MRI scan hazard

Sir, I came across a case when it was not possible to perform Magnetic Resonance Imaging due to previous routine dental treatment. One of our patients stated that during the MRI scan procedure 'the magnet nearly pulled his crowned teeth out'. The procedure was stopped due to the potential hazard. We tracked the patient's record down and discovered that a non-precious alloy with high nickel content (82%) was used in this case to make cast posts and crowns on 12 and 11. The interaction between dental restorations and MRI scans is an interesting topic which has not received much attention in the dental literature.

MRI units use strong magnetic fields and radio-frequency waves to create images. The magnetic field generated by the MRI scanner will attract objects containing ferromagnetic metals (iron, nickel, cobalt) with considerable force. While the MRI examination is a very useful non-invasive imaging technique with no known side effects, it may sometimes provide confusing results due to dental restorations.

Since the MRI scan was introduced in the 1970s, numerous studies have confirmed that precious alloys, amalgams and titanium implants generally cause minimal artefacts. Non-precious dental alloys have the potential of causing image deformation or image voids.

Dentists are not the only professionals implanting metal devices. Heart pacemakers and defibrillators, aneurysm clips, cochlear implants, insulin pumps, vascular stents, artificial joints etc are widely used in other branches of medicine. MRI technicians must conduct a careful evaluation of each patient and may alter the field strength to ensure the safety of the procedure. In some cases it is not possible to perform an MRI scan due to the risk of device dislodgement (eg some aneurysm clips) or malfunction (pacemakers). Extensive dental hardware with a high content of ferromagnetic metals, in some rare cases, can become a reason for a patient's ineligibility for an MRI procedure as well.

Every imaging modality can produce artefacts. Dental restorations can generate artefacts on both MRI and CT scans, with CT images being more affected by dental alloys due to the high attenuation of X-ray beam by metals.6 Severe image distortion or inability to perform the MRI scan due to dental restorations are rare problems, but cannot be completely eliminated. Precious alloys are superior not only in terms of biocompatibility, but also as they produce fewer artefacts on the MRI scan.

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Sinkiewicz, D. MRI scan hazard. Br Dent J 214, 376 (2013). https://doi.org/10.1038/sj.bdj.2013.388

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