Effect of high-speed sintering on the flexural strength of hydrothermal and thermo-mechanically aged zirconia materials

To investigate the influence of high-speed and conventional sintering on the flexural strength (FS) of three zirconia materials initial and after artificial aging. Milled zirconia specimens (3Y-TZP: ZI and Zolid; 4Y-TZP: Zolid HT+; Amann Girrbach AG; N = 288, n = 96/group) were sintered in a high-speed sintering protocol (final temperature 1580 °C, n = 48/subgroup) or a conventional sintering protocol (control group, final temperature 1450 °C, n = 48/subgroup). FS was tested initially and after artificial aging (10 h in an autoclave or 1,200,000 chewing cycles; n = 16/subgroup). Univariate ANOVAs, post-hoc Scheffé, partial eta-squared, Kolmogorov–Smirnov-, Kruskal–Wallis- and Mann–Whitney-U-test were performed (p < 0.05). ZI showed the highest and HT+ the lowest FS, regardless of the sintering protocols and aging regimens (p < 0.001). High-speed sintered HT+ showed higher initial FS than the control group (p < 0.001). ZI (p < 0.001–0.004) and Zolid (p < 0.001–0.007) showed higher FS after thermo-mechanical aging. High-speed sintered HT+ showed higher FS in the initial stage (p < 0.001). The Weibull modulus of the three thermo-mechanically aged materials was negatively influenced by high-speed sintering. As shorter sintering times represent a cost and time efficient alternative, high-speed sintering is a valid alternative to conventional sintering protocols.