There are many factors that affect the color of teeth and cosmetic dentistry. When we select the shade of a crown, for example, the “color” is determined by hue, chroma, and value. However, what we cannot control is a physical property of light passing through a prism. This is called metamerism.
The shades of teeth are usually grouped under different hues, or broad categories. For instance, in cosmetic dentistry – teeth tend to fall in the yellow, brown, grey, or red categories. True “white” has no hue and is not a realistic color. Hues tend to be based predominantly on the dentin color, the inside of the tooth. Hue selection is very difficult, however, when large restorations are present on the tooth which may stain the tooth dark grey or brown. When a crown is being made, the hue is usually selected to match the adjacent tooth.
Chroma is the actual amount of pigmentation that is in the tooth. Most frequently, a tooth has a higher chroma value closer to the gumline where the translucent layer of the tooth, the enamel, is the thinnest. Many teeth do not have predictable chroma patterns. Therefore, the skill level of the dentist is tested because he or she must accurately describe the chroma of the tooth to a lab technician in writing, with photographs, etc., to get an esthetic restoration.
Value is the lightness or darkness of a tooth. Metamerism changes the value of a tooth. For instance, a ceramic restoration will look whiter under fluorescent light and darker in daylight. The phenomenon of metamerism is the reason that dentists prefer not to restore just one front tooth at a time. Even the best porcelain restoration will look different in certain lighting situations than a natural tooth next to it. The effects of metamerism can be minimized if all of a person’s front teeth are made of the same material: enamel, resin, or porcelain.