COLUMBIA LIBRARIES OFFSITE HEALTH SCIENCES STANDARD m NTAL Surgery SEWILL iV.V Columbia (HnitJem'tp College of ^Si^^icmng mh ^urgeonjs l^ilirarp NO/H. dJukaek DENTAL SURGERY Digitized by the Internet Archive in 2010 with funding from Columbia University Libraries http://www.archive.org/details/dentalsurgeryincOOsewi DENTAL SURGERY: INCLUDING SPECIAL ANATOxAIY AND PATHOLOGY. A MANUAL FOB STUDENTS AND PBACTITIONEBS. HENEY SEWILL, M.E.C.S., L.D.S.Exg. I'AST PRESIDENT OF THE ODONTOLOGICAL SOCIETY OF GREAT BRITAl.V FORMERLV DENTIST TO THE \\'EST LONDON HOSPITAL. THIRD EDITION. London: BAILLIEEE, TINDALL eV. COX, 20 AND 21, KING WILLIAM STREET, STRAND. 1890. CD -J Q CD C';> TO JONATHAN HUTCHINSON, LL.D., F.R.S., PRESIDENT OF THE EOYAL COLLEGE OF SURGEONS, WHOSE LABOURS HAVE CONTRIBUTED TOWARDS ELUCIDATION OF MANY PROBLEMS IN SURGICAL AND DENTAL PATHOLOGY. THIS BOOK IS DEDICATED WITH SINCERE REGARD AND IN GRATEFUL ACKNOWLEDGMENT OF LONG CONTINUED FRIENDLY KINDNESS. PEEFACE TO THE THIRD EDITION. Encode AGED by the success of previous editions, and guided by the kindly criticism and suggestion which they evoked, I have endeavoured to extend the original design and scope of this work in the hope that it might adequately fulfil the requirements of a complete Manual of Dental Sm-gery and Pathology. My aim has been to supply all the information on these subjects which can be needed by the surgeon or practitioner of medicine, and to provide a solid founda- tion of knowledge from which the dental student may proceed to that fuller study which ought to be under- taken by everyone intending to devote himself to the practice of Dental Surgery. Although I have not neglected to collate authorities, I have personally investigated many of the subjects of dental physiology and most of the problems of dental pathology. Into the natm-e of Caries I have particu- larly made a thorough research. Numerous obligations for assistance must be acknow- ledged. To Mr. Arthm- Underwood and Mr. Charters White I owe an equal debt. From the former, whose Tiii. Preface. labours with Mr. Milles did so much to clear away obscurity from the subject, I have received great help in the study of caries ; from the latter I have obtained friendly aid in examination of physiological questions, and from both I have derived [most material assistance in free use of the extensive cabinets of microscopical preparations which they possess. My research into the pathology of Caries would pro- bably have been far less complete and conclusive had I not fortunately secured the co-operation of Mr. Pound, of the Bacteriological Laboratory, King's College ; an expert of experts in bacteriological microscopy, he fur- nished me for examination with a vast number of ex- quisitely prepared sections. A considerable number of original illustrations have been added to this edition, amongst which are facsimile reproductions of photo -micrographs by Mr. A. Pringle and Mr. Charters White. Mr. England has contributed a series of diagrams illustrating the operation of stop- ping. The engravings of syphilitic and honeycombed teeth are taken from original drawings, for the loan of which I have to thank Mr. Jonathan Hutchinson. For several valuable cuts from '^ Notes on Dental Practice," I am indebted to Mr. H. Quinby. Other wood-cuts have been obtained from various sources, all of which have been duly acknowledged. Whilst it is hoped that no fact of importance has been omitted, the anatomical chapters are intended to be merely introductory to Pathology and Surgery, not ex- haustive of the subject. In this edition, as in the preceding, I have striven to keep closely to the proper theme of the work and Preface. ix. not to enter into purely surgical topics further than seemed necessary to make clear questions in the patho- log}', diagnosis, and treatment of diseases connected with the teeth. I have thought it well not to encumber the pages and needlessly add to the bulk of the book by insertion of a great number of wood-cuts of instruments. Every prac- titioner can provide' himself with the illustrated cata- logues published by the principal manufacturers. All the classes of instruments mentioned are fully figured in the lists published by Messrs. Ash, of Broad Street, Golden Square; Messrs. White, of Philadelphia, U.S.; and the Dental Manufacturing Company, of Lexington Street, Golden Square. Messrs. Ash and the Dental Company have supplied numerous new illustrations for this edition. WiMPOLE Steeet. June, 1890. PREFACE TO THE SECOND EDITION. This Edition has been revised throughout, re-written, and amphfied where necessary. In its preparation the author has had the advantage of the assistance of Arthur Underwood, M.E.C.S., L.D.S., Assistant- Sur- geon to the Dental Hospital of London. Mr. Under- w^ood's investigations of dental pathology, and his w^ork with Mr. Milles in elucidation of the phenomena of caries, are well known as among the most valuable contributions within late years to our knowledge of these subjects. Abundant evidence has been forthcoming that the First Edition of this book was useful to the practitioner as well as to the student ; and it is hoped that the altera- tions in the Second Edition may render it still more acceptable to both classes of readers. WiMPOLE Street. March, 1883. PllEFACE TO THE FIRST EDITION.* No department of physiology or surgery has of late years made greater progress than that connected with the teeth, and this advance has been necessarily at- tended by a corresponding increase in the literature of the subject. ^Yhich has now become so voluminous as to form a source of embarrassment to those who are entering upon a course of dental education. Under these circumstances the projectors of the ** Students' Guide" manuals have considered a work on Dental Anatomy and Surgery a desirable addition to the series. It is designed that these manuals should be free from needless technicalities ; that they should facihtate the labours of the student ; and that whilst each volume — although presenting merely an outline of the subject — should be complete in itself, it should at the same time lead the reader to desire, and direct him in seeking, the fuller knowledge afforded by more extended treatises. These designs I have striven to accomplish in this volume. * This and the second edition were published in the '" Students' Guide Series" (Churchill). xiv. Preface. It must, however, not be supposed that the student can profitably peruse even the most rudimentary text- book on any special branch of pathology or surgerj'- without an adequate knowledge of the fundamental principles of those sciences ; and evidently it can but confuse him to encounter such terms as ''nucleus'' and "cell," or "inflammation" and "abscess," unless he have a clear conception of their signification. Such knowledge must be obtained previously from elementary works on physiology, pathology and surgery. Whilst in a work of this kind it is essential that, as far as practicable, facts only should be laid before the student, it is not possible to avoid altogether the dis- cussion of controverted points, or at least the descrip- tion of subjects that have as yet been insufficiently investigated. Amongst these subjects must be placed the development of the teeth. The description of this process, which is found in physiological text-books, even the latest editions, is entirely based upon the investiga- tions of Goodsir, which were published by him in the " Edinburgh Medical and Surgical Journal," in the year 1838. Since that date the subject has been investigated by numerous physiologists, among whom may be specially mentioned Marcusen, Dursy, Kolliker, and Waldeyer, and they are agreed with regard to the main facts of the process. Aided by the advance of microscopical science since the time of Goodsir, they have traced the pheno- mena of dental evolution from a period of embryonic life much earlier than that at which it was supposed to commence by that renowned physiologist, and have thus necessarily overthrown much of his theory. Messrs. Legros and Magitot have issued the latest Freface. xv. monograph on the subject — a most elaborate and minute description, entirely based upon original observations — and the corroboration it receives from previous investi- gations leaves no doubt that ^ it is substantially accurate. The section which I have in this manual devoted to the development of the teeth is merely a summary of the work of these physiologists. The histogenesis of the dental tissues — the changes which take place in the tooth-germ by which its elements are gradually converted into these tissues — has been, like the preceding subject, investigated by numerous physiologists, and like it has given rise to considerable difference of opinion. The majority of more recent observers (Lent, Kolliker, Marcusen, Huxley, Eobin, Magitot, Tomes, and Waldeyer) are, however, in accord with regard to essential points, and in the account which I have given I have attempted to epitomize the main facts elucidated by these authorities without enter- ing upon controverted topics. The theory of the etiology and pathology of caries w^hich I have adopted is entirely based upon generally admitted facts ; it is that which I believe can alone be arrived at by reasoning upon such facts ; it is that w^hich recently has been enunciated by the best authorities, and eventually must be, in my opinion, universally accepted. It will be perceived that decay of the teeth is a process entirely dissimilar to caries of bone, and that although the term caries is retained for the sake of convenience, it is not really indicative of the true character of the disease. No more than passing reference has been made to those injuries and diseases of the mouth and jaws that xvi. Preface. are not intimately associated with dental pathology and surgery. Although these affections necessarily fall much. under the notice of the dental surgeon, who is therefore required to possess a knowledge of their nature, their full discussion belongs more properly to works on general surgery than to those devoted entirely to dental subjects. Knowledge having been obtained of the principles upon which operative procedures are carried out, and of the materials and instruments employed, the student cannot commence too soon to acquire skill by practice and experiment. This practice is easily obtained by the dental student. He may begin by plugging with tinfoil cavities cut in bone or ivory or in extracted teeth, each stopping after completion being carefully broken up to discover in what detail it has failed, or in what direction it is capable of improvement. In the same way such operations as capping the pulp, extirpation of the pulp and fang-filling may also be practised. For this purpose extracted carious teeth are best preserved in spirit, which prevents the pulp from drying and shrivelhng. As soon as the student can with rapidity and certainty fill difficult cavities in extracted teeth fixed in a vice, he may safely proceed to operate upon simple cavities in the mouth of the living subject. Similar remarks may be made with regard to the operation of extraction. The anatomy of the teeth and of the parts around being understood, the student may proceed to apply the forceps to the diff"erent kinds of teeth, and familiarize himself with the mode in which the instrument is held, the tooth grasped, and the force applied. Every student should subsequently go through a course of extracting Preface. xvii. operations on the dead subject, opportunities for which are afforded at every school of medicine. Of the illustrations some are original, some are copied, and some are borrowed from works the property of the publishers. Those illustrating the development of the teeth are copied from Messrs. Legros and Magitot's monograph. For some of the most valuable I am indebted to the admirable works of Messrs. Tomes, Mr. Christopher Heath, and Mr. Salter. Figs. 34, 36, and figs. 74 to 78, are taken by permission from the "Transactions of the Odontological Society." Among the original engravings, those in the sections on prepar- ing cavities and gold filling have been most kindly contributed by my friend Mr. Howard Mummery. WiMPOLE Steeet. Feh. 1876. CONTENTS. HE TEETH PAGE 1 17 28 49 Q2 Ill 163 ... 171 \SES OF THE PULP 228 ANATOMY AND HISTOLOGY OF THE TEETH DEVELOPMENT OF THE TEETH GROWTH OF THE JAWS ... ABNORMALLY FORMED TEETH IRREGULARITIES OF THE TEETH CARIES PREVENTION OF CARIES ... TREATMENT OF CARIES ... EXPOSURE OF THE PULP. DISE DISEASES OF THE DENTAL PERIOSTEUM. PERIODONTITIS. AL- VEOLAR ABSCESS. PERIOSTITIS AND NECROSIS OF THE MAXILLiE. DENTAL EXOSTOSIS. NECROSIS. ABSORPTION OF ROOTS OF PERMANENT TEETH. ABSORPTION OF ALVEOLI. PYORRHCEA ALVEOLARIS CARIES AND ITS SEQUELS IN INFANCY AND EARLY CHILDHOOD DISEASES OF THE GUMS AND BUCCAL MUCOUS MEMBRANE. RANULA. GLOSSITIS ABRASION. EROSION. INJURIES— CONCUSSION, DISLOCATION, AND FRACTURE OF TEETH PIVOTING TEETH. PORCELAIN INLAYS. CROWN, BAR AND BRIDGE WORK 259 281 288 291 301 XX. Contents. PAGE SALIVARY CALCULUS OR TARTAR 306 MORBID GROWTHS CONNECTED WITH THE TEETH 311 DISEASES OF THE ANTRUM 328 TOOTHACHE. NEURALGIA, AND DISEASES OF THE NERVOUS SYSTEM 336 EXTRACTION OF TEETH 348 DISLOCATION AND FRACTURE OF THE JAW. CLOSURE OF THE JAW ... 385 appp:ndix ... 391 LIST OF AUTHORS. f Action of Agents for Devitalization of the < Tooth-Pulp, Transactions, International [ Congress, 1881. (Papers on Dental Physiology and Histology, Dental Cosmos, 187-1-1880. f Relations of Fifth Cranial Nerve, Transac- I tious Odontological Society, 1889. ( Injuries aud Diseases of the Jaws, 3rd Edition, \ 1884. Papers on Syphilitic, Stomatitic, and Mercurial Teeth, &c. Ophthalmic Hospital Reports, 1859. Transactions, Pathological Society, 1875. Transactions, Odonto. Society, 1889. Caries der Ziihue, 18 67. . Histology, 1889. 6b. Klein and 1 , . ,t- , -. , oor xT^r^rx, c. r Atlas of Histology, 1880. InobleSmithJ '='^' 7. Legros and f Origine dii Follicule Dentaire. Journal (] « > 6 •gg o ,£3 31 a;) ,—1 +3 Qj •=p^ OJ^ ^'H S ^^ Ol id W ^ '*' ^ tu X o III c 'd 3 c a o -5 .2 .-■ o -4J c>. '-M o T tM X) x o r. tC r/5 2 2 o l-H o t- oj c3 -s^^ - ® J . 10^:3 ^ t>. -M "^ ^ P-^ X t; ^ OS -^ ,-: tt> .i^ 2 ^ " 33c a '^ ■ i.' ' i rt c 3 ii2 ^ '+-' c/: p -. o -IS ^ X •r-j rt' C^' <4-l ►^ bfl ^ o p ■ — ■^ -i-> ^ -u ^ 3 fi ■s Zj ^ J3 ^ 11 6 _ Z- "^ OJ - ^ -y. K^ .• / "c — ■ '^ 2^1 ii i) -T=< — > z^^ ^ P-^ " c -r^ ^S - 3 b .X X ^ r—^ -i^ ~ ~ "5 3 X +3 ~ o if. ct = o *-5 '^ ?-• ^ -u OJ !> X i^ c3 c X c:p r!5 To fair 2). 10. w ,-'-■ ^ L-» ^ ^ O ^ > ;-■ •-i ^"^ ■> ^ «^ 5 '' S^ .^ • , ^ u ^ CJ '-' "" , S i fl ^ 5o Q ^'S o o .-—J «— ' - 5 3 5 o =* 6 .„ ^ +s '*— • -►^ = o -'"— ? xf- 3 'JL ."^ Z^ ^ CO c ^V^J?^ '■■■:::m. •.. .— «l' ':».■■.•" ;•.:>'•': 's-.- . tViivv, V\'^S'' ,-;'\."v» ^^'^.^^^ ". -v- ■V.-V-- >^^t•.■ iilui-l.lil-'-^A o m 1-H o P=i n >, o , — ! -M lo J2 X ?s ^ if; K- 1) o — o 'l\)JiiIloir Fi-J. 11. ANATOMY AND HISTOLOGY OF THE TEETH. 11 Examined microscopically (figs. 9, 10, 11, 12, 13), den- tine is found to consist of innumerable minute tubes having apparently distinct walls, and running close together through an intermediate substance — the inter- tubular substance or matrix. Commencing by open orifices on the walls of the pulp cavity, the tubes radiate outwards in an undulating course, giving off numerous branches, which freely anastomose. In the upper part of the crown they have a vertical direction, towards the sides they become oblique, then horizontal, finally incline downwards towards the point of the root. Each tube as a rule extends throughout the whole thickness of the tissue. Their diameter is about -^-^q^ of an inch, being larger at the inner ends than at a distance from the pulp cavity. They are also more close together near the pulp, there being less matrix between them. The distance between adjacent tubes is about two or three times their width. The tubes and their branches are occupied by soft fibrils which anastomose ; and it can be shown, by staining with chloride of gold, that they form a continuous network. These fibrils seem to spring from the central pulp, and they appear to be continuous with elongated processes of the odontoblasts, the special cells of the pulp. The inner surfaces of the tubes sur- rounding the fibrils are called the dentinal sheaths or sheaths of Neumann. These sheaths are probably in an intermediate condition between the fully calcified matrix and the w^holly uncalcified fibril. It is stated that the only difference between these three tissues, matrix, tube, and fibril, is that they represent different degrees of calci- fication of the same tissue. That there must, however, be some further difference is obvious from the fact that the tubes are plainly discernible in interglobular spaces where no calcification w^hatever has taken place. The sheaths can be demonstrated most clearly after removal of the fibres by maceration, and they remain as a white 12 DENTAL SUEGEEY. fibrous felt even after boiling in strong muriatic acid, or in caustic alkalies. Vascular canals proceeding from the pulp (common in the teeth of some mammalia) some- times occur as rare abnormalities in human dentine. They are usually minute. The dentinal tubes terminate in the crown by fine pro- cesses (fig. 11) which either anastomose or become ex- tremely minute, and are lost beneath the enamel, into which tissue, however, a few may penetrate. In the root (figs. 9 & 14) they end beneath the cement, by opening into the irregular spaces of the granular layer, and frequently passing through to anastomose with the contents of the canaliculi. The intertubular substance or matrix is translucent and without any visible structure. It contains the greater part of the earthy constituents of the dentine. The granular layer of the root (figs. 9 & 14), which ex- sists between the dentine and cement, may be said to con- stitute the line of transition where these tissues blend. The layer is made up of granules or minute globules, and contains numerous spaces apparently due to imperfect coalescence of these elements. Into these spaces (as above mentioned) the dentinal tubes open, and the spaces are again connected with the lacunae of the cement by fine canaliculi. Dentine is endowed with a considerable amount of sensibility, due to the soft fibrils which permeate its tubes, and which, as we have seen, directly emanate from the pulp. The sensibility of healthy dentine varies very much in the teeth of different individuals and in different parts of the same tooth. It is always more marked immediately beneath the enamel than deeper, until the pulp chamber is approached. The sensibility disappears when death of the pulp takes place. Owing to their minuteness it has hitherto been impos- sible to demonstrate the exact character of the dentinal fibrils, although the attempt has been made to prove ANATOMY AND HISTOLOGY OF THE TEETH. 13 that they are really extremely fine filaments proceeding from the nerves of the pulp. It has however been conclusively shown that whatever their structure, to them the sensibility of dentine is due. Mr. Charles Tomes has pointed to some facts which establish this view, and prove that the sensibility is not, as has been suggested, due merely to transmission of vibrations through an inert conductor to the pulp. For instance, the peri- pheral sensibility of dentine can be allayed by applica- tions which do not affect the pulp ; and it often happens that a sensitive layer of dentine overlays a less sensitive portion placed deeper and closer to the pulp. These circumstances can only be explained by the supposition that the seat of sensibility lies within the tissue. Cement (figs. 9 & 14) forms a thin layer, which, commencing at the neck, where it slightly overlaps the enamel, gradually increases towards the apex of the root. It is a true bone structure, having the same chemical and microscopical characters as that tissue. Existing only in a thin layer in man, cement is, however, des- titute of Haversian canals. It contains, as a rule, canaliculi throughout, and lacunae at its thicker parts, enclosing during life protoplasmic contents which form by anastomosis a continuous network. Canaliculi and lacunae may be wanting where the tissue is extremely thin. In the latter case it presents on section a per- fectly homogeneous appearance. The cement is invested with periosteum which is directly continuous with the periosteum of the jaw. It unites the cement to the socket, and consists of a single layer, not two as used to be supposed. The fibres of this periosteum run obliquely upwards from the cement to the socket. It is a delicate connective-tissue mem- brane, containing abundance of vessels and nerves, which are derived from those of the submucous tissue, from those which supply the pulp, and from those of the con- tiguous alveolar wall. 14 DENTAL SUEGEEY. Nasmyth's membrane is an extremely thin homo- geneous layer, covering the enamel. It exists only on young teeth which have not been long used in masti- cation. It resists the action of the strongest mineral acids, but softens when boiled in caustic potash. Al- though other theories as to its nature exist, the majority of authorities are agreed that Nasmyth's membrane is merely a thin layer of cement modified in structure, and exactly homologous with the thick coronal-cement found on the teeth of herbivorous animals. This theory has been confirmed by the investigations of Mr. Charles Tomes (16), who has especially pointed out that coronal cement of well-marked structure, containing lacunaB and canaliculi, occasionally occurs in human teeth, and that when such a layer does not exist it may be often found that sulci or fissures of the enamel such as commonly exist beween the cusps on the masticating surface of molars are filled with a bone-like tissue continuous with Nasmyth's membrane. The dental pulp which occupies the central cavity consists of the remains of the original papilla from which the dentine was developed. It is composed of fine fibrous connective tissue, containing numerous cells, and is well supplied with blood-vessels and nerves, which enter through small foraminse in the apices of the roots. Mr. Charles Tomes describes the pulp as being made up of "a mucoid gelatinous matrix" containing cells in abundance, and but little connective tissue. The outermost cells of the pulp — that is, those that immediately line the dentine — are of a special form, larger and more regular than the others, and are known as the membrana eboris, or odon- toblast layer. Each odontoblast is oval or pear shaped, with a well marked nucleus at the end farthest from the dentine, and has several sets of processes ; some of these processes seem to penetrate the canals in the dentine to become the fibrils, although (as above stated) some obser- ANATOMY AND HISTOLOGY OF THE TEETH. 15 vers believe it probable the fibrils are really nerve endings derived from the pulp beneath the odontoblast layer through which they pass. Boll has especially supported the latter view. He was the first to point out the great number of non-medullated nerves in the superficial part of the pulp tissue, and to show that they ascend between the odontoblasts towards the tubuli into which he be- lieved they entered as fibrils. Boll's opinion receives support from recent demonstrations of the peripheral terminations of intra-epithelial nerve fibrils of the skin, cornea and mucous membranes. These fibrils which Fig. 15. V^5^^^~^«- -^-^^^•-^^■' ^-^^1^^ cannot be much less minute than those occupying the dentinal tubes, might be considered, perhaps, homologous with them. Processes connect each cell with its odontoblast neigh- bom's on either side while others again join the processes of underlying pulp cells. By means of these last men- tioned anastomoses, it may be presumed the odontoblast layer is directly continuous with the terminal nerve filaments in the pulp, while, in the other direction, the fibrils extend through the dentine and anastomose with the protoplasmic network of the cement. Fig. 15 from Tomes (20) illustrates the anatomy of the pulp. The drawing represents a section from a half 16 , DENTAL SUEGEEY. formed human incisor stained with carmine. From the surface of the odontoblast layer which in the preparation is detached from its connection with the wall of the pulp cavity project dentinal fibrils, torn ends of which hang from the orifices of the tubes above. A vessel ramifies close to the surface. Lymphatics have not yet been . demonstrated in the pulp. As age advances, gradual calcification of the pulp takes place, until at last it is reduced to a few fibrous filaments, with the remains of vessels and nerves. Mr. C. Tomes describes a process of degeneration which occurs in the remains of the pulp in advanced age, by which it becomes reduced to a shrivelled un vascular insensitive mass. The tissue resulting from calcification of the pulp is called secondary dentine. In some cases calcification commences in the external layer of odontoblasts, and the new formed tissue coalesces from the first with the pre- viously formed dentine, and the tubes of the two are continuous. In other cases secondary dentine is deposit- ed in isolated nodules scattered through the pulp. These nodules sometimes unite and form larger masses, which again may become attached to the walls of the pulp cavity. The masses of secondary dentine are occasionally traversed by canals containing blood-vessels, and sur- rounded by concentric lamellae, like the Haversian canals of bone. 17 DEVELOPMENT OF THE TEETH. The first trace of dental development in man is visible to the naked eye as early as the seventh vreek of intra- uterine life, when the embryo is not more than one inch and a quarter in length. This trace consists of a smooth oval ridge extending along; the whole length of the Fig. 1G. ,^^: Section of the incisive region of the lower jaw of an embryo sheep, magnified eighty diameters. (Dental development in the sheep and in man is identical.) a. Epithelial ridge or band which extends the whole length of the maxillary arch, but of which the section only is here visible. From this band the epithelial lamina will be given off later. rudimentary alveolar border {a, fig. 16). Section of this ridge shows it to be a continuous vertical band composed of a thick layer of epithelial cells, and it is, in fact, a pro- longation of the epithelial layer of the mouth which has sunk into the embryonic tissue of the jaw. Before the end of the eighth week there has become developed, at about the middle of the buried or deep surface of the ridge, a projection or lamina (b, fig. 17), which, like the 2 18 DENTAL SUEGEEY. layer from which it is derived, extends the whole length of the maxillary border. Its shape is a little flattened Fig. 17. Section of the incisive region of the lower jaw of an embryo sheep, magnified eighty diameters. A. Epithelial ridge. B. Epithelial lamina originating from the epithelial ridge. Fig. 18. Section of the ramus of the lower jaw of an embryo sheep, magnified eighty diameters. A. Buccal epithelium and epithelial ridge. B. Epithelial lamina. c. First appearance of the enamel organ. from above downwards, with its extremity rounded and curved in the form of a crook. It is composed externally DEVELOPMENT OF THE TEETH. 