Mercury in Dentistry
Preface
Many materials commonly used in dentistry today are considered toxic and
harmful to health. Among those materials are the base metals mercury, nickel,
lead, chromium, cobalt, beryllium, zinc, tin, copper, and many others. We also
apply sterilizing agents such as phenol, formocresol and chlorine directly into root
canals. All of the phenols and most of the halogens are considered toxic to some
degree.
This profession has a long history with regard to the use of mercury.
Although the focus of this presentation is on the heavy metal mercury, the concepts
applied can be readily transferred to most of the other dental materials. A recent
Louis Harris poll reported that a clean environment is second only to a happy home
life among the desires of adults. It is the dentist’s responsibility to protect
themselves and their staff as well as the patients from exposure to toxic materials.
Most of the technology used by scientists today to uncover hidden
environmental hazards was not available even ten years ago. Numerous new
illnesses have cropped up from unknown causes, among which environmental
exposure to toxics seems to be a most likely suspect. As these investigations
continue you can expect to find that many of the most common dental materials
will no longer be considered appropriate for use due to their potentially toxic
nature.
Modern technology has focused on developing techniques for evaluating
biocompatibility that look for minimal damage rather than gross disease. But in the
telling words of astronomer Carl Sagan, "Absence of evidence is not evidence of
absence."
In this paper I will review the state of the research on the patient's exposure
to mercury from dental fillings, the occupational hazards of dentistry, the
environmental impact, and how best to protect the dentist, the patients, and the
dental staff from injury. This subject has been a source of controversy for over a
century. The reason the argument has lasted so long is because investigators did
not rely upon the documented scientific literature. Through the use of modern
science we can dispel many of the common myths about dental amalgam.
The Chemistry of Mercury
1
Mercury in Dentistry
Mercury is an unusual base metal that is molten at room temperature. It is
highly volatile and vaporizes readily. The fumes from elemental mercury are
uncharged atoms (Hg0) that are easily (75% to 100%) absorbed from lung and
nasal tissues1. Once absorbed, this uncharged form may enter the bloodstream and
penetrate cell membranes, the blood-brain barrier, the placental membrane, and
fetal tissues.2 When combined with the other metals used in a dental amalgam it
has the unique property of forming what could be termed a solid suspension. This
filling material is not an alloy but rather a mixture. When compressed or heated
free vapor mercury will be released.
Mercury combines readily with many compounds, and it has a particular
affinity for sulfur. When it attaches to protein molecules, it alters their tertiary
structure. This is one way it exerts its poisonous effects. Regardless of the source,
once mercury enters the body, the body tries to detoxify the poison. The process of
detoxification involves the production of mercurous or mercuric (Hg+ and Hg++)
forms which are not as easily absorbed through cell membranes. Consequently, the
biological removal of mercury form tissue is inhibited.
Neurological tissues have a high sulfur content. For this reason, mercury
tends to accumulate in the central nervous system.3 Less than 1 ppm of mercury
absorbed into the bloodstream can impair the blood-brain barrier within hours,
permitting substances from the plasma that would normally be excluded to enter
into the cerebral spinal fluid.4 5 All mercury compounds appear to cause the same
kind of damage in the brain.6 7 8 Other organs and systems adversely affected by
mercury are the immune system, kidneys, liver, and the reproductive and
cardiovascular systems. 9 10
How Does It Poison?
1)
2)
3)
Neurological
Immunological
Endocrine
Because of mercury's effects on the central nervous system, many divergent
neurological and psychological symptoms are common findings in mercury
2
Mercury in Dentistry
poisoning. In 1926 the famous German scientist Dr. Alfred Stock meticulously
cataloged and classified these symptoms through conducting experiments on
himself. He identified confusion, memory loss, and irritability as associated with
inhaling a single 10 ppm dose of mercury. He termed these symptoms micromercurialism..11 Mercury is also associated with depression, suicidal thoughts,
nervousness, fits of anger, shyness, and emotional outbursts.
In addition to the psychological symptoms associated with exposure to low
doses of mercury, the immune system appears particularly sensitive to this toxin as
well. It responds to mercury with an antigen/antibody reaction in an attempt to
remove the foreign substance. Two types of white blood cells are involved. T-cells
are endowed with special qualities that allow them to migrate to sites of infection
and defend against invading microorganisms, viruses, and toxins. B-cells produce
antibodies specific for the unwanted invader or foreign substance, which circulate
in the plasma.
The immune system's response works like this. When T-cells recognize the
presence of an antigen, they stimulate the B-cells (memory cells) to produce
antibodies to the antigen. The B-cells, along with a special class of T-cells called
helper cells, then surround and engulf the antigen and neutralize it. Once the job is
complete, other T-cells (suppressors) suppress further production of antibodies.
The used-up B-cells, along with the antibodies and toxins or dead germs, are
excreted through the kidneys and feces. An allergic reaction is similar, except that
the B-cell antibodies also cause a release of histamines. Histamines are what
causes the tissue breakdown and red skin reaction.
White blood cells are very sensitive to mercury exposure and as a result,
their numbers at first increase and later, as they die, the numbers will decrease.
Other toxic effects on the white blood cells also result from exposure to mercury.
