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 of the missing structure can be achieved with a variety of treatments. Restorations may be created from a variety of materials, including glass ionomer, amalgam, gold, porcelain, and composite. Small restorations placed inside a tooth are referred to as "intracoronal restorations". These restorations may be formed directly in the mouth or may be cast using the lost-wax technique, such as for some inlays and onlays. When larger portions of a tooth are lost, an "extracoronal restoration" may be fabricated, such as an artificial crown or a veneer, to restore the involved tooth. When a tooth is lost, dentures, bridges, or