Page 343 - Demo

General discussion 34113coating, which could then chip, fracture or even delaminate.(47,49) This problem can however be overcome by applying a gradient in the DLC-layer with more Ti-C bonds near the underlying Ti surface and C-C bonds near the implant surface. Which even further increases the wear resistance.(46) Thus, in the development of the TMJR, a proprietary protocol using a DLC-coating (HadSat®) was developed for the condylar articulating surface.(50) A second surface modification technique that was applied, was large-grit sandblasting and acid-etching (SLA) of the bony interface of the mandibular component. By increasing the surface roughness, both cell adhesion and bone ingrowth are promoted, thus reducing stress on the screw-bone interface.(50,51)Our literature analysis revealed that the risk of developing metal hypersensitivity is higher in metal-on-metal TMJR than in metal-onUHMWPE combinations.(9,26,27) Several researchers found that although the total wear volume was considerably less in the CoCr metalon-metal Christensen prosthesis compared to for instance the TMJ Concepts CoCr-on-UHMWPE prosthesis, a significantly higher amount of metal ions such as Co and Cr were found in the first group. Whereas only 3% metalosis was seen in the metal-on-UHMWPE group, 33% of all patients with a metal-on-metal system needed explantation of the TMJR.(52,53) Interestingly, five systems discussed by Elledge et al.(1) still rely on a metal-on-metal articulation. All but one other TMJR rely on a UHMWPE articulating surface for the fossa.(1) UHMWPE is a wellresearched material with high stiffness and high impact strength, low coefficient of friction, good impact load damping capability, and good resistance to body fluids.(32) Over time, these properties have even been improved upon through high-grade crosslinking (also called highly crosslinked polyethylene or HXLPE).(32) However, UHMWPE, and HXLPE, are not without flaw, as oxidative degradation over time due to reactive free radicals formed by common γ-irradiation sterilization procedures, also known as “shelf aging”, leads to loss of mechanical strength and wear resistance. This issue can be overcome by incorporating α-tocopherol (vitamin E) in UHMWPE, greatly increasing oxidation resistance. As a result, an increase in mechanical strength and less deterioration occurs, compared to non-treated UHMWPE.(54) Nikolas de Meurechy NW.indd 341 05-06-2024 10:15