Impact of Sintering Protocol on the Mechanical Properties of Hydrothermally Aged High- Translucent Zirconia Materials

To evaluate the effect of high-speed and conventional sintering on the biaxial flexural strength of high-translucent zirconia materials before and after artificial aging (low-temperature degradation [LTD]).

A total of 156 zirconia specimens (disk shaped, 12-mm diameter × 1.2-mm thickness) were prepared from three materials (4Y-TZP: Nacera DD-cube-ML-HT; 5Y-TZP: Nacera DD-cube- X2ML-HT; 6Y-TZP: Nacera Pearl-Q3-ML-HT; n = 52 each). Specimens were sintered using either a high-speed sintering protocol (1,580°C; n = 26) or a conventional sintering protocol (1,450°C; n = 26). Specimens were artificially aged (LTD; 10 hours, 134°C; n = 13) or not aged (control group). Microhardness and biaxial flexural strength were measured, and phase composition was characterized using x-ray diffraction (XRD) with Rietveld refinement. ANOVA, post-hoc Tukey, and Shapiro-Wilk tests were performed (P < .05). The survival probability was determined using Weibull analysis.

Conventional sintering of 4Y-TZP and 5Y-TZP zirconia resulted in similar mechanical characteristics after LTD. The Weibull modulus of high-speed sintered zirconia specimens decreased following LTD. Among the groups, 4Y-TZP specimens exhibited the highest stability and strength, whereas 6Y-TZP showed the lowest performance.

Speed sintering and LTD can lead to degradation of the physical and mechanical properties of zirconia, potentially compromising its durability in clinical applications. Conventional sintering preserved higher flexural strength and phase stability compared to high-speed sintering under LTD conditions and therefore appears more favorable for long-term performance.