DENTAL PATHOLOGY AND SURGERY LONDON: PRINTED BY 8POTTISWOODE AND CO., NEW-STREET SQUARE AND PARLIA~MENT STREET BY S. JAMES A. SALTER, M.B., F.R.S. MEMBIER OF THE ROYAL COLLEGE OF SURGEONS, AND EXAMINER IN DENTAL SURGERY AT THE COLLEGE; DENTAL SURGEON TO GUY'S HOSPITAL NEW YORK WM..WOOD & CO., PUBLISHERS 56 AND 58 LAFAYETTE PLACE PREFACE. IT is just twenty-three years since I determined to devote myself to the practice of Dental Surgery as the profession of my life. Having previously practised surgery in its general and broader aspect, both in private and with hospital appointments, I was at once impressed by the too narrow and circumscribed view, which was comprehended by the literature of the speciality I had adopted. It had appeared to me that even eminent hospital surgeons were scarcely aware how serious are some of the maladies directly dependent on tooth-disease, and how largely the pathology of the teeth is associated with serious morbid changes in contiguous structures. The fairness of these remarks may be briefly illustrated by saying that'Warty teeth' had been mistaken for Exostoses of the jaw; that Dentigerous Cysts had scarcely been recognised, and that the external orifice of an outward-pointing alveolar abscess, dependent on a carious tooth, was. still constantly attributed to necrosed bone. Vi PREFACE. These are a few examples of a general imperfection of knowledge among surgeons. On the other hand, the pathology of the teeth themselves was very imperfectly investigated by dentists. The many morbid changes, both chronic and acute, which occur in the tooth-pulp, were either undescribed, or but imperfectly known. The same may be said of the series of tumours of the hard tissues of the teeth, now grouped together under the title'Odontomes.' And many more instances of the like kind might be enumerated. It appeared to me that there was a considerable field of surgery and pathology-a sort of debatable ground between that occupied by the surgeon and by the dentist-which was open to further research, and which would amply repay the labour of investigation. My appointment to Guy's Hospital, as Dental Surgeon, gave me abundant opportunities for prosecuting such researches. The population tributary to Guy's Hospital is immense, and the poor patients, whom I have there attended, have given me a rich reward in cases and pathological specimens-an ample return for any services I may have rendered them. The records of these, and those furnished by private practice, supplemented by communications and specimens sent me by kind friends, have constituted many single and serial papers, which have been published in the Transactions of learned Societies and in medical periodicals. The Medical and Chirurgical Society have published PREFACE. 911 some of my papers. Several have appeared in the'Transactions of the Pathological Society,' and more numerous communications have found publicity in the pages of the'Guy's Hospital Reports.' Others have been given to the profession in the' Archives of Dentistry' and the'Dental Journal.' When it was determined, some fifteen years since, to publish a large concrete work on Surgery, consisting of essays written by different authors, and which ultimately assumed the shape of the System of Surgery, so ably edited by Mr. Holmes, I was solicited to contribute the article on'Surgical Diseases connected with the Teeth.' This again appeared in 1870, much enlarged, in the second edition of that work. The present volume is a digested collection of all my previous essays and papers, arranged in the form of chapters; and several more chapters have been added to previously published matter. I have ventured to think that, after the many years devoted, not without some diligence, to the study of the pathology and surgery of the teeth, I should be justified, without presumption, in publishing my views in a distinct and authentic form; and I have thought it the more desirable to do so, as I have been incorrectly quoted-by high authority, and in some instances my scattered writings have been used without acknowledgment. In the following pages it will be found that some subjects are not considered which may perhaps be fairly held to belong to dental surgery. It would have been Viii PREFACE. easy to have supplied chapters on such subjects by compilation; but it has been my desire as far as possible only to express views and to record observations where 1 could do so with authority; or, at least, as the result of independent thought and investigation. And I have wished, too, that my book should be on Dental Surgery rather than on Dentistry proper. How far this work may be of benefit to others, I leave for them to decide. For myself, the researches upon which it is based have been a constant source of pleasure and of mental profit. My obligations are due to Mr. Christopher Heath for some of the illustrations in this book; and to Mr. Charles James Fox for much kind assistance in the revision of the proofs. S. J. A. S. CONTENTS. CHAPTER I. General anatomy of the teeth- Human dentition diphiodont-Structure of enamel, dentine, and tooth-bone-Enamel destitute of vitality-Dentinal tubers contain protoplasm-Dentine a sentient tissue-Tooth-bone laminated, and containing lacunse, non-vascular-Incremental lines in the hard tissues of the teeth-Soft contiguous structures-Tooth-pulp, Gum, Periosteum. Page 1-14 CHAPTER II. Functions of the teeth: mastication, touch, passive organs of speechModes of application of tongue to the teeth in articulation. 15-25 CHAPTER III. Supernumerary teeth: conical, and cuboid, mimicking normal teethSingle-fanged-Temporary and permanent-Treatment-Third sets of teeth, impacted teeth mistaken for-Recorded cases of —Deficiencies of teeth, partial and complete-Associated with baldness of hair. 26-35 CHAPTER IV. Irregularities in the position of teeth-Causes-Simple and contingent irregularities-Underhung jaw-Separation of the teeth in the two jawsV-shaped jaw-Transposition of teeth-Inversion of teeth-Treatment: by extraction, pressure with plates, cap-gag, elastic spring. 36-51 CHAPTER V. United teeth —Temporary and permanent-Union may occur with any contiguous teeth, partial and complete-Primary, dentinal, and congenital union: secondary-Tooth-bone union of fangs.. 62-60 X CONTENTS. CHAPTER VI. Secondary dentine: Dentine of Repair, Dentine-excrescence, Osteodentine — Intrinsic calcification of the tooth-pulp.... Page 61-72 CHAPTER VII. Congenital defects of Structure and Form-Rocky enamel-Imperfect calcification of dentine-Vascular dentine-Dentine replaced by bone-Large teeth-Small teeth-Supernumerary cusps and fangs-Curved fangsDilaceration of tooth-Syphilitic teeth. 73-82 CHAPTER VIII. Caries: its chemical and physical. characters —Acidity of caries —Isolation and dilatation of dentinal tubes in-Growth of Leptothryx buccalis onCauses, predisposing and exciting-Artificial imitation of caries-Relative frequency in different teeth-Treatment-Abscess in dentine-Red patches in dentine..... 83-98 CHAPTER IX. Mechanical injuries to the teeth-Surface wear (abrasion and erosion)Polish of surface-Peculiar forms of wear-Semi-transparency of dentine in —Dentine of Repair developed in worn teeth-Treatment-Fracture: simple, compound-Exposure of pulp-Treatment... 99-104 CHAPTER X. Necrosis of teeth: partial, complete-Death and decomposition of pulp-, Altered colour of necrosed teeth-Dislocation of dead teeth-Absorption of fangs-Treatment.105-108 CHAPTER XI. Odontomes: Congenital-Warty teeth, Hernia of fang, Enamel Nodules on fangs —Secondary odontomes-Exostosis, Deniine-excrescence-Literary history of warty teeth: structure of: partial and complete warty condition-Hernia of fang: variety of-Structure of tumour-Enamel Nodule on fang: essentially a submerged cusp-Exostosis, varieties of: general, nodular, vascular- Neuralgia from- Dentine-excrescence, structure of-Cases of neuralgia caused by.... 109-138 CONTENTS. Xi CHAPTER XII. Diseases of the tooth-pulp-Intrinsic calcification-Calcification islandsObliteration of all the soft tissues-Sphacelus and suppuration of the pulp-Rapid purulent solution of the pulp —Line of demarcation between healthy pulp and pus-Clot-filled ampullae of capillaries —Necrosis of pulp: Fatty decomposition of dead pulp-Polypus of pulp: its structure -Treatment-Sensitive sprouting of pulp: occurs after fracture of tooth-Treatment.. Page 139-158 CHAPTER XIII. Tumours of-the gum-Epulis: essentially fibro-myeloid: recurrent, but nonmalignant-Treatment-Polvpus of the gum-Fibro-mucous in character-Treatment-Vascular tumours: two forms —nsevus-like, and aneurisms-by-anastomosis-Treatment-Warty tumours: innocent and malignant-Other affections of the gum —Scrofulous ulceration, Syphilitic affections, True Scurvy, False Scurvy, Transparent Hypertrophy, Stomatitis in children..... 159-189 CHAPTER XIV. Congenital Hypertrophy of the gum and alveolar borders of the maxillee. Rarity of the disease —Treatment.. 190-195 CHAPTER XV. Impaction of permanent teeth in the substance of the maxillary bonesSeries of examples-Occasional results: neuralgia, maxillary abscess, enlargement of jaw-bone.. L96-208 CHAPTER XVI. Dentigerous cysts-Literary history-Series of examples-Caused by impaction of permanent teeth: rarelytemporary or supernumerary teeth —Fluid, serous, or sero-purulent, secreted by enamel pulp-Symptoms-Diagnosis -Treatment...209-225 CHAPTER XVII, Painful and difficult eruption of the wisdom teeth-Symptoms: pain, swelling, trismus —Burrowing abscess-Treatment-Maunder's Screw Gag..... 226-234 Xii CONTENTS. CHAPTER XVIII. Alveolar abscess —Gum-boil-Causes —Symptoms-Mistaken for diseased bone-Opening externally, varieties of orifice —Sometimes ending as a serous cyst-Diagnosis-Treatment —Large palatal abscess in childrenOccasional accompaniments-Erythema, Abscess in cheek, CarbuncleSuperficial gum-boil....... Page 235-245 CHAPTER XIX. Abscess of the antrum-Anatomy of the antrum-Essential nature of the affection-Causes-Complications: injury to the orbital nerves, blindness -Necrosis, of upper jaw-Treatment —Fang of tooth passing into the antrum......... 246-254 CHAPTER XX. Affections of the nervous system dependent on diseases of the teeth —Less common with permanent than with temporary teeth-Reflex, Direct and Mixed nervous affections-Facial neuralgia-General neuralgia-Brachial neuralgia-Trismus-Tetanus-Epilepsy-Brachial paralysis-Deafness -Perverted nutrition-Facial paralysis-Amaurosis. 255-282 CHAPTER XXI. Phosphorus disease: maxillary necrosis from phosphorus fumes-Literary history-A new disease, coeval with the manufacture of lucifer matches -Caused by oxidised phosphorus vapour, acting on exposed pulps of carious teeth-' Amorphous' phosphorus innocuous-Symptoms like ordinary bone-necrosis —Supplemental bone forming only when lower jaw is affected-Prevention of the disease-Treatment. 283-2~9 CHAPTER XXII. Necrosis and exfoliation of the alveolar processes and portions of the maxills after the attacks of the Eruptive Fevers-Relative frequency after smallpox, measles, and scarlet fever-Usually symmetrical-Narrative casesTreatment........ 300-312 CHAPTER XXIII. Syphilitic Alveolar Periostitis —Diffuse suppurative periostitis-Extensive bone necrosis-Narrative cases..... 313-317 CONTENTS. Xiii CHAPTER XXIV. Saliva: a compound fluid-Chemical characters-Microscopical and physical characters-Salivary calculus or tartar-Varieties-Chemical composition- Salivary gland duct stones-Effects - Operation of'scaling'.......... Page 318-322 CHAPTER XXV. Extraction of teeth-Circumstances necessitating the operation-Instruments employed: Forceps, Key, Elevator, Fang-dividers, Screw-Methods of use as adapted to individual teeth-Stumps-Stump-forceps. 323-334 CHAPTER XXVI. Casualties that may arise in the operations of tooth-extraction-Breaking a tooth; breaking jaw-bone; taking out a wrong tooth; taking out two teeth instead of one; removing capsule of growing permanent tooth in extracting its temporary predecessor; tearing gum; wounds produced by slipping of elevator; extracted tooth falling into the air-passages; ex, tracted tooth falling into the pharynx and being swallowed; crushing the inferior maxillary nerve; dislocating the lower jaw; breaking one tooth in extracting another; cutting lip in removing a jagged, extracted tooth; forcing a tooth or tooth-fang into the antrum; forcing a toothfang into an abscess excavation in maxilla....335-361 CHAPTER XXVII. Haemorrhage after extraction of teeth —Its diathetic character-Narrative cases —Vicarious with menstruation-Treatment: pressure, stypticsAlveolar tourniquets-Astringent medicines... 362-368 CHAPTER XXVIII. Cleft and Perforate Palates-Congenital and accidental-Congenital clefts the result of arrested foetal development-Varieties in degree-Single and double clefts-Absence of intermaxillary bones-Accidental lesions of palate: causes of-Literary history of mechanical appliances for remedying defective palates-Effects on voice of defective palatesTreatment: Radical cure, Obturators, False palates-Combinations to supply lost palate, portions of jaw and teeth-Narrative cases. 369-394 LIST OF ILLUSTRATIONS. FIGURE PAGE 1 Diagram of dentinal tube, showing the illusive ring round cut extremity...... 4 2 Decalcified dentinal tubes from tooth of Ancient Briton.. 3 Diagram of dentinal tube, showing its relation to caries and its source of nutrition.....8 4 Diagram of canine tooth, displaying' incremental lines' of the three hard tissues...... 10 5 Capillary blood-vessels of gum, as seen on the dental surface 14 6 Diagram of section of mouth, showing the relations of the teeth to the tongue in the formation of articulate sounds 17 7 Front of utipper jaw, with conical supernumerary tooth in itu. 27 8 Conical supernumerary tooth... 27 9 Supernumerary tooth with many conical cusps... 27 10 Minute supernumerary tooth from front of lower jaw... 27 11 Upper jaw, with two cubic-crowned supernumerary teeth in situ 28 12 One of these teeth after extraction,-posterior view.. 28 13 The same,-front view....... 28 14 Upper jaw with supernumerary united incisors.... 30 16 Superior bicuspid tooth, with minute supernumerary bicuspid attached......... 31 16 Irregularity of teeth in upper jaw, canine too high and too prominent i.. 38 17 Irregularity of superior incisors..... 43 18 Plate for regulating the same.. 43 19 Upper jaw with lateral incisor tooth placed obliquely. 44 20 Plate for regulating the same.. 44 21 Upper jaw, showing distortion and separation of central incisor teeth.... 45 Xvi LIST OF ILLUSTRATIONS. FIGURE PAGE 22 Upper and lower incisor teeth, with intersecting bite, in situ. 45 23' Cap-gag' for separating the jaws in contingent irregularities of the teeth... 46 24 The same, as fastened to the second lower temporary molar tooth........ 46 25 Plate for the treatment of intersecting, or underhung bite. 46 26 Upper jaw, with permanent canine teeth appearing in the palate, the temporary canines remaining in the dental arch 47 27 Plate for the treatment of V-shaped upper jaw.. 50 28 Upper jaw, exhibiting transposition of the left canine tooth between the two bicuspids.... 60 29 Superior canine and lateral incisor, exhibiting congenital union 65 30 Section through the crowns of the same... 65 31 Section through the fangs... 55 32 Microscopic section through the crowns of the foregoing specimen......... 56' 33 Fangs of first and second upper bicuspid teeth, united by hypertrophy of crusta petrosa (secondary union), seen in face 58 34 The same seen endwise... 68 35 Microscopic section of the foregoing specimen. 59 36 Diagram of canine tooth, in vertical section, showing the position of the several forms of Secondary Dentine... 62 37 Outline section of canine tooth, enlarged, showing Dentine-ofrepair in its relation to the primary dentine when worn away by friction.. 63 38 Outline section of superior central incisor tooth, enlarged, showing Dentine-of-repair induced by fracture of the angle of the tooth......... 655 39 Microscopic section of inferior canine tooth, showing Dentine-ofrepair, the result of friction-wear and caries. 66 40 Microscopic section of Osteo-dentine.,. 70 41 Portion of the same, showing the obliteration of the vascular canal in the axis of a single system of Osteo-dentine. 71 42 Teeth exhibiting rocky enamel.. 74 43 Microscopic section of canine tooth showing rocky enamel and imperfectly calcified dentine ~.. 77 44 Microscopic section of globular dentine... 78 45 Molar tooth. with perforations in the neck.. 79 46 Microscopic section of the previous specimen, showing cancellated bone in the crown and neck of the tooth.. o 80 47 Superior central incisor tooth, showing dilaceration of the fang; enlarged two diameters.... 81 LIST OF ILLUSTRATIONS. Xvli FIGURE PAGE 48 Front teeth of upper and lower jaws, displaying peculiar wearing of edges (after Bell). 100 49 Necrosed incisor tooth, exhibiting absorption on the fang, and dilatation of the root-foramen..... 107 50 FWarty molar tooth (after Wedl)..... 111 51 Upper lateral incisor tooth, with warty growth; enlarged two diameters......... 11 52 Microscopic section of the last specimen.... 117 53 A portion of one of the laminig from the warty growth, more highly magnified......... 118 04 Wisdom-tooth, from which a wrarty growth had been removed. 120 55 Section of the same, showing by a black bristle the communication between the warty growth and the pulp cavity.. 120 56 Upper wisdom-tooth with warty growth attached to the crown. 120 57 Upper lateral incisor tooth, with warty growth sprouting from the side of the crown...... 120() 58 Molar tooth, with' Hernia' of the fang..... 125 59 Section of the Hernia, showing its structure.... 125 60 Enamel nodule, or submerged cusp on fang of molar tooth. 12.9 61 Superior central incisor tooth with Nodular Exostosis on fang; enlarged two diameters....... 13 62 Microscopic section of the same....... 132 63 Superior bicuspid tooth with Cancellated Exostosis; enlarged two diameters......... 133 64 Microscopic section of the Exostosis...... 134 65 Dentine Excrescence in the pulp cavity of a superior central incisor tooth; enlarged two diameters..... 135 66 Microscopic section of the Excrescence..... 136 67 Crown of molar tooth, with the partially calcified fang-pulps attached..... 141 68 Molar tooth from which the crown has been removed, leaving in view the completely calcified pulp. 141 69 Partially calcified pulp, magnified eighteen diameters.. 142 70 Slightly calcified pulp, magnified forty diameters... 142 71 Portion of tooth-pulp in the last stage of calcification; magnified 200 diameters........ 143 72'Calcification Islands' from a tooth-pulp; magnified 200 diameters.......... 143 73 Calcification Islands on a plexus of nerves.....145 74 Calcification in the axis of a plexus of nerves... 145 75 Diagram exhibiting the arrangement of parts in suppuration and sloughing of tooth-pulp....... 149 a Xviii LIST OF ILLUSTRATIONS. FIGURE PAGE 76 The same in a more advanced stage.,,.. 149 77 The same occurring in a very slight degree in a temporary molar tooth........... 150 78 Minute blood-vessels from the sloughing fang-pulp of a tooth. 151 79 The same from the central chamber of a molar tooth.., 151 80 Molar tooth with Polypus of pulp.... 155 81 Upper jaw with Epulis tumour...... 