Incisor

“ Mr. Salter [5] gives an account of an extensive fracture of the jaw which occurred in a lady æt. 35. The fracture occurred in connection with the removal of the superior central incisors. The right central incisor required some force for its removal, and when it came away the whole of the front of the alveolus was firmly attached to the root. In removing the left central incisor considerable force was required during the exertion of which the bone was fractured. ”

“ The remarkable conformation of the teeth will be easily seen by reference to the annexed figure. The upper incisor teeth, four [249] in number in the young animal, become reduced to two in the adult, but these are of enormous size, prominent, triangular, and very sharp. The lower incisors, on the contrary, are small and have a two-lobed crown. The canines of the upper jaw are nearly of the same form as the incisors, but rather smaller; those of the lower jaw present no remarkable peculiarity. ”

“ They appear worn not so much on the outer edge or line of the tooth, as inside this line; but, after this, the edge begins gradually to lose its sharpness, and to present a more flattened surface; while the next outer teeth wear down like the four central ones; and at three months this wearing off is very apparent, till at four months all the incisor teeth appear worn, but the inner ones the most. ”

“ The tooth, which previously seemed to be on the eve of piercing the gum, after the extraction of the milk incisor never came up,—nor will any person who has thought for an instant, wonder if the violence, necessarily used, does occasionally injure or rupture the delicate vessels and gelatinous tissues of the pulp. More often the breeder’s impatient interference breaks the tooth off at the neck and leaves the fang in the jaw. ”

“ Upper Incisors.—The roots of both the upper central and lateral incisors are usually cone shaped, the anterior surface being the arc of a greater circle than that of the posterior. Forceps for the removal of these teeth ought therefore to have the blades made in a corresponding manner (see fig. 17) . The lateral incisor is smaller than the central, and has at times a root somewhat flattened. In removing upper incisors the posterior blade is applied first, care being taken to{20}
Fig. ”

“ The small twigs which penetrate into the roots of the incisor and canine teeth are less slender than those which enter the roots of the molars, and are easily to be seen not only in large animals, but also in man. If the tooth of an ox or that of a ram be split through the middle, the mucous substance contained in the interior is seen to be traversed by small bloodvessels; and one perceives, besides, certain fibers, which are probably nerves. All these things, says Eustachius, I have observed many times in different animals, in some cases more, in others less distinctly. ”

“ Their length in the jaw is great, to insure solidity without actual union with the bone. The loss of an incisor results in the abnormal lengthening of the opposing one, which may finally interfere with mastication and cause starvation. Ruminants have no incisors in the upper jaw; the elephant has none in the lower jaw, but the tusks are upper incisors. ”

“ The Ox has no cutting or incisor teeth in its upper jaw, as every one knows, and the tongue touches a hard and moist gum there. The incisor teeth of the Calf are never cut, but they are gradually absorbed in the gum with age. ”

“ In the adult the dentition (fig. 11) is i. 3/1, c. 1/0, p. + m. 4/3, total 24. The first upper incisor is much larger than the others; canine and first two premolars rudimentary. In the lower jaw there are also one or two small and early deciduous premolars; third premolars of both jaws formed on the same type as that of the rat-kangaroos, but relatively much larger; molars rudimentary, tubercular. The functional teeth are reduced to one pair of large cutting incisors situated close to the middle line, and one great, cutting, compressed premolar, on each side above and below. ”

“ The dentition is very peculiar and characteristic: there are in all thirty-two teeth, tipped with deep crimson; of which twelve belong to the lower jaw; of the remaining twenty ten occupy each side of the upper jaw, and of these the first three are incisors. The first incisor is large, with a long anterior canine-like cusp and a small posterior one; then follow two small single-cusped teeth; which are succeeded by three similar progressively smaller teeth, the first being a canine and the other two premolars ”

