*.i:< , .(U\;i;i;^;;>;..;/; l ' (l ;: < ,;,v. u y 4 ;,»;';-:; ' .'• • •'■X '■.'■:'. : x .' ■ Class, WV\ Book _ GopyrightN°_ COPYRIGHT DEPOSIT. PRINCIPLES AND PRACTICE OF Operative Dentistry BY JOHN SAYRE MARSHALL, M.D. (Syr. Univ. DENTAL SURGEON UNITED STATES ARMY PRESIDENT ARMY EXAMINING BOARD FOR DENTAL SURGEONS PHILADELPHIA AND LONDON J. B. LIPPINCOTT COMPANY 1901 1 (TO I av THE LIBRARY OF CONGRESS, Two Cowea Received OCT. 8 1901 Copyright entry CLASS O-XXc No. 9997 COPY J. Copyright, 1 901 BY J. B. Lippincott Company ' LEC 1 UNTYPED AND PRINTED LIPPINCOTT COMPAN PHILADELPHIA, Zo tbe flUemon? of m^ more tban tfrienD THE LATE DR. JAMES W. WHITE EDITOK OF THE DENTAL COSMOS WHO THROUGH THE NOBLENESS OF HIS CHARACTER BECAME THE INSPIRATION OF EVERY YOUNG MAN WHO CAME WITHIN THE SPHERE OF HIS INFLUENCE THIS VOLUME IS AFFECTIONATELY DEDICATED BY THE AUTHOR PREFACE. In the preparation of this volume the author has kept in mind the needs both of students and of practitioners of dental surgery. It has been his endeavor so to present the subject-matter as to give the student a comprehensive view of the principles and practice of operative dentistry, arranged in a natural and orderly sequence. This plan has also been carried out in the presentation of each individual topic, in the hope that the student will thereby be helped in his understanding of the various phases of each department of the subject and likewise taught to be me- thodical in his studies and operations. It is also hoped that the dental practitioner will find in the work material which will assist him in his investigations of those pathologic conditions of the teeth and their con- tiguous parts, and the surgical methods employed in their treatment, that occupy so large a part of his time, energy, and skill. The methods of constructing artificial crowns and bridge- work have not been included in this volume, because in the opinion of the author they properly belong to the department of prosthetic dentistry. The subject of orthodontia has also been excluded, for the reason that this branch has assumed the proportions of a separate specialty, and would therefore occupy more space than could be given to it in a work of this size and character. The author desires to acknowledge his great indebtedness to his friend Dr. Vida A. Latham, of Chicago, for her valuable services in the prepara- tion of numerous original and interesting photomicrographs of normal and pathologic dental tissues and of bacteriologic specimens ; also to his friends Dr. E. E. Andrews, of Cambridge, Massachusetts, and Mr. James S. Shearer, of Bay City, Michigan, for the use of a number of original photo- micrographs from their valuable collections ; to Dr. W. D. Miller, of Berlin, Germany ; to Dr. J. Leon Williams, of London, England ; to Dr. Filandro Vincentini, of Naples, Italy ; to Dr. Matt H. Cryer, of Philadel- phia, and to Dr. Frederick B. Noyes, of Chicago, for the privilege of reproducing and using several illustrations from the published accounts of their investigation^. The author also acknowledges the courtesy extended by Dr. Wilbur F. Litch, Dr. G. V. Black, and the publishers of the "American System of VI PREFACE. Dentistry ;" by Dr. Edward C. Kirk and the publishers of the u American Text- Book of Operative Dentistry ;" by the late Dr. Henry H. Burchard and the publishers of his "Dental Pathology, Therapeutics, and Pharma- cology ;" by Mr. Charles Tomes, F.B.C.S. , of London, England; by the S. S. White Dental Manufacturing Company, and by others, for the privi- lege of reproducing many valuable illustrations. Acknowledgment is also due to his friend Dr. Bertha E. Bush, of Chicago, for much valuable and time-saving assistance in reading and correcting the proofs. Chicago, August 1* 1901. CONTENTS. CHAPTER I. PAGE Classification and Descriptive Anatomy of the Teeth 1 Number and Classification of the Teeth — Descriptive Anatomy of the Teeth — Architectural Design of the Teeth — The Incisors — The Cuspids —The Bicuspids— The Molars— The Deciduous Teeth. CHAPTER II. Origin, Development, and Morphology of the Teeth 26 Evolution of Epithelial Tissue — Evolution of the Jaws — Evolution of the Teeth. CHAPTER III. Histology of the Dental Tissues 34 Enamel — Striae — Chemic Composition of Enamel — Calcification of Enamel — Stratum Intermedium — Blood-Supply of the Enamel-Organ — Dentin — Matrix — Dentinal Tubuli, Sheaths, and Fibrils — Interglobu- lar Spaces — Development of the Root — Dentinification — Cementum — Cementification — Chemical Composition of Calcified Tissues — Nas- myth's Membrane — The Teeth-Pulp — The Peridental Membrane- The Gums. CHAPTER IV. Eruption of the Teeth 59 Deciduous Teeth — The Eruptive Process — Growth of the Jaw — Morbid Primary Dentition — Exuviation or Shedding of the Deciduous Teeth — Eruption of the Permanent Teeth. CHAPTER V. Bacteriology of the Mouth Parasites — Classifications — Mouth Bacteria Proper — Bacteria which affect the Integrity of the Dental Tissues— Sterilization of Hands and Instruments — Technique of Sterilization. CHAPTER VI. Examination of the Teeth and Mouth 107 Position of Patient and Operator — Instruments used in Examinations — The Examination. vii Vlll CONTENTS. CHAPTER VII. PAGE Dental Caries 115 Distribution — Results of the Examination of Ancient Crania— Preva- lence of Dental Caries— Etiology — Constitutional Predisposing Causes — Local Predisposing Causes. CHAPTER VIII. Dental Caries (Continued) 135 Theories of Caries — Caries of Enamel — Caries of Dentin — Penetration of Caries — Caries of Cementum. CHAPTER IX. Dental Caries (Continued) 161 Varieties — Stages — Symptoms — Diagnosis — Prognosis. CHAPTER X. Treatment op Caries. Prophylaxis 166 Cleanliness of the Mouth and Teeth — Dentifrices— Antiseptics. CHAPTER XL Treatment of Caries (Continued) 171 Medication— Excision. CHAPTER XII. Treatment of Caries ( Continued) 174 Methods of Separation of Contiguous Teeth — Exclusion of Moisture. CHAPTER XIII. Hypersensitive Dentin 184 Causes of Hypersensitive Dentin — Treatment— Palliative Treatment — Chemical Treatment — Heated Air, etc. CHAPTER XIV. Cataphoresis 193 Osmosis — Anodal Electrolysis — Cathodal Electrolysis — The General Principles or Laws which govern the Generation and Transmission of Electricity — Rheostats ; Current Selectors ; Current Controllers — Electrococaine Ansesthesia — Method of Administration — General Ansesthesia. CHAPTER XV. The Classification of Cavities 217 Simple Cavities upon Exposed Surfaces— Simple Approximal Cavities — Compound Cavities. CONTENTS. CHAPTER XVI. PAGE Preparation of Cavities 234 Opening the Cavity — Removing Decay — Retentive Shaping — Forming Cavity Margins. CHAPTER XVII. Treatment op Caries by Obturation, or Filling 250 Filling-Materials and their Introduction — Non-Plastic Materials — Physical Characteristics of Gold — Properties of Gold-Foil — Non- Cohesive Foil — Cohesive Foil — Plugging Instruments — Crystal or Sponge Gold — Gold-and-Platinum Foil — Annealing. CHAPTER XVIII. Considerations in Filling Special Classes op Cavities 272 Simple Cavities upon Exposed Surfaces — Simple Approximal Cavi- ties — Compound Cavities — Matrices — Tin-Foil — Tin and Gold — Finish- ing Fillings — Repairing Defective Gold Fillings. CHAPTER XIX. Plastic Filling-Materials. Amalgam 296 The Nature and Properties of Amalgam — Chemic Relations — Com- position of Alloys— Making Dental Alloys. CHAPTER XX. Manipulation and Introduction op Plastic Filling-Materials 321 Especial Uses of Amalgam — Mixing Amalgams — Introduction of Amal- gams—Copper Amalgam — Gutta-Percha — Zinc Cements — Varnishes. CHAPTER XXI. Inlays 346 Metal— Porcelain— Glass— Methods of Manipulation. CHAPTER XXII. Denudation or Erosion of the Teeth, and Attrition or Abrasion 359 Causes — Pathology — Treatment. CHAPTER XXIII. Diseases and Injuries of the Dental Pulp and Their Treatment 373 Hyperemia of the Dental Pulp— New Formations — Calcifications. CONTENTS. CHAPTER XXIV. PAGE Inflammation op the Dental Pulp 397 Table of Inflammatory Phenomena— Inflammation of the Pulp— Sup- puration of the Dental Pulp— Chronic Inflammation of the Dental Pulp. CHAPTER XXV. Exposure of the Dental Pulp and its Treatment 416 Secondary Dentin, or Dentin of Repair — Devitalization and Extirpa- tion of the Pulp — Physical Effects of Arsenic upon the Pulp. CHAPTER XXVI. Pulpless Teeth and Filling Pulp-Canals 431 Preparation and Treatment of Pulp-Canals — Materials Employed for Filling Pulp-Canals and Methods of Introduction— Mummification of the Pulp. CHAPTER XXVII. Bleaching Discolored Teeth 446 Preparation of the Tooth for Bleaching— Method of Bleaching — Chlo- rine Methods— Truman Method— Dioxide Methods — Sulphurous An- hydride Method — Cataphoric Method. CHAPTER XXVIII. of the Pericementum 459 Pericementitis— Subacute and Chronic Pericementitis— General Non- Septic Pericementitis — Tubercular Pericementitis— Scorbutic Perice- mentitis— Mercurial Pericementitis. CHAPTER XXIX. Dento- Alveolar Abscess 474 Causes — Varieties— Pathology — Formation of Pus— Location — Chronic Dento- Alveolar Abscess — Treatment. CHAPTER XXX. Replantation of the Teeth 490 Indications calling for Replantation — Persistent Alveolar Abscess. CHAPTER XXXI. Transplantation and Implantation of the Teeth 494 Transplantation of Teeth — Implantation of Teeth — Requirements for the Operation — Method of Operation. CONTENTS. XI CHAPTER XXXII. PAGE Dislocation of the Teeth 501 Partial and Complete Dislocations — Treatment — Prognosis. CHAPTER XXXIII. Fkactukes of the Teeth 505 Simple, Compound, and Comminuted Fractures— Treatment — Union of Fractured Teeth. CHAPTER XXXIV. Resorption of the Roots of Permanent Teeth 509 Causes — Pathology — Symptoms and Diagnosis— Prognosis — Treatment. CHAPTER XXXV. Hypercementosis 513 Causes — Pathology — Inostosis — Symptoms and Diagnosis — Treatment. CHAPTER XXXVI. Necrosis of the Teeth 518 Causes— Partial Necrosis — Treatment. CHAPTER XXXVII. Deposits upon the Teeth. Green Stains. Calcic Deposits 521 Composition of the Saliva— Salivary Calculus — Varieties — Treatment — Scalers. CHAPTER XXXVIII. Pyorrhea Alveolaris 530 Constitutional Origin of the Disease— Local Origin of the Disease- Bacterial Origin of the Disease — Ptyalogenic Calcic Pericementitis : Causes — Pathology and Morbid Anatomy — Symptoms and Diagnosis — Prognosis — Treatment. CHAPTER XXXIX. HEMATOGENIC CALCIC PERICEMENTITIS 550 Causes— Varieties — Pathology and Morbid Anatomy — Symptoms and Diagnosis — Prognosis — Treatment. CHAPTFR XL. Phagedenic Pericementitis 568 Causes — Pathology — Symptoms and Diagnosis — Prognosis — Treatment. CONTENTS. CHAPTER XLI. PAGE Anaesthetics, Local and General 578 Local Anaesthetics — Anaesthesia by the Local Abstraction of Heat- Richardson's Method — Letamendi's Method— Anaesthesia by the Local Narcotic Effect of Drugs — Cocaine — Eucaine — Chloretone — General Anaesthetics — Nitrous Oxide — Hewitt's Method — Examination of the Physical Condition of the Patient — Precautions against Accidents— Administration of Ether. CHAPTER XLII. Extraction of Teeth Indications which call for the Extraction of Teeth — General Condi- tions Unfavorable to Extraction — Instruments used in the Operation of Extracting — Selection of the Proper Instruments for the Extraction of the Various Classes of Teeth, their Proper Adjustment, and the Kind and Direction of the Force applied — Extraction of the Roots of Teeth — Difficulties, Complications, and Accidents. LIST OF ILLUSTRATIONS. PLATES. PLATE PAGE I. Varicosed enamel-rods, magnified 36 II. Varicosed enamel-rods, very highly magnified 37 III. Normal dentin showing tubuli in cross-section, highly magnified 44 IV. Normal dentin showing tubuli in longitudinal section, highly magnified 45 V. Leptothrix racemosa, early stages 96 ' VI. Leptothrix racemosa, later stages 97 VII. Abnormal root-canals 435 FIGURES. FIG. 1. A T ertical section of inferior maxilla and teeth of mole, X 15 2 2. Deciduous teeth of the left side 2 3. Permanent teeth of the right side ■ 2 4. Structures of a tooth 2 5. Occlusion of the teeth 3 6. Superior left central incisor, labial surface 3 7. Superior right central incisor, labial surface 3 8. Superior left central incisor, labial surface 6 9. Superior left central incisor, lingual surface 6 10. Superior left central incisor, mesial surface 6 11. Superior left central incisor, distal surface 6 12. Superior right lateral incisor, labial surface 7 13. Superior right lateral incisor, lingual surface 7 14. Superior lateral incisor with exaggerated cervical ridge 7 15. Superior right lateral incisor, mesial surface 7 16. Superior right lateral incisor, distal surface 7 17. Inferior right central incisor, labial surface 8 18. Inferior right central incisor, lingual surface 8 19. Inferior right central incisor, mesial surface 8 20. Inferior right central incisor, distal surface 8 21. Inferior right lateral incisor, labial surface 9 22. Inferior right lateral incisor, lingual surface 9 23. Inferior right lateral incisor, mesial surface 9 24. Inferior right lateral incisor, distal surface 9 25. Superior right cuspid, labial surface 10 26. Superior right cuspid, lingual surface 10 27. Superior right cuspid, mesial surface 10 28. Superior right cuspid, distal surface 10 29. Inferior right cuspid, labial surface 11 30. Inferior right cuspid, lingual surface 11 31. Inferior right cuspid, mesial surface 11 32. Inferior right cuspid, distal surface 12 33. Superior right first bicuspid, buccal surface 12 34. Superior right first bicuspid, lingual surface 12 35. Superior right first bicuspid, mesial surface 12 36. Superior right first bicuspid, distal surface 12 xiii XIV LIST OF ILLUSTRATIONS. FIG. p AGE 37. Superior right first bicuspid, morsal surface " 13 38. Superior right second bicuspid, buccal surface 13 39. Superior right second bicuspid, lingual surface 13 40. Superior right second bicuspid, mesial surface 13 41. Superior right second bicuspid, distal surface 14 42. Superior right second bicuspid, morsal surface 14 43. Inferior right first bicuspid, buccal surface 14 44. Inferior right first bicuspid, lingual surface 14 45. Inferior right first bicuspid, mesial surface 15 46. Inferior right first bicuspid, distal surface 15 47. Inferior right first bicuspid, morsal surface 15 48. Inferior right second bicuspid, morsal surface 15 49. Inferior right second bicuspid, buccal surface 16 50. Inferior right second bicuspid, lingual surface 16 51. Inferior right second bicuspid, mesial surface 16 52. Inferior right second bicuspid, distal surface 16 53. Superior right first molar, buccal surface 17 54. Superior right first molar, lingual surface 17 55. Superior right first molar, mesial surface 17 56. Superior right first molar, distal surface 17 57. Superior right first molar, morsal surface 18 58. Superior right second molar, buccal surface 18 59. Superior right second molar, lingual surface 18 60. Superior right second molar, mesial surface 18 61. Superior right second molar, distal surface 19 62. Superior right second molar, morsal surface 19 63. Superior right third molar, buccal surface 19 64. Superior right third molar, lingual surface 19 65. Superior right third molar, mesial surface 20 66. Superior right third molar, distal surface 20 67. Superior right third molar, morsal surface 20 68. Inferior right first molar, buccal surface 20 69. Inferior right first molar, lingual surface 21 70. Inferior right first molar, mesial surface 21 71. Inferior right first molar, distal surface 21 72. Inferior right first molar, morsal surface 21 73. Inferior right second molar, buccal surface 22 74. Inferior right second molar, lingual surface 22 75. Inferior right second molar, mesial surface 22 76. Inferior right second molar, distal surface 22 77. Inferior right second molar, morsal surface 23 78. Inferior right third molar, buccal surface 23 79. Inferior right third molar, lingual surface 23 80. Inferior right third molar, mesial surface _ 23 81. Inferior right third molar, distal surface 24 82. Inferior right third molar, morsal surface 24 83. Deciduous teeth of the left side 25 84. Graafian follicles, or ova, in various stages of development, X 80 26 85. Division of mammal ovum 27 86. 