Comparison of stress distribution on articular disc between the Hunsuck/Epker and NM-Low Z plasty technique for mandibular setback procedure

Abstract

Novel modification of Low Z plasty (NM-Low Z) technique is a bilateral sagittal split osteotomy (BSSO) technique in which the incision line is designed to create more inferior support at the proximal segment compared to the Hunsuck/Epker (HE) modification. This study aimed to evaluate and compare the stress distribution patterns at the articular disc of the temporomandibular joint (TMJ) using the NM-Low Z technique and HE modification in mandibular prognathism models. Finite element models of the mandible including the TMJ from a CT scan of a patient with skeletal class III deformity that required mandibular setback surgery, were segmented using the NM-Low Z and HE modification techniques. The mandible was moved 7 mm posteriorly and fixed with 2.0 mm miniplates
and screws. The material properties of the articular discs were simulated as homogenous, isotropic, and linear elastic materials. Finite element analysis was used to evaluate the equivalent von Mises stress on the articular disc of the TMJ. Various muscular and biting forces were applied to simulate 1, 3, and 12 months postoperatively in both models. The maximum von Mises stresses of the articular disc in the NM-Low Z model were 60.64, 36.43, and 76.38 MPa, while those of the HE modification model were 73.40, 29.94, and 82.51 MPa at 1, 3, and 12 months, respectively. Both techniques resulted in normal stress distribution patterns on the articular disc surface. In conclusion, the NM-Low Z technique is an option for BSSO in terms of providing a lower maximum von Mises stress at the articular disc than the HE modification technique, while also providing a normal stress distribution pattern similar to the HE modification technique.