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

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.

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.

Twistflex caused large artifact volumes (AV_mand: 13530 mm³; AV_max: 15642 mm³; 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 mm³; 394 mm³; 39; 31), grade-5 titanium (110 mm³; 126 mm³; 12; 12) and nickel-titanium (54 mm³; 78 mm³; 12; 14) both produced very small artifact volumes.

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.

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.