DENTAL AND OEAL EADIOGRAPHY DENTAL AND ORAL RADIOGRAPHY A TEXTBOOK FOR STUDENTS AND PRACTITIONERS OF DENTISTRY BY JAMES DAVID McCOY, M.S., D.D.S., F.A.C.D. PROFESSOR OF ORTHODONTIA AND RADIOGRAPHY, COLLEGE OP DENTISTRY, UNIVERSITY OF SOUTHERN CALIFORNIA, LOS ANGELES, CALIFORNIA WITH 116 ILLUSTRATIONS THIRD EDITION ST. LOUIS C. V. MOSBY COMPANY 1922 Copyright, 1916, 1918, 1922, by The C. V. Mosby Company (All rights reserved) Printed in U. S. A. Press of The C. V. Mosby Connpany St. Louis, Mo. A/ ^0 PREFACE TO THIRD EDITION During the past few years, much of value has been added to dental radiography. This has not come entirely from new in- ventions or new developments in technic, but has been the result of its more universal adoption in dental practice with a consequent closer analysis of its true values and possibilities. With the development of any new science there is always born an enthusiasm which is apt to get out of bounds and carry its victims beyond the range of good balance, but with the back- ward swing of the pendulum w^hich comes with more complete knowledge, affairs assume more rational proportions. This is true of the present status of dental and oral radiography. Without depreciating its value, for in many instances it is abso- lutely indispensable, we must realize that it is but one important link in the chain of successful diagnosis. To regard it other- wise is both unjust to it and to our profession. In the revision of the text and illustrations, the writer has endeavored to condense the material as much as would be just and consistent with the subject and has kept uppermost in mind the needs of the dental student. The dental practitioner of ex- perience has many avenues for increasing his knowledge of this field and it is hoped that the contents of this volume may inspire the dental student to do likewise when more ample opportunities are offered. The author gratefully acknowledges the assistance given him by Dr. Leo M. Baughman, Dr. A. R. Ebenreiter and Dr. Carroll W. Jones who aided him in the selection of many of the radio- grams used as illustrations in Chapter X, and for their valuable counsel. James D. McCoy. Los Angeles, California. 663185 PREFACE TO SECOND EDITION During the preparation of the second edition of this book the author has endeavored at all times to keep in mind the needs of the beginner in radiography rather than consider matters of in- terest to those who have progressed beyond this stage. That radiography is essential in the practice of dentistry is no longer a debatable question. The wide interest being mani- fested in it by our profession and the numerous instances where dentists are installing their own x-ray laboratories bear elo- quent testimony of this fact. While the author is willing to plead ''guilty to a great degree of enthusiasm" regarding the value of the x-ray in dentistry, he feels that he is within reasonable bounds in asserting that the x-ray has done more to improve dentistry than any other agent that has come into it during the past ten years. If it were of value ''in root canal operations only" the benefits to this field alone would justify the foregoing statement, for we must all acknowledge that as commonly prac- ticed in the past this branch represented the greatest short- coming of our profession. Fortunately root canal work does not represent the only field in dentistry where the radiogram is a benefit, for it has been demonstrated that it is of equal value and in fact is often abso- lutely essential in the other branches of practice. These facts are not only now fairly well appreciated by dentists, but the laity have been quick to grasp them with the result that den- tists who attempt certain operations without radiographic guid- ance are open to censure from their patients. The awakening of the rank and file of the profession to the necessity of a more universal adoption of the x-ray has been slow, and it is doubtful if some will ever become fully conscious, as they continue to exhibit a lethargy toward this field which is either indicative of lack of foresight or sheer laziness. In contrast to such, it is refreshing to recall that some mem- bers of our profession were quick to see the possibilities to den- 6 PREFACE i tistry offered through the adoption of the x-ray. Conspicuous among these was Dr. C. Edmond Kells, of New Orleans, who in 1896 (within the year following the discovery of the x-ray) installed x-ray equipment in his office and applied it to his dental practice. So great were his convictions and so genuine was his enthusiasm that in July, 1906, he took his x-ray equip- ment to Ashville, N. C, and there gave a clinic before the South- ern Dental Association. Dr. Kells was the first dentist to make radiograms by placing small films in the mouth, and he also originated the plan of placing diagnostic wires in the roots of teeth. Among those who shared Dr. Kells' foresight during those pioneer days and adopted the x-ray as part of dental practice are numbered such men as Drs. Van Wort, M. L. Rhein, E. W. Caldwell, T. P. Hinman, and Weston A. Price. Within the last few years a large number of our dental schools have included radiography in their teaching curriculums and some have even shown the foresight of establishing it as a dis- tinct department with equal rank and consideration with the other important branches. This will in time bear fruit which will result in a more adequate appreciation of the merits and possibilities of the x-ray and its inseparable relationship to dentistry. The author wishes to gratefully acknowledge the assistance given him in the preparation of this edition by Dr. Julio Endel- man, whose friendly criticism and interest have been a constant source of help. Grateful acknowledgment is also made to Dr. Richmond C. Lane, who was kind enough to contribute several radiograms from practical cases illustrating root canal opera- tions, root resections, and cysts. The author has also been aided by various manufacturers of x-ray equipment who have fur- nished many cuts of value to the text, and last, but not least, the publishers have by their cooperation and patience through many delays rendered less irksome the task of the writer. James D. McCoy. Los Angeles, CaJ. PREFACE TO FIRST EDITION This book has been written primarily as a textbook for stu- dents of dentistry. It is essentially a book for beginners, and as the majority of the dental profession are at present to be regarded as beginners in this comparatively new branch of den- tistry, the author entertains the hope that it will prove of inter- est to practicing dentists Avho appreciate the value of the x-ray, and are desirous of adding radiography to their accomplish- ments. A few years ago the x-ray was considered in the light of a cultural asset to dentistry, but today the far-seeing members of our profession have awakened to the fact that it is a real necessity. The x-ray will give the maximum amount of service in dental practice only to such of our profession who master the technic of radiography, and in addition are possessed of an accurate knowledge of the anatomy and pathology of the dental and oral structures. The author is indebted to the pioneers in dental radiography who have so generously contributed to its literature. Of these, much of value has been derived from the writings of such men as Drs. A. H. Ketcham, Weston Price, Sidney Lange, Howard R. Raper, F. L. R. Satterlee and Edward H. Skinner. During the preparation of this work, the author has been aided by various manufacturers of x-ray equipment who have generously furnished cuts whenever requested. Grateful ac- knowledgment is also made to Dr. J. R. McCoy and to Laura Spruill who have made the drawings used as illustrations, and last and by no means least, to the publishers who have, through their forbearance and many courtesies, lessened the burdens of the writer. James D. McCoy. Los Angeles, Cal. CONTENTS PAGE CHAPTER I Introduction 17 CHAPTER II The Nature OF THE X-RAY AND Its Discovery 23 CHAPTER III High Tension Electric Currentsi Magnetism Electromagnetic Induction . . 32 CHAPTER IV Rhumkoepf or Induction Coil Tesla or High Frequency Coil Interrupterless Transformer 44 CHAPTER V Requisites of the Dental X-ray Laboratory 61 CHAPTER VI Technic of Dental and Oral Radiography The Intra-oral Method 77 CHAPTER VII Technic of Dental and Oral Radiography The Extra-oral Method 93 CHAPTER VIII Technic or Dental and Oral Radiography (Continued) Proper Tube and Current Conditions 110 CHAPTER IX Correct Exposure and Development of X-ray Plates and Films 123 CHAPTER X The Interpretation of Dental and Oral Radiograms .... 133 CHAPTER XI Indications for the Use of the X-ray in the Practice of Dentistry 154 CHAPTER XII Dangers of the X-ray and Methods of Protection 186 ILLUSTRATIONS FIG. PAGE. 1. William Conrad Eoentgen 24 2. Michael Faraday 25 3. Sir William Crookes 26 4. Hcinrich Hertz 27 5. The action of iron filings in forming definite curved lines about an ordinary bar magnet 35 6. Diagrammatic illustration of the magnetic lines of force . . 36 7. Diagrammatic illustration of the magnetic field surrounding a coil of wire through which an electric current is passing . 37 8. An iron bar placed within the windings of a solenoid is subject to its magnetic field and becomes a magnet 38 9. Magnet with diagrammatic illustration of ' ' magnetic lines of force" surrounding it 39 10. Battery from which an electric current is passing through the solenoid 40 11. Diagrammatic illustration of the essential parts of an induction coil 44 12. Diagram of the electrolytic interrupter 46 13. Diagram of the induction coil 47 14. Induction coil adapted for use in the dental x-ray laboratory 50 15. Diagram of the high frequency coil 53 16. The working principles of the interrupterless transformer . 55 17. Interrupterless transformer adapted for use in the dental x-ray laboratory 56 18. Interrupterless transformer adapted for use in the dental x-ray laboratory 57 19. Step-up transformer unit 58 20. Step-up transformer unit 58 21. Step-up transformer unit 59 22. Diagram of an x-ray tube 64 23. Coil or transformer tube 65 24. The high frequency tube 66 25. Connecting the tube to the x-ray machine 67 26. The hydrogen tube 67 27. The Coolidge tube 69 28. The tube stand 70 29. Illustrating reasons for using the tube shield, compression dia- phragm, and compression cylinder 71 30. Leaded glass tube shield 73 11 12 ILLUSTRATIONS FIG. PAGE. 31. A convenient manner of arranging the necessary apparatvs when not in use ' . . 74 32. The portable dark room 75 33. The patient holding the film in position against the upper teeth 81 34. Correct and incorrect technic 82 35. Technic for the upper molar teeth 84 36. Special compression cylinder made of leaded glass .... 85 37. The patient can hold the film in position against the lower teeth by exerting slight pressure with the finger 86 38. The Leach film holder 88 39. The Dorr film holder with detachable handle 89 40. Diagram of complete exposure of the dental arch .... 89 41. Method of obtaining radiograms using the bite method ... 90 42. The head-rest of the dental chair with its many adjustments can easily be arranged so that the patient 's head may rest easily and firmly upon it 93 43. Tube stand with plate-rest and head-support 94 44. The arrangement of the apparatus preparatory to seating the patient 96 45. The patient seated and the apparatus arranged for making a radiogram of the left side 97 46. Plate and head-rest support for extra-oral radiograms ... 98 47. Plate and head-rest support adjusted to the arms of the dental chair 98 48. Technic for the left side 100 49. Technic for the right side . 101 50. The result of correct technic 102 51. Incorrect technic 103 52. The result of incorrect technic 104 53. Technic for radiographing areas in the upper and lower jaws extending from the median line to the first premolar . . 105 54. The structures at the median line including the incisors, both above and below may be secured in this way 106 55. Supporting the patient's head with a bandage of gauze to pre- vent movement 107 56. The tube connected with the x-ray machine 112 57. Diagrams of the x-ray tube 115 58. The radiator type Coolidge tube 116 59. Radiator Coolidge tube, right angle type 116 60. X-ray-proof film and plate chest 124 61. Intra-oral radiograms of groups of teeth and adjacent tissues, under normal conditions 140 ILLUSTRATIONS 13 FIG. PAGE. 62. Instances where inflammatory processes have resulted in a hypertrophy of the peridental membrane and resultant en- croachment upon the alveolar structures 142 63. Chronic dento-alveolar abscesses with cystic formation . . . 143 64. Three instances of true cysts occurring in the mandible . . 144 65. Eadioluceut areas adjacent to the roots of teeth which are characteristic of necrosis or rarefying osteitis .... 145 66. Radiopaque areas about the roots of teeth or in the alveolar bone indicating defensive bone reaction 146 67. Characteristic appearance of the investing tissues in well de- veloped pyorrhea alveolaris 147 68. A cuspid tooth lying against the anterior wall of the antrum . 149 69. A radiogram to determine the state of dentition of the right side in the mouth of a child eleven years old 150 '70. Root canal fillings 151 71-B. Instances where the roots of teeth lie in close proximity to the antrum or accessory antral cells 152 72. Extra-oral radiogram of the right side made for purposes of general examination 156 73. Intra-oral radiogram used as a means of confirmation of the findings of the extra-oral radiogram 157 74. Alveolar abscesses at the apex of each bicuspid root . . . 157 75. Upper bicuspid teeth with abscesses 157 76. Severe inflammatory process in progress about upper lateral incisor 157 77. Extra-oral radiogram of the lower molars showing the presence of a large alveolar abscess 158 78. Radiograms showing imperfectly filled canals, diagnostic wires in place, and same teeth after being filled 159 79. Radiograms showing imperfectly filled canals, diagnostic wires in place, and same teeth aftdr being filled 160 80. Radiogi'ams showing imperfectly filled canals, diagnostic wires in place, and same teeth after being filled 160 81. Radiogram showing condition present, diagnostic wires inserted, root canals filled, and resection of roots 161 82. Radiograms showing central incisor before resection, after re- section, and several months later, showing regeneration of osseous tissue 162 83. Upper central root before resection, and after resection, show- ing partial regeneration 163 84. A well-developed case of pyorrhea alveolaris involving the molars and incisors 164 85. An unerupted cuspid tooth making an attempt to erupt under a bridge 166 14 ILLUSTRATIONS no. PAGE. 86. Radiogram made to be sure no root fragments were present in the tissues under the bridge 166 87. Inflammatory process under a small bridge 166 88. Extra-oral radiograms of impacted and unerupted third molars 168 89. lutra-oral radiograms of impacted lower third molars . . . 169 90-A. Large cyst in the mandible lying below a molar tooth . . 170 90-B. Same case as shown in 97-A, six months after curettement, showing partial regeneration of the osseous structure . . 170 91. Large abscess with cyst formation, involving the upper central, lateral and cuspid roots 171 92. Radiogram revealing the fact that there is a congenital absence of permanent molars on the left side 172 93. Radiogram revealing the fact that all but one of the permanent molars are congenitally absent on the right side . . . . 172 94. Unerupted lower second bicuspid for which space must be made to permit its eruption 174 95. Unerupted cuspid for which si)ace must be made if it is to erupt in its normal position 174 96. Unerupted lower lateral incisor for which space must be made 175 97. Unerupted lower second molar prevented from erupting through impaction against the lower first molar 175 98. Unerupted upper bicuspid teeth Avhich are being deflected to the lingual 176 99. Unerupted bicuspid teeth which are rotated and erupting to the lingual 176 100. Radiograms showing unerupted cuspid, same tooth after re- moval of lateral incisor and deciduous cuspid, showing at- tachment for moving the unerupted tooth; cuspid tooth moved down to the point of eruption 177 101. Supernumerary teeth. Case after extraction 177 102. An unerupted lower second bicuspid in a patient twelve years old 179 103. Unerupted upper and lower bicuspids in a patient eleven years of age 179 104. Unerupted cuspid teeth whose relationship to the roots of the incisors must be taken into consideration during tooth move- ment 180 105. An unerupted lower third molar which is crowding the incisors 181 106. An erupting lower third molar which has been responsible for the crowding of the lower incisors and cuspids . . . . 181 107. Non-vital tooth being used as an anchor tooth and non-vital tooth which was considered unsafe for anchorage . . . 183 108. Supernumerary upper second bicuspid 183 109. Lower deciduous central incisors having the appearance of super- numerary teeth 183 ILLUSTRATIONS 15 FIG. PAGE 110. Eadiogram showing either an anomalous central incisor or a central incisor lying in a horizontal position to the other teeth 183 111. Patient seated and the apparatus arranged to make a radiogi'am to the left side 184 112. Patient seated and the apparatus arranged to make a radio- gram of the right side 184 113. An x-ray tube inclosed within a leaded glass tube shield . . 191 114. Lead-lined protection screen 192 115. Lead-impregnated glove 193 116. X-ray protection apron 194 DENTAL AND ORAL RADIOGRAPHY CHAPTER I INTRODUCTION When AVilliam Conrad Roentgen announced to the world the discovery of a new and hitherto unsuspected form of energy, he called it the x-ray, but the scientific world has for the most part seen fit to designate it the "roentgen ray" in honor of the discoverer. Roentgen- ology is, therefore, defined as ''the study and practice of the roentgen ray as it applies to medicine and surgery." For purposes of study, roentgenology may be divided into two distinct fields, depending upon the purpose for which the roentgen ray is to be utilized. In the first, which is the one enlisting the interest of dentists, it is used for the production of shadow pictures or radio- grams. In other words, it embraces what is commonly called the "field of radiography," or "roentgenog- raphy." The other branch mentioned includes the use of the roentgen ray for therapeutic purposes, and is known as "radiotherapy," or "roentgenotherapy." With this field, the dentist is happily not directly concerned, and, therefore, his responsibilities are not so great as the medical roentgenologist. Of the various collateral sciences of medicine, there is perhaps no other which has developed as rapidly, or which has assumed a more important bearing in many branches of practice as has the science of roentgenology. This was no doubt due to the fact that the more progres- 17 18 DENTAL AND ORAL RADIOGKAPHY sive members of the medical and dental professions were quick to realize its possibilities and adopted it so universally that a great stimulus was given to its per- fection and development, with the result that although but a comparatively short time has elapsed since its dis- covery, this branch has been evolved to the state where it can now be regarded broadly speaking in the light of an exact science. In spite of this fact, there is still apparent in some quarters a great degree of misconception as to the re- sponsibilities of one who is to actively engage in this work. This is evident by the influx into this field of a large number of the laity who in spite of the fact that they are without medical or dental training or experi- ence, have for purely commercial reasons attempted to establish themselves as radiographers. To such, this field of labor apparently presents allur- ing possibilities as is evident by the numerous instances where laymen have engaged in such work without ade- quate preparation. To these, the reward of bitter dis- appointment must eventually come for the time is fast approaching when the intelligent public will realize the grave responsibilities encumbent upon the '' dispenser of x-rays" and will demand expert service. It is encumbent upon the dentist therefore, not to be satisfied with the acquiring of a *' partial knowledge" of the subject, which at best can only carry one half-way upon the journey of success, but he should early come to a realization that the practice of roentgenology or any of its branches re- quires much more than a mere training in the mechanics of the x-ray laboratorj^ Undoubtedly, many a man has, in the contemplation of x-ray apparatus for his office, given serious thought to the type of equipment which he wished to install, and has assumed that with a modern laboratory, he would be in INTRODUCTION 19 a position to render the best of service. Such a mis- guided individual all too soon learns that a very large part of the battle lies within himself, and if his own knowledge is deficient, the finest equipment in the world will not make him a roentgenologist. It is important, therefore, that those who contemplate any indulgence in this field should not underestimate the task that con- fronts them or consider lightly the responsibilities it entails. In addition to becoming familiar with the electro- physics of x-ray laboratory equipment, its practical ap- plication in his chosen field, the dangers which surround it if improperly used, one should realize that the real practice of roentgenology begins when the x-ray picture, or radiogram, has been produced. It is quite impos- sible for such an image to be of value unless the roent- genologist is thoroughly familiar with the anatomy, phys- iology, and pathology of the field, under examination; and even these qualifications are not adequate unless backed up by practical clinical experience. For those who can qualify, it will be found that there is a real field and a rare opportunity for useful service. It will also be found that everyone who engages in this work will receive just that amount of recognition and respect from his colleagues to which his abilities entitle him, for, as already alluded to, this is an exacting voca- tion and is no fit place for the mediocre or ill prepared. At the very outset the beginner should become familiar with the terminology of the subject, and cultivate the habit of using terms correctly. Failure to do this soon stamps one as a presumptuous amateur. For instance, instead of using the term ''x-ray picture," such an image should always be spoken of as a ^'radiogram/' or as a '' roentgenogram/' or if the area involved is but of one 20 DENTAL AND ORAL RADIOGRAPHY or more teeth and their investing tissues, the term "odontogram" might be appHed. The physician or the dentist maintaining an x-ray laboratory should not be called an '* x-ray specialist," but should be spoken of as a "medical or a dental roent- genologist." A dental roentgenologist may also be prop- erly spoken of as a radiodontist, or the broader term "oral radiographer" may be used. Not infrequently, we hear physicians or dentists speak- ing of a dental radiogram as a ''dental x-ray." Such an expression should be avoided as it is crude and devoid of any real meaning. It is thought by some terminologists that in addition to always speaking of the x-ray as the roentgen ray, in honor of the man who discovered it, we should include the name roentgen in every descriptive word connected with the work. To such, the term "radiograph" (verb) and "radiogram" (noun) will doubtless appear improper, but the author feels justified in continuing their use, as these words are thoroughly descriptive and less cum- bersome than "roentgenograph" and ''roentgenogram." For the same reason, the