Page 341 - Demo

General discussion 33913concerns when opting for Co or Cr. (7,25) Firstly, due to a high elastic modulus, stress shielding might occur in CoCr prostheses. Secondly, animal studies indicate that CoCr particles can exert toxic effects in the exposed tissues, with Co-containing implants being classified as possibly carcinogenic for humans and metal hypersensitivity occurring significantly more in the metal-on-metal CoCrMo prosthesis (like the Nexus CMF).(26–28) Furthermore, a meta-analysis investigating implantrelated metal sensitivity revealed that 10% to 15% of the population has an allergy to one or several alloy components, with nickel, chromium and cobalt leading to allergic skin reactions in respectively 20%, 7% and 4% of Europeans and 14%, 9% and 4% in Americans.(29,30) In comparison, an allergy for titanium remains very rare.(31)Titanium alloy has an even better biocompatibility compared to CoCr prostheses, thanks to the Ti-Oxide layer that is formed. By combining Ti with aluminum and vanadium, the strength and fatigue resistance are improved. (16,32,33) In addition, both commercially pure Ti and Ti-6Al4V boast an elastic modulus of respectively 105 and 115 GPa, which is closer to that of bone, compared to Co-Cr alloys. For said reasons, we found titanium alloys to be preferable over cobalt-chromium alloys. Important to notice is that the biocompatibility of commercially pure Ti is higher, compared to that of Ti-6Al-4V, due to the more stable Ti-oxide layer and thus higher corrosion resistance. In comparison, Ti-6Al-4V has both a higher tensile strength and fatigue strength.(16) By opting for grade 23 Ti-6Al-4V extra-low interstitials, the amounts of oxygen, nitrogen and iron are reduced, resulting in an enhanced biocompatibility compared to industrial Ti-6Al-4V.(34) Despite these properties making Ti (alloys) the more interesting option for implantation, Ti is a softer material compared to CoCr, thus resulting in a lower wear resistance and making it less suitable as an articulating surface.(16) This might also explain why 19 of the discussed TMJR by Elledge et al.(1) used a Ti ramal component, though altered the material for the condylar head in 9 systems. To overcome this flaw, two possible solutions were discussed. Nikolas de Meurechy NW.indd 339 05-06-2024 10:15