161 82 Right side of upper jaw, with large Polypus of the gum.. 164 83 Upper molar tooth with pedunculated Vascular tumour attached 167 84 Papillary tumour from the lower jaw..... 169 85 Upper jaw with Warty tumour on the side of the hard palate. 171 86 Section of the same......... 172 87 Outlines of papillae from the foregoing specimen; enlarged six diameters...,.. 172 88 Warts from the gum......., 174 89 Another specimen of the same.. 174 90 Upper jaw, exhibiting Scrofulous Ulceration of the gum, with loss of incisor teeth........ 177 91 Spring for compressing bleeding gum..... 184 92 The same in situ, with ideal section of lower jaw... 184 93 Large congenital hypertrophy of the gums, and alveolar border of the upper jaw, seen on the palatal surface... 192 94 Section of a portion of the same, showing the papillary surface and an imbedded tooth...... 194 95 Lower jaw, with an impacted bicuspid tooth.... 197 96 Lower jaw, with an impacted permanent canine tooth, the temporary canine being retained.... 198 97 Lower jaw of a child, with a deeply impacted molar tooth. 199 98 Upper jaw, with impacted canine tooth, the temporary canine being retained......... 199 99 Front of upper jaw of an aged person; both canines being impacted in the substance of the bone... 200 100 Palatal aspect of an upper jaw, in which the crown of an impacted canine tooth pierced the palate, and the fang the lateral surface of the jaw...... 200 101 Upper jaw of a very aged person; a canine tooth is seen lying on the edge of gum, which is otherwise edentulous.. 201 102 Portrait of a patient who had suffered from dentigerous cysts expanding both antra (after Glaswald),. 214 103 Central incisor tooth with aborted fang from a dentigerous cyst 216 LIST OF ILLUSTRATIONS. Xix FIGU1RE PAGE 104 Second lower molar tooth (posterior view), showing absorption of the fang occasioned by a dentigerous cyst which had expanded around an impacted dens sapientime... 217 105 Oblique view of the same........ 217 106 Superior maxilla, with dentigerous cyst growing into the antrum 219 107 Dentigerous cyst of lower jaw, seen from above (after Heath, from Mr. Fearn's preparation)..... 219 108 Side view of the same....... 219 109 Section of a dentigerous cyst (after Heath, from Mr. Underwood's model)..... 220 110 Portrait, from a photograph, of a person suffering from abscess, opening externally, dependent on an impacted inferior wisdom-tooth......... 29 111 Maunder's'Screw-gag'........ 234 112 Molar tooth, with pyriform alveolar abscess-sac embracing extremity of fang (after Bell)..... 236 113 Superior maxilla, showing the excavations in the bone occasioned by alveolar abscess; taken from a specimen in the museum of Guy's Hospital (after Bell)..... 238 114 Intermaxillary bones and crowns of incisor teeth, necrosed after small-pox.......... 304 115 Portion of lower jaw and right lateral inferior incisor tooth, necrosed and shed after measles..... 305 116 First superior temporary molar tooth and crown of immature bicuspid, shed after measles..... 306 117 Portion of lower jaw with temporary molar teeth, necrosed and shed after scarlatina........ 306 118 Small sequestra of jawbone, shed after scarlatina.., 307 119 Greater portion of right upper jaw and temporary teeth shed after scarlatina....... 307 120 Immature central incisor tooth of the upper jaw, with its bony loculus and temporary predecessor, shed after scarlatina. 308 121 Superior central incisor tooth, blighted by scarlatina... 309 122 Elevator, with serrated edges; side and face views., 328 123 Screw for extracting hollow tooth-fangs,-section showing form of worm...... 330 124 Baly's molar stump-forceps...... 333 125 Stevens's molar stump-forceps...... 33.3 126 First lower permanent molar, with first and second temporary molars, united by fibrous tissue.... 347 127 Perforated palate, from syphilis..... 385 XX LIST OF ILLUSTRATIONS. FIGURE -PAGE 128 Obturator, for the treatment of the perforation shown in previous figure. 386 129 Congenital cleft palate, with deficiency of right incisive bone and teeth 388 130 Artificial palate (hard and soft) for the foregoing, shown on oral surface..389 131 The same in profile..... 389 132 Palate with two perforations and loss of alveolar bone, after syphilis 391 133 Apparatus to supply the losses in foregoing case.. 392 DENTAL PATHOLOGY AND SURGERY. CHAPTER I. GENERAL ANATOMY OF THE TEETH AND CONTIGUOUS STRUCTURES. THE dentition of man is diphiodont; that is to say, there are two sets of teeth, the temporary and permanent, numbering respectively twenty and thirty-two teeth. In the temporary set there are four incisors, two canines, and four molars in each jaw; in the succeeding set these are replaced by others-incisors succeeding incisors, canines succeeding canines; the temporary molars are replaced by premolars or bicuspids, and behind these are developed in succession, as the maxilla elongate, three permanent molars on each side of each jaw. The formulae of human dentition may be thus expressed. The temporary set:I 22; C 1-; M2 2-20 22 11 22 The permanent set:22 11 22 33 I; C; 22; M=32. 2 2 H' 22 33 In histological development, in structure, in physiology, and in their diseases, the teeth have certain resemblances to bones, and, at the same time, characteristic differences from them. B 2 DENTAL PATHOLOGY AND SURGERY. A considerable portion of each tooth is naked, whilst bones are wholly clothed by periosteum; the hard tissues of human teeth are destitute of blood-vessels —bone is highly vascular; teeth are perishable, and may be shed-bones last the life-time of the, individual; lost substance of two of the tissues of teeth, enamel and dentine, is never restored, though in the latter there is a curious process of internal repair, in this resembling some bones and differing from others. Teeth certainly are not extraneous organs, as suggested by Hunter, but have a distinct vitality: they undergo nutritional changes by virtue of a plasmic circulation in their tubular structure, and two of their hard tissues manifest sensibility, which, in disease, may he exalted to extreme painfulness. The teeth are not parts of the true skeleton, but may be considered as elements of a dermal skeleton. They are developed from the tegument of the mouth; and though closely embraced by the alveolar processes of the maxillary bones, are never, in man, united to them. It is not my intention to enter upon a description of the development, the structure, and the physiology of the teeth, further than as illustrating their diseases. Human teeth are composed of three hard elementary substances, enclosing a soft fleshy mass in the centre. The three sclerous substances are enamel, dentine or ivory, and crusta-petrosa or tooth-bone. Enamel is the hardest tissue in the body; it contains above 95 per cent. of earthy matter. In structure it consists of a series of dense fibres, running with a somewhat wavy course, but generally at right angles to the dentine surface of the crown of the tooth upon which they rest, radiating outwards, and ending free upon the masticating surface of the crown of the tooth. Close to the dentinal surface the fibres are frequently separated from each other by the protrusion between them, for a short distance, of the dentinal tubes, and the latter are sometimes large and bulbous in that situation.* There is every reason to believe that enamel is totally destitute of vitality; that it undergoes no nutritional changes after * This may account for the fact, stated by Retzius, that the enamel close to the dentine contains more animal matter than elsewhere. GENERAL ANATOMY OF THE TEETII. 3 it is once formed, and that it is only influenced by the physical and chemical agencies to which it is exposed. Dentine or ivory, which constitutes the bulk of a tooth, is a tissue of bony hardness; it consists of earthy matter to the extent of not less than three-fourths of its weight. Histologically it is composed of a series of minute tubes about — ~ of an inch in diameter, radiating from the central hollow chamber or pulp-cavity, in which. is lodged the soft vascular organ, the pulp, which is mainly concerned in the nutrition of the tooth. Between the dentinal tubes is a hyaline structure called the intertubular tissue. The tubes pursue a wavy course, and branch more or less, especially in the crowns of the teeth near the surface, and occasionally they exhibit dilatations somewhat like bone-lacunee. The dentinal tubes have extremely thin walls, which can scarcely be said to be visible in the hard tissue when seen in profile, but which, in transverse section, as viewed by high powers of the microscope, display a broad brilliant ring of considerable thickness around each. This appearance is an optical illusion, and has given rise to much error in interpreting the histological elements of dentine. Whether the broad ring is the- result of the curious phenomenon, irradiation, or the diffraction of light by the thin cut edge of the tube, I am not prepared to say; but the appearance is not without parallels, which are thus explained. This fact was first pointed out by Henle,* in i841, and is easy of confirmation. It can be demonstrated both by analysis and by synthesis. In some fractures of sections of dentine these fine tubes are seen standing out rigid and calcified from the broken edge. The animal basis of the dentinal tubes and that of the intertubular substance are different; the former is considerably denser, and, after decalcification, strong hydrochloric acid will remove the intertubular substance, or render it absolutely transparent —thus the tubes can be isolated, and their minute diameter, corresponding with the dark dentinal tube as seen in the profile view of hard sections, is at once recognised. If tubes, thus distinctly free from all surrounding ewalls, be * Allgemeine Anatomie, von J. Henle; constituting the sixth volume of SSmmerring's Baue des mnenschlichen KEorpers. Leipsig, 1841. B2 4 DENTAL PATHOLOGY AND SURGERY. traced along their course, occasionally some are seen turning their broken ends towards the observer; the rings in question are apparent, and the illusion is manifest. The accompanying diagram will explain this perhaps better than a description. Fig. 1. Synthetically this question of histology is demonstrated with equal clearness. In studying the development of dentine, it is found that upon the formative pulp there is arranged a series of columnar cells constituting the membrana eboris, from the distal extremities of which minute tubular threads project; and, as the dentine forms from without inwards, these are prolonged centripetally, a homogeneous blastema separating them and being calcified with them. These prolongations are the dentinal tubes,* and the calcified blastema is the intertubular tissue. No other elements hitherto discerned enter into the formation of dentine,.and the minute tubes, freed by the decalcification and the solution of the intertubular tissue in dentine, through the action of hydrochloric acid, are identical with the thread-like prolongations seen on the ends of the columnar cells of the dentinal pulp. These minute tubules of dentine, when free and soft, have a certain resemblance to nerve fibres, and this circumstance, combined with the belief that the luminous rings around the tubes represent the walls of comparatively large hollow canals, has led a distinguished microscopist to conclude that they are nerves, or the equivalents of nerves, occupying the cavities of such canals. And, unaware that the histological facts had been recorded both in description and illustration by Henle long previously, he presented to the Royal Society a memoir " On the Presence of Fibrils of Soft Tissue in the Dentinal Tubes," t and in that memoir he speaks of them as "organs of sensation." But the truth is they are the dentinal tubes themselves, and * This was discovered by Lent, " Ueber die Entwickelung des Zahnbeins und des Schmelzes," in Siebold and Kdlliker's Zeitschrift, 1854, p. 121. t By John Tomes, F.R.S. In the Philosophical Transactions of the Royal Society, vol. cxlvi., 1856. GENERAL ANATOMY OF THE TEETH. 5 there is nothing whatever separating these bodies from the intertubular substance. In the observations made by this author, great stress was laid upon the examinations being made on perfectly fresh specimens, so that the soft structures may not have suffered injury or decay. The minute tubules may, however, be demonstrated just as well in the oldest specimens of dentine. The accompanying illustration (fig. 2) is from a specimen, prepared by myself, of a portion of decalcified dentine from the tooth of an Ancient Briton, that had been. entombed probably for not less than two thousand years; all soft uncalcified tissues must have perished for ages. Fig. 2.:. In this figure the dentinal tubules are free to the left of the dotted line, but to the right they are still held in position by the intertubular substance, which, though perfectly hyaline and transparent, has not yet dissolved away.* The dentinal tubules are hollow and appear to contain a dense plasma. Mr. Tomes has contributed a valuable record in support of this view: " When accidentally stretched between two masses of dentine the diameter of the fibril (decalcified tube) becomes much diminished, and, when broken across, a minute globule of transparent but dense fluid may sometimes be seen at the broken end, gathered more or less into a spherical form." The axis of the tube, therefore, whatever may be its disputed nature, being occupied by fluid. * For a more lengthened discussion of this subject, the reader is referred to a paper by the author "On some Points in the Anatomy and Physiology of the Dentinal Tubes," in Truman's Archives of Dentistry, 1865. 6 DENTAL PATHOLOGY AND SURGERY. Human dentine is non-vascular, that is, it is destitute of blood-vessels; though occasionally, as an abnormal condition, erratic vascular canals are seen in its substance. This will hereafter be referred to, as well as that peculiar form of secondary dentine, osteo-dentine, which is produced by the intrinsic calcification of the tooth-pulp, and which is abundantly vascular. Dentine exhibits vital phenomena, which show it to be part of the living body. I. It is sentient. II. It is susceptible of nutritional changes. III. It takes cognisance, so to speak, of injuries done to its outer surface, leading to a renewal of ivory-growth on the surface of the pulp. Hunter* denied that dentine is sensitive, and that view was long entertained. I believe it was M. Duval t who first prominently pointed out that the ivory of human teeth is endowed with sensation; and he particularly mentioned that the external layer, just beneath the enamel, and which he named " Dictyodont," manifests the most acute sensibility. This circumstance may arise from the fact that the outer layer is often imperfectly calcified, and that some of the tissue here remains soft and more impressible; for it is found that the same exalted sensibility is displayed when the surface of any exposed dentine is acted upon by acids, and again it is seen in pale soft decay. I believe that both the periosteum around the fangs of the tooth and the pulp itself hlave a nervous connection with the substance of ivory. The destruction of the pulp very much reduces the sensitiveness of dentine, and generally seems to destroy it; but in not a few instances I have found masses of dentine still intensely sensitive when their direct connection with the pulp has been severed by lesion of intervening tissue; and it has occurred to me as probable that the sentient perception has, in such cases, been through the periosteum. It does not necessarily follow, however, that the nervous connection * The Works of John IIunter, Palmer's edition, vol. ii. p. 50. London, 1835. t Observations Pratiques sur la Sensibilite des Substances Dures des DI)ents, par J. R. Duval. Paris, 1833. This paper was originally read before the Royal Academy of Medicine of Paris, 1831. GENERAL ANATOMY OF THE TEETH. 7 between the pulp and the dentine should be by a direct radiation in the same course as the tooth-tube structure: it may be diffuse and circuitous, and thus an outlying mass of dentine may still maintain a sentient connection with the pulp. I am inclined, however, to believe that the periosteum shares in this function, as it does in the nutrition and general vitality of the teeth; and this opinion is supported by the fact that Czermak has found a large supply of nerves in the periodontal membrane, and has traced them to the hard substance of the fangs.* The mode in which the hard tissues of the teeth are supplied with nerves is still an enigma; but that there is some supply is certain, on physiological grounds. Tomes mistook the decalcified tubes for nerves, or their equivalents. Other anatomists, especially Neumann, have described cylindrical processes as projecting from the ends of the tubes (sheaths); and Boll has figured the same with clear definition.t It is assumed that these are nerves. It should be remembered, however, that minute branches of the tubes might easily be mistaken for emanations from within the tubes, as I have myself seen; and, further, that the viscid contents of tubes, drawn out especially after induration by chromic acid (as employed by Boll), might readily be mistaken for fibrils, and, indeed, might so appear. The nerves of the tooth-pulp form loops towards its periphery, which may be readily demonstrated by the action of caustic alkali, and from these, according to Boll, large numbers of very minute fibrils proceed outwards, passing between the ivory cells and their tubular prolongations. It is highly probable that these are the nervous elements distributed to the dentine; but whether they pass into the intertubular substance, or, fastening upon the tube walls, are so piloted into the ivory structure, is quite uncertain. It is, however, highly improbable that they pierce the wall of the ivory cell, and occupy the axis of the tube. The sensibility of dentine has some peculiarities:iit is exalted * "Beitriige zur mikroskopischen Anatomie der menschlichen Ziihne," von Dr. Johann aziOrlakr, in KI11ilrer and Siebod'a Zoiisci hr;ft, p. 317. Leipsig, 1850. t "Untersuchungen uber die Zahnpulpa," von'Franz Boll, in Schultze's Archiv fiir Mikroskopische Anatomtie, p. 73, Tafel v. fig. 45. Bonn, 1868. 