A comparison of skeletal stability after mandibular advancement and use of two rigid internal fixation techniques

Purpose: Two different methods of rigid fixation were compared for postoperative stability 6 months after mandibular advancement for treatment of Class II malocclusion. Material and Methods: Sixty (30 + 30) patients from two different oral and maxillofacial units treated for a Class II malocclusion by bilateral saggital split osteotomy (BSSO), and two different methods of internal rigid fixation were prospectively investigated. Two groups (S1, n = 15; S2, n = 15) had bicortical noncompressive screws inserted in the genial area through a transcutaneous approach, and the other two groups (P1, n = 15; P2, n = 15) had the bone segments fixed with unicortical screws and miniplates on the lateral surface of the mandibular body. Cephalograms were taken preoperatively, 2 days postoperatively and 6 months after the operation. A computer program was used to superimpose the three cephalograms and to register the mandibular advancement and postoperative change both sagittally and vertically. Results: These were minor differences in the advancement and postoperative changes between the four groups, but statistically no significant difference was shown in either sagittal or vertical directions, However, statistically verified differences proved that increasing age was associated with a smaller amount of postsurgical relapse, Low-angle cases (ML/NSL < 25 degrees) had a bigger amount of surgical (P = .0008) and postsurgical (P = .0195) movement compared with the patients in the high-angle group (ML/NSL < 38 degrees). Using a multiple regression test, a positive con-elation was also shown between the amount of surgical advancement and the amount of postsurgical instability (P = .018). Conclusion: This prospective dual-center study indicates that the two different methods of internal rigid fixation after surgical advancement of the mandible by BSSO did not significantly differ from each other, and it is up to the individual operator to choose the method for internal rigid fixation.