[Study on low temperature degradation of dental zirconia ceramic].

Objective: To evaluate the properties of low temperature degradation (LTD) of dental Y-TZP by experiments.

Methods: According to ISO 13356-2008 standards, 72 blanks of Y-TZP were sintered at different temperature (1 400 °C,1 450 °Cor 1 530 °C) and in different heat preserving time(2 h or 5 h), and then the specimens were grounded and polished. The blanks were divided into 12 groups according to the different sintering temperature, heat preserving time and aging time. The surface of specimens was observed by SEM to evaluate the grain size of specimens; Each group of specimens was exposed to 140 °C hydrothermal aging environment for 0 h, 5 h or 24 h. After aging, XRD analysis was undertaken to determine the amount of phase transformation from tetragonal to monoclinic for each groups. At last, the biaxial flexural strengths of all specimens were measured and calculated.

Results: The SEM showed that the grain size of each group of Y-TZP increased with the increase of sintering temperature and heat preserving time, however, all of them were below 1 μm. The XRD analysis showed the contents of monoclinic of each group varied with different sintering temperatures, heat preserving times and aging time. The flexural strength of 24 h aging groups declined significantly; but that of 5 h aging group showed increase or decrease according to the different sintering temperatures and heat preserving times.

Conclusion: Different sintering procedures to some extent may affect the Y-TZP aging properties.