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Published on: January 28, 2020
Postoperative Mandibular Positional Changes after NM-Low Z Plasty: Implications for Interpreting Skeletal Stability
Sarunpong Imampai1, Narissaporn Chaiprakit2, Siripatra Patchanee3
1Department of Dentistry, Phayuha Khiri Hospital, Ministry of Public Health, Nakhon Sawan, Thailand.
Objective:
This article compares skeletal movement after mandibular setback surgery using the NM (novel modification)-low Z plasty technique between patients treated with the surgery-first approach (SFA) and the conventional orthognathic surgery (COS) approach.
Materials And Methods:
This retrospective study included 42 skeletal class III patients (ANB < 0°) who underwent mandibular setback using the NM-low Z plasty technique between 2017 and 2022. Consecutive lateral cephalograms were obtained at three time points: preoperative (T0), immediate postoperative (T1), and 6 to 12 months postoperative (T2). Horizontal and vertical movements at the dentoalveolar point of the mandible were defined as primary outcomes. Data distribution was evaluated using the Shapiro-Wilk test and Q-Q plots. Within-group changes were analyzed with paired t-tests. Between-group comparisons were performed using Mann-Whitney U tests according to data distribution. Statistical significance was set at p < 0.05.
Results:
The mean mandibular setback was 9.34 mm in the COS group and 13.89 mm in the SFA group, respectively. Horizontal mandibular forward movement was 2.8 mm in COS (30%) and 2.06 mm in SFA (14.8%). Vertical movement at T2 showed upward movement of 1.68 and 2.8 mm, respectively. No statistically significant differences were found between groups for horizontal or vertical movement (p = 0.072). Changes in incisor inclination were also not significantly different between groups.
Conclusion:
Mandibular setback surgery using the NM-low Z plasty technique demonstrated comparable skeletal stability in both orthodontic-driven treatment protocols. The findings further suggest that postoperative mandibular positional changes in SFA were reflected as a consequence of planned orthodontically occlusal adaptation. Furthermore, vertical mandibular changes after surgery appeared to be primarily governed by postoperative orthodontic tooth movement rather than being attributable to the surgical technique itself.
