Fracture load of two thicknesses of different zirconia types after fatiguing and thermocycling

Abstract Statement of problem A direct relationship has been reported between yttria concentration and translucency in zirconia restorations. However, increased yttria concentration also increases the cubic phase of the zirconia, which reduces its strength. The effect of increased yttria content on the fracture resistance of zirconia as a function of material thickness after fatigue testing requires evaluation. Purpose The purpose of this in vitro study was to use the biaxial flexural test to evaluate the effect of yttria concentration on the mean fracture load (N) before and after fatiguing and thermocycling as a function of zirconia thickness. Material and methods Disk-shaped specimens of 5 mol% yttria partially stabilized zirconia (5Y-PSZ, BruxZir Anterior Solid Zirconia) and 3 mol% yttria partially stabilized zirconia (3Y-PSZ, BruxZir Shaded Zirconia) were prepared to thicknesses of 1.2 and 0.7 mm. For each thickness, the biaxial flexural test was used to measure the fracture load (N) before and after fatigue testing, with 1.2 million cycles at a 110-N load and simultaneous thermocycling at 5 °C to 55 °C (n=20). The data were analyzed by repeated-measures ANOVA (α=.05). Results Yttria concentration, thickness, and exposure to fatiguing had a statistically significant effect on the mean biaxial flexural load (yttria concentration: P Conclusions Yttria concentration had a significant effect on the strength of zirconia. 5Y-PSZ was considerably less resistant to fracture before and after fatigue testing than 3Y-PSZ. Decreasing the thickness of zirconia reduces its fracture resistance, regardless of the zirconia type.