TEETH

The teeth (dentes) are accessory structures of the digestive system located in sockets of the alveolar processes are covered mandible and maxillae. The alveolar processes are covered by the gingivae, or gums, which extend slightly into each socket forming the gingival sulcus. The sockets are lined by the periodontal ligament, which consists of dense fibrous connective tissue and is attached to the socket walls and the cemental surface of the roots. Thus, it anchors the teeth In position and also acts as a shock absorber to dissipate the forces of chewing.

A typical tooth consists of three principal portions. The crown is the exposed portion above the level of the gums. The root consists of one to three projections embedded in the socket. The neck is the constricted junction line of the crown and the root near the gumline.

Teeth are composed primarily of dentin, a calcified connective tissue that gives the tooth its basic shape and rigidity. The dentin encloses a cavity. The enlarged part of the cavity, the pulp cavity, lies in the crown and is filled with pulp, a connective tissue containing blood vessels, nerves, and lymphatic vessels. Narrow extensions of the pulp cavity run through the root of the tooth and are called root canals. Each root canal has an opening at its base, the apical foramen. Through the foramen enter blood vessels bearing nourishment, lymphatic vessels affording protection, and nerves providing sensation. The dentin of the crown is covered by enamel that consists primarily of calcium phosphate and calcium carbonate. Enamel is the hardest substance in the body and protects the tooth from the wear of chewing. It is also a barrier against acids that easily dissolve the dentin. The dentin of the root is covered by cementum, another bonelike substance, which attaches the root to the periodontal ligament.