Release of the migratory inhibitory factor appears reduced, and antinuclear
antibodies are formed, so that the immune system appears to attack itself. And the
respiratory burst of the white blood cells (the mechanism by which white blood
cells attack bacterial invaders) is inhibited.12 Exposure to mercury causes the
chromosomes of white blood cells to break and form unusual combinations and
genetic aberrations.13 14 15 White blood cells from mercury-diseased rats show a
significant decrease in ability to replicate their own chromosomes, and 90% of the
3
Mercury in Dentistry
cells develop autoimmune antibodies for their own nuclei.16 17 Mercury also
suppresses the primary humeral antibody response.18 19 20 21 22
In a preliminary study Dr. David Eggleston demonstrated that both mercury
and nickel dental restorations suppress the quantity of circulating T-cells present in
humans.23 Vera Stejfkal, M.D. of Sweden has documented the immunological
response to mercury in humans. She has even found an adverse reaction in infants
when a mercury preservative (thimerosal) is used with the inoculum. While further
research is badly needed in this new area of science, it is clear that mercury plays a
very important role in immunosuppression. Its adverse effects on human resistance
to diseases and tumors cannot be overlooked.24
The endocrine system is also affected by the accumulation of mercury in
certain critical tissues. Not only does inhalation of this volatile substance allow
transport from the lungs into the bloodstream. In addition, the nasal mucosa can
apparently transport it directly to the brain and pituitary. It is here that critical
hormone balances can be damaged. (See Reproductive Defects)
How Toxic Is Mercury Compared to Other Metallic Compounds?
To answer this question, Sharma and associates studied the cytotoxic effects
of several compounds on chick ganglia. They stated in their conclusions: Our study
showed mercury, cadmium, and lead in decreasing order of toxicity.25
SEVERELY TOXIC MODERATELY TOXIC
MERCURY
CADMIUM
ARSENIC
VANDEX-TIN
SLIGHTLY TOXIC
THALLIUM
ARSENIC
SELENIUM
COPPER
LEAD
ARSENIC
TIN OXIDE
Industrial Exposure
In order to protect workers from excessive exposure to toxic materials, the
governments of all the developed nations and the World Health Organization
(WHO) have adopted adult industrial standards for mercury exposure. In addition
to these industrial exposure standards, many governments have also enacted
4
Mercury in Dentistry
legislation called environmental standards, or simply EPA, to protect the general
populace from excessive pollution.
Environmental standards are strictly enforced in California, and our state
government at the request of the people has placed even more stringent
requirements on many emissions than the federal government has. In the United
States the U.S. EPA standard is the only non-occupational standard, and as a result
it is the only exposure considered appropriate for the majority of the population.
When looking at the question of toxins in dental restorations, it is reasonable to
conclude that restorations should certainly not increase the patients' exposure to
levels of toxic materials that exceed the EPA health standards. Beyond that, it
should be noted that both the U.S. EPA and WHO have stated that no amount of
exposure to mercury can be considered totally harmless, and it is not possible to
establish a level at which no response will be seen.26
Some individuals in society are at higher risk from toxic exposure than
others. Such groups include the elderly, pregnant women, women of childbearing
age (for possible unsuspected or near future pregnancy), infants, children, the
hypersensitive, immunosuppressed, and those already occupationally exposed. The
Occupational Safety and Health Act (OSHA) has recommended no exposure of
fertile women to amounts of mercury greater than 10 micrograms per cubic meter
of air, and pregnant women should be occupationally exposed to no mercury.
Individual Intra-oral Exposure
Although evidence that mercury was leaking from dental fillings was
previously discovered in 1926 by the aforementioned Dr. Alfred Stock, and again
noted in 1979,27 in 1981 Dr. Carl Svare28 partly by chance made a rediscovery that
shocked the dental community. To conduct a series of experiments on the amount
of mercury in expired air, he had asked for volunteers from among his dental
students. One woman waiting at the end of the line saw that it would be some time
before she was to be tested. So she went across the street the have a pizza for
lunch. When she returned, the line was gone and Dr. Svare tested the mercury in
her exhaled breath. Her mercury measurement was so high it blew out his
equipment.
5
Mercury in Dentistry
When he learned that she had just eaten a pizza, he recovered some of the
uneaten pizza and could find no mercury contamination. With further
experimentation, Dr. Svare noted that the student's mercury vapor level began to
drop. He then gave her a piece of rubber tubing and instructed her to chew on it for
a while. He was amazed: her mercury level shot right back up. The other students
were recalled and re-measured after chewing sugarless gum with similar results.
This landmark study became known as the Chewing Gum Study. It led to
subsequent findings that mercury release from fillings increases dramatically by
15-fold whenever the fillings are stimulated by chewing, brushing, hot fluids,
bruxism, etc. Numerous other investigators have confirmed these results.29 30 31 32 33
Low doses of mercury are almost completely absorbed from the lungs before
exhaling. Therefore, Dr. Svare's exhaled air measurements represent only a small
fraction of the dose absorbed by an individual. We also know that personal habits
such as night grinding, gum chewing, and mouth breathing can greatly affect the
rate of release of mercury from fillings. Because of wide variations in such
personal habits, it is not possible with present technology to predict which patients
will release the most mercury. But an average daily dose can be estimated.
In 1985 Dr. Murray Vimy, et al. took the examination several steps further
by subjecting the chewing to a standardization technique and plotting the increase
of mercury release with respect to time.34 35 He discovered that fillings take only 10
minutes to reach maximum output and do not immediately stop releasing when
chewing stops, but rather continue for a period of up to 90 minutes. This was
termed the "cool down" period.
