A permanent retainer is a thin wire custom-bonded to the back of the front teeth, typically on the lower arch, designed to maintain alignment after orthodontic treatment. These fixed appliances are made of metal alloys, leading patients to worry about safety and image quality during Magnetic Resonance Imaging (MRI). Undergoing an MRI with a permanent retainer is generally considered safe, but image complications may arise depending on the scan location. The specific materials used and the area being imaged determine if the procedure requires special consideration.
Safety of Permanent Retainers During an MRI
The primary safety concern during an MRI is whether a metallic object is ferromagnetic, which could cause movement or excessive heating. Most modern permanent retainers use non-ferromagnetic or weakly ferromagnetic materials, such as specific stainless steel alloys, titanium, or nickel-titanium (NiTi) alloys. Titanium is highly compatible with MRI technology and is a popular choice. Because these materials are not strongly magnetic, the risk of the retainer shifting or causing a dangerous reaction is negligible. The small size and fixed position of the wire further reduce the low risk of thermal injury or movement, meaning the retainer is not considered a contraindication for an MRI scan.
How Retainers Cause Image Distortion
The retainer can negatively affect the quality of the resulting images, a degradation technically known as a magnetic susceptibility artifact. These artifacts occur because the metal locally distorts the uniform magnetic field created by the MRI machine, even if the metal is non-ferromagnetic. The distortion appears on the scan as a signal void, or dark shadow, that obscures surrounding anatomical structures. The size of this artifact is directly related to the retainer’s material, with stainless steel alloys causing substantially larger artifacts than those made of titanium or nickel-titanium. This issue is most problematic when the scan targets the head, neck, jaw, or upper cervical spine, though distant scans, such as the knee or abdomen, are unaffected.
Essential Steps Before Your Scan
The most important step for any patient is full disclosure during the MRI pre-screening process. Inform the ordering physician and the MRI technologist about the fixed wire before the procedure begins. If possible, try to find out the specific material the retainer is made of, as this information is vital for the radiology team. Once informed, the technologist and radiologist can mitigate potential image artifacts by adjusting the scanning sequence, altering the slice angle, or utilizing specific artifact-reduction software techniques. Temporary removal might be recommended only in rare cases, such as when the retainer is made of an unknown or strongly ferromagnetic alloy, or if the diagnostic area is immediately next to the wire.