Effect of preparation angles on the precision of zirconia crown copings fabricated by CAD/CAM system.

The aim of this in vitro study was to evaluate the effects of different preparation angles on the precision of fit of zirconia crown frameworks. Dies were fabricated with three different preparation angles: 4, 8, and 12 degrees total taper. Ten copings were fabricated for each angle by a laboratory and a milling-center CAD/CAM system. After cementation, cross-sections were obtained and cement gaps were measured. Preparation angle (ANOVA, p < 0.01) and measurement location (ANOVA, p < 0.01) exhibited statistically significant influence on the precision of fit. On the other hand, no statistically significant influences were detected between copings prepared using the laboratory and milling-center CAD/CAM systems (ANOVA, p = 0.92). All groups showed marginal openings ranging between 36.6 and 45.5 microm. In light of the results obtained in this study, a preparation angle of 12 degrees is hence recommended with the confidence that the marginal gap will be consistently less than 50 microm.