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rently less and less saturated until it appears almost gray. Simultaneously, the chroma (intensity) of complementary colors appears greater, a phenomenon that has led to the suggestion that shade selection can be enhanced if the operator walls are painted pale blue (complementary to yellow) or a pale gray-blue card is glanced at between looking at the color choices.
Deceptive color perception
Surrounding color, particularly complementary ones, influence color. When, for example, blue and yellow are placed side by side, their chroma may appear to be increased. The color of teeth can appear different if the pat5ent is wearing brightly colored clothing or lipstick.
Metamerism
Two colors that appear to be a match under a given lighting condition but have different spectral reflectance are called metamers, and the phenomenon is known as metamerism. For example, two objects that appear to be an identical shade of yellow may absorb and reflect light differently. normally a yellow object reflects yellow light but some may, in fact, absorb yellow light and reflect orange and green. To an observer the orange and green combination looks yellow, although when the light is changed the metamers no longer match. This means that a sample that appears to match under, for example, the operator light may no longer be satisfactory in daylight. The problem of metamerism can be avoided by selecting a shade and confirming it under different lighting conditions such as natural daylight and fluorescent light.
Colorblindness
Defects in color vision affect about 8% of the male population, and less of the female population. Different types exist, from achromatism (complete lack of hue sensitivity) through dichromatism (sensitivity to only two primary hues, usually either red or green not perceived) to anomalous trichromatism (sensitivity to all three hues with deficiency or abnormality of one of the three primary pigments in the retinal cones). Thus all dentists should have their color perception tested, and any that are found to be deficient in a particular range should obtain assistance when selecting tooth shades.
SHABE SELECTION
Because shade matching is sub3ective, consistency is difficult to achieve. It has been demonstrated that considerable variation exists among dentists and some are unable to duplicate even their own shade selection from one time to another. Fortunately, a lifelike restoration does not have to be an exact color duplicate of the adjacent of contralateral teeth. It should, however, blend with the teeth as a result of the distribution of ceramic materials in the restoration. Shade selection can be improved by knowledge of the principles of light and color, and of the techniques involved in dental ceramics.
Commercial shade guide
The most convenient method for selecting a shade is to use one of the modem commercially available porcelain shade guides. Each shade tab has an opaque backing color and a neck color, body color, and incisal color. Shade selection consists of picking the shade tab that looks the most natural and having this reproduced in a laboratory with the help of the materials and techniques recommended by the manufacturer. The procedure is made easier if the shade guide is arranged with specimens of the same hue grouped together.
Hue selection
In the popular Vita Lumin vacuum shade guide AI, A2, A3, and A3. 5, and