8 DENTAL PATHOLOGY AND SURGERY. to pain (especially when softened in early decay) by certain sapid bodies, which have no particular effect upon nerves of rig. 3. ordinary sensation, such as salt and sugar, especially a* the latter, which is remarkably irritating in its low uncrystallised forms. Again, the sensibility is numbed in a singular degree by some of the pungent hydrocarbons, such as creasote and phenole, which,' priori, would not have been expected to produce such a result. Dentine, that is matured, afterwards undergoes nutritional changes under certain circumstances as far as the tubes are concerned, but apparently not in regard to the intertubular tissue. It is very common for dentinal tubes, leading from the pulp to a slight superficial decay, or an abrasion, in the crown of a tooth to be sealed up by a deposit of calcified material for a short space at the distal end of the tube, while the whole of the rest of the tube has remained patent. A section of a dry tooth, in which this has occurred, shows the tissue around the decay, or abrasion, clear and transparent, the tubes being filled with material apparently of the same, or nearly the same, density as the surrounding structure, while leading to the pulp the tubes are opaque and air-filled. Now, where this occurs in the crown of a tooth, the only source of nutrient material is the vascular supply of the pulp; and the calcific matter must traverse the whole length of the tube before deposition at its terminal extremity. This will be more intelligible by reference to the accompanying diagram. The asterisk represents the spot of decay, or abrasion; a b, that portion of the tube closed by calcific deposit; b c, that portion of the tube filled with air in a dry specimen, and with plasm in the living state; d, a capillary loop. This may seem too diagrammatic and mechanical a method of expressing what occurs; but it is not so. A figure illustrative,,/7 ~ of this is seen under the head "Dentine of Repair," where the clear tissue, close to the carious surface, has been thus produced. GENERAL ANATOMY OF TIIE TEETH. 9 The tube in the diagram is drawn as terminated towards the blood-vessel by the persistent developmental cell, which appears to remain through life, and ever ready to resume a continued growth by centripetal elongation, when the outer surface of the dentine is injured, producing " dentine of repair." The entrance of nutrient material into the tube must therefore be by endosmosis through this cell-wall. A similar filling-up of the tubes by calcified material takes place in the fangs of teeth, especially after inflammatory action. This produces a semi-transparency; the dentine looks like horn. In jaundice the plasm in the tubes is stained yellow by the bile; and where the pulp becomes disorganised, the colouring matter of the blood often imparts a red or purple hue to the contents of the tubes. The development of dentine of repair is another indication of vitality. When the surface of the dentine is injured either by decay, by friction, or by fracture, an impression is conveyed to the formative pulp, by which a fresh growth of dentine is started, having a definite relation to the external injury. This will be further illustrated in the chapter on Secondary Dentine. When dentine is removed by absorption from the external surface or the end of the fang of a tooth, it is never restored; but the erosion may be filled up by a deposit of crusta petrosa. Crustapetrosa, or tooth-bone, is a structure closely resembling the bone of the skeleton; and it clothes the dentine of the tooth's fang just as the enamel covers the crown. The tissue contains about 70 per cent. of earthy matter. Crusta petrosa consists of bony laminve, which in transverse section constitute a series of rings around the dentine of the tooth's fang, and in vertical section display elongated wedgeshaped processes, broad towards the apex of the fang. Among these are interspersed true bone lacunae, large and oval, with their long axes parallel to that of the fang: they usually have a profusion of canaliculi mostly passing from within outwards, and from without inwards. Among the lacunae are frequently seen tubes, sometimes numerous and parallel to each other, radiating from centre to surface, and much resembling dentinal tubes. These when cut across present the same broad ring as is seen in a similar section of dentinal tubes. The lacunae are wanting towards the neck of the tooth, where 10 DENTAL PATHOLOGY AND SURGERY. the crusta petrosa is a thin, nearly transparent layer, and they appear and increase somewhat rapidly about the middle of the fang and towards its extremity. The tooth-bone is not always an even layer on the dentine, but is often thick at places, obliterating the folds of the latter, and not infrequently uniting fangs together. Crusta petrosa is normally non-vascular, but towards the apex of the fang it is occasionally pierced by a few bloodvessels in the teeth of old people, where the tissue is often much thickened. These constitute Haversian canals, which generally terminate in blind extremities. The tubes of the dentine and those of the tooth-bone, as well as the canaliculi of the latter, frequently anastomose. Tooth-bone is very liable to absorption and re-deposition. This tissue is sensitive, and, when exposed by the recession Fig. 4. of the gum and alveoli, is irritated to pain by the same sapid bodies as affect dentine, especially by salt. The manner in which nerve-tissue enters the substance of toothbone, and is distributed among it, is unknown. Its chief source of supply is probably from the periosteum; but it may have some connection with the nerves of the pulp, just as dentine seems to have with the nerves of the periosteurn. The hard tissues of the teeth have a general radiating character in their structure, and are at the same time laminated. The radiation indicates the ultimate his/ 1 \ tology and the structure as associated with x\/11 the nutrition of the tissues: the lamination indicates the increments of their development-the successive portions by which the tooth is built up. These indications may be fairly called incremental lines, and are indicated in the accompanying diagram.* Theoretically, the process of a tooth's growth is continuous, * Professor Owen has called these markings in dentine " contour lines." The term is scarcely admissible, as they only approximate remotely the contour of the tooth. GENERAL ANATOMY OF THE TEETH. 11 the three hard tissues being evenly produced upon the surface of the formative pulps; but really that is not so, the enamel, dentine, and crusta petrosa indicating, by a sort of lamination, a distinctly repeated periodicity, as though the tissue were formed perfectly and imperfectly, or of different density, at intervals of time more or less evenly repeated. This is especially the case with dentine. This repetition of different nutritional conditions, a sort of alternate plus and minus, so to speak, is a phenomenon of very general existence in the growth and nourishment of tissues; but it has been scarcely dwelt upon by physiologists with the importance that it deserves. As regards the tissues of the teeth, it is of extreme interest from the clearness of its demonstration in them, and from the fact that they retain through life a permanent register of alternate growthcomplete and incomplete. This alternation of developmental force is most marked in the dentine, and manifests itself in the matter of calcification. That is to say, a layer of dentine will form over the entire area of the pulp, and its calcification will be complete; and then another layer will form, in which the calcification is incomplete, the earthy impregnation being partial and defective, either from the growth of the animal basis being too rapid, or the supply of calcareous matter being deficient. And so on alternately. Now this imperfect calcification of the alternate layers is demonstrable from the fact that the animal matter of dentine is not evenly impregnated by the earthy in a general and progressive manner; but as the histological elements are formed on the surface of the pulp, the earthy matter impregnates the soft mass at a series of isolated points, which gradually enlarge into spheres of perfectly calcified dentine, while the intermediate portions remain unchanged. It is by the progressive enlargement and fusion together of these spheres-" calcification globules "-that normal dentine is completed. If, however, the animal matter is imperfectly supplied by the calcareous, while the tissue progresses in growth, the calcification is permanently imperfect; the matured structure remains as a series of hard globules with soft interspaces. And when such specimens of dentine are dried, these interspaces become airfilled, from the shrinking of the very soft tissue occupying them, and are white and opaque as seen with reflected light, and dark 12 DENTAL PATHOLOGY.AND SURGERY. with transmitted light. These interspaces have been often mistaken for lacunae. Now this layer of imperfectly formed dentine occupies the area of the pulp at a given time throughout, though most marked near the margin of the forming toothcap where the tissue is forming fastest, and it illustrates the successive increments of which the tooth is built up. See fig. 43, where this is shown in the vertical section of a canine tooth. The histological characters, as seen with the microscope, are displayed in fig. 44, where they are treated among the vices of original tooth development. A somewhat similar effect is produced in enamel by these alternations of nutritional force: the enamel is calcified first as a cap on the summit of each tooth-cusp, and then in a series of rings down the crown of the tooth; and the markings, more in colour and transparency than in difference of structure, which are thus produced, display at the summit an arch and then a series of rhomboidal forms, as shown in figure 4. Where there is any grave fault in the structure of the enamel, it is usually found to abut upon the extremity of a severely marked incremental line in the dentine. The lamination of crusta petrosa is likewise, in all probability, a manifestation of periodicity and alternation. The Soft Structures connected with the teeth have a very important bearing on Dental Disease. They are the Pulp, the Gum, and the Periosteum. The Pulp is a soft mass, which exactly fills the chamber in the fang and crown of the tooth; it is of a pinkish colour, and rather translucent. It contains a large amount of fluid, and dries to a mere film. Nerves and blood-vessels are very abundant throughout the structure. The blood-vessels form long plexuses, the larger vessels in the centre of the pulp giving off irregular loops towards the surface. They are extremely numerous, and a pulp treated with acetic'acid shows the nuclei of vascular muscle in all directions. Indeed, the structure of minute blood-vessels is well exhibited for study in the pulp. The nerves form a large element of the mature pulp; they enter the apex of the fang in small bundles of various size and number, and these divide and subdivide in plexuses forming long meshes, which ultimately, near the surface, break up into GENERAL ANATOMY OF THE TEETH. 13 primitive fibres. Here they form very distinct loops immediately beneath the membrana eboris. From these loops, according to Boll, very minute fibrils pass outwards between the cellular elements of the extreme surface of the pulp. There appear to be no lymphatics in the tooth-pulp. A very pale ill-defined areolar tissue, pervaded by numerous round and oval cells, or nuclei (the granules of Purkinje) occupies the spaces between the vessels and nerves. These cellular bodies towards the surface are enlarged and more oval, increasingly so as they become more superficial, where they assume the form of columnar epithelium. From the extremities of these project minute tubular prolongations which constitute the animal basis of the dentinal tube wall, and are in direct continuity with the calcified dentinal tubes of the indurated dentine. The Gum is the mucous membrane which surrounds the necks of the teeth, and is continuous with that of the rest of the mouth; it has no exact limit, but may perhaps be said to be from a quarter to a third of an inch broad from its free edge. In structure it consists of an elastic layer of fibrous tissue intimately connected and continuous with the periosteum of the jaw; upon this is placed a regular and strongly marked papillary structure, covered in by a dense.epithelium. The papillae are long and cylindrical near the edge of the gum, like the fingers of a glove, and they become shorter and expanded in passing towards the jaw and palate. Each papilla contains a single capillary loop. The epithelium is soft and small and round immediately upon and between the papillae, becoming larger and flatter towards the surface, where it is squamous and cuticular, and completely covers in the papillae, forming an even surface. The change in form and size of the deep and superficial epithelium is very gradual, and there is no distinct line of demarcation-nothing like a rete nzucosum, as in the skin. Where the gum is in contact with the necks of the teeth, the structure is very much modified; the papillae cease and the hard squamous epithelium is wanting. The surface is here soft and clothed with a smaller and rounder epithelium: there are no true glands, such as Serres described, but the surface is 14 DENTAL PATHOLOGY AND SURGERY, cupped and folded between the ramifications of a beautiful capillary network. This surface emits a profusion of those globular cells which are constantly found in the fluids of the mouth, and which are called by authors mucous corpuscles. Whether they all come from this source I cannot say; but they are certainly largely produced here and constitute the bulk of that yellow oozy material which collects around the necks of the teeth in uncleanly people. The accompanying illustration shows the vascular arrangement of the gum on the dental surface; and the sudden change Fig. 5. from the papillary loops to the glandlike plexus is very manifest. The alteration in the disposition of the vessels exactly coincides with the modification of the surface and of the epithelium. This is probably a truly glandular structure, but of the simplest kind. The supply of nerves to the gum is -.,ji,~ small, and it is insensitive unless the surface is ulcerated, when, like some -~~5~r-> ~ # other tissues slightly furnished with nerves, it is intensely painful. The Periosteum lines the socket of the tooth and ministers to its nutrition, and to that of the surrounding alveolar process. It has been customary to take too artificial a limit, and to make too exact a definition of the fibro-vascular tissues surrounding the fangs of the teeth, and to divide them into periodontal membrane, periosteum, endosteum, and gum. With exception of the mucous membrane of the gum, they are really one and continuous; they share, to a great degree, the same vascular supply and the same general influences of health and disease. The membrane which intervenes between the alveolus and the tooth-fangs has, however, some characteristics which distinguish it from ordinary periosteum. It is entirely devoid of fat cells, it consists of connective tissue in which the elastic element is wholly wanting, and it has a very large supply of nerves. CHAPTER II. FUNCTIONS OF THE TEETH. MASTICATION is the most important of the functions of the teeth, and is so obvious that it need not be dwelt upon. The teeth have, moreover, a tactile faculty which is exercised in detecting the texture of food and the presence of foreign bodies. Another function of the teeth, hitherto too little dwelt upon, is that they play a very important part in the formation of articulate sounds: they constitute an essential element in the organs of speech. Without them the precise and clear pronunciation of a great many letters, particularly consonants, would be impossible, and the resources of the oral cavity, as an organ of speech, greatly circumscribed. Accordingly we find that, when the teeth are lost, certain imperfections in articulation are immediately entailed; and thus the knowledge of the particular way in which the teeth help to form articulate sounds is of much practical importance to the dentist, as it is only by this knowledge that the imperfections of articulation will enable him to tell what is amiss, how to correct it, and, indeed, whether the teeth are in fault or not. With the formation of many articulate sounds, both' vowels and consonants, the teeth have nothing to do, and, therefore, into the discussion of the mechanism by which these are produced it will not be necessary to enter. Nevertheless I think it well, before describing how the sounds are effected in which the teeth are immediately concerned, to say a few words on the mechanism of articulation generally, as it will render the more special part of the subject clearer and more intelligible. Articulate sounds are essentially produced by the passage of air through the oral canal.. Now, there are chiefly three parts 16 DENTAL PATHOLOGY AND SURGERY. of the oral canal that may severally impress certain characters on air passed through them, and these are the three points where closure,perfect, imperfect, and modified, may be produced at will-namely, the soft palate, the front teeth and gums just behind them, and the lips. Certain characters are also given to the sounds by the relation of the size of the oral cavity to the size and shape of these orifices. Articulate sounds have been divided into vocal and consonantal sounds, or vowels and consonants, and to a certain extent the distinction is a good one and based on physiological truth; but as it is usually understood, and as we find it explained in grammars, it is quite incorrect. It is usually stated that vowel sounds are the true voice sounds, and that consonants are merely the method of commencing and terminating vowels; that vowels are open sounds, and consonants closed sounds; that vowels are capable of prolonged utterance, and that consonants are incapable of pronunciation without the aid of vowels. We see this implied in the very names themselves-vowels (zocales), voice sounds; consonants (con sono), something necessarily sounded with something else. Now, this error has arisen, as shown by Miller, from the supposition that voice sounds were necessary to articulate utterance; that articulation was, in fact, nothing more than the modification of laryngeal vibrations; whereas in truth almost all articulate sounds, both vowels and consonants, may be pronounced in a whisper without any vocalisation, as anyone may satisfy himself in a moment; thus, V or S may be pronounced as well in a whisper as with the superaddition of the voice, and the sound prolonged with as much facility as the vowel sounds E or O. Indeed, in following my remarks on this subject and verifying for himself my description of the way in which the sounds of the different letters are produced, I should advise the reader to pronounce them in a whisper, and not to speak them "out," as by eliminating the laryngeal vibrations he will get the oral element of the sounds more unmixed and simple, and their analysis will be.easier and more precise. In what, then, does the essential difference between vowels and consonants consist? I think mainly in this —that while vowel sounds depend on the relation of the size of the oral cavity to the size of its orifices, consonantal sounds depend on FUNCTIONS OF THE TEETH. 17 some superadded condition of orifice quite independent of size. To take an example-in far and fear the difference is in the vowel sound, and the difference of condition is in the size of the oral cavity and aperture, both being more capacious in far,; but in oth and oss, where the difference of sound is consonantal and the vowel sound the same, we find the size of the cavity and its relation to the orifice to be unchanged, but that the dental orifice is modified by the altered relations of the tongue to the teeth. I am aware that this definition can only be stated approximatively; for as there is no real physiological distinction between some vowels and some consonants, so no definition can be laid down that would separate the whole of the one class from the whole of the other. This is illustrated in the accomnFig. 