By Dr. Murray J. Vimy DMD
Clinical Associate Professor
Faculty of Medicine,
University of Calgary.
Are mercury-based fillings slowly
poisoning their owners? Evidence suggests that, far from
being the best material to use in the mouth, these
fillings should be banned.
The issue of mercury exposure from
dental "silver" fillings has gained
considerable notoriety in the general media during the
last decade. Specific attention has focused on the
potential for human health consequences and the general
well-being of the global environment. The modern silver
amalgam (amalgam meaning mixed with mercury),
traditionally known as a "silver" filling, has
been employed as the principal tooth restorative
material for over 180 years and presently accounts for
75-80% of all tooth restorations.1 These
"silver" fillings contain approximately 50%
mercury by weight, 35% silver, 13% tin, 2% copper and a
trace of zinc.2 Each tooth restoration has a
mercury mass of about 750-1000 mg and should more
properly be called a mercury filling. They have a
functional life of approximately 7-9 years, after which
they are usually replaced with another mercury filling.3,4
Hundreds of metric tonnes of mercury are placed into
teeth world wide each year and some of this material, as
particulate waste from the dental office, finds its way
into the sewerage and refuse systems.
Within the dental profession, the
issue of mercury filling safety has cyclically recurred.
After the introduction of the modern dental amalgam in
1812 by a British chemist, a "silver paste",
which was a combination of silver filings from coins and
mercury, became fashionable for tooth restoration. Since
the coins were not pure, expansion of the material often
resulted in tooth fracture and/or a "high
bite". In America during the 1800s, concern
regarding the possibility for mercury toxicity caused
the American Society of Dental Surgeons to make mercury
usage an issue of malpractice, mandating that its
members sign an oath not to use mercury-containing
materials. However, mercury fillings usage increased
because it afforded an economic advantage to those
dentists employing it; it is user friendly; and because
of its durability in the mouth. By 1856, the American
Society of Dental Surgeons was forced to disband due to
dwindling membership over the mercury filling issue. In
its place arose the American Dental Association, founded
by those who advocated silver amalgam - mercury use in
dentistry.5-7 Again in the 1920s, a controversy
erupted after the publication of articles and letters by
a German chemistry professor, who attacked mercury
filling usage for possible toxic effects.8-13
That debate abated and the dental profession's opinion
still remains unchanged.
Today, 182 years later, the
American Dental Association has amended its Code of
Ethics to make the removal of serviceable mercury
fillings an issue of unethical conduct, if the reason
for removal is to eliminate a toxic material from the
human body and if this recommendation is made solely by
the dentist.14 In the American Dental
Association's view, a dentist is "ethical" to
place the mercury material and recommend its safety.
But, if the dentist suggests that the mercury fillings
are potentially harmful or that exposure to unnecessary
mercury can result, then the dentist is acting
"unethically". Clinically serviceable mercury
fillings can be "ethically" removed if: done
for aesthetic reasons; at the request of a physician; or
at the patient's request (without prompting). ***
Release of mercury from dental fillings. Mercury
vaporizes continuously from dental fillings, being
intensified by chewing,15,16 tooth brushing17 and
hot liquids.18 After mastication or tooth brushing
ceases, it takes almost 90 minutes for the rate of
vaporization to decline to the lower prechewing level
(Fig. 1).16 Also, the greater the number of fillings and
the larger the chewing surface area, the larger the
mercury exposure.15,16 Thus, the average
individual is on a roller coaster of mercury vapor
exposure during the day. Breakfast will cause the
release rate to increase and just as the rate is slowing
again it is time for the midmorning coffee break. Lunch,
mid-afternoon coffee or tea, the evening meal, and a
snack before bedtime all contribute to the daily
exposure to mercury from dental fillings.
It is estimated that the average
individual, with eight biting-surface mercury fillings,
is exposed to a daily dose uptake of approximately 10
micrograms mercury per day from dental fillings.19
Select individuals may have daily doses 10 times higher
(100 micrograms per day) because of factors which
exacerbate the mercury vaporization. Some of these
factors are: frequency of eating, chronic gum chewing,
chronic tooth grinding behavior (usually during sleep),
the chewing pattern of the individual, consumption of
hot foods and drinks, mouth and food acidity.16
Corroborating human autopsy evidence20-22 showed
that brain and kidney tissues contained significantly
higher mercury in individuals who had mercury fillings.
Furthermore, the concentration of brain mercury in the
subjects with mercury fillings correlated with the
number of these fillings present.