He then began the extremely complicated process of estimating how much
mercury a person might absorb daily from mercury fillings. For the conversion
from intra-oral air exposure to absorbed intake, consideration was given to such
factors as respiratory volume, absorption rate, oral-nasal breathing ratio, frequency
and duration of chewing, and cool down period following stimulation. In each
instance the lowest possible estimate was chosen to avoid overestimating the risk
posed by the release of mercury from fillings. Vimy concluded that by the most
conservative estimate, the average person with 12 fillings would absorb
approximately 11 micrograms per day from the fillings alone.36 37
To put this estimate in perspective I have prepared the following graph. It
compares the EPA maximum daily dose of mercury from: sources other than air,
6
Mercury in Dentistry
air alone(i.e. smog), and all sources combined. Note that the EPA standard is based
on an adult weight of 165 lb (75 kg). To be applicable to small children, it should
be reduced in proportion to their weight.
The most obvious result of
mercury/silver dental implants is an
increase in the individual's exposure to
mercury. This is demonstrated by
elevated blood levels that are measurably
higher for those with fillings than those
without.38 The following graph shows
the findings of three different researchers
measuring intra-oral mercury vapor.
In his reports, Vimy stressed the concept of "average intake" to allow for the
fact that some of the people examined were definitely not average. For example,
Dr. Svare's young dental student was well over 100 µg/m3, where the average
person was measured at 32 µg/m3. Thus, the daily intake for this young woman
would be 3 times 11 or 33 µg of Hg per day.
Sellers discovered an even more disturbing phenomenon. His experiment
involved children aged 11 to 13 with mixed dentition. Of the children with
amalgams, Sellers found 33% with intra-oral levels above 50 µg/m3.39 In fact, 47%
of the children who had 6 fillings or more tested above 50 µg/m3. Sellers failed to
fully appreciate the seriousness of such high exposure levels, however. He
commented that "Such concentration may not be any more dangerous than briefly
walking through a contaminated
workplace --an interpretation
revealing an apparent disregard
for the safety of children. (It is of
interest to note that Sellers denies
writing these words and contends
that the conclusions of his article
were changed after submission to
the Texas Dental Journal40)
7
Mercury in Dentistry
In my opinion, the most important feature of this study is that it clearly
demonstrated children with fewer teeth and fillings rapidly reach higher mercury
vapor levels than adults.
It is important to keep in mind that the industrial standard is not an
environmental standard and was never meant to protect the health of children.
Rather, it is clearly a workplace standard meant for consenting adults who work 40
hours a week and are medically monitored. They are presumably paid a salary
commensurate with the obvious risks to which they are exposed.
It is the policy of the State of California to destroy school buildings that
cannot achieve compliance with the EPA standards. It is unlikely that any informed
parents would give their children permission to play in a toxic waste dump 4 to 10
or more hours daily. Should toxic poisons be placed in their mouths instead?
Sellers' experiment is further flawed since the chewing terminated after only
4 minutes and therefore did not allow the children to chew for the full 10 minutes
necessary to maximally stimulate the fillings. Vimy's previous research had
demonstrated that the dramatic increase in output continues to rise for 10 minutes.
One can only speculate the levels that would have been achieved had the author
allowed the children to reach maximum output. In the United States today many
children chew gum all day. It is clear from the discussion that the author failed to
recognize the inherent medical, legal, and moral liabilities of exposing the children
to such high levels of this toxic material.
Abraham, et al. provided additional information regarding blood levels and
the release of mercury from fillings. In their experiment, baseline blood and breath
air samples were taken after subjects had not eaten or drunk anything for the
previous 12 hours. Then the subjects were required to chew gum for three minutes
at 120 beats per minute, followed by post-chewing blood and breath air samples.
Subjects with amalgam measured higher both before and after chewing than
those without, and there was no change in the no-amalgam group following
chewing. Those with amalgam fillings measured post-chewing levels higher than
prechewing levels in both blood and breath. Abraham, et al. concluded their report
by stating: Given these facts, the small increase in blood mercury levels that is
statistically associated with dental amalgam restorations should be a matter of
concern for dentists as well as for the recipients of these restorations.41
8
Mercury in Dentistry
It should again be pointed out here that three minutes of chewing does not
correspond to normal chewing and would not have allowed the fillings to reach
their maximum output.
Previous studies by Kroncke, et al. and Ott and Kroncke42 43 had failed to
find a connection between blood levels and the number of amalgam fillings,
although they did find that those with amalgam had higher blood levels than those
without. Their work has not been verified by other investigators, and the
preponderance of scientific data suggests that they failed to find correctly.44 There
is also a question about their sampling technique, which may have caused the loss
of mercury from their samples. In addition, blood alcohol was not recorded.
Alcohol will greatly reduce blood levels and perhaps increase tissue levels. Their
experimental group may also have had some additional external exposure to
mercury.
Does Dental Amalgam Contribute Significantly to the
Body Burden?
One way to evaluate this question is to analyze human autopsy tissues for
mercury accumulation. Till sectioned tissues and human jawbone around teeth with
and without amalgam fillings and found high levels of mercury around teeth with
fillings. Surprisingly he found even greater amounts if a gold crown covered an
amalgam.45
The biological half-life of mercury in human nervous tissues appears to be
over 10,000 days (27 years).46 47 Since the brain is sensitive to mercury, many of
the first symptoms of mercury poisoning are neurological and psychological in
nature. The action of mercury on the brain may occur by blocking the metabolism
in nerve tissue which frequently causes irreversible damage.48
Certain areas in the brain tend to collect much more mercury than others.
