In vitro optical characterization of dental resin composite aged in darkness

The overall objective of this study is to confirm the method of determining the accuracy of Kubelka-Munk reflectance theory (KMRT) for composite materials after undergoing aging unrelated to surface exposure. The specific aims of this study include comparisons of optical characterizations for two dental resin composite materials before and after aging in darkness. Aging of five shades of two nanohybrid dental resin composite materials was accomplished under relatively normal room conditions in a dark enclosure for over 3 years. The accuracy of KMRT was assessed and optical absorption and scattering and color and translucency characterizations were performed. The magnitudes of the error of nonlinear regression of reflectance after aging to KMRT are well within the limits of expected measurement error as applied to regression analysis. The characterizations of inherent optical scattering, inherent color, and translucency indicate that aging in darkness will have some effect for at least some shades of the materials studied. KMRT is a reliable method to predict the reflectance of dental resin aged in darkness and permits subsequent clinically relevant optical characterizations of materials aged in this manner. Although changes in optical scattering were detected due to this aging, such changes appear to have a negligible clinical effect on color and translucency.