A New Look at Mercury Dental Amalgams

A year after 17 groups petitioned the agency to reconsider that rule, the center has agreed to consider an updated risk assessment being prepared by a team from Montreal-based SNC-Lavalin Environment, a division of SNC-Lavalin Inc.
The team is headed by G. Mark Richardson, the author of Health Canada’s 1995 assessment of mercury exposure and risks from dental amalgam that recommended a lower safe mercury exposure level from amalgam than FDA used in its final rule.

The study was slated to be complete in time for a December 14–15 Dental Products Panel advisory committee meeting, which was called to consider scientific issues presented in the groups’ petitions. According to petitioners, Richardson’s new study used the latest statistical information on the U.S. population taken from the National Center for Health Statistics.

The petitioners complained that the safe mercury exposure levels used by FDA for the final rule were significantly outdated and failed to take account of more recent published data. The SNC-Lavalin study reviews the most recent studies on the toxicology of mercury vapor, building on work by Health Canada that was published in 2009, and also considers very recent studies on the use of dental amalgam in children.

Petitioners say the intention is to apply these recent toxicological studies to the dose-response assessment methods recently recommended by the National Research Council and published by the National Academies Press.
According to the petitioners, three recent studies published in 2008 or later substantially lower the recommended safe exposure level for elemental mercury vapor, the primary form of mercury from amalgam fillings. These studies were not discussed in FDA’s final rule but are being considered by the SNC-Lavalin team.

“Additionally, SNC-Lavalin will estimate mercury exposures to children as young as 26 months, the youngest age at which NCHS recorded restored teeth,” a news release said in October. “The team will also estimate exposures for people with as many as 28 filled teeth, the maximal dental filling load recorded for the U.S. population. FDA did not consider children younger than 6 years or estimate exposure levels derived from greater than 10 fillings.”

The petitioners said that the SNC-Lavalin team was also reviewing the available data to determine whether an estimate of mercury exposure to a fetus is possible. The petitioners complained that fetuses are exposed to mercury by the placement of mercury fillings in the mother. “The U.S. EPA recognizes the fetus as vulnerable or sensitive and recommends consideration of the fetus in the assessment of neurotoxins, including mercury,” the petitioners said. “FDA’s final rule did not include an estimate for this exposure.”

Using published health statistics, SNC-Lavalin plans to identify the proportion of the U.S. population treated with mercury fillings that exceed the safe exposure levels determined by various national and international government agencies. The team will also offer its opinion on the number of fillings that may be safely used in toddlers, children, teens, and adults. “The risk assessment will be disseminated to the FDA advisory committee for consideration prior to the public hearings,” according to SNC-Lavalin.