In vivo ageing of zirconia dental ceramics - Part II: Highly-translucent and rapid-sintered 3Y-TZP

3Y-TZP ceramics with reduced alumina content have improved translucency and are used in monolithic dental restorations without porcelain-based veneers. The workflow can be further streamlined with rapid sintering. This study was designed to assess how these approaches affect ageing when the materials are exposed to the oral environment in vivo.

43 discs were fabricated from 3Y-TZP powder with 0.05% Al₂O₃ and sintered with conventional or rapid regimens (1450 °C 2 h, 1530 °C 2 h, or 1530 °C 25 min). Their surfaces were polished or airborne-particle abraded with 50 μm Al₂O₃. The discs were incorporated in complete dentures of 16 volunteers and worn continuously for up to 48 months. Ageing changes on disc surfaces were monitored every 6 months by X-ray diffraction, scanning electron microscopy and atomic force microscopy. Data was statistically analysed with linear models.

The amount of monoclinic phase on polished surfaces increased linearly, reaching up to 40% after 48 months in vivo. The ageing process observed for rapid sintering was 1.6 times faster compared to conventional sintering. A nano-scale increase in roughness with microcracking was also detected on polished surfaces. Airborne-particle abraded surfaces did not exhibit clear signs of ageing during the course of the study.

Highly-translucent 3Y-TZP ceramics are more susceptible to ageing than classic 3Y-TZP. After 4 years in vivo, the extent of degradation did not yet constitute grounds for clinical concern, but was more pronounced in materials prepared with rapid sintering.