Teeth

The primary function of teeth is to prepare food for digestion by chewing (mastication). Mastication breaks down tough connective tissues and fibers and helps saturate these materials with lubricants and enzymes.

Parts of a tooth

Crown is the white part that is seen. It is covered by a layer of enamel which contains a crystalline form of calcium phosphate (the hardest biologically manufactured substance). Adequate amounts of calcium, phosphates, and vitamin D3 are essential during childhood in order for the enamel coating to form and resist decay.
Neck marks the boundary between the root and the crown.
Root consists of a layer of dentin that extends up into the crown, the pulp cavity which contains the root canal, nerves, and blood vessels.

Dentin is a mineralized matrix similar to that of bone, differing only in that it does not contain living cells. Instead, cytoplasmic processes extend into the dentin from cells within the pulp cavity. The pulp cavity receives blood vessels and nerves via the root canal at the base (root) of the tooth, which sits within a bony socket called an alveolus.

Collagen fibers of the periodontal ligament extend from the dentin of the root to the surrounding bone. A layer of cementum covers the dentin of the root, providing protection and firmly anchoring the peridontal ligament.

Cementum also resembles bone, but it is softer. Where the tooth penetrates the gum surface, epithelial cells form tight attachments to the tooth, preventing bacterial access to the easily eroded cementum of the root.

Types and Functions
Each of the four adult types of teeth has specific functions:

Incisors are blade-shaped found at the front of the mouth. They are useful for clipping or cutting off bits of food.
Cuspids are cone-shaped with a pointed tip. They are useful for tearing or slashing food not totally separated by the action of the incisors.
Bicuspids are premolars.
Molars have flattened crowns with prominent ridges. They are useful for crushing, mashing, and grinding food, thus preparing it for the digestive process.

Tooth Development
Two sets of teeth are formed:

Twenty (20) deciduous teeth (primary) are the first to form.
Thirty-two (32) secondary, or permanent teeth, with the addition of three (3) molars on each side, up and down, replace the primary.

Primary teeth and their approximate appearance

Lower Jaw
- Central incisors – 6 months
- Lateral incisors – 7 months
- Cuspids – 16 months
- Primary or first molars – 12 months
Upper Jaw
- Central incisors – 7½ months
- Lateral incisors – 9 months
- Cuspids – 18 months
- Primary or first molars – 14 months

Permanent teeth and their approximate appearance

Lower Jaw
- Central incisors – 6-7 years
- Lateral incisors – 7-8 years
- Cuspids – 9-10 years
- First premolars – 10-12 years
- Second premolars – 11-12 years
- First molars – 6-7 years
- Second molars – 11-13 years
- Third molars – 17-21 years
Upper Jaw
- Central incisors – 7-8 years
- Lateral incisors – 8-9 years
- Cuspids – 11-12 years
- First premolars – 10-11 years
- Second premolars – 10-12 years
- First molars – 6-7 years
- Second molars – 12-13 years
- Third molars – 17-21 years

This page was updated in December 2005.