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Esthetic Restorative Material Shade Changes Due to Photopolymerization
Howard E. Strassler, DMD
Watanabe H, Covey D. Gen Dent. 2008;55:260-266.
This study sought to measure color values (before and after photopolymerization) and variations of A1 shade polymeric dental restorative materials. The L*a*b* values of polymeric dental restorative material disks were measured by a spectrophotometer with the specular component excluded (SCE) geometry under D65 illumination over a standardized white background before and after photopolymerization. Color differences (ΔE*ab) due to photopolymerization were calculated using the CIE color-different formula. ΔE*ab indicates differences between two colors in the L*a*b* color space. In this system, L*a*b* indicate lightness, red-green, and yellow-blue respectively. Color differences (ΔE*ab ) were calculated by the equation ΔE*ab = [(ΔL* ) 2 + (Δa* ) 2 + (Δb* ) 2]1/2 . Eight resin composites, three flowable resin composites (FRCs) and two resin-modified glass ionomers (RMGIs) were utilized. L*a*b* and ΔE*ab values of the test groups were analyzed using ANOVA and Newman-Keuls multiple comparison tests. ΔE*ab values before and after photopolymerization ranged from 3.01-17.76. All RMGI and two FRC materials displayed greater color changes than resin composites (P < .05). Photopolymerization produced measurable increases and decreases in all test groups after polymerization, while most red-green (a*) values increased. Color differences between polymerized A1 shade materials ranged from 0.76-25.51 ΔE*ab. The color difference between the test materials and a widely used tooth shade guide (the Vita Lumin) was averaged at 12.66 ΔE*ab.
Our patients take shade and color matching for granted. They assume that it is easy to match the color of the tooth. This couldn’t be farther from the truth. We know that tooth color changes with dehydration of the enamel during treatment. We know that one needs to evaluate and note the shade early in treatment. Over the years, clinicians and manufacturers have tried to standardize office lighting by using color-corrected bulbs, provided for a standard lighting source to pick shades using standard shade guides, provided for shade guides with their restorative materials, and provided even more sophisticated dental spectrophotometers to choose dental shades. While the standard shade guides are excellent, clinicians have made shade chips with the actual restorative material to provide for better shade matching.
This is an excellent study with a well-thought-through and executed study design. The authors provide a good explanation of how colors/shades of restorative materials can be compared using a spectrophotometer and what these values mean. When I note a Vita Shade A1 and ask a dentist if they can picture a Vita Shade A1, the answer is usually yes. Unfortunately, this study points to the reality of restorative material shades. They don’t match the standard and they don’t match each other. Of equal importance, the shade dispensed into the tooth preparation will change during photopolymerization. It may increase or decrease in value and hue. So how do you choose a shade to match? Based upon all the available data, the most predictive technique to choose the shade of a resin-based restorative is to use the standard shade guide provided with the restorative material or, if no shade guide is available, use the Vita Lumin standard shade guide before initiating restorative treatment. In some cases where esthetics is critical, take the next step and place the restorative material on the tooth and light-cure to get the true color match. When light curing, the photoinitiator (usually camphoroquinone) will be color changed from its inherent yellow-orange color to clear.
|About the Author|
|Howard E. Strassler, DMD |
Professor and Director of Operative Dentistry
Department of Endodontics, Prosthodontics, and Operative Dentistry
University of Maryland Dental School, Baltimore, Maryland