Influence of Full-Contour Zirconia Surface Roughness on Wear of Glass-Ceramics

Purpose The purpose of this study was to evaluate the influence of full-contour (Y-TZP) zirconia surface roughness (glazed vs. as-machined) on the wear behavior of glass-ceramics. Materials and Methods Thirty-two full contour Y-TZP (Diazir (R)) specimens (hereafter referred to as zirconia sliders) (phi = 2 mm, 1.5 mm in height) were fabricated using CAD/CAM and sintered according to the manufacturer's instructions. Zirconia sliders were embedded in brass holders using acrylic resin and then randomly assigned (n = 16) according to the surface treatment received, that is, as-machined or glazed. Glass-ceramic antagonists, Empress/EMP and e.max/EX, were cut into tabs (13 x 13 x 2 mm(3)), wet-finished, and similarly embedded in brass holders. Two-body pin-on-disk wear testing was performed at 1.2 Hz for 25,000 cycles under a 3 kg load. Noncontact profilometry was used to measure antagonist height (mu m) and volume loss (mm(3)). Qualitative data of the zirconia testing surfaces and wear tracks were obtained using SEM. Statistics were performed using ANOVA with a significance level of 0.05. Results As-machined yielded significantly higher mean roughness values (R-a = 0.83 mu m, R-q = 1.09 mu m) than glazed zirconia (R-a = 0.53 mu m, R-q = 0.78 mu m). Regarding glass-ceramic antagonist loss, as-machined zirconia caused significantly less mean height and volume loss (68.4 mu m, 7.6 mm(3)) for EMP than the glazed group (84.9 mu m, 9.9 mm(3)), while no significant differences were found for EX. Moreover, EMP showed significantly lower mean height and volume loss than EX (p < 0.0001). SEM revealed differences on wear characteristics between the glass-ceramics tested. Conclusion e.max wear was not affected by zirconia surface roughness; however, Empress wear was greater when opposing glazed zirconia. Overall, surface glazing on full-contour zirconia did not minimize glass-ceramic wear when compared with as-machined zirconia.