The objective of this study was to assess the influence of alumina sandblasting on the flexural strength of the latest generation of highly translucent yttria partially stabilized dental zirconia (Y-PSZ). Fully-sintered zirconia disk-shaped specimens (14.5-mm diameter; 1.2-mm thickness) of four Y-PSZ zirconia grades (KATANA HT, KATANA STML, KATANA UTML, all Kuraray Noritake; and Zpex Smile, Tosoh) were sandblasted at 0.2 MPa with 50-μm alumina (Al2O3) sand (Kulzer) or left as-sintered (control). For each zirconia grade, the yttria (Y2O3) content was determined using X-ray fluorescence (XRF). Surface roughness was assessed using 3D confocal laser microscopy. Micro-Raman spectroscopy (μ-Raman) and X-ray diffraction (XRD) were used to assess potentially induced residual stresses. Biaxial flexural strength (n = 20) was statistically compared by Weibull analysis. Focused ion beam - scanning electron microscopy (FIB/SEM) was used to observe the subsurface microstructure. Fracture surfaces after biaxial flexural strength testing were observed by SEM. KATANA UTML had the highest Y2O3 content (6 mol%), followed by KATANA STML and Zpex Smile (5 mol%), and KATANA HT (4 mol%). Al2O3-sandblasting significantly increased surface roughness of KATANA UTML and Zpex Smile. μRaman and XRD revealed the presence of residual compressive stress on all Al2O3-sandblasted surfaces. FIB/SEM revealed several sub-surface microcracks in the sandblasted specimens. Weibull analysis revealed that Al2O3-sandblasting increased the characteristic strength of KATANA HT, KATANA STML, whereas it decreased the strength of KATANA UTML. The strength enhancement after Al2O3-sandblasting of KATANA HT was the highest, followed by KATANA STML. For Zpex Smile, the influence was statistically insignificant. The impact of Al2O3-sandblasting on the Weibull modulus was controversial. The strength of zirconia after Al2O3-sandblasting is determined by the balance between microcrack formation (decreased strength) and surface compressive stress build-up (increased strength).
Keywords: Biaxial flexural strength; Compressive stress; Translucent; Weibull; Zirconia.
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