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

Purpose: This pilot investigation was designed to apply several, newly developedand more sophisticated methods of measuring muscle structure, function and fibreorientation to a situation where adaptation of muscle is pivotal to the success of atherapeutic approach.Materials and Methods: Patients attending the combined orthodontic / orthognathicsurgery clinic at Clitrofa – Centro Médico, Dentário e Cirúrgico, in Trofa - Portugalwere screened using Magnetic Resonance Imaging protocol. Ten patients scheduledfor a bimaxillary osteotomy involving a combination of maxillary Le Fort I impactionprocedure coupled with a sagittal split advancement of the mandible were select toform the study group. An Experimental design used to provide information in relationto masticatory muscle adaptation following orthognathic surgery. The study involvedthe contribution of two independent examiners that measured the changes in fibreorientation at the different jaw positions using AnatomicsTM software, at three differenttime moments. A combination of different parametric tests has been used to comparethe different experimental variables.Results: Statistical differences have been identified between examiners measurementsand between operations. There were no significant differences testing different times.Conclusions: The discrepancies between examiners probably arise from smallvariations in the experimental methodology used by them. The differences betweenoperations reveal masseter muscle adaptation following orthognathic surgery. Themeasurement of “P1 masseter muscle/ zygomatic bone / process mastoid anteriorangle” and “P2 masseter muscle / mandibular angle” can therefore be a valuable toolfor controlling the reworking of masseter muscle upon orthognathic surgery.