A critical comparison of methods for the determination of the ageing sensitivity in biomedical grade yttria stabilized zirconia

Abstract

Since the recent failure events of two particular series of zirconia femoral heads for total hip replacement prosthesis, a large decrease in the use of zirconia ceramics for orthopaedic implants has been observed. In spite of the biomedical success of this material during the last ten years, this was required for safety reasons, until the cause of the failures is known. It has been shown that these failures were related to the low temperature hydrothermal degradation (also known as ageing). Thus it is crucial to better understand the ageing behaviour, in order to be able to assess its importance and then control it if required. In this paper, various techniques relevant to assess the hydrothermal degradation sensitivity of biomedical grade yttria stabilized zirconia are discussed and compared. The expected outputs of conventional methods, i.e. X-Ray diffraction and scanning electron microscopy are examined. More recent methods like optical interferometry and atomic force microscopy are presented, with their respective benefits and drawbacks. An up to date comparison of these different techniques is provided, and their use for ensuring the long term reliability of a particular batch of zirconia in terms of ageing degradation is demonstrated.