance (see Fig. 341). To maintain the correct relation between wire bow and loop a lug on the former may be necessary (see Fig. 341). (iii) The wire enters a tube, closed or per- forate ; when the latter form is used it may be essential to solder a lug on the wire, or to have the wire threaded and carrying a nut, which shall engage one of the extremities of the tube (see Fig. 340). There is great advantage in appliances of this type because they permit of slight indi- vidual movement of the teeth, allowing them to take up a position of equilibrium, whilst main- n Q, p - 3. Fig. 340. — Methods of movable attachment between short tubes and retaining wires. 1. Retaining wire entering a closed tube. The object of the closed end is to enable the tooth to wliich the tube is attached to resist any pressure brought against it by other teeth exerting pressure on the lingual wire. The attach- ment on the first left molar (see Fig. 356) could be of this nature and would resist anj' tendency of the incisors to move lingually were there no attacliment to the first left premolar. 1. Retaining wire passing through a perforate tube with lug on the wire to serve the same purpose as the tube with closed end. The attacliment on the second right premolar (Fig. 356) could be of this nature. The object of the wire passing through the tube is to retain the adjacent molar in its buccal position. Retainmg wire passing tlirough a perforate tube and then bent over. The buccal attaclunent on one or both sides to the second premolar (see Fig. 'Hi, III), could be of this nature. The incisors would in this way be prevented from moving labially. The wire used with this object in view must be sufficiently thin to be easily bent when the appliance is in the mouth. Tlireaded wire passing through a perforate tube, one end of which is engaged by the nut on the wire. The applica- tion of this method is shown in Fig. 341. This type of attaclunent has the advantage of being adjustable. W^hen cii'cumstances demand, the nut may engage the distal end of the tube ; its fixation in the mouth would be more difficult. taining their general relationship to one another. Li the text, soldering all the parts to the base wire is assumed, to avoid constant repetition, but it must be bonie in mind that it is preferable not to attach the ^\ire rigidly to all the bands unless this is specially referred to. B. Removable. liemovable Appliances consist of — - 1. Vulcanite Plates; 2. Metal plates of tlie same tjiie as vulcanite plates, or of the Jackson type with a skeleton base ; 230 3. Plates combining the features of (1) and (2) (see Figs. 342, 343). Wire attachments are used in connection with the plates when necessary, and may be fixed directly to the teeth or to the plate ; the former method implies a combination of fixed Fig. 341. — Retention of buccal movement of all the teeth. — Reciprocal reinforced and .simple reinforced anchorage. The retainer consists of a lingual wire and plain bands with accessories on 5 ] 15. The wire is not soldered to any of the bands. On the right premolar band the accessory is a short tube, engaged medially by a nut on the lingual wire, which in this position is threaded ; on the left premolar band the accessory is a wire loop to engage the lingual wire, on which there is a lug engaging the loop. The lug and nut prevent lingual movement of the incisors. A cross-section of the left central incisor, having cemented to it a plain band with loop, before closing, and lingual wire in position, is shown on the right of the figure. The gingival end of the loop is left free so that if the loop is not efficient a wire ligature may engage this free end and the lingual wire to secure the two together. Notice that the loops are arranged diagonally across the tooth, whereby they are longer and so more easily adjusted. and removable appUances, which is frequently a desirable plan. Attachments, whether removable or fixed, . should be made for preference to deciduous teeth. The tooth movements to be retained are the same as those referred to on p. 181. This part of the subject need not be dealt with seriatim as tooth movement has been treated, but the table given for that purpose (p. 182) wUl now be followed in the case of retention, and the numbers used refer to it. I and n— MOLARS. PREMOLARS, CANINES, AND INCISORS A. Buccal Movement 1, 3, 5, 7, and 3S. Fixed Appliances. (a) (See Fig. 344, I, without the labial wire from canine to canine.) Clamp or plain bands are fitted to the first permanent molars and plain bands to the canines. A complete lingual wire bow is bent up to fit the dental arch almost at the necks of the teeth, and then soldered to the lingual surfaces of the four bands. If the clamping portion of the clamp-band extends forwards then the lingual wire bow is attached to this ; if it goes distally, the lingual wire is attached to the medio-lingual comer of the band. Wlaere there has been considerable buccal movement of the canines this arrange- ment of the bands is desirable, as the efficient retention of these teeth is very important, especially in the upper jaw. (6) (See Fig. 341.) Plain bands are made for the two second premolars and for one of the incisors, the one selected having been moved lingvially or moved least in a labial direction. A lingual wire is bent up so that it will hold all the teeth as desired ; it may be maintained in place without solder if constructed as follows. To the lingual surface of one pre- molar band a short horizontal tube is soldered (when fixing the appliance in the mouth it may be necessary to put this band on last, even Fig. 342. — Vulcanite saddle retention plate with platinized gold wire to hold the incisors in their labial positions. There are accessory wires soldered to the main base-wire to engage those tooth surfaces that are next to the spaces for the uneiupted canines, so that these spaces may be preserved. The wire on the first right premolar is also a spring to move that tooth distally. The wire on the left lateral, which has been rotated, is bent round to engage the labial surface of that tooth closely, and hold it in its new position ; the lingual wire against the lingual surface of the tooth holds the other comer. There are wire clasps on the first permanent molars to hold the plate in position. after the lingual wire has been put in ; the tube on the band is slipped over the end of the wire and then the band itself rotated into place on the tooth) ; one end of the lingual bow sliould be threaded and carry a nut to engage this short tube medially (see p. 238 (3)); the wire then 231 passes across the lingual surfaces of all the teeth, being engaged by loops, open occlusal ly and soldered to bands, one on an incisor, preferably a central, and the other on the other second premolar. To maintain the medio-distal posi- tion of the -wire a lug is soldered to it to engage the loop on the premolar so that it cannot slip distally through the loop ; this also secures the retaining \\ire in position against the incisors, Mliich are now prevented from relapsing in a lingual direction. These loops shoidd be placed as near the cervical edge of the tooth as possible and be open only sufficiently to permit the bow wire to pass, or else there will be the possibility of the patient dislodging it with the tongue. If of sufficient length and made of thin wire (19 gauge B. & S.), these loops may be closed after the lingual bow is in position. The lug to engage the medial aspect of the loop on the premolar may be given an inclination distally, ■\\hen it will also act as a locking device. If there is any difficulty in maintaining the wire bow in position it may be tied to the loops by a fine wire ligature of brass or gold. The incisor loop is more applicable to the lower jaw than the upper, where the use of any appliance but that occupjing the least space (the wire soldered to the band) may be contra-indicated on account of the bite. (c) (See Figs. 345 and 350.) Labial move- ment of the incisors and canines may be retained by banding the first premolars or canines and joining the two bands by a lingual wire ; if the canines are banded the wire may be extended distally to include the first pre- molars if it is necessary to retain those teeth in position. 2, 4, 6, 8, and 39. Removable Appliances. (See Fig. 342.) A simple plate, metal or vul- canite, is made to engage all the teeth to be retained on their lingual surfaces. It may be held in position by clasps or cribs on molars or premolars. In the case of the upper jaw, if all the teeth have to be retained at one time, the plate may be a saddle one with a platinized gold wire attached, at both extremities, to the anterior edge of the plate, and passing round beliind the incisors and canines to en- gage these teeth at a point just beyond the free edge of the gum. Wlien necessary, addi- tional attachments may be soldered to this lingual wire. In the case of the lower jaw a similar principle, but varied to meet the different conditions, may be employed (see Fig. 343). The sides of the plate are made in vulcanite or metal as usual to retain these teeth, and these two portions of the plate are coiuiected by an oval wire, as used in making wire lower dentures, passing across the lingual surfaces of the canines and incisors so as to rest on the cingula of these teeth. Methods such as these considerably reduce the amount of soft and hard tissue covered by tlie plate, and so there is less liability of any harm being caused thereby. In some cases it will he possible to replace vulcanite in contact with tlie jiremolars by wire. Fig. 343. — Vulcanite and metal retention plate. The sides, in the position of the premolars and molars, are of vulcanite ; the intervening portion is an oval wire resting on the eingnla of the incisors. On the right lower molar there is a cleat to prevent the plate sinking ; on the base wire there is a spring to push out the two central incisors. Against the distal surface of the first left premolar there is a sliort spur to prevent that tooth falling distally. On the first left molar there is a complete crib clasp. which will still further reduce the amount of tissue, covered by plate, that there is any possibility of damaging. B. Lingual Movement. 9, 11, 13, 15, and 40. Fixed Appliances. This is the reverse of that just described, but it seldom involves more than individual teeth, except in the case of the upper incisors. For this purpose a wire must extend from canine to canine or more distal teeth, on their labial surfaces. In many cases expansion of the molar series and canines will also have to be maintained at the same time. The ways in which the appliances may be arranged for this purpose are numerous ; tho.se shown in Fig. 344 may be mentioned. (I) is probably the mo.st efficient ; the lingual wire behind the incisors is to give added strength and to remove any chance of the molar series collapsing, and the labial wire may be a very light one^ The cases in w hicli these movements have to be retained are usually complicated by close bite, so that there is every probability of the lower incisors striking this lingual wire ; if it serves the purpose of opening the bite this 232 arrangement is satisfactory, but it throws con- siderable strain on the canine bands. (II) and (III) avoid the use of a lingual wire for the incisors. The retention of the buccal movement of the molar series and canines, as well as of the lingual movement of the incisors, depends entirely on a buccal wire, which must therefore be of heavy iridio-platinum ; the short Fig. 344. — Upper arch, which has been expanded in the molar and canine regions. The incisors have been moved lingually. Retention — Reinforced recipro- cal and simple reinforced. I. Clamp-bands on the first molars ; plain bands on the canines ; a lingual wire bow from molar to molar to retain all the teeth except the incisors, which are retained in their lingual positions by a labial wire from canine to canine. II. Plain bands on first molars, first premolars, and one central ; a complete buccal wire from molar to molar. This retains all the teeth as desired except the second premolars, which are held buccally by lingual spurs from bands on the molars or pre- molars. If the canines need retaining, lingual spurs must extend to these also, (a) Shows the arch resting in a notch in the seam of the central band instead of being soldered to it. III. Plain bands on the second premolars and central, to all of which a buccal wire is soldered. To each premolar band a lingual wire is soldered, which engages the first molar, first prertiolar, and canine. In I, II and III the incisors are held lingually by the canines and premolars (also by the molars in I and II), whose position has not been changed in the direction (medio-distal) that corresponds to bucco- lingual direction of movement of the incisors, as regards their efficiency for retention purposes. Fig. 345. — Retention of lingual movement of incisors by combined labial and lingual wires, the required resistance being obtained from the canines. Anchorage — Simple reinforced. Plain bands on the canines and one central ; a lingual wire unites the three bands. A labial wire is attached to the central band and engages all the incisors that have to be held in a lingual position. Without the labial wire this appliance will hold the incisors labially. lingual .spurs in (II) to engage the second pre- molars may be attached to the first molar band or first premolar band ; if the former be a clamp- band, the threaded wire of the clamping mechan- ism will serve this purpose. The lingual wires in (III), when they extend to the canine, are some- what long and liable to be displaced by the stress to which they will be subjected ; con- siderable strain is thrown on the premolar bands with such an ai^phance. In both cases the length of buccal wire needs a support, w hich may a Fig. 346. — Retention of lingual movement of one incisor. Anchorage — Simple reinforced. (a) Before treatment. (6) After treatment. The tooth that was in labial occlusion is banded, and a spm-, soldered to the lingual surface of the band, extends to one adjacent tooth on either side. This also prevents the left central and right lateral closing together again. be provided by a notch in the seam of a band on one of the centrals. (See Fig. 345.) Another method of retaining all the incisors in a position lingual to the original is to band the canines, or any teeth distal to them, and coimect them by a lingual wire which is soldered to a band on one of the cen- trals. From this band a wire extends on each 233 side to engage the laliial surfaces of all the incisors that have been moved lingually. This is especially satisfactory if one of the laterals has not shared in the lingual movement; but, if the spur wire must extend over two teeth, there is less danger of impairment of the appliance on account of the comparatively slighter stresses of mastication compared with those experienced in other situations. \\lien only one or t^^•o teeth have to be held in a lingual position, a band (on the tooth that was misplaced) ^\ith a lingual \\ire to one or two of the approximal teeth is sufficient (see Figs. 346, 347) ; or two bands with a labial wire may be employed (see Fig. 348, a), and this plan is indicated when the bite would be dis- turbed by lingual appliances, especially if the various parts are separate from one another, as these are greater in bulk. The original irregu- larity is shown at Fig. 348, A. Fig. 348, b shows another method of retaining this irregularity. Fig. 349 shows how the retainer in Fig. 348, a, may be constructed of three separate parts ; the loop on the band is such that the wire may be just forced into it and held so that it will not slip out of its own accord, but can be removed with a gentle pull. These loops must be made accurately, as there is danger of damaging the appliance if an attempt is made to bend them much after 4, 6, 8, 39, are employed with the addition of a buccal ^^ire to engage the teeth that have been moved lingually. The wire should be attached at both ends, passing from the lingual ^ c::^ Fig. 347. — Three methods o£ retention of lingual movement of one premolar. Anchorage — Simple in (a) and (6) ,■ Simple reinforced in (c). A. Original abnormality. In each case there is a plain band on the tooth that was misplaced. To the lingual surface of the band is soldered in — (a) a lingual spur to engage the adjacent premolar; (6) a lingual spur to engage the adjacent canine ; (c) a lingual spur to engage the adjacent premolar and canine. A fourth method would be to band the canine and second premolar and luiite these two bands with a buccal wire, which would hold the first premolar in its new position. Fig. 348. — Retention of two buccally misplaced central incisors. Anchorage — -Simple reinforced. A. Original abnormality. (a) The centrals retained by the laterals, which are banded and miited by a labial wire. (6) One central is banded and has a labial spur engaging the other central. A Ungual wire engages all four incisors, so that the laterals again retain the centrals. This form has the advantage of only requiring one band. to the buccal surface where two teeth ap- proximate. The buccal wires should not include more teeth than absolutely necessary, as the longer they are the more difficult they arc to manipulate. It may be an advantage at times to make the buccal \\ire in two or three sections, any teeth intervening be- tween them being engaged by an extension. Some o])erators prefer to cast w ires of this nature rather than to bend them, as great accuracy of fit may be obtained, tliough it should not be overlooked that for the pur- pose of retaining teeth in position it is not necessary that the wire be carried into the approximal spaces, but only be in contact \\ itli each tooth at one point ; as regards cleanliness the latter method is the more desirable. they are in situ. The thinner the wire of which they are made the less chance there is of dam- aging the band or its attachments ; in no case should it be greater than gauge 20 (B. & S.). 10, 12, 14, 16, and 41. Removable Appli- ances. — Plates such as those described for 2, C. and D. Medial and Distal Movements. {laques arti- ficially upon whole teeth suspended in cultures of the organism, and found also that active symbosis takes place with many acid-producing organisms; its role in dental caries is thus evident. In its cultural characters the organism some- what jesembles the micrococcus catarrhalis, but it grows with difficulty both on broth and milk, and does not grow on gelatin. It does not grow below the ordinary incubator temperature, 37° C. Sarcinae. — The group of sarcinae form the lowest scale of the cocci with regard to patho- genicity. With one or two exceptions, they are not found causmg suppuration. Tlie sar- cinae are fairly active fermenters of carbo- hydrates, and, as they occur with considerable regularity in the mouths of persons suffer- ing from dental caries, and are found in the cavities of carious teeth with great frequency, they may be certainly regarded as organisms associated with the destruction of the teeth. Furthermore, the majority of the sarcinae are organisms producing proteolytic enzymes, and although they do not liquefy blood serum, they are still capable of digesting decalcified dentine. Typical sarcinae are organisms occurring in packets of eight, this form being produced by their method of divi.sion in three planes at right angles to one another ; but in the ordinary smear preparations made from cultures the typical sarcinal form is not preserved, the small packets becoming broken up in making the films. To obtain a proper idea of the typical sarcinal form, recourse must be had to the method of the hanging -drop preparation, when beautiful packets of cocci arranged symmetri- cally in small cubes can be seen. Like the closely allied staphylococci, the sarcinae are pigment-producers. Three well- known varieties of pigment-producing sarcinae are recognized — (a) Sarcina Aurantiaca, producing an orange pigment. (6) ^'arc!M« Z,w7ca, producing a yellowish pig- ment. (c) Sarcina Rosa, producing a rose-pink pig- ment. In addition, Sarcina Alba, with a colourless, or whitish porcelainous growth, is also common. Like the nearly allied staphylococci, the sarcinae vary very considerably in the size of the individual cocci. Ordinarily, the .sarcina lutea is the largest, the aurantiaca holds an inter- mediate position, and the alha is usually the smallest. The sarcina aurantiaca is not so common in the mouth as the sarcina lutea, while the most commonly occurring form of the three is the sarcina alba. This is a small sarcina, and the growth closely resembles the granular appearance of the saccharomyces. All the sarcinae grow readily on gelatin, with the exception of the peculiar sarcina alba found in the mouth. The sarcina lutea and sarcina aurantiaca produce their pigment only at the room temperature, and not at the temperature of the body. The most typical colour is pro- duced on the surface of boiled potato. Gelatin is, as already stated, rapidly liquefied, and the growth on broth is heavy, the whole of the fluid being rendered turbid, and a thick deposit produced ; at 20° C. tliis deposit is often pig- mented. The inocidation of considerable quantities of these sarcinae into animals, such as rabbits and guinea-pigs, produces no fatal result. Sarcinae may be found in acne pustules. The colonies of the sarcinae are, as a rule, large, and often marked with a central projection, the surface being smo and glistening. Little or no chflficulty is expa -need in isolating these organisms owing to t j large size of their colonies and their rapid growth, and their typical morphology. Streptococcal Group. — The group of strepto- cocci comprises a large number of diverse bacteria, many of them highly pathogenic both for man and the lower animals, as well as a number that are simple saprophytes, and are to be found widely distributed in Nature. The first description of the streptococci was made by Billroth in 1874, when he described the organism as a "cocci bacteria septica ". From this time onwards much attention was paid to the bacteriology of wounds and septic processes, and Fehleisen (17) and Rosenbach (36), by the use of pure cultures, demonstrated the pathogenicity of the.se chain-forming organisms. The streptococcus, as its name implies, is an organism growing in a chain, 'i'ho mor})hology, however, shows considera))le variation : isolated cocci may be found, or short chains of only three or more elements; at other times, inter- spersed throughout the chahi, are to be found elongated forms closely resembling bacilli, the chain having the appearance of a sentence in Morse code. On the other hand, scattered 264 throughout the chain may be swollen and irregular forms, oval or elliptical, sometimes described as arthrospores, a moditied and more resistant form of the organism ; this view is doubted by other observers, who regard these swollen elements in the chain as being merely involution forms. On the surface of agar and on other solid media, the organism may closely resemlile the staphylococcus, the cocci being arranged in masses with very Uttle sign of chain formation. But the typical form is in chains, best seen upon liquid media, the organisms growing out to their maximum length in fluids. In many races of streptococci the individual chains show special characteristics. Occasion- ally, chains of diplococci are to be seen ; some- times tangled masses, with a number of swollen forms as well, and to this particular type the term Streptococcus Conglomeratus has been given. Some varieties of streptococci have been recognized as associated with special diseases, and as having cultural characters sufficiently well marked to separate oE the given strepto- coccus into a sub-species. The most typical form of streptococcus differentiated in this manner is the streptococcus — or, as it is most often termed, the diplococcus — pneumoniae. The Diplococcus Pneumoniae was first de- scribed by Frankel (19). Previously, the diplo- bacillus of Friedlander, which had been described as occurring constantly in pneumonic aiTections, was regarded as the cause of pneumonia ; but Frankel showed by animal experiments that although the Friedlander bacillus, or bacillus pneumoniae, may be often found in pneumococcal affections, the diplococcus pneumoniae was really the exciting cause of the disease. The organism occurs typically in pneumonia as diplococci, pear-shaped in form, with the broader bases turned towards one another, and the whole diplococcus surrounded by a gelatinous capsule, which only stains by sjDecial methods. The capsule is not formed on ordinary laboratory media, but may occasionally be found in gelatin cultures grown in the hot incubator, and also on serum cultures — water of Hiss, — particularly milk to which serum has been added. On fluid media this diplococcus grows out into streptococci, and even in pneumococcal affec- tions streptococci may be found comprised of five or six elements, the whole of the chain being surroimded by a capsule similar to that described in the diplococcal form. The organism stains rapidly by Gram's method, and by the ordinary aniline dyes ; it does not, however, grow with ease upon the ordinary laboratory media, but requires some- what special treatment. It is exceedingly sensitive to the degree of alkalinity of the medium in which it is growing, and further requires (especially the higlily pathogenic forms) some admixture of serum, ascitic fluid, or hydrocele fluid to the medium in which it is grown. A typical growth of the organism may be obtained on agar smeared with fresh blood, as originally described by Washbourn (42), (43). The organism grows but jioorly on gelatin. It is to be found with singular frequency in the saliva of normal individuals ; and Washbourn and Eyre (16) have shown that about five per cent of normal inchviduals harbour typical pathogenic pneumococci in their saliva. Many other observers have found virulent pneumo- cocci in the mouths of normal persons unaffected with chsease ; others, again, go so far as to say that it is present in all mouths. The pneumococcus may be raised to an extraordinary pitch of virulence by passage through the bodies of susceptible animals, the method of procedure being as follows — An animal is uifected with a pure culture of pneumococcus, and after a .short interval — one to two days — it is killed, and the body incubated for twenty -four hours ; blood is then taken from the heart under aseptic precautions, and inoculated directly into another animal. By this means the \'irulence of the organism may be raised considerably ; in fact, Wash- bourn and Eyre were able to raise the virulence of numerous strains of pneumococci to such a pitch that jTnjxTTrTrcr o^ ^ milligramme, corresponding to about fifty to eighty cocci, was sufficient to cause the death of susceptible animals (rabbits) in forty-eight hours, with all the typical signs of pneumococcal infection. The pneumococcus is often to be found in- fecting the gum margins in certain forms of alveolar infection, often as a mixed infection in cases of so-called " jjyorrhoea alveolaris". The form found in the mouth is, however, rarely so pathogenic as that found in the pneumonic lung ; Washbourn and Eyre, in the paper referred to above, found that the organism required the passage through a larger number of animals to raise it to a given standard of \-irulence, than did the organism obtained from the lung of a person who had died of pneumonia ; in the latter case only seven passages were re- quired, whilst in the former some twenty-eight were necessary. The pneumococcus ferments a number of carbo-hydrates used in testing bacteria, but differs from the streptococcus, to which it is so closely related, in the fact that it rarely clots milk, and does not ferment manitol, cane sugar, salicin, and inulin. Pneumococcal sore throat, and pneumococcal gastritis are not uncommon ; whUst meningitis 265 and pyaemia, besides classical pneumonia, may all be caused by the pneumococcus. It may be that residence in inflammatory lesions of the mouth tends to increase the virulence of the pneumococcus, for when testing the blood of persons in whose mouths the pneumococcus has been found associated \\ ith an inflammatory lesion, distinct variations from the normal in the pneumo-opsonic index have been found ; the blood of such persons occasionally jiroduces agglutination of the pneumococcus. Tlie pneumococcus, hke other streptococci, may produce a haemolytic ferment, but this is not so common as with the other varieties of streptococci. Streptococci. — The first division of the strepto- cocci into varieties was made by von Lingelsheim (29), who separated the streptococci into t\xo main varieties, using as criteria the length of the chains. His two divisions were therefore Streptococcus Loiujus and Streptococcus Brevis. The typical form of the streptococcus longus was the Streptococcus Pyogenes, occurring in infective processes in the human subject, whilst the streptococcus brevis was the organism typically found inhabiting the mouth. A great deal of work has been devoted to the different classes of streptococci, and following the method of Gordon, and later Andrews and Horder (2), an attempt has been made to separate the cocci of this class into groups according to the fermentation of various carbo- hydrate media, the carbo-hydrate media used by Gordon consisting of glucose, lactose, galactose, inulin, salicin, coniferin, and manitol ; the organisms were also growii on neutral red broth anaerobicalh', litmus niUk, and gelatin. By using the carbo-hydi'ates, Andrews and Horder obtained about twenty-six species of streptococci, and suggested an arrangement of the streptococci into certain groups according to the type of fermentation produced by them. The groups were found to merge into one another very greatly, but the fermentations allowed grouping, which, although not con.sistent, was exhibited by a large number of the species tested ; and it was thought that just as species in the animal kingdom show considerable variation from the typical form, so the strepto- cocci might be considered to show de\-iations from the main grouping. By the adoption of this method the following streptococcal groups are suggested : — 1. Streptococcus Pyogenes. 2. Streptococcus Faecalis. 3. Streptococcus Angiosus. 4. Streptococcus Salivarius. 5. Streptococcus Mitior. On examining a large scries of cultures, it was found that the division into long and short 9 * chains did not coirespond witli the pathogenicity and non-pathogenieity of the species; for whilst several non-pathogenic forms of .streptococci were found to show very long chains, liighly virulent streptococci that grew only in very short chains were also discovered. It is, how- ever, very difficult to form any proper con- ception of the grouping of streptococci witliin the limits of this chapter, and for the general purpo.se of description, therefore, the strepto- cocci of the mouth may be considered as — (1) Non-pathogenic streptococci occurring commonly in the mouth ; (2) Pathogenic streptococci rarely presented in the mouth. Non-Pathogenic. — In practically all mouths the organisui called by Lingelsheim Streptococcus Brevis, and iiy Gordon and Holder Strepto- coccus Salivarius, may be found. In the mouth the typical form of this organism is diplococcal, and if a smear is taken from the inside of the mouth and stained, a number of epithelial cells will be found surrounded by diplococci. If a small amount of saliva is placed in a drop of melted agar and smeared over a coverslip, and the coverslip is placed on a hanging-drop slide, an epithelial cell may be found surrounded by these cocci. If this is marked, and the prepara- tion placed in the incubator, in the course of twenty-four hours the diplococci grow out into streptococci. This particular form of strepto- coccus was also originally described by Miller as the Streptococcus Xcvijer, on account of the chains formed. The organism stains by Gram's method, and by the usual anihne dyes. In- jected into animals it is non-pathogenic, and produces no localized lesion, and no general infection of the blood stream, even when very large quantities are used. It is one of the commonest of all streptococci, and is difficult to eliminate from colonies of other bacteria on plating out impure cultures made from the mouth. The organism closely resembles the .streptococci found in the mucous membranes in other parts of the body. In crowded assem- blies, it has been found in the air by Gordon and others. The organism ferments a number of carbo-hydrates with ease. It is frequently found not only in the superficial layers, but in the deep layers, of carious dentine, where, owing to its power of fermenting carbo-hydrates, it may be regarded as one of the chief organisms concerned in the actual dissolution of the lime salts of the teeth by its active acid fermentation. Pathogenic Streptococci of the Mouth. — from time to time streptococci having a defuiite degree of pathogenicity are to be isolated from the oral secretions. In pathological processes of the mouth, tongue and throat, the strepto- 266 coccus is often an active agent ; in various forms of recurrent sore throat, the streptococcus may be the only infecting organism, and in a number of cases of so-caUed " pyorrhoea alveolaris " an almost pure culture of the streptococcus pyogenes may be obtained, differing in many respects from the ordinary accepted type of the strepto- coccus brevis or salivarius. Culturally, the more pathogenic streptococci differ from the sapropliHic streptococci in their less active powers of carbo-hydrates fermenta- tion ; and although this is not an absolute test, yet it is found as a matter of fact that the less actively fermenting streptococci are always found amongst the pathogenic varieties. On the other hand, the streptococcus faecalis, often found as an infecting agent, and occurring typically in the alimentary canal, particularly in its lower third, may be sometimes found in the mouth, its chief differential point from the other streptococci being its power of fermenting manitol. The normal mouth streptococcus rarely forms chains in the mouth itself, and if a defuiite streptococcus is found on examining smears from the pus of a pathological process in the mouth, such a streptococcus is almost invariably of a pathogenic nature, and is causing some, if not all, of the inflammation present. A number of the pathogenic streptococci, and a few also of the non-pathogenic, produce haemolytic ferments, and as William Hunter has shown in pernicious anaemia, streptococcal infection of the mucosa, and even the deeper layers of the tongue, is not uncommon ; the haemolytic function of the streptococci is there- fore of extreme importance in all secondary anaemias associated with oral infection. The Streptococcus Erysipelatus, a most highly pathogenic streptococcus, is the chief cause of generalized septicaemia, and of pyaemia, bone infections, cerebral infections, and many forms of so-called septic processes affecting various parts of the body ; and, as streptococci often defuiitely virulent may be obtained from the mouth, it must always be borne in mind as a source of infection in such diverse diseases as streptococcal peritonitis, chronic infective endocarditis, acute meningitis, etc. A species of streptococcus closely allied to the ordinary streptococci, but coming generic- ally between them and the pneumococcus, is an organism described by Burger (10). The organism has many of the characteristics of , the pneumococcus, and others of the strepto- coccus, but it differs from the latter in de- veloping a capsule in an ordinary culture medium, and is found to vary in many other particulars from the typical streptococcus; for further particulars the student is referred to the original jjapers. Tlie thermal death-point of the streptococci' is not high, 58° C. for half to three-quarters of an hour being sufficient to destroy the organism, and this temperature may be used in the preparation of vaccines. The great increase in attention to the strepto- cocci coincident \nth the adoption of vaccine therapy in the treatment of many chronic diseases has Ijrought to light many facts re- lating to the strejDtococci that were hitherto unknowii, but the production of vaccines and the control of the dosage are perhaps more difficult with this class of organism than any other, mainly because of the great difficulty of standardizing the vaccines. The streptococci produce definite toxins, and owing to this fact it is possible to use cultures of the streptococci for the production of anti-streptococcal serum. In reported cases of therapeutic use of anti- streptococcal serum, great divergence is found in the curative effects produced by the injection of such serum. This is not surprising, in view of the great variation in the cultural characters of the various streptococci, as brought out by the work of Andrews and Horder ; and it is probaljle that in the cases in which a strepto- coccal serum acts with curative effect, the organisms used to produce the serum happen to coincide with the particular type of strepto- coccus causing the infection ; it is for this reason that in producing anti-streptococcal serum, as many varieties of streptococci as possible are made use of in immunizuig the animals (horses) [polyvalent vaccine]. For further details about the streptococci the student is referred to the various papers in the Cenlralhlalt fiir Bakteriologie, and also to the work of von Lingelsheim, in KoUe and Wassermann's Hawlhuch. GROUP II~BACILLI Among the organisms found in the mouth as adventitious forms, by far the largest number belong to the group of bacilli. Certain organ- isms commonly found in the throat, and in other parts of the body, are from time to time found inhabiting tlie mouth, and require to be briefly mentioned ; but as they are all of them fully described in the text-books on general Ijacteriologj^, only a general reference to them is necessary. At the same time, lesions of the mouth are often attributable to one or other of these particular bacteria. So far as is known, the organisms occurring in the mouth do not produce spores m the mouth, and although some of them are capable of sporulation outside the mouth, the presence of spores in the salivary secretions is very uncommon. Morphologically, bacilli are rod- shaped or cylindrical organisms, in \\hich the 267 length is at least twice the diameter. As with the cocci, they may be arranged in different groups according to their method of develop- ment — Bacilli — single organisms witli the above characters. Diplobacilli — two organisms attached to one another end to end. Streptobacilli — bacilli in chains of three or more elements. Many of the mouth organisms also belong to the class of anaerobic bacilli, but these will be described separately ; most of the pathogenic forms met with in the mouth are facultative anaerobes. Various races and genera of bacilli isolated from the oral cavity, although exhibiting the main cultural characteristics of the group, do not all conform to type ; moreover, a number of species related to certain groups are to be found. The latter statement is particularly true of the diphtheria bacillus, and the colon bacillus ; and for this reason it is common to speak of diphtheroid bacilli, meaning organisms resembling in both morpho- logical and cultural characters the true diph- theria bacillus, but differing from that organism both in the power of producing toxins and pathogenic effects in animals, and also in ceitain peculiarities in the general cultural characteristics. A considerable amount uf discussion has raged around the group of organisms that may be regarded as the diphtheria group, and much research has been directed towards this par- ticular family. The chief organism of the group is the diphtheria bacillus. Bacillus Diphtheriae {Klehs-Loefjler Bacillus). This is a bacillus of 5 to 6 /«, in length, and about '75 /x in width, staining by Gram's method and l)y the ordinary aniline dyes. It grows best on the surface of Loeffier's blood serum, a medium consisting of nutrient broth and normal serum mixed together, and inspissated at a temperature of 70° C, and afterwards sterilized by the intermittent method in streaming steam. On the surface of this medium the organism rapidly develops, and in making cultures from throats of persons suspected of clinical diph- theria, this medium is commonly used. At the end of twenty-four hours typical colonies of the di])htheria bacillus develop, for on this medium they grow more quickly than the other organisms, streptococci and staphylococci, which are invariably present. With Loeffler's methy- lene blue, or with ordinary carbolic methj'lene blue, the diphtheria bacillus stains in a typical manner, showing a series of darker-stained areas throughout its length; three or more of these areas are present in the typical organism. Another constant form is the so-called " sheath " form or diplobacillary form, the organisms being tapered and triangular, and the two bacilU approximated to one another by their bases; the whole organism is surrounded by a fine unstained area when methylene blue is used. In addition, the bacilli may be found arranged in so-called palisade form, in which several lie with their long axes parallel to one another in groups. The ends of the bacilli in many instances show slight enlargement, producing club-shaped forms ; the cluljs as a rule stain deeply. The deeper staining granules in the I diphtheria bacillus may be also stained typically j by means of Neisser's stain (acid methylene blue, I followed by a watery solution of Bismarck brown). By tliis method the granules .stain deep blue, and the rest of the organism a faint yellow. In coverslip preparations made from true diphtheritic membrane, this specific stain- ing is invariably seen, and is of great use for the rapid preliminary diagnosis in the determmation 1 of clinical chphtheria. The members of the diphtheroid groujj, a large number of which closely resemble the diphtheria ))acillus, do not stain in this typical manner. If pure cultures of the organism itself, or filtered broth cultures, are inoculated into an animal (guinea-pig), death results in the course of twenty-four to seventy-two hours, with typical haemorrhagic inflammation of the supra- renal capsules, and signs of general toxaemia. If a sub-minimal fatal dose of toxin is ad- ministered to a susceptible animal, the animal recovers ; and if the process is repeated on several occasions, the dose being gradually increased, the animal finally becomes immune to large quantities of fully virulent and living cultures. Wien the animal has been immun- ized in this maimer, its blood serum, obtained under a.septic precautions, is capable of pro- tecting a susceptible animal from many times a fatal do.se of cliphtheria toxin, and advantage is taken of this circumstance in the treatment of diphtheria in the human being. Horses are immunized by means of the diphtheria toxin and bacillus, their blood is then obtained aseptically, the serum separated off under aseptic precautions, and standardized by test- ing its protective power on susceptible animals (guinea-pigs). The standardized serum is known as diphtheria antitoxin, and is used both during the disease itself and as a prophylactic to i prevent its development in fiersons exposed to infection by the diphtheria bacillus. The Diphtheroid Group. — A certain number of organisms belonging to this group are found in various parts of the tod}', ajid in certain infective concUtions, but differ from the true diplitheria bacillus by non-production of toxin. 268 Tlie growth of many of them on caibo-liydrate media is more energetic than the diphtheria baciUus, which only ferments ghicose. Hoffmanns Bacillus, or Pseudo- Diphtheria BaciUus. — This organism, closely resembling the diphtheria bacillus, is often found in the mouth. It is not pathogenic for man or the ordinary laboratory animals, and differs from the true diphtheria bacillus in producing the fermentation of several carbo-hydrates. The Hoffmaim bacillus does not give the usual stain- ing reaction with NeisserV stain, and is nmch shorter and tends rather to polar staining ; but it exliibits the same banded staining \\ith methy- lene blue as the diphtheria bacillus — in fact, *<*^%%l 'vr>i''">,-o; ' Fig. 382. — Bacillus Hoffmann, U hrs. serum agar, Gram, x 1000. on agar the tw o organisms closely resemble one another. HolTmami's bacillus is constantly found in conditions of sore throat resembling the diph- theritic throat, but without membrane ; it may often be found existing in the throats of individuals a long time after an attack of diph- theria, and for this reason some observers are of opinion that it is merely a non-virulent degenerated form of the true diphtheiia bacillus ; most observers, however, consider the organism to be a distinct species. Xerosis Bacillus. — This organism was de- scribed by Uhthoff (39) as commonly found in trachoma and forms of conjunctivitis. It closely resembles the diphtheria bacillus, but is non-virulent ; it shows clubbing, and partial staining in a high degree ; it does not react to Neisser's stain. It may be found in the mouth from time to time in cases of chronic eye disease, gaining entrance, no doubt, by passing down the nasal duct into the nose, and thence into the mouth. A large number of other varieties of diph- theroid bacilli exist. They are often found in suppuration. Thus Dudgeon (14) describes a diphtheroid-like bacillus causing cellulitis. C4ra- ham-Smith (Jour. Hygiene, 1904) describes an organi.sm bacillus auris resembling bacillus diph- theriae as occurring frequently in chronic sup- puration of the ear ; a large number of these ear cases are found to be associated with a bacillus conforming to a particular tj^ie. Caiitley (11) describes a bacillus, bacillus coryza .segmentosa, or bacillus septus, occurring in common colds. The writer has frequently found it also in suppur- ation of thealveolar margin, often associated with the micrococcus catarrhalis. Inoculations with this organism frequently cause symptoms of acute coryza. The organism produces no fermen- tation with carbo-hydrate, according to Cautley ; j on the other hand Bentham states that an ' organism of a similar type ferments glucose only, and that other similar ones produce an acid fermentation in glucose, lactose, cane-sugar, and manitol. Bacilli of this type are by no means inicommon in the mouth, and may be found causing a species of pseudo-membrane on the anterior surfaces of the alveolus in some forms of chronic septic mouth. They stain by Gram's method, and grow readily on the ordinary media providing they have an alka- linity of -|- 3. For further particulars of the cultural characters of these oi'ganisms the reader is referred to papers in The Lancet, by Bentham, who gives references. De Simoni (12) describes a diphtheria-like bacillus in the nose, whilst Ritter (35) describes diphtheria-like bacilli occurring in the mouths of a number of children examined. Diphtheroid bacilli are also to be found in the intestinal and genitourinary canals. Bacillus Tuberculosis. — The bacillus tuber- culosis is one of the well-known pathogenic organisms ; it is found causing lesions in the buccal cavity, .such as tubercular ulcers of the palate, tongue, and fauces and very occasionally tubercular osteitis of the bone of the jaws. Primary tubercular disease of the jaw is very rare ; most of the cases of tubercular osteitis and ulceration of the soft parts of the mouth occur in persons suffering from tubercular lesions in other jjarts of the body. Tubercle bacilli may be found in the mouths of persons suffering from pulmonary tuberculosis, and they have been demonstrated in the mouths of nurses employed in a phthisis hospital but unaffected by the disease. The tubercle bacillus belongs to the group of organisms known as acid-fast, owing to the fact of its retaining a dye, carbol-fuchsin, after 269 treatment with a mineral acid, siicli as dilute sulphuric acid, 25 per cent. In its usual form the organism is a tine rod, slightly curved, and exhibiting irregularity of staining, which gives it a slightly beaded appearance. Like its some- what near relative, the diphtheria liacillus, it exhibits branched forms, and owing to this tendency to branching exliibited by l)oth these organisms Lehmami and Xeumami have classed them under a new group of corny-hacteriiim. 'I'he organism docs not stain with the ordinary aniline dyes used, but may be stained by Gram's method, although l»ut feebly. It does not grow on the usual culture media, hut re- quires the addition of 10 % glycerine. The method of obtaining pure cultures is somewhat laborious. It is best performed by plating sputum having a high tubercular content, and after twenty-four hours removing portions of the agar that are free from colonies of the ordinary rapidly growing bacteria ; the small portions are placed in other tubes, and the organism slowly develops. Its growth much resembles that of streptothrix, being hard, wrinkled, and lichen-like in appearance. It grows easily on the surface of glycerine broth, and this medium is made use of for the prepara- tion of tuberculin. For the treatment of chronic tubercular lesions tuberculin is often made use of, or else a bacillary emulsion, the solution being in the one case the filtered toxin of the organisms (T. R.), and in the other a triturated culture containing the bodies of the organisms themselves (B. E.). The tubercle bacillus is pathogenic for the lower animals, as well as for man, and for the purposes of diagnosis, when the organism cannot be found microscopically by the Ziehl Neelson method of staining, an animal (guinea-pig) is inoculated. In a large number of cases in which no l)acilli can be demonstrated by staining methods, the injected animal exhibits well- marked tubercular lymphangitis ; and it is supposed by some observers that in such cases a |)ecuharly small form of the bacillus exists, which does not stain by the usual methods adopted. Tlie peculiar acid-fast staining of the tubercle bacillus is due to a wax-like body that it contains. BaciUwi Lepra. — The bacillus of leprosy closely resembles the tubercle bacillus in its staining characters, in that it is acid-fast, but it more ra])idly undergoes decolorization with dilute mineral acids than the tubercle bacillus. It is found in vast numbers in the lesions of leprosy, and generally arranged in characteristic masses. Leprous lesions are not common in the mouth, but in cases of advanced leprosy, where the tonsils are aifected, and also in ca.ses of nasal leprosy, it is common to find the bacillus in the mouth. According to Bayon (7) (8) the leprosy bacillus may be gro\\'n in pure culture. The organism undergoes a curious variation, which no doubt accounts for the failure of many persons to obtain cultures of the organism. Some of the cultures that Bayon obtained exhibited varia- tion in the acid-fast staining ; this was absent in the early cultures but gradually developed as the organism became accustomed to the artificial media. Inoculation of the pure cultures into animals produces characteristic lesions with the char- acteristic grouping of the leprosy bacilli. Bacillus Pyocijaneus. — This is a fine rod- shaped organism with square or round ends, 3 to 4 yx in length, or less, about 0'3 /j, wide, and possessed of peritricheal flagella. It does not form spores, is decolorized by Grams method, and stains by the ordinary aniline dyes. Two pigments are produced, as well as a toxin. Several non-pathogenic organisms are closely allied to the bacillus pyocyaneus ; these produce one or other, but never both, of the pigments produced by the bacillus pyocyaneus. The pig- ments are the green tluorescin, and the orange or brown pigment, pyocyanin; the latter \Ag- ment is not formed unless a considerable amount of proteid is present. The organism occurs sometimes in suppura- tive lesions, such as dento-alveolar abscesses, but is not very common. Wien it is present in the mouth, it may also be found in the faeces ; it may be an infecting organism in ear disease, and may then gain entrance to the throat. Filtered cultures of the organism injected into animals j^roduce symptoms similar to those caused by inoculation of the living bacillus. A considerable amount of early bacteriological work on toxins and immunity was performed with the bacillus pyocyaneus. Its recognition gives little difficulty ; the bright green fluorescent pigment, its non-Gram staining, its motility, etc., are all points that render it easy of determination. Bacillus Coli Communis. — The bacillus coli communis is an organism constantly found in the faeces and in the large intestine, hut only occasionally in the mouth; and although a curious foetid smell may be met with in fluid media cultures made from the mouth, the odour is only very rarely due to tiie bacillus coli commune. A number of organisms are closely related to the colon group, dilYering from the colon bacillus it.self in their special fermentation of carbo- hydrates, and the carbo-hydrate tests are used with, perhaps, greater atlvantage in the differen- tiation of tiie colon group than any other series of organisms. The organism itself is an exceedingly short bacillus, often arranged as diplobacilli, about 270 rS /x in length, and "5 /i in width. It does not stain by Gram's mctliod, ahhough by careful decolorization a certain number of the individual bacilli are found partly to retain the stain. The organism is highly motile, possessing peritricheal flagella. It produces gas and acid when grown on glucose, lactose, malto.se, inulin, manitol, etc., but according to MacConkey (30) rarely produces fermenta- tion of cane-sugar. The organism is frequently found in mUk and water, and its presence shows faecal contamination. It is pathogenic for animals, when injected in large doses, and may be raised to a considerable pitch of virulence by tlie method of passage. For a full description of this organism see the text-books on Bacteriology. Bacillus Friedlii ruler. — The bacillus Fried- lander is closely allied to the colon group in its carbo-hydrate fermentation, but differs from the bacillus coli in many respects, and is, as a rule, a much longer organism. It was first described by FriedJiinder as the cause of pneu- monia. It is present in many cases of lung infection, often associated with the pneumo- coccus, and wlien found in the sputum is. as a rule, surrounded by a gelatinous capsule staining by the ordinary methods of capsule demonstra- tion. When grown in gelatine stabs, large buljbles of gas form along the length of the stab ; it does not hquefy the gelatine. It is Gram-negative, and jiroduces localized tissue necrosis wlien inoculated into animals. It is by no means an uncommon organism in the mouth, and may be often found as the cause of localized suppuration, ulceration, or post-nasal catarrli. The bacillus rhinosclcroma and tlie bacillus ozoenae are generally considered to be variants of the Friedlander bacillus, and are found associ- ated with the pathological conditions from which they derive their names. They all rapidly ferment a number of carbo-hydrates, w ith the production of acid and gas. The chief difference between these organisms lies in the question of carbo-hydrate fermentation, and for particulars in this direction the student is referred to the literature on the subject. The other closely allied organisms occasion- ally found in the mouth are bacillus cloacae of Jordan and bacillus ox^i^ocus perniciosus ; their differentiation depends upon their carljo-hydrate reactions. Bacillus Influenza. — The bacillus influenza may be regarded as one of the mouth bacteria. It is found in the sputum and saliva of persons suffering from typical influenza, as well as in the mouths of perfectly healthy persons. The organism is exceedingly small, being only about 1 /x in length, and about '25 fi or less in breadth; it occurs as diplobacilli, and is typically found lying amongst and in the cells of the sputum. The organism is exceedingly delicate in its growth, and will only grow on blood-agar or normal blood-serum-agar (one part of normal unlieated serum to two parts of agar, mixed at 40° C). On the surface of thia medium the organism forms round colourless transparent globules, often compared to drops of dew, which rarely become confluent into a definite streak. The organism is Gram-negative, and stains best with carbol-fuchsin. The usual method of demonstrating its presence in sus- pected material is by means of prolonged stain- ing with very dilute carljol-fuehsin, the speci- mens being left from one to four hours in the hot incubator. The organism is not very pathogenic for animals, but has been definitely determined as the exciting cause of tnie influenza. The organism is occasionally found in the blood of persons suffering from clinical influenza. The organism is rapidly killed by a short exposure to 60° C, and ceases to grow below 22° C. The influenza bacillus undoubtedly produces a toxin of extreme virulence, and a large number of cases of post-influenzal nervous affection are known — in tact, nerve diseases are particularly prone to occur as sequelae of genuine influenza. Bacillus Necrodentalis.- — This organism is con- stantly found in the mouth, and is particularly associated with dental caries. The organism is a small oval bacillus, 2 to 2' 5 /t long and 0'75 /JL wide, occasionally occurring in pairs, with almost a coccal appearance — more par- ticularly in aerobic cultures. The organism is facultative anaerobic, and often oiJy develops in preliminary cultures under anaerobic or semi- anaerobic conditions. It is to be found along the gum margins, and typically in the deeper layers of carious dentine, and associated \\ith the streptococcus salivarius of the mouth. On agar the growth closely resembles that of the streptococcus, but no turbidity occurs in broth, and very little deposit, what is formed being of a stringy consistency and remaining attached to the bottom of the tube on shaking. An- aerobically the organism tends to grow out into longer bacillary forms than under aerobic environment, and well marked irregular bacilli may be observed in .such cultures. The organism is not motile, produces no spores, and stains by Gram's method and ordinary aniline dyes. It is slightly pathogenic for animals, pro- ducing locahzed tissue necrosis, and occa.sionally generalized infection when inoculated into rabbits. In guinea-pigs, an occasional local abscess is formed, but only when a considerable quantity of the organism is injected. The organism rapidly ferments glucose, lac- tose, and suchrose, but not inulin and manitol ; acid only, and no gas, is formed. 271 It is often found in the nose ; and Lewis (28), in the examination of a number of cases of disease of the maxillary sinus due to various tyjies of in- fection, found this organism in many of the cases. Tlie organism does not liquefy gehitine, but produces coagulation of litmus-milk. Colonies on the surface of agar closely resemble those of the streptococcus, but have an eroded and irre- gular outline, and occasionally a small central point ; the characters of the colonies are extremely inconstant. From the frequency with wliich it is found in tlie deep layers of carious dentine, and the fact of its being an anaerobic, or faculta- tive anaerobic organism, and the ease with which it ferments many earbo-hvdrates, it is highly >^Jkr I * , it,^ %fl^ ■J^ ^"6v, ^ *' ^V'vo, *^ ,•;># A » -''v •-•vv Fig. 383. — Streptobacillus malae, 48 hrs. egg agar. Gram, x 1000. probable that this organism is one of those concerned in the production of dental caries. Slreplohacillus Malae. — This streptobacillus closely resembles in its morphological characters the streptobacillus ulcus moUe of Ducrey, but differs from it in the fact that it will grow on ordinary agar ha\'ing an alkalinity of -f 3, Ducrey s organism requiring blood-agar. Cultivations on the ordinary media, -r 10, do ' not give typical cultures, as the bacillus is extremely sen.sitive to small degrees of alkalinity. Tlie appearance of the colonies on the surface of agar is somewhat characteristic ; they are irregularly eroded, with a finely granular appear- ance, but frequently exhibit microscopically an irregular central area, darker in colour and with an irregular crystalline appearance. After several days on the surface of agar they may be as wide as three to four millimetres, having an ill-defined irregular outline, composed of a darker bluish ring, with a central greyish granular area. The colonies are somewhat tenacious and granular, and when removed from the .surface, show a tendency to run into small flakes. It typically ferments glucose, lactose, cane-sugar, glucose, and lae\iilo8e, with the production of acid, but does not ferment manitol, inulin, salicin, and caffein. Litmus-milk is rendered acid, but coagulation does not always occur. Tlie morphology of the organism is irregular; its tj7)ical form consists of short bacilli joined together in long chains, often of twenty or thirty elements ; and interspersed in the ele- ments are long shuttle-shaped forms taking the stain deeply. Polar-staining types are also fre- quently met with, as \\ell as large swollen and irregular masses, Mhich may be seen at the ends of threads. The organism stains by Gram's method, and by the usual aniline dyes. It is commonly found in the infective processes of the jaw, particularly those in ^\■hich a large amount of destruction of bone lias taken place around affected teeth (rarefying osteitis). The wTiter has also isolated the organism on several occasions from the urine of infected cases ; it resembled in some respects the streptobacUlus isolated by Pfeiffer from the urine. Pure cultivations of the streptobacillus, when inoculated into the knee-joints of rabbits, or into the periarticular tissues, produce secondary changes in the joint and articular structures; no suppuration results, but a low type of inflam- mation with hypertrophy of the synovial membranes, great thickening of the joint cap- sule, and rarefaction of the articular ends of the bones. Wlien the injections are made intra- venously, as well as into the articular tissues, the changes are more rapid, and secondary joint affections have resulted in many of the animals inoculated by the ^^■riter, including definite periosteal nodes on the ribs, and the organisms have been recovered in pure culture from the heart, blood, and periarticular structures as long as six months after inoculation. In several animals the joint swelling and thickening has disappeared after two or three months, but in others progressive changes have taken place exactly similar to those produced in infective arthritis, and arthritis deformans of slow onset. Furthermore, the use of vaccines prepared from the streptobacillus. in cases of arthritis deformans of oral origin, have beenattended with a consider- able degree of success in the writer's liands ; the preliminary inoculations have been often associ- ated with exacerbation of the local joint affec- tion. There is, therefore, a good deal of evidence that this streptobacillus is one of the organisms causing arthritis deformans of oral origin. Non-Pathogenic Bacilli ok the Modth The writer has already stated that many varieties of bacilli may be found in tlie mouth 272 as adventitious species, and it is quite impossible to tabulate all the organisms that have been described by various observers as occurring in the mouth. A certain number of organisms of the non-pathogenic group are to be found re- siding ill the mouth and oral secretions for long periods, and may be found in the same mouth time after time if sought for. Such may appear in films made from pus or buccal secretions, or in cultures made from diseased tissues in the mouth. A few of the more commonly occurring forms will be re\aewed. For this purpose the organisms may be considered as belonging to several main groups — ■ 1. Mesentericus Group. 2. Proteus Group. 3. Acidi Lactici Group. 4. Chromogenic Bacilli. 1. The Bacillus Mesentericus Group. — Tliis group has three well marked varieties — Bacillus Mesentericus Vulgatus, Bacillus Mesentericus Ruber, Bacillus Mesentericus Fuscus, and to this group in all probability belongs the organism described by Arkovy (3) as the bacillus gangrenae pulpae, an account of which is given in Lehmami and Neumaiui's handbook. The bacillus mesentericus group, also called potato bacilli, are very \\idely distributed in nature. The organisms are rod-shaped bacilli, 3 to 5 /i in length, and '5 /t or less in breadth, and retain the stain of Gram's method. They are liighly motile, and all of them form spores, which resist considerable concentration of dis- infectants, and are even resistant to boiling for as much as half an hour. They produce proteolj'tic enzymes, and digest a number of proteids with considerable rapidity. They do not clot milk, but gradually peptonize it. The particular characteristic of the group is the curious WTinkled appearance of the growth on various mecUa, especially on the surface of boiled potato. Two meml^ers of the group, the bacillus ruber and bacillus fuscus, both stain the substratum of the potato deeply, the first a reddish -brown colour, and the latter a blackish- brown. When present in association with other mouth bacteria they rapidly grow them down, and cover the whole surface of the medium. They are more common in carious dentine than in the oral secretions, and may be very frequently obtained from superficial cavities in molar teeth that have been under- going rapid caries. Even considerable quantities of the cultures, when inoculated into animals, produce no lesion. The position of the spores in the organism is variable, but as a nde they are centrally placed ; the spores may be stained by the usual spore- staining methods. The Subtilis Group is oiJy rarely found in the mouth, and probably only as an adventitious species. In its gro\^'th it resembles somewhat the bacillus mesentericus ruber on potato, and grows rapidly. The size of the organism makes it easy to chfferentiate from the bacillus mesen- tericus. By itself it cannot be regarded as a mouth organism, but a large bacillus, in some ways resembling the subtilis bacUlus in its size and sporulation, though entirely different from it in growth, is the bacillus rnaximus buccalis, which, so far as the «Titer is aware, is only found in the mouth. Bacillus rnaximus buccalis is a large bacillus, 1 n- in width and 5 to 6 /u. in length, forming definite chains. Spores are produced, wliich %\ithstand a temperature of 80° C. for over an hour ; sporulation does not take place in the mouth. Tlie organism ferments certain carbo-hydrates, coagulates milk, liquefies gelatine, and is not pathogenic for animals. It is by far the largest of all the organisms met \\ith in the mouth, and is the organism originally described morpho- logically by Miller as bacillus rnaximus buccalis. It is non-motile, and Gram-positive. Bacillus Plexijormis (Goadby). — These are curved and twisted baciUi, which may be associated with or grow out into pairs 30 yu. or more in length. On gelatine, at the tem- perature of the room, a small white punctiform colony apjDears, producing gradual liquefaction. On agar, the organism tends to grow out into very long irregular threads. These threads are frequently swollen in the centre, and form long terminal fine filaments, curved and twisted. Their growth on agar is thick, and tends to be sUghtly fluorescent, no definite pigment, how- ever, being produced. The organism is Gram- negative. 2. Proteus Group. — The term bacillus proteus comprises a very large number of bacteria of various types. Among them are several defi- nitely pathogenic forms, and the group may, therefore, be regarded as coming midway be- tween the pathogenic and non-pathogenic bacilli of the mouth ; the majority of the proteus group are not pathogenic. Tliree forms were originally described by Hauser (26) and the strains were termed — Proteus Mirabilis. Proteus Vulgaris. Proteus Zenkeri. The special feature of these organisms is the curious " wandering colonies ", which are formed on the surface of nutrient media in Petri dishes ; the colonies are termed amoeboid. 273 . Certain workers, as Jordan, included under the proteus group all organisms that ferment sucrose and dextrose, and rarely lactose, and that are also vigorously proteolytic, rapidly liquefying gelatine and blood serum, and precipitating and then dissolving casein. Practically all authors agree in laying special stress on the proteolytic and fermentative properties of the group. None of the organisms of this group are more than 1 jx in diameter, and they do not form spores; they are all motile. They are non- chromogenic, and most of them produce an unpleasant foetid odour. They are all facultative anaerobes, grow at the body temperature, and are al)le to withstand a very considerable variation in the alkalinity or acidity of the media in which they are grown. They jji'oduce a generalized turbidity and precipitate in nutrient broth. Jlemljers of tliis group may be commonly isolated from carious dentine, more especially the superficial layers, and are to be regarded as active agents in the destruction of decalcified tooth tissue. 3. The Bacillus AcidiLactici Group. This group is closely related to the bacillus coli group, and to the bacillus lactose aerogenes, the bacillus pneumoiuae of Friedlander, and the bacillus cloacae of Jordan. MacConkey, \\ho has made a very complete study of these groups of organ- isms, is of opinion that both the acidi lactici and a somewhat similar organism, the liacillus lactis aerogenes of Hiippe, may be differentiated from the bacillus coli communis, and are not, as is sometimes suggested, non-motile forms of that organism. Both the bacillus lactis aerogenes and the bacillus cloacae give the Voges and Proskauer " kalilaugerothreaktion ". \The V oges-P roskauer Reaction. — The method of performing this test is to add caustic potash to the broth tube, and allow it to stand for twenty-four hours or longer ; a fluorescent colour somewhat similar to a dilute alcoholic solution of eosin is produced.] The growth of bacillus acidi lactici differs from that of bacillus coli in its viscid character on agar; the organism is non-motile, but Gram- negative, producing a much denser growth on gelatine than bacillus coli. Tliese organisms are often present in milk, and are non-sporulat- ing, they often gain access to the mouth, \\here they persist, and may be obtained in pure culture. For further information on this interesting group see MacConkey's paper in The Journal of Hygiene, 1905, giving the cultural reactions in fermentations, etc., of a mimberof allied species. 4. Chromogenic Bacilli (Iroup. The other chromogenic bacilli of the mouth, in addition to the bacillus pyocyaneus already cited, are not very numerous ; amongst them the commonest is the organism df scribed by Dobrzynicki (13), a bacillus (bacillus lutcns) 1-5 /x long^ irregular in size, non-motile, and staining l)y Grams method. The organism pioduces a \\ell-niarked sulphur- yellow colouiation when grown at room temperature. This organism is occasionally found causing the yellow stain in some varieties of salivary calculus ; it does not liquefy gelatine, and is not pathogenic when inoculated into animals. Bacillus Roseus, or Micrococcus Roseus, is a very short plump l)acillus, or oval coccus, and is a widel}' distrii)uted organism found in air and water as well as in the mouth. It stains by the ordinary aniline dyes and by Gram's method, and produces a very slow liquefaction of gelatine. The colonies are rather ty])ical, being raised, cone-.shaped, and of a beautiful rose-red colour, particularly when grown on potato. The rose-red colour is only produced aerobically, and at a temperature of 20° C. Tlie organism is not pathogenic. It differs from the bacillus prodigiosus, «hich the wTiter has never met with in the human mouth. In addition to these two chromogenic bacilli, several of the organisms already described l^roduce pigments, namely : — Staphylococcus A ureus, Staphylococcus Citreus, Sarcina A urantiaca, Sarcina Liitea, Sarcina Rosa ; and to these may be added the common pink torula of the air, and a pink saccharomyces producing mycelium, as well as several forms of streptothrix. GROUP III— SPIRILLA Among some of the most interesting bacteria to be found in the human mouth are the group of spirilla. Tliese organisms differ from other bacteria in their curious morphological form, consisting of spiral threads ; the turns of the spiral frequently exhibit great regularity and beauty, while in others the spiral form is less well marked, the turns of the thread being unequal and irregular ; in others, again, comma forms are found, these organisms resembling an inverted comma, and no doubt arise from the breaking up of a spiral thread into its component parts. The spirilla are closely allied to the Spiro- chaetes, and it has been thought that the true spirochaete is not a bacterium, and does not belong to the .schyzomyccs, or even to the fungi at all, but to the protozoa ; this view is usually held concerning the spirochaeta pallida, the organism discovered by Schaudin, and shown to be the cause of syphilis. Some observers. 274 amongst them Miihlens and Hartmann (25), regard these mouth spirochaetes as closely related to the spirochaeta pallida, and claim to hav'e shown that the mouth spirochaete possesses an undulating membrane : and in the figures given by Miihlens in the Zeitschrift fiir Hygiene, these spirochaetes are so figured (33). A large number of spirochaetes have been found in the mouth, the first reference to them being that of Lewis in the Lancet. They were further described by Miller as belonging to two varieties, (1) Spirochaeta Dentium, an irregular thread without definite motility, and (2) Spirillum Sputucjenum, a well-marked spiril- lum possessing motility. In making films from ulcerative processes of the mouth, especially ulcerative stomatitis and gangrenous stomatitis, as well as from a number of cases of alveolar pyorrhoea, large numbers of spiral-formed organisms are found in the preparations. The spirilla and spirochaetes have been found in other parts of the body affected by gangrenous processes — the in- testinal canal, the genito-urinary tract, and even the surface of the body. Spirilla forms are also known as the infecting cause in certain fevers, as for instance in relapsing fever, in the West African tick fever, and in a disease of geese. Most of these organisms exhibit the same general peculiarities, in that they do not grow readily, and only a limited number have been cultivated on artificial media. Very little attention had been paid to the spirochaetes before Schaudin's discovery of the spirochaeta pallida ; since then a good deal of work has been done on the family of spirilla and spirochaetes, and has resulted in the addition of a number of species to the list of known spirochaetes, as well as to the re-naming of a number of species already known to exist. Spirochaeta Pallida (Treponema Pallidum), This organism is found regularly in the various lesions of syphilis, both primary and secondary, and has also been found in tertiary lesions. The term treponema has been applied to it to indicate an organism midway between the true spirilla and the protozoa of the treponazome type — organisms that are frankly protozoal, and show nuclei and nucleoli when stained by Romanowski's and Giemsa's methods. The spirochaeta pallida is a long spirochaete showing twenty or more turns in each individual thread. So far the organism has not been grown in pure culture, although ArnJieim (4) claimed to have obtained it in impure cultures. The organism stains by Romanowski's method, and best by Giemsa's modification, or better still by the silver nitrate method. The organism is found, after special staining and in favourable sections, as large masses of delicate spirochaetes infecting the tissue in all directions. By taking the material contauiing the spiro- chaete, as shown by staining reactions, and in- oculating monkeys, the primary and secondary lesions of syphihs have been produced ; and the spirochaete has been demonstrated not only in the primary lesion at the seat of inoculation; but in the secondary lesions at a distance. The opinion generally accepted at the present time is that this organism is the true cause of syplulis. Primary lesions have been produced on the conjunctivae of raljbits by inoculating them with the serum from the primary lesion in monkeys. The ulcer when examined microscopically is found full of long motile spirochaetes. Since the discovery of the organism, con- siderable steps have been made in the direction of treatment and early diagnosis, based on certain general bacteriological facts. I^iagnosis has been furthered by Wassermann's appUca- tion of the method of Bordet — deviation of com- plement — to the detection of a sypliihtic virus in the blood. This reaction, known as the Wassermann reaction, depends upon the j)resence of sypliilitic virus circulating in the blood and determining the presence of anti-bodies towards the spirochaetes. Tlie method of testing is somewhat complicated. Use is made of the fact that the specific virus, if present, absorbs complement added to an inactivated haemolytic serum, and thereby prevents the occurrence of haemolysis. Should no antigen be present to fix the complement, it becomes attached to the inactivated haemolytic serum and re-activates it ; haemolysis then takes place, with the result that the fluid in the tube, instead of containing a precipitate of red cells, becomes uniformly coloured with the haemoglobin of the dis- integrated red cells. The treatment of the disease has gained considerably through the researches of Ehrlich, who has found that the intra-venous injection of certain specific drugs breaks up and destroys the organisms in the tissues, the substance used,tetra-niethyl-diamino-ari3eno-benzaldehyde (" 606 "), being an organic preparation of arsenic. As the immediate result, the Wasser- mamireaction — complemental deviation — which was before well marked, is rapidly lost, and only reappears if the substance used has been in- sufficient to destroy the spirochaeta palUda infecting the tissues. The spirochaeta pallida may be demonstrated in mucous patches about the mouth and in primary lesions of the mouth, and has occasion- ally been found in gummatous ulceration, etc., of the palate. Tlie other spirochaetes found in the mouth may be divided into two classes — ■ Spirochaeta Dentium. Spirillum Sputugenum. 275 These two classes of organisms are frequently found associated with the Ijacillus fusiforniis, more particularly the spirochaeta dentiuni, and it has been thought by several observers that the bacillus fusiformis and the spirochaete are forms of the same organism (38). There is no doubt that it is exceedingly difficult to separate the various forms of spirochaete in pure culture. They are all anaerobic, and, moreover, will only grow in culture medium containing normal (unheated) serum, or at any rate not heated above 60° C. The organisms are so strongly anaerobic that it is necessary to heat the agar as well as the serum before mixing (agar 3, serum 1), to drive off tlie entangled oxygen. Shake cultures, Vignal tubes, or deep agar plates covered with paraffin, are the best methods of isolating the organism, and by one of these metliods the organism may be obtained in pure culture, but transference to other media or any attempt to continue the cultures is not always satisfactory ; moreover, there is a great tendency for the colonies to be impure, and the fusiform bacillus and long threads of the bacillus hastahs (bacillus necrosis), to be described later, are frequently found mixed with the spirochaetes. Several definite morphological forms of the spirochaetes may be observed in film prepara- tions made fiom the mouth, namely : — (1) Threads with wavy undulations and irregular twists, '1 to "2 /u in diameter and some 7 to 8 /i long, the form corresponding to Miller's original description of the spirochaeta dentium. (2) Well-marked spiral forms with 4 to 5 turns of the thread, the whorls of the thread being regular, and the organism having pointed extremities, furnished ^\■ith terminal flagella. This organism corresponds to Miller's original description of spirillum sputugenum. (3) A minute spirochaete, ' 1 /x in diameter and about 2 /x in length, possessing not more than three to four turns to the thread. This organ- ism is the one described by Veszpreni (40, Bd. 45, p. 17) as spirochaeta gracilis. All these spirochaetes are Gram-negative, and the staining is best carried out by Leishman's modification of Romanowski's, or with dilute carbol-fuchsin for some little time. If staining with fuchsin, it is better to clear the films thorouglily with alcohol and ether and 1% acetic acid before staining. (4) Comma-shaijed bacUli, resembling in many respects the second form of Miller's spirillum sputugenum. This organism has recently been grown in pure cultures by Miihlens (34), who claims that it is a distinct species. (.")) The E bacillus of Miller, an organism of spirillum form, non-motile, and frequently found in carious dentine, and growing easily on potato -gelatine. Of thes:' spirochaetes, the last only is aerobic, the other four being anaerobic. The spirochaeta dentium has been grown in pure culture by Miihlens and Hartmann (25). wlio describe the cultures. They were unaljle to obtain any growth on the ordinary culture media, unless serum was added and air rigorously excluded. Inocula- tion experiments carried out with pure cultures produced no lesions in animals. The colonies are somewhat typical in the depths of the serum-agar, being small, circular, slightly granu- lar, and greenish, and exhibiting as a rule a tangled mass of threads, which only later show a distinct spirochaetal form. The threads tend to show irregular staining, and may be grouped in masses, in which the spirochaetal form is almost lost. The spirillum sputugenum, except in its comma-shaped variety, does not seem to have been grown l)y either of these observers ; but more recently Miihlens, in the paper referred to above, gives particulars of an organism that he has obtained, which closely resembles and probably is identical with this comma form. The E bacillus of Miller was obtained by the writer in pure culture some time ago, by the use of potato-agar, and was at first thought to be the spirochaeta dentium ; but the later work of Miihlens and Hartmann, whicli to some extent the \mter has been able to confirm, has afforded evidence that this parti- cular spirillum belongs to the type described by Miller as the E bacillus. The organism, like the others, is Gram-negative, and in old cultures grows out into quite long threads and spirochaetes, as well as spirilla, and shows curious enlarged cocci-like bodies in the course of the thread, closely resembling the so-called arthrospores descriljed by Pfeiffer in the cholera bacillus. Inoculations with this organism were found to be distinctly pathogenic for guinea- pigs, and the orgamsm was obtained in pure culture from the bone-marrow of the femur, but not from the blood. Tliere is consideraljle difficulty at the present time in separating the various groups of spiro- chaetes and spirilla into their proper genera, and it will be necessary to refer to them again in dealing with the next group of organisms, amongst which comes the bacillus fusiformis. A considerable amount of further research on the mouth spirochaetes is required before one can regard tlie several species as being satisfactorily separated. For further parti- culars, as well as tiu' literature on the sul)ject, see the papers of Miihlens and Hartmann, and Veszpreni. Anaerobic Bacilli In addition to the spirochaetes just described, which are obligatory anaerobes, two organisms !276 of fairly common occurrence in the mouth are obligatory anaerobes, whilst a number of others, so far ungrowni, probal)ly belong to the group as well. Cliief amongst the anaerobic bacilli that have been cultivated on artificial media with success, are the liacillus fusiformis and bacillus hastalis. In addition to these, the bacillus perfringens, found in the alimentary tract, has been de- scribed as occurring in the mouth, but is more common in the intestinal canal (47). Bacillus Fusijormis. — As has been premised in discussing the spirochaetes and spirilla of the mouth, the bacillus fusiformis is commonly found associated with the spirillum, particularly in infective processes of a gangrenous nature, namely, gangrenous stomatitis, ulcerative stoma- titis, ulcerative gingivitis, and Vincent's angina. Fig. 384. — Bacillus fusiformis in pus with spirochete dentium, gentian violet, x 1000. The organism is a diplobacillus, frequently with tapered ends, the two halves of the bacilU being roughly triangular with their bases in apposition — not at all unlike the sheath form of the diphtheria bacillus, but much larger. It does not stain by Gram's method, although if the decolorization is carried out very quickly, a certain amount of stain may be retained, more especially in smears made from infective processes in the mouth, which are full of mucin and albumin. Tlie organism may be as much as 1 /i in ■vsidth in the widest part, tapering off to fine pointed ends. In sections of tissues undergoing an ulcerative process the bacilli are found in the deeper layers, together with, but in advance of, the spirochaetes. Wlien cultivations are made on the ordinary laboratory media under aeroljic or anaerobic precautions, no growth takes place. When, however, serum-agar is u.sed, under strict anaerobic precautions, growth of colonies of the bacillus fusiformis takes place, together with a small number of the spirochaetes. The colonies are frequently im- pure, and show a mixture of fusiform baciUi and long threads — doubtless, involution forms of the spirochaetes. From the constant occurrence of curved and spiral threads with the bacillus fusiformis, Turnecliffe and others have been led to suppose that the fusiform bacillus and the spirochaete ^vere identical. On the other hand, Miihlens and Hartmami, who isolated the spirochaete by the serum-agar method, were able to com- pare the growth ^^•ith bacillus fusiformis, a pure culture of which had been supplied to them by Ellermann, and the organisms showed very chstinct differences both in their colonies and in their cultural characters. The cultural characters of the bacillus fusi- formis are mainly of the negative type. The organism does not grow unless serum is added ; it \\ill grow, however, on glucose-agar with a slight addition of serum, or in milk broth, or in carbo-hydrate peptone water if serum has been added, but only under anaerobic conditions. Xo development of acid takes place. In older cultures the organism tends to grow out into longish threads, these threads sho\nng curious transverse and dotted markings %\hen stained with methylene blue or Leishman's stain. In addition, curious rounded swollen forms appear in the course of the thread, and these particular forms may often be observed in impure cultures, when streaks are made on ordinary agar from idcerative stomatitis. If organisms other than the anaerobes are present, particularly obligatory aerobes, the oxygen-loving bacteria apparently use up so much of the oxygen in the immediate vicinity that a limited development of the anaerobes takes place. This may be well seen in making a broth culture from a case of ulcerative stomatitis, when at the end of two or three days, long threads and various other involution forms of anaerobic bacteria may be met ^^•ith, forming a thick deposit at the bottom of the tube. Attempts to separate these by the ordinary methods of aerobic process never result in the growth of the anaerobic organisms. In these broth cultures an exceedingly foetid smell is produced, and various observers who have dealt with the bacillus fusiformis — Veszpreni (40. Bd. 44. p. G60), Abel (1) and Ellermann (15) — all agree about the relation of this foetidsmell to cultures of bacillus fusiformis. Perhaps the best method of isolating the organism is by the use of Vignal tubes, when the individual colonies may be selected. The 277 colonies of the bacillus fusiformis in the depth of the medium are of a disc-like form, biconcave in shape, yellowish, finely granular, and with a somewhat darker centre, the colonies of the spirochaetes being greenish and non-striated, and tending to send out processes into the surroundiiig media. The bacillus fusiformis and the spirochaetes are always to be found in ulcerative stomatitis, and in Vincent's angina; from their constant association with each of these diseases, and from their position histologically in the depths of the tissues, there seems to be little doubt that the organisms themselves are concerned in the tissue necrosis. So far, however, the various observers are not in agreement as to the pathogenicity of these organisms. Miihlens and Hartmann, working with pure cultures, were unable to obtain pathogenic effects by inoculating large quantities into laboratory animals. On the other hand, Eller- mann and Veszpreni both succeeded in pro- ducing very definite pathological results, but Miihlens and Hartmann are inclined to regard the pathogenic effect as due to an admi.xture with other organisms. There is no doubt that the bacillus fusiformis is concerned with tissue necrosis; in several rabbits that the writer has inoculated with cultures containing the bacillus fusiformis and the spirochaete in large numbers, together with certain strepto- cocci, which are exceedingly difficult to eliminate from the cultures, he has produced much greater pathogenic effects than when a pure culture of either the streptococcus or bacillus fusiformis itself has been inoculated. If the pus from a case of ulcerative stoma- titis, or the triturated necrosed tissue, is inocu- lated subcutaneously into an animal, patho- logical results follow, the tissue necrosis often extending over very wide areas ; in one of the writer's rabbits the abscesses spread from the cricoid cartilage to the pubes, and into both axillae. Bacillus Ha-stalis {Bacillus Necrosis). — This organism is closely related to the bacillus fusi- formis, and may be obtained in pure culture by the same serum method. It is strictly anaerobic and serophile, and forms long threads, but without the characteristic diplobacillary form of the bacillus fusiformis. The threads are very long and pointed, and, as witii bacillus fusiformis, an unpleasant foetid smell is pro- duced. The organism is, no doubt, similar in all res])ects to that described by many observers as bacillus necrosis, and found in parts of the body other than the mouth. ■ It has been de- scribed in diseases of cattle, by Vogcs (41), and in man, in lung gangrene, necrotic con- ditions of the liver, etc. (27). The organism belongs to the class of anaerobic thread-forming bacteria — a class as yet ill- deiuied, and containing many organisms that have not received sufficient investigation. The best method of demonstrating these necrotic bacteria in diseased organs is l>y means of smear preparations made from a small piece of necrosed tissue, and stained by Leishman's modification of Romanowski's method. The diagnosis of diphtheritic membrane or Vincent's angina may be thus easily made, but it must not be forgotten that the fusiform bacillus may often be found associated with true diphtheria. These anaerobic organisms already described — bacillus fusiformis, bacillus hastahs, and the spirochaetes — occur in the mouths of man in various races : the writer has obtained them from the mouths of men of the native races of Central Africa, of India, and of China ; and recently Gustav Meldorf (31), on examining the mouths of persons in Greenland suffering from ulcerative stomatitis, has described organ- isms that, from their morphology, are evidently those under discussion. GROUP IV— STREPTOTHRICAE The streptothrix group comprises a series of organisms liiglier in the scale than those already considered, and coming intermediate between the yeasts or blastomyces, and the fission- fungi or bacteria, the schizomyces. The characteristics of the group are increased complexity of form, the filamentous mycelium showing true brandling. The ends of the threads of the mycelium undergo differentia- tion into cocci-like bodies, or gonidia, which in certain groups contain a quantity of dark pigment. The grow-th of the whole group is character- istic. The colonies are cartilaginous and tough, and as they become old tend to crater-like form, splitting across and showing various stages of pigmentation, from chalky-wliite through various shades of yellow and pink to dark brown. Some members of the group cau.se distinct staining of the media in which they are growing, whUst others produce no such change. The white or coloured powder on the surface of the colonies, which may be easily scraped off, contains the cocci-like bodies, which, when sown on the surface of nutrient media, rapidly develop into the tangled myce- lium. As the mycelium becomes old, it under- goes gradual fragmentation into portions bearing a morphological resemblance to the bacteria. A number of members of the grouj) are patho- genic, and a few retain the stain when stained by the tubercle bacillus method, and are termed acid-fast. In not a few instances they have been showii to be the infecting organism in 278 a disease of the lung closely resembling pulmon- ary tuberculosis. Tlie streptothrix adinomyces, or ray fungus, the first organism of this group, produces the well-known disease of the jaw known as actino- myces, or sometimes actinomycosis. The disease is commoner in the lower animals than in man, and produces the so-called " woody tongue " in cattle, and when affecting the bone causes enormous swelling, and tunnelling of the hypertrophied mass. In pus from a case of actinomyces, the strepto- thrix may be found in the form of small granules of golden yellow or lighter yellow colour, about •5 of a millimetre in diameter. Inspection with the microscope shows these granules to be com- posed of tangled masses of threads (mycelium) exhibiting true branching ; the outer ends are thickened and club-shaped. The organism is supposed to gain entrance to the mouth and soft tissues through the medium of one of the cereals, and in many instances an &\vn of barley has been discovered in the centre of the tumour. The disease often makes its first appearance in some organ or gland associated with the alimentary tract, and when once established is exceedingly difficult to eradicate. The true streptothrix actinomyces grows best anaerobically, and two types are described — • Streptothrix Actinomyces Bovis. Streptothrix Actinomyces Hominis. It is probable that the two organisms are closely related. The organism stains with the ordinary anihne dyes, and best by Gram's method, Weigert-Gram being the best stain for tissue preparations. It grows readily on the ordinary laboratory media, forming gelatinous colonies, which turn yellow after four or five days ; and it presents no difficulty in recognition. (See Chapter LI, p. 767.) A large number of species of the genus strepto- thrix are known, and some of them occur in the human mouth ; amongst these, one first de- scribed by the writer in the Transactions of the Odontological Society, 1899, as cladothrix huccalis, was found by him later to be a true streptothrix. This organism is often present in the mouth, and differs from a number of other strepto- thricae in its cultural peculiarities. It stains by the usual methods, and by Gram's method. It is not acid-fast to carbol-fuchsin. Filaments of this organism may be ob.served in preparations from the white deposit found along the gum margins in neglected mouths, where its fila- ments are associated with an organism to be described later, namely, crenothrix polyspora. The streptothrix buccalis produces well-marked gelatinous white colonies on agar, but no staining of the medium occurs ; the colonies very soon become covered with a white flour-like fluorescence. So far it has not been found pathogenic for animals. The cultures give off a characteristic smell, much like that of a damp cellar. A number of other streptothricae have been found in the mouth — some of them isolated from bone and gum inflammation. The writer has, on several occasions, found a streptothrix closely related to the streptothrix actinomyces, but differing from it in cultural characters, in acute inflammation of the bone of the mandible. Foulerton (18) made a study of the strepto- thrix group, and describes twenty-five species in his original paper, some of them pathogenic. Fig. 385. — Streptothrix buccalis, 24 hrs. agar. Gram. X 1000. Amongst these, two had been obtained from dento-alveolar abscesses. For the full de- scription of these species, the cultural reactions, and epitome of the literature to that date, as well as the micro-photographs of the organism, the student is referred to the original paper. GROUP V— BLASTOMYCES The blastomyces, or yeasts, form a group of organisms higher in the scale than the strepto- thricae. The organisms develop by budding, one or more secondary cells being formed from the main cell ; and in most species of saccharomyces definite mycelial formation takes place, the myce- lium showing a roughly articulated form, closely resembling the hyphomyces, or mould fungi. The organisms are all comparatively large, being 10 /J, or more in diameter ; they are round, oval, or lanceolated, and when stained with poly- 279 chromatic methylene lihie show a distinct nucleus in the centre taking a red colouration, and suriounded by Ijlue c\'loplasni in which are a nuniher of finely refractile granules. The chief representatives of this group associ- ated with the pathology of the mouth are the saccharomycrs albicans, oidium albicans, or so- called thrush fungus, and sacclmroinycef! r/ingivae. The first organism is an occasional inliabitant of healthy mouths, and the writer has met with it in about one per cent of unclean mouths. It is not common, and is rarely found in "pyor- rhoea alveolaris ", or ah'eolar osteitis. Tlie other saccharomyces is occasionally found in discharge of pus along the gum margins ; it has many of the cultural characteristics of the saccharomyces neoformans of San Felice, from •••. 4» Fig. 380. — Saccharomyces neoformans, 24 hrs. glucose agar. Gram, x 1000. which organism, however, it differs in several important respects, and may, therefore, be considered to be a species esjiecially related to tlie mouth. Saccharomyces Albicans (Oidium Albicans, Thrush Fungus). — The growth of this organism on artificial media is exceedingly characteristic Its colonics form delicate rayed masses with a minute central point, the fine filaments radiating regularh- from the centre. It stains by Gram's method, and by the ordinary aniline dyes. When examined microscopically, the organ- ism is found to consist of an irregular mycelium having a large munber of joints ; the individual joints are somewhat elongated, tajjered, and many /jl in width, and at the ends show a slightlj^ protruding rim. This portion of the cell takes on a deeper stain than the other part of the organism. Tlie organism grows fairly well on ordinary laboratory media, but nuich the best results are obtained on media containing sugar, glucose, or lactose, both of which it rapidly ferments. It is slightly pathogenic for the low'cr animals, and in man grows with greatest frequency in the terminal stage of certain debilitating dis- eases, such as pulmonary tuberculosis, causing a white membrane in the mouth. In other cases, in underfed children, it may produce a white membrane in the fauces and buccal mucous membrane, closely simulating the membrane of diphtheria. A coverslip prepara- tion will rapidly clear up the diagnosis. The whitish membranous deposit produced by the saccharomyces albicans must not be confused with the white necrotic patches associated with ulcerative and gangrenous stomatitis, in which the bacillus fusiformis and spirochaeta sputugemim are invariably found. Saccliaromyces Gingivae. — This organism is a. large, oval, lanceolated, or rounded yeast, frequently forming defiiute mycelial filaments, which are often found in smears from the margins of hypertrophied gums. The organism grows best on maltose, or lactose-agar. It does not liquefy gelatine, and on the surface of agar and gelatine containing one per cent of maltose produces a coarsely granular growth. The individual colonies are rounded, opaque, with sharply defined edges, soft in consistency, and giving a granular appearance when mixed with water for the purpose of making coverslip preparations. This yeast is frequently patho- genic ; when isolated from the gum margins, and inoculated in pure culture into animals, it may produce secondary growths in various parts of the animals" bodies, notably in the spleen, kidney, and lung. The appearance of these growths is highly characteristic, and closely resembles sarcoma. Tlie pathological condition of the mouth w ith which the organism itself is most frequently associated is hyper- trophy of the gums, and one particular form of hypertrophic gingivitis is probably caused by it. It gives the ordinary staining reactions of the yeast, particularly with polychrome methylene blue, or Leishman's modification of Romanow- ski's stain, a well marked chromatin .staimng being exhibited by the latter method. For the cultural characters see the Transactions of the Odontological Society, 1908. Certain other members of the saccharomyces family are occasionally found, but are non- pathogenic. Chief amongst them is a yeast producing bright red colouration, as well as one producing a pink colour, closely resembling the ordinary pink torula. Both of these organisms are of little interest, except for their pigment production. 280 GROUP VI— LEPTOTHRICAE Zoph defines as a leptothrix " thread-like, filamentous forms showing distinct differentia- tion between the two ends, one end of the thread being apparently modified for attachment, and the other forming a variety of arthro-spores or gonidia." The so-called leptothiix epidermidis alba, is a large bacillus growing out into threads. Miller's original description of the leptothrix also in- cluded definite bacterial forms, without any differentiation into a higher type of cryptogam. Tlie term '" Leptothrix " is used loosely, as synonymous with any thread form, and has been appUed, therefore, to the thread form of any bacterium. Although it is not uncommon to find '" leptothrix of the mouth", " the leptothrix of tooth decay "', cited as definite entities, such an entity has no more real existence than any j of the category of heraldic beasts. If stained preparations are made from the white material found adhering to the necks of the teeth in some mouths (particularly those where there is a good deal of caries but no definite gum suppuration), or from the surface | of artificial dentures, or even from scrapings | from the tongue, a large mass of threads may frequently be seen. These threads stain by i Leishman's method, and show a general simi- larity. If. as Leon Williams first pointed out, considerable care is exercised in making the films, and the material to be examined is sus- pended in distilled water instead of being smeared on to the slide or coverslip, a certain amount of structure may be seen, which in the ordinary method of making smears is lost through the breaking up of the threads. In ordinary preparations stained with either gentian-violet or Leishman's stain, curious felted masses of threads may be seen, a number of these threads being surrounded by a mass of cocci-like bodies ; and by careful focussing the threads may be seen pas.sing through the centre of the mass. If the material is rather more broken up, and Leishman's stain (especi- ally) made use of, a large number of morpho- logical forms of bacteria are seen. These may be grouped as follows — Irregular cocci-like bodies, diplo- and single cocci of various sizes, staining not a deep blue but a faint violet with the reagent used ; a number of bacilH, diplobacilli, and various- sized threads, some of them quite fine (not more than -2 /x in diameter), others very much larger, up to 1-5 /x (the bacilli may show irregular staining, well-marked purplish dots highly suggestive of a chromatin staining being observ- able in their interior) ; long articulated threads, some of them very large, and showing in their interior numerous darkly stained bodies. Wlien stained by Gram's method, most of the bacilli and cocci-like bodies remain un- stained ; the threads take a faint stain, but the internal structure stains deeply — in all proba- bility it decolorizes with greater difficulty than the rest of the organism, for if the decolorization is carried too far, this curious punctate appear- ance is lost. The threads do not show definite branching, but have the appearance of an internal struc- ture consisting of small cUvisions passing across the thread at right angles to its long axis. Practically all varieties of the schizomyces mor- phology are seen in such a preparation ; this led Vicentini to the remarkable supposition that all micro-organisms of every known species, in- cluding of course the tubercle bacilli and all other pathogenic forms, were only fragments of the organism that he termed " Leptothrix racemosa ". Prom careful examination and consideration of a number of preparations, and comparison of the preparations \\ith photographs and draw- ings of the liigher bacteria derived from other sources, particularly water, the writer has come to the conclusion that the organism producing this wonderful medley of morphological forms is a variety of the group of bacteria described by Cohn, and figured by Zoph, as crenothrix poly- spora. This organism has the same curious irregular threads, which seem to proceed from a central parent, the internal portion of the thread showing a large number of cocci-like bodies ; and the apparent branching is produced by the development of these cocci-like bodies into threads, which undergo transverse fragmen- tation, become .spht off, and hence form the various morphological types. Rullermann (37) gives figures of the crenothrix polyspora, according to Zoph, and also figures of a crenothrix obtained from a waterworks in Bavaria. The photograph gives the exact morphological type that is met «ith in a number of mouth preparations — the jointed threads, the cocci-like bodies situated in the interior of the threads, and the curious packets of threads sprouting from the centre ; all of which may be met with in the smears made from the normal human mouth. If comparison is made of the illustrations given by Leon Williams and Vicentini, as well as the earlier diagrams given by Miller of the leptothrix innominata and leptothrix gigantia of the mouth, and of lepto- thrix buccalis, in each case close similarity to the diagram of Zoph and the photographs of Rullermann is observed. So far, the organism has not been grown, and it is impossible from merely stained preparations from the mouth to be absolutely certain as to its identity, but there is little doubt that the curious morpho- logical forms that have been described as the 281 leptothrix racemosa belong to the group of crenothrix polj-spora (Cohn). K. W. G. BIBLIOGRAPHY (1) Abel. Cenl. far Bakt., Abt. 1, Bd. XXIV, 1898. (2) Andrews & Horder. Lancet, Sept. 15, 1906 p. 708. (3) ArkiiVY. Vierteljahrssch. jiXr Zahnheilk., 1893, Heft 11. (4) Arnheim. Berl. Klin. Woch., 1909. (5) AXENFELD. Archiv jur Opklhalm., 1896, Bd. 42. (6) Babes. Zeits. fiir Hygien., 1889, Bd. V. (7) Bayos. Proc. Hoy. .Sor. Met!. (Path. Sec), 1912. (8) Bayon. Jour. Soc. Trop. Medicine, 1912. (9) Bulloch. Proc. Roy. Soc. Med., 1910, Vol. Ill, p. 75. (Discussion on Vaccine Therapy.) (10) Burger, Leo. Cent, jur Bakt., Bd. 41, p. 414. (11) Cautley. L.G.B. Reports, 1894. (12) De Simoni. Vfficiale Samlaro, 1899. (13) DoBRZYNicKi. C'en^/«r-BaA(., Bd. 21, p. 835. (14) Dudgeon. Jour, of Hyi/iene, 1911, p. 137. (15) Ellermann. Cent, fur Bakt., Bd. 38, p. 383. (16) Eyre. Brit. Med. Jour., Nov. 4, 1899. (17) Fehleisen. KoUe & Wassermann's Harulbuch der pathogenen Mikroorganismen, Bd. Ill, pp. 304-5. (18) FouLERTON. Trans. Path. Soc, 1902, p. 50. (19) FrXnkel. Zeits. fur Klin. Med., 1886, Bd. XI, Heft 5 and 6. (20) Freund. hiaugiiral Dissertation, Freiburg, 1898. (21) GoADBY. Layicet, Jlarch 9, 1907. (22) GoADBY. Proc. Roy. Soc. Med., 1910, Vol. Ill, p. 85. (Discussion on Vaccine Therapy.) (23) GoADBY. Hunterian Lecture. Lanct'^ March 1 1, 1911. (24) Graham-S>uth. Jour, of Hygiene, Vol. IV, 1904, p. 289. (25) Hartmann. Deutsch. Med. Woch., 1906, No. 20. (26) H.AUSER. Munchen. Med. Woch., Bd. 39, 1902, p. 103. (27) KoLLE & Wassermann. Handbuch der patho- genen Mikroorganismen, Vol. II, p. 699. (28) Lewis. Jour, of Path. , Cane sugar Dextrose Laeviilose These then undergo fermentation into lactic acid as previously indicated. Grape-sugar, dextrose, laevulose, and glucose, as stated, undergo direct fermentation into lactic acid. It will be observed that the fermentation of the grape-sugar group is direct, and that of the cane-sugar indirect ; and Stanley Colj'cr has suggested that the directly ferment- able sugars are more destructive to the teeth than cane-sugar ; but according to Miller, there seems to be no considerable difference of time in respect to the beginning of fermentation in the two groups, and the one is apparently about as detrimental to the teeth as the other. Except in the case of the fermentation of starch into dextrose and maltose, the decom- positions are the result of the action of bacteria, and the products are not exactly simple ; traces of other substances are produced at the same time wliich do not seem to be of any im- portance in the aetiology of caries. There is one fermentation, however, that should be noted, namely, the mannitic or viscous fermenta- tion of cane-sugar, as the gummy product prevents the normal self-cleansing processes. This may be represented by the folio whig formula — 25(C,„H2,0„) -t- 25(H.,0) = Cane-sugar 12(C„H.,„0,„) + 24(C,H„0,,) + 12(C0,) + 12(H,0) Girni Mannite 282 283 While tlie fermentation of carbo-hydrates in immediate contact \( ith the enamel (occasion- ally with the dentine or cementum) constitutes wliat may be considered the ])rimary stage of dental caries, it is in the conditions that favour the undue loihjement of carbo-hyckates and bacteria that the aetiological factors must be sought. As acid-forming micro-organisms are ubiquitous, and carbo-hydrates practically always constitute part of a meal, it is neces.sary particularly to note why in some mouths there should be undue retention of carbo-hydrates and micro-organisms leading necessarily to fermentation, and why in other mouths carbo- hydrates should not lodge undidy. Attention must therefore be directed to the conditions that favour — (1) The undue retention of carbo-hydrates in the mouth, or more especially in the crevices of, and between, the teeth ; and (2) The proliferation of the acid-forming micro-organisms. (1) The undue retention of carbo-hydrates m the mouth results from the nature of — (a) The food. (b) The form and arrangement of teeth. (c) Arrested or insufficient flow of the saliva. (d) The dietetic habits. (a) The most important factor in causing the midue retention of carbo-hydrates in the mouth is the nature of the food itself. In considering this subject reference to the albu- minous foods will for simplicity be more or less omitted, as their lodgement is not of the same positive importance with regard to the aetiology of dental caries. Certam classes of foods are now recognized as being peculiarly liable to lodge in the crevices of, and between, the teeth. In general it may be said that fibrous and acid foods, such as fresh fruit and vegetables, do not tend to lodge, except when the teeth are abnormal in their arrangement ; and even when such foods do lodge they are practically harmless from the point of view of dental caries, for during mastication the sugary and starchy matters are the first to be expressed from the bolus and swallowed, while the shreds which may lodge are relatively free from fermentable carbo-ln^diates. On the other hand, many of the prepared foods, especially those in which the fibrillar element has been destroyed or eliminated, tend to lodge unduly about the teeth ; thu.s biscuits, soft or doughy bread, and almost all prepar- ations of cereal food, are liable to lodge in the crevices of the teeth (35). The firm and fibrillar nature of certain foods encourages mastication, and stinudates the natural self- cleansing of the mouth, whereas highly refined and, more especially, soft, bland, alkaline foods — porridge, milk puddings, potatoes and gravy, bread soaked in milk, etc. — are liable to be con- sumed without that amount of mastication and insalivation which is necessary for the dislodge- mcnt of food that may be of a sticky nature. Some foods are not sticky in themselves, but they may become sticky in the mouth ; thus sugar, in addition to becoming fermented in part into lactic acid, also undergoes a mamiitic fermenta- tion, resulting in the formation of a gummy sub.stance, which is liable not only to stick about the teeth, but also to retam the other food particles about the teeth. Thus a combination of starch and sugar, as found in cake and sweet biscuits, is likely to be particularly liable to lodge about the teeth. Similarly, combina- tions such as bread and marmalade, or jam, are liable to lodge about the crevices of the teeth if they form the last part of the meal. Further reference will be made to the relative lodgeability of foodstuffs ; enough has been said to indicate how the nature of the foods may lead to the undue lodgement of carbo-hydrates, which are necessary for the production of acid by bacteria, while on the other hand, food of a detergent nature may not only be eaten with- out leavmg food particles, but may also clean the mouth of sticky carbo-hydrates and bacteria, which may have been lodging about the teeth before the fibrillar foods were eaten. • (h) With regard to the form and arrange- ment of the teeth, it is obvious that pits or abnormally deep crevices predispose to the undue retention of food particles. The abnormal relation of one tooth to another generally may be said also to predispose to the undue lodgement of food, for the normal inverted V-shaped space is replaced by some other arrangement. Tilted molar or premolar teeth are peculiarly liable to give rise to undue lodgement of carbo-hydrates, because the normal V-shaped inter-space, filled as it normally is with the gum, is the most perfectly adapted for least lodging and easiest self-cleansing. Recession of the Gums, by removing the inter- dental pad of gum, favours the undue retention of carbo-hydrates and therefore jsredisposes to caries. Abnormal Relation of the teeth, more especially of the thu'd molars, to the surrounding soft parts or to the opposing teeth, is a frequent cause of the undue retention of carbo-hydrates. (c) More or less complete arrest of the flow of saliva from constitutional causes is a rare condition except during fevers ; when it is pro- nounced or prolonged, caries correspondingly tends to be rapid and general. (d) Dietetic Habits have a considerable infiu- ence over the lodgement of food particles. Thus, for example, the taking of a meal immedi- ately before going to bed, or the eating of sweets 284 in bed before going to sleep, when the self- cleanhig processes are in abeyance, tends to give rise to undue lodgement of carbo-hydrates. Frec|uency of meals may also be mentioned, not that the meals need necessarily leave carbo- hydrates ill the mouth, but if the meals are of such a character as to leave starch or sugar, each successive meal renews the supply. Still further is this an important consideration when sweets are eaten more or less continuously, thus supplying the bacteria \\ith a corresponding supply of food. Other habits such as the con- suming of food with little or no mastication, or the cb-inking of liquids m ith, rather than after, meals may be mentioned. (2) The Undue Retention of Micro-Organ isms about the Teeth. — The proliferation of micro- organisms is markedly influenced by the environ- ment in which they exist, and this is jjarticularly true of the micro-organisms of the mouth. Notwitlistandmg repeated efforts, it has been found impossible to cultivate certain bacteria outside tfie mouth, so sensitive are they to alterations m their environment. Although nearly all the bacteria found in the mouth may cause acid fermentation, or putrefactive changes, according to the medium in which they exist, they may for convenience in elucidating certam aetiological details all be mcluded in the following divisions — (1) Those most generally active in the pro- duction of acid ; and (2) Those most generally active in the putre- factive processes. As these groups of micro-organisms flourish best in the media that permit of their most active development, it follows that the acid producers are favoured \\hen carbo-hydrates (their natural food) remain in the mouth. When, therefore, carbo-hydrates lodge unduly about the teeth, then correspondingly, acid fermentation is marked and caries tends to be induced ; the acid-forming bacteria are specially favoured and proliferate unduly, thus increasing the rapidity and intensity of the acid fermenta- tion. E. C. Ku'k suggested that the type of micro-organisms was modified by the presence of glycogen in the saliva ; but it would appear that glycogen is not present (19) in the saliva as it issues from the salivary ducts, and except in diabetics such cause of modification of the oral flora cannot be presumed. On the other hand, acid foods tend to prevent the proliferation of the acid-forming bacteria, for acids and alkalies, especially the former, even in very dilute solution retard the develop- ment of bacteria. So, too, the growth and fer- ment activity of bacteria are always more or less influenced by theu- own waste products, and the bacteria themselves are often destroyed by the action of the acid that they have pro- duced (20). It follows that the acid-forming bacteria, more esjiecially, are retarded in activity by the acids that are present ui so many food-stuffs (fruits and vegetables). The effect of acid may, however, be counter- balanced by the presence of easily fermentable carbo-hydrates ; thus, for example, grajies, which are acid and contaui some 20 per cent of sugar, seem under certain circumstances, as in grape-cure treatment, to induce dental caries. Agam, a diet of an albuminous nature favours those putrefactive bacteria whose natural habitat is an albuminous medium. It may be said that the putrefactive micro-organisms are normally ah^ays favoured in a clean and healthy mouth, because of the albuminous nature of the mucus, salivary corpuscles, proteid bodies, and epi- thelial cells, which are constantly being shed into the buccal cavity. Under abnormal cir- cumstances they may be specially favoured ; thus, hi case of gingivitis and pyorrhoea, except when recession of the gum has given rise to places particularly favourable to the retention of food particles. In this is found an explana- tion of the frequently observed fact that the Ul-cared-for and dirty mouths of hospital patients may l)e remarkably free from dental caries. Another pouit should be noted. To have the production of acid kept up it is necessary to renew the supply of carbo-hydrates periodi- cally, otller^\■ise putrid decomposition is set up and alkalinity results. It is probably on this account that when there is more or less com- plete stagnation in the crevices of the teeth, e. g. when there is no opposing tooth, caries is rarely rapid. Independently of the particular kinds of micro-organisms that are favoured by lodguig food particles, there is an important general effect produced on the bacteria of the mouth by different kinds of diet. In the presence of carbo-hydrates acid is produced even when mixed with a large proportion of albuminous food, while in the presence of purely albuminous food the resultmg products are alkaline. Food that demands vigorous mastication and insalivation is most effective in dislodging the bacteria that may be clinging about the more or less exposed parts of the teeth, while the bacteria of a less adhesive nature are effectually washed away ; and it would appear that some of those bacteria that are most adhesive are of the putrefactive rather than of the acid-forming kind (11). It thus seems j)robal)le that the putrefactive bacteria may help to prevent caries by forming a coating, which tends to become alkaline over unrubbed parts of the enamel ; although at places lodging carbo-hydrates frequently, it would be unlikely to find the putrefactive 285 bacteria only. After the bacteria are effectu- ally dislodged by food that demands vigorous mastication, it is obvious that even though the carbo-hydrate foods lodge after a meal, the amount of fermentation wUl be much less than when soft food is masticated and incorporated with the bacteria without dislodging them. Although the type of bacteria has a certain importance from an aetiological point of view, it should be remembered that the bacterial flora, or the relative predominance of any particular type, may be quickly altered by the lodgement of different kinds of foods. As a matter of experiment it is found that the saliva of immunes, a^ a rule, produces less acid Ijy fermentation in a given time (18) than average saliva, yet this is principally in the first t\^enty- four hours. Correspondingly, too, it may be said that tho.se who are generallj' called immune are those who as a rule do not eat such tj^es of meals as A\ould induce the undue proliferation of acid-forming bacteria. DIET IN INFANCY AND CHILDHOOD Diet in infancy and childliood plays an im- portant part in the aetiology of dental caries (37). Mother's milk is, of course, the best possible diet for infants, and it may be said that this ampl}', perhaps lavishly, supplies all the re- quirements of all the organs of the growing child ; but it may not be possible for tlie child to be provided with mother's milk, and the question immediately arises whether the artificial substitutes supply these requirements, and more especially ^^hether bottle-feeding supplies the developing teeth with such nourish- ment as will ensure thek perfect development. When due precautions as to sterilization and general cleanliness are taken, it is said that the chUd always thrives (6), but when the methods and surroundings are unhygienic various dis- turbances may take place ; if then, an effect is produced on the developing teeth it would appear to result from such disturbances. Whether again these dLsturbances produce an effect on the developing teeth such as will, after the eruption of the teeth, predispose to dental caries has further to be considered. As has just been said, when all goes well the general bodily development of the infant does not suffer; nor do the teeth suffer as far as it is known ; that is to say, they appear on eruption to be perfectly normal. There is, however, a certain projjortion of cases both in bottle-fed and breast-fed children in which the teeth are not perfectly formed, but emerge through the gums pitted or grooved (hypoplasia). (See Chapter III, p. 47.) It nuiy be that the pro- portion of hypo])lasic teeth Ls greater among the bottle-fed than among the breast-fed, because such bottle-fed children are, through neglect of necessary precautions, more subject to grave constitutional disurbances, which may be presumed to affect the developing teeth, and Xorman Bennett attributes the com- monest type of hypoplasia to a condition of general ill-health and digestive derangement brought on, no doubt, in many ca.ses by errors in feeding. The specific fevers that would appear to give rise most frequently to hypo- plasia are measles and scarlet fever, but it is not definitely known that these are proportion- ately more frequent among the bottle-fed children than they are among the breast-fed. However, while recognizing the want of definite knowledge, it may be said that bottle-feeding may somewhat predispose to measles, scarlet fever, and other constitutional diseases, which maj^ be presumed to affect the teeth in such a way as to gi\-e rise to hypoplasia, though it is impo.ssible to say that bottle-feeding can be considered an aetiological factor in dental caries of any importance, especially with regard to the deciduous teeth (which are oidy hyijoplasic in one or two per cent of cases). The question of bottle-feeding, however, as an aetiological factor in dental caries, has been studied in another way. R. B. Hunter examined some 5U0 .school-children's teeth and concluded as follows. Of the children who were breast-fed only, the teeth were "good" in 4-1 per cent, ■" moderate " in 35 per cent, " poor " in 17 per cent, and " bad " in 5 per cent. Among the children who were artificially fed only, the teeth were " good " in 33 per cent, " moderate " in 43 per cent, " poor " in 16 per cent, and " bad " in 8 per cent. From this it will be ob- served that the comparison does not lend itself to any deduction of practical importance ; at least it does not appear to throw much light on the extraordinary prevalence of dental caries at the present day. The next stage to be considered is the period of transition from the purely milk diet to the mixed and varied diet of later life. This takes place concurrently with the eruption of the de- ciduous teeth and concomitant changes in the alimentary canal. It should be noted that the change is not precisely from liquid milk to the solid and varied diet of adult life, but from sucking liquid out of the mother's brea.st to the taking of solid food into the anterior part of the mouth and subjecting it to a gnawing and sucking in a maimer similar to the sucking of the mother's breast. When an infant is tirst given a piece of solid food, say a piece of Ijread or a crust, it gnaws, insalivates, and sucks it, thereby making the first stage in the tran- sition from breast-feeding to solid food. Later, when the molar teeth come into position, a further change is brought about, for the infant 286 then takes the sohd food uito the mouth and throws it on to the molar teeth to be more rapidly disintegrated, insalivated, and prepared for swallo\\ing in a more or less liquid state. As the teeth give a definite indication of the nature of the food for which the infant is at any particular age adapted, it is obvious that untU the incisors erupt milk diet alone is indi- cated. Similarly, when only incisor teeth have erupted, food that can be gnawed and sucked (in addition to milk) is ^\'hat may be regarded as the type of food for which the child is obviously adapted at that age. With the eruption of the deciduous molar teeth a proportionately greater amount of solid food is indicated. Divergence from these uidications as to diet is not conducive to the best results, and the specially harmful results with regard to caries may be briefly alluded to. From the time of the eruption of the incisor teeth to the eruption of the molar teeth the diet should be mother's milk supplemented by an increasing amount of solid food that can be gna-\\ed and sucked, e.g. crusts, bread rolls, toast, rusks and butter. If such food is not given in a form in which it may be gnawed and sucked, in other words if it is soaked in milk, the incisor teeth are not subjected to the normal cleansing resulting from the gnawing of the food, and carbo-hy- drates may lodge about the necks of the teeth and undergo acid fermentation, while from want of use (assuming that the child is not per- mitted to chew other things) they may even become relatively tender. But the incisor teeth on account of their small size and shape do not tend to lodge food much, and bread soaked m milk is not likely to do much harm by inducing dental caries in these teeth ; never- theless even at this stage dental caries may be initiated near the gum margins. It is however when the molar teeth come into position that the harmful results of a diet almost exclusively of a " short " or soft nature is most obvious, for the crevices of the molar teeth and the spaces between them are liable to retain carbo- hydrate foods ; and if no food that will stimulate the self -cleansing processes is eaten, caries is almost mevitable m these situations. Thus, therefore, a child's diet between the twelfth and thirteenth months (exclusive of the milk) should not be restricted to porridge, bread soaked in mOk, milk puddings, potatoes and gravy ; much less should the child be given, in addition to these, sweet cake and sweets. If such a diet is adopted caries wiU gradually make its appearance, first in the crevices most liable to retam the carbo- hydrates, and later even in less retentive places such as the necks or buccal sides of the teeth. In addition to this, when young children are restricted to soft foods they soon tend to avoid foods that require much mastication, e.g. crusts. After all the deciduous molars have come into place it is particularly necessary to avoid restrictmg chUdxen to a dietetic regime that will favour the onset of dental caries ; and as by this time the dental armamentarium is, in relation to the size and needs of the child, practically the same as or greater than in adults, so corre- sponduigly should the diet approximate in type to that which is physiologically correct for adults. Three meals a day are from the point of view of dental caries, as probably also from other points of view, to be preferred to more frequent meals, for, as usually happens when a larger number of meals are taken, they are to a certain extent necessarily restricted to kinds of food that tend to digest (and ferment) quickly and to lodge about the teeth, and therefore to induce dental caries. Moreover, with more than three meals daily it is generally found necessary with children to let one of the meals be taken imme- diately before going to bed ; and as the child naturally, from other physiological considerations, is only able to take a light meal at this time, it is usually given bread-and-milk or something else of a fermentable and non-detergent type. With regard to meals in general, it may be said that from the age of two years onwards they should always contain, firstly, a sufficiency of food that will stimulate thorough mastication sufficiently well to dislodge, as efi'ectually as possible, bacteria that may be clinguig about the teeth and mucous membrane of the mouth ; for m so far as this is not done the fermentation of the carbo-hydrates that may lodge after the meal wiU be proportionately intense and rapid. Secondly, the meals should not end with food of a sticky or pasty nature, for other- wise the bacteria will be supplied with all that is requisite for their rapid development and, consequently, for the initiation of dental caries. In order to put these principles into a clear light, the type of diet that tends to induce dental caries may be outlmed. Diet Table. — Breakfast. — Porridge and mUk, bread and marmalade. Then a supplementary breakfast, a few- hours later, of a glass of mUk and a sweet biscuit. Dinner. — Mashed potatoes and gravy, mUk and mUk-pudding, jam-roll or preserved fruit. Supper. — Bread soaked in mUk, or bread -and-jam, cocoa, and cake, and perhaps a supplementary supper, on going to bed, of a glass of mUk and a biscuit. It should also be remembered that the taking of soft, sweet, sticky foods, such as malted foods, medicated syrups, etc., tends to induce dental caries, more especially when they are taken three times a day after meals. To illustrate and impress upon those who may have to do with children the danger of sticky 287 carbo-hydrates taken at the end of meals, they may be advised to kiok into the mouth of a cliild a few minutes after it has eaten, say. biscuits, sweet cake, or cliocoh\te, and they will observe a visible amount in the crevices of the molar tcetl). If then they give the child a piece of an apple to eat and then look into the mouth, they will find that the crevices are clean and no particles of the food are to be seen. An apple not only stimnlates mastication, and thus the mechanical and hydro-dynamical self- cleaning processes, but on account of its acid and aromatic flavours, it also stimulates the chemico-physiological self - cleanuig processes most effectually. In order to be able to direct the attention of parents to the particular dietetic errors that are responsible for caries in any given child, it will be found useful to ask first with regard to the physical con- sistency of the food : Does the child not eat much crisp toast ? Does it try to avoid eating crusts ? Does it not eat meat, or vegetables, or fresh fruit ? Then ask how each meal is terminated : Does it finish breakfast with bread-and-marmalade ? Does it finLsh dinner with milk-puddings or jam-rolls ? Does it finish its ne.xt meal with cake, bread-and-jam, or bread-and-milk ? If not, with what foods or li(iuids does it terminate its meals ? Lastly, ask iJE the child eats sweets or biscuits between meals or before going to bed ? The parents may direct your attention to the fact that the child's teeth are brushed before going to bed ; this may in general tend to prevent caries, but when caries exists it cannot have been effectual — it .seldom is in children, and does not appre- ciably simplify the problem as to what dietetic errors have to be corrected. CIVILIZATION It is a well-recognized fact that caries is most prevalent among the civilized races, and accord- ingly civilization is generally mentioned as an aetiological factor. Various explanations of how civilization induces caries have been ad- vanced, and may be briefly reviewed. It has been contended that the soft nature of the food of the civUized races gives rise to deterio- ration or degeneration of the teeth. Two ex- planations of tliLs have been made. One is that the pressure brought to bear on the teeth during vigorous mastication increases the circula- tion of the blood in the pulp and induces increased deposit of lime-salts or more perfect calcifi- cation. Another is that the comparative disu.se of the teeth among the civilized gives rise to degeneratioti of structure according to the Lamarckian hypothesis of heredity. It may be said however, that, if either of the.se two explanations is correct they cainiot account for the prevalence of caries in the deciduous teeth, which, among savage tribes as among the civilized, have the enamel completely calci- fied before solid food is eaten at all ; nor can they account for any supposed degeneration of the enamel, which is formed before it becomes functionally active. Another theory of the degeneracy of teeth resulting from the influence of civilization, which is also widely accepted, may be mentioned. It is contended that on account of humane sentiments among the civilized, those who would naturally in savage comnumities be extermi- nated before maturity, are, among the civilized, rendered fit by artificial aid to marry and pro- pagate their kmd. It is pointed out that among the savages the tough nature of their food renders it almost imperative to have an efficient masticatory apparatus, while among the civil- ized not only are the foods softened and, as it were, presented in a semi-masticated condition, but also the patients themselves may have their teeth restored by fillings, crowns, bridges, etc. Difference of opinion exists with regard to this explanation. Those opposed to it contend that, dental caries being comparatively rare among the uncivilized (as among animals), there can be but little elimination on this account (25) ; whOe on the other hand they contend that the unhygienic conditions of the mouth a.s.sociated with, and resulting from, the state of the mouth when the teeth are more or less ravaged by dental caries, frequently lead to premature death among the civilized. The last, and no doubt the most tenable, theory to which reference may be made does not recognize that there is any degeneracy of the teeth. On the contrary it is contended that the foods of the civilized provide an ample and adequate supply of nourishment for the develop- uig teeth, but that unfortunately they are pre- sented in a form that renders them liable to lodge unduly and undergo acid fermentation in the mouth. The fine milling of flour, the sugar refining, etc., together with the preparation by cooking of foods already highly refined, tend to decrease the foods of a detergent nature and hicrease those that tend to lodge about the teeth. In addition, there is a gratuitous advocacy of types of food that result in producuig an unhygienic state of the mouth. This, however, will no doubt soon be rectified throughout civilized nations when the hygiene of the mouth and the .science of dietetics m relation to dental hygiene are more thoroughly appreciated and studied by the medical profession. Reference may here be made to the well- known fact that caries is a.ssociated w ith certain occupations. .Millers and bakers (who are habitually hi-cathing flour dust), sugar refiners and confectioners, are particularly subject to 288 caries. How this results is so obvious to those who have become acquainted with tlie pathology of the disease and conditions favourable to the activity of the exciting cause, that it has been recognized as superfluous to assume the exist- ence of susceptibility to dental caries among those who follow these occupations. RACE Several investigations have been made with regard to caries among the various races of mankind. The most important of these was that undertaken by the late J. R. Mummery. Although he came to the conclusion that general hygienic conditions are often as much concerned in the growth of healthy teeth as food, hLs investigation has supplied us with facts of con- siderable importance in the elucidation of the problem of the aetiology of dental caries. Mum- mery's investigations, together with others, show that no race is exempt from dental caries, and further that the degree to which the various races are afflicted does not correspond in any way with the natural racial divisions as recog- nized by anthropologists, except in so far as racial divisions are associated with civilization. WHien, however, races are classified according to certain dietetic customs a general conclusion is arrived at, namely, that meat-eating races are less frequently affected by dental caries than mixed feeders. This is a generalization subject to exceptions ; thus, among modern savage races South Americans (aboriginal) are principally meat eaters, yet show 27 per cent of caries, while some mixed feeders, e.g. East Indians (North), show only 5-92 jjer cent; still, on the whole the truth of the generalization is well established. Similarly, it may be ob- served that races subsistmg on uncooked foods are more or less exempt from caries ; thus the Pygmies of Central Africa are free from the disease. It should be noted, however, that the same race may have within itself groups that show remarkable differences. Thus, those Kaffirs who have been supplied with civilized foods have in one generation become totally different (9) with regard to caries from those who are still not subjected to similar dietetic customs. Similarly, the aristocracy of ancient Egypt were much affected with dental caries, while those not belongmg to that class were comparatively free from the disease (30). Thus, although it has been generally assumed that the different extent to which the various races of mankind suffered indicated a corre- sponding susceptibility or immunity to the disease resultmg from hereditary or con- stitutional differences, yet an analysis of the facts revealed in the light of our present know- ledge of the aetiology of the disease shows that what was attributed to susceptibility and im- munity may now more properly be regarded as resulting from different dietetic habits ; for those races that are more or less exempt from the disease are seen to live chiefly on food of a kind (meat, uncooked roots, and fruits) that is detergent in its effects, and moreover does not readily encourage the development of acid-forming micro-organisms, nor undergo rapid acid fermentation in the mouth. Heredity. — The dental profession has long been acquainted with the fact that the children of parents with carious teeth are more liable to have carious teeth than the children of parents with teeth free from caries. This fact was so well recognized that the hereditary nature of the disease came to be considered as settled beyond question. The knowledge of the pathology of the disease precluded the possi- bility of maintainmg its direct inlieritance, so that it came to be believed that it was the hereditary ■predisposition that accounted for the apparently hereditary nature of the disease. Two theories to account for tliis predisposition were advanced : the first that it resulted from certain hereditary structural deficiencies of the teeth, the second that it resulted from hereditary peculiarities of the oral secretions. When the hereditary nature of the disease was assumed as a fact it was of course necessary to account for it by one or other of these suppositions, but which of them should be considered correct was the subject of much controversy. The most thorough investigations seemed rather to nega- tive both views, yet the conviction remamed that the jDredisposition to caries, whether in- duced by structural deficiency or perverted secretion, was strongly inherited. It is a well- known fact that living organisms are able to produce their like, and that the resemblance between a child and its parents, though never perfect, may nevertheless extend to the most minute details of construction and function (40) ; this seemed to indicate how the markedly hereditary nature of the disease could be ac- counted foi', although the nature of the structural or functional variation might not have been discovered. At the present, however, no know- ledge exists of inherited functional variations that might predispose to dental caries, though assiduous search has been made for them ; but certain hereditary structural variations that predispose to the disease are recognized. It is obvious that variations in the sizes of the teeth, and more especially the depth of the crevices, predispose to dental caries by favouring the undue retention of food particles and micro-organisms (in conditions favourable to fermentation). Simihirly, pits, when resulting from hereditary causes and not the result of 289 ill-health, may be considered as hereditarily predisposing to dental caries. And although it may have to do rather with the rapidity of the progress of the disease tlian witli its cause, mention may liere be made tliat tliere is no reason for doubting hereditary variation in the chemical or molecular constitution of tlie teeth. All these variations within normal limits have, however, peculiarly little to do with tlie prevalence of the disease in some mouths and not in others, for it is found that those wlio are free from the disease have likewise similar variations in the depth of the crevices, etc. Many observers now believe that the here- ditary nature of the disease is rather apparent than real, and that what had been taken to indicate inheritance may better be explained by similarity of environment (7) ; or, more explicitly, that the dietetic habits of parents and children being similar, the results as regards caries are also similar. Moreover, certain facts with regard to the pathology of the disease make it impossible to believe that there is an\'thing hereditary beyond the predisposition that various conditions might produce for the undue retention of food particles. Dental caries has been shown to be essentially a mutilation in its initial stages, and therefore the belief that its increasing prevalence had anjiihing to do with the fact of the ancestry having been the subjects of the disease, cannot be accepted. Nor could it be maintained, even by those who believed in the inheritance of acquired characters, that the soft nature of civilized food tended after .several gcTierations to produce a sort of enamel but feebly resLstant to caries, for the enamel is passive in its function. Tho.se who maintain that the apparently hereditary nature of the disease may best be explained by similarity of environment — dietetic habits — believe that the nature of the food in relation to whether it leaves the mouth in a hygienic state at the end of a meal, or other- wise, is by far the most important factor in the causation of the disease. Those, on the other hand, who consider that the differences in dietetic customs cannot account for the facts, believe that ultimately the causes of susceptibility and immunity will be found in something that may be discovered in relation either to the tooth substance itself, or to the oral secretions. They further consider that variations in sus- ceptibility at different periods during a life- time are to be explained by differences in the constitutional states, while those who practically deny the hereditary nature of the disease attribute such apparent su.sceptibility almost entirely to hitherto unsuspected changes in dietetic habits that are of importance from the point of view of caries. Thus, for example, the fact that children are much more subject to 10 caries than adults, whose teeth from irregu- larities and other causes are more predisposed to the undue retention of carbo-hydrates, is attributed to the custom by which children as a rule are fed on the softer and more fermentable foods, f . (J. bread soaked in milk, milk-puddiags, sweets, potatoes and gravy. Before the role played by the physical characters of the food and the arrangement of the meals was ajjpreciated, naturally the differences that tended to bring on or stave off caries were unobserved, and a belief in some um-ecognized susceptibility and immunity was required to account for the prevalence of caries in some mouths and its absence in others. THE CHEMICAL CONSTITUTION OF THE TEETH That the incidence of dental caries depended more or less completely on the perfection of the calcification of the teeth was the all but universal belief of the dental profession until the results of G. V. Black's investigations into the chemical and physical properties of the teeth were published in 1895. The revelations that he made with regard to the chemical constitution of the teeth have received sub- stantial and authoritative corroboration ; and though the correctness of his findings from a chemical point of view is now universally admitted, yet certain objections have been made, not only to his inferences, but also with regard to the qualitative, rather than the quan- titative, chemical composition of the teeth. The questions involved are of great importance. For very good reasons set forth in the original papers. Black selected sections of the neck of the teeth as the part most suitable for analysis, and with regard to this part he set forth in detail the specific gravity, the percentages of water, of lime-salts, and of organic matter. He contrasted sections of teeth that had been taken from carious, and those that had been taken from sound, teeth, but found no such difference as had been supposed to exist. He summarized his results with regard to the point in the follow- ing «ords : The teeth of persons wJw suffer much from caries are just a.s hard, just a-s heavy, and contain just as much lime-salts, as the teeth of persons wJw do not suffer speciall;/ from caries. The objection that the part of the tooth specially analysed by Black is not the part that is of vital importance with regard to the aetiology of dental caries, may be referred to. It is true that the enamel is by far the most important from this point of view. At the same time it seemed reasonable to infer that the neck of the tooth is in general representative of the state of calcification at other parts, and as far as the dentine is concerned this has been 290 experimentally substantiated by Charles Tomes. 