87, 88. Transverse section of embryo of chick 26 89, 90. Vertical sections of human skin 27 91. Squamous epithelium from buccal cavity, X 162 27 92. Longitudinal section of lip of a kitten 27 93. Transverse section of hairs of scalp, X 50 28 94. Epithelial layer of the mucous membrane 28 95. 96. Columnar epithelial cells, X 670 28 LIST OF ILLUSTRATIONS. XV FIG. PAGE 97. Goblet-cells, X 500 28 98. Section of jaw of rabbit embryo 2S 99. First rudiments of a hair from human embryo 28 100. Lower jaw of human embryo, X 80 29 101. Vertical section of skin, showing bulbous ends of hairs, X 55 29 102. Head of human embryo 29 103. Vertical section through head of human foetus, X 80 29 104. Lower jaw of human foetus, X 80 29 105. Involution of the Malpighian stratum 30 106. Lower jaw of human embryo, X 75 30 107. Vertical section of epithelial cord, or primitive enamel-organ, X 300 30 108. Cross-section of epithelial cord, X 300 30 109. Primitive epithelial cord, X 45 30 110. Section through lower jaw of embryo mouse 31 111. Evolution of dental follicle (ninth week), X 70 31 112. Developing human cuspid 31 113. Follicle of human molar (eleventh week), X 50 31 114. Human embryo (twelfth week) 32 115. Vertical section of human molar at junction of enamel-organ with dentin papilla?, X 300 32 116. Vertical section of incisor of human foetus 32 117. Oblique section of a dental follicle 32 118. Vertical section of human molar, early stage of calcification, X 90 32 119. Vertical section of cuspid of human foetus, budding of primitive epithelial cord, X 70 32 120. Vertical section of human foetal maxilla, X 70 33 121. Vertical section of human foetal incisor, X 50 33 122. Section of human developing tooth 33 123. Section of dental follicle of cat, X 9 33 124. Vertical section of cuspid, human foetus, X 50 33 125. Vertical section of molar, human foetus, X 70 33 126. Section of dental follicle, first layers of ameloblasts and odontoblasts, X 100.. 34 127. Section of f cetal femur, showing odontoblasts, X 109 31 128. Forming dentin, showing odontoblasts, X 1900 35 129. Enamel-cells, with nuclei 35 130. Dentinal sheaths 36 131. 132. Enamel-columns, highly magnified 36 133. Developing molar, ends of enamel-rods, X 1000 36 134, 135. Sections of enamel-rods, odontoblasts, and dentin 37 136. Section of enamel, striations of Retzius, X 1 10 38 137. Section of dental follicle, first layer of ameloblasts, X 325 3S 138. Teased section of developing molar, showing ameloblasts, X 1000 38 139. Developing enamel, Tomes's processes 38 140. Section of developing human molar, X 1000 39 141. 142. Section of developing tooth, ameloblasts highly magnified 39 143. Transverse section of developing tooth, X 275 39 144. Developing tooth of embryo lamb, X 105 40 145. Section of human foetal incisor ; blood-supply of enamel-organ 40 146. Section of dental follicle of rat, papillary layer, X 90 40 147. Section of forming enamel (rat), X 325 40 148. Section of incisor of rat, X 80 41 149. Ground section of developing tooth of rat, X 97 41 150. 151, 152. Forming enamel, calcoglobulin, formation of enamel-rods 41, 42 153. Longitudinal section of incisor 42 154. Longitudinal section of inferior molar 42 155. Section of root of bicuspid, radiation of dentinal tubuli 43 XVI LIST OF ILLUSTRATIONS. FIG. PAGE 156. Dentinal tubuli at dento-enaruel junction, X 760 43 157, 158. Sections of root, parallel to dentinal canals 43 159. Section of dentin and enamel, tubuli entering the enamel 44 160. Section of developing tooth, dentinal fibres passing from dentin to enamel, X 1000 44 161. Dentinal sheaths, X 273 45 162. Section of enamel and dentin, interglobular spaces, X 50 45 163. Section of enamel and dentin, interglobular spaces, X HO 48 164. Section of dentin and cementum, X 97 48 165. Section of enamel and dentin, incremental lines, X 500 48 166. Vertical section of foetal face, X 7 ! 48 167. Section of human lower jaw, X 9 49 168. Section of developing human cuspid, X 100 49 169. Teased section of developing molar, X 1000 49 170. Truncated odontoblasts and fibril cells 49 171. Section of tooth-follicle, nuclei of odontoblasts, etc., X 325 50 172. Odontoblasts 50 173. 174. Sections of bone, X 60 51 175, 176. Sections of cuspidati, magnified 52 177, 178. Sections of molars, magnified 52 179. Section of root of tooth and alveolus, X 80 53 180. Section of alveolar process and cuspid, X 100 53 181. Developing bone from scapula, X 50 53 182. Section of enamel and Nasmyth's membrane, X 250 54 183. 184. Sections of normal pulp-tissue, X 143 54 185, 186, 187. Sections showing blood-supply of the pulp 55 188. Injected dental pulp, X 8 56 189. Nerves of dental pulp 56 190. Pericementum and alveolar process between teeth, X 100 56 191. Section through pulp-chamber of cuspid 56 192. Periosteum surrounding ulnar and radius, X 13 56 193. 194. Peridental membrane of forming tooth 56 195. Section through alveolar process, X 30 57 196. Section of root of tooth in situ 57 197. Blood-vessels and nerves entering at base of dental follicle, X 96 57 198. Section of pericementum in situ, X 408 57 199. 200. Sections of peridental membrane, highly magnified 58 201. Section of jaw through alveolar process, X 60 59 202. Section of dental follicle and mucous membrane, X 26 59 203. Glands of Serres, X 50 59 204. Epithelial layer of embryonic mucous membrane 59 205. Section of jaw, showing forming root, X 15 ■ . 60 206. Follicles of permanent teeth at period of eruption of primary teeth, X 22.. . . 60 207. Lower jaw of foetal mouse, X 80 61 208. 209. Section of erupting tooth of mouse, area of resorption at cusp, magni- fied 61, 62 210. Vertical section of human cuspid, X 75 62 211. Rami at various ages 63 212. Jaws of a young child 64 213. 214. Sections of jaw of embryo cat, showing deciduous tooth and follicle of permanent tooth 64 215. First and second dentition 66 216-220. Eruption of teeth 71 221. Gum-lancet 72 222. Curved scissors 73 223. Peculiar exuviation of a kitten's tooth, X 35 76 LIST OF ILLUSTRATIONS. XVII FIG. PAGE 224. Absorbent organ and portion of dentin, X 65 76 225. Calcification and decalcification of teeth 78 226. Fruit mould, X 130 84 227. Forms of bacteria 85 228. Various forms of yeast fungi 86 229. Torula, or yeast fungi 84 230. Bacterium typhosus, X 1000 88 231. Bacillus pestis and blood-cells of rat, X 1000 88 232. Pneumococcus, capsule form, X 1200 88 233. Diplococcus pneumoniae, X 1000 88 234. Streptococcus pyogenes, X 1000 80 235. Streptococcus in pyaemia after erysipelas, X 660 89 236. Bacteria in pus, X 700 80 237. Bacillus tuberculosis, X 1000 89 238. Flagellated spirillar and vibrio, X 2100 90 239. Bacillus of hog cholera, X 1000 90 240. Staphylococcus pyogenes, X 1000 91 241. Streptococcus pyogenes, X 1000 91 242. Streptococcus hominis, X 218.75 91 243. Leptothrix buccalis, X 193.75 92 244. Mouth bacteria (diplococci, leptothrix) 92 245. Bacillus buccalis maximus, 1800 : 1 93 246. Spirochaeta dentium (denticola) and leptothrix threads, X 1000 94 247. Spirochasta dentium, showing flagella, X 1000 94 248. Leptothrix gigantea, from dog, X 750 94 249. 250. Leptothrix gigantea, X 1000 95 251. Micro-organisms from enamel surface 100 252-258. Leptothrix racemosa, fructification heads, etc 100 259. Instrument-sterilizer 105 260, 261. Dental mirrors 105, 109 262-264. Magnifying-glasses 110 265. Explorers Ill 266. Electric mouth-lamp Ill 267. Parr's universal separator 112' 268. Perry's two-bar separators 113 269. Syphilitic teeth 120 270. 271. Caries following crack in enamel, X 95 132 272, 273. Caries of enamel and dentin 156 274. Undermining caries of enamel 157 275. Section of a molar crown with caries 157 276-293. Infected dentin and dentinal tubules 157-161 294. Section of a molar showing stages of caries 162 295. Corundum disks 173 296. 297. Tooth-separators 176 298, 299. Napkin clamps 178 300. Rubber dam applied 180 301. Rubber-dam holder 180 302. Ivory clamps 181 303. Ottolengui's clamp applied 181 304. How's cervix screw-clamp 181 305. Elliot's clamp and forceps 182 306. Rubber-dam applier 182 307. Ainsworth's rubber-dam punch 182 308. Sizes of holes in rubber darn 183 309. Depressed rubber dam 183 310. 311. Denham coffer-dam shield 183 XV111 LIST OF ILLUSTRATIONS. FIG. PAGE 312. Mirror 183 313, 314. Hot-air syringes 189 315. Improved electric hot-air syringe 1 90 316. Jewell graphite rheostat 205 317. Weston's milliamperemeter 207 318. Cataphoric electrodes 208 319. Cataphoric outfit without milliamperemeter 209 320. Arrangement of apparatus for cataphoric work 210 321. Syringe electrode 213 322. Flexible face-piece for inhalers 215 323. Allis's ether inhaler 210 324-344. Simple cavities in teeth 218-225 345, 346. Small chisels and hatchet excavators 226 347. Cavity prepared for filling 227 348, 349. Cavity near morsal edge of cuspid 227 350-353. Cavities on mesial and distal surfaces of bicuspids and molars 228 354-366. Compound cavities 229-233 367. Water-syringe 241 368, 369. Burs for opening small cavities 241, 242 370, 375. Cleavage of enamel 242, 249 371, 372. Chisels 242, 243 373. Excavators 245 374. Instruments for setting screw-posts 248 376. Crowns restored with cohesive gold-foil 257 377. Cylinders of gold-foil 258 378. Foil-carriers 258 379. Cylinders and mats being introduced into a cavity 258 380. 381. Bing pluggers ; Butler pluggers 259, 260 382. Herbst burnishers 262 383, 384. Varney pluggers ; Webb pluggers 264 385. Steel mallets 264 386, 387. Darby-Perry pluggers ; Chappell pluggers 265 388. Royce plugger-points 265 389. Snow & Lewis automatic plugger 266 390. ,391. Abbott automatic mallet 267 392, 393. Bon will electro-magnetic and mechanical mallets 267 394, 395. Electric gold annealers 271 396. Gum retractor 272 397-401. Clamps for keeping rubber dam in position 272, 273 402-411. Filling simple cavities upon exposed surfaces 273-276 412-414. Filling simple approximal cavities 277, 278 415-429. Filling compound cavities 279-282 430-433. Matrices and forceps 284, 285 434. Hand-burnishers 288 435, 436. Engine-burnishers ; disk burnishers 289 437. Plug-finishing burs 289 438. Wood polishing-points 289 439. Corundum points and wheels 290 440. Arkansas, Hindostan, and Scotch stones 290 441. Soft rubber polishing-cups 290 442^144. Plug-trimmers and finishing files ' 291 445. Right and left plug-finishing files 292 446. Thickened- rim sand-paper disks 292 447. Disk mandrels 293 448. An inoculated gelatin plate showing antibacteric effects of copper amalgam. . . 313 449. Creager loop matrices 322 LIST OF ILLUSTRATIONS. XIX FIG. PAGE 450. Flagg wafering pliers 324 451. Glass mortar and pestle 324 452. 453. Amalgam-carriers 326 454. Flagg amalgam instruments 326 455. Kirk's instruments for plastics 327 456. Revised set of amalgam instruments 327 457. Heating spoon — cone-socket handle 329 458-461. Built-up molar crowns 330 462. Flagg' s gutta-percha softener and tool-heater 354 463. How's thermoscopic heater 335 464. 465. Glass mixing-slab ; spatulas 338 466. Details of process for making cast filling for incisor 347 467^470. Restoration of incisors and molars by cast fillings 348 471, 472. Bridge-work 349 473, 474. Porcelain stoppers ; inlay rods 350 475, 476. Inlay trephines and burs 351 477, 478. Electric oven ; electric furnace f 352 479, 480. Erosion of teeth 365 481, 482. Erosion of teeth from gout 366 483. Abrasion by tooth-brush 371 484, 485. Hyperemia of dental pulp 3S0 486. Secondary growths in pulp-chamber 390 487, 488. Secondary dentin on wall of pulp-chamber, X 100 390 489. Secondary dentin in base of pulp-chamber, X 50 391 490, 491. Pulp-nodules 391 492. Section of pulp with pulp-nodule, X 70 392 493. Section of pulp undergoing fibroid degeneration, X HO 392 494^98. Calcification of dental pulp 393, 394 499, 500. Osteodentin 395 501. Bone-tissue in place of resorbed dentin 396 502-505. Suppuration of dental pulp 408-411 506. Incisor with enlarged pulp-chamber 414 507. Pulpitis, X 300 414 508. Fibrous degeneration of pulp, X 50 415 509. Metallic caps for capping teeth 418 510. 511. Sections showing formation of secondary dentin in coronal portion of pulp- chamber, X 100 422 512. Section of pulp treated with arsenic 425 513. Barbed nerve-broaches 430 514-525. Longitudinal sections of teeth 432 526. Peculiarities in cuspids and bicuspids 433 527-534. Sections of bicuspids, showing pulp-chamber and canals 433 535-550. Sections of first, second, and third molars 434 551-557. Abnormalities of dental roots and canals 435 558, 559. Donaldson bristles ; Gates-Glidden drills 435 560. Donaldson pulp-cleansers 435 561, 562. Nerve-extractors 436 563. Pulp-canal pluggers 439 564. Canal probe guage 439 565. Syringe electrode 456 566. Bleaching electrode 457 567. Duplex syringe 457 568. Nipple-expander 458 569. Bleaching electrode in position 458 570. Rubber band causing cementitis 460 571. Dental artery supplying pulp and pericementum 462 XX LIST OF ILLUSTRATIONS. FIG. PAGE 572. Dunn capillary or drop syringe 463 573. Metal cap to prevent occlusion 464 574. Shreddy sac of tooth abscess 476 575 r 576. Spear-pointed drills ; trephines 484 577. Puncturing alveolar abscess 484 578. Rollin circular knives 498 579. 