title: A comparison of simulated jaw dynamics in models of segmental mandibular resection versus resection with alloplastic reconstruction.
abstract: BACKGROUND
  Composite mandibular resection resulting in mandibular discontinuity can alter jaw motion, occlusal forces, and mastication, whether or not the jaw is reconstructed. The biomechanical events associated with these changes are difficult to assess clinically and, therefore, are not well documented or researched.
  
  
  OBJECTIVE
  The purpose of this study was to model movements of a mandible with a discontinuity defect, and to compare them to movements of a mandible with its continuity restored by alloplastic reconstruction.
  
  
  METHODS
  Computational models were created with a novel simulation platform. The variables designed into the models included gravity, external forces, and jaw muscle activity. Each jaw was observed at rest, when opened by external force or by muscle drive, and during the generation of unilateral occlusal force on the nonoperated side. Scarring was simulated with springlike forces. Outputs included individual muscle forces and torques, as well as mandibular incisor and condylar motions.
  
  
  RESULTS
  Both models displayed plausible resting postures, and jaw opening with deviation toward the defect side when scarring was simulated. Opening caused by downward force on the incisors differed from that due to muscle activation. Jaw rotations during unilateral molar contact on the unaffected side were muscle specific and influenced by mandibular discontinuity.
  
  
  CONCLUSIONS
  Plausible jaw movements after hemimandibulectomy and/or alloplastic reconstruction could be predicted by dynamic modeling. The effect of soft tissue forces on jaw posture and movements varied with the condylar support available. In both models, different opening trajectories were produced by external force on the jaw and by jaw muscle activation. Mandibular rotation during unilateral molar contact depended on which muscles were activated, and the availability of bilateral condylar support.
authors.affiliation: Department of Oral Health Sciences, University of British Columbia, Vancouver, British Columbia, Canada. ahannam@interchange.ubc.ca
authors.forename: Alan G
authors.initials: AG
authors.lastname: Hannam
authors.forename: Ian K
authors.initials: IK
authors.lastname: Stavness
authors.forename: John E
authors.initials: JE
authors.lastname: Lloyd
authors.forename: S Sidney
authors.initials: SS
authors.lastname: Fels
authors.forename: Arthur J
authors.initials: AJ
authors.lastname: Miller
authors.forename: Donald A
authors.initials: DA
authors.lastname: Curtis
mesh_terms: D001696:Biomechanical Phenomena; D001732:Bite Force; D001860:Bone Plates; D018786:Bone Substitutes; D003198:Computer Simulation; D006801:Humans; D008334:Mandible / Q000503:physiopathology* / Q000601:surgery*; D008335:Mandibular Condyle / Q000502:physiology; D008410:Masticatory Muscles / Q000502:physiology; D008954:Models, Biological; D009068:Movement / Q000502:physiology
chemical_list: D018786:Bone Substitutes