Dental surface restorations composed of dental amalgam, a mixture of mercury, silver, tin and other metals, significantly contribute to prolonged mercury levels in the body, according to new research from the University of Georgia's department of environmental health science in the College of Public Health.

This research, which analyzed data from nearly 15,000 individuals, is the first to demonstrate a relationship between dental fillings and mercury exposure in a nationally representative population. The results were published online last week and will be available in the print edition of the journalEcotoxicology and Environmental Safety in December.

"Tooth decay is one of the most prevalent chronic diseases," said Lei Yin, a scientist in the department of environmental health science and the study's lead author. "I think a majority of people have experienced dental fillings, but the kind of materials the dentist uses isn't something that's really discussed."

Mercury exposure from dental fillings is not a new concern, but previous studies were inconsistent and limited, according to Xiaozhong "John" Yu, assistant professor of environmental health science and co-author of the study.

"This study is trying to provide the most accurate levels of exposure, which will form the scientific basis to make future risk assessment," Yu said, adding that the study was the first to also control for age, education, ethnicity, race, gender, smoking and seafood consumption, which is a known contributor to mercury levels in the body.

The researchers further analyzed exposure by specific types of mercury and found a significant increase in methyl mercury, the most toxic form of mercury, 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's 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.