580. Younger trephines and reamers 499 581. Eollin spiral knives 499 582. Ottolengui combined drill and reamer 499 583. 584. Torsion forceps; bullet forceps * 503 585. Gooch's double canula snare 503 586-596. Macroscopic appearances of permanent teeth the roots of which are being resorbed 510 597, 598. Osteoclasts, producing resorption of dental roots '. . . 511 599, 600. Transverse sections of roots of teeth, near apex, X 175 514 601-603. Macroscopic appearances of hypercementosed teeth 514 604, 605. Sections of molar roots, hypercementosis, magnified 514 606. Transverse section of molar roots, near apex, X 75 515 607. Transverse section of root of hypercementosed tooth, X 75 515 608. Transverse section of alveolus and apex of root of abscessed molar, X 96 515 609. Inostosis, with formation of a pearl-like globule resembling enamel 515 610. Inostosis, section of root of tooth, X 80 515 611-614. Necrosis of teeth, macroscopic appearances 520 615. Epithelial scales and salivary corpuscles from sordes of mouth, X 50 520 616-619. Salivary calculus 526 620. Glands of Serres, X 50 526 621. Small scalers 518 622. Small rubber disks, wheels, and cups 528 623. Small revolving brushes 528 624. Inflamed peridental membrane from a case of pyorrhoea alveolaris, X 50 544 625. Removing subgingival salivary deposits 546 626-628. Pyorrhoea alveolaris instruments 547, 548 629. Medicinal drop syringe 548 630-632. Splints for supporting loosened teeth 549 633-636. Gouty pericementitis before and after treatment 563 637. Underlying condition in pyorrhoea alveolaris 564 638. Fibroid degeneration of pulp in pyorrhoea alveolaris, X HO 572 639. Pulp in situ showing calcic degeneration, X 65 572 640. Hyaline degeneration of the pulp, X 100 573 641. Colloid degeneration of the pulp, X 21.25 573 642. Airport's bur ' 576 643. Improved dento-electric cautery 577 644. Spray apparatus — hand instrument 578 645. Spray apparatus — foot instrument 579 646. Glass tube with capillary point 581 647. 648. Nitrous oxide apparatus 587 649-651. Gas-inhalers 588 652, 653. Hewitt's apparatus for the administration of oxygen with nitrous oxide 589, 590 654, 655. Mouth-props 592 656. Towel folded as a cone 592 657, 658. Lente's and Allis's inhalers 593 659. Aseptible ether inhaler 594 660. Mouth-mirror 600 661. Gum-lancet 600 662. Curved scissors 600 LIST OF ILLUSTRATIONS. XXI FIG. PAGE 663-665. Mouth-props and gags 601 666. Laryngeal forceps 601 667. Turnkey 602 668. Aseptic forceps 602 669. Root-elevators , 603 670. Dental screw 608 671. 672. Relation of teeth to alveolar processes 604 673, 674. Superior incisor forceps 604 675-678. Inferior incisor forceps 605, 606 679-681. Superior cuspid and bicuspid forceps 606, 607 682-685. Inferior cuspid and bicuspid forceps 607, 608 686, 687. Superior first and second molar forceps 609 688-694. Inferior first and second molar forceps 609-611 695-697. Superior third molar forceps 611, 612 698, 699. Inferior third molar forceps 612, 613 700, 701. Screw-forceps '. . 613 702-705. Superior root forceps 614 706, 707. Inferior root .forceps 615 708. Superior alveolar root forceps 615 709. Deciduous inferior universal forceps 616 710. Inferior alveolar root forceps 616 711. Deciduous superior anterior and root forceps 616 712. Deciduous superior molar forceps 616 713. Deciduous inferior anterior and molar forceps 617 714. Deciduous and superior universal root forceps 617 715. 716. Common deformities of teeth 617 717-721. Common malpositions of teeth 617 722. Skiagraph showing misplaced superior cuspid 617 723. Misplaced inferior second and third molars 618 724. 725. Forceps for extracting misplaced molars 618 PRINCIPLES AND PRACTICE OPERATIVE DENTISTRY. CHAPTER I. CLASSIFICATION AND DESCRIPTIVE ANATOMY OF THE TEETH. Nearly all of the mammalia possess a more or less complicated dental system. These organs are applied to various purposes, mainly, however, to that of procuring food by seizing and killing living prey, or gathering and biting off portions of vegetable material, and more indirectly in tearing or putting through the hard protective coverings of food substances, such as the husks and shells of nuts, or in grinding, crushing, or otherwise mechanically dividing the solid materials before swallowing, so as to prepare them for digestion in the stomach. Fig. 1 shows the peculiar form of the teeth of the mole. In many animals certain teeth are excessively developed, and are used as weapons of offence and defence ; in others the presence or excessive development of certain teeth mark the male sex. Man is an omnivorous animal (the term omnivorous comes from the Latin omnis, all, and voro, I eat), and, as the term implies, eats all kinds of food. He has been endowed by nature with organs of mastication suited to the requirements of cutting, tearing, and grinding these various forms of food. Man's teeth, therefore, represent in part those of the carnivora, or flesh-eating animals, and those of the lierMvora, or vegetable- eating animals ; in other words, certain of his dental organs are represent- ative of both of these types of animals. The incisors and molars are typical of the herbivora, and are suited to cutting and grinding vegetable fibre and grains, while the cuspids and bicuspids represent the teeth of the carnivora, and are adapted to seizing, tearing, and cutting animal food. NUMBER AND CLASSIFICATION OF THE TEETH. Man, like many others of the mammalia, is endowed with two distinct sets of dental organs, one designed to serve the purposes of the economy during infancy and early childhood, the deciduous, temporary, or milk teeth ; and the other a larger, stronger, and more numerous set, which re- places the deciduous teeth, and is designed to serve the purposes of the economy from childhood to old age ; these are designated as the permanent teeth. l 2 OPERATIVE DENTISTRY. The deciduous teeth are twenty in number, ten in each jaw, and are expressed by scientists in the following formula : I.?? 11 M .22 = 20 2 2 11 22 The formula is read as follows, beginning at the median line : incisors* two above, two below ; cuspids, one above, one below ; molars, two above, two below, which equals ten on either side of the median line, or twenty in all. Fig. 2. Deciduous teeth of the left side. (Gray.) 1 and 2, incisors ; 3, cuspidati ; 4 and 5, molars. The permanent teeth of man are thirty-two in number, sixteen in each jaw, the formula for which is written thus : Permanent teeth of the right side. (Gray.) 1, third molars ; 2, second molars ; 3, first molars ; 4, second bicuspidati ; 5, first bicuspidati ; 6, cuspidati ; 7, lateral incisors ; 8, central incisors. Beginning at the median line, it reads as follows : incisors, two above, two below ; cuspids, one above, one below ; bicuspids, two above, two Fig. 1.— Vertical section of inferior maxilla and teeth /// xifu of mole. A Fig. 4.— Showing structures of a tooth. 1, enamel ; 2, cementum ; 3, dentin ; 4, pulp- chamber. Fig. 5.— Occlusion of the teeth. (After Cryer.) Cutting i Fig. 6.— Superior left central incisor, labial surface. (Enlarged.) Fig. 7. — Superior right central incisor, labial surface, showing short root. ( Enlarged. ) CLASSIFICATION AND DESCRIPTIVE ANATOMY OF THE TEETH. 3 below ; molars, three above, three below, equals sixteen on either side of the median line, or thirty-two in all. The ten anterior permanent teeth of each jaw are sometimes called the teeth of replacement, or succedaneous teeth, from the fact that they replace the deciduous teeth. The permanent incisors and cuspids take the place of the temporary teeth of the same name, while the bicuspids assume the positions occupied by the temporary molars. The permanent molars appear one by one behind the position occupied by the second deciduous molars. DESCRIPTIVE ANATOMY OF THE TEETH. The teeth are specialized organs of mastication implanted within the alveolar processes of the superior and inferior maxillce in man and in many animals. The teeth are composed of five tissues (Fig. 4) : a vitreous-like substance which comj)letely covers the crown — the enamel (1) ; a bone-like substance which envelops the root — the cementum (2) ; and a hard substance, less dense than enamel but harder than bone, which forms the interior or body of the organ — the dentin (3) ; while a small mass of soft tissue occu- pies a central cavity (4) within the crown and the root — the pulp ; and a fibrous membrane covers the cementum of the root — the pericementum. In a normally developed individual of the genus homo the teeth are arranged in the form of two parabolic or elliptical curves, the superior arch describing a trifle larger curve than the inferior, so that the teeth of the former slightly overreach their antagonists in the latter. The buccal cusps of the upper bicuspids and molars close over the buccal cusps of the lower teeth ; this brings the buccal cusps of the lower teeth within the sulci of the upper, and the palatal cusps of the upper teeth within the sulci of the lower. The incisors, cuspids, and bicuspids of the lower jaw are smaller than the corresponding teeth in the upper, the greatest differ- ence being in the size of the incisors. The superior incisors and cuspids are slightly longer than the inferior and overlaid them, while the cuspids and molars not only overreach their opposites in the inferior maxilla, but so interlock at their occlusal surfaces that each tooth, except the third superior molars, occludes or antagonizes with two of its fellows in the opposite jaw, when the teeth are brought into their normal occlusion. (Fig. 5.) This arrangement permits the whole of the occlusal surfaces of these teeth to be brought into contact by the various movements of the jaws in mastication, thus rendering the function of triturating the food and pre- paring it for digestion most effective. A normal incisor tooth presents certain characteristics which are com- mon to all the dental organs of man ; it will therefore serve the purpose of illustrating the anatomical divisions of the teeth, which are as follows : the crown, the cervix, the root, the pulp -chamber, the pulp-canal, the morsal* or cutting edge, the apex, and the apical foramen. A more minute description relative to the cusps, surfaces, angles, margins, grooves, fissures, etc., will be reserved for the special anatomy of the individual teeth. * The term morsal is used, following the suggestion of Dr. Thompson, in the place of incisive or cutting edge and occlusal surface. 4 OPERATIVE DENTISTRY. The crown is that portion of the tooth which is visible within the mouth, projecting beyond the gum ; the cervix or neck is that part repre- sented by a constriction between the crown and the root at the point where the enamel and the cementum meet, or, in other words, the portion grasped by the margin of the gum ; the root is that part which is implanted within the alveolar process of the jaw and covered by the gum ; the morsal edge or cutting edge is that portion of the crown which occludes or antagonizes with a tooth in the opposite jaw ; the apex is the terminal end of the root, that portion farthest removed from the crown (Fig. 6) ; the pulp- chamber is a cavity or cul-de-sac located within the crown, and may be termed a coronal enlargement of the pulp-canal which extends through the centre of the root from its apex to the pulp-chamber within the crown ; the apical foramen is the orifice or entrance to the pulp-canal located in the apex of the root. ARCHITECTURAL DESIGN OF THE TEETH. It is important to the dental student that he understand and appreciate the architectural design upon which nature has constructed the dental organs. The more closely he studies this design, in both their gross and minute anatomy, the more will he become impressed with the perfection of the general plan and the admirable adaptation of their form, their structure, and their tissues to perform the functions for which they were created. The form of the teeth is designed upon the plan of the cone, modified to meet the individual requirements of the several classes of teeth ; some are composed of a simple cone, like the incisors and cuspids, while others are a combination of two or more cones, as in the bicuspids and molars. In no way can these facts be taught so well as by modelling in clay the forms of the various classes of teeth, commencing with the sinrple forms as expressed in the single-rooted teeth, and progressing to the more com- plex through a series of double and multiple cones in the formation of the bicuspids and molars. THE INCISORS. There are eight incisor teeth in the dental series of man, four in the upper jaw and four in the lower, two situated upon either side of the median line of the jaw ; the first are termed the central incisors, and those next in order upon the distal side of the centrals are known as the lateral incisors. The situation of the central incisors in the extreme anterior portion of the jaw upon opposite sides of the median line causes their mesial sur- faces to approximate each other. The function of the incisor tooth is to cut or incise the food, — hence its name, which is derived from the Latin, incido, to cut. These teeth are all designed upon the form of the truncated cone, with slight modifications, to meet the requirements of the individual organ. The Superior Central Incisor. — This tooth is in form a modified truncated cone with its base flattened out to form the morsal or cutting edge. It presents for examination four surfaces, — labial, lingual, mesial, and CLASSIFICATION AND DESCRIPTIVE ANATOMY OF THE TEETH. 