Color changes in post-cure heat-treated resin composites

The purpose of this study was to determine the color changes that arise from post-cure heat treatment of selected light-cured resin composites by using colorimetric as well as observational methods. Brands of composite were selected that were solely Bis-GMA-based and Bis-GMA/urethane based. These materials also represented a range of filler content (low, medium, and high). The RGB values of cured resin discs were obtained immediately after light-curing as well as after a 5-minute post-cure heat exposure. The range of post-cure temperature was from 100-300 degrees C in 25 degrees C increments. The mean delta L*, delta a*, delta b* and delta E* were determined from red, green and blue data using triplicate replications for each heating condition. Twenty-one observers were asked to determine if the randomly arranged post-cure heated specimens differed in color from the unheated, cured control specimen for each brand. The results indicate that a delta E* value of approximately 3 resulted in greater than 50% of the observers noting a color difference between the post-cure heated specimen and the unheated control. The degree of color change was influenced more by the amount of resin content in the composite systems rather than by the particular resin composition. Microfill resins showed greater potential for color change than did the other types of materials. If clinicians are considering using conventional light-cured composite materials for inlays, the choice of material as well as the post-cure temperature will influence the ability to match the inlay with the original shade of composite selected.