6. Tsam ieeo r, This diagram is intended to illustrate, by section, the relation of the tongue to the teeth and palate in the production of several sounds. a. Superior incisor tooth. b. Inferior incisor tooth. c. Uvula. 1. Application of tongue to incisor tooth in producing the sound " th." 2. Tongue to palate, sound " d "- closure complete; sound " s " —closure incomplete. 3& Sound " ch " (German), as in "Liebchen." 4. Sound German and Scotch guttural, as Oh! " 5. Sound "g " hard and "k." panying diagram. It represents a vertical section, in the middle line, of the upper jaw, the soft palate, and the tongue c 18 DENTAL PATHOLOGY AND SURGERY. in various positions, and shows that the apposition of different parts of the upper surface'of the tongue along the under surface of the soft or hard palate, or to the gum behind the teeth and upper incisors, produces the sounds of various letters, five of which are consonants and one a vowel. Thus, if the back of the tongue is applied to the soft palate, the sound of K is produced; if the sound of the Scotch Och is pronounced, it will be seen that the apposition takes place a little further forwards; for the pronunciation of the German ch, as in Liebchen, the apposition is still further in front; if, now, the upper surface of the front of the tongue is brought close against the front of the palate, whilst the tip is pressed against the back of the lower incisor teeth, so that a narrow horizontal chink is formed, on breathing through it the sound of E is produced; if the tip of the tongue is-placed close against the gum behind the upper incisors, we get S; lastly, if we carry it a little further forwards and place it against the edge of the incisors themselves, projecting the tongue a little beyond the teeth, we get th. Thus, the apposition of the tongue to the upper wall of the mouth at six successive points, from behind forwards, gives six definite articulate sounds, one of which is a vowel. Thus, while the teeth have far more to do with the formation of consonants than vowels, the associated distinction between oral cavity and orifice, as connected the one with the formation of vowel sounds, the other with that of consonants, is lost. The principal way in which the teeth assist in the production of articulate sounds is by acting as an arch, or horseshoe-shaped ridge, within which and against which the tongue may act as a valve, and by pressing against which it may produce modified and variously-placed partial or complete closure. The outline of the tongue, when flaccid and in a state of rest, coincides with that of the alveolar arches both in size and shape; and as its border is on the same level as the line of meeting of. the upper and lower teeth, the teeth and the edge of the tongue are always, when this natural condition of rest is not disturbed, in close juxtaposition. This is not strictly and absolutely true with regard to the anterior extremity of the tongue, which is slightly depressed, so that the tip of it rests, not against the line of meeting of the incisors of the two jaws, but against the back of those of the lower one. It is this approximate coinci FUNCTIONS OF THE TEETH. 19 dence of shape and close propinquity that make the instantaneous application of any part of the edge of the tongue to the corresponding part of the dental arch of either jaw so easy, and this it is also that makes any considerable dental irregularity or deficiency destroy, by preventing this application, the power of producing certain articulate sounds. Hence (to state this proposition conversely) we may lay down the practical rule that all measures taken with a view to restore imperfect articulation due to the teeth must have for their object to restore this coincidence between the entire dental arch and the entire border of the tongue. Although the tongue is so placed that its edges may be pressed with equal facility against the teeth of either jaw, it is against various parts of the dental arch of the upper jaw that it is, in actual fact, pressed in the formation of most of the dental consonants. Whenever the border of the tongue is closely applied to the inside of any of the teeth, then closure is produced, and air cannot pass; whenever this closure is not produced, then air can pass, and then it is that the particular sound produced by this modification of aperture is generated. Thus, the seat of the sound is always, not where the tongue is in contact with the teeth, but'where it is not in perfect contact with them. This is a point that it is of importance to bear in mind in drawing an inference, as to the whereabouts of a deficiency in the teeth, from the particular defect of speech that the patient may exhibit. Upon the principles that I have laid down I have endeavoured to construct what may be called a physiological alphabet. The arrangement is based upon the situation of the closure by which the sound is produced, upon the completeness or incompleteness of the closure, and upon whether the breathing is soft or aspirate, and the table shows how completely symmetrical the whole subject is, and what a parallelism runs through it. It shows, too, to the formation of how large a number of letters the teeth contribute. 20 DENTAL PATHOLOGY AND SURGERY.'TABLE. a. terminally dental. e. wholly dental. Vowels............ i. terminally dental. l~~~~~~~~ ~~~~o. not dental. Lu. inceptively dental. (b. labial.. u Closure Soft...d. dental. ~ ~ Closure complete, [g (hard), palatal. mutes. p. labial. I J Aspirate t. dental. - ~. {k. palatal. nm. labio-nasal. Consonants Nasal. n. denti-nasal. ng. palato-nasal. J fv.... denti-labial. Closure incomplete, ngi dental. L semi-vowels.j I j. English th. (in thou) I Lzh. (=Fr.j.)J Oral ] f.. denti-labial. 1...... } a cth. English r ch th (in through) sh.... J ch. (German), palatal. Of the consonants it will be seen that nine-B, D, G, P, T, K, M, N, NG —-are subdivisible into threes in a very orderly and regular way. Three are labials, B, P, and M; three are dentals, D, T, and N; three are palatals, G hard, K, and NG (as in thing). Of the labials, one, B, has a soft breathing; the other, P, an aspirate breathing; and in the third, M, the sound is continued through the nose after the labial closure, and I therefore call this a "labio-nasal." In the same way the dental has a soft, an aspirate, and a denti-nasal; and the palatal a soft, an aspirate, and a palato-nasal; so that there are three with a soft breathing, three corresponding ones with an aspirate breathing, and three nasal, in which the sound is continued through the nose after the oral closure. In all these nine the oral closure, whether at lips, teeth, or palate, is complete, and those of them (the first six) in which the sound is not continued through the nose are therefore called mutes, because they produce complete arrest of sound. FUNCTIONS OF THE TEETH. 21 In all the other consonants the oral closure is incomplete, and the characteristic sound of the letter is produced, not by the method of closure, as in the others, but by the particular shape and seat of the orifice or constriction produced by the partial closure. The sound in these is therefore continuous, and may be protracted any length of time, and the letters are thence called " semi-vowels," or continuous consonants. Putting aside the German ch (in English we do not possess it), they are fourteen in number, and may be coupled two and two, seven having the soft and seven the aspirate breathing, and each aspirate letter corresponding to one with a soft breathing. Thus V corresponds to F, Z to S, &c.; so that there are really only seven distinct consonantal sounds of this class and seven modifications of the parts engaged in their production, each of these sounds being doubled by the substitution of one breathing for the other. Two of the letters, V and F, are produced by certain relations of the teeth and lips, and I therefore call them "denti-labial;" the other twelve depend upon the relation of the teeth and tongue, and I therefore call them "dentals;" perhaps with more correctness they might be called "denti-linguals." Let me now analyze more particularly and in order the way in which all these letters are formed. As my object is only to show the part which the teeth play in their formation, I shall not say anything about the labials and palatals. In pronouncing D the tip of the tongue is placed firmly against the gum behind the upper incisors, and its edges against the upper alveolar arches and teeth, so as to produce complete closure, and these parts are then suddenly opened. In T exactly the same is done, only the breathing accompanying the opening is more forced. In N the method of oral closure is exactly the same, only after the closure is established the sound is continued through the nose. Thus T may be said to be 1)-aspirate, and N may be said to be D with nasal prolongation. This is how it is that when the nose is obstructed by cold or otherwise, N becomes D; thus, "nonsense" pronounced " dodsedse" gives an idea of cold in the head, Conversely, in cases of cleft palate, in which the posterior nares cannot be closed, and the sound is therefore not prevented from prolongation through the nose, D cannot be 22 DENTAL PATHOLOGY AND SURGERY. sounded, but is pronounced like N, so that a person with cleft palate, instead of saying "How do you do?" says, "How noo you noo?" In the pronunciation of V and F the upper front teeth are brought against the lower lip, and the air is driven through them-in V gently and in F forcibly. For this sound therefore the uppers incisors are necessary. In old people who have completely lost all their upper incisors the gum answers nearly or quite as well; but the loss of a single incisor or of the two central incisors materially interferes with the pronunciation of these letters. It is perhaps in consequence of being unable to bring the thick and prominent lower lip against the upper teeth that Africans (negroes) are unable to say these letters. In the pronunciation of consonants in which the sound depends upon air driven through a chink between the tongue and the teeth, the closure may be lateral and the aperture mesial, or vice versA: thus, in TH and S the aperture is mesial; in L the closure is mesial and the aperture is lateral. In the pronunciation of TH the tip of the tongue is brought against the upper teeth, and the air is driven through the chink thus formed; in TH, as in " thou," with the soft breathing; in TH, as in " thick,' with the aspirate. If now the tip of the tongue is a little retracted and brought close against the gum behind the upper teeth, and a slight chink still permitted while the sides of the tongue are firmly applied to the side teeth of the upper jaw (especially, as it seems to me, the bicuspids), and the air driven through this chink, the sound of S will be produced; if we substitute the soft breathing for the aspirate, we shall have Z. Let the tip of the tongue be still further retracted, so as to be brought against the edge of the gum where it makes an angle to pass up and form the roof of the palate, we shall get the sound of R; but in this case, from the way the tip of the tongue is twisted up, I think the lateral closure is not perfect, or at any rate that the chink is more laterally extended than in the pronunciation of S. In sounding L, the closure is mesial and the aperture lateral. We make it by applying the tip of the tongue firmly against the gums behind the upper incisors, but exercising no lateral opposition-in fact, leaving a space open on each side: through FUNCTIONS OF THE TEETH. 23 these two lateral apertures the- air is driven, and' so the sound is generated. Thus the difference between 1) and L is, that in the former there is lateral closure, in the latter lateral aperture, but the mesial closure is the same in both; and in pronouncing D and L in succession, as in " candle," we merely have to libeiate the sides of the tongue from their contact with the upper alveolar arch and teeth. SH is perhaps the most purely dental sound of any; for in its formation the air is simply driven through the closed or nearly closed teeth. In S the chink through which the air is driven is exceedingly slender and also laterally circumscribed. In SH we have a larger or coarser sibilation, the tongue not narrowing the chink, nor being concerned in the production of the sound at all. I think it is only through the teeth in front of the bicuspids that the air is driven in this sound (SH), and that it is prevented from lateral escape.through the bicuspids and molars by the pressure of the cheeks, by means of the buccinator muscle, against the outsides of the teeth. Anyone pronouncing the sound will feel that his cheeks are pressed against the outsides of his teeth, and that his buccinators are in a state of action; and this, no doubt, is how it is that the lips are protruded in uttering it; for, to fix the commissures of the mouth, that the buccinators may act from them with advantage, the orbicularis oris contracts, and when this is the case either the mouth must be closed, or, to prevent this, the lips must be protruded. In the lateral apertures between the teeth being closed, and the air prevented escaping through them by the pressure of the cheeks against their outsides, instead of the edges of the tongue against their inside, the formation of this sound differs from that of all others. That the lateral escape of air between the molars interferes with the firmness and integrity of the sound may be shown by introducing the finger between the cheeks and the teeth, and so holding the former out; the lateral escape of air at once alters the sound. The French J, which would be spelt in England ZH, is the soft breathing of which SH is the corresponding aspirate. The English J is really a compound sound, and begins with the sound of D; it is, in fact, DJ. Anyone analysing in his own person how the J in "'judge" is sounded, may satisfy himself of this, and that the movements of the parts concerned are 24 DENTAL PATHOLOGY AND SURGERY. those that would produce D and the French J in succession. CH, as in " church," is the correlative aspirate of the English J, and might be spelt TSH. Of the five English vowels, A, E, I, O, U, together with the additional vowel sounds in AH, AU, 00, only one can strictly be said to be dental. In the pronunciation of E it will be observed that the tip of the tongue is pressed against the back of the lower incisor teeth, so as to be flattened and expanded, and the air driven through a horizontal chink formed between. the upper surface or the front of the tongue thus flattened out and the gum behind the upper incisors; and it would be extremely difficult to pronounce this vowel without thus pressing the apex of the tongue against the lower front teeth. But, if the pronunciation of the vowels A, I, and U be analysed, it will be observed that the sound of E enters into them all-A and I terminating with the E sound, and U commencing with it. Thus E is a pure dental vowel; A and I terminally dental; and U inceptively dental. To these must be added Y, which so commonly has the sound of E, as in " yes." and "'joy." Now, the loss or injury of any of the passive organs of speech produces a corresponding defect in the articulation of the sufferer; and, if the teeth are the organs affected, then dental sounds are interrupted or interfered with. This is always very manifest, and by far most manifest immediately after the loss of a tooth or teeth has taken place; for by degrees the loss is, to a certain extent, compensated by the adaptation of the soft parts, and the cultivated skill of the speaker. The injury inflicted on the speech is always more marked when the loss consists of a few teeth, and especially those towards the front of the mouth-there being thus produced a marked gap between teeth still standing. The loss, for instance, of the superior central incisors while the laterals remain, puts an end to the F's and V's of the speaker, and a blowing sound through the opening takes their places, or is superadded. When, however, several teeth are removed, and a considerable surface of gum is left free, the tongue or the lips, as the case may be, can be applied to it somewhat as they had been previously to the teeth; thus, if all the upper incisors and canines are gone, the upper gum rests on the lower lip, so as to imitate the sounds of F and V; but the want of the teeth with the little intervals FUNCTIONS OF THE TEETH. 25, between them deprive those sounds of the slight sibilant accompaniment which properly attends them, and which is produced by the passage of air between the teeth; the sound is dull and short; thus, V has somewhat the sound of B, and F of P: still the sound is approximately correct. When lateral teeth (molars and bicuspids) are lost, the flattening out of the tongue, and the in-sinking of the cheek remarkably fill up the gap and compensate for the loss; and thus, to a considerable extent, the consequent defect in articulation is remedied. These compensating changes in the soft parts are not sudden, but progress by time. After a gap or a lateral vacancy hag existed some months, the tongue, if the loss of teeth be on one side, loses its symmetry and bulges so into the hiatus as to fill it -at least so as to meet the cheek. Everyone who has supplied artificial teeth in such a case must have observed what is the consequence-how frequently the tongue and cheek are at first bitten by the substitutes for those natural teeth, the removal of which has allowed the soft parts to enlarge and expand. These changes in the soft parts are merely instanced as some of the compensatory conditions by which the effects on speech of the loss of teeth are remedied. Without carrying this subject further, it may be stated in general terms that, though the loss of the teeth will injure or destroy those elements of sound which it is their office passively to assist in forming, the plasticity of the soft parts will greatly relieve or remedy such injury. Further, that an individual adapted by habit and long use to speech without teeth, is at first incommoded by their artificial restoration. But that those persons will ultimately have the best articulation who, having lost teeth, are supplied artificially by that which is the nearest approach to a perfect dentition. 26 DENTAL PATHOLOGY AND SURGERY, CHAPTER III. SUPERNUMERARY TEETH-THIRD SETS OF TEETH-DEFICIENCIES OF TEETH. THE number of the human teeth being definite and fixed, a departure from that number is an abnormality. This more often occurs as an excess than a deficiency. Supernumerary teeth occur as additions to the temporary set; as additions to the permanent set; but more commonly than either as superadditions to the permanents-superadded, that is, as regards both time and character. The only instances with which I am personally acquainted, where this condition has affected the temporary teeth, have consisted in a repetition of one of the lower milk incisors, ranging with the others, and not to be distinguished from them. Many years since, I saw this in a young cousin of my own; and it was impossible to say which of the two left lower lateral temporary incisors was the supernumerary, and which the normal tooth. They were nearly or quite coincident in time of advent, and ranged in unbroken arch.