Hard tissue human tooth enamel is one of the primary concerns of dentistry. In humans, enamel varies in thickness over the surface of the tooth, often thickest at the cusp, up to 2.5 mm, and thinnest at its border with the cementum at the cementoenamel junction (CEJ). The normal color of enamel varies from light yellow to grayish (bluish) white. At the edges of teeth where there is no dentin underlying the enamel, the color sometimes has a slightly blue tone. Since enamel is semitranslucent, the color of dentin and any material underneath the enamel strongly affects the appearance of a tooth.
Human tooth is commonly called an alveolus, or "socket". Lying over the bone is the gingiva or gum, which is readily visible in the mouth. The periodontal ligament is a specialized connective tissue that attaches the cementum of a tooth to the alveolar bone. This tissue covers the root of the tooth within the bone. Each ligament has a width of 0.15–0.38mm, but this size decreases over time. The functions of the periodontal ligaments include attachment of the tooth to the bone, support for the tooth, formation and resorption of bone during tooth movement, sensation, and eruption. The cells of the periodontal