The historically espoused opinion
of dentistry insists that, once mixed, the mercury is
locked into the fillings.23 The aforementioned
body of experimental evidence suggests that their
opinion is totally without merit. Despite these
replicated research findings, many national dental trade
associations still claim that mercury fillings are safe.24
They base their conviction on the anecdotal facts that
mercury fillings have been used for over 150 years,
billions of fillings have been placed, and they do not
see sickness or death from the mercury exposure.25
But, the diagnosis of mercury toxicity lies outside the
purview of dentistry, falling more appropriately within
the jurisdiction of medicine. Dental institutions do not
have the scientific expertise or the resources to
undertake the necessary studies to scientifically
resolve this issue. Thus, the issue of mercury filling
safety has not been suitably addressed until recently,
when academic medicine became aware of this insidious
exposure to mercury. From the medical perspective,
dental amalgam fillings are a significant mercury
source, having potential medical consequences.
Tissue uptake of mercury from
dental fillings. Recent investigations in sheep and
monkey animal models demonstrate that dental mercury
accumulates in all tissues of the adult, being highest
in the kidney and liver. This accumulation is so
extensive that it can be visualized on a whole-body
image scan (Fig. 2).26,27 Research also shows
that a high level of dental amalgam mercury in monkey
kidney is still present at one year after mercury
filling placement.28 Also, mercury from dental
amalgam will cross the placenta and begin accumulating
in the developing fetus within two days after the
filling placement in pregnant sheep and is highest in
the fetal liver then the kidney. The mother's milk also
showed evidence of mercury, suggesting that the newborn
would have an additional exposure to mercury.29
Recent human chelation studies show a association
between urinary mercury excretion and the presence of
mercury fillings.30-33 For example, one study
showed that, after a chelation challenge with DMPS,
urinary mercury excretion is significantly higher from
subjects with mercury fillings than from those with no
such fillings. It was concluded that at least two-thirds
of the excreted mercury originates from the dental
On the basis of the research cited
here, there is now international scientific consensus
that the mercury from dental tooth restorations
constitutes the largest non-occupational source of
mercury in the general population, being greater than
all other environmental sources combined!34-36
Yet, the dental profession still insists, without
evidence, that the exposure is insignificant and has no
potential to produce harm.
Pathophysiological consequences of
mercury from dental fillings. During the last several
years, medical research has demonstrated a relationship
between mercury exposure and pathophysiology in various
In sheep exposed to mercury from in
situ tooth fillings, kidney function has been shown to
be impaired. After 30 days of chewing the sheep lost 50%
of their kidney filtration ability; they began to have
difficulty regulating sodium and they demonstrated a
reduced albumin excretion. Control sheep treated with
non-mercury dental fillings did not show such effects.37
In a study of 10 humans with mercury fillings, it was
demonstrated that the plasma mercury level dropped by
50% and the urinary mercury level declined by 25% over a
twelve month interval after filling removal compared to
the pre-removal level. Most notable was the finding that
12 months after filling removal, the urinary albumin
level was significantly higher than the level 4 months
prior to removal.38 In the sheep, the placement
of mercury fillings caused a fall in the urinary
albumin, signifying renal pathophysiology. In humans,
the removal of mercury fillings results in an elevation
in urinary albumin, indicating a renal homeostatic
readjustment. The agreement between this sheep and human
data is remarkable.
In a recent collaborative paper
between three North American universities, it was
demonstrated in a primate model that oral and intestinal
bacteria (eg. streptococci, enterococci,
enterobacteriaceae) exhibit a significant increase in
mercury and antibiotic resistance within two weeks
following mercury filling placement.39 The
mercury resistant bacterial species exhibited resistance
to various antibiotics such as, ampicillin,
tetracyclines, streptomycin, kanamycin, erythromycin,
and chloramphenicol, which they had not demonstrated
prior to placement.. This is the first direct
experimental confirmation of a non-antibiotic factor,
mercury, producing antibiotic resistance. This occurs
because in some bacteria mercury-resistance and
antibiotic-resistance are encoded on adjacent small
genetic sites within plasmids.40 When exposed to
environmental mercury, this genetic material is
activated to protect the bacteria from the lethal
mercury. The plasmid is also replicated and passed on to
other bacteria, insuring species survival. In so doing,
the antibiotic resistance also spreads to the other
bacteria. Antibiotic resistance is a important issue in
medicine today.41 It has been estimated that 80%
of mercury-resistant bacterial strains also show an
increased resistance to one or more conventional
antibiotics. Thirty percent of all hospitalized patients
in North America receive antibiotic therapy42 and
antibiotics compromise 10% of the total $5.1 billion
drug sales in Canada during 1992.43 Moreover, ten
of the top 20 generic drugs prescribed during 1990 in
the U.S.A. were antibiotics.44 Yet, antibiotics
appear to be losing their clinical potency and stronger
antibiotic medications at increasing dosages are
necessary to combat many common infections.41
Recently, investigations have
suggested that mercury may be involved in common brain
pathologies and that the source of the mercury is likely
the dental fillings45-47 In a human autopsy
study, brain tissue from persons having Alzheimer's
Disease at death were compared to an age-matched group
of control brains from subjects without Alzheimer's
Disease. The only significant difference in metal
content between the two groups was mercury, being
considerably higher in the Alzheimer group. The mercury
concentration was prominent in the hippocampus, the
amygdala and particularly in the nucleus basalis, all
brain structures involved in memory function. Other
metals examined were not significantly different in the
two groups of subjects. The effect of mercury on central
nervous system neuron membrane integrity has been
examined and shown that mercury specifically affects
tubulin, a brain neuronal dimer protein responsible for
proper microtubule formation of brain neurons.48 Both
in vivo and in vitro experiments demonstrated that
mercury chelated to amino acids maintains an abnormal
polymerization state of tubulin. This effect may produce
neurofibrillar tangles. Such tangles are a recognized
lesion of Alzheimer's Disease. Inorganic mercury affects
ADP-ribosylation of the rat brain neuronal proteins
tubulin, actin and B-50, in both in vivo and in vitro
experiments.49 ADP-ribosylation is the rate
limiting process involved in polymerization of tubulin
and actin monomers into the structure of the neuron
membrane. Most recently, our laboratory has demonstrated
that ionic mercury and elemental mercury vapour markedly
diminishes the binding of tubulin to GTP and thus
inhibits the polymerization of tubulin which is
essential for the formation of microtubule in the
central nervous system50 These studies are direct
quantitative evidence for a connection between mercury
exposure and neurodegeneration.
