Page 135 - Demo

Animal experiment: Surface wear analysis1335IntroductionSince the first implantation of alloplastic material as a means to treat temporomandibular joint (TMJ) disease, many different prosthetic concepts have been developed, including a total joint replacement (TJR) with both condylar and fossa component. Although the indications for TMJ TJR remain limited, an increase in case numbers has been observed in recent years−including younger patients (1–3)−raising concerns about the lifespan of the used prostheses. A recent meta-analysis on total knee prostheses reported 95% and 92% survival of the implant at 15 and 20 years, respectively. They concluded that, when the patient is first treated at a young age, at least one replacement surgery in a patient’s lifetime might be necessary.(4) This is of significant importance, as the expected lifespan of a TJR decrease is inversely correlated to the number of revision surgeries.(5) The rate at which wear appears, can be influenced by both material-related factors such as material choice, surface roughness, and the geometry of the articulating surfaces, as well as patient related factors such as the amount of force that is generated and the amount of activity and movement(6). Wear debris also can lead to foreign-body giant cell reactions, bone resorption, and aseptic implant loosening, contributing to long-term implant failure.(2,7–9)Despite several TMJ systems being available on the market, there is a clear lack of both proper in vivo and in vitro wear analysis. (10,11) This lack of testing is a significant shortcoming, as mechanical properties and wear resistance play a pivotal role in determining the long term outcomes of TJR and, therefore, the need for revision or replacement surgery (2,7). As far as the authors are aware of, Van Loon et al.(12,13) are the only group to publish their in vitro TMJ TJR wear results, prior to commercial release of their prosthesis. They designed a wear testing machine, which simulated the articulation of the mandibular head against the UHMWPE disc, while the implant was submerged in bovine fetal calf serum, diluted with distilled water. The UHMWPE disc was weighed both before and after a 7 million cycle-run, which corresponds to ten years in vivo functioning, resulting in a wear rate of 0.65mm3 per year or linear wear of less than 0.01mm/year (13). While they afterwards also conducted an in vivo sheepNikolas de Meurechy NW.indd 133 05-06-2024 10:14