Orthodontic springs and auxiliary appliances: assessment of magnetic field interactions associated with 1.5 T and 3 T magnetic resonance systems

The objective of this paper is to evaluate magnetic field interactions at 1.5 and 3 T for 20 orthodontic devices used for fixed orthodontic therapy. Twenty springs and auxiliary parts made from varying ferromagnetic alloys were tested for magnetic field interactions in the static magnetic field at 1...

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Bibliographic Details
Published in:European radiology 2007-02, Vol.17 (2), p.533-540
Main Authors: Kemper, J, Priest, A N, Schulze, D, Kahl-Nieke, B, Adam, G, Klocke, A
Format: Article
Language:English
Subjects:
Deflection
Electromagnetic Fields
Equipment Design
Equipment Failure Analysis
Equipment Safety
Evaluation
Ferromagnetic materials
Ferromagnetic resonance
Gravity
Humans
Magnetic alloys
Magnetic fields
Magnetic Resonance Imaging
Materials Testing
Orthodontic Appliances
Orthodontic Wires
Orthodontics
Rotation
Stainless Steel
Torque
Translation
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Summary:The objective of this paper is to evaluate magnetic field interactions at 1.5 and 3 T for 20 orthodontic devices used for fixed orthodontic therapy. Twenty springs and auxiliary parts made from varying ferromagnetic alloys were tested for magnetic field interactions in the static magnetic field at 1.5 and 3 T. Magnetic translational force F(z) (in millinewtons) was evaluated by determining the deflection angle beta [American Society for Testing and Materials (ASTM standard test method)]. Magnetic-field-induced rotational force F(rot) was qualitatively determined using a five-point scale. beta was found to be >45 degrees in 13(15) devices at 1.5(3) T and translational force F(z) exceeded gravitational force F(g) on the particular object [F(z) 10.17-261.4 mN (10.72-566.4 mN) at 1.5(3) T]. F(z) was found to be up to 24.1(47.5)-fold higher than F(g) at 1.5(3) T. Corresponding to this, F(rot) on the objects was shown to be high at both field strengths (> or = +3). Three objects (at 1.5 T) and one object (at 3 T) showed deflection angles or = +3 at both field strengths. For the remaining objects, beta was below 45 degrees and torque measurements ranged from 0 to +2. Of 20 objects investigated for magnetic field interactions at 1.5(3) T, 13(15) were unsafe in magnetic resonance (MR), based on the ASTM criteria of F(z). The implications of these results for orthodontic patients undergoing MRI are discussed.
ISSN:0938-7994
1432-1084
DOI:10.1007/s00330-006-0335-x