COLUMBIA LIBRARIES OFFSITE HEALTH SCIENCES STANDARD HX00043877 ■ ,^y rocess. The bodj^ of this bone con- tains a large cavity, the antrum of Wghmore, obviously for the purpose of minimizing the weight of the bone, and at the same time of increasing its proportionate strength. The external or facial surface (Fig. 1) shows above the incisor teeth a slight depression, called the incisive fossa. Outward from this is another depression, the canine fossa, which is deeper than the incisive, and separated from it by a vertical ridge, the canine eminence, corresponding to the socket of the canine or cuspid tooth. At the upper portion of the canine fossa we observe the infra-orhital foramen, through which pass the infra-orbital nerve and artery. The posterior or zygomatic surface is pierced by several aper- tures, the orifices of the j^osterior dental canals, for the transmis- sion of the posterior dental vessels and nerves. The lower part 2 1 1: THE ANATOMY AND PATHOLOGY OF THE TEETH. of the /ygoniatii.' surface gradually develops into the ma:rlllary (iihirosit;!, which is most conspicuous after the eruption of the wisdom or third molar tooth. The superior or orbital surface is made up of a thin triangular plate of bone. It is traversed by the iitfra-orhitai groove, carryings the infra-orbital nerve and artery. This groove terminates in a canal, dividing into two branches ; one of which, the wfra-orhital, opens l:)elow the border of the orbit, while the other, Avhich is- smaller, pierces the anterior wall of the antrum, and bears the name of anfcrior denial camd, transmitting the anterior dental vessels and nerve to the front teeth. Fiu. 1. ExTERSAL OR Facial Scrface op the Right Superior Maxillary Boxe. /, Incisive fossa : t', canine fossa : £, canine eminence : F, iufra-oibital foramen ; P, posterior- dental canals: G, infra-orbital groove; ,1/, malar process. The /mdar proce.-<.^ is a prominent rough eminence servino- for the articulation with the malar bone. The descending ridge constitutes the boundary between the facial and zygomatic siu'- faces. ^ From this ridge a small portion of the masseter muscle takes its origin. The nasal process, directed upward, has a concave external sur- face. The anterior border of this process articulates Avith the nasal bones ; the posterior is hollowed out by a o-roove in which the lachrymal duct lodges. This groove is converted into a THE SUPERIOR MAXILLARY BONES. 3 canal by the lachrymal and a part of the inferior turbinated bones. The palate process (see Fig, 2) is a strong piece of bone project- ing horizontally from the inner surface of the superior maxilla. It is especially thick anteriorly, the upper surface forming a large portion of the Hoor of the nasal cavity, while the lower surface makes up the greater portion of the roof of the oral cavity. The lower surface is slightly concave, and is channeled at the posterior part of its alveolar border for the passage of the pos- terior palatine vessels and the anterior and external palatine Fig. 2. IxFERiaR Surface of the Right Scpeeior Maxillary Boxe. P, palate proaess: S, anterior nasal spine; A, opening of antrum: .1/, lower meatus of nasal cavity ; L, laehr3-mal groove. nerves. The two palate processes assist in forming an orifice in the median line, the anterior palatine canal This canal is divided into four compartments, two of which run laterally to the right and left nasal fossae, while the anterior and posterior compartments run along the median line. The anterior one serves for the transmission of the anterior branch of the descend- ing palatine arteries. The anterior and the posterior compart- ments transmitthe naso-palatine nerves, the left running through the anterior, the right through the posterior canals. The roof of the mouth is pierced by a number of small canals which THE ANATOMY AND I'ATIIOLOCiY OF THE TEETH. carry the vessels for the nutrition of the bone. The upper sur- face of the palate process is concave and smooth, exhibiting the openings of the canals above mentioned. The inner border of the palate process is raised into a central ridge which supplies a space of attachment to the vomer. Anteriorly, this process pro- duces a sharp prolongation, the mdcrior nasal spine. The pos- terior border serves for articulation with the palate bone. The upper portion of this surface shows a large, irregular opening, that o-f the antrum. The upper border of the opening is par- tially closed by the cellular cavities of the ethmoid bone. Below this opening a smooth concave surface presents itself, the Inirer meatus of fhe nasal eaelUj. Behind the opening we notice a rough surface that articulates with the perpendicular Fig. 3. The Alveolar I'hocess ok the Right Slperior Maxillaky Bone. View from Below IS Natural Size. plate of the palate bone, being traversed by a groove which, with a corresponding portion of the adjacent palate bone, forms the posterior palatjm canal, directed obliquely downward and for- ward. In front of the opening of the antrum a groove is seen, which with the lachrymal and inferior turlnnated bones consti- tutes the lachrymal or nasal duet. At the base of the nasal pro- cess is the horizohtal or inferior turbinated crest for the articulation of this process with the inferior turljinated bone. The wall of the inferior meatus of the nasal cavity is perforated by numer- ous small foramina, which serve as carriers of nutrient vessels. The alveolar process is the portion of the jaw which holds the teeth. It contains eight excavations or sockets for this purpose (Fig. 3). The deepest of these excavations is the socket of the THE SUPERIOR MAXILLARY BOXES. 5 canine or cuspid tooth ; the sockets of the molars are the widest, and are usually subdivided into three smaller cavities, corre- sponding in number with the roots of the teeth. The socket of the third molar is usually single, while that of the first bicuspid exhibits two cavities, and that of the second bicuspid usually but one. The sockets for the incisors are always single. They are of roundish form for the central, but for the lateral incisors the sides of the receptacles are somewhat compressed. The ant r II III is the largest of the so-called pneumatic spaces of the skull. It is a cavity of four surfaces, — the upper or orbital surface ; the posterior surface, produced by the maxillary tuber- osity ; the anterior or facial surface, which is slightly depressed bv the canine fossa; and the inner or nasal surface. When regularly formed, the antrum has the shape of a triangular pyramid, and either the upper orbital or the inner nasal sur- face may be considered the base of the pyramid. The inner wall of the antrum is divided by the articulation of the turbi- nated bone into an upper and a lower half (pars supra- and pars infra-tarbinalis). The lower half is made up anteriorly by the superior maxillary, and posteriorly by the vertical lamella of the palate bone. The upper half is supplied with several openings, which are quite large in the skeleton, but much smaller in the vital state, in which condition the bones are covered by their lining membrane. If the mucous covering closes these gaps, such membranous portions Zuckerkandl* terms fontanelles. Of these, he designates one as anterior and one as posterior. There is left only a longitudinal opening, the ostium maxillare, within the unciform process of the ethmoid bone, and one ethmoidal cell, invested by a mucous membrane, communicating with the frontal sinus and the nasal cavity. The lower surface or floor of the antrum is formed by a thin bony plate. Between this and the alveoli of the teeth is a layer of spongy bone. The latter substance, as a rule, is thinnest over the roots of the molar teeth. The roots of the incisor teeth are not within the boundary of the antrum. The canine and the first bicuspid, though near the floor of the antrum, do not quite reach it, the floor being overlaid by a bulky osseous structure. The apices of the roots of the second bicuspid and the buccal roots of the molars are in contact with the floor of the antrum. The second bicuspid *]Srormale unci Patholoffische Anatoniie der jSTasenhole. Wien, 1882. 6 THE ANATOMY AND PATHOLOGY OF THE TEETH. an.l tlie first molar, as a rule, correspond to the deepest portion of the antrum. Variations in the Size of Antra. — The difterence in size of the upi-er jaws of various individuals is not great, but of the antra the shapes and sizes vary considerably ; nay, sometimes there are marked differences in the two antra of the same head. Zuckerkandl publishes the following table of variations in the size of antra, some of the figures of this table being quoted from C. Reschreiters : Heights of Upper Jaw?. Heights Breadths Depths of Antra given in Millimeters. 64 19 25 21 64 29 25 21 64 32 28 83 64 32 25 34 64 32 24 32 64 38 22 34 64 39 25 SO 56 13 15 14 59 37 29 18 Communication between the Antrum and the Nasal Cavity. — The opening termed ostiojii ma.rjjlart is situated in the middle meatus of the nose. It leads into the hiatus semilunaris in com- pany with the ostium fronUde, which communicates with the frontal sinus (see Fig. 4). The latter is situated superficially in the frontal portion, while the ostium maxillare lodges backward and is somewhat hidden in the infundibulum. The best view of the ostium maxillare is obtained from the antrum (see Fig. 5, M), where Ave observe it a little below the orbital surface, on the upper border of the nasal surface of the antrum. Its shape is irregular, most frequently semilunar, but often oval, and sometimes round. According to Zuckerkandl, this opening varies from three to nineteen millimeters in length, and from three to five millimeters in breadth. Sometimes there exists, between the antrum and the nose, an accessory communication, which is usually small and round (see Fig. 5, A). This acces- sory opening generally is situated in the posterior fontanelle, somewhat lower than the ostium maxillare. In rare instances the communication bet^veen the antrum and the nasal cavity is closed, the result either of a chronic infiammatory process or of a malformation during development. THE SUPERIOR MAXILLARY BONES. The Lining Membrane of the Antrum has a double function, — i.e., it serves as a periosteal cover, supplying the nutritive vessels to the bony walls of the cavity, and at the same time secretes mucus. It is continuous with the mucous lining of the nasal cavity, and is closely adapted to the depressions and eleva- tions in the bony wall of this cavity. According to Sappey, the mucosa of the antrum is supplied with glands, which in appear- ance are much like the Meibomian glands of the eyelids. They Sagittal Section through the Xasal and Oral Cavities, partly after Zuckee- KAVDL. H, semilunar hiatus ; U, upper lip, the ethmoidal bulla ; L, lowpr lip, the unciform process ; M. insertion of middle turbinated bone ; T, lower turbinated bone ; E, mouth of Eustachian tube. are irregularly distributed, and much scantier than those of other mucous membranes. The antrum is supplied with blood-vessels, principally derived from the mucous membrane of the nasal cavity, although some of the smaller branches arise fi-om the posterior dental arteries through the alveoli. 8 THE ANATOMY AND rATIIOLCxiY OF THE TEETH. Development. — The superior maxilla is one of the earliest bony formations, and, as anatomists suppose, it starts from four centers of ealcitication, namely : the j^'cmoxilUm/, the palatine, the /na.rillaiy, and the inalar portions. With the exception of the maxillary portion, all these develop from and around hyaline eartilair-e. The prcmaxilla, to the presence of which the great LKFr Slpebior Maxillary Bone, kxhibiting thk Commumcatioxs between Aktkum AND Nasal Cavity. (After Zuckeekaxdl.) O.orbital cavity; i/, maxillary cavity or antrum of Highmore ; M, slit-like opening or ostium maxillare; A, accessory opening between antrum and nasal cavity. German philosopher and poet, Goethe, first drew attention, holds the two incisor teeth on each side. In young subjects its articu- lation with the palatine portion is still visible. In the eon- genital malformation of the upper jaw termed deft palate, this portion is separated from the remainder of the maxillary bone by a single or double fissure, usually associated with a corre- sponding fissure of the upper lip, called hare-lip. - THE INFERIOR MAXILLARY BONE. \) The antrum begins to develop in the maxillary portion of the bone at about the fourth month of fcetal life. Involution.'^ — By this term is indicated a retrograde change leading to a partial or complete disappearance of tissues and organs. It is of frequent occurrence in embryonal develop- ment, the same as in senile reduction of the size of organs, especially that of the skeleton, whereby bone-tissue is brought back to iibrous and myxomatous tissue preceding absorption. The studies of the authors herein named were made on the upper jaw of a woman who died when seventy-five years of age. The thickness of this jaw, between the oral and the nasal cavi- ties, was not more than from four to five millimeters. The sur- face of the oral cavity was perfectly smooth, without a trace of a tooth or socket. The bone was present only in thin ledges, arranged in an irregular line, and without distinction between the compact and the cancellous structures. Xumerous pieces of hyaline cartilage were present in the same stratum with the bony tissue, which proves that the cartilage grows from a pre- vious bony structure, and that it replaces the latter. CHAPTER II. THE INFERIOR MAXILLARY BOXE. This is the largest bone, and the only movable one, of all the facial bones. It consists of a horizontal hody and Ul-q perpendicu- lar -projections, the '/■«//(/,, arising from the body nearly at right angles to it. The body presents for examination two surfaces, the external and the internal ; and two borders, the alceolar and the inferior. The external surface (see Fig. 6) is convex from the median line to the ramus, and slightly concave from above downward. In the middle line we observe a shallow vertical ridge, indicative of the junction of the two pieces of bone from which the body de- velops. The ridge terminates below in a protrusion termed the mental process. Outward of this central ridge is a slight depres- sion, the incisive fossa. Farther backward we find the large * " Senile Atrophy of the Upper .Jaw. - ' By Carl Heitzmann and Frank Abbott. Dental Cosmos, 1892. 10 THE ANATOMY AND PATHOLOGY OF THE TEETH. mental foramen for the transmission of the mental nerve and artery. The location of this foramen corresponds with the in- terstice l)et\veen the roots of the first and second bicuspid teeth. Posterior to this foramen begins a carved ridge, the external oblafuc V.iie, which runs backward and upward, being continuous with the anterior border of the ramus. The alveolar process is more massive posteriorly than in its anterior portion. It is pierced by sixteen sockets for the recep- tion of the teeth. The inferior border of the body is rounded and quite massive anteriorly; posteriorly it becomes more narrow. In the vicinity Fig. 6. The In-ferior Maxillary Boxe— External Surface of the Right Side. M, mental process : /, incisive fossa ; F, mental foramen ; L, external oblique line ; G, groove for facial artery ; A, anterior or coronoid process ; P, posterior or condyloid process. of the rami this border exhil^its a shaUoiv groove, in which the facial artery is located. The internal surface of the body is markedly concave from the median line to the ramus, and slightly convex from above downward. (See Fig. 7.) In the central line we observe four tubercles, two above and two below, the genial fuhercles, which vary greatly in size and arrangement in different individuals. Laterally to the tubercles we notice a shallow depression, the sublingual fossa, in which the sublingual gland rests. Posterior THE INFERIOR MAXILLARY BONE. 11 to this depression is the beginning of the internal oblique line or rnylo-hijoid ridge, which becomes more distinct as it passes up- ward and backward. The portion above this line is smooth and covered by the oral mucous membrane, whereas the portion below shows a shallow depression, the submcLrillory fossa, corre- sponding to the site of the submaxillary gland. The perpendicular projections, or rami, have a more or less quadrilateral shape, each ramus presenting two surfaces, four borders, and two offshoots. The external surface is ridged, and serves for the attachment of the masseter muscle. The internal Fig. 7. The Inferior Maxillary Boxe— Isterxal Surface of the Right Side. 0. genial tubercles ; M, mylo-hyoid ridge : 0, opening of the inferior dental canal ; H, mylo-hyoid groove ; A, anterior or coronoid process ; P, posterior or condyloid process. surface is pierced about its center by an oblique aperture, the opening of the inferior dental canal. Anteriorly this aperture is surmounted by a ridge terminating in a sharp spine, which at its lower part shows a notch leading to the mylo-hyoid groove, for the mylo-hyoid vessels and nerve. The lower border of the ramus exhibits a large rough surface for the attachment of the internal pterygoid muscles. The inferior dental canal takes an oblique course downward and forward in the ramus, and a horizontal one in the body. This canal is located underneath the sockets of the teeth, with 12 THE ANATOMY AND PATHOLOGY OF THE TEETH. which it communicates by small openings. At a point about level with the first bicuspid tooth it ends in the mental foramen. In the posterior two-thirds of the bone the inferior dental canal runs near the internal surface, while in the anterior third it is near the external surface. This canal holds the inferior dental vessels and nerve, from which small branches pass to the apices of the roots of the teeth through the small openings at the bases of the alveoli referred to above. The upper border of the ramus is thin, and shows two pro- cesses, the anterior or coronoid, and the posterior or condyloid. Situated between these processes is a deep depression, the sig- moid notch. The coronoid process is a thin piece of bone serving mainly for the attachment of the temporal muscle, and — at its outer surface — for the attachment of the masseter muscle. The condyloid process is more massive than the coronoid, and terminates in the condyle, which is covered with hyaline carti- lage. The condyle, placed upon a constricted portion of the neck, is of an oblong shape. Its long axis is set obliquely upon the neck, the outer extremity being higher and directed more forward than the inner. Its surface is convex both antero-pos- teriorly and from side to side. The lower border of the ramus is thick and continuous with the body of the bone. At the angle of the jaw it is marked by oblique ridges on each side, for the attachment of the masseter and internal pterygoid muscles. The posterior border of the ramus is covered by the parotid gland. Development and Involution. — The lower jaw, one of the first-formed bones of the embryo, is developed principally from a hyaline cartilage, which, in honor to its discoverer, is termed Meckel's cartilage. The formation of osseous tissue begins about the sixth week of intra-uterine life. (See Fig. 8.) Meckel's cartilage, invested by perichondrium, — which at this stage is not as yet fibrous, but made up of spindle-shaped proto- plasmic bodies, — forms a ledge, from and around which ossifica- tion takes place. The perichondrium plays as great a part in the production of bone-tissue as the cartilage itself. The first step toward the development of bone is the calcification of the basis-substance around the cartilage-corpuscles. Il^ext a reap- pearance of protoplasm takes place in the non-calcified portion of the basis-substance, whereby the entire territory of the car- THE INFERIOR MAXILLARY BONE. 13 tilage-corpiiscle is rendered graiiiilar. An increase in the size of the granules results in an augmentation of the nuclei, and at last the entire cartilage-corpuscle is transformed into a cluster of medullary or embryonal corpuscles, which furnish the mate- rial for bone-production. A preliminary stage of ossification is Fig. 8. FiEST Formed Teabecul.e of Bone, in Lower Jaw of Hcmax Ejibryo, Six Weeks Old. //, hyaline, or primordial, or Meckel's cartilage ; N, non-calcified basis-substance around the territories of hyaline cartilage ; L, calcified basis-substance of territories of cartilage-corpuscles; B. cartilage broken up to embryonal or medullary corpuscles; ij, coarsely granular cartilage- corpuscles: C, calcified embryonal corpuscles; T, trabeoulfe of bone-tissue with territories; M, M, M, myxomatous or medullary connective tissue. Magnified 200 diameters. a deposition of lime-salts in a number of embryonal corpuscles, derived either from the hyaline cartilage or the perichondrium. By the coalescence of a number of such bodies territories of globular shape are formed, the center of the globules being 14 THE ANATOMY AND PATHOLOGY OF THE TEETH. occupied by bone-corpnscles, while the peripheral portion is transformed into glue-vielding basis-substance, saturated with lime-salts. This change does not alter the structure of the pro- toplasm. The trabecule!? of bone are originally small and irreg- ular ; later they unite into cancellous tissue, inclosing medullary spaces tilled with protoplasmic bodies and carrying blood-vessels. In the second half of the third month the Fig. 9. maxilla is as yet a minute ledge of bone, but -r rj^^"^'^^ with indications of future sockets, and of the coronoid and condyloid processes.- (See Fig. 9.) In the first half of the seventh month the Infekior Maxilla OF AN Embryo ix the Second Halk of the Third Month. future sockets of the teeth are wide and irreg- ular excavations. Both the coronoid and condyloid processes are plainly seen, the latter being almost horizontal. The mental foramen is already established. (See Fig. 10.) At the time of birth the lower jaw is made up of tw^o pieces, articulating in the center line. The upper border of these pieces is grooved, without being subdivided into sockets. The cortical portion is imperfect and pierced by numerous medullary spaces, especially near the central symphysis and in the region of the rami. The coronoid is more advanced in size than the condyloid, which latter retains a nearly horizontal position. (See Fig. 11.) In the sixth year ot" life the inferior maxillarj' bone has at- tained a considerable size, and the condyloid process is inserted at an obtuse amile. Of the teeth we observe on either side of Fig. 10. Fig. 11. Inferior Maxilla of a Fcetus in THE First Half of the Seventh Month. Inferior Maxilla at the Time of Birth. the jaw the two temporary incisors, the cuspid, and three molars, — two temporary and one (the sixth-year) permanent. (See Fig. 12.) In the adult the condyloid process is- conspicuous by its almost rectangular junction with the ramus, whereas with advancing age this process appears inserted again at an obtuse angle. In old age the lower jaw gradually returns to its embryonal THE i>;ferior maxillary bone. 15 shape. (See Fig. 13.) After the teeth are lost, the sockets become obliterated, and are replaced bv small pits and grooves, the points at which the conversion of the bone into medullary tissue begins. The mental foramen is now seen to be near the previous alveolar surface, and to be considerably widened. The body, as well as Fro. 12. Inferior Maxilla of a Boy Six Years Old. Fig. 13. Ikferioe Maxilla in Senile Age. the ramus, is reduced to a thin ledge of bone, mostly smooth at the surface. The laws of development, as well as of senile involution, are not as yet fully understood. It is certain, how- ever, that all changes take place by juxtaposition, and not by interstitial growth. All phenomena become intelligible, if we admit the fact that not only are the bone-corpuscles endowed M^ith properties of life, but so also is the basis-substance, and thus both are enabled to be reconverted into protoplasm, and ao;ain to scive rise to connective tissue. 16 THE ANATOMY AND PATHOLOGY OF THE TEETH. CHAPTER III. THE TEETH. The tooth, macroscopically considered, consists of a crown, a neck, and a root. Tlie crown of a tooth is that portion which is covered with enamel, and, when the tooth is fully erupted, is exposed above the margin of the gum. The neck is the part that is covered by the gum. It begins at the border of the enamel and extends to the alveolar process. The root, in its normal condition, is entirely inclosed by the alveolar process. The Right Tekth of ax Adult Twexty-tato Y'eaks Old. External View. Labial (Buccal) Surfaces.* Between the neck and the root of a tooth we observe no distinct macroscopical boundary, but for descriptive purposes and for practical convenience we employ differentiating terms. The dental formula that represents the permanent teeth of the human mouth is noted as follows: (See Figs. 14 and 15.) Ci; B|; M| = 32 -The teeth Xos. 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, and 24, in shape correspond with their fellows of the opposite side of the dental arch, except that the general shape of their crowns is reversed, and it has therefore been deemed imnecessarv to illustrate them. THE TEETH. 17 Upon examining the crown of a tooth, we observe on it five surfaces. First, the outer surface in regard to all teeth, called the " labial" surface of the front teeth, and the " buccal" surface of the bicuspids and molars. Second, the inner surface, in con- tact with the tongue, and therefore called "lingual." Thirds the " grinding-surfaces" and the "cutting-edges," the former name being applied to the under surfaces of the upper bicuspids and molars and the corresponding grinding-surfaces of the lower bicuspids and molars, while the second term is given to the similarly opposed edges of the front teeth. The two surfaces of each tooth still to be named are those that are in contact with the neighboring teeth. The surface of each tooth directed toward 25 26 27*' 28 29 The Right Teeth op an Adult Twenty-two Years Old. Internal View. Lingual Surface. the center of the jaw is called " mesial"; that toward the poster- ior portion of the dental arch is known as the " distal." There are four incisors in the upper and four in the lower jaw. The two middle ones are termed " central incisors" ; the two outer, " laterals." Their cutting-edges, when the teeth are erupted, usually exhibit three protuberances, which, in use, soon become smooth through wear. The upper incisors, especially the centrals, are much larger than the lower ones, and in normal articulation overlap the latter. The upper incisors are inclined toward the median line, rendering the mesial surfaces somewhat longer than their corresponding distal surfaces. The incisors are wedge-shaped, thinning from the base at the gum toward 3 18 THE ANATOMY AND PATHOLOGY OF THE TEETH. the cutting-edges. These edges, in adult teeth, viewed anteriorly, represent a straight line. The general shape of an incisor thus anteriorly seen is, approximately, that of a square, though it narrows toward the neck. The mesial angle of the cutting-edge always inclines more than the distal. From this tapering of the crowns of the teeth toward their necks result more or less V- shaped spaces, which vary in diiferent mouths. In some instances we meet with teeth of which the crowns are almost square, in which case the intervening spaces at the necks are quite small ; while between teeth which exhibit broad cutting- edges and narrow necks we observe large Y-shaped spaces. The upper incisors usually have single roots, which are more or less conical toward the apices. The labial surfaces of the upper incisors, especially in young subjects, are mostly marked by slight longitudinal depressions and elevations, which, through wear, gradually disappear with advancing age. In adults the labial surfaces are more or less smooth and slightly convex. In some instances we meet with transverse furrows or pits in these surfaces, which, however, must be regarded as abnormalities. The enamel at the gingival border of the labial surface terminates in a curved, somewhat elevated ridge. The lingual surfaces are irregularly concave. The periphery is bounded by a more or less prominent ridge of enamel, which, toward the margin of the gum, forms what is known as the hasaJ ridge or cim/ul'i/n. This basal ridge is frequently found to be divided by a deep groove or pit, which, in the majority of such cases, soon becomes the seat of caries. The boundary line of the enamel on the lingual surface is curved similarly to that of the labial surface. These ridges, as they turn into the mesial and distal surfaces of the incisors, take a down- ward course, following the festoons of the gum, and meet with the enamel ridge of the labial surface, producing a Y-shaped appearance in both the mesial and distal surfaces of the teeth. The a2:)2)er central incisors (Kos. 8 and 9) occupy the center in the dental arch, being the broadest of the incisor teeth. Their roots are almost cylindrical, and gradually taper from the neck toward the apex. The upper lateral incisors (Xos. 7 and 10) are smaller than the centrals. The mesial angle of their cutting-edge usually over- hangs more than that of the central incisors, in consequence of which their distal angles appear more rounded. Their roots THE TEETH. • 19 are compressed laterally, and taper frora crown to apex, corre- sponding in length to those of the central incisors. The lower central incisors (Nos. 24 and 25) are the smallest teeth in the dental arch. They are even smaller than the upper lat- erals. Their general outline is the same as that of the upper laterals, but the angle of their mesial surfaces is much less over- hanging. Their lingual surface is usually smooth and but slightly concave. The roots of these teeth are more compressed laterally than those of the upper laterals. The lower lateral incisors (iSTos. 23 and 26) are somewhat wider than the centrals of the lower jaw, yet in every other respect their appearance is the same as that of the central incisors, although their roots are a little longer and heavier. The upper canines, eye-teeth, or cuspids (Nos. 6 and 11) occupy a prominent position on either side of the incisor teeth. They form the corners of the dental arch, and are in every respect more stoutly built than the incisors. The crown terminates in a more or less blunt point, from either side of which a rounded cutting-edge slopes away and becomes continuous with the mesial or distal surface. The cuttino^-edsre of the mesial surface is somewhat shorter than that of the distal surface. By this diiference in the length of the cutting-edges we are enabled to distinguish the teeth belonging to the right from those of the left side of the mouth. Upon the labial surface of an upper cuspid tooth we observe a somewhat prominent ridge, which extends from the summit of the cusp to the neck. This ridge renders the surface more convex than the corresponding labial surface of an incisor tooth. In the median line of the lingual surface of an upper cuspid we also observe a ridge, the direction of which is identical wdth that of the labial surface. In some instances, where this ridge joins the cingulum, it develops into a regular small cusp, which in shape is not unlike that of a lower first bicuspid tooth. The mesial and distal surfaces are of a triangular form, similar to those of the incisor teeth ; but their base is much broader. The roots of the upper cuspid teeth are much stouter and longer than those of the incisors, and are usually somewhat compressed laterally. The position of these roots in the mouth can easily be determined, since they are marked by a prominent ridge upon the external surface of the maxillary bones, the canine eminences. The shape of the lower cuspids (il^os. 22 and 27) does not dififer 20 THE ANATOMY AND PATHOLOGY OF THE TEETH. much from that of the upper ones,- although they are smaller -in ever}' respect. The ridges upon their lingual surfaces are not so prominently developed, and their roots are shorter. The premolars or bicuspids, eight in number (jSTos. 4, 5, 12, 13, 20, 21, 28, and 29), are arranged in pairs, both in the upper and lower jaws, posterior to the cuspids. Their crowns are quadrilateral; but the buccal portion of the crown is larger than its lingual half, as is especially noticeable in the first bi- cuspids. The shape of the buccal surface of a bicuspid is similar to that of the cuspid of the same side of the mouth ; the ridge, however, extending from the summit of the cusp to the margin of the gum, is not so strongly marked. The grinding-surface of a bicuspid, as the name implies, exhibits two cusps, of which the buccal is the largest. These cusps are separated from each other by a furrow which, in some teeth, is quite deep, and often becomes the seat of caries. The mesial and distal portions of this furrow are bounded by a small ridge of enamel, continuous with the sloping lingual and buccal edges of the cusps. The cutting-edges are similar to those of the cuspid of the same side of the dental arch. The upper bicuspids (Nos. 4, 5, 12, and 13) are somewhat larger than those of the lower jaw, and their lingual cusps are more developed. The lingual portion of the crown of the fi.rst upper bicuspid is narrower antero-posteriorly than its buccal half. The shape of the crown of the second bicuspid is more nearly square, and the entire tooth a little stouter than the first. The root of the first upper bicuspid always is much compressed laterally, and, as a rule, contains two pulp-canals. Sometimes- its root is bifurcated, while the upper second bicuspid seldom has more than one root, or one pulp-canal. The lower bicuspids (ISTos. 20, 21, 28, and 29) are smaller than those of the upper jaw. Their crowns are roundish and some- what bent inward. Their roots are conical. The first lower bicuspid is the smallest of the bicuspids. Its outer cusp is much higher than the inner one, which is but slightly developed. From the buccal to the lingual cusp extends a small ridge, on either side of which is sunken a little pit, a favorite seat of decay. The second lower bicuspid is larger than the first, and its lingual cusp is more developed than that of the first lower bicuspid. If we compare the incisors with the cuspids and bicuspids, THE TEETH. 21 we find that there exists a typical analogy between their shapes, which, however, is not the case if we compare the incisors with the molars. The molar teeth QSo^. 1, 2, 3, 14, 15, 16, 17, 18, 19, 30, 31, and 32) are the largest in the mouth, and occupy the posterior por- tion of the dental arch. jS^orrnally there are six molars in each jaw, three on either side. The third molar, also called wisdom- tooth, is, however, frequently missing, and in a crowded dental arch may remain unerupted. This deficiency is, in some fami- lies, characteristic and hereditary. The crowns of the first molars are larger than those of the second, and, in turn, the crowns of the second are larger than those of the third. The grinding-surface of a molar is of a more or less square shape, with rounded angles, and is made up of four or five cusps. The mesio-buccal cusp of a molar usually is a little larger than the others, which fact enables us to determine to which side of the mouth the tooth belongs. The crowns of the upper molars (Nos. 1, 2, 3, 14, 15, and 16), especially the first and second, usually exhibit a cusp upon each of their angles, of which the mesio-lingual is the largest. The mesio-buccal cusp is connected with the mesio-lingual one by a ridge which runs along the mesial border of the grinding-sur- face. Sometimes we observe upon the mesio-lingual border of the crown of the first and second upper molars a small extra cusp, separated from the large mesio-lingual by a deep furrow. The furrows separating the cusps run over the buccal and lingual borders of the grinding-surface. The furrow upon the lingual surface usufilly terminates in a more or less deep pit, which, together with the above-described fissures of the grind- ing-surface, famishes a favorable locality for the development of caries. The roots of each upper molar are usually three in number, — two buccal, much compressed antero-posteriorly, and one lingual or palatal. The lingual root is the stoutest of the three, conical in form, diverging from the axis of the crow^n toward the palate, and often slightly curved in the direction of the buccal roots. The crown, as well as the roots of the upper third molar, or wisdom-tooth, is liable to great variations. In the majority of instances we find the crown of a third upper molar much smaller and shorter than that of the first or second molar. This molar sometimes has only one straight, short root, but in some instances it is supplied with three, — the typical 22 THE ANATOMY AND PATHOLOGY OF THE TEETH. number, — four, or even live. Occasionally the roots of the wisdom-teeth are normally developed, like those of the first and second molars; mostly, however, they are but rudimentary and more or less compressed, or even conglomerated into one root. The grinding-surfaces of the lower molar ieefh (Nos. 17, 18, 19, 30, 31, and 32) usually exhibit five cusps, separated from one another by deep farrows, representing a regular cross. The posterior arm of this furrow, as a rule, bifurcates and winds around the fifth cusp. The lingual and buccal portions of the farrow extend into the lingual and buccal surfaces of the tooth. Especially upon the buccal surface of the lower molars the fur- row is quite deep, terminating in a pit, which, like that of the upper molars, frequently decays. The cusps are placed, one at each of the four angles of the grinding-surface, while the fifth cusp, the smallest, is situated upon the posterior border of this surface. The lower molars, with the exception of the third, usually are implanted with two roots, which in the jaw occupy an antero-posterior position and are much compressed in the antero-posterior direction. Occasionally we observe that the mesial root of the first lower molar is bifurcated. The Temporary, Deciduous, or Milk Teeth. — In the mouth of an infant, about the sixth month after its birth, we observe the appearance of the first teeth, which belong to the so-called " ternporari/" or " deciduous" set. The complete denture of a child is comprised of twenty teeth, which are noted as follows : T II; TCI; T M # = 20. (See Fig. 16.) The temporary incisor and cuspid teeth are similar to those of the permanent set, though much smaller. The bicuspids are absent. Their arrangement in the dental arch is the same as that of their respective successors ; but the temporary molars occupy on either side of the cuspids the places which in the permanent set are filled by the bicuspids. The crowns of the temporary teeth are large in proportion to their necks and roots, the enamel terminating in a rather thick ridge, which is a characteristic feature of all the temporary teeth. In the illastration I have adopted the numbering of the tem- porary^ teeth from one to twenty, adding a T, to distinguish them from the permanent teeth. No. 1 T, the right up-per second molar, is the largest of the upper THE TEETH. 23 molars. In shape its crou^ii resembles that of the first perma- nent upper molar ; but its roots, besides being smaller, diverge much more from the center than do those of the permanent teeth. The grinding-surface is surmounted usually by four, sometimes by five, cusps, arranged in the same manner as those of the first permanent upper molar. JVo. 2 T, the right upper frst molar, is considerabh' smaller than Xo. 1 T. Upon the grinding-surface we usually find but two cusps, one upon the buccal, the other upon the lingual aspect. They are divided by a deep furrow. There are three roots, which in shape and arrangement are similar to those of molar !N"o. 1 T, but somewhat smaller. 20.T. I9.T. I8.T. I7T. I6.T. The Right Temporary or DECiDuors Teeth. No. 3 T, (he right upper cuspid, while in its principal character- istics similar to its successor, in proportion is much smaller and shorter than the permanent cuspid. It is implanted by a single, almost cylindrical root. Nos. 4- Tando T, the right upper lateral and central incisors, excep)t in being smaller than their successors, are in their general out- lines much like the latter, only their crowns are shorter in pro- portion to those of the corresponding permanent teeth. They invariably have but one root, of a conical shape. Temporary teeth Nos. 6, 7, 8, 9, and 10 of the upper jaw, as well as Nos. 11, 12, 13, llf, and 15 of the lower jaw, are identical in character with their fellows of the opposite side, with the excep- tion that the forms of their crowns are reversed. Nos. 16 T and 17 T, the right lower central and lateral incisors. The principal difference between these teeth and their permanent 24 THE ANATOMY AND PATHOLOGY OF THE TEETH. successors is that the former are much smaller, have a more or less conical root, and their enamel terminates at the neck in a thick ridge, which is common to all temporary teeth. No. 18 T^ the right lower cuspid. Its crown usually is some- what longer than that of the upper temporary cuspid, but not so stout; while its root, like that of No. 3 T, is nearly conical. Xo. 19 T, the right lower first molar. Its crown is smaller than that of ]^o. 20 T. Upon its grinding-surface we commonly lind four small cusps. It is implanted by two roots, flattened antero- posteriorly, and diverging considerably from the center. i\o. 20 T, the right lower second mohu\ is the largest of all the temporary molars. Its grinding-surface is surmounted by four, sometimes five, cusps, arranged in the same manner as those of the first permanent lower molar. It has two roots, which in shape and position are similar to those of the first temporary molar, though much larger, and in some instances almost as stout as those of the permanent lower molars. CHAPTEE lY. INDIVIDUAL CHARACTERISTICS OF THE TEETH. Disting-uishing Features between the Temporary and the Permanent Teeth. — The main peculiarity of temporary teeth is that they are much smaller than the permanent ones. The enamel of the temporary teeth terminates at the neck in a rather thick ridge, whereby the necks of these teeth appear much smaller in proportion than those of the permanent teeth. The temporary incisors oflier another marked characteristic in their smooth cutting-edges, while those of permanent teeth, in the juvenile condition, are each of them surmounted by three small protuberances. The temporary cuspids are much shorter, narrower, and have a less pointed cusp than their permanent successors. The crown of a first temporary molar is so typical that it scarcely will be mistaken for a permanent tooth. Its roots are much smaller than those of a permanent molar, and diverge considerably from the center. The second temporary molars, on the contrary, while in the jaws, may sometimes be confounded with a permanent sixth-year INDIVIDUAL CHARACTERISTICS OF THE TEETH. 25 molar ; but as this always is the fifth tooth from the center, its position will aid us in making the distinction. Distinguishing Peculiarities between the Upper and Lower Permanent Teeth. — The principal difference existing betw^een the incisors of the upper and those of the lower jaw is that the crowns of the former are much broader than those of the lower incisors. While the crowns of the latter are the smallest in the mouth, they are, at the same time, noticeably compressed laterally toward their necks. The upper cuspids, or eye-teeth, are the stoutest teeth possess- insr sino;le roots, much lar2:er than the lower ones. The cingulum and the ridge upon the lingual surface of the lower cuspids, which are so marked in the upper, are but little devel- oped. The main difference between the bicuspids of the upper and those of the lower jaw is that the crowns and roots of the former are somew^hat compressed antero-posteriorly, w^iile the roots and the crowns of the latter are nearly cylindrical. There is also a difference in their lingual cusps, which in the upper bicuspids are long, in the lower short, sometimes merely rudimentary. This last is especially often the case with the first lower bicuspid. To discriminate between the first and second molars of the upper and lower jaws, it is only necessary to notice the number of their roots, since the former usually exhibit three, the latter mostly but two. Another peculiarity of the upper molars is the arrangement of the furrow upon the grinding-surface, which somewhat resembles the letter H, w^hile the fissure of the lower molars represents a cross. The upper and low^er wisdom-teeth, or third molars, might sometimes be confounded with each other, because both are often implanted with a single conglom- erated root. The crown of a lower third molar, however, even though altered, usually represents the general type of the lower molars. Upon the grinding-surface of a lower third molar, therefore, we mostly see the fissure between the cusps more or less in the form of a cross. In numbering the teeth, the writer has adopted the system employed in dental registers and examination tables. (See Figs. 14 and 15.) JSfo. 1. Right upper third molar, or wisdom-tooth. This is the smallest of the three molars. The crown usually exhibits but three cusps, one upon the lingual and two upon the buccal aspect. 26 THE ANATOMY AND PATHOLOOtY OF THE TEETH. The mesial cusp is the largest of the three. Usually the third molar has one root, sometimes it has two ; in well-developed teeth three roots may be present. In the last case the grinding- aurface is surmounted by four cusps, similar in arrangement to those of the other molars. No. 3. JRight upper second molar. This is a trifle larger than jSTo. 1, but smaller than Eo. 3. Its cusps and roots are similar to those of jSTo. 3, though its crown is more rounded. Its mesio- buccal cusp is larger than the distal one, and the tooth, as a rule, is possessed of three distinct roots. No. 3. Bigld upper first molar. This is the largest of the upper molars. Its grinding-surface is of a rhomboidal form, the mesio-buccal and linguo-distal angles being acute, while the disto -buccal and mesio-lingual angles are obtuse. Its mesio- buccal cusp is larger, somewhat lower, and more rounded than the disto-buccal one. It has three distinct roots. No. 4- mght upper second bicuspid. The crown of this tooth is larger than that of any other bicuspid. Its lingual cusp is slightly higher and better developed than that of the first upper bicuspid. The mesial portion of the buccal cusp of the cutting-edge is more obliquely inclined than the distal. The root is usually single, somewhat compressed laterally, and holds but one pulp- canal. No. 5. Right upper frrst bicuspid. This tooth is a trifle smaller than jSTo. 4, especially in the lingual portion of its crown. The mesial cutting-edge of the buccal cusp is directed more obliquely downward than that of the distal. The root is usually bifurcated, or a groove runs longitudinally on both sides of the root in the median line, indicative of two pulp-canals, which, in most instances, are present. No. 6. The right upper cuspid has a single, pointed cusp, of which the mesial cutting-edge is directed more obliquely down- ward than the distal. It has one long, stout root. No. 7. Right upper lateral incisor. Its crown is much smaller than that of a central, l^o. 8 or 9. The mesial angle of the cut- ting-edge is more overhanging than the distal one, the latter being more rounded. It has a single compressed root. No. 8. Right upper centred incisor. The crown, like that of No. 9, is broad and square in its labial aspect. The mesial angle of the cutting-edge is more acute than the distal, which is some- what rounded. It has a single, more or less conical root. INDIVIDUAL CHARACTERISTICS OF THE TEETH, 27 The teeth Nos. 9, 10, 11, 12, 13, II,., 15, and 16 are identical in shape Avitli the corresponding teeth of the opposite side of the dental arch, with the exception that the general shape of their crowns is reversed. No. 17. Left hirer third molar, or wisdom-tooth. Its crown is somewhat larger than that of the npper wisdom-tooth, but it is always the smallest of the lower molars. The grinding-surface is surmounted by four or five cusps. When there are four, the mesio-buccal cusp is the largest; if, however, five cusps be present, three of them usually are upon the buccal portion of the crown. In most instances it has one or two more or less conical roots, curved toward the posterior portion of the jaw. No. 18. Left lower second molar. The crown is nearly scjuare, somewhat larger than that of 'No. 17, but not quite as large as that of No. 19. The grinding-surface is surmounted by four or five cusps, of which two are situated upon the lingual and two or three upon the buccal portion of the crown. The lingual cusps are always a little higher, but more pointed, whereas the buccal cusps are broad and round. By the shape and posi- tion of these cusps we are enabled to determine correctly to which side of the dental arch the molar belongs. This molar usually has two compressed roots, of which the anterior some- times holds two pulp-canals. No. 19. Left lower first molar. Its crown is almost square. It is the largest of the lower molars. It usually has five cusps, of which two are situated upon the lingual and three upon the buccal portion of the crown. The lingual cusps are pointed, and a little higher than the three buccal ones, the latter being rounder, broader, and a little lower. Of the buccal cusps, the mesial is usually the largest. This molar generally has two, but occasionally three roots, two anterior and one posterior, and it almost always contains one posterior and two anterior pulp- canals. No. 20. Left hirer second bicuspid. The crown is larger than that of No. 21, its lingual cusp a little lower than the buccal. The lingual cusp of this tooth is much more developed than that of the first lower bicuspid. The mesial cutting-edge of the buccal cusp usually is more oblicjuely inclined than the distal. The root is mostly single and conical. No. 21. Left lower first bicuspid. The crown is the smallest of any of the bicuspid teeth, nearly round in circumference, 28 THE ANATOMY AND PATHOLOGY OF THE TEETH. and somewhat bent upon the root toward the lingual portion of the dental arch. The lingual cusp is very small, though pointed, and connected with the buccal cusp by a ridge of enamel which divides the grinding-surface and thereby produces two deep pits. The mesial cutting-edge of the buccal cusp is more ob- liquely inclined than the distal. It usually has a single conical root. Xo. 2'2. Left lower cuspid. The crown is narrower, but some- times longer than that of an upper cuspid. Its lingual surface is almost flat, or slightly concave, and the mesial cutting-edge is more obliquely inclined than the distal. Its root is mostly single, but flattened. No. 23. Left lower lateral incdsor. Its crown is somewhat narrower than that of an upper lateral, but not quite so narrow as that of a lower central incisor. The mesial angle of the cutting-edge usually is similar to that of the distal. The root is much more compressed laterally than that of an upper lateral incisor. No. 24-. Left lower central incisor. The crown is narrower than that of any other incisor tooth, being much compressed laterally at the neck. Its root is similar in shape to that of a lower lateral incisor. The teeth Nos. 25, 26, 27, 28, 29, 30, 31, and 32 are identical in shape with the corresponding teeth of the opposite side of the dental arch, with the exception that the general configuration of the crowns is reversed. It should be noted, however, that in the lower laterals and central incisors both angles of the cutting-edges are about equal. It is in most cases impossible to determine to which side of the dental arch a lower incisor belongs. CHAPTER V. THE PULP-CHAMBERS OF THE TEETH. Every tooth incloses a central cavity, of which the shape corresponds to that of the exterior of the tooth. The coronal portion of this cavity is called the j^ulp-chamber, while the portion in the root of the tooth is known as the root-canal. It is of the utmost importance to the dental practitioner to be thoroughly THE PULP-CHAMBERS OF THE TEETH, 29 familiar with the forms and positions of the pulp-chambers of the teeth, since a proper diagnosis of the different diseases of the dental pulp cannot be made without this knowledge. Furthermore, a dentist not well acquainted with the anatomy of the pulp-chamber is liable to expose a pulp unintentionally dur- ing the preparation of a cavity for filling. Within every cusp of the molars, bicuspids, and cuspids we find a corresponding elevation in the pulp-chamber, while in the crown of an incisor the cavity is somewhat bifurcated. The pulp-chambers, as well as the root-canals, are filled by myxomatous connective tissue, interwoven with blood-vessels and nerve-fibers, termed the dental pulp. This tissue also fills the Fig. 17. Left Teeth ix Linguo-Labial and Lisguo-Buccal (Sagittal turning to Frontal) Sections. Reversed to the Right Side- protuberances under the cusps of the teeth, these portions being called the horns of the pulp. The latter are the points which, through caries, easily become exposed and diseased. Although we often find carious cavities, and, consequently, exposures of the pulp, about the necks of the teeth, nevertheless in the majority of instances the dental pulp becomes exjDOsed at one or more of its horns. G. Carabelli"^ w^as the first to give illustrations of the pulp- chambers of the teeth, in their various places, but without cor- rect measurements. He published elaborate drawings of the pulp-chambers of both the temporary and the i:>ermanent teeth. Upon comparing the charts of Carabelli, however, we find that * Systematisches Handbuch der Zahnheilkunde, 1844. 30 THE ANATOMY AND PATHOLO(^^Y OF THE TEETH. tlie pnlp-eliaml)ers of tlie teetli tliere depicted do not correspond to those usually met Avitli in this country, which difference may perhaps be explained by the fact that the teeth used by Cara- belli were of a different type from those of our generation. To arrive at satisfactory conclusions in the study of the pulp- chambers of the human teeth, it would be necessary to examine many complete sets of different ages, constitutions, and shapes. But the author has only been able to obtain a single set of thirty- two perfect teeth, which were imported from Tramond, of Ptiris. These teeth are alleged to have come from the mouth of a girl about twenty-two years of age. Correct drawings were made of them, as represented in Figs. 14 and 15. Afterward the sixteen teeth of Fig. 18. mi/ iir III Right Teeth in Lixgcal axd Buccal (Feoxtal tuexing to Sagittal] Sections- the left side were ground upon a corundum-wheel, exposing the mesial or frontal aspects of the pulp-chambers, as represented in Fig. 17. The other sixteen teeth, belonging to the right side of the dental arch, were prepared as represented in Fig. 18, exposing the labial aspect (respectively buccal or sagittal) of the pulp-cham- bers. It is a well-known fact that, at different ages of the individ- ual, the pulp-chambers vary greatly in size and shape ; yet, with the knowledge derived from observations made on other teeth, as well as from the chart published by Arkovy,* we may regard the above teeth as normal for the age of twenty-two years. It is likewise established that the pulp-chambers of the teeth decrease in size with advancing age, and especially when the *Diao-nostik der Zahnkrankheiten, 1885. THE PULP-CHAMBERS OF THE TEETH. 