A
tooth (plural,
teeth) is a structure found in the
jaws of many
vertebrates that are used to tear, scrape, and chew
food. Some animals, particularly
carnivores, also use teeth for hunting or defense. The roots of teeth are covered by
gums. Teeth are among the most distinctive features of
mammal species.
Paleontologists use teeth to identify
fossil species and determine their relationships. The shape of an animal's teeth is related to its diet. For example, plant matter is hard to digest, so
herbivores have many molars for
chewing.
Carnivores, on the other hand, need
canines to kill and tear meat.
Humans are diphyodont, meaning that they develop two sets of teeth. The first set (the "baby," "milk," or "deciduous" set) normally appears at about six months of age, although some babies are born with one or more visible teeth, known as neonatal teeth. Normal tooth eruption at about six months is known as teething and can be quite painful for an infant.
Some animals develop only one set of teeth (monophyodont) while others develop many sets (polyphyodont). Sharks, for example, grow a new set of teeth every two weeks to replace worn teeth. Rodent incisors grow and wear away continually through gnawing, maintaining relatively constant length. Some rodent species, such as the sibling vole and the guinea pig, have continuously growing molars in addition to incisors.
