Dental amalgam has been embroiled in controversy for
long periods during the 160 years since its
introduction. The fact that it is still in use tends to
be regarded as evidence that it has actually passed the
equivalent of a very long clinical trial. This
conclusion may not be well founded. The methods of
medical research are not very sensitive when the problem
is to assess the long-term safety of a substance to
which a large proportion of the population are exposed.
The difficulties encountered in such situations are
particularly well illustrated by the history of research
on tobacco and health, but other examples can be found
in cancer research.
The epidemiology of chronic diseases is in itself a
difficult field of study because of the relatively long
interval between the induction and the manifestation of
such diseases. The classical criteria of causality known
as Koch's Postulates are often hard to apply in
non-infectious, non-acute disorders .
But there is also a structural problem in science
itself, which in many cases tends to prolong the process
of coming to a conclusion. Research operates within a
kind of adversarial system. This is inevitable as there
would be no growth of knowledge without a battle of
ideas. If scientists were perfect people who were only
motivated by love of truth, there would be no great
problem. Personal ambition may be a disturbing factor,
but this is nothing compared to the effects of various corporate
interests on the process of scientific inquiry.
Smoking and Disease
The scientific community has at long last reached
consensus on the seemingly interminable question of
smoking and disease. The tobacco industry has not given
up yet, but their rearguard action is no longer a
serious threat to the integrity of science. Asbestos has
been banned, as well as a fairly large number of other
carcinogens. Are we winning the war on cancer?
Unfortunately not. The partial victories just mentioned
have not been enough, and they have furthermore been
much delayed by the influence of corporate interests on
the scientific process. Robert N. Proctor's book
"Cancer Wars"  is a
great source on this rather unflattering chapter in the
history of science.
The research process is very vulnerable to situations
where "for every Ph.D. there is an equal and
opposite Ph.D." Trade associations know this and
act accordingly. Some 30 years ago the following
appeared in an internal document produced by a cigarette
"Doubt is our product since it is the best means
of competing with the 'body of fact' that exists in the
mind of the general public. It is also the means of
establishing a controversy. If we are successful at
establishing a controversy at the public level, then
there is an opportunity to put across the real facts
about smoking and health."
I am not suggesting that the dental organizations are
as cynical as the tobacco industry, but when they make
pronouncements on the safety of amalgam we should not
forget that they enjoy the privilege of being regarded
as more or less scientific bodies. Everybody knows that
the tobacco industry is protecting its own commercial
interests, but so is every guild from time immemorial.
The dental associations have it in their power to retard
the growth of knowledge about the side effects of
amalgam. In my view, the only decent attitude is to
assist the critics of amalgam in every way in their
efforts to reveal the truth. This does not mean that a
great deal of active professional help will be needed,
since the work will mainly be done by researchers from
medical fields such as neurology, psychiatry, gastro-enterology,
immunology, and several more. If indeed amalgam has
non-trivial side effects, this is an old, neglected
problem of both medicine and dentistry. We have
inherited this from previous generations of scientists,
and our liability is clearly limited to the consequences
of any avoidable delays in the process of uncovery, once
the suspicion has taken root.
Diseases of Civilization
Dental amalgam entered the scene during the
Industrial Revolution. This was an era of unbridled
environmental pollution. Chimneys spewed out smoke from
coal fires which brought fresh mercury into the global
circulation . Mercury compounds
were in widespread medical use. Many of the so-called
diseases of civilization probably emerged, or
became common, during this era. There is a general lack
of reliable information on changes in the incidence of
various diseases over such long periods of time, and
medical researchers often hesitate to draw any
conclusions from historical data. Parkinson's disease,
which is easily recognized in typical cases, was first
described in 1817. Alzheimer's disease was described in
1906 as a relative novelty among people below the age of
60. Multiple sclerosis has a geographic distribution
with a higher incidence in the temperate zones in which
industrialization started. Its epidemiology shows
interesting parallels to that of dental caries .
These are examples of diseases in which a role for
mercury and amalgam has been suggested.
In my own specialty, psychiatry, two important
diseases, schizophrenia and major depression, are
historically remarkable for possible long-term changes
of incidence. Schizophrenia got its modern name in 1911,
but it can be clearly recognized in 19th century sources
back to 1809. It has proved quite hard to find even
earlier descriptions of this very severe, common
disease, which of course suggests that it was relatively
rare before that time. In the 19th century it was often
taken for granted that the rise of "insanity"
was a real phenomenon, and a cause for great concern .
The infamous eugenic movement, which arose 100 years
ago, was motivated by a perceived decline of the mental
health of Western populations.
There is epidemiological evidence of a quite
remarkable rise in the incidence of depressive disorders
during recent decades. Anxiety disorders have probably
also become more common .
Cancer is a complex field, but several forms of
malignancies have certainly increased in incidence
during the present century. Asthma and allergies in
young people show an almost explosive rise at the
The causes of the diseases mentioned above are
largely unknown. It is interesting that genetic
contributions appear to be fairly well substantiated in
many of them, but of course this does not explain why
they have become more common. The fact that something
"runs in families" is relatively easy to
demonstrate, but the crucial factor may nevertheless be
environmental. If the environment deteriorates, genetic
factors of resistance and susceptibility will often
become decisive at the individual level. Tuberculosis
tends to run in families, but still the solution of this
very serious health problem proved to be environmental.
As long as we don't have an obvious chief suspect,
genetics may be playing the role of a red-herring, as in
cancer research .
Why are the causes of many of the major killers and
disablers of humanity unknown? A difficult question, but
two partial answers were suggested at the beginning of
- our methods are not sensitive enough for complex
- it is rather too easy to be thrown off the scent
or delayed by factors having to do with vested
interests or sheer conservatism.
The second of those explanations is clearly relevant
to cancer research, including the tobacco story
But why should the sensitivity be too low?
Adapting the Methods of
Important discoveries don't grow on trees. There is
always an element of surprise in new knowledge, and we
have heard about such things as Serendipity, and the
importance of having a Prepared Mind. On the other hand
we tend to think of "the scientific method" as
composed of rigorous procedures and accepted routines,
which is a quite different angle on the subject. In
medicine many relatively simple problems have been
solved, but the complex ones remain. It may be that our
methods will have to be made more flexible in order to
The traditional medical attitude implies that we
should rather throw away a few babies with the
bath-water than accept a spurious causal relationship.
This may look like a prudent and responsible attitude,
worthy of a true scientist, but it may in fact be too
conservative for today's problems. We all, collectively,
pay a price if the rules are too rigid and confining,
first of all by having to wait longer than necessary for
a solution, but also more directly by supporting
research that is handicapped by mistaken methodological
notions. In my opinion medical research will have to
draw some general conclusions from the tobacco story.
It is important to realize that research is not
objective in such a way that the truth will force itself
upon you, willy-nilly, if you just abide by the rules.
That is of course one reason why money from the tobacco
industry is not welcome in the world of science
. But irrespective of the source of funding, it
is a waste of both time and money when people are
looking for something they rather hope not to find, as
can be the case with serious side effects of dental
amalgam. This simply won't work in actual practice, and
scientific progress would be much better served if we
gave all the money to researchers who are biased against
amalgam! No amount of research can ever prove
that a foreign substance which is implanted in the body
will have no adverse effects.
Side Effects and
Even the least toxic of drugs have serious side
effects in some cases, so why should mercury be an
exception? If none have been found so far, we shall
probably have to change our approach to the problem. A
first step in this direction would be to start
collecting case reports of suspected side effects, as is
routinely done with drugs. There is traditionally a
disdainful attitude to "anecdotal evidence" in
medicine. However, the safety of drugs and medical
interventions cannot be monitored without an input of
anecdotal material. This very important function would
be paralyzed if controlled studies were to be required
as evidence throughout. There is little or no discussion
about these things, but the necessity of case reports is
tacitly accepted by everyone concerned.
Side effects of drugs usually appear rather promptly,
which makes them relatively easy to recognize. When the
drug is discontinued, the side effect will fade away,
which confirms that there was a causal relationship.
Catching and reporting a side effect is often as simple
as that. With amalgams the time scale is rather
different, and it is often impossible to establish any
significant temporal relationship between amalgam
placement and the emergence of symptoms. The research
problems are therefore quite similar to those of
carcinogenesis, but if amalgam effects are reversible,
we still have the opportunity to observe what happens
after amalgam removal. This is where the
defenders of amalgam have invoked placebo effects in
order to explain the very numerous reports of remarkable
results in cases with long-standing symptoms.
The placebo concept came into prominence after WWII
and seems to have been accepted without much resistance
as a kind of universal principle that would apparently
account for a very wide range of phenomena for which
medicine lacks a scientific explanation. There is a
diffuse medical tradition which tells of the remarkable
powers of placebo, and the need to be critical of such
stories is rarely recognized. Some of the original work
on placebo has turned out to be of very doubtful quality
. However, nobody could seriously maintain that
a mere placebo treatment is enough to bring about
permanent improvements in any illness of long duration,
except in very rare cases. There is simply no scientific
basis for this. The placebo argument has the added
disadvantage of being a patronizing insult to the
intelligence of those people who have recovered from
Nobody knows exactly what the effects might be of
chronic low-dose mercury exposure in sensitive
individuals. Today dental amalgam is a dominant source
of such exposure in the West. In my opinion medicine and
dentistry will both have to change their attitudes to
this problem. The scientific debate has been much too
defensive. It cannot yet be ruled out that mercury from
amalgam is partly responsible for some of the health
problems which have emerged as so-called "diseases
of civilization" during the last 150 years. This is
a scientific problem of the highest order, and our
treatment of this will be of crucial importance for the
future goodwill of the health sciences.
 Dalén, P. (1969) Causal
explanations in psychiatry: A critique of some current
concepts. Brit J Psychiat 115, 129-37. I am offering
this old reference because to my knowledge the
discussion of Koch's postulates has not changed very
much since I wrote this paper.
 Basic Books, New York, 1995. See also an
on-line interview with Dr. Proctor at http://www.trimaris.com/~ussw/bc/bcwars.html.
 Proctor 1995, page 110.
 Goldwater, L.J. (1971) Mercury in the
environment. Scientific American 224(5), 15-21; Airey,
D. (1982) Contributions from coal and industrial
materials to mercury in air, rainwater and snow. Sci
Total Environ 25, 19-40; Lindqvist, O & Rodhe H
(1985) Atmospheric mercury - a review. Tellus 37B,
 Craelius, W. (1978) Comparative epidemiology
of multiple sclerosis and dental caries. J Epid Comm
Hlth 32, 155-65.
 Torrey, E.F. (1980) "Schizophrenia and
Civilisation", New York, Jason Aronson; Hare, E.H.
(1988) Schizophrenia as a recent disease. Brit J
Psychiat 153, 521-31.
 Hagnell, O. et al. (1982) Are we entering an
age of melancholy? Psychol Med 12, 279-89.
 Proctor, op. cit., ch 10.
 See for instance several indignant comments
(editorial, news, letters) on a proposed donation of
tobacco money to Cambridge University (British Medical
Journal vol 312, No. 7027, 23 March 1996). The editorial
started as follows: "Most people would agree that
Cambridge University would be ill advised to launder
money for a Colombian cocaine cartel."
 Kienle, G.S. (1995) "Der sogenannte
Placeboeffekt", Stuttgart, New York; Schattauer.