Tooth

From ArticleWorld

A tooth is one of several hard structures, collectively known as teeth, that are located in the mouth for the purposes of chewing. Not all teeth look the same; the particular structure and placement of a tooth is related to the particular chewing activity they are used for.

Development

In humans, the tissue that eventually becomes teeth begins in the seventh week of gestation. Humans usually get visible teeth beginning around the age of six months. The twenty teeth that eventually surface are called “baby teeth” or “milk teeth”. These teeth begin to fall out around 6 years of age and are replaced by adult teeth. There are 32 adult teeth.

While humans have two sets of teeth, other animals develop teeth differently. Some animals develop only a single set of teeth. Sharks, on the other hand, grow a new set of teeth every two weeks. Still others, such as rodents have one set of teeth that continually grows as the chewing surfaces wear away.

Anatomy

The part of the tooth that is visible is known as the crown. The root of the tooth is the portion that lies beneath the gum line. The crown is covered by hard enamel, made from calcium and phosphate, which is generally resistant to breakage. Underneath the enamel is the bulk of the tooth—a softer dentin layer that extends down into the gums. The pulp is the central core of the tooth through which nerves and blood vessels travel. A thin layer, called cementum, surrounds the tooth at the root and helps to keep it firmly anchored to the jaw.

As mentioned, all the teeth in humans do not look the same. In adults, there are four different tooth shapes that have different functions. There are eight incisors in the front, four cuspids (or canine teeth), eight bicuspids on the sides and 12 molars located in the distant sides of the mouth. The last four molars are often called the “wisdom teeth”. These teeth sometimes do not erupt at all. At other times, the teeth erupt but do not fit well into the mouth, resulting in their surgical removal.