Teeth

Teeth, specialized hard structure used for biting and chewing food. The number of teeth varies from species to species and from age to age, but in most cases an immature set of teeth (milk teeth) is replaced during growth by a permanent set. In humans the latter consists of 32 teeth, comprising 8 incisors, 4 canines, 8 premolars or bicuspids, and 12 molars, of which the rearmost are the late-erupting wisdom teeth. Each tooth consists of a crown (the part above the gum line) and a root (the insertion into the bone of the jaw). The outer surface of the crown is covered by a thin layer of enamel, the hardest animal tissue. This overlies the dentine, a substance similar to bone, and in the center of each tooth is the pulp, which contains blood vessels and nerves. The incisors are developed for biting off food with a scissor action. The canines are for maintaining a hold on an object. The molars and premolars are adapted for chewing and macerating (separating) food. The most common disease of the teeth is dental decay, ot caries, in which acid produced by bacteria dissolves the tooth enamel, causing a cavity.