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Dental amalgam controversy

The dental amalgam controversy centers around the use of dental fillings containing mercury. An amalgam is a mixture of metals, 50% of which is typically mercury. It has been used in dentistry for nearly 200 years because it is malleable, durable and more affordable than gold or composites. The American Dental Association has supported the use of amalgam since its inception in 1859. Proponents once thought the combination of metals in an amalgam rendered the mercury inert. This is now known not to be the case; mercury vapors do leach from fillings into the body, although their levels are not high enough to cause mercury poisoning.

The ADA's position states that the amount of mercury released by amalgam fillings is negligible (ADA). As of December 2002, FDA investigations reported that, "no valid scientific evidence has ever shown that amalgams cause harm to patients" (FDA) Critics associate long-term exposure to the low levels of mercury vapor with neurodegenerative diseases, birth defects, and mental disorders. There is no debate on the danger of high concentrations of mercury in any form, and both sides agree that amalgam may cause an allergic reaction in mercury-sensitive individuals.

History of dental amalgam

For centuries dentists have been cleaning out decay and filling cavities, using filling material such as stone chips, resin, cork, turpentine, gum, lead and gold leaf. The renowned physician Ambroise Paré (1510 - 1590) used lead or cork to fill teeth. Amalgams were the first true standard filling material. The first people to use amalgams to fill cavities appear to be the French. In 1816 Auguste Taveau developed the first dental amalgam from silver coins and mercury. This early amalgam was low in mercury and had to be heated in order for the silver to dissolve at any appreciable rate. Modern dental amalgams are mixed cold.


One obvious disadvantage of using amalgams for fillings is they look unattractive. The material is black (silver if an abrasive toothpaste is used) and can clearly be seen on, and sometimes behind, a tooth. For this reason, amalgam fillings are seldom used in the front teeth. They are, however, still very popular for use in the back teeth, especially since dental amalgams are generally considered to be tougher wearing than composite fillings. Another advantage of amalgam fillings is the antiseptic properties inherent in them due to the presence of silver and mercury ions. Any microbes present on the surface of the tooth will be killed by the trace amounts of these elements released when the filling is applied; preventing further decay of the tooth. Since teeth are largely composed of inorganic minerals, this is harmless to the tooth.

This assumption has been challenged, since the number and type of composite (or "white") fillings available has been rapidly growing since the 1980s. For the first time in history there are competitors to amalgam, such as the 'Diamond' range of composites, which according to one comparative study were demonstrated to be superior to amalgams in terms of toughness, rate of corrosion ('wear'), three different measures of strength and other measurements. Other more commonly used brands of composite also compared favourably in some aspects, but not in others.

History of controversy

In 1840 the only official dentist organisation in existence, The American Society of Dental Surgeons, which had promoted mercury amalgams since its inception, had members sign a mandatory pledge promising not to use mercury fillings because of fear of mercury poisoning in patients and dentists. It must be noted that in 1840 dentists mixed the amalgam themselves in their office, making the office a source of poisonous levels of mercury.

The American Society of Dental Surgeons however claimed amalgams were toxic in the mouth and should be removed. Such claims have been controversial for over a century because the removal exposes the patient to abundant mercury vapors unless special precautionary measures are employed. These measures cannot eliminate exposure to mercury vapors but can nowadays minimize it. They may include the use of an oxygen mask, rubber dam, extensive rinsing, high volume suction, cutting and sectioning the filling rather than drilling it all out, and other precautions.

In 1856 the American Society of Dental Surgeons disbanded because dentists who supported the use of amalgams deserted the ASDS ranks until it had too few members to exist.

In 1859 the American Dental Association (ADA) formed from dentists who wanted to continue the use of amalgams. Their position is that amalgams were proven to be completely safe and leaked no mercury at all. No such proofs existed in 1859, because the scientific methods of medicine in 1859 were not as advanced, and toxicity of amalgams or exposure to the mixing process could not be proven or disproven. Therefore, no substantial medical studies were funded. The ADA position on the safety of amalgam itself never changed.

