title: Biomechanical analysis of asymmetric mesio-distal molar positions loaded by a symmetric cervical headgear.
abstract: OBJECTIVE
  The plane 2D model and 3d finite element model of the headgear attached to two molars with different mesio-distal location are studied to show the asymmetric mechanical effects produced by symmetrically loaded headgear. In daily dental practice the asymmetrical location of molars is usually ignored.
  
  
  METHODS
  Six 3D finite element models of a symmetric cervical headgear were designed in SolidWorks 2011. The models showed symmetric molar position (model 1), 0.5 to 2 mm of anterior-posterior molar difference (models 2-5) and a significant asymmetry with 10 mm of difference in the locations (model 6). The head gear was loaded with 3N of force applied at the cervical headgear. The forces and moments produced on terminal molars are assessed.
  
  
  RESULTS
  It is shown the difference between the forces acting at the longer and shorter outer arms of the headgear increases with increase in the distance. The significant numeric difference in the forces has been found: from 0.0082 N (model 1) to 0.0324 N (model 5) and 0.146 N (model 6). These small forces may produce unplanned distal tipping and rotation of the molars around their vertical axes. The most important funding was found as a clockwise yaw moment in the system when is viewed superio-inferiorly. The yaw moment has been computed between -0.646 Nmm (model 1) and -1.945 N mm (model 5).
  
  
  CONCLUSIONS
  Therefore even small asymmetry in location of molars loaded by a symmetric cervical headgear will produce undesirable movement and rotation of the teeth that must be taken into account before applying the treatment.
authors.affiliation: Warsaw University of Technology, Faculty of Power and Aeronautical Engineering, Warsaw, Poland.
authors.forename: Natalya
authors.initials: N
authors.lastname: Kizilova
authors.affiliation: Tehran University of Medical Sciences, Dentistry Research Institute, Department of Orthodontics, Tehran, Iran.
authors.forename: Allahyar
authors.initials: A
authors.lastname: Geramy
authors.affiliation: Kharkov National Polytechnical University, Faculty of Mechanical Engineering, Ukraine.
authors.forename: Yurij
authors.initials: Y
authors.lastname: Romashov
mesh_terms: D019245:Compressive Strength / Q000502:physiology; D003198:Computer Simulation; D017076:Computer-Aided Design; D003799:Dental Stress Analysis / Q000379:methods*; D005115:Extraoral Traction Appliances; D006801:Humans; D008954:Models, Biological; D008963:Molar / Q000033:anatomy & histology / Q000502:physiology*; D016382:Orthodontic Appliance Design; D013314:Stress, Mechanical; D013718:Tensile Strength / Q000502:physiology; D014087:Tooth Movement Techniques / Q000295:instrumentation* / Q000379:methods