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|Permanent teeth of right half of lower dental arch, seen from above.|
|The permanent teeth, viewed from the right.|
|Gray's||subject #242 1115|
Incisors (from Latin incidere, "to cut") are the front teeth present in most heterodont mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, whereas armadillos have none.
Adult humans normally have eight incisors, two of each type. The types of incisor are:
- maxillary central incisor (upper jaw, closest to the center of the lips)
- maxillary lateral incisor (upper jaw, beside the maxillary central incisor)
- mandibular central incisor (lower jaw, closest to the center of the lips)
- mandibular lateral incisor (lower jaw, beside the mandibular central incisor)
Children with a full set of deciduous teeth (primary teeth) also have eight incisors, named the same way as in permanent teeth. Young children may have from zero to eight incisors depending on the stage of their tooth eruption and tooth development.
Among other animals, the number varies from species to species. Opossums have 18, whereas armadillos have none. Cats, dogs, foxes, pigs, and horses have twelve. Rodents have four. Rabbits and hares (lagomorphs) were once considered rodents, but are distinguished by having six — one small pair, called "peg teeth", is located directly behind the most anterior pair. Incisors are used to bite off tough foods, such as red meat.
Cattle (cows, bulls, etc.) have none on top but a total of six on the bottom.
In many omnivorous mammals, such as a gorilla, they are adapted for shearing sharply. In cats, the incisors are small; biting off meat is done with the canines and the carnassials. In elephants, the upper incisors are modified into curved tusks (unlike with Narwhals, where it is a canine that develops into a straight and twisted tusk). The incisors of rodents grow throughout life and are worn by gnawing.
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- Nweeia, Martin; Eichmiller, Frederick C.; Hauschka, Peter V.; Tyler, Ethan; Mead, James G.; Potter, Charles W.; Angnatsiak, David P.; Richard, Pierre R. et al. (30 March 2012). "Vestigial Tooth Anatomy and Tusk Nomenclature for Monodon Monoceros". The Anatomical Record 295 (6): 1006–1016. doi:10.1002/ar.22449. PMID 22467529.