Controversy has never disappeared on this subject, with ardent views on both sides, but the mainstream view in most countries (with some exceptions such as Japan, Switzerland, Norway and Sweden) has since 1859 maintained that dental amalgam is not only safe for use but desirable, since it is cheap, easy to use, fairly durable and strong and, above all, fast to insert into the oral cavity, and hence more profitable than alternative materials which need to be layered in and so take longer to place in general.

In California in 2001, in a lawsuit over California Proposition 65 and dental amalgam, Superior Court Judge James A. Robertson II ruled that all dental offices with more than nine employees must provide warnings on the dangers of mercury dental fillings to patients. The wording of the warning was argued between the California Dental Association and Shawn Khorrami, attorney for the plaintiff. The accepted warning follows:

Notice to Patients, Proposition 65: Warning on dental amalgams, used in many dental fillings, causes exposure to mercury, a chemical known to the state of California to cause birth defects or other reproductive harm. Root canal treatments and restorations including fillings, crowns and bridges, use chemicals known to the state of California to cause cancer. The U.S. Food and Drug Administration has studied the situation and approved for use all dental restorative materials. Consult your dentist to determine which materials are appropriate for your treatment.
Efforts continue from some legislators to make amalgam fillings illegal. In 2002, eight members of the U.S. House of Representatives introduced the Mercury in Dental Filling Disclosure and Prohibition Act (Bill H.R. 4163, 107th Congress, 2nd Session, April 10th 2002), which would prohibit any mercury in dental fillings starting in 2007. In an interim period between July 1, 2002 and 2007, it would require labeling of amalgam with the following warning. The bill was referred to a subcommittee and did not emerge.

Dental amalgam contains approximately 50 percent mercury, an acute neurotoxin. Such product should not be administered to children less than 18 years of age, pregnant women, or lactating women. Such product should not be administered to any consumer without a warning that the product contains mercury, which is an acute neurotoxin, and therefore poses risks.


In 1895 the multitude of formulas for making amalgam were standardised:

The gamma-2-phase amalgams contain approximately equal parts 50% of liquid mercury and 50% of an alloy powder containing:

  • 65% silver (Ag)
  • 29% tin (Sn)
  • 6% copper (Cu)
  • 2% zinc (Zn)
  • 3% mercury (Hg)

Around 1970, the ingredients changed for manufacturing cost reasons to the new non-gamma-2 form:

The gamma-2-free amalgams (sometimes referred to as "high-copper" amalgams) contain approximately equal parts 50% of liquid mercury and 50% of an alloy powder containing:

  • 40% silver (Ag)
  • 32% tin (Sn)
  • 30% copper (Cu)
  • 2% zinc (Zn)
  • 3% mercury (Hg)

The possible difference in toxicology between the two has not been studied conclusively. Around the late 1970s, the gamma-2-free amalgam became common. The leaking of poisonous substances other than mercury, or of combined compounds of the various metallic components, has less often been the subject of tests than mercury on its own, which further adds to the lack of conclusive data.


This change in the amalgam formula was introduced without having to undergo FDA approval because amalgams are classified as a device, not a substance. Device modification does not need FDA approval. As far as the U.S. Code of Federal Regulations is concerned amalgams are a prosthetic device.

Amalgam Alloy, (a) Identification. An amalgam alloy is a device that consists of a metallic substance intended to be mixed with mercury to form filling material for treatment of dental caries. (b) Classification. Class II (21 CFR 872.3050 (2001)).

This prevented amalgams from undergoing the testing which had been used for all other dental materials invented since.

Environmental impact

The World Health Organization, OSHA, and NIOSH, all agree that mercury is an environmental poison and have established specific occupational exposure limits.

Mercury enters the environment as a pollutant from various different industries, since it has been applied to many different uses. For details see the article Mercury.

The Environmental Protection Agency has declared amalgams removed from teeth to be toxic waste. Even the American Dental Association warns that amalgam filling material is hazardous to dental office personnel before and after its presence in patients' mouths.

