Proximal segment position after distraction with the MD-DOS device

We investigated cephalometrically the movement of the proximal segment in t he sagittal plane in patients treated with distraction (MD-DOS device) for mandibular lengthening. The proximal segment was anteriorly rotated, whilst the distal segment was posteriorly rotated after the lengthening procedure . Thus the angle of the jaw was advanced half the distance of the advanceme nt of the distal segment. One possible reason for the anterior rotation of 3.3 degrees on average is the repositioning of the proximal segment during application of the anterior fixation unit in the cases where mobilization w as complete. Another more plausible reason is the anterior pull by the mast icatory muscles and elastic bands being greater than the reactive distracti on vector component in concert with a flexible telescopic distraction modul e and a single posterior screw anchorage. The positional movements of both distal and proximal segments were similar to those observed after mandibula r advancement with bilateral sagittal split osteotomies. (C) 1999 European Association for Cranio-Maxillofacial Surgery.