LTD results in an adverse cascade reaction involving Y-TZP grain pull out,
roughening of the surface, increased wear and microcracking.
When the microcracked and damaged zone reaches the critical size for slow crack growth to proceed,
degradation in mechanical properties of the material will occur.
It was claimed that the ageing process was limited and not critical in the in vivo situation until the year 2001,
when roughly 400 orthopaedic femoral heads failed in a very short period.
Upon investigation of the reasons for failures of these heads, Chevalier found it to be associated with an
accelerated ageing related to the changes in the processing techniques used.
The latter led to changes in the microstructure of the Y-TZP material [71]. Thus, the author emphasized the importance of accurate processing techniques in avoiding accelerated ageing as compared to normal ageing processes.