People with more than eight dental fillings may have 150 per cent more mercury in their blood, increasing the risk of brain, heart and kidney damage, a new study has found.
Dental surface restorationsor, commonly known as dental fillings, is composed of dental amalgam - a mixture of mercury, silver, tin and other metals.
The research by University of Georgia in the US, analysed data from nearly 15,000 individuals and is the first to demonstrate a relationship between dental fillings and mercury exposure.
"Tooth decay is one of the most prevalent chronic diseases. I think a majority of people have experienced dental fillings, but the kind of materials the dentist uses is not something that is really discussed," said lead author Lei Yin, a scientist at University of Georgia.
Mercury exposure from dental fillings is not a new concern, but previous studies were inconsistent and limited said Xiaozhong Yu, assistant professor at University of Georgia.
"This study is trying to provide the most accurate levels of exposure, which will form the scientific basis to make future risk assessment," said Yu.
It was the first study to control for age, education, ethnicity, race, gender, smoking and seafood consumption, which also contributes to mercury levels in the body, he said.
Researchers further analysed exposure by specific types of mercury and found a significant increase in methyl mercury, which is the most toxic form, related to dental fillings.
Yu said this result suggests the human gut microbiota, a collection of microorganisms living in the intestines, may transform different types of mercury.
Dental amalgam has been the go-to dental filling material for more than 150 years, because it is affordable and durable.
However, about half of the compound contains mercury, a heavy metal known to be toxic at high levels, causing brain, heart, kidney, lung and immune system damage.
New research suggests that methyl mercury may cause damage even at low levels.
"As toxicologists, we know that mercury is poison, but it all depends on the dose. If you have one dental filling, maybe it is ok. But if you have more than eight dental filings, the potential risk for adverse effect is higher," Yu said.
People with numerous dental fillings who are also exposed to mercury from other sources, such as seafood or work environments, are most at risk.
The results show that individuals with more than eight fillings had about 150 per cent more mercury in their blood than those with none.
The study also looked at dental composite resins, a mercury-free alternative for dental fillings that can release small amounts of bisphenol A which may cause developmental or reproductive damage. The research appears in the journal Ecotoxicology and Environmental Safety.