19 of colmnnar cells of the deep or Malpighian layer of the mucous membrane, internally of squamous cells. ^Yithin a few more days there can be demonstrated along the border of the epithelial lamina m each jaw a series of ten small club-shaped enlargements (c, fig. 18). These en- largements or buds are the rudimentary enamel organs of the temporary teeth, and they are situated at intervals corresponding to the position of the futm'e teeth. The Section of the ramus of the lower jaw of an embryo sheep, magnified eighty diameters. Buccal epithelium. B. Epithelial lamina. Enamel organ. d. Dentinal pulp. First appearance of the enamel organ of the permanent tootb. Fibrous tissue whence is derived the dental sac. shape of each bud is at first hke the fioger of a glove pushed into the submucous tissue, then the end swells, becoming much bigger than the neck, and it is flask- shaped, with its central or lowest point directly over the futm-e dentine papilla. The apex of the future papilla arrests the further descent of this central part, but the sides continue to descend all round the papilla, envelop- 20 DENTAL SUEGEEY. ing it in a double layer, and assuming the shape that an india-rubber ball takes if a finger be pushed against it. The annexed drawing (fig. 20) represents diagram- matically four stages of the descent of the enamel organ on to the dentine papilla. It must be borne in mind that this is supposed to be only a section of the object, and also that the papilla is not visibly differen- tiated so early. Fig. 20. A The buds — the rudimentary enamel organs of the tem- porary teeth — are composed of the same epithelial ele- ments as make up the lamina, and they are destined by subsequent deposit of calcareous matter tc become the external or enamel layer of the crown of the tooth. They remain for some time united to the lamina by a narrow portion in the form of a neck, which grows longer as the enamel organ increases in size. The enamel organs soon begin to assume the form of the crowns of the future teeth, but at first their shape is not well defined, and resembles a cap with the concavity directed towards the depths of the jaw. By this time (the ninth week) the first appearance of the dentinal pulp may be detected. This pulp (d, fig. 19) eventually becomes converted by calcification into the dentine or ivory forming the bulk of the tooth. Its elements first manifest themselves in the depths of the jaw independently of the enamel organ, but directly contiguous to its deeper surface. The pulp at first con- DEVELOPMENT OF THE TEETH. 21 sists of a small papilla composed of nucleated cells, and penetrated by a vascular loop, and it is, in fact, at this stage merely a special division of the mucous tissue unusually rich in vessels and cells. Later on, when it has assumed more definite shape, nerve filaments can be traced into it. It grows until it impinges upon the enamel organ, which becomes moulded upon it like a cap, whilst the papilla gradually assumes the form of the crown of the future tooth. Thus, for the incisors it becomes conical, and for the molars develops outgrowths corresponding to the cusps of these teeth. By the beginning of the fourth month each rudi- mentary temporary tooth has become enveloped in a distinct closed sac composed of sub-epithelial connective tissue. This sac begins to appear as soon as the dentinal pulp is shghtly advanced in development. An opaque fibrous outgrowth springs from each side of the base of the pulp, and grows towards the summit of the tooth, where it unites with that of the opposite side, and so forms the dental sac. By this time the connection between the enamel organ and the epithelial process from which it emanated has become severed, owing to absorption of the uniting neck or band of epithelium at the surface of the sac, and this absorption slowly pro- gresses until the whole of the process disappears, leaving the sac completely isolated. The origin of the permanent set, consisting of sixteen teeth in each jaw, has now to be described. The enamel organs of the ten teeth v/hich replace the temporary set — namely, the incisors, canines and bicuspids — originate from a bud for each tooth, which is given off from the elongated extremity of the epithelial lamina at its point of junction with the enamel organ of the temporary tooth .(e, figs. 19 and 21). The enamel organ of the first permanent molar is .given off from the posterior extremity of the same 22 DENTAL SUEGEEY. epithelial band as gave origin to the temporary teeth. Erom the epithelial process of this enamel organ a bud springs for the second permanent molar in exactly the Fig. 21. Section of the incisive region of tlie lower jaw of a human embryo. (In this preparation the epithelial cord or process whence is developed the enamel organ of the permanent tooth, is seen partly isolated from its origin in the follicle of the temporary tooth.) A. Buccal epithelium. B. Epithelial process or cord of the temporary follicle. C. Enamel organ. D. Dentinal pulp covered by a small cap of dentine. E. Epithelial cord, whence is developed the enamel organ of the per- manent tooth. F. Eudimentary cartilage of the jaw. G. Section of the dental artery. n. Traces of ossific matter in the jaw. I. Section of the dental nerve. DEVELOPMENT OF THE TEETH. 23 same manner as the permanent successors of the tem- porary set were evolved from the epithehal processes of that set. In a precisely similar fashion the enamel organ of the third molar, or wisdom tooth, arises from the epithelial process of the second molar. These sixteen germs in each jaw constitute the first traces of the permanent teeth, and they each pass through the same phases of development as we have seen undergone by the germs of the temporary set, . these phases being the appearance of the dentinal pulp, its junction with the enamel organ, and their enclosure in the sac. The only further difference to be noted between the development of the permanent and deciduous teeth is in the time which particular teeth take to pass through the successive stages of evolution. For example, the temporary teeth are usually all cut by the third year, whilst the first permanent molar, although its germ appears at the fifteenth week of foetal life, is not erupted until the sixth year. Similar remarks apply to the rest of the permanent set ; but it will suffice now to give the dates of the phases of their development so far as above described. The enamel organs of the incisors, canines, and bicuspids make their appearance about the sixteenth week of intra-uterine life ; those of the first permanent molars about the fifteenth week ; those of the second molars about the third month after birth ; and those of the wisdom teeth can be demonstrated towards the third year. The dentinal pulps of the ten first-mentioned teeth appear at the twentieth week of foetal life ; those of the first molars at the seventeenth week ; those of the second molars about the first year after birth ; and those of the wisdom teeth towards the end of the sixth year. The complete closure of the sacs of these teeth is ac- complished in the order in which they have been above mentioned at the following dates— 9th month, 20th week, 1st year and 6th year. 24 DENTAL SUEGEEY. The preceding figures illustrating this subject, although sufi&ciently correct, are diagrammatic in character. The appearances and anatomical relations of the parts in the later stages of evolution of the teeth, are shown with exquisite clearness and exactitude in Mr. Charters White's photographs (figs. 22, 23 and 24). The histological changes which take place in the tooth germ by which its elements are gradually converted into the dental tissues, must be now more fully described. It has been seen that the enamel organ (figs. 18 and 19) when first formed is composed entirely of epi- thelial cells — externally of the columnar, internally of the squamous variety. It retains its epithelial nature throughout the process of calcification. This process begins at the surface of the dentine, and progresses outwards. Prior to deposition of earthy matter the columnar cells immediately in contact with the dentine increase greatly in length, and form six-sided prismatic bodies so arranged as to constitute a columnar epithe- lium, which, according to Waldeyer, is the most beau- tiful and regular found in any part of the body. This layer is called the internal epithelium of the enamel organ. The external cells of the enamel organ (termed external epithelium) are shorter and more cubical in form. Numerous vascular papillge, arising from the contiguous tissue of the dental sac, penetrate to a slight depth the external epithelium, and serve doubtless to provide nutriment to the developing tissue. The cells forming the interior of the organ undergo transforma- tion during the formation of the enamel. At first small and round, they soon become stellate in form, united with each other by their processes, and from the cells of this layer (called stratum intermedium), in contact and united with the internal epithelium, a continuous development of columnar' enamel cells proceeds. It has been just stated that the deposition of calca- Fig. 22. ^s:_J Section of Lower Jaw of Foetal Kitten, with Temporary Tooth and permanent successor in situ, x 24 diameters. Phofo-micrograph by Mr. Charters AVhite. a. — Gum. b. — Enamel, c. — Dentine. d. — Dental pulp. e. — Permanent Tooth enclosed in Sac. /, — Jaw partly ossified : and Section of Inferior Dental Artery and Nerve. Tofiiccp. 2!t Fig. 28. Section of Lower Jaw of Kitten, witli Teniporary Canine fully erupted and permanent successor ifi sitn. X 10. Photo-micrograph by Mr. Charters White. a. — Deciduous Canine. b. — Mucous Membrane of Gum. c. — Inferior Maxilla cartilao;inous : with islands of forming Osseous Tissue. d. — Pernmnent Canine in its sac. c. — Inferior Dental Canal, and Section of Dental Artery and Nerve. T<^ JhUnir philc 32. Fig. 24. Developing Perninnent Tooth, shown in Fitr. 23, more higlily mngnified. x 3-1 diameters. Photo-micrograph by j\Ir. Charters White. a. — Dsntal 8ac. h. — Enamel Organ. c. — Formed Enamel. d. — Formed Dentine. e. — Odontoblast layer. /. — Dentinal Pulp with trace:? of Vessels. To follow plate iHJ, DEVELOPMENT OF THE TEETH. 25 reous matter commences in the enamel organ at the sm'-face of the dentine and proceeds outwards. The com- pleted tissue results from direct calcification of the in- ternal epithelimn. The calcification progresses from the periphery of each cell towards its centre, at the same time uniting together the contiguous columns. Prior to the completion of the enamel the external epithelium and remaining portion of the stratum intermedium un- dergo atrophy. These cells ultimately disappear, or per- haps, as some observers state, they take part in forming Nasmyth's membrane (cuticula dentis), the thin layer of tissue which envelops new-formed enamel. Although the difference of opinion has no practical bearing on dental pathology or surgery, since all observers are agreed on the main point, namely, that enamel is developed through the medium of the cells of the enamel organ, it may be mentioned that some investigators be- lieve that the ca,lcareous matter is deposited by the cells, and that the cells do not themselves undergo calcification. Let it be here noted as a point the importance of which, in discussing the nature of dental caries, will be apparent later, that study of the histogenesis of enamel shows that the tissue once formed is entirely cut off by the intervening mass of dentine from direct vascular con- nections, and that when fully calcified, the completed tissue being devoid of cellular or protoplasmic elements, cannot afterwards be the seat of physiological processes or undergo any change due to influences arising from within. The later stages of the histogenesis of enamel are illustrated in figs. 25 and 26. Calcification of the dentinal pulp begins before that of the enamel organ. The process by which the conversion is effected closely resembles the histological formation of bone. It commences at the external surface and pro- ceeds inwards, the central portion with the vessels and nerves remaining to constitute the persistent dental pulp 26 DENTAL SUEGEEY. or "nerve " of the tooth. The dentinal pulp (as already mentioned) at first consists of a special division of the rudimentary mucous tissue, rich in vessels and cells. Its fibrous elements consist of a fine connective tissue,through which the cells are scattered. When the pulp has ar- rived at a certain stage of development the cells begin to be specially organised and arranged. By this time the pulp contains numerous nerve fibrils besides blood-vessels. The latter form a plexus close to the surface. The spe- cialized cells are termed odontoblasts. They are de- veloped from the cells lying at the periphery, where they become arranged in a layer so as to form a kind of columnar epithelium. This layer is termed the mem- brana eboris. The cells are finely granular, have no membrane, and contain a large rounded nucleus. They are each provided with numerous processes, which unite them with the contiguous odontoblasts, and with sub- jacent developing cells. The nuclei of the odontoblasts gradually disappear, and the cells become converted into a gelatinous material which undergoes direct calcification, and forms the whole of the hard constituents of the den- tine. The changes take place from the periphery of each cell towards the centre. It is believed by most inves- tigators that the central portion of each cell remains un- calcified, and forms the soft fibril which occupies the completed dentinal tube. The other views regarding the nature of the fibrils have been given in previous pages. The membrana eboris is constantly fed from the deeper layer of cells, which, united with the odontoblasts by means of their processes, form an uninterrupted series, and provide for the continuity of the dentinal tubes and fibrils. The layer of matrix immediately around the fibrils becomes converted into the dentinal sheaths — the lining walls of the tubes. It has not yet been ascer- tained whether the sheaths are calcified or not, since their structure cannot be examined except after maceration. Fig. 25. Section of Developing Tooth of Dog. x 260. Cut and stained by Mr. A. Underwood. Photographed b}' Photo. Company. a. Outer layers of enamel cells. h. Stratum Intermedium. c. Enamel Cells. d. Formed but Uncalcified Enamel. e. Calcified Enamel. f. Calcified Dentine. [/. Formed but Uncalcified Dentine. h. Odontoblasts. i. Pnlp Tissue. To face p. 30. 2 To foUoic FitJ. ^>;j. THE DEVELOPMENT OF THE TEETH. 27 The later stages of the histogenesis of dentine are illustrated in figs. 25 and 27. By the end of the seventeenth week of intra-uterine life a cap of dentine may be demonstrated on the pulps of all the temporary teeth. By the sixth month the first permanent molar has advanced to a similar stage of development. By the first month after birth the perma- nent incisors and canines are advanced to the same stage ; and at the third year and twelth year respectively, calcification has commenced in the second molars and wisdom teeth. The entire crown of each tooth is represented in soft tissue before deposition of earthy salts commences, and as the tooth elongates by growth of the pulp from below successive portions undergo calcification to form the root. The development of cement has not been made out beyond dispute. It probably takes places in a matrix formed by the investing fibrous coat of the dental sac. A special cement pulp has not been demonstrated in man. Cement is, in fact, a thin layer of bone, and the process of its formation is in all probability similar to intra-membranous ossification of other bones. The cuticula dentis (Nasmyth's membrane), is be- lieved by some authorities to be formed from the resi- duum of the pulp of the enamel after the completion of that tissue. It is, however, much more probable, as stated on a previous page, that it is merely a thin layer of modified osseous tissue continuous with the cement, having a similar origin, and homologous with the coronal cement found on the teeth of certain herbi- vorous animals. 28 GROWTH OF THE JAWS. FIRST AND SECOND DENTITION. CoMMENCiNa as early as the fifth week of foetal life, ossification of the maxillary bones proceeds rapidly, and is well advanced at birth. The lateral halves both of the upper and lower jaws at this period are, however, still united in the median line by cartilage, and the growing alveoli of the temporary teeth are indicated by a deep trench, divided by incomplete bony plates into large crypts, in which the teeth lie enclosed by the dental sacs and submucous tissue. The temporary teeth are repre- sented by their partly calcified crowns, the stage of de- velopment varying in the different teeth according to the period at which their eruption is destined to take place. Thus the crowns of the central incisors are nearly com- plete, whilst, as yet, the apices alone of the rudimentary crowns of the canines have become converted into a cap of calcified material. During the first few months after birth, the develop- ment of the maxilla is most active at the surface adjacent to the connecting cartilages and at the alveolar border. The alveoli increase in depth, and by the growth of their free margins overhang and protect the contained teeth. A little later they become nearly closed. The age at which eruption of the temporary teeth commences varies somewhat in different individuals, but it is rarely earlier than the fifth, or later than the ninth month. Eruption of the teeth is a process of gradual elongation of the teeth on the one hand, and of simulta- neous absorption of the superimposed tissues on the other. GROWTH OF THE JAWS. 29 The absorption commences first in the overhanging mar- gins and front walls of the alveoli, which gradually disappear until room is afforded for the free passage of the advancing tooth. The growth of the tooth keeps j)ace with this absorption, and the crown at length press- ing against its membranous coverings these undergo atrophy, and, becoming by degrees thinner, and at last transparent, give way and disclose the advancing crown. It occasionally happens that these various actions are not perfectly harmonious in their course, the advance of the tooth being more rapid than the disappearance of the enclosing bony and soft tissues. The tooth is thus mechanically held in position, and irritation is set up, which manifests itself by inflammation and induration of the gums, and even by reflex nervous disorders, and constitutional disturbance of various kinds. This ex- planation, which, it must be admitted is far from satis- factory, is perhaps the best that can be given of the occasional undeniable connection between ''teething" and infantile disorders ; for although the connection seems taken as proved by most writers on infantile diseases, it is rare to find any attempt to trace the nervous phenomena to their source, and to explain the correlation between eruption of the teeth and the varie- ties of trivial and grave disorders commonly ascribed to this physiological process. That eruption of the teeth is a physiological not a pathological process, and need not, more than other similar processes of growth and development, necessarily be attended with morbid phe- nomena, is however a fact which is commonly lost sight of ; and there can be no question that in a vast number of cases infantile diseases are ascribed to "teething" which have no relation whatever to the process of denti- tion, many of them being due to such causes as improper food and feeding. It is, however, the opinion of physi- 30 . DENTAL SUEGEBY. cians who have had the opportunity of watching large numbers of children, that even in perfectly healthy and well-managed infants a certain amount of local irritation, manifested by more or less slight swelling of the gums and augmented flow of saliva, is noticeable in most instances at the time of eruption of each tooth, and it is not difficult to understand that in some instances an increase of the local irritation may give rise to reflex disorders of various kinds. It is for the relief of dis- orders of dentition that the operation of lancing the gums of infants is performed. This operation has for its object the division of the abnormally indurated gum, and the release of the advancing tooth. It is obvious that the utility of this procedure must be extremely doubtful when it is carried out prior to the passage of the crown through the contracted bony orifice of the crypt in which the tooth lies ; but that the operation may be reasonably expected to afford relief in cases where the advancing tooth can be distinguished beneath the tense and swollen gum. The order in which the temporary teeth are erupted seldom varies. The lower central incisors are the first which appear. They are followed, after an interval varying between a week and two or three months, by the corresponding members of the upper set. After another similar lapse of time, the lower, quickly fol- lowed by the upper lateral incisors, present themselves. Next, after like intervals, the first molars, and then the canines are protruded. Lastly, the second molars take their places, and complete the series. The annexed dia- gram (fig. 28) from Dr. Louis Starr's well known work, ''Hygiene of the Nursery," maybe helpful in fixing. in the memory the order in w^hich the teeth appear, and the approximate length of the pauses which intervene between the eruption of the different classes. . By the time that the eruption of the temporary teeth GROWTH OF THE JAWS. 31 is completed (between the second and third years), con- siderable progress has been made in the development both of the jaws and permanent teeth. The maxillae have increased in size, and the fibro-carfcilages uniting the lateral halves are completely ossified ; the alveoli which had been absorbed to give exit to the teeth, have since Fig. 28. Diagram showing order of eruption of temporary teeth. 1 1, between fourth and seventh months. Pause of three to nine weeks. 2 2 2 2, between eighth and tenth months. Pause of six to twelve weeks. 3 3 3 3 3 3, between twelfth and fifteenth months. Pause until the eighteenth month. 4 4 4 4, between eighteenth and twenty-fourth months. Pause of two to three months. 5 55 5, between twentieth and thirtieth months. The numbers 1 to 5 in- dicate the order of eruption of the groups of teeth, and the letters a and h the precedence of eruption of members of each group. grown up with the advancing organs, and now closely invest them; the angle of the lower jaw, which recently after birth is very obtuse, has become more acute, coin- cident with the development and lengthening of the ramus, and of the articular and coronoid processes. 32 DENTAL SUEGEKY. Excepting those of the wisdom teeth, the crowns of" the permanent set are all well advanced in calcifica- tion, their progress being, however, proportionate to the periods at which their complete evolution is due. The incisors, canines, and bicuspids are completely enclosed in bony crypts. The incisors are situated in the upper jaw above and behind, and in the lower jaw below and behind the roots of the teeth, which subsequently they respectively replace. The canines are deeply placed between the crypts of the lateral incisors and first Fig. 29. ' Well developed set of deciduous teetli (projected upon a plane), ■with crowns of permanent teetli enclosed in their crypts exposed by removal of alveolar wall. (Natural size.) bicuspids. The bicuspids lie within the divergent roots of the temporary molars. The molars, surrounded by incomplete casings of bone, occupy the portion of jaw posterior to the temporary set, extending into the ramus of the inferior, and the tuberosity of the superior maxilla. The anatomy of the jaws at this period is admirably dis- played in figs. 29 and 30 from Wedl. It may be noted that this is the epoch at which the greatest number of teeth are GEOWTH OF THE JAWS. 33 held in the ja^YS at one tune. The whole of the deci- duous set, and the whole of the permanent set are present, and of these the wisdom teeth alone are still totally unealcified. Within two years after the completion of the tempo- rary set a process is commenced hy which their roots are gradually removed by absorption, until in time the teeth lose their attachment to the jaws, and are cast off one by one, to be afterwards replaced by the advancing members of the permanent set. The absorption does not begin simultaneously throughout the whole set, but attacks the teeth according to the order in which they are to be shed. It commences and proceeds, as a rule, at that part of the root tow^ards w^hich the permanent tooth is advancing, but occasionally it affects other parts at the same time. The wasting surface, which on examination is found ir- regular in outline and broken up into minute pits or de- pressions, resembles that seen in bone when undergoing absorption. Closely applied to the whole of this surface there is found a vascular papilla of slight depth, the ab- sorbent organ, the active agent in the removal of the tissues. This papilla consists of a vascular and cellular structure, the portion in contact with the teeth being entirely made up of large multiform nucleated cells. These cells occupy the pits in the wasting tissues. The papilla originates from the contiguous vascular layer of the alveolar periosteum, and it constitutes a special pro- vision in the economy for the removal of the deciduous teeth. Abundant evidence exists that the absorption is not (as was once supposed) due to the pressure of the advancing permanent teeth, and the following are some of the main facts composing this evidence : — 1st. In some of the lower animals, notably in the serpent, con- ditions exist during the evolution of successive sets of <^) teeth, which prove beyond doubt that absorption of deciduous teeth, similar to what occurs in man, takes 3 S4: DENTAL SUKGEEY. place independently of pressure. This fact has been clearly demonstrated by Mr. Charles Tomes (15). He has pointed out that the succession of teeth in snakes is endless, new teeth continuing to be developed at the inner side of the teeth already in place throughout the Fig. 30. Commencement of second dentition. Profile view from right side ; front alveolar wall removed, (a) First permanent molars of upper and lower jaws erupted, (b) Upper permanent canine, (c) Lower permanent canine, (d^ Mental foramen. Crowns of bicuspids are seen embraced by the roots of temporary molars. Second per- manent upper and lower molars are (in their crypts) imbedded in the maxillary tuberosity and coronoid process. Considerable absorption of the roots of the temporary incisors has by this time taken place. (Natural size.) lifetime of the animal; that when a tooth is about to be shed, both it and the bone at its base are attacked by absorption, this taking place at its inner side before the outer side is at all involved ; and that the advancing GROWTH OF THE JAWS. 35 tooth moves forward, the dehcate cells of its enamel organ remaining in situ, even after absorption has been effected to such an extent that the inner side of the old tooth has been cut away, and the successional tooth has passed into the space thus gained. "It is obvious that if the successional tooth had ever come into contact with its predecessor, these cells, at the point of impact, could not have escaped destruction." 