Amalgam (Silver) Fillings

/Home/Specific Dental and Oral Conditions/Mercury Fillings

Amalgam (Silver) Fillings

Summaries of the latest research concerning amalgam fillings
By Hans R. Larsen MSc ChE
International Health News

Mercury sources and toxicity
ROCHESTER, NEW YORK. Mercury is a highly toxic metal associated with damage to the kidneys and central nervous system. Mercury vapour is emitted from volcanoes, coal-burning power stations, and municipal incinerators and returns to the earth through rain contaminated with metallic mercury. Metallic mercury is methylated to methyl mercury in oceans and lakes and enters the food chain via fish and other seafood. Long-lived predator fish such as shark, swordfish, tilefish, king mackerel, and pike and bass in fresh water are the main sources of methyl mercury. Dental amalgams are an important source of mercury vapour and the vaccine preservative thimerosal is a significant source of ethyl mercury.

Researchers at the University of Rochester School of Medicine recently published a review of what is currently known about mercury toxicity. Among the highlights:

Mercury vapour, methyl mercury and ethyl mercury all target the central nervous system and mercury vapour and ethyl mercury also target the kidneys. Inorganic (metallic) mercury primarily targets the kidneys and stomach.
Chelators such as DMSA are effective in removing all forms of mercury from the body, but cannot reverse central nervous system damage.
The allowable or safe intake of mercury has recently been reduced to 0.1 microgram/day per kilogram of body weight.
The concentration of mercury in the brain, blood and urine correlates with the number of amalgam fillings in one's mouth. The concentration increases markedly with increased chewing. Long-term use of nicotine gum by people with amalgam (silver) fillings may increase levels by a factor of 10, thus approaching occupational safety limits.
There is concern, but no clear evidence, that mercury emitted from amalgam fillings may cause or worsen degenerative diseases such as ALS, Alzheimer's disease, multiple sclerosis, and Parkinson's disease.
Ethyl mercury (thimerosal) is used as a preservative in vaccines. Recent concerns about its toxicity have caused US authorities to take steps to remove it by switching from multi-dose vials to single-dose vials that do not require a preservative.
A recent move by power companies to replace mercury containing pressure-control devices for domestic gas supplies has led to numerous spills of mercury in homes. Some 200,000 homes were affected in one recent incident. The liquid mercury is difficult to remove and gives off highly toxic vapours, which are particularly harmful to infants and children.
Several studies have found an association between mercury exposure and cardiovascular disease, but other studies have failed to confirm the connection.
Clarkson, Thomas W., et al. The toxicology of mercury Ò current exposures and clinical manifestations. New England Journal of Medicine, Vol. 349, October 30, 2003, pp. 1731-37

Editor's comment: The review makes it clear that exposure to mercury is detrimental, but hard to avoid. Nevertheless, avoiding the placement of new amalgam dental fillings and gradually replacing old ones with composite fillings, avoiding gum chewing if amalgam fillings are present, and limiting the intake of fish with high mercury levels are all steps that can be taken by everyone. It is important to realize that consuming just one 7 oz (198 grams) can of tuna per week translates into a mercury intake of 0.1 microgram/day of mercury per kilogram of body weight Ò equivalent to the currently recommended maximum daily intake.

ADA fighting the mercury battle
GAITHERSBURG, MARYLAND. The American Dental Association (ADA) has launched an advertising campaign to discourage patients from having their amalgam (silver) fillings removed. Many patients and sometimes even their physicians believe that mercury, the main component of amalgams, plays a role in promoting such varied diseases as Alzheimer's, multiple sclerosis, and autism. The ADA says the evidence is not there and their Code of Ethics forbids dentists from advising their patients that there could be a link. Scientists at the University of Milan disagree with the ADA and point out that several studies have confirmed that mercury from amalgam dental fillings does enter tissues and that the mercury content of brain, thyroid, kidney, and pituitary gland tissue is proportional to the number of amalgam fillings. They conclude that the health effects of amalgam fillings are not at all clear and need further investigation. German researchers point out that some of the composite materials used in the replacement of amalgam fillings may in themselves be toxic.
Larkin, M. Don't remove amalgam fillings, urges American Dental Association. The Lancet, Vol. 360, August 3, 2002, p. 393
Guzzi, G, et al. Should amalgam fillings be removed? The Lancet, Vol. 360, December 21/28, 2002, p. 2081
Editor's comment: Mercury and removed amalgam fillings are classified as hazardous materials and require extreme caution in disposal. Why they would be hazardous outside the mouth, but not inside defies comprehension. It is also a scientifically proven fact that the blood level of mercury is twice as high in dentists as in non-dentists. This fact and the fact that savvy patients don't want mercury in their mouths is no doubt what is leading many dentists to put a, albeit discrete, sign in their waiting rooms "Mercury-free practice"!

