Buccal Cavity – Teeth
Two different sets of teeth form during development. The first set, the primary teeth (deciduous teeth), usually erupt through the gums at regular intervals between the ages of six months and two to four years. There are twenty deciduous teeth—ten in each jaw. The primary teeth are usually shed in the same order they erupted. After their roots are resorbed, then, the secondary teeth (permanent teeth) push the primary teeth out of their sockets. This secondary set consists of thirty-two teeth—sixteen in each jaw. The secondary teeth usually begin to appear at six years, but the set may not be complete until the third molars (wisdom teeth) emerge between seventeen and twenty-five years .
Teeth begin mechanical digestion by breaking pieces of food into smaller pieces. This action increases the surface area of food particles, allowing digestive enzymes to react more effectively with the food molecules. Table 15.1 summarizes the number and types of teeth that appear during development and their functions.
Each tooth consists of two main parts—the crown, which projects beyond the gum (gingiva), and the root, which is anchored to the alveolar process of the jaw. Where these portions meet is called the neck of the tooth. Glossy white enamel covers the crown. Enamel mainly consists of calcium salts and is the hardest substance in the body. Enamel damaged by abrasive action or injury is not replaced. Enamel also tends to wear away with age. The bulk of a tooth beneath the enamel is dentin, a substance much like bone but somewhat harder. Dentin surrounds the tooth’s central cavity (pulp cavity), which contains blood vessels, nerves, and connective tissue, collectively called pulp. Blood vessels and nerves reach this cavity through tubular root canals extending into the root.
A thin layer of bone like material called cementum, surrounded by a periodontal ligament, encloses the root. This ligament contains blood vessels and nerves as well as bundles of thick collagenous fibers that pass between the cementum and the bone of the alveolar process, firmly attaching the tooth to the jaw.