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

Purpose: It has been previously demonstrated that distractors placed parallel to the mandible in the transverse plane, without regard to the vector of distraction create lateral displacement tendencies at the appliance-bone interface, leading to potential clinical problems and complications. The purpose of this study was to evaluate the biomechanical effects of linear distractor orientation in the sagittal plane relative to the anatomic axis of the mandible (mandibular plane) and the maxillary occlusal plane. Materials and Methods: A 2-dimensional model of the human mandible was generated for computer simulation of osteodistraction. Positional changes of the distal mandibular segment were then analyzed during 10 mm of incremental lengthening based on distractor orientation relative to the maxillary occlusal plane. Results: Distractors placed parallel to the inferior border of the mandible without regard to the maxillary occlusal plane created a vertical translation of the distal bone segment resulting in an anterior openbite. The magnitude of the anterior open bite was proportional to the angle between the vector of distraction and the maxillary occlusal plane, and to the amount of distraction. Placement of the distractors parallel to the maxillary occlusal plane eliminated the tendency for an anterior openbite. Conclusions: The orientation of the distractors relative to the maxillary occlusal plane is one of the important biomechanical parameters that must be included in preoperative planning for mandibular osteodistraction.