Influence of Orthodontic Appliance-derived Artifacts on 3-T MRI Movies
Objectives: MRI movies enable evaluation of temporal/spatial movement of multiple articulating organs. This study aimed to assess the influence of artifacts caused by orthodontic appliances on 3-T MRI movies.
Methods: Nine healthy adults with normal occlusion were recruited. Four types of customized maxillary (Mx) and mandibular (Md) plates made of Biostar® (DURASOFT PD®, ©Rocky Mountain Morita) were prepared. The plates incorporated (a) nothing, (b) a fixed canine-to-canine retainer (HI-TTM II TWIST-WIRE®, 0.015" in diameter, ©3M), (c) 0.018"-slot metal brackets (CLEAR BRACKET SL+®, ©Dentsply) for anterior teeth and metal brackets for molars (OPA-K®, ©Tomy), or (d) 0.018”-slot clear brackets (CrystaBrace3, ©Dentsply) for anterior teeth and the same metal brackets for molars as (c). No archwire was applied. Subjects were scanned using a 3-T MRI scanner during production of a vowel-consonant-vowel syllable (/asa/) under 6 conditions with the plate in (1) neither Mx or Md, (2) a in both Mx and Md, (3) a in Mx and b in Md, (4) b in both Mx and Md, (5) c in both Mx and Md, and (6) d in both Mx and Md. A gradient echo sequence with a segmented cine and a parallel imaging technique was used. The subjects performed the tasks without knowing the plate type.
Results: A large artifact was observed in MRI movie images over the entire oral region around the metal orthodontic appliances. The artifact size was in the order 6>5>4>3>2 and 1, and there was no significant difference between 1 and 2. Velar heights in both 5 and 6 were significantly longer than that in 1.
Conclusions: Orthodontic appliances including metallic materials may produce a significant error on measurement of articulatory organs using MRI movie images. The degree of artifact depends on the type of orthodontic appliances, the distance between the organs, and appliance and scanning parameters.