Borosilicate glass as a surface finishing alternative for improving the mechanical properties of third-generation zirconia

Objective: This study evaluated the effect of an experimental borosilicate glass on the mechanical and optical behavior of 5Y-PSZ zirconia and comparing it to commercial glaze and as-sintered. Methods: Disc-shaped specimens of a 5Y-PSZ (Zpex Smile) were prepared and sintered (1550 degrees C, 2 h). The zirconia discs were randomly divided according to the surface treatment: as-sintered (C), commercial glaze (G), and experimental borosilicate glass (SL). Glaze and experimental glass powders were mixed with building liquids and applied to zirconia with a brush. G specimens were fired at 950 degrees C and SL at 1200 degrees C. An extended dwell time of 20 min was applied to both groups. Biaxial flexural strength, roughness (Ra and Rz), translucency (TP00), color alteration (Delta E00), Vickers hardness, fracture toughness, residual stresses, and x-ray diffraction analyses were conducted. Statistical analyses were performed with Weibull statistics, Kruskal-Wallis, or ANOVA tests (alpha = 5%). Results: SL yielded the highest flexural strength (799.35 MPa), followed by G (662.34 MPa), and C (485.38 MPa). The fracture origin of SL specimens was in the bulk zirconia, while G and C showed fractures starting at the surface. As-sintered reached the highest fracture toughness and hardness. Glaze and borosilicate glass provided surface compressive stresses. Borosilicate glass application led to phase transformation (t -> m). SL and G showed the lowest roughness. TP00 and Delta E00 were similar among groups. Significance: Borosilicate glass improved strength without harming the optical properties of third-generation zirconia. Toughness and roughness provided by the experimental glass were similar to those from commercial glaze.