term "radiography" is pre- ferred rather than "roentgenography" to designate the art of making radiograms. To some, the term "radiogram" seems improper, the claim being made that this term is used in Wireless ter- minology to imply a Marconigram. However, there should be little chance for confusion as the subjects are sufficiently segregated so that there is small chance for misinterpretation of the word. Briefly summarized, the following roentgen terminol- ogy will be found to be quite adequate : Roentgen ray, or A phenomenon in physics discovered by X-ray: William Conrad Roentgen. INTRODUCTION 21 The study and practice of the roentgen ray as applied to medicine and surgery. One skilled in roentgenology, or radi- ology. One skilled in use of the roentgen vay in making roentgenograms or radiograms. One skilled in the art of making roent- genograms or radiograms of the dental and oral structures and interpreting the findings. The shadow picture produced by the x- ray upon the photographic emulsion. The shadow picture of teeth and their investing tissues produced by the x-ray upon the photographic emulsion. (Verb.) To make a roentgenogram, or radiogram. The art of making roentgenograms, or radiograms. The art of making roentgenograms or radiograms of the dental and oral structures. Treatment by the application of the roentgen ray. Skin reaction due to too strong or too often repeated application of the roent- gen ray. Roentgenographic examination, or The examination and study of the shadow Roentgenology, or Radiology : * Roentgenologist, or Radiologist : * Radiographer : Radiodontist : t Roentgenogram, or Radiogram : Odontogram : Roentgenograph, or Radiograph : Roentgenography, or Radiography : Radiodontia : i Roentgenotherapy, or Radiotherapy : * Roentgen dermatitis, or X-ray dermatitis: Radiographic examination : Roentgen diagnosis, or X-ray diagnosis: Pathoroentgenography, or Pathoradiography : t pictures produced by the x-ray upon the photographic emulsion. Diagnosis by aid of the roentgen ray. The study of pathologic lesions as re- vealed by the radiogram, or roentgeno- gram; it implies and renders impera- tive a knowledge of the pathology and of the interpretation of normal and abnormal tissue densities as recorded in the radiogram. *The term is rather confusing, as it could also refer to the practice and therapy of radium or other radiotherapeutic agents. tTerms suggested by Dr. Julio Endelman. JTerms suggested by Dr. Howard R. Raper, 22 DENTAL AND ORAL RADIOGRAPHY Eadiopacity: Implying an increased resistance of the tissues to the penetration of the rays. Badiolucence : A decreased resistance of the tissues to the penetration of the x-rays. Boentgenize : To apply the roentgen ray. Roentgenization : The application of the roentgen ray. Roentgenism: The untoward effect of the roentgen ray. Some writers add other descriptive terms to the fore- going list, but the author feels that a terminology should be just as brief as is consistent with adequate descrip- tion ; hence, several terms appearing in current literature on different phases of roentgenology have been omitted. Terms suggested by Dr. R. Ottolengui. CHAPTER II THE NATURE OF THE X-RAY AND ITS DISCOVERY In order to gain an intelligent conception of the x- ray, it is quite necessary that the student start with a consideration of certain phases of electrophysics, and radiant energy, or in fact the very foundation of matter itself. According to the most plausible theories and beliefs, all matter is suspended or contained in the medium known as ether, which is an elastic medium filling all space, interatomic and interelectronic, as well as all other space of which we have any knowledge. Furthermore, many facts brought out by the close study of chemistry and physics seem to justify the be- lief that all substances of matter are composed of mi- nute particles called ''molecules," and that each mole- cule is made up of two or more elements called * ' atoms, ' ' while these atoms are also further divided in particles known as electrons. These electrons, or units of matter, are never still, but are in a constant state of motion or vibration, each sub- stance having its own specific atom and the electrons of such atoms having their own rate of vibration. The vibration of these electrons produces disturbances in the ether know as ''ether waves" which vary in length according to the rate at which electrons are vibrating. If the rate of vibration of the electrons be changed or disturbed, there is a change in the ether waves, resulting in a corresponding change in the phenomenon produced. If this theory of matter is correct, as the evidence of 23 24 DENTAL AND ORAL RADIOGRAPHY modern science would lead us to believe, all matter then is made up of the same constituents, and its various forms are determined, not by any essential difference of com- position, but by the number, arrangement and amount of motion of the ultimate particles making up the atom. All this has a practical significance to us in under- standing the phenomenon which we call the x-ray. As stated before, it is known that a certain rate of vibra- tion of electrons will produce other waves resulting in a definite phenomenon, while a change in this rate will produce an entirely different phenomenon. For instance, a slow rate of vibration (75,000,000 per second) produces what are known as electromagnetic waves. A little higher up the scale where the electrons are made to vi- brate faster, heat waves appear. Another increase, and light waves appear. If we continue to accelerate the rate of vibrations of the electrons, there will be pro- duced successively ultra-violet, or Finsen rays ; then cath- ode, or radium, rays, and finally the x-ray. It will then be seen that the x-rays are produced as the result of the most rapid rate of vibration of which we have any knowledge. In the laboratory this phenomenon is produced by the sudden stopping of a stream of rapidly moving free electrons in a vacuum tube which has been exhausted to one millionth of an atmosphere. The x-ray, therefore, may he defined as that form of radiation which emanates from a highly exhausted tube when an electric current of high tension is passed through the tube. The object of the vacuum tube is to establish a medium in which all source of resistance is removed, so that the electric current may excite the exquisitely rapid vibrations necessary to produce the phenomenon desired, the electric current being the source of excita- tion. The radiation thus produced gives neither heat nor NATURE OF X-RAY AND ITS DISCOVERY 25 light, nor can it be deflected, reflected, or polarized. In fact, it can only be recognized by its effect npon the photographic plate and npon such chemicals as willem- ite, calcium, and tungstate, which fluoresce or glow un- der its influence. The Discovery of the X-ray The x-ray was discovered in 1895 by William Conrad Roentgen, Professor of Physics, at the Royal University Fig. 1. William Conrad Roentgen. of Wiirzburg, in Germany. This discovery, marking as it did, a distinct epoch in the science of medicine, was re- ceived by the world with incredulity and amazement, for 26 DENTAL AND ORAL RADIOGRAPHY its reported possibilities savored almost of the oc- "A new ray had been discovered by means of was possible to look through opaque substances/" While it fell to the lot of Professor Roentgen to make this discovery, there is no doubt but that other experi- menters in the field of physics, unconsciously produced Fig. 2. Michael Faraday. this same ray. In fact, its discovery was made possible by the work of other scientists who preceded Roentgen and laid the foundation for its advent. Of these, Michael Faraday was the pioneer. In 1831 he discovered electro-magnetic induction, which made possible the induction coil and the other electric machines NATURE OF X-RAY AND ITS DISCOVERY 27 .^cjd tra^ generate currents of great potential. As early IB conducted a series of experiments to deter- mine the effect of electric discharges upon rarified gases, and invented the terms ''anode" and "cathode" for positive and negative electrodes. In 1857 Geissler constructed the first vacuum tubes and it was noted at this time that an electric discharge passed through these tubes would produce a peculiar -^^Hlto ^^|i^^^ . ; .:. _.' . . -g jBHgBg ' i^^ <^,..i- . ^f i^^" #';*'a W r" |W ^K/^Hf M m p^^ ' 1 \' Fig. 3. Sir William Crookes. glow or phosphorescence, the coloring of which depended upon the character of the rarefied gas contained in the tube. This phenomenon became known as ''fluores- cence." A few years later (1860) Professor Hittorf, a cele- brated physicist of Miinster, conceived the idea of ex- hausting the Geissler tube to a higher degree of vacuum and found as a result an increased resistance to the pass- 28 DENTAL AND ORAL RADIOGRAPHY ing of the electric discharge, and that the color of the rarefied gases under fluorescence, varied with the degree of rarefication. He also discovered another fact which was to have an important bearing upon the work of later experimenters, and that was that the luminous discharge in a Geissler tube could he deflected hy a magnet. The important work of these early experimenters was followed later (1878) by Sir William Crookes, who suc- Fig. 4. Heinrich Hertz. ceeded in constructing a more perfect vacuum tube, that is, one that could be exhausted to a much higher degree of vacuum. "With these improved tubes, Crookes discov- ered that with a sufficiently high vacuum the luminous glow within the tube disappeared, and demonstrated that within it there was a rectilinear radiation from the cathode, which he conceived as being a projection of par- ticles of highly attenuated gas at exceedingly high veloc- NATURE OF X-RAY AND ITS DISCOVERY 29' ity. To this radiation he gave the name ' * cathode rays, ' ' and because of the peculiar behavior of gas in this ex- ceedingly rarefied state, he concluded that it vt^as as dif- ferent from gas in its properties as ordinary air or gas is different from a liquid. He found that the impact of the cathode rays against the wall of the tube would pro- duce within it a greenish "phosphorescence" or ''fluores- cence" and an increase in temperature; also that these rays could be intercepted by metallic plates within the tube. By concentrating the rays at the focus of a con- cave cathode, he was able to produce a brilliant fluores- cence and a very high temperature, both at the walls of the tube and in various substances within it. Without douht, Sir William Crookes unconsciously produced the x-ray in the course of these experiments. In 1892 Professor Heinrich Hertz discovered that cathode rays would penetrate gold leaf and other thin sheets of metal placed within the tube. Soon after this discovery. Hertz died, and his experiments were con- tinued by his assistant, Lenard, who was able to demon- strate that many of the phenomena of the cathode rays could be observed outside of the Crookes tube. By clos- ing a vacuum tube at the end opposite the cathode with a thin sheet of aluminum, he demonstrated that a radia- tion proceeded through or from the aluminum walls of the tube which would pass through many substances opaque to ordinary light, and after passing through such substances, it would excite fluorescence in crystals of ba- rium platino-cyanide, and would affect sensitive photo- graphic plates in much the same manner as ordinary light. Lenard considered that all these phenomena were due to the cathode rays alone, although in the light of our present knowledge, there is no douht tlmt, not only in his experiments^ hut in those of Crookes, Hertz, and other investigators, x-rays were produced. However, 30 DENTAL AND ORAL RADIOGRAPHY they were not recognized as such until 1895 when Pro- fessor Roentgen startled the world by the amioimcement of his discovery. Upon the memorable day of his discovery, Professor Roentgen was duplicating one of Lenard's experiments in the laboratory of the Wiirzburg University. The ex- periment consisted of passing an electric current through a Crookes tube covered with black cardboard, to test its fluorescence upon a piece of cardboard coated with ba- rium platino-cyanide. A fresh specimen of this chemical had been prepared and spread upon the cardboard which was placed against the wall on the opposite side of the room to dry. The room was darkened and the current was passing through the tube, when to his amazement. Roentgen noticed that the chemically covered cardboard on the other side of the room was glowing with a wierd fluorescence. He approached the cardboard, and in doing so, passed between it and the Crookes tube, and beheld his shadow upon the cardboard. Picking up a book, he held it in front of the screen and noticed that it also cast a shadow. He then discovered that the luminous glow or fluorescence on the cardboard appeared and disappeared with the turning on and off of the current. With the tube operating, he picked up the cardboard, and ivhile examining it, noticed the shadow of his hand on its surface, the hones appearing much darker than the soft parts of the hand. He also found that the fluorescence was produced in the cardboard regardless of whether the chemically coated side was turned toward or away from the Crookes tube, showing that the rays had the power to penetrate substances at a distance from the tube. Further investigation proved that the radiation pro- ducing these phenomena emanated from the point of im- pact of the cathode rays against the glass wall of the Crookes tube; that nearly all substances were trans- NATUKE OF X-EAY AND ITS DISCOVERY 31 parent to it, although in widely different degrees, varying roughly with their density ; that the radiation was recti- linear; that it could not be refracted, reflected, or de- flected by a magnet. Hence it was plain to Roentgen that these rays were quite different from the cathode rays of Crookes, Hertz, or Lenard. Using photographic plates wrapped in black paper to protect them from ordinary light, he obtained with these new rays shadow pictures of metallic objects in a wooden box, and of the bones of the hand. He continued his experiments both with the fluorescent screen and the photographic plate, and in December, 1895, communicated his discovery to the Physico-Medical Society of Wiirzburg. Being unable to determine the exact nature of this new ray other than classing the phenomenon as longitudinal vibrations of ether. Roent- gen called it the x-ray, the letter ^'x" representing the unknown in the mathematical formula. Even today the exact nature of the rays has not been determined, al- though the concensus of opinion seems to be that they are violent ether pulses set up by the sudden stoppage of the cathode rays as they strike upon the walls of the tube or upon any intervening obstruction. If this theory be correct, x-rays are of the same general nature as light waves, but of such short wave length that they lie out- side the visible spectrum. CHAPTER III HIGH TENSION ELECTRIC CURRENTS- MAGNETISM ELECTROMAGNETIC INDUCTION High Tension Electric Currents As stated previously, the x-ray is produced when an electric current of high tension is passed through a vac- uum tube. Therefore, let us consider the character of this current and the means employed to produce it. There are several kinds of electric currents, but of these we need concern ourselves only with two the direct current, commonly designated by the abbreviation D.C. ; and the alternating current, designated as A.C. The direct current is one in which the electricity flows along a conductor in one direction at a uniform rate of pressure, while the alternating current flows along a con- ductor first in one direction, then reverses and flows in the opposite direction, these changes taking place with great rapidity (50 to 120 per second). Such a current in making these changes is said to have completed a cycle, and its frequency is designated by the number of alter- nations which occur each second. A high tension current is one which has high voltage, or, as it is expressed in electrical terms, has great elec- tromotive force, or pressure. The Volt is defined as the unit of electromotive force, and is analogous to the pressure caused by a difference in level of two bodies of water connected by a pipe the pressure tends to force the water through the pipe and 32 HIGH TENSION ELECTRIC CURRENTS 33 the electromotive force or voltage tends to cause the elec- tric current to flow along a conductor. The Ampere is the unit of current strength, or in other words, the amount of current passing a given point on a conductor in a given time. If we again use the analogy of the two bodies of water at different levels connected by a pipe, it would be the amount of water which could pass through the pipe in a given time. The Ohm is the unit of resistance. Just as the water in flowing through a pipe is resisted somewhat in its pas- sage by the friction offered by the surface of the pipe, or by the limited capacity of the pipe, so, likewise, the electric current is resisted in varying degrees in its pas- sage along a conductor, the degree of resistance depend- ing upon the degree of conductivity of the material used as the conductor, its length, cross section, etc. The Watt is the unit of electromotive poiver or the ability of a current to do work. The wattage of a cur- rent is determined by the voltage, or pressure, and the amperage or quantity, the wattage of a given current be- ing determined by multiplying the voltage by the am- perage. From the foregoing, then, we see that the character of an electric current is determined by several factors, all of which must be taken into consideration. If we wish to know the strength of a given current, we have but to remember this strength will depend upon the pressure or electromotive force and the resistance of- fered by the conductor through which the current is pas- sing, just as the strength of a stream of water flowing from a tank would depend upon the pressure and the size of the pipe carrying the water. In other words, the strength of the electric current equals the pressure di- vided hy the resistance. Reducing this to an equation we have 34 DENTAL AND ORAL RADIOGRAPHY volts E.M.F. Amperes = ^y^^^^g or C equals ^ This is known as ''Ohm's Law" and is one of the fun- damental laws upon which electrical science is based. This important law has two other forms which make it possible to learn the relationship and amount of any of these three units, provided two are known. For instance, by transposing the formula of Ohm's law, we have Volts = amperes x ohms, or E.M.F. = C x R. If we wish to determine the resistance offered by a given conductor, we apply the formula as follows : E.M.F. E.M.F. Resistance = or R = ^ amperage C As stated before, the current which is passed through the vacuum tube to generate the x-rays must be a cur- rent of high tension, or great pressure ; or, expressed in the terms of the units just described, it must have very high voltage. The ordinary lighting current of 110 volts is inadequate, as this current is of far too low potential to pass through the tube, as the vacuum offers great re- sistance, a resistance which to the ordinary current amounts to an absolute nonconductor. We are obliged, therefore, to make use of some means which will pro- duce a current of great voltage, a current, we will say, of at least 75,000 to 150,000 volts. To do this, Ave must make use of one of the electric machines which can generate such a current by utilizing the principle of electromagnetic induction. Lest the stu- dent become confused, we will first review very briefly some of the elementary principles of electromagnetism and its relation to the production of the high tension cur- rent necessary in x-ray production. HIGH TENSION ELECTRIC CURRENTS 35 Magnetism Magnetism is the term applied to substances which have the property of attracting small pieces of iron. A material possessing this property was first found by the ancients at Magnesia, in Asia Minor, from which fact arose the name magnet. The natural magnet is an oxide of iron and is also called the lodestone. Artificial magnets can be made by rubbing a bar of hard steel with a lodestone, or with an- other artificial magnet, or by means of an electric cur- rent. Artificial magnets acquire the same magnetic properties which the lodestone or natural magnet pos- sesses except that they acquire them to a much greater extent, and are, therefore, always used in preference to natural magnets. In addition to the property of attracting small pieces of iron, magnets have other characteristics worthy of mention, such as polarity, or the property of assuming, when suspended and perfectly free to move, a north and south position. The compass is quoted as a familiar example. At the ends of a magnet, or in other words at its poles, the greatest power or attraction exists. This is easily illustrated by placing one end of an ordinary magnet in some iron filings and withdrawing it. The filings will cling to it in great numbers, as they will likewise do to the other end of the same magnet if it too be placed in the filings. The middle of the magnet (or that portion midway between the two poles), however, does not pos- sess this property; but as the ends are approached, the attraction increases until the poles are reached, where it reaches the maximum. In observing the action of the two poles of a magnet in attracting the iron filings, no particular difference is 36 DENTAL AND ORAL RADIOGRAPHY observed. They both attract the iron filings. There is a difference, however, which may be shown by experiment- ing with two magnets, one of which should be suspended at its center like an ordinary compass, while the other is held in the hand. If the north pole of the magnet held in the hand is moved near the north pole of the sus- pended magnet, they will repel each other. Likewise if their south poles are approached, they will repel each other. But if the north pole of one be placed near the south pole of the other, they will attract each other. Fig. S. The action of iron filings in forming definite curved lines about an or- dinary bar magnet indicates that the magnetic field exerts its influence in certain definite directions which are called "the magnetic lines of force." This shows that like poles repel each other, while unlike poles attract each other. The space surrounding a magnet which is subject to its influence i^ known as its magnetic field. The presence of this magnetic field is easily demonstrated by placing a magnet under a sheet of paper upon which iron filings have been evenly spread. By tapping the paper lightly, the filings will form into a series of curved lines extend- ing from one pole of the magnet to the other pole, as il- lustrated in Fig. 5. The formation of these definite HIGH TENSION ELECTRIC CURRENTS 37 curves indicates that the magnetic field exerts its influ- ence in certain definite directions which are called the lines of magnetic force. These lines of force start at one pole of the magnet, pass in curved lines around to the opposite pole, where they re-enter and pass on through the magnet again, so that if any line is followed through its entire length, one will eventually come back to the starting point, as shown in Fig. 6. It is by virtue of its magnetic field, that a magnet has the power of attracting pieces of iron. "When a piece of ^x; / I I I Fig. 6. Diagrammatic illustration of the magnetic lines of force. iron is brought under its influence, it becomes a tem- porary magnet, and for the time being has its two poles. If the north pole of a magnet is brought close to a piece of iron, a south pole will be induced in the iron next to this north pole, and a north pole in the portion farthest from it. The attraction is then exactly similar to the at- traction between two permanent magnets when two un- like poles are brought together. This action of a mag- net in developing magnetism in iron placed in its magnetic field is called magnetic induction. When a piece of iron is in contact with a magnet, the attraction is greatest; but actual contact is unnecessary 38 DENTAL AND ORAL RADIOGRAPHY to magnetize the iron, as it need only be placed within the magnetic field, or, in other words, within the mag- netic lines of force of the magnet. Magnetism may be induced in iron in another way not yet described, and to ns this is of great importance. If an ordinary electric current is passed through a coil of wire, the coil becomes equivalent to a magnet and is sur- rounded by a magnetic field similar to that of a bar mag- net. Such a coil of wire is called a helix, and if its length is many times its diameter, it is called a solenoid. /.