Teeth

(teth,) pl. of TooTH. [From A. S. teth, pl. of toth; L. dens; Gr. odo us, odontos.] (Anat.) The bony organ with which vertebrate animals seize or prepare their food. In the higher mammals, a tooth is composed of three ti ues, viz.: dentine, which forms the body of the T.; cement, which forms the outer crust; and enamel, which is placed between the dentine and the cement. The cement resembles in texture the bones of the same animal, and in adult man it is confined to the outer part of the fangs. The enamel is the hardest of the dental ti ues, and, like the others, consists of earthy matters deposited in minute cells. The typical number of T. in the mammal i a is 44 (the hog, for example, having this number), but the average one of that cla is 32, as we find in man, the Old World apes, and the true ruminants. In each of the jaws of the adult man are four cutting T., or incisors, in front, followed on 56 5L each side by one canine tooth and five grinding T., or molars, of which the two next the canine tooth are termed premolars. All the T., except the true molars, are shed early in life, and are replaced by others which grow up from beneath them. The first set of T. are denominated the temporary deciduous or milk T. The method adopted by anatomists for expre ing the number and kind of the T. may be thus illustrated by the dental formula of man: 2-2 1-1 2-2 3-3 m = 32, 2-21-1 1-12-2 3-3 where the letters indicate the names of the T., as given above, and the numbers above and below the lines respectively indicate the T. in the upper and lower jaws, while the short lines separating the figures serve to point out the different sides of the jaws. The T. of different animals vary greatly in shape, according to the uses to which they are applied. Take the molar T., for example. Among the true carnivora, they are compre ed laterally, and have sharp cutting edges, which shut like the blades of sci ors, and set over the other. By this structure these animals are able to divide their food with great facility. The insect i vor a, such as the mole and bat, have molars terminated by several sharp points. Herbivorous animals have the summits of their molars flat with prominent ridges, a structure that enables them to crush and triturate their food. An omnivorous animal, like man, has several rounded tubercles on the grinding surfaces. From this variety in the shapes of T., and the constancy of their correspondence with the structure of the body, it happens that a single molar will always indicate the group to which any animal belongs. [s. 881]