Ageing of dental zirconia ceramics

An in vitro study was designed to monitor the t–m transformation of biomedical grade 3Y-TZP ceramics produced from two ready-to-press granulated powders of the same nominal chemical composition, but differing in their specific surface area. Disc-shaped specimens were formed by uni-axial dry-pressing and sintering in air for 2 h in the temperature range 1400–1550 °C, resulting in a mean grain size of 0.26–0.57 μm. The sintered specimens were subjected to accelerated ageing in deionized water at 134 °C for up to 48 h and verified in terms of the amount of the transformed monoclinic fraction, the thickness of the transformed layer, and the bi-axial flexural strength. The sintering-temperature-dependent transformability during ageing was confirmed, whereby the role of the starting-powder characteristics was more pronounced at lower sintering temperatures and was almost negligible at higher sintering temperatures.