5 distal; two angles, — mesial and distal; and a morsal edge. The general form of the crown is that of the wedge or chisel, the edge being quite thin, the angles rounded, and the thickness rapidly increasing to the cer- vix of the tooth. It is also slightly curved from the cervix to the morsal edge, and curved over mesio-distally, so that the labial surface is somewhat convex and the palatal concave. The labial surface (Fig. 7) of the crown is in general outline an imper- fect quadrilateral, the cervical margin being rounded. Tins surface has four margins, — mesial, distal, cervical, and morsal or incisive. (Fig. 8.) The mesial margin begins at the morsal margin or cutting edge, and extending upward, usually with a slight distal inclination, unites with the cervical margin. The distal margin also begins at the morsal mar- gin, and extends upward with a slight mesial inclination, uniting with the cervical margin. Both of these margins are more or less convex. The cervical margin is somewhat rounded, the form following the outline of the gingival border, where it unites with the mesial and distal mar- gins. The morsal margin extends from the mesial margin to the distal margin. The union of the mesial and morsal margins form the mesial angle, while the union of the distal and morsal margins form the distal angle. The mesial angle is usually pointed and square, while the distal is much more obtuse. Two shallow grooves or depressions — the labial grooves— traverse the labial surface in a longitudinal direction, dividing it into three lobes, the mesial, median, and distal. These grooves extend from the morsal edge to the middle or upper third of the labial surface, where they broaden out and disappear. They are termed developmental lines (Black), and represent the three primitive plates of calcification in the develop- ment of the tooth, the grooves being formed by the union of these plates with each other. Occasionally one or more transverse ridges are found upon the cervical portion. The lingual surface (Fig. 9) of the crown is triangular in outline, smaller than the labial surface, and presenting a more or less angular concavity, the lingual fossa. This fossa is bounded by three marginal ridges and the morsal or cutting edge. The mesio-marginal ridge extends from the mesial angle upward to the cervico-marginal ridge, following the curvature of the mesial margin. The disto -marginal ridge extends from the distal angle to the cervico- marginal ridge, following the curvature of the distal surface. The cervico-marginal ridge forms -a curved line at the cervix or base of the crown, uniting by its extremities with the mesial and distal marginal ridges. The marginal ridges are often high and conspicuous, and the cervico-marginal ridge is sometimes developed into a cusp, the ridge at the base forming a girdle or cingulum. The lingual fossa is usually smooth, but occasionally it forms a deep depression or pit, while a fissure may extend from it into the cervico-marginal ridge. Two longitudinal grooves are sometimes seen traversing the lingual fossa, which correspond to the developmental grooves upon the labial surface. The Mesial and Distal Surfaces. — The outlines of these surfaces (Figs. b OPERATIVE DENTISTRY. 10 and 11) are irregular triangles, with the base directed towards the root and the apex terminating at the incisive or morsal edge. The base of the triangle is concaved at the cervical margin, and the apex rounded or con- vex at the morsal edge. These surfaces have three margins, — labial, lingual, and cervical. The mesial surface is slightly longer than the distal surface, and presents a more or less convex and rounded form, slightly flattened near the cervical margin. The distal surface is rounded as in the mesial, but more curved in its longitudinal axis. The labial margins of these surfaces are convex, following the outline of the labial surface, while the lingual and cervical margins present concave outlines, following the curves of the lingual surface, and the cervical line. The incisive edge or morsal margin of the crown is formed by union of the labial and lingual surfaces, and extends in a nearly straight line from the mesial to the distal surface, with a slight downward pitch towards the median line. In a recently erupted tooth this line is often broken by the presence of the developmental grooves ; these, however, soon disappear with use, leaving the line comparatively straight. In a normal occlusion these teeth shut over the lower incisors, but occasion- ally they will be found to occlude squarely with their fellows of the lower jaw. The cervix or cervical line or margin is clearly and distinctly marked by the free extremity of the enamel which covers the crown of the teeth. The termination of the enamel at the neck of the tooth marks the extent of the peridental membrane. The enamel edge, which slopes off more or less abruptly to meet the cementum, does not form a straight line around the tooth, but curves upward upon the root at the labial and lingual surfaces and downward at the mesial and distal surfaces, thus forming in outline a double convexity and a double concavity. The root in section of the tooth at the cervix shows it to be broader on the labial than the lingual surface, — pear-shaped, — and this condition is maintained throughout the greater length of the root. In general outline the root has the form of a slender cone. The aver- age length of the superior central incisor is 0.88 inch (2.23 centimetres), of the crown 0.39 inch (0.99 centimetre), and of the root 0.49 inch (1.24 centimetres).* The pulp-chamber is large, and the pulp-canal usually gives free access to the apex. In young teeth the cornua extend well towards the angles, while in old persons the pulp-chamber and canal is often constricted, making it difficult of access. The Superior Lateral Incisor. — This tooth is the second in the dental arch from the median line, and approximates the central incisor upon its distal surface. It is a little shorter, and about a third narrower than the central incisor, has the same general form and architectural design, and is possessed of the same developmental grooves. * All measurements of the teeth are taken from Black's Dental Anatomy. Cervical margin Cervico- rnarginal ridge Distal margin Distal angle Disto- marginal ridge Mesial angle Morsal edge Labial grooves Fig. 8. — Superior left central incisor, labial surface. (Enlarged.) Lingual fossa -Superior left central incisor, lingual surface. (Enlarged.) Fig. 10.— Superior left central incisor, mesial surface. (Enlarged.) Fig. 11. — Superior left central incisor, distal surface. (Enlarged.) ^atrial grooves Morsal edge Fig. 12. — Superior right lateral incisor, labial surface. Fig. 13. — Superior right lateral incisor, lingual surface. (Enlarged.) (Enlarged.) Fig. 15.— Superior right lateral incisor, mesial surface. Fig. 16.— Superior right lateral incisor, distal surface. (Enlarged.) (Enlarged.) CLASSIFICATION AND DESCRIPTIVE ANATOMY OF THE TEETH. 7 The crown presents for examination four surfaces, labial, lingual, mesial, and distal ; a cervical margin, an incisive or morsal edge, a mesial and a distal The labial surface of the crown (Fig. 12) is more rounded than in the central, the mesial angle is acute, and the morsal edge slopes upward to a rounded and obtuse distal angle. The mesial half of the crown seems to partake of the form of the central incisor, while the distal half approaches the form of the cuspid. In the young tooth the morsal edge, as in the cen- tral, presents three tubercles, more or less distinct, with the developmental grooves passing between them. The lingual surface (Fig. 13) in a majority of instances is the broadest part of the crown. It is less concave than in the central, but more de- pressed at the base of the cervical ridge. The mesial and distal marginal ridges are in proportion to the size of the tooth, broader and stronger than in the centrals. The cervical ridge is also well marked and propor- tionately broader and stronger than in the central. Occasionally, however, the marginal ridges are but slightly developed ; the surface is then quite smooth. The lingual fossa may be divided by a longitudinal ridge with slight depressions upon either side between it and the marginal ridges. The cervical ridge is sometimes very prominent, forming a cingulum, at the centre of which a tubercle is often developed. An exaggerated development of this cusp or cingule is shown in Fig. 14, a, from a case reported by W. H. Mitchell. As a consequence of this greater prominence of the cingulum, and the marked depression or pit so often found at its base, caries is more liable to occur upon the lingual surfaces of the superior laterals than upon those of the central incisors. The mesial and distal surfaces (Figs. 15 and 16) present a triangular or V-shaped outline similar to that of the central incisor. The mesial surface is rounded near the morsal edge, but considerably flattened near the cervix. A slight depression sometimes exists at this point, while the mesio-labial angle occasionally presents a flattened or depressed point midway between the morsal edge and the cervix. The distal surface is convex in all directions, and quite full at the morsal or incisive third ; from this point it slopes towards the cervical line, where it becomes quite flat. The morsal edge is divided into two parts by a more or less prominent tubercle. The mesial half is straight, like that of the central, while the distal half has a slight upward slope, terminating in a rounded distal angle. When the tubercle becomes worn off, the edge is straight, with a pitch towards the median line. The cervix is considerably flattened mesio-distally. Section of the root at this point shows the form to be a flattened oval. The cervical line follows the same course as in the central incisor, having an upward curve upon the labial and lingual surfaces, and a downward curve upon the mesial and distal surfaces. 8 OPERATIVE DENTISTRY. The enamel margin does not, as a rule, end so abruptly as in the central incisors, although occasionally it will end in a sharply defined ridge. The root of the tooth is conical, but more or less flattened mesio- distally ; its labio-lingual diameter at the neck is about one-third greater than its mesio-distal diameter. The root is generally straight, but in many specimens the apex has a slight distal curvature. Occasionally it is very crooked. The average length of the superior lateral incisor is 0.85 inch (2.15 centimetres), of the crown 0.34 inch (0.86 centimetre), and of the root 0.51 inch (1.29 centimetres). The lateral incisors are the most variable in size and form of all "ie dental series of man, and they more frequently fail to appear in the dental arch— suppressed— than any others except the third molars. They are often imperfectly developed, and not infrequently present a conical or peg- shaped form. In one instance which has come under the observation of the writer, the superior lateral incisors have been absent in certain mem- bers of a family for three generations. The father had never erupted these teeth, his only daughter had the same deformity, and of her four children, two boys and two girls, the eldest son and both daughters have never erupted them, while these teeth in the second son are developed and peg-shaped. The pulp-canal partakes of the shape of the root, which is generally flattened, and when the root is straight it can be readily entered and fol- lowed to the apex ; but in operating for the removal of the pulp, the possibility of encountering a root with a curved apical end must not be overlooked. THE LOWER INCISORS. The lower incisors have the general outlines of the superior laterals, but they are in every way smaller, the roots are much more flattened mesio- distally, and often have a groove upon the mesial and distal surfaces run- ning from the cervix to the apex. The labio-lingual diameter of the root is much greater than its mesio- distal diameter. They are located in the anterior portion of the lower jaw upon either side of the median line, opposite the superior incisors, with which they occlude in cutting food. The developmental lines are the same, but the tubercles upon the morsal edge and the labial grooves are less strongly marked than in the superior incisors. The lower central incisor is the smallest tooth of the dental series of man. It is chisel-shaped in form. The crown, viewed mesio-distally and labio-lingually, is composed of a double wedge. The widest portion of the crown is the morsal edge, which is thin and straight. From this point it slopes slightly to the cervix, where it is only about one-half as wide as at the edge. The labial surface (Fig. 17) has the outline of a slender wedge, its widest portion at the morsal edge, and its narrowest at the cervix. It is nearly straight, or only slightly convex near the edge, but as it approaches the cervix it becomes more rounded and convex. The cervical margin is well defined and concave towards the root. The mesio-labial and disto-labial !>abial grooves Fig. 17. — Inferior right central incisor, (Enlarged.) riuiit central incisor, lingual surface. (Enlarged.) right central incisor, (Enlarged.) Fi<;. 20.— Infcri. right central incisor, di (Enlarged.) Mesio- narginal ridge -M , v .-^_ Lingual fossa Disto- marginal ridge Fig. 21. — Inferior right lateral incisor, labial surface. (Enlarged.) Fig. 22. — Inferior right lateral incisor, lingual surface. (Enlarged.) Fig. 23. — Inferior right lateral incisor, mesial surface. (Enlarged.) Fig. 24.— Inferior right lateral inciapr, distal surface. (Enlarged.) CLASSIFICATION AND DESCRIPTIVE ANATOMY OF THE TEETH. 