Evaluation of the effect of mandibular length and height on the sagittal splitramus osteotomy rigid internal fixation techniques: A finite element analysis

The stress distribution on the fixation units after sagittal split ramus osteotomy and its relation with mandibular height and length is considered to be an important factor regarding post-operative outcomes. To assess this relation, finite element models of mandibles with different heights and lengths were created. Sagittal split ramus osteotomy and 7 mm advancement was simulated on these models prior to fixation with miniplate, hybrid or inverted L system. 200 N force was applied from the incisal edge and the stress distribution on the fixation systems and the adjacent bone was evaluated. The maximum stress was measured on the miniplate system and the least stress was measured on the inverted L system. The stress was higher in the longer and thinner models, also the increase in length affected the stress change unfavorably comparing to the decrease in height. The mandibular models with greater alveolar height shared the stress with fixation units resulting a homogenous stress distribution. The least displacement was seen in hybrid system and the stress was reduced when a bicortical screw was used with a miniplate system. Based on the results of this study, when sagittal split advancement osteotomy is planned for a rather long or thin mandible, using the hybrid system for fixation should be considered since it is biomechanically advantageous. Key Words: orthognathic surgery, FEA, hybrid technique