The pituitary gland which regulates the human hormonal system preferentially
collects mercury at a rate 10 times greater than the brain as a whole.49 It is also well
recognized that mercury has an adverse effect on fetal neurological development.
It can be assumed that if mercury is present and the source is amalgam
fillings, then autopsy tissue samples taken from individuals with amalgam fillings
would contain more mercury than samples from those without fillings. In one of
9
Mercury in Dentistry
the largest human autopsy studies conducted so far, University of Southern
California professor Dr. David Eggleston performed over 100 human brain
biopsies and analyzed them for mercury. The results showed a high positive
correlation between the amount of mercury in the brain and the size and number of
fillings in the mouth. The experiment found a 3- to 4-fold greater occipital lobe
brain burden of mercury for those with an average number of fillings than for those
without fillings.
These results are also particularly significant because they confirm earlier
studies and show unquestionably that dental mercury does escape from fillings, is
absorbed, and does contribute significantly to the total body burden of mercury.50
The U.S. EPA has established the optimum intake of mercury is 0 µg/day!
They have suggested that 30 micrograms is the maximum allowable daily dose of
mercury from all sources, with just 10 of these µg allocated to sources other than
air. All sources and forms of mercury are considered equal and cumulative.
WHO expert committee calculated that the human daily dose of mercury
from various sources is:
Dental amalgam
= 3.0-17.0 µg/day (Hg vapor)
Fish and seafood
= 2.3 µg/day
(methylmercury)
Other food
= 0.3 µg/day (inorganic Hg)
Air & water
= Negligible traces
The WHO also noted that "A specific No-Observed--Effect Level (NOEL) for
mercury cannot be established."51 In other words, because the effects of
mercury poisoning are cumulative and long-term, the only definitely safe exposure
is no exposure at all. We can now definitely state that as a direct and persistent
result of amalgam implants the patient's immune system is altered, gingival tissues
and jawbone adjacent to the tooth are saturated with mercury, and the mercury
content of the brain increases by three- to fourfold. And as a result of extensive use
of this material, silver/mercury fillings are now considered by the World Health
Organization to be the predominant source of human exposure.52 53
10
Mercury in Dentistry
In 1987 an expert committee instructed to review the safety of dental
amalgam by the Swedish Socialstyrelsen (Department of Health) concluded that
from a toxicological point of view, mercury is too toxic for use as a filling material
and dentists should use other materials as soon as they are available. As a first
step amalgam work on women who are pregnant should cease because of danger
of damage to the brain of the fetus.54
Dentists and Personnel Exposure
While the issue of patient exposure is still the subject of intense
investigation, there is no question that dentists are at risk. Let me preface my
remarks regarding the urinary excretion of mercury in dental personnel by quoting
a short excerpt from Goldwater, et al.: Urinary mercury levels may give some
indication of the degree of exposure. They are of limited value in the diagnosis of
poisoning, since high levels can be found in human subjects who are symptom-free,
and low levels in those exhibiting marked evidence of mercurialism. It has been
suggested that, in some cases, failure to excrete mercury is a factor in the
development of poisoning. Those investigators who have studied the subject are in
almost unanimous agreement that there is poor correlation between the urinary
excretion of mercury and the occurrence of demonstrable evidence of poisoning. 55
56
Urinary excretion may, however, provide some information on a group basis
as to degree of exposure. This has been publicly acknowledged at the National
Institute of Dental Research (NIDR) workshop on the biocompatibility of metals in
dentistry.57
As part of the ADA's Health Assessment Program held at ADA annual
sessions in the years 1975 through 1983, the urinary mercury levels of 4,272 U.S.
dentists were measured. The mean level was 14.2 micrograms/liter with a range
from 0 to 556 micrograms/liter. An increase in the mean mercury level was found
to be correlated with increase in age of the office, the practice, and the dentist. The
highest mean was found in general dentists, at 15.3 µg/l, and the lowest was found
in orthodontists, at 3.9 µg/l. Blood samples of l,555 dentists found that the mean
for all dentists was 8.2 ng Hg/ml blood, and the mean for general dentists was 8.8
11
Mercury in Dentistry
ng Hg/ml.58
That is
approximately 12
times greater
than the mean
blood level
of 0.7 ng/ml
Abraham
found for those
with
fillings.59
In the
U.S. the average
urine level
for the general
population is
0 to 5 µg/l, with
above 20
µg/l considered
abnormal. 4
µg Hg/l is
considered
excessive in the
Federal Republic of Germany.60 The U.S. Center for Disease Control has published
the opinion that 30 µg Hg/l urine is the maximum accepted level. 50 µg/l is
associated with load-induced tremors, and 100 µg/l is generally associated with
outright tremors.61 Furthermore, a study by Berlin showed that inhalation of
mercury vapor selectively increased the uptake in the brain.62 The recent animal
study by Vimy shows why there is no blood or urine threshold for mercury which
can be considered totally safe. In Vimy's sheep study, the blood levels remained
low and urine level never exceeded 10 ng Hg/g, yet high levels of mercury were
found accumulated in critical organs.63
In their report on the Biocompatibility of Metals in Dentistry, the NIDR
published the opinion that The distribution of mercury into body tissues is highly
variable and appears to be of little correlation between levels in urine, blood, or
hair and toxic effects. On the other hand, high urinary output on a group basis may
indeed indicate high exposure. If exposure is prolonged, then urinary levels will
eventually drop as the kidneys lose their ability to remove mercury from the blood.
