Structure of the Teeth and Supporting Tissues

READING ASSIGNMENT: AFP 162-6, Vol. 1, pages 84 - 85

MORPHOLOGY 115

Teeth: A tooth is divided into two parts, the crown and the root. The anatomical crown is the part of the tooth covered with enamel. The root of a tooth is embedded in alveolar bone and covered with cementum. NOTE: In young people, areas of the 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. The term clinical crown applies to the part of the tooth that is visible above the gingiva to include root surface.

The bulk of the tooth is composed of a bone-like substance called dentin which is covered by enamel to form the crown and cementum to form the root. The line of division between the crown and the root is called the cervical line or cementoenamel junction (CEJ). The dividing line is found in a somewhat constricted region on the tooth’s surface called the cervix or neck.

The tip of the root is known as the apex. The tooth contains an aggregate (herd) of blood vessels, nerves, and cellular connective tissue called the dental pulp. The dental pulp is housed within a pulp chamber and root canal of a tooth. Anterior teeth ordinarily have one root canal; multiple canals occur in posterior teeth. The nerves and blood vessels enter and leave the tooth through an opening called the apical foramen at or near the apex of the root.

Supporting Structures of the Teeth: The supporting tissues of the teeth are collectively called the periodontium (perio = around – dontium = teeth). The periodontium consists of the alveolar process of the maxillae and the mandible, the periodontal ligament, the cementum of the tooth, and the gingiva.

Alveolar process: The alveolar process is the portion of the maxillae or mandible in which the roots of the teeth are embedded and by which the tooth roots are supported. An alveolar process consists of three kinds of bone. They are the outer cortical plate, lamina dura, and spongy bone. The outer cortical plate is a compact layer of bone on the bone’s surface. The lamina dura is a thin, dense layer of bone that lines tooth sockets. The lamina dura is a specialized continuation of the cortical plate. Spongy bone is the less dense, cancellous (porous) bone representing the alveolar process’ central mass.

Periodontal Ligament: The periodontal ligament is a thin, fibrous ligament connecting a tooth to the lamina dura of the bony socket. Normally, teeth do not contact the bone directly; a tooth is suspended in its socket by the fibers of the ligament. This arrangement allows each tooth limited individual movement. The fibers act as shock absorbers to cushion the force of chewing impacts.

Cementum: The cementum is the only tissue considered as both a basic part of the tooth and a component of the periodontium. It is a thin, calcified layer of tissue that completely covers the dentin of a tooth’s root. Cementum is formed during the development of the root, It functions as an area of attachment for periodontal ligament fibers.

Gingiva: The gingiva is the specialized mucous membrane covering the alveolar processes and encircling the necks of the teeth. It aids in the support of the teeth, and protects the alveolar process and periodontal ligament from bacterial invasion. Healthy gingiva is pale pink, firm, and resilient. It is divided into two types, free and attached.

Free Gingiva: Free gingiva is “free” to the extent that it can be displaced; it is not tightly bound to anything underneath it. Free gingiva extends from the gingival crest to the bottom of the gingival sulcus. At the bottom of the sulcus, and epithelial attachment joins the free gingiva to the tooth surface. The interdental papilla is the portion of the free gingiva that fills the proximal space below the contact areas of adjacent teeth. It helps prevent food from packing between the teeth.

Attached Gingiva: Attached gingiva covers the labial and lingual cortical plates of the alveolar process. It is firmly fixed to underlying bone.