1 Chemical analysis of the enamel is apparently ! extremely difficult, and discrepancies in the published results of such analyses seem to indicate this difficulty, rather than real differ- ences m the chemical constitution of the enamel itself. As, however, the enamel of man, horse, and elephant, shows no difference (32) with regard to the amount of organic matter and water accompanyuig the lime-salts, it is probable that little difference exists between different specimens of enamel from the teeth of animals of the same species. The difficulty in the chemical analysis of the enamel being recognized, it seems more satisfactory that Black's experi- ments on the enamel were also directed towards the amount of crushing strain that the enamel would bear, for in this way his results are a more effective reply to those who object to his con- clusions on account of his not taking into con- sideration the molecular constitution of the tooth. His exjjeriments seem to show that no relation whatever exists between the crushing strain and the tendency of the teeth to caries. Sunilarly, it may be presumed that the teeth of the present day are no more susceptible to caries as a result of their mmute constitution, for " the ffiiest lenses reveal not the slightest difference between enamel ground moist from a living tooth, and tliat which has lain in the earth for a hundred centuries" (41). One of Black's findings, \\'hich was considered specially surprising by those who believed in susceptibility and immunity existing in the tooth substance, ^^•as the fact that the incisor and canine teeth are less highly calcified than the molar teeth. Tomes gives the percentage of lime-salts for the incisors as 11-5, and for the molars 73'2. These results are practically the same as those recorded by Black, and more recently by Gasmann. Associated with the belief that a deficiency in lime-salts is resjionsible for the prevalence of caries there were certam explanations of how this came about. Thus it was generally believed that deficient calcification was associ- ated with a lack of the mineral constituents in the food or in the ^\ater. It was also assumed that white bread, from wliicli all the bran con- taining a large amount of jjhosphates ^\•as removed, was responsible for defective calcifica- tions ; but it has been shown that less phosphates were assimilated from the \\ hole-meal bread than from the white bread (16), so that this explana- tion could not have been maintained even though defective calcification of the teeth had been associated \\ith caries. It «"ould indeed appear from experiments carried out on rats l)y Chalmers Watson that an exclusively meat diet^ — that is, one very deficient in lime-salts — although affecting the development of the bones (rickets), had no apparent effect on the development of the teeth. Deficiency of lime- salts in the drinking water has been advanced as a cause of deficiency of the mmeral con- stituents of the teeth. Rose supports this view and has brought forward a great number of figures to sho\\- that in districts having a large proportion of lime-salts in the water the teeth of the inhabitants showed less caries than in those localities where the drinkmg water was poor in lime-salts. It has, however, been pointed out that in certain districts (Gothland) where the water does contain a large amount of mmeral matter caries is very prevalent, while in certain other districts (Delarne, Sweden) where the water was relatively free from lime- salts the teeth are relatively free from caries. Rose, on havmg his attention called to this, explained the prevalence of caries among the Gothlanders by pointing out that they lived on black bread, which was soft and sour and moreover contained sugar ; but it is not clear that the dietetic customs in this respect are essentially different in those districts m Germany in which the teeth are most carious. It is just possible that deficiency of lime-salts in the water miglit favour the progress of dental caries, masmucli as it might be presumed that the lime-salts m the water and in the foods would neutralize or modify the effect of acid formed from the fermentation of carbo-hydrates. It is possible also that when lime-salts are abundant m any district the inhabitants might instinctively tend to eat more food containing a deficiency of lime-salts, e. g. meat ; and vice versa. Whether either of these possibilities throws any light on Rose's statistics or not, it is difficult, as Tomes and Nowell observe, to reconcile them \\ith the chemical analyses of the teeth already referred to. In this connec- tion it may be mentioned that the Esquimaux have particularly excellent teeth, though they live largely on meat and fat — that is, food very deficient in lime-salts, — and are practically I debarred from aU the kinds of foods — e. g. cheese, peas, vegetables, cow's milk, etc. — that Rose recommends on account of their richness in lime-salts, while they drink water (melted snow) that is about as free from lime- salts as though it had been distilled. A more plausible theory of defective development of teeth is that which blames a disease — rickets — for the defects. Some have held this view, but while they have cited the effect of rickets on developmg bone as justifymg this assumption, they have not brought forward statistical evidence such as could be considered sufficient to establish the claim. StUl, although it cannot ] be said that rickets has been proved to interfere with the development of the enamel, as do tiie [ e.xanthemata, which have a specific effect on 291 epithelium, yet inasmuch as rickets is a disease acting during the formation of tlie teeth, the possibility of such effect cannot be excluded. iShould rickets be shown to be a cause of hypo- plasia of the enamel, then of course it would predispose to caries, inasmuch as pits and grooves tend to favour the undue lodgement of food particles. At the present time, however, several authors (2, p. 51) claim that defective enamel formation is not specially associated with rickets (24), while others (33, p. 229) are of the contrary opinion. Although the chemical composition of the tooth does not appear to have the effect in pre- disposing to caries that was previously assumed, yet the form of the tooth, more especially pits, crevices, and rough enamel surfaces, obviously predisposes it to caries by promoting the undue lodgement of carbo-hychates and bacteria. It is equally obvious that, the enamel being absolutely passive, it can have no in- fluence ^^hatever on the active fermentative process, nor can any enamel resist decalcifica- tion provided such fermentation is sufficiently intense and prolonged. Certain defects in the enamel, however, influence the rate and progress of the decalcification. Thus a crack or bruise of the enamel (22) vnder a focns of fermentation allows of the easy ingress of the acid, and consequently leads more rapidlj- to its decalci- fication. The enamel cuticle, too, offers a certain resistance to the ingress of acid (22), so that when this is removed or abraded the decalcification is made more easy. 8o again, w hen the outer crust of the enamel is worn off, it would appear from experiments made by Stanley Mummery that the action of acid is more rapid than when the enamel has not been subjected to abrasion. This is of interest, because it is frequently assumed that the crevices of the teeth offer least resistance to the action of acid, on the assumption that there is generally defective formation of the enamel between the cusps ; however, it appears that the worn cusps of the enamel are least resistant to acid. This should be remembered, because a generalized presence of carbo-hydrates and bacteria in the saliva, together with points of least resist- ance in the teeth to the action of the acid formed, has often been assumed to determhie the incidence of caries. In view of what has just been said this idea cannot be maintained. SALIVA AND MUCUS The influence of the saliva in relation to the causation of dental caries has been the subject of much research, but the conclusions of the different investigators have not alwaj's been the same. As, however, those of AliUer are both most thorough and authoritative, an abstract of them may be given, together with the con- clusions of some other investigators, which are not in harmonj'' witli his. Miller makes the following summary — 1. Mixed human saliva does not possess the power to prevent or retard processes of fermenta- tion and putrefaction. 2. Potassium sulphocyanide does not possess any appreciable antiseptic action even in the greatest strength in which it is found in the human mouth. 3. Growths of bacteria, and fermentative and putrefactive processes, take place in the oral mucus quite as readily as in the mixed saliva of the same persons, if not more so. 4. The saliva of immunes develops, in the presence of carbo-hydrates, on an average, a little less acid than that of highly susceptible persons ; the difference is, however, not con- stant, and not sufficiently marked to account for the great differences of susceptibOity. According to Michaels, variations in the standard of health make corresponding changes in the composition and reaction of saliva. \Vlien the saliva is normal there is immunity to caries, when abnormal the teeth show various changes as an effect (13). Hugenschmidt, how- ever, came to the conclusion that the antiseptic action of saliva is most problematical. If, however, there is still any doubt as to the reliability of the conclusions of such investi- gators as Miller and Hugenschmidt, opinions may be formed from other considerations. At least it may be said that if there is any antiseptic action m the saliva it mvist be exceedingly weak, and in view of the fact that the mouth of man, and animals also, whether susceptible or immune to caries, always contains micro-organisms in abundance, it may be doubted whether the search for antiseptic properties in saliva is likely to lead to positive results. But it does not necessarily follow that because the saliva is not antiseptic it is not antagonistic to the uiception of caries ; thus the alkaline salts may to a certain extent inhibit the carious process ; and Joseph Head comes experimentally to the conclusion that the saliva has decided powers of protecting the teeth from acid decal- cification, which can hardly be e.xplaitied by its contained alkaline salts. In this there may be a partial explanation of the fact that the starches are less harmful to the teeth than the sugars, because starch cannot give rise to acid fermentation except when incorporated with saliva, while sugar is convertible into acids solely by the action of micro-organisms. It has been contended b\' F. VV. Low that sulphocyanide of potassium prevents the in- ception of caries because it is a solvent of the gelatinous plaques, or that it inhibits the plaque formation which, it is held, precedes the 292 decalcification of the enamel (I). This subject has not been fully worked out, however, and the results are in a certain proportion of cases conflicting (27). Similarly, the class of micro-organisms con- tained in the mouth may be influenced by the saliva and mucus. The albuminous mucus, salivary corpuscles, and desquamated epithe- lium, form a nutrient medium for certain bacteria, which find albuminous material the most suitable soil for tlieir growth ; and as there is no carbo-hydrate (normally) secreted by the salivary or mucous glands, bacteria that find their nutrient medium in carbo-hydrates are not encouraged ui their development. It may be presumed from this, and from the fact that the fermentation set up by saliva rich in mucus gives place more rapidly to putrefaction, that mucus contains a relatively larger proportion of saprogenic bacteria than the clear saliva. The glutinous coating of a somewhat slippery nature (the basis of which is probably mucin) to be found on the less rubbed parts of the teeth may also help to prevent the lodgement of certain food particles, and thus protect the teeth. The nature of this coating is no doubt very variable. It must contain different species of bacteria, but except when it is habitually bathed in fermentable carbo-hydrates tliese bacteria are probably not of a pronouncedly acid-forming character ; and being somewhat imjaegnated with saliva and salts, \\hich when excessive in amount result in the coatmg becommg soft tartar, it is no doubt inimical to the carious process. When tested witli litmus paper this coating shows a distmctly alkaline reaction, and when it is artificially brushed away from the necks of the mcisors, canines, and pre- molars, these teeth appear to sliow a distinct predisposition to become carious. A totally different view of the significance of this coating is held by Black (3). He strongly suspects that this glutinous deposit may afford coverings, which will shield micro-organisms and their products from the washmgs of the saliva. But, inasmuch as carbo-hydrates are presented to the outside of this slippery coating, they are liable to be washed away altogether ; it thus seems difficult to see how this coatmg can aid the micro-organisms in the retention of acid in contact with the teeth. It should be noted that this glutinous coating is entirely different from the gelatinoid plaques formed by certain micro- organisms, and from the gummy coatmg which is formed by the mannitic fermentation of cane- sugar. This latter coatmg is highly favourable to the inception of caries, because it prevents the saliva diluting, or washing away, the acid formed from the sugar under the gummy coating. In general, it should be noted that the saliva and mucus are secreted in quantity and quality proportionate and appropriate to the necessity for the removal from the mouth of certain sub- stances, wliich if they lodged unduly would be injurious to the teeth. Thus, acids and carbo- hydrates, more especially the sugars, stimulate a copious flow of saliva. Caries may be said, in general, to be mduced by those agencies that hinder the cleansmg action of the saliva, such as the depth of the crevices of the teeth, or the nature of the food itself — for example, excess of sugar, or absence of fibrous matter, «hich during mastication helps the saliva to reach relatively inaccessible crevices in the teeth. SUSCEPTIBILITY AND IMMUNITY Disappointment may be felt that the present knowledge of tlie chemical constitution of the teeth and of the oral secretions does not throw mucli light on the question why the teeth in some moutlis succumb to caries while in others they remain free from this disease, and tliat, notwith- standing the most persistent and careful investi- gations, the question of " susceiJtibUity " and " immunity " is still as far from solved as ever. But the negative results of these investigations appear to confirm the beliefs of those who think tliat the existence of susceptibility and immunity has been assumed, \\hen a simple confession of lack of knowledge of the aetiology of the dis- ease was alone justified. Whetlier in the future anything at all analogous to susceptibility and immunity, as iniderstood in medical literature, may be discovered, Ls doubtful. At all events, at the present time such discovery has not been made, and in the present state of knowledge susceptibility or immunity should never be assumed, at least untU all the conditions that are known to promote the undue lodgement of fermentable carbo-hydrates have been mvesti- gated. Unless the well-known conditions that predispose to the undue lodgement of food are included, such as pits, fissures, malarrangement of the teeth, arrested flow of saliva, etc., probably it is umiecessary to believe that there is any appreciable susceptibility and immunity to caries at all. It has been seen that what was once considered hereditary predisposition is now recognized to be entirely, or almost entirely, a matter of similarity of environment in families, and even in races ; and this was what most necessarily demanded the assumption of a con.stitutional susceptibility to the disease. Since the kinds of differences in foods and dietetic customs that lead to different results as regards caries have become more accurately known, it has been recognized that what once would have been attributed to susceptibility and immunity may now be attributed to variations in diet and dietetic habits. Those who assume that susceptibility or immunity 293 results from the constitution of the saliva are confronted with the fact that caries is a markedly local disease, and may be advancing rapidly in some teeth while it is actually becoming arrested in others. Indeed, in one single tootli the greater part may frequently show arrested caries \\hile at one or two points caries may be actively progressing. Under the impression that there was practi- cally no such thing as inherent or constitutional susceptibility to caries — no matter how much the parents might have been afflicted \\ith the disease, — and basing a system of prevention on the aetiology of the disease as presented in these pages, the writer persuaded the parents of four- teen infant children to adopt the method he sug- gested and to test it. In every one of these cases the children \\ere free from all traces of caries at ages varying from five to seven years (38). RELATIVE LIABILITY OF DIFFERENT TEETH TO CARIES The relative liability of the various teeth to caries is a subject that has received con- siderable attention. Generally the relative fre- quency of caries in different teeth has been deduced from the number of extractions of particular teeth on account of caries. Con- sidered in this way there are, of course, sources of inaccuracy; thus a first molar, for example, is likely to cause much more severe toothache than a third molar, because of its lial)ility to become carious in early life ; this would lead more certainly to its extraction. 80 again, carious third molars are more likely to remain during life ; or, indeed, they may never have erupted at all when death is premature. Never- theless, on the whole a fairly good general know- ledge of the prevalence of caries in particular teeth may be arrived at in this \\ay. The following analysis of over 30,000 extractions made by Wallis and Pare indicates the relative frequency of caries in the various teeth (33. p. 229)— Per C«nt. 1st upper molar .... 18'7 1st lower molar .... 17'4 2nd lower molar. . . . 11-62 2nd upper premolar . . . 8-33 2nd upper molar . . . 8'04 1st upper premolar . . . 7'62 2nd lower premolar . . . 5-58 3rd lower molar .... 4-4 3rd upper molar. . . . 4-38 Upper lateral incisor . . . 3' 37 1st lower ])remolar . . . 3-07 Upper canine .... 286 Upper central incisor . . . 2'51 Lower canine .... '78 Lower lateral incisor . . . -62 Lower central incisor. . . '44 From the foregoing table it may be observed that the teeth most predisposed to caries are those that tend to induce the prolonged lodgement of food and micro-organisms. Thus, for example, the lower incisors and canines are particularly unlikely, both from the manner in which they cut through the food and from their shape, to favour the lodgement of food, whUe the molars on the other hand are par- ticularly liable to induce the undue lodgement of food, and consequently to become carious. Further comment on this aspect of the subject (36) is hardly necessary, for in general it may be said that if the movements of the jaws, lips, cheeks, and tongue, together with the normal forms and arrangement of the teeth with regard to each other and the surrounding mucous membrane, are considered, it is obvious that the lial)ility of the various teeth to caries is just what might be de- duced from a consideration of the aetiology of the disease as already set forth. If, further, note is taken of the parts of the teeth (3) tliat are most frequently attacked, the conclusion is deduced that in proportion to the relative liability of any particular part of a tooth to lodge food, so, to a corresponding degree, is dental caries likely. In conclusion, a word maybe said with regard to the cause of caries from the patient's point of view. Patients constantly ask why the teeth of the present generation are so bad, and dentists should always be willing to answer the question. But the intelligent layman only wants to know — and ought accurately to be told — important points. Consecjuently he need not be confused with an exposition of conditions that are present whether the disease occurs or not. To him the cause of a disease is that or those controllable antecedents, which being present, the disease invariably follows. Atten- tion should therefore be directed to the abnormal or prolonged lodgement of fermentable carbo- hydrates hi the crevices of, and between, and about, the teeth, for this condition being present, the disease will sooner or later arise. It is, moreover, the alterable condition that is of importance from the point of view of preven- tion. This ' condition explains whj' the teeth of the present day are so bad, for the cooked and prepared foods as so generally consumed tend to lodge unduly and undergo fermentation under circumstances that lead to the destruc- tion of the teeth. Technical knowledge is not really required to appreciate the cause of caries when presented thus, and it is of cour.se the duty of the profession to the public to see that they do become acquainted with the knowledge that for their own welfare thev require. J. s .w. 294 BIBLIOGRAPHY I (21 (1) Beach, J. Wright. Saliva and Tooth Decay. Dental Cosmos, 1908, Vol. L, p. 469. , (22 (2) Bennett, Norman G. Aetiology of Lamellar Cataract. Trans. Ophth. Soc, Vol. XXI. (3) Black, G. V. Operative Dentistry. Vol. I, p. 136. (23; (4) Black, G. V. Chemical and Physical Properties of the Teeth. Dental Cosmos, 1895, Vol. XXXVII, p. 353. I (24 (5) Bunting, R. W. Dental Caries. Dental Cosmos, 1909, Vol. LI, pp. 314-317. (6) Cheadle, W. B. Artificial Feeding and Food (25 Disorders of Infants, p. 45. (7) CoLYER, J. F. Recent Views on Heredity and Variation in Relation to the Study of Disease. (26 Dental Becord, 1908, Vol. XXVIII, p. 1. (27 (8) CoLYEB, S. The Problem of Dental Caries. Dental Becord, 1904. Vol. XXIV, p. 301. (28 (9) Fbiel, G. Tlie Teeth of South African Natives. Brit. Dent. Jour., 1910, Vol. XXXI, p. 729. (10) Gasmann. The Chemical Composition of Teeth. (29 Zeitschrift f. Phys. Chcm., 1908, Vol. LV, p. 455. (11) GoADBY, K. W. Mycology of the Mouth, p. 139. (12) Head, J. Miller's Observations on the Wasting (30 of Tooth Tissue. Dental Cosmos, 1907, Vol. XLIX, p. 801. (31 (13) Howe, H. L. Hyper-acidity of Saliva. Dental [ Cosmos, 1906, Vol. XLVIII, p. 143. [ (32 (14) HuGENSCHMiDT, A. C. Experimental Study of the Different Modes of Protection of the Oral (33 Cavity against Pathogenic Bacteria. Dental (34 Cosmos, 1896, Vol. XXXVIII, p. 797. (15) Hi'NTEH, R. B. Condition of School Children's Teeth and their Food during Infancy. Brit. (35 Jour, of Dent. Sci., 1908, p. 632. (16) Hutchison, R. Principles of Dietetics, p. 205. (36 (17) Kirk, E. C. The Predisposing Factor in Dental Caries. Dental Summary. Feb. 1903, p. 93. (37 (18) Miller, W. D. Immunity to the Diseases of the Mouth and Teeth. Dental Cosmos, 1903, Vol. (38 XLV, p. 88. (19) Miller, W. D. Further Experiments in Relation (39 to the Question of Immunity. Dental Cosmos, 1903, Vol XLV, p. 695. (40 (20) Miller, W. D. Micro-organisms of the Human ' (41 Mouth, pp. 12, 14. [ Miixer, W. D. Study of Certain Questions relative to the Pathology of the Teeth. Dental Cosmos, 1904, Vol. XLVI, p. 990. Miller, W. D. Study of Certain Questions relative to the Pathology of the Teeth. Dental Cosmos, 1905, Vol. XLVII, p. 18. Mummery, J. R. Relation of Dental Caries to Food, etc., among Aboriginal Races. Trans. Odont. Soc, 1869-70, Vol. II. p. 7. Mummery, S. Experiments on Susceptibility to Dental Caries. Proc. Boy. Soc. of Med. (Odont. Sec), 1910, p. 71. Mummery, S. Heredity and Dental Disease. Discussion. Proc. Boy. Soc. of Med., 1908, Part III, p. 119. Pedley', R. D. Hygiene of the Mouth, p. 21, Report of Committee on Scientific Research. Dental Cosmos, 1908, Vol. L, p. 1418. Rose, C. The Teeth of the Inhabitants of Delarne and Gothland. Brit. Dent. Jour., 1905, Vol. XXVI, p. 119. Rose, C. Deficiency of Mineral Salts and Degeneracy. Dental Cosmos, 1909, Vol. LI, p. 135. Smith, Elliott. The Cause and Prevention of Dental Caries. Lancet, 1908, p. 1846. Tomes, C. S. Dentine and Enamel. Trans. Odont. Soc, 189.5-6, Vol. XXVIII. p. 114. Tomes, C. S. Chemical Composition of Enamel. Jour, of Physiology, 1896, p. 217. Tomes & Nowell. Dental Surgery, 5th ed. Turner, J. G. Causes, Effects, and Treatment, of Dental Diseases in Childliood. Brit. Med. Jour., 1907, p. 1488. W.allace, J. Sim. Cause and Prevention of Decay in Teeth, p. 7. Wallace, J. Sim. Supplementary Essays on the Cause and Prevention of Dental Caries, p. 46. Wallace, J. Sim. Diet in Infancy and Childliood. Brit. Dent. Jour.. 1908, Vol. XXIX, p. 641. Wallace, J. Sim. The Prevention of Dental Caries, p. 33. Watson, Chalmers. Meat Diet and the Teeth. Lancet, 1907, Vol. I, p. 119. fl^EisM.ANN, A. The Germ Plasm, p. 20. Williams, L. Formation and Structure of Dental Enamel, p. 79. CHAPTER XIV THE PATHOLOGY OF DENTAL CARIES The process and progress of dental caries — essentially external in its origin — is one of disintegration and loss of substance of the teeth, prodnced and accompanied by chemical means and bacterial action in the mouth — changes which can be experimentally repeated in vitro. Its commencement is clinically noted by a softenmg of a mmute portion of the hard circumference of the enamel, which generally. whether it be occlusal or mterstitial, is easily detected by the carefid examination with an explorer of the fissure, sulci, pits, and the in- equalities of surface. The presence of a small area of discoloration does not necessarily imply the mception of the condition. If situated on the coronal portion, this would appear to indicate some colour change in Xasm^-ths membrane, either by the action of cliromogenic bacteria, sucli as the liacillu.s lititiejuckns /luurcscens molilis or jwn-motilis, the Bacillus prodigiosus, the Staphy- lococcus pyogenes aureus or citreiis ; or by adven- titious materials taken into the moutli, such as the oil of nicotine ; or by an organic change due to the perversion of the salivary secretions. On approximal surfaces, as for example in the premolars, it is common to note that whereas, say, a cavity of " decay " has occurred on the distal portion of the first premolar, there is no actual breach on the medial aspect of its posterior neighbour, but that a more or less small area of brown or black stain Ls observed. This is, probably, merely a superficial chromatic alteration, which is of little or no importance. The first real indication of the onset of caries is, to repeat, the decalcification of the enamel, whereby the fine extremity of an explorer can enter the sufficiently disintegrated tissue. The softenmg may be, and often is, accom- panied by a pigmentation, or loss of translu- cency or polish of the parts. On exposed, fiat, or convex surfaces an opaque condition may obtain. In the fissures and pits of the occlusal or buccal surfaces, especially in the molar region of the dental arches, the former changes are frequently seen ; and in the later stages the white opacity itself may assume a greyish or more or less pronounced brown or yellow tinge. The "bacterial plaques" of some authors, notably Black and Leon Williams, are believed to be due to the zoogloea formations of masses of bacteria, which, collecting in favourable situations, are able, by a precipitation of muci- laginous compounds, to focus in a more or less widespread but yet well-defuied fashion the operations of the destructive agencies (15). But all writers do not recognize the existence of these so-called plaques, as such, and Kirk has recently shown that it is possible to manufac- ture bacterial plaques to any size or extent (8). If allowed to continue unchecked, dental caries proceeds at a varying rate, m the same mouth, and in similar teeth; or it becomes spontaneously arrested. If the former occurs, the loss of the enamel at the original pouit of entrance of the destroying medium is succeeded by invasion of the dentine, when, on account of its tubular character, the condition advances much more rapidly, extendhig downwards and laterally, and thus undermining the enamel to a certam extent. If it still continues, areas of dentine become devastated and disappear, 295 296 and subsequently the enamel, having been deprived of its support, fractures at its edge, and shares the same fate. If tlie condition is arrested, through mcreased physiological resistance of the parts as a conse- quence of an amelioration of the health of the individual, the process and progress simul- taneously cease, and the teeth, denuded of the main portions of their crowns, become perman- ently discoloured, and do not admit of penetra- tion by the point of a steel instrument, whUe the previous softness of the tissues now gives place to a polished density which is truly remarkable. Fig. 388. — An early stag<^ in cariet: E, Enamel ; D, Dentine. X MICROSCOPICAL PHENOMENA Nasmyth's Membrane in Carles. — It is not known whether tlie translucent pellicle of Nasmyth's membrane (its outermost epithelial lamma of cells is a negligible structure where caries is concerned) becomes peptonized by the bacterial action. It is highly resi.stant to acids. If, however, it is of the same chemical constitu- tion as the sheaths of Neumann in the dentine, it is capable of being acted upon by the enzymes of the micro-organisms and split up and dis- solved, probably with the production of a small quantity of amido-acetic acid. The role played by Nasmyth's membrane with regard to caries is not at present understood. It is, however, extremely probable that were tliis tissue to remain intact on the surface of the enamel, no penetration by micro-organisms could take place. It is too thick, measuring generally 50 /x in thickness, not 1 /x or 2 /x as KoUiker described ; but it is so loosely adherent to the periphery of the enamel, that it is extremely easily damaged by mechanical agencies, and bacteria are at once brought into immediate contact with the enamel. In the writer's opinion, however, it constitutes the first line of defence against dental caries. It may be argued that on approximal sur- faces, where, it may be surmised, no traumatism could exercise much, if any, effect on the teeth, and m the depth of pits and fissures, etc., caries should never be found. It is common knowledge that interstitial caries is of more frequent occurrence than that on the labial, buccal, or lingual surfaces. This frequency may be ex- plained by the belief that, once having effected an opening through the pellicle of Nasmyth's membrane — say, for instance, on the summit of a cusp of a premolar — the micro- organisms would quickly travel down to the future site of caries. Black's gelatinous plaques, which both he and Leon Wil- liams lay so much stress upon, are probably no- thing more nor less than fragments of this mem- brane, which, covered with bacteria, still re- main adherent to the surface (1). Walkhoff has demon- strated the presence of organic pigment on Nasmytirs membrane (14). This is probably identical with tlie stain seen sometimes on the teeth of chUdi'en, which does not necessarily indicate the first stage of caries. It is probably generated by the chromogenic bacteria before mentioned, and is more adherent to the translucent pellicle of the membrane than to the free surface of the enamel itself, occurring, curiously enough, most frequently on the labial surfaces of the maxillary incisors — a fact which would suggest that the colour was due to the action of an air micro- organism. The {precise effects of caries on Nasmyth's membrane remain as yet unknown. Many text-book statements are purely conjectural. Pickerill believes, perhaps with some reason, that it acts as a dialysing membrane to certain structures, which may disintegrate the surface of the enamel, and pave the way for carious changes — an hypothesis that is apparently sliared of enamel 45. 297 by Tomes and Nowell (12). But the difficulties of proof are, at present, exceeding!}' great. Microscopically there is nothing to distinguish the structure of the component parts of the mem- brane in the case of normal tLssue, and in the case of that associated witli caries. Enamel A. — On the Occlusal Surfaces. In vertical section of the crowns of teeth in which the earliest phenomena of caries appear, it is obvious that these occur in the neighbourhood of the fissures. Examination of a deep fissure nearly prolonged to the amelo-dentiiial junction, reveals the presence of broad brown patches similar to the " white spot " surrounding the entrance. These extend some distance out- wards. Beneath any remaining shreds of Nasmyth's membrane the colouration is not so intense ; it is the innermost region of the affected area that is most deeply pigmented. Beyond this band an area of unstained tLssue supervenes between it and a large territory of coloured enamel. In shallow pits with a less truncated aperture the pigmentation is more pronounced, and there is but little lateral extension ; it may happen that the area of unstained tissue is absent. The sub-lying dentinal tubules are rendered inconspicuous, their refractive indices approximating to that of the matrix ; the colourless area may, how- ever, be present. As loss of surface takes place the discolora- tion increases, until the enamel that .still remains undisintegrated assumes a yellowish or cinnamon colour ; it thus occupies the base. so to speak, of a triangle, the apex of which is directed downwards towards the dentine. The figure itself is formed by the distribution of the dentinal tubules, which are occluded with air and debris, as they show up most clearly under a low power objective of the microscope. There may be an actual separa- tion of enamel and dentme at their junction. Fragments of Nasmyth's membrane always remaui at the bottom of a pit or fissure. B. — On Approximal Surfaces, and on the labial, but seldom on the lingual aspects of the teeth, the phenomena of '" white spots " appear. The pathological process is probably identical with that just described. The ap- pearances presented are as follow : A band of pigmentation of varying thickne.ss extends into tiie enamel in an arcuate form, having on both sides paler zones, of which the innermost is perhaps the more translucent of the two. Whether this represents a decalcification or not, is difficult to determhie, but it probably does, the pigmented band being due most probably to post-mortem changes common to all dead matter. The enamel rods are them- selves exceedingly granular, having lost a 10* large part of their characteristic structure. Individually they are pigmented, and there is irregular fusion of their enamel globules. By transmitted light a " white " spot is rendered a dark spot, as light penetrates but feebly through the enamel rods and their cementing substance. Not all " white spots " are evidences of caries. Those seen in permanent teeth may have a different origin. J. G. Turner has shown that a septic condition of the deciduous series wUl, at times, leave a mark upon the crowns of their successors. He attributes many Fig. 389. — Caries of the enamel. II, Micro-organisms; E, DecalciBed enamel. X 90. of the discoloured patches classified as " white and coloured spots "' to this cause (13). The means by which the enamel rods beconie detached from one another, and thus begin to fall away, is the action of the caries-producing micro-organisms. A multitudinous tunnelling of the tLssue of parallel-sided or V-shaped channels of different lengths penetrates the line of least resistance, viz. that of the cementing substance, and not at first— unless the tissue is incompletely developed— the actual axes of the rods. 'These channels at their outer ends mav measure more than 5 /u, in width ; but this naturally in acute caries Ls ([uickly exceeded in amount, and in chronic conditions less rapidly. The morphological detaUs of the rods undergo 298 less change in the former than in the latter class of caries, where they assume, according to Leon Williams, a "sponge-like " structure, and viewed by transmitted light appear to be greyish or discoloured, and by reflected light, white. By the absence or presence of colour, therefore, an acute or chronic condition may usually be diagnosed. As caries advances, the transverse striae of the individual rods become more pronounced. " Secondary enamel decay " is thus termed from the fact that an extension from within outwards of the carious processes has taken place. It consists almost enthely of broken- down rods and ma.sses of bacteria. Between this area and that just described, the changes M, Micro-organisms in a tube ; LF, Liquefaction focus. X 450. in the structure of the enamel are truly re- markable. Tlie rods have lost their outlines, are exceedingly granular, are broken up, and are either isolated or confluent — all evidences of the structure of a zone of complete de- calcification. Dentine The pathological variations in the dentine, similarly to those of enamel, are concerned with two distuict chemical and histological elements. Unlike tho.se of enamel, however, the presence of tubes renders the process, perhaps, more easily comprehensible. The changes affect the walls of the dentinal tubes, the matrix, and the inter-globular spaces. The tubular nature of human dentine permits the free entry of bacteria, and as the process deepens, its rate increases, on account of the gradual enlargement of the tubes as they approach the pulp. Tlirough the peptonizing action of the bacteria, the sheaths of Neumann become thickened, their elastin being probably converted into immeasurable quantities of amido-acetic acid. That there is a definite swelling and dilatation of the sheaths of the tubes admits of no doubt, the thickening being due to the action of the bacteria on the walls themselves, and also on the adjacent matrix, which, becoming decalcified and therefore soft, allows the expansion of the diameters of the tubules. A "liquefaction focus" is an area where the matrix is softened to such an extent that the collagen, rid of its lime salts, has probably become of the nature of calcoglobulin. The tubules here are so enlarged that apparently the mechanical accumulation of bacteria and their pro- ducts causes their physiological resistance to be diminished, and they break and fuse with their neighbours. Thus are pro- duced, in the fir.st instance, oval or balloon-shaped bodies in the courses of the tubules, and usually, but by no means invariably, with the longer diameter placed longitudmally. A continuation of the process involves a greater number of tubules and a more extensive portion of raatri.x, and ultimately ends in tlie formation of a small cavity. The matrix, at all times, suffers first ; the tubules are secondarily affected. The microscopical features of these enlarged tubules give the so-called " pipe-stem " appearance to carious dentine. The chief interest in the changes in the matrix lies in the controversy that has arisen over the cause of the .so-called "translucent zone". Two schools of thought have occupied themselves with this question : (i) the Vitalists, who consider that it represents the physiological resistance of dentme to morbid changes, being due to an actual calcification of the dentinal fibrils — the belief of Sir John Tomes, Miller, Walkhoff, Magitot, etc. ; and (ii) the others, who deem it an area of partial decalcification produced by the advancing army of bacteria, with consequent and concomitant obliteration of the tubules, through tlie swelling of the matri.x. Wedl, Black, Charles Tomes, Leber and Rottenstein, and F. J. Bemiett, among others, hold this view. Into this diversity of opinion it is unnecessary, here, to enter. Suffice it to say that the facts connected with it would appear to be that 299 around the cone-shaped carious region there is an alteration in the appearance of the dentine, wiiicli becomes more transparent and indicates an increase in the homogeneity of the tissues. If this be compared with adventitious dentine — which is so frequently an accompaniment of dental caries, an effort on the part of tlie pulp to withstand the bacterial intrusion, as described in Chapter XVI — it is seen that it possesses the same lustre and translucency, prol)- ably indicating that its chemical constitution is similar, if not identi- cal. Translucent zones occur at the presence of opaque zones in the near proxi- mity of the translucent zone, which seem to arise from the uiclusion in the tubules of certain times in abrasion of the teeth. It would be thought that all doubt about the method of their formation would be set at rest by ascertaining ^^hethe^ the tubules were patent or otherwise — by immersion of carious teeth in aniline dyes or carmine solutions. This apparently has been done by the advocates of both hypotheses, with the astonishing result that both admit the possi- bility of the staining of the interiors of the tubules in many instances. In the vanguard of the advancing micrococci, the traversing of the inter-globular spaces by the tubules can sometimes be beauti- fully observed. At an early stace, individual KiG. 391. — Mi?^ mm Fig. 394. — Transverse section of carious dentine. C, Micro-organisnas in tubes, x 180. — those growing only at very high or very low- temperatures , or on media very poor m nitrogen, perhaps excepted — will do so if the necessary 301 degree and form of immunity is not present. A pathogenic organism is one which can grow in the living tissues, and it can do so only because those mechanisms of immunity which are sufficient in the case of the saprophytic bacteria are powerless to resist it ; but ill most cases, a liigher degree of immunity can be produced artificially, and the microbe in question then becomes non- pathogenic to that particular animal. So, too, will the bacteria ordinarily regarded as non-pathogenic. Under certain circum- stances, some of whicli are known and some still unknown, the resistance of the body or of a part of it may be broken down to such an extent that these organisms may gain access, flourish, and give rise to disease. Thus, the Bacillus proteus may give rise to phlebitis, growing in the thrombosed vein, and giving off toxins which have an injurious action on the ti.ssues " (3). If these data are remembered, it will be at once obvious that the intricacies, such as those afforded by a study of the real caries-producing micro-organisms and their actions, are very great, especially when one is reminded that the bacteria of the diges- tive tract enter the mouth. At present it is impossible to say why many persons who are ignorant of the necessities of ordinary oral hygiene, and also never perform the usual dental and oral toilet. are free from dental caries ; and the opinion. of the immune individual is so great as to render their action inoperative, is purely conjectural. Fig. 390. — A late stage of caries of the dentine. C, Cavity; P, Pulp-chamber. X 45. Fig. 395. — Transverse section of carious dentine, x 250. that either a special bacterium or group of bacteria provocative of dental caries may e.xist, or that the physiological resistance on the part As far as is known, however — thanks largely to Miller, Goadby, and others — it may be briefly stated that the micro-organ- isms foiuid in the superficial parts of carious dentine are either liquefiers of that tissue, when it has already been decalcified to a certain extent, or are merely acid-producers. To the former groufj belong, in alphabetical iirder, the Bacillus furvus. Bacillus gingivae jii/ogenes, Bacillus liquejaciens fluorescens tnotilis ; Bacillus mesentericus fuscus, ruber, and vulgatus ; Bacillus plexiformis. Bacillus suhiilis, and Proteus vulgaris : to the latter, the Sarcina alba, auranliaca, and lulea ; Staphylococcus albus and aureus, and Strepto- coccus brevis. Those discovered in the deeper layers of dentine are the Bacillus necroden- talis. Staphylococcus albus, and Staphylococcus brevis. A third class includes the chromo- genic bacteria mentioned on an earlier page. Of the above, the Bacillus liquejaciens fluorescens motilis, the Bacillus plexiformis, and the Proteus vulgaris are Gram-negative, all the others being Gram-positive. Round the edges of carious surfaces are found 302 many thread-like forms. These often include such organisms as tlie Leptothrix innominata and racemosa, Leptothrix buccalis maxima, the Strepto- thrix buccalis, and the vibrios described as the Spirillum sputugenum, and Spirochaete dentium, which may be identical. Choquet has isolated five varieties of bacteria from beneath fillings (2). Caries of Cementum. — Dental caries occurs less frequently here than in the two other hard tissues. The reasons are mainly anatomical. If the periodontal membrane remams in situ over the roots, and if it becomes inflamed, or otherwise undergoes morbid changes, it is possible — though as yet not demonstrable nor demonstrated — that a bacterial infection might Fig. -Ml -Vi-'i'i ical snclitm t)l' .■ti;iiii<] J E, Enamel; D, Dentine. X 90. pass into the substance of tlie cementum. Sections can be obtained for microscopical examination of this tissue covering the dentine of the palatine roots of maxillary molars, when, on account of absorption of the bone of their sockets, and denudation of the sub-lying parts, the cementum becomes exposed. A certain amount of softening occurs, but this differs, physically and chemically, from the like phe- nomena that are seen in enamel and dentine, although it more closely approaches that in the latter tissue. Cocci have been demonstrated by Gram's method, in these circumstances, in the short canals in which the Sharpey's fibres lie. The means of penetration is more or less mechanical. Small cocci gam quite an easy entrance into the widely-open apertures of the canals and proceed for a short distance only, for these channels are, roughly speaking, trumpet-shaped, and narrow down very rapidly as they extend inwards to the homogeneous layer of the cementum. Thread- forms have never been seen entering the canals. " Arrested " Caries. — The macroscopical char- acteristics are recognized without difficulty by the dental practitioner ; but little is known concerning the physical, chemical, and histolo- gical phenomena, or their courses. The enamel, dentine, and cementum, together with the pulp, may all be influenced by the condition. For if caries has advanced but little in a tooth, the enamel is often partially retained. Permanent molars afford good opportunities for the exam- ination of the microscopical changes. They should be treated by the Koch- Weil method, which here pos- sesses the advantages of en- abling the observer to dis- tinguish between the chemical and physical alterations of teeth affected by acute and chronic caries. In such cases the enamel is stained uniformly for varying depths. In its widest portions, certain areas over the cusps of the dentine may remain un- coloured, although the whole of the superficial parts of the tissue are stained. Under a high power, the stained por- tions show very clearly — the cement mg substance between the individual rods appearmg as dim black longitudinal Ihies running in a parallel direction on a red background. The transverse striae of the rods are ^ird (-iinrs ■'. indistinguishable, the struc- tural alterations giving them a homogeneous appearance. In the unstained areas, the boundaries of the rods are observed without any difficulty, but they themselves, while losing their transverse mark- ings, are distinctly granular. The brown striae of Retzius, as well as Schreger's lines, are invisible in stained sections. Beneath the amelo-dentinal junction, which may itself, at times, be pigmented, a thick band of unstamed dentine is found. Nearer the pulj], the whole of the dentine is coloured a bright carmine, which differs in intensity from the scarlet of the enamel. It is quite prol^able that the cu'cumferential dentinal tubes have their lumina comjjletely obliterated, for their' out- lines are absorbed in the general homogeneous appearance of the matrix. Here and there, in many places, their shapes are well defined by the presence of broken or contiiuious greyish lines 303 filling tlieir interiors. The stained portions contain multitudes of delicate granules of the staining reagents. In the pulp, adventitious dentine may or may not be found. The breach of surface of the enamel does not, ho« ever, seem to produce a correspond- ing development on the part of tlie pulp in early cases, because the formative cells of the latter organ have not been called upon to provide a physiological barrier to tlie carious attack. The pulp is not inflamed. If, ho\\ever, events should occur rapidly, and acute conditions should super- vene upon the arrested state, the usual micro- scopical changes of acute caries are evident. The dentine and cementum of the radicular portions of the teeth are frequently unstained, showing changes somewhat similar to those of senile teeth, or those affected by disease of the periodontal membrane. There is no pene- tration of reagents, and large uncoloured areas are found. Defective Formation of Teeth. — The developmental defects of enamel may or may not assist the process and progress of caries. Ac- cording to the envkonment, and not so much the struc- ture of enamel, does this occur. Black has seen '"white spots", and "dead- paper wliite " enamel, free from caries ; thLs he con- siders to be due to lack of cementing material between the individual rods. He wTites : '"This condition of the enamel had not rendered the teeth more than ordin- arily liable to caries, etc." If the colouration is of a dead lustreless character, Nasmyth's membrane is absent ; if not, it is present as usual. Unusual Situations for Dental Caries. — As throwing some light on the aetiology of this condition, it is necessary to observe and note cases that present bacteriological and cliemical changes in parts of the teeth that are commonly unaffected, viz. the admittedly self-cleansing surfaces, such as the labial aspects of the anterior teetli, the extremities of the pointed cusps of the canines, the lingual sides of the cro\\iis of the mandibular incisors, etc. The writer has per- sonally observed instances of caries commencing to attack, among others, the palatine surface of the second left maxillary permanent molar in a mouth otherwise apparently innnune ; the lingual surface of the left maxillary deciduous incisor ; the disto-buccal surface of the second left maxil- lary permanent molar ; the labial surface of the first right mandibular permanent incisor ; and the tip of the maxillary permanent canine, etc. The collection of evidence such as that just adduced is much needed to help to elucidate many of the still serious problems surrounding the pathological phenomena of dental caries. A. H-S. BIBLIOGRAPHY (1) Black. Operative Dentistry, Vol. I, 1908. (2) Choquet. a Study of Certain Microbes in Dental Caries. Proc. Int. Dent. Cong. Paris. 1900. (3) Emery. Immunity and Specific Therapy, 1909. (4) GoADBY. The Mycology of the Mouth, 1903. (5) Hewlett. A Manual of Bacteriology, 1898. (6) Hopewbll-Smith. The Histology and Patho- Histology of the Teeth and Associated Parts, 1390. Fig. 398.- -Vertical section of enamel of " arrested caries ' E, Enamel ; D, Dentine. X 90. (7) Hopewell-Smith. The Pathology of the Pulp in Relation to Clinical Dental Surgery. Dental Cosmos, 1909, Vol. LI, p. 13h6. (8) Kirk. A Consideration of the Question of Sus- ceptibility and Immunity to Dental Caries. Dental Cosmos. 1910, Vr>l. LII, p. 729. (9) Low, F. W. Prophylactic Value of Potassium Sulphocyanate in Saliva. Dental Cosmos, 1911. Vol. LIII p. 12(59. (10) Miller. The Micro-Organisms of tlie Human Mouth, 1894. (11) Rose. Deficiency of Mineral Salts and De- generacy. Dental Cosmos, 1909, Vol. LI. (12) Tomes and Nowell. A System of Dental Surgery, 1906. (13) Turner, J. G. Aetiology and Pathology of Defects of Teeth of Children. Brit. Med. Jour., No. 23, 1907. p. 1488. (14) Walkhoff. Mikrophotographischcr Atlas d. path. Histologic menschlichcr Ziihne 1901. (1.")) Willi \MS. Dental Caries. Dnilnl ('n.inios, 1897, Vol. XXXIX. CHAPTER XY THE PATHOLOGY OF EROSION, ATTRITION, AND ABRASION Erosion may be defined as "a progressive destruction of the exposed surfaces of teeth, ])ro(iiieini; cavities tliat are peculiarly dense and polished, and in the majority of instances hypersensitive on receiving tactile impressions " (5). The causes are predisposing and exciting. Of the former it may be said that, in all pro- bability, certain anatomical relationships of the parts are concerned in its production. Thus if the enamel and dentine do not meet bout a bout, as is commonly the case, but fail to toiicli one another, a minute surface of dentine at tlie necks of the teeth is denuded of its usual covering, and may in certain circumstances prove to be the seat of the lesion. Much con- troversy has arisen over the nature of these circumstances, being mainly due to the con- fusion existing in the minds of some writers, who regard attrition or abrasion of the teeth as synonymous ternis. It has generally been believed that there is a chemical solution of the three hard tissues at their point of junction, caused by the fermen- tation of mucus and the production of acid sodium phosphate, or by an acid fermentation occurring in the material located in the area of denudation, through the action of the mucus. Others, inchuling Miller, per contra, consider it to be entirely mechanical in origin (6); while others again would ascribe it to both these agencies. Kirk has found acid sodium phosphate in vhat he has termed hydroglyphic (graphic) erosion. He considers that this acid is produced during diseases of sub-oxidation, when, as a result of the })erversion of metalxilism, the blood contains more carbonic acid than is normal. In other words, gout and rheumatism are the nuiin prcdisjiosing causes. He would suggest that in genei'al erosion lactic acid is generated, and is the solvent of the enamel ; that in localized conditions acid sodium phosphate or acid calcium piios]>ha(e are the agents involved (2). Black is of the opinion that it seems highly probable that the .solution of the question will be found to be associated with " some systemic dyscrasia ", and that if it is so, "the conditions leading to its strict localization will require explanation " (1). Erosion nuist be clinically distinguished from abrasion and attrition. If the definition just given be accepted, it is possible to describe the maeroscopical appearances as those presented by a wedge-shaped cut or gioove, as if made by a file, at the necks of the teeth, especially on their labial or buccal aspects. \'ery occasion- ally, the lingual surfaces of the crowns of the maxillary canines or premolars may be affected. The cavities are smooth, and brightly polished, and at first possess everted edges, a relatively greater portioTi of the enamel being lost than the dentine. These cavities may be coloured yellow, brown, black, or green, in various shades. Hypersensitive to tactile impressions, but not so much to thermal, chemical, or electrical stinudation. they may rarely be (piite insensi- tive. Pain seems to be associated with the earliest and not the latest manifestation of their development. Histologically, the edges of the cavity exhibit the presence of numerous clefts described by Baume — minute cracks in the dentine, on the floor of the cup-.shaped depressions that go largely to form the component parts of the eroded surface. The enamel margins, at first everted, may later become somewhat inverted, but they never simulate those due to caries. The dentinal tubules that proceed from the floor of the cavity become obliterated — they cannot be stained. Adventitious dentine, here truly a ''dentine of repair", is deposited upon the surface of the pulp that corresponds with the breach of surface. It roughly, also, equals this in amount. It is constructed of an irregular fine-tubed material, and many spaces frequently cxi.st similar to those found in areolar adventitious dentine connected with lesions due to dental caries. As these cavities are seen on labial surfaces, the use of porcelain inlays is generally indicated in the treatment of this conclition. Attrition. — The term attrition may be applied to tiie gradual wearing away of the hard parts of teeth through the physical and physiological agencies of mastication of food. A certain amount of faceting of the occlusal surfaces of teeth is often the forerunner of a larger attrition, which develops in the course of a few years. The teeth of those whose food is hard and unrefined often suffer severely 304 305 from this physioloi^ical masticatory effort. Those of preliistoric man commonly present bri^'htly pohshed flat table-lands of dentine bordered by enamel, whicli have become dis- coloured by age. Tlie niandilMilar incisors of modern man frequently exhibit a narrow strip of brown discoloration ruruiini; in a medio- distal direction. As tiie lesion advances, com- plete wearing down of t lie crowns may sometimes be seen. Tlie enamel that lemains at the edges of the surface of attrition is deeply pigmented, and tlie dentine, naturally stained tlirougliout its entire thickness, presents a sharp smooth surface with its tubules cut tangentially or transversely. Secondary dentine, as distinguished from adventitious dentine, is fretiuently deposited in the Jjulp ; it is generally well formed and consists <)f a fine tube formation with delicate termi- nations, and but few Ijranches. '' Transhicent zones '' may l)e found in tlie ])rimarv dentine. Abrasion means the rapicl wasting and de- struction of enamel and dentine l)y friction set up by the presence of foreign bodies in the mouth. In complete contradistinction from the two jjreceding conditions is abrasion, in which the affected surface of the teeth is rough, dull, flat, extensive, and stained yellow or brown. It speedily b(!Coines carious, atVordhig ideal attachment for the caries-producing organisms. If sections are examined before a bacterial attack, it will be found that the edges of the dentine and cementum have disappeared, and the extremities of the dentinal tidjules are levelled flat w ith the floor of the abraded sur- face, and that the matrix is softened and can be easily stained by means of aniline dyes. This staining can be effected without sectioning the specimens. Micro-organLsms can be demonstrated lining the floor of the cavity. A. H-S. BIBLIOGRAPHY (1) Black. Operative Dentistry, Vol. I, 1908. (2) BuBCHABD. ,4 Text-book oj Dental Pathology and Therapeutics, 1912. (3) CoLYER. Dental Surgery ami Pathology, 1910. (4) Heide. Erosion. L'Odontologie, 1908. (5) Hopewell-Smith. The Histology and Patho- Histology of the Teeth and Associated Parts, 1903. (b) MiLLEB. Experiments and Observations on Erosion, etc. Dental Cosmos, 1907, Vol. XLIX, pp. 1, 109, 225 and 677. (7) Ottofy. Oriental Erosion. Dental Cosmos, 1905, Vol. XLVII, p. 71. (8) Talbot. Constitutional Causes of Erosion, Abra- sion, and Attrition. Dental Cosmos, 1905, Vol. XLVII, p. 47. (9) Talbot. Causes of Erosion and Abrasion, Dental Cosmos, 1907, Vol. XLIX, p. 122.'). CHAPTER XVI DISEASES OF THE DENTAL PULP INTRODUCTORY It can be but a small matter for surprise that the pulp — the most important part of a human tooth, from every pomt of view — should be particularly susceptible and predisposed to disease, when it is remembered that its ana- tomical situation in the animal economy is with- out a like or equal elsewhere, in consequence of its being a peripheral organ, implanted m a peripheral environment, subjected to perijjlieral structural metamorphoses — through the unique vascular and nervous mechanism that it possesses, — surrounded by dense, unyielding walls, and rendered easily accessible to changes of a thermal, bacteriological, chemical, and elec- trical character. The pulp of a tooth — yea, the whole tooth itself — is a peripheral organ — in much the same way, properly sj^eaking, as is the external ear, — a true epidermal structure, placed not always in the oral cavity. The ancestors of fishes had dental appendages, closely homologous with dermal appendages. The mouth of a young dog-fish displays the fact that the oral teeth are the homologues but not the analogues of the spines on its skin ; the saw-fish {Pristis) at the present day possesses certain dental ^\eapons of offence and defence on its rostrum or snout, in addition to numerous minute teeth of a less functional type on the surface of its jaws. In the Gymnodonts the teeth are not covered by the lips. It is not difficult to conceive that Nature intended the teeth to last throughout the life of an animal ; even perhaps that of a member of the highest orders of Mammalia, such as the Primates and Carnivora. But it is a universal rule that the older the creature the less efficient is its masticatory apparatus, on account of the impairment or the lo.ss of its functions, or the shedding of the teeth themselves. That this is so, is further demonstrated by the fact that the osseous foundations of the teeth of man, being peripherally jjlaced in the alveolar processes of the jaws, in which the diploetic bone is, at its margins, of poor construction and quality and feebly supplied vith blood, are anatomically and histologically deficient in those properties that tend to a jiermanent condition of life. A third remarkable peculiarity is sho\^n in the microscopical .structure of the pulp. There is no collateral circulation hi its blood stream, which might, in the event of uijury, attempt to induce a restoration of the vitality of the affected parts ; the veins are valveless and non-collap- sible (10) : no lymphatic system is present; and the apical foramina of the teeth, which transmit the blood vessels, are often so e.xceedingly small in adolescence or old age, that it seems a mar- vellous thing that, m these circumstances, the pulp, and therefore the tooth, is kept alive at all. In addition, the arrangement of the principal elements of its nervous system is such as to render impossible a dkect neurotic control over, or influence upon, the greater portion of the tooth, viz. the dentine. Dentine is secondarily vitalized by lymph — a protoplasmic exudation from the pulp itself, — while enamel, still more remote, is entirely outside the pale of nutrition. Finally, it is, on mature reflection, not an extraordinary thing that it so comparatively frequently, as the march of so-called civilization proceeds, becomes a prey to the attacks made upon it by the changes of temperature that the oral cavity may daily experience, a temperature ranging from zero to 40° C. ; a locus principii for one of the most distressing pains that man can suffer ; a territory constantly invaded by many diseases mainly of an inflammatory character ; and an organ that, more commonly than is generally supposed, undergoes retro- gressive changes. AETIOLOGY The causes of diseases of the pulp may be conveniently considered under the two great classifications. Predisposing and Exciting, of which the former may be cliiefly congenital, and the latter are always acquired and dependent somewhat on the former. The exciting causes may be further sub-divided into — • (a) Tho.se clue to exogenetic disturbances. (h) Those due to endogenetic disturbances. Regarding these, the former largely predomi- nate in point of view of frequency of occurrence, are purely local in origin, and are influenced mainly by pathological conditions of enamel and dentine induced by dental caries (bacteriological) or thermal, chemical, electrical, and other stimu- 306, 307 lation ; give rise to immediately referred symp- toms ; and yield successfully to local treat- ment. The latter are only occasionally met with, are constitutional in origin, and depend largely on general circulatory variations of the blood stream, which act in a limited, circum- scribed sphere. The causes may be summarized as follows— A. — Predisposing : — ■ 1. General. (a) Physiological, e. g heredity, sex, age ; and (h) Patho logical, e.g. marasmus, long-con- tinued fevers, etc. 2. Local. Anatomical individual- ities of hard and soft parts, etc. B. — Exciting : — 1. General. Endogenetic : effects of disease of — (a) Vascular sys- tem, e.g. anaemia, chlorosis, etc.; and (6) Nervous system, e. g. neurasthenia, etc. 2. Local. Exogenetic. [u] Appar- ent : Effects of dental caries ; and (6) Non-apparent : Ther- mal, chemical, and electrical stimulations, etc. '' A. — Predisposing Causes 1. General. — While the relationship be- ^- tween cause and effect is fairly well under- ', stood, it is impossible to ascertain very strictly the nature of the complex jarocesses that may develop in pathology. Especially is this so with regard to those cases associ- ated w ith heredity. The effects of parent- age on progeny are so difficult to follow, and involve such large issues, that general- izations only can properly be made as to plausible beliefs respecting the question. It is true that heredity can be reduced by some to a mere porism ; it is also true that heredity has a control over circumstances that markedly influence the determination m the shapes, sizes. and j)ositions of the crowns and roots of teeth, and that the consequences of disease are fre- quently handed down from father to son. But probably the pulp suffers in this manner very little, although there may be, at times, some recondite transmission of susceptibility to the onset of morbid conditions existing on its part. Regarding sex, one cannot recognize with facUity the differences either macroscopically or microscopically between male and female teeth. In a less degree than the hard parts, it may, however, be assumed that the pulps of the teeth of the two sexes do really differ (11). There is some support for the theory of this differ- ence when the morphology of tlie dental tissues is considered ; and it would seem as if there were some good grounds for the belief that the fact of vascular alterations taking place in women at definitely-recurring intervals of time would constitute a fundamental difference be- tween the two. There is a widespread belief in Great Britain that in parturient women a loss of a tooth coincides with the bii'th of each child. Age plays a somewhat more prominent part in the determination of pulp diseases than the factors just mentioned. There can be no deny- ing that, as time goes on, acute inflammation "t."^ .¥■ Fig. 399. — Calcareous degeneration of deciduous molar. D, Dentine ; P, Pulp, x 45. j becomes rarer, and odontalgia, its main symptom, 1 less frequent, whilst degenerations of various kinds become more and more common. These conditions are not necessarily connected with the actual number of years of the individual's life, but with the age of the tooth and its pulp. Children's deciduous teeth often show his- tological evidences of calcareous infiltration, fibroid degeneration, and other morbid condi- tions coincident with, and incidental to, old age. Predisposition to disease on the part of the l^ulp is dependent on the connections existing between it and other parts of the body, as evidenced by the vascular and, in a limited degree, by the nervous system. The general disorder of these systems at or about the age of puberty in both boys and girls renders the pulp favourable to organic disease. In women at the cata menial periods and the menopause I the same thing happens : repeated elevations 308 of the blood pressure in its substance, succeeded by frequent falls, are aetiological factors that cannot possibly be ignored. Certain chronic diseases in which grave evi- dences of katabolic metabolism occur, in addi- tion to general disturbances of metabolism originating in infections or auto-intoxications accompanied or iniaccompanied by fever, may leave their marks on the life histories of the pulp and dental tissues. Degenerations, such as fatty or albuminous, may arise in this organ during the course of acute general pyrexial or Fig. 400. — Fibroid degeneration of tlie pulp in a deciduous tooth. D, Dentine ; P, Pulp. X 45. apyrexial maladies : degenerations of a fibroid type may follow in the train of anaemia, chlorosis, leukaemia and the like ; and gout, rheumatLsm and allied conditions become a.sso- ciated with nodular deposits of calcified material within its substance. It may be truly remarked that tlie general health of an individual is as important for the welfare of the teeth, and their sockets, as it is necessary for the welfare of the heart, the in- testines, the lungs, the kidneys, and the liver. The teeth suffer as a result of rickets and syphOLs, and of the exanthematous fevers, in the early stages of their growth and development ; and, later, chlorosis, anaemia, long-continued fevers, certam neurotic influences, etc. A vicious circle may absolutely be established by the anaemic conditions of the immediate osseous environment of a tooth, giving rise to atrophy and symptoms of dLsease of the bone and periosteum, and setting up, if infected with jiyogenic bacteria, a pyorrhoea alveolaris, and forms of oral sepsis, \\'hich, in their turn, are lielieved by some to induce, at times, secondary anaemia or be associated with it. In marasmus, which is a pathological lesion when occurring in the young, the pulp may undergo retrogressive changes like other organs ; such are the epidermis, which becomes dry and cracked and rapidly desquamates ; the blood vessels and epithelial linings of the alveoli of the lungs, as well as their elastic fibres: the lamellae of bone, which disappear; etc. Finally, in general cachexia the chemical composition of the blood is changed and may jjioduce thrombosis, multiple capUlary haemorrliages. and even go so far as to diminish the volume and weight of the pulp itself. 2. Local. — It has already been hinted that the pulp differs in several exceptional ways from any other organ of the body. These are principally anatomical, as already noted ; and the influence of these curious structural features on the general well-being of the pulp leads the writer to the conclusion that it is rare to find a healthy normal pulp in a tooth of a European, Asiatic, or American, after the age of twenty-five years. The vast majority are degenerating, or have already undergone retrogressive metamorphoses. It must be so ; for if the apices of the roots of teeth after that age be examined, it will at once be obvious that the foramina are so diminutive that it is impossible to insert a fine needle-point through their apertures into the root-canal. The openings will certainly not admit a horse's or a camel's hair; measured, they may only possess a diameter of 5 fi. In many — almost the majority — of the specimens examined, the apical foramina are macroscopically invisible, whUe even a lens, in numerous instances, fails to detect traces of their presence. And this is a universal fact ; thus, in a miscellaneous collection of permanent teeth of adults, rich and poor alike, sent to the WTiter from India for the special purpose, no less than 24 per cent had closed and completely obliterated foramina. It is quite inconceivable that the natural nutrition of the soft parts in the interiors of teeth can be projjerly carried on, if the afferent and efferent vessels are restricted to so limited an area of ingress and egress. After the apical 309 foramina have become closed, ' the blood supply, ] hitherto abundant, or at all events adequate, I becomes sooner or later insufficient, and there- 1 fore inefficient, and the first stages of degenera- j tion and disease begin. Many children's teeth show these initial changes ; different teeth from the same mouth also exhibit them. It would be interestmg to attempt to ascertain why the foramina become contracted and oc- cluded as years pass by. It may be suggested in the absence of definite clinical and laboratory data, that the growth and consolidation of the osseous frame\\ork of the jaws may press upon the " formative rings " of growing dental tissue — as a result of the shortening of the jaws and the absence of diminution in the standardiza- tion of the size of the teeth — and gradually bring about tliis constriction and actual occlusion of the orifices. Added to this, there are also, most commonly, areas of pathological cementum deposited on the surface of the roots, a fact that might itself be a contributing cause. Anotlier sign of degeneracy, too, is seen on examining the portions of the teeth by transmitted light ; a great number reveal a tendency to a trans- parency of the tissues. Among local predisposing causes of pulp disease may be mentioned the presence in the enamel and dentine of one or more metallic or porcelain fillings, whether pure gold, or mi.x- tures of tm, copper, etc., or the lute of an inlay placed in situ as obturations for carious cavities. If the pulp has escaped the effects of the caries, and is in a more or less physiologically responsive condition, it has a propensity to be secondarily affected by the presence in its neighbourliood of a mechanical, inert, dead mass, and its blood- pressure to be subject, at times, to certam exacerbations and declines in varymg circum- stances. A tooth containing a filling is almost certain to have a degenerate or degenerating pulp ! B. — Exciting Causes 1. General. — These — endogenetic in origin — are necessarily associated with disturbances of the vascular and nervous systems. Tlius, anaemia, chlorosis, or other conditions due to alteration in the chemical constituents of the blood, which may or may not lead to diseases of the vessel walls, or elevation or depression of the blood-pressure in the pulp, ' Closiire of tlie apical foramina occurs approximately as follows: — Maxilla — first incisor, 11th year; second incisor, Uth year; canine, 13th year; first premolar, 12th year; second premolar, 12th year; first molar, 12th year; second molar, l.ith year; third molar, 19th year. Mandible — first incisor, 10th year; second incisor, 11th year; canine, 13th year; first premolar, 12th year; second premolar, 12th year; first molar, 11th year; second molar, Kith year; third molar, 21st year. belong to the first group ; while neurasthenia, hysteria, or repeated undue excitability of the nervous system reacting locally, belong to the second. After due consideration of the peculiar ana- tomical conditions of the parts as already re- counted, it is not surprising that lesions arising from variations in the blood stream or in the blood-pressure itself should be fairly common. So much is this the case, that it is probably true to assert that, while teeth are very frequently the victims of dental caries, they may also equally and simultaneously be subjected to internal retrogressive metamorphoses induced by a lowered or altered physiological resistance, or lack of it, on tlie part of the pulp, through the unusual characteristics of its blood supply. This does not always apply to the normal indi- vidual, but applies more especially to those who suffer from disturbances of the circulatory system. Many persons undergo a certain transitory discomfort brought about by hyperaemia of the pulp. For some reason the ves.sels become vicariously overfilled and undergo hypostatic congestion, which presently disappears when j the cause is removed or when there is an effective outlet provided for an uninterrupted flow. If, however, the intra-dental pressure is so severe, and so sudden, as to prevent the occurrence of a rapid and permanent relief, then the tissues degenerate and perhaps die, as they are unable, on account of their dentinal envelopment, to accommodate tliemselves to their engorged state. Ferdinand Tiinzer (17) has recently em- phasized this point. The introduction of metallic fillings and cement floorings into carious cavities, to which j reference has already been made, is sometimes followed by local pain, and the work of obtu- ration Ls credited by the uninformed with being j the cause of the odontalgia, while it is often due I merely to either reflex nervous irritation or a rise in the local blood-pressure. It is thus clear that temporary engorgement j of the vessels of the pulp tends to produce odontalgia of varyuig degrees of severity ; but if this congestion is still continued, death of the parts ensues, \^ith complete cessation of pain. I This may be occasioned, (a) slowly, when the tis.sues pass through the various stages of fibroid degeneration, or (&) rapidly, when moist gan- grene supervenes as a result of thrombosis and ! arterio -sclerosis, and sudden death en masse takes place. Fortiuiately, gangrene as a perma- nent termination of thrombosis Ls a contin- gency of comparatively infrequent occurrence from a clmical point of view. It is believed that a slight rise of blood -pressure produces no symptoms of neuralgia, though it can be readily I conceded that pain from other areas may be 310 reflected to a tooth that is sound, but whose pulp is somewhat liyperaemic. Exaininatiou of sections showing these vascuhir lesions under the microscope displays the engorgement of the capillaries and small veins that are distributed to the peripheral parts of the pulp, and particularly to the coronal region. The corpuscles and blood platelets are appreciably altered in shape and size — due, no doubt, very largely to certam haemic changes, which favour coagulation ; they may partially or completely fill the lumina of the vessels and are sometimes arranged in rouleaux ; frequently Fig. 401. — Longitiulmal snliiMi of pulp Kliowing tlirom- bosis of capillaries and other vascular lesions. D, Dentine. X 45. they have escaped into the surrounding tissues as a result of the rupture of the vessel walls. Small arterial haemorrhages are often seen, at times among the odontoblasts, at times in the basal layer of VVeU, and at times in the sub.stance of the pulp it.self. The haemorrhagic infarcts may vary in composition from a punctiform collection of a dozen or more corpuscles to many hundreds clustered together to form a large mass. The endothelium of the ttinica intima of these arteries and capillaries is altered, and the nuclei of its cells are indi.stinguLshable. The larger arteries and larger veins are empty, and hyaline areas of degenerated material in many places extend across them, and as they become smaller, entirely occlude their lumina. The arteries and veins have lost their distinguishing coats, both having thinner walls than usual, showmg a truly hypoplasic or hyaline degenera- tive change. The odontoblasts are enormously multiplied, are vacuolated, are flattened laterally, and possess planiform nuclei ; they are colligated into sheaves. The basal layer of Weil — free in normal conditions — is rich in small cells with large round nuclei, and its fibrous parts are prominent. The cells of the pulp proper possess nuclei that are degenerate in shape and small in size ; their branches are well marked and increased in number. The nerve bundles are degenerating. Organization of thrombi pro- ceeds in places, leaving only a thin fibrous ccird or hyalme mass coherent with the walls (ir completely filling the lumina of the vessels. Al^sence of a collateral circulation predisposes t(i the onset of thrombosis. Any increased \ olume of fluid (blood) must be compensated by a corresponding outpouring, as there cannot be an adequate displacement of the surround- ing parts to afford the room required. A thrombus may be the cause or the result of arteritis or jjlilebitis ; it may be due to chemical changes in the blood itself, or to lesions in the vessel walls, as in degeneration. ( )sler (13) has observed that durmg thrombus Inrmation the blood platelets described by Hizzozero (1), and Eberth and Schimmelbusch (7), are the first of all the blood elements to accumulate upon the vessel walls during coagu- lation, and that the filaments of fibrin spread principally from these plate masses. They undergo viscous metamorphoses and also conglutination, as explained by Thoma. The thrombi in the pulp consist of corpuscles, platelets, fibrin filaments, and a colourless semi-transparent homogeneous material. They are of the hyaline variety, and are non- infected. Thus it ^vould appear that in the dental pulp chemical haemic changes, plus the unusual arrangement of the termmal vessels, assisted by the vis a tergo, which naturally leads to a certain retardation of the flow, and therefore — as first pointed out by Virchow — coagulation, are the originators of atrophic influences. Marantic, anaemic, and debilitated conditions, which often form the sequelae of long-continued and en- feebling diseases, have the same or similar efl'ects on the vascular system. Other diseases of the vessel walls occur in the pulp, such as chronic arteritis, atheroma or endarteritis, phlebitis, and varicosity of the veins. Un- fortunately they are undiagnosable, and all terminate in degenerative clianges or inflam- mation and death of the tissue. Regarding the effects produced by diseases of the nervous system, little need be said. In 311 so far as the trophic influence of the vascular mechanism Ls a permanent, predominant, de- termining, and important factor, by so much is the ciiculatory system affected ; the two are interdependent. In short, the diseases of the pulp depend upon the impaired vitality of the body generally, and the circle is completed by the diseases of the former producing at times various forms of dyscrasia in the latter. 2. Local — (a) Apparent- — Effects of Dental Caries. — The action of micro-organisms on Nasmyth's mem- brane and the enamel — no matter whether they be liquefying or non-liquefying — produces prob- ably no direct effect on the pulp ; there are no evidences to show it. When the outer zone of dentine is reached, however, and the micro- organisms are able easily to penetrate its depth, on account of its tubularity, changes at once originate. Tlie first phases of the plienomena associated with breach of surface are concomitant with cellular activity ; and a barrier to the bacterial incursions, composed of adventitious dentine conveniently classified as areolar, cellular, fibril- lar, hyaline, and laminar (10), is thrown up on the pulp side as a rampart. But the con- structive do not proceed pari passu witli the less rapidly accomplished, and an entrance to the pulp cavity is effected, in spite of the lowered physiological resistance, and in spite of the Af.' mm^ L Fio. 402. — Blood \essols iii liyperaoiuia of the pulp. X 250. destructive transformations ; for the cells appear to lose their power of forming dentine and offering physiological resistance to the demolition of enamel and dentme, wliich becomes more or Fio. 403. — Areolar adventitious dentine. X 180. limited area occupied by the adventitious dentine. Thus it is never observed that the soft tissues become enth-ely obliterated, but only partially so at the spot oppo- site to the breach of surface. Com- plete calcification of the jiulp can and does take place in entirely dLssimilar circumstances. The appearance of hyperaemic foci is tlie very next indication that the pulp is becoming affected by disease. There is a bacteriological irritation of the protoplasm in the dentinal tubes. Long before the micro-organisms reach the innermost portion of tlie dentine their toxic products liave passed on- wards in the vanguard of the advancing destructive host. At first this uivasion is slight, because the diameters of the tubes and their branches are so minute (about 2'5 fi. to immeasurability) that only the smallest of micrococci can effect an entrance. As, however, the matrix becomes peptonized and re- moved, and the tubes become larger in diameter at their distal extremities, mixed infections of bacteria occur, greater numbers gather together, and the individual liquefaction foci are increased in size. By tliis time, in the majority of cases, pain has been ex- perienced, indicating that hvperaemia has begun. The immediate effect of the invasion of bacteria, therefore, is a toxic infection of tlie pulp, which endeavours to make an immediate effort to repel the attacks of the enemy. 312 Wlien bacteria invade the cementum, as some- times happens in the roots of maxillary permanent molars, through exposure due to loss of bone on the internal aspect of the alveolar socket, they penetrate the tissues by means of the canals that contain Sharpey's fibres. This invasion, unlike that via the coronal surface, is unaccom- panied by a deposition of adventitious dentine, probably because it occurs later in life, and the cells of the pulp are, therefore, unable to lay do^m fresh dentine on the pulp surface. (b) No7i-apparent — Effects of Thermal, Chemi- cal, and other Stimulations. — The variations of temperature that the mouth may undergo during the course of a fashionable English meal, in which scalding hot fluids are succeeded shortly by icy cold confections, exercise a deleteri- ous influence on the pulp. Hence, while normally the pulps are proljably maintained at a temperature a fraction of a degree higher than blood lieat, the result of its elevation or lowering is to act partly on the arterial supply and partly on the nervous system — heat, of course, producing vaso- dilatation and a tendency to hyperaemia and pam ; and cold, producing vaso-con- striction and anaemia and al.so pain. Pulps constantly liable to experience these thermal vicissitudes cannot but be rendered amenable to the attack of disease or degeneration, slow at first but nevertheless sure. The nerve bundles become easily sensible to exogenetic irritation and lose their tonic authority over the blood vessels ; vaso-dilative and vaso-constrictive influ- ences, alternating in a struggle for supre- macy, lead in the end — which may be soon — to the loss of the normal physiological equilibrium of the parts, and, as a result of one being overcome, the pulp suffers irreparably, and the way is paved for one or other of the exciting causes. The effects of chemical stimulation of the hard parts in an apparently sound tooth are probably negative. The combined application of lukewarm alkalies, and natural and mineral acids, cannot, per se, unless Nasmyth's mem- brane and the enamel have been removed, prove inimical to the pulp. The acids only act as solvents — as, for instance, in the case of 1% lactic acid — by first destroying the enamel and then the dentine : while lactic acid, 1 in 1000 parts, probably has no ill effect what- ever, it is likely that malic and citric acids in weak solutions continuously applied have. It is evident that in this instance, however, the pulp would repair itself so thoroughly, that its whole coronal or cervical portions might become calcified by successive deposi- tions of adventitious dentine on its surface, and remain to the end a normal organ, as far as its radicular regions are concerned. The liability to an attack of disease, therefore, as the result of chemical .stimulation, is perhaps reduced to a minimum. This is, however, different in the case of a carious tooth ; the pathological conditions set up by the repeated accidental or purposeful application of acids to a carious cavity \\ould ultimately end in the death of the pulp. The above remarks apply also to voltaic irritation. A tooth that does not contain a metallic substance on its surface is not subjected to retrogressive changes, and the pulp will not respond by exhibiting a nerve-storm on the application of such a current. Fig. 404. — Hyperaemia of the pulp. D, Dentine ; P, Piilp. X 45. HYPERAEMIA WliUe it has been already claimed that on account of its anatomical surroundings the pulp occupies a unique position in the human economy, it may be predicated at once that pathologically no such distinction can be made. Pathological events and phenomena are observed here occurring in precisely the same way as in other soft organs, with the exception that they are modified by the en- vironmental factors previously enumerated. Essentially the morbid processes are identical, their causes similar, their courses analo- gous, their results alike, and the variations due to tlieir anatomical peculiarities of little con.sequence, though clinically important. The nutritional well-being of the pulp — a normal condition — depends upon the proper 313 regulation of its blood supply, which is governed by the influence of the vasomotor nerves of the unstriped muscle fibres in the walls of the arteries, the normal elastic tissue in the tunica media of these vessels maintaining simul- taneously the necessary " tone ". When the usual amount of blood exceeds this physio- logical limitation, pathological hyperaemia — a frequent forerunner of inflammatory or de- generative changes — Ls induced, and is called arterial, active, or congestive hyperaemia. Arterial hyperaemia may be brought about by any condition that either paralyses the vaso-constrictor nerves, or stimulates the vaso-dilator nerves, or \\eakens the tunica media, or removes the extra-vascular pres- sure. In dental caries, «hen a sufficiently large area of dentine has been exposed, various forms of irritation may set up a localized regional hyperaemia, which is known as coronal, cervical, or cornual, ac- cording to the parts of the pulp affected ; such as the chemical or bio-chemical pro- ducts of decomposition of liquid or soft food, vitiated oral secretions, thermal changes in the mouth, and drugs medicin- ally or artificially applied for curative or experimental purposes. Cold paralyses the vaso-constrictors, heat the vaso-dUators, while the protoplasmic irritation of the dentine (via the tubules) caused by the products of bacteria and the use of chemical reagents probably weakens the vessel walls. Venous hyperaemia, or passive conges- tion, occurs much more frequently than arterial hyperaemia, and is due to an abnormal obstruction to the outflow of blood from the veins of the jKilp. depending upon local conditions. The seat of the obstruction is at the apical portion of the roots of the teeth, where the mechanical pressure of hard dentinal walls, combined with the absence of a collateral circulation, causes its development to the fullest degree. The microscopical changes iii the pulp due to venous congestion need not now be detailed ; they have been fully described elsewhere (11). Suffice it to say that here, as in other soft parts, there is a capillary and venous dilatation, the pulp becomes deeply reddened, the axial and peripheral blood cur- rents in the veins become confused, the red corpuscles are densely crowded together, and stasis (the cessation of flow of the blood stream) and diapedesis (the emigration of corpuscles through the vessel walls) supervene. The dUatation of the veins and capillaries arises from the loss of balance of haemodynamic pres- sure, caused by the les.sened resistance of the blood stream to friction, through its slowing down. A transudation of serum is favoured by the intra-vascular pressure ; and more or less oedematous conditions soon ensue, because of the absence of lymphatics from the pulp. If the conditions remain unrelieved, acute inflam- mation takes place, and deatli and moist gangrene conclude the attack. Clinically, the symptoms are those of odontal- gia coming on as a direct result of stimulation by cold. The pain may cease at once on removal of the cause, or persist for some hours and assume a neuralgic character. FK! C, . 40.5. — Vertical .st'ctioii of carious tnotli with pulp (71 situ. Cavity; CD, Carious dentine; P, Pulp which is very hyperaemic. X 45. INFLAMMATION Inflammation is the com])lcx local reaction of tlie tissues to injuries and lesions of various kinds. " In recent years it has become more and more evident that the only theory that allows the full meaning of inflammation to be grasped is the broad biological conception which recognizes in inflammation an adaptive, pro- tective, and reparative tendency common to the reactions to injury among all animals." Hektoen and Riesman (9). To Cohnheim (tj) and Metchnikoft" (12) belong 314 the credit for a great deal of the early and late knowledge of tliis subject. " Inflammation brings mto operation a num- ber of factors to counteract harmful agents, protect the organism at large, and effect healing. The common mode of origin, the similarity of the changes (though combmed in difl^erent proportions), and the evident tendency of the inflammatory processes to protect and repair, justify fully the teaching that inflammation is essentially an adaptive, protective, and repara- tive process, a means of self-preservation. Yet it must not be forgotten that the mechanism of defence and preservation is far from perfect : the exudate may possess but little bactericidal power ; the j)hagocytes may be po\\erless or the bacteria may multiply freely ^\ ithin them ; extensive destruction of tissue may occur before the virulence of the bacteria is neutralized ; the fixed cells may form imj)erfect material for repair or multiply in excess. . . . The inflam- matory reaction does not respect the re- lative importance of the tissues. . . . Hence inflammation, though biologically an adaptive and preservative process, may appear harmful, requiring the intervention of medical art. Tak- ing all things into consideration, \\e may con- clude that inflammation is a reaction to local injuries, calling forth protective and reparative measures ; but that it is an imperfect patho- logical adaptation, often leading to consequences that are dangerous per se and defeat its purpose." Hektoen and Riesman (9). As this is true for the tissues in general, so does it apply to the dental pulp in particular. It has been pointed out that venous hyper- aemia may soon pass into a condition of inflam- mation. A brief sketch of the roles that are severally played by (a) the blood vessels, (b) the leucocytes, (o) the exudates, ((/) the fixed cells, and (e) the nervous system m this important condition must now be given. (a) The Blood Vessels. — It is believed that the vessel \\a\]s are structurally altered during the course of inflammation to allow of and facilitate the emigration of the blood cells and plasma. Their endothelial cells are contractile (Klebs) and, according to Metchnikoff, mobile and phagocytic, and by frequently enlarging, cause an increased resistance to the vascular stream. {b) The le.ucocytes play a fundamental part in the process, by passing mto the perivascular tissues, as first pointed out by Dutrocht in 1828. Cohnheim laid great stress on this phenomenon. Detaching themselves from the marginal current, which they normally occupy on account of their low specific gravity, they become attached to the enclothelial lining of the walls ; and, as a result of a localized positive chemiotaxis produced by diffusible products of bacteria, drugs, etc., emanating from the seat of the lesion, pass through the inter-cellular cementing substance. Leucocytic emigration is a complicated pro- cess, and varies with the nature of cells actively engaged in it ; thus there may be more eosino- philes than neutrophiles, etc. This emigration is favoured by the dilatation of the blood- vessels, and the contractility and mobility of the endothelial cells ; and is determined by chemiotaxis, by which the leucocytes advance towards the foci of greatest attraction. Tlie red corpuscles foUow the white ones at greater or shorter intervals of time. Phagocytosis is the action of certain leuco- cytes and wandering cells — with endothelial and fixed connective tissue cells to a limited degree, — wliich occurs in the presence of patho- genic bacteria and other particles of matter. A kind of intra-cellular digestion takes place, alexins — protective bactericidal bodies — being formed, either by a process of secretion, or, as Hardy believes, excretion, and the adventi- tious material being destroyed. Tlie function is carried out by the neutrophile cells and the polymorphonuclear leucocytes, and also, per- haps, the mononuclear hyaline cells. Negative chemiotaxis, the antithesis of jjositive chemio- taxis, implies the insensibility of phagocytes to tlie toxins jiresent in any particular part. The inflammatory exudate (plasnia) ]3ossesses also bactericidal properties, as shown by the experiments of Buchner, Xissen, and others, and assists the phagocytes in their beneficent work. All leucocytes are not phagocytes — - eosinophiles are not ; they probably possess excretary functions, and may diminish the vitality of the micro-organisms. (c) The inflammatory exudates contain more proteids than physiological lymph, also fibrin, iibrinoplastin, etc., and certain digestive fer- ments and peptones, etc. The quantity is very insignificant in the pulp tissue ; the serous and sero-fibrinous and fibrinous exudates are small in quantity and poor in quality, but the haemorrhagic exudates, originated by the in- tensity of tlie primary lesion, and due to an enormous diapedesis of the red corpuscles, is very marked. After traumatic exposure of the pulp, durmg excavation of a deep carious cavity, where a small amount of dentine re- mains in the floor, there is often a large flow of arterial and caiiillary blood, signifying extensive changes in, and injuries to, the vessel ^^•alls, and also a large quantity of haemorrhagic exudate. (rf) Fixed Tissue Elements .—RetTogiessive and progressive changes may go on side by side, but the former are more pronounced in the earlier stages of acute inflammation. Inflam- mation follows injuries that produce lesions 315 not sufficiently great to induce complete necrosis or death of the part. No inflammation of the pulp is set up by cocaine pressure-anaesthesia ; it is anaesthetized, and removed ahve. But in carious encroachments that give rLse to an acute inflammation, the mesodermic pulp cells become greatly damaged and undergo extensive retro- gressive changes. Necrosis and necrobiosis of the fixed cells and leucocytes occur. The odon- toblasts at the site nearest to the lesion become fatty and degenerate ; while further away they become " sheaved ", and show signs of prolifera- tion. This is probably an attempt on their part to heal the uijury or prevent furtlier damage from taking place by warning the pulp, so to speak, of the oncoming dangers ; and perhaps even to stimulate the dormant dentine-depositing cells arranged about them to functionate, and produce adventitious dentine. (c) That the nervous si/stem exercises a certain amount of influence in inflammation cannot be denied. Hyperaemia and exudation are inter- fered with by the uncontrolled action of the vaso-con.strictors, the toxins are not removed, and repair of the injury cannot be proceeded with. If, on the othei hand, the vaso-dilators exceed their functions, congestion takes place enormously, and a strangulation of the vessels in the radicidar region soon leads to moist gangrene of the entire organ. The Galenic signs of acute inflammation are manifested m the pulp as in the other parts, but ^ary greatly in intensity. Thus pain (dolor) is the greatest, whilst swelling and heat {tumor et calor), owuig to its circumscribed environment, are the least. The former is due to the pressure upon tlie nerve bundles, and the great tension caused by the hyperaemia ; while the latter are due to hyjieraemia, leuco- cytic emigration, serum exudation, prolifera- tion of fixed tissue elements, and the relatively large amount of blood in the part. The Terminations of Inflammation The effects of an acute inflammatory attack upon the pulp are disastrous to that tissue. It is too small, it suffers too severely and too entirely, its reparative powers are ordinarily too feeble, for its complete recovery. The whole organ is usually lost, because it is im- possible to treat at all satisfactorOjr an ulcer, say, or a eircumseriljed inflammation of its surface. Hence pulp diseases generally end in death, with or without suppuration, as the case may be. Rarely, however, remarkable instances of the partial or complete healing of \ lesions may be met with. Elsewhere the writer has drawn attention to these reparative pro- cesses (10). It would seem that under favour- able conditions, when a large area of the pulp surface has been exposed, attempts at healing [ begin within the first twenty-four hours after the receipt of the injury. Organization of the inflammatory i^roducts has taken place. A firm, fine, fibrous stroma, retaining many blood cells and much exudation in its reticulum, may be formed ; or the surface may show the liisto- logical character of ulceration, many layers of degenerated cells and pus cells being produced ; while, centrally, masses of the nature of calco- globulin may exist. Black and Woodhead believe that these nodules are associated with the venous congestion, and are analogous to the phleboliths found sometimes in varicose veins. It may be that they are the local ex- pression of all that is implied by the production of callus after the fracture of a bone. Russell's fuchsuie bodies are also occasionally seen. At times, a kmd of calcification of a plastic exudation may heal the lesion, as reported by Tomes in connection with a case extending over three years : at times, a sort of catagmatic autoplasty may be set up between the parts of a fractured tooth that have been kept in apposition for some period of time after an accident. In these latter cases, where an impaction of the fragments has occurred, it is probable that the calcified unitmg material is the product of the cells of both pulp and periodontal memlirane. Generally speakuig, however, acute inflam- mation means death of the pulp, especially if there has been any considerable amount of serous exudation, for, to repeat, this organ possesses no lymphatics to carry such exudation off. In many instances, nevertheless, progressive metamorphoses may suiservene on an '" expo- sure " of the pulp. They are all in accordance with the laws that govern cellular prolifera- tion ; viz. that they follow the jjhysiological types of cellular division ; that the law of cellular specificity is usually obeyed ; that ]5roliferation occurs most actively in young, well-nourished, slightly differentiated, elementary cells — such as those of the epithelium and connective tissues ; and that proliferation occurs under conditions that are opposed to those that kill the cells, such as dii'ect traumatism or necrosis or gangrene, and that are not opposed to those that stimulate the formative activities, such as increased function, or that, if con- tinued, operate simultaneously both ways. These metamorphoses are characterized by the formation of new tissue, apparently for tlie purposes of regeneration or replacement of old lost tissue. Thus, surface ef)ithelium and con- nective tissue cells are remarkably reparative. The new substance is called granulation tissue, and is found developing in inflammatory pro- liferations that occur in large coronal cavities, principally in the permanent molar series. 316 Clinically, the growth (Roraer's Pulpitis granu- lomatosa, 14) is kno\vn as " polypus " of the pulp — an incorrect but common term. It is composed largely of cells of the mesodermic type of variable size, round or oval, derived diiectly from pre-existing cells and chiefly concerned in the formation of the bulk of the mass of the new tissue ; of the plasma cells of Umia ; of many polymorphonuclear hyaline leucocytes ; of large mononuclear hyaline leu- cocytes, which are considered by MetchnikofT to be able to become transformed into fixed comiective tissue cells; of "mast-cells" so- called; and, finally, if necrotic material is present, or if foreign bodies — e. g. a splinter of dentine — exist, of multinucleated giant-cells, Fig. 406. — Cliroaic inflammation of the pulp. D, Dentine ; P, Pulp ; E, Epithelium. X 45 whose function is somewhat of a phagocytic type. This granulation tissue undergoes but little change after it has once formed. It slowly increases in bulk until it may actually rise above the lunits of the walls of the cavity and extend over its sides. Its free surface usually has upon it some degenerated cells and pus corpuscles ; but when it has come into direct contact with the epithelium over the surface of the gum near by, either as a consequence of the destruction of the dentinal wall beneath the gingival margm, or as the result of exuberant granulation tissue spreading itself over the sides of the wall, it acquires an epithelial cover- ing of cells, which may form a single or several layers, or even copy, with faithful accuracy, the normal oral epithelium of the neighbour- hood. The presence of this adventitious epi- thelium on the surface of a mesodermic body was formerly attributed to the results of skm- graftmg ; but it is in consequence of the irrita- tion of a sharp dentinal edge that the implanta- tion of new cells occurs, and growth begins, the latter passing by an unbroken continuity from the gingival margm over the edge and on to the pulp surface. THE RETROGRESSIVE CHANGES IN THE PULP Anabolic metabolism of the cells of the pulp — as in cells generally — gives rise to certain activ- ities, which carry on the proximate principles underlying nutrition, function, and reproduc- tion. The direct result of disturbances in the activities of cells leads to different varieties of dis- integration and atrophy and death. These are retrogressive changes, which are distinguished from progressive changes, inasmuch as the latter are concerned in building up alinormal growths and j)roliferations. The death of cells may be occa- I) sioned : (1) directly and rapidly, ajjart from morbid changes taking place in cellular struc- tures — this is necrosis, as exemjjlified in the appli- cation of .strong caustics or arsenious acid ; or (2) indirectly and slowly, either by atrofhy, or by a gradual shrinking of their size, or by altera- tions in structure produc- ing either degeneration through the oncoming of certain abnormal chemical processes in the protoplasm, or infiltra- tion, that is, the deposition of foreign materials from without — this is necrobiosis, and is ex- emplified in many of the degenerations, such as fibroid, fatty, and the like (18). Imperfect nutrition induces atrophy, which in its turn may lead to necrobiosis or destruction of cells. Perverted intra-cellular metabolism produces degeneration of the protoplasm, which is conv'erted into abnormal and useless sub- stances; this, too, may terminate in necrobiosis. Infiltration favours the death of cells. For a long time it has been known that the pulp is peculiarly liable, on account of the unique nature of its circulatory apparatus, to undergo necrobiosis through degeneration and infiltration. Many teeth, apparently not in- fected by disease, in old and young alike. 317 reveal this condition, wliich has been described by Weil as reticulai- atrophy, and by the wTiter as fibroid degeneration. It wiU now suffice briefly to indicate the pathological lesions that manifest themselves in connection with this common condition. Four main types have been observed : Fibroid, Atrophic, Fatty, and Hyaline or Colloid. The Degenerations 1. Fibroid Degeneration or Sclerosis. — This probably occurs, in the first place, as a complica- tion of thrombosis of the capillaries and veins, and permanent dilatation of the arteries through atony (due to impairment of the vaso-motor mechanism) or disease of the walls, with or without minute haemorrhages. It seems often to be succeeded or accompanied by a con- densation or fibrification of the pulp-tissue that lies between the basal layer of Weil and the substance of the pulp proper. A hyper- plasia of the connective tissue fibres of the parts occurs. " Sheaving " of the odontoblasts, with or without fatty degeneration, permanent dis- tension of the arteries and arterioles, and rapid overgro\\th of the fibrous tissue, supervene, until a well-marked reticular atrophy appears, and, m later stages, complete fibrosis of the organ, \\ ith disappearance of all cells and nuclei Fio. 407. — Longitudinal section of fibroid degeneration of the pulp. D, Dentine ; P, Pulp. X 45. and every vestige of nerve bundle and vascular system. The condition may be considered to be a natural old-age termination of the life of a healthy pulp, dependent not upon the age of its possessor, but on the constitutional lesions already noted. In complete fibrosis no traces of cellular organization of cell nuclei, or inter- stitial cementing substance, can be found any- where. Nerve fasciculi, odontoblasts, pulp Fig. 408. — Transverse section of fibroid degeneration of the pulp. D, Dentine. X 45. cells, blood vessels, equally share the process of fibrification, and are no longer recognizable under the microscope. But the connective tissue stroma, which is merely a loose net\vork in normal circumstances, has either become grossly hyperplasic or quite obliterated, and its place occupied by a new firm fibrous struc- ture devoid of cells, nuclei, or any regular arrangement of the constituent parts. Large alveolar spaces (areolae) appear ; rows of long thick fibres of various shapes and sizes, some bifurcated, others plain, others possessing fibrous offshoots, are visible; the odontoblasts are "'.sheaved" at first, and then reduced to thin fibrous cords or bundles of fibres. The areolae at times may measure from 220 ^ x 160 /x to X 10 /i 5 /x, and abound in the central portions of the pulp in the \acinity of the blood vessels and nervous systems. The basal layer of WeU and the odontoblasts themselves are the last to undergo the change. As has already been pointed out, complete fibrosis may occur in deciduous teeth. 2. Degenerative Atrophy of the Pulp. — This 318 is similar to the preceding, and has been care- fully demonstrated by Wedl (21) and Walkhoff (20). Shrinkage of the odontoblasts is followed, later on, by their total disappearance. The freely anastomosing capillaries in the peripheral regions often, even before dilatation, present varicosities through contraction of the con- nective tissue stroma. The pulp beneath the odontoblasts becomes condensed and infiltrated with cells, and vacuolation of the healthy tissues occurs. Rothmann (15) describes an Atrophia pulpae sderoticans, which bears a general resemblance to this condition, especially as. if chronic, it passes into a state of complete fibrosis — the cellular elements diminishing in size and numbers, and the normal connective i'lG. 40y. — Two solid pulp nodules P, Pulp ; N, Nodules. X 45. tissue fibres becoming coarsely fibrUlated. Calcific deposition often takes place simul- ' taneously. 3. Fatly Degeneration. — This is an incidental necrobiotic condition in senile permanent teeth and deciduous teeth undergoing absorp- tion, and in pulps whose " exposures " have been "capped". The pulp recedes from the dentinal walls, and is of a pale colour ; the odontoblasts are degenerated, and fat globules appear in their substances and interstitially, and the walls and sheaths of the capillaries and nerves undergo, to some extent, a form of degenerative lipogenesis. Accordmg to Thoma (18), " in fatty infiltration free fat, deposited in the form of drops, may be formed from an excess of circulatory albumen, while in albumin- ous and fatty degeneration the organized albumen is attacked and broken up into granular albumin ous or albuminoid and fatty molecules." It is this latter, and not the former, condition that obtains m the dental pulp, and even there only to a very limited degree. 4. Hyaline or Colloid Degeneration. — The writer possesses a section of which the histological elements exhibit appearances dissimilar to the above, tlnis enabluig the condition to be placed in a different category. The pulp appeared to present signs of undergoing what, in the absence of a further classification, may be described as a hyaline or colloid degeneration of its elements. It is probably a coagulated fibrinous exudation, which subsequently be- comes hyaline m character, and bears a super- ficial resemblance to the hyaline tube-casts found in disease of the renal glomeruli, or in the alveoli of the thyreoid gland. The degenerations briefly described repre- sent in the pulp certain disturbances of tissue nutrition that are retro- gressive, as opposed to progressive or formative metamorphoses. They are unexposed to ex- ternal influences, are not dependent on bacterial cau.ses, and possess no clearly marked symp- toms, bemg capable only of being demonstrated post mortem. Calcification, Petrifaction, or Calcareous Infiltration Common as is fibrosis of the pulp, perhaps even more general is that pathological condition which has been variously described as calcareous infiltration or calcification of the pulp. The former presents no operative difficulties ; the removal of pulps affected by what may be termed soft degenerative processes is easy of accomplishment and can, as a rule, be thoroughly carried out. This is not so, however, \\ith the latter ; repeated attempts at devitalization of the sensitive — even hypersensitive — surface are often required to achieve the end in view. It would save a confusion of ideas if three kinds of calcific deposition were generally recognized : (I) Calcareous mfiltration, entirely produced by changes in the pulp alone — a constant accompaniment of caries, but also found occasionally in apparently sound teeth as the result of vascular changes due to con- 319 stitutional or idiopathic causes ; (2) secondary dentine, occurring not only as a pathological process in cases of attrition, abrasion, or fracture, but physiologically as the result of senOe changes in permanent and in long-retained deciduous teeth ; and (3) adventitious dentine the product of caries solely. Under the microscope, pulps affected by calcification present in varying degrees the appearance of nodules, smooth and round or irregular, solid or hollow, attached or unattached to the dentinal waUs, transparent, laminated, or granular. They are frequently very refractUe and exceedingly hard — as hard as the neigh - bouring dentine. They arise in all cases — either partially or completely filling up the pulp-cavity, or arranged in masses or clusters or fused together into homogeneous \^liole, or large or small — from the deposition of finely granular particles of carbonate and phosphate of lime between the cells and fibres of the pulp. Their frequent presence in this region is no doubt due to the fact that there is a pro- pensity, elevated in early stages of life into an actuality, for the pulp cells to be concerned in the buUding- up of hard dense osteoid substances ; and their histological resemblance to the dentinal walls of the teeth is at times particularly striking. Thus, not only are they marked by more or less concentric laminae, but they contain radiating tube-like lines, which may be actual tubes or merely traces of con- nective tissue fibres, which, partially stiffened by impregnation ^\ith lime salts, have become incorporated in the general calcification. It is possible to stain them with borax-carmine, but an immersion for years is required to render them apparent. It is impos- sible to say ^^■hether they are hollow ; the probability is, however, that they are solid structures. Calcification may exist in one or two teeth in a given denture ; or it may affect many, or even all. There are usually pronounced clinical symptoms, which come on after the en- largements of the nodules have produced some considerable pressure m the pulp cells and fibres. It is not known whether the actual mechanical pressure of the nodules on the nerve l)undles in the immediate vicinity (thus producing a slight amount of nerve stretching) sets up pain and discomfort ; or whether pam may be due to an increased volume of tissue ui the pulp effecting an alteration in the blood pressure. Probably both factors are in operation, espe- cially the former, as instances occur, in other parts of the body, of pain being induced by the slow gradual pressure on nerve trunks issuing from foramina — say, in the skull — where symp- toms of epileptiform neuralgia are produced. Pain may also be due to mere mechanical pressure on the pulp itself, induced by the en- croachments made upon, and the diminution of, the cubic contents of that organ. The interest of this retrogressive meta- Fiii. 41U. — Calcification of tho pulp. P, Pulp; N, HoUow nodule. X 90. morphosLS lies in this element of pain, which is almost always manifest in the later stages. The change is due to a general circulatory cause, viz. lime salts ch-culating in solution in the blood, and is proljably associated with the gouty or rheumatic diathesis. In this respect it is probably analogous to those bodily condi- tions that give rise to arterioliths and phlebo- liths in arteries and vehis, and the concretions that at times occur in the efferent ducts of the parotid and other salivary glands, in the urinary passages, and in the bUe-ducts of the gall- bladder. 320 Necrosis and Putrefaction of the Pulp Tliis proceeds very rapidly by means of three ■distinct chemical and biological stages — primary, Fig. 411. — Complete calcification of the pulp. E, Enamel; D, Dentine; AD, Adventitious dentine. secondary, and final. The fir.st begins as a post-mortem change, and does not necessarily depend upon the presence of schizomycetes, the fact being that both the liquid and solid constituents of the pulp, immediately after its death, are capable of destroying many micro- organisms. The changes partake more of a chemical dissolution than a result of bacterial infection, and are dependent upon the action of the unformed soluble ferments found in the pulp, as in other soft tissues of the body. Tliese soluble ferments or enzymes are present in all living tissues, and have a great deal to ■do with the processes of metabolism. Thus ■albumen becomes converted by these enzymes into peptones and hemi-albumens, and this probably sums up the changes in the early stages. Pathogenic bacteria are capable of developing in tlie soft parts and producing the changes just noted ; but in order that they may develop sufficiently to produce these chemical stages in sufficient amount before they themselves are destroyed, there must be some local focus of disease or area of chemical decomposition present, which becomes largely invaded by the pus-forming micro-organisms. It is therefore obvious that if the balance between the biological actions of the invading and invaded forces is mam- tained in equilibrium, simple death of the pulp will occur ; that is, its general functions will cease, its physiological resistance to disease or injury will be in abeyance, its powers of undergoing pro- gressive or further retrogressive meta- morphoses will be ended, and it will remain, perhaps for many years, an inert, innocuous, ineffectual remnant of its former self — pale and shrunken. The hard parts surrounding it will, at the same time, be affected by the loss of nutrition, and the enamel — probably through changes in the subjacent dentine, certainly not through actual alteration in its own structure or chemical composition — wUl become dark and lustreless. On the other hand, if the bacterial infection is great and the albuminoid bodies produced are voluminous in amount, toxic enzymes result. These are very active poisons, which give rise in a short space of time to the usual chemical products of decomposition, viz. X 45. Fig. 412. — Vertical section of necrotic pulp M, Masses of micro-organisms. X 45. carbonic acid, ammonia, sulphuretted hydrogen, and certain other salts and water. The evolu- tion of these is dependent upon the access of oxygen, heat, and moisture. 321 The chemical changes of putrefaction are those of hydration — the taking-up of one or two molecules of water ; reduction — the breaking-up and decomposition by nascent hydrogen ; and oxidation — the formation of carbonic acid, acetic, nitrous, nitric, and similar acids. Other substances manufactured simultaneously, in varying degrees, are globulins, toxic enzymes, peptones, the nitrogenous amido-acids, leucin and tyrosin, the nitrogenous amines, niethyl- amine, propylamine, etc. ; and organic and fatty acids, such as formic, propionic, butyric, valerianic, palmitic, and other fatty acids ; and also putrescLtie (C^HjoN.,) and the isomers, cadaverine and neuridine (CjHjjN.,). These substances quickly become converted into ammonia and its derivatives. Buckley believes that not only is the pulp tissue thus destroyed, but the contents of the dentinal tubules also ; and that the pulp- chamber, the root-canals, and the dentinal tubules, are more or less filled with these end-products of decomposition (2) (3) (4). A. H-S. BIBLIOGRAPHY (1) BizzozEBO. Virchoius Archiv., Vol. XC. (2) BocKLEY. Trans. Fourth International Dental Congress. Dental Cosmos, 1905, Vol. XLVII, p. 223. (3) Buckley. Dental Cosmos, 1905, Vol. XLVII, p. 1302. (4) (5) (6) BtJCKXEY. Johnson's Operative Dentistry. Bukchard-Inglis. Text-book of Dental Pathology and Therapeutics, 1908. CoHNHEiM. Archiv. fiir Pathol. Anat., Vol. XV, 1867, andXLV, 1869. (7) Eberth AND ScHiMMELBUSCH. Virchow's Arckiv., Vol. cm. (8) Fischer und Laxdois. Zur Histologie der Gcsunden und kranken Zahnpulpa, 1908. (9) Hektoen- .\nd Riesman. A Text-book of Patho- logy, 1901. (10) Hopewell-Smith, A. The Histology and Patho- Histology oj the Teeth and Associated Parts, 1903. Hopewell-Smith, A. The Pathology of the Pulp in Relation to Clinical Dental Surgery ; Pyor- rhoea Alveolaris ; and other Essays. 1911. Metchnikoff. L'Imniunite dans les Maladies Infectieuses, 1904. Pathologic comparative de V Inflammation, 1891. Osler. Cartwright Lectures on the Physiology of the Blood Corpuscles. Medical News, 1886. RoMER. Ueber die Pathologie der Zahnpulpa. Trans. Fifth International Dental Congress, Berlin, 1909. Atlas der pathologisch-anatom- ischen V erdnderungen der Zahnpulpa, 1909. RoTHMANN. Patko- Histologic der Zahnpulpa u. Wurzelhaut, 1889. Sieberth. Mikro-organismen d. kranken Zahn- pulpa, 1900. ) Tanzer. The Increased Intra-dental Blood Pressure. Oester-Ung. Vierteljahrsschrift fitr Zahnheilkunde. 1906. Thoma. General Pathology and Pathological Anatomy. 1896. Tomes and Nowell. A System of Dental Surgery. 