<-' ^."-^xN y /' y / Fig. 7. Diagrammatic illustration of the magnetic field surrounding a coil of wire through which an electric current is passing. Since a solenoid is surrounded by a magnetic field sim- ilar to that of a magnet (see Fig. 7) it follows that a solenoid is capable of magnetizing pieces of soft iron and attracting them in the same way as does an ordinary steel magnet. The magnetic field of a solenoid is strongest within its windings and therefore if a bar of soft iron is placed within the coil, the bar will be much more strongly magnetized than if placed in any other position about the coil. Such a coil adapted to carry a current and 'provided with a soft iron bar or core is called an electromagnet (Fig. 8). HIGH TENSION ELECTRIC CURRENTS 39 In order to permit the wire to be closely wound and at the same time to allow the current to pass through each turn, the wire must be covered with insulation throughout its length. It should also be remembered that the iron core ivithin the solenoid remains a magnet only ivhile the current is passing through the coil, as "only electric charges in motion produce magnetic effects." Electromagnets are much more powerful than ordinary- magnets ; that is, their fields have much greater strength, for the field of the electromagnet is equal to the sum of Fig. 8. An iron bar placed within the windings of a solenoid is subject to its mag- netic field and becomes a magnet. the field due to the core, plus the field due to the current passing through the coil. Thus far we have discussed the fact that a magnetic substance in the field of an ordinary magnet, or a con- ductor carrying an electric current, is magnetized. This phenomenon, we know, is due to magnetic induction. It is also a fact that an electric current may he induced in a conductor by causing the latter to move through a mag- netic field. It makes no difference whether this field comes from an ordinary magnet or from an electric charge passing through a conductor. This action of a 40 DENTAL AND ORAL RADIOGRAPHY magnet or of a current on a conductor moved in its field is called electromagnetic induction. Principles of Electromagnetic Induction If the ends of a coil of wire are connected with a gal- vanometer (Fig. 9) and the coil is moved down over an ordinary magnet, the galvanometer will show that a mo- mentary electric current has passed through the coil. Fig. 9. A, magnet with diagrammatic illustration of "magnetic lines of force" sur- rounding it. B shows a coil of wire connected to a galvanometer, C. The current continues as long as the coil is in motion, and ceases as soon as the coil is brought to rest. If the coil is withdrawn from the magnet, a current is also in- duced which flows in an opposite direction to the current which was induced when the coil was carried down over the magnet. These induced currents are produced by the field sur- rounding the magnet moving or cutting across the wires composing the coil. If a current is passed through the coil, it creates a magnetic field, and, on the other hand. HIGH TENSION ELECTRIC CURRENTS 41 the movement of a magnetic field within the coil produces a current. As a solenoid is surrounded by a magnetic field similar to an ordinary bar magnet, it follows that if a solenoid carrying a current were thrust within (Fig. 10) another coil, induced currents will be produced in the latter. These induced currents, as in the case where the magnet is used, only flow while there is a relative movement be- tween the magnetic field and the conductor. "When the Fig. 10. A, battery from which an electric current is passing through the solenoid, B; C, large coil into which the smaller coil B is passed; D, galvanometer. solenoid is passed into the other coil, the induced cur- rent will flow in an opposite direction to the current flowing in the solenoid, and upon withdraiving the sole- noid, the induced current will flow in the same direction as the current in the solenoid. Suppose the two coils just described are placed one within the other (there being no current passing) and while in this position a current is started in the inner coil. Upon the passage of the current in the inner coil, a momentary current is induced in the outer coil, just the 42 DENTAL AND ORAL RADIOGRAPHY same as if a magnet had been moved within it, as shown in Fig. 9. This induced current remains only while the current in the inner coil is increasing in value from zero to its normal strength. As soon as this normal strength is reached, the induced current ceases to flow. Now if the circuit of the inner coil is broken and its current ceases to flow, at this instant another momentary cur- rent is induced in the outer coil, which flows in a direc- tion opposite to the current which was induced by start- ing the current. These two induced currents created by starting and stopping the primary current, or in other words, by *' making" and ''breaking" the current, are not of equal strength, the one produced by the '^ break" of the current being much the stronger. Such an instrument arranged with one coil within the other, but without any connection between the two coils, is known as an "induction coil." The inner coil which is usually supplied with an iron core, is known as the ''primary coil;" and the outer coil, in which the current is induced, is known as the "secondary coil." Induced currents are greatly intensified when soft iron cores are placed tvithin the primary coils, as the cores become m^agnets and increase the strength of the field by adding largely to the lines of force therein. If an induction coil is constructed with the same num- ber of turns of wire in the "secondary" as are present in the "primary," the current induced in the secondary will be exactly equal to the current passed through the primary. The voltage will not be increased. On the other hand, if the secondary contains twice as many turns as the primary, the induced current will be double the voltage of the primary, as each turn of the secondary induces a current in the turns directly adjacent to it, which must be added to the current induced in the first layer by the action of the primary current. Therefore, HIGH TENSION ELECTRIC CURRENTS 43 it should be apparent that as we increase the number of turns in the secondary, we increase the E.M.F., or volt- age. This increase of E.M.F., or voltage, is due to the phenomena of "self-induction" which is the principle utilized in all x-ray machines or other electrical appara- tus used to ''step up" the E.M.F., or voltage. CHAPTER IV X-RAY MACHINES RHUMKORFF OR INDUCTION COIL TESLA OR HIGH FREQUENCY COIL INTERRUP- TERLESS TRANSFORMER STEP UP TRANSFORMER UNIT The Rhumkorff or Induction Coil The Rhumkorff, or ''induction coil," was for many years the most popular and widely used type of x-ray machine. AVhile it is gradually being supplanted by other types, many are still in use and for this reason a description of its principles is not deemed out of place. Furthermore, a knowledge of its mechanism cannot but aid in understanding the other types of apparatus. The induction coil may be said to consist of two princi- pal parts, each of which is a coil of wire, one being con- tained within the other, although they have no electrical connection (see Fig. 11). The inner coil, or "primary," as it is called, consists of a few turns of very coarse insulated wire wrapped about a bundle of soft iron which is known as "the mag- netic core." The outer coil, or "secondary" is made up of a great many turns of fine insulated wire. It has been estimated that in a 12-inch induction coil the secondary coil is wound with between twenty and thirty miles of wire. This, of course, makes possible an enormous number of "turns of wire" so that when we consider that each turn of the secondary induces a current in the turn directly 44 X-RAY MACHINES 45 Fig. 11. Diagrammatic illustration of the essential parts of an induction coil. A' and A are the terminals of the "primary coil." D represents the windings of the "primary" about the magnetic core C. The insulating medium between the "pri- mary" and "secondary" is shown at B. The windings of the "secondary" coil are designated by F, and the "secondary" terminals by B and B'. 46 DENTAL AND ORAL RADIOGRAPHY adjacent to it, which must be added to the current in- duced in the first layer by the action of the primary cur- rent, the sum total of the current coming from the sec- ondary amounts to something tremendous. To compute the E.M.F., of the induced current (or that coming from the secondary), we have but to remem- ber that ''the E.M.F., of the induced current is to that of the primary current, as the number of turns in the secondary coil is to the number of turns in the primary." For instance, suppose we have an induction coil with 10 turns of wire in the primary, and 100 turns of wire in the secondary. If we pass a current of 110 volts through the ** primary," the voltage of the ''secondary" current will be 110 -j^xlOO=1100 volts. Notwithstanding the great change in voltage, the wat- tage of the secondary current is the same as it was in the primary (except for a small loss due to internal re- sistance). This is not true, however, of the amperage. For example, if the primary current of 110 volts carries 5 amperes, its wattage would be 550. The wattage of the secondary current would also be 550, and since wattage equals amperes multiplied by volts, the amperage of the secondary current would be 550 jjQQ- = V2 ampere. Thus it will be seen that as the voltage, or E.M.F., is increased in the before described manner, the amperage or current strength is decreased in equal ratio. It should be plain, therefore, that the original current running to the primary is not changed in actual value, hiU is simply transformed to a state or condition tuJiere it will do the special work required of it. X-RAY MACHINES 47 In our consideration thus far we have considered the manner in which an electric current may be transformed from a low to the high voltage necessary to energize an x-ray tube. We have not, however, named one important requisite of a current to be used for this purpose, namely, that the current must flow continuously and in the same direction* In considering the manner of obtaining a current in the secondary, we learned that such a current is produced by ''making" and "breaking" the primary current. If a continuous current is to be kept flowing, we must utilize some instrument which will rapidly ''make" and "break" the current in the primary circuit. Such an instrument is known as an "interrupter" and is essential to any in- duction coil. There are two classes of these instruments, both of which utilize some automatic principle, and are known as "mechanical" and "electrolytic." Mechanical interrupters, a simple illustration of which is the ordinary vibrator used on small coils, electric bells, etc., will rapidly make or break the primary current and thereby induce a fairly constant current in the secondary ; but this form of interrupter has not been found to be so satisfactory for x-ray work as the electrolytic type. Of the various forms of electrolytic interrupters, the Wehnelt type is the one most universally used. It con- sists of a large battery jar which is nearly filled with a solution composed of sulphuric acid one part and water six parts. Into this solution are introduced two elec- trodes. The negative electrode is constructed of lead and has a large surface exposed, while the positive electrode is contained within a porcelain or hard rubber tube ex- tending down into the solution with only the tip or end of the electrode exposed. The tip of this electrode is usually made of platinum. (See Figs. 12 and 13.) *The exceptions to this rule will be given later. 48 DENTAL AND ORAL RADIOGRAPHY The electrolytic interrupter is connected in the primary- circuit and operates briefly as follows: As the current passes from the platinum point (the positive electrode) through the solution to the negative electrode, by virtue of its chemical action upon the solution bubbles of gas are formed around the exposed platinum point. These bubbles act as a source of insulation and the current Fig. 12. Diagram of the electrolytic interrupter. P, terminal of the positive electrode; A'^, terminal of the negative electrode; T, porcelain sheath or tube cov- ering the positive electrode; /, platinum point of the positive electrode; L, negative electrode constructed of lead. ceases to flow ''It is interrupted." At the instant it is interrupted, the bubbles are dispersed, the solution again comes in contact with the electrode, and the current is re- established only to be broken again and so on, these changes taking place with tremendous frequency. With such an instrument the primary current may be inter- rupted from 60 to 30,000 times a minute. These inter- rupters are sometimes constructed with several platinum X-KAY MACHINES 49 1 ^ ^ 'W \ Fig. 36. Special V compression cylinder made of leaded glass. When it is desirable to obtain a radiogram of the buc- cal roots in their exact length, they must be assumed as being the plane of the tooth {B) and the rays must pass in perpendicularly to a plane lying midway between them and the film. In this event, the image of the lingual root is elongated. If the lingual roots are under scrutiny (C), they must be considered the plane of the teeth, and the rays passed in perpendicularly to a plane lying midway between the lingual root and the film. In this event, the image of the lingual root luill have its correct proportions, but the image of the buccal roots will be slightly shortened. 86 DENTAL AND ORAL RADIOGRAPHY The upper molars are hy all means the most difficult teeth to radiograph; that is, to obtain radiograms that are as coynprehensive as those made of the other teeth. However, by going to the extra work entailed by the foregoing procedure, valuable radiographic information can oftentimes be gained. The task of radiographing the upper molars and pre- molars can be rendered less difficult by using a special compression cylinder made of leaded glass, as shown in Fig. 37. The patient can hold the (ihii in position against the lower teeth by exert- ing slight pressure with the finger. Fig. 36.* The end of the glass cone or cylinder is beveled at the end so that it can be placed close to the face and still remain at the desired angle, its glass construction enabling the operator to view the area under exposure at all times, and thereby lessen the liability of inaccurate work. AVith the lower teeth (Fig. 37) we do not have this diffi- culty to contend with to so great a degree, as the films can be placed for the most part in such a position that Suggested by Dr. F. K. Ream. DENTAL AND ORAL RADIOGRAPHY TECHNIC 87 they lie parallel to the long axis of the teeth, and the rays can be directed in a perpendicular direction both to the plane of the teeth and the plane of the film. In placing the films in the mouth preparatory to mak- ing radiograms of the lower teeth, difficulty is sometimes encountered, owing to the fact that the tissues are usually quite sensitive. Inasmuch as the film must be pressed well doivn hehveen the tongue and the teeth, it is advis- able to first see that no sharp corners exist on the film covering, or better still, provide a rubber envelope or film holder ivhich has no sharp corners. Such an en- velope is easily improvised by the use of ordinary black vulcanite rubber. A piece of this rubber which should be a little more than double the size of the film, is wrapped about it and the free edges pressed together. These edges are then trimmed with a pair of scissors so that the cor- ners are rounded. Such an envelope containing the film can be introduced into the mouth and placed well down on the lingual side of the teeth with a minimum amount of discomfort to the patient. Realizing the discomfort to patients arising from the film comers, manufacturers are now making films with soft metal backs with the corners rounded. Such films are decidedly preferable for the lower teeth. Film Holders. Some operators prefer to use a film holder to support the film during exposure. Of these, there are several varieties upon the market, all of which will accomplish the work for which they are intended. The Leach Film Holder (Designed by Dr. F. D. Leach). The Leach film holder is very simple in design, and two film holders constitute a set. (See Fig. 38.) AVith these, the patient holds the film in position by grasping the handle part of the holder, and the operator can by noting the angle of the handle, determine the di- rection in which the rays must be directed. 05 DENTAL AND ORAL RADIOGRAPHY The smaller holder is designed for the upper six and lower eight anterior teeth, and the larger holder is de- signed for the posterior areas of the mouth. The Dorr Film Holder (Designed by Dr. P. P. Dorr). The Dorr film holder is designed so that the film is held in position for exposure by closing the teeth upon a flange which is part of the holder. (See Fig. 39.) A removable handle is attached to the edge of the flange and assists in placing the film holder (carrjdng the film) Fig. 38. The Leach film holder. in the desired position in the mouth, after which the handle can be removed. Two film holders constitute a set of which one has an obtuse angle and is designed for the upper teeth, while the other is placed at right angles to the flange and is intended for use upon the lower teeth. Where it is necessary to make a complete radiographic examination of the dental arches, it can be accomplished in the average case, by making six exposures of each arch. The procedure to be followed is diagrammatically DENTAL AND ORAL RADIOGRAPHY TECHNIC 89 shown in Fig. 40. The numbers 1, 2, 3, 4, 5, 6 indicate the position of the x-ray tube in its relation to the dental arch, and the ends of the lines coming from the numbers show the position of the mesial and distal edges of the film used for each exposure. It will be noted that each adjacent film position overlaps its neighbor which is ad- visable so that no area is left out. Fig. 39. The Dorr film holder with detachable handle. Fig. 40. In making radiograms of the anterior part of the arch, it is a mistake to attempt to radiograph more than two or three teeth at a time, as the curvature of the arch usually renders it impossible to get more than that num- ber free from distortion. Another point in technic which should not be over- 90 DENTAL AND ORAL EADIOGRAPHY looked if sharp outlines are to be obtained, is the one in regard to having the tube placed at the proper distance from the structures to be radiographed. To establish the best focal distance for work about the teeth or jaws, the target of the tube should be about twenty inches from the plate or film. Another method of holding a film in position for ex- posure which has not been alluded to so far is known as Fig. 41-/1. --Method of obtaining a radiogram of the npper incisor region using the bite method. the "bite method," and while it is limited in its useful- ness can sometimes be employed to advantage. It con- sists of placing a large film about 1^2 ^ ^V^ i^i ^i^e in the mouth and having the patient close the teeth against it and thereby hold it in place during the exposure. Owing to the fact that a film held in this manner is not brought in close contact with the teeth except at their occlusal surfaces the images of the apical portions DENTAL AND ORAL RADIOGRAPHY TECHNIC 91 cannot be shown as clearly as they should be if the higli- est possible degree of detail is desired. Furthermore, the x-raj'S must be passed in through the tissues at a much more decided angle than is necessary where the standard technic is used. However, occasions may arise where this plan will prove advantageous especially where deeply imbedded or impacted teeth in the mandible lie out of reach of the I'ig. 41-B. Method of obtaining a radiogram of the lower incisor region using the bite method. ordinary small films placed between the tongue and the teeth. The technic employed in such cases is shown in Figure 41-B. The time factor will not be discussed at this juncture except to say that with a good x-ray machine, and a properly regulated tube, good radiograms can be ob- tained by very short exposures in using the intraoral method, as the rays need only penetrate a comparatively 92 DENTAL AND ORAL RADIOGRAPHY short distance before reaching the fihns. In fact, with the apparatus now available, radiograms can often be obtained by instantaneous exposures. However, instan- taneous exposures are not necessary for good radiog- raphy. X-ra}^ apparatus which is capable of producing sharp, clear "intra-oral" radiograms in from two to five seconds, is efficient enough for use in the x-ray lab- oratory of the dentist. CHAPTER VII TECHNIC OF DENTAL AND ORAL RADIOGRAPHY (Continued) Extra-oral Method The extra-oral method is, in tlie author's opinion, one which offers a very wide range of usefulness in our work. As stated previously, this is the method used to obtain radiograms of large areas. Not only can larger areas be Fig. 42. The headrest of the dental chair with its many adjustments can easily be arranged so that the patient's head may rest easily and firmly upon it. obtained by this method, but locations and structures in- accessible to the small films are reached and their images accurately and clearly recorded upon the larger plates. Therefore, the advantages of becoming familiar with this method are well worth Avhile. 93 94 DENTAL AND ORAL RADIOGRAPHY Fig. A3-A. ^Tube stand with platerest and head support. (Eisen and Ivy.) Fig. 43-B. Position of head and angle for left side of jaws. (ICisen and Ivy). DENTAL AND ORAL RADIOGRAPHY TECHNIC 95 The technic is simple when once mastered, but must be adhered to accurately if the results are to be depended upon for diagnosis. In using the extra-oral method, large plates or films are used and the areas desired are brought in as close contact as possible with the plate, hy pressing or resting the side or portion of the face upon ivhich the structures desired are located, against the plate. First of all, the patient must be placed in a position so that the head can he held perfectly still. The dental chair with a few adjustments offers an excellent means for accomplishing this and may be used in any one of several ways. For instance, one of the chair arms can be lowered down against the side of the chair or removed, and the patient placed sideways in the chair. The chair back is then adjusted so that the patient lies against it in an easy position, and the headrest wings are adjusted so as to lie flat and thereby form an excellent resting place for the plate. The headrest with its many possible adjustments can easily be placed so that the patient's head rests easily and firmly upon the plate, rendering it an easy matter to remain perfectly quiet. This position is shown in Fig. 42. For this character of work some operators prefer to use a platerest and head supporting device attached to the tube stand as shown in Fig. 4'S-A. Where such a method is followed, the head is supported in its proper relationship to the plate as shown in Fig. 43--^.