COLUMBIA LIBRARIES OFFSITE HEALTH SCIENCES STANDARD HX00043834 I II! |: nil' 'ti l;iilili;a;lluli[lil;lllllllllllliL Columbia ^nibersiit in t!)c €itp of i^eto |9orfe ^cfjool of Bental anb (j^ral ^urgcrp Digitized by the Internet Archive in 2010 with funding from Columbia University Libraries http://www.archive.org/details/textbookofoperatOOjohn A TEXT-BOOK OF OPERATIVE DENTISTRY LIST OF CONTRIBUTORS. J. p. BUCKLEY, PH. G.. D. D. S.. Professor of Materia Mcdica and Therapeutics, Chicago College of Dental Surgery. W. A. CAPON, D. D. S.. Lecturer and Instructor of Dental Ceramics, Dental Department, University of Pennsylvania. GEORGE W. COOK, D. D. S.. Dean of the Cc^llege of Dentistry, University of Illinois, Chicago. FERDINAND J. S. GORGAS. A. M., M. D.. D. D. S.. Dean and Professor of Principles of Dental Science, Oral Surgery and Dental Prosthesis in the University of Maryland, Dental I)ej)artnicnt; Author of "Dental Medicine." ELLISON HILLYER, D. D. 5.. Professor of Prosthetic Dentistry and Orthodontia, New York College of Dentistry. GEORGE EDWIN HUNT. M. D.. D. D. S.. Dean of the Indiana Dental College, Indianapolis. C. N. JOHNSON, M. A.. L. D. S.. D. D. S.. Professor of Operative Dentistry in the Chicago College of Dental Surgery; Editor of "The Dental Review." C. EDMUND KELLS. JR., D. D. S., New Orleans. GARRETT NEWKIRK. M. D.. Member of the California State Board of Dental Examiners, Former Dean and Professor of Operative Dentistry, College of Dentistry, University of Southern California. JOHN EGBERT NYMAN, D. D. S.. Chicago. ALFRED OWRE. D. M. D.. M. D.. C. M.. Dean and Professor of Operative Dentistry and Metallurgy, College of Dentistry, University of Minnesota. JOHN DEANS PATTERSON, D. D. S.. Professor of Dental Pathology, Kansas City Dental College. HERMANN PRINZ, M. D.. D. D. S.. Professor of Materia Medica, Therapeutics and Pathology, Dental Department Washington University, St. Louis. HERBERT A. PULLEN, D. M. D., President of the American Society of Orthodontists, 1906-07 ; Instructor in the Angle School of Orthodontia, Session of 1900; Member of the New York State Dental Society, Buffalo Dental Association, National Dental Association, etc. CHARLES R. TURNER. D. D. S.. M. D.. Professor of Mechanical Dentistry and Metallurgy, Department of Dentistry, University of Pennsylvania. A. E. WEBSTER. L. D. S., D. D. S.. M. D., Professor of Operative Dentistry and Dental Pathology in the Royal College of Dental Surgeons of Ontario; Editor of "The Dominion Dental Journal," etc. GEORGE H. WRIGHT, D. M. D.. Former Assistant in Embryology and Histology, Harvard Medi- cal School. A TEXT-BOOK OF OPERATIVE DENTISTRY BY VARIOUS AUTHORS EDITED BY C. N. JOHNSON. M. A., L D. S.. D. D. S. PROFESSOR OF OPERATIVE DENTISTRY I.\ THE CHICAGO COLLEGE OF DEXTAL SURGERY; EDITOR OF THE "dEXTAL REVIEW'" WITH SIX HUNDRED AND EIGHTEEN ILLUSTRATIONS PHILADELPHIA P. BLAKISTON'S SON & CO. 1012 WALNUT STREET 1908 Copyright, iqo8, by P. Blakiston's Son & Co. Printed by The Maple Press York, Pa. PREFACE In preparing this book for the profession the aim has been to condense the latest thought on the various subjects into the closest possible limit consistent with a clear elucidation of the ideas presented. It has been the constant effort to bring the work strictly up to date, and with the rapid evolution of dental thought in progress at the present time this has been no small task. As an illustration it is only necessary to mention the circumstance that one entire chapter ^ — that by Dr. Nyman on the gold inlay — was wholly rewritten after it was in type and the illustrations made for it. The original article was discarded as being out of date the moment the cast method became a demonstrated fact. This is only indicative of the great care taken by the various authors in the revision of their work, and for which the editor wishes at this time to express his great appreciation. Particular attention is called to the illustrative character of the work. Most of the cuts were made specially for the book, and many of them are striking in their originality. Those, for instance, illustrating Dr. Turner's chapter on "The Anatomy of the Human Teeth" were made from photographs of natural teeth, a typical specimen of each tooth being selected for this purpose and photographed on its different surfaces. The effect has been to present something perfectly true to nature. Mention might be made of distinguishing features in each chapter in the book, but this would appear unnecessary with the work in the reader's hands. It seems appropriate, however, to call attention to Dr. Pullen's chapter on "Orthodontia" which we believe is one of the most concise and practical presentations of this important subject that has yet appeared. To the contributors the editor feels under deep obligation for their cordial cooperation in preparing the work, and to the publishers for their uniform courtesy and painstaking care in every detail of publication. C. N. J. Chicago, August, 1908. CONTENTS. PAGE Introduction, xi BY C. N. JOHNSON, M. A., L. D. S., D. D. S. CHAPTER I. The Anatomy of the Human Teeth, , i BY CHARLES R. TURNER, D. D. S., M. D. CHAPTER II. The Histolog)' of the Human Teeth, 59 BY CHARLES R. TURNER, D. D. S., M. D. CHAPTER III. Hygiene and Arrangement of Light in the Operating Room, 85 BY C. N. JOHNSON, U. A., L. D. S., D. D. S. CHAPTER IV. Asepsis in the Operating-Room 89 BY A. E. WEBSTER, M. D., L. D. S., D. D. S. CHAPTER V. Hygiene of the Mouth, 97 BY GEORGE H. WRIGHT, D. M. D. CHAPTER VI. Dental Caries, 117 BY C. N. JOHNSON, M. A., L. D. S., D. D. S. CHAPTER VII. Examination of Teeth for the Finding of Carious Cavities, 127 BY GARRETT NEWKIRK, M. D. CHAPTER VIII. Separation of Teeth Preparatory to Operating on Cavities in the Proximal Surfaces, 133 BY GARRETT NEWKIRK, M. D. CHAPTER IX. Exclusion of Moisture from the Teeth during Operations, 145 BY GEORGE EDWIN HUNT, M. D., D. D. S. vii Vlll CONTENTS. CHAPTER X. PAGE Pre])arati()n of Cavities for Fillings i6i BY .^. E. WEBSTER, M. D., L. D. S., D. D. S. CH.^PTER XI. The Treatment of Sensitive Dentin 215 BY J. p. BUCKLEY, PH. G., D. D. S. CH.\PTER XII. Filling Materials: Their Characteristics, Indications for Their U.se and the Methods of Manipulation, 225 BY ALFRED OWRE, M. D., C. M., D. M. D. CHAPTER XIII. The Use of the Matrix in Filling Teeth, 255 BY GARRETT NEWKIRK, II. D. CHAPTER XIV. Inlays, 263 BY C. N. JOHNSON, M. A., L. D. S., D. D. S. CHAPTER XV Preparation of Cavities for Inlays, 267 BY C. N. JOHNSON, M. A., L. D. S., D. D. S. CHAPTER XVI. The Porcelain Inlay 277 BY W. A. CAPON, D. D. S. CHAPTER XVII. Construction of Gold Inlays, 301 BY JOHN EGBERT NYHAN, D. D. S. CHAPTER XVIII. The Treatment of Exposed or Nearly Exposed Pulps, 311 BY J. p. BUCKLEY, PH. G., D. D. S. CHAPTER XIX. The Anesthetization and Devitalization of Pulps, Their Removal and the Subsequent Treatment, 317 BY J. p. BUCKLEY, PH. G., D. D. S. CHAPTER XX. The Treatment of Ordinary Pericementitis, 335 BY J. p. BUCKLEY, PH. G.. D. D. S. CHAPTER XXI. The Chemistry of Pulp Decomposition, 341 BY J. p. BUCKLEY, PH. G., D. D. S. CONTENTS. IX CHAPTER XXII. P^Qj, The Treatment of Putrescent Pulps; Acute and Chronic Alveolar Abscess, with Complications; and the Filling of Root Canals, 347 BY J. p. BUCKLEY, PH. G., D. D. S. CHAPTER XXIII. The Causes and Treatment of Discolorations of Teeth, 367 BY J. P. BUCKLEY, PH. G., D. D. S. CHAPTER XXIV. The Treatment of Children's Teeth 377 BY C. N. JOHNSON, M. A., L. D. S., D. D. S. CHAPTER XXV. Local Anesthesia, 3^5 BY HERMANN PRINZ, M. D., D. D. S CHAPTER XXVI. The Extraction of Teeth, 399 BY FERDIN.^ND J. S. GORGAS, A. M., M. D., D. D. S. CHAPTER XXVII. The Planting of Teeth, 439 BY C. EDMUND KELLS, JR., D. D. S. CHAPTER XXVIII. Pyorrhea Alveolaris, 45 ^ BY JOHN DEANS PATTERSON, D. D. S. CHAPTER XXIX. Erosion, 47^ BY GEO. W. COOK, D. D. S. CHAPTER XXX. The Management of an Office Practice, 483 BY ELLISON HILLYER, D. D. S. CHAPTER XXXI. Orthodontia 5o5 by herbert a. pullen, d. m. d. Index ... - 747 INTRODUCTION. Operative Dentistry may be defined as the science and art which aims at the preservation of the natural teeth in a state of heahh and beauty. Its highest ofhce is to prevent disease or deformity, but where either of these has already occurred it is then its function to remedy the evil, and check its further progress. The dentist who does the best for his patient is the one who, in addition to the develop- ment of the highest manipulative skill, studies most carefully the conditions surrounding the field of his operations. To fill a cavity in a tooth in the most perfect manner possible, when the surrounding tissues are in an abnormal condition, without a recognition of this fact and the most careful attention to the abnormality, is far from good practice. To attempt to remedy any disorder in the mouth by confining attention solely to the immediate seat of the trouble is fre- quently to court failure. The human economy is so complicated that cause and effect are often remote from each other, and the practitioner who does the best service to his patient is the one who in addition to being an acute observer extends his observation over the widest field. The conscientious dentist, when he finds himself baffled in dis- covering the cause or relieving the symptoms of any affection of the mouth will not hesitate to call in consultation a specialist in dentistry or medicine as the case indicates, and particularly is it desirable in instances of peculiar idiosyncrasies to consult with the family physician of the patient. No individual practicing a profession like dentistry should think lightly of his obligations, and no practitioner can properly fulfil his obligations without developing the habit of painstaking care in all his work whether of diagnosis or treatment. It should early be recognized by the young practitioner that dentistry demands of those who aim to excel in its practice a more diversified order of talent than any other calling. To be a good dentist an individual should develop the scientist's attitude toward the intimate and sometimes intricate relationship between cause and effect, he should be a close observer of phenomena, a mechanician of the first order, an artist with the sense xi INTRODUCTION. Operative Dentistry may be defined as the science and art which aims at the preservation of the natural teeth in a state of health and beauty. Its highest ofhce is to prevent disease or deformity, but where either of these has already occurred it is then its function to remedy the evil, and check its further progress. The dentist who does the best for his patient is the one who, in addition to the develop- ment of the highest manipulative skill, studies most carefully the conditions surrounding the field of his operations. To fill a cavity in a tooth in the most perfect manner possible, when the surrounding tissues are in an abnormal condition, without a recognition of this fact and the most careful attention to the abnormality, is far from good practice. To attempt to remedy any disorder in the mouth by confining attention solely to the immediate seat of the trouble is fre- quently to court failure. The human economy is so complicated that cause and effect are often remote from each other, and the practitioner who does the best service to his patient is the one who in addition to being an acute observer extends his observation over the widest field. The conscientious dentist, when he finds himself baffled in dis- covering the cause or relieving the symptoms of any affection of the mouth will not hesitate to call in consultation a specialist in dentistry or medicine as the case indicates, and particularly is it desirable in instances of peculiar idiosyncrasies to consult with the family physician of the patient. No individual practicing a profession like dentistry should think lightly of his obligations, and no practitioner can properly fulfil his obligations without developing the habit of painstaking care in all his work whether of diagnosis or treatment. It should early be recognized by the young practitioner that dentistry demands of those who aim to excel in its practice a more diversified order of talent than any other calling. To be a good dentist an individual should develop the scientist's attitude toward the intimate and sometimes intricate relationship between cause and effect, he should be a close observer of phenomena, a mechanician of the first order, an artist with the sense XU INTRODUCTION. of harmony hi^^hly cuhivalcd, a physician in his diagnosis of disease, a humanitarian in his ministrations to others, and above all a cultured gentleman of the liiglu'st mental and moral fiber. This does not imply that in the beginning he must be endowed with great brain capacity or natural attributes of an unusual char- acter. The encouraging thing about dentistry is that most of the qualities necessary for achievement are capable of cultivation, and the man who will apply himself with sufficient zeal and perseverance is certain of at least a reasonable measure of success. The chief recjuisite is the patience to i)lod. If every dentist would bring to his work a real sincerity of purpose to serve his patients to the highest possibilities of his art, the future of the profession would be secure. There would be less need than there is today of artificial teeth, and the full functional use of the natural organs in mastication and in harmony of expression would be more generally recognized and appreciated. As we develop dentistry along the lines of prevention and conservation we shall bring it nearer and nearer to its highest mission. To do the greatest good to the largest number, to do this good without thought of self advancement, to w'ork for the love of it and for the benefit it brings to humanity — this is the acme of faithful service and the only kind of effort which will bring permanent satisfaction. Unless a dentist is willing to do this he will fall