The Tissues of a Tooth

A tooth is made up of five different tissues, each with a specific and important function. Serious disease in any of these tissues can affect the entire tooth and result in its decay and/or destruction. These tissues are as follows:

1. Enamel, which is a hard white outer covering surrounds the crown of the tooth and protects it from wearing away as a result of the pressure of chewing. It consists largely (96 to 98 percent) of inorganic substances, mainly calcium and phosphate.

Figure 1 The permanent teeth showing the orderly arrangement of the various types in the upper and lower dental arches.

Figure 2 Lateral or side view of the permanent teeth showing the four types of teeth, their arrangement in the dental arch, and differences in size and shape.

Figure 2 Lateral or side view of the permanent teeth showing the four types of teeth, their arrangement in the dental arch, and differences in size and shape.

2. Dentin, a yellowish bone-like tissue under the enamel, provides support and forms the bulk of the tooth structure, extending almost to its entire length. It is covered by the enamel on the crown and the cementum on the root. Chemically, dentin is composed of 20% organic and 75% inorganic matter, or collagen and calcium phosphate, respectively. The remaining five % is mainly water and other mucosubstances.

3. Pulp, a soft tissue within the center of the crown and root, contains nerves, blood vessels and lymph vessels that produce dentin and provide nourishment for the tooth throughout its life. Because of its rich supply of blood and nerves, the pulp also functions as a defense system against bacterial invasion and as a sensory signal of injury by causing toothache.

4. Cementum, a thin, bone-like tissue that covers the root, serves as a means of attaching the tooth to the surrounding bone.

5. Periodontal ligament, a layer of connective-tissue fibers, stretches between the cementum and the bone connecting the tooth root to the jawbone. It also cushions the tooth from the pressures exerted during chewing (Fig. 4).

Enamel

Dentin

Pulp

Cementum

Periodontal ligament

Jawbone

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