title: Influence of changing the chewing region on mandibular movement.
abstract: BACKGROUND
  In the shortened dental arch condition, little is known of how patients adapt their jaw function during mastication to the new oral environment. This study aimed to investigate the changes in mandibular movements when the chewing region was changed from the first molar to the first premolar.
  
  
  METHODS
  Thirty clinical residents with natural dentitions were recruited. The subjects were asked to chew a piece of beef jerky using either the first molar or the first premolar on the preferred chewing side. Three-dimensional trajectories of lower incisors and both condyles were analysed using a jaw movement tracking device with six degrees of freedom during the period between the onset and offset of electromyographic bursts from the masseter and anterior temporal muscles.
  
  
  RESULTS
  The closing angle of the lower incisors for first premolar chewing was narrower in comparison with that for first molar chewing (p < 0.05). The lengths of the condylar trajectories and the maximum velocities of the condylar movement for first premolar chewing were smaller and slower, respectively, in comparison with those for first molar chewing (both sides; p < 0.01).
  
  
  CONCLUSIONS
  The mandibular movement during mastication might be changed to adapt the premolar chewing because of a loss of posterior occlusal supports.
authors.affiliation: Department of Oral and Maxillofacial Biology, Matsumoto Dental University, Nagano, Japan. hashii8020@po.mdu.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Hashii
authors.forename: M
authors.initials: M
authors.lastname: Tomida
authors.forename: S
authors.initials: S
authors.lastname: Yamashita
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D001641:Bicuspid / Q000502:physiology; D003799:Dental Stress Analysis; D004576:Electromyography; D005260:Female; D006801:Humans; D007576:Jaw, Edentulous, Partially / Q000503:physiopathology*; D008297:Male; D008334:Mandible / Q000503:physiopathology*; D008406:Masseter Muscle / Q000503:physiopathology; D008409:Mastication / Q000502:physiology*; D008963:Molar / Q000502:physiology; D009068:Movement; D013703:Temporal Muscle / Q000503:physiopathology; D055815:Young Adult