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The 60 minutes exposé
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| In December, 1990, the news program "60 Minutes" ran a
shocking exposé on the most common dental
restoration in the world. It alleged that silver amalgam,
because of its mercury content, is poisonous and is responsible for many
of the diseases that have not yet been cured by medical science. |
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The protagonist in this piece was a researcher from a
respected Canadian university who had done some sheep research to discover the
effects of mercury poisoning from silver amalgam placed in the sheep's' teeth. He was
followed by other crusaders who linked the use of silver amalgam to Multiple
Sclerosis, Alzheimer's disease, Chronic Fatigue Syndrome and various vague ailments
including fatigue, anxiety, insomnia,
depression, and loss of appetite. Many people who watched this piece were appalled, and contacted their
dentists to have their amalgam restorations removed, or even to have
their teeth extracted! This, in turn benefited many dentists. It also
lit up the lives of many tort lawyers. Unfortunately, it did not benefit the
patients in the least!
After the airing of the program, experts in biochemistry,
toxicology, physiology, general medicine and dental medicine descended on
these researchers en masse. Their consensus was that this research was poorly done
and the results were misinterpreted and contradictory.
Mainstream researchers and public health experts who looked at this research
concluded that it did not prove that amalgam is harmful or that it poses
a public health threat as was implied by the Canadian researchers. On the
contrary, the nature of the methodology used in the study as well as the nature
of the misinterpretation of the results (and the fact that the amalgam used by
these researchers contained a higher proportion of mercury than that used in
humans) suggested that the researchers entered
into the study with an anti-amalgamist agenda:
In 1991, Murray Vimy and other researchers published a study in
the Journal of American Physiology ("Mercury from Dental 'Silver'
Tooth Fillings Impairs Sheep Kidney Function," Am J Physiol 1991;
261: R1010-R1014) that investigated mercury's poisonous effects on
sheep. Researchers placed 12 occlusal (top surface) fillings in each
of six female sheep and two glass ionomer restorations in two
control sheep. Before surgery and at 30- and 60-day intervals after
amalgam placement, scientists checked the animals' renal (kidney)
function.
They then evaluated how effectively the sheep cleared a substance
called inulin (not insulin), a chemical not metabolized by the body.
They found that plasma inulin clearance fell by about 60 percent
after 30 days and remained so at the 60-day checkup. Among the
control sheep, baseline clearance stood unchanged after 30 days.
They concluded that the amalgams damaged the animals' renal (kidney)function.
But the study drew quick criticism. In a letter to the editor of the
journal, professor Richard Malvin from the University of Michigan's
department of physiology and other scientists cited numerous flaws
in Vimy's research methods and analysis. In particular, Malvin and
the others wrote, "in these experiments, as the clearance of inulin
decreased with time, the clearance of urea increased with time to
the point that it actually exceeded the inulin clearance. This is a
physical impossibility."
Also, Malvin recalls today, "they measured two enzymes that did not
change [y-glutamyl transpeptidase and alkaline phosphatase]. And
that's evidence of good kidneys, not bad kidneys." In addition,
Malvin says the study's controls were inadequate. "They should have
had six control sheep, not two. And they [the controls] had only one
post-amalgam measurement, at 30 days. That's totally insufficient."
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There was also considerable concern about the validity of using sheep as a
proxy for humans in this study. See box below for details:
The
sheep kidney showed 10 to 20 times as much mercury compared with
concentrations reported for kidneys from humans with many
dental amalgam restorations. However, brain tissue mercury
concentrations in the sheep were similar to those in persons with few amalgam dental restorations.
Several factors may explain the relatively higher levels of mercury
detected in the sheep kidneys as compared to human kidneys. These
factors could include
1) The temporal (timing) relationship of the study to
the placement of the amalgam restorations. The 12 occlusal amalgam dental restorations
were placed all at the same time, and the study was initiated
immediately upon the placement of those amalgams:
Newly placed amalgam fillings leach much more mercury than those
which have been in the mouth for several months, and the tests were
conducted immediately after placement of the amalgam.
2) The test
animals were followed only briefly:
60 days
3) The chewing patterns of the
ruminants (sheep) and the abrasiveness of the ruminant diet are very
different from those of humans:
Unlike humans,
ruminants chew and grind their teeth constantly. They
wear their
teeth down in order to create sharp cutting edges.
4) The organ distribution of
mercury in the sheep appears to reflect gastrointestinal uptake of
elemental (inorganic) mercury rather than lung uptake of
mercury vapor:
Inhaled mercury vapor accounts for
most of
the mercury absorbed by the human body from dental amalgam whereas
in the sheep almost all of the mercury was absorbed through the
stomach. This was apparent due to the organ distribution of
the absorbed mercury.
Therefore, the results of these studies may not be relevant to
humans. [red text is added for clarity.] |
It should be noted here that the experts doubt whether the sheep experienced
any kidney damage at all. The changes reported in the sheep's renal
function were just the opposite of what happens when kidneys are impaired.
Damage to the kidneys' filtering function generally causes the blood levels
of urea (a waste product) to rise. Instead the blood concentration of urea fell
contradicting the researchers' claims of kidney damage.
Since no dissenting opinions were presented in the 60 Minutes piece,
the airing of the program caused quite a stir, and for a
while there was a push to remove dental amalgam from the market. In the
end, nothing of the sort happened. As of this writing (winter 2005),
amalgam continues to be the most popular material in the world for repairing
decayed and broken teeth. Amalgam has been the
premier filling material for over 200 years because it is strong, durable and
able to withstand the tremendous pressures of chewing and grinding. It is
also easy to place and has minor
decay inhibiting properties. For more particulars on
the debunking of this 60 minutes hatchet job, please click
here
or
here.
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