Abstract: PURPOSE: To evaluate maxillary skeletal stability after downward Le Fort I (LF1) osteotomy and to use three-dimensional measurements to investigate the effects of factors on postoperative stability. METHODS: Fifty patients were treated with LF1 osteotomy with downward and setback bilateral sagittal split osteotomy. The position of the maxilla was measured using spiral computed tomography data from preoperative (T0), 3 days postoperatively (T1), and more than 6 months postoperatively (T2) time points. To assess the postoperative maxillary changes, there 3-dimensional alterations in the landmarks [bilateral greater palatine foramen (GP), anterior nasal spine (ANS)at follow-up were measured. Statistical analysis was performed using SPSS 12.0 software package. RESULTS: In all 50 cases of downward LF1 osteotomy, the vertical dimensional relapse of the ANS from T2-T1 was 1.11 mm. The relapse was correlated with the amount of anterior maxillary vertical surgical movement and type of posterior vertical movement. CONCLUSIONS: LF1 osteotomy to move the maxilla downward is a high-risk surgical procedure that might result in relapse. Some factors contributing to relapse patterns include the amount of downward surgical movement, movement in the posterior maxilla. All of these factors should be considered during surgical treatment planning.

Key words: Orthognathic surgery, Three-dimensional measurement: Maxiilary vertical dysplasia, Stability, ROC analysis