title: Magnetic field interactions of orthodontic wires during magnetic resonance imaging (MRI) at 1.5 Tesla.
abstract: BACKGROUND
  Orthodontic appliances pose a potential risk during magnetic resonance imaging (MRI) due to forces on metallic objects within the static magnetic field of MRI systems. The aim of the present investigation was to measure forces on orthodontic wires caused by the static magnetic field of a 1.5-Tesla MRI system, and to assess the safety hazards associated with these forces.
  
  
  METHODS
  Thirty-two different orthodontic wires (21 arch wires, eight ligature wires and three retainer wires) were investigated in a 1.5-Tesla MRI system (Magnetom Symphony, Siemens Medical Solutions, Erlangen, Germany). The translational forces were measured using the deflection angle test (ASTM F2052-02); rotational forces were assessed on a 5-point qualitative scale.
  
  
  CONCLUSIONS
  All retainer wires and the steel arch wires (the Noninium arch wire being the exception) were subjected to considerable rotational and translational forces within the MRI system's magnetic field. Translational forces were from 9.1- to 27.6-times as high as gravitational forces on these objects. Steel ligature wires and arch wires made of cobalt chromium, titanium molybdenum, nickel-titanium, and brass alloys showed no or negligible forces within the magnetic field. The translational and rotational forces within the MRI magnetic field should pose no risk to carefully-ligated arch wires. Steel retainer wire bonds should be checked to ensure secure attachment prior to an MRI investigation.
authors.affiliation: Department of Orthodontics, University Hospital Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany. klocke@uke.uni-hamburg.de
authors.forename: Arndt
authors.initials: A
authors.lastname: Klocke
authors.forename: Jörn
authors.initials: J
authors.lastname: Kemper
authors.forename: Dirk
authors.initials: D
authors.lastname: Schulze
authors.forename: Gerhard
authors.initials: G
authors.lastname: Adam
authors.forename: Bärbel
authors.initials: B
authors.lastname: Kahl-Nieke
mesh_terms: D001672:Biocompatible Materials / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D004574:Electromagnetic Fields; D019544:Equipment Failure Analysis; D004869:Equipment Safety; D008279:Magnetic Resonance Imaging; D009969:Orthodontic Wires; D011874:Radiometry; D013314:Stress, Mechanical
chemical_list: D001672:Biocompatible Materials