Magnetic Resonance Imaging (MRI) uses powerful magnetic fields and radio waves to create detailed images of organs and tissues. A permanent retainer (bonded or fixed retainer) is a thin metal wire bonded to the back of the teeth, usually the lower front teeth, to maintain alignment after orthodontic treatment. The presence of metal near the strong magnetic field of an MRI machine raises questions about safety and image quality. Understanding how the retainer’s metal interacts with MRI technology is necessary before undergoing a scan.
Is It Safe to Get an MRI With a Permanent Retainer?
It is generally safe to undergo an MRI scan with a permanent retainer, depending on the wire’s material and the scan’s location. Most modern retainers use non-ferromagnetic materials, such as stainless steel alloys or titanium, which do not strongly react to the magnetic field. These materials do not pose a risk of movement or injury within standard 1.5 Tesla (T) or 3T MRI machines.
The primary concern is not physical safety, but the potential for compromised image quality, especially when scanning the head, neck, or upper spine. For body parts below the neck, the retainer is typically far enough away to have minimal effect on diagnostic quality. If a retainer contains older, strongly magnetic materials, the technician may need to take precautions or advise against the scan if the head or neck area is the target.
How Metal Retainers Interact With MRI Technology
The interaction between the retainer’s metal and the MRI machine results in two consequences: artifacts and the risk of heating. Image quality is primarily affected by magnetic susceptibility artifact, which occurs because the metal distorts the local magnetic field of the scanner.
This magnetic field distortion creates dark patches, bright spots, or a signal void on the image, obscuring surrounding anatomy in the mouth, jaw, or lower brain. The artifact’s severity relates directly to the retainer’s material. Strongly ferromagnetic metals cause severe distortion, while paramagnetic materials like titanium cause minimal artifacts. Common stainless steel retainers produce considerable artifacts, particularly in head or neck imaging.
The second concern is the risk of radiofrequency (RF)-induced heating. RF energy can induce electrical currents in conductive materials, potentially leading to localized heating of the wire and surrounding tissue. However, for the small, fixed, non-looped wire of a permanent retainer, this heating risk is considered very low or clinically insignificant at standard field strengths. Studies show that fixed retainers made of stainless steel do not cause clinically significant heating during 1.5 T and 3T body MRIs.
Patient Preparation and Communicating With the MRI Team
Patients must inform the referring physician and the MRI technologist about the permanent retainer before the scan is scheduled. This disclosure allows the imaging center to assess potential risks and plan for image optimization. The technologist will ask about the metal in the body during the mandatory safety screening process.
It is beneficial for patients to obtain documentation from their orthodontist detailing the exact material composition of the retainer. Knowing whether the wire is titanium, gold, or a specific stainless-steel alloy helps the MRI team determine the degree of risk and anticipated artifact. This information is important for high-field MRIs, such as 3T scanners, or when the scan targets the head or neck region.
To mitigate the image artifacts caused by the retainer, the MRI center may employ specialized techniques. These include adjusting the scanning sequence parameters, changing the imaging angle, or utilizing artifact-reduction sequences designed to minimize the metal’s impact on the images. While image distortion cannot always be eliminated, these adjustments often ensure the final images are diagnostically useful.