Page 49 - Demo

Historical evolution of the TMJ prosthesis472only 3 years. They also noted that while Vitek-Kent reported a 3% failure rate per year, most clinicians reported an annual failure rate of up to 18%.(22,80,82,86) These findings resulted in the FDA recommendation to remove PTFE implants from all symptomatic patients and from asymptomatic patients showing radiological changes, as well as the discontinuation of the VitekKent replacement system in 1992.(37)Polymethyl methacrylatePMMA was first used as an implantation material by Judet(87) in 1946, as a replacement for the femoral head. Although this system was far from a success, with significant breakage and tissue reaction to wear debris, the material still found its way into the field of TMJ surgery.(88) It was first introduced in 1954 by Healy(89), who used it to reconstruct the mandible after ablative surgery. Ten years later, in 1965, Christensen used it as the condylar head of his prosthesis. Several other surgeons such as Kiehn, Silver, and Kummoona used this acrylate as a cement to better fix the ramal or fossa component, and to achieve a better fit between the fossa and the base of the skull.(18,19,31,35) For PMMA to function as a cement, unpolymerized PMMA had to be combined with a catalyst, causing a polymerization reaction with heat being produced and dissipated to the surrounding tissues. Although a cadaver study by Mercuri et al.(90) confirmed that the amount of heat released was not sufficient to increase intracranial temperature, caution was strongly advised when using PMMA cement. Also, if the cement was unable to completely polymerize, it would not only result in a weakened state of the material, but residual monomers could also be washed out, leading to local and systemic reactions.(18) Furthermore, there were several reports that PMMA was not able to cope with normal functional loading, leading to fragmentation of the acrylate. As a result, the use of PMMA has been abandoned by all current implant systems.(18)Nikolas de Meurechy NW.indd 47 05-06-2024 10:14