An assessment of the predictability of maxillary surgery

The purpose of this investigation was to determine the ability to perform the surgery that is planned based on the prediction tracing and model surgery when using the mandible as a guide to maxillary repositioning and internal reference points to establish the vertical dimension at the time of surgery. One hundred 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 and measurements made on the lateral wall of the maxilla (internal reference points, IRP) to determine the maxillary vertical dimension. Tracings of all cranial structures were made of the preoperative cephalograms and superimposed on the postoperative cephalogram and on the prediction tracing using cranial base structures. Points were digitized to compare the preoperative, postoperative, and predicted position of the maxillary central incisor and first molar of each patient by computer. Comparison between the predicted and actual change in the position of the incisor and molar was calculated. Statistical analysis showed that there were significant differences between the predicted and actual change in vertical and horizontal position of both the incisor and the molar (P less than .0001). The results of this investigation indicate that the ability to determine vertical repositioning of the maxilla with internal reference lines is limited.