Dental News - High-strength MRI may cause mercury release from amalgam dental fillings

Dental Tribune International

Wed. 4. July 2018

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OAK BROOK, Ill., U.S./ANTALYA, Turkey: Exposure to ultrahigh -strength MRI may release toxic mercury from amalgam fillings in teeth, the Radiological Society of North America has cautioned. The warning is in reference to the findings of a new study conducted by Turkish researchers.

Amalgam fillings have been a staple of dentistry for many years. Despite amalgam containing 50 percent mercury, a known toxin that can cause a host of harmful effects in humans, the U.S. Food and Drug Administration considers it a safe filling material for adults and children older than 6.

“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,” said the study’s lead author, Dr. Selmi Yilmaz, a dentist and faculty member of Akdeniz University in Antalya. “Therefore, any mercury leakage is minimal.”

Previous research has found that exposure to magnetic fields in MRI could cause mercury to leak from amalgam fillings. This concern has been heightened by the recent arrival of ultrahigh-strength 7 T scanners in the clinic. The stronger magnetic field of 7 T MRI yields more anatomical detail, but its effects on amalgam dental fillings have not been studied.

To learn more, Yilmaz and his colleague Dr. Mehmet Zahit Adisen evaluated mercury released from dental amalgam after 7 T and 1.5 T MRI in caries-free teeth that had been extracted from patients for clinical indications. While 7 T MRI was approved by the FDA in 2017, it has extremely limited availability. The lower-strength 1.5 T MRI is widely available and commonly used for patient examinations.

The researchers opened two-sided cavities in each tooth and placed amalgam fillings. After nine days, two groups of 20 randomly selected teeth were placed in a solution of artificial saliva, immediately followed by 20 minutes of exposure to 1.5 T or 7 T MRI. A control group of teeth were placed in artificial saliva only.

When the researchers analyzed the artificial saliva, the mercury content in the 7 T, 1.5 T and control groups was 0.67 ± 0.18, 0.17 ± 0.06 and 0.14 ± 0.15 ppm, respectively. The mercury content in the 7 T group was approximately four times that in the 1.5 T and control groups.

“In our study, we found very high values of mercury after ultrahigh-field MRI,” Yilmaz said. “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.”

An important point of discrimination concerning safety and hazard to human health is the amount of mercury that is absorbed by the vital tissues. “It is not clear how much of this released mercury is absorbed by the body,” Yilmaz said.

Further studies may be warranted, the researchers added, to evaluate the relationship between high-field MRI and release of mercury from dental amalgam. The researchers have three ongoing projects focused on phase and temperature changes of dental amalgam across different magnetic fields.

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

The study, titled “Ex vivo mercury release from dental amalgam after 7.0-T and 1.5-T MRI,” was published online on June 26, 2018, in Radiology ahead of inclusion in an issue.

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