2nd. Absorption of human temporary teeth frequently goes on at points remote from the permanent successors. 3rd. The permanent do not impinge upon the tem- porary teeth during their advance, and, on the contrary, are separated from them throughout by the bony walls of the crypts in which they are enclosed. It happens occasionally without assignable cause that temporary teeth retain their positions long after the period at which they ought to be shed, and even until middle age. Sometimes they apparently form the sole obstacle to the eruption of their permanent successors, the presence of which may then be usually recognised from the contour of the external alveolar plate within which they are hidden. Every now and again an adult patient presents himself having one or more healthy looking and firmly fixed temporary teeth in position with absence of the members of the second set which should occupy the places. A reasonable time should be given for nature to take its course, but temporary teeth ought not to be allowed to remain beyond childhood — beyond the period when the second permanent molars are well in place. Extraction of such retained temporary teeth may be followed by one of two results — either the ex- cluded permanent tooth will emerge, or the space which is left will Jbecome in time much diminished, and in a crowded set will be surely filled up by spreading of the teeth, which always takes places in these circumstances in youthful jaws. 36 DENTAL SUEGEEY. Eetained temporary teeth rarely endure beyond ap- proach of manhood. In many cases in which long re- tained temporary teeth have been at last shed, artificial teeth are called for, to fill towards the front of the mouth unsightly gaps which have shown no tendency to close, but which might have become obliterated had the temporary teeth been removed during youth. 3 3 Dqwq^ t» 'i. 2 2 ^\ ^ Fig. 31. Diagram of second dentition, showing relation between per- manent and temporary teeth. Figures 1, 2, 3, &c., indicate the groups of teeth and the order of their appearance. Eetained temporary crowns may be of good colour, and look healthy; they occupy usually a lower level than the adjacent permanent teeth, and sometimes a temporary molar seems held in place mainly by its neighbours, which, leaning towards each other keep it in position. On seizing such a tooth with forceps it will commonly be recognisable that the only resistance to its. removal is formed by this condition. When the tooth comes away it is often found to have little or no roots,, and the permanent crown may be perhaps seen or felt in the socket beneath. GKOWTH OF THE JAWS. 37 The process of eruption of the permanent teeth closely resembles that which has been described as occurring in the first dentition. By the time each temporary tooth is shed, absorption has commenced in the plate of bone which up to this period has closed the cr}^Dt of the permanent successor, and this absorption proceeds until the opening is large enough to permit the free passage of the emerging crown. When the crowns of the teeth have become fully protruded the development of the alveoli again becomes active, and the bone in time closely embraces the necks of the teeth, and invests the roots in accm'ately fitting sockets. The age at which second dentition commences varies like the first, in different individuals, but the order in w^hich the teeth appear is rarely irregular (see fig. 31 from Dr. Starr). The following maybe taken as average dates at which the eruption of the different teeth is completed. The teeth of each class appear somewhat later in the upper than in the lower jaw : — YE.IES First molars .... Central inferior incisors Central superior incisors Lateral incisors . Anterior bicuspids Canines .... Posterior bicuspids Second molars Wisdom teeth . . The eruption of the permanent teeth is very rarely, if ever, attended with constitutional disorders due to reflex nervous disturbance, such as commonly accompany first dentition ; and local irritation is rare, except in the case of the lower wisdom teeth. Impacted Wisdom Teeth. — The protrusion of the lower wisdom teeth is often attended by considerable to 6 to 8 7 to 9 8 to 10 9 to 12 10 to 12 12 to 11 17 to 25 38 DENTAL SUEGEEY. suffering. They make their appearance after the com- pletion of dentition, at the time when, owing to insuffi- cient backward development of the horizontal ramus of the jaw, crowding of the teeth in many cases exists, and the space which should remain for the wisdom teeth is encroached upon by the second molar. The wisdom teeth in their advance thus become wedged between the distal surface of the second molar and the coronoid process. This condition — commonly spoken of as ''im- paction" of the wisdom tooth — appears sometimes enough alone to give rise to considerable swelling and inflam- mation of the gum, and the mischief becomes aggra- vated when the opposing teeth of the upper jaw during mastication come forcibly in contact with the swollen tissues which overhang the emerging crown. In many cases the inflammation arises from cold, and it is some- times difficult to determine whether it has commenced around the tooth or has spread forward from the tonsil or pharynx. The inflammation, starting at the gum, if allowed to run on, spreads to the alveolar periosteum, and to the uvula, soft palate, and tonsil ; and the neigh- bouring lymphatic glands become swelled and painful. The wisdom tooth and often the molars in front become- exquisitely sensitive to the touch. Movement of the lower jaw is always more or less impeded by the swell- ing, and sometimes force is needed to open the mouth. Closure of the jaws of this kind, whilst inflammation exists in connection with an impacted wisdom tooth, may endm^e for many weeks. The closure may be altogether due to inflammatory swelling in and around the muscles, but it is very often spasmodic in its nature. The masseter and internal pterygoid muscles are mainly affected in spasmodic closure. The nature of the case becomes apparent when the patient is put fully under the influence of an anaesthetic ; for then in a spasmodic case the muscles relax and the mouth is easily opened, GROWTH OF THE JAWS. 3^ whereas if the closure be due to inflammatory sweUing or adhesions, force will be still necessary to separate the jaws. The pain, which varies with the amount of inflam- mation, is often severe, and sometimes throbbing in character, and is increased by attempted movements of the jaw and by swallowing. During the acute stage the pain is mostly localised, but in chronic inflammation around impacted wisdom teeth, and even in cases where very slight or no traces of inflammation are detectable, neuralgic pain spreading over the side of the face, and par- ticularly affecting the ear, is a very common symptom. The acute symptoms are attended with considerable febrile disturbance. If the disease run on suppuration takes place, and pus flows or may be pressed from within the gum and alveolus ; or in some few cases pus may burrow and point externally through the cheek, or at some distant part. I have seen many cases of this kind. In one (reported in British Dental Journal, 1869) an abscess arising from an impacted lower wisdom tooth, formed, pointed and burst upon the cheek about an inch from the corner of the mouth. In some cases suppuration with extensive burrowing of pus through the tissues of the neck takes place. In all cases of inflammation of the face and neck in the region of the angle of the jaw in patients between the ages of seventeen and twenty- five, unless other sufiicient causes be evident, a careful examination of the teeth should be made, lest the true origin of the mischief be overlooked. On occurrence of suppuration the symptoms may slowlj' subside, or the inflammation may remain chronic, in- creasing again into the acute form from time to time, under the influence of cold or other irritation. In a few instances necrosis of the wisdom tooth results, and in rare cases others of the adjacent teeth, and more rarely again portions of the alveoli or jaw may also lose their vitality. 40 DENTAL SUEGEEY. It must not be supposed that in every case of impac- tion — every case in which, owing to want of space, the full eruption of a wisdom tooth is rendered difficult or impossible — inflammation necessarily follows. It is only in a small minority of cases that inflammation at any time supervenes. Many cases occur in which lower wisdom teeth remain throughout life either partly hidden or completely buried behind the second molar, without the patient being aware of their presence. Ex- amples where the tooth was rising vertically rather than those where it lay in a sloping or horizontal position have most often in my experience been attended by inflammation. On the other hand, the absence of in- flammatory or other objective symptoms does not ne- cessarily imply in these cases that the impaction is not a cause of irritation. On the contrary, the cause of neuralgia of the side of the face, and particularly pain referred to the region of the internal ear, is in a con- siderable number of cases clearly traceable to an im- pacted lower wisdom tooth, in the neighbourhood of which no inflammation or other sign of disease may be discoverable. The neuralgia in these cases seems really due to pressure upon or irritation of the trunk of the inferior maxillary nerve by the root of the wisdom tooth. The apex of the root is even in normal cases in very close propinquity to the nerve canal, and in some instances encroaches upon it.''' Treatment. — In a great number of simple cases of impaction immediate relief may be afforded, and, at the same time, a permanent cure effected by excising the thick flap of gum which overlays to a greater or less degree the posterior portion of the tooth. The mere lancing or division of the gum rarely does permanent good, as the divided parts fall at once again into apposi- * See chapter on Neuralgia. GROWTH OF THE JAWS. 41 tion and become rapidly re-iinited. The flap of gum should be seized with a pair of strong narrow-bladed dissecting forceps, and cut away with a small bistoury or curved scissors. I have in some cases used an artery forceps to grip the flap of gum, pushing one blade beneath and then closing the forceps. The gum is usually tough, slippery and difficult to hold; and un- less firmly fixed, it is often by no means easy to dissect the flap cleanly off, and at the same time to avoid cutting the cheek. Sometimes the fixing may be done with a small tenaculum or hook. The hemorrhage on the first incision is enough usually to hide the part, and an as- sistant should be at hand provided with small sponges held in a dressing forceps, to wipe away the blood, and give the operator a view of the part. The operation is sufficiently painful to justify use of an anaesthetic. Nitrous oxide answers well and affords enough time, if the surgeon stands ready with instruments in hand. If a wisdom tooth, as sometimes happens, be mal-placed, and with the crow^n so directed as to render it useless in mastication, it should, if the cause of inflammation, be removed. The extraction of a tooth may also be called for in cases which take a rapid, bad course, or which have been neglected until extensive inflammation and suppuration are present. It often happens, how- ever, in these instances, that the tooth is so impacted as to render its extraction extremely difficult or impos- sible. This is especially the case where the tooth is advancing in an oblique direction — sometimes it may be nearly horizontal — and with the anterior margin of the crown impinging upon the distal surface of the second molar. A careful examination must be made before an operation is attempted. In one or two cases of this kind, I have succeeded in breaking the crown from the root, the patient being under the influence of an anaes- thetic, and extracting the root in a second operation. 42 DENTAL SUKGERY. But, with few exceptions, cases of impacted lower wis- dom teeth, in which rehef afforded by space is called for, are best treated by extraction of the second molar. This allows the impacted tooth to advance slowly inta the vacant space. Where the second molar is exten- sively carious, there seldom need be hesitation in pro- posing this operation. A crown of a wisdom tooth advancing obliquely and impinging upon the distal sur- face of the second molar will in some instances be found partly lodging within a carious cavity, which is apt in these cases to form at the point of contact. This con- dition renders impaction more complete, and it will under these circumstances be found impossible in some instances to remove one without the other tooth. Ex- traction of the first molar or even of a bicuspid, which may be chosen if decayed, will give relief, but more^ slowly, to the crowding. To reach the tooth when the jaws are closed they must be carefully forced apart with a screw gag, the patient being anaesthetised. When suppuration has been going on for some time round an impacted wisdom tooth, it is often sc loosened and extruded that it may be extracted with comparative ease.''' Beyond the operative procedures just described, the treatment of inflammation associated with impacted wisdom teeth is the same as that of ordinary dental and maxillary periostitis given in a later chapter, and consists mainly of assiduous use of hot fomentations, confined as much as possible to within the mouth, and incisions through the gum and swollen periosteum of the jaw, in order to relieve tension, to give exit to pent-up pus, and prevent it from burrowing or bursting externally through the skin. In cases of intractable neuralgia (particularly in young * See chapter on Extraction. GKOWTH OF THE JAWS. 43 subjects) affecting the side of the face and the ear, in which no local cause can be discovered, but in which an apparently healthy although impacted wisdom tooth is present, it may be right to extract the tooth or the second molar, in the hope of relieving irritation of the nerve trunk, which may exist without recognisable local signs. Throughout the entire period of their growth the pro- cess by which the maxillae are moulded into their des- tined form is similar to that which takes place in all developing bones. It consists, on the one hand, of con- tinuous deposition of bone, and on the other of occasional absorption. It has been already explained how the pro- cesses of growth and absorption alternate during denti- tion and the development of the alveolar border of the jaws. Enlargement of the maxillary arch is produced mainly by deposition of bone upon the facial surface, and as new layers of bone are deposited absorption takes place upon the lingual surface. In the same way in the development of the posterior portion of the lower jaw, whilst the ascending ramus is increasing in size by the deposition of bone upon the posterior surfaces of the coronoid and condyloid processes, absorption is going on upon these parts anteriorly, and thus the bones are moulded into their destined form. The depo- sition of new material is principally subperiosteal, but it also takes place beneath the articular cartilage of the lower jaw, and at the surfaces contiguous to the car- tilag3s, which in the infant unite the separate portions of bone in both maxillae ; and the increase in the bulk of the jaws is thus entirely affected, not by interstitial growth or expansion of the bones, but by constant addi- tions to the external surfaces. Up to a certain period in the growth of the jaws, as 44 DENTAL SUEGEEY. previously explained and illustrated, there is not suffi- cient room in the alveolar arch for the crypts of the developing permanent molars, which, therefore, are en- closed in the base of the coronoid process of the lov^er, and in the tuberosity of the upper jaw. The space taken up by the ten anterior permanent teeth almost exactly corresponds to that occupied by the milk teeth, and it is, therefore, in the backward direction that the required increase in size of the arch takes place. The depth of the bones becomes greater in accordance with the dental and muscular development. Examination of a large series of human maxillse of different ages enabled Sir J. Tomes to demonstrate the fact, first pointed out by John Hunter, that the growth of the alveolar border, during both first and second dentition, follows and is dependent upon the growth of the teeth, and that the position of the teeth is not, as was once believed, pre- determined by independent growth of the bone. This fact has also received confirmation from the obser- vations of Mr. Chas. Tomes, upon the mode of attach- ment of the teeth in fishes and reptiles. He has proved that in the attachment of a tooth by simple anchylosis, or by ever so rudimentary a socket, as it takes place in the varied species, the bone is modelled] to the tooth in full subserviency to the position of that tooth, and that the tooth does not come to take its place upon a spot predetermined for it by any disposition of the bone, made prior to its advent. The portions of bone which give attachment to the muscles of mastication increase in bulk as these organs develop in size and power. When the teeth are lost from age or other causes, the alveoli waste by absorption ; and at the same time mas- tication being gradually discontinued, the muscles, to- gether with the portions of bone to which they are attached, undergo atrophy, and the jaws assume the peculiar form characteristic of age. GEOWTH OF THE JAWS. 45 It happens occasionally that permanent teeth remain imbedded within the jaws instead of making their aj)- pearance at the natural epoch of their eruption. It has been just explained, and illustrated in figs. 29 and 30, that at one period in the growth of the maxillae, before the jaws have attained their full size, enough space for the extended arrangement of the set in an unbroken arch does not exist, and the teeth are crowded within Fig. 32. the jaw, the canines and bicuspids being deeply placed, whilst the upper and lower wisdom teeth are situated in the tuberosity of the upper and in the ramus of the lower jaw respectively. If, owing to arrest of develop- ment or other cause, the jaws remain unduly small or contracted, there may never exist enough room for the 46 DENTAL SUEGEEY. entire set of teeth to take their places in the dental arch, and some of the set, although fully formed, may remain buried within the bone. This condition, al- though it may happen in the case of any tooth, most commonly arises, as might be expected, with those teeth — such as wisdom teeth, canines, and bicuspids — which are cut at a late stage of dentition, when the whole available space in an abnormally small maxilla may be taken up by the rest of the set. The eruption of such teeth may be also in the same way prevented by the presence of supernumerary teeth or by temporary teeth holding their position after the time at which they ought to be cast off. Fig. 33. In another class of cases imbedded teeth hold such ab- normal positions within the bone that, although room may exist for them in the dental arch, their eruption is impos- sible. In some of these instances there is evidence that the malposition is due to deflection of the growing tooth from GBOWTH OF THE JAWS. 47 its normal course by obstacles, such as temporary teeth or supernumerary teeth, but in others the tooth is sit- uated far from the alveolus, and its misplacement cannot be accounted for. Fig. 32, from Mr. Heath's work (4), shows an upper canine situated within the jaw in a position which it may have possibly assumed in con- sequence of want of space, whilst fig. 33 from the same work, exhibits an upper canine, lying horizontally in the floor of the nose, with the crown directed backwards — -a misplacement which cannot be accounted for. Fig. 34 from Salter (12) shows an imbedded molar in the lower jaw. In all these specimens the bone has been cut away to expose the buried tooth. Similar specimens are pre- Yh-i. served in the Museum of the College of Surgeons, show- ing teeth imbedded in almost every position in the maxilla). Imbedded teeth, especially those regularly situated within the bone, sometimes make their appear- ance after a lapse of time when room is afforded by the 48 DENTAL SUEGEEY. loss of other teeth, and the eruption of such teeth late- in life has given rise to the unfounded belief in the occasional occurrence of a third dentition. ' Every dental surgeon becomes familiar with cases in which in a patient with edentulous gums, and perhaps wearing a complete set of artificial teeth, one or other buried mem- bers of the set — most often wisdom teeth or canines — begin after a time to emerge or become exposed through the wasting of the alveolar border of the jaw. In the majority of instances, imbedded teeth remain through life, without the patient being aware of their existence. In some cases, in consequence of extension of periostitis from around overlying or neighbouring- teeth or other causes, inflammation may be set up in the cyst of a buried tooth; and in all cases of deep- seated inflammation within the jaws where the cause is not evident, possibility of the presence of a buried tooth must be therefore borne in mind. The diagnosis would be confirmed by exploration; and the thin ex- ternal plate of bone covering the tooth can be easily penetrated for this purpose, if it have not at some point already given way to pressure of confined exudations or pus. A tooth being discovered its extraction presents as a rule no serious difficulty. The enclosing bone must be opened to the slight extent necessary, either with a dental drill, a small trocar, or bone forceps, and the tooth being gripped at a convenient point must be care- fully detached and withdrawn. A cure will be hastened by antiseptic lotions, such as Condy's fluid or carbolic acid (1 in 50), with which the mouth may be frequently rinsed and the cavity syringed. In some few individuals buried teeth become the centre of cystic disease or of other morbid growths. Such growths connected with teeth are described in a later chapter. 49 ABNOEMALLY FOEMED TEETH. Abnormalities in Size of Teeth. — The size of teeth varies very much in different individuals. In the vast majority of cases teeth composing a set are of sizes proportional to each other ; but a set may be dis- proportional relatively to the size of the jaw, being made up of comparatively very large or very small teeth. A large set in a small jaw gives rise to crowding — a con- dition discussed in the next chapter. Single members of a set may in proportion to the rest be abnormally large or small, but variations in this respect are very rare, except in the upper laterals and in the wisdom teeth. The laterals occasionally are very small, round, conical and pointed in shape, resembling a class of supernumerary teeth (figs. 50 and 51), with which they must not be con- founded. In some uncommon cases the incisors and canines and, in still rarer instances, a whole set has par- taken of this character. Such teeth have been likened to rats' teeth. Wisdom teeth are, above all, most vari- able in size. They are sometimes represented by stunted conical teeth, also not unlike in character the peg-shaped supernumerary teeth illustrated in this chapter (figs. 48 and 50). Wisdom teeth are less frequently of great size; every now and then, however, they are met with having crowns half as large again as the second molar. Such large teeth often — although by no means always — have stunted roots. It will commonly be found that teeth of any class with small crowns may possess roots 4 50 DENTAL SURGERY. of full or great size and vice versa — a point which must be borne in mind in several operations of dental surgery. Syphilitic and Honeycombed Teeth. — A peculiar malformation associated with hereditary syphilis affecting the incisors and canines of the permanent set only, and Fig. 35. Typical syphilitic upper and lower incisors. Fig. 36. Syphilitic upper central incisors, and mercurial (honeycombed) permanent molars, carious, from boy «t. eleven. At one side the temporary molars, carious, are still in place. being most marked in the upper central incisors, was first described many years ago by Mr. Jonathan Hutchinson (5). Syphilitic teeth (figs. 35 and 36) are short, small and peg- shaped. Their cutting edges are narrow and marked by a characteristic broad crescentic notch. Horizontal notches, or furrows, and honeycomb pits not of syphihtic ABNORMALLY FORMED TEETH. 