■S,sSfiSl"'ia%'^ RK501 K6Tf9^rS, The American (ext-bo RK ^01 \iG'3 intt)fCtipoflfttigork College of $f)p£(ician£f anb burgeons; Dr. C.F. M».cD ^m^.Tfi^iW-";' Digitized by tine Internet Archive in 2010 witii funding from Open Knowledge Commons http://www.archive.org/details/americantextbook1911kirk LIST OF rOXTRIBUTORS. ANGLE, EDWARD H., M.D., D.D.S. ; CAPON, W. A., D.D.S. ; CASE, CALVIN S., M.D., D.D.S.; CRENSHAW, WILLIAM, D.D.S.; CRYER, M. H., M.D., D.D.S.; DARBY, EDWIN T., M.D., D.D.S. ; GODDARD. C. L., D.D.S. ; GUILFORD, S. H., A.M., D.D.S., Ph.D.; INGLIS, OTTO E., M.D., D.D.S.; JACK, LOUIS, D.D.S.; KIRK, EDWARD C, D.D.S., Sc.D. ; NOYES, FREDERICK B., B.A., D.D.S.; OTTOFY, LOUIS, D.D.S.; PRINZ, HERMANN, M.D., D.D.S.; THOMPSON, ALTON HOWARD, D.D.S. TRUMAN. JAMES, D.D.S., LL.D. ; WARD, MARCUS L., D.D.Sc. ; WEEKS, THOMAS E., D.D.S. THE AMERICAN TEXT-BOOK OPERATIVE DENTISTRY. m CONTRIBUTIONS BY EMINENT AUTHORITIES. EDITED BY EDWARD C. KIRK, D.D.S., Sc.D., Professor of Dental, Pathology, Therapeutics, and Materia Medica, and Dean of the Dental Department of the University of Pennsylvania, Philadelphia; Editor of " The Dental Cosmos;" Officier de l'AcadiSmie de France. FOURTH EDITION, REVISED AND ENLARGED. ILLUSTRATED WITH 1015 ENGRAVINGS. LEA & FEBIGER, PHILADELPHIA AND NEW YORK. 1911 T K ^'0 i \< (. 3 1S\I Entered according to Act of Congress in the year 1911, by LEA & FEBIGER, in the Office of the Librarian of Congress at Washington. All rights reser\^ed. WITH THE CONSENT OF THE CONTRIBUTORS THIS BOOK IS DEDICATED TO JAMES TRLTjMAISr, D. D. S., L.L. D., THE CHARACTERISTIC OF WHOSE LONG PROFESSIONAL CAREER HAS BEEN THE INCULCATION OF THE PRINCIPLES UPON WHICH THE WORK IS BASED. PREFACE The demand for a new edition of the American Text-book of Operative Dentistry has necessitated much more than a mere revision of the previous text. The work has been largely ^e^^Titten, and the fourth edition is therefore practically a new book. Such a radical change has been rendered necessary by the rapid evolution which has taken place throughout the entire domain of the science and art of dentistry since the publication of the previous edition. The accumulation of new data, the investigation of the deeper problems of dental science, and the modification exerted by these factors upon the practice of dentistry have wrought changes that in certain departments are little less than revolutionary. So rapid and far-reaching in their effects are many of the changes which have taken place that the whole subject of operative dentistry has been and still is in a state of flux. The mirroring of the progressive movement in operative dentistry will be evident in the plan as well as in the text of this work. The subject of cavity preparation is treated as a technic procedure, first, because it can be most intelligently comprehended as such, and further, because the work is primarily intended for the instruction of the undergraduate student. It is fully recognized that the scientific basis of such subjects as pyorrhea alveolaris, tooth discoloration, tooth extraction, root-canal treatment, orthodontia, etc., is much more fully elaborated in the present work than would be justifiable in a treatise or text-book devoted exclusively to operative dentistry as an art; but as there still appears to be a demand upon the part of students for a volume furnishing a comprehensive view of the fundamental principles upon which alone an intelligent and rational practice may be based, the treatment of the subject of operative dentistry in the present work has been extended to include those principles. Certain differences of opinion will be occasionally manifest in the work in the treatment of allied subjects by difterent authors. ^\liile such differences are, of course, not desirable in a work intended for the use of untrained students, and while no conflict of opinion will be noticed with respect to established scientific principles, it is manifestly impossible to secure unanimity upon subjects which have not as yet (vii) . viii PREFACE reached a stage of development entitling them to classification among the exact sciences. For example, the imsettled (luestion whether under any circumstances extraction is a justifiable operation in connection with the correction of malocclusion, has led to dift'erences of opinion that are not at present reconcilable, and cannot be until a larger body of evidence based upon observation and experience has been submitted at the bar of professional judgment. The Editor takes this occasion to express his deep sense of appre- ciation of the uniform courtesy and spirit of helpfulness which have characterized the attitude of all of his collaborators in this work, for their patience under his suggestions, and their willingness to sacrifice personal interests to the thoroughness and accuracy of the work as a whole. To the publishers his thanks are due for their unhesitating cooperation in every effort which tended to the completeness of the work in all its phases, and he is likewise und(>r obligation to his colleague, Dr. Riethmiiller, for the preparation of the accurate and copious index. The Editor assumes personal responsibility for the nomenclature used throughout, and in submitting the \olume to the critical consideration of his fellow-teachers and his larger circle of fellow-students he can hope for it no more generous treatment, nor, indeed, could he expect more, than has been so freely accorded to its predecessors. E. C. K. University of Pennsylvania, 1911. LIST OF CONTRIBUTORS EDWARD H. ANGLE, M.D., D.D.S., Presuiont of the Angle School of Orthodoiif ia, Now Tvoiidon, Conn. W. A. CAPON, D.D.S., Lecturer on Dental Ceramics in the University of Pennsylvania, Phila(le!j)liia. CALVIN S. CASE, M.D., D.D.S., Professor of Orthodontia, Chicago College of Dental Surgery, Chicago, 111. WILLIAM CRENSHAW, D.D.S., Dean and Professor of Operative Dentistry and Dental Pathology, Atlanta Dental College, Atlanta. M. H. CRYER, M.D., D.D.S., Professor of Oral Surgery in the Dental Department of the University of Pennsylvania, Philadelphia. EDWIN T. DARBY, M.D., D.D.S., Professor of Operative Dentistry and Dental Histology in the University of Pennsylvania, Philadelphia. C. L. GODDARD, D.D.S., Late Professor of Orthodontia, University of California, College of Dentistry, San Francisco, Cal. S. H. GUILFORD, A.M., D.D.S., Ph.D., Professor of Operative and Prosthetic Dentistry and Dean of the Philadel- phia Dental College, Philadelphia. OTTO E. INGLIS, M.D., D.D.S., Professor of Dental Pathology and Therapeutics in the Philadelphia Dental College, Philadelphia. LOUIS JACK, D.D.S., Pliiladelphia. EDWARD C. KIRK, D.D.S., Sc.D., Professor of Dental Pathology, Therapeutics, and Materia Medica, and Dean of the Department of Dentistry in the University of Pennsylvania, Phila- delphia; Officier de I'Academie de France. FREDERICK B. NOYES, B.A., D.D.S., Professor of Dental Histology in the Northwestern LTniversity Dental School, Chicago, III. LOUIS OTTOFY, D.D.S., Professor of Clinical Therapeutics, Chicago College of Dental Surgery, Chicago; Attending Dental Surgeon, St. Luke's Hospital, Manila, P. I. (ix) X /-/.ST OF COXTRIIiUTORS HERMANN PRINZ, M.D., D.D.S., Professor of Materia Medica, Therapeuties, ami I'alliolo^^y in (lie \\ asliirinton University Dental School, St. Louis, Mo. ALTON HOWARD THOMPSON, D.D.S., Professor of Dental Anatomy, Kansas ( 'ity 1 )eiital ( "olIcKe, Kansas C'it^', Mo. JAMES TRUMAN, D.D.S., LL.D., Emeritus Professor of Dental Pathology, Therapeutics, and Materia Medica in the University of Pennsylvania, Philadelphia. MARCUS L. WARD, D.D.Sc, Profe.ssor of Dental Physics and Chemist r^- in the University of Michigan, Ann Arbor, Mich. THOMAS E. WEEKS, D.D.S., Professor of Dental Anatomj-, Operative Technique, and Clinical Dentistrj' in the Philadelphia Dental College, Philadelphia; Author of Weeks' Technique. CONTENTS CHAPTER I HUIMAN ODONTOGRAPHY • 17 By Alton Howard Thompson, D.D.S. CHAPTER n DENTAL HISTOLOGY ^YITH REFERENCE TO OPERATIVE DEN- TISTRY 56 By Frederick B. Noyes, B.A., D.D.S. CHAPTER HI ANTISEPSIS IN DENTISTRY 118 By James Truman, D.D.S. , LL.D. CHAPTER IV EXAMINATION OF THE TEETH AND ORAL CAVITY PRELIMINARY TO OPERATION— REMOVAL OF DEPOSITS— APPLIANCES AND METHODS— RECORDING RESULTS 135 By S. H. Guilford, A.M., D.D.S., Ph.D. CHAPTER V CREATING INTERDENTAL SPACES PREPAJIATORY TO FILLING — GRADUAL SEPARATION — IMMEDIATE OR FORCIBLE SEPARATION 140 By S. H. Guilford, A.M., D.D.S., Ph.D. CHAPTER VI MODIFICATION OF DENTINAL SENSITIVITY BY DEHYDRATION — TOPICAL MEDICATION — ELECTRICAL OSMOSIS — GEN- ERAL ANESTHESIA 145 By S. H. Guilford, A.M., D.D.S., Ph.D. (xi) xii CONTENTS CHAPTER \\\ TECHNIQUE OF CA^ rrv PREPARATION lo.l By Thomas E. Weeks, D.D.S. CHAPTER \\U EXCLUSION OF MOISTURE— EJECTION OF THE SALIVA— APPLI- CATION OF THE DAM IN SIMPLE CASES, AND IN SPECIAL CASES PRESENTING DIFFICULT COMPLICATIONS— NAPKINS AND OTHER METHODS FOR SECURING DRYNESS .... 191 By Louis Jack, D.D.S. CHAPTER IX THE OPERATION OF FILLING CAVITIES WITH METALLIC FOILS AND THEIR SEVERAL MODIFICATIONS 201 By Edwin T. Darby, D.D.S., M.D. CHAPTER X USE OF THE MA^IllTX IN FILLING OPERATIONS 23') By William Crenshaw, D.D.S. CHAPTER XI PLASTICS 202 By Marcus L. Ward, D.D.Sc. CHAPTER XII COMBINATION FILLINGS 324 By Marcus L. Ward, D.D.Sc. CHAPTER XIII RESTORATION OF TEETH BY CEMENTED INLAYS 333 By W. a. Capon, D.D.S. CHAPTER XIV THE TREATMENT AND FILLING OF ROOT CANALS .... 391 By Otto E. Incjlis, D.D.S. CONTENTS xiii CIIAITKR XV PYOKIMII'IA AI.VMOI.AIIIS 464 By Edwaki) C Kirk, D.D.S., Sc.l). CHAPTER XVI DISCOLORED TEETH AND THEIR TREATMENT 519 By Edward C. Kirk, D.D.8., Sc.D. CHAPTER XVH EXTRACTION OF TEETH 545 By M. H. Cryer, M.D., D.D.S. CHAPTER XVHI LOCAL ANESTHESIA 623 By Hermann Prinz, M.D., D.D.S. CHAPTER XIX PLANTATION OF TEETH 546 By Louis Ottofy, D.D.S. CHAPTER XX MANAGEMENT OF DECIDUOUS TEETH 664 By Clark Goddard, A.M., D.D.S. CHAPTER XXI ORTHODONTIA 683 By Edward H. Angle, M.D., D.D.S. CHAPTER XXII DENTO-FACIAL ORTHOPEDIA 873 By Calvin S. Case, D.D.S., M.D. CHAPTER XXIII ORAL PROPHYLAXIS 910 By S. H. Guilford, A.M., D.D.S., Ph.D. I N T K () D U C T (3 R Y. A STUDY of the advances which have of recent years taken place in the field of Operative Dentistry will reveal, besides the important addi- tions to our knowledge in the shape of novel methods and improved technique, a vastly more important advance manifested in a better and more general understanding of scientific principles, and the application of dental science to dental art, resulting in a more rational practice. Especially is this true in regard to the etiology of dental and oral pathological conditions, and the rationale of the modes of treatment indicated for the morbid states constantly confronting the dental practitioner. The modifications in surgical methods and the greatly improved results "which are the outgrowth of modern scientific studies in bacterial pathology, while they have made a considerable impress upon dental operative methods, have not, however, received that universal practical acceptance among dental operators which their immense importance demands. There is no field of special surgery in which the import- ance of exact knowledge wdth respect to aseptic and antiseptic treat- ment is more marked than in the practice of dentistry. The dental operator is continually confronted with septic conditions, so that pre- cise knowledge of their origin, causes, i^henomena, and treatment are essentials to the legitimate practice of the profession. The performance of any operation, and especially those which are classified as capital, with unclean hands or infected instruments would in the present stage of surgical art be regarded as criminal malpractice. It should be so considered in dentistry. The loss of a patient's life as the result of surgical septic infection is no longer permissible. Lack of antiseptic precautions, in certain dental operations may directly lead to and as a matter of fact has been the cause of fiital results. It has been shown conclusively ^ that a large variety of pathogenic micro- organisms are almost constant inhabitants of the oral cavity. In addi- tion to the numerous forms which bring about an acid reaction, there are many specific organisms which produce in inoculated animals pyemia and septicemia in their several clinical classes. But while the dental practitioner is not often called upon to face the issues of life ^ W. D. Miller, Dental Cosmos, November, 1891. 15 16 lyTRODCCTOliV. and (lentil in tlic course of his woi-k, his reil)ilities as related to the issues with which he docs deal demand ol" him the same care and thoroughness in order to attain tiie character of result which the pos- sibilities of modern dentistry require of him. In the following pages the importance of asepsis and antisepsis in dental operations is con- stantly impressed upon the mind of the student. By the term nsqms is specifically meant the condition under which are excluded those influences or causes which induce infection by patho- genic micro-organisms ; when a tissue or surface has been rendered germ-free it is said to be in an aseptic condition. By (inti.srp.sis is meant the means by which the septic state is comljated or the aseptic state is attained. Under the aseptic condition repair of tissues takes place normally without interference, wounds and injuries heal with a minimum of dis- turbance, and the inflammatory concomitant is of the simple traumatic type, without suppuration or tendency to diffusion. The aseptic state, in many operations in the mouth, is not readily attainable and cannot be maintained for anv lentjth of time ; but in all operations which involve the pulp and pulp chamber, as well as the periapical region through the pulp canals of teeth, strict aseptic con- ditions, as regards external infection, are perfectly attainable through exclusion of the oral secretions by means of rubber dam, the use of suitable disinfectants, and sterilized instruments. It is the class of operations here alluded to which are most prolific of disturbance from infective inflammations caused by ignorant or careless manipulation. The time is at hand, if indeed it has not already arrived, when puru- lent inflammations fi)llowing dental treatment will be regarded with the same condemnation by the dentist as by the general surgeon. The operative section of this work is written in full recognition of the prin- ciples here indicated. OPERATIVE DENTISTRY CHAPTER I HUMAN ODONTOGR.IPHY By ALTON HOWARD THOMPSON, D.D.S. The teeth are located at the portal of the alimentary system of the animal organism. They help to differentiate in the choice of the elements of nutrition and reduce these elements to digestible condition. The dental armament is, therefore, the first and chief factor in the mechanism of alimentation. The teeth are, morphologically, transformed tissues belonging to the tegmnentary system of animals, and are hard, calcareous bodies, situated in the oral cavity at the anterior orifice of the alimentary canal. In the lower vertel)rates they may be scattered over all of the bones and cartilages surrounding the mouth, l)ut in the mammals, as in man, they are confined to the upper and lower jaws only. Tlie name teeth, is therefore, in the latter, especially applied to those structures located in the oral cavity which contain a calcified tissue known as dentine. Tlie mai)i function of the teeth is the prehension and mechanical sub- division and reduction of substances employed for food, preparatory to digestion. The main divisions of this function are: (1) Prehension, or the seizing of food sulistances ; (2) division, or cutting into pieces; (3) mastication, or comminution into small particles, and (4) insalivation, or the mixing of food with the oral secretions. For the performance of these various functions, diflFerent forms of teeth are developed in different animals in great variety. For the office of prehension, long trenchant canines are developed in lower mammals, but in man these teeth are reduced to the level of the other teeth. Division and cutting are per- formed by the incisors, which are well developed in man. Crushing and mastication are performed by the premolars and molars, which in man are much reduced and modified, owing to his omnivorous diet. The denture of man is midway between the extreme form of the carnivora, on the one hand, and herbivora, on the other. Food selection has reduced the denture of man to a simple type, which is quite primitive, showing evidences of reversion. The functions of the teeth in man being less 2 (17) 18 IIUMAX ODOSTOGRAPIIY specialized (liaii in lower, hifjhly speeiali/ed animals, his (jentiire is eorrespoiulin^ly reduced, function Ix'inii iiere, as ever, the cause and sustainer of structure. The primitive tooth form is that of the simj>le cone. This is still found in the teeth of fisiies, reptiles, and some lower mannnals. The more complicated teeth of the hii^her mammals have been formed hy the modification of the single cone. Thus the incisors and canines are com- posed of single cones, the bicuspids of two cones fused together, and the molars are formed of three or more cones arranged to form triangular or (juadrangular crowns. In the genesis of tooth forms, theiefore, the complex teeth, as the bicuspids and molars, are formed by the repetition and addition of cones and their accompanying cusps, both laterally and longitudinally of the jaw. The transition from single to complex teeth is accomplished by the repetition of the single cone in various directions. Thus a bicuspid is formed 1)V the evolution of a cingule upon the lingual side of the buccal cone, which gradually develops into a lingual cone with cusp and root, as illustrated in the double cone shape of the upper first bicuspid of man. The upper molar crown is developed as follows: The primitive simple cone, the primordial element, is called the protocone. The first cone (Fig. 1, A) and the first step in molar formation is the growth of cusps upon the mesial and distal aspects of the protocone (Fig. 1, B). The mesial cusp is called the paracolic and the distal the mciacone. This gives three cusps in a mesio-distal line, forming a three-coned crowai called the triconodont type. This is the type of the early forms of the mammalian molar teeth, and is still preserved in some of the car- nivora, seals, lemures, etc. The next stage is the shifting of the cones so as to alter their relative positions to form a triangle (Fig. 1, C). In the upper jaw the protocone moves to the lingual side and becomes the mesio- lingual cusp, leaving the paracone as the mesio-buccal cusp and the metacone as the disto-buccal cusp, which come together on the buccal side, thus forming the trigon of the upper molar. This is the trituber- cular crown of early geological times from which all other molar types were developed, and is still preserved in the opossum, some insectivora, and some other modern mammals. In the lower molars the primitive cone is called the protoconid, but it moves to the buccal side and becomes the mesio-buccal cusp. The paraconid has l)een aborted in man, so that the metaconid becomes the mesio-lingual cusp, which forms the trigonid of the lower molar crown. Thus the triangles of the upper and lower molars alternate — the apex of the upper molar being directed lingually and the lower bucally, so that they pass each other with a shear-like motion. The next stage in the evolution of the molar crowns is the addi- tion to the trigon of the upper molar on its disto-lingual face, of a heel, or talon (Fig. 1, Z)), which supports the fourth cusp, the hypocoiie, which strikes into the centre of the trigonid of the lower molar, like a pestle into a mortar. Then there is added to the trigonid of the lower molar on its 77/ A' 1)I-:NT.