Magnetic Resonance Imaging (MRI) is a sophisticated medical tool that produces detailed images of internal body structures without using ionizing radiation. The technology relies on a powerful static magnetic field and radiofrequency pulses to measure the energy released by the protons in water molecules within the body. Given the widespread use of dental restoration materials, the question of whether these materials can safely enter a high-field magnetic environment is common. The powerful magnet creates a potential for interaction with any metallic or magnetic material present in the patient’s body. This interaction does not typically result in physical danger but rather creates a complex challenge for the diagnostic quality of the resulting images.
Safety First: Can You Get an MRI Scan?
Yes, in the vast majority of cases, a patient with dental fillings or restorations can safely undergo an MRI scan. The primary concern is the potential for diagnostic interference, not patient safety. Older or larger ferromagnetic objects elsewhere in the body, such as certain aneurysm clips or pacemakers, pose a serious risk of movement or heating. However, the risk of thermal heating or movement from dental fillings is minimal, especially with non-ferromagnetic materials like titanium. It is important to inform the technologist about all dental hardware, as this information helps them manage the scan parameters and minimize image degradation.
Why Dental Materials React to MRI Fields
The reaction of dental materials to the magnetic environment is governed by their inherent magnetic properties, which are categorized into three main types. Ferromagnetic materials (e.g., iron, nickel, and cobalt) are strongly attracted to the static magnetic field and should generally be avoided. Paramagnetic materials (e.g., magnesium) are weakly attracted, while diamagnetic materials (e.g., gold, silver, and copper) are weakly repelled. The powerful magnetic field causes an effect known as magnetic susceptibility, which is the degree to which a material becomes magnetized when placed in a magnetic field. When a dental material has a susceptibility significantly different from the surrounding soft tissue, it causes a distortion in the local magnetic field lines, leading to signal loss and image quality problems.
Which Fillings and Devices Cause the Most Issues
The most significant problems arise from materials containing high concentrations of iron, nickel, or cobalt, which are strongly ferromagnetic. Stainless steel alloys, often used in older crowns, wires, and orthodontic brackets, fall into this high-risk category, as do older dental amalgams. These materials can cause large, severe distortions that extend far beyond the physical boundaries of the filling itself. The size and number of the restorations also play a role, as multiple large pieces of metal will compound the overall field distortion.
In contrast, many contemporary dental materials are considered low-risk because they exhibit diamagnetic or non-ferromagnetic properties. Pure gold, ceramic, porcelain, and composite resins typically cause minimal or no artifact. Titanium, commonly used in dental implants, is non-ferromagnetic and only causes minor image distortion. The location of the material is also highly relevant; a small metal restoration on a back tooth will cause more concern if the MRI is focused on the nearby brainstem or spinal cord than if the scan is focused on the knee.
Understanding Image Artifacts and Diagnosis
The consequence of this magnetic field distortion is the creation of image artifacts, which are systematic errors in the image that do not represent true anatomy. Radiologists often observe a “signal void” or area of signal loss, which appears as a large, black region where no diagnostic information can be seen. This signal void can be much larger than the filling itself, obscuring adjacent anatomical structures like the jawbone, nerves, or soft tissues. The other common artifact is distortion or “streaking,” where the image appears warped or blurred near the metallic object.
When the area of diagnostic interest falls within the artifact zone, the scan can be rendered non-diagnostic. To mitigate this, technologists employ specialized protocols, such as advanced artifact suppression sequences like Slice Encoding for Metal Artifact Correction (SEMAC). Adjusting scan parameters, such as increasing the readout bandwidth, can also shrink the size of the artifact. Communicating the precise location and material type of the dental work to the technologist is the most effective step in ensuring the highest quality scan possible.