51 ■origin often exist on the same teeth. The colour of the teeth is bad — often a dirty grey shade. The central in- cisors Mr. Hutchinson considers the " test teeth." The tissues of syphihtic teeth are soft and ill-made, so that they soon become worn down and lose in great part their characteristic marks. The enamel towards the neck is usually smooth and free from visible defect. A striking connection has been observed between this deformity of the teeth and a syphilitic disease of the cornea — inter- stitial keratitis. The subjects of inherited syphilis w^ho present marked examples of interstitial keratitis, have almost invariably typically malformed teeth, and those who have such teeth scarcely ever escape interstitial keratitis ; whilst syphilitic children who are liable to suffer in after life from phagadaenic affections of the mouth and throat usually show nothing peculiar in their teeth. Although the characteristic appearances of true syphilitic teeth are of unequivocal significance, and can hardly be mistaken by an experienced observer, it must not be forgotten that many honeycombed and malformed teeth resemble syphilitic teeth ; and caution is therefore necessary in pronouncing a diagnosis from the teeth alone. It is only in a small proportion of undoubtedly syphilitic children that teeth of this special type appear. A considerable variety of malformed teeth with de- fective surfaces — pitted, rocky, ridged or spinous — are usually classed as "honeycombed" teeth. These teeth are almost sufficiently described by their names. In spinous teeth the cusps of molars seem pinched, drawn out and pointed, and the crowns of incisors and canines flattened and elongated into thin processes towards the cutting edge. The defects rarely involve the whole crown. They are mostly confined in the molars to the cusps and masticating surface. In the incisors and canines the markings may be confined to a narrow space along the cutting edge. At this point the disfigurement 52 DENTAL SUEGEEY. always starts, thence extending to a varying degree over the surface towards the neck. The rest of the tooth is often well formed and of good structure. The defect is mainly confined to the enamel. These teeth have been styled by Mr. Jonathan Hutchinson " sto- matitic" or ''mercurial" teeth. He believes that, in cases in which great and general damage to the enamel of the permanent set of teeth is observed it ought to lead us to suspect that the patient has in early in- fancy passed through an attack of stomatitis, attended with inflammation of the tooth sacs. Mr. Hutchinson believes that if all the bicuspids have good white enamel, while all the first permanent molars show absence of enamel and spinous discoloured surfaces, it may with confidence be assumed that the child took mercury in infancy, or that some cause for a similar kind of stoma- titis then existed. As to the cause of the stomatitis, although he does not assert that mercury is the only cause, he believes that by far the most important cause of defects in enamel development in the permanent set of teeth is the use dmdng infancy of mercury in one or other form. The "test teeth" in these cases are the first permanent molars. The bicuspids often and the second molars usually are unaffected. The disease of the eye known as lamellar cataract, which is not con- genital and not s^^philitic, has been observed in concur- rence with honeycombed teeth, particularly in children who have suffered from con\ailsions in infancy. It is to some extent still an open question whether there is any correlation of development between the eyes and teeth, but Mr. Hutchinson holds to the belief that the connection between the two phenomena referred to is not to be so explained, but that the lamellar catar- acts are due to convulsions in infancy, and the damage to the enamel of the teeth is due to stomatitis which may be caused by mercury given for the convulsions. ABNORMALLY FOEMED TEETH. 63 Mr. Hutchiusoii has found that some adult patients with honeycombed teeth display an unusual suscepti- bility to the action of mercury, and believes that it is owing to this idiosyncrasy that the teeth have suffered from what was given in infancy. If this view be correct, honeycombed teeth may rank as revealing symptoms, and may be of value in giving information as to individual susceptibilities which could not have been otherwise recognized. To sum up the more important of these facts it would appear : — 1. That syphilitic teeth are mostly accompanied by other evidences of the inherited taint, such as skin affections and interstitial keratitis, while honeycombed teeth are frequently associated with a nou- syphilitic eye disease, lamellar cataract, with infantile convulsions, and with stomatitis often but not always caused by mer- curial treatment during the enamel forming period. 2. That in inherited syphilis the teeth most affected are the upper incisors, the honeycombed condition being most conspicuous in the first permanent molars. 3. That these conditions may both be present in the same individual. 4. It by no means happens that every case of inherited syphilis is marked by typical mal-development of the teeth. Many instances occur in which no characteristic defect is visible. 5. Syphilitic teeth are due to causes acting upon the entire tooth germ during development, whereby not only the structure but the whole form of the tooth is modified. Honeycombed teeth are due to causes acting upon the enamel during calcification and interfering with the proper formation of the tissue. Syphilitic and honeycombed teeth are well illustrated in the accompanying engravings, taken from patients at Moorfields Ophthalmic Hospital. Figs. 35, 36, show- 54 DENTAL SUKGEEY. ing typical teeth, are from patients undoubtedly subjects of hereditary syphilis, and in one (Fig. 36) there is a history of mercurialism also. Eigs. 37 and 39 — honey- combed teeth — are from patients with lamellar cataract and to whom mercury had been given in large quantities in early childhood. Pig. 35 may be contrasted with fig. 39 ; the former syphilitic, the latter mercurial, or- FiG. 37. Eidgecl and honeycombed teeth, boy aet. sixteen, subject of lamellar- cataract. Had fits in connection with very late dentition in early childhood. Much calomel was given during a whole year (from, one to two years of age). Fig. 38. Honeycombed teeth, girl set. nine, subject of lamellar cataract.. No evidence as to fits or mercury. stomatitic central incisors. Fig. 38 well illustrates the common occurrence of w^ell-made bicuspids in honey- combed sets of teeth. Treatment. — Syphilitic aud honeycombed teeth do not necessarily call for interference. Pits, fissures and grooves, especially if they extend to the dentine, are of course very apt to become the seat of carious action, which must be dealt with as it appears ; but enamel- ABNOEMALLY FORMED TEETH. 55 covered pits and depressions often remain permanently unaffected. The flattened, pitted and drawn out or spinous edges of front teeth often as time goes on present an unsightly appearance. The surface becomes covered with discoloured tartar which, filling the small pits, is difficult to dislodge. It is a good plan in some cases at the approach of adult age to file or cut down and polish these ragged surfaces and edges, with care not to approach the pulp chamber. This may leave the teeth unnaturally short but will vastly improve their appearance. Fig. 39. Stomatitic or mercurial teeth of type sometimes mistaken for syphilitic. Dilaceration. — When the mode of development of the teeth is considered, and it is remembered that they are liable to injury at the period when they are but partially calcified, it is easy to understand why teeth are occasionally met with the crowns and roots of which are m.ore or less distorted. In such cases some force — such as a blow — has been transmitted to the developing organ, by w^hich a part or the w^hole of the crown has become displaced, without severance of its connection with the uncalcified portion of the pulp, and has become sub- sequently fixed in its malposition by completion of the process of calcification. This kind of injury has been termed dilaceration. Section of such teeth displays evi- 56 DENTAL SUEGEEY. dent marks of the bending which the tissues underwent in the soft state. It is possible that a tooth might be distorted during growth to the extent of dilaceration in consequence of crowding and pressure within the jaw from want of space, and this opinion is strengthened by the fact that the deformity seldom or never occurs except in teeth situated at the front of the jaw where a crowded condition is common. Figs. 40 and 41. Teeth which have undergone dilaceration are of course easily recognised when the injury affects the tissues of the crown, but when the crown is well formed and merely bent at an angle with the root, careful examina- tion is sometimes required to distinguish the case from one in which a well formed tooth is lying in an abnormal Figs. 42 and 43, position. The latter case might be amenable to treat- ment, which would be inapplicable to dilaceration. Teeth the subject of dilaceration often present marked bulgings upon either surface close to the neck, which is frequently constricted and well defined; they occa- ABXOKMALLY FOEMED TEETH. 57 sioually display marked mobility under slight pressm-e, and the distorted root may be in some cases traced by the finger through the alveolar wall. Fig. 40, from Wedl, represents a case of dilaceration or flexion occur- ing in an upper central incisor, of which a side view is presented. The crown is perfectly developed, but the root is short and thick and much curved, its apex being directed towards the lips. Fig. 41, from Wedl, shows a lower central incisor the seat of dilaceration. The crown is bent at a right angle to the root, and the cutting edge is directed towards the lips. Figs. 42 and 43, from Wedl, illustrate similar malformations of the roots of upper central incisors. Gemination, apparently the result of organic union of two neighbouring teeth during development, sometimes occurs. It rarely affects any but incisors, and the union may extend through crowns and root, or may affect only a part of the teeth. Blended crowns contain as a rule a common pulp cavity, but in blended roots the chamber is divided or distinct. Gemination does not necessarily give rise to marked deformity in the appearance of the Figs. 44, 45. 4(5 and 47. teeth. Figs. 44, 45, 46 and 47, from Tomes (21), show examples of these malformations. Supernumerary teeth are frequently met with. They are as a rule easily recognised, being mostly of an irregular conical form, unlike any member of the normal 58 DENTAL SUEGEEY. set of teeth. They may occur in any position, but their most common situation is towards the front of the mouth, where they are usually placed irregularly among the other teeth. Sometimes a supernumerary tooth is symmetrical in form, and placed within the dental arch,, and hardly distinguishable from its neighbours — an individual in this way possessing an extra or supple- FiGS. 48, 49 and 50. mental incisor or canine. Figs. 48, 49 and 50, from Salter,, illustrate common types of supernumerary teeth. Fig. 51, from Salter, and fig. 52, from the Transactions of the Odontological Society, show supernumerary teeth in position in the upper jaw. Fig. 51. Mr. Bland Sutton (14) — to whom I am indebted for the illustration fig. 54 — believes that the origin of gem- inated teeth and of some supernumerary teeth is ex- plicable on the theory that a dental germ or papilla may occasionally bifurcate, but it does not necessarily follow that two distinct teeth arise in consequence of the dicho- ABNOKMALLY FORMED TEETH. 69 tomy, for duiing development the two teeth may fuse and produce gemination. This opinion is supported by the fact that dichotomy of a similar kind is to be observed in the feathers of some species of birds, and has been occasionally noticed in the hairs of man. The dichotomy is not always equal or complete. In the case Fig. 52. of teeth when dichotomy is equal and complete the teeth are as like each other as twins, and difficulty arises as to which shall be regarded as supernumerary. In such a specimen as Fig. 47 the dichotomy of the papilla was equal, but in the case represented in Fig. 53,. from Tomes, a lower molar, with a small tooth projecting Figs. 53 and 5-}. from its side, the dichotomy was unequal, and in both specimens probably only partial. Complete and unequal dichotomy would produce the small mis-shapen super- numerary teeth such as above described and illustrated. 60 DENTAL SUEGEEY. Other abnormal teeth, presenting several forms, vary^ ing between so-called warty teeth, studded with nodules of enamel, and monstrous teeth, mere shapeless masses of dental tissue, must be considered identical with the morbid growths termed odontomes, the nature of which is more fully discussed in a later chapter/'' The specimen shown in fig. 53 recently described by Mr. Bland Sutton, throws some light upon this subject. This tooth was removed from a lad aged nineteen years ; it was situated in front of the right upper bicuspid, dis- placing the lateral incisor and canine, so as to occupy their position in the dental arch. It has no fang, and appears to consist merely of a crown and neck, but the crown bristles with cusps, and as many as nine distinct enamel-covered eminences can be detected. The appearance of the specimen is as though a group of supernumerary teeth had become confluent. Had such a tooth been dislodged from a swelling below the gum, it would have been described as an odontome, and re- garded as an odontome which had cut the gum and taken rank with the normal teeth. Mr. Bland Sutton has pointed out that odontomes resemble teeth in this way — for a time during their development they remain hidden below the mucous membrane, and give no evi- dence (or very little) of their existence. To this con- dition succeeds an eruptive stage, when perhaps sup- puration, with the constitutional disturbance dependent thereon, draw attention to the part. If this view be correct, this remarkable structure must be regarded as an odontome which has cut the gum and taken a position in the dental series. This specimen is further interesting in that it consists of a conglomeration of denticles. Mr. Sutton has urged that those remarkable cases in which denticles have from time to time been erupted from a tumour connected with the jaw should be classed as ■odontomes. It is easy to imagine that if the cusps of "^ See chapter on Morbid Growths. ABNOEMALLY FORMED TEETH. 61 this odontome remained distinct and each had heen separately erupted, they "would have heen called super- numerar}- teeth. Indeed, many of the cusps can he easily detached from the main mass. This strange specimen serves to bridge the gap hetween ^vhat he calls compound fillicular cysts and composite odontomes. The sole treatment available in each variety of the above described abnormalities is extraction, an operation "vvhich is of course not called for unless the faulty tooth is unsightly, a cause of deformity, or of disease. 62 lEEEGULAEITIES OF THE TEETH. Irregularities of the teeth may, to facilitate des- cription, be divided roughly into two great classes. 1st. Those in which teeth occupy abnormal positions in ^well-formed jaws ; 2nd, those associated with mal- formation either of the alveolar border or of the body of the jaw. The first class of irregularities rarely occurs in the deciduous set, for the reason that in this case a chief cause of irregularity — obstruction by preceding teeth — is absent. Instances of the second class in the infant, although seldom manifest to casual observation, are often perceptible on careful examination, especially when the deformity affects the jaw generally. Irregularities of the temporary teeth, whatever their character, are, however, of little practical importance, since the teeth are shed in early life, and the deformities do not call for treatment. Irregularities of the First Class. — It was ex- plained in a previous chapter that, during the process of eruption the teeth are not closely embraced by bone, and that it is not until some time after the crowns have fully emerged from the wide orifices of the crypts that the alveoli become fully formed, and invest closely the necks and roots of the teeth. During this stage of growth, when the advancing teeth are surrounded only by soft, readily yielding tissues, any slight obstacle to their progress suffices to deflect them from their proper direction, and to retain them in a wrong position. The most frequent of such obstacles consists of temporary IKKEGULARITIES OF THE TEETH. 63 teeth, or decayed portions of temporary teeth, which have retained their places, after the time at which they ought to have been cast off. The most common example of this kind of irregularity, is illustrated in fig. 55, from Tomes Fig. 55. (21), where the permanent incisors of the upper jaw are seen to occupy a posterior position, owing to the per- sistence of the temporary teeth. A corresponding irre- gularity occurring in the lower jaw, is shown in fig. 56. Fig. 56. By similar causes teeth may be rotated upon their axes, crowded together so as to overlap, or deflected in almost any direction. Other causes of this class of irregularities are to be traced to injuries, which may be due to blows upon the mouth, or may be inflicted during untimely extraction 64 lEEEGULAEITIES OF THE TEETH. of temporary teeth. Supernumerary teeth form a fre- quent cause of irregularity. Then again, inflammation and alveolar abscess connected with a temporary tooth may cause displacement of the developing permanent successor ; whilst lastly, some cases of simple displace- ment of one or more teeth in well-formed jaws can only Fia. 57. be ascribed to remote causes acting during development. Some in the latter category are undoubtedly hereditary — malposition of one or more in a set of teeth forming often a characteristic trait common to several members of a family. But the causation of irregularities of the class under discussion is, it must be acknowledged, often as difficult or impossible to discover as that of total Fig. 58. displacement of teeth buried within the bone, described and illustrated in a previous chapter. IRREGULABITIES OF THE TEETH. 65 • Figs. 57 and 58 illustrate the typical variety of irregularity ultimately resulting from unchecked progress of the condition shown in fig. 55. Upper front teeth fully erupted inside the normal line pass on closure of Fig. 59, the jaws within instead of without the lower incisors, and the teeth being held in malposition by the bite," a deformity is produced, which can only be overcome by the mechanical treatment presently to be described. Fig. 59, from Quinby (11a), illustrates general irregu- larity of incisors and bicuspids. Fig. 60, from Salter (12), shows a rare example of displacement of the upper canines, which appear within the dental arch and pos- terior to the persistent temporary canines which hold their places. Figs. 61 and 62, ^he latter from Quinby, show typical irregularities of upper canine and bicuspid. Fig. 63, from Wedl, exemplifies irregularity caused by presence of a supernumerary tooth (a) and a retained temporary tooth — the canine (d). The right permanent * The arrangement of the upper and lower teeth when in com- pletely close contact is termed the '* bite." 5 66 DENTAL SUEGEEY. central incisor (6) is displaced upwards and forwards ; the lateral incisor (c, too large in the drawing), is twisted on its axis, and the permanent canine (e) pushed out- wards. Other examples of this first class of irregular!- Fig. 60. ties are shown in figs. 77, 78, and 81 from Quinby, figs. 82 and 84 from Mason (9), and in fig. 89 from Talbot (22). A very fruitful source of irregularity is untimely ex- traction of temporary teeth, and therefore the first thing Fig. 61. to be avoided by the young practitioner is unnecessary interference of this kind. It is very easy to sweep away temporary teeth and to produce a transient improvement in appearance ; but it may be laid down as a rule sub- ject to rare exceptions that it is extremely bad practice to extract any temporary tooth for the cure of irregu- IKREGULAEITIES OF THE TEETH. 67 larity unless it be a direct cause of displacement, or form an evident obstacle to the regular advance of its proper •permanent successor. During the progress of second dentition, in most instances a child's mouth necessarily presents a more or less unsightly appearance, and the Fig. 62. parents over anxious and ready to imagine that every passing irregularity may become a permanent de- formity, ^Yill often urge that treatment should be com- menced. Clear explanation of the nature of the case, and of the advantage either of delay or of total non- interference when one or other of these may be the proper course, will bring the young practitioner in the end more credit and profit than he could derive from any less ingenuous line of conduct involving the wanton infliction of unnecessary pain and injury upon the patient. Each tooth ought to be left until the last moment at which its presence can be safely allowed. Absorption of the roots progresses rapidly from week to week as the time approaches for shedding of the teeth. It is both right and expedient to spare a child unnecessary pain and terror. To push or pick from its weak attachment the crown of a temporary tooth of which the roots are completely absorbed need neither excite fear nor give appreciable pain ; both of these are likely when the use of instruments becomes necessary. 6$ DENTAL SUEGEEY. The evils as well as the benefits which may arise from- premature removal of temporary teeth, will be perhaps brought out more clearly by examination of some par- ticular instances. In the case shown in fig, 55 it would be right and expedient to extract the temporary central incisors even if still very firm, immediately the eruption of their per- manent successors were impending; but the like haste- would be by no means called for in the similar condition affecting the lower jaw seen in fig. 56. In the one case delay might lead to an irregularity incapable of sponta- neous cure (fig. 57) ; in the other case the normal posi- tion of the lower incisors being within the uppers, the obstructing temporary teeth might with safety be left. for a much longer period with the certainty that in the end the displaced teeth would assume the correct position. In neither of these cases would extraction of the tem- porary laterals be expedient for the purpose of increasing the space available for the forward movement of the centrals. Whatever relief might be given to the centrals,, the effect of this operation would probably in the end be to give rise to more serious irregularity of the laterals,, which deprived of room, would be forced backward or seriously deflected in some irregular direction. IKBEGULARITIES OF THE TEETH. 69 Untimely extraction of the temporary canines is usually a very injm'ious procedure. The operation is one which is very often improperly performed at the urgent request of parents who, whilst ignorant of the evils which result from ill-timed interference are anxious to •avert a deformity w^hich may seem imminent. The -first bicuspids come into place from one to four years before the permanent canines. The effect of removing •temporary canines soon after the appearance of the per- manent laterals to relieve what is often only transient ■crowding of these and the central incisors, is to allow the first bicuspids to move gradually forw^ards until they come into contact with the permanent laterals, thus occupying the places which should be filled later on by the permanent canines. This happens in almost •every such case but with more certainty in undersized jaws, and here in the end the mischief is commonly most serious. The ultimate result is that the permanent canines being excluded from their proper places become erupted more or less high up externally over the position through which they ought to descend, and in conse- quence occasionally assume so faulty a direction that their regulation becomes difficult, or even their extrac- tion becomes necessary. In the lower jaw^ a correspond- ing condition may be in the same way induced. To make room after this mismanagement, sacrifice of per- manent teeth which might perhaps have been avoided had the temporary canines been preserved for thek full period, will be called for. In the majority of well- managed cases where owing to lack of space there is on completion of dentition merely general crowding as in fig. 70 and no other irregularity the only treatment called for is, as a rule, extraction of a first permanent molar or bicuspid at each side as soon as the second molars are fully erupted. A case of this kind will usually right itself in from a few months to a year by 70 DENTAL SUKQEEY. the gradual spreading of the whole set after room is afforded. On the other hand, in instances aggravated by untimely extraction of the temporary canines long mechanical treatment may become necessary unless in- stead of the molars the first bicuspids are removed ; but if the bicuspids as so often happens are sound and the molars badly decayed, the last named procedure can hardly be entertained. The extraction of permanent canines unless they are hopelessly mal-placed is unjus- tifiable, for these teeth are relatively among the strongest of the set and they contribute much to the character and symmetry of the front of the mouth. Mechanical treatment — long and tedious — which might have been avoided, thus becomes often, in these cases, necessary not only to force the canines in the desired direction,, but as a preliminary step to make room by pushing back, the bicuspids which may have besides become locked in their too forward position by the bite. It is, therefore, clearly preferable to allow continuance of considerable irregularity of the permanent incisors for a time rather than relieve it by removal of the temporary canines ; for in any case in which the irregularity might be likely to remain after childhood it would not be cured by the operation, but on the contrary, the general condition of the set must be in the end made worse. Cases of an opposite character, in which evidently nothing but good could arise from removal of the temporary canines arfr exemplified in figs. 60 and 63. Too early extraction of the temporary molars gives. rise to evils similar to those just described ; for then the first permanent molars move forward as they are erupted and encroach upon the space which should be occupied by the bicuspids, which appear later. This no doubt, besides causing displacement of the bicuspids, sometimes leads to crowding of the whole front range of teeth. lEREGULAKITIES OF THE TEETH. 