Fish, mercury, and heart disease
BALTIMORE, MARYLAND. Several studies have shown that regular fish consumption protects against cardiovascular disease. Other studies have shown that consuming mercury-contaminated fish increases the risk of coronary heart disease. The beneficial effect of fish consumption is believed to be due to the presence of the omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the tissue of fish and shellfish. Two recent studies have attempted to answer the question "Are the beneficial effects of fish oils (EPA and DHA) outweighed by the negative effects of mercury"?

The first study, carried out by a team of researchers from eight European countries, Israel and the United States, involved 684 men who had suffered a first non-fatal heart attack and 724 matched controls. All participants had their mercury level measured in toenail clippings and their level of DHA measured in a fat tissue sample taken from the buttock. Participants with a mercury level of 0.66 mcg/gram were found to have twice (odds ratio of 2.16) the risk of having a first heart attack when compared with participants having a mercury level of 0.11 mcg/gram. This risk assessment was arrived at after adjusting for age, DHA level in adipose tissue, body-mass index, waist:hip ratio, smoking status, alcohol intake, HDL cholesterol level, diabetes, history of hypertension, family history of heart attack, blood levels of vitamin E and beta-carotene, and toenail level of selenium.
The research team also found that participants with a high (0.44% of total fatty acids) fat tissue content of DHA had a 41% lower risk of having a first heart attack than did those with a low (0.10% of total fatty acids) fat tissue level of DHA. This risk assessment was arrived after adjusting for all other known risk factors including toenail mercury level.
The researchers point out that the main sources of mercury are occupational exposure (dentists), exposure to silver-mercury amalgam in dental fillings, and fish consumption. They conclude that the health benefit of fish consumption is significantly diminished if the fish is high in mercury. They also confirm the cardioprotective effect of fish oils (DHA).

The second study was part of the Health Professionals Follow-Up Study begun in 1986 as a cooperative venture between the Harvard School of Public Health, the Brigham and Women's Hospital, and Harvard Medical School. The study involved 33,737 male health professionals who had toenail clippings analyzed for mercury in 1987. After 5 years of follow-up 470 participants had been diagnosed with coronary heart disease. The researchers observed that dentists, who are habitually exposed to mercury, had toenail mercury levels (0.91 mcg/gram) that were twice as high as the levels found in non-dentists (0.45 mcg/gram). They also found a direct relationship between fish consumption and mercury level with participants consuming an average of 357 grams (3/4 lb) of fish per week having a level of 0.75 mcg/gram while those who consuming 145 grams (1/3 lb) per week had a level of 0.29 mcg/gram. After adjusting for age, smoking and other risk factors for heart disease the researchers conclude that there is no clear association between total mercury exposure and the risk of coronary heart disease, but that a weak relation cannot be ruled out.
Guallar, E, et al. Mercury, fish oils, and the risk of myocardial infarction. New England Journal of Medicine, Vol. 347, November 28, 2002, pp. 1747-54
Yoshizawa, K, et al. Mercury and the risk of coronary heart disease in men. New England Journal of Medicine, Vol. 347, November 28, 2002, pp. 1755-60
Bolger, PM and Schwetz, BA. Mercury and health. New England Journal of Medicine, Vol. 347, November 28, 2002, pp. 1735-36


Editor's comment: The two studies clearly do not agree as to whether high mercury levels are associated with an increased risk of coronary heart disease. I am inclined to believe that they are. Furthermore, there is compelling evidence of significant associations between high mercury levels and Alzheimer's disease, Parkinson's disease, congestive heart failure, kidney damage, hearing loss, and high blood pressure. So definitely, mercury, from whatever source, is a very bad actor and should be avoided. The joint European/Israeli/US study clearly confirms that DHA (fish oil) is protective against a first heart attack, so regular consumption of low-mercury-level fish is still a healthy option. An alternative approach to obtaining DHA (and EPA) on a regular basis is to supplement with 1 gram/day of a high quality, molecular distilled, non-rancid fish oil containing a minimum of 220 mg EPA and 220 mg DHA. Reliable sources of such fish oils can be found at www.consumerlab.com/results/omega3.asp and at www.coromega.com
To be on the safe side it is best to eat fish and shellfish with an average mercury content of less than 0.10 ppm. Unfortunately, there are not too many species left that fulfill this requirement. King crab, scallops, catfish, salmon (fresh, frozen and canned), oysters, shrimp, clams, saltwater perch, flounder, and sole are all good choices. Salmon is my favourite because of its combination of a low mercury content with a high level of beneficial EPA and DHA. The following fish species should be avoided: tilefish, swordfish, king mackerel, shark, grouper, tuna, American lobster, halibut, pollock, sablefish, and Dungeness and blue crab. Limited sampling of the following also indicated high mercury levels: red snapper, marlin, orange roughy, saltwater bass. Atlantic cod, haddock, mahi mahi, and ocean perch have mercury levels around 0.18 ppm, so should be eaten in moderation.

More information is available online.