Mechanical behaviour of zirconia and zirconia-toughened alumina in a simulated body environment.

The mechanical properties of a zirconia-toughened alumina (ZTA) and three tetragonal zirconia polycrystal ceramics (TZPs), together with a biograde alumina, have been assessed in a simulated body solution (Ringer's solution). The hardness and fracture toughness of these materials were unchanged from the values in air when the tests were carried out in Ringer's solution; there was an instantaneous fall in strength in Ringer's solution but this was considered acceptable. However, ageing for long periods in Ringer's solution promoted a surface layer of monoclinic zirconia. This was accompanied by a strength decrement and it is concluded that these yttria-stabilized ZTA and TZP materials are unsuitable as implant materials.