\L Mi'C/l 19 distal side, a licel, or taioiiid, which suj){)()rts two or three cusps the buccal, which is called the hypocunld; the disto-huccal, the liypoconu- lid; aud the disto-lingual, the cntucuidd. Sometimes there is developed on the liiiji^ual face of the upper molar a fifth cusp which is called the hypoconule. This is the counterpart of the fifth cusp of the lower molar, the hypoconulid. This is the phylogenetic history of the molars in man, which are quite primitive in type, but their evolution can be readily traced in beautiful completeness. A Fig. 1 • • • • o o o o -# •- VqVqV The phylogenetic history of the molar cusps: A, the single cone, the reptilian stage; B. lower mammals, the triconodont crown; C, the tritubercular molar, the trigonodont crown; D, the quadri- tubercular molar crown. The Dental Arch. — The teeth of man are arranged around the margins of the upper and lower jaws in close contact, and have no interspaces between them. The basal arch is a graceful parabolic curve, with some variations which lead from the round arch to the incomplete parallel- ogram or even to a well-defined V-shape. These variations may be classified as follows: First: The Square Arch (Fig. 2, a). This is found usually in persons of strong osseous organization, of Scotch or Irish descent — i. e., of Gaelic extraction — and is probably derived in the first instance from a doli- chocephalic people. The squareness is more or less dependent upon the prominence of the large canines, which stand out very markedly at the 20 HUMAN ODONTOdHAl'llY anjrles of (ho scjiuire. 'i'lie incisors prt'snit a Hat front and j)r()j{'ct sli(^rli(lv, witii little or no curve of the incisive line. The bicuspids and molars fall backward from the canines with no perceptible curve. The two sides are quite parallel, but sometimes there may be a shVht diveragile enamel margins should not be retained, of course, but when backed l>y dentine the walls should be preserved — especially when parts of the supporting columns of the crown. Fig. 9 Fig. 10 d ■ ^ The mechanical design of the crown of the upper central incisor: a, the blade; b, the two columns supporting the blade; c, the marginal ridges acting as guys, bracing the columns; d, the basal ridge at the base of attachment for the guys. Diagram of the labial face of the upper central incisor. The neck of the central incisor is a rounded pear-shape in outline, the labial half being wider (Fig. 11, a) than the lingual. There is not much constriction of the tooth at the neck. The enamel edge curves upward on the root on the laliial and lingual sides, and dips downward on the mesial and distal faces. It terminates abruptly on all sides, especially on the lingual, where a considerable ridge is sometimes raised (Fig. 10, c). The root is cone-shaped and tapering (Fig. 11, ^). The rounded pear- shaped section continues almost to the end. The pulp chamber is spacious and open, and of the general form of the tooth (a and c). The radical portion of the canal gives free access, but the flattened coronal portion is difficult to clean.se. In young teeth the cornua or horns of the pulp may project far toward the angles (c). The Lateral Incisor. — This tooth approximates the central incisor on its distal side, and is also implanted in the intermaxillary bone. It is of similar spade-like form and of the same architectural design as the 77/ A' LATIJRAL INC ISO Ji 27 central, modified by the distal half heiiio' more louiided in every direc- tion. As the crown is narrower than the central, the destruction of the marginal ridges on the lingual face weakens the edge still more, so that it breaks off more easily. The crown is narrower in the mesio-distal diameter than the central, but, still almost as wide labio-lingually, the relative difference of thickness in the two directions is more apparent. The tooth has the appearance of being compressed mesio-distally. The thickness increases rapidly from the edge to the neck (Fig. 12, B). Fig. 11 Fig. 12 .d E The root of the upper central incisor. 3-^A B C D Tlie upper lateral incisor. The lahlal face (Fig. 12, C) is more rounded than that of the central. It is half incisor and half cuspid («), the mesial half toward the central incisor resembling that tooth (h), and the distal half toward the cuspid resembling it (c). The mesial angle of the edge is quite acute, while the distal ang-le is rounded and obtuse. The three lobes may be well devel- oped, similar to those on the central incisor, but are usually indistinct, although the central ridge is prominent. The lingual face (Fig. 12, D) is much de- pressed, but less concave than that of the central incisor. The marginal (d) and basal ridges (e) are quite prominent. The basal ridge is often raised into a permanent cingule or talon, an exaggerated example of which is shown in Fig. 13, which is a revival of the basal talon found in the apes — and the insectivora. This cingule occurs more fre- quently on the lateral incisor than on any other of the anterior teeth. The depression above it is often the location of a fault, a fissure or pit, which becomes the seat of caries. The basal ridge is sometimes cut by a fissure which leads down quite upon the neck of the tooth (Fig. 12, /). Sometimes the entire surface is full and rounded without any concavity whatever. The mesial face (g) is of triangular form similar to that of the central incisor. It is rounded toward the edge labio-lingually, but flattened at the neck, with a depression at the enamel line which leads upward upon Showing unusual devel- opment of the cingule or basal talon on an incisor. (From case reported by Dr. W. H. Mitchell, Dental Cosmos, vol. xxxiv. p. 1036.) 28 II UMAX ODOSTUaUM'IIY the root. The labial an^le is sometimes the seat of a depression (A), which u;ives the angle a hook shape. The depression varies in width and depth, and may become the seat of caries. The point of contact with the central incisor is at the junction of the lower with the middle third of the length of the face. The distal jace is more convex in all directions, and reseml)les the canine in form, being in harmony with the general form of the distal half of that tooth. From cervix to edge it is rounded and the contact eminence in the middle third is very full (/). From this point it rounds off rapidly to the edge. The upper third is depressed rapidly toward the cervix, with a considerable depression at the enamel litie leading off to the distal groove on the root. The edxje is divided into two portions by the prominent tubercle (y) in the middle which terminates the prominent central ridge of the labial face. The mesial half is straight, like that of the central. When worn, these features disappear and the edge becomes almost straight. The pitch of the edge, like that of the central, is toward the median line. The same mechanical structure of the crown is found in the lateral as in the central, except that the crown is more slender and weaker, so more precaution must be observed to prevent breaking during and after operating upon it. The neck is much flattened mesio-distally, and is of a compressed pear shape, or flattened oval on section. The enamel margin pursues the same course as on the central incisor, rounding upward toward the root on the labial and lingual sides and dipping downward on the distal and mesial. It does not terminate so abruptly as that of the central incisor, and presents less of a ridge at the gingival margin. The rooi is commonly longer than that of the central incisor, is nar- rower, flattened mesio-distally (Fig. 12, A, B). It tapers gradually, not rapidly like the root of the central incisor. It is a flattened oval on section (E). Sometimes there is a hook at the end, curved distally. (Grooves sometimes occur on the mesial and distal sides. The pulp canal is flattened in conformity to the shape of the root, but is readily entered if the root ])e straight. The lateral incisor is very irregular as to form, presenting various degrees of deformity or abnormality, and may sometimes be reduced to a mere peg. It is also erratic as to eruption, being sometimes suppressed, not appearing for several generations of a family. It follows the third molar in the frequency of its irregularities both as to form and frecpiency of non-eruption. The third incisor of the primitive typal mammal sometimes reappears in man, and is known as a supernumerary. It rarely assumes the proper incisor form and position in the arch, but usually erupts within the arch, and is a mere pointed peg-shapetl tooth. THE LOW EH INCLSOltS 29 The lower incisor. The Lower Incisors. — These are most conveniently described as a group, as they are very similar in form, having but slight variations between the central and lateral incisors to be noted. They are located in the anterior portion of the lower jaw, upon each side of the median line, opposite the incisors above. Their function is the same as that of the upper incisors, the cutting of food, which they perform by opposing the upper. The lower central opposes only the central above; the lateral, both the upper central and lateral incisors. The lower central incisor is the smallest tooth in the dental series. It is ()f spade-like form (Fig. 14), the crown being a double wedge shape (a, /;). The first wedge (a) is observed on viewing the crown from the front, the widest portion being at the morsal edge and the point at the cervix. The second wedge is observed from the side (b), the widest part being at the neck and the point at the morsal edge of the crown. The edge is thin, but the labio-lingual diameter increases rapidly to the cervix, which is the widest part. The crown is widest mesio-distally at the edge, but dimin- ishes to the neck, which is scarcely more than half the width of the edge. The tooth cone is therefore compressed in one direction at the edge, and in another at the cervix. The mechanical elements are the same as those of the upper central, but with the parts less strongl}' marked. The labial face is a long wedge shape (a), the widest part at the edge and narrowing to the cervix. It is usually straight, or nearly so, longi- tudinally, and straight across the edge, but round and convex at the neck and the cervical half. Sometimes vertical ridges are found on these teeth when they are first erupted, but these soon wear off. The lingual face is depressed and concave from edge to cervix (c), but less so from side to side. The marginal ridges are often well marked. In the lateral incisor the fossa is often more marked and the marginal ridges more distinct. The mesial and distal sides are of wedge-like form, straight from edge to cervix and widening in the same direction. A depression runs across the neck just above the enamel line. The neck is much compressed disto-mesially, and the root partakes of this flattening through its entire length. The section presents a compressed oval (e), The enamel line dips downward on the labial and lingual sides, and curves upward on the mesial and distal in a manner characteristic of the incisors. The edge is perfectly straight from side to side, after the three tuber- cles, found when first erupted, are worn off. The root is flattened like the neck, and frequently a groove runs the 30 HUMAN ODOATOGRAJ'in- entire length on the mesial and di.stal sides. Oeeasionallv conijjlete hifnreation resuhs, wiiieli recalls the form of this tooth tonnd in lower animals. The pulp canal [c) is of similar form to the root, and is flattened and thin, so that it is often difheult to effect an entrance to it with instru- ments. The lateral incisor is similar in form to the central incisor, hut is wider at the edge, and the distal corner of the edge is slightly rounded {(I). In all other features it resemhdes the central incisor. The canine, or cuspid, appears very early in the history of vertel)rate life in its prototype, the single conical tooth of fishes and reptiles. The conical form of the canine is maintained down through all the suc- ceeding stages to man, with mere variations as to contour, as manifested in the higher vertebrates. It is the tooth of prehension from the lowest to the highest forms. As prehension is the most primitive of tooth func- tions, so the conical, canine tooth is the primitive tooth. In the higher mammals it is probably modified from the premolar series, as it is the first tooth posterior to the intermaxillary suture. In the lower mammals it is variously modified, but it is in the carnivora that it attains its highest specialization. Its greatest development was found in the extinct felidse, where it was long and sabre-shaped, with sharp serrated edges, as in the cave lion and bear and the fossil forms of America. The living cats, the lion, tiger, leopard, etc., have the highest forms of this tooth, but it is reduced in the dogs and bears and other omnivorous forms. In the quadrumana the canines are well developed, and in the apes they are very large and strong, and are formidable weap- ons. Owing to the continued absence of the "missing link," there is a sudden transition between the higher apes and man, as they are much reduced in the latter, being brought down to the level of the other teeth. Indeed, the canine presents more points of divergence from the form of this tooth in the anthropoid apes than any of the other teeth, all of which resemble those of the apes very closely. It is practically a crushing tooth in man as prehension is in abeyance as a human dental function. The Upper Cuspid. — This is the third tooth from the median line, and approximates the lateral incisor on its distal side. It is the first tooth posterior to the intermaxillary suture, and is embedded in the maxilla proper. It is commonly said to form the spring of the arch, and conveys the impression of great strength, as is indicated by its strong implantation. It is more strongly implanted, and l)y a longer and larger root, than any of the other teeth. Zoologically it is the largest tooth in the dental series, but in man is much reduced from its proto- type, the larger carnassial canine of lower animals, especially the car- nivora. It is the principal prehensile tooth, and is therefore first in order of function in the dental series. The crown has a spear-head shape (&), hence its name, cuspid, from THE UPPEli CUSPID 31 the Latin cv.spis, "point, pointed end." It is constructed essentially for piercing and tearing. The central cusp or point is braced in all directions; the edges leading up to it both mesially and distally (which serve for cutting as well), the strong labial ridge coming downward from the cervix (c) to the median ridge leading up on the lingual sur- face (rf), all support it in the office of prehension and the laceration of flesh. The labial face (b) presents the outlines of the spear shape, more or less rounded in different cases. Starting from the well-defined cusp just in front of the central axis of the tooth, it widens sharply for about one- third of its length, whence it narrows gradually to the gum line, w^hich is fully rounded. In some cases the mesial and distal angles are rounded and the outlines are more of a leaf shape (e). The surface is slightly rounded mesio-distally, so that the sides slope roundly or flatly away from the central ridge. This ridge descends from the middle of the cervical margin, curving slightly