Human tooth missing or diminished enamel on a permanent tooth usually from a prior infection of a nearby primary tooth. Hypoplasia may also result from antineoplastic therapy. Tooth destruction from processes other than dental caries is considered a normal physiologic process but may become severe enough to become a pathologic condition. Attrition is the loss of tooth structure by mechanical forces from opposing teeth. Attrition initially affects the enamel and, if unchecked, may proceed to the underlying dentin. Abrasion is the loss of tooth structure by mechanical forces from a foreign element. If this force begins at the cementoenamel junction, then progression
Human tooth ligaments include osteoblasts, osteoclasts, fibroblasts, macrophages, cementoblasts, and epithelial cell rests of Malassez. Consisting of mostly Type I and III collagen, the fibers are grouped in bundles and named according to their location. The groups of fibers are named alveolar crest, horizontal, oblique, periapical, and interradicular fibers. The nerve supply generally enters from the bone apical to the tooth and forms a network around the tooth toward the crest of the gingiva. When pressure is exerted on a tooth, such as during chewing or biting, the tooth moves slightly in its socket and puts tension on the periodontal ligaments. The