* Author's Methods of Seating the Patient In the author's opinion, there is another method of seating the patient for this character of work which will be found to be advantageous where such special ap- paratus is not available. It is accomplished by using an Kisen, I'". J., and Ivy, Robert IT.: American Journal of Roentgenology, May, 1916. 96 DENTAL AND ORAL RADIOGRAPHY ordinary chair with a straight back and small arms, placed against the back of the dental chair. The head- rest of the cliair is turned over and adjusted to the proper height, position and angle, so that the patient's head can rest against it in any desired position. In this way the patient is afforded the firm support of the heavy Fig. 44. The arrangement of the apparatus preparatory to seating the patient. dental chair, and, therefore, has little difficulty in re- maining perfectly quiet, and the operator can by making a few changes in the position of the small chair, by mov- ing and readjusting the tube stand and the headrest, have radiographic access to any part of the oral cavity or associated structures. The arrangement of the appa- DENTAL AND ORAL RADIOGRAPHY TECHNIC 97 ratns preparatory to seating the patient is shown in Fig. 44. The fact that this requires but a few moments, does not material!}' disarrange the office, or put the patient to discomfort, justifies the author in feeling that it is an Fig. 45. The patient seated and the apparatus arranged for making a radiogram of the left side. The comfortable position of the patient renders it an easy matter to remain perfectly quiet. excellent method for use in the average dental office. (Fig. 45.) In order to expedite the making of radiograms of this character the author has designed a special "plate and head rest table" which is shown in Fig. 46. In using 98 DENTAL AND ORAL RADIOGRAPHY Fig. 46. Plate and head-rest support for extra-oral radiography. Fig. 47. opiate and head-rest support adjusted to the arms of the dental chair. DENTAL AND ORAL, RADIOGRAPHY TECHNIC 99 this apparatus the patient is seated in an ordinary office chair and the table is then moved close up to the patient so that the elbows and forearms rest upon the table and the face is allowed to rest upon the head and plate sup- port, which is adjustable in height. The apparatus can be so arranged that the patient rests in an easy com- fortable position and therefore can remain perfectly quiet as long as necessary. When not in use the table is placed against the wall where it is out of the way. After satisfactorily using this method of supporting the head for some time, the author modified this table so that it could be adjusted to the arms of the dental chair as shown in Fig. 47. This is proving a distinct advantage as it requires but a moment's time to place the table in position and renders it unnecessary to re- move the patient from the chair regardless of the char- acter of radiography which is to be attempted. With the head thus supported, as shown in Figs. 45 or 46, the rays are directed from the opposite side of the head, and, therefore, must pass through the entire face or skull in transit. The question naturally arises, how is this to be accomplished without superimposing the shad- ows of one side upon the shadows of the other side, and thereby producing a chaotic result. For instance, let us suppose that we wish to obtain a radiogram of the left side of the upper and lower jaws extending from the cuspid region in front to the angle of the jaw behind, and from the floor of the orbit above to the inferior margin of the mandible below. If we are to get a correct shadowgraphic representation of this area, it should be free from the shadows of the opposite side, and this can only he accomplished hy directing the rays in such a manner that they will miss the areas not desired and will pass through those we wish to record. In accomplishing this, we must take into consideration 100 DENTAL AND ORAL RADIOGRAPHY Fig. 48-^. Fig. 48 -B. Fig. 48-B. Technic for left side. M-L, median line; .S", the spine; A, ascending ramus and angle of lower jaw; P-F, plate or tilm. DENTAL AND ORAL RADIOGRAPHY TECHNIC 101 Fig. 49-A. Fig. 49-B. Fig. 49-B. Techiiic for right side. M-L, median line; S, the spine; A, ascending ramus and angle of lower jaw; P-F, plate or film. 102 DENTAL AND ORAL RADIOGRAPHY two structures; viz., the spine and the ascending ramus of the mandible (on the right side in this instance as the left side is to be radiographed) and cause the rays to pass in through this opening and thereby reach the Fig. SO. desired area. The way in which this is accomplished is shown in Fig. 48, A and B, and Fig. 49, A and B. An important factor in accomplishing this is the posi- tion in which the patient's head is held as it is pressed against the plate. Held in the manner shown, the rays DENTAL AND ORAL RADIOGRAPHY TECHNIC 103 Fig. 51-A. Fig. SIB. Fig. 51-S. Incorrect tcchnic. The shadows of both sides will be imposed upon the plate. 104 DENTAL AND ORAL RADIOGRAPHY can be made to pass in between the ascending ramus of the mandible and the spine, and can pass in at approxi- mately a perpendicular direction to the long axis of the teeth and the plate, giving correct shadow lengths upon Fig. 52. The result of incorrect technic. This is a radiogram of the same subject as shown in Fig. SO. the plate. Fig. 50 shows a radiogram made by using this technic. If this rule is disregarded and the rays passed through the structures, as shown in Fig. 51, A and B, the shadows DENTAL AND ORAL RADIOGRAPHY TECHNIC 105 Fig. 53-^. Fig. 53B. Fig. 53. The areas in the upper and lower jaws extending from the median line to the first premolar can be radiographed by utilizing this technic. A, technic for left side; B, technic for right side. 106 DENTAL AND ORAL RADIOGRAPHY of the opposite side will be superimposed upon the shad- ows of the structures desired, and a chaotic result pro- duced. The result of such technic is shown in Fig. 52. In a similar manner as shown in Figs. 48 and 49, with slight adjustments in the position of the plate, the head, and the tube, the areas in the upper and lower jaws ex- tending from the median line to the first premolars, and from the nose above to the inferior margin of the man- dible below, can be radiographed (Fig. 53, A and B). Lil^ewise the structures at the median line including the A Fig. 54. The structures at the median line including the incisors, both above and below, may be secured in this way. incisors, both above and below, the anterior portions of the mandible and maxilla, the nasal cavity and its ac- cessory sinuses, may be radiographed by passing the rays directly through the skull, as shown in Figs. 54 and 55. In this instance, the shadow of the spine will be superimposed upon the dental structures, but owing to the fact that it is so far removed from the plate, its shadow does not interfere seriously. It is important, in making these pictures, to have the patient's head sup- ported in such a manner that it can be held still for a DENTAL AND ORAL RADIOGRAPHY TECHNIC 107 longer period than is required in making the exposures of the other areas mentioned. When ready to make the exposure for extra-oral radio- grams, the apparatus is arranged with the anode of the tube about twenty inches from the plate. The patient Fig. 55. In following out the technic illustrated in Fig. 54, the patient's head may be supported by a bandage of gauze of necessary to secure more complete im- mobility. is instructed to heep the mouth closed ivith the teeth together in their natural occlusion. They should also be warned as to the approximate length of time the ex- posure will require, and that they must remain perfectly quiet. 108 DENTAL AND ORAL RADIOGRAPHY With the more powerful types of apparatus, extra-oral radiograms require but short exposures, but if an oper- ator does not possess high power apparatus, he should not hesitate to use this method, as a patient properly seated and supported, as shown in Fig. 47, can easily re- main quiet for five or ten seconds, or perhaps even longer, should it be necessary. In making a complete radiographic examination of the teeth, the maxilla and mandible, the author suggests the following procedure. Extra-oral radiograms should be made of each side, using the technic illustrated in Figs. 48, 49, and 53. This would mean two plates for each side. Then by the use of intra-oral films, the region ly- ing between the cuspids both above and below, should be radiographed. These plates and films should then be developed and examined. If the procedure has been car- ried out with due regard for all the elements involved, the result should constitute a general radiographic sur- vey of the teeth, the maxilla and the mandible. Should any of the plates or films exposed fail to result in good radiograms, additional exposures should be made, as nothing but good radiograms should be depended upon for diagnosis. It is sometimes advisable after making a complete radi- ographic examination by the method just advocated, ' ' to check up" the findings of extra-oral radiograms by the use of the intra-oral films. For instance, suppose a large plate shows what appears to be a dento-alveolar abscess upon the root of an upper bicuspid or molar tooth. An intra-oral radiogram of this particular area will often settle any doubts, as a higher degree of detail can often be obtained by concentrating upon the small area in question. The author would not wish to imply by the preced- ing remarks upon technic, that the few rules enumerated DENTAL, AND ORAL RADIOGRAPHY TECHNIC 109 constitute a safe and never failing means of producing good radiograms. There are many points to be consid- ered which cannot be included in so limited a text, but which must be learned in the school of experience, such as the necessary variations from the given rules of tech- nic because of anatomic variations in the dental and oral structures of patients. Therefore, the rules of technic which have been presented must be accepted only in the light of principles. CHAPTER VIII TECHNIC OF DENTAL AND ORAL RADIOGRAPHY (Continued) Successful radiography depends upon a sequence of operations, each of which must be carried out with scien- tific accuracy. These steps, upon which the finished prod- uct depends, may be enumerated as follows : 1st Correct technic of position. 2nd Proper tube and current conditions. 3rd Correct exposure and development of plates and films. It would be difficult to determine which of these steps is the most important ; in fact, they are all so important that a radiogram is a success or failure in accordance with the degree of accuracy with which each is carried out. In the preceding chapter, the actual technic of radiog- raphy, so far as the arrangement of apparatus is con- cerned and its relative position to the patient and the plate (or film), has been discussed. We will, therefore, proceed to the next factor for consideration. Proper Tube and Current Conditions The character of the x-rays produced in a tube de- pends upon the degree of its vacuum and the current which passes through it. We know that the x-rays are produced by the cathode stream striking the anode or target, and that this cathode stream (Fig. 57-M) is gen- erated by the flow of the current in the tube. The veloc- ity of the cathode stream depends upon the voltage of the current entering the tube, therefore, the higher the 110 DENTAL AND ORAL RADIOGRAPHY TECHNIC 111 voltage, the faster the cathode stream travels, and the more intense or penetrating are the x-rays produced. The quantity of x-rays produced depends upon the mil- liamperage of the current. In considering the role enacted by the voltage and mil- liamperage in the x-ray production, we have assumed that the tube is exhausted to a high degree of vacuum, for the degree of vacuum determines to a large extent, the value of the other two factors. It is highly important therefore that a uniform degree of vacuum be maintained so that all the factors for proper x-ray production shall be known to the operator. The degree of vacuum of a tube is designated as high, medium, or low, a "high tube" being one in which the vacuum is well nigh com- plete; in a "medium tube" the vacuum is less complete, while a "low tube" is one in which the vacuum is far from complete. For dental radiography a medium or a fairly high tube is indicated, as with such a tube x-rays may be produced having a degree of penetration sufficient to pass through the oral structures and produce the desired effect upon the emulsion of the plate or film. When a current of high voltage and proper milliam- perage is passed through an ordinary gas tube whose vacumn is "medium" or "fairly high" it should light up in a characteristic manner forming two hemispheres which have a definite line of demarcation. The hemi- sphere in front of the target which is the active hemi- sphere, is evident by a fluorescence deep apple green in color, while the other hemisphere should be evident by a lack of greenish light. To Determine the Vacuum of a Tube The comparative degree of vacuum of a tube can be determined in the following mariner: Connect the tube 112 DENTAL AND ORAL RADIOGRAPHY to the X-ray machine as shown in Fig. 56. See that the third terminal (/S") is moved well away from the nega- tive terminal (S), or better still, disconnect the wire run- ning to the regulation chamber (R). Now, move the sliding rods {B and D) of the secondary spark gap, to- ward each other until they are about three inches apart, and start the current. Unless the tube is loiv, the cur- rent will jump the spark gap instead of passing through the tube. If the tube resists the current and causes it Fig. 56. to jump the spark gap, it is said to have '' backed up" three inches of spark. Thus a "low tube" will back up two or three inches of spark, a ''medium tube" five or six inches, while a high tube will back up six or eight inches. In fact, the vacuum of a tube may be so great that only the most powerful x-ray machines will operate it. Such a tube, however, is not useful for dental radiog- raphy. The vacuum of a tube may also be determined by the use of an instrument known as a milliamperemeter. DENTAL AND ORAL RADIOGRAPHY TECHNIC 113 This instrument which is usually an accessory of either the induction coil or transformer, is connected in circuit with the tube, and measures the current passing through the tube. "With a "low tube" the milliamperemeter will show a reading of 15 to 18, while with a "medium tube" the reading will be from 10 to 12, and with a "high tube" the milliamperemeter will register 5 or less. Relative Merits of Low, Medium, and High Tubes A ' ' low tube ' ' in operation under average current con- ditions gives a clear sharp hemisphere of pale greenish in front of the target, with usually a trace of bluish light in the region of the assistant anode. If the tube is very low the cathode stream shows blue, and there is a bluish light back of the active hemisphere. Such a tube Avill not do good radiographic work, as the x-rays produced by it are lacking in penetration. A "medium tube" gives a clear, sharp hemisphere of light greenish color, and there is an absence of bluish light back of the target. The rays emanating from such a tube are more penetrating than those from the "low tube," but are not so well suited for "bone radiography" as those which come from a tube fairly high in vacuum. When such a tube is operating, it gives a clear sharp hemisphere deep apple green in color, with a lack of greenish light back of the target. The x-rays emanat- ing from such a tube are of degree of penetration tuJiich is best suited for bo)ic radiography^ for they penetrate and pass through the soft tissues and to a sufficient de- gree through the hone structure to give good contrast. It is very important that the vacuum of such a tube be kept uniform, for if it becomes low'ered, the power of penetration of the rays is decreased, and, on the other hand, if the vacuum gets too high, the penetrating power of the rays will be increased. Variation either up or 114 DENTAL AND ORAL RADIOGRAPHY down is unfortunate as it makes it impossible for the operator to proceed with any assurance of uniform results. Regulating the Tube Prior to seating and arranging the patient, the tube if it be of the gas type should be tested out and any needed change in its vacuum effected. This is easily ac- complished by utilizing the third terminal of the x-ray machine. The tube should be connected to the machine as shown in Fig. 56. The terminals of the regulating spark gap (S'S) should be placed about four inches apart, and the current (of correct working strength) turned on for an instant. If a line of sparks jump be- tween S' and S, it shows the vacuum of the tube is too high. In this even the regulating spark gap (S'S) should be reduced to about two inches, and a small amownt of current turned on. This weaker current will pass across the spark gap {S'S), travel down the mre connected to the regulating chamber, and by heating the abestos (impregnated with chemicals), will liberate enough gas to reduce the vacuum. Unless the tube is very high, a few seconds will suffice to reduce it to the vacuum desired. To be sure the vacuum is right, the regulating spark gap {S'S) should be widened to about four inches, and the desired working current again passed through the tube for an instant. If the tube lights up with a clear sharp active hemisphere deep apple green in color with a lack of greenish light back of the target, and if it carries the desired amount of working current, you then know it is ready for work. If an x-ray machine is not equipped with a third termi- nal, the same results in regulating the tube may be ef- fected by using the regulating adjuster (Fig. 57), the end of which can be placed at the desired distances from DENTAL AND ORAL RADIOGRAPHY TECHNIC 115 negative wire near its point of attachment to the tube. The tube may also be lowered by attaching the negative wire directly to the regulating chamber and passing a small amount of current through the circuit. These manipulations should be carried out with the greatest caution, for a tuhe is an extremely delicate and sensitive piece of apparatus and ivill not stand abuse. A careless operator can quite easily reduce the vac- uum to such a degree that the tube is useless. Such a tube has a purple appearance when the current is passed through it. If such a tube has not been too greatly ^.l A Anode. B- -Assistant Anodi C Calhodi- D-RfRulalini? Chamber r Rrgulalint juslcr r, Hfmisphc- H-ConncclK, Wire I- Assistant Ano.lr - Cap K Anode ('ai L Caihodr Ca|i M Cathodr Sirrain N Focal I'oini abused, it will often regain its vacuum if given a rest. If this does not bring the vacuum up, it can often be brought back in the following way: The spiral spring (Fig. 57) connecting the anode and assistant anode should be re- moved and the positive wire from the machine attached to the assistant anode (Z). The negative wire is at- tached as usual (at L) and a light current is run through the tube for a minute or two at a time. If this is done once or twice a day for several days, the vacuum will usually come up. Any increase in vacuum will be indi- cated by the milliampere readings dropping off, or by 116 DENTAL AND ORAL RADIOGRAPHY the increased length of spark gap the tube will "back up." If a tube does not respond to this treatment but con- tinues to be purple Avhile operating, it indicates that it is practically non vacuous or "punctured." It is then useless and should be sent back to the manufacturer for repairs. In the event a tube is "completely punctured," the current in passing through it simply jumps the gap between the anode and cathode, and is evident as a line of white sparks. One tube complication not yet mentioned is sometimes encountered in the use of induction coils. This is known I'lg. 58. Radiator type Cooliilge tube. Fig. 59. Radiator Coolidge tube, right angle type. as "inverse in the tube," and is the result of the pres- ence of inverse current (current in the wrong direction) in the secondary circuit of the coil. "Inverse" is evi- dent in the tube by the appearance of rings of light back of, and usually running at an angle to, the active hemi- sphere, or by a fullness of greenish light back of the ac- tive hemisphere, with rings about the assistant anode. Inverse current in a tube will generate secondary rays which have the tendency to make the outline of the image on the plate hazy or "less sharp," as these rays are pro- duced in the tube elsewhere than at a focal point on the DENTAL AND ORAL RADIOGRAPHY TECHNIC 117 target. It also produces heat in the tube which lowers the vacuum and hence lessens the penetration of the rays coming from it. "Inverse" in the tube can usually be controlled or pre- vented by the use of "a multiple spark gap" or "a valve tube" arranged in series with the x-ray tube, and by using a tube which is fairly high in vacuum. If it still persists after these precautions are taken, it indicates an imperfect adjustment of the induction coil or some of its accessories. All manufacturers of x-ray tubes furnish full instruc- tions as to the care of and manner of using x-ray tubes. These instructions should be carefully read and explic- itly folloived. In order that uniform results may be obtained, it is advisable to always use the tube at the same vacuum, with the same amount of current. The proper ' ' working current" for dental and oral radiography may be deter- mined in the following way : AVith the tube disconnected, set the sliding rods [B and D of Fig. 56) of the machine about four or five inches apart. Then start the current in the machine, and beginning with a low current in- crease it until a fat fuzzy "caterpillar spark" is pro- duced across the spark gap. As soon as this spark or discharge appears, the switch should be pulled out, but the rheostat or other controlling apparatus left as it was when the spark appeared, so that when the tube is connected, the proper working current will come from the machine. The tube should then be connected up and given a trial. If it is not too high in vacuum, it should take the cur- rent, or in the event it is too high, it will "back up" the spark, and the discharge instead of passing through the tube will jump the gap. If the tube requires regulating, it can be done by the methods before described. 