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Chapter 378bioactive. Furthermore, stainless steel alloys have a high elastic modulus (E = 210 GPa), which promotes stress shielding.(34,48) Also Proplast/Teflon, despite its beneficial properties such as its low elastic modulus (E = 0.5 GPa) and the occurrence of rapid soft and hard tissue ingrowth, had proven unsuitable as PTFE was found to be unable to withstand the compressive loads the TMJ is subjected to. As a result, perforations located mainly on the central aspects of the implants developed, and originating from these perforations, a great many fracture lines and fiber extrusions could be seen. A significant amount of layer tearing was also noted.(23) Spagnoli et al.(53) reached similar conclusions after removing 96 implants: 44% of implants showed signs of wear involving either the Teflon or both the Teflon and Proplast layers, and nearly 15% of removed implants exhibited fractures.(53) Furthermore, animal studies have shown an increase in the incidence of sarcomas associated with the use of implants containing PTFE. The incidence was significantly increased when the implant had a large PTFE surface area with a flat and smooth surface morphology. This led McGregor et al.(54) to conclude that PTFE implants, when used as thin smooth films, are possibly carcinogenic for humans. Currently, Ti, Ti6Al4V, CoCrMo, and UHMWPE are considered the gold standards among the materials used for low-friction orthopedic total joint replacements.(13,18,38,40) Cobalt-chromium alloysCoCr alloys were one of the first materials used in load-bearing total joint implants because they combine high strength and fatigue resistance with good biocompatibility, owing to the passivating Cr-oxide layer.(41,42) Moreover, because of their relatively high hardness, CoCr alloys have excellent wear resistance and can be applied as the joint-bearing surface. All current FDA-approved TMJ devices still make use of more recently developed CoCrMo alloys for their condylar components.(6,34)While the Nexus CMF (Christensen) system implemented a cast American Society for Testing and Materials (ASTM) F75 CoCrMo alloy containing Nikolas de Meurechy NW.indd 78 05-06-2024 10:14