Human Physiology

Lesson 18 : Dentition

Layers of the Tooth

Enamel

The crown of each tooth has a coating of enamel of varying thickness. Enamel is the hardest substance in the human body. It is harder than even bone. It is the enamel which protects the tooth from being affected by normal food. It gains its hardness from calcium and phosphorus crystals. An unfortunate thing about enamel is that once the tooth erupts, the cells forming enamel get destroyed. So if enamel is lost due to any reason, it cannot grow back. However, scientists are experimenting with stem cells and forming an entire new tooth may become a reality.

Dentine

The major component inside the tooth is the most sensitive part known as the dentine, a ‘live’ tissue. Dentine lies directly below the enamel. This substance is slightly softer than enamel and resembles bone in composition. It is elastic and compressible in contrast to the rigid nature of enamel. It contains tiny tubules throughout its structure that connect with the central nerve of the tooth within the pulp.

Pulp and the Root Canal

Within the dentine, at the centre of the crown and root, is the pulp. The pulp is made of soft tissue and contains blood vessels to supply nutrients to the tooth, and nerves to enable the tooth to sense heat and cold. It also contains small lymph vessels which carry white blood cells to the tooth to help fight bacteria. The pulp is the only living part of the tooth. The extension of the pulp within the root of the tooth is called the root canal. The root canal connects with the surrounding tissue via the opening at the tip of the root. This is an opening in the cementum through which the tooth’s nerve supply and blood supply enter the pulp from the surrounding tissue.

Cementum

Cementum is the layer which covers the root surface similar to enamel which covers the tooth surface. However cementum is not as hard as enamel. The periodontal ligament is attached to the cementum.

The Periodontal Ligament:

The tooth is not directly attached to the bone. The periodontal ligament is a fibrous membrane attached to the bone on one side and to the cementum on the other. It contains elastic fibres to allow some movement of the tooth within its bony socket. This gives the springiness to the teeth, and load-bearing capacity to the teeth. That is also why teeth feel a bit mobile when you grasp it between your thumb and finger.

Alveolar Bone

This is a special type of bone that has two important functions: keep the tooth in its place; feed it and protect it. It absorbs the high forces generated during chewing.
The Gum

The gum is the pink soft tissue covering the tooth and alveolar bone. It is a general misconception that the tooth is anchored to the pink soft tissue, actually the gum is just a covering. The technical name for gum is gingiva. Healthy gums are coral pink in colour. They remain firmly attached to the underlying bone and support the tooth structure inside. Gingiva is affected by hormonal and other changes occurring in the body.