Double layer effect and other optical phenomena related to esthetics.

A number of optical phenomena have been applied to an understanding of the appearance of dental porcelain restorations. Chromatic adaptation by observers has been identified as a major source of error in taking shades under artificial light. The measurement of tooth color by means of an instrument appears to be a long range solution, but is not yet practical. Surface gloss interferes with the correct identification of tooth and porcelain color due to specular reflection. Diffuse illumination is recommended for color matching. The color of teeth and porcelain crowns is determined by the "double layer effect." This means that the apparent color is the result of diffuse reflectance from the inner dentin or opaque porcelain layer through the outer translucent layer. Therefore, changes in the translucency of dental enamel due to illumination or desiccation alters the overall color of the tooth. Chromatic adaptation, translucency changes, and the double layer effect appear to be the major effects rather than metamerism. An understanding of these effects is needed to improve the esthetics of dental restorations.