forward and then backward to the Fig. 15 c d e The upper cuspid. point of the cusp (c). This curve recalls the curving shape of this tooth in the felidse. It is usually a sharp, prominent ridge, but may be re- duced and rounded so as to be scarcely perceptible. The three lobes of the surface are imperfectly marked — the central ridge dominating and dwarfing the lateral ones. The lateral furrows on each side of the central ridge separating it from the lateral lobes are more or less marked, especially toward the edge. Wear reduces in time the promi- nence of the lobes and ridges and obliterates the furrows. The lingual face is of similar spear-shape (cT), but is more flat. It is rarely concave. The thickness of the crown increases gradually to the lateral prominences, which gives a blade-like edge, then rapidly to the shoulder at the base. A strong vertical ridge extends from the cusp to the basal ridge (d), with a slight concave depression on each side. The basal ridge is well marked and sometimes develops into a cingule, more or less marked. The marginal ridges lead up on each side only so far as the lateral protuberances. They are not strongly marked as a rule. The 32 I/IM.W (JDOSTOCRM'IIY fosste oil each side of the \(>rtical median rid^re, between it and the mar- ginal ridges, may he (juite deep, init are usually shallow and ill defined. The me.sldl faee in outline is not unlike the central incisr)r, hut its contotu' is very diii'erent, for it is more or less rounded in all directions, and the lateral eminence in the lesser third makes this part especially full (/'). From this point the surface is depressed roundly to the eii,imel line at the neck, where a depression of greater or less depth is found. It is somewhat flattened at the cervix. The point of contact is at the eminence, which touches the lateral incisor. The distal face is of similar form to the mesial, except that it is more full and the eminence more pronounced, which gives the increased width of the crown on that side. The surface descends rapidly toward the neck and is rounded labio-lingually. The point of contact with the first bicuspid is on the lateral protuberance. The morscd edge presents a prominent cusp, which is almost central to the long axis of the tooth. The side facets slope away, but still retain their cutting edge (h). The distal side of the edge is longer than the mesial, by reason of the increased size of the distal protui)erant angle. The sharp point is soon worn oft' to a rounded cusp, and, as wear increases with age, it may be reduced to a straight surface between the mesial and distal protuberances (r/). The neck is a flattened oval on section, or the lateral direction of the labial ])ortion may be greater than tiiat of the lingual {h). The enamel line preserves the same curves as on the incisors, /. c, rounding upward on the labial and lingual surfaces and dipping downward on the mesial and distal. The enamel terminates gradually with but a slight ridge, unless it should be on the lingual side. A depression occurs on both mesial and distal sides above the curve, which may lead up as a groove on the root. The root is longer than that of any other tooth, and it is at least one- third larger than that of the central incisor. It is of a rounded trihedral form, or irregularly conical. It is usually straight, and tapers t(; a slender point, which may be curved or very crooked. In well-arranged dentures, where it has erupted naturally, it is usually straight. The 'puly canal is large and open, of the same form as the tooth, and easily entered. It is regularly formed except in those cases where the root is curved, and even in these it can be filled if not too crooked, as it is so open and acce.ssible. The Lower Canine. — This is similar to the upper in form and outline, except tiiat it is somewhat smaller, more slender, and uK^re rounded in form (Fig. 16, a). It differs also in being more compressed mesio-distally and in being flattened in the neck and root. The crown leans l)ackward on the root so that the mesial face is almost straight the entire lengtii of root and crown. It forms the spring of the lower arch, and is strongly built to oppose the strong upper canine in the act of prehension and THE LOWER CANINE 33 Fig. 16 teariiijj. It opposes the mesial surface of the canine al)ove and the distal surface of the upper lateral incisor. The Idbidl face is a long oval (r/), the cusp beino^ hlunt and the neck rounded Avhile the mesial side (c) is flattened. The lobes are indistinct and the central ridge is rounded from side to side. The entire face is in- clined inwanl to accommodate the occlusion. The crown in manv cases presents the appearance of being blunt toward the distal side. The Ungnul face [h) is flat, sometimes cup-shaped, and the marginal ridges are not prominent. The central ridge sometimes stands out strongly. The basal ridge is weak and is rarely developed into a cin- gule. The crown increases gradually in thickness from the point to the neck. The mnrsal siirfdcc presents a mere rounded eminence; the cusp may be sharp in childhood, but usually it is soon reduced by wear. Some- times it remains sharp and prominent. The lateral edges are not devel- oped, but are mere ridges lead- ing down to the lateral faces, which are not prominent, except the distal {d), which is often full. The mesial face is quite flat, and straight with that face of the root. The eminence is not marked. It is rounded only at the eminence, but flattened at the cer\'ical third {c). The distal face has the most prominent eminence {d), the crown being bent in that direction. The cervical third of this face is Hat. It descends rapidly from the eminence. The neck is usually oval (/), or, when compressed, spindle-shaped upon section {g), being depressed on the mesial and distal sides at the origin of the grooves nmning up on the root. The enamel line is not so variable as on the incisor, but more nearly on a level on all four aspects. The root is long, flattened, and tapering (a, h, c). It is shorter than that of the upper cuspid. It is grooved on the mesial and distal sides — so much so as to tend toward bifurcation. This, indeed, sometimes happens in man, thereby recalling the form usual to the primates and some other lower animals. The pulp canal is of the same general form as the root, often presenting the spindle-shape on section. It is somewhat difficult to enter on account of its flattened shape and narrowed channel. The canine being larger, stronger, and more robust than the incisors, presents fewer elements of mechanical weakness of the crown than those teeth. The body of the crown is thicker from the cervix 3 The lower canine. 34 HUMAN ODONTOGRAPHY to the inorsal point, and is well supported laljially hy the rounded emi- nence of this face and lingually by the columns on thai face. The median third of the erown is stronu; enou) on tliroiioh varions degrees of development, nj) to a full ensp as large as the huecal eusp, when the tooth becomes a Jiiie bicuspid. The tooth is therefore essentially a ])rimitive nnieuspid premolar, (jf tiie form of this tooth in some of the lower primates. The buccal face (c) is caniniform, or a long oval in outline, with the cusp rising as an abrupt point above it. The angle of the Junetion of the marginal ridges may stand out prominently. The face curves markedly toward the lingual side, so that the buccal cusp becomes central to the long axis of the tooth (a). The cervical border is rounded at its margin and convex from side to side. The lol)es are not marked. The lingual face (d) is convex from side to side and straight vertically, but is not perpendicular, as it is directed toward the lingual side. Its height depends upon the height of the lingual cingule, which varies from a mere buccal ridge through various degrees up to the full-sized cusp. The mesial and distal surfaces are of similar form, convex from side to side (a, h), slightly Hattened at the cervical border and flaring out to meet the full marginal ridges, which are round and prominent. The prominence of these ridges and the inward inclination of the lingual face gives the crown a decided bell shape, tapering to the neck (c/). The morsal surface (e) is peculiar and differs from every other tooth in its great variability and the extremes which it may present, from being that of a full bicuspid to a mere canine. This face is nearly circular in outline, the widening of the lateral surfaces by the spreading of the marginal ridges (/, /) adding to the width. The buccal cusp (g) is large and prominent, and is also drawn toward the centre of the tooth to accommodate the occlusion. Sometimes it is high and sharp when the lingual cusp is reduced, and is low and blunt when the latter is en- larged — appearing to have an inverse ratio in size to the inner cusp. The lingual tubercle or cingule varies much in size, from a mere point on the basal ridge, above the cervical border, to a pronounced cingule, a larger cingule, a small cusp, then a fidl cusp, the basal ridge (h) being raised with it. The ridges are the mesial and distal marginal ridges (i. i), which are bowed out round and full and are always pronounced; the buccal marginal ridges (/, /), leading down from the buccal cusp to form an angle with the mesial and distal marginal ridges; the basal ridge, when the lingual cingule is lowered (h); and the triangular ridge of the buccal cusp, which is always large, and when the inner tubercle is reduced leads down as a high central eminence. The lingual cingule, as a rule, possesses no triangular ridge. The central groove usually crosses the central ridge (k), but not always, being often bowed around its lower termination. Sometimes the ridge is crossed by a sulcus. The groove terminates in a sulcus at each end, with slight triangidar grooves branching up on the buccal cusp. The neck is usuallv oval on section, being much constricted, the crown 77/ A' TUBERCULATK TEETH 39 Hiiring upward from the corviciil portion, i;ivint>' the crown the well- known bell sha})e. 'I'he enamel line dips but slightly, being usually level on all foiu' sides. The buccal border sometimes presents a promi- nent ridge. The root is single, long, tapering, and may ])e nearly round, but is usually flattened mesio-distally. It is sometimes thick the greater part of its length, and terminates in an abrupt, round, blunt apex (c, d). It is very liable to be crooked. It is rarely bifurcated and does not pre- sent grooves on its lateral faces. The pulp canal is constricted and flattened at the neck, and the back- ward inclination of the teeth makes it difficult to enter. The possibility of the root being crooked and the peculiarity of its anatomical relation- ships^ also increase the uncertainty of treatment, which makes the pulp canals of the lower bicuspids difficult to deal with. The lower second bicuspid approximates the first on its distal side. It resembles the first as regards the general form of the crown, its taper- ing bell shape, the constriction of the neck, and the shape of the root. In all these features there is little difference be- tvv^een these teeth, and the description of the first ^i«- 20 will apply also to the second bicuspid. The morsal surface (Fig. 20), however, differs very materially from that of the first. This is circular in outline like the first, and the buccal cusp is full and rounded (a), but the inner cusp is divided by a groove (b) running over it, into two parts, so that it is really divided into two , '■ , ,_-, . Ill 1 1 • The morsal surface of the tubercles. 1 his makes the lower second bicus- lower second bicuspid. pid in its typal form a tricuspid tooth, so that it differs from the lower first, which has but one cusp, and from the others, which have but two cusps. The lingual tubercles vary much in size, so that one may be suppressed and the tooth seem a bicuspid. The mesial lingual tubercle (c) may be of large size and be devel- oped at the expense of the distal ((I); this may be a mere cingule on the distal marginal ridge and appear on the distal side, but it is always present. The morsal groove is (e) triangular in design, passing between each of the three tubercles. A well-marked triangular ridge descends from each of the cusps. The tricuspid form of the morsal surface of this tooth is, of course, a reproduction of the trituberculate premolars of the lower primates, and of still lower mammals, although the triangular form of the crown is lost in man. The Molars. — The molars in man are twelve in number, three on each side of each jaw, and are placed at the rear of the arch, opposite the strong 1 See Chapter on Extraction of Teeth. 40 HUMAN ODONTOCRA PlI ] ' tritunifing musck's, for the j)urj)().s<' of criisliiiiu- nud iii;i.sticatiiiute to the func- tion of diij^estion hy prepaiino;ularity and uncer- tainty of the form of the roots make this tooth difficult to deal with in treating its pulp canals. The Lower Molars. — The lower first molar apj)r<)ximates the lower second hicuspid on its distal side. It is the first of the true grinders of the lower jaw and the largest tooth in the dental series. Unlike the upper molars the transverse diameter is less than tlie mesio-distal. The greater width is fyund across the hase of the disto-huccal tuhercle. The crown is square or trapezoidal in form, depending on the size of the fifth tuhercle. Being quinquetuherculate, the crown is l)roadened hy the multicuspid grinding face. The l)uccal face is inclined toward the centre of tlie tooth, for its morsal half, to accommodate the occluding teeth. Fig. 24 Architectural diagram. S f B The lower first molar. Architecturally, the tooth is formed of four cones (Fig. 24, A), and may he roughly divided into four quarters. There are four primitive cones with their tuhercles and one cingule in the structure. The morsal surface (B) is trapezoidal in outline, the buccal line heing the longest. The huceal angles are acute, while the lingual are rounded and ohtuse. There are five tuhercles, two on the lingual margin and three on the buccal. They are named the mesio-huccal (r), median buccal (c/), disto- huccal (e), disto-lingual (f), and mesio-lingual (e well anchored on the morsal surface and undercuts avoided. Attention must also be given to the lingual occlusion of these teeth, which increases the stress upon all operations upon them. The upper molars are of beautiful and wonderful architecture, as before de- scribed, and present an interesting study. The greatest point of weakness in these teeth is the disto-lingual cusp, the hypo- cone, which often breaks away when undermined by distal caries, as the fusion with the oblicjue ridge and the protocone is weak. This should l)e obviated, after filling, by grinding down the point of the cusp. It is danger- ous to cut the oblicjue ridge, for when the marginal ridges are destroyed it becomes the main binding girder of the crown. When this is under- mined by caries the crown becomes so weakened that it readily splits. The introduction of the inlay, however, has greatly lessened the mechan- ical dangers of operating uj)on these teeth that cannot be avoided with the pressure fillings. Mesial inlays should, of course, be carried into the mesial sulcus and the buccal border preserved as much as possible for the esthetic effect. Indeed, extensive caries on this tooth can be better treated with the inlay than with the shell crown, and the natural crown be better preserved. The lower molar is different from the upper in its mechanical design, and the lingual occlusion presents different problems. In the evolution •**- Negro top jaw with fourth molar. THE TUBEUCULATE TEETH 51 of its crown it will he remembered that the protoconid shifts to the buccal side and becomes the mesio-biiccal cusp. The triangle of the lower molar is just the opposite, therefore, of the upper and carries two cusps, the two mesial, the third having been lost in the process of evo- lution. The talonid, therefore, supports three cusps, the two distal buccal and the disto-lingual, which are, therefore, weaker than those of the trigonid. Hence we have more breakdowns of the distal half of the lower molars than of the mesial. This must be considered in operating on this tooth, not making deep undercuts to weaken the cones, but depending upon occlusal retention. The cutting of the transverse ridges does not weaken the crown except when the cones are separated too deeply, which results in the splitting off of the lingual half of the crown, which is not uncommon. So the grinding of the lingual cusps must again be resorted to to prevent the danger of the wedging of food. The crown of the lower molar is essentially weak and the conservation of its weakest points, the junction of the cones, must be considered at all times. A knowledge of this weakness is obtained by a study of the evolution of the crowns of the molars. The mechanical resistance of the molars, as well as their effective- ness in the mastication of food, depends much upon the accuracy of their occlusion. It is needless to say that this very rarely obtains in ordinary dentures. Malposition, extractions, abrasion, dental mutila- tions, imperfect and indolent use in the performance of the function of mastication, all contribute to the malocclusion of the molars which is so prevalent. Imperfect occlusion is productive of abnormal stress upon various parts of the crown and its consequent frequent breaking down along the lines of the junction of the cones. It follows, of course, that the proper procedure is to restore the normal occlusion as completely as