Patients with dental crowns often worry if their restorations will interfere with a magnetic resonance imaging (MRI) procedure. A dental crown is a cap placed over a damaged tooth to restore its shape, size, strength, and appearance. Since MRI machines use powerful magnetic fields, the presence of metal-containing crowns raises valid questions about patient safety and image quality. The good news is that having dental crowns does not prevent a patient from safely undergoing an MRI scan in most cases. Modern dentistry uses materials largely compatible with the imaging process, though the specific composition of the crown dictates the potential for interference.
Material Composition and MRI Safety
The primary concern regarding patient safety during an MRI relates to the material used in the dental crown. Metals are categorized by their magnetic properties, and only certain types pose a potential risk in the strong magnetic field of an MRI machine. Ferromagnetic metals, such as iron, cobalt, and nickel, are highly magnetic and interact strongly with the scanner’s field.
Crowns containing these ferromagnetic metals, often found in older restorations, theoretically carry a small risk of movement, heating, or vibration during the scan. Heating occurs if the metal absorbs the radiofrequency energy, potentially causing thermal burns to the surrounding gum tissue. However, the likelihood of a crown dislodging or causing significant heating is extremely rare, especially with modern crowns.
In contrast, non-ferromagnetic materials are considered safe for MRI procedures. Modern crowns are often made from non-metallic substances like porcelain, ceramic, zirconia, or composite resin, all of which are entirely non-magnetic. Even metal alloys used today, such as gold and titanium, are non-ferromagnetic or only weakly magnetic. The use of these materials in contemporary dentistry has made the issue of patient harm during an MRI largely obsolete.
How Crowns Affect Diagnostic Image Quality
While modern crowns are safe for the patient, their presence can still affect the diagnostic quality of the scan, particularly if the MRI focuses on the head, neck, or brain. Any metallic material, even non-magnetic ones like titanium, can disrupt the uniformity of the magnetic field. This disruption leads to the creation of “artifacts” on the resulting image.
Artifacts appear as distortions, signal voids, or dark areas, essentially creating a shadow around the crown’s location. These signal voids obscure anatomical details in the immediate vicinity, making it difficult for a radiologist to interpret the image in that specific region. The severity of the image distortion depends on the crown’s material, the size and number of restorations, and the strength of the MRI scanner.
Metal-based crowns, including porcelain-fused-to-metal restorations, are the most common cause of significant artifacts. For example, a scan targeting the jaw, brainstem, or inner ear could be compromised by a nearby crown, though a scan of the knee would not be affected. Artifacts are not harmful to the patient, but they limit the diagnostic utility of the MRI, which is a significant factor in medical decision-making.
Essential Patient Preparation and Communication
The most proactive step a patient can take before an MRI is to communicate thoroughly with their healthcare providers. Patients must inform the MRI technologist and the referring physician about all existing dental work, including crowns, bridges, and implants. This disclosure allows the facility to assess the potential for interference before the scan begins.
Patients should attempt to determine the specific material used in their crowns by contacting their dentist. Dental offices typically keep records detailing the composition of the restorations, which is the most useful piece of information for the MRI team. Knowing the material allows the radiologist to potentially adjust the scanning parameters or sequences to minimize artifact formation. This preparation helps ensure the highest quality diagnostic images are obtained.