RESUMEN
The orthognathic surgery not only can alter facial appearance and occlusion, but also can affect the morphology, physiology, and biomechanics of craniofacial skeleton and the muscles of mastication. The purpose of this study was to investigate the changes in maximum bite force and electromyographic activity of masticatory muscles after sagital split ramus Lefort I osteotomy in patients with mandibular prognathism. A clinical trial was conducted on 14 patients with mandibular prognathism. Maximum bite force in 7 predefined points of dentition as well as electromyographic activity of masseter and temporalis muscles preoperatively, and at 3- and 6-month follow ups were measured in the patients. The analysis of variance for repeated measures and paired T-test served for analysis of longitudinal changes in maximum bite force and electromyographic activity of muscles. Three months after surgery, both bite force and electrical activities of mandibular muscles of patients were significantly less than those of before surgery [P <0.05]. Although all parameters were improved 6 months after surgery, maximum bite force in molar region did not reach the preoperative value. All other parameters at 6-month follow up increased by 10 to 15 percent compared to preoperative measurements. The findings of this study suggest that the maximum bite force and electrical activity of masticatory muscles in patients with mandibular prognathism may adapt to the new situation resulted from orthognathic surgery in six months after surgery; yet their return to the preoperative measurements is possible