31 enamel of the teeth becomes worn away. In these instances, not only all the horns of the pulp gradually disappear, but sometimes almost the whole pulp-chamber becomes obliterated by the formation of secondary dentine. This condition of the pulp-chambers does not so much depend upon the age as upon the habit of the individual to whom the teeth belong, and upon the articulation of the teeth. Some individuals, especially those Fig. 19. Key to the Measurements of the PtTLP-CH.iiiBERS of the Teeth. A. sctfiittal section of the rigid lower first molar. — DN. diameter of neck ; DP, diameter of pulp-ehamber ; a, diameter between pulp-chamber and mesial surface: h, diameter between anterior horn of pulp-chamber and external surface of cusp : c. diameter between posterior horn of pulp-chamber and external surface of cusp ; d, diameter between the pulp-chamber and distal surface. ^, frontal, section of tlie left lower first molar. — Z>iV, diameter of neck ; DP, diameter of pulp-chamber: a, diameter between pulp-chamber and buccal surface; h, diameter between buccal horn of pulp-chamber and external surface of cusp : c. diameter between lingual horn of pulp-chamber and external surface of cusp ; d, diameter between pulp- chamber and lingual surface. of a nervous temperament, have the habit of griuding their teeth during sleep, whereby the enamel of the antagonizing surfaces soon becomes worn off. In other instances a person loses some of the molars and bicuspids, with the result that he is able to masticate with the front teeth only, in which case the enamel of these teeth is soon worn away. In such cases, we observe in the vicinity of the pulp-chamber corresponding to the place of injury 32 THE ANATOMY AND PATHOLOGY OF THE TEETH. on tlie grinding- or cutting-surfaces of the teeth, a formation of secondary dentine, although the individual may not be more than thirty or thirty-five years of age. On the other hand, it sometimes occurs that with people from forty-five to fifty-five vears of age there remains a complete set of teeth, with their cusps, as well as the horns of the pulp, still present. Further- more, where we find defects upon the neck of the tooth, called erosion, we observe a great diminution in the size of the pulp- chamber, and especially that portion corresponding to the place of injury in the neck of the tooth. In some chronic constitu- tional diseases, particularly in anaemia, we often meet with teeth the pulp-chambers of which are unusually large. Notwithstanding the great dilferences existing in the size and form of the pulp-chambers of the teeth, it is of great value to know, approximately, the thickness of the dental tissue between the pulp-chamber and the periphery of the tooth, and conse- quently the author has made correct measurements of the thirty- two teeth in twelve different places, as explained by Fig. 19, ^ and B. Table of Measurements of Puljp-Chamhers in Millimeters. IS Labial Sections, respectively Buccal or Sagittal. 02 OS 1 klesial or Frontal Sections. s '^ a 2.1 b " d 2.1 D P 2.9 DN 7.1 a 6 e d DP D N 1 4.7 4.6 9 23 4.1 2.6 1.6 6.5 2 2.0 5.4 5.6 2.3 8.5 7.8 10 1.9 5.6 2.0 1.9 5.8 3 2.8 4.8 5.0 2.4 2.3 7.5 il 2.5 5.8 ... 2.8 2.2 7.5 4 2.0 4.7 2.1 1.0 5.1- 12 1.6 3.9 4.5 2.1 4.6 8.3 5 1.9 4.9 1.7 1.0 4.6 13 2.0 5.2 5.8 2.3 4.2 8.5 6 2.1 6.9 2.4 1.5 6.0 14 3.4 5.5 5.4 3.2 4.6 11.2 7 1.6 3.6 1.7 1.5 4.8 15 3.4 5.4 6.4 2.4 5.6 11.5 8 2.4 6.5 2.2 1.9 6.5 16 2.5 5.5 5.8 2.4 59 10.8 25 1.4 4.1 ... 1.6 1.0 4.0 17 2.2 5.1 4.9 2.5 3.2 7.9 26 1.6 4.0 1.7 0.8 4.0 18 2.4 6.3 7.0 2.1 43 8.8 27 1.9 6.1 2.4 1.0 5.1 19 2.3 5.0 6.2 2.0 4.4 8.7 28 2.0 3.5 1.8 0,9 4.7 20 1.3 4.0 5.1 2.5 2.5 6.8 29 1.8 4.0 2.0 1.2 50 21 1.7 4.7 4.4 1.9 2.5 6.1 30 2.4 5.1 4.9 2.5 3.6 8.5 22 2.6 4.4 2.7 2.5 7.8 31 2.3 5.4 6.5 2.5 3.8 8.6 23 2.0 3.5 2.4 2.1 6.5 32 2.2 5.2 6.0 2.6 33 8.1 24 1.8 3.8 2.1 1.3 5.3 THE PULP-CHAMBERS OF THE TEETH. 33 TaELE of MEASrREMEXTS REGARDING THE SITUATION OF THE HORXS OF THE Pulp. o2. P o « S ffi age with normally j- developed teeth. ) A man 33 years of ) age with normally >- developed teeth. } A man 37 year.s of ] age with teeth >■ very much worn. J A man 17 years of] age with normally > developed teeth. ) A man 33 years of") age with normally r developed teeth. J A man 37 years of 1 age with teeth r very much worn. ) 1 1 1 1 1 1 1 -^ n: 1 CO o p .*-* .=■-* .*-* 1 1 .•» Di* * * lid p" 1 jn 0-. *- *. J^ ! Vt 1 -. E cn Oi W ii J- *. F 1 Cji p Oi 1 1 *. = ' o 2 o p" \n ' ' :.T ^-1 ' P i p, O. *- 4- _.*. ^ 1 « * K ra f' f' f~ 9^ f^ ^ P* J- Oi J- J~ ^ en i.T C7I C.T bi en ' S-. 2 1 1 rf^ >(>. ^ -L. 4^ 4^ p" o« cj> *. :ri 4- *- ni 1 , 4^ C»= CO *- *- w 1 ■ en ■ ' ' bi » _*- _i.'i *^ ^ en 4>. V» ' en ui en ^ 1 2d Bicusp. 00 — 05 4>. *^ W j in ■ ■ ■ en en p* ] 4- 4- o; 4- en *- p: 1st Bicusp. ; 4- ^ i; j_ 4>. CO 1 ■ en ■ ■ ■ en p ■ ji. *. (o 4- en CO en "en ■ " en Cuspid. i 4- _4- o; 4- C-. CO 1 " cn ■ en ' * Lateral Incisor. 4- en tc . en -a Co bi Central Incisor. CO en ls3 en ~4 CO Central Incisor. CO en CO en Oi CO bi ■ ■ ... Lateral Incisor. 4^ 4^ CO 4^ en |sS b" Cuspid. 4^ CO CO 4a. en CO bi p" 1st Bicusp. *- 4^ CO *,. 4^ rf^ bi ■ bi ■ ::: : CO en cc CO en CO bi ' bi bi ' en p 2d Bicusp. en 4^ 4- CO ^ 4.- bi =r. 4^ CO CO *- en co bi bi " ' bi p s 5 p* y1 *- en 4>- en *- CO bi ■ ■ ■ ■ b" =-. *. 4^ jP^ *. en *- p 1 4^ ^ 4>. .^ en en en en bi en en *- en 4k en O' *- 1 P p* 4*. O *. ZJi pi f- cn - b» * * * cn^ *.. *- 4a. en ej' 4* bi h< bn ■ ■ P en C-. I 111 -• en en 1 1 P" 1 P ^ ' g p" Ol Oi , 1 •'^ 1 1 1 en . 1 1 = en* o. 1 111 1 ^ D 1 g 1 111 1 =^ H i^ a p ^ 3 hi R M 9 ij > 4 S" iz! ►1 Q 34 THE ANATOMY AND PATHOLOGY OF THE TEETH. CHAPTEE VL THE ARTICULATION OF THE TEETH. When we examine the occluding surfaces of a perfect set of human teeth and the manner in which they articulate, we come to the conclusion that the articulation of the teeth is a most wonderful device of nature, forming quite a complicated piece of mechanism. The principles of articulation, both from a practical and a scientific standpoint, are of the greatest impor- tance, and therefore ought to be studied closely by every dental student. The articulation of the teeth is based, upon certain geometrical and mechanical laws first described by W. G. A, Bon will.* Fig. 20. Articulation of a Perfect Set of Teeth of the Right Side— External Surface. In observing this articulation, we find that, in the human jaw, a straight line drawn from the buccal surface of the first bi- cuspid to the internal angle of the condyloid process of the lower maxilla will almost touch all the buccal surfaces of the bicuspids and molar teeth. Tliis shows that the teeth named are arranged in an almost straight row from the cuspid to the inner angle of the condyloid process of the lower jaw. We also observe that, with the exception of the upper third molars, every tooth articu- lates with two in the opposing jaw. (See Figs. 20 and 21.) Thus, if a tooth is lost, the antagonist, being retained in its position, is useful to a certain extent, and the regularity of the * '^Tlie Geometrical and Mechanical Laws of the Articulation of the Human Teeth." HaiTis'.s •■Principles and Practice,'' twelfth edition THE ARTICULATION OF THE TEETH. 35 dental arch is not materially disturbed. Again, articulation has been wisely arranged in this manner to offset the work of another law of nature, by the operation of which every tooth not articulating with at least one opposing tooth gradually elon- gates, and eventually is cast out of the jaw. We observe that, in a normal articulation, all the teeth of the upper jaw more or less overlap those of the lower, although it must be admitted that a perfectly articulating set of teeth is a rarity in the human mouth. In studying the articulation of the bicuspids and molars, we find that every cusp correctly fits between cusps in the opposing jaw ; and by this arrangement of cusps and depres- sions the grinding-surface is materially increased. The external or buccal cusps of the upper bicuspids and molars are arranged a little outside of the lower arch, — a disposition which enables Fig. 21. Articulation of a Perfect Set of Teeth of the Right Side— Internal Surface. the teeth of the upper jaw, when the pterygoid muscles are brought into action, to articulate with all the teeth of the lower jaw. The lingual cusps of the upper bicuspids and molars are somewhat higher and less pointed than the corresponding outer cusps. In the lower teeth we find this arrangement reversed, and observe that the outer cusps of the bicuspids and first molars are the longer and rounder, while the inner or lingual cusps are the shorter and more pointed. The result of this reciprocation evidently is that, when the lower jaw is moved laterally by the pterygoid muscles, the buccal and lingual cusps of the upper teeth on one side of the mouth play upon the buccal and lingual cusps of the lower teeth, while the lingual cusps of the upper jaw on the opposite side of the mouth articulate with the buccal cusps of the lower teeth. 36 THE ANATOMY AND PATHOLOGY OF THE TEETH. Hence the teeth not only possess a larger extent of grinding- surface with small proportional bulk, but considerable energy is saved in mastication. At the same time, the pressure upon the teeth exerted by the muscles of mastication is more or less equalized through the entire dental arch. If we examine dif- ferent sets of teeth, we shall notice that great variations exist in the lengths of the so-called overbites. If the upper front teeth overlap the lower ones but little, we invariably find short cusps upon the bicuspids and first molars, while, on the contrary, when the overbite is long these cusps are long and pointed, provided all the teeth occupy their proper positions. On examining the plane of the grinding-surface of the lower bicuspids and molars, we find that the second and third molars stand considerably higher than the first, yet the three crowns form a gradual slope. Regarding the position of the roots of the low^er second and third molars, we observe that while their crowns are tilted forward, their roots, on the contrary, are directed toward the condyloid process of the jaw, by which arrangement this grad- ual slope is accomplished. In consequence of this slope in the low^er dental arch, the second and third molars of the upper jaw also assume a slanting position upward, rendering the first upper- molar the longest of the molar teeth. The object of this arrange- ment evidently is that, when by the sliding movements of the lower jaw the condyloid process is brought forward, the second lower molar articulates against the first upper one, which, being longer than the second and third, opens the jaw sufficiently to allow the articulation of the cutting-edges of the upper and lower front teeth as well as the points of the cusps of the bicuspids. Hence the pressure, which otherwise would bear upon the molars only, is equally distributed upon the side as well as the front por- tion of the dental arch. When, because of the loss of the back teeth, a patient for a number of years masticates entirely with the front teeth, the muscles of mastication gradually become contracted, the condy- loid process leaves its normal place in the glenoid fossa, and occupies a more anterior position. In such cases we observe a slight protrusion of the lower jaw, and the remaining teeth to be considerably reduced in length through mechanical abrasion, brought about by the lateral movements of the lower jaw^. Their cutting-edges, formerly more or less sharp, are now Inroad and flat, similar in form to the grinding-surface of a THE ARTICULATION OF THE TEETH. 37 much-worn bicuspid. In this instance an acquired abnormal articulation of the lower jaw is present, which, upon the restora- tion of the teeth to their original length, will cause the condy- loid processes of the lower jaw to resume their former position in the glenoid fossie. From the article published by W. G, A. Bonwill I quote the following : " The Equilateral Triangle ivithin the Main Triangle. — The out- line drawing (Fig. 22) may be thought ideal. But any one at all acquainted with geometry must be struck with wonder at the marvelous ingenuity of the contrivance based alone on the equilateral triangle. It will be seen that perfection must Fig. 22. Diagram showing Equilateral Triangle of the Lower Jaw. (After W. G. A. Bonwill.) be the result, since each part is complete within itself and the whole supporting each individual part. " How have I arrived at this divination ? The law is based upon the measurement of over two thousand human skulls. First make an equilateral triangle, four inches; A, A, F. Draw a line from T to F. What is the guide to form the arch ? Know the actual width of the superior central, lateral, and cuspid at their greatest diameter from the mesial to distal surfaces, say H", as in Fig. 22. Measure this off with the dividers, and place one arm at F and describe an arc from D to D through I. Then place dividers at I, and intersect the line just made from 88 THE ANATOxMY AND PATHOLOGY OF THE TEETH. F, and it will be found that at D will be found the extremest point of the arch D, F, D, and will be the distal surface of the superior cuspid. Place the dividers at I, and describe the arc from D to D through F, which will constitute the normal and positive arch of the superior jaw. There wall be an equilateral triangle from D, F, I on either side of the mesial line at F. The same will be found the base of each superior incisor. " I^ext draw a line from A to D on either side, which will be the guide for the bicuspids and molars as to width and depth. Then, by placing the dividers at A and B, describe another arc to C, which will give the width of iirst superior bicuspid. The line from A to D passes through its palatal base, and will pass through center of base of triangle of this tooth. Form another triangle by drawing a line from H to H, through B, which wnll pass through the center of the first molar, and will give the width between the palatal surfaces or their depth or thickness. Placing the dividers at I and F, we intersect the line from F to T at Y. Draw a line through Y to E, E, forming another equi- lateral triangle. From B to F is now the radius of another arc, which intersects the line from D to A at Y, and the line A to D at 0. A line now drawn E to E through Y intersects the center of the second molar at E, E. " Get half the distance between the points at E on the line from D to A, and the width of the first molar is made, and also the second, which is the angle of the equilateral of each. This leaves room between the first bicuspid and first molar, and is the width of second bicuspid ; or it is shown by placing the di- viders at A and Y, and intersecting line from D to A at W, same as from B to C, for the first bicuspid's width. The distance from D to D is the same as from D to the distal surface of the second molar. P to P through Z forms another equilateral tri- angle, giving the wisdom-tooth's place in the arch. " The arrangement of L and J on the left shows the teeth in the act of mastication, while on the right the inner cusp of molars of the upper and outer of the low^er molars come in con- tact when not in use. There is double the surface touching at every lateral movement." GENERAL AXATOMY OF THE HUMAN TEETH. 39 CHAPTER VIL WENERAL ANATOMY OF THE HUMAN TEETH. I. The sockets of the teeth are made up of a thin layer of cortical bone, distinctly lamellated, and blending with trabeculse of the cancellous bone in the central part of the alveolar pro- cess. The latter we find filled with freely vascularized medul- lary tissue in the juvenile condition ; whereas, in advanced age, this tissue is transformed into fat, which, as a rule, is likewise supplied with numerous blood-vessels. The socket-walls are of the greatest possible strength, with the least mass, since a hollow cylinder is stronger than a solid one. The blood-vessels of the medullary spaces are continuous with those of the periosteum, pericementum, and gums. This explains why sockets easily become necrotic after suppurative periostitis and pericementitis, in event of which maladies a certain amount of the socket is deprived of the nourishing material carried to it by the blood- vessels. (See Fig. 23.) II. The compact hone of the socket is covered with a layer of dense connective tissue of broad bundles. This is continuous with another layer of fibrous connective tissue composed of bundles that run obliquely toward the apex of the root of the tooth. The latter tissue bears the name of pericementum, root- mem.brcme, or alreolar dental periosteum. Its bundles are firmly attached to the walls of the socket and the root of the tooth. Thus it becomes comprehensible that the teeth can stand enor- mous pressure without injury, as in the process of mastication, in the lifting of heavy weights, or in the suspension of the whole body on a rope, by means of the dentures. We further- more understand why sometimes a portion of the bony structure is carried away upon the extraction of a tooth. At the same time the pericementum gives a considerable degree of elasticity and a limited amount of mobility to the teeth. This explains the presence of facets upon the approximal surfaces of the crowns of teeth in crowded dental arches. III. Similarly the upper and the lateral portions of the alveolar process are covered by fibrous connective tissue, the periosteum , which blends with the dense fibrous connective tissue of the gum, composed of broad and straight interlacing bundles. 40 THE ANATOMY AND PATHOLOGY OF THE TEETH, This firm cushion, the (/".in, in a normal condition is but scantily supplied with blood-vessels. The superficies of the gum exhibit numerous finger-like elevations, the so-called papillae, Fig. 23. Diagram of the Structure and Implantation of a Normal Incisor Tooth. L, cuticle of enamel, Nasmyth's membrane ; E, enamel ; D, dentine with uniformly dis- tributed canaliculi ; /, interzonal layer between enamel and dentine ; B, border-line between enamel and cementum of neck ; 5, cementum of neck ; Ce. cementum of root ; Z, interzonal layer between dentine and cementum ; P, pericementum ; A, arteriole of pulp, brancbing into capillaries; F, vein of pulp, taking up capillaries; xV, meduUated nerve-fibers of pulp: Eg, stratified epithelium of gum ; P^r, papillary layer of gum ; Pe, periosteum ; Co, cortical bone of alveolus or socket; 6'a, cancellous bone-tissue of alveolus; ilf, medullary spaces of can- cellous bone. GENERAL ANATOMY OF THE HUMAX TEETH. 41 which contain loops of capillary blood-vessels. The sum-total of the papillse is termed the papillan/ layer. At its outer surface it is covered with a layer of stratified epithelia. In the strata we observe three forms of epithelia, as in the skin and in the mucous membranes generally. The innermost layer is made up of a single row of columnar epithelia, much elongated in a ver- tical direction and resting upon the connective tissue. This row of columnar epithelia is covered by several rows of cuboidal epithelia, so termed on account of their shape. The layers of cuboidal epithelia are coated by several strata of flat or pave- ment-epithelia, so called because their length and width are much greater than is their thickness. The pavement layer is composed of a horny substance, and it exhibits properties of life only in the nuclei of the epithelia, the same being the case throughout the flat epithelial covering of the oral cavity. The surface of the gum appears to the naked eye either smooth or slightly granular, since the papillary elevations of the connective tissue and the valleys between them are but slightly pronounced upon the epithelial surface. Continued irritation, as in the too frequent application of the tooth-brush, is, in many instances, sufficient to give the surface of the gums a more or less pro- nounced papillary aspect. lY. Dentine is the tissue which composes the main mass of the tooth. It consists of a glue-yielding basis-substance (not carti- laginous, as is often stated), richly infiltrated with lime-salts. The chemical constituents, according to Bibra,* of perfectly dried dentine are, — Organic matter (tootli-caitilage) .... 27.61 Fat 0.40 Phospli. iluoride calcium 66.72 Carbonate of calcium 3.36 Phosphate of magnesium ...... 1.08 Other salts 0.83 The basis-substance is traversed by the dentinal canaliculi, which take their general course from the pulp-chamber toward the summit of the crown, running horizontally in the neck, and in a portion of the root. It is only near the apex that the canaliculi are inclined toward the end of the root. Each canali- culus curves in the general shape of the letter S, slightly toward the pulp-chamber and abruptly toward the periphery of the * From Tomes 's •• Dental Anatomv." 42 THE ANATOxMY A^'D PATHOLOGY OF THE TEETH. dentine. In the region of the crown, upon approaching the peri- phery of the dentine, almost without exception, the canaliculi divide into tw^o or three branches, this branching being termed bifarcatioiL In the region of the neck such a bifurcation of the dentinal canaliculi is exceptional. It is a peculiarity there that the canaliculi do not reach the periphery of the dentine, but stop short of the latter at a distance varying in difi'erent teeth, w^hereas in the root bifurcation is of frequent occurrence. Each dentinal canaliculus contains a slightly beaded fiber, the deritinol fibrilla, or, in honor of the discoverer, ./. Tomes\s fiber. In the crown the dentine is surrounded by the enamel, and in the regions of the neck and root by the cementum. The border-line between these tissues has been termed by W. H. Atkinson the interzonal lagev. This layer has been also termed the granular hnjer by J. Tomes. It is usually marked by shallow excavations along the periphery of the dentine. Occasionally the ultimate branches of some dentinal canaliculi transgress the interzonal layer, producing either loops or club-shaped enlarge- ments in the adjacent portion of the enamel. The interzonal layer between the dentine of the root and the adjacent cementum may be marked by shallow excavations similar to those in the dentine of the crown, or there may exist no distinct boundary line between the two tissues. V. Enamel. Whereas dentine is undoubtedly a form of con- nective tissue closely allied to bone, enamel bears no resemblance to any other tissue in the animal organism. It starts from epi- thelium, becomes transformed into connective tissue, yet exhibits features characteristic of epithelial structures. The enamel covers only the crown of a tooth. It is thickest upon the sum- mit of the crown, gradually becoming thinner toward the region of the neck, "where it terminates in a sloping line, slightly over- lapped by the cementum. The enamel is composed of so-called enamel-prisms, exhibiting transverse striations, the striee of Retzius. Between these enamel-prisms there are narrow interstices which hold delicate beaded fibers, the enamelfibrillce. The enamel- prisms run a wavy course, and we meet with transverse sections intermixed wdth longitudinal ones so frequently that the idea of interlacing bundles of enamel-prisms forced itself upon previous investigators. Frank Abbott was the first to assert that no such interlacing occurs, and that the appearance of transverse sections intermixed with longitudinal ones is due to the pro- GENERAL ANATOMY OF THE HUMAN TEETH. 43 nouncedly wavy course of some of the bundles, being cut both longitudinally and transversely. The outer surface of the enamel is covered by a thin, horny layer of epithelial tissue, the so-called XasmijiJi's membrane, or enamel-cuticle. This layer can be rendered visible by the appli- cation of strong chemical agents, and is present only in teeth not as yet worn off by mastication. It is in direct union with the outermost epithelial layer of the gum, which is likewise composed of flat, hornitied epithelia, to a varying degree. The enamel-cuticle is, therefore, the only laj^er which closes up the fissure between the neck of the tooth and the adjacent gum. VI. Cementum. This is a stratum of bone-tissue covering the dentine of the root of the tooth. It starts in an oblique line at the neck, gradually increasing in thickness toward the apex, where it borders upon the beginning of the root-canal. The cementum is, as a rule, covered at its outer periphery by a single layer of calcified protoplasmic bodies, similar to the so-called osteoblasts (Gegenbaur), which are in connection with the fibrous connective tissue of the pericementum. At the neck it is com- posed of a calcified basis-substance, pierced by spindle-shaped protoplasmic bodies. In the root portion of the cementum we observe a distinct lamellation, and here we meet with numerous branching protoplasmic bodies, the cement-corpuscles, bearing a close resemblance to bone-corpuscles. Even in low amplifica- tions by the microscope we frequently notice a union of the ends of the dentinal canaliculi, with oftshoots of cement-corpus- cles. From these facts we may infer that each root of a tooth represents a large Haversian system, in which the Haversian canal corresponds to the central pulp-canal and its soft tenants, whereas the outermost laj'er of the cementum represents the concentrically lamellated cortex. Between these, two layers is inserted a broad layer of dentine, traversed by dentinal canaliculi, , which we may consider as elongated oftshoots of bone-corpus- cles. If viewed in this light, dentine may justly be considered a modified bone-tissue, peculiar to the structure of the teeth. VII. The Pulp. The central cavity is called pulp-chaniber in the crown, and root-canal in the root of a tooth. It is filled 5vith a myxomatous connective tissue, in which are distributed blood- vessels and nerves. These enter the pulp-canal at the apex of the root of the tooth. At about the middle of the root-canal a small afierent artery, the arteriole, splits up into capillaries, 44 THE ANATOMY AND PATHOLOGY OF THE TEETH. producing throughout the pulp-tissue a rich net-work, termin- ating at the summit of the coronal portion in loops. The capil- laries coalesce with the vein. This vein is a branch of the alveolar vein, into which it carries the blood through the root- canals. There is a large number of bundles of nerves in the pulp, entering the apical foramen in the shape of raedullated nerve-fibers. Upon approaching the periphery of the pulp they lose their medullary sheaths and become non-meduUated, as is the rule with all meduUated nerve-fibers in peripheral organs. During the development of the tooth, the outer surface of the pulp exhibits a row of large protoplasmic bodies, the so-called odontoblasts (J. Tomes), which are in direct connection with the tenants of the dentinal canaliculi. In the fully-developed tooth the odontoblasts are not always present, being mostly replaced by irregular rows of medullary corpuscles. The ultimate ter- mination of the nerve-fibrillee can be traced between these me- dullary corpuscles or odontoblasts, but never to a direct union with the dentinal fibers. This fact sufficiently proves that the dentinal fibers are not true nerves. Lymph-vessels are un- questionably present in the pulp, but nothing positive has as yet been ascertained as to their course and origin. Anomalous though not Pathological Formations in the Teeth (see Fig. 24). — Among the most frequent occurrences of such formations, we notice in the crown of the tooth fields filled with a non-calcified basis-substance. They are known as the inter- r/lobular spaces of Czermak. They appear as irregular spots, varying in size and shape, but always bordered by concave con- tours. These so-called spaces occur near, though never directly at, the periphery of the dentine toward the enamel, and occa- sionally blend with much smaller spaces at the interzonal layer of the neck, or even the root of the tooth. They are traversed by the dentinal canaliculi without the slightest deviation of the latter. Of common occurrence in the dentine are fields of calcified basis-substance, lacking dentinal canaliculi. Much rarer are parallel striations of the dentine, indicative of the successive formation of the layers of this tissue. In the enamel at the interzonal layer we not infrequently meet w^ith globular or club-shaped spaces filled with protoplasm. In the highest expression of this abnormality we find every branch of the dentinal canaliculi to have a club-shaped termina- GENERAL ANATOMY OF THE HUMAN TEETH. 45 tion. Pigmentation and stratification of the enamel are not rare. J. Retzius first drew attention to their presence. The brown pigmentation of the enamel always is most pronounced Fig. 21. Diagram of an AyoMALous though sot Pathological Incisor Tooth. 6', cuticle of enamel, Nasmyth's membrane : E, stratified and pigmented enamel; /, inter- zonal layer between enamel and dentine, with club-like terminations of dentinal canaliculi : G, dentine with interglobular spaces along the outer periphery : -V, cementum of neck, over- lapping the enamel; 5, basis-substance of dentine, destitute of canaliculi ; .S' (upper), stratifi- cation of dentine; S (lower), secondary dentine; Z. interzonal layer between dentine and cementum, with club-like enlargements of the canaliculi; Ce, cementum of root; P, peri- cementum ; 0, row of odontoblasts at the outer periphery of the pulp ; M, meduUated nerves of the pulp; Eg, stratified epithelium of gum; Pa, papillary layer of gum; So, socket or alveolus. 46 THE ANATOiMY AND PATHOLOGY OF THE TEETH. along the periphery and along the strife of the enamel. What the cause of such pigmentations and stratifications may be, we do not know. In rare instances the cement of the neck considerably over- laps the enamel. This feature explains certain occurrences in the process of absorption of temporary teeth. Along the inter- zonal layer between the dentine and the cementum we occasion- ally meet with club-shaped spaces filled with protoplasm, and in union with the terminations of the dentinal canaliculi. All these features, including the interglobular spaces, may be con- sidered as the result of an imperfect calcification during the process of development. CHAPTER VIII. GENERAL HLSTOLOaY. The animal body is built up of four main varieties of tissue, viz : I. Connective Tissue. IL, Muscle-Tissue. III. Nerve- Tissue. IV. Epithelial Tissue. According to the views of most histologists, both the connec- tive and muscle tissues are products of the mesoblast, the middle layer of the germ, and the nerve-tissue originates from the epiblast, whereas the epithelium arises from both the epi- and the hypoblast. This view, however, cannot be strictly adhered to, since we know that the central nerve-organs, though originally products of the epiblast, in further development are composed of a tissue of their own, closely allied to connective tissue. The enamel of the teeth is of an epiblastic or epithelial origin, but during further development it changes to a type of connective tissue. I. Connective Tissue. — This tissue composes the main mass of the organism. It forms the bony frame or skeleton, the articular surfaces of the joints, or cartilages. As the derma of the skin, it covers the body ; as perimysium and perineurium, it accompanies the muscles and nerves ; and as periosteum, it en- GENERAL HISTOLOGY. 47 velops all bones. Fat is likewise a sub-variety of connective tissue. The latter is the only tissue serving as a carrier of both blood- and lymph-vessels. Up to the year 1873, connective tissue was believed to be made up of cells, — the so-called connective-tissue corpuscles, — and an apparently inert intercellular or basis-substance, varying con- siderably in consistency and chemical constitution. This basis- substance generally is termed glue, a nitrogenous matter for which there exists as yet no chemical formula. Until that time, also, the cells were believed to be isolated individuals, imbedded in cavities of the basis-substance. In the year mentioned, Carl Heitzmann showed that protoplasm in general pbssesses a reti- cular structure, a fact which has since been proved by photo- micrography. In the basis-substance Heitzmann likewise has shown the existence of a reticulum identical with that of the protoplasm, a fact not as yet generally accepted by histologists. The reticulum, its points of intersection, the granules, and the nucleus are the living or contractile matter proper, and it is this which pervades the basis-substance, as well as the protoplasm. In this view^ both the animal and the vegetable organisms are a continuous net-work of living matter, — a delicate reticulum, the meshes of which are filled with a lifeless nitrogenous liquid in the protoplasm, while in all varieties of basis-substance these meshes contain a solid or semi-solid nitrogenous matter. We distinguish four varieties of connective tissue, viz : A. 3Iyxomatous, or mucoid. B. Fibrous, or striated. C Cartilaginous, or chondrogenous. D. Osseous, or bong. Under the last head belong the dentine and the ceinentuni of the teeth. While the character of any variety of connectire tissue is ex- clusively defined by the peculiarities of its basis-substance, it is to be understood that its corpuscles, though varying in size, shape, and arrangement, are made up everywhere simply of protoplasm, or, as in dentine, of fibers of living matter alone. A. Myxomatous, or 31ucoid Tissue, is the earliest formation ia the embryo, and all varieties of connective tissue are of myxo- matous origin. This tissue shows fields of basis-substance cor- responding in size and shape to medullary corpuscles, or. proto- plasmic bodies, which have been transformed into a jelly-like mass, though their minute structure has remained unchano-ed. 48 THE ANATOMY AND PATHOLOGY OF THE TEETH. The reticular myxomatous tissue is composed of branching protoplasmic bodies, the meshes of which hold a gelatinous (myxomatous) basis-substance with central nuclei, the rem- nants of previous protoplasmic bodies. (See Fig. 25.) To this type belong the tissue of the placenta, the umbilical cord, the lymph-ganglia, the so-called adenoid laj^ers and follicles of the mucous membranes, and the pulps of the teeth. Fat is a variety of myxomatous tissue held as a basis-substance in a protoplasmic net-work. Fig. 25. Reticular Myxomatous Tissue of a Villus op the Placenta op a Human Embryo, Four Months Old. (From C. Heitzmann.) E, E, epithelial cover of the yillu? ; B, solid bud of a growing villus ; C, C, capillary blood- vessels, overlapped by the myxomatous reticulum. Magnified 500 diameters. B. Fibrous, or Striated Tissue, derives its name from the striated appearance of the basis-substance, which upon being torn asunder has the aspect of fibrillse. The bundles of such fibers may be thin and arranged loosely, as in the so-called areolar variety of connective tissue (pia mater, arachnoid, and peritoneum), or they may be densely put together and traversed by large branch- ing protoplasmic bodies. The bundles are either arranged per- GENERAL HISTOLOGY, 49 fectly parallel, as we observe in the tendon (see Fig. 26), or interlacino- and interwoven in all directions, as we find them in Fig. 26. Texdox of Achilles of a Young Person. Loxgitudixal Section. Chromic Acid Specisien. (From G. Heitzmann.) B, bundles of striated connective tissue, here and there finely dotted; TC, tendon cor- puscles within the bundles or between the smallest bundles; 72', interstitial medullary tissue carrying capillary blood-vessels, C. Magnified 500 diameters. the derma of the skin, the periosteum, the perichondrium, the articular and the interarticular ligaments, etc. C. Cariilaginous, or Chondrogenous Tissue, is composed of proto- plasmic bodies imbedded in a dense and tough basis-substance. (See Fig. 27.) In the juvenile condition it is traversed by medullary spaces containing blood-vessels. The existence of connections between the protoplasmic bodies, as well as of the reticulum in the basis-substance, was proven by the method of staining with a solution of chloride of gold and treatment with absolute alcohol. There are three varieties of this tissue, viz : The Hyaline Cartilage. The Fibrous Cartilage. The Reticular Cartilage. D. Bong or Osseous Tissue. — Of this there are two main varie- ties, viz : The cancellous, epiphyseal, or spongy, and the compact, or cortical, bone-tissue. Cancellous bone is the first bone formed in the embryo, long 5 50 THE ANATOMY AND PATHOLOGY OF THE TEETH. before the cortical bone makes its appearance. (See Fig. 28.) In human beings it is the only variety of bone present up to the fifth, sixth, or even the seventh month of intrauterine develop- ment. In dogs, cats, and rabbits, at birth, none but cancellous bone is found in the skeleton. This tissue consists of small, interconnected trabeculie of bone, surrounding and inclosing spaces of medullary or myxomatous tissue, supplied with capil- lary blood-vessels. The trabeculse are faintly lamellated, and FiCx. 27. -M '>"^J ^ <^-^ %i1 f " '^^^iV ^-^^V. ■i^fjl ir^iie Hyaltxe Cartilage from the Condyle op Femtje or a Ne^lt-born Pup. Chromic Acid Specijien. (From C. Heitzmanx.) C, the tissue of the hyaline cartilage, with scattered groups of cartilage-corpuscles; lf» medullary spaces, containing blood-vessels and medullary tissue. Magnified 100 diameters. hold a number of branching protoplasmic bodies, the bone-cor- puscles. The latter have been known only since 1870, and w^ere discovered by S. Strieker. Previous to that date dry bones, ground thin and mounted in Canada balsam, w^ere resorted to for microscopical examination. In such specimens only the spaces holding the protoplasmic bodies and their offshoots, the so-called canaliculi, were visible. To-day we know that not only each lacuna holds a bone-corpuscle, but that every canaliculus GENERAL HISTOLOGY. 51 contains a small fiber of living matter, and the entire basis-sub- stance is traversed by an extremely delicate net-work of such matter, the meshes of which are filled with a ghie-yielding basis- substance, saturated with lime-salts. Cortical hone-tissue is composed of parallel lamellae, bunched together in the shape of so-called Haversian systems, extending longitudinally with the longitudinal axis of the bones. (See Fig. 29.) The center of each Haversian system is occupied by Fig. 28. Tibia of a Newlt-borx Pup. Longitudinal Section. Chromic Acid Specimen. (From C. Heitzmann.) T, trabecule of bone-tissue containing bone-corpuscles: J/, medullary spaces filled with medullary tissue, holding blood-vessels in the most central portions. Magnified 200 diameters. a medullary canal that holds, besides a straight capillary blood- vessel, a varying amount of medullary tissue. The older the individual, the scantier is this medullary tissue. The lamellated region contains the branching bone-corpuscles, the same as the trabeculfe of cancellous bone. The offshoots of these corpuscles are arranged radiately, interconnecting not only all protoplasmic bodies within the bone, but also the medullary corpuscles, and, indirectly, the walls of the blood-vessels. This is an im- 52 THE ANATUMY AND rATHOLU(JY OF THE TEETH. portant fact, since it explains the nutrition of the compact bone, which is sparingly supplied with blood-vessels, though endowed with properties of life. Each large bone, the shaft-bones as well as the lower maxilla, contains in its center a large medul- lary space traversed by cancellous bone-structure. In youth the medullary spaces hold the so-called red medulla, while in more advanced age they contain fat-tissue. Epiphyseal ex- tremities of bones are mainly cancellous and covered by a thin layer of cortical structure, while articular ends are directly coated with hyaline cartilage. TnjiA OF A Grown Dog— Cortical Portion, Transverse Section. Chromic-Acid Spe- cimen. (From C. Heitzmann.) S, Haversian system of lamellje, containing the bone- corpuscles, C, with their radiating off- shoots; ilf, central medullary, so-called Haversian canal, containing a capillary blood-vessel ; /, interstitial bone-tissue indistinctly lamellated. Magnified 500 diameters. II. Muscle -tissue is the motor apparatus proper, and occurs in two varieties, — viz, the smooth or involuntary , and the striated or vohmtari/ masele-tissae. The former is composed of spindle- shaped protoplasmic bodies, often holding rod-like nuclei in their interior. The contraction of these spindles results in a slow movement of the muscular walls of the cavities of the body, and the larger blood-vessels, arteries, and veins. The striated or voluntary musdes consist of large spindle-shaped fibers, in which there are disks made up of small prismatic GENERAL HISTOLOdY. 53 pieces, the so-CiTlled " sarcous elements." In longitudinal section the disks of the sarcous elements appear in great regularity of arrangement, separated from one another by a slight interstice tilled with a liquid. (See Fig. 30.) The shape and arrangement Fig. 30. Muscle op Tongue op Max— Chromic-Acid Specimen. (From C. Heitzmann.) L, longitudinal musele-fiber, broken otf and exhibiting its structureless sheath, the sarco- lemma, S ; N, medullated nerve-fiber, terminating in the motor hi]], H ; T, transverse section of a muscle-fiber; P, the perimysium, holding capillary blood-vessels, C, and nerves, iV^. Magnified 500 diameters. of the sarcous elements greatly vary, depending upon the posi- tion of the muscle-fiber at death. "Whatever the configuration of the sarcous elements be, they are invariably interconnected by extremely delicate conical threads, both in the longitudinal 54 THE AXATOMY AND PATHOLOGY OF THE TEETH. and transverse directions. The sarcous elements, like the spindles of the involuntary muscles, are formations of con- tractile or living matter. The structure of the muscle-fiber is, according to Heitzmann, identical with that of protoplasm. Fig. 31. Branch of the Motoe Oculi Nerve of Man. (From C. Heitzmann.) L, longitudinal, T, transverse section of the bundle ; PE, external perineurium; PJ, inter- nal perineurium; ML, myelin investment; A, axis-cylinder; M, transverse sections of muscle-fibers. Magnified 600 diameters. The only difference is that in protoplasm the granules and the points of intersection of the minute reticulum are small and arranged without regularity; whereas in the striated muscle the points of intersection are large and of a prismatic or disk- GEXERAL HISTOLOGY, 55 like shape. The contraction of tlie protoplasm and that of the muscle-fibers are based upon the same principle. III. Nerve-tissue. — As the writer intends to confine himself to but a brief description of the nerves, he will not dwell upon the central nervous organs, the brain and the spinal cord. "We distinguish two varieties of nerve-fibers, — viz, the medid- lated and the non-medullated. The medidlated nerre-fibers exhibit to the naked eye a white color, owing to the presence of m>/elin, or nerve-fat, which sur- rounds the central conducting fiber, the so-called axis-cylinder. In transverse sections of bundles of meduUated nerve-fibers we observe around the periphery of the bundle a sheath of delicate fibrous connective tissue, the external j^erineurium. From this Fig. 32. Medullated and Non-Medullated Nerte-Fibers from the Retina of a Bull. (From C. Heitzmann.) S'^, myelin sheath, with oblong nuclei and (S-) transverse septa. The myelin oozed out. JV, non-medullated nerve-fibers, with varicose enlargements. Magnified 600 diameters. layer arise minute offshoots which encircle each nerve-fiber, as \h.Q internal perineurium. (See Fig. 31.) Next follows a thin laj'er of nucleated connective tissue, Schwann's sheath. After this a laj^er of myelin or nerve-fat, which surrounds the central axis- ment of reticular cartilage. — «, territory originally composed of a number of embryonal corpuscles,— protoplasm containing a reticulum of living matter; &, peri- pheral protoplasmic bodies in the beginning inflliration with glue-yielding basis-substance, the chemical change taking place in the fluid, filling the meshes of the reticulum ; the central pro toplasmic body left unchanged, — cartilage-corpuscle; c, infiltration with basis-substance further advanced ; d, infiltration with basis-substance accomplished, the reticulum present, but ren- dered invisible. B, structure and development of fibrous connective tissue. — a, branching and interconnecting protoplasmic tracts; 6, fibers composed of protoplasmic spindles, holding the reticulum of living matter, all interconnected by living matter; c, advanced infiltration with basis-substance, the reticulum present, but rendered invisible. afterward, when they could not any longer deny it, they said that it was not originally observed by Heitzmann, but was discovered by C. Frommann in 1867. Frommann, it is true, speaks of a reticulum in connective tissue, and in ganglionic cells, but with- DEVELOPMENT OF COXXECTIYE TISSUE. 63 out giving an illustration thereof. He afterward declared that he had never used lenses of a higher power than 450 diameters. To observe the reticulum in the protoplasm with such a power of the microscope is simply impossible, even to an experienced eye. Indeed, from 800 to 1000 diameters are required for the study of the reticulum under consideration. That the reticulum exists is to-day a settled fact, the more so as Strieker, in 1890, succeeded in reproducing it by photography, magnifying a livino- colorless blood-corpuscle of the proteus by means of the electric microscope, with a power of 2500 diameters.* In this photo- micrograph the reticulum in the protoplasm is exactly the same as discovered and described by Carl Heitzmann in 1873. That the nucleus is made up of living matter became appar- ently doubtful when, in 1875, the so-called karyokinesis of the nucleus was discovered by Strassburger,Biitschli, Flemming, and others. It was shown that the nucleus is composed of loop-like threads representing stars and double-stars preceding its divi- sion. Since these loops could be stained deeper by certain anilin dyes, especially safranin, than the granules of the protoplasm, it was asserted that the nucleus is composed of a substance of its own, called " nuclein" and "chromatin." It is plain that a substance capable of changing its shape and place must be living matter. The karyokinetic threads assumed a deeper color only on account of their being more bulky than the rest of the reticulum in the surrounding protoplasm. Besides, it was shown that even at the height of karyokinesis, the loops remain interconnected with the surrounding reticulum of the protoplasm, which again proves their identity, ^ot only do all movements occur in consequence of contraction and extension of the reticulum, but all new formations and outgrowths start from this substance, respectively from the granules, the points of intersection of the reticulum. This again proves that the reti- culumis the living matter proper, in the meshes of which there exists a liquid holding nitrogen, but, being a liquid, not endowed with the properties of life. Originally every so-called cell is a solid granule of living matter, which in turn becomes vacuoled by an accumulation of liquid, and, at last, is reticulated, in consequence of perforations of the walls of the vacuoles. Another discovery of Carl Heitzmann, in 1873, was that the * Arbeiten aits dem Institute fur experimentelle Pathologie. 1890. 64 THE ANATOMY AND PATHOLOGY OF THE TEETH. intercellular or basis-substance of tlie connective tissue is not dead or inert, as hitherto supposed, but is alive in the same sense as the cells themselves. The reticulum of living matter visible in the latter is present also in the basis-substance, though ren- dered invisible by chemical changes and a solidification of the originallv liquid contents of the meshes in the protoplasm. It has been proven that in all varieties of connective tissue, in the muscles, the nerves, and the epithelia, the so-called cells are interconnected by means of delicate threads of living matter, or indirectly by the reticulum pervading the basis-substance. (See Fig. 37.) In the development of all varieties of basis-substance, the protoplasm shares, by a process of chemical transformation which" renders it more or less firm and solid. It has also been proven that in the formation of basis-substance the protoplasm does not perish altogether, but only the lifeless liquid portion which is held in the meshes of the reticulum becomes solidified, whereas the reticulum itself remains unchanged. Development of Bone-Tissue. — While all varieties of connec- tive tissue develop directly from indifferent or medullary tissue, bone is a secondary formation, originating either from previous hyaline cartilage or from fibrous connective tissue. The latter is the case with the fiat bones of the skull ; the former, with all the rest of the skeleton, including the lower jaw and the greater portion of the upper jaw. In both instances the process is identical ; indeed, W. X. Sudduth* has shown that even the lower jaw may, in part, develop from fibrous connective tissue, inde- pendently of hyaline cartilage. AYhenever hj^aline cartilage is about to be transformed into bone-tissue, as in the case of the lower jaw in the sixth week of embryonal life, the cartilage becomes reduced to medullary tissue, a process frequently, though not always, preceded by a deposition of lime-salts at the border of the territories of the cartilage-corpuscles. Sometimes, before the cartilage begins to change into embryonal tissue, a calcified frame of basis-substance is produced. In former years, histologists encountered great difficulties in explaining the origin of the medullarv tissue. Some of them — A. Rollet, for example — have gone so far as to assert that the cartilage-cells perish altogether, and that into their places colorless blood-cor- puscles migrate, giving rise to bone-tissue. To-day all such *"The American Svstem of Dentistry, " 1886. DEVELOPMENT OF CONNECTIVE TISSUE. 65 difficulties have vanished, since we know that not only are the cartilage-corpuscles traversed bj a net-work of living matter, but that so also is the dense basis-substance. Nothing is required but a liquefaction of this basis-substance to liberate the reticu- FiG. 38. ^ -J' ^i \S\ 'k^ ^■ Humerus of a Human Embryo, Five Moxths Old. Sagittal Sectiox. Chromic Acid Specimen-. (From C. Heitzmanx.) C, rows of cartilag-e-corpuscles in elongated groups, due to their territories : F, frame of calci- fied basis-substance, around which, in the lower portions, the first traces of bone-tissue are noticeable; J/, medullary space, containing medullary corpuscles. Magnified 300 diameters. lum, whereupon the protoplasmic condition of the tissue is re- established. The newly-appearing medullary corpuscles, in this view, are nothing but the result of the return to the embryonic condition of the cartilage-tissue. (See Fig. 38.) , This process is 6 66 THE ANATOMY AND PATHOLOGY OF THE TEETH. followed by an outgrowth of living matter into threads, which afterward, by vacuolation, become hollowed, and thus blood- vessels are formed holding red blood-corpuscles, even before union with the already permeable capillary system. The spaces filled with embryonal or medullary tissue are bordered by the calcified basis-substance of the previous cartilage, this evidently serving as a support of the cartilage, which, to a considerable degree, has been reduced into protoplasm. Around this calcified Fig. 39. Vertebra of a Human Embyro, Five Months OLd. Horizontal Section. Chromic Acid Specimen. (From C. Heitzmann.) M, medullary space, with central blood-vessels and medullary tissue ; B, first-formed globular territories, containing one or two central bone-corpuscles, with radiating ofishoots. The terri- tories lie against the trabeeulte of the original calcified basis-substance of the cartilage, F. Magnified 500 diameters. frame the first-formed territories of bone-tissue are seen, with their convexities lying against the calcified basis-substance. (See Fig. 39.) Later a number of such medullary corpuscles unite, coalescing into globular masses of so-called nu/eloplaxes (Robin), or giant cells (Yirchow), in which we frequently notice a large number of nuclei placed at nearly regular intervals. (See Fig. 40.) Such a globular bod}^ is the beginning formation of a territory DEVELOPMENT OF CONNECTIVE TISSUE, 67 of future bone-tissue. In the center of the territory a certain amount of protoplasm remains unchanged, representing the future bone-corpuscle, whereas the peripheral portion of the territory becomes infiltrated, first with a glue-yielding basis- substance, and afterward with lime-salts. The latter portion is traversed by radiate protoplasmic oftshoots, all of which com- municate with the central bone-corpuscle. The formations formerly termed lacriue^ therefore, are nothing but the central Fig. 40. Surface OF THE sciPULA OF ilv TTE\ Chp mic \cid ;?pecimen (From C. Heitzmaxx.) C, lamellated bone, with bone-eorpuscles ; G, a single territory of bone-tissue liquefied, result- ing in the formation of a multinuelear plastid or cell ; M, coalesced masses of multinuclear plastids or cells. Magnified 600 diameters. cavities in the basis-substance, holding the bone-corpuscle. What have been termed canalicuU are the offshoots of the central cavities, holding threads of living matter. In fully-developed bone, the bone-corpuscles and their offshoots are quite conspicu- ous. By decalcifiication and staining there is rendered visible throughout the whole territory a delicate reticulum of living matter, identical with that seen in the protoplasm itself LameUaffd bone arises by an arrangement in rows of medullary 08 THE AXATOMY AND l'ATH0L0(4Y OF THE TEETH. corpuscles adjacent to the already formed bone. The large medullary bodies termed osteoblasts are a preceding stage of bone, just as the odontoblasts are of dentine, and the ameloblasts are of enamel. Either of these bodies, which resemble epithelia, must Fig. 41. Skull of Hvman Embryo, Four Moxths Old. Horizontal Section. Chromic Acid Specimex. (From C. Heitzmanx.) F, fibrous connective tissue of the pericranium : M, medullary space, with central blood- vessel : B, first-formed trabecula of bone : 0. row of osteoblasts ; C, medullary corpuscles of the inner pericranium, infiltrated with lime-salts. Magnified 500 diameters. break up into indifferent corpuscles in order to give rise to permanent bone, dentine, or enamel. Whenever bone develops from fibrous connective tissue, the latter is first reduced to embryonal tissue in the same manner as THE .MINUTE STRUCTURE OF DENTINE. 69 hyaline cartilage previous to the formation of bone. The far- ther stages of the production of bone from fibrous tissue are identical with those in the development from hyaline cartilage. (See Fig. 41.) The law here laid down is but a brief sketch of the history of development as first established in 1873 by Carl Heitzmann. Every tissue originates from protoplasm in the state of indiffer- ence, — the so-called embrijonaL or iiiedullar;j tissue. No tissue can be transformed into another unless it has first been reduced to the em- bryonal condition. This law holds good not only in the pro- gressive evolution of the tissues, but also in their retrogressive changes, and in all morbid processes, — i.e., in inflammation or in the formation of new tissue, as the result of an inflammatory process termed " hyperplasia,"" or in the formation of tumors. CHAPTER X. THE MINUTE STRUCTURE OF DENTINE.* Methods. — The best method in the preparation of bone-tissue for microscopical purposes is doubtless the treatment with chromic-acid solution of the strength of from one-half to one per cent. The same treatment has repeatedly been resorted to by different investigators of tooth-substance. The writer has used this solution extensively for this purpose, adopting precautions suggested by his experience in dealing with bone. These are, to immerse only a few teeth in a large vessel containing a consid- erable amount of chromic-acid solution ; to renew the supply of this every third or fourth day, and to add, to enforce the action of the fluid, very small quantities of dilute hydrochloric acid. Under this treatment the teeth, after a few months, become dark green from the reduction of the chromic acid to the sesqui- oxide of chromium. This method is most effective for softening teeth, both human and animal, when they are still in the jaw. Wonderful results can be obtained by cutting at the same time bone and tooth prepared in this process; also in preparing *--The Distribution of Living Matter in Human Dentine, Cement, and Enamel." Dental Cosmos, 1878-1879. 