1906. (20) Walkhoff. Mikrophotographischer Atlas d.pathol. Histologie Menschlichcr Znhne, 1901. (21) Wedl. Pathologie der Zahne, 1903. (11) (12) (13) (14) (15) (16) (1 (18) (19) 11 CHAPTER XYII THE DENTAL OPERATING ROOM: ITS APPOINTMENTS AND HYGIENE The choice of the operating room is a matter of very great importance to the dental surgeon, inasmuch as he ]ias to spend the great part of his working life in it. The room selected should be of good size and well ventilated ; it should liave the advantage of whatever public services there may be in the district, such as gas, water, electricity, etc., and a satisfactory drainage for the wash-basin and fountain spittoon. Light Natural. — A good light is an absolute neces- sity, and there are certain conditions which must be fulfilled if the lighting of the room is to be satisfactory. (1) The amount of light must be sufficient for the operator to see all the details of his work, but should not be great enough to cause " glare " ; as a matter of fact, this is unlikely with anything short of direct sunlight. (2) The actual area of operation must be the most brightly illuminated jjart of the operator's field of view. This is a most im- portant condition, because, if other parts of the fi( Id of view are brighter than the operation area, that area will by contrast appear darker than it really is, and fatigue and eye-strain may be caused by the extra effort that has to be made. (3) The light must be diffused, that is, it must come from a source large enough to sub- tend a wide angle at the chair head-rest, or else from several sources at sufficient distance from one another to produce the same effect. If the light comes from too small a source it tends to make all shadows of an equal degree of black- ness ; a more diffused light will cause a grading of the shadows corresponding with the different amounts o{ surface irregularity that cause them. This is the reason why a diffused light w ill show the details of a cavity better than that coming from a single lamp, however powerful. If pushed beyond a certain point, diffusion of light tends to obscure detail by lighting hollows and projections alike, as everyone kno-\\'s who has tritd to make out the surface details of a crown in a hot furnace. The fulfilment of these conditions will depend partly on the window and the ))osition of the chair in relation to it, and ])artly on the sur- roundings of the chair, including the wall decorations. The window should be of good size, say not much less than 5A ft. by 4J, with its lower mar- gin not more than 3J ft. from the floor, and it should command a view of sky unobstructed by buildings or trees. There appears to be some difference of ojsinion as to what is the best aspect, but anything between north and east or even south-east will ans^\er the purpose. If one is obliged to have a window with such an asjject that sunlight falls on the chair during part of the day, much may be done to mitigate the glare by the use of shades or of some kind of window glass that breaks ujj the direct rays of the sunlight. The chair should be placed facing the window and near to it in such a way that while the light falls full on the work, no part of the ^\•inclow is in the operator's field of view while he is in his usual position of "right side front". A bay window is not altogether satisfactory in this respect, although it gives a large quantity of light. Besides the main window, there need be no others in the room at all. There %\ill be no actual disadvantage in having extra windows at the operator's back, but should there be any facing him, they shoidd be fitted with opaque blinds that will completely shut the light from them during working hours. The surroundings of the chair and the wall decorations — that is, everything that helps to form the background to the actiuil work — should be of some quiet tone ; this does not necessarily mean dull and inartistic, but it does mean that there should be nothing glaring or glittering ; Black says very truly that the worst possible wall surface would be glazed white. There is perhaps too much tendency at the present day to use ^^■hite enamel, white tiles, white opal glass, and such-like materials. These things no doubt show the dirt better than dark t-n s, and in that way may be a useful means of educaticn, both to the dental surgeon and to the public ; but anyone who really under- stands surgical cleanliness, can just as easily i keep a dark object in a clean condition as a ] light on". Artificial. — In most localities artificial light will be requind at some time or other. Inas- 22 323 much as the intensity, position, and size of the ilhiminating agency, can be controlled, there need be no difficulty in getting a light satis- factory for \\ork. Here again the same rules must be followed in the matters of sufficiency and diffusion of light, and relative brightness of the operation field. Most of the methods of arti- ficial lighting in common use transgress these rules to some extent. If the source of light be a single lamp, or several close together, there will be insufficient diffusion of light, and the operator will experience difficulties from the blackness and definition of the shadows ; he will be constantly getting in his own light, and Fig. 413. moreover A\ill find that even with a brilliant lamp it \\'i!l be difficult to see clearly the details of his work, especially if he is doing a gold filling. \'ery often, in order to get intensity of illumi- nation, the lamp is brought too close to the work, and consequently is liable to come into the opera tors field of view. Inasmuch as the dentist has arranged both the chair and his o\\'n position in relation to the window for daylight work, the ideal artificial light shoidd also come from the \\-indow, and that not from one point of it, but from all the corners of its upper half, so as to imitate as far as possible the directions of the rays of daylight that pass through the window from the sky. By far the best artificial light the \\riter has ever worked by is afforded by six fifty-candle- power glow-lamps, attached to alight rectangu- lar frame 4i ft. broad and 3 ft. high, hung just inside the upper part of the window, and capable of being moved up or down some little distance. The lamps are arranged one at each corner, and one in the middle of each horizontal side. (See Fig. 413.) The light from this arrangement is very soft and easy to «'ork by, producing no feeling of strain to the eyes and causing neither more nor less shadow than the ordinary diffused daylight coming from the window. For instance, an ordinary small instrument .such as an excavator held just in front of a piece of ^\•hite paper on the head-rest casts hardly any shadow at all. Wliatever lamps are used, they should be sur- rounded by fro.sted globes of fair size, to prevent the patient being dazzled by the intense bright- ness of the filaments, or mantles. If this is done there need be little fear of having too powerful a light. As a matter of fact many lights in common use do not give sufficient illu- mination, although, on account of being too close and not shaded, they may be dazzling to both patient and ojierator. In arranging the other appointments of the room, and in the general conduct of dental operations, three considerations demand atten- tion. These are the comfort of the patient, the comfort and convenience of the operator, and cleanliness. The comfort oj the patient, altiiough a most important matter, can be dismissed in a few words. In the general fittings and appearance of the room any suggestive display of instru- ments or appliances should be avoided. Al- though the dental surgeon likes to be up to date, he must always remember that the apjja- ratus he is so proud of seems to many people nothing but a collection of instruments of tor- ture ; to some nervous patients the v^ery odour of a dentist's room may suggest all sorts of horrors. Much discomfort may be saved the patient by proper adjustment of the chair, especially of the head-rest. This should always be arranged so that both head and neck are ^\•ell supported ; if only the head is supported, the neck has to be kept stiff by muscular effort, which soon causes great fatigue. One of the most comfortable tj-pes is the \\'ell-known " roll " head-rest, which has the additional advantage of serving as an arm-rest for the operator. In cold weather a foot-warmer or rug will prove of great use ; it is not always jjleasant to sit for an hour or so on a cold winter's day with the feet to^\ards a window. It need liardly be suggested that time and pain-.saving a])pliances and methods should be used to tlic utmost possible ext( nt . The convenience and comfort of the operator 324 depend largely on the efiSciency and methodical arrangement of his instruments. Everything should be in perfect condition and exactly in the jDlace where he expects to find it, so that he does not waste time groping for things, perhaps first in one drawer and then in another. The cabinet should be placed so that instru- ments can be reached from it without the operator moving his position at the chair side ; this may seem to some a trifUng matter, but the extra work of moving backwards and for- wards a step or two, each time anything is wanted from the cabinet, will amount to a good deal in the course of a day. Cleanliness Cleanliness is a matter that calls for most careful consideration. There are two sorts of cleanliness, real and apparent, and both are necessary. A tarnished or even rusty instru- ment, just sterilized, is actually cleaner, in the surgical sense, and safer to use than one that is bright, but has only been polished in the ordi- , nary household way ; nevertheless out of re- spect to the patient's feelmgs, everything ought to look as bright and clean as possible ; many a dentist allows his appliances to get into a con- dition that an ordinary housekeeper would be ashamed to see. While a bright and cleanly appearance is most deshable, the all-important matter is the real or " surgical " cleanliness. Before gomg into details as to the way in which this may be secured, it wUl be necessary to understand clearly the nature of the problem that the dental surgeon has to face, and the limitations that are imposed on him by the conditions under which he is working. In the course of a day's work a busy dental surgeon will see and treat a number of different cases, and will be at work pretty continuously for several hours at a stretch. Some of these cases are almost certain to be purulent ; he may have to extract an abscessed tooth, or , perform a scaling for a patient ^\ith septic | gingivitis, and every day he will be treating ordinary septic dead teeth. From these patients there will be projected from time to time bits of tartar, tooth shavings, or droplets of saliva, blood, or pus, some large enough to be visible, but the greater number of microscopic size. These ■rtU settle in various places according to their size and the directions of the air cur- rents they may meet with. Many will come to rest on the clothes of operator and patient, others on the cliaii-, bracket table, and cabinet, still more on the floor; the finest ones wiD eventually settle on the walls, curtains, and in fact in any place where dust can collect. Many of these particles are loaded with pus- producing bacteria, but they are not the only source of danger, as many otlier pathogenic organisms are occasional denizens of the mouth. It is a well-kno\^Ti fact that people apparently in perfect health maybe " carriers " of infection. Scarlet fever and diphtlieria are of especial interest in this connection, because the organisms which cause them may lurk about a patient's throat long after he has recovered from his actual illness. At any time a i^atient suffering from sjrphilis may present himself for dental treatment ; fortunately most dental surgeons would be able to recognize the manifestations of this disease, and w^ould be on their guard against it. From the fact that a patient carries patho- genic organisms in his own mouth, it is obvious that really " aseptic " dental surgery is not possible, and fortunately the oral mucous membrane seems to possess an extraordinary power of resistance to infection. On the other hand there is one thing that the dentist can and must do, and that is to prevent the carrying of uifection from one patient to another. This is part of the problem that is continually pre- senting itself to the general surgeon, and it will be instructive to consider what measures he takes to prevent access of infective material to his operation wounds. If the operating theatre of a hospital is visited, it will be noticed that the precautions taken may be classified in four groups : those relating to the fittings, the instruments, the surgeon, and the patient. Without going too much into detail it may be said tliat the theatre floor, walls, tables, and aU fittings generally, are made of very easily cleansed substances, such as tiles, glass, or enam- elled iron ; there are no corners, crevices, or mouldings to catch dust, and everything in the way of curtainis, drapery, and upholstering is absent. Instruments are sterOized by boiling, and are then placed in trays of antiseptic fluid to be taken thence as the surgeon requires them. It is an education in itself to watch the elaborate cleansing of the surgeon's hands, and the don- ning of overalls, and perhaps cap and mask as well. Theoretically, nothing would be easier than to sketch out an ideal set of arrangements and rules for dental practice on these lines, but it must be remembered that the conditions of dental practice are widely different from those of general surgery. A surgeon may spend half an hour or more prejjaring himself and his instruments for one case, but the dentist is obliged to treat case after case throughout the day, with but very short breaks between them. Hence whatever plan is proposed must not take up too much time, or it will be dismissed by the average man as a " counsel of perfection ". The scheme suggested in the following 325 remarks has at least the merit of having been put into actual everyday practice. No claim is made that it is ideally perfect, as improvements are continually being made in it, both in tlie direction of greater thoroughness and greater facility. Furniture ami Fittings. — One most important prbiciple m cleanly workuig, in the surgical sense, is, as we have seen, the avoidance of dust ; and a good deal may be done to miti- gate this evU, witliout sacrificing the artistic appearance of tlie room, or its feeling of comfortr. One of the first things to be thought about is the floor, and this sliould not be covered with that worst of all dust-catching contrivances, a fixed carpet. Wood blocks form an almost ideal flooring. These are not always to be had, but there are several ex- cellent substitutes that answer the purpose just as well, such as a veneer of small boards J-inch thick, carefully fitted together, m orna- mental patterns, on the top of the existing deal floor, and subsequently well polished. Simpler still are inlaid Unoleum and cork carpets, which are made in colours and patterns hardly distinguishable from parquet flooring itself. All these materials can be cleaned as frequently and as thoroughly as one may wish. A thin rubber mat at the chair will be comfortable to stand on, and will prevent any possible slipping of the operator's feet, or of the foot- switch of the electric engine. One or two rugs on the floor will give an appearance of comfort, and as they can be taken out into the air every day and well shaken, they will be practically unobjectionable from the hygienic point of view. Although dust can be reduced to a mmimum, the actual floor surface is bound to be unclean ; and it should be made an absolute rule that whatever falls on the floor should go at once either into the sterilizer or the waste-container. It is as well to avoid wall coverings that have patterns m strong relief ; smooth materials, such as " duresco ", or flat-varnished paper, not shiny, are clean, and also lend themselves to artistic treatment. Curtains and drapery should be dispensed with as far as possible ; it is best to have none at all, but whatever there are should be frequently clianged. For chairs and couches leather or removable covers are perhaps the best, and plush about the worst that can be imagined ; this also applies to the operating chair itself ; its left arm-rest in parti- cular is in continual danger of being soiled by drops that escape the spittoon. A great im- provement will be made by substituting rubber for the carpet with which the foot-rest is gener- ally covered. The bracket-table should be as simple as possible ; the best of all is a plain sheet of glass with a removable metal rim, so that the whole arrangement can be easily and quickly sponged after each case. This Ls very necessary because the table is just in the position to catch a good deal of contamination ; for this reason it is well to avoid a table with drawers, as they are more likely still to catch dht, and increase the diffi- culty of cleansuig tenfold ; in fact it is fairly safe to say they are never clean at all. The cotton-ivool and waste holders deserve some little attention. It hardly seems the best plan to have the day's supply of wool on the bracket table, where it will be sure to get fouled by contact with soiled fingers. A better plan is to take a little fresh supply for each case, an orduiary wool roll formmg a most convenient source from which to take small portions for the various needs that are continually aris- ing. Whatever may be said in favour of the wool-holder, there is no doubt that most ' waste-receivers are objectionable m the extreme, inasmuch as the tweezers are freed from the piece of wool sticking to them, by scraping them along the slot in the top of the receiver, which is already fouled by the material from the last case. Fortunately, there is now a perfectly satisfactory, simple, and cheap device for this purpose in the shape of little cardboard waste- holders made by some of the supply houses ; a fresh one is used for each case and thrown away when soiled. Of the various kinds of spittoon the liest is some variety of the fountain bowl, with constant water supply. In fitting the fountain spittoon there must be a good downfall for the waste- pipe, which sliould be of large size. The bowl and pipe should be periodically flushed out with strong soda and water. If hand spittoons are used, they should be frequently changed, and well cleaned, and before being used again should have placed in them a small quantity of some disinfectant fluid. A most important article of furniture is the instriiment cabinet. Of these there can be nothing better and cleaner than the enamelled iron and glass cabinets now supplied. The chief objection to tliem is their obtrusive appear- ance, which of course can be easily altered, as coloured enamel is just as clean as wliite. The use of formalin, or ratlier of its solid polymer, paraform, has made it possible to keep a ^^•ooden cabinet hi as clean a condition, from the sur- gical point of view, as a metal one. If a few tablets of paraform are placed in each drawer, and an ounce or so in the space underneath the lowest one, the air in the cabinet will be kept continuously charged with formaldehyde gas ; there should be a fairly strong odour of formalin every time a drawer is opened, and they should be kept shut, when not actually in use, so that the strength of the antiseptic vapour may be kept up to its proper level. Experiment has 326 shown that no cultivations can be made from dust taken from a closed space in which para- form has been kept for some hours. Tliis method of keeping sterile is equally applicable to metal cabinets, or any other kind of closed receptacle whatever. If a wooden cabinet is used it is an excellent plan to have the drawers lined with glass ; the same purpose will be an- swered by the movable porcelain trays now supplied, or by having detachable linings of enamelled iron. By the side of the cabinet is usually the most convenient place for the table on which the sterilizer is kept, so as to be within easy reach of the operator. The metal tables supplied by the manufacturers are admirably suited for this purpose. It is better however, to have marble or slate for the top and shelf, in place of glass, which is liable to be cracked by the heat of the sterilizer. histruments. — The care of the instruments may now be considered. This is the most im- portant of all because, whatever may be the ulti- mate source of infection, it is usually conveyed to the patient by an instrument of some kind. By far the most convenient and most gener- ally satisfactory method of sterilization is by boUing ; hence the sterilizer is one of the most important pieces of apparatus in the room. The oblong shape, wliich allows instruments of the largest size to be quite submerged in the boiling fluid, is preferable to the "pot" shajae, which only allows the points to be covered. Gas and electricity are equally useful as sources of heat. The addition of sodium carbonate (ordinary washing soda) to the water both ren- ders the sterilization more rapid and prevents the tarnishing of steel instruments ; as a matter of fact individual instruments have been boiled hundreds of times in the course of a year or two without being deteriorated in any way whatever. This is the case with almost all articles made of metal, with the exception of aluminium. Many things not made of metal \\ill stand repeated boiling ; materials that will not, such as cellu- loid, had better be avoided in the construction of dental instruments. Directly the patient is out of the chair, all in- struments, with a few exceptions to be mentioned later, should be collected together and placed in the sterilizer, and the table sponged with an antiseptic. Wliile the next patient is being seen, the surgery attendant, who for this p\irpose need be no more than the servant who opens the door, can take the in.struments out, dry them, and return them to their places. There are certain instruments that it is either impo.s.sible or inconvenient to boil, and these must be treated in some other way ; these exceptions had better be discussed in detail. Gold- filling instruments, inasmuch as they never touch anything wet, will hardly need further care than keeping in a closed drawer with some paraform ; this does not apply to files and trimmers, which are sometimes used after the rubber is taken off. Burrs, nerve instruments, and such-like very small articles, can be boiled with the rest or treated by being placed in 2 "J, lysol or lysoform directly after use, and allowed to remain there until the next day, when tliey may be brushed and dried. This method involves the keeping of more of these instruments in use than some other methods do, but it is not less economical, as tlie instruments are not actually used more in the long run. Lysol, owing to its alkaline reaction, possesses the great advantage that steel and nickel-plated articles can be kept in it for an indefinite time, without appreciable rusting or tarnishing. This method of keeping is particularly convenient for two classes of instruments, namely (1) Forceps : these should always be boiled after use, and then placed in the anti- septic ; they are then ready for use at a moment's notice. Otherwise they ought certainly to be boiled immediately before using, and this takes up valuable time. Convenient shallow glass dishes, with glass or metal tops, are supplied in various sizes, and will be found most useful for this purpose. (2) Hand-pieces : these are often liable to get very much soiled. A convenient plan is to have two or more of these in use, and to take them in rotation ; when not actually being used, they should rest in lysol ; this will ensure their being at least moderately clean when their turn comes to be taken out. This treatment, moreover, keeps them in excellent working order. Some makers are suppljang right-angle at- tachments with detachable heads, which can be boiled, but even then the handle part should be kept immersed in anti- septic. The hypodermic syringe, if septic, is perhaps the most dangerous carrier of infection in the dental surgeon's outfit. Both all-metal and all-glass and also combination glass and metal sjrringes are made. These can be sterilized by boiling, with the exception of the glass, which can be cleaned with carbolic or other antiseptic. If a fresh quantity of solution is required for the same case, a new needle should be fixed before refilling the syringe ; this wall prevent the inside from getting soiled by septic matter being drawTi into the barrel. Mirrors have hitherto been difficult to ster- ilize, but the difficulty has been greatly dimin- ished by the use of cone-socket handles ; the 327 handle can be unscrewed and boiled after each case, and the glass placed in some antiseptic solution ; three or four glasses should be kept and used in rotation. Anaesthetic apparatus is more difficult still. The masks should be most carefully cleansed with antiseptic solution, and the rubber face- pad taken off and boiled. The ga.s stopcock frequently does not get the attention it deserves ; Vernon Knowles has designed one made entirely of metal, which can be boiled witliout injury to any of its parts. The gas-bag is not likely to get fouled, unless " re-breathing " is prac- tised. If this is the case the bag ought certainly to be well cleansed, and bags are supplied that can be turned inside out for this purpose. Trays are easily sterilized by boiling ; com- position should be new for each patient, unless it has been kept for an hour and a half at boiling- water temperature, as Kenneth Goadby suggests. Napkins should be of a material that can be tlirown away after use, or else well boiled after each case. Rvbher-dam may quite well be used again if ihorougJily sterilized ; in fact, as J. H. Badcock has pointed out, it is then jirobably much cleaner than when it comes from the factory ; this is the case with many other things, as factory workmen camiot be expected to have much idea of surgical cleanliness. The water-syringe is certain to get fouled, either from the patient's mouth or the operator's fingers ; all-metal syringes, which can no\\' be obtained, cause no difficulty; if one with a leather washer is used, the piston part can be soaked in antiseptic fluid ^^•hiIe the barrel is being boiled. As is the case in general surgery, certain pre- cautions in connection with the operator's person and methods are essential. While at work the dentist should wear a coat made of some light washable material. The care of the hands is quite a serious problem. The dental surgeon has to clean his hands so many times in the day that the metliods used by the general surgeon are inadvisable on account of their destructive action on the skin ; they are, be- sides, unnecessary. The ^^■ash-basin sliould be conveniently close to the chair, and if possible fitted with taps operated by foot-pedals. The ordinary nail-brush, kept in the open, is little better than a germ trap, as bacteriological examination has shown that there are often more organisms on the hands after its use than before. This is not the case \\-ith a brush kept in an antiseptic fluid, and brush-containers are made by the surgical-instrument makers for this purpose. Lysol is one of the best fluids to keep the brush in, and is sufficiently antiseptic in a strength that does not injure the skin. The chief objection to lysol is its odour, but this can be masked by dipping the hands into a bowl of glycerine and rose-water after lirushing them with the lysol. This treatment may be repeated almost any number of times a day \\-ithout injury, in fact it will keep the hands in excellent condition. WHiile operating it is well not to allow the .soiled fingers to touch one's face or clothes, or anjrthing else beyond the actual work in hand. Especial care should be taken to avoid contamination of the instrument cabinet from this source. It is quite easy to open the trays, especially of metal cabinets, and take instru- ments from them with a pair of stout straight tweezers similar to those used in the laboratory for soldering. As far as possible, the instru- ments required should all be taken from their places before the operation is begun. For the operator's own sake, the use of the chip-blower should be avoided except for the necessary drying of cavities ; yet one often sees a cloud of what must be intensely septic dust thrown out into the aii- that both patient and operator are breathing all the time. Many other details will suggest themselves, but the main principles of surgical cleanliness have now been indicated. Perfection has cer- tainly not been attained, but improvements are constantly being made, and the A\liole practice of dental surgery is in process of evolu- tion towards better hygienic conditions. J. B. P. BIBLIOGRAPHY (1) Badcock, J. H. Brit. Dent. Jour., IQOU, Vol. XXVII, p. 433. (2) Black, G. V. Operative Dentistry. Vol. I, p. 172. (3) Law, W. J. Brit. Dent. Jour., 1906, Vol. XXVII, p. 394. (4) Ottolengui, R. jDentai Cosmo*, 1905, Vol. XLVII, p. 388. (5) VoYLES, S. H. Dental Cosmos, Dec. 1909, Vol. LI p. 1408. (6) Webster, A. E. Johnson's Operative Dentistry, pp. 85, ff. (7) Webster, .1. Forbes. Dental Record, 1909, Vol. XXIX, p. 214. CHAPTER XVIII ORAL HYGIENE AND PREVENTIVE TREATMENT OF DENTAL CARIES It has been truly said that " tlic mouth is the vestibule of life ", and therefore it behoves dental surgeons, as the potential guardians of that important cavity and its contents, to take every possible means to keep its various func- tions in as thorough working order as possible. It may be noted that every piece of food pass- ing into the stomach, and part of the air breathed into the lungs, fu-st passes through the mouth, and therefore neither should have normally any chance of becoming contaminated. The two main objects in oral hygiene and prophylaxis as practised in the mouth are, firstly, to jsrevent oral sepsis and its many sequelae ; and secondly, to prevent dental caries and consequent destruction of the masticating power of the mdividual. The evils of oral sepsis are very frequently met with and are often serious. But the resist- ing and recuperative po^\'ers of the mucous membrane of the mouth often act as a barrier, and are important factors in the prevention of grave results. The mouth itself is the normal habitat of a very large number of different micro-organisms, and, on account of its situation and functions, it must necessarily be very frequently contaminated with patho- genic bacteria, which, in a suitable nidus, wOl cause serious trouble ; and it is perfectly justifiable to expect that on the slightest lowering of the Natality of the individual his tissues will become immediately invaded by the micro-organisms present in his moutli, and some form of disease be brought about. And again, the arrangement of the teeth and gums is often such that, unless certain pre- cautions are taken to prevent it, micro-organisms will be readily harboured and allowed to propa- gate in the very situation that is most suitable for their existence. Neglect of the teeth and gums is a most frequent source of trouble. If food is left undisturbed in crevices and inter- stitial spaces, it Mill readily ferment or jnitrefy according to its composition, and thereby the soft tissues N\'ill be irritated or the teeth them- selves destroyed; and it axtII generally be observed, in the mouths of those N^ho take no precautionary measures to prevent tlie harbour- ing of foreign matter, that there is gingivitis present in greater or less degree. The above conditions, then, constitute oral sepsis, and may affect the patient in many ways. By direct septic infection of neighbouring tissues, general gingivitis, stomatitis, trouble m the maxillary sinus, necrosis, cellulitis of the tissues of the cheek or neck, may all be brought about. By remote septic infection, the lymphatic glands, the stomach, the intestines, and lungs, may severally be affected ; and from septic absorption, either septicaemia, pyaemia, septic anaemia, septic neuritis, septic pleurisy, septic nephritis, or puerperal fever, may supervene. All tliese are the residt of pyogenic infection. (See Chapter XLVI.) The conditions most necessary for pyogenic infection are — (a) an abrasion of the mucous membrane, (b) lowered vitality from any cause, and hence diminished resist- ance of the tissues, and (c) continuous expo- sure to the doses of infection (11). These are exactly the conditions so frequently found in a septic mouth, and therefore constitute the reason why oral sepsis so often leads to general pyogenic infection. It is, therefore, of the gravest importance that the mouth, which can be so easily treated, should be continually tended, and hygienic measures taken to pre- vent it becoming the source of uifection. The opinion is strongly upheld (II) that if oral sepsis could be overcome the other chamiels by which " medical sepsis " gains entrance might be left to chance. It is seen from the above that the import- ance of prophylactic measures cannot well be over-estimated ; and ajjart from the individual, there are few problems of greater public import- ance than the hygiene of the mouth. The gospel of the clean mouth and clean teeth shoidd be for ever preached, for " the influence of the training of the patient in the proper care of the mouth wUl be productive of much good to the teeth and general health of generations to come " (16). Absolute cleanliness, therefore, should be the watchword; but as absolute cleanliness is probably impossible of attainment, the nearest approximation to it must be aimed at. The reports of the Diamond Match Factories in the United States make interesting reading in this connection. Great care and supervision is taken with the teeth of all employees ; each individual lias a three-monthly inspection, all 328 329 teeth are scaled and filled when necessary, and oral hygiene is attended to, every patient being carefully charted. In comparing the condition of the employees since these measures ^^'ere adopted, with that formerly obtaming, the following observations were made — (a) much less caries, {b) the gums all healthy and pink i in colour, (c) fewer days lost through illness, and (d) much better general health. The means of attaining the desired result of a clean mouth and clean teeth may be broadly indicated under two headings — (a) by natural means, that is, by proper mastication of a rational diet ; and (b) by artificial means, that is, by hygienic, chemical, and bacteriological methods. Natural Means of Cleansing. — -The beautiful conformity and arrangement of a normal den- tition indicate that the teeth were intended to be of great service to the individual ; but the advance in civilization, and with it the culinary art, has lessened their use ; hence the food tends to cling about the mouth, and tartar to collect, and the necessity for artificial means almost invariably arises. But if it were possible to return to a dietary that necessitated vigorous mastication, the surfaces of the teeth would be continually polished by the friction of the food, ■ and the gums stimulated to their proper func- tion, and thus the integrity and environment of the teeth maintained in their normal con- ditions. There would then be less dental caries and fewer diseases of the soft tissues of the mouth. Sim Wallace (25) sums the whole c^uestion up in the following words : " If children are fed accordmg to physiological principles, Awhile hygiene requirements are not neglected, the teeth will not decay, nor wiU the other diseases which result from the infringement of physiological laws be at aU likely to be prevalent." A diet that will teach the child how to masticate is the surest means of preven- tion of caries, for not only will the teeth be properly cleansed, but the jaws, being efficiently used, ^^ill develop to their fullest extent, and the possibility of irregularity in position of the teeth, and therefore predisposition to caries, be reduced to a minimum. (See Chapter XIII.) I The method adopted in the early rearing of the uifant is of considerable importance from the point of view of prophylaxis of dental caries. There is considerable evidence to support the contention that breast-fed children are less liable to caries than artificially fed children, probably on account of a larger percentage of lime salts in their teeth. Cow's milk, besides being " humanized ", should therefore receive an addition of lime-water; and patent foods should be avoided. And again, a wholly hygienic mode of liv^ing will lessen the tendency to rickets and fevers in the infant, and tliereby reduce to a \ 11* minimum the risk of hypoplasia of the teeth and their consequent predisposition to caries. From about nine months of age the mfant can be given a little solid food, such as bread or toast with butter, from A\"hich he can gnaw and suck as from tlie breast ; the thorough insalivation and liquefaction of the bread, brought about by the sucking, renders it per- fectly digestible on jjassing into the stomach. This can be increased up to about twelve months, and then, with the advent of the first deciduous molar teeth, toast and milk-pudding can be given as a meal, and not merely as a small adjunct to the breast ; and by the time the second deciduous molars are in place boiled fish or other simple albuminous food can be given, as the mouth then possesses its full function (26). From this time onwards the diet naturally becomes more varied, but tliere are certain articles of food that are especially deleterious and should be avoided, or at least eaten in such a way that they become a lesser latent source of harm. The most important is the sticky carbo-hydrate food, from which all fibrous material has been eliminated, and which has, therefore, no cleansing properties, but only tends to cling about the teeth and gums and be fermented in situ on the teeth into lactic acid, etc. It is well recognized that roUer-miUed flour, which has almost entirely displaced stone-milled flour during the last thirty years or so, is very much more easily fermented into acid in the mouth than its predecessor, and not only that, but tends more to cling than the stone- milled flour, which contains a certain proportion of the fibrous husk of the grain (21 )i Therefore the white loaf, ^^•hose falsely praised whiteness indicates the use of roller-milled flour, should be avoided, and the bread made from stone- miUed or whole-meal flour exclusively used. Sugar and sweets, although rapidly fermentable into acids in the mouth, if taken in moderation ^^■ill do no harm, as they are generally easily dissolved and washed away. But the more sticky forms, especially if very frequently eaten, may greatly aid the destruction of the teeth by caries ; if taken at all they should as far as possible be taken during and not bet-\\een meals. Medicines containing free mineral acids, although easily washed away, should, never- theless, be taken in such a way as not to be allowed to flow about the teeth, or the mouth should be freely rinsed after their use, in order to minimize the risk of decalcification. The acid in fruit which is masticated stimulates a flow of alkaline saliva; this acts probably as a neutral- izing agent, and no harm results. It is difficult definitely to outline a typical meal, as the age and taste naturaUj' pl^J so large a part in eating ; but it may be pointed out that the sticky carbo-hj'drates mentioned above, 330 namely, bread, biscuits, thick sugary articles, etc., should always be taken at the beginning or middle and never at tlie end of a meal, which should be finished with food of a cleansing nature such as fresh fruit. Sim Wallace (27) suggests the following as a tj^ical meal for a child — Breakfast. — Fish, bacon, toast and butter, coffee or tea. Luncheon. — Meat or poultry, potatoes, salad, well-baked milk-pudding, fresh fruit, water. Supper. — Rusks, toast or bread-rolls and butter, chicken or fish, water, milk-and-water or tea, fresh fruit. Whatever the solid food, however, it should always be followed by liquid of some sort as the last ingiedient of a meal. The regularity m the arrangement of the teeth, and the correct occlusion, are important factors in the prevention of food lodgement. With a perfectly normal arrangement of the two arches the food is so worked upon the teeth in mastication that there is little tendency for the food to lodge, the lips, cheeks, tongue, and inter-proximal papillae of gum, tending to keep the teeth tree from adherent food, except of course the more sticky carbo-hydrates, which will lodge in any crevice. It is, therefore, important from a dtntal hygienic point of view, quite apart from aesthetic and utilitarian reasons, that every abnormality in position of the teeth should be corrected, so as to make the arch as nearlv nornifil as possible. Artificial Means of Cleansing. — The natural means of keeping the mouth in a hygienic con- dition having now been discussed, the artificial means will be taken in detail. As stated above, the necessity for the latter arises on account of the unnatural, but usual, mode of feeding of both children and adults. In almost every text-book or article on the subject one reads the well-worn sentence — " clean teeth will not decay " — , which cannot be disputed if read literally. It therefore behoves dental surgeons to do all in their power to see that then patients' teeth are clean. The ordinary means at the patient's disposal for cleansing the mouth are tooth-brushes, with or without powders, tooth- picks, floss silk, dragon canes, and mouth washes. Tooth-brushe.s. — 'The tooth-brush is an imple- ment that is frequently abused. Experiments conducted by Miller (18) conclusively proved that by vigorous cross-brushmg, especially in conjunction with powders or pastes, great injury was done to the teeth in the form of so- caUed erosion cavities, and he attributed all erosion cavities to this cause. The gums like- wise will be caused to recede. Healthy gums will stand a considerable amount of brushing and will be benefited by it if used in a judicious manner. To avoid injury it is not sufficient, however, merely to instruct patients, as is so often done, to brush the teeth up and down as well as across ; they sliould be taught to make the brush rotate against the surfaces of the teeth, at the same time passing the bristles as much as possible from the gums to the teeth and not in the reverse direction, and to give special attention to the buccal surfaces of the third molars, which are least accessible; the occlusal surfaces should be freely brushed in all directions. The size of the brush should be commensurate with the size of the patient's mouth, so as to be freely used; it should, for preference, be a moderately stiff one with a serrated edge, whose bristles will thereby more readily penetrate between the teeth than those of closely set brushes. It should also have a lengthened tuft of bristles at its end for more efficiently cleansuig the lingual surfaces of the incisors ; or, better still, a separate brush with a tuft only may be kept for that purpose. The usual times for brushing the teeth are night and morning. No food should be taken after the cleansing at night, which is by far the more important time, as the rest and stagnation in the mouth during the sleeping hours give the fermentative bacteria the opportunity they require for their growth. In those especially susceptible to caries, the teeth should be brushed after every meal and on retiring. The age at which to start brushing the teeth is the time of the appearance of the teeth ; the early use of the brush in the young child is very im- portant, for not only will the few teeth present be cleansed, but also the chUd will be brought up to the habit and appreciation of its use. Patients will sometimes be encountered with very septic mouths, with abundance of tartar, and much soft deposit around the necks of the teeth, who will profess to clean their teeth two or three times a day. Under these circum- stances one must, as a rule, discount entirely any intention on the part of the patients to deceive, for almost invariably they are speaking I the truth as far as they are aware. It merely means that their method of cleansing is wTong ; but any doubt can be removed by requesting I them to illustrate their methods. A definite demonstration should then be given to such patients on the proper hygienic mode of cleans- ing the mouth and teeth, models and brushes being used if thought necessary. Floss Silk. — It must be borne in mind, in using the tooth-brush, tliat its bristles wUl not penetrate between the teeth to any appreciable extent, and therefore if it is used alone the inter- proximal spaces, the most vulnerable spots, re- mam uncleansed. The best way to cleanse these spaces and remove the bacterial plaques lurking there is by means of waxed floss silk. The great difficulty and discomfort of correctly using the silk precludes its general adoption. 331 but where patients will take the trouble it is of extreme utility. It should be passed into every inter-proximal space to a little below the gum, and then pulled from the gum to the biting surface with a light saving motion against the medial and distal surfaces of every tooth ; if it is soaked in perchloride of mercury, 1 in 500, before use, fermentation is stUl more likely to be prevented (7, p. 206). If this process, in conjunction «ith brushing and efficient rinsing, were carried out thoroughly every day, probably caries would cease to exist in the mouth. In- stead of floss silk, thm rubber bands may be used in a similar manner, but it is merely a matter of choice. Toothpicks. — Toothpicks are useful adjuncts to the above, especially with those who lind a difficulty in the use of the silk, as they may be used to clear the plaques from the inter-proximal spaces ; but they are more prone to injure the gum. The quUl picks should be used, as a fresh one can always be taken, and they are much less likely to injure the gum than a gold one ; the wooden ones tend to leave splinters in the gum and are more septic. Dragon Canes. — Where the teeth readily become discoloured with tobacco smoke or tea stain, tlie patient may more or less frequently use a cane, frayed out at one end and cut flat at the other, to rub the teeth with a little powder, using the flat end for the interstitial spaces and the frayed end for the free surfaces. Although these stams tiiemselves do no harm to the teeth or gums, the roughening that they create increases the readiness of tartar and other deposits to collect. Tooth-powders and pastes. — Opinions are found to vary with regard to the advLsability of habitually using tooth-powders and pastes ; they can be almost as much abused as tooth- brushes. The writer is of opinion that with those whose teeth show no soft white deposit or discoloration, and but little tartar, the use of powders is superfluous, but otherwise they are a necessity, though always in moderation. The abrasive effect of powders and pastes upon the teeth, if used in excess, and especially if there is the smallest amount of grit in them, may lie very liarmful to the teeth, as proved by Miller's experiments and observations men- tioned above. Moreover, precipitated chalk, of which most are largely composed, if used in excess, becomes lodged between the teeth and is liable to irritate the gum margins, for it is insoluble in the saliva. Tooth-powders and pastes are mostly used for their mechanical properties, but antiseptics, astringents, deodorants, etc., may be added with marked benefit. The following makes an efficient powder, which may be used with the brush once or twice a day, as the necessities of the case demand, and 6 !]• 5 J- 5 ]• gr. V. Ill V. 3 J- whose ingredients may be varied for reasons detailed below — R Mag. Carb. Pond. Pulv. Saponis Dur. Pot. Chlor. Ac. Carbolici 01. Rosae. . Calc. Carb. Precip. ad M. Fiat pulv. The heavy carbonate of magnesia is an antacid, and may tend to counteract fermentative acidity ; it is also a cleansing agent. The powdered soap is also an antacid, and very materially assists the scouring action and helps to dissolve the mucous plaques of bacteria. For patients who object to the frothy condition brought about by the soap it may be omitted. The potassium chlorate is a slight astringent, and tends to counteract any abrasive effect upon the gums, and is especially beneficial if there is any marginal gingivitis. If the gingi- vitis is very marked, thirtj' grams of tannic acid may be substituted for the potassium chlorate. The carbolic acid is an antiseptic and deodorant ; the actual amount that can be used with comfort in a tooth-powder will have but little effect in inhibiting the growth of bacteria present, but it is useful in impartuig a refreshing sensation to the mouth and certainly helps to prevent the tooth-brush from becoming foul. With a few people it will be found that carbolic acid causes a slight stomatitis, or eczematous con- dition at the angles of the mouth, when it must be omitted, and a similar quantity of one or more of the essential oils substituted, such as the oils of bergamot, cinnamon, cloves, euca- lyptus, peppermmt, or wintergreen, according to the patient's taste ; or, of course, one or more of these may be primarily incorporated in the powder instead of the carbolic acid, if the patient so desires it from choice, as they are aU antiseptics, as well as powerful flavouring agents. The otto of rose is used principally as a flavour- mg agent, it being only very slightly antiseptic. The precipitated chalk, which forms the principal mgredient, is used as the scouring agent ; it is also antacid. For those who prefer a paste to a powder the following may be used, but the efficiency is approximately the same — R Calc. Carb. Precip. . . 5 j. Pulv. Saponis Dur. . . 3 ss. Glycerini . . . . 3 ss. Thvmol gr. iv. 01." Gaultheriae . . . H) x. 01. Rosae .... Ill j. Sp. Rect q. s. Misce. 332 In the above, as with the powder, the essential oils may be varied according to taste. The thymol is substituted for carbolic acid as the antisej)tic. At no time should any grit m the form of powdered cuttle-fish, pumice, etc., be incor- porated m the tooth-powder or paste for habitual use. Where a powder or paste seems contra- indicated, either on account of irritable gums or rooted objection on the jjart of the patient, a liquid dentUrice may be prescribed for use with the tooth-brush, such as — R Tr. Quillaiae. , § J- Tr. Krameriae . 5 ss. Aq. Cologn. ad . 5 ij- Fiat dentifricium. isig. — "A few drops to be placed on a moLst tooth-brush used vigorou sly 5 J The tincture of quillaia is a cleansmg agent and becomes very frothy m the mouth, and the tincture of rhatany is an astringent. Mouth-washes. — The use and value of mouth- washes as a hygienic measure \\ill now be con- sidered. For patients whose ordmary methods of cleansmg are efficient the use of moutli- washes is superfluous, but they become very useful adjuncts to those who experience a difficulty in cleansing then teeth and gums, or whose efforts are not equal to their mten- tions, and who suffer from much caries or gingivitis in consequence. But the habitual use of mouth-washes, purely as a hygienic measure, is to be deprecated, as liable to do injury in time to the mucous membrane of the mouth ; and those jjatients whose moutlis seem to be especially needing the use of a mouth- wash are just those who should be urged to use more efficient means of natural and artificial mechanical cleansmg. In jirescribing a mouth- wash for a patient's habitual use, it is necessary that its object, methods of use, and limitations, be first explained, as otherwise it may result m nothing but a delusion and a snare ; for the careless and uninitiated may, and often do, consider the antiseptic properties of the wash all that is to be desired to counteract the fer- mentation and putrefaction in the moutli, and do not realize that the wash will not, to any appreciable extent, penetrate the mucous plaques of bacteria and deposits of food about the teeth. It is essential, therefore, that the mouth and teeth should be cleansed, as described above, a-id the debris about the teeth removed or at any rate loosened, prior to the use of all moutli- washes, which, if antiseptic, will then inhibit the growth of the bacteria lying loose or in the now thinned film that may be left between the teeth. Thus, if the bacterial colonies are removed every twelve hours and mouth-washes used, the teeth and gums should remam healthy ; for a mass of bacteria such as would be dangerous as uifection or as an acid-producer can hardly grow from a thm bacterial film m less than twenty-four hours (10). It is impossible to get rid of all the bacteria by the use of anti- septic mouth - w ashes. Rliller's experiments proved that they could be apparently removed for tlie time bemg, but that after a few hours they were as plentiful as before ; this was at any rate true of those bacteria habitual to the mouth ; those \\hose natural habitat is not in the mouth can be eSectually removed by anti- septic washes and mechanical cleansing (4, p. 158). One cannot, therefore, hope to sterilize the oral cavity, but its condition can be im- proved. The difficulty lies in the choice of drugs; for most of those that are able to kill bacteria or uiliibit their growth are liable to damage the mucous membrane of the mouth. There are two distmct kmds of mouth-washes : firstly, those that will neutralize the acidity caused by fermentation in the mouth ; and secondly, those whose antiseptic properties wiU kiU or inliibit the growth of bacteria. The former are of special use where there is hyper- acidity from fermentation or otherwise, and where caries is rampant, especially in those cases where caries is proceedmg extensively around the cervical marguis of the teeth. The alkaline salts that have been found to be of most service are the magnesium salts ; all others are so readily soluble that they are very easily washed away, if used alone. Tlie most convenient and effective form to use is the hydroxide or hydrate of magnesia (Mg (H0)o), sometimes called " milk of magnesia " when ui solution. This is prepared by the mteraction of magnesium sulphate and solution of ammo- nia, and collection of the precipitate, which is washed until the washing ceases to give a reaction to sulphates (7, p. 90). The following is the strength that should be used — R Magnesii Hydroxidi Aquam ad gr. xxiv Sig. M.d. utend. A teaspoonful of this should be taken into the mouth night and mornmg after cleansing the teeth, and allowed to run around and between all the teeth, and not washed away by further rinsing. Of the antiseptic washes only weak solutions can be used, owing to tlie risk of injury to the mouth. Either carbolic acid (1 in 200), formalin (1 m 4000), or hydrogen peroxide (two volumes), may be used once or twice a day after cleansing the teeth. A combmed and more 333 elegant wash may be made up as follows for the same purpose — R Liq. Formaldehydi (40 »;) 1 ._. :. g_. Tr. Ivrameriae. . . . | ' ' >> ' " 01. Gautheriae . . . | .. - 01. Menth. Pip. . . .1 ''^ '^ Sp. Rect 5 i^'- M. Fiat collutorium. Sig. — Add a few drops to a third of a tumblerful of water. Any of these should be kept moving about the mouth for at least a minute, and it is important that the action of the cheeks, lips, and tongue, should always be brought vigorously uito use in order to keep the wash forcibly passing be- tween the teeth. Wadsworth (23) was the first to advocate that a 30 per cent, solution of alcohol in water, to which is added glycerine, sodium chloride, and sodium bicarbonate, was a much more efficient wash than the ordinary antiseptics for removing the secretion and infectious deposits from the mouth, and de- stroying the bacteria, the salts aiding the dissolution of the mucm, epithelial debris, and coagula. The writer suggests the following, which he has found most useful, being more pleasant to use, but somewhat weaker than Wadsworth recommended — R Sod. Chlor. . Sod. Bicarb. . Aq. Cologn. . Sp. Pect. Aq. ad . . . M. Fiat collutorium. Sig. — " Use a large teaspoonful with an equal quantity of water to swill round the mouth and between the teeth for at least a minute." During illness, especially all febrile conditions and pregnancy, the saliva is more mucoid and stickj% and therefore acid fermentation Ls much more likely to take place in situ upon the teeth, esjiecially as the diet is probably of the soft carbo-hydrate variety, or milk alone. The absence of true mastication will cause stagnation in the mouth, and the teeth may be rapidly destroyed. It is essential, therefore, that special attention be paid to the teeth at such times. The tooth-brush should be freely used after each meal if possible, and the mouth ^\ell rinsed with some antiseptic wash. If the patient is too ill to do this himself, the nurse should cleanse the mouth, either with a brush or lint dipped iti some aTitiseptic. Periodical Cleansing. — Apart from the daily treatment adopted by the patient, it is advisal)le that the teeth and mouth should be clean.sed - aa gr. xxx. 3 vnj. periodically by the dentist. The frequency will vary according to the adequacy and thor- oughness of the patient's own daily cleansing, and the tendency to caries and the accumu- lation of tartar. But the more frequent the treatment, the less will be the liability to caries or oral sepsis. G. H. Wright of Cincinnati and D. Smith of Philadelphia advocate fort- nightly, or at least monthly, visits by their patients for extreme cleansing and massage, and they describe their treatment as "an enforced, radical, and frequent change of environ- ment for the teeth and perfect sanitation for all oral conditions ". They claim that by this continual polishmg of all the aspects of the teeth they have reduced the tendency to caries in their patients to a very great degree. In practising such prophylactic measures as these, or even to a less degree, the theory of it must first be j^ropounded to the patients, and their interest aroused comjiletely to its importance and utility ; otherwise the treatment will meet with little or no success, for they will be apt to rely too much upon the periodical scour, and too little upon their own cleansing. The result is due as much to the patient's zeal and thorough- ness in carrying out daily the instructions given, as to the dentist's professional skill and handi- work. For projjhylactic treatment to be suc- cessful all conservative work in the mouth must be as perfect as possible, so as to allow no chance for lodgements ; all septic roots must be extracted, and abscesses and pyorrhoea alveolaris cured. At the periodical visit, whether it be fortnightly, monthly, or at greater intervals, the teeth should first be completely freed from all calcareous deposits above and below the gum margins with suitable scalers, and attention then paid to all the aspects of the teeth, special care being given to the approxi- mal surfaces. The method of affecting this cleansing varies ■^^•ith different practitioners, but the essential matter is that all surfaces must be completely freed from plaques, whicli gener- ally consist of decomposing food, mucus, epithe- lial debris, and bacteria, and must then be left in a polished condition. Tlie simplest method is by the use of engine brushes, aided by finely ground " flower of pumice," moistened with a little Eau de Cologne, which is both antiseptic and fragrant. The bruslies the \vi-iter has found most useful are those whose bristles are set end on, and therefore spread out on being applied to the teeth; and those whose bristles are arranged like the base of a small cone ; both of these penetrate bet^^•een the teeth better than most others. The approximal surfaces are then further polished with waxed floss silk as described above, and finally freely sjTinged with hydrogen peroxide (ten volumes) or other suitable anti- 334 septic solution to remove all traces of powder and debris. For tliose who possess a com- pressed air plant, tlie antiseptic sjjray Ls a very useful adjunct to this periodical cleansing. It is applied to all parts of the teeth and gums, any mOd antiseptic solution being used, at a pressure of about thii'ty or forty pounds, and is employed to advantage before and after the scaling, and again after the polishing. It is advised (12) that before the polishing the spray should con- sist of warm ^\•ater with a little aromatic spirit of ammonia, in order to dissolve the mucous coating of the plaques of bacteria. In using the spray, especially in cases of marked oral sepsis, the precaution is adopted by some operators of wearing a celluloid or fine gauze mask to protect themselves from infection of eyes or air passages by the spray passing back from the patient's mouth. There is a prophylactic method of oil polishing (13) which is claimed by its author to give beneficial results. Fine precipitated chalk is mixed with vaseline oil to form a stiff paste and applied by rotary brushes after drying the teeth, special attention again being given to fissures and approximal surfaces. Quarterly applications are advised for children, bakers, vegetarians and during pregnancy, and half- yearly applications for all other patients ; and one daily application also is recommended for use by the patients themselves. Treatment Silver Nitrate. — There are other methods, which are occasionally adopted by some, for the preventive treatment of dental caries and the treatment of small cavities other than by filling. The principal of these is by the use of silver nitrate. MUler (19) conducted some experi- ments by rubbing a saturated solution of silver nitrate upon teeth, allowing it to dry, and subjecting the teeth to artificial caries, and then again treating with silver nitrate. The pro- tective action was found to be greater when there was already some slight decalcification, and in many teeth so treated it was found that established caries was completely arrested. Therefore, this treatment seems to be specially indicated for readily accessible and superficial caries, and for carious deciduous teeth that cannot readily be treated otherwise. Black (4, p. 231) advises the following method of use : Apply the rubber-dam and thoroughly dry the surface with hot air ; apply a saturated solution of silver nitrate with the pomt of an orange- wood stick ; leave in direct sunlight for ten minutes or in daylight for one hour till deep black. If not black the silver nitrate has not been reduced and is soon dissolved out ; the black precipitate is insoluble. It is uncertain whether the protective action is due to the coagulation of the contents of the tubules or to the formation of an insoluble precipitate therein. There is another method of use advised by L. C. Bryan (5), of Basle, for children, where deep fissures or rough surfaces invite caries. He uses a 40 per cent, solution of silver nitrate as follows : Apply rubber if possible ; heat shreds of asbestos wool to burn off organic matter ; with these apply the silver nitrate solution to the teeth ; \^'ork to the bottom of the fissures with a quill pick ; if possible let it dry on the teeth ; repeat twice a year. The writer has had no experience of this method. Potassium Sulplwcijanide. — A treatment for the staying and prevention of dental caries has been devised by Michaels of Paris (17), based upon investigations on the biochemical states of the saliva. He found that the chief chemical variations associated with caries were the relative amounts of alkaline sulphocyanides and ammonia in saliva. In those cases where caries was rampant the ammonia was in excess of the sulphocyanide ; and in those cases where caries was absent, the sulphocyanide was in excess of the ammonia. He also found that potassium sulphocyanide given internally was excreted by the saliva, and went on being excreted for some considerable time afterwards. He there- fore devised the treatment of giving three times a day to patients with rampant caries tablets containing half a grain of potassium sulpho- cyanide ; the caries in these cases was checked and no further cavities developed. These facts have since been confirmed by many in- vestigators. (See Chapter XI.) Gliange of Mouth " Flora ". — Another form of treatment \\ith a similar purpose, ba.sed on the principle that one set of micro-organisms will crowd out another, has been devised by Kenneth Goadby (8), who essays to eject the acid- producing bacteria from the mouth by means of others of a less virulent type. His method is, first, to determine the type of organism that j is present in largest numbers ; then to carefully , cleanse the mouth of all bacteria as much as possible, especially the most prevalent form ; and freely to " sow " the mouth from time to time \\ith the spores of a specially selected and innocuous form of organism. In this way he claims to have had excellent results in the stay- ing of rampant caries. The treatment, though ingenious and highly scientific, does not seem likely to be universally or even commonly adopted, on account of the technical difficulties for the ordinary practitioner. Excision. — The excision of dental caries to prevent further ravages is somewhat limited in its scope, though useful when adopted judiciously. It is only in treating quite shallow cavities by this method that any degree of success can be hoped for ; the depth of the 335 caries in the dentine should not be greater than the tliickness of the enamel (22). The carious spot should be excised by means of small files, carborundum stones, emery discs and strips, and finally ])olished with pumice powder and whiting on wood points. Only those situations that can be easily and habitually cleansed afterwards should be attempted ; otherwise, with the dentine exposed caries may readily recommence. It will be well to recapitulate briefly the essentials of dental hygiene. Its importance for preventing both pyogenic infection and dental caries is without question. The natural, and probably the mo.st efficient, mode of cleansuig, is by the proper mastication of a rational diet. The artificial methods of cleansing by brushes, .silk, picks, and canes, are laborious if efficiently done, but generally necessary on account of irrational diet and insufficient mastication. Dentifrices and mouth-washes are useful ad- juncts, though not a necessity for many people. Periodical cleansing by the dentbt is essential, but must not be relied upon by the patient as the most important factor. Other methods for the prevention or inhibition of dental caries, such as by silver nitrate, altered states of the saliva (by drugs or bacteria), and excision, have all a somewhat limited application, though useful in their places. The technicalities of efficient dental hygiene are sucli that at the best it is the few who can profit by it to its fullest extent. It has been well said (28) that with regard to the masses of the people, if it was possible to get rid of dental caries by altering the character of the people's food, then there was some hope ; but if it was necessary to rely upon elaborate methods of cleansing, prevention of caries was hopeless. E. B. D. BIBLIOGRAPHY (1) Austen, H. Effects of Drugs in Causation of Dental Caries. Brit. Med. Jour., Sept. 1910, p. 772. (3 (9 (10 (11 (12 (13 (14 (15 (16 (1" (18 (19 (20 (21 (22 (23 (24 (25 (20 (27 (28 Badcock, .1. H. The Need for Correction of Malposition of the Teeth. Brit. Med. Jour., Sept. 1910, p. 771. Bennett, Norman G. Dental Hygiene and National Physique. Brit. Dent. Jour., 1904, Vol. XXV. p. 888. Black, G. V. Operative Dentistry, Vol. I. Bryan, L. C. Dental Review, 1904, p. 1. BuRCH.\RD. Dental Pathology. 1908 ed., p. 393. Gabell and Austen. Dental Materia Medica. GOADBY, Kenneth. The Buccal Secretions and Dental Caries. Brit. Med. Jour., Sept. 1910, p. 769. Godlee, Sir B. J. Surgical Aspect of Oral Hygiene and Oral Sepsis. Brit. Med. Jour., Nov. 1904, p. 1367. Head, J. Dental Prophylaxis. Dental Cosmos, 1908, Vol. L. p. 317. Hunter, W. Oral Sepsis. Brit. Med. Jour., 1904, p. 1358. Kelly. Prophylaxis. Dental Cosmos, 1909, Vol. LI. p. 1283. Kleinsorgen. Dental Cosmos, 1908, Vol. L, p. 881. Marshall, J. S. Operative Dentistry, p. 176. McKenzie, H. Care of the Mouth during General Disorders. Brit. Med. Jour., Sept. 1910, p. 620. Meerhof, C. E. Oral Prophylaxis. Dental Re- view, 1908, p. 198. Michaels. Transactions of Third I nternatioruil Dental Congress, 1902. Miller, VV. D. Experiments and Observations on the Wasting of Tooth Tissue. Dental Cosmos, 1907, Vol. XLIX. pp. 1, 109, 225, 677. Miller, W. D. Preventive Treatment of Teeth. Dental Cosmos, 1905, Vol. XLVII, p. 913. Mummery, J. H. Susceptibility and Immunity to Dental Caries. Brit. Med. Jour., Sept. 1910, p. 773. Read, T. .1. Chemical Changes in the Mouth during the Mastication of Bread. Brit. Dent. Jour., Aug. 1901, Vol. XXII, p. 590. Tomes and Nowell. Dental Surgery, 5th ed., p. 280. Journal of Infectious Diseases, Dental Cosmos, 1907, Vol. XLIX, Wadsworth. Oct. 1906. W.\dsworth. p. 415. Wallace, J. Sim. Causes and Prevention of Dental Caries, p. 73. W.ALLACE, J. Sim. Prevention of Dental Caries. Brit. Dent. Jour., 1910, Vol. XXXI, p. 241. Wallace, J. Sim. Effect of Food Stuffs in Pre- vention of Dental Caries. Brit. Med. Jour., Sept. 1910. p. 617. Wheatly. Brit. Med. Jour., Sept. 1910, p. 621. CHAPTER XIX TREATMENT OF CAVITIES IN THE TEETH BY FILLING I.— EXAMINATION OF THE MOUTH AND TEETH Too much importance cannot be attached to the care, skill, and judgement required in the thorough examination of the mouth ; it must be accurate, compreheiLsive, and exhaustive, so that any opinion or advice founded upon it may be of the utmost advantage to the patients who entrust themselves to the dental practi- tioner. It is in all cases advisable that the ex- amination should be periodical, the intervening periods vaiying in different cases, according to the age of the patient and the predisposition to caries and other pathological conditions. In children and through early life it is usually necessary every three months, later on every six months, and in some cases an annual ex- amination may suffice. At the first visit com- prehensive views of the patient should be taken, and general note should be made of any special feature in walk, manner of speech, habits, etc., as well as any special condition such as preg- nancy, or any general pathological state such as diabetes, etc. More detailed exammation may take place then or at a subsequent sitting. A systematic record should be made of every case, the card system now so much used in almost every department of life being the most convenient form. A useful card is 8 in. by 5 in., and on the left-hand side may be a diagram of the mouth, the rest of the card being ruled ^\itll famt blue Imes on which details of treatment, etc.. may be entered. A note should be taken of the conditions mentioned iDreviously, and in the case of chOdren especially the exact age should be entered. It is also a good plan to take models at stated intervals ; these, to- gether with the wTitten record, afford very valuable data at a subsequent time. The general condition of the teeth and gums should also be entered, especially conditions such as hypoplasia of the enamel, abnormalities in size or shajie, suppression or early erujition, etc. The examination of the mouth should always be conducted in an orderlj' manner. Some practitioners recommend that it should com- mence at the third left mandibular molar and proceed to the third right mandibular molar, and then return from right to left in the max- illa ; others prefer to commence at the middle line and work in a posterior direction. Very little importance need be attached to the order providing some system is used, so that nothing shall be overlooked and that each tooth shall receive individual examination. As j)ointed out by Johnson, each tooth has five surfaces, therefore time must be devoted to this matter, or important conditions may very easily be overlooked. Nothing is more likely to bring discredit upon a practitioner than the occur- rence of pain that might have been prevented by a more thorough examination. The appliances required are a mouth mirror, one or more exploring instruments, floss silk, water syringe, and in some cases an electric mouth-lamp. The mouth should be free from deposits of salivary calculus, etc., and should be in a generally clean condition. If it is not so, before a systematic exammation can be made it must be brought into that condition by suitable scaling and cleansing. The recently introduced method of using compressed air medication is a very good preliminary, and will soon be looked upon as a sine qua non in dental practice. Some sort of aii- compressor must be employed, the simplest type being a hand pump attached to an air receiver capable of with- standing an internal pressure of at least forty to sixty poinids to the square mch. The air, under pressure and capable of being controlled, is conveyed to a spray bottle by a strong mdia-rubber tube. The bottle sliould contain some suitable non-irritant antiseptic, such as hydrogen peroxide or comf)ound glycerin of thymol, and should be warmed to about blood- heat electrically, or otherwise. Variously shaped nozzles may be used, and the drug, in a fine state of division, and delivered with considerable force, is applied to the surface of the teeth and gums, and very successfully removes food debris, etc., the thorough examination of the mouth being thus very greatly facilitated. Many other uses may be foinid for the compressed air atomizer, such as in the treatment of pyorrhoja. An automatic compressor, the pump being actuated by an electric motor, has also been introduced. This is the most convenient form, as the pressure can be easily controlled and kept uniform. The mouth having been rendered clean in the maimer indicated, the examination may be 33(i 337 commenced at the predetermined tooth, a mirror being in the left hand and held in siicli a position that it may be used either as a rcfl(?ctor of light, or to give an image of the tooth, by an alteration of the angle at ^diich it is held. An exceedingly useful form of mirror is one having a double surface, with a reflector at what would be the back of a mirror made in the usual way. This is especially valuable in the examination and treatment of buccal cavities, where the mirror can also be used as a retractor of the cheeks. If preferred, t«'o mirrors may be used, each with one of the reflectmg surfaces as indicated. The exploring instruments should be very sharply pointed, and so bent near the extremity that all positions may be reached with ease ; it is not well to have the handles too thin, as it is important that the sensations conveyed through the instrument should be conducted to a sufficiently large area of the fingers to enable the touch sensations to be accurate. Each tooth should be looked upon as occupying an isolated position, and all the five surfaces should be examined by the probe, the most difficult being of course the medial and distal ones when the teeth are tightly placed, especially the area between the actual point of contact with the adjacent tooth and the cervical margm. The fine point of the probe should be introduced here with as great thoroughness as possible, but even with the greatest care a small cavity may easily be over- looked. If the point of the probe can be made to stick in any fissure or other pit, and so reveal a softening through the enamel, that may be taken as a general sign that a carious cavity is forming, and that treatment should be under- taken. Frequently the fissures in molars and premolars may be deep and stained, but unless softening is found treatment by filling should be deferred, as with suitable care on the part of the patient (his attention having been directed to it by the dentist) the fissures may never degenerate into carious cavities. After careful examination as above, unwaxed floss silk may be passed between the teeth and drawn to and fro ; if any rough place be detected it probably indicates a carious cavity, but the absence of such a fraying is not conclusive evidence of a perfect condition, as frequently in very early caries the enamel edges are not sufficiently marked to catcli the silk. In case of doubt the best method is to dry the teeth thoroughly with absolute alcohol, after intro- ducing a napkin, wool roll, or even rubber-dam ; then by the aid of the mirror and the electric mouth-lamp a slight difference in translucency may be detected if caries is commencing. Before doing this it may be helpful to put in separating material for a day or two, or an immediate separation may be made at the time if thought desirable. Frequently very definite opacity is found when the actual opening of the cavity is not reached by an exploring instrument, witliout separation. Particular care should be given to examining the edges of existing fillings (if present), more particularly if they extend below the gingival margin ; the same remark applies to crowns and bridges. Artificial dentures, if worn, should of course be removed before the examination, and note should be made of their construction and design, especially the portions coming in actual contact with the natural teeth. The occlusion should also be examined. For this purpose the patient should be asked to close the teeth in a natural manner, leaving the muscles of the lips and cheek in a lax state (care must be taken to see that the " bite " is a correct one) ; the lips and cheeks should then be lifted up and retracted by the mirror and the forefinger of the left hand. While this is being done, the condition of the gums and gingival margins may be noted, and any sinuses or cicatrices of old abscesses may be investigated ; the condition of the palate, tongue, fauces, etc., should also receive attention. It is well to pass the tip of the first finger over the buccal surfaces of the gums, as by this method alveolar abscesses, exostoses, etc., may sometimes be detected. Finally, any sign of discoloration, or loss of translucency, suggesting the death of a pulp, should be looked for. If an examination is conducted in this mamier the first time the patient is interviewed, and careful notes are made both as to present conditions and also weak spots that may require attention at a future visit, the best interests of the patient wiU be studied, and much time may be saved later on when the case comes for further con- sideration and advice. II.— EXCLUSION OF SALIVA In the treatment of teeth it is necessary to isolate them from the fluid that normally bathes all their exposed surfaces. It is neces- sary in order that a perfect and unrestricted view of the cavity or surface may be obtained ; the presence of saliva both obscures and distorts. It is necessary in order that the cavity may be storUized and dehydrated ; it is found in practice that live dentine is generally more sensitive when wet (this however is not always the case, and the very act of dehydration may cause considerable pain). It is necessary to keep the tooth in a dry state in order not to interfere with the chemical action of cements during setting ; and also when cohesive gold is used, as any moisture will quite prevent the thorough welding that should take place between all the laminae as the filling is built up. 338 A large variety of methods liave been intro- duced from time to time to secure the desired result. It is impossible to go into all the details, but a general indication will be given of the methods vvhicli have been found of greatest { -'■■ ■ / / / ^ Fig. 414. — Method of folding a napkin before intro- duction into the mouth. It should be folded upon itself once or twice more than shown in the bottom figure, so as to form a long pointed cone. service. Occupying the foremost place is, of course, "rubber-dam"; this was introduced many years ago in the United States b^^ Barnum and since that time has never been superseded. Its use is essential in many cases, more particu- larly in cohesive gold filling and in certain root-canal treatments, but its application is always attended with considerable inconveni- ence and discomfort to the patient, and there- fore for short operations, and particularly in young children, other methods are frequently to be preferred. The Napkin. — Except in the case of those patients who have an abnormally free flow of saliva, the napkin may be found of the greatest possible service. The most useful size is seven or eight inches square : it should be made of " bandage muslin " cut into suitable pieces and should be quite free from "dressing." It can be obtained ready prepared from the depots. This is much superior to the washable napkin made of damask, either from a sanitary or economic point of view. Some operators have suggested the placing of a piece of rubber-dam in the folds of the napkin ; this sometimes gives good results. In applying a napkin to the upper jaw, it should first be folded diagonally, and then upon itself to form a long pointed cone (see Fig. 414) ; a portion about three inches from the point is then taken between the thumb and first finger of the right hand and introduced into the sulcus while the cheek is held away from the teeth by the left hand of the operator (see Fig. 415). It should be tucked up opposite the orifice of Stenson's duct ; the rest of the point should then be snugly packed into tlie sulcus above the anterior teeth, the lip being lifted out to enable that to be done. The tliicker portion of the napkin is then spread out over the lower incisors. V Fig. 415. — Shows napkin in situ for upper teeth. and acts as an " apron " if any debris is dropped during the excavation or filling of the tooth. In applying the napkin to the lower posterior teeth (see Fig. 416) somewhat the same pro- cedure should be followed, but when the napkin 339 is being tucked along the lingual side of the teeth the patient must be requested to lift up the tongue; this enables it to be introduced quite Fig. 416. — Shows napkin in situ for lower posterior teeth. The pointed end of the folded napkin should be introduced into the sulcus after the other portion has been introduced on to the floor of the mouth. on the floor of the mouth, thus more readily blocking the flow of saliva from the sub- maxillary and sub-lingual glands, and also being kept in place by the tongue. A few folds of white blotting paper, say, one inch square or less, placed over Stenson's duct on the side to be operated on, will frequently be found a valuable addition to the napkin in the lower jaw, as the parotid gland is a very active one and readily responds to the stimulus of pam, and always on the side from which the stimulus arises ; that is to say, the increased flow is unilateral, in contradistinction from the bDateral flow produced by mental stimuli. The use of a clamp, either with or without the addition of "wings" or other devices, is frequently a great help in the retention of the napkin in the lower jaw. Wool Rolls, a large variety of which have been introduced, are preferred by some operators to napkins ; they may be retained in place by being either tucked into the sulcus between cheek and gum or used in connection with clamps and springs (see Figs. 417, 418). Small discs of unglossed pipe-clay have also been advocated for application to the orifices of the salivary ducts. Wliere any of these methods are used it must not be forgotten that the moisture around a tooth is not due only to the salivary glands, but that the mmute mucous glands found in the flap of gum that surrounds the cervical Fig. 417. — Harvard wool-roll clamp. (Robert Richter's.) Made in four sizes. To fasten the cotton roll to the clamp the wire is bent somewhat outwards, the roll pierced lengthways, and the pin, with roll attached, pressed back under the hook. Either two separate rolls or one long roll (as shown in the figure), may be used. {Dental Manufacturing Co., Ltd.) portion of the teeth are also active : it may therefore be necessary to place small pledgets of wool saturated with mastic varnish in the 340 inter-spaces of adjoining teeth, or if the cavity approaches the cervical margin, the surface of the mucous membrane may be thoroughly dried and pahited over with " liquid amber " (a sort of varnLsh used by jewellers). A 14 % solution of trichloracetic acid has also been recommended for application to the free edge of gum to prevent " weepmg " ; this gives very satisfactory results where for any reason rubber-dam cannot be applied. The Saliva Ejector when first introduced met with considerable oj)position, but its use is now almost universal, and if simple aseptic pre- cautions are taken no objection can possibly be found to its adoption. It is important that the orifices of the tubes should be so placed that the Fio. 418. — Simmons' wool-roll clamp. For application of wool rolls to lower teeth. The upper teeth rest upon the upright of the clamp ; the mouth is thereby held open, and the clamp held firmly down in place. The clamp does not touch the lower teeth — simply presses the rolls firmly against the gimis below the teeth. The rolls are slipped upon the sharpened points before the clamp is placed in the mouth. [Dental Manufacturing Co., Lid.) soft tissues of the floor of the mouth are not sucked into the holes, as in this way considerable pain may be caused. Rubber-dam. — As indicated above, the most thoroughly satisfactory method of obtaming dryness of a tooth or teeth is by the use of rubber-dam. It is necessary that only rubber of a good quality be used, so as to minimize as far as possible the liability to split ; for the same reason it must be fresh and kept in a well-fitting tin case when not in use. If in good condition it should be capable of returning to the flat after being stretched over the forefinger ; if it " bags " its quality Ls doubtful. A light-surfaced rubber has been supjjlicd, and for use in the back of the mouth has some advantages. Again, some operators advocate a " twill " surface, but each operator, getting accustomed to a particular make, finds that he can get the best results with. it. Rubber-dam is usually supplied in three weights, viz. so-called thin, medium, and thick; the latter is rarely if ever used, the medium being the most popular, but the thin, if carefuUy manipulated, is both less painful and more easUy adapted, especially in the case of upjier and anterior teeth. Before any attempt is made to apply the dam, the teeth in the neighbourhood should be carefully examined and a scaler passed over them, as even a small portion of calculus under the cervical flap of the gum may prevent the proper adjustment of rubber and ligature. VVliere approximal cavities exist in the teeth to be treated, it is also most important to smooth over any sharp cervical edges, as otherwise the rubber wiU be torn at each attempt. Much trouble is saved if the rough excavation of the cavities is made before the application of rubber ; edges can then be trimmed approximately and much waste of time avoided. It is well always . to test the teeth by passing silk vip in the approximal spaces ; if this runs into place readUy, without any fraymg or catching, the rubber may be expected to do the same. For the upper anterior teeth some operators prefer to use a triangular-shaped piece, but a square, 6 in. by 6 in., is most universally useful ; for molars, especially in the lower jaw, a piece even larger may be required, measuring 6 in. by 7|in. Rules have been laid down by some as to the number of teeth on either side of the one to be operated upon that should be included in the rubber. No general rule will suit all cases, but it must be borne in mmd that if too few teeth are included easy access to the cavity may be prevented ; and if too many are allowed for, the possibility of leakage is somewhat increased, and the pain and discomfort of an unnecessary number of ligatures are also incurred . Generally speaking it is necessary to include a minimum of three teeth, that is to say, one on each side of the tooth to be treated ; in a few cases, however, it may only be necessary to pass it over two teeth ; while in isolated teeth, or for a cavity on the occlusal surface of a premolar or molar, only the one may be necessary. When applied to a lower molar it is generally advisable to include a molar posterior to the one to be treated, as the " bag " forward of the rubber is apt seriously to inconvenience the operator ; this is more particularly so if the cavity is a distal one. It is also desii-able, where applied to the upper teeth, to finish on a premolar rather than a canine, as a ligature is more difficult to retain upon the latter than the former. The position in which to punch the holes is not without importance. For the upper in- cisors they should be from one inch to one inch and a quarter from the edge of the rubber; the holes should be nearly a quarter of an inch apart (between centres) unless the size or position of any of the teeth is abnormal ; the distance apart should be even greater if the 341 teeth are spaced, or if much recession of gum has taken place. The important point to bear in mind is that there should be sufficient width of rubber completely to cover the gum between the teeth, and also to turn under the free edge of gum to form a watertight joint (see Fig. 420) ; at the same time, any snqjlus rubber only " bags " and prevents free access to the cerv^ical portion of the cavity, and is much more likely to be caught and torn by instruments than if it were taut. The holes ought also to be punched in an arch correspond- ing to the arch of the teeth. A frequent error is to make the holes too small, in fact the Ains\\-orth punch as ordLnarUy supplied by the depots should have at least two more holes of Fig. 4Ht. — To illustrate position in which holes should generally be punched in rubber-dam. Upper incisors Upper premolars and molars Lower premolars and molars the same, but 3 inches from edge of rubber, instead of \\ inch as above. Lower incisors in arc of a circle 2 to 3 inches from the edge of the rubber. increasing size, so that the rubber when stretched over an Ivory's molar (or other large) clamj) is not so liable to split (see Fig. 421). Just as satis- factory a watertight joint may be made as with the smaller holes, without the increased liability to this annoying accident. An easy method of determining the position of the holes is slightly to stretch the dam over the teeth to be included, and then to mark the centre of the cutting edge of each by touching lightly with a tine-pointed probe. The same method may be used if there are any spaces between the teeth due to the loss of some members of the series. Upper or Lower Anterior Teeth. — The rubber should be slightly stretched and gently passed over each of the teeth in turn — sometimes a slight smear of vaseline on the under surface of the rubber will considerably facilitate this stage. In case of nausea in the application of rubber-dam, Louis Jack recommends a few drachms of aqua camphora used as a gargle in mouth and throat. The retractors should then be applied, but with- out any "pull" on the rubber; this enables both hands to be kept free for tlie adjustment INCORRECT METHOD CORRECT METHOD Fig. 420. — To illustrate the method of tucking in edge of rubber-dam under free edge of gum to form a watertight joint or " valve ". of ligatures. If the edge of the rubber does not turn under the free edge of gum readily, a few touches with a blunt flattened burnisher (so- called battle-axe pattern) will usually suffice ; it is always desirable to do this before the ligature is applied rather than to trust to its carrying the rubber before it, for leakage is then liable to occur, because sometimes the ligature masks the position of the " valve " of rubber. The ligature is usually formed of waxed floss silk, but waxed " twist " sOk is equally good and sometimes seems to retain its position more readily. Cobblers' thread, with thek special wax, has also been used by some. The knot should be a surgeon's one, and a double twist in the first portion of it will prevent slipping while the burnisher is again used to adjust the ligature into place ; when this is satisfactory the knot should be completed, and the ends cut off quite close, so as to be out of the way of instruments later. For very sensitive patients it may be advisable to apply o Fio. 421. — Plate of Ainsworth's punch showing correct range of holes that should be supplied. novooaine or other local anaesthetic to the edge of the gum before adjusting the rubber-dam and ligature. It is not always necessary to ligature each tooth included in the dam, but it is generally advisable to put one on the tooth to be treated. Small pledgels of cotton- wool saturated in varnish and placed in the inter-spaces of the 342 other teeth will frequently take the place of ligatures, and be very much less pamful in application ; this method is especially applicable wliere much recession of the gum has taken place. Soft copper or iron " binding wire " may be used with advantage in some cases, where there is a difficulty experienced in the application or retention of silk, or where tlie cavity is near the cervical margin. In order that "the rubber may not slip over the ligature, knots may be tied on the silk before application ; these knots should be so placed as to come on the lingual surface of the tooth. Small glass beads may be tied in instead if preferred. After all the ligatures have been adjusted the retractors may be tightened, and an unrestricted view of Fig. 422. — Rubber-dam holder. {H. P. Fernald's.) Co., Ltd.) the cavity should result. A napkin should be placed under the rubber where it passes over the lower lip, and if weiglits are employed they will keep it in place by catching it in the clips. Many operators prefer Fernald's wire frame holder to take the place of retractors and weights (see Fig. 422). Uf-per Posterior Teeth. — To apply the rubber- dam to these teeth is a little more difficult than the foregoing. Ligatures can be used near the front of the mouth, but are much more difficult to adjust further back. For the molars, there- fore, and also frequently for the premolars, " clamps " must be used. A very large number of these have been designed and intro- duced from time to time, and much difference of opuiion has resulted from a comparison of their supposed merits. It is most important that a clamp should accurately fit the neck of the tooth to which it is to be applied. It should have sufficient " spring " to retain its position against the strain of the rubber, and it should hold the rubber out of the way so that easy access may be obtained to the tooth. A selec- tion of different shapes, therefore, must be kept, and the clamp should always be tried on the tooth before being used. Where a clamp is to be applied the procedure may be in either of two ways : [a) The rubber may be passed over the tooth and held in position by the left hand while the clamp, previously placed on the forceps, is passed over the tooth, care being taken to see that the edges of the rubber are turned under the cervical edge of gum ; (6) the " blades " of the clamp may be passed through the hole in the rubber so that the points of the forceps may just pass through the holes in the clamp; the rubber is gathered together and held in the left hand, while the blades of the clamp are adjusted exactly in place on the tooth ; the rubber is then spread out and carefully worked over the tooth and clamp with a burnisher or other blunt instrument ; in this way a water-tight joint may be more readily made and there is less likelihood of the clamp " pinching " the edge of the rubber. Ivory's clamps were introduced to facilitate the application of rubber, and are made with a little process of metal on each side, so that the rubber is held clear of the blades until the clamp is in correct position; the rubber is then released by a blunt instru- ment and sprmgs into its correct place. It is necessary to punch rather larger holes for these clamps, but their use greatly facilitates the application of rubber in many cases. Where more than one clamp is to be used the posterior one should be introduced first and the rubber brought over the anterior teeth afterwards. The procedure in the case of lower molars or premolars is the same as described above, except that it is almost always necessary to pass the clamp through the rubber unless an Ivory's pattern is used. Cervical cavnties, especially those in the posterior teeth, frequently present great diffi- culties in the application of rubber-dam ; some- times it is quite impossible to apply it without (Dental Manufacturing 343 great pain and inconvenience to the patient, besides considerable damage to the periodontal ?nembrane. In these cases some other treat- ment has to be adopted, and possibly a filling chosen that does not demand absolute dryness for its insertion. For the anterior teeth various cervical clamps have been introduced, and by their use some otherwise difficult cervical cavities may be kept quite dry durmg the building of the filling (see Fig. 423). The cavity should be partly ex- cavated, and a temporary gutta-percha filling inserted and left rather full and packed against the free edge of gum. In a day or two when this is removed, the cervical margin of the cavity will be better defined by the lifting back Fig. 423. — Ivory's adjustable cervical clamp. This clamp is tightened to the tooth by a slide. It may be adjusted to slide higher up the tooth without being removed by loosening the set-screw and pushing the arm attached to the labial jaw farther through the slide, and then tightening the screw again. Pin-holes are made in the arm to prevent any tendency to slip on large teeth. (Dental Manufacturing Co., Ltd.) of the soft parts, and the application of the rubber-dam and cervical clamp much facilitated. Where some posterior teeth are missing, as for instance in the case of a distal cavity in an upper canine \\ith both the premolars on the .same side absent, much time may often be saved if, instead of punching a hole for the first molar, the rubber is merely stretched over the molar and a blunt- edged clamp placed upon that tooth outside the rubber. This serves to hold the rubber out of the way, and the adjustment of it over the intervening space is easily made, whereas if a hole is punched some difficulty may be ex- perienced in finding the exact position for it ; if it is made too near the canine hole the rubber will be pulled away from that tooth, and if too far away the rubber will " bag " and interfere with the clear view of the cavity. Where rubber is applied to the lower jaw it is usually necessary to use the saliva ejector, as the difficulty of swallowing is sometimes con- siderable ; this may also be necessary in the case of the upper teeth. III.— SEPARATION Before a tooth can be successfully filled, it is frequently necessary to obtain a certain amount of separation ; this is especially the case where the teeth are somewhat tightly placed or crowded together. The ideal tillmg entirely restores the tooth to its original contour, and as, generahy speaking, the teeth have tended to ajjproximate to each other with the progress of caries and loss of tissue, so it is necessary to separate to allow for the correct building up to replace this lost tissue. Wliere gold is used for the restoration of contour sufficient separation must be obtained to allow for the correct polishing of the contact points before the teeth come into their normal position agam. Good separation also avoids the neces- sity of cutting away unich tooth tissue before the introduction of the filling or inlay. The methods may be divided into Gradual and Immediate. Gradual In the gradual method, some material is introduced between the teeth, and by its change of shape the desired result is brought about. It is usually the less painful and more satis- factory plan where it can be used, but care must be taken not to produce too much pressure on the process of gum between the teeth or per- manent recession of the gum may result. Some writers lay great stress on this point, which should not be overlooked. In certain cases, however, where the interstitial gum tissue has become abnormally thickened, o\\ing for instance to the irritation of a rough cervical edge, it may be necessary deliberately to produce pressure upon it, in oi-der that a clear view of the margins of the cavity may be afterwards obtained. The most certain and rapid material to use for separation is undoubtedly rubber, either in the form of wedges or blocks of various thick- nesses, or rubber-dam rolled up to the required size. In either case the rubber is stretched and passed up between the teeth, a space being allowed to remain between it and the gum ; the ends are then cut off quite close to the teeth. As a rule one to two days is the utmost time that should be allowed to elapse before the patient is seen again, as the action is rapid, and much pain and inconvenience may result if the rubber is left in too long. Even after twenty -four hours it may be advisable to substitute some non- expansUe material, which may be left in untfi the periodontitis has passed away. An opera- tion on a tooth immediately after separation 344 by rubber is sometimes exceedingly paiuful. In order to jDrevent the rubber slipping out after separation has commenced, or to prevent pressure on the gum, it is often a good plan to open ujj and partly excavate the cavity, and fix tlie iiibber with gutta-percha packed in nearly cold while the rubber is kept on the stretch. Another way of avoiding undue pressure on the gum where there are two adjacent carious cavities is to place a small metal bridge across the floor of the space with its ends resting in both cavities. Another means of effecting separation is by the use of cotton-wool. It is best applied in the following manner. Firstly, roughly excavate the cavity, cutting away sharp edges of enamel. Then wipe out -v^dth carbolized resin, next pass a piece of waxed ligature sUk between the teeth, and pack in cotton-wool from the lingual surface ; when the space is quite full tie the silk tightly around the cotton-wool, making it into a " bale ", so that the expansion wUl be in a medio-distal direction. If the cavity is very deep or sensitive, a sedative dressing may be applied, and temporary gutta-percha packed into the deeper portion before the wool is packed in. It is necessary, however, to leave room for a certain bulk of wool, or the resulting separation wUl not be -sufficient. Tape folded upon itseK until just thick enough to pass tightly up between the teeth is another material that may be used. This may be put in by the jMtient instead of rubber after the latter has been in a few hours, if much pain has resulted. A wooden wedge made from a lucifer match may also be easily put in by the patient if tape is inconvenient. Wedges of orange-wood lightly tapped into place with a mallet, or pressed into position with specially designed forceps, are also used; they tend, however, as rubber does, to press on the inter-proximal gum tissue, and care must be exercised to prevent this. Gutta-percha packed between the teeth, if left in position for a sufficient length of time, wUl produce separation, but this is brought about more by the pressure of occlusion and mastication upon the gutta-percha than by any power of expansion inliercnt in the material. In Immediate immediate separation some form of mechanical appliance is used to force the teeth apart. Here the danger is that the enamel may be injured at the point of contact with the instrument, or that such force may be used as to cause severe periodontitis. In young patients there is least danger of either, as the degree of mobility of teeth is greater than in those of more advanced age, but in all cases the greatest care should be exercised. Combination of Gradual and Immediate Probably a combination of both methods is the most desirable — the use of a separator to obtain the preliminary opening, and whOe it is still in situ the packing in of gutta-percha with cold instruments ; at the next visit of the patient all inflammation will have passed away and the fillmg may be completed. The separators as supplied are either in the form of a double wedge, gradually approximated by the tightening of a screw (as in the " Uni- versal ", etc., see Fig. 424), or in the form Fio. 424. — The "Universal" separator. (Dental Manufacturing Co., Ltd.) of " cribs " applied to teeth and then gradually separated by means of double -threaded screws (as in the " Perry ", see Fig. 425). In the latter type the j)ressure is spread over two points on each tooth instead of only one, and therefore it is claimed that less damage is likely to result ; by means of rubber or impres- sion composition placed between the " bow " of the instrument and the occlusal surfaces of the teeth, the jaws can be prevented from sliding up and injuring the soft parts. The " Perry " is Fig. 425. — The " Perry " separator. (Dental Manufacturing Co., Ltd.) especially useful for the posterior teeth, while the so-called " Universal " is sometimes more readily applied in the anterior region. IV.— GENERAL PRIKCIPLES OF CAVITY PREPARATION It frequently happens that when a patient presents himself for dental treatment, examina- tion of the mouth will reveal a number of teeth that require attention. Before a reliable opinion can be given it may be necessary (and in most cases it is necessary) to open up the cavities, and thus determine the extent of the 345 disease, and form a mental picture of the most suitable after-treatment. If the moutli is not in a clean state, suitable scaling should be undertaken, the teeth should be polished, and the mouth sprayed with the compressed air atomizer previously referred to. It may also be advisable to give the patient instructions as to the use of the tooth-brush, etc., so that on the next visit aU the teeth may be found in a more suitable condition for treatment. All the cavities should then be opened up, and those in which the pulp is not involved may, after slight excavation, be dressed vdth oil of cloves or other suitable obtundent, and sealed with temporary gutta-percha. Attention may then be directed to those requiring root-treatment. In this way a more comprehensive view may ' be obtained of the condition of the dentition, and while treatment is being undertaken in the teeth ^^■ith the most advanced caries, or in those that have been giving pain, the others, partly excavated and sealed up wdth antiseptic obtundent dressings, are tending to become more amenable to future treatment. During the preliminary opening up and excavation the carious cavity should be freely syringed out with tepid water in ANhich some pleasantly flavoured antiseptic has been dissolved. It is important that the water should be kept near to the temperature of the blood, as even a ' comparatively slight variation from this may ! cause pain, especially if there be an exposed and inflamed pulp in the tooth. A chisel, either straight or curved, is the most useful instrument for the preliminary opening up of most cavities. It must be kept very sharp, and a thumb-rest must be found before any force is applied, so that the blade shall never reach the floor of the cavity, nor the cutting edge slip from its correct position in case of , any sudden movement of the patient. The j direction and " cut " of the chisel must always be so arranged that the line of cleavage shall j be in a Ime with, and so between, the enamel prisms, and never across them. The chisel should only be used for the breaking down of enamel that is unsupported by dentine. A few bold cuts \\ill usually suffice to give thorough access to most approximal cavities, and also those on the occlusal surface where fairly extensive caries has taken place. In ! some fissure cavities, howev^er, it is necessary ' first to use a cross-cut fissure-burr. These are of very hard steel, and consequently care must be taken when using lateral pressure to I avoid fracture. The point should be intro- duced into that part of the fissure which offers most opportunity, and the burr should be di- rected along the line of tlie fissure ; a slight saw- ing motion facilitates the cutting. The cariou.s floor of the cavity should be avoided, as the l cross-cut burrs are liable to give pain when used in dentine. It will be found that enamel is most readily cut from the itiside ; the burr should, therefore, be so directed along the fissure that it tends to cut the enamel from within outwards. The cross-cut burrs require frequent renewal as they soon become dull ; when this has taken place they should be discarded. Breaking off the terminal y,, inch will sometimes allow another unworn portion to come into use and give a fissure-burr another short period of usefulness. Carborundum wheels and points may sometimes be used in the preliminary treatment of enamel walls, more especially in molars where clearance for the opposing tootli has to be made. Enamel walls can be reduced in height very readily by this means. Wlien free access has been made, the softened dentine should be very carefully removed. Sharp, straight or curved, spoon excavators are generally the best for this purpose. They should be so directed that the carious decalcified portion is flaked up around the edges first, and then gradually all removed towards the centre of the cavity, special care being taken when the instrument has to approach near to the pulp. After the removal of all softened tissue the cavity has to be shaped to receive the filling, or inlay, or whatever treatment has been decided upon. This further excavation is done by the use of round, oval, or inverted-cone burrs, and hatchet or hoe excavators. Again it is all-important that every mstrument should be exceedingly sharp, for in this way much pain and time may be saved. Dentine when cut is much less painjul than tvhen scraped; therefore all instruments should be applied at such an aiu/le that real cutting takes place. Too much stress caimot be laid upon this point. The shaping of a cavity demands great care and consideration ; the outlines of the subse- quent fUlLng should be graceful (this is specially important for gold fillings in the anterior teeth), and the walls should be sufficiently strong, not only to retain the filling, but to bear the stress and stram of mastication, etc. In approximal cavities endeavour should be made to arrange the junction of the tooth and filling in such a position that it may easily be kejit clean. The cervical margins of cavities demand special attention; the position of the junction of the enamel and cementum must be clearly defined, judgement being necessary to direct the excava- tion so that on the one hand weak edges of enamel may not be left, and on the other that the junction of filling and tooth shall not be too far under the gum margin. In approximal cavities in premolars and molars the buccal and lingual walls should be kept as nearly parallel as possible. Any softened patches in the enamel in the vicinity of a cavity should also 346 be excavated and if necessary included in it ; likewise some developmental pits may have to be cut out and included in the cavity outline. Where grooves are cut in the dentine for reten- tion purposes they must not be too deep, as there is great danger of \\'eakening the wall and of leaving inaccessible portions of the cavity, especially when cohesive gold is to be used. The final treatment of the enamel edges varies in accordance with the nature of the filling material to be used, and it will be sufficient in this place merely to lay stress upon the import- ance of smooth well-finished edges, so that there may be a perfect junction between the tooth and filling. Very sharp chisels are again required, and now the edges may be " planed ". Fine-cut '" finishing " burrs are also very useful, and very small stones mounted on thin mandrels give excellent results. Strips and discs are some- times necessary, but enamel edges bevelled in this way are apt to be uneven, as it is difficult to direct the cut at the same angle with the surface in the different parts of the cavity. v.— SENSITIVE DENTINE AND THE AVOIDANCE OF PAIN [For Electro-therapeutical Treatment, see Chap. XXXI.] Much has been written on this subject, and many methods have been introduced to over- come the po«er of transmission of pain through the hard portions of a tooth during excavation or other necessary treatment. It has been stated that perfectly normal dentine is not sensitive ; for example, in fracture of a portion of the cutting edge of an incisor where dentine is exposed, at first this tissue does not give rise to pain, but a short exposure to the fluids of the mouth makes it hypersensitive. Again, all the teeth in the same mouth may show different degrees of sensibility, and even cavities in different jjortions of the same teeth vary in tlie same way. The dentine near the cervical margin is invariably more capable of trans- mitting f)ain than the rest, especially on the buccal surface of molars. These A\ell-known clinical facts can be explained, to a certain extent only, by the structure of the teeth ; it can be readily believed that dentine in the neighbourhood of the " granular layer ", and at tlie amelo-dentinal junction, would be more capable of transmitting sensation than in a somewhat deeper portion of the tooth. Authorities are not yet agreed as to the exact nature of the contents of the dentinal tubules ; the outstanding clinical fact, however, is that the contents, whether nervous tissue (according to the recent researches of Howard Mummery) or merely protoplasmic, are capable of trans- mitting as pain to the sensorium certain stimuli, which may reach them. Another fact to bear in mind is that not infrequently, especially over the cusps of the j)osterior teeth, there is pene- tration of the enamel by the so-called " enamel spindles " ; these spaces in the enamel, being filled with the same tissue as the dentinal tubules and connected with them, are capable of giving rise to considerable pain when sub- jected to cutting, or grinding with a stone. There is jirobably considerable tactile sense about the teeth, quite apart from the sense of pressure that may be recognized through the pericementum ; for instance, the crunch of sugar may be readily differentiated from the crunch of a cinder. A pulpless tootli has much less power of discrimination in this way than a normal one. Dentine reacts to thermal stimuli, which however are interpreted as jMin, not as a thermal change. It also reacts to bacterial products, such as lactic acid, and to salt, sweet, or acid substances or fluids, as well as to mechanical stimuli. The exact method of transmission has not yet been determined ; nor have the exact histological contents of the dentinal tubules. Burchard gives two theories of the jihysical phenomena that may be con- cerned in the process, the second one being favoured by him — (a) That a contraction of the whole cell, fibril and odontoblast, occurs, sensory nerve-endings being pressed upon in the act ; (6) That a wave-like motion along the pro- toplasm is set up, causing excitation of the sensory nerves, and due to the incompressibility of the water (Gysi). There is no doubt that if excessive sensibility of dentine could easily be avoided, many of the difficulties of operative dental surgery would vanish ; the nervous strain on both patient and operator would be reduced enormously. Very many methods have been introduced, and all have given a certain amount of success, but nothing so far has proved thorouglily and uni- formly satisfactory. The ideal method should conform to the following conditions — ■ (1) Ease and painlessness of application. (2) Rapidity of action. (3) Limitation of action to the dentine, with sufficient penetration to allow for the painless shaping of the cavity. (4) Non-irritation of the pulp, botli at the time of application and afterwards. (5) Absence of discoloration. So far no drug or method has been introduced that conforms to the above rather exacting requirements ; the failures have been so many that some of the best operators have come to rely principally on gaining the confidence of 347 the patient and on firm, decisive, and rapid cutting with perfectly sharpened instruments, by wliich they claim that more can be done than by the use of any special drug, etc. The advantage of sharp instruments lies largely in the fact that pressure is avoided, as this causes more pain than cutting. Carious dentine is often more sensitive if cut in one direction than another. Generally speaking, the part just under the enamel is the most sensitive, and cutting outwards causes less pain than driving an instrument between the enamel and dentine and then cutting inwards. Neverthe- less, many individuals, especially children, present tliemselves for treatment for whom it is impossible to excavate a cavity correctly with- out the use of some method for reducing the sensitiveness of dentine. It is impossible to mention all the methods that have been employed, but the following are the more important — Hot Air, especially if a dehydrating agent (e. g. alcohol) is used in conjunction with it ; the application at first may be very painful, and sometimes the pain may be rather prolonged. Cold has been used in the form of ethyl chloride spray directed upon the sensitive cavity, which has been liglitly filled with wool. It is frequently very painful in application, and as the effects are somewhat transient, rapid excavation has to be done before recovery of sensation; there is also danger of causing inflammation of the pulp. It is only used for shallow cavities in tlie anterior teeth. Phenol is very nuich used, especially in con- junction with hot air ; it may also be .sealed into the cavity \\-ith temporary gutta-percha with advantage. Oil of Cloves is used in the same way. A combination of both di'ugs in equal parts sealed into the cavity for some days seems to give better results than either used separately. Zinc Chloride. — F. N. Johnston recommends the following — R Zinci Chloridi . . . gr. xx. Alcohol . . . . f.T iv. ClJoroformum ad . . f 3 j. M. (If the zinc salt does not make a clear solution with alcohol add a drop of hydrochloric acid.) Silver Nitrate may be applied either in the solid form or in a 50 % solution. If in the former, the most con\'enient method is to melt a small bead of the salt upon a roughened silver point, care being taken not to allow it to become dish)dged. This is important, because a dis- lodged portion might easily set up larjaigeal spasm if it remained in tlie air passage, or if swallo^\■ed might set up ulceration of the stomach ; a prompt dose of sodium chloride would of course counteract the latter. The resulting discoloration of the dentine when silver nitrate is used limits the use of this drug very considerably. Fortunately, however, as it is extremely efficient in many cases, the dis- coloration is usually limited to the decalcified dentine, which is removed on a subsequent occasion in the preparation of the cavity. Cocaine has been advocated and may be used in several ^\ays ; the mere application of a .solution of hydrochloride of cocame to the dentine, even if sealed in for some time, does not appear to have any effect. If, however, pressure is used, by tlie introduction of a plug of unvulcanized rubber pressed into place with a large-headed plugger, anaesthesia of the dentine may result ; this is, however, brought about in many instances by the cocaine reaching the pulp tissue, and it is therefore not truly an anaesthesia of the dentine. The use of the so-called "' high pressure " syringe is followed by anaesthesia of the pulp. Its use is only justifiable when the removal of the pulp is intended; it should not, therefore, be employed in ordinary cases of hypersensitive dentine, if the pulp is to be left intact. Paraform is a polymer of formaldehyde and occurs as a white amorphous po\\der with a pungent odour. It is exceedingly powerful, and must be used with the utmo.st caution and with a definite know ledge of its action. It is especially useful in shallow hypersensitiv^e cavities where a dressing can be left in contact for a week or more. It should be mixed with some form of temporary filling but never in a greater propor- tion than five per cent ; care must be taken that the paraform is evenly distributed through- out, so as to avoid the possibility of a concen- trated dose upon a small portion of dentine. The most convenient preparation is that made with temporary gutta-percha ; it should not be heated more than neces.sary, as the paraform tends to volatilize. Another preparation may be made by mixing it with ox\^-sulphate of zinc ; this, when mixed into a paste with an aqueous solution of gum arable, may be introduced into the sensitive cavity and covered with temporary gutta-percha. Paraform should not be used in a deep cavity, and if used in a two per cent or five per cent proportion should be left in from seven to fourteen days ; the penetration is sufficient to allow of excavation, but is localized to the cavity treated, i. e. treatment of a cavity on the occlusal .surface of a molar would not render the dentine in the buccal region insensitive. Trichloracetic Acid, 10 to 15 % solution, some- times gives good results if the dentine be saturated with the acid, which is afterwards 348 evaporated by the hot-air syi'inge. The appli- cation may, however, be rather painful. General Anodynes, such as opium, morphine, or the bromides of potassium, sodium, or ammonium, have been used ; in ordinary cases, however, such treatment is not indicated. In the same way general anaesthetics have been employed, but are now rarely necessary. Local Anaesthesia. — The introduction of drugs like novocaine, and the improvement in sjTinges and technique, have naturally opened up a field of usefulness in application to conservative dentistry. It has been found that a deep injection m many cases results in complete anaesthesia of several teeth ; this of course eiaables perfect excavation to be made without any inconvenience to the patient. A. H. Parrott, of Birmingham (16) (17), by means of a special syringe, makes injections into the bony septum, by means of which he claims to get perfect anaesthesia of the part extending to the pulp, and thus to render the dentine insensitive. It may be by such methods, rather than by means of drugs applied directly to the dentine, that success may be achieved, but at the moment it is impossible to forecast with any degree of certainty. J. A. W. VI.— OBJECTS AND INTENTIONS OF TOOTH RESTORATION The objects and intentions in filling a carious tooth are : firstly, to arrest the progress of the caries that is taking place in the tooth ; secondly, to restore the usefulness of the tooth for mastica- tion and other purposes ; and thii-dly, to prevent the recurrence of the caries, that is, so to alter the conditions, that having been once arrested it wUl not commence afresh. In considering this subject, therefore, it is necessary to distinguish between— (1) Arrest of the caries (for the time being) ; (2) Prevention of its recurrence (at some future time) ; (3) Restoration of function. 1. Arrest of Caries. — It is the general experi- ence of dentists that caries in a tooth may be inhibited for the time being by removmg from the tooth all the tissues affected, and replacing them by a watertight plug. It is obvious, liow- ever, that in doing this the pulp must not be injured or exposed to mjury, and that the tooth must be left strong enough, when fiUed, to with- stand the stresses of mastication, as failure in either of these particulars would render useless the success gained in arresting the caries. To remove completely all that part of the tooth that is affected by caries is not easy, and, as will presently be seen, is not always desirable, nor is it possible in all cases to be sure that the fillings inserted are watertight ; but it is admitted that the more nearly perfect the operation of filling a tooth is in these two par- ticulars, the more certain is it to be successful in arresting the caries. It is worth while, there- fore, to consider the amount of latitude that may be allowed — how far, in fact, the fillings may fail in being watertight, or the removal of carious tissues fail in being complete, without endangering success. The affected tissues to be removed may be either enamel or dentine, and to ensure their complete removal it is necessary to distinguisli them from those parts of the tootli that are still sound. The first effect of caries on enamel is a partial decalcification, probably of the inter- prismatic substance, which renders the enamel to a certain extent porous, and causes this dense and translucent substance to look more opaque ; this appearance is brought about by the per- meation of the enamel by a substance (saliva) with a lesser coefficient of refraction of light than has enamel itself (just as air mixed with water wiU cause the opacity of foam), and one of the incidental advantages of the use of the rubber -dam is that it causes the carious enamel to be more easily recognized, since dry, porous enamel is even more opaque than w et (air having a lesser coefficient of refraction of light than saliva). As the decalcification proceeds the enamel is gradually disintegrated and broken up into minute fragments ; on the external surface of the tooth these are washed away by the saliva, but should the decalcification of the enamel take place from the side of the dentine (secondary enamel caries), the fragments can be seen as a I white cheesy layer between the enamel and the I dentine. Owing to its opacity, therefore, carious 1 enamel in any position can be easily recognized, and in its case ocular evidence is more trust- worthy than tactile, since partly decalcified enamel, even though opaque, is capable of opposing great resistance to an excavator or a burr, and even to a chisel. The question how enamel affected by primary caries should be dealt with, is easily answered : it should be entirely removed. It has been shown that enamel in which there is only slight loss of translucency may be quite porous, and this bemg so, it is almost certain sooner or later to become disintegrated and break dowai alto- gether; there can, therefore, be no justification for leaving any such opaque enamel at the edge of a filling (26). Nor must any of the debris of secondary caries of enamel be left in the cavity ; in addition to tlie fact that such debris are loaded with micro-organisms, their presence shows that the enamel fibres under which they are seen — from which in fact they have been broken off — are unsupported, i. e. are not con- tinuous with sound dentine. It is known that 349 such fibres, if not removed (and their removal ia generaUy the safer course), should be sup- ported by an adhesive filling-material, such as oxy-phosphate of zmc, this being the treatment that gives them the best chance of resistmg fracture duruig mastication ; and in order to make such a filling adliere, all trace of the cheesy material must be carefully scraped from the under-surface of the enamel. The rule, therefore, Ls, without exception : all enamel that shows any signs of decalcification — any loss of translucency — should be removed. To distinguish sound from affected dentine, reliance is placed not on sight, but on sense of touch ; it is, in fact, assumed, that hard dentine is sound, while dentine in any degree softened, i. e. decalcified, is unsound ; and for present purposes, it is probably justifiable to make this assumption, though Mller (14) has shown that the tubules of even hard dentine may be invaded by bacteria. The best means of estimating tlie hardness of dentine is by the use of a sharp spoon-excavator ; with this instrument, better than any other, the educated touch can tell when all the decalcified dentine has been removed and tissues of normal hardness have been reached. No decalcified dentine, i. e. no dentine at all soft under the excavator, should be left under the enamel or in the walls of the cavity ; this is a rule that admits of no exception, since it is plain that such dentine, even should the process of caries become arrested in it, would not give sufficient support to the overlying enamel to enable it to withstand mastication, and would also, owing to the large amount of moisture in it, greatly increase the difficulty of inserting a watertight filling. As regards the floor of tlie cavity, and by floor is here meant the pulp wall, the course is not quite so clear. It has until lately been the accepted teaching (23, pp. 286 and 402) that a certain amount of soft dentine may safely be left ui this position as a protective covermg for the pulp agamst thermal irritation, provided that under the soft dentine a layer of hard den- tme remams to protect the pulp from pressure ; it was recommended that the soft dentme left should be soaked with oil of cloves or some other antiseptic, and by some authors the hope was even held out that in course of time it might become recalcified (10). Lately, however, these views have undergone considerable cliange. It is pointed out that softened dentine is charged with products of bacterial growth, which act as irritants to the pulp ; that these can pene- trate to the pulp even through a layer of hard dentine (20) ; and that there is no proof that they can be in any way neutralized by antiseptic treatment. It is also stated that the results of this treatment in the past have not been good (11, p. 141); that in most cases, when much soft dentme has been left, the pulp has either degenerated, as the result of chronic inflamma- tion, or has been destroyed by acute septic inflammation (21). The practice of leaving softened dentme to protect the pulp seems to have been fostered by the belief that pulp trouble following on a filling is generally due to thermal hritation ; whereas there is reason to believe that in most cases these troubles are of septic origin, and more likely to be caused than prevented by leaving, under the filling, material charged with micro-organisms and their products. It is, therefore, now generally taught, that it is better to remove completely (11, p. 141) (3, vol. i, p. 206) (15) (22, vol. u, p. 379) aU the softened dentme from the floor of the cavity, when this can be done without exposmg the pulp, and to insert a lining of non- couductmg material underneath the fillmg, should thermal irritation be feared. When complete removal would cause an expo.sure, there is perhaps justification for leaving over the pulp a very small quantity of decalcified dentine, more especially in young patients, in whom the pulp has greater vitality, and in whom root-filling involves greater risks ; such treat- ment, however, should be restricted to those cases in which there is no history of the spas- modic pam characteristic of mflammation of the pulp, and, as a measure of precaution, the dentine left should be rendered sterile as far as possible ; it is generally recognized, however, that if any large quantity of softened dentme is left, resulting injury to the pulp is almost certain to occur. Should no trouble arise from the pulp, the leaving of a small amount of decalcified dentine on the floor of the cavity does not seem to interfere with the power of the fillmg to arrest caries (3, vol. i, p. 206). To sum up, then : in order to arrest the progress of the caries, all carious enamel must be removed and all carious dentine, save ui some cases a minute portion covering the pulp, and even this should be removed if it can be done without exposmg the pulp. The second question — Must the plug be water- tight m order to arrest caries ? — is a more difficult one to answer. It can hardly be doubted that many fUIings that have rendered excellent service in the mouth for years, are not, and indeed have never been, watertight. But it is pointed out that this good service is only rendered ia mouths m which there is a jjractical immunity from caries, and that the fiUhig only remauis serviceable as long as this immunity lasts : should the immunity disappear, the leak serves as a starting point for the renewal of caries. The fact indeed seems to be, that in im- mune mouths almost any filling that {prevents 350 effectively the lodgement of food, is sufficient to arrest the caries for the time being. It must also be admitted to be improbable that most iillmg-materials are an effective barrier against micro-organisms (25), and indeed they are not used by the ordinary operator in such a way as always to make perfectly watertight joints (23, p. 298) ; but in spite of this there is a consensus of opinion among dentists that the efficiency of a filUng in causing arrest of caries depends largely on the amoiuit of success attained m making it watertight (22, vol. ii, p. 400) (3, vol. i, p. 192) (11, p. 153) (23, p. 383). With the present limited knowledge of the exact conditions under which caries takes place, it is impossible to be too dogmatic ; but it is probably true that in most mouths a leaking filling will lead sooner or later to a renewal of the carious process in the cavity, while with a watertight filling no such result need be feared, and, if caries recurs, it does so by a fresh decalcification of the enamel taking place at the edge of the filling. 2. Prevention of Recurrence. — Even when it has been arrested for the time being by a suc- cessful operation, caries may recur later at the edge of the filling. This may happen because an uneven joint between the enamel and the filling-material affords lodgement for ferment- able material, and must in such a case be attributed to faulty technique on the part of the operator, or to defects in the filling -material he has used ; it may also, however, happen when the joint is perfect, and in this case the recurrence of the caries must be due to the non- removal of the conditions that caused it. It is to remove these conditions that " extension for prevention " has been suggested, and it is v\orth « hile to consider this proceeding in some detail. The principles on which extension for preven- tion is based were given out many years ago (18) (24), but in more recent times they have been much insisted on by G. V. Black, and it is from his writings that the followmg account of them is mainly taken. It is pointed out by him that carious cavities may be divided into two groups, according to their origin — 1. Pit and fissure cavities. 2. Smooth surface cavities. Pit and fissure cavities are those originating in the pits and fissures to be found m the teeth; these occur normally on occlusal sur- faces of molars and premolars, on Iniccal surfaces of molars, and sometimes on lingual surfaces of upper incisors — m irregularly calcified teeth they may be found in any part of the enamel. Although these pits and fissures do not generally extend completely through the enamel, they act as starting-points for cavities, since they afford lodgement for colonies of micro-organ- isms, which grow on the carbo-hydrates that have found entrance into them, and which are supported by the fresh supplies of sugar and other carbo-hydrates coming in from the mouth. The acid generated by these micro-organisms gradually decalcifies the enamel, and this it does more quickly in the direction of the enamel fibres (that is towards the dentine), perhaps because the cementing substance between the rods is more easily decalcified than the rods themselves. When the dentine is reached, the process of softening is more rapid : it spreads most rapidly in the direction of the tubules and under the enamel, the result being an area of softening in the dentine of pyramidal shape, with its base to- wards the opening in the ennmel (see Fig. 426). Fig. 420. — C'arums dentine under fissure in a molar tooth showing pyramidal shape of softened area. In these cavities, given a thorough removal of the softened dentine and the frail enamel, and a watertight filling with perfect edges, there is no tendency to recurrence, since in making such a filling, the pit or fissure, the predisposing cause of the caries, is of necessity removed. In them, therefore, no extension for prevention is required. Smooth surface cavities are cavities not commencing in pits or fissures ; they occur on the buccal, labial and approximal surfaces of all the teeth, and rarely on the lingual surfaces also. The caries appears first as an opaque spot on the smooth translucent surface of the enamel. For such spots to occur, it is believed to be necessary that micro-organisms should have become attached to the tooth in a gela- tinous matrix (zoogloea formation), which pre- vents the washing away of the acid they produce, and so leads to the decalcification of the enamel 351 on which they are fixed. The opaque spot gradually enlarges and finally the enamel breaks down, generally at the point where the opacity first appeared, and the cav-ity in the dentine is formed in the usual way. If a section of such a tooth is made, it will be found that the cavity or softening in the dentine is of the usual pyramidal shape — the apex towards the pulp and the base towards the enamel ; but it will also be found that the enamel is more ex- tensively carious on the surface than in its deeper layers, so that the area of caries in it is more or less cone-shaped, and on the surface may even be of greater extent than the dentinal softening (see Figs. 427, 428). In this particular, therefore, these cavities differ markedly from pit and fissure cavities, in which the decay does not spread on the external surface of the enamel. any quantity of enamel may ultimately break down, but on the surface the caries only spreads to a certain limited extent. There are, KiG. 427. — Diagram showing largo extent of carious enamel iu smooth-surface cavities. (G. V. Black : Operative Dentistry.) but on its dentinal surface, where it is secondary to that of the dentine. It is supposed that the acid generated by the micro-organisms penetrates the enamel more easilv in the direction of the fibres, since the Fig. i2H. — i'hotograph of a cross-soctiuii of a pre- molar, showing broad whitened areas of caries of enamel on the approximal surfaces. (G. V. Black : Operative Dentistry.) decalcification is greater under the older zoogloea formation in the centre of the opacjue spot than under the more recent i^eripheral portion. Owing to the softening of the dentine and to consec|uent secondary caries of enamel, ' ^iiiiiiiiiiiiiiiiiiiuiijDjjjjg- / ViiiSiJSSiiSilSffllli^ Fig. 429. Fig. 430. A diagrammatic representation of caries of the bucca surfaces, Fig. 429, and of cross-sections of the crowns. Fig. 430, of tlie lower first and second premolars and first and second molars, showing the location of caries and tendency to spread in a direction aroimd the crowns of the teeth, following the free margin of tlie gingivae. In Fig. 429 the dotted line represents the gingival line, or Ime of the attachment of the gum tissue to the teeth. The continuous dark line represents the line of the free margin of the gingivae, which arches toward tlie occlusal surface in passing between the teeth. The double Ime represents a saw-cut dividing the crowns through the areas of carious enamel. Fig. 430 represents the areas of carious enamel exposed by cutting away the crowns. The portions darkened represent the parts of the enamel most liable to caries, while the areas left white at the medio- and disto-buccal angles of the teeth represent areas that are almost always immune to caries. (G. V. Black : Opera- tive Denti.strij.) in fact, certain boundaries that it does not cross : on buccal and labial surfaces it starts near the gum margin and sjjreads medio- distally and occlusally, but stops short of the angles of the tooth, and does not extend oc- clusally beyond the ghigival third nor reach underneath the gum (see Figs. 429, 430) ; on approximal surfaces it generally starts just underneath the contact point and spreads in every direction, but stops short of the angles of the tooth, and does not encroach on the occlusal surface or reach beneath the gum (see Figs. 431, 432). The non-immune area, therefore, or area over which the caries may spread, may be seen in both these cases to correspond to the area of the tooth over which food is not driven in mastication, or that is not covered by gum. It is probable that the gum-covering and the friction of food both prevent the zoogloea forma- tion necessary for the production of surface caries, and it is noticed in confirmation of this theory that the non-immune area varies under different conditions : for instance, it is relatively 352 smaller in teeth in which the embrasures or re-entrant angles are large (see Fig. 433), since the approximal surfaces of such teeth are more exposed to the friction of food; and it is extended gingivally on approximal surfaces when the inter-proximal gum has been so flattened by the impaction of food as to be pushed away from tlie neck of the tooth. In preparing a smooth surface cavity accord- ing to the ordinary rules, all the surface enamel Figs. 431, 432. Diagrammatic representation of the areas of liability to caries on the approximal surfaces of the pre- molars and molars. Fig. 431, and on the buccal surfaces of the premolars and molars, Fig. 432. The arching of the free border of the gum tissue as it passes between the teeth is iUustrated in Fig. 431. The form of this arch varies greatly in different cases. In many, and particularly in young persons, the summit of the arch is nearly flat for a more or less considerable space. (G. V. Black : Operative Dentistry.) that shows signs of decalcification must be removed ; but, at least in shallow cavities, it is not an uncommon practice to polish the carious surface with tapes or discs, so as to diminish as far as possible the area over which such removal need be made, since such polishing completely removes the opacity at its most peripheral part. According to the doctrines of Fig. 433. — Caries in the distal surface of a second premolar, which makes a broad contact with the first molar. a. Large en^brasures or re-entrant angles. 6. Small re-entrant angles. The second premolar and first molar should be sepa- rated, the premolar cut away for prevention, and the original contour restored by filling material. (G. V. Black : Operative Dentistry.) extension for prevention, by acting in this way the operator is courting recurrence of caries, since the edges of the filling are placed in a non- immune area. In such a case what piobably happens is that the zoogloea formation starts again in much the same place as before, which will be somewhere on the surface of the filling ; as before, also, it gradually spreads peripherally, and attains or even exceeds its original extent, so that unless the area of the cavity has been made at least coextensive with this, there is good reason to expect recurrence. It is true that filling the tooth may alter the conditions under which tlie decalcification went on, by enabling the patient to masticate with greater vigour, or that, on buccal and labial surfaces, special instructions as to the use of a tooth- brush may have the same result ; but it is un- wise to trust very much to the effect of this alteration of conditions, whicli at the best is but problematical. To carry out the principle of extension for prevention in its entirety it is necessary to go yet further; even if the surface decalcification has not extended all over the non-immune area, all that area should be cut out and included in the cavity, so that the edges may be placed in positions immune from caries. Thus, on a buccal surface the cavity should be extended medially and distally almost as far as the angles of the tooth ; occlusally it should extend at least one-third of the distance from the gum to the occlusal edge ; and gingivally it should reach as far as just under the free margin of the gum. Similarly, ajiproximal cavities should be ex- tended below the gum, above the contact point, and out to the angles of the tooth ; this will have the effect of placing all the cavity edges clear of the non-immune area, on the so-called self- cleansing surfaces, which are protected by friction from the feltmg of micro-organisms. It is believed by the upholders of this doctrine, that in susceptible mouths such extended fillings are the only ones that are effective ; and they hold that in these mouths the extension should be made even at the expense of sound tissue. It is true that in all mouths a layer of micro-organisms wiU be found felted to the crowns of the teeth in those parts less exposed to friction; but it is only in non-immune or susceptible mouths that tliese plaques seem to have the power of causing decalcification of the enamel to which they are fixed. This would also account for the facts already mentioned, namely, that enamel fissures and the edge of fillings not strictly watertight do not always act as startmg-points for caries. On the whole, the advocates of extension for prevention would seem to have established their position, and it is now generally recognized that fUlings inserted according to their principles are most to be relied on in preventing recurrence of caries at the cavity margin. In spite of this, however, it must be admitted that in practice the com- plete carrjdng out of the 23rocedure is not always possible or perhaps to be recommended. In young patients and in those with sensitive teeth — often in fact in those very cases where it is most desirable — the difficulty of extending a cavity is so great that the operator must be content with cutting out the carious tissues and inserting a filling as best he can. A period of 353 immunity may be approaching, in which case ' the filling will stand, or, should the worst happen and recurrence take place, the filling can then be extended ; the first filling will not have been useless, since by arresting the caries in the deeper parts it wiU have prevented the involvement of the pulp. 3. Restoration of Function. — In order to re- store the function of the tooth, the tissues lost by caries must be replaced, and the crown of the tootli be built up to its original shape. On buccal and labial surfaces this is so obviously necessary that no comment on them is needed. On occlusal surfaces the exact reproduction of the original shape of the tooth is somewhat subordinated to considerations of strength, in so far that the cusps need not always be reproduced in their entirety ; but any great alteration in the shape of the surface should be ; avoided, as the effectiveness of the tooth for mastication is thereby impaired. On approxi- i mal surfaces the restoration of the original shape is a matter of the greatest importance, and indeed much of the success of the operation depends on the contouring of the filling ; it has already been shown how insufficient ! building out of the approximal surface may increase the area predisposed to caries, and so be a cause of recurrent caries, and it will be found that this is not the only ill result that is to be feared. In a healthy mouth the triangular, or rather pyramidal, spaces, whose apices are the contact points and whose bases are the portions of the alveolus between the necks of the teeth, are completely filled by muco-periosteal tissue — the inter-proximal gum ; the contact points of the teeth by their apposition protect the apices of these p3Tamids of inter-proximal gum,. so that food in mastication camiot impinge on the apex but only on the sloping sides, off ^^•hicll it glides; should the adjacent teeth, however, not be in contact, food will be forced on to the apex of the p\Tamid in mastication so as to flatten it dowTi, and will become impacted be- tween the teeth, and a so-caUed food pocket will be formed (see Fig. 434). The inter-jDroximal gum being very sensitive, such a pocket wUl render the teeth useless for mastication ; in addition to this the fermentation of tlie impacted food, if it be acid, may cause decalcification and caries of the adjoining teeth, or, if alkaline, may cause periodontitis in their root-membranes ; indeed some cases have been recorded in which such a pocket is believed to have been the source of a septic inflammation of the gravest char- acter (1). The ideal contact between teeth is like that between two marbles firmly pressed together, which only touch each other at one small point. If the areas in contact are flat surfaces 12 instead of points, the inter-proximal gum will soon be no longer protected : food driven be- tween such surfaces sticks fast and cannot be easUy removed, and acts as a wedge, causing slight separation of the teeth ; more food is then driven down during mastication on the top of what is already there, forcing it on to the inter-proximal gum, which it flattens down and pushes away from the approximal surfaces of the teeth ; in this way a pocket is formed. Contact points, therefore, to be effective must be quite small — points and not surfaces. Again, the full medio-distal diameter of the tooth must be restored ; if this is not done, the teeth will not be in sufficiently firm contact with each other to protect the inter-proximal gum, nor Fig. 434. 1. a. Inter-proximal space. b. Inter-proximal gum driven away from contact point : commencing food pocket. c. Healthy inter-proximal gum in position. 2. Approximal surface. Gum driven away from eon- tact point — black line shows original position. 3. Inter-proximal gum in position. (Feiesell : Dfntal Cosmos.) will the formation of a food pocket be long prevented in any case, since, if tlie diameters of the crowns are lessened, the teetli come together at their necks, and again flat surfaces are in contact ; a narrow crevice is in fact thereby formed, from which it is almost im- possible to dislodge with tongue or lips such pieces of food as must now and then be forced past the contact points, and the final result is a food pocket. In order, therefore, to seQure restoration of function, small contact points and restoration of the full inter-proximal space are required (3, ^'ol. ii, p. 296) (8). Methods The procedures by ^hich it is souglit to arrest caries, to prevent its recurrence, and to restore the function of the tooth, having been discussed, it will now be well to describe the 354 methods by which these procedures may be carried out. The general priaciples of cavity Fig. 435. — Ivory's Matrix and Retainer. {Messrs.Claudius Ash, Sons foot-plugger will be found necessary to pack and sliape tlie gold at the gingival margin in beginning the contour. In such cavities as these, semi- cohesive gold in small pellets may be used to make some edges of the fresh piece «eld so that it will not curl up when the condenser is applied to the middle. Sucii a condenser as No. 7 is excellent in building contour, wliiie a form like No. 5 has an advantage along walls or margins. The direction of f(nve in condensing gold should mostly be nearly, but not tiuite, parallel with the long axis of the tooth. Force should always be directed so as to drive the gold into the cavity, and no force should at any time be Fig. -4 44. : against the walls and in the angles, while annealed or fully cohesive gold fori'ns the main body of the tilling. In all cases the cohesive gold should be tlirust firmly into the semi- cohesive with small pluggers where an angle or an undercut is to be filled. In building contour larger pieces of gold may l)e used than are permissible elsewhere. Such an instrument as No. 8, or the Varney foot-plugger, is con- venient to pack or mould frcsii pieces to the form desired. Enough pressure should be used used tending to loosen or move the filling from the cavity. This should be especially borne in mind when malleting upon the periphery of a contour, where a blow in the wrong direction, though unnoticed at the tinu", will move the filling, causing it to leak and impart a stained appearance to the tootii afterwards. Huilding along the lingual wall should be kept in advance, as indicated in the lateral. Fig. 445. When tiio incisal undercut is reached, the small right-angle for the lateral, or the No. 2 point for the central, will be suitable. Small jiellets of semi-cohesive gold followed by small pellets of coiiesive should be forced in the lingual direction to wedge the gold in the cavity and ct)nipletely till the retentive undercut. The last i)art of tiu' cavity to be filled is indicated in the central, Fig. 445. [Previous to this stage the incisal )indere\it is entirely filled, the filling being tinis tinally locked, and a cohesive surface being left to receive further additions of gold to conipleto the contour. By this ])rocedure good oppor- tunity is secured to build the contact ]ioiat and the remainder of the lingual and incisal margins and finish t he work when' there is no obstrui^t ion. When the filling is thought to be conipletcly built, the nuirgins should 1h^ examined. Any soft or unfilled spots should receive a suital)ly small pellet of well-annealed gold by hand pressure, so that the filling nuiy be finished without any pit [!