Structure of a typical tooth

A tooth consists of two main parts - the crown and the root. Vertical section through a molar tooth showing internal structure The crown is the portion extending above the gum and root is the portion extending below the gum. It is further divided into the following laye..

tructure of a typical tooth

A tooth consists of two main parts - the crown and the root.

Vertical section through a molar tooth showing internal structure

The crown is the portion extending above the gum and root is the portion extending below the gum. It is further divided into the following layers:

Enamel

is white in colour. It is the hardest substance in the human body and covers the outer portion of the crown. It is made up of mineral salts (of calcium and magnesium) and keratin. It can withstand high pressure.

Cement

is the layer present covering the root portion of the tooth. It is made up of mineral salts and water and is almost as hard as bone.

Periodontal membrane or ligament - It consists of fibres which extend across the cement and anchor the tooth in the bony socket. They also allow a certain degree of movement while chewing thereby acting as shock absorbers.

Dentine

is yellow and is a bone-like material which is present along the full height of the tooth. It is enclosed by the enamel in the crown portion and cement in the root portion. Dentine can also be composed of living cells which show divisions with new cells being added to it regularly.

Pulp cavity

is the innermost region of the teeth and shows the presence of blood vessels and nerve endings. The blood vessels serve to nourish the tooth and the nerves transmit messages of heat, cold and pain to the brain and back. The pulp cavity in the root portion is also referred to as the root canal. The number of root canals may range from 1 to 3 depending on the type of tooth. The blood vessels and the nerves enter the root canal through a small hole at the tip of the root canal.

In a set of adult human teeth, four types of teeth can be found. This condition is called heterodont. The different types of teeth are-

Incisors

There are two pairs of incisors in each jaw. They are teeth, which have chisel-like ends and are meant for cutting and biting. They have a single root canal.

Canines

There is a pair of canine in each jaw. They are teeth, which are pointed and are meant for tearing the food. They are well developed in carnivores. They too have a single root canal.

Premolars

There are two pairs of premolars in each jaw. They are bigger than incisors and canines and are flattened on top. There are four pre-molars each on upper and lower jaws, two on either side. The first pre-molar on the upper jaw has two root canals. All others have one. The surface has small humps which facilitates grinding and mastication of food. These humps are called the cusps. The pre-molars are normally bi-cuspid, having two cusps.

Molars

There are three pairs of molars in each jaw. Molars are also flattened on top. However, the number of cusps is more ranging from three to five. They are bigger teeth and appear only in the permanent set of teeth. In fact, the last molar in each side, appears only much later in the adulthood. Hence, they are commonly called the wisdom tooth.

During the life span of man, he grows two sets of teeth. This condition is called diphyodont. The teeth, which appear during the infancy, number only 20 and are temporary. They start falling from around the age of 5. They are thus called deciduous teeth (also called milk teeth). In each jaw there are 10(4 incisors, 2 canines and 4 pre-molars).

The permanent teeth take the place of the milk teeth after they fall. The types of teeth remain the same. In addition to these 20 teeth, the permanent set have 12 molars which are present 3 on each side. Thus, a total of 32 teeth are present in the normal human adult.

The following diagram shows the full complement of teeth on one jaw-