Incisor

Structure

Adult humans normally have eight incisors, two of each type. The types of incisors 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. Typically, the mandibular central incisors erupt first, followed by the maxillary central incisors, the mandibular lateral incisors and finally the maxillary laterals. The rest of the primary dentition erupts after the incisors.

Apart from the first molars, the incisors are also the first permanent teeth to erupt, following the same order as the primary teeth, among themselves.

Other animals

Distinct incisors first emerged among early therapsids during the Permian period.

Among mammals, 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.