Masseter Muscle Adaptation Following Orthognathic Surgery

Abstract

After facial deformity surgery, long-term skeletal stability relies heavily on the structural and functional adaptation of the facial muscles. If these muscles, particularly the pterygo-masseteric sling comprising the masseter and medial pterygoid, cannot adjust to post-surgical changes in length or orientation, they may exert undesirable forces on their attachments. This failure to adapt can cause skeletal instability and compromise surgical outcomes. While treatment options have expanded to include myofunctional appliances for children and orthognathic surgery for adults, a fundamental principle of adult surgery is avoiding the stretching of the pterygomasseteric sling, which increases the risk of relapse. If muscles revert to their original functioning length faster than they can adapt organically, or if their attachments migrate, bone resorption can occur due to inadequate muscle support. Consequently, capturing functional adaptation accurately requires multiple sophisticated assessment measures.
Academic support from UCL Eastman Dental Institute helped identify the project topic, structure the four developments presented, define repeatability tests, and conduct pilot studies. Technical support from CEiiA supervised the construction of two devices used in Phase 1: the Occlusal Force Diagnostic System and the Bite Training Machine. The development of the MRI protocol at the John Radcliffe Hospital - MRI Centre, presented in Phase 3, enabled the identification and visualisation of muscle fibres and their orientation. The Medical, Dental, and Surgical Center – Clitrofa, Portugal provided clinical support by selecting patients, performing surgical interventions, and conducting follow-ups for the four phases presented.
The selected patients for the pilot and follow-up studies underwent a bimaxillary osteotomy, combining a maxillary Le Fort I impaction procedure and a sagittal split advancement of the mandible.
Future studies with larger patient cohorts are actively assessing surgical efficacy further. These evaluations will increasingly employ ultrasonography, a portable, radiation-free method that provides real-time, cross-sectional assessment of soft-tissue thickness and adaptation.

Date of Award	7 May 2026
Original language	English
Awarding Institution	University of Portsmouth
Supervisor	Chris Louca (Supervisor) & Mahdi Mutahar (Supervisor)