In summary, then, since the ADA Health Assessment Program's studies of
dentists and dental personnel found urinary output 3 to 15 times that of the general
population,64 there seems to be little question that we are excessively exposed. The
following percentages reveal the extent of that overexposure.
19.1% measured over 20 µg/Hg/l
10.9% measured over 30 µg/Hg/l
12
(29,500 U.S. dentists)
(16,500 U.S. dentists)
Mercury in Dentistry
4.9% measured over 50 µg/Hg/l
1.3% measured over 100 µg/Hg/l
( 7,500 U.S. dentists)
( 2,000 U.S. dentists)
For the last 20 years dental offices have been tested for compliance with
various industrial standards. In addition, several statistical surveys of dentist’s
exposure levels have been conducted. Dentist’s offices do not fare too well when
compared to these safety standards. As you may have noted, the U.S. has one of
the highest exposure standards in the world. Despite this, over 10% of dentist’s
dental offices exceed this standard. A 1983 survey of British dental offices found
that 10% of those also violated that country's industrial exposure standard of 50
µg/Hg time-weighted average (TWA).65
Many procedures common to
the practice of dentistry are known to
release mercury vapor. Such routine
duties as condensing, polishing,
grinding, and mixing amalgam will
send an invisible shower of mercury
droplets into the air.66 These droplets
may be inhaled or may fall to the
floor and vaporize. Dental offices
have been studied extensively in the
scientific literature to see how the
handling of mercury affects the ambient level of mercury vapor found in the
workplace. Theoretically, the type of flooring should make a difference. However,
this did not seem to be one of the critical factors.67 68 Research indicates that the
process of mixing, packing, drilling, and polishing a mercury/silver filling will
expose everyone present to
high levels of mercury.69 70 71 72
73 74 75 i
In his lecture at Tuffs in
Boston, Mass., Dr. Patrick
13
Mercury in Dentistry
Störtebecker discussed the Direct Transport of Mercury from the Oronasal Cavity
to the Cranial Cavity as a Cause of Dental Amalgam Poisoning .76 He further
discussed the valveless venous passage of mercury into the pituitary and other
areas of the brain from the nasal passages in his book Silver Mercury Fillings: A
Hazard to the Human Brain.77 Störtebecker confirmed his theory of the nasal
pathway through conducting experiments with dogs.78 The dogs were sacrificed
soon after inhaling low levels of mercury vapor. The graph demonstrates the ability
of the brain to selectively accumulate mercury. Those areas closer to the nasal
passages had considerably more mercury than the areas farthest away.
In an earlier experiment,
Dr. Alfred Stock had studied the
transport of mercury to the brain
via the nasal mucosa by
applying a mercury-containing
ointment to the nasal mucous
membrane during the final
hours of a terminal cancer
patient's life. Postmortem
examination for mercury
content revealed a
considerable accumulation in
that short time in both the
pituitary and frontal brain.
Dr. Stock concluded that the high concentration of mercury in the pituitary
was best explained by the assumption that it was transported there from the
olfactory bulbs, since they too contained a larger quantity of mercury.79 (While
such types of experiments may be criticized by today's standards, they were
considered the norm at that time. Still, the information they provided was virtually
14
Mercury in Dentistry
ignored for 50 years until a young Swedish scientist, Magnus Nylander, D.D.S.,
devised a way to study dentists.)
Our present level of exposure to mercury is associated with many health
problems, most notably birth defects and neurological disorders.80 81 82 83 84 A 1987
study by Sikorski identified a significant positive correlation between mercury
levels in the hair of occupationally exposed women and the occurrence of
reproductive failures and menstrual cycle disorders.85 Recently reported in the
literature is the case of a young dentist, professionally exposed to mercury for 35
weeks during her pregnancy, who delivered a severely brain-damaged infant.86
Could this tragic outcome possibly have been prevented if dentists were more
aware of the hazards of mercury poisoning in their practices?
The authors of the textbook Occupational Hazards in the Health Professions
cautioned against comprehensive amalgam work during pregnancy.87 Koos and
Lango stated as early as 1970 that their research indicated that fertile women
should be exposed to no more than 10 Hg µg/m3, and pregnant women should be
exposed to no mercury at all.88
In this modern day when most offices have several mechanical mixers,
exposure seems to be increasing nevertheless. Some authors have felt that the type
of amalgam capsule is of critical importance.89 Precapsulated mixes appeared to
reduce exposure if handled properly.90 Other investigators have found no
correlation between the care with which mercury is handled and exposure levels.91
It is likely that the use of this material makes exposure inevitable.92
Furthermore, at present no known procedure will permit this material to be
implanted in the mouth and still keep the patient's breath within the EPA standards
for the air.
Clearly, women in dentistry are at the greatest risk from exposure to
this toxic substance. One assistant's death has been reported.93 The United
States Environmental Protection Agency states that Women chronically
exposed to mercury vapor experience increased frequency of menstrual
disturbances and spontaneous abortions; also a high mortality rate was
observed among infants born to women who displayed symptoms of mercury
poisoning.94 It would be interesting, then, to examine the literature for
evidence that dentists and dental personnel are absorbing higher than normal
amounts of mercury.
