Y-TZP ceramics for artificial joint replacements

Due to their excellent mechanical properties, Yttria-stabilized Tetragonal Zirconia Polycrystal ceramics (Y-TZP) are used in ball heads for Total Hip Replacements. It is known that Y-TZP materials may show strength degradation due to ageing or to hydrothermal treatment. Also high wear of UHMWPE sockets coupled to steam sterilized Y-TZP ball heads after a short implantation period was recently reported. This effect may be related to ball head surface phase transformation, due to corrosive attack. The aim of this study is the evaluation of Y-TZP ceramics stability. Y-TZP made out of Yttria coated powders were aged at 140°C under 0.2 MPa water pressure, in Ringer’s solution at 37°C, in NZW rabbits. Samples made out Yttria coated powders show lower strength degradation than samples made out coprecipitated powders, and UHMWPE discs coupled to Y-TZP rings made out coated powders do not show increase in wear after repeated sterilization cycles of the ceramic rings.