short of all that his profession has to offer him, if he does it he may be certain of an encouraging measure of attainment. But to accomplish anything of note he must be progressive. The methods of yesterday will not suffice for today. No profession is developing more rapidly than dentistry and he who would give the best service must ever be alive to the latest advances. The foremost thinkers of the profession are constantly placing their ideas before their fellow practitioners, and the man who keeps abreast must be alert to avail himself of the results of their matured thought. It is with the purpose of presenting this thought in the most condensed form as it relates to the different departments of operative dentistry that the present volume is issued. OPERATIVE DENTISTRY. CHAPTER I. THE ANATOMY OF THE HUMAN TEETH. BY CHARLES R. TURNER, D. D. S., M. D. The teeth of man are hard masses of calcified tissue attached to the mandible and maxilla and having as their chief function partici- pation in the work of his masticatory apparatus. His food, as intro- duced into the mouth, the beginning of the digestive tract, consists of articles of various degrees of physical consistency. In order that this may be prepared for subsequent stages in the digestive process, much of it must be mechanically subdivided into particles of convenient size to go through the alimentary canal and be acted upon by the di- gestive ferments and solvents. Such subdivision is performed in the mouth by the act of mastication and it is with this function that the teeth are chiefly concerned. They afford hard opposed surfaces which are brought into contact in the approximation of the jaws by the muscular apparatus and by this means the food is cut or crushed into particles of the desired size. The teeth also have a functional relationship with the apparatus by which voice and speech are produced and bear a cosmetic relation to the features of the face. The adult human denture consists normally of thirty-two teeth which are divided in number equally between the upper and the lower jaw. These are known as the permanent teeth, in contra-distinction to the temporary or deciduous teeth which serve for purposes of mas- tication during the earlier years of life and are subsequently exfoliated to give place to their permanent successors. The permanent teeth are divided anatomically into classes and these divisions largely correspond with their functions as portions of the masticatory apparatus. Thus, there are eight incisors, which NOTE.^The author desires to acknowledge his indebtedness for Figs, i to 84 inclu- sive to Dr. George J. Paynter, of the Department of Dentistry, University of Pennsyl- vania, who selected and dissected the specimens, and to the Department of Dentistry, University of Pennsylvania, for whom the photographs were made, for permission to reproduce them. 2 THE ANATOMY OF THE HUMAN TEETH. serw in the incising of ihc food; four cuspids, whose chief function in the carnivorous animals is to pierce and hold the food, a function wholly rudimentary with man; eight bicuspids, which are intermedi- ate in position and function between the cuspids and the molars, and lastly twelve molars which are the crushing and grinding teeth pro])er. The formula for the permanent human dentition is expressed: 2—2 I-I 2-2 ^-? I ^-=, C - , B , M -^-^ = 32 2-2 I-I 2-2 ^-;^ The deciduous denture consists of twenty teeth — eight incisors, four cuspids and eight molars. As all the teeth possess certain characteristics in common it will be well to refer to these before undertaking a description of the in- dividual teeth. The crown of a tooth is that portion which projects beyond the gum margin and is normally covered with enamel. The root or roots of the tooth are imbedded in the alveolar process and are attached thereto by a fibrous membrane, the pericementum. The root and crown of a tooth unite at its neck, a point w^hich corresponds to the point of juncture of the enamel and the cementum. This is also called the cervix and also the gingival margin of the crowm. The sharp- ened extremity of a root is know^n as its apex, and this is the seat of an opening which transmits the nerves and blood vessels of the pulp of the tooth and is known as the apical foramen. The surface of a tooth which comes into contact with the corresponding surface of teeth in the opposing jaw is referred to as the occlusal surface. This term is also applied to the analogous portion of the incisor teeth although strictly speaking it should only apply to that of the low^er incisors, in- asmuch as this edge of the incisors of the upper jaw does not touch the teeth of the lower jaw, when the teeth are in occlusal contact, but normally is only brought into this relationship when the mandible is protruded. This is also referred to as the incisive edge of the incisors. Molar and bicuspid teeth have large tubercles upon their occlusal surfaces and these are known as cusps. The adjoining surfaces of teeth are known as their proximal surfaces, the most prominent point of which is called the angle of the tooth. If a vertical plane is passed between the central incisors of both jaws, those proximal surfaces of the teeth which are directed toward this are know-n as mesial surfaces, while those proximal surfaces directed away from it are known as distal surfaces. The surfaces of the six anterior teeth of each series which are in relation with the lips are called labial, while the corre- THE UPPER CENTRAL INCISOR. 3 spending surfaces of the remaining teeth which arc in relation with the cheeks are called buccal surfaces. Those surfaces of the teeth which are directed inward toward the cavity of the mouth arc known as their lingual surfaces. The surface-form and internal anatomy of the permanent teeth will now be given in detail. THE UPPER CENTRAL INCISOR. The crown of this tooth is wedge-shaped; the base of the wedge is at its cervical margin from which the broad labial and kngual sur- faces converge to a straight cutting edge. Fig. I.- -Left Upper Central Incisor. Labial Surface. Fig. 2. — Left Upper Central Incisor. Lingual Surface. The Labial Surface (Fig. i). — Irregularly quadrilateral in shape, this surface has four margins. The incisive edge which forms its lower margin is nearly straight; it is marked in the newly erupted tooth by two developmental grooves which disappear early in life be- cause of the wearing down of the three tubercles which are found on this edge. The mesial margin is nearlv straight or mav be a long 4 THE ANATOMY OF THE HUMAN TEETH. curw; ihc- ciTxital border is conwx roolward, wliilr llir distal marj^in is more convex than iIk- mesial and is a liltle shorter. 'i"he surface itself is convex from the cer\ix to the incisive ed<^e, the lower ])ortion of it being, howi'ver, nearl\- ilat, while that portion near the cervix is more curved and is marked hy a cervical ridi^e. This face of the crown is convex from side to side and is marked by two longitudinal grooves which correspond to the lines of union of the three developmental lobes of the crown. The Lingual Siirjace (Fig. 2).— This is irregularly triangular, the mesial and distal margins uniting with the cervical to form a rounded Fig. 3. — Left Upper Central Incisor. Mesial Surface. Fig. 4. — Left Upper Central Incisor. Distal Surface. apex, while the base of the triangle is formed by the incisive margin. The mesial and distal margins are marked by rounded ridges of enamel which extend from the angles of the crown in a graceful curve rootward to unite with the cervical ridge. The mesial is .slightly the longer of these two. The cervical is more pronounced than the other marginal ridges. It is .sometimes cut near its center by a fissure and .sometimes it is the^seat of a rounded elevation of enamel, the cingulum. The THE UPPER CENTRAL INCISOR. I'lG. 5. — Left Upper Central Incisor. Occlusal View. lingual surface is concave occluso-gingivally and mcsio-distally. Its center is occupied by a pronounced fossa, the lingual fossa, which is traversed by two longitudinal grooves. Occasionally a lingual pit is present and this occupies a position at the juncture of the cervical ridge and the lingual fossa. The Mesial Surface (Fig. 3). — Being shaped like a spear-head or irregularly tri- angular in outline, this surface has three margins. The labial presents a long curve ending in the mesial angle of the tooth and rs shorter than the lingual which it meets at this point. Both are bowed in a labial direction and the labial margin is the more pronounced, the lingual being rounded and marking less distinctly the boundary of the surface. The cervical margin is concave in an oc- clusal direction and at its terminations unites with both the labial and lingual bor- ders at an acute angle. Near the incisive edge the surface is convex but this convex- ity decreases as the root is approached and the surface becomes either a plane or is marked by a slight depression at the gingival margin. The most prominent point of the surface is located one-third the distance from the mesial angle and this establishes the point of contact with the central incisor of the opposite side. The Distal Surface (Fig. 4). — While this is of the same general shape as the mesial surface, it is slightly smaller because of the location of the distal angle nearer to the cervix. Its margins arc less distinct and the surface is more rounded and the poin_ of contact with the lateral is relatively nearer the cervix. The Incisive Edge (Fig. 5). — The in- cisive edge is formed by the intersection of the planes of the labial and lingual sur- These do not meet at an acute angle but their Fig. 6. — Left Upper Central Incisor. Longitudinal section cut labio-lingually showing pulp cavity. faces of the crown line of intersection is .somewhat rounded. This edse extends from THE ANATOMY OF THE HUMAN TEETH. the mesial to the di.s/al angle, usually almost in a straight line. In young subjects it is marked by the developmental grooves, but these usually disappear from the wearing of the surfaces. When the crown is viewed from below, the line of the incisive edge is oc- casionally bowed in a labial direction. The Cervical Margin. — Beginning at the mesio-labial portion of this line, it extends with an upward curve u])on the labial sur- face, downward on the distal, upward on Fig. 7.— Left Upper Central the lingual, and downward again on the Incisor. Cross-section at cer- . , \ . . ^ r 1 • ■ t. • vix showing pulp chamber in m^'Sial to the j^oint of begmnmg. it is crown. Looking crownward. marked by the bulging of the cervical ridge on the labial and lingual surfaces. While there is usually a well- defined constriction on the tooth at this point, the 7ieck of the tooth is not so marked as in some of the distal teeth. The Root. — This is conical in shape, and when viewed from the labial surface (Fig. i) its sides converge in almost straight lines to a rounded point; but viewed from the mesial (Fig. 3) or distal side the outlines of the root curve to a rounded point. When viewed in cross-section at the neck the labio- lingual diameter of the root is greater than the mesio-distal and the root outline is that of a rounded triangle with its sides corresponding to the labial, mesial, and distal faces of the root. Of these the mesial is the longest and nearly straight, the labial and lingual being approximately equal in length but the labial is the most curved of all. The Pulp Cavity. — The form of the pulp cavity of the central incisor corresponds in general with the external form of the tooth itself (Fig. 6). It is divisible into the pulp chamber and the pulp canal, but the line of division is not clearly marked. The pulp chamber occupies the crown of the tooth and, as seen in a labio-lingual section of the tooth (Fig. 6) follows the form of the crown closely. The pulp canal is conic in form, with its base joining the pulp chamber and its apex Fig. 8. — Left Upper Central Incisor. Cross-section at cer- vix showing small pulp cavity in old tooth. Looking crown- ward. Fig. 9. — Left Upper Cen- tral Incisor. Cross-section made at middle of crown (looking rootward) showing form of pulp chamber. THE UPPER LATERAL INCISOR. 7 reaching the apex of the root where it terminates in the. apical foramen. In a mesio-distal section of the tooth the flattening out of the occlusal end of the pulp chamber to follow the incisive edge of the tooth, is seen. (Fig. 9.) The portions extending in the direction of the angles of the tooth are known as the "horns" of the pulp. In the young subject there are three concavities in its occlusal end, correspond- FiG. 10. — Right Upper Lateral Incisor. Labial Surface. Fig. II. — Right Upper Lateral Incisor. Lingual Surface. ing to the three tubercles and the three developmental centers of;the incisive edge of the crown, A cross-section of the root at the cervix shows the pulp cavity almost circular in outline (Fig. 7), and this form characterizes it to the end of the root. The pulp cavity of this, as of all the teeth, diminishes in size from the time of completion of the root through old age because of the deposit of dentin upon its walls (Fig. 8). THE UPPER LATERAL INCISOR. The Labial Surjace (Fig. 10).