Methods: Sixty metal ceramic crowns were fabricated to the same shade specifications by 5 commercial dental laboratories. Color differences (DE) were determined between crowns and the prescribed shade tab. A test for homogeneity of variance was used to assess within lab consistency. Analysis of variance was used to determine if differences in color reproduction existed among labs.
Results: Color reproduction was significantly different among laboratories. Color reproduction for the incisal third was not consistent within the work of the individual technicians; however, no differences in within lab variability existed for the middle third of crowns. Mean color differences from shade tabs for individual labs ranged from 3.5 to 11.1 DE units. Labs were better at matching shades in the incisal third.
Conclusions: The ability to reproduce the color of the target shade tab differed among laboratories. Mean color difference variance among labs was approximately 6 DE units for both middle and incisal thirds. A color discrepancy of this magnitude would be considered a just-tolerable shade match under intraoral conditions. However, the cumulative effect of the variation among labs and the variation within individual technicians was sufficient to have rendered many of the crowns assessed in this study as clinically unacceptable shade matches. This places a premium on accurate shade selection by the dentist.