Mandibular Lengthening: 3-D Planning
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Douglas P. Sinn, DDS, Wichit Tharanon, DDS

Introduction

Currently, distraction osteogenesis of the craniofacial skeleton is an accepted alternative treatment modality for patients who have hypoplastic craniofacial skeletons. Numerous publications of mandibular distraction (McCarthy, 1994; McCarthy et al., 1992; Moore et al., 1994; Havlik & Bartlett, 1994; Pensler et al., 1995; Klein & Howaldt, 1995, 1996; Molina & Ortiz Monasterio, 1995) and other craniofacial bones (Cohen et al., 1995; Polley et al., 1995) have been reported. Additionally, different types of devices (uni-, bi-, or multi-directional; extraoral or intraoral) for distraction of the mandible have been reported (Klein & Howaldt, 1996; Diner et al., 1996; Dinner et al., 1997; Schmelzeisen et al., 1996). Recently, Losken et al. proposed a mathematical formula, which was used to preoperatively calculate the location of pin placement in the mandible (Losken et al., 1995a, 1995b). The data for calculations was obtained from lateral cephalometric radiographs and three-dimensional computed tomographs. They reported three cases of bilateral mandibular distraction and one case of unilateral mandibular distraction. In the unilateral mandibular distraction, they had difficulty identifying the points for measurement and calculation due to asymmetry of the mandible.

Prediction tracings and details of treatment planning for mandibular distraction osteogenesis in hemifacial microsomia patients have not been previously published. The purpose of this chapter is to present three-dimensional planning and prediction tracings using conventional (panoramic, PA and lateral cephalometric) radiographs. Two cases of hemifacial microsomia treated by this approach are demonstrated. Preoperative prediction tracing of mandibular distraction will provide the surgeon with important information such as proper location of the osteotomy, the location of pin placement, the sequence of distraction vectors, and the actual distance of osseous distraction. These prediction tracings are used as a guide during the distraction period to direct appropriate appliance adjustments.