('«)]. Procedure in cavities that arc much extended lingually while the labial enamel and the incisal angle are intact and sound will vary from the 382 foregoing. Lingual approach, hand pressure, and proportionally more non-cohesive gold in larger pieces, will be used, anchorage being obtained bet^¥een opposing walls of retentive form ; cohesive gold will be added only to form the contour, contact point, and surface exposed to attrition. Finishing. — Restoration of contour and con- tact point should be kept constantly in mind during the preparation of the cavity, the inser- tion of the gold, and the finishing of approximal surfaces (2). The cavity being filled, and the proper contour built, the first part of finishing should be to burnish the whole surface. Beginning with a flat burnisher (see No. 3, Fig. 446) at the contact point, move the instrument towards and over the margins in all directions, except at the gingival margin, where, to avoid injury of the gum, the burnisher may be drawn labially at one side and lingually at the other; No. 2 is a form of burnisher convenient for labial or lingual margins. The advantages of burnishing are the complete condensation of the surface and the tendency to fill slight pits left by pluggers, and also the final and complete closure effected between the gold and the enamel margins. Any considerable excess of gold overlying the enamel after burnishing may be cut away at the gingival margin with small safety back files {see Nos. 6 and 7, Fig. 446), which should be operated only in a labio-lingual direction for the safety of the gum. Excess along the labial or the lingual margin may be most satisfactorily cut away by suitable knives or draw-cut scalers used always towards the enamel and never in the opposite direction. Emery-paper discs of small diameter and lubricated liberally with vaseline may next be used to dress the labial and lingual margins. If separation is sufficient, | inch paper discs may be used to dress the approximal surface. In doing this much care is necessary to avoid undue cutting of the contact point. A little pressure, as from finger-ends or a burnisher upon the back of the disc at its edge, will make it cut more rapidly the part against which the pressure is applied. Such pressure is usefully introduced in dressing the approximal surface at or near the gingival margin with the edge of a wide disc not allowed to cut the contact point. Margins extending to the lingual fossa are dressed by application of a ball burnisher to the back of a small thin disc near its rim, so as to force the grit side to the form of the fossa while the disc revolves. In most cases the disc should be mounted with its grit side towards the hand- piece. Vaseline minimizes frictional heat, and also the tendency of the disc to catch and wmd the rubber-dam. A thin finishing strip may be used upon the gingival portion ; this strip should be so narrow as to ^^•ork witlaout cutting the contact point, and should be well vaselined ; care is necessary in the use of strips to avoid injury of the gum or the pericementum. Cuttle- fish or crocus discs may be used, and finally a thin strip charged with fine grit may be drawn a few times over the whole filling, provided no pressure of the adjacent tooth is allowed upon the back of the strip at the contact point, to give Fig. 447. a satisfactory surface to the whole of an incisor filling [l(p)]. When removing the rubber-dam, be sure to remove all shreds of rubber or ligature, or any foreign matter, that may have found its way under the gum margin during the operation. Vigorous streams of water from a syringe serve 383 well for the removal of grit used in finishing, or other matter that should not be allowed to remain where it may cause injury to the sur- rounding parts. Fig. 447 is an approximal view of the finished fillings. Figs. 448 and 449 are labial views of the filled teeth in situ. Fig. 450 is a lingual view of the filled teeth in situ. Note in Figs. 448, 449, and 450, that contact of the filled teeth occurs upon the fUlings only ; cavity outlines should in all cases be managed so as not to allow contact of the teeth to occur at or near the joint between filling and enamel. The Fig. 448. medial filling in the central. Fig. 450, shows extension to the lingual surface for the removal of tissue too much damaged by caries to remain. The lingual and gingival extension seen in the other fillings in these teeth is ordinarilv sufficient, Fig. 449. and need not be exceeded except in cases of extreme susceptibOity or for the removal of tissue unfit to remain. The labial extension seen in Figs. 448 and 449 is the maximum to be used for prophylactic reasons. In extreme cases indicated by ext;nsion of caries of the enamel along the gum line the cavity should be extended to include all carious enamel. Fig. 451 shows the relation of the cavity out- line to the gum margin, and the appearance of fillings thus extended labially. Note that the free margin of gum covers the gingival margin Fig. 45'J. of the filling ; while the joint is thus covered gingival recurrence of caries will not take place. The maintenance of the inter-proximal space and of the health of the tissues occupying it are therefore of the first importance in the preven- tion of both caries and pyorrhoea alveolaris. Fig. 451. The student is advised to note well tlie form of the gingival lines upon the incisors as seen in these figures, so that in the application of ligatures, finishing instruments, etc., he may the better guard against violence to the peri- cementum, which, if wounded or separated from the cementum,is likely to remain in a permanently diseased condition (2). Class 2. — Pit and Fissure Cavities Typical examples of the smaller pit and fissure cavities prepared for filling are seen in Fig. 452. The filling of these ca\'ities with foil is a com- paratively simple operation. The end of a roll of very slightly cohesive foil is introduced and 384 with thrusts of such a phigger as Nos. 5 or 6, Fig. 442, packed until the cavity is one-half or two-thirds filled. Into the gold thus packed cohesive gold is thrust with a small point and by hand pressure until the whole is solid and the cavity has a firm grip of it. By mallet or hand pressure the remainder of the cavity is filled with cohesive gold. No considerable ex- cess of gold should be allowed to extend over the uncut enamel ; by the addition of small pieces at the last the desired fullness may be obtained without excess. Serrations at the edges of the plugger faces should 'not be sharp, Fig. 452. but rather smooth or rounded, so that in sliding upon the inclines leading into the cavity they will not catch or injure the enamel. In the larger occlusal cavities of Class 2 in molars non-cohesive gold may be used for the greater part of the filling. Cylinders long enough to reach the cavity margins are placed on end and forced to the walls. Wlien the greater part of the cavity is thus filled, the walls and floor being covered, a pellet of cohesive gold is fii-mly thrust into the mass at the centre. Cohesive gold is added in an outward direction until the Fig. 453. non-cohesive is forced solid against the walls and margins and partly covered by cohesive gold. The welded surface ^vill stand attrition better than will non-cohesive gold, while the adaptability and rapid filling qualities of the latter are fully utilized (4) (7). To finish this kind of filling a hand burnisher with rounded point such as No. 1, Fig. 446, may be used, so as to leave a good finish with no occasion for cutting or further polish. A straight instrument with a smooth and somewhat flattened end may often be used with mallet blows to condense and smooth tlie surface of this kind of filling. Any excess of gold overlying enamel in grooves or depressions can be cut away with a discoid excavator or such an instrument as No. 5, Fig. 446, and complete finish made by burnish- ing. Fig. 453 shows the cavities filled, and finished by burnishing. Treatment of buccal pits in molars, or lingual pits in lateral incisors, is essentially the same as in the examples illustrated. Class 3. — Labial and Buccal Cavities Fillings in these cavities are exposed to little friction or wear, and to no stress, in mastication ; therefore strength and hardness in the material used are not essential. The situation at the gum margm, where these cavities begin, is unfavourable for easy or harmless application of the rubber-dam ; and, except in the upper incisors and canines, quite as unfavourable for the safe or harmless use of the usual means of finishing gold. The colour of gold is sometimes, and its conducting properties are always, objectionable in these cases. The pulp is separated from the filling by a very thin body of dentine at the neck of the tooth. Considering the difficulties and the liability of adjacent parts to injury, gold foil can hardly be recommended as generally suitable to such cavities, especially in the lower teeth. Inlays, gutta-percha, amalgam, and oxy-phosphate of copper, afford alternatives where such obstacles are promi- nently in the way of foil-work. Labial cavities in upper incisors or canines may, however, be filled with foil without using the rubber-dam. It has been found quite practicable to work foil in these cases without the rubber for patients whose control of lips and tongue is good, and from whose gums there is no abnormal exudation. Having the cavity prepared, wash the moiith with warm water, dry the gum and lip, place a cotton-wool roll under the lip, and the edge of a napkin below the upper teeth. Dry the cavity and gum margin with alcohol and warm air. Begin at once with a large pellet or cylinder of very slightly cohesive, or non-cohesive, gold against the gingival wall. Let this piece pro- trude a little from the cavity, even if it is against the gum, to ensure complete filling of the cavity at the gingival margin. Use a plugger in each hand and rapidly pack the semi-cohesive gold, adding only enough cohesive gold to bind or toughen the filling and render it stable for finishing. A cavity may thus be well filled in a few niinutes, or at least before there is any oozing of moisture to prevent the ^\•orking of gold. When all the gold is in moisture can do no harm ; it may be wiped away while the filling is being finished. Having the contour restored, burnish the whole surface, remove any excess at the gingival margin with files or points of knives, and burnish 385 smooth all gold covered by gum. The rest of the filling may be finished with the edges of small paper discs mounted on a small neat mandrel with thin screw-head ; thorough control of the disc should be maintained, but no attempt made to operate a paper disc under the gum. W. C. G. BIBLIOGRAPHY (1) Black, G. V. Operative Dentistry, Vol. II: (a) Cavity Preparation, pp. 105 ei seq. (6) Re- tention Form, pp. 113, 126, 182, 208. (c) Modification of Alloys, p. 312. (d) Inlays, pp. 330 et seq. (e) Filling Materials, p. 224. (/) Injuries by Use of Clamps, p. 51. [g) Liga- tures, p. 86. {h) Nature of Blows, p. 237. (i) Application of Force, p. 251. (/) Plugger Points, pp. 2.54 ct seq. {k) Forms of Gold, p. 227. {!) Preparation of Foil, p. 249. (m) Filling Incisors and Canines, p. 282. (n) Cavities in Approximal Surfaces in Premolars and Molars, pp. 143 et seq. (o) Filling Approximal Cavities in Premolars and Molars, pp. 265 et seq. (p) Finishing Gold Fillings, pp. 291 et seq. (2) Black, G. V. The Contact Point and its Func- tion considered with Reference to Caries and its Treatment. Dental Review, 1909, pp. 595- 663. (3) Clack, W. R. Gold Fillings. Dental Cosmos, 1909, Vol. LI, pp. 1274-1304. (4) Clapp, D. M. Various Kinds of Gold in Combina- tion. Kjrk^s Operative Dentistry, 3rd ed., p. 345. (5) COE, Ika J. New Feature in Retention of Gold FiUings. Dental Cosmos, 1906, Vol. XLVIII, p. 563. (6) Darby, E. T. Gold and Tin Fillings. Kirk's Operative Dentistry, 3rd ed., p. 227. (7) Dunning, W. B. Manipulation of Non-cohe- sive Gold. Dental Cosmos, 1906, Vol. XLVIII, p. 558. (8) Enomoto, Sekichi. Annealing Gold. Dental Cosmos, 1905, Vol. XLVII, p. 233. (9) Geayston, VV. C. Gold Filling. Brit. Dent. Jour., 1909, Vol. XXIX, p. 241. (10) Gbayston, W. C. Gold Fillings (Tests). Trans. Odont. Soc, 1901-2, p. 47. (11) Johnson, C. N. Principles and Practice of Filling Teeth. 3rd ed. (a) Crystal Golds, pp. 174-5. (6) Experiments with Various Mallets, p. 178. (c) Automatic and Rapid Mallets, pp. 182-3. (d) Hand Pressure, pp. 185 et seq. (e) Protecting Periodontal Membrane, p. 187. (/) Matrices, pp. 201 et seq. (gf) Finishing Filhngs, p. 214. (h) Manipulation of Tin and Gold, pp. 228 et seq. (i) Manipulation of Amalgam, pp. 232 et seq. (/) Manipulation of Gutta-percha, pp. 239 et seq. (12) LiTCH, Wilbur F. American System of Dentistry, Vol. II. (a) General Principles concerning Packing of Gold, pp. 107-123. (6) Hprbst Method of Gold Filling, pp. 207-217. (13) Matheson, L. Gold Fillings. Trans. Odont. Soc, 1903-4, p. 220. (14) Noel, L. G. Methods of combining Cohesive with Non-cohesive Gold or with Tin, or Tin with Non-cohesive Gold. Dental Cosmos, 1908, Vol. L, pp. 320-6. (15) Ottolengui, R. Methods of Filling Teeth. (a) Gold as a Filling Material, pp. 69-77. (6) Uses of Heavy Gold, pp. 77-81. (c) Lining Cavity with Oxy-phosphate, pp. 82-3. (d) Con- densing Gold, pp. 85-9. (e) Preparing Cavities for Gold, pp. 114-184. (/) Finishing Gold Filling, pp. 187-9. (16) Owre, Alfred. Johnson's Operative Dentistry. (a) Gold Filling, p. 225. (6) Tin Filling, p. 245. (17) Parfitt, J. B. Mechanical Principles (Gold Fillings). Trans. Odont. Soc., 1906-7, p. 34. (18) Sachs, Prof. Wilhelm. Adjusting Matrix for Approximal Cavities in Molars and Premolars. Dental Cosmos, 1908, Vol. L, p. 531. (19) Wedelstaedt, E. K. Methods and Principles of Packing Gold. Dental Cosmos, 1905, Vol. XLVII, p. 985. 13 CHAPTER XXIII PLASTIC FILLINGS Easily moulded filling - materials, which undergo a process of self-hardening, are known as " Plastics ". Great as are the advantages pertaining to these two properties something further is demanded of the ideal fillmg. Thus, it should resemble m colour and appearance the adjacent tooth tissue ; harden fairly rapidly ; maintam its form, i. e. neither contract, expand, nor warp, and be insoluble in the oral fluids ; be strong enough to stand the mechanical stress of mastication without fracturing or becoming defaced ; be capable of receiving and maintaming a high polish ; and exert no mjurious effects on the hard or soft dental structures. AU these desu'able qualities are not to be met \\ ith in any single filling ; the plastics, how- ever, combme many of them, and as will be shown, some have jjroved the most generally useful of all the fillings at present in use. Plastic fillings may be divided into three mam classes — 1. Dental Amalyams — metallic alloys con- taming mercury. 2. Osteo-plastic Cements — inorganic com- pounds resulting from the union of a powder with a liquid. 3. Compounds — largely organic, containing gutta-percha. 1. DENTAL AMALGAMS In its widest sense an amalgam is an alloy of one or more metals with mercury. A dental amalgam is such an alloy, ui which, however, the mercury is present as one of the chief constituents. The other metals usually employed are silver, tin, copper, gold, zinc, platinum, palladium, and bismuth. Of these, copper is sometimes used alone, as is also palladium, to form simple binary amal- gams, but the ternary alloy of mercury, silver, and tin, occasionally modified by the addition of small amounts of certam other metals, has i proved the most reliable in practice. 1 Amalgamation. — Mercury is in several re- I spects a remarkable metal ; fluid at ordinary I temperatures, it volatilizes at 360° C, and will combine to some extent, even in the cold, with nearly all the other metals. Amalgamation is facilitated and rendered more thorough by heat, ; 386 and by the other metals being in a fine state of division. In the case of copper and palla- dium, ^precipitates of the metals obtained from solutions of their salts are used ; with ternary and other alloys, the metals other than the mercury are alloyed fu'st by fusion, and then reduced to a fine state, by filing, drilling, or turning the mgot. The production of this primary alloy is a matter of some importance. Wlien the meltmg is conducted in an ordinary crucible oxidation of some of the base metals is very liable to occur, with the result that the composition of the alloy is varied ; hence it is best to employ (4, f»- 307) a closed electric crucible and fuse the metals together under hydrogen. Further, it is very difficult to obtam an ingot that is perfectly homogeneous, one m which the metals are evenly alloyed throughout the mass. Two pomts only, liavmg a bearmg on this matter, may be mentioned here. When two metals of differing densities are melted and poured together into a vessel, preferably higher than it is wide, the metal with the greater specific gravity tends to collect at the bottom, and the lighter metal at the top, but it ^\ill be found on analysis that the separation is not complete — some of the heavier metal has passed up into the lighter metal, whilst a portion of the lighter metal has combined with the heavier metal below. Again, by means of the readings of a pyro- meter it is possible to construct a curve illustrat- ing the behaviour of a cooling mass of metal or aUoy. When a single metal cools, the coolmg curve becomes practically horizontal at the point of the metal's solidification. But in tlie case of an alloy several interruptions of the curve may be noticed ; these breaks correspond with the formation of crystals of a definite composition, and may be observed after the mass has solidified. It has been shown by Black that an amalgam made from filings cut from previously prepared alloy possesses physical properties different from those of an amalgam made from the precipitates of the same metals, the proportions of the metals being the same in each case (4, p. 307) ; so that it is possible that the manner in wliich the primary alloy is cooled, quickly or slowly, may have some influence on the properties of the resultant amalgam. 387 For the supj)ly of these alloys the dentist is entii'ely iii the hands of the manufacturers, and it is to be feared that many of them are prepared in a wholly empirical manner, with no regard to their perfect homogeneity. When the filhigs or turnmgs from a previously prepared alloy are brought into intimate contact with a sufficiency of mercury, either by tritura- tion with pestle and mortar, by shakuig the filuigs together m a test tube, or by simply nibbing them together in the palm of the hand, the other metals go into solution with the mercury very much in the same manner as do metals when fused in a crucible, a soft plastic mass being formed. Sooner or later, but usually in a few mmutes, tlie time varymg with the composition and treatment of the primary (silver-tin) alloy, and the amount of mercury, a process of crystallization ensues, and the mass becomes harder, feeling crystalline \^'hen rubbed between the fingers, and finally sets. In this way is formed a solid metallic alloy, which may be a chemical compound, or series of com- pounds, composed of mercury and the other metals in the alloy, crystallized, and dissolved in the excess of mercury present. There is, and always must be, some excess of mercury present in the original mix, over and above that requu-ed to satisfy the chemical affinities of the other metals, in order that the alloy may be rendered sufficiently plastic to be workable. This excess is usually partly removed by squeezing it out, through chamois leather or linen, before packing the amalgam into the tooth cavity ; and as will be seen later, much care is taken to remove, as far as possible, the remainder of the excess during the insertion of tlie filluig. It is jjossible that the variations in the amount of mercury used, over and above that which is necessary, and the alteration in the constitution of the alio •, consequent upon the extraction of small qua titles of the other metals with the expressed mercury, account in some degree for the differii "■ results achieved with amalgam fillings. It has already been mention 'd that amalgam- ation is facilitated by heat, uid Fenchel has pointed out that an alloy \\ith a low melting- point will combine more readily and more completely with mercury than one with a high melting-point ; further, that as a result of the complete solution of the alloy in the mercury, a true homogeneous amalgam may be expected by recrystallization out of a perfect solution, thus obviating the formation of masses of amalgam uniting imamalgamated crystals of the primary alloy ; and he advocates the use of a primary alloy compo.sed of silver 48, tin 52, which melts at 470° C. (14). The majority of alloys in use to-day possess a nmch larger content of silver. These high- (jrmh alloys, as they are called, set rapidly, particularly so if the filings are coarse and are used when freshly cut. There is a possible advantage to be derived from rapid setting, inasmuch as the amalgam mass is under the control of the operator and may be condensed during a critical jseriod, when many changes in form are liable to occur; further, it is less likely to be defaced by use before it has hardened. Alterations in Form. — Just as other alloys undergo changes in density at the time of solidification, so amalgam alloys exhibit changes of form whUst hardening; and although it is true that these changes are very marked at and about the period of setting, yet in some instances they continue to occur for some considerable time after the mass has apparently fully hardened. Thus a dental amalgam may either contract, exj)and, or warp. Many alloys contract at first, but subsequently expand and recover their original density, or may go be- yond it ; a few expand at first and then contract ; others expand or contiact only. Black has shown that expansion and con- traction are mainly due to the composition of the primary alloy, and partly to its method of preparation and the amount of mercury used. Speaking generally, in a ternary alloy of mer- cury, silver, and tin, the silver promotes ex- pansion, whilst the tin tends to induce contrac- tion. It has been found by experiment that with an alloy composed of silver, 65 parts, and tin, 35 parts, mixed with 52 per cent of mercury, the tendency towards expansion and contraction on the part of these two metals is approximately neutralized, and that such an alloy yields an amalgam that is practi- cally unalterable. This result, however, is only achieved when the amalgam is made with filings that are freshly cut, or with shavings newly turned (4, p. 308). Fresh-cut alloys containing over 65 jjer cent of silver and less than 35 jJcr cent of tin, as a general rule, form amalgams that expand, the expansion being very marked when the silver exceeds 70 per cent ; whilst those containing less than 65 per cent of silver and more than 35 per cent of tin contract. Tomes has shown that there is a minimum of shrinkage resulting from the use of pieces of old silver-tin amalgam, which have been heated and softened in the same manner as that adopted when working copper amalgam (23). Silver -tin amalgam, however, when so used, sets so rapidly that it is almost impossible to pack it into any but the simplest and most accessible cavities. The same observer has also found that shrinkage may be partly con- trolled by inserting hard metallic bodies, such as pieces of already hardened amalgam, small 388 iron rinrrs, etc., into the amalgam mass whUe it is still soft. The form of shrinkage or of expansion de- pends somewhat on the shape of the ping, and, if it is packed into a cavity, on the shajoe and character of that cavity. Thus amalgam packed into a simple mould, slightly undercut, with approximately straight walls, and a flat base, will exhibit shrinkage after the form shown in Fig. 454. On the other hand, should the alloy used be one that expands, the expansion will take place in the dhection of least resistance, and hence it wUl rise from the of)en end of the mould ; further, it will experience some resist- ance at the sides of the mould, and wUl as a result of this rise more easily and to a greater extent in the centre, very much in the same way as ice forms at the open end of a tube when the water that it contains is frozen. This Fig. 454. appearance gave rise to the idea that there was a tendency on the part of some amalgams to " spheroid". The Amount and Distribution of the Mercury. With an unalterable alloy, such as one composed of sil\er, 65 per cent, and tin, 35 per cent, when the filings are used freshly cut, variations in the amount of mercury incorporated with tliem have no effect upon the volume of the amalgam made, that is to say, upon its con- traction or expansion ; variation in the amount of mercury, however, seriously affects its rigidity and strength. The quantity of mercury required to f)roduce the strongest plug differs with the formula and method of preparation of the primary alloy ; it is usually bet\^een 30 per cent and 60 per cent. Freshly cut and finely com- niiiuited alloys, and also those that contam much silver requue a large amount of mercury. Alterations in the quantity of mercury used V ith alloys that have a greater or lesser content of silver than 65 per cent, however, increase the contraction and expansion resjaectively of these alloys, and these changes caimot be controlled by the percentage of mercury employed. It is of the utmost importance that the mercury should be evenly distributed through- out the mass. As the plug hardens, there is apparently a tendency for the excess of mercury in what may l)e termed the wetter portion to migrate to the drier portion, and this spon- taneous equalization of the distribution of the mercury is often accompanied by some warping or twisting of the plug (lit). Changes in Form due to Mechanical Stress. — A mass of amalgam, when fuUy set, possesses in some curious way the two opposite physical properties of brittleness and flow. Thus, when a piece of amalgam is struck a smart blow with a hammer, or subjected to very great pressure, it win fly to pieces ; yet it Ls almost malleable when the j^ressure is limited to an amount below that required to produce fracture (5). Further its malleability is of a distinctive kind. When a cube of pure gold is compressed, it yields to an extent limited by the amount of the pressure to which it is subjected, and camiot be made to yield further unless the pressure is increased. Many dental amalgams, on the other hand, will yield or flow under pressure so long as the pressure is maintained, no matter whether it is constant or intermittent, and that without any increase m the amount of the stress applied. It will be evident that this prof)erty of molecular motion under stress is one of extreme importance from the point of view of the stability of an amalgam filling. For whilst an amalgam may be sufficiently strong to withstand the strain of mastication without fracturing, its strength will be of no avail, so far as its tooth-saving properties are concerned, if it is liable to be defaced, and to flow away from the cavity margins. The tendency to flow is at zero in the binary amalgam of copper and mercury ; is less marked in those silver-tin alloys that contain from two per cent to five per cent of cof)i5er ; and also in those amalgams that are made from freshly cut filings. The flow is increased by using an excess of mercury, and by unevenness in its distribution throughout the mass ; it is also greater in amalgams made from very finely comminuted filings or from those that have been annealed. Increase in the percentage of tin increases the flow, as does also the addition of gold to a sUver-tin alloy. The following table from Black shows some of the results obtained by him, the percentage of flow being that per hour, \\ith a pressure of 60 lb. Silver 60 42-45 70 Tin 40 57-55 30 Percentage of Mercury 38-58 39-05 50 Percentage of Flow 2-91 9 4-12 Crushing Stress. — It is very rarely that an amalgam filling, when once fully hardened, frac- tures under the stress of mastication. Before it has fully set, however, it passes through a stage in which it is very friable, and is then easily broken if bitten upon. Amalgams made from alloys containing a high percentage of 389 silver possess a good crushing stress, but it is reduced by increasing the amount of tin, by using filmgs that have been freshly cut, and by incorporating too much or too little mercury A^itli the mix. The addition of five per cent of gold to a silver-tin alloy slightly raises its crushuig stress, whilst the addition of a similar amount of copper raises it very considerably. No other metal appears to have any beneficial effect in this respect. A cube of amalgam measurmg '085 inch will withstand a pressure of from 200 lb to 400 lb before crushmg, varymg of course with the composition of the alloy and the methods adopted in its preparation. It will thus be seen that amalgam fillings usually possess sufficient strength for the purposes required of them. The Ageing or Annealing of Comminuted Amalgam Alloys. — When an amalgam is mado with filings immediately after they have been cut, an alloy is produced that possesses pro- perties differmg from those possessed by an aUoy made from the same batch of filings some weeks or months after they have been cut. Two explanations have been offered to account for these changes, one being that they are due to the surface oxidation of the filings, and the other that they are the result of a slow process of annealing, \\hich the filings undergo when left at rest in a moderately warm room. It is probable that the second of these two ex- planations is the correct one, the argument being that as the filings come off from the file they are rendered hard and harsh, and that the displaced molecules of the alloy subsequently readjust themselves (4, p. 309) ; thus filings may be artificially aged by annealing them as soon as they are cut, and it has been found by experiment that this may be efficiently accom- plished by placing the filings in a test tube, and the latter in boiling water for twenty minutes. Tlie following table shows the effects of annealing on the physical and working properties of the same alloy (4, p. 310) — Percentage Flow Crush- of Shrink- Expan- per- ing Silver Tin Mercury age siou centage Stress Fresh-cut 65 35 52 1-5 3-67 290 Annealed 65 35 33 6-10 5 335 Thus it wUl be seen that as the result of annealing less mercury is required to make a working mi.x ; that the expansion of an expand- ing alloy is reduced ; and that both the flow and the crushing .stress are increased. Further, the setting of the mass is delayed. The effects of annealing are proportional to the temperature to which the filings are sub- jected. It is possible to carry the process so far as to oxidize the tm and render the alloy useless ; this is safeguarded against by adoptmg the method described above. From the fore- going it will be seen that an unmodified silver- tin aUoy, which is to be comminuted and re- served for future use, will be one containing a larger amount of silver than 65 per cent. It will be found to be somewhere in the neighbourhood of 70 per cent, but the actual amount wfil depend on the purity of the metals employed, and must be determined independently for each batch of metals as received from the refiners. The Action of the Oral Fluids on Dental Amalgams. — With the exception of the binary alloy of copper and mercury, dental amalgams are practically insoluble in the oral fluids. Most of them, however, become tarnished more or less speedily in the mouth, owing to the action of the sulphuretted hydrogen i^resent, and it is difficult to see how this can be entirely prevented, so long as silver forms one of their principal constituents. A content of copper also tends to increase then- liability to discolour. Zinc, on the other hand, even in quite small quantities, owing to the fact that it forms a white sulphide, helps to maintam the colour of the alloy, as jjrobably also does the addition of a little gold. It is possible, too, that the presence on the surface of the filling of uncom- bined portions of silver, in an imperfectly amalgamated alloy, may be a factor increasing discoloration. Stauiing of the tooth tissue is due to the penetration of the sulphides of the metals used, resulting from the presence of moisture between the filling and the cavity walls. It may follow shruikage of the plug, imperfect adaptation of the fUling, or want of care in the preparation of the cavity. Discoloration is more marked in pulpless teeth, and in those portions of the dentme in which dead dentinal fibrils are pre- sent, such as frequently occur when the cavity is large, and the fibrils have been cut off from their connection with the pulp (4, p. 315). The character of the staining depends upon the constituents of the alloy ; it is usually a greyish black. Certain acids, however, acting upon copper, produce staming of a blue, green, or purple colour. All discoloration may be pre- vented by properly lining the cavity with one of the osteo-plastic cements. Another point that must be taken into con- sideration when dealing with the action of the oral fluids, is the electro-motive force that is occasionally established between two fillings made from different metals, such as amalgam and gold, or between an amalgam filling and a gold clasp on a denture, or a metal crown. Such galvanic action not uncommonly occurs when the reaction of the oral secretions is acid and the amalgam is new and untarnished. It is induced by the different metals acting as electrodes, and the oral fluid as the electrolyte, and is most marked when the two metals are 390 widely separated in the voltaic series. It thus happens that the impact of a newly made amalgam fillmp; on another fiUiiig made of gold in a different tooth, or similar conjunction of two metals, results m a sharp pain being felt in the tooth containing the amalgam. A similar residt ensues when the filling is touched with a steel instrument, or with the nickel rim of a mouth mirror. The action is very marked ■with high-grade silver aUoys that also contain zinc, and particularly so when these alloys are used to repair old fillings made from copper amalgam. It is quite jjrobable that some of the wasting of copper amalgam in the mouth may be due to electrical action, and the darken- ing of gold fillings when coexistent ui the mouth with amalgam fiUmgs may be attributed to the same cause. Conductivity for Heat. — As might be expected, amalgam fillings are good conductors of ther- mal changes ; in this respect, however, they are inferior to gold, but possess a higher rate of conductivity than do the osteo-plastic cements. Modified Silver-tin Alloys. — Small quantities of other metals are often added to sUver-tin alloys in order to secure or enhance certain desirable properties. Such metals are gold, copper, zinc, occasionally j)latmum, and more rarely bismuth. Cadmium also was used for- merly, but has been abandoned owmg to the fact that it forms a yellow sulphide, \^hich under certam conditions stained the dental tissues. Considerable difference of opinion exists as to the results accruing from such modifications. It is claimed that gold, when added to the extent of five per cent, renders amalgamation more easy, improves the colour of the filling, hastens its settmg, and reduces any tendency it may have to contract. Black on the other hand, is of opinion that gold has no influence on the contraction of the alloy, whilst it increases the liability to flow, and to some extent raises its crusjiing stress. It has been already indicated that the binary alloy of copper and mercury forms the most rigid amalgam — one showing the least tendency to flow. The addition of five per cent of copper to a silver -tin alloy makes it much more rigid, and at the same time increases its crushing stress, and apparently also hastens the settmg of the mass. It is the most useful of all the metals added to modify a sUver-tin alloy. Its presence, however, promotes discoloration of the filling, although this may be partly con- trolled by a small content of zinc or gold. Some observers claim that the mclusion of copper in a dental amalgam lessens the liability to a recurrence of caries, as the salts of the metal have a preservative and antiseptic action on the tooth tissue ; this, however, needs corrobora- tion. The addition of zinc to a silver-tm aUoy materially helps to preserve its colour. As a general rule it promotes expansion, which is contmued over a long period and renders the amalgam so unstable as to contra-mdicate its use. Alloys contaming zmc are much harsher when commuiuted, they amalgamate less readily, requu'ing more mercurj' than an unmodi- fied alloy, their tendency to flow is reduced, but their crushing stress remains practically unaltered. Fletcher first introduced platinum as a constituent of amalgam alloys, claiming that its presence, when combined with a small percentage of gold, both hastened the settmg and rendered the mass more rigid (16, p. 39). Black is of of)inion that platinum increases the flow and yields a plug that contracts steadily, whether gold is present in the alloy or not. Bismuth is very seldom used. It facilitates amalgamation, but makes a somewhat dirty and sticky mix (16, p. 64). The following table shows the results obtained from experiments conducted by Black (4, p. 312)— Formulae How pre- Percentage Shrink- Expan- Flow Crushing Modifying Metal Silver Tin pared of Mercury age sion Stress 65 35 Fresli cut 52-33 1 3-67 290 65 35 Annealed 33-00 10 5-00 335 66-75 33-25 Fresh cut 51-52 4 3-35 329 66-75 do. Annealed 33-53 7 5-06 380 Gold 5 . 61-75 33-25 Fresh cut 47-56 1 4-62 330 do. do. Annealed 30-35 7 6-07 395 Copper .") . do. do. Fresh cut 53-65 23 2-38 300-343 do. do. Annealed 35-60 5 3-50 416-450 Zinc 5 do. do. Fresh exit 56-65 68 1-83 200-290 do. do. Annealed 40-65 9 2-07 250-345 Platinum 5 do. do. Fresh cut 51-87 9 9-68 200-273 do. do. • Annealed 37-33 7 8-20 250-352 Bismuth 5 . . do. do. Fresh cut 46-26 4-78 250-288 do. do. Annealed 23-67 6 5-58 308 391 The follovvmg list gives the formulae of some of the modified silver -tm alloys in general use — surface of the mercury ; whilst the anode con- sists of copper turnings enclosed in a muslin 1 Silver Tin Copper Gold Zinc Platinum | C.A.S. Alloy . . 1 67-18 27-24 4-48 1-1 Tulloeh's Alloy (1) . j 69-5 25-5 4 1 (2) . . j 66 29 4 1 Fletcher's Gold Alloy . . j 40 56 4 Platinum and Gold Alloy 43-35 50-35 1-65 3-35 1-3 Fellowship Alloy . 67-73 ■ 27-24 4-71 1-23 True Dental Alloy . 1 65-82 27-94 3-86 2-38 : Flagg's (Submarine) . 60 35 5 1 „ (Contour) . 58 37 5 (Facing) . 37 35 5 3 Eckfeldt's (Standard) . . 1 52 40-6 3 4-4 1 Binary Amalgams. — The only buiary amal- gams employed in dentistry as filluig materials are those of copper and palladium ; the latter, however, is now but seldom used. Both con- sist of a combmation of the precij)itates of the metals with mercury. Copper Amalgam. — This, which was intro- duced under the name of Sullivan's Cement, may be prepared by precipitating metallic copper from a weak and slightly acid solution of copper sulphate by rods of pure zinc or iron. The precipitate is collected and thoroughly washed with sulphuric acid, and finally with water ; it is then dried and mixed with twice its weight of pure mercury, by trituration m a mortar. Amalgamation does not take place very readily at first, but may be facilitated by heat, or by the addition of a small quantity of mercuric nitrate. When thoroughly mcorporated, the mass LS made mto pellets of suitable size, which are then allowed to harden. These pellets possess the property of becoming softened again when strongly heated, and may then be tri- turated in a mortar and worked up uito a plastic mass, \\hich is then ready for packing into a tooth cavity. Boyd-Wallis is of opinion that copper precipitated by iron produces an amalgam superior to that made from copjser precipitated by zinc (6). Another method of preparation consists in depositing the copper electroIyticaUy directly into the mercury. A quantity of mercury is placed at the bottom of a suitable vessel, and covered with a saturated solution of copper sulphate. The mercury is made the cathode by introducing a copper wire, which is attached to tlie zinc pole of a battery, beneath the bag, which is suspended from a wire attached to the carbon pole of the battery. The action is contmued until the mercury at the bottom of the vessel is completely saturated with the precipitated copper (20). The mass is collected and thoroughly washed, and the excess of mercury squeezed out. It Ls then made mto pellets of a requked size. Copper amalgam possesses many jjroperties that render it suitable as a fillmg material. It is the most rigid of all dental amalgams and undergoes no change of volume whilst hardening. Its colour is objectionable from the fact that it quickly becomes coated with a black sulphide, from exposure in the mouth, and unless special precautions are taken, it is liable to stain the tooth tissues. The first of these undesirable properties, however, is of minor importance when the use of the material is restricted to cavities that are at the back of the mouth and hidden from view ; whilst the second may be obviated by properly Iming the cavity \vith one of the osteo-plastic cements. Unfortunately, however, the amalgam undergoes dismtegration in the mouth, which renders it inadmissible as a permanent filling material. As the surface of the filling is attacked by the sulphuretted hydrogen present, it becomes converted into copper sulphide, and the combined mercury is liberated. In crown cavities the sulphide is washed away as formed. In approximal cavi- ties, particularly at cervical margins, the dis- integration is very marked, resulting m the formation of a new cavity, partly from the loss of fiUmg material, and partly owing to the recurrence of caries. In this cavity, little globules of free mercury may frequently be 392 observed. The rate of wasting of the plug appears to depend upon the density of the filling, the amount of copper it contains, the Fig. 455. {Trans. Odont. Soc.) amount of sulphuretted hydrogen present, and the degree of friction to which it is subjected. In short, copper amalgam should never be used in a cavity of which any of the margms are hidden from view. As already mentioned, certain therapeutic and preservative pro- perties have been claimed for this material. It is more probable that its preservative qualities are due to the fact that it does not contract, and hence, so long as it remains intact, forms a watertight plug (2). It is stated tliat the addition of from two per cent to five per cent of tm to a copper amalgam lessens its tendency to waste in the mouth, and also improves its colour. Palladium Amalgam. — An amalgam composed of precipitated palladium and mercury was formerly much used in this country ; it is now but seldom employed. This is no doubt partly due to the great advance in the cost of the metal. The precipitate is prepared by dissolving palladium foil in nitro-hydrochloric acid, and precipitating the metal from a dilute and slightly acid solution of its salt by rods of zinc. The grey- black powder thus obtained is col- lected, and thoroughly washed free of all acid with hot water. It is then dried, and should be kept in a tightly stoppered bottle, as it seems to lose its affinity for mercury after exposure to the air. When triturated together in a mortar, paUadium and mercury do not combine at once ; when the union does occur, it is somewhat sudden, and a certain amount of heat is generated, indicating a chemical union. Palladium amalgam sets rapidly, yielding a plug that exliibits a large degree of expansion, which continues for a fairly long period. In the mouth the fiUmg becomes jet black in colour ; it does not, however, stain tlie tooth tissue. The Mixing of Dental Amalgams. — It has already been indicated that the amount of mercury required to make a mass that is easily manipulated and that may be condensed without diffi- culty varies with the constitution, character, and method of preparation of the primary alloy. Some excess of mercury over and above what is neces- sary to satisfy the chemical affinities of the constituent metals is required, as otherwise the mass cannot be rendered sufficiently plastic ; but the limitation of this excess to a uniform minimum, as well as evenness m its distribution, are matters of Fig. 456. — TuUoch's amalgam alloy measure. (Trans. Odont. Soc.) the first importance. Amalgamation is effected in various ways : by trituration with pestle and mortar ; by shakmg the finely divided alloy 393 and mercury together iii a test tube ; or by merely rubbing tliem together ui the palm of the hand. The first of these is the method most generally adopted and is the best ; further, the mortar should be warmed. The filings having been incorporated with the mercury, it is a common practice to express some of the excess mercury by squeezing it out through a cloth or piece of chamois leather. Such a procedure cannot but lead to a lack of uniformity in the results achieved. If some of the expressed mercury Is exammed, and a globule of it made to roll do«ii a smooth incline, it will at once be observed that it is contanimated by some other metal, as evidenced by the fact that, when rolling, it does not main- tain the form of a perfect sphere. With the mercury have been extracted varying propor- tions of the other constituents of the alloy, gold and tin being the chief losers. This may be confirmed by treating a little of the expressed mercury in a test tube w ith dilute nitric acid ; the mercury, together with any silver, is dis- solved, \\liilst a residue is left, which m the case of tui alone is white (metastannic acid), and in the event of gold also being present is purple (Purple of Cassius). The amount of tin removed ^^ith the excess of mercury is proportional to the quantity of the latter metal of silver 38-8 per cent, tin 49 per cent, gold 12 per cent, it was found that, after amalgama- tion with a large quantity of mercury, and _^_^^p^ Fig. 457. — ^Tulloch's amalgam alloy measure. (Trails. Odont that is expressed, being approximately one per cent (17). As the result of an experiment conducted by Brisleo, with an alloy composed 13* Fig. 458. removal of the excess by squeezing, the alloy then contained silver 67 per cent, tin 31 per cent, gold 2 per cent (7). It is obvious that with such haphazard methods as those commonly adojited, the amount of mercury removed being dependent upon the caprice of the operator, uniform results with dental amalgam fiUmgs caimot pos- sibly be obtained ; and the differ- ences will be further accentuated by variations m the amount of mercury expressed during the actual insertion of the filling. In order to ensure a uniform mix, from which it is unnecessary to ex- f)ress any mercury, several balances for easily weighing definite quantities of mercury and alloy filings have been devised ; that designed bv J. B. Parfitt is excellent (Fig. 455). Of a similar nature are the appliances introduced by Tulloch (24) (see Figs. 456, 457). These machines may be adjusted to throw a desired amount of mercury or alloy, and prove very satisfactory in use. The appliance for measuring the filings may be replaced by the little spoon (Fig. 458) ; the weight of the filings it contains when quite full having been ascertained, the mercury appliance may be adjusted to throw the required amount to produce the desired mis. A spoon with Soc.) 394 t< [ a capacity of five grains will prove most convenient. Methods of Packing. — The technique involved in the preparation of cavities for the reception of fillings is dealt with in Chapter XIX. Briefly it may be said that such cavities should possess strong and as nearly as possible straight walls, with squared edges, whilst as broad a seat as may be is secured for the fillmg. The cavity should be com- pletely lined with one of the osteo-plastic cements, prefer- ably an oxy-phosphate of zinc. The packing of the amalgam should be commenced before the cement has hardened, in the mamier recommended by Baldwui (3), ui order to take advantage of the adhesive qualities of the cement, which also serves to reduce the con- ductivity of thermal changes through the amalgam to the tooth-pulp. The best results are obtained by using the alloy in small pieces, and thoroughly condensing them into place with heavy pressure. Plugger points with finely serrated flat surfaces are to be preferred to ball- headed burnishers (Fig. 459), and here agam the importance of properly mixed amalgam is seen. If the mix is too soft, it cannot be made to stay in close apposition with the cavity walls : as soon as the pressure is removed there is a tendency for the compressed mass to rebound, as it were, after the manner of a sponge (18). Pre- cautions must be taken to remove any portions of the cement lining that may have encroached on the enamel mar- gins, in order that the whole of the exposed surface of the filling may be of metal. With compound cavities a matrix (see Chapter XIX) is indis- pensable, not oiJy to assist in securing the desired contour, but also to allow of the amalgam being evenly condensed. There are many methods of packing amalgam, all of which are directed towards securing an even distribution of the mercury and a rapid setting of the plug. KLirby was the first to suggest using two mixes, one containing more mercury than the other, and employing the former for commencing the filling, and the latter for finish mg ; by this means the excess of mercury, which always n Fig. 459.- -Hopson's Amalgam Pluggers. (Messrs. Claudhis Ash, Sons e possible. In the matter of strength, the high-fusing porcelains on the whole take the lead, although it must not be forgotten that some of them are actually inferior to the Jenkins body in both strength and density. In spite of individual preferences, it would not be far wTong to say that while low-fusing bodies have the advantage of convenience, the high make better porcelain ; and this is appar- ently the opinion of the manufacturers, who invariably use high-fusing materials in the making of thek artificial teeth. The follo^vulg table will give some idea of the fusing points of several of the porcelain bodies in common use : the figures may be regarded as approximate and are collected from various authorities, who do not always agree ^^■ith one another. Packing the Porcelain. — The aim is to get the maximum density, or in other words the greatest amount of body in a given space. The difficulty to contend with is that the grains are of irregular shapes, so that air spaces are inevitably left lietween them. If the body is merely placed in the mould with brush or s^satula, the grains will lie in a perfectly haphazard fashion, like Fusibility Table F. Dazzling White Heat 2600° C. Wliite Heat 2500°- . 2400°- 2300°- Orange Yellow Heat . 2200°- 2100°- Orange Heat 2000°— 1900°— 1800°— Bright Red Hrat . . 1700°— 1600°— i Red Heat . I. 500°— -1400° -1300° -1200° -1100° -1000° -900° -800° -Parker's Body (1420° -Allen (1280°). -Dental Manufacturing Co. Foundation (1260°). Close (1260°). -Brewster Foundation (1215°). -Dental Manufacturing Co. High Fusing (1170°). ^Consolidated Inlay (1170°). -S.S.W. High Fusing (1150° 1) -Brewster Enamel (1140°). Fellowship Fusible Filling. -Dental Manufacturing Co.'s Mediiun (1093°). -Gold melts, S.S.W. Medium (1065°). -Ash High Fusing (1035°). Brill's Plastic Porcelain. -Brewster Gold Matrix (960" -Ash Low Fusing, Jenkins (850° to 900° 412 bricks tipped out of a cart. The best way to get the grains packed as closely as they can go is to have the body damp and the mould kept ui constant vibration ; under these conditions the grains settle themselves together, and the moisture that occupied their inter-spaces appears on the surface. A simple way of vibrating the Fig. 478. — Settling porcelain solidly in matrix by vibration. mould is to hold it, or the tray in which it is invested, in a pair of spring tweezers, and gently draw a .serrated rod, or coarse file, across their handles. As the moisture appears it can be soaked up «'ith blotting paper. Even when the grains are packed as closely as they can go, the mass is still far from solid, and if heated to its fusmg pohit will show a considerable contraction, corresponding in amount to that of the air spaces obliterated. If baked free from a mould, as artificial teeth are baked, the mass contracts uniformly to- wards its centre and attains its maximum den.sity. If baked wt a mould, the contraction still takes place, and causes fissures or spaces to appear in the substance of the porcelain, or between it and the mould ; or else the mould itself is drawn out of shape. The latter result would be disa.strous to an inlay, so that the best way to counteract the effect of shrinkage is to cut the mass into two or more sections, by a fine division running right down to the floor of the mould. Each section is then free to contract towards its own centre, and the result- ing chinks can be filled up at a subsequent bakmg. The Firing of the Porcelain. — In the process of firing, the "fused silicate ", of Fickes' defini- tion, must be properly melted so as to get the necessary cohesion, but the particles of " sili- cious substances " must retain their identity so that the essential structure of the porcelain is not lost, as it would be if the whole mass were melted into a homogeneous glassy mixture. The correct point to stop the firing is when all the contraction has taken place, and the surface become properly glazed, but before any change of shape, or loss of sharpness of outline, has occurred. Both over- and under-fusmg produce a material deficient in strength ; for instance, Weston Price (18) found that both Brewster and Jenkin bodies were nearly twice as strong if properly fused than if over- or under-baked to the extent of 85° C. ; Bluell (1) gives similar results. Time has an importance only second to that of temperature in the fusing of porcelain ; some experiments of J. Byram (2) show that bodies that normally fuse at or above 1200° C, can be satisfactorily fired by keeping them at the melting-point of gold for a long time. Close body and Bre%\.ster foundation requiring about an hour. White and Whiteley about three hours, and Consolidated six hours or more. There are many kinds of furnace for the firmg of porcelain. The heating is effected either by electrical means, or by the burning of gas, oil, or (in the older furnaces) coke. Excellent electric furnaces are on the market ; among many may be mentioned the Pelton, the Price, and the Hammond. The principle of all of them is the same, the heating being effected by the passage of an electric current through a platinum wire embedded in the furnace walls. In the best furnaces the heating of the interior is made uniform by a closer winding of the wire towards the entrance. Loss of heat is guarded against by having a thick A BCD Fig. 479. — Stages of firing of porcelain. (A) Plaster cast of mould showing original size of pellets B, C, D. (B) Pellet of S.S. white medium-fusing porcelain fired to 1050° C. (" biscuited "). (C) Similar pellet fired to the proper fusing point, 1070° C. ; note the glaze without loss of shape. (D) Over-fired pellet, heated to 1130° C. ; note loss of sharp outline. non-conducting jacket and a close-fitting door; the less loss of heat there is, the greater is the temperature that can be obtained without undue heatmg of the platinum wire. The amount of power required to run a furnace will, of course, vary with its size ; a moderate-sized one might take anything up to half a kilowatt. Custer (4) and others (6 and 8) give directions for making a furnace ; the writer has known a home-made 413 furnace last several years, in spite of heating many dozens of times to 1100° C. and over. While the electric furnace is far the most convenient, results just as good can be obtained by heating with gas or oU, provided the burnt or partly burnt gases are excluded from the interior of the muffle. Various kinds of gas and oil furnaces are to be obtained, some of them caj)able of firing the most refractory bodies on the market. The methods used for gaugmg the temperature are — (1) Inspection. — This is satisfactory only if the porcelain fuses at a red heat. It is practi- cally impossible to see details with sufficient accuracy in a white-hot furnace, even if a strong beam of light is thrown on the work from an external source, as has been recommended. (2) Test Pieces. — These consist of small pieces of the same body placed on a tray or in a loop of platinum wire and fired side by side with the work. The test piece is taken out from time to time and the progress of the baking judged thereby. This is a fairly satisfactory method, although the small piece fires more quickly than the work itself ; it is much better than the plan of taking the work itself out for in- spection, which cools it down to quite an un- known degree, so that it is most difficult to judge just how long it must be baked again to raise it, first to its former temperature, and then as nuich more as may be necessary, especially as the furnace has been getting hotter all the time. (3) Melting of Substances of Known Fusing Point. — (a) Tlie simplest of these methods is to use a pellet of pure gold as the test, and if the body fuses at a higher temperature than 1065° C, to leave it in the steadUy heatmg furnace for a certain definite time after the meltmg of the gold, which must be determined by trial for the particular furnace, body, and current voltage. (b) Seger's cones of the proper fusing pomt for the particular body may be obtained. (c) Le Cron's pellets of gold and platinum alloy afford a very simple and reliable means of gauging the temperature. The proportions given by Le Cron are as follows — Percentage Body. Composition of Pellet Gold Platinum Allen . 89 11 Close . 90i 9.^ Wliite Inlay 91 9 Brewster Foundation OU 8i Brewster Enamel 98 o ^Vhiteley Inlay . 921 n Consolidated Inlay 92i 7i White Medium . mo The pellets are used in connection with an ingeniously shaped crucible, which is placed on the furnace floor next to the work that is being fired. The crucible has two oj)enings, one in the roof, which is just too small to allow the pellet to pass, and the other larger one in the side. At the commencement of a bakmg the pellet is placed on the top of the crucible, resting in the smaller hole ; when its fusing point is reached it falls into the well ui the crucible floor, from which it can be recovered, when cold, for use m the next baking. As the pellets do not tarnish, they can be used over and over agam. [d) If the furnace always heats up in a perfectly regular mamier, its temperature can be gauged by the melting of a piece of metal of low fusing-point such as lead, placed in some position where the temperature bears some definite relation to that of the interior of the furnace. Such an arrangement can be made to actuate an alarm or an automatic cut-out. (4) Thermo-electric Pyrometer. — This consists of a platinum-rhodium couple, the junction of which is placed in tlie furnace at the point Fio. 480. — Le Cron's Pyrometer PeUet in crucible, ready for use. Nat^u'al size. whose temperature is required to be known. The free ends of the couple are connected with a very delicate galvanometer, and as the current is proportional to the difference between the temperatures of the hot and cold junctions, the excursion of the needle of the galvanometer can be made to indicate degrees of temperature. As the electro-motive force of the couple may be only about '02 volt, it will be understood that the pyrometer is a somewhat delicate instrument ; nevertheless, if well made, it wiU last a very long time. This is one of the most satisfactory and easy ways of gauging the temperature, and if used with reasonable care and intelligence w ill enable the operator to get a properly fused piece every time. Effects of Over-firing. — These are loss of shape, loss of colour, loss of strength, and porosity. Loss of strength and shape have already been mentioned, loss of colour can to some extent be remedied by painting with coloured enamel and refiring. The most mischievous defect of all is porosity, although this may be due to other causes besides over-firing. The bubbles may have been in 414 the mass from the first, owing to bad packing, and this is a much more frequent cause than most workers might imagine. They may be due to steam generated by putting a moist mass into the hot furnace. Porosity may also be caused by insufficient allowance for contraction ; m this case it ^^■ould take the form of fissures rather than a diffuse sponginess. If not due to either of these causes the bubbles must result from the evolution of gases, owing to the de- composition of some constituent of the porcelain, or of some foreign substance mixed with it. Most ordinary volatile substances would dis- appear before the body had become viscous enough to imprison the bubbles, but possible gases that might be given off at a high tempera- ture are water and sulphur dioxide, the latter being readily provided by the accidental in- clusion of a little plaster of Paris. If the body has become porous, there is nothing to do but dissolve it out of the mould, wholly or in part, by hydrofluoric acid, and replace it with fresh porcelain, or else to start a new inlay altogether. THE MAKING OF A FUSED INLAY The mould or matrix is usually made of gold or platinum foil, and there are two ways of adapting it to the proper shape. The ordinary one is to swage it into the cavity or some reproduction of it ; in this case the inlay is necessarily smaller than the cavity by the thickness of the foil lining. The other way, generally associated with the name of Peck, is to adapt the foil to a cement impression, which might be called, by a photographic analogy, the "negative" of the cavity, as opposed to the " positive " ob- tained by first taking an impression and then casting a model from it ; if the matrix is made by this method, its inside measurement will exactly equal that of the original cavity, no matter what the thickness of the foil may be. Ordinary Method. — The cavity having been prepared, the matrix may be swaged directly into the cavity or into a model of it. If a model is used, an imjiression must first be taken in some plastic material, the ones most used being ordinary mcdellmg composition, den- tal lac, gutta-perclia, and osteo-plastic cement. To prevent undue adhesion the cavity must be either dusted with French chalk, wetted, or, if cement is to be used, vaselined. In a labial cavity, an impression in one of the materials that "soften by heat can be obtained by the simple process of warming one end of a stick of the impression material and using the other one as a handle to press it into the cavity. In approximal cavities, and in the case of cement in all cavities, a metal strip or tray is required, both to press the material into the cavity and to prevent undue thickness of the impression, which might hinder its \\ithdrawal from the cavity. In some cases Dowsett's trays aaIII be found useful. In others, especially approximal cavities in which there is not too much space, a convenient plan is to press the material in with a band of thin steel or German silver, wide enough to reach from the tip of the tooth down over the cervical margin, and long enough to project on the labial and lingual sides, so that it can be gripped by the finger and tliumb of each hand when pressing the material into the cavity. The strip, preferably vaselined, is placed in the space first, and then the small j^ellet of softened modelling material is quickly packed into the cavity and pressed well home with the strip. From this impression the model is made, cement, Spence metal, or amalgam being most commonly used for the purpose. Cement is a very satisfactory substance to make a model of ; it is easily manipulated, and is quite hard enough to stand the necessary Fig. 481. — Taking impression of cavity with composition or lac, and metal strip. piessure. Care must be taken to smear it well into the parts of the impression that represent the enamel margins. If cement is cast into cement, the impiression must be well vaselined, and the model part mixed rather thick, rolled in the fingers with French chalk, and packed with considerable pressure. Spence metal, or sulphide of iron, can be poured into a dental lac impression, and gives a very sharp model. A little practice is re- quired to pour it satisfactorily. If heated in a spoon it will be observed that it is in the best condition for pouring M'hen just above its melt- ing point, a higher temperature causing it to become thick and full of bubbles; M'hen it is melted the ladle should be taken oif the flame and gently tapped on the bench to get all the bubbles to the surface ; when these have all disappeared and while the material is still quite fluid, it should be quicldy poured into the impression, care being taken to avoid inclusion of air in the deeper parts. Amalgam requires no special description; it is not so satisfactory as either Spence metal or cement, for general use. The use of a model has several great 415 advantages. It is far more easy to swage the foil to a model than to the cavity itself, partly because there are no adjoining or opposing teeth to get in the ^vny, and no patient to consider, and partly because the mechanical swaging press can be used instead of the much more tedious method of hand instruments. Moreover, the work can be done at leisure at any convenient time, or better still the den- tist can get some one else to do it for him. On the other hand, no method of swaging on a model can, as a rule, give as good a fit and as sharp a margin as can be obtained by directly burnishing the foil to the cavity itself. The method about to be described combines the advantages of the use of a model with those of direct swaging into the tooth ca\'ity. The preliminary fitting is done to a model. The matrix may be made from gold, platinum, or some combination of the two. Gold is easier to swage, but its very pliability makes it neces- sary to use a thicker sheet than would be the case with platinum ; it can, moreover, only be used Avith lo^\•-fusing bodies. Platinum has the great advantage that it allo^\■s the use of porcelain of any degree of fusibility. Strength for strength, it is thinner than gold, and although a little more care may be required, it is safe to say that any matrix that can be made at all can be made mth platinum; the difference is at a minimum in the beautifully soft platinum now made for the purpose ; the full iiliability is brought out by careful annealing, preferably in the electric furnace. The thickness is a matter of importance ; a certain thickness is necessary to give the mould strength to keep its shape during the various manipulations ; moreover, it is of no use at all to have a mould thinner than the average size of the grains of the cement forming the lute. Head (10) and Poundstone (17) have made careful measurements, both of the size of the grains and of the minimum thickness of a cement film setting between two plane surfaces under pressure. From their estimations it appears that foil up to jy^gTy inch thick may be quite safely used. It so happens that soft platinum foil of this thickiaess is pliable enough for all cavities of ordinary size, and stiff enough to keep its shape if used ■\\dth reasonable care, and this is the foil that on the \\-liole will be found most suitable for general work ; in making very small inlays, foil ^^jyjj inch thick may be used, on account of its greater pliability, this quality being much more than doubled by halving the thickness. WTien freed from the matrix, the inlay wiU go further into the cavity by an amount represented by the foil thickness, and this wiU reduce the discrepancy between the sizes of the inlay and cavity in all except those that have absolutely parallel walls. In order to make the matrix, the model of the cavity should first be fixed to the bed plate of the swaging press ^v-ith plaster or composition. _ A piece of the foil is then cut, of sufficient size to leave a margin all round the cavity. This is at first carefully adapted by hand, mth the aid of ball-ended tweezers, and pieces of cotton- wool, amadou, or chamois leather. The middle parts should be worked down first, and advance made gradually towards the margin. A piece of the thinnest china silk jslaced between the foil and the cavity during the preliminary part of the hand fitting will greatly help in the prevention of tears. A few small tears are almost inevitable, and unless they are near the margin they will not prejudice the fit of the Fig. 482. (A) The tooth cavity. (B) Impression of cavity iia composition. (C) Cement model of tlie impression moimted on bed-plate of swager. inlay ; in fact it may be said that the relief they afford to the foil prevents the necessity of having so much fullness at the margin, v^ith consequent wrinkles that must be flattened out. The fitting of a foil matrix is not quite comparable to the swaging of a metal denture, which is entirely a matter of stretching of the material. Of course some amount of stretching of tlie foil does take place, but, except in a simple case, there is almost bound to be some \\Tinkling or folding at the edge or some tear in the floor ; the best plan is to get as much real stretching as possible, and for the rest make a compromise between too much wrinkling on the one hand and too much tearing on the other. \Vlien the fltting is complete, any ^Tinkles on the margin must be carefully burnished out, so that the outline of the enamel edge is shaqaly and evenly defined the whole way round. For this purpose, as also for the greater part of the fitting, Booth Pearsall's rotary burnishers are very useful ; failing these, a perfectly smooth instrument must be employed. 416 so that the foil may not be cut or torn at the margin. The metal plate carrying the model and foil matrix is now transferred to the swaging press, and any warp or sjiringiness removed by press- ing \\ell \\ith the water-bag plunger. The matrix, which should now fit perfectly, must at this stage be removed from the model. In order to prevent distortion, it should first be filled with some substance that ^^'ill sufficiently support it, and that can be easily and com- pletely removed after the matrix is invested. Wax, gutta-percha, or camphor may be used for this jnirpose. Of the various kinds of gutta- percha the most suitable is the pink " base- plate " ; it should be packed into the matrix comparatively cold, so that it will not adhere too firmly to the platinum. After the invest- ment has set it can readily be removed if it is (A) Asli's Inlay Press. (B) The bed-plate, to which is fixed the cement model. (C) The water-bag plimger for fitting thin foil. (D and E) Iron plunger and hard rubber block for heavy swaging. warmed on the top surface ; if the mould itself is heated, there is danger of the gutta-percha sticking to the platinum foil and pulling it away from the investment. If wax is used it should be that supplied for casting and guaranteed to leave no fixed residue on ignition. The most convenient substance of all is camphor. If small pieces are packed into the mould, they can readily be made to cohere into a solid mass which acts as a very satisfactory support to the foil ; after investment the camphor can easily be removed with a blast of hot air, as it volatilizes at a low temperature without melting to a liquid and so rumiing into the pores of the investment, as wax does. Various substances are used for investing the matrix, such as asbestos powder, alone or mixed with plaster, clay, or kaolin, or either of these two latter by themselves. As useful an invest- ment as any is a mixture of three parts of powdered silica and one part of plaster. The investment should be mixed with water to make a stiff batter, a portion placed in a little platinum tray, and the matrix with its contained camphor gently settled into place by vibration. The camphor may be removed directly the invest- ment has set. It may be observed that the chief function of the investment is to give a ready means of handling the matrix \\dthout bending it ; it cannot really be relied upon to counteract A B Fig. 48-i. (A) The foil matrix. (B) Matrix invested in small platinmn tray. the tendency of the porcelain to warp the foil. The first part of the porcelain should have a much higher fusing-point than that used for the more superficial layer. The matrix should be wetted, and tlie body thoroughly packed by vibration in the manner already described. Wlien completely solid it is carved to shape so as roughly to represent the dentine of the ntissing part of the tooth, a margin of t;V of an inch or more being left free from porcelain all the way round inside the actual cavitj' edge. The object of this is to allow the refitting of the foil to the enamel margin of the tooth cavity after the foundation body has been fired, and consequently after all possibility of ^^■arping has passed, as the foundation body is never heated to its fusing point in the firing of the subsequent layer. Finally, the resulting core is cut into two or more sections, according to Fio. 485. — End of first baking; core in two sections. its size and shape, by carefully scratching through the hard packed body with a fine point until it is completely divided down to the platinum. With regard to the colour of the foundation, a very safe rule, especially for beginners, is to have it the same colour as the rest of the inlay. Another good plan is to make the foundation always white, and put all the colour into the overlying layer ; the advantage of this arrange- 417 ment is tliat it lessens or does away with the " shadow effect " of the cement lute. For this purpose " dead " white foundation body is supplied by the manufacturers, but the same effect may be obtained by mixing oxide of tin with an ordinary translucent body of light colour. Tliompson and others, (juoted by Smreker (21, p. 137), attempt to imitate the natural translucency of the tooth by building in layers, beginning -i^ith dark in tlie centre and advancing to lighter on the outside, in some cases going .so far as to put a spot of red in the floor to in\itate the colour of the blood- vessels of the pulp shining tlu'ough. The foundation is now fiixd, and it will be found that the sections into which it had been cut liave contracted, each to its o^^•n centre ; the resulting chinks are now solidly filled with the same body as before, and the completed core fused to a rough glaze. The matrix containing the core of foundation is now removed from the investment and well cleaned. The easiest way to clean it, both from investment and from stray particles of body, is to soak it for a few moments in hydrofluoric acid, and as this leaves a film of insohible earthy fluoride on the surface, it may with great advantage be boiled in strong sulphuric acid and then \^'ashed in plenty of plain water ; this treatment takes very little time and leaves the mould beautifully briglit and clean in the parts free from porcelain, %\hicli is itself roughened in a manner that greatly helps the adhesion of the next layer. The foil is, moreover, rendered over the whole area of the cavity and held by the fingers of the free hand. The matrix is now removed from the cavity, the greatest care being taken to prevent distortion of the edge ; as a rule it is best to pack it ^^■ith camphor under the rubber strip, or if any difficulty is likely to be experienced in getting it out, it may be jjacked with cement in tlie same way ; this of course holds the foil margin .so strongly that it will bear quite a lot of handling \\ithout -S^J^/i Fig. 486. — End of second baking ; core complete, but edges of matrix free from porcelain. Matrix and core are now ready for trying in cavity and reburnishing of edges. very pliable by the annealing it has received in the furnace. Tlie half-finished inlay is now tried in the cavity. A little trimming of the surplus foil may be necessary, especially at the side that goes in first and at the cervical margin ; there is no need to have more surplus any\\here than is just necessary for judging what cf)ntour is required. The foil is well burnished against the margin of the cavity so as to get the edge sharply defined without any break in its con- tinuity. A final dead fit is obtained by burnish- ing with a steel instrument through a double fold of rubber-dam which is tightly strained 14 F'lO. 487. — Reburnishing nuuf^iii., uf matri.x luider strip of rubber-dam, after second baking. distortion. The cement is removed by boiling with a little nitric acid. The matrix is now ready to receive the remainder of the porcelain. The body chosen should fuse at a temperature about 50° C. or so below that of the foundation. The tip and base of the tooth must generally be matched separately, and the whole inlay made a trifle dark for medial cavities, and light for di.stal ones. The first layer after tlie tryiiig-in should consist of a thin coating round the foil margin, great care being taken in this, as in all other j stages, not to get tlie slightest particle of body over the sharp edge of the cavity. This layer should be fired to a "high biscuit", i. e. some- thing short of the complete glaze. The next layer should bring the porcelain right out to its proper .shape, any surplus being carved away so that the sharp edge of the matrix stands out the ^\llole way round as a bright, slightly prominent line. This layer is also fired to a "high bi.scuit ". Some sliiinkage will have taken place, and this mu.st be made right, and the inlay fired to a good glaze, or, what is perhaps a safer plan, brought to a rough glaze, and the actual smooth surface obtained by painting on a very thin layer of body of a still lower fusing point and firing this to a high glaze. The inlay should now be ready for removal of the matrix, grooving, and setting in the cavity- The Peck Method. — The es.sential feature of this method consists in the fact tliat tlie inside dimensions of the matrix are equal to those of the ca\'ity itself. Consequently, neither the thickness of the foil nor the presence of folds in it make any difference to the fit of the inlay. 418 The use of thick foil minimizes the tendency to warping, so that this method is extremely useful for making any kind of inlay in -which A\arping is liable to occur, such as those that are shallow in jjroportion to their ai-ea, and on account of the parallelism of their walls do not permit the use of thick foil in the ordinary A^ay. Both these conditions are present in many labial festoon cavities in which it is very desirable to place porcelain fillings, and it will be found that in these cases the Peck method gives an accuracy and uniformity of fit that is other^vise very difficult to obtain. Let it be su^jposed that the cavity has been prepared. The matrix is swaged on to an impression of the cavity ; this impression must witlistand a good deal of lieavy pressure in the course of staging, so that cement is the only material both strong enough and quick-setting enough for the purpose. To get the impression, the cavity is first vaselined, and the cement mixed to a thick The Peck method. (A) The tooth cavity. (B) Tile cement impression, fixed to the bed-plate of the press (C) The foil matrix freed from cement. (D) The finished inlay. putty-like consistency, and in order to over- come still further the tendency to stick to the dentine, it is rolled between the fingers, and the surface made smooth with a little French chalk. WliLle .still plastic, it is packed into the cavity, preferably in one piece, and pressed home v,ith a little disc or strip of metal large enough to cover the margins of the cavity, and if necessary bent to the contour of the tooth surface. When the cement has set the impression is gently removed, and transferred to the bed-plate of the swaging press. It is supported on and fixed to tlie plate with cement ; if plaster or composition be used, the impression \\ ill ahuo.st certainly crack in swaging. A piece of foil is now cut out, ygVo inch thick for small inlays, and -^}ij, inch for larger ones. This is first carefully fitted d(n\n by hand. It must be remembertd that the | work is being done on a " negative " of the cavity, so that the prominent enamel margin is represented by a deep groove, into the bottom of which the foil must be taken. The fitting should proceed from the centre outwards, finish- ing up with the groove. The thick foil rec|uires a certain amount of pressure to adapt it ; folds and crinkles are of no consequence at all, as the final s^\aging vnil obliterate all traces of them on the inside of the mould. Burnishers, and pads of wool held in the tweezers, will be found the most useful means of adapting the matrix. As the fitting proceeds, the surplus foil round the edge may with advantage be trimmed away. Opposite j)laces where the marginal groove is very deep it is best to trim the foil until there is hardly any surplus at all ; this ^vill greatly facilitate the carrying of the matrix down to the bottom of the groove without tearing. Hand fitting should be persevered in until, on removing the matrix, the margin of the cavity is well defined the whole way round. It is now ready for SAvagmg ; this must be very thorough, as the smallest failure of adaptation of the foil Mill result in making an inlay that will not go into the cavity at all. The plate carrying the impression and matrix is placed in the floor of the swaging press, and the solid rul)ber block, 7iot the water-bag, used under the iron plunger. The pres- sure must be very considerable, such as that produced by a large tail-vice, or a hydraulic or differential plate- swager. If the pressure has been sufficient, the matrix will be found absolutely adapted to the cement impression. Foil and cement are removed to- gether from the iron plate and boiled in strong nitric acid ; the acid dis- solves the cement and leaves the matrix free. Some authors recommend that the matrix should be detached from the im- pression by the aid of investment poured over it and alloA^'ed to set, or viith gutta-percha; but if the foil has really been adapted well, both these methods render the matrix liable to fatal distortion. If the cement contains an insoluble silicious material, the addition of a drop or two of hydrofluoric acid to the nitric will soon make it dissolve. When free from cement the matrix is ready to receive the porcelain. It may be invested or not, as may be most convenient. The further stages are similar to those of the ordinary method, with the exception that it is impossible to try in and re-burnish when tlie inlay is half finished. Although thick foil has been used, no chance must be given to the porcelain to A\ar)) tlie matrix, so the body must be at once carried u]) to the cavity edge and the mass well sectionizrd for the first baking ; the first layer should also be of a higher fusing point than the rest of the inlay. A little care may be 419 necessary in removing the thick foO, especially from a broad shallow piece of porcelain ; the best plan is to loosen the matrix gently all round the margin to commence with. RETENTION This matter has of necessity been alluded to ■while considering the preparation of the cavity. There are two kinds of retention : grooving, with or without etching ; and fixing with a metal post, pin, or some such means. Grooving and etching are suitable and suf- ficient for inlays that have in cross-sections ver- tical to the floor, an outline of the Dall type. The grooves should be in the middle of the lateral walls, parallel to tlie surface and floor, as narrow as they can be made, and about as deep as their width. They are most easily made witli a thin diamond disc. They may also be made by placing in a suitable position in the matrix some substance that can be sub- sequently removed, or is burnt out in the firing. Fig. 489. — Thin section of porcelain etched witli hydrofluoric acid, showing the rough siu-face produced. (Magnified (i diameters.) Such are pieces of starch, as recommended by Le Cron (14), clay, or powdered silica. Rolls of platimnu foil, or pieces of platinum wire or in low-fusing body gold foil or wire (or even copper wire (21, p. 297),) have been used for the same purpose, the metal being subsequently dissolved out with aqua regia. If the inlay is being made by the Peck method, the grooves may be cut in the sides of the cement impression, and will be accurately reproduced in the finished inlay. Besides grooving, it is well to take advantage of the additional lioldfast given by etching the surface next to the cavity. This may easily be done by pouring a few drops of strong hydro- fluoric acid on the parts to be roughened ; the outer surface, and a narro\\' area just inside the edge all the way round, should be protected from the action of the acid by mdliiuj a thin layer of wax on to them. After a few minutes, according to the strength of the acid, the inlav is \\ashed, the wax removed, and the roughened surface made still rougher by boiling for a moment in strong sulphuric acid; this is to remove the chalky layer of earthy fluoride that would otherwise be left on the surface. The inlay is no^\- ready for drying and cementing in the cavity. The other method of anchorage, as aheady stated, is by a metal post ; this may or may not A B Fig. 4'JO. (A) Bosch pin for retention of inlays. (B) Diagrammatic section of Bosch pin in inlay. be fixed in a special hole drilled in the dentine for it. If there is no special hole for the post, the cavity must be shaped in just the same way as if the holdfast consisted of etching and groov- ing only, but a considerable dei^ression must be left on the under side of the inlay to contain the metal anchor and the cement in which it holds. The post has to l)e kept in place in the matrix while the body is being packed; this is most easily done by making one end of it long and sharp, and pushing it through the floor of the matrix, so that it holds in the investment, the surplus length being cut oif before the inlay is fixed in the cavity. The cement space is obtained by building investment material, or thin gold or platinum foil, round the part of the anchor near the floor, the other part being left free, so that it is smrounded by, and solidly held in, the porcelain body. Bosch (15) has devised some double-headed Ijlatinum pins for this purpose. The part from A to B is pushed through the floor of the matrix and holds the pin in place Fig. 4'Jl. (A) Double-ended platinum wire loop answering the same purpose a~s Bosch pin. (B) Section of inlay with loop in situ. while the body is being packed ; when the inlay is finished, it is cut off. The part from B to C is surrounded by investment or other material during the firing, and later on is held in the cement lute. Tlie part from C to D is baked into the ])orcelain. A pin that answers the same purpose may be made by bending a piece of platmum wire in a loojj ^ith the two ends 420 projecting, one for fixing through the matrix and the other for holding in the porcelain body. The fitting of a pin into a hole specially drilled for it affords a very secure anchorage indeed. The governing principle of this kind of anchorage, and the necessary cavity pre- paration, have already been considered. Let it be .supposed that the cavity has been prepared and the hole drilled for the post. An impression is taken ^\■itll the post in position ; the latter necessarily comes away in the im- pression and then appears in its proper place in the cement model. To facilitate its removal from the model it should be coated with a thin layer of wax, and this should be applied be/ore the taking of the impression, the hole in the tooth being made sufficiently easy to permit this being done. The pin is now removed from its hole in the model, and the matrix fitted ; the post is then pushed through the floor of the matrix into its place, and the camphor packed in as usual. Matiix and jiost are no\\' removed from the model, the camphor keeping them in their proper relative positions ; they are then invested, and after the camphor has been volatilized the post is found firmly fixed in its proper position. The core of foundation body is then made, fixing matrix and post together with porcelain, and the inlay tried in and finished in the ordinary way. It has been suggested that the pin should be pushed through the matrix after it is in- vested, and the hole drilled in the tooth to accommodate the pin. If this plan is adopted, it will be found that it is a very difficult matter to drill the hole in its exact position ; in fact, the attempt generally results in having a hole much too large for the pin. In a dead tooth this will not matter, as there is plenty of tooth substance to cut, and opportunity to have a large and strong post ; but in a living tooth, where space between the pulp and the enamel wall is so limited, it will generally be found best to take the impression with the pin in its place to commence with. If two pins are required it is well to let their ends join together inside the porcelain ; that is to say, the two pins should form the two ends of a staple. This arrangement greatly helps to prevent warping of the porcelain. In cases that allow of it the staple may be reversed, so that the two eyids are baked in the porcelain, while the loop lies in a groove cut in the tooth to receive it. FIXING OF THE INLAY The inlay has now been grooved, and its underneath surface well etched with hydro- fluoric acid to about one millimetre from the margin. As dryness is an essential condition for the adliesion of cement, the tooth must be satis- factorily isolated from moisture. The question now arises whether the cavity shall be undercut or not. It has been stated by some authorities that the cavity should be left just as it is, in order to ensure the accurate " keying " of the inlay into the tooth substance. Head's researches (II), however, show that cement is not at its be.st in a thin film, but requires a certain thick- ness of substance to develop its full strength. Moreover, a slight space under the floor of the inlay allows its margin to be pressed into very close apposition with the enamel edge, thus making a better inlay and further minimizing the chance of solution of the cement. Hence a little freshening and roughening of the surface of the cavity is altogether an advantage. The cenient chosen should be of fine grain, not too cjuick-setting, and of such a nature that it develops its full strength when mixed to a thin creamy consistency. There are various special inlay and crown cements on the market, which are said by their makers to possess these properties. The colour may be such as to harmonize with that of the inlay, or a white cement may be used for all cases, the advantage of the latter plan being that the white ground reflects the greatest amount of light without changing the colour tone. In any case of doubt it is best to try the inlay in with some of the cement ponder mixed with water, so that the actual effect may be noticed and a powder of different colour used if necessary. The cement having been chosen, it should be mixed fairly thin, and then smeared on the etched surface of the inlay, and over the walls of the cavity. The inlay is now placed in the cavity and pressed gently and firmly into its correct position, especial care being taken to avoid any tilting, \\'hich Mould make one edge too high and the opposite one too low, and so spoil the whole fit of the fillini;. If the cavity has been properly prepared, this accident is not very likely to happen. In approximal cavities it is best to tie the inlay in place while the cement is hardening. After the cement has thoroughly set, the exce.ss is removed. If fitted as it can quite well be fitted, the inlay itself .should not require either dressing down or polishing of any kind. If the edge projects above the level of the enamel, it is a sign of faulty workman.ship, either in making the inlay or in cementing it into place. COMBINATION FILLINGS Some difficult cavities are most easily treated by filling each half of them separately. Both fillings may in some cases be made of 421 porcelain. This can be done by first filling one half of the cavity with cement or artificial dentine, then making and fixing an inlay in the other part, and finally cutting the temporary filling away and making the inlay for the second half. As a rule it is only necessary to put porcelain in the half that shows most. The other half ^\ould in these cases be filled ^\ith amalgam or gold before the preparation of the rest of the cavity for the inlay. Gold and porcelain inlays may be combined in this way, the gold inlay being made and fixed first. CJold and porcelain can also be joined together and cemented into the tooth as one mass. There are two ways of doing this. In the first method a wax foi'm is made for the whole cavity, but before casting, a portion of the wax is removed from the labial surface, so as to make a depression in the finished inlay, care being taken to preserve the rim of the mould intact. The resulting depression in the cast gold inlay is filled ^\ ith low -fusing body, so that nothing of the gold is visible but the fine line at the edge. By the other method the porcelain inlay is made first ; the side of it that fits against the gold is then cut into a dovetail, and the inlay put into its place in the cavity. The renu\ining part of the space is then filled with casting wax ; porcelain and wax are removed together and invested, and the gold is cast in the ordinary manner. The gold runs into the dovetails of the porcelain, and the two form one solid mass, which is then groo\ed for retention and cemented like anv other inlav. J. B. P. (1 (2, (3 (4 (5 (6: (" (8 (9 (10 (11 (12 (13 (14 (15 (16 (1- (18: (19 (20 (21 (22 (23 BIBLIOGRAPHY Bluell. Dental Cosmos, 1910, Vol. LIl, p. 84. BYR.4M, J. Plienoinena observed in fusing Porcelain. Dental Review, 1906, pp. 223, 338. Capon, W. A. Porcelain after Eighteen Years. Dental Cosmos. Sept. 1008, Vol. L, p. 909. Custer, L, E. Construction of Electric Furnaces, Dental Rciueic, 1906, p, 878. FiCEES, W. h. Chemical and Physical Character- istics of Porcelain and their Relation to its Manipulation. Dental Cosmos, 1910, Vol. LIT, p. 48. Garhart, W. E. Construction of Electric Fur- naces. Dental Review, 1906, p. 891. GuTTMANN, A, Progrls Dentaire, 1904, pp. 257, 326. Hammond, J, F. Construction of Electric Fur- naces, Dental Review, 1906, p. 883, Head, Strength of Porcelain, Dental Cosmos, 1906, Vol, XLVIU, p, 130, He.\d, Tests on tlie Inlay Cement Problem. Dental Cosmos, 1905, VoLXLVlI, p, 775, Head, Dental Cosmos, 1908, Vol, L, p, 812, Jeffery, L, Duplex Inlays, Brit. Dent. Jour., 1904, Vol, XXV, p, 767, Jenkins, Dental Cosmos, 1902, Vol. XLIV, p, 456, Le Cron, Porcelain Work. Published by Dental Manufacturing Co,, Ltd. Machwurth, Porcellanfiillung mit Platinstiften, Deutsche ilonatsschrijt fur Zahnheilkunde, 1902, p, 531, McCuxLOUGH. Dental Cosmos, 190(>-7, Vols, XLVIII-XLIX. p, 143, PouNDSTONE, Tile Cement Problem in Porcelain Work, DcntM Cosmos, 1904, Vol, XLVI, p, 760, Price, Weston A, Dental Brie), 1904, p, 136, RoBBiNS, C, Aji Improved Porcelain Inlay Tip, Brit. Dent. Jour., 1907-8, Vols, XXVIU - XXIX, p, 611, Robin, Pierre, Progri's Dentaire, 1901, p. 257. Smreker, E, Handbiich der Porzellan/ idlang und Goldcinlagen. Underwood, A, S, Trans. Odont. Soc, April 1904, p, 179, Wheeler, Dental Cosmos, 1904, Vol, XLVI, p, 547, CHAPTER XXV GOLD INLAYS Treatment of caries, or restoration of lost portions of teeth, by inlaying gold is not alto- gether new (13). Gold inlays were made as early as 1868, notably by the late Dr. Swazey of Chicago, whose work was found in good condition in teeth of his patients more than thirty years afterwards. The durability of inlaid fillings cannot therefore be regarded as untried (6). In respect of technique the gold inlay is yet in the developmental stage. Inlay technique in use prior to the advent of pressure casting is now abandoned, and even the technique of the latter process has undergone many variations since its introduction. Hence any description of technical jirocedure written now may soon become obsolete by reason of further change or improvement. Pressure casting renders prac- ticable certain changes in tlie interior form of an important class of cavities, and these changes tend to enlarge the limits within M'hich gold inlays may be used. The advantages of the cast inlay over the large or complex foil fillmg may be briefly stated as follows : The inlay lessens the work to be done in the mouth ; better protects frail walls against wear or fracture ; restores projjer contour and contact ^vith more certainty ; lessens pain by the form and manner of cavity preparation in Hve teeth ; and minimizes waste of tissue and encroachment upon the region of the pulp, more especially in buccal, lingual, and gingival extension of cavity margins to areas of comparative immunity. It minimizes irritation of live dentine or pulp by inter- position of cement. It renders the rubber-dam, with its clamps and ligatures, unnecessary. It is inserted without the irritation of the periodontal membrane incident to the condensation of foil. By the use of suitably alloyed gold the cast inlay is harder, stronger, and less conspicuous, by reason of colour, than is the foil filling. The comparative advantages of the inlay do not, however, hold good for all cavities, but only for the larger or more complex kinds hereafter described. Generally speaking, the smaller and simpler the cavity the less will be the advantage of the inlay (12). Wliile it is trae that gold inlays are made more accurately and easily by casting than they were by any other method, it does not follow that less knowledge, 422 skill, or attention to detail wUl suffice to attain the desired results. Dimension Changes in Gold Investments and Wax. — The follo\\ing statements of dimension changes occurring in gold or accessories in process of casting are derived from Weston A. Price's report of his investigation recently published in the Dental Cosmos. As sf)ace allows only brief mention of these important matters here, the reader is referred to Price's interesting account of the newly discovered properties of these materials, and the principles upon which errors in practical results are to be avoided (23). No process now in use yields gold castings that exactly fit all jsarts of the cavities they are made for. Gold, whether alloyed or not, contracts upon solidification and cooling. According to Price's figures the total linear contraction of 24-carat gold in passing from the liquid state to 0° C. is -0384, or 3-84 per cent; contraction in change of state is r64 per cent, and in cooling 2'20 per cent. This contraction, though not preventable by any means no^\' known, may be off-set, compensated, or controlled, so as to lessen or minimize the errors in fit otherwise inevitable in a cast inlay of complex form (19). Off-set is here used to mean expansion or enlargement of the mould, as by crystallization or heating, so that the molten metal is introduced while cxjjansion of the mould is greatest. The expansion available in the best moulds at pre- sent is effected by heating, and is generally equal to less than one-third of the contraction of gold. By compensation is meant the effect of sus- tained pressure upon the molten gold in the mould. As solidification is not instantaneous but gradual, and accompanied by contraction, additional metal is forced into the mould by pressure upon the surjilus in the gate. In other Mords, sustained pressure keeps the mould full until the metal becomes so solid as to resist the pressure used, the inevitable contraction occurring in the sprue more than in the casting. The greater the pressiu'e, the larger is the fraction of total contraction of the casting compensated for. The contraction of a gold casting is reduced to "013 or 1'3 per cent by an effective pressure of five and a half pounds per square 423 1^ incli upon the casting, as developed in a centri- fugal machine (19). The direction of contraction can be to some extent controlled. Such control depends upon the figure of the casting, the hardness of certain parts of the mould, and the contractile strength of the metal. If a band of gold is cast iipon a hard stone core, contraction of the gold in one direction is ojjposed or ^^'ithstood by the core, and does not lessen the inside diameter of the band ; the contraction of the gold takes place in directions where it is unopposed, making the band narrower and thimier. This kind of control has a useful application in casting an inlay to fit two or more surfaces of a tooth. A hard stone model, by holding the cooling gold, maintains certain inside dimensions of the inlay that are essential to its fitting the cavity ; hence effectiveness of control may depend upon cavity preparation and consequent shape of the inlay. Complex ca\aties should therefore be prepared ^\'ith due regard for the control of contraction and the consequent transfer of its effects to parts where they do no harm (20). Off-set, comi)ensation, and control, may all be used at once in casting complex inlays. Their combined effect, with present facilities, wOl be equal to less than the total contraction of gold, plus the contraction of wax impression or model. Investment Materials. — Expansion or con- traction of any investment now in use varies with the temperature to which it is heated. The investment mixtures supplied by dealers differ froni one another in the extent to which they contract or expand when heated, and also in the temperature at which maximum expansion or contraction occurs. In the best investment tested by Price a maximum expansion of "0085 was reached at 1000° F. ; in others the maximum expansions were much less and occurred at loM'er temperatures ; in some contraction began at 900°. After reaching a temperature of 1000° and cooling to ordinary temperature, all con- tracted to an extent var\dng from -005 to '035 of their original linear dimensions when set. If heated to burn out the wax and then cooled before casting, a mould made of such an in- vestment \\\\\ contract, increasing the errors in dimension due to contraction of the gold ; the mould sliould therefore not be allowed to cool before casting, which should be done at the temperature of maximum expansion (21). Wax. — The volume of any wax varies with its temperature. " The rate of expansion of all waxes changes rapidly with increase of temperature, but at different rates for different base waxes and different formulae of mixtures." Inlay waxes for use in making models or jiatterns are composed of base waxes according to different formulae. These differ from one another in the maximum and minimum temperatures at which they are M'orkable, and also in the degree to ^^'hich they contract in cooling from lowest working temperature to room temperature, or 67° F. The linear contractions recorded within these limits of temperature vary, for the ^^'axes tested, from Tl to 2-3 per cent. A wax model prepared in the mouth and chilled for removal will at 67° F. have linear dimensions from 1-1 to 2'3 per cent (according to the wax used) less than the dimensions of the cavity in which it was made. If invested at 67° or a lower temperature the error in dimensions will be carried forward. If left uninvested for several hours in a warm room, or warmed to or near its lowest working temperature for expansion, the model will be distorted. Distortion cannot be corrected by a subsequent step. Inlay waxes have considerable elasticity. Stretched, compressed, or bent, while warm, and then chilled, tliey retain the new form only •\\hile kept cold ; if warmed they tend to resume original form ; stretched parts shorten, com- pressed parts expand, and bent parts tend to straighten, ^\•hile the volume of the wax in- creases M'ith rising temperature. For im- pressions, as distinguished from models, a wax may be used having only half the contraction of the best model ■\\-ax, or 0'6 per cent linear, and less than one-fourth the elasticity of inlay waxes. Cement. — Cement exposed to the fluids of the mouth disintegrates ; the greater the area exposed, the thinner the mix of cement, or the nearer the exposure to the gum margin, the more rapid will solution or ^\■asting be. The quality of the cement, its manipulation, or the character of the oral fluids, may one or all hasten or delay solution ; but the general experience of the dental profession ^Aith cements seems to warrant the caution to treat them all as soluble in the fluids of the mouth. For this reason the margins of all gold inlays must fit so closely to the prepared enamel as to exclude oral fluids from contact with the cement (26) (30). Qualities of Metals for Inlay Casting. — Ideal alloys for inlay castings have not, so far as is known, been produced ; that such alloys will be developed does not, however, seem impossible. The qualities desirable in metals for this use are- — Malleability, strength, and hardness, varying from tliat of pure gold to about that of an alloy composed of ninety-five parts gold and five parts coin silver, to satisfy the needs of various situations. Immunity from chemical attack or change in the mouth, as complete as that of pure gold. Contraction upon solidification and cooling to an extent of one-third that of gold, or about one per cent. 424 Colour, that of a white metal or alloy that would be inconspicuous in the mouth. Conductivity, electrical or thermal, the minimum. Especially undesirable qualities are brittleness and elasticity. Pure or 24-carat gold, by reason of its malleability and softness, is easily moulded or burnished to close contact \^ith cavity margins. Exposed to stress on incisal angles or marginal ridges, however, it is too soft, and is ajjt to spread or .stretch so as to fail where the bite is strong. Reinforcement is suggested by Price as a remedy for this. Small threaded platino-iridium wire bent to the form of the letter L is j)laced in the cavity of the stone model before waxing, so that the gold when cast will enclose it. The wire strengthens parts otherwise lial)le to stretching oi' bending, and also restrains contraction along the wire, without changing the mouklable qualities of the inlay at the margins (21). For inlays not exj)osed to stress, or those surrounded by strong walls, as in buccal or some occlusal cavities of molars, pure gold is best a,i\d needs no reinforcement. The addition of five per cent of either platinum or coin silver to gold gives it strength and hard- ness equal to the needs of almost any situation without rendering it too hard for burnishing. The harder the metal in an inlay, the thinner its edges should I)e to allow effective burnish- ing; and the liarder the alloy of gold, the greater are the difficulties due to shrinkage or to .slight inaccuracies in technique. Therefore, thick or bulky inlays, if made at all, .should not be made of hard metal (32). Inlays that are to support ends of bridges should be of alloyed gold, or else reinforced with wire. But no alloy to be used for an inlay should be harder than the situation requires. The harder the gold, the more elastic it is and the less effectively burnished ; an edge of elastic metal pi-essed against the enamel %\'ith a burnisher tends to return or spring away, leaving the joint imperfectly closed. Scraps containing .solder, or zinc, or any ba.se metal should nut be added to inlay gold. Special Instruments. — For preparation of inlay cavities, abrasives, where they can be used, are superior to steel cutting instruments. Especially useful are thin steel discs charged upon one side with carborundum ; these can be used upon an approximal surface without injury to the adjacent tooth. " Vulcarbo " discs are excellent for their rapid cutting qualities ; these and the charged metal discs are to be preferred for their thinness. Small square- edge wheels and cones should be of vitrified carborundum ■ Abrasives cut with less irritation and vibra- tory jar than burrs do. Enamel margins cut with abrasives are stronger against attack of any kind than when cut with steel instruments, as will be obvious upon consideration of the .structure of enamel (29). The friction of any rotary cutter used dry rapidly generates heat, which is largely, sometimes wholly, responsible for the pain suffered. Therefore, water should be applied to minimize frictional heat and keep the cutter clean for rapid progress ; a medicine dropper held in the left hanel will conveniently supply A\'ater for this purpose. CAVITIES SUITABLE FOR GOLD INLAYS (1) Approximal cavities in meilars and pre- molars that involve the contact point. Science and experience both teach that the occlusal surface is the proper place for the fillings of these cavities to terminate at, whether it is carious or not. These cavities, and tho.se in whicli the occlusal surface also is carious, "will be treateel as approximo-occlusal. (2) Occlusal cavities extending to buccal or lingual surfaces, or other^xise so large as to render any wall weak or unsafe for foil filling. (3) Any large portion of tooth-crown lost by fracture, abrasion, or caries, where an artificial crown is not indicated, and exposure to view or to stress contra-indicatcs amalgam or porcelain. (4) Certain buccal ca\'ities in molars or pre- molars. (5) Certain approximal cavities in incisors or canines involving the incisal angle, or the pulp, or both, especially where the fillings are exposed to stress, anel aesthetic considerations are not paramount. (6) Cavities in molars or premolars in which death of the pulp has occurred. Special Requirements in the Preparation of Cavities for Gold Inlays. — According to current teacliing cavdties for gold inlays are prepared in much the same way as for foil, but \\ithout undercuts or convenience points (2). This teaching needs amendment in so far only as it relates to complex cavities : a cast inlay of complex form differs from the corresponding foil filling in tensile strength, retention, manner of insertion, and form necessary for resisting stress (3). Gold alloyed with five per cent of platinum or coin silver, or reinforced with platino- iridium wire, and ca.st under high pressure, is stronger in all ^^•ays than a foil filling of like size and form. The interior dimensions of a cavity may, so far as the strength of the filling itself is concerned, be smaller for an inlay than for foil. Certain interior dimensions and form of cavity that are not necessary for the insertion of an iiday are necessary for the insertion of foil. 425 To withstand masticatory stress approximo- occlusal foil fillings require as a foundation a broad flat gingival ^^■all at right angles ^\ith the tooth's axis, and need a dovetailed step, or occlusal portion, as a brace. An inlay, on the other hand, being a single rigid piece, is supported by the whole area covered by it ; its hook-like hold in the occlusal portion of the cavity is much stronger than that of a foil filling, so that unless much dentine is lost by caries, little Fig. 492. gingival wall is needed to supjaort the inlay against occlusal stress. \Vlien the dentine underlying a marginal ridge is not destroyed by caries, it is obvious that broad or deep cutting Fig. 4'J3. of the approximal part of the cavity only trans- fers so much stress-resisting area from the step to the gingival wall. \\'ithoiit at all increasing tlie support of the inlav. Much is lost by such 14* cutting for an inlaj', however necessary it may be for other fillings, and nothing is gained except convenience in preparing the wax model in the mouth, an object likely to be abandoned. Fig. 4Tinge, care being taken to isolate as far as possible the tooth intended to be tested ; and a large heated burnisher, or better, an instnrment with a copper bulb at its extremity, A\ill be found useful for convej-ing heat. It is ^^■ell to bear in mind that teeth in ^\■hich the pulp has undergone degenerative changes respond after an appreci- able interval to thermal tests, as compared with the rapid reaction of healthy teeth. Percussion with a heavy steel instrument affords much valuable information, and should never be neglected ; for this purpose it is well to bear in mind that light taps are quite as efficient as heavy ones, and less disagreeable to the patient. Thus, in periodontal mflamma- tion, the tooth on either side of the one affected may respond to percussion, and appear almost equally painful, but a little care will bring out the fact that the centre one is the most tender. It is also useful to nin the index finger of the right hand lightly over the gum about the level of the apices of the roots of the teeth, when a slight s^A■elling or tenderness over a particular tooth w-ai help to clear up the diagnosis. Per- cussion is also of considerable value in cases of inflammation of the pulp, as the root-membrane is frequently involved to a greater or lesser ex- tent in these cases ; but if the pulp has been aflected for some time all teeth on that side may be more or less sensitive to percussion. The character of the note produced by percus- sion of a doubtful tooth may advantageously be contrasted with that of a healthy one, and the sensation conveyed by the percussion mstru- ment, of tapping against a pad of thickened membrane, is quite distmct from the clear ring of a sound tooth. 444 Colour is a point that should always be noted about teeth as contrasted with their fellows. Thus, frequently a slight opacity ^\-ill reveal the beginning of a cavity that the probe has not detected, and a trifling difference in trans- hicency \\ill nlvny that a pulp is not quite healthy, and thus lead to more exhaustive tests as to its vitality. A good mouth-mirror is generally sufficient for this purpose, but the use of an electric mouth-lamp is also valuable. It is perhaps scarcely necessary to add that in all doubtful cases the use of X-rays will afford the practitioner most valuable help, by giving trustworthy information about pathological changes, otherwise unobtainable. But a radio- graph, to be of value, must be correctly inter- preted by the expert who takes it ; to those unfamiliar with its meaning it is useless. In the following case the use of novocaine as an aid to diagnosis is, as far as is known to the %mter, original : "In April, 1909, a young lady consulted me for constant pain on the right side in both the upper and lower jaws, with occa- sional remissions. The jiain was better at night in bed, but it was steadily becoming worse, and while it affected both the maxillary and mandi- bular divisions of the trigeminal nerve on the right side, it extended beyond the median line in the mandible. All teeth seemed to be equally sensitive to percussion and thermal tests, but if an\'thing the second upper molar a little more than the rest. My suspicions fell on the second upper premolar as the possible delinquent, owing to the fact that it was a shade darker in colour than the others. But there was really little to choose between it and the second upper molar ; so I made a further exhaustive examina- tion of all the teeth, and filled a small cavity in the crown of the third right ujiper molar; taking into account the fact that the neuralgia extended Ijeyond the median line of the lo\\er jaw. and al.so that it was relieved by the ad- ministration of stimulants and aspirin, I came to the conclusion that the neuralgia was probably the result of anaemia and overwork for an examination ; consecjuently I referred her to her physician before deciding on local treatment. Two days later the pain was more severe all day in the regions I have already indicated, but with the addition of an occa- sional sharp boring pain towards the right eye. She came to me late in the evening, as I had been away from town all day. In consecpience of the pain in the infra-orbital direction I decided to remove a filling from the second right upper premolar. I drilled in without causing any pain, and found the lining of cement ^^■as intact under the amalgam filling. There was a slight trace of softening at the cervical edge, which, on being touched, gave rise to a severe paroxysm of pain. As it was not yet clear whether this tooth or the second molar was at fault, for purposes of diagnosis I decided to isolate this tooth «ith novocaine, as I thought that if the pain ^^•as due to another tooth it ^\ould continue in sjjite of the premolar being anaesthetized, but if the premolar were the real source of the pain it would immediately cease. Accordingly I injected into the gum on each side of the pre- molar 0'125 of a gramme of novocaine, with the result that the pain immediately ceased and my diagnosis ^^■as confirmed. I at once drilled into the pulp, ^\hich I found to be inflamed, but without the formation of pulp-stones. I re- moved the greater portion of it, but was afraid to go to the apex, owing to the complete anaes- thesia produced by the novocaine ; so I dressed the root ^\ith pui'e hot carbolic acid, gave the patient some phenacetin and cafEein, and sent her to bed. The result \\"as complete relief (4) ". Head's Areas. — As any enumeration of the aids to diagnosis, in cases of neuralgia, would be obviously incomplete if it did not include some I'eference to the important work done by Henry Head, -what are familiarly known as " Head's Areas " vriW now be considered. It is an established fact, and familiar to most dentists, that in neuralgia depending on dental causes there are certain points of anatomical interest upon the head and face where the pain is of maximum intensity. This was first drawn attention to by Valleix ; but more recently Henry Head, in a series of jiapers communicated to the Neurological Society and published in Brain, has most ably systematized the subject, and has shown that these areas of skin tenderness are not only to be found on the head and face, but may likewise be found all over the body, \N'here they correspond to visceral disturbance. As Head's first article dealt with pain and ten- derness of the first dor.sal segment, it is proposed not to do more than allucle to it here, but to start at once from the point where his observa- tions have a special interest for dental surgeons, viz. in the region of the head and face. The system that he adopted in determining the areas associated with any particular organ of the head was first to exclude all pain and tender- ness in the thorax and abdomen ; then to note the presence or absence of general conditions, e.g. anaemia; and, lastly, to exclude the dis- turbances of organs other than the one under observation. After determining that certain pain and tenderness were due to disturbance of a certain organ, he noted the results of treat- ment of that organ. Thus, it was not sufficient to say that a headache was due " to the eye " or " to the teeth", unless the direct effect was noted by treating the eye or removing the teeth. Head found that each organ in the head stands in relation to one or more areas on the surface. To these areas pain is referred, 445 and over them the skin may become tender when the normal condition of that organ is •disturbed. For testing superficial tenderness on the fore- head and hairy scalp, where there is a firm bony substratum, the blunt end of a pin is used; this is felt as a blunt touch until the tender area is reached. The patient then complains either that the touch hurts and the skin is "tender", "like a bruise '', or he may say that he is being pricked. In carrying out these tests it is necessary to use a pin \\ith a spherical head ; the ordinary pin has a head that is a segment of a sphere and its edge may be definitely sharp to the normal skin, unless care is taken not to use it obliquely to the skin surface. If the tender area lies over the hairy scalp, a useful method is gently to pull upon or lift tlie hair ; this is perfectly painless in the normal human being, but becomes painful if superficial tender- ness is present over the scalp. Thus patients suffering from referred pain and tenderness \\ ill complain that their hair is sore when tliey brush it in the morning. On the cheeks there is a clanger that the head of the pin may exert pressure upon tender underlying structures such as the teeth, and it is therefore advisable to support the cheek ^^•ith the finger placed inside the mouth. Now the areas that are concerned w ith dental practice are eight in number. These it is hoped to make clear with the help of a couple of diagrams and a brief description. If some general idea of their position and boundaries is obtained, it will render subsequent reference to them comparatively simple. Head has named these areas — (1) Fronto-nasal. (2) Naso-labial. (3) Temporal. (4) Maxillary. (5) Mandibular. (6) Mental. (7) Hyoid. (8) Superior laryngeal. (1) Fronto-naml. — This area forms a racquet- shaped patch, with the larger part lying over tlie forehead. It extends for about two inches above the root of the nose, reaching the junction of the scalp with the forehead. It meets its fellow of the opposite side, excepting just over the root of the nose. At the level of the eye- brow it extends out for about an inch from the middle line of the forehead. A downward flap occupies the side of the nose, but does not reach the median line ; and ends below, al)ove the upper part of the ala nasi. (2) Xaso-Uthial. — This area lies over the U])))er lip, tip and under-surface of the nose, and the cheek. It includes part of the lower lip, and extends as a patch on tlie cheek as far back as a line dropped vertically from the external canthus of the eyje. Its limits can be best under- stood from the diagram. ^/rO'^^rf'^^-" ^^jf/u^/^y -*>f/VZ2'^(^XW Fig. 514. — Diagram to illustrate the area of tenderness as mapped out by Head on the face and neck, front view. When tenderness is [jresent, the patient com- plains ■■ that his upper lip is swollen and tender, and that the tip of the nose is sore." -^^KiVra-'MSj^L **^Jr/^i^//r vAsO'^/iem Kic. 515. — Diagram to illustrate the "maxima' front view. spots, (3) Temporal. — Tliis area lies directly over the temporal fossa, and extends upwards for a distance of three to four inches above a line joining the lateral canthus of the eye with 446 the upper part of the insertion of the ear. Its anterior border is about three mches from the median Ime of the forehead, and about half an hich in front of a vertical Ime drawn up^^•ards from the uisertion of the ear. Its breadth is about two inches at the widest part. The maximum lies in the temporal fossa, just above the upper border of the zygoma. The pain is said to be " in the temple ", or, if bUateral, to shoot through from " temple to temple ". (4) Maxillary. — This is a very easy area to defuie. It lies over the maxilla, extendmg as far forwards as the lateral fold between the nose and the cheek. Its upper border is formed by the lower margin of the bony orbit. Its lower border is a curved Ime jommg a pomt on the clieek, close to the fold between the ala nasi and the upper lip, ^\■ith a point just posterior to the bony orbit. At the level of the eyebrow the apex lies about three inches from the middle Ime of the forehead. To this area also belongs that part of the maxilla contaming the pre- molar teeth, together with a portion of the hard palate. When it is affected by other causes than caries of these teeth (e. g. lesions of the eye), these teeth may ache, and the hard palate in their neighbourhood may be tender. (5) Mandibular. — This area is also roughly triangular, and lies over the coronoid process, and the ranuis and part of the body of the man- dible. Below, it extends as far forward as a line dropped vertically from the external canthus of the eye. The apex of the triangle lies about half an inch in front of the insertion of the ear. From this point the posterior border dips back to include the tragus of the ear, and then swings forwards and downwards in front of the posterior border of the mandible. The anterior border of this area abuts on the posterior border of the maxUlary area, except at its lower portion. The maximum spot of this area lies about on a level with, and a little in front of, the tragus of the ear. The pam is referred to the cheek, just in front of the ear. This area becomes tender with disease of the last two molars of the maxilla. (6) Mental. — This area swings almost directly back from the angle of the mouth to a point on a line drawn vertically downwards from the lateral canthus of the eye. Thence it drops slowly to a point on the posterior body of the lower jaw, about three inches from the middle line. It then runs forwards along the fold separating the chin from the neck. In front it does not include the lo\\er lip or that part above the elevation of the cliin. When tliis area is affected, the anterior one and a quarter mches of the tongue are tender on the side affected. This area is tender in connection with disease of the anterior part of the tongue, and of the mcisor and canine teeth of the mandible. (7) Hyoid. — This area lies partly over the ramus of the mandible, and partly behmd its posterior border. The limits are best gathered from the diagram. Posteriorly it runs up on to the mastoid, and hence superficial tenderness over this area may give rise to fictitious " mas- toid tenderness ". The lobule of the ear is also tender. The anterior border of this area lies m front of the lobule, but does not include the Fig. 51(1. — Diagram to illustrate the area of tenderness as mapped out by Head on the face and neck, side view. tragus, whicli belongs to the mandibular area. The posterior portion of the meatus is intensely tender, and the insertion of an aural speculum will give much pain. There is also tenderness, as a rule, over the edge of the tongue. The maximum spot lies just behmd and below the angle of the mandible. A second most import- ant maximum lies ui the external acoustic meatus. The patient complains of pain in the ear, and of pain ■' just behind the jaw " ; hence the lialjitual complaint of pain in the ear with affections of tlie tonsils, side of the tongue, and molar teeth of the mandible ; and also the pain 447 in the ear so commonly met witli in diphtheria. This referred pain is liable to lead to errors of dia(;nosis, as the membrana tympani has Ijeen perforated without relief, when the fault lay in the molars of the mandible. (8) Superior Laryngeal. — The area next below the hyoid is roughly triangular in shape. The apex of the triangle reaches posteriorly to a line dropped vertically from the posterior attachment of the ear. The posterior part of its lower border lies just behuid the anterior border of the sterno-mastoid, and thence swings dowii- wards ajid forwards to the level of the lower part si//)rfi/curijiffKva;tt Fk;. 517.- -Diagramto illustrate the "maxima " spots, side view. of the thyreoid cartilage . The upper border runs forwards from the posterior angle, and just laps up on to the extreme posterior border of the body of the mandible. It then skirts the fold between the chin and neck, and seems to meet its fellow on the other side about the thyreo- hyoid space. From this anterior sujierior angle the base of the triangle curves downwards to meet the termination of the lower border a little to one side of the middle line at the level of the lower border of the thjTcoid cartilage. If this area is alTected by any cause \\hatever, the patient complains that he has difficulty in swallowing. Tlic paui is said to be " m the throat ". and the patient points to the situation of the maximum spot, which is just in front of the anterior border of the sterno-mastoid at the level of the thyreoid prominence. Tliough anatomically a small area, and one that has been crowded in the course of develop- ment, it is stUl functionally important, for into it refer the third molars of tlie mandible, and the jjosterior part of the dorsum of the tongue. The following table exhibits the teeth of the maxilla and mandible, and the areas to which pain is referred in the event of their being diseased : — Teeth. (1) Uppc?r incisors.] (2) Upper canines and fii'st premolars. (3) Upper second premolars. (4) Upper first molars. (5) Upper second molars. (6) Upper third molars. (7) Lower incisors, canines, and first premolar.^. (8) Lower first and second molars. (9) Lower third molars. (10) Lower second premolars. Areas. Fronto-nasal. Naso-labial. Temporal, also Maxil- lary. Maxillai'y. ManiUI)ular. Mandibular, also Hyoid. Mental. Hyoid. Pain in ear, edge of tongue tender. Superior Laryngeal. (Doubtful) Mental or Hyoid. Anatomy. — Li order to understand how these skin areas are associated witli visceral disturb- ance, it will be necessary to refer briefly to some anatomical facts connected with the nervous system. These are taken from Prof. Dixon's admirable address on the " Distribution of the Perijjheral Nerves ". The late Prof. His pub- lished some papers in which he drew marked attention to the fact that in the early human embryo the nerves run almost straight courses from thek origins to their terminations. He showed very clearly that the complications found in the courses of the nerves in the adult arose gradually, and were due to unequal rates of growth m the various parts of the developing embryo, and to the consequent bendings of the tissues and the displacements of the organs during their development. He conclusively proved it to be possible to demonstrate that the various organs and parts of the body in the embryo receive their nerve supply from the nerves belonging to the region in which the organs or parts originate, and that the complica- tions in the courses of the nerves in the adult are due to the fact that the various organs and parts during then- development often become removed far from the regions where they are first found. It has been established that in the lower vertebrates all the spinal nerves are built upon the same plan, and that each nerve — formed by 448 the junction of its two roots — divides into a dorsal and a ventro-lateral sub-division. The dorsal sub-division has been traced to the skin and muscles of the back, while the ventro- Abducent nerve Trigeminus Optic cup and len: Trochlearis Within recent years surgeons, by removal of the semilunar ganglion and the trigeminal nerve roots in cases of trigeminal neuralgia, have afforded opportunities for precise observations concerning the Hind-brain Acoustic nerve I otic capsule Second post-oral cleft Glossopharyngeal nerve ird post-oral cleft Auricular branch of vagus Telencephalfii Oculo-motor ner^-e*-^ Froriep's ganglion Ophthalmic nerve ■" Diencephalon Eoot and trunk of the first cervical spinal nerve _/ Accessorius [nerve anaesthesia; p'l runk of 2nd cervical spinal -Hypoglossal nerve actual distri- bution of this nerve in man. Ki'ause, Lynn Thomas, Gush- ing, and others, have in such cases carefully mapped out the areas of Roots and trunks of cfivieal spinal nerves 3-7 Olfactory bulb / Fronto-nasal process Nasal pit [ Ocular fissure Lateral nasal process Maxillary nerve Maxillarv process Mouth cleft Mandibular trunk Mandibular arch Fourth post -oral < I Vagus nerve Second branchial arch lea Fig. 518.- First branchial arcli Thyreo-liyoid arch Facial nerve Hyoid arch First post -oral cleft -Hivnian embryo, four weeks old, showing the distribution of the cerebral and spinal nerves. From a drawing by Professor His. (Dixon.) lateral has been shown to divide into a larger and more superficial branch for the body wall, and a smaller, deeper, visceral branch for the supply of the internal organs. It has been shown that this type of spinal nerve distrilnition occurs also in the embryo, of higher mammals, including man ; and it is kno\\-n that each spinal or segmental nerve sup- plies the various structures that arise from the segment to which the nerve belongs — skin, muscle, viscera, and probably also blood-vessels. In the head there are motor and sensory nerves, and some of these, at all events in the embryo, seem to arise in fundamentally the same manner as the segmental nerves of the trunk. It would, therefore, be of interest to inquire whether it has been found possible to establish for the cerebral nerves a tyi^e of distri- bution at all comparable with that which has been proved to exist in the case of the spinal .segmental nerves. This is a suliject that has received nuich attention ; and most conflicting views are held concerning it. Although certain of the cerebral nerves at first sight do appear to resemble spinal nerves, both in regard to their formation and their mode of attachment to the brain, Di.xon is of opinion that it would seem to be wiser, with present knowledge, to be careful not to push the comparison too far, and for the most part to be content to consider the cerebral nerves by themselves. and the most recent papers of Gushing on this subject probably give the most ac- curate pictures as yet available of the sensory distribution of this great nerve, both on the face, and in the mouth, nose, and pharynx. It is most satisfactory to note that as regards the surface of the face Kic. 519. — Cutaneous distribution of the trigeminal nerve in man as determined by Gushing. Over the dotted areas sensation was not completely lost, but painful sensations were interpreted as tactile sensations. (After Professor Di-xon.) and head, the minute anatomical dissections of Frohse enabled him almo.st quite accurately to map out the sensory field of the trigeminal nerve ; 449 and Gushing remarks that the outline given in one of Frohse's figures is practically the counter- i part of the skhi-field demarcated in nearly all his cases of trigemuial neurectomy. A consideration of these facts sliows that there is a close analogy between the trigeminal and a segmental nerve. The trigemmal nerve is distributed to the internal organs of the mouth — ■ teeth, tongue, etc., and sends branches to supply the skin and the face ; so that in cases of neuralgia or referred paui it might naturally be expected that the areas of tenderness traced out by Head would be found. It will be noticed that the area of anaesthesia mapped out by Gushing for the trigeminal stops at a well- defined Ime, which lies over the ramus of the mandible. The curious alteration in sensation that has been observed posterior to this line in cases where the semilunar ganglion has been re- moved, may be accounted for by considering the nerve supply of this region ; for the skbi over the angle of the jaw is supplied by the great auricular nerve, and communicating branches of the trigeminal, facial, and glosso-pharyngeal nerves. This would also explaui how the mandibular, hyoid, and superior laryngeal areas become affected by dental causes. In investigating the relations between the different teeth and then- areas of superficial tenderness, it is found that these organs stand in a curious position compared with other organs of the body, in that they lie in a cavity where the necessary conditions for the develop- ment of powers of localization are fulfilled. It is for this reason believed that a local pam will persist in the teeth later than in any other organ of the body. The first stage of caries of a tooth may be roughly said to consist of the removal of the enamel and excavation of the underhmg den- tine. During this process pain may or may not be present ; but provided the dentme is affected, pain can generally be elicited by stimulation. The most effectual stimulus in these conditions is heat and cold ; for in many cases \\ here a carious portion may be cut away without pain, a jet of hot or cold water, or the blast of the chip-sjTinge, will produce a twinge of pain. Xow as long as the pulp-cavity is not exposed the pain remains local. The patient complains of an aching tooth, and will point to the one affected. The pain may " dart and shoot ", but the darting and shooting are practically confined to the aching tooth. Local stimulation produces local pain. Neuralgia is absent, and no tenderness appears in the skin of the face. In this stage the pain jjroduced by the tooth is exactly analogous to tliat produced by injuries to the conjunctiva or outer layer of the cornea. It is purely local, and points to the seat of the injury. 15 If, however, the pulp-cavity is exposed, the paui alters in character and distribution. It starts ui the affected tooth, and darts and shoots into the face, forehead, neck, or ear. Each stab of pain lasts a few moments only, to be followed more or less rapidly by a second twinge. This is the well-known "neuralgia", caused by affections of the teeth. On testmg the face or teeth during the " neuralgia " some one or more of the areas described will be found more or less tender. On the face thLs tenderness is superficial, but parts of the jaw, mouth, or tongue may be tender at a distance from the affected tooth, owing to their intimate connection with the distribution of these areas. Thus teeth at a distance from the one affected may ache and be tender to the touch. The tender areas are not developed until the neuralgia has lasted several hours, and when a test is made for them the patient may refer the pain to a particular spot on the face or head, saying '" When you touch me there it seems to make my tooth worse". Tenderness usually ceases within twenty-four hours after the removal of the tooth, or it may be absent if the pain has ceased for several hours. For diagnostic purposes the patient's account alone may frequently be of value ; for referred pain is localized by the patient in the maximum spot or spots of the tender area affected. Thus, given a knowledge of the distribution of the tender areas and their " maxima ", it is easy to determine to what area the referred pain must have belonged, and thus indirectly to arrive at the diseased tooth. For instance, if the patient says that he has had ear-ache, he has probably suffered from the referred pain that is frequently associated with tenderness in the hyoid area. Now tenderness here is associated with disease of the second premolar and first and second molars of the mandible ; and thus it is possible to argue back that the patient with referred pain in the ear is suffering from disease of one of these teeth. Head's theories, and his explanation of these tender areas, are certainly fascinating, but up to the present they do not appear to have given the results that Head so confidently predicted. This may be partly due to the fact that they have not been sufficiently tested, and the areas carefully examined for, in neuralgic cases. Whether they will be of real value as an aid to diagnosis will depend upon the results obtained from the examination of a fairly large number of cases, which, as far as the writer is aware, has not been attemjjted up to the present. Notwithstanding the lack of successful dental cases, and that clinical physicians have reported that their results have not been encouragmg, there is no doubt that the subject will amply repay further investigation, even if it leads to 450 nothing more than a better acquaintance with the nerve-supply of the head and face ; it is not unlikely that it may demonstrate the existence of a valuable aid to diagnosis m obscure cases of neuralgia. A. W. W. B. BIBLIOGRAPHY (1) AcLAND, W. R. Notes on Some Causes of Neur- algia. Brit. Med. Jour., 1907, p. 1499. (2) Amoore, J. S. Dental Record, 1900, Vol. XXVI, p. 73. (3) Andrews, E. Two Cases of Removal of Gasse- rian Ganglion. Brit. Dent. Jour., 1892, Vol. XIII, p. 620. (4) Baker, A. W. W. A Case of Neuralgia. Dental Record, 1910, Vol. XXX, p. 217. (5) Baker, A. W. W. A Clinical Lecture on "Head's Areas". Med. Press, June 22, 1910. (6) Baker, A. W. W. Neuralgia. A Communica- tion to the Dublin Biological Club. (7) Baldwin, H. Neuralgia. Trans. Odoni. Soc, 1890-1, Vol. XXIII, p. 84. (8) Black, G. V. Litch's American System of Den- tistry. Vol. I, p. 923. (9) Brownlie, J. D. Odontalgia. Dental Record,Ma,Tc\i, 1910, Vol. XXX, p. 168, Discussion, p. 195. (10) BuECHARD, H. H. Dental Pathology, p. 500. (11) Dixon, A. F. The Distribution of the Peripheral Nerves. Dub. Jour. Med. Science, Feb., 1905. (12) Fereier, Sir David. On Some Relations of Fifth Cranial Nerve. Trans. Odont. Soc, 1889-90, Vol. XXII, p. 225. (13) Hayman, C. A. Neuralgia. Brit. Dent. Jour., 1900, \ ol. XXI, p. 721. (14) Head, H. Disturbances of Sensation and the Pain of Visceral Disease. Brain, 1894. (15) Heath, C. Injuries and Diseases of the Jaws. 4th ed. Chap. XII, p. 89. (16) Hopewell-Smith. Histology and Patho-Histology of the Teeth. (17) HoRSLEY, Sir Victor. Neuralgia. Brit. Med. Jour., Sept. 9, 1905. (18) Marshall, J. Clu-onic Neuralgia of Upper Lip. Brit. Dent. Jour., 1890, Vol. XI, p. 34. (19) Mummery, H. Brit. Med. Jour., Sept. 9, 1905. (20) Partsch, C. Diseases of the Antrum. Handbuch der Zahnheilkunde. Vienna, 1892. (21) RiLOT, C. F. Neuralgia. Trans. Odont. Soc, 1890-1, Vol. XXIII, p. 84. (22) Rose, W. Removal of Gasserian Ganglion for Severe Neuralgia. Brit. Dent. Jour., 1890, Yo]. XI, p. 740. (23) Russell, Risien. Neuralgia. Brit. Med. Jour., Sept. 9, 1905. (24) Salter, S. J. A. Dental Pathology and Surgery. (25) Smale, M. & CoLYER, J. F. Diseases and Injuries of the Teeth. (26) Tomes, C. S. & Nowell, W. S. Odontalgia and Neiu-algia. A System of Dental Surgery, 5th ed., p. 663. CHAPTER XXVII TREATMENT OF THE DENTAL PULP The normal human tooth contains a live jnilp. The function of the pulp, according to a few his- tologists, has ceased when the tooth is fully developed ; upon this hypothesis many practi- tioners do not liesitate to devitalize the pulp of a tooth for reasons that others would consider unjustifiable. The experience of the great majority of practitioners is that a pulp should not be devitalized unless there is no hope of retaining it permanently in a normal vital condition. It may be justifiable sometimes to attempt to retain the vitality of a pulp, even for a few years, if the tooth is not fully developed. Not\\-ithstanding the arguments set fortli by histologists and some radical practitioners, observation shows tliat both the enamel and the dentine of a tooth that has lost its pulp lose in strength and endurance. The earlier in life a tooth loses its pulp, the fewer years it will last. A tooth that loses its pulji before the normal closure of the apex, or shortly after its eruption, does not usually give many years of useful service ; both the tooth structure and the periodontal membrane lose in strength and in endurance. Teeth that have lost their pulps are not so useful for mastication as those with live pulps. Black (1 ) has shown that molars upon which a patient could bring to bear in closure a pressure of over two hundred pounds could only withstand a jiressure of less than a hundred pounds after devitalization of the pulji. Crowns supported by roots of teeth that have lost their pulps, and bridges sup- ported by abutments without pulps, are not as useful for mastication as if the pulps had remained alive. WliOe all teeth do not dis- colour equally when their pulps have been devitalized, yet sufficiently large numbers discolour badly enough to make the careful operator consider the possibilities of a darkened tooth. The degree of discoloration depends largely upon the mode of operating, but, perhaps, almost as much upon the striicture of the tooth. The younger the patient the greater are the possibilities for discoloration ; no conscientious operator lightly undertakes the devitalization of the pulp of an anterior tooth for a young patient. It is well recognized to-day that the cases of devitalization that give the best results are those of single-rooted teeth in mature persons. No preservative yet dis- covered vnll keep dead pulp tissue free from infection in a root-canal; as the difficulties of removing all the pulp tissue from root-canals increase, so do the chances for ultimate failure. The foregoing reasons, and those of the pain, discomfort, loss of time, and the expense, are enough to dissuade the dentist from needlessly devitalizing a dental pulj). Strong as the reasons are for retaining a pulp alive ^^•here it is indicated, yet they are not as strong as those for devitalization where such an oi^eration is demanded. The pain and discomfort, the ijossibility of an alveolar abscess and its consequences, are sufficient to cause the dentist to use all the knowledge and experience obtainable before deciding upon his course of action. In few cases is the den- tist's misjudgement fraught with such bad consequences as in not devitalizing a pulp that should be devitalized. MANAGEMENT OF PULPS ALMOST EXPOSED, OR EXPOSED WHEN THE OPERATOR BE- LIEVES THAT CONSERVATION IS DESIRABLE Dental Caries. — It can be laid down as safe practice to jjrotect or cap a pulp that has not caused pain lasting some hours, and is not exposed when all the carious dentine has been removed. It is always necessary to make a careful examination of the dentine covering the pulp in deej) cavities, to be sure that an exposure does not exist ; this should be done with a magnifying lens where it is possible. A fine pointed explorer or broach may be care- fully passed over the area where the pulp would seem to be nearest. Care should be taken not to allow the fine point to penetrate, as un- necessary pain would then be caused. Pressure should not be directed towards the pulp ; the point should rather be drawn cro^^'nwards. The most likely point of exj)osure is at one of the horns of the i^ulp ; in teeth that are angular in form with long cusps the horns of the pulp run almost to the enamel. Factors that Influence the Location of the Pulp.