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CHICAGO — Silver tooth fillings have been placed in the mouths of Americans since before the Civil War, an inexpensive, durable and reliable material that helped form the foundation of modern dentistry.
For nearly as long, they’ve been a source of controversy.
Because elemental mercury — a toxic substance — makes up about half of a silver filling, its use has been the subject of hundreds of scientific and academic studies examining their safety. The results have done little to settle the dispute.
What’s not up for debate is that silver fillings, commonly called dental amalgam, contribute mercury pollution to the environment.
Global consensus on that issue has led some anti-mercury crusaders, who long have sought to ban the material from dental products because of health concerns, to shift their focus to a fight they think they have a better chance of winning.
“The approach to getting to the end of amalgam is the environment,” said Charlie Brown, president of the World Alliance for Mercury-Free Dentistry, a multinational group that lobbies to ban the use of mercury in dentistry.
Recent developments suggest momentum is building against silver fillings based on environmental concerns:
More than 140 nations agreed in January to a U.N. treaty calling for decreasing use of dental amalgam.
One major U.S. dental school announced it is putting less emphasis on teaching students about preparation and placement of silver fillings.
Two large, nonprofit Catholic hospital chains are waging proxy battles with the two leading American makers of dental amalgam. The hospital chains’ investment arms are seeking a shareholder vote that would mandate each company detail plans to phase out mercury.
Norway, Denmark, Sweden, Japan and Finland have either banned dental amalgam or restricted its use within the last five years. (Other countries, such as Canada and Germany, recommend keeping amalgam out of the mouths of certain people — including pregnant women, children and those with kidney impairment — as a precaution.)
The Food and Drug Administration and the American Dental Association, which represents more than 150,000 dentists, maintain that silver fillings should remain an option, saying that they are safe and effective and that they often outperform other restorative materials.
“From a patient safety and efficacy perspective, the (ADA) takes the position that it should advocate for patients’ overall oral health,” said Dr. Dan Meyer, the association’s senior vice president of science and professional affairs. “There is no reason, based on current scientific information, to do anything other than advocate ... to make all treatment options available that are safe and effective.”
The ADA acknowledged that mercury waste is a problem but noted that as of 2010, about half of dentists were filtering out more waste mercury through the installation of relatively inexpensive equipment.
Twelve states have mandatory dental amalgam reduction programs. The Environmental Protection Agency is working with the ADA to draft a federal rule that would require dental offices that handle products containing mercury to install the equipment.
About half the mercury entering municipal wastewater treatment plants, or about 3.7 tons annually, comes from dental amalgam waste, according to a 2010 EPA estimate.
While treatment plants capture about 90 percent of amalgam, some mercury settles into sewage sludge that is deposited in landfills, incinerated, applied as fertilizer or flushed into waterways.
Once in water, it can transform into methylmercury, a neurotoxin that builds up in fish, shellfish, and animals that eat fish, including humans, according to the EPA.
Although it’s impossible to calculate the contribution of dental amalgam to mercury pollution in waterways, the EPA points to a 2002 New York Academy of Sciences study that estimates that as much as 40 percent of the total mercury load in the New York-New Jersey harbor and watershed may have originated in dental offices.
Several studies have linked methylmercury to health and developmental problems, especially in pregnant women, fetuses, infants, and children.
Research shows that the human body absorbs mercury vapor released from dental amalgam, though most studies suggest it’s not at a level that could be linked with adverse health effects, except in rare instances of allergic reactions. Still, numerous studies raise concerns about mercury exposure from amalgam, especially in children and fetuses.
In toxic doses, elemental mercury breathed in as vapor can cause symptoms including tremors, mood swings, neuromuscular changes, and cognitive deficits, according to the EPA.
Students at New York University’s College of Dentistry were told last summer that they would no longer have to place amalgam fillings in patients as part of final exams. The university cited concern for the waste stream, consumer demand for tooth-colored fillings, and the less invasive nature of composite fillings.
“I took a lot of heat from a lot of people for it,” said Dr. Mark Wolff, chairman of the Department of Cariology and Comprehensive Care at NYU. Dentists can place amalgam in a quarter of the time it takes to place a composite, he said.
Dr. Wolff said amalgam still will be taught because there are cases in which it is impossible to keep the tooth dry to allow a plastic restoration. Saliva can cause such restorations to fail. But composite resins have advanced enough to be a better alternative in most cases.
Dr. Markus Blatz, chairman of the Department of Preventive and Restorative Sciences at the University of Pennsylvania School of Dental Medicine, said he thinks dental schools will follow NYU, as dentistry strives to be more aesthetic and less invasive.
Dr. Wolff and Dr. Blatz emphasized that studies have not shown mercury fillings to cause illness.
But Dr. Blatz said patients are increasingly concerned about the cumulative exposure to environmental toxins, so “why be exposed when there are viable alternatives?”