118 DENTAL AND ORAL RADIOGRAPHY With the working current and vacuum established, it is a good idea to separate the sliding rods on the ma- chine to at least eight inches, to insure against the tube backing up the current, for in the event the tube should start going up during the time the exposure is being made, the startling noise made by the discharge jumping the gap, may cause the patient to move and thereby blur the radiogram. If several exposures of five or ten sec- onds each are made, the tube, if it be a gas tube, should be given sufficient rest between exposures so that it will not heat up. This is important. With proper tube and current conditions, the length of time required for the exposure will depend somewhat upon tlie type of x-ray machine used, and the thickness and density of the parts to be radiographed, varying with different patients according to age and structural make up. In order tliat uniform and dependable radiograms shall be produced, tlie operator sliould adopt a technic of tube operation suited to his needs and adhere to if. If this habit is acquired early it will be foxmd that the re- quired exposiire for any given case will after a little ex perience become a simple matter. Such a technic requires the selection of a definite amoimt of *' spark back up" or"^" working current" and the use of a definite number of milliamperes of current passing through the tube, the ''back up" as stated before representing the voltage or pressure of the current and the milliamperage the volume. These two factors when combined Avith uniform tube vacuum make possible ac- curate and definite results, provided the tube is operated at the same distance from the parts being radiographed. In other words, a definite ivorlinff distance must he main- tained if results are to be duplicated. While different operators have prefei*ences, the writer has found it ad- DEXTAL AND ORAL RADIOGRAPHY TECHXIC 119 vantageous to keep the target of the tube approximately 18 to 20 inches from the plate or film. If this factor is varied, the intensity of the rays will change with it in definite ratio, for they will vary inversely as the square of the distance from the target of the tube to the plate or film. Thus if the distance is doubled, the intensity of the rays will be one-fourth as great as it was previously, or if the distance is tripled, the intensity will be but one- ninth as great as at the original distance, etc. For intra-oral radiograms, a ''spark back up" of four or four and a half inches with twenty milliamperes will give very satisfactory results. If extra-oral radiograms are to be made, a higher degree of penetration is neces- sary and, therefore, five or even six inches of "spark back up" should be employed either with the same milli- amperes (twenty) or with an increase of ten or even fif- teen milliamperes for dense objects. The Use of the Coolidge Tube The introduction of the Coolidge tube has proved to be the greatest addition to x-ray equipment of recent years for it has made possible uniform results in a man- ner which greatly lessens the burdens of the radiog- rapher. While the radiograms produced by it do not exceed in excellence those made with other tubes, its ease of operation, hardy construction and nev^er varying re- sults made possible by its perfect control, promise to make it the most popular of all x-ray tubes. This tube is built and operated in quite a different manner from the ordinary gas tube. (See Figure 27). The target or anode is smaller and is constructed en- tirely of tungsten, while the cathode is placed well out in the tube but a short distance from the anode and con- sists of a spiral filament of flat closely wound tungsten wire located with a small shell or short metal tube. 120 DENTAL AND ORAL RADIOGRAPHY The tube is energized by two distinct currents, one cf high voltage which is derived from the x-ray machine, and the other a low voltage current derived from a stor- age battery or "step-down" transformer. The object of the low voltage current is to electrically heat the spiral filament in the cathode for the filament heat governs the amount of current ivhich can pass through the tube. A rheostat is connected in series with the filament heat current supply as well as an ameter, both of which make possible a fine degree of current control and scale read- ing so that the filament of the cathode can be brought to any desired heat and maintained there. When the desired amount of "voltage" or "w^orking current" or "back up" has been determined as well as the milliamperage to be used for the character of work at hand the filament current is turned on and the catliode heated to the point where the tube will take the current. AVlien this is once done and the meter readings of the "Coolidge control" (the apparatus governing the heat- ing of the filament) noted as well as the milliamper- meter on the machine, it is only necessary on subsequent occasions to set the controls at the same points and pro- ceed. The vacuum of this tube does not undergo change as the milliamperage of the current which passes through it is governed absolutel}^ by the filament heat, the higher the heat the larger the number of milliamperes will flow through the tube and consequently the shorter will be the exposure required to produce the desired effect upon the photographic emulsion. Owing to the fact that the flow^ of the current is con- trolled so positively, this tube may be used for repeated exposures or in fact it may be used for hours if necessary without its vacuum being affected, which would of course be impossible Avith any other type of tube. From the DENTAL AND ORAL RADIOGRAPHY TECHNIC 121 standpoint of durability it is in a class by itself, its length of life being practically without limit providing it is not roughly handled and broken. There are two distinct types of Coolidge tubes, the first of which is kno^^Tl as the "universal type" and the other as the "radiator type." The universal type is the older of the two and has proven highly satisfactory for general all around usage. It is obtainable with a broad, medium and fine focus, the term ' ' focus ' ' referring to the area upon the anode from which the x-rays emanate. As a high degree of detail is necessary in dental and oral radiography a fine focus tube is preferable for our use. Such a tube should be energized by an interrupterless transfomier with the addition of the special Coolidge control apparatus which has already been mentioned and described. Coolidge tubes of the "radiator type" while similar in principle are different in several respects from the "universal type." They are energized by an x-ray ma- chine which is a "step-up transformer" but has no recti- fying switch such as is employed in the interrupterless transformer. This apparent discrepancy is overcome by the tube itself which in addition to its other functions rectifies the current. The filament of the cathode is heated from a "step-down" transformer arranged in conjunction with the machine, all of which makes possible a very compact unit which gives promise of becoming very popular especially where but a small amount of space can be given up to x-ray equipment. Radiator tubes are made in both straight and right angle form as shown in Figs. 58 and 59 and as stated before they must be operated on machines especially adapted for them. Such outfits or "step-up transformer units" are usually operated with a set amount of "spark hacli up" and current milliamperage. This is made nee- 122 DENTAL AND ORAL RADIOGRAPHY essary by the fact that such tubes are limited in the amount of current they will rectify. Such units are usually made in two sizes, the smaller of which operates with three inches of spark back up and ten milliamperes of current, while the other operates with five inches of spark back up and has a capacity of thirty milliamperes of current. While they no doubt give excellent service for certain classes of work they cannot be regarded as flexible or powerful as the interrupterless transformer with a va- riable spark back up used in conjunction with the uni- versal type of Coolidge tube. CHAPTER IX CORRECT EXPOSURE AND DEVELOPMENT OF X-RAY PLATES AND FILMS X-ray plates and films differ from those used in or- dinary photography in that their emulsion is more sen- sitive and better adapted to record the shadows produced by the x-ray. Therefore, they should always be used in preference to ordinary plates and films. The same general photographic rules apply to x-ray plates and films as apply to the ordinary kind, except perhaps that they demand a greater degree of accuracy and care throughout the process of exposure and devel- opment, if the very best results are to be obtained. X-ray Plates X-ray plates are supplied by the manufacturers, packed in lightproof boxes containing one dozen plates. They are obtainable in any desired size, but for dental and oral radiography, a 5x7 plate is large enough. If stored in the laboratory, they should be kept in a lead-lined box prior to their preparation for exposure, or they will be- come *' fogged," as lightproof boxes offer no protection whatever from the x-ray. A suitable plate and film storage box is shown in Fig. 60. Such a box should be about twelve inches square and five inches deep. This will enable the storage of several boxes of 5x7 plates, and in addition, three or four dozen dental films. In their preparation for exposure, each plate is placed in two lightproof envelopes, one of which is black and the other red or orange in color. Such envelopes are 123 124 DKNTAL AND ORAL ItADIOGRAPII Y furnished by plate manufacturers and are obtainable in the desired size. The transference of the plate from its original box to the envelopes must, of course, only he done in the photographic darkroom. The plate is first slipped into the smaller envelope which is usually the black one, with the emulsion side of the plate facing the smooth side of the envelope (the side free from seams or over- lapping edges). The envelope containing the plate is then placed in the larger or yellow envelope, flap-end first, with the smooth side of the inner envelope facing the smooth side of the outer one. Plates prepared in Fig. 50. X-iayproof film and plate chest. this way are then ready for exposure and can be placed back in the lead-lined box until needed. In "loading these envelopes," care should be taken lest the emulsion of the plate become scratched, as scratches even though they be very slight will often cur- tail the value of the finished radiogram. It is not advisable to keep large quantities of plates loaded in envelopes, unless they are to be used within a few days, as the contact of the paper with the emulsion will in time affect it adversely. All ''brands" of x-ray plates are not the same, there- fore, if the best results are obtained in using any par- ticular kind, they must be handled in strict accordance DEVELOPMENT OF PLATES AN^D FILMS 125 with the manufacturers' instructions. For dental and oral radiography, a plate should be fairly rapid (that is, it should not require a long exposure), give a high de- gree of detail and good contrast, and should be uniform in its reaction to the x-ray. X-ray Films In making intra-oral radiograms, a film is preferable to a plate as it is flexible and, therefore, can be more easily adapted to the inside of the mouth. These films are obtainable in several convenient sizes, wrapped in lightproof and dampproof coverings ready for exposure. Like plates they should be kept in a lead-lined box for protection. With these "dental films" as they are called, you have the choice of two different emulsions, one of which is much more ''rapid" than the other. The ''rapid" or "fast film" requires only about one- fourth or one-third as long an exposure as the "regular" or "slow film," and therefore is an advantage to the radiographer who uses one of the less powerful types of x-ray machines. However, such a film does not have as much latitude as the slow film, and is therefore more easily overexposed. If properly exposed, either one will give satisfactory results. When arranging a plate or film for exposure, the emul- sion side should lie next to the structures being radio- graphed. If this rule is systematically followed, it is an easy matter to identify radiograms, i. e., whether they represent structures on the right or left side of the me- dian line. The Exposure of the Plate or Film The actual time required to properly expose a plate or film depends upon several factors as has already been 126 DENTAL AND ORAL RADIOGRAPHY made plain in the discussion of tube and current condi- tions. Assuming that the before mentioned conditions are kno^\^l to the operator and are under control, the next factors for consideration are the character of the emulsion of the plate or film being used and the density of the parts through which the x-rays must penetrate. It is well for the beginner in this work to use standard plates and films of known ''speed" and the slow variety is recommended. After becoming thoroughly familiar with these it will not be difficult for the operator to modify his technic to handle the other varieties. The vast majority of exposures may be figured as re- quiring an average amount of time especially if they are being made of adult patients. Young children of course require shorter exposures than adults and those cases among adults where the patients are thick and heav}^ and show evidence of strong osseous development will re- quire a little longer exposure than the average. Judg- ment in this matter as well as in other phases of this work will naturally come with experience. Many operators prefer to figure their exposures in ''milliampere seconds." Under known tube and current conditions a "milliampere second" is one milliampere of current passing through the tube for one second. Let us suppose therefore that with a certain speed of plate or film, the exposure required for the average patient is eighty milliampere seconds. If ten milliamperes are be- ing passed through the tube the required exposure would be eight seconds. If twenty milliamperes are being utilized, four seconds will be required, etc. Not infrequently manufacturers of plates and films for dental and oral radiography include among their in- structions and suggestions the approximate number of milliampere seconds required for proper exposure. Such instructions should be carefully followed for they will DEVELOPMENT OF PLATES AND FILMS 127 oftentimes save the operator the necessity of determin- ing the time factor by experiment. Intra-oral radiograms of the lower teeth usually re- quire less time than is required to expose the upper teeth, as the mass of the tissues to be penetrated is not so great. Of the upper teeth the molars require the longest ex- posure as the x-ray must penetrate a greater distance before reaching the emulsion. In making intra-oral exposures the author uses the same milliamperage and '^ spark back up" for both the upper and lower teeth but varies the time slightly as sug- gested above and has found the method very satisfactory. For such work twenty milliamperes of current with four or four and a half inches of ''spark back up" are used. For intra-oral work where children are the subjects for exposure the factors are kept the same but for adults the "spark back up" is increased to five or even six inches and the milliamperage increased to thirty as added penetration and volume are needed. Development of Plates and Films The process of "development" of either plates or films may be briefly described as follows: At a con- venient time following the "exposure," the plate or plates (or films) are taken into the "darkroom." Such a room has all white light excluded from it, and is illu- minated only by a so-called "ruby light" or darkroom lantern. The darkroom should be supplied with a shelf or table about two and a half feet wide and three feet long placed at ordinary table height from the floor, so that the operator may sit upon a stool while at work. Upon this shelf there should be four trays, one for the "developing solution," one for the "fixing bath," and the other two for water. Where a darkroom is supplied 128 DENTAL AND ORAL RADIOGRAPHY with running water and a sink, only three trays are nec- essary. "With all light excluded from the room except the ruby light coming from the darkroom lantern, the plate (or film) is taken out of its envelope and immersed emulsion side up in the devoloping solution. In order to insure a uniform action by the developer, the tray should be fre- quently rocked with a gentle motion. If the plate (or film) has been properly exposed, development should be complete in about five minutes (although the time varies with different formulae). The plate or film is then removed from the developer and placed in a tray of water to thoroughly wash the developing solution from it. This, of course, requires but a moment, and it is then immersed in the ''fixing bath," keeping the emulsion side up. As soon as the plate has been in the fixing bath a few seconds, the dark- room door may be opened and light admitted without in- jurious effects. However, the plate (or film) must still remain in the fixing bath until it has "cleared" (until all milkiness is gone from the back of the plate), which will usually require from five to ten minutes. In fact, it is better to let it ''fix" for at least five minutes longer than is required for it to become clear. When the fixing process is complete, the plate must be placed in water and thoroughly washed to remove all the fixing solution from it. This can be accomplished by washing it in several changes of water, or better still, place it in a basin or tray of cold "running water" for ten or fifteen minutes. When the washing process is complete, the emulsion side of the plate or film should be gently rubbed with a clean piece of wet cotton, holding the plate (or film) under a cold water faucet during the act. The developed radiogram is then ready to dry. Plates should be stood DEVELOPMENT OF PLATES AND FILMS 129 on edge or placed in a suitable rack so that nothing will come in contact with the emulsion side, and left until perfectly dry. Films may be pinned to the edge of a shelf, or secured to a line with suitable clips. The drying process should take place in a room free from dust or soot, for these will prove injurious to the drying emulsion. The size of the trays used in the darkroom will depend upon the number of plates or films which are to be carried through the developing process at a time. For plates, the author uses trays 8x10 inches in size. With such trays two 5x7 plates can be carried through at a time. Where a large number of plates are being devel- oped, additional trays can be used and if necessary 'Hanks" capable of holding a dozen plates, utilized in the fixing or washing process. In developing "dental films, ' ' small trays will be found convenient, and unless a large number are to be developed at a time, a 4x5 or 5x7 tray will be large enough. Trays should be labeled according to the purpose for which they are to be used, and used for that purpose only. Tliat is, developing trays should be used, for the de- veloper only, and fixing trays, only for the fixing bath, if troublesome chemical reactions are to be avoided. Any one of several good formulas may be used in the developing and fixing process. The following has given satisfactory results in the hands of the author, and is easily prepared: Developer Water (distilled) - 20 oz. Metol 20 gr. Hydroquinone 80 gr. Sodium sulphite (dry) 1 oz. Sodium carbonate (dry) 1 oz. Potassium bromide 10 gr. 130 DENTAL AND ORAL RADIOGRAPHY Fixing Bath Solution A: Water (distilled) 30 oz. Hyposulphite of soda 1 lb. Solution B: Water (distilled) 15 oz. Chrome alum 1 oz. Sodium sulphite (dry) 2 oz. Solution C: Water (distilled) 5 oz. Sulphuric acid (C.P.) Vs oz. Add C to B (when cold) and the mixed solutions to A. If the best results are to be obtained in developing, the temperature of the solution should be kept between 65 and 75 F. If the temperature gets much over 75, the plate will develop too fast, while if the temperature goes much below 65, development will be retarded. It is a mistake to try to develop a large number of plates with the same mixture of developer, for after it has developed a half dozen plates, it will become weak and not give the best results. Therefore, do not hesitate to use plenty of fresh developer if you expect to get satis- factory results. The same rule applies to the fixing solution. It must be fresh and clean to give good results. Under proper tube and current conditions, and with correct length of exposure, a plate or film should require about five minutes for its development. To get the most out of a plate, it should be developed until fairly dense, that is, until it is about the same color on each side. If, after it has cleared in the fixing bath, it appears too dark or dense, you know that it has been overexposed. Therefore, in making subsequent expo- sures of similar patients and structures decrease the DEVELOPMENT OF PLATES AND FILMS 131 length of exposure. If, upon clearing, the image on the plate is faint and indistinct, you have reason to think it has been underexposed. Therefore, in subsequent ex- posures of similar cases increase the length of exposure. Plates or films which as the result of overexposure are too dark or dense for diagnostic purposes may be greatly improved by the use of "a reducing solution." Where the reducing process is to be employed the fixing bath solution should be removed from the plate or films by placing it in running water for several minutes. The reducing solution is then prepared as follows : Solution A : Distilled Water 1 quart Potassium Ferricianide 1 oz. Solution B: Distilled Water 1 quart Hypo Crystals 1 oz. Use equal parts of Solution A and Solution B. A sufficient amount of solution is placed in a tray to cover the plate or film and the process carefully watched until the desired density is obtained. It is unnecessary to carry out the process in the dark room as ordinary light does not hamper the reduction. When brought to the proper density the plate or film should be placed in running water for about thirty minutes. AVhile the reducing process can often times be em- ployed to advantage it is safe to say that plates and films so treated are not as highly satisfactory as those which are correctly exposed and correctly developed and therefore need no such treatment. Sometimes after development plates and films appear very thin and lacking in contrast. If this is the result of underdevelopment or the use of a weak or stale develop- 132 DENTAL AND ORAL RADIOGRAPHY ing solution their usefulness can be increased by the use of an intensifying solution. Such a solution may be made as follows : Solution A : Distilled water 16 oz. Bichloride of Mercury 120 grs. Potassium Bromide 120 grs. Solution B : Distilled water 16 oz. Sodium Sulphite (dry) 2 oz. The plate or film to be intensified is first well washed so that all the fixing bath solution is removed from it. It is then immersed in a suitable amount of solution A where it is allowed to remain until it becomes thoroughly bleached. AVhen this has been accomplished it is well washed with water and placed in solution B, a sufficient amount being used to cover it well. This will cause it to become cleared and darkened after which it is thor- oughly washed in cold running water, the entire process being permissible outside of the dark room. The intensifying process is most useful where the pa- tient is not available for additional exposures, but plates and films so treated cannot be regarded as being on a par with those where all the factors of correct exposure and development have been observed and therefore it should be regarded in the light of an emergency proceeding. By keeping the tube and current conditions right, the approximate length of exposure for any given case is usually easily determined by the operator, after a little experience. As stated before, this will depend upon the type of x-ray apparatus used, the thickness and density of the parts to be radiographed, and the age and struc- tural make up of the patient. CHAPTER X THE INTERPRETATION OF DENTAL AND ORAL RADIOGRAMS The ability to correctly interpret dental and oral ra- diograms is an accomplishment which every dentist should possess. In fact, it should be viewed, not only in the light of an accomplishment, but as a requisite of modern dentistry. Unfortunately, the assertion is not infrequently made by certain ill-informed members of the dental profession that only minor importance should be attached to the findings of the radiogram, their claim being that such images can be construed as shomng conditions which do not actually exist. Such an attitude can be explained as being the out- growth of several things, among which a lack of knowl- edge of the fundamental principles