title: Torque differences according to tooth morphology and bracket placement: a finite element study.
abstract: BACKGROUND
  Torque of the maxillary incisors is essential in esthetics and proper occlusion, while torque expression is influenced by many factors. The aim of this finite element study was to assess the relative effect of tooth morphology, bracket prescription, and bracket positioning on tooth displacement and developed stresses/strains after torque application.
  
  
  METHODS
  A three-dimensional upper right central incisor with its periodontal ligament (PDL) and alveolus was modelled. The tooth varied in the crown-root angle (CRA) between 156°, 170°, and 184°. An 0.018-inch slot discovery® (Dentaurum, Ispringen, Germany) bracket with a rectangular 0.018 × 0.025-inch β-titanium wire was modelled. Bracket torque prescription varied between 0°, 12°, and 22°, with bracket placement at the centre of the middle, gingival or incisal third of the crown. A total of 27 models were generated and a buccal root torque of 30° was applied. Afterwards, crown and apex displacement, strains in the PDL, and stresses in the bracket were calculated and analysed statistically.
  
  
  RESULTS
  The palatal crown displacement was significantly affected by bracket positioning (up to 94 per cent), while the buccal apex displacement was significantly affected by bracket prescription (up to 42 per cent) and bracket positioning (up to 23 per cent). Strains in the PDL were affected mainly by CRA (up to 54 per cent), followed by bracket positioning (up to 45 per cent). Finally, bracket prescription considerably affected the stresses in the bracket (up to 144 per cent).
  
  
  CONCLUSIONS
  These in silico results need to be validated in vivo before they can be clinically extrapolated.
  
  
  CONCLUSIONS
  Tooth anatomy and the characteristics of the orthodontic appliance should be considered during torque application.
authors.affiliation: Clinic of Orthodontics and Pediatric Dentistry, Center of Dental Medicine, University of Zurich, Switzerland.|Department of Oral Technology, School of Dentistry, University of Bonn, Germany.
authors.forename: Spyridon N
authors.initials: SN
authors.lastname: Papageorgiou
authors.affiliation: Department of Orthodontics, School of Dentistry, National and Kapodistrian University of Athens,Greece.
authors.forename: Iosif
authors.initials: I
authors.lastname: Sifakakis
authors.affiliation: Department of Oral Technology, School of Dentistry, University of Bonn, Germany.|Department of Prosthetic Dentistry, Preclinical Education and Materials Science, School of Dentistry, University of Bonn, Germany.
authors.forename: Ludger
authors.initials: L
authors.lastname: Keilig
authors.affiliation: Clinic of Orthodontics and Pediatric Dentistry, Center of Dental Medicine, University of Zurich, Switzerland.
authors.forename: Raphael
authors.initials: R
authors.lastname: Patcas
authors.affiliation: Clinic of Orthodontics and Pediatric Dentistry, Center of Dental Medicine, University of Zurich, Switzerland.
authors.forename: Stefan
authors.initials: S
authors.lastname: Affolter
authors.affiliation: Clinic of Orthodontics and Pediatric Dentistry, Center of Dental Medicine, University of Zurich, Switzerland.
authors.forename: Theodore
authors.initials: T
authors.lastname: Eliades
authors.affiliation: Department of Oral Technology, School of Dentistry, University of Bonn, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Bourauel
mesh_terms: D003198:Computer Simulation; D004955:Esthetics, Dental; D020342:Finite Element Analysis; D006801:Humans; D007180:Incisor / Q000473:pathology* / Q000503:physiopathology; D016382:Orthodontic Appliance Design; D009967:Orthodontic Appliances; D016910:Orthodontic Brackets; D009969:Orthodontic Wires; D010513:Periodontal Ligament / Q000503:physiopathology; D013314:Stress, Mechanical; D014025:Titanium; D019228:Tooth Crown / Q000503:physiopathology; D014087:Tooth Movement Techniques / Q000295:instrumentation / Q000379:methods*; D014092:Tooth Root / Q000503:physiopathology; D019415:Torque
chemical_list: C023988:beta titanium; D014025:Titanium