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.