Long-term in vivo and in vitro aging of a zirconia ceramic used in orthopaedy.

A detailed study of a commercial zirconia (Y-TZP) aged at 37 degrees C held in Ringer's solution or transplanted in animals or humans is reported. No degradation in strength was found for MOR bars or for hip joint heads subjected to stresses caused by pressing titanium alloy trunnions into the head tapers with loads up to 30 kN. Polished specimens also showed no increase in the monoclinic phase percentage upon aging for 1 year. Small specimens transplanted in animals experience no change in the micro-indentation KIC toughness value, suggesting no degradation. Zirconia heads recovered after 2 years of human implantation showed no loss of strength. The difference between the excellent performances of this ceramic presented here and other studies can be accounted by the microstructural design and quality of the zirconia.