 The objectives of this research are to test the following hypotheses: 1 differences between mean wear of antagonist enamel by polished monolithic zirconia crowns and by the polished veneer surface of metal-ceramic crowns are statistically significant; 2 differences between mean wear of antagonist enamel by opposing polished monolithic zirconia crowns and enamel by opposing enamel are statistically significant; and 3 differences between mean antagonist wear of enamel by opposing polished veneer surfaces of metal-ceramic crowns and enamel by opposing enamel are statistically significant. 