title: Impact of the Static and Radiofrequency Magnetic Fields Produced by a 7T MR Imager on Metallic Dental Materials.
abstract: OBJECTIVE
  We examined safety issues related to the presence of various metallic dental materials in magnetic resonance (MR) imaging at 7 tesla.
  
  
  METHODS
  A 7T MR imaging scanner was used to examine 18 kinds of materials, including 8 metals used in dental restorations, 6 osseointegrated dental implants, 2 abutments for dental implants, and 2 magnetic attachment keepers. We assessed translational attraction forces between the static magnetic field and materials via deflection angles read on a tailor-made instrument and compared with those at 3T. Heating effects from radiofrequency during image acquisitions using 6 different sequences were examined by measuring associated temperature changes in agarose-gel phantoms with a fiber-optic thermometer.
  
  
  RESULTS
  Deflection angles of the metallic dental materials were significantly larger at 7T than 3T. Among full metal crowns (FMCs), deflection angles were 18.0° for cobalt-chromium (Co-Cr) alloys, 13.5° for nickel-chromium (Ni-Cr) alloys, and 0° for other materials. Deflection angles of the dental implants and abutments were minimal, ranging from 5.0 to 6.5°, whereas the magnetic attachment keepers were strongly attracted to the field, having deflection angles of 90° or more. Increases in temperature of the FMCs were significant but less than 1°C in every sequence. The dental implant of 50-mm length showed significant but mild temperature increases (up to 1.5°C) when compared with other dental implants and abutments, particularly on sequences with high specific absorption rate values.
  
  
  CONCLUSIONS
  Although most metallic dental materials showed no apparent translational attraction or heating at 7T, substantial attraction forces on the magnetic attachment keepers suggested potential risks to patients and research participants undergoing MR imaging examinations.
authors.affiliation: Department of Prosthodontics and Oral Implantology, Iwate Medical University.
authors.forename: Kenta
authors.initials: K
authors.lastname: Oriso
authors.forename: Takuya
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Makoto
authors.initials: M
authors.lastname: Sasaki
authors.forename: Ikuko
authors.initials: I
authors.lastname: Uwano
authors.forename: Hidemichi
authors.initials: H
authors.lastname: Kihara
authors.forename: Hisatomo
authors.initials: H
authors.lastname: Kondo
mesh_terms: D002858:Chromium Alloys / Q000737:chemistry; D003442:Crowns; D000044:Dental Abutments; D003722:Dental Alloys / Q000737:chemistry; D015921:Dental Implants; D003764:Dental Materials / Q000737:chemistry*; D017267:Dental Prosthesis Design; D006047:Gold Alloys / Q000737:chemistry; D006358:Hot Temperature; D006801:Humans; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D059346:Magnets; D008670:Metals / Q000737:chemistry*; D055100:Optical Fibers; D010165:Palladium / Q000737:chemistry; D019047:Phantoms, Imaging; D011846:Radio Waves; D012449:Safety; D012834:Silver / Q000737:chemistry; D013821:Thermometers
chemical_list: D002858:Chromium Alloys; D003722:Dental Alloys; D015921:Dental Implants; D003764:Dental Materials; D006047:Gold Alloys; D008670:Metals; D012834:Silver; D010165:Palladium