Host: The Japanese Society for Dental Materials and Devices
Ideal esthetic restorative materials should have similar properties of light reflection, scattering, fluorescence and opalescence to those of natural teeth. Instrumental technologies that quantify color and color-difference are widely used. However, parameters for the size of perceptible and acceptable color-differences in esthetic restorations are varied; therefore new color-difference formulas were introduced. Metamerism was proposed as the largest single cause of industrial color matching and acceptance problems. In addition to the color and color coordinates, enhanced opalescence and fluorescence may result in color-reactive material that looks natural and esthetic in any light and reacts to light in the same manner as the natural dentition. Opalescence was reported as a contributor to the vitality of a restoration, and was included as a parameter for the dental color determination. The following topics were studied to evaluate varied optical properties of esthetic dental materials.The correlation between color-difference values calculated with delta E*ab (CIELAB) and delta E00 (CIEDE2000) formulas was measured after polymerization and thermocycling of dental resin composites, and the order and correlation of influencing variables on the discrepancy of color-difference values calculated by two formulas (delta E00-delta E*ab) were determined. As a result, significant changes in weighing functions and parametric functions were involved during polymerization and thermocycling of resin composites. Since delta E00 formula was proved to be more matched to observer responses, the new formula should be considered for evaluating color-difference of dental substances. Metameric color changes between resin composites and dentin was determined and the changes in lightness, chroma, hue and hue angle under the three standard illuminants (D65, A and F2) were evaluated. As a result, metameric effect between dentin and resin composites varied depending on the shade of dentin and resin composite, and on the color parameters of lightness, chroma, hue and hue angle. Therefore these factors should be considered in color matching. Fluorescence of resin composites was measured with a color measuring spectrophotometer. From the spectral reflectance values, the difference in reflectance by the inclusion and exclusion of UV component of the illuminant was calculated. As a result, some commercial resin composites showed fluorescence, and others did not. Opalescence of resin composites was measured with a color measuring spectrophotometer. Colors measured in the reflectance and transmittance modes were compared, and a parameter that could predict the opalescence of resin composites was determined. As a result, opalescence varied by the material and shade of the resin composites, and contributed to the masking of background color along with translucency parameter.
