title: Static and dynamic loading of mandibular condyles and their positional changes after bilateral sagittal split advancement osteotomies.
abstract: This study analysed the effects of change of direction of masseter (MAS) and medial pterygoid muscles (MPM) and changes of moment arms of MAS, MPM and bite force on static and dynamic loading of the condyles after surgical mandibular advancement. Rotations of the condyles were assessed on axial MRIs. 16 adult patients with mandibular hypoplasia were studied. The mandibular plane angle (MPA) was <39° in Group I (n=8) and >39° in Group II (n=8). All mandibles were advanced with a bilateral sagittal split osteotomy (BSSO). In Group II, BSSO was combined with Le Fort I osteotomy. Pre and postoperative moment arms of MAS, MPM and bite force were used in a two-dimensional model to assess static loading of the condyles. Pre and postoperative data on muscle cross-sectional area, volume and direction were introduced in three-dimensional dynamic models of the masticatory system to assess the loading of the condyles during opening and closing. Postsurgically, small increases of static condylar loading were calculated. Dynamic loading decreased slightly. Minor rotations of the condyles were observed. The results do not support the idea that increased postoperative condylar loading is a serious cause for condylar resorption or relapse.
authors.affiliation: Department of Oral and Maxillofacial Surgery/Pathology, Academic Centre for Dentistry Amsterdam and VU University Medical Center, Amsterdam, The Netherlands. med.bib@elkerliek.nl
authors.forename: G J
authors.initials: GJ
authors.lastname: Dicker
authors.forename: M
authors.initials: M
authors.lastname: Tuijt
authors.forename: J H
authors.initials: JH
authors.lastname: Koolstra
authors.forename: R A
authors.initials: RA
authors.lastname: Van Schijndel
authors.forename: J A
authors.initials: JA
authors.lastname: Castelijns
authors.forename: D B
authors.initials: DB
authors.lastname: Tuinzing
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D001732:Bite Force; D003799:Dental Stress Analysis; D005260:Female; D006801:Humans; D008297:Male; D019186:Mandibular Advancement / Q000379:methods*; D008335:Mandibular Condyle / Q000502:physiology*; D008406:Masseter Muscle / Q000502:physiology; D008409:Mastication / Q000502:physiology; D008875:Middle Aged; D008953:Models, Anatomic; D019340:Osteotomy, Le Fort / Q000379:methods; D059229:Osteotomy, Sagittal Split Ramus / Q000379:methods*; D011626:Pterygoid Muscles / Q000502:physiology; D016059:Range of Motion, Articular; D013704:Temporomandibular Joint / Q000502:physiology*; D055815:Young Adult