Alternatives to amalgam
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:
teeth, such as molars
personal oral hygiene is poor. (Silver is cheaper and easier to place, more resistant to decay than other materials, such as composite plastic, tooth-colored fillings, and 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-beating 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.
A literature review of amalgam research by 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 the 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.
No single material can completely replace dental amalgam. Gold and
ceramic inlays and crowns can replace amalgam in larger back cavities or in medium-sized cavities on other stress-bearing tooth surfaces. Smaller cavities in premolars and molars can now be restored with resin-based composite materials, glass ionomers, or compacted gold.
Alternatives to dental amalgam are not as durable, however, especially
in larger cavities, and can cost significantly more.
"A wholesale conversion to non-amalgam materials would drive up
national dental health-care costs by about $12 billion in the first year, a tremendous cost impact," says Robert C. Eccleston, assistant to the director at FDA's Center for Devices and Radiological Health. "The cost would also increase in the years following any across-the-board conversion."
Also, according to the PHS report, it is possible that alternative
dental restorative materials could have long-term toxicity problems of their own that have not yet been discovered. Since no definitive data exist to show that mercury in dental amalgam is directly linked to illness, and since amalgam is less expensive, easier to place, and more durable than alternatives, dental amalgam should continue to be used.
Composites, made from synthetic resins, are used to make attractive
restorations in the front teeth. Dentists use a combination of composites and sealants, technically known as preventive resin restorations, to treat small cavities and conserve tooth structure. But the use of composites as substitutes for restorations in stress-beating areas may be inappropriate because composites can leave a tooth susceptible to recurrent decay.
Pit and Fissure Sealants
In its report, PHS recommends dental sealants to prevent caries.
Sealants prevent cavities by sealing with thin plastic coating the natural pits (round holes) and fissures (grooves) in their molars. Pits and fissures in permanent first molars account for 91 percent of the surface cavities in children up to 11 years of age.
"The best restoration that is ever placed cannot be as good as the
sound tooth structure that was there in the beginning," Corbin says. "But some of the preventive materials sealants actually improve tooth structure."
Glass ionomers, introduced to dentistry in the 1970s, chemically bond
to the tooth structure and have the beneficial side effect of releasing fluoride.
Ionomer placement technique requires limited drilling, so the
procedure is quick and the result fairly attractive. Because glass ionomers are generally not used in occlusal surfaces (biting surfaces), their use is limited to baby teeth and primarily root surfaces.
Although not widely used today, gold foil restorations (compacted
gold) date back many centuries. These fillings may last 20 years or longer, but are not used for large or very visible areas. Gold foil restorations require more skill and careful attention to detail during placement to prevent harm to the tooth pulp (nerve) and gums. Its high cost also makes gold foil a less popular choice.
Cast Metal and Metal-Ceramic
Cast metal and metal-ceramic restorations generally require two or
more dental appointments and are typically used for inlays, onlays, crowns, and bridges. Use of metal and metal-ceramic materials depends on the degree of tooth destruction from decay, breakage, or amount of tooth removed by drilling. It is also determined by the number of missing teeth, how important looks are to the patient, and the patient's oral hygiene and financial situation.
These restorations cost approximately eight times more than amalgam
and are most often used:
Cast metal or metal-ceramic restorations are generally not used if: * there is a danger of exposing the tooth pulp while preparing the
tooth for restoration for example, in patients under 18 whose pulp is higher in the tooth
alloys (gold and certain non-precious casting metals).
The PHS report recommends that FDA require restorative material
manufacturers to identify the ingredients used in their products, and FDA is considering such an action. Industry disclosure of product ingredients would provide dentists with information necessary to prevent sensitivity reactions in allergic patients.
The PHS findings indicate that it is inappropriate to recommend
restrictions on the use of dental amalgam unless more studies show a definite link between amalgam and illness.
"The science simply doesn't justify such an action," FDA's Eccleston
points out. "There are several reasons for not restricting amalgam. First, current evidence does not show that exposure to mercury from amalgam restorations poses a serious health risk in humans, except for a very small number of allergic reactions. Second, there is insufficient evidence that alternative materials have fewer potential health effects than amalgam. And, as stated previously, amalgam use is declining."
Laura Bradbard is a member of FDA's public affairs staff.
PHS REPORT AVAILABLE
For a copy of Dental Amalgam: A Scientific Review and Recommended
Public Health Service Strategy for Research, Education and Regulation from the Department of Health and Human Services, January 1993, write to:
Les Grams HFZ-220 Subcommittee on Risk Management/ CCEHRP 5600 Fishers Lane Rockville, MD 20857