Vector Control in Internal Midface Distraction Using Temporary Anchorage Devices

Abstract

Le Fort III and monobloc distraction osteogenesis serve as the primary surgical treatment for children with severe midface hypoplasia. The orbital retrusion and class III malocclusion of patients with midface hypoplasia is best addressed with bodily advancement of the midface segment parallel to the cephalometric Frankfort horizontal plane. Use of internal distraction devices allows for advancement of the midface without extensive external hardware but comes at the cost of less vectorial control, resulting in a distraction vector that can cause a clockwise rotation of the entire midface or frontofacial component creating hollow appearing orbits. To counteract this clockwise rotation, we have developed a technique using orthodontic microimplants to anchor interarch class III relationship elastics. We report our experiences with this technique on a cadaveric model and as a case series of 17 patients who underwent midface distraction. A Le Fort III distraction procedure was carried out on a cadaver, and the orbital height was measured at 0-, 10-, and 20-mm distraction advancement with and without elastics in a class III relationship. Improvement of both subjective hollow appearance of the orbits and objective measurement of the orbital height with class III relationship elastics demonstrated the efficacy of class III relationship elastics in counteracting the clockwise rotation of the midface segment. A review of 17 patients with midface or frontofacial hypoplasia treated with Le Fort III or monobloc distraction with simultaneous microimplant anchored class III relationship elastics revealed correction of malocclusion and improved midface projection without significant increase in vertical height of the orbits.