71 There seems good reason to believe that during untimely extraction of a temporary molar the bicuspid which lies in its crypt within the roots may be displaced. In this way the irregularity illustrated in fig. 62 might be ac- counted for. It has also been suggested that after premature extraction of temporary teeth the alveolus becomes filled up with dense osseous tissue, through which the permanent tooth when the period of its erup- tion arrives cannot penetrate and thus becomes deflected through the more yielding internal or external alveolar plate. Some of the evils which may arise from per- sistence of temporary teeth long after the period at which shedding ought to take place, were described in the chapter on dentition, and to these evils may be added the possibility of a permanent tooth being forced to take a course outwards or inwards through the al- veolar wall. Although it may be necessary to extract necrosed temporary teeth before their time for the relief of disease, the same rules apply to them as to healthy teeth in rela- tion to irregularity, and they must not be removed as a rule until the period at which they ought normally to be shed. The physiological process of absorption described in a previous chapter, by which the roots of deciduous teeth are gradually removed, ceases on the death of a root. The cessation of the physiological process is, how- ever, usually followed by absorption such as mostly affects dead teeth and bone, but this is slow and often ineffectual. Necrosed teeth and roots are therefore more than living teeth likely to be retained and form obstacles to the proper progress of their successors, and on this account they call for greater watchfulness. All the reasons against ill-timed treatment must be kept steadily in view, and yet while uncalled-for inter- ference should be guarded against with the utmost care, there need be no hesitation in extracting temporary teeth 72 , DENTAL SUEGERY. the removal of which is demonstrably necessary for the cure of irregularities. It is a somewhat popular belief that the premature extraction of these teeth may act as a cause of contraction of the jaw, and thus of subsequent irregularity of the teeth of the worst kind ; hence, as just pointed out, whilst some parents will urge treat- ment, others will strenuously oppose the performance of the most necessary operations. The belief is refuted by physiological fact as well as by practical experience. The growth of the alveoli of the permanent teeth (as ex- plained on a previous page) goes on quite independently of the temporary set, and cases are on record in which even after the premature loss of the entire temporary set the jaw attained its normal development and the per- manent teeth assumed their proper positions. A knowledge of the order in which the teeth are erupted and of the characteristics which distinguish the per- manent from the temporary set, will prevent the mis- take against which it is necessary caution should be exercised, of extracting one of the former instead of one of the latter. An error of this kind is, however, hardly possible, except in the case of incisors and canines. The permanent molars may be known from their posi- tion at the posterior extremity of the jaw beyond the range of the temporary teeth ; whilst the bicuspids may be easily recognized since no such tooth exists in the deciduous set. The permanent if present during the persistence of the temporary incisors will be found in the vast majority of cases behind the teeth which they re- place, and their cutting edges are serrated, whilst those of the temporary set by this time are worn smooth. The permanent canines may be distinguished by their great size in comparison with the corresponding temporary teeth, and by their position, which is external and pro- minent the root being marked by a vertical projecting ridge on the external alveolar wall. The occasional lEKEGULARITIES OF THE TEETH. is occurrence of anomalous cases must not however h& forgotten — rare cases like that for example shown in fig. 60 where the permanent canines have presented themselves within instead of as is usual without the arch. The presence of supernumerary teeth already referred to, forms an occasional complication which must not be overlooked ; and a neglected mouth in which numerous temporary teeth also are retained w^hilst the crowns of the permanent set are appearing through the gums in various directions will sometimes need close examina- tion, even by an experienced practitioner, before the real nature of the case can be determined. A very large proportion of cases of simple irregularity of one or more teeth spontaneously recover in the com'se of time when room is afforded for the movement of the teeth, and if they are not locked in their malposition by the bite — as for example in the cases shown in tigs. 57 and 58. The movements of the tongue, the pressure of the hps and the effects of mastication — all or either of these help to press the teeth in the proper direction to which they indeed tend in their natural growth. Unless, therefore, it be clearly evident that mechanical treatment is unavoidable — that the deformity cannot be mended, or may be aggravated by delay — the teeth are better left until about the twelfth year; or until the period at which the second permanent molars are in place. By this time it will have become possible to decide whether other teeth will need treatment and whether sacrifice of permanent teeth will be called for, and if so upon which the choice should fall ; and the preliminary necessary operations having been completed an instru- ment may be constructed to act at once upon all those teeth which need mechanical treatment. A tooth merely deflected in its course, the crown mal- placed, but the apex of the root in its natural position can in a majority of even extreme cases be in time drawn 74 DENTAL SUEGEEY. into its proper place. The nature of the case may be determined usually by careful examination, the outline of the root being often sufficiently indicated through the overlaying bone. The possible existence of dilaceration in these instances must be kept in view. Numerous instances, however, present themselves in which one or more teeth are so far displaced as to preclude^ the possibility of their reduction by any means to their proper positions. Such instances are specially those in which not only the crown, but the entire root is out of its normal position. Eor example, an upper canine being- erupted after the lateral incisor and bicuspid are in position, often presents itself external to and prominent over the space between these teeth, which is too narrow to contain it. When the direction of the canine is correct it will in time take its proper place if room be afforded, but should it appear in an oblique direction and with its root lying at an angle across the alveolar border and the apex far aw^ay from its right position, in the- direction somewhat roughly indicated in fig. 61, it is un- likely that it could be brought into the desired position even were mechanical treatment employed. In such cases the extraction of the malplaced tooth is the sole resource. An example of irremediable displacement of a bicuspid — a kind of irregularity which is also frequently met with in the case of other teeth is shown in fig. 62 from Quinby. In most cases where early mechanical treatment is called for, but particularly in the typical variety exem- plified in figs. 57 and 58, it ought not to be commenced until the crown of the tooth has well emerged. Before that period the crown will be too short to overlap suffi- ciently its lower opponents, and although it may be easily pressed forward it will probably relapse into its old position as soon as mechanical treatment is with* drawn. IRREGULAEITIES OF THE TEETH. 75 The main points in treatment of irregularities of the first class may be summed up as follows : — 1. Bearing in mind the cautions above given against indiscriminate and untimely extraction of apparently- obstructive temporary teeth, real obstacles, whether formed by temporary or supernumerary teeth, must be removed. 2. Unless fixed in mal-position by adjacent permanent teeth or rendered incapable of movement by the bite^ irregular teeth ought, after removal of obstacles, to b& allowed time to assume spontaneously their normal position, to which when free they always tend. 3. Mechanical treatment ought never to be commenced before the full eruption of the second molars, except in such cases as evidently cannot spontaneously recover, or in which after lapse of time no tendency towards im- provement is manifested. The principles of mechanical treatment being the same in all varieties of irregularity the two classes in this connection are discussed together on later pages. Irregularities of the Second Class. — Irregularities due to malformation of the alveoli or of the body of the jaws themselves have now to be described. It has been before stated that the normal dental arch is semi-elliptical in shape. The front portion of the figure, containing the incisors, canines, and biscupids, forms an almost perfect semicircle ; whilst the portions containing the molars continue the line backwards at each side. Flattening or contraction of this arch, or abnormal development of any part of it, necessarily gives rise to irregularities of the teeth. This class of irregularities is most commonly congenital, and at the same time often hereditary, a peculiar abnormality in the form of the jaws being in this manner sometimes reproduced in many members of a large family. It is not necessary to dwell upon the fact that the jaw of civilised races has in com'se of ages become 76 - DENTAL SUEGERY. greatly diminished in size, so that crowding and mal- position of teeth in consequence have become, especially in women, the rule rather than the exception. Deformity may exist in one or both maxillae, or may be confined to one side only of the bone. Deformities may be due to injury or other accidental causes. The almost marvellous manner in which the jaws (like other bones) may be modified in shape, especially during early life, by the continued application of force in one direc- tion, is not uncommonly exemplified in surgical cases. Fig. 6i. 'The sequel of extensive burns of the neck occasionally furnishes a striking instance in point. The cicatrix resulting from such an injury has a constant tendency to contract, and unceasingly drawing the chin towards the chest, causes the body of the jaw gradually to curve downwards. In cases from time to time met with, the curvature is so great that the alveoli are completely everted, and the teeth directed outwards, or even downwards. One of these cases is figured in the annexed engraving (fig. 64), taken from Mr. Tomes's work (21). Cases like this serve to show that any suffi- . c >. ^ .5 ^ ci ^ &4 QJ) S .U3 o .2 o ^' p ^ a> © ~l^ 02 %i hi 'i ^. ee 3 'S O >> ^ c5 I— 1 ^ %^ fee aT e- -d o X e3 o , o p a >-5 o 5 c <» 3 4H r^ 6 QJ -(J fe 03 1^ ci o J3 > -k3 O ■c c3 «2 •>> m c3 o 0) S -M 5 t». o c: (U o -M CO X r^ rO a ^ • o H *5 o o c3 o > , o r— • CO o 5 o o i—t iJ: a ,• •^ <^ ^.-Tn iD ^^ '-'JU C •" if^ o a, ^'■^' e4H o > Is c > rt K .2 o tc p '-*3 0) Si X TJ ~ > tv To follow Fig. OS. CI o o 3 ax ^g l-( To tottoio Fig. 100, o t-l To follow Fig. 102. J= X CAKIES. 129 vanced caries, but where the dentine is still far from broken down. The magnification ( x 650) is here large enough to allow micro-organisms to be clearly visible under the microscope, and many are distinctly indi- vidualised in the photograph. In this specimen they are mostly cocci. The dark-shaded patches are masses of organisms lying on different planes, so that to produce photographic distinctness of individual organisms is im- possible. In fig. 100 there is shown a section (x600), in which the tubes are mainly occupied by leptothrix. In the vast majority of carious teeth cocci form the great bulk of organisms within the tubes, and although leptothrix is invariably present on the surface it is only in rare cases that it alone occupies the tubes. In the photograph (fig. 101) are clearly exhibited the appear- ances of carious dentine at an early stage of decay. The less affected portions of such a section would present, to the naked eye, no evidence of disease. A similar section under a much higher power ( x 650) showing the point of junction of carious and healthy tissue is shown in fig. 102. Under this power micro-organisms are clearly differentiated, and in the photograph cocci (which pre- dominate in this section) can be distinguished. In fig. 103 is seen a transverse section of carious dentine (x650). The organisms are so closely packed that they cannot be differentiated within the tubes ; but in sec- tions like this many organisms can always be seen at points where the tubes are breaking down. The advance of organisms in caries may be likened to the progress of an invading army. On the surface are massed the main hordes, with smaller bodies pushed for- ward along every avenue (tube) ; whilst at the farthest limits of the invaded territory, beyond the sphere of decay distinguishable to the naked eye, a few narrow files of bacteria may be discovered by the microscope 130 DENTAL SURGEEY. penetrating like the advanced guard of an invading host. This simile was first suggested by Mr. A. Underwood, who also pointed out the fact that the tubes of dentine around the immediate sphere of decay were always penetrated by organisms before showing morbid changes recognisable without the microscope. It was noticed by the earlier dental pathologists that certain changes apparently take place prior to actual disintegration in that portion of dentine through which the disease is advancing, and which is situated im- mediately contiguous to disorganised tissue. This altered dentine which has a translucent appearance, is however visible only under a low power, and forms either a regular zone, or exists in isolated patches around the walls of the cavity. This phenomenon was once thought to indicate invariably a vital or patho- logical action, a natural effort to arrest the disease by calcification of the dentinal fibrils. It is found, however, that a precisely similar alteration occurs in caries of dead teeth and is always produced during the gradual softening of dentine by acid, and to this softening, and not to consolidation, the effect is due. Transverse sections of dentine at the deeper parts of a cavity, where carious action is in the incipient stage and before micro-organisms have penetrated, mostly exhibit in patches a peculiar appearance which has been likened to that which would be shown on section of a multitude of tobacco-pipe stems united by an intervening substance. This appearance also was once thought to indicate pathological activity, but it has been proved that it occurs in dead teeth, and can be produced by chemical reagents which render prominently visible the dentinal sheaths — the sheaths of Neumann. This appearance was first described by Sir J. Tomes, who characterised it in the manner which is here adopted. The drawing with which he illustrated his description is reproduced in CARIES. 131 fig. 101. The exact appearances presented under the microscope are shown in the photograph, fig. 105. Pain in Dentine during Caries and Reaction in the Pulp. — Enamel being devoid of sensibility, pain during caries does not begin before the dentine is affected, and it may be absent in the earlier stages of the disease. In these stages it is due solely to exposure of this sensi- tive tissue to sudden changes of temperature and pressure Fig. lOi. of foreign particles and contact with irritating substances. In the later stages of caries pain arises from the trans- mission of similar irritation to the pulp, leading to inflammation, when that stru cture is either insufficiently protected by a layer of dentine, or actually exposed . Finally, if the disease runs on, there is added the pain due to extension of inflammation from the pulp to the dental periosteum. The amount and character of the pain in all the phases. 132 DENTAL SUKGEBY. of caries are much diversified in different persons. In some individuals when dentine is reached, there is, almost from the beginning, constant pain of a dull aching character, which increases from time to time as decay advances into more severe attacks, whilst in others teeth are altogether destroyed without any suffering beyond slight occasional aching and uneasiness. It is the belief of many competent observers that carious dentine in some cases displays exalted sensibility — hypersesthesia. It has also been shown that healthy dentine may present at parts areas displaying unusual sensibility, apparently due to presence of an abnormal amount of organic structure. Although the possibility of hypersesthesia of carious dentine cannot be denied, my observation leads me to doubt whether it really occurs ; and its occurrence certainly cannot be in any case demonstrated. Perfectly healthy dentine is sensitive, and the sensibility is much greater in some teeth than in others, and greater in some parts of a tooth than in others. All observers recognise, for instance, that the tissue is as a rule more sensitive immediately beneath the enamel than deeper. In cut- ting through carious dentine it is very common to pass through a highly sensitive layer into tissue displaying less feeling ; but I have never observed the excitation of greater pain in this than commonly seems inflicted in many instances by excision of healthy dentine, whilst dentine the seat of incipient caries shows, as often as not, no increase of sensibility whatever. It is often difficult to distinguish pain referred solely to dentine from that which arises from irritation of a pulp when closely approached by decay. It is impossible to account fully for the difference in the amount of pain arising during the progress of caries through dentine ; but there can be no doubt pain is often due to irritation by vitiated secretions. The application of some substances — such as sugar— to carious dentine CAEIES. 133 notoriously excites pain. In some disorders of health, notably in pregnancy, for instance, where superficial caries so often gives rise to considerable pain, this may be presumably due to vitiated buccal secretions, such as in many of these instances are present. Mr. Arthur Underwood has clearly shown that where extreme sensibility of dentine exists it may, in rare cases, be traced to the existence within the tissues of what he styles " aberrant filaments " — anomalous nervous filaments — radiating from the surface of the pulp even as far as the deep surface of the enamel. On the other hand, he has pointed out that in some cases the pulp may be insufficiently innervated, so that not only the dentine, but the pulp itself displays little sensibility. Leaving out exceptional cases it may be broadly stated, however, that in the vast majority of instances there comes on from time to time, after dentine is affected, slight attacks of transient aching, particularly after entry into the cavity of irritating substances, such as sugar and salt, and a smart pang slowly subsiding is often inflicted when a hard fragment of food is forced in during mastica- tion. The pain of this phase of caries is never of a throbbing character. The etiology, symptoms and pathology of irritation and inflammation of the pulp and of dental periostitis asso- ciated with caries are discussed in a later chapter. It may be repeated that the most severe pain which arises during the progress of caries is due to inflammation of the pulp. It is by the extension of this inflammation that the dental periosteum becomes involved. It must, however, be here noted that reaction in the pulp and vascular connections of the teeth are not necessary accompaniments of caries as they would be if this malady were of inflammatory origin. When they occur they arise in the later stages as the results — the sequelae — of the disease, and they take no part in pro- moting or retarding the destruction of the hard tissues. 134 DENTAL SUKGEKY. There need be no difficulty in believing that during progress of caries irritation may be communicated through the dentinal fibrils, and that in some cases the stimulus may excite calcification of the pulp. This. beHef is sufficiently supported by the fact that an occur- rence of this kind is very common where sound teeth, in the course of years, become worn down by attrition, until the level of the pulp chamber is reached. In these cases the pulp almost invariably becomes converted into dentine over the surface in danger of exposure ; and the new-formed tissue coalesces with the surrounding dentine, and is evidently the result of a natural reparative effort. It is, however, very rare indeed to meet with protective calcification of this kind in caries. There are few, if any, specimens in the museum of the Odonto- logical Society, and though I have examined a vast, number of carious teeth in hospital practice, I have never encountered a single example. It is very common ta find isolated nodules of secondary dentine in the pulp of carious teeth, but such nodules, are almost equally common after a certain age in teeth perfectly free- from disease. Cement in Caries. — Dental caries very rarely, if ever, has its starting place in cement, although the disease very often begins at the necks of teeth, in close contiguity to this tissue. Cement may become necrosed through stripping of its periosteum during inflammation, and the roughened surface, if exposed, at the neck of a tooth might, by giving lodgment to debris, lead to caries of the underlying dentine. Cement, be it recollected, is identical in structure with bone, but it forms so thin a layer until the apex of the root is approached, that it has. little effect in influencing or modifying the progress of caries. It must also be remembered that cement is. capable of pathological activity, and any morbid| pheno- mena which it displayed would not be analogous to caries in enamel and dentine. CAEIES. 135 Owing, no doubt, to the vitality of cement and its in- vesting periosteum, decay advancing along the exterior of a tooth usually becomes checked at the border of this tissue. The walls of roots hollowed to the depths by decay thus often remain until the supporting dentine within being nearly destroyed, the thin external shell enveloped by cement, becomes gradually crushed in or broken down. Spontaneous Arrest of Caries. — Cases of spon- taneous arrest of caries were alluded to further back, when it was implied that in rare instances the disease might come to an end without treatment. Such cases are of the following description : — The decay occasion- ally commences on the grinding surface of a tooth the external portion of which alone is of inherently defective structure. The occurrence is most common in honey- combed teeth, particularly in the first permanent molars. The decay spreads over the whole of the ill-made enamel composing the masticating surface, which gradually breaks down until the denser, better formed dentine beneath the defective tissue is laid bare. The surface so exposed being more or less used in mastication, con- stantly swept by the tongue and washed by saliva, becomes in time worn smooth and highly pohshed, and frequently endures for many years in that condition without any renewal of disease. The surface of dentine thus laid bare, often from the first, shows little sensi- bility, and in time frequently becomes insensitive. It is possible that in these cases, as in the analogous condition produced by simple wearing down of the teeth from attrition alone, the pulp becomes calcified over the vsurface towards which the waste of tissue is progressing. It is not uncommon to find caries on the mesial and distal margins of molars in the situation where foreign particles lodge, whilst over the greater part of the surface exposed to friction decay has become sponta- neously arrested. 136 DENTAL SURGERY. Epitome of Researches. — A large number of ob- servers have demonstrated the fact, which is, however, very easy of verification by anyone, that acids which commonly exist in the mouth are capable of dissolving the earthy constituents of enamel and dentine. Many of the earlier investigators wrote at a time — not many years ago — when fermentation and putrefaction were believed to be purely chemical processes. Magitot's researches (8) were among the most valu- able of this period, and they are interesting as fore- shadowing future discoveries and presenting facts which, at the time, were inexplicable. He produced close imi- tation of caries by submitting teeth — sometimes protected at all but one part of their surface — to the action for prolonged periods of very dilute solutions of mineral and vegetable acids. He produced similar effects with fer- mentable solutions composed of sugar with organic matter. He incidentally proved that when an acid solution is kept from fermentation by the addition of an antiseptic, such as creosote, the enamel of an immersed tooth is entirely dissolved and the dentine gradually decalcified, but not entirely destroyed. We now know — what was not recognised at the date of these experi- ments—that the different results were due to the presence or absence of micro-organisms, the result being brought ■ about in one case by chemical action, in the other by putrefaction and fermentation. Magitot held the opinion that caries is due to purely chemical action. He believed that he had produced experimentally in extracted teeth all the phenomena of the disease except the zone of translucent dentine. He considered the zone indicative of vital reaction — an attempt at natural arrest of the disease by calcification of the dentinal fibrils. Leber and Rottensteia's work (6), written at a time when the study of bacteriology was in its infancy, formed a valuable and suggestive contribution, especially in directing attention to the development of one species of micro-organism in carious tissues, and to its effects in supplementing the action of acids. The initial stage of caries, they proved, is due to the solvent action of CARIES. 137 acid, and when a breach of substance has been pro- duced leptothrix penetrates into the interior of the tissues, and by proliferation, particularly in the dentine, occasions more rapid disintegration than would have been the case under the action of acid alone. They treated sections of dentine by staining with iodine, and demonstrated enlarged dental canals filled with what they described as minutely granular masses, composed of leptothrix and its developing elements. They clearly showed that masses of organisms proliferate within the canals and enlarge and distend them. They, in fact, described most of the phenomena which later discoveries have proved to be due to a great variety of bacteria, and they made a single mistake in classing all these as one species — leptothrix. They also proved that human teeth ■artificially inserted in the mouth, and also teeth manu- factured of ivory blocks, displayed when carious all the microscopic changes which earlier writers had regarded ■as proof of a vital process in dentine. Leber and Eottenstein's illustrations of sections of •carious tissue under low magnifying power, although somewhat diagrammatic, correctly represent the appear- ances. Professor Wedl,''' in his great work (28) on dental pathology, classes caries under the heading " Anomalies of the Secretions." Caries, he believed, has its origin chiefly in abnormal secretions of the gums, of the oral mucous membrane, and salivary glands. He looked upon the secretion of the gums as most active, this secretion coming in immediate contact with and often forming a viscid covering on the teeth. In consequence of decomposition of the secretions, mingled with organic debris, acids are formed, which extract the calcareous salts from the hard tissues. The tissues are passive * Written by one of the most distinguished professors of areneral pathology, this work is free from the narrowness so difficult for any specialist, however philosophical, to avoid. It is exhaustive, based on a foundation of original investigation beginning with anatomy, and it leaves no fundamental fact of any kind, no observation of any respectable investigator unexamined. To dispute the clearly stage of direct disintegration. During the latter stage the tubes become enlarged and varicose and filled with leptothrix, which also he believed was to be found in all the ramifications of the carious cavity, although he had not discovered its presence in the earliest stages of the disease. Although Wedl, who also wrote before the science of bacteriology had far advanced, did not posi- tively identify any form of micro-organism except lepto- thrix in carious dentine, he described the presence of minute bodies within the tubes, which he specifically referred to as highly suggestive of micrococci. It can hardly be doubted that these were really organisms of that kind, the presence of which is now easily demon- strable. Fig. 108. Wedl pointed out that, although the living pulp does react against external agencies, still the interpretation of writers, according to whom an inflammation of the pulp can manifest itself by pathological effects in the dentine, is incorrect. Pursuing this subject further, Wedl clearly explained that irritation and inflammation of the pulp, when they occur during caries, form a sequel to and are caused by destruction of dentine, and he showed that there are no grounds for ascribing changes CARIES. 