The American text-book of operative dentistry

Front matter

Class _L_

Book. \JZ>

Copyright N°_Ji2Jl

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 rewritten and the fifth 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 constantly growing demand for preventive dentistry has made it necessary to treat several subjects in a much more extensive manner than has been done in former editions in order that the undergraduate student may more intelligently comprehend preventive dentistry in its relation to all other operative procedures.

It is fully recognized that the scientific basis of many of the subjects which constitute preventive dentistry in its broadest sense 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 appears to be a demand upon the part of students and practitioners 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 different authors. While such differences are, of course, not desirable, and while no conflict of opinion will be noticed with respect to established scientific principles,

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x preface

it is manifestly impossible to secure unanimity upon subjects which have not as yet reached a stage of development entitling them to classification among the exact sciences, and which are subject to the variations in methods of procedure of different individuals. For example, it will be observed that all the contributors to this work have used the nomenclature advocated by Dr. G. V. Black ia describing the teeth and their anatomy except the three who have written chapters who are associated with departments of general and comparative anatomy. The latter have used the words canine, premolar, etc., which appear to some general and comparative anatomists as the logical terms, while the former have adhered to the use of the terms cuspid and bicuspid, etc., in accordance with more common usage. As dentistry continues to develop as a branch of medicine, it appears possible that the opinion of the anatomist will prevail and some of the terms now generally used by the dental profession to describe the teeth, and which seem to have been useful in the development of operative dentistry, will be displaced by terms more accordant with the fundamental subjects of general and comparative anatomy. Such differences of opinion are not at present reconcilable, and cannot be, until the bar of professional judgment has decided which school of thought ia based upon the better observation and experience.

The progress in the development of the fundamental principles and technic of correcting mal-occlusion has been so rapid that orthodontia has become a specialty with a scope so broad that it has seemed wise to include in this work only the principles of orthodontia that a general practitioner should know in order to enable him to advise intelligently those who are in his care. In submitting this work to the critical consideration of former contributors to the subject, fellow-teachers and students, it is the desire of the editor to do so with the highest respect for orthodontia as a progressive and preventive measure— his only reason for curtailing the subject in this volume being inability to allow a sufficient space for an appropriate presentation of the subject in its present state of development.

The progressive movement in operative dentistry is still further reflected in the chapter on roentgen diagnosis. A study of the advances which have taken place in the field of roentgenology reveals, besides important additions to our knowledge, a vastly more important advance manifested in a better understanding of the value of the roentgenogram in determining pathologic conditions, the result being more rational practice.

Chapters XII and XIV are devoted to an equally progressive development in the discovery of new substitutes for cocain which are less toxic and equally effective in the removal of pain. With marked

PREFACE xi

improvement in the teehnic of handling these new products local anesthesia has become much more generally used by practitioners of dentistry than before. It has been recognized that local anesthesia was more desirable than any other anesthetic in many respects when the operation was to be performed in the dental office where it was difficult to prepare the patient properly and equally difficult to protect him after the operation. Xot until the advent of the new product novocain or procain, together with improved teehnic, however, could local anesthesia be used so satisfactorily for so many operations, especially the extraction of teeth.

The recent attention given to work in cavity preparation by studying the location and direction of progress of caries and the extension of the cavity walls into relatively immune areas for caries prevention has seemed to warrant a somewhat lengthy consideration of this subject, first, because in itself, it is a preventive measure, and second, because it has been regarded fundamental to all work which involves restorations for lost tooth tissue.

To have made this work in true monographic style with references to all of the authors of every statement would have resulted in a book of impracticable size and form. The policy that has been adopted provides, as a rule, for reference to authorities for facts that have not received general recognition.

The editor takes this occasion to express his deep sense of appreciation of the uniform courtesy and spirit of helpfulness which have characterized the attitude of all his collaborators in this work, and their willingness to sacrifice personal interests to the thoroughness and accuracy of the work as a whole. To express adequately my appreciation of the generous support accorded by my colleagues, Drs. Bunting and Lyons and Miss Nita Faught and Miss Hazel Y. Kramer in the preparation of this work is not possible. Second, only to the contributors, should these persons who have been intimately associated with me, receive credit for any help that this work may be to the progress of dentistry.