- — There are manj^ factors that may influence the location of the pulp. Any irrita- tion that is not sufficient to destroy living tissue is a stimulant. All the slight irritations 451 452 that occur to the pulps of teeth tend to make them throw out secondary dentine to protect themselv-es. The chief irritant or stimulant to the dental pulp is change of temperature. The pulps of old people have sometimes receded to the level of the neck of the tooth, while in all cases recession goes on as years advance. Teeth that are worn away have their pulps receded ; in fact, the horns of the pulp are usually obliterated in such teeth. The pulps of teeth of " mouth-breathers " are usually more receded than others. Large metal fillings ; cavities that have not developed rapidly enough to cause an exposure or too much irritation ; erosion and pyorrhoea alveolaris ; salt, acid, and sugar, applied to the dentine of a tooth, all cause recession. If these influences on the size and position of the pulp, and an exact knowledge of the thickness of the tissues of the normal tooth, are borne in mind, there should rarely be any doubt as to the location of the horns. Temporary Treatment of Exposures from Dental Caries. — If in the case of the young, tlie weak, or very old, the removal of all the carious dentine would expose a pulp that had not previously caused pain, and if, for good reasons, a temporary operation is desirable, all of the carious tissue — which means soft and discoloured tissue — need not be removed. It is desirable that large spoon-shaped excavators should be used to remove carious dentine from cavities in which there is any likelihood of exposing the pulp. The instrument may be cut into the tissue close to the enamel, thus avoiding pressure upon the pulp, and a pulling force applied to the instrument rather than a cutting one ; with a little care and observation the de- calcified dentine may be removed from deep cavities without pain. Wlien all the decalcified dentine has been removed that is possible without an exposure, there are t-\\o courses of practice open to the operator. In either case it is necessary to sterilize the remaining tissue, but this cannot be done immediately; he may apply a disinfectant and seal the cavity for a few days, or he may apply a disinfectant mixed with some solid substance and insert the filling at once. Since the operations under consideration are looked upon as temporary, the method of mixing the disinfectant with a non-irritating solid is the most satisfactory. It must be borne in mind that tlie main hope in these cases is for the pulp to die painlessly and not afterwards become infected with pyogenic organisms, or that it may remain in a quiescent condition until a more convenient season. It is believed by Black (2) and others, that if the ptomaines remaining in the sterilized tissue are not sufficiently irritating to destroy the pulp, the disinfectant is. The disinfectant used in such cases must be as non-irritating and as permanent as possible. Shalloiv Cavities. — Shallow and saucer-shaped cavities, or those in small teeth, are best managed by disinfecting, and filling at a subse- quent sitting, because there is not room for a layer of a disinfecting material and the filling. A layer of oxy-phosphate or oxy- sulphate of zinc should be used as a protection in any case. Some operators cover the part of the cavity next to the pulp with a varnish, such as benzo-balsam, sandarac, copal, or chloro-iiercha, and then apj)ly the filling ; this method is only advisable after disinfecting for several hours. If the cavity is deep and the immediate operation is decided upon, there is no method that gives better results than mixing oil of cloves with oxide of zinc or \\ith oxy- sulphate of zinc, and applying this to the pulp wall with a round-ended instrument, and covering with oxy-phosphate of zinc. Teeth not Fully Developed. — Deep cavities fre- quently occur before the apex of the tooth is normally closed ; in such cases it is very desir- able to keep the pulp alive until calcification is completed. If the pulp is removed from an incompletely developed tooth, the canal is larger at tlie apex than it is at a point nearer the crown, and as a consequence cannot be j)erfectly filled with a solid substance. Besides this, it is difficult to devitalize and remove the pulp, and the canal cannot be perfectly dried at the end. The chances for permanency are very remote ; every possible effort should there- fore be made to keep the pulps of the young alive. (See Chapter XXVIII.) First molars are often so carious in children less than ten years of age that if all the de- calcified dentine were removed the pulp would be exposed. In tlie great majority of such cases it is good practice to remove all the carious dentine possible -v^ithout exposing the pulp, cover the pulp wall with a paste of oil of cloves and oxide of zinc, and fill the remainder of the cavity with oxy-phosphate of zinc. After the time for the full calcification of the root is passed, it is well to open the cavity and remove all the filling and anyr emaining carious material, and if the pulp is clearly exposed, devitalize it and insert a permanent filling ; if there is no exposure, oxy-sulphate of zinc should be placed next to the pulp, and over this a j^ermanent filling. The same jjractice may be followed in the anterior teeth of the young. Many deep cavities in the young are so sensitive that it is impossible to excavate them properly even though the pulp is not exposed. The pulp in these cases may be capped with oxide of zinc and oil of cloves, and the cavity filled with oxy-phosphate of zinc for a few months or a year, after which the 453 cement should be removed and a permanent filling inserted. During the time the test fill- ing is in place, the pulp will have been stimu- lated to throw out secondary dentine to protect itself ; the decalcified dentine can then be re- moved with much less pain. If hypersensitive ca\'ities are filled with oxy-sulphate of zinc mixed with thymol crystals, and this is allowed to remain in place for a few ^\■eeks or months, the carious tissue can then be removed ^\■ith less pain. Such temporary filling may be covered with oxy-phosphate if the cavity is large enough and there is any danger of dis- lodgement of tlie filling. Discoloured Dentine Covering the Pulp. — If a permanent operation is intended it is not good practice to leave any soft tissue in the cavity, even if its removal would expose the pulp. Some authorities go so far as to say that no discoloured dentine should be left in a cavity. The tendency at the present time is to be more thorough in removing carious material than in the past. Many of the older writers on this subject advanced peculiar theories to support their views ; some went so far as to say that decalcified dentine would be recalcified inider a capping of zinc cUoride. No such views are held to-day, but many continue to cap exposed pulps ^^-ith zinc chloride, believ- ing that the irritation of the drug stimulates the pulp to throw out calcium salts to cover the exposure. The success of the practice, if it ever had any, more likely depended on the disinfecting jDroperties of the zinc chloride, which retained such capped jnilps in an aseptic condition for a long time, even though they were dead, than on recalcification of the dentine. The practice of removing all discoloured dentine covering a pulp is equally unwise, besides being distressing to the patient. Every observer of the progress of caries in teetli has noticed streaks of discoloration, extending from a superficial attack of caries, which it would ho very un\\ise to cut out. It must be borne in mind, however, that such discoloured tissue has been influenced by the carious process — the part near the surface much more than that deeply placed. There is a wide range between decalcified tissue that is compressible when removed, and the hard discoloured tissue of the penetrating variety just mentioned. It is safe practice to leave discoloured dentine covering a pulp, when it is hard enough to give a distinct clink or ring to the instrument as it is cut. Such tissue is undoubtedly infected, and con- tains waste products of bacteria, \\hich may be irritating to the pulp. The bacteria should be destroyed, and the ptomaines neutralized. The bacteria may be destroyed by placing a paste of creosote or oil of cloves and oxide of zinc over the tissue before inserting the per- manent filling. Until more is known of the chemistry of the ptomaines in such tissue little else can be done. Intermediate Fillings. — There is a growing tendency among careful operators to place some non-metallic or plastic .substance betA\een the vital tissue of the tooth and a metallic filling. Not a few ojDerators have followed the practice of placing oxy-phosphate or gutta-percha be- tween amalgam or gold fillings and the tooth tissues. One of the important advantages of the gold or porcelain inlay is that the inter- mediate cementing substance does not conduct heat and cold as rapidly as the metal, and thus protects the pulp from shock ; besides the safe- guard against changes of temperature, it pro- tects the tooth pulp from a certain effect of irritation that all metals have on living tooth- structure. Every operator has noticed that some teeth are not comfortable under metal fillings for months after they are inserted, while in others there is little or no discomfort ; others, again, are never comfortable while a metal filling is in contact with the dentine. The WTiter has more than once set up a violent pain by jalacing amalgam on living dentine, which Mas not relieved until every particle of the amalgam was removed and a soothing dressing inserted. It is good practice to place some non-conducting substance betAveen every large metal filling and the dentine. This cannot be done with large gold fillings in the anterior teeth, but fortunately such fillings are not now necessary. Accidental Exposures. — The rule generally laid down is to devitalize an exposed pulj). This rule, however, admits of a few exceptions. An exposure by caries is hopeless. An exposure by a clean instrument cutting sound dentine, which does not destroy more than a square micro-milli- metre of the membra na eboris in a young patient, may be looked upon as a favourable case for capping. If the instniment has wounded the pulp so as to cause haemorrhage, the insertion of a capping covered with a permanent filling is courting trouble. If the tooth is fully developed the removal of such a pulp is impera- tive. It might, if capped, remain comfortable for years, but the tooth would turn dark and would be less likely to give as long service as if the pulp liad been removed at once. Acci- dental exposures from clean instruments in teeth not fully dev^eloped should be capped ; if perfect dryness and surgical cleanliness cannot be secured, results are proportionately less likely to be satisfactory. The exposure should be dried by means of absolute alcohol and warm air; and an aseptic, non-irritating, easily adapted substance should be applied to the exposed surface ; the most suitable are the varnishes, such as benzo- 454 balsam, sandarac, or copal; or gutta-percha dissolved in oil of cajuput. If the exposure is clean when made there is no need to ajDply strong disinfectants or caustics. The varnish sliould be covered with a layer of oxy-sulphate of zinc if there is room ; if not, the cavity should be filled with oxy-phosphate of zinc alone. Accidental exposures are so rare %vith careful operators that they would not occur more than once or twice a year, and in fully ninety per cent of them the pulj) ought to be immediately devitalized. This leaves the number to be capped very small. Fractures of the Teeth. — -Fractures of the teeth that immediately or subsequently involve the pulp are not infrequent. They usually occur in childhood or young adult life ; they are more frequent among boys than girls, because boys play more hazardous games than guls and are generally more careless of their jiersonal safety. The upper anterior teeth are more often in- volved than any others; children often fall, or have missiles thrown at them, which fracture one or more of their upper incisors. The fracture may not expose the pulp, but the shock is often sufficient to cause it to die subse- quently ; in some cases the pulp dies from irritation of the exposed dentine. If the pulp is not exposed by fracture, the exposed dentine should be covered %\ith oxy- phosphate of zinc, which should remain until there is an assurance that the pulp is not going to die from shock or irritation of the dentine. If the pulp has been but very slightly exposed in a tooth not fully developed, an attempt should be made to retain the pulp alive until develoi^ment is completed. If there has been much j)ain, or protrusion of the jiulp through the exposure, or if more than a few hours have elapsed since the accident, there is little hope of success. Even slight exposures in mature teeth call for devitalization, and all large exposures demand it. Technique. — Freshly exposed dentine be- comes exceedingly sensitive in a few hours if the fluids of the mouth are in contact with it. This hypersensitive condition may be reduced to a normal state by dryness. The rubber should be adjusted, and the dentine dried with warm air. Applications of oil of cloves heli^ to protect the dentine from stimulation by the air. Phenol cauterizes the dentinal fibrils and protects them from irritation. When the exposed dentine has been thus protected and dried with alcohol, thinly mixed oxy-phosi)hate will usually adhere to a fractured surface if no contour of the cement is attempted. If space permits, the cement may be pressed into place with the forefinger. If an exposure is to be treated, the method described under accidental exposures may be followed, except that com- plete dLsinfection is necessary, which may take twenty-four hours. DEVITALIZATION OF THE DENTAL PULP As soon as it was discovered that many pains m and about the teeth were caused by the pulp, attempits were made to destroy its vitality. The early methods seem to us barbarous, but even in present methods there is great room for improvement ; they do not cope satisfactorily with pulps that have been subject for a long time to i^aroxysms of pain from slight irrita- tions. All the earlier methods were surgical, and had been j)ractised for many years before the discovery of the action of arsenic on the pulp by Spooner, a dentist practismg in Mon- treal. He found that the destructive action rarely if ever passed beyond the apex of the root. This was one of the greatest discoveries ever made in dentistry. It has made possible the restoration to usefulness of millions of teeth that would otherwise have been lost, and has relieved more pain than many general anaesthetics. The next advance in the method of devitalization of the pulp was the discovery of pressure anaesthesia by Funk of Chicago. The pulp may be devitalized by or with the aid of (a) Surgery, (b) Poisons, (c) Anaesthetics. Surgical methods of devitalizing the dental pulp have dropped into disuse since the intro- duction of arsenic and need not be further •considered. Many poisons have been used for the purpose of devitalizing the dental pulp, but none have proved as satisfactory as arsenic. Though arsenic has many drawbacks it stands to-day as the most universally satisfactory method. Cocaine anaesthesia stands easily in the second place. Among the objectionable features of arsenic as a devitalizing agent are its irritatmg properties, its failure to act upon mflamed tissue, the possibility of destroying more tissue than desired, its toxic or destructive action on the periodontal membrane, its frequent failure to devitalize completely the whole of the pulp, and the long time required for its action. Drugs that devitalize tissue by their cauterizing properties are too slow in action and mostly too irritatmg to be of much value ; they do not penetrate — a property so essential in devital- izing tissue some distance from the pomt of application. Among such drugs are caustic potash, sulphuric acid, hydrochloric acid, nitric acid, chromic acid, zmc chloride, nitrate of silver, and phenol ; of these phenol is the least irritating, while the strong acids are more 455 destructive. These drugs are only used where there is danger of too much destruction if arsenic is used, or where cocame wiU not act. They have been highly recommended for the destruction of the j)ulps of deciduous teeth, but hke many another recommendation handed down from text-book to text-book, they are of little value. If the pulp of a deciduous tooth is to be devitalized, arsenic is the most satis- factory ; there is no danger m using arsenic, where it is indicated, in deciduous teeth. The only requu'cment of the operator to use arsenic safely in deciduous teeth is knowledge of dental anatomy and histology and the action of the drug. This leads to a discussion of the action of arsenic when applied to living tissue. The reader need not be particularly concerned with whether arsenic devitalizes the pulp by conges- tion or strangulation. It has been held in many long and cleverly ^^Titten articles that arsenic caused the death of the pulp by creating an irritation that stopped or hindered the circula- tion of the blood in the veins. It has been as vehemently held that arsenic causes pulps to die by irritating the tissues until so much blood is forced into the j'ulp-cavity through the fine opening at the apex that the return circulation is cut off and the pulp is thus strangulated. For further discussion on this subject the reader is referred to works on therapeutics. The power of arsenic to devitalize a pulp depends upon — (1) the quantity and purity of the drug; (2) the vitalitj' of the tissue to which it is applied ; (3) the length of time it remains in contact with the vital tissues ; (4) the physiological condition of the tissues to be devitalized. Each of these factors must be considered in every application of arsenic. Success or failure depends more often upon the pathological state of the tissue of the pulp than anything else. The variations in the action of arsenic are so great that ^'^ of a grain, if applied just beneath the enamel m a normal first molar, may devitalize the pulp in twenty-four hours, while the same quantity may not devitalize the pulp of another tooth in the same mouth, even though it be applied to the exposed pulp and left in position for three months. It is often sagely said, if a pulp is inflamed do not at once apply arsenic , but reduce the inflammation and then make the application. The first difficulty is to make the diagnosis and the next is to reduce the in- flammation. Every pulp that has caused pain is not inflamed, and every inflamed pulp does not cause jjain, and if the inflammation has reached the stage of passive congestion neither time nor drugs will reduce it. Sometimes a free haemorrhage will cause the tissues to absorb the arsenic (or an anaesthetic), but there are many pulps — unfortunately they are the ones upon which drugs have the least effect — that will not bleed freely, and are too sensitive to allow of haemorrhage being promoted. Since , the action of arsenic on the pulp is so variable and depends upon so many factors, no definite rule can be laid down for the quantity to be used or the time it should be left in position. If the application is made directly to a normal pulp accidentally exposed in a young or middle- aged patient, ^hu oi a grain will devitalize it in twenty-four hours, while .},j of a grain may be applied to the dentine of a tooth with a pulp that has been hypersensitive to changes of temperature for months in the mouth of an old patient, and be left for weeks with safety. Only general rules can be laid doT\ii for quantity and time : yijj to tt^j of a grain, for twenty-four hours in deciduous and immature teeth, up to two weeks in the aged and in teeth with inflamed or partially dead pulps. Formes in which Arsenic is used. — Arsenic as used for devitalization of the dental pulp is a fine white powder, -tthich is sometimes adulterated with chalk. The powder may be mixed with antiseptic anaesthetic liquids, such as oil of cloves or creosote, until a paste is made ; a little of this may be taken on a small round- ended mstrument and placed upon the desired spot in the cavity of the tooth to be treated. Some operators prefer to mix the jjowder and liquid for each application, while others mix enough at once to last for years ; it is doubtful whether arsenic retains its full devitalizing power if mixed for a long time. A smaU [ pledget of cotton-wool may be moistened with creosote, and then touched with the arsenic powder, and carried to the cavity and sealed. Pastes are made of arsenic, creosote, oil of cloves, and thymol ; instead of the creosote or cloves, glycerine or lanolm may be used, because they are solvents of arsenic. The following is a useful formula for a paste — Arsenii Trioxidi . . 5 J- Cocainae Hydrochloridi gr. x. Thymol . . . . gr. v. M. Fiat unguentum. The objection to all forms of pastes is the liability of their being squeezed out of the cavity in attemjDts at sealing. For several years arsenic pastes were used in the Royal College of Dental Surgeons (Toronto), and it was no inicommon thing to have several cases of arsenical poisoning for treatment every week. Since 1897 arsenical fibre has been used, and 456 cases of poisoning are so infrequent that many students graduate without having seen one. Arsenic fibre when rolled up the size of a pin's head wiU contain sufficient arsenic to devitalize a pulp. For general use the fibre is the most satisfactory ; it is convenient to handle, easy to seal in the cavity, does not tend to leak out of the cavity when being sealed, and is easily removed. The fibre should be sufficiently dry to prevent liquid being exjjressed from it in the act of sealuig. It is made by workmg arsenic paste into a short-fibred cotton. Methods of Applying and Sealing in Arsenic. The method of application and the means of sealing depend largely upon the pathological state of the pulp as gathered from the history of the case, and the presence or absence of a cavity and its size and position. Carious Cavities m teeth approaching or reachmg the pulp are the chief reason for its devitalization. Cavities that are so deep as to endanger the vitality of the jJulp are usually large enough to make the problem of application and sealing a simijle one, but in cases where a great deal of the tissue of the tooth has been lost and the gum tissue has encroached upon the cavity, as is frequently found in the disto- buccal surface of the third lower molar, the problem of apfjlication and sealmg is a difficult one. It is often difficult on the labial surface of anterior teeth, and in excessive caries com- bined witli fracture in jjremolars. In most cases the application of arsenic is best made to the dentine in the cavity ; but if the cavity is so situated that the application cannot be made without the possibility of pressure on the pulp, or leakage of the arsenic, it is much wiser to drill a small hole through the enamel at a convenient spot, and pack the arsenic fibre in this, and place a dressing of oil of cloves and phenol in the cavity A\here the pulp irritation occurred ; this method will be found advisable in distal cavities of second molars, and sometimes in the first and third molars. Any j)re-existing pain will soon sub- side, and hi three or four days the cavity may be fully excavated, and if necessary an applica- tion made directly to the pulp, which may need to be left in position for days. If a pulp has been giving pain, it is not wise to make the application directly to an exposure if it exists, nor is it ■v\ise to attempt to make an exposure, unless the operator suspects an ulceration or abscess of the coronal portion of the pulp. If, however, it seems to be fully alive and is ex- posed, or if it has been exposed surgically and is bleeding freely, the application should then be made directly to the exposure, otherwise the arsenic is better applied to the dentine, and if possible an anodyne applied to the pulp, or as near as can be to it. Incisor teeth, especially lowers, do not give much room for application and sealing ; a very small quantity of arsenic should be used, and if there is room, this should be covered with a small piece of cotton-wool moistened with oil of cloves, and the whole covered with cement. If the overhanging enamel of the cavity is not broken away any more than is necessary to gain access to the cavity, it will assist greatly in retaining the dressing. The chief cause of pain m devitalization of a pulp \\'ith arsenic is pressure on the pulp, or the application to semi-vital or infected tissue when there is not an exposure of fuUy vital tissue. Wlien applica- tions are made directly to an exposure, the effort to seal effectively often results in pres- sure, while if the application is made to the dentine and an anodyne applied to the pulp, undue pressure is not so likely to be made. Leakage of arsenic most frequently occurs at the time of application. This is especially true in approximo-occlusal cavities ; the gingival wall of the cavity is often not sufficiently dry to ensure adhesion of the sealing material, and as it must be pressed into place from the occlusal opening after the arsenic has been placed, there is every chance of displacement, and if a paste is used it is almost impossible to avoid its being squeezed out of the cavity. In the anterior teeth the application can in most cases be made from the lingual or labial aspect ; and in deep cavities a small portion of the sealing material may be placed over the gingival wall of the cavity, the application made on the occlusal aspect of this, and the remainder of the sealing applied. Sealing. — Almost every kind of plastic sealing material has been used and advocated to retain arsenical applications. Among the most fa- voured are osteo-plastic cement, gutta-percha, sandarac varnish and cotton- wool, chloro- percha and cotton-wool, and ^^■ax and plain cotton-wool ; each of these (and others) has its advocates. That material is most suitable \^hich may be the most easily applied without pain, and will the most securely seal the appli- cation. Cement takes first place for small cavities and cavities upon which mastication might dislodge a less strong material. Sandarac and cotton-wool is most suitable for all cavities that have to withstand little or no force of mastication, and that are deep enough to retain it ; it is most easily applied and attaches itself most securely to the tooth's surface. If arsenic fibre is to be sealed with sandarac and cotton-wool, it is well to cover the fibre with some substance that is insoluble in alcohol (or ether, as the case may be), so that the sandarac may not spread through the fibre and prevent it coming into contact with the live tissues. If glycerine or lanolin is used in 457 the fibre, or if it is covered with a few shreds of cotton-wool dipped in vaseline or creosote, there is not likely to be any penetration of the cotton-wool by the sandarac. Gutta-percha may be used, but it does not usually become sufficiently plastic at a moderate temperature, and requires so much pressure to adapt it to the cavity wall that there is some difficulty in avoiding pressure on the pulp : this, however, may be overcome by placing a small convex metal or celluloid cap over the fibre, with its edges resting on hard tissue. Tetth with Fillings. — If a tooth is filled and the pulp needs to be devitalized, consideration should be given, in choosing the direction of approach, to the convenience of getting access to the pulp and root-canals, and the strength of the tooth after an opening has been made. Usually the nearest approach to a painful pulp in a frUed tooth is through the filling, which can be removed with less pain than is caused by cutting through live dentine ; if an exposure exists under the fiUmg or can be easily made, the pain can be at once relieved. If the pain is not severe, and the fiUmg is not such as will give free access to the pulp, it is better practice to cut through the enamel to the dentine at the most convenient site, and there apply the arsenic. If devitalization is advisable for any other reason than to relieve immediate pain, and the filling is in good condition, the only considera- tion left is the strength of the tooth after a sufficient opening has been made to remove the pulp. If good approximal or approximo- occlusal fillings exist in the incisors or canines, it is generally advisable to open the pulp- chamber from the Imgual aspect. If premolars have double approximo-occlusal fillings, and the pulp-chamber is opened from the occlusal surface, either cusp will sooner or later break away ; it is better in these teeth to gain access to the pulp through the medial filling, even though it is perfect. Upper molars are best opened at a part slightly medial to the central fossa, whether the filling is a good one or not : there is room in the molar teeth to cut into the pulp-chamber from the occlusal surface without making the tooth so weak that it is liable to fracture. Lower molars may be opened on the medio-occlusal aspect regardless of the filling ; in most cases of medio-occlusal cavities or fillings it is advisable to cut away the medio-buccal cusp ; this is especially ad- visable if the tooth is tipped lingually, or the cusp has been undermined by caries. No Cavity or Filling. — If no cavity or filling exists, and it is thought advisable to remove the pulp, the opening should be made at the part of the tooth's surface that will give the freest access to the pulp-chamber and the root- canals, and will at the same time not unneces- 15* sarily reduce the strength of the tooth. Hence the anterior teeth should be opened on the lingual surface just occlusal to the cingulum. If the teeth have been much worn by attrition, as sometimes occurs in the aged, the cutting edge may be selected as the site of opening : this is especially true in the lower incisors and canines. When an opening on the lingual aspect is used through which to remove the pulp, much care must be taken to remove all the pulp from the coronal portion of the tooth ; otherwise discoloration will occur. If the pulp is alive there is no need to cut through live dentine so as to expose tlie pulp before applying the arsenic ; all that is necessary is to cut a small opening through the enamel with a drill and pack this with arsenic fibre. In three or four days this may be removed, and the dentine cut away painlessly to a sufficient depth to ensure devitalization in forty-eight hours more. There are a few cases in which pulps are so sensitive to thermal changes that it is impossible either to grind or drill a hole sufficiently deep to retam arsenic, without causing severe pain ; these cases are found in highly sensitive people who have pyorrhoea, and in whom the necks of the teeth have been exposed for some years. The surface of the neck of the tooth should be wiped dry with cotton-wool, a little piece of arsenical fibre placed against it, a pledget of sandarac and cotton- wool applied over the fibre, and the whole tied to the tooth by three or four strands of floss silk. In a few days the surface will be so desensitized that an opening may be made deep enough to permit of a proper application. Since arsenical applications nearly always cause more or less irritation, and sometimes give violent jjain, it is wise to warn tlie patient that he may have some discomfort from the tooth for an hour or so, but that if it becomes violent he should call for relief. With some experience the operator will be able to foretell whether much pain is likely to occur. In the case of children, or patients who are in a highly nervous state, it is well to tell some other member of the family of the possibility of pain. Removal of Arsenical Applications. — It is well to evmce some interest in each case under- taken, and at tlie same time gain information, by asking the patient if he has experienced any irritation from the treatment. If some pain was felt for an hour or two and nothing since, excej)t, perhaps, that the tooth may have become slightly sensitive to pressure during the last day, the pulp is dead. If changes of tem- perature have ceased to cause pain it may be judged that the pulp is dead. If changes of temperature were not noticed for a few days and have smce returned, and the tooth is also ' slightly sensitive to pressure, it means not only 458 that the pulp is dead, but that it has died some days previously, and the quantity of arsenic has been sufficient to irritate the periodontal membrane and the living tissue at the junction of the livmg with the dead. In such cases, if the dressmg is removed and an exposure made, there will be an almost immediate relief of the membrane irritation and the sensitiveness to changes of temperature. But if the application has been in position only for a short time, or i was placed upon partially dead tissue, or if | the pulp tissue was much inflamed, then irrita- tion from changes of temperature probably indicates that the pulp Ls not dead. A tooth that was exceedingly sensitive to touch before treatment should be carefully handled in the removal of the dressing, even though the pulp is known to be dead ; and if there is doubt about the condition of the j)ulp, it is stin more important to use such care as \ will enable the patient to say whether sensations felt are from the periodontal membrane or a live pulp. Just because some pain is felt durmg the removal of the dressing or ui removing the carious dentine covering the pulp, it does not follow that the pulp is still alive ; the procedure may cause variation of pressure of the dead tissue upon the living irritated tissue at the apex. Sandarac and cotton-wool dressing can be readily removed with tweezers or a hoe-shaped excavator. Cement may be cut away with I sharp excavators or a drill in the engine ; it is well not to use the engine if it can be avoided. Gutta-percha can be easily removed with a hot instrument, but the temperature or pressure may cause pain ; it is important not to cause the slightest pain at this stage of the operation, i As soon as the dressing has been removed, a drop or two of cold water may be allowed to run mto the cavity, and if this causes no dis- ^ comfort a full stream may be applied. If an | exposure exists, a very fine, smooth broach should be gently passed into the pulp-cavity, and if no sensation occurs as the pohit reaches the apex there is a positive assurance that the pulp is dead, and that if there is any pain afterwards during the removal of the pulp, it is probably due to pressure on the living tissue at the apex, or tension on the same in attempts at removal, or to jarring an inflamed peri- , odontal membrane. If no exposure exists, all the carious material over the pulp should be removed with large spoon-shaped excavators ; it should be remembered that pressure over an j almost exposed dead pulp, or a sudden plunge into a pulp-chamber, will probably cause pain and frighten the patient. The dentine may be tested for sensation with fine sharp ex- cavators, ^^hich hurt a sensitive surface without pressure enough being used to make them cut. As the cavity is excavated it should be washed out with tepid water, and if an exposure is made the pulp should be tested with a fine broach as previously described. If the cavity is large, and some thickness of solid dentme exists between it and the pulp, a large round burr should be used until a horn of the pulp is exposed. If a small burr is used it is liable to be plunged into the pulp-chamber and cause pam ; moreover, the operator will not know whether it comes from the periodontal mem- brane, the j)ulp, or pressure at the apex. If the pulj) is dead, an o23ening should be made the full size of the pulp-chamber ; the cavity washed out with peppermmt water and dried ; and an antiseptic dressmg applied. If the pulp has not been devitalized, or is only partially dead, a second application of the devitalizing agent is necessary ; it is important not to make a second application if it can be avoided. It is thus realized why so much care should be bestowed upon the operation of removing the dressing and gaining access to the pulp-chamber, because it is so easy to misjudge the meanmg of the symptoms. Every pulp should be devitalized with as little arsenic as possible, because there is always danger of devitalizmg not only the pulp and dentine, but also tlie cementum and periodontal membrane, thus leaving a lame tooth with a limited number of years of probable service. If a second application of arsenic is made to a pulp or dentine when the former is already dead, an excessive absorption is likely, followed by an apparent return of hypersensitiveness of the pulp, and the permanent maiming of the tooth ; an accurate diagnosis of the condition of the pulp is more essential at this time than at the time of the fu-st application. If , however, the pulp is alive on tlie surface, the arsenic may be there reapplied, and if the surface tissue is dead but sensation is reached farther up the pulp-cavity, a small shred of fibre should be pushed up to the live tissue with a fine broach, and the pulp covered with an antiseptic dressing and sealed so that no pressure may come upon it from mastication. Some good authorities give the general rule that arsenical applications should not be made to pulp tissue in the root-canal, because of the danger of the poisonous efl^ect on the periodontal membrane or beyond the apex. If, however, a very small quantity is used, the danger is no greater than from a large quantity m the pulp-chamber. A broach may be dipped into arsenic paste, and pricked into the pulp two or three times as near to the live tissues as possible. This will carry enough arsenic to complete the devitalization, if the tissue has not been previou.sly inflamed. Management of the Devitalized Pulp. — Among the best operators and the best authorities 459 there is not a full agreement as to when a | pulp should be removed after it has been devitalized with arsenic. Such a well-knowii authority as the late A. W. Harlan recommended that no attempt should be made to remove the pulp at the time of the removal of the arseni- cal application, but that instead an application of a saturated solution of tannic acid in either alcohol or glycermo should be made for at least a week or ten days. ThLs \\as to give sufBcient time for the dead tissue to become separated from the livmg at the apex. The tannic acid was supposed to toughen the tissue sufficiently to allow it to come away in one piece ; and the glycerine so to act upon the red blood-corpuscles that discoloration of the tooth did not occur. Buckley, in his recent work on therapeutics, says in reference to this practice : " Let us consider the rationalism of such treatment. The pulj) tissue ui all large canals is sufficiently tough to be removed m its entirety, and it must be disorganized or removed piecemeal in small canals, whether it has been previously con- stringed or not. Hence, there is no advantage in using tamiic acid, and there is no serious objection. If those who follow this practice are observant, they wiU notice after they remove the tannic acid dressing, that the pulp tissue is dark m appearance. They wiU also observe that many teeth thus treated subse- quently discolour. The cause of this Is found in the fact that tannic acid and iron in any form are chemically incompatible, the resultmg compound being iron tamiate, one of the most msoluble substances known to chemistry. In the presence of moisture a form of ink is pro- duced, which is a great staining agent for the dent me, and one that it is almost impossible to remove by any known process of bleachmg." Few operators have noticed the peculiar tamimg effect of the tannic acid, but many have recognized the advantage of not attemptmg to remove the pulp for two or three weeks after it has been devitalized. It is then detached | from the tissue at the apex and comes away without pain ; and if disintegration has occurred, the apical contents can be absorbed with cotton- wool. The pulp may be kept aseptic during this period under a dressing of oil of cloves, creosote, or thymol ; no drug should be used that might discolour the dentine. Though this waiting method has been recommended by the highest authorities, few seem to follow it. The general rule is to attempt to remove the pulp when the arsenical application is removed. This method, though painful, is perhaps more suited to the anterior teeth, because the tissue can be taken away with one pull, and, besides, there is less likelihood of discoloration ; the canal can be at once wiped out and dried, no opportunity being left for the disintegration of red blood- corpuscles. The waiting method has a distinct advantage m molars and upper premolars. At best it is a tedious operation to remove the pulp from these teeth, and if it is still attached to the walls of the chamber and the apex, and, in addition, pain Is caused every time the broach is moved in the canal, the operation is distressing to both the operator and the patient. Anaesthetics. — About ten years after the introduction of cocame, as a local anaesthetic. Funk of Chicago, U.S.A., discovered pressure anaesthesia. Since then the method has under- gone many modifications, and a great variety of drugs has been used ; among these are cocaine, eucaine, stovaine, novocame, nervocidin, and a combination of phenol, cocaine, and adrenalin. Funk's original method is the most universally applicable : Remove the decay from the cavity untU an exposure is obtained. Dissolve a few crystals of cocaine in a drop or two of alcohol or water, and absorb the solution with a small piece of spunk. Place this on the exposure. Take a piece of raw ^iilcanizing rubber (soft and sticky) larger than the cavity, so as to occlude the outside of it. When this is in place, select as large an instrument as wiU enter the orifice of the cavity, or a large flat instrument, and gradually brmg pressure to bear upon the rubber, keeping in mind that success wOl not come unless the rubber acts as a piston, and forces the cocaine solution into the pulp. Use steady pressure, gradually increasing it, and finaUy kneading the rubber into the cavity. If the final kneadmg causes no pain, the rubber and spunk should be re- moved and the pulp tested with a fine broach for vitality. If haemorrhage occurs at this time the pulp is not fully desensitized, and a further application had better be made at once. If the pulp Is fully desensitized, the cavity should be freely opened until access can be obtained to the pulp-chamber and root-canals. Removal of the Pulp must be accomplished I within a very few minutes, or sensation wiU return. The most satisfactory method of domg this is by means of cotton-fibre wound on a fine smooth broach, as described below, under " Removal of Pulps ". If success has not come after five or si.x attempts, another method should be tried. Cotton-wool saturated with phenol should be carried to the apex to prevent return of sensation ; then a barbed or hooked broach may be tried, or if this fails, a fine reaming broach may be rotated to the ape.x, an attempt being made to separate the pulp from the } tissue at the apex. In all round or single- rooted teeth the fii'st or the second method wiU usually succeed. Excessive Haemorrhage may follow the removal of the pulp ; several drops of blood may come away. It may liave been noted that the 460 haemorrhage did not occur immediately after the pulp was removed. Cocaine acts as an astringent when first applied, but a reaction soon takes jjlace and the vessels dilate, and there is then excessive haemorrhage. As soon as the haemorrhage seems to be stojjping of its own accord, the cavitj' should be washed out and dried, a mild dressing inserted, and the cavity securely sealed for a few days. If excessive haemorrhage occurs it is an indication that a good deal of the drug has been absorbed, which may be sufficient to irritate the tissues at the apex and cause a soreness of the tooth last- ing for several days, or even weeks. In such cases the canal should not be immediately filled, because there is then no opportunity of removing mechanically the waste products of inflammation, which might go on to suppura- tion and permanent laming of the tooth. Immediate root-filling is only permissible after cocaine anaesthesia when the pulp was not previously infected, and there was not excessive haemorrhage, and also when the apex is small and absolute dryness is obtainable. If the pulp has an ulcerating surface, or is infected, pure phenol, or phenol and cocaine, should be used for pressure anaesthesia of the pulp. If cocaine alone is used the infection may be forced through the apex and an alveolar abscess result ; if phenol is used the absorption of the drug is limited, and disinfection occurs. Novoeaine and adrenalin chloride are used together for local anaesthesia with satisfactory results ; the adrenalin hinders the dissipation of the anaesthetic and limits its action to the part where it is needed. In cases of accidental exposure of the pulp, as in fracture, or by the excavator or burr a few crystals of cocaine may be placed upon the exposure, and in a few minutes the pulp may be jjainlessly removed. This will only act immediately after the exposure occurs; if several hours have elapsed absorption of the anaesthetic will not take place. Some years before Funk introduced pressure anaesthesia Manning Burge suggested injecting a cocaine solution into the pulp with a hypo- dermic syringe : If the pulp-chamber is suffi- ciently open, the needle is inserted, and gutta- percha or raw vulcanizing rubber is packed aroiuid the needle, and held while force is brought to bear upon the j)iston of the syringe. This method is very successful with partially devi- talized pulps if phenol is u.sed. High-Pressure Anaesthesia of the Dentine. About 1903 Myer of Cleveland, U.S.A., intro- duced high pressure anaesthesia of the dentine : A small tapering hole is drilled througli the enamel to the dentine, and into this is inserted a needle that fits tightly ; and by means of a specially constructed syringe sufficient force is applied to drive a cocaine solution into the dentine so as to desensitize it and the pulp. Anaesthesia of the Pulp from Surrounding Tissues. — The dentine and iHilp may be desen- sitized by injecting cocaine solution into the gum tissue around the tooth. Some operators recommend drilling through the process and injecting the solution into the diploe, so as to anaesthetize several teeth at once if they are to be operated upon. Occasions for Use of Pressure Anaesthesia. Cocaine anaesthesia is best suited for single- rooted teeth with exposed pulps that are not inflamed. In multi-rooted teeth, sensation often returns before all the canals are cleared out. If any shred of such a desensitized pulp is allowed to remain, severe pain may be felt until the piece is either dead or removed. On the other hand, with arsenic the finest portions die, and even if they are not removed immediate pain does not occur. Pressure anaesthesia of the pulp is rarely accomplished without some pain. It has advantages over arsenic in its rapid action and in the smaller probability of discoloration of the tooth. Toxicity. — Cocaine pressure-anaesthesia can- not be accomplished without some danger of local and general poisoning. It is almost impossible to know what patients will be poisoned and what quantity can be borne with- out ill-effect ; even the smallest quantity will cause the profoundest effect in one patient, while ten times the dose will not affect another or the same patient at another time ; the smallest quantity should be used that will produce the desired result. Care should be taken that none of the solution is allowed to escape into the mouth or be swallowed. Phenol has been known to produce an area of anaesthesia in the distribution of the inferior alveolar nerve, when squeezed into the pulp of the third lower molar. The local absorption may be sufficient to destroy the vitality of the tissues at the apex of the tooth, and result in a tooth that may remain sore for weeks and never return to a normal condition. Novoeaine, eucaine, and stovaine, are less toxic than cocaine and are more generally used. Refrigeration. — Pulps of teeth may be desen- sitized by the application of such refrigerating drugs as ether or ethyl chloride. The tooth may be isolated with the rubber-dam and the drug apijlied in a spray. If a pulp is inflamed and causing pain, and is relieved by cold, there is nothing better than the application of a spray of ether for a few minutes, and then of ethyl chloride while the tooth is being cut into and the pulp made to bleed freely, when arsenic may be apj)lied \\ith an assurance that no more pain Anil occur. Ethyl cliloride has often been used with good effect on partially dead pulps 461 in anterior teeth. The nostrils must be shielded, or else the evaporating ethyl chloride ^\ ill pro- duce a general anaesthesia. General Anaesthetics. — Highly inflamed pulps that are causing acute pain can only be satis- factorily treated by the administration of a general anaesthetic ; during its influence the pulp-chamber is cut into, and if f)ossible the pulp removed. Partially dead and inflamed pulps, and cases of pulp-stone, may be similarly treated. If several pulps are to be devitalized in the same mouth, they may be most expe- ditiously treated under a general anaesthetic. For all ordinary cases nitrous oxide anaesthesia is sufficient ; it is the safest, and altogether the most satisfactory. CONDITIONS REQUIRING DEVITALIZATION OF THE DENTAL PULP (1) Exposure of the pulp. (2) Inflammation that is indicated by pain or hypersensitivity to changes of tem- perature. (3) Hypertrophic inflammation of the pulp. (4) Atrophic inflammation of the pulp. (5) Recession of the pulp. (6) Ulceration of the pulp, and abscess of the pulp. (7) Erosion or abrasion. (8) Pulp-stones and pulp-nodules. (9) Pyorrhoea alveolaris. (10) Crowns with dowels. (11) Abutments for bridges. (12) Posts for large fillings. Management of Exposed Pulps. — Pulps exposed by caries in the anterior teeth and not causing pain are best devitalized by cocaine anaesthesia, provided the cavity is of such a form that pres- sure can be applied. In multi-rooted teeth arsenic is usually the most suitable, but if there is any reason for haste pressure anaesthesia may be used with satisfactory results. Pulps recently exposed by accident or by surgery may be desensitized by placing a few crystals of cocaine on the exposure for a few minutes, and if suffi- ciently anaesthetized, removed at once ; if not, a hypodermic needle may be passed a short distance into the pulp-cavity and a solution of cocaine injected ; if this fails, or the pulp is still sensitive, a broach dipped into arsenical paste may be j)ricked into the surface of the pulp, or a fine shred of arsenical fibre slipped into the pulp-chamber beside the pulp, and the whole covered, when possible, with cement. If a pulp has been exposed by accident for some hours or days, and has been irritated by changes of temperature, fluids of the mouth, and food, the tissue usually protrudes from the cavity and is so exceedmgly sensitive that it is impos- sible to touch it with anything. If the pulp is accessible at all, a few grains of cocaine may be placed upon it ; but the difficulty in such cases is that so much pain is caused by exposure to air that it is necessary to cauterize the surface at once «ith phenol to relieve the pain, and this prev^ents the action of the cocaine. The phenol should be gradually worked into and around the pulp until the pain stops ; arsenic can then be applied in the pulp-cavity beside the pulp. If this method is not successful a general anaesthetic may be administered, and the pulp at once removed if in an anterior tooth ; and if in a molar, as much taken out as possible, and the remainder devitalized with arsenic. A high- pressure syringe may be used satisfactorily if there is good enough circulation in the pulp to carry the cocaine solution. Injections of cocaine solutions into the gum tissue about the apex of the tooth will produce the desired result. Refrigerating sprays are too painful. Management of Inflamed Pulps. — As a general rule all painful pulps are inflamed, and so are almost all pulps exposed from caries. All pulps that are exposed should be devitalized (except as on p. 452), and all pulps that are in- flamed or have caused pain for some hours should be devitalized. Pulps that are exposed from caries, or are painful from pressure of food or other substances, may be relieved by removmg carious dentine or the substance causmg pres- sure. If the paui is caused by salt, sugar, or fermentations in the cavity, it may be relieved by gently washing out the cavity with tepid water and removing any loose carious material, and applying an anodyne, such as oil of cloves, phenol, or cocaine. Relief is not certahi in any of these cases unless haemorrhage is obtained. It is remarkable that sometimes if arsenic is placed upon the dentine, the pain, which has been gonig on perhaps for hours will be relieved in a short while. It the pain is not too severe to be borne, an anodyne should be applied to the pulp, and arsenic applied to the dentine and sealed, so that the patient cannot remove it. The pain may last for a short while, but it usually sub- sides in an hour or two. If the pain is severe, attempts should be made to relieve it. Appli- cations of cocaine, oil of cloves, phenol, and other tried remedies having failed to give relief, pressure anaesthesia with phenol may be tried. If this fails, a spray of ethyl chloride will gener- ally work admirably ; the tooth nuist be acces- sible, and the rubber-dam should be in position ; and it is well first to cover the tooth with cotton- wool and apply the spray gently, then gradually to remove the cotton- wool until a full spray can be applied to the tooth. When the pulp is anaesthetized, a round l)urr as large as will enter the pulp-chamber, rapidly revolving in the engine, should be plunged into the pulp. This will secure a free haemorrhage and relieve 462 tlie paiii, and ensure a certain and rapid action of arsenic, wliicli should be at once applied. General anaesthesia is also satisfactory for this operation. Inflamed and Painful Pulps that are not exposed are often difficult to locate. There are so many causes of pain in an unexposed jjulp, and they are so obscure, and the symptoms are so bewilder- ing to both the patient and the dentist, that it Ls little wonder they are so often undiagnosed. (For the pathology of the dental pulp see Chapter XVI, and for referred pain see Chapter XXVI.) Pulps that are actively congested are hyper- sensitive to cold and may be soothed by mild warmth ; pulps that are passively congested are soothed by cold and irritated by warmth or heat. Pulps that are hypersensitive to either heat or cold are in a pathological state. All j)ersons' teeth are not equally responsive to changes of temperature ; each person has his own standard of sensibility. The sensitivity of the suspected tooth must be gauged by the action of the same degree of heat on normal teeth in the same mouth. A tooth that has an actively congested pulp, and has not ached violently for some hours, need not be devitalized ; such a tooth should be protected from thermal shocks by drying it and covering it with a varnish ; and a cathar- tic and one-grain doses of quinine, or small doses of aconite or belladonna should be ad- ministered to the patient. When passive con- gestion exists or pressure from gases, the pulp- chamber must be opened, and if the pulp is alive it must be devitalized. If no cavity exists in the tooth, a convenient point from which to reach the pulj) is selected, and a hole drilled directly towards the pulp. During the drilling, cold water or a spray of ether or ethyl chloride should be cast upon the tooth to reduce the pain of drilling and the shock of puncturing the jnilp. Here again general anaesthesia may be used. If a cavity exists, the carious dentine may be removed and an exposure made vA\.\\ large spoon excavators ; as soon as this occurs relief is obtained. An anodyne and arsenic may be applied with the assurance that there will be no further pain. Management of Hypertrophied Pulps. — An irrita- tion that is not sufficient to destroy vitality is a stimulant. Pulps of the young are often exposed by caries and remain so exposed for years, gradually increasing in size until they protrude through the pulp-chamber and almost fill the cavity in the tooth. These hypertrophies most often occur in first molars. They have become accustomed to their surroundings, and are not easily irritated by chemicals, changes of temperature, or mechairical irritation. The patient avoids masticating upon the affected tooth. It is difficult to differentiate a hyiJertropliied pulp from gum tissue that has grown into the cavity of the tooth, either from an approximal surface or from between the roots. Gum tissue irritated by lying upon the sharp edge of a cavity bleeds as freely and is quite as sensi- tive to manipulation as a hj-^jertrophic pulp. In both cases the tissue is pedunculated, and cocaine crystals may be slipped under the flap to reach as near to the neck as possible. In a few minutes a fine-pointed excavator may be slipped under the tissue, and the position of the neck made out. A thorough knowledge of dental anatomy will now be of assistance. If the operator is satisfied that the tissue comes from the root-canal or the pulp-chamber, a few strands of arsenic fibre may he slipped under the flajj, and the cavity sealed with cotton- wool and sandarac varnish. If he is not satis- fied, more cocaine should be used, and with a large spoon-shaped instrument the tissue should be cut out of the cavity. TOien the haemorrhage, which will be profuse, has been controlled by hot water, another examination may be made ; and if the operator is still not satisfied, the cavity should be packed with phenol and san- darac vamish for twenty-four hours, when all haemorrhage will have ceased and a diagnosis can be made. If the tissue is pulp, arsenic may be applied to the remainder, and the case treated in the ordinary way. Management of Atrophic Pulps. — Owing to irritation or diminished circulation, chlorosis of the dental jiulp sometimes occurs. The fibrous elements increase ; the tooth does not respond to changes of temperature ; and the pulp decreases in size. There is little or no blood, and no sensation in certain places, but excessive hypersensitiveness in others, so that the pam may be exceedingly violent when the pulf) is touched with, a broach. Neither cocaine nor arsenic has any effect : there is not sufficient circulation to absorb the drags. This condition often occurs under metal fillings that have been placed close to the pulp or on an exposure. Treatment. — The cavity should be flooded with pure phenol, which should be gradually worked into the pulp-cavity with a broach, and finally forced in with soft rubber. No other drug is nearly so satisfactory as phenol in these cases. Phenol may be forced into the canal with a hj'podermic syringe. Management of Receded Pulps. — On p. 452 are given the reasons for the recession of the pulp. There seems to be a certain physiological reces- sion of the pulp, and if more than this occurs atrophy and death supervene. Pulps that have receded because of the nearness of a cavity or metal filling, or on account of exposure of dentine to irritation, are prone to become atrophic and 463 die. Pulps that have been exposed may recede and live for years, but in no case does the original exposure become covered with calcific material ; if the cavity is opened, a broach can be passed down the exposure, and though it may strike calcific material, if it is worked around an opening -will be found. It would seem that the membrana eboris when once destroyed does not reproduce itself laterally; or if this occurs, it does not seem to have the power of depositing lime salts. If, -when a filling has been removed, there is evidence of the pulp having been at one time exposed, pressure anaesthesia can at once be applied witli success. The general rule has been laid do\\Ti by some authorities, that pulps that have receded to within one or two millimetres of the neck of the tooth should be devitalized ; it has been observed that in- fections from pulps that were much receded or atrophic before death, are especially severe and of the streptococcus variety. Management of Ulceration and Abscess of the Pulp. — Wien a pulp that is exposed, or almost exposed, becomes infected with pus organisms, and as a result there is an exudation of pus from the surface, it is said to be ulcerated ; if the infection has penetrated a layer of leathery dentine to reach the pulp, and pus is formed in the substance of the pulp tissue around it, the condition is then called " Abscess of the Pulp ". If an ulcerating pulp by any means becomes covered, so tliat the exudate cannot get away freely, pain will supervene, which is relieved by cold and increased by heat ; the symptoms of abscess of the pulp are the same. The pain is of a deep throbbing character, and if it goes on for several hours the tooth becomes tender to touch. In fact, if there have been several attacks, the tooth vnll become tender and elon- gated almost as soon as the pain begins ; in such cases all the pulp tissue in the crown of the tooth, and perhaps for some distance into the root-canals, may be a dead and infected mass. The treatment is essentially the same as for an inflamed pulp. The pressure must first be relieved. If there is a cavity, the carious material should be removed, and the cavity washed out \\ith cool water. As soon as the pulp-chamber is opened (which should be done with a great deal of care lest pressure cause excessive pain) pulsations can be seen in the liquid exiidate or blood. Wlien these pulsations begin tlie patient will feel extreme jiain, and it is well not to continue to operate after an exposure has been made, lest the patient should tliink the operator is causing the pain. If an ab-scess exists on the surface, the exiidation of the pus will be followed by blood ; the exudation should be wiped away, and the patient assured that the pain will subside in a few minutes and not return. Cocaine, oil of cloves, or phenol, may be placed in the cavity for a few minutes while waiting for the pain to subside. The cause of the pain is the stretching of the nerves back to their normal state after being compressed. It is sometimes difficult to know whether the pus and blood are coming from a small portion of pulp in the root-canal, or from the apex. If there is any doubt, a broach should be passed up tlie canal, and if there is sensation in tlie pulp<-liamber or not too far up the canal, a very small piece of arsenical fibre may be worked up until it is in contact with the live tissues. If only a small portion of the pulp at the apex is alive, it is \\iser to jiack the cavity with phenol until the next sitting, and then try pressure anaesthesia, using phenol. Arsenic may be placed on an ulcerating or abscessed pulp in which the pressure has been relieved and a liaemorrhage has occurred, with an assurance that there will be no further pain. If there is no cavity in the tooth, or a large filling to be cut througli to reach tlie pulp- chamber, it must be borne in mind that the rotat- ing drill will cause pain from heat, or the jarring may cause pain to the periodontal membrane ; each of these may be confounded with the pain of cutting sensitive dentine, and might thus cast .some doubt on the diagnosis. Small sharp drills sliould be used. Management of Pulps containing Calcific Deposits. Calcific deposits occur in the pulps of teeth at almost any age, but more frequently in advanced years ; such deposits are an indica- tion of a degeneration of tlie pulp, which becomes inflamed or sclerotic. Pulp-stones are often associated with an inflammation of the pulp that is difficult to diagnose ; tliey usu- ally occur in teeth whose pulps are subjected to some form of chronic irritation, such as abrasion, erosion, exposure of the neck or roots of a tootli, a large cavity or filling. Teeth may have i3ulp-stones in them for a lifetime and cause no inconvenience ; it is only when degeneration has gone so far that death or infection supervenes that any treatment is necessary. The only certain means of diagnosis before the pulp- chamber is opened is a radiograph. The whole pulp may become a solid calcific mass sur- rounded by degenerated tissue, which is ex- ceedingly sensitive, but does not bleed. In single-rooted teeth it is often cone-shaped, and any movement at the orifice of the cavity acts like a spear tlinist into the nerves at the apex ; in multi-rooted teeth the pulp-chamber may be filled with one piece, while the canals may have several granules or be entirely free, or the whole pulp may be literally filled with fine granules like grains of sand. i The only treatment, when any is necessary. 464 is devitalization of the remaining living tissue, and removal of all of the contents of the canals. If the tissues become inflamed, all the difficulties of devitalizing an inflamed pulp are met with, and in addition those due to the presence of calcific tissue, which will not absorb arsenic nor become devitalized beyond the point of ap- plication. If the pulp tissue contains granular deposits no unusual difficulties mil occur. If there are no acute symptoms, it is best to rely upon applying the arsenic to the dentine for a long time ; pressure anaesthesia -n-ill very rarely succeed. If acute symptoms are present , and pulp-stones are diagnosed, either local or { general anaesthesia is the oijy hope ; while the pulp is thus anaesthetized, a rapidly revolv- ing burr should be plunged into the pulp- chamber, and as soon as free haemorrhage is obtained arsenic may be applied with an assur- ance of no more pain and a fair certainty of devitalization; it may be advisable to pass a fine reamer up the canal if nodules are suspected. Management of Pulps in Pyorrhoea. — It is thought by many operators of long experience in the treatment of pyorrhoea, that better results are obtained when the pulps are removed ; it is explained that the periodontal membrane gets additional stimulation or nourishment when the pulp has been devitalized. In many cases of pyorrhoea the pulp becomes irritated from changes of temperature or from chemicals, because so much of the root of the tooth has become exposed. In multi-rooted teeth one root may become the seat of pyorrhoea until even the apex is reached, while the other root or roots may be perfectly normal aiad secure in position. Pain may occur in the pulp of the diseased root, which will need devitalization. A small hole may be cut through the enamel, and arsenic applied for a few days, and then a further cut made until sensation is reached, when another application may be made. At the next sitting the pulp will probably be found dead, if there has not been too much previous inflammation. Management of Pulps of Teeth used as Abutments for Bridges or to support Crowns or Large Fillings with Posts. — It has been observed that the pulp of teeth used as abutments for bridges and covered with a gold cap very frequently lose their vitality. In fact it is believed by some that the pulp of every tooth that is covered with a gold cap, or that is to receive a large metallic filling, should be devitalized, because sooner or later it will die. Such is a most radical view. No tooth that has lost its pulp will bear as much jjressure, last as long, or feel as comfortable, as if its pulp had been alive. It has been suggested that pulps die under gold caps and large fillings because the oxide of zinc used in the oxy-phosphate contains arsenic ; this view has not been substantiated by analysis of oxides or phosphates used. A more reasonable explanation of the death of pulps of teeth used as abutments is overwork of the abutment ; in the case of single caps or large metal fillings, thermal changes are probably responsible. In both classes of work it might be wise to devitalize. If the pulp is devitalized, the patient will certainly not bring so much pressure to bear upon the bridge, and the abut- ment will last longer, but the bridge will be less useful while it does last. Notwithstanding the arguments that have been advanced by such authorities as Hungerford, Goslee, and Broomell, the experience of a large number of careful observers is that no pulp should be devitalized that can be retained alive, and that even in cases of abutments, cap crowns, and large fillings, better results may be secured with live pulps. Discoloration of the Teeth during Devitalization. Other things being equal, the later in life devitalization occurs, and the shorter the time the pulp remains in the tooth after it is dead, the less are the chances of discoloration. It is impossible to give a patient an assurance that a tooth will not become discoloured after the pulp has been devitalized. Teeth whose pulps are dead are always a different colour from those having living pulps ; the discoloration in some cases is very slight, while in others it is of a deep bluish-blacit. Some teeth are so open in struc- ture that the red blood -cells seem to penetrate the dentine as soon as the pulp has been devital- ized ; they become pink in colour, and no amount of bleaching will prevent them from finally turning black. If one tooth in the mouth turns pink by devitalization, all the rest are likely to do the same if devitalized. If the pulp could be desensitized and removed without haemorrhage, and the root and cavity filled at once, discoloration would not be likely to occur. Baird (Canada) devitalized the pulp of a central incisor for a young girl, and the tooth turned pink and afterwards black. The pa- tient was deterred from having conservative operations done, and applied to Baird about fifteen years afterwards to have all the teeth and roots remaining in the maxilla removed. Baird, remembering the pink colour that followed an arsenical api^lication, determined, before extracting, to find out whether the same result would occur if any of the remaining pulps were devitalized. He found that not only devitalization by arsenic caused the teeth to become pink, but also desensitization by cocaine and immediate pulp removal gave the same result. When the teeth were extracted they were sent to the laboratory of the Royal College of Dental Surgeons (Canada), where 465 sections were made, and examination under the microscope revealed enlarged tubules and an abundance of inter-globular spaces. If the pulp of an anterior tooth is to be removed, it should be done as expeditiously as possible, neither moisture nor any other sub- stance being allowed access to the canal or cavity, except \^'hat the operator intentionally puts there. He should know what drugs and what treatment are the least likely to cause discoloration ; if at all possible cocaine anaesthesia should be used ; blood should not be allowed to remain in the cavity; dryness is the key to success; dnigs that coagulate albumen, or leave a resinous deposit, or are discoloured by exposure, should not be used. Phenol, chloride of zinc, and bichloride of mercury, are objectionable ; colourless oil of cloves, oil of cajuput, or non-coagulating campho-phenique, may be used as mild anti- septic dressings, if the canal cannot be at once filled. The root-filling should be a yellowish- white oxy-chloride of zinc. The cavity in the tooth should be at once filled ; if this is impos- sible an impermeable temporary filling should be used. REMOVAL OF PULPS Opening into Pulp-chambers. — Tlie first essen- tial in opening into pulp-chambsrs for access to the root-canals is complete, free, and un- obstructed access; the second essential is to gain such access with as little loss of strength of the tooth as possible. Access to the pulp- chamber does not always give access to the canals ; this should be kept in mind when cut- ting through the crown of the tooth to the pulp- chamber. The strength of the tooth is in the dentine ; large openings may be made at or t near the occlusal surfaces, but if much cutting is done near the neck of the tooth the support of the crown is gone. By choice, the pulp- chamber should be reached through a cavity or a filling, when such a position will give access to the canals. If, however, a good filling exists in a molar or premolar, it is not necessary to remove it ; the tooth should be cut into as if the filling did not exist. Access to the canals of the anterior teeth cannot be obtained by drilling through an approximal filling, without dis- lodgement of the filling ; if the filling is in good condition, a direct opening to the canals can be made from the lingual aspect. Technique. — If the enamel is not broken, the most suitable instrument wdth which to reach the dentine is a stone. If the situation will not permit the use of a stone, a drill made from an old burr ^^■ill cut through the enamel better than any form of burr ; the drill must be frequently sharpened ; if the point is dipped into oil or \ vaseline it will cut better and generate less heat. | As soon as the dentine is reached a round burr will cut more satisfactorily than any other instrument. A drill will cut amalgam or gold better than a burr. Before the pulp-chamber is reached, if there is any reason why the instru- ment should not be allowed to plunge into it, the opening should be enlarged with a large round burr. As the pulp is reached, a horn will be opened before the instrument drops into the cavity; a small burr may be passed into the opening, cutting sideways to avoid pressui-e into the pulp-chamber. The chamber should be opened the full size of the occlusal wall in molars and premolars. The inexperienced operator often believes that he has found the root-canals of an upper premolar when he has only opened into the chamber through the buccal and lingual horns ; the same mistake may occur in a molar. Even the experienced operator may be in some doubt in cases where the pulp has much receded ; all doubt can be set aside by passing a hooked broach or a small hatchet- excavator through the oiiening ; if after being turned round it catches when withdrawn, there is evidence that the occlusal wall of the pulp- chamber has not been all cut away. If a cavity exists in the tooth large enough to expose the pulp, all the overhanging enamel and carious dentine should be cut away with chisels and large spoon-excavators. The cavity should be washed out with tepid water, and dried with an absorbent or a blast of warm compressed air. As much tooth tissue should be cut away as will be necessary for the final preparation of the cavity for the reception of the filling, or for access to the pulp-chamber or canals. The pulp-chamber should now be opened from the exposure laterally with a round burr (not allowed to drop into the chamber, and drawn outwards as it cuts). No sharp-cornered rotating instrument should be used for this purpose, lest corners be made in the chamber against which broaches ^^■ill strike when attempts are made to reach the canals. If the canal of a single-rooted tooth is to be reached from an ap- proximal cavity, and the approximo- occlusal corner of the tooth is to be preserved as much as possible, there vfiW be no opportunity to get direct access to the canal. To assist in getting access, a small round burr may be passed up the canal as far as possible, and pressed against the approximal wall of the canal as it is drawn towards the occlusal surface ; this will enlarge the canal towards the Fig. 520. approximal surface, and give access without cutting away tissue that is of assistance to the strength of the tooth (see Fig. 520). In young anterior teeth the horns of the jjulp are often very thin labio-lingually, and require a 466 good deal of attention to remove the pulp, esjiecially if the opening to the chamber is made from the lingual aspect or from an approximal cavity near the neck of the tooth. Removal of Pulps. — Of all the ojierations in dentistry, removing pulps requires the most skill and perseverance. It is necessary to have a good kno^^•ledge of dental anatomy, familiarity with the strength of instruments, skill in their use, and a cultivated sense of touch. Wlien one thinks of a cone-shaped or slit-shajjed cavity of unknown length and often so fine and tortuous that the finest steel bristle will not pass into it, placed in a position awkward to get at, and filled with, a tissue that is attached at a fine opening at the end, and is not often strong enough to break at the attachment when pulled upon, it is no wonder that so much attention is devoted to the subject. One of the chief difficulties is to pass an instrument into the canal that is already full, and get hold of the pulp, without pressing it into the fine end of the canal. It is not usually difficult to remove the pulp from single-rooted teeth of young patients. The difficulties increase as the canals become smaller, flatter, more tortuous, and more diffi- cult of access. It is physically impossible to remove all the pulp from some flat tortuous canals in molar teeth, without taking the risk of puncturing the root or breaking a jjroach in the canal, or of causing an irritation with chemicals that would be more detrimental to the longevity of the tooth than the small amount of tissue that might have been left. It must not be understood from the fore- going that the writer would recommend leaving dead pulp tissue in a canal from which it is possible to remove it : dead organic matter cannot be retained in the human body in the presence of moisture without danger of septic infection. The possibilities of infection are in proportion to the amount of tissue left, and the possibilities of sterilization are inversely so. It is impossible to sterilize pulp tissue perman- ently by any known method : because a tooth so treated gives no trouble in one patient, it does not follow that the same treatment -ndll be equally successful in another. A tooth that does not remain in a perfectly normal condition for the remainder of the patient's life caimot be said to have been treated v.-ith entire success. Many teeth that have lost their jjulps do not ache violently, but gradually lose their useful- ness; they get tender to bite upon now and again, heavy pressure always hurts, the roots become discoloured, the gum recedes from the neck, the periodontal membrane becomes detached, the tooth loosens, and has finally to be removed because it gets very tender or is a nuisance; the end of such a root is markedly absorbed leaving a rough honeycombed surface. This is the history of a tooth devitalized in early life, or of one in which there was irritation by arsenic or cocaine, or some pulp tissue remained but never caused pus-formation — a chronic inflammation; the cementum and periodontal membrane gradually die and the root is exfoliated as a foreign substance. An improperly filled root-canal with a large apex may bring about the same result. Fig. 521. — Donaldson Bristles, hooked, rough- ened, and spiral (S. S. White make). (Dental Manufacturing Co., Ltd.) Fig. 522. — Donaldson Root-canal Cleansers (S. S. White make). [Dental Manujacturing Co., Ltd.) Dentists are better able to cope with this difficult operation now than at any previous time, because of a better knowledge of dental anatomy, and a better training; and more especially because of the great improvement in instruments during the past ten or fifteen years. Instruments. — An instrument to be useful as a pulp-extractor must be fine, strong, flexible, tough, and sufficiently rigid to be forced into the canal. Pulp-extractors are designed to entangle or hook on to the pulp. They are hooked, barbed, or spiral ; and are made of steel — round, square, or triangular in section (see Figs. 521, 522, 523, 524). 467 Technique. — Pulps that have been recently devitalized or desensitized may be removed by winding a few strands of a long-fibred cotton- wool on a smooth broach, and gently j)assing Fig. 523. — DonaldsOH pattern Root-canal Cleanser with extra short handle. (Dental Manujacturing Co., Ltd.) it up the canal with a rotary motion until the pulp is entangled in the fibres of cotton and thus extracted when the broach is withdrawn; this operation may have to be repeated several FlQ. 524. — Broaches, barbed and spiral, with flexible handles (magnified). (Dental Manujacturing Co., Ltd.) times before the pulp is caught. Barbed broaches are passed up the wall of the canal when there is room, and rotated and withdrawn. It is necessary to take great care of broaches, because the steel is so fine that the slightest rusting or corroding might cause them to break at a critical moment. They should be kept clean and bright at all times. Broaches are made short, with a knob at the end, for use in the molar region, and long and flexible for placing in a holder. Broach-holders should be light, easily adjusted, and of convenient length; a heavy broach-holder is so much out of balance with a fine broach that sensations are not readily appreciated. Each broach should be placed in its own holder, and not removed until it is no longer serviceable. There should be ready for use at all times at least four smooth broaches : a very fine, long, flexible one ; another just as fine at the end, but gradually becoming thick and rigid, and intended for forcing its way into fine canals; a third of ! A A \ il Fig. 525. — Beutelroo Drills for straight hand-piece. (Messrs. Claudius Ash, Sons cfc Co., Ltd.) medium size for general use ; and a fourth heavy and strong with a square end. Two hooked broaches, one fine and one coarse, will meet most conditions. Two or three barbed \ I 1 II ^1 ' 1 LJ [3 n U C I LI Fig. 526. — Beutelroc Drills for right-angle hand-piece (Messrs. Claudius Ash, Sons .6i\. (6) Carmalt-Jones and Humphreys. Treatment (19) of Pyorrhoea Alveolaris by Inoculation with Bacterial Vaccine. Brit. Dent. Jour., 1908, Vol. XXIX, p. 63. , (20) (7) CoLYER, J. F. Dental Surgery and Pathology, p. 5^^. (8) Coi-YER, J. F. The Treatment of Periodontal Disease. Proc. Roy. Soc. of Med. (Odont. Sec.), , (21) Feb. 1912. (9) Croftan, a. C. The Gingival Manifestations of Certain Metabolic Disorders. Dental Cosmos, (22) Dec. 1911, Vol. LIII, p. 1365. (10) Endelman, J. Uratic Deposits upon the Roots (23) of Teeth. Dental Cosmos, Aug. 1905, Vol. XLVII, p. 935. (11) Eyre, J. W. & Payne, J. Lewin. Some Observa- (24) tions on the Bacteriology of Pyorrhoea Alveo- laris and the Treatment of the Disease by Bacterial Vaccine. Proc. Roy. Soc. of Med. (25) (Odont. Sec), 1909, p. 29. (12) Feiler, Erich. Treatment of Alveolar Pyorrhoea. Ash's Monthly, Jan. 1911. (26) (13) Fryd, (Hamburg). Artificial Hyperaemia in Dentistry. Dental Cosmos, April 1909, Vol. LI, (27) p. 483. (14) Gardiner, F. D. Case of Pyorrhoea of Lower ! (28) Incisors and Canines. Dental Cosmos, A^TiW^ll, (29) Vol. LIII, p. 473. (15) Goadby, Kenneth. Pyorrhoea Alveolaris. Pro- gress Report. Trans. Odont. Soc, April 1902. (16) Goldberg, H. A. Treatment of Pyorrhoea < (30) Alveolaris. ZJe^fa/ Cosmos, May 1911, Vol. LIII, 1 p. 551. I Hardgrove, T. A. Pyorrhoea Alveolaris. Dental Review, Feb. 1906. Hartzell T. B. The Practical Surgery of the Root Surface in Pyorrhoea. Dental Cosmos, May 1911, Vol. LIII, p. 513. Head, J. A Tartar Solvent especially useful in Pyorrhoea Work. Dental Cosmos, Jan. 1909, Vol. LI, p. 41. Hopewell-Smith, A. Pyorrhoea Alveolaris : its Patho-Histology. Dental Cosmos, April 1911, Vol. LIII, p. 397. Hopewell-Smith, A. Pyorrhoea Alveolaris : its Interpretation. Dental Cosmos, Sept. 1911, Vol. LIII, p. 881. HoRDER, T. J. Pyorrhoea Treatment by Specific Inoculation. Lancet, Dec. 28, 1907. Houston, I. F. Immobilizing as a Cure for Pyor- rhoea Alveolaris. Dental Cosmos, April 1909, Vol. LI, p. 445. Merritt, a. The Protective Substances of the Blood in their Relation to Pyorrhoea Alveolaris. Dental Cosmos, Jan. 1909, Vol. LI, p. 44. PiERGiLi (Rome). Massage and Bismuth Paste in Pyorrhoea Alveolaris. Dental Cosmos, Dec. 1911, Vol. LIII, p. 1459. Senn, A. (Ziirich). On Pyorrhoea Alveolaris. Ash's Quarterly Circular, June, 1907. Sims, H. Pyorrhoea and Some Investigations into its Bacteriology, 1906. Tombs & Nowell. Dental Surgery, 1906, p. 636. Turner, J. G. Some Clinical Notes on Pyorrhoea Alveolaris. Proc. Roy. Soc. of Med. (Odont. Sec), Vol. 1, 1908, p. 104. Discussion, pp. 105 et seq. Williams, W. R. The Vaccine Treatment of Pyorrhoea Alveolaris. Dental Cosmos, Sept. 19II, Vol. LIII, p. 1076. 17 CHAPTER XXXI DENTAL ELECTRO-THERAPEUTICS NATURE OF APPARATUS In order to apply electricity in an intelligent manner, it is essential that more than a super- ficial knowledge should be acquired of the means of production, the methods of application, and the effects obtauiable by the current. It is beyond the scope of this work to undertake more than a curtailed description of the par- ticular forms of electricity that concern the dental practitioner, but the student of electro- therai^eutics should interest liimself iiithe whole subject of medical electricity, a knowledge of which will greatly enhance his capability of dealing with this special subject as applied in dentistry. Galvanic Electricity. — For dental purposes it is necessary to have a continuous current that can be controlled at ^^■ill and reduced to the muiimum of electro-motive force ; this is obtainable from a collection of cells or from current dynamos, controlled by a rheostat or some form of current- resistance in circuit. Primary Cell. — Of the many forms of primary cells that exist, those that concern the dental student most are the Leclanche for generathig galvanic current, and the chromic acid and allied forms for cautery work. The Lecla7iche' Cell. —The Leclanche ceU con- sists of a glass jar half filled with a strong aqueous solution of ammonium chloride, in which is placed a porous pot containing a rod of carbon surrounded by powdered carbon and peroxide of manganese, formmg altogether the " negative element ", and a rod of amalga- mated zinc, forming the " positive element ". The fluid m the jar is the " electrol3^e ", or excitant and conductor of electricity formed within the jar. Thus the internal parts of the cell consist of a positive (+) and a negative (— ) element and an excitant conductmg fluid (see Fig. 580). Tlie ammonium chloride solution acts chem- ically on the zinc rod to form zinc chloride and to liberate hydrogen and ammonia ; the hydrogen coOects at the carbon {— ) element, uniting there with oxygen liberated from the manganese peroxide, to form water. The formation of zinc chloride on the positive element is called polarization; and the union of hydrogen with 5 oxygen at the negative element, by which bubbles of gas are dispersed instead of beuig allowed to cover the surface and make it in- effective, is called depolarization. No polarization takes place in this form of cell when in disuse, but directly the circuit is closed rapid polarization takes place, in con- sequence of hydrogen being liberated more rapidly than the oxygen of the manganese peroxide is formed to unite with it ; thus the cell becomes weak if it is short-circuited for any great length of time, but it recovers rapidly Fig. 580. — Leclanche cell. on the circuit being again broken, and is con- sequently a very lasting form of cell. The choice of zinc and carbon in the con- struction of the Leclanche cell is based on Volta's contact law, which points out that when two very dissimilar metals are brought in contact through an electrolyte, the one becomes positively and the other negatively electrifled. By this is meant, not that two kinds of current are formed (for it should be remembered that there is only one kind of electricity), but that the difference of potential, 14 515 or electro-motive force, is greater in the one (zinc) than it is in the other (carbon). Current. — It has been stated that no current flows when the Leclanche cell is not in use ; the ends of the carbon and zinc outside the cell are called the terminals, and as soon as the terminals are connected by a conducting agent (copper and silver wire being the best conductors) the current flows in the direction from the + to the — element internally, i. e. from the higher potential to the lower ; passing to the terminals of the — it becomes + , and is returned to the + terminal forming a circuit. Current will thus flow until equilibrium is established, and the Fig. 581.- -Direction of flow of current inside and outside cell. cell is then said to have " run down " (see Fig. 581.) Electro-motive Force. — The force that causes the current to flow from the element of higher potential to the element of lower potential is termed electro -motive force (E.M.F.). The electroljrte within the cell is the conducting medium between the two producing elements. The E.M.F. varies in different kinds of cells, and this variation depends on the kinds of plates used and the exciting fluid. The E.M.F. of one Leclanche cell is said to be 1-47 volts, the Daniel cell about 1 volt, and the Grenet or bichromate cell about 2 volts. Units — The unit of E.M.F. Is one volt. The unit of current strength is one ampere. The unit of resistance is one ohm. The unit of quantity of current is one coulomb. The unit of capacity is one farad. These names have been applied in honour of the great early workers in electrical science, Volta, Ampere, Coulomb, and Faraday. Resistance. — In studying electricity it must be remembered that resistance forms a very important factor in the production of cuiTents ; not only has the resistance beyond the terminals (R) external to the cell to be calculated, but also the internal resistance (r) that the currents meet within the cell in passing from the + to the — element through the electrolyte. The passmg of current from the terminals of the cell depends on the nature of the conducting medium ; thus copper wire offers little resistance to current and is much used as leads to convey current, whilst Gferman silver and graphite are poor conductors, and advantage is taken of this fact in their use for constructing resistance in circuit to reduce tlie current strength. Glass and many allied substances are non-conductors of current. The resistance varies directly with the length of the conducting wire ; thus 5 metres of wire wiU offer twice the resistance of 2-5 metres of wire of the same thickness. Resistance of the Body. — The resistance of the human body varies greatly, not only in different individuals but also in the same individual at different times ; it may be noted tliat a patient at one time will permit 5 niilliamperes of current to be conducted through tlie body without noticing it, whilst at another time he will object to less than half that amount. The average resistance of tlie body is said to be over 1200 ohms. GuOleminot says : " Resistance depends on the degree of polarization and number of free ions in the tissue ; the determination of the resistance of the body is, therefore, a very complex problem " (4, p. 201). Ctirrent Strength. — The current strength is measured in amperes, one ampere being the unit. This amount of current, however, is more than can be used in electro-therapeutics ; it is therefore divided into niilliamperes (toth) ampere). The various units that have been mentioned depend upon one another for calcula- tion of the current in use. By the application of Ohm's Law, which says, " The current varies directly as the electro-motive force and inversely as the resistance in a circuit ", a definite know- ledge of the different units concerned may be arrived at. If any two terms are knowai, say (E) electro-motive force and (R) resistance, the third (C), current strength, may easily be found ; or if (C) current strength and (R) resistance are 516 known, (E) electro-motive force may be deter- mined. To calculate these, by working accord- ing to Ohm's Law, an ordinary algebraic calcu- lation wiU give the required factors. Say, for example, there are 18 Leclanche cells of 1 volt each passing a current througli a patient with a resistance of 1500 ohms, what amount of current m m.a. will pass ? C = 1 8 X 1 v olt 1500 ohms = -012 amperes = 12 m.a. So also, to find the E.M.F. of 18 cells when the other two factors are knov\n, resistance bemg 1500 ohms and current strength -012 amperes. E.M.F. = -012^ X 1500" = 18 volts. Li like manner resistance can be determmed when E.M.F. and current strength are known. 18 V. ■ -0121 R: 1500 ohms. These figures are only taken as an example, and are not accurate as far as the Leclanclie ^^^56^^^^^ Fig. 582. — Connection of voltaic cells in series. cell is concerned, for internal resistance (r) of each cell must be added ; but on this principle, any two factors being known, the third can be ascertamed. On a thorough knowledge of the application of Ohm's Law in electro-physics depends the scientific use, and indeed the successful use, of electric current in electro- therapeutics (11). Batteries. — The E.M.F. obtainable from one Leclanche cell is insufficient for practical pur- poses, and to make the cell larger would not increase the E.M.F., because the increase of current strength depends on the kind of plates and the electrolyte used, and not on the size of the cell. In order to obtain sufficient amperes it is necessary to collect the current from a number of cells by connecting them in series ; this constitutes a battery. The most convenient form of cell for a battery is the Leclanche, either dry or wet cell. The dry cell consists of a zinc canister, measuring 3f x H x H inches, which forms tlie positive element of the cell. This is lined with a paste of some composition of ammonium chloride, the exciting material or electrolyte. In the centre of this is ihe carbon and manganese dioxide, which forms the negative element. This cell is more compact and cleaner than the wet cell, but does not last as long, and cannot be renewed. The wet cell, already described, can be renewed, and lasts for years «ith a little attention. To construct a battery take 18 to 24 cells and connect the carbon of one with the zmc of the adjoining one by means of msulated wire ; repeat this until the whole number are joined in succession ; to the carbon of the first cell comiect a copper conducting wire, which will be the -f pole, and to the zuic of the last cell a similar wire, which will be the — pole of the now completed galvanic battery (see Fig. 582). The current strength from such a battery will be far m excess of what can be used in dental electro-therapeutics ; in order to reduce it to practical proportions a rheostat must be con- nected in circuit, and must be of a type that will admit of only a fraction of a milhampere of current to start with, and be so arranged that the increase shall be exceedingly gradual. Batteries that have only current collectors attached, by which one cell at a time is switched into use, are not adapted to many dental opera- tions, because the turnmg on of each cell causes too sudden an increase of current and gives a pauiful shock, which would make some operations impossible. A graphite rheostat or volt-selector should be jjlaced in circuit with the battery, and the current worked through it. Rheostats. — Of the different forms of rheostats for cell batteries those constructed of graphite are the most suitable ; a simple form is one made of lead pencils with a gliding metallic spring, by Siark +' Schwa ch. M Fig. 583. + P G- -Graphite Rheostat. {Schall.) which the finest graduations of current are obtainable (see Fig. 583). One of German make, of graphite with mer- cury contact, having a resistance of 100,000 ohms, which can be reduced to 20 ohms by turning a glass dial, is a very reliable one (see Fig. 584). The positive ( -i- ) wire is connected to one 517 attachment screw of the rheostat, and to the other screw the wire conveying the current to the patient. The negative (— ) wire is attached to the electrode that is to be held by the patient to complete the circuit. 3Iilliampere-meter. — No one should attempt electric treatment without a milliampere-meter, by which can be seen exactly what current strength is being applied. The mterest in the work centres a great deal in noting the variations of current in different operations. To attach the milliampere-meter connect the + of the battery to the rheostat, thence to the m.a. meter and to the patient (see Fig. 585). Current-Beverser. — Tlie battery, to be complete, should have a current-rev^erser, so that the poles may be changed at will. Tliis contrivance is found on most batteries on the market. Current from Dynamos. — A con- tinuous current from the main (that is from dynamos) for ordinary lighting purposes may be used with perfect safety and comfort, provided the resistance of the switchboard is great enough to reduce the current strength to about one volt, and can be switched on to register from a frac- tion of a milliampere with the resistance of the patient's body in circuit. Switchboards for ejector should not be used. With these few precautions, which are, some of them, doubtful sources of danger, and with the current passing through a properly constructed switchboard, the street current may be used with perfect safety. If the current is an alternating current, it Fig. 584. — Graphite Rheostat. {Schall.) thLs jjurpose are supplied by instrument-makers, and are admirably adapted to dental work. A few ordinary precautions are necessary in using current from the main. The chair should be insulated from earth, as all dental chairs usually are. The patient should not be brought ui contact with gas or water pipes, which are connected usually with earth; running water should be avoided, and the saliva Fig. 585. — Illustration of connections. must be converted into a continuous ; this is done by motor-transformers, of which there are many kinds on the market. Electrodes. — Suitable electrodes for operations ui the mouth are of cardinal importance. In selectmg an electrode for a particular operation, the nature of the tissue must be considered in determining the size of the electrode, for the density of current at tlie point of contact varies according to the area of the electrode ; the smaller the area the greater is the density, and conse- quently the more intensely will the current be felt at tlie point of contact. For example, if an electrode of the diameter of a pulp-canal in- strument is placed in a cavity of a tooth with sensitive dentine, and -5 m.a. of cuiTent is applied, the patient will be more likely to feel pain than if the same amount of current is passed with an electrode of a diameter of one millimetre, because in the latter the current is diffused over a larger area, and the density is thereby lessened. Forms of Electrodes. — For root-canals fine platinum wire (or an ordinary steel nerve- instrument) is suitable ; for obtunding sensitive dentine, or bleaching, round jjlatinum wire about 1 millimetre in diameter. For treating periodontal membrane and gums, platinum, zinc, or copper wire, about 1 millimetre in diameter, flattened at the end for an inch, tapered, spear-shaped, and bent to a slight curve, makes a useful active electrode. They should be insulated on the shanks, and inter- changeable to suitable ebony or vulcanite 518 handles to which the wire is connected (see Fig. 586). The indifferent electrode should be a cylinder of metal, which should contain at the free end a moistened sponge, and should be held by the Fig. 586. — Author's pattern Electrode and Handle. patient. The skin in the palm of the hand has a greater resistance than in most parts of the body, and is less liable to be affected by the electrolytic action of a moistened electrode (see Fig. 587). much reduced, and the current strength is very great. The cells are connected in parallel arrangement, that is, all the + plates are connected and all the — plates (see Fig. 588). When cells are connected in parallel the E.M.F. is the same as one cell, but the internal resistance (r) is reduced by as many times as there are cells in the combination, in consequence of the area of the cross-section of the plates being increased by so much in what is practi- cally one cell. If, say, 4 cells are connected in parallel, and each cell is 2 volts with internal resistance (r) of 1 ohm, and external resistance (R) of i ohm, this would amount to one large cell of 2 volts with an internal resistance of one- fourth of that of an individual cell ; worked out according to Ohm's Law these cells would yield a current strength of 2-6 amperes, thus — Fig. 587. — Hand indifferent Electrode. Testing the Poles. — To determine the correct poles of a l^attery, or current from dynamos, one of the following sample tests will suffice to dispel any feeling of doubt that might enter the mind of one unfamiliar with electricity, and will en- sure accuracy and so will inspire confidence. 1. Put a few drops of phenol - phthalein in a glass of water, and place two small electrodes a little apart in the water ; switch on a few milliamperes of current, and a bright purple colouring of the water will take place at the negative pole. The positive ele- ment is of acid, and the negative of alkaline, reaction ; it is the alkaline reaction on the plienol- phthalein that causes the colouring. 2. Electrolysis of Water. — The pole that collects twice as much gas as the other is the negative pole ; the H„0 is split up into H.^ ions, which are attracted" to the negative element, and O ions, A\hich are attracted to the positive. 3. The mniiamperemeter needle always deflects in the same direction for the same pole, usually to the left for the positive pole ; if the needle deflects in the direction opposite to the known positive pole direction, then the poles have been changed, and simply reversing the plug will correct the poles. Cautery. — For cautery work, cells with low internal resistance and high current strength are necessary. For this purpose, Leclanche cells are of little use on account of the high internal resistance. The chromic acid or Grove's cells are generally used ; the plates used in tlieir construction being of large area and placed close together, internal resistance is very E.M.F. R + 1- = C 2 volts :_ = 2-6 amperes But if the same cells are connected in series, the E.M.F. will be greater, but the yield of current will be less, on account of the internal resistance being greater, thus — E. M.F . R + r I'l amperes Fig. 588. — Cells in parallel. The cell battery in parallel form for cautery work has been partly superseded by accumu- FiG. 589.— Accumulator. {Sctiall.) lators, or secondary batteries, which can be recharged and are very effective. 519 A 4-volt accumulator of 45 ampere-hours' capacity, sold by most instrument-makers, is a useful form (see Fig. 589.) A simple platinum loop burner is all that is required for most dental operations (see Fig. 590). The cautery has its useful place in dental surgery ; in orthodontic work, the fraenum labii is often found to be the cause of separation of the central incisors, its attachment being well between the two teeth ; the most effective means of dividing and eradicating this ligament is by the cautery. The operation can be painlessly done by anaesthetizing the tissue previously. Many other minor operations m the mouth find a use for the cautery. CATAPHORESIS Li electro-therapeutics as applied to medical treatment the current is used principally m the form of faradic, static, and galvanic electricity, and the effects sought are chiefly stimulating, sedative, ionic, and trophic; in dental electro- therapeutics galvanic electricity is used prm- cipally, and the effects sought are electro -osmosis, electro - diffusion or cataphoresis, and ionic medication. These are physico - chemical effects pro- duced by the current. Cata- phoresis may be defined as the property possessed by electric current of transporting non-dissociated molecules of liquid en masse through a tissue in the direction of flow of the current. The direction of transport is from the positive to the negative pole ; certain substances have been described as passing from negative to positive, e. g. iodine, peroxide of hydrogen, chlorine, etc., but those substances correspond with those which in ionization are termed electro- negative ; the effects obtained by the use of the negative pole are altogether due to the transporting of ions, and not to cataphoresis. The cataphoretic effect is one of pressure in the direction of current — the passing of mole- cules from the greater to the lesser potential, by which " liquids and whatever they may contain in solution " (9, p. 77) are transported en masse. Little attention is paid to cataphoresis in medical electricity, principally because the skin is difficult to penetrate, and the effect is not far-reaching enough to medicate deep-seated tissues, on account of the absorption that takes place in transit ; but in treatment of mucous and periodontal membrane of the mouth the penetra- tion is rapid and the effect far-reaching enough, if sufficient current can be passed without producing pain. Many interesting experiments have been performed by Morton (9, p. 91), Gautier (2), Edison, Bacquerel, and others to show the physical and physiological effects of cataphor- esis. Dawson Turner (11, p. 294) refers to the treatment of cases of gouty concretions with solution of lithium chloride by cataphoresis, in which lithium urate was detected in the urine. It has been applied in dental practice for obtunding sensitive dentine for over twenty years, and the author has used it for many years "for treating pyorrhoea alveolaris. Amongst the early workers in cataphoresis for obtunding dentine were D. F. McGraw of California (8), A. C. Westlake of Elizabeth, New Jersey (12), W. H. Gillett of Newport, Rhode Island (3), W. J. Morton of New York (9, p. 197) and many others. IONIC MEDICATION Whilst taking into account the osmotic effect of the current, the more important electrolytic effect must not be overlooked. The body must be regarded as an electrolyte of homogenous nature, in which certain chemical changes take Fig. 590. — Cautery loops. (Schall.) place when an electric current is passed through it, in the same way as chemical changes take place in a voltaic cell. When a current is passed through a conduct- ing liquid or electrol}d;e, it has the property of splitting up the molecules into atoms of the chemical component parts, which are charged with electricity and become dissociated, certain kinds being attracted by the + pole, and others going to the — pole ; these atoms constitute the ions m electrolysis. If an electrode of gold is connected to the positive pole of a battery, and another of German silver to the negative pole, and the current is passed through a solution of cyanide of gold as the electrolyte, the molecules of cyanide of gold in solution are split up into the chemical com- ponent parts. Ions of gold are attracted to the German silver electrode at the — pole, where they give up their charge of electricity, and pure gold is deposited on the kathode, " plating it with gold " ; whilst cyanogen ions are attracted to the + pole, where it attacks the gold anode in consequence of its chemical affinity for the metal, uniting chemically with it once more to form molecules of gold cyanide in solution. Electrolysis of water also takes place at the same time. Ho ions forming at the — electrode 520 and O ions collecting at the + electrode. This is the process that takes place when a metal electrode is placed in contact wdth a tissue, with a liquid electrolyte as conductor of the current. Certain ions are repelled from the anode (+), while others are repelled from the kathode (— ). A knowledge of the direction of the ions obtain- able from a compound in solution is necessary for ionic medication. The investigations of many recent workers m medical electricity have furnished a list of these, which serve the purposes of dental \\ork. Under the head of Electro-positive, that is, ions that migrate from the + to the — pole, are the following : hydrogen, zinc, copper, silver, gold, iron, mercury, potassium, sodium, and magnesium. Under the head of Electro-nega- tive, that Ls, ions that migrate from the — to the + pole, are the following : oxygen, chlorine, sulphur, nitrogen, bromide, iodine, arsenic, phosphorus, and fluorine. Salts of certain oxidizable metals, brought m contact with moist tissue with an electric current become dissolved by chemical reaction of the metallic salts with the chlorine or oxy- gen constituents of the tissue, and liberate free ions which penetrate the tissue ; of these zinc and copper are the most useful for ionic medication in dental treatment. The theory and practice of ionization has been brought up to date by Lewis Jones, in a paper read before the Royal Society of Medicine, February 28, 1908, in a very ex'plicit and most instructive manner, and much information on the subject is also to be found in his book, Medical Electricity. Dawson Turner explains the origm and action of ions in his book. Manual of Practical Electricity; and useful hiformation is to be found on the theory of ions ui Guille- minot's book. Electricity in Medicine. W. J. Morton ascribes electric medication solely to the cataphoretic effect, but in the case of anaphoresis, where the direction of the flow of current is reversed, ionization is probably the only effect, whilst in cataphoresis both electro-osmosis and ionic medication may go on at the same time. A convincmg experiment to show the cataphoretic and ionic effect of the current consists m placing two small copper electrodes one inch apart into the white of a hard-boiled egg and turning on 3 or 4 m.a. of current ; the albumen at the + pole will be immediately stained a bright green, which will extend in every direction but chiefly towards the position of the — pole ; at the same time at the — pole drops of liquid will accumulate. The green stain is composed partly of chloride of copper, formed by chemical union of the solu- ble electrode witli chlorine in the albumen, and partly of ions of copper migrated in the direc- tion of the attracting negative pole ; this pro- ■ cess illustrates ionic medication. The drops of water formed at the — pole consists of liquid driven en masse towards the pole of lower poten- tial, and the process illustrates cataphoresis. TREATMENT Obtunding of Dentine. — To obtund sensitive dentine, first apply the rubber-dam, dry the tooth and cavity, and place in the cavity a pellet of cotton-wool saturated with a 20'!ii solution of codraline, novocaine, or cocaine that has been slightly warmed, allowing no excess of the solu- tion to leak out at the neck of the tooth ; apply to the cavity a suitable platinum electrode con- nected with the + pole and direct the patient to hold the — electrode ; press the electrode firmly into the cotton-wool, without allowing the metal to come into actual contact with the dentine ; turn on the current slowly through a finely graduated rheostat until a slight sensation is indicated by the patient, when only a fraction of a m.a. of current may be registered by the m.a. meter. After a minute or two at this stage the current may be further increased mitil it is felt ; in this way gradually mcrease the current, untU from -5 to 3 m.a. are registered, a process that may take from 5 to 10 minutes, according to the density of the dentine or the thickness of the layer over the pulp. Current strength in milliamperes necessary to induce anaesthesia in dentine varies greatly ; it may be only -5 m.a., or as much as 4 m.a. In large cavities, a good plan is to place a pellet of platuium foil over the cotton-wool containing the anaesthetic, and press it firmly into the cavity with the metal electrode ; the object of this is to lessen the density of the current, for the greater the area of the electrode the less concentrated is the current, and consequently the less painful. In obtunding dentme by electri- city the pulp is often anaesthetized, and care should be taken in preparmg the cavity not to expose it. The current must be reduced to zero by reversing the rheostat before removing the electrode from the cavity, in order to prevent the paiirful shock that would occur by suddenly breaking the contact. Pulp Anaesthesia. — Clean.se the cavity of superficial debris and dry it ; apply the anaes- thetic in the same manner as for obtunding dentine. If the cavity approaches the im- mediate vicinity of the pulp, the apfilication should be continued until 3 or 4 m.a. are regis- tered, which will be sufficient evidence that anaesthesia is complete ; if the layer of dentine over the pulp is of considerable thickness, a portion of it should be removed after 5 or 6 minutes' application, and another application made to complete the operation ; if the pulp is actually exposed, very gradual application of 521 current of low E.M.F. should be used at first ; it should be slowly increased after 2 or 3 minutes, without producing pain, until 3 or 4 ni.a. are registered, which will be sufficient proof that tlie pulp is anaesthetized. The current must be reduced to zero before removing the electrode in all treatment of live teeth. Electro-sterilization of Root-Canals. — A perfect method of sterilizing root-canals is to be found in ionic medication. In a tortuous or con- stricted canal, the application of 2 or 3 m.a. of current for 5 or 6 minutes is sufficient to produce ions from a compound solution of antiseptic salts, which will penetrate the length of the canal and sterilize it effectively. The saturation of the tubules with septic matter in long-standmg purulent canals often makes ordinary antiseptic dressings too superficial and imperfect to accomplish complete steriliza- tion ; but by ionic medication with some powerful antiseptic salt, such as zinc chloride or silver nitrate, the tubules are penetrated by zinc or silver ions, and perfect sterilization of the lining walls of the canals is effected. In treatmg root-canals, the rubber-dam should be applied when there is any chance of moisture from the mouth interfering ; and the canals should be cleared of all available fragments of diseased tissue without using reamers or drUls. A fine root-canal instrument, wrapped with a little cotton-wool saturated with the antiseptic solution should be passed into the canal to the apex, or as far towards it as space will permit ; and the current should be applied by comiecting the + electrode to the instrument in the canal, and switching on the current gradually until 2 to 4 m.a. are indicated by the m.a. meter. Five or six minutes will be suffi- cient to sterilize the canal, and two or three canals m one tooth can be done at the same time by placing electrodes in each and connect- ing them all m ith the current electrode. A 5% solution of zinc chloride for anterior teeth, or a solution of silver nitrate for posterior teeth, are effective drugs for this treatment. Some autliors have advocated the use of the current in electro-sterilization without antisep- tics, claiming that it is sufficient in itself to sterilize root -canals ; but as normal salt solution is generally used by them as the solution electrode, it is possible that sodium ions formed by the electrolytic effect are resjjonsible for the results obtained. Josef Peter, of Vienna (10), in advocating electric current for sterilizing roots, states that " solution of common salt is a suitable elec- trolyte ". Zierler and Letemann (13), experi- menting with the current on agar-cultures of anthrax bacilli, micrococcus pyogenes aiireus and albus, and bacillus coli, found that " two mUliamperes acting for 10 minutes created at 17* the anode a sterile region from 1 to r5 cm. in diameter ". There is, however, no objection to usmg antiseptic salts in solution as the solution electrode, and the results are likely to be more certain by the addition of ions obtainable from them. Lewis Jones (5) refers to root sterUization as advocated by E. Zierler, who used the negative electrode applied to the gum, in the vicinity of the tooth containing the positive electrode ; this technique is likely to be more painful and not more effective than directing the patient to hold the negative electrode in the hand. Acute Periodontitis. — In septic mfection at the apex of the root threatening alveolar abscess, a single application of zinc ions, in the same manner as for sterilizing roots, wUl sometimes terminate the disturbance and give rapid relief ; a 5% solution of zinc cliloride with 2 to 4 m.a. of current should be applied for 10 minutes, and from this ions of zinc are driven through the foramen at the apex into the affected perio- dontal membrane. A more effective antiseptic, and at the same time one more easily tolerated by the tissues, would be hard to find. Chronic Alveolar Abscess. — Chronic alveolar abscess with fistulous opening on the gums should be first treated in the same manner with zinc ions passed into the canals. In addition, afterwards, pass a fine copper probe along the ' fistulous tract to its origm at the apes of the I root ; leave it in position, and connect the -f electrode to it, and very gradually turn on the current until from 1 to 4 m.a. are recorded (or less, if painful), for five minutes. The soluble copper electrode will be dissolved by the electro- lytic action, and free ions of copper will pass into the tissue, effectively sterilizing the infected tract ; two or three such treatments will often permanently cure a long-standing chronic abscess. Should the copper probe adhere to the tissues, it can be released by reversing the poles and applying the — current for a minute. Treatment of Pyorrhoea Alveolaris. — Of the many important uses to which electro-theraijeutics lends itself in dental practice, probably the most important is the treatment of chronic suppura- tive affections of the gums, periodontal mem- brane, and alveolus, in which these tissues are involved in a form of septic infection that is difficult to deal with in the ordinary way. In the early stages of pyorrhoea alveolaris ionic medi- cation is most effective in curing the disease, and even in the worst stages, the pus can be checked and the tissues rendered healthy. Constitutional disorders of more or less grave character often accompany pyorrhoea alveolaris, due to absorp- tion mto the system of micro-organisms ; ui these cases, if the system is rendered immune to the organism or organisms predominating in the uifection by vaccine therapy (as described 522 ia Chapter XXX), and if at the same time local treatment is vigorously kept up by ionic medication, the disease will yield to treatment. The technique of electrical treatment here is as follows : A limited number of teeth, say six upper or lower incisors, are dried, and the saliva is kept away by cotton-wool rolls or napkms ; the patient should hold the negative electrode in the hand, and a suitable positive electrode should be w rapped with a few threads of cotton- wool moistened with the antiseptic drug ; this should be introduced mto the pockets and spaces between the teeth, and the current switched on gradually until the patient indicates that it is bemg felt. According to the sensitiveness of the teeth and tissues, the current strength necessary will vary between 1 and 4 milliam- peres ; the former strength is sufficient to liberate ions, although it is desirable to iise a stronger current if possible. The electrode should be slowly passed around the necks of the teeth and mto the depth of the pockets, and kept in constant contact with the tissues, except when it is necessary to replenish the liquid. The time required to sterilize the tissues varies according to the severity of the disease ; ions of salts are formed uistantaneously, and the amount of sterilization required must be de- termmed by the operator. Where the disease is deep-seated and the discharge considerable, the electrode should be kept in contact at that particular part for one to three minutes, accord- ing to the amount of penetration of ions it is deemed necessary to procure. A good plan is to keep the electrode in a pocket to be treated until this is tlio roughly sterihzed, reduce the current to zero, and move the electrode to the next position before turning on the current again. It must be distmctly understood that no amount of treatment will do any lasting good if the calcareous deposits are not com- pletely removed ; it should be the aim of the operator to remove every particle of deposit, a process that may take a portion of the time at every sitting during a long course of treatment, and still be imperfect. The surfaces of the teeth should also be polished. For the first treatment, ^^'hen the tissues are more or less lacerated from extensive scaling operations, a soothing drug, such as argyrol, 5% aqueous solution, should be used. A period of thirty to forty-five mmutes of this treatment is as much as most patients will endure, even it not painful ; the operation should be repeated on the third day, when 5% aqueous solution of zinc chloride should be used, from which ions of zmc are obtained ; this is probably the mo.st effective antiseptic, and at the same time the one best tolerated by the tissues. Of zinc ions S. Leduc (6) says : " This ion is an antiseptic of the first rank, and when applied electrically, it can be made to penetrate the tissues of the skin to any desired depth. There is no wound or ulcer which cannot be disinfected by its em- ployment, provided its surface can be reached by the electrodes. One of its peculiarities is that it provokes but little inflammatory reaction. When I have experimented with zinc upon the skin of animals, and have caused superficial or even deep idceration, I have observed that the wounds produced show no inflammatory effects or signs of mfection from germs, even if they are left completely uncovered ; on the contrary they remain aseptic, so that it appears as if the ions of zinc which they contam serve as the best possible of antiseptic agents." The writer's experience with the use of zinc ions m the treatment of pyorrhoea is tliat there is no other antiseptic that wiU stop the discharge of pus so effectively or so quickly. Three treatments the first week, two the second and third weeks, and one every five or six days subsequently, until the tissues have resumed a perfectly healthy appearance, form a sequence that is as near as possible to any rule that can be laid down for the intervals of treatments. The operator should be guided by his judgement in each mdividual case, two or three treatments being all that wiU sometimes be necessary when only one or two teeth are affected. In cases of wasting of the gums on the labial and buccal aspects of the teeth where no dis- charge of pus is visible, ionization obtained by passing the electrode under the thin margin of gum and using a 5% solution of zmc chloride as the electrolyte will effectively stop reces- sion and relieve the sensitiveness of the necks of the teeth that nearly always accompanies this form of pyorrhoea. A low current strength, '5 to 1 m.a., will often be all that can be endured at first ; but gradually the use of more wUl be possible, and the effect is lastmg, for after a year or two the teeth will often be found to have lost all sensitiveness, and it will then be possible to apply 2 or 3 m.a. if further treatment is necessary. Other drugs that can be used with good effect in the treatment of pyorrhoea are tincture of iodine (diluted with equal parts of water), caprol, and copper sulphate. In using iodine the negative electrode must be applied to the tissues, as iodine ions are liberated at the — pole. Caprol, from which ions of copper are obtamed by the current, is a powerful antisep- tic salt ; it should be used in 5% aqueous solu- tion, to which should be added five per cent of chloretone. Copper sulphate, from which copper ions are obtained, may be used in very dilute aqueous solution (1 in 500). The whole principle of electro-therapeutic treatment of suppurative affections of the gums and periodontal membrane is based on the penetration of ions procurable by the electrolytic effect of the current on compounds 523 of antiseptic salts, by which the micro-organisms contained in the tissues are effectively destroyed, and the tissues stimulated to repair. Further- more, the dead bacteria are probably absorbed into the general circulation, and have an effect on the opsonins. Bleaching by Electric Current. — To bleach discoloured teeth with the aid of the electric current, due consideration must be given, as in ordinary bleaching, to the cause of tlie discoloration and the nature of the stain. If the colouring matter responsible for tlie dLscoloration is of purely organic origin, the possibility of bleaching by this method is a valuable aid in this difficult problem ; if, however, it is inorganic, the difficulty of trans- formmg such matter into translucent substance is very much increased. Where organic stams are concerned, bleaching can readily be effected by using 25% ethereal solution of hydrogen peroxide made into an aqueous solution by adding half the volume of water, with a small quantity of sodium sulphate, and then dispelling the ether of the liydrogen peroxide by evapor- ating over a warm water bath. The hydrogen peroxide is practically a non-conductor of current in tlie pure state ; the addition of water and sodium sulphate makes it highly conductive. A tooth to be bleached requires special prepara- tion : the rubber-dam should be applied, and the root-canal cleansed, and filled at the apex only with gutta-percha ; the bleaching liquid, which is the solution electrode, should penetrate the length of the root-canal to the filling of gutta- percha, because a dead tooth offers great resist- ance to current. (Six to ten volts applied m a cavity of a dead tooth will only admit of perhaps one milliampere of current strength, but if the current is conducted well into the root the resistance is lessened and a greater current strength obtained with less volts.) The peroxide of hydrogen should be applied on cotton-wool passed weO into the canals, and a platinum electrode used in the same mamier as for obtunding. Care should be exercised that the electrode is not brought into contact with soft tissues, because of tlie high voltage required to overcome the increased resistance. The positive pole is applied, and the liquid bleaching solution is driven towards the pole of lower potential. The wTiter has observed that ionization with hydrogen peroxide is sometimes more effective than cataphoresis : the ions are repelled from the negative pole and seem to have a more penetrat- ing effect on the dentine. Hence it has been stated that when bleaching will not succeed with the positive electrode, by reversing the poles and applying the negative electrode the desired effect can be brought about in a remarkable manner. The current is also a valuable aid in bleach- ing with calcium hypochlorite (" bleaching powder "), from which chlorine is liberated to act chemically on the discoloured matter in the tubules. The value of the current in this respect seems to depend on the electrolytic effect on the water in the dilute acetic acid. Chlorine has a great affinity for hydrogen, and \\iLl unite with tlie H._, molecule of water, hbera- ting under ordinary circumstances. When electrolysis is employed in a mixture m which chlorine is being set free, the H., molecules combme with the chlorme to form hydrochloric acid ; oxygen m its nascent form is liberated, and has great affinity for organic matter, uniting ^\■ith it to change it uito a translucent substance. Continuous Current and Ionization for Neu- ralgia. — Galvanic current has been advocated by many authors for treatment of trigeminal neuralgia. The difficulty in diagnosmg whether the pain is of reflex origin, or arises from some affection of the semilunar ganglion or the nerves connected with it, makes tlie treatment of facial neuralgia by the current of uncertain prognosis. Drastic measures are often resorted to, by the extraction of numerous sound teeth, in the hope (often a vain one) of relieving persistent chronic facial neuralgia. Tliis is the class of case that calls for electric treatment. The technique consists ui placing a large active electrode over the whole surface of the affected side of the face, whilst another indifferent electrode is placed on the neck, and a contmuous current of 30 to 80 milliamperes apf)lied for a dura- tion of 30 to 45 minutes. Tliis treatment should be repeated daily until the pain dis- appears. Guilleminot (4, p. 34(3) says : "In most cases . the treatment par excellence for neuralgia is that by the galvanic current." Ionic medication \\ith sodium salicylate, and also bichloride of quinine, in severe cases of tic douloureux has been advocated by Leduc of Nantes (7), who details remarkable cures of very severe cases of this painful disease by salicylic ions and quinine ions. E. S. BIBLIOGRAPHY (1) Archives D'ELECTRiciTiMEDiCALE. July 25, 1904. (2) Gautier. Technique d'Electrotherapie, VI. p. m. (3) GiLLETT, W. H. Cataphoresis for Obtunding Sensitive Dentine. Dental Cosmos, 1896. Vol. XXXVIIl, p. 132. (4) Guilleminot. Electricity in Medicine. (5) Jones, Lewis. Medical Electricity, p. 463. (6) Ledtjc, S. Arch. d'Electricile me'dicale, Sept. 25, 1904. Les ions de medecine. (7) Leduc, S. La Semaine M,'dicale. Nov. 22, 1905. (8) McGr.\w, D. F. Denta/ Co«mo«, Feb. 1889. Vol. XXXI. (9) Morton, W. J. Cataphoresis. (10) Peter, Josek. Odontologische Blatter, Berlin, July 1905. (11) Turner, Dawson. Practical Medical Electricity. (12) Westlake, a. C. Dental Cosmos, 1892. Vol. XXXIV. p. 887. (13) ZiBRLER & Letemann. Dental Cosmos, 1905. Vol. XLVIl. p. 1136. CHAPTER XXXII INJURIES OF THE TEETH DUE TO VIOLENCE In common \\itli other hard structures of the body, teeth are liable to accidental injuries, the upjJer incisors, owing to their shape and position, particularly when unduly prominent, being the chief sufferers. It is usual to classify such injuries under three headings : Con- cussion, Dislocation, and Fracture. These again may be subdivided in accordance with the severity of the injury, as evidenced by the age of the patient, the degree of dislocation, the position of the fracture, and the extent of the lesion, if any, inflicted on the soft structures of the dental pulp. Such mjuries occasioned by direct violence are of frequent occurrence ; but they may also result from indirect violence, as when a blow or fall upon the chin causes the teeth in the mandible to be brought into contact with those of the maxiUae with great force, or by muscular effort when the teeth are subjected to improj)er or unexpected uses. CONCUSSION By concussion is meant an injury resulting from direct or indirect violence, but of a degree insufficient to dislocate or fracture the tooth. Such accidents are exceedingly common, but even the most trivial may result in the subse- quent death of the pulp. Usually the injury is followed by some periodontitis — the tooth becomes tender and slightly loose ; under favourable circvimstances the inflammation may be arrested at this stage and speedily subside. Should the inflammation continue, the tooth becomes more tender and elongated ; the pulp may become involved, as shown by its extreme sensitiveness to thermal changes, the mere drawing in through the lips of cold air starting acute pain, which radiates to adjacent teeth or is referred to some other area of the nerve distribution. Fmally, the pulp may die, and the periodontal mflaramation progress to the forma- tion of an alveolar abscess. Sometimes the continuity of the soft struc- tures of the pulp with those external to the tooth is severed at the apical foramen when the injury occurs ; there may then be a periodontitis un- complicated with inflammation of the pulp. Not uncommonly the concussion may lie apparently so slight as to produce no periodontitis, and yet be sufficient to destroy at once the vitality of the 524 pulp ; or this organ may die shortly afterwards without any manifestations of acute mflamma- tion. Such a tooth may remain quiescent for many years, and then suddenly become affected with acute periodontal inflammation. It nearly always shows some discoloration, rangmg from grey to black. The discoloration would seem to be greater, howev^er, in those cases in which the pulp died as the result of acute inflammation, than when it has been killed outright at the time of the injury. In all cases of concussion it is necessary to determine the extent of the lesion, if any, received by the pulp. Should it be dead the sooner it is removed the better. This may be ascertamed by the absence of response to thermal tests. A hole having been punched m a small piece of rubber-dam, the suspected tooth is passed through it and so isolated from its neighbours, when it may be easily tested by spraying a little ethyl chloride upon it, or by placmg a small piece of superheated temporary gutta-percha in contact with it. Access to the canal of an incisor for the purpose of removal of the pulp is obtained best through the cin- gulum ; in the case of a premolar or molar, directly through the crown. Should perio- dontitis be present, the operation may be rendered less painful by making a small splint from impression composition, and using it to steady the affected tooth. If when employing thermal tests an undue response is elicited, some hyperaemia of the pulp may be suspected, and an attempt should be made to allay it by the application of counter- irritants to the gum immediately over the tooth, such as tmcture of aconite, tincture of iodine, and chloroform, in equal parts, or a capsicum plaster. Similar applications are also indicated when periodontitis is present. Should this treatment fail, and acute inflammation ensue, the pulp should be removed under an anaesthetic. DISLOCATION Dislocation of a tooth is usually caused by direct rather than indirect violence. It may be partial or complete, and it is not un- commonly accompanied by some fracture of the alveolar process ; or the root of the tooth itself may be fractured high up in its socket. 525 In partial dislocation the displacement may occur in any direction, but most frequently it is inward towards the tongue, or the tooth is driven into its socket. Treatment consists in thorouglily cleansing the parts, reducing the dislocation, and mauitaining the tooth in absolute rest until it has become firm again in its socket. An imjjortant factor to be taken into consideration is the age of the patient. A very large percentage of teeth that have suffered dislocation die, and should this occur m the case of a young tooth not yet fully formed, further growth is arrested, and the successful filling of the root-canal is rendered difficult and sometimes impossible. In such circumstances it may be wise to extract the tooth, and either allow the space to close up by the falling together of the adjacent teeth, or adopt some means for preserving such space, with a view to providing an artificial substitute later on. In coming to a decision attention should be paid to the sex of the patient, the crowding of the teeth, and aesthetic considerations generally. In this connection the following case is of interest. A small boy aged six years fell and struck his mouth against the leg of a table, completely dislocating his left upper central incisor, which had erupted early. It was, naturally, only partly formed, but it was replaced and subsequently became quite firm. It re- mained, however, in its original position, and failed to erupt further; nor was there any further growth of the root, as was proved when the tooth was removed ten years later, owing to its unsightly appearance due to its shortness in relation to its neighbours. Teeth that have been driven into their sockets may be brought into alignment by suitable forceps. In tlie case of upper canines, premolars, and molars, it must be remembered that these may have perforated the floor of the maxillary sinus ; care, therefore, is needed when grasping these teeth to prevent their slipping upwards into that cavity. Teeth that have been dislocated upwards, and allowed to remain, have a tendency to come down of themselves into a more or less natural position. Some years ago the -wTiter saw a smaU boy aged eight and a half j'ears who a month before had fallen on a stile and driven his right central incisor upwards and outwards practically but of sight. The tooth was then quite firm, and as he was going away to school the following day it was decided to leave it until his next holidays. Wlien seen three months later it had come down considerably, and was therefore left alone for a further period of four months ; at the end of this time it had taken up what was practically its normal position ; the tooth, however, was dead. A careful examination should be made in those cases in which a tooth has apparently been knocked out and lost, to ascertam that the socket is really empty, and that the tooth has not been merely driven upwards out of sight. The wTiter saw a man who four months previously had been kicked by a horse and had had his mandible fractured, who stated that his left upjjer lateral incisor and canine had been knocked out. He came to the hospital on account of a swellmg m his cheek, with a sinus openmg externally and discharging pus. Aii examination with a probe revealed the jjresence of a tooth, which was removed without difficulty through a small incision, and jjroved to be the canine tooth that the patient imagined he had lost. Methods of Retaining Partially Dislocated Teeth, As already indicated, a tooth that has Ijeen partially dislocated should be brought into correct alignment, the alveolus if fractured carefully moulded around the root, and measures taken to secure perfect rest until repair of the injured tissues has taken place. Thus the tooth may be ligatured to the adjacent firm teeth by wir- ing in the manner shown in Fig. 591. The tendency, always present, for the tooth to re- al a i n slightly elongated is in a measure guarded agamst by using an extra loop of wire, passing it through the other loops, which fix the tooth to its neighbours, bringing it downwards, and finally twisting it tightly at the incisal edge of the tooth. Fi'equently it is necessary to afford greater support than can be obtained by simply ligaturing the tooth to its fellows, particularly when the force of occlusion of the oj)posing teeth is heavy, or when the affected tooth is unduly prominent ; in these circumstances it is often better to employ some kind of metal splint, such as that described below (Fig. 592). In ca,ses of complete dislocation the same consideration nuist be given to the age of the patient as in tliose of partial dislocation. Should the accident occur at the hands of the dentist, as may occasionally happen, the tooth should be immediately re2:)laced, as there are grounds for believing that in young patients the pulp structures, which have been severed at the apical foramen, occasionally reunite. Thus, an upper left central incisor was extracted from the mouth of a boy aged eleven years, in order to facilitate the thorough removal of a recurrent epuloid growth ; after the operation the tooth was replaced and retained in position by a splint previously prepared. Four months later the tooth was quite firm and of normal colour, and it responded to thermal tests equally with the 526 other incisors. At any rate, teeth thus re- planted frequently undergo little or no sub- sequent discoloration. This may be due partly to the fact that the amount of blood extravasa- tion in tlie pulp is but slight, compared with those cases in which the death of the pulp has been gradual and has followed acute hyperaemia of that organ. Should the patient not be seen until some time after the injury, the socket should be syringed witli hot water and rendered as aseptic as possible, after the removal of all clots. The pulp of the tooth should be extir- pated, and the canals sterilized and filled in the usual manner, before the tooth is replanted. This may be done either through the apical foramen or through the most accessible portion of the cro«n ; the latter usually gives tlie better Fig. 592. result. The tooth itself should be carefully and thoroughly cleansed by some warm anti- septic .solution, such as lysol two per cent, and durmg the filling of the canals held in lint soaked in tlie same. The chances of success are undoubtedly greater in those cases in which the tooth is replanted shortly after the injury, since the peri- odontal membrane adherent to the root of the tooth retains its vitality for some time, and a membranous connection between the tooth and its socket is often secured. The direct trans- plantation of teeth from one mouth to another has not only been advocated but successfully accomplished. However, the necessity and the opportunity for such an operation can arise but seldom, and its ethics are open to question. A replanted tooth may serve for many years, but not infrequently its root becomes absorbed, this resulting in its ultimately being lost. Absorption occurs more frequently when the replantation has been delayed for some time. Examination of such a tooth reveals the fact that there has been chronic inflammation in the socket, and that an alternating process of absorption and deposition of cementum has taken place ; and it may well be that some replanted teeth are kept in place partly by the hold afl^orded by the filling in of these absorption spaces. Retention is secured better by means of a specially constracted splint than by simple ligaturing ; the most efficient is made by striking a piece of German silver plate to fit over the replaced and the adjacent teeth, and cementing it in position with one of the osteo- plastic cements (Fig. 592). An impression for producing a model of the parts can be taken readily if the tooth is ligatured temporarily into place. The advantage of such a splint is that it relieves the " bite " and secures absolute rest. Its disadvantage is that it is somewhat large, but as a rule it may be dispensed with in a week or ten days. Another useful splint is one made of thin German silver bands soldered together and ^'°- 5^•'• cemented in place (Fig. 593) ; or a small modified Hammond splint may be employed. Dislocation of Unerupted Teeth. — A developmg tooth may be partially dislocated by an injury received while it is still buried in its crypt. In such cases, the part of the tooth already calcified is forced out of its proper alignment with, and partially detached from, the re- mamder of the tooth yet uncalcified, thus giving rise to certain forms of dilacerated teeth (see p. 49). FRACTURE The causes of fracture of the teeth are similar to those producing the injuries just described. Teeth undermmed by caries, and those possessmg large fillings placed in im- properly prepared cavities, are often fractured by biting upon hard substances, especially when they are pulpless : occasionally perfectly sound teeth may be fractured in the same manner. The degree of injury shows considerable variation. A mere crack in the enamel may be disregarded, and a slight chip simply requires to be smoothed down with a stone and then polished. More extensive lesions may be grouped as follows: (1) Transverse, (2) Oblique, and (3) Longitudinal fractures. Transverse fractures may occur in the crovra or in the root ; in the former the pulp may or 527 may not be exposed, whilst in tlie latter an impacted fracture is sometimes produced. Oblique fractures may involve the crown only, or both crown and root. The pulp may or may not be exposed. Longitudinal fractures are comparatively rare, and are met with more frequently in the premolar and molar regions. In the treatment of these cases, the extent of the lesion, if any, suffered by the soft tissues of the dental pulp is a matter of first importance, for it must be remembered that a tooth that has been fractured has been concussed also, and although the pulp may not have been exposed, due observation must be made for subsequent changes in that organ, such as described under " concussion " and " dislocation ". Further, the pulp of the tooth may be directly exposed by tlie line of the fracture rumiing across it. In the event of such fracture involving the crown, the patient sliould be anaesthetized, and the pulp removed. A general anaesthetic, such as nitrous oxide, is to be preferred as a rale to a local anaestlietic, altliough in some cases of anterior teeth an injection of the latter, high up near the apical foramen, may serve. It frequently happens, however, that some peri- odontitis is present, and under these circum- stances the action of a local anaesthetic is not so efficacious as one would wish. Again, pressure anaesthesia is difiicult to employ, inasmuch as there is no cavity in which to place the medicament and the unvulcanized rubber, by means of which the necessary pressure is exerted. The root-canals are then treated in the usual manner, and the missing i portion of the crown is restored by means of a filling, inlay, or crown, as the extent of the injury necessitates. Again, the treatment may be complicated stLU further, owing to the age of the patient and the fact that the root of the tooth may not ' be fuUy formed. In the case of an upper front tooth it is desirable, from many points of view, 1 that the root should be retained if possible. The pulp having been removed, an examination of the canal should be made with a fine broach to determine the length of the root and the degree to which the apical foramen is closed. If the apical foramen is found to be compara- tively small, an attempt should be made to fiU ' the canal, either by a "sponge graft" (2) or one of the methods described on p. 481. Fail- ing this, the tooth must be removed, and as a general rule means should be taken to preserve the space, in order that an artificial substitute may be inserted at a later date. This may be done by adapting two metal bands of the Angle type to the adjacent teeth and uniting them by a crossbar, the whole being cemented in position (Fig. 594). When the tooth involved space may sometimes be in the mouth of a boy Fio. 594. is a lateral incisor the allowed to close, e. g. when there is evidence that there will be a general crowding of the teeth. The fact. however, that the loss of such a tooth would lead to a driftmg of the central incisors from the median line of the face, must be borne in mind, and, if possible, steps should be taken to minimize this by the judicious extraction of a premolar on the opposite side. A similar injury to a lower incisor in the mouth of a young patient is best treated by extraction and allowing the space to close naturally. Its loss is not very noticeable subsequently, although it is true that it may lead to some abnormalities of position of the teeth in the upper arch. When the fracture is trivial in extent, involv- ing but a small portion of the incisal edge of an upper front tooth, it is possible in a young patient to elongate the affected tooth by mechanical means, trim the ragged edge with a stone in the engine, and bring the tooth into alignment with its fellows. A simple appliance for such purpose consists in banding the fractured tooth as well as its immediate neigh- bours, and applying traction force by means of a rubber band as shown in Fig. 595. It is neces- P'ik. .