Effect of mandibular setback surgery on occlusal force

Purpose: This study investigated the effect of mandibular setback surgery on occlusal force and evaluated the extent to which postsurgical changes in such force can be explained by the type of operation, the duration of maxillomandibular fixation (MMF), and the changes in the mechanical advantage of the jaw musculature. Materials and Methods: Maximal molar bite force was measured before surgery and at MMF removal, and 3, 6, and 12 months thereafter in 26 patients with mandibular prognothism. To correlate bite force and skeletal change, the cephalometric tracings were measured, tabulated, and statistically analyzed. Results: Mean bite force was 13.7 kg before surgery, 7.6 kg at MMF removal, 14.2 kg at 3 months, 19.7 kg at 6 months, and 26.1 kg at 12 months postsurgery. The bite force was positively correlated with the surgical change in mandibular plane angle and mandibular body length. The recovery of bite force was significantly affected by the type of operation and duration of MMF. Conclusions: To hasten recovery and increase bite force after orthognathic surgery, long periods of MMF and injury to the masticatory muscles should be avoided.