Incisors

Incisors are the type of tooth located in the front part of the mouth that function in cutting food. Their crown is flat and chisel-shaped like a small blade, which enables food to be cut before it is swallowed. The back teeth then break down the food and mix it with saliva.

An adult human typically has eight incisors: four in the upper jaw and four in the lower. The two closest to the center of the mouth are called central incisors, and the other two are called lateral incisors. Incisors usually have only one root, which differs from back teeth that can have two or three roots.

Structure

Like other teeth, incisors consist of a hard outer layer called enamel, which is the hardest substance in the body; beneath it lies dentin; and in the center of the tooth pulp chamber containing living tissue of the root and blood vessels. The root is held in place by bone and the periodontal ligament.

Eruption and replacement

Incisors are the first teeth to erupt in children. Among the deciduous teeth are three incisors that later fall out and are replaced by permanent teeth. This replacement typically occurs in the early school years.

In animals

Different animal species have incisors shaped to suit their diet. Rodents and gnawing animals have large incisors that grow continuously and which they use to gnaw. Herbivores that eat plants such as cattle and sheep lack upper incisors, instead having a hard pad where the upper incisors would be, while their lower incisors are used to cut plants. The elephant's long forward-pointing incisors are its tusks.

Health and practice

Incisors are most visible when a person speaks or smiles, and therefore have a significant effect on appearance; orthodontic treatment often focuses on arranging the incisors. They also play a role in certain sounds, particularly those involving the lips and teeth. Many cultures, including in parts of Somalia, have customs related to the appearance or beautification of incisors.