Measurement of opalescence of resin composites

Objectives Opalescence is an optical property, where there is light scattering of the shorter wavelengths of the visible spectrum, giving the material a bluish appearance under reflected light and an orange/brown appearance under transmitted light. The objective of this study was to determine the opalescence of resin composites with a color measuring spectrophotometer. Methods Colors of A2 and enamel or translucent shades of four resin composites and of an unfilled resin measured in the reflectance and transmittance modes were compared, and the opalescence parameter (OP) was calculated as the difference in blue-yellow coordinate (Δb*) and red-green parameter (Δa*) between the reflected and transmitted colors of 1-mm thick specimens. The masking effect was calculated as the color difference between the color of a black background and the color of specimen over the black background. Results The range of OP in resin composites was 5.7–23.7, which was higher than that of the unfilled resin. However, there were significant differences among the brands and shades of the resin composites. Significance Opalescence varied by brand and shade of the resin composites, and contributed to the masking of background color along with translucency parameter. Some of the resin composites actually displayed opalescence.