Effect of Sintering Temperature on Reliability and Aging of 3Y-TZP

Objective: to evaluate the effect of sintering temperature and resultant grain size on the reliability and aging sensitivity of zirconia (3Y-TZP) for dental applications. Methods: Cylindrical blanks of cold isostatically-pressed zirconia (3Y-TZP) were sectioned into discs (2x25mm; n=20 per group) and sintered at temperatures in the range 1300º to 1550ºC (50ºC increments for 2h). Density was measured by Archimedes' method. The ratio of monoclinic to tetragonal phases was determined by XRD after aging in a steam autoclave at (137ºC @ 2Atm). The mean biaxial flexural strength was determined in air with a Universal testing machine (0.5mm/min). The flexural strength data was analyzed using Weibull statistics. The microstructure was investigated by SEM and AFM. The real grain size was determined by the lineal intercept method. Results: Density was greater or equal to 99.2% of theoretical density for all groups. ANOVA and Tukey's test showed that the mean flexural strength was not statistically different between groups, except for the group sintered at 1550ºC which was highest (1159±90MPa; p<0.0001). The mean grain size was statistically different between all groups, varying from 0.23±0.02 microns for the group sintered at 1300ºC to 0.75±0.04 microns for the group sintered at 1550ºC. The Weibull modulus was highest for the group sintered at 1550ºC (m=15.0) and lowest for the group sintered at 1300ºC (m=6.8). Both mean grain size and Weibull modulus increased linearly with sintering temperature (R-square=0.97). Accelerated aging led to increasing amounts of monoclinic phase as sintering temperature increased. Conclusion: Higher sintering temperatures led a larger grain size, higher flexural strength and reliability, but greater sensitivity to aging.