9 margins are rounded off at the expense of the labial surface. The mesial angle is quite acute, and the distal angle slightly obtuse and rounded. The lingual surface (Fig. 18) is concave from the mesial edge to the cervix, but is nearly flat, or only slightly concave mesio-distally. The marginal ridges are not strongly marked. The mesial and distal surfaces (Figs. 19 and 20) are V-shaped in outline, with the apex directed towards the morsal edge of the crown. They are convex near the edge, but become flattened and even slightly concave at the cervix. The cervix is flattened mesio-distally, the greatest diameter being the labio-lingual. Section at this point gives the form of a compressed oval. The root is flattened like the cervix, for its entire length. The apex sometimes has a distal curve. The groove upon the mesial and distal surfaces is sometimes quite deep and occasionally results in bifurcation. The pulp canal is thin and flattened, partaking of the form of the root ; in some instances it is with great difficulty that the canal can be entered with the most delicate instruments. The average length of the inferior central incisor is 0.81 inch (2.05 centimetres), of the crown 0.34 inch (0.86 centimetre), and of the root 0.47 inch (1.19 centimetres). The inferior lateral incisor (Figs. 21, 22, 23, and 24) is similar in form to the inferior central, but, unlike the superior incisors, it is distinctly larger than the centrals, not only in width of crown, but also in the length of the root, while the marginal ridges are more strongly marked and the fossa more distinct. The morsal edge has a slight distal pitch, and the distal angle is obtuse and rounded. The average length of the inferior lateral incisors is 0.85 inch (2.15 centi- metres), of the crown 0.35 inch (0.88 centimetre), and of the root 0.50 inch (1.26 centimetres). THE CUSPIDS. There are four cuspids in the dental series of man, two in each jaw. They are situated just in front of the angle of the mouth, between the lateral incisor and the first bicuspid tooth ; they are the third in order from the median line, and form the spring of the superior dental arch. These teeth are variously known as cuspids, cuspidati, canines, and eye- teeth. The term cuspid comes from the Latin cuspis, a point. The cuspid teeth are in all respects larger and stronger than the incisors, the crown is thick and spear-pointed, and the root long and heavy. The architectural form of these teeth adapts them for seizing, piercing, and tearing animal food, and they represent the carnivorous element in man. The Superior Cuspids. — The crowns of the superior cuspids present for examination four surfaces, the labial, lingual, mesial, and distal, two margins, the cervical and morsal, and two angles, the mesial and the distal. The general outline of the crown is that of a short cone with its base at the gum line, and it represents the primitive conical teeth of many of the fishes. 10 OPERATIVE DENTISTRY. The labial surface (Fig. 25) of tlie crown in outline is spear-shaped. It is convex in all directions, and is much more rounded mesio-distally than the incisors. The developmental grooves and ridges are often quite promi- nent. The distal groove is usually most strongly marked, which brings the central and distal lobes into greater prominence. This surface is bounded by five margins, the mesial, distal, cervical, mesio-morsal, and disto-morsal. The mesial and distal margins are rounded and convex from the morsal edge to the cervical margin ; the convexity being greatest in the distal margin. The distal margin is slightly shorter than the mesial on account of the sharper slope of the disto-morsal edge. The cervical margin follows the contour of the gum line, and unites with the mesial and distal margins. The morsal margin is divided by a prominent cusp, from the summit of which gradually slope away the mesio-morsal and disto-morsal margins. The mesio-morsal margin slopes slightly upward, and is usually a trifle concave, though occasionally it is convex. The disto-morsal margin may be described in the same manner, except that it is a little longer, and has a slightly more pronounced upward slope and a deeper concavity. The widest part of the labial surface is at a line drawn from the mesial to the distal angles ; the narrowest part is at the cervical margin. The Ungual surface (Fig. 26) presents nearly the same general outline of the labial surface, with the exceptions that it is more fiat, sometimes concave, and has three generally well-defined marginal ridges. The mesio-marginal and disto-marginal ridges arise at the mesial and distal angles, and pass upward, where they unite with the cervico-marginal ridge, which may be said to be formed by the union or continuation of the two former ridges. The cervico-marginal ridge is sometimes quite prominent, terminating in a more or less pronounced tubercle or cusp. Between the mesio- and disto- marginal ridges there is a prominence known as the lingual or triangular ridge, upon either side of which are sometimes deep fossa or fissures, but more frequently they are shallow and ill-defined. The mesial surface (Fig. 27) resembles that of the central incisor in many respects. It is convex in all directions at the mesial angle, but as it ap- proaches the cervix it becomes flattened and occasionally concave. The distal surface (Fig. 28) in general outline is similar to the mesial surface, except that it is more rounded, and, as it nears the cervix, not quite so flat. The distance from the cervix to the distal angle is nearly one-third shorter than the distance on the mesial surface from the cervix to the mesial angle. The morsal edge by its form gives to the cuspid tooth a double function, that of incising and penetrating. The morsal edge combines a cusp which is placed near the centre, to the long axis of the tooth, and two cutting or incisive edges which slope away from it in an upward direction, and termi- nate at the mesial and distal angles. The distal edge is longer than the mesial, and it has a more acute upward slope. The sharp cusp is soon worn off, and in old age the morsal edge may be reduced to a straight line. Disto mor margin Morsal margin -Superior right cuspid, labial surface. (Enlarged.) Fig. 26.— Superior right cuspid, lingual surface. (Enlarged.) Fig. 27. — Superior right cuspid, mesial surface. (Enlarged.) Fig. 28. — Superior right cuspid, distal surface. (Enlarged.) Disto- morsal edge Distal angle Cervical margin M edge Mesial angle Labial ridge Cervical ridge -Inferior right cuspid, labial surface. (Enlarged.) -Inferior right cuspid, lingual surface. (Enlarged.) Fig. 31.— Inferior right cuspid, mesial surface. (Enlarged.) -Inferior right cuspid, distal surface. (Enlarged.) CLASSIFICATION AND DESCRIPTIVE ANATOMY OF THE TEETH. 11 The cervix on section presents a flattened oval. The enamel line maintains about the same outline as in the central incisors, curving upward upon the labial and lingual surfaces, and downward upon the mesial and distal. Occasionally it presents a slight depression both mesially and distal^, which may be continued upon the root as a groove. The root is the longest of all the human teeth, and is irregularly coni- cal in form, tapering to a slender point ; it is usually straight, but may be curved or very crooked. In size it is about one-third larger than the central incisor. It is flattened slightly mesio-distally, and occasionally grooved. The pulp-canal is large and accessible, usually of the same form as the root, and except when the root is curved or crooked, can be easily followed to its apex. The average length of the superior cuspid is 1.05 inches (2.66 centi- metres), the average length of the crown is 0.37 inch (0.94 centimetre), and of the root 0.68 inch (1.72 centimetres). The Inferior Cuspids. — There is probably a greater similarity be- tween the superior and inferior cuspids than between any other class of teeth in the human mouth. They are alike in form and outline, though the inferior are somewhat smaller. The crowns are a little longer, and this makes them appear more slender ; they are also more flattened mesio-dis- tally at the cervix and in the root. These teeth are heavily built and firmly set in their alveoli, in order to enable them to perform the double function of incising and tearing food. The cusp is generally more promi- nent and pointed than in the superior cuspids. The crown opposes the mesial surface of the superior cuspid and the distal surface of the superior lateral incisor. The labial surface (Fig. 29) of the crown is smooth and convex, the de- velopmental grooves are less prominent than in the superior cuspids ; the labial ridge, however, is well developed, and extends from the cusp to the cervical margin, giving additional strength to the crown. Transverse ridges are also occasionally present in the cervical region. To accommo- date the occlusion of the superior teeth, the labial surface of the crown is inclined inward. The lingual surface (Fig. 30) is quite smooth, the ridges and grooves being less strongly marked than in the superior cuspids. The lingual ridge, which extends from the cusp to the cervical ridge, is, however, sometimes quite prominent. In exceptional cases the cervical ridge is strongly developed, forming a fossa at its base. The mesial surface (Fig. 31) is rounded at the eminence, flattened at the cervical third, and nearly straight with the surface of the root, which gives the crown the appearance of being bent backward or having a distal in- clination. The distal surface (Fig. 32) is quite convex and the disto-morsal angle prominent ; as it approaches the cervix it becomes more or less flattened, and at the cervical margin may present a slight concavity. The morsal edge presents a more or less prominent cusp and a mesial and a distal incisive edge. The distal edge is longer than the mesial, and 12 OPERATIVE DENTISTRY. slopes away rapidly to the distal angle. The differences, however, are not so marked as in the superior cuspids. The angles are pronounced, but the mesial less so than the distal. The cervix is generally found on section to be oval in form, although sometimes it is flattened mesio-distally, and when the root is grooved it may present a modified hour-glass outline. The curves of the enamel line are not so variable as in the incisors, nor the termination of the enamel quite so abrupt as in the superior cuspids. The root is long, straight, tapering, and flattened mesio-distally. It is shorter than the superior cuspid, and not infrequently presents a decided depression or groove upon its mesial and distal surfaces, showing a ten- dency towards bifurcation. The apex is slender and sometimes curved in a labial direction. The pulp-canal has the same general outline as the root, and when the longitudinal grooves upon the mesial and distal surfaces are deep, the canal is constricted in the middle, making it more or less difficult to enter with instruments. The average length of the inferior cuspids is one inch (2.53 centimetres), of the crown 0.40 inch (1.01 centimetres), and the root 0.60 inch (1.52 centimetres.) THE BICUSPIDS. The bicuspids, or premolars, as they are sometimes termed, are the fourth and fifth teeth from the median line, and are situated between the cuspid and first molar teeth. There are eight bicuspids in a normal denture of man, two upon each side in the upper and lower jaws. The one which is situated next to the cuspid tooth is termed the first bicuspid, and the one located between the first bicuspid and the first molar is known as the second bicuspid. The term bicuspid is derived from the Latin bi, two, and cuspis, a point, — two-pointed or bi-cusped ; a tooth, therefore, with two cusps. Architecturally the bicuspid tooth is formed of two cones fused together. This structure, from the mechanical stand-point, is weak and faulty, as its power of resistance to the mechanical force applied in mastication depends upon the strength of the mesial and distal marginal ridges which bind the cones together upon the morsal surface ; when these for any reason have been destroyed, the greatest weakness of the structure is developed, ending in the separation of the cones under stress and the loss of one or both cusps. Fractures of this character occur more frequently in the bicuspids on account of their mechanical weakness than in any of the other teeth. The bicuspids succeed and replace the deciduous molars, and by reason of their smaller size give extra space in the jaws for the permanent cuspids, which are much larger than their deciduous predecessors, and are, as a rule, erupted at a later period. The function of the bicuspids is to divide the food into small pieces and prepare it to be triturated by the molars. The superior first bicuspids, viewed from the morsal surface, have the form of a rounded quadrilateral, the buccal margin being broader than the lingual. Section through the crown just beyond the cusps shows a somewhat pear-shaped outline. The design of this form is to make it pos- iperior right first bicuspic (Enlarged.) Lingiuu cusp 'M. — Superior right first bicuspid, lingual surface. (Enlarged.) Lingual cusp Fig. 35.— Superior right first bicuspid, mesial surfac (Enlarged.) Fig. 36. — Superii Buccal cusp right first bi'cuspi< (Enlarged.) Buccal triangular ridge Fig. 37. — Superior right first bicuspid, morsal surface. (Enlarged.) -Superior right second bicuspid, buccal surface. (Enlarged.) Lingual cusp -Superior right second bicuspid, lingual surface. (Enlarged.) Fig. 40. — Superior right second bicuspid, mesial surface. (Enlarged.) CLASSIFICATION AND DESCRIPTIVE ANATOMY OF THE TEETH. 