— This surface is somewhat similar in outline to that of the central incisor except that it is smaller, being narrower from side to side and shorter, and its distal angle is more rounded. It is bordered bv four margins. The incisive margin is 8 THE ANA TOMY OF THE HUMAN TEETH. almost slraiglu, beinji;, ho\vc\-er, inclined sli. mature the pulp cavity becomes more flattened here. Otherwise it is very much like the external form of the tooth, extending well toward the mesial and distal angles, and closely resembhng that of the central incisor. At the level of the cervix it is oval in cross-section and ex- tends gradually diminishing in size to the apex. There is no line of demarcation between the root and coronal portion of the cavity. THE LOWER CUSPID. The crown of the. cuspid of the lower series is very similar to that of its upper, except that it is narrower, more delicate and slightly longer, and usually not so well marked. The Labial Surjace. — The markings of this surface are not so pro- nounced as those of the upper cuspid. The outline is less angular than that of the upper, with the exception of that portion formed by the mesial and distal incisive edges, for its cusp is more pointed than that of the upper cuspid. The developmental grooves are usually poorly defined, the labial ridge being the most prominent mark- ing of this surface and giving to it a marked convexity. This ridge, as in the upper cuspid, is located decidedly nearer the mesial than the distal margin. The mesial margin is more pronounced than the distal, the labial surface meeting the mesial somewhat more abruptly than the distal into which it passes by a rounded curve without definition. l8 THE ANATOMY OF THE HUMAN TEETH. Till' Liiii^iiiil Siirjacc— 'Vhv oullinc is more rounded and tlu- sur- face markings less bold than those of the upi)er cuspid. The marginal ridges arc usually poorly deiined, that at the cervix being more prom- inent than the mesial or distal. The lingual ridge extends from the eusp lo the. cervix, dividing this surface and forming two very shallow grooves or fossa?, the lingual grooves; but the surface is less convex than that of the upper, especially at the occlusal end, which is some- times ilal mesio-distally. TJie Mesial Surjace. — Similar in shape to that of the upper, yet differing from it in some particulars, this surface of the lower cuspid possesses the peculiarity of being almost flat and being continuous as an almost ]jlane surface with the root. At the cervix it is slightly con- cave or it may be simply flat, but it assumes a convex character as the mesial angle is approached. The cervical outline is much less concave rootward than that of this face of the upper cuspid, but similarly it extends to a lower level lingually than labially. The lingual margin is well defined but the labial is rounded. TJie Distal Surface. — The convexity characteristic of this surface of the u])i)er cuspid is observed here, except that the cervical portion is sometimes slightly concave. The surface is smaller in extent than the mesial, a fact due to the lower location of the distal angle. The cervical margin is pronounced, the surface of the root usually forming a decided angle with that of the crown. The lingual margin is more marked than the labial, but by comparison they are less clearly defined than those on the mesial surface. The Cusp. — The prominent point of the tooth occupies a line al- most in its long axis. From it descend the mesial and distal incisal edges of which the latter is slightly longer, but the difference is not so marked as in the upper cuspid. The Cervical Margin. — This is concave in the direction of the root on the labial and lingual sides and convex on the mesial and distal. On the lingual and distal sides the root and crown join more abruptly than on the mesial and labial. The Root. — The root is shorter than that of the upper cuspid and is flattened on its mesial and distal sides. Viewed in profile from any of the four surfaces its sides slope gradually to the apex which is frequently inclined to the distal. The Pulp Cavity.— This resembles that of the upper cuspid except that it is narrower mesio-distally, a difference in form likewise ob- servable in the crowns of the two teeth. It has no horns of the pulp chamber but terminates in a pointed extremity beneath the cusp. THE UPPER FIRST BICUSPID. I9 The pulp canal is flattened mesio-distally at the cervix but becomes circular in its apical portion, THE UPPER FIRST BICUSPID. The crown of this tooth presents for examination five surfaces, namely, occlusal, buccal, lingual, mesial and distal. It is irregularly cuboidal in shape. The Occlusal Surjace (Fig. 29). — When viewed from the occlusal surface the crow^n appears ovoid in outline, whereas the occlusal sur- face proper is trapezoidal, the oval appearance being due to the pro- jection of the upper portion of the buccal J ill roMnB^^^M^M^aBapMgiM^y iiiiiiuiu.i 1^^^ — — i face of the tooth. The most prominent I ^iniHi^ • features of this surface are the two cusps sur- j|fc|pP^''^^^^l|k mounting its buccal and lingual portions, the Br 1 1 buccal and lingual cusps, which are separated B. ...^mt^, by the central groove and which give to the ■ 'W^- ■^ tooth its distinguishing character (bicuspid). ■ »|f' The margins are formed by the buccal cusp ^L with its descending mesial and distal inclines, ^^^^^^^^i^^^-- the mesial and distal marginal ridges, which are well-defined ridges of enamel joining the BifuspS'^o^ccL^arsurSS ridges of the buccal cusp at the mesial and distal angles of the crown and converge to join descending ridges from the lingual cusp and the lingual cusp itself. The buccal cusp is the larger, sharper and more prominent. From its summit four ridges descend; the buccal ridge, which is partly responsible for the prominence of the buccal surface of the crown; the triangular ridge, which extends dowmward toward the central groove and usually terminates there; and one each mesially and distally to reach the mesial and distal angles respectively. Of these latter two, the distal is usually the larger and the more inclined, the point of the cusp being usually nearer the mesial than the distal face of the crown. The lingual cusp is lower and much more rounded than the buccal and the three ridges descending from it are less pronounced. The triangular ridge is often missing but when present it descends toward the central groove to meet the ridge from the buccal cusp. Occasion- ally these two triangular ridges unite and form the transverse ridge, but usually they are separated by a fissure in the central groove. The ridges descending mesially and distally from this cusp join and are continuous with the marginal ridges, being curved so that the lingual outline of the occlusal surface is much rounded. The lingual aspect 20 THE ANATOMY OF THE HUMAN TEETH. of the lingual cusj) is convex and rounded and gradually blends with the lingual surface. The mesio-distal groove separates the cusps and extends from the mesial to the distal marginal ridges. It is sometimes extended at each extremity into the mesial and distal developmental grooves which when present are line lines crossing the marginal ridges to reach the mesial and distal surfaces of the crown. The triangular grooves are short, cross the central groove at its terminations at right angles, ex- FlG. -Left Upper First Bicuspid. Buccal Surface. Fig. 31. — Left Upper First Bicuspid. Lingual Surface. tend toward the angles of the crown, and separate the mesial and distal marginal ridges from the triangular ridges. The junctions of these grooves with the central groove are often spoken of as the mesial and distal pit. The Buccal Surface (Fig. 30). — This closely resembles in form and outline the labial surface of the cuspid tooth, being smaller and more compressed occluso-gingivally. It is bounded by four margins, the occlusal, the cervical, the mesial and the distal. The occlusal is formed by the mesial and distal inclines of the buccal cusp and is well defined. The mesial incline is usually a straight line or is slightly convex. THE UPPER FIRST BICUSPID. 21 while the distal may be marked with a concavity caused by the distal buc- cal groove. The mesial border is more sharply defined than the distal. It descends from the mesial angle to the cervical border, which latter is nearly straight or may be slightly convex rootward and is not distinctly marked by an abrupt termination of the enamel. The distal margin is usually shorter and more rounded than the mesial, because of the lower position of the distal angle, and the fact that the buccal surface rounds into the distal without a sharp line of definition. The buccal Fig. 32. — Left Upper First Bicuspid. Alesial Surface. Fig. 3- -Left Upper First Bicuspid. Distal Surface. ridge, descending from the buccal cusp and flanked by the buccal developmental grooves, which are forced well towards the angles of the crown, contributes towards the convexity of this surface. It usually disappears by blending whh this convexity about the center of the surface, but occasionally in well-marked teeth it extends almost to the cervical margin. The greater mesio-distal diameter of the crown at the level of the angles than at the cervical margin gives to the crown its characteristic bell-shape, which may be well observed when looking at the buccal surface. The Ungual Surjace (Fig. 31).— This face is smaller than the buccal, being both shorter and narrower. It is convex mesio-distall 22 THE ANATOMY OF THE HUMAN TEETH. and rounds into the mesial and distal face without line of demarcation. Its occlusal margin is also rounded, being formed by the lingual cusp and the ridges descending from it, while the gingival margin is either nearly straight or is only slightly convex rootward. The surface is curved from the summit of the lingual cusp, which is slightly nearer the mesial face of the crown, lo the cervix, its outline when seen in pro- f.le being a long gentle curve. It is usually quite smooth and without grooves. The Mesial Surface (Fig. 32). — Ir- regularly quadrilateral in shape, this face of the crown is bordered occlusally by the mesial marginal ridge and a portion of the ridge from the lingual cusp, and gingivally by the cervical line which is usually nearly straight or slightly concave in the direction of the root. The occlusal margin is concave, the concavity being about midway be- tween the cusps. Frequently this margin is broken by the mesial de- velopmental groove which reaches this face from the occlusal surface and usually terminates about its center. The buccal margin is fairly well de- fined and extends from the mesial angle to the cervix, while the lingual is Fin. 24. — Left Ujjper First Bicuspid. i i i ,i i i • • • r B ucco-lingual longitudinal section, SO roundcd by the gradual jommg of s howing pulp chamber, its horns, and the lingual surface as to be indistin- f he pulp canals. , guishable. Near the occlusal margin the surface is full and rounded, giving a point of contact for the proximal side of the cuspid, but it flattens out as the cervix is ap- proached and in this location is usually the seat of a depression which is continued up the face of the root. The Distal Surface (Fig. 33). — While this is much like the mesial surface, it is smaller in extent and more convex. The buccal margin is not so pronounced as that of the mesial face and is usually shorter. The cervical, lingual and occlusal margins are very much like those of the mesial face and the lingual is poorly defined and much rounded. In its occlusal third the surface is quite convex in all directions and this usually extends in decreasing degree to the cervix, although the com^sponding portion of the mesial face is usually concave bucco- THE UPPER FIRST BICUSPID. 23 lingually. The distal developmental groove sometimes crosses the upper margin from the occlusal surface and disappears about the center of the surface. The Cervical Margin. — -This is more nearly straight around the tooth than that of any of the teeth so far described, usually having, however, a slight curve rootward on both buccal and lingual surfaces and being curved toward the occlusal surface on the mesial and distal faces. The Root. — The upper first bicuspid usually has two roots (Fig. 32) or two branches of its root, which are located beneath its two cusps and are called the buccal and lingual roots. Occasionally the tooth has only one root or the division may occur very near its apex. In the former instance the central portion of the root between the two pulp canals is thin and usually consists only of cementum. The occurrence of two separated roots is most frequently noted and in this instance the roots are delicate and taper gradually to a somewhat sharp apical extremity and are usually curved in several directions. These curves are usually first in a buccal and lingual direction, serving to separate the roots which again approach each other at their termi- ^ ^ ^ t^ '^ r^ _ FiGt 35. — Left Tjpper nations. There is often a gentle distal curve in First Bicuspid. Cross- 1 ,1 , /-Til 1 •£ ,• • 11 1 4^ 1 sectionof root near cervix, both roots. The bifurcation is usually located growing shape of pulp about one-third the distance from the cervix, and canal, is accomplished by a meeting of the groove noted on the mesial face of the root and originating in the crown, with one which develops above the cervix on the distal side of the root. The Pulp Cavity.— T\ie pulp chamber and the pulp canal are usually differentiated in this tooth (Fig. 34), the chamber correspond- ing to the general shape of the crown, the canals to the form of the roots. The chamber is a cavity with flattened mesial and distal walls and curved buccal and lingual walls. In the mature tooth these latter are nearly parallel and terminate occlu.sally in the buccal and lingual horns of the pulp chamber, which are cone-shaped projections of the cavity penetrating the two cusps. The occlusal wall of the chamber is marked by a projection corresponding to the central groove of the occlusal surface of the crown. In horizontal cross-section at this level, the cavity is larger than at the cervix, the mesial and distal walls converging to this point in correspondence with the external surface of the crown. 24 THE ANATOMY OF THE HUMAN TEETH. 