“ Lower Central Incisors placed similarly to that shown in fig. 43 may be removed with ordinary lower root forceps (hawk’s-bill pattern) , the blades being placed on the mesial and distal surfaces of the root, and movement applied in a direction to and away from the median line of the mouth. When the crowding is not so extreme as shown in fig. 44, forceps of the hawk’s-bill pattern with a strong but narrow inner blade should be used (fig. 45) , and the principal extractive movement made in an outward direction. For an incisor placed as shown in fig. ”

“ The wife of a Protestant minister gave birth to a female child which already had a fully developed tooth, a lower middle incisor, equal in size to that of a child of two years old, and which interfered with the sucking by injuring the nipple of the mother’s breast and the tongue of the child itself. So it was necessary that it should be removed. But it was found to be so firm that the surgeon sought in vain to extract it with a thread, and was obliged to have recourse to the forceps.343
Observation XXXI of the third centuria relates a case of rhinoplasty. ”

“ In the lower dentition, none of the teeth are reduced, and all are in a continuous series, except that there is a small diastema either side of pm. 1. The incisors are simple, compressed teeth, with but a trace of a cingulum. The canine is incisiform and a trifle larger than the incisors. Premolar 1 is also incisiform, and is isolated by a small diastema on either side. ”

“ There is never more than one pair of incisors in the mandible, and except in the Hares and Rabbits, there is similarly only a single pair in the upper jaw. These animals are, too, the only rodents which have well developed deciduous incisors. There is always a long diastema separating the incisors from the grinding teeth. ”

“ The scalpriform incisors of the rodents, already alluded to, have the enamel band on the front face of the tooth; the softer dentine behind wears away more rapidly, keeping the cutting surface bevelled, like the edge of a chisel, while the hard enamel forms the sharp edge. In some instances the enamel is absent altogether and the teeth are composed entirely of dentine, as in the elephant tusk. ”

“ It is, however, impossible to examine the molar teeth satisfactorily during life. Far less frequently an incisor tooth becomes loosened; more often it loses its glistening appearance and looks dull and yellowish. ”

“ They are readily recognized by their large incisors. These teeth grow throughout life, and if they are not constantly worn away by gnawing upon hard food, they become inconveniently long, and may prevent closing of the mouth and cause starvation. The hard enamel is all on the front surface, the dentine in the rear being softer; hence the incisors sharpen themselves by use to a chisel-like edge. ”

“ Incisors very large, curved, with persistent pulp, and enamel only in front, growing up as fast as worn away; canines absent (the last two characters as in the Rodents) ; long vacuity between incisors and pre-molar; pre-molar much smaller than molars; molars with flat crowns and very indistinct tubercules; milk-teeth agreeing more in number and form with those seen among Lemurs than with the permanent set; the upper jaw having its full set of two incisors, one canine, and a pre-molar tooth present; the lower jaw having one incisor, no canine, and one pre-molar tooth on each side. ”

“ Sufficient of the tooth itself remains in four of the sockets to show that these incisors, like the nearly perfect one (fig. 5) , had only a partial investment of enamel; but though in this respect, as well as in their curvature and perpetual growth, they resemble the dentes scalprarii of the Rodentia, they differ in having a prismatic figure, like the inferior incisors of the Sumatran Rhinoceros, or the tusks of the Boar. ”

“ The incisors and canines, as we have said, exhibit no difference of importance, but the last premolar and all the molars, instead of having the sharp cutting character they have in the Cat, and to a less degree in the Dog, have comparatively flat crowns, raised up into a number of little elevations or tubercles; even the “carnassial” teeth (last premolar in the upper jaw, and first molar in the lower) have entirely lost their scissor-blade character, and become true grinders. ”

“ In front there is a series of small pointed incisors, usually three in number, on each side of both jaws, of which the first is always the smallest and the third the largest, the difference being most marked in the upper jaw; these are followed by strong conical, pointed, recurved canines; the premolars and molars are variable, but generally, especially in the anterior part of the series, more or less compressed, pointed and trenchant; if the crowns are flat and tuberculated, they are never complex or divided into lobes by deep inflexions of enamel. ”