141 in the dentinal fibrils to irritation of the pulp. The pulp seldom becomes implicated until the dentine has suffered a considerable loss of substance, and, indeed, in most cases is in no way affected until exposed to external irritation. Fig. 109. By an elaborate series of observations, completely illustrated by accurate drawings of the histological ap- pearances of the tissues, Wedl conclusively demonstrated that carious dentine of dead human teeth, and of artificial teeth made of ivory, presents the same appearances as are formed in ordinary caries, in respect of pigmentation, granular condition of dentinal fibrils, and thickening and varicose enlargement of the tubes. Figs. 108, 109, may be taken as examples of these illustrations ; these are sections of carious dentine x 500 from human incisors reinserted as artificial substitutes on a gold frame. Their accuracy may be gauged by comparison with the photo- micrographs on earlier pages. The difiiculty of drawing 142 DENTAL SURGERY. aud reproducing truthfully microscopical sections of this kind is of course extreme. It is now many years since Sir J. Tomes (21), basing his investigations on the exact knowledge of the dental tissues which his previous researches had largely helped to establish, demonstrated very clearly and laid it down as his belief, " that caries is an effect of external causes, in which so-called * vital ' forces play no part ; that it is to a great extent due to the solvent action of acids which have been generated by fermentation going on in the mouth, the buccal mucus probably having no small share in the matter ; and when once the disintegrating process is established at some con- genitally defective point, the accumulation of food and secretions in the cavity intensify the mischief by furnish- ing fresh supplies of acid." This opinion still remains unchanged. It has been confirmed and adopted by Mr. Charles Tomes (21), who, however, recognises the share which micro-organisms take in production of fermenta- tion — phenomena of which, for years after Sir J. Tomes first wrote upon caries, were regarded as purely chemical. The presence of globular masses of calcareous salts, which are sometimes found iu dentinal tubes near a carious cavity, and which were relied upon by some of the older writers as evidence of vital action, they regard as probably depositions from solution of salts, and they maintain that even if it were conclusively shown that dentinal fibrils become obliterated by calcification, this would not be absolute proof of vital action; for they point out that albumen, even when out of the body, is able to form with calcareous salts combinations having a definite structure. They show that all the appearances of ordinary caries may be traced in the tissues of human teeth which have been inserted in the mouth on pivots or plates ; and, therefore, inasmuch as no characteristic appearances can be found to distinguish caries occurring in living from that in dead teeth, the hypothesis of vital action in any way modifying the disease must be aban- doned in toto, and " dental caries cannot, strictly speak- ing, be said to have any * pathology.' " Mr. C. Tomes points to. the fact that caries occurs C-YEIES. 143 in the same mouth in teeth with and without living pulps, and he suggests the impossibihty of regarding such cases as belonging to two diseases ''in their very •essence different : that the caries of the living tooth is an internal inflammatory change, and that the caries of the dead tooth is an effect of external chemical and physical causes alone." He remarks that this difficulty has never been fairly faced by any advocates of the ^' vital" theory. Messrs. Tomes regard as the main predisposing cause of caries structural imperfections in the tissues ; and they recognise that the physical signs visible at the onset of the disease vary mainly in consequence of the disintegration commencing sometimes on an unbroken surface, sometimes on a surface the seat of congenital •defect. The other great predisposing cause is vitiation of the secretions of the mouth. The mucous membrane, when irritated or inflamed, throws out an acid secretion capable of injuring sus- ceptible teeth. They prove by experiment that this secretion is alone enough to give origin to caries. If a small pellet of cotton wool, or other foreign substance, be forced between two teeth, and left so as to press upon the gum, the secretion from the mucous membrane at that point will be found in the course of a few hours increased in quantity and strongly acid ; and it will be seen after a short time that the enamel of the adjacent teeth is undergoing slow solution. Messrs. Tomes point to the fact that, in a superficial cavity subject to friction of mastication and swept by the tongue, decay will be slow, or may even be arrested, if the friction be made more thorough and constant, by the breaking down of the low walls. On the other hand, the mere persistent retention of decomposing products in contiguity with the tissue, is enough to originate and keep up carious action. This they prove by experiment. With regard to microscopical appearances, Messrs. Tomes compare carious enamel to enamel which has been slowly decalcified, but it is pigmented in a manner that cannot be imitated artificially. The solvents in caries attack the axial portions of the prisms before the 144 DENTAL SUEGEEY. periphery. In the dentine they describe as one of the earhest changes enlargement of the tubes, which become dilated to many times their original dimensions, and the parietes of the enlarged tubes having undergone partial decalcification, the so-called "tobacco-pipe" appearance is produced. To Messrs. Arthur Underwood and Milles (25), of whose research (commenced some four years earlier) the fruits were presented to the International Medical Congress in 1881, belongs the great credit of haviug been the first thoroughly to investigate the subject of caries in the light of the then recently-established knowledge of the true nature of the processes of fermentation and putrefaction. They pointed out that although the old " vital " theory — the theory that caries is a real disease, a pathological process due to causes acting from within — had been abundantly disproved, yet the chemical theory — the theory which supposes mere solution of the tissues by acid — could not be considered wholly satisfac- tory. They proved that destruction of teeth by action of acids, without the aid of septic ageuts, does not result in producing naked eye appearances or minute tissue changes exactly like those occurring in true caries. Sec- tions of dentine so decalcified show disappearance of the matrix, but not enlargement of the tubules, and there is an absence of pigmentation throughout. They repeated and confirmed the experiment first performed by Magitot, who, however, at the date of his investi- gations could not, of course, account for the result — the experiment which proves that it is impossible to pro- duce artificially caries resembling natural caries when septic influences are excluded. They from this assumed that two factors are in operation in caries — the action of acids and the action of germs. Their theory they put forth rather as an amplification of the chemical theory than a contradiction. The work of decalcifica- tion, they proved, is entirely performed by acids, but the acids are generated by germs, which, as is now known, are essential to the processes of putrefac- tion and fermentation. These considerations led the investigators next to seek for the presence of organisms CARIES. 145 in carious dentine. They cut a vast number of sections from fresh carious teeth immediately after extraction without use of any softening or decalcifying reagent, and subsequently stained them with an aniline dye — methyl violet. Examination of these preparations under a one- eighth lens disclosed the fact that the tubes were in- variably infiltrated with organisms, for the most part micrococci and oval and rod-shaped bacteria. The accompanying diagrams (figs. 110, 111 and 112), =:- from Fig. 110. the Proceedings of the International Medical Congress, 1881, may help to show how clearly these observers described the morbid anatomy of caries. In decay in blocks of hippopotamus ivory worn on a plate, they observed similar appearances. These ob- servers also made a large number of experiments and established important facts. In teeth exposed to the action of weak acid with perfectty aseptic conditions, solution of enamel went on so loner as the acid was * Owing to a mistake of the draughtsman the rods in theso diagrams are depicted with square instead of rounded ends. 10 146 DENTAL SUKGEEY. Tinexliausted and then ceased. On the other hand, where extracted teeth were exposed to septic influences immersed in organic debris such as exists in the mouth, the action of the organisms (" which constitute a Uving factory of acid") caused gradual decalcification of the whole tooth and destruction of the organic basis of den- tine, the microscopical appearances very closely resem- bling those of natural caries. Mr. Underwood has shown that the "tobacco-pipe" appearance is not peculiar to caries, but is to be seen whenever a re-agent renders prominent the sheaths of Neumann. Fig. 111. By a simple experiment -cultivation of organisms derived from carious dentine, Mr. Underwood also demonstrated the fact that organisms cause the charac- teristic pigmentation of caries — several varieties of organisms produce special colours, some black, some brown, some green. Professor Miller (10), of Berlin, was the first investi- gator to follow the lines traversed by Messrs. Underwood and Milles. Dr. Miller first traced the derivation of the acid, the prime agent in caries. He demonstrated the CARIES. 147 presence in the mouth of an acid-formmg ferment of organic origin, and obtained a pm-e culture of the active organisms. He showed that these organisms, added to a fermentable mixture, gave rise within a few hours to formation of acid capable of decalcifying enamel and dentine. Fig. 112. By a series of experiments in production of caries artificially Professor Miller has carried investigation in this direction further than Messrs. Underwood and Milles. Tubes containing sterilised starch solution were attached to teeth within the mouth, access of saliva being allowed, and were left for six or eight hours. At the end of that time the contents of the tubes were found to display strong acid reaction, and this was easily proved to be due to fermentation with the presence of bacteria. By similar methods applied to dead teeth out of the mouth, Dr. Miller has produced artificial caries which cannot be distinguished by the microscope from true caries. Opposing Theories. — In a recent work'-^ I examined Dental Caries," second edition. 18S8. 148 DENTAL SUKGEEY. exhaustively all the theories promulgated in late years which go counter to the views on caries which I have set forth in this book. I quoted the authors extensively, and the quotations alone sufficed to show the worthless- ness, as well from a literary as from a scientific stand- point, of most of the writings. There exists altogether a vast mass of literature on the subject, out of which I selected what seemed most worthy of notice, but found that the greater part of it, when not purely fanciful hypothesis, consisted merely of the record of superficial impressions without foundation of demonstrable fact and unsupported by logical reasoning. These writings- would be quite unworthy of notice under ordinary cir- cumstances in any book which did not include among its readers inexperienced students. But unfortunately the writings in question have been put prominently forward, and without any indication of their real character, have been cited among recognised authorities in works ad- dressed to students. I have therefore felt constrained to notice here such arguments from these writers as could be put into shape — and I have done so as briefly and generally as possible — so that the intelligent student may gauge their value for himself, and -not imagine (as he otherwise might have done) that they had been passed over because unanswerable.* Theories which have been set forth either in early or recent times, and which would, if proved, show the * It is hardly necessary the student should trouble himself with fantastic theories such as that propounded and worked out at great length by the late Mr. Bridgman, and recently revived in America. Briefly stated, the hypothesis was to the effect that the dental tissues exist in different electrical conditions, and are liable under some circumstances — in conjunction with!. the fluids of the mouth — to develop a process of spontaneous electrolysis, resulting in de- struction of the teeth through disintegration (caries) of the enamel and dentine ! CAEIES. 149 falsity in part or entirely of the view which I have tried to make clear, may be divided into three categories. First, those that would make out caries to be a true disease, carried on by pathological action initiated within the tissues ; second, those admitting the disintegration of enamel and dentine to be due to external agents, but insisting that these agents are powerless without prior occurrence of morbid changes in the tissues, which lessen their power of resistance and predispose them to attack ; and thirdly, theories which admit that caries is entirely due to external agents, but maintain that the tissues — or at least dentine — are not passive under the process of disintegration, and assert that the process is accompanied by inflammatory phenomena, or some kind of vital reaction. I am, however, not aware of any modern author bold enough to support the first of these theories in its entirety. This view is confined almost exclusively to obsolete works composed before the anatomy of the teeth had been clearly made out, or their physiology properly understood. Eegarded in the light of modern science, the opinions of the early dental pathologists are not more absurd than those of workers in other departments. It was first necessary, before exact knowledge of disease could be obtained, that complete acquaintance with the struc- ture of the tissues in health should be gained ; and this was impossible before the perfection of methods of his- tological investigation. It was natural for old writers, ignorant of the real structure of enamel and dentine, to look upon these tissues as more highly organised than we now know them to be ; to speak of their " vitality," to suppose that they underwent constant nutritive changes; to identify the phenomena which disease made visible in the tissues with similar effects in more highly organised parts, and to classify these appearances as inflammation, atrophy and gangrene — conditions to which they, perhaps, bore a superficial resemblance. 150 DENTAL SUEGEKY. It would be probably in most cases very unsafe to try to establish on a priori grounds alone the truth of an ex- planation of any series of morbid phenomena. But if the conclusive mass of evidence (set forth in previous pages) derived from observation and experiment did not exist, an argument based on consideration of the anatomy and physiology of enamel and dentine would alone suffice to prove that caries could be due only to external agents, and that the view which I have endea- voured to set forth must be essentially correct. The student cannot have failed to perceive that enamel and dentine are anatomically quite peculiar, and are not closely comparable to any other human tissues. In their physical and chemical characters they most closely resemble dense bone ; but even the densest bone is. permeated by a free vascular supply, while these have none. Between them and other avascular structures,. such as cartilage and the cornea, there is the vast difference that the latter are largely composed of cells, and are capable of carrying on physiological processes and of undergoing intrinsic degenerative and reparative changes. Enamel is totally devoid of any elements whereby physiological changes could be brought about in it. A tissue incapable of physiological activity cannot become the seat of true pathological change. Not only is enamel incapable of intrinsic changes, but it is not in relation with any physiological organisation capable of acting upon it from within. To believe in the possibihty of physiological activity in enamel, we must first believe that it contains the necessary elements, and next con- ceive some means by w^hich the calcareous basis could assimilate nutritive material when conveyed to it ; and we must then imagine the conveyance of new and effete material to and from the vessels of the pulp by way of the dentinal fibrils to its destination within the substance CAEIES. 151 of the enamel. To dentine the tissue with which alone enamel has relation similar remarks apply with almost equal force. The great bulk of dentine is composed of a homogeneous calcareous matrix, in which no trace of active cellular or other living structure can be detected. It is a tissue in which the minute fibrils alone can be said to possess any " vitality." Structures constantly undergoing physiological changes contain tissue elements whose activity is demonstrable. They require for their maintenance in health a proper supply of nutritive material from the blood, as well as provision for removal of effete material. It is from failure or perversion of necessary physiological activity of this kind, and by this means alone, that parts can be brought into a state predisposing them to disease, or actual pathological change can be produced in them. We have only first to think of the anatomy of a tooth as a whole, and of that of enamel and dentine in particular, and more especially to think of the structure of enamel — the starting place of caries — and then to realise the nature of the physiological factors necessary in the pro- duction of malnutrition or impaired vitality leading to pathological change — we have only to bring these things vividly before our minds to perceive the absurdity of a belief in the possibility of such morbid processes originat- ing in enamel. It is beyond all things necessary, before adoption of any theory, that its foundations should be proved abso- lutely secure ; and, as pathology must have its basis on anatomy and physiology, it is evident that no apparent pathological phenomenon irreconcileable with incontro- vertible facts of those sciences can be accepted as real. The account of caries given in this vvork starts from the established anatomical facts which are set forth in the opening chapters, and it has been recognised by the better class of recent writers, who have brought 152 DENTAL SUEGEEY. forward arguments in opposition, that it would be ne- cessary to overthrow those facts before a new theory- could be founded. An attempt to do this has been made. An American observer — referred to in an earlier X^age — stated some years ago that by staining the tissue with chloride of gold he had demonstrated the presence of active organic matter regularly distributed between the enamel fibres. And this observation has been held by some writers to prove the possibility of physiological and pathological activity in enamel. There are, how- ever, in the first place, grave doubts as to the correct- ness of the observation. It has neither been accepted nor confirmed by authorities, and from the result of my own researches I have no hesitation in denying its correctness. In this opinion I am confirmed by Mr. T. Charters White, one of the most accomplished dental histologists of the day. We agree in the opinion, founded upon careful obser- vation, that the amount of protoplasm between enamel fibres is really nil. The amount of organic material in enamel is altogether only from three to six per cent. It is in the vast majority of cases nearer the lesser than the greater amount. If even the whole of this material were '' active protoplasm " equally distributed, it must exist in a state of such extreme tenuity that it might well be disregarded as an agent. Mr. White has stained very thin sections of recently extracted teeth with chloride of gold, but while the contents of the dentinal tubuli were coloured, not a trace of stain could be de- tected between the enamel fibres under the higher microscopical powers.'-' The difficulties in believing in * It is possible to tint euamel in thin scetion with, chloride of gold, and a section thus coloured (by Mr. Arthur Underwood) is shown in a reproduction from a photograph on an earlier page. To stain the whole texture uniformly is, however, a different thing from differentiating protoplasm regularly distributed between the prisms. CARIES. 153 necessary nutrition of physiological elements in enamel have been already dwelt upon. Gallippe and Hoppe-Seyler both have made some observations going to show that teeth (enamel and den- tine) increase in density as age advances ; but these observations are incomplete and fallacious, and it would be unsafe to base conclusions upon them. Since indi- vidual teeth of a set in the vast majority of cases vary considerably in structural character, it would be neces- sary in order to prove alteration in density to cut sections from the same tooth at different periods of its existence. But even this experiment would not be con- clusive, for as we have seen, the density of different portions of a tooth may vary very much. The result of the experiment would be determined in accordance with the innate structural characters of the tooth. At one part it might yield enamel and dentine of the densest quality, at another it might yield tissue less dense owing to the presence of defective strata such as have been described on a previous page. An experiment which every dental smgeon performs in practice daily is without any other evidence almost alone enough to prove that not only enamel but also dentine is too lowly organised to be capable of physio- logical action. This experiment consists of the common operation of filling or stopping teeth. It cannot be believed that tissues so highly organised as the hypo- thesis in question supposes would passively tolerate the presence of a foreign body like a mass of gold or other stopping forcibly wedged into their substance. Relying upon the undoubted clinical fact that caries is very often started or accelerated during morbid states of the system, not accepting as sufficient the effects of the predisposing causes described in previous pages, and disregarding the experimental and clinical facts which negative the hypothesis, some writers argue that caries 154 DENTAL SUEGERY. must be influenced by causes acting from within. It bas^ been already explained that all the phenomena of caries, including appearances visible to the naked eye and those disclosed by the microscope, are to be observed not only in pulpless teeth and in dead teeth replaced in the mouth as artificial substitutes, but also in blocks of ivory used for the same purpose. And not only is this the fact, but the remote as well as direct causes of decay in these dead substances when worn in the mouth are precisely the same as govern the onset of caries in living teeth — teeth with living pulps and living periosteum. Dead teeth and ivory blocks are under similar conditions neither more nor less liable to decay in the mouth than their neighbours implanted in the alveoli. Some few years ago, before the general use of vulcanite, artificial teeth were much more frequently constructed of gold plates with human teeth mounted upon them, and it was a fact of common observation — one which I was able fully to verify — that the durability of this kind of work varied much in different individuals and under changing circumstances in the same individual. Every dentist recognised that their durability depended very largely upon the quality of the enamel and ivory of teeth and blocks employed; if these were of the most solid structure they lasted much longer than if inherently weak. Their durability depended, secondly, on the health and personal habits of the wearer. In a mouth habitually neglected and where the frames were allowed to remain for long periods coated with decomposing debris, the teeth and blocks were speedily softened and destroyed, whilst on the other hand where the mouth and teeth were kept scrupulously clean the beginning of decay was relatively less frequent and its. progress in like degree less rapid. A combination of bad health with neglect, giving rise to extreme vitiation of the buccal secretions, was with certainty accompanied CAKIES. 