[AS.] A small, hard body in the jaws, used for biting and chewing food. Like the nails and hair, teeth may really be considered as portions of the skin made compact and dense by the deposit of various mineral substances. Man has two sets of tee t h; the first set, the milk-teeth or temporary teeth, are twenty i n number. They are got when two years old. At six years the permanent teeth, growing up from beneath the milk-teeth, push the latter out, and at ten all the temporary teeth have been replaced by permanent teeth, altogether thirty-two in number - sixteen being placed in the upper, and sixteen in the lower jaw. Teeth are of different shapes, because some are intended for one purpose, and some for another. The part of the tooth imbedded in the gum is called the fang, while that above the gum is known as the crown ; the crown of each tooth is overlaid with a pearly-white enamel. The eight teeth in the front of the mouth - four in the upper, and four in the lower jaw - have sharp cutting edges like chisels, and are called incisors ; they are useful for biting or separating food. One on each side above and below are the four canine teeth or eye-teeth, called canine because they are so large and prominent in the dog (Latin canis, a dog), and also in all beasts of prey. These canine teeth are useful for tearing and for biting the food. Farther back in the jaws are eight teeth (two on each side above and below) called pre-molars, because they are next to the molars, twelve large teeth which occupy the hinder parts of the jaws. Both molars and pre-molars are mainly useful in grinding the food ; whence their name, from the Latin word mola, a mill. The four last molars at the ends of the jaws are called the "wisdom teeth," because they are the last to be cut, usually not making their way through the gum till the age of twenty one. The teeth are not perfectly solid. Inside of each tooth there is a little hollow called the pulp-cavity, which contains several nerve-branches. These nerves pass along each fang into the gum, and are there connected with other nerves which go to the brain. When from any cause the enamel of the tooth is worn away, the delicate contents of the pulp cavity are exposed to the air, and to pressure from any little hard bits of food which may get inside the hollow place. Cold or pressure on the nerves produces the intense pain called toothache.