Zirconia and zirconia-apatite (hydroxyl- and fluor-) composites were sintered at 1225-degrees-C by glass-encapsulated hot isostatic pressing. In addition to the general assessment of the mechanical properties of the materials, the static fatigue behaviour of the zirconia-hydroxylapatite composite was evaluated by measuring the slow crack propagation at different loads in a circulating 0.9% NaCl solution at 37-degrees-C. The mean fracture strengths of the materials in three-point bending mode were 770, 860 and 910 M Pa for zirconia-fluorapatite, zirconia-hydroxylapatite and zirconia, respectively. The high value of the slow crack growth stress exponent, calculated from the average strength at the different loading rates, indicates that the zirconia-hydroxylapatite has excellent fatigue resistance in addition to high strength. The even distribution of the apatite phases as islets in the zirconia matrix may contribute to mineralization and direct bone apposition to this type of ceramic composites. The machinability of zirconia materials is discussed.
