Effect of dopants and sintering temperature on microstructure and low temperature degradation of dental Y-TZP-zirconia

Accelerated ageing of dental TZP were investigated at 134 °C for 2 h under 2.3 bar water vapor pressure. The TZP blanks were sintered in the range from 1350 to 1580 °C. The average grain size of 1350 and 1400 °C sintered materials were <0.3 μm whereas higher sintering temperatures led to larger grain sizes. The grain size and dopants influence the stability of tetragonal phase of zirconia under LTD conditions. The Y-TZP with average grain sizes <0.3 μm did not reveal the martensitic tetragonal-monoclinic phase transformation after ageing, whereas zirconia with grain sizes larger 0.3 μm showed fractions of monoclinic phase. Alumina and Ceria stabilized grain size and Y-TZP against LTD. Y-TZP with low amounts of Fe2O3 (<0.15%) used for coloring did not show any detrimental effects under LTD conditions. As the Y-TZP ceramics with grain size larger than 0.3 μm are not stable under LTD conditions they are not recommended for long term use in moist environment.