Marcus L. Ward.

LIST OF CONTRIBUTORS.

RUSSELL W. BUNTING, D.D.Sc,

Professor of Dental Histology and Pathology, University of Michigan.

WILLIAM A. CAPON, D.D.S.,

Assistant Professor of Dental Ceramics, The Thomas W. Evans Museum and Dental Institute, School of Dentistry, University of Pennsylvania.

JOHN V. CONZETT, D.D.Sc,

Author of Many Valuable Articles on Operative Dentistry.

EDGAR D. COOLIDGE, D.D.S.,

Professor and Head of the Department of Materia Medica and Therapeutics, University of Illinois.

ARTHUR HOPEWELL-SMITH, Sc.D., L.D.S., M.R.C.S., L.R.C.P.,

Professor of Dental Histology, Histopathology and Comparative Odontology, The Thomas W. Evans Museum and Dental Institute, School of Dentistry, University of Pennsylvania. ■

CHALMERS J. LYONS, D.D.Sc,

Professor of Oral Surgery and Consulting Dental Surgeon to the University Hospital, University of Michigan.

FREDERICK B. NOYES, B.A., D.D.S.,

Professor and Head of the Department of Orthodontia and Dental Histology, University of Illinois.

HERMANN PRINZ, A.M., M.D., D.D.S.,

Professor of Materia Medica and Therapeutics, The Thomas W. Evans Museum and Dental Institute, School of Dentistry, University of Pennsylvania.

KURT H. THOMA, D.M.D.,

Lecturer on Oral Histology and Pathology, Harvard University.

ROSCOE H. VOLLAND, M.D., D.D.S.,

Professor of Oral Pathology and Operative Technic, Iowa University.

MARCUS L. WARD, D.D.Sc,

Professor of Dental Metallurgy and Crown and Bridge Work, Dean, College of Dental Surgery, University of Michigan.

Chapter I. The Anatomy Of The Teeth Of Man

By ARTHUR HOPEWELL-SMITH ; ScD., L.R.C.P., M.R.C.S., L.D.S.

Introduction.— In determining the nature of his contribution to this volume the author has been actuated by the main conception of presenting the subject with due regard to the scope and character of the entire work, to the average requirements of the general reader, and to the limitations of allotted space. It is obvious that for a fuller treatment of the subject text-books especially dealing with dental anatomy should be consulted. Complete discussions of many of its branches are not germane to the consideration of special technical methods of immediate interest to the practitioner, important though they undoubtedly are to the anatomist, pathologist and surgeon.

Consequently, this chapter includes brief descriptions of the anatomy of the dental organs which should influence daily clinical work, and omits much of purely academic interest. The facts of dental histology and histogenesis, the problems of dental physiology, and the resultant principles of dental pathology cannot be here set forth: they must be sought for elsewhere.

At the same time it must be noted that the earnest, progressive seeker after truth should not be contented with what is here so concisely detailed. Many recent advances have been made; but many debated and debatable side issues increasingly demand attention. Many old theories have been, and will still continue to be relegated to the past, and the newer teachings of anatomy, medicine, surgery and pathology employed and applied to the study of the science and art of dental surgery.

The reader will be well advised, therefore, to refer to modern text-books, written for the specific purpose of providing an enlarged, sure, clarified, common-sense and scientific basis for the building up of the 2 (17)

higher degrees of knowledge and learning demanded today of the practitioner of dental surgery.

The use of a stricter nomenclature, the appeal of a closer correlation of science and practice, the recognition of the fact that the teeth are orgaus of the body, acting in suis modibus as part controllers of its wellbeing, should be strongly insisted upon, if advancement in the interpretation of symptoms and the diagnosis and treatment of diseases of the oral cavity is desired, as it is certainly desirable.

