Evaluation of postoperative mandibular positional changes after mandibular setback surgery in a surgery-first approach: Isolated mandibular surgery versus bimaxillary surgery

Publication date: Available online 20 September 2018

Source: Journal of Oral and Maxillofacial Surgery

Author(s): Jeong Joon Han, Seunggon Jung, Hong-Ju Park, Hee-Kyun Oh, Min-Suk Kook

ABSTRACT

Purpose

The aim of this study was to compare postoperative positional changes in the mandible after isolated mandibular surgery (IMS) or bimaxillary surgery (BMS) in a surgery-first approach (SFA).

Materials and Methods

The investigators designed and implemented a retrospective cohort study composed of patients who underwent mandibular setback surgery using the SFA. Surgical and postoperative changes were evaluated using lateral cephalograms taken 1 month before surgery (T0), 1 week after surgery (T1), and immediately after the debonding of orthodontic appliances (T2, 16.6 ± 8.7 months after surgery). To predict postoperative mandibular positional changes due to the increase in vertical dimension (VD) in surgical occlusion, the mandible was rotated counterclockwise to the preoperative VD on the lateral cephalogram at T1, and resultant mandibular positional changes were measured. To evaluate actual postoperative mandibular positional changes between each time point and compare them between the two groups, an independent t test, a paired t test, and repeated measures analysis of variance were performed.

Results

Thirty patients were evaluated (16 in the IMS group and 14 in the BMS group). Both groups showed significant time-course mandibular positional changes from T0 to T1 and from T1 to T2 within each group (point B, P < 0.001), although no statistically significant differences were observed between the groups. There was no statistically significant difference between groups in the predicted and actual postoperative rotational movements. In addition to the mandibular forward movement that resulted from the postoperative mandibular counterclockwise rotation, additional horizontal relapse occurred.

Conclusion

The present findings suggest that the mandible exhibits significant postoperative forward movement during the postoperative orthodontic treatment, regardless of the extent of the orthognathic surgery in the SFA, and it is necessary to consider mandibular forward movement due to the VD increase in surgical occlusion and additional relapse during the treatment planning stage.

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