It’s relatively normal to be scared of going to the dentist. But what if we told you it could lead to a mouthful of mercury?
Researchers in Turkey published in the journal Radiology, showing that a new type of MRI scan has the slightly worrying effect of, er, making your fillings leak mercury into your mouth. Yes, it turns out a simple medical scan might give you a free helping of delicious heavy metals.
First, a quick recap: MRI – which stands for Magnetic Resonance Imaging – is a technique for scanning the body that has been around for nearly 50 years already. It relies, as the name suggests, on using strong magnetic fields to generate images of internal organs.
So how strong is a “strong magnetic field”? A standard MRI uses a magnetic field of 1.5T (Teslas – the unit of measurement for magnetic field strength). For comparison, the magnetic field surrounding the entire planet is only about 0.00005T. So, pretty strong.
But since the early 2000s, a new type of MRI scanner has been in commercial production – and it can produce magnetic fields of 7T and higher. In 2003, the FDA declared strengths of up to 8T a “non-significant risk”, and the new machines quickly proved popular for research and clinical use – despite concerns that not enough research had been done into their safety. In particular, researchers questioned whether enough was known about how the ultra-high magnetic fields would affect surgical and dental implants in patients.
This is where the new study comes in. The researchers took 60 “human teeth that had been extracted for various reasons”, which sounds very fine and not suspicious, and gave them all amalgam fillings – that’s the silver type you probably think of as a “normal filling”. They then divided the teeth into three groups: one underwent a normal 1.5T MRI scan, one had a 7T scan, and a control group had no scan at all. After nine days brewing in vials of artificial saliva, the amount of mercury that had leaked out of the teeth was measured and recorded.
The results were … not great. Although the mean amount of mercury that leaked in a normal MRI was a little higher than the control group, the teeth that had the ultra-high MRI scan had lost nearly five times as much. The researchers also noted that problems have been found with other dental implants, with gold and platinum crowns becoming hotter under the higher magnetic fields.
Despite the worrying results of the study, it’s important to remember that mercury-based fillings have been in common use for hundreds of years, and are declared safe by the FDA, the American Dental Association, the UK's NHS, Health Canada and many more – and although ultra-high field MRI scans might be on their way, you’re unlikely to undergo one for a very long time.