ORAL HISTOLOGY

Histology is the study of anatomy that deals with the minute structure, composition, and functions of tissues. Oral histology describes in detail the tissues of the teeth, periodontium, and the surrounding oral mucosa.

Figure 4-2.\Average periods for emergence and exfoliation of primary teeth.

Figure 4-3.\Average periods of emergence of permanent teeth.

STRUCTURE OF TEETH

A tooth is divided into two parts: the crown and _{one or more roots.} Figure 4-4 illustrates the tooth crown and root.

The Crown

The crown is divided into the anatomic and clinical crown. The anatomical crown is that portion of the tooth encased in enamel. In young people, areas of the

Figure ^{4-4.\Tooth crown and root.}

anatomical crown are frequently buried in gingival tissue. As a person gets older, it becomes common for a tooth's enamel to be completely exposed above the gingiva and to have root surface showing (gingival recession). The term clinical crown is applied to the part of the crown exposed (visible) in the mouth.

The Root

The root of a tooth is embedded in alveolar bone and is covered by cementurn. The tooth may have a single root or it may have two or three roots. When teeth have more than one root, the region where the roots separate is called the furcation. When a tooth has two roots, the root portion is said to be bifurcated. When it has three roots, the root portion is said to be trifurcated (fig. 4-5). If a tooth has four or more roots, it is said to be multirooted. The tip of each root is called apex. On the apex of each root, there is a small opening that allows for the passage of blood vessels and nerves into the tooth. This opening is called the apical foramen.

The Cervix

The cervix or cervical line (fig. 4-4) is a slight indentation that encircles the tooth and marks the junction of the crown with the root. The cementum joins the enamel at the cervix of the tooth. The point at which they join is called the cementoenamel junction or cervical line.