title: Changes in the mechanical advantage of the masseter and temporal muscles following surgical correction of mandibular prognathism.
abstract: The purpose of this study was to determine if the mechanical advantage of the masseter and temporal muscles is altered and improved as expected in patients subjected to surgical correction of mandibular prognathism. It aimed also to detect any relationship between (1) the moment arms of the masseter and temporal muscles, the moment arm of the bite force, and any morphologic characteristics considered to be factors in determining the size of the moment arms; and (2) the changes in the moment arms and the changes that the combined orthodontic-surgical treatment could induce in the morphologic characteristics. Presurgical and postsurgical lateral cephalograms of 51 consecutive orthognathic surgery patients with severe mandibular prognathism were used. The radiographs were taken 1 week before surgery and approximately 1 year after surgery. The results indicated that the mechanical advantage of the masseter and temporal muscles had a tendency to increase following correction of the dysplasia. The changes in the moment arms of the masseter and the bite force seem to be dependent on the changes in some morphologic parameters such as the angle between the mandibular line and ramal line, the angle between the anterior cranial base and the mandibular line, and the angle between the anterior cranial base and the functional occlusal plane. The combination of changes in these angles together with the shortening of the mandibular length could also lead to a decrease of the advantage of both muscles.
authors.affiliation: Department of Orthodontics, Royal Dental College, Faculty of Health Sciences, Aarhus, Denmark. mavreas@matrix.kaputel.gr
authors.forename: D
authors.initials: D
authors.lastname: Mavreas
authors.forename: B
authors.initials: B
authors.lastname: Melsen
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D001732:Bite Force; D002508:Cephalometry / Q000379:methods / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D008297:Male; D008406:Masseter Muscle / Q000503:physiopathology*; D011184:Postoperative Period; D011378:Prognathism / Q000175:diagnosis / Q000503:physiopathology* / Q000601:surgery; D012044:Regression Analysis; D013703:Temporal Muscle / Q000503:physiopathology*