13 sible for these teetli to follow the curve of the alveolar arch. The bucco- lingual diameter of the crown is about one-third greater than its raesio- distal diameter. The buccal surface (Fig. 33) of the crown is almost a counterpart of the corresponding surface of the superior cuspid, with the exception that the cusp is placed nearer the centre of the crown, thus making the mesial and distal morsal margins nearly of the same length. The central or buccal ridge which springs from the cusp is prominent, while the mesial and distal ridges or lobes are rarely conspicuous. The developmental grooves or furrows between them are, therefore, shallow and extend only about half-way to the cervix, where they are lost in the smooth convexity of the cervical half of this surface. The surface is considerably narrower at the cervical margin, which gives it the general outline of a cone, with the apex at the cervical margin. This difference in the width of the buccal surface at the angles and at the cervix gives the -'bell-shaped" form to these teeth. The Ungual surface (Fig. 34) is mesio-distally regularly convex. From the lingual cusp to the cervix it presents a nearly straight line, though many times it is slightly convex, and occasionally fully as much so as the buccal surface. Mesio-distally the surface is not so broad as the buccal surface, and the lingual cusp is not quite so long. The mesial surface (Fig. 35) bucco-lingually is much flattened, but slightly convex ; from the mesio-morsal marginal ridge to the cervix it is also slightly convex, although examples are numerous in which a shallow concavity is presented at the cervical margin, which extends to the side of the root in a more or less sharply defined groove. The marginal angles formed by the union of this surface with the buccal and morsal surfaces are well defined, but the mesial and lingual surfaces are so blended and rounded that it is difficult to designate their line of union as an angle. The distal surface (Fig. 36) is so nearly like the mesial surface that it needs no especial description except in the points of difference. It is rather more convex than the mesial surface, has rarely a convexity at the cervical margin, and the disto-morsal angle is more prominent than the mesio-morsal. The morsal or occlusal surface (Fig. 37) presents an abrupt change in form and function as compared with the morsal edge of the cuspid tooth. This surface is composed of two well-defined cusps or points divided by a deep sulcus having a mesio-distal direction, and bound together at their bases mesially and distally by two strong and prominent ridges termed the mesio-morsal and the disto-morsal ridges. One of these cusps is situated at the buccal margin, and the other at the lingual, and from their situation are designated as the buccal and the lingual cusps. The buccal cusp is usually sharper, longer, and more prominent than the lingual cusp. The lingual cusp is broader and more rounded. From the summit of the buccal cusp four ridges slope away at right angles, one mesially to form the mesio-morsal edge of the crown ; one distally to form the disto-morsal edge ; one to the buccal surface, forming the central buccal ridge, and another slopes downward in an opposite direction to form 14 OPERATIVE DENTISTRY. the buccal triangular ridge, which ends either in the central sulcus or joins a similar ridge descending from the summit of the lingual cusp, and forms the transverse ridge. The mesio-morsal aud disto-morsal edges enter into the formation of the mesial and distal morsal angles at their extremities. The lingual cusp is usually blunt, and its margins, which are not sharply- defined, unite with the marginal ridges at both angles. The lingual trian- gular ridge arises at the summit of the lingual cusp, and either terminates at the central sulcus or joins its fellow of the buccal cusp to form the trans- verse ridge. The lingual triangular ridge is seldom prominent, and some- times is entirely absent. The central sidcus extends from one lateral rid°:e to the other in a mesio- ;tal direction, and widens into the mesial a The mesial and distal sulci are not alwayi passing over the central portion of the mesial and distal marginal ridges. The mesial and distal triangular grooves are situated at the base of the marginal ridges, and are directed towards the mesial and distal angles, dividing the marginal ridges from the triangular, where they are either lost or may be traced as slight depressions near the angles. These sulci often become the seat of caries. The cervix is flattened laterally, its bucco-lingual diameter being some- what greater than its mesio-distal. The enamel line curves slightly upward at the buccal and lingual cervical margins, and dips downward a very little, or may describe a nearly straight line at the mesial and distal cervical margin. The root is considerably flattened laterally, and is generally more or less deeply grooved from the cervix to the apex, and often bifurcated for from one-third to two-thirds of its length. The root over the buccal cusp is the buccal root, and that over the lingual cusp is termed the lingual root. Bifurcated roots in the first superior bicuspid is the rule in the negro and other races of a low order of intelligence, and also in the apes. It is often very crooked, or may be triple-rooted. The pulp-canal usually takes the form of the root, and may be either single or double. It is narrow at the neck, and often constricted in the middle, giving it the outline of an hour-glass. More often, however, it has two distinct pulp -canals. The coronal portion of the canal terminates in two well-defined cornua or horns which point towards the cusps of the crown. The average length of the first bicuspid is 0.80 inch (2.03 centimetres), of the crown 0.32 inch (0.81 centimetre), and of the root 0.48 inch (1.21 centimetres). The superior second bicuspid so nearly resembles the first that its differences only need to be noticed. It is in every way a little smaller ; the cusps are reduced, while the lingual cusp equals or exceeds the buccal cusp in size and length. The marginal ridges are broader, and the morsal surface more flattened, and often presents several shallow wrinkles or supplemental grooves and ridges, which radiate from the central sulcus. The triangular ridges are often united, thus increasing the strength of the tooth. The crown is narrower mesio-distally, and the cervix more oval, Buccal cusp Fig. 41.— Superior right second bicuspid, distal surface. (Enlarged.) Lingual cusp Fig. 42. — Superior right second bicuspid, morsal surface. (Enlarged.) Buccal ridge Transverse ridg< Fig. 43. — Inferior right first bicuspid, buccal surface. (Enlarged.) -Inferior right first bicuspid lingual surface. (Enlarged.) angular or transverse ridge Buccal cusp Lingual Disto- cusp morsal ridge Fig. 45. — Inferior right first bicuspid, mesial surfaei (Enlarged. ) Fig. 46. — Inferior right first bicuspid, distal surface. (Enlarged.) Buccal cusp Buccal cusp ridge ridge Lingual ridge or cusp Fig. 47. — Inferior right first bicuspid, morsal surface. (Enlarged.) Lingual groove Fig. 48.— Inferior right second bicuspid, morsal surface. (Enlarged.) CLASSIFICATION AND DESCRIPTIVE ANATOMY OF THE TEETH. 15 while the cervico-inarginal line curves slightly downward upon the mesial surface only. The greatest difference between these teeth is in the root, which is a little longer than the first ; very rarely bifurcated ; is much flattened from the cervix to the apex, and often deeply grooved upon the mesial surface at the apical third. (See Figs. 38, 39, 40, 41, and 42.) Occasionally the root is rounded and conical. Crooked roots are of more frequent occurrence than in the other bicuspid, and it has a tendency to be rotated in its alveolus, more frequently in a distal than in a mesial direction. The pulp-canal is usually single, and gives free access to its apex. The average length of the tooth is 0.84 inch (2.13 centimetres). The average length of the crown is 0.29 inch (0.73 centimetre), and of the root 0.55 inch (1.39 centimetres). THE INFERIOR BICUSPIDS. These teeth occupy the same relative positions in the lower jaw that the superior bicuspids occupy in the upper jaw. They are the smallest of the bicuspid teeth, and are distinctive in form, particularly in their morsal surface. The transition in form from bicuspids to molars is more marked in the lowers than in the uppers. In the inferior first bicuspid the lingual cusp is rudimentary, and in the second it is large and broad, and divided bucco-lingually through the centre by a more or less deep furrow, giving it the appearance of a tri- cuspid tooth. In architectural form, these teeth are constructed from a single cone, the peculiarities of the crown being the result of various additions or cingules to the primitive cusp. Unlike the superior bicuspids, the buccal and lingual cusps are connected by a transverse ridge. The Inferior First Bicuspid. — This tooth is the smallest of all the bicuspids, and more nearly resembles a cuspid than a bicuspid, on account of the imperfect development or supx>ression of its lingual cusp, which is often little more than a cingule. In general outline the crown is much more rounded than the superior bicuspids, and its bucco-lingual and mesio-distal measurements are nearly equal. The buccal surface (Fig. 43) viewed from the buccal aspect, looks like a cuspid. In form the buccal surface is a long oval, surmounted by an acute point. It is convex in all directions. The buccal cusp is situated a little to the distal of the centre of the crown, while the curvature of the buccal surface towards the lingual side places the buccal cusp nearly in a central position to the long axis of the tooth. The Ungual surface (Fig. 44) is convex mesio-dis tally, and nearly straight from cervix to morsal margin. The tooth is slightly bent at the cervix in a lingual direction, which gives the crown a lingual inclination. The length of this surface depends upon the length of the lingual cusp or cingule ; usually it is only about half as long as the buccal surface. The mesial and distal surfaces (Figs. 45 and 46) are convex bucco- lingually, slightly flattened at the cervix, and becoming convex towards the morsal margin, which gives a bell shape to the crown when viewed from the buccal aspect. 16 OPERATIVE DENTISTRY. The morsdl surface (Fig. 47) is so different from the superior first bicus- j)id that a separate description is necessary. In general outline this surface approaches a rounded triangle, the width at the buccal, mesial, and distal margins being greater than at the lingual margin. It is surmounted by a prominent buccal cusp which is located nearly in the centre of the surfaee, and a small lingual cusp, though this is sometimes entirely absent, and its place occupied by a more or less prominent lingual ridge. The buccal cusp has four well-defined ridges descending from it like those of the superior first bicuspid. The buccal ridge arises from the summit of the cusp and descends to the buccal surface ; the mesial and distal morsal ridges usually form a curve with its concavity towards the lingual, and are merged into the marginal ridges to form rounded angles ; the tri- angular or transverse ridge descends towards the lingual cusp or ridge. On either side of this ridge are pits, the mesial and distal pits. The mar- ginal ridges are usually well defined. The central groove sometimes crosses the transverse ridge ; at other times the ridge is divided by a deep sulcus. The cervix is very much constricted, and the cervical line but slightly curved except at the buccal margin. The enamel at this point sometimes forms a prominent ridge. The root is single, flattened laterally, long and slender, occasionally grooved mesio-distally, is rarely bifurcated, and inclined to be crooked. The pulp-canal is small and flattened, and difficult of access. The diffi- culties are increased by the lingual inclination of the crown and the ten- dency of the root to be crooked. The average length of the inferior first bicuspid is 0.84 inch (2.13 cen- timetres), of the crown 0.30 inch (0.76 centimetre), and of the root 0.54 inch (1.37 centimetres). The inferior second bicuspid resembles the first so closely in general form of both the crown and the root that an especial description, except of its morsal surface, would be unnecessary. The morsal surface (Fig. 48) of the tooth presents the most marked devia- tion in form of any of the bicuspid teeth. It is triangular in outline, like the first, but a trifle larger. The buccal cusp is larger and rounded ; the lingual cusp not quite so fully developed, and divided bucco-lingually, through the centre, by a deep groove, which gives the crown the appear- ance of being a tricuspate. The mesio-lingual cusp or tubercle is some- times developed at the expense of the disto-lingual, but it is always present. Occasionally it appears as a mere cingule on the disto-marginal ridge. A well-defined triangular ridge descends from each of the cusps, and terminates at the central groove. The marginal ridges are well marked. The central groove is generally straight, but often curved or angular ; the lingual groove is straight, and united with the central groove, forming at the point of union the central fossa. The other surfaces are shown in Figs. 49, 50, 51, and 52. The average length of the inferior second bicuspid is 0.87 inch (2.20 centimetres), of the crown 0.31 inch (0.78 centimetre), and of the root 0.56 inch (1.42 centimetres). Buccal cusp -Inferior right second bicuspid, buccal surface. (Enlarged.) lferior right second bieuspii surface. (Enlarged. ) Fig. 51. — Inferior right second bicuspid, mesial surface. (Enlarged.) Fig. 52. — Inferior right second bicuspid, distal surface. (Enlarged.) Lingual Lingual Buccal groove -Superior right first molar, buccal surface. (Enlarged.) Lingual groove Fig. 54. — Superior right first molar, lingual surface. (Enlarged.) Mesio- buccal cusp Disto-lingual cusp Disto-buccal cusp -Superior right first molar, mesial surface. (Enlarged. ) Fig. 56.— Superior right first molar, (Enlarged.) CLASSIFICATION AND DESCRIPTIVE ANATOMY OF THE TEETH. 