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The 60 Minutes Expose on Dental Amalgam

The following piece is now more of a historical reference since it happened over a quarter century ago, however it serves as a warning of just how easy it can be for “junk scientists” to deceive legitimate news organizations.  In this case, “60 Minutes”, one of the most widely watched and respected  network news organizations of the late twentieth century presented a disgracefully inaccurate news piece that “scared the hell” out of an entire nation.

In December, 1990, the news program “60 Minutes” ran a shocking exposé on the most common dental restoration in the world.  It alleged that silver amalgam,  because of its mercury content, is poisonous and is responsible for many of the diseases that have not yet been cured by medical science.

The protagonist in this piece was a researcher from a respected Canadian university who had done some sheep research to discover the effects of mercury poisoning from silver amalgam placed in the sheep’s’ teeth.  He was followed by other crusaders who linked the use of silver amalgam to Multiple Sclerosis, Alzheimer’s disease, Chronic Fatigue Syndrome and various vague ailments including fatigue, anxiety, insomnia, depression, and loss of appetite. Many people who watched this piece were appalled, and contacted their dentists to have their amalgam restorations removed, or even to have their teeth extracted! This, in turn benefited many dentists. It also lit up the lives of many tort lawyers. Unfortunately, it did not benefit the patients in the least!

After the airing of the program, experts in biochemistry, toxicology, physiology, general medicine and dental medicine descended on these researchers en masse. Their consensus was that this research was poorly done and the results were  misinterpreted and contradictory.  Mainstream researchers and public health experts who looked at this research concluded that it did not prove that amalgam is harmful or that it poses a public health threat as was implied by the Canadian researchers.  On the contrary, the nature of the methodology used in the study as well as the nature of the misinterpretation of the results (and the fact that the amalgam used by these researchers contained a higher proportion of mercury than that used in humans) suggested that the researchers entered into the study with an anti-amalgamist agenda:

In 1991, Murray Vimy and other researchers published a study in the Journal of American Physiology (“Mercury from Dental ‘Silver’ Tooth Fillings Impairs Sheep Kidney Function,” Am J Physiol 1991; 261: R1010-R1014) that investigated mercury’s poisonous effects on sheep. Researchers placed 12 occlusal (top surface) fillings in each of six female sheep and two glass ionomer restorations in two control sheep. Before surgery and at 30- and 60-day intervals after amalgam placement, scientists checked the animals’ renal (kidney) function.

They then evaluated how effectively the sheep cleared a substance called inulin (not insulin), a chemical not metabolized by the body. They found that plasma inulin clearance fell by about 60 percent after 30 days and remained so at the 60-day checkup. Among the control sheep, baseline clearance stood unchanged after 30 days. They concluded that the amalgams damaged the animals’ renal (kidney)function.

But the study drew quick criticism. In a letter to the editor of the journal, professor Richard Malvin from the University of Michigan’s department of physiology and other scientists cited numerous flaws in Vimy’s research methods and analysis. In particular, Malvin and the others wrote, “in these experiments, as the clearance of inulin decreased with time, the clearance of urea increased with time to the point that it actually exceeded the inulin clearance. This is a physical impossibility.”

Also, Malvin recalls today, “they measured two enzymes that did not change [y-glutamyl transpeptidase and alkaline phosphatase]. And that’s evidence of good kidneys, not bad kidneys.” In addition, Malvin says the study’s controls were inadequate. “They should have had six control sheep, not two. And they [the controls] had only one post-amalgam measurement, at 30 days. That’s totally insufficient.”

There was also considerable concern about the validity of using sheep as a proxy for humans in this study.   See box below for details:

The sheep kidney showed 10 to 20 times as much mercury compared with concentrations reported for kidneys from humans with many dental amalgam restorations. However, brain tissue mercury concentrations in the sheep were similar to those in persons with few amalgam dental restorations.

Several factors may explain the relatively higher levels of mercury detected in the sheep kidneys as compared to human kidneys. These factors could include

1) The temporal (timing) relationship of the study to the placement of the amalgam restorations.  The 12 occlusal amalgam dental restorations were placed all at the same time, and the study was initiated immediately upon the placement of those amalgams:

Newly placed amalgam fillings leach much more mercury than those which have been in the mouth for several months, and the tests were conducted immediately after placement of the amalgam.

2) The test animals were followed only briefly: 60 days

3) The chewing patterns of the ruminants (sheep) and the abrasiveness of the ruminant diet are very different from those of humans:

Unlike humans, ruminants chew and grind their teeth constantly.  They wear their teeth down in order to create sharp cutting edges.

4) The organ distribution of mercury in the sheep appears to reflect gastrointestinal uptake of elemental (inorganic) mercury rather than lung uptake of mercury vapor:

Inhaled mercury vapor  accounts for most of the mercury absorbed by the human body from dental amalgam whereas in the sheep almost all of the mercury was absorbed through the stomach.  This was apparent due to the organ distribution of the absorbed mercury.

Therefore, the results of these studies may not be relevant to humans.  

It should be noted here that the experts doubt whether the sheep experienced any kidney damage at all.  The changes reported in the sheep’s  renal function were just the opposite of what happens when kidneys are impaired.  Damage to the kidneys’ filtering function generally causes the blood levels of urea (a waste product) to rise. Instead the blood concentration of urea fell contradicting the researchers’ claims of kidney damage.

Since no dissenting opinions were presented in the 60 Minutes piece,  the airing of the program caused quite a stir, and for a while there was a push to remove dental amalgam from the market.  In the end, nothing of the sort happened.  As of this writing (Summer 2011), amalgam continues to be the most popular material in the world for repairing decayed and broken teeth.  Amalgam has been the premier filling material for over 200 years because it is strong, durable and able to withstand the tremendous pressures of chewing and grinding.  It is also easy to place and has minor decay inhibiting properties.  As to the 60 Minutes Expose on Dental Amalgam, it has never been shown again or even referred to by any main stream media, medical or scientific organization since it first aired.  For more particulars on the debunking of this 60 minutes hatchet job, please click here.

Next Page (Minimata and the safety of eating fish)==>>

Dental Amalgam and Mercury pages 12345678