title: Positional changes of the masseter and medial pterygoid muscles after surgical mandibular advancement procedures: an MRI study.
abstract: This study evaluated whether surgical mandibular advancement procedures induced a change in the direction and the moment arms of the masseter (MAS) and medial pterygoid (MPM) muscles. Sixteen adults participated in this study. The sample was divided in two groups: Group I (n=8) with a mandibular plane angle (mpa) <39° and Group II (n=8) with an mpa >39°. Group I patients were treated with a bilateral sagittal split osteotomy (BSSO). Those in Group II were treated with a BSSO combined with a Le Fort I osteotomy. Pre- and postoperative direction and moment arms of MAS and MPM were compared in these groups. Postsurgically, MAS and MPM in Group II showed a significantly more vertical direction in the sagittal plane. Changes of direction in the frontal plane and changes of moment arms were insignificant in both groups. This study demonstrated that bimaxillary surgery in patients with an mpa >39° leads to a significant change of direction of MAS and MPM in the sagittal plane.
authors.affiliation: Department of Oral and Maxillofacial Surgery/Pathology, Academic Centre for Dentistry Amsterdam (ACTA) and VU University Medical Center, Amsterdam, The Netherlands. med.bib@elkerliek.nl
authors.forename: G J
authors.initials: GJ
authors.lastname: Dicker
authors.forename: J H
authors.initials: JH
authors.lastname: Koolstra
authors.forename: J A
authors.initials: JA
authors.lastname: Castelijns
authors.forename: R A
authors.initials: RA
authors.lastname: Van Schijndel
authors.forename: D B
authors.initials: DB
authors.lastname: Tuinzing
mesh_terms: D000293:Adolescent; D000328:Adult; D002508:Cephalometry / Q000379:methods; D002680:Chin / Q000601:surgery; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008334:Mandible / Q000473:pathology / Q000601:surgery; D019186:Mandibular Advancement / Q000379:methods*; D008335:Mandibular Condyle / Q000473:pathology; D008406:Masseter Muscle / Q000473:pathology*; D008875:Middle Aged; D056948:Orthognathic Surgical Procedures / Q000379:methods; D019340:Osteotomy, Le Fort / Q000379:methods; D059229:Osteotomy, Sagittal Split Ramus / Q000379:methods; D011626:Pterygoid Muscles / Q000473:pathology*; D012399:Rotation; D014716:Vertical Dimension; D055815:Young Adult