Confirmation of Theoretical Color Predictions for Layering Resin Composite Materials

Objective: The aims were to confirm the color agreements with colors predicted from corrected Kubelka-Munk (K-M) reflectance theory for light and dark shades on a gray backing (single-layer model), and for intermediate shades as a second layer on the dark and light layers (double-layer model).  Methods: Two shades A1 and C3 were selected as the single layer on a gray backing for two brands of resin composite, Kalore (n=3, GC America) and Herculite Ultra (n=3, Kerr Corporation). For the double-layer model, three intermediate shades A3, B2 and C2 were applied as a second layer on a single layer, which was treated as the backing to the second layer.  Predicted reflectance spectra were calculated using corrected K-M theory, absorption and scattering coefficient spectra of each layer, measured thickness of each layer and the effective reflectance of the gray backing, and these configurations were measured for spectral reflectance.  Predicted and measured reflectance spectra were used to calculate the predicted and measured CIE color parameters respectively. CIE DeltaEab color differences (measured vs. predicted) were calculated and summarized and their confidence limits were used for comparison to acceptability and perceptibility limits. Results: The mean, standard deviation, and lower and upper confidence intervals of DeltaEab for all 12 specimens were for single layer models 1.75, 0.80, 1.24 and 2.26, respectively, and for the double layer specimens 1.89, 0.71, 1.44 and 2.34, respectively.  Conclusion: Although the agreement between the predicted and measured may be perceivable, the upper confidence limits are below acceptability limits found for tooth color matches to restorative materials.  The good agreement found for this reflectance theory reinforces the application of this theory to the prediction of the color of layered composite and would aid in the selection of the shades which, when layered, may be used to best match a desired tooth color.