Abstract
Background
As the number of ceramic THR bearings used worldwide is increasing, the number of implants that experience off-normal working conditions, e.g. edge loading, third bodies in the joint, soft tissues laxity, dislocation/subluxation of the joint, increases too. Under all such conditions the bearing surfaces can be damaged, leading eventually to a limitation of the expected performances of the implant.
Methods
We characterised the damage resistance of different bearing surfaces (alumina matrix composite BIOLOXdelta, alpha-alumina BIOLOXforte, zirconia 3Y-TZP, oxidized zirconium alloy Zr-2.5Nb, CoCr-alloy) by scratch tests performed following the European standard EN 1071–3:2005. Also the scratch hardness of same materials has been assessed.
Results
The Lc1 value (i.e., the load for the onset of a scratch) measured for BIOLOXdelta is about fivefold the one measured for the oxidized zirconium alloy (OXZr) surface and about tenfold the Lc1 measured for the CoCr alloy. The height of ridges along the scratch edges due to plastic flow in the composite ceramic BIOLOXdelta are only 21% in height than in CoCr, and only a small fraction (0.04%) of the height of ridges measured on OXZr surfaces. The scratch hardness of the metal samples tested (CoCr, OXZr) results one order of magnitude lower than the ones of ceramics. This behavior is not influenced by of the presence of the coating on OXZr surface.
Conclusions
The transformation toughened ceramics tested (BIOLOXdelta, 3Y-TZP) are the materials that exhibit the higher resistance to scratching. Ridges at scratch edges are lower in ceramics than in coated or uncoated metals. The result show the superior scratch resistance behavior of toughened ceramics for THR wear couples with respect to coated or bare alloys.
Level of Evidence
Level 1.