'Vhv lloor of the pulp chamber, which is usually about on a level with llu- cervix, differs in character in accordance with the root forma- tion of the loolh. In teeth with two roots or in those with two root canals, the buccal and lingual walls of the chamber are continued as the corresponding walls of the two pulp canals, but in old teeth a line of definition between the two is caused by an inward projection of the wall. The openings to the two canals are funnehsha])ed and are sej)arated by a ridge corresponding to the root bifurcation. The canals are usually about circular in cross-section, and follow the directions of the roots, occupying their centers. When the tooth has only one root, it sometimes has only one pulp canal (Fig. 35), which is flat and ribbon- like in its gingival portion, becoming more nearly round as the apex is reached. Often in single-rooted teeth there arc two jnilp canals, which either terminate in separate foramina close together or coalesce just before reaching the apex, a single canal making exit at the apex. THE UPPER SECOND BICUSPID. This tooth so closely resembles the upper first bicuspid that it will only be necessary to point out the differences between the two. The crown of the tooth is smaller and its prominences are more rounded than those of the first bicuspid. It is always shorter from cusps to cervix but the bucco-lingual diameter at the cervix is sometimes slightly greater than that of the first. (3n the occlusal surface (Fig. 36) both cusps are more rounded, B '^ st^^^ ^x\(S., unlike the first bicuspid, are usually wk. Wf^M^/Km of equal length. The lingual cusp is usually '^^^^^^ equal in size to that of the first bicuspid while the buccal is smaller, in consequence of which facts the two cusps of this tooth are approximately ec^ual in size. The tri- ^ ^. , ^. ^ , angular ridges usuallv unite to form a trans- it iG. 36. — Kigrit L yjper Second . Bicuspid. Occlusal Surface. verse ridge, the central groove is shortened mesio-distally, and usually terminates in pits instead of well-marked triangular grooves. The buccal (Fig. 37) and lingual (Fig. 38) faces of the crown are smaller and more rounded than those of the first bicuspid, the mesial (Fig. 39) and distal (Fig. 40) faces being similar to those of the first except that the concavity on its mesial face near the cervical margin is missing. This is one of the chief distinguishing features of the tooth. The cervical margin more nearly occupies a horizontal plane than that of the first bicuspid, being THE UPPER SECOND BICUSPID. Fig. 37. — Right Upper Second Bicuspid. Fig. t,S. — Right Upper Secund Bicuspid. Buccal Surface. Lingual Surface. Fig. 39. — Right Upper Second Bicuspid. Fig. 40. — Right Upper Second Bicuspid. Mesial Surface. Distal Surface. 26 THE ANATOMY OF THE HUMAN TEETH. sliglitly curwd roolward on buccal and lint^ual surfaces and being almost straii/ht on the mesial and distal sides. A single root is char- Fio. 41. — Right Upper Second Bicuspid. Bucco-lingual longitudinal section, showing pulp cavity. Fig. 42. — Right Upper Second Bicuspid. Mesio-distal longitudinal section, looking buccally. Showing pulp cavity. acteristic of this tooth. It is much flattened on its mesial and distal sides and is usually marked with a longitudinal groove on each of these surfaces. Its extremity is usually rounded and occasionally bifid. Its buccal and lingual surfaces converge much more in reaching the ^ ,j^ apex than do its mesial and distal. The root W ^1 sometimes has a curve in a distal direction near ■ iH its termination. ' ^H Inasmuch as this tooth normally has but one root, the pulp cavity consists of a pulp chamber corresponding in shape to that of the crown and a single pulp canal (Fig. 41). While the pulp chamber is similar in form to that of the first bicuspid, the horns of the chamber are less pointed and penetrating, because of the differ- ences in the cusps of these two teeth. The pulp canal has its walls continuous with those of the chamber, no definite demarcation be- FiG. 43. — Right Upper Second Bicuspid. Cross- section of root above cer- vix, showing pulp canal. THE LOWER FIRST BICUSPID, 27 tween the two existing. It is narrow mesio-distally and ribbon-like at the cervix but is usually easy to enter (Fig. 43). Occasionally this tooth has two roots, in which case two root canals can be found, and their existence should be considered among the rare possibilities in the treatment of these teeth. THE LOWER FIRST BICUSPID. While partaking of the characteristics of the upper bicuspid teeth, the lower iirst bicuspid departs from the typical bicuspid design in the rudimentary development of its lingual cusp. The great variation in th-e development of this cusp accounts for the variations in form so commonly observed in this tooth. The Occlusal Surface (Fig. 44). — Viewed from the occlusal surface the outline of the crown appears almost circular or ovoid but this is due to the fact that the upper portion of the bulging buccal face is visible. The surface presents for examination a buccal cusp, cither a lingual cusp or a lingual ridge, a mesial and distal pit and marginal ridges bordering the surface. The summit of the buccal cusp is nearly in the line of the long axis of the crown. Four ridges descend from it, one each in a buccal, lingual, mesial and distal direction. The two latter unite at the mesial and dista angles with the marginal ridges. The buccal extends upon the buccal face of the crown and , ,. , . 1111- Fig. 44. — Left Lower First the ImgUal is more strongly developed, is not Bicuspid. Occlusal Surface. crossed by a groove, reaches the lingual ridge or lingual cusp, and separates the mesial and distal pits. The mesial and distal marginal ridges converge to unite and form a semicircle with a lingual prominence of enamel, which when much elevated above the adjoining margin ridges is considered the lingual cusp and when only existing as a ridge is called the lingual marginal ridge. The Buccal Surface (Fig. 45).^ — This corresponds so closely to that of an upper bicuspid that detailed description would be superfluous. The cusp is not so pointed, the buccal developmental grooves are poorly developed, the crown is shorter and narrower than its fellow of the upper series, the cervical line is almost straight, and the surface is convex and slopes inward to the summit of the buccal cusp which is usually in line with the long axis of the root. The Lingual Surface (Fig. 46). — This is small because of the small 28 THE ANATOMY OF THE HUMAN TEETH. Fig. 45-- -Left Lower First Bicuspid. Bucc:al Surface. Fig. 46. -Left Lower First Bicuspid. Lingual Surface. Fig. 47.- -Left Lower First Bicuspid Mesial Surface. Fig -tS Left Lower First Bicuspid. Distal Surface. THE LOWER FIRST BICUSPID. 29 size and low position of the lingual cusp. The occlusal margin is well defined and the surface is nearly straight from this point to the cervix and in manv instances is continued without marked division into the surface of the root or it may make an obtuse angle with this face of the root. Mesio-distally it is much rounded passing into the proximal surfaces with a gentle curve. The Mesial Surface (Fig. 47). — Irregularly c^uadrilateral in out- line, with only its occlusal margin well defined by the marginal ridge, Fio. 49. — Right Lower First Bicuspid. Mesio-distal longitudinal section, showing pulp cavity. Fig. 50. — Right Lower First Bicuspid. Bucco-lingual longitudinal section, show- ing pulp cavity. this surface is generally convex. The most prominent point of the convexity is located centrally just below the occlusal margin from which the surface inclines inward toward the central axis of the tooth, con- tributing therebv to give the bell-shape which is observed of this crown as it is viewed from the buccal or lingual side. At the cervix the surface is flattened. The Distal Surface (Fig. 48). — -This is almost similar to the mesial except that its convexity is usually less pronounced. The Cervical Margin. — The juncture between enamel and cemen- tum in this tooth occupies nearly a horizontal plane, being continued 3© THE ANATOMY OF THE HUMAN TEETH. around the tooth in almost a straight line. 'Jliere is frequently a dip rootward on the buccal face. The Root. — A single root normally characterizes the lower first bicus])i(l although in rare instances two roots are found. When single it is conical, the buccal and lingual sides being uniformly in- clined toward each other and continuing these faces of the crown. The lingual is the narrower, which is caused by the fact that the flat- tened mesial and distal faces converge in passing lingually. These latter are usually slightly con- vex and uniformly taper to the apex, but occa- sionally they are marked with a shallow longit- udinal depression. The end of the root is sharply pointed and is frequently deflected dis- tally. The cervical portion of the root is oval in cross-section. Fig. 51.— Kight Lower j^j^^ p^ip Cavitv.—As in all single rooted First Bicuspid. Cross- -^ '^ ... , section at cervix showing teeth there is no sharp division between the P'^^P '^"^^- pulp chamber and canal (Fig. 49). The cham- ber has one well-defined horn situated beneath the buccal cusp and when a lingual cusp exists there is a small projection of the cavity in its direction (Fig. 50). At the level of the gingival margin the cavity is oval in cross-section whence it continues diminishing in bucco- lingual diameter to the apical foramen (Fig. 51). It is usually small and thread-like in the apical third of the root. THE LOWER SECOND BICUSPID. While this tooth bears a close resemblance to the lower first bicus- pid tooth in many particulars, in some details it is quite different. These chiefly pertain to the lingual portion of the occlusal face of the crown and the adjacent surfaces which are related therewith. In general the crown of the tooth is smaller and more rounded than the first. Viewed from the occlusal face it will be seen that this surface is larger and even more nearly circular in outline than the first. In some instances this is due to the presence of a well-developed lingual cusp and prominent marginal ridges mesially and distally. In other instances the same rounded outline is caused by the presence of two lingual cusps, a fissure dividing the lingual portion in its center. The buccal cusp is less prominent than that of the first bicuspid, and has a well-defined triangular ridge which seldom unites with that of the lingual cusp. When present the lingual cusp is smaller than and THE UPPER FIRST MOLAR. 3 1 not so prominent as the buccal and is usually separated from it by a mesio-distal groove. This latter terminates in pits, the mesial and distal pits, and is curved lingually. When the face presents three cusps the groove has three branches meeting in a central pit or fossa. The angles of the crown are not well marked. The buccal surface is more rounded and shorter and wider than that of the first bicuspid. The lingual surface is proportionally larger than the lingual of the lower first bicuspid, being longer occluso-gingivally because of the lingual cusp at the base of which it is also wider mesio-distally. The mesial and distal faces of the crown are similar to those of the first bicuspid except that they are wider bucco- lingually and are both slightly more convex. The cervical margin encircles the tooth almost in a horizontal plane, but a curve rootward may usually be made out on the. buccal face. The single root is con- ical, proportionately longer than that of the first bicuspid, flattened on its mesial and distal sides, and usually bent distally in its lower portion. The pulp cavity is larger than that of the first bicuspid, the chamber being shaped to correspond with the external surface of the crown and having the rudimentary lingual horn better developed. The canal is oval or circular in cross-section at the cervix from whence it tapers gradually to the apical foramen. THE UPPER FIRST MOLAR. The crown of the upper first molar is roughly cuboidal in shape and offers for examination five surfaces — occlusal, buccal, lingual, mesial and distal. The Occlusal Surjace (Fig. 52). — This is irregularly rhomboidal in outline as may be seen when the crown is viewed from this surface. The mesial and distal margins are nearly straight and parallel; the buccal and lingual margins are curved. At the mesio-buccal and disto-lingual juncture of these margins acute angles are formed while the angles at the disto-buccal and mesio-lingual juncture are obtuse. The surface is marked by the presence of four cusps, four marginal ridges, two fossae, and several developmental grooves. The mesial marginal ridge is a rounded and well-defined elevation of enamel extending from the summit of the mesio-buccal cusp to that of the mesio- lingual cusp, and is curved rootward between these points. It is often crossed near its center by the mesial developmental groove which ex- tends from the occlusal to the mesial surface. The buccal marginal ridge unites with the mesial at the mesio-buccal angle of the tooth. It 32 THE ANATOMY OF THE HUMAN TEETH. extends from tliis point to the ])oint of the me.sio-buccal ciisj), then in a slightly lingual direction to the bottom of the buccal groove, then buccally to the j^oint of the disto-buccal cusp and then to the disto- buccal angle, being cur\'e(l latterly in a lingual direction to unite with the distal marginal ridge. It is the sharpest of the marginal ridges, a fact in large part due to the sharpness of the buccal cusps. The distal marginal ridge is similar to the mesial in that it is curved rootward between its terminations and is a rounded ridge of enamel. It is marked to the buccal side of its center by the distal groove, which passes over upon the distal face of the crown. The lingual termina- tion is well rounded and consequently less easily differentiated from the disto- lingual cusp in which it terminates. The lingual- marginal ridge completes the periphery of the occlusal surface, ex- tending from the disto-lingual to the mesio-lingual angle of the crown. From its mesial end it curves lingually to the summit of the mesio-lingual cusp, then buccally to the point where it is divided by the disto-lingual cusp and then lingually again to the top of the disto- lingual cusp. It is the most rounded of the marginal ridges. The Cusps. — The upper iirst molar may be said to possess four cusps nor- mally but in a large number of cases it has live. The mesio-buccal cusp, located near the mesio-buccal angle of the tooth, is sharp and from its summit descend four ridges. These latter are the buccal, which continues upon the buccal surface of the crown, the triangular which descends into the central fossa, and the two ridges descending mesially and distally forming portions of the buccal marginal ridge. The disto-buccal cusp is somewhat smaller than the one just described, but like it is sharp and has four ridges descending from its point. The buccal ridge descends upon the buccal face, the mesial and distal ridges are portions of the buccal marginal, while the fourth ridge unites with one from the mesio-lingual cusp to form the oblique ridge. The disto-lingual cusp is usually the smallest (except the fifth) and is rounded. But two ridges descend from it, one each in a mesial and lingual direction to form the marginal ridge of these boundaries. Its lingual and distal aspects fade off into these respective faces of the Fig. 52. — Left Upper First Molar Occlusal Surface. THE UPPER FIRST MOLAR. 