Page 51 - Demo

Historical evolution of the TMJ prosthesis492characteristics of the CoCrMo-UHMWPE combination in TMJ articulation. The same conclusion was reached by Westermark et al.(95) after histologic analysis of soft tissues surrounding Biomet and TMJ concept prostheses. These findings were further supported by several in vitro and in vivo studies showing that CoCr particles could exert toxic effects in exposed tissues. In animal studies, McGregor et al.(96) found sufficient evidence for the carcinogenicity of metallic Co and limited evidence for the carcinogenicity of Co alloys; thus, Co-containing implants were classified as possibly carcinogenic for humans. These findings led to withdrawal of FDA approval for the Nexus CMF system in 2015. DesignInterpositional prosthesisBetween 1840 and 1980, the main purpose of the TMJ prosthesis was as a treatment for TMJ ankylosis.(7,97–99) The rationale behind the development of the intrapositional implant was that if something was placed between the fossa and condyle recurring ankylosis could be prevented, and this offered a less invasive alternative to procedures such as gap arthroplasty and condylectomy.(6,98) A recent meta-analysis by Ma et al.(98) concluded that interpositional arthroplasty could be considered a superior treatment to gap arthroplasty, as it resulted in a better maximal inter-incisal opening and lower rate of recurring ankylosis. Alternatively an autogenous interpositional graft, of which the temporalis flap is considered the most favorable, could also be used.(97,100) Yet these autogenous interpositional grafts are not without problems; the muscle may start to shrink and even develop fibrosis, cartilage could calcify or develop fibrosis and fascia might lack the necessary bulk.(101) In comparison, alloplastic materials are easy to use, do not incur donor site morbidity, and are abundantly available. When evaluating the evolution of interpositional materials, we can observe two distinct phases. First, different materials were tested, leading to the development of suitable materials for implantation. Second, from the middle of the 20thcentury onward, the volume of the prosthesis was reduced,(6) leading to the development of prostheses such as ultra-thin silicon sheets.(101)Nikolas de Meurechy NW.indd 49 05-06-2024 10:14