MRI Metallic Artifacts of Crown Shaped Alloys and Magnetic Keepers

Objectives: The objective of this study was to evaluate the artifacts generated by crown-shaped dental alloys and a magnetic keeper quantitatively by analyzing digital MRI data around samples.

Methods: Four clinical dental alloys (gold-silver-palladium: GC, Japan, casting gold alloy Type3: Sankin Industry, Japan, cobalt-chromium: GC, Japan, gold porcelain alloy: Pentron, USA) and one pre-fabricated magnetic keeper (Hitachi, Japan) were selected. The alloys of the former were cast into a similar lower first molar using a same shell crown (Crown-S #5 GC, Japan). Identically shaped resin crowns were used as a control. Twenty metal crowns and 5 magnetic keepers were analyzed. The samples were set in an acrylic phantom (150mm x 150mm x 150mm) filled with agar, and then placed in a 1.5T MRI apparatus. Various image slices were selected from the center (0mm) to 70mm at steps of 5mm. The phantoms with samples were imaged in T1 and T2 weighted methods. The distribution of signal intensity in the region of interest (ROI approximately 2780pixels) was calculated with ImageJ software and the mean coefficient of variation of each sample was obtained.

Results: Repeated measures one-way ANOVA found significant effect of artifacts in MRI (p<0.05). Dunnett's test found significant difference between control and cobalt-chromium up to 40mm in coronal T1-WI images (p<0.05) and up to 70mm in axial T1-WI images for the magnetic keeper (p<0.05). The signal intensities of gold-silver-palladium and casting gold alloy Type3 were not significantly different from the control. The signal intensity of gold porcelain alloy was significantly different from the control at 0mm and 5mm in coronal T1,T2-WI, and in sagittal T1-WI at 0mm (p<0.05).

Conclusion: The artifact generated by magnetic keeper and cobalt-chromium crown might disturb the MR images of TMJ when they are used in the upper second molars.