* In one instance the supernumerary tooth was organically united to its normal neighbour. I am not aware that supernumerary teeth of the character of temporaries, ever follow upon the milk set as others- do upon the permanents. Where supernumerary teeth occur in connection with the first set, I believe it may be stated that they are coincident with those that are contiguous to them and similar in form and general characters; ranging, moreover, in the same arch.t They are usually found in the lower jaw. When the supernumerary * The permanent lower incisors were afterwards normal in number. t An interesting exception to this has occurred in the practice of Mr. Ibbotson. The temporary supernumeraries were followed by supernumerary teeth. SUPERNUMERARY TEETH. 27 teeth appear later in life, they are generally, though not always, behind the range of the normal teeth. And as to time of advent, they may appear just before, with, or soon after the true teeth which are near them, and with which their genesis has been associated. Most often they follow the normal teeth in date of eruption: least often they antecede them. In their relation to the proper teeth of the permanent set, they are by far the most commonly connected, both by proximity and apparent resemblance, with the incisors; less commonly with the molars; and still more rarely with bicuspids and canines. They are far more common in the upper than in the lower jaw. These permanent supernumeraries, if they may be so called, are divisible intoConical teeth-canine-like; Cubic-crowned, resembling lower bicuspids; and Teeth mimicking those of the true set in their immediate neighbourhood. The conical supernumerary teeth are usually found towards the extreme front of the upper jaw, and frequently single between the two superior central incisors, as seen in the accompanying illustration (fig. 7). When behind the arch of Fig. 7. the true teeth they are still generally well forward; but instead of being single, are sometimes in pairs. Or rather, it should Fig. 8. Fig. 9. Fig. 10. be said, they are in twos, which often differ considerably in form. Thus, one will be a single conical cusp, while the fellow tooth will be broken up into several small cusps: as is illustrated by the left and central figure in this series (figs. 8 and 9). .28 DENTAL PATHOLOGY' AND SURGERY. These canine-like supernumeraries usually consist of a short. conical crown and a long conical root, and there is seldom any distinct indication which is the front and which the back of the tooth. It is uncommon to find supernumerary teeth in the lower jaw' associated with the permanent set. The minute figure to the right (fig. 10) represents a central supernumerary tooth which I extracted from deep down in the front of the lower jaw: it was projecting forwards, and had pierced a hole in the lower lip. This example occurred in a boy, ten years old, at Guy's Hospital. The point of the supernumerary tooth had appeared a few months after the permanent incisors were cut. The incisors were not separated, as the little supplemental tooth pierced the gum nearly half an inch below their necks. The cubic-crowned teeth, resembling lower bicuspids, are, I believe, always found in the upper jaw immediately behind the central incisors or slightly to their outer edges, and usually in pairs. The accompanying illustration (fig. 11) shows their geneFig. 11. ral situation. The form of these teeth is very characteristic, and pretty constant. In front the crown presents a smooth oblong surface; behind it is lumpy and corrugated; while at the summit the enamel surface is bulged-in in the form of a pit. The roots are usually long, cylindrical, and straight. The accompanying figures (12, 13) represent the left tooth taken from the mouth, which is illustrated by the foregoing woodcut. The left figure represents the back of the tooth when in situ, the right its front. The tooth was extracted before the end of the fang was completely formed. SUPERNUMERARY TEETH.'29 The supernumerary teeth which mimic those in their own.immediate neighbourhood are the most interesting, involving the practical question as to which of two teeth, close together and just alike, should be considered the normal tooth, and so retained; and as bearing upon the curious theoretical question, how far their formation may be considered as an effort to produce a third set of teeth; or at least how far their presence may explain those reputed instances in which a third set has been said to have occurred. The only supernumerary teeth which resemble the normal form of the true teeth, are those which sometimes occur towards the front of the mouth. The superior incisors sometimes; more often the laterals than the centrals: the upper canines very rarely, and still more rarely the bicuspids. Further back in the mouth, and associated with the molars, the supernumeraries are usually but small conical cusps, and sometimes appear to be actual cusps belonging to the neighbouring teeth, as if thrown off by fission. I have seen three instances in which the superior permanent central incisor has been mimicked. They were all three exactly alike. Upon the shedding of the temporary incisors one of the apparent permanent successors was cut in advance of its fellow: this was followed by the tooth on the other side; and then appeared a third incisor over the first that had come. The event proved that the second and third were the normal central incisors; the first that was cut being a supernumerary tooth, but like the true tooth on the same side, excepting that the back of the crown was more corrugated, and the serrations at the edge rather deeper than usual. As I have said, I have seen this three times, with scarcely any variation of the circumstances. I have in my collection one plaster cast, and two teeth illustrative of this condition. The supernumerary lateral incisor, however, completely imitates the true tooth. I have seen five instances of this, and in two cases both laterals were thus repeated. I have four such supernumerary laterals in my possession. One of the cases in which both laterals were repeated was very interesting. A young lady about twelve years of age was brought to me respecting the irregularity of the teeth in the front of her mouth, and this consisted in the presence of four superior lateral incisors-two 30 DENTAL PATHOLOGY AND SURGERY. very prominent, and two backward. When the mouth was shut, the lower incisors divided the two in front from those behind. I extracted the latter, and those in front soon fell back into their places. The teeth I had extracted were perfect lateral incisors, and could not be distinguished in any way from those that remained. In the other instance, where two supernumerary laterals were present, they were in the true dental arch, and they were rather smaller than those which I took to be the normal teeth. In the other three instances the imitation was on one side only-there was one supernumerary lateral incisor. A very remarkable example of supernumerary incisor development came under my notice some time since, which can be best understood by reference to the accompanying figure taken from Fig. 14. a plaster cast of the boy's mouth. The patient was about twelve years old. Describing the front of this patient's mouth, and beginning from the left (the right of the figure), there was first the anterior bicuspid, then the left canine just through the gum, then a large broad incisor tooth, then a similar one just a trifle smaller; after that two small incisors of the form of central incisors united together organically, then another incisor wider than either of the two latter, and smaller than either of the first two, but still resembling a central rather than a lateral. Still further to the right (the left of the figure) is seen the projecting gum over the right canine just about to pierce, and then the right anterior bicuspid. It is difficult to interpret the incisor elements of this dentition; all the teeth resembled centrals. Their edges were faceted by direct application to the summits of the lower teeth. The patient was to have come to me again; but he did not return. Supernumerary canines are far less common than incisors. It does not follow that — a supernumerary tooth, because it is SUPERNUMERARY TEETH. 31 opposite a canine, is therefore a supernumerary cuspidatus. Again, many of the supernumerary teeth are pointed, and resemble to some extent canine teeth; still they have none of the moulding of a true eye-tooth. However, genuine repetitions of the cuspidatus do occur. I have seen two in the same individual. In the autumn of 1866, a German gentleman applied to me on account of the annoyance which his tongue (in a state of syphilitic ulceration) experienced by contact with two teeth projecting from the palate on either side, just within the eye-teeth. Upon examining the mouth, I found two supernumerary pointed teeth in the situation indicated. I extracted them, and found that they were exactly like the true cuspidatus that remained in the normal position. The patient claimed one of these teeth, and I have retained the other. The supernumerary teeth were cut a few years after those in proper place. The only example of a supernumerary bicuspid tooth which has come within my knowledge is the specimen here figured. There is a minute tooth with two cusps attached to a second upper bicuspid. The crown is free, but the Fig. 15. root fused to the larger tooth. This little super-, numerary is truly bicuspid, inasmuch as its crown presents two eminences with an intervening depression; but it cannot be said that the form of the crown is exactly like that of a full-sized normal premolar. Such, then, are the supernumerary teeth which mimic those of the true set; and they add, as far as their number and simili. tude go, a certain weight in favour of the authenticity of those instances of third sets of teeth which are reputed to have occurred. Of this more will be said presently. I have never seen or heard of an instance in which a supernumerary tooth had more than one fang. The structure of the tooth is generally very compact, and the enamel thick. Where the surface is irregular, it is usually produced by tubercular masses of enamel. In one instance only have I seen the enamel rocky and pitted: in this instance, there were two supernumeraries in the same mouth, and both similarly affected. In one instance, in which I made a section of a supernumerary tooth for the microscope, I found the dentinal tubes passing into the 32 DENTAL PATHOLOGY AND SURGERY. enamel to a remarkable extent; and those sacculated, clubshaped cavities sometimes seen extending from the dentine into the enamel, were extremely numerous. As regards the treatment of supernumerary teeth, I know but of one plan-extraction. Excepting where a supernumerary tooth is organically connected with a normal tooth, it is, I believe, always in the way, and better removed. In the front of the mouth they usually dislocate the incisors, protruding them, and even altering the expression of the face, and, when central, separating them in the middle line. They should therefore be extracted as soon as possible, when it will be found that the normal teeth soon assume their proper position. Third Sets of Teeth.-The doubtful question as to the occurrence of third sets of teeth may well be considered here. It is of small practical importance, but is very interesting physiologically; and the uncertainty which attaches to the disputed circumstance is not a little remarkable as a matter of scientific observation and evidence. There is no recorded instance of the occurrence of a third set of teeth in the writings of any modern observer of scientific repute; but the authorities of earlier date, who have asserted the fact, are so respectable, that it is difficult altogether to discard from one's mind the idea that the circumstance has occurred in some shape. At the same time, it must appear to any scientific reasoner as most remarkable, that in the immensely increased population of more recent times, subjected far more than formerly to acute professional scrutiny, no such occurrence has been seen. The fallacies by which a mistaken judgment may happen in this matter (at least, as regards partial third sets of teeth) are such as would be not unlikely to lead to errors. Supernumerary teeth, and still more impacted teeth, which, though belonging to the normal set of permanents, have not been previously missed, and have, late in life, pierced the gums from the prolonged absorption of alveolar process, would be, and probably have been, considered as representatives of a third set of teeth. These fallacies would not, however, explain those instances where complete third sets have been recorded. Hunter has had the credit of stating that he himself saw one instance in which a complete third set of teeth was developed. THIIRD SETS OF TEETH. 33 He has, however, recorded no such observation; but, having expressed himself rather ambiguously, Dr. Mason Good misunderstood his remarks, and incorrectly attributes to him this statement. Subsequent writers,* copying Dr. Good's resume of the subject, have repeated the error, until Hunter has been regularly accredited with the assertion. All that Hunter did assert on his own observation was, that he once saw an instance in which " two fore teeth shot up in the lower jaw." These he supposed to be portions of a third set. The following instance of a complete third dentition is thus recorded, in the third volume of the " Edinburgh Medical Commentaries," t on the authority of the editor:-" A country -labourer, who was an inhabitant of the town of Hawick, in the south of Scotland, lost all his teeth by the time he arrived at the sixtieth year of his age. But, about half a year afterwards, a new set made their appearance. All of them appeared within the space of twenty days; but during this time he suffered the most excruciating pain. His new set of teeth continued fresh and firm for a period of thirty-four years. He is still alive, has entered the ninety-sixth year of his age, and has all his teeth except three, which he has lost within these two years, one of them very lately." In another instance, recorded by Dr. Bisset, a physician at Knayton, in Yorkshire, in a letter to Dr. Duncan, an old woman of ninety-eight is stated to have cut twelve molar teeth, and two upper incisors. Six months afterwards, four molars had been shed, and the remainder were somewhat loose. Dr. Mason Good ~ saw a lady, seventy-four years of age, who cut 1" several straggling teeth." And he records another instance that occurred to him:-" A lady of seventy-six, mother of the late Henry Hughes, Esq., printer of the Journals of the House of Commons, cut two molars, and at the same time completely * Dr. Harris in his Dental Surgery has repeated this assertion in edition after edition. (Dental Surgery, by C. A. Harris, Philadelphia. Several editions.) t Edinburgh Medical Commentaries, vol. iii. pt. i. p. 105. Lond. 1784. t Published in Edinburgh Medical Commentaries, vol. viii. p. 371. Lond. 1787. ~ The Study of Medicine, by John Mason Good (4th edit.), vol. i. p. 40. D 34 DENTAL PATHOLOGY AND SURGERY. recovered her hearing, after having been for some years totally deaf." This latter case was probably an instance of impacted teeth being laid bare through the prolonged absorption of jaw-bone in old age. No such explanation, however, can apply to the marvellous history, which Dr. Stare has recorded in an early volume of the " Philosophical Transactions of the Royal Society," and of which the following is an abstract.* The subject of this curious abnormality was " a Bedfordshire gentleman of an old English family," and he was grandfather of Dr. Stare, who records the case. When eighty years of age all his teeth were sound and firm: at eighty-two he lost first one, and then a second front tooth. After this, in the succeeding three years, the whole of the front teeth were shed. They were subsequently replaced by an entire new set of teeth, which, it seems, he retained till his death in his hundredth year. This singular history is narrated in a letter to Sir Hans Sloane, with earnest assurances of its truthfulness, by Dr. Stare, who refers to the circumstance, not only from his own observation and inspection, but as notorious at the time. Deficiencies of Teeth.-It is by no means rare to find certain of the teeth wanting from the set; and this may arise fromn the tooth being embedded in the jaw, and not projected; or from its not being formed: to the latter I now refer. This is more common'with the permanent than the temporary teeth. The latter may be complete, and the succeeding set deficient. The superior lateral incisor is more often absent than any other tooth. I have no right permanent upper lateral; but the temporary was present. Deficiency, like all other congenital peculiarities of the teeth, is very apt to run in families. I have three near relatives in whom the superior laterals are wanting; and in some others they are small and imperfectly formed. I am acquainted with three sisters, two of whom have no upper wisdom teeth; in the third they are very minute. I had a patient whose mouth contained no inferior incisor teeth, and no upper laterals. The wisdom teeth were absent * Letter from Dr. Frederick Stare to Sir Hans Sloane, " Concerning a person who had a new set of teeth after eighty years of age." In Phil. Trans. vol. xxviii. p. 273. DEFICIENCIES OF TEETH. 35 from both jaws; but as the patient was only twenty years of age, the latter might still appear. Two other examples show the hereditary character of these defects. A young lady, thirteen years of age, was brought to me by her father. She had no central incisors of the lower jaw, but the laterals were separated to the full extent. The temporary centrals had come out, but from the condition of the alveolar border it was clear that their successors were totally wanting. The father, fifty-six years old, also had no lower central incisors; neither had he the second molars or wise teeth on either side of the lower jaw; the second bicuspids were wanting, and their place held by the second temporary molars, still sound and firm. In the upper jaw the wisdom teeth were absent. This gentleman had never had a permanent tooth extracted. Two interesting cases, in which great deficiency of teeth was associated with almost complete alopcecia, are recorded in the thirty-first volume of the "Transactions of the Medico-Cbirurgical Society " (p. 71). The subjects of these peculiarities were cousins, and each had four molars in the upper jaw, and no other tooth. Otto * mentions, on the authority of others, two cases in which teeth were wholly wanting. The first occurred in a woman who at sixty years of age had never had any teeth.t The other two were brothers, adults, members of a Jewish family. Neither of them had teeth or hair.: * Lehrbuch der Path. Anatomie, Sc,, von Dr. A. W. Otto. Berlin, 1830. t Borelli, Hist. et Obs. Med. Phys., Cent. II. Obhs. XI. i., p. 144. 