Three-Dimensional Evaluation of the Postsurgical Stability of Mandibular Setback With the Surgery-First Approach: Comparison Between Patients With Symmetry and Asymmetry.

PURPOSE: The purpose of the present study was to evaluate the 3-dimensional postsurgical stability of mandibular setback with a surgery-first (SF) orthodontic treatment approach in patients with skeletal Class III malocclusions and facial asymmetry using cone-beam computed tomographic (CBCT) images.

PATIENTS AND

METHODS

Thirty-six patients who underwent mandibular setback with an SF approach for the correction of mandibular prognathism were enrolled in the present study. Patients were divided into symmetrical (n = 18) and asymmetrical (n = 18) groups according to their degree of menton deviation. CBCT images were acquired before surgery, 1, 6, and 12 months after surgery, and at the end of treatment. After reorienting of CBCT images using automatic volume-based registration, the position of the mandible at each time point was evaluated relative to its post-treatment position. MATLAB (MathWorks, Natick, MA) was used to represent all sequential changes in postoperative mandibular position. The increase in posterior vertical dimension at surgery was measured and then correlated with postsurgical mandibular stability.

RESULTS

For up to 6 months after surgery, the position of the mandible differed considerably from its post-treatment position. At 12 months after surgery, the position of the mandible no longer differed substantially from its post-treatment position. The asymmetry group exhibited greater outward displacement of the proximal segment. The symmetrical and asymmetrical groups exhibited a positive correlation between postsurgical mandibular instability and the increase in posterior vertical dimension.

CONCLUSION

These results indicate that mandibular position stabilizes 12 months after surgery performed with an SF approach. It is necessary to consider mandibular forward movement from the increase in posterior vertical dimension in surgical occlusion during the treatment planning stage. Moreover, clinicians should maintain the surgical position of proximal segments during postsurgical orthodontic treatment at least until 12 months after surgery.