17 THE MOLARS. The molars, or tuberoulate teeth, as they are sometimes termed, are very different in form and architectural design from those which have been pre- viously described. The most simple form of tooth is that designed from the single cone. This is the architectural form of the incisors and cuspids. The bicuspids are more complex, being formed of two cones. But the inferior first bicuspid has but one well-developed cusp and a lingual cin- gule. The superior bicuspids have two well-developed cusps, and the inferior second bicuspids have three cusps. The superior molars are still more complex, being formed by the addition o* a third cone to the bicuspid type. This gives the tooth three roots, upon which three or four cusps are supported. The inferior molars are the most complicated in form of all the teeth, being composed of four cones supporting four or five cusps. There are twelve molars in man, three upon either side of each jaw, above and below. They are situated in the posterior part of the jaws, behind the bicuspids, and are designated as the first, second, and third molars. The third molar is sometimes termed the dens sapientia, or wis- dom-tooth, because of its late eruption. The molars occupy the sixth, seventh, and eighth places, respectively, from the median line ; the first molar approximating the second bicuspid distally, the second molar ap- proximating the first molar distally, and the third molar occupying a similar position to the second molar. The function of the molars is to crush and triturate the food, and fit it to be acted upon by the gastric juice of the stomach. The loss of these teeth, therefore, seriously impairs the function of mastication, and inevitably leads to various derangements of digestion, and these again to imperfect assimilation and nutrition. The preservation of these teeth, therefore, becomes of vital importance to the individual. The superior first molar is located upon the distal side of the second b^uspid. It is the largest and most strongly marked of the superior molars, and may therefore be taken as the typical form. It possesses three strong roots, and the crown is surmounted by four more or less prominent cusps. In general contour the crown is an irregular cpiadrilateral, having its angles rounded, two of its sides convex, and two slightly flattened. The bucco-lingual diameter is a little greater than the mesio-distal, while ie height of the crown is about equal to the mesio-distal diameter. It presents for examination five surfaces, — buccal, lingual, mesial, distal, and morsal. The buccal surface (Fig. 53) is formed by the union of the mesio- and disto-buccal developmental lobes, and is divided by the buccal groove into a mesial and a distal half, which are quite similar in outline. This surface about twice the width of the bicuspids. It is widest at the morsal aargin, narrowing towards the cervix, giving a bell shape to the tooth. The morsal margin is surmounted by the mesio- and disto-buccal cusps, which are separated by a deep notch, through which passes the buccal groove to the cervical margin. Sometimes this groove terminates in a pit 18 OPERATIVE DENTISTRY. midway between the morsal and cervical margin. Descending from each buccal cusp is a longitudinal ridge, — the buccal ridges, — which are at first well defined, but gradually disappear in their course towards the cervix. The Ungual surface (Fig. 54), like the buccal surface, is formed by the union of the two Ungual developmental lobes, and is divided into a mesial and a distal half by the Ungual groove. Both halves are smoothly convex in all directions. The morsal margin is surmounted by the mesio- and disto- the mesial being the larger. The mesial lobe often carries a -a rudimentary fifth cusp. The mesial and distal margins converge rapidly towards the cervix, conforming to the palatal root. The mesial surface (Fig. 55) is nearly flat, except near the morsal margin, where it is slightly convex, and at the cervical margin, where it is some- times depressed towards the lingual or j)alatal root. The buccal and lingual margins are rounded. The morsal margin is concave in the direction of the root, while the cervical margin is concave in the direction of the morsal surface. The distal surface (Fig. 56) is similar to the mesial surface, except that it presents a somewhat greater convexity, converging more sharply towards the cervix, and more rounded towards the lingual root. The morsal surface (Fig. 57) is surmounted by four rounded cusps or tubercles designated as the mesio-buccal, the disto-buccal, the mesio-lingual, and the disto-lingual cusp ; the latter being, as a rule, smaller than the others, and sometimes only arjpearing as a small tubercle. The surface is bounded by four marginal ridges of nearly equal length, — the buccal, the lingual, the mesial, and the distal, — which unite the bases of the cusps. Arising from each cusp and descending towards the centre of the tooth is a triangular ridge. The triangular ridges of the mesio-lingual and disto- buccal cusps unite to form the prominent oblique ridge. On the mesial and distal sides of the oblique ridge are two fossse, the central and distal. The bottom of the central fossa is deeply lined by two of the developmental grooves, the mesial and buccal grooves. The former arises on the mesial surface, crosses the mesio-marginal ridge, and continues in an irregular line to the bottom of the fossa ; the latter begins upon the and terminates also in the iangular groove. A supple- mental groove arises from the central pit of this fossa, extending distally across the oblique ridge, which is termed the distal groove. It is rarely well defined, but occasionally it may divide the oblique ridge. The distal fossa is not so large as the central, and is of an entirely differ- ent form, partaking more of the outline of the sulcate groove. This fossa is traversed by a deep develop mental groove, the disto-lingual groove, which arises on the distal margin, follows the line of the fossa, crosses the lingual margin, extending on to the lingual surface- to form the lingual groove. "When a fifth cusp is present — the mesio-lingual — it is separated from the lingual surface by a groove designated as the mesio-lingual groove. Various supplemental grooves or wrinkles are found upon the morsal surface of the molars, which radiate from these fossse. Lingual groove Fig. 57. — Superior right first molar, morsal surface. (Enlarged.) Fig. 58.— Superior right second molar, buccal surface. (Enlarged.) Disto- Mesio- buccal buccal root root Lingual groove -Superior right second molar, lingual surface (Enlarged.) Fig. 60.— Superior right second m (Enlarged.) lar, mesial surface. P,llrc;il grc>< >ve Lingual Disto-lingual groove Fig. 61.— Superior right second molar, distal surface. Fig. 62.— Superior right second molar, morsal surface. (Enlarged.) (Enlarged.) Buccal groove Fig. 63. — Superior right third molar, buccal surfaci Lingual cusp Fig. 64. — Superior right third molar, lingual surface. (Enlarged.) CLASSIFICATION AND DESCRIPTIVE ANATOMY OF THE TEETH. 19 The cervix of this tooth, on section, shows the form of a rounded rhom- boid, widest upon its buccal aspect. The cervical line is nearly straight upon all four surfaces. A concavity occurs on the buccal side at the bifur- cation of the buccal roots, and a slight depression upon the mesial and distal sides, with an inclination towards the lingual root. The root is divided into three prongs or radicles, two upon the buccal side, which are small, tapering, and either flat or rounded, the mesio- buccal and disto-buccal, and one upon the lingual side, large, round, and tapering, the lingual. The roots are usually separated ; their apices stand wide apart. Occasionally, however, they are united for some distance by a bridge of cementum ; this most frequently occurs with the buccal roots. The mesio-buccal is the largest of the buccal roots. All of the roots may be more or less bent and crooked. The Pulp- Chamber and Canals. — The pulp-chamber is large and divides into three branches, one for each root. The Ungual canal is the largest, and is freely entered to its apex, except in those cases in which the root is bent or crooked. The mesio-buccal is the next largest canal, and can often be entered with ease, but occasionally it is small and narrow, and when the root is crooked it often becomes difficult or impossible to follow it. The disto-buccal canal is almost always so small and fine as to require great skill and much patience to properly cleanse it preparatory to filling. Many times the canal cannot be followed to the apex by any degree of skill or patience, thus making the proper treatment and filling of these roots one of the most difficult problems in the whole range of dental practice. The average length of the superior first molar is 0.81 inch (2.05 centi- metres), of the crown 0.30 inch (0.76 centimetre), and of the root 0.51 inch (1.29 centimetres). The superior second molar is so nearly the counterpart of the first molar that the differences in its form need only be described. It is a little smaller than the first molar, not so nearly quadrilateral in form, but rhomboidal, being somewhat compressed mesio-distally. The buccal surface (Fig. 58) is almost identical with that of the first molar. A slight difference is noticed in the mesio-distal width of the sur- face and in the location of the buccal groove, which in many instances is at the distal third rather than at the mesio-distal centre. The lingual surface (Fig. 59) presents a greater convexity mesio-distally, and particularly so from the linguo-morsal margin to the cervix. The lingual groove is not so constant in its location, often being found between the mesio-distal centre and the extreme of the distal third of the surface. The mesial and distal surfaces (Figs. 60 and 61) have only slight differ- ences. The mesial is inclined to be concaved bucco-lingually ; into this concavity the distal surface of the first molar closely fits, while the only difference in the distal surface is that it is more markedly convex. The Morsal Surface. — The most marked differences in the character of the morsal surface (Fig. 62) of the second superior molar is the almost con- stant tendency to the suppression of the disto-lingual lobe. This carries the oblique ridge farther to the distal side, and enlarges the central fossa. The cusps are also not so prominent, and when the disto-lingual cusp is 20 OPERATlVE dentistry. only rudimentary in size, and the oblique ridge prominent, the tooth be- comes practically a three-cusped tooth. The various grooves are the same as on the first molar in the normally developed organ. The cervix is less regular in outline and more constricted and flattened mesio-distally than in the first molar. The roots are the same in number and general form as in the first molar ; they spread less, however, and are quite inclined to be crooked or converge towards each other, or to be fused together. Sometimes the buccal roots only are fused, while in others the mesial and lingual are joined, or all of the roots may be united in a single root, the outlines of the roots being marked only by shallow grooves. The pulp-canals in a normally developed superior second molar are, as a rule, smaller and more difficult to enter than those of the first molar. When the roots are fused together, all of the canals may coalesce, making a single canal, or when union of the buccal roots takes place these canals may unite. The uncertainty, however, as to their regularity in form adds greatly to the difficulties to be surmounted in the treatment. The average length of the superior second molar is 0. 79 inch (two centi- metres), of the crown 0.28 inch (0.71 centimetre), and of the root 0.51 inch (1.29 centimetres). The superior third molars are smaller than either of the other su- perior molars, and show greater deviations from the normal type, being very erratic as to the time of their appearance and in their form and struc- ture. It is the eighth from the median line, and the last tooth of the upper dental arch. This tooth, when well formed, is a tricuspid, the clisto-lingual cusp being suppressed. The oblique ridge then becomes the disto-marginal ridge. The crown is triangular in form and the angles well rounded. The buccal surface (Fig. 63) is like that of the second molar, but more rounded and the lobes less strongly marked and the buccal groove shallow. The lingual surface (Fig. 64) is usually full and convex in all directions. It has but a single lobe on account of the suppression of the disto-lingual cusp. The Mesial and Distal Surfaces. — The mesial surface resembles the same surface of the second molar but is reduced in size, while the distal surface is shorter and more rounded (Figs. 65 and 6G). The morsal surface (Fig. 67) in a well-developed third molar presents a ?nesio -buccal, a disto-buccal, and a mesio-lingual cusp, with the suggestion of a disto-lingual cusp, in the form of a cingule or tiny tubercle. In this case it will also present a central and distal fossa, with the developmental grooves more or less distinctly marked. More often, however, the disto- lingual cusp is entirely suppressed, and with it the distal fossa. Many times the cusps will be so blunted around the central fossa as to give the appearance of a continuous marginal ridge, occasionally sharply defined, or it may be broadly rounded. The cervix is constricted, and in form, on section, gives the outline of a rounded triangle. The roots have very rarely the form of the typical molar in the higher civilized races. As a rule, the roots are fused together to a greater or less Mesial groove Fig. 65. — Superior right third molar, mesial surfac (Enlarged.) Distal groove -Superior right third molar, distal surface. Disto-huccal gr< Mesio-lingual cusp Fig. 67. — Superior right third molar, morsal surface. (Enlarged.) Fig. 68. — Inferior right first molar, buccal surface. (Enlarged.) Mesio-lingual cusp Disto-lingual cusp Lingual Fig. 69.— Inferior right first molar, lingual surface. Fig. 70.— Inferior right first molar, mesial surface. (Enlarged.) (Enlarged.) Median- Buccal groove buccal cusp Disto-buccal groove Mesio- buccal cusp Mesial groove B..„ '- jE Mesio- fi cusp Disto- buccal cusp Distal groove Central Disto- lingual cusp Fig. 71.— Inferior right first molar, distal surface. (Enlarged.) Lingual groove Ftg. 72. — Inferior right first molar, morsal surface. (Enlarged.) CLASSIFICATION AND DESCRIPTIVE ANATOMY OF THE TEETH. 21 extent, sometimes forming a single root, and they are often curved distally towards the maxillary tuberosity. Sometimes they have multiple roots, which may be curved in various directions. The pulp-canals are usually blended into one, but when the roots are separate there are individual canals. The difficulties presented in the treatment of the root- canals of these teeth are greatly enhanced by the positions which they occupy in the jaw and their great liability to have crooked roots. The average length of the superior third molar is 0.68 inch (1.72 centi- metres), of the crown 0.24 inch (0.6 centimetre), and of the root 0.44 inch (1.11 centimetres). THE INFERIOR MOLARS. The inferior molars are three in number, and are designated according to their positions in the jaw as the first, the second, and the third. They occupy respectively the sixth, seventh, and eighth positions in the inferior arch from the median line. As already stated, these teeth are constructed upon the architectural de- sign of a combination of four cones united at their bases to form the crown, while the apices are united in pairs to form the mesial and distal roots. The inferior molars differ from the superior in that they have two roots instead of three ; are inclined to have multiple cusps ; have a greater diameter mesio- distally than bucco-lingually ; and the buccal surface slopes towards the centre of the tooth to accommodate the over- locking of the cusps of the occluding teeth. The inferior first molar is the sixth tooth from the median line, and approximates the second bicuspid upon its distal surface. " Next to the superior first molar it is the largest tooth in the denture." (Black.) The buccal surface (Fig. 68) is an irregular trapezoid in form, the morsal margin being wider than the cervical, due to the convergence of the mesial and distal surfaces towards the cervix. The surface is convex in all direc- tions, and the mesial and distal margins are rounded. The morsal margin is usually surmounted by three cusps or tubercles, the mesio-buccal, the me- dian-buccal, and the disto-buccal, which are separated by the buccal and disto- buccal grooves. The buccal groove is a little to the mesial of the centre of the tooth, while the disto-buccal groove is near the disto-buccal angle. These grooves generally terminate near the middle of the surface in pits, which often become the seat of caries. The lingual surface (Fig. 69) is slightly convex in all directions, and in- clines towards the lingual. The surface is not so wide as the buccal sur- face on account of the convergence of the mesial and distal surfaces towards the lingual. The morsal margin forms a rather sharp angle with the mor- sal surface ; it is surmounted by two cusps or tubercles, the mesial and dis- tal, and is divided through its centre by the lingual groove, which separates the mesial and the distal cusps. This groove is shallow and rarely extends farther than the middle of the surface. The mesial and distal surfaces (Figs. 70 and 71) are flattened bucco-lin- gually and convex from morsal margin to cervix, the distal surface more than the mesial. They are wider at the morsal margin than at the cervix. 