1676. I Daaz, in Stark's Archiv. f. d. Gebzertshiilfe, vol. iv. p. 684. Jena, 1792. 36 DENTAL PATHOLOGY AND SURGERY. CHAPTER IV. IRREGULARITIES IN THE POSITION OF THE TEETH. IRREGULARITIES of the teeth, as regards their relation to each other and to the jaws containing them, constitute some of the most important considerations in the practical treatment of the teeth, and they are not without interest theoretically. Irregularities of the temporary teeth are uncommon, and are not of'much importance. The incisors sometimes have a distorted position, but the commonest form of irregularity in the teeth of the first set is that which is relative in the two jaws. It is not very rare in families, where there is a strong tendency to what is known as an "underhung bite," for the temporary incisors, or even the canines of the lower jaw, to project beyond those of the upper. And though this may not be attended by any irregularity of the relative position of the teeth in either jaw, it still constitutes a serious irregularity of the teeth as taken collectively. These irregularities of the temporary teeth may not require immediate interference, but they indicate the propriety of most careful superintendence during the advent and progress of succession. Irregularity of the teeth appears to be one of those conditions induced by artificial life, and progressing in degree during the lapse of time in successive generations. It is almost unknown among the lower animals in a wild state; but it has been induced in some through domestication. This subject may be treated with almost endless extension, and with profuse illustration, as the conditions of irregularity are almost without limit in their variety, and may be complicated in cause. IRREGULARITIES IN THE POSITION OF TIIE TEETH. 37 I propose to consider them here briefly and practically, and principally by illustrative cases that have occurred in my own practice. The causes of irregularities may be (1) congenital and hereditary, (2) the prolonged retention of temporary teeth, (3) accidental mechanical influences, (4) disproportion of the size of the teeth and jaws, (5) faulty development of the jaw-bones. There are few conditions in which hereditary influences are more manifest than in the irregularities which occur in the teeth; and these show themselves often in minute particulars, and are displayed with distinctness by collateral relations. The prolonged retention of temporary teeth is frequently associated with irregularity in their successors or their permanent neighbours, and is probably often the cause of such irregularity; though perhaps the imperfect or tardy growth of the permanents may be at least partially the reason why the temporary teeth are so retained. Accidental mechanical influences, such as thumbsucking or hypertrophy of the tongue, will cause certain irregularities. But by far the most common cause of irregularities in the teeth is their being disproportionately large in comparison with the jaws. This is a condition which has been progressing in development for a long period of time and very many geatat, aevm w pf een in sanf e All Nmuenient o& m Mi% life. The disparity is such as to lead to the crowding of teeth so constantly seen, and which is sometimes so excessive as to altogether exclude some member of the dental series from eruption, and hold it permanently impacted in the substance of the jaw. This condition is not infrequently induced by the premature extraction of the temporary teeth, which permits contiguous permanent neighbours to approximate each other to the displacement or partial exclusion of the successor of the extracted tooth. Malformation of the jaws is much less common, and is only certainly displayed in some peculiar irregularities, as in the V-shaped jaw. In considering irregularities of the teeth in regard to their treatment, they may be divided with much practical advantage into (1) Simple and (2) Compound or Contingent. Simple irregularities are those in which the misplacement is 88 DENTAL PATHOLOGY AND SURGERY. absolute as regards the jaw affected, and independent of the position of the teeth in the opposite jaw. They may affect both jaws in the same individual, but they are uninfluenced by each other. Compound irregularities are contingent on the position of the teeth of the opposite jaw, as to cause or maintenance, and are dependent on the " bite." The importance of these distinctions will be manifest in considering the treatment of these cases. In curing irregularities it will be necessary toa emove all obstructions which prevent the teeth from assuming a regular arrangement; and it may be necessary to apply mechanical elastic force to complete that result. Both these elements of treatment may be requisite in a single case. Again, there is a peculiar method of applying mechanism where no force is involved, namely, in those cases in which the irregularity is contingent on the bite, and where the closure of the mouth causes its maintenance. In such cases the jaws must be kept apart during treatment, and this is accomplished by the passive mechanism of gagging. Very much depends on the age of the patient when the irregularity comes under treatment. For instance, where it is brought about by crowding, the mere removal of some tooth or teeth in a young patient may allow the remainder to assume the natural arch, and this they will generally do without assistance; whereas the same condition in an older patient will require mechanical pressure to place the teeth in proper range, and it may be necessary to maintain them in this position by similar means for a considerable period, as when once firmly established they have a tendency to return to their original relations. It has appeared to me that this subject may be conveniently Fig. 16. treated by the consideration of typical examples of irregularity; and the accompanying figure (16) illustrates one'i | of the commonest forms -where the upper canine tooth, from insufficient room, makes its appearance high up, and in front of the range of contiguous teeth. I refer to this form of irregularity, first, not only from its frequency, but because its consideration involves many general IRREGULARITIES IN THE POSITION OF THE TEETH..39 questions of importance bearing on the whole subject. It may arise from the premature removal of the temporary canine tooth, thus allowing the bicuspid and lateral incisor to approach close to each other. This condition usually manifests itself between ten and thirteen years of age, and, if uncomplicated, it is readily cured by the extraction of a tooth behind the coming canine; and in the simplest cases the removal of the first bicuspid effects the remedy at once. Circumstances, however, may suggest the desirability of sacrificing another tooth, the second bicuspid, or even the first molar; and this point requires careful consideration. And it should further be remembered that much may be done by nature, through the expansion of the jaw itself; and this is especially the case where the permanent teeth make their appearance very early, and at a time when the jaw, from the age of the patient, may be supposed to be too soon invaded by its large and many occupants. I have sometimes known bicuspid teeth removed to make room in young patients with much crowding, when afterwards it has been apparent that such a proceeding was unnecessary, —the jaw growing to such an extent that considerable spaces were developed between the remaining teeth-spaces which in the aggregate would have accommodated the teeth that had been extracted. It is a question, therefore, with young patients to consider how much may be done by nature in time, before a sacrifice is entailed which cannot afterwards be remedied. In estimating which of the three teeth (first or second bicuspid, or first molar) should be extracted in any. given case, many points arise which should be carefully balanced in the mind of the operator before he makes his selection. The respective value of the teeth must be considered as features, as organs of masticcation, and in relation to their prospective durability and their soundness at the time. These are all important points for consideration, irrespective of the cardinal question as to which tooth would, by its removal, best effect the required object, furnish the needed room, and allow the misplaced anterior tooth, or teeth, to range in proper order with the others. Unquestionably the bicuspid teeth are superior as features to the molar; indeed, the farther forward in the mouth a tooth is situated, the more does it modify the form of 40 DENTAL PATHOLOGY AND SURGERY. the lips, the more is it seen in expression, and consequently the more would its absence be remarked. It must be recollected, however, that there are two bicuspids, so much alike that when one is lost the other takes its place as far as appearance goes. As an organ of mastication a molar is of greater value than a bicuspid. The present soundness or otherwise of the bicuspids and molar is a question of the greatest importance, and must often decide finally and peremptorily the question under consideration. Provided the loss of either a bicuspid or a first molar would give the necessary space with equal ease and certainty, or nearly so-one being carious and the other sound -there can be no hesitation as to which should be extracted. The decayed tooth should be taken out, and a double good will thus be effected, the regulation will be achieved, and a source of future or perhaps present pain will be removed. It must be recollected, however, that it will take a far longer time for the crowding of the canines and incisors to obtain relief by the removal of a molar tooth than by the loss of a bicuspid; and in patients who have reached some fourteen or fifteen years of age, or in whom the irregularity has existed for some time, it may even be doubtful if the loss of a molar will extend forward the required relief. And this leads to the consideration of another very important point. The''te " of the bicuspids in the two jaws may be interlocking; the cusps of the lower bicuspids may so abut, when the mouth is closed, upon the posterior aspect of the cusps of the upper bicuspids as to prevent the latter from moving backwards after the removal of the first molar; and thus, though the room may be firnished, the crowded upper front teeth are mechanically prevented from obtaining the benefit of it. The operator, therefore, should well look to this point before deciding on the removal of a molar. I urge this, not on theoretical grounds, but because I have more than once seen a molar removed under these circumstances; and,. the bite keeping the upper bicuspids immovably forwards, no improvement in the irregularity took place. Finally, the question of relative prospective durability, as between the bicuspids and first molar, supposing each to be sound, is a point the importance of which cannot be over-estimated. This matter isnot so easily decided by the statistical records regarding the decay of the two teeth as has been imagined. No doubt first molars are more IRREGULARITIES IN THE POSITION OF THE TEETH. 41 prone to decay than bicuspids, and it may be prognosticated as probable that at the time any particular first molar is cut its term of soundness will be shorter than that of any particular bicuspid, when it first comes into the mouth. But that does not state the case fairly. The question is, which tooth, supposing both to be sound at the time when the regulation is required (say at about twelve years of age), has the best prospect of prolonged soundness and usefulness? It should be remembered that a first molar tooth at that time has been in the mouth some six years, and if then sound, it has for that long period resisted the influences of decay. The bicuspid, though also sound, has only been exposed to like influences for a year or a few months. The existing evidence therefore, though negative in its nature, is, as a matter of probability, altogether in favour of the molar on the score of prospective soundness; and my own experience is that if a first molar is free from decay at twelve years of age, it is nearly as likely to remain sound as any other molar; whereas no such estimate can be formed of the prospective durability of a bicuspid that has been in the mouth only a few months. This is the real question as between a sound bicuspid and first molar at the usual time for removing one of them to make room, and it is in favour of the retention of the molar. I would, therefore, say, as a summary of these arguments: Provided the removal of either tooth would be equally efficacious, or nearly so, remove a decayed tooth rather than a sound one; this will lead to the very frequent extraction of the first molar. If both the bicuspids and first molar are sound, extract one of the former; and the regulation, though not more effectually perhaps, will be more speedily accomplished than by removing the molar. The foregoing observations have been written with special reference to the upper teeth, but they may be applied to those of the lower jaw. The greater durability of the inferior bicuspids, however, and the more easy cutting and more forward position of the lower wisdom-tooth which result from the removal of a first molar, would tend to balance more evenly the claims of the two teeth respectively; still, where both are sound at twelve years, I would remove a bicuspid and retain the molar. As regards the first and second bicuspids respectively, the removal of the former I consider preferable. 42 DENTAL PATHOLOGY AND SURGERY. This crowding of the canine tooth in the upper jaw upon the lateral incisor, entailing the loss of a tooth to remove unsightly irregularity, not infrequently involves another question of much nicety and requiring a judicious balance of opposing arguments. The question I refer to does not relate to the loss of a bicuspid' or a molar, to make room for more forward teeth, but it is this: In a confirmed irregularity in a patient of more advanced years, when posterior room cannot be expected to allow the canine and lateral incisor to range in proper arch, the disfigurement being great, which of the teeth in question ought to be sacrificed? Such cases constantly occur. Take the following as an example: A young lady eighteen years of age has been entirely neglected as to her teeth. The first bicuspid tooth of the right side, upper jaw, is almost in contact with the lateral incisor; the canine is in front, high up, and rather to the outside of the lateral, while the latter tooth is so far forced back as to shut behind the lower teeth when the mouth is closed, having an intersecting bite. Such cases, with or without the latter complication, are but too common. Now, the lateral incisor is of the first importance as a feature tooth; its loss makes a marked deficiency; its replacement by the large pointed canine is a disfigurement. On the other hand, the lateral incisor is a perishable tooth in comparison with the canine. The cuspidatus is also a marked feature tooth; but the large pointed cusp of the bicuspid makes a fair substitute for it in that respect. There are many points, therefore, to be balanced in the mind before deciding which tooth to sacrifice, lateral incisor or canine. Another circumstance occasionally arises in these cases of much importance. The fang of the lateral incisor becomes absorbed from the pressure of the canine; it is very common to a slight degree, occurring then upon the outer and front surface of the fang, about the sixth or eighth of an inch from the neck of the tooth. I have at least a dozen such specimens, and they were all removed in cases similar to those I am now discussing. But sometimes the whole root is absorbed, the crown of the lateral incisor merely adhering loosely to the gum. I have known an instance in which the operator was manipulating the canine and lateral incisor, in doubt which to remove, when the crown of the latter tooth came off in his hand, the whole fang having been absorbed. Before, IRREGULARITIES IN THE POSITION OF THE TEETH. 43 therefore, removing a canine tooth to make room for the lateral incisor in such irregularities as these, it should be clearly ascertained that the incisor holds its place in the jaw by a firm root. My own practice, in these confirmed cases, is to remove the canine, when the lateral is sound and bites in front of the lower teeth; to remove the lateral when it is either carious or loose, or bites within the lower teeth. If the canine be retained, the point of its cusp should be rounded off by the file, so as to resemble as much as possible the lateral incisor of the other side. On the ground of symmetry, where interference is necessary on both sides, it will be well (unless there are positive indications to the contrary, such as much difference of position or soundness of the respective teeth) to sacrifice the same tooth on the right as on the left. An overlapping and crowding of the upper incisor teeth is Fig. 17. Fig. 18. not uncommon, and may exist in very various degrees and forms. The accompanying illustrations are of a sufficiently characteristic 44 DENTAL PATHOLOGY AND SURGERY. example (figs. 17, 18), and show the treatment which rectified the irregularity in this instance. The left central incisor projected beyond the normal arch, while the right central and both laterals were within it. To obtain room the first left bicuspid was extracted, and then a plate (fig. 18) was adapted, in which processes a and b pressed out the in-standing teeth, while a band of hard elastic gold, c, drew in the projecting incisor. An incisor tooth being twisted and placed more or less across the line of the maxillary arch, is another not uncommon irregiularity. The accompanying figure (fig. 19) illustrates this condition, where the right lateral incisor was thus placed. The tooth was Fig. 19. readilyestoredtoitsnrmalpoitio b ei, readily restored to its normal position by the plate (fig. 20), the small process, a, pressing out the receding angle of the tooth, Fig. 20. and the elastic band, b, forcing in the projecting angle, the points of pressure being increased from time to time, following up the movement of the tooth. The sudden, forcible twisting of the tooth into its right posi-.tion, by means of forceps, has been adopted in many of these cases with better results than could have been anticipated; but IRREGULARITIES IN THE POSITION OF THE TEETH. 