The effect of sagittal orientation of the distractor on the biomechanics of mandibular lengthening

Purpose: It has been previously demonstrated that distracters placed parall el to the mandible in the transverse plane, without regard to the vector of distraction create lateral displacement tendencies at the appliance-bone i nterface, leading to potential clinical problems and complications. The pur pose of this study was to evaluate the biomechanical effects of linear dist racter orientation in the sagittal plane relative to the anatomic axis of t he mandible (mandibular plane) and the maxillary occlusal plane. Materials and Methods: A 2-dimensional model of the human mandible was gene rated for computer simulation of osteodistraction. Positional changes of th e distal mandibular segment were then analyzed during 10 mm of incremental lengthening based on distracter orientation relative to the maxillary occlu sal plane. Results: Distracters placed parallel to the inferior border of the mandible without regard to the maxillary occlusal plane created a vertical translat ion of the distal bone segment resulting in an anterior openbite. The magni tude of the anterior open bite was proportional to the angle between the ve ctor of distraction and the maxillary occlusal plane, and to the amount of distraction. Placement of the distracters parallel to the maxillary occlusa l plane eliminated the tendency for an anterior openbite. Conclusions: The orientation of the distracters relative to the maxillary o cclusal plane is one of the important biomechanical parameters that must be included in preoperative planning for mandibular osteodistraction.