A federal advisory panel is trying to decide whether the U.S. Food and Drug Administration relied on adequate science when it determined last year that mercury amalgam can safely be used to fill cavities in healthy people. At the time, the FDA didn't find evidence that dental mercury hurts developing fetuses, young children and those more sensitive to its potential health effects.
The FDA's scientific review of evidence about dental amalgam fillings, commonly called "silver fillings" because of their silver-gray color, found them safe for adults and children at least 6 years old. Dental amalgam is an approximately 50-50 mixture of liquid mercury and powdered metal alloy of silver, tin and copper. When mixed, it forms a pliable putty-like substance that hardens into place.
The mercury in amalgam fillings, called elemental mercury, releases small amounts of mercury vapor – a substance that at high levels can be toxic to the brain and kidneys. Vapor levels are highest right after fillings have been placed in a tooth, and later if they're being removed or replaced. People trying to stop the use of mercury in dentistry say mercury vapor levels are boosted by chewing, eating, brushing teeth and drinking hot liquids. The mercury that accumulates in the bodies of fish is methylmercury, which is generally considered more toxic.
"Even in adults and children ages 6 and above who have 15 or more amalgam surfaces, mercury exposure due to dental amalgam fillings has been found to be far below the lowest levels associated with harm," according to an FDA document titled "About Dental Amalgam Fillings." The document says mercury levels in breast milk also fall below those considered safe by the Environmental Protection Agency and the federal Centers for Disease Control and Prevention. In addition, the World Health Organization has said that amalgam restorations are safe and effective.
However, many Americans still worry about dental mercury exposure, and some have sought out mercury-free dentists who advise them to have their amalgam fillings removed and replaced with other types of fillings. Some mercury amalgam opponents fear that having the heavy metal in the mouth is related to higher rates of autism and behavioral problems in children, although there hasn't been proof it causes neurological injury in youngsters.
In the summer of 2009, the FDA moved dental amalgam from a low-risk category to one of elevated risk, under which it began requiring warnings for patients, dentists and dental assistants about inhaling mercury vapors, disclosure of mercury amalgam's health risks to dental patients, and assurances that the material is handled in properly ventilated areas and isn't used in patients with a known mercury allergy or sensitivity. But the new rule didn't warn that any particular groups faced higher risks than others.
Soon afterward, the FDA received four petitions asking it to reconsider the rule and ban or restrict mercury's use in dentistry.
On Tuesday, the dental products panel of the FDA's Medical Devices Advisory Committee began reviewing the science upon which the agency made its most recent determination about mercury safety. Among the witnesses testifying at the meeting were three of the petitioners for restricting dental mercury, as well as three outside researchers asked by the FDA to review levels of mercury exposure from dental amalgams, evaluate the science used to establish daily exposure levels, and discuss the thresholds at which mercury exposure might be harmful.
Among dental mercury opponents was Dr. Richard F. Edlich, a distinguished professor emeritus of plastic surgery, biomedical engineering and emergency medicine at the University of Virginia. He urged the FDA to prohibit the use of mercury amalgam, citing legislative bans enacted in 2008 in Norway and Denmark, and last year in Sweden, as well as six U.S. states' decisions to require dental patients to read about mercury's benefits and risks before undergoing dental restorations.
The city of Costa Mesa, Calif., adopted a resolution in October opposing dental mercury and asked local dentists to voluntarily stop using it.
"In the very least, the Food and Drug Administration should developed informed consent brochures that are used in every dental office in the United States," Edlich said.
Another opponent of continued mercury use in dentistry accused the FDA of "covering up amalgam's mercury from the American people." James S. Turner, a Washington attorney and chairman of a group called Citizens for Health, said, "What keeps amalgam sales going is that most Americans are understandably deceived by the term 'silver fillings,' a grossly misleading marketing term approved by the FDA."
He proposed that by January 2011, the FDA's website should spell out the risks of mercury and mercury vapor; that by March 2011, the FDA should say mercury amalgam is risky for children, young women and people with kidney disease, or at least adopt strict warnings about it; and that by May 2011, the agency should contact every U.S. dentist about the dangers to pregnant women, children and those with kidney disease, and urge the dentists to use alternative materials for tooth restorations.
FDA Invites Outside Experts to Testify
In response to a request from the FDA's Olga Claudio, William Farland, vice president for research at Colorado State University and a former EPA official, recommended that the FDA re-evaluate how well its 2009 mercury rule protects those who might be most sensitive to mercury's effects, such as fetuses and young children.
Farland said the modest increases in mercury levels when fillings are inserted or removed would still fall within exposure levels the EPA considers acceptable, and that this level would still protect the kidneys and immune system. That view was echoed by another outside expert, Robert A. Yokel, a professor at the University of Kentucky's College of Pharmacy and specialist in the neurotoxic effects of metals.
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.