of radiography and its various branches, and especially of the science of in- terpretation, stands as an important factor. Therefore, opinions of the x-ray and its application in dentistry ex- pressed by those unqualified, should not be regarded seriously. The idea also seems to prevail among many poorly in- formed members of the dental profession as well as among medical men of the same type that the interpreta- tion of dental and oral radiograms is an extremely simple matter, requiring little if any preparation on the part of the one who is to make the interpretation. This erroneous idea is doubtless responsible for many errors being committed which naturally has the tendency to put this work in disrepute. Without doubt, many useful 133 134 DENTAL AND ORAL RADIOGRAPHY teeth have been needlessly sacrificed through sheer in- competence on the part of some diagnosticians. Hence, the importance of careful study and judgment in this particular phase of our work. The first requisite of interpretation is an accurate knoivledge of the anatomy and physiology of the struc- tures involved, for a radiogram is a shadoiu picture, and a shadoiu picture is meaningless unless one is thoroughly familiar with the main characteristics of the original. The radiogram may be said to vary from an ordinary shadow picture, as, in addition to mere outlines, varying densities are shown due to the fact that the x-ray pene- trates all matter in inverse ratio to its mass or density. If one is possessed of an accurate knowledge of the anatomy and physiology of the dental and oral struc- tures, the next step toward acquiring the ability to cor- rectly interpret radiograms of these structures, would be to become familiar with their radiographic appear- ance under normal conditions, for unless one be familiar with the appearance in the radiogram of the structures under normal conditions, it is obviously impossible to in- telligently recognize pathologic or anomalous conditions unless they be of a glaring nature. When we speak of the radiographic appearance of the structures under normal conditions, we refer, not only to a freedom from pathologic or anomalous involvement, but also to the character of the radiogram itself, which must be normal in that it must he made in accordance with a technic which results in the shadoivs of the structures under scrutiny being imposed upon the plate or film in their correct proportions. Therefore, it is essential that in addition to the before mentioned requisites, one ivho ivould intelligently inter- pret radiograms must understand enough of the funda- mental rules of radiographic technic to know ivhen IISrTERPRETATIOX OF RADIOGRAMS 135 examining a radiogram, whether or not the technic in- volved in its making was correct or faulty, and if faulty, ivhether or not the degree of fault is sufficient to render it so inaccurate as to he useless. In correctly made radiograms, the dental and oral structures under normal conditions have a characteristic appearance, for, owing to the varying densities of the contained structures in our field, they appear upon the plate or film in a manner most advantageous for obser- vation. For instance, it will be noted upon the examina- tion of such a radiogram, that metallic fillings, if they are present, appear as white masses, and root fillings as somewhat less dense lines. The enamel and dentin are next in density, while root canals show plainly as dark channels in the dentin, and the. alveolar process and max- illae show their fine uniform cancellous structures in vari- ous degrees of density, depending upon their thickness. In examining a radiogram, it is essential that the original plate or film only be used, and this should be examined carefully and in a proper light, if the maximum amount of information is to be obtained from it. This is best accomplished by utilizing some sort of illuminating box or cabinet from which varied degrees of light are obtainable. The face of such a cabinet should be covered with ground glass, so that the light transmitted will be equally distributed and free from shadows. As a radiogram is a transparenc}^, a dim light behind it will bring out one set of shadows to their greatest clearness. An increase in the light will show forth still other effects ; while a high degree of illumina- tion will bring out the more dense portions. In this manner each portion of the radiogram may be studied under a degree of light destined to bring out the maximum amount of detail. Now with a *' print" or ''lantern slide" one can study 136 DENTAL AND ORAL RADIOGRAPHY the field only from a one light aspect and oftentimes in order to secure any detail in the higher or less dense areas, it will be found that the dense areas must be printed almost to an inky blackness. This fact accounts for the unsatisfactory appearance of many radiograms used as illustrations in our journals and text books, for when reduced to halftone engravings, 7niicJi of their val- uable detail is lost. In examining intra-oral radiograms, it is an advan- tage to place them in a film mount which will hold them securely and render it unnecessary to vieAv them while being held between the fingers. Such a *' mount" should preferably be made of celluloid with one side clear and the other side dull, which allows the light transmitted to be of the same character as that coming through ground glass. If one be unfamiliar with the fundamental rules of ra- diographic technic, he cannot know, when examining a radiogram, just what portions of it are to be relied upon to give dependable information, for as a rule, owing to anatomic arrangement of the structures in our field, only limited areas can be relied upon to be "in focus" in each radiogram. But if one is possessed of an accurate knowledge of the anatomy and physiology of the parts involved, understands the fundamental rules of radio- graphic technic, and is familiar with the appearance in the radiogram of the dental and oral structures under normal conditions, it should hy no 7neans he difficult to see any alterations or changes ivhich occur in these struc- tures as a result of anomalous or pathologic conditions. The mere ability to note an alteration, or change, in the structures does not fulfill the requirements of intelli- gent interpretation, for these alterations, or changes, can have their full significance only to one who under- stands the pathologic conditions ivhich may develop in INTEKPRETATIOI^ OF RADIOGRAMS 137 these structures, and the character of the anatomic changes which they bring about. Therefore, it should be apparent that the ability to intelligently interpret ra- diograms is not a thing to be acquired overnight, but must come as the result of study in several important branches, and anyone who attempts it otherwise as- sumes responsibilities unworthily. The essential requirements of radiograms to be used as an aid in diagnosis may be briefly considered under two classes. In the first, we maj^ place those which may be useful in determining the presence or absence of grosser lesions or anomalies, such as fractures of the maxillae, impacted or unerupted teeth, large cysts or tumors, the presence of foreign bodies, etc. In the sec- ond class, would be included individual teeth and their investing tissues, the peridental membrane and alveolar bone. Both of these classes are important and essential if the x-ray is to render the maximum service. In either instance, a standardised and exact technic are essential. In the first class mentioned, viz., the grosser lesions or anomalies, extra-oral radiograms frequently prove highly advantageous for they render accessible areas and structures, the images of which may not always be satisfactorily impressed upon the smaller films. The diagnostician should therefore familiarize himself with the appearance of the structures as they appear in such radiograms under normal conditions for, owing to the fact of the difference of technic required, greater dis- tances of penetration of the raj^s, with the resultant dif- fering appearance of the finished product when com- pared to intra-oral radiograms, some confusion may occur. However, when one is really familiar with the ap- pearance of the grosser structures in such radiograms under normal conditions, the anomalous and pathological is not difficult to discern. 138 DENTAL AND ORAL RADIOGRAPHY In the second class, viz., where individual teeth or groups of teeth with their investing tissues are under examination, it is extremely important that not only the tooth (or teeth) be reproduced in the film, but that the peridental membrmie and alveolar hone surrounding the roots, both marginally and apically he shoivn to the hest advantage. When such a result is not accomplished, the radiogram cannot be considered a safe or suitable diag- nostic aid. One error which frequently proves a stumbling block for the young diagnostician is due to the fact that cer- tain types of lesions are supposed to have a more or less stereotyped appearance in radiograms and while this may be true of some of the grosser conditions, it still re- mains a fact that really dangerous and unhealthy condi- tions may exist which do not manifest themselves in any marked manner. In other words, it is essential that the most even degree of detail possible shall be obtained and that in the examination of the finished radiograms, care- ful study of them shall be made. This does not mean merely illuminating the radiogram for an instant but it means the carefid study of it under light conditions favoring the maximum detail. The normal alveolar process when correctly radio- graphed has a distinct appearance owing to its anatomi- cal structure and chemical composition. There is an irregularity of the cancellations and a harmonious blending of lights and darks in the picture. The irregu- larity of the cancellations, is due to the fact that the spaces which constitute spongy bone ai:e irregular in shape and size for spongy bone is made up of lamellae, which instead of being laid down in an orderly manner as in compact bone, are arranged in an irregular man- ner. These groups of lamellae form strands of bone tis- sue which unite, and in uniting, form irregular shaped INTERPEETATIOlSr OF RADIOGRAMS 139 cavities. For this reason, a picture of spongy bone when normal, shows white lines composed of thin and delicate strands of bone tissue enclosing dark areas, no two of which are exactly alike. So it may be definitely stated that the appearance of the normal alveolar process pre- sents an appearance of irregularly shaped minute cavities surrounded by fine delicate white strands of bone struc- ture. (Fig. 61.) It is a demonstrated fact that when the bone is sub- jected to injurious influences, the cancellations lose their clear-cut borders and become smaller and closer together. Therefore, whenever cancellated structure tends to be- come regular, ill-defined and homogeneous, the suspicion of pathological processes is entirely justified. As the presence of calcium salts in the bone tends to obstruct the passage of the rays, any increase or de- crease of this factor will become apparent upon the sensi- tive photographic emulsion, an increase being visible as an area of greater density, (a lighter area) while a de- crease of this element shows a lessened density or darker area. These radiographic changes are spoken of in the former instance as radiopaque areas and in the latter in- stance as radiolucent areas, terms which are quite de- scriptive and have found a permanent place in our nomenclature. In the study of radiograms therefore, a definite effort should be put forth to determine whether or not varia- tions from the normal have occurred, and if it can be definitely demonstrated that such is the case, the next prol)lem is to determine ivhy such changes should have occurred. While in numerous instances, the cause may be apparent in the radiogram, many others may be en- 140 DENTAL AND ORAIi RADIOGRAPHY countered where the cause is obscure or subject to ques- tion. This brings the diagnostician face to face with an Fig. 61-A. Intra-oral radiograms of groups of teeth and adjacent tissues under normal conditions. important factor very frequently overlooked, viz., the clinical findings. Kegardless of the value we place upon INTERPRETATION OF RADIOGRAMS 141 the x-ray, ^ye should never commit the error of failing to take into full consideration all circumstances connected Fig. 61-B. Intra-oral radiograms of groups of teeth and adjacent tissues under normal conditions. with the case under examination, including its history, conditions of dentition and occlusion, as well as the physi- cal state of the soft tissues of the mouth. 142 DENTAL AND ORAL RADIOGRAPHY Unfortunately, this has not always been done, or at least it has not been universally practised during that hysterical era just passed during which so many pulp- less teeth have been needlessly slaughtered. Fortunately Fig. 62. Instances where inflammatory processes have resulted in a hypertrophy of the peridental membrane and resultant encroachment upon the alveolar bony structures. In the instances shown, the clinica'i findings gave confirmation of the fact that these were chronic dento-alveolar abscesses. INTERPRETATION OF RADIOGRAMS 143 for our patients we are now entering upon a period of greater conservatism as a result of past experience and a more accurate knowledge of the subject which this ex- perience has brought. One eminent investigator* in this field has demon- strated a very important fact in regard to radiographic variations which the student should bear in mind, viz., that infection is not the only cause for radiographic vari- ations in films and that infection and inflammation are not necessarily synonymous. In radiographic variations, Fig. 63. Chronic dento-alveolar abscesses with cystic formation. such factors as hj-perocclusion, disuse, chemical influ- ences and pressure are likewise influences which must be considered possibilities in interpreting such changes. In judging the relationship of individual teeth to any suspected condition, two structures having a character- istic radiographic appearance should be carefully scru- tinized. These are the peridental membrane, showing as 1922 Dr. Joseph Pollia. The Journal of the National Dental Association, January, 144 DENTAL AND ORAL RADIOGRAPHY a fine black line, and the peridental lamella,* visible as a fine tvhite line A The characteristic appearance of these if Fig. 64. Three instances of true cysts occurring in the mandible. two structures is due in the former instance to the fact that the soft tissue of the membrane offers little resist- *Terms suggested by Dt. Joseph PoUia to be used instead of cribriform plate. tThe white line of demarcation which is intact around a normally disposed tooth was first called to the attention of the profession by Dr. Iceland Carter. (Interna- tional Journal of Orthodontia, July, 1917.) IlSrTERPRETATIOjSr OF RADIOGRAMS 145 ance to passage of the rays and therefore throws no radiopaque impression, while in the latter instance, the thin compact bone resists the passage of the rays and is visible as a thin radiopaque line. About a healthy tooth, these two structures shoiv no variation of thickness or contour. If a pathological process has its origin from within a tooth, the first structure to be subjected to its influence Fig. 65. Radiolucent areas adjacent to the roots of teeth which are characteristic of necrosis or rarefying osteitis. is the peridental membrane which naturally makes it the first structure to show abnormality. This is indi- cated by a thickening of the fine black line at the point of irritation. As the membrane is closely encased by the peridental lamella, its thickening or hypertrophy pushes out the peridental lamella, causing it to sag or lose its normal contour at the seat of the inflammatory process. If the inflammatory process is unchecked and continues 146 DENTAL AND ORAL RADIOGRAPHY to progress, the hypertrophy of the peridental membrane continues with a resultant encroachment upon the alveo- lar bony structures. (See Fig. 62.) With the changes in nutrition which accompany pro- gressive inflanmiatory processes, there is a resultant de- crease of calcium salts in the adjacent alveolar bone as ^S^^^^^V^ 1 ^^HkH^^^t Fig. 66. Radiopaque areas about the roots of teeth or in the alveolar bone indicating defensive bone reaction. well as a diminution of the bone units or lamellae which lessens the resistance usually offered by these structures to the passage of the rays. For this reason, the photo- graphic emulsion is more readily affected and the area is rendered more radiolucent than is characteristic of normal structure. While the changes described above INTERPRETATION^ OF RADIOGRAMS 147 are perhaps more frequently due to infection than to other causes, it is possible for them to be the result of other conditions such as trauma or hyperocclusion, pres- Fig. 67. Characteristic appearance of the investing tissues in well developed pyor- rhea alveolaris. sure, or chemical influences so that all clinical facts should be carefully weighed before coming to a definite conclusion. 148 DENTAL AND ORAL RADIOGRAPHY Cysts and tumors of the maxillae, owing to the char- acter of tissue changes which characterize their develop- ment are visible radiographically as radiolucent areas. Differentiation of the character of the lesion however is not to be judged by this feature alone but more by the extent of the area affected and the clinical findings. (Fig. 63.) It will be recalled that the true cyst differs from the cystic formation frequently accompanying chronic dento- alveolar abscesses in that it has an epithelial lining which definitely limits its extent although it usually attains considerable size, depending upon its character and cause. On the other hand, cystic formation accompany- ing chronic dento-alveolar abscesses are usually less ex- tensive as they result from the necrosis and liquefaction of the central portion of the inflammatory process due to lack of nutrition. In either event, such lesions are radiographically demonstrated as radiolucent areas, but their definite character must, as has already been em- phasized, be determined by their size and by such other clinical signs as may be indicative of their true character. (Figures 63 and 64.) Necrosis, Rarefying Osteitis, or Caries within the al- veolar bone or its supporting structures are manifest in the radiogram as radiolucent areas but differ in appear- ance from cysts or dento-alveolar abscesses in that there is a less distinct line of demarcation between the radio- lucent area and the surrounding tissue. In such in- stances, the borders of the radiolucent area show a grad- ual increased radiopacity until normal tissue is shown. | This fact is easily understood when we recall the pro- gressive character of these lesions and the character of tissue changes which accompany them. Thus far only those conditions which might be termed progressive inflammatory processes and which are ap parent as radiolucent areas have been discussed INTERPRETATION OF RADIOGRAMS 149 Another type of radiographic variation sometimes en- countered and which is apparent as an area of increased radiopacity is important. In such instances the reaction of the alveolar bone may be defensive in character re- sulting in an increase in the number of bone units and hence to an increased resistance to the passage of the Fig. 68. A cuspid tooth lying against the anterior wall of the antrum. rays. In this defensive process there is an increased deposition of lamellae which in some instances may ren- der the bone structure in the area affected very dense and compact in character. This condition which is doubtless due to a morbid increase of nutrition may as in the case of the progressive inflammations be due to infection, trauma or hyperocclusion, thermal shock, de- 150 DENTAL AND ORAL RADIOGRAPHY fensive reaction, or to such unknown influences as may produce such bone changes. In any event, such condi- tions when demonstrated require no small degree of study and judgment in correctly accounting for their existence. (Fig. 66.) Either of the above mentioned types of radiographic variations (i. e., the progressive or defensive) may be encountered in alveolar bone even after all the teeth have been removed especially so if one or more of the roots of Fig. 69. A radiogram to determine the state of dentition of the right side in the mouth of a child eleven years old. The developing second molars pre shown, likewise the upper second bicuspid and the lower first bicuspid about to erupt. It will be noted that the lower second deciduous molar has no successor, nor is there an upper first bicuspid present in the jaw. teeth previously held had been the source of an infectious process. If upon the removal of such teeth, the infected area is not eliminated either through natural means or through curettement, the condition may persist and if such is the case, may be demonstrated by properly made radiograms. INTERPRETATIOlSr OF RADIOGRAMS 151 Where a destructive process has ensued in the peri- dental membrane, or in the bony wall of the alveolus (pyorrhea pockets), the extent of the changes occurring may be quite definitely determined through a study of the structures first affected, viz., the peridental membrane (the fine black line) and the peridental lamella (the fine white line). In such instances, the progress of the lesion extends from the margin of the alveolus in an apical di- rection, hence its extent is not difficult to determine es- pecially if occurring upon the mesial or distal side of the tooth. (Fig. 67.) Visualizing the s:rosser lesions should offer little dilfi- Fig. 70. Fig. 71-A. Fig. 70. Root canal fillings in a lower first molar. Fig. 71-A. Root canal filling material forced beyond the root apex of an upper second bicusoid. culty for as a tooth is much more dense than the bony structures of the jaw or adjacent parts, any anomaly of form, size or position is easily discernible even though it occupy a position far from what might be expected, as for instance, in the case of impacted molars, teeth in the antrum, etc. (See Figure 68.) Likewise, and for the same reason, the presence in or absence from the jaws of successors of the deciduous teeth can easily be deter- mined, as well as the state of development of any un- erupted tooth. (Fig. 69.) Fractured roots or fractures of the bone even without ]52 DENTAL AND ORAL RADIOGRAPHY displacement are often discernible at the line of fracture, owing to the fact that the line of fracture offers less re- Fig. 71-B. Instances where the roots of teeth lie in close proximity to the antrum or accessory antral cells. Not infrequently, serious errors of diagnosis are made in such instances. sistance to the penetration of the rays, and therefore, is apparent upon the plate or film as a dark line. INTERPKETATIOlSr OF RADIOGRAMS 153 The different filling materials vary but little in relative gradation of density, and when used as root filling mate- rials, are plainly visible as light lines. Because they differ in density from cementum and dentin, the extent to which they have been introduced into the root canals is easily discernible. (See Figs. 70 and 71.) Broken off broaches and other instruments, or small wires intro- duced into root canals to determine their length or the extent to which they have been opened, because of their great density, appear very white and are easily differ- entiated from root canal fillings or tooth structure. In the study of radiograms of the alveolar bone, and their supporting bony structures, caution should be ex- ercised in the misinterpretation of such natural cavities as the antrii, nasal cavities, or nerve openings or canals such as the mental foramina, etc. Owing