“ When the upper incisors are fairly presented to the sight, a partial view only of the lower teeth is obtained, [116] and as the age advances even that is lost. Further inspection also shows additional changes in position, shape, and tint. The grooves are broad, deep, and well marked by their dark colour. Between the upper incisors there are interspaces in which the food has accumulated and become black, giving to the mouth the appearance represented in the coloured plate. ”

“ In different individuals, the lower jaw varies greatly in height, but this seems to me to be individual and sex variation. The three incisors and the canine are subequal in size, closely crowded, and each with a small cingulum near the base of the enamel. ”

“ The horse incisors do not occupy the same cavities in which the milk incisors were placed, but are developed in cells formed especially for their reception, and come up rather behind than absolutely under the primary teeth. The form of the anterior part of the jaw in the foal admits of such an arrangement, and its greater comparative bulk gives all the space that was required. The space, however, between the branches of the lower jaw where the molars are developed, is filled by important muscles ”

“ THE MILK TEETH.—We are provided with two sets of teeth. The first, or milk teeth, are small and only twenty in number. In each half jaw there are two incisors, one canine, and two molars. The middle incisors are usually cut about the age of seven months, the others at nine months, the first molars at twelve months, the canines at eighteen months, and the remaining molars at two or three years of age. The lower teeth precede the corresponding upper ones. The time often varies, but the order seldom. ”

“ The teeth (Figs. 45, p. 95; 154, p. 306) are extremely high-crowned, or hypsodont, and do not form roots till an advanced age; the incisors have a deep, enamel-lined pit, the “mark” in the centre of the grinding surface; the first premolar in each jaw is very small and of no functional importance; the other premolars have the same pattern as the molars, which is excessively complex in the arrangement of the enamel ridges and the areas of dentine and cement. ”

“ In this character, as in the number of incisors, the South- African Karoo fossil resembles the Marsupial genus Didelphis. The lower incisors are subequal, subcompressed, and elliptical in transverse section, at least at the base of the crown, with the long-axis of the section directed from the fore to the hind part of the alveolar border; and they are close-set, as in carnivorous mammals. As in these, also, the dentine, in both canines and incisors, is of the hard unvascular kind, and the enamel as distinct in tissue and as thick. ”

“ The incisors are chisel-shaped, and the canines tend to become isolated, so as in the more specialized forms to occupy a more or less midway position in a longer or shorter gap between the incisors and premolars. ”

“ They are remarkable, not only for having enormous tusks, and for the development of a large excrescence, or wart, under each eye, but also for the peculiar construction of their last grinding teeth. These are massive, and composed of prisms of enamel surrounding a central mass of dentine, and embedded in the cement which unites them into one tooth. There is only one pair of upper incisors, and the last molars are the only ones which are not shed in the old animal. The canines are large, recurved, sharp, and project eight or nine inches beyond the lips. ”

“ I use it in the grinding surface of molars and bicuspids, buccal cavities in molars and bicuspids, cervical fissure pits in superior incisors, proximal cavities in bicuspids and molars. If proximal cavities are opened from the occlusal surface, the last portion of the filling should be of cohesive gold to withstand mastication. In simple cavities I place as many pieces as can be easily introduced, using my pliers as the wedging instrument to make room for the last pieces, and then condense the whole. ”

“ The accompanying illustrations well indicate this arrangement of sutures and teeth (Figs. 26 and 27) ; the importance of these facts will be emphasized later. All traces of the facial aspect of these sutures disappear quite early in life.
Figs. 26 and 27.—Diagrams to represent the normal human upper jaw of a child, with four and six incisors respectively, and also indicating the five intermaxillary sutures. (After Albrecht.)
EG, MG, XG. Endo-, meso-, and exo-gnathion. e. Inter-endognathic suture. f. Endo-mesognathic suture. g. Exo-mesognathic suture. i1. Central incisor. i2. Lateral incisor. ”