Shika Hoshasen

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Objective: Dental materials produce metal artifacts which are serious problems in diagnostic of head and neck region using magnetic resonance imaging (MRI). However, there are few reports about the effect of metal artifacts caused by self-ligation brackets. The purpose of this study was to assess the influence of metal artifacts on MRI caused by orthodontic appliance's using phantom.
Methods: Subjects consisted of 9 types of orthodontic appliance. Six MRI sequences, which are commonly employed in the head and neck MR examinations, were used for this study on 1.5 Tesla MRI. The range dimension of metal artifacts on each image was measured on CRT.
Results: Most orthodontic appliances such as a bracket, a tube and a wire, produced severe metal artifacts on phantom study except for brackets of ceramic and titanium, wire of nickel-titanium and cobalt-chromium. These appliances mainly consist of iron. In scanning sequence, the largest dimensions of metal artifacts were diffusion weighted imaging (DWI) sequences.
Conclusions: Band with welded single tube, direct-bonding single tube, metal bracket, resin bracket and stainless steel wire which have ferromagnetism, caused the significant metal artifacts. Brackets of ceramic, titanium, wire of nickel-titanium and cobalt-chromium produced slight metal artifacts. These results suggest that orthodontic appliances including self-ligation brackets impair evaluation in the DWI techniques.

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