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The importance of the geometry of the screws in TMJ implant fixation

Several diseases can affect the temporomandibular joint (TMJ) and the last option is then a total replacement. The main goal of the replacement of the TMJ includes the improvement of the mandibular function (Mercuri 2009). In the design of a new TMJ, the muscular forces and the geometry of the articular surfaces of this joint increase the difficulty of finding a good solution. The TMJ implant fixations available in the market use screws and should guarantee the stability of the implant (van Loon et al. 1995; Mercuri et al. 2007). The implant fixation in TMJ remains controversial, since it is important to minimise the stress and strain changes when compared to the natural joint (Jui-Ting Hsu et al. 2011). The screws in the condyle are critical in TMJ fixation and important in the implant stability (Jui-Ting Hsu et al. 2011). In the fixation with screws, the primary stability is a mechanical interlocking (fixation) in the surrounding bone, which is influenced by several factors especially by the implant geometry, number of screws and bone quality (Marco et al. 2005). Some studies analyse the screw diameter influence and consider the screw as a pin (Chowdhury Roy et al. 2011), with a minimum diameter of 2mm to guarantee enough stabilisation. According to these points, the aim of this study is to analyse the effect of the screw geometry in the fixation of the TMJ implant.