■)itr). sary to retain the tooth in its new position for some time, as other- wise it tends to relapse into its original place. Agam, a small fracture of the incisal edge of a central incisor, when both centrals are longer than the laterals, may be treated by truemg the edge of the one fractured and reducmg the length of the other to matcli. Transverse fractures through the root of a tooth usually demand treatment by extraction. Wien the fracture occurs in an incisor, but slightly above the neck of the tooth, it may be possible to adapt a crown ; in such a case no attempt should be made to employ one of the banded varieties, a much better chance of success bemg afforded by one of a porcelain type, " flush " fitted. WTien the fracture occurs in the upper third of the root, it is commonly accompanied by partial dislocation of the remainder of the tooth, as already mentioned. Occasionally, however, there is complete im- paction, and under such circumstances reunion may take place, the uniting tissue being derived partly from the pulp and partly from the peri- odontal membrane ; the length of service rendered by such teeth, however, is comparatively short. 528 Storer Bemiett (1) has described a case of united fracture, which occurred in the practice of W. E. Harding. Tlie patient was a girl aged seventeen years wlio in falling struck an upper incisor tooth, whicli was driven upwards into its socket, and fractured obliquely at the neck ; it remamed impacted for ten months, until it caused so much irritation that its removal was called for. A microscopic examuiation showed that reunion of the fracture had taken place, the unit- ing substance consisting of a calcified material of a spongy or cavernous character, with numerous spaces for blood-vessels. The cavernous spaces had apparently been occupied by"a substance somewliat resembling pulp. In various positions slight absorption of the edges of the normal dentine had taken place, the spaces thus formed being filled « ith cementum. showing well-marked lacunae and canaliculi. (See Fig.s. 596, 597, 598.) pain, however, caused the patient to consult Mr. Tomes, who removed the tooth, an examina- tion of which revealed the fact that the pulp Fig. 59(i. {Trans. Odont. Soc. {Trans. Odont. Soc.) Very occasionally, a pulp laid bare by fracture of the tooth undergoes repair by calcification of the exposed surface. Charles Tomes (3) has recorded such a case. In attempting the removal of a lower molar, the tooth was fractured slightly below its neck, thereby producing a large exposure of the pulp. Tlie remauider of the tooth was allo^^•ed to remain, where it gave but little trouble for three years. Paroxysmal Fig. 598. {Trans. Odont. Soc.) had not died, and that its exposed surface had become completely calcified over with secondary Fig. 599. {Trayu. Odont. Soc.) dentine, in which were embedded several minute pieces of fractured dentine (see Fig. 599). M. F. H. BIBLIOGRAPHY (1) Bennett, C. Storer. Trans. Odont. Soc, 1S95-Q6, Vol. xxviir, p. 181. (2) Brttnton, G. Jour. Brit. Dent. Assoc, 1892, Vol. XIII, p. 352. (3) Tomes, C. S. Trans. Odont. Soc, 1895-96, Vol. XXVIII, p. 183. CHAPTER XXXII r THE MECHANICAL STRESSES OF MASTICATION In considering tlie amount, incidence, and effects of the mechanical stresses to whicli the teeth are subjected in the process of mastica- tion, it is important to bear in mmd that each dental arch must be viewed both as (1) a unit in itself; and (2) an aggregation of 16 units. Stresses applied at certain positions of the arch tend to wear and displace the units upon which they act ; but when the full complement of teeth remaui in normal occlusion, there are compensating resistances in other parts of the arches, which tend to minimize these evil effects, and which, together with the mutual support afforded to each other by well-placed teeth, enable the arch in proportion to its perfection to approximate to the condition of a single rigid masticating mechanism. IN NORMAL ARCHES AND UNDER NORMAL CONDITIONS A. — The amount of the mechanical stress to which the teeth may be exposed when the bite Ls closed has been estimated by the gnatho- dynamometer and found to be (on an average of 1000 cases) 171 lb in the molar region and, of course, somewhat less in the mcisor region.— Black. The maximum possible j)ressure is rarely reached, and the slightest condition of tender- ness of the teeth dimmishes at once the force voluntarily exerted by means of the muscles of mastication. On the other hand, the figures ascertained by a dynamometer are misleading as clinical guides, since the teeth are necessarily separated more or less by the msertion of the instrument, and the pressure recorded is there- fore less than the true maximum force of the bite, because the muscles act at the greatest mechanical advantage -when the teeth are at the point of closure. Moreover, such measurements as have been made relate to the vertical movement of the mandible, and this is less important clinically than movements other than vertical, the stresses of which are even more difficult to measure. B. — The direction of impact of stresses. (1) In the Incisor Region. — Here, the stresses to which the teeth are subjected are, in the main, lateral stresses, and owuig to the natural over- bite they are exercised on the palatal aspects of the upjDer and the labial aspects of the lower teeth. Any pressure exercised on an oblique surface can be resolved into two components — one parallel with, and the other at right angles to, the oblique surface, in this case formed by the palatal aspect of the upper mcisor crowns. The first component (AB,Fig. 600) can be neglected as of no effect as a stress on the ui^ijer tooth, and the cumulative effect of the second (AC) is sho\vn in the later years of life in the gradual moving forward and spacing of the uf)per teeth, and often in the gradual moving backward and crowdmg of the lower teeth. The effect is more pronounced in the upper than the lower teeth, since in the latter the units of the arch are com- pressed together and so support one an- other. (2) In the Pre- molar and Molar Regions. Here, also, owing to the obli- quity of the cusp surfaces, any stress is split up into com- ponents parallel to and at right angles with the cusp surface, and the latter com- ponents similarly tend to lessen the stability of the tooth. That this effect is consider- able is shown by the way in which the buccal cusps of the lower molars and the palatal cusps of the upper molars are worn away when the teeth have been subjected to much attrition. In the operation of masticating on, say, the right side of the mouth, the mandible is carried to the right and the teeth are closed, bringmg the outer and inner cusps of the molars and 529 Fig. goo. 530 the outer cusps of the premolars first together (see Fig. 601). The outer cusps of the lower teeth then slide up to the sulcus of the uppers, whilst their ioner cusps slide up the lingual aspect of the Fig. 601. inner cusps of the uppers. The slidmg contact between the inner cusps usually takes place in the molar region only, since the inner cusps of the premolars are too short to make a contact in this part of the movement. Fig. 602. When the outer cusps of the lowers have reached the upper sulcus, the teeth are in the position of the resting bite (see Fig. 602). But the sliding movement may be contmued in the same direction, and the contact trans- ferred to the lingual aspect of the outer cusps of the lower teeth and the buccal aspect of the inner cusps of the upper teeth. This contact is shared also by the premolars, smce it can be made when the longer cusps of both upper and lower teeth are articulating. The movement ends with apical contact between the lingual upper cusps and the buccal lower cusps. The foregoing description deals with what takes place on the side of the mouth employed m mastication. But during this movement the teeth are also in contact on the opposite side, and the various contacts take place m an order the reverse of that described above (see Fig. 601). Commonly, however, the contacts are less numerous on the non-masticating side, owing to the descent of the condyle on that side. Fig. 603. These stresses regularly at work show them- selves in time in the wear on both sides of the lingual upper and buccal lower cusps. In the same movement there Ls contact first between the tips of the upper and lower canines, then between the medio -lingual surface of the upper canine and the disto-huccal surface Fl.:, (id I. of the lower, resulting in wear of these cusps and surfaces ; and also a sliding contact (from side to side) resulting in wear of the palatal aspects of the upper incisors and the lingual aspects of the lower. These latter effects become more 531 marked as the wear of the molars allows of more forcible contact between the upper and lower front teeth. It will be seen that while the stresses on the molars and premolars are bilateral (outwards and ui wards in both upper and lower), and so tend to neutralize one another, the stresses on the canines and incisors are unilateral (out- wards in the upper and inwards in the lower Fig. 605. teeth). Hence displacement of the premolars and molars is rare in normal dentures, while displacement of the front teeth may occur in any denture after wear or loss of the back teeth has allowed undue approximation of the jaws. This will always be slight in a normal and complete denture, but is rendered much more obvious under abnormal conditions to be sub- sequently dealt with. Fig. •iO(i. E.xamples of tlie wear of teeth that ultimately takes place under the masticating stress in nearly normal dentures is shown in — Fig. COS, 3 . rig. 604, 53,; Fig. 605, jS ] and Fig. 606, Note that in the upper canines the stresses are such as to exert pressure from the median line, and in the lower canines towards the median line of the mouth. Attention has been drawn to the fact that the stability of the molar and premolar teeth in the perfect arch is due to the lateral stresses upon them being alternately inward and out- ward in both upper and lower teeth, the forces thus tending to neutralize each other ; while the evil effects of the unilateral outward and inward stresses upon the upper and lower front teeth respectively are only limited by the closure of the back teeth determining the amount of stress that can fall on the front. UNDER ABNORMAL CONDITIONS A. — Effects of malposition on the incidence and amount of stivss cui indixidual units of .m ai'ch. Fig. 607. These are seen — (1) In the increased wear of cusps malpoised teeth. Fig. 607 is a case where the deciduous canmes were unduly long as compared with the other the Fig. 608. teeth, and being thereby subjected to an ab- normal amount of ^Dressure at the commence- ment of the lateral movement of mastication, became worn at the tips, and, in the lower canines, on the disto-labial aspect. Fig. 608 shows the effect of increased lateral 532 stress due to slight local irregularity, resulting in a little forward displacement of | 1 and marked labial wearing of | 1. (2) In the increase of the malposition, or in its recurrence if rectified, owing to the abnormal stress exercised at that point, or to the greater range or length of time over which the stress is applied. When cases of superior protrusion were treated by merely drawing the upper incisor crowns back without reducing the long over- bite of the front teeth, relapse was quite usual. Here, the condition represented in Pig. 609 (I) was changed to that shown in Fig. 609 (II) , and the lateral stresses exercised over the long sliding contact from A to B speedily drove the upper incisors forward again. But when the bite of the back teeth is raised, or the upper incisors are driven uj)wards as well as backwards, and the overbite in front is thus reduced, the condi- tion is as shown in Fig. 609 (III) , -where the chance of relapse is much less owing to the lateral stress bemg limited to its normal range of action. The tendency of upper incisors to move forward if the stress upon their palatal surfaces becomes too great applies equally of course to artificial incisor crowns. It is frequently seen that in Logan crowns, where the pin is often made of platinum too soft for the purpose, the stress has been sufficient to bend the pin, the crowna has been tilted forwards, and its palatal margin raised from the end of the root. This tendency is often dealt with by adjusting the crowii so that its palatal aspect clears the bite altogether; but such provision is likely to be of only temporary effect, smce the root will probably descend from the socket till the crown meets the lower incisor bite. To counteract the double tendency to gradual lengthening and displacement forwards, the provision of a small palatal cusp to the crown has sometimes been practised. When the bite is closed this cusp articulates on the lingual side of the cutting edge of the lower incisor, and obviously prevents the upper crown from moving forward and lengthening. The tendency of crown-posts to bend or break under lateral stress, or, where the post itself withstands the stress, the tendency of the root to split, furnishes the reason for the addition of a collar round the root or a partial collar on its palatal aspect. The need for collars in addition to posts, would seem to be greater in the incisor region, where the stress is unilateral, than in the premolar region, where it is alternately outwards and inwards. Another effect of lateral stresses is seen m the splitting off of one ~ " cusp of a weakened tooth, e. g. where an upper premolar has large medial and distal cavities joining each other across the masticating surface, through caries in the sulcus. In such cases the fracture is produced by the wedging of food particles between the cusps of the weakened tooth. Fig. 610 shows a method of filUng designed to avoid this accident. The lingual cusp is cut down sufficiently to allow the filling material to be extended over it, and stUl to leave a space between itself and the mner cusp of the lower premolar. From this space the food particles can escape in a lingual dnection, and so injurious wedging is avoided. The outer cusp of the up- per premolar is cut away lingually, so that the bite of the outer cusp of the low er is borne by the filling material, and the stress taken off the upper cusji. B. — Effects of loss of some of the units of one arch on — (1) The remaining units of that arch. (2) Tlie various units of the opposing arch. (1) ^\'Tien some of the units in an arch are lost, there is obviously an in- crease in the stresses on the remaining units, owing to the lesser number over which the stresses are distributed. This results in — • (a) Greater wear of the remaming units. (b) Movement in position of some of or all the remaining units, owing to increased stresses and loss of lateral contact with other units of the arch. Fig. 610. 533 Where both upper and lower first molars have been lost from tlie same side, the inter- action of the cusps of the premolars on the inclined planes of their opponents soon causes separation and backward displacement of these teeth ; for this to occur, however, both upper and lower premolars must be free to move. If either upper or lower first molar is retained, and the premolars in front of it are tliereby kept in proper position, the stresses exerted by these will in turn preserve their opponents from backward disijlacement, notwithstanding the absence of the opposing first molar. (c) Tendency to loosening of the various units, owing to the increased stresses, both lateral and vertical. (2) In the opposite arch, the units that have lost their opponents tend to elongate. Since these elongated teeth may be not corn- ward the upper incisors acts by wearing exten- sively the labial surfaces of the lower incisors. Fig. lill. pletely unopposed, there are developed abnormally long slidmg contacts between them and partially opposing teetli. This means that the lateral stress is here in- creased in the range of its action ; and abnormal wearmg or loosening results. Fig. 611 shows a case where the front teeth developed an abnormally long over- bite, owing to loss of opposition between upper and lower back teeth. As the over- bite in front became deeper and deeper, tlie lateral stresses, outwards m the upper and inwards in the lower, came to act over a greater and greater range of sliding contact ; as well as bemg absolutely in- creased on these teeth, owing to the diminished number of teeth remaining. The result is seen in the unnatural spacing of 3.2.1. Fig. 612 shows tlie lower arch of the same case. Here the lateral stress that forced for- FiG. Cil2. This difference in the effect of the same force acting on upper and lower incisors is frequently seen, since, as already pointed out, it is much easier to force the units of an arch out by pressure from withui, than to force them in by pressure from w ithout. So, in the latter case, tlie force rather exhausts itself in wearing the teeth. Fig. 613 shows undue approximation of the jaws owing to loss of opposition between back teeth. This has developed increased stresses in the incisor and canine region, resulting in forward movement and spacing of the upper front teeth. It also shows that as the bite has closed, an abnormally long slidmg contact has_been developed between the distal surface of 5 j and the medial surface of 5 I partly articulating with it. The displacement back- FiG. 013. wards of the latter and the wearmg away of both teeth are obvious. 534 It is to be remembered that the lengthening of a tooth may be actual or relative. The tooth may be actually extruded from its socket owing to loss of aU its opponents. But if the arch is partly supplied by artificial teeth on a plate, and this denture slowly " rises " or " settles " in the mouth, owing to the pressure exerted by opposing teeth and the gradual absorption of the alveolar ridge, the remaining natural teeth in the composite arch v,iR become relatively longer than their artificial companions, even though no actual extrusion from their sockets has occurred. In this case they will encounter the force of the bite sooner than the teeth on the plate, and durmg the part of the movement in which they supply the sole antagonism to the opposing teeth, wUl have the stresses upon them increased owing to their smaller number ; and, taking the wliole range of the masticatory movement, it wUl be of longer duration in the case of the natural members of an arch than in the artificial ones, where the plate has sunk. Hence results of abnormal wear — displacement and loosening — Fig. liU. are likely to occur amongst these natural units of the arch. Fig. 614 shows the lack of opposition amongst back teeth which may be caused by the rising and sulking of plate dentures. Here " " are artificial teeth on plates. The space be- tween the molars caused by smking of plates does not exist between 5 | and 5 | , because the latter tooth was added later as a repair, and was placed at a higher level than 6 | and 7 | so as to be in articulation with the upper. Of course 6 | and 7 | should have been raised at the same time. rig. 615 shows virtual or relative elongation of I 3 and | 6, owing to the rising of an upper plate carrying artificial incisors and premolars. Here the closing of the bite has allowed an abnormally long sliding contact to develop between | 3 and | 3, resulting in great wear of the disto-labial aspect of | 3, and in medio- palatal wear and loosening of | 3, though these latter points cannot be verified from the figure. Fig. 615. Such cases show the results of a method of artificial replacement that allows of actual or relative lengthening of the remaining natural teeth, and the consequent development of in- creased lateral stresses ui^on them. To over- come these is one of the objects of bridge-work, which transmits the stress of mastication to the roots of natural teeth on which it is mounted, instead of to the surface of the slowly atrophymg alveolar ridge. STRESSES OF MASTICATION IN TO BRIDGE-WORK RELATION It is not intended here to discuss the whole of the advantages or disadvantages of bridge- work, but only to examine them in relation to the stresses of mastication and their effects. It is evident that so long as a bridge lasts, it can more efficiently perform its proportional share of the work of the arch than can substi- tutes on a plate. Its level, as compared with the natural teeth, will not change, and so these are not exposed to the increased stresses, with consequent wear, displacement, and loosening, which follow the actual or relative lengthen- ing of natural teeth when a partial plate is used. But bridge-work has the great disadvantage that the stresses of mastication are trans- mitted to a smaller number of roots than were intended by Nature to bear them, and so it is 535 found that the roots upon which the bridge is mounted ultimately loosen, and the work is rumed. As m the case of natural teeth, so in the roots upon which a bridge is mounted, the lateral stresses are those that chiefly operate hi loosen- ing the roots ; and these can best be combated by extending the bridge as far as possible round the arch, thus increasmg the number of its root supports, and arranging that these shall not be in a straight line or slight curve, but shall be so placed that the appliance has the stability of a "three-legged stool", or better stiU, of one with more than three legs. Thus, two antero-posterior bridges should not be placed at the sides of the jaw ; they should be connected across the middle line. An in- cisor, or incisor and canine, bridge should, if Fig. (iia. possible, be prolonged round the jaw, and take in some tooth in the premolar region of one or both sides. In this way the whole bridge will not be expo.sed to the force of mastication at the same time ; and the portion remote from the site of stress will liave some of that stress transmitted to it, and will serve to support and " key " the portion of the bridge that is exposed. The adoption of this plan will in- crease the number of roots over which the stress is distributed, and must materially lengthen the life of the work. The history of the case shown in Fig. 616 illustrates some of the points made in the fore- going statement. The patient is a smoker who has for years been in the liabit of holding his pipe with the left incisors and canines. The combhied loosen- ing efifects of tlie masticating stresses, the pipe stresses, and alveolar absorption, caused first the loss of I 1.2, which were replaced by a small lower plate. Then 1 | also loosened, and the lower bridge was uiserted, by means of which 5.1 I 1.2 were supported on 4.3 | 3. All the upper and lower molars were subsequently lost and replaced by dentures, the lower denture also replacing | 5. Then followed the loss of I 2, which was replaced by the bridge shown in the figure, by means of which | 2 was supported by |J^.3, and which was inserted about three years later than the lower bridge. The teeth supportmg the upper bridge soon loosened, so that the appliance failed altogether and had to be removed The natural teeth and bridge are included in the model. The lower bridge has remahied firm and satisfactory throughout, and has been in use some years longer than the upper. Its extent has been indicated by colouring the metal parts on the model, the bridge itself bemg still in the patient's mouth. There are several reasons for this failure and success. Firstly, as has been pointed out, the loosening and displacing effects of the lateral stresses are more marked iia upper than in lower front teeth, since it is easier to dislodge the segments of an arch by pressure from within than from with- out. Secondly, since the upper bridge is the shorter and is at one side of the mouth only, it is more likely that the whole of the bridge will be acted upon by stress at any one time, than would be the case if an extension passed across tlie middle Ihie. Thirdly, nearly aU the stress on such a bridge wiU be of the most damaging kind, namely, unilateral outwards at right angles to the plane of the palatal aspect of the bridge. The greater permanence of the lower bridge is accounted for by the following facts. Firstly, the main stress on the bridge is from without inwards, which cannot have so great a loosen- ing effect as stress ui the opposite direction. Secondly, the bridge is prolonged to the first premolar on the right side, and thus lias the "three-legged stool "quality; though the arm of the bridge from 3 | to 4 | is shorter than might be desired, still the support of 4 | must be very efficacious hi counteracting the back- ward stress on the front teeth. Thirdly, the stresses on this bridge are of a mixed character. If the facets visible in Figs. 608, 603, 604, and 605, are examined, it will Ije seen that they indicate stresses directly backwards on the lower incisors, but backwards and towards the middle line on the lower canines. Now, all the stresses applied to one end of a bridge in the direction of the length of the 536 bridge will be adequately resisted by the supports at the other end. It is manifest that if a hurdle is implanted by two stakes, one at each end, it is easier to throw it down by pres- sure applied to one side at right angles with the plane of the structure, than to one end in the direction of the other end. All the pressures acting on the upper bridge are of the first kind. Pressures of this kind in the lower bridge are resisted by its distal arm fixed to 4 | and ending m 5 I . 3 | and 3 form supports for each other against " end on " stresses, such as those thrown on the lower canines in normal movements of mastication. The histories of this and other cases show conclusively that in bridge-work the stability and success of the appliance do not depend merely upon not overloading the supporting roots with too many additional artificial teeth. The success depends at least as much upon such design of the .structure as will bmd the supporting roots into a unity of form calculated to resist most efficiently the combined wrecking stresses from all sides that it wUl have to en- counter. In the above case the upper bridge, by which one tooth was attached to two contiguous ones, proved far less durable than the lower one, by which five teeth were attached to three. G. G. C. C. H. P. CHAPTER XXXIY ARTIFICIAL CROWNS GENERAL CONSIDERATIONS Prefatory Remarks. — Perhaps the most fas- cinating field in the domain of operative dentistry is that of crowning. The term covers j two main ideas : first, the substitution for the natural crown of an artificial one fixed on the root ; second, the covering of a natural crown by a fixed cap or shell of metal such as gold or platinum. The attractiveness of the subject is due chiefiy to the perfect restoration of function, and also, when desired, of normal natural ap- pearance tliat is attamable. Added to these almost unique merits is the interest that is excited by the nature of the technical pro- cesses involved, which enter into all the refined arts nowadays brought to bear on operative prosthetic dentistry. Li most cases of crownmg the result may be expected to prove of a durable nature, even when the natural crown is in such an advanced state of demolition and decay, or total loss, that any other operation for its restoration would give but a very poor result or be entirely impossible. Appreciation of such an operation well performed is a feeling that can be shared alike by both operator and patient. Again, the inherent difficulties of the subject provide unlimited scope for the best efforts and ingenuity of the most skilled, most inventive, and most artistic of operators. The restoration of both function and natural appearance to the point of perfection that is attainable may justly be said to place this operation of crowning in the position of being the most perfect substitutive operation in surgery, either dental or general. Very often, teeth that have become the merest wrecks, and that may have been filled and refilled, and still further damaged by frac- ture and caries until more filling is a hopeless proposition, may be saved from their otherwise derelict condition by crowning, and thereby restored to a condition that virtually equals that of the perfect organ. Crowning Compared with Filling. — A crown, by surrounding a root or part of a tooth, helps to hold the particles of the tooth together, and so strengthens it. A crown also takes its attachment from the strongest remaining part of the tooth. A filling, on the other hand, 537 is in a much less advantageous position, because both of these conditions are reversed. Relative Merits of Crowning and Extraction Compared. — First and foremost let it be stated in crownuig versus e.xtraction, that when crowning is likely to be a successful operation, and when it will obviate the necessity for wear- ing a plate, it is of such enormous advantage to the patient that no words can be too strong to express condemnation of extraction. Thus, the operator who wUI break into an unbroken row of the six or eight front teeth in the mouth of, say, a young lady, by extracting one of them for some remediable defect, such as exijosure of jKilp, or fracture of the crown, or primary acute abscess, deserves to be severely censured. The tooth could be satisfactorily treated with- out extraction in the vast majority of such cases, and the operator should be under no delusion as to the absolute truth of this point of view. With regular care and attention on the part of both operator and patient, it should become but very rarely necessary to extract a firm tooth. Crowning should be resorted to when the safety of the root would otherwise be im- perilled, so long as teeth remain tight in the jaw. A tendency downward on the path of decay and dissolution should at all events be arrested by cro«iiing ; and in the case of a young person the wearing of a plate witli artifi- cial teeth should but rarely be allowed to become a necessity. With this end in view, every tooth should be crowned as soon as it is recog- nized that further filling will not restore it to proper and permanent function. By this means extraction will be obviated, with the possible exception of the third molars, which may not, as a rule, be worth crowning. If, however, a molar has already been lost from the same range of molars, then at all events even the third molar is well worth crowning. When a Partial Plate is already being worn. In those cases w here a plate is being \\orn and a natural tooth breaks down in the vicinity of the plate, the question arises whether it is better to add the new tooth to the plate or to restore the tooth by cro\viiing. In the case of an old and feeble patient it will often be in- advisable to incur the discomfort and exhaustion attendant upon a long operation; crowning. 538 therefore, will be ruled out ; but in other cases, crowTiing will generally be the better propo- sition. The reasons for this are as follows — (a) extraction is avoided ; (b) having a root under the plate is avoided ; (c) the removal at night of this particular tooth is avoided ; (d) the plate is steadied and supported by the presence of the crown ; good crown forms the best kind of abutment for the embrace of a clasp- band, if such an assistance to steadiness of the plate is desired, partly because the crown can be made of a favourable shape with parallel sides, and partly because, inilike a natural tooth, a crown is not liable to have caries induced by the band. If not crowned, the root should generally be extracted. The prematurely senile cast of countenance that results from wholesale extraction and consequent absorption of alveolar processes is well known, and forms a strong argument in favour of crowning as against extraction. (e) a A B Fio. 617. A. Shows the regular distribution of occlusal force over the whole socket in the case of an erect-standing tight tooth and normal occlusion. B. Shows the increased force applied to one side of the socket in the case of an obliquely standing tooth, leading to premature loosening. The disadvantages of leaving a root under a plate are — (a) the liability of the root to decay and to become septic ; (b) the constant tendency of the root to be extruded, causing the plate in time to rock upon it ; (c) the increased liabiUty of the artificial tooth to get broken, owing to its being nipped between the root on the one hand and the occluding tooth on the other. Fig. 618. — Site of extracted tooth, showing gum re- ceded from cervix of neighbouring t«eth, exposing root. Few people will require argument to convince them of the advantages of teeth as compared with no teeth ; but all the disadvantages of losing a tooth are not immediately apparent, and therefore it is necessary to mention at least some of the evils that are caused by extraction to neigh- bouring teeth. Firstly, extraction will often cause the neighbourmg teeth to fall from their normal positions, to become oblique by tilting towards the gap. This will cause an abnormal contact of approximal surfaces and so induce caries. It will also destroy the closeness of their occlu- sion and therefore their effectiveness as part of the masticatory organ. Secondly, extraction will be likely to cause premature loss of neighbouring teeth by loosening. An obliquely leaning tooth cannot support the strain of the occluding force so well as an erect- standing tooth ; for part only of the socket has to receive the force, which should be distributed over the whole of it, and so the tooth will become pre- maturely loosened (see Fig. 617). Thirdly, extraction damages the neigh- bouring teeth by causing the gum and alveolar process to recede from them, especially on the side of each tooth towards the vacancy, thus not only partly depriving them of their attachment, but also uncovering a surface of dentine or cementum, which may give pain and trouble through its sensitiveness and is specially liable to caries (see Fig. 618). Fourthly, extractions are detrimental to teeth in tlie occluding jaw, which are deprived of their antagonists, and wUl on that account protrude from their sockets and lose their correct level, until they nearly bite the gum of the opposite jaw, and also lose part of their attachment. 539 Fifthly, extraction, by reducing the numbec | of teeth, greatly aggravates that tendency of < the rest to wear down, which, especially in the I mouths of strong and active patients, becomes so often a troublesome condition, it bemg so difficult to arrest and treat. Pulplessness not a Disadvantage. — The condi- tion of " pulplessness ", which is a condition generally presupposed to a crowned tooth, need be considered no detriment to its "ex- pectation of life ", so far as its retention as a useful organ is concerned. The lesson that experience teaches is that with scrupulous care in the treatment of root-canals and the elimma- tion as far as possible of liability to sepsis at the apex of the root, the pulpless tooth will last quite as long and quite as efficiently as the live tooth. It is oidy too true that infection of the periodontal membrane will cause either acute abscess or chronic inflammation of the socket, but modern instruments and modern methods in this regard have arrived at such a degree of efficiency that the chance of this kind of uifection can, in the great majority of cases, be reduced to a negligible quantity. If premature loosening of a dead tooth does happen, it is probably due to chronic septic irritation of the socket set up by decomposition at the apical portion of the canal, or to arsenic - irritation of the socket ; and not to the 7nere fact of the tooth being pulpless. The writer be- lieves that "dead" teeth, when carefully treated and free from septic contamination resist the loosening that might result from pyorrhoea alveolaris, and also from what may be called senile atrophy of the socket, better than teeth with living pulps. A loosening similar to that of senile atrophy frequently attacks the teeth of persons of middle age ; but still this kind of loosening seems to be due to no other cause than atrophy, and therefore senility, so far as the tooth-socket is concerned, must be considered to have arrived prematurely. The writer has observed that this kind of loosening attacks " living " teeth to a far greater degree than " dead " ones. That pulplessness qua pulplessness is not a cause of premature loosening, requires but one instance for its proof. Here it is : An old gentleman pre- sented himself first to the writer at eighty years of age, with all his front teeth still in his mouth. One of these had been "pivoted" fifty years before, i. e. crowned with a metal post inserted in the enlarged root-canal to its apex. All the teeth at the time of his presentmg himself were loose ; but the "pivoted " tooth was the tightest of them all ; the other teeth were all still "alive ". The pivoting had been beautifully done in the early manner ; septic trouble had not super- vened ; hence the pulplessness had been no detriment to the tooth, but apparently a benefit. ROOTS SUITABLE FOR CROWNS General. — Any root that is sufficiently acces- sible, that offers a good proportion of sound dentine, and is tight enough to stand the strain of mastication, can be crowned ; but seeing that the root is to afford the sole support for the crown, it is obvious that the sounder, the larger, the longer, and the tighter the root, the better chance is there of the result being, so far as such a term is applicable to a portion of the human frame, permanent. Determination of the Desirability of Crowning any Particular Root. — In making an estimation of the desirability of crowning a given root, the following points are to be considered. (1) Tlie soundness of the root — its fixity, its length, its freedom from caries. (2) The probable length of life when crowned. (3) The value in function and appearance to the patient of the prospective crown. In estimating the amount of sound dentine present in a root, it must be recognized that if the pulp is alive, the root is almost sure to be "good for crowning ". A root that has been neglected, and whose pulp has been dead, with the root-canal open to the mouth for a long time, may be so extensively softened from within, through the canal being filled with debris of food and micro-organisms, that it will be unfit for crowning. Moreover, the chronically septic condition may have caused absorption of the tip of the root by an inflarned periodontal membrane. The presence of a live pulp is, therefore, a favourable feature because it denotes the soundness of the dentine with which it is in organic connection, and the preservation of the root from the attacks of micro-organisms and their resultant acids. In this case the pulp of course wiU have to be extirpated preparatory to crovraing. The degree of fixity of the root, if doubtful, must be tested by moderate attempts to shake it. Its length can be tested by probing the canal with a Donaldson bristle and feeling for the end. Tliis process may indicate that the root is too short for crowning, even though the dentine is hard and comparatively free from caries. The root may have lost much of its length, not only by caries at the surface, but by absorption at the apex. When the canal is" felt to te enlarged at the apex by absorption, the actual length can be measured by passing up to the apex a hooked Donaldson bristle. This hook can be hitched over the end of the root and the length indicated on the bristle by sliding to the mouth of the canal a small washer of rubber-dam through which the bristle 540 lias been previously passed (see Fig. 619). On removang the bristle from the root the length will be denoted by the distance of the washer from the hook. The depth of caries on the surface and in the interior must be judged by fairly hard pressure with the point of a sharp stiff steel explorer. If the amount of softening is still in doubt, the question must be settled by removing all the carious portion with a sharp round burr. The probable " length of life " when crowned will be estimated largely on the result of the examination as above, but sometimes a very poor root will repay crowiiing when the advantage to the patient of Rubber havuig the crown would be great, even washer though the " expectation of life " be but a few years. On the other hand, many a doubtful root, when crowned, will last mucli longer than might have been ex- pected ; and a previously neglected root will often actually tighten some- what in its socket after bemg crowned. This improvement probably ensues partly by reason of the thoroughness with which the root is rendered and kept aseptic by the processes attend- ant upon crowning, and also partly by reason of the root being restored to function. The amount of fixity of a root that will enable it to withstand the force of the bite will depend largely upon the nature of the bite ; for instance, a root that could not stand the impact of a bite when powerfully delivered by strong natural teeth of a vigorous person, would, perhaps, be quite equal to the strain when the bite is delivered by artificial teeth on a plate, or in the Fig. 019. case of a less vigorous person. The value of crowning is especially evident when it saves the patient from the wear- ing of a plate. A tooth ideally crowned is not only the acme of comfort and efficiency, but is as mnocuous to the remaining teeth as the natural tooth itself. On the other hand, a plate must always lack such a full measure of comfort and efficiency ; must also always be a source of some trouble and solicitude to the patient, and in a great number of cases will ultimately damage the adjacent natural teeth. The amount of dis- comfort occasioned by wearing a plate is a very variable quantity in different cases, and while some patients will assert that in actual wear their plates occasion them no discomfort, it is certainly true that other patients never get reconciled to the feeling of having a plate in the mouth, and are incurably afflicted by dis- comfort thereby. The writer substituted two central incisor crowns for a gold plate that had been fitted over the roots of these two teeth and adjacent gum for a friend of his who is a medical man. The plate was rather small, and well made, and fitted well, and had been worn for many years. Yet the patient's grati- tude for being relieved of it was quite touching, and he declares that the enhancement of his comfort is enormous. Without scrupulous at- tention and unremitting cleanliness on the part of the patient, a plate is certam to do damage to adjacent teeth ; and even with the greatest care damage often ensues, not only by caries, but by recession of the gum caused by the pressure of the plate. The pressure increases the recession that naturally follows the mere extraction of the teeth. PRINCIPLES OF CROWNING General. — Crowns should be endowed, if possible, with an excess of strength, both in themselves and in their attachment to the root ; so that they may defy not only ordinary strains of mastication, which are m cumulative effect destructive enough, but also unexpected shocks and casualties. Provision should be made to prevent rotation of the crown upon the root. The root-face should be shaped so that the crown can be conveniently fitted to it. The cro\vn should be so fitted that it rests fairly and squarely on the root. Provision should be made to prevent the crown from bemg forced out of place upon the root hy the bite. In the case of the upper front teeth, the bite being delivered in an outward Fig. 620. — Central " pivot " tooth with " pin-wire " post. Pin bent by force of bite, and crown thrown out of position. direction as well as upwards, this condition is met by providing a cap or half -cap to the neck, or by merely usmg a sufficiently thick and un- bendable post. Vast numbers of failures of anterior crowns are due to the tyraimy of an old idea, viz. that pin-size wire is the proper wire of which to make posts (see Fig. 620). The wire should, as a matter of fact, be much thicker. In the case of upper premolars the condition is met, in addition, by providing a naturally shaped two-cusped masticatory sur- face. If the inner cusp is not represented. 541 but the tooth finished iii shape like a canine, the bite will very probably in time shift the tooth outwards either upon the root, or root and all, on account of the bite being always delivered on an unopposed inclined plane. The occlusal surface therefore of the crown should be a close copy of the normal. This will be referred to again under the head of " Occlusion". Where a crown is fixed for a young person whose teeth are still lengthening, it is important to be able to remove the crown easily, as in the course of time it will be necessary to remove it to cut down the root, which will have elongated and become visible and unsightly, and to refix the crown, or make another. In these cases the crown can be made easily removable by fixing it with gutta-percha instead of cement. Then, on warming the crown, it can be with- drawn from the root without injuring either the root or the crown. Fig. 621. A. Properly backed. Backing thick and extending to edge of porcelain. Edge of porcelain ground thin and repohshed. B. Improperly backed. Flat tooth, and porcelain improperly left thick on incisal edge. In the great majority of cases crowned teeth are dead teeth, i. e. the crowns will have been fixed on pulpless roots, and when a root pre- sents itself for crowning containing a live pulp, it is nearly always best to kill and remove the ■pulp. When in douht, kill — is a useful working rule wherever pulps are concerned. Provision against Fracture of the Porcelain. Wliere it is desirable to fi.x a porcelain or porcelain -faced crown with cement, but the likelihood of subsequent fracture of the porce- lain by the bite or other causes of stress is recognized, the porcelain part should be made removable and replaceable independently of the metal part, so that the porcelain may be easUy replaceable m the mouth without interfering with the essential part of the crown. This is in the interest of the root itself, and also saves trouble should fracture occur. (For detaOs of removable facings see pp. 590-5.) Sometimes, but rarely, teeth containing live pulps are crowned, and then the metal post has to be dispensed with, and the whole attach- ment effected by a closely fittmg cap plus the cementing medium. Very often the dowel or post forms part and parcel of the finished crown, and the whole is inserted and fixed together; but in the case of molars with divergent roots, and of certain very carious single roots, or under certain difficult circumstances, or where it is desired to screw the post into the roots, the post or posts are fixed first and allowed to project, and U-J A B Fig. 622. A. Section of first upper premolar crown with collar. B. Same without collar. the crown is subsequently attached. As a rule the post is not screw-cut but is merely forced in, luted with cement. The subsequent fixuig of the crown to the post is sometimes effected by a screw-nut, but generally by cement only, or by cement and amalgam in the combination known as " PcA ". The crown should foUow as nearly as possible the normal original contour of the tooth. It must not project beyond the edges of the root, but be finished absolutely flush with it, excepting Fig. 623. — Improperly constructed crowns projecting beyond edges of roots, affording a lodgement for food, etc. the very slight projection m the case of cap- crowns, which is caused by the edge of a closely fitting collar. In this case the edges of the cap should be bevelled and the projection reduced to the smallest possible amount (see Figs. 622 and 623). The crown should be large enough to cover the whole root-face so that none of the root-face will remam exposed. Wliere no cap is used, care must be taken not to allow any portion of the crown to project beyond the edges of the root-face, either 542 labially or lingually. No gratuitous nidus for the lodgement of micro-organisms or debris of food can be allowed. Hygienic Considerations. — Any roughness or projecting ledges or faultily shaped interstitial surfaces, which tend to cause retention of food between tlie teeth and the harbourmg of micro- organisms, and any undue encroachment upon the gum, must be avoided. This is true univer- sally and applies to fillings just as much as to crowns. If a nidus is formed for the lodgement of decomposing food and septic organisms Fig. 624. — Sections of properly constructed crowns showing ends of roots " coned " and caps fitted close with no projecting edges. much mischief may ensue ; for local irritation will be set up, which may not stop at a mere local gingivitis, but may cause more or less periodontitis and even osteitis of the alveolar bone — inflammations that manifest themselves in tenderness of the tooth on pressure and gradual loss of attacliment. The systemic mischief that may result from absorption of the noxious products of micro-organisms, and from swallowing these poisons and the germs themselves, may become the graver side of the question ; and to escape condemnation on these two counts, crowns must be constructed so as to present no salient projections or encroach- ments upon the gum, and the greatest care must be exercised to get a very accurate fit at the junction of crown and root, particularly if a collar or cap on the root-end is used. \\'hen a collar is to be used, it must not be forced into the soft tissues, but must be fitted only to parts of the tooth that can be see7i or felt. The edge of the root or cervix of the tooth, or any other part of the tooth that is to be grasped by the hand, must be so shaped as to have parallel sides, or sides slightly coned, so that it is as easy as possible to secure a very close adaptation of collar to tooth (see Fig. 624). Wlien crowns are fitted and made as perfectly as possible, wliether they have collars or no, they are quite free from objection as regards their effect on the hygiene of the mouth ; in fact, owing to their optional contour and their smooth indestructible surfaces, they are dis- tinctly superior in this very respect to the patched-up apologies for natural crowns that they generally supersede. Let it be, there- fore, the ambition of the operator to produce crowns that shall not only be useful, durable, and artistic organs, but shall be also free from the important objection of insanitary encroach- ments upon the inter-dental spaces, gum, and periosteum. Previous writers on crowning, when describing collars, have erred in recom- mending and figuring collars far too deep, and in allowing that collars may to some extent be forced into the soft tissues. Collars should never be so deep as to injure the soft tissues or cause pain. The Use of Collars and Caps. — The advantages of collars and caps tightly fitting the root-end, when that root -end presents a strong edge, are — (1) They very greatly add to the strength and stability of the crown. (2) By covermg up the joint they protect the sectioned edge of cementum and dentine from the deleterious action of acids and caries-producing organisms. (3) They greatly reduce the liability of a root to split under the strains of mastication or accidental violence. These advantages take effect to the full when the root is strong-edged and sufficiently acces- sible for a projjer accuracy of fit to be obtained, but vanish pari pa^sii with the reversal of these conditions. Therefore, it is necessary to dis- tinguish the occasion on which it is and is not proper to apply a collar or cap to the end of the root. When Caps are Contra-indicated. — (1) In those cases where the root is carious much Fig. 625. — Showing how a collar may appear to fit the edge of the root tightly, and yet by being forced too deeply may have a projecting edge under the gum. (J. H. Badcock.) under the gum, and the soft tissue is adherent to its edge, a cap is not admissible. To place a collar here would mean cutting away a considerable part of the attachment of the periodontal membrane to the root, and owing to the more or less buried position of the root, it would be an unpractical proposition to shape the sides of the root properly to parallelism or conical form, without which the collar would probably not fit well enough to justify its existence. It must be remembered that under the gum 643 most roots are curved by Nature in the direction opposite to what is required for tlie fitting of a collar, and a collar forced on in such a position will have its edge standing widely away from the root (see Fig. 625). (2) In those cases where the root is hollowed out into crater-like form, leaving very thin edges it is not to be expected that a collar encircling those edges will add much to the holding-power of the crown, nor will it add appreciably to the resistance to splittmg of the root. It «ill be seen then, that the contra-indica- tions to a collar are all centred in the mechani- cal difficulties that sometimes accrue from an advanced state of caries of the root, which precludes the possibility of properly fitting the collar without damaging its attachment to the soft tissues. The question of appearance also arises, but is not fundamental, because when the appear- ance of a collar on the external part of a tooth would be objectionable, the collar can always, with a little extra trouble, be nearly or quite covered by the porcelain portion of the crown (see Fig. 626). Shape and Depth of Collars. — When the gingival margin is irregular, festooned, or higher at one part than Fig. 026. another, the band or collar of a crown must have its edge shaped accord- ingly, or else corresponding to the attachment of the periodontal membrane, which is generally much the same thing. This means that the band is not to be fitted by crudely jamming it on, so as to detach portions of the membrane from the root. The band must be so festooned as to follow the attachment, if necessary, of this A B Fio. 627. A. Shell crown " festooned " to follow the edge of the gum. B. Shell crown improperly forced under gum at back, owing to absence of proper " festooning". delicate and sensitive membrane without de- taching it at all (see Fig. 627). If any slight detachment from root is desired, it must be done with a tiny knife and not by the collar itself. The tendency of crown workers who use caps is to use them of too great depth, and writers giving instructions upon making cap crowns are at fault m recommending this. A cap of a porcelam crown on an incisor or pre- molar should hardly ever be more than ^^ of an inch m depth, and very often not more than ^V of an inch, when the edge of the root is level with or slightly under the gum. In such a case the object is to place the collar under the free edge of the gum, and that only. In Defence of the Collar. — When either free from the gum or placed under the naturally free edge of the gum, fitted quite close to the root, bevelled at the expen.se of the outer sur- face, and properly luted with cement, no objection can be reasonably urged against the collar. It produces no kind of irritation, and can be kept clean in the dental sense. It is scarcely more prominent than the cingulum of natural enamel in the same situation. It is by no means comparable to a layer of tartar. Tartar is an offensive accretion containuig a large proportion of animal matter, is absorbent, rough, and eminently prone to harbour micro- organisms, and, most serious of all, creeps deeper and deeper along the root, causing dis- appearance of the tooth-socket and often pyorrhoea. The collar should be m all these respects the antithesis of calculus. As age advances an apparent lengthening of all teeth ensues by gradual recession of gum and socket. Apart, therefore, from all question of irritation, the most properly fitted collar, if it lasts long enough, will in time be found free, if not origin- ally so, from the gum ; but this inevitable result of the flyiug years must not be confounded with what it is not, and ascribed to the maleficent efl^ect of the harmless and often necessary collar. Occlusion. — The occlusion of the bite must be specially studied. The finished crown should receive just its normal amomit of the bitmg force — neither more nor less. If more, the crowiied tooth or the opposing one or both, will be in danger of becoming tender in the socket by the setting up of periodontitis. If less, the crowned tooth or the opposing one will tend to become, in time, partially extruded from its socket, and its roots thereby partially exposed. A normal firm bite keeps the teeth in place in their sockets, but a shirking bite tends to cause the teeth apparently to lengthen — " feeling for the bite ". The lengthening, however, is not real, and merely represents a partial exti-usion of the teeth from their sockets and a loss to that extent of their stability. The shape of the masticating surface of a crown should be as nearly as possible a reproduction of the normal, so that the bite shall strike it naturally, and not tend in time to shift the root into a vicious position. For instance, in an upper premolar the inner cusp should be faithfully reproduced and not finished off like a canine ; otherwise, the impact of the bite upon it wUl be received 544 by a simple inclined plane unopposed, which will tend in time to shift the tooth outwards. The presence of a proper inner cusp will neu- tralize this tendency by presenting an inclined plane in the opposite direction (see Fig. 628). Properly formed cusps, also, made after Nature's \ A B Fig. 628. A. Shows correct antagonism of upper and lower premolar. B. Shows faulty antagonism of upper and lower pre- molar owing to absence of inner cusp of upper premolar, causing upper premolar to be gradually pushed outwards in direction of arrow. pattern, give the bite in its various positions that continuous antagonism so admirably arranged by Nature. Crowns for Teeth not Exposed to View. Crowns for back teeth, which are not ordinarily exposed to view even during speaking, laueh- ing, etc., are generally made entirely of metal for the sake of simplicity and strength ; but where exposed to view they should be either made of porcelain chiefly or of metal porcelain- faced. The commonest form of crown for molars is the all-metal "cap" or "shell" crown. This is a hollow shell of gold or platinum or other suitable metal made in the form of a molar tooth and filled with cement and puslied on to the root, so enclosing the remains of the natural crown and any iiUmgs that it may contain. Additional aid to its fixity may or may not be provided in the form of metal posts set in the roots. These are fixed in the roots previ- ously and allowed to project, the projecting ends being enclosed in the cement within the crown. This crown in its simplest form without posts is suitable where the remams of the natural crown are sufficient with the aid of the cement to hold the crown securely. Wliere the natural crown is very much hollowed or very deficient on one side, or reduced nearly to the level of the gum, a post or posts should be fixed, as otherwise under the strain of mastica- tion the crown will probably either come off simply, or will come off with the remains of the natural crown embedded in it (see Fig. 629). The edges of the crown should extend as a nile sufficiently deeply to include all the visible por- tion of the tooth and also slightly under the free edge of the gum, but on no account should the soft tissues be damaged by forcing the edges into the periodontal membrane. The edges of the crown should fit absolutely closely to the root all round, and be bevelled off at the expense of the outer surface, so that no abrupt margin is left. The crowned tooth when finished should present as nearly as jjossible the appearance of a natural tooth of which the crown has been gilded. These crowns are often made of platinum instead of gold, when the less ob- trusive colour of the platinum is preferred. The gold or j)latinum sliell crown is equally applicable for premolars whenever it happens, owing to the conformation of the mouth, that they are sufficiently out of siglit. Crowns for Teeth Exposed to View. — Teeth that are exposed to view are treated by an entirely different method for the sake of appear- ance. The portion exposed to view, or the whole crowii, is then made of porcelain, and a metal intermediate portion is made to attach the porcelain to the root. In the case of upper premolars it is ordinarily the outer face (labial face) alone that shows, and this is the only part that must of necessity A B Fio. 629. A. Shows section of molar with lingual portion missing. Here a post fixed in the palatine root is imperative. B. Same with post fixed in palatine root. be constructed of porcelain ; but in the case of lower premolars it is the top or masticating surface that often shows the most, and there- fore in such cases it is very desirable that the top should be made of porcelain also. A porcelam or porcelain-faced crown is indi- cated in the majority of premolar crowns, and in some cases also of first molars, both upper and lower. In the case of the six front teeth porce- lain or porcelain-faced crowns are almost universally required. They are attached to the root by one metal post or dowel, and may or may not be provided with a closely fitting 545 bell shaped in section. In the anterior roots of lower molars this is so marked as frequently to amount to there being two canals, circular Fig. 631. — Section of lower molar showing canal in anterior root taking a course downwards and forwards where it starts from the pulp-chamber. in section, the " handle " of the " dumb-bell " being obliterated. The canals of this anterior root present an exception to the rule that the shallow cap to cover the end of the root. These cro\vns should in colour, size, shape and position, be hfelike in appearance, so that arti- ficiality is incapable of detection under ordinary observation. Certain Points in the Anatomy of the Roots of Teeth. — As the roots of the teeth form the princi2)al and often the only attachment of cro-ivns, it is important to understand thoroughly then- usual arrangement and shape, and also the position, shajje, and direction of their canals. The canal in every root is situated centrally, i. e. axially in the longitudinal direction, and of course follows any curvature the root may take. In all the incisor and canine teeth the canal is coincident with a line drawn from the centre of the incisal edge (or cusp) to the tip of the root. In lower pre- molars the canal is coincident with a line drawn from the tip of the external cusp to the tiji of the root. Shape of Canals in Section. The canals of the six upper front teeth m section are for all practical purposes circular; as also are those of each root of the two -rooted first upper premolars. Tlie vast majority of second upper premolars are single-rooted, and have a single canal, but the possi- bility of encountermg ab- normalities must always be borne in mind. As an example of two separate canals in each second upper premolar occur- ring as an abnormality, observe the photograph (Fig. 630). The canal of the single- rooted second upper jjremolar is oval. Those of the three-rooted upper molars i canals follow the general direction of the roots, are chcular. m that while the general direction of the root. The canals of the loioer incisors, canines, and ' like most lower molar roots, is downwards and backwards, the pulp-canal when starting from the jjulp-chamber at first goes dow^lwards and forwards, then soon changes its direc- tion and follows the direc- tion of the root downwards and backwards (see Fig. 631). Three-rooted uj^per molars have canals tliat Fig. 630.— Foiu- upper premolars^ all Jrom the same patient, sliowing the second deserve .special attention, owing to the difficulty often Fig. 632. — Simple cervical sections of all the upper permanent teetli. as well as the first to be two-rooted. premolars, are oval in section, the long axes of the oval being in the labio-lmgual dkection. Those of the lower molars, having ribbon- shaped pulps, are very fiattened or else dumb- 18 experienced in discovering the buccal canals, or one of them. Tlie largest or palatine canal is generally quite easy to find. The buccal canals are often very difficult. Wlien this 546 is the case tlie anterior buccal will generally be found more anteriorly and more externalhj than was suspected, and the pulp-cbamber should be enlarged with a round burr antero- externally in order to find it. When the posterior buccal is difficult to find it will generally be found by probing more internally than was suspected, i. e. mucli nearer to an Fig. 633. — Simple cervical sections of all the lower permanent teeth. imaginary straight line drawn from the anterior buccal to the palatine canal (see Fig. 63i). Danger of Perforating the Anterior Wall of an Upper Incisor Root. — When enlarging the canal of a front upper tooth, especially the cen- tral upper incisor, the inexperienced operator will be almost certain to imagine the canal as running in a more anterior direction than actually is the case. Hence, while perforation of the wall of the root posteriorly is almost Fio. 634. — Cervical section of first right upper molar showing actual position of canals. The dotted circle shows position one would natiu-ally expect to find posterior buccal canal. rest till the patient's head lies nearly horizontal ujjon it, the face being turned up nearly parallel to the ceilmg. Take a largish smooth round burr, look at the tooth or root by du'ect vision, reflecting the light upon it by a mouth-mirror held in the left hand. With the burr make a shallow depression where the mouth of the canal is supposed to be. This will clean the site and either show up the canal, or if the canal is quite obliterated, will show up the dark spot of secondary dentme that denotes its former site. Supposing the canal to be quite obliterated, take a largish spear "ijointed drill and run it on a short way in the estimated direction of tlie canal, re- membering that the direction will run more posteriorly than it is natural to expect. Remove the drill. Reflect the light from the mouth-mirror quite up this hole and look at the end of it for the dark spot of secondary dentine. Take a smaller spear drill ; place the jjoint of it in the dark spot and driU a little further. With- draw the di'iU ; reflect the light to the top of the hole and again see the position of the dark spot. If it is at the end of the hole all is well. Proceed in this way, frequently changing the di'ill, usmg the smaller and the larger alternately, and always keeping the dark spot at the absolute end of the hole. In this way the centre of the root can be kept until the hole unknown, perforation of the anterior wall is all too common. Therefore, while followhig along this canal with a sharp-pointed drill it is neces- sary to direct the point further back and to hold the handpiece of the engine further forward than would be expected (see Fig. 635). Technique — to follow with a Sharp-pointed Drill the almost {or quite) Obliterated Canal of an Upper Incisor. — Raise tlie operating chair till the patient's head is a little above the operator's when operating. Lower the head- FiG. 635. — Section of upper central incisor showing direction (by dotted hne) in which there is a danger of perforation. is deep enough for any purpose without en- dangering the root by eccentric drilling and possibly by perforation of its wall. The im- portant points in this j)roceedmg are : the position of the head of the patient ; the use of direct vision by the operator ; the reflection of the light to the top of the hole ; the keeping the hole large enough with the larger spear- 547 pointed drill to allow the light to reach the terminal spot. Surface Indications of the Direction of a Buried Root. — Where doubt exists as to the direction of a root it is a useful plan to palpate the surface of the gum over the root with the tip of the finger, gently rubbuig the gum laterally. In this way some indication, perhaps a strong indication, of the position and length of the root ^\ill be given by tlie feeling of an / \ Fig. 636. — Shows roots of central incisors symmetrically diverging. eminence on the surface, wliich corresponds to it exactly. Agahi, if one is dealmg ^\dth a root of which the fellow tooth on the opposite side of the mouth is mtact (and the du'ection of the root obvious), a clue will often be given to the direction of the root in question, as fellow teeth are generally placed symmetrically in the mouth. Again, when a tooth has been extracted Fig. 637. — Shows second upper molar root tilted towards a space made by extraction. some years previously near to a root that it is desired to crown, the coronal end of the root will often have acquired a tilt towards the space from which its neighbour was extracted, and the knowledge of this fact, together \\ith palpation of the gum over the root, will often give a clear idea of its direction. When the canal is not cjuite obliterated, but so nearly that the finest Morey drills « ill not follow it, a passage may be forced as a rule by the finest Beutelroc drill (see Fig. 638), or Kerr drill ; or by a straight Donaldson \\ ith the point sharpened to a root-shajie, used by twistmg between the finger and thumb and at the same time forcing Fig. 638. — Beutelroo's root -canal instruments. {Dental Manufacturing Co., Ltd.) upwards. This must be done \\ith a sensitive touch, and when the Beutelroc, Kerr, or Donald- son has reached a short distance further u^j the canal, it should be followed to that distance II Fig. 639. — I. Nomenclature of parts of root prepared for crowning (in section), (a) End of root-hole; (6) Root-hole; (c) Sides of root-end; (d) Labio- cervical edge ; (e) Linguo-cervical edge ; (/) Mouth of root-hole ; (g) Root-end, root-face, or coronal end of root. II. Root-face. by Morey cli-Uls, and so on, till the furthest pouit is reached. N. S. Jenkins says that to i^erf orate a root (meanmg laterally) is a great and inexcusable blunder, and the wTiter agrees with him. 548 Preparing a Root for Crowning. — As in filling, so in crowning, all carious dentine must be removed from the root. Even slightly carious dentine is always a source of weakness, tending to renewed caries and fracture. In the further prejjaration of the root a guiding principle is that as much of the sound substance should be conserved as jiossible, because the greater the bulk of root-substance, the easier it is to secure a fu'm attachment to it, and the less will be the tendency of the root to split. Other principles, however, conflict to some extent with this, and the extent to which sound dentine should be removed will be for the operator to decide. Thus, (a) great obliquity Fig. 040. — Nomenclature of a diaphragm and pin crown (" pivot " crown) (in section), (a) " Tip " of post; (b) Post or dowel; (f) Diaphragm, radical surface; (d) Coronal end of post; (c) " Face '" of porcelain facing; (/) Pins of porcelain facing; (g) Lingual contouring; (/() Backing; (J) "Tip" of porcelain tooth. of the root -face is an evil, and therefore, if one side of the root-face is deeply invaded by caries or fracture, it will be necessary to cut away the opposite side to a considerable extent to produce an apjjroximate balance and prevent undue obliquity (see Fig. 642) ; (6) to produce an mvisible joint between crown and root on the labial aspect requires that the root be cut down till the labial edge is overlapped by the "free" edge of the gum (see Fig. 643) ; (c) where it is required to cap the end of the root, the part of it that is to be enclosed by the cap must have its sides demided of projecting enamel, and further reduced if necessary to produce parallelism of those sides, or even trimmed still further so that the root-end is slightly coned in a direction opposite to the natural taj^er of the root ; {d) where a porcelain crowai is required, the greater Fig. G41. — Nomenclature of a "removable" porce- lain crown and of its metal fixing with cap (in section), (o) Post or dowel; (6) "Inside" or radical siu'face of cap ; (c) Band of cap ; (d) dia- phragm of cap; (e) Coronal surface or "top" of cap; (/) Tenon; (g) Base or radical surface of crown ; {h) Mortise. Fig. 642. — Section of tooth (below dotted line) to be removed to prevent great obliquity of root. If a cap is to be used remove to b. If no cap remove to a. Lm^uaL. Lahial. Fig. 643. — Labial edge of root cut down so as to be overlapped by free edge of gum ; lingual edge not so much. the bulk of solid porcelain, the better is it for the strength of the porcelam, and, therefore, the root must be cut do^vii till a sufficiently solid bidk of porcelain is capable of being accommodated. 549 Principles Concerned in Drilling the Dowel- hole. — 111 most crowning operations it is re- quii'ed to fix a metal dowel or post into the root or roots, and in drilling the hole for this the following principles must be kept in view — (1) To foUow accurately the canal of the root as this is the guide to its central axis. (2) To reach almost, but not quite, to the tip of the root, or so far as is possible to drill along the central axis in a root that is curved or crooked. (3) To remove the smallest possible amount of tooth substance compatible with greatest strength of combined root and dowel. This implies that the hole must be finished to a gentle taper correspond- ing roughly to the taper of the root itself. Techyiique of Drilling the Dowel-hole. — It is assumed that the canal has been j'roperly cleansed and dismfected. Proceed to estimate the length of the root by probing to the end if possible with a smooth Donaldson bristle. A small disc of paper or rubber-dam may be impaled upon the bristle and the bristle pushed through it into the canal, an index of length thus being provided (see Fig. 619). Open the mouth of the canal if necessary with a bud-shaped burr (see Fig. 644) or with a medium-sized Morey drill. Then gently drill along the canal with a graduated series of Morey d details of procedure are all directed towards ensurmg proper clearance of the drills, and the prevention of jammhig, and also the provision of a hole wide enough throughout the greater part of its length to facilitate the removal of a broken portion should breakage of the instru- ment unfortunately occur. Great care should be taken only to use drills that are sharp, and free from rust and other blemishes. (Li purchasing Morey drills always see that their weakest part is in the centre of the flexible shank or nearer the mandrel, and not near the " head ", so that in case of fracture a sufficient length of shank will be attached to the head to allow of (1 u Fig. 644. — Bakhvin's Right-angle Canal Burr. For funnelling out mouths of canals. The shank is long to reach deep cavities. {Dental manufacturing Co., Ltd.) driUs, using a small one as the pilot and fre- quently changing this for a larger one, so that the canal is followed in short stages, first by the smallest drill, then by the larger sizes. During the whole of this drilling let the dental engine be run at a moderately high speed, but let the forward pressure be slight and sensitive, so that the drill is allowed to cut its way easily, and not be jammed or broken by being forced faster than it is able to go. Also let the forward pressure be uitermittent, alternating with a slight withdrawal, a sort of "touch-and-go" action being in fact used. Frequently clear the leaves of the drills and clean them, so that they are not clogged ^\ith their own debris. These Fig. 645. — Taper Drill, or Reamer, for shaping the hole to the exact size or shape of the post. easy withdrawal.) Thus guarded against, a troublesome breakage can almost always be avoided. After enlarging the canal with moderate- sized Moreys to as near the tip of the root as is considered desirable, still further enlarge the hole at its coronal end only with a large Morey, so as to leave the hole with an incipient taper. Now cut the whole length of the hole to a definite taper with a special smooth-sided reamer made to the exact size of the dowel that is to be used (see Fig. 645) . This comijletes the prepara- tion of the hole for the dowel. If it is desued to roughen the inside of the hole for greater attach- ment of the cement, this is better clone just before fixing the crown. Standardized taper reamers, and taper dowels to fit the holes made by the reamers, should be kept in stock ready for use. It is important that the posts should not be shaky in their holes, and should not fail to reach the end of their holes, but should be an accurate fit throughout their ivhole length. On Amputating the Crown of a Tooth. — It is necessarj' to remove the natural crown, or what remains of it, by amputation, when a porcelain or porcelain-faced crown is to be fitted. Never use " excising " forceps for this pur- pose. The use of this brutal instrument tends to cause pain and shock to the patient ; it also frequently causes a false line of fracture, and is often followed by traumatic periodontitis. 550 Technique. — Firstly, cut through the enamel on the lingual side with a knife-edge carbo- rundum stone or diamond startmg-point near the gum (see Fig. 646). Then take a trochar- drill, dead-hard and pointed as a three -sided 5 sa*1W Fig. 040. — Diamond Starting Point. (Dental Manufacturing Co., Ltd.) pyramid; from the labial side, with this drill, cut a series of holes through the enamel at the cervix of the tooth along the gmgival margui. George Pedley's trochar-i^ointed drill (see Fig. 647) is suitable for the purpose, or a drill serving ^ Fig. 647. — Pedley's Triangular or Trocar Drills. The form of point prevents tlie drill running about when commencing to bore, even on a hard and sloping surface of enamel. (Messrs. Claudius Ash, Sons ct Co., Ltd.) the same end may be readily extemporized by grinding the point of an old cross-cut fis.sure-burr to a three-sided pjTamid, and then hardening it dead-hard. Take a small spear-head ch'iU (see Fig. 648), and centreing it in the holes through Fio. 648.- -Spcar-head Drill, for drilling holes through the tooth. the enamel, drill through the tooth a series of parallel tumiels (see Fig. 649). Care must be taken to incline the drill, so that the gum will not be injured when the drill emerges on the lingual side, as the gum is nearer the incisal edge lingually than labially (see Fig. 650). Then take a sharp, small, cross-cut fissure- burr (No. 2 or 3), run it rapidly, pass it into one of the holes, and with lateral pressure and a sawing motion cut away the intervenmg Fig. 649. — Broken-down central incisor, showing series of drill holes made on labial side. dentine, and so jom up the holes (see Fig. 651). Wlien the crown is nearly detached by these means, take a stiff straight enamel-chLsel, and insert it into the slot, and lever off the crown. This last should be done only when but Fig. 650. — Showing obliquity of gum level, and obliquity of drill necessary to avoid wounding gum on Ungual side. slight force is required. In this way all shock is avoided, and the section made to follow the actual line intended. The trimming of the root-face is then pro- ceeded with, and is best done with steel root- Fig. 651. — Cross-cut Fissure-burr for joining up the holes. facers and carborundum wheels. The best root-facers are those of Raulie (see Fig. 652), which have a wheel-shape with a fine Ime of teeth running spirally round the working sur- face. After the steel tool, the edges, especially 551 the labial edge, should be finished very smooth with a carborundum wheel, and the gum must not be injured (see Fig. 653). The best general shape for the root-face is slightly domed or obtusely roof-shaped, with tlie labial edge just overhung by the "free" edge of the gum (see Fig. 654). This shape allows maximum Uu Fig. 653. — C'arboriindimi Stump Wheels. (Dental Manujacturing Co., Ltd.) crown should always be in mind in shaping the root-face. Great obliquity of root-face must be guarded against, as a great obliquity gives a less firm seat for a crowii than one that is roughly at right angles to the dowel. Labi at side Palatal side Fig. 652. — RaiUie's Root-facers. length of dowel, but frequently the root-face wiU be found seriously encroached upon by fracture or caries, and this will prevent an ideal shape beuig arrived at, and will largely determine what the resulting shape may be. The prevention of rotation of the finished surface, or surfaces, of one of them from the occlusal surface to the gum, the best way by far is by use of the diamond disc in the dental engine (see Fig. 655). Technique. — The liandijiece hokUng the dia- mond disc must be held firmly in the fingers as in holding a pen, with the uidex finger and the middle finger firmly supporting each other behind, and the thumb in front. The risk to be guarded against is that of the disc running away from its icork and injming the soft tissues of the mouth. The disc should be wetted with a solution of soap or weak "lysoform", and sprinkled with fine carborundum powder to increase its cutting power. The engine should be run moderately fast, and the disc allowed to cut its way easily and without hurry or forcing. A safe-sided disc may be used to guard against shaving off part of the contiguous surface of the next tooth, and as an extra precaution against this an Ivory's No. 2 steel- band matrix can be put around it. As a pre- caution against wounding the tongue, a Claude Rogers shield-clamp may be applied to the tooth behind the one being operated on, and the " Toomey-safety-device " should be used to guard the disc. In using the diamond disc for cuttmg away the enamel of an approximal surface that is in contact with the neighbouring tooth, there is the risk of the disc jamming momentarily and Fig.' 654. — Shows root-face slightly domed or roof- shaped and cut down slightly under free edge of gimi on labial side. Cutting a Space between Contiguous Teeth. Instead of entirely excising all that remains of the natural crown, it may be desired to conserve as much of it as possible and to en- close it within a hollow metal shell. This particularly ai^plies to molars, as will be de- scribed later in dealing with the gold shell crown. When the teeth are in contact with each other, and it is desired to cut down the interstitial Fig. 655. — Diamond Discs. [Dental Manufacturing Co., Ltd.) then kicking away from its work and badly damaging the soft tissues of the mouth. Suf- ficient practice, however, will soon give confidence to the ojoerator and security to the patient, enabling the hardest enamel to be cut down between the closest of teeth without fear of accident. As the disc rapidly revolves, the operator should feel that it is cutting its way really easily and freely and is not behig forced ; a slight variation of direction should frequently be given to the disc to ensure the division being cut wider than the thickness of the disc, and the disc frequently \\ithdra\\ai altogether for dipping in the lubricant and sj>rinkling with carborundum grauis. Jammmg will thus be guarded against. In case of a jam being felt the disc must at once be slightly removed from its work, and the engine stopped at the same instant. If the electric engine is 552 being used, and the operator is standing, the whole weight of the operator's body must be resting on the foot that is not operating the switch, so that the operator will be in the most advantageous position for immediately releasing the balance of the switch without altering the body. If the operator is seated, the switch must be placed in such a position on the floor that it can be instantly released without dis- turbing the balance of the body. Flat diamond discs are the most generally useful, and next to these, those forming a flattened hollow cone. Frequent dipping of the disc in soapy solution and sprinkUng with fine carborundum grains will be found greatly to increase the speed and facility with which C D Fig. 656. A. Disc-dowel for fixing gutta-percha on end of root. B. Tinned tack for same purpose. C. Disc-dowel roughly fitted to root and padded with gutta-percha. D. Tinned tack similarly padded. even the diamond disc will do its work, and this is, if possible, more forcibly true for carborun- dum discs. The unpractised hand, in order to avoid accidents, should adjust the engine-cord slack, so that its degree of tension will only suffice to rotate the disc when workmg easily and freely, and will cease to hold on the slightest suspicion of a jam. Exposing a Buried Root. — Wlien a root to be crowned is buried under the gum it must first be exjjosed by prelimmary treatment, which may occupy several days. Technique. — After cleansing and disinfect- ing the root-canal enlarge it by means of a graduated series of Morey drills followed by the taper drill or reamer. Then take a tem- porary brass or German silver disc -do \\ el, a stock of which should be made in the workroom and kept ready for use. Roughly fit this to the supposed sliape of the root-end and length of the hole. Apply a softened wad of gutta- percha to the dowel and disc, and tightly jam it into the canal, and so cause the gutta-percha to fit itself to the root -face and press on the gum all round (see Fig. 656). A tinned tack can be used with gutta-jaercha instead of the disc-dowel, and will generally require its spike to be reduced laterally with a file and its point blunted. This must be left m for a A B Fig. 657. A. Lateral perforation caused by parallel-sided drill. B. Lateral perforation avoided by using taper drill. day or so, and then removed, and the process repeated if necessary, and perhaps the root may be partially trimmed after each applica- tion, but the application must be persisted in vintil the root-end is clearly exposed in its entirety. Fig. 658. — (a) Root reamed to correct taper ; (b) Post of correct taper (magnified) ; (c) Post of incorrect taper and objectionable sharpness; (d) Post of too abrupt a taper, affording little retention. Where the root has been exposed in this way, the gum has a great tendency to roll quickly over the edges again when the wad is removed ; therefore, until the crown is fixed, the wad must be refixed at the end of each sitting, and the patient never allowed to leave the chair without it. Fig. 659. — Gauge made of ivory for testing taper when making posts. The test hole through the laminae of the gauge is drilled with the reamer that is used for the root. Even after amputation of a natural crown where the root is ground do^v^l ever so slightly beyond the free edge of the gum, it is best to fix a wad of gutta-percha in this way to be worn during the intervals between the sittings, so great is the tendency of the gum to roll over the edges of a root when allowed any opportunity of doing so. 553 1 Fig. 660. Taper Reamer. On Posts or Dowels 0)1 the Material of which Iknvels should be made. — It is of great importance that the material used for dowels should be the strongest and sliffest that can be obtained. It must also be non-corrosible. Tlie best materials at present in use are platinized gold and iridio-plati- num. The strength of German silver and dental alloy is far below these. Every jjost must be fixed axially in its own particular root to avoid weakening and risk of perforation. Wlien a crown is to rely mainly on posts for its attach- ment every root should have its post — single - rooted teeth, one post ; multi-rooted teeth, a post for each root. CMracter of Post or Doivels.— The character of a post or dowel should be such as to afford the strongest possible attach- ment for a crown consistently «ith the root retainuig its maximum of strength. It is useless to provide a dowel so large that the root is greatly weakened for its accommoda- tion . What is ^^-anted is maxi- mum strength in combined root and dowel. The strength of the attachment of the dowel to the root largelj^ de- pends upon its length ; and the longer the post, not only the stronger will it be, but the less Hkely to split the root under strain. Therefore posts should be as long as possible, short of the actual tip of the root. Strength should be at its maximum at the part that has to bear the maximum strain, i. e. at the coronal end. The shape should be such as will necessitate sacrificing the min- imum amount of tooth sub- stance ; therefore, the bulk of the post should not be greater at any part tlian is necessary for maximum strength. No^\■, the strain that a post will and Wire Hokler! "chiefly be Called upon to resist for holding wire is a shearing strain caused by while being filed leverage of the crown upon to a taper. ^^j^g pgg^ under lateral strain, and this leverage is exerted most strongly at the end of the post nearest the crown, and least at the tip. The shape of post that entirely fulfils 18 * Fig. OUl. — Uroach {Dental Manufac luring Co., Ltd.) all these requirements is a shape roughly corre- sponding to the root itself, i. e. a gentle taper and a taper that fits the hole. The hole that is requu-ed is a taper hole, as this sacrifices the mhiimum amount of root-substance and runs the least risk of perforating the root later- ally near the apex (see Fig. 657). A post that fits its hole will hold more tightly than one that does not, and is obviously stronger; and for these reasons j)osts should be made accurately to fit the whole length of the taper hole. Tlie post must resist withdra^^'al, when cemented, as strongly as possible ; therefore the taper must be very gradual and not abrupt, and the rough file-cut surface should be left upon it. The pomt should be blunt and rounded and not sharply acute (see Fig. 658) . The method of correctly making the tajser of the posts LS by filing them to fit the gauge (see Fig. 659) in which the hole is made by the drill to be used on the patient. The taper post has, more- over, great advantages tech- mcally, as when kept in stock of standard taper, made to fit the hole produced by the reamer (also of standard taper) (see Fig. 660), it acquires an immediate and automatic fit when inserted in either long or short holes, and its thick- ness at the line of greatest ^ Fig. G62. — Shownig two taper Fig. 663. — Special posts firmly fixed together, Pliers for manipu- wluch can be inserted or with- lating posts or drawn from their taper holes, dowels, though shghtly divergent. shearing strain increases ua proportion to its length. I Consider the deskability of the posts being taper m the case of a crown that requires two posts slightly divergmg from one another. This 554 is the condition that generally obtains in the first upper premolar (one of the crowns most frequently in demand). Here the taper will often allow the two posts, when fixed together, to be withdrawn and reinserted without the divergence causmg them to bmd m their holes, as would necessarily be the case if the posts were cylmdrical (see Fig. 662). Grist le between the band and the root at any j)oint. Wlien fitted to this degree of perfection, the next pro- ceeding is to "contour "it, ?'. e. to round its buccal and lingual sides, and to bulge its medial and distal sides so Fig. 695. — Serrated that they Can form a natural Pluggers for press- contact with adjoining teeth, ing band to buccal Contouring the Band. or liiigual wall of The necessary rounding and / r^ °° , ' , ^ , bulging of the sides to "S CoTluiT' P™d"ce a natural contour can be done by the judicious use of contouring pliers (see Fig. 699), but great care must be taken not to alter its sliape or size at the cervical portion. Occlusion : Taking the " Bite ".—Try the band on the root and adjust it so that it does not interfere with the " bite ". Now take the " bite ". First nearly fill up the band inside with pink wax. Then place either a small quantity of plaster of Paris or of composition on the top and let the patient close the teeth tightly home. The mechanic will now cast a model from this, and a " bite ", either on a crowii articulator or by making the simple plaster articulation. After separating the " bite " from the model, cover the forms 1^ ■'■ Fig. 696.- — (a) Boxwood tool for "rocking" snaall bands on to roots; (6) Large boxwood " rocker". {Dental Manujacturing Co., Ltd.) of the cusps that will occlude with the crown with tin foil stuck with wax. Rhodes' s Crown Tray. — Instead of taking the " bite " in the simple way mentioned above, a better way is to use a Rhodes 's crown tray (see Fig. 673), and with it secure an impres- sion of all the adjacent teeth with band in situ and of the occluding teeth at one and the same time by the patient's ovm act of 567 occlusion, but before doing this fill the band almost completely when in situ in the mouth with wax, to prevent the impression material entering it much. On removing the tray from the mouth the band will be found still on the root. Therefore, detach it from the Fig. 697. — Peeso's so-called " Stretching " and Contouring Pliers. (Dental Mamifacturing Co., Ltd.) root and carefully replace it in its bed in the impression and fix it there by meltmg wax inside before casting the plaster model. Suf- ficient wax in a thin film should be melted inside to allow the band to be easUy removed from the model \\hen desired. (a) Supplying the Top by Striking up Plate. Strike up a top to form the occlusal surface out of Xo. 6, 7, or 8 gold plate, 22-carat, usmg a zmc die (see Fig. 687) made from a natural tooth of suitable size and shape, and a flat piece of lead as a "counter". Or the striking up may be done by striking a button of lead into a steel or gun-metal die plate (see Fig. 700) ; or by striking with a zinc cast of the actual tooth being crowned and a lead counter, Fig. 698. — Band embedded in composition, which is cut away between two marks where it is desired to expand the band. this last being the method to adopt when the masticating surface or much of it is preserved, and it is desired not to cut it dowii. The need for this arises when, owing to the tooth beino- still alive and sensitive, or the patient being easily tired or nervous, it is desired to do a minimum of the grmding down that ^^-ould otherwise be necessary, and at tlie same time Fig. 699. — Johnson's Contouring Pliers. (Dental JManiifacturing Co., Ltd.) to prevent the bite from being raised by the additional thickness of metal. Adjust the top, when struck, to the edge of the band and to the bite, and then solder it on with gold solder, holdmg the parts together meanwhile either with bindmg wire or a soldering clamp. Reinforce the cusps by melting gold solder into the inside of them. {b) By the Gold Pressure-casting Process (see 568 Fig. 702) — alternative to (a). — Fill the band with gold-casting investment. Build up the rest of the form. i. e. the occlusal surface, with the same, {5r ff^ #* *»- ^>' K % % C, 5/ 7, C^ C^ ^ ^ ff p ^. 7^ a C^ ^ ^ #•*♦#• ^ #^ *^ /*■ 6f<«- 1^ m y::^ ♦*? tM? *?!*' C" CT f/, :r ^ '- c^ iC^ s; JT J? ST ^ 5? tr-c*. C^ ^ r. «^ .C t e c C cr ;? * c ■«. •• ir •f V wr * •> w . A «» ^ #> <» ^ 4» Jk #•> « IT H*^ W V «• « « «^ w <• • W IT V w <•'«-- ♦ V■5»l^ mi W Z' ^ m ererr^re f. ?i e e e e e e «■ « » * » ,. ,» f'c'eff'r. e*f ■ c? ffr ^ ct C 5^ r^ fTn 0* ^m ^m 0* »*.i»' Vin V^F- *»!^' \it# '- "■ Fio. 700. — Ajax Die-plate. {Dental Manufacturing Co but making it short of the bite by the thickness it is desired the top sliall be. Cover this with Fig. 701. — Contouring Pliers, for contoiu-ing occlusal surfaces. {Messrs. Claudius Ash, Sons ds Co., Lid.) casting-wax and articulate the wax to the bite. Attach a sprue to some part of this wa.x and pressure-cast it either m Solbrig's pliers or one of the numerous machines devised for pressure- casting. In this way the top is cast direct on to the band, and it can be managed at the same time to thicken the band on the outside to any desired extent and to improve the lateral contours by added gold. J. E. Dunwoody, PhUa- delj)liia (10), recommends makmg the occlusal portion in the following way : After the band is made, j)ut it on the tooth. Place in it a small amount of modelling composition. Let the patient close the teeth upon it. Re- move band and separate the composition from the band. Carve the composition to fit the opposing teeth and to fit the band. Remove all com- position from uaside. Lay the composition flat down on a glass slab. Pour over it two- thirds of plaster of Paris and one-third of medium marble dust. Lito the mould thus made, melt gold without borax and produce pressure on it with a piece of charcoal to force ' ^^ Ltd.) (3) (4) Fig. 702. — (1) Band filled with investing material, with tinfoil inserted between the investing material and the counterpart. (2) The band with masticating surface in wax, and sprue-wire attached with sticky wax. (3) The band with the masticating surface in wax is shown placed upon the cone and sur- rounded by the cylinder. (4) Section of the cyUnder filled with embedding material, with the cone and the metal point removed, (a) Plaster of Paris ; (6) Tinfoil; (c) Investing material; {d) Wax; (e) Sticky wax ; (/) Sprue-wire ; (S. White Denial Manulacturing Co.) the attempt is made to secure a perfect fit — diffi- culties that can only be surmounted by unduly sacrificing valuable tooth substance. They -can be fitted to the root direct in the mouth or to a model in the workroom. In either case the sharp edges of the platinum pin should first Ije removed with a file to lessen the necessity for making such a very large hole in the root. Fig. 724. — Lugan Crown. Shows the unsnitabihty of a Logan Crown for a Ijifid root. The pin of the Logan has been spht and the two halves have been bent away from each otlier. To accommodate this an excessive amount of root-substance would have to be removed, and the root lamentably weakened. (- l' .' J C.ASM & SONS.L? I'll:. ,.:;:_;. I Hittnn' ( Mh\ h m-l nnii.'iil-. (Messrs. Claudius Ash, Sons da Co., Ltd.) over that. To the model thus obtained, make a restitution of the original contour of the root outside the cap where necessary with cast gold, so that the \\ork may be finished flush with the root. The lingual contouring with gold and the attachment of the porcelain face can all be made by one and the same operation of casting. J. Leon Williams' Modification of the Buttner System (see Fig. 735). J. Leon Williams has desired to retain the advantages of the Biittner system of a ready made circular cap and root cut mechanically to fit it, and at the same time to eli- minate the disad- vantages of the want of circular- ity of the root- face, by sinking the cap well with- in the edges of the root, and combining it with a thin diaphragm over the whole root-face. He has also provided a taper j)in and a taper root-hole. These principles are all good, but as supplied the pin is too thin, too abruptly tapered, too sharply pointed, and altogether too small. The Partial Cap, Pin, and Porcelain Crown. — Wlien it is desired to get some of the advantages of a cap without the disadvantages of its showing at aU on the labial aspect, a partial cap is used by some operators, notably William Hern. The proper way to make a partial cap is first to make a complete cap and then to cut away as much as is desired to prevent sliowing. Some operators make a jJartial caj3 by bend- ing a narrow strip of gold t(i a model of the tooth, jilacing it in position on the lingual aspect of the edge of the root, and soldering it to the diaphragm, but this method is not so accurate as the preceding, and there- fore not recommended. If a partial cap is justified at all, it must fit very perfectly indeed. C. A.' Baker (2) recommends a diaphragm 587 with a partial cap, and prepares the root-face in a slightly different maimer from usual, as follows : Prej)are the root as if for a Richmond crown. Notch (i. e. cut a step in) the anterior part of the root-face about half-way anterior to the root-canal opening with a sharp inverted cone burr. Solder a diaphragm of gold, 24-carat 32 gauge, to an iridio-platinum post. Place on the root and burnish first to the notched surface. Remove and stiifen that part with solder. Split the surplus portion covering the posterior surface so as to allow the surj)lus jJortion to be turned up and burnished to the lingual wall of the root, thus forming a partial band. Thoroughly burnish to root, remove and invest in whitening. Flow solder to stiffen it and to reinforce the portion that forms the partial band. If the porcelain is to be fused on it, use platinum for the cap. i 1 1 ' 1 Vl V v) Fig. 735. — Leon Williams' Porcelain-faced Crown. (Dental Mmnikiclurihrj Co., Ltd.) The "Pivot" Tooth, or Diaphragm and Pin Porcelain Crown. — The old method of making and hxing a "' jjivot " tooth is no longer prac- tised. It consisted of making a hole in the root with a twist-drill to fit pin-size wire, and fixing upon a piece of plam pin-size wire a diaphragm and a tooth. This " pivot " tooth then had its pivot jagged with a penknife, and had floss silk wrapped round the pivot. The pivot was then dipped in copal or mastic varnish, and was wxiggled and jammed home. The modern improvements consist in using a taper pin of much greater strain-resistmg power than the pin-size wire, and m usmg oxy- phosphate cement as the medium of fixation in the root. A large number of roots present themselves for crowning that are too much decayed below the gum to warrant their being fitted with a cap. The diaphragm and pin crown is then indicated. Technique; Shaping the Boot. — Cut down the root to form a face on which the crown can rest steadily. Any great obliquity of the root-face is objectionable as dimmishing steadiness. Make the taper hole for the pin (described on p. 549). Method I. Making to a Model. — Take an impression in t\\o parts as described on p. 554. Pack with amalgam or Harvard cement, and Fig. 736. — " Pivot "Crown with pin secured in po-sition and with the wax back modelled to shape. Fig. 737. — The same with sprue-wire inserted in the wax. cast model and bite. Make the post of iridio- platuium or platinized gold and of as large a cross-section as the hole in the root will allow. Fit a diaphragm of thin soft platinum or pure gold to the root-face and solder it in proj)er position to the post. Burnish the diapliragm into a perfect fit witli the root -face. Fit a backed flat tooth, and solder together, flushing up a lingual contour with the solder. An alternative to this is to dispense with the Fig. 738. — The same with sprue-wire inserted in centre of cone. Fig. 739. — The same with metal cylinder placed over cone. backmg, and pressure-cast the diaphragm and backing direct on to the porcelain tooth and post, to form the lingual contour (see Figs. 736, 737, 738, 739). Metliod II. Making to the Mouth without a Model. — -Prepare the root as m Method I. Make a taper pin as above of as large a section as possible to fit the hole in the root. Bend a thin piece of soft sheet platmum y^^ of an inch m thickness roughly to fit the root-face. Prick a hole through it opposite the hole in the root. Push the taper pin 588 through it uj) to its place in the root ; this will drive the diaphragm close to the root round the hole, and will attach the diaphragm to the post Fig. 741. — SpringTweezers for same purpose. Fig. 740.— Tongs for hold- (S. S. White Dental mg pm while soldering. Manufacturing Co.] (S. S. White Dental Manufacturing Co.) firmly enough to allow both to be removed together and soldered without investment. Solder with a very small bit of solder in a Bunsen flame. Place again in position on the root, and j)ress the diaf)hragm to a fine fit on the root- face by means of serrated foot- plugger and serrated sjionge-gold packer (see Fig. 742). Trim any surplus edges of the diaphragm with scissors. Select a f)Iate tooth, back it, and grind it to fit the root in the mouth. Attach it with sticky wax to the diaphragm and pin. Por this pur- pose it will generally be found Fio. 743. — Le necessary to reduce the labial side of the projecting pin by filmg, and to bend the remainder backwards (Imgually), and to notch the back of the tooth and the backing in order to get the tooth sufficiently 1 far back. When correctly fitted and waxed ! together, remove from the mouth, invest in the usual way, and solder. By this method a crown can be produced at one sitting. These crowns are generally best fixed with gutta-percha, as afi'ording a better protection agamst further caries in the root. William Hern recommends soldering a tag of metal to the lingual edge of the diaphragm, and allowing it to project over the edge of the root, representing what may be called about a ^ Fig. 742. — Serrated Pluggers for swaging diaphragm to root-face. (Dental Mamifacturing Co., Ltd.) one-third cap, the object being to resist the bite that normally, in the case of the six upper front teeth, forces outwards as well as upwards. His method of fixing these crowns is : first to place a thin disc of white base -plate gutta-percha on the diaphragm, and force this, warmed, into place on the root ; then, to remove the work from the mouth and cool the adherent gutta- percha ; and then, with the gutta-percha still adherent to the crown, fix with cement. Building-up the Lingual Contour with Porcelain Body instead of with Gold. — A more translucent crown is produced by fusing porcelain between the back of the porcelain face and the diaphragm, using no metal backing or only a verv small one. Cron's Nitrous Oxide Blowpipe, for use with platinum. (Denial Mamifacturing Co., Ltd.) but in any case soldering the pins of the facing to the post previously and using no metal but platinum and platmum solder. Technique. — Proceed as before, making a 589 diaphragm and a post, but taking care that no metal is used except platinum soldered with platinum solder or pure gold. Either solder the pins of the tooth firmly to the post, or back the tooth with the smallest possible backing, and solder that to the post. Then solder a wire round the edge of the diaphragm on the coronal side, and several short lengths of wire across. Build up the contour at the back of the tooth entirely with porcelam body, and fuse it in the furnace. The porcelain wiU attach itself, when fused, very strongly to the pre- existing porcelain, and the wires will cause it to be attached to the diaphragm ; the actual adhesion of porcelain to platinum is a negligi- ble quantity. Partly this fact, and partly to increase the translucency of the crown, are the reasons why the metal backing is either dispensed with or reduced to the smallest dimensions. George Northcroft recommends crowns for anterior teeth made by fusing up the contour at the back with porcelain, and says " they are so strong that even an edge-to-edge bite will not smash them ". The All-Porcelain Cast-Gold Crown, when made with detachable porcelain crown to the mouth without a model. Technique. — Prepare the root as before, aiming at a domed root-face. Then countersink the orifice of the root-hole, when there is plenty of root-substance to deal with ; also cut a transverse groove in the dentine of the root-face, not neces- sarily extending to the periphery of the root, half-way between the root-hole and the lingual edge. Connect this groove with the orifice of the root-hole by means of another groove at right angles with it. Fit a taper post (iridio-platinum or platinized gold), allowing it to project about liy inch to form the tenon. Fit the crown closely to the root at the labial edge, leaving a distinct space behind of, say, Jg inch. Soap-solution the inside of the canal and root-face. Place softened casting wax on the tajjer post. Soap-solution the ba.se and mortise of the crown. Use the crown as a pliuiger and force the post nearly home on the root with it. Remove all from the mouth and trim off the excess of wax. Replace in the mouth and force the crown quite into place. Burnish the wax with a smooth burnisher to make it accurately flush with the edges of the root-face. Cool ; remove the crown only from the mouth. Clear away enough casting wax from the tenon of the post to get a good grip of it with cutting pliers. Force the crown on again. Remove it. Seize the tenon with pliers, and remove post and wax from the root. Replace the crown on the post and wax. Melt the edge of the wax to the edge of the porcelain crown, takmg care not to interfere with the fit of the wax to the root-face. Remove the porcelam. Attach sprue to the lingual part of the wax, invest the whole, and cast with gold. Attach the porcelam with oxy-phosphate. The counter-sinking of the root-face is to give a secure seating for the crown ; the grooving is to increase the strength of the attachment of the crown to the root and to prevent rotation, and bemg situated behind the line of greatest weakness of the root, it does not increase the liability to fracture. ^ Another way is to fill the mortise in the porcelam crown with an Alexander gold inlay, and to pressure-cast direct on to tlie porcelam. Porcelain-faced Cast-Gold Crown. — This is pro- duced m a manner similar to the preceding, but usmg an ordinary flat plate tooth instead of a dowel crowri. The casting should be done direct to the porcelain, and if the wax is not allowed to overlap the edges of the porcelain, and the work is sufficiently heated up in the investment before forcing in the molten gold, no harm will result. F. E. Roach (15) assumes that it is necessary to remove the porcelain tooth from the wax and the rest of the work before casting, pre- sumably because he fears fracture, and recom- mends puUuig the porcelain flat tooth away from the casting-wax by means of a piece of sticky wax attached to the facing. Carbon points are then inserted into the pin-holes in the wax before investing and casting. He secures the facing to the backing by one of two means. If the backing is thick enough to cover the full length of pin, the facing can be securely attached in the following manner : With a twist-drill two or three sizes larger than pin-holes, drill out the carbon points, thus making the holes slightly larger than the pins, to accommodate a sort of head that is made on the ends of the pins by pinching with pliers. Then carefully fill the holes with cement, and with the entire back of the facing covered with cement press it into place. In case of a thin backing, the holes, he says, sliould extend through to the lingual surface and be slightly countersunk. The puis are cut off flush with the surface of the backing, and the facing is secured to the backmg by cementation and rivetmg, which should be done before the cement sets, by embedding the facing in a softened mass of modelling composition with the backing up\iards, and with a small jeweller's hammer riveting the ends of the pins and finishing flush with the lingual surface of the backing. Making to a Model. — All these processes, when no cap is used, can be satisfactorily performed to a model and a bite, made from a good impres- sion of the parts, provided the root-face is repre- sented on the model by an amalgam or fusible metal surface, or by Harvard cement. CHAPTER XXXVI ARTIFICIAL CROWNS {continued) REPLACING PORCELAIN FACINGS When a crown has been fixed with gutta- percha, it can easily be removed by simply {(') (b) tmr U) (fc) Fig. 744. — Replacing a broken ordinary flat tooth with a Steele's facing in the mouth, (a) To replace the broken tooth; (6) Cut off pins and stone the backing to a flat surface; (c) Grind a Steele facing to fit the space ; (d) Flow a very thin layer of wax on the fiat svu-face by means of a hot spatula; (e) Moisten facing and press the wax in its correct relative position ; (/) Slide facing downward off the wax, disclosing a wax impression of slot on the backing ; (g) With drill or handpiece mark location of hole slightly above lower end of the slot as indicated by the wax. Mark another midway to the gingival margin ; {h) Remove wax, lubricate with drop of oil, drill holes to the depth of the shank of drill. Hold drill straight and steady to avoid enlarging holes ; (/) Thread holes with tap after oihng; (j) Slip on facing. If screws are correctly seated, fill hole and slot in facing and cover the back with cement, slide to position, holding it until the cement begins to set ; (t) Where a heavy tip has been used, proceed as above, but leave the tip untouched. Grind a bevel on the facing to correspond with the bevel of the tip. Set the screw nearest the incisal edge farther back from the edge than in ordinary cases, and do not set deeper than required to seat facing against backing. lieating, and the necessity for retaining it in the mouth during repairs will not arise ; but when fixed with cement, it is generally im- possible to remove it without destroying it, and much ingenuity has been expended on the problem of replacmg the porcelain facing without removal of the metal work from the root. The problem has been met on various Imes — By originally constructing the crown with a special removable facing: Steele's, Bloom's; or on metal slides, J. D. Logan's, Rose's. By applying fresh facings when ordinary plate teeth have been iised : ^'arious methods and devices, viz. Ash's facing, Leon Williams' facing ; soft soldering in the mouth (Baldwin) ; use of part of a J. D. Logan slide (Baldwin) ; use of a 590 Fig. 745. — Bloom's Interchangeable Facings. (Dental Maimjacturinij Co., Lid.) jacket crowii to enclose the old back ; Zentner's riveting; Bryant's nvits and screws; Steele's method. Devices Providing for Easy Refacing Incorporated in the Original Construction of the Crown Steele's Facing (see Pig. 744). — The porcelain facing has a longitudinal groove at the back, extending from the radical end to near the tip; this groove is shaped in section like half a dumb- bell. A metal backing is supplied with a ridge upon it, in shape corresponduig with the groove. Tlie porcelain facing slides on to the ridge and when cemented is firmly held. Bloom's Facing (see Fig. 745). — This is similar in principle to Steele's. The difference is that the shape of the groove in the porcelain and ridge on the backing is simf)ly wedge-shaped 591 in section, and the groove in the porcelain is lined with platinum foil. J. D. Logan's Slide (see Fig. 746). — ^\ny ordinary plate-tooth can be made removable by the use of this device. It consists of a gold slide in two pieces, one .sliding within the other. The tooth is backed with the inner member ; and Fig. 746. — Logan's Slide for fixing Removable Porce- lain Facings. (Dental Manufacturing Co., Ltd.) the outer member is soldered to the diaphragm of the crown, or whatever else it is desired to fix it to. The slide is beautifully made of plati- nized gold, and while affording an absolutely Fig. 747. — Rose's Two-part Backing. (F. Rose.) reliable hold for the tooth, is hardly thicker than an ordinary No. 8 backing. Rose's two-part backing (.see Fig. 747) is another device that j)rovides any ordinary plate -tooth with a sliding attachment, and so makes it removable. It is not so suitable for crowns as the J. D. Logan, as it is irregular in surface, and therefore does not lend itself to neat finish. It is also much thicker (16). Devices for Refacing when an Ordinary Plate-tooth has been used in the Original Construction of the Crown Leon Williams' Facing (Dental Manufactur- ing C'omi)any"s, see Fig. 748). — This device has been made by Harry Rose for many years for his own use, and also by Leon Williams. It is a flat tooth in all respects like an ordinary plate-tooth, except that it has no pins ; but has instead of pins two undercut holes at the \ Fig. 748.- ^ ' I w '~ ■ -Leon Williams' Porcelain Facings. (Dental Manujacturing Co., Ltd.) back, where, in a plate-tooth, the pins would be. These holes are large enough for the headed pins to enter. Technique. — When a facing is broken in the mouth, remove all fragments of porcelain, but do not remove the pins. Select a Leon Williams' facing that will suit the case, and that has the holes in similar positions to the pins of the broken facing. Fit the new facing into place and cement it in. The Dental Manufacturing Company supplies pairs of facings, one with pins, and one with Fig. 749. — Ash's Repair Facings. (Messrs. Claudius Asli, Sons & Co., Ltd.) holes, but otherwise exactly alike. The idea is, when making a crown, to procure a pair of facings, using at first the one with pins in the ordinary way, and handing the one with holes to the patient to be kept in case of fracture of the first. Ash's Facing (see Fig. 749). — This is similar to the preceding, except that instead of having two holes to accommodate the two pins, it has an undercut transverse slot into which the pins are received. This slot gives greater latitude in selection of a facing, owing to its being able to accommodate puis of diverse widths apart. 592 Technique. — Same as the preceding. Long-pin Facings (S. S. White's, see Fig. 751) (19). — These can be used for replacing a crowii inside of the holes with a cross-cut fissure-burr. Cement the facing into place. Bryant's Crown or Bridge .Repair Process (see ^;^ Fig. 750. — Ash's Dowel Crowns, premolars. {Messrs. Claudius Ash, Sons <& Co., Ltd.) in the mouth when there is a sufficient body of metal to enclose the whole length of the pin. Technique. — Remove all fragments of broken Fig. 751. — S. S. White's Long-pin Facings. {S. S. White Dental Manufacturing Co. Fig. 752). — Bryant's set consists of two screw- cutting dies (Nos. 1 and 2), a reamer (No. 3), a nut-driver (a choice of two forms, Nos. 4 and 4a), and two gold nuts (No. 5) ; Nos. 1, 2, and 4 are manipulated bet\\'een the tliumb and finger ; Nos. 3 and 4.\ with the right-angle hand-piece on the engine. The larger of the two dies. No. 1, is for starting the thread on the pin of the repair tooth, and No. 2, \^•hicll is smaller, for completing it. The reamer. No. 3, is for shaping the lioles drilled in the backing for tlie pins so that tliey will receive the nuts (No. 5). to the taper of which it corre- 6 5 4 porcelain, and reduce the old backing to a flat sur- face, removmg the jjro- jecting pins. With a fine spear-drill only slightly larger than the pins of the facing, drill two small horizontal holes into the old backing and body of the crown in exactly the right position to receive the pins of the long-pin facing .selected. Letdown the facing into position, allowing the whole length of the pins to enter the holes. Roughen the pins thoroughly, or cut a screw upon them with a Bryant's screw cutter. Roughen the 2 «S 4a 5 Bryant's Crown or Bridge Repair Process. {S. S. White Dental Manufacturing Co.) sponds. The nut-driver (No. 4) is for sending the nuts (No. 5) home upon the pins. A holder (No. 6) keeps the nut in line while being started. 593 The process is suitable where the metal work at the back of the crown is thick, amounting to one sixteenth of an inch or more. The old backing is cleared of all fragments of broken FiC!. 753. — Shriver's Bridge-repairing Drill and Pliers. (.S. S. White Dental Manufacturing Co.) porcelain and overhanging edges and is trimmed flat. The projecting pins of the old tooth are cut away and ground flat. A new ordinary flat tooth is selected to replace the old one. Two holes are drilled right through the old backing at the correct positions to take the pins of the new tooth. The new tooth is fine-fitted into place. The holes are deeply countersunk from the lingual .side. The pins of the new tooth are threaded with small screw-cutting dies. \Vhen in place, the tooth is secured by small nuts of conical shape, which are screwed on to the pins, and sunk into the countersunk holes in the backing. Thin cement or thick chloro-percha can be used as a luting material. After the cement has set, the portions of the nuts pro- jecting above the level of the backing can be ground down with small stones. Shriver's Bridge-repairing Drill and Pliers (see Fig. 753). — This method can be used for refacing a crown in the mouth. The old backing is trimmed, and holes to take the pins of the new tooth are drilled, as in Bryant's method, but the holes are only slightly countersunk on the lingual side. The new facing is fitted, and its pins are cut short so that they project only very slightly beyond the back. The ends of the pins are now converted into tubes for a short distance by drilling along their centres with a fine trochar- ended drill, which is held in position while doing its work by a small piece of tube slipped over the pin. The tooth is now smeared at the back with cement, and put in position in the mouth, and the tubular projecthig ends of the pins are quickly spread out and riveted down by the pressure of the point of the pliers made for the purpose. The set of tools consists of a little drill to countersink the ends of the pins, a pair of pliers for spreading the countersunk pin to clinch it to the backing and for burnishing the A^ork down smooth, and a detached sleeve, which is set over the tooth-pin to centre the drill in coiuiter- sinking. The pliers are much like the old-style rubber- dam punch in appearance. One jaw is provided with a pocket or bowl to receive a mass of modelling composition to serve as a cushion for the lingual face of the crown in fixing the new facing. The other jaw has two removable punches — the first \vith a cone-shaped end to spread the countersunk end of the j^in and rivet it to the backing ; the second with a smooth rounded face to burnish the riveted end down. Refacing by Soldering in the Mouth (Baldwin). This method cannot be used in those rare cases where the pulp is still alive in the root. The old backing is trimmed down smooth and flat, and the old pins are cut off' and ground smooth. An impression of the labial aspect only of the old backing and adjacent teeth is taken in composition, and a plaster model cast. A new, thin, flat tooth is backed with a thin backing (No. 6 or 7), which is brought well to the tip of the tooth ; the pins are cut short and riveted down into countersunk holes in the Ijacking and soldered with gold. The new backing is now 594 filed smooth and flat. This tooth is fitted on the model. The new backing is then '• tinned " by melting a low-fusing soft solder, called " pearl solder ", all over it with a copper solderuig bit (see Fig. 754 A), using hydrochloric acid and zinc as a flux. 1 he outer surface of the old back in the mouth is similarly coated with pearl solder. The new tooth is then placed in position in the mouth, and while it is held by a finger of the left hand with a small piece of bibulous paper intervening, the two metal sur- faces in contact are made to unite by melting the intervening pearl solder by the application of a molten bead of pearl solder on the tip of the copper bit ; this bead of solder nmst come 01.0 e.n<-<^ ,soi- DE.K ,0,EW CHCK fi!i,L(LHlH FACE iCuPtKiNt Fig. 754. — A, Soldering Iron ; B, Method of use. The " tinned " copper bit must toucli the solder on tlie tips of the two backings, and must not be placed behind. {Dental Mamijacturing Co., Ltd.) in covtact from the first with the pearl solder already upon the two backings (see Fig. 754 B). The moment of thorough melting can be in- stantly told by feeling the tooth sink down under the pressure of the finger. Directly this is felt, the hot copper bit is removed and a swab of cold water dashed upon the work. A swab of cold water is used in the same way immediately after each operation of " tinning " the old back in the mouth. The copper bit must be used very hot, short of redness. Precautions against heat being conducted to serusitive neighbouring jiarts should be taken as follows : The rubber-dam should be put on the crown and the adjacent teeth. If the adjacent teeth are live teeth, the old backing should be reduced with a dividirg file or diamond disc if necessary to prevent its touching them. Pieces of thick l)lotting-paper can be put between the old backing and the adjacent teeth. All the applications of heat in the mouth must be done quickly, and the cold swab applied immediately afterwards without loss of time. No attempt nuist be made to apply the heat for the final fusing through the old backing. The writer has performed this operation many times successfully, and has never had trouble by causing pain to the patient. It would be possible, of course, to make a preliminary injection of novocaine. Befacing by Means of Part of the J. D. Logan Slide (Baldwin). — This is an excellent way of refacing in the mouth. The old back is trimmed flat in front and the pins are removed. The outer member of a J. D. Logan slide is then selected that will go in between the adjacent teeth. The old backmg is ground clowai at each side with a diamond disc until it will fit the slide. To facilitate this the imier member of the slide can be used as a pattern ; laid upon the old back, its lateral outlines can be scratched with a fine steel point on the old back, and the old back can then be ground away up to these lines. The ground edges nui.st be bevelled at the expense of their Ungual surfaces to make them fit the hollow dovetail of the outer member. The outer member must be pushed on as far as it will go. An impression is then taken of the labial surfaces of this and the adjacent teeth ; the impression is removed, and the outer member is withdrawn from the mouth and fitted mto the impression, which is then cast in plaster. A new fachig is then fitted and fixed on to the outer member, the outer member being used as a backuig. The pins must be cut short and riv-eted down into countersunk holes and gold-soldered. The outer member should 1 e kept full length, projectmg beyond the incisal edge of the porcelain. Any irregularity of surface inside the slide caused by riveting and soldering must be removed by filmg or grinding. The projecting part of the slide can be notched at the sides to facilitate removal of the redundant portion after fixing. The new tooth should tlien be fixed by sliding it on m cement, and the redundant portion of the slide trimmed away with a wheel. One of the merits of the method is that it does not thicken the metal-\\ork at the back, which is of great importance in close bites. Another Method of Befacing Incisors and Canines by making a Slide. — In cases where some extra thickness at the back is not contra- indicated. Instead of using a ready-made Logan slide, 595 the new tooth may be backed with No. 4 soft platmum, the pins being cut short, riveted down into countersunk holes, and soldered, and the back left considerably wider than the tooth. The old back having been reduced laterally, the excess of platinum is then bent round the sides of the old back, and may either completely cover the old back, in which case the edges should be neatly fitted together and soldered, or may be only just large enough to lap over the edges of the old back. In either case the platinum should be well squeezed by pliers on the old back, and well burnished, to ensure a good fit. The new \\ork is finally cemented on. Some operators adopt the method of com- pletely covering the old back with the new metal, but instead of cutting the jiins short, they merely solder them to the new metal, allowuig them to project straight across the space between its two layers. Two vertical slots are then cut with a fissure-burr in the old backing from the incisal edges sufficiently deep to allow the pins to slide up. Cement is used as the uniting medium. H. H. Bethel makes a new facing of inlay body, fusing it, in cases «here the backing is thin and therefore some of the other methods are contra-indicated (8). He proceeds thus : Straighten the old back and bend it free fiom bite. File up the heads of the pins till they are the same diameter as the rest of the pins. Burnish lyVrr '"• platinum (or No. 30 gold for low-fusing) to the old back, lettmg the old pins project through it. There are t\\ o ways of getting the holes in the facing for the pins to enter. The first is as follows : Place small platinum tubes over each pin and a little longer than the puis. Pinch the ends and so close them. Remove the matrix and tubes together by pressing beeswax, slightly softened, on them when in place on the old backing. Place a steel-wire pin in each tube. Coat with moistened whitening the end that goes in the tube. Remove and invest in pow- dered asbestos two parts, plaster of Paris one part. Bake porcelain in such a manner as to avoid drawing the tubes away. The second method is as follows : Use no tubes, but press hard wax on to the matrix in place of the backing. On withdrawing the wax, place a pure gold pin in each hole, a little thicker than the tootli-pins and long enough to be held by the investing material. These become embedded in the porcelain, and are afterwards cut off and drilled out. Roughen the tooth-pins before cementing on the facing. A "BRACKET FIXTURE" (Baldwin) Where it is desired to fix an artificial tooth without a plate to a live premolar in such a way that the metal will not come to the front or show at all, a fixture may be made (to fit the natural tooth) to which the artificial tooth is to be soldered. The writer's plan is as follows : For Pre- molars. — Shave oft with a diamond disc enough of the approximal surfaces of the premolar to produce parallelism of its sides, or even to produce surfaces slightly approachmg each other in the direction away from the root. Then cut out the fissure running between the two cusps with a smooth fissure-burr, making a groove of about j',; in. wide and the same in depth. Now construct a gold partial band with a cross piece, to fit the medial, lingual and distal surfaces, and the groove, as follows — Take an impression of the tooth, soaped, oiled or vaselmed, in a smaO copper cap, with dental lac or crown comjjosition. When chilled and quite set, remove this and pack it full of amalgam or Harvard cement, and set on a basis of plaster. Having obtamed this metal model, make the partial band of thin pure gold to it, and make a small tongue of pure gold to lie in the groove between the cusps, and lightly solder it to the band at each end. Fit this band and tongue as «ell as may be by burnishing it to the model. Then try in the mouth, bend a rather narrower 18-carat plate band of the same length round it ; place a bit of gold wire m the groove^ uivest, and solder all together. If a castmg machine is available, after thoroughly fitting the inner pure gold shell, place it on the model, and on the model buUd up the outside of the partial band, and fill up the groove with castmg wax. Attach a sprue and pressure-cast. Trim up the resulting arrangement, and try it ui the mouth. Adjust it to the bite and rock it completely home ; if necessary, fit it on by means of vermilion j^aint as some contraction will have taken place. Burnish the edges close to the tooth all round ; consisting as they do of pure gold of the original band, this can easily be done. Then take a plaster impression over it and the adjacent teeth. The mechanic will be able to add the porcelam tooth to it by soldering. Wlien finished the work is set with cement ; but before this is done, the edges, filed thin, should again be closely burnished to the tooth. This produces a reliable fixing, and leaves the buccal surface and both the cusps entirely free and unafi'ectcd. Another way of producing this is by making the first partial band of crown gold and making it quite a loose fit, and having the casting wax in- side it instead of outside, thereby producing the fitting portion and cross-bar entu'ely by casting. THE CARMICHAEL CROWN For Premolars. — This device is for the same purpose as the preceding, and like it has a 596 Fig. 755. — The Carmichael Crown, three-quarter band, but it differs from it by requiring the inner cusp to be cut away and replaced by a gold cusp, and also by having a strong rib of gold running vertically on the inside of both medial and clistal portions of the partial band. These ribs are accommodated in the tooth by deep grooves cut by embedding a fissure-burr vertically in both medial and distal surfaces of the natural crown. Technique for Premolars (see Fig. 755). — Trim the tooth as for the Bracket Fixture, except that the groove across the occlusal surface is to be cut a little to the buccal side of the transverse groove. Grind off the inner cusp flat, and also the inner jiortion of the base of the outer cusp. Cut a groove with a fissure-burr in the medial and distal enamel, continuous with the transverse groove, as shown in the diagram, and deep enough to form a full half - circle in section. Take an im- pression and make an amalgam or fusible metal model. On this make the three-quarter band of pure gold and burnish it into a fit, and also carry the gold over the site of the inner cusp and into the grooves. Lightly solder it together and try it in the mouth. Fine-fit it by burnishing it to the natural tooth. Then remove ; make up the necessary thickness and contour, and fill the grooves with casting wax and cast it. In the absence of a pressure- casting appliance, the added gold may consist of plate bent round to fit, and soldered. A variety of the Carmichael crown is called the " Staple " crown, because a staple-shaped piece of gold wire is first made to fit the tri- partite groove, and the rest of the crown fixture is constructed over it as before. For Incisors and Canines. — These fixtures can be constructed by making the transverse groove across the palatal surface near the cuttmg edge, but not near enough to weaken the cutting edge, and the medial and distal grooves in contiiniation of this. If the bite is normal, accommodation for it must be made, partly by reducing the tips of the antagonizing teeth if necessary, and partly by removing with a carborundum wheel the occluding part of the tooth that is to hold the fixture, before taking the impression. For Molars. — The transverse groove is made antero-posteriorly right across the masticating surface. PARTIAL CROWNS Partial crowns are described in various books ; they consist of a shield of metal, with a tag soldered to the inside, for the purpose of protect- ing the surface of large cement fillings. These, in the opinion of the present writer, are not of much value, but there is one form of partial crown that he has found useful. It is designed for those cases where there is a very large open cavity in a " live " molar tooth, and it is apparent that there would be great difficulty in providmg for the retention of a filling without killing the pulp, or further ^\eakening the tooth by grooving the edge of the cavity and so providing it with walls ; it may also be desired to preserve the whole of the remaining occlusal enamel as an occkiding surface. Here the object is to band the tooth, and by means of the " cire perdu " casting j)rocess, to strengthen it inside, and fit it more perfectly, and attach to it a mass of gold, which shall form a gold inlay for the cavity. Possibly there may be two cavities to be filled on opposite sides of the same tooth, and then both are fiUed with the one fixture. Technique.- — Remove all caries and softened tooth substance, particularly all weak enamel of the occlusal surface. Then if the rest of the tooth presents any bulge, remove all the bulge \\itli carborundum stones and carborundum powder, and if necessary slice down the ap- proximal enamel both medially and distally, so that a band can be fitted properly round the tooth. If any enamel overhangs the cavity or cavities, fill all the undercuts with Fletcher's artificial dentine and carefully trim it away from all the edges. Make a band of No. 4 gold, 22 -carat, and fit it accurately and tightly at the cervical edge ; solder its ends ; contour it neatly to the buccal and lingual surfaces, and give it a jjroper contact approximally with the next tooth, but allow its occlusal edge to stand free from the tooth. Adjust it to the bite. Dry it and melt into it casting wax. \Miile the tooth is wet press this home upon it, keeping the thumb (wetted) over the occlusal end tightly to confine the wax ; then let the patient bite home and rub the teeth together. Cool off with ice-water or ethyl-cliloride spray, and trim away surplus wax with a warm scraper. Let the patient bite again and grind the teeth together. Now carefully remove from the tooth. If it is desired to economize gold, remove some of the wax that entered into tlie deepest part of the cavity, Ijut take great care not to damage or interfere with the wax at the cervical and occlusal edges. If it is necessary to add wax to any part of the outside, do so. Try on the tooth again, if necessary. Attach a sprue or sprues to the occlusal part of the wax and pressure -cast it. File up and polish, and rock it into place on the tooth and verify the bite. If properly done, the result win be a band with gold inlays in the cavities, I all fitting with great exactness. Any artificial dentine is to be removed from the cavities in the tooth, and the work cemented on to the 597 tooth with oxy-phosphate, the band being firmly rocked home under the usual j)i'ecau- tion of absolute dryness, and tlie joints, if pos- sible, varnished with chloro-percha before being allowed to get wet. CROWNING SPLIT TEETH Wien a tooth is split vertically through the natural crown, it will generally be found that one portion is much looser than the other, owing to the fracture being quite oblique under the gum, and in this case the looser portion will have but a small portion of root attached to it. In such a case the looser portion should be removed and the remainmg portion crowned. When, however, it is manifest that the fracture extends really between the roots of a multi-rooted tooth, and eacli portion of the cro«n is attached to a valuable root, then it becomes necessary to crown the whole in order to hold the two parts tightly together. The present wTiter has been successful in crowning various cases of split teeth with both shell crowns and porcelain crowTis, some of which are doing perfectly good service after the lapse of many years. In such a case, if some days have elapsed since the fracture, it will often be found that the two halves have become separated some\\hat from each other ; this means that the roots also have travelled some- what apart. The first thing then to be done is to bmd the two portions tightly together with silk or thread or binding wire, and leave the case for further treatment for some days. When the parts have been thus brought together absolutely, the crownmg can be pro- ceeded with. The all-gold (or platinum) shell crown, made in the usual way, is the simplest and best for the purpose. Part of tlie treatment of the fractured halves should consist in cutting a groove round them parallel with tlie gum, fitting a soft platinum or Angles bronze regulating ligature wire in the groove, twisting the wire tight with pliers, and causing it to lie snugly in the groove ; but before fixmg it, the space between the broken parts must be very thorouglily cleaned by prising them apart, syringmg, disinfecting and drying, and then introducing chloro-percha containing chinosol or thymol between the fractured surfaces, and squeezing the parts tightly together with for- ceps. When there are pins fixed in the roots, these should be bound together tightly with fine platinum or other soft wire before super- imposing the crown. In the case of an upper first premolar fractured between the roots, where it is desired to crown with a porcelain cro\\n, a Richmond cap crown is indicated, or a porcelain -faced shell crown. When possible, first bind the two halves together with a single wire under the free edge of the gum, twisting it tight with fine-nosed pliers on the outside. This wire will greatly assist during the trimming of the root for the cap and the enlarging of the root-canals, and during the fixing of the crown (or posts), and should be removed after the crown is finally fixed. FIXING CROWNS Crowns are almost always fixed for a per- manency with either — ( 1 ) Oxy-pliosphate of zinc cement ; (2) Oxy-phosi^hate of copper ; (3) Gutta-percha ; (4) A combination of gutta-percha and ce- ment ; or — (5) Pc-A. (For details see p. .561.) Fig. 756. — Rogers's Wool-roll Long Ann Clamps (right and left lower molar). ■ rrr,->i {Messrs. Claudius Ash, Sons cfc Co., Ltd.) Before fixmg any crown, the root and the crown must be thoroughly cleaned and dried with hot air, or ^^■ith absolute alcohol followed Fic. 757. — Gross's Wool-roll Clamp. (Messrs. Claudius Ash,' Sons tSi Co., Ltd.) by hot air. In some cases it is possible to apply the rubber-dam to the root, when the stump is sufficiently preserved, but not often. To Achieve Dryness of the Root. — Have several 598 roughened Donaldson liristles ready wrapped with absorbent cotton- wool, say three for each root. If an upjier tooth, place a roll of soft bibulous paper, or a cotton-A^ool roll, under the lip or cheek, to hold these jmrts away from the site of operation. If a lower, place a roll, li ins. long, on each side of the root, to keep both tongue and cheek or lip a\\ay . Whether upper or lower, it is advi.sable to place a pad be- tween the cheek and the upper back teeth on hoth sides of the mouth to absorb the secretion from Sten.'