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dentes incisivi
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Permanent teeth of right half of lower dental arch, seen from above
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The permanent teeth, viewed from the right
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Incisor
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(from Latin ''incidere'', "to cut") are the first kind of
Tooth in
Heterodont Mammal s. They are located in the
Premaxilla .
In many
Herbivorous or
Omnivorous mammals, such as the human and the
Horse , they are adapted for shearing sharply. In
Cat s, the incisors are small and do not do much; biting off meat is done with the
Canines and the
Carnassial s. In
Elephant s, the upper incisors are modified into curved
Tusk s, just as is the case with
Narwhal s, where normally one of them develops into a straight and twisted tusk. The incisors of
Rodent s grow throughout life and are worn by gnawing.
Human s normally have eight (8) incisors, two of each type. The types of incisors are:
Among other animals, some other
Primate s, cats and horses have twelve. The
Rodent s have four. Rabbits and hares (
Lagomorph s) were once considered rodents, but are distinguished by having eight--1 small pair, called "peg teeth" is directly behind the most anterior pair.
The rodent incisor is one of the evolutionary adaptations that make rodents such a successful group. There are two incisors in the upper jaw and two in the lower jaw. The incisors are separated from the molars by a
Diastema region, an area without any teeth. The tissue of the incisor is regenerated from the apical end and constantly wears down at the distal tip. The ever-growing incisor can be subdivided into two areas, the crown analogue and the root analogue.
The crown analogue is the labial half of the incisor. It is characterized by an enlarged cervical loop at the apical end. The cervical loop is the epithelial stem cell niche. The epithelial progeny of the crown analogue's cervical loop differentiates into ameloblasts that produce enamel.
The root analogue is the lingual half of the incisor. It's cervical loop is much smaller and the epithelium does not differentiate into ameloblasts, but instead forms a root sheath and fragments into epithelial cell rests of Malassez typical of root epithelium. The root analogue is covered in dentin and cementum like a normal root.
