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Chapter 13342Roughly half of the fossa components discussed by Elledge et al.(1) are metal-backed, whereas 10 are fully made out of UHMWPE. The latter poses a risk however, as deformation of UHMWPE can occur due to long term exposure to loading, called creep. The risk of creep occurring is increased when opting for a solely UHMWPE fossa. This deformation can result in a diminished fit, possibly leading to micromovements and in turn loosening of the fossa component, thus resulting in implant failure. Furthermore, due to the hydrophobic nature of UHMWPE, poor surface fixation between the UHMWPE fossa and bone/bone cement can occur, once again leading to the increased risk of micromovements.(17,55–57) Thus a Vitamin E-enriched articulating surface for the fossa component was opted for, which was then hot pressed onto a custom designed Ti6Al-4V scaffold to be fitted onto the cranial base. Implant development – DesignEqually important to the material choice is the design of the prosthesis. By performing a systematic historical review, a better understanding was gained of the design flaws in the past. Whereas the first alloplastic TMJ replacements were interpositional materials that were used after a condylectomy, just to prevent reankylosis, Smith and Robinson were the first to focus on restoring joint dynamics.(2,25,58) This led to the development of the fossa component, which aimed to further improve joint function and stability.(2) Hoping to further improve mandibular form and function, condylar prostheses were developed. However, as it became clear that the solitary use of a condylar prosthesis led to resorption of the glenoid fossa, total alloplastic TMJ replacements were developed.(2,25,59) These TMJR were designed as stock implants at first. Thus, the patient’s anatomy needed to be adapted to achieve a good fit of the implant. With the development of CAD-CAM, patient-specific custom made TMJR came to the market as well. These systems were developed to fit the patient’s anatomy specifically, thus needing no alterations during placement.(19,60) Also, these patient specific implants (PSI) allow for optimization of the fixation screws, thus minimizing the risk of damaging the inferior alveolar nerve.(19,32,61) Nikolas de Meurechy NW.indd 342 05-06-2024 10:15