Objective. The objective of the present study was to evaluate the jaw function anatomical changes subsequent to orthodontic treatment combined with mandibular advancement or set-back surgery. Study design. The sample consisted of 67 combined skeletal and dental malocclusion patients, who had received orthodontic and surgical treatment previously. Three and 6 months following jaw surgery, the following jaw functions were evaluated: the level of occlusal force developed, the efficiency of masticatory function, the size in the temporomandibular joint (TMJ), the rdlationship between occlusal force and maxillo-mandibular skeletal change, and the range of mandibular movement. Results. The results revealed that after surgery the occlusal force, masticatory function, TMJ positioning, and mandibular movement distance were all different from presurgery values. The surgical set-back group jaw function recovery proved to be more rapid than that for the mandibular-advancement group. Conclusion. Surgical mandibular advancement and set-back by sagittal-split osteotomy influence subsequent mandibular function.