155 by destruction of the artificial teeth. It was proved, moreover, that when such dead teeth were attacked by caries decay began precisely in those situations where it would be most likely to attack a living organ — namely, in places favourable to the lodgment of decomposing par- ticles, and on surfaces where a solution of continuity allowed access to exposed dentine ; and that if cut sur- faces were finely polished, so as not to allow the ready adherence of debris, these surfaces would, like those of a living tooth under similar circumstances, be much less liable to decay. In short it was amply proved that dis- turbances of the general health and local conditions exercised the same indirect influence upon ivory blocks as upon living teeth, and the effects were traceable on- wards through the same series of events, namely, vitia- tion of the buccal secretions and putrefaction and fermentation of organic matter attended by development of micro-organisms, and formation of acids in the vicinity and on the surfaces of the teeth. To all this must be added the fact that no observer has ever produced a specimen of enamel and dentine in which degenerative changes were present. If in some systemic states teeth were to undergo softening or de- generation, owing to abstraction of their solid con- stituents through the vascular system, the morbid process would surely begin, if not always, at least very often on the surface nearest the vessels — in the dentine forming the walls of the pulp cavity. No such appear- ances have ever been detected, but on the contrary, where softening or disintegration of a tooth takes place, it is always progressive from the external surface, the situation where agencies exist capable of producing the effects. Some writers dwell much upon the occurrence of what they style acute caries, associated with general ill-health. A very common example is seen sometimes in patients 156 . DENTAL SUEGERY. subjects of long-standing chlorosis. A set of delicate teeth extensively filled, which have gone on v^ithout serious outbreak of decay from late childhood till beyond puberty, in such cases often suddenly show renewed signs of general decay ; well-made stoppings fail, and tooth after tooth is attacked by rapid caries. Precisely the same thing is often seen in women with delicate teeth during the child-bearing period. It must be recollected that a cause, however slight, if in action sufficiently long is enough to account for great effects, and ill-made enamel from the moment of a tooth's eruption is exposed to the constant or intermittent action of destructive agents. These cases of acute caries are fully accounted for by the action of the predisposing causes which have been discussed, and may be safely ascribed firstly to presence of innate structural defects in the tissues ; and secondly, to gradual solution of weak enamel by acid. It is easily conceivable that, in the course of months or years, patches of ill-made porous enamel become further weakened by gradual solution and allow readier access of acid-forming products, even into the substance of the tissue. Given such extensive areas of organically weak tissue, allowing infiltration of fluid and undergoing slow solution, and we can understand that a change in health involving vitiation of the secretions of the mouth and encouraging formation of acid, should often be accom- panied by rapid breaking down of the previously weakened enamel. Enamel inherently defective often covers dentine of equally bad formation ; and the enamel of ill-made teeth once penetrated by caries, the rapid destruction of the soft imperfectly calcified dentine which often follows need excite no astonishment. All these facts added to others given in previous pages, have not sufficed to prevent acceptation of the theory that caries may be brought on by changes in the CAEIES. 157 dental tissues arising from within. It may be impossible to prove the falsity of these views. The reader must form his own judgment upon the facts which I have tried to lay fully and impartially before him. The student conversant with the nature of inflamma- tory action — with the objective phenomena and the sub- jective symptoms which are comprised in the term inflammation — can hardly have failed to perceive that the physiological facts just discussed suffice to prove the impossibility of the occurrence of vital reaction of the nature of inflammation in dentine. The following facts may be recapitulated : Caries never commences in proximity to the vessels (on the walls of the pulp chamber), but always at the external surface, the point furthest removed from vascular influence ; signs of in- flammation, which invariably arise speedily in vessels bordermg avascular tissues the seat of inflammation, are absent in caries ; there are no tissue elements in dentine except the fibrils, which are capable of inter- stitial change ; caries goes on unaltered and with pre- cisely the same microscopical appearances when the pulp and therefore the fibrils are dead. If inflammatory corpuscles are present in carious dentine they must arrive there by traversing intervening dentine by way of the tubes from the vessels of the pulp — a supposition which is manifestly absurd. The sole observation which could support the belief in question is the doubtful fact that carious dentine in some cases displays hyperaesthesia. The errors of the few older although modern obser- vers, who have believed in occurrence of inflammation in caries, arose from misinterpretation of the significance of apparent changes in the tissues. The masses of organisms, for instance, in the dilated tubes of carious dentine readily taking up colour might possibly be mis- taken for inflammatory corpuscles by observers writing 158 DENTAL SUEGEEY. at a period before the existence of micro-organisms was suspected in such a situation, and before their real nature had been ascertained. It is scarcely credible, but nevertheless true, that in face of all facts and considerations an American writer* within late years has elaborately described what he styles inflammation of enamel and inflammation of den- tine, and has described the constant presence in carious dentme of ' ' nodulated protoplasmic bodies with nuclei and threads running from one to another," and states that in his judgment ''it is this living matter which has been mistaken for organisms." The publication of a statement of this kind seems hardly compatible with possession of an adequate know- ledge of microscopical and bacteriological science, for not only are the tubes in caries filled with organisms and only with organisms, the forms of which are per- fectly familiar to all competent observers, but each and all of them (except leptothrix, which will not grow transplanted from its peculiar habitat) can be separated, isolated and cultivated out of the mouth by the method now commonly practised by bacteriologists. By the per- formance of this simple yet crucial experiment this writer might have convinced himself of the falsity of his observation. Relative Frequency of Caries in different Classes of Teeth. — It is a remarkable fact, and one that has some practical application (as was seen in the chapter on Irregularities), that the teeth are not all equally liable to be affected by caries. Series of cases have been tabulated from time to time by various observers, and these agree in the main with each other. * This author must be taken as a fair sample of the class of writers just alluded to, and his statement as a specimen of the kind of fact upon Tv'hich theories have been based, and thea set out before students with a show of authority. CARIES. 159 Central incisors The following statistics of 10,000 cases collected by Magitot show the relative frequency of caries in the different kinds of permanent teeth. g^2 I Superior 612 [ Interior 30 rjr-rj { Superior 747 ' ' ^ \ Inferior 30 p;-j f. f Superior 445 ^^^ [ Inferior 70 1310J?T'^°^^ ^70 [ Inferior 370 1 Qi n J Superior 810 ^"^^^ \ Interior 500 qo-A J Superior 1540 "^■^'"^ 1 Inferior 1810 -irjor ^ Superior 690 ■^'"^^ I Inferior 1046 Lateral incisors Canines . . First bicuspids . Second bicuspids First molars. Second molars . Third molars . orc) \ Superior 220 \ Inferior 140 10,000 10,000 The first point which attracts attention in these tables is the great relative frequency of caries in the first molars ; the next the much greater frequency of the disease in the front teeth of the upper than in those of the lower jaw. The latter circumstance may perhaps be partly accounted for by the fact that the lower front teeth are protected from the action of acid by the saliva with which, owing to their position, they are constantly bathed. It must, however, be admitted that no entirely satisfactory explanation of the ratio of frequency in the several classes of teeth has yet been afforded. The localisation and the incidence of caries are certainly deter- mined mainly by the presence of inherent flaws in the enamel of the teeth attacked ; but we cannot yet account for the fact that certain classes of teeth are more than others the seat of these defects. 160 DENTAL SUEGEEY. • Diagnosis. — The Diagnosis of Caries is usually simple. In a considerable proportion of cases patients are aware at an early stage of the disease that a tooth is affected, and more especially where food is apt to. lodge in the cavity during mastication, or when decay begins on a part exposed to exploration by the tongue, which quickly perceives a roughened surface. But as many cavities are hidden, either under the free edge of the gum or in interstitial situations ; as caries of enamel is unattended with pain, and as neither exposed dentine nor exposed pulp is invariably accompanied by pain, it is impossible to be sure that caries is not active in a mouth without careful examination of the teeth. For this purpose a mouth mirror and dental searching probes are needed. The probes are thin and needle-pointed, and bent in curves to pass round the contours of the teeth. In examining a mouth for caries each tooth should be separately explored : its fully exposed surfaces, the neck under the free edge of the gum, and the mesial and distal aspects. In these latter places the greatest care is often required : the fingers are apt to be deceived ; small cavities are easily overlooked, or on the other hand a deposit of tartar or some other accidental roughness of outline, particularly along the neck of the tooth, may give a false impression of the existence of caries. In some few cases, to facilitate examination of surfaces in very close apposition, it is a good plan to press teeth apart by one or other of the methods described in a later chapter. The electric light in the form of a miniature incandescent lamp held within the mouth, which is now so commonly employed in dentistry is occasionally a useful aid in diagnosis. It renders the teeth semi-transparent and discloses discoloured surfaces in hidden situations. Some appearances on the surface of the teeth and conditions of enamel which simulate caries occasion- ally present themselves ; it is important they should not CAEIES. 161 be mistaken for decay. Patches of enamel of a yellow colom- or of a white or opalescent hue differing from the shade of the rest of the tooth are not infrequently met with as innate structural markings on perfectly sound tissue free from other blemish. These marks are to be distinguished by their hardness and polish and by the absence of other signs of caries. When on front teeth, the existence of these markings is often well known to patients, who are aware the spots have remained un- changed since the eruption of the teeth. Thin layers of hard black or brown tartar often simulate incipient caries ; careful examination will of course show the real nature of the case. Discoloured pits and fissures not the seat of decay may be mistaken for carious cavities. In teeth of the most delicate structure, and in inouths where caries begins early in life and attacks many of the set, it becomes a question sometimes, especially when the patient is not kept under frequent observation, whether it may not be better to anticipate the onset of decay, and prepare and fill all fissures, whether carious or not, which give a lodgment to decomposing debris. Such a procedure would be quite unjustifiable in dealing with a set of strong teeth little affected by caries. The depths of the sulci between the cusps of molars and bicuspids are in a large proportion of teeth, the enamel of which is of first-rate quality, more or less stained and often have the appearance of decay. By careful exploration with a sharp-pointed probe it may be ascertained whether softening exists. Such discoloured lines often endure through life free from decay — some- times they become gradually obliterated as the surface is worn by mastication. Every now and again, in one or another tooth, a fissure or a pit with smooth rounded walls will be found which is evidently merely a depres- sion in the contour of the tooth, being covered with 11 162 DENTAL SUEGEEY. dense polished enamel, although very often discoloured by deposit of tartar. Pits in *' honeycombed " teeth are often of this character, and do not then call for im- mediate treatment. 163 PEEVENTION OF CARIES. The remote or predisposing causes of caries, fully- described in previous pages, are (1) innate structural weakness and defects in enamel ; (2) vitiation of the buccal secretions ; (3) crowding and irregularity of the teeth. The immediate cause of caries is the lodgment of acid, or of acid-forming debris, on the surface of the teeth or within defective spots — pits and fissures — inherent in the enamel. The prophylaxis of caries must be based on prevention of these causes. The origination of ill-made dental tissue is a large subject, which cannot be more than touched upon in this work. There is gradual decrease in size of the jaws and teeth through savage and primitive races to those of the highest civilised type, and there seems good reason to believe, although it has not been demonstrated, that the teeth are of relatively inferior structure ; but in this respect the dental development of the different civilised peoples seems to vary considerably.* Ill-made dental tissues are often hereditary, and struc- tural characteristics may often follow those of one parent only. Nothing is more common than to find, in members of the same family, teeth of one general type and quality, or teeth presenting in exactly the same situations flaws or patches of inferior formation. The * Professor Flower, after examination and measurement of many thousands of skulls, has constructed a dental index, and in this the average size of the teeth of the gorilla being represented by 50'8, the Tasmanian by 47"5, and other savage races holding intermediate positions, the European stands at iO'5. 164 DENTAL SUKGEET. effects upon the teeth of hereditary syphihs and also of stomatitis occurring during the progress of enamel cal- cification have been discussed in an earlier chapter ; and although the typical teeth of Hutchinson — the signi- ficance of which is unquestionable — are present in only a small proportion of undoubtedly syphilitic children, their occasional occurrence clearly shows the power of hereditary disease to influence the development of enamel and dentine. An intimate connection between dental mal-develop- ment and any other diathesis, besides the syphilitic, can- not be fully demonstrated, yet there are some of these constitutional conditions with which badly made teeth seem more or less associated. In this matter I am recording the results of my own observation alone. My experience goes to show that imperfect dental tissues are found in the majority of cases of scrofula. Phthisis is now known by no means to indicate invariably the tuberculous diathesis, and keepnig distinctions in view, I would say that ill-made teeth are not at all a constant accompaniment of any form of phthisis, nor are they especially noticeable in a majority of patients of un- doubted tubercular tendency. With rickets I have gene- rally found inherently defective teeth, I can in no way associate faulty tooth development either with the rheu- matic or gouty constitution. Indeed, with the latter both teeth and jaws are often of unusually massive and solid character. In view of our limited knowledge of the causation of degeneracy of enamel and dentine, what general measures can be suggested likely to lead to improvement in the quality of the tissues, and to aid in the prevention of dental caries? Such a general question can be answered only in general form. Whatever tends to improve the physical development of a race should cause a relative improvement in the structural qualities of the teeth. PREVENTION OF CAEIES. 165 It may next be asked can we, by treatment, influence beneficially the developing teeth of the foetus in utero, through a mother? The answer must be that little reliance can be placed upon treatment specifically directed to this end, and we must depend mainly upon measures for the amelioration of the mother's general health, and the eradication of any definite morbid con- stitutional taint. The treatment of these conditions is quite beyond the province of the dentist, although it is the duty of the dental physiologist and pathologist to ex- plain the laws which should govern treatment directed to the developing teeth. To show that defective teeth might occasionally result from deficient supply of the necessary pabulum through the mother, several cogent facts have been brought forward. It has been pointed out that in a pregnant woman the union of a fracture is slow, the inference being that the lime salts are all required for the formation of the bones of the foetus ; and this is borne out by the fact that osteophytes and bony thickenings sometimes present in the early months of gestation become absorbed as pregnancy advances and bone begins to form in the foetus. In presence of these facts a rule may be established that in every case of dyscrasia or cachexia during pregnancy, and particularly where there is a tendency to atrophy and bony wasting, there should be administered mineral nutrition, both through the medium of a suitable dietary and of the preparations of lime salts to be found in the pharma- copoeia. In previous pages the reasons have been given for the opinion that enamel once fully calcified is physiologi- cally unalterable, and if this opinion is correct it follows that after the formation of enamel any attempt to prevent caries by improving the quality of that tissue must be futile. The exteriors of the crowns of all the temporary teeth — from caries of which children suifer so 166 DENTAL SUEGEEY. much — are fully formed at birth ; these teeth can there- fore be influenced only through the mother. By this time the first permanent molars and the permanent in- cisors and canines are so far advanced in development that it is open to doubt whether treatment can have any effect upon the enamel. It is difficult to believe that any treatment could influence cases in which a strong hereditary influence proceeding from the father gives a bias to dental develop- ment. A mother with good dental tissues will often bear children with defective teeth having the closest resem- blance in form and structure to those of the father, who may be perfectly healthy, and in whom this may be the sole physical defect. When the child is born, syphilis and specific diseases will receive their appropriate treatment, whilst the well- known rules of hygiene are enforced for the improvement of the general health. We are ignorant of the actual causation of defective enamel. It cannot be always due to lack of lime salts, or the whole skeleton would in every case be equally defective with the teeth. But as uncertainty exists, it may be better to err on the right side — especially as the error would be harmless — and en- force the rule that in every case in which ill-made tooth tissues are likely to appear an attempt by diet and therapeutics should be made to supply to the develop- ing tissues the mineral constituents of which they may stand in need. This rule should, of course, especially be enforced in those diseases, such as rickets, in which the whole skeleton is ill-constructed. There is no diffi- culty in administering lime to an infant from birth. A child should have no food except its mother's milk, if this is of proper quality, up to at least the ninth month. Practically in the majority of cases this source is supplemented by cow's milk ; which, of course, with well-managed children, is diluted and prepared in the PEEVENTION OF CAKIES. 167 usual way to resemble human milk. It happens that lime water (liquor calcis) is found to be an admirable aid to the digestion of milk in infancy, and this can either be added to the supplementary food, or can be given separately. It is impossible, particularly when both causes are present, to determine in any case the exact share which inherently weak enamel and vitiation of the secretions severally take in causation of caries, and when discussing the association of ill-made dental tissues with certain diatheses, it must therefore not be forgotten that some of these diatheses have as a common constant accom- paniment vitiation of the secretions of the mouth. Thus one type of scrofulous subject — that with coarse features, muddy complexion, and long thick upper lip — has usually a chronic condition of congested buccal mucous mem- brane with secretion of viscid mucus. Again, rickets is often preceded and attended by a virulent form of acid dyspepsia. In this way the prevalence of caries is to be accounted for among certain individuals or portions of the com- munity whose physique and general health in other respects are not to a corresponding degree inferior, and whose dental tissues are not evidently of the w^orst struc- ture. For example, the constant presence of dyspeptic troubles in some classes of factory operatives is enough to account for the rapid tooth decay from which they suffer. Dyspepsia due to sedentary habits and improper dietary — superabundance of coarse food and alcohol — is so common in some of these communities that it is re- garded as a matter of course, and endured as one of those evils from which there is no escape. The broad facts must be kept in view, that without acid, without a septic condition of the secretions of the mouth, caries is impossible ; and that acid capable of dissolving enamel — and of more rapidly dissolving 168 DENTAL SUEGEEY. enamel in proportion as the tissue is soft and ill-made —is always being formed in greater or less quantity in every mouth in which perfect cleanliness does not uniformly exist. In combating this cause of caries, the patient's general health must first be considered. Probably every lapse from a perfect standard will be accompanied by a pro- portionate vitiation of the secretions of the mouth. The question of general health, is, however, for the physi- cian, not the dentist. But even with perfect health and perfect dental tissues, caries may appear if organic debris be allowed to remain and decompose in contact with the teeth. The first thing, therefore, in the prevention of caries is to ensure mechanical cleanliness by the use of tooth-brush and tooth-pick. A tooth-pick properly em- ployed is important. The use of those of quill or wood only should be allowed ; metal may scratch and break the enamel. They should be used at night to clear away remains of food from between the teeth, before they receive their final brushing. Where the teeth are crowded and are of delicate structure, the use of fine silk thread passed between the teeth and rubbed to and fro supersedes the tooth-pick. A simple inexpensive tooth powder calculated to do all that such a preparation can do to remove debris of food and to neutralise acid secretions may be composed of soap powder and precipitated chalk — about a drachm of soap to the ounce. To this may be added a few drops of carbolic acid or oil of cloves and of oil of eucalyptus. Care should be taken that the soap powder is fresh and of good quality, or a disagreeable flavour may be pro- duced. A more pleasant and efficacious mixture would be represented by the following — powdered Castile soap one to three drachms, boric acid two drachms, powdered orris root one drachm, precipitated chalk one ounce. With fastidious patients it is well to add perfumes PREVENTION OF CARIES. 169 which they prefer. Attar of roses, and oils of lavender, cloves, geranium and eucalyptus afford a choice, and with one or several of these it is possible to impart a delicate perfume to the powder and make it highly agreeable — an important matter with preparations in- tended for habitual use in the mouth. A dentifrice ought of course to be thoroughly triturated and re- duced to impalpable powder. In fevers and other diseases in which the patient is either too feeble or too listless to clean his teeth for him- self, this should be done by an attendant. In such cases, and in all those where great vitiation of the secre- tions is present, as in the zymotic fevers and the dyscrasia of pregnancy, extra means should be adopted to prevent putrefaction and fermentation in the deposits which form upon the teeth. Thorough cleansing of the teeth in this way will often suffice to prevent toothache, which in certain conditions — particularly during pregnancy — is sometimes clearly due to irritation of carious cavities by the products of decomposition. Perchloride of mercury is by far the most potent drug for this purpose, and may be used in a few exceptionally severe cases. A solution of a strength of 1 in 5,000 is antiseptically equivalent to a 2 per cent, carbolic acid solution, which latter, although not more powerful than needed to pre- vent fermentation, is too strong to be used as a mouth- wash. A not unpleasant mixture of perchloride can be made if one grain be dissolved in one ounce of eau-de- Cologne or tinctm-e of lemons. Of this a tea-spoonful is to be mixed with a wineglassful of water, and the mouth after thorough brushing of the teeth to be rinsed with it several times a day. The mixture approximates a strength of 1 in 5,000. Some patients complain of a lasting disagreeable metallic taste following use of the perchloride wash. To overcome this, and also to guard against the swallowing of even a minute quantity of 170 DENTAIi SUKGEKY. this very poisonous drug, the mouth may be well rinsed with warm water, or warm water to which has been added a little spirit of wine or eau-de-Cologne. Mouth- washes may be prepared with any of the antiseptics in common use — carbolic acid, chloride of zinc, or per- manganate of potash. Pleasant and efficacious lotions, may be composed of boric acid and tincture of myrrh, with lavender water and eau-de-Cologne, or tincture of lemons ; and all lotions are much more likely to fulfil the desired end when used with a tooth-brush, friction being necessary to cleanse the teeth from shreds of food and adherent mucus. Por this reason a powder, when it can be used, is to be preferred to a lotion, and in every case the importance of systematic sweeping and cleansing of the teeth and interstices by means of a thin flexible wooden or quill toothpick cannot be too strongly insisted upon. The third main predisposing cause of caries — crowding and irregularity of the teeth — has been discussed in pre- vious chapters. The measures which may be taken in prevention and cure of these conditions have been des- cribed ; and the danger of setting up decay by prolonged or careless use of regulating instruments having been sufficiently dwelt upon, calls for no further reference here. 171 TEEATMENT OF CAEIES. The treatment of incipient caries may be con- fined in some instances to cutting away the diseased tissues, polishing the surface, and leaving it of such a form that it may be readily cleansed, and may not allow the adhesion of decomposing particles of food. This pro- cedure is in imitation of the process of spontaneous arrest sometimes effected fortuitously during the pro- gress of the disease which was described on an earlier page. The treatment of caries by the simple operation of excision is applicable only in rare cases to the grind- ing surfaces of the teeth, but is commonly resorted to with success in dealing with decay of contiguous surfaces, especially those of the incisors and canines. The operation is performed under the most favourable circumstances when the enamel alone is affected, but it may be occasionally carried out with permanent ad- vantage even when the dentine has been penetrated to some slight depth. As a rule it should not be undertaken in mouths where chronic inflammation and sponginess of the gums prevail ; neither should it be proposed in any case when the carious surface ex- tends below the gum. At the level of the gum it is desirable in most cases that a portion of sound tissue should remain projecting from each tooth, so as to prevent the cut surfaces from again gradually falling into close apposition, which they are apt to do in crowded jaws. The rest of the surfaces should be left perfectly 172 DENTAL SUEGEEY. plane, and with such an inchnation towards each other that the space between teeth is V-shaped, the wider part so directed as to be easily accessible to the tooth-brush and to the tongue, and subject to the constant benefi- cial friction of mastication. In forming surfaces in this manner it is sometimes necessary to cut away a con- siderable quanity of sound tissue. The amount which may be safely removed varies with the size of the tooth, but it must be borne in mind throughout, that if too much be removed the tooth may be left unbearably sen- sitive, owing to near exposure of the pulp. In the case of incisors and canines the excision of tissue may be con- fined always to a great extent, and sometimes entirely, to lingual surfaces, the teeth being thus preserved from perceptible disfigurement. The instruments required in the operation consist of enamel chisels and files ; with the chisels — when applied in the direction of the enamel Fig. 113. fibres — the decayed tissue may be rapidly and pain- lessly broken down; with files of different degrees of coarseness the operation may be continued, and the surface made ready for the final polishing. This latter process is accomplished by rubbing the surfaces first with finely powdered pumice, carried on wet tape or on a strip of cane, to remove the file-marks, and afterwards with a strip of wet slate-stone, to make it perfectly smooth. The whole process of cutting and polishing is TEEATMENT OF CAEIES. 