70 THE ANATOMY AND PATHOLOGY OF THE TEETH. specimens from embryos, in order to stuclj" the history of development of teeth. This method is highly recommended, although the chromic acid only softens the cement and dentine to a certain depth, so that a tooth kept howsoever long in the chromic-acid solution never is fit to be cut throuo;h its whole substance at one time. The sections so obtained are ready for staining wdth carmin or hpematoxylin after they have been immersed in and washed with distilled water, also for staining with chloride of gold, which latter may be done in the following wa}- : Thin sections, after having been washed in distilled water for twenty-four hours and thus freed from the remnants of chromic acid, are to be placed in a solution of chloride of gold of the strength of half of one per cent., by means of glass rods, as metals must be avoided in the treatment with chloride of gold. These sections are to remain in the solution for from half an hour to an hour, and must then be thoroughly washed with distilled water and exposed to daylight for several days, when they are ready for mounting in the ordinary' way in chemically-pure glycerin. The greatest objection to the chromic-acid treatment is that enamel never can be obtained in connection with the dentine. If hydrochloric acid has been used in addition to the chromic- acid solution, the enamel is almost completely dissolved. If chromic acid alone has been used, the enamel becomes so brittle that it crumbles into small particles under the knife. Under such circumstances the outer surface of the dentine looks bay- like, owing to the curved lines on the boundary between the dentine and enamel. Lactic acid, if diluted sufiiciently, so acts upon teeth as to dissolve the lime-salts much faster than chromic acid does. Specimens prepared in this waj', however, in the writer's expe- rience, are not distinct enough for study with high powers ; hence a tooth, after being softened with lactic acid, has to be immersed in chromic-acid solution for several weeks. But the o-reatest objection to the use of the lactic-acid solution is the formation of mildew in a relatively short time, and the dissolving of the enamel from the teeth. The only method which has enabled the writer to obtain speci- mens of teeth provided with all hard tissues is the following: A fresh tooth, or one kept a short time in chromic-acid solution, is sliced under water by a watch-spring saw, and ground as thin as THE MINUTE STRUCTURE OF DENTINE. 71 possible upon a corundum-wheel of a lathe, always being kept under water. The lamella thus obtained should be placed in a large quantity of chromic-acid solution of the strength of half of one per cent, for one or two days, with the view of harden- ing the soft parts of the tooth and dissolving the lime-salts. After this the specimen may be stained with carmin, hfema- toxylin, chloride of gold, etc., as above described, and mounted in glycerin. The saturated solution of picric acid in water may also be used for the decalcification of a ground slice of a tooth, though the precipitated acid must be afterward removed, either by a brush or the blade of a knife. Very handsome specimens can be obtained by staining them with carmin after the treatment with picric acid. Examination. — We know that the basis-substance or matrix of the dentine is analogous to that of bone, — i.e., that it is glue- yielding, and at the same time infiltrated with lime-salts. We learned from the researches of E. Neumann that the basis-sub- stance is denser at the walls of the canaliculi, and more resistant to the action of strong acids, which cause the appearance of a sheath around each canaliculus after the solution of the inter- mediate substance of the matrix between the tubuli. Analogous relations also exist in bone-tissue, in which the basis-substance is decidedly denser on the walls of the lacunae and Haversian canals. With low powers we cannot see in the dentine anything more minute than the dentinal canaliculi. These run in curved sig- moidal lines from the boundary of the pulp-cavity to the per- iphery of the dentine ; they are directed obliquely upward in the crown, and assume a more horizontal direction in the region of the neck, while in the root they remain horizontal or some- times turn downward to a varying extent. Besides the main sig- moidal curvature, each individual canaliculus exhibits a more or less wavy course in its way through the dentine, and the individ- ual curvatures are, as a rule, very marked on the outer periph- ery of the dentine. The dentinal canaliculi reach the outer surface of the dentine only on the circumference covered by enamel. On the periph- ery coated by cementum, including also the neck, the canaliculi terminate b'^.fore reaching the cementum, and are replaced by a finely-granular basis-substance greatly varying in width. 72 THE ANATOMY AND PATHOLOGY OF THE TEETH. The distribution of the dentinal canaliculi is in the great majority of teeth uniform throughout the dentine, although ex- ceptionally the writer has met with specimens of dentine in which there were smaller or larger territories devoid of dentinal canali- culi ; which latter looked as if arranged in bundles or groups within the basis-substance. This relation is especially visible on transverse sections of the dentine. An irregular arrangement of the dentinal canaliculi is more common in the roots than in the crowns. Each canaliculus contains a dentinal fiber. These fibers, when viewed with a power of 500 on good chromic-acid speci- mens, exhibit a pale-gray color, and run without ramification through the middle of the canaliculi up to the outer surface of the dentine. The outlines of these fibers alwa^'s look beaded and fringed. On specimens treated with chloride of gold, the fibers and their delicate offshoots show a distinct violet color, characteristic of living matter within protoplasmic formations, while the space between the fiber and the wall of the canaliculus remains unstained, and the basis-substance between the tubuli only assumes a slight violet tinge. Longitudinal sections of dentine, stained with carmin or chloride of gold, if examined with high powers, — from 1000 to 1500 diameters (immersion lenses), — exhibit the following : The canaliculi of the dentine run in a more or less wavy course through the basis-substance, and are, as a rule, bifur- cated only at the periphery of the dentine, both toward enamel and cementum. Each canaliculus contains a central, slightly beaded fiber, which on its whole periphery sends delicate thorn- like elongations through the light space between the central fiber and the wall of the canaliculus. The thorns are distinctly conical, their bases being attached to the dentinal fibers, and their points directed toward the basis-substance. The smallest thorns spring in an almost vertical direction from the dentinal fiber, while somewhat larger ofishoots may run obliquely through the basis-substance, and directly unite neighboring fibers with one another in the vicinity of the enamel and cementum. The basis-substance shows a distinct net-like structure. The light spaces surrounding the dentinal fibers send delicate elonga- tions into the basis-substance, in which, through repeated branch- ing, a light net-work is established, the meshes of which contain the decalcified glue-yielding basis-substance. The finest off- THE MINUTE STRUCTURE OF DEXTIXE. 73 shoots of the dentinal fibers can be traced only mto the months of the elongations of the canaliculi ; on the periphery of the latter, owing to their great delicacy, the offshoots are lost to sight. Coarser offshoots of the dentinal fibers, at the localities mentioned before, traverse the basis-snbstance within its light net-work, at the same time uniting dentinal fibers directly, and sending slender conical offshoots into the light net-work of the basis-substance. (See Fig. 42.) The dentinal fibers are either in direct connection with coarser ri' Fig. 42. ■D '1 4} \ ■ j ': y^ Root of Molar staixed with Chloride of Gold. D, dentine ; C. cement with branching bone-corpuscles : F^, dentinal fibers with their trans- verse offshoots ; F-, ramifications of dentinal fibers and their union with the oflFshoots of cement- corpuscles. Magnified 1200 diameters. offshoots of the protoplasmic bodies of the cementum, or the light net-work of the basis-substance of the dentine is in communi- cation with that of the basis-substance of the cementum." The latter condition prevails at the periphery of the neck of the tooth, where the basis-substance of the dentine is pierced not by larger offshoots of the dentinal fibers, but only by a deh- cate net-work, through which the connection between dentine and cementum is indirectly established. Where the dentine is in contact with the pulp, the dentinal 74 THE ANATOMY AND PATHOLOGY OF THE TEETH. fibers communicate directly with the odontoblasts (John Tomes) in a growing tooth, and with the protoplasmic bodies of the pulp in a fully-developed condition, where no regular odontoblasts can be seen. In cross-sections of dentine the dentinal canaliculi are visible in the shape of circular or oblong holes ; the center of each is occupied by the dentinal fiber, wdiich has the shape of a small roundish dot. Again we see that the periphery of the dentinal canaliculus is sharply marked, and repeatedly interrupted by light offshoots leading into the light net-work that pierces the basis-substance between the canaliculi. The central fibers look very distinct and dark violet in specimens stained with chloride of gold, and send slender, conical, radiated offshoots through the surrounding dentinal canaliculi, respectively toward the mouth of the light interruptions in their walls. Fig. 43. ^3 1^" \f^-^~^r—I' _S- "1 ^^^vLt„- ^- uoK/^^'^^^:' ■£■ Ckoss-Sectiox of Dextine of Incisor. Cross-Sectio\ of Dentine of Incisor. Stained ■vfith Chloride of Gold. Stained with Chloride op Gold. Main Mass of Dentine. View from Outer Periphery of Dentine, near Enamel. F, dentinal canaliculi with the central dentinal fibers, the latter with star-like offshoots ; E, the basis-substance between the canaliculi, pierced by a delicate light net-work. Magnified 2000 diameters. In directly transverse sections, one, two, or sometimes even three such offshoots can be seen in a star-like arrangement. Each offshoot springs with a broad base from the central den- tinal fiber, while its pointed end always is directed toward the perforation in the wall of the canaliculus, where, as a rule, it is lost to sight. Slightly oblique sections of the canaliculi exhibit both transverse and longitudinal projections of the dentinal fibers. In such an oblique section we may succeed, by cautiously changing the focus, in seeing star-like radiated offshoots up to five in number, all arising from a single dentinal fiber. Toward the boundary between dentine and enamel, and dentine and cementum, as is well known, the dentinal canaliculi THE MINUTE STRUCTURE OF DENTINE, 75 niraify, and according to their ramifications also the dentinal fibers bifurcate, becoming the thinner the nearer thej are to the surface of the dentine. Both longitudinal and transverse sec- tions of this part of the dentine show details identical with the main mass of the dentine, the only difference being that near the periphery of the dentine the fibers are more delicate and more closely arranged. (See Fig. 43.) In some teeth I have met on the periphery of the dentine of the crown with the so-called " interglobular spaces" (Czermak), which may be considered as remnants of the embryonic con- dition of the dentine. They represent lacunae of greatly vary- ing sizes, bounded by curved lines, the convexities of which are directed toward the central cavity. These spaces sometimes contain protoplasm, — that is to say, embryonal elements which have not been transformed into basis-substance and not calcified. The dentinal fibers enter the protoplasmic bodies, and each fiber is united with the net-work of the protoplasm by means of deli- cate thorn-like projections. At other times the 1)asis-substance of the dentine is developed within the interglobular spaces, but devoid of lime-salts. In this instance the dentinal fibers, with- out investment and without changing their course, pierce the basis-substance and send ofiTshoots to this through the surround- ing light spaces. The dentine shows, in general, though not constantly, peculiar formations where it approaches the enamel and cementum. These formations, however, being in close relation to the cover- ing tissues of the tooth, I prefer to describe in the chapter on cementum and enamel. Results. — The dentinal canaliculi are excavations in the basis- substance of the dentine, each containing in its center a fhei^ of living matter. Besides the dentinal canaliculi, there exists an ex- tremely delicate net-work within the basis-substance of the den- tine, into which innumerable ofi:shoots of the dentinal fibers pass. Although evidently, by reason of its delicacy, we cannot trace the living matter throughout the whole net-work in the basis- substance, we are justified in assuming that not only are the den- tinal canaliculi, but so also is the whole basis-substance of the dentine, pierced by a delicate net-work of living matter. The living matter of the dentine is in direct union with that of the protoplasmic bodies of the pulp, of the cementum, and of the enamel. tb THE ANATOMY AND PATHOLOItY OF THE TEETH. Further researches into the minute structure of dentine have been made by John I. Hart,* of which the following is an abstract : "Method. — A freshly extracted tooth, preferably a deciduous one, is sawed into sections, either vertical or transverse, with the precaution that the tooth, and the instrument employed, are kept constantly moist with a one or two per cent, solution of sodium chloride. The object of this procedure is to prevent the drying up and consequent shrinkage of all soft constituents of the dentine, — viz, the dentinal fibers and their offshoots. The slab thus obtained is ground first with a coarse corundum-wheel on the lathe, and afterward on a corundum-slab of medium grit, always under a weak solution of table-salt. I wish to lay stress upon the fact that the ground slabs should not be kept longer than two hours in the salt solution, lest the dentinal fibers should become hydropic, and, swelling up, completely fill the canalieuli. Before staining, with a camel's-hair brush cleanse the specimen of the adhering debris resulting from the grinding. The next process is staining with a one-half of one per cent, solution of chloride of gold, or a one per cent, solution of hyperosmic acid. Since the latter has proved inferior to the former, it has been abandoned, and chloride of gold is ex- clusively employed. Two waj's have been adopted. Pour the chloride-of-gold solution over the slab and leave it immersed two hours, carefully shutting ofi" the light; then transfer the slab with a wooden spatula, carefully avoiding all metallic instru- ments, into a six per cent, solution of glacial acetic acid for two hours. Repeat this procedure, — viz, staining with the gold salt and decalcifying with acetic acid from ten to twelve hours, after which the now pliable slab is left exposed to strong day- light in distilled water until it has assumed a dark-violet color; or expose the slab to the action of the gold salts for ten hours, and then to the solution of acetic acid for the same length of time, and expose to light in distilled water. The latter method is preferable, although the specimens are sometimes partially overstained and become too dark for examination. After the required color is reached, brush the specimen gently in order to remove the precipitations of the gold salt, and mount in chemi- cally-pure glycerin. " There is a marked difference in the behavior of enamel and that of dentine in the process of decalcification by acetic acid. * •• Minute Structure of Dentine. ' Dental Cosmos, 1891. THE MINUTE STRUCTURE OF DENTINE. 77 Enamel at first breaks up into prisms with transverse blocklets, similar to those obtained by treatment with dilute hydrochloric acid. Upon the approach of complete decalcification, the enamel becomes extremely brittle, and breaks up into small pieces if the least pressure is exerted upon it. After complete removal of the lime-salts, there is left, as first seen and described by Dr. Frank Abbott as early as 1878, only a delicate reticulum, — the last residue of organic material. " Dentine resembles enamel only in this particular, that in incomplete decalcification, blocklets of lime-salts are seen throughout the basis-substance. After complete decalcification a tough, pliable slab is left, which, even though exposed to some pressure, will not break asunder. Obviously the glue-yielding basis-substance and its tenants are not corroded or affected in the least by the six per cent, solution of acetic acid. All this acid accomplishes is the removal of the lime-salts deposited in the basis-substance, thereby rendering clear its minutest struc- ture. Exposure of a ground slab of dentine to the action of the gold solution for three hours renders the dentinal fibers plainly visible and tinted a pale violet. Exposure of six hours will stain the dentinal fibers dark violet, and will bring out clearly the broader offshoots. An exposure of from nine to ten hours is necessary to bring forth the more minute conical off- shoots emanating from the dentinal fibers and the minutest structure in the basis-substance. " Main Mass of Dentine.— If successfully stained portions are placed under an amplifying power of from 1000 to 1200 diameters, striking features become recognizable in the dentinal fibers themselves. Should the method described above be faith- fully carried out, we will invariably see portions of a varying extent suitable for the amplification just stated. It makes no difference whether water or cedar-oil immersion is resorted to. " The dentinal fibers in the main mass of the dentine do not look homogeneous, as in the unstained condition, but appear hollowed out in their interior by light spaces, so-called vacuoles, of greatly varying sizes. These vacuoles are plainly visible if the ground slab is left exposed for the shortest possible time to the salt water. If this exposure is protracted for days, the vacuoles will appear enlarged and almost continuous within the dentinal fibers. Both longitudinal and transverse sections exhibit the vacuoles: I have obtained the most distinct image, 78 THE ANATO.MY A^'D PATHOLOGY OF THE TEETH. however, in thin lougituclinal sections, where but one layer of dentinal fibers was visible. (See Fig. 44.) "From the rather uneven periphery of the dentinal fibers arise a smaller number of broad and a large number of delicate conical offshoots, all of a dark-violet tint. These offshoots pierce in an almost rectangular direction the light space of the dentinal canaliculus, and inosculate with a minute dark-blue net- work pervading the whole basis-substance of the dentine. This net-w^ork being present throughout the basis-substance, serves Fig. 41. Main Mass of Destine of a Temporary Tooth, Stained with Chloride of Gold, Decalcified -with Acetic Acid. F, F, dentinal fibers, partly vacuoled ; B, B, basis-substance, traversed by a reticulum. Magnified 1200 diameters. for a direct interconnection of all dentinal fibers. The net-work appears uninterrupted wherever sufficiently stained, although w^e may fail to trace the connections in some limited portions ot the basis-substance. In transverse sections of the dentinal canaliculi, such as we invariably obtain in longitudinal sections of the crown, and, as a matter of course, in transverse sections of any part of the tooth, we notice features identical with those of longitudinal sections. (See Fig. 45.) THE MINUTE STRUCTURE OF DENTINE. 79 " The dentiaal fibers of somewhat varying diameters exhibit hollow centers in many instances. From their periphery, broad and narrow offshoots spring forth in a considerabh' larger number than ever visible in sections of teeth not treated with chloride of gold. The basis-substance appears to be traversed by a dark-violet reticulum of the same character as that of longi- tudinal sections. Oblique sections will of necessity show an apparently larger number of dentinal canaliculi and their tenants than longitudinal or transverse sections in a given area of den- tine. Here we often obtain the impression that rectangular off- shoots of one dentinal fiber inosculate directly with neighboring fibers, thus furnishing a pretty figure of a ladder with minute rungs. Fig. 45. Dentike of Temporary Tooth. Transverse Section of Canaliculi, Stained vrirH Chloride of Gold, Decalcified with Acetic Acid. F, F, dentinal fibers, with radiating oflFshoots piercing the space of the canaliculi ; B, B, basis- substance traversed by a delicate reticulum, in connection with the dentinal fiber. Magnified 1200 diameters. " x\ll that I have described thus far as being present in the main mass of the dentine is plainly visible only in the dentine of teeth that were alive at the time of extraction. If life has been destroyed to a varying extent by an alveolar abscess or pyorrhea alveolaris, the image furnished by the dentine is so characteristic that we recognize at the first glance the extinction of life. Several times have I ground teeth without knowing that they were dead. The microscope revealed the fact. (See Fig. 46.) " In longitudinal sections, only the canaliculi are conspicuously prominent, exhibiting delicate and numerous interruptions along their walls. The dentinal fibers appear shriveled up to 80 THE ANATOMY AND PATHOLO(:^Y OF THE TEETH. rows of minute granules, not always in the center of the canali- culus, but frequently quite near to one of the walls. The gran- ules often appear interrupted to a considerable extent, and some- times the remnants of the dentinal fibers are missing altogether. IS^o conical offshoots emanate from the remnants of the dentinal fibers. The basis-substance shows a rather faint and indistinct reticulum, lacking connections in numerous places. In trans- verse sections of dead portions of the dentine we obtain a strik- ing image. (See Fig. 47.) Fig. 46. Destine of a Dead Temporary Tooth. Stained -n-iTH Chloride of Gold, Decalci- fied WITH Acetic Acid. (J, C, canalieuli, holding shriveled dentinal fibers ; B, B, basis-substanee, holding a shriveled reticulum. Magnified 1200 diameters. " AVe see the dentine pierced by light spaces at almost uniform distances, many of which contain dark-violet granules or ves- tiges of a previous dentinal fiber. There are but scanty and incomplete indications of conical offshoots emanating from the shrunken dentinal fibers. The basis-substance is of the same character as found in longitudinal sections. The basis-substance shows a rather indistinct dark-violet reticulum with numerous interruptions. The facts here described suffice, in my judg- THE MINUTE STKUCTURE OF DEXTIXE. 81 ment, to determine the nature of the reticulum pervading the whole of the dentine ; it is of necessity the living matter which is plainly marked in living, and shriveled and reduced to a row of granules in dead teeth. Since we know of no tissue consti- tuted of nerves, we cannot support the suggestion of John Tomes, that dentinal fibers are but nerve-fibers carrying sensa- tion from the periphery to the center. Since we know that non- medullated nerve-fibers have the same structure as the dentinal fibers, we must conclude that both the nerves and dentinal fibers are made up of living or contractile matter, the contraction of which is facilitated by the presence of vacuoles. For, according to modern researches, the conduction of sensation centripetally Fig. 41 Dentine OF a Dead Temporary Tooth. Teaxsveese Section of Caxaliculi, Stained •WITH Chloride of Gold, Decalcified iriTH Acetic Acid. C, C, dentinal canaliculi, holding shriveled dentinal fibers ; B, B, basis-substance, containing a shriveled, indistinct reticulum. Magnified 1200 diameters. and of motion centrifugally is ver}'' probably instituted by the contraction of living matter. " Interzonal Layer between Dentine and Enamel. — In all the provisional teeth that I have examined, a zone of varying breadth was visible along the outer periphery of the dentine, conspicuous by a darker violet stain than the rest of the dentine. In fact, this region is rather prone to be overstained and become too dark for examination with high powers ; hence, we should ex- amine this region before it has assumed a deep stain, owing to a protracted exposure to light. The first feature which strikes us upon approaching the outer periphery of the dentine is the 7 82 THE ANATOMY AND PATHOLOGY OF THE TEETH. beaded appearance of the dentinal fibers, lacking vacuoles in this situation. The fibers are bifurcating, as is Avell known, and, becoming more and more delicate, correspondingly exhibit more and more beads. The reticulum into which the lateral conicnl ofl:shoots of the dentinal fibers inosculate is extremely dense, — much more so than in the rest of the dentine. The densely reticulated zone usually corresponds to the depth of the bifur- cations of the dentinal fibers; in other words, it commences in a rather abrupt line in the height in which bifurcations begin to appear. (See Fig. 48.) Fig. 48. Dentine of Temporary Tooth, near Enamel, Stained ■^vith Chloride of Gold. De- calcikied avith Acetic Acid. B.B, boundary of dentine toward enamel; /, /, interzonal layer (Atkinson \ with a dense reticulum, dentinal fibers bifurcating ; D, D, main mass of dentine, holding beaded dentinal fibers. Magnified 1200 diameters. " The presence of this dense reticulum of living matter evidentlj^ explains the fact that the interzonal layer between enamel and dentine is so extremely sensitive. I am sure that every dentist is made aware of this striking fact when cutting into dentine. The dentinal fibers rarely enter the enamel in human teeth, but the reticulum of the dentine is continuous with that of the enamel. This connection, however, I w^as unable to trace THE MINUTE STRUCTURE OF DENTINE. 83 myself, as in all mj specimens the enamel was dissolved and removed by the camel's-hair brush prior to mounting. "Interzonal Layer between Dentine and Cementum at the Neck of the Tooth. — Ever since John Tomes drew attention to the peculiar fact that the dentinal fibers stopped short of the cementum, special attention has been paid to this region of the dentine, since it is also known to be more sensitive than the rest of the dentine. According to Tomes, ' the greater degree of sensitiveness observable in the dentine immediately below the- enamel, — that is, at the point of ultimate distribution of the den- tinal " tubes," and consequently of their contents, — may be fully accounted for on the supposition that the latter are organs of sensation, the highest sensibility of which is confined to their branches.' " This hypothesis does not find foundation in the region of the neck, where bifurcations of dentinal fibers are often missing or are scanty. There is only a uniformly granular layer visible in unstained and ground specimens between the surface of the dentine and the terminal points of the dentinal fibers. Still, the sensitiveness at the neck is undoubtedly even greater than that of the interzonal layer of the crown. Bodecker drew attention to the fact that in the great majority of teeth the finest ter- minations of the dentinal fibers are lost to sight in a net-work somewhat coarser than that of the basis-substance of ordinary dentine. Sometimes, he says, the dentinal canaliculi upon ap- proaching the periphery become slightly dilated, so as to pro- duce slender pear-shaped cavities, in accordance with which the terminating dentinal fibers exhibit slight enlargements. " I can corroborate this statement from what I have seen in my own specimens of temporary teeth. Several times I have met with peculiar formations in this region, which, as far as I am aware, have not as yet been described. (See Fig. 49.) In unstained slabs of temporary teeth I have seen coarsely granular layers in the dentine at the region of the neck, with which the dentinal fibers directly inosculated. After deep staining with chloride of gold, the granular layers became dark violet and easily recognizable with low powers of the microscope. I found, as a rule, one or two granular layers like narrow ribbons run- ning along the outer periphery of the dentine, close to the cementum. A much more irregular and broader granular layer was seen at a certain distance below the surface, produc- 84 THE ANATOMY AND PATH0L0C4Y OF THE TEETH. ing wavy lines, and being in connection externally witli a more uniformly granulated layer, and internall}^ with the dentinal fibers. This peculiar configuration was plainest at the portion of the cementum made up of spindles at the neck of the tooth, and gradually faded downward, where the lamellated layer of the cementum began to make its appearance. High powers of the microscope revealed the intimate structure of this portion. (See Fig. 50.) Fig. 49. Neck of Texiporary Tooth. Loxgitudinal Ssctiox, Stained with Chloride of Gold, Decalcified with Acetic Acid. D, D, dentine, main mass ; N, N, dentine of neck, bordered upward and downward by coarsely granular layers; C, C, cementum of neck; P, P, shreds of pericementum. Magnified 400 diameters. " The fi.bers in this situation appear reduced in caliber, and show a beaded structure much the same as at the periphery of the crown. These fibers either terminate in pear-shaped en- largements, or in irregularly-shaped dark-violet lumps, which send delicate ofi:'shoots in all directions, serving as an intercom- munication between them. The large number of these lumps causes the granular appearance of the dentine. The following broader zone, which with lower powers has appeared uniformly granular, is now dissolved into a rather coarse reticulum — much coarser than that of the interzonal layer of the crown. This reticulum shows stray irregular fibers. Both the latter and the lumps are in close connection with the reticulum. THE MINUTE STRUCTURE OF DENTINE. 85 "At the outermost periphery we again notice one or two rows of enlargements, which, judging from the regularity of their arrangement, correspond to the bases of the spindles, building up the cementum of the neck. This large amount of living matter satisfactorily explains the extreme sensitiveness of the region of the neck. "Results. — To sum up my observations, I must maintain the presence of a reticulum of living matter throughout the dentine. Fig. 50. Dentine of Neck op Temporary Tooth, Stained with Chloride of Gold, Decalci- fied WITH Acetic Acid. D, D, dentine; G, G, coarse globules, into which the dentinal fibers inosculate; N, jV, den- tine of neck, with a coarse reticulum, lacking fibers; C, C, cementum of neck, bordered by a granular layer toward the dentine. Magnified 1200 diameters. It is decidedly coarser than that seen and described by Frank Abbott in the enamel. It is most delicate in the interzonal layer of the crown between dentine and enamel, and coarsest in the region of the neck bordering on the cementum. " My assertion finds proof by comparison of living with dead teeth, for in the latter the dentinal fibers were reduced to a series of granules, and the basis-substance appears irregularly dotted or spotted, instead of being reticular. The microscope 86 THE ANATOMY AND PATHOLOGY OF THE TEETH. therefore easily reveals the difference between living and dead teeth. Another point of confirmation is that the portions of the dentine being most sensitive are richest in the supply of living matter, not in that of the fibers which are missing in the inter- zonal layer of the dentine of the neck, but in that of the basis- substance." Further researches into the presence of the reticulum in dentine have been published by Carl Heitzmann,* as follows : " Dr. Bodecker had collected a large number of teeth that were filled for months and years. The first tooth he ground thin was a bicuspid with two cavities in its crown; one filled with cement, the other with silver amalgam, — both plugs having been in the cavities for years. How great was his surprise when, examin- ing the border of the cavity previously filled with amalgam, he saw a dark-brown discoloration of the dentine, not directly along the border of the cavity, but some distance away from it, and in this brown zone the dentinal canaliculi, respectively their tenants, the dentinal fibers, crowded with black dots, and their offshoots rendered wonderfully plain by a black deposit. In the darkest portion the reticulum was easily seen with compara- tively low powers of the microscope, — viz, 500 diameters. (See Fig. 51.) " The border of the cavity is, in the upper portion, seen in the breadth of the specimen, and here it holds a number of black metallic particles, evidently not of the amalgam itself, but of a sulphur-combination of the silver or quicksilver. The zone of the dentine directly bordering the cavity is, apparently, destitute of structure, showing but faint traces of canaliculi ; of a high refraction, obviously in a state of consolidation, a reactive process subsequent to the filling. Close beneath this consolidated layer follows a dark-brown zone, diffusively pig- mented, and here we see the dentinal canaliculi crowded with black metallic particles, considerably widened and sending black ofi^shoots into the basis-substance between the canaliculi. The ofl'shoots are comparatively scarce and large toward the enamel, where the unstained canaliculi show only the usual bifurcation. The offshoots are more numerous upon entering the dark-brown region of the dentine, and in the darkest portion are so numer- * " Demonstration of the Reticulum in Dentine with Low Powers of the Micro- scope." Transactions of the New York Odontological Society, 1892. THE MIXIITE STRUCTURE OF DENTINE. 87 ous and so delicate tliat the power of five liiindred diameters is iiisufiicient to dissolve the minutest branches, all of which in- osculate into an extremely delicate hlack reticulum. All the features, the coarse and tine offshoots and their union into a re- Fio. 51. Ground Bicuspid. Cavity of the Crown previously filled with AMALGAXf. E. enamel; D, D, dentine ; B, border of cavity ; .S", solidified dentine along the border of the cavity ; R, reticulum, brought forth by the amalgam. Magnified 500 diameters. ticulum, are identical with the image obtained by John I. Hart in living dentine, treated with chloride of gold. "How did the metallic particles reach the dentinal canaliculi, 88 , THE AXATOMY AND PATHOLOGY OF THE TEETH. and produce such an image at a certain distance away from the border of the cavity ? There is but one answer possible to this query. The metallic particles were taken into the living matter, probably before the consolidation was accomplished at the bor- der of the cavity, and carried farther, at the same time render- ing visible the reticulum, interconnecting the dentinal fibers. It would be impossible to understand the loading of the den- tinal fibers, which run a parallel course and are separated from one another by the intervening basis-substance, unless by the presence of transverse connections of the fibers, as actually shown by the reticulum. This reticulum is, in fact, so plain that any tyro must see it, and the specimen alone is suflicient to remove the doubts of even the most skeptical minds. " Fig. 52 represents the neck of a molar whose pulp years ago was treated by AYilhelm Herbst, of Bremen, Germany, with his method, made known in this country by Dr. Bodecker. Dr. Herbst applies cobalt upon the exposed or inflamed pulp of the crown ; a few days afterward he excises the pulp down to the root-canals; introduces tin foil, which he grinds down at the bottom of the cavity, thus shutting off the pulp of the root- canals from contact with air, or other filling-materials placed into the cavity of the crown. The remarkable outcome of Bodecker's examination of the teeth sent by Herbst is that the pulp remains alive in the root-canal, and is sufiicient to endow with life the whole tooth, though its crown is entirely deprived of its pulp. This fact becomes intelligible only upon the pres- ence of interconnections between the parallel dentinal fibrillfe ; for the dentinal fibers could not possibly be kept alive in the crown, unless by unions with the fibrillse of the roots, the only ones kept directly alive by the pulp-tissue of the roots. This is an indirect, though stringent proof of the presence of the reticu- lum. The direct proof is furnished by the visible interconnec- tions of the fibrillse along the neck of the tooth, of a brownish color, in a slightly brownish basis-substance. After having examined many hundreds of teeth under the microscope in all sorts of pathological changes, I have never met with such a dis- coloration in the dentine so frequently observed in the enamel. It is quite possible and reasonable to assume that the metallic salt, originated at the border of the cavity, was transferred into the dentinal fibers and their offshoots, and was, at last, depos- ited in the fibrillte and their offshoots in the region of the neck, THE MINUTE STRUCTURE OF DENTINE, 89 wliicli, as John I. Hart's researches prove, abounds'^in living matter far in excess of any other portion of the dentine. This, I admit, is a hypothesis, to which I resort for lack of a better Ground Molar. Thk Pulp previocslt treated by the Heebst Method. The Cav- ity FILLED TTITH AMALGAM. C, pericementum ; 0, osteoid layer of eementum ; P, protoplasmic bodies at the interzonal layer between eementum and dentine ; G, granular layer of dentine of tbe neck ; JD, dentine of neck. A few club-shaped enlargements of dentinal canaliculi. The reticulum brought forth by the amalgam. Magnified 500 diameters. explanation ; it is nearest to my mind, after thirty-two years of study of the teeth, having become so thoroughly convinced of 90 THE ANATOMY AND PATHOLOGY OF THE TEETH. the life of all constituent tissues of the teeth. The specimen under consideration exhilnts an ill-calcified dentine, for it shows numerous protoplasmic bodies at the border of the dentine toward the osteoid layer of the cementum, and club-shaped enlargements of some dentinal fibrillse. The granular layer of Tomes in the dentine of the neck destitute of dentinal canali- culi is narrower than in thoroughly calcified teeth; but present, nevertheless." CHAPTER XI. THE MINUTE STRUCTURE OP ENAMEL.* The best specimens for examination of enamel I obtained by grinding fresh teeth, and staining them for one hour with a half per cent, solution of chloride of gold. Up to this time the impression of most examiners has been that the enamel is built up of bundles of rods, or prisms, cross- ing one another, and traversed by faint vertical lines, which give each of them the appearance of a column, subdivided into small squares. The enamel-rods doubtless exist, and are wavy near the dentine, and straight on the periphery and the main mass of the enamel. They may be considered as columns of a calcified substance, between which minute spaces are left, analogous to the cement-substance of epithelial formations. In longitudinal sections we see delicate beaded fibers, which occupy the central portion of the interstices between the enamel- rods. These fibers I propose hereafter to term the " enamel- fibers." (See Fig. 53.) From such a fiber arise very minute conical fibrillse, which traverse the tiny intervals between the fiber and the neighboring outlines of the rods, and fade away where they enter the latter. The columns of the basis-substance themselves are pierced by delicate canaliculi, running in an almost vertical direction to the enamel-rods, regularly enough to give the appearance of squares, although these are much smaller than usually represented iji the books. In the midst of a minute square, light canals are seen, not infrequently running parallel witli the outlines of the * " The Distribution of Living Matter in Human Dentine, Cement, and EnameL" Denial Cosmos, 1878-1879. THE MINUTE STRUCTURE OF ENAMEL. 91 enarael-rocl. The square lields thus produced by the rectangular crossing of light channels look, under the power of 1200 diame- ters, finely granular. In specimens not fully decalcified it is impossible to decide whether there is a light net-work within the enamel-prisms analogous to that in the basis-substance of the dentine and cementura, or whether the granular appearance is merely due to the deposition of lime-salts. In thoroughly de- calcified specimens of enamel, however, such as were first made by Dr. Frank Abbott, there is no difficulty in seeing, with high powers, the reticular structure of protoplasm. Cross-sections of the enamel, which we obtain also in longi- tudinal sections of the tooth, on account of the different direc- tions of the bundles of the enamel-rods, plainly exhibit the irregular polyhedral fields of the intersected enamel-rods. The FiC4. 53. LOXGITUDIXAL SeCTIOX OF ExAMBL. ER, enamel-rods, traversed by prevailing vertical spaces; EF, enamel-fibers, branching and partly uniting by delicate offshoots. Magnified 1200 diameters. light interstices between the polyhedral fields contain in many instances delicate beaded fibers, surrounding the polyhedral fields of the enamel-rods. The fibers, if cut transversely, have tlie appearance of dots. They connect with one another directly or by means of intervening delicate threads. Extremely fine thorns traverse in a vertical direction the light space between two neighboring enamel-rods, even where a fiber is not visible (see Eig. 54). The rods of the enamel are, on an average, half the diameter of the columns of the basis-substance in dentine ; therefore four columns of the former will correspond to two of the' latter, and consequently two dentinal fibers will answer to four enamel- fibers. Sometimes in the cross-section of an enamel-rod I have met with roundish formations occupying the center of the rod, one or two in number, which, owing to a denser granulation and a surrounding shell, had the appearance of nuclei. The 92 THE ANATOMY AND PATHOLOGY OF THE TEETH. enamel-fibers run a very straight course toward the surface, and are, on the average, a trifle thicl^er here than near the boundary of the dentine. The outermost surface of the enamel is covered by flat epi- thelia (Nasmyth's membrane), which in the transverse section have the appearance of shallow spindles ; not infrequently there occurs also a stratified epithelium on the surface of the tooth. The enamel-fibers are in connection with these epithelial bodies, which, if detached, show delicate ofishoots adhering in regular intervals — the broken enamel-fibers. Sometimes the surface of the enamel is coated by a thin uniform layer of protoplasm, with regularly scattered nuclei. In such an instance single epi- thelia are not traceable, though scarcely any doubt can arise about the epithelial nature of this layer. Fig. 54. SI" Ceoss-Sectiox of Enamel. EIi,rods of enamel, partly exhibiting formations like nuclei ; the light interstices between the rods traversed by delicate beaded fibers, EF, or by vertical thorns. Magnified 2000 diameters. • At the place of junction of the enamel with the dentine a direct connection is not infrequently seen between the enamel- and dentine-fibers. The latter, through repeated bifurcations, being closely brought together, continue their course into the enamel-fibers without any interruption. The direction of the fibers of the two tissues, however, is almost never identical, in- asmuch as the enamel-rods, and consequently the enamel-fibers, as a rule, owing to their wavy course in this situation, are ob- liquely intercepted upon the dentine. "We can often trace dentinal fibers up into the enamel for a varying distance, without finding a distinct union between the enamel- and dentine-fibers, as the former do not reach the sur- face of the dentine, but terminate above its level in dififerent heights, while the zone close above this is occupied by a delicate, THE MINUTE STRUCTURE OF EXAMEL. 93 irregular net-work, analogous to that of the dentine. Here no rods of enamel are visible either in longitudinal or transverse sections, but with low powers of the microscope only a finely- granular layer is presented. In many places the dentinal canaliculi, upon entering the enamel, suddenly become enlarged, and form more or less dis- tinctly spindle-shaped cavities of greatly varying diameters, an- alogous to the spindle-shaped enlargements on the boundary of the cementum. (See Fig. 55.) These enlargements either run Fig. 55. 2L. ■-BB H F Union of Dentine with Enamel. B, dentine ; E, enamel ; BF, dentinal fibers, in union with large protoplasmic bodies, P, or directly running into enamel-fibers, EF ; the latter often are lost in the delicate, irregular net- work on the bottom of the enamel. Magnified 1200 diameters. in the main direction of the dentinal canaliculi or deviate ob- liquely. They invariably contain protoplasmic bodies which plainly show the reticular structure, and sometimes contain one or more compact clusters to be considered as nuclei. The spindle-shaped protoplasmic bodies are in direct connection at their proximate ends with the terminations of the dentinal fibers that have arisen from their repeated bifurcations, while on the distal end they may show delicate fibers, viz, enamel-fibers, or delicate conical thorns, traversing the light space between the surface of the protoplasmic body and the wall of the cavity. These thorns are lost to sight on passing into the net-work at 94 THE ANATOMY AND PATHOLOGY OF THE TEETH. the bottom of the enamel. In some places, especially on the cusps, the spindle-shaped enlargements of the dentine-fibers are quite numerous, and of an almost uniform size and direc- tion, forming regular rows of spindles within the enamel. In the teeth of younger individuals, the spindle-shaped enlarge- ments are comparatively larger and more regular than in the teeth of old people. The boundary-line between the dentine and enamel is either straight or slightly w^avy, and with more or less deep ba^-like excavations, analogous to those on the boundary between dentine and cementum. The concavities of the bays are directed toward DI i), dentine; E, enamel; P, protoplasmic formations at the boundary between both tissues ;: EF, union -with enamel-fibers ; BF, with dentine-fibers. Magnified 1200 diameters. the dentine. (See Fig. 56.) In this interzonal layer at the bottom of the bays we meet with fibers occupying the curved spaces between dentine and enamel, or we see in a correspondingly bent course protoplasmic bodies directly connected with the dentinal fibers downward, and with the enamel-fibers upward. In specimens stained with chloride of gold, the dentine is always much deeper in color than the enamel, hence the relations de- scribed are plainly marked on such specimens. Results. — The enamel is traversed by fibers of living matter located in the interstices between the enamel-rods. The fibers are connected with one another by delicate fibrillfe, piercing the enamel-rods in a vertical direction. Besides these rectangular THE MINUTE STRUCTURE OF EXAMEL. 95 unions, the basis-substance is traversed bj a minute net-work of living matter. The enamel-fibers send conical thorns toward the enamel-rods, and such thorns are visible in all interstices between the enamel-rods. The enamel-fibers are continuous on the outer surface with the covering ]ayer of flat epithelia, and on the inner surface with the dentinal fibers. The latter con- nection is either direct or indirect through a net-work of living matter, or through intervening protoplasmic bodies in the inter- zonal layer. Further researches in this field have been made by Frank Abbott.* Of their results the following is an abstract : " As to enamel, I have never seen the minute relations marked so plainly in permanent as I find them in temporary teeth. Here the enamel-rods are narrower, and the interstices between them wider, than in permanent or adult teeth. A power of 500 diameters of the microscope is sufiicient to show plainly in the temporary teeth relations rendered visible in permanent teeth, only by very much higher powers. " The cut, Fig. 57, is made from a drawing taken with a power of 1200 diameters (immersion). In the enamel the enamel-rods, the fibers in the interstices between the rods, the lateral offshoots of the fibers, and the light reticulum within the rods are represented. As a striking feature, I wish to em- phasize the direct connection of the fibers of the dentine with those of the enamel. Thus the width of an enamel-rod is in full correspondence with the width of the fields of basis- substance of the dentine, after the bifurcation of the dentinal fibers, near the boundary between dentine and enamel. In preparing this specimen, it happened that on several portions of the crown a larger portion of the enamel was ground away than was intended; so much so that only shreds of enamel in con- nection with the dentine were left. On one of these places delicate beaded fibers (F) were seen, isolated at their upper ends, while their lower ends could be traced into interstices between the enamel-rods, and into connection with the ends of the dentinal fibers. Xo doubt here the mechanical injury done to the enamel has luckily led to a tearing out of a few enamel- fibers, which accident plainly illustrates their presence.'"' * " The Minute Anatomy of Dentine and Enamel.'- Dental Cosmos, 1880. 96 THE AXATOMY AND PATHOLOGY OF THE TEETH. The same author, in an article, " A Contribution to the Study of the Minute Anatomy of Enamel,"* says, — "Dr. George W. "Weld, in a paper entitled ' The Destructive Energy of the Tincture of the Chloride of Iron on the Teeth : an Experimental Study,' read before the iS^ew York Odontologi- cal Society, June 8, 1886, and published in the Dental Cosmos for October, 1886, page 627, draws attention to a novel method of treating enamel for the purpose of decalcification. Fig. 57. \ V ^ X D, D, dentine, with bifurcating fibrillar toward the enamel ; E, E, enamel with beaded fibrillaj between the rods ; /", free fibrillse of enamel, the rods being torn away. Magnified 1203 diameters. " Dr. Weld minutely describes how a specimen (thin slab) of enamel previously treated with a six per cent, solution of acetic acid, while watched under the microscope, in consequence of a jarring of the instrument, became broken in pieces, and the enamel-rods isolated, so as to resemble a ' bunch of sticks.' He asserts that ' this method will perhaps ultimately be the means * Dental Cosmos, 1887. THE MIXUTE STRUCTrRE OF ENAMEL. 97 of throwing some light on tlie matter of the distribution of lime-salts and living matter in the enamel,' but he does not, so far as is known, follow up the study. "The method, as I have used it, is as follows: A freshly- extracted tooth, or one placed, immediately after its extraction, in dilute alcohol for a time, is ground, under water, as thin as practicable; then placed in a six per cent, solution of acetic acid, and left there for at least twelve hours even if the speci- men be very thin, and for eighteen hours if slightly thicker ; the acid is then poured off and the specimen repeatedly washed with distilled water, and then placed in a concentrated ammo- niacal solution of carmin for twelve hours. After its removal from the carmin solution it is again washed with distilled water, and the enamel detached from the dentine with two needles. This process is easily accomplished, but a slight frill of the organic substance of the enamel is usually left attached to the dentine, and we obtain the enamel itself in small pieces. I have used- two other reagents, — viz, a one-half per cent, solution of chloride of gold, and a one per cent, solution of hyperosmic acid. The specimens are subjected to the action of the former from twelve to twenty hours, and to the latter from one to three hours; after which they are carefulh' washed with distilled water; then treated with the acetic-acid solution as before stated. They are again washed; then mounted in glycerin, care being taken that they are not broken during this part of the process, their weakened condition from the action of the acetic acid having rendered them very brittle. Such a speci- men, when viewed with a power of from 400 to 500 diameters, presents the following features: The enamel-rods are plainly recognizable (running their usual way, slightly wavy near the dentine, and straight toward the periphery), owing to the fact that the interstices between them are widened. Another feature presents itself which is quite striking, — viz, that the cross-bars within the enamel-rods also are widened, and plainly marked. " We often meet with specimens of enamel where, toward the dentine, the rods are entirely lacking, or very indistinct, and much narrower than those a little distance from the dentine. Should the bundles of rods assume a fan-shaped appearance, as is sometimes seen in the neighborhood of the dentine, the inter- stices between such bundles may' be found filled with a granular material, or with oblique or transverse sections of rods, occupj'- 8 98 THE ANATOMY AND PATHOLOGY OF THE TEETH, ing comparatively a small field. This latter appearance has undoubtedlj led previous observers to conclude, and to make the statement, that the enamel is composed of interlacing bundles of rods. In a longitudinal section of enamel we find comparatively few transversely-cut bundles of rods, whereas obliquely-cut bundles are met with quite frequently. This fact leads to the conclusion that the appearance of interlacing is simply due to the presence of bundles of rods running in a more than usually wavy course, but never transversely to the general direction of the rods, " The manner in which the acetic acid acts to produce the widening of the interstices, in my judgment, is as follows : In the process of grinding, the edges or borders of the rods are more or less exposed in every specimen, and probably the organic basis-substance is more or less disturbed. The edges being thus exposed to the action of the acid, the same as the ground sur- faces of the rods, are dissolved away, and the interstices become widened, while the flat surfaces of the rods themselves are not jierceptibly afiected. This serves to explain also the widening and bringing so distinctly to view the ' cross-bars' in the rods, which also contain a minute amount of organic matter. Thin specimens of enamel . treated with the same solution of acetic acid, if viewed with a power of from 500 to 600 dia- meters, clearly establish the above facts, since we can invari- abl,y trace all degrees of dissolution of lime-salts, from a slight widening of the interstices to the coarse granulation of the rods, then to the fine granulation, with the preservation of their general appearance, and finally down to their complete disap- pearance, nothing being left but the organic portion. The appearance in the field of the microscope is now very striking, it being finely granular, pale, and traversed by innumerable parallel filaments. Even moderately thick specimens may be utilized for bringing to view completely decalcified fields, by exerting a gentle pressure upon the covering-glass. I would not, however, recommend broken enamel-rods for microscopical research, as in my judgment such specimens are entirely worth- less, I prefer to confine my studies to shreds in which either the traces of the previous rods are recognizable, or the fibers run a parallel and unbroken course. The foregoing description holds good for the majority of specimens of enamel. There are exceptions, however. Occasionally we find specimens with THE .MINUTE STRUCTURE OF EXAMEL. 