title: Magnetic displacement force and torque on dental keepers in the static magnetic field of an MR scanner.
abstract: OBJECTIVE
  To evaluate the effect of the static magnetic field of magnetic resonance (MR) scanners on keepers (ie, ferromagnetic stainless steel plate adhered to the abutment tooth of dental magnetic attachments).
  
  
  METHODS
  Magnetically induced displacement force and torque on keepers were measured using 1.5 Tesla (T) and 3.0 T MR scanners and a method outlined by American Society for Testing and Materials (ASTM). Changes in magnetic flux density before and after exposure to scanner static magnetic field were examined.
  
  
  RESULTS
  The maximum magnetically induced displacement forces were calculated to be 10.3 × 10(-2) N at 1.5 T and 13.9 × 10(-2) N at 3.0 T on the cover surface. The maximum torques exerted on the keeper (4 mm in diameter) were 0.83 N × 4 mm at 1.5 T and 0.85 N × 4 mm at 3.0 T. These forces were considerably higher than the gravitational force (7.7 × 10(-4) N) of the keeper but considerably lower than the keeper-root cap proper adhesive force. The keepers' magnetic flux density remained less than that of the Earth.
  
  
  CONCLUSIONS
  Magnetically induced displacement force and torque on the keeper in the MR scanner do not influence the keeper-root cap proper adhesive force.
authors.affiliation: Radiological Technology Section, Reseach Center Hospital for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Mika
authors.initials: M
authors.lastname: Omatsu
authors.forename: Takayuki
authors.initials: T
authors.lastname: Obata
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Minowa
authors.forename: Koichi
authors.initials: K
authors.lastname: Yokosawa
authors.forename: Eri
authors.initials: E
authors.lastname: Inagaki
authors.forename: Kinya
authors.initials: K
authors.lastname: Ishizaka
authors.forename: Koichi
authors.initials: K
authors.lastname: Shibayama
authors.forename: Toru
authors.initials: T
authors.lastname: Yamamoto
mesh_terms: D003722:Dental Alloys / Q000528:radiation effects*; D017268:Dental Prosthesis Retention / Q000295:instrumentation*; D003799:Dental Stress Analysis / Q000379:methods*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D059346:Magnets; D009038:Motion; D013314:Stress, Mechanical; D019415:Torque
chemical_list: D003722:Dental Alloys
keywords: displacement force; magnetic denture; magnetic resonance imaging; soft magnetic material; torque