173 of course much more perfectly and easily performed with the dental engine and the wheels, burs, and discs with which it is provided. Fig. 113 (from Arthur) indicates the most favourable form in which the interstices of the teeth can be left after this treatment. The sensibility of exposed dentine, varying in amount in different cases, which often remains for a time after the operation, may be rapidly diminished by application of zinc chloride, and the use of a lotion containing spirit. One or two thorough applications of zinc chloride usually suffice to permanently deaden the surface. A small portion of solid chloride in powder, carried on a strip of wood or cane, may be rubbed over the moistened sm-face. A spirit lotion — rectified spirit or eau-de- Cologne ansvrer well — may be used to moisten a length of tape with which the surfaces may get a daily rubbing. The operation of stopping or filling/' — When, owing to its extent or to other circumstances, caries cannot be dealt with by the method just described, it must be treated by the operation of stopping or filling the tooth. This operation comprises cutting out the diseased tissues and forming the cavity for retention of a filhng, drying the cavity, and filling it with some suit- able material. It also includes pressing teeth apart in * The operation of stopping or filling teeth which forms a special complex branch of surgical handicraft, cannot be entirely learnt from books. Books can only supply instruction in general principles, with explanation of methods aud description of means of operating. Book knowledge must be supplemented by tuition at the chair side, such as is provided at dental schools. Upon this part of his educa- tion the student enters prepared by previous training in mechanical dentistry; and by this time — unless he is devoid of natural aptitude and has mistaken his vocation — his fingers will be so trained that the simpler operations of dentistry, when understood, may appear easy to him, and he will be prepared to profitably commence a course of operations on extracted teeth as recommended in the Preface to the First Edition. 174 DENTAL SUEGERY. order to gain access to cavities in interstitial positions. The operation of filling is conducted always on the same principles, but its details vary considerably according to the position, character, and extent of decay. The present chapter will be restricted to the treatment of cases in which the central chamber of the tooth has not yet been laid open by caries, and in which the dental pulp is free from disease.''' The operation of filling, throughout all its details, is much facilitated by the use of a dentist's chair, which allows the patient to be firmly and comfortably placed in the most suitable position, raised when a tooth of the upper jaw, and lowered when a tooth of the under jaw, is to be filled, with the head tilted forwards or Fig. 114. backwards, the face turned towards or from the operator, according to the position of the tooth and of the cavity of decay. The instruments used in excising carious tissues con- sist of enamel — chisels, drills, and excavators. The chisels are sufficiently described by their name, both as * To facilitate description more or less arbitrary division of the subject is necessary; but no student will attempt operations without thorough knowledge of the pathology, symptoms and diagnosis of the inflammatory sequels of caries. TREATMENT OF CAEIES. 175 regards their nature and use. They are made with blades of different sizes, bent at various angles, so as to reach the decay wherever situated. A set sufficient for ordinary use is shown in fig. 114. With them the I [.: I carious enamel of the walls of cavities can be speedily broken down with but little pain to the patient. The chisel should be held firmly with the handle in the palm of the hand, the thumb being lodged securely against the tooth to control the instrument and to prevent it from slipping. It should be applied in the direction in which the enamel fibres run. Dental drills are mostly of two kinds, the rose or bur- head, and the sharp-bladed drill. The cutting point of the rose-head forms a circular or conical file. It is used to open up the ragged orifices of cavities and to grind away the carious tissues within. Sharp drills 176 DENTAL SUKGERY. serve to open np small cavities and fissures in the enamel, to shape the cavity, and to cut retaining points, into which the filling is to be dovetailed. The general character of these drills is sufficiently exemplified in the selection depicted in figs. 115, 116 and 117. These drills and many other useful varieties of cutting, filing and Fig. 117. polishing instruments, are now usually employed in conjunction with the dental engine. This machine con- sists of a flexible shaft rotated by a band, which is driven by a treadle and fly-wheel. The extremity of the shaft which carries burs, grinding- wheels, drills and discs and cones of any desirable size and shape, revolves with great rapidity, and enables the operator to excise tissue with great facility, and speedily to reduce to smoothness the ragged or rough margins ; and afterwards to polish all surfaces with exquisite nicety. Wheels, discs and cones are illustrated in figs. 118, 119, 120, 121. All these shapes and patterns, and many others, are made in a variety of materials. For grinding TREATMENT OF CAEIES. -1 rrr It they are made of corundum of different degrees of coarse- ness; some having rapid cutting power, others, of finer texture fitted to reduce rough surfaces to smoothness Fig. 118. preparatory to pohshiug. For pohshing purposes they are made of wood and of vulcanised india-rubher, and are used with levigated pumice, and with chalk or whitening. Fig. 119. Others made of Arkansas stone produce a surface read}- for burnishing. Again mandrils are provided which carry small discs of emery and sand paper admirably adapted for polishing some surfaces, especially in narrow inter- spaces. 12 178 DENTAL SUEGEEY. Excavators serve to pare away dentine. They are made of all sizes, some with flat blades, some hoe-shaped, some spoon-shaped, and others sharp-pointed, and they are curved and bent at various angles to reach the differ- FiG. 120. ently situated cavities, and some to cut with a pushing, others with a drawing movement. Useful forms of ex- cavators are shown in fig. 122. With regard to the performance of the preliminary step in the operation of filling, at present under dis- FiG. 121. cussion, it may be laid down in the first place as a rule, subject to important exceptions to be mentioned further on, that the whole of the carious tissues should be removed. If the orifice at least of the cavity be not formed of sound tissue, decay will proceed unchecked after the insertion of the filling. The beginner is most liable to err, by too limited use of the chisel and excava- TREATMENT OF CARIES. 179 tor at the orifice, too free use in the depths of a cavity. It will be perceived at once that carious cavities are in form rarely either regular or symmetrical. Most often they assume an irregular star-shape, with numerous horizontal branches or carious channels running in ■different directions from the main cavity. If only one such shaft communicating with the exterior or covered with a thin shell of enamel be left, the durability of a stopping must of course be much curtailed. The danger of overlooking and leaving unsound enamel is greatest at the margin of the free edge of the gum, and more espe- cially in cavities on the mesial or distal surfaces. In these positions, although the difficulty of examining the seat of decay is great, the operator must satisfy himself that no unsound enamel remains. It is between the teeth and beneath the free edge of the gum that decay after filling is most apt to recur, for it is there that in spite of a patient's care particles tend most to lodge and -decompose ; and there that incipient caries if present i-s certain to progress. The more the tissue towards the neck of a tooth is excised the more diflicult it becomes to form a solid foundation for a stopping, hence the young operator may be tempted to leave enamel about the condition of which he may feel doubtful. 180 DENTAL SUEGEKY. To cut away solid tissue without sufficient reason is un- justifiable ; but to carry the excavation as far as the margin of the cement is better than to leave exposed a layer of partly decalcified enamel, certain to speedily break down. It very often happens that dentine beneath disor- ganised tissue appears stained to a brown or darker shade, whilst showing neither appreciable softening nor other physical change. It is seldom necessary to cut away tissue in this state ; but whilst it must not be forgotten that the nearer the pulp is approached by a filling the greater becomes the risk of loss of a tooth, it must be also borne in mind that very nice discrimina- tion is needed in leaving carious dentine in close proximity to the pulp. A pulp covered only by a layer of disor- ganised tissue must be looked upon as virtually exposed ; being accessible to micro-organisms and septic matter. In cases where there is a history of inflammation of the pulp characterised by occasional attacks of throbbing pain, diagnosis is easy; but this symptom is often absent. Before inserting a permanent filling the operator must strive to satisfy himself not only by negative evidence — absence of symptoms of pulp irritation and inflam- mation — but also by careful exploration that the pulp is in no sense exposed, and that it is covered by a layer of dentine in which caries is not and has not been active. In cases in which the pulp cavity is closely approached by decay and when the pulp is beheved to be free from disease the greatest care must be exercised to avoid lay- ing open the chamber, for if this accident happen the chances of saving the tooth are much diminished. When danger of the accident exists, the softened den- tine from the depths of the cavity must be slowly and cautiously removed, and for this purpose excavators with spoon-shaped blades should be used, to avoid the danger TEEATMENT OF CAKIES. 181 of a sharp point pluuging through the softened tissues, and through a thin layer of sound dentine into the pulp chamber. If it be found that excision of all the ajffected dentine cannot be accomplished without risk, a general rule may be laid down subject to the cautions ^nd reservations dwelt upon in previous paragraphs, that it is better to leave a layer of partly decayed tissue in the depths of the cavity. Carious dentine in the earliest stages of decay may be always left with safety in the deeper parts of cavities, for it can be brought into such a conchtion, and placed under such circumstances, as will prevent it from decaying further. Caries cannot go on without the influence •of external agents, and all that is wanted in the case in question is to harden the partly decalcified dentine by abstracting completely its moisture, to render it perfectly aseptic, and to protect it by a filling from the action of external agents. Partially disorganised dentine may be treated by filling the cavity with a plug of cotton wool, saturated with a solution of gutta-percha and tannin in chloroform, or gum mastic in spirits of wine, with a dressing beneath, and the whole being re- newed at intervals of a few days over as long a period as necessary. The dressing may be composed of ab- sorbent cotton with absolute alcohol and iodol taken up on the moistened pellet. In many cases the drying of the tissue by means of a hot-air syringe, aided by application of alcohol, will suffice. This process is described on a later page. There are no grounds upon which the deliberate ex- posure of a healthy pulp during the process of excavation can be justified. It is probable that a healthy pulp, <3xposed to the atmosphere alone, and no other irritation, will certainly pass into a condition of disease if not kept ■aseptic by art. This always happens in the case of a joint or other analogous structiu'e wounded in a like 182 , DENTAL SUEGEllY. manner. The condition of an exposed pulp may be fairly compared to that of the tissues exposed in such a wound or in a compound fracture. The difficulties of rendering an exposed wounded pulp aseptic, and of keeping it in that condition during and after filling operations are very great. These are spoken of under the heading of treatment of exposed pulp. On the other hand the existence of a layer of slightly affected tissue treated as described, and enclosed beneath a filling in the depths of a cavity, can be productive of no harm. If the tissue be cut away it must be afterwards replaced by an artificial substitute. The application of this is difficult, it often sets up irritation, and even w^hen of the most perfect construction it must be necessarily less adapted to its purpose than a layer of imperfect dentine. In previous pages the sensibility of dentine in health and disease was described, and the fact W'as mentioned that the sensibility (which depends on the existence of a living pulp) varies very much in different individuals. Excision of carious tissue is thus always a more or less painful operation. In most cases, however, it will be found that it inflicts no more than an easily bearable amount of pain, when it is done rapidly with instruments, thoroughly sharp. The suffering may be lessened in the few cases in which there appears hyperaesthesia or in which the patient cannot endure the pain, by a]o- plications w^hich diminish the sensibility of dentine. Amongst applications in common use may be mentioned chloride of zinc and arsenious acid. But these sub- stances, especially the latter, must be used always with extreme caution even in superficial caries, and being very apt to penetrate to the pulp and excite inflammation, they are entirely forbidden w^hen the pulp is nearly approached by decay. Sensibility of dentine may be most safely and effectually lessened during excision by the use of ab- TEEATMEXT OF CAKIES. 183 solute alcohol and the hot air syringe, as described in the section on drying the cavity. Excavation will then be best done with the saliva entirely excluded throughout the operation, although a very considerable effect may be produced by drying the cavity and applying alcohol at intervals. Some operators prefer to exclude saliva throughout the operation of excising decay ; and this plan answers well with sensitive dentine which needs obtunding. In excavating the tissues preparatory to the insertion of filling it is not only necessary to remove decay, it is necessary often to cut away a considerable amount of sound tissue to render access to the cavity sufficiently easy, and it is mostly necessary to modify the form of the cavity to adapt it for the retention of a stopping. It will be presently seen that with one exception no class of materials used in filling teeth adhere as cements to the walls of a cavity — they are all retained by either plugging, wedging, or dovetailing. The simplest kinds of cavities are such as after removal of the decay assume the form of a hole or trench with vertical walls ; and those which require most modification are such as have a narrow irregular orifice, and those which either wholly or partly take the form of a shallow saucer-shaped exca- vation. To pack a filling beneath the overhanging mar- gins of a cavity being often impossible, these portions must be, when necessary, freely cut away, whilst, as it is also impossible to fix a plug upon a shallow concave depres- sion, the walls of such a cavity must be rendered either vertical or slightly undercut, or retaining points must be formed. Eetainiug points are made by drilling small pits in different parts of the cavity. Into these pits portions of filling are packed, and to these portions more and more being securely joined, the whole mass is fixed immovably in position. The number, size, and depth of retaining points must be regulated according to the 184 DENTAL SURGEEY. circumstances of the case. They need never be very- deep, and of course due care must be taken in using drills to avoid laying open the pulp cavity. The annexed diagrams may serve to make this sub- FiG. 123. Fig. 124. Fig. 125. ject more clearly understood. Fig. 123 exhibits the aspect of the commonest form of simple cavity in the grinding surface of a molar. In such a cavity the over- hanging enamel would require cutting back to the extent shown by the dotted lines. A section of same tooth (fig. 124) through line A — B (fig. 123) shows about the extent to which decay in such a case usually extends beneath the enamel. Fig. 125 shows section of same tooth, and TEEATMENT OF CARIES. 185 illustrates the preparation of a typical cavity for filling with cohesive gold. The walls are slightly divergent towards the floor of the cavity, sufficiently to give a wedge shape to the filling. On the other hand the enamel walls are bevelled back at the orifice sufficiently Fig. 126. Fig. 127. to avoid leaving a sharp edge against which it would be difficult to pack cohesive gold without chipping the •enamel. If the cavity were intended for stopping with non-cohesive gold or any other filling, particularly amal- gam, the edges should not be bevelled back, but should Fig. 128. run in a line with the dentine walls. A thin edge of amalgam round the plug is likely, owing to the brittle- ness of the material, to gradually break away and leave a rough margin." Fig. 126 illustrates the preparation of a cavity when the * The materials used for stoppings are described ia later pai-a- jraphs. 186 DENTAIi SUEGEEY, decay is situated in the fissures of the crown of a molar. The dotted Unes indicate about the extent to which it is necessary to cut back the enamel walls. Pig. 127 shows the same cavity prepared. In cutting out such a cavity Fig. 129. care should be taken to leave no sharp corners; they should all be well rounded off, to facilitate packing of the stopping. Fig. 128 shows a cavity after excavation on the distal surface of an incisor. The cavity is of some depth towards its centre, but from that point slopes gradually Fig. 130. in every direction towards the lingual and labial margins,, and towards the cutting edge and neck of the tooth. It forms, therefore, a uniformly concave saucer- shaped cavity incapable of retaining a filling. Such a cavity TREATMENT OF CAKIES. 187 might well be prepared by giving it the form of a trench, as shown in fig. 129, with slightly undercut walls, render- ing it a little smaller at the orifice than within. The next diagrams illustrate the formation of retain- ing points. A cavity of typical character on the distal sm-face of an incisor is shown in fig. 130. After removal of the carious tissues it forms a shallow concavity, broad at the upper part and sloping and narrowing towards the cutting edge of the tooth, near vrhich point it terminates. Fig. 131. The preparation of such a cavity would consist, after slightly deepening the labial and lingual walls, in drilling- two pits (as shown in fig 131) in the upper aspect, and one in the lower angle, of the depth and in the direction indicated by the dotted lines. In the examples just illustrated the cavity is bounded by four solid walls ; in the following there are only three walls, and consequently the mode of preparation is modi- lied in some details. Fig. 132 is an example of decay occurring in the side of an upper bicuspid. In these situations, and particularly with cavities on distal surfaces of bicusj^ids and molars, it is generally necessary to cut through the crown in order to get free access to the cavity. Enamel forming the grinding surface of a bicuspid or molar, unsupported 188 DENTAL SUBGEEY. by a considerable thickness of dentine, will not long withstand the force of mastication even after insertion of a filling, and for this reason alone must be in many cases cut away. Small cavities, particularly on mesial aspects and where decay has not closely approached the masticating surface, may, however, often be effectually treated without cutting through that surface. The dotted lines indicate the extent to which it is usually necessary to cut back the enamel walls in the case Fig. 132. Fig. 133. K illustrated. This being done and decay removed, the cavity must be shaped as shown in fig. 133 and in sec- tion fig. 131. The floor of the cavity should be slightly wider than the mouth, and at the junction of the side walls with the inner one retaining grooves should be cut as indicated in dotted lines in fig. 133 and G in fig. 134. At the bottom of these grooves retaining points should be drilled (figs. 133 and 134, P P). The edges of the cavity should be finally rounded and well smoothed off. TREATMENT OF CAIIIES. 189 Figs. 135, 136, 137, illustrate the preparation of a cavity where a portion of the side and cutting edge of a Fig. 135. Fig. 13G. tooth are destroyed, and consequently part of the filling- has no supporting walls. Fig. 1137, The dotted hues in fig. 135 show the extent to which the enamel walls will have to be cut back in the prepara- tion of the cavity. 190 DENTAL SUKGEEY. Fig. 136 shows front view of tooth with cavity pre- pared showing the extent of tissue removed. Fig. 137 is a side view of same tooth showing cavity prepared. In preparing a cavity of this nature for gold, if after the removal of decay there is left only a thin shell of enamel unsupported by dentine at the cutting edge, it will be necessary to cut it away, as illustrated in figs. 136 and 137. A thin shell of enamel in an incisor or canine which would not bear the force neces- sary in packing gold, may often be preserved by use of plastic cement and gutta percha. In order to secure a gold plug in such a cavity it will be necessary to excavate an undercut groove all round. This groove should be cut in the dentine between the enamel and the pulp, so as to leave a supporting layer of dentine under the enamel and a protecting layer over the pulp, see figs. 137 and 152, in which the groove is marked G and U respectively. Three retaining points must then be drilled in positions indicated in figs. 136 and 137, marked AAA, care being taken not to ap- proach the pulp or crack the enamel. Preparation of the cavities of this type is designed to provide for fixa- tion of an immovable wedge-shaped mass of gold in the depths, upon which can be built more and more until the tooth is restored to its original form. The later section on gold filling will be further ex- planatory of this subject. Separating Teeth. — The difficulties which present themselves in dealing with cavities, which, being situ- ated on the contiguous surfaces of teeth, are neither fully visible nor sufficiently accessible, must be overcome either by free chamfering, or by temporarily forcing the teeth apart. The beneficial effect of permanently separating teeth was explained in the section on the treatment of incipient caries, and the procedure there described must be adopted in the majority of cases TREATMENT OF CAEIES. 191 preparatory to the filling of the cavities in question. In treating incisors and canines the plan described in the section on incipient caries must be adhered to, and the chamfering must be as far as possible con- fined to the lingual aspect of the teeth. This suffices in most cases to render the cavity accessible to the filling instruments from behind, whilst the labial sur- face remaining intact, the normal appearance of the tooth is preserved, and the filling, unless large, is ren- dered invisible to casual observation. The instances in which it is better to force the teeth temporarily apart are those in which small cavities exist in teeth — es- pecially front teeth — of otherwise sound structure, and where permanent separation would cause disfigurement. Sometimes the plan may be well adapted of chamfering the affected surfaces to some extent, and pressing the teeth apart in order to obtain the further space necessary for the use of the filling instruments. The temporary separation of front teeth — incisors, canines and bicuspids is easily affected by slipping be- tween them a strip of india-rubber, and allowing it to remain for twenty-four hours. A very slight amomit of pressure suffices for [the* object ; the rubber should not therefore be thicker than the space which it is