^on's ducts. Dry the root-face and mouths with pellets of alisorbent cottoIl-^\ool or fill the cap or shell with it ; then apply some of the cement to the mside of the root-canal or canals with the cotton -^^Tapped wire. Place the crown in position and press home with a notched handle or a boxwood "rocker", using Fig. 758. — Stokes's Clamp for use with absorbent paper. {Messrs. Claudius Ash, Sons tSk Co., Lid.) Then dry the canals with the cotton-wrapped Donaldsons. Blow hot air on the root-face and into the canals (after using absolute alcohol if desu-ed). If any point of gum threatens to e.xude moisture, touch it with Merck's perli^drol (William Hern) and dry again. (1) To Fix with Cement {Oxy-jihosphate of Zinc). — Place everytliing to hand that v,il\ be required. Have one stout specially roughened Donaldson, wrapped with cotton-wool, for the sole purpose of aiDplying cement to the inside of the canals, and a white porcelain slab within easy reach of the right hand, and fixed down to the table on which it rests. On this place the fluid and powdered portions of the cement side by side in two patches, and a little hydro- naphthol ; also a notched handle for front teeth or a boxwood " rocker " for back teeth. After drying, rub the root-face and the inside of the canals, and also the post of the crown and the inside of the cap or base of the crown, with the fluid part of the cement to be used ; then remove any excess of this fluid with dry cotton-wool. The effect of this is to make the cement attach itself much more easily and quickly to the surfaces to be cemented. Mix the cement by grinding the powder little by little with considerable pressure into the fluid, using a large stiff steel spatula elliptical in section. When mixed first apply some of the cement to the post and base of the crown, and Fig. 759. — Goodhugh's Clamp. {Messrs. Claudius Ash, Sons & Co., Ltd.) considerable force. A front tooth requires the notched handle and a slight rotation in each direction, accompanied by strong pressure in the direction of the length of the root. A back tooth requires the "rocker" with forcible pressure and a rocking motion. The surplus 599 cement should squeeze out all round and may at once be wiped away with a pellet of cotton- wool, whOe the pressure is maintamed for a few minutes. The remaining excess of cement should then be removed, and the cervical edge of the crown and the gum in contact with it flooded with chloro-percha, which should be evaporated off with hot air. The film of gutta- percha is to jH-otect the edge of the cement from saliva until thoroughly set, and so increase its durability. (2) Oxy-phosphate of Copper. — This is said to be more insoluble in the saliva than oxy-phos- phate of zinc, and also antiseptic and non- absorbent. It has the disadvantage of being coal-black in ccilour and showincr an ul'Iv lilack Fig -Evans's Gutta-percha Cement, and outfit for setting crowns and bridges. {Dental Mariufacturiny Co., Ltd.) line. The manipulations are the same as for the preceding. (3) Gulta- percJia is a very valuable medium or fixing crowns as — - (a) It holds very securely in all cases, except short crowns witli poor attachments and subjected to great strains ; (h) It protects the root very reliably from caries ; (c) It makes the crown easily removable at the will of the operator; (d) It is quite insoluble. The disadvantage is that it is sometimes very difficult to get tlie crown to go quite so close to tlie root as with cement. The best kinds of gutta-percha at present are base-plate gutta-percha, and Hill's. Evans's gutta-percha "cement ' is an impure gutta- percha, similar to Hill's (see Fig. 760). Technique. — ilake dry and keep diy as before both the stump and the crown. Place the cro^vn on a heater to keep hot (a hot block of steatite or hot copper slab). Coat the inside of the root-canal, and all the parts to be united, with cliloro-percha. and put a little column of gutta-percha into the canal or canals. Pack a sufficiency of hot gutta-percha on to the base of the crown and round the pin or pins. Heat it all finally and slowly press the crown home. If there is evidence of pain from heat, slightly withdraw the crown and wait a little ; then press it home again. It may go right home, and give evidence of there being sufficient gutta-percha by this squeezing out all round; but if either there is no surplus expressed, or the crown fails to go quite home, it must be with- drawni from the mouth, and either a little more gutta-jjercha added, or a little taken away, as the case requires. After reheating press it home again. It is generally best to remove it and adjust the amount of gutta-percha, and reheat, and again press home, several times, to ensure that the crown shall get quite into its proper place. White or red base-plate gutta- percha is excellent where there is no cap, and no great accuracy of fit (e. g. Logan crown), but being much tougher than Hill's, it will not readily displace from under a cap, and in such cases should not be used. Where it is desired to increase the adhesion of gutta- percha to a tooth or crown, apply to the surface a solution in chloro- form of ordinary resin (rosin). All impure gutta-percha, which softens at a low heat, for fixing erowiis and bridges, with instru- ments to work it, is sold; it is called Evans's Gutta-percha Cement. The wTiter recommends a mixture of chloroform and eucalyptus oil to be placed on the gutta-percha while' it is being heated. L. G. Noel (13) recommends for setting crowns and bridges — gr. x\. Chloroform Eucalyptus Oil . Aristol Gutta-percha . . . q.s. This takes a week to dissolve and is used cold. In using this pour some of it out on a slab and work into it zinc oxide till it is of the con- sistency of cold butter. (4) Gombina'ion of Gulta-percJia and Cement. Where a crown fits loosely, it is recommended fii-st to coat the pin and base with gutta-percha and force it home completely on the wet root ; 600 then withdraw it ; repeat this ; dry it and also the root ; smear a little thin oxy-phosphate over the base and pin; and quickly force it home. A crown fixed in this way is removable at the will of the operator on reheating. WilHam Hern, when fixing a diaphragm and pin crown (pivot crown) or a half-collar crowii, always first places a thin washer of gutta-percha over the base of the crown only ; heats this, and forces the crown home ; then removes it ; trims off the surplus at the edges ; and then fixes the crown in the ordinary way with cement. This he does to give special protec- tion to the root against REMOVING CROWNS Wlien a crowned tootli is the cause of chronic ui- flammation or abscess, it is necessary to remove the crown, or di'ill vertically through it, in order to open out the canals and rectify the septic condition there. When a crown has been fixed with gutta-percha, it is only necessary to warm it for' a sufficient time by holding a hot copper bit against it. The metal will gradually conduct the heat to the remotest portion of the crown, and then it can easily be pulled off. When the crown has been fixed with cement, and re- c|uires removing, it is per- haps worth while trying a preliminary wriggle upon it with a pair of extracting forceps, taking care not to use enough force to cause Fig. 7(il. — Copper- pai" or risk loosening the ended instrument root. for holding crown When it is desired to and maintaining remove a crown, and it '"'■ cannot be done in either of the ways mentioned, proceed as follows — For Shell Croivns. — Slit the whole depth of the crown at the part most easily accessible, with crown-.slitting forceps (see Fig. 762) (or with a fine fissure-burr). Turn up the cut edges with a stiff sharp instrument and prise off. If the crown still rcfu.ses, drill a largLsh hole hori- zontally vvith a spear-drill from the slit, under the occluding surface, and as close under the metal of the occluding surface as possible. Let the hole go in to a point just short of perforating the opposite side. Into this hole insert a stiff strong instrument, which can be used as a lever, and tTien the crown can be levered off. For Dowel Crowns. — A dowel crown remover may first be tried, to remove the whole crown and pins together. If this fails, drill a hole horizontally under the crown so as to strike the post, with the object of completely severing it. Fig. 701!. — Crown- ting Forceps. [Dental Manujacturinq Co., Ltd.) Fig. 7ti3. — Screw-driver used for levering off crown. (S.S. White Dental Manti- jacturing Co.) If the drill-hole fails to sever the post com- pletely, use a small fissure-burr in the hole laterally. Wlien the post has been completely severed, the crown can be easily pulled away. The post left in the root must then be drilled out. For Cap and Pin Crown. — Proceed as above, and, if necessary, cut through the cap and turn up its edges, or, if necessary, cut horizontally right through root, pin, and cap, close to the porcelam, and so completely amputate the crown from the root. Then remove any portion 601 of the collar still remaining and drill out the post. TREATING WORN AND BROKEN CROWNS Uld shell crowns sometimes present them- selves with holes \\orn through the occlusal surface. Usually it is a satisfactory proceeding to burr out with a round burr any decay that may have supervened, or to make a satisfactory hole in the cement exposed, and then to fill the hole with amalgam. If, however, extensive caries has supervened, it is best to remove the crown. The mechanic can then mend up the old crown, or a new cro\\'n can be made. Where a dowel crown has broken, leaving the dowel tightly fixed in the root, either the dowel Fig. 7ij4. — Jlosley's Crown Remover. {Messrs. Claudius Ash, Sons & Co.. Ltd.) may be pulled out, or, if this is impossible, a new crown can be fixed on to the old post. Types of crowns available for fixing to an old 2)ost still in situ in the root are — The ordinary sheU crown ; The BonwUl crown, the Davis, Ash's dowel cro\ni, etc., or a crown to be specially made for the case, with tube or mortise to receive the projectmg end of the old post, and if desh-ed a porcelain face. WQien an old " pivot " crown has broken off, leaving the post tight in the root, either drill out the old post with a sharp stiff spear-drill after grinding it down flush ; or proceed as follows — Take a small trephine and trephine round the post to a distance of | or \ inch. Fit an iridio- platinum tube in the space thus made, and construct a crown upon this with a diaphragm, in the same way as descriljed in making a diaphragm and pin crown, except that the tube takes the place of the pin. Fix the new crown with cement. H. B. BIBLIOGRAPHY Dent. (1) Badcock, J. H. Molar Crowns. Brit. Jour., 1900, Vol. XXI, pp. 429-34. (2) Baker, C. A. Dental Cosmos, 1907, Vol. XLIX, p. 578. (3) Baldwin, H. On Cement and Amalgam Filling. Trans. Odont. Soc, 1896-7, Vol. XXIX, p. 93. (4) Baldwin, H. Bicuspid Crowns. Brit. Dent. Jour., 1900, Vol. XXI, p. 429. (5) Baldwin, H. Further Experience of Cement and Amalgam Filling. Brit. Dent. Jour., 1904, Vol. XXV, p. 781. (6) Baldwin, H. A New Method of Refacing Porcelain-faced Crowns in the Mouth. Brit. Dent. Jour., 1910, Vol. XXXI, p. G73. (7) Bennett, Norman G. Difficult Crowns. Brit. Dent. Jour., 1908, Vol. XXIX, p. 49. (8) Bethel, H. H. Dental Cosmos, 1907, Vol. XLIX, p. 280. (9) DosKow, Samuel. The Banded versus the Band- less Crown. McCullough's Crown. Dental Cosmos, 1907, Vol. XLIX, pp. 270 et seq. (10) Dttnwoodv. J. E. Dental Cosmos, 1907, Vol. XLIX, p. 197. (11) Hern, William. Incisor Crowns. Brit. Dent. Jour., 1900, Vol. XXI, p. 417. (12) McAfee, S. H. Dental Cosmos, June, 1906, Vol. XLVIII, p. 656. (13) Noel, L. G. Dental Cosmos, 1907, Vol. XLIX, p. 453. (14) RiETHMULLER, R. H. and Hough, H. The All- Porcelain Jacket Crown. Dental Casinos, 1909, Vol. LI, p. 1258. (15) Roach, F. E. Elliott's Quarterli/, October, 1910. (16) Rose, Frede. Brit. Dent. Jour., 1906, Vol. XXVII, p. 865. (17) TuLLER, R. B. Ainer. Dent. Jour. ; Dental Cosmos, 1909, Vol. LI, p. 1016. (18) Weekes, T. E. Dental Siimmari/. 1910, j). 105. (19) White, S. S. Catalogue of Instruments used iti Crowning. CHAPTER XXXYII BRIDGE-WORK GENERAL BRIDGE-WORK Selection of Cases. — Tlie most important part of the work in the construction of a bridge is undoubtedly the proper preparation of the roots on Avhich it is to be buUt up ; unless the abutments are in a sound condition and properly " coned up ", the work cannot have any lasting quality ; for no matter how good the actual mechanical construction may be, sooner or later the bridge will fail if the root-treatment and prefiaration have been faulty. Xow in coming to a decision whether a case is a suitable one for bridge-work, the type of patient must be considered ; a neurotic person or anyone in bad general liealth would hardly put up with tedious and tiring, if not actually painful, work incident to careful root-f)reparation. Then it must be considered whether, by put- ting a bridge in a certain position, the whole denture is thereby made good ; in a j)atient badly in want of a masticatory apparatus, to put a liridge on one side of the mouth leaving the other side with a considerable space would be bad treatment ; yet one often sees it done. It must be remembered that the chief use of the teeth is for masticating purposes, and bridges should be made to that end; to put practically only facings in the molar region for show, is extremely wrong, as very often some form of plate would give both use and appearance. The articulation must be taken very care- fully into account — i.e. whether it is normal or nearly so. In so many otherwise suitable cases the teeth opposite the space to be bridged have elongated considerably, making the attain- ment of proper occlusion almost impossible without too much mutilation of the lengthened teeth ; a little grinding of the prominent cusps, however, is quite allowable, but good occlusion must be got, and in extreme cases it might be necessary to devitalize and "crown " or other- wise properly prepare the opposing teeth, rather than liave the occlusion faulty. The front upper teeth should not be bridged if the lower l^ack teeth are missing, and are not going to be replaced with a denture or saddle bridge, as in this case a greater strain is brought to bear on the front of the mouth, and the life of the bridge very much shortened. The probable length of life of a bridge in a given case must be considered, and the patient made to understand thoroughly the condition ; bridges may be made with only a comparatively short life in view, provided that this is explained, and that the case does not admit of more per- manent treatment. All roots not to be used as abutments must of course be removed, and never must a bridge span a root buried in the alveolus. The question of employing unblemished teeth as abutments is a difficult one, and as a general rule, v,\\en two sound teeth «ould have to be employed as abutments, a bridge is contra- indicated ; an exception would be a case where for some reason it would be difficult to make a satisfactory plate, and where the space is only on one side. There is no doubt that far too many sound teeth are sacrificed to serve as abutments, and very often a plate is indicated when the patient would perhaps prefer a bridge. Then again it nmst be remembered and taken into account that the value of a well -constructed bridge as a masticatory apparatus is about four times greater tlian that of a plate, by reason of resistance to pressure of occlusion. The use of the cantilever prmciple in bridge- work is not to be recommended as a general rule ; that is to say, when it is possible to anchor the bridge at both ends by means of abutment pieces, or by one abutment piece at one end and some variety of " spur " at the other end, it is desirable to do so. At the same time the cantilever principle has its use in bridges ; for example, in a bridge from canine to first molar, where the remaining molars on the same side are absent, an extension of the biting surface of the molar may be made backwards to the extent of the breadth of the second molar, sufficient strength being obtamed from the two abutments to take the additional strain, and especially so if there is an opposing artificial denture. Were the force opposing a cantilever bridge applied only in one direction, viz. in a direction parallel with the axes of the teeth, the principle could be employed to a much greater degree ; but in the moutli there is a side-to-side move- ment during mastication and a pressure sideways from the tongue, which must certainly preclude their employment to any great degree, although some wTiters contend that they are perfectly satisfactory even under these conditions. 002 603 General Condition of Mouth and Teeth. — The more healthy and clean the mouth, the better will a bridge last. In case.s where there is distmct recession of the gums going on, bridge- work cannot be made very lasting ; the re- cession will continue around the abutments at the same rate as before, if not faster, leaving undesirable pockets for food to collect in, and very great care will have to be taken to keep the parts clean ; but still, as a means of deferring the wearing of a plate, it is sometimes desirable. A bridge acting as a splint maj^ in some cases of pyorrhoea, considerably improve the condition when in conjunction \\ith other treatment. The mouth nuist lie put in as healthy a con- dition as possible, and in cases of gingivitis or pyorrhoea, removable ^^•ork should be inserted where possible. A bridge should not be put in the mouth of a patient who does not keep the teeth absolutely clean, for it is certain that care will not be taken to keep the bridge so. Strain or Stress. — Teeth are designed by Nature to support each a certain amount of strain or stress — the incisors an outward and inward stress, the jiremolars a lateral and vertical, and the molars chiefly vertical, ^yith a certain amount from all sides according to tlie position and length of their cusps. When the articulation is interfered \\ith by loss of teeth or by irregularity, the stress upon individual teeth, more or less unsupported by neighbours, is increased. This is important when considering the advisability of bridge-work in any given case — for instance, a first premolar as the anterior abutment of a bridge, and having a space betw-een it and the canine, would make the bridge as a whole not so strong as when the premolar abutment knuckles firmly with its neighbour. The greater the length of overbite, the greater the stram on the bridge, and if the cusjjs of the bridge and those of the opposing teeth inter- digitate too pronouncedly, the strain is again increased ; of course if all the remaining teeth in the mouth articulated perfectly, one could articulate the bridge anatomically, but it is rare to find the remaining teeth so, and therefore it is better not to have the artificial cusps too pronounced. Two centrals can .support two laterals. Two laterals can support two centrals. A central will support a lateral with a spur in the canine. A lateral will support a central with a spur in the other central. Two canines will support centrals and laterals if the arch is not V-shaped and if the overbite is only very slight, and presuming there is the normal amount of posterior occlusion. If the arch is V-shaped a removable saddle-piece only can be used. A central and fiist premolar may support the lateral and canine, but a removable piece made with a saddle is better than a fixed piece. A canine and first molar can support the two premolars, and also the lateral, without (but better with) a spur in the central. A canme and second molar can supj)ort the intervening teeth if the bite is not too strong. The canuie to the third molar should only be employed in a removable piece with a saddle, and if the third molar has come forward somewhat. The two canines and two second molars can supi^ort a full removable piece with saddle. The two lower premolars can supf)ort the two molars in a removable piece with saddle. The second premolar and second molar can supj)ort the first premolar (without spur) and first molar. Any one tooth can sujDport another tooth with a spur in adjacent tooth. It is always advisable in a doubtful case to have an extra abutment piece when possible. Devitalization. — Teeth should practically always ))e devitalized before being used as abutments for bridges. In the earlier methods of bridge- work this was not considered essential, but it is impo.ssil)le to " cone up " a live tooth properly without causing a great deal of pain, and even if the patient will stand it there is great risk, almost a certainty, of the pulj) dying from chronic irritation after a varying period of time. Open-faced abutment pieces were formerly used, and it was not considered neces- sary to kill the jiulp, as they were put on with very little grinding ; but even if this form of abutment piece were sound (and, as will be seen later, it is not), more grinding away of the tooth must be done for proper fitting of the gold than can be accomplished without endan- gering tlie pulp from constant slight irritation of possible thermal changes. In the rare cases in which a patient would stand the proper preparation of the roots, a fixed bridge put on with gutta-percha cement would be mdicated. Those forms of bridges that do not necessitate the mutilation of the abutment teeth can be used without, of course, interfering with the pulps ; they will be described later. Bridge-work in suitable cases has distinct advantages over " plate- work ". It admits of greater masticatory power and it does away with the difficulty in some cases of becoming accustomed to the " management " of a plate; also it is occasionally (but only rarely) found that a plate apparently alters, or the patient thinks it alters, the power of speech and of taste. Then, again, a plate in some mouths will cause a con- siderable amount of abrasion of the remaining 604 natural teeth, although theoretically this should not hapjjen in a well -adapted piece. The main disadvantages are devitalization of teeth that would otherwise be kept alive ; the extra strain that is brought to bear on the abutments ; unhygienic conditions that may supervene in mouths that are not kept scrupulously clean; and the difficulty and tediousness of the work necessary to proper adaptation. Varieties of Bridges. — A dental bridge is a masti- cating or incisive surface of gold or other material, bridgmg (or spaiming) a space in the alveolo- dental arch caused by loss of one or more teeth, and firmly anchored at either end to one or more teeth; if "removable", it may receive additional support from an alveolar " saddle plate ", and in the case of a removable " ex- tension " bridge it may be anchored to teeth only at one end, receiving its chief support from an alveolar saddle. The natural teeth or roots supporting the bridge are called the "abutments", and the anchorage to them the " abutment pieces ", the intervening portion being called the " body ", and the several pieces composing the body the " dummies ". A fixed bridge is one in which the body and abutment pieces are one, and that is fixed to the abutment teeth by some form of cement, and is not removable by the patient. A removable bridge is one in which the iiuier abutment pieces only are permanently fixed to the roots, the body and outer abutment pieces being removable at will by the patient for cleansing purposes. The complicated struc- tures sometimes seen, which are only removable by the dentist, are not included in the term " removable " in this article. Fixed and removable bridges may be sub- divided into — (a) All metal — gold, or gold and platinum. (b) Gold, or gold and platinum, with porcelain faces . (c) Fused porcelain on platinum base. General Shapes of Bridges. — In all bridges as many so-called "self-cleansing" spaces should be allowed as possible ; contours of abutment pieces should Ije arranged so that the inter-dental spaces between them and the adjoining natural teeth are preserved. This is of very great importance, and just as much care must be exercised to obtain a proper contact with the natural teeth as would be done in the case of a " crown ". ^^ When possible in posterior fixed bridges, a " bar " bridge, i. e. a biting surface without dummy facings, should be used ; it is more comfortable and allocs the food to be managed more easily, and is certainly far more cleanly ; the thickness of this bar should be only sufficient for requisite strength, thereby leaving as much space between the " bar " and the gum surface as possible, and the under-surface should be made slightly convex. By this means the under- surface is kept clean more easily ; the patient can get the tooth-biiish around the abutments and also pass the floss silk everywhere. It is not so artistic, but one of the main points to observe in all bridge-work is tlie question of cleanliness. A piece of linen can be passed underneath a " bar," and the abutment pieces and under-surface can be kept comparatively clean on a fixed bridge, whereas if there are facings the under-surface is extremely difficult to keep clean — indeed, in many cases it is im- possible — with the usual results of gum surface irritation and consequent recession around the abutments. However, in so many cases the teeth show, and there is then no alternative but to put facings. In removable work this does not apply, as the bridge can be removed at will and kept clean. Facings on bridge abutments should be kept absolutely flush with the band en- circling the root, and never allowed to stand out over the gum as is so often seen ; the gum becomes unhealthy and food collects, and the piece never looks well after a short time in the mouth ; even at the expense of showing a little gold, this metliod should be adhered to. As mentioned elsewhere, the overlapping facing may be allowed in removable work when necessary, and an improved appearance can sometimes be obtained by it. Broad surfaces of metal should never, in fixed bridges, be allowed to rest on the mucous membrane of the alveolus or palate, such as a " saddle " for instance, and, indeed, one might almost say that no metal of any sort should be allowed so to rest, although other writers advocate it — explaining that the metal could be fitted so closely to the gum surface that the fiuids of the mouth are even excluded. It is only necessary to see a few cases fitted in this way that have been worn for a short time, to realize the fallacy of the argument ; slight absorption takes place, food begins to collect, and the gums then become inflamed and the piece unhygienic in every way. An exception to this rule may be made in cases of extension of the bridge behind a natural tooth not included in the bridge, by means of an oval wire, and carrying a facing attached only to the \\ire, so that floss silk can be passed under it and around and so keep it clean ; for instance, a posterior bridge, one abutment of which is the first premolar, from which the extension conies around the canine and carries a lateral facing. The extension bar should be 605 kept well free from the tooth that it encircles so that food will he removed by the tongue. In removable work the resting of metal on the mucous surface does not matter, and it is an additional benefit as a support to the piece. Goslee (5) says, referring to Saddle Bridges in connection with " fixed " bridge- work — " The practicabihty of this metliod has long been, and indeed, perhaps still is, a somewhat debatable question, but it may nevertheless be safely asserted that whUst the possible virtues of the principle involved wUl increase or dimuiish in proportion to the degree of accuracy obtained in the adaptation, the utility when judiciously employed is unquestionable." And again — " Upon the removal of such bridges worn from three to five years where the adaptation has been good, the surfaces of the saddles have been found clean and comparatively free from accumulations except some little exfoUated epithelium ; the patients had experienced no particularly unpleasant taste nor offensive odours. And the tissues, while presenting a slightly reddened, somewhat congested appear- ance, due, perhaps, to a superficial capillary stasis, as the result of the pressure, indicated no marked evidences of soreness, inflammation, hypertrophy, nor resorption. Such results could only be expected, however, when a good, close adaptation without irritating influences existed." It seems to the writer that this description of a piece worn " from three to five years " points to the fact that the conditions found were distinctly mihygienic and extremely un- desirable, and that they show the advisability of not employing saddles in fixed bridge-work, rather than being an argument in favour of so doing. Relative Value of Large and Small Bridges. As a general rule it is better to make two relatively small bridges in a mouth rather than a single large bridge, but the operator must, of course, be guided by the conditions. A root not sufficiently strong as an abutment by itself becomes a very useful adjunct to a large bridge. Relative Value of Bridges and Bridge-plates. Bridge-plates or saddles, which should only be used in removable work, often give greater strength to the piece ; for instance, a bar across the palate, uniting two saddle bridges, will aid in giving strength in many cases of shaLlo\\' bridges, and enable simpler forms of removable abutments to be used. Then agam, in bridges from canine to canine in the maxilla when a V-shaped arrangement of the teeth is necessary, much greater strength Ls obtained by a saddle over the alveolar margin, and very often in these cases a more aesthetic arrangement of the teeth can be obtained. Variety of Abutment Pieces, and Forms of Anchorage. — The chief abutment pieces for fixed bridges are the all -gold crown, and the Rich- mond crown — the Richmond crown may be varied by having only a half-band — , and the " porcelain-faced " crown. " Pin and Plate " crowns in anterior teeth may be employed ; they are not nearly so satisfactory from the point of view of strength, but as they can be easily made, and with the certainty of show- ing no gold cervically, they have their uses. In these days of pressure-casting, however, such an accurate diaphragm and half -band may be made, with no discomfort to the patient, and with the certainty of obtaining a good fit medially and distally (a thing that Ls difficult to obtain by the ordinary method of making a half-cap), that it is really very seldom one would be justified in using them. Another form of anchorage in both fixed and removable work is the spur resting m a hole or groove ui a gold fiUmg or cast-gold inlay placed in the abutment tooth. The use of the spur or bar built into a gold filling is highly unsatisfactory and practically obsolete, as it is almost impossible to build a really solid filling around a spur or bar, and they so often work loose. The iridio-platinum bar fittmg mto a slot in a cast-gold filling, and so arranged that it " locks " when in place, is an excellent form of support where the strain is not too great and where it is desirable not to crown the whole tooth ; this is more particularly used in remov- able work and is so much simplified by the castmg process. It is of great use in those cases where one abutment is a shallow tooth and does not lend itself to a telescopic cap. In removable work the best forms of abut- ment are the telescopic caps, and the half- round cap and split pin. The " key " anchorage ui cases of shallow occlusion is very useful. The gold inlay as an anchorage when united to a cast bridge by solder is of considerable use in fixed and removable bridges. Relative Value of Banded and Non-banded Abutments. — In all cases of abutments for bridge-work the banded variety is preferable to the non-banded, from the point of view of strength. It is undoubtedly difficult to fit in such a way that gold does not show, and in process of time there is apt to be a certain amount of recession, which wiU expose the gold ; this is the chief disadvantage, bnt the amount of recession caused by the band diminishes pari passu with the accuracy of the fit of tlie band, and if it were possible in all cases to have the gold extending under the gum only to the exact extent of the enamel that has been removed, 606 and that the band replaces, this recession would liardly ever take place in consequence of the band. There is also of necessity more pain infhcted in fitting, but this can be reduced to a minimum by careful manipulation and by the use of obtundents. A half-band is the next best thing in cases where a full band camiot be used, and in the incisors protects the root from the direction of the greatest strain. In most cases a banded crown can always be used on the molars and premolars. " Pin and plate " teeth may very seldom be used, as, for the same reason that applies to their use in crown-work, they are not so strong, and their weakness is accentuated by the greater strain brought to bear in bridge-work, and it is only in the cases where there is practically no " bite " that they can be used. In removable bridge-work the band is a necessity for really good work, but the difficulty of the gold showing may sometimes be got over by having the facing fitted over the inner cap, and just resting hghtly on the gum, providing it does not make the tooth seem too prominent. Li a fi.xed piece this is absolutely inadmissible : the band and facing must always be flush. Relative Value of Fixed and Removable Bridges. — There can be little doubt that a well- made removable bridge, built on the proper lines to suit the case in hand, is far superior in most cases to a fixed one ; it is true that some patientslike so much the idea of " fixture ", that it is sometimes difficult to make them see the advantages of a removable piece, but this diffi- culty can almost always Ijc overcome. In cases in which it is essential to make the work removable, it is advisable to refuse to do the work rather than run the risk of failure by not so doing. The two main advantages of a removable bridge are the ease of repair and the greater longevity of the piece from the point of view of the alnitments lasting better, and the chief disadvantages are the greater difficulty of construction and the longer time taken and number of visits that a patient must make. These points must be weighed carefuUy in each individual case, the jjatient's temperament being taken into consideration. With regard to the ease of repair, an accident may happen to the very best-constructed bridge — a facing may break ; but if removable this is easily put right. Some may say that re- movable facings do away with this difficulty — they do partially, of course ; but then there is always the fact that there is a much smaller selection of colour in removable facings, and this is a great difficulty to many operators and of very great importance for the aesthetic result. It can be got over by making special removable facmgs or two-part backings for the case in hand, but this is a much more lengthy process, and cannot always be used. However, the facing question is not the most important from the repairing point of view ; it is this — that sooner or later in most mouths recession of the gum at the cervical margins will take place. Now when this happens, for exam{)le, on the medial surface of a second lower molar abutment, the removable bridge is taken off, and either the tooth is filled or the inner cap is removed and repaired or a new one made, and the piece is then as good as before ; and it must be remembered that the daily (or several times daily) removal of the bridge very often prevents the occurrence of caries in this position — the patient can pay particular attention to that part of the tooth when there is recession, and it can be kept scrupulously clean. In a fixed piece any recession of the gum in this position means certain caries at an early date, and when it has taken place the whole bridge must be removed — a difficult operation and one that means that in many cases the bridge is rendered useless, and a new one must be made if it is to be satisfactory. Then again, the longevity of a fixed bridge is probably very much influenced adversely by the fact of both the abutment teeth being always held firmly in one position and of having no move- ment at all apart from each other. In the normal condition in the mouth a tooth has a certain amount of rao\omcnt in its socket, and this condition of individual movement is more nearly approximated in a removable bridge ; because, when the piece has been sprung into j)lace there is undoubtedly, after it has been worn for a time, a certain amount of movement of the outer on the inner caps — not sufficient to be uncomfortable or insecure, but enough to give each abutment piece a small amount of play. And again, by leaving it out at night when possilile, the roots are rested and the mucous memljrane is refreshed and stinuilated by being left uncovered and perfectly clean — undoubtedly a very important point to be taken into consideration. The cases in ^^■hich a fixed bridge is perhaps preferable to a removable one are those in the front of the mouth consisting of one abutment piece and one facing, with a spur in a filling on an adjouiing tooth. Unless two abutment pieces are made in these small cases they are apt to work loose on the iimer caps and be a constant source of aiuioyance, and the employ- ment of two abutments means often the un- necessary mutilation of a practically sound tooth. IMPRESSIONS With regard to impressions in bridge-work, one thing is of great importance, and that 607 is to realize that a plaster impression repays one in every way for the extra time em- ployed in taking it ; there is absolute accuracy and no chance of " dragging " or \\arping, as with modelling composition ; then again, the final model, on which the piece is to be finished, can be made from an imf)ression and bite in one piece, ■with the certainty, if properly done, of a perfectly true occlusion. With any othei' material, a " squash bite " impression, or even one taken in the ordinary way in a tray, is very easily distorted in removing from the mouth, and it is very difficult to be sure that the abutment pieces or bands, as the case may be, are replaced in their proper position in the impression before casting, when they have not come away in the imjjression. For instance, supposing composition were used in a case of two gold crowns as abutment pieces, the bands of these crowns are put in the mouth for the last impression, and if properly fitted should hug the roots tightly ; they are also contoured ; if the composition comes away leaving the bands on the roots, as it should as a rule, it is i^ractically impossible to replace the bands tightly in the impression owing to the dragging of the material. For rough models, of course, composition is very useful. Some ojierators complain that a bridge made from a plaster impression goes into place in the mouth \\ith more difficulty. It is not easy to see how this is, for the bridge either fits or it does not, and the slight shrinkage of the solder is allowed for by the natural spring of the teeth in their sockets ; the abutments often require a little touching up on their sides to allow the caps to go over them, but after that they sliould fit snugly into place under the gum with the aid of firm pressure, or perhaj^s a little gentle tapping. The taking of plaster impressions for ordinary work is described elsewhere, but the taking of a " squash bite " in plaster is here described as being chiefly used for bridge-work. The plaster is of the soft variety, and coloured with carmine in the bulk ; the abutment pieces being in the right position on the roots, the mouth is rinsed with mUk of magnesia, thus facilitatmg the removal of the plaster from the mouth. The plaster is now mixed to the consistency of thick cream, in water to which has been added a few drops of eau de Cologne, and a pinch of salt to hasten the .setting. The plaster is then taken on a broad spatula (an agate one is best) and spread over and around the abutment pieces and the space be- tween, and on the adjoining two or three teeth, being left pretty thick along the palatal aspect of the teeth. The patient is then directed to turn the tip of the tongue as far back as possible against the median line of the palate. and at the same time to close the teeth tightly and keep them closed. More plaster is then applied along the buccal aspect of the teeth to be included ; jjl^nty of plaster everywhere facilitates removal and the reassemblmg of the fractured pieces. The plaster should be mixed to such a consistency that by the time it is in place in the mouth it is getting hard, and in a minute or t«o is ready for removal. Mixmg the plaster in warm water also hastens the settuig and is pleasanter for the patient. Wlien the surj)lus plaster m the bowl breaks with a clean fracture, remove the impression from the mouth in as few pieces as possible, carefully placing the pieces m order on a piece of blotting-paper. When the plaster is quite hard, and before the impression has dried, rinse in water and brush away carefully with a camel's-hair brush any loose pieces adhering. As the abutment pieces will probably not have come away in the impression, clean them carefully, place in position, and put the pieces of the broken impression together, waxuig them with hard wax at points not required on the model. Now run a thin film of pink wax inside the walls of the crowns or bands, but leaving uncovered with wax an area of the under-surface of the cusps of the crown (or of the flat tojj of a removable abutment). The edges and inner surface of the band portion of the crowns, to the extent of about the thickness of thick note-paper, should be scraped free of wax. If in the abutment pieces there are tubes or pins, these should also be waxed over with a thin film. After casting, this aUo«s the wax to be burnt away, and the abutment pieces can then be taken off the model and replaced ■ndthout any danger of getting them in the ^^■rong position. This very carejid waxuig of the caps before casthig cannot be emphasized too strongly, as on it depends largely the accuracy ■with which the piece will go mto position m the mouth ; the necessary removals of the piece from the model dining the makmg cause a certain amount of "rubbing" and accurate waxmg reduces this to a minimum. That part of the impressions containing the caps should now be varnished until glazed with sandarac varnish, in which has been dissolved a piece of " indelible ' pencil sufficient to colour it, and which has been diluted onc-haLf with alcohol from that usually supplied by the manufacturers. The model and overbite are now cast and separated in the ordinary way. The abutment pieces are warmed, and removed, and the wax is cleaned off — the best way is to heat the crown several times, putting it on the model each time until the wax on the model and cap is burnt away. 608 It is very essential that all the details that go to securing a good model should he faithfully adliered to, as a bridge should be finaUy waxed up and invested straight from the model, and never tried in the mouth just before investmg, as is so often done, so that an accurate model is all-important. Goslee (4) advises that in all cases the im- pression with the finished abutment pieces in position should be taken in plaster, a wax bite being also taken {i. e. a '' squash bite " m wax), and that the model and articulating model should be mounted on an anatomical articulator in correct occlusion by means of the " wax bite ", and the work then fuiished in the ordinary way. Li cases where a very large bridge, or a series of bridges comprising practically aU the teeth, is being made, thLs method is necessary; but in case of a bridge of, say, three or four teeth, or a small bridge in the incisor region, it is distinctly unnecessary, and is inferior to the "squash bite" in plaster for the following reasons : The amount of the lateral movement of the mandible, and the consequent necessary length of the cusps of the bridge, can be easily noted in the mouth ; and if it is allowed for in the construction of the bridge, any slight shortenmg of the cusps can be done in the mouth before cementmg the bridge. By the other method much unnecessary work is done : fu-stly, the whole of the teeth must be included in the plaster model, as otherwise the lateral move- ments may not be even approximately true, and unless the path of the condyle is taken, and even if it is the lateral movements are only approximate; then the "wax bite " admits of much inaccuracy in cases where the articulation is abnormal — it can be so easily adjusted wrongly to the models if there has been the slightest distortion of the wax in cooling, and removal from the mouth. Then again, as has been pointed out, if there is any great abnormal- ity m the bite, a bridge should not be constructed unless this can be remedied by cutting down the cusps of the opposing teeth, or by crowning them, or otherwise making the condition as nearly normal as possible. If there is any doubt as to the right height of cusps, etc., the finished abutment pieces can always — and in some cases should — be tried in the mouth and articulated there, and the final model taken with them in position on the roots, the dum- mies being afterwards fitted and soldered with- out further trial in the mouth. DESCRIPTION OF MAKING A TYPICAL FIXED BRIDGE In order to describe the making of a tyjjical fixed bridge, the case will be taken of a mouth in which the left upper premolars have been lost, and there is also a carious first molar, broken away distally and labially to below the gum margin, and a carious and hoUow canine. The occlusion is normal, the lower premolars not having elongated. It is jsroposed to construct a bridge having a Richmond crown abutment piece on the canine, a gold crown on the molar, and two premolar dummies with porcelain faces. The devitalization of teeth and treatment of septic pulps, and the general methods of root-canal treatment are dealt with elsewhere (Chapter XXVII), and need only be touched upon here in so far as the j)rocesses bear upon actual bridge -construction. With regard to the sealing of the root-apex, it is best, in cases in which the canal is to be used for a pin or tube, to defer the sealing until the canal has been partially reamed ; it is so much easier to place whatever material is used (generally gutta-percha) at the extreme end of the canal after it is enlarged, and fuial sterilization where necessary can be better carried out. Also, and more important, there is no risk of removing the root-filling during subsequent reaming for the pin or tube ; theo- retically one could not do so without drilling through the apex, but practically it may hap- pen, the gutta-percha for instance being dragged away. A rough squash model and " bite " is first taken in composition, or better still in plaster ; this is useful for reference during the work, and in cases of any difficulty as to methods of treat- ment it is advisable to study the model before deciding just how the bridge is to be constructed. The pulps of both teeth, if alive, having been destroyed and removed, or if dead teeth, the canals having been cleaned and sterilized, the roots of the molar are fiUed in the ordinary way, the tooth is cleared of caries, and a tem- porary gutta-percha filling placed in it, so as to force the gum well away from the cervical edges that are under the gum. The apex of the canine is then sealed temporarily with absorbent cotton- wool dipped in antiseptic. The crown is cut off, and the root " dressed down " so that about one-sixteenth of an inch of root is left projecting from the gum. The root is then dried and the absorbent cotton removed ; a very fine flexible broach is passed to the apex ; a small piece of rubber -dam having first been placed on the shank of the broach, the exact length of the canal is then measured off from this on the shank of a Beutelroc or similar drill by this piece of rubber, and a similar length also measured off on graduated sizes of other drills, up to the largest ; by this means, the danger of subsequently perforating the apex is reduced to a minimum. 609 Successive size drills are then used in the ordinary way, and the canal is enlarged. It is advisable, after the first three or four drills have been used, not to pass the others quite to the apex, a sufiScient enlargement of the canal only being obtained to allow of the apex being easily sealed w-ith gutta-percha. The enlargement must be made gradually tapering to the end ; this is quite easily done provided that each drill is only slightly larger than the preceding ; but should too large an increased size be used, a ridge will be formed, and if there is any curve towards the end of the root, it is then extremely difficult to pass even the smallest drill again to the apex (as will be seen by the rubber measurement), and the risk is run of a faulty root-filling. This root-filling is now inserted, gutta-percha being generally chosen. Care must be taken to use only just enough, as, if too much is put in, the length of the canal is diminished, and, as a rule, one cannot have a root-canal too long. One thirty-second to one-sixteenth of an inch of gutta-percha is enough, this being measured by passing up a drill and noting the difference in length before and after filling. At this stage gutta-percha may be pressed well over the root surface, and held in place by a blunted tin-tack, or a pin with a flat disc attached, passing up the canal. In twentyrfour hours the gum is mcely pressed away from the root ; a novocaine tabloid is then ground to a powder and a little dabbed between the gum and the tooth, sufficient to prevent the pain incident to removal of the enamel. The next step is the " coning up " of the canine. Too much trouble cannot be taken in doing this, as it is not an easy thing to prepare a root perfectly for the fitting of the band. The shape of the teeth seen in trans- verse section at the gum level is more or less the same in each individual (see Figs. 765 and 766), and it is essential to have a clear idea of the shape of a given tooth from this aspect after the enamel has been removed. In the removal of all the enamel lies the secret of making a well-fitting band, and the omission to remove all is the chief cause of failure at this step. Once this is realized the main difficulty disappears, and it is surprising how comparatively easily a band may then be made to hug the root tightly, so that an explorer passed beneath the gum will reveal no greater ridge than that caused by the thick- ness of the gold. Root preparation is tedious work both for the patient and operator, but its importance cannot be insisted on too strongly, and the extra time spent in properly so doing is more tluin made up during the process of fitting the band. The removal of enamel is best accomplished 20 by means of heavy "enamel cleavers" with curved blades, right and left, cutting on one side only, and having short thick handles that can be firmly grasped ; the rounded edge passes under the gum margin and causes little or no injury to the tissues. This form of cleaver was Fio. 765. — Upi^er ; right side. first suggested by Peeso and is undoubtedly the most useful. Case's enamel cleavers are in addition very useful. The point of the blade is used to start the cleavage by forming a Fig. 766. — Lower; right side. groove or cut in it, and then bit by bit it is pulled off. Wlien the " bulge "of the enamel is thick, it may be thimied down by a stone — this greatly facilitates removal. A firm sup- port for the thumb or fingers must be got on the adjoining tooth. By passing the blade of a spatula under the gum and noting whether 610 the ridge has disappeared, and by the " feel " of the root to a probe, one can tell when the enamel is all removed. The enlargement of the root-canal is now continued, the next sizes of the drills are used up to the largest, and then the reamers, enlarg- ing the canal sufficiently to enable pin-wire (sile 3 Ash) tempered well to be passed up, giving a length of pin as much more as possible than the length of the facing when finished. In a canine, pin-wire size (between No. 3 and 4 Ash) may be employed, but care must be taken not to weaken the canal in a small tooth. Iridio-platinum (10% iridium) is better than gold for fixed bridges ; there is no danger of fusing when using a high carat solder, and a thinner pin with equal strength may be used in necessary cases. The Peeso root reamers will be found the most useful, as the tip of the reamer does not cut, there being a small thin point, which acts as a guide and helps to prevent cutting through the wall of the canal, and it is impossible with ordinary care to go through the apex. The coning up of the molar is at this stage proceeded with. First, the occlusal surface of the tooth is ground freely away to allow for the necessary thickness of gold cusps. As will be seen later, these cusps are made solid with gold of the carat and constitution of coin gold, so that plenty of space must be allowed ; the common practice of allowing only sufficient room for cusps of about No. 4 (Ash) " crown " (22-carat) gold, reinforced with a little solder, is entirely wrong ; tliey wear through very quickly in the mouth and of course are not strong. The objection to reinforcing cusps with low carat solder to obtain the required strength is that if any grinding has to be done in the mouth to "adjust the bite, and it sometimes happens that there is a sort of "alternative" bite, the aesthetic appearance of the bridge is impaired by the discoloration of the solder. In preparing the waUs the procedure is some- what similar to that for the preparation of the canine, but stones are more freely used, and do the greater part of the work; for, as the abutment piece on a molar is in most cases a gold crown, as much of the walls of the tooth as possible is left standing, and the cleaving of the enamel in such cases without its being thumed down is almost impossible. Now, were the teeth used as abutments always parallel, the removal of the enamel would leave the walls in proper alignment; but in many cases, when it is desired to put a bridge, there has been more or less tilting of the teeth, especially in the molar region. It will be easily seen, therefore, that if the walls of the prepared root and the root -canal are not parallel or slightly less than parallel, the finished piece would not go into place ; hence this must be kept in mind during the process of coning up. By merely examining the teeth in the mouth, the amount of removal necessary is very diffi- cult to estimate, so that the model must there- fore be carefully examined in order that a general idea may be obtained. Much time is saved by so doing, and where a molar, for instance, leans considerably in any direction, a bold slice of tooth may be cut off by a plane- faced disc, and the tooth roughened up into its approximate shape. Help is obtained in getting alignment by bending a piece of soft wire, of a size that easily fits the canal of an incisor or premolar, into such a shape that the two ends will be parallel jf^.^ 767. (see Fig. 767), one end being placed in the canal of the first abutment tooth and the other in or against the second abutment tooth. German silver plate cut into narrow strips and bent to suit the particular case, is useful for molars and premolars when shell cro\vns are to be used. In the bridge under descrij)tion the molar is so shaped that its walls are nearly parallel with those of the canine and its root-canal. To get exact parallelism is impossible, and indeed not desirable, for by making the walls slightly less than parallel, a shght natural spring is obtained when the finished piece is put into place. The teeth are now ready for the fitting of the bands. The rough fitting is best done on a model ; it saves the patient considerable dis- comfort and pain and saves the operator's time, as it can he done by the mechanic. Flu. 7I3S. The method is as follows : A piece of ordinary modelling wax is made into a cone about an inch long, and, when at a temperature slightly above that of an ordinary warm room, the point of the cone is passed 07ice through the flame of the spirit lamp and then placed in the centre of the root ; continuous pressure is exerted against the root and gum until the wax gives and spreads over the surface, when the outline of the root is shown on the wax on removal. In the case of the molar, one side being below the surface of the gum, par- ticular attention must be paid to getting this edge defined in the wax : by placing the wax near the edge in the first instance and then 611 pressing, this result will be obtained. This is done both for molar and canine. Each wax impression is cast separately in plaster, and when it is quite hard, the base of the model is warmed and the wax removed. Fig. 7G9. The outline of the root is now seen clearly in the plaster, even the part that is under the gum in the mouth (see Fig. 768). A fine-pointed instrument is now taken, and, by keeping it flat against the root and in the same plane, the plaster is gradually " pared " away, forming a groove all round the root to the depth of about a thirty-second of an inch. The plaster base is then cut away all round the Fig. 770. root until the bottom of the groove is reached, when the model will be as in Fig. 769, i. e. one thii'ty -second of an inch more from the model than when first cast. If the root in the mouth has been properly " coned up '", this model will pretty faithfully represent the condition in the mouth, with that part of the root under the gum exposed. These models are dried slowly overnight, and then coated with sandarac varnish several times (the vaniish usually sup- plied should be diluted one-half with alcohol), the hollow parts of the roots are filled flush with hard wax, and they are then ready for fitting the bands. Measurement is taken with a thin strip of annealed " brush copper " (which can be got at an electrician's) and the length marked out on the gold. Gold of approximately the same carat and fine-fitted and let down so that it follows the gum line. Twenty-one carat solder is used here if the soldering method is employed. The gold is cut from the main piece on a slant (see Fig. 770) so that when fitted it flares out all round and gives the commencement of the contour. If the cone is made from a curved piece of gold (see Fig. 771), great care must be taken to see that the measurement is accur- ate, as it is more difficult to obtain on the curve. Only a very slight " flare " must be given, as the remaining necessary contour is done in the mouth by " contouring pliers " ; this contour- B ■C ing only applies to the molar band, the canine not requiring it (see Fig. 772). The sweating of the edges together instead of soldering is desirable, and may be described here. The end of the band A (see Fig. 773), after being bent roughly round the plaster root, is chamfered at B, to about the extent of the thickness of the gold. At C it is also chamfered, but on Fig. 771. hardness as coin gold rolled into plate form jiji^ inch thick is the best to use (about size 4, Ash) ; it is hard and a good colour, and, as will be seen later, solders that work well with it can be made with the scrap. A piece of the right length having been cut off, and of sufficient depth to allow for fitting, it is annealed, bent round the model, and either soldered or sweated, and then the reverse side. These ends are then " sprung " against each other into perfect contact all along ; to do this only requires a little knack, straight ends to the band, and perfectly flat bevels of the same width, made by a flat fine-cut file. 61i A small amount of "liquid flux" (sorosis is one of the best varieties) is then run between the ends, and the point of the blowpipe applied to the gold at the edge that is not going to be fitted to the root (see Fig. 774), and as soon as the gold "sweats " at this point the flame is run firmly along the line of junction, just as if there were solder there, until the metal fuses all along. A small pointed blue flame {and no draught of any sort to divert it) is necessary, and the gold must be well fused at the point of commencement, and the whole thing done with one sweep of the flame ; otherwise oxida- tion takes place and the band has to be carefully pickled and refluxed before the edges can be further united. The ends need not be " cham- fered ", but it gives a much better finish if done, as little or no filing is necessary. Both bands being fitted to the model, they are transferred to the mouth and fine-fitted to the roots. If the previous stages have been carefully done this will be a comparatively simple matter, and they should be fitted up under the gum to the extent of about a thirty- second of an inch ; if anything, they should be fitted on the tight side to the model, as they can then be slightly enlarged if necessary at the cervical edge, in fitting to the mouth, by means of stretching (contouring) pliers or by means of a small anvil and hammer. The molar band is now pressed with the fingers, while on the root, until it is somewhat the shape of a first molar tooth, and not merely a round ferrule (in tran.sverse section like Fig. 775), and it should then be contoured with Peeso contouring pliers (short heavy-beaked pliers, which stretch the gold) untO it is in proper contact with the second molar. Tliis proper contact and contouring is of great importance, firstly, for the aesthetic effect, and secondly, and more important, for the proper preservation of the inter-dental space ; by shaping the band and contouring it carefully, and by selecting and applying the right sort of cusps or "top", the natural shape of the tooth can be faithfully reproduced. The band should be contoured exactly to touch the contiguous tooth at the normal point of contact of the natural teeth, and to extend a little beyond it ; then by " pinching " the edge of the band all round, this extended portion only is brought away again from the contiguous tooth, so that when the cusp is soldered, the actual contact point need not be interfered with during filing up and polishing, as the part of the band immediately below the junction with the cusp will be known to be contact point and can be left severely alone, with the o Fig. certainty that when the bridge goes into place this most important adjustment will be right (see Fig. 776). The proper alignment of the pin and two bands must be here carefully noted in the mouth. The band and root of the canine are now cut down labially by root-facers (Peeso), so that (when the "top" is soldered on) the surface of the gold labially is just below the gum, and the band is left standing about one-sixteenth B' Fig. 770. — A, Contact point; B, Edge of band. of an inch above the gum on the palatal side ; the band is then taken off the root and filed absolutely flat (in a slanting plane) on that side on which the " top " is to be placed, and then replaced on the root ; it will now appear in vertical section as in Fig. 777, the dotted line representing the " top ", which will be put on presently. The molar band is filed flat on the edges on which the cusps are to go, and a space sufficient for the thickness of the cusps left between it and the opposing teeth (note previous remarks as to contact point). The canine band is now made into a cap as for an ordinary Rich- mond crown, the top being sweated or sol- dered on (if soldered, 21 -carat must be used) ; the top must be of slightly thicker gold than for the band, viz., yi^jy inch, (about size 5, Ash), to allow for any slight filing flat later on (in order to get an easy adaptation of the base of the facing when it comes in contact with the cap), in case there is any warping during the sweating of top to band. In sweating the top on, care must be taken that the band and the piece of gold for the top are flat, and so come in absolute contact all round (the depots supply a small swager or " plunger " for flattening small pieces of gold for this purpose). The top is held in iridio- platinum-boaked pliers at the extreme edge, plenty of surplus being allowed ; the band is dipped in liquid flux and placed on it, when they will be in absolute contact everywhere, and they are then held over a Bunsen burner flame Fig. 613 (see Fig. 778,) the points of the phers being brought to a red heat first, so as not to absorb heat when the actual sweating takes place. As the gold is heated to the required degree, the corners of the square " top " begin to curl up, and just at that moment the gold is given a " dip " into the flame, when the band and Fig. 778. " top " will be seen to fuse together just as if there were solder between. It is then trimmed and placed on the root, and a pin is fitted and soldered in the ordinary way with 21 -carat solder, care being taken to bend the pin before soldering it, so that it will not have to be ground away when the facing is fitted ; as much room as possible must be left for the facing by this bending, as it is often difficult to get room for both pin and facing. (See Fig. 779.) This being done, it is replaced in the mouth, and another jjlaster model is taken with both cap and the molar band in position. The molar band is now made into a finished crown by the following method. A molar crown die is chosen from an assort- ment, which it is desirable to have, and the method of making these dies will be here described : An extracted molar tooth with crown surface intact is selected, and with a saw the cusps and a little less than half the crown are cut off (see Fig. 780). This half tooth is then placed in a " Badcock " water swager, and a matrix in thin copper made, appearing as in Fig. 781. Into this copper matrix is flowed soft Fig. 779. solder, the surplus edges are cut off, and the surface is filed quite flat ; it will then appear as in Fig. 782. A large selection of molar and premolar dies should be made and kept ready. To return to making the gold top : A die is selected large enough to be in contact with the gold band at all points (a little overlapping Fig. 780. does not matter at all), and more or less right as to the bite (as seen by the plaster model). This die is placed in the Badcock swager and the same process gone through as was employed in making the copper matrix, oifly pure gold (thickness ixnin) '^ "^^^ ! ^ gold matrix is thus obtained. This matrix is painted with whiting on its under-surface (or embedded in plaster and sand) and placed on a soldering block (see Fig. 783). The same gold as is used for making a band is fused into about six or nine separate pellets, each about twice ^^ Fig. 782. A, Copper matrix ; B, Soft sokier. the size of a pin's-head, and these pellets are placed in the matrix (see Fig. 784). A steady whitish flame is played on the pellets from directly above (not at an angle) until the pellets begin to melt and '' settle " into the matrix, making one solid piece. No flux is used at first, but towards the end a little may be used, and care must be taken not to overheat and fuse the pure gold. It is not very difficult to do, and with a little practice may be done quite 614 quickly, but if once the matrix is fused the whole thing is spoiled. The surj)lus gold matrix is cut off, and the bottom filed absolutely flat by drawing it along a fine-cut file. Pressure-casting has of course rendered this method much less C Fig. 783. A, Gold Matrix embedded in B, Investment material ; C, Soldering block. useful than it was, but it is still one of the quickest ways of making the cusps. The cusps and band are now wired together and fluxed, a very small piece of 21 -carat solder is placed in the inside, and the whole held over Fig. 785. Fig. 784. the Bunsen until the solder fuses, appearing now as Fig. 785. The surplus cusp is cut off (see dotted line. Pig. 785), the crown placed on the model, and the occlusion adjusted by cut- ting away the cusp. Wlien this has been done, and after the final polishing, there will be very little left of the pure gold matrix, and a crown is thus obtained all of the same gold — band and solid cusps. Any further carving of the gold cusps may be done with stones and finishing burrs. The next step is the selection of suitable facings as to colour and size. That part of the cap anterior to the pin is ground perfectly flat (if any solder has got on it), and the canine facing fitted first and waxed temporarily into place ; the premolars are next fitted to the gum so as to rest lightly on it at their cervical edges, but they must neither touch each other nor the abutment pieces on either side ; they are held in place with wax, and a plaster wall is built up on the buccal side to hold them and the canine facing in position. When the plaster is hard, the facings are removed, and the occlusal ends of the premolar ones ground off about one tliirty-second of an inch at an angle of 75° with the back of the facing (see Fig. 786). The occlusal bevel of either facing should not be higher than the other. The facings of the premolars are then backed with platinum about y^u inch thick, by placing the platinum on a little block of Fig. 780. Fig. " india-rubber " and pushing the pins through, and then conforming it to the facing by bending over the pins, flowing a little wax on to the platinum, and pressing with the fingers until the wax is hard. The backing should extend just over the edge which has been ground to fit the gum, and be continuous with the occlusal bevel (see Fig. 787). Gold camiot be used in this way for backing, as sufficiently thin gold would be in danger of fusing during soldering. On the side they should touch each other and the abutment pieces. The canine facing is backed in the same way, only the backing is extended beyond the tip (but not bent over it), and is fiush with the flat under- surface that fits on the cap (see Fig. 788). If it is then waxed accurately in place on the cap, two perfectly flat surfaces are in contact, and after soldering, the contraction during cooling will cause the facing to be as in Fig. 780, leaving a very unsightly space (in the illustration the space is exaggerated to show what is meant) ; therefore in waxing the facing, just before the wax is cool, lever it ever so slightly away from the cap at the back, as in Fig. 790, and the result will be that, after soldering, the facing and cap will be in exact contact (see Fig. 791). The plaster supjjort, which is now put back, will just have to be altered a little to allow for this ; the premolar facings are put in place, a piece of oiled paper is placed on the cast, 615 and all are waxed firmly together, the wax bemg kept liigh enough to allow the cusps of the premolars to be put on. Suitable cusps are then made in the same gold by the method described for making the top of the molar abut- ment piece, and these cusj)s are then ground Fig. 789. Fig. 790. or filed to fit the bevel on the facmgs (see Figs. 792, 793), the same space being left for the con- traction of the solder as was done in the case of the canine and its cap. All the parts being now as- .sembled, viz. the canine cap and facmg, the dummy facings backed and waxed up with their gold cusps in position, and the molar crown abut- ment piece, and all firmly united with hard wax, the piece is invested in plaster and sand (two parts sand and one part plaster), the facings having first been pamted with whiting to keep the surfaces from being roughened, and is then soldered in the ordinary way with 20- carat solder. In investing, only an amount of investment sufficient for strength is used, and the sides of the mvest- ment are pared flat so that it can be more easily tipped in any direction required during soldering ; soldering is done on an iron " grill " on a small gas "plate-heater", i.e. the piece is not removed from the heater to a soldermg block to do the actual soldering ; it is much easier to keep the piece up to the required degree of heat on a heater, with the gas lighted Fig. 791. only so much as will not interfere with the flame of the blow-pipe. It is better not to wash out the wax with hot water, Init merely to heat up until the bulk of the wax can be removed with a spatula, and then allow the remainder to burn off in the further process of heating up. Wien the mvestment is partially dried, it is dusted with powdered borax, and the solder applied in the ordinary way, and then the heating up and soldering are continued. With a high-carat solder it is unnecessary to use pieces of metal across the joints in soldering, and the necessary thickness of solder at the proper points should be obtained by tilting the invest- ment, and draw ing the solder w here it is wanted by means of the flame. A few small pieces of solder should be placed in the inaccessible places before starting to solder, and care should be taken to see that these are thoroughly fused to commence with. It does not matter how quickly the investment is cooled down after soldering. In " finishing up ", revolving stones on the dental handpiece Fig. 792. Fig. 793. are used to do the fuie finishing, and the wheel is revolved from the gold to the porcelam. Polishing is done with discs and buff-wheel on the lathe in the ordinary way. An excellent way of makuig suitable-sized felt wheels for polishing on the lathe is as follows : A broad felt wheel is taken and cut into four slices by holding the point of a very sharp knife against it while revolving on the lathe ; it is then dipped into shellac dissolved in alcohol, and taken out immediately and dried thoroughly on a glass slab; it is then "trued up " on a lathe with a piece of flat wood, and coned with a sharp knife, the flame of a blow- jDipe being kept on the wheel to soften it while being " trued up ". This makes a hard wheel with a narrow edge, which will go in between the cusps and narrow places, and will only polish where it is required. An extra finish may be given to a Ijridge by filling \\\y the spaces between the facings, and between the facmgs and abutment pieces, with pure gold, i. e. by making an ordinary gold filling with " mat " gold at these points ; as a rule there is sufficient hold for the gold when the bridge comes out of the investment, but to make quite sure of the hold the sides of the 616 facing may be ground slightly just before waxing up, so as to give a slight undercut at these points when soldered. This method makes a very beautiful finish to a bridge. Post for Crown- and Bridge-work. — Mention may be here made of a post for crown- and bridge -work, suggested by George Brunton of Leeds (1), and described by him as follows — " The ijost is made taper, hollow, and open in front and at the labial aspect, the taper f)0st fits into a correspondingly taper hole in the root, and the hole is notched with a \\heel burr opposite the opening in the post. Wlien setting the crown or bridge the hollow post and the notched hole in the root are filled with cement, and when set the post is firmly locked in the root, and rotation is prevented. " The advantages from the use of this post are great strength, simplicity of construction, and easy removal when necessary. The great superiority of this form of post to operators lies in the fact that it can be used in roots that are not parallel. Should a post break, and have to be removed, it is very easy to do so by drilling out the cement from the inside of the hollow post at the back or lingual aspect. It is then easy to force in the two halves of the post, and remove it. There is thus no weakening of the root by the use of the trephine or drilling around the post to loosen it. This method leaves the root ready for the insertion of a new post. The construction is very simple, requiring only such tools as are to be found in any workshop, namely, a hand-vice, taper man- drel, shears, a small anvil, hammer, and file." The British Dental Journal says of this post : "... The interesting point of novelty consists in the abandonment of any necessary attachment by adhesion of cement between the external surface of the post and the internal walls of the root -cavity, dependence being placed ujJon the keying of the cement in the interior of the post with the notched position of the root interior. Should this in use prove to be sufficient in strength, it would become almost impossible, in silting, to force any excess of cement into the apical foramen, and the sheet metal used need not only be quite thin, but also perfectly smooth. There can be no doubt about the novelty and great mechanical interest of this device, especially where, as in all porcelain bridge- work, absolute inflexibility is a requisite, " It is obvious, however, that the special features of the post are only developed when the most perfect accuracy of adjustment in direction is secured. Though failing this, with provision made for a surrounding of cement and inserted as the usual forms, it still appears to have conspicuous advantages over the other well-known tjrpes." CHAPTEII XXXYIII BRIDGE-WORK {continued) DESCRIPTION OF MAKING A TYPICAL REMOVABLE BRIDGE Canine to molar. Half-cap and split piu on canine and telescope-cap on molar. The preparation of the abutments is the same as described in the making of a fixed bridge, but even greater care must be taken in getting the proper alignment. Gold of the same carat and hardness as coin gold is the best to use. crown gold (22-carat) being too soft. The canine band is first fitted, having plenty of surplus and having the sides slightly less than parallel, and quite smooth and even from the top to the bottom edge (». e. keep the beaks of the j)liers embracing the full length of the gold in bending up, so that there is no " bulgi- ness " anywhere ; other\\-ise the telescopic fit, to be described later, will be interfered with). The molar band is then fitted in the same way, and with slightly conical sides, and the exact alignment obtained ; the canal of the canine is enlarged and notice taken that it is in align- ment with both bands. The canine band is now cut down ^^ell below the gum in front {,'.f inch), and standing out from the gum on the palatal aspect about yV inch or more. This band is converted into a cap, and the top should be j^^^j inch thick. A hole is made through the top, and the tube (in length as nearly as possible the length of the crown to be used) placed in the canal and \vaxed in position, the alignment being noted. The hole tlirough the top for the tube should be large, and in waxing up the wax should be allowed to go well through, so that \\hen soldered there will be plenty of solder at the junction underneath — the reason for this will be seen later. The cap is carefully removed from the mouth and soldered with 20-carat solder. The tube here referred to, and the split pin to be later mentioned, had better now be described. Three or four steel mandrels (sizes 52 and 53 Stubbs' steel wire-gauge) are obtained, and kept smooth and polished ; the smaller sizesiare used for small teeth and narrow root-canals, and the larger for large teeth. A piece of iridio-platinum plate (size iri>,jT inch) in breadth the required length of the tube, is filed to a knife-edge, and with half-round pliers the edge is turned slightly upwards ; a mandrel is placed against this 20* 617 upturned edge, the plate placed on a bench anvil or piece of fiat steel, and then by pressing with a broad fine-cut file on the iridio-platinum plate, and holding the mandrel tightly against it with Fig. 7'j4. A. A. Iridio-platimim; B. Mandrel; C. Rladeof file; Arrow — direction of movement of tile. the left hand, the plate is gradually rolled round the mandrel to form a tulje (see Fig. 794). This is soldered with pure gold, and the next-sized mandrel gently tapped through it, so as to stretch it and make the inside perfectly smooth. The surplus is then cut off, and a piece of the same plate soldered with pure gold to one end to form the floor ; the surplus is cut off and the whole filed smooth. The split pin is made from half-round wire — iridio-platinum or platinized gold (10% platinum) — as follows : a piece of wire a little longer than twice the length of the tube is bent over, and the flat sides are brought almost to- gether, by tapping gently on a bench anvil, and frequently annealing ; the ends are then united by a very small piece of the band or pure gold ; the flat surfaces are tapped into contact all along — if this is done before uniting the ends it is difficult in soldering to avoid uniting the surfaces all along. The pin is placed on a vice on the lathe and filed to fit the tube ; it is then left with the ends closed, and is tightened, if required, after the piece has been worn a little, by introducing a fine instrument between the halves (see Fig. 795). If the pin is a particularly short one, it is better to cut off the closed end, and tighten Fig. 795. 618 Fig. 796. by spreading the ends apart slightly with an instrument. The molar band is now cut down to allow room for the top to be put on, and for the outer cap and cusps ; judgement will have to be exercised as to how much space to leave ; as a rule it will be found that the difficulty is to have sufficient depth of telescopic cap and at the same time plenty of room for nicely shaped cusps. The requisite space having been obtained, the top is sweated or soldered on. This molar cap (which is the " inner cap ") should now appear as in Fig. 796. The canine and molar caps are then placed in the mouth, and a plaster impression is taken ; the caps are waxed and a model is cast. The caps are removed from the model by heating — a piece of iron wire heated and passed into the tube of the canine cap will remove it easily; the wax is burnt out by heating and replacing several times on the plaster roots. The caps are now ready for the outer caps to be made. Canine. — The excess of tube is stoned away about level with the cap, and the top surface of the cap is then made perfectly flat by gently passing it over the surface of a fuie-cut bench- file held flat on the bench. The entrance to the tube is enlarged somewhat by means of a finishing-burr, the bulk of solder that is under- neath allowing for this. A piece of the same gold as is used for the band, ^^§^7 inch thick, is made perfectly flat, and cut distinctly larger than the surface of the cap ; a hole is made through it to take the split pin, and the pin passed through into the tube and allo\\ed to fit as tightly as possible. The pin and top are waxed together, care being taken that the con- traction of the wax does not draw the surfaces of the gold from absolute con- tact ; the pin and top are removed and soldered with 21- carat. The piece is then replaced on the inner cap and filed | to a size just larger. A crescent-shaped piece of gold (r^,{J(7 inch) is cut, and fitted around the palatine, medial, and distal sides of the inner cap, being brought round the sides a little more than half way ; this must be carefully done, and must fit well at B, B (see Fig. 797) . A better way than fitting by hand is to cast a piece to the required shape. A surplus of gold is left at C (see Fig. 797). The top and crescent-shaped gold are waxed together (care being taken that the wax does not run through), removed, invested, and soldered with plenty of solder. One has now a removable half-cap and split-pin abutment piece. Molar. — The cap is removed from the model, and 20-carat solder is flowed around the line of junction of band and top inside ; this reinforces the junction and allows for rounding the " corner " later, so that the outer cap finds its way on better when in the mouth. A very thin film of wax is flowed over the inner surfaces of the cap — to prevent union « ith the fusible metal to be poured into it ; the cap is then placed in a paper cone, having the base of the cap towards its narrow end (see Fig. 798), and is forced fu-mly down, the cone being held together by means of an elastic band. The cone is placed in an upright position (the hole of a cotton-reel is a convenient way of holding it), and fusible metal is poured in; a metal cone is thus formed with a gold cap as a ferrule ; any fusible metal over the outer edge is scraped away, and the cap is rounded oft' all round the junction of the band and top, the solder previously flowed inside allowing for this without fear of makmg a hole (see Fig. 799). It is then polished properly, as after this no further polishing can be done except with rouge. Measurement around the middle of the cap is taken and another band made and gently tapped over it, being frequently annealed so that the one collar is forced over the other, gradually stretch- ing the gold and obtain- ing a perfect telescopic fit. The outer cap is made slightly shorter than the inner, i. e. so that it will, when placed in the mouth, reach to gum margin only, and is J.! inch shorter all round than the inner cap. The inner cap and outer band appear as in Fig. 801 ; the outer cap is cut down to the level of the inner at A, A (see Fig. 802), and by Fig. 798. 619 gradual burnishing made to fit closely there. The tightness of the outer cap is overcome by burnishing firmly all round until the requisite degree of looseness is obtained. The outer band is removed, and a top, xuhi ^^^^ thick, Fig. 799. Fig. 800. Fig. 801. Fig. 802. The next step is to put the contour on the molar cap ; this is done by adding flanges on to it by means of solder, as follows — A piece of gold is cut the same size as the outer band and in length about half the circumference. It is cut the same shape as in Fig. 803. The lower edge of Fig. 803. this is bent a little, so that it only touches at two points when placed against the band (see Fig. 804). It is now held in this position against the medial surface of the band in a pair of pliers, a liquid flu.x is flowed in, and the gold held in the Buiisen flame until the flux steadies the " wing " piece of gold in position ; it is gently placed on a soldering A. Fusible metal; B. Band; A. Band; B. B. Roimded C. Solder around jiinc- comers of band, tion inside. sweated or soldered on, according to whether the band has been soldered or sweated, and one has an accurately fitting telescopic cap. The edges of the floor are now trimmed flush with the sides of the band. A — block, and a minute piece of 21 -carat gold placed at the point A (see Fig. 805), and carefully fused. The solder at this point should really only just tack the band and " wing " together, and not Fig. 804. flow up between to any appreciable extent. A similar piece is soldered on the distal surface of the band. This outer cap with the attached wings is now placed on the inner cap (which is stUl on the fusible metal die), and the wings are pressed outwards to give the required amount of contour medially and distally. The ends are then bent in buccally and lingually to the required amount, the whole giving the natural shape of the tooth. The outer cap is re- moved from the inner, and the ends of the wings are held firmly against the band with pliers, fluxed well, and held in the flame until the flux dries off ; this also anneals the gold, and the ends of the wings now remain close to the band and do not spring away ; it is then placed on a soldering block and further pieces of 21 -carat solder are placed at the juncture Fig. 806. A, Telescopic cap ; BB, Contour pieces of Gold ; C, Solder. lingually and buccally (see Fig. 806). This solder is flowed well round by fusing and drawing the flame round, starting at the lingual or buccal aspect as the case may be, but never putting any more solder medially or distally, as there is so little room to solder that it may easUy flow inside the band and so spoil the fit. Plenty of solder is used to allow for filing up and finishing. The surplus contour or wing is cut off, and the whole made flush with the floor of the cap ; a cusp of gold is made as previously de- scribed for a fixed bridge, fUed flat accurately to flt the cap, wired to it, and soldered with 20- carat solder. The soldering is best accomplished by placing the abutment piece on the soldering block and using the blowpipe. The casting process can be used advantageously here, as the contour can be cast directly on to the outer 620 cap ; or it can be cast separately and soldered on, and the cusps then soldered as previously described ; or again, contour and cusps can be cast directly in one piece on to the cap. It is best to reinforce the junction of the cast part \nth the cap with a little solder, in case the union is not perfect, as is sometimes the case ; a better finish can also be thereby obtained. The further steps in the bridge are the same as for a fixed bridge, except of course that when waxed up for soldering the imier cap must be carefully removed before investing. This is a delicate operation as it is easy to distort the wax unless great care is used, but by employing a hard and brittle wax that will break and not stretch, and by leaving enough of the imier cap showing to enable one to get a firm hold of it, it can usually be done without nuich trouble. Fig. 807. Fig. 8U8. Figs. 807 and 808 show an upper removable bridge, with a telescopic premolar abutment- piece, and a split pin in the molar (it being supposed that the molar was too shallow to allow of a telescopic abutment-piece being used satisfactorily). Drill Guide. — A very u.seful form of "drill guide " is that devised by P. S. Campkin (2) ; it is used for obtaining proper parallelism of the canals in removable cases, where each abutment piece is to consist of a split pin and half-cap. Campkin describes this guide and its method of employ- ment as follows — " It consists of movable bars united by a hinge joint controlled by a nut, with two small tubes at each extremity, the inside diameter of which corresponds to pin-size, and is used as a ' drill guide ' in the following mamier : Each canal is opened the entire length, and after suitable treatment, each apex is perma- nently plugged with gutta-percha or other form of filling ; this prevents any foreign material being pushed through the apex in subsequent treatment. The available depth of each canal is noted, and a small twist-drill used as a commencement of the enlargement. A second twist drill is now used, larger than the first, but smaller than pin-size. The canal of one root is now enlarged to pin-size by twist- drill No. 3. The pin of the guide is passed through the tube at the extremity of the other bar, and into the canal of the root. The tube at the extremity of the other bar is adjusted over the entrance of the root-canal to be reamed, and the position fixed by tightening the nut in the centre ; the pin-size twist-drill is passed through this and allowed very gradually to enlarge the canal to its available depth, any pressure or undue force being avoided." ABUTMENTS FOR REMOVABLE BRIDGES Telescope and Split-Pin Combination. — In the foregoing description of a typical removable bridge, the ordinary haK-cap and split pin, and the telescope-cap abutment pieces, have been described ; mention will now be made of other forms of abutment pieces that are used in removable work. The combination of the telescope-cap and split pin in cases where the teeth are short is very useful, and is made in the following manner : The imier cap is made in the ordinary way ; a hole is made through the top, the cap placed on the root, and a tube passed through the hole into the pulp-chamber or a canal of the tooth and waxed firmly in place, having the tube parallel with the sides of the cap ; this is removed and soldered, and then the tube is cut flush with the top. The outer cap is now constructed, the exact position of the tube being located by tapping with a piece of wood over the entrance to the tube ; a hole is cut for the split pin, which is passed through the outer cap into the tube, fitting the tube loosely, but the outer cap tightly ; it is waxed in place, the outer cap is removed without disturbing the wax, and the two are soldered together. The piece is then finished as before described. Inlays. — Another form is the Inlay Attach- ment, which is specially useful in molars — 621 Fig. S09. The tooth is devitalized and treated, and the pulp-chamber filled flush with gutta-jjercha. A non-retentive cavity is cut in the crown surface, and brought through to the medial or distal surface, as the position of the bridge may require. In this cavity is put burnished platinum foil as for an ordinary inlay ; a platinum tube is passed through the floor of the matrix and through the gutta-percha to the floor of the pulp-chamber, care being taken that the alignment with the other abutment f)iece is correct ; wax is flowed into the matrix, and the edge carefully adapted, and the whole removed, invested, and filled with hard band gold. A groove is then cut in the inlay from the edge to the tube sufficiently deep to take a split pin, which has been made to fit the tube (see Fig. 809). A split pin is then adjusted, the inlay placed in the mouth and the impression taken. A somewhat easier way is to " cast "the inlay in 22-earat gold, having the tube in position in the wax, and partially to form the groove for the pin in the wax, making it quite smooth and even afterwards by means of stones. " Key and Shoe." — A form of attachment known as the " Key and Shoe " is described by Peeso (6, p. 799) as follows " The key is made of iridio-j)latinum, and filed smooth to form a dovetail, as in Figs. 810, 811. A strip of the same metal. No. 32 American gauge, is bent to fit the side of the key perfectly, and filed off even with the face or broad side of the key, and a floor of the same ^^ -, V I metal fitted to it and \ ' \ \ / / soldered with a little Fig. 812. Fig. 813. P"re gold (see Figs. 812, 813). " In using this form of abutment-piece the side of the crown to which the key is to be attached should be .straight, from the gum line to the tojj of the cusp, and should be reinforced _ with a piece of coin gold, No. 28 i\ American gauge, soldered across the ] whole face of the crown (see Fig. / S14). , " The key is then put in place, and a hole drilled through it and the Fio. 814. side of the band, and it is fastened with a small platinum rivet, such as a toothpin, the under surface of the key having first been covered with pure gold, as the union between iridio-platuium and solder is not strong. It is then soldered to the cap, very little solder being used (see Figs. 815, 81b). P'iG. 810. SO Fig. 811. " The shoe is then slipped over the key, and a thin piece of platinum cut out to shp down over the key next to the crown, and this is A Fig. 815. o Fig. 81(3. LnJ burnished closely to it (see Fig. 817). It is then waxed to the shoe, removed, invested, and covered %vith pure gold, after which it is trimmed to its proper dimensions, and rejilaced on the crown, the facings are ground in, and the bridge is constructed. " If a saddle is to be used, it is first waxed carefully to the shoe, removed, and soldered, after which it is replaced on the model, and the bridge constructed as before described." Split Pin and Tube. — For a case where the two roots that are to serve as abutments are out of the parallel to such an extent that it is impossible to insert tubes sufficiently deeply and yet have them parallel, Peeso (6, p. 802) describes as follows an attachment of a split pin and tube, but the tube is embedded in the bridge and the pin is in the root and attached to the inner cap — " The roots are prepared in the same way as when they stand in a normal position, \vith this exception — the approximal angles are cut Fig Fig, 818. away, in order that the bands may be adjusted with their sides nearly parallel to each other. The bands are then fitted, the roots cut down, and the canals enlarged to receive a strong pin, and a plaster impression is taken with the bands and pins in position, as in Fig. 818. " A cast is then made, the bands are cut flush with the top of the stump, and a flow of 28 American gauge coin gold is sweated or soldered to them. An opening is then made through the floor to fit the pins tightly, and the pins are bent first beneath the floor, so that when 622 they pass through they will be parallel with each other or nearly so (see Fig. 819). They are then waxed together, invested, and soldered from the under side. Fig. 819. ' ' In niakuig the outer cap, the floor of y^^ inch coin gold is drilled so as to fit the pin easily but not loosely. It is then cut flush with the sides of the inner cap, and tlie half-band made and soldered to it, after which it is replaced on the iimer cap. The tube is next placed over the pin, and is made to sit down closely on the floor all around, and is waxed to it with hard wax ; it is then removed, a little investing material carried into the tube, and a small iron wire iiLserted, and allowed to extend about one quarter of an inch below the floor (see Fig. 820). This will hold the tube in position, and is Fig. 820. Fig. 821. embedded in the investment, the tube being soldered to the floor with 22-carat solder (see Fig. 821). The facing is then ground to the floor of this cap, and when the bridge is invested for soldering, a small iron wire is inserted in the investment to prevent the tube from shifting, the same as when attaching it to the floor." In cases where one end of the bridge is supported by means of a spur resting on a filling in the abutment, iridio-platinum wire is u.sed, of a size varying from 1 to 4 gauge (Ash), according to the size of the bridge it has to support. It is best to let the spur rest in a gold fining or gold iiJay, and, as a rule, it wfll be found that the inlay answers the purpose best ; it is absolutely solid, and the requisite grooving can be made more easily in a smaller filling than could be managed if the gold were inserted in the ordinary way, because of the danger of weakening the filling by cutting the countersunk part. The inlay can always be perfectly made, as there is no contiguous tooth. Ready-made Attachments. — Many ingenious devices for attachment have been described from time to time by different writers, but most of them have the great fault of being unnecessarily complicated and difficult to make properly and adapt, and in most cases when it is advised that they can be used, other and more simple methods can be employed. In discussing the.se methods Goslee (4, pp. 492 et seq.) ably sums up their advantages and dis- advantages, and speaking more particularly of devices made by the manufacturers he says — " These attachments vary considerably in design, but are usually composed of two parts that telescope into or over one another, of which one is to be securely attached to the supporting tooth and the other to the removable fixture. Advantages. — The advantages that are to be derived from the use of such forms of attachment lie in the facility with which anchorage to the supporting teeth may be obtained ; in the more or less secure means of fixation that they afford ; in the fact that the parts are usuaUy machine-made and therefore accurately adjusted in their relation to one another, and that they may be obtained ready for immediate use directly from the manufac- turer or dealer, thus saving the expenditure of time and energy in devising a means of otherwise retaining such pieces. Disadvantages. — • Notwithstanding the nu- merous possible advantages, however, such attachments as are even yet used and recom- mended are neither universally applicable, nor, as a rule, free from objectionable features. These are usually, firstly, inherent weakness, \\ hich results in their soon becoming broken ; secondly, a demand for such precise and ac- curate parallelism when two are to be on a single piece as to require the use of a ' parallel- ing ' instrument, and the exercise of a greater degree of skill than is ordinarily possessed by the average dentist, thus making their use too intricate and uncertain; thirdly, the extent of space occupied by the attachment itself, and obtained at the expense of the adjustment of the teeth to be supported by the fixture ; fourthly, the possible subsequent loosening of the parts in their inter-relation, as a result of continued friction and stress, which may soon render them useless; fifthly, a lack of provision or opportunity for easily overcoming this, or for tightening the adjust- ment ; and sixthly, the leverage imposed upon the supporting teeth, which may be so severe as to result in their subsequent loosening, or ultimate loss. Indications. — Whenever opportunity for 623 minimizing these objectionable features seems to be present, and whenever suitable anchorage teeth remain in the mouth, and the form of attachment best adapted to the case is judi- ciously selected and properly and skilfully adjusted, such attacliment may be success- fully employed." SADDLE BRIDGES In a bridge in the maxilla from canine to canine where the arch is of the V-shaped variety, a very useful form of bridge can be constructed by making a saddle of heavy gold and soldering it to the half-caps on the two canines, having the saddle fitting tightly on the ridge. On the saddle may be mounted tube-teeth in the ordinary way ; or flat teeth or gum sections may be fitted on the gum and soldered to tlie saddle, in which case the piece must be built up very solidly with solder to give sufficient strength, the natural shape of the teeth behind being obtained by means of stones on the dental engine. The saddle in different forms may be made use of in the molar and premolar region also, a useful form of bridge being made by vul- canizing teeth on to a gold saddle attached to the removable abutments. A point to note in connection with taking the models for all these forms of saddles is as follows : After the first model and the removable abut- ment pieces have been made, another model is taken in modelling comjjosition used fairly hard (with the abutment pieces on the roots). This procures a model of the alveolar ridge in which the soft tissues have been forced well aw ay by the composition ; the outline of the required plate is marked, and a little wax placed along it to ease the edges of the jjlate. The alveolar ridge is also waxed slightly, and then dies and counter-dies are made in the ordinary way, and the plate is struck ; this, when placed in the mouth and held firmly there, will be seen to have no " rock". In the form of saddle to be next described — that of two premolars on the same side being employed as abutments and attached to an extension saddle supplying the lost molars — • this accurate fitting of the saddle on the alve- olar ridge is highly important ; here, if not correctly made, the saddle will " settle ", carry- ing posteriorly with it the two premolars, bringing a great strain on them, and „ „,- thereby causing their earlv Fig. 822. i • loss. Peeso's method of obtaining this accurate adjustment is to strike up the saddle in soft platinum, about yJ;-,,y inch thick, having the edges shghtly turned up (see Fig. 822) ; gold of the carat and constitution of coin gold is Fig. 823. flowed over the surface of the plate so as to fill the edges flush with the plate (see Fig. 823), and then it is tried in the mouth, the amount of rock noted, and the saddle adjusted by pressing the sides together with the fingers. The inner caps having been made, they j are placed in the mouth to- ' gather with the saddle ; the saddle is held in place by the tip of the finger, and a plaster impression taken, the finger being kept on the saddle until the plaster has set. This is cast, the outer telescope -caps are made, waxed together and also to the saddle, and the whole is taken off the model ; the inner caps are then re- moved from the outer, the piece is invested, and the two caps and saddle are joined by 20 or 21 carat solder ; the inner caps are then replaced in the outer, the whole is placed in the mouth, and another model with articulation taken (which need not now be in plaster). If this method is not followed, and if the abutment pieces are soldered to a saddle that has been made on the original model and has not been adjusted in the mouth (as one would do in the case of a plate and bands), it will be seen that the saddle does not sit firmly on the alveolar process when the piece is finally finished and placed in the mouth, and conse- quently the strain of mastication is all brought to Ijcar on the abutments, and the advantage of the alveolar process taking part of the strain is thereby lost, although this support from the alveolar process should be part of the advantage of the saddle bridge ; a bridge, of course, cannot settle to the mouth as a plate would. The subsequent steps for finishing the piece may be by means of tube-teeth (in which case it is advisable to re- inforce the saddle further by strikmg up a piece of plate gold to fit the upper a __--' surface of the saddle, and then soldering it as one would an ordinary bar lower), or by a method Peeso employs, which will be now described, and which makes a very beautiful result, although the amount of gold used makes it a very expensive method. Peeso (6, p. 806) sa^'s — ■' In constructing a saddle bridge it is better that the facings should not be ground to fit the saddle exactly, but should stand away from it for a little distance (see Fig. 824), the object of Fig. 824. 624 which \vill be seen later. The tips of the facings should be high enough to touch the Hngual side of the buccal cusps of the upper molars, as in Fig. 824, A. " After the facings have been ground they are held in place with wax, and a wall of plaster is built up on the buccal side so as to retam them m position after the wax has been removed (see Fig. 825). The facings are then removed, and Fig. 825. the occlusal ends ground off at an angle of about 45° with the backs or lingual side, as in Fig. 825, A, leavmg them so that they will clear the occludmg teeth by about ^,\, of an inch. " The facings arelthen backed with thin platinum, the backings touching each other and extending from the begimiing of the level at the occlusal end to the saddle, which they Fig. 82(). Fig. 827 should touch closely all along (see Fig. 826). The facings are then waxed firmly to the saddle with hard adhesive wax, the wax being high enough to support and hold the cusps (see Fig. 827). " A solid cusp must be used (of coin gold), the buccal side ground or filed to fit the bevel of the facing, and waxed in place. " The buccal and lingual sides are next covered with wax, the pink paraffin wax being preferable, as it is not sticky and carves nicely. Both sides are then carved to represent the natural gums. This should be done very carefully and the wax made perfectly smooth in order to secure a clean die, so that when the plates are struck up they will require no finishing other than with pumice and rouge. On the buccal side it should be carried above the lower Fig. 829. Fig. 828. edge of the facings, and well up between them, as in Fig. 828 ; the carving on the lingual side should correspond in depth and breadth with the facings on the buccal side. " An impression is then taken of each side separately, the plaster being carried well above the gum line and over the heel on the buccal side, and on the lingual side well above the cusps and below the saddle, and far enough over the heel to meet the impression from the buccal side (see Fig. 829). " The impression should be deep enough to serve as a model from which to get good strong dies. The dies and counter- dies are made, the buccal plate is strack up from coin gold y r, Jf ,7 inch, and festooned carefully to fit around the facings. The lingual plate is struck up from coin gold t-J4jj inch and fitted care- fully, the f)art going over the heel being brought in contact with that from the buccal side. '' After they have been cleansed in acid, the buccal plate is placed in position and held with small iron-wire clamps, as in Fig. 830. The saddle is then held over a small flame for a moment to loosen the wax from the plate, and the teeth and ^^•ax are removed and laid carefully aside. The saddle is then invested, lingual side down, only just enough of the investment being used to keeji it from springing (see Fig. 831)'. " The investment is thoroughly dried out, Fig. 830. 625 the piece well fluxed, and some pieces of 18-carat solder dropped in between the saddle and plate. It is then well heated up, and when it has reached a red heat the lilowpipe flame is thrown on the under-side of the saddle next to the invest- ment, and the solder drawn through all round. ^Vhen cool, it is cleansed in acid and the saddle warmed slightly, and the teeth are pressed back into place until the fitting of the lingual plate shows that they are in their correct position. The bridge is now ready for the final solder- ing. The piece is invested, buccal side down, the investment on the occlusal side covering about two-thirds of the cusps and the saddle, to within about ^ inch of the lingual edge (see Fig. 832, Aand B). After the investment has hardened it is warmed up a little, and the wax lifted out. Fig. 832. It is then thoroughly heated up to a light-red heat, fluxed and soldered between the cusps \vith 20-carat solder, the backings being united and connected with the saddle with the same solder, of which enough must be used to give sufficient strength and support the bridge (see Fig. 833). Some 18-carat solder is then melted Fig. 833. over the lingual side of the saddle and cusps at A and B, Fig. 833, and the lingual plate carefully put in place, having been previously fluxed on the inner side. The whole investment is then thoroughly heated to a bright-red heat, and the flame of the blowpipe passed along the under- side of the saddle and the exposed portion of the cusps (see Fig. 834), until the .solder has been drawn through and has united the lingual jslate all round. The greatest care must be exercised in putting on this plate as it has to be heated so very hot that it is easily burned. " After it has cooled it is removed from the investment, boiled in dilute acid, washed, and then dipped in alcohol and thoroughly dried. The points of the buccal plate that have been Fig. 834. carried up between the facings are now bent outwards, and the space between the plate and the saddle and under the facmgs is filled with oxy -phosphate of zinc. While the cement is yet soft, the points of the plate are pressed back again between the facings. After it has hardened, the cement is cleaned out from between the teeth, and plastic gold is packed in and over the points of the plate. "The bridsje is then readv to articulate and finish." PRESSURE-CASTING A description had better be given here of the modifications of bridge -work brought about by the advent of pressure-casting ; this method of work is undoubtedly revolutionizing all previous methods, and by its means many beautiful results may be obtauied — results which are more aesthetic, stronger, easier of repair, and easier of application, in difierent cases ; the problem of the change of colour of the tooth, both when making the bridge and by the lapse of time, is much simplified, as methods may be adopted that admit of the facing not going through any " firing ". The description of the making of abutment pieces from the point of view of casting has been referred to, and w ill not be given in further detail, as that is dealt with under " Artificial Crowns " (Chapter XXXV, pp. 567-70). In anterior teeth, where a half-cap and pin are used for fixed bridge-work, this can be made all in one piece by castuig, and a very accurate adaptation of the half-cap can be obtained; the facing can also be made re- movable, that is the gold can be cast on to the backing of some form of removable facing, or an ordinary facing can be used and removed from the wax before casting, bemg afterwards 626 cemented into place ; by this means, too, supple- mentary facings can be easily adjusted for use in case of fracture. With reference to the " body " of a bridge, the employer of the casting process will see many ways of using it. It is particularly 1 useful in "forming " saddles " combined with " tube " or " dowel " teeth, the perfect adapta- tion of the teeth to the saddle being easily obtained, and the strengthening of the saddle at the requisite pomts much more easily made. The aesthetic effect also can be enhanced by employing " tubes " or " dowels ", combined with equal, and in many cases greater, strength. Large gold uilays may be used as abutments with great advantage. To get the best results, however, the inlay must be cast separately from the body of the bridge, and united to it by solder; otherwise, owing to the slu-inkage of the gold during casting, the inlay will not go accurately into place. If a minimum of high- carat solder is used to join the inlay and bridge body, an excellent result is obtained. This method api^lies more particularly to cases where the inlay is of a large size ; with a small inlay an accurate result is extremely difficult, in addition to its not being strong enough. But even where every care is taken, and with the best possible manipulation and workmanship, the soldering of a bridge to an inlay must mean that the inlay is ever so slightly altered in its relationship to the bridge, and hence when placed in the mouth the inlay is certain not to go absolutely accurately into place. However slight this inaccuracy is, it is particularly undesu-able, inasmuch as it is situated at a most vulnerable part of the bridge; hence the " bar and slot " previously mentioned is to be preferred in both fixed and removable work, because the very slight alteration of relationships of the bar and slot is immaterial to the success of the piece. For the inlay itself to be at fault is to invite disaster. Then again, a great advantage of a cast inlay is that very often the abutment tooth need not be devitalized, if sufficient strength of "seat " for the inlay can be obtained ; this strength requires great nicety of judgement, and in doubt- ful cases it is better to devitalize and secure with a pin in the pulp-chamber ; some writers advise drilling holes in the dentine of a live tooth and placing pins therein attached to the inlay, but this is of doubtful utility, as it is so often in- applicable on account of danger to the pulp and the weakening of the tooth. The different methods of inlay formation are described in Chapter XXV, and the technique will not here be gone into. Some points, how- ever, must be remembered particularly : very great strength of " seat " is necessary for use as an abutment piece ; extension for prevention. when possible, must be carefuUy carried out ; and, as pointed out before, whenever possible the inlay abutment and bridge should not be united together. CEMENTING OF BRIDGES In cementing bridges it is advisable to use a hydraulic cement and one that does not set too quickly. The inner surfaces of the caps are washed thoroughly, swabbed out with chloroform and then slightly roughened with the point of a sharp instrument ; the abutments are made perfectly dry mth chloroform or absolute alcohol. The oozmg of the gum may be controlled by means of 25% pyrozone on a wisp of absorbent cotton-wool. The cement is mixed and placed in the abut- ment pieces first, then it is applied to the root and canals and the bridge quickly forced mto place. It is advisable always to see that the bridge goes properly home before the cement is mixed ; edges and corners have very often to be rounded off to allow of this ; in cases where the bridge fits exceedingly tightly it may be left in the mouth uncemented for twenty-four hours, when the taking on and off wiU be much easier. In removable bridges the imier cap is placed in the outer, and the junction between them 1 must be protected with a film of wax, as other- wise the cement squeezes in and converts the movable bridge into a fixed one, at any rate for a considerable time, an accident that is extremely disconcerting. The film of wax must be only " plastered " on lightly, not heated and run on, for if made too hot it also makes it very difficult to remove the bridge when the cement has hardened. j No attempt should be made to take off a ! removable bridge for several hours after cement- ing it. j REPAIRING OF BRIDGES One of the greatest difficulties in bridge-work of the fixed variety is properly to repair a broken bridge, and many ingenious methods for so doing have been devised ; some of these necessitate the use of specially formed instruments, and are in consequence not so convenient of application, for the occasions on which they can be used are of necessity limited. In those cases in which the fracture of the bridge has taken jalace right through the body of the piece, owing to faulty soldering or uisufficient strength of metal, it is necessary to remove the whole bridge and resolder, or in most cases remake ; but very often the gold wears through, if soft gold in- sufficiently reinforced has been used, and a repair can then be effected by inserting a gold filling at the weak pomt. The commonest 627 form of fracture, however, is the broken facing, and the chief methods of repair will be given, presupposing of courae that it is not desirable to remove the bridge, and as a rule that is what one does not wish to do. In the case of a broken premolar or incisor facing, and where there is a good thickness of gold, the following method is one of the most satisfactory. The remainder of the facing is removed, leaving the pins in position in the gold ; the puis are then cut flush with the backing, and with spear- head and rose-head burrs dipped in oil the pins and intervening gold are cut away, and a hole is made ui the backing about ^V of an -A- ta V^ Fi(i. 835. inch deep, or more if the backing allows of it (see Fig. 835), but the hole must be made right through the gold ; the width of the hole must be kept only slightly wider than the pins of the new facing ; this new facing having been selected, the pins are made quite parallel, and the facing is put in place, the pins going as far into the hole as the depth of it «ill allow. The facing being correct as to thickness, etc., i. e. so that when later on it is tight up against the backing it will not be too prominent, it is laid aside, and the gold is hollowed out (or under-cut) laterally, to a distance on each side of about .'.r of an inch or more (see Fig'. 836). The pins of the facing are flattened and the ends bent at right angles (see Fig. 837, transverse section). One pin is made slightly shorter than the other, and by putting the long pin in the opening and pressing it side- ways, the short pin wiU also be enabled to pass into the opening, and the facing cannot then pull out ui a direct forward line (see Figs. 838 and 839). The hole and under-cuts hav- ing been made sufficiently large, the porcelain ^^ill go right up against the backing. It must be ascertained now that the fit is good ; if the back of the facing is quite flat, and in good pin-teeth it usuaOy is (except just round the pins, which does not matter), and if the backing itself has not been bent by attrition, etc., it will be found that very little fitting is needed, but Fig. 836 A, Undercut part of gold back- ing ; B, Hole into backing ; C, Gold back- ing. in some cases a little grinding of the backing is necessary. The facing havmg been ground for the " bite ", the glaze is taken off the back -with a stone, the backing roughened slightly with a burr, and the pin then cemented into place with an oxy- phosphate cement, a very strong and serviceable repair bemg effected. In order to shorten the work in the mouth, an impression may be taken of the surface of the broken backing, and after a model has been cast in metal or cement it may be cut out exactly as it will be in the mouth, and the facing may then be accurately fitted to this model, only the actual fitting of the gold being left to be done in the mouth. This method also helps one by showing exactly where to cut the hole in the gold, and about what size to make it. Another method is, as follows : Firstly, the pins of the broken facing are cut flush as in the previous method, and then a cast is made ; the pins of the new facing are then made exactly parallel and passed through two holes made in the metal cast in such a position that they allow of the facing being fitted properly to the cast. After this has been done a back- ing is made of paper to fit the new facing. Fig. 838. Fig. 839. with holes exactly fitting the pins ; this back- ing is taken off the facing and transferred to the backing in the mouth, the holes in the paper showing exactly where to drill the holes in the gold; this is done by means of spear- pointed drills, care being taken to keep them quite parallel, and the holes must go right through the gold. Notice should be taken that the pins project on the lingual side of the gold to allow of their being bent together over it, and then a groove should be cut on the lingual surface joining the two holes. After the tooth is cemented into place it is firmly held while the cement is soft, and with pliers the two pins are bent together in the groove prepared for them ; they are then burnished down lightly and smoothed over with a stone. Instead of the pins being bent over to hold the facing in place they may be riveted by means of a plate punch, the" lingual ends of the two holes having hrst been countersunk. This makes a very firm repair, but it is difficult to do the riveting properly ; it is best in so doing to have only just as much extra length of pin as is re- quired, and to start by very slightly grooving the ends of the pin with a knife. Outfits are supplied by the depots for 628 Fig. 840. threading the pins, and securing them to the backing by means of a cone-shaped nut, which is screwed home into the two holes from the lingual side, the holes having been enlarged and made cone-shaped to receive the nuts ; this method is very often inapplicable, and the weak point of it is that the threading of the pins must necessarily weaken them very much. A useful method of repairing a facing in those cases «heie the backing is thin, owing to the " bite '". is as follows : The pins are ground flush with the backing ; then with a spear-pointed drill two holes are made right through the backing in the exact position of the two pins (see Fig. 840) ; these holes are converted into grooves by means of fissure-burrs, as shown by the dotted lines in Fig. 840. A facing is selected, and the pins hiving been made parallel, it is slipped into jjlace, the pins resting in the bottom of the grooves and going right through the thickness of the backing, and being allowed to project considerably on the lingual side ; if the backing is too thick for the pins so to project, it is stoned down from the lingual side until the condition is effected ; a sectional view would appear as in Fig. 841. The facing having been properly adjusted as to fit, bite, etc., and ])lenty of room having been left between the occluding teeth and the lingual surface of the stoned- down backing, a piece of thin soft platinum (about inW oi an inch in thickness) is cut to size, and the facing being held in position, the platinum is pressed against the lingual surface of the backing, the pins are forced through it, and it is roughly adapted to the backing. The pins are secured to the platinum by a little hard wax apphed to their ends where they emerge from the platinum ; the platinum backing or foil is then cut to the proper size and closely adapted to the gold backing by burnishing, and brought to the cutting edge of the tooth. \Vlien this has been done more wax is flowed over the whole lingual surface of the platinum (the tooth and platinum being removed for this), and it is then replaced, and while the wax is fairly soft held in close apposition everywhere until cold ; it is then thoroughly chilled, removed, and invested, and a high carat gold is flowed over the lingual surface to replace the wax, and so make a solid diaphragm. The facing and diaphragm are then cemented into place with a good hy- draulic cement, the surfaces of the gold having been thoroughly dried and roughened. This process makes a serviceable repair and is Fig. 841. quickly done, but should not be employed if a more thorough method can be used. Ash's mineral teeth can often be used advantageously ; they are practically ordinary facings made in the shape of flat teeth, but in lieu of pins they have an oval cavity in the porcelain, which corresponds to the position of the pins, and where the pins are left standing in the backing, a suitable tooth is selected and cemented into place with an oxy-phosphate cement. PORCELAIN BRIDGES In considering the question of porcelain bridge- work, it is necessary to remember that its application is strictly limited. The comparative ease with which porcelain will fracture under strain and stress requires that in a given case there must be no mis- judgement of all the forces it will be called upon to bear ; everything must be considered — the articulation, the occluding teeth, whether natural or artificial, and as nearly as can be ascer- tained the amount of force exerted in the normal movements of mastication. Now this is very difficult to gauge ; in ordinary bridge-work, doubt as to strength can be removed by rein- forcing Hkely points of weakness by means of more metal, but with porcelain this is not possible in the same way, for the requisite strength can only be obtained by having the iridio-platinum base-work, on which the porce- lain is fused, sufBciently strong of itself to with- stand all the likely force ; this, of course, neces- sitates ample room between the abutments and the opj)osing teeth, and this is just \\hat is not usually obtainable in what would otherwise be suitable cases for the work. Then again, allowing that the necessary strength of base has been obtained, it must not have been done by encroaching on the space required for the proper amount of porcelain body, for, in apply- ing the body, everything must be so arranged that in the finished piece the piorcelain is not intersected by the underlying base at points where the continuity of the porcelain is essential for strength. The possibility of the repair of a bridge must be taken into consideration ; it may be safely said that no porcelain bridge should be put in the mouth fixed by cement alone — that is, no so-called fixed bridge ; cement combined with gutta-percha, or gutta-percha " cement ", should always be used, for the enormous difficulty of removing a bridge cemented in the ordinary way absolutely contra-indicates it, so that if for any reason it is considered that gutta-percha can- not bo used another form of \\ork is desirable. Comparative Value of Fixed and Removable Porcelain-work. — The same points for con- sideration arise when deciding the advisability 629 of making a piece removable or fixed in porce- lain-work, as arise ^^•hen ordinary bridge-work is being considered (and having been dealt with in the earUer part of this chapter need only be slightly touched upon here), but in addition it must be remembered that it is much more difficult to work in iridio-platinum and platinum solder than it is in gold, and, as has been seen when considering repairs, a "fixed " piece must not be permanently fixed in the mouth by ordinary cement alone ; thus it often happens that in the front of the mouth a fixed bridge put on with gutta-percha will be preferable to a "removable" one, and occasional removal by the dentist for thorough cleansing purposes is of course highly desirable. On the other hand, in bridges at the side of the mouth, say from canine to first molar, which of course show very much, and at the same time take a large amount of the strain of mastication, sufficient strength is only to be obtained by the use of a " saddle ", and to put a " fixed " bridge in the mouth with a saddle is as culpable in porcelain-work as in ordinary gold-work, although some writers (Evans, Goslee) maintain that the amount of absorption that takes place is negUgible (if the teeth have been extracted a proper length of time), and that under jjlatinum the mucous membrane simply becomes shghtly hyj^eraemic, and that the piece remains perfectly hygienic. Thus, if the necessary strength can only be obtained by means of a saddle, a removable bridge is indicated. Then again, if there has been much absorp- tion, especially in the anterior part of the mouth, a saddle becomes necessary in order that the gum may be properly reproduced by means of the porcelain. Main Points in the Construction of Porcelain Bridges Fixed. — A thorough knowledge of the working of high-fusing porcelain and the management of platinum solder is essential. Iridio-platinum is used (about 10% iridium), about T^JfjT to ^4ttij thick for the plate, and as strong as possible for the pins. The Rich- mond cap and pin is used wherever possible (or the half-cap and pm) on the ten anterior teeth, and on molars a cap, also with one or more pins, as long as can be obtained, going into the pulp-chamber. The soldering is done by means of platinum solder, of at least 20 per cent., and in making the bands the ends are overlapped for soldering. A model with the caps in position is obtained as for ordinary bridge- work. The facings are selected and fitted and coaxed into place ; the piece is removed from the model and invested in a good strong investment, and the wax re- moved, the pins having been left straight and no tackmg used. An iridio-platinum bar, not less than No. 1 size (Ash), or 16 (American) gauge, is fitted so that the ends (which have been flattened) rest securely on the top of the cap and the bar runs close to the facings under- neath the pins, but not quite touching them or the facings. The pins are then bent down on to the bar until they touch it ; if absolute con- tact is difficult to obtain, platinum plate must be fixed firmly between, the bar being held in position by means of additional investment at suitable points. The whole is then strongly soldered with platinum solder, removed, and cleaned, and any rough points of solder or the edges of the pins ground down, so that it presents everywhere a smooth surface, when the piece is ready for the application of the body. This is done as for a single crown, high-fusing body of two different fusing pomts being used, and the material worked as dry as possible, and in as few bakings as possible. If one of the abutments is the second pre- molar, the first premolar should be left as a facing, and no attempt made to build out the cusps of the tooth, as they would only fracture. Removable. — The chief abutment pieces are the half -cap and split pin. Taking a case from canine to canine, the caps are made in the same way as for gold-work, except of course that the pin and outer caj) is made with iridio-platinum soldered with platinum solder. An iridio-platinum saddle is used, made as before described (in thickness j^~ to yig„ inch), and 30 to 32 (American) gauge, adapted to the mouth, soldered to the outer caps, and tried again ; a model is then taken, facings are fitted, and a bar, between 3 and 4 (Ash), or 14 (American) gauge, is fitted so that it rests as described for fixed work, on the abut- ment pieces, and between the pms and the saddle, and as near to both as it can be got. A piece of wire may be fitted along the lingual edge of the saddle also, to act as a sort of support for the body during the fusing. The piece is soldered strongly, and thoroughly cleansed, and the body is fused in the ordinary way. Further back in the mouth, say, from first premolar to second molar, the method would be the same, except that for the abutment pieces of the molar, a strong iridio-platinum bar fitted into a deep and broad groove in either a crow n or inlay is preferable to soldering the bridge (after fusing) to an ordinary telescope- cap, be- cause even a high-grade solder does not hold well on platinum, and pure gold cannot be fused over the contact point of the platinum with the cap, on to which the solder would hold, as the gold would disappear in firing the high-fusing 630 body, and a sufficiently low -fusing body is not strong enough ; for the same reason pure gold cannot be used as a solder, as was previously taught. G. P. P. BIBLIOGRAPHY ( 1 ) Betjkton, G. a Kew Post for Crown- and Bridge- work. Brit. Dent. Jour., 1906, Vol. XXVII, pp. 1057, 1105. (2) Campkin, p. S. Brit. Dent. Jour., 1907, Vol. XXVIII, p. 3. (3) Evans. Artificial Crown, Bridge, and Porcelain Work, 7th ed., pp. 188 et seq. (4) GOSLEK. Principles and Practice of Crown- and Bridge-work, 3rd ed., 1910, p. 336. (5) GosLEE. Principles and Practice of Crown- and Bridge-work, 7th ed., pp. 394, 397. (6) Peeso. Turner's Text-book of Prosthetic Dentistry, 1907. CHAPTER XXXIX CAST SECTIONAL BRIDGES Before describing the technique in the con- struction of cast sectional bridges, it is advisable to point out some of the advantages of this method of constructing bridge- work — 1 . It is not necessary to muti- late the teetli intended to serve as abutments. 2. The bridge can be easily and accurately fitted to the abutments. 3. The bridge can be so con- structed that all parts can be readily cleaned. 4. The bridge can be easily removed without destroying it. 5. The time of the patient and operator can be economized, as the greater part of the work can be done in the laboratory, the bridge being fitted and ad- justed to models. To obtain these results, it is absolutely necessary that the im- pressions of the spaces and the abutments be accurate, and that the materials of which the models are made be sufficiently taking Case 1 as an example, and afterwards describing other cases in practice to which this method, with slight variation, has been applied. Fig. 842. hard to withstand the friction and rough usage to which they are subjected in the laboratory. Herewith is given a detailed description of the method used in making these bridges, 631 Fig. 843. Trays for Impressions. — In most cases, an impression of the mouth is first taken in the ordinary way, and special trays are made as in Fig. 842. These are cast in tin or lead with a piece of brass or nickel wire embedded to form a handle, A. Impressions. — The impression is then taken in plaster of Paris in two halves — lingual surface first. The plaster in the lingual half is allowed to set, and is then trimmed in the mouth, until only the lingual, and half the medial and distal, surfaces are covered, Fig. 843, A, so that the buccal half of the impression B will \nthdraw easOy. When this has been done, the surface is vaselined, and the buccal half of the impression is then taken. A little aniline colour is used in one of the mixings to facilitate the assembling of the parts together. When the two halves are withdrawn, they must be secured firmly together with sealing wax, and a low- 63;] fusing alloy poured in to form the model. After the model has been cast, it should be compared with the mouth, and trimmed where necessary. An impression of the antagonizing teeth should be taken, and correct occlusion ascertained at the same visit. A saliva ejector is useful to assist in keeping the mouth dry whilst the impression is being taken. By taking the impression in this manner all risk of dragging is eliminated, and however undercut the teeth may be, a correct result is obtained. Metliod of Preparing Wax Patterns for Casting. It is usually the best plan to make the lingual half of the'bridge first, as in Fig. 844, A, with articulating surfaces formed ; carbon points are inserted where screws (1) and locking-pin (2) are intended to be. (See Case 1, Fig. 846, A Fig. 844. and B.) If porcelain facings are to be used, these should be fitted to the model and carefully removed from the wax mould, and carbon points inserted where the pins have been (3). The porcelain faces can then be cemented in when the bridge is complete. This half should be quite finished and polished, the holes tapped, and the screws fitted. Wlien that is done, the buccal half is built up, as in B, Fig. 844, with the impressions of screw-heads (4) and hole for locking-pin (5) formed in the wax mould. A carbon point is put in the hole for the locking-pin, but the holes for the screw-heads are filled up with investment material. The form and position of sprues are shown at (6). The buccal half is then cast, and a locking-pin (see Case 1, Fig. 846, C) soldered to it. Fig. S45. — Case 1. ■SEC" inn SH'^v^irif^ ^ 1 »if^->^^SEfs»>^ - t L0CKIM(^ Pin Fig. 84(). — Case 1. Fig. 847.— Case 1. 633 Case 1. This is a case where the lower lateral, second premolar, and first and second molars are absent. A porcelain facing is fitted to replace the lower lateral in the lingual half of the bridge ; the buccal half is secured to the lingual half by two screws, and a locking-pin between the screws. All ■pressure is taken off the screws by extending the articulating surface as a flange over the upper portion of the buccal half (Fig. 846), and lateral stress resisted by the locking-pin (Fig. 846). In this case the lower premolar is very carious, so it is built up and covered with a gold cap. A lug is soldered on the distal side to prevent the bridge being driven down by the force of masti- cation, or raised by the action of the tongue. Fig. 845 shows model with crown on premolar. Fig. 846 shows the lingual half finished and fitted to the model. A; the same apart from the model, B ; and the buccal half completed, with locking-pin soldered to it, C. Fig. 847 shows the completed bridge on model with porcelain face cemented at (1). Vir.. 840.— Case 2. Fig. 850.— Case 2. Case 2. Fig. 848. Molar crowned, with lug on medial surface, and centre portion cast to fit over lug and lower premolar. Fig. 849 shows the lingual half in position on the model A, and off the model 13. In this case the locking-pin is in the lingual half. Fig. 850 shows the bridge in position. Fi.!. 848.— Case 2. 634 Fig. 851.— Case 3. Case 3. Bridge to fill up space between first lower premolar and third lower molar. In this case the articulation of the molar does not allow of its being wholly covered, and the distal surface of the premolar is too nearly vertical to retain the bridge in position, so a shallow groove is cut in the distal surface of the premolar, and the molar is covered as much as the bite will allow. Fig. 851 shows the model with groove cut in the lower premolar (1), Fig. 852 shows the lingual half in position, A, and off the model, B, and the buccal half ready for fixing, C. Fig. 853 shows the bridge completed and in position. Fici. 8.52.— Case 3. 853.— Case 3. Fig. 854. — Case 4. 635 Fic;. 857 -Case 5. Fig. S55. — Case 4. Fig. 858. — Case 5. Fig. 850. — Case. 4. Case 4. Fig. 854. Model. This case is typical of what is met with in everyday practice. The space has been vacant for some time, and there is considerable tilting of the lower molar and premolar. The two halves are secured by a strong screw, and lateral movement is pre- vented by a square groove, Fig. 855 (1), cast in the hngual half, into which the buccal half is keyed. Fig. 856 shows the bridge in position. Fig 859. — Case 5. 636 Case 5. Fig. 857. Model. This is a somewhat simOar case to the last, but the abutments are much shorter. In this case the molar is covered by the bridge, and the two halves are secured by a single screw, Fig. 858 (1), and a locking-pin, Fig. 858, (2) prevents lateral movement. Fig. 859. Completed case. Fig. SG2. — Case G. Fig. SUU. — Case U. Case 6. ! Fig. 860. Model. Fig. 861. Similar to the last, but more teeth are absent. The lingual half covers the greater part of the molar abutment. i I The two halves are secured by two screws and a locking-pin. Fig. 862. Completed case. Fig. 861.— Case 6. Fig. 863.— Case 7. fi:?7 Fig. 865.— Case 7. Case 7. Fig. 863. Model. This is a useful method of replacing a lower incisor and, at the same time, supporting adjacent teeth. The impression is taken in two halves, as described in Case 1. The lingual half is cast first with a porcelain tooth in position as described in Case 1, Fig. 864. To prevent lateral movement a boss is shaped as in Fig. 864 (1). This half is finished and polished, and then the pattern for the labial portion is adapted to it, with the hole for screw-head moulded in and filled with a car- bon point (2). The method of keying the two halves is shown at (3), Fig. 864. Fig. 865 shows bridge in position. Case 8. Figs. 866 and 867 represent a retaining appli- ance for loose lower incisors, made in a similar way, and secured by two scre\\s passing between the teeth. S(i8. — Ca 638 Fig. S70.— Case 9. Fig. 871. — Case <». Case 9. Fig. 868. This is a modification of the method described, and is more suitable for upper cases, where it is desirable to avoid showing gold. The space to be filled is from the first pre- molar to the second molar. The first premolar is cut do^vn level \vith the gum margin, and a strong pin fitted in the root. A pattern in wax is then fitted over the face of the root, Fig. 868 (1), and cast on to the pin. This is shaped and finished as in (1) and (lA). An impression is taken in two halves, as in Case 1, and the model made in the usual way. The porcelain faces are then fitted, and the wax pattern for the buccal portion made first, as in A, Fig. 869. Carbon points are inserted where the screws are intended to be. Fig. 869 (1) ; the porcelain faces carefully removed from the wax pattern ; and carbon points inserted where the pins have been. Fig. 869 (2). This half is then cast, screws are fitted, and the piece is finished and polished, A, Figs. 870 and 871. The pattern for the palatal portion is then made as in B, Fig. 871. The two halves are secured by two screws through the palatal half. The completed case in position is shown in Figs. 872 and 873. 