22 OPERATIVE DENTISTRY. The rnesio-inorsal margin is deeply concaved, and the disto-morsal margin is notched, sometimes deeply, by the distal groove. The morsal surface (Fig. 72) is trapezoidal in form, the buccal side being the longest. The surface is surmounted by five cusps, designated as fol- lows : the mesio-buccal, the median-buccal, the disto-buccal, the mesio-lingual, and the disto-lingual ; three are arranged upon the buccal half of the sur- face, and two upon the lingual. The cusps are united at their bases by four marginal ridges, the mesio-marginal ridge, joining the mesio-buccal and the mesio-lingual cusps ; the bucco-marginal ridge, uniting the mesio-buccal, median-buccal, and disto-buccal cusps ; the linguo-marginal ridge, joining the mesio-lingual and disto-lingual cusps ; and the disto-marginal ridge, uniting the disto-lingual and disto-buccal cusps. These ridges slope towards the centre of the teeth to form the central fossa. There are five triangidar ridges which descend from the five cusps towards the central fossa. The morsal surface is traversed by five developmental grooves, the mesial, buccal, disto-buccal, lingual, and distal. The mesial groove arises in the central fossa and crosses the mesio-margi- nal ridge to the mesial surface ; the buccal groove begins at the central fossa, crosses the bucco-marginal ridge between the mesio- and median-buccal cusps to the buccal surface ; the disto-buccal groove takes a disto-buccal di- rection from the central fossa, dividing the bucco-marginal ridge between the median- and disto-buccal cusps ; the lingual groove has its origin in the central fossa, crosses the linguo-marginal ridge in a deej) sulcus between the mesio- and disto-lingual cusps, and is lost upon the lingual surface. The distal groove arises also from the central fossa, crosses the disto- marginal ridge dividing the disto-lingual cusp from the disto-buccal. Various other pits and supplemental grooves are occasionally observed. The cervix on section is rectangular in form, with the sides slightly con- caved in the centre, and deepest at the buccal and lingual sides at the begin- ning of the bifurcation of the roots. The cervical line is convex upon the buccal and lingual sides, and concave upon the mesial and distal. The roots are two in number, the mesial and the distal. They are long, flattened mesio- distally, and often have a decided distal curvature. They are implanted in their alveoli, with their long diameter in a trans- verse direction to the jaw. The distal root is larger and more rounded than the mesial, the latter having deeper grooves and a greater tendency to bifurcation. The pulp-canal is formed like the teeth, with two branches. Occa- sionally the mesial root will have two canals. The distal canal is the largest and quite readily entered, while the mesial canal is inclined to be flat or hour-glass-shaped, showing the tendency of this root to bifurcate. When separate canals are formed, they are usually very small, and often cannot be followed. The average length of the inferior first molar is 0.82 inch (2.08 centi- metres), of the crown 0.30 inch (0.76 centimetre), and of the root 0.52 inch (1.32 centimetres). The inferior second molar differs from the first in that it has but four instead of five cusps, is more quadrangular, rounded, and symmetrical. Mesio-buccal cusp groove Mesio-lingual cusp Central fossa Cervical lingual Buccal &ro°v< gual Fig. 73. — Inferior right second molar, buccal surface. Fig. 74. — Inferior right second molar, lingual surface. (Enlarged.) (Enlarged.) Mesial groove Fig. 75. — Inferior right second molar mesial surface. Fig. 7(">. — Inferior right second molar, distal surface. (Enlarged.) (Enlarged.) Mesial groove Median Disto-lingual cusp buccal cusp Mesio-buccal cusp Central fossa Distal pit Fig. 77. — Inferior right second molar, morsal surface. (Enlarged.) Fig. 78.— Inferior right third molar, buccal surface. (Enlarged.) Mesio-buccal cusp Disto-lingual cusp Mesial groove Mesio- lingual cusp '■ ' Disto- buccal cusp Fig. 79.— Inferior right third molar, lingual surface (Enlarged.) Fig. 80. — Inferior right third molar, mesial surface. (Enlarged.) CLASSIFICATION AND DESCRIPTIVE ANATOMY OF THE TEETH. 23 The buccal surface (Fig. 73) is convex in all directions, but is divided into two lobes by the buccal groove, which is usually shallow. A deep buccal pit is often observed in the centre of the surface. The morsal mar- gin slopes towards the centre of the tooth as in the first molar, and the surface is widest at this point, while the convergence of the mesial and distal surfaces makes it narrowest at the cervix. The lingual surface (Fig. 74) is similar to that of the first molar, with the exception that it is proportionately wider, being nearly as broad as the buccal. The mesial and distal surfaces (Figs. 75 and 76) are similar to those of the first molar, except that the distal surface does not have the distal pro- tuberance due to the presence of the fifth cusp ; both surfaces are smoothly convex. The morsal surface (Fig. 77) is surmounted by four cusps, placed at the four corners of the surface. The cusps are rounded and symmetrical, the lingual being a little more pointed than the buccal. The marginal ridges are well formed and enclose a central fossa. The central fossa is traversed by four developmental grooves, all arising from the central pit, which cross the four marginal ridges. The triangular ridges are well marked, being more prominent than in the first molar. The cervix is similar to that of the first molar, but more constricted. The cervical line describes about the same irregular curves. The roots are about the same as the first molar, except that the diver- gence is not so great. There is also a tendency to fusion of the roots. Examples of complete fusion are not rare. The roots are usually curved distally, or otherwise crooked. The pulp-canals are similar to those of the first inferior molar, the distal the largest, and the mesial usually much constricted. The same difficulties are encountered in opening the canals as are found in the first molars, which are augmented by the irregularity in the form of the roots. The average length of the inferior second molar is 0.77 inch (1.95 cen- timetres), of the crown 0.27 inch (0.68 centimetre), and of the root 0.50 inch (1.26 centimetres). The inferior third molar is similar in many respects to the other lower molars. It is the eighth from the median line, and the last tooth in the lower dental arch. It approximates the second molar upon its distal sur- face. It is x3robably the most erratic in its form of any tooth in the whole dental series. There are tivo typical forms, one having four cusps, and sepa- rated by four developmental grooves, like the second molar, and the other having five cusps andfive developmental grooves like the inferior first molar. While these two forms are the most common, there are many variations from these types ; the morsal surface is often divided by numerous develop- mental grooves, so that six, seven, and even eight well-defined cusps are presented. The buccal surface (Fig. 78) of this tooth is more convex than either the first or second molars, but in all other respects it has the same form. When the tooth has four cusps, this surface partakes of the outlines of the second molar, being surmounted at its morsal margin by two cusps, divided 24 OPERATIVE DENTISTRY. by the buccal groove. When it has five cusps it is like the buccal surface of the first molar, being surmounted at its morsal margin by three cusps, which are divided by the buccal and disto-buccal grooves. The lingual, mesial, and distal surfaces (Figs. 79, 80, and 81) correspond so nearly to the same surfaces of the other lower molars that no separate description is necessary, except to notice that the distal surface is more convex, and when the fifth cusp is present, often very prominent. The morsal surface (Fig. 82) exhibits the greatest variations from the other lower molars. In the four-cusped tooth, which is the more common form, it is the counterpart of the second molar, with the exceptions that the distal cusps are rarely so large and well formed as the mesial, and the central fossa is sometimes occupied by a central tubercle. In the five-cusped tooth, it partakes of the form of the first molar, and is frequently larger than the second. The distal cusp is usually placed more disto-lingually, the buccal surface is more rounded, and numerous supplemental grooves and ridges are often present. The morsal surface is sometimes surmounted by six, seven, or eight cusps, as many supplemental grooves, and one or more supplemental ridges within the central fossa. Such teeth are always very large, the grooves deeply fissured, and the structure poorly organized, predisposing them to early destruction from caries. Occasionally the inferior third molar is much smaller than the second, having a circumference of not more than two-thirds as large as this tooth. A common feature of the crown is its inclination towards a circular form. The cervix is similar in shape, in the typical forms, to the second molar. The roots are, in comparison, smaller and more rounded than in the other lower molars. They are generally divided, but have a greater convergence, and in some instances are fused together in the form of a single cone, but in either case they are almost invariably curved distally, sometimes very considerably, so that their extraction is often a difficult operation. Occa- sionally the tooth may have three or more roots. The pulp-canal is sometimes single, but usually it is divided. The canals are, as a rule, difficult to enter on account of the location of the tooth, the generally small size of the canals, and the almost certain distal curvature of the roots. The average length of the inferior third molar is 0.62 inch (1.57 centi- metres), of the crown 0.26 inch (0.66 centimetre), and of the root 0.36 inch (0.91 centimetre). THE DECIDUOUS TEETH. The deciduous teeth resemble in every way the same class of teeth in the permanent set, with the exception of the first molars. They are, however, all much smaller than the permanent teeth, and are much whiter in color. The incisors and cuspids of both jaws are similar in form to the teeth which succeed them. The cervix, however, is more constricted, and the enamel ends more abruptly. The process of resorption of the roots of the Disto-lingual cus Disto-buccal cusp FlG. 81.— Inferior right third molar, distal surface. (Enlarged.) Disto-lingual cusj ])i>tn hueeal cus Mesio-lingual cusp Mesial groove Mesial cusp Mesio-buccal cusp Median-buccal cusp Buccal groove Fig. 82.— Inferior right third molar, morsal surface. (Enlarged.) CLASSIFICATION AND DESCRIPTIVE ANATOMY OF THE TEETH. 25 deciduous teeth, which allows their crowns to fall away, begins in the cen- tral incisors at about the fourth year, and is completed at about the seventh. In the lateral incisors this process begins at about the fifth year, and is completed at about the eighth ; while in the cuspids it is delayed until the ninth year, and completed at the twelfth. Fig. 83. The superior first deciduous molars are unlike the molars of the permanent set in that the crown has but three lobes or cusps, mesial, distal, and Ungual, which are divided by three developmental grooves, the mesial, distal, and buccal. The cusps converge towards the centre of the crown, giving the morsal surface the appearance of being smaller than the base of the crown. The cervix is constricted, while the enamel ends so abruptly at the bucco- cervical margin as to form a prominent ridge, —the buccal ridge. Another distinctive feature is that the marginal ridges, triangular ridges, and angles are more acute than in the permanent molars. Its greatest diameter is bucco-lingually. The superior second deciduous molars are larger than the first ; the morsal surface is wider, and is surmounted by four cusps, and in other ways the prototype of the superior second permanent molar. The inferior deciduous molars are similar in general form and out- line to the permanent molars. The first molar has four cusps irpon its morsal surface, while the second molar, unlike the second permanent molar, has five cusps. The cusps and the marginal and triangular ridges are more marked and prominent ; the central fossa is large and deep, being sometimes divided by the triangular ridges forming two or more fossoe or pits. The cervix is constricted and the bucco -marginal ridge prominent. The mesio-distal diameter of the crown is greater than the bucco-lingual. The roots of the deciduous molars differ from the permanent in that they are relatively thinner and longer, and are much more spread or divergent to accommodate the crowns of the succeeding bicuspids. The pulp-chamber is proportionately much larger than in permanent molars, but the root-canals are thin and narrow, making their treatment difficult. The process of resorption in the roots of the first molars begins at about the sixth year, and is completed at the tenth, while for the second molars it begins at about the eighth year and is completed at the eleventh. CHAPTER II. ORIGIN, DEVELOPMENT, AND MORPHOLOGY OF THE TEETH. Definition. — Morphology (from the Greek fj.»p7j, form, and X6yo