In view of the foregoing the subject may be shortly considered under the following headings: (I) Definitions. (II) Numeration. (Ill) Morphology. (IV) Articulation. (V) Descriptive Gross Anatomy. (VI) Relationships.

I. DEFINITIONS.

A. Collective. — Teeth may be defined as hard bodies generally* found in the mouth, developed from the ectoderm and mesoderm, articulated to the skeleton but not forming part of it, whose major general functions are concerned with the comminution of food.

B. Individual. — The teeth of man, as of all the primates, are classified as incisors, canines, premolars and molars — so-called from their predominant anatomic and physiologic characteristics, viz., those used for sectorial purposes, those greatly developed in the canidce (dogs, wolves, etc.), those occupying a position in front of the molars, and those used after the fashion of a flat millstone for grinding food.

The maxillary incisors in each half of each jaw are two in number,

in articulation with the premaxillary bones, that is, the bones which

intervene between the right and left premaxillary suture. They are

called the first and second incisors. The older terminology — " centrals"

and "laterals" — is incorrect for several reasons. The words have

no specific meaning. The so-called "central" is central to no anatomic

entity. It occupies a position either to the right or to the left of

the interpremaxillary suture — which corresponds to the midline of the

jaws and face — on the endognathion, 1 and is probably the homologue

of the first incisor of mammalian dentitions. The so-called "lateral"

s ; lilarly may assume a position in the dental arch on either side of the

&r palatal surfaces of the first incisor, appears to be the homo-

the second incisor in the mammalian dentitions, and is in

with the mesognathion. 1 The mandibular incisors are those

o the lower jaw which, in occlusion, correspond directly

ceeth.

so be found in the nasal fossae, 10 sigmoid notch of the mandible, 12 .j. ta, 4 and testes, 5 and attached to the temporal bone 6 and external audi-

DEFINITIONS

The maxillary canine is that tooth — no matter what its shape or size — which is in articulation with the maxillary bone (the exognathion) ,* in that region immediately beyond the premaxillary suture. The mandibular canine is that tooth in the mandible which in occlusion passes in front of its maxillary congener. In the carnivora, for instance, a space exists between the maxillary incisors and canine for the purposes of the accommodation of this tooth. This space is termed a "diastema/' literally meaning "an interval." It is occasionally found in man as a normal interruption to the regularity of the dental arch. In the typically herbivorous animal there are no incisors or canines in the upper jaw. The front portion of the mandible, however, carries four teeth on each side of the suture at the symphysis menti. Of these the fourth or outermost, is small and incisiform in shape. It is, nevertheless, a canine, its period of development and eruption being considerably later than that of the three incisors, it being impossible for mammals (except the polyprotodont marsupials) normally to possess more than three incisors on each side of the middle line of the face.

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Fig. 1. — Palatal aspect of maxilla? of child aged five and a half years, showing various sutures. 1, interpremaxillary suture; 2, endognathion; 3, mesognathion; 4, exognathion; 5, premaxillary suture; 6, median maxillary suture.

The premolars are two in number on either side of each jaw. They are so-called because they are situated immediately in front of the permanent molars, and in eruption have displaced two predecessors, viz., the deciduous molars. They are termed the first and second premolars, though they probably represent the third and four+1 premolars of the typical mammalian dentition. These teeth been generally known as "bicuspids," But recent trend of t 1 determined by a careful examination of many specimens i v of man, and by a study of the anatomic relationships ( primates, show that the term is a misnomer, for the folk the crowns of many maxillary canines possess a promL their lingual aspects. Incisors frequently have a well-define lingual tubercle. In both instances this is an elevation of the it part of the cingulum. They are, therefore, bicuspidate. Further, the first mandibular premolar has often the lingual cusp so ill-defined and underdeveloped that it appears merely as a raised tubercle and cannot properly be called a cusp. The second mandibular premolar is frequently tricuspidate, and may on occasion be multi-tuberculate. These objections cannot be raised, however, if the teeth are considered as the homologues of the mammalian dentition.

