title: Magnetic forces on orthodontic wires in high field magnetic resonance imaging (MRI) at 3 tesla.
abstract: BACKGROUND
  In a previous investigation we reported on magnetic forces in the static magnetic field of a 1.5 Tesla MRI system. The aim of the present investigation was to assess forces on orthodontic wires in a high field strength MRI system at 3 Tesla.
  
  
  METHODS
  Thirty-two different orthodontic wires (21 archwires, eight ligature wires and three retainer wires) were investigated in a 3 Tesla high field strength MRI system (Intera, Philips Medical Systems, Best, The Netherlands). Translational forces were measured by the deflection angle test (ASTM F2052-02), and rotational forces assessed on a 5-point qualitative scale.
  
  
  CONCLUSIONS
  Translational forces ranged between 43.5 mN and 136.1 mN for retainer wires and between 0.6 mN (Noninium) and 208.4 mN (Orthos Stainless Steel) for steel archwires. Translational forces were up to 53.8 times as high as gravitational forces for retainer wires and up to 54.5 times as high for steel archwires, associated with marked rotational forces for the most part. Archwires manufactured from nickel-titanium, titanium-molybdenum and cobalt-chromium and different ligature wires showed no or negligible forces in the magnetic field. Carefully ligated wires should not present a risk due to translational and rotational forces in the high field MRI system at 3 Tesla.
authors.affiliation: Department of Orthodontics, Center of Dentistry, University Hospital Hamburg-Eppendorf, Pavillon 0 53, Martinistrasse 52, 20246 Hamburg, Germany. klocke@uke.uni-hamburg.de
authors.forename: Arndt
authors.initials: A
authors.lastname: Klocke
authors.forename: Bärbel
authors.initials: B
authors.lastname: Kahl-Nieke
authors.forename: Gerhard
authors.initials: G
authors.lastname: Adam
authors.forename: Jörn
authors.initials: J
authors.lastname: Kemper
mesh_terms: D000497:Alloys; D002858:Chromium Alloys; D003300:Copper; D006801:Humans; D008279:Magnetic Resonance Imaging; D008280:Magnetics; D008982:Molybdenum; D016382:Orthodontic Appliance Design; D018704:Orthodontic Retainers; D009969:Orthodontic Wires; D013193:Stainless Steel; D014025:Titanium; D019415:Torque; D015032:Zinc
chemical_list: D000497:Alloys; D002858:Chromium Alloys; D013193:Stainless Steel; C048399:brass; C013616:nitinol; D003300:Copper; D008982:Molybdenum; D014025:Titanium; D015032:Zinc