|
By Francesca Lyman
Anyone who has ever had a tooth cavity
has probably seen a dentist who drilled it and packed it with
a "silver" filling. But how many patients know what's
in that silver? And whether it could have consequences for
your health?
Could silver dental fillings be causing,
or contributing to, health problems? Holistic health advocates,
environmentalists and a growing cadre of "mercury-free"
dentists fear amalgams emit dangerous
levels of mercury, stirring up a health
controversy that goes back 150 years.
Scientists agree that when absorbed in
high enough doses, mercury, in all its chemical forms, can
damage the brain, nervous system, kidneys and other organs,
especially in infants and children. But they differ on not
only how much mercury must be absorbed to cause adverse health
effects, but also just how much of the amalgam's mercury is
absorbed by the human body to begin with.
Dental associations pooh-pooh alleged
dangers. The ADA considers it "a safe, affordable and
durable material" that has been used for "more than
150 years and during that time has established an extensively
reviewed record of safety and effectiveness."
ADA quotes the U.S. Public Health Service's
1993 report stating that amalgam has no
health consequences other than for a small percentage
of people who might be allergic to the metals.
Others, however, like Boyd Haley, a chemist
at the University of Kentucky, argue that it is harmful to
more than just sensitive populations. Most people with amalgam
fillings get an unsafe dose of the heavy metal because mercury
vapor leaks continually from the fillings, says Haley, who
recently testified before Congress on mercury exposure in
children.
Consumer groups
argue, meanwhile, that dental patients ought to be told about
what's going into their mouths.
In June, a coalition of citizens' health
and environmental groups filed suit against the American Dental
Association for allegedly deceiving consumers into thinking
amalgam fillings are made of silver, when in fact the major
component (about 50 percent, according to the suit) is mercury.
They also claim that the ADA has failed
to disclose information regarding the significant risk of
harm associated with the fillings in order to promote the
continued use of amalgams, a product in which it has a financial
stake as a paid endorser.
"If
mercury is so safe, why do they try to hide it?"
says Charlie Brown, one of the lawyers representing Consumers
for Dental Choice (CDC), a plaintiff in the suit. Brown notes
that CDC has already succeeded in winning a state ruling that
requires the California state dental board to advise participating
dentists to tell their patients about the mercury content
of amalgam fillings as well as discuss with them any sensitivities
and the potential for adverse reactions, including suspected
links to birth defects.
Although mercury has been known to be
poisonous since ancient times, dentistry associations claim
that the mercury is tightly bound with other metals, rendering
it safe. Silver fillings usually contain a mix of silver,
tin and copper as well as zinc and other metals, according
to the Journal of the American Dental Association.
Mercury is essential to make the amalgam
harden and adhere, says ADA spokesman J. Rodney Mackert, professor
of dentistry at the Medical College of Georgia and an expert
in materials science.
Tracking Mercury's
Vapors
It wasn't commonly known that amalgam
released mercury vapor until recently, although the issue
was raised more than a century ago. In 1985, Fritz Lorscheider,
a fetal physiologist, and Canadian dentist Murray Vimy showed
that mercury in amalgam continuously vaporizes; measuring
mercury in the mouths of 46 people, they also found that the
amount of vapor released from fillings rose when the subjects
chewed gum or brushed their teeth.
In 1990, the same scientists reported
that studies on sheep using radioactively tagged mercury revealed
that the highly volatile
and unpredictable element travels to the gastrointestinal
tract, kidney, liver and brain.
"Whether those [latter] studies are
applicable to humans is a matter of serious importance to
public health," says Dr. Norman Braveman, a research
administrator at the National Institute of Dental and Craniofacial
Research (NIDCR), which has two studies underway on the subject.
At issue, he says, is what dose of mercury
a typical patient gets in the dentist's office, how much he
is exposed to daily and potential health effects that might
arise from this dose. And there isn't much agreement on any
of those questions.
"There's no question that mercury
is not healthy for us," says Vasken Aposhian, a professor
of cellular and molecular biology at the University of Arizona
who has studied how mercury acts on the body. How many amalgams
you have makes a big difference in terms of how much mercury
your body's absorbing, he maintains.
"Some people are hyper-sensitive
to metals and can get very sick" from amounts that others
can safely handle, he says. "Most are at risk from multiple
exposures from fish, food and other sources."
