The fact mercury makes up roughly 50 percent of the content of dental amalgam is a contentious subject for many, and a new study that found MRIs can release the toxic heavy metal from fillings is sure to give those in the anti-amalgam camp even more to chew on. But before you start digging all the fillings from your teeth with a chisel, it's worth noting that this effect was only found to relate to new ultra-high-strength MRIs.

Most current MRI machines are rated as 1.5-T and 3-T, where the 'T' stands for Tesla, the unit of measurement used to describe the strength of an MRI's magnet. Any mercury leakage as a result of exposure to a 1.5-T or 3-T MRI is minimal, however, there are new 7-T MRI machines capable of producing more detailed images whose effect on amalgam fillings has not been studied. Dr Selmi Yilmaz and Dr Mehmet Zahit Adişen set out to change that.

"In our study, we found very high values of mercury after ultra-high-field MRI," Dr. Yilmaz says. "This is possibly caused by phase change in amalgam material or by formation of microcircuits, which leads to electrochemical corrosion, induced by the magnetic field."

The researchers began with a collection of teeth, opened two-sided cavities in each and applied amalgam fillings to the cavities. After nine days, three groups of 20 randomly selected teeth were placed in a solution of artificial saliva. One group of teeth was then subjected to 20 minutes of exposure to a 1.5-T MRI, the second was exposed to a 7-T MRI, while the control group of teeth received no exposure.

The artificial saliva from each batch was then analyzed for mercury content and it was found that the 7-T group had approximately four times the mercury levels of the 1.5-T and control groups.

While the mercury levels found were high (at around 0.67 ppm) Dr. Yilmaz stated, "It is not clear how much of this released mercury is absorbed by the body." Clearly, further investigation is needed to determine the real-life risk that such exposure could pose.

These newer 7-T MRIs represent the latest in imaging technology, but while stronger magnets mean better images, stronger is not always better. Implants and foreign bodies (like shrapnel) can be problematic for more powerful MRI machines, and some body parts – due to different compositions – require careful selection of MRI strength in order to generate the best diagnostic images. All implants need to be tested for safety before being allowed near an MRI machine due to the magnetic field strength. Implants must be rated Safe, Unsafe or Conditional).

The researchers also point out that, although the effects of 7-T MRIs on amalgam fillings requires further research, such machines were only approved by the FDA last year so are still extremely rare. Therefore, patients shouldn't be unduly worried about having an MRI exam.

The study was published in the journal Radiology.

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