幼齒 and 恒齒

Baby Teeth:
 


Permanent teeth, which are also known as adult teeth, are the second and final set of teeth in the human mouth. There are generally 32 permanent teeth in an adult mouth—16 in the upper jaw and 16 in the lower jaw. The permanent teeth replace the 20 primary teeth, which are also known as baby teeth, milk teeth, or deciduous teeth.

 


Types of teeth

The shape of the crown determines the purpose of the tooth:

·Incisors have a straight edge to incise or cut food. The two central incisors in each jaw are also known as the front teeth, indicating their location in the mouth. A lateral incisor is located on each side of the front teeth. There is one root in each incisor.


·The canine teeth are located in the corners of the mouth, with two in each jaw. The canine teeth have pointed crowns and are longer than the other teeth. These teeth are used to grip and tear food. They are also known as cuspids or eye teeth. Each canine tooth has a single heavy root.
 

·On each side of the six front teeth (incisors and canines) are five molars known as the back teeth. The crowns have wider surfaces that are used to chew food. On the surface of the molar are two or more cusps, slight elevations in the crown that are used to grind and pulverize food before it is swallowed.


·The premolars, which are also known as bicuspids, are located behind the cuspids (canine teeth). They help the canine teeth to grip and tear food. There are eight premolars in the adult mouth, with half in the upper jaw and half in the lower jaw. A premolar has one or two roots.


·The remaining molars in each jaw are used to grind food. The first molar, also known as the six-year molar, is adjacent to the second bicuspid. On the other side of the first molar is the second molar, the twelve-year molar. At the back of the mouth are the third molars, which are also known as wisdom teeth. The upper molars generally have three roots, and there are usually two or three roots in the lower molars. These roots help bolster the teeth for the heaviest pressure of chewing and grinding food.