Low-fusing porcelain glaze application does not damage the fatigue strength of Y-TZP

This study evaluated and compared the effects of two glaze application methods (brush and spray) on the fatigue strength and surface characteristics (topography and roughness) of a translucent yttrium stabilized partially tetragonal zirconia polycrystal ceramic (Y-TZP) prior to and after grinding. Disc-shaped specimens of translucent Y-TZP (Vita YZ-HT; Vita-Zahnfabrik) were processed (ISO 6872-2015) and randomly allocated into 6 groups, according to the surface treatments performed on the tensile surface: Ctrl - as-sintered (no treatment); Gr - grinding with a diamond bur (181 mu m-grit; #3101G); Br - glaze obtained from a powder-liquid mix and applied by brush (Vita Akzent; Vita Zahnfabrik); Sp - glaze application via spray (Vita Akzent Plus; Vita Zahnfabrik); Gr + Br and Gr + Sp - association of grinding + respective glaze method. Analyses of surface roughness (Ra and Rz), fatigue strength (staircase method), surface topography and fractography were carried out. The assintered condition had the smoothest surface, while grinding led to the rougher and more heterogeneous topography. Both glaze application methods showed a potential for topography evenness (smoothening effect), while the glaze spray method led to thinner layers of material, showing a limitation in reducing the roughness compared to the brush method. No deleterious effect on fatigue strength of the Y-TZP could be observed, as the glaze-spray application on the as-sintered surface showed the highest values. Fractography depicted two distinct fracture origin regions: from defects in the surface/sub-surface region for the Ctrl and Gr groups; and at the zirconia-glaze layer interface for Br, Sp, Gr + Br and Gr + Sp. The clinical relevance of this work is that the tested glaze application methods did not damage the fatigue strength of the tested Y-TZP.