Biomechanical and finite element analysis of mandibular vertical ramus marginal resection designs

This study aims to know the post-surgical Von Mises stress of the mandible after two different vertical ramus marginal resection designs, analyze the results, compare with stress pattern of normal adult mandible without simulation and infer regarding the better of the two. Three groups of 3D finite element models of human adult mandibles were created. Group I (control)-normal mandible. Group II: Mandible with a quadrilateral vertical ramus marginal resection simulated. Group III: Mandible with an arc shaped vertical ramus marginal resection simulated. Finite element analysis (FEA) models were subjected to a point load of 475 N over right and left first molars, along with masticatory loads of masseter, medial pterygoid, anterior belly of digastric and temporalis loads in varying combinations (with and without bilateral temporalis and without right temporalis). The models were analyzed to infer the overall Von Mises stress in (a) the mandible (b) the sigmoid notch (c) postero-inferior resection corners. Results of our present study provides scientific evidence for the common practice of using arc form for marginal resection of vertical ramus of mandible whenever executed. Scientific evidence behind the concept of marginal resection of horizontal ramus is available but only scanty biomechanical evidence using finite element method (FEM) is available behind the same when performed in the vertical ramus, as magnitude and direction of loads in this region vary when compared to the horizontal ramus. The results ratify that incorporating arc shaped design pattern and removal of ipsilateral temporalis load by removal of coronoid, an area prone to stress concentration on loading, significantly decreases the post surgical Von Mises stress and hence would reduce the progressive micro-damage of the mandible after marginal resections of the vertical ramus of mandible.