Incisors (from Latin ''incidere'', "to cut") are the front

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, ...

present in most

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

s. They are located in the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

above and on the

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

below. Humans have a total of eight (two on each side, top and bottom).

Opossum Opossums () are members of the marsupial order Didelphimorphia () endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 93 species in 18 genera. Opossums originated in South America and entered No ...

s have 18, whereas

armadillo Armadillos (meaning "little armored ones" in Spanish) are New World placental mammals in the order Cingulata. The Chlamyphoridae and Dasypodidae are the only surviving families in the order, which is part of the superorder Xenarthra, alo ...

s have none.

Structure

Adult

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, cultu ...

s 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 The maxillary lateral incisors are a pair of upper ( maxillary) teeth that are located laterally (away from the midline of the face) from both maxillary central incisors of the mouth and medially (toward the midline of the face) from both maxil ...

(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 Deciduous teeth or primary teeth, also informally known as baby teeth, milk teeth, or temporary teeth,Illustrated Dental Embryology, Histology, and Anatomy, Bath-Balogh and Fehrenbach, Elsevier, 2011, page 255 are the first set of teeth in the ...

(primary teeth) also have eight incisors, named the same way as in

permanent teeth Permanent teeth or adult teeth are the second set of teeth formed in diphyodont mammals. In humans and old world simians, there are thirty-two permanent teeth, consisting of six maxillary and six mandibular molars, four maxillary and four mand ...

. Young children may have from zero to eight incisors depending on the stage of their tooth eruption and

tooth development Tooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. For human teeth to have a healthy oral environment, all parts of the tooth must develop during appropriate st ...

. 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

Among other animals, the number varies from species to species.

s have 18, whereas

s have none. Cats, dogs, foxes, pigs, and horses have twelve.

Rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...

s 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 Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Adult females are referred to as cows and adult ...

(cows, bulls, etc.) have none on top but a total of six on the bottom.

Function

In cats, the incisors are small; biting off meat is done with the canines and the carnassials. In

elephant Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantida ...

s, the upper incisors are modified into curved tusks (unlike with

Narwhal The narwhal, also known as a narwhale (''Monodon monoceros''), is a medium-sized toothed whale that possesses a large " tusk" from a protruding canine tooth. It lives year-round in the Arctic waters around Greenland, Canada and Russia. It is ...

s, where it is a canine that develops into a straight and twisted tusk). The incisors of

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...

s grow throughout life and are worn by gnawing. In humans, the incisors serve to cut off pieces of food, as well as in the grip of other food items.

Additional images

File:3D Medical Animation Still Showing Types of Teeth.jpg, Arrangement of incisors in an adult human. File:Illu mouth.jpg, Mouth (oral cavity) File:Gray157.png, Left maxilla. Outer surface. File:Gray187.png, Base of skull. Inferior surface.

References

External links