Wear-testing of a temporomandibular joint prosthesis: UHMWPE and PTFE against a metal ball, in water and in serum

For a temporomandibular joint prosthesis, an estimation of the wear rate was needed, prior to patient application. Therefore, we determined the in vitro wear rate of the ball-socket articulation of this prosthesis, consisting of a metal head and an ultra-high molecular weight polyethylene (UHMWPE) cup. The basic testing configuration consisted of one 8-mm diameter stainless-steel ball. rotating between two conforming cups with a minimum thickness of 5 mm. For validation of the testing apparatus, two cup materials, in two lubricants, were tested. Both cup materials, UHMWPE and polytetrafluoroethylene (PTFE) were tested in deionized water, as well as in a serum-based solution. For UHMWPE in serum, eight samples were tested, for the other combinations four samples. For UHMWPE, the tests ran for 7 million cycles, for PTFE between 0.8 and 1.7 million cycles. For UHMWPE, the wear rate was 0.006 and 0.47 (mm³/10⁶ cycles), in water and in serum, respectively. For PTFE, the wear rate was 2.8 and 47 (mm³/10⁶ cycles), in water and in serum, respectively. For reason that testing in serum simulates the in vivo situation best, it was concluded that the wear rate of the TMJ prothesis articulation is 0.47 (mm³/10⁶ cycles), which is considered acceptable.