33 crown without demarcation. It is separated from the oblique ridge by the disto-lingual groove. The mesio-lingual cusp is frequently the largest cusp of this tooth. It is much rounded and has ridges descending from it as follovv^s: one to the mesial to join the mesial mar- ginal ridge and one distally forming a portion of the lingual marginal ridge, while one passes in the direction of the disto-buccal cusp, meet- ing a ridge from the latter to form the oblique ridge. The buccal Fig. 53- —Left Upper First Molar. Buccal Surface. Fig. 54. — Left Upper First Molar. Lingual Surface. aspect of the cusp forms a wall of the central fossa, while the lingual side is rounded and descends without demarcation into the lingual surface of the crown, or in teeth with a fifth cusp descends into the groove dividing the latter from the crown. The fifth cusp, or lingual cingule as it is sometimes called, varies much in size and occurrence. When present it is an elevation of enamel on the lingual surface of the crown, near and just distal to the mesio-lingual angle and at the lingual base of the mesio-lingual cusp from which it is separated by a groove, the mesio-lingual. The Fossa and Grooves. — The central fossa is triangular in shape and occupies the space between the mesio-buccal, disto-buccal and mesio-lingual cusps, its walls being formed by the central inclines of 3 34 THE ANATOMY OF THE HUMAN TEETH. these cusps and ihc mesial marginal ridge. In its center is the central pit from which radiate ihe mesial de\elopmental groove, which passes forward over the mesial marginal ridge to the mesial face of the crown, the buccal groove which divides the mesio-buccal from the disto-buccal cus]) and reaches the buccal surface of the crown, and the distal which is less well marked and jjasses distally over the obli([ue ridge. Each of these grooves may be the seat of a fault or fissure, the buccal exhibiting it more commf)nl\- and the distal less commonly than the others. The distal fossa is smaller than the central and is located between the disto- lingual and disto-buccal cusps and the distal marginal and oblique ridges. Its longest di- mension is disto-lingually in which direction it is traversed by the disto-lingual groove. This latter has its terminations in the lingual pit near the cen- ter of the lingual surface and a pit in the distal fossa. It is parallel to the oblique ridge, dividing the disto-lingual cusp from this, and is usually the seat of a fissure, the result of faulty union of the develop- mental lobes of the crown. The distal groove passes through this fossa, crossing the oblique ridge anteriorly and the distal marginal ridge posteriorly. The Buccal Surface (Fig. 53). — This is bounded by four margins, of which the occlusal is irregular, sharp and prominent, being formed by the buccal marginal ridge and the two buccal cusps, the cervical is almost straight, while the mesial and distal are not well marked, the distal being less so than the mesial. The two latter are rounded and fade into the respective faces of the crow^n. They converge from the occlusal surface to the cervix, so that when the tooth is viewed from the buccal face the bell-shape of its crown is noticeable. For the most part the surface is slightly convex having, however, a depres- sion near its center in which is frequently located a buccal pit. The buccal groove divides it into two lobes and usually terminates in the Fig. 55. —Left Upper First Molar. Mesial Surface. THE UPPER FIRST MOLAR. 35 buccal pit, but the depression is sometimes continued rootward and is continuous with that between the two buccal roots. At the cervix there is a ridge of enamel, the cervical ridge, which gives prominence to this line. The Lingual Surface (Fig. 54). — This is somewhat similar in out- line to the buccal, but is narrowed mesio-distally at the cervix as the sides converge to a single root instead of two as upon the buccal surface. The surface is more convex than the buccal, but, like it, is often the seat of a pit near its center, the lingual pit, in which the disto- lingual groove terminates. Tlic depression caused by this groow is often continued rootward, dividing the surface into t^^•(> lobes, and being continuous with a longitudinal depression upon the lingual root. The distal lobe is rounded in every direction, its distal portion be- ing continuous with the distal face of the crown without de- marcation. The mesial lobe resembles this in character ex- cept that its anterior margin is more defined. In those teeth with five cusps this lobe pre- sents near the occlusal margin a rounded cingule, whose lin- gual side is continuous with the lingual face of the crown, but which is separated from the mcsio- lingual cusp by a groove, the mesio-lingual groove. This latter often terminates distally by uniting with the disto-lingual groove, but frequently at each extremity it fades away ipto the surface of the tooth. The cervical line is almost straight, the mesial and distal margins are curved and converge toward the cervix, while the occlusal margin resembles that of the buccal face except that the cusp points are not so sharp and the marginal ridge is more rounded. The Mesial Surface (Fig. 55). — While this is generally convex bucco-lingually near the occlusal margin, in its gingival two-thirds it is either flat or it may be slightly concave. It is either convex or nearly flat occluso-gingivally, and the most prominent point is Fig. 56. — Left Upper First Molar. Distal Surface. 36 THE ANATOMY OF THE HUMAN TEETH. slightly aboNX' the occlusal margin where the tooth is in contact with the second bicuspid. The surface is bounded by four margins — the cervical is usually concave in an occlusal direction, while the occlusal is concave in a cervical direction because of the mesial groove which is sometimes continued for a short distance upon this surface. The buccal and lingual margins are convex and converge to the occlusal surface. They are rounded, the former being better defined than the latter. The lingual margin is modified by the presence or absence of the lingual cingule, the location of the notch caused by the mesio- lingual groove varying according to the height of the cingule. The Distal Surface (Fig. 56). — Four sided, this surface resembles the mesial in general outline. It is generally con- vex, except that often the distal groove is continued and makes a slight longit- udinal depression near its center. The occlusal margin is more deeply notched than that of the mesial surface, the cer- vical line is nearly straight or concave occlusally while the buccal and lingual margins are rounded, the former being less well defined than the latter. The Roots (Figs. 53 and 54). — These are three in number and are named from their location, the mesio-buccal, disto- FiG. 57.— Right Upper First Molor. , , , , . Cross-section below cervix, showing buccal and Imgual. They are not given the pulp chamber and entrances to Qff directlv from the base of the crown, the pulp canals. but the division which results in them occurs usually about one-third the distance from the cervix to the root apices. The mesio-buccal root (Fig. 55) is flattened antero-posteriorly, and is next to the lingual in size and length. Viewed from its mesial side, it is nearly equal in width to half the crown and its sides slowly converge to near its end when they meet in a blunt, rounded point. From this view the root is inclined buccally, while viewed from the buccal side, it is seen to have a mesial inclination in its first third, curving then in a distal direction to its extremity. It is thin and flat mesio-distally. The disto-buccal root (Fig. 56) is the smallest. It is narrower bucco-lingually than the mesio-buccal and is short. Its sides gradually incline to a more or less pointed apex, and it is sligtitly flattened mesio- THE UPPER FIRST MOLAR. 37 distally. In its first third it is inclined distally, but in the remainder of its extent it is usually inclined mesially, approaching the mesio- buccal root. The lingual root (Fig. 54) is the largest and usually the longest of the three roots. It is somewhat flattened bucco-lingually, and it is either nearly straight or slightly curved, in which latter instance its extremity is inclined buccally. It diverges markedly from the buccal roots in a lingual direction. Viewed from the lingual face the sides of the root are markedly convergent, sloping from the base of the crown to a somewhat rounded apex. This face of the root often pre- sents • a longitudinal depression which is continuous with that on the lingual side of the crown. The Pulp Cavity (Fig. 57). — The pulp cavity is easily separable into the pulp chamber and the pulp canals, of which the former is ap- proximately the shape of the exterior of the crown of the tooth, while the latter, which are three in number, correspond to the general external shape of the roots. The pulp chamber is characterized by four horns or depressions in its occlusal wall, one entering each of the four cusps. Its four lateral walls are parallel to the sides of the crown and are generally fiat. In bell- shaped teeth they converge from the occlusal wall to the floor (Fig. 58) which is much smaller than the occlusal wall, while in teeth whose crown walls are nearly parallel without constriction at the neck, the lateral pulp chamber walls are similarly disposed. The horns of the pulp chamber are marked and penetrating and often persist in mature teeth as deep recesses in the dentin. The floor of the pulp chamber presents the three openings for the pulp canals. In the young adult tooth these are in the form of funnel-shaped open- ings. As age increases, the size of the pulp chamber decreases. The thickening of the lateral walls encroaches upon the pulp chamber, the Fig. 58. — Right Upper First Molar. Longitudinal section cut through the pulp canals of the buccal roots, showing the pulp chamber and its horns. 38 THI-: ANATOMY OF THE HUMAN TEETH. funru'l-likc openinj^s to the canals become simjjly small apertures and the canals are much reduced in size. The lingual canal (Fig. 57) is the largest and most accessible. It does not conform to the flattened shape of the root but is usually cir- cular, decreasing gradually in caliber to the apex, and following the curvature of the root already noted. The entrance to it is directly under the middle of a line drawn from the summit of one lingual cusp to the other. The mesio-buccal canal (Fig. 58) is next in size and length. The entrance to it is very near the mesio-buccal angle of the tooth, slightly anterior to the summit of the mesio-buccal cusp. It is iiat and ribbon-like and follows the curvature of the root. The disto- buccal canal (Fig. 58) is small and thread-like. Its entrance is approx- imately under the disto-buccal cusp. It is short and difficult to enter. THE UPPER SECOND MOLAR. The crown of this tooth differs from the first molar in any given denture in that it is flattened mesio-distally, with a rounding of the mesio-lingual and disto-buccal angles; its cusps are not so long and their summits are nearer the center of the tooth; it almost never pos- sesses a fifth cusp or cingule, and the disto-lingual cusp is relatively smaller than that of the first molar. The Occlusal Surface (Fig. 59). — When the crown is viewed from the occlusal surface this latter is seen to be rhomboidal in outline but with the angles more rounded than those of the first molar and with the lingual margin almost semicircular. The mesial marginal, the distal marginal, the buccal and the lingual marginal ridges are formed as they are in the first molar. In this tooth they are more rounded. The mesio- buccal cusp has four ridges descending from its summit, one each in a buccal, lingual, mesial and distal direc- tion. It is smaller and less sharp than the corresponding cusp of the first molar. The disto-buccal cusp is usually small and pressed in toward the center of the crown by the rounding of the disto-buccal angle. Its buccal ridge is absent or barely distinguishable. The mesio-lingaul cusp is usually the largest cusp and is well rounded and without a clearly Fig. 59. — Left Upper Second Molar. Occlusal Surface. THE UPPER SECOND MOLAR. 