DIFFUSE REFLECTANCE BY ESTHETIC DENTAL MATERIALS

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The purpose of this research is to study the accuracy and sensitivity of an experimental technique for determining the color parameters of teeth clinically. Color control is central to the emerging field of aesthetic restorative dentistry and is a major problem with the present visual color matching for determining a patient's tooth color. Research done in this laboratory and others indicates the main source of the problem is that the accuracy required is greater than the error of visual discrimination under clinical conditions. Instrumental methods have not been successful in several studies due to optical effects arising from direct application of probes to the tooth surface and the irregular thickness of teeth. Teeth make poor samples for colorimeters. The method to be studied in this research combines visual matching using color standards for determining approximate color matches along with a photocolorimetric measurement to make the final selection. This is a major simplification of the method proposed in the previous application and combines the advantages of the visual and instrumental approaches. Statistical evidence from our pilot studies indicates that CIE L*a*b* measurements made on carefully made photographic images can be used to make accurate color matches of pairs from groups of color samples. The clinical procedure of this proposal involves photographing restorations with known color parameters in patients' mouths along with the two closest visually selected shade guide color standards. Measurements with a small electronic colorimeter on the photograph in CIE L*a*b* units are then made to match the teeth to the closest standard in the photograph. This technique does not require the accurate photographic color reproduction but instead is based upon the relative measurements of the teeth and color standards. The hypothesis of this research is that measurements of CIE color coordinates made on photographic images can be used to choose the closest matching color standard in the same photograph. The experiments in this study are designed to accomplish two purposes. First, to determine the optimum experimental conditions for color matching with photocolorimetry including illumination geometry and type of photographic process. The second purpose is to determine the sensitivity and accuracy of the refined procedures in clinical trials with different observers. The experimental designs include factorial experiments with 30 observers and several variables to determine sensitivity, accuracy and precision. The outcome measure is numerical CIE deltaE* color difference units which can be related to other studies in the color science literature.