99 Fig. 58. e^v\-' ^,^ BEGI^M^u Decalciiu ATiox of ExASfEL, Br A Six Per Cext. Solution of Acetic Acid. The interstices between the enamel-rods and the cross-bars of the rods widened. The rods exhibit slight organic structure, in consequence of the abundant presence of lime. Magnified 500 diameters. Fig. 60. ExAMEL Completely Decalcified, through THE Agexct of a Six Per Cent. Solution OF Acetic Acid, Slightlt Staixed with Chloride of Gold. The upper portion of the figure shows slightly obliciue, and the lower very oblique, sections of the enamel-rods. The boundary lines of the prisms are made up of highly glistening elastic ledges, at the sides of which there are visible oblique sections of enamel-fibers in connection with a delicate grayish reticulum pervading the rods. This reticulum is especially dense in the central portion of the rods, as shown in the lower half of the figure. Magnified 1200 diameters. Advaxced but not Complete Decalcifica- tiox of Enamel, through the agexct of a Six Per Cext. Solutiox of Acetic Acid. The interstices very marked, but not mate- rially widened; their tenants, the enamel- fibers, plainly visible. The cross-bars do not appear in the shape of interstices, but in deli- cate transverse lines. The organic structure begins to appear, owing to partial removal of the lime-salts by solution. Magnified 500 diameters. Fig. 61. Completely Decalcified Enamel Deeply Staixed with Chloride of Gold. The enamel-fibers appear in the shape of dark-violet, beaded threads, in connection with a grayish-blue reticulum within the enamel- rods. The transverse threads corresponding to the cross-bars are but slightly marked. In the lower portion of the figure the reticulum is partly torn away, leaving the enamel-fibers protruding and rendered plainly visible. Mag- nified 1200 diameters. 100 THE ANATOMY AND rATHOLOGY OF THE TEETH. unusually narrow prisms, or perhaps lacking them altogether, in comparatively large districts. "Whether this feature is due to advanced age, malformation, or some pathological condition, I am unable to say. The higher powers of the microscope (1200 to 1500 diameters) ffive a hio-hlv s-ratifving imao;e of the structure of enamel. Partially decalcified rods appear to be composed of irregular lumps, of high refraction, invariably arranged in the shape of irregular squares, which serve to complete the rods ; the irregular interstices separating the glossy lumps are traversed by delicate grayish threads. The interstices causing the appear- ance of cross-bars through the rods are traversed by minute grayish, beaded filaments, sending oflshoots into the fields of the rods between them. The longitudinal interstices between the enamel-rods, in many places, show long, beaded filaments, on either side of which we observe a light space. This space again is traversed by conical threads arising from the enamel- fibers, and penetrating the interior of the rods themselves. " In thoroughly decalcified enamel, I have often met with a pe- culiar appearance. "Whether carmin, chloride of gold, or osmic acid hud been used for staining the specimen is immaterial, — the rods appear to be surrounded by a .glossy, smooth, or beaded border, between which can be seen the light interstices. Sometimes there is one such ledge for two neighboring rods, without any intervening interstice. In oblique sections the ledges are best marked on the distal portions of the rods, over- lapping their neighbors in a shingle-like manner; while in transverse sections the gloss}' border may be seen all around the rods. It is evident that these ledges cannot be mistaken for the enamel-fil)ers proper; nor can we conclude that the ledge is an optical phenomenon, caused, as it were, by the thickness of the rods, since the ledge is often found slightly protruding beyond the border of the specimen. The only explanation I can sug- gest for this is that the borders of the rods are made of a denser kind of basis-substance, kindred to the elastic substance, and similar to that which we observe in the basis-substance of the dentine surrounding the canaliculi. In the center of the rod we not infrequently see a somewhat more compact accumulation of a pale gray substance than in the rest of the rod. " Completely decalcified portions of the enamel exhibit a most beautiful reticulum, especially in specimens treated with chloride of STold, and not the least doubt can arise as to the fact that the THE MIXUTE STRUCTURE OF CEMEXTUM. 101 enamel-fibers, being the most conspicuous formations, are in an uninterrupted continuity with the reticulum of living matter pervading the whole enamel." CHAPTER XIL THE MINUTE STRUCTURE OF CEMENTUM.* The zone of dentine is not continuous everywhere about the pulp-cavitv. Around the apices of the roots the cementum, although the outermost layer of the tooth, immediately lines the cavity. In the cementum delicate parallel striations are to be seen, identical with the lamellae of a Haversian system, and, as a rule, more plainly marked near the periphery than near the dentine. The lamellae exhibit a more or less concentrical arrangement around the pulp-cavity, easily demonstrable on cross-sections. Within the basis-substance of the cementum there are numer- ous branching spaces, in correspondence with the lacunie of bone. The oiFshoots of these spaces in the cementum, like the spaces themselves, are very marked in dry specimens, because of their being filled with air. In chromic-acid specimens, on the contrary, the offshoots are much less prominent, and the less so the more thoroughh' the decalcification has been effected by the acid. jSTo essential difference is noticeable in the lacunae and canaliculi of ordinary bone from those of the cementum ; in both tissues there exists great variety in the general arrangement, in the size of the lacunae, and in the number and ramifications of their offshoots. The walls of the lacunae and the coarser offshoots, if viewed with a highh^ magnifying lens (immersion 1000 to 1500 diam.), appear interrupted at their peripheries by light openings, which lead into a light, delicate net-work, piercing the whole basis- substance to such an extent that the meshes have to be con- sidered only as fields of calcified glue-yielding basis-substance. Each lacuna contains a protoplasmic body, with a central nucleus, — the cement-corpuscle. The nucleus sometimes is * • ' The Distribution of Living Matter in Human Dentine. Cement, and Enamel. ' ' Dental Cosmos, 1878-1879. 102 THE ANATOMY AXD PATHOLOGY OF THE TEETH. relatively large, and surrounded only by a narrow seam of proto- plasm ; while in some small lacunae a body of the appearance of a nucleus is present without a noticeable amount of surround- ing protoplasm. The net-like structure of both the nuclei and the protoplasm is plainly visible in all cement-corpuscles. From the periphery of each corpuscle arise conical offshoots, of which the coarser ones penetrate into the larger offshoots of the lacuna, while the finest offshoots of the protoplasm traverse the light rim between the wall of the lacnna and the peripher}- of the jDrotoplasm, being directed toward a light interruption on the boundary of the lacuna. Cement-corpuscles, on the average, are round or spindle- shaped bodies, the long diameter of which corresponds to the direction of the lamellse. In the teeth of juvenile and middle- aged persons we meet with cement-corpuscles three or four times surpassing the size of ordinary ones, in which two or three nuclei are visible. Instead of multinuclear bodies, a number of meclallary nucleated elements may fill a large lacuna, all these elements being connected with one another by very delicate threads. The longitudinal diameter of such large lacunae is sometimes, therefore, an axis from which those elements radiate vertically to the direction of the lamella?. IN'umerous cement-corpuscles send broad and branching off- shoots through the basis-substance in a direction perpendicular or oblique to the lamellae, and not infrequently a direct union is established between two or three cement-corpuscles by means of such large oftslioots. (Fig. 42, page 73.) In some teeth broad, spindle-shaped spaces pierce the ce- mentum radiately, all of them containing protoplasm with deli- cate oft'shoots directed toward the net-work in the basis-substance. l!^ay, sometimes medullary spaces traverse the lamellfe in difi'er- ent directions, which spaces contain, besides a varying number of medullary elements, capillary blood-vessels evidently in con- nection with the capillaries of the pericementum. These forma- tions may be considered as remnants of the embr^'onic condition of the cementum, and are never present in large numbers. All protoplasmic formations within the cementum, though greatly varying in shape, are alike in being connected with one another by the delicate net-work that pierces the basis-substance. At the periphery of the cementum, on the line of its connec- tion with the pericementum, the net-work of the protoplasm is THE MIXUTE STRUCTURE OF CEMEXTUM. 103 usually veiy broad, and the fields of the basis-substance show a prevailing globular appearance. Also numerous spindle- shaped protoplasmic bodies are seen in connection with the cementum in an oblique arrangement, forming the transition into the structure of the pericementum. Between the calcified cementum and the striated connective tissue of the pericementum there often exists a narrow zone, occupied by closely-packed spindle-shaped protoplasmic bodies only. In the pericementum itself there are less numerous, partly nucleated protoplasmic Fig. 62. Teassition of Dextise into Cemextum, tvithoct a Marked Bouxdary. C, branching cement-corpuscle ; P, spindle -shaped cement-corpuscle ; both in direct connec- tion with dentinal fibers, F, which bifurcate within the eanalieuli of the dentine, D. Magni- fied 1200 diameters. bodies, between which the fields of an apparently homogeneous glue-yielding substance are seen. (See Fig. 62.) The connection betAveen dentine and cementum is established either by a gradual change of one tissue into the other, without a distinct line of demarcation, or there exists a boundary formed by a more or less marked wavy line, presenting irregu- lar bay-like excavations. Lastly, it occurs that between the bay -like excavations and the dentine there is interposed a 104 THE ANATOMY AND PATHOLOGY OF THE TEETH. stratum of tlie structure of cementum, with a gradual change of the tissue of the former into that of the' latter. (See Fig. 63.) Where a gradual change takes place, the dentinal canaliculi show irregular, mainly spindle-shaped enlargements, which stand in the direction of the dentinal canaliculi themselves, or run obliquely through the basis-substance of the cementum. The distal end of such a spindle is, as a rule, in connection with a Fig. G3. \1 E^^:;^ Teassitiox of De.ntixk into Cement, with an Intermediate Layer of Cement-stric- ture. U, dentine ; F, bifurcating dentine-fibers, in union with elongated cement-corpuscles, C^ ; these are imbedded in a basis-substance blending with that of dentine. The regular cementum is characterized by branching corpuscles, C-. Magnified 1200 diameters. regular lacuna of the cementum, or with an analogous forma- tion of a neighboring dentinal canaliculus. Many of the latter simply pass into the light, delicate net-work characteristic of the basis-substance of cementum. The dentinal fiber is in direct union with the protoplasm, which fills the spindle-shaped spaces, or it is lost to sight upon entering the net-work of the basis- substance of the cementum. THE MINUTE STRUCTURE OF CEMENTUM. 105 Where a boundary with bay-like excavations is present be- tween dentine and cementum, spindle-shaped enlargements of the dentinal canaliculi may be seen, much smaller than in the former instance. The majority of the dentinal canaliculi, however, reach the boundary of the cementum after repeated bifurcations, by which the caliber both of the canaliculi and of their central fibers is gradually diminished. A connection of the dentinal fibers with the coarser oflishoots of the cement-corpuscles is often observed. The light net-work of the basis-substance of the dentine always passes into that of the cementum. ^IsTot rarely, also, on the bottom of a bay-like excavation, partly nucleated protoplasmic bodies are present, into which the dentinal fibers inosculate. The connection between these and the coarser oftshoots of the cement-cor- puscles under these circumstances is established by such inter- vening protoplasmic bodies. The Neck of the Tooth. — There are certain peculiarities about the minute anatomy of the neck of the human tooth which, so far as I can judge from the literature within my reach, have not heretofore been mentioned. John Tomes* in describing the distribution of the dentinal tubes, says, "Near the neck they stop short of the cementum." This assertion is in accord with the v^a-iter's observations. In the great majority of teeth neither the canaliculi nor their tenants, the dentinal fibers, reach that part of the cementum which surrounds the neck. I^ear the periphery of the dentine bifurcations of the canaliculi — and consequently also of their tenants, the dentinal fibers — take place, some of the finest ter- minations of which run to the boundary between the dentine and cementum. As a rule the finest terminations of these fibers are lost to sight in a net-work somewhat coarser than that of the basis-substance of ordinary dentine. The minute elonga- tions of the dentinal fibers can also be traced into the light net- work with more distinctness than elsewhere in the dentine. Sometimes the dentinal canaliculi, upon approaching the periph- ery, become slightly dilated so as to produce slender pear-shaped cavities, in accordance with which the terminating dentinal fibers exhibit slight enlargements. The boundary between dentine and cementum presents a wavy line, traversed by delicate threads, or occupied by spindle- * " System of Dental Surgery," 1873. 106 THE AXAT03IY A^'D PATHOLOGY OF THE TEETH. shaped protoplasmic formations, all of which are in union with direct or indirect elongations of the dentinal fibers. The cementum around the neck forms a narrow layer, which is cut ofi" obliquely at the place of junction with the enamel. Both the cementum and enamel in this situation — being of the same width — are separated by a boundary w^hich runs from the outer periphery obliquely downward to the dentine. This rela- tion I found in the majority of teeth, and it is only exception- ally that I have met with cementum regularly overlapping the enamel. The cementum on the neck is built up of delicate prisms, or spindles, arranged verticallj^ to the surface of the dentine. The prisms represent the fields of the basis-substance, and are separated from one another by light rims, holding beaded fibers, or traversed by delicate vertical threads. In transverse sections, when the prisms are cut obliquely, they exhibit irregu- lar opaque fields separated from one another by light rims. These formations closely resemble the protoplasmic bodies of the pericementum next to the cementum, alluded to in the former chapter ; hence I do not hesitate to consider the bony formation on the neck as being produced by calcification of the osteoblasts of the pericementum. The cementum on the neck of the tooth is devoid of lamellae and lacunae, which appear deeper below, together with all the characteristic features of the fully-developed structure of the cementum. The lamellae become the more distinct, and the lacuna, with their contents (the cement-corpuscles), the more numerous, the broader the diameter of the layer of the cementum. The outer surface of the cementum is covered on its upper part with epithelial elements closely resembling those of jSTas- myth's layer of the enamel. This layer turns over into the epithelial coat of the gum. Farther down, the cementum, though still endowed with properties characteristic of the neck of the tooth, is surrounded by the fibrous connective tissue of the pericementum. I have met in one instance with striking formations on the neck of a tooth, which I consider anomalous, but not quite pathological. Here the ordinary cement of the neck is inter- rupted by grooves or pits containing the elements of perice- mental tissue. The inner periphery of the pit is covered with a well-developed, evidently isolated formation of cementum. The island of the cementum is broadest above the bottom of the THE MIXUTE STRUCTURE OF CE.MEXTUM, 107 pit, and slopes down along tlie walls of the pit, until it is lost within the layer of the cementum of the neck. (See Fig. 64.) Results.— -The cementum, as well as ordinary bone, is provided with lacunfe and canaliculi. The lacunas contain nucleated proto- plasmic bodies, and the canaliculi hold offshoots of the living matter of the protoplasm. The whole basis-substance of the cementum is traversed by a delicate net-Avork, which in all pro- bability contains living matter, though this is traceable only in Fig. 64. ^ ^- '' - ^ ■■ ^.,; V \-?i \ 1 K. -—d:b Anomalous Foematiox of Cementu.vi ox the Xeck of a Hcmax Tooth. B, dentine; DF, dentinal fibrillfe; JV, cementum on neck of tooth, with spindle-shaped or prismatic fields of basis-substance ; DP, depression in the cementum of the neck, filled with elementsof pericementum surrounded superiorly by a zone of regularly developed cementum, C; P, pericementum. Magnified 1200 diameters. its thorn-like projections from the periphery of the protoplasm and its larger offshoots. The living matter of the cementum is uninterruptedly connected with that of the periosteum, and continuous with the living matter of the dentine, either through intervening protoplasmic bodies in the interzonal layer, or directly with the dentinal fibers. The cementum covering the neck of the tooth is devoid of lamellae and protoplasmic bodies. It is built up of directly calci- fied osteoblasts of the pericementum, presenting their prismatic shapes, and everywhere traversed by a net-work of living matter. 108 THE AXATOMY AND PATHOLOGY OF THE TEETH. This is ill connection either with the epithelium of i^Tasmyth's layer or the pericementum, and with the dentine mainly through the intervening net-work in the basis-substance of the latter. Investigations concerning the structure of the cementum have been published by Carl Heitzmann and F. A. Roy,* of which I otter the following : " Method. — A recommendable method for the study of the microscopical structure of the cementum is to grind a tooth as thin as possible, always keeping it moist with a one per cent, solution of table-salt. First, with a fine saw or with a corundum - stone in the lathe, a coarse slab is made of the freshly-extracted tooth, which afterward is ground thin on a corundum-slab, and finished on an Arkansas stone. The specimen is not allowed to become dry for a moment. After brushing away the debris from grinding, the specimen is directly mounted in chemically-pure glycerin, or staining with ammoniacal carmin may be resorted to, though such a stain is of comparative!}' little value in the study of cementum. Some of our illustrations are made from specimens prepared in the manner just described. The}' are especially plain when examined immediately after mounting, but rarely fit for higher powers of the microscope, — powers exceeding from 500 to 600 diameters. After several weeks, when the glycerin has thoroughly saturated the specimen, the minute features are, as a rule, less conspicuous than in the freshly-mounted specimen. " The method first employed by William Carr, in 1889, for bringing to view the minutest structure of the dentine, is a pro- tracted stain with a one-half of one per cent, solution of chloride of gold, of plates ground thin with the finger on grinding-stones and corundum-slabs, and a subsequent complete decalcification by means of a six per cent, solution of glacial acetic acid. This method has also enabled John I. Hart to obtain perfect speci- mens of dentine. The same procedure we have adopted for clearing up the minutest features in the structure of the ce- mentum. Freshly-extracted teeth are placed in a one per cent, solution of talile-salt and ground thin, as before stated. It is important to leave the extracted teeth a short time only in the salt solution, — a few hours at the utmost, — since the protoplas- mic formations of the cementum become hydropic and unstain- able with chloride of gold if left in the solution for days. This * Transactions of the New York Odontological Society, 1892. THE MINUTE STRUCTURE OF CE.MENTUM. 109 tissue, being directly exposed to the salt solution, is altected by it sooner than the dentine. Special care must betaken in keep- ing the slabs moist ^Yith a weak solution of table-salt, lest the specimen become dry, and the lacune? and the coarser canaliculi filled with air, by which the details are rendered indistinct, or obliterated completely. After the slab — immaterial whether a longitudinal or a transverse section — has attained a sufficient degree of thinness, as proven by mounting on a slide and cover- ing with the thinnest possible covering-glass, it must be washed carefully and repeatedly with a camel's-hair brush, under con- tinuous renewal of the salt solution. Xext the slab is placed in a one-half of one per cent, solution of chloride of gold, in which process all metallic instruments must be avoided, the simplest spatula being a match shaped with a penknife. If several sec- tions should be ready for treatment with chloride of gold, it is necessary to see that each one be in free contact with the gold solution. Specimens overlapping one another prevent a perfect stain, because they will not allow the desired contact and pene- tration with the gold solution." " The time required for exposure to the gold-salt is somewhat different with different teeth, probably because of the variable amount of lime-salts infiltrating the cementum. The best re- sults we have obtained were on temporary teeth left in the gold solution from six to seven hours, — certainly a shorter time than is required for staining the dentine. The following exposure for ten hours to a six per cent, solution of glacial acetic acid is, as a rule, sufficient for complete decalcification of the cementum, and now the specimen may be exposed to broad daylight for a number of days, until it has assumed a dark-violet or dark- purple color. The only precaution required at this stage of the procedure is to renew every day the distilled water in which the specimen lies, in order to prevent the growth of mildew. A drop of chemically-pure glycerin added to the distilled water is a sure means of keeping away the mildew. The mounting of such specimens is invariably done in glycerin, — the only medium which allows the examination with the highest powers of the microscope. " We admit that the results obtained in the described manner of treating cementum were not uniformly satisfactory, in contra- distinction to those in the preparation of dentine, in which failures are exceptional. We cannot account for the fact that specimens 110 THE ANATOMY AND PATHOLOGY OF THE TEETH. of difterent teeth which we knew to be alive and perfectly fresh, yielded good images only occasionally. Cohnheim, the dis- coverer of the gold-stain, met with the same accidents. Some- times the basis-substance assumes a deeper color than the con- tents of the lacunae ; the latter may remain so pale even as to imitate features of devitalized teeth. Specimens well stained, however, exhibited all features so handsomely that we thought best to describe this method, leaving the invention of new pro- cedures to other observers. It is especially the acetic acid which we suspect of yielding unsatisfactory results, and other acids — perhaps diluted sulphuric acid — may have to be resorted to in future trials. Owing to the unequal efficiency of the method employed, we will abstain from statements which are of the utmost importance to the practitioner, — viz, the definition of the living from the non-living part of the cementum in pulpless teeth. The results of our examination seem to be sufficiently interesting, however, so far as they go, to deserve presentation. " Cement of the Roots. — We have examined quite a number of roots of teeth, both deciduous and permanent, in specimens ground thin under the protection of an indiflierent liquid, — a one per cent, solution of table-salt. Our intention has been to study the features of the cement-tissue in freshly-ground specimens, before they were exposed to the influence of a solution of chloride of gold. What we saw in many instances has not up to this time been described. (See Fig. 65.) " With low powers of the microscope, we find on the surface of the cementum shallow pits that render the border-line, in a longitudinal section, hilly or wavy. This corresponds to the rough, slightly-pitted aspect of the surface of the roots, viewed with the naked eye. The lamellated portion of the cement tapers toward the neck of the tooth, and becomes the broader as it approaches the apices of the roots. In this portion of the cement-tissue the parallel lamellae are conspicuous, and we notice scattered in the basis-substance a number of cement-corpuscles which differ from ordinary bone-corpuscles only in being more irregular, often elongated, apparently arranged without regu- larity, certainly without parallelism to the lamellse. Besides the cement-corpuscles, we notice a number of lines running from the surface to the dentine, and piercing the lamella? at right or acute angles, often in union with the cement-corpuscles. The course taken by these lines, which in their parallelism bear THE 3IIXUTE STRUCTURE OF CEMEXTUM. Ill somewhat the aspect of dentinal fibers, is always devious from the latter, with which they produce obtuse angles. We have failed to find an immediate union of dentinal fibers with the fibers pierciug the cementum. The lamellated portion is fol- lowed by a layer, indistinctly lamellated or striated, likewise con- taining cement-corpuscles, and likewise traversed b}' radiating lines. This layer, either indistinctly lamellated or entirely destitute of lamellae, we propose to term ' the osteoid la;yer of the cementum.' At the boundary of the osteoid layer, toward Fig. 65. Root of a Ground Bicuspid, showixg a Combixatios of Lamellated axd Osteoid Cemextum, P, pericementum; T, thickness of the specimen; L, lamellated cementum; 0. osteoid ce- mentum; Z, interzonal layer between cementum and dentine: D, dentine. Magnified 200 diameters. the dentine, a layer of numerous small protoplasmic bodies is seen in our specimen, similar to those of an ill-calcified enamel, and probably due to a deficient calcification of the cementum. This layer is rather exceptional. The dentinal canaliculi either stop short of the interzonal osteoid laj^er, or a limited number of canaliculi is seen to directly run into the interzonal layer, where they inosculate with the coarse protoplasmic reticulum. " The aspect of the cement-corpuscles in the distinctly lamel- 112 THE AXAT03IY AND rATHOLOGY OF THE TEETH. lated portion is rather peculiar in ground specimens, mounted in glycerin, when viewed with medium powers of the micro- scope, 500 to 600 diameters. The lacuna appear filled with protoplasmic bodies, in the center of which we notice oblong nuclei. From the periphery of the bodies numerous offshoots break forth, which either directly connect neighboring cement- corpuscles, or are lost in the basis-substance. Innumerable fine oftshoots are seen to emanate from the coarse ones, and by Fig. 66. Lamellated Cemextum of the Root of a Ground Bicuspid. C, C, cement-corpuscles branching and interconnecting; R, incomplete reticulum, produced by the finest offshoots of the cement-corpuscles ;"X,'X, boundary-lines of the lamellae. Mag- nified 600 diameters. these finest ofishoots an indistinct net-work is established, par- ticularly plain in the vicinity of the cement-corpuscles. The basis-substance appears coarsely granular, but no reticulum proper can be made out with this amplification. The basis- substance is pierced by peculiar fibers which intersect the lamellae at right or acute angles, often are bifurcate, and in many instances are independent of the cement-corpuscles or their ofl:shoots, while in other instances they distinctly inoscu- late with the two last-named formations. (See Fig. QQ.) THE MINUTE STRUCTURE OF CEMENTUM. 113 " The question arises, AVhat are these fibers iu the cementura ? The first idea suggesting itself is that we have to deal with per- forating fibers, first described by Sharpey in specimens of dry bone-tissue. Charles S. Tomes* says, 'Like bone, cementum is also sometimes found to contain Sharpey's fibers ; that is to say, rods running through it at right angles to its own lamina- tion, and, as it were, perforating it. These are probably calcified bundles of connective tissue.' " Sharpey's fibers are never seen in specimens decalcified by solutions of chromic acid. Histologists assert that they are elastic fibers, not perishable after treatment of the specimen with caustic potash. The fibers in the cementum, on the con- trary, are caualiculi in the basis-substance, holding protoplasm, or rather living matter, which feature renders them akin to dentinal fibers. AVe propose the name of ' piercing cement- fibrillai' for their designation. " The ultimate analysis of the tissue of cementum is possible only after exposure to a solution of chloride of gold and subse- quent decalcification with acetic acid. (See Fig. 67.) " TVe see the cement-corpuscles, the nuclei of which often appear a trifie lighter than the rest of the protoplasm. The reticular structure of the latter is plain in many corpuscles. Xumerous coarse and innumerable fine oft'shoots break forth from the periphery of the cement-corpuscles. Close around the latter and their coarse offshoots a light rim is present, tra- versed by the minutest conical oft'shoots, Avhich rim obviously corresponds to the wall of the lacunse and canaliculi. The walls are rendered indistinct by the decalcification of the specimen. The whole basis-substance is traversed by an extremely minute reticulum of a dark-violet color, interconnecting all cement- corpuscles. The behavior of this reticulum toward chloride of gold clears up the nature of it : living matter produces the net- work in the protoplasm, as well as in the basis-substance. Of this reticulum, however, the meshes must be considered as the basis-substance proper, composed of what we term glue or gela- tin, and saturated with lime-salts. The boundary zone or interzonal layer between dentine and cementum is conspicuous by its bay-like excavations. In this region we easily recognize the union of most of the dentinal fibers with coarser offshoots '■A Manual of Dental Anatomy.'" PhiladelpMa, 1876. 9 114 THE ANATOJIY AND PATHOLOGY OF THE TEETH, of the eement-eorpiiscles, — a fact already established by Bo- decker. An immediate union of the living matter of the den- tine with that of the cementum is fairly plain, since from six to eight hours' exposure to the solution of chloride of gold was sufficient to bring to view the reticulum in the cementum, whereas ten hours' exposure is needed, accordmg to John I. Hart, to stain the reticulum of the dentine to a satisfactory degree. jSTo doubt, in a living tooth, the whole cementum is a Fig. 67. Root of a Molae in Loxgitudixal Section. Stained -nrrH Chloride op Gold. P, nucleated protoplasmic body with coarse, dark -violet ofiFshoot?; C, basis-substance of ce- mentum, pierced by a violet delicate reticulum; i>, D. dentine. Most of the dentinal fibers unite with offshoots of cement-corpuscles. Magnified 12C0 diameters. tissue, endowed with properties of life, the same as is dentine. Life is not conlined to the cement-corpuscles and their coarser otishoots, but extends all through the basis-substance, being active within the reticulum that pervades the protoplasm ; and active also within that of the basis-substance. The study of the pathology of cementum has furnished ample proof for the cor- roboration of this statement. " Osteoid Cementum. — The tissue of the cementum covering THE MINUTE STRUCTURE OF CEMENTUM. 115 the neck of the tooth is diit'erent in its microscopical structure from the main mass of the cementum. It is known that the thin layer of this tissue gradually blends with the cementum proper. First the prisms of the neck-layer disappear, and a granular layer makes its appearance, destitute, as yet, of lamellae and cemeut-corpuscles, exhibiting a few faint striations, and tra- versed, as in our specimen, occasionally, though not always, by piercing cement-librills?. (See Fig. 68.) " This formation is probably what Charles S. Tomes* Rout of a Ground Bicuspid ix Loxgitudixal Sectiox. Traxsitiox of the Cemextum OF THE Neck ixto that of the Root. P, pericementum : T, thickness of the specimen : 0, osteoid layer of the cementum; D, den- tine ; L, protoplasmic bodies at the interzonal layer between dentine and cementum. Magnified 200 diameters. describes in the following words : ' The matrix of the cementum is sometimes apparently structureless, at others finely granular or interspersed with small globules.' We wish to term it the ' osteoid layer' of the cementum. By the name 'osteoid' the histologists designate a tissue kindred to bone, saturated with lime-salts, lacking bone-corpuscles or showing but few of them, and without lamella?. All this characterization holds good for the portion of the cementum under consideration. Its history * " A Manual of Dental Anatomy. ' " Philadelphia, 1876. 116 THE ANATOMY AND PATHOLOGY OF THE TEETH. of development will be cleared up some day, when the develop- ment of eementum will be studied in human teeth, — a study not as yet accomplished. " The osteoid layer shows, as it nears the lamellated eementum, a few irregular bone-corpuscles. The lamellated portion starts from the periphery of the root, and soon becomes broader and supplied with regular, freely-branching cement-corpuscles, with the result that the osteoid structure, in the majority of the teeth examined, is lost to sight. In the specimen from which the Fig. 69. KooT OF A Geousd Molar in Longitudinal Section. Transition of Osteoid into Lamellated Cementum. P, pericementum ; T, thickness of the specimen ; X, lamellated eementum ; 0, osteoid ee- mentum ; Z, interzonal layer between dentine and eementum; D, dentine. Magnified 200 diameters. illastration is taken, the dentinal iibrill?e stop short of the osteoid layer, a feature so characteristic of the anatomy of the neck. ISTear the interzonal layer, between the dentine and the osteoid tissue, a few small protoplasmic bodies are seen, into which dentinal fibers inosculate. " ISTot infrequently the osteoid layer does not perish, even though lamellated eementum has made its appearance ; nay, the osteoid layer may be seen all around the root, as an intervening formation between dentine and eementum. Fie;. 69 is taken THE MINUTE STRUCTURE OF CEMENTUM. 117 from sucli a specimen. Here we see the beginning of a lamel- lated formation, between which and the dentine are protoplasmic bodies, with a number of long and parallel offshoots, of the aspect of piercing fibers. The interzonal layer, in this instance, is conspicuous by a large number of interconnecting protoplas- mic bodies, in union on their upward course with cement- corpuscles, and on their downward course with dentinal fibers. This peculiar formation is traceable all along the roots, and signifies an incomplete deposition of lime-salts at the time of Fig. 70. p Osteoid Layer of the Root of an Incisor. L(jngitudinal Section. Stained with Chloride of Gold. P, protoplasmic body, with scanty, coarse oifshoots; 0, coarse oifslioot, apparently in no con- nection with a protoplasmic body ; B, basis-substance of the osteoid layer, traversed by a deli- cate reticulum. Magnified 1200 diameters. the formation of the cementum. The dentine of this tooth is fully developed, lacking even the so-called interglobular spaces in the crown. " In order more thoroughly to understand the structure of the osteoid layer, we have applied to such specimens the protracted gold stain, with subsequent decalcification by means of diluted acetic acid ; the image thus obtained was a striking one indeed. (See Fig. 70.) 118 THE ANATOMY AND PATHOLOGY OF THE TEETH. " We observe small, odd-sliaped protoplasmic bodies of a dark- violet color, exhibiting but a limited number of coarse oftshoots. Besides, coarse dark-violet fibers traverse the basis-substance, making a coarse net-work, arranged without apparent regular- ity, and also, as it seems, lacking connections with larger proto- plasmic masses. This latter feature may be due to a curved course of the fibers, the union with cement-corpuscles being severed by the process of grinding. The whole basis-substance is seen to be traversed by a, comparatively speaking, coarse, dark-violet reticulum, in union with the protoplasmic bodies, as Fig. 71. Osteoid Cementum op the Root op a Ground Bicuspid. C, osteoid layer of the cementum, with scanty protoplasmic bodies and piercing cement- fibrillas ; Z, interzonal layer between dentine and cementum, with numerous branching proto- plasmic formations ; B, dentine with scanty protoplasmic bodies. Magnified 600 diameters. well as with the coarse fibers. Unquestionably the reticulum is the living matter proper, which endows the osteoid layer with a considerable degree of vitality and sensibility. " The peculiar interzonal formations, represented in Fig. 69, we have also examined with higher powers of the microscope. (See Fig. 71.) " We notice small protoplasmic bodies branching and inter- connecting. Upward their offshoots run into cement-corpuscles, or into piercing fibers of the cementum, whereas, downward the oftshoots blend with the dentinal fibers. Even the dentine is THE MINUTE STRUCTURE OF CEMENTUM. 119 possessed of protoplasmic formations, a certain distance away from the interzonal layer; all of which proves a deficient calci- fication just at the time of the beginning of the development of the cementum. The specimen from which the drawing is made was not stained with chloride of gold, and not decalcified ; hence the reticulum of the basis-substance is only indicated, not con- spicuous. A^o doubt, however, can arise about its presence. " Cementum of the Neck. — Bodecker was the first to accurately describe the minute anatomical features of the cementum of the neck. How defective the knowledge of this region was, even sixteen years ago, is best shown by a quotation from Charles S. Tomes, who says,* ' Where the cementum is very thin, as, for instance, where it commences at the neck of a human tooth, it is to all appearance structureless, and does not contain any lacuna?.' The cementum of the neck, as is well known, forms an extremely thin layer, sharply bordered toward the enamel, and sometimes even overlapping the latter. Bodecker speaks of directly calcified prisms in the neck-cementum, which, in his opinion, may be considered as osteoblasts, infiltrated with lime-salts. Sometimes the prismatic structure is not pronounced, but a row of spindles is seen arranged in a direction almost perpendicular to the surface of the tooth. Larger and smaller spindles alternate, the latter sometimes being so small as to con- vey the impression of fibers. " There is a slight discrepancy between the statements of Bodecker and our own observations. We fully concur with him as to the calcified prisms; but the spindles, sometimes very con- spicuous even to medium powers of the microscope, we cannot consider as formations of the basis-substance. Rather, we should regard the spindles and alternating fibers as protoplasmic formations, which fill the interstices between the prismatic pieces of the cementum of the neck. This tissue, in our opinion, is either composed of prisms alone, with intervening light and parallel spaces, or of prisms, between which are protoplasmic bodies of spindle shape, alternately broad and narrow, in the latter instance having the aspect of coarse fibers of living mat- ter. Thus the uniformity in the structure of the cementum of the neck is established. We hope Dr. Bodecker, with whom we thoroughly concur in all other points, will pardon our heresy * "A Manual of Dental Anatomy. "■ Philadelphia, 1876. 120 THE ANATOMY AND PATHOLOGY OF THE TEETH. and eventually satisfy himself that our conception renders this structure more comprehensible than does his. (See Fig. 7-.) " Considerable interest attaches to the layer of dentine directly subjacent to the prismatic layer of the cementum of the neck. AVe are indebted to John Tomes for the knowledge of , the fact that the dentinal fibers, in this situation, stop short of the cementum. AVe may say that nowhere does the structure of the teeth vary in aspect so greatly as in the dentine in the region of the neck. There are scarcely two teeth perfectly alike in this region. The simplest form is when the prismatic layer is directly followed by a granular layer of dentine, lacking Fig. 72. Neck op a Bicuspid in Loxgitudixal Sectiox. Staixed with Chloride of Gold. /", pericementum ; T, thickness of the specimen: JV, cementum of the neck, composed of prisms and intervening spindles and fibers: Z, stratified interzonal layer: .D, coarsely reticu- lated layer of dentine, destitute of dentinal fibers. Magnified 3200 diameters. canaliculi. That the granulation means a rich reticulum of li^^ng matter, coarser than in any other part of the dentine, and rendering the neck excessively sensitive, John I. Hart has proven, fully in accordance with Bodecker's statements. This simple arrangement, however, is rare. In many instances there are layers of stratifications between the cementum and the granular dentine, greatly varying in breadth and in numbers. The appearance of strata, in accord with the conception of John I. Hart, means that alternate layers, rich in living matter, and others scantily supplied with it, build up the neck-region of the THE MIXUTE STRUCTURE OF CEMENTUM. 121 dentine. Club-like or pear-shaped spaces, filled with proto- plasm, are often seen to pervade the granular layer of the den- tine with a peculiar regularity, and often in connection with dentinal fibers, which otherwise do not reach the boundary of the cementum. In Fig. 72 we find represented in the granular layer of the dentine coarse, dark-violet dots, forming points of intersection, and far too small to be termed protoplasmic bodies or cells in the sense of older histologists. All these features Fig. 73. Neck of a Grouxd Bicuspid. Anomalous Arraxgemen't of Layers of the Cementum AXD the Dentine. P, pericementum ; T, thickness of the specimen ; .9, stratified layer of cementum, composed of halved prisms; L^, outer lamellated layer; G, outer granular layer; L-. inner lamellated layer; (?-, inner granular layer; D\ thoroughly calcified glossy layer; D-, inner prismatic layer ; D, normal dentine. Magnified 200 diameters. seem to mean a markedly augmented amount of living matter, which renders all surgical interference in the region of the neck so painful. " The most complicated structure that we have ever seen in the region of the neck is illustrated in Fig. 73. " The figure is taken from a ground bicuspid, which shows at its crown a distinct mechanical abrasion. The stratifications 122 THE ANATOMY AND PATHOLOGY OF THE TEETH. extend all over the root. It is impossible to bring them into a relation with the mechanical abrasion, and we should consider this formation a rather anomalous one. The layers are as fol- lows : The outermost portion, directly bordering the cementum, is composed of large, regular prisms, which show faint longi- tudinal lines and are halved by distinct fissures in a direction parallel to the surface; this layer extends to the close vicinity of the enamel, and far down along the root, directly changing into stratified cementum, devoid of cement-corpnscles, so far as the specimen shows. This is the only la^^er that belongs to the cementum, since in the neighborhood of the enamel the dentinal fibers are traceable up to the prisms, pervading a granular basis- substance as yet but slightly stratified. Soon afterward the dentine begins to exhibit a number of layers, which may be defined as composing a narrow outer, and a broad inner, lamel- lated stratum, between which strata lies the ' outer granular' zone, somewhat varying in breadth along the root. These three strata are pierced by extremely delicate radiating lines, which closely resemble dentinal fibers. The next layer to form is the 'inner granular,' greatly changing in breadth in different por- tions of the root. This layer holds small, angular protoplasmic formations, and, obviously, corresponds to the granular layer subjacent to the cementum of the neck in normal teeth. In- wardly there follows a zone (D^) marked by a high gloss due to an intense calcification of the basis-substance, pierced by scanty angular protoplasmic bodies. The innermost stratum appears to be composed of prisms or spindles, far less regular than those of the cementum. A sharp line of demarcation, in which not the slightest anomaly can be made out, closes this layer at its approach to the normal dentine. All these layers are seen down to nearly half the length of the root, where the specimen is cut off. " Exceptional!}' there is observable in the dentine of the roots stratification, consisting of narrow, light lines, arranged nearly parallel to the surface, causing an interruption in the course of the dentinal fibers, but never a change in their direction. Strati- fication of the dentine at the neck is far more common, but has never been seen as yet in such perfection as in the specimen illustrated in Fig. 73. What the cause of such stratification is, future studies in the history of development of the dentine of the roots and the cementum will elucidate. THE MINUTE STRUCTURE OF CEMEXTUM. 123 " Devitalized Cementum. — We have ground a number of teeth which, to judge from their naked-eye appearance, were pulpless and devitalized. After the exposure of thin slabs obtained from such teeth to the solution of chloride of gold, with subse- quent decalcification with acetic acid, the image under the microscope was striking. (See Fig. 74.) " The most conspicuous features were the empty lacuna, desti- tute of nucleated protoplasm, but containing granular clusters Cemextum of the Root of a Devitalized Molar. Staixed with Chloride of Gold. L, lacuna, holding shriveled protoplasm ; C, empty canaliculi ; B, basis-substance, pierced by a light reticulum. Magnified 1200 diameters. of a dark-violet color, obviously the shriveled remains of pro- toplasm. iSTumerous canaliculi arose from the lacunae, all of which were empty. The finest oftshoots of both the lacunae and canaliculi produced alight net-work in the dark-violet basis- substance, — an image which corresponds to dry and also to ne- crotic bone. Unfortunately, some specimens of living, freshly- extracted teeth furnished, after the same chemical treatment, identically similar figures. Such an untoward result has also 124 THE ANATOMY AND PATHOLOGY OF THE TEETH. occurred to other investigators who resorted to the gold method. The cause of such failure may have been that the extracted teeth were left too long under the influence of the table-salt solution ; or, possibly, the acetic acid worked in a wrong way. All we can say is, that whenever such a negative result was obtained, the whole cementum had been affected, so much so that we are at a loss to state whether or not the devitalized cementum is dead all through, up to the pericementum. Future examina- tions, carried out with improved methods, vdll probably settle the question where the boundary between dead and living tissue is, this being a matter of the greatest importance to the prac- titioner." CHAPTER XIII. SYNOPSIS OF THE DEVELOPMENT OF THE TEETH. From a morphological point of view, we might, as several writers have done, consider the teeth to be dermal structures. Their analogy to the skin is, indeed, striking, if we compare the crown of a tooth with a papilla of the skin, especially when the former is in a state of formation, — viz, about the fifth month of intra-uterine development. Here we observe a knob-like for- mation of connective tissue, the dental papilla, similar to a skin- papilla, supplied with blood-vessels and covered by an epithelial tissue, the enamel-organ. The teeth, during their early stage of development, are com- posed of only two tissues, — i.e., the enamel and the dentine, the cementum of the root being developed after birth. The first process in the formation of teeth in the human sub- ject is the evolution of a furrow extending the whole length of the future alveolar process. This furrow appears at about the sixth week of intra-uterine life. (See Fig. 75.) Shortly afterward we observe along the furrow a row of hillocks in the oral epi- thelium, growing down into the substance of the future jaw. This hillocked epithelial formation is called an enamel-cord, and as development proceeds, the enamel-cord is formed which becomes the enamel-organ of each tooth. About the third month this epithelial cord widens at its distal extremity, which assumes the shape of a bell-jar at the end of the cord. The for- SYNOPSIS OF THE DEVELOPMENT OF THE TEETH. Fig. 75. 125 Transverse Section of Furrow on Lower Jaw op a Human Ejibkto Six "Weeks Old. E, epithelium of oral mucosa; T, tongue: V, blood-vessels; B, base of oral cavity: F, fur- row in transverse section. Magnified 75 diameters. Fig. 76. Epithelial Cord tei;minaii.\i. THE Future ExAiiEL-OKLrAX of a Human Embryo Three Months Old. 0, stratified epithelium of the oral cavitj- ; Co, epithelial cord of the enamel-organ ; .S", short secondary offshoot of the epithelial cord ; SP, broad secondary offshoot of the epithelial cord ; EE, external or outer epithelium ; £■ (lower), internal or inner epithelium; J/, medullary tissue sprung from previous epithelia, the future stellate reticulum : /'.dentine-papilla; Ca, capsule or tooth-sac; £" (upper), embryonal tissue, the future fibrous connective tissue of the mucous membrane. Magnified 75 diameters. 126 THE ANATOMY AND PATHOLOGY OF THE TEETH. mation tlirougliout is composed of two distinct layers of colum- nar epithelia, continuous with the oral mucous membrane. (See Fig. 76.) At the period in which the bell-shape begins, we see the first trace of the dentinal papilla. About the end of the third month of intra-uterine development we observe that the enamel-organ has changed considerably in shape and size, and we now distinguish the following formations: 1, the epithelial cord; 2, the external epithelium; 3, the internal epithelium; 4, the stratum intermedium ; and 5, the stellate reticulum. (See Fig. 77.) We also notice the beginning formation of the tooth-sac, which grows upward from the dentine papilla, gradually encircling the enamel-organ. About the fifth month the external epithelium of the enamel-organ, together with the epithelial cord, begin to break into epithelial nests and buds, amid which a pro- fuse formation of red blood-corpuscles and blood-vessels takes place. At this period the internal epithelium covering the crown of the future tooth undergoes a change consisting in a prolongation of the single epithelia, and their sum-total is now called the amdohlast h'lU'r., while those elongated formations covering the dentine papilla are termed odontoblosf.'--. The amelo- blasts and odontoblasts have been originally in close contact, but with progressing development the dentine begins to form from the periphery toward the center of the tooth ; the enamel, on the contrary, grows from the surface of the dentine outward. These changes appear in about the fifth month, wherein also the first trace of dentine is seen, while the enamel begins to form at about the sixth month. Before calcification takes place, there becomes visible on the outermost portion of the ameloblasts a delicate light zone, consisting of embryonal or medullary cor- puscles, from which the enamel originates. The odontoblasts at the periphery of the dentine papilla likewise undergo a transformation into medullary corpuscles, and by their calcifica- tion give rise to the basis-substance of the dentine. The odonto- blasts, as well as the medullary corpuscles sprung from them, are interconnected by delicate threads of living matter. These threads, in coalescence with the ofishoots of the odontoblasts, produce the dentinal fibers. The odontoblasts and ameloblasts, therefore, are not directly transformed into the tissues, dentine and enamel, which they respectively represent, but must be con- sidered as provisional formations. During development, the den- tine is formed of globular territories, proven by the occurrence .SYNOPSIS OF THE DEVELOPMENT OF THE TEETH. 127 of interglobular spaces, and by the retrogressive processes of absorption in temporary teeth, in caries and ebiirnitis. In this process, the similarity of dentine-tissue with bone-tissue is ren- dered evident. The cementum is formed after birth ; the remains of the Fig. 77. 'i^^'"?^ NX^ ;:>-^ Epithelial Coed teemisatixg is the Examel-Orgax of a Hcman Embryo Five Months Old. 0, stratified epithelium of the oral cavity : SP, secondary offshoot of the epithelial cord : Co. epithelial cord of the enamel-organ; J/, myxomatous tissue of the enamel-organ: EE, external or outer epithelium; IE, internal or inner epithelium; /, stratum intermedium, between inner epithelium and myxomatous tissue; /-'.papilla; Ca, capsule or tooth-sac; F. fibrous connective tissue of oral mucosa. Magnified 75 diameters. 128 THE ANATOMT AND PATHOLOGY OF THE TEETH. tooth-sac changing into meclnhary corpuscles, from which the cementuni is developed in the same manner as bone-tissue. The twenty anterior permanent teeth are developed from enamel-organs, being oifshoots from those of the temporary teeth. All the permanent molar teeth are an offspring of the enamel-organ of the second temporary molar teeth. The Avriter's views concerning the development of the teeth, as here propounded, differ considerably from those entertained by previous authors. To enable future investigators to satisfy themselves of the correctness of his assertions, the result of eight years of labor, the following is presented as the method resorted to in the pursuit of this study, one of the most fascinating subjects of microscopical research : To prepare microscopical specimens of embryonal jaws for researches in the history of the development of the teeth, the jaw-bones (preferably the lower) are excised from the foetus, — care being exercised not to squeeze the specimen, — and are placed in a one-iifth of one per cent, solution of chromic acid. The liquid must be changed every third or fourth day, and the strength of the chromic-acid solution gradually increased to one- half of one per cent., until the hard tissues, by the removal of the lime-salts, are sufficiently soft to be cut with a razor. All trials to determine the degree of softness of such a specimen must be made by means of a needle, and not with the fingers. The epithelial structures are especially liable to be crushed, unless handled with the utmost care. The greatest obstacle to obtaining perfect specimens is caused by the fact that the enamel- organ is withdrawn from the dentinal cap, and the epithelia are detached from the connective-tissue structures, a cavity beino- thus formed whose walls offer no resistance to the cuttino-- instruments, and are thus easily detached from their normal position. After having tried different methods of imbedding, the author has come to the conclusion that the best material for this purpose is celloidin, softened in absolute alcohol and dissolved in sulphuric ether. The specimen, previous to imbedding, must be dehy- drated by immersion in absolute alcohol for twenty-four hours. It is next kept in a mixture of equal parts of sulphuric ether and absolute alcohol about twenty-four hours longer. Then it is held in a rather thin solution of celloidin for about two days, after which it is ready for mounting upon a cork. When DEVEL0P3IEXT OF DEXTIXE. 