to their prox- imity to the roots of the teeth, the error is not infre- quently conmiitted of confusing them with radiolucent areas of pathological significance, an error which natu- rally proves disastrous to patients if operative measures are carried out. In seeking out the various anomalies and pathologic conditions to which the teeth and oral structures are subject, ive should not be misled by indefinite shadows in radiograms. The very nature of these structures, their gross, as well as minute anatomy renders them somewhat difficult to radiograph, and necessitates a refinement of technic greater than that demanded with most of the other portions of the human anatomy. Therefore, only radiograms made in accordance with a definite and exact- ing technic should be relied upon as diagnostic aids. If a doubt exists in any given instance, an additional or even several more exposures should be made, so that any conclusions reached tvill be founded upon definite evi- dence. CHAPTER XI INDICATIONS FOR THE USE OF THE X-RAY IN THE PRACTICE OF DENTISTRY Prior to the discovery of the x-ray and its adoption in dental practice, the diagnosis of many abnormal condi- tions in tlie alveolar process and in the maxilla or mandi- ble proper had to be accomplished, or at least attempted b}^ the dentist largely by relying upon his ''judgment" and "experience." As these excellent attributes are not infallible, the progessive members of the profession were quick to recognize in the x-ray, a veritable godsend, be- cause it rendered more positive and accurate than here- tofore, the diagnosis of many pathologic conditions. It has also aided just as materially in prognosis and treat- ment. In fact, so indispensable has it become that if the dentist attempts certain operations without its aid, he assumes unworthily his professional responsibilities. In enumerating the many instances where this agent should be used, the author will not attempt to give preference or importance to any particular field, or to classify the indications in the order of their frequency of occurrence, for this Avill depend largeh^ upon the character of practice enlisting the efforts of different men. "Wlien the need arises for its use, it should he iised whether the need arises in the practice of the or- thodontist, prosthedontist, oral surgeon, or general practitioner, etc., for the obligation is the same if the dentist expects to do his full duty by his patients. For Purposes of General Oral Examination Not infrequently the dentist is consulted by patients who are undergoing no discomfort or pain from their ld4 INDICATIONS FOR X-RAY IN DENTISTRY 155 teeth, but realizing their importance as etiologic factors of systemic disease, wish to undergo a thorough exami- nation. In many instances, such an examination will not be complete without a radiographic survey of the mouth. Especially is this true where such patients have pulpless teeth, or where large fillings, bridge work or crowns are present. Notwithstanding the fact that often the clinical history of such cases reveals nothing that will lead the dentist to believe that active septic foci have existed in such mouths, the radiographic examination should, nevertheless, be made, for in the light of our present knowledge, it must be concluded that these con- ditions frequently exist without subjective or objective symptoms. Such examinations are particularly important in the case of patients suffering from some systemic conditions, who are referred by a physician to determine whether or not the teeth are an etiologic factor. Where such an examination reveals no active septic foci, but shows the presence of one or several pulpless teeth with root canal fillings which do not measure up to the full requirements of such fillings, it is important that such teeth be resubjected to radiographic examina- tion at regular intervals to see whether or not they re- main in a healthy state. Radiographic Requirements. In order to do justice to such cases, extra-oral radiograms should be made of each side. These should show the upper and lower teeth and adjacent structures posterior to the cuspids. Intra- oral radiograms of the upper and lower incisors and cuspids should also be secured, and the whole series de- veloped and examined. (See Fig. 72.) Where the extra-oral radiograms show suspicious areas about the teeth which do not show with sufficient clearness to meet the demands of diagnosis, intra-oral 156 DENTAL AND ORAL RADIOGRAPHY radiograms may then be made of these areas, as a means of confirmation. (See Fig. 73.) Some operators prefer to use the intra-oral method entirely, in making a general examination, but this, in the author's opinion, is a mis- take, for the reason that all areas of pathologic impor- tance are not accessible to these small films. Fig. 72. Extra-oral radiogram of the right side made for purposes of general ex- amination. Suspicious areas are to be seen above the upper first bicuspid and about roots of the lower second molar. An unerupted upper third molar is also visible. To Determine the Seat of Pericemental Infections Not infrequently it is a difficult matter to determine the tooth responsible for a pericemental infection or an alveolar abscess, as the inflammatory process may be in progress in the region of several teeth, each of which may be under suspicion, or the infected area may be at a point remote from the suspected tooth. A radio- graphic examination will quickly settle all doubts, for the radiogram will reveal the source and determine whether INDICATIONS FOR X-RAY IN DENTISTRY 157 or not one or more teeth are involved. It will likewise show the extent to which the periapical tissues have be- come involved and will often shed valuable information on the prognosis of the case. (See Figs. 73, 74 and 75.) Fig, 73. Fig. 74. Fig. 73. Intra-oral radiogram used as a means of confirmation of the findings of the extra-oral radiogram. Fig. 74. Alveolar abscesses are shown to be present at the apex of each bicuspid root. Fig. 75. Fig. 'G. Fig. 75. Upper bicuspid teeth with abscesses. Fig. 76. Severe inflammatory process in progress about an upp-er lateral incisor. The root end shows a marked hypercementcsis. Radiographic Requirements. ^Intra-oral radiograms will usually suffice. Where the lower molars and bicus- pids are under examination, and the tissues under the tongue are very tender, the extra-oral method can be used to advantage, if the patient's comfort is a consideration. (See Fig. 77.) 158 DENTAL AND ORAL RADIOGRAPHY Root Canal Treatment Of the various dental operations, there is none that is more universally in need of further elucidation than the treatment and filling of root canals. As generally prac- ticed at the present time, this work can easily be termed the ''greatest shortcoming of dentistry." To those who recognize the uncertainty of results in this field, and the serious results which accompany failure to render sterile Fig. n. 15xtra-oral radiogram of the lower molars showing the presence of a large dento-alveolar abscess. and to completely fill root canals, the x-ray offers indis- pensable aid. Before considering the treatment of a tooth (or teeth), a radiogram should be made to show the topography of the roots to be treated. If these are proved to be ana- tomically within the range of treatment, an attempt may then be made to remove all organic material from the canals and to open them up to the very apical foramen. Fine diagnostic wires should then be inserted and car- ried to the end of the canal, or as far as the operator has INDICATIONS FOR X-RAY IN DENTISTRY 159 been able to introduce the broaches. After sealing them in with gutta percha, a second radiogram should be made. Because of their greater density, the wires will show distinctly in the radiogram and will enable the operator to determine to what extent the canal or canals have been opened. It will likewise determine whether any opening leading from the pulp chamber is a canal or a perforation. A. C. Fig. 78. A, two upper bicuspid teeth with inipcTfectly filled canals; B, the same teeth with the canals cleaned out and diagnostic wires in place; C, the same teeth after the root canals have been filled. When the canals are open to the end (as shown by the inserted wires) and the necessary treatment and sterilization has been completed, the root canal fillings can then be inserted. Another radiogram should then be made to determine whether or not the root fillings ex- tend to the apical foramina and seal the canals. If they do not, they should be removed and the before-men- 160 DENTAL AND ORAL RADIOGRAPHY B. Fig. 79. A, lower second bicuspid needing root canal treatment and filling; B, same tooth with canal cleaned out and diagnostic wire in place; C, same tooth with the root canal filled. c. Fig. 80. A, an upper first bicuspid needing root canal treatment and filling; B, canals have been cleaned out and diagnostic wires put in place; C, canals filled. INDICATIONS FOR X-RAY IN DENTISTRY 161 tioned operative and roentgenographic process repeated until success is obtained. Even when all precautions are taken and results seem eminently satisfactory, several radiograms should be made at regular intervals of from three to six months following the filling of the roots, to determine whether or not the operation has been successful, so far as the periapical tissues are concerned. This is especially im- '^W 1 1 C. D. Fig. 81. A, showing condition present; B, diagnostic wires inserted; C, root canals filled; D, resection of roots. portant where roots have been the seat of periapical in- fections prior to the time when treatment was inaugu- rated. (See P'igs. 78, 79 aiul 80.) Radiogfraphic Requirements. Intra-oral radiograms exclusively should be used for this work. An excep- tion might be made in the case of the lower molars and bicuspids, if the tissues under the tongue are sufficiently 162 DENTAL AND ORAL RADIOGRAPHY tender to make the placing of the films for exposure a hardship to the patient. Excellent extra-oral radio- grams of this area may be obtained, providing the opera- tor has the ability and constancy to master the neces- sary technic. Root Resection Where root resection is contemplated, the intelligent dentist should first obtain accurate radiograms of the A. Fig. 82. A, upper central incisor before resection; B, radiogram made immedi- ately following resection; C, radiogram made after several months, showing regen- eration of osseous tissue. roots under consideration. These aid him greatly, pri- marily in determining whether or not a resection is in- dicated, and if it is, it will give him a fairly concrete idea of the field of operation as well as the extent of the root to be resected; secondarily, in determining whether or INDICATIONS FOR X-RAY IN DENTISTRY 163 not the root canal has been sufficiently well filled so that the filling extends past the point where resection is to take place. Following root resection, a radiogram should be made as a matter of record and be used for purposes of com- parison as the process of healing progresses. Subse- quently, additional radiograms should be made every three months to determine whether or not the process of bone-regeneration is progressing in a satisfactory manner. (See Figs. 81, 82 and 83.) ^ ^^^" x^ i ''4 l0 Fig. 83. A, an upper central root before resection; B, the same root six weeks after resection, showing partial regeneration. Radiognraphic Requirements. Intra-oral radiograms should be used exclusively. In fact, the necessity for anything else could hardly arise, as root resection is usually confined to the anterior teeth. For Purposes of Examination and Diagnosis in Pyorrhea Alveolaris and Allied Diseases A radiographic examination of the teeth and their in- vesting structures is of great advantage in diagnosis and treatment. In the first place, accurately made radio- grams will often show the extent to which the destruc- tive process has progressed, especially if areas of ab- 164 DENTAL AND ORAL RADIOGRAPHY sorption and ** pockets" exist upon the mesial or distal aspects of teeth. Even where such areas are visible to the eye, the radiogram serves an important function in acquainting the patient with the true state of affairs, thereby securing the patient's cooperation in the treat- ment. (See Fig. 84.) When the destructive process is shoMH to be exten- sive about certain teeth, the operator can more safely Fig. 84. A well-developed case of pyorrhea alvcolaris involving the molars and in- cisors. (After Arthur H. Merritt.) judge whether or not the treatment of such teeth should be attempted or whether they should be extracted. Where suppuration is occurring at the gingival margin, the radiogram is often indispensable in helping to deter- mine (by showing the contents of the root canals) whether the adjacent teeth are vital, and if nonvital whether or not the suppuration is due to a chronic alveo- lar abscess. INDICATIONS FOR X-RAY IIST DENTISTRY 165 In cases of gingival irritation about crowned teeth or teeth carrying large fillings or inlays, a radiogram will reveal jagged or overhanging edges, the removal of which is so essential if the tissues are to be restored to health. Finally, the radiogram or a series of radiograms will be of value after active treatment has been completed, to determine whether or not the destructive process has been successfully checked. Radiographic Requirements. Intra-oral radiograms will suffice for such cases, as pockets seldom extend be- low the apical area of the roots. Such radiograms should be made in series, so that no area about the teeth is left unsurveyed. In Crown and Bridgework Where teeth are to be crowned individually, or as bridge abutments, the radiogram will give valuable in- formation, not only as to the length and shape of the roots, and the condition of the investing structures, but also as to that of the periapical tissues. Where the neces- sity for the devitalization of such teeth occurs, the op- erator can also judge by the shape and condition of the roots whether or not the prognosis for successful root treatment and filling is favorable. Where ** posts" are to be placed in the roots, their extent and direction can be noted, and where the ana- tomic peculiarities of such roots make them liable to perforation, precautions for avoiding such calamities may be taken. Where spaces are to be bridged, and the exact status of the area which is to lie beneath the bridge is not known, a radiogram should be made to be sure that un- erupted teeth or root fragments are not present. (See Figs. 85, 8(), and 87.) Radiographic Requirements. Intra-oral radiograms are indicated for this character of work. 166 DENTAL AND ORAL RADIOGRAPHY Reflexes of Obscure Origin Where painful reflexes occur about the face or head, and a clinical examination does not immediately deter- mine their possible origin, a radiographic examination of the teeth and their adjacent structures is indicated. Where such reflexes are the result of unerupted, im- pacted, or anomalous teeth, the presence of any of these Fig. 85. Fig. 86. i'ig. 85. An unerupted cuspid tooth making ?.n attempt to erupt under a bridge. The patient was twenty-eight years of age. Fig. 86. Radiogram made to be sure no root fragments were present in the tis- sues under the bridge. Fig. 87. Inflammatory process under a small bridge. An extensive pocket is shown upon the mesial aspect of the root of the bridge abutment. is quickly demonstrated. Likewise, if the reflexes are caused by an alveolar abscess, its presence can be thereby determined. Where pulp stones are producing the trouble, they can often be detected, if intense care is exercised in making the radiograms. If these reflexes are the result of ''hid- den caries," the radiogram will frequently suggest the INDICATIONS FOR X-RAY IN DENTISTRY 167 presence of such a condition, providing the cavities occur upon the mesio-or disto-approximal surfaces of the teeth, and are sufficiently extensive so that the density of the tooth structure in the region of the cavity is decreased, or the contour of the tooth is altered. Radiographic Requirements. Approximately the same plan of examination should be used as where a general radiographic examination of the mouth is made ; viz., extra-oral radiograms of each side with intra-oral radiograms of the anterior teeth. These can be further augmented with confirmatory intra-oral radiograms, if necessary. (See Figs. 72 and 73.) In Oral Surgery Perhaps the most frequent indication for the use of the x-ray in oral surgery occurs in cases in which the extraction of certain teeth is necessary. For instance, if one or more third molars are to be removed, a radio- gram of these teeth and their surrounding structures will acquaint the operator with any abnormalities of po- sition or formation, and will make it possible to proceed with the operation without unknown handicaps. Following the removal of teeth, a radiogram of the field of operation is often of value as a matter of record, to make sure that no root fragments or bone fragments are left remaining. Where necrotic areas are to be curetted, a radiogram not only aids greatly in confirming the diagnosis, but gives the operator a more comprehensive idea of the extent to which the curettement must be carried out. As a postoperative precaution, the radiogram is also fre- quently of value, especially where the process of healing does not progress in a manner satisfactory to the pa- tient or operator. Such postoperative radiograms are 168 DENTAL AND ORAL RADIOGRAPHY Fig. 8S-A. Fig. 88-B. Fig. 88-A. and B. F,xtra-oral radiograms of impacted and unerupted third molars. INDICATIONS FOR X-RAY IN DENTISTRY 169 particularly advantageous where patients move from one locality to another, and, therefore, must change surgeons. In handling fractures of the mandible, the x-ray is seldom necessary for purposes of diagnosis, but it can often be used to advantage, and in some instances, is quite indispensable. As a postoperative precaution it should be used so that no doubt may arise as to the proper placement of the fractured parts. Where fractures of the maxilla occur, a radiogram may be of value as a means of confirming the clinical diag- nosis. Where cysts or tumors are suspected, the radiogram will confirm the clinical findings, and comprehensively I'ig. ?. Intra-oral radiograms of impacted lower third molars. Such radiograms are not as satisfactory as those made by the method shown in Fig. 95. outline the field of operation. Following operations for the relief of those conditions, radiograms should be made at frequent intervals to determine whether or not the process of healing is progressing satisfactorily. In gunshot wounds about the face or mouth, properly made radiograms will localize the bullets or shot, and thereby aid in their removal, as well as in determining the extent of injury to the osseous structures. Where drills, hypodermic needles or other instruments are broken off and left remaining in the tissues, they may be easily located by correctly made radiograms, and their removal rendered more certain. 170 DENTAL AND ORAL RADIOGRAPHY Fig. 90-/4. Ivarge cyst in the mandible lying below a molar tooth. Fig. 90-S. Same case six months after curettemer.t, showing partial regeneration of the osseous structure. INDICATIONS FOR X-RAY IN DENTISTRY 171 Radio^aphic Requirements. Both the extra-oral and intra-oral radiograms are indicated in this field. For impacted third molars, the extra-oral method is best, as it will clearly show not only the third molar, but its re- lationship to all other adjacent structures. In the case of single-rooted teeth, such as incisors, cuspids, etc., where hypercementosis is suspected, the intra-oral method will prove adequate. (See Figs. 88, 89 and 90.) Where a curettement is to be carried out, intra-oral radiograms will prove sufficient, provided the field is not largo. (Fig. 91.) Fig. 91. lyarge abscess v/ith cyst formation involving the upper central, lateral and cuspid roots. In fractures of the mandible, the extra-oral method should always be used, so that the entire field in the re- gion of the fracture can be visualized. For fractures of the maxilla, intra-oral radiograms will usually suffice. In the Practice of Orthodontia The necessity for using the x-ray in orthodontic prac- tice varies with different patients, but, generally speak- ing, may be summarized under ten different headings as follows : 1. As a means of determining the presence or ah- 172 DENTAL AND ORAL RADIOGRAPHY Fig. 92. This radiogram reveals the fact that there is a congenital absence of per manent molars on the left side. Fig. 93. This radiogram reveals the fact that all but one of the permanent molars are congenitally absent on the right side. INDICATIONS FOR X-RAY IN DENTISTRY 173 sence of unerupted permanent teeth before treatment is undertaken. The majority of patients requiring orthodontic treat- ment usually have a mixed dentition ; viz., the deciduous molars and cuspids are usually present. It is essential, therefore, to determine whether or not these deciduous teeth have their permanent successors. If the upper and lower incisors have erupted, information concerning the other permanent teeth is easily obtained by making a radiogram of each side by the extra-oral method. Such radiograms are shown in Figs. 92 and 93. Such radiograms give the operator a very adequate survey of these unerupted teeth, and leave no doubt as to their presence or absence. 2. As a means of determining the approximate size of unerupted teeth, for ivhich space must he made in the arches. Where the deciduous molars or cuspids have been shed prematurely, with the usual resultant loss of space in the arch, the radiogram can be made to show quite accurately the amount of space which it will be necessary to pre- pare for the unerupted teeth. (See Figs. 94, 95 and 96.) 3. To determine the state of development of unerupted teeth ivhich are tardy in their eruption. Not infrequently permanent teeth fail to erupt when expected. By utilizing the radiogram, their state of de- velopment is easily determined, and often the cause for their noneruption is determined. Steps can then be taken to open up spaces and to hold them until such a time as the teeth involved progress in their development to the point of eruption. (See Fig. 97.) 4. To determine the approximate direction in ivhich teeth are erupting and the relationship which they will hear to the line of occlusion when erupted. 174 DENTAL AND ORAL RADIOGRAPHY Fig. 94. Unerupted lower second bicuspid for which space must be made to permit its eruption. Fig. 95. Unerupted cuspid for which space must be made if it is to ertipt in its normal position. INDICATIONS FOR X-RAY IN DENTISTRY 175 Fig. 96. Unerupted lower lateral incisor for which space must be made. Fig. 97. Unerupted lower second molar prevented from erupting through impaction against the lower first molar. 