possible by artificial means. The Deciduous Teeth. — The deciduous teeth are those wdiich appear in infancy and serve the purpose of dental organs during the first years of the development of the individual, until the jaws and their environ- ment are ready for the larger, permanent teeth to come into place. They bear a direct relationship to the conditions of the digestive appar- atus and the food required at that early stage. The food of infancy being simple and requiring little mastication, the deciduous set are small and insufficient for the reduction of more resisting substances. As these foods come to form part of the dietary, the larger teeth of the permanent set appear and perform the duties of higher functional activity. The crowns of the deciduous teeth resemble, in a general way, those of the permanent teeth which succeed them, except the deciduous molars (Fig. 30, a, d), which are very different from the bicuspids of the per- manent set which displace them. The incisors of both jaws precede the analogous teeth of the same series of the permanent set. They are similar in form, but reduced ib), 52 Hi' MAX ODUXTOGRM'ffV and <1() not have tlic main ftaturt's so cliaracteristically marked. Tliey art" infantik' in form and function. The nnAs of these teeth are resorbed at from the fifth to the ninth year, when the permanent incisors come into pkice, l)eiriiniin<; witli tlie k)wer centrals. Tlie cuspids {<■) of l)oth jaws are still more reduced from the strong, full form of their j)ermanent successors, and are hut little more .spe- cialized than the incisors. They are of the same general form as the permanent cus]:)ids, hut much less developed. But in the deciduous molars are found some important features which mark distinctive differences. They are of true molar form as com- parefl with the permanent molars, hut they occu])y the place of the bicuspids. Tiiere are no bicuspids in the deciduous set, the molars being of full molar pattern {n, d). Fig. 30 The deciduous teeth. The deciduous molars of both jaws are of irregular, cjuadrangular form on the morsal surface, diverging rapidly outward to the neck, which presents a large buccal ridge .standing out at the margin of the enamel, and is rounded off suddenly to the neck, which is much con- tracted. This thick ridge is characteristic of the deciduous molars and is ab.sent in those of the permanent denture. It is somewhat more prominent and bulging on the buccjal than on the other faces. In ad- justing ferrule crowns to these teeth the gold need not be carried beyond this ridge, but burnished over it slightly. The morsal surface (e) of the upper deciduous grinders pre.sents the characteristic pattern of the upper molars, four tubercles, oblicpie ridges, etc., but reduced and contracted. A distinctive feature is that the mar- ginal ridges and angles are more acute and sharp than in the perma- nent molars. Sometimes the two lingual cusps are reduced to one and the lingual border is rounded and crescentic. THE VARIATIONS OF TOOTH FORMS 53 The second inolai- is lai'^vr than the first and tlie niorsal surface is wider. The transverse diameter of the crowns of the upper molars is the longest. 'J'lie luurr iiiolars Ul) are similar to the permanent molars in pattern, but are more irrei>;ular as to the contour of the morsal surface (/). Tiie tubercles may be hi(>;her than in the upper molars, and the tri- angular ridges more marked. The central fossa maybe large and wide, or tlividetl by the triangular ridges. The second molar is five-Iobed, unlike the second permanent molar, which has but four cusps. The morsal face is decidedly trapezoidal in outline, the mesio-distal diameter beino- greater than the transverse. The roofs of the deciduous molars are similar to those of the other molars, except that they are very divergent to accommodate the crown of the advancing bicuspids. They are thin and long, and difficult to enter and fill. The pulp chamber is large and open in the crown; as a consequence of this caries soon reaches the pulp. Treatment and fillino- of the canals is difficult and uncertain. THE VARIATIONS OF TOOTH FORMS The teeth mai/ vary quite extensively from the typal forms which have been described, and these variations may be due to a number of causes. Through all degrees of variation, however, the type is still pre- served, unless the tooth form is cjuite destroyed by pathological causes. The general causes of variation may be enumerated as follows- 1. Incompleteness of development. 2. Reversion to primitive types. 3. Temperamental impress. 4. Pathological lesions. i. Under incompleteness of development may be grouped all those varieties of stunted growth which are the effect of disuse and the con- sequent effort of Nature to reduce and suppress the teeth as useless parts. The third molar teeth suffer most from these suppressive attempts of Nature in the effort toward economy of growth; next to these teeth the upper lateral incisors are most frequently affected by reduction of size, stunted growth, and suppression. Other teeth are not affected, or but very slightly, by this influence, except in rare cases. 2. Under the second head, reversion to primitive types, we have a variety of interesting phenomena in the form of parts of the human teeth which seem to be a zoological legacy. These consist of conspic- uous features which reappear and seem to recall forms of the teeth observed in some of the lower animal orders, especially the quadrumana and insectivora. 54 IIVMAX ODONTOGRAI'IIY Ainon^ these features may l)e mentioned the curved uj)[)er central incisor with the ])roniinent cino;iile on the lin^nial-huccal ridoc, niakin<,' a notcli whic-li recalls the incisors of the moles; the prominent cinf,nile on the linoiial face of the lateral incisor, which is not imcommon and recalls the form found in the insectivora and some of the (|uadrumana; the extra lonu', curved canine with extra larnc median ridt^cs, which recalls the larue forms of this tooth in the hahoons and in the carnivora; the double root sometimes found in this tooth is also a reversion to the insectivorous type; the three-rooted bicuspid is a (|uadrmnanous rever- sion; the upper tricuspid molar is a primitive typal form, leadini^ Iniek to the lemurs and beyond them to the early typal mammals found in fossil formations; the notched and grooved incisor recalls the divided incisor of the galeopithecus; the double-j-ooted lower incisors and canines recall insectivorous forms; the unicuspid lower first bicuspid is an insect- ivorous type and is often quite marked in man; the fifth cusp on the lower second molar is a cpuuh'umanous reversion; the wrinkled surface of the lower tliird molar is like that of the orang, etc. There are other features that might be named illustrating the work- ings of the law of atavism, by which parts once lost in evolution may reappear and be reproduced. 3. Under the third head, temperamental impress, may be noticed those differences of form and structure which have relation to the domi- nant temperament in the constitution of the individual, (ireat difi'er- ences exist between the teeth of diiferent persons, and these are mainly dictated by temperament. The teeth of the primary basal temperaments present the following physical peculiarities, which are characteristic of the particular tempera- ment : The bilious temperament presents teeth that are of a strong yellow; large, long, and angular, often with transverse lines of formation, with- out brilliancy, transparency, and of but slight translucency; firm and close set, and well locked in articulation. The sanguine temperament has teeth that are symmetrical and well proportioned, with curved or rounded outlines, and round cusps; cream color, inchned to yellow, rather brilliant and translucent; well set, and occlusion firm. The nervous temperament has teeth which are rather long, the cutting edges and cusps long and fine; color pearl blue or gray, very trans- parent at the apex; the occlusion very penetrating. The lymphatic temperament presents teeth that are pallid or opaque, dull or muddy in coloring; large, broad, ill shaped, cusps low and rounded; the occlusion loose and flat. Of the binary combinations: The sanguitieo-bilious has teeth which are large, with strong edges and large cusps; color dark yellow, and quality good. THE VARIATIOXS OF TOOTH FORMH 55 The ncrvo-hUlous lias tcetli that are \on^y and narrow, with long cusps; color yellowish or bluish, or both combined; the enamel stroni^, the dentin soft. The lijmphu-hUious has teeth that are laro^e, with thick edt);es and short thick cusps; yellowish in color; enamel of good structure and polish, and dentin fair. The hlUo-sangu'uicous has teeth of average size, round arch, well- developed cusps and edges; rich dark-cream color; excellent in (juality. The nervo-sanguiiicoiis has teeth of average size, good shape, round arch, gootl edges and cusps; rich cream color; enamel and dentin of excellent structure. The lympho-sanguhu'oiis has teeth of more than average size, shapely edges and cusps, rounded arch; color grayish cream; enamel and dentin fairly good. The bilio-iicrvous has teeth variable in size and form, sometimes broad, again very long with more pointed and long cusps; the color generally bluish; enamel fairly good, dentin soft and sensitive. The sanguhieo-nervous has teeth of average size, good shape, round arch; color grayish blue; soft and frail. The biUo-hjmphatic has teeth usually large, with thick edges, short, thick cusps, and flat arch; color yellowish; quality good. The sangmnco-lijmphaiic has teeth of more than the average size, broad round arch; color gray; enamel and dentin poor. The nervo-lymphatic has teeth of average size, good shape, average length, rather round arch; color bluish gray; soft and poor. Combinations of the binary temperaments are of the most common occurrence in individuals, but there is usually one basal temperament that preponderates over the others and gives its characteristic to the teeth as a predominating influence. 4, Under the fourth head, pathological lesions, are to be included all those disturbances of nutrition which eventuate in faulty formation of the teeth, whether due to specific hereditary diseases, mere malnutri- tion, idiosyncrasies, predispositions, defective functional life, etc. But this leads beyond the province of this chapter into the field of special pathology and embryology. CHAPTER II DENTAL IIIST()L()(;Y WITH REFERENCE TO OPERATIVE DENTISTRY.^ By FHEDERICK B. NOYES, B.A., D.D.S. The development of our knowledoe of the eell has had a most pro- found effect upon the entire practice of medicine; in fact, the progress of modern medicine dates from the studies of cell biology, the germ theory of disease being only one of the phases of this development. In terms of the cell theory the functions of the body are but the manifest expression of the activities of thousands or millions of more or less independent but correlated centres of activity; if these centres or cells perform their functions correctly, the functions of the body are normal; but if they fail to perform their office, or work abnormally, the functions of the body are perverted. In the last analysis, then, all physiology is cell physiology; all pathology cell pathology. To modern medicine his- tology, or the cell structm-e of the organs and tissues of the body, together with cell physiology, is the rational foundation of all practice. This is as true for the dentist as for the physician so far as regards all of the soft tissues of the mouth and teeth that he is called upon to treat and handle. With caries of the teeth, the disease which most demands the attention of the dentist, the case is somewhat different. Caries of the teeth is an active destruction, by outside agencies, of formed materials which are the result of cell activity (the tissues themselves being passive). The cellular activities of organs and tissues of the body may have an influence, but this is only in producing those con- ditions of environment which render the acdvities of the destructive agents efficient in their action upon tooth tissues. Though the enamel and dentin are passive, we can understand the phenomena of caries only as we understand the structure of the tissues; and not only must the treatment of caries be based upon a knowledge of the structure of the tissues, but the mechanical execution of the treatment is facili- tated by that knowledge. In the preparation of cavities the arrange- ment of the enamel wall is determined by our knowledge of the direction of enamel prisms in that locality, and to a certain extent the position of the cavity margins must be governed by our knowledge of the structure ' In the prep.aration of this material I am indebted to Or. O. V. Bhick for the use of his large and valuable collection of microscopic slides, and for much advice and many suggestions. (56) DENTAL HISTOLOGY AND OPERATIVE DENTISTRY 57 of the enamel. Jn the execution of the work a mniute knowledge of the direction of enamel rods becomes the most important ("lemcnt in rapiditv and success of operation. From the standpoint of comparative anatomy, the teeth are found to be not a part of the osseous system, but appendatijes of the skin, and are to be compared with such structures in the body as the nails and the hair. The teeth are a part of the exoskeleton, and their rela- tion to the bones of the endoskeleton is entirely secondary, for the pur- pose of strength, the bone growing up around the tooth to support it. If we examine the skin of such an animal as the shark, we find the entire surface covered with small calcified bodies which are really small simple cone-shaped teeth The mouth cavity is to be regaixled, Fig. 31 Shark's skull (Lamna eornubica), showing succession of teeth. when viewed in the light of its development, as a part of the outside surface of the body which has been enclosed by the development of the neighboring parts, and the dermal scales or rudimentary teeth which were found in the skin covering the arches which form the jaws have undergone special development for the purposes of seizing and masti- cating the food. In the simplest forms there is only a development in size and shape of these scales, and they are supported only by the connective tissue which underlies the skin. These teeth are easily torn off in the attempt to hold a resisting prey, and, as in the shark, they are constantly being replaced by new ones (Fig. 31). In the more highly developed forms there is a growth of the bone of the arch forming the jaw upward around the bases of these scale-like teeth, to support them more firmly and render them more useful. 58 DEXTAL HISTOLOGY AXD OI'ERATIVE DEXTISTRY If we coinparc the structure of the liiiir with that c)f the tooth, we find, \\\ the ease of the hair, a horny structure eouipose*! of ('jjithehal cells restini^ uj)on a paj)illa of couueetive tissue; in the ease of the tooth, a calcified structure formed by epithelial cells resting; upon a j)apilla of coiuiective tissue which is also j>artially cah-ified. The relation of the hones of the jaws to tiie teeth is entirely a secondary and transient one. The hone ^rows up around the roots of the teetii to support them, and is destroyed and removed with the loss of the teetli or the cessation of their function. In this way the development of the Fig. 32 m. ^ te. jft. ^w Changes in the mandible with age; buccal and lingual view. alveolar proce.s.s takes place around the temporary teeth; all of this hone surroundint]^ their roots is absorbed and removed with the lo.ss of the temporary dentition, and a new alveolar process grows up around the roots of the permanent teeth as they are formed. This development of bone around the roots of the teeth leads to the changes in the shape of the body of the lower jaw, increasing the thickness al)ove the mental foramen and the inferior dental canal. Wiien the teetli are finally lost this bone is again removed and the body of the jaw is reduced in thick- ness from above downward ( F'ig. 32). These phenomena are of im- portance in their bearing upon the causes and treatment of diseased conditions of the teeth, particularly those which involve the supporting tissues. ENAMEL 59 Dental Tissues. — The human tci'tli ai-c made up of four tissues (Fio-.^:«): 1. 'i'lio cudiiicl covers tlie exposed j)ortioii of the tooth, oi- ci-owii, and i>;ives the detail of crown form. Its function is to jjrotect the tooth against the wear of friction. 