Color formulation and reproduction of opaque dental ceramic

The purpose of this study was to determine the validity and accuracy of mixing opaque feldspathic dental ceramic to obtain specific shades using two methods: (1) Concentration Additivity of Optical Parameters (CALAB) and (2) Concentration Additivity of Kubelka-Munk Optical Coefficients (CAK/S).

A total of 25 opaque feldspathic dental ceramic specimens were fabricated by mixing six different pure shades in different concentrations. The reflectance spectra were measured and the actual CIELAB L*, a* and b* coordinates were obtained for the 25 specimens. The CALAB and CAK/S methods were used to predict the L*, a* and b* values with reference to the concentrations of the pure shades. Correlation analysis was carried out between the actual and predicted L*, a* and b* values for both methods. The color differences (DeltaE*) between actual and predicted L*, a* and b* values were also calculated and analyzed using repeated measures ANOVA.

Pearson's correlation coefficients between predicted and actual values for both methods were greater than 0.98. The mean DeltaE*s were 0.24 (0.11) for CALAB method and 0.21 (0.11) for the CAK/S method. The repeated measures ANOVA revealed a statistically significant difference (P=0.0213) between the mean DeltaE*s from the two methods.

Both methods produced mean DeltaE*s between the actual and predicted methods that were below the threshold of human perceptibility. The simpler CALAB method can be used to determine the opaque ceramic mixture for specific shades with accuracy.