39 defined point. It has ridges which pass mesially, distally and buccally, the latter is hea\T and strong and assists in forming the oblique ridge. The lingual surface of the cusp is much rounded. The disto-lingual cusp varies much in size and form. It is usually relatively smaller than that of the first molar. Often it is little more than an enlarge- ment of the distal marginal ridge, with which its buccal ridge is contin- uous. Its distal and lingual faces are much rounded. The central fossa is not so deep as that of the first molar, though similarly its walls are formed by the two buccal cusps and the mcsio-lingual together with Ufc, fS Fig. 6o. -Left Upper Second Molar. Buccal Surface. Fig 6i. — Left Upper Second Molar. Lingual Surface. the mesial marginal and oblique ridges. The mesial groove, the buccal groove and the distal groove all pass from it in these respective directions. It has a pit, the central pit, in its center, and the distal fossa has, simi- larly, the distal pit. From the latter fossa the distal groove passes to the distal surface and the disto-lingual to the lingual surface, ending on the latter usually in the lingual pit. The Buccal Surface (Fig. 60). — This resembles that of the first molar so closely that only their points of difference need to be pointed out. The occlusal margin has the same outline as that of the first 40 THE ANATOMY OF THE HUMAN TEETH. Fig. 62. — Left Upper Second Molar. Mesial Surface. from that of the first molar ex- cept that it is much more con- vex and the fifth cusp is almost never present to modify the form of its mesial portion. The Mesial Surface (Fig. 62). — This resembles closely the cor- responding surface of the upper first molar, but is relatively smaller and is often concave from buccal to lingual side. Its lingual margin is less well de- fined than its mesial. The Distal Surface (Fig. 63). — Usually more convex than this surface of the first molar, and relatively shorter occluso-gingi- vally, the distal surface of this tooth resembles in other respects molar exce])t that the smaller proportionate size of the disto- buccal cusp causes this ])ortion to be slightly altered. The distal margin is more rounded and less ])ronounced than that of the first molar, but llie other two margins are similar, 'i'he buccal groove continues upon the buccal face, from the occlusal surface, some- times to the jjoint of bifurcation of the roots, less rarely ending in a buccal pit. The lobe of the crown mesial to the depression is always larger than the distal lobe. The cervical ridge is not so frecjuently marked. The Lingual Surface (Fig. 61). — This dift'ers in no wise Fig. 63. — Left Upper Second Molar. Distal Surface. THE UPPER THIRD MOLAR. 41 its mesial neighbor. The varying size and portion of the disto-lingual cusp influence the exact form of this face of the crown. The Roots. — Alike in number and gen- eral form to those of the first molar, the roots of the second differ in some respects from them. The mesio-buccal (Fig. 62) is flattened antero-posteriorly, the disto- buccal (Fig. 63) is nearly conical, while the lingual root (Fig. 61) is longest, largest and flattened bucco-lingually but seldom ex- hibits the depression observed on this root of the first molar. The two buccal roots have a distinct distal inclination and tend to converge at their apices. The disto- buccal root occupies a position relatively Fig. 64. — Right Upper Second Molar. Cross-section at cervax showing pulp chamber. Fig. 65. — Right Upper Second Molar. Longitudinal Section cut through mesio- buccal root canal, showing pulp chamber. more lingual than that of the first molar because of the flattening of the disto-buccal angle of the crown. Tlie Pulp Cavity. — The dift'er- ences between the form of this and that of the first molar correspond to the differences in the surface forms of the two teeth. The pulp chamber is flattened mesio-distally (Fig. 64) and the entrances to the canals are rela- tively nearer together and that of the disto-buccal canal is more lingually located. The horns of the pulp chamber are four in number but arc smaller and less penetrating than those of the first molar. The root canals have the same shape as those of the first molar but are smaller and more difficult to enter (Fig. 65). THE UPPER THIRD MOLAR. Greater variation occurs in the form of this tooth than in that of any other in the dental series. In its typical form it has only three 42 THE ANATOMY OF THE HUMAN TEETH. cusps, tlic (listo-lingual cusp having (lisa])pcure(l, while in its most strongly developed form this is j)resent but is much reduced in size by comparison with the other cusps of thi> tooth. Many atypical teeth arc observed in which the cusp development is difficult to classify. A description will be gi\en of the typical tooth. The Occlusal Snrjace (Fig. 66). — This is marked by the presence of a mesio-buccal, a dieto-buccal and a mesio-hngual cusp. The disto- lingual is represented only in the distal marginal ridge, or may be en- tirely absent when the oblique ridge forms the posterior margin of the surface. The buccal cusps are like in form to those of the lirst and second molars except that they are shorter and smaller. The mesio- FlG. 60. — Left Upper Third Molar. Occlusal Surface. Fig. 67. -Left Upper Third Molar. Buccal Surface. lingual cusp is large and rounded and the central fossa is well defined; usually many small ridges descend from the cusps into it. The mesial marginal ridge is well defined, the buccal depends in character upon the buccal cusps and the lingual is usually poorly discernible. The posterior margin may be either formed by the triangular ridge or the distal marginal ridge may be present. The Buccal Surface (Fig. 67). — In typical teeth this resembles the buccal face of the second molar but is smaller in extent, more rounded, and its distal lobe is poorly defined. The Lingual Surface (Fig. 68). — Variations in the form of this surface are caused by the presence or absence of the disto-lingual cusp — when present, this cusp surmounts a lobe of this surface which is partially divided from the mesial lobe by the disto-lingual groove. In this event the mesial lobe resembles that of the second molar but THE UPPER THIRD MOLAR. 43 is even more convex. When the h'ngual side is surmounted onlv by one cusp, it is much rounded and convex and joins the mesial and distal faces almost without line of demarcation. The Mesial Surface (Fig. 69). — This resembles that of the second molar in being flat and sometimes concave from buccal to lingual sides, but it is smaller in extent of surface. The Distal Surface (Fig. 70). — While it is usually rounded from buccal to lingual side, being always so when the disto-lingual cusj3 is absent, this surface may also be flat or even concave, when the crown has four cusps. It is always smaller in area than the mesial surface or than the distal surface of the first and second molars. Fig. 68.— Left Upper Third Molar. Lingual Surface. Fig. 69.— Left Upper Third Molar. Mesial Surface. The Roots. — These vary much even in teeth which are typical in regard to thier crowns. There are sometimes three roots, a mesio- buccal, a disto-buccal and a lingual, which are usually short and have a distal and a lingual curvature. These are sometimes fused together throughout most of their length. Occasionally only one root is seen caused by the complete fusion of the roots. Occasionally also four roots may be found (Fig. 71). The Pulp Cavity. — The external form of the crown largelv deter- mines the form of the pulp cavity, so that in trituberculate teeth this cavity is triangular in cross-section while in quadrituberculate teeth, it has the general form of the pulp chamber of the other upper molars. Its lateral walls converge more to the floor of the pulp chamber which is situated at a higher level than that of the pulp chamber of the second molar. The horns of the pulp chamber are less well defined and are 44 THE ANATOMY OF THE HUMAN TEETH. shorter than those of the other upper molars and correspond in number to the number of cusps in any given tooth. The ])ulp canals usually correspond in number with the number of roots except that in teeth in which the roots have fused into a single one, there may be three or even four root canals, which sometimes have separate apical fora- mina, or asiain mav unite before this is reached and have a common Fig. 70. — Left Upper Third Molar. Distal Surface. Fig. 71. — Left Upper Third Molar. With roots not completely developed and atypical in having four roots. Showing large patulous openings into root canals. termination. Occasionally in the single rooted tooth there is only one large canal, the walls of which are continuous with those of the pulp chamber and converge to a small foramen at the root apex. Where more than one canal exists, they are small and thread-like, quite short as the roots are short, and the openings from the pulp chamber into them are verv close together. THE LOWER FIRST MOLAR. The largest tooth of the human series is the lower first molar, which is longer mesio-distally than the upper fir.st molar, and is of about ec{ual width. The five surfaces of its crown may be described. The Occlusal Surface (Fig. 72).— This is irregularly trapezoidal in outline, its four margins usually being rounded. The buccal and lingual are more convex than the mesial and distal which may be al- most straight. These latter converge toward the lingual side in consequence of which this is shorter than the buccal. Five cusps are usually present, three upon the buccal side and two upon the lingual. A central fossa is formed and occupies nearly the center of the surface and from this radiate grooves separating the cu.sps. Four ridges THE LOWER FIRST MOLAR. 45 bound the surface. The mesial marginal ridge is the best defined of these. It passes from the mesio-buccal to the mesio-lingual angle of the crown, is concave rootward and is usually crossed near its center by the mesial groove. It is continuous at its buccal and lingual ex- tremities with the marginal ridges of these names. The buccal marginal ridge is poorlv defined, is bowed in a buccal direction, and is made up of the ridges descending mesially and distally from the three buccal cusps. The distal marginal ridge is not so prominent as the mesial but is like it in other respects. It is commonly crossed by the distal groove. The lingual marginal ridge is made up of the ridges descending ante- riorly and posteriorly from the two lingual cusps. It is cut near its center by the lingual groove and is somewhat sharper than the buccal marginal ridge. The mesio-buccal cusp i> usually the largest and some- times the longest cusp of thi> tooth. It is a rounded elevation with ridges descending mesiall}-, buccally, and distally, and some- times two or more toward thr central fossa from its lingual sides. The names of these ridges correspond to the direc- tion in which they descend from the point of the cusp, except that the lingual ridge is usually spoken of as the triangular. It is the most sharply defined of all. The buccal cusp is next in size of the buccal series of cusps, being intermediate in size and position between the mesio-buccal and the disto-buccal cusp. It has also four ridges which pass in a buccal, lingual, mesial and distal direction respectively. The lingual ridge descends into the central fossa and is called the triangular ridge. The disto-buccal cusp is separated from the last described cusp by the disto-buccal groove. It varies in size and position. It is more prominent buccally where it is of greatest size, but when found of small size it is located nearer the distal face of the tooth and there is a corresponding increase in the size of the buccal cusp. The disto-buccal is always the smallest cusp. Three ridges, a mesial, a distal and a triangular, may usually be observed, but its buccal surface is rounded and convex. The lingual cusps are sharper than the buccal cusps. The mesio- FiG. 72. — Right Lower First Molar. Occlusal Surface. 46 THE ANATOMY OF THE HUMAN TEETH. lingual is shar]) and jjroniinrnt in the unworn toolh and ils summit is near the mcsio-lingual angle. Its lingual surface is continuous witli that of the crown but ridges descend mesially, distally, and buccally. The triangular ridge passes into the central fossa and ter- minates at the mesial groove opposite the triangluar ridge from the mcsio-buccal cus]). These two ridges arc separated from the mesial marginal ridge by a shallow depression running bucco-lingually. The disto-lingual cusp is usually smaller than the mesio-lingual, Fig. 73. — Right Lower First Molar. Buccal Surface. Fig. 74. — Right Lower First Molar. Lingual Surface. but like it, is pointed and has three ridges descending from its summit, and otherwise resembles it in shape. The central fossa occupies approximately the center of the occlusal surface, and is broad and shallow. The mesial and distal marginal ridges and the five cusps contribute to form its walls. The mesial groove passes from it to the mesial surface, the buccal groove is well marked, usually the seat of a fissure, and passes buccally between the mesio-buccal and buccal cusps; the disto-buccal groove, also frequently the seat of a fissure, passes between the buccal and disto-buccal cusps; the distal groove crosses the disto-marginal ridge and the lingual groove THE LOWER FIRST MOLAR. 47 passes between the lingual cusps, although in some instances it is very poorly marked. The floor of the central fossa is flat and frequently small tubercles of enamel arc found divided from each other by fine grooves. The central pit, a fault in the enamel, is usually found where the buccal and lingual grooves meet and a distal pit often at the occlusal termination of the disto-buccal groove. The Buccal Surface (Fig. 73).