Other investigations have examined
the mercury hypersensitivity from dental amalgam in
patients with and without oral lichen planus lesions.51-53
These studies showed that patient groups having oral
lichen planus had a much higher incidence of mercury
patch-test reactivity (16-62%) than did control groups
(3-8%). Removal of the mercury fillings resulted in
amelioration of the oral symptoms.
Governmental regulatory action
concerning mercury fillings. In 1987, the government of
Sweden commissioned an "expert panel" to
evaluate the available evidence regarding mercury
filling safety. The panel concluded that mercury
fillings were "unsuitable from a toxicological
point of view". Based on this panels advice, the
Swedish Socialstyrelsen announced that steps would be
taken to eliminate dental amalgam usage and recommended
that comprehensive mercury filling treatment on pregnant
women should be stopped to prevent mercury damage to the
fetus.54 Shortly thereafter, the German Ministry
of Health (Bundesgesundheitsamt, BDA) issued an similar
advisory.55 In October of 1989, the Swedish
Director of Chemical Inspection (KEMI), responsible for
environmental protection, declared that amalgam would be
banned.56 In January of 1992, the German Ministry of
Health (BDA) informed manufacturers of its intention to
ban the production of amalgam.57 The BDA removed
low copper non-gamma-2-amalgam from the market and
published a pamphlet recommending avoiding mercury
filling use in individuals with kidney disease, children
to age 6, and pregnant women.58 In August of 1992, the
Swedish government suggested a timetable to phase out
mercury fillings. Environmental concerns were used as
the official reason for amalgam discontinuation, but the
government did acknowledge the toxicological risk to
patients and stated that mercury fillings should no
longer be used in children by July 1993, in adolescent
to age 19 by July 1995, and in all Swedish citizens by
1997.59 The Austrian Minister of Health announced
that the use of mercury fillings in children would be
banned in 1996 and discontinued in all Austrians by the
year 2000.60 In 1994, the Swedish Dental Association
acknowledged that its leadership had previously been
incorrect in their position regarding mercury filling
safety. They now support a discontinuation of mercury
use in dentistry.61 Other industrialized
countries, for what ever reason, appear to be side
stepping the issue.
Conclusions. As one might expect,
the dental profession has not responded well to these
data. Some national dental associations have attempted
to influence public and governmental opinion by
endorsing quasi academic symposia pervaded with amalgam
advocates. These gatherings are non-consensus meetings
often under government auspices, where the moderators
responsible for drawing the conclusions are typically
inclined toward the prevailing dental orthodoxy and the
conclusions reached often blatantly disregard the
experimental data presented.62 Most damning to
the dental profession is that they have not advanced any
reputable experimental evidence of their own to support
their belief in mercury filling safety.
The medical research evidence has
been clear for some time. Dental amalgam - mercury
fillings - constitute a significant source of chronic
exposure to mercury in the general population. This
exposure is unnecessary and can not be justified by
risk/benefit analysis. While incriminating medical
research continues to be published, the dental
profession persists in placing itself in the untenable
predicament of advocating an anecdotal position of
mercury filling safety. The mercury filling advocates
can be criticized for their shortage of supporting
research evidence; however, so can many mercury filling
opponents, who irresponsibly go far beyond the limits of
the experimental data, by suggesting that miraculous
cures will occur after removal of the fillings. Still,
the mercury exposure from dental silver amalgam is
toxicologically significant and research into its
possible effects is at an early stage. Perhaps a 1000
years from now, historians will look back and draw
comparisons between the chronic lead poisoning of the
Roman Empire and the insidious mercury poisoning from
our toxic teeth.
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