2. The dentin forms the mass of the tooth and determines its chiss form, the number of cusps and the number of roots beinn; indicalcd by the dentin form. '>]. Cemcnium covers the dentin beyond tlie border of the enamel, overlapping it slightly at the gingival line and forming tlie surface of the root. Its function is to furnish the attachment of the fibers of the peridental membrane, which fastens the tooth to the bone. 4. The pu/p, or soft tissue, filling the central cavity in the dentin is the remains of the formative organ which has given rise to the dentin. Its functions are the formation of dentin and a sensory function. In describing the structure of the teeth and the arrangement of the structural elements of the tissues directions are described with reference to three planes: The mesio-disto-axial plane, a plane passing through the centre of the crown from mesial to distal and parallel with the long axis of the tooth. The bucco-linguo-axial plane, a plane passing through the centre of the crown from buccal to lingual and parallel with the long axis of the tooth. The horizontal plane, at right angles to the axial planes. The Supporting Tissues. — The human teeth are supported on the maxillary bones, their alveolar processes growing up around the roots of the teeth, so that the roots fit into the holes in the bone. The calcified structures of the tooth and the bone are not, however, united, but the roots are surrounded by a fibrous membrane, the peridenfal membrane, or pericementum, which fastens the tooth to the bone. ENAMEL The enamel differs from all other calcified tissues in the nature of the structural elements of which this tissue is made up, in the degree of calcification, and in origin, being the only calcified tissue derived from the epiblast. The enamel is formed from an epithelial organ derived from the epithelium of the mouth cavity and indirectly from the epiblastic germ layer, w^hile all other calcified tissues are products of the mesoblast. In the case of bone and dentin the formative tissue is persistent. It is possible in bone at least, therefore, to have degenerative and regen- erative changes, or the removal of part of the calcium salts and their replacement through the agency of the formative tissue; while in the ()() DKXTAL IJlSTOLOaV AXJ) OI'KRATIVK DEXTISTRY Vw. 33 Ground section of :i canine: E, enamel; Cm, cementum; D, dentin; Pc, pulp chamber; De, dento-enamel junction; Ed, enamel defect; G. junction of enamel and cementum at the gingival line; Gt, granular layer of Tomes. (Reduced from photoniicrograph made in three sections.) ENAMEL (31 fiKiiiirl no Mich ro^ciu'rativt' chaiigv is possiMc, as flic Formative tissue clisapiH'arcd when (he tissue was eoinpleti-d and heforc the eruption of the tooth. The enamel is the hardest oF human tissues. Chemicallv it is ecMii- posed of the pliosphates and earhonates of calcium and ma<,niesium and a very small amount of the fluorides, water, also a very small amount of organic matter if any.^ The enamel in the natural condition, hathed in the fluids of the mouth, contains a considerable amount of water. If dried at a litUe above the boiling point of water, it gives up part of it and shrinks considerably, so as to crack in fine checks. If heated almost to redness, it suddenly giyes of¥ from 3 to 5 per cent, (of the dry weight) of water with almost explosiye violence. These facts were demonstrated some years ago by Charles Tomes,^ and account for most of what was formerly recorded as organic matter in old analyses. If we observe under the microscope the action of acids upon thin sections of enamel, when the inorganic salts are entirely removed, the structure of the tissue vanishes, there being no trace of organic matrix left as in the case of bone or dentin. In the growth of bone and den- tin the formative tissue produces first an organic matrix in the form of the tissue, and into this the inorganic salts are deposited, combining with the organic substances of the matrix. This union is compara- tively weak, howev^er, for by the action of acids the combination is broken up and the inorganic salts are dissolved; or by heat the organic matter is removed, and in either case the form of the tissue will be maintained. In the case of the enamel, the formative organ produces organic substances containing inorganic salts, and the substances are arranged in the form of the tissue after the manner of a matrix; but finally under the action of the formative organ all of the organic matter is remo.\ed and substituted by inorganic salts, whatever organic matter is found in the fully formed tissue being the result of imperfect execution of the plan. The enamel is composed of two structural elements, the enamel rods, or prisms, sometimes called enamel fibers, and the inferprismatic or cementing substance, both of which are calcified. It is to the arrange- ment of these structural elements that the characteristics of the tissue with which we are most concerned in operative procedures are due. 1 Von Bibra gives the following analysis of enamel: Calcium phosphate and fiuorid S9.82 Calcimn carbonate 4.37 Magnesium phosphate 1 . 34 Other salts 0.88 Cartilage 3.39 Fat 0.20 Total organic 3.r>9 Total inorganic 96.41 - Journal of Physiology, 1896, 02 DESTAL HISTOLOGY AND Ol'EI{ATI\ E DE.XTISTRY Wliile both the prisnis and intcrprisinatic .sul).stance of tlic enamel are ealciiied, or, lietter, eoinposed of iiior±^_-_ " 1 •.i^iv ■'■ 1 Hj —lii^^H 'k=L^. ■ -^^J.- '- '■ ■ ....-l— IWBi H Enamel showing direction of cleavage. (About 70 X) ment of the rods causes the greatest difference in the feeling of the tissue under cutting instruments. Such a specimen of enamel as shown in Fig. 40 can be cut away easily, the tissue breaking through to the dentin and splitting off in chunks; while a specimen like Figs. 41 and 42 wiD not cleave if supported upon sound dentin. If the outer ends of the rods are straight, they will split part way to the dentin (Fig. 42); but where they begin to twist around each other they will break across the rods. If the dentin is removed from under such enamel, it will break in an irregular way through the gnarled portion. From a study of the arrangement of the enamel rods in the forma- tion of the crow'n it is apparent that the plan is such as to give the greatest strength to the perfect structure, and may be likened to an arch. At the gingival border the rods are short and are inclined apically G to 10 07 Straight enamel rods. (About 80 X) Vin, 11 Gnarled enamel. (About 80 X) 68 DENTAI. UlSTOLOCY AND Ol'Kli AT I V l<: DhWTISTh'V ceiitifrrades' (20 to o5 det-rccs) from the horizontal phme. 'i'liese short rods lire overlapped for a short dkstance by theceinentuin. This inclination grows less and less, and at some place in the ginf>;ival half of the middle third of the surface they are in the horizontal plane. Al this jjoini they Fig. 42 Gnarled enamel. (About SOX ) are also usually perpendicular to the surface of the dentin. Passing from this point they become inclined more and more occlusally from the horizontal plane, at the junction of the occlusal and middle thirds about 8 to 12 centigrades (28 to 40 tlegrees) in bicuspids and molars, and 8 to 18 centigrades (28 to 65 degrees) in incisors and canines. In the occlusal third ' In the centigrade division the circle is divided into one hundred parts, each calleil a centigrade. One centigrade is equal to .'^.f) degrees of the astronomical circle, 25 centi- grades to 90 degrees, 12 centigrades to 4.5 degrees. The cut gives a comparison of the two systems of measuring angles. 2 70 180 Centigrade division. EN A MEL 69 the inclination increases rapidly, and often the outer ends of the rods are inclined more Uian the inner ends. Over the point oF the cnsps and the crest of the marginal rid<>es the rods reach tlu- axial plane, though they are often very nnich twisted about each other in the inner half of their length. This j)()sition does not always correspond with the highest point of the cusp, but is inclined slightly axially from that posi- tion, and corresponds with the highest j)oint of the dentin cusp. Fig. 43 Diagram of enamel rod directions, from aphotograph of a bucco-lingiial section of an upper biscupid. Passing down the central slope of the cusp, or ridge, the rods become again inclined away from the axial plane toward the groove, or pit, leaning toward each other where the two plates meet. The degree of inclination of the rods on the central slope of the cusps depends upon the height of the cusps; the higher the cusp the greater the inclination from the axial plane. Fig. 43, a diagram from a photograph of a bucco- lingual section of an upper bicuspid shows the plan of arrangement and illustrates the arch principle in the construction. In the study of longitudinal sections of the teeth, one of the most conspicuous structural features is the stratification bands, or brown bands of Retzius. These bands are not parallel with either the outer surface of the enamel or the dento-enamel junction. They begin at the tip of the dentin cusps and sweep around in larger and larger zones. 70 DENTAL IIISrOLOGY AND OPERATIVE DENTISTRY These stratification bands are better seen in comparatively tliick sec- tions, and are caused by the varying amount of pio^incnt (lej)osited with die calcium salts in the development of the tissue. 'I'hev record the growth of enamel of the crown as a whole, as each line was at one time the surface of the enamel cap. These stratifications, or, better, incre- mental lines, are shown in Figs. 44 to 40. Fig. 44 Stratification of enamel; the cusp of a biscupid: De, dento-enamel junction; Ed. enamel defect showing in the heavy stratification band; IN 73 74 DENTAL HISTOLOGY AND OPERATIVE DENTISTRY Preparatiou uf unauiel wall in snarled enamel : 1. Knnmel wail as el-aved, shnwinpr breaking across rods and sliverintj at a. J. Wall as smoothed but not extended to reniov short rods whose inner ends are cut off at /-. :>.. Wall extended and trimmed to a i^osition of strength. D, dentin; /)e, dento-enamel junction : <•, cavo-surface angle; 6, point where inner ends of rods are cut off; a, sliveriiii,' of the tissue. (About 80 <.) HISTOLOGICAL REQUIREMENTS IN ENAMEL WALLS 75 direction indicated hv the direction of the cracks in Fitr. 49. 'i'lic outer ends of the enamel rods must he sha\'ed away, to hrinn- the j)hiiie of the enamel wall parallel with the dentin wall or into the axial plane. When this has been done a strong margin has been formed, for the rods which form the point of die cavosurface angle are snpported by the piece A, B, C (Fig. 50), made up of rods resting upon sound dentin Fig. 49 Occlusal fissure in an upper bicuspid, showing direction of rods. (About 80 X) and covered by the filhng material. Often the angle will be too sharp, however, and the cavosurface angle should usually be bevelled to pro- tect the margin from accident. This illustration may be taken as typical of occlusal cavities. Fig. 51 shows a cavity prepared in the buccal surface of an upper molar. The occlusal margin is placed in the occlusal half of the middle third, and the gingival margin in the gingival half of the gingival third 76 DENT A I. lllsrOLOaV AM) OPERATIVE DENTISTRY of the surface. In the occhisal wall (lie nids an- incliiK-d occhisally about 8 centi^rrades ( 2S dcirrccs) from the lioii/.oiilal |)laiK-. After cleav- iiifj^, the broken and sHvered rods should be shaved away, but the an^de cannot be increased without makin^^ the margin of fiUing material too Yir.. 50 I / :\^^A J Preparation of enamel walls in occlusal fissure cavities (the same as Fig. 49). thin ; the rods forming the mart^in shouhl tiierefore be protected by bevel- iintj the cavosurface angle. At the gingival wall the rods are inclined apically from the horizontal plane about 6 centigrades (20 degrees). The wall should be shaved in that plane, increasing the angle a little, and the cavosurface angle should be bevelled. Fig. 52 shows the occlusal IIISTOLOCICAL h'KQl/h'KMK.XTS J .\ EXAMKL WALLS 77 Fig. 51 Preparation of enamel walls in a buccal cavity in a molar: (?, gingival wall; 0, occlusal wall (About 70 X.) 78 DKXTAL IIIST()L(H;Y AM) OI'KHAriVK DICXTISTRY enamel wall alone, after cleavintj and triinniin^r into form. Sueli enamel walls may be taken as typical of axial siuface cavities, the angle of the Fi<;. 5 2. Wall OS trimmed. Preparation of occlusal wall of Fig. .51. (.-Miout 70 X ) enamel with the dentin wall being determined by the direction of the enamel rods in the position where the margin is laid. Grooves, fissures, and pits are always positions of weakness, and when a cavity approaches a groove or pit a good margin, histologically, HISTOLOUIVAL RKQ^IREMENTS IN ENAMEL WALL^ 79 cannot he prepared witliont cntting beyond it. V\\f^. 5;i shows an occlusal fissure in a bicuspid, which illustrates the conditions of structure characteristic of these positions. The rods are inclined tcnvard the fissure, and between the bottom of the fissiu-e and the dentin are very irregular. If a cavity wall were made to approach this fissure from the lingual side, so as to come to the dotted line, the wall would hav(; to be inclijied (\ to , and is made up of a solid organic matrix impregnated with about 72 per cent, of inorganic salts^ and pierced by minute canals or tubules, which radiate from a central cavity which contains the remains of the formative organ, or pulp. The minute canals, or dcniinid fnhules, are occupied in life by protoplasmic processes from the ()dontol)lastic cells which form the Fic. 57 Dentin at dento-enamel junction, showing tubules cut longitudinally: Dt, dentinal tubules; D, dentin matrix. (About 760 X) outer layer of the pulp. Dentin contains two kinds of organic matter, the contents of the tubules and the organic basis of the matrix. The dentin matrix, after the removal of the calcium salts by acids, yields gelatin on boiling and resembles the matrix of bone, reacting in a similar, though not identical, way with staining agents. The portion of the 1 Von Bibra gives the following analysis of dentin: Organic matter 27 . 61 Fat 0.40 Calcium phosphate and fluorid 66.72 Calcium carbonate 3.36 Magnesium phosphate 1 . 08 Other salts ., , . . 0.83 84 DENTAL HISTOLOGY AND OPERATIVE DENTISTRY matrix immediately .surrounding the tul)ules shows (h'fferent chemical characteristics from the rest of the matrix, resembling elastin, and resisting the action of strong acids and alkalies after the rest of the tissue has been destroyed. This portion of the matrix .surrounding the tul)ules and lying next to the fibrils is known as the sheaths of Neumann. The dentinal tubules are from 1.1 to 2.5 microns in diameter, and are separated from each other by a thickness of about 10 microns of dentin matrix. This is fairly unif(jrm throughout the dentin. The character of the tubules is different in the crow'n and root portions. In the crown the tubules branch but little through most of their course; but in the outer part, close to the enamel, they branch and anastomose with each other (juite freely. Fig. 57 shows a field of dentin Fig. 58 Dentin showing tubules in cross-section: Dt, dentinal tubules; D. dentin matrix; .S', shadow of sheaths of Neumann, (.\bout 11.50 X) just beneath the enamel, as .seen with a high power, and shows the diameter of the tubules, their branching, and the amount of matrix between one tubule and the next. The relation of one tubule to each other is shown also in .sections cut at right angles to their direction (Fig. 58). In the crown portion the tubules pass from the pulp chamber to the dento-enamel junction in sweeping curves, so as to enter the pulp chamber at right angles to the surface, and end next to the enamel at right angles to that surface. This produces S- or F-shaped ( \ or curves, which are known as the primary curves of the tubules. Through- out their course the tubules are not straight, but show a great many wavy curves, known a^ the secondary curves, "^rhese appear as waves DENTIN 85 when seen in longitudinal sections, but are really the effect of an open spiral direction, as is seen by changing the focus of the microscope in studying sections cut at right angles to the direction of the tubules. The branches throughout their length are few and small, and are given oif at an acute angle to the direction of the tubule; but just before the enamel is reached the tubules fork and branch, producing an appearance similar to the delta of a river. These branches are given off from the tubules for some little distance back from the enamel, and they anas- tomose with other tubules very freely. The branching of the tubules in their outer portion causes the spreading of caries just beneath the Fig. 59 Crown of a molar, mesio-distal section, showing penetration of caries: A, caries penetrating dentin; B, line of abrasion; P, pulp chamber. (About 20 X ) enamel, the microorganisms growing through the branches from tube to tube, and so spreading sideways beneath the enamel plates, and then penetrating the dentin in the direction of the tubules. Fig. 59 shows the penetration of caries in the dentin. It will be noticed that in decay starting at the contact point there has been more spreading under the enamel than in that starting at the gingival line, but in both positions the penetration has followed the direction of the tubules. In the root portion the tubules pass out from the pulp canals at right angles to the long axis of the tooth and pass directly out to the cemen- tum, showing only the secondary curves. Throughout their course they give off a great many fine branches passing through the matrix in all 8G DENTAL HISTOLOGY AND OPERATIVE DENTISTRY Fig. 00 Dentin from the root, showing tubules cut longituilinally. (About TOO • ) Fr of cementum Gt. Rranular layer of Tonics; l(i. inter- globular spaces. (About 200 X ) In many specimens made bv ^riiuling dried teeth lar<]je irregular spaces are very conspicuous in the dentin. They usually occur in lines or zones at al)out uniform depth from the surface. These have been called the interglobular spaces. They are really not spaces at all, but are areas of imperfect development in which the dentin matrix has not been calcified. The dentinal tubules pass through them without interruption. In a dried specimen the organic matrix shrinks, and the resulting space becomes filled with the debris of grinding, so as to give the appearance of black spaces. Fig. ()2 shows two (|uite distinct layers of interglobular spaces, the second much more marked than the first; and in the enamel at a position corresponding to the first is .seen an imperfection of structure marked l\v the very dark stratification band. This is shown best in the region of the cusp (Fig. 44) from the same section. Interglobular spaces in the root portion of the dentin are shown in Fig. 63, close to the granular layer of Tomes. PULP 89 The formation of dentin is not complete at tlie tim(> of enijition of the tooth, hut continues for an indelinite period, thickenin-staining Fi.;. (17 Diagram of \\w liloodvessels of the pulp. (Stowell.) y^^ y* • —5/ ! • ' iA A pulp bloodvessel, showing the thin wall: C, blood corpuscles in the vessel; Bl, bloodvessel wall showing nuclei of endothelial cells; .V, nuclei of connective-tissue cells in the body of the pulp; /, intercellular substance, showing a few fibers, (.