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Biomaterials in TMJ replacement813is prioritized over the load-bearing capacity of the material, resulting in the selection of cp Ti for these parts. Furthermore, cp Ti and Ti6Al4Vhave an elastic modulus of 105 GPa and 115 GPa, respectively. This reduces the risk of stress shielding, compared with stainless steel or CoCr alloys, although these modulus values are still clearly different from that of bone.(48,59)It should be noted, however, that despite of its advantages, Ti is not a material without flaws. Ti and its alloys are rather soft and have a low wear resistance, meaning that the material is not suited for articulating surfaces.(48) A second potential problem of Ti6Al4Vrelates to its alloying components. The alloy contains both V and Al, which can be released over time because of corrosion. Release of these ions has been found to be associated with long-term health problems, such as osteomalacia and neuropathy, as they are respectively toxic and neurotoxic. McGregor et al.(54) found no reports of tumors in animal studies with either Ti or Ti alloys, except for one study with Ti-6Al-4V, in which the alloy was implanted in the femur of rats, resulting in an increased incidence of local tumors. Loosening of the implant resulted in a further increase in the incidence of tumors. However, no other study showed the occurrence of tumors with the use of Ti-6Al-4V. Based on both epidemiological evidence and animal experiments, these authors concluded that there is inadequate evidence to indicate that Ti or Ti alloys (Ti6Al4Vincluded) are carcinogenic for humans.To overcome Ti’s shortcomings both β-Ti alloys and surface modification are currently being developed and discussed further below in the “Future Directions for Temporomandibular Joint Materials” section.Ultra-high-molecular-weight polyethyleneAfter UHMWPE was first used in orthopedic surgery in 1962(60), the Techmedica device was the first to make use of this material for TMJ purposes in 1990, using the material as the articulating surface of the fossa component. Not long after, the Biomet system followed suit.(6,38,60)Nikolas de Meurechy NW.indd 81 05-06-2024 10:14