title: Articular disc displacement in mandibular asymmetry patients.
abstract: Mechanisms of disc displacement in temporomandibular joint (TMJ) internal derangement (ID) in mandibular asymmetry have not been clearly defined. This study examines the degree and direction of disc displacement and their relationship with vertical asymmetry in terms of both clinical and biomechanical aspects. A retrospective study of disc displacement was performed in 31 mandibular asymmetry patients using MR imaging. The degree and direction of disc displacements on the shifted side and contralateral side TMJ were investigated with the degree of vertical asymmetry. Furthermore, three-dimensional finite element models of entire mandible include TMJ and maxillary teeth in occlusion were created to simulate displacement of the articular disc during clenching condition. The direction of displacement on the shifted side and contralateral side were significantly different. Articular disc has tendencies to displace more on the shifted side even in mild degree of vertical asymmetry. The degree of displacement was correlated with the amount of asymmetry. The MR results were consistent with the tendencies of disc displacement predicted from the finite element models. We suggest that disturbance in the direction of stress distribution through asymmetry of the mandible is one of the mechanisms related to disc displacement.
authors.affiliation: Orthodontic Science, Department of Orofacial Development and Function, Division of Oral Health Science, Graduate School, Tokyo Medical and Dental University, Japan. boonsi.orts@tmd.ac.jp
authors.forename: Boonsiva
authors.initials: B
authors.lastname: Buranastidporn
authors.forename: Masataka
authors.initials: M
authors.lastname: Hisano
authors.forename: Kunimichi
authors.initials: K
authors.lastname: Soma
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D002508:Cephalometry; D003766:Dental Occlusion; D005146:Facial Asymmetry / Q000150:complications*; D005260:Female; D020342:Finite Element Analysis; D006801:Humans; D004204:Joint Dislocations / Q000209:etiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008336:Mandibular Diseases / Q000150:complications*; D008410:Masticatory Muscles / Q000502:physiology; D008875:Middle Aged; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology; D012189:Retrospective Studies; D019224:Temporomandibular Joint Disc / Q000473:pathology*; D013705:Temporomandibular Joint Disorders / Q000209:etiology*; D014716:Vertical Dimension