Assessment of Alteration in Pediatric Temporomandibular Joint (TMJ) Stress Distribution Secondary to Mandibular Advancement Surgery
Date of Award
Dissertation - Restricted
Doctor of Philosophy (PhD)
Harris, G. F.
Maxillofacial deformity occurs as a result of a differential in the growth of the upper facial skeleton to the lower facial skeleton. Normal anatomical relationship can be restored by reconstructive surgery. The resultant aesthetic improvement is straightforward and the anatomical restoration can be predicted using current surgical planning system. However, prediction on functional improvements is still not available and the mechanism of the functional alteration is still unclear. The biomechanical response secondary to the mandible advancement has been selected as the topic for studying. From the clinical observation, the TMJ symptoms of the patient with mandible hypoplasia and Class II malocclusion can be alleviated as a result of mandible advancement surgery. The hypothesis is that the mandible advancement significantly reduces the contact pressure along the TMJ. To verify this, both analytical and FE models of a pediatric patient-specific stomatognathic system have been established based upon clinical available CT scan data. Using medical imaging techniques, the mandible advancement surgery has been simulated and thus both pre- and post-operation model have been established. The muscle force information including their directions and application sites as well as physiological cross-section areas have also been extracted from the pediatric patient-specific CT scan data. Employing an optimization technique and force-squared based objective function, the magnitude of the muscle forces and the joint reaction forces have been determined subjected to a given occlusal force. The results of the analytical model have been used as a part of the boundary conditions imposed on the FE models. The articular disks have been modeled as non-homogeneous objects with hyperelastic body and a linear elastic soft layer. The FE analyses have been carried out using two independent sets of boundary conditions to approach the real alteration of the contact pressure on the TMJ. Under both conditions, the comparison study between pre- and post-operation models indicated that the mandible advancement results in a significant reduction of the contact pressure on the TMJ, and an anterior shift of the high contact pressure area. This proves the hypothesis and provides an explanation for the alleviation of the TMJ symptoms from the biomechanical response point of view.