3D Simulation, Postoperative Stability and Bone Healing after the Maxillary Setback Movement

Abstract

Purpose: Maxillary setback surgery is necessary for patients with maxillary protrusion to improve the aesthetical facial harmony. However, it is technically difficult surgery with intra- and post-operative complications because of complicated anatomical structures. Adequate amounts of bone around the pterygomaxillary junction should be removed to avoid bony interferences, and descending palatine artery also should be identified and isolated carefully under narrow surgical field. Moreover, bone reduction of pterygoid plate can lead to moderate but continuous bleeding which control is frequently difficult. Even though maxillary setback movement is frequently conducted in the orthognathic surgery, the amount of bone interference using simulation surgery and postoperative stability have not been reported The purpose of this study was to evaluate the amount of bone interference by simulation surgery, postoperative stability including bone healing at pterygomaxillary suture after maxillary setback surgery.

Patients and Methods: 41 patients who underwent maxillary setback surgery combined with BSSRO for orthognathic surgery were included in this study. For the evaluation of postoperative stability, patients were divided into two groups with maxillary setback less than 3 mm (Group I) and greater than 3 mm (Group II), and we lateral cephalograms taken before surgery, immediately, 6 weeks and more than 6 months after surgery were analysed. After simulation surgery in 15 patients using pre- and postoperative CT, the amount of bony interference between maxillary tuberosity and pterygoid plate was calculated after maxillary setback movement with and without consideration of autoroation of maxillomandibular complex. For the evaluation of bone healing at the pterygomaxillary junction, CT images taken immediately postoperatively and at 3 months after surgery were evaluated in 15 patients using image analyzing program.

Results: The mean surgical movements of the maxilla were 2.80 mm, 1.25 mm, 0.54 mm and 2.35 mm posteriorly at upper central incisor edge, point A, PNS and upper first molar. At 6 months after surgery, there are no significant horizontal relapse at point A and PNS. And there was no significant difference of the relapse between Group Ⅰ and Group Ⅱ. In 3D simulation surgery, the bony interferences were more in maxillary setback with consideration of autoroation of maxillomandibular complex than in simple maxillary setback, and it was increased when the distance between condylar rotation center and pterygomaxillary suture. And there was statistically significant bone healing at the pterygomaxillary junction three months after surgery (p<0.001).

Conclusions: Although maxillary setback surgery has technical difficulty with postoperative complications, it could be a selective treatment option for the balanced facial aesthetics in the patients with maxillary protrusion.