The permanent molars are three in number in each half of each jaw, erupt in typical diphyodonts behind the milk molars, and have no predecessors. The existence of a fourth molar is impossible; no typical mammal possesses such a tooth. The "fourth molar" of some authors 8 is a more or less molariform supernumerary tooth. The deciduous molars are those teeth which have been displaced during the growth and eruption of the subjacent premolars. They are correctly termed the first, second and third molars in the first instance and the first and second molars in the second instance.

H. NUMERATION.

There is a marked reduction in the number of the teeth of man compared with that of the typical mammalian dentition, as seen, for example, in the mole, young horse and pig. Here the full dental formula gives on one side of either jaw three incisors, a canine, four premolars and three molars. Adopting the usual symbols this may be represented graphicallv: 1, Pm i, M, f

The normal human permanent dentition is denominationally and numerically expressed thus:

1 f, C h Pm h M | = 16, or X 2 = 32; and the deciduous series:

I |, C f , Pm 1 M, | = 22 or X 2 = 44 in the entire oral cavity

Reasons for the Departure from the Typical Mammalian Formula- Examination of the preceding formula? shows that man has twelve permanent teeth less than the typical number — four incisors and eight premolars. The factors in the production of this condition are probably 26 as follows:

1. Incomplete evolution of certain teeth which are practically functionless, such as the third molars, following the rule of degeneracy of other organs of the body, as exemplified, for instance, in the vermiform appendix and the plica semilunaris, which are important in the rabbit, and as the third eyelid of birds and lizards, etc.

MORPHOLOGY

2. The progressive enlargement of the most actively functional organs, as typified in the comparatively great size of the fourth premolar in the felidce, the dynamic effects of unusually great muscular action in the zygomatic region; and

Fig. 2. — Left side of jaws of man with permanent teeth in situ.

3. The shortening of the length of the entire jaw of man in comparison with that of many of the mammalian series of animals. This reduction in the antero-posterior direction results in the crowding out of teeth which, as organs for the comminution of food, can best be spared. While the general size and shape of the teeth of modern man have undergone little change during his evolution, his jaws have. There is less room in his mouth for the attachment of his teeth than there was in the more spacious oral cavity of his prehistoric simian ancestor.

m. MORPHOLOGY.

In attempting to affix the conception of a geometrical basis to any consideration of the shapes of the organs of man, it must be remembered that, in spite of the necessity, when describing such organs, of adopting mathematical ideals, it was probably never the intention on the part of nature to construct an architectural type which would be completely subservient to geometrical pattern or design. If it were so, then of all the organs of the body his teeth lend themselves most to this treatment; more so than his palate or his dental arches.

It is usual, however, to describe the shapes of the teeth as being dependent, especially as far as the roots are concerned, on the morphological variations of that geometrical figure known as a cone. The roots of human teeth are conical, thoroughly adapted to their unique articulation with the alveolar processes of the jaws. Roots may be cylindrical, flattened laterally, straight, curved or twisted.

With regard to the evolution of the pattern of their crowns three schools of thought may be cited as holding concurrent views, varying chiefly by reason of the differences of the viewpoint of their genesis and development.

Of these the simpler is the theory of (A) the fusionists, 20 21 25 27 who hold that in consequence of the decrease in shape and size of the jaws, haplodont (cone-shaped) teeth may exist per se, or, becoming fused, may produce a molariform pattern. (B) The trituberculists 11 23 have advanced the theory that, during the course of evolution from the primitive type, haplodont teeth may develop on the chief cone, subsidiary cusps in anterior, posterior and lateral directions. A further extension of the tubercular theory may be called (C) the multitubercular theory, 14

A discussion as to the merits of, and objections to, these views is not relevant to this article. It may, however, suffice to say that probably the crowns of the human incisors are merely flattened cones, that the canine largely retains its primitive shape, while the molariform crowns of the three posterior teeth are chiefly due to a longitudinal fusion of original haplodont cones. In the case of the premolars it is believed that the internal cusp is a modification of the cingulum, in which an elevation of its inner part produces a tubercle of varying proportions.

