Head and neck cancer is a growing health problem; tumours in this region usually require extensive resections. Tumour-related injuries may require the removal of the mandibular bone, which in turn require understanding the biomechanics of the mandible and investigation on its response under mastication loading conditions. It is also important to evaluate existing reconstruction procedures, such as the performance of the usual fixation plate, or innovative ones, such as determining the behaviour of filing materials, like Polycaprolactone (PCL), Poly(lactic acid) (PLA), bone graft (BG) or Titanium (Ti). This work started from medical imaging exams of patients with mandibular problems. In detail, finite element (FE) models of 5 cases were reconstructed and those with mandibular lesions were analysed in terms of the effect of the filling material. The focus was on analysing the von Mises stress values of the remaining bone under the different conditions. It was observed that, in the filled models, there was a reduction in von Mises stress in the bone due to the filling, and that the studied materials were able to effectively withstand masticatory forces. However, it was also possible to observe that each material had a different behaviour: over the long term, PLA is most likely the indicated material for mandibular filling, as it generally showed the same behaviour as the BG. Contrarywise, the Ti fillings would cause stress shielding, which in turn could damage the surrounding bone tissue (and others), making it an inadequate candidate over both short and long term. The behaviour of the mandible bone with the use of a common fixation plate was also studied, by simulating the before and after of a partial mandibulectomy. It was found that the Ti fixation plate reduces the von Mises stress, as it is designed to withstand forces and protect the bone during healing. This is again because Ti has a much higher Young's modulus than bone, which increases the stresses in the plate and reduces them in the surrounding bone, promoting stress shielding as happened with the filling. Therefore, this study has contributed not only to an in-depth understanding of the biomechanical behaviour of the mandible, but also to improving reconstruction strategies and clinical interventions in patients with head and neck tumours; to conclude, it provides a solid basis for future research and advances in medical practice concerning mandible reconstruction and materials.