However, Gary Ginsberg, a toxicologist with the Connecticut Department of Public Health, who serves on the EPA's Science Advisory Board and has been on its Children's Health Protection Advisory Committee, said he didn't think the threshold was "adequately protective," especially in early-life exposures, given differences in gender, pre-existing diseases and exposures to other chemicals that could affect the body's response to mercury. He said even low mercury doses may have bad effects and, therefore, "a more robust risk assessment is needed."
Yokel said regulators are facing a dearth of studies documenting patients' or dental workers' exposure to mercury in the air or inside their mouths "as well as the clear presence or lack of adverse effects." Yokel said he believed that the variable that most influences mercury exposure is the number of dental fillings on tooth surfaces.
Since the late 1800s, dentists have mixed liquid mercury and powdered metals in their offices and inserted the amalgam into tooth cavities after they've drilled away dental decay. Dentists continue to use amalgam because it's the most durable material for fillings, capable of withstanding the pressure of biting without shrinking or allowing bacteria seep in and cause further decay, and because it's relatively inexpensive when compared with alternatives. Other materials that can be used are gold, porcelain (ceramic); composite resins (called tooth-colored or white fillings), which contain combinations of powdered glass and plastic resin; and glass ionomer cement and resin-ionomer cement, which also more closely resemble natural enamel than amalgam fillings.
The state of California has included elemental mercury on its Proposition 65 list of chemicals known to cause cancer, birth defects or reproductive harm – meaning they can be toxic to a developing fetus. In 2002, the Dental Board of California mandated that all dental patients receive a dental materials fact sheet so they could make informed choices about filling materials. The American Dental Assn. and the California Dental Assn. oppose removing amalgam fillings and replacing them with other materials because of the elevated exposure to mercury vapor from the removal process.
But the problem with alternative materials is that some of them also may pose health risks. For example, some of the composite resins contain crystalline silica, which also is on the Prop 65 list of known cancer-causing chemicals.