Following an oncological resection or trauma it may be necessary to reconstruct the normal anatomical and functional structures of the mandible to ensure the effective and complete social reintegration of patients. In most surgical procedures, reconstruction of the mandibular shape and its occlusal relationship is performed using a free fibula flap. The bone segments must be taken with extreme accuracy and, for this reason, it is often done using a cutting guide which allows the surgeon to easily identify the cutting point and angle. This thesis focused on the development of a mixed reality headset application that facilitates the process of positioning the cutting guide on the fibula during surgery.