— This is trapezoidal in shape, and is convex mesio-distallv and occluso-gingivallv. The mesial and distal Fig. 75. — Right Lower First Molar. IMesial Surface. Fig. 76. — Right Lower First Molar. Distal Surface. margins are much rounded and ill defined, the occlusal margin is marked by three elevations, the cusps, and two grooves, and the cer- vical is usually convex rootward and marked with a prominent ridge of enamel, the cervical ridge. The buccal groove crosses the surface a little mesial to its center and, decreasing in depth, is continuous with the depression caused by the bifurcation of the roots, or it terminates half way between the occlusal and cervical margin in a well-define;d de- pres-sion, the buccal pit. The disto-lingual groove is less deep at the occlusal margin and 48 THE ANATOMY OF THE HUMAN TEETH. terminates by disappearing about half way from the cervix. These grooves divide the buccal surface into lobes of which the mesial is most strongly marked, the central and distal being more rounded and usually uniting at the cervical portion, being separated at their occlusal portion by the disto-buccal groove. TJie Lingual Surjace (Fig. 74). — This is convex in all directions but is less so occluso-gingixally than the buccal because of the sharp- ness of the lingual cusps. Its mesial and distal margins are much rounded and converge to the cervical which is convex rootward. The occlusal margin is marked by the two cusps and the lingual groove. The latter is often poorly marked although it is occasionally deep, but usually disappears about the center of the surface, and the division of this surface by it into two lobes is not usually distinct. The Mesial Surjace (Fig. 75). — While it is generally convex and usually so near the occlusal margin where it affords a point of contact with the second bicuspid, this sur- face is sometimes fiat and usually a concavity may be noted near the Fig. 77. — Right Lower First Molar. . Cross-section at cervix, showing the cervical Ime. The occlusal margm pulp chamber and entrances to the pulp jg notched by the mesial groOVe canals. ■' _ '^ between the two mesial cusps, the lateral margins are rounded and convex in an occlusal direction. The Distal Surface (Fig. 76). — This resembles the mesial face of the crown in outline, but is more convex. Its cervical and lingual margins are like those of the mesial but the varying size and position of the disto-buccal cusp determine the occlusal and buccal margins. The latter is rounded and the former is marked by the distal groove. These unite at the disto-buccal cusp, the position of which determines whether the occlusal margin is long or short. The Roots. — There are two roots (Fig. 73), named from their posi- tions, mesial and distal. They are both broad and much flattened mesio-distally. The point of bifurcation is about one-fourth the dis- tance from the cervix to the root apices. The mesial root when viewed from the mesial surface (Fig. 75) is seen to be flat, its sides converging but slightly to a blunt apex. On both its mesial and distal surfaces a longitudinal depression running the length of the root may be ob- served. The mesial and distal sides are nearly parallel until the apex THE LOWER SECOND MOLAR. 49 is reached. The root is curved mesially so that its lower third has a decided distal turn. The distal root is usually straight and is flattened also mesio-distally. It is not marked by longitudinal depressions on its mesial and distal sides, terminates in a sharper apex than the mesial root, and is not so long. The Pulp Cavity.— The chamber corresponds in general to the shape of the crown, being quad- rilateral in horizontal cross- section (Fig. 77). The occlusal wall of the chamber in young teeth has five horns which are in relation with the five cusps, but these are very poorly marked because of the shortness of the cusps. The lateral walls are four in number, the buccal wall being of greatest extent. These converge to the floor (Fig. 77) which is concave bucco-lin- gually and convex mesio-distally. The buccal and lingual walls meet in a troughdike depres- sion which dips down anteriorly and posteriorly to the entrance into the pulp canals. In any but old teeth the mesial and distal walls (Fig. 78) are contin- UOUS with the walls of the pulp dis'ta?" longui^ilaV section cut through the canals. The openings to the buccal cusps and the pulp canals, showing , ^ , ,., rr^, pulp chamber and canals. latter are funnel-like. 1 here are usually two canals in the mesial root which are fine and thread- like and round. They occasionally meet before the apex of the root is reached and terminate in a common foramen although they usually make exit by separate foramina. The distal pulp canal is larger and ovoid in cross-section and easilv entered. THE LOWER SECOND MOLAR. The crown of the lower second molar differs from that of the first in that it has four cusps of nearly equal size instead of five. In other particulars its surface form is very similar. The Occlusal Surface (Fig. 79). — The occlusal surface presents 50 THE ANATOMY OF THE HUMAN TEETH. for examination four cusjjs of nearly ecjual size, silualed near its four anL:;les. The summits of the cusps are nearer the center of the crown than are those of the first molar and are more rounded. The out- line of this surface is more rounded than that of the first molar, the mesial and distal margins being of equal length and convex. The buccal and lingual are also usually of equal length but in some instances that of the former is greater. The mesial and distal marginal ridges arc similar to those of the first molar, and the surface has a central fossa from which a mesial, distal, buccal, and lingual groove pass to these respective borders. The central fossa is well defined but shallower than that of the first molar. The triangular ridges from the cusps are well marked and between these the grooves meet forming a cruciform sulcus. Occasion- ally the tooth has five cusps when the anatomy of this sur- face is similar to that of the first molar. The Buccal Surface (Fig. 80). — This has the same general form of tliat of the first molar, but is less complicated because of the absence of the fifth cusp. It is more convex than that of the first molar, is relatively smaller in extent and is not so definitely divided into lobes by the buccal groove. This latter usually terminates by blending with the buccal surface about its center and rarely terminates in a buccal ])it. The Lingual Surface (Fig. 81). — Except that it is smaller, this resembles the lingual face of the first molar crown so closely as to require no separate description. TJie Mesial Surface (Fig. 82). — This is more convex than that of the first molar but is like it in other respects. The Distal Surface (Fig. 83). — The absence of the fifth cusp is responsible for the dissimilarity between this and the distal surface of the first molar. It resembles, however, the mesial surface of the second molar, being slightly more rounded. The Roots. — These are two in number and closely resemble the roots of the first molar. They are not quite so long, do not exhibit the longitudinal depressions seen upon the roots of the first molar, Fig. 79. -Right Lower Second Alolar. Occlusal Surface. THE LOWER SECOND MOLAR. >I Fig. 8o. — Right Lower Second ^lolar. Buccal Surface. Fig. 8i. — Right Lower Second Molar. Lingual Surface. Fig. 82. — Right Lower Second Molar. ^Mesial Surface. Fig. 83. — ^Right Lower Second ]Molar. Distal Surface. 52 THE ANATOMY OF THE HUMAN TEETH. terminate in sharper apices and arc usually inclined to the distal at their extremities. The Pulp Cavity (Fig. 84). — -The occlusal wall of the pulp chamber has only four rudimentary horns, the floor of the chamber is smaller and the openings into the pulp canals are closer together but in other particulars this is similar to the chamber of the first molar. THE LOWER THIRD MOLAR. No tooth in the human denture is subject to greater variation than the lower third molar. The form most commonly found is that with four cusps, in which instance the crown much resembles the second molar. Rarely it is possessed of five cusps, being somewhat similar to the first molar in form. Often its occlusal surface is much broken up and exhibits a fossa surrounded by a number of cusps and is nearly circular in outline. The Surfaces. — When four cusps are present, and this is the commonest form, the occlusal surface resembles that of the second molar except that the cusps are shorter, the fossa is shallower and the outlines of the sur- face are more rounded. When several cusps exist the grooves separating them radiate from the central fossa. The buccal, lingual, mesial and distal sur- faces resemble those of the second molar if the tooth has four cusps, or those of the first if it has five. In other forms of the tooth the tendency to roundness of these surfaces is to be noted and it is usually difficult to perceive any line of demarcation between them. The Roots. — There are two which usually resemble the other lower molar roots except that they are shorter in proportion to the size of the crown, and generally have a marked distal curve which complicates the extraction of the tooth. Often the roots are fused and sometimes throughout their whole extent, giving thus only one actual root. The Pulp Cavity. — It can only be said concerning this that the chamber corresponds to the external form of the crown, being similar to this cavity of the first or second molar according as the crown re- FiG. 84. — Left Lower Second Molar. The roots have not been completely developed. Longitudinal section through mesial root showing pulp cavity and method of its division into two pulp canals. THE DECIDUOUS TEETH. 53 sembles one or the other of these teeth. In other instances it is usually a rounded cavity resembhng the external form of the crown. The pulp canals are similar in number to those of the first molar and may be found separated even if the roots of the tooth are fused. In rare instances a single large canal terminating in a single small apex is found. THE DECIDUOUS TEETH. ■ The temporary or deciduous teeth serve for purposes of masti- cation during the earlier years of life and are exfoliated between the fifth and the twelfth years to give way to their permanent successors. Fig. 85. — The permanent teeth in occlusion. External View. (American Text-book of Prosthetic Dentistrj'.) They are less highly developed for functional purposes than the per- manent teeth but entirely satisfy the requirements of the food habit of these early years. They are necessarily smaller than the permanent teeth and are but twenty in number. They resemble in many respects the permanent teeth as regards external form and internal anatomy, but differ in some particulars and these latter must be pointed out. They are in general less well developed as to surface markings. They have relatively longer roots but these are relatively smaller than those of the permanent teeth. 54 THE ANATOMY OF THE HUMAN TEETH. This latkT fad accounls for the t-onslrirlcd neck and bell-sha])cd crown characteristic of the deciduous teeth. The crowns of tlie teeth are shortcT in relation to their wicUh than are those of the permanent teeth. The Upper Central Incisor (Fig. 88). — In addition to being much smaller than the ])ermanent central incisor, the crown of this tooth is less well marked upon its surface. The labial grooves, the lingual marginal ridge and fossa and the distal angle are especially lacking Fig. 86. — The Occlusion of the Teeth. Lingual View. (American Text-book of Prosthetic Dentistry.) in development. Its surfaces are much rounded and its neck is con- stricted. The root is relatively longer and smaller than that of the permanent tooth but resembles it in other particulars. The Upper Lateral Incisor (Fig. 88). — This resembles both the permanent lateral and the deciduous central incisor. It has the characteristics of the former except in a modified degree. Its surface markings are less pronounced than are those of the permanent lateral and it resembles the deciduous central except that its wddth is less and its distal angle is more rounded. It is a more delicately shaped tooth but is usually equal in the length of its crown to the central and fre- quently its root is longer. The latter resembles that of the permanent THE DECIDUOUS TEETH. 55 lateral incisor in other particulars except of course that it is relatively smaller. The Upper Cuspid (Fig. 88). — The resemblance between this tooth and that of the permanent series is marked, but sufficient ditTerences exist between them to easily differentiate the two teeth. The crown of this tooth is proportionately shorter and more rounded than that of the permanent cuspid. The labial surface presents a marked labial ridge ascending from the point of the cusp, and the labial grooves are much nearer the angles of the tooth. The angles of the crown are much nearer the cervical line than those of the per- manent cuspid in consequence of which the mesial and distal cutting edges are relatively longer and the mesial and distal surfaces are smaller. The lingual surface has a marked lingual ridge and the surface is generally rounded and convex. The root is pro- portionately smaller than that of the permanent cuspid and the pulp canal is small in conse- quence, but the pulp chamber, like that of all the deciduous teeth, is relativelv large. ^ig. 87.— Occlusal surface of the upper " deciduous teeth. The Upper First Molar.— The molar teeth of the deciduous series are totally unlike their suc- cessors, the bicuspids, and partake chiefly of the characteristics of true molar teeth. The crown of the first upper molar usually has three cusps, two on the buccal and one on the lingual side. (Fig. 89.) The surface is almost quadrilateral because the large size of the lingual cusp serves to balance the two buccal on the opposite side. The corners of the figure are much rounded, the sharpest corner being the mesio-buccal while both the lingual corners are much rounded. The buccal cusps are sharper than the lingual which is full and rounded, although all are more pointed than those of the upper permanent molars. A central fossa occupies the space between the cusps. It is broad and shallow. A groove passes from it to the buccal, mesial and distal sides respectively, and these serve to separate the cusps from each other. The buccal surface resembles that of the upper molars except that the occlusal margin is sharp, the surface is more rounded, the buccal groove is very shallow and poorly defined, and at the cervical margin a ridge of enamel passes from the mesial to the distal border. 