Effect of different finishing/polishing techniques and glaze application on the flexural strength of ultratranslucent zirconia after hydrothermal aging

Purpose: To evaluate the effect of different finishing/polishing procedures and glaze on the surface roughness, flexure strength, and microstructure of an ultratranslucent zirconia (UZ) submitted aging. Methodology: Two hundred and forty (240) UZ bars were sintered (8 × 2 × 1 mm) and treated according to the factors (n = 15): Type of finishing/polishing procedure (Control - Ctrl; Ultra-fine Diamond Burr - FG; Medium grit diamond burr- MG; Stone Bur - Stone; Rubber - Rub; FG + Rub; MG + Rub; Stone + Rub), and “Glaze” (Without and With - Gl). The bars were hydrothermally degraded (24 h, 127 °C, 1.7 bar), submitted to roughness analysis and 3-point mini flexural strength (FS) test. Scanning Electron Microscopy (SEM), X-ray Diffraction (XDR), and Weibull analysis were performed. Data were analyzed by 2-way ANOVA and Tukey test (5%). Results: Finishing/Polishing’ and its interaction with ‘Glaze’ were statistically significant (P < 0.0001) for FS, unlike ‘Glaze’ alone (P = 0.8827). Rub (602.11 MPa^A), Stone + Rub (555.50 MPa^AB), and Ctrl (621.72 MPa^A) showed superior FS, while FG_GL showed the lowest FS. Stone + Rub showed the highest Weibull modulus (13.15^a). Ctrl_Gl (0.18 ± 0.02^F μm) and Ctrl + Rub_Gl (0.29 ± 0.07^F μm) showed the lowest roughness. Glaze (0.48^B) reduced the roughness of the groups that did not receive it (1.56^A), with MG (2.60 ± 0.69^A μm) and FG (2.50 ± 0.7^A μm) exhibiting rougher surfaces. Conclusions: Rubber polishers are ideal for minor adjustments to UZ while Stone followed by rubber is effective for greater abrasion without compromising mechanical strength. The application of glaze did not reduce mechanical strength and resulted in lower surface roughness compared to the non-glazed groups, with the exception of the FG groups.