Regardless of which system of shade selection is used, there should be general adherence to the following principles:
1. The patient should be viewed at eye level so that the most color-sensitive part of the retina will be used.
2. Shade comparison should be made under different lighting conditions. Normally the patient is taken to a window, and the color is confirmed in natural daylight after initial selection under incandescent and fluorescent lighting.
3. The teeth to be matched should be clean. If necessary, stains should be removed by prophylaxis.
4. Shade comparisons should be made at the beginning of a patient's visit. Teeth increase in value when they are dry, particularly if rubber dam has been used.
5. Brightly colored clothing should be draped and lipstick removed. The operatory walls should not be brightly painted.
6. Shade comparisons should be made quickly, with the color samples placed under the lip directly next to the tooth being matched. This will ensure that the background of the tooth and the shade sample are the same, which is essential for accurate matching. The dentist should be aware of eye fatigue, particularly if very bright fiber-optic illumination has been used. The eyes should be rested by focusing on a gray-blue surface immediately before a comparison, because this balances all the color sensors of the retina and resensitizes the eye to the yellow color of the tooth.
COMMERCIAL SHADE GUIDES (FIG. 23-18)
The most convenient method for selecting a shade is a commercially available porcelain shade guide. Each shade-tab (Fig. 23-19) has an opaque backing color, neck color, body color, and incisal color. Shade selection consists of picking the shade tab that looks the most natural and reproducing this in a laboratory with materials and techniques recommended by the manufacturer. The procedure is easier if specimens of the same hue are grouped together in the shade guide. In the past, shade guides were produced in response to the demand for denture teeth rather than on the range of natural tooth color . 36 More recently, shade guides have covered the color space occupied by natural teeth,* such as the Vita-pan 3D-Master shade guide (Fig. 23-18, C).
Hue Selection. In the popular Vita Lumin vacuum shade guide (Fig. 23-18, A), A1, A2, A3, A3.5, and A4 are similar in hue, as are the B, C, and D shades. Choosing the nearest hue first and then selecting the appropriate match of chroma and value from the tabs available is the recommended technique.
*Shades that match artificially bleached teeth are also available.
If its chroma or intensity is low, accurately determining a given hue may be difficult. Therefore, the region with the highest chroma (i.e., the cervical region of canines) should be used for initial hue selection (Fig. 23-20, A).
Chroma Selection. Once the hue is selected, the best chroma match is chosen. For example, if a B hue is determined to be the best match for color variety, there are four available gradations (tabs) of that hue: BI, B2, B3, and B4 (Fig. 23-20, B). Several
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