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Historical evolution of the TMJ prosthesis412Another recently introduced system is the Groningen TMJ prosthesis, which was released in 1999.(48) (OCEBM LOE IV) Both a stock implant and patient-specific implant were developed. The latter was used when the patient had an insufficient amount of bone to use the stock device. The system used a titanium fossa with a zirconia plate on the articulating side. The ramal component was also made of titanium, with the condyle being composed of a zirconia ball. A UHMWPE disc was placed between the zirconia fossa and condyle.(18,48) Adapting Falkenström's 1993 design, which placed the point of rotation more inferior to the middle of the natural condyle, creating a translation movement when the mouth was opened, the center of rotation was placed more inferiorly compared to other TMJ prostheses.(19,48) Falkenström also calculated that by lowering this point of rotation, the use of a unilateral prosthesis would no longer overload the contralateral healthy joint over time.(19) Evaluation after 8-year follow-up of the Groningen TMJ prosthesis showed that it was mechanically successful in 87.5% of patients, and patient satisfaction was scored high.(48) Due to a lack of perceived financial viability, however, “mainstream” manufacturing ceased. DiscussionTo understand the evolution of the alloplastic TMJ prosthesis, several different aspects of its development must be highlighted. Changes in materials and designs over time will be discussed in an attempt to explain why certain systems failed whereas other systems were successful and are still used today. MaterialsWhen evaluating the evolution of the TMJ prosthesis, be it a fossa prosthesis or a TJR device, it is apparent that each new design utilized the newest materials that were available at the time of its conception.(7) However, not all of these materials were suitable for implantation, as became abundantly clear through postoperative results. For a material to be suitable for implantation, it must meet several criteria. First, proper fixation of the implant system (to preventing micromotions) Nikolas de Meurechy NW.indd 41 05-06-2024 10:14