WEAR OF HUMAN ENAMEL OPPOSING MONOLITHIC ZIRCONIA, GLASS CERAMIC, AND COMPOSITE RESIN: AN IN VITRO STUDY

Statement of problem. Demand is increasing for ceramic and composite resin posterior restorations. However, ceramics are recognized for their high abrasiveness to opposing dental structure. Purpose. The purpose of this study was to investigate the wear of enamel as opposed to dental ceramics and composite resin. Material and methods. Twenty-four test specimens (antagonists), 6 each of monolithic zirconia, glass ceramic, composite resin, and enamel, were prepared into cylindrical rods. Enamel specimens were prepared from 24 extracted human permanent molar teeth. Enamel specimens were abraded against each type of antagonist with a pin-on-disk wear tester under a constant load of 25 N at 20 rpm for 4800 cycles. The maximum depth of wear (Dmax), mean depth of wear (D-a), and mean surface roughness (R-a) of the enamel specimens were measured with a profilometer. All data were statistically analyzed by 1-way ANOVA, followed by the Tukey test (alpha=.05). A paired t test was used to compare the Ra of enamel at baseline and after testing. The wear of both the enamel and antagonists was evaluated qualitatively with scanning electron microscopic images. Results. No significant differences were found in enamel wear depth (D-max, Da) between monolithic zirconia (2.17 +/- 0.80, 1.83 +/- 0.75 mu m) and composite resin (1.70 +/- 0.92, 1.37 +/- 0.81 mu m) or between glass ceramic (8.54 +/- 2.31, 7.32 +/- 2.06 mu m) and enamel (10.72 +/- 6.31, 8.81 +/- 5.16 mu m). Significant differences were found when the enamel wear depth caused by monolithic zirconia and composite resin was compared with that of glass ceramic and enamel (P<.001). The Ra of enamel specimens increased significantly after wear tests with monolithic zirconia, glass ceramic, and enamel (P<.05); however, no difference was found among these materials. Conclusions. Within the limitations of this in vitro study, monolithic zirconia and composite resin resulted in less wear depth to human enamel compared with glass ceramic and