For more than two decades, the Food and Drug Administration, under pressure from consumer activists and some medical experts, has wrestled with how to regulate dental fillings containing mercury.
Last week, just 18 months after FDA declared such fillings safe, an advisory committee of outside experts recommended that the agency revisit the question.
Why is mercury even in fillings?
Mercury, which is liquid at room temperature, binds amalgam alloy — silver, tin, copper and sometimes zinc — into a mass that is malleable enough for the dentist to work it into a cavity but then hardens to make a durable filling. The American Dental Assn. and other supporters of amalgam say that in binding with other metals mercury is rendered stable and safe.
Why is it controversial?
Mercury is a well-known toxin in sufficiently large doses, such as those received when eating large amounts of mercury-contaminated fish. But information about the health impacts of mercury vapor arising from amalgam is much sketchier. FDA's current guidance, released in July 2009, is that the fillings are safe for people 6 and older, but it notes that very young children and developing fetuses may be more sensitive to mercury vapor from amalgam.
Opponents of amalgam fillings say that FDA has misread scientific evidence that points to harm.
What are some of the challenges in sorting this out?
There's a dearth of human studies showing how much mercury vapor it takes to trigger toxic effects such as brain and kidney disorders. In addition, the amount of mercury vapor produced by fillings and absorbed by individuals can vary depending on genetics, the number of fillings and their surface area, and by factors like grinding teeth and chewing gum.
Are there alternatives to amalgam?
Yes. Amalgam use has been decreasing, in part out of concern about the mercury content and in part because of a consumer preference for other kinds of fillings, including ones made from composite resin, which can be matched to tooth color.
But amalgam fillings, which are silver-colored, still are the cheapest and longest-lasting patches for tooth decay.
What are the issues beyond public health?
Tens of millions of people have amalgam fillings and an FDA determination that they cause harm would raise questions about whether they should be removed and who should pay for pay for it. In addition, a finding that amalgam is harmful could set in motion a barrage of litigation against dentists, amalgam manufacturers and the ADA.
What recommendations did the advisory committee make?
First, FDA should consider requiring dentists to tell patients what is known and not known about mercury exposure through amalgam, so that patients can give informed consent.
Second, the agency should attempt to identify a safe dose of mercury from fillings by reviewing existing studies of amalgam and research on mercury vapor exposure. The advisory committee said that the current mercury vapor safety metric, which was calculated by the Environmental Protection Agency and last modified in 1995, "needs to be updated with the latest studies."
Is the FDA required to follow these recommendations?
No. Its expert panels are purely advisory. But their recommendations usually carry great weight with the agency and are seldom entirely ignored.