Planning mandibular distraction: preliminary report.

Normal lengths of the vertical ramus, body, and angle of the mandible at different ages are presented. Before mandibular distraction is embarked on, the extent of the deficiency of the mandible is assessed. The length of the vertical ramus and body are measured on cephalometric radiographs or three-dimensional computed tomography (3D CT) scans. Deficiency of the length of the mandible is calculated. The position of the pin placement angle (from the horizontal ramus) is calculated by means of the following formula: 180 degrees minus mandibular angle times vertical ramus deficiency divided by total deficiency. Placing the pins correctly will result in correction of the vertical ramus and body deficiency of the mandible and the excessively obtuse angle of the mandible will become more acute.