YTTRIA, CERIA DOPED ZIRCONIA-ALUMINIA CERAMIC COMPOSITES FOR DENTAL APPLICATIONS

摘要

At present, zirconia-based ceramics are gaining popularity in dentistry, particularly in fixed prosthodontics. Clinically, it is important that ceramic restorations reproduce the translucency and color of natural teeth. At ambient pressure, unalloyed zirconia can assume three crystallographic forms depending on the temperature. At room temperature and upon heating up to 1170°C, the symmetry is monoclinic (P21/c). The structure is tetragonal (P42/nmc) between 1170 and 2370°Cand cubic (Fm-3 m) above 2370°C and up to the melting point. The transformation from the tetragonal (t) phase to the monoclinic (m) phase upon cooling is accompanied by a substantial increase in volume (～4.5%), sufficient to lead to catastrophic failure. This transformation is reversible and begins at ～950°C on cooling. Alloying pure zirconia with stabilizing oxides such as CaO, MgO, Y_2O_3 or CeO_2 allows the retention of the tetragonal structure at room temperature and therefore the control of the stress-induced t→m transformation, efficiently arresting crack propagation and leading to high toughness.