\bout 200 X ) nucleus, the protoplasm stretching out into slender projections in two directions to form the spindle cells, or in more than two ilirections to PULi' 93 form the stellate cells. Th(> stellate forms are more eotnmoii in the body of the j)ulj), tiie spindle form in the canal portions. The round cells are comparatively few in number, and are pi-obably young cells which have not yet accjuired the adult form. The Bloodvessels of the Pulp. — 'J'he blood supply of the pulp is extremely rich, several arterial vessels entering in the region of the apex of the root, often through several foramina. These large vessels extend occ-lusally through the central portion of the tissue, giving oif many branches which break up into a very close and fine capillary plexus (Fig. 67). From the capillaries the blood is collected into the veins, which pass apically through the central portion of the tissue. A very striking peculiarity of the blood- vessels of the pulp is the thinness of their walls. Even the large arteries show scarcely any condensation of fibrous tissue around them to form the usual adventitious layer, and usually contain but a single involuntary muscle fiber representing the media, while the walls of even the large veins are made up of only the single layer of endothelial cells forming the intima, and are in structure like large capillaries (Fig. 68). This peculiarity of the bloodvessel walls is of great importance, as it renders the tissue especially liable to such pathological conditions as hyperemia and inflammation. The Nerves of the Pulp. — Several comparatively large bundles of medul- lated nerve fibers, containing from six or eight to fifteen or twenty fibers, enter the pulp in company with the bloodvessels and pass occlu- sally through the central portion of the tissue. These bundles branch and anastomose with each other very freely. Most of the fibers lose their medullary sheath before reaching the layer of Weil, in which position they form a plexus of non-medullated fibers ; from these fibers free endings are given off, which penetrate between the odontoblasts. In some cases these have been followed over on to the dentinal ends of the odontoblasts, but in no instance have they been followed into the dentinal tubules. The Functions of the Pulp. — The pulp performs two functions, a vital and a sensory. The vital function is the formation of dentin, and is performed by the layer of odontoblasts. This is the principal function of the pulp, and it is first manifested in the development of the tooth before the dentinal papilla is converted into the dental pulp by being enclosed in the formed dentin. After the tooth is fully formed the vital func- tion is not manifested unless the pulp is stimulated by some excitation affecting trophic centres and which causes the formation of secondary dentin. There are some exceptions where the formation is entirely local. The Sensory Function. — In regard to sensation, the pulp resembles an internal organ. It has no sense of touch or localization, and responds to stimuli only by sensations of pain. The pain is usually localized correctly with reference to the median line, but, aside from that, is 94 DKXTAL IIIST()IJ)(;Y AM) Ol'KR Ml V F. D/JXTISTRY locali/ed only us it is referred to some known lesion. If several j)nlps on the same side of the mouth and in teeth of both the upper and lower arches were exposed so that they could be irritated without impressions reaching the peridental membrane, and the patient were blindfolded, it would be impossible for him to tell which of the pulps was touched. The pain originating from a tooth jndp may be referred to the wrong tooth or to almost any point on tiie same side supplied by the fifth cranial nerve. The pulp is especially sensitive to changes of temperature, but is incapable of differentiating between heat and cold; this fact is often made use of in differential diagnoses. The pulp is also very sensitive to traumatic and chemical irritations, even when these are conveyed to it through the agency of the dentinal fibrils. I )r. Huber has suggested^ that this transmission may be accomplished by the traumatic or chemical action upon the fibrils setting up metabolic changes in the odontoblastic cells, which act as stimuli to the sensory nerves ending between the cells of that layer. CEMENTUM The cementum covers the surface of the dentin apically from the border of the enamel, lapping sliglitly over the enamel at the gingival margin (Fig. 69). It forms a layer, thickest in the apical region and Fir.. 69 Gingival border of enamel, showing the cementum overlapping it: E, enamel; C, cementum; D, dentin. (About 40 X) > Dental Cosmos, October, 1698. CEMENT UM 95 between the roots of biciisj)Ld.s and molars, and heeoniino' thinner as the gingival line is approached. The eenientuni resembles subperiosteal bone in structure, but differs from it in the character and arrangement of the lacuna^ and in the absence of Haversian systems; the layers, or lamella% of the cementum also are less uniform in character than those of bone. The function of the cementum is to furnish attachment for the fibers of the peridental meml)rane which holds the tooth in its position. The surrounding tissues are never in physiological connection with the outer surface of the dentin, except to form cementum over it or to Fic. 70 Cementum near the apex of the root: Gt, granular layer of Tomes; L. lacunae, b, point at which fibers were cut off and reattached. (About 54 X ) remove its substance by absorption; and when absorption of the dentin has occurred on the surface of a root it is never repaired except by the formation of cementum to fill up the cavity and reattach the membrane. The cementum is intermittently formed during the functioning of the tooth, being added layer after layer over the entire surface of the root, the difference in thickness of the tissue in the gingival and apical portions being chiefly, though not entirely, due to the difference in thickness of each layer in the two positions (Figs. 69, 70). The cemen- tum on the roots of newly erupted teeth is thin, and on the roots of teeth of old persons is thick. This continued formation of cementum 96 DENTAL niSTOLOUY AX U Ul'EliATl\ E UEXTISTRY Fu.. 71 Thic-k liimella' of cementum witli inany laciin*, tiliniLr an alisdrption iii ikiuhi; i.. iacunse; //, Howship's lacunse filled ; D, dentin. (About 250 > .) Fig. 72 Two Melds ot cenientuui sii(i\vin'4 in'iu'tratin!,' lihers : (jf. tiianiiiar layer ot 1 omcs ; C, ceineliluni not showing fibers ; F, pciH'lT«M»g fibers, (.\bout 54 •;.) PERIDENTAL MEMBRANE 97 is duo to the necessity for cliange and reattaclinient of the fibers of tlie membrane. In the ging'ival j)()rtioiis, where the cementuin is thin, the tissue is clear and apparently structureless, and usually contains no lacunar; while in the apical half and between the roots the lacunae are numerous. In general, wherever the lamelhe are thin, the lacuna" are absent; but where the lanieihe are thick they are found. The canaliculi which radiate from the lacunae are not as regular as in the case of the lacunae of bone. Sometimes they are numerous, sometimes few; they may extend from a lacuna in all directions, or they may be confined to one side, usually the side toward the surface of thecementum (Fig. 71). The cementum is penetrated through all its layers by fibers of the peridental membrane which have been embedded in the matrix of the tissue and calcified along with it. The first layer — that is, the one next to the dentin — is usually structureless and shows no fibers in it, at least in its inner half. In ground sections the embedded fibers often appear in a number of layers, while they are not apparent in the rest of the thickness. This is because just before and just after the forma- tion of the layers in which they appear the fibers were cut oft' and reattached, changing their direction, so that in the other layers the fibers are cut transversely or oblicjuely. This is illustrated in Fig. 72. These embedded fibers are very numerous in some places. If properly stained, the tissue seems almost a solid mass of fibers. In ground sections these have sometimes been mistaken for minute canals from the fact that they are not always as fully calcified as the cementum matrix, and shrinkage causes the appearance of little open canals. Hypertrophies of the cementum (formerly often called exostoses, or excementoses) are very common. The increased thickness may be of one lamella or of several lamellae in the region of the hypertrophy, or all of the layers from first to last may take part in it. Small local thick- enings of a single lamella are seen in connection with the peridental membrane wherever a specially strong bundle of fibers is to be attached to the root to support the tooth against some special strain. PERIDENTAL MEMBRANE The peridental membrane may be defined as the tissue which fills the space between the root of the tooth and the bony wall of its alveolus, surrounds the root occlusally from the border of the alveolus, and supports the gingiva. It has been referred to under many names, as pericementum, dental periosteum, alveolodental periosteum, etc. While this tissue performs the functions of a periosteum for the bone of the alveolus, it differs in structure from the periosteum in any posi- tion, so that any name including the word periosteum or implying a double membrane should be avoided. 7 98 DENTAL IIISTOUKIY AND OrERATIVE DENTISTRY The peridental rnenil)rane belongs to the class of fihrous membranes, and is made uj) of the followiiif; structural elements: Fic. 73 Diagram of the fibers of the peridental membrane: G. KinRival portion; Al, alveolar portion; Ap, apical portion. (From a jjliotograph of a section from incisor of sheep.) 1. Fibers. 2. Fibroblasts. 3. Cementoblasts. 4. Osteoblasts. 5, Osteoclasts. 0. Epithelial structures which have been called the glands of the peridental membrane. 7. Bloodvessels. .S. Nerves. The peridental membrane performs three functions — a 'physical PERI DKNTA L MEM Bit A NE 99 function, maintaining the tooth in rehition to the adjacent hard and soft tissues; a vital function, tiie formation of bone on the alveolar Fir;. 74 Longitudinal section of peridental membrane from young sheep, showing fibers penetrating cementum: D, dentin; C, cenientum, showing embedded fibers; F, fibers running to outer hiyer of periosteum covering the alveolar process; F', fibers running to the bone at the border of the process; 5, bone. (About 80 X) wail and of cementum on the surface of the root; and a sensor]/ function, the sense of touch for the tooth being exclusively in this membrane. 100 DENTAL IIISTOUHIY AS I) ()I'KRATI\ E DESTISTRY The fibrous tissue of the membrane is of the white variety, and may be divided into two chisses, the j)riii(ij)al fibers and the indifferent or interfibrous tissue. The principal fibers may l)e (K'fined as those which spring from the cementum and are attached at their other end to the bone of the alveolar wall, to the outer layer of the periosteum covering the surface of the alveolar process, to the cementum of the approximating tooth, or become blended with the fibrous mat of the gum supporting the epithelium. They were so called by Dr. Black, not only because they form the principal bulk of the tissue, but they also perform tne principal function of the membrane, the support of the tooth and sur- Fi<:. 75 ^ ^ \ «v>- ' -'■ »v- ..'•>^"^ ' M. ' ' /•-• •' 4 ■•i.- / T''- J ■ ■f-f '',-^' & ■ /...■^^'., 0? Longitudinal section of the peridental membrane in the gingival portion: £), dentin; A'^, Nasmyth's membrane; (', cementum ; F, fibers supporting the gingi\ us; f, fibers attached to the outer layer of the periosteum o\er the alveolar process; F-, fibers attached to the bone at the rim of the alveolus; B, bone. (About 30 X ) rounding tissues. The interfibrous tissue, also of the white variety, but made up of smaller and more delicate fibers, is found filling spaces between the principal fibers and surrounding and accompanying the bloodvessels and nerves. For convenience of description and study, the peridental membrane is divided into three portions: the gingival, that portion which surrounds the root occlusally from the border of the alveolar process; the alveolar, the portion from the border of the process to the apex of the root; and the apical portion, surrounding the apex of the root and filling the apical region (Fig. 73). PERIDENTAL MEMBRANE 101 The principal fihors sj)riiio- from the (•ciiumiIiiim, the (•(Miiciitohlast.s building u{) tlic matrix around (hem and tlicn calcifvino; hoth matrix and fibers, in this way iinplantino- their ends inio the surface of the root. In Fig-. 74 the fibers are seen passing through the last-formed layer of cenientuni. In most positions the fibers as they spring from the cementum appear as well-marked bundles of fine fibers. A short distance from tiie surface of the root they break up into smaller bundles, which interlace and are reunited into laro'er bundles, to be attached at their other extremity to the bone, cementum, or fibrous tissue. Fig. 76 Transverse section of the peridental nienil>rane in the t;inKi\ ai portion (from slieep): E, epithe- lium: F. fibrous tissue of gum; B, point where peridental membrane fibers are lost in fibrous mat of the gum; P, pulp; F' , fibers extending from tooth to tooth. (About 30 X ) To arrive at an understanding of the arrangement of the fibers of the peridental membrane, they must be studied in both longitudinal and transverse sections. In longitudinal sections of the membrane, in the gingival portion (Fig. 75), the fibers springing from the cementum at the gingival line pass out for a short distance at right angles to the long axis of the tooth and then bend sharply to the occlusal,^ passing 1 In describing the direction and inclination of peridental membrane fibers they are always traced from the cementum to the bone, the angle with the horizontal plane being formed at the surface of the cementum. 102 DENTAL HISTOLOGY AND Ol'EUATIVE DENTISTRY into the gingiva to .siij)j)()rt it and hold it closely against the neck of the tooth. These fihers are most numerous on the lingual side, where food is brought against the gingiva with force in mastication and tends to crush it down. In the middle of (he gingival portion the fibers pass out at right angles to the axis and are blended with the fibrous mat of the gum on the labial and lingual sides, or arc attached to the cementum of the adjoining teeth on the approximal sides. A little farther from the gingival line the fibers are inclined slightly apically, ])assing over the border of the process to be attached to the outer layer of the ])eriosteum. These fibers are especially large and strong. Just at the rim of the alveolus the fibers are inclined slightly aj)i(ally and aic inserted into the bone, forming the edge of the process. Fig. 77 Fibers at the border of the alveol.ir process (from sheep): />, dentin; C, eementuin; F, fibers extend- ing from cementum to bone; Bl, bloodvessel; h, bone. (About 81) X) In transverse sections of the membrane in the gingival portion (Fig. 70) the fibers spring from the cementum in large bundles; at the centre of the labial surface they extend directly outward, breaking up into smaller bundles, passing around bloodvessels and bundles of hl)ers, and blending wiUi the fibrous tissue sup|)orting the epithelium. Passing mesiaily and distally toward the corners of the root, the fibers swing around laterally and pass to the cementum of the next tooth. On the approximal sides the fibers suddenly divide into smaller bundles, which wind in and out around bloodvessels, and bundles of fibers which pa.ss into the gingiva and are reunited into large bundles to be inserted into the cementum of the next tooth. On the lingual side the arrangement is like that of the labial, except Uiat the distance to which the fibers of PERIDENTAL MEMBRANE 103 Fi(!. 78 Om Transverse section of the peridental membrane in the occlusal third of the alveolar portion (from sheep): J/, muscle fibers; Pec, periosteum : .4/, bone of the alveolar process; Pti, peri- dental membrane fibers ; P, pulp ; D, dentin ; Cm, cementum. 