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Chapter 7200Unlike sheep, humans can be asked to consume a liquid to soft diet and only perform depression and elevation of the mandible during the first 6 weeks after surgery. This restriction can prevent LPM micromovements and maximize the chances of good ingrowth. However, restoration of the maximal ‘range of motion’ during the post-operative recovery period could be delayed.(34) While a limitation in movement might lead to concerns with regard to HO and possible ankylosis, several remarks have to be made. Firstly, none of the patients that were included in the study by Mommaerts that were treated with LPM reinsertion, showed heterotopic bone formation.(7) Secondly, with consideration of the per-operative difficulties that were experienced as to evaluate if the enthesis came in direct contact with the subcondylar lattice structure, sometimes residual bone chips were added to the assumed gap. This in turn might have led to a hyperostotic reaction in some sheep. Thirdly, evidence seems to indicate that by filling out the negative space around the joint, by means of an autologous fat graft for instance, the risk of heterotopic ossification can be reduced as well.(35)Lastly, while five ewes developed heterotopic bone formation, four of these sheep presented themselves with an aseptic loosening and subsequent displacement of the fossa (Table 5). Despite the fossa being designed to achieve a perfect anatomical fit, the aseptic loosening most likely occurred due to micromovements between the fossa and the underlying bone. This resulted in bone resorption underneath the titanium surface of the fossa.(36) A possible cause was the use of 2mm diameter screws for fixation of the zygomatic component. Considering the higher mastication rate and mainly laterotrusive movement, the fossa is subjected to higher forces compared to its human counterpart. While a higher screw diameter increases the fatigue resistance and lessens the risk of failure as excessive stress in the bone surrounding the screw, the opposite is true for screws with a smaller diameter.(37,38) This excessive stress can lead to bone resorption and implant failure.(36,39) As a result, using 2mm diameter screws under this higher load compared to its human counterpart, can very well have resulted in insufficient fixation of the fossa in four out of 13 ewes. Furthermore, in humans a soft diet can be maintained during the period of osseointegration, limiting the amount of force the TMJ is Nikolas de Meurechy NW.indd 200 05-06-2024 10:14