129 such a specimen is cut, it will usually be found that the spaces between the dentine and enamel, which are due to the shrinkage of the myxomatous tissue of the enamel-organ, are filled with celloidiu. If, however, it is found, upon cutting, that such a space has not been completely filled, a very thin solution of cel- loidin may be poured into it. A section-cutter is of great advantage, since bv its use a laro^e number of thin and uniform specimens can be obtained in a comparatively short space of time. Chemically-pure glycerin is considered far superior to Canada balsam as a mounting medium, the tissues of the object pre- senting in this medium a more distinct appearance. If high powers of the microscope are to be employed, only glycerin- mounted specimens will give satisfactory results. CHAPTER XIV. DEVELOPMEXT OF DEXTIXE.* Dentine, as is universally admitted, is strictly an offspring of connective tissue produced by the papilla, a formation of embryonal tissue, crowded with medullary corpuscles. (See Fig. 78.) It appears about the end of the second and the beginning of the third month of intra-uterine life, at a time when the extrem- ity of the epithelial cord has flattened and assumed a cup-shape. The cavity of this cup is filled with the papilla, which sends prolongations along the outer wall of the cup, the future sac of the tooth. The more this is deepened and widened, the larger will be the papilla., If the cup of the enamel-organ shows de- pressions corresponding to a bicuspid or molar tooth, we shall find corresponding elevations upon the papilla extending into them. The papilla is originally supplied with but few capillary blood-vessels. With advancing growth, however, the vascular supply becomes greater, especially in its peripheral portions, where a delicate fibrous connective tissue is developed, — the so- called tooth-sac. In the seventh month of fcetal life, we observe * • ■ Contributions to the History of Development of the Teeth. ■ " By C. Heitzmann and C. F. W. Bodecker. Tlie Indejyendent Practitionei^ vols, viii and ix. 10 130 THE ANATOMY AND PATHOLOGY OF THE TEETH. a perfect vascular apparatus traversing the papilla, consisting of arteries, veins, and capillaries. If examined with low powers of the microscope, the papilla appears to be composed of small, globular, highlj-refracting corpuscles, amid which is seen a scanty basis-substance. With high powers of the microscope, we observe globular or oblong corpuscles of small size, which are either compact and homogeneous, or possessed of a distinct reticular structure in their interior. Between small groups of such medullary corpuscles, spindle-shaped tracts appear, corre- sponding to the boundaries of the future territories of the myxo- matous tissue, the reticulum of which in the human subject is always incomplete, never attaining the degree of development Fig. 78. Medullary Tissue of the Papilla of a Human Embryo of Four Months. The small shining medullary corpuscles form clusters, around which we observe an irregularly developed ms'xomatous net-work. Magnified 1200 diameters. seen in the enamel-organ. The largest medullary corpuscles are observed in the middle of territories surrounded b}^ a certain amount of basis-substance. Both these corpuscles and the basis- substance have a distinct reticular structure. (See Fig. 78.) The more the papilla increases in size and advances in devel- opment, the less frecjuent are the homogeneous and small medullary corpuscles, while the granular corpuscles are larger, each being surrounded by a small amount of basis-substance. Along the periphery of the papilla, however, there is invariably present a narrow zone, in which the medullary corpuscles are more numerous and more shining than in the rest of the papilla. itEVELOPMENT OE DENTi:SE. 131 In the fifth month the outermost periphery of the papilla is fre- quently found to be composed of a hyaline rim, beneath which is a narrow zone of medullary corpuscles. The hyaline rim corresponds to the so-called structureless layer, or basement membrane so often seen between epithelial and connective-tissue formations. When the enamel-organ is detached from the papilla, — and this detachment is, as above said, very frequent, — the outer surface of the basement membrane appears beset with an extremely delicate fringe, evidently the torn connection be- tween the papilla and the adjacent enamel-organ, or the amelo- blasts. High powers of the microscope reveal in the apparently structureless layer a faint reticular formation, and marks of a division into medullary corpuscles. At the iDCginning of the fifth month, we usually find along the periphery of the papilla the first traces of peculiar, elongated corpuscles, known as odontoblasts. These formations are ob- long, pear-, club-, or spindle-shaped, arising from the coalescence of a number of medullary corpuscles, including that portion which has been previousl}^ transformed into basis-substance. The odontoblasts are sometimes seen directly beneath an already- formed layer of not yet calcified dentine. The latter, in this case, is sufiiciently characterized by the presence of delicate branching dentinal canaliculi, holding the slender dentinal (Tomes) fibers. AYe often observe these fibers to be in direct connection with adjacent odontoblasts. If an odontoblast ter- minates in a sharp point, one ofi'shoot directly connected with a dentinal fiber is seen to arise from the point. If an odonto- blast has a broad basis, two or more offshoots may arise from it and run, in the shape of dentinal fibers, into the adjacent dentinal canaliculi. It may also happen that an offshoot of an odontoblast takes another direction, and instead of passing into a dentinal canalicukis, runs parallel with the border of the already-formed dentine. Fully-developed odontoblasts are not often seen in direct union with dentine, and this is especially true along the lateral portions of the dentinal cap. It is far more common that medullary corpuscles are present between the odontoblasts and the dentine, and that the offshoots of the odontoblasts run between these medullary corpuscles in order to reach their respective dentinal canaliculi. Fully-developed odontoblasts are rarely seen at the apex of the papilla. Usually medullary corpuscles only are present in this locality, or they 132 THE ANATOMY AND PATHOLOGY OF THE TEETH. are interposed bet^'eeii the odontoblasts and dentine. Not in- frequently we observe in the forming dentine layers as are represented in Fig. 79. The odontoblasts have arisen from the fusion of a number of First-Formed Dentine of a Human Fcktus of Six Months. D, calcified layer of dentine with marked globular territories ; DT, dentine composed of a non-calcified basis-substance, likewise globular ; DM, row of medullary corpuscles before the formation of basis-substance ; 0, odontoblasts, the ofi'shoots of which run between the medul- lary corpuscles into the dentinal canaliculi ; E, enamel. Magnified 1200 diameters. medullary corpuscles, and are present where, at the time, the for- mation of dentine is not actively in progress. "Whenever this is the case, the odontoblasts break up into medullary corpuscles. DEVELOPMENT OF DEXTIXE, 133 which are directly transformed into the basis-substance of the dentine. The oiFshoots of the odontoblasts, that are seen to run directly into the dentinal canaliculi, appear between the medullary corpuscles as soon as the odontoblasts split up into such corpuscles. The offshoots are formations of living matter seen to emanate from a compact layer at the base and the borders of the odontoblasts. The dentinal fibers remain in situation after the formation of medullary corpuscles, or they are newly formed between the medullary corpuscles, as soon as the dentinal canaliculi are formed. The odontoblasts are not direct dentine-formers, but provisional formations, from which arise the medullary corpuscles, and these are changed into the basis- substance of the dentine. Odontoblasts, therefore, the same as ameloblasts, are provisional formations, and dentine, as well as enamel, originates from medullary corpuscles in the same manner in which all forms of connective tissue are known to arise. It is the rule that the medullary corpuscles are at first trans- formed into a basis-substance, which is as yet destitute of lime- salts. In specimens stained with carmin, this zone of non- calcified dentine assumes a bright red color, in contradistinction to the calcified portion, which either remains unstained or assumes a greenish tint by the reduction of the chromic acid. Another distinction between the non-calcified and the calcified basis-substance is that the latter has a markedly higher degree of refraction than the former. When we examine such a speci- men with high powers of the microscope, we at once become convinced of the identity of the structure of both the non-calci- fied and the calcified dentine. We observe a markedly reticular structure in both, and in many instances fine filaments, emanat- ing from the dentinal fibers, are seen to penetrate the reticulum. At the periphery of ttie dentine, the bifurcations of the dentinal canaliculi and their tenants are always plainly marked. This feature obviously arises from an aggregration of smaller medullary corpuscles than those appearing at a later period of development. At the same time, the reticulum in the basis- substance is more delicate in the region of the bifurcations, and consequently the meshes of the basis-substance appear narrower in the first-formed dentine than in that which is formed at a later period. We sometimes observe, in connection with longi- tudinal sections of dentine, transverse sections which are of great interest. (See Fig. 80, BC.) Here it is seen that the 134 THE ANATOMY AND PATHOLOGY OF THE TEETH. calcification first starts at the periphery of the fields farthest from the dentinal canaliculi. Thus a comparatively coarse net- work of calcified basis-substance is established, in the meshes of which we observe either an uncalcified basis-substance or unchanged protoplasm, whereas the central portions of the Tig. 80. First-Formed Dentine of the Molar Tooth op a Human Fcetus op Six Months. DB, basis-substance of non-calcified dentine ; BL, basis-substance of calcified dentine, both in longitudinal section : I)C, calcified dentine in crois-section. Magnified 1200 diameters. meshes are occupied 1)y the dentinal fibers in transverse or oblique section. The latter appear larger in inverse ratio to the amount of calcareous matter that has been deposited. From their periphery arise the spokes, also seen in fully-devel- DEVELOPMENT OF DEXTIXE. 135 oped dentine, wliieh traverse a light rim — the future canali- culus. The horder of the canaliculus is often marked hy a circular or crescentic formation, possildy the future rim of elastic substance of the dentinal canaliculi. The line of the non-calcified basis-substance forming the l)onndary toward the medullary corpuscles is found to be either straight, stair-like, or slightly wavy. This feature is never observed close to the periphery of the dentine, Ijut always some distance awaj' from it. These wavy contours unquestion- ably correspond to the globular territories of which the basis- substance is composed. Previous researches regarding dissolu- tion of the dentine of temporary teeth, in caries and in the process of e1)urnitis, especially in the latter, have strongly pointed toward the presence of globular territories in the dentine, the same as in l)one-tissue. The history of develop- ment corroborates the presence of such territories, since they are of very common occurrence in developing dentine of man, as well as of diiferent animals. Their origin- is explained in a grouping together of a certain number of medullary corpuscles previous to their transformation into basis-substance. Each glol:)ular territory is pierced by a number of dentinal canaliculi, without the least interruption in their course. We desire to lay special stress .upon the fact that such territories become conspicuous only after calcification of the basis-substance has taken place. Under the theory that tlie odontoblasts are directly transformed into dentine, the formation of globular territories was inexplicable. In morbid processes, we observe the globular territories of the dentine breaking up into a num- ber of medullary corpuscles. The history of development teaches us that each territory arises from a number of smaller corpuscles. Thus the formation, . dissolution, inflammation, and reformation of dentine become plain. Since Czermak has drawn attention to uncalcified fields in the dentine of many teeth, and called them " interglobular spaces," a great deal of speculation has been indulged in to explain this occurrence. Such spaces are never present, as far as the writers have observed, close to the periphery of the den- tine, l:)ut are always found some distance from the lufurcations of the dentinal canaliculi, and sometimes are scattered through- out the dentine. These spaces are filled with a non-calcified basis-substance, or with medullary corpuscles that have not 136 THE ANATOMY AND PATHOLOGY OF THE TEETH. been trant>formed into basis-substanee. We have often observed within these spaces irregular globular territories, invariably marked bv the contours of such territories, but never causing a deviation of the course of the dentinal canaliculi. Fig. 81. GD CD Anomalous Foematiox of Dentine fbom a Human FffiTus of Six Months. r, papilla of the tooth, with a few blood-vessels, and no odontoblasts. The medullary cor- puscles, close below the dentine, are arranged in groups, corresponding to the future territories of the dentine; CI), non-calcified basis-substance of the dentine; D, calcified dentine ; S, 1, 2, and 3, stratifications of the dentine ; GD, ill-calcified basis-substance of the dentine, in con- nection with S'2, composed of globular territories. Magnified oUO diameters. The origin of such interglobular spaces is traceable to the earliest stages of the formation of the dentine. (See Fig. 81.) In exceptional cases even fully-developed dentine will appear composed of layers, or with faint concentrically-arranged marks, DEVELOPMENT OF DENTIXE. 137 traversed without interruption bv the dentinal eanalieuli. Both the stratification and the interglol)uhir spaces are caused by a taulty deposition of lime-salts in the embrvonal development of the dentine. Their cause is probably a temporary interruption of deposition of lime-salts, owing to transient ailments of the mother. These rather anomalous formations of dentine again prove that the basis-substance is made up of globular territories, and these, again, of medullary corpuscles. In the foetus of the cat, the sheep, and the dog, the process Fig. 82. Papilla axd Adjacext Dextixe op Foetus of a Pig. P, myxomatous tissue of the papilla, with irregularly branching corpuscles, and an abun- dance of myxomatous basis-substance ; C, €, capillaries, partly fully formed, and partly in the process of formation ; 0, layer of odontoblasts : J), dentine. Magnified 500 diameters. of the formation of dentine is the same as in man, in all essen- tial features. The same rule holds good for the history of the development of dentine in swine. This dentine, in develop- ment, differs slightly from that of man, mainly in the structure of the papilla. (Fig. 82.) The papilla of the foetus of a pig is composed of irregular, branching, and partly connecting protoplasmic bodies, some- what resembling the stellate reticulum of the enamel-oro-an. 138 THE ANATOMY AND PATHOLOGY OF THE TEETH. These corpuscles are nniforml}' distributed in an abundant mass of basis-substance, which, with lower powers of the micro- scope, appears finely granular. High powers, however, reveal the delicate net-work essential to all the varieties of a myxo- matous basis-substance. This tissue is traversed by a moderate number of blood-vessels, mainly capillaries, which show in some places characteristics of the stages of development from the original solid cords of protoplasm to the vacuolization and ap- pearance of endothelia upon their walls. Toward the periphery of the papilla, spindle-shaped bodies make their appearance. Fig. Fig. 84. Odoxtoblasts, wns Adjacext Dextine, from the Fcetus op a Pig. 0, odontoblasts ; D, dentine. Magnified 1200 diameters. evidently arising (at least to a great extent) from the living matter previously hidden in the myxomatous basis-substance. By an increase in the size of one, or the confluence of several, such spindle-shaped corpuscles, the odontoblasts arise, and they are often seen in contact with the already-formed dentine. Close study of specimens has satisfied us that the odontoblasts do not directly form the basis-substance of the dentine, but here, as well as in men and other animals, are merely transi- tional formations. DEVELOPMEXT OF DEXTINE. 139 111 the condition of rest the odontoblasts oft'er an excellent opportnnit}' to study their relation to the dentine. If they lie against the dentine with a broad basis, four or five offshoots (as represented in Fig. 83) may be seen to enter the adjacent canaliculi, all of which arise from one odontoblast. If, on the contraiy, the odontoblasts terminate, toward the dentine, in a point, a single dentinal fiber will spring therefrom, as repre- sented in Fig. 84. It may also happen that a single odontoblast exhibits no offshoots, in which instance we observe, between the base of the odontoldast and the dentine, delicate filaments which run along the border of the dentine, and from ^^dlich arise the dentinal fibers. The opposite ends of the odontoblasts are, roughly speaking, pointed, and likewise elongated into delicate fibers. These fibers, as well as the lateral portions of the odonto- blasts, are interconnected with all their neighbors by means ot delicate thorn}' offshoots. The results of further researches in this field , as follows, have been published by Frank Abbott : * " The only formations deserving of the term ' cells' are the •odontoblasts, those peculiar, elongated bodies (of a shape and size to remind one of columnar epithelia) usually seen at the periphery of the papilla in developing, and at the periphery of the pulp-tissue in developed teeth. " We know of these peculiar protoplasmic bodies that they send offshoots (the dentinal fibers) upward into the dentine, off'shoots laterally connecting one with another, and other off'shoots down- ward, uniting them with the medullary elements of the papilla. " The first to see and describe all these offshoots was Franz Boll, in 1868, and he was corroborated by Waldeyer, in 1869. Before these offshoots were known, attempts at explaining the formation of dentine were made, first by A. Kolliker, in 1852, in his hand-book of histology. On page 385 he says, ' In the formation of dentine not the whole pulp is concerned, but only its outermost layer of epithelium-like cells, which, by a contin- ual prolongation of the original cells, under a continuous midtipli- cation of the nuclei, apparently keep up the same thickness. " ' I am not willing to maintain that one and the same cell is suflB.cient for the whole duration of the formation of dentine, for I consider it as quite possible that, from time to time, the * " Odontoblasts in their Relation to Developing Dentine.'' Deidal Cosmos, 140 TJ[E AXATOMY AND PATHOLOGY OF THE TEETH. dentine-cells are replaced by others forming at their inner side. What I deny is, that the whole pulp is transformed and ossified from without inward.' " Kolliker, at that time, knew nothing about the presence of dentinal fibers. To explain the formation of the dentinal canali- culi, he, on page 386, discusses the following three possibilities : " 1. The canaliculi are the remnants of the cavities of the den- tinal cells, which, in the process of ossification, become thickened and hardened in their walls, but are not perfectl}' closed. " 2. The canaliculi originate from the nuclei of the dentinal cells, which elongate and coalesce, but retain their central cavities. " 3. The canaliculi are produced by a process of resorption in the previously homogeneous dentinal tissue, in a manner analo- gous to the formation of the Haversian canals, or the canaliculi in the cementum. " Of these three possibilities, Kolliker considered the first as the most probable for the formation of the main canaliculi, and was convinced that the third possibility alone can explain the origin of the fine-branching canaliculi. He distinctly states that no other tissue is concerned in the production of dentine but the cells which later were dubbed odontoblasts, and that these, by a successive taking up of the lime-salts, become dentine. He therefore, as early as 1852, although upholding until then the secretion theory, adopted, and from that time up to date has unswervingly maintained, as regards the formation of dentine, the opposite or transformation theory. About ten years later, he and John Tomes discovered the dentinal fibers, and, with the acknowledged evidence of these fibers within the canaliculi, and their connection with the odontoblasts, the difiiculties in ex- plaining the formation of dentine have considerably increased. '' Are the dentinal fibers remnants of the central portion of the odontoblasts, whose lateral portions become transformed into basis-substance ? Are the dentinal fibers formed between the odontoblasts after the latter have become basis-substance ? So great, indeed, seemed the puzzle, that quite recently R. R. An- drews deemed it advisable to reiterate a previously-expressed opinion of E. Klein and others, that there are two sets of odon- toblasts, some with broad bases which become basis-substance altogether, and others pear- or spindle-shaped, with long pro- jections, which become the dentinal fibers. These latter they termed ' fibril-cells.' DEVELOPMENT OF DENTINE. 141 " It would seem to require a very limited amount of histo- logical or microscopical experience to satisfy oneself of the uu- tenableness of these views, as, with not a very high power, projections may be seen running from every odontoblast into the canaliculi of the formed dentine, some giving off one, some two, some three such projections; while even as many as five offshoots have been seen arising from a very broad end of an odontoblast, and penetrating the canaliculi. The ' fibril-cells,' therefore, are nothing but narrow wedges between broad-based odontoblasts, especially numerous where the periphery of the papilla forms a sharp curvature, as on the pointed cusps. " Several questions, however, require our close attention in the history of the development of dentine. One of these is, Are the odontoblasts absolutely necessary as a stage preliminary to the formation of dentine ? And secondly, how is it that the odontoblasts produce a continuous mass of dentine from the periphery to the pulp, if they are converted into basis-substance in layers ? For we know that the dentine is only in exceptional cases stratified, whereas one would expect such lines of stratifi- cation to be of common occurrence, if one row of odontoblasts after another were to be converted into basis-substance. " As to the first question, we are unable to give a positive answer, but take it for granted that the response should be affirmative, and that the odontoblasts are a prerequisite to the formation of dentine. We often see, at the summit of the papilla, medullary tissue bordering the already-formed dentine without a trace of odontoblasts. Through the researches of John Tomes, we know that the odontoblasts originate in the coalescence of medullary corpuscles of the papillarv tissue; and we know, furthermore, that the odontoblasts again return to the medullary condition before becoming infiltrated with lime-salts. It appears possible that previous odontoblasts have been transformed into medullary tissue, and no new ones pro- duced at that particular period. " To the second question, whether or not the odontoblasts form a single row for the time being, thus involving au interruption in the appearance of the basis-substance of the dentine, a positive answer can be given, in accord with the observations of Kolli- ker in 1852, above quoted. The difference, however, between his views and ours is, in our judgment, sufficiently marked to demand attention. 142 THE ANATOMY AND PATHOLOGY OF THE TEETH. " lie declares that there is hut one row of odontohhists capable of producing dentine, and that these become continuous by a proliferation of the nuclei of the original single row. He dis- tinctly denies that the pulp as a whole can be converted, layer after layer, into odontoblasts. We, on the contrary, agree with John Tomes in the view that the medullary corpuscles of the papillary tissue are progressively converted into odontoblasts, — a view which explains the fact that, with the advancing growth of the dentine, the bulk of the papilla diminishes. We add another point, — viz, that each odontoblast, while being reduced to medullary corpuscles at its distal or jperipheral end, is being added, to by an attachment of medullary coiyuscles of the papillary tissue at its proximal or central end. " Undoubtedly there are periods of comparative rest, in which a fhllv-developed odontoblast borders the dentine, and dips into the papillary tissue with sharply-defined contours, with its nar- row and pointed end. As soon, however, as the building of dentine is resumed, the peripheral end of the odontoblast is seen to have di^uded itself into medullary bodies again, and, simul- taneously, rows of medullary corpuscles are superadded to the opposite or central end. " A beautiful illustration of this process may be seen in the developing tooth of a pig's foetus, ten centimeters long. (See Fig. 85.) Here we see several rows of odontoblasts, bordering the non-calcified portion of the basis-substance of the dentine. At that portion, in which unchanged odontoblasts stand against the dentine, others are attached to the uppermost row, likewise in full development. This we consider as a condition of compar- ative rest. At that portion, on the contrary, in which the odontoblasts are replaced by medullary corpuscles toward the dentine, Avithout a distinct boundary -line between the two, we see rows of medullary corpuscles attached to the inner ends of the odontoblasts, whereby the transverse diameter of the odonto- Idastic layer is noiiceably broadened. In the former instance, the layer of odontoblasts is fairly well marked toward the pap- illary tissue ; in the latter instance it is indistinct, the odonto- blasts blending with the papillary tissue. "■ High powers of the microscope still better illustrate this view. (See Fig. 86.) At the same time it becomes evident that the den- tinal fibers, originally attached to and connected with the odontoblasts, become situated between the medullary corpuscles- DEVELOPMENT OF DENTINE. 143 ±iiG. 85. BO Tooth of a Pig's Fcetus 10 Centimeters Long. B, D, calcified dentine : DC, non-calcified dentine : 0, row of odontoblasts, partly fully formed, partly forming ; M, odontoblasts broken up into medullary corpuscles in the process of forma- tion of dentine ; P, yascularized myxomatous tissue of papilla. Magnified 4i!KJ diameters. 144 THE ANATOMY AND PATHOLOGY OF THE TEETH. Fig. 86. DC^> DM Tooth of a Pig's Ecetus 10 Centimeters Long. />, I>, calcified dentine ; DC, non-calcified dentine ; DM, dentine in the process of formation from medullary corpuscles; 0, odontoblasts in multiple rows, spindle-shaped elements wedged in between the broad odontoblasts ; M, medullary corpuscles arisen from odontoblasts, such corpuscles also attached to the distal ends of the odontoblasts. Magnified 1200 diameters. DEVELOPMENT OF DENTINE. 145 Fig. 87. Tooth of a Humax Fcetus Six Moxths Old. B, D, calcified and stratified dentine : DC, DC, non-calcified dentine, the border of the calci- fied dentine being marked by globular formations : (9, odontoblasts splitting into medullary corpuscles toward the dentine, and showing rows of such corpuscles at the distal ends; M, medullary corpuscles ready for the transformation into basis-substance of dentine; P, P, myxomatous tissue of papilla. Magnified 600 diameters. 11 146 THE ANATOMY AND PATHOLOGY OF THE TEETH. Fig. 88. Tooth op Human Fcetus, Setex Months. D,D. dentine calcified; DC, non-calcified basis-substance of dentine, close above the capil- lary blood-vessels broadened and visibly made up of medullary corpuscles ; C, capillary blood- vessel in transverse and longitudinal section ; M, M, medullary corpuscles ready for infiltration with basis-substance ; MO. MO, medullary corpuscles a,rranged in rows for the formation of odontoblasts. Magnified 1200 diameters. DEVELOPMENT OF DEXTINE. 147 as soon as tlie former are converted into the latter. Wher- ever we notice rows of medullary corpuscles at the inner ends of the odontoblasts, delicate fibrill',e are seen coursing between their rows or groups. Since, according to our views, the myxomatous basis-sub- stance of the papillary tissue is supplied with living matter, the same as are the so-called cells, there is no difficulty in explain- ing the origin of new protoplasmic bodies from tbe previous myxomatous basis-substance, for the benefit of continuous addi- tions to the odontoblasts. The facts just descriljed are well illustrated in the developing teeth of a human foetus from six to seven months old. (See Fig. 87.) The cusp of the dentine shows stratification, although no odontoblasts are seen at the summit of the papilla. At the sides of the cusps, odontoblasts make their appearance, broken up into finely-granular medullary corpuscles, toward the non- calcitied basis-substance of the dentine, and augmented in their bulk by rows of glistening, almost homogeneous, medullary corpuscles, toward the papillary tissue. Occasionally we meet with a basis-substance of. dentine not yet calcified, and still ex- hibiting its composition of medullary corpuscles. (See Fig. 88.) Upon studying this specimen, all doubts as to the origin of the basis-substance of the dentine must vanish. All previous attempts at explaining how the odontoblasts are converted into dentine must prove futile in the face of such a specimen. Although we admit that such a plain instance is only excep- tionally seen, we thought it to be so instructive and so con- vincing that we had an illustration made with a very high power. With the facts advanced, a hitherto mooted question seems to have found solution. As to the question why dentine in all its stages of develop- ment appears to be a continuous mass, and but exceptionally interrupted by marks of stratification, the explanation is that the odontoblasts themselves are continuous. ISTot that the original odontoblasts are preserved and augmented from the periphery toward the center ; but all that is converted of an odontoblast into dentine, at its peripheral portion, is made good by the addition of medullary corpuscles at their central ends or portions, from the tissue of the papilla, — protoplasmic bodies and basis-substance, both. 148 THE ANATOMY AND PATHOLOGY OF THE TEETH. CHAPTER XV. DEVELOPMENT OF THE ENAMEL.* The history of the development of the tissues of the teeth is not intelligible on the basis established by the researches of Remak. According to this oliserver, the epiblast and the hypoblast are epithelial formations, and give rise to epithelial tissues and their derivations only. The mesoblastis connective tissue, including the muscles, the blood-vessels, and the lymph- vessels. Early investigators in embryology were embarrassed in attempting to explain the origin and formation of the central nervous system (brain and spinal cord), which unquestionably has its origin in the epiblast, although in full development it contains a large amount of connective tissue, and blood-vessels,, which are intermixed with nerve-substance proper, such as the gray substance, the ganglionic corpuscles, and the axis-cylin- ders. For that portion of the e})iblast which gives rise to the nerve-centers, some authors have proposed the name " neuro- epithelium." This would imply that trom an original epithe- lial structure, tissues may arise which have no resemblance to epithelia, and do not contain any, except in the ventricular lining of the brain and the central canal of the spinal cord. It is admitted, therefore, that a certain portion of the epithelium of the embryo contains protoplasm, which, in turn, becomes gray substance, forms the ganglionic corpuscles and axis- cylinders, as well as the investment of the latter, — the myelin or nerve-fat, — and the perineurium or neuroglia, which all authorities admit to be a delicate fibrous connective tissue. The history of the development of the enamel likewise furnishes striking proofs of the fact that the theory of exclu- siveness, so tar as the epiblast is concerned, is not tenable. We have demonstrated that the original epithelial cord of the enamel-organ serves for carrving a certain amount of buildino; material into the depth of the connective tissue. This material, however, loses its epithelial nature as soon as it gives rise to the enamel-organ proper, which is myxomatous connective tissue. The fact was established that the tissue termed enamel * " Contributions to the History of Development of the Teeth." By C. Heitz- mann and C. F. "W. Bodecker. The Independejit Pracfitioner, vols, viii and ix. DEVELOPMENT OF THE EXAMEL. 149 is epithelial in its origin only, and that it is changed from its original character ^^hortly hefore becoming enamel proper. We must admit that enamel will not he formed unless upon an epithelial basis, the epithelium in this instance being the conveyer of the protoplasm from which enamel originates. But to assert that enamel is an epithelial structure throughout, wi 'uld be as erroneous as to call the brain and the spinal cord epithelial structures. From an organo-genetic point of view, we may say that the outer senses of the animal organism, serving for perceptions from the outer world, are formations of the outer investment of the animal, its epiblast. The brain, being the most highly perfected organ of sensual perception, continuously takes its growth from the epiblast. The same may be said of the teeth. Fig. 89. Human Embryo Six Weeks Old. Fhoxtal Sectiox. T, tongue ; L, lip ; B, base of oral cavity : F, furrow, in transverse section, funnel-shaped. Magnified 25 diameters. which, in some lower order of amphibious organisms, such as Chelonia, are nothing Init horny ledges, or a thickening of the epithelium. Even at the height of development their growth is continuous from the epiblast, and they are, at least as far as the enamel is concerned, derivations from it. Let us now consider the direction taken by the epithelial cord of the enamel-organ into the depth of the connective tissue, up to the time when the enamel-organ is ready for the formation of the enamel. The first trace of the future tooth in the human embryo is visible about the sixth week of intra- uterine life, when the epithelium of the oral cavity is as yet little developed. Here we notice a furrow, which is situated close behind the lip, and is succeeded by an elevation of medul- lary tissue. (See Fig. 89.) 150 THE ANATOMY AND PATHOLOGY OF THE TEETH. After this period follows the formation of an epithelial peg, appearing not at the bottom of the primitive dental furrow, but at some distance from the latter. This peg appears as a reduplication of the epithelial layer covering the elevation behind the furrow. (See Fig. 90.) Shortly afterward, the epithelial hill has gained in height considerably, and from the point which connects the hill with Fig. 90. Base of Oral Cavity op Human Embryo Two Months Old. Feontal Section. T, tongue ; L, lip ; B, base of oral cavity ; F, furrow ; EH, epithelial hill ; EP, epithelial peg. Magnified 25 diameters. Fig. 91. o Base op Oral Cavity op Human Embryo Two and a Half Months Old. Frontal Section. EH, epithelial hill ; 0, epithelial lining of base of oral cavity ; F, furrow ; EC, epithelial cord of enamel-organ ; EO, club-shaped enlargement of the epithelial cord, the future enamel- organ. Magnified 25 diameters. the rest of the oral epithelium, the original peg has elongated into an epithelial cord. A striking feature of this cord is that from its periphery arise blunt or slightly-pointed offshoots, while at the same time its distal end is noticeably broadened, the epithelia being arranged in radiating tracts throughout, but most markedly in the club-shaped enlargement of the distal end. (See Fig. 91.) DEVELOPMENT OF THE EXAMEL. 151 In the third month of embryonal life, the epithelial hill still remains a prominent formation. From the point of its junc- tion with the other epithelium arises the epithelial cord, which varies, to some extent, both in width and in its course. Some- times the cord runs nearly parallel with the base of the oral cavity, becoming devious on the way to its club-shaped distal end. Its periphery is slightly fluted, and from its lower contour arise scanty but strongly-marked epithelial oftshoots, the signi- ficance of which is not perfectly plain. "We may assume that a large secondary oftshoot forms the epithelial cord of a future permanent tooth, but as to the significance of the short second- ary oftshoots we can only suggest that the epithelium primarily Fig. 92. Base of Oral Cavity of a Humax Embryo Three Months Old. £3. epithelial hill : F, furrow, sharply marked and lined by a heavy layer of flat epithelium ; 0, base of oral cavity ; EC, epithelial cord ; £0, club-shaped end of the epithelial cord, the future enamel-organ ; S, secondary oflfshoot ; SP, secondary offshoot, possibly a germ of the permanent tooth ; P, papilla. Magnified 25 diameters. producing the cord at first assumed a direction which afterward was changed. This much is certain, that such short secondary offshoots perish and disappear in the course of farther develop- ment. It woidd certainly be a bold hypothesis to consider all such short secondary oftshoots germs of supernumerary teeth, or of third dentitions. They are too common as compared with the rare cases in which supernumerary teeth are found. At this stage of development the first trace of the papilla (the future dentine) is noticeable. (See Fig. 92.) Sometimes the epithelial cord is broad, exhibiting compara- tively few blunt secondary ofiishoots. Its course is more or less 152 THE ANATOMY AND PATHOLOGY OF THE TEETH. vertical, into the depth of the connective tissue of the jaw. The epithelium within the cord is arranged into groups sepa- rated by trabeculae somewhat resembling those of true myxoma- tous connective tissue. The club-shaped end of such a cord at this period shows a slight separation of the columnar epithelium into an outer and an inner layer, whereas the center of the club- shaped enlargement is occupied by medullary corpuscles, which as yet do not exhibit the characters of a myxomatous reticulum. Unquestionably, tliis medullary tissue has arisen from epithelia, which originally filled the club-shaped end of the cord, and it is Fig. 93. Floor of Oral Cavity of a Human' Embryo Three Months Old. EH, epithelial hill ; F, furrow; 0, oral epithelium ; EC, epithelial cord : S, short secondary oflfshoot; EO, medullary tissue of enamel-organ; P, papilla, detached. Magnified 25 diameters. this medullary tissue from which, soon afterward, the myxoma- tous reticulum of the enamel-organ proper originates. (See Fig. 93.) We found an epithelial cord of a three-months' embryo pre- senting points of interest, since it showed e^ddences of the germ of a temporary molar. A short offshoot arose at the place of origin of the epithelial cord, while the latter made a few shallow convolutions and then abruptly turned downward in a direction almost at right angles to its former course. At the place of the turn a broad epithelial laj^er was per- ceptible, showing the rather thin epithelial tracts before alluded DEVELOPMENT OF THE EXAMEL, 153 to, and in part, toward the adjacent mednllary tissue, indis- tinctly bordered. Tlie club-shaped end of the epithelial cord was divided into two segments by an intervening deep fissure. The broadest segment, again, showed blunt protuberances, to which corresponded shallow hills of the subjacent papilla. The club admitted of an indistinct differentiation into an ex- ternal and internal epithelium, whereas its center exhibited a few faint tracts of epithelia and a large amount of medullary tissue, which as yet had nowhere begun the formation of a myxomatous reticulum. (See Fig. 94.) When the embryo has reached about the fourteenth week, Pig. 94. Base of Deal Cavity of a Humax Embryo Threk Months Old. £'£r, epithelial hill; /'.furrow: 0, oral epithelium: EC, epithelial cord of enamel-organ; -S', short secondary offshoot ; SP, broad secondary offshoot, possibly the germ of a permanent molar; EO, dub of the epithelial cord filled with medullary tissue (the future enamel-organ) ; P, papilla. Magnified 25 diameters. the epithelial cord is of special interest, on account of the ap- pearance of two distinct layers at its distal end, the internal and the external epithelium, between which the myxomatous enamel-organ makes its appearance. The papilla, at this point of development, has a distinct neck, being of a mushroom shape. At its distal periphery it is bordered by a thin layer of fibrous connective tissue extending upward along the external epithelium to a certain height, and producing what has been termed the follicle, or tooth-sac. In one of our specimens the epithelial cord emanates with a broad base from the epithelial 164 THE AXATOMY AND PATHOLOGY OF THE TEETH. liill, having at this point several short and bkmt oiishoots directed downward. Its general course is almost parallel to the floor of the mouth. The enamel-organ originates from its distal end in an abrupt rectangular manner, with a somewhat narrow neck. The external epithelium extends into a solid peg, with a slight sigmoidal curvature, obviously the germ of the future permanent tooth. (See Fig. 95.) In another specimen of the same period, the epithelial cord arises from the base of the epithelial hill, with a narrow neck, in immediate connection with a solid epithelial peg, running a downward vertical course, with a slight sigmoidal curvature. The epithelial cord itself shows blunt offshoots upward as well as downward, the former being characterized by a distinct con- centric arrangement of their epithelia. The general course of Fig. 95. Base of Oral Cavity of a Human Embeyo Three and a Half Months Old. EH, epithelial hill : 0, oral epithelium ; EC, epithelial cord ; SP, secondary offshoot of a permanent tooth, arising from the external epithelium of the enamel-organ ; EO, enamel- organ of a distinctly myxomatous character ; P, papilla ; F, follicle. Magnified 25 diameters. the epithelial cord is slightly downward. Its cup-shaped distal end is marked, by three prolongations, the concavities of which correspond to two myrtle-leaf-shaped papillae. Evidently, this is the germ of a future temporary molar. No trace of a corre- sponding permanent tooth was visible at the distal end of the epithelial cord. The external epithelium is very broad, and visible only along the broad cup. The enamel-organ is narrow,, but possesses a pronounced mjTfomatous structure. (See Fig. 96.) The fourth month of embryonal life differs from the previous stage only as the myxomatous enamel-organ gains considerably in volume, with a simultaneously-marked differentiation into its two boundary layers, the external and the internal epithe- lium. The papilla, at this stage, likewise, has gained in bulk^ developme^:t of the enamel. 155 and its enveloping layer of fibrous connective tissue extends farther up along the convexity of the cup of the enamel-organ. In one of the specimens, the epithelial hill is extremely marked, and contains a central vacuole, possibly the first step toward its destruction, since shortly afterward no trace of it is found. Tig. 96. Floor of Oral Cayitt of a Hdiax Embryo Three and a Half Months Old. EH, epithelial hill : 0, oral epithelium ; EC, epithelial cord of enamel-organ ; SP, second- ary offshoot, possibly the germ of the permanent tooth ; EO, enamel-organ ; P^ and P^, double papilla ; F, follicle. Magnified 25 diameters. Fig. 97. Floor of Oral Catity of a Human Embryo Four Months Old. EH, epithelial hill ; 0, oral epithelium ; EC, epithelial cord with numerous offshoots ; SP, secondary peg of permanent tooth ; EO, myxomatous enamel-organ : P, papilla : F, follicle . Magnified 25 diameters. The epithelial cord begins with a narrow neck, and has numer- ous oblique secondary offshoots, mainly at its upper periphery. The arrangement of the epithelia into tracts is marked along the epithelial cord, not only of the temporary but also of the permanent tooth. (See Fig. 97.) 156 THE ANATOMY AND PATHOLOGY OF THE TEETH. In another specimen of the same age, the epithelial hill is absent. The cord has but a limited number of offshoots, some of which are pediculated, and some have the shape of a lancet. The peg of the permanent tooth is conspicuous by its devious course, (See Fig. 98.) When the embryo is at the age of four and a half months, the development of the enamel-organ has still further pro- ceeded: its myxomatous tissue is plainly marked, and the papilla has correspondingl}' gained in bulk. The specimen illustrated is noteworthy for its short vertical epithelial cord, which is directly in connection with the lining epithelium of the oral cavity. The secondary offshoots are but short, and no trace of a peg for the permanent tooth is visible in this section. The cup of the enamel-organ is lobulated, evidently belonging to a future molar. (See Fig. 99.) The next question to be considered is, How does epithelium grow from an originall}' small point into a comparatively long epithelial cord ? Most observers agree that epithelium has an independent growth, and that its elements by division and multiplication will produce epithelium, and no other tissue. During the last fourteen years many microscopists have studied the so-called indirect division of " individual cells," which became traceable after the application of certain reagents, especially safranine. This dye rendered visible a filamentous structure in the nucleus, apparently independent of the sur- rounding protoplasm, which did not take up the stain of the safranine. The filaments produced beautiful star-shaped figures, with equatorial divisions leading to a fission of the original nucleus, and the process has been termed Jiaryokinesis or mitosis. In fresh specimens, or those preserved in a chromic-acid solu- tion, the filamentous structure of the nucleus does not exist, or, at least, is not plainly visible, although Bizzozero, of Italy, <3laimed that safranine will bring out the filamentous structure of the nucleus even in chromic-acid specimens. The filaments taking up the dye were termed chromatin, and all those remain- ing pale, achromatin; and it was claimed that these were two different substances. Considering the fact that the filaments are produced only by certain reagents, we should be loth to assume that the structure thus rendered visible really corre- sponds to the unstained and living epithelium. The doubts become still stronger, if we recall the fact that living matter is DEVELOPMENT OF THE EXAMEL. Fig. 98. 157 Floor of Oral Cavity of a Human Embryo Four Months Old. 0, oral epithelium ; EG, epithelial cord ; S, short pediculated offshoot ; 5,5, secondary off- shoot, lancet-shaped ; SP, secondary peg of permanent tooth : EO, enamel-organ ; P, papilla ;. F, follicle. Magnified 25 diameters. Fig. 99. Examel-Orgax and Papilla of Human Embryo Four and a Half Months Old. 0, oral epithelium : EC, short epithelial cord ; S, secondary offshoot ; EO, enamel-organ : P, papilla ; F, follicle. Magnified 25 diameters. 158 THE AXATOMY AND PATHOLOGY OF THE TEETH. stained deeply bj the same reagent, if present in a compact mass, where thin layers of it remain unstained, as is the case in the protoplasm which surrounds the central nucleus. From this point of view the terms chromatin and achromatin be- come superfluous, especially if we admit that the living matter during life is in constant motion, particularly in the process ot growth, although its continuity may temporarily be interrupted. "V^^hat we see in a growing epithelial cord, with high powers of the microscope, is depicted in Fig. 100. Fig. 100. Epithelial Cord of the Examel-Orgax of a Human Embryo Three and a Half Months Old. E, epithelial cord ; C, connective tissue. Magnified 800 diameters. We observe epithelia along the borders of the cord which are elongated and bear the name of columnar epithelium ; while the central portion is tilled with epithelia which exhibit about an ecjual diameter in all, directions, and are termed cuboidal. Both varieties show difterences in the size and structure of their nuclei. Some nuclei are very large and distinctly reticu- lar, others are small and nearly compact, often appearing as if split up into several lumps, with a vacuole or plasmatic space. Sometimes a nucleus is elongated or irregular in shape, another DEVELOPMENT OF THE EXAMEL. 159 T)eing globular or vesicular. Again, we see epithelia much en- larged, holding in their interior several nuclei. An epithelium in this condition has been termed by previous observers " the mother cell." i^ot infrequently we observe solid, spindle-shaped bodies in the cement-substance, between two epithelia. All these forms become intelligible only under the assumption that epithelium is composed of proto[>lasm, in which the living- matter greatly varies in size and shape, according to the state of growth and new formation. The cement-substance is often absent, and thus large protoplasmic masses become conspicuous, TV'ith a varying number of nuclei. Where the cement-substance is present, it is usually traversed by radiating lines, which are the connecting bridges of the living matter. Again, these lines may coalesce into solid masses, presenting spindle, pear, or club shapes, from which new epithelia arise, as shown by Louis Elsberg. The way, therefore, in which epithelium grows is by the augmentation of its living matter, and the appearance of new cement-substance, — that is, new lines of demarcation, in which process the continuity of the living matter, though temporarily interrupted in certain foci, in the whole remains preserved and unbroken. In the epithelial cord of the enamel-organ the connecting spokes in the cement-substance are prominently marked in all its layers and stages of development. We now proceed to consider the changes of the enamel-organ about the beginning of the fifth month. If we examine the cup-shaped enlargement of the enamel-organ at this period, we observe a distinctly-marked border composed of columnar epi- thelia, whereas the interior of the cup is filled with medullary corpuscles, which, in the center, present the so-called stellate reticulum. At the end of the fourth and the beginning of the fifth month, we invariably find some epithelial cords, which, at their interior ends, are broadened and contain a distinctly marked stellate reticulum. (Fig. 101.) The first question to be entered into is, Whence comes the myxomatous tissue known as the stellate reticulum in the inte- rior of the cup ? According to our present knowledge of the tissues of the mammalian organism, we are entitled to call the stellate reticulum a myxomatous tissue, which is a variety of connective tissue. This tissue occurs most extensively in the embrvonal organism, and remains throuo^hout life in the fullv- 160 THE AXATO.MY AXD PATHOLOGY OF THE TEETH. developed body only in a limited number of organs, sncli as the Xmlp of a tooth, the hinph-ganglia, and the so-called adenoid tissue, which properly ought to be called lymph-tissue, and is- Fig. 101. EE Epithelial Cord terminatin-g ix the Examel-Orgax. Human Embryo at the End of THE Fourth or the Begixxixg of the Fifth Month of Intea-Uteeine Life. 0, stratified epithelium of the oral cavity; TT, epithelial cord of temporary tooth; PT, epithelial cord of permanent tooth ; N, epithelial nests and buds at the bottom of the furrow and along the cords of both the temporary and permanent teeth ; .1/, myxomatous tissue of the enamel-organ (stellate reticulum); EE, external i outer) epithelium; IE, internal (inner) epithelium ; /, intermediate layer between inner epithelium and myxomatous tissue ; P, papilla with numerous blood-vessels : E, embryonal or medullary tissue crowded with medullary cor- puscles at a certain distance from the epithelial formation. Magnified 50 diameters. DEVELOP.MEXT OF THE EXAMEL. 