176 DENTAL AND ORAL RADIOGRAPHY Where the deciduous teeth have been retained in the mouth longer than the normal time and where the roots of these teeth have not been entirely absorbed, the erupt- ing permanent teeth will sometimes be deflected from their normal course. It is an advantage to know the di- rection in which they are deflected, so that if retaining appliances are to be placed, they may be arranged in I''ig. 98. Unerupted upper bicuspid teeth which are being deflected to the lingual. A. \ B. Fig. 99. Unerupted bicuspid teeth which are rotated and erupting to the lingual. such a way and in such a relationship to the erupting teeth that they will not interfere with them. In fact, it is sometimes possible to construct the retainer in such a way that the tooth which is deflected from its course may be guided towards its normal position or moved there before the inclined planes of the opposing teeth be- come a factor in establishing it entirely out of its normal position. (See Figs. 98 and 99.) INDICATIOlSrS FOR X-RAY IN DENTISTRY 177 Fig. 100. A, unerupted cuspid; B, same tooth after the removal of the lateral incisor and the deciduous cuspid showing the attachment for moving the unerupted tooth; C, cuspid tooth moved down to the point of eruption. A. B. Fig. 101. A, two supernumerary incisors are present with the normal central lying above them; B, the same case after the extraction of the supernumerary teeth. An attachment has been made to the central preparatory to moving it down into place. The patient was fourteen years of age. 178 DENTAL AND ORAL RADIOGRAPHY 5. As a guide where it is necessary to make attach- ments to unerupted teeth, to aid in their eruption. "While it is not often necessary to secure attachments to teeth lying beneath the gingival tissues, the occasion for this sometimes arises, as shown in Figs. 100 and 101. In such cases, radiograms should be made as a guide in securing the attachment. After the attachment is se- cured, others should be made to determine the direction in which force should be applied to accomplish the desired tooth movement. 6. To determine the most opportune time for the ex- traction of the deciduous teeth. Where the deciduous tooth persists in the mouth, and shows no sign of being shed, it is an advantage to deter- mine the extent of absorption of the roots, as well as the development of its successor, so that if extraction is re- sorted to, it can be done with the knowledge that the de- veloping tooth will not be disturbed or injured, and that the successor has reached a degree of development which will insure its eruption within a reasonable time. (See Figs. 102 and 103.) 7. To observe the movement of the roots of teeth and their relationship to other roots and structures. In the bodily movement of teeth, and particularly of the incisors, it is important in young subjects that these roots do not encroach upon each other or upon other teeth; for instance, an unerupted cuspid. It is there- fore, advisable, where any doubt exists, to determine the exact status of this relationship. (See Fig. 104, A, B, C.) 8. To determine the relationship of developing third molars to certain recurrent malocclusions, and also as a precaution so that steps may he taken to prevent these teeth from becoming a cause of malocclusion during their eruption. The pressure exerted by developing lower third molars INDICATIOlSrS FOR X-RAY IN" DENTISTRY 179 Fig. 102. An unerupted lower second bicuspid in a patient twelve years old. Fig. 103. Unerupted ui)per and lower bicuspids in a patient eleven years of age. 180 DENTAL AND ORAL RADIOGRAPHY is often sufficiently great to cause a crowding of the lower incisors and cuspids. (See Figs. 105 and 106.) This can be true, even though malocclusion has not existed in this region previous to the development of the third molars. By making radiograms from time to time of patients at the age of the eruption of these teeth, the status of the developing teeth can be determined and the I'ig. 104. Unerupted cuspid teeth whose relationship to the roots of the incisors must be taken into consideration during tooth movement. necessary precautions taken to prevent the crowding of the incisors and cuspids. 9. To observe nonvital teeth prior to tooth movement, to determine their fitness for movement or anchorage, and their state of health during the process of ortho- dontic treatment. INDICATIONS POR X-RAY IN DENTISTRY 181 Fig. 105. All unerupted lower third molar which is crowding the incisors. Bf m \ ^^^^^B' -'"^''ini [? * I |_ <. :J^J*- 'A,^rL^M i Fig. 106. An erupting lower third molar which has been responsible for the crowding of the lower incisors and cuspids. 182 DENTAL AND ORAL RADIOGRAPHY Where it is necessary to either move nonvital teeth, or utilize them as anchorage, it is essential to the patient's welfare and comfort to know that snch teeth and their investing tissues are in a healthy condition. By determin- ing this prior to instituting orthodontic treatment, much trouble, both to the patient and operator, can often be avoided. (See Fig. 107.) 10. In cases ivhere anomalous teeth are present, to dif- ferentiate hetiveen anomalous and normal teeth. In a majority of instances, this can be done without the aid of the radiogram, unless the teeth in question have failed to erupt. Under such conditions, by utilizing ac- curacy in the technic of making the radiograms, little dif- ficulty is encountered in determining the difference be- tween normal and anomalous teeth. Examples are shown in Figs. 108, 109 and 110. Radiographic Requirements. Owing to the fact that patients undergoing orthodontic treatment are usually children whose ages necessitate their being handled with tact and gentleness, if confidence is to be maintained, precaution should be taken to rid every operation of fear or discomfort. Especially is this essential in mak- ing radiograms, for any considerable degree of move- ment on the part of a patient will either curtail the value of the finished radiogram, or render it useless. In selecting a method of procedure for making radio- grams of children, the child's comfort must be taken into consideration, and with this idea in mind, the author has found it an advantage to use the extra-oral method quite universally. In fact, he has used it in nearly all cases except where the region embracing the upper anterior teeth is under scrutiny. The wisdom of this course will be apparent to anyone who has experi- enced the discomfort of having intra-oral films placed lingually to the lower teeth, where the tissues are very IISTDICATIONS FOR X-RAY IN DENTISTRY 183 Fig. 107. A, nonvital tooth being used as an anchor tooth; B, nonvital tooth which was not considered safe for anchorage. Fig. 108. Fig. 109. Fig. 108. Supernumerary upper second bicuspid. Upon the extraction of the supernumerary, the normal tooth erupted. Fig. 109. Lower deciduous central incisors having the appearance of supernu- merary teeth. The radiogram leaves no doubt as to their identity, and also shows that these teeth have no permanent successors. Fig. 110. Fig. 110. Radiogram showing either an anomalous central incisor or a central incisor lying in a horizontal position to the other teeth. The patient was sixteen years of age. 184 DENTAL AND ORAL RADIOGRAPHY Fig. 111. The patient is seated and the apparatus arranged to make a radiogram of the left side. Fig. 99 shows the extent of radiograms made by using this technic. Fig. 112. The patient is seated and the apparatus is arranged to make a radiogram of the right side. Fig. 100 shows the extent of radiograms made by using this technic. INDICATIONS FOR X-RAY IN DENTISTRY 185 sensitive, or has had them placed posteriorly in the molar region, against the palate, where they so fre- quently induce gagging. These unpleasant features are all eliminated by using the extra-oral method, and good radiograms of the structures can be secured on the larger plates. (See Figs. Ill and 112.) This statement should not be construed as a protest against the use of intra-oral films in dental radiography, for it is very often necessary to use such films with adult patients where a high degree of detail is essential, in determin- ing the condition about nonvital teeth, root canal fillings, etc. In orthodontic practice, however, where we are dealing with young subjects entirely, a sufficient degree of detail can be obtained in the majority of instances to satisfy the needs of the operator, by using the extra-oral method. CHAPTER XII DANGERS OF THE X-RAY AND METHODS OF PROTECTION Almost invariably when any phase of x-ray work is discussed, some one raises the query as to the dangers connected with it and the injuries resulting from its use. In fact, the impression is still quite broadcast among the laity, and to a degree among the profession, that the x-ray is a dangerous agent and as such should only be employed in cases of dire emergency. This impression, erroneous as we know it to be for the most part, gained credence as a result of the first few years' use of the x-ray, during which period its dangers were not suspected nor the laws governing its use well understood. During this period a sufficient number of patients and operators were injured so that, notwithstanding the fact that with our present knowl- edge of the subject and with the marked improvement in x-ray apparatus these accidents are no longer neces- sary, the early impression still prevails to a certain extent. In order that we may not underestimate the dangers of this valuable agent and consider lightly our responsi- bility in using it, we will now consider the character of injuries possible through its misuse. We should bear in mind the fact that the x-ray in medicine serves a double purpose. It is used as a diag- nostic agent; that is, in making radiograms and fluoro- scopic examinations, and as a therapeutic agent. In the latter capacity patients are subjected to repeated ex- posures, the length of which are very far in excess of 186 X-RAY DANGERS METHODS OF PROTECTION" 187 that required in making radiograms. In fact the length of exposure in one average x-ray therapy treatment will more than out-total the necessary exposures to radio- graph a half dozen patients for diagnostic purposes. Therefore, the responsibility of the x-ray therapist, and the danger connected with his work are far in excess of the man who limits his activities with x-ray to radiog- raphy alone. Of the various ill effects attributed to the x-ray, the so-called "x-ray burn" or dermatitis is the most com- mon. This injury occurs in various degrees of severity, depending upon the amount of overexposure to which the one afflicted has been subjected, and is designated as "acute" and "chronic." Acute X-ray Dermatitis Acute x-ray dermatitis in its simplest form manifests itself in somewhat the same way as ordinary sunburn. There is a slight pinkish erythema, dry in character, accompanied oftentimes by the sensation of tingling or burning. If x-ray exposures are continued, this condi- tion is augmented by the appearance of vesicles and the affected surface becomes moist or "weeping," and the patient has similar sensations as those produced by any blistering burn. If exposures to the ray be discontinued at this stage, the affected area will slowly clear up with no permanent ill effect except perhaps a slight pig- mentation. If the exposures be continued, the next degree of der- matitis will ensue. The affected area becomes an angry red in appearance, congestion is intense, and the surface is covered with a yellowish white necrotic membrane, which is epithelial in character. In fact, up to this point the connective tissue is not affected except for more or less swelling. This degree of dermatitis is exceedingly 188 DENTAL AND ORAL RADIOGRAPHY slow in healing, months being required for the necrotic membrane to disappear, and when this has occurred it is followed by a horny epidermis which appears in spots over the area affected, eventually covering it. This new skin while smooth and natural looking is usually char- acterized by the absence of all hairs and follicles. The most severe form of acute x-ray dermatitis is char- acterized by somewhat the same symptoms as those just described, except that they are greatly exaggerated. The degree of congestion is very great, the necrotic membrane extends deeper into the tissue, necessitating the surgical removal of masses of dead tissue to prevent gangrene. This sloughing or necrotic area shows a strong tendency to spread and according to some authors, is apt to become malignant. With such a der- matitis patients often suffer very intense pain. Inju- ries of this degree of intensity are exceedingly slow in healing, a number of years sometimes being necessary for the process of reconstruction. Even after it occurs, the skin is not natural in appearance, but hard and horny and covered in places with scar tissue. Chronic X-ray Dermatitis After a person has been exposed to the x-ray a great many times covering a period of perhaps months or years, and has had one or more "burns" which were not allowed to heal before new effects were added by additional exposures, the dermatitis which results be- comes "chronic." This chronic x-ray dermatitis is con- fined almost entirely to x-ray operators and others con- stantly associated with the x-ray. The hands because of their exposed position are most often the seat of this affection. The skin becomes thin and atrophic with red patches of a vascular nature, and there is usually an entire absence of all follicles and hair. Codman describes X-RAY DANGERS METHODS OF PROTECTION 189 this condition as follows: ''In the less pronounced forms the skin appears chapped and roughened, and the normal markings are destroyed ; at the knuckles the folds of skin are swollen and stiff, while between there is a peculiar dotting resembling small capillary hemorrhages. The nutrition of the nails is affected so that the longi- tudinal striations become marked and the substance be- comes brittle. If the process is more severe, there is a formation of blebs, exfoliation of epidermis, and loss of nails. In the w^orst form the skin is entirely destroyed in places, the nails do not reappear and the tendons and joints are damaged." Another author states that "while the condition in chronic forms of x-ray irritation is as a whole atrophic, there is usually a peculiar tendency to hyperkeratosis, which shows itself in increased horniness of the epi- dermis about the knuckles and in the formation of kera- totic patches. In some cases this is very marked, so that the affected parts, usually the backs of the hands, have scattered over them many keratoses with or without in- flamed bases. The appearance is very similar to that seen in senile keratosis where the patches are inflamed and have a tendency to epitheliomatous degeneration. The development of epitheliomas in these patches of x- ray keratosis has within the last few years been well established." Carcinoma may also have its origin from the same source, in fact many x-ray operators who have failed to take the proper precautions have been subject to this dreaded malady, the hands being the parts most often affected. Other 111 Effects In addition to the before described injuries, there are still other ill effects attributed to the x-ray, such as loss of hair, sterility, and certain systemic effects. The loss 190 DENTAL AND ORAL RADIOGRAPHY of hair due to x-ray exposure is not to be regarded seri- ously, unless it is associated with a dermatitis of suffi- cient severity to destroy the hair follicles, for unless this complication is present, the hair comes back within five or six weeks. The x-ray has a deleterious effect upon developing em- bryonic cells and can therefore be the cause of sterility in the male by destroying the spermatozoa, and in the female by the destruction of the primordial ovules. This condition is brought about by continued exposures, and x-ray operators are the ones usually affected. It is not accompanied by impotence, is temporary in duration, and can be avoided entirely by adopting protective measures. Regarding the so-called injurious systemic effects pro- duced by the x-ray, too little evidence of a convincing character has yet been presented to really fasten the blame upon the x-ray for conditions other than those before enumerated. Therefore, until its guilt is scien- tifically substantiated, we must not indict it for condi- tions which may be but coincident with its use. Methods of Protection The evil effects of the x-ray can be entirely avoided by utilizing the protective measures afforded in modern x- ray apparatus. Inasmuch as lead is impervious to the rays, it can be used in different forms and in various pieces of apparatus in such a way as to control or con- fine the rays according to the will of the operator. Tube Shield The most essential piece of protective apparatus is the tube shield (Fig. 113). This is constructed of lead glass, there being a sufficient amount of lead salts incor- porated in the glass to prevent ordinary rays from pass- X-RAY DANGERS METHODS OF PROTECTION" 191 ing through it. The sides extend up over the highest part of the tube and the opening at the top is often cov- ered with a rubber cap, in which lead is also incorporated. At the bottom directly opposite the target of the tube an opening of the proper size is left to allow the desired ra^^s to pass out. The size of this opening may be con- trolled by interchangeable diaphragms of various sizes, which are constructed of sheet lead about one-sixteenth of an inch in thickness. Fig. 113. An x-ray tube inclosed within a leaded glass tube shield. This apparatus is usually augmented by a compres- sion cylinder, which is attached to the base of the tube shield, against or in contact with the lead diaphragm. Such a cylinder is usually constructed of aluminum with a lead lining, is made in various lengths and diameters according to the character of the work for which it is to be used, and serves the purpose of confining the rays coming through the diaphragm from the target of the tube. 192 DENTAL AND ORAL RADIOGRAPHY These pieces of apparatus are usually integral parts of the modern tube stand, sold by all reliable manufac- turers of x-ray apparatus. It should be apparent to anyone that with such apparatus, the only rays which leave the area of the tube are those which pass through Fig. 114. lycad-Iined protection screen. the diaphragm and cylinder and are used upon the pa- tient. In radiographic work these do not injure the patient, as the exposures are too short to produce ill effects, even if numerous exposures are necessary. On the other hand the radiographer who fails to use X-RAY DANGERS METHODS OF PROTECTION 193 these protective measures, or who carelessly places him- self in the direct path of the rays will in time through the accumulative effect of the x-ray be very apt to reap as a result of his folly some of the dread injuries before described. Other Means of Protection In addition to the protective measures thus far de- scribed, there are other means that afford additional pro- tection, and if a person is working constantly with the x-ray these should be used. Among these is the leaded screen behind which the operator stands during the time exposures are made (Fig. 114). Such a screen is usually Fig. 1 15. r.tacl-iinpregnaled glove. placed in front of the controlling apparatus and has a leaded glass window, so that the operator can watch the patient during the exposure. Lead-impregnated gloves (Fig. 115) and aprons (Fig. 116) are also used by some as a precaution, but such extreme measures are not nec- essary for the dentist doing his own radiography. "With a properly constructed leaded glass tube shield, lead diaphragm, and lead-lined cylinder the operator is safe, provided he takes the precaution of avoiding the direct rays. "We all realize that many very useful agents in medi- cine and surgery are dangerous when used carelessly, indiscriminately, or may we say igiiorantly. The old say- 194 DENTAL AND ORAL RADIOGRAPHY ing that * ' fools rush in where angels fear to tread, ' ' per- haps applies with greater significance in many branches of medicine than we would care to admit. But the fact that through the misuse of dangerous agents, many- patients have met death, or have been subjected to need- less suffering, is no argument against their use when Fig. 116. X-ray protection apron. placed in competent hands. In such hands the x-ray stands today as one of the greatest adjuncts to the mod ern art of healing, a blessing to humanity, even if in its early history it left its martyrs here and there ; its bene- fits and triumphs far out-balance any evils connected with its use. INDEX A Alternating current, 32 Alveolar abscesses, 142, 143 Ampere, 33 Anode, 27 Anomalous teeth, 151, 182 Arrangement of aj^paratus, 73, 96 B Broken-off broaches, 153 C Cathode, 27 Cathode rays, 28, 29 Coil, 38, 39 primary, 44, 45 secondary, 44, 45 Compression cylinder, 72 Compression cylinder, special, 85 Compression diaphragm, 72 Coolidge tube, 68, 116 Crookes, Sir William, 27 Crookes' tubes, 28 Crown and bridgework, 165 Current conditions for radiography, 110 Cysts and tumors, 143, 144 D Dangers of the x-ray, 186 Darkroom, 75 portable, 75 Developer for plates and films, 129 Development of plates and films, 127 Drying plates and films, 129 Electric currents, 32 alternating, 32 Electric currents Cont 'd. amperage, 33 direct, 32 high tension, 32 voltage, 32 wattage, 33 Electrolytic interrupter, 48 Electromagnetic induction, 40 Electromagnets, 39 Electromotive force, 32 Electrons, 23 Extra-oral radiograms, 93 Faraday, Michael, 26 Filling materials, appearance of, 153 Film holders, 87 Films, x-ray, 125 film chest, 124 preparation for exposure, 123 Fluorescence, 27 Fractures, 151 Gcissler, 27 G H Hertz, Heinrich, 28 High frequency coils, 52 diagrams of, 53 Hittorf, 27 Hydrogen tube, 67 Illuminating cabinets, 135 Impacted teeth, 168 Induced currents, 39, 40 Induction coils, 44 diagram of, 45, 49 195 196 INDEX Induction eoils Cont 'cl. essential parts of, 44 illustrations of, 50 Interpretation of radiograms, 133 Interrupterless transformer, 54 illustrated, 55 Interrupters, 47 electrolytic, 47 mechanical, 47 Intraoral radiograms, 81, 82 L Lead apron, 194 Lead compression diaphragm, 72-191 Lead gloves, 193 Lead screen, 192 Leaded glass tube shield, 72, 191 Lead-lined compression cylinder, 71 Lines of force, magnetic, 37 Low vacuum tuljcs, 113 M Magnet, electro, 38 poles of, 36 Magnetic effect of electric current, 38 Magnetic field, 36 Magnetic force, lines of, 37 Magnetic induction, 37 Magnetism, 35 Milliamperemeter, 112 Missing teeth, 171 N Nature of the x-ray, 23, 31 Necrosis, 148 O Ohm, defined, 33 Ohm 's law, 34 Oral examination, 154 Oral surgery, 167 Orthodontia, 171 radiographic requirements in, 182 Pathoradiography, 21 Penetration of x-rays, 113 Pericemental infection, 156 Photographic darkroom, 75 Plate chest, 124 Plates, x-ray, 123 care of, 124 development of, 127 drying, 128 preparation of, 124 Portable darkroom, 75 I'ower rating of coils, 51 Primary coil, 44 Protection from x-rays, 190 Pyorrhea pockets, 151, 163 B Radiogram, 21, 77 examination of, 138 extra-oral, 93 interpretation of, 133 intra-oral, 80, 81 proper tube and current condi- tions for, 113, 114 rules for making, 82 Radiographic examination, complete, 108 Rectifier, chemical, 51 Rhumkorfi; coil, 44 Roentgen, William Conrad, 25 Roentgenogram, 21 Roentgenograph, 21 Roentgenology, 21 Root canal treatment, 158 Root resection, 162 Rotary converter, 54 S Secondary coil, 44 Self-induction, 43 Solenoid, 38 Spark gap, 51 Technic of radiography, 77, 93, 110 correct and incorrect, diagram of 82 INDEX 197 Tcriiiiiiology, 20 Tesla coils, 52 Transformers, iiiterruptcrless, 54 Tube, connection to x-ray machine, 63 inverse in, 116 regulation of, 114 Tube conditions for radiograms, IK) Tube shield, 72 Tube stand, 69 with platerest, 98 Tubes, low, medium, and high, 113 U Unerupted teeth, 173 Unit of electromotive force, 32 current strength, 33 resistance, 33 V A-'acuum of tube, how to determine, 111 relative merits of low, medium, and high, 113 Vacuum tubes, 63, 110 Volt, 32 Voltage, 32 W Watt, 33 Wattage, 33 X X-ray, dangers of, 1S6 defined, 24 dermatitis, acute, 187 chronic, 188 discovery of, 25 effect upon photographic plates, 31 machines, 44 nature of, 23, 31 penetration of, 30 production of, 24 protection from, 190 tube, 61 connected to the coil of trans- former, 63 essential parts, 61 types of, 61, 65, 60, 67, 68 vacuum of, 61 \ UNIVERSITY OF CALIFORNIA LIBRARY Los Angeles This book is DUE on the last date stamped below. 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