title: Optimization of unilateral molar rotation correction by a trans-palatal bar: a three-dimensional analysis using the finite element method.
abstract: OBJECTIVE
  The main goal of this study was to optimize unilateral molar rotation correction by modifying a trans-palatal arch (TPA) design using the finite element method.
  
  
  METHODS
  Three-dimensional analysis of different TPA designs was carried out using the finite element method.
  
  
  METHODS
  Department of Orthodontics, Tehran University of Medical Sciences, Iran.
  
  
  METHODS
  For this investigation, 13 three-dimensional finite element models were produced for different TPA designs without pre-activation bends. Each model contained a palatal bar and two tubes. Optimizing unilateral molar rotations was achieved by five separate different paths: incorporating U-loop(s), 'R' loop(s) or helix/helices, a reverse action of the helix/helices and adding a straight wire to the design. The mesial part of the left side tube was displaced 0·1, 0·25, 0·5 and 1 mm, successively towards the midline, simulating palatal bar tab engagement in a mesio-palatal rotated maxillary left molar. The mesio-distal force, moment and energy produced in the normal side (right) molar were recorded for each of the models.
  
  
  RESULTS
  Findings showed that in all designs, the associated mesializing force was lower than that seen in the traditional design and the moment showed an increasing pattern when compared with a simple palatal bar. Regarding energy levels, the same increasing pattern was observed in the designs between activations of 0·1 and 1·0 mm.
  
  
  CONCLUSIONS
  According to our optimized system, the TPA design with the highest energy and moment, but the lowest mesializing force associated with derotating a maxillary molar tooth was a parallel wire II design (i.e. adding a straight wire).
authors.affiliation: Orthodontics Department, Tehran University of Medical Sciences, Tehran, Iran. gueramya@yahoo.com
authors.forename: Allahyar
authors.initials: A
authors.lastname: Geramy
authors.forename: Tahura
authors.initials: T
authors.lastname: Etezadi
mesh_terms: D001696:Biomechanical Phenomena; D003722:Dental Alloys / Q000737:chemistry; D020342:Finite Element Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008310:Malocclusion / Q000628:therapy*; D008963:Molar / Q000473:pathology*; D016382:Orthodontic Appliance Design; D009969:Orthodontic Wires; D012399:Rotation; D013193:Stainless Steel / Q000737:chemistry; D013314:Stress, Mechanical; D014087:Tooth Movement Techniques / Q000295:instrumentation*
chemical_list: D003722:Dental Alloys; D013193:Stainless Steel
keywords: Asymmetric activation; finite element method; rotation; transpalatal bar; unilateral