161 distributed througiiont the mucous membranes, especially during the early periods of life. Unless we assume that the enamel-organ is a tissue entirely different from all others enter- ing into the structure of the body, we must call it myxomatous connective tissue. Those who adhere strictly to the teachings of Thiersch and Waldeyer will l)e loth to admit that epithelium can ever change into connective tissue. Researches thus far, however, have led us to the conviction that such a transformation is by no means impossible. The thyroid gland, for instance, is originally com- posed of alveoli lined by epithelia. Shortly after birth, how- ever, the epithelium is replaced by a medullary or lymph- tissue. The whole central nervous system (the brain and spinal cord) originates from the embryonal epiblast, which is strictly epithelial in nature. ^Nevertheless, nobody will maintain that the central nervous system, so richly supplied with blood-ves- sels, is an epithelial structure, except in the lining of the ven- tricles of the brain, and the central canal of the spinal cord. There may be advocates of the exclusive nature of epithelial tissue who might think of an immigration of medullary cor- puscles between the epithelia of the enamel-organ for the bene- fit of the formation of the stellate reticulum, but there is not the least indication of such a process in any of our specimens. On the contrary, we can prove a gradual transformation of the epithelia into myxomatous tissue. In the third month of intra-uterine life, we observe, inside of the epithelial cup of the enamel-organ, a zone entirely occu- pied by medullary corpuscles, and even in the fourth and fifth months such a gradual transition is distinctly traceal)le (Fig. 102). Those who still adhere to the cell doctrine will never l:)e al)le to understand how medullary tissue arises ti'om epithelia. Ac- cording to our views, however, there exist no individual cells, but layers of protoplasm, in which the living matter is dis- tributed in a reticular arrangement. Every particle of the li^^ng matter is able to grow from the size of a minute granule to that of a solid lump, in which afterward takes place a dif- ferentiation into a peripheral protoplasm containing compara- tively little living matter, and a central body, termed nucleus, with a larger amount of li^ing matter. The inner epithelia, at the period mentioned above, exhibit augmented nuclei and small glistening'granules near the fold, 12 162 THE ANATOMY AND PATHOLOGY OF THE TEETH. Fig. 102. EE EM Lower Edge of the Cup of the Exajiel-Orgax, showing the Recurvation of the- External into the Internal Epithelium, at the End of the Fourth Month of Ixtra-Uterine Life. EM, embryonal or medullary tissue ; EE, external epithelium, composed of cuboidal epi- thelia ; T, cuboidal epithelia turning into columnar epithelia : IE. inner epithelium breaking- down into medullary tissue and giving rise to the spindles composing the intermediate layer, close above the internal epithelium : M, myxomatous tissue, or stellate reticulum, bounded toward the external and internal epithelium by the intermediate layer, and continuous with the- medullary tissue filling the border of the cup ; P, papilla. Magnified 500 diameters. Fig. 103. Inner Epithelium or the Enamel-Organ of a Human Embryo of Four Months of Intra-Uterine Life. E, inner epithelia connected with each other by delicate thorns, traversing the cement-sub- stance. In their interior vacuoled lumps are seen of greatly varying sizes, which toward the enamel-organ are split up into smaller reticulated corpuscles, all being interconnected by deli- cate offshoots ; /.intermediate layer composed of spindle-shaped medullary corpuscles; M,. beginning formation of the myxomatous reticulum, in the meshes of which we observe nucle- ated protoplasm. Magnified 1200 diameters. DEVELOPMENT OF THE EXAMEL, 163 corresponding in position to the neek of the fntnre tooth. The more we turn to the center of the cup, the more shall we be struck by the presence of glistening homogeneous lumps in the epithelia, until we have reached the center of the cup, where we observe that epithelium has been transformed into a number of such lumps in a regular arrangement, which reminds us of their origin from previous epithelia. The original epithelia gradually become enlarged, and at last are split up into a number of medullary corpuscles. As a rule, this process of transformation is most marked in the original epithelia at the portion directed toward the stellate reticulum, whereas, in that portion nearest the papilla, the epithelial character ma}^ still be preserved, (Fig. 103.) The medullary corpuscles first assuming a spindle shape, constitute the intermediate layer {stratum i/itermediu/n). The innermost spindles are in connection with a comparatively coarse net-work, representing the first trace of the stellate re- ticulum. The trabeculsB of this reticulum are composed of solid or vacuoled spindles, inclosing spaces which appear to be filled with a distinctly reticulated protoplasm, holding central nuclei. The latter exhibit a varying number of coarser gran- ules, the so-called nucleoli. Xot infrequently the intermediate layer is missing, which fact affords the best opportunity for observing the gradual transition of the homogeneous globules arising from the epi- thelia into nucleated protoplasmic bodies, and finally into the myxomatous reticulum. Changes similar to those described take place in the central portions of the external epithelia, and, as it seems, even precede the changes of the inner epithelia. Thus the original columnar bodies of the outer epithelium are reduced to a row of cuboidal epithelia, as seen in Fig, 102, ^E. The medullary corpuscles are slightly enlarged ; their nuclei, at first plainly visible, are likewise split up into a delicate re- ticulum, and both become infiltrated with a myxomatous basis- substance. The peripheral portions of the original medullary corpuscles, on the contrary, are solidified into nucleated forma- tions of living matter, representing the stellate reticulum proper. The meshes of the myxomatous tissue in the stellate reticulum are originally small, and correspond in size to the medullary corpuscles, from which they arose. The corpuscles of the stellate reticulum are mostly solid. ater, several medullary 164 THE ANATOMY AND PATHOLOGY OF THE TEETH. corpuscles are required for tlie formation of a large field of basis-substance. The original stellate reticulum, in this view, must fall back to an embryonal or medullary tissue before changing into a more perfect myxomatous tissue, such as we observe from the end of the fifth month of foetal life up to the full development of the enamel. (Fig. 104.) Toward the end of the fourth and the beginning of the fifth month, the stellate reticulum is composed of nucleated proto- plasmic bodies, with a varj-ing number of branching and inter- connecting offshoots. With low powers of the microscope, the basis-substance in the meshes, inclosed l)y the corpuscles and Tig. 104. Stellate Reticulum, or Myxomatous Tissue, of the Enamel-Organ of a Human Foetus of Five Months of Intra-Uterine Life. Magnified 1200 diameters. their offshoots, appears to be homogeneous and structureless. The highest powers, however, reveal in this basis-substance the presence of a delicate reticular structure, even without the addition of any reagent. This structure has arisen by a direct transformation of the original medullary corpuscles into basis- substance. In the highest development of the stellate reticulum, such as seen in the seventh and eighth months of foetal life, the nucleated corpuscles are more slender, and the reticulum is com- posed mainly of delicate branching and interconnecting fibers. The further changes of the external epithelium are of con- DEVELOPMENT OF THE EXAMEL. 165 siderable interest. While about the fourth month of intra- uterine life the inner portions of the external epithelium are, as mentioned above, transformed into medullary tissue and participate in the formation of the myxomatous enamel-organ, a single row of cul)oidal epithclia is left. From the remains of Fi< 105 Budding of the Extern i.L Epithjlium f the E\ -imel Ortw of i Human F(etus Seven Momhs Old. M, myxomatous reticulum of the enamel-orgm ; C, delicate fibrous connective tissue : E, epithelial bud arisen from the external epithelium; P, large protoplasmic body filled with glistening coarse granules ; B, newly-formed blood-vessel. Magnified 500 diameters. this external epithelium, a new growth takes place, of a markedly centrifugal character. By a multiplication of the epithelial elements, solid buds and knobs are formed, well known to pre- vious observers. (Fig. 105.) 166 THE ANATOMY AND PATHOLOGY OF THE TEETH. The^se l)uds are at first in continuity with the external epithe- lium, and have a distinct layer of outer columnar and a varying number of inner layers of cuhoidal epithelia. They are characterized by a brownish color, common to all epithelial formations. "We observe that, both in the central portions of these buds and along the original row of the external epithe- lium, a transformation takes place into medullary corpuscles, the same as we observe toward the myxomatous enamel-organ. This medullary tissue develops into connective tissue of a decidedly fibrous character. Thus we oliserve numerous inter- ruptions in the external epithelium, partly filled with medul- lary and partly with fibrous connective tissue. The latter is in direct connection with the myxomatous reticulum, or this con- nection is established by spindle-shaped corpuscles, resembling those of the intermediate layer close above the internal epithe- lium. At the time when the buds sprout from the external epithe- lium, an active new formation of blood-vessels and blood- corpuscles takes place in the immediate vicinity of the buds. At first we notice large protoplasmic bodies with coarse gran- ules, which were known to Theodore Schwann, in 1839, by the name of blood-cells. With the increase of the size of tliese bodies, the granules likcAvise become coarser, and assume the properties of the so-called haematoblasts. Tliese grow up to the size of red blood-corpuscles, and we not infrequently en- counter in the bays between the buds, groups of h^ematoblasts, or fully-developed blood-corpuscles, apparently isolated and in no connection with blood-vessels. At last, capillary l)lood- vessels arise from the conference of blood-cells, which are filled with red blood-corpuscles. The splitting of the external epithe- lium into isolated buds and nests of an epithelial character is especially marked near the neck of the future tooth. (Fig. 106.) At this place the amount of myxomatous enamel-organ in a seven-months foetus is usualh* small, since' a great quantity of it has already been transformed into enamel-tissue. But even here a few small and isolated epithelial nests are seen, sur- rounded by a large numljer of capillary blood-vessels, filled with blood-corpuscles. It is evident that all these blood-vessels are newly formed, and indeed we can trace the formation of blood-vessels in this situation step by step. Even the myxo- matous trabeculse of the enamel-organ participate in the forma- DEVELOPMENT OF THE ENAMEL. 167 tioii of capillaiy blood-vessels. "We liave seen closed spaces, or vesicles, sprung from the basis-substance of the myxomatous tissue, filled with liaematoblasts and red blood-corpuscles, partly in connection with already-formed or forming capillaries, ^o Fig. 106. I-BV LE LE Isolated EpiiHELiii Nests, of the Plvce or the Ewmel Oec a_\ c rrespondixg to THE Neck cf the Fiture Tioth of a Hlman Fcetls Se^e\ M nths Old. M, my.xomatous reticulum of the enamel-organ ; J., row of ameloblasts ; /, intermediatelayer composed of spindles and fibers ; B, vesicle filled with haematoblasts and red blood-corpuscles ; V, capillary blood-vessel forming from trabecular of the myxomatous reticulum : B V, irregular spaces filled irith ha?matoblasts and red blood-corpuscles, lined by endothelia and in an incom- plete connection with forming capillaries ; EE, epithelial nests, the remnants of the external epithelium. Magnified 500 diameters. doubt the living matter inclosed in tire basis-substance has grown into hsematoblasts. This process is indicated by the appearance either of coarsely-granular or of compact glistening nuclei in the meshes of mvxomatous reticulum. 168 THE ANATOMY AND PATHOLOGY OF THE TEETH. Wherever we observe epithelial nests, they are invariably enlarged, toward the enamel-organ, by spindles and fibers of an intermediate layer. Their scarcity and diminutiveness at the place corresponding to the neck of the tooth indicate that they are completelv transformed into mednllary tissue. Con- sidering the fact that at the end of the intra-uterine develop- ment the enamel-organ is nearly exhausted, and the enamel which is formed up to that time is comparatively thin, there is good reason for the assumption that the medullary tissue Dissolution of Epithelial Cord of the Examel-Orgax into Isolated Clusters of a HuMAX Fcetus Five Months Old. Horizontal Section. C, fibrous connective tissue with scanty blood-vessels ; iV, epithelial nest composed of large, flat, almost epidermal-like scales, producing onion-like layers around the central group ; this nest is surrounded by tracts composed of cuboidal epithelium ; E, clusters of cuboidal epi- thelia holding concentrically arranged epithelial nests ; R, remnants of epithelia transformed into clusters of medullary corpuscles. Magnified 100 diameters. Sprung from the previous external epithelium is the source for the completion of such enamel as we observe upon temporary teeth when they emerge from their sockets. Of special interest are concentrically stratified globular nests and buds, in which the epithelia appear flattened and arranged in the shape of an onion. Such nests are often lacking alto- gether, and sometimes they are present in small numbers in the center or at the periphery of the epithelial cord. Some- DEVELOPMENT OF THE EXAMEL. 169 times their number is very large. The centers of the nests are occasionally filled with globules of high refraction, possibly colloid material or eleidin (horn tat). In some specimens the Fig. 108. FiKST-FoRMED Dentii^k axd Enamel of Humax FffiTus, Sevex Months. E. enamel-cap ; D, calcified dentinal cap ; DD, non-calcified dentine ; 0, row of odontoblasts ; P, papilla, with blood-vessels ; M, stellate reticulum of enamel-organ ; IE, inner epithelium ; EE, clusters of the remains of the outer epithelium ; C, fibrous connective tissue. Magnified 50 diameters. epithelial structure of the peg is little marked, especially in places where the epithelial peg produces broadened layers, with- out sharp contours toward the surrounding connective tissue. 170 THE ANATOMY AND PATHOLOGY OF THE TEETH. In such places tracts are seen composed of ro^vs of solid nuclei, or solid cords, Itetween which line granular protoplasm is visi- ble. Such tracts have been repeatedly alluded to in the descrip- tion of the early forms of development of the epithelial cord of the enamel-organ. It is quite possible that in such places a transition takes place from the epithelial to the medullary, and from this to connective tissue. This is rendered probable by the fact that the broadened portions of the epithelial cord have sharp contours only on one side, whereas the opposite peripher}^ almost blends with the adjacent connective tissue, without a distinct line of demarcation l)etween the two kinds. While we admit that the original epithelial peg and cord are of a marked epithelial structure, at the same time Ave claim that in the advancing process of growth the epithelium does not retain its speciiic structure, but l)lends with or is transformed into connec- tive tissue. (See Fig. 107.) The formation of enamel commences about the sixth month of foetal life, at a period when the dentine, which begins to form about the tifth month, has assumed a certain thickness. About the seventh month, we observe at the summit of the papilla a comparatively broad cap, the dentine, and above this a some- what narrower layer of enameL (Fig. 108.) Investigations of the development of enamel are rendered difficult by the fact that the enamel-organ is almost invariably found to be detached from the enamel and the papilla. This perplexity may be obviated, at least to a certain extent, by fill- ing the cavity between the enamel-organ and the enamel with cilloidin. The cavity or space is evidently the result of shrink- age of the delicate myxomatous tissue in the enamel-organ. A peculiar asymmetry is often met with, one side l^eing very broad and the other very narrow. Peculiar indentations, also, are often seen in the course of the inner epithelium. Whether or not all of this is artiiicial, and due to shrinkage, we are unable to state, but it is certain that as soon as the enamel begins to appear there are marked differences in the structure of the inner epithelium. At the bottom of the enamel-organ, corre- sponding to the future neck of the tooth, the inner epithelium is found to l)e transformed into medullary tissue, and the edge between the inner and outer epithelium is likewise filled with medullary tissue. Higher up, along the border of the papilla, where there is as vet no enamel, we find formations that DEVELOPMEXT OF THE EXAMEL. 171 resemble the original epithelia, but which iu this condition are termed ameloblasts. The intermediate layer, in connection with the ameloblasts in this stage, is alwa^'s markedly devel- oped. Still higher up, where ready-formed enamel is present, the ameloblasts are much less regular, and we observe that they again split up into medullary corpuscles. From this we draw the conclusion that the original inner epithelium is trans- formed into medullary corpuscles, which give rise to the amelo- blasts, and that the latter, before being transformed into enamel, once more break up into medullar}' tissue. In a specimen prepared from a human foetus of five months, there is scarcely a trace of the inner epithelium left : we see nothing of that tissue except a succession of small glistening medullary corpuscles, which, by their arrangement in rows, remind us of their origin from previous epithelia. This tissue remains plainly visible even in the sixth and seventh months of foetal life, especially, as mentioned above, at the fold correspond- ing to the edge of the enamel-organ in the region of the future neck of the tooth. Higher up, the medullary corpuscles, which previously were scattered, once more assume a line-like arrange- ment, and gradually take the shape of narrow elongated cor- puscles, not always distinctly nucleated, and these elongated bodies, somewhat resembling the original columnar epithelia, are termed ameloblasts. (Fig. 109.) One of the striking features in this process of transformation is the presence of a layer forming the outermost portion of the enamel-organ toward the papilla (Fig. 109, P). This layer, with low powers of the microscope, appears to be made up of finely-granular protoplasm with interspersed granular nuclei. Above this, marks of division appear in the protoplasmic layer, and the marks correspond to the boundary lines of the rows of the glistening medullary corpuscles, the forerunners of the future ameloblasts. There is a transitional stage, as referred to In Fig. 109, in which the inner portions of the ameloblasts are made up of several glistening medullary corpuscles, whereas the outermost portion is finely granular, or made up of a deli- cate reticulum. The ameloblasts in the seventh month of foetal life are distinctly-marked formations, and are present only on places where enamel has not yet been formed. They are in junction, side by side, from the region of the neck to the sum- mit of the crown. They are composed of finely-granular pro- 172 THE AXATOMY AND PATHOLOGY OF THE TEETH. toplasm, Avitli one or several nuclei, or sometimes without any distinct nucleus. Their general form is columnar, slightly broadened toward the papilla. Often, however, they exhibit parallel contours, or a wedge-shape, between two neighboring Fig. 109. Segment near the Fold of the Enamel-organ, corresponding to the Neck of the Future Tooth of a Human Fcetus of the Seventh Month. PP, papilla; 5*, stellate reticulum in an early stage of development ; 31, medullary corpuscles in a nearly uniform distribution, becoming elongated higher up, and arranged in rows; A, ameloblasts at an early stage of formation, composed of medullary corpuscles ; P, protoplasmic bodies producing the outermost portion of the enamel-organ. Magnified 1200 diameters. funnel-shaped ameloblasts (see Fig. 106, A). All ameloblasts are interconnected by delicate conical threads traversing the light interstices between them. Their layer is easily distin- DEVELOPMENT OF THE EXAMEL 173 guislied from the stellate retic-uluni hy the intermediate layer, which is composed of spindles and libers. From their Ijases delicate short ofishoots often emanate (Tomes's processes), which, however, do not exhibit any regnlar arrangement. Where the layer of ameloblasts is detached from the surface of the papilla, similar short processes emanate from the surface of the latter, and it is obvious that all these fine oftshoots serve for an inter- connection between the ameloblasts and the medullary cor- puscles of the papilla. Fig. 110. EiRST-EOEMED EXAMEL OF A HuMAX FcETUS OF SiX Mo.XTHS. B, dentine bounded toward the enamel by bay-like excavations ; E, enamel composed of prismatic pieces ; -1, rows of medullary corpuscles sprung from previous ameloblasts. Magni- fied 1000 diameters. Still nearer the summit of the crown the ameloblasts once more lose their character, and once jiiore break up into medul- lary corpuscles, more or less retaining their row-like arrange- ment. We observe that the medullary corpuscles which lie nearest to the already-formed dentine are finely granular, whereas the rows some distance above are coarsely granular or homogeneous. These finely-granular medullary corpuscles are at last infiltrated with lime-salts, and thus is produced the enamel proper. (Fig. 110.) 174 THE ANATOMY AND PATHOLOGY OF THE TEETH. The first trace of enamel, as is well known, appears about the sixth month of intra-uterine life, at a period when a certain amount of dentine has already been formed. The outer sur- face of the dentine exhibits bay-like excavations, in which we often observe a flat layer of a finely-granular protoplasm, analo- gous to that found in the teeth of adults. Above this layer we see prismatic pieces of calcified basis-substance irregularly dis- tributed, since the enamel-prisms, as a rule, do ,not reach the surface of the dentine, luit are replaced by a homogeneous (Tomes's granular) layer. Yet above this the enamel-prisms are easily recognizal)le, and appear to be composed of more or less regular square pieces. We can see a deposition of lime-salts along the borders of the prisms, while their central parts often exhibit one large nucleus, or several coarse granules. The interstices between the rows of these square pieces frequently exhibit delicate fibrillse, the enamel-fibers, which are in connec- tion with broader protoplasmic tracts, lying in the boundary between the enamel and the dentine. These enamel-fibers send branches through the transverse interstices of the square pieces. Everywhere delicate offshoots are seen, indicating that the living matter of the previous medullary corpuscles is preserved, even after their infiltration with lime-salts. In the eighth and ninth months of foetal life, both the enamel and the dentine form solid caps, corresponding to the summit of the crown of the tooth, and the one is superimposed upon the other. In decalcified specimens of these tissues, when they have been stained with carmin or chloride of gold, we observe a striking analogy in the structure of the enamel to that of the dentine. With a magnifying power of 500 diameters, it is difil- cult to difl:erentiate between dentine and enamel. The fibers in the canaliculi of the dentine closely resemble those of the interstices between the enamel-rods. Even the highest powers of the microscope exhibit a close resemblance of both tissues, more especially after the Jime-salts have been completely re- moved by means of reagents. Let us now ask the question, What is the ultimate fate of the epithelial cord of the enamel-organ? In the earliest stage of its development we meet Avith num- erous lateral offshoots and sprouts, which, preceding their ultimate disappearance, are visible in the shape of medullary corpuscles. The destiny of the cord is obviously to produce DEVELOPMENT or THE ENAMEL. 175 the enamel-organ for the formation of the enameL This pro- cess is accomplidied with the lifth month of intra-nterine Kfe. In the latter part of the fourth, and in the lifth month, the orio:inal epithelial cord undergoes peculiar changes, which have attracted the attention of many previous observers. The main change consists in the breaking up of the epithelial cord into innumerable clusters of a more or less markedly epithelial structure, between which fibrous connective tissue has appeared, completely isolating the clusters. Changes of this description are best seen in horizontal sections of the jaws. (See Fig. 107.) With low powers of the microscope, we observe a large number of clusters which are distinctly marked in specimens preserved in chromic-acid solution. They have a brownish color, and may be either sharply outlined or more or less blended with the adjacent connective tissue. Many of these clusters hold concentrically-arranged epithelial nests, and, judged by their size and shape, they must have originated from a very active new gro"\^i:h of epithelium, which is indicated also by a number of buds sprouting from the original clusters. The buds have been j)^^shed apart by librous connective tissue, since many of them appear entirely isolated, and as if imbedded in the fibrous connective tissue. Higher powers of the microscope reveal the fact that the process of dissolution of the original epithelial cord is identical with that of the disso- lution of the external epithelium, the only difference being that in the latter process numerous newly-formed blood-vessels participate, whereas in the breaking up of the epithelial cord the new formation of blood-corpuscles and blood-vessels is not very conspicuous. (See Fig. 111.) The smallest isolated clusters, still recognizable by their brownish color, only show traces of a division into epithelia through an intervening cement^substance. Most of them rep- resent protoplasmic masses, with nuclei of varying size, inter- spersed at more or less regular intervals. Such clusters are often found surrounded by an almost homogeneous layer of a so-called basement-membrane. In the next stage, the cluster splits up into medullary corpuscles at its periphery, whereby its size is considerably diminished, and the basement-membrane lost. Ultimately the multinuclear protoplasmic mass, or the medullary corpuscles, split up into delicate spindles, which become infiltrated with basis-substance, thereby assuming the 176 THE AXATOMY AND PATHOLOGY OF THE TEETH, cliaraoteristie features of fil)rous connective tissue. Some- times we meet with single brownish corpuscles imbedded in fibrous connective tissue, and in size surpassing the nuclei of the latter. Such formations are possibly the last remnants of previous epithelia, that have escaped transformation into con- nective tissue. The ultimate fate, then, of the epithelial cord of the enamel- Fro, in. Dissolution of the Epithelial Coed of Examel-Organ of a Human Fcetus Five Months Old. Horizontal Section. C, capillary blood-vessel holding red blood-corpuscles; B, B, multinuclear protoplasmic masses arisen from the original epithelial buds; R, remnants of previous epithelia partly transformed into medullarj' corpuscles ; E. single protoplasmic body, probably epithelium ; M, medullary corpuscles in transition to fibrous connective tissue. Magnified 800 diameters. organ is the same as that of the external epithelium, the cord being partly transformed into connective tissue. The further the development of the enamel and the enamel-organ proceeds, the less is visible of the original epithelial cord, although small epithelial clusters may be recognizable even in the sixth and seventh months of fcptal life. DEVELOPMENT OF THE EXA.MEL. 177 We have already alluded to tlie possibility tliat the epithelium present between the outer surface and the enamel serves as stored-up material for the increase of the enamel, a possibility assumable since at the time of birth this tissue has by no means attained the full thickness which we observe at the time of the Fig. 112. r ■vCtr.m Tooth of a Hl'man Fcetcs Seven" axd a Half Months Old. Vertical Sectiox. P, papilla : B, dentine : E, enamel ; IE, internal epithelium ; EO, enamel-organ ■ EE external epithelium: R, remnants of epithelial cord: EN, epithelial nest: EP, pit filled loosely with flat epithelia : RM, rete mueosum ; Ep, horny layer of the oral mucosa. Magnified 50 diameters. eruption of the tooth, and since, also, on that part of the surface corresponding to the summit of the enamel there is no proper enamel-organ left for the further growth of enamel-tissue. The epithelial cord does not, however, completely disappear 178 THE ANATOMY AND PATHOLOGY OF THE TEETH. toward the end of intra-nterine life. Near the surface of the oral mucosa we ofteu meet with comparatively large spaces filled with loosely-arranged flat epithelia of the character of epidermal scales, as illustrated in Fig. 112. Thus far we have heen unable to trace the connection of such a large pit with the rete mucosum, or surface of the oral epithelium. But there can he no doubt as to the origin of the pits. They must have arisen from the original epithelial cord, since the epithelial cord of the permanent tooth may be traced from their periphery. The cord in our specimen is broadened at its distal end and surrounded by a small papilla correspond- ing in every respect to the developing temporary tooth in an embryo of about three and a half months. The epithelia filling the pit are arranged loosely, similar to those of the horny layer of the oral mucosa, and many of them hold glistening granules of what possibly is eleidin. The boundary of the pit is made up of a single row of cuboidal epithelia, which in some places may produce stratified hills and protrusions. The pit corresponds to the summit of the temporary tooth, and its destiny seems to be to prearrange the route for its eruption. Between the lower periphery of the pit and the upper bound- ary of the enamel-organ, or rather its external epithelium, the connective tissue is loose and approaches the myxomatous structure, containing very small groups of epithelium or medul- lary corpuscles sprung therefrom. Such clusters are especially conspicuous in the space between the epithelial cord of the permanent tooth and the external epithelium of the enamel- organ, where a large number of capillary blood-vessels is also visible. Among the different animals in whose jaws we have examined the process of formation of the enamel, we may mention the following : Kittens, at the time of birth, show all stages of the formation of teeth, and especially the breaking up of the inner epi- thelium into medullary, and afterward into myxomatous, tissue, which is easily traceable. All the details, however, correspond to those observed in human beings. In a newly-born pup the formation of enamel was found to be, in all essential points, identical with its formation in man. The foetus of a pig affords an excellent example for the study of the formation of ameloblasts from medullary corpuscles. DEVELOPMENT OF THE EXAMEL. 179 (Fig. 113.) The ameloblasts are arranged with great regularity, l)eing alternately wedge-shaped in opposite directions. Their reticulum is very wide, and the horizontal threads traversing the interstices are quite plain. From their bases arise a varying number of offshoots, directed toward a peculiar tissue which occupies the space between the ameloblasts and the already- formed dentine. This tissue appears granular with low powers of the microscope. High powers, however, plainly reveal a Fig. 113. A.MELOBL.A.STS OP A Pig'S FffiTUS, ABOUT TeX CeXTIMETERS LoxG, BEFORK THE FORMATION OF EXAMEL. M, Myxomatous enamel-organ ; A, A, rows of ameloblasts of a markedly reticular structure ; G, granular layer between the dentine and the ameloblasts. Magnified 1200 diameters. reticular structure, traversed by delicate fibrillae in connection with the reticulum. The presence of nuclei in this tissue indi- cates its origin from medullary corpuscles. The foetus of a lamb, about ten centimeters long, shows a large layer of ameloblasts. (Fig. 114.) In places where the ameloblasts lie close to the dentine, no filDrill^e are seen, but where the layer of ameloblasts is detached, a large number of fibrillae appear, e^-idently belonging to the dentine. This is less calcified and takes up a deep carmin stain, contrary to the fully-calcified central portion of the dentine, that usually re- 180 THE ANATOMY AND PATHOLOGY OF THE TEETH. mains unstained. Here is wedged in between the dentine and the ameloblasts a hirer found only as bek^nging to the sheep. The amelobhists break up into medullary corpuscles before forming enamel, in the same manner as in human beings and other animals that we have examined. Sectiox of a Tooth of 4. Sheep's Fcftus, 4.B0bT Ten Centimeters Long. D, dentine in transverse section ; F, fibers drawn out from the non-calcified portion of the- dentine; A, layer of ameloblasts partly in connection with the dentine. Magnified 1200 diameters- Valuable researches in the study of the development of the enamel have been published by Frank Abbott,* as follows : * "Growth of Enamel." Dental Cosmos, 1889. DEVELOPMENT OF THE EXAMEL. 181 " A. Kolliker, in liis ' Handbook of Histology of Man' (1852), speaks of development of enamel in the following terms : * The development of the dental substances has always been considered a rather difficult topic. The relations are the simplest in the enamel, where not the slightest doubt prevails that the enamel-cells, bj a complete calcification, become transformed into enamel-fibers (enamel-rods). As soon as a small portion of the cells, without am' preliminary deposition of lime-parti- cles, is being ossified, we recognize a small lamella of enamel over the somewhat larger dentine cap, which has also recently originated. The deposition of lime proceeds in the cells from within outward till they have at last been transformed into enamel-fibers and simultaneously transgress on new cells, by which means the layer of enamel is broadened. AVhile this is going on, the enamel-membrane has not disappeared at the place where the ossification has started. On the contrary, we find this membrane always of the same In-eadth so long as the deposition of the enamel lasts, which proves that the ossified portion of the membrane is continuously being replaced by an additional mass. Apparently this is done, not l;)y the produc- tion of new cells, but by a continual outgrowth of the original ones. The enamel-organ (stellate reticulum) is certainly of great importance in the building up of enamel, and owing to its richness in albumen and a gelatinous mass in its meshes is, so to speak, a pantry from which the enamel-membrane derives the material for its growth, being at some distance from the blood-vessels. In fact, we see this spongy tissue losing in its bulk during the development of enamel, and finally disappear- ing when the formation of enamel is completed.' '' I will here add that to Kolliker the enamel-membrane means a layer of epithelia. He describes the enamel-organ as being made up of anastomosing star-shaped cells, or a reticular con- nective tissue, which in its meshes contains a large amount of albumen and a liquid rich in mucus. The same author, in his work on the ' Historj' of Development of Man and Higher Animals,' in 1879, claims that the stellate reticulum of the enamel-organ in appearance is identical ^^ith connective tissue, but is really nothing but a peculiarly transformed epithelium. Kolliker, therefore, in 1852, held an opinion that we consider to-day the correct one, which he very materially modified, almost to the point of al)andonment altogether, years later. 182 THE AXATOMY AND PATHOLOGY OF THE TEETH. This author was the first to announce that the theory of exehi- siveness is not tenable, in the process of development from the three original embryonal layers, the ' ectoderm,' the ' meso- derm,' and the ' entoderm,' or, using Balfour's terminology, the ' epiblast,' the ' mesoblast,' and the ' hypoblast' ; and still he narrows his views to an almost incredible degree, in the chapter upon development of enamel. ''John Tomes, in his 'Dental Physiology and Surgery' (Lon- don, 1848; Philadelphia, 1853), gives wonderfully accurate drawings of what he calls enamel-pulp, or columnar tissue, now known as ameloblasts. On page 102 he explains the develop- ment of enamel-rods or fibers in the following words : ' The cells being formed in lines, eventuall}" become confluent; the points of union being somethiies transverse, and at other times oblique, At this stage the earthy elements are received, and the lines of union between the component cells of the fibers become less distinct, and are eventually lost, leaving a continu- ous fiber. The nuclei, from the first very small, are altogether lost in the formation of the fibers, or exist as very fine tubes passing through the length of each.' " On page 104 we read :. ' To the best of my belief the trans- verse striae are due to the alternate dilatation and contraction of the fibers, — each dilatation corresponding to the center of a formative cell, and each contraction to the junction of two cells.' "From these cpiotations it becomes evident that John Tomes was a most careful observer. Even at that early date, with the limited powers of his microscope, he conceived the full truth when he stated ' that each enamel-rod is the result of a juxta- position of formative cells, between which are left the stride.' He considers the formative cells as the recipients of the cal- careous matter in exactly the same way as we see it to-day. " F. "Waldeyer, in his ' Handbook of Histology,' edited by Strieker, in Leipzig, JL869, page 347, describes the formation of enamel in the following manner : ' The formation of enamel is done exclusively by the enamel-epithelium, since the enamel- prisms are the result of a direct calcification of its long cylin- drical cells. The boundary of petrifaction on the cells is by no means linear, but extends downward to an irregular depth, — a fact which likewise is not in favor- of the view that a secretion of the enamel-cells is being calcified. After treatment of young DEVELOPMENT OF THE ENAMEL. 183 enamel with dilute acids, the enamel-prisms slightly swell and resume entirely the form of the previous cylindrical cells. The disappearance of the nuclei, in the process of the calcifica- tion of the cells, is of so common occurrence that their absence in the enamel cannot cause any wonder. Enamel, therefore, is to be considered as the petrified dental epithelium.' " This author explains the formation of the stellate reticulum by a transformation of the epithelia, and considers its gelatin of a merely mechanical importance, since it keeps an open space for the growing tooth. " John and Charles S. Tomes, in their ' System of Dental Sur- gery' (London, 1873, page 253) say, ' The conclusions respect- ing the development of enamel which are most in accordance with appearances observed are these : The columns of the enamel-organ (enamel-cells, internal epithelium of the enamel- organ) are subservient to the development of the enamel-prisms, into which they by calcification become actually converted. This conversion goes on in the folloA^dng method : The proxi- mal end of the cell undergoes some chemical change prepara- tory to calcification, and is subsequently calcified ; but this cal- cification does not go on uniformly throughout its whole thick- ness, but proceeds from its periphery toward its interior, the central portion of the cell thus being calcified later than the external portion, which lies at the same level. At the same time that calcification is proceeding inward, in each individual cell, it has united the contiguous cells to each other. The cal- cification of the central portions of the enamel-fibers does not keep pace with that of their exteriors, nor even in fully-com- pleted enamel does it attain to precisely the same characters. In the progress of calcification the nuclei of the enamel-cells disappear, and it is probable, as is believed by Waldeyer, that the internal epithelium of the enamel is reunited by the cells of the stratum intermedium as it becomes itself used up by ad- vancing calcification, converting it into enamel-fibers.' " These authors give credit to KoUiker as the originator of the idea that the enamel-cells do not undergo direct conversion into enamel-fibers, but that the enamel is, as it were, shot out from their ends, — that is, it is a secretion from them, not a deposition of lime-salts into their own substance. Our quotations from Kolliker's original German- work, issued in Leipzig in 1852, plainly show that he at that time believed fully in the conver- 184 THE AXATOMY AXD PATHOLOGY OF THE TEETH. sion tlieory. Since the Tomeses quote from the fitth German edition of Kohiker's histology, issued in 1867, it is obvious that he has changed his views, much, in my judgment, to his own disadvantage. " The views announced b}' C. Heitzmann and C. F. W. Bo- decker are in harmony with my own observations, and fur- nish the foundation of what I have to add, in the way of a more comprehensive idea of the building process of enamel, than has heretofore been advanced. "Fig. 115 gives an illustration of the views just alluded to. The figure, it must be emphasized, is not diagrammatic, but copied with the utmost care from a specimen of a human foetus six months old, the period at which enamel begins to appear. The diiferent layers, it will be observed, appear separated from one another. This is usually the case even in the most care- fully prepared specimens, o'^^'ing to slight mechanical injury in cutting, and to shrinkage of the soft parts ; the relations, how- ever, are absolutely correct in this drawing. "After the epithelial peg has grown into the depth of connec- tive tissue of the oral mucosa, in the twelfth week of embry- onal development, the distal end of this peg becomes club- shaped, and then appears the first trace of medullary tissue, which two weeks later plainly shows the stellate reticulum. The club at this period assumes a cup-shape, Avhose concave surface is lined by the internal epithelium, while the outer sur- face is made up of the so-called external epithelium, which is in uninterrupted continuity with the internal epithelium at the most prominent l)order of the cup. If we examine the lower edge of the cup of the enamel-organ at al)Out the sixteenth week of embryonal life, we observe a peculiar change in the columnar bodies of the internal epithelium, which consists in the appearance, in a more or less row-like arrangement, of highly-glistening globular bodies, replacing the previous col- umnar epithelia. These bodies are either solid or slightly vacuoled, and are formations of living matter such as we are accustomed to look upon as medullary, embryonal, or indifter- ent corpuscles in their earliest stage of appearance. Obviously these glistening globules have originated from the reticulum of living matter of the columnar epithelia themselves. We feel justified in this conclusion from the fact that we can trace, step by step, the growth of these glistening granules up to the for- DEVELOPMENT OF THE ENAMEL. 185 matiou of o-Usteiiiug lumps, such as we have termed medullary corpuselesr The niore the cup of the euamel-orgau is eularged, Fig. 115. ^t^^il^'r Tooth of Humax Fcetcs, Six Moxths. P, papilla; D^, non-calcified dentine: X>2, calcified dentine: E. enamel: ^, row of amelo- ■blasts; 3/, medullary corpuscles at the peripheral portion of ameloblasts; ■, .S', secondary dentine at the borders of both pulp -chambers : i?, narrow laj-er of cementum. Magnified 6 diameters.- 200 THE ANATOMY AXD PATH0L0C4Y OF THE TEETH. had a weak constitution, and during the period of early child- hood was often seriously ill. The boy did not have the upper central incisors till he was four years of age, and their perma- nent successors only made their appearance about the tenth year of age. It appears to be improbable that general or local disturbances should have influenced the malformation of this tooth. On the other hand, there is a strong corroboration of the theory of traumatic origin of the anomalous development of the tooth under consideration. At the cutting-edge we observe four channels, or rather vestiges of channels, where a series of foreign bodies were forcibly thrust into the enamel-organ shortly after birth, or at least during the first year of life. Judging from the arrangement of the slighth' devious channels^ I should infer that the foreign bodies were pliable, though rather firm and pointed. Such bodies are the bristles of a tooth-brush, which may have been either bitten into by the infant, or may by other accidental means have obtained entrance into the enamel-organ of the tooth. This view is the more plausible since we find a detached nodule of pigmented enamel at the floor of the central pulp-chamber, which evidently took origin fi'oni a torn-off" piece of the enamel-organ. A portion of the dentine being destitute of enamel, this view gains the more ground, because the detached nodule of enamel corre- sponds in its devious direction to the other tracts of the channels. The tooth has a wide bifurcated pulp-chamber and a small cen- tral one, both exhibiting narrow layers of secondary dentine. The cementum is extremely narrow all over the root, and nowhere developed beyond the formation normally seen at the neck of the tooth. The root was somewhat compressed and grooved laterally. The arrangement (>f the channels and the injuries produced in the enamel are illustrated in Fig. 123. The enamel is colored a light brown, and its prisms, besides- being conspicuously wa\w, exhibit irregularly-scattered pigmen- tations. In the vicinity of the channels the enamel is of a deep yellow-brown color; its prisms are but scantily developed, and in most places are replaced by a deep-brown amorphous mass. The dentine along the borders of the enamel-globules and pegs shows slight irregularities, consisting in a widening of the canaliculi, or in coarse conical ofishoots filled with granules of lime-salts emanating from the enamel-pegs. Around the enamel-pegs the canaliculi converge. At the border between FAULTY DEVELOPMENT. 201 the enamel and dentine there is a globular formation, deeply stained with an ammoniacal solution of carmin. Higher powers of the microscope reveal that this globule is an anoma- lous formation of dentine. (See Fig. 124.) The basis-substance appears finely . granular and arranged concentrically. It is Fig. 123. Portion of Enamel from Cuttixg-Edge of Crown of Fig. 122. E, enamel, deeply pigmented ; C^. vestige of channel surrounded by a dark yellow-brown irregular enamel ; C", vestige of channel bifurcating ; G, globule of ill-calcified dentine ; D, normal dentine. Magnified 25 diameters. traversed by extremely faint dentinal fibers running a radiating course. The periphery of the globule is surrounded by in- tensely-calcified globular masses, between which are seen inter- globular spaces filled with protoplasm and granular deposits of 202 THE ANATOMY AND PATHOLOGY OF THE TEETH. lime-salts. The globules are pierced by scanty and irregularly- formed dentinal canaliculi, wliicli, however, keep the general direction of those of the normal dentine. Both the. intensely- calcified zone around the globule, and the normal dentine, are traversed by broad routes of protoplasm pervaded with coarse granules of lime-salts. Fig. 124. Globule of Ill-Calcified Dentine op Fig. 122. (r.Sbasis-substance uncalcified, with scanty and faint dentinal canaliculi ; P, globular calca- reous deposits around tbe uncalcified basis-substance ; T, T, tracts filled with calcareous granules ; B, normal dentine. Magnified 500 diameters. That the protrusions and pegs penetrating the dentine really are a formation of enamel-tissue, as is the nodule at the floor of the"central pulp-cavity before alluded to, is proven by examina- tion with higher powers of the microscope. (See Fig. 125.) FAULTY DEVELOPMENT. 203 Furthermore, we notice enamel-prisms of an extremely devious course, the deviousuess being most pronounced in the center of the peg, where a number of transverse sections of enamel- prisms are met with. Instead of such transverse sections, we frequently notice amorphous and deeply-pigmented granular Fig. 125. ^ ^^ ^ "^ Portion of Ixterzoxal Later betweex Destine and Enamel of Cutting-Edge of Fig. 122. G, G, globular protrusions of pigmented enamel; T, tract of anomalous enamel; A, amor- phous, deeply pigmented masses, replacing transverse sections of enamel-prisms; H, highly refractive rims between enamel and dentine ; I>, normal dentine. Magnified 500 diameters. masses, which probably are the result of crushed ameloblasts. The yellow-brown color of the anomalous formation of the enamel is everywhere due to the presence of such amorphous masses, whereas the enamel-prisms appear of a lighter dusky- 204 THE ANATOMY AND PATHOLOGY OF THE TEETH. brown color. There is but little doubt that the pigment of the masses is due to a hemorrhage produced at the time of the injury. A noteworthy feature is the presence of an intensely- calcified rim between the globules and the pegs of the enamel and the dentine, which is traversed by the bifurcations of the dentinal canaliculi. The writer has observed an interesting incident of faulty development in a family of four children and two grandchildren. The four children have no enamel upon their permanent teeth, while the teeth of both parents were covered with normal enamel. The teeth of all the children were abnormally small, and the incisors and cuspids even smaller than ordinary tem- porary teeth. Their external surface is smooth, of a dark-yellow color, and not abnormally sensitive to thermal changes. The molars mostly have the form of a lower first temporary molar, while the bicuspids are of normal form, but quite small. The cusps of all the molar teeth, when they made their appearance through the gums, were quite sharp, and, becoming a source of irritation to the tongue and cheeks, they had to be rounded ofi". These teeth soon decayed where the pointed cusps had been removed, and the inner portion of the dentine was extremely sensitive to the touch of the bur. The writer has lately seen the two grandchildren of this family, one of which is five and a half, the other six years of age. The latter child has normal temporary, and, as far as erupted, good permanent teeth, while the former has inherited the faulty-developed teeth of his father. This child, although only five and a half years of age, had its upper and lower permanent central incisors and the first per- manent molars fully erupted. The remaining temporary teeth are the smallest teeth the writer has ever seen in any child's mouth. Their enamel, with the exception of the upper second temporary molars, appears to be normal. The latter four teeth each exliibit two pointed cusps, and seem to be devoid of enamel. The four permanent molars, which in general size and shape are nearer normal than those of his father's, are sur- mounted by four or five cusps respectively, and appear to be entirely devoid of enamel. The upper and lower permanent central incisors exhibit a bright-yellow color, and are also much larger than those of the father, while their surfaces seemingly lack enamel. They are marked by transverse grooves, princi- pally upon their labial surfaces. FAULTY DEVELOPMENT. 205 I shall make use of two valuable contributions to this topic by Frank Abbott.* The first deals with anomalous occurrences in the enamel, as follows : "I. Anomalous Relation between Dentine and Enamel. — In examining a large number of specimens of ground teeth, I met with formations in two instances which are to be considered as rather anomalous, though not strictly pathological. In one instance, that of a temporary molar, there was on the buccal Fig. 126. Protrusion of Dentine into Enamel. E, enamel ; D, dentine ; H, hill of dentine with fluted summit ; P, protoplasmic bodies in the dentine. Magnified 400 diameters. surface a protrusion of dentine into the enamel with a fluted surface, or a surface fluctuating in a series of bay-like excava- tions. This fluting was present also at the junction of the dentine with the enamel in general, but not so marked as in this protruding spot. The center of this protrusion was occu- pied by an eccentric protoplasmic formation, differing in shape from the ordinary interglobular spaces. The dentinal fibers at the periphery were bifurcated in the usual manner, but very * "Studies of the Pathology of Enamel of Human Teeth, with Special Eefer- ence to the Etiology of Caries." Dental Cosmos, 1885. 20(3 THE ANATOMY AND PATHOLOGY OF THE TEETH. few of them penetrated the enamel. The portion of the enamel nearest to the protrnsion was destitute of prisms, while in the immediate vicinity, again, of this portion such pr'sms were traceable almost in contact with the dentine. The zone immediately above the protrusion was but slightly brownish, whereas the prisms of the enamel exhibited a very distinct brown pigmentation. Fig. 127. #i^ 'jji)/"' " .f .T'^^^VS / '^ "I'll o /I 44 — ^*+-t. Wl^ ' Protrusion of Dentine into Pathological Enamel. E, enamel ; D, dentine ; G, granular enamel ; A, summit of the dentine ; S, sloping borders of the granular enamel. Magnified 200 diameters. " In a second case, that of a permanent cuspid, a protrusion of dentine was observed, as in the former instance, on the buccal surface near the edge, occupying nearly one-half of the breadth of the enamel. This protrusion was of a conical shape, and without a distinct boundary, but blended with an oblong field of enamel of quite remarkable structure. The dentinal canaliculi exhibited at their peripheral portions numerous bi- FAULTY DEVELOP-ME^JT. 207 furcations, and terminated in small pear-shaped enlargements, many of which conld be traced in connection with dentinal fibers, whereas the most peripheral ones, owing to their devious course, looked isolated. The adjacent enamel showed but very indistinct rods, the main mass of the enamel being occupied by brownish globular fields, separated from one another by irreg- ular interstices closely resembling the interglobular spaces of dentine, though of considerably smaller size. The deepest pig- mentation and the largest number of such interprismatic spaces occurred along the periphery of this anomalous formation, especially toward the outer surface of the enamel. The yicinity of the enamel proper was marked by the presence of slightly pig- mented rods, more wavy in their course than is normal. Toward' the dentine the anomalous formation was sloping, and the line of demarcation between the normal and anomalous enamel exhib- ited either brown and yery wayy prisms or small inferprismatic spaces, decreasing in diameter the nearer they approached to the dentine. I wish to emphasize and call particular attention to the fact that the dentine of this tooth was nowhere traversed by interglobular spaces, the anomalous construction being confined to the enamel. "II. Stratification of Enamel. — It is known that dentine, without exhibiting pathological features, yet slightly deviating from its normal structure, is sometimes composed of strata that are more or less distinctly marked, and are altogether independ- ent of the formations known as secondary dentine. We often meet with similar formations in the enamel. We observe, varying in width and more or less sharply marked Ijy a straight line, layers which in longitudinal sections of teeth are concen- tric, the broadest part corresponding to the cusps, the narrowest to the neck of the tooth. " At the outer periphery of the enamel there may occur strata, which, contrary to the general construction as above described, are broadest toward the neck and narrowest toward the cusp, though never reaching its summit. In transverse sections the enamel shows simply concentric lines, separating from one another layers of greatly varying diameters. With higher powers of the microscope we ascertain the fact that the lines of stratification, as a rule, do not alter the general course of the enamel-prisms, — in other words, a single enamel-prism will show an oblique line of demarcation, corresponding to the 208 THE ANATOMY AND PATHOLOGY OF THE TEETH. Fig. 128. iHl m Diagram of Stratification op Enamel. P, "pulp-chamber ; B, denting ; CL^, CL^, CL^, CL\ cusp-layers of enamel ; NL\ NL^, neck- layers'of enamel. FAULTY DEVELOPMEXT. ' 209 general line of stratification, without being altered in its con- struction or its course. An exception to this rule will occur only at the peripheral portions of enamel, occupied hy the tapering ends of the ahove-described secondary strata, which I would like to term neck-layers, in contradistinction to the central casp-Vvjers. The tapering ends of the neck-layers may exhibit enamel-rods, almost parallel with the surface of the enamel, a feature which is never seen at the outer periphery of the cusp- layers, where the enamel-rods are invariably directed more or less perpendicularly to the surface. •• An understanding of the stratification of the enamel is of the utmost importance in aiding the understanding of its pig- mentation and granulation. As I will show later on, both the pigmentation and granulation correspond to the general strata of the enamel, thus showing in longitudinal sections of teeth a fan-like appearance. '• It can scarcely be doubted that the stratification of this tissue is in close relation to the history of its development. A\^e know that the first appearing enamel-cap of temporary teeth, in the seventh month of intra-uterine life, has the configuration of the innermost cusp-layer,^ — i.e., it is broadest in the direction of the future cusp, and tapers toward the future neck of the tooth. It seems reasonable to assume that the subsequent layers of enamel form on the plan of the first, but there may be a tempor- ary stoppage of its construction, due. perhaps, to slight ailments of the mother before delivery of the child, or slight ailments of the infant after delivery, which causes interruptions in its organi- zation. Slight ailments of a general nature will not interfere with the final result of an otherwise sound enamel: whereas severe ailments, particularly local ones, may lead not only to stratification, but to a decidedly pathological condition, which I have before called pigmentation and granulation. These condi- tions invariably involve a deficient deposition of lime-salts. "III. Anomalous Arrangement of the Enamel-Rods. — In normal enamel, longitudinal sections "will, in the majority of cases, exhibit slightly wa^-y rods, interlaced by comparatively small bundles, cut in a transverse direction. Toward the periph- ery the curvatures of the rods gradually become less, until, when close to the surface, they present a nearly straight course. I have never seen transverse sections of enamel-rods directly in contact with the interzonal layer. 