639 Various Practical Points. — A hard gold 18- carat alloy should be used. The screws should be made of a hard metal, such as platinum- iridium or 12-carat gold. In practice, the latter has proved very satisfactory. They can be cut out of the solid wire by using special cutters, such as are supplied to watchmakers. A small watchmaker's lathe, such as the Lorch, is very useful for this work. The most suitable screw-cutting appliances are Card's Diamond Screw-plates, ^^■ith taps and dies to conform to the British Association Standard. The useful sizes are 9 to 14 inclu- sive. Morse drills to correspond with these sizes should be used to enlarge the lioles before tap- ping, as better results are obtamed by using the carbon cores a size smaller than the screws are intended to be. The carbon points can be obtained from any good stationer. Cementing the Bridge in Position. — The two halves are comiected by engaging the screws in a few threads only, thus facilitating the placing of the bridge in position. All surfaces intended to come in contact \vith the abutments, are covered mth cement, care being taken to avoid the cement coming in contact with the screws. \Vlien the two halves are connected it is a simple matter to place the bridge in position, and the operation is completed by driving the screws home. E.H. CHAPTER XL EXTRACTION OF TEETH Extraction of a tooth or of teeth is one of the few remamiiig operations of surgery calling for the possession of such a degree of skill and dexterity on the part of the operator as will enable him to act with celerity as well as certitude. It is true that any operation is quickly enough done that is well done, but the conditions attendant on this particular procedure are pecidiar, and, speaking generally, render rapidity in its execution eminently desirable. Thus it is frequently done with- out any anaesthetic, or with a local anaesthe- tic, and in either of these cases the dentist should endeavour to shorten, so far as possi- ble, the period of the patient's bodily anguish or mental perturljation. If a general anaesthe- tic is employed, it is usually one affording a short available anaesthesia, so that quick- ness and skill are essential if the operation is to be completed before the patient returns to con- sciousness. None the less, as Moynihan has said : " Speed should be the achievement, not the aim of the operator." Consideration for his patient and regard for his own reputation should stimulate every practitioner to perfect himself in the technique of extraction. It wiU be well in the first place to consider what the conditions are that may call for the removal of teeth. The broad proposition may be laid down that any tooth that is non-func- tional and incapable of restoration to functional activity, or causes pain or marked discomfort and is not amenable to treatment, or is septic and cannot be made aseptic, should be ex- tracted. The dictum of Smale and Colyer, "No teeth are better than septic teeth," is a wise pronouncement, which should be ever present to the mind when one has to decide, in respect to any tooth, for conservation or extrac- tion. A more detailed examination of the conditions calling for extraction reveals the extraordinary number of pathological changes that depend upon diseases of the teeth as a primary or contributory cause. Teeth may of course require to be extracted from either the deciduous or permanent dentition ; in the case of the former, undue retention, extensive caries, and sepsis, are the commonest conditions demanding extraction ; in the case of the latter it will be necessary to enumerate a long list of affections, some of which may be associated also with diseased deciduous teeth. Conditions Calling for Extraction. — The imme- diate relief of pain from inflammation of the pulp, or periodontal membrane, or from pulp- stone ; extensij/e caries, alveolar abscess, sepsis, abscess of the maxillary or other accessory sinuses ; post-exanthematous necrosis, syphilis, epuhs, polypus, glossitis, leukoplakia ; ulcera- tion of the tongue, cheek, or lips ; maUgnant dis- ease; pyorrhoea alveolaris, alveolar osteitis or osteomyelitis. Supernumerary, unsightly, or deformed teeth ; irregularity, overcrowding, or malocclusion ; interference with articulation, impaction (commonest ^dth third lower molars, and sometimes associated with trismus), acci- dental fracture or splitting of a tooth, extrusion, looseness, salivary calculus. The preparation of the mouth for the insertion of dentures ; the effective removal of septic crowns or bridges. General sepsis associated with dead or abscessed teeth or roots. Extraction is frequently required for the relief of conditions arising from or comiected with dental disease. As the result of the emigration or conveyance of septic material from the teeth to adjacent or remote parts there are : tonsillitis, pharyngitis, lymphadenitis, neuritis, gastritis, appendicitis, pernicious anaemia, anaemia and general debility or malnutrition. So too, as the result of reflex nervous irritation, or tox- aemia, there are : facial neuralgia, cranial neur- algia, neuralgia affecting remoter parts, chorea, epilepsy, facial paralysis, trismus, torticollis, histrionic spasm, hysteria, neurasthenia, mania, amaurosis, glaucoma, mydriasis, strabismus, ptosis, corneal ulcer, keratitis and possibly many other ocular affections, otalgia, otorrhoea, deafness, nasal catarrh, coryza, and some skin diseases, e. g. herpes and psoriasis. In all of these extraction of teeth may be the appropriate treatment. Extraction may become necessary in cases of excessive or painful erosion or abrasion, exo- stosis, or absorption of roots ; as a prophylactic measure in phosphorus workers; as a prelim- inary to excision of the jnaxilla or mandible ; to facilitate the introduction of a tube for the conveyance of liquid nutriment in cases of trismus, tetanus or anchylosis of the mandi- bular articulation ; in cases of purpura, hyper- 040 641 trophy of the gum or acromegaly ; and in the removal of dental cysts and odontomes. General Principles of Extraction. — The object of the operator is the removal of the tooth from its bony socket with the minimal disturbance or injury of the bone, and without destruction or laceration of the soft parts. This is usually effected by forceps, and the principle on which the use of the instrument is based is as follows — The roots (or root) of the tooth are grasped by the blades of the forceps, the points of which are pushed or driven with firm and steady pressure weU beyond the neck of the tooth, the gum and periodontal membrane being pushed aside or stripped away as the sharp blades go home. The handles are compressed and the tooth becomes, as it were, an integral part of the forceps. Tooth, forceps, the hand, wrist, forearm, upper arm, and shoulder girdle of the operator, now constitute one long rigid bar or lever, the conical, bifid or trifid extremity of which is embedded, fastened, and cemented, in a rather dense but also some\^'hat yielding and elastic medium. In the case of the upper jaw the fixed extremity is in the long axis of the lever ; in the lower jaw the fixed end, i. e. the tooth, is embedded almost at right angles with the long axis. Regarded thus, the problem of how to extricate the distal extremity of the lever from its surroundings resolves itself into a determination of the method by which the most economical application of force in the direction of least resistance will effect a solution of continuity between the end of the lever and the strvicture in which it is lodged. The method will vary with the shape and situation of the end of the lever, but the principle enunciated remains constant. Particulars must be given for the different teeth ; but as a broad proposition it may be laid down that the upper incisors and canines are rotated, with a slight outward movement if necessary ; the upper cheek-teeth move out- wards and do\rawards, and all the lower teeth, with the occasional exception of the third molar, move outwards and upwards durmg extraction. The late Sir John Tomes was the first dentist to devise efficient extracting forceps. He insisted that these forceps should embrace as much as possible of the lingual and labial aspects of the tooth at its neck ; that the jaws should present an inclined plane terminating in an edge ; and that the length of the jaws should on no account be greater than is neces- sary to allow sufficient space for the reception of the crown and the neck of the tooth. He also observed that as the roots of all teeth have a general conical form, forceps when well made and applied should be but as a lengthening of 21 the cone to its base ; and that forceps should be used and constructed upon the jjrinciple of lengthening the tooth for the extraction of which they are intended. He impressed upon his students the absolute necessity of laying hold of the tooth as far down towards the roots as they could possibly get tlie instrument, and quoted with apjjroval an old and successful operator as saying, " Push the jaws of your forceps into the sockets as tJiough you intended they should come out at the top of the head or below the chin " (12) (13, pp. 551-554). The statements are as true and the advice is as good to-day as in 1848. The writer may be permitted to observe that in the case of the beaked forceps commonly used for molars, the presence of the beak offers an obstacle to the smooth passage of the blades along the roots. Forceps havmg a smooth, sharp, uninterrujjted, curved outline at the extremities of the jaws can usually be made to slip under the edge of the alveolus where it embraces the neck of the tooth ; but the beak of beaked forcejjs impinges on the margin of the alveolus and prevents the driving on of the forceps except at the expense of slight fracture or splitting of the alveolar border, or at least of its more violent displacement. He believes that in practice these beaked forceps are seldom driven past the neck of the tooth, which, indeed, they are made to fit and to which they are instinctively adjusted. Antiseptic Precautions. — It may be conceded that it is not possible to secure an absolutely sterile condition of the field of operation in extraction. But though sterilization or com- plete asejjsis is unattainable, the dentist is not absolved from the duty of using such antiseptic precautions as are at his disposal. He may be unable to annihilate the micro-organisms of the mouth ; he can, nevertheless, reduce their numbers and refrain from introducing new- comers of a j)ossibly more dangerous type. If the opportunity occurs, the patient should be instructed to attend carefully to the cleansing of the mouth and teeth for some time before the operation. The use of the tooth-brush and toothpick should be supplemented by frequent irrigation and gargling, with a view to the promotion of asepsis and the pro- duction of a healthy condition of the buccal mucosa. In the attempts made by Miller and others to sterilize the oral cavity, mercuric chloride (corrosive subUmate), in a strength of 1 in 2500 of water, was found to be the most efficacious agent. The use of this salt in a mouth-wash is, however, barred to the dentist by reason of its poisonous nature. Sterihzed boric acid solu- tion (1 in 40) or salicylic acid (1 in 300), is useful. 642 Carbolic lotion (1 in 80) may be used, or this prescription — B Acidi Carbolici . . . . o i^^- Liquoris Potassae . . . 3 ^J- Aquam ad 3 i"^- Misce, fiat collutoriiim. Sig. — One teaspoonful in half a tumblerful of warm water to be used as a mouth-wash. In the writer's experience phenol sodique is of proved value and may be prescribed. R Phenol sodique (Boa) . . 3 vj. Sig. — Two teasj)oonfuls in a wine-glassful of water to be used frequently as a mouth-wash. Hydrogen peroxide, zinc chloride, zuac sulpho- carbolate, benzoic acid, thymol, saccharin, hydronaphthol, izal, and the essential oils of cassia, cimiamon, and cloves, may be included in the list of efficacious antiseptics suitable for use in the mouth. Permanganate of potassium and Condys fluid are sometimes used ; they have the decided disadvantage of producing a black, dirty, messy appearance. All instruments should be carefully cleansed before and after use liy scrubbing at a running tap of hot water wth a stiff brush. They must then be placed in the sterilizer and boUed in a solution of potassium carbonate (gr. v in 5 j) for fifteen minutes. For the operation they are placed ready to hand in a dish or instrument tray containing carbolic lotion (1 in 40) sufficient to cover them. The hands of the operator must be cleansed and sterilized. Dirt and loose epitheUum are got rid of by washing and scrub- bing with a nail-bnish and soap at a stream of hot water. The nails should be carefully cut short. The naU-brash should be sterilized and kept in 1 in 1000 mercuric chloride. The hands when thoroughly clean should be washed in 85 % alcohol and rinsed in sterilized water. For very septic cases with foul f)us present, or for sjqjhilitic cases, the operator must wear india-rubber operating gloves. THE OPERATION OF EXTRACTION The operation of extraction will be described with reference to — (1) The examination of the patient; (2) The instruments ; (3) The position of the patient ; (4) The positions of the operator; (5) The introduction and application of the forceps ; (6) The extraction. 1. Examination of the Patient This should be conducted methodically by : (o) inquiry, (b) inspection, (c) palpation, \d) auxihary means, e. g. probe, thermal tests, radiography. In many cases (a) and (b) wiU suffice to identify the tooth or teeth to be extracted, and to justify extraction without further examination, and they should always come first, and should be conducted in gentle and considerate fashion. Nothing is more discon- certing to a patient than to be told to open the mouth, and forthwith find the operator's hand plunged therein. Besides, such conduct betrays a want of fine feeling. The surgeon's motto, " Eyes first, then hands," should be always remembered. Removal of dentures from the mouth should accompany inspection, and it may be necessary to wash or syringe out the mouth with warm water or antiseptic lotion. Palpation reveals the degree of fixity or loose- ness, and the presence or absence of pain on pressure ; a probe, the situation of a buried root, the direction of a sinus, the existence of necrosed bone, the definition of obscure edges, the condition of the tooth qua soundness, decay, separation of roots, etc. ; while in some instances of imijaction or apparent suppression a radio- graph may be required before the appropriate operative procedure is determined. 2. Instruments These are forceps and elevators. Forceps consist of blades, joint, and handles. Fig. 874. — Curved Elevators— All Metal (writer's pattern). The length and curve of the blades should be such as to permit them to accommodate, with- 643 out touching it, tlie crown of the tooth to be extracted when the blades are adjusted to the root or roots. The joint is a strong pin-joint or hinge. The handles are serrated witli crossed serrations for the greater part of their lengtli, to ensure a firm grip and prevent the hand or fingers sHpping. The serrations begin about one inch from the joint. The forceps are, over all, 6i— 7 ins. in length, but for large hands may be made longer. For the anterior maxillary teeth, handles and blades may be made in the same straight line ; for uf)per cheek teeth, the blades and handles are just so much curved as to permit the easy application of the blades, and the clearance of the anterior teeth by Fig. 875. — Curved Elevators — All Metal (writers pattern). the handles. For mandibular teeth, the blades are at right angles to the handles. In the " hawk's-bill " lower forceps the blades are so placed that \Ahen they are applied the handles are at right angles to the line of the arch ; in the " straight " lower forceps, when the blades are applied the handles are more or less in a line with, or tangential to, the arch. The "hawk's-bill" form is more generally effective, and is preferred by most operators. The elevator (.see Figs. 874, 875) consists of handle and blade. The handle, about four inches long, is serrated or cornigated, and whatever its shape it must afford a firm grip. The blade is about two inches long. If the handle is all metal the blade is in one piece with it, but if the handle is, as it still is sometimes, of wood or ivory, a long tang. the full width of the handle, should run the whole length of the handle. The point of the blade is rounded and its edge sharp. A spear- headed or beaked shape of point is sometimes preferred. Elevators are either straight or curved. In both, the side of the blade m contact with the tooth to be removed is flat or slightly concave ; the htxek of the elevator blade is convex. The straight elevator can be used on either side of the mouth, but a pan- of curved elevators is required. 3. Position of the Patient The patient should be seated in a dental chair, in as comfortable and easy a position as possible. The head and trunk should be in the same line, that is to say, the neck should be neither bent forward nor stretched backward. It is of great importance that the head should never be thrown far back and the neck stretched, especi- ally when an anaesthetic is given, as this impedes both deglutition and respiration. Besides this, the risk of teeth or portions of teeth, loosened fillings, blood or jjus, being swallowed, or worse stOl, drawn into the respiratory passages, is greatly increased. A dental chair of the Morri- son type, unencumbered by bracket-table or fountain-spittoon is the form best suited for the extraction operation. The chair should be placed in the best available light before a window. The head-rest should be of such a form and be so adjusted as firmly to support and maintain the head in position. The chair should be slightly tilted back. The top of the patient's head should be about on a level with the operator's breast. 4. Positions of the Operator For the maxillary teeth, the operator stands on the right front of the patient, both his thighs are against the arm of the chair, and the jjoise of his tmnk and head is instinctively that best adapted to secure a good view of tlie parts to be operated on (see Fig. 87(3). For the right mandibular cheek teeth, the operator stands behind the patient, bending his body and head forward over the patient's right shoulder to enaljle him to look downwards and backwards into the mouth ; his left arm surrounds, embraces, supj)orts and fixes the patient's head, the forefinger of his left hand is on the buccal, the thumb on the lingual, side of the alveolus in relation to the tooth, and the remainmg fingers are under the jaw. In this way complete control of the mandible is ob- tained. A kidney-shaped stool that can be placed beside the chair is a great convenience, as standing on it the operator attains the necessary elevation ; failing a stool, the chair must be lowered till the operator standing on 644 Fig. 876. the floor can assume the desired position (see Fig. 877). The anterior mandibular teeth can be taken out with the operator standing behind, and the jaw controlled in the same way (see Fig. 878) ; or the operator may stand on the right or left front of the patient grasping the alveolus in the mamier sho^^ai (see Figs. 879, 880). Some operators, indeed the majority, advise that the lip be kept out of the way with the forefinger of the left hand, and the tongue with the second finger, the thumb being used to support the chin ; but the writer favours the principle of Fio. 877. Fig. 878. always graspmg the alveolus between the finger and thumb of the left hand as giving a firmer grip, better support, and more complete control. For the extraction of the left mandibular cheek teeth the operator has the choice of two positions. He may stand on the right front, with the second finger of the left hand on the lingual side and the first on the labial side of the tooth to be extracted, the thumb being placed under the chm ; the operator leans slightly across the patient while extracting. The writer much prefers, and strongly advises the operator, to take his stand on the left side of the chair. His left knee should be slightly bent, the side of his left thigh pressing against 645 the arm of the chair, his right foot thrown a little forward, and his trunk inclined a little backward and to his left. The alveolus, as always, is hrnily grasped between the finger and thumb of the left hand, with the other fingers under the jaw (see Fig. 881). He considers that in this position the operation can be performed in a more gainly and workmanlike manner, and he has never been able to follow the reasoning of Tomes and Nowell \\ho, speakmg of it, say : " This is indeed a disadvantageous position, it is difficult to see where the blades of the forceps are, and the operator is encumbered by i'^ his own body being between the operating hand and the patient's mouth." He has never experienced any difficulty in seeing the whereabouts of the blades of the forceps, or even demonstrating it to a class, and he has never succeeded in so contorting his body as to bring it into that undesirable position between his hand and the patient's mouth. Consequently, he must decluie to admit the cogency of the objections stated. He does not dispute the fact that many experienced and skilful operators work "across", standing on the right front, but he cannot imagine tliat their reasons for preferring this stance are those above quoted. Conduct of the Left Hand. — The generalj'prin- ciple on wliich this may be founded is : that Fig. 880. Fig. SSI. 646 Fig. 882. in any and every case the alveolar border at the point where the forceps are to be apphed should be firmly grasped between the fore- finger and thumb of the left hand. Taking first the anterior maxillary teeth, the forefinger on the labial side carries away the lip, keeping it out of harm's way, and by firm pressure supports the outer table, preventing its fracture or excessive displacement, while the parts are grasped and controlled by the opponent thumb on the lingual aspect. The thumb is kept slightly bent, thus affording a shelf or inclined plane, which directs teeth that "jump", or Fic. 88:1. Fig. 884. slip, forwards out of the mouth into safety and bars tlieir passage towards the floor of the mouth or the j)harynx (see Fig. 882). For right mandibular cheek teeth, the fore- finger and thumb must be passed well into the mouth ; the forefinger should carry away, and keep away, the cheek, while the thumb keeps the tongue out of the way and guards against injury of that organ. The other fingers pass under the jaw, support it against the downward pressure of the forceps, and steady it during the extraction (see Fig. 883). For left mandibular cheek teeth the roles of forefinger and thumb are exchanged (see Fig. 884). For right maxillary cheek teeth, the wrist is bent and the elbow raised, the thumb is on the buccal side and holds away the cheek, and the QVi I'Ui. 885. forefinger is on the lingual side (see Fig. 885). For left maxillary cheek teeth, wrist and hand are nearly horizontal ; the forefinger is on the buccal, the thuml) on the lingual, side (see Fig. 886). \^^aen the finger and thumb are introduced into the mouth, they should be carried well back first, and then opened out to grasp the alveolar margins at the point desired. With an ex- perienced operator these movements become automatic, so too do the adjustments whereby he keeps away the tongue and cheek by a slight bending of the phalangeal joints. The educated touch and muscular sense of the finger and thumb greatly assist him in the accurate Fig. 88(). Fig. 887. adaptation of the forceps, and also apprise him of the strength of the resistance encountered and of the moment of yielding, and enable him to restrain haemorrhage and at once to compress the margins of the alveolus when the extraction is completed. 5. Introduction and Application of the Forceps The method of taking up, opening, and hold- ing the forceps is shown in the illustrations (see Figs. 887, 888). The butt of the loft handle should lie in the centre of the palm of the hand, and from this position it should never shift or slip, as on its maintenance depends the steady application of the driving power and pressure, which persists during the operation. As is the case with almost every tool in the hand of a skilled worker, the long axis of the instrument crosses the hand at an angle and in such a 648 position that when grasped for use the thumb comes to lie along it. The forceps held as shown are introduced into the mouth for application to the tooth. In the case of the upper cheek teeth the blades of the forceps should always be entered in a plane parallel to the occlusal surfaces of the tooth, and so carried to the tooth to be extracted, when a slight depression of the hand enables one instantly and correctly to apply them. For the anterior teeth above and below, the blades are presented in a plane parallel to the long axes of the teeth. The lower forceps are picked up, grasped, and applied in an exactly similar maimer ; the blades, which, be it remembered, are at right angles to the handles instead of in a straight or curved line with them, are for cheek teeth carried to the back of the mouth in the hori- zontal position, or parallel to the occlusal Fig. S88. surfaces, when a turn of the wrist brings them into line with the roots of the teeth to \\hich they are to be applied. To open the forceps to the required extent, the end of the little finger is used to move away the butt of the right handle, the left handle being now gripped by the thumb and fore- finger, while the outward movement of the right handle, and consequently the opening of the left blade, is controlled liy the second and third fingers on the outside of the right handle. The fleshy part of the thumb may with advan- tage lie between the handles, the upper edge of the right handle impinging on the point of the thumb at its side and on its palmar aspect. The forceps being introduced, opened, and applied, the operator firmly grips the handles and drives the blades well home along the root or roots, beyond the neck. He must remember to keep the butt of the left handle in the middle of the palm of his hand. If he does not he will find his hand sHpping up the handles till he is grasping them near the joint instead of near their ends, when he will be depriving himself of every mechanical advantage the instrument is designed to afford him. He can neither drive them home with the same nice calculation, efficiency, and strength, nor exercise his ex- tractive force with such precision, delicacy of direction, and power, as he can when he grips the handles near their distal extremity, and constitutes them an extension of his hand and forearm by holding them as described, with the butt of the left handle in the palm of the hand right in front of the middle of the carpus. The forceps should be driven home " in once ", without ineffectual prods. In the case of conical roots this driving home of the blades often evicts them at once, the blades acting as a pair of wedges, and the principle involved being the well-known one that two (or in this case three) bodies cannot occupy the same space at the same time. But as a rule some extractive force has to be appUed. 6. Extraction A knowledge of the anatomy of the teeth and associated parts is essential. It must be remembered that : (a) the buccal surfaces of the teeth are disposed on the circumference of a larger arch than that on which the lingual surfaces lie, or, in other words, the teeth are rouglily wedge-shaped ; (6) the alveolus (except of the third lower molar) is thinner and more easily displaced on the buccal than on the lingual side ; (c) the roots of upper incisors and canines are conical ; {d) the roots of lower incisors and canines are conical, and flattened very much laterally ; (e) separate roots of cheek teeth are conical ; (/) roots of lower cheek teeth, when they curve, curve distajly ; {g) the medio -buccal root of a maxillary molar is larger than the disto-buccal root, and the lingual or palatine root lies m most cases behind the middle of the tooth. Extraction with forceps comprises (a) adapta- tion to the tooth or root ; (b) solution of con- tinuity between the tooth or root and the socket ; (c) removal of the tooth or root from the socket and the mouth. The instruments and methods most in vogue in this country will be described as they are applicable to individual teeth. Upper Incisors. — Straight forceps (as shown in Fig. 889) are advised. The inner blade is applied first, then the outer. The blades are diiv'en forcibly past and under the edge of the alveolus, and as far as may be along the root. While strong upward pressure is maintamed, a firm hold of the handles is taken, and tooth, forceps, hand, wrist, and arm, become, as it were, one long rod with a conical termination. This conical end is fixed in a more or less dense medium by accurate or tight implantation ; it is also secured by Sharpey's fibres, which cross 649 from alveolus to cenientiiin in a direction transverse to its length. It is obvious that a very slight degree of rotation of the root will sever all these fibres, since they are hardly, if at all, extensile. It is equally obvious that a little Fig. 889. — Forceps for Upper Incisors, Canines, and First Premolars. {Messrs. Claudius Ash, Sons, d- Co., Lid.) - Forceps for Upper Pre- FiG. 890, Second molars. (Messrs. Claudius Ash Sons & Co., Ltd.) outward movement of the distal extremity of the rod or lever will slightly displace outwards the thin outer wall of the bony socket at its free margin, thus enlarging the aperture of emergence. At the same time the point of the cone will move downwards and inwards, and if unimpeded its track would lie along a curve. But it impinges on the dense un- yielding inner wall, and as the result of the principle set forth in the proposition known as the parallelogram of forces, is impelled do\\n- wards. The operator, therefore, rotates, hold- ing the forceps firmly, but refraining from a crushing stress, and rotating the tooth from him, because his supinator muscles are so much more powerful and better trained than his pronators. Simple rotation, combined with the ^Acdge-like action of the blades, oftens suffices, but if it is insufficient it is supplemented by a steady outward movement. Upper Canines. — The same instrument and the same method are employed, but rotation is not always so useful, because the root more often departs from the circular conical form. It may be flattened or curved, and it is usually 21* longer and stronger tlian the incisor roots, and hence offers more resistance. First Upper Premolars. — The same forceps are used. The tooth is usually two-rooted, and flattened medio -distally; the roots may be confluent. The inner blade is applied first. The blades must lie driven well home ; then forcep-handles, hand, wrist, arm, and shoulder, are carried steadily outwards. Second Upper Premolars. — The root is usually single, but may be bifurcated ; it is not so much flattened as that of the first premolar. The forceps must be a curved pair (see Fig. 890), in order that they may be more easily intro- duced, applied, and used, and that without injuring the lips or lower teeth. The extraction is carried out in the same way as for the first premolar. Upper Molars. — These teeth have normally three roots, two buccal and one lingual. Of the two buccal roots the medio-buccal is the larger, and the disto-buccal lies on a plane slightly internal to the medio-buccal. The Imgual root is the largest of the three, and diverges from the crown at a greater angle than the other two ; it lies in a plane distal to the medio-buccal root, Fig. 891. — Forceps for Right Upper Molars. (Messrs. Claudius Ash, Sons est left to the medical attendant. Post-extraction Haemorrhage. — In patients who are haemoijliiliacs the risk of haemorrhage is a somewhat serious consideration. It will not be wise to extract more than one tooth at a time for such patients. A haemophiliac should be put on a preliminary course of treatment of chloride or lactate of calcium, grs. x to xv, thrice daily for a week previous to operation. The extraction should bo done in the morning, and the patient kept under observation for the re.st of the day. If the tooth is one with a single circular conical root, an india-rubber band, made by snipping off about jV i'l- from the end of a piece of small drainage-tube, may be sUpped on to the neck of the tooth and allowed to work its way up the root. Peri- odontitis accompanies this procedure, which is not without pain and discomfort, but the tooth becomes so loose that it may be removed with much diminished risk of bleeding. In all cases of know n or suspected haemopliilia it is probably good practice to plug the socket at once, whether haemorrhage occurs or not. Wright states that the inhalation of CO., for a few seconds will always check the bleeding in haemophilia. Ordinary alveolar haemorrhage may be : (1) Primary, which occurs at the time of extrac- tion ; (2) Reactionary or Intermediate, coming on some hours afterwards, often during the night ; and (3) Tnie Secondary Haemorrhage, which is the result of ulceration or sloughing of the walls of the vessels, does not occur till a week or ten days after the operation, is always of most serious import, and is certainly of extreme rarity after tooth extraction. In both primary and reactionary haemorrhage the treatment will be to endeavour to control the bleeding by the application of very hot or very cold water, or by the use of various stj'ptics or haemostatics, and if these fail to arrest it by direct pressure. This direct pressure is usually exercised by means of an alveolar plug, which may be supplemented either by one or more sutures passed through the gum from side to side and tied on the surface, or by an inter- dental pad of gutta-percha or cork held in place by opijosing teeth, the mandible being secured and pressure kept up by a four-taUed bandage. Very hot water should always be tried first. The patient should not be allowed to spit out violently, but rather should the water and blood trickle or flow from tlie mouth. Many styptics and haemostatics have been used. Clot and debris should be removed, the socket dried as quickly as possible, and the chosen re- agent carried in on lint, cotton- wool, or gauze. Perchloride of iron should never be used ; it is dirty and messy and causes sloughing, and, moreover, the clot that it produces to block the lumen of the vessels is soluble in scrum, .so that the haemorrhage is likely to recur. Tannic acid, adrenalin chloride, alum, and turpentine, are perhaps the standard haemo- statics for dentists. Hamamelis (witch-hazel, hazeline) is sometimes used. Tomes and Nowell extol the virtue of matico-leaf. As a general rule it is not sufficient to apply a haemostatic without plugging, if the haemorrhage is of any importance. The writer uses a plug of cotton-wool, which is first wTung out of an alcoholic solution of perchloride of mercury (1 in 1000), then dipped in thick mastic varnish, and finally rolled in powdered alum till it has a good coating of the salt. This plug is forced well home with vaseUned instruments; an elevator is an excellent tool for this purpose. The alum is the coagulant, while the resin of the varnish, being precipitated from its alcoholic solution, makes the plug quite firm and soUd. This treatment in the writer's hands has been uni- formly successful. The plug should be removed when it becomes loose by itself. Gauze, adrenalin, and tamun, make an effective plug as advised by Norman G. Bennett (1, p. 448). Walter Pye (10) speaks very highly of a metliod suggested by Sir A. E. Wright, which consists in filHng the socket with formaha and gelatin. Commercial gelatin will not do as it often contains the spores of bacillus tetani ; the gelatin used must be bacteriologically sterile. The procedure given is as follows — " Place a test-tube containing the gelatin in a bowl of water sufficiently warm to melt the gelatin. Care must be taken that the water is not too hot, for, if overheated, gelatin loses its power of solidifying when cooled. When the contents of the tube are fairly fluid add to them .■V part of pure formalin, i. e. if the test-tube contains 40 c.cm. gelatin, add 2 c.cm. formalin. Shake the tube so that the two mix. Now with the patient's mouth wide open, sponge away the blood with gauze or wool pledgets until the socket is fairly dry, and then, soaking a thin strip of gauze in the mixture in the test- tube, press it well home to the bottom of the cavity. Keep it thus for one or two minutes, 660 withdraw it, and pour in the mixture of gelatin and formalin, which is now nearly solid. A little care ^\^ll enable the operator to fill the whole socket with^this_valuable styptic, which soon solidifies." As an adjuvant to plugging, gallic acid may be administered internally in 15-grain doses re- peated every two or three hours for twelve hours. The patient should be kept sitting up, or propped up in bed with the head cool and the feet warm, and fed on cold liquids. The extracted tooth has often been used as a i)lug ; if this is done it should at least be well washed before being put back. If the measures recounted fail, surgical assistance must be invoked ; it may be neces- sary to plug the inferior alveolar or palatine canal, or even to tie the carotid. Wliere the loss of blood has been excessive, and the patient is in a state of syncope, restorative measures must be taken promptly ; it may even happen that transfusion, or infusion of normal saline solution, may afford the only chance of saving the patient. Sepsis following Extraction. — In dealing with this subject one is confronted by the apparent anomaly that while it is impossible to maintain the field of operation in a sterile condition, yet there is no area of the body more tolerant of in- jury, or in which a septic condition so rarely leads to systemic infection. Nevertheless, the dentist is culpable who neglects to endeavour by the judicious use of antiseptics before and after operation, and by rigid adherence to aseptic technique, to minimize the risk of local sepsis, or general infection from the wound. The pre- cautions advised on pp. 641 and 642 must be always taken, and an antiseptic mouth-wash before and after extraction should form part of the ritual. The wound should bo inspected from time to time. Whatever mouth-wash is chosen, the patient should be directed to hold it in the mouth for a minute at a time, not violently swilling it round, but merely allowing it to lave the wound ; and then to let it gently flow or trickle out of the mouth ^\ithout ener- getic suction or expectoration. It is well to wash out the mouth after every meal, to prevent particles of food lodging or decomposing in the wound ; cold or tepid water — or better still water sterilized by boiling — may be used for this purpose, followed by the mouth- wash. This should bo done five times a day till healing is complete. Although the tissues exhibit wonderful re- cuperative power, and healing is usually un- eventful, yet, as the result of trauma and sepsis, one must be prepared to meet and deal \\ith excessive inflammation, suppuration, ulceration, osteitis, osteo-myelitis, or necrosis. The so-called "dry socket ", in which the alveolar margins of bone are exposed, bare, inflamed, and sensitive, is generally due to disturbance and septic liquefaction of the clot (often caused by injudicious packing of the socket), followed by inflammation of the de- nuded bony surface. Careful cleansing and stimulation to a healthy reaction by the use of such remedies as orthoform, or touching with trichloracetic acid, supplemented by curetting of granulation tissue, is the appropriate treat- ment. If the exposed edge has undergone superficial necrosis it wiU be non-sensitive, and may be curetted or burred away as recom- mended by 0. E. Inglis (6). The same author uses nitric acid to dissolve the dead bone and promote granulation. In the writer's experi- ence, if necrosis has taken place, antisepsis and the expectant line of treatment, \vith removal of the necrosed bone when it separates, are indicated. Sloughs must be removed, abscesses evacuated, and sinuses washed out. For pack- ing sinuses or abscess cavities, either a bismuth sub-nitrate and vaseline paste, or a paste of orthoform, zinc oxide, and vaseline has been recommended Where necrosis causes the death of any con- siderable portion of alveolar bone, precipitation in its removal is to be deprecated ; the seques- trum should not be removed until it has separated. General experience confirms the conclusion long since arrived at by the writer, that cases of excessive inflammation, sloughing, and necrosis, are much commoner after extrac- tions when a local anaesthetic has been injected : the paralj'sis, impaired vitality, and arrested circulation, sufficiently explain this result. Suppuration of the socket calls for surgical cleaidiness and antisepsis. The socket should l>e gently syringed out with hydrogen dioxide (10 vols.) ; it may be dried and touched with zinc chloride or trichloracetic acid, and anti- septic lavage thereafter assiduously practised. Should the floor of a lower molar socket be in close relation to the inferior alveolar canal, care must be taken not to implicate the mandilnilar nerve in the application of escharotics or curet- tage. While general infections are admittedly rare, they do occur from time to time. Whether in respect of the operation they are post hoc or propter hoc, it must often be difficult to deter- mine. Septicaemia, pyaemia, sapraemia, septic thrombosis, metastatic abscesses, septic and embolic pneumonia, glossitis, tonsillitis, pharyn- gitis, gangrene, meningitis, phlebitis, and tetanus, are not only possible sequelae of the extraction operation, but stand recorded as having occurred. Their treatment is not for the dentist. The most dreaded infection of all, perhaps, is syphilis, and the importance of the dentist being acquainted with and ready to recognize 661 the manifestations of this disease cannot be urged too insistently. Ignorance or carelessness may result either in the infection of one patient from another, or in the inoculation of the operator himself. Surgical Shock. — That a certain degree of surgical shock attends the extraction operation, should never be forgotten. It must be regarded as contra-indicating extensive extractions in frail weak subjects. Syncope or fainting sometimes happens. The chair should be tilted back so that the patient's head is lower than his trunk and extremities, smelling-salts or ammonia should be held to the nose, and restoratives — brandy or twenty drops of sal volatile in water — adHiinistered. If syncope is profound and pro- longed, medical aid should be summoned. For faintness the patient should be directed to bend forward, bringing the head between the knees or lower, so as to facilitate the flow of blood to the brain. Mania. — Dentists should be alive to the danger of transitory deferred mania consequent on the exhibition of cocaine as an analgesic. The writer recalls a case in which the patient, a big, strong farmer, ^^■as referred to him by a surgeon who had for diagnostic purj)Oses cocain- ized the nasal passages by spraying. The patient sat down in the chair to have his teeth examined, but before anything was done suddenly rose and savagely attacked the nurse who accompanied him, and, had he not been forcibly restrained, might have killed or seriously injured her. In another case that was brought to his notice, the driver of a char-;x-banc who had had a tooth removed ^nth cocaine injected locally in the morning, was, an hour or two after- wards, driving his conveyance over a high bridge spaiuiing a deep vaUey, when he pulled up his horses, and remarking to his passengers that he would show them something they had never seen before, committed suicide by jumping from the parapet. Less frequent Sequelae. — Menorrhagia, amenor- rhoca, a fit in epileptic subjects, and hysteria, are occasional post-extractional manifestations. EXTRACTION UNDER GENERAL ANAESTHETICS Choice of Anaesthetic. — The selection of the most suitable anaesthetic for a given operation will depend on several factors, such as the extent or difficulty of the operation, the age and bodily state of the patient, the skill of the operator, and the knowledge and experience of the anaesthetist. For operations that can be performed in thirty seconds, nitrous oxide is generally used. For longer operations lasting up to ninety seconds, gas and ethyl chloride is. in the experience of the writer, the best anaes- thetic. It nuist, however, be used under strict limitations as to dose of ethyl chloride (3 c.cm. being regarded as the maxinmm), and time of administration, which should never exceed twenty-five seconds breatliing of the mixture. The ethyl chloride, in a measured dose, should be poured, not squirted, into the bag, after five to-and-fro respirations of gas.i While believing that the mixture, if given in the apparatus and according to the technique advised by him, is as safe as nitrous oxide, pleasant to take, and free from after-effects, the writer would not advise its indiscriminate use by all and sundry ; Ijut, as in the case of all anaesthetics, would limit its employment to those who have had sufficiently extended oijportunity of seeing its adminis- tration by experts, of themselves giving it under supervision, and of receiving adequate instruc- tio'nin the admmistration of general anaesthetics, the difficulties and dangers comiected v,hh an- aesthesia, and the methods of preventing their occurrence or dealing with them \\hen they arise. In short, a man can only practise suc- cessfully what he has been \\e\\ taught, and to no procedure is this remark more aijplicable than to the administration of anaesthetics. According, therefore, to his school of origin and experience, it \\ ill be found that the anaes- thetist prefers continuous gas, gas and oxygen, gas and ether, ether preceded by gas or ethyl clUoride, or gas and ethyl chloride. These may all be given with the patient in the sitting position. Chloroform is at once the most unsuitable and the most dangerous anaesthetic to employ for tooth extraction, and sliould never be so used. In gas, alone or in combina- tion with oxygen, ethyl chloride, or ether, the dentist has a choice of reagents of proved efficiency and safetv. Procedure in Administration. — A general an- aesthetic should not be given shortly after a fuU meal. Midday, after a light breakfast at 8 a.m. or 9 a.m., is perhaps the best time for dental operations. All tight clothing should be loosened ; collar, necktie, hat, artificial teeth, spectacles, and brooches, should be re- moved. The clothing should be opened to give a view of the neck and episternal notch, so that the presence of any s\\ elling, e. g. goitre, may be detected. The chair should be upright, or very slightly tilted back; the patient's cranium and trunk should be in a straight line ; the head must not be tlirown back nor the neck stretched. The crown of the patient's head should be on a 1 Since this was written the author has devised a method and apparatus for administering gas and oxygen alone or in combination witli ethylcliloride or ether. He believes that this method gives eve greater safety and freedom from aftereffects than tlie method described in tlie text. 662 level with the operator's breast. The hands should be clasped, with the fingers interlaced, on the lap. The legs should rest easily, not crossed, and the feet should not be braced against the foot-rest. The patient should clear the throat and blow the nose ; it may be necessary to Fig. 906. remove from the mouth such objects as lozenges, tabloids, sweets, or quids of tobacco. The cloth- ing must be protected by a waterproof, washable, sterihzable cover ; two yards of Batiste Mosetig, invented by Prof. Mosetig of Vienna, serve this purpose admirably. A mouth-prop must be in- serted previous to adjusting the face-piece. If the mouth-prop is placed at one side, Sir Frederic Hewitt's are the best (see Fig. 906). The writer always places it centrally and uses a prop with surfaces at right angles to the stem. The props should be attached to a neat strong chain instead of the dirty string or catgut often seen. An inch of red rubber tubing with a hole cut in one side makes the best cover for these props. All props with springs, racks, or other complica- tions, are anathema. A small gag should be used as a rule, the larger size being reserved for cases in which the incisors are wanting. A patient cannot breathe comfortably with the mouth widely propped oiDen. The small prop at the front of the mouth does not impede the swallow- ing movement of the tongue, as does the prop at the side. Here let a protest be made against the expression, so often heard, " the tongue falling back." The tongue does not fall back ; if it did, every one would Ije asphyxiated in sleep ; in anaesthesia the swallowing reflex is interfered with or abolished, and the tongue, arrested in the middle of the swallowing move- ment, blocks the faucial aperture of the air- passages, wlule at the same time the larynx is closed by the epiglottis. ^Vhen this happens the forefinger should be passed to the back of the mouth and the base of the tongue depressed. It is advised that tongue-forceps be at hand to draw forward the tongue ; but the writer, though he accepts and endorses the advice, has never had occasion to use the instrument. For opening the mouth further during anaesthe- sia, or keeping it open independently of the mouth-prop, a Mason's or Heister's gag, or a wedge mouth-opener of pewter, aluminium, or Britannia-metal, will be needed. An expe- rienced anaesthetist will assist the extractor by holding the patient's head and manipulating the mouth-opener. Most anaesthetists stand on the right of or behind the chair to administer, and hold the facepiece in the left hand. It is more con- venient to stand to the left side holding the face- piece in the right hand (see Fig. 907) . Many men never apply the face-piece properly. It should be firmly grasped in the right hand, and the point placed on the bridge of the nose ; then gentle pressure downwards and towards the face secures accurate adaptation without constriction of the nose or compression of the cheeks. Procedure in Operation. — It is not the writer's province in this article to deal with the administration. He may, however, be per- mitted to emphasize the importance of elimi- nating the asphyxia element from any and 663 every anaesthesia. The dentist must take care that there is no raechaiiical or physical obstniction to respiration, and that the blood is sufficiently aerated during induction and operation. He must guard against a block- ing of the airway by the tongue, blood, saliva, mucus, pus, extracted teeth, or foreign bodies, such as swabs or sponges. He must not, while extracting, force back the tongue against the fauces, or neglect to support the mandible with the left hand. He must train the finger and thumb of his left hand to take charge of the tooth, and prevent its backward passage, to the pharynx or air-passages. He must refrain from throwing the patient's head far back, thereby increasing the risk of this accident. He must make certain that the whole of the extracted tooth is in every case out of the mouth; if a tooth or root fall on the tongue, or into the sulcus of the cheek, the head must be thrown forward and the tooth removed before another extraction is attempted. Patients ought to know that the bladder should not be full or the lower bowel loaded. In cases where the removal of one or more teeth is imperative, and of others advisable, it is often wise to make sure of the more im- portant ones first ; but, speaking generally, if a number of teeth are to be removed, it is best to adopt a definite order of procedure. Take the extreme case of " clearing a mouth ". The fewer instruments the operator uses, the less time «dll he consume in changing them. He should begin on the left side of the mandible and work from the back forwards. He need not strain this rule, if for example the extrac- tion of the second molar first would facilitate the removal of the third molar. Assuming tlie prop to be centrally placed, he extracts the left lower teeth to the canine inclusive, and crosses to the right side, behind the chair. He should never pass in front of the patient, be- cause it takes longer, and involves the risk of stumbling over the foot-rest ; or, worse still, of disarranging his dress by catching on the arm of the chair — an accident that, occurring to a dentist imprudent enough to give an anaesthetic to and operate on a female patient without the presence of a third party, preferalily of the gentler sex, may involve his being charged with a criminal assault. The lower teeth on the right side are taken to the canine. The operator steps dowii, takes his upper forceps, and re- moves first the cheek teeth on the left, then the same teeth on the right side, begiiming always at the back and working forwards. The anaes- thetist or assistant inserts a Mason's gag or a wedge on the left side, the central prop is re- moved, and the operation completed by the extraction of the anterior teeth, upper and lower. The procedure described may be varied by extracting all the mandibular teeth before proceeding to the upper teeth. The operation of "clearing the mouth" is, or should be, rare in private practice, and attention to dental hygiene would render it very infrequent in hospital patients. Even when it ajjpears necessary, it will often be more judicious to do it at two sittings, taking the lower teeth at the first, and the upper teeth at the second, or the upper and lower teeth of the same side at each sitting. Inasmuch as the risk of sepsis is increased in extensive extrac- tions in dirty mouths, every antiseptic precau- tion inculcated in the earlier part of this chapter must be strictly observed. The collective area of an extensive extraction wound is large ; till the gums heal, solid food is impossible, and nutrition is apt to be impaired ; haemorrhage and .shock are also factors antagon- istic to speedy recovery. The importance of the operation and its attendant risks need not be exaggerated to the point of frightening the patient and paralysing the operator, but on the other hand they need not be minimized or recklessly ignored. One word of advice in conclusion : during the administration and extraction, " Watch the breathing " ; after the operation, " Attend to the wound ". W. G. BIBLIOGRAPHY ( 1 ) Bennett, Norman G. Pye'a Surgical Handicraft, 1909. (2) BowDEN, G. H. Case of Deafness following Bilateral Dislocation after Extraction of Molars. Trans. Odonl. Soc, 1896-7, p. 90. (3) Coleman, F. Extraction of the Teeth. (4) Davies, .John D. Pulmonary Abscess caused by a Tooth. Brit. Dent. Jour. Dental Cosmos, 1907, Vol. XLIX, p. 98. (5) Endelman, Julio. Notes on Therapeutics of the Accidents of Extraction. Dental Cosmos, 1905, Vol. XLVII, p. 348. (6) Inolis, O. E. Post-extraction Sequelae. Dental Cosmos, 1909, Vol. LI. p. 695. (7) J.\MES, W. W. Extravasation of Blood into Neck following Extraction of Third Lower Molar. Trans. Odont. Soc, 1906-7, p. 104. (8) LiNiATSCHECK. Post-extraction Pain. Deutsche Monatschrift far Zahnheilkunde, Nov. 1904. Dental Cosmos, 1905, Vol. XLVII, p. 145. (9) Parfitt, J. B. Mechanical Principles of Extrac- tion. Trans. Odont. Soc, 1906-7, p. 44. (10) PVE, Walter. Pye's Surgical Handicraft, 1908, pp. 31, 32. (11) Smale and CoLYEB. Diseases and Injuries of the Teeth, 2nd ed., p. 567. (12) Tomes. Dental Physiology and Surgery, 1848, pp. 325-327. (13) Tomes and Nowell. Dental Surgery, 1906. (14) Vorslund-Kj.\er, Prof. Permanent Insensi- bility of Inferior Dental Nerve, caused by Extraction of Lower Wisdom. Dental Cosmos, 1908, Vol. L, p. 1151. CHAPTER XLI LOCAL ANAESTHESIA Local anaesthetics may be defined as sub- stances tliat temporarily destroy sensation in a circumscribed area of tissue, by interfering with the functions of the terminations of the sensory nerves. From early times many methods have been adopted, and various substances used in an endeavour to bring about a freedom from pain during a surgical operation. The methods in use in dentistry at the present time are : Firstly, the application to the part, of volatile substances, which act by lowering the tempera- ture of the tissues, and thus paralysing the terminations of the sensory nerves; this is merely a further advance on older methods, which attempted by the application of cold substances to the part to be operated on, to bring about a certain degree of numbness. Secondly, the application to mucous surfaces of drugs cajjable of being absorbed, and by their action on the nerve fibres producing local anaesthesia. Thirdly, the injection into the tis- sues themselves of solutions of drugs capable of causing local anaesthesia of the part. The first of the volatile substances to be used for freezing the tissues was the ether sjiray introduced in 1866 by Sir W. Richardson. This spray, when allowed to play on the part, caused intense cold, brought about by the rapid evaporation ; and anaesthesia was produced by the paralysis of the terminations of the sensory nerves. Although there is no record that this particular spray was ever used in dentistry, the substances introduced later, which were even more volatile, such as ethyl chloride and methyl chloride, and also various mixtures of the two in varied proportions, have been extensively used to produce local anaesthesia in dental operations. Ethyl Chloride is a gas at ordinary tempera- tures, but under pressure is condensed into a colourless liquid, having a sweet burning taste, and a characteristic pungent odour. It boils at about 50° F., and is very inflammable, burning with a green flame and setting free hydrochloric acid. It readily volatilizes when liberated at ordinary temperatures, more readily if it is aided by a little heat, such as that of the hand. It is usually supplied in glass or metal capsules, either sealed or fitted with some form of metal stopcock or screw stopper. The 664 opening from the capsule is exceedingly minute, in order to allow the gas to escape in a fine spray. It is used for the extraction of teeth, and for many minor operations about the mouth, but its use is rather restricted to the anterior part of the mouth, on account of the difficulty of directmg a spray on to the tissues in the posterior region. The freezing should not be too prolonged, nor used for patients who have a poor circulation, as the blood-supply may be so cut off as to bring about a condition which has been likened to a chilblain, or frost-bite, and which may lead to gangrene of the part, unless the circulation is restored in time. For the same reason it is not advisable to employ it where there is extensive inflammation, as the circulation may be more readily cut off in tissues where vitality is already lowered and stasis has occurred. Its use is not advised in acute inflam- mation of the pulp, or acute periodontitis, on account of the intense pain produced during its application. Where it is to be used for the ex- traction of a tooth with an exposed pulp, or in the neighbourhood of one, care should be taken to protect the pulp first, by means of some fiUing, and an endeavour should be made to direct the spray towards the apex of the tooth and away from the crown. The inhalation of the vapour, even though only a small quantity, may bring about a jjartial general anaesthesia, and for this reason the method should not be used for patients who are habitually mouth- breathers. Method of Ajyplication. — The part to be sprayed should first be thoroughly cleansed, and then dried. Wool rolls and napkins should be so arranged as to protect the surrounding tissues, and to prevent the vapour being sprayed on the back of the mouth or throat. The glass capsule is held in the hand with the nozzle directed away from the patient, and the warmth of the hand hastens the volatilization of the liquid ; the spray is then directed on to the tissues," the capsule being held some six or eight inches away, so as to ensure the ethyl chloride reaching the tissues in the form of vapour. When the tissues appear white and covered with crystals, the spray should be arrested, and the operation quickly performed, as the anaesthesia is not of very long duration. The second metliod employed is that of the 665 application to the mucous membrane of drugs, or solutions of drugs, that are capable of being absorbed, and by their action on the sensory nerves dull the sensibility to pain. Cocaine is one of the chief drugs used for this purpose, but the result is merely superficial, and does not render it of very great value in the mouth, except for very slight operations. A very much stronger solution of the drug may be used in this manner than would be injected, but care should be taken to limit its action to a small area, by protecting the surrounding parts. Sufficient time must also be allowed for ab- sorption. Electrical currents have been used to aid the diffusion of the drugs, but the un- certainty of the results produced, and the time required, have rendered this method, in dentistry at any rate, almost olisolete. ANAESTHESIA BY INJECTION The method most in practice at the present time is the injection, by means of a syringe, of solutions of drugs, which by infiltration of the tissues, and by their action on the nerve filaments in close proximity to the part to be operated on, bring aliout the desired result. In general surgery this is carried further, by the injection into a nerve-trunk, in order to produce anaesthesia in the course supplied by the nerve, and is known as " regional anaes- thesia ". This method, however, is not em- ployed in dentistry. Before discussing the various drugs used for this purpose, it may be as well to consider what are the advantages and disadvantages of this method as compared with a general anaesthetic, and in doing this it will be taken for granted that its chief use would be for the extraction of a tooth or teeth, though of course its use is not limited to this. The advantages of this method over nitrous oxide inhalation are : No special preparation on the part of the patient is necessary ; in contradistinction from nitrous oxide anaesthesia it is rather preferable to inject after a meal than some time before, as this enaljles a patient better to withstand any shock. The length of time the anaesthesia lasts by this method is considerably longer, thus allowing ample time for a difficult extraction ; it also permits a very careful preliminary exploration to be made painlessly. The patient remains quieter during the operation ; this, with the additional time, enables the extraction to be accomplished with less laceration of the tissues. The after-pain of extraction is very much diminished, if only a suitable strength of the drug has been injected, and not more than a sufficient quantity of the solution. Some writers maintain that the pain is often very severe some hours after the operation ; but except in a very few cases this does not occur, and when it does it rather points to some error in judgement, such as injecting in an unsuitable case, or the use of a too powerful strength of the drug. Besides the cases in which the injection of any particular di'ug is contra-indicated, one of the disadvan- tages of this method over a general anaesthetic is that a nervous patient is conscious of the manipulation of the instruments, although not feeling pain. This difficulty can, however, as a rule be overcome, except in the case of neur- asthenic patients, to whom should be given a general anaesthetic. Against this may be placed the fact that a patient who has once experienced local anaesthesia has less dread of it than many patients have of a second administration of a general anaesthetic. It is claimed against this method that it is more dangerous, but this need not be so now, if its use is limited to suitable cases. It was undoubtedly true before it was recognized that nothing like the dose of the drugs formerly given was necessary, and also before the addition of adrenalin chloride to solutions to limit the action of the ckug to a circumscribed area ; now, however, with a minimum amount of the drug in an isotonic solution it need be no more dangerous than any other anaesthetic. The healing is said by some to be delayed by this method, but this is not borne out clinically. Where such was the case it may have been due rather to an unsuitable strength of the drug, or to the condition of the tissues having been un- healthy, thus not permitting the return of the blood to the part sufficiently soon for healthy healing. Although it may be conceded that this method has many advantages to recommend it, yet it should in no wise be looked upon as a simple and easy operation. Great care should be exercised, and experience is necessary in the use of drugs, which are in many cases strong protoplasmic poisons. Warning is necessary in the case of multijjle extractions, as there is great danger that, on account of the prolonged anaesthesia that can be obtained, too much may be attempted at one time. It is frequently not realized that the operation of tooth extraction entails consider- able shock to the system, and although symptoms of it may not appear at the time, the effects of it are often felt for some considerable period afterwards. This is perhaps one of the greatest dangers of local anaesthesia, and it cannot be too strongly urged that where it is necessaiy to extract several teeth at one time, the patient should be kept under observation afterwards, and should be treated exactly as he would be after a minor surgical operation, and where possible, kept in a reclining position. 666 The use of this method of produchig anaes- thesia is not recommended for young cliildren, as although they are frequently good subjects for it, yet the technique of the injection, and their consciousness of aU that is being done, is rather apt to frighten them ; whereas in the case of a general anaesthetic they veiy soon reach an unconscious state, and rarely dread a repetition of it at a future date. It is not advisable to inject into, or near, very inflamed tissues, as besides the pain caused by so doing, the vitality of the tissues, already lowered, is liable to be further reduced by the action of the drugs used ; moreover, the absence of blood-supply for some time may cause sloughing and death of the tissues. There are other factors to be taken into consideration in injecting certain drugs, which will be con- sidered when these drugs are discussed. Cocaine was the first drug to be used, by injection, to produce local anaesthesia. Cocaine Hydrochloride is the hydrochloride of an alkaloid extracted from coca-leaves (Erythroxylon Coca). It was first obtained in 1860 by Gaedeke, but its use by injection was first suggested by Koller in 1884. It consists of colourless crystals or a crystalline powder, soluble 2 in 1 of water, 1 in 3 of alcohol and 1 in 3 of glycerine. It has a bitter taste and produces on the tongue a tingling sensation, followed by numbness. Aqueous solutions are neutral to litmus jmper. Solutions do not keep well on account of the growth of a fungus in them ; to prevent this, boric acid or salicylic acid is added to the solution ; it is, however, better to make fresh solutions from the salts as they are required. Prolonged boiling breaks it up into ecgonine and other compounds ; but it is maintained by some writers that such boiling as is necessary for sterilization does not impair its anaesthetic action, and that the ecgonine is present in such a small quantity as to be non- irritant. Its local action on injection is a selective one for some of the terminations of the sensory nerves, especially those conve_>dng impressions of pain and touch. It has a vaso- constrictor action on the vessel walls, producing contraction of the vessels and a perceptible blanching of the tissues. Its general action is, firstly, one of stimulation of the central nervous system, which may be evidenced by some excitement in either speech or movement ; this is followed by depression. Respiration is accelerated owing to central .stimulation, and the rapidity and depth of breathing is increased ; later, depression follows, and as it progresses the amount of air in- spired with each breath becomes less, and may cease altogether. The circulation is altered owing to its action on the heart and on the vessels, and the pulse is quickened; later, it becomes slow and \^•eak, and collaj)se may take place. The dose by the stomach is | gr. ; for dental operations J gr. is considered a safe dose, in a weak solution of | per cent or 1 per cent ten to fifteen minims being usually required. Sauvez (15) recommends that not more than 1 c.cm. of 1% solution should be injected at one time in a sitting position ; if more is required the patient should be placed in a recumbent position, and kept in that position for some time afterwards. All clothes that impede respiration should be loosened. The toxic action of cocaine even in small doses is very uncertain, and it is this that makes cocaine a dangerous drug to use indiscriminately. Symptoms of toxic action differ in different individuals. They may first appear as some excitement or restlessness on the part of the patient ; or there may be merely a calm languid condition. The pulse is quickened, the breath- ing is quick and deep, the pupils are dilated, headache and a feeling of sickness may be com- plained of, the mouth is often dry, and there is a profuse perspiration. The breathing becomes rapid and dyspnoeic, and may finally be arrested during convulsions. Li other cases there may be no convulsive movements, merely faulting and collapse, with the heart-beat slow and weak and the respiration feeble ; either of these may gradually cease. There is no known antidote for cocaine. Place the patient quickly in a recumbent position, loosen all clothes that may in any way impede respiration, allow plenty of air to get to the patient, cover tlie lower limbs and keep them as warm as possible, give stimulants and inlialations of ammonia, and if necessary employ artificial respiration. Cocaine should never be emjjloyed for people with heart-disease, nor for those suffering from any affection of the lungs, or other organs of respiration ; nor should it be injected in anaemic people, or those weak- ened by iUness ; and because of its depressive action it should not be used for neurasthenic people, or where there is locally intense in- flammation, such as spongy inflamed gums. Wlien cocaine was first extensively used as a local anaesthetic, the dose injected was usually too great, and sufficient care was not perhaps taken to ensure that the patient was in a fit condition, with the consequence that the cocaine was absorbed into the system, and toxic symptoms occurred rather frequently. Tluis cocaine came to be looked upon as too dangerous ; later, adrenalin chloride was added to solutions to cause further contraction of the vessels, and so limit the action of the drug to a small area. Adrenalin Hydrochloride, known also as epi- nephrine, suprarenin, and under many other names, is the hydrochloride of a substance 667 obtained from the suprarenal capsules of sheep and oxen. It is a greyish powder, slightly soluble in cold water, but more freely in warm water. Aqueous solutions ^^•hen fresh are colourless ; if allowed to be submitted to the action of light or air, they become oxidized and lose their properties. It remains stable much longer in the dry state. It is a powerful vaso- constrictor, acting on the muscular coat of the smaller arteries, and when applied to a mucous membrane, even in dilute solution, produces a local ischaemia ; on injection its action is increased, causing complete contraction of the vessels. If used in weak solutions and not in too great quantity its action is only local ; but when injected in large doses it causes great acceleration of the heart's action, and a rapid rise in blood pressure, wliich is followed by a slowing or arrest of the heart ; respiration slows and may cease with expiration. For applica- tion to mucous membranes an aqueous solution of 1 in 1000 is used, but for injection this should be diluted to 1 in 10,000 or 1 in 100,000, in normal saline solution. Adrenalin possesses no anaesthetic value itself, but when injected in combination with other drugs, it not only restricts their absorption to a limited area, but at the same time permits them to exercise a much more jjowerful action by so doing ; it also permits the operation to be performed bloodlessly. This latter may or may not be of advantage, but it is claimed that its jjower of restricting absorption has had a marked influence on the usefulness of local anaesthetics. Cocaine, though good from an anaesthetic point of view, has disadvantages, both from its limitation of u.se in certain cases, and the uncertainty of its toxic effects ; so that many substances have been introduced with the object of supplying an anaesthetic without these disadvantages. Among these are eucaine and tropacocaine, stovaine, and novocaine. Eucaine is a synthetic product artificially produced from a base analogous to ecgonine. At first two alkaloids were used, alpha and beta, but the former was discarded on account of its irritant properties. Of beta-eucaine the hydrochloride and lactate are Ijoth used. The former appears as small, white, opaque crystals soluble in water, 1 in 30 ; it is usually used as a 3 or 4% solution for injection, and i gr. may be safely injected. A good anaesthesia may, however, be obtained with a 2% solution, but to obtain this solution, the salt must be dissolved in warm water, and it is more readily dissolved in a sodium chloride solution. The lactate is preferred by many on account of its greater solubility, 1 in 5 of water. The lactate contains in 119 grs. the .same amount of the eucaine base as 100 grs. of the hydro-chloride. The properties of eucaine are similar to those of cocaine, except that it has a vaso-dilator action instead of a vaso-constrictor. It has been extensively used, the advantages claimed for it being a lesser toxicity, and also that it does not decompose on boiling. Its disadvantages are, that it is rather more irritating to the tissues, that it does not diffuse so readily as cocaine, and that swelling is more likely to occur. Anaesthesia is not produced so rapidly ; at least seven or eight minutes must be allowed to elapse after injection before operating. Its effect does not last nearly so long as cocaine. Adrenalin is often used in combination with eucaine, but its addition has not the same effect as in the case of cocaine ; eucaine lessens the action of adrenalin while cocaine enliances it, probably because eucaine has a vaso-dilator action and so retards the action of adrenalin. Tropacocaine is derived from a source similar to cocaine ; it is obtained from the leaves of Java coca. The hydrochloride is the salt used, it is freely soluble in water, solutions of it may be boiled without change, and solutions are said to keep well. Sauvez considers it inferior to cocaine in anaesthetic value, and equally to.xic ; others have placed its toxicity between that of cocaine and eucaine. It has been extensively used in dentistry in Germany, and has been found successful without being dangerous. It is used as a 3% solution, 10-20 minims being injected. Anaesthesia lasts about ten miiuites ; it has a vaso-dilator action, and is said to differ from the other drugs by preventing the action of adrenahn cliloride when used in conjunction with it. Le Brocq, however, found that if fresh solutions were used the two drugs could be successfully combined. Stovaine, discovered by Fourneau in 1904, is the name given to a hydrochloride of beta- amyline, which is a derivative of the tertiary series of amino-alcohols. It crystallizes in scales, and is easily solulile in water, 1 in 13, and is slightly acid in reaction. Aqueous solutions can be sterilized by boiling without decomposi- tion. It has less to.xicity than cocaine, and ha? a slight vasodilator action; it is said also to possess slight germicidal properties, and a tonic action on the heart. The anaesthesia produced is not so good as with cocaine, and there is some pain (in injec- tion. Gangrene has been noted at the point of injection, but po.ssibly too strong a solution was used; Reclus (14) recommends a 1% solution, and says that its injection caused only a slight sensation of smarting, and that gangrene does not take place. He came to the conclusion that anaesthesia w'as .slower in coming, and quicker in disappearing, than with cocaine. Braun (1) considered it weaker in anaesthetic action, and that it possessed no advantages over cocaine and eucaine. 668 It has been extensively used in_surgery to produce spinal anaesthesia. Novocaine is a synthetic product discovered by Eiiihorn ; it is an amino-alcohol of the ethane series combined with the radicle of para-amido- benzoic acid. The hydrochloride consists of a white crystalline powder, which is readily soluble in cold water. Solutions react neutrally to litmus paper, and can be boiled without decomposition. It has a slight vaso-dilator action, and possesses the same action on the peripheral nerves as cocaine. The resjiiratory and circulatory systems are only affected by very large doses. It has no harmful action on the tissues, causing no irritation or sweUing on injection. The drug is usually used in combina- tion with adrenalin chloride, and it is claimed that a smaller amount is then required ; the action of the adi'enalin is not lessened by the novocaine, and as the anaesthetic properties of the latter are not interfered with, and the adrenalin limits the action of the novocaine to a circumscribed area, a very small quantity is needed. In dental operations it is usually used either as a 2 % or 1 % solution ; the latter is ample for most operations, and J gr. is usually sufficient, though it may safely be used up to 1 grain. Li a large series of experiments, Le Brocq (8) has investigated the relative suitability of drugs used as a substitute for cocaine in local anaesthesia. The points that he investigated were based on the postulates laid down by Braun as being essential, viz. — (1) That it should have a lower toxicity than cocaine, in proportion to its local anaesthetic value. (2) That it should possess sufficient solubility in water, and that solutions should keep without deterioration and be capable of sterilization by boiling. (3) That there should be no mjury to the tissues, and that it should be easily absorbed, without causing any after- effects. (4) That it should be capable of being com- bined with adrenalin. (5) That it shoulcT penetrate mucous mem- brane rapidly, and be suitable for medullary anaesthesia. Among the drugs he investigated were beta- eucaine lactate, novocaine, stovaine, and tropa- cocaine. In anaesthetic action alone, he came to the conclusion tliat stovaine was more powerful, weight for weight, than the others, wliich were about equal to cocaine. With regard to toxi- city, after numerous experiments on animals to find the minimum lethal dose, he found that by taking the toxicity of cocaine as 1-0, stovaine would be rejjresented by 0-625, tropacocaine by 0'500, novocaine by 0-490, and beta-eucaine lactate by 0-414. In solubility he ruled out those not capable of forming a 2 % solution in cold water, thus excluding eucaine hydro- chloride, as a 2 % solution of this drug can only be obtained in warm water. The others are all freely soluble, and their solutions are capable of being boiled and are stable. As to their irritant action, he found by experiments on animals with antiseptic precautions, inject- ing 10 minims of a 10 % solution, that cocaine caused swelling and hyperaemia ; stovaine caused intense hyperaemia with dilatation of blood- vessels, followed by sloughing ; beta-eucaine lactate caused swelling and thickening about the j)oint of injection, followed by sloughing; tropacocaine caused swelling and some thicken- ing, followed by sloughing ; and novocaine caused no sweUing or hyperaemia, and the part remained perfectly normal. From this it will be seen that novocaine was the onlydrug showing less irritant action than cocaine ; and though the strength of the solutions used was considerably in excess of those usually employed, yet the experiments tend to show which drugs possess the least irritant action. He found that all the drugs named were capable of being combined with adrenalin, if fresh solutions were used. His conclusions summed up were briefly as follows : The toxicity and anaesthetic action of novocaine and tropacocaine are about equal, but the latter is more irritant. Comparing novocaine with beta-eucaine lactate, the anaes- thetic action is about equal, but while the toxicity of eucaine is slightly less, its irritant action is much greater; he considers that the lack of irritation caused by the novocaine outweighs its slightly greater toxicity. In comparing novocaine with stovaine, the latter has a greater anaesthetic action, but its toxicity is greater and it has a greater irritant action. On the whole, therefore, he came to the con- clusion that novocaine was the most satisfactory. It is perhaps not safe to take these conclusions as final evidence, as with experiments on animals, even though they be mammals, the drugs may not react in quite the same mamier as on man. Clinical experience can be the only final guide as to which is the better drug to u.se. The solutions used for injection have been very much improved by the recognition of the fact that they must be capable of being absorbed into the tissues quickly and freely, and to attain this nuist therefore be of the same density as the fluids of the body ; in this way also the irritation, pain, and swelling caused by injection are minimized. These results are brought about by making a solution of the drug in normal saline, or by adding to the tablet of the drug sufliciont sodium chloride to make the sola- 669 tion the same density as the blood-serum, and so facUitate the diffusion of the solution. Having the solution of the right density also prevents change in the tissue-cells, other than that which is supposed to take place when these drugs are injected. The drugs when eliminated after action are probably not in the same form, some change having taken place \\hile they were in conjunction wth the tissue-cells. Another means of aiding the rapid absorj)tion of drugs is by making the solution to be injected slightly warmer than blood heat, so that by the time it has passed through a cold syringe it is about the temperature of the blood. Syringe and Needles. — The syringe used for dental purposes must be stronger than those used for hypodermic injection, as the tissues are much denser and a great deal of resistance has often to be overcome. A good many have been evolved for this jDurpose, so that it is hardly necessary to describe one in detail ; it is sufficient to say that it must be strongly made, and capable of being readily taken apart for cleansing purposes. It must be capable of being held in the hand with comfort, and have finger-rests so that sufficient force may be exerted ; it should be graduated to show the amount of solution used, and should be so jointed as to exclude leakage under the force exerted. Needles should be very strong and sharp-pointed, as unnecessary pain may be caused by using a blunt needle ; a disc or stone run over the point ensures a sharp edge. Needles should not be too long, as they are more apt to bend and break, nor should they be too short, for if they are they tend rather to obscure the view and render the injection more difficult ; I in. is perhaps the best length for most f)urposes. Needles that can be attached to the nozzle are best, and it is better not to use them a second time. Some operators prefer a needle fixed to the nozzle, but these require very careful sterilization after use. All needles should be immersed in formalin or some other antiseptic before use. Technique of Injection. — The mouth should first be rinsed with an antiseptic solution ; when the injection is for tooth extraction, the tissues surrounding the tooth should be further cleansed and dried, and a napkin arranged in such a way as to leave the tissues exj)osed to view, and at the same time effectually ab- sorb any of the solution that is not forced into the tissues. The point or points where the needle is to be introduced should be painted with a solution of iodine, to prevent the carry- ing of septic matter into the tissues. This usually also has the effect of diminishing the pain of inserting the needle, but if desiral)le a pledget of wool soaked in a strong solution of the drug to be used, may be applied to the part for some minutes to prevent even the prick of the needle being felt ; this is perhaps necessary where the f)atient is at all nervous. The amount of solution to be injected is drawn into the syiinge ^\itli a small quantity in excess, to allow for leakage ; the piston is then pressed down until a drop appears on the end of the needle. The gum where the needle is to be inserted is, where possible, rendered tense by the thumb and a finger of the left hand ; this makes the insertion of the needle easier. The needle is then pressed a little way into the tissues, and at the same time force is exerted on the piston ; when a few minims have been injected, a short time is allowed for the absorp- tion of the solution, pressure being maintained on the piston meanwhile to keep the fluid in. The needle is introduced still further, and so on, until the tissues become blanched. The needle is then witlidra\\n, pressure being still maintained on the piston. If the needle is not introduced deeply enovigh, a portion of the mucous membrane is raised like a blister, con- taining the liquid. When this happens it is best to withdraw the needle and insert it in a new position, and deeper. The first insertion should be made on the labial aspect of the tooth, about midway bet\\een the gum margin and the apex of the root. The needle should be directed obliquely to the long axis of the tooth, and gradually forced more deeply into the tissues. Considerable force is often needed to overcome the resistance of the tissues to the introduction of the liquid, and intervals should be allowed for its absorption from time to time. Care should be taken that the needle does not strike the bone, as not only is there danger of the needle breaking, but also very little fluid is able to escape in that position. For the incisors one puncture is often sufficient, but for a canine two are usually necessary, one on the labial aspect and one on the palatal, on account of the length of the root. The premolars usually require two ; the upper molars three, two on uhe buccal side and one on the palatal. For the lower molars two, and sometimes more, are necessary ; they are the most difficult to anaesthetize successfully, and the needle should be passed in a direction down- wards and backwards, and if possible in a straight nozzle, though the use of a curved nozzle is sometimes necessary. Wlien there are two or more injections, care should be taken to introduce the needle on the subse- quent occasions within the area anaesthetized by a j)revious injection ; and to enable this to be afterwards done, when introducing the needle the first time, the orifice of the needle should be made to point towards the position where it is intended to make the second injec- tion, as the liquid wiU escape more readily in f)70 that dii-ection; in fact, by turning the needle round, an anaesthetic zone equal in all directions may be obtained. After the injections have been accomplished, the i^atient should be asked to rinse the mouth again, in case any of the solution has escaped. The time to allow be- tween the finish of the injection and the per- formance of the operation varies with the drug used, and also with the strength of the solution. Clinical experience will soon teach the necessary time to allow. Before actually performing the operation it is as well to make an e.xploration witli a blunt probe, in order to test the depth of the anaesthesia ; this also, when necessary, helps to make sure of the configuration of the root. Where the tissues are in an inflamed state the engorged vessels will not readily permit of any further infiltration, and indeed it is too painful ; but sometimes this may be overcome by in- jecting in small quantities in several positions around the inflamed area, but outside it, till gradually an anaesthetized area will be formed, which will reheve most of the pain. It is better, however, not to attempt this in the case of a tooth, as the area around it is so limited. Anaesthesia for Conservative Operations The injection of local anaesthetics, besides being used for extractions and other minor operations in the mouth, is also used in con- servative dentistry, to enable either a cavity to be prei^ared, or a pulp removed, or other painful operations performed on a tooth. A small quan- tity of a weak solution of one of the drugs men- tioned, injected into the gums surrounding a root that is to be banded for a crown, enables this to be done painlessly. For the removal of a pulf) in a single-rooted tooth, injections made in the neighbourhood of the apex of the root, with the needle inserted deeply, in many cases enables the pulp to be removed without sensation. An injection made deeply between two teeth, until the needle reaches the alveolar septum separat- ing them, often has the effect of rendering operations on these teeth painless for some con.siderable time. The injection into the gum around the neck of a tooth j)ermits tlie excava- tion and preparation of cervical cavities. A. H. Parrott (11) (12) and other writers recommend what they term intra-alveolar injections for many purposes in conservative dentistry. Parrott uses a high-pressure syringe, and makes a preliminary injection into the sub- mucous tissue at a convenient spot, and injects a few minims of a 2 % novocaine solu- tion. He then changes the needle used for this injection, for one with a heavier point unsharpened and bevelled. With a round burr corresponding in size with this needle, he makes a perforation through the soft tissues, where possible near the apex of the tooth, and also through the outer layer of compact bone, into the cancellous bone beyond. The heavier needle is inserted into the entrance of the per- foration in the bone, the bevel on the needle preventing it entering far and also ensuring a tight joint, and about four or five minims of the solution are injected. The syringe he uses works on the ratchet principle, and is so arranged that for each movement of the ratchet only one minim is injected. Anaesthesia is produced in a few minutes, and lasts sufficiently long for the removal of a puljj or the preparation of a cavity. This method has been extensively used by many operators, and successful results are reported from many of them. It appears, however, to many others as rather a drastic operation for the preparation of a cavity or the removal of a pulp ; and although it is at present the surest method of producing anaes- thesia of the f)ulf)s of lower molars, perhaps in the near future some modification \\ill be de- vised, which, while producing the same effect, \vill not necessitate drilling and injecting into the bone. F.J. P. BIBLIOGRAPHY (1) Bratjn. Die Lokalanaesthesis. (2) BuRCHABD, H. H. Kirk's American Text-book of Operative Dentistry, 3rd ed., p. 631. (3) CusHNEY. Text-book of Pharmacology. (4) FiscHEB, G. Technique of Injection. Deutsche Zahnarztliche IVochenschrift. Trans. Dental Cosmos, 1909, Vol. LI, p. 1341. (5) Gabell and Austen. Materia Medica for Dentists, p. 89. (6) Hey, S. D. Local Anaesthesia and Methods of producing it. Brit. Dent. Jour., 1910, Vol. XXXI, p. 405. (7) HowKiNS, C. H. Local Anaesthesia in Dentistry. Brit. Dent. .Jour., 1907, Vol. XXVIII, p. 1013. (8) Le Brocq, C. N. Substitutes for Cocaine. Brit. Med. Jour., 1909. Dental ReconI, Aug. 1909. (9) Luke and Ross. Anaesthesia in Dental Surgery. (10) Pare, J. W. A New Local Anaesthetic. Trans. Odont. Soc., 190B-7, Vol. XXXIX, p. 120. (11) Parrott, A. H. Injection Anaesthesia in Con- servative Dentistry. Brit. Dent. Jour., 1910, Vol. X.XXl, p. 1201. Dental Record, 1910, Vol. XXX, p. 181. (12) Parrott, A. H. Proc. Roy. Soc. of Med. {Odont. Sec), 1912. (13) Prinz, Hermann. Johnson's Operative Dentistry, Chap. XXV, p. 385. (14) Reclus, p. Brit. Dent. Jour., 1906, Vol. XXVII, pp. 170, 225. (15) Sauvez, E. A Study of the Best Means of Local Anaesthesia for Extraction of Teeth. Brit. Dent. Jour., 1905, Vol. XXVI, pp. 373, 445. Dis- cussion, 679. (16) Struthers. Local Anaesthetics. (17) White, Hale. Materia Medica and Pharma- cology, p. 99. CHAPTEll XLIl ALVEOLAR ABSCESS Alveolar abscess occurs in connection with any tooth, deciduous or permanent. The tooth, or particular root, with which it is con- nected is always septic as a result of death of the pulp — a sequel generally of caries, sometimes of violence. A few cases of alveolar abscess occurring in connection with living teeth are recorded in dental literature, but these should probably be classed with paradental abscess of pyorrhoea. Alveolar abscess may be expected at any time, from a few months after eruption of the first deciduous incisor to the close of life. Six months suffices for caries to destroy the crown of any young tooth, deciduous or permanent, so that the disease may be found in connection with any tooth at any time from six months after its eruption. The particular incidence of alveolar abscess follows dental caries : the simplest teeth — the lower six front teeth, deciduous or permanent — are the least frequently attacked ; the rest may for practical purposes be classed together as equally liable. General health has little practical influence, but as with most diseases, lowered resistance may be the precipitating cause ; in general, however, the dose and virulence of the microbic infection are sufficient to overcome the healthi- est resistance. As with abscess elsewhere, pus formation is generally definitely due to germ infection. The organisms incriminated include staphylococcus aureus and albus, streptococcus longus, and di25lococcus pneumoniae. In some cases, both acute and chronic or quiet, but always unopened cases, no organisms have been found. This may be due to the fact that the germ has destroyed itself by the products of its own activity. COURSE AND PATHOLOGY OF ALVEOLAR ABSCESS Most commonly the pulp of the tooth dies as a sequel of germ infection after exposure by caries ; in some cases as the result of infection through the yet hard dentine via the dentinal tubules. When the pulp dies as a result of violence, germ infection probably takes place through a crack in the tooth, or along the injured periodontal membrane. In the case of a two- or three -rooted tooth, abscess formation may begin at the apex of one or every root, or there may be a live pulp strand in one root and an abscess comiected with the dead pulp in another. In a few cases part of the pulp itself has been found alive as well as the nerve of one root, while there has been abscess formation at the apex of the root whose nerve and blood vessels were distributed in the gangrenous portion of the pulp. Abscess forma- tion begins by infection of the peri-apical tissue through the apical foramen ; germs may (1) spread through by growth, (2) be forced through by pressure of gaseous products of putrefaction, or (3) be forced through by mani- pulation. At first there is only inflammation of the periodontal membrane and bone surrounding the apex. In acute cases this soon gives way to suppuration and destruction of bone tissue, forming a central l)one abscess. In cases that are chronic from the beginning, there is a slow rarefying osteitis, leading to considerable forma- tion of granulation tissue, for some time before pus formation commences. The bone is de- stroyed by molecular necrosis ; very rarely is there any tangible necrotic fragment. In a few cases the pus finds a vent through the canal of the root ; in a few others along the side of the root, between it and the bone of the socket ; most frequently the abscess enlarges in the direction of least resistance and eventually perforates the hard outer bone casing. Most frequently this perforation occurs through the outer side, even when the abscess arises from the palatal root of an upjoer tooth ; this may be due in j^art to the direction of the leash of vessels and nerves entering the root foramen, and in part to the density of the hard palate. In the maxilla the pus may also perforate in the following positions : (1) The palatal aspect ; more usually such an abscess arises from the lateral incisor or first molar, but may arise from any one of the teeth. (2) The nasal floor ; arising from an incisor, canine, or a premolar, and possibly the palatal root of a first molar. (3) The floor of the maxillary sinus ; arising from any of the cheek teeth, i. e. premolars and molars. In the mandible exit on the lingual side is rare. After perforating the outer bone case the pus strips up the periosteum to a greater or less extent, forming a sub-periosteal abscess, and in 671 672 general, finding the least resistance in the direction of the alveolar buccal sulcus (vesti- l)ulum oris), perforates the alveolar muco- periosteum — hence the use of the term " alveolar abscess ". The point of exit through the muco- periosteum is very seldom opposite that through the bone. Fascial or muscular attachment to the bone — cervical fascia, buccinator — may prevent sub- periosteal spread in the vestibular direction, especially in the case of long -rooted teeth ; the pus on perforating the periosteum then forms an interstitial abscess among the fascial layers of the face or neck, and issuing again from beneath the fascia by the same process -of destroying the tissues in the line of least resist- ance, may form a sub-cutaneous abscess before eventually opening on the surface. Thus the possible "stages of an alveolar abscess are : (1) central abscess of bone, (2) sub-periosteal abscess, (3) exit into mouth ; or — (1) central abscess of bone, (2) sub-periosteal abscess, (3) interstitial abscess, (4) sub-cutaneous abscess, (5) exit through the skin. (2) (3) and (4) will only be distinguishable from one another in the less acute cases. Alveolar abscess may be acute or chronic from the beginning ; chromcity frequently follows on an acute commencement, and an acute phase may complicate a chronic case. Wlien dose and virulence are low the process will be chronic from the begimiing, and " point- ing " will be correspondingly delayed ; otherwise the clinical symptoms are acute in inverse ratio with drainage. \Vlien an acute or chronic abscess bursts, unless the cause is removed a fistula or discharging sinus forms ; so long as this is patent the course of the abscess will be chronic, but if the fistula is blocked in any part of its course, as soon as pus has collected in sufficient quantity to cause tension, i. e. to determine absorption, the course becomes acute. The microscopic appearances of the tissues round an acute or chronic alveolar abscess differ in no way from those found in inflammatory processes of bone or soft tissue elsewhere. In the most chronic cases of peri-apical or peri- radicular infection, there is a free formation of interstitial granulation tissue replacing the bone and almost entirely obliteratmg the periodontal membrane. In parts this granulation tissue may break down into pus, forming what is at first a minute, almost miliary, abscess. On extraction, such an abscess may be brought out entire in a mass of granulation tissue adherent to the root. This is the only sense in which a "pus sac " is ever found adherent to a root; what is generally so described is a small dental cyst. CLINICAL COURSE AND SIGNS OF ACUTE ALVEOLAR ABSCESS The first stage, infection of the periodontal membrane and bone round the apex, causes a tenderness of the tooth, at first relieved by pressure, but rapidly increasing, and soon followed by rising of the tooth in its socket, so that biting becomes painful, and by tenderness of the overlying bone and gum. The pain, at first dull and shght, rapidly becomes severe and throbbing, increased by each pulse -wave, and continuous, but remains local, whereby it is in general differentiated from the pain of an inflamed or irritated pulp, which is often referred or neuralgic ; in some cases an abscess as it forms may involve a mmute nerve-trunk and give rise, especially in the early stage, to a true neuralgia (see also involvement of inferior maxUlary trunk later). The severity of the pain is due to tension of the inflammatory exu- dation within the unyielding bone, and marks the inception of pus formation. There is now an acute central abscess of the bone. Within a few hours there is some swelling of the over- lying soft tissues — a slight swollen face. In from twelve to twenty-four hours from the be- ginning there is a sudden relief of acute pain, followed by rapid increase in the swelling of the soft tissues. This marks the relief of tension by perforation of the outer plate of the bone and the formation of a sub-periosteal collection of pus. In proportion to the amount of pus the swelling of the soft tissues is extreme ; hence fluctuation is a sign that is not to be expected. This is due to the looseness of the cellular tissues of the face, which allows oedema to spread even to the eyelids. The soft tissues, cellular and muscular, are now mfiltrated with inflammatory exudation, and tender on movement ; hence difficulty of opening the mouth is a very usual symptom of alveolar abscess. Generally the abscess points in the mouth, on the outer side of the alveolus, directed by the attachment of the buccinator. Not infrequently pus perforates the periosteum beyond the attachment of the buccinator, and then points externally. A second lower deciduous molar or a first lower permanent molar is a common source of such an abscess, but in proportion to its frequency abscess of a lower permanent incisor is most often followed by external evacuation. When the pus points externally on the outer side of the mandible, it is superficial to the deep cervical fascia, and the disease runs a more rajiid and easy course than when the pus issues below the mandible and so gets beneath the deep cervical 673 fascia. Pus finding its way externally towards the skin will give rise to the usual symptoms of inflammation and abscess — redness, swelling, local lieat, and pain, followed by fluctuation. If poulticed tiU it breaks, or allowed to burst naturally, the abscess will degenerate into a discharging sinus, and later, when healing occurs, there wiU be a puckered scar adherent to the bone. There may be an accompanying glan- dular abscess. Pus (usually from a third lower molar) finding its way beneath the deep cervical fascia wiU give rise to a hard, brawny, tender, painful swelUng below the mandible, finding but little relief from tension on its exit from the bone ; some days must elapse before the tissues are sufficiently softened to allow the abscess to point. In these cases there is a persistent raising of the general temperature of one or two degrees, and enlargement of lymphatic glands, which may run on to suppuration, giving rise to a second and distinct collection of pus ; but both suppurating foci will be enclosed in one uniform and tense inflammatory swelling. A rise of temperature and an enlarge- ment of lymphatic glands probably occur in all cases of pus formation, but owing to the rapidity of the process are of such a transitory nature as to escape detection. CLINICAL COURSE AND SIGNS OF A CHRONIC ABSCESS These are often limited to a discharging sinus, with perhaps some inflammatory redness and swelling of overlying gum. In the most chronic cases it may be years before a sinus appears. Opposite the apex of the root of the affected tooth a small tender inflammatory nodule of the periosteum is often found. Occasionally, sometimes at regular intervals, when drainage faUs after once becoming established, there is a more acute phase. In the mandible, deposi- tion of new periosteal bone is to be expected, but not in the maxilla. Tangible glandular swellings may be found, but quite generally the glandular swelling escapes notice. Diagnosis of Acute Alveolar Abscess. — This is to be made from (I) the existence of a septic tooth, and (2) local acute inflammatory symp- toms ; and in the early stage before swelling, by acute tenderness of the tooth and a history of local pain and tenderness gradually increasing from discomfort to agony. The inflamed tissues are very sensitive to sudden changes of tempera- ture. Difficulty arises where the abscess is due to a buried root (in this case a radiograph will assist diagnosis) ; or when inflammatory trouble of the neighbouring part (c. g. maxillary sinus, nasal duct, necrosis of nasal process of maxillary bone, superficial abscess, or deep acne abscess) encroaches on the area usually occupied by a 22 dental swelling. In general the most tender and prominent part of the swelling is opposite the offending tooth. Fluctuation is not to be expected in the acute stage, and the amount of pus is very smaU compared with the swelling of the soft parts. If the sub-periosteal stage is prolonged, fluctuation will become evident. Diagnosis of Chronic Abscess. — A chronic alveolar abscess very commonly escapes notice till the patient's attention is called to a dis- charging sinus. In the vestibuhim oris the end of the sinus is often drawn out into a long nipple-like process. A chronic discharging sinus of the face or neck, or even further afield, should always lead to a careful examination of the teeth. Other clinical signs are frequently absent, but there is generally some alveolar tenderness and some slight sweUing and blood injection of the surrounding gum, obscuring the so-called health-line of the gums, i. e. a line marking the limit of the attachment of the muco-periosteum to the bone, beyond which on the cheek side the mucous membrane is free and shows greater vascularity than where it is intimately bound down to the periosteum. In inflammatory conditions of the gum this contrast is lost by increased vascularity of the gum. In the mandible a chronic alveolar abscess may be accompanied by considerable bony swelling and actual deposition of new periosteal bone. In some cases where there has been no sinus formation there is a hard limpet-like swelling on the bone due to periosteal new bone capjjed by inflamed periosteum. Such cases have a subacute history of six weeks to two months. In more chronic cases the bone swelling is more diffuse, and may be apparent on all sides. A sujjpurating dental cyst may be mistaken for an alveolar abscess. Evidence of true tumour growth, thimied and expanded bone-shell, negatives simple abscess. Clinically it is difficult or impossible to distinguish the early stage of a dental cyst from chronic abscess before sinus formation. In the mandible it is impossible, smce there will be bone swelling in both cases, and the early stage of a dental cyst may be accompanied by signs of inflammation due to the periodontitis that originally started its growth. In the maxilla after early life a bone swelling indicates tnie tumour growth, the periosteum of the maxilla early ceasing to deposit inflammatory new bone. A sinus opening remote from the originating tooth is generally the pomt of exit of a chronic abscess — at least by the time the opening is recognized the symptoms have ceased to be acute. Remote openings may be found (1) in the floor of the nose ; (2) on the back of the soft palate (rare, and recorded as due to an incisor) ; (3) on the cheek over the maxilla or malar bone, and in these cases pus is very liable to track in 674 different directions, and besides forming an external opening it is liable to form several blind pockets (healing is slow and the chronicity of the process may suggest streptothrix infec- tion) ; (4) outside or under the mandible ; (5) along the neck as far down as the clavicle, limited then by the attachment of the deep cervical fascia. Generally a probe can be passed from the point of exit to the tooth of origin, but some- times the remote abscess is entirely cut off from the source of the trouble. In these chronic cases the tooth itself is generally free frorn pain and tenderness owing to freedom of drainage. A pulp that has died painlessly as the result of infection via the dentinal tubules, under only a small filHng, may initiate a chronic, practically painless, suppurative process, eventuating in remote sinus formation. RARER FORMS OF CHRONIC ABSCESS Sometimes a quiet abscess, generally due to an incisor or canine, hollows out the entire body of the maxilla of one side (the process appears to be unable to pass the suture-lme) producing no clinical symptoms till a small sinus forms, perhaps years after its inception. Such an abscess may be found at the root of a tooth that has been left untreated after traumatic death of the pulp, or in slow pyorrhoea, as well as in connection with teeth dead as the result of caries. It may be mistaken for a suppurating maxillary sinus or cyst. Residual Abscess. — The minutest apex of a tooth left in at the time of extraction, a minute central necrosis, or a residual germ infection, may, years afterwards, cause an abscess. Hence it becomes important to note every fractured root at the time of extraction. Such an abscess may be acute, or may be chronic or subacute. Wlien chronic or subacute, it gives rise to the same symptoms as chronic central abscess of bone in other parts, i. e. intermittent pain and tenderness, worse at night, shght swelling of soft parts and of lymphatic glands similarly intermittent, and in the mandible some deposition of the periosteal bone. Li the more acute cases the intermissions of pain are sometimes so regular as to suggest malaria. A chronic abscess of the mandible may in- volve the inferior alveolar nerve and set up most acute neuralgia- — such an occurrence has not been recorded in the case of an acute abscess. Injection Abscess. — Sub -periosteal or inter- stitial abscess may follow the use of local injec- tions, as the result of infected needle or fluid, or of injecting into or through an infected area, when fluid under pressure or the passage of the needle may cause a diffusion of the infecting virus beyond the area that has been protected by inflammatory reaction. TREATMENT In general terms, remove the cause and secure drainage. This is best done by extrac- tion ; a tooth may be extracted at any stage of the process ; there is no reason for waiting until tlie inflammation is gone. If there is difficulty in opening the mouth, gentle per- sistent force will overcome it, and a general anaesthetic may be used to obviate unconscious resistance. In aU inflammatory cases local anaesthetics will be worse than useless, unless regional anaesthesia can be secured by injection behind the lesion. After extraction in the case of an acute abscess syringing is seldom necessary. With a chronic abscess opening externally, a silver probe should, if possible, be passed till it finds the opening in the jaw, and the tract well syringed to make sure that there is no inter- mediate collection of pus left. To syringe — B Acid Carbol. liq. Sod. Bicarb Aquam ad . M. ft. lot. "l vj. gr. X. 5 J- When it is desired to save the tooth, treatment depends on the stage at which the abscess presents itself. In the early stage of an acute abscess, before pus has made exit from the bone, the tooth is too tender to admit of much manipulation. With a sharp instrument worked on a smooth-running engine, a hole may be drilled vertically through the crown to the pulp- cavity, or a root-canal may be partly reamed out, the tooth being meanwhile steadied in such a way as to afford aU possible reUef from pressure. The pulp-cavity may be syringed, and perhaps the abscess aspirated by means of a hypodermic syringe thrust into a root-canal, after which the tooth may be dried and some antiseptic intro- duced, and if feasible gently pumped up the root-canal. The tooth may eventually be left open to secure drainage and to relieve any pressure that may be caused by gaseous pro- ducts of decomposition ; or paraform paste (paraform and tricresol) may be lightly sealed in. Paraform is said slowly to liberate formaUn vapour, which penetrates and exerts its anti- septic action ; but the success of early treatment probably depends far more on the establishment of drainage at an early stage than on any particular ding used ; indeed, the success of rhizodontrophy — drilling a hole laterally through the neck of the tooth into the pulp-chamber — depended entirely on early drainage and relief of gas pressure. 675 111 case this treatment fails to afford relief, the patient may be given the following — B Tinct. Opii. . Aqiiam ad M. ft. mist. 5J- IV. Sig. — One ounce %\hen needed, followed in half an hour by anotlier ounce if there is no relief. All four doses may be taken during the night. Opium is the only reliable drug for the relief of pain. Hot fomentations may give some reUef , used both in the mouth and over the face. In these cases capsicum plasters and strong iodine liniment probably owe their reputation to the accident of being used shortly before natural relief occurs. In some cases it may be possible by cutting down on the bone and perforating it to reach the pus, but even with a single-rooted tooth the success of this operation is uncertain, and if early treatment ina the crown fails, the dentist will generally have to wait till the pus makes its own way out, trusting to opium for relief of pain. To perforate the alveolus a small incision is to be made on to the bone, and with a sharp spear-pointed drill on the dental engine, the alveolus is jjerforated at a spot as near as possible to the root-apex. An anaesthetic is desirable, but if not available, it may be possible to effect an entrance in the following way. Apply to one spot of the mucous membrane a very little pure carbolic acid ; wait till the spot is well whitened and then scrape away the dead tissue ; repeat this till the bone ' is reached ; then proceed similarly, but use a rose-head burr in the engine. A serrated gold- plugger may be used both to apply the carbolic acid to the gum, and by rotating it to scrape away the dead tissue. When relief of pain has occurred, tliat is, when the pus has perforated the bone, it may be well, in order both to expedite matters and to secure evacuation into the mouth, to cut on to the pus. The incision should be made doAni to the alveolar bone opposite the most prominent part of the s-nelling ; if pus is not found it should be sought for with a director, the point of which is kept in contact wth the bone. In opening a palatal abscess the position of the posterior palatine artery at the base of the alveolus should be remembered : the artery may be stripped up with the muco-periosteum by the pus. In dealing with abscesses that are pointing on the face a small external incision should be made early : time is not to be wasted in trying to draw the abscess to a point in the mouth. An early incision need be but a punc- ture, through which the abscess may be gently evacuated and syringed, and which will eventu- ally leave practically no scar ; delay wiU result I in much destruction of tissue and a j)uckered scar adherent to the bone. In these cases the 1 position of the facial artery passing over the man- dible at the anterior edge of the attachment of the masseter muscle must be borne in mind. For treatment of septic roots see Chapter XXVII, pp. 471 et. seq. Wlien the tooth is to be saved, treatment of a chronic abscess is best carried out by securing ! a free flush through the root-canal and out by the alveolus. Where there is no fistula already existing, an attempt may first be made to clear out the abscess via the root-canal by aspiration, antiseptic solution being injected and with- drawn by means of a hypodermic syringe, and the root thoroughly treated ; but generally it will be found necessary to make an external opening, which may often be done under novocaine anaesthesia. After establishment of an external sinus, a weak alkaline carbolic lotion is to be forcibly syringed through from the root-canal to the external opening every day till pus formation ceases. Generally this occurs in three days. In difficult cases fluid may be made to flow through under pressure by packing round the nozzle of the syringe with gutta-percha. Before syringing pass a fine probe as far as jJossible through both root and external opening- — a small flake of coagulated lymph may entirely obstruct the flow. Creosote used in tliis manner, either by pumping or syringing under pressure till it appears on the gum, sometimes effects a cure in one or two sittings. Often the roots are curved, or blocked by secondary dentine, or the canal is too minute to follow. The introduction of 10 % suljshuric acid is said to be useful in the two last cases in assisting to open up the root-canal, but in the absence of stereoscopic radiographs the diagnosis is at best but guess-work. Before using solvent agents, after reaming out the root antiseptic dressings should be applied for a week. Unless the drill is felt easOy to follow the root-canal there is no sure guide to its course, and when a root is perforated laterally loss of the tooth is certain. The abscess meanwhile must be syringed from outside. These cases are sometimes treated by cutting down on to the root through the alveolus and excising its terminal jiart. Laying the abscess cavity open from the buccal side, and plugging lightly till it heals from the bottom, is an equally successful method of treatment, and both measures probably depend on the establishment of efficient drainage. In the writer's experience these operations are seldom necessary. Abscess of a third lo^^•er molar (wisdom tooth) has characters that need special mention (see Chapter II) . These it owes to its situation, which 676 renders stagnation round the partly erupted tooth almost mevitable, and to the tendency that pus from a radicular abscess of the tooth has to get beneath the deep cervical fascia. Owing to want of space the third lower molar finds great difficulty in reaching full eruption. This gives stagnant germs time to infect the partly obliterated tooth-sac, and an abscess round the partly erupted crown results. The existence of "pyorrhoea alveolaris " greatly increases the probability of such a stagnation abscess. An abscess following on caries of the third molar frequently finds its exit from the bone below the attachment of the deep cervical fascia, giving rise to a tense brawny swelling and pro- tracted suffering, and perhaps tracking far down the neck before evacuation occurs. Both these forms of abscess are accompanied by more or less inability to open the mouth owing to tenderness, which may induce reflex protective spasm of the muscles (an inflamed part is instinctively kept at rest), and to inflammatory infiltration, which mechanically interferes with movement. If the abscess becomes subacute by reason of partial drainage, trismus may last for weeks. Cellulitis of the neck and throat, or tonsillar abscess, not infrequently follows this form of dental abscess, the original cause remaining undiscovered owing to the difficulties of clinical examination. A radiograph should always be taken in doubtful cases. Pus in the mouth, often seen as a tliin film spread over the gum in the neighbourhood of the third lower molar ; inflammatory swelling of the gum and surround- ing tissues — cheek and fauces ; inflammatory swelling and pointing of pus externally near the angle of the jaw or lower down the neck, should raise a suspicion of a third molar as the prime cause. As far as the teeth are concerned extraction is the best treatment. This may need the use of a bone chisel and mallet. Before attempting an operation, pus must be evacuated and the parts rendered as aseptic as possible. The bone should be laid bare and gently chiselled away from the outer and upper side of the tooth. Stereoscopic radiographs will give valuable information as to the position of the tooth, which generally lies with its coronal surface forward. No great force should be exerted either \nth forceps or elevator, since injury to the bone in so undrainable a situation is gener- ally followed by necrosis. Syringing will have to be practised for six weeks or more after the operation. SEQUELAE OF ALVEOLAR ABSCESS Alveolar abscess, acute or chronic, may be followed by any of the sequelae, local or general, that are common to germ foci in all parts of the body, the anatomy of the part giving rise, in addition, to distinctive local diseases, and food contamination to a special possibility of intestinal symptoms. Local Sequelae. — Glandular enlargement and glandular abscess. Probably glandular eidarge- ment occurs in all cases of alveolar abscess, acute or chronic, but is often so transient or slight as to escape notice. On the other hand, in acute cases the enlargement may rapidly run on to suppura- tion, and in chronic cases an insidious eidarge- ment slowly spreading from gland to gland may lead to a diagnosis of lymphadenoma — a disease that may, indeed, be originated by chronic dental sepsis. The possibility of infective lymph taking an alternative route, whereby certain groups of glands may be entirely left out, may lead to the appearance of swollen glands remote from and apparently unconnected with the septic tooth ; this is seen in the case of the lower cervical glands. Acute glandular abscess, especially sub-mental, may, in common with the originating abscess, be so embedded in a mass of inflammatory tissue as to give rise to no suspicion of a second pus focus. Not infrequently the glands enlarged by infection of acute or chronic abscess fail to regain their normal size, even after removal of the primary cause. If excised and exammed, such glands are generally found to be tuberculous ; when left to themselves they may caseate, and eventually form a cold or tubercular abscess. The source of tubercular infection in these cases seems not to be the tooth or its infected socket — the tubercle bacillus may gain an entrance by the tooth socket, but the rarity of tubercular disease of the gum or alveolar bone negatives this view, and observations as to this mode of entry have not been subjected to the crucial test of inocula- tion into guinea-pigs. The probabiHty is that the germs find an entry through the tonsils or naso -pharyngeal mucosa or may be brought by the general blood-stream. Glands that have enlarged rapidly as the result of acute dental abscess, and later have been excised, have jjresented tuberculous changes, leaving no doubt that the tuberculosis, though unsuspected, long antedated the secondary dental infection. Ob- servations have been made indicating that the circulation of tubercle bacilli in the blood-stream is a commoner phenomenon than is generally believed. Septic teeth must be extracted in all cases of obstinate cervical glandular enlargement. Scarring. — A disfiguring scar adherent to the bone is a common sequel to the formation of an external sinus. It is best prevented by early evacuation of pus, if necessary externally. Sometimes it is possible, by stripping up the periosteum in the direction of the centre of the inflammatory swelling, to reach a sub-periosteal abscess that threatens to burst externally, and 677 so evacuate its contents into the mouth. The use of a two-way cannula will assist syringing. When a scar has formed, its adhesion to the bone may be divided by means of a tenotomy knife, and the part massaged, that is, rubbed and drawn in various directions to j^revent con- traction of cicatricial tissue ; probably massage will be needed daily for some years. In recent cases fibrolysin may be tried. Acute Spreading Osteitis may originate in the same infection as gave rise to the original abscess, and generally ends in necrosis. The persistence or aggravation of pain and tender- ness, and, still more, the spread of these symp- toms, indicates a serious condition of osteitis, and is a warning of probable necrosis. Chronic Osteitis may follow an acute or chronic alveolar abscess, and may end in the incej>tion of an intractable neuralgia, either tnie neuralgia major, or a neuralgia due to com- pression of nerve filaments by the chronic formative osteitis — sometimes referred to as " toothache without teeth ". Persistent chronic osteitis is more generally due to periodontal infection than to infection tlirough the tooth-pulp. Septic Phlebitis. — Spreading septic phlebitis may originate in a dental abscess, and by extension along the deep facial plexus of veins may cause intra-cranial abscess and thrombosis of the cavernous sinus. Infective or Spreading Cellulitis. — Cellulitis may spread in any direction from an alveolar abscess as the focus, and may be started by injudicious injection into an inflammatory area. It may be of any degree of virulence. Spreading to the orbit it sometimes gives rise to orbital cellulitis, or in less acute cases to apparently causeless optic neuritis or retro-bulbar neuritis. In the mandibular articulation it may cause a destructive arthritis. Spreading down the throat to the naso-pharynx, larynx or pharynx, according to the degree of severity, it gives rise to forms of cellulitis that vary from an almost transient oedema of the mucous mem- brane to a rapidly sloughing cellulitis. This severe form is often known as Ludwig"s angina, or acute cervical cellulitis. It starts more commonly as an infection from teeth foul and uncleaned, coated with tartar, and affected with pyorrhoea, than from alveolar abscess, but is conveniently described here. Its spread is gener- ally rapid and accompanied by oedematous inflammatory exudation, giving rise to a painful swelling, but at first to little or no pus formation. Wlien originating from the lower teeth, there may be extremely rapid swelling of the loose tissues , of the floor of the mouth and tongue. If spread takes place backwards, from whatever part ' originating, there wiU be oedema of the fauces. epiglottis, and base of the tongue ; of the larynx reaching to the glottis, where it is arrested by the intimate union of the mucous membrane to the vocal cords ; and of the walls of the pharynx, giving rise to imminent danger of death by suffocation on the one hand, and on the other, to dysphagia or actual aphagia. Spread of the disease externally down the neck ! may also lead to suffocation by j)ressure of the tense inflammatory exudation beneath tense cervical fascia. Symptoms of general intoxica- tion rapidly supervene. At the commencement there may be shivering or an actual rigor ; the temperature may rise to 105° F., but more generally to about 101° ; the patient may complain of headache and general malaise. Wlien infection is very virulent, the disease may be rapidly fatal either by suffocation or by acute intoxication. In less acute cases widespread pus formation and gangrene of soft parts may follow. In the more favourable forms, where resistance is good, complete resolution occurs in a few days. The dangerous cases are those in which there is lividity and dysphagia, pointing to such swelling of the larynx and pharynx as to obstruct respiration, and those in which the general temperature is low (100° or lower, asthenic), as compared with the extent of the local lesion. On cutting into the tissues in search of pus or to relieve inflammatory tension, they will be found unresilient and matted to- gether, and there will be a free escape of serous fluid ; but at first pus formation is absent, except at the focus of the disease when its origin is an alveolar abscess. Every intermediate form of clinical reaction may be met with between the wide-spread and varulent type described above and a transient erythema, the area affected varying, but all owning the one cause (septic teeth), and all being dependent on infection by similar germs ; dose and virulence are balanced against resistance. The treatment of these conditions usually requires the aid of a surgeon. Infection of the Maxillary Sinus is a not infrequent sequel of alveolar abscess, and is to be suspected when an acute "face-ache" suddenly clears up without external discharge (see Chapter XLIII). Blood infections, acute, subacute, and chronic (septicaemia, sapraemia), depending on the greater or less amount and relative quantities of germs and toxins absorbed, pyaemia with distant abscesses and mfarcts, may result from a dental abscess. These processes are more fre- quently the result of general dental sepsis than of a single dental abscess (see Chapter XLVI). For an account of intestinal symptoms due to food contamination see same Chapter. J.G.T. CHAPTER XLIII EMPYEMA OF THE MAXILLARY SINUS Empyema, or " abscess of the maxUlary sinus ", are terms used to signify the presence of pus within the sinus and produced by acute or chrome inflammation of its lining mucous membrane. Aetiology. — It is ahnost universally agreed that acute inflammation of the maxillary sinus is most frequently due to intra- nasal infection arising during the course of one of the acute specific fevers, and of these influenza has proved itself by far the most prolific factor, while pneumonia, diphtheria, measles, scarlet and enteric fevers, account for a smaller number of cases. Further- more, there can be little doubt that empyema may be produced by the infective organisms that give rise to acute coryza or "cold in the head ". Less commonly the inflammation is induced by infective elements derived from a diseased tooth in the immediate neighbour- hood of the sinus. Stroebel's (Dresden) statistics show that intra- nasal infection ^\ill account for 64-6 per cent of inflammations of the maxillary sinus, while only 29 per cent are due to dental causes. The remainder arise from rarer factors, such as traumatism, syphilis, tubercle, mahgnant dis- ease, etc. It will thus be noticed how completely this view is opposed to the old notion that abscess of the maxillary smus was invariably caused by a diseased tooth. The error probably arose from the facts that dental surgeons rarely saw any cases but those that were really due to diseased teeth, and were therefore impressed with this mode of origin, while general surgeons, as \vell as their confreres who devoted special study to the diseases of the nose, were quite satisfied to regard an empyema as of dental origin if a premolar or molar tooth possessed a small focus of caries or any other sign of disease. To-day it is known "that, with very rare exceptions, e. g. pyorrhoea alveolaris, only a dead tooth with a septic i3ulp-cavity can cause suppuration of the corresponding maxillary sinus. In certain cases it will be doubtful which aetiological factor has played the more promi- » The writer wishes to state that lie has endeavoured to treat this subject from tlie point of view of the dental surgeon, and only to emphasize those aspects of It that should be of interest to members of that branch of the profession. 678 nent part, and under such circumstances the best interests of the patient and of his medical and dental advisers wiM be served if the latter bring together those special experiences which have been gained by each working from opposite sides of a somewhat neutral territory. Leaving aside empyemata of intra-nasal origin, those that are caused by diseases of the teeth may now be reviewed in more detail. EMPYEMA DUE TO DENTAL CAUSES Wlien it is remembered that there is a close comiection between the vascular system of the deeper muco-periosteal layers of the lining membrane and the coarse-meshed vascular system of the spongy bone of the alveolus, and also of the latter with the fine network of vessels of the alveoli and the roots of the teeth, it is not surprising that inflammation may readUy travel from a dental focus to the maxillary sinus without any direct continu- ity of surface. Still more easily will such in- fection be transmitted if a diseased root-apex projects into the sinus and is only separated from its cavity by a very thin layer of bone or even of mucous membrane. This intimate anatomical relationship has led many distinguished rhinologists to the beUef that the maxillary sinus may be infected from carious foci in a living tooth, the materies morbi being conveyed along the blood or lymph vessels, or nerves. But, as has already been stated, there are very few exceptions to the rule that only a dead tooth with a septic puljj-cavity can cause suppuration in the superjacent sinus. Empyemata of dental origin may be divided into two main forms ^ — ( 1 ) Those due to acute inflammatory changes around the diseased root of a tooth. (2) Those caused by chronic inflammatory changes. 1. Acute Inflammatory Changes (a) Acute root abscess. (h) Acute periostitis. (c) Circumscribed or diffuse osteitis of the alveolar process. ' The writer wishes to acknowledge the use he has made in this classification of Hajek's treatise. Patho- logic und Tlierapie der entzundlichen Erkrankungen der Nebenhohlen der Nase, 1909. 679 (a) Acute Root Abscess. — This condition develops as a result of periodontitis secondary to inflammation of the pulp of a carious tooth. The roots of the second premolar and the molars are in close contact with the floor of the maxil- lary sinus, and emjiyema of that cavity is a not infrequent result of septic periodontitis con- nected with them. The well-known symptoms of severe toothache, pain on pressure, sensation of elongation of the tooth, possibly a painful swelling over the alveolus, and the relief of these symptoms simultaneously with a dis- charge of foul pus from the nose or into the nasopharynx, are too well known to need description here. If the tooth is extracted a probe may find easy access to the sinus, but, on the other hand, the communication between the alveolus and the sinus may barely admit a fine probe, and then only after patient and careful mani- pulation. In some instances no direct communi- cation can be found, and the question will arise : Has the infection entered by way of bone, blood or lymph vessels, or nerve-sheath ? (b) Acute Periostitis may aSect the alveolus as a result of dental disease, and the resulting abscess may break into the maxillary smus as well as externally on the gum. Wlien periostitis appears after extraction, the sinus seems especially liable to inflammation, possibly on account of infection having taken place during the operation or shortly afterwards. (c) Circumscribed or Diffuse Osteitis of the Alveolar Process resulting from dental disease, trauma, or septic osteomyelitis of the upper jaw, may induce suppuration of the sinus. 2. Chronic Inflammatory Changes (a) Chronic inflammation of the periodontal membrane. (6) Infection of the maxillary sinus by way of the root-canal of a dead tooth. (c) Empyemata caused by dental treatment. (d) Pyorrhoea alveolaris. (a) In periodontitis there frequently develops a small suppurating cyst on the root-apex, or possibly only a small mass of granulations. In either case these may by their growth reach and infect the mucous membrane of the sinus, owing to slow and often painless absorption of the intervening bone. (6) The Traversing of the Alveolar Process by Infection derived from an Inflamed Dental Root. WTien a pulp becomes septic — even under a harmless looking filling — communication may be established with the siiuis by way of the root-canal, and a fine passage through a con- siderable thickness of alveolus. Here agam the diseased tooth may not be unduly sensitive to pressure, tapping, or thermal changes. (c) Empyema following Dental Treatment. Instances of this have arisen when a bristle or di'ill has been pushed up too far through an unclean pulp-cavity, and an apical granuloma has been infected or a root abscess caused, either of which may eventually infect the sinus. (d) Pyorrhoea Alveolaris. — That this condition may lead to empyema is now an estabUshed fact. EMPYEMA OF TRAUMATIC ORIGIN In this category must be included empyemata following upon nasal and dental operations. The application of the galvano-cautery to the middle meatal region, and other operations in this vicinity, have occasionally j)roduced inflam- mation of the sinus, and the same may be said of skilful as well as unskilful extraction of difficult upper molar roots. In the latter the sinus may have been opened and infected at the time of operation ; or, at a subsequent period septic material may have gained access from the mouth. Similarly, projectiles and other sharp bodies may find their way into and cause infection of the sums. In these instances, as weU as those of dental origin, there is some laceration of the lining mucous membrane, with consequent bleeding and infection of the blood-clot. In malignant disease of the maxillary sinus the pus is often very foetid and blood-stained, while the intense pain, and later on the distension of the walls, soon indicate the serious nature of the malady. In syphilitic and tuberculous disease of the upper jaw, there are generaUy present other unmistakable signs of the general disease, while locally sequestra of necrosed bone, forming some part of the alveolus or the walls of the sinus, may frequently be recognized. Pathology. — In acute inflammation there is marked hyperaemia and oedema with scattered points of interstitial haemorrhage. Microscopic examination shows ceU infiltration and oedema in the superficial layer and around the glands. The \viiter believes that the infiltration of the mucous membrane may be so great as practicaUy to obliterate the lumen of the maxillary sinus, because occasionally on puncturing such cases there has been great resistance to the injection of the fluid used for irrigation, and this in spite of any change of position of that portion of the camrala witliin the sinus. In chronic inflammation a purulent deposit will be found on the mucous membrane. The latter is often greatly thickened, and may contain scattered spaces indicating lymph or cystic cavities. The ciUated epithelium may be absent in parts, or in others approximate 680 to the squamous type, while active leucocytic exudation takes place between the cells. A certain amount of engorgement of the vessels will be present, and around their walls small- celled infiltration is generally well marked. \Mien the chronic inflammatory changes spread to the muco-periosteal layers, there may be some thickening of the underlying bone, or this may appear to be eroded with numerous lacuna-like depressions. Readers interested in this matter should consult references 2, 3, 7, 14. Other pathological sequelae of chronic sup- puration are — (a) Cysts in the siiius, due to cicatricial stenosis of the mouths of lymjihatic gland ducts. (6) Nasal polypi, which are usually met with in the neighbourhood of the opening (ostium). (c) Osteophytes, which are found in the deeper or muco-periosteal layers. ((/) Serious complications — a rare occurrence ; these are generally due to an infective spreading periostitis. Dental Cysts. — These formations are not primarily due to suppuration within the sinus, but they may cause it, and have to be differ- entiated from chronic empyema. They are most probably developments from the epithelial remains of the enamel-germ ; and arising in connection with the roots of a tooth, they may by their growth extend into and encroach on the sinus so as entirely to fill its lumen. These cysts contain a clear fluid and cholesterin crystals, but repeated attacks of inflammation may alter the colour and consistency of the fluid, or even induce suppuration. Bacteriology. — In acute empyema of influenzal origin pure cultures of the influenza bacillus have been found (11). As a general rule a mixed infection is present, in which the diplo- coccus pneumoniae is prominent, together with the staphylococcus pyogenes aureus and albus, streptococcus pyogenes, and baciUus coH. Lewis and Turner (10), amongst other con- clusions, have shown " that the pus obtained from some cases of suppuration witliin the sinus may contain organisms similar to those occurring in the buccal cavity ; that occasionally bacilli distinctive of dental caries may be isolated from the pus ; that in the cases of chronic suppuration streptococci were found in 80 per cent, while in the more recent cases they occurred in 60 per cent ; that in recent cases virulent organisms are met with twice as often as in cases of chronic suppuration ; that clinical evidence supports the view that the sinus is more frequently infected by way of the nasal cavity; and that this opinion is corroborated by bacteriological investigation." Since the symptoms, diagnosis, prognosis and treatment vary so -widely according as the inflammation of the sinus is acute or chronic, it may conduce to clearness if the two conditions are discussed separately. ACUTE INFLAMMATION Symptoms. — These are both local and general. (1) Subjective Local Symptoms — (a) Pain is nearly always present when the inflammation is due to acute influenzal or to dental infection. In the latter case acute toothache, associated with tender- ness and swelling over the alveolus, may precede the suppuration of the maxillary sinus, and be quickly relieved by a discharge of pus from the corre- sponding nostril or into the naso- pharynx. The pain of acute inflammation of the sinus is often very severe and is felt deeply in the cheek. As a rule it is of a tense throbbing nature, and is much increased if the patient bends the head downwards and forwards. It is also accentuated by pressure applied over the canine fossa, the malar bone, and especially over the ascending process of the superior maxiUary bone. The pain may radiate to the supra-orbital region even though the frontal sinus and ethmoidal cells are free from inflammation. The offending tooth wfll generally be painful if pressed upon or tapped, and will often feel as if it were too long when a firm bite is made upon it. (b) Discharge of Pus.- — A discharge of foul pus from the corresponding nostril or into the naso-pharynx is generally associated with rehef of the pain. Tliis symptom is nearly always noted by the patient. (c) Foul Smell or Impairment of Smell. — If the discharge escapes into the naso- pharynx or is small in amount, the patient may not notice it and will only complain of a putrid smell — in fact, this may be the one nasal symptom that he is aware of. On the other hand loss or impairment of smell may be due to obstruction of, or acute inflamma- tory changes in, the olfactory region of the nose. (2) Objective Local Symptoms — (a) The dental conditions that have already been referred to as aetiological factors. 681 (b) Examination of the nose will usually reveal pus in the middle meatus, or on the posterior phar\^lgeal wall in those cases where the discharge is prevented from flowing for\\ards by various forms of intra-nasal obstruction {vide Chronic Inflammation). (3) General Symptoms. — There may be acute pyrexia rising to 102°-104°, with its attendant symptoms of general malaise, anorexia, etc. ^Vhen the inflammation is caused by one of the acute specific fevers, the local symptoms are often largely overshadowed by those due to the general constitutional infection. This is well marked in influenza, enteric fever, and pneumonia, although in the first named the " neuralgia ", as it is frequently termed, may be intense in its severity. Diagnosis. — In dental cases this will largely depend on the history of an antecedent tooth- ache, which was relieved by the appearance of a purulent discharge from the nose. Examination of the nasal cavity may reveal a collection of pus in the middle meatus, l)ut if this sign be want- ing, it may yet be possible to establish it by asking the patient to turn the affected cheek upwards for a minute, so that the pus may be encouraged to flow into the nose. The transillumination test (vide Chronic Em- pyema) is not of great value in acute inflam- mation, although a slight diminution in translucency may be noticed on the affected side. If there is still doubt as to the diagnosis, the maxillary sinus should be explored by trocar and cannula {vide Chronic Suppuration). Prognosis.^Acute empyema of dental origin nearly always recovers quickly if the diseased tooth is removed, and the sinus is freely drained and cleansed once or twice daily with a mild, non-irritating antiseptic. Wlien the infection occurs in the course of an acute specific fever, the prognosis must be guarded, because a more intimate inflammation of the mucous membrane takes place and the general resistance of the patient is lowered. Treatment. — It will be obvious that the i Fig. 908. {Mayer & Meltzer.] diseased tooth .should be at once removed, and communication made ^^ith the maxillary sinus by way of the alveolus (see Fig. 908). It can- not be impressed too firmly on the dental surgeon that a free communication should be made, i. e. at least equal to the calibre of an ordinary slate-pencil. If a small puncture is made it will rapidly contract, and the pain in passing the nozzle of a syringe through the alveolus will be so great that the patient will discontinue the necessary after-treatment before the mucous membrane of the sinus has returned to its normal condition. Fig. 909.— H. Tilleys Vulcanite Plug. (Mayer