15
Mercury in Dentistry
Dental Personnel Health Risks
The kidney filters the blood, and as a result chronic exposure to chemicals
might eventually induce kidney damage. A 1988 study by Verschoor, et al.
evaluated the kidney function of 68 dentists (63 men, 5 women) and 64 female
assistants who were apparently healthy, not pregnant, and taking no drugs. They
compared the results of their kidney function analysis to 250 workers known to be
exposed through the workplace to lead, cadmium, or chromium. Their conclusion
was that Dentists and dental assistants appear to have a higher potential risk of
kidney function disturbances than the workers in these industries. Although this
study did not present evidence for changes of renal function parameters in dental
practice in relation to Hg-urine levels below 20 µg/l, it certainly suggests that
dental practice may carry a risk of renal dysfunction. There is a need to assess the
renal hazard of the potential nephrotoxic chemicals used in dental practice.95
Kuntz followed 57 prenatal patients with no known exposure to mercury for
changes in whole blood from initial prenatal examination to delivery and
postpartum hospitalization. The mothers' whole blood total mercury increased
during pregnancy from .79 ppb at initial examination to 1.16 ppb at delivery. This
represents a 46% increase during pregnancy. Mercury has previously been
recognized for its particular ease of crossing the placental membrane. The
umbilical cord blood was also sampled at birth and found to have even higher
levels of mercury at 1.5 ppb.96 After careful analysis of the data, Kuntz concluded:
Previous stillbirths, as well as history of birth defects, exhibited significant positive
correlation with background mercury levels. He further stated that patients with
large numbers of dental fillings exhibited a tendency to higher maternal blood
levels, which agrees with both Ott and Abraham.97
Vimy has confirmed the transport of mercury from fillings to the fetus in
experimental animals (sheep and monkey) and the additional exposure through
mothers milk.98 Berlin has shown the fetal blood content of mercury was raised
dramatically at the end of pregnancy exceeding that of the mother at delivery by a
factor of at least five. Early abortion, premature birth, low birth weight with a
perinatal death have been observed in monkeys.99
16
Mercury in Dentistry
A criticism of the earlier Kuntz study is that the levels of mercury found
were too close to the controls to conclude without further study that a definite
correlation with stillbirths had in fact been proven to exist.
Women Exposed to Mercury Vapor Have a
Higher Incidence of Menstrual Disturbances
Mikhailova, et al. found that 26.8% of women working in a mercury
polluted atmosphere suffered from menstrual disturbances. Marinova, et al. found
that 29% had hypermenorrhea.100 The controls found only 0.3% with the same
condition. Hypomenorrhea occurred in 15.3% of the exposed group and only 0.6%
of the nonexposed group. This could mean that more than 44% of female dental
personnel working under these conditions will suffer from reproductive disorders
due to mercury in the dental office. This hypothesis is corroborated by two other
studies of women occupationally exposed to mercury which found that 36% to
45% will develop these types of disorders within 6 months of employment, a
proportion that increases to 67% within 3 years of employment.101 102
This hypothesis has been further confirmed a recent study of 418 women
working in dentistry who became pregnant during the previous four years. Detailed
information was collected on mercury handling practices and the number of noncontraception menstrual cycles it took the women to become pregnant. Dental
assistants not working with amalgam served as unexposed controls. Women
working in offices with poor mercury hygiene factors took longer to become
pregnant. The fecundability (probability of conceiving in any given menstrual
cycle) of this high exposure group was only 50% of that for unexposed women
after controlling for age, smoking, race, frequency of intercourse, history of pelvic
inflammatory disease, year the attempt began, and occupational exposure to cold
sterilants, x-rays, and unscavanged nitrous oxide. No relationship was found
between the number of amalgam surfaces and in a woman’s own mouth and her
fertility. Unfortunately no intra-oral assessment of mercury exposure was made.103
17
Mercury in Dentistry
The most common symptoms were dysmenorrhea (painful menstruation),
hypermenorrhea, anovulation
(infertility >40%),
and hypomenorrhea. These
symptoms are known to increase in
populations additionally exposed to
lead.104 The relationship between
spontaneous abortion, stillborn
infants, and mercury has also been
confirmed.105
Problems that may develop
in the fetus from maternal exposure
are not always evident at birth. Prenatal exposure to mercury vapor has been
shown to have an effect on brain development.106 Such delayed problems include
diminished learning capacity, muscle spasms, and altered
electroencephalograms.107 Exposure continues to increase if the infant is nursed,
since mercury concentrates 8 fold in breast milk.108 109
Proper Handling of Amalgam
The ADA and others have repeatedly pointed out that dentists are exposed to
large amounts of mercury both in school during their training and in their
profession through the use of this restorative material. In addition, mixed dental
amalgam has been ruled a hazardous substance by the U.S. EPA. Specific
instructions in the disposal and handling of dental amalgam have been given.110 111
112
1)
A no-touch technique of handling amalgam should be used. Direct contact
or handling of mercury, amalgam, or other mercury-containing materials should be
avoided.
2)
All amalgam scraps should be salvaged and stored in a tightly closed
container. They should be covered with a sulfide solution such as X-ray fixer solution.
3)
Skin exposed to mercury should be washed thoroughly.
4)
Precapsulated alloy should be used, and used capsules resealed.
18
Mercury in Dentistry
5)
Water and high-volume evacuation should always be used, both when
removing old fillings and when finishing new restorations. Evacuation systems should
be passed through filters, strainers, or traps, and not exhausted into the office or directly
into the sewer.
6)
A face mask should be used to avoid breathing amalgam dust.
7)
The dental office should be monitored for mercury vapor once a year or
more often if contamination is suspected.
8)
Periodic urinalysis of all dental personnel should be conducted.
Unfortunately these steps are insufficient since they do not protect the
patient or the dentist and the dental staff from elemental mercury vapor and
respirable particles that are created when amalgams are manipulated with highspeed drills and diamonds since the mask that they wear does not protect against
either.
