The effect of surface grinding and sandblasting on flexural strength and reliability of Y-TZP zirconia ceramic

Objectives: This study was conducted to evaluate the effect of grinding and sandblasting on the microstructure, biaxial flexural strength and reliability of two yttria stabilized tetragonal zirconia (Y-TZP) ceramics. Methods: Two Y-TZP powders were used to produce fine grained and coarse grained microstructures. Sixty discs from each material were randomly divided into six groups of ten. For each group a different surface treatment was applied: dry grinding, wet grinding, sandblasting, dry grinding+sandblasting, sandblasting+dry grinding and a control group. Biaxial flexural strength was determined and data were analyzed using one-way ANOVA, followed by Tukeyʹs HSD test (p<0.05). In addition, Weibull statistics was used to analyze the variability of flexural strength. The relative amount of transformed monoclinic zirconia, corresponding transformed zone depth (TZD) and the mean critical defect size ccr were calculated. Results: There was no difference in mean strength between the as sintered fine and coarse grained Y-TZP. Significant differences (p<0.05) were found between the control group and ground fine grained material for both wet and dry grinding. Sandblasting significantly increased the strength in fine and coarse grained materials. All surface treatment procedures reduced the Weibull modulus of Y-TZP. For both materials, the highest amount of the monoclinic phase and the largest TZD was found after sandblasting. Lower amounts of the monoclinic phase were obtained after both grinding procedures, where the highest mean critical defect size ccr was also calculated. Significance: Our results indicate that sandblasting may provide a powerful technique for strengthening Y-TZP in clinical practice. In contrast, grinding may lead to substantial strength degradation and reduced reliability of prefabricated zirconia elements, therefore, sandblasting of ground surfaces is suggested.