BIOMECHANICAL CONSIDERATIONS OF MANDIBULAR LENGTHENING AND WIDENING BY GRADUAL DISTRACTION USING A COMPUTER-MODEL

Purpose: Experience using distraction osteogenesis for limb lengthenin g has shown the importance of appliance orientation. Although successf ul results of mandibular lengthening using osteodistraction have been reported, optimal orientation of the distracters relative to the mandi ble has not been determined. The purpose of this study was to evaluate the biomechanical effects of linear distracters placed parallel to th e body of the mandible or parallel to the axis of distraction. Materia ls and Methods: A two-dimensional model of the human mandible was gene rated for computer simulation of mandibular osteodistraction. Linear d istracters were then analyzed based on their orientation, either paral lel to the body of the mandible or parallel to the axis of distraction . In addition, two types of distraction osteogenesis procedures for ma ndibular reconstruction were analyzed: 1) bilateral mandibular lengthe ning, and 2) bilateral mandibular lengthening in combination with midl ine mandibular widening. Results: Distracters oriented parallel to the body of the mandible caused a lateral displacement of the posterior c omponents of the distraction devices and a reduction of the midline di straction gap during mandibular lengthening. These effects were elimin ated when the device was oriented parallel to the axis of distraction. Midline symphyseal widening created axial rotation of the mandibular condyles regardless of the orientation of the distracters. Conclusions : Distraction appliances must be oriented parallel to the axis of dist raction to prevent adverse biomechanical effects during bilateral mand ibular lengthening. Additional ramus osteotomies, using hinged devices for angular correction, may be necessary to compensate for rotational movements of the mandibular condyles secondary to midline osteodistra ction.