A COMPARISON OF SKELETAL STABILITY AFTER MANDIBULAR ADVANCEMENT AND USE OF 2 RIGID INTERNAL-FIXATION TECHNIQUES

Purpose: Two different methods of rigid fixation were compared for pos toperative stability 6 months after mandibular advancement for treatme nt of Class II malocclusion. Material and Methods: Sixty (30 + 30) pat ients from two different oral and maxillofacial units treated for a Cl ass II malocclusion by bilateral saggital split osteotomy (BSSO), and two different methods of internal rigid fixation were prospectively in vestigated. Two groups (S1, n = 15; S2, n = 15) had bicortical noncomp ressive screws inserted in the genial area through a transcutaneous ap proach, 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 a nd vertically. Results: These were minor differences in the advancemen t and postoperative changes between the four groups, but statistically no significant difference was shown in either sagittal or vertical di rections, However, statistically verified differences proved that incr easing age was associated with a smaller amount of postsurgical relaps e, Low-angle cases (ML/NSL < 25 degrees) had a bigger amount of surgic al (P = .0008) and postsurgical (P = .0195) movement compared with the patients in the high-angle group (ML/NSL < 38 degrees). Using a multi ple regression test, a positive con-elation was also shown between the amount of surgical advancement and the amount of postsurgical instabi lity (P = .018). Conclusion: This prospective dual-center study indica tes that the two different methods of internal rigid fixation after su rgical advancement of the mandible by BSSO did not significantly diffe r from each other, and it is up to the individual operator to choose t he method for internal rigid fixation.