MRI scans may release toxic mercury from dental fillings

High-powered MRI scans may pose a potential poisoning risk to people with silver dental fillings, warns new research.

The study shows that ultra-high-strength 7-Tesla MRI scanners may release toxic mercury from amalgam fillings in teeth.

The scanners rely on strong magnets to work and researchers suggest the magnets could break down amalgam fillings – metal-looking fillings in hundreds of millions of people around the world.

Amalgam, which has been commonly used in dentistry for over 150 years, is 50 per cent mercury, a highly toxic heavy metal.

A lab study showed ‘unsafe’ levels of mercury were found in saliva after a tooth with a filling was scanned by a 7-T machine, which is more than four times as powerful as a normal hospital scanner.

It is not clear whether there would be enough to cause mercury poisoning, but if it did severe cases can increase the risk of brain damage, heart attacks or infertility.

The researchers said the effects of the stronger MRI on fillings had not been studied, but they found it could be a risk to people with filled teeth.

High-powered MRI scanners may have such strong magnetic fields that they corrode fillings in people’s mouths and release the toxic mercury inside them, researchers say

The same effect is not seen in the lower strength, 1.5-Tesla MRI scanners which are commonly used in hospitals.

For now, the powerful 7-T machines are used primarily for research and there are only a handful in the country: St Thomas’ Hospital in London and the universities of Glasgow, Cardiff and Nottingham are among those which have the machines.

The machines, which were approved for use in 2017, create clearer images for medics to study but may carry a risk if used in practice, scientists claim. 

Fillings seal mercury inside when they are in the tooth 

Researchers at Akdeniz University in Turkey explain that when an amalgam filling hardens, the mercury is sealed inside it and a protective film layer covers the filling’s surface. 

The study’s lead author Dr Selmi Yilmaz, a dentist and faculty member at Akdeniz University said: ‘In a completely hardened amalgam, approximately 48 hours after placing on teeth, mercury becomes attached to the chemical structure, and the surface of the filling is covered with an oxide film layer.

‘Therefore, any mercury leakage is minimal.’

However, they say the magnets in the stronger scanners – nearly five times as powerful as a normal hospital scanner – cause corrosion in the amalgam, which allows toxic mercury to leak out. 

Mercury poisoning can cause brain damage 

High levels of mercury in the blood can cause brain damage such as paralysis or slow reflexes, may increase the risk of heart attack or heart disease, and can reduce men’s sperm counts or increase the risk of a woman having a deformed baby.

‘In our study we found very high values of mercury after ultra-high-field MRI,’ Dr Yilmaz continued.

HOW DOES AN MRI SCAN WORK? 

Magnetic resonance imaging, known as MRI, works by using magnetic fields and radio waves to take details pictures of the inside of the body.

During a scan people lie inside a large tube in which they are surrounded by a machine which contains powerful magnets.

The magnets in the machine hold steady tiny particles called protons inside the body’s cells, lining them up in the same way a magnet controls a compass.

Short bursts of radio waves are then bounced off these magnetic protons, and back to a reciever – the scanner – which builds a picture of how different types of tissue look inside the body, similarly to an x-ray.

MRI scans are painless and safe, and do not use the same radiation as x-rays. Some people cannot have them, however, such as those with pacemakers.

Source: NHS  

‘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.’

Based on Environmental Protection Agency standards, the amount of mercury released would far exceed levels considered safe for people.

Dr Yilmaz added: ‘Although it is not clear how much of this released mercury form is absorbed by the body, the study findings indicate that amalgam fillings may pose a risk not only to patients, but to staff too.’

How the research was carried out

Dr. Yilmaz and colleagues evaluated mercury released from dental amalgam after 7-T and 1.5-T MRI in teeth that had been extracted from patients for clinical indications. 

The researchers applied amalgam fillings to a number of extracted human teeth with cavities.

After nine days, two groups of 20 randomly selected teeth were placed in a solution of artificial saliva, then put in either a 1.5-T or 7-T MRI scanner for 20 minutes.

Another group of teeth was placed in artificial saliva only.

When the scientists analysed saliva afterwards, mercury levels in the 7-T group were around four times the levels found in the 1.5-T group and the saliva-only group.

Patients should not worry about MRIs in hospitals 

As no evidence of harmful effects was found in the 1.5-T group, the researchers said patients with amalgam fillings should not be concerned about having an MRI exam.

The researchers said further studies may be needed to confirm the relationship between high-field MRI and the release of mercury from dental amalgam.

The team has three ongoing projects focused on the effects of magnetic fields on amalgam fillings. 

The findings were published in the journal Radiology. 



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