title: Radiofrequency heating and magnetically induced displacement of dental magnetic attachments during 3.0 T MRI.
abstract: OBJECTIVE
  The aim of this study was to estimate the risk of injury from dental magnetic attachments due to their radiofrequency (RF) heating and magnetically induced displacement during 3.0 T MRI.
  
  
  METHODS
  To examine the magnetic attachments, we adopted the American Society for Testing and Materials F2182-02a and F2052-06 standards in two MRI systems (Achieva 3.0 T Nova Dual; Philips, Tokyo, Japan, and Signa HDxt 3.0 T; GE Healthcare, Milwaukee, WI). The temperature change was measured in a cylindrical keeper (GIGAUSS D600; GC, Tokyo, Japan) with coping of the casting alloy and a keeper with a dental implant at the maximum specific absorption rate (SAR) for 20 min. To measure the magnetically induced displacement force, three sizes of keepers (GIGAUSS D400, D600 and D1000) were used in deflection angle tests conducted at the point of the maximum magnetic field strength.
  
  
  RESULTS
  Temperature elevations of both coping and implant were higher in the Signa system than in the Achieva system. The highest temperature changes in the keeper with implant and keeper with coping were 0.6 °C and 0.8 °C in the Signa system, respectively. The temperature increase did not exceed 1.0 °C at any location. The deflection angle (α) was not measurable because it exceeded 90°. GIGAUSS D400 required an extra 3.0 g load to constrain the deflection angle to less than 45°; GIGAUSS D600 and D1000 required 5.0 and 9.0 g loads, respectively.
  
  
  CONCLUSIONS
  Dental magnetic attachments pose no risk due to RF heating and magnetically induced displacement at 3.0 T MRI. However, it is necessary to confirm that these keepers are securely attached to the prosthesis before imaging.
authors.affiliation: Department of Partial Denture Prosthodontics, Nihon University School of Dentistry, 1-8-13 Kanda, Surugadai, Chiyoda-Ku, Tokyo 101-8310, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Miyata
authors.forename: M
authors.initials: M
authors.lastname: Hasegawa
authors.forename: Y
authors.initials: Y
authors.lastname: Abe
authors.forename: T
authors.initials: T
authors.lastname: Tabuchi
authors.forename: T
authors.initials: T
authors.lastname: Namiki
authors.forename: T
authors.initials: T
authors.lastname: Ishigami
mesh_terms: D003734:Dental Casting Investment / Q000528:radiation effects; D015921:Dental Implants; D003764:Dental Materials / Q000528:radiation effects*; D017268:Dental Prosthesis Retention / Q000295:instrumentation*; D004869:Equipment Safety; D006047:Gold Alloys / Q000528:radiation effects; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D059346:Magnets; D010165:Palladium / Q000528:radiation effects; D019047:Phantoms, Imaging; D011846:Radio Waves / Q000009:adverse effects*; D012307:Risk Factors; D012834:Silver / Q000528:radiation effects; D013314:Stress, Mechanical; D013821:Thermometers; D014025:Titanium / Q000528:radiation effects
chemical_list: D003734:Dental Casting Investment; D015921:Dental Implants; D003764:Dental Materials; D006047:Gold Alloys; D012834:Silver; D010165:Palladium; D014025:Titanium