title: Quantification of translational and gliding components in human temporomandibular joint during mouth opening.
abstract: OBJECTIVE
  In humans, the opening movement of the mouth requires a complex combination of rotation in the lower temporomandibular joint compartment and of translation in the upper compartment. The aim of the current study was to quantitatively assess the percentage contribution of rotation and translation movements of the mandible at maximum mouth opening in normal, healthy individuals.
  
  
  METHODS
  Free, habitual movements of mouth opening were recorded in 12 men and 15 women aged 19-30 years using an optoelectronic three-dimensional motion analyser. All subjects had a sound, complete, permanent dentitions with Angle Class I jaw relationships, without cast restorations or cuspal coverage, TMJ or craniocervical disorders. For each subject, the mandibular movements at the interincisor point (occlusal plane) were reconstructed, and, using suitable mathematical algorithms, divided into their rotation and gliding components. The relative contribution of the two components to the total movement was calculated for each frame of motion. In particular, the situation at maximum opening was assessed.
  
  
  RESULTS
  At maximum mouth opening, on average, men had significantly larger displacement of the mandibular interincisor point (56 mm versus 46 mm) and angle of rotation (34 degrees versus 32 degrees), than women. The percentage of mandibular movement explained by rotation at maximum mouth opening (77%) was not influenced by sex. The degree of rotation was significantly related to the displacement of the interincisor point: in women r2 = 87%, in men, r2 = 45%.
  
  
  CONCLUSIONS
  Overall, in normal subjects with a healthy stomatognathic apparatus, mouth opening was more determined by mandibular rotation than by translation.
authors.affiliation: Laboratorio di Anatomia Funzionale dell'Apparato Stomatognatico (LAFAS), Functional Anatomy Research Center (FARC), Dipartimento di Morfologia Umana, Facoltà di Medicina e Chirurgia, Università degli Studi di Milano, Milano, MI, Italy. farc@unimi.it
authors.forename: Virgilio F
authors.initials: VF
authors.lastname: Ferrario
authors.forename: Chiarella
authors.initials: C
authors.lastname: Sforza
authors.forename: Nicola
authors.initials: N
authors.lastname: Lovecchio
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Mian
mesh_terms: D000328:Adult; D000465:Algorithms; D000886:Anthropometry; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007259:Infrared Rays; D008297:Male; D008334:Mandible / Q000033:anatomy & histology / Q000502:physiology; D008335:Mandibular Condyle / Q000033:anatomy & histology; D008954:Models, Biological; D009068:Movement / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D012727:Sex Characteristics; D013704:Temporomandibular Joint / Q000502:physiology*