104 DEXTAL IlISTOLOCY AM) OI'Kh'ATl \ K DKXTISTh'Y the mcmhraiic can he followed hct'orc (licv arc lost in the lil)i-()iis mat of the ^uiii is usually ^M-ea(er than on t\\r lal)ial. In the occlusal third of the alveohir j)ortioii of the nienihrane the fibers pass, at riirht anolcs to the axis of the tooth, directly from the cementuin to the hone. In this jjosition the fibers are hir(,^e and do not break up into smaller bundles, but the original fibers can be followed uninterruptedly from the eementum to the bone (Figs. 74 and 77). In the middle third the fibers are inclined occlusally, and this inclina- tion increases as the a])ical third is ap])roaclied. In the apical third the inclination is i«;reatest, and the lil)ers as they arise from the eemen- tum are very large and break up into fan-shaj)ed fasciculi as they pass across to the bone. Tn the apical portion the fibers radiate from the apex in all directions across the apical region and sj>read out in fan- shaped bundles like those in the apical third of the alveolar portion. In a transverse section near the border of the alveolus (Fig. 7S), at the centre of the labial surface of the root, the fibers are seen to extend directly out from the surface of the root to tlie bone of the process, excepting where they are diverted to pass around bloodvessels. Passing around distally at the corner of the root, the fibers swing laterally so as to be almost at a tangent to the surface of the root, and are inserted much farther to the distal on the wall of the alveolus. A similar arrange- ment is noticed at the other corners of the root, though these tangential fibers are usually more marked at the distal than at the mesial corners. wStudying the arrangements of the fibers with reference to the physical function of the membrane, it is seen to be the best that could be devised to support the teeth against the force of mastication and to support the tissues about them. In the gingival portion the fibers passing from tooth to tooth form the foundation for the gingivae between the teeth filling the interproximal spaces; so that if these fibers are cut off from the eementum, by extending a crown band too far, or by the encroachment of calculary deposits beginning in the gingival space, the gingiva drops down and no longer fills the interproximal space. In the alveolar portion the fibers at the border of the process and those at the apex of the root together support the tooth against lateral strain, while those in the rest of the alveolar portion are so arranged as to swnng the tooth in its socket and suppt)rt it against the force of occlu- sion (Fig. 73). As seeii from the transverse section, the fibers of the occlusal third of the alveolar portion are so arranged as to support the tooth against forces tending to rotate it in its socket. Cellular Elements of the Membrane. — The Jihroblasts are spindle-shaped or stellate connective-tissue cells which are found between the fibers as they are arranged in bundles. In sections stained with hematoxylin they take the stain deeply, and the fibers, unstained, are differentiated by the cells lying in rows between them. The number of fibroblasts in the membrane decreases with age. They are large and numerous in the PKRIDESTM. MEMIiliA SK 10- inenil)ranc of a newly (Mii|)ti-(1 tootli. and (■()iiii)arati\('y small and few in the membrane around an old tooth. This is eharaeteristic of fibro- blasts in other positions. The Hbroblasts are shown as they appear in a hematoxylin-stained section witii low powers in Fif^. 79, which Fig. 79 Fibers and fibrobhists from trans\ erse ^ci Uua uf membrane: F, fibers cut transversely: F\ fibers cut longitudinally, showing fibroblasts. (About 80 X ) gives part of the membrane in the gingival portion between two teeth. The cells are seen as spindle-shaped dots which mark out the fibers; at F they are seen in a position where the fibers are cut transversely. With higher powers these cells appear as in Figs. 81 and 90. Fig. so :^Y^ -C Cementobkists. (Drawing by Dr. Black.) The cementoblasts are the cells which form the cementum, and are found everywhere covering the surface of the root between the fibers which are embedded in the tissue. ^Miile these cells perform the same function for the cementum as the osteoblasts do for bone, they are in form very different from the osteoblasts. The cementoblasts are always flattened cells, sometimes almost scale-like, and when seen from above 106 DENTAL HISTOLOCY AND OPERATIVE DENTISTRY are very irrefrular in oiitliiic. Tliis irrci^nilarity of outline is caused by the cells fittiii",^ aroiind the attached fibers of the membrane so as to cover the entire surface of the cenientuni between the fibers. Fig. 80, from a drawing by Dr. Black/ shows several cementoblasts as seen when isolated bv teasing. The cementoblasts have a central mass of protoplasm containing an oval nucleus, and short irregular proces.ses which fit around the fibers as these spring from the surface of the cemen- tum. Fig. SI shows diem in section ])erpendicularly to die surface Transverse section, showing the cellular elements: Fb, fibroblasts; Ec, epithelial structures; Cb, ceinentobla-sts; Cm, cenientum; D, dentin. (About 900 X) of the root, where they are crowded between the fibers. The cemento- blasts often have processes projecting into the cementum like those from the osteoblast, but processes projecting into the membrane have never been demonstrated. In the formation of the cementum occasionally a cementoblast be- comes enclosed in the formed tissue filling one of the lacuna', in which position it becomes a cement corpuscle. > Periosteum and Peridental Mpnil>rane. PERIDENTAL MEMBRANE 107 Fig. 82 PclB EB ^Per Border of growing process : Cm, cementum : Prf, peridental membrane : Prf.B, solid subperidental and subperiosteal bone with imbedded fibers; Ms, medullary space formed by absorption of the solid bone; -ff.-B, Haversian-system bone without fibers; Pec, periosteum. (About 50 X.) 108 DEXTAL lIISTOLOdY AS I) Ol'ERATIVR DKSTISTUY 'i'lic ().sfc(ihla.s/.s ot" the iii<'iiil)r;iiic cover tlic siirt'acc of tlic l)oiic, t'oniung the wall ot" the alveolus, lyiiiu- iK'twccn tlic fiUcrs which arc hiiilt into the bone. In form and fiiiiction they are like the osteoblasts in attached portions of the periosteum. They form bone around the ends of the peridental-memV)rane fil)ers, buildirif; them into the substance of the bone. The bone thus formed over the wall of the alveolus is like the Fi... s:; r^i M o/>'-^ 1> Epithelial structures: Ec, epithelial coil. ai)!,iarently showing a lumen; Cm, cementum; D, dentin. (About 500 X) cords are invested with a delicate basement membrane, but no special relation to bloodvessels has been demonstrated. The attempt to show their connection with the surface epithelium has thus far failed. As the gingiva is approached (Fig. 92), they seem to swing out from the sur- face of the root and are lost between the projections of the epithelium lining the gingival space. There is evidence that these structures are, at least in some cases, of importance as the primary seat of pathological conditions of the membrane. PERIDENTAL MEMBRANE Fi(i. 1)2 115 Longitudinal section: Ep, epithelium lining the gingival space; Gg, gingival gland, so called, D, dentin ; S, Nasmyth's membrane ; Du, duct-liko structure, stretching away toward the gin- giva from the epithelial cord, seen at Ec : Cm, cementum, separated from the dentin by decalcification. (About 50 X ) 110 DESTAL HISTOLOGY AND Ol'KRATlVl': DESTISTUY Fig. 93. Fig. 94. Young and old membranes (from sheep): D, dentin: Cm, cementum : CvO, thickening of cemen- turn to attach fibers at the corner; Pd, peridental membrane ; B, boue forming the wall of the alveolus ; P, pulp. (About 80 X ) PERIDENTAL MEM lilt AN E 117 Bloodvessels and Nerves of the Membrane. — Bloodvessels. — The hlood supply of tlio peridental membrane is very abundant. Several vessels enter the membrane from the bone in the apical region. These arteries ])raneh and divide, fonniiio; a rieh network, from which the ca}>illary ves- sels are given off. The arterial network is constantly receiving vessels which enter the membrane through Haversian canals opening on the wall of the alveolus, and in this way the size of the vessels passing oeclusallv is maintained. Arterial vessels also enter the membrane over the border of the process. This double or triple supply of the membrane is impor- tant, as it maintains the health of the membrane when the supply entering through the apical region is entirely cut oif by alveolar abscess. While the arterial supply of the membrane is very rich, the capillaries in the membrane are comparatively few. This is, however, a characteristic of connective-tissue membranes. The nerves of the peridental membrane have not been sufficiently studied to be described in detail. Six to eight medullated nerve trunks enter the apical region in company with the bloodvessels, and they receive other trunks through the wall of the alveolus and over the border of the process, but the manner of their distribution and the nature of their endings are not known. The Changes which Occur in the Membrane with Age. — When a tooth is erupted the roof of the bony crypt in which it was enclosed in the body of the bone is removed by absorption and the crown advances through the opening. The diameter of the alveolus at that time is, therefore, greater than the greatest diameter of the crown, and the peridental membrane which fills the space is very thick. By the forma- tion of bone on the wall of the alveolus and the formation of cementum on the surface of the root, the thickness of the membrane is reduced. In the young membrane most of the large bloodvessels are found in its outer half, forming a rather defined vascular layer near its centre. In the old membrane most of the bloodvessels are found very close to the surface of the bone, often lying in grooves in its surface. Both young and old membranes are illustrated in Figs. 93 and 94, which are taken from the temporary teeth of a sheep, one just after eruption and the other shortly before the time of shedding. CHAPTER III ANTISEPSIS IN DENTISTRY Bv JAMES TRUMAN, D.D.8., LL.D. Antisepsis has now become recognized as of \'ital importance in all operations connected with the human organism. The oral cavity, with its contents, has been considered, of recent years, one of the most important factors in producing disease, and hence both dental and medical practitioners have realized that hygienic and prophylactic measures must begin with this, the vestibule of the entire system. It is here that the pathogenic organisms find a prolific culture field and with the possible result of equally infecting many important organs. That this was not, in earlier dental practice, fully recognized is due to the fact that the part played by bacteria was not known thirty years ago, as it is now, hence cleanliness, as then understood, was held to be sufficient. This, however, will not meet the requirements of the present, and the dental practitioner neglecting to avail himself of all means and appliances necessary to affect antisepsis is assuming a grave responsibility. The skepticism which formerly prevailed as to the value of antiseptic measures had its origin in the prevailing idea that the oral fluids were, with ordinary cleanliness, sufficient to prevent infection. This has never been proved through laboratory experiments, but clini- cal observation and long experience have demonstrated that injuries in the mouth ordinarily heal rapidly. It seems unreasonable to suppose that a fluid peculiarly subject to fermentation should have this effect, and this has led some to ascribe it to a vital influence. ]\Iiller^ says of this: "It is a very fortunate provision that the gums in a healthy state offer so powerful a resistance to the invasion of the germs of most iiifrcfious rJis- eases. For this reason a wound in the gums may be followed by scarcely any reaction whatever, while a similar wound on the hand with the same instrument may produce most disastrous results. It has been attempted to account for this fact on the supposition that the saliva has an anti- septic action, in evidence of which we are often reminded that dogs lick their wounds, and that these heal rapidly. . . I doubt if there is anyone who would wish us to believe that the dead saliva has even the slightest antiseptic properties, in consideration of the fact that saliva, J Dental Cosmos, July, 1831. (118) /1/V77.s'7?/'.SV.S' IX DENTISTRY 119 especially when it contains much organic matter, readily j)utrcfies. If the saliva possesses any such property, it must be sought for in its living histological elements — i. e., in the living leukocytes or phagocytes.'" AVhile it is true that there exists a degree of exemption from serious results, leading to indifference and careless management of cases, it is e(iually true that infection has resulted in the experience of almost every operator in dentistry. Prior to the period when Lister announced that all operations in surgery should be performed antiseptically, and made modern sin-gery possible, this ignorance was excusable; but at the present time, with the accumulated knowledge in bacteriology, it should be impossible for any dental operator to neglect the procedures under this head considered absolutely essential for the general surgeon. The difficulties attending antisepsis in dentistry far exceed those in other branches of surgery. The dentist is necessarily obliged to meet conditions hourly that seem to preclude absolute freedom from sources of contamination. If he were to take the same precautionary measures now regarded as necessary for the surgeon, he would find practice almost impossible. While this is true, it does not follow that every ett'ort should not be made to approach absolute surgical cleanliness. The usual methods employed to accomplish this, while valuable to a limited extent, are by no means equal to what could readily be secured without consuming much time or patience. The dentist is usually sat- isfied that he has fulfilled all antiseptic precautions when he has dipped his instrument in some antiseptic fluid, generally carbolic acid. Little or no attention is paid to the possibility of infection from the rubber dam, towels, hands, and the variety of instruments that enter into dental operations. Some of the latter, as, for instance, the separator, are more liable to carry infection than the excavator, the one generally regarded as most important. The appliances ordinarily in daily use are the rubber dam, excava- tors, broaches, pluggers, clamps, ligatures, separators, drills, hand- pieces, napkins, and forceps. It is safe to assume that but few of these will receive any attention beyond ordina.ry washing. The rubber-dam is too often used as it is furnished by the manufacturer. If an attempt at cleanliness is made, it consists in washing the dam in cold or warm water, this being regarded as sufficient. The boiling of the rubber in water has the effect of reducing the absolute tenacity of the material. The continuation of the boiling for fifteen minutes, while it does not seem to aftect immediately the elasticity, renders the rubber apt to tear, a very objectionable feature. If kept for a few da^'s it deteriorates rapidly. The writer has tested 1 For an elaborate study of this problem see Experimental Study of the Different Modes of Protection of the Oral Cavity against Pathogenic Bacteria, by Arthur C. Hugenschmidt, M.D., Dental Cosmos, xxxviii, p. 797. 120 ANTISEPSIS IN DENTISTRY this at various periods of Ixjilinf^ without any marked difference in results. The boiHiig of rubber cannot, therefore, })e recommended. This is to be regretted, for it is evident that tlie rubber, as it comes to the dentist in sheets, is a \ery unsafe material to place in the mouth. To meet this objection there remains but one remedy, and that is thor- ough washing in water with a good antiseptic soap. This has no injurious effect on the material, but while this is true, it cannot be regarded as effective sterilization, but with other aids may answer the purpose. The dam should never be applied without first bathing the gingivae of the teeth to be covered by the rubber with a good antiseptic wash. The most effectual is, probably, a 1 per cent, alcoholic solution of hydronaphthol. Upon the removal of the dam this bathing should be repeated, saturating thoroughly the free margin of the gums. This is especially recpiired after the use of ligatures and clamps. It is needless to add that the rubber should never be used a second time on a different patient. \Vlien it is remembered that this is passed between teeth and usually forced up under gingival margins with ligatures, or clamps, fre(juently lacerating the surface, it becomes evident that the possibility of infection is always present. If infection does not occur from the rubber, it is almost certain to produce a wound in a locality extremely favorable for the growth of pathogenic germs. The result is innumerable lesions that may extend to pericemental inflammations. The great increase in the past twenty-five years of gingival inflammations subsequent to operations in mouths of more than ordinary health must be partly ascribed to this cause. Excavators ordinarily receive the most attention, and yet, when their use is considered, they possibly require the least. It is rarely necessary to use the excavator outside of a cavity, where infection, if at all pos- sible, would do the least harm, for the continual washing of the cavity, as the operator proceeds, reduces the danger to a minimum. Broaches and all instruments intended to enter the pulp canals, require the most careful attention, and this applies with equal force to drills; yet it is fe.ired that both of these, loaded though they are with septic matter, receive but indifferent care. When the dangerous possibilities which mav result from this negligence are considered, it I)econies a serious, if not a criminal offence. The difficulty in making these instruments germ- free and in keeping them from becoming contaminated is fully appre- ciated; yet the effort must be made, and it is not a difficult procedure, nor does it require a large consumption