Magnetic Resonance Imaging (MRI) is a powerful diagnostic tool that utilizes strong magnets and radio waves to generate detailed images of internal body structures. Many individuals have dental fillings, leading to questions about how these metallic restorations might interact with an MRI scan. This article clarifies the relationship between metal fillings and MRI, addressing common concerns and explaining the considerations involved.
How Metal Fillings Interact with MRI Scans
Metal fillings can interact with MRI scans in two primary ways: by affecting image quality and through potential safety considerations. These interactions are important for both diagnostic accuracy and patient well-being during the scan.
One significant interaction involves the creation of image artifacts, which are distortions or obscurations in the MRI images. Ferromagnetic materials found in some dental restorations can cause a phenomenon known as susceptibility artifacts. This results in signal voids, streaks, or blurry areas around the filling, making it difficult for radiologists to interpret images of tissues near the dental work. The extent of these artifacts depends on the magnetic properties, size, shape, and position of the metallic material, as well as the specific MRI sequence used.
Safety concerns, while generally low, include the potential for heating and, in rare instances, slight movement of the metal. Radiofrequency pulses can induce a small amount of heat in metallic objects within the body. Studies have shown that temperature elevations for amalgam restorations and dental implants during 1.5T MRI are typically minor, ranging from 0.21°C to 0.70°C for amalgam and 0.35°C to 0.47°C for implants, which are considered within acceptable safety limits. While mechanical displacement of fillings is exceedingly rare with modern MRI machines, especially for well-bonded restorations, it remains a theoretical consideration for highly ferromagnetic materials.
Understanding Different Dental Materials
The impact of dental fillings on an MRI scan varies significantly based on the specific materials used in their construction. Not all “metal” fillings behave the same way within a strong magnetic field.
Amalgam fillings, often called “silver fillings,” consist of a mixture of metals, including silver, tin, copper, and mercury. While silver is diamagnetic, the setting reaction with mercury can render the material paramagnetic. Amalgam fillings can cause image distortions, but generally pose minimal safety risks during an MRI. Some research indicates a very small, statistically significant increase in mercury release from amalgam fillings during high-field MRI (7T), but this release is considered negligible at the standard 1.5T and 3T MRI strengths commonly used.
Gold fillings and crowns typically pose minimal to no issues during an MRI because gold is a non-ferromagnetic material. Although gold can potentially cause minor image distortion due to its high electrical conductivity leading to eddy currents, this effect is usually limited. Similarly, composite resins and ceramic restorations, being non-metallic, are generally considered safe and do not cause significant distortions in MRI images.
Other dental metals, such as titanium and zirconia, commonly used in implants and some crowns, are also non-ferromagnetic and are largely compatible with MRI, generating only minimal artifacts. However, materials like stainless steel, frequently found in older orthodontic appliances, contain ferromagnetic elements and can produce substantial image artifacts, potentially affecting diagnostic clarity in the head and neck region.
Navigating an MRI with Dental Fillings
Undergoing an MRI with dental fillings often requires specific considerations to ensure both patient safety and the diagnostic quality of the images. Clear communication with medical professionals is a cornerstone of this process.
It is important to inform the MRI technologist and the referring physician about all dental work, including fillings, crowns, bridges, and implants, before the scan. This information allows the medical team to make informed decisions regarding the scan protocol. Patients typically complete a detailed screening questionnaire that asks about any metallic objects in their body, including dental restorations.
The radiologist assesses the location of the dental fillings relative to the area being scanned. In such cases, the radiologist may adjust specific scan parameters, such as increasing readout bandwidth or utilizing spin-echo sequences instead of gradient-echo sequences, to minimize artifacts. This careful adjustment helps improve the clarity of the images despite the presence of metallic materials.
Patients with fillings can generally expect a safe MRI experience. While a slight warmth near the filling might be felt, significant discomfort or risk is uncommon. In situations where severe artifacts from dental work could obscure the target area and hinder a clear diagnosis, alternative imaging methods, such as a CT scan, might be considered to provide the necessary diagnostic information.