Effect of Glazed Full-Contour Y-TZP on Wear of Glass-Ceramics

The use of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP), normally employed as a framework for all-ceramic restorations, have now started to be used without any veneering ceramics in patients with parafunctional activities.

Objective: To evaluate the influence of Y-TZP surface roughness on the wear behavior (volume/height loss) against glass-based ceramics (i.e., IPS Empress CAD and IPS e.max CAD, Ivoclar-Vivadent).

Method: Thirty-two Y-TZP full-contour zirconia (Ardent^®) sliders (ϕ=2mm, 1.5mm in height) were milled in a CAD/CAM unit and sintered according to the manufacturer instructions. Sliders were embedded in brass holders using acrylic resin and then randomly allocated into 2 groups according to the surface treatment (n=16): G1-as-machined and G2-glazed (Diazir^®). Empress and e.max antagonists were cut into tabs (13×13×2mm) wet-finished and also embedded in brass holders. Two-body pin-on-disc wear test was performed at 1.2Hz for 25,000cycles under a 3-kg load. Non-contact profilometry was used to measure antagonists height (mm) and volume loss (mm³). Qualitative data of the testing surfaces and wear tracks were obtained using SEM. Statistics were performed using one- and two-way ANOVAs (a=0.05).

Result: G1 yielded significantly higher mean roughness values (R_a=0.83mm, R_q=1.09mm) than G2 (R_a=0.53mm, R_q=0.78mm). Regarding antagonist loss, G1 caused significantly less antagonist mean height and volume loss (68.4mm, 7.6mm³) for Empress than G2 (84.9mm, 9.9mm³) while no significant differences were found for e.max. Moreover, Empress significantly showed lower mean height and volume loss than e.max (p<0.0001). SEM data revealed morphological differences on wear characteristics between the two ceramics against Y-TZP.

Conclusion: Within the limitations of this study, e.max wear was not affected by Y-TZP surface roughness. However, Empress wear was greater when opposing glazed Y-TZP. Overall, based on our findings, surface glazing on full-contour Y-TZP did not minimize glass-ceramic antagonist wear when compared with as-machined group.

Study was partially funded by Ivoclar-Vivadent