Y-TZP CERAMICS FOR ARTIFICIAL JOINT REPLACEMENTS

Due to their excellent mechanical properties, Yttria-stabilized Tetrag onal Zirconia Polycrystal ceramics (Y-TZP) are used in ball heads for Total Hip Replacements. It is known that Y-TZP materials may show stre ngth degradation due to ageing or to hydrothermal treatment. Also high wear of UHMWPE sockets coupled to steam sterilized Y-TZP ball heads a fter a short implantation period was recently reported. This effect ma y be related to ball head surface phase transformation, due to corrosi ve attack. The aim of this study is the evaluation of Y-TZP ceramics s tability. Y-TZP made out of Yttria coated powders were aged at 140 deg rees C under 0.2 MPa water pressure, in Ringer's solution at 37 degree s C, in NZW rabbits. Samples made out Yttria coated powders show lower strength degradation than samples made out coprecipitated powders, an d UHMWPE discs coupled to Y-TZP rings made out coated powders do not s how increase in wear after repeated sterilization cycles of the cerami c rings. (C) 1998 Published by Elsevier Science Ltd. All rights reserv ed.