Newer dental composites are continuously being introduced by manufacturers in order to improve esthetic quality. Kubelka-Munk theory also known as K-M theory has been applied to certain dental materials to provide descriptions of color and translucency. This study applied this reflectance model to translucent composite materials used in dentistry.
Three interfacial reflection methods are proposed to correct for the internal reflectance predicted by K-M theory. An aim of this study is to determine which of 3 interfacial reflection correction methods provides the least error. Reflectance values corrected with interfacial reflection correction method suggested by Richmond for composite resin material had the least error to the actual measured reflectance values.
Using this correction method the scattering and absorption coefficients of two composite brands (Herculite Ultra and Kalore) for five shades (A1, A3, B2, C2 and C3) was used to calculate perceptual color parameters at infinite thickness L*, a* and b* and translucency parameter. A second aim of this study is to determine the color difference between each brand and Vita shade guide data published by O’Brien in 1990. Color difference was generally found to exceed the acceptability limit.
K-M theory provides a reflectance model for translucent materials placed on backings of different colors. It is hypothesized that K-M theoretical reflectance spectra of single and double layers of dental composite resin material are in good agreement with observed reflectance. Another aim was to compare the measured values of reflectance of composite resin material specimens with K-M theoretical values simulating a clinical situation. Color difference values obtained by the method where the optical properties of each layer were used to predict the reflectance of the layered composite showed a barely perceivable color difference which was deemed acceptable in dentistry.