Phase transformation, roughness, and microhardness of artificially aged yttria- and magnesia-stabilized zirconia femoral heads.

Yttria-stabilized zirconia ceramic (Y-TZP) has been used in total hip arthroplasty for many years but is susceptible to low-temperature aging. Medical-grade magnesia-stabilized zirconia (Mg-PSZ) is less commonly used; however, it has been shown to resist phase transformation. The purpose of this study was to directly compare the effects of artificial aging on phase transformation, surface roughness, and Vickers microhardness on Y-TZP and Mg-PSZ femoral heads. Y-TZP and Mg-PSZ heads were artificially aged in an autoclave in stages up to a total of 49 h. The surface roughness of Y-TZP significantly increased with each stage of artificial aging. Y-TZP heads aged for 49 h had a significantly higher monoclinic phase concentration and roughness, and a significantly lower microhardness, than nonaged Y-TZP heads. Artificial aging also caused the surface of Y-TZP to exhibit a lumpy "orange peel"-like appearance with a significantly higher mean peak height, suggesting that artificial aging causes individual grains to be pushed out of the surface. In contrast, artificial aging did not significantly affect the properties of Mg-PSZ heads. These findings suggest that Mg-PSZ is a satisfactory material for orthopaedic implant use, while Y-TZP, in the form tested, is not adequately stable for use as a bearing surface.