45 necrosis and loss of the tooth sometimes follow; and I think the proceeding scarcely justified, when the same result can be accomplished safely by gradual pressure. Simple separation of the central incisor teeth is not uncommon, and they may be readily drawn together by an indiarubber ring; but they are very prone to return to their former position, even after prolonged and repeated use of the appliance. This plan of treatment, moreover, is not free from serious risk: the india-rubber ring is apt to pass up far on to the neck of the tooth, peeling the gum from the tooth, which, if continued, leads to its loosening and may even entail its loss. I have known an instance in which a young lady lost both the central incisor teeth from this cause. Where the separation of the incisors is Fig. 21. attended with obliquity of axis, as in the accompanying illustration (fig. 21), it is desirable to apply a plate with processes pressing the projecting angles and edges towards the centre, adding increased length to the processes as the teeth yield. The case here figured was thus treated with the best results. In contingent irregularities, where the bite is intersecting, or altogether " underhung," where some or all of the upper six front teeth shut behind the lower in closing Fig. 22. the mouth, it will be necessary to adopt the passive mechanism of gagging, either alone,, or in combination with elastic pressure; for, if the jaws are not separated somewhat, the misplaced teeth are persistently held in their wrong position every time the mouth is closed. The accompanying illustration (fig. 22) shows how this occurred with the superior lateral incisors on each side. If such a case as this is taken early, say from seven to ten years of age, and there is sufficient room for the backward laterals to come forward, or if room be made by extracting the temporary canines, it is generally quite sufficient to separate the jaws by a '46 DENTAL PATHOLOGY AND SURGERY. gag, and the teeth then spontaneously come forward in proper range. This passive mode of treating these cases originated with Mr. Bell, and it is wonderfully successful as well as simple. The gag consists of a little'cap' (fig. 23) made to a model of one of the molar teeth, and upon it are soldered thicknesses of Fig. 23. Fig. 24. metal enough to separate the front teeth; it is made to clip firmly the neck of the tooth, and it remains on permanently. In fig. 24 the cap is seen embracing the second temporary molar tooth, which is the one I usually fasten it to. When the displaced upper teeth have advanced sufficiently to allow the lowers to shut behind them, the gag should be removed, and then closure of the mouth completes the cure, by forcing forward the teeth which had been too backward. If the upper tooth obstinately remains in its wrong position, it will be necessary to force it forward by pressure, and this may be accomplished by a plate such as is represented in fig. 18. Another and very powerful method of bringing forward upper teeth in an underhung, or an intersecting bite, is by placing upon the lower incisor teeth a plate from the upper edge of which a process passes obliquely upwards and backwards, so Fig. 25. that when the patient closes his mouth the upper teeth rest on the sloping surface and are pushed forwards. This may be done for one particular tooth, as shown in the accompanying illustration (fig. 25), or it may be applied to all the front teeth, as in a complete underhung jaw. In the latter cases I have found it very efficacious. It should be applied early-before the lower permanent canines have appeared. It will be necessary generally to remove the lower temporary canines, so as to get fastenings around the permanent lateral incisors. The force thus exerted on the upper teeth is very great, and I have by IRREGULARITIES IN THE POSITION OF THE TEETH. 47 this method completely rectified the underhung condition, even where it was a marked inherited condition. Crowding and overlapping of the-inferior incisor teeth is a common form of irregularity. It very frequently occurs as a transient condition in changing the teeth; but, when it threatens to become permanent, treatment should be adopted, either by giving lateral relief, removing a bicuspid tooth, or by extracting one of the irregular incisors, and of these it is usually desirable to remove the most prominent. The gap readily fills up, and the loss of the tooth is scarcely to be observed. The canine teeth are very prone to assume a wrong position and direction, and this is frequently associated with retention of their temporary predecessors. This displacement may vary from the slightest departure from a correct position to a complete impaction in the substance of the jaw. The accompanying illustration (fig. 26) shows the permanent canines occupying a Fig. 26. place in the palate, with the temporaries remaining in the arch. In this case I removed the temporary teeth; and, though the patient was seventeen years of age, I succeeded with a plate in forcing the permanent teeth into their proper place, and they were retained there by the bite. Irregularities of the bicuspids are not uncommon, and they usually consist of a too inward position or direction. Persistence of a temporary molar or its fangs may be a cause, or a general crowding of the teeth. Not infrequently an upper bicuspid, usually the second, is found in the palate, resting against the lingual surfaces of the contiguous teeth, and sometimes twisted on its axis. In the lower jaw a bicuspid may lean inwards, so as to present its masticating surface to the tongue. In any :48 DENTAL PATHOLOGY AND SURGERY. case, if inconvenience is experienced, it is better to extract the irregular tooth; and it will be most readily accomplished by operating from the opposite side of the mouth, and drawing the tooth towards the operator. Of the molar teeth the first and second very seldom present irregularity of position, but it is common with the wisdomtooth. These latter misplacements are of much surgical importance, and are treated of in a separate chapter on "Difficult Eruption of the Wisdom-teeth." The position assumed by the third molar is sometimes very singular. It has been found imbedded in the ascending ramus of the lower jaw; and in another instance it pierced the cheek and the crown was exposed on the surface of the face. Separation of the teeth of the two jaws in the front of the,mouth, while the molars are in contact, is occasionally met with. It may arise from (1) congenital malformation of the lower jaw. It may be induced (2) by contraction of the cicatrix of a burn in the throat, pulling down the front of the lower jaw; or (3) by the protrusion of an hypertrophied tongue. I have seen cases from all three causes, and have treated both the first and last varieties. The plan consisted in placing a padded leathern cup under the chin; this was connected by tightening bands with a cap on the head. In each case there was slight temporary improvement; but the least suspension of the pressure allowed a return of the deformity, and no ultimate benefit resulted. In the case produced by hypertrophy of the tongue, a large portion of that organ was removed by the galvanic ecraseur, and this was followed by a slow, but considerable spontaneous improvement in the form of the lower jaw, the front teeth ultimately approximating the uppers very closely. The V-shaped jaw, or " rabbit-mouth," as it has been called, from the prominence and exposure of the incisor teeth, constitutes an irregularity of a most serious character, and one which is difficult of treatment. It is a condition which is apt to affect many relations of the same generation, especially the brothers and sisters of one family, and in a certain sense is inherited; but I have frequently observed (as is the case with harelip) that many children of the same parents will exhibit the V-shaped jaw, while neither the father nor mother have it. IRREGULARITIES fN THE POSITION OF THE TEETH. 49 This is an irregularity which has developed with the progress of civilisation. It did not exist in the earlier races of mankind (Mummery), and it is now especially seen among those of refined and delicate organisation (Coleman). It is generally associated with enlarged tonsils, spongy gums, and offensive breath; and Dr. Langdon Down has pointed out that it is very frequently concurrent with congenital idiocy. It must be observed, however, that this form of jaw is often seen in persons of the highest intellectual capacity. The altered form of the jaw and position of the teeth consists of a lateral flattening of the arch and a projection of its centre; the bicuspids and molars, especially the former, approach each other, and the incisors project. It mostly affects the upper jaw, the roof of which is narrowed and much vaulted. Not infrequently the lower jaw is shorter than usual, with a peculiarly close bite, the lower incisor teeth resting on the palate behind the upper incisors. Not only do the incisors of the upper jaw project, but they assume an oblique direction, so as to rest on and overlap the lower lip. The treatment of these cases is tedious and often unsatisfactory. It may be sought to obtain two results-an increase in the width between the bicuspid teeth, and a diminished projection of the incisors and their sockets. The first object may be accomplished more or less by a palatal plate pressing the teeth outwards, the force being established and maintained by the width of the plate being in excess of that of the interval between the teeth, and the -pressure kept up by increasing the width as the teeth yield. This may be accomplished either by a metal plate, or by vulcanite or ivory, with the addition of compressed wooden pegs. The drawing in of the incisor teeth and a rectification of their direction of growth is, as it seems to me, of more importance, and in my experience is more easy of attainment. This may be achieved by keeping up persistent pressure on the teeth in front, and removing all resisting influence behind. A plate fastened to the first molar and second bicuspid may be the fixed attachment, from which the force is applied, and this may consist of metal bands extending round the front of the teeth, bent in from time to time as the teeth yield; or, what I prefer, an apparatus such as is here figured (fig. 27), In E DENTAL PATHOLOGY AND SURGERY. this a frame, c, fits over the incisor teeth, and from this a spiral spring, b, extends to a swivel and screw, a. The elasticity of Fig. 27. the spring soon brings in the teeth, and it should be tightened by shortening as the case progresses. Care should be taken that the bar across the palate does not obstruct the recession of the teeth and alveoli. As the incisors come in it will be desirable to prevent any hindrance which further-back teeth might occasion. It may be necessary to extract a bicuspid on either side. In a severe case I have extracted both bicuspids on each side, and have subsequently drawn the front teeth and their sockets so as to closely approximate the canines to the first molars. The teeth have a tendency to go back to their former position, and it is often necessary to wear the apparatus for a long period to prevent this. As long as the incisors project beyond the lower lip this will happen, and an intelligent patient will much assist the Fig. 28. treatment by pressing in the teeth with the lower lip, and taking care that they never rest upon it. IRREGULARITIES IN THE POSITION OF THE TEETH. 51 Transnposition, of teeth is an occasional though rare form of irregularity. It is confined, when complete, to the upper canine tooth, which may occupy a position between the bicuspid teeth, as in the accompanying figure (fig. 28), or it may separate the central from the lateral incisor. The former case is of no importance, but the latter may be somewhat unsightly. Still, no treatment is available. I have seen an incomplete transposition, in which the lateral incisor was nearer the mesial line of the mouth than the central; but it was behind it, and out of the alveolar arch. Inversion of the teeth is another and very rare form of irregularity. I have seen both the superior lateral incisors completely inverted and growing upside-down; the crowns of the teeth appeared in the nostrils, from which I removed them. 52 DENTAL PATHOLOGY AND SURGERY. CHAPTER V. UNITED TEETH. CONTIGUOUS teeth are sometimes united together. This fact, though now not called in question, was seriously disputed and denied after its publication by Mr. Fox, who was, I believe, the first to describe it in a systematic work on dental surgery. In 1803 Mr. Fox wrote, " Sometimes in the formation of the teeth two pulps unite, and upon their surfaces appear as two distinct teeth; but upon attempting to remove one it is discovered to be united to the next." It is this statement that was called in question. M. Maury t (1828) described united teeth, speaking of them as "soldered together," and he figured six examples of this condition. The next observation that was made upon this subject was by my relative, Mr. Bell, in 1829: "The intimate and inseparable connection of two teeth by means of a true bony t union of their roots and sides, though not a frequent occurrence, is too well established by facts to admit of a moment's doubt. I have met with six instances of it in my own practice." ~ But though this circumstance appears to have escaped the notice of previous writers on dental surgery (even that of Hunter), it was nevertheless recognised by some early anatomists: ~ The Natural History of the Human Teeth, p. 29. By Joseph Fox. London, 1803. t Traite' Complet de l'Art du Dentiste. Paris, 1828. t It is evident that the term " bony union," used by Mr. Bell, was not intended to convey the idea that the union was effected by crusta petrosa, or by true bone. At the time Mr. Bell wrote, what we now know as dentine was considered dense bone of a peculiar kind. ~ On the Anatomy, Sc. of the Teeth, p. 107. London, 1829. UNITED TEETH. 53 thus, instances are mentioned by Rhodigius,* Eustachius,t and Haller.t Where teeth are united together it is usually confined to two contiguous individuals, but sometimes more are involved. Otto ~ mentions three, and Eustachius four, in a state of union. There are two distinct kinds of united teeth: two methods by which the union is effected: the one congenital, in which the pulps are originally fused together, and in which the dentine is continuous in the two teeth; the other in which the union is secondary, occurring in after life,- and brought about by an exuberant growth.of crusta petrosa, encircling and coupling contiguous fangs which have ceased to be separated by alveolar plates. The minute structure and the development of these two forms of united teeth will be considered more fully presently. I allude to them now before detailing instances so as to point out which are congenital and which secondary. It is not a little remarkable that, considering how comparatively few cases are on record, almost all classes of teeth appear to have been subject to this condition; a circumstance which shows that there is nothing in the form or development of any particular teeth, or any region of the mouth, more calculated to produce it than any other. Otto saw three incisive teeth in a child united together: this was probably congenital: indeed, I believe whenever the temporary teeth are united, it is an ivory and congenital, and not a cemental or secondary union. Of the three cases that occurred to Mr. Fox, one consisted in a union of the central incisors of the lower jaw by their fangs and the sides of their necks and crowns (congenital). In another, the second and third molars of the upper jaw were united by their fangs (probably secondary). In the third, the fangs of the second lower bicuspid and first molar were completely fused together (congenital). These specimens are still to be seen in the Museum at Guy's Hospital. The six instances described and figured by Maury are* Lectiones Antigquce. Basel, 1517. t De Dentibus: Opuscula Anatomiea. Venet., 1574. t Elementa Physiologice, Sc. Bernze, 1764. ~ Lehrbuch der Pathologischen des Menschen uend der Thiere. Berlin, 1830. 54 DENTAL PATHOLOGY AND SURGERY. Ist. Two superior central permanent incisors, union throughout and congenital. Planche VIII. fig. 4. 2nd. Second and third lower molars united at the roots; probably cemental and secondary. Fig. 7. 3rd. First upper molar and second bicuspid; the latter embraced by the roots of the former, and the union probably cemental. Fig. 12. 4th. Inferior temporary central incisors; union congenital. Fig. 15. 5th. Two inferior bicuspids, the roots fused into one and clearly congenital. Fig. 18. 6th. First upper molar and supernumerary tooth; apparently congenital. Fig. 23. In the six examples referred to by Mr. Bell, three consisted in the lateral union of the temporary superior central incisors. The other three are undescribed; but I am informed by Mr. Bell that they were in one case the permanent superior central incisors; in another the permanent inferior central incisors (all these congenital); and the second molar and dens sapientice of the upper jaw: the nature of this union I cannot say. I have myself seen nine examples of dental union: a permanent lateral and canine of the upper jaw; a permanent dens sapientice of the lower jaw and supernumerary tooth; superior second bicuspid and supernumerary tooth, the latter being itself a miniature bicuspid (see fig. 15, p. 31); right central and lateral permanent incisors of the lower jaw; two supernumerary teeth, mimicking permanent upper incisors (see fig. 14, p. 30); two examples in which the temporary superior central incisors were anchylosed their entire length, crowns and fangs, with common pulp-cavity; temporary lateral of the lower jaw fused to a similar supernumerary tooth: all these being ivory union and congenital. One other case of union of teeth has occurred to me, to be more fully described elsewhere. It consisted in a coupled pair of bicuspid teeth, the uppers of the right side: these were soldered together by an excessive development of crusta petrosa embracing the fangs of the two as one. Thus, in these few examples, we see that individual teeth of each kind have been the subjects of this peculiarity: temporary and permanent teeth; regular and supernumerary; teeth of the upper and of the lower jaw; molars, premolars, canines, and UNITED TEETH. 