We deposited multilayer Nanocrystalline Diamond (NCD) thin films on Ti-6Al-4V substrates that were machined to imitate the shapes of the condyle and fossa of the temporomandibular joint (TMJ). We performed low stress wear assessment experiments on condyle/fossa pairs mounted in a custom-built mandibular movement simulator (MMS) for 5 x 105 loaded cycles at 1.2 Hz, which is equivalent to 4.4 years of clinical use. Analysis of wear surfaces on the control and the NCD-coated pairs indicated that no film delamination occurred on the NCD-coated condyle/fossa couple and that wear damage was extensive on the uncoated condyle/fossa pair. The high stress wear tests performed using the Ortho-POD machine at loads of 80 and 165 N showed that loss of film on the condyle specimens occurred after 3300 and 341 cycles, respectively. A subsequent evaluation of the influence of condyle curvature on wear by articulating a multilayer condyle/disk pair at a load of 50 N and 250 000 cycles at 1.2 Hz, showed that film delamination on the condyle occurred after 12500 cycles and no loss of film was observed on the disk after 250 000 cycles of articulation. Our results show that the observed lower film lifetimes on the condyles at high stresses are not related to intrinsic stresses in the film but probably due to lower film adhesion on the curved surfaces of the condyle.
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