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Fundamentals of Esthetic Implant Dentistry
Environmental Effects on the Perception of Color Metamerism Color-corrected lighting is designed to match the wavelengths and relative quantity of visible light coming from the sun; however, a person’s smile will be viewed under any number of different lighting conditions, causing restorations to appear completely different in terms of hue, value, and chroma, as shown in Figures 11.9A–B. Like the restorations themselves, traditional shade tabs will appear different when viewed under various lighting conditions, creating difficulties in shade matching. The phenomenon of two objects appearing to match in color in one setting, place, or environment, but showing apparent differences in others, is termed metamerism. This is known in some circles as the “jacket and pants problem.” What can appear to be a perfectly matched pair under the fluorescent lighting of a clothing store can look significantly different in natural light. The two objects are referred to as a metameric pair.
In dental terms, metamerism occurs when a restoration is matched to the natural dentition under incandescent light, but, when viewed under color-corrected or fluorescent light, appears different in color when compared to the natural teeth. This can occur frequently, and mistakes can often be glaring, resulting in a return visit, an unhappy patient, and unproductive chair time. The only sure way to avoid metamerism is to achieve a spectral curve match. Pairs of colored objects that have the same spectral curve always match, regardless of the light in which they are viewed. Advanced technology in dentistry has greatly increased the chances of achieving a spectral curve match. Pairs of colored objects that do not have the same spectral components may or may not match under different lighting conditions. Although some manufacturers have tried to combat metamerism by developing materials that exhibit a chameleon effect by taking on the color of their surroundings, metamerism continues to be a problem in the dental operatory. (See Figure 11.10.) Metamerism complicates shade selection and, on the whole, can only be
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Figure 11.9A, B. A color temperature meter measures the quality of lighting. The proper color temperature for the dental operatory is about 5,500°K. Here we see the same two maxillary anterior central incisors viewed under artificial daylight, fluorescent light, and incandescent light, respectively, demonstrating that operatory lighting conditions have a big impact on tooth shade and color perception. Reproduced by permission of Quintessence Publishing, copyright Quintessence.