Dental Amalgam: Filling a Need or Foiling Health?

by Food and Drug Administration (FDA)

Amalgam restorations — better known as "silver fillings" — are probably more familiar to millions of Americans than they would like.

Dental amalgam is the most widely used material to fill cavities in decayed teeth, technically known as caries. It has been used for 150 years; only gold has been used longer.

Amalgam is composed of approximately equal parts of liquid mercury and alloy powder containing silver, tin, copper, and sometimes lesser amounts of zinc, palladium or indium. Despite amalgam's long history of use, some scientists and consumers are concerned that the mercury from amalgam restorations might be harmful. Nearly half of 1,000 adult Americans surveyed by the American Dental Association in 1991 said they believed amalgam could cause health problems. Besides having the broadest range of use in dental procedures, "amalgam is the most forgiving to place," says William Kohn, D.D.S., National Institute of Dental Research, part of the National Institutes of Health. "It is not as sensitive to moisture [saliva], which can be a problem. With other restorations the dentist has to be more meticulous or the restoration fails when the filling is placed."

Dental amalgam, which the Food and Drug Administration regulates as a medical device, is used in children and adults alike for:

• stress-bearing areas and small-to-moderate-sized cavities in back teeth, such as molars severe tooth damage
• when finances prohibit use of more expensive alternative filling materials as a foundation for cast-metal, metal-ceramic, and ceramic restorations
• when patient cooperation during the procedure or commitment to personal oral hygiene is poor. (Silver is cheaper and easier to place, more resistant to recurring decay than other materials, such as compositie [plastic, tooth-colored fillings], and it is less costly to replace.)

"Dental amalgam is the only material I'm aware of that, when it initially degrades, the restoration improves," says Corbin. "A byproduct builds up and seals the interface between the tooth and the restoration. There may be drawbacks, but amalgam has allowed people to keep teeth in their mouths."

Amalgam is not used when appearance is important (as in front teeth), in patients allergic to mercury, or for large restorations when use of costlier materials is not prohibitive. In 1990, nearly half of the more than 200 million tooth fillings performed in the United States involved dental amalgam. This is down 38 percent from 1979.

Dental amalgam use began to decrease in the 1970s, primarily because dental caries among school children and young adults declined and new alternative materials were developed and improved.

Not only has the incidence been reduced, but also the type of dental caries has changed, possibly as a result of fluoride used in toothpaste and topical gels and in water, sealant use, improved oral hygiene practices, and dietary changes.

Stephen Corbin, D.D.S., from the national Centers for Disease Control and Prevention, says that dentists see fewer caries, which are generally less aggressive once they start, and that today early caries can actually be reversed clinically.

The decision to fill a tooth is complex, whether you are replacing a filling, repairing a damaged tooth, or filling a tooth for the first time. "The decision was simpler in the past. Today there are more choices to make because we see different disease patterns." says Kohn.

Alternative dental restorative materials (composites, glass ionomers, ceramics, and others) are being used more often because cavities are usually smaller and amalgam is therefore not the only choice. Since the alternatives are not as durable as amalgam, the most commonly used alternatives are not used for large fillings or stress-bearing areas. According to Kohn, this is often an inappropriate choice.

Approximately 70 percent of the fillings performed each year are replacements. Most replacements require amalgam or other metallic materials because, as more tooth is drilled away, the new area is larger with each replacement. Some patients do not want the silver showing in their teeth and choose other filling materials that match the natural tooth color.

Amalgam Risks and Benefits

According to Dental Amalgam: A Scientific Review and Recommended Public Health Service Strategy for Research, Education and Regulation, published January 1993 by the Department of Health and Human Services, scientists have shown that dental amalgam emits minute amounts of mercury vapor. "The toxicity of high-dose mercury levels in industrial settings has been established. Although mercury vapor can be absorbed through breathing and eating, research has not shown that low levels of mercury-containing amalgam are harmful except in rare cases of mercury allergies.

In a literature review of amalgam research, the U.S. Public Health Service found no sound scientific evidence linking amalgam to multiple sclerosis, arthritis, mental disorders, or other diseases, as has been suggested by some critics of amalgam.

The PHS subcommittee, which prepared the amalgam report, reviewed the research of low-dose mercury toxicity. According to the findings, a fraction of the mercury in amalgam is absorbed by the body. People with amalgam fillings have higher concentrations of mercury in their blood, urine, kidneys, and brain than those without amalgam. A small proportion of patients may manifest allergic reactions to these restorations, but, Corbin says, there are only 50 cases of amalgam allergies reported in scientific literature. According to the PHS report, the few human studies done to determine a possible public health risk from amalgam have been flawed or contained too few subjects. If there are long-term effects from the mercury in amalgam, they likely are subtle — slight neurological or behavioral changes — and difficult to detect.

The subcommittee could not conclude with certainty that mercury in amalgam fillings poses a health threat or that removing them is beneficial. Removal itself may, in fact, expose patients to additional mercury absorption since drilling into the amalgam filling releases mercury into the air. Many questions remain unanswered, but for now the PHS report does not recommend either removing or not using amalgam. The report does, however, recommend more research into what the specific health effects of low-level mercury exposure might be, whether these effects can be produced by amalgam, and whether certain population groups, such as women and children, might be particularly sensitive. The report also recommends research on the safety of amalgam alternatives.

About the Author

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FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.