of time — an important item to the dental operator. Pluggers cannot be regarded as a source of infection. They are used solely in connection with metal, and therefore strict cleanliness is all that is absolutely required. It is fortunate that this is so, for these instruments require unusual care to protect them from rust. ANTISEPSIS IN DENTISTRY 121 Hence immersion in an antiseptic fluid may he deleterious and not required. Separators — and under this head are included metal ones with screw attachments and wedges — require special attention, but probably receive the least. They should be made as nearly sterile as possible before their use upon a patient. Hand-pieces, of the various kinds in use, are probably the most difficult to keep thoroughly clean. While they do not come in direct contact with the tissues of the mouth, they may indirectly, by contam- inating the hands, produce unpleasant results. Frequent taking apart and boiling are essential, and should not be omitted. Napkins from the ordinary wash have been and are used with con- fidence that no bad results from use can follow. If the laundry is con- fined to the home, this may ordinarily be true, but the indiscriminate mingling of washes indulged in by the commercial laundryman is always a menace to health. Where napkins of the latter character are to be used they should be subjected to the sterilizing process. The chair occupied by a variety of patients may be a source of dis- ease, and should be carefully cleansed, especial care being taken with the head-piece. The latter should be covered with a clean napkin, to be changed for every patient. The cuspidor, where the fountain is not used, is ordinarily an abom- ination, for here, if anywhere, will carelessness be manifest. There can be no excuse for this, as thorough daily scalding with boiling water and the use of antiseptics will keep it measurably free from unpleasant consequences. Glasses require to be thoroughly boiled both before and after use. Boiling should never be neglected with ejector tubes, either metal or glass, glass being generally used. Hard boiling in water for twenty minutes should be sufficient. The lancet is an instrument demanding especial care, as it may become a dangerous source of infection. This instrument should be thoroughly sterilized by boiling in water in which sodium bicarbonate has been added. This must never be neglected, mere dipping in carbolic acid, or a milder antiseptic, has very little value. The fact that the lancet must frequently be employed on infants during the eruptive stage of the deciduous teeth, demands special care, and before attempting its use the gums should be thoroughly washed with an antiseptic of a non-escharotic character. The difficulty attend- ant on lancing these teeth in private families, where this is generally required, can be in a measure overcome by the preparatory boiling process in the office and careful wrapping the blade in antiseptic cotton, and, before its final use, dipping it in an antiseptic solution, 1 per cent, solution of formalin preferred. 122 ANTISEPSIS IX DENTISTRY Fig. 95 The forceps employed in extraction should he so constructed as to render the blades readily scj)aral)lc at tiie joint, and they should be boiled in soda bicarbonate solution for an hour. The recorded cases of infection from these instruments render this care imperative in all instances. Fig. 95 shows a convenient form of apparatus for sterilizing ordinary dental instruments by a l)oiling soda solution. The writer has found that a half to a teaspoonful of sodium bicarbonate to a pint of water, and kept at boiling temper- ature for fifteen minutes, is amply suffi- cient for sterilization and with no injury to instruments. The amount of sodium bicarbonate to be used will depend on the character of the water in a given locality. Abbott^ in his valuable chapter on steri- lization, thus briefly describes those agents which will "prove of value in rendering infectious materials harmless; they are: Heat, either l^y burning, by steaming for from half an hour to an hour, or by boiling in a 2 per cent, sodium carbonate solution for fifteen minutes; 3 to 4 per cent, solution of commercial carbolic acid; milk of lime and a solution of chlorinated lime con- taining not less than 0.25 per cent, of perchlorine." It must be evident that the only available method, in this list, for the dentist is by boil- ing in sodium carbonate solution. ORAL DISEASES AND THEIR TRANSMISSION The possibility of carrying disease from one person to another seems so self-evident that it ought not to require more than a word of caution, and yet it is clear that the attention given to this source of danger is by no means commensurate with the risks assumed constantly in practice. The peculiarly transitory character of much of dental practice precludes the possibility of any previous history of patients, and therefore every one should be regarded as a possible source of infection. Diseases the result of pathogenic bacteria independent of possible external infection are now in the main well understood, but by no means equally appreciated by medical practitioners, nor are they properly con- sidered by dental operators. ]\Iiller states that " many facts favor the Downie steam sterilizer. I The Principles of Bacteriology, 1902. * The Microorganisms of the Human Mouth, p.ige 275. ORAL DISEASES AND THEIR TRANSMISSION 123 .supposition that a considerable numl)er of pathop;enic microorganisms may tiirive in the juices of the mouth without showing in tlieir vital manifestations any distinction from the common parasites of the oral cavity as long as the mucous membrane remains intact. If, however, the soft tissues have been wounded, as in extraction, or if the resistance of the mucous membrane has been impaired, these organisms may gain a point of entrance and thus become able to manifest their special actions." This fact, now well recognized, is being constantly demon- strated in the use of the various appliances that may, through careless handling, injure the mucous membrane. So much is this the case that a large proportion of gingival inflammations have undoubtedly had their origin from this cause. It has come under the observation of the writer that injuries thus received, although apparently unnoticed by dentist or patient, have resulted in the course of forty-eight hours in very disturbing pericementitis, confusing to the operator and very painful to the patient. The necessity for such antiseptic precautions here as are taken in general surgery is almost entirely overlooked. Before placing the coffer-dam, the clamp, or ligature, that portion of the mouth should be thoroughly washed with an antiseptic -solution and an effort made to render the appliances equally sterile, or at least to inhibit develop- ment for a definite period. (See Treatment of Rubber Dam.) The evidence is abundant that many cases of pyorrhea alveolaris have had their origin from this careless indiff'erence to accepted and necessary precautions. The mouth, as a source of disease to the general system, does not properly belong to this article to discuss, but its importance cannot be overlooked. Dental writers have devoted much attention to this sub- ject. It is for the dentist to understand that he is, to a large degree, responsible for the general health of his patient as far as the mouth is concerned, and he should insist on prophylactic measures that will at least reduce this source of disease to a minimum. The constant danger of what IMiller aptly calls "auto-infection" from the collection and propagation of pathogenic bacteria in the fluids of the mouth should suggest to the dentist constant efforts to effect the removal of all deposits on the enamel, gingival margins, tongue, and mucous membrane. This line of study will bring about in the future an entirely different dentistry as to hygiene and prophylaxis from that practised at the present time. The pulp of a tooth is not ordinarily regarded as a point of infec- tion, and yet it is well known to be a serious menace to the health of an individual. Israel, quoted by iMiller,^ asserts that "the root canal furnishes a point of entrance even for the ray-fungus, actinomyces, and in one case the microscopic examination revealed the elements of this organism in the canal of a pulpless tooth." ^^llen it is considered 1 The Microorganisms of the Human ^louth, p. 285. 124 ANTISEPSIS IX DENTISTRY that some individuals have decomposed jjulps in a nnmher of teeth at the same time, and tre<|uently a seore of dead and broken roots, sendinj^ out their infectious material, it is not surprisini^; that disease of a serious nature may supervene. While there is no record of cases coming within the observation of the writer of pulps produeini^ pyemia directly, it is a well-known fact, supported by a lotii;' list of recorded cases, that alveolar abscess, with its concentration of putrid material, is liable to be followed by blood poisoninj^. There is no question that diseases of the digestive organs, of the lungs — in fact, of all the organs of the body — may be produced by infected material germinated in the mouth, and, indeed, through sputum ejected, may affect individuals remotely situated. Miller,* in considering this portion of the subject, says: "We know that under certain circumstances saccharomycetes may directly colonize in the mucous membrane of the mouth, and that in the mouths of enfeebled individuals bacteria may occasionally obtain a foothold. The mucous membrane of the mouth and pharynx is especially sus- ceptil)le to the action of certain germs of infection (those of diphtheria, syphilis, etc.), and large portions of the mucous membrane and the submucous tissue may be wholly destroyed by parasitic influences." The extended use of fixed dentures in the mouths of patients, of so-called bridge-work, and crowns of varied character, are prolific in mouth disorders. The removable bridge-piece, in a measure, over- comes liability to infection, provided the patient is properly instructed in its use and care, but the average patient has no real conception of the danger from infection from this source. It becomes the duty of every dentist, upon inserting such a piece, to insist on careful anti- septic methods of cleanliness. There is a phase of this subject that requires more extended inves- tigation. Inflammations of the mouth are not infrequent where great swelling is present. This may be observed around the lower third molars with no explainable cause in dead pulps, overlapping mucous membrane, retarded eruption, or malpresentation. It is evidently produced by bacterial invasion, but has not always yielded to anti- septic measures, and at times has resulted in abscess entirely independent of pulp devitalization. Crowns improperly placed are a continued source of disease, result- ing not only in the loss of the roots upon which these are placed, but in gingival and peridental inflammations, involving not only local pathological conditions, but extensive gastric disturbance. A recent report of three cases by Dr. John A. AlcClain' in the medical practice of Dr. M. G. Tull is interesting as indicating possibilities. The first case was an extensive swelling posterior to the lower third • The Microorganisms of the Human Mouth, p. 295. - International Dental .Journal, October, 1900. INFECTION FROM MOUTH TO MO I Til 125 molar. He could not coiiiiect it with that tooth, and suspt'ctcd auto- infection, lie had cultures made with negative re.sult,s. Hi.s theory was that it was diphtheritic; and, although laboratory evidence wa.s wanting, he determined to inject antitoxin. This injection was fol- lowed in twenty-four hours by an entire reduction of the sweilinc- All other efforts had previously failed to effect any result. Two other similar cases yielded to the antitoxin treatment in the same speedy manner. If this can be regarded as something more than a coincidence in practice, it may lead to an explanation of many similar anomalous pathological cases arising posterior to the third inferior molar, yet apparently not connected with it. Similar conditions have been the cause of much uncertain diagnosis and still more empirical ti'eatment. The more the writer has considered this subject the more important it has appeared; and he is convinced that, when the proper prophy- lactic measures come into use for the prevention of tuberculosis, in all its protean forms, antisepsis of the mouth will be given primary importance. The fact is very apparent that very little attention is given to anti- sepsis of the mouth in hospital treatment, and what is equally remark- able, our health authorities, in all cities in this country, have not until recently awakened to its importance in connection with the public schools. The authorities are usually quite sufficiently active as to the general health of the children, but pay not the slightest attention to the condition of the mouths and necessary dental care. When this care is given one of the open doors to tuberculosis will be closed. INFECTION FROM MOUTH TO MOUTH Infection from mouth to mouth through instruments is a difficult matter to prove by cases, but theoretically there can be no cause for disputation. The question will always arise. Was the lesion occasioned by auto-infection or by transmission ? The answer can rarely be given with the assurance desirable. In one instance, at least, in the writer's experience the origin was clearly traceable. This was in a patient of the better class, presenting for treatment in the clinic of the Dental Depart- ment of the tjniversity of Pennsylvania. Her teeth were remarkable for structure, regularity, and cleanliness; gums perfectly healthy. Necrosis of the anterior alveolar plate was threatened when first seen, and finally resulted in the entire destruction of the alveolar border and all the anterior upper teeth, but did not involve the maxilla. The history of the case as given was that a bicuspid had been extracted from the right superior region by a dentist notorious for his uncleanly habits. Not long thereafter the patient noticed a serious inflannnation. These symptoms indicated a syphilitic infection, and the family physician was consulted, who insisted that no history of this disease existed and that 126 ANTI^EI';Sl;S IN DESTISTHY iiitVctioii iiuLst 1)0 the cause. The patient, tlir()ii Dental Cosmos, July, 1S91. 2 The Principles of Bacteriology. 1909. 3 Dental Cosmos, July, 1891, page 520. AGENTS USED FOli STERILIZATION 129 The three previously named, carbolic acid, trichlorphenol, and mer- cury bichlorid, were the only ones that gave any satisfactory results, and these only partially so. In regard to the rest, Prof. Miller says: "They all fall far short of those already mentioned. The 10 per cent, solution of the 'peroxide of hydrogen came next to carbolic acid, but is considerably inferior to it. The essential oils, in emulsions as well as in pure form, utterly failed to produce the desired action." The results obtained by Miller are not wholly in accord with those of some others. Charles B. Nancrede, M.D., in an article' gives a list of agents which have "proved most reliable clinically, can be resorted to in any emergency, or are peculiarly applicable to meet exceptional indications:" Marked inhibition. Complete inhibition. Mercuric chlorld 1 to 1,600,000 1 to 300,000 Oil of mustard 1 to 333,000 1 to 33,000 Thymol 1 to 86,000 Oil of turpentine 1 to 75,000 lodin 1 to 5,000 1 to 1,000 Salicylic acid 1 to 3,300 1 to 1,500 Eucalyptol 1 to 2,500 1 to 1,251 Borax 1 to 2,000 1 to 700 Potassium permanganate 1 to 1,400 Boric acid 1 to 1,250 1 to 800 Carbolic acid 1 to 1,250 1 to 850 Quinin 1 to 830 1 to 625 Alcohol 1 to 100 1 to 12.5 At the time these tables were prepared one agent not mentioned was practically unknown as an antiseptic — formaldehyd, or in solution known as formalin. Dr. Elmer G. Horton, B.S., assistant in bacteriology, Department of Hygiene, University of Pennsylvania, undertook, at the request of Dr. Edward C. Kirk, a series of investigations with formaldehyd,^ the results of which are given, omitting the details of experiments. "We employed the gas generated by heating over an alcohol lamp a pastil which contained five grains of paraform. The lamp was placed in a tin box of nearly one cubic foot capacity . . . (Fig. 96). Among the instruments employed in the tests were various chisels, excavators, and burs. These were boiled, shown by cultural method to be sterile, then either dipped into bouillon cultures or infected from selected cases found in the operative clinic of the Department of Dentistry, University of Pennsylvania. After infection each instrument was placed in a sterile tube and kept at incubator temperature (37.5° C.) for three hours , . . In a single test with moist instruments we found sterilization complete. After the infection and subsequent drying the tubes containing the infected instruments were separated into two lots, one to be subjected to the method of disinfection and the others to be kept as controls, by 1 Treatment of Wounds: Antisepsis and Asepsis, Surgery by American Authors, Park, page 365. ' Dental Cosmos, July, 1898. 9 130 ANTISEPSIS IN DENTISTRY wliic-h would be shown that no step other than the action of formal- tlehvd destroyed the vitaHty of tlie ^ernis. . . . After exactly ten or fifteen minutes, according to the experiment, the door was opened and theinstrument(|uickly removed. . . . Each instninient (controls like- wise) was placed in a considerable amount of sterile bouilhm and these cultures, to