Masseter muscle adaptation following orthognathic surgery - Biomodelling analysis - A pilot study

Purpose: This pilot investigation was designed to apply several, newly developed and more sophisticated methods of measuring muscle structure, function and fibre orientation to a situation where adaptation of muscle is pivotal to the success of a therapeutic approach. Materials and Methods: Patients attending the combined orthodontic / orthognathic surgery clinic at Clitrofa – Centro Médico, Dentário e Cirúrgico, in Trofa - Portugal were screened using Magnetic Resonance Imaging protocol. Ten patients scheduled for a bimaxillary osteotomy involving a combination of maxillary Le Fort I impaction procedure coupled with a sagittal split advancement of the mandible were select to form the study group. An Experimental design used to provide information in relation to masticatory muscle adaptation following orthognathic surgery. The study involved the contribution of two independent examiners that measured the changes in fibre orientation at the different jaw positions using AnatomicsTM software, at three different time moments. A combination of different parametric tests has been used to compare the different experimental variables. Results: Statistical differences have been identified between examiners measurements and between operations. There were no significant differences testing different times. Conclusions: The discrepancies between examiners probably arise from small variations in the experimental methodology used by them. The differences between operations reveal masseter muscle adaptation following orthognathic surgery. The measurement of “P1 masseter muscle/ zygomatic bone / process mastoid anterior angle” and “P2 masseter muscle / mandibular angle” can therefore be a valuable tool for controlling the reworking of masseter muscle upon orthognathic surgery.