Mechanical characteristics of the mandible after bilateral sagittal split ramus osteotomy: Comparing 2 different fixation techniques

Abstract

Using finite element (FE) computer model simulation, we compared the mechanical characteristics of the mandible after bilateral sagittal split ramus osteotomy (BSSRO) through the use of 2 different techniques to stabilize the osteotomy. Based on the reconstructed geometry from computed tomography scans of dry adult skull with a mandibular deformity requiring surgical correction, we developed 3-dimensional FE models that simulate BSSRO with 2 different techniques to stabilize the osteotomy. Technique 1 uses 3 bicortical titanium screws. Technique 2 uses a curved titanium plate with 4 monocortical screws. Five different load cases were applied to the mandible after the simulated BSSRO with the mandible being constrained at both temporomandibular joints. To evaluate the efficacy of these 2 stabilization techniques, we compared 1) the resulting deflections at the central incisor, 2) the mechanical stresses developed in the bone in the vicinity of the stabilizing implants, and 3) the mechanical stresses developed within the screw/plating system themselves. Technique 1, using 3 bicortical titanium screws, leads to smaller deflections at the central incisor for all 5 load cases, suggesting higher mechanical stability. Technique 1 also leads to lower mechanical stresses in the bone and in the implanted screws, whereas technique 2 is associated with higher values in each of these quantities. To stabilize osteotomies after a 3-dimensional simulated BSSRO, 3 bicortical screws forming an inverted-L configuration are shown to offer more effective load transmission in the mandibular construct. This technique, when examined in an FE model, leads to higher stability with lower mechanical stresses in the bone near the bicortical screws.