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

The three basic radiographs used for three-dimensional prediction tracings are the panoramic, PA and lateral cephalometric. Magnification error of each radiograph is calculated and subtracted prior to determining the actual distance of distraction in all directions. In hemifacial microsomia patients, mandibular hypoplasia presents in both the vertical and horizontal dimensions. Therefore, the plan of distraction is usually in both dimensions.

Panoramic Radiograph

The panoramic radiograph is used as a general survey of the mandible since it provides better visualization of mandibular morphology than the PA and lateral cephalometric radiographs. The actual distance of distraction is determined from lateral and PA cephalometric radiographs due to their decreased distorsion. A diagnostic tracing of the panoramic radiograph is made and includes both the maxilla and the mandible. A preoperative planned osteotomy is drawn on the diagnostic tracing. The location of the four distraction pins should be located near the posterior and inferior border of the mandible. The preoperative planned pin position should be placed in the best possible position on the diagnostic tracing. The location for pin placement may be limited in some patients who have had previous jaw surgery and/or have retained hardware. An alternative location for pin placement should be planned as a second option. After osteotomy and pin placement location are planned, the prediction of distraction is completed from the PA and lateral cephalometric radiographs.

FIG. 6.1.1.1. Diagnostic tracing of a panoramic radiograph used as a general survey of mandibular structures such as the inferior alveolar canal and morphology of the abnormal ramus, and for planning the osteotomy location (A) and pin positions (B, C).