title: Effect of different advancement positions on the maximum retrusive force of the mandible.
abstract: BACKGROUND
  Functional appliances lead, in different degrees, to loss of anchorage in the lower arch. By anchoring them to the mandibular bone, any dental side effects may be avoided and the skeletal effect enhanced. Stability of bone-borne fixation would be affected by forces created by the pull of the masticatory muscles. We aimed to identify mean maximum forces produced by mandibular retrusive muscles, at different degrees of advancement.
  
  
  METHODS
  Eighteen healthy adult volunteers participated in the study. Maximum retrusive force was measured using a splint/load cell system. Readings of the maximum forces of retrusion were taken from five mandibular positions: unstrained retruded position, and 4, 5, 6, and 7 mm anterior to the unstrained position. Data were presented as means ± SD and anova was performed to examine statistical significant differences between means of the maximum retrusion force.
  
  
  RESULTS
  Mean maximum retrusion force ranged between 63.3 and 198.2 newtons at the unstrained and 7 mm positions, respectively. It increased as the distance of advancement increased, being statistically significantly (p < 0.05) less at unstrained position compared with all advancement distances, 4 mm of advancement than 6 and 7 mm advancement, 5 mm of advancement than at 7 mm advancement.
  
  
  CONCLUSIONS
  Magnitude of the forces exerted by muscles during voluntary maximum retrusion movement from different advancement positions increased proportionately as the retrusion distance increased up to 7 mm. Such range of high forces might be important to consider when designing a bone-borne functional appliance.
authors: Orthodontics, Prince Philip Dental Hospital, University of Hong Kong, Sai Ying Pun, Hong Kong, SAR, China.
authors: A A
authors: AA
authors: Al-kalaly
authors: J E
authors: JE
authors: Dyson
authors: R W K
authors: RW
authors: Wong
authors: M
authors: M
authors: Schätzle
authors: L K
authors: LK
authors: Cheung
authors: A B M
authors: AB
authors: Rabie
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001732:Bite Force; D019245:Compressive Strength; D003768:Dental Occlusion, Centric; D003799:Dental Stress Analysis; D005260:Female; D006801:Humans; D007574:Jaw Relation Record; D008297:Male; D008334:Mandible / Q000502:physiology* / Q000601:surgery; D019186:Mandibular Advancement; D008410:Masticatory Muscles / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology*; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation*; D017289:Orthodontic Appliances, Functional; D018709:Statistics, Nonparametric; D013718:Tensile Strength