title: Unilateral Outer Bow Expanded Cervical Headgear Force System: 3D Analysis Using Finite Element Method.
abstract: OBJECTIVE
  Headgears are among the effective orthodontic appliances to achieve treatment goals. Unilateral molar distal movement is sometimes needed during an orthodontic treatment, which can be achieved by an asymmetric headgear. Different unilateral headgears have been introduced. The main goal of this study was to analyze the force system of unilateral expanded outer bow asymmetric headgears by the finite element method (FEM).
  
  
  METHODS
  Six 3D finite element models of a mesiodistal slice of the maxilla containing upper first molars, their periodontal ligaments (PDLs), cancellous bone, cortical bone, and a cervical headgear with expanded outer bow attached to maxillary first molars were designed in SolidWorks 2010 and meshed in ANSYS Workbench ver. 12.1. The models were the same except for the degree of outer bow expansion. The outer bow ends were loaded with 2 N force. The distal driving force and the net moment were evaluated.
  
  
  RESULTS
  A decrease in the distalizing force in the normal side molar from 1.69 N to 1.37 N was shown by increasing the degree of unilateral expansion. At the same time, the force increased from 2.19 N to 2.49 N in the expanded side molar. A net moment increasing from 2.26 N.mm to 4.64 N.mm was also shown.
  
  
  CONCLUSIONS
  Unilateral outer bow expansion can produce different distalizing forces in molars, which increase by increasing the expansion.
authors.affiliation: Professor, Dental Research Center, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran; Department of Orthodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Allahyar
authors.initials: A
authors.lastname: Geramy
authors.affiliation: Assistant Professor, Dental Caries Prevention Research Center, Qazvin University of Medical Sciences, Qazvin, Iran.
authors.forename: Omid
authors.initials: O
authors.lastname: Mortezai
authors.affiliation: Assistant Professor, Department of Orthodontics, Lorestan University of Medical Sciences, Khorramabad, Iran.
authors.forename: Masomeh
authors.initials: M
authors.lastname: Esmaily
authors.affiliation: Postgraduate Student, Orthodontics Department, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Hojat
authors.initials: H
authors.lastname: Darvishpour
keywords: Asymmetric; Extraoral Traction Appliances; Finite Element Analysis