The reasons for the diversities in shape of the crowns of teeth may be ascribed to the operations of the laws of adaptive modification, which demonstrate that, following the deterioration and suppression of disused and unwanted organs and the more complete morphological development of really necessary and much used organs, certain slow, progressive modifications from few and simple forms occur. Of all the teeth the third maxillary molar and probably the second maxillary incisor are the least used as mechanical agents. These teeth, particularly the former, have a tendency to undergo suppression and to evince in their coronal patterns traces of retrogressive and unstable characteristics. In short: the law which governs the fixed morphological features of the teeth is founded upon the requirements of nature in connection with the provision of an organ or of several

ARTICULATION 23

organs most suitably designed and constructed to accomplish the very definite purpose for which they were intended.

Succession. — Man, like most animals, is a diphyodont animal, i. e., he possesses two sets of teeth, the deciduous or milk, and the permanent series. A third set, occasionally spoken of by the unlearned, cannot exist. Vestigial dental remains are exceptionally found in the human jaws and are believed by some evolutionists 21 to point to a reversion to a reptilian dentition in which a polyphyodont condition obtains.

IV. ARTICULATION.

Teeth are attached to the jaws by means of a unique joint or articulation, termed "gomphosis," exactly imitating the arrangement of a nail or peg when received into a hole or mortise in a piece of wood; hence the term. Gomphosis is a variety of synarthrosis 15 24 — a fixed, immovable joint, as exemplified in the methods of union of the bones of the cranium. It is limited to the teeth. The socket containing the cone-shaped root is termed the alveolus, and those portions of the jaws which support the sockets are called the alveolar processes. The teeth are immovably held in position through the cementum on the inner side by a strong fibrous attachment to the lamina dura — a thin sheet of compact bone surrounding their alveolar sockets on the outer side — through the intervention of a dense, firm layer of connective tissue called the alveolo-dental periosteum.

Just as it may be affirmed without fear of refutation that the masticatory organs of modern men are degenerate and unfitted to perform properly their functions throughout the lifetime of the individual, so may it be stated that their sockets are equally unsuited to their desired requirements. It is the rule that they should atrophy and disappear with the incidence of age.

The terminal margins of the sockets of the teeth of man are of a degenerate character for the following reasons: 17

1. Absence of muscular attachment. No muscles or parts of muscles arise from or are inserted into the alveolar processes of the jaws, except a few stray fibers of the buccinator in the neighborhood of the maxillary molars. The fundamental function of bone is therefore entirely absent in this situation.

2. The unique character of the structure of the bone does not completely conform either to the compact or cancellous varieties.

3. Inadequacy of the blood supply tends to produce anemia of the parts, and this, when long continued, is likely to lead to atrophy.

4. Physiologic resistance to disease and nutritional equilibrium are easily and readily lowered and disturbed by the extreme tenuity and other histologic features of the external and internal alveolar plates.

5. There is a modification of the usual function of bones, which, in this particular instance, is only required to support and afford attachment to the roots of teeth.

V. DESCRIPTIVE GROSS ANATOMY.

A. The Permanent Series. — 1. The Maxillary Teeth. — The First Incisor. — In articulation with the endognathion and placed on either side of the intermaxillary suture, which corresponds to the midline of the jaw and face, this tooth with its congener of the opposite side forms one of the most striking objects of the dental series. The graceful size and shape of its crown make it of great importance in its relationship to the other teeth and to the aesthetic bearing it has on the features generally.

It is usually placed in close proximity to its fellow in the other maxilla, but frequently in early life a space exists between the two first incisors. This is due to an excessive development and consequent enlargement of the bone of the alveolar sockets of the teeth, particularly at the side nearest the suture, a hypertrophy probably induced and continued by the presence and action of a large frenum labii, which is inserted into the soft tissues of the labial aspect of the alveolar process.

