Dental Amalgam: Filling a Need or Foiling Health?
by Laura Bradbard

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.

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 exists 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
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-
bearing 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
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.

Gold Foil
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:
  in teeth involved in the stress from chewing and biting
  when moderate to severe breakdown of the tooth requires
replacement
  if the patient demands a more pleasing appearance than that
produced by amalgam.
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
  the patient shows evidence of extensive teeth grinding or
clenching
  the patient is known to be allergic to the metals used in casting
alloys (gold and certain non-precious casting metals).

 Regulation
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.

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

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