1-5 210 THE ANATOMY AND PATHOLOGY OF THE TEETH. " Deviations from this rule seem to be rare. Where they exist,, the enamel-rods seem to lack all regularity in their arrangement. It may occur that close to the interzonal layer the enamel-rods show extensive fields occupied by these transverse sections, which gradually blend with oblique and longitudinal ones, producing a wavy appearance, to such an extent that beautiful figures arise,. reminding one of the grain of lignum-vitce. Still more compli- cated figures arise if the transverse bars of the longitudinal rods are unusually conspicuous. In such enamel it may occur that the curvatures of the rods remain very marked up to the surface ; and, consequently, groups of transverse sections may be seen directly at the outer surface. " Enamel of this description may be seen only on one portion of the tooth, while the rest is normal. In all my specimens, pigmentation is combined with this curly appearance of the enamel-rods as a marked feature, and the interstices between the rods are a trifle wider than normal. Both of the latter features must imply a deficient calcification, and, consequently,, extreme brittleness. It is very ditficult to obtain perfect speci- mens of such enamel. The dentine subjacent to such anomalous formations is freely supplied with interglobular spaces, which fact is likewise a sign of deficient calcification. " IV. Deficient Calcification of the Enamel, without Pigmen- tation. — The friability alluded to under the previous heading is in some instances very marked, — so much so that it is impos- sible to obtain an unbroken slab of a tooth, even with the finest grinding-stones. With low powers of the microscope we observe that the broken ends of the enamel-rods look as if cor- roded, or as if some of them had been displaced or torn ofi" by the process of grinding. ISTeither pigmentation nor an anoma- lous course of the enamel-rods is necessarily connected with such a condition of the tooth. The most striking feature, how- ever, — a feature visible even with low powers, — is that the enamel-rods are unusually narrow, the interstices between them unusually wide, and their tenants, the enamel-fibers, very promi- nent. The cross-lines of the enamel-rods are likewise consider- ably widened and irregular, so that the fields of basis-substance look unusually small and irregular. The reticulum in the immediate vicinity of the interzonal layer is also unusually prominent. " Such a condition of the enamel may occur both in tempo- FAULTY DEVELOPMENT. 211 rarv and permanent teeth, and may be combined ^vith pigmenta- tion. It is a feature of such deficient enamel that it readily stains with an ammoniacal sokition of carmin, something that normal enamel will not easily do. The subjacent dentine, under such conditions, may either be perfectly developed, as before stated, or be deiicientin its formation, as shown by the presence of more or less numerous interglobular spaces. " All clinicians have observed, in the enamel of teeth, con- FiG. 129. Extremely Ikregui.ae Course of Rods tx Slightly-Pigmested Examel. The longitudinal rods deviating to a great extent from the field of the specimen, show • oblique and transverse sections. The interstices are widened and contain conspicuous enamcl- iibers. Magnified 1200 diameters. genital white or yellow spots, which, if broken into, are found to be of the consistence of chalk. Such spots have been termed ' white decay,' although they do not correspond to the process of caries as we usually understand it. They mean nothing but deficient calcification. Again, all clinicians have seeo teeth across which runs a row of pit-holes, in the bottom of which depressions, in many instances, no enamel is to be found. This condition, also, is always congenital, and closely related in its 212 THE ANATOMY AXD PATHOLOGY OF THE TEETH. origin to pigmentation and the white or yellow spots. In other instances an originally smooth enamel is mutilated mechanicallv by the process of mastication, with the result of loss of substance, with abruptl}' broken, jagged edges. Again, we see teeth with a great portion of their crowns covered by a brown- ish-yellow substance in place of enamel, this substance being so soft as to be easih' remoyed, leaving the dentine bare of its covering and extremely sensitive to the touch of an instrument, the pressure of food in mastication, etc. These conditions, again, are, in most instances at least, connected with the presence of pigmentation and the white or yellow spots. "We might call them exaggerated cases of the same condition. Obviously these congenital defects are dependent upon deficient deposition of lime-salts in the basis-substance, rendering the enamel less resistant and more friable. "V. Pigmentation of Enamel. — One of the most common anomalous conditions of the enamel is its pigmentation. Some- times it is so slightly marked that the naked eye discovers only a slight yellow-brown discoloration : in other instances it is quite prominent and readily discernible. Correspondingl}', specimens of such teeth under the microscope will exhibit either a dim yellow tint in the enamel or a marked brown discol- oration. The pigmentation may occur either in non-stratified or in stratified enamel. In the first instance there is no demar- cation of the brown spot toward the colorless enamel ; only faintly-marked oftshoots of the main spot, tapering toward the dentine, and running in an oblique direction, will indicate the fact that pigmentation has occurred during its formation. In the second instance, on the contrary, if pigmentation invades stratified enamel, there is a close relationship between the two, inasmuch as the deepest stain invariably corresponds to the boundary line of the strata, tapering toward the neck, and gradually fading toward the proximal end of each stratum. Thus, in longitudinal sections, a beautiful fan-like configuration is produced. " The pigmentation may invade all layers of the enamel, often being more marked in the deeper than in the superficial por- tions. Higher powers of the microscope reveal the following facts : First, that the brown discoloration concerns the basis- substance of the enamel-rods only. Secondly, that the inter- stices between the pigmented enamel-rods are widened, — not FAULTY DEVELOPMENT. 213 merely to seeming, and in consequence of the contrast in color, but because of a deiiciency in the formation of the basis-sub- stance. Thirdly, that the transverse lines of the enamel-prisms likewise are (at least in many instances) enlarged. Fourthly, that the enamel-fibers and their lateral offshoots are more con- spicuous than in normal enamel, and more so even than in the enamel of temporary teeth, and in many places distinctly beaded. Pigmented portions of the enamel are rather prone to take up a red stain on being treated with an ammoniacal carmin solution. Fig. 130. iiii|i||iil4lit!lil4ii^ J) Pigmented axd GEAxrLAE Examel. D, dentine ; EE, layer of slightly pigmented rods broken off; EG, layer of highly pigmented and granular enamel ; EP, stratified pigmented enamel. Magnified 400 diameters. " As to the origin of the brown discoloration, I have to say, as a suggestion simply, that at the time of the formation of this tissue there must have been a disturbance in the enamel-organ which interfered with the proper construction of the basis-sub- stance and the deposition of lime-salts. What this disturbance really was, I am unable to say. Many pigments of the body de- pend upon and are closely related to the coloring-matter of the blood. I am loth, however, at this time, to attribute pigmen- 214 THE ANATOMY AND PATHOLOGY OF THE TEETH. tation of enamel to the extravasation of blood-corpuscles or diff'usion of the coloring-matter of the blood. Careful studies in the history of the development of this tissue must be made, before an attempt at a solution of this question will be admis- sible. One point I am positive about, however, is that this pig- mentation is congenital, invading temporary as well as perma- nent teeth. Acquired pigmentation of enamel seems to be ot comparatively I'are occurrence, except as a result of caries. I have seen pigmentations of its surface, of a deep orange color, not penetrating the enamel-tissue in the least. Caries on the surface often causes an orange discoloration, diffused and fading toward the normal portions. Several of my specimens plainly show an invasion. of the enamel by caries, on spots pigmented congenitally ; secondarily, an orange diffused discoloration has taken place, and here the enamel is likewise prone to take up the carmin stain ; thus beautiful shadings of brown, orange, and red are to be seen, the brown being congenital substances, the orange acquired, and the red artificial. What chemical may lead to an acquired pigmentation or discoloration of the enamel I caunot say. " VI. Granulation of Enamel. — Under this heading I propose to describe a peculiar abnormality, which, so far as my speci- mens indicate, is by no means rare. It consists of pear-, spindle-, and club-shaped spaces in the middle of the substance of the enamel. Such spaces were known to exist heretofore at the junction of the dentine and enamel only. They may appear in pigmented, and invariably do in stratified, enamel; the strati- fication in the latter instances being due to their presence. Club-shaped spaces may appear at the distal boundary of one ol the cusp-layers, or there may be several rows of such spaces, varying in extent and degree, but it sometimes occurs that only the outermost cusp- or neck- layers are freely supplied with them, whereas the rest of the enamel is normal or more or less pig- mented. " Higher powers of the microscope demonstrate that the spaces are enlargements of the interstices between the prisms and the tenants of the interstices. The enamel-fibers are in direct connection with the contents of the spaces, — i.e., with living matter. The spaces, at their stem-like beginnings, run, accordingly, parallel with the interstices; but in their broader portions ma^y cross the enamel-prismS in different directions. FAULTY DEVELOPMENT. 215 If they are few in number tliey may protrude from the bound- ary Ime of a cusp-layer, and penetrate the adjacent cusp-layer obliquely to the main direction of the enamel-rods. In this in- stance I could trace the connections of the enamel-fibers even with the club-shaped ends projecting into the neighboring cusp- layer. If these spaces are present in large numbers, the enamel, with lower powers of the microscope, will look dark and granu- lar; hence the name, 'granulation of enamel,' which I have given it. Pig. 131. Geanular axd Slightly Pigmented Examel. Club-, spindle-, pear-shaped, and irregular spaces at the boundary of a cusp-layer in the middle of enamel. Magnified 1200 diameters. " Fig. 127 represents this condition of granulated enamel, with a low power. " Fig. 131 shows the condition under a high power. "• In stratified and granular enamel, single strata may be pro- duced by an interruption of the pigmented enamel-rods, by con- vex ends directed toward the adjacent peripheral cusp-layer. (See Fig. 130.) " The interprismatic spaces of the enamel bear some resem- blance to the interglobular spaces of the dentine. I have seen 216 THE ANATOMY AND PATHOLOGY OF THE TEETH. both conditions in a highly-marked degree present in one of my specimens. Whenever these interprismaiic spaces are present along the border of a cusp-layer, they considerably lessen the degree of consistence of the enamel, which, npon being ground, easily breaks oif along the dark granular line. " The nature of the mterprismath: spaces is plain enough. They mean an incomplete formation of the enamel, owing to some deficient-y of function in the enamel-organ during its for- mation. Obviously, not only the basis-substance is deficient, but also the amount of lime-salts is considerably less than nor- mal; hence its brittleness and proneness to decay. " Under the foregoing headings I have described a number of anomalous conditions of the enamel, which, at least so far as stratification, pigmentation, and granulation are concerned, mean a deficient formation of the basis-substance, together with decreased deposition of lime-salts. These conditions are, in my judgment, of the utmost importance in the etiology of caries. Ailments either of the mother during gestation or of the infant in the earliest periods of life, obviously cause such anomalies in this tissue. These ailments are known to occur far more fre- quently in refined people, debilitated, as it were, by civilization, than in strong, hard-working, plain-living people, continually engaged in a struggle for life. Thus, I have directly demon- strated and anatomically shown, in a measure, at least, the reasons why refined people are far more subject to caries of the teeth than people lacking such refinement." The other contribution, by Frank Abbott, to the knowledge of faulty development of enamel is Congenital Defects in Enamel.^ " Every dental practitioner is more or less familiar with the condition of imperfect or defective enamel upon the crowns of permanent teeth (more especiall}^ the incisors and first molars), which I propose to consider under the above heading. These imperfections usually concern the summit of the crown or its vicinity. We see upon an otherwise well-developed crown an almost circular ridge, above which the enamel appears of a grayish-brown color, and in the shape of numerous pointed, thorny projections, the masticating surface of molars appearing as if provided with numerous minute stalactites or stalagmites. (See Fig. 132.) * Dental Cosmos, 1891. FAULTY DEVELOPMENT. 217 " In some cases there are only a few blunt or pointed protru- sions of enamel, between which the dentine is entirely destitute of such covering. In others the dentine is nearly covered with enamel, leaving rows of small round or oblong holes through it to the dentine. These features appear, as before stated, only in permanent teeth, and very seldom are any except the incisors and first molars involved. Whether or not the complete absence of enamel from the crowns of incisors, as is sometimes seen, is Fig. 132. CONGENITALLY IMPERFECT CkOWS OF LOVTEE MOLAB. ^■, shortened crown ; C, C, cones of enamel ; 1), dentine without enamel covering. Magnified 4 diameters. of the same nature, and due to the same causes, I am not pre- pared to say, although it seems probable. " In looking with the naked eye at a longitudinal section through a molar, aifected as just described, we at once recognize the deficiencies of enamel, the stalactite or stalagmite appear- ance, and the shortening of the crown by about one-eighth of an inch, caused by these deficiencies. " These blunt and pointed elevations are made up partly of 218 THE AXATOMY AND PATHOLOGY OF THE TEETH. healthy-looking and partly of a yellowisli-brown enamel. Be- tween the elevations are areas partly covered by an extremel}'^ thin layer of enamel and partly destitute of it. By grinding the crown of such a tooth in longitudinal section for microscopi- cal examination, the masticating surface presents an extremely striking image. (See Fig. 133.) "A well-developed, though slightly-pigmented, enamel is seen to be gradually tapering toward the masticating surface, show- FiG. 133. Section or Masticating Surface, shotting Partial Covering of Enamel. E, well-developed enamel ; L, isolated lumps of enamel ; D. D, dentine : /, 1. interglobular spaces. Magnified 100 diameters. ing marked deficiencies of the outermost layer. These deficien- ' cies consist of conical depressions at the surface and granula- tions near it. Obviously this condition was caused by an incom- plete calcification of the enamel, iTom the fact that it has taken up or absorbed a deep brown pigmentation. The tapering layer of enamel stops abruptly, leaving the dentine entirely un- covered, as is seen in several places; besides, there are irregular hilly protrusions of an enamel of a deep brown color. These are the protrusions furnishing to thegrinding-surfacethe appear- FAULTY DEVELOPMENT. 219 ance of groups of stalactites. Slabs exposed to the action of a half per cent, solution of chloride of gold for one hour, exhibit a dark violet color of the dentine in the crevices between the enamel-lumps, which means that a portion of the lime-salts has been dissoh^ed out, although no destruction of the organic por- FiG. 134. Isolated Lump of Enamel, Very Imperfect. P, P, P, protoplasmic projections into the enamel from the dentine ; C, transverse section of enamel-prisms ; B, dentine. Magnitied 500 diameters. tion of the dentine has taken place. At the usual distance from the mterzonal layer are seen interglobular spaces. " L*et us magnify a lump of enamel in this locality live hun- dred diameters. (See Fig. 134.) " "We notice in this specimen narrow prisms, markedly wavy, and interrupted by faint concentric striations. The prisms, as 220 THE ANATOMY AND PATHOLOGY OF THE TEETH. usual, do not reach the surface of the dentine, but at a given distance from it they are replaced by irregular angular pieces. The outermost portion of the lump is of a dark brown color. Penetrating the enamel at varjing heights are seen numerous pear-shaped prolongations of the dentinal canaliculi, some ex- tending nearly to the surface. These spaces contain protoplasm, and have become stained a deep violet color by the chloride of gold. Aside from these irregularities the lump seems to be thoroughly calcified, except in a few spots upon the surface, Fig. 135. Imperfect Enamel. E, well-developed enamel, transverse section ; G, G, granular layer of enamel, with pear- shaped protoplasmic enlargements; 7), dentine, canaliculi in transverse and oblique sections; /, interglobular spaces. Magnified 800 diameters. which have taken a slight violet stain. The exposed dentine is also deeply stained the characteristic violet color in this locality, denoting insufficiency of lime-salts, or an excess, over the ordi- nary, of organic material. " In some instances the crown of the tooth may be nearly covered with a well-developed or a stratified and slightly-pig- mented enamel, the other portions being coated with a thin layer highl}" pigmented, again denoting deficiency in lime-salts. (See Fig. 135.) FAULTY DEVELOPMENT. 221 " We present here a transverse section of the crown of a molar. The thin and irregularly-contoured enamel exhibits only transverse sections of prisms, of a deep brown color. At the interzonal layer numerous pear-shaped protoplasmic spaces are seen penetrating the enamel, and in the region nearest the den- tine the prisms appear as if granular or sieve-like (perforated with numerous small holes), indicative of a lack of proper calci- fication. " I will now call attention to some extremely interesting and instructive anomalies in the formation of this tissue, — viz, two distinct varieties of enamel, one upon the other. First we have the anomalous portion grafted or deposited upon a normal enamel, and again anomalous enamel first deposited, with the peripheral portion fairly normal. (See Fig. 136.) " This represents a cusp of a molar, with a conspicuously deficient enamel, deposited upon a nearly normal one. The normal portion is slightly pigmented, slightly stratified, and supplied with a moderate number of granulations, near the interzonal layer. The outer or peripheral portion exhibits a layer which ends abruptly on one side, and gradually blends with the normal enamel on the other. This portion is remark- ably deficient in its structure. At the boundary-line between the two portions the enamel-prisms become abruptly devious, their longitudinal course being suddenly changed to a trans- verse one. In the latter portion a few oblique sections are seen alternating with the transverse. The whole portion superadded to the normal is pierced by innumerable granulations, which, owing to their violet color, we must conclude as protoplasmic in structure, and, of course, deficient in lime-salts. The granu- lations are, in some places, arranged in rows, in others scattered irregularly. If a large mass of enamel exhibits prisms almost rectangular to their original normal direction, it is not an evi- dence of interlacing of such prisms, but of their unusually wavy courses. An originally deficient enamel, upon which is deposited a normal one, is represented in Fig. 137. " Here we observe numerous layers made up of extremely narrow, interrupted prisms, and at a given line prisms of normal width appear, first in transverse, then in longitudinal sections. This specimen affords a good opportunity to trace one and the same prism in longitudinal, oblique, and transverse section. " In all the teeth with imperfect enamel that I have examined. 222 THE ANATOMY AND PATHOLOUY OF THE TEETH. the so-called interglobular spaces were present in the dentine, indicating a deficient calcification of territories at the period of development which corresponds with that of the formation of enamel. In only one specimen have I seen a devious course of the dentinal fibers and stratification of the dentine. Fig. 136. Imperfect, Grafted upon Perfect Enamel. D, dentine ; B, boundary zone (interzonal layer) ; E, perfect enamel : E^, imperfect enamel. Magnified 100 diameters. " In one instance peculiar formations were seen in the ce- mentum. (See Fig. 138.) " The cementum here exhibits distinct lamellations and scat- tered cement-corpuscles, with their longitudinal diameters mostly arranged perpendicular to the direction of the lamellte. The cementum was abruptly interrupted by the dipping downward FAULTY DEVELOPMENT. 223 of the pericementum to the close vicmity of the dentine. In this situation the prolongations of the pericementum were hardened by globular depositions of lime-salts, which were conspicuous by a high degree of refraction. " This anomaly — altogether different from the process of absorption of the roots of temporary teeth, or that of bone — Fig. 137. Perfect, Grafted cpox Imperfect Examel. E'^, irregular and imperfect layer of enamel ; E-, regular layer of enamel ; D, dentine ; 1, interglobular spaces. Magnified 500 diameters. must have occurred at the time of the development of the ce- mentum, which, as is well known, takes place after the forma- tion of the dentine. "A remarkable feature in connection with this case was the apparently perfect condition, in the mouth, of the gum and 224 THE ANATOMY AND PATHOLOGY OF THE TEETH. alveolus. In the pericementum the microscope revealed noth- ing anomalous except a few scattered calcified patches. It is hardlj possible that there is any especial connection between this and the morbid process in the enamel, as the enamel is com- pletely formed at a much earlier period than this could have happened. As to the causes which lead to the imperfections in the enamel and other portions of the teeth during the process of development, I will quote as follows from an article on ' Den- tition and its Derangements,' by A. Jacobi, M.D., 1862. He says,— Fig. 138. Irregularities of Cementum. P, pericementum ; C, stratified cementum with cement-corpuscles ; E, excavations of cementum filled with pericementum; G, globular stratified depositions of lime-salts; D, D, dentine. Magnified 100 diameters. " ' The enamel of the teeth is subject to several anomalies. It may be either defective or discolored. Its defective formation ap- pears either in excavations dispersed over the surface of the tooth, or there are complete furrows or transverse notches around the crown of the tooth, the body being still covered with or entirely deprived of enamel. This atrophy is the result of those severe diseases which the child may have been suffering from during the development of the enamel. Acute exanthems are said to FAULTY DEVELOPMENT. 225 produce the dispersed excavations; acute inflammatory diseases, the furrows; and rhachitis has often been observed to be the cause of the entire absence of the enameL The incisors ot rhachitic children are usually small, appear late, and are verj'^ liable to become carious. Acute exanthems are counted among the causes of this anomaly, especially by such writers as classify the teeth with the dermal tissue. Smallpox is related to produce isolated excavations which have a great similarity to the cica- trices remaining after smallpox. To vaccination, also, some have attributed the defective development of the enamel. . . . The mucous membrane of the mouth is verj^ irritable, being accustomed only to amniotic liquor in foetal life, and to milk in the early stage of extra-uterine existence. Every change in the diet, therefore, the bad quality of the material, or artifi.cial nipples, the use of candy, sucking-bags, or alcoholic beverages, cofiee, or stimulants of whatever kind, will act as irritants, pro- ducing hyper?emia or inflammation in a more or less severe form. ... A more severe form is that known by the name of aphthous stomatitis. The superficial layers of the epithelium are not thrown otf during the hypersemic swelling of the mucous membrane, as in erythematous stomatitis, but a real and visible change takes place in the anatomical structure of the follicles. There is a circumscribed, punctated, vascular injection around a follicle which is gradually infiltrated by exudation. The con- secutive swelling increases in proportion, the follicles will burst and exhibit a superficial erosion or ulceration, and the adjacent mucous membrane will be sympathetically aflfected.' " Edmund Lesser says, ' In the majority of haired men, which means congenital grow^th of hair all over the face (hirsuties), I hitherto have observed that defects or irregularities of the dental system were present, since not only a number of teeth, but the corresponding alveoli, were missing. In some cases of normal dentures a broadening of the alveolar processes was apparent.' " Although of epithelial origin, the enamel-organ is of a myxomatous structure, and thus represents a variety of connect- ive tissue. The history of development of enamel (which makes its appearance about the seventh month of foetal life) is well understood, as far as temporary teeth are concerned, up to the time of birth of the child. Still we know nothing as to the progress of the lateral pegs in laying the foundation of the 16 226 THE ANATOMY AND PAIHOLOOY 0¥ THE TEETH. enamel-organ and the enamel of the permanent teeth. We simply conclude that the process is identical with that of the tem- porary teeth, in its development during the earliest years of extra- uterine life. Since the imperfections of enamel, as described, are observable upon permanent teeth only, I, without fear of contradiction, venture the hypothesis that diseases of the oral cavity only affecting the epithelial layers, and the pegs derived therefrom, must -cause these defects. Such diseases occur in the oral cavity of young children, under the headings of inflamma- tion (stomatitis), from many causes, leading to the formation of blisters, ulcers, and abscesses. Growth of mildew (so-called thrush) is known to be a fertile source of both such superficial and deep-seated disturbances. " Acute exanthems, which sometimes spread to the mucous membrane of the oral cavity, undoubtedly play an important part in causing inflammation of the enamel-organ, which results in producing defective enamel. "We can appreciate the probability that inflammation will partially destroy either the original epithelia or the enamel- organ derived therefrom, and thus be the direct cause of defect- ive enamel. A simple obliteration of a number of blood- vessels which freely surround this organ would suffice so to interfere with its proper function as to diminish the amount of lime-salts deposited; the enamel-prisms in such case might develop normally as to size, but show deficiency in calcification. If, with the inflammation and obliteration of blood-vessels, hemorrhage takes place into the enamel-organ, or effusion of haemoglobin should occur, pigmentation of the deficiently calci- fied prisms would become intelligible. " We can realize that the medullary tissue giving rise to enamel-prisms will, in consequence of inflammation, be so altered or misplaced that the outcome would be imperfect, in- complete, or devious prisms. As I showed in 1885 that the formation of enamel takes place in the shape of layers for the crown and layers for the neck, we may grasp the possibility that the earliest crown-layers may be fully and regularly developed, while the last crown-layers are interfered with and become defective. Should, therefore, an inflammatory process start at the time of the appearance of the earliest crown-layers, and soon abate, the enamel nearest the dentine will be found imperfect. If the inflammatory disturbance continues for a long period, the DEVELOPMENT OF CEMENTUM. 227 result will be a thin and incompletely calcified layer of enamel. Should portions of the enamel-organ be completely destroyed by suppuration, entire absence of enamel at such points will be the result. A number of so-called miliary abscesses in the enamel-organ will lead to a porous or ' pitted' enamel. A limited number of somewhat laro-er abscesses would cause laro^er holes or pits, or possibly the entire enamel-organ might be destroyed, leaving the dentine entirely unprotected. '' In all the cases of teeth with defective enamel that I have ex- amined, the dentine has been found fully developed and perfectly calcified, with the exception of quite numerous interglobular spaces. These appear in the dentine at the same period ot development during which the enamel-organ was ati:ected. This positively indicates the disease or diseases which caused the production of imperfect enamel to have been local rather than general, as has been supposed by some pathologists.'' CHAPTER XVII. DEVELOPMENT OF CEMENTUM.* Our researches into the history of the development of the teeth extend over a period of eight years, and a large collection of specimens has been at our disposal, IsTevertheless, until re- cently, we hesitated about saying anything upon this topic, as none of the specimens of which we were then possessed revealed anything of interest concerning the development of cementum. This tissue, in human beings, is developed after birth, when the root and its dentine have been fully formed. We know that at the time of birth only the crowns of the temporary teeth are present, but there is no trace of the roots. At what time the tissue in question begins to appear in the human subject, we are unable to state. The only specimens at our disposal, in which the question of the development of the cementum could be studied, were obtained from the lower jaw of a kitten about six weeks old. As the course of development of dentine and *" Contributions to the History of the Development of the Teeth," by C. Heitzmann and C. F. W. Bodecker. The Independent PractHloner, vols, viii, ix. 228 THE ANATOMY AXD PATHOLOGY OF THE TEETH. enamel is almost identical in cats and men, we feel justified in the assumption that the formation of cementum is likewise the same in both. "We are the more confident because of the knowl- edge that the development of bone exhibits the same features in cats as in men, and because, as is well known, cement is nothing: but bone-tissue. ^\G. 139. 13 \ c fcfe)"J>[ ^^/^' M '\'}' i\ ¥^k^ UU, PO \ \ ^l M^&XiKKm Apex of the Root of a Tempoeaey Tooth of a Kittex Six "Weeks Old. Vertical Sectiox. Z>, dentine: C, cementum, in part thoroughly calcified, and partly made up of medullary corpuscles: CB, basis-substance of the cementum, composed of medullary corpuscles; PC,- pericementum. Magnified 200 diameters. In the above-mentioned specimens, taken from a kitten six weeks old, we observed both the temporary and permanent teeth in place. The temporary teeth were fully developed and their roots perfect, whereas the permanent teeth only exhibited a small cap of dentine and enamel over the papilla, correspond- DEVELOPMENT OF CEMENTUM. 229 ino; to a human foetus between the seventh and eis^hth months of intra-uterine life. Both the dentine of the crown and that of the root, especially of the latter, were partly absorbed, and they exhibited bay-like excavations, which were filled with multi- nuclear protoplasmic masses. The cement at the cervix of the teeth in cats is a compara- tively narrow formation, made up, as in the teeth of men, of delicate spindles arranged perpendicular to the longitudinal axis of the root, between which spindles we observe no cement-cor- puscles. This layer is evidently developed from spindle-shaped medullary corpuscles, of which a whole row is visible in the neighboring pericementum, A direct calcification of these medullary corpuscles leads to the formation of the cementum of the neck. Farther down, the cementum becomes broader by the addition of a row of medullary corpuscles greatly vary- ing in size, and without distinct lines of demarcation between them. "With lower powers of the microscope their protoplasm appears finely granular ; with high powers, however, a distinct reticulum is recognizable, the same as in all protoplasmic for- mations. Toward the dentine the medullary corpuscles assume ■a high grade of refraction, indicative of a deposition of lime- salts, which latter have been removed by the treatment with the ohromic-acid solution. The boundary-line between the dentine and cementum is nowhere distinctly marked. Still farther down toward the apex of the tooth scanty cement-corpuscles make their appearance, invariably surrounded by a number of finely-granular medullary corpuscles, without any marked terri- torial formation around each bone-corpuscle. IsTearer to the apex the cementum becomes very broad, exhibiting a number of cement-corpuscles. Here this tissue is fally developed around the dentine, but is yet in the process of formation at the periph- •ery of the root. The latter portion plainly reveals the manner in which the cementum is developed. Like all the tissues of the body, including the dentine and the enamel, the cementum arises from medullary tissue. In this respect cementum and bone-tissue show a striking likeness. The medullary corpuscles from which bone-tissue arises bear the name of osteoblasts, and should any one desire to give a special name to the formers of the cementum, that of cemento- blasts should be admissible. These corpuscles become the seat of a deposition of lime-salts before any cement-corpuscles are 230 THE ANATOMY AND PATHOLOGY OF THE TEETH. conspicuous. We observed that the previouslj^-calcified medul- lary corpuscles are decalcified, and after a second calcification some of them remained unchanged, exhibiting an angular shape characteristic of bone- and cement-corpuscles. This stage, how- ever, still represents an incomplete form of cementum. Lastly', another decalcification of the medullary corpuscles takes place, and this time distinct groups of medullary corpuscles become visible, the centers of which are occupied b}' the cement-corpus- cles, and in this manner the territories of the cementum as well as those of bone-tissue arise. After calcification of the medul- lary corpuscles has been accomplished, neither the medullary corpuscles nor the boundary-lines of the territories are conspicu- ous; but when calcification is incomplete, both the medullary corpuscles and the territories are easily recognizable. With high powers of the microscope we more readily observe the manner in which the cementum is developed. As long as this tissue is imperfect, and not fully calcified, a number of the medullary corpuscles assume a certain degree of refraction which marks partial calcification, whereas some of the medullary cor- puscles retain their protoplasmic nature, and thus represent the cement-corpuscles. Nearer to the dentine the medullary cor- puscles are arranged in clusters, in the center of which we observe the cement-corpuscles. As a rule, each cement-corpus- cle is surrounded by a number of medullary corpuscles repre- senting a territory. ISTot infrequently a territory is indistinctly defined. This is the case wherever the cement-corpuscles are separated from each other by a single row of medullary corpus- cles only, or where the deposition of lime-salts has been com- pleted, whereupon both the medullary corpuscles and the boundary-lines of the territories are lost to sight. (Fig. 140.) The question arises, How are the otfshoots of the cement-cor- puscles formed ? In order to understand this process, we must bear in mind that the medullary corpuscles, even when incom- pletely calcified, exhibit the reticular structure characteristic of all protoplasmic formations. They greatly vary in size, and are separated from one another by light rims, which invariabl}' appear traversed by delicate conical ofifshoots. It is obvious that the oiFshoots are formations of living matter, serving for the interconnection of all medullary corpuscles. Whenever lime- salts are deposited in the meshes of the reticulum of the medul- lary corpuscles, the interstices between them remain free from DEVELOPMENT OF CEMENTUM. 231 MB sueli a deposit. The conical offshoots between the medullary corpuscles coalesce at the centers of the latter into a filament of living matter, — the offshoot of the bone- or cement-corpuscle. Such a delicate offshoot remains interconnected by the lateral filaments running into the reticulum of the medullary corpus- cles, the same as is the case with dentine- and enamel-fibers. Even where the calcification of the medullary corpuscles has assumed its highest degree, and where all boundary' lines Fig. 140. CO Cementum i.v the Process of FoRM.iiiox of a Temporary Tooth of a Kitten' Six Weeks Old. J/, medullary corpuscles incompletely calcified, but still recognizable; MB, medullary cor- puscles thoroughly calcified in parts and transformed into basis-substance ; CV, cement-corpus- cles partly lying in a completely-calcified basis-substance, and partly occupying the centers of groups of medullary corpuscles, the so-called territories ; B, basis-substance. Magnified 1200 diameters. between them have disappeared, the reticulum in the basis- substance remains unaltered, and plainly visible with a good immersion lens, without the addition of any reagent. The results of our researches concerning the history of development of the cementum of the temporary teeth of a kitten six weeks old are as follows : I. The cementum arises from medullary tissue, the same as bone- and all other tissues of the bodv. 232 THE ANATOMY AND PATHOLOGY OF THE TEETH. II. The medullary corpuscles first become the seat of a deposi- tion of lime-salts before any cement-corpuscles are visible. III. The lime-salts are dissolved and redeposited again in the medullary corpuscles, which are arranged irregularly around the cement-corpuscles, the latter, however, remaining free from calcareous infiltration. IV. Still later the medullary corpuscles are arranged in groups, the centers of which are the cement-corpuscles, the sum total furnishing the territories around the cement-corpuscles. Y. The offshoots of the cement-corpuscles are filaments of livino- matter, orio-inatino; from the briclo:es traversing the inter- stices between the medullar}' corpuscles. VI. The reticular structure of the original medullary corpus- cles is preserved in the basis-substance even after the completion of the calcification of the latter, and the disappearance of the original medullary corpascles. The development of the roots of the temporary as well as the permanent teeth has been carefully studied, as far as naked-eye appearance goes, by C. i^. Peirce. The illustrations published by him I have copied in the chapter on " Faulty Development," Fig. 120, page 196. My rather limited knowledge of this topic will excuse mv reference to an author known to be reliable. CHAPTER XVIII. THE DEVELOPMENT OF TEETH IN EMBRYOS AFFECTED WITH EHACHITIS.* Amono the numerous embryos whose teeth the writers have examined, there were three aftected with so-called congenital rhachitis. One of these was a seven-months" foetus, another seven months and a half, while the third was eight months old. Macroscopically the two former did not exhibit any symptoms of rhachitis, and it was only upon microscopical examination of the jaw-bones that we were enabled to recognize the morbid process, whose characteristic feature is a new formation of hya- * " Contributions to the History of Development of the Teeth, "' by Carl Heitz- mann and C. F. TT. Bodecker. Indepenrlent Practitioner^ vols, viii and ix. DEVELOPMENT OF RHACIIITIC TEETH IX EMBRYOS. 233 line cartilage in the place of bone-tissue. The trabecular of the cancellous bone-tissue were scantier, and the lione-corpuscles within them were much larger, than those iu normal bone-tissue. In many places, however, hyaline cartilage was present instead -of bony trabeculte, and in the medullary spaces between them. The cartilage-corpuscles often were of a brown color, caused either by previous hemorrhage or by a new formation of blood- corpuscles and haemoglobin. The third foetus, which was eight months old, showed the symptoms of congenital rhachitis in such a degree that all l»one-tissue throughout the l;>ody was lacking, and only in the lower jaw were found a few trabeculEe. This foE-tus was delivered l)y a healthy woman, who, during her pregnancy, for a nural»er of months furnished dogs, cats, and rabbits with soup, meat, bread, and vegetables, mixed respect- ively ^^ith lactic acid, for the purpose of artificially producing rhachitis and osteomalacia in these animals. These experiments were made by Carl Heitzraann (see '' Microscopical Morphol- ogy," 1888) and proved to be successful. Dogs and cats, treated with lactic acid soon after birth, became rhachitic, and treated with lactic acid for several months in succession, l)ecame affected with osteomalacia. The woman who gave l;»irth to this ftjetus was healthy during pregnancy, and remained so after delivery. The f* etus, on the contrary, died shortly after Ijirth, from intracranial hemorrhage caused by pressure during labor, on account of the complete absence of cranial bones. The abnormal occurrences in the teeth of these three rhachitic embryos were so striking and so numerous that we made an attempt to arrange them under a number of headings, being aware of the fact that diiferent chronic ailments both of a mother and of a foetus, more especially rhachitis of the foetus, reflect on the growth of the teeth, and leave marks in the shape of transverse grooves or furrows upon them. I. Premature Eruption of Ill-developed Teeth, found in the lower jaw of a rhachitic fptus. seven mimths old. (See Fig. 141.) This tooth had reached a stage of development corresponding to about the seventh month of intra-uterine life, but had grown above the level of the gum, and was plainly visible to the naked eye. This specimen helped to settle a mooted question con- cerning the origin of Xasmvth's membrane, — the c-uticle of the 234 THE ANATOMY AND PATHOLOGY OF THE TEETH. tooth. The writers observed that the flat epithelial layer cov- ering the summit, and the dentine at the deeper portion of the tooth, is a direct reduplication of the flat epithelial layer of the gum. The papilla is moderately supplied with blood-vessels. Fk 141 Premature Eruption of a Lower Incisor of a Ehachitic Fcetus, SevenIMoxths Ol.D. G, gum ; G, fibrous connective tissue ; EO, myxomatous enamel-organ. Magnified '50 diameters. and is of a markedly myxomatous structure, especially at its lower part, which appears lobulated. It is bordered by a structureless layer at its lower portion, which we consider a normal feature, and w^hich is always present previous to the DEVELOPMENT OF RHACHITIC TEETH IN EMBRYOS. 235 appearance of odontoblasts. The gum is composed of a loose, delicate, fibrous connective tissue. At the right side of the specimen, near tlie lower portion of tlie papilla, there appears an isolated layer of invxomatous tissue, which extends below the papilla, bearing the characteristics of the enamel-organ. Its outer periphery shows a number of buds or nests, which are the offspring of the external epithelium. II. Double Papillae. — In the same foetus the writers observed two papillae of lower bicuspids, which at their bases were united into one continuous l>road mass, whereas higher up there was seen a cancellous bony structure, separating the papillae, which proves that they belonged to two separate teeth. The struc- ture of these papillae was markedly myxomatous, similar in appearance to that of the papillae of pig's teeth. The enamel- organ appeared to be in full development, being lined by the internal epithelium, which was broken up into medullary tissue, and an external epithelium broken up into epithelial nests. Along the internal epithelium peculiar folds and indentations are visible, which the writers propose to describe later on. iSTo trace of dentine or enamel was visible upon these germs. III. Dwarf Teeth. — In the rhachitic foetus which was seven and a half months old, the writers met with minute teeth which were in a stage of development corresponding to the age of the foetus. (See Fig. 142.) The papillae are of very irregular shape, being partly blunt, partly elongated, and sharply marked by a constriction at the place corresponding to the neck of the future tooth. Above the neck the papillae are of the usual lancet or myrtle-leaf shape, exhibitino; alonsr their borders either odontoblasts or rows of medullary corpuscles, and showing comparatively few blood- vessels. The dentine is curved around the constriction in a marked degree, surrounding the neck of the tooth like a cap. Its canaliculi are wide, but without pathological features. The enamel is likewise to be considered normal, but the enamel- organ is missing in all of these specimens, which indicates that the myxomatous reticulum was exhausted. The external epi- thelium only shows its presence by small epithelial nests and buds along the already-formed enamel. A peculiar feature of both the papilla and the surrounding connective tissue is the presence of rusty-brown, needle-shaped crystals of haematoidin, sometimes clustered together in numer- 236 THE ANATOMY AND PATHOLOGY OF THE TEETH. oa3 masse?. These are the result of a previous hemorrhage, although it is not expHcable how they appear in the papilla, where the blood-vessels are extremely scanty and just in the process of formation. IV, Malformations and Malpositions of the Enamel-Organ. — In the teeth of a rhachitic foetus we not infrequently meet with enamel-organs markedly differing from normal ones, the difference mainly consisting in the lack of a myxomatous reticulum. This tissue appears in the shape of small, glistening Tig. 142. D^TARFED Teeth of a Ehathitic Fcetus, Seyex and a Half Months Old. A, blunt foot-shaped papilla, with a constriction, from which the dentine starts; i?, elon- gated narrow papilla, from which grows at an acute angle the tooth, again marked by a con- stricted neck. Magnified 50 diameters. granules, arranged either in the shape of clusters or of an indis- tinct reticulum. The granules themselves vary somewhat in size, and among them larger granular corpuscles may be seen, which, without any regular arrangement, are yet entitled to the name of nuclei. The meshes of this irregular reticulum hold an apparently structureless mucoid basis-substance. Besides these irregular formations of the enamel-organ, we sometimes meet with malpositions of it, either in a normal or an anomalous condition. (See Fig. 143.) DEVELOPMENT OF RHACHITIC TEETH IX EMBRYOS. 237 In this specimen the enamel-organ is located entirely above a tooth, which is likewise anomalous. It is widened in a horizontal direction, nearl}^ parallel to the outer surface of the mucosa. It Fig. 143. Anomalous Location and Foematiox of the Examel-Oegan of a Human Fcetus Seven AND A Half Months Old, affected -n-iTH Congenital Rhachitis. EO, enamel -organ ; EE, external epithelium; E, enamel; D, dentine; P, papilla. Magni- fied 100 diameters. extends downward along the newly-formed dentine and along the upper portion of the papilla. It is lined with medullary tissue and with clusters of epithelia, both being derived from the external epithelium, whereas the internal epithelium is com- 238 THE ANATOMY AND PATHOLOGY OF THE TEETH. pletely exhausted for the formation of the enamel. The layer of medullary tissue arising from the external epithelium is broad, but short on one side, and narrow and much elongated on the other side of the enamel-organ. The tooth is anomalous not in its size, nor in respect to the stage of development it is in, but on account of its devious papilla, resembling the teeth illustrated in Fig. 142. The specimen was obtained from the same embryo as those illustrated in Fig. 142. The papilla is constricted at the place where the dentine begins, at the neck of the tooth, below which the. papilla suddenly widens and pro- duces a bluntly-elongated body of considerable size, composed of medullary tissue, and holding a number of clusters of hsema- toidin crystals, which are also seen in the neighboring fibrous connective tissue. Another misplacement of the enamel-organ is illustrated in Fig. 141, in which it is depicted as located beneath the base of the papilla. V. Folds, Convolutions, and Reduplications of the Epithelium of the Enamel-Organ. — In both rhachitic embryos from which specimens have been taken, we have encountered in the enamel- organ peculiar formations, which we propose to describe under the above heading. JSTear the external epithelium, which at the age designated is invariably split up, we have sometimes found concentrically-arranged epithelial nests, or clusters of medullary tissue, imbedded in an otherwise normal myxomatous reticulum. Far more common than these formations, which depend upon a reduplication of the external epithelium, are foldings and con- volutions of the internal epithelium. (See Fig. 144.) The internal epithelium shows, sometimes, simple indenta- tions, which are also observed occasionally in normal teeth of the same stage of development. At other times there is a series of successive convolutions of the internal epithelium. IS'eighboring this epithelium the myxomatous tissue of the enamel-organ, as a rule, is in a medullary condition, with and without a pronounced intermediate layer. Obviously, such sinuosities correspond to furrows of the enamel-organ, and very probably may cause the ridges and furrows often observed upon this tissue. The highest degree of reduplication of the internal epithelium is sometimes seen, together with apparently isolated buds of dentine, surrounded by and inclosed in a layer of amelo- blasts and myxomatous tissue. The dentine consists either of a narrow calcareous rim, or a cap in which we may observe dis- DEVELOPMENT OF RHACHITIC TEETH IX EMBRYOS. 239 tinct dentinal canaliculi. If the dentinal cap appears as a thin calcified ledge, it is composed of calcified medullary corpuscles, beneath which odontoblasts are perceptible. If the ledge of the dentine is broader and supplied with dentinal canaliculi, we notice close beneath it a layer of medullary corpuscles followed by a layer of odontoblasts which are usually in process of break- FiG. 144. Reduplication of the Inteexal Epithelium of a Rhachitic Fcetus Sevex and a Half Months Old, around a Bud of Dentine. ^(9, myxomatous enamel-organ; -E^, external epithelium ; A.layer of ameloblasts; /X, in- terstitial layer composed of spindle-shaped elements surrounding the ameloblasts ; A^, A^, layer of ameloblasts toward an already-formed enamel ; M, myxomatous tissue approaching the structure of medullary tissue ; D, dentine with underlying odontoblasts. Magnified 200 diam- eters. ing up into medullary corpuscles. It may be possible that such formations are the starting points of the transverse furrows ob- served upon the labial surfaces of the temporary teeth of rickety children, although these occurrences are far more common on permanent teeth. VI. Anomalies of Enamel. — It is a common feature in teeth 240 THE ANATOMY AND PATHOLOGY OF THE TEETH. of rhacliitic children that the interstices between the enamel- prisms are wide, and their tenants, the enamel-libers, are very distinct, often running a wavy course independent of the con- tours of the enamel-prisms. The prisms themselves are finely granular, without distinct cross-lines. These features are ex- plained by the evidence of a deficient calcification of the enamel^ Anomalous ExAMf:L or a Rhachitic F(etus Seven and a Half Months Old. EE, enamel-organ of medullary character arisen from the external epithelium ; E, enamel composed of prisms of a markedly wavy course ; M, cluster of medullary corpuscles,— {.c, non- calcified enamel-tissue ; IL, interzonal layer filled with medullary corpuscles ; D, dentine. Magnified 500 diameters. • which allows the cutting of thin sections of the enamel after it has been softened in chromic-acid solution, whereas it is impos- sible to obtain sections of normal enamel in the same manner. In a rhachitic foetus eight months old, we have observed in the enamel dark-brown colorations, which are to be considered as DEVELOPMENT OF KHACHITIC TEETH IX EMBRYOS. 241 pigmentations of the enamel-rods. Another feature in the ■enamel of rhachitic embryos is a markedly wavy course taken by the enamel-prisms, — so much so that in a strictly longitudinal section alternate layers of enamel-prisms appear, some of which are cut longitudinally, while others are transverse. (See Fig. 145.) Frank Abbott has already drawn attention to the fact that transverse sections of enamel-prisms, alternating with longitu- dinal sections, are not caused by an interlacing of the enamel- prisms, but by a wavy or devious course of the enamel-prisms themselves, and our specimens have furnished satisfactory proof of the correctness of the latter view. jSTot infrequently we observe at the summit of the dentine, in the interzonal layer, medullary corpuscles, either arranged in rows or irregularly scattered in the vicinity of the dentine. Such formations scarcely admit of any other interpretation than that the medullary elements, from which the enamel-prisms originate, have not been calcified, but have remained in an embryonal state. (See Fig. 145, M and IL.) In specimens from- a rhachitic foetus seven and a half months old, the enamel appeared bordered by a medullary tissue, whose orio;in could be directlv traced from the buds and clusters, the remains of the external epithelium. Here, therefore, our pre- vious assumption, that the external epithelium likewise furnishes material for the increase of the enamel, can be directly proven. VII. Anomalies of the Dentine. — The dentine of all rhachitic teeth is conspicuous by wide dentinal canaliculi, in which the den- tinal fibers and their lateral offshoots are easily discernible. The basis-substance shows a more or less marked reticular structure, without the application of any reagent. In a foetus eight months old we found peculiar formations of dentine, which evidently are caused by a deficient calcification of this tissue. (See Fig. 146.) Such spaces send offshoots upward and downward in the den- tine, which represent either conicall^'-widened dentinal canals, or broad routes replacing the same. The spaces and their larger branches are filled with medullary corpuscles in all stages of development. Where the space inosculates with dentinal canaliculi, the tenants of the latter are coarse fibrillas, with spindle-shaped widenings composed of large granules. Both within these spaces and in their vicinity we observe 'globular 17 242 THE ANATOMY AND PATHOLOGY OF THE TEETH. formations which exhibit the features of badlj-developed secondary dentine, or globular dentine, resembling the structure of the dentine of the so-called pulp-stones, or denticles. Spaces Fig. 146. Medullary Space and Globular Mass in the Dentine of a Tooth of a Rhachitio FcETUs Eight Months Old. M, medullary corpuscles filling a crescentic space in the dentine ; B, branch of the creseentic space replacing a dentinal canaliculus ; G, globular, concentrically-striated mass. Magnified 600 diameters. of this description resemble the interglobular spaces of Czermak, but thev are more irregular and much larger. VIII. Anomalies of the Papilla. — The writers have described and illustrated, in Fig. 142, anomalous papillse of peculiar shapes. In such papillfe we often observe crystals of heematoidin grouped together in clusters, the origin of which must be sought for in an imbibition by the tissue of the coloring-matter of the blood at a very early stage of development. The writers furthermore wish to draw attention to peculiar formations met with in the medullary tissue of the papilla. . (See Fig. 147.) Such globules we have observed only at the summit of the DEVELOPMENT OF RIIACHITIC TEETH IN EMBRYOS. 