At a Congressional hearing on the use
of mercury in medicine last year, Aposhian told legislators
that Americans' greatest exposure to mercury is from fillings
- a serious threat, he says, because it can cross the placenta
and harm the developing nervous system of the fetus.
ADA, however, maintains that the
amount of mercury that vaporizes from the amalgam is trivial,
and less significant than exposures in food, water and air.
"Yes," acknowledges ADA's Mackert, "mercury
is a poison," and amalgams vaporize, "something
only recently discovered." But, he argues, "there
is no convincing evidence that the small amount of mercury
vapor from amalgams has any effect on humans."
Further, says Mackert, repeating the mantra
of the ADA, "there have been no studies conclusively
linking mercury from dental amalgams with any diseases."
But concerns about possible effects "can't
be dismissed," as the U.S. Public Health Service noted.
Studies show that people with more dental amalgam fillings
have higher levels of mercury in their bodies. And researchers
at the University of Calgary School of Medicine showed that
mercury could be found in the blood and tissues of pregnant
mothers and their fetuses within a few days after mercury
fillings were placed.
Mercury in
dental fillings has been linked to other adverse health effects.
Anne Summers, a microbiologist at the
University of Georgia, for example, found that mercury from
fillings can inhibit the effectiveness of antibiotics.
Scientists at the Battelle Centers for
Public Health Research and Evaluation in Seattle linked exposure
to mercury vapor from dental amalgam fillings to central nervous
system toxicity among dental personnel.
The Battelle team also found "convincing
new evidence of adverse behavioral effects associated with
mercury exposures from amalgam fillings within the range of
that received by the general population." And researchers
at the Colorado State University, Department of Physiology,
in Fort Collins, Colo. have linked dental amalgam exposure
to mental illness.
Haley and other scientists, including
Vimy and Lorscheider, found in experiments on rat brains that
chronic inhalation of low-level mercury ã at levels
that simulate exposure to amalagam fillings ã can inhibit
brain chemistry, producing lesions similar to those in Alzheimer's
diseased brains. Mercury inhibits the efficiency of tubulin,
a protein vital to brain cells, they explain.
'Safe' For
Human Use
Despite such studies, though, the National
Institutes of Health, the U.S. Public Health Service, and
the World Health Organization have all concluded that amalgams
are safe enough to use. There is "no
solid evidence of any harm for millions of Americans who have
these fillings,"
wrote the U.S. Public Health Service, and "no persuasive
reason to believe that avoiding amalgams or having them removed
will have a beneficial impact on health."
By contrast, Canada recently restricted
the number of amalgams that could be placed in children and
pregnant women, following similar laws passed in Sweden, Germany,
the United Kingdom and other countries.
But having produced its new guidelines,
the U.K. government then qualified that it had no evidence
that there was a risk from amalgam, complicating the issue
even further.
While the battle for reliable science
rages, many dentists are switching away from mercury. A 1995
survey of dentists found 8.7 percent wanting to ban amalgam
and 12.3 percent
uncertain about its safety, according to a report
published in the March issue of the Journal of the American
Dental Association.
Discussion Board Remembering how he had
to dispose of his scrap amalgam as hazardous waste, he says,
"It's OK to place these in people's mouths yet it's considered
hazardous when you take it out. Go figure that one out."
Looking To
The Future
Given amalgam's long track record, however,
the government is hesitant to ban it without greater evidence
of harm to human health.
"If we ban this material," said
NIDCR's Braveman, "what
are our alternatives, and will they do the job
as well?"
For now, he says, two government-funded
studies are tracking 1,000 children -- half with mercury amalgams,
half with alternative materials -- for such traits as behavior,
intelligence, antibiotic resistance, immune function and memory.
The results, he says, will be available in about four years.
In the meantime, if you're concerned that
you have a great many mercury fillings, Bronte suggests checking
yourself for symptoms of mercury toxicity and having your
fillings replaced with non-toxic materials.
"If your regular dentist really isn't
familiar with these materials, you are better off finding
a dentist who is familiar with them," advises Bronte,
who went on to write "The
Mercury in Your Mouth" after her health improved.
As more patients find out what's in mercury
fillings, adds advocate Brown, "more dentists will make
it their business to know about the alternatives."
MSNBC
July 11, 2001
| 