An assessment of the predictability of maxillary repositioning.

The purpose of this investigation was to compare our ability to perform the surgery that is planned in the prediction tracing and model surgery when using the mandible as a guide to maxillary repositioning, using internal and external reference points to establish the vertical dimension at the time of surgery. A total of 146 consecutive patients who underwent maxillary repositioning by means of Le Fort I osteotomy were selected. In all patients the unoperated mandible was used to provide anteroposterior and transverse maxillary position. In 100 patients, measurements made on the lateral wall of the maxilla (internal reference points--IRP) were used to determine the maxillary vertical dimension. In 46 patients, the vertical dimension was established by measuring between a Kirschner wire in the nasal bridge and a maxillary incisor (external reference points--ERP). Comparison between the predicted and actual change in the position of the incisor was calculated. Statistical analysis showed that there were significant differences between the predicted and actual change in vertical and horizontal position of the incisor (p less than 0.0001) for both experimental groups. However, there was a significant difference between the 2 experimental groups (p less than 0.001) for the accuracy of vertical repositioning. The use of an external reference point proved to be a more accurate method for vertical maxillary repositioning. The results of this investigation indicate that the ability to determine vertical repositioning of the maxilla with internal reference lines is limited.