The crown has four surfaces, six borders, and two angles, named respectively (1) labial, or vestibular, or external, or anterior, (2) lingual, caval, internal, or posterior, (3) mesial 1 and (4) distal; incisive edge or inferior border, gingival edge or superior border, and mesio-anterior and mesio-posterior and disto-anterior and disto-posterior borders. The angles are mesial and distal.

Surfaces. — The labial is the largest of all the surfaces. It is markedly convex from above downward and from side to side. Its upper border is narrow and rounder than the lower, thus making it triangular in outline. Smooth usually, it may be traversed by numerous horizontal ridges or pits or depressions, and is frequently discolored and pig-

1 The terms "mesial" and "distal," common in clinical parlance, are not strictly anatomically correct. It is the rule in general anatomy to designate that part or surface of a long bone nearest to the larger joint as "proximal," that away from the large joint "distal." Thus, in the femur the part of the bone at the hip is called the "proximal extremity," that at the knee the "distal extremity." So it should be with the teeth. Owing to the shape of the dental arches the mesial surfaces of the incisors face in exactly the same direction — toward the midline — as do the lingual surfaces of the premolars and molars, their distal surfaces as the buccal surfaces of these teeth. It is more in accordance with anatomic usage to consider the so-called "mesial surface," i.e., the part further away from the joint, viz., the temporo-mandibular articulation — as the "distal surface," and the so-called "distal" as the "proximal surface," For the convenience of the reader, however, the usual clinical terms will be here adopted.

mented as the result of either congenital or acquired conditions. Occasionally a median vertical ridge may divide the surface into two unequal parts.

The lingual surface is remarkable for its pronounced double concavities. Smaller than the above, with thickened and elevated boundaries, it is triangular in shape, the base being at the incisive edge. A diminutive cusp or tubercle frequently appears at the gingival margin. It represents an elevation of the cingulum.

On the mesial aspect the crown is slightly convex in both vertical and lateral directions. It is enclosed by the rounded mesio-anterior and mesio-posterior borders, which in many instances are scarcely elevated from the general level of the surface and therefore indistinguishable to any extent. The upper borders follow more or less closely the outline of the surface itself. Of its two parts, that directed to the external side is shorter than that directed to the internal side.

The distal surface is more convex than the former, a little larger generally, as a consequence of the superior border not curving downward so markedly. The whole of this doubly-convex surface passes into the disto-anterior and disto-posterior borders without any perceptible interruption.

The incisive edge is blunt, slightly convex and slightly thicker toward the mesial side. Three tubercles may be present here at birth.

The gingival edge varies over the different aspects of the crown. On the labial side it forms part of the circumference of a circle. Lingually it is considerably flattened — nearly in a straight line, mesially it dips down some considerable distance near the middle portion toward the mesial angle, and distally it is less curved than in the last-named situation.

The mesio-anterior, mesio-posterior, disto-anterior and disto-posterior borders are all rounded and smooth, and in the majority of instances are not elevated over and above the surfaces which they enclose.

Of the angles, the mesial is nearly a right angle, the distal is obtuse.

The neck of the tooth is clearly defined, on account of the prominence of the free edge of enamel and its relationship with the cementum above. It does not lie in the same horizontal plane, but as it passes around the tooth it is elevated or depressed, according to the situation. Thus labially and lingually it is very much raised, distally and mesially it is considerably depressed toward the incisive border of the crown.

The root is normally almost a cylindrical cone and the alveolar socket also necessarily cylindrical. Usually straight, it may be deflected slightly toward the middle line. Flattened laterally, it becomes at times somewhat triangular in outline. It may rarely be bifurcated, the second root being placed on the lingual side.

The pulp cavity generally follows in shape the outline of the tooth itself, viz., two cones of dissimilar size placed together at their bases. Of these the radicular portion is considerably the larger. Viewed in a mesio-distal direction the lower part of the pulp cavity is the broadest, and is divided into three cornua, of which the central — the smallest — disappears at about the fifteenth year. The root canal is tube-like, narrow and straight.

A B C D

Fig. 3. — Maxillary first incisor. A, labial surface; B, lingual surface; C, mesial surface;