Comparison of two methods of profile prediction in surgical treatment of mandibular prognathism.

Two methods for prediction of the soft tissue profile subsequent to oblique subcondylar osteotomy for correction of mandibular protrusion were evaluated. The first one included distalization of the mandible into an Angle Class I relationship. The amount of distalization and any vertical changes were transferred to the tracing, and the anticipated new profile was drawn. The second method was based on the profile means of a group of "normal" persons and was aimed at correction of both sagittal and vertical discrepancies. Fifty patients were studied. A double set of prediction tracings was made according to both methods; and the results were compared with the actual postoperative results and with a "normal" control group. Both methods were usable, as the predictions were considered satisfactory if they were within one standard deviation from the mean of the control group. The sagittal changes were somewhat exaggerated by both analyses. The vertical changes were much better expressed by the profile prediction. Such changes are difficult to create by the vertical subcondylar osteotomy. Consequently, the model prediction seems most suitable for planning profile changes in surgical techniques that include mobilization of one main mandibular fragment.