title: Metallic artifacts in MRI caused by dental alloys and magnetic keeper.
abstract: OBJECTIVE
  To evaluate the artifacts generated by crownshaped dental alloys and a magnetic keeper quantitatively by analyzing digital MRI data.
  
  
  METHODS
  One pre-fabricated magnetic keeper and four clinical dental alloys (gold-silver-palladium, casting gold alloy Type 3, cobalt-chromium, gold porcelain alloy) were selected. Twenty metal crowns and 5 magnetic keepers were analyzed. The samples were placed in an acrylic phantom (150 mmx150 mmx150 mm) filled with agar, and then placed in the MRI apparatus. Various image slices were selected from the center (0 mm) to 70 mm at steps of 5 mm. The distribution of the signal intensity in the region of interest was calculated using ImageJ software and the mean coefficient of variation of each specimen was obtained. Statistical analysis was performed by Dunnett's test (p<0.05).
  
  
  RESULTS
  Compared to the resin control, cobalt-chromium showed significantly greater signal intensity up to 40 mm in coronal T2-WI images and up to 70 mm in axial T1-WI images for the magnetic keeper. The signal intensities of gold-silver-palladium and casting gold alloy Type 3 were not significantly different from that of the control. The signal intensity of gold porcelain alloy was significantly different from that of the control at 0 mm and 5 mm in coronal T1,T2-WI and in sagittal T1-WI at 0 mm.
  
  
  CONCLUSIONS
  The artifacts generated by the magnetic keeper and the cobalt-chromium crown when they are used in a second molar can disturb the MR images of the temporomandibular joint.
authors.affiliation: Department of Removable Prosthodontics, Masticatory Function Rehabilitation, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan. mztn.rpro@tmd.ac.jp
authors.forename: Darline
authors.initials: D
authors.lastname: Destine
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Mizutani
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Igarashi
mesh_terms: D016477:Artifacts; D003722:Dental Alloys; D008279:Magnetic Resonance Imaging; D008280:Magnetics; D008670:Metals; D019047:Phantoms, Imaging; D011476:Prosthodontics
chemical_list: D003722:Dental Alloys; D008670:Metals