Loading frequencies up to 20 Hz as an alternative to accelerate fatigue strength tests in a Y-TZP ceramic

Considering the interest of the research community in the fatigue behavior of all-ceramic restorations and the time consumed in low-frequency cyclic fatigue tests, this study aimed to investigate the influence of the loading frequency on the zirconia fatigue strength. The biaxial flexural fatigue strength of Y-TZP discs was determined by the staircase approach after 500,000 cycles. The investigated frequencies were 2 Hz (control-simulation of the chewing activity; n=20), 10 Hz (n=20), 20 Hz (n=20), and 40 Hz (n=21). The fatigue strength data were analyzed using one-way ANOVA and post-hoc Tukey׳s test (α=0.05). Pearson coefficient (r) was calculated to assess the existence of a correlation between fatigue strength and loading frequency. X-ray diffraction analysis was used to determine the relative amount of monoclinic phase under each fatigue test condition. The fatigue strength was significantly higher for 40 Hz group (630.7±62.1 MPa) and did not differ among the groups 2 Hz (550.3±89.7 MPa), 10 Hz (574.0±47 MPa) and 20 Hz (605.1±30.7 MPa). Pearson correlation coefficient indicated a significantly moderate correlation (r=0.57) between fatigue strength and loading frequency. The percentage of monoclinic phase was similar among the groups. Therefore, the use of loading frequencies up to 20 Hz seems a good alternative to expedite the cycling strength fatigue tests in polycrystalline ceramics without significantly changing the fatigue behavior showed by zirconia in tests employing the frequency of the masticatory cycle.