56 THE ANATOMY OF THE HUMAN TEETH. Thv lobe of this surface mesial to the buccal groove is proportion- ately larger than tliat of the permanent molar, as it is both wider and larger from occlusal to cervical margin than the distal lobe. The lingual surface is full and convex in every direction and passes into tlie mesial and distal faces witliout demarcation. These latter resemble those of the upper permanent molars, the mesial being flattened with a convexity near the occlusal margin, the distal being rounded. Tliree roots are possessed by this tooth. They are mesio-buccal, disto-buct al and lingual. The buccal roots are flattened mesio-distally. Fig. 88. — Skull showing deciduous teeth in occlusion. the lingual being llattened bucco-lingually, and they diverge mark- edly in order to give a space for the permanent tooth which succeeds. The pulp chamber is rounded and large, corresponding with the general external form of the crown. The root canals are small and thread-like and difficult to enter. The Upper Second Molar (Fig. 89). — This tooth is larger than the first temporary molar and resembles the first permanent molar so exactly that a separate description is unnecessary. It has not the lingual cingule or fifth cusp, it is smaller, more constricted at the neck and its roots are widely separated at their apices, but in other particu- lars the description of the permanent tooth will suffice. The Lower Central Incisor. — Except for the fact that the tooth is smaller, has more rounded angles, and has its labial and lingual grooves THE DECIDUOUS TEETH. 57 poorly defined, the description of the permanent tooth would equally apply to this. It must be added, however, that its root is relatively smaller than that of its successor. The Lower Lateral Incisor. — The resemblance between this and the upper deciduous lateral incisor is marked. It is wider than the lower central and its distal angle is rounded like that of the upper lateral. Its various surfaces and its root are like those of its upper opponent and further description is unnecessary. The Lower Cuspid. — The upper and lower deciduous cuspids are much alike. The latter is narrower mesio-distallv and its surfaces Fig. 89. — Dissected specimen of maxillae and mandible showing the deciduous teeth. are not quite so convex but in other particulars its anatomy is identical with that of the former. The Lower First Molar (Fig. 89). — This tooth has the general molar form but a detailed description is necessary for its identifica- tion. Its crown is a much rounded cuboid and exhibits four cusps, one near each of its rounded angles. On the occlusal surface these four cusps are seen to be divided by grooves which unite in the fossae. The mesio-buccal cusp is the largest. A ridge descending from it anteriorly curves and meets one from the mesio-lingual cusp to form a mesial marginal ridge. Triangular ridges from these two cusps meet at the bottom of a mesial groove, and a small depression is formed between these and the mesial marginal ridge. This is often called 58 THE ANATOMY OF THE HUMAN TEETH. ihe mesial fossa but is very small as compared to the distal fossa which is located between the two distal cusps and these triangular ridges. A distal, a buccal and a lingual groove, all poorly defined, emanate from the distal fossa in these several directions. The buccal and lin- gual grooves are not continuous because the greater size of the mesio- buccal cusp carries the former too far distally. The disto-buccal cusp is small, the mesio-lingual is usually the sharpest and longest, and the disto-lingual is not well defined as the lingual groove is always shallow. The distal marginal ridge is cut by the distal groove. The buccal surface is convex and has near its cervical margin a pronounced ridge of enamel, the cervical ridge. The mesial margin is longer than the distal in conseriuence of the greater size and length of the mesial lobe, a condition similar to that of the first upper decid- uous molar. The buccal groove is shallow and either terminates in a pit or disappears upon the center of the surface. The lingual surface is convex, and the lingual groove marks its occlusal portion about the center when it is present but often it is almost indistinguishable on this surface. The mesial and distal sur- faces are very similar to those of the second permanent molar. The mesial is flat with a pronounced occlusal edge; the distal is more rounded and the distal groove usually marks decisively its occlusal margin. The tooth has two roots which are similar to those of the first permanent molar except that they are smaller and quite divergent to give space for the bicuspid which follows. The pulp chamber cor- responds in shape with the external surface of the crown. The en- trances to the three canals are near together, the two mesial ones being small and very difificult to enter, the distal canal being more accessible. The Lower Second Molar (Fig. 89). — Beside the constriction of its neck, the divergence of its roots, and its smaller size, this tooth resembles the first permanent molar in almost every particular. The description of the latter tooth will apply to the deciduous tooth and the reader is referred to it. CHAPTER II. THE HISTOLOGY OF THE HUMAN TEETH. BY CHARLES R. TURNER, D. D. S., M. D. A knowledge of the minute anatomy of the tissues of the human teeth is as important as an acquaintance with their surface forms, for it paves the way to an understanding of their several physiological rela- tionships in the tooth, to a knowledge of the pathological conditions arising in them, and to a rational conception of the various operative and therapeutic measures used in the treatment of these conditions. The tissues of the human tooth are the enamel, which is the hard external covering of the crown; the dentin, which composes the bulk of the tooth and largely determines its form; the cementum, which forms the external covering of the root and to which is attached the peri- cementum, a membrane intervening between the tooth and its bony socket in the alveolar process; and finally the dental pulp, a mass of soft tissue occupying the internal chamber of the tooth called the pulp- cavity. A clearer understanding of the relationships of these tissues may be had if we first become acquainted with the method of their develop- ment in the embryo. This also confers a better knowledge of their structure. About the fortieth to the forty-fifth day of intra-uterine life, there is a thickening of the stratum Malpighii of the oral epithelium over the site of the future jaw. This forms a band of epithelial cells extending from one end to the other in each jaw. About the forty-eighth day a budding is seen to take place from the under surface of this tooth-hand, and ten rounded buds appear attached to it, marking the beginning of the tooth-germs for the deciduous teeth. These buds dip further into the substance of the underlying connective tissue, and becoming invagin- ated upon their advancing surfaces, finally enclose in this invagina- tion a mass of mesoblastic connective tissue and become the tooth- germ. This epithelial cup which has descended from the mucous membrane remains connected with it for some time by a cord of epithe- lial cells, the epithelial cord, but this cord soon disappears, and the tooth-germ is enclosed by a fibrous membrane developed from the 59 6o THE HISTOLOGY OF THE HUMAN TEETH. surrounding tissue. The epithelial cup becomes the enamel organ of the future tooth, the connective tissue enclosed by it becomes the dentin organ or papilla. The whole tooth-germ enclosed in its sac is known as the dental jollidc. (Fig 90.) The enamel organ takes on the form peculiar to the tooth which it is to assist in forming, and its cells begin to alter in character. Those Fig. 90. — Section of upper jaw of human embryo near the seventh month of fetal life, showing development of temporary cuspid. A. Ameloblasts showing beginning of enamel formation. B. Dentin. C. Showing beginning of dentin formation. D. Walls of tooth sac. E. Dentinal papilla. X 50. (Williams. Dental Cosmos.) next to the dentinal papilla become columnar in form, those on the ex- terior disappear by atrophy, while the intervening ones are changed from polygonal to stellate cells and become the stellate reticulum. This latter finally almost entirely disappears, leaving however next to the inner columnar layer a small layer of cells which now comes to be knowm as the stratum intermedium. The inner columnar cells now become enlarged and elongated, their nuclei move to their outer ends THE ENAMEL. 6l and they become the ameloblasts, which are the cells directly concerned with the formation of the enamel. The dentin organ which occupies the space within the enamel organ, and which is formed from the mesoblastic connective tissue, is composed of embryonal connective tissue cells of various kinds; spindle shaped, round, and stellate cells are scattered through its substance, while over its entire periphery there is a layer of specialized club-shaped cells, the odontoblasts, which are specifically concerned in the forma- tion of the dentin. In the development of the tooth, a deposit of dentin initiates the proc- ess, a layer of dentin being calcified about the external surface of the odontoblastic layer of the papilla. The function of the odontoblasts in this process is imperfectly made out. It is known that lime salts are deposited about their external processes and that these become the dentinal fibrils. Furthermore, as said by Broomell, they are be- lieved to superintend the dentin formation, but just what is their rela- tion to the deposition of the lime salts is not known. After the dentin cap is begun it grows by additions to its interior, while upon its periphery enamel formation begins. This is by a process of secretion in which globular masses of calco-globulin are formed in the ameloblas- tic cells; these escape from the external ends of the ameloblasts and, becoming packed together one after another, form the enamel prisms. An albumen-like substance, according to Williams, is secreted in the stratum intermedium, and flows about the partially formed prisms, "supplying the cement substance and probably the mineral matter for the calcification of the whole." Cementum is formed upon the completed dentin root of the tooth by specialized odontoblastic cells, the cementohlasts, which have devel- oped in the wall of the tooth follicle. Its growth is similar to that of subperiosteal bone. The pulp is what remains of the dentin papilla, after the latter has been reduced in size by the growth of the dentin walls. The periph- eral layer of odontoblasts persists during the life of the pulp, but after the mature tooth is formed, these cells remain inactive unless called into activity by some pathologic stimulation from without. THE ENAMEL. The enamel constitutes the external covering of the crowns of the teeth. It is by far the hardest of the animal tissues and for this reason it is particularly suited to resist the wear incident to the use of the teeth in the comminution of food. Its distribution over the crown 62 THE HISTOLOGY OF THE HUMAN TEETH. of a tooth is not uniform, as it is thinnest at the cervical margin, where it is slightly overlapped by the cementum; from this margin it increases in thickness, until over the cusps and cutting edges of the teeth, where it is most exposed to wear, it is thickest of all. It is also slightly thicker at the site of the elevations and ridges upon the crowns of the teeth. In the newly erupted tooth it is faintly and delicately ridged transversely, and in some teeth it presents other evidences of its develop- ment, but it soon wears smooth and lustrous. When a tooth is erupted the enamel is entirely completed over the whole of its crown. No portion of the tooth is erupted until the enamel covering it is fully formed. When once formed enamel is a fully completed substance, and no physiologic change in its structure or composition ever occurs thereafter. Williams remarks, "Enamel is a solid mineral substance, and the finest lenses reveal not the slightest differences between enamel ground moist from a living tooth, and that which has laid in the earth for a hundred centuries." Defects in the structure of the enamel, in consequence of which the value of its protective of^fice is lessened, are commonly observed at the site of the fissures and pits upon the surface of the tooth-crown which marks the points of union of the several centers from which calcification began. These faults are frequently found in the sulci of the molar and bicuspid teeth, in the buccal pits of the molar teeth, and in the Ungual fossae of the upper lateral incisors. These defects are favor- able sites for the beginning of caries, the break in the integrity of the enamel affording lodgment for the bacteria and a favorable starting point for their activity. While enamel is formed in an organic matrix, not the least trace of this remains chemically in the completed enamel. This accounts for the lack of sensitivity of this structure, for it is not capable of trans- mitting physiologically any sensations whatever. These facts demon- strate its value as a vital protective covering for the teeth. Chemically it consists chiefly of the phosphate and carbonate of calcium as the following analysis by von Bibra shows: Man. Woman. Calcium phosphate and fluorid, 89.82 81.63 Calcium carbonate 4.37 8.88 Magnesium phosphate, 1.34 3.55 Other salts, 88 .97 Cartilage, 3.39 5.97 Fat, 20 a trace Organic, 3.59 5.97 Inorganic 96.41 94-03 THE ENAMEL. 63 Charles Tomes has shown that the organic matter obtained in this and the older analyses is simply the water which is combined with the lime salts. He has proven that it will be suddenly given off upon ignition of the specimen under analysis. Enamel is not a homogeneous mass of calcified tissue but, under the microscope may be seen to consist of a collection of prisms or rods, Fig. 91. — Section of enamel of huiii