Acceptability of shade differences in metal ceramic crowns

Statement of problem. Application of technology that quantify color and color differences is currently used in esthetic restorative materials research. However, parameters for the size of perceptible and accept able color differences in metal ceramic crowns have not been determined. Purpose. The CIELAB colorimetric system was used to study the relationship between instrumentally measured color differences (Delta E) and human observer assessment of color differences in metal ceramic crowns. Material and methods. Subjects were shown pairs of metal ceramic crowns whose color difference varied from indistinguishable to obvious. The subjects attempted to discern a difference in each pair's color and indicated the clinical acceptability of the shade difference between the crown pairs. Results. Correlations between instrumental and visual assessment of color differences in these crown pairs did not agree in all dimensions of color space. Thresholds acceptability of color differences were 1.1 Delta E units for red-varying crowns and 2.1 Delta E units for yellow-varying crowns. Thresholds for perceptibility judgments were significantly lower than thresholds for acceptability judgments. Conclusions. Acceptability thresholds were found to be dependent on chromaticity. Observers were more sensitive and critical of crowns whose color differed in redness as opposed to crowns whose color differed to the same extent in yellowness.