243 papilla, and in close connection with medullated nerve-fibers. The globules are pale, finely granular, and with either smooth or lobulated contours. Their interior shows faint marks of division, which indicate that the globules have arisen from medullary corpuscles or clusters thereof. We are unable to de- termine the nature of such corpuscles, which seem to be in relation to newly-forming medullated nerves. All the nerve- FiG. 147. Globules in the Papilla in a Rhachitic Fcettjs Seyen" and a Half Months Old. G, G, granular globules, partly smooth, partly lobulated; iV, iV, medullated nerves. Magni- fied 600 diameters. fibers seem, however, to run between the globules, although it appears in the drawing as if a bundle of nerves inosculated with a globule. This may be explained by the assumption of a de- vious course of the nerve-bundle. The most interesting feature of such papillae is that the medul- lated nerves first appear at the summit of the papilla, ^whereas the lower portions of the papillae are free from nerves, and only 244 THE ANATOMY AND PATHOLOGY OF THE TEETH. exhibit scanty capillary blood-vessels. The nerves still appear to be composed of rows of medullated corpuscles, without any trace of the niyelin sheath. Whether or not axis-cylinders are present, we could not determine from the longitudinal sections before us. This much is certain, — that the nerves grew inde- pendent of the central nervous sj'stem ; that they were in no connection with alreadj'-formed nerves of the central nervous system, and, therefore, that they must have arisen from medul- lary corpuscles in essentially the same manner as other tissues. Those who strictly adhere to the doctrine of exclusiveness in embryology — the doctrine that development proceeds from the three original layers — will try in vain to explain such an inde- pendent formation of nerves in the middle of connective tissue. CHAPTER XIX. THE DENTAL PULP.* Methods. — The best method of preparing pulp-tissue for ex- amination is to place the tooth, immediately after its removal from the mouth, in an aqueous solution of chromic acid of from one-half to one per cent, strength. To this mixture may be added, every third or fourth day, one or two drops of dilute hydrochloric acid, to hasten the process of decalcification. It is important to use a large quantity of the liquid, — not less than a quart for one tooth or a few, — and to renew the same at least every second or third day. After the teeth have been in the chromic-acid solution a few weeks, the peripheral portion of the dentine will become sufficiently soft to be cut by a razor. When the hard parts of the dentine are reached by the cutting-instru- ment, the extraction of the lime-salts must again be continued in the manner described above, until the pulp- cavity is reached. Another method is to split the tooth, as soon as possible after its extraction from the mouth, with a strong pair of excising- forceps. The teeth best adapted for this method are the incisors, cuspids, and bicuspids. By an experienced manipulator the * ' ' The Minute Anatomy, Physiology, Pathology, and Therapeutics of the Dental Pulp." Dental Cosmos, 1882. THE den;tal pulp. 245 pulps of molars can be extricated from their inclosing walls, but with less success than in the teeth before mentioned. In split- ting, put the cutting-edges of a sharp pair of excising-forceps in the longitudinal direction near the apex of a single-rooted tooth, then exert a sharp and quick pressure, when, as a rule, the tooth will split into halves with the pulp-cavity exposed. Immediately moisten the pulp with a solution of chloride of sodium in water, of the strength of about one-half of one per cent,, and then remove the pulp. The greatest care must be taken, in picking the fragments of the tooth from the pulp-tissue, to avoid tearing the organ, as tearing greatly alters the micro- scopical aspect of nerve-tissue. If the pulp is to be stained with carmin,li8ematoxylon,fuchsin,hyperosmic acid, picro-indigo, or chloride of gold, etc., place it in the staining-fluid immediately after its removal from the hard parts of the tooth. Among the reagents mentioned, I have found but one of con- siderable value, — viz, the solution of chloride of gold of the strength of one-half of one per cent. This reagent may be applied to fresh pulps as well as to very thin sections obtained after hardening in chromic acid. These specimens, however, must, as a matter of course, be carefully washed with distilled water before the chloride-of-gold solution is added. The re- agent may be allowed to remain in contact with the specimens for from twenty to thirty minutes, when they should again be washed in distilled water and exposed to daylight. In a few days fresh specimens assume a bright violet color, while sections which have previously been in a chromic-acid solution become brownish-violet. Osmic acid, in solution, one per cent, strong, renders the contours of the constituent tissues, and especially those of the medullated nerve-fibers, more distinct, as it stains the nerve-fat dark green. Both fresh and chromic-acid speci- mens may be treated with osmic acid. Thin sections do not require more than an hour's exposure to this reagent, while whole fresh pulps may be left in it for two or three hours. Ex- cept the ammoniacal solution of carmin, which is known to be excellent for staining certain parts of the tissue, I would not lay stress upon applying any of the other reagents mentioned. If we wish to examine the pulp, together with the inclosing dentine, or a pulp-stone, the specimen, previously softened by chromic acid, must be imbedded in a mixture of paraffin and wax, which is best done in the following manner. Place the 246 THE ANATOMY' AND PATHOLOGY OF THE TEETH. softened tooth in absolute alcohol for about twenty-four hours ; then, of rather thick paper, prepare a box somewhat larger than the specimen ; warm the imbedding mixture, which consists of about eight parts of paraffin and one of white wax, until it is barely liquid ; pour enough of it into the paper box about to half-fill it: then take the specimen out of the alcohol, and as soon as it begins to dry, place it in the paper box and pour over it some more of the paraffin and wax, so as to cover it com- pletely. Care must be taken not to have the imbedding mixture too hot, as it may injure the specimen. The latter, after the mixture has become sufficiently hard, is ready for cutting, when very thin sections can easily be obtained. To-da}^ imbedding in celloidin is used almost exclusively. If a fresh pulp is thin enough, it may, immediately after its removal from the split tooth, be transferred to the slide, with the addition of an indifferent fluid, such as the solution of chlo- ride of sodium, etc. But a slight and careful pressure upon the cover is necessary in order to spread fresh specimens. The fresh pulps of lower incisors, being the thinnest, are the best adapted for examining the system of blood-vessels. In a short time, however, they fade away, and the specimen becomes unfit for preservation. Isolated pulps may be placed between two plates of velvet cork, and thus cut into thin sections with the razor. I would recommend chemically-pure glycerin as the best preserving-fluid for pulp-specimens. The Minute Structure of Pulp -Tissue. — The dental pulp repre- sents the remains of the former dentine papilla, and occupies the central cavity of the tooth. It is richly supplied with blood- vessels and nerves, which enter the pulp-chamber at the apex of every root through one or more openings. The tooth for its supply of nourishing material depends upon the pulp and the pericementum. In many instances a tooth, after the death of the pulp, may be retained in its place for years, deriving its blood-supply from the pericementum only. If we exaiTiine a thin longitudinal or transverse section of the pulp with low powers of the microscope (200 diameters), we recognize a large number of blood-vessels and bundles of medul- lated nerve-fibers. The majority of these blood-vessels are capillaries; the veins are less numerous, and arteries are scarce. Often we find in a pulp only one arteriole.; frequently arterioles lie in the midst of the medullated nerve-bundles. The medul- THE DENTAL PULP. 247 lated nerve-bundles mostly run in a longitudinal direction, but not in frequently ^we observe smaller bundles, or single medul- lated nerve-fibers, to diverge from tlie longitudinal direction, and to run obliquely tbrough the pulp-tissue. In transverse sections of the pulp we meet witli arteries, veins, Normal Pulp ix Transverse Section, Stained with Chloride of Gold. From a Molar of a Youth Sixteen Years Old. 0, layer of odontoblasts, arranged in rows of medullary corpuscles; B, granular layer; M, M, myxomatous, erroneously termed "adenoid," tissue; C, C, capillary and venous blood-vessels; T, r, bundles of medullated nerves in cross-section; i, i, bundles^of medullated nerves in longitudinal section. Magnified 75 diameters. and capillaries, the first cut across, the others distributed in all directions. The bundles of medullated nerve-fibers are seen most distinctly in transverse sections. They often hold in their interstitial tissue capillary vessels and arterioles, which also appear in transverse sections. In very thin sections it often hap- 248 THE ANATOMY AND PATHOLOGY OF THE TEETH. pens that the nerve-fibers fall out, and then we see a roundish empty space bounded by the sharply-defined external perineu- rium. The absence of an endothelial coat renders such spaces easily recognizable in distinction from blood-vessels. (See Fig. 148.) The main mass of the pulp, as seen with low powers, is com- posed of a delicate fibrous reticulum, containing a large number Fig. 149. Segment of the Pulp of a First Molar Tooth. Longitudinal Section. M, myxomatous connective tissue ; V, vein ; C, capillary blood-vessel ; N, bundle of medul- lated nerve -fibers ; i^, terminal non-meduUated nerve- fibers; 5, protoplasmic layer, contain- ing the terminations of the nerves ; 0, layer of medullary corpuscles in rovys, termed odonto- blasts. Magnified 200 diameters. of bright corpuscles. Longitudinal sections in many instances exhibit delicate fibrous bundles scattered throughout the reticu- lar structure of the pulp, mostly in the neighborhood of large blood-vessels and nerve-bundles. The fibrous reticulum, in the crown portion, is evenly distributed ; in the root-portions, on the contrary, it is much elongated. Pulps composed of a fibrous connective tissue only, are rather exceptional, and, as it seems, THE DEXTAL PULP. 249 their occurrence is without any relation to the age of the per- son. They are always the result of morbid processes. Toward the outer surface of the pulp the reticular structure is, as a rule, denser than in the middle portions. This peripheral part is Fig. 150. Normal Pulp ix Traxsverse Szctiox, Staixed with Chloride of Gold. Eeom a Molar of a Youth Sixteex Years Old. 0, layer of odontoblasts, arranged in rows of medullary corpuscles ; B, granular layer ; well- developed myxomatous lymph-tissue ; M, myxomatous lymph-tissue, basis-substance still pro- toplasmic ; CL, capillary blood-vessel in longitudinal section; CT, capillary blood-vessel in transverse section; iV'i, bundle of medullated nerves in longitudinal section; iV'T, bundle of medullated nerves in transverse section. Magnified 500 diameters. surrounded by a wreath of elongated formations arranged in a radiating manner all around the pulp, — the so-called " odonto- blast layer." (See Fig. 149.) f250 THE ANATOMY AND PATHOLOGY OF THE TEETH, Higher powers of the microscope (500 to 600 diameters) re- veal a minute reticular structure, consisting of delicate fibers or anastomosing protoplasmic cords, Avith verj^ small oblong nuclei at their points of intersection. The mesh-spaces inclosed by this reticulum either look pale and finely granular throughout, or there is, besides the pale granular substance, a bright yellow- ish body, either homogeneous or granular, of the size and as- pect of a nucleus. The number of the latter formations varies greatly in diflerent pulps. "Where bundles of a fibrous tissue traverse the reticulum, there the latter blend with the former. In the fibrous bundles, besides the delicate fibrillee, we see scanty and small oblong nuclei. (See Fig. 150.) As mentioned before, the fibrous connective tissue prevails at the periphery of the larger blood-vessels and nerve-bundles. In transverse sections the latter invariably exhibit a distinct fibrous sheath containing oblong nuclei, — the so-called external perineu- rium. The nuclei imbedded in the sheath do not project above the level of the sheath, as is plainly observable on empty ones where the fibers have fallen out, while the endothelia of blood- vessels of any description invariably protrude toward the in- closed space, thus affording an excellent means of distinction between blood-vessels and empty nerve-sheaths. The arteries are characterized by the presence of a layer of smooth muscles, outside of which is seen a slight fibrous coat. The layer of smooth muscles necessarily thickens the walls of the blood-vessels, thus rendering them easily recognizable in transverse sections. The veins, marked by their large caliber, their scanty muscle-fibers, and a fibrous coat, are usually filled with blood-corpuscles. The capillaries are composed of a single endothelial layer, which is separated from the adjacent reticu- lum by an extremely delicate light rim. They are found either empty or containing a few blood-corpuscles. In longitudinal sections the medullated nerve-fibers show the well-known fluted double contour of considerable refraction (the sheath of Schwann). Inside of this is the myelin (nerve-fat) concealing the central axis-cylinder. Schwann's sheath exhibits delicate oblong or spindle-shaped nuclei, and external to this we observe a very delicate layer of fibrous connective tissue, — " the internal perineurium." In cross-sections of the nerve-bundles a more or less circular group of medullated nerve-fibers is seen, each of which in its center exhibits the axis-cylinder in the shape THE DENTAL PULP. 251 of a roundish, glistening dot, the single nerve-fibers being sepa- rated from one another by the delicate internal perineurium. Not infrequently capillary and arterial blood-vessels are met with between the nerve-fibers which, at the periphery of the bundles, blend with the nucleated sheath of the external peri- neurinra. As to lymphatics of the pulp, I can say that in some speci- mens I have seen branches of vessels of the size of veins with- out an adventitial coat,^ and composed of large, flat, slightly- protruding endothelia. These vessels I believe to be lymphatics, as they contained a finely-granular coagulated albumen, scanty granular corpuscles, and a very limited number of blood-cor- puscles. As to the distribution of lymphatics, I must abstain from positive statements. It seems that pulps containing calcareous globules afford the best opportunity for the study of the lymph-vessels, owing to their dilated condition. Fig. 151 is taken from the coronal por- tion of such a pulp, and beautifully shows the relation of the lymph- and blood-vessels to the bundles of medullated nerves. At the periphery of the pulp the delicate reticulum consti- tuting the pulp-tissue is very dense, and its small meshes are supplied with numerous corpuscles looking like nuclei. In this layer we meet with only narrow capillary blood-vessels. The outer surface of this layer is bounded by radiating rows of shining -corpuscles of the size and appearance of nuclei. These rows are separated from one another in a longitudinal direction by light rims, in which, frequently, delicate fibrillse may be observed. • In chromic-acid specimens stained with carmin, or, still better, in those treated with chloride of gold, high powers (1000 to 1200 diameters) reveal an extremely minute reticular structure pervading all formations of the pulp-tissue. The formations at the periphery of the dental pulp, which Avere termed " odontoblasts" by J. Tomes, and which by some observers have been considered as epithelium-like formations, under high amplifications exhibit the following: Longitudinal bodies, somewhat resembling epithelia, border the pulp in a radiatory direction. Such a field may appear in the shape of a finely-granular protoplasm or basis-substance, in which there are imbedded oblong nuclei in varying numbers. The nuclei exhibit coarse granules and a dense reticulum of living matter, while the elongated fields inclosing the nuclei exhibit 252 THE ANATOMY AND PATHOLOGY OF THE TEETH. pale granules and a delicate reticulum. Between these latter formations a narrow light rim is seen, wherein we observe some- times broad, sometimes delicate, fibrillse in connection with the reticulum of neighboring formations, accompanied by delicate conical offshoots, which penetrate the surrounding rims at right Fig 151 Vessels and Nerm.s of the CRO'\^^ of a Pulp contaimng Calcareous Globules. N, N, large and small bundles of medullated nerves ; A. arteriole ; F, V, veins ; C. eapillarj- blood-vessel; i, Z, lymph-vessels ; J/, 3f, myxomatous lymph-tissue. Magnified 200 diameters. angles. In many instances these formations between the odonto- blasts may be traced into the dentinal fibers, lodging in the middle of the dentinal canaliculi. It is evident, from what I have seen, that the odontoblasts THE DEXTAL PULP. 253 furnisli the matrix for the basis-substance of the dentine, whereas the dentinal fibers, being formations of living matter, originate between the odontoblasts. (See Fig. 152.) In specimens of a nine-months' foetal pulp, sufficiently stained with chloride of gold, I have observed that the medullated nerve- fibers upon approaching the peripherv of the pulp are destitute of their myelin sheath, and now, being bare axis-cylinders, split into numerous extremely delicate beaded fibrillte, — the '• axis- FiG. 152. ■<^f Skgiiest of the Pclp of a Tempoeaet To:r>:. .^liiyEo with Chlobidb of Gold. M, myxomatous conneetiTe tissue : X. terminal non -medullated nerve-fibers, in a uniformly granular protoplasmic layer : 0, rows of medullary corpuscles, termed odontoblasts : F, dentinal fibers between the odontoblasts ; I), dentine. Magnified 12C0 diameters. fibrillje.'" They are marked by a dark-violet color, and run in the light rims between the rows of the odontoblasts near the pulp-tissue proper, and are connected with the odontoblasts by means of delicate conical ofishoots. In some instances I have observed that these axis-fib rilliEe terminated in knob-like extremi- ties. But whether the nerve-fibers directly anastomose with the dentinal fibers I am unable to say. That an indirect connection of the two is established by the intervening reticulum of living matter. I positively assert. 264 THE ANATOMY AND PATHOLOGY OF THE TEETH. The results of mv researches of the normal pulp are as fol- lows: I. The dental pulp is a variety of connective tissue termed myxomatous, representing an embryonal form of it. Some authors have called this form of tissue " adenoid," but this term is admitted to be erroneous. II. The myxomatous tissue of the pulp is intermixed with a delicate fibrous connective tissue in varying amounts. III. The pulp-tissue is traversed b}^ a closed system of blood- vessels, — viz, arteries, veins, and capillaries. At least one artery is invariably found in the pulp, and it is by no means of excep- tional occurrence that the pulp contains several arteries. Lym- phatics in srnall numbers are also present. IV. The pulp-tissue is richly supplied with nerves, which, in the shape of bundles of medullated nerve-fibers, traverse the myxomatous tissue. Toward the periphery of the pulp they lose their m3^elin sheaths, become non-medullated, and, in the shape of minute beaded fibrillse, branch between the odonto- blasts. V. The odontoblasts at the periphery of the pulp are elon- gated protoplasmic formations with rows of nuclei. They are medullary corpuscles such as we see wherever a new tissue arises from a former one. They build up the basis-substance of the dentine by solidification (transformation into glue, and infiltra- tion with lime-salts). The reticulum of living matter traversing the odontoblasts remains unchanged in the basis-substance of the dentine. VI. The dentinal fibers originate between the odontoblasts. Being formations of living matter, they are in direct connection with the reticulum of living matter, — first of the odontoblasts and afterward of the basis-substance of the dentine. The con- nection between the ultimate nerve-fibrillse and dentinal fibers is very probably an indirect one by means of the intervening reticulum of livino; matter. THE PERICEMENTUM. 2od CHAPTER XX. THE PERICEMENTUM.* The pericementum (root-membrane, or alveolo-dental peri- osteum, or periodontium, etc., as it has been termed by former writers) is a formation of fibrous connective tissue, identical with the periosteum which covers all bones. It consists of a layer interposed between the roots of the teeth and their corre- sponding bony alveoli, and is common to both. It is continu- ous with the connective tissue — the so-called sub-mucous layer of the guni — and with the periosteum of the maxillse. Its fibers are connected with the cementum of the root as well as with the wall of the alveolus. A few writers have described the pericementum as a double membrane, one portion of which belongs to the root, the other to the alveolus: we ourselves have not been able to see anything that justifies such a discrimination. In many of the specimens examined, the connective-tissue bun- dles of the pericementum may be traced from the socket to the cementum of the root of the tooth, or in connection with the reticular structure in the vicinity of the root. Exceptionally we see, close around the root, a thin layer of very dense and fine fibers, the general direction of which is not quite identical with that of the connective tissue which produces the main mass of the pericementum. The relations between the soft and the hard formations of the jaws are very plain in specimens obtained from grown cats, and in all essential points are in accordance with those perceived in specimens taken from the liuniau jaw. The course pursued by the connective-tissue bundles is slightly wavy and oblique, starting from the cementum and running up- ward toward the alveolus. The bundles of this tissue are dense, without many decussations. The parallel direction of the bun- dles begins to change into a diverging one at about the height of the border of the socket, where the bundles become coarser, decussate, and thus produce the elastic connective-tissue cushion, termed the gum. From the anatomical disposition of the pericementum, con- clusions may be drawn as to its physiological action. It is evident that the relatively soft and elastic layer between the two bony * " Pericementum and Pericementitis.' Dental Cosmos. 1879-1880. 256 THE ANATOMY AND PATHOLOaY OF THE TEETH. formations — the cementum and tlie alveolus — is designed to lessen the concussion upon the jaw-bones during mastication. The oblique direction of the connective-tissue bundles is the most favorable for the suspension of the tooth within its socket, as the bundles correspond to the funnel shape of the socket, in the center of which is situated the conical root of the tooth. The elasticity of the layer of pericementum admits of a slight degree of motion of the roots; hence we understand the forma- tion of facets on the approxiraal surfaces of the crowns of the teeth in crowded maxillary arches. Fig. 153. Pekicemextum of Myxomatous Structure. D, dentine ; C, cementum of neck ; P, pericementum ; M, multinuclear body ; V, capillary blood-vessel ; F, fat-globule ■uith a vacuole. Magnified 500 diameters. We observe two varieties of pericementum, — one of a reticu- lar structure, termed myxomatous; the other altogether fibrous. The myxomatous variety I have met with, as a rule, in young individuals. It consists of delicate fibers, or bundles of fibers, in a net-like arrangement, and having, in many instances, round or oblong nuclei at the points of intersection. The meshes con- tain either a hyaline, apparently structureless, sometimes finely- granular basis-substance, or they hold protoplasmic bodies, pro- vided with a varying number of nuclei. The nearer to the THE PERICEMENTUM. 25/ cementum, the narrower is the myxomatous reticulum, and the smaller, therefore, are the inclosed protoplasmic bodies. The latter, in the immediate vicinity of the cementum, stand in more or less regular rows, entirely analogous to the protoplasmic bodies around the developing bone-tissue, known, since Gegen- baur, as "osteoblasts." Some of the meshes of the myxomatous tissue are considerably larger and contain multinuclear proto- plasmic bodies, termed " myeloplaxes" by Robin, of Paris ; " giant-cells" by R. Virchow, of Berlin, and " myeloid cells" by English authors. Other meshes hold fat-globules, which, in specimens preserved and hardened in a solution of chromic acid, very often contain closed spaces, — so-called vacuoles. The myxomatous reticulum is traversed by numerous blood-vessels, mainly capillaries and veins, some of which may be seen enter- ing the medullary spaces of the compact bone of the wall of the alveolus, and in connection with the capillary system of the can- cellous portion of the alveolus. I have met with but few nerve- fibers in my specimens. Fig. 153 illustrates a portion of the myxomatous variety of pericementum as shown with a relatively low power. High amplification of the microscope plainly demonstrates the delicate reticular structure of all protoplasmic bodies; the reticulum being visible not only in the contents of the meshes, but also within the fibers of the myxomatous reticulum. The latter feature is best recognizable on specimens deeply stained with chloride of gold. The apparently structureless or indistinctly granular myxomatous basis-substance, held in the meshes of the myxomatous reticulum, proves to be of a reticular structure just as well as the protoplasm itself. The second variety of pericementum is built up of fibrous connective tissue, which prevails in adults and persons of ad- vanced age. The bundles of the fibrous connective tissue may be uniform in width throughout the whole pericementum ; or there exists a zone of tissue of myxomatous or indistinctly fibrous character close around the cementum. The bundles are built up of a number of fibers which hold a varying amount of protoplasmic bodies ; as a rule, more numerous the nearer to the cementum. On the latter there maybe found rows of osteo- blasts or scattered protoplasmic bodies alternating with bundles of a delicate connective tissue, which are directly attached to the cementum. In a few instances we see rows of osteoblasts, 18 'lol THE ANATOMY AND PATHOLOGY OF THE TEETH. the refracting power of which has been considerably augmented. Such corpuscles look shining and structureless, evidently because of a deposition of lime-salts. The fibrous variety of the perice- mentum also contains fat-globules, sometimes in a surprisingly large quantity. High magnifying powers of the microscope reveal a struc- ture of the fibrous connective tissue, as follows : The fibers, a certain number of which combine in the formation of a bundle, are delicate spindles, directly connected wdth one another at their pointed ends. These spindles are separated from each other by narrow layers of a light substance, to the presence of which Tomsa first drew attention, and for which he proposed the term " cement-substance." This substance is doubtless kindred to the gluey basis-substance which mainly builds up the spindles of the connective tissue. The interstices between the spindles are traversed in a vertical direction by extremely minute threads every way analogous to the thorns in the cement-substance sur- rounding epithelial elements. These threads in many instances are visilolc in specimens hardened by the chromic-acid solu- tion ; they become very plain when thin sections have been im- mersed in a half per cent, solution of chloride of gold for one or two hours, or until the specimen has assumed a dark-violet color. If the stain be complete, we also recognize that the spindles are not homogeneous, as they look in fresh, unstained specimens, but are rather traversed by a delicate, dark-violet reticulum, the points of intersection of which are slightly thick- ened, and thus represent granules. (See Fig. 154.) Between the spindles of the basis-substance protoplasmic bodies are seen the formerly so-called connective-tissue cells. Some of these bodies exhibit shining, compact, oblong nuclei, with a certain amount of surrounding protoplasm, while others are devoid of nuclei, and split into spindle-shaped or polygonal lumps, which in size and shape fully correspond to the element- ary formations of the fibrous basis-substance. Where there is a central nucleus, it is invariably bounded by a light rim, which is pierced by radiating thorns. The latter connect the circum- ference of the nucleus with the granules of the protoplasm next to the nucleus. The protoplasm under all circumstances exhib- its the well-known reticular structure. From the periphery of a protoplasmic body, each being surrounded by a light rim, minute threads spring forth, and run into the reticulum within THE PERICEMENTUM. 259 the spindles of the basis-substance. The same relations are seen in protoplasmic bodies next to the cementum, — the so-called osteoblasts. The offshoots of these formations run partly to the spindles of the basis-substance and partly into the light reticu- lum within the cementum. In some instances, between the cementum and the osteoblasts there is interposed a small layer of fibrous basis-substance in the shape of delicate slender spin- dles. The walls also of the capillaries, consisting of a single layer of endothelia, are connected wdth the neighboring spindles of the basis-substance by means of delicate threads, which tra- verse the light rim around the blood-vessels, — the so-called peri- EiG. 154. Pericementum of Fibrous Structure. f C, cementum of root; PX, pericementum, the fibers of which are built up of spindles, in longitudinal sertion ; PF, pericementum, the elementary spindles of which are finer, and cut obliquely ; P\ P-, protoplasmic bodies, either so-called connective-tissue corpuscles or so-called osteoblasts. Magnified 1200 diameters. vascular space. Last!}', such offshoots run also into the light reticulum of the bone-tissue, where the pericementum is attached to the wall of the alveolus. In its juvenile condition the pericementum represents a myxo- matous connective tissue, the fibrous portion of which is rela- tively scanty, while the protoplasmic portion prevails. In this instance two varieties of basis-substance occur, — viz, the fibrous, building up the reticulum, and the myxomatous, filling a cer- tain portion of the meshes. This condition arises, first, from the indifierent or embryonal tissue, not only in the pericementum, but in all formations of connective tissue which, when fully de- 260 THE ANATOMY AND PATHOLOGY OF THE TEETH. veloped, exhibit a fibrous structure. The only way to explain the formation of the myxomatous tissue is that a part of the proto- plasm constituting the embryonal elements remains unchanged, a part is transformed into spindles of myxomatous reticulum, and a part into myxomatous basis-substance. "Whereas the myxomatous variety of pericementum is rich in blood-vessels, the fibrous variety is bat scantily provided with them. The broadest portion of the pericementum, that around Fig. 155. Coils op Arterioles ix the Pericementum. Horizontal Section. C, eementum at the apex ; L, longitudinal fibers of pericementum ; T, transverse fibers of pericementum ; <7, C, coils of arterioles ; N, N, bundles of meduUated nerves in transverse sec- tion. Magnified 100 diameters. the apex of the root, shows peculiarly tortuous arteries and arterioles, in some places coiled into tuft-like formations. C. Wedl was the first to describe such arterial tufts in the perice- mentum. Fig. 155 is an illustration of two arterial coils. Tor- tuous arteries we invariably find in tissues and organs exposed to frequent changes in their bulk, and it seems that the slight mobility of the tooth, owing to the varying amount of perice- mentum, accounts for the presence of arterial coils. ERUPTION OF THE TEETH. 261 CHAPTER XXL ERUPTION OF THE TEETH. For the first eight or ten mouths after birth, infants require only liquid food, and in a normal condition they have during that period no teeth above the gums. Instead of teeth, upon the anterior portion of the jaws we observe comparatively hard and rough eminences of the mucous membrane, designed to hold the nipple of the mother's breast in the process of sucking. At the time of birth the cusps — cutting-edges — of the crowns of most of the temporary teeth are situated on a level with the alveolar process, covered only by the mucous membrane. The calcification of the teeth commences at their cusps or cutting- ,30ms Diagram of Eruption of the Temporary Teeth. edge, and gradually extends to the root. The first teeth usually make their appearance about the sixth or seventh month after birth, although no definite time can be predicated. There are several cases on record of children born with teeth; while on the other hand, the author has seen children who began to cut their teeth no earlier than at the age of twelve or sixteen months. When the crowns of the temporary teeth make their appearance through the gum, the roots are but partially formed, as is illus- trated in Fig. 120, taken from an article by C. X. Peirce.* The time considered normal for the eruption of the tempo- rary teeth is as follows. (See Fig. 156.) "^Dental Cosmos, Auo-ust, 1884. 262 THE ANATOMY AND PATHOLOGY OF THE TEETH. -4-5 y LiAGRAM OF Eruption of Permanent Teeth of the Upper Jaw. Fig. 158 Diagram of Eruption of Permanent Teeth of the Lower Jaw. ERUPTIOX OF THE TEETD. 263 The central incisors from the fifth to the seventh month. The lateral incisors from the seventh to the ninth month. The first molars from the twelfth to the fourteenth month. The cuspids from the fourteenth to the eighteenth month. The second molars from the twentieth to the thirtieth month. The temporary teeth, under normal conditions, remain in their respective places in the mouth until they are replaced by the permanent teeth, the first of which are usually erupted at about the sixth year. Occasionally we meet with children who shed their teeth earlier, — at the fifth year or even before ; while in other instances the permanent teeth do not appear before the Fig. 159. Sheddixg of the Temporary and Appearaxce of the Permanent Teeth, between THE Fifth and Sixth Years. eighth or ninth year. We frequently find that a patient has re- tained one or two temporary teeth up to the thirtieth or fortieth year of his age, these being sometimes quite firm in their sockets. The time considered normal for the tem.porary teeth to fall out and to be replaced by their successors is as follows. (See Figs. 157 and 158.) The central incisors from the sixth to the seventh year. The first molars from the sixth to the seventh year. The lateral incisors from the seventh to the ninth year. The upper first bicuspids from the eighth to the tenth year. 264 THE ANATOMY AND PATHOLOGY OF THE TEETH, The lower cuspids from the eighth to the eleventh year. The lower lirst bicuspids from the ninth to the eleventh year. The upper cuspids from the tenth to the twelfth year. The second upper and lower bicuspids from the tenth to the twelfth year. The second molars from the twelfth to the thirteenth year. The third molars from the fifteenth to the forty-fifth year. On the first appearance of the permanent teeth, their roots, like those of the temporary teeth at that period, are not com- pleted. A consideration of the time of calcification of the roots of the teeth is therefore important, especially as the teeth of young patients often are attacked by caries, and sometimes by pulpitis. (See Fig. 159.) It is evident that when the pulp of a tooth with an incomplete root dies, the saving of that tooth becomes very problematical. CHAPTER XXII. ABSORPTION OF TEMPORARY TEETH. At a certain age the temporary teeth become loose, and some- times fall out without causing pain or loss of blood. A temporary tooth shed in this manner usually exhibits only a croAvn somewhat hollowed out underneath, in the place whence the former root united with it, or a small portion of the root may still be present. Upon macroscopical examination we find the concave bottom of the crown worn away into irregular grooves and pits. Some of these bays may contain small pieces of vascularized soft tissue, the " carneous hody^' of older writers. Originally, the temporary teeth, like those of the per- manent set, are possessed ■ of roots which gradually become shortened by absorption, as the growth of the permanent teeth proceeds. Frank Abbott has thoroughly studied the appearances of the absorption of the deciduous teeth, and has published his results ABSORPTION OF TEMPORARY TEETH. 265 in an essay.* I fall}^ concur with the author in all essential points, and quote from him as follows : " The assertion of Tomes, that absorption is due to the pres- ence of a freely-vascularized papilla, does not explain the decrease of the dental tissues, for the papilla is nothing but medullary tissue, such as we meet with in any part of the organism, where one tissue is about to change into another. Such a papilla may be the cause of the absorption, as well as its result. Another assertion, that the medullary cells eat out the dental tissues by their active growth, or by their amoeboid motions, is insufficient to explain the loss of the lime-salts in the dental tissues, as well as to explain the presence of circular or semi-circular excava- tions and bays so characteristic of the melting process of the cementum and dentine of deciduous teeth. "Since we know that pieces of dead bone or ivory may be absorbed, with figures similar to those found on the surface of temporary teeth, the idea possibly becomes admissible that, owing to the presence of an acid, first the lime-salts are dissolved away within certain territories of the dead bone-tissue, in a merely chemical or passive manner, whereupon the soft medul- lary tissue penetrates the spaces thus established. Quite differ- ent, however, will be the conception of this process, if we bear in mind that the temporary teeth, as well as the permanent ones, are made up of living tissues, and an active participation of these tissues must be expected in the process of transformation of the dental into the medullary tissue. As the process of absorption is closely allied to the process of inflammation, and active changes of the dental tissues have, beyond any doubt, been proven to follow inflammation, we may a 2)nori expect such changes of the bone-tissue of the temporary teeth in the process of absorption also." The process of absorption of deciduous teeth is, indeed, closely allied to the inflammatory process, and may be considered as a physiological type of tissue-changes owing to the presence of some irritating agency. The dissolution of lime-salts in bone, as well as that of the hard tissues of the teeth, probably is due to the presence of lactic acid. The dissolution of the lime-salts may invade dead bone-tissue, or invade pieces of ivory implanted *•' Microscopical Studies upon the Absorption of the Eoots of Temporary Teeth." 266 THE ANATOMY AND PATHOLOGY OF THE TEETH, in a living tissue. In such dead bone or ivory we likewise^ob- serve the disappearance of the lime-salts in the bay-like'excava- tions, which later are tilled with a living tissue growing into the excavations from without. When a temporary tooth begins to be absorbed, its constituent Fig. 160. Absorption of Cementum of a Temporary Tooth. D, cement-corpuscles in division ; iV, cement-corpuscles unchanged ; B, basis-substance of cementum ; M, M, multinuelear protoplasmic bodies ; F, fibrous connective tissue. Magnified 500 diameters. tissues unquestionably are alive, and consequently it is reason- able to assume that the outermost layer of the root, first ex- posed to the irritation, will react as other living tissues do in the inflammatory process. ABSORPTIOX OF TEMPORARY TEETH. 267 Whether or not dentine and enamel actively participate in the process of absorption is doubtfnl, and np to the present day unproven. Absorption of Cementum. — The first changes due to absorp- tion are semi-circular excavations or bays on the surface of the root of a temporary tooth, filled with embryonal corpuscles or multinuclear protoplasmic bodies, in connection with the myxo- matous or fibrous connective tissue of the pericementum. According to Abbott, isolated excavations may be seen, the connection of which with the outer surface, though not observa- ble in the specimen, may be present above or below the plane of the section. He says, " By closely watching excavations of a more recent date, at the periphery of earlier ones which are in communication with the pericementum, we notice that the lime- salts and the basis-substance proper are missing, and are replaced by a uniformly-granular protoplasm, or a varying number of faintly-marked medullary elements, each of which may contain a central nucleus." Another proof that the tissue of the cementum reacts upon the irritation is that the cement-corpuscles nearest to the eroded surface frequently are found enlarged, glossy, and split up into smaller pieces. (See Fig. 160.) The result of such changes is the appearance of embryonal or medullary corpuscles at the border of the excavation, or of multinuclear bodies, formerly the territories of the cementum, now reduced to protoplasm. This indifferent tissue appears connected with fibrous tissue, abundantly supplied with newly- formed blood-vessels. ]^ot infrequently the latter tissue also holds trabeculse of newly-formed bone, sometimes to such an extent that the widened sockets of the temporary teeth are filled with a considerable amount of cancellous bone-tissue. Absorption of Dentine. — Dentine, during the process of absorption, if examined with low powers of the microscope at the corroded surface, exhibits a number of bay-like excavations similar to those seen in bone-tissue and the cementum in this process. (See Fig. 161.) Since we know that dentine, like bone, is formed from medul- lary tissue clustered together in territories, we are not surprised to find such semi-circular excavations at the exposed surface of dentine during the process of absorption. The bays are filled either with clusters of embryonal corpuscles, or multinuclear 268 THE AXATOMY AXD PATHOLOGY OF THE TEETH. protoplasmic bodies, frequently observed in growing as well as in inflamed bone-tissue. These formations are continuous with fibrous connective tissue holding the shortened temporary tooth in position. An important question is, whether or not the den- tine of deciduous teeth participates actively in the production of Fig. 161. Absorption of Dentine of Temporary Tooth. U, unchanged dentine ; D, decalcified dentine : B, zone of bay -like excavations ; F, fibrous connective tissue. Magnified 100 diameters. embryonal elements, which afterward develop into fibrous con- nective tissue. This question is as yet unsettled. If, however, we bear in mind that a deciduous tooth with a living pulp, as a rule, remains sensitive up to the time of detachment from the pericementum, the possibility of such participation cannot be ABSORPTION OF TEMPORARY TEETH. 269 denied. Abbott is iu favor of assuiriing it, since he observed a widening of the dentinal canaliculi at the borders of the bays, with an increase of the living matter of the dentinal fibers. Fields of absorption are frequently met with in the dentine, some distance away from the eroded surface, and apparentlv Fig. 162. Absorption of Dentine of a Temporary Tooth. -D, dentine without signs of reaction ; /, isolated medullary spaces; .S", medullary space filled with indifferent corpuscles and fibrous connective tissue : M, multinuclear body filling a bay ; T, newly-formed territories of bone-tissue; X, lamellated bone-tissue: F, fibrous connective tissue. Magnified 500 diameters. isolated. Again, we cannot deny the possibility that such ex- cavations may have been in connection with the surface, and^are filled with ingrowing embryonal or myxomatous tissue. (See Fig. 162.) "270 THE ANATOMY AXD PATHOLOGY OF THE TEETH. It is known since J. Tomes, that the bays of the eroded den- tine are often found filled with bone-tissue, either in the shape of territories or of laraellated bone. The latter may reach such a degree of development that it produces an almost continuous layer all around the absorbed tooth. Absorption of Enamel. — This process is but little studied, on account of its exceptional occurrence, which has been mostly observed in the temporary molars. Bay-like excavations, similar to those observed in the dentine and cementum, occur in absorbed enamel. Chas. Tomes has noticed such bays of the enamel filled with newly-formed bone- tissue, the same as we observe in absorption of dentine. He attributes this rare occurrence to the overlapping of the cement on the edffe of the enamel. CHAPTER XXIII. PHYSIOLOaY OF THE HARD DENTAL TLSSUES. The latest researches into the minute anatomy of the dental tissues — researches described in previous chapters — necessarily alter the views hitherto held concerning the nutrition of those tissues. Enamel has been considered to be a mere deposit, as it were, of purified lime-salts ; a coat of mail destitute of life. The authors in the, foregoing chapters have demonstrated the presence of living matter between and within the enamel- prisms, and consequently affirm that enamel is a tissue with properties of life, although in minimum degree. Dentine has long been known to be a tissue extremely sensitive throughout, especially at the interzonal layer bordering the enamel. Xothing, however, was known as to the seat of life in dentine, until myself and others endeavored to prove not only that the dentinal fibers and their coarse ofishoots are formations of living matter, but that the basis-substance, so rich in lime-salts, is traversed by an extremely delicate filigree of living matter as well. With the facts before us, we may attempt to approach the solution of a hitherto insoluble riddle, — viz, the nutrition of the PHYSIOLOGY OF THE HARD DEXTAL TISSUES. 271 dentine and of the enamel. N"o close observer will doubt that the nutrition of the hard tissues of the teeth is — and must be — an active one. This is proven not only by the growth of these tissues, but also by the same tissues' strikingly rapid loss of lime- salts in constitutional diseases, such as neurasthenia, antemia, etc., and even in pregnancy. How are the lime-salts deposited in the dentine, and how can they be removed to such a degree that dentine, originally hard, becomes in a few months soft and brittle ? Looking at the dentinal canaliculi with . the highest obtain- able powers of the microscope, we see between the dentinal liber and the walls of the canaliculus a narrow, light space, evi- dently filled with liquid, which serves for the carrying of nour- ishing material to the dentine, and for the carrying of effete material away from it. More than this, even the ultimate fib rill as of living matter within the basis-substance are sur- rounded by a delicate light space holding substances that serve the same purposes. If, besides these points, we observe that the dentinal fibrillee are of a vacuoled structure, and that the ultimate fibrillse have a rosary or beaded appearance, we are prepared to acknowledge the possibility that in living dentine the living matter proper is at no time perfectly at rest ; that, on the contrary, it is contract- ing, slowly but continuously, and that through its contractions it not only stirs the surrounding column of liquid, but pumps, as it were, nourishing material into the minutest fields of the dentine, or away from them. The chemical character of the liquid may explain the dissolution of a certain amount of the lime-salts deposited in the blocklets of the basis-substance, which salts, thus being rendered effete, may be carried into the lymphatics of the pulp, and thence into the ly-mph-system of the body for further elimination. Why, in one instance, nourish- ing material should be carried from the blood-vessels of the pulp into the dentine, and in another instance carried away from the dentine into the lymphatics, w^e are as yet unable to under- stand. What I have stated concerning the tissue of dentine unques- tionably holds good for the tissue of the enamel also. The latter being at the periphery of the crown of the tooth, farthest away from the source of nutrition, and but scantily supplied with living matter, its nutrition must be extremely slow. Still, 272 THE ANATOMY AND PATHOLOGY OF THE TEETH. every dentist must have observed instances of softening of the enamel as the result of constitutional ailments. Ee-calcification, re-hardening of the enamel, though denied by E. Baume, is certainly a fact. The structure of the enamel- fibers between the prisms, as well as of those traversing the latter, points to the identity of the process of nutrition and de- nutrition with that in the dentine. To preserve the life of the dentine and of the enamel, it is not necessary to have the entire pulp of a tooth intact. The experiments of W. Plerbst jjrove, on the contrary, that only a portion of the pulp-tissue left alive in the pulp-canals is capable of keeping alive the dentine and enamel of the crown of a tooth, as I will show in a subsequent chapter. Another important point seems to be explained satisfactorily by our researches into the structure of the dentine, — i.e., the sensitiveness of this tissue. So striking is this fact that a thoughtful observer such as J. Tomes alluded to the possibility of the dentinal fibrillse being nerves. Such a view is not tenable, for two reasons : First, it is, according to our advanced conceptions of histology, impossible to admit of the existence of a connective tissue hold- ing nerves alone in its constitutent soft parts. Second, neither have we, nor has G. Retzius in his recent investigations been able to trace a direct inosculation of the dentinal fibrillse with the axis-fibrillse of the nerves, so abundantly distributed through- out the periphery of the pulp-tissue. As soon, however, as we admit that the dentinal fibrillfe are formations of living matter, the same as are the nerves, all ditficulties vanish in explaining the transmission of sensation from the periphery of the dentine to the nerves of the pulp-tissue. Living matter is contractile matter, according to Heitzmann. Nerves are made up of living matter, and, owing to their reticulated or beaded structure, are fittest for that transmission of contractions from the periphery to the nervous centers which we call sensation. Contraction of the dentinal fibers transmitted into the reticulum of the protoplasm at the periphery of the pulp, and thence into the ultimate nerve- fibrillfe, — all of which formations are proven to be continuous, — are suificient to explain the transmission of sensation, or, speak- ing bluntly, of pain. As to the sensitiveness of enamel, very little is known. It is denied altogether by E. Baume and others. ISTevertheless, the PHYSIOLOGY OF THE HARD DENTAL TISSUES. 273 simple experiment of eating a sour apple tends, in my judg- ment, to prove sensitiveness of the enamel. The sensation which attends what is called " setting the teeth on edge," following in this instance, is noticed not oiily in permanent teeth whose enamel is ground oiF, but also in children having perfectly sound enamel upon their temporary teeth. Nobody will explain this sensation on the assumption of a solution of the lime-salts of the enamel, and a penetration of the apple's acid to the surface of the den- tine. It is far more probable that the pain is due to the irrita- tion of the living matter of normal enamel, and the transmission of its contractions to that of the dentine, with which it is con- tinuous. That enamel, under morbid conditions, may become extremely sensitive, is a fact known to every dental practitioner. A third point may be cleared up by these researches, — i.e., the discoloration of devitalized teeth. The discoloration concerns not only the dentine, but also the enamel ; indeed, the latter is the first to show the stain. The absence of a nourishing fluid, and the shrinkage of the fibrillfe of living matter in both tissues, may account for their opacity and change of hue. The minute anatomy of the hard tissues of the teeth, lastly, throws light upon the nature of their senile changes. In temporary teeth the dentinal canaliculi are noticeably wider, and their tenants, the fibers, larger than in permanent teeth. In the enamel-tissue the interstices between the prisms are widest, and their tenants, the enamel-fibrillse, largest, in developing teeth, at the seventh month of intra-uterine life. In the enamel of per- manent teeth the interprismatic spaces are very narrow, and their tenants so delicate that both the spaces and the fibrillsB have escaped the notice of previous observers. With advancing age, all formations of living matter diminish in bulk, whereas the basis-substance, and the lime-salts held therein, increase in amount. This explains the fact that the teeth of old people have but extremely narrow dentinal cana- liculi, and that the total number of these is noticeably lessened by a transformation of previous dentinal canaliculi into basis- substance. This has been before proven to be likewise true in the case of bone- and cartilage-tissue, by Heitzmann and Spina. The pulp-tissue gradually decreases in amount with advancing age. This is due, as I shall show in a future chapter, to a suc- cessive transformation of the pulp into secondary dentine. Nevertheless, not a single instance is known of the complete 19 274 THE AXATOMY AND PATHOLOGY OF THE TEETH. solidification of a tooth in old age, even thougli the pulp-tissue be reduced to a minimum, and the pulp-canals barely accessible to the finest broach. Eegardiug the physiology of the cementum, little can be said, since there are no anatomical facts as yet observed upon which we can base conclusions. The dentine and the enamel derive their nutrient material from the blood-vessels of the pulp. The cementum has an additional source of nutrition in the blood- vessels of the pericementum. Should the pulp-tissue perish, either in consequence of disease or of the application of arseni- ous acid, etc., the dentine and the enamel become devitalized. In the case of the cementum, devitalization from such cause is not an inevitable result, since there remains a possibility of its being kept alive by the pericementum. ISTothing positive has as yet been ascertained fixing the boundary at which life ends in the hard dental tissues. That with advancing age the teeth become loose and fall out, may be due to a lack of nutrition in the pericementum, as well as to a shrinkage of the sockets in their transformation into fibrous connective tissue. Not a single instance is known in which, with advancing age, the pericementum ossifies, and the teeth become anchylosed; but, on the contrary, in all instances they loosen and are shed. - CHAPTER XXIY.