Many skeptics maintain that if mercury were as dangerous a poison as
numerous medical, environmental, occupational, health, and safety agencies have
concluded, then there should be overt symptoms of mercury poisoning in the dental
profession. Although that is not a very scientifically valid approach, it appears to
be a reasonable hypothesis. The next area we will examine, then, will be additional
evidence of mercury poisoning and related injuries in the dental profession.
Allergy/Hypersensitivity
Some authorities believe that mercury/silver fillings are not a problem
except for the rare individual who is hypersensitive to mercury.113 There is no
scientific evidence to support this contention. However, assuming that it were true
for the general public, it would also be true for dental personnel.
A hypersensitive response is an abnormal immune reaction to an allergen.
Mercury is an allergen. Numerous health problems have been related to allergic
reactions to mercury. Idiosyncratic responses to metallic mercury have been
documented since the last century. In 1943 Bass submitted a case report of
urticaria response in a child after receiving dental amalgam fillings.114 Also
documented in the scientific literature are chronic atrophic dermatitis115, contact
dermatitis116 117 118 119, eczematous dermatitis120, multiple polyposis121, generalized
19
Mercury in Dentistry
allergic reactions122 123 124 125, oral lichens planus (62% of those with lichens planus
tested allergic)126 127 128 129, chronic oral ulcerations130, and burning mouth131.
Two studies have examined the risk of hypersensitivity to inorganic mercury
in dental personnel. The first tests were by White and Brandt, who patch tested
dental students with mercuric chloride and silver amalgam to determine their
hypersensitivity.132 As you can see by the table, freshmen tested lower than seniors
in mercury hypersensitivity. The study concluded that exposure during training in
dental school could lead to increased hypersensitivity response in students.
A more recent study by Miller, et al. found an increase in hypersensitivity
corresponding not with
years in school, but rather
with increasing number and
age of the subjects'
amalgam restorations.133
Overall, they found an even
greater percentage of the
171 dental student
participants who tested
allergic/hypersensitive to
mercury.
Miller's study considered freshmen dental students to be representative of
the general public. He found that 31.4% of freshmen tested positive to mercuric
chloride.
Djerassi also tested for allergy and found that of those with amalgams,
16.1% tested allergic, whereas none of the 60 control subjects without amalgams
tested allergic.134
Neuman, a dental professor
and spokesperson for the ADA,
contended at the California Dental
Association meeting in 1987 that
the positive patch test is actually a
chemical burn and is not related to
mercury hypersensitivity.135 The
20
Mercury in Dentistry
protocol of this and other studies has precluded that possibility. The negative
controls for both the Miller study and the Djerassi study found that 0% of those
who had no fillings tested positive for hypersensitivity. (As an interesting side
note, in California it is against the law for tattoo artists to use red dye in their
designs, because it contains mercury. There are reported cases of the development
of hypersensitivity to dental fillings after placement of a red tattoo.136)
Miller concluded that hypersensitivity is apparently related to subjects'
number of amalgam fillings and the length of time they have been in place, rather
than to the number of years spent in the dental profession. The risk of developing
an abnormal response increases with both time worn and number of fillings.
Contact dermatitis has indeed forced a number of dentists out of practice, since
they could no longer wear gloves or handle amalgam. It is considered an
occupational hazard, with approximately 11% of all dentists displaying an allergic
hypersensitivity reaction to gloves.137
Neurological Damage
In a study of 298 dentists, Shapiro measured their mercury levels by X-ray
fluorescence. Of those dentists with greater than 20 µg Hg/liter tissue levels, 30%
had polyneuropathies, while those dentists with no detectable mercury levels had
no polyneuropathies. Shapiro concluded that these findings suggest that the use of
mercury as a restorative material is a health risk for dentists.138
Dr. Magnus Nylander devised a series of experiments utilizing neutron
activation analysis (NAA) to study the mercury content of brain tissues of
amalgam bearers, non-amalgam bearers, and dentists. NAA was the most accurate
method currently known to science at that time to evaluate trace minerals. What he
found in the cases of 7 dentists and 1 dental nurse was that all had a surprisingly
high pituitary mercury content, totally out of proportion to the content found in
other parts of the brain. Values ranged from 135 to 4,000 nanograms Hg per gram
tissue.139 140 He also found in a related study of dentists and dental assistants in
Sweden that they have twice the incidence of brain tumors as non-dental
personnel.141
Table
21
Mercury in Dentistry
Pituitary
1) Dentist
4,040
2) Dentist
3,650
3) Dentist
2,700
4) Dentist
350
5) Dentist
350
6) Dentist
350
7) Dentist
135
8) Assistant
1300
Amalgam bearers 7-77
Cases 9-23 Mean 28
24)
10
25)
5
Occipital
300
84
16
40
5
17
19
18
3-23
11
6
6
Ratio
14:1
43:1
169:1
9:1
70:1
18:1
7:1
72:1
2.5:1
2:1
1:1
The evidence is clear that dentists are exposing themselves, their staff and
their patients to a known toxic material through the use of mercury in dentistry.
One of the principal reasons this has happened is the strong advocacy position of
the American Dental Association in support of the use of this material.
The ADA was formed in 1859 by mercury-placing dentists to support their
belief that mercury fillings were safe. In the last 132 years the organization has
championed the cause of mercury fillings and its spokesmen have on many
occasions made numerous statements proclaiming amalgam's safety. The most
recent and comprehensive article appeared in the April 1990 issue of the Journal of
the American Dental Association.