Environmental Health Criteria 118, a report prepared by Dr Lars Friberg, Karolinska Institute, Sweden, and published under the joint sponsorship of the United Nations Environment Programme, the International Labour Organisation and the World Health Organization, in Geneva, 1991, concluded that amalgam fillings constitute the main average exposure risk to humans (3 to 17mcg), exceeding fish and seafood (2.3mcg), other food (0.3mcg), air and water sources combined.

Amalgams and Alternative Medicine

Dental amalgams have been suspected by some medical practitioners, particularly of integrative or alternative medicine, of causing many physical and/or psychological problems. They reason that, since mercury is poisonous, so must be anything in the mouth which contains and releases mercury; hence, that amalgams in the mouth are poisonous. While amalgam fillings are universally regarded as hazardous waste outside the mouth, after removal, and as hazardous material before insertion into the mouth, the dispute rests on whether they can also be hazardous to the health once inside a person's mouth.

Part of the difficulty is that toxicologists have catalogued a great many health effects of mercury poisoning, hence the range of possible symptoms is very diverse and, in addition, all of them can equally be produced by other causes, making it difficult to draw definite conclusions. Hence critics of the view that dental amalgams may cause such symptoms have said that the type of problems attributed to amalgam poisoning tend to be too vague, often comprising multi-systemic effects. While most dentists acknowledge that a small proportion of patients may suffer from local symptoms due to mercury sensitivity/allergy, they would not agree with alternative practitioners who suspect a larger range of local and non-local health effects in a larger proportion of people.

Similarly, some proponents feel that the mercury contained in amalgam fillings is safer than pure mercury compounds due to the difference between a metal and an alloy. Many of the discussions on this topic have centered, historically, on whether the amalgam mixture is stable, or whether any metals are released from the fillings after being placed in the oral cavity. However, the release of mercury, especially in vapor form, was eventually widely accepted to be a process which does take place in the mouths of patients with amalgam fillings, hence the focus of the debate has in recent years shifted to discussing whether the amount released is significant or not. Some integrative and alternative practitioners claim that it is, while most mainstream dental authorities, physicians and chemists maintain that it is too small to cause any symptoms beyond rare cases of local irritation in mercury-sensitive patients.

Various diagnostic methods exist to detect the presence of mercury in the body, and/or the degree of mercury sensitivity, including blood tests, urine tests, stool tests, saliva tests, MELISA tests, lymphocyte sensitivity tests, DMPS or DMSA chelation urine tests, a hair analysis and others. Opinions differ on which of these tests, if any, is the best, although mainstream scientific research tends to place the most weight on chelation urine tests or stool tests when trying to assess chronic levels, or on blood or urine tests when trying to assess recent acute exposure. None of these tests, however, can be linked specifically to mercury of dental origin, except (a) on an epidemiological scale; or (b) through measuring levels before and after dental work. Studies have been attempted to investigate both angles, and results have differed, again fueling the controversy on both sides, since the scientific data remains inconclusive and has not yet proven either safety or danger.

Nevertheless, alternative practitioners, in some cases with tests and in others without, sometimes recommend their patients to consider removing their dental fillings, saying they suspect mercury poisoning from them.

Most dentists, on the other hand, still feel that while there is no denying that, when placing the fillings, both patient and dentist are exposed to a small amount of mercury and mercury vapor, once the alloy has hardened (which takes less than a minute), most of the mercury is captured in the filling and, being bound in the alloy, cannot get out except in small amounts they would not deem significant except for the hyper-sensitive.

Conventional authorities maintain that no medical research has yet provided any conclusive evidence of significant physical problems caused by amalgam fillings. Legal bodies such as 'Consumers for Dental Choice', however, claim to have over 65,000 studies on file implicating amalgam fillings in diverse health conditions, which have been used in various lawsuits, and which were the main contributing factor both to the Californian legislation concerning the issuing of warnings to patients about mercury, and the federal bill introduced in 2002 proposing that amalgam fillings be made illegal after 2006. Critics have described some of these studies as scientifically invalid. The most recent meta-study has concluded that after studies with methodological flaws are discounted, the evidence indicates that amalgams should not be used.