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Biomaterials in TMJ replacement733OsseointegrationFor any type of alloplastic bony implant to be successful and achieve good longevity, osseointegration is required. Direct bone anchorage, without formation of an intervening fibrous tissue layer, is the key to establishing a rigid connection between the implant and the bone, which augments the load-bearing capacity of the prosthesis. Achieving good osseointegration relies on the interrelationship of a number of factors, such as the implant (biocompatibility, surface topography and chemistry), status of the bone bed (bone quantity and quality), surgical technique (primary stability, surgical trauma, aseptic environment), and loading conditions after implantation (immediate loading or not).(49,50)Implant surface characteristicsThe implant–tissue interaction (and therefore also osseointegration) is largely determined by a cascade of events at the implant surface, ranging from protein absorption to cellular adhesion, proliferation, and differentiation to tissue development. As indicated above, the surface chemistry governing a material’s biocompatibility is a crucial parameter, but other surface characteristics, such as topography and surface energy, are important as well. It has been shown that micro-topography favors cellular adhesion, whereas macroscale roughness (e.g., porous coatings) offers the advantage of bone ingrowth, leading to mechanical interlocking of the implant with the host bone. A higher surface energy (hydrophilicity) is more favorable for cell attachment.(50)Primary stabilityTo ensure osseointegration, the device must be well fixated at the moment of implantation (primary stability). This reduces micro-motions, allowing load transfer from the implant to the bone and vice versa without a risk of bone degeneration and fibrous tissue formation, leading to implant loosening and eventually even failure.(6,10,12,13,34,38,48) While in orthopedic surgery, fixation can be achieved by using cementation or press-fitting, this is not possible for TMJ implants. Current TMJ implants are fixated using screws,(6,12,13,34,38) which provide good primary stability. Nikolas de Meurechy NW.indd 73 05-06-2024 10:14