In response to the numerous false and misleading statements contained in
that article the International Academy of Oral Medicine and Toxicology prepared a
scientifically documented response. That paper is still today the most complete
scientific review of the myths and falsehoods regarding the use of dental amalgam.
For your further information it is available for download from Saveteeth.org and
on the web sight of the International Academy of Oral Medicine and Toxicology at
www.IAOMT.org.
22
Mercury in Dentistry
Responsibility
Who is responsible?
The American Dental Association in 1992 declared their position in response to a
lawsuit (Tollhurst vs. ADA). Their attorneys pleaded: “The ADA has no legal
duty of care to protect the public from allegedly harmful dental materials.
The ADA did not manufacture, distribute or install the amalgam fillings.” The
judge agreed and dismissed the ADA as a defendant in the case.
Dentsply Caulk has informed the
dental profession in their Material Safety
Data Sheet for Dispersalloy,142 one of the
most popular high copper dental
amalgams, of the contraindications for
amalgam use. Their warnings are
dramatically different from the procedures
commonly taught in dental schools, found
in many dental practices and as advocated by the ADA. This information certainly
can be used in court to deflect liability suits away from the manufacturers toward
the dentist.
California, after arguing in court for over 10 years with the California Dental
Association, has won and now requires that dental clinics with 10 or more
employees inform patients who might be exposed to mercury that, “Dental
amalgams contain mercury. Mercury is known to the State of California to
cause fetal brain damage, infertility and birth defects”.
It is clear that few if any mercury-placing dentist give accurate informed
consent or full disclosure to their patients prior to implanting this time-release
mercury filling.
The United States Food and Drug Administration has defined an implant as,
“any substance implanted into a natural or man made body cavity.” The ADA
asked for amalgam to be exempted from this definition. The FDA refused. By law
manufacturer must have proof of implant safety.
23
Mercury in Dentistry
The FDA committee which was suppose to approve amalgam did not
approve mixed dental amalgam. Their explanation was that the finished product
(filling) is manufactured by individual dentists and therefore could not be
approved.
It is safe to say that the burden of responsibility for material selection rests
with the trained professional. The Supreme Court of Sweden ruled in a case of
adverse patient reaction to dental materials that selection of proper materials is the
individual dentist's responsibility and not the government's. If that responsibility is
shirked or ignored, both the patient and dentists' reputation will suffer.
Dr. Vimy's research clearly indicates that the issue of dental filling safety is
a medical issue, not a dental one. It is clear from the research that dental schools
and dentists lack the necessary training or facilities to adequately evaluate dental
materials. Replacement of non-biocompatible materials with more compatible
materials is one viable option however that course is further complicated by the
fact that the patient will be exposed to mercury during the removal unless the
International Academy of Oral Medicine and Toxicology’s Patient Protection
Protocols are followed. Certainly, as a first step, As a first step the profession as a
whole should immediately comply with the manufacturers MSDS
recommendations and the further placement of toxic materials in children and
pregnant women should cease immediately.
Whatever the outcome, failure to act prudently will surely diminish the value
of this profession in the long run. Dentistry's long history of flagrant disregard for
industrial exposure standards must end. Dentisty’s 20-year failure to bring the
dental offices into compliance with the present lenient law has resulted in injury to
patients, dentists and dental staffs.
One can only speculate at this point as to why this failure has occurred.
Certainly professional organizations and educational institutions must share a
significant portion of the responsibility. In the years when I attended the University
of Missouri at Kansas City from 1967 to 1971, the subject of mercury toxicity was
never even mentioned. To this day, few of the facts reviewed in this presentation
are common knowledge among dentists. New graduates are equally unfamiliar
with the problems and issues discussed here. A colleague of mine in France writes,
"It's not easy to speak about the problem of mercury in France." It has never been
"easy" to reject conventional wisdom and follow the path dictated by science and
24
Mercury in Dentistry
knowledge. All that is required is detailed scientific knowledge, moral conviction,
and the courage to be criticized by those who lack the former.
While this paper has focused primarily on mercury, it is important to point
out that several other common dental materials should also be subjected to closer
scrutiny. Many materials in use today have failed to pass even the most elementary
biocompatibility testing. In my own practice I have meticulously attempted to
remove all such agents from my office.
Dr. Max Planck developed the quantum theory of physics in 1901. Albert
Einstein read Dr. Planck's theory and in 1905 used quantum physics to arrive at
E=mc2. Quantum physics has only recently become widely recognized as a valid
scientific theory. After trying for years with only limited success to have his new
concepts accepted by the "established scientific community," Dr. Planck was
quoted as saying, New ideas enter science not by old men considering new data
and arriving at new conclusions, but by old men dying.
It is true that a word to the wise is sufficient, but a fool you can tell a
thousand times. Let us not become a profession of fools, but rather let us listen to
the words of the scientific community. We should abandon materials which do not
meet the highest biocompatibility standards or which increase the patient's body
burden of toxins--for the safety of the patients, the families, and the staff.
I wish to express my sincere thanks to the International Academy of Oral
Medicine and Toxicology for the opportunity to again address this excellent
organization of physicians and dentists on this timely subject, and to Drs. Murray
Vimy and Michael Ziff for expanding my knowledge of the science of dentistry.
Contact the author:
David Kennedy, DDS
Davidkennedy-dds@cox.net
3243 Madrid Street
San Diego, CA 92110
(619) 222-8177
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