55 incisors. Considering how few instances have been reported, this diversity is remarkable. I now describe more particularly two of my specimens, one congenital, the other secondary. The first consisted in a united cuspidatus and lateral incisor. The teeth were completely united by a very-broad union. When viewed superficially, the crowns of the teeth appeared distinct: the division on the surface which separated them down to the necks was so marked that a casual observer or careless operator would probably be unaware of their junction. Below the necks the fangs were completely united together; Fig. 29. and though the junction of the roots at the upper twothirds was indicated by a groove, the rest of them was ( so completely fused as to obliterate all indication of a double origin (see fig. 29). On dividing the teeth at the points indicated by the transverse lines in the figure, it was seen that there were two pulp-cavities in the crowns, and but one in the fused roots, as is shown in the accompanying little diagrams (see figs. 30 and 31). Fig. 30, Fig. 31. I made sections of these teeth for the microscope, by which I had an opportunity of observing, what I believe had never been seen before, the histological character of the uniting medium (fig. 32). A section through the crowns of the teeth, made transversely midway between the summit and the neck, exhibited the form of the figure 8, and it displayed to the naked eye a mass of dentine surrounded by enamel, and interrupted only by a small pulp-cavity in each of the teeth. Between these pulp-cavities, where the union existed, there was no break of surface, and nothing in the aspect of the dentine to indicate that the teeth were distinct individuals. The enamel did not appear to pass between them. The question was settled by microscopical scrutiny. A thin section of these teeth, viewed with low magnifying powers, displays within the enamel a mass of dentine, consisting of tubes radiating from each pulp. cavity, and passing across the 6;6 DENTAL PATHOLOGY AND SURGERY. union, without interruption. Near the edges of the teeth this continuity of tissue is most obvious: the tubes from one pulp can be followed across the line of junction, and are seen to end upon the inner surface of the enamel of the opposite tooth. In the centre, however, between the teeth, the section divides the tubes in an oblique direction: they are thus seen more or less cut across, and cannot be traced in lines; but there is clearly no interruption of tissue. This will be better understood by referring to the accompanying illustration (fig. 32). rig. 32. There is one point in this section which is curious and interesting: it is, that at the margin of the teeth, where they come in contact-at the extremities of the line of union-there are two small mammillary projections, one on each side, occupying the interval left by the curving inwards of the outline of the teeth. These appearances suggest the idea that, when in a soft and plastic condition, the pulps were firmly pressed together within their sac, and that where they met they were pressed out, as it were, into these little eminences. I sacrificed another specimen of teeth, united congenitally, to make sections for the microscope: the union was here also by continuous dentine.* These specimens then establish the fact, not only that the ~ The description and illustrations of these specimens were published by me in the Transactions of the Medico-Chirurgical Society, vol. xxxv. p. 201. Plates I. and II., 1852. UNITED TEETH. 57 teeth are occasionally united together, but that the union is effected, in certain instances, by a fusion of the dentinal tissue of the two individuals. As regards the development and formation of teeth thus united, it can but be concluded that the two pulps were within one and the same sac; and that though they were distinct at their summits, they were as one, except outward moulding, through most of the crown and the whole of the fang. Although the congenital union of two contiguous teeth is an abnormal condition, it can scarcely be considered pathological: it can simply be considered as the result of some modifications in the papillary and follicular mouldings of the surface which occur in the earliest stages of tooth-development. And considering that the near proximity of two pulps, or the imperfect formation of the septa between the sacs, would furnish circumstances favouring, if not determining, its production, it may rather be a matter of surprise that this deviation from the natural condition is not much more frequent. The union of distinct teeth, formed upon separate pulps, and exhibiting the outward anatomical form of certain recognised teeth, is merely an exhibition of the same sort of process on a large scale, as is seen in miniature in the formation of every tooth with more than one cusp. Each cusp commences, as each tooth, by a separate calcific centre, upon a single eminence of pulp —upon, in fact, a miniature tooth-pulp: and when these become confluent, they show through a very short space, near the summit of the crown of the teeth, the same relation in section as I have just described in these united teeth: it only needs a deeper fissure between the cusps to render the analogy more complete. The secondary union of contiguous teeth-that which occurs in after life-is brought about by the encasement of mature tooth-fangs within a common growth of crusta petrosa. Normally, each fang is separated from every other fang by a tube of alveolar bone, a portion of the true skeleton bone. Many morbid conditions of the fangs of teeth occasion absorption of the alveolar plates, and this occurring immediately between two, may place them in a common socket. It is but necessary for this apposition of neighbouring fangs and a union of the periodontal membranes of the two teeth to occur, when a fusion of the cemental blastema from the two sources, in 58 DENTAL PATHOLOGY AND SURGERY. active development, would accomplish the encasement of the two teeth-fangs as one. This secondary union of contiguous teeth is perhaps scarcely as frequent as the congenital form, though, from its affecting the fangs of the teeth, it is less likely to be observed when present. It more often affects the molar teeth than others, and I believe is seen, when present, in those Who are affected with. a general excess of cemental formation on the teeth. The accompanying illustrations (figs. 33, 34) represent two fangs-those of the two superior bicuspids, before alluded to. The figure on the left represents them in face; that on the right Fig. 33. Fig. 34. i J shows the extremities of the fangs seen endwise. These fangs were separate at both extremities, but united in the middle by a band of crusta petrosa, enveloping the two in a common sheath, very clearly shown in the right figure. The dotted lines in the left figure indicate the crowns of the teeth, which had long been decayed and broken away. I extracted several other stumps and decayed teeth from the patient on the same day (preparing for artificial teeth), and they all presented an immense amount of general crusta-petrosal hypertrophy. I have made a section for the microscope of the two united bicuspid fangs-the plane of section being indicated by the line in the foregoing fissure. The illustration (fig. 35) shows the arrangement of the fang-tissues in this specimen, and implies the method and sequence of their formation. In this instance, as is common, th'e first bicuspid had two roots, and the second but one. Starting from each narrow pulp-cavity, there is first a ring of dentine; then rings of crusta petrosa belonging to each fang, and then a belt of the same tissue involving the whole. The dentine circles, with a certain amount of cement, were the original fangs: the enlarged cemental rings indicate the progressive hypertrophy of the toothfangs, and the contingent atrophy of the alveolar plates, which UNITED TEETH. 59 issued in a common socket, and a structural fusion of the two teeth. Fig. 35. The anatomical condition, which I have now described, is_ not without important practical bearing. Two teeth may be united side by side, though apparently distinct organs: one may be diseased, and require extraction, and the other be sound: or one may be out of place, and (in a young mouth) may suggest the propriety of its removal for regulation. Now, in many of the recorded cases, perhaps the majority, it would have been impossible to have ascertained the union of the teeth while in the jaw: in the great majority it would surely have been overlooked by an ordinary observer. In all the recorded instances it would have been impossible to have separated the attached teeth before extraction. These propositions involve an inevitable accident; and the rarity of that accident, and the fact that it has not yet been recorded, results from the abnormality, which would induce it, being itself so rare. Two teeth may be extracted where one was intended, because they are joined together. On the 24th of June 1867, a maiden lady, about forty years of age, came to me to have her jaws cleared of stumps and decayed teeth, preparatory to wearing artificial substitutes. I had extracted several, all coated about the fangs with excessive cement, when I removed the first upper bicuspid root on the right side: with it came away the root of the second bicuspid: 60 DENTAL PATHOLOGY AND SURGERY. they were united together by a common cemental sheath, and are represented in the previous figures. The gum was so full, and the tongues of gum passing up between the two buried fangs were so complete, as to mask this union entirely. The possibility of such an event as this must have occurred to every one in contemplating united teeth; but I am not aware of any recorded instance where it has occurred in actual practice. CHAPTER VI. SECONDARY DENTINE. WHEN a tooth is completely formed, but as yet has never been subjected to wear of the ivory, or inflammation or irritation, the pulp remains a soft, vascular, nervous mass. This fleshy body then contains no schlerous elements,* but it does contain elements which are capable of transformation into ivory of essentially the same nature (both chemical and anatomical) as the dentine previously formed. Such fresh growth differs, however, in some of its anatomical characters; it is, moreover, an after-growth, or secondary formation, and it is divisible into varieties. The terms " Osteo-dentine," and " Secondary Dentine," have been applied respectively by Professor Owen and Mr. Tomes to designate some of those forms of dentine which are thus found within the primary single system of the tooth,-formed from the one original pulp. The former referring, and being applied to structures normal and abnormal, both in man and other animals, and the latter being used by its author in relation to those quasi-morbid, or truly morbid products, which are found in the injured and diseased teeth of the human subject. The two terms have been applied by anatomists, in respect to human teeth, as synonyms and parallel expressions, but really they are not so; for whereas osteo-dentine refers to an inconstant anatomical condition, secondary dentine has a general physiological meaning, and refers to period of formation. " Secondary dentine" is, as it were, generic of the whole; " Osteodentine " is specific, and applies to that one form of secondary * A few calcification islands are said occasionally to be present in the pulps of developing teeth; but I have not met with them. 62 DENTAL PATHOLOGY AND SURGERY. dentine, in which the new tissue consists of a series of dentine systems arranged around isolated blood-vessels, or secondary pulpules. This nomenclature is not only incomplete, but inaccurate. Considering Secondary Dentine as applicable to all the after-formations of dentine by which the pulp-cavity is diminished or obliterated, subsequent to the tooth having attained a mature and adult condition, I would subdivide it, according to the anatomical distinctions which the different forms exhibit, into Dentine of Repair, Dentine Excrescence, and Osteo-dentine. I first suggested this arrangement in the " Guy's Hospital Reports" for 1853. The accompanying diagram- (fig. 36) shows these three forms of Secondary Dentine. The tinted triangle at the top of the Fig. 36. pulp-cavity represents a mass of Dentine of Repair compensatory for the wear of the summit of the cusp. The nodule projecting from the side into the pulp-cavity is a Dentine Excrescence; and the dark cylinder in the axis of the pulp shows where the intrinsic calcification of that organ usually commences in the formation of Osteo-dentine. The illustration must be considered as simply diagrammatic. IDENTINE OF REPAIR has been recognised and described by Hunter and subsequent writers; and its meaning, as a remedial effort of nature, has been understood; but recent observers, even with the assistance of 3 the microscope, have not described many interesting points concerning its anatomy. The amount of knowledge till recently obtained has scarcely been added to since the time of Hunter. He remarks: "A tooth very often wears down so low, that its cavity would be exposed, if no other alteration were produced in it. To prevent this, nature has taken care that the bottom part of the cavity should be filled up with new matter, in proportion as the surface of the teeth is worn down." *'.unter on the Teeth, 4to, 1771, p. 108. SECONDARY DENTINE. 63 Mr. Bell, with rather more definition, observes: " It is first deposited in that part of the cavity towards the worn surface, and becomes gradually more and more filled as the tooth becomes abraded." * The circumstance of repair, as thus generally expressed, had not received a more exact description until 1853, though the microscope discloses the laws which regulate its development; laws which are exact, regular, and intelligible. Before the publication of Mr. Tomes's Lectures on the Teeth, the filling up of the pulp cavity by new dentine was only recognised as the result of abrasion from wearing. Mr. Tomes, however, has shown that decay of the tooth may produce the same result, and I have had many opportunities of verifying the correctness of this observation. I have also found that fracture of the crown of a tooth, so long as it does not open the pulpcavity, causes a similar result: there is an internal repair in proportion to the external lesion. Correctly to understand the laws which are followed in the formation of dentine of repair, it is necessary to examine sections of teeth variously worn and variously broken. Sections should be made carefully, so as to cut the dentine parallel with the radius from the centre of the pulp cavity to the point of injury, and not obliquely or on one side. The injury and the corresponding point in the pulp cavity should be disclosed at once. A very /" slight magnifying power, from ten to twenty diameters, will suffice to exhibit the general arrangement. Those teeth which are partially worn at the summit of their cusp, or cusps, and are likewise grooved at the neck, when cut vertically and so mounted, are the most illustrative; and, on that account, I have selected a tooth thus worn for the subject of an outline figure. The accompanying drawing (fig. 37) represents a section of a superior canine tooth, of which the apex of the crown is worn by attrition in mastication; and by friction of the tooth-brush it has been * Bell on the Teeth, 8vo. 1835, p. 193. 64 DENTAL PATHOLOGY AND SURGERY. grooved along the anterior surface of the neck. This amount, and this position of wear are extremely common, and are, in all cases where the tooth is a living one and the dentine pulp is alive, accompanied with a development of dentine of repair. In this specimen it is seen that the friction at the apex of the crown has removed all the enamel from the summit, and a small amount only of the dentine. In the section some ten or fifteen tubes correspond to the worn surface; a large mass of tissue intervenes between the wear and the repair, but yet the latter (in the shape of a triangular mass of secondary dentine in the summit of the pulp cavity) has appeared, and in proportion to the former. Wear, which is the mere result of mechanical friction, has no relation to the structure of the dentine-it occurs simply in the place and in the direction of the rubbing-but the consequent repair has a direct relation to its intimate anatomy. Now, of the tubes that abut upon the worn surface, the central would correspond to those most worn down; those which in the entire tooth had reached the extreme point of the cusp, and had consequently, by the removal of the top, been more shortened than any others. The contiguous tubes have been reduced next in amount, whilst those at the extremity of the worn surface have been least shortened. Upon tracing the tubes which have thus been rubbed down, from their outer extremities to the pulp cavity, it will be found that the amount of secondary dentine laid on, so to speak, upon their inner extremities, is in proportion to the amount removed externally. Thus, in this specimen, the central tubes abut upon the apex of the triangular mass of secondary dentine, while those at the sides of the wear, and next to the yet unbroken enamel, terminate internally at the edges of the new repair tissue. And it should be observed that, not only does the repair tissue correspond with the amount of injury done to each tube, but that it is generally limited by the internal abutment of those tubes which are at the edge of the worn surface. And this correspondence of the repair with the individual tubes injured is illustrated with peculiar clearness by the situation which the secondary dentine obtains where the injury has consisted in a groove in the neck of the tooth. The tortuous direction of the dentinal tubes in this situation, and SECONDARY DENTINE. 65 their elevation out of the horizontal line, as they pass from within outwards, present circumstances which admirably test and illustrate the manner in which the structural direction of the tissue determines the position of the repair. By tracing the curves and the convergence of the tubes as they pass inwards to the pulp cavity, they are found on the interior to correspond to the dentine of repair far below the horizontal line of lesion. The next figure, 38, represents a central incisor of the upper jaw, in which one of the angles has been broken off. The section is vertical and from side to side. The fracture has injured at the extremity a large number of tubes, but, by their convergence as they approach the pulp cavity, it will be seen how much smaller is the area of resulting repair. Now, in all these instances, it will be seen that the dentine of repair has a very close relation both in amount and position to the injury that has caused it. When, however, the amount of wear, or fracture, or decay, is great, there ceases to be that exact and proportionate recompense, the new tissue forming over a large surface of the pulp-cavity, and often much in excess: and it may be stated, as a general rule, that even where the injury is slight, if the repair be not in accurate proportion, the difference is on the side of excess, and corresponds to a larger surface than is indicated by the internal abutment of the injured tubes. The next illustration (fig. 39) is an accurate representation of an interesting specimen, a vertical section of an inferior canine tooth, in which dentine of repair is seen in three situations-in two developed as the recompense or repair for lesion, the result of mechanical friction, and in one as a compensation for the inroads of superficial caries. At the summit of the cusp and the front of the neck the dentine has been worn into by friction; at the back of the neck there is a crescentic cavity eaten out by caries. In making the section, from the bending of the fang, it was not possible to open the pulp cavity from end to end. The upper half is exposed in about its centre; in the lower half the dentine of the fang is exhibited, just on one side of the pulpcavity. The external injury, and the plano-convex masses of F 66 DENTAL PATHOLOGY AND SURGERY. dentine of repair in the pulp cavity are so clearly defined, that the specimen does not need further description. Osteo-dentine and dentine exrig. 39. crescence are not infrequently seen in teeth that are worn and exhibit dentine of repair; they are evidently associated, and have a similar exciting cause. Dentine of repair, however, always forms pon that portion of the pulpcavity next to the lesion, and is adherent, and in direct structural continuity with the primary dentine; whereas osteo-dentine and f dentine excrescence occur almost 1 \