Introduction
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 critera 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
company.
"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
Civilisation
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 civilisation
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 present time.
Genetics
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 this paper:
- our methods are not sensitive
enough for complex problems,
- 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
Science
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 tackle this.
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
"Anecdotal Evidence"
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 paralysed 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.
Placebo?
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 serious illness.
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
civilisation" 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.
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