Evaluation of magnetic resonance imaging artifacts caused by fixed orthodontic CAD/CAM retainers—an in vitro study

OBJECTIVES: Magnetic resonance imaging (MRI) image quality can be severely impaired by artifacts caused by fixed orthodontic retainers. In clinical practice, there is a trend towards using computer-aided design/computer-aided manufacturing (CAD/CAM) retainers. This study aimed to quantify MRI artifacts produced by these novel CAD/CAM retainers. MATERIAL AND METHODS: Three CAD/CAM retainers and a stainless-steel retainer (“Twistflex”; clinical reference standard) were scanned in vitro at 3-T MRI using a high-resolution 3D sequence. The artifact diameters and three-dimensional artifact volumes (AV) were determined for all mandibular (AV(mand)) and maxillary (AV(max)) retainers. Moreover, the corresponding ratio of artifact volume to retainer volume (AV/RV(mand), AV/RV(max)) was calculated. RESULTS: Twistflex caused large artifact volumes (AV(mand): 13530 mm(3); AV(max): 15642 mm(3); AV/RV(mand): 2602; AV/RV(max): 2235). By contrast, artifact volumes for CAD/CAM retainers were substantially smaller: whereas artifact volumes for cobalt–chromium retainers were moderate (381 mm(3); 394 mm(3); 39; 31), grade-5 titanium (110 mm(3); 126 mm(3); 12; 12) and nickel–titanium (54 mm(3); 78 mm(3); 12; 14) both produced very small artifact volumes. CONCLUSION: All CAD/CAM retainers caused substantially smaller volumes of MRI artifacts compared to Twistflex. Grade-5 titanium and nickel–titanium CAD/CAM retainers showed the smallest artifact volumes. CLINICAL RELEVANCE: CAD/CAM retainers made from titanium or nickel–titanium may not relevantly impair image quality in head/neck and dental MRI. Artifacts caused by cobalt–chromium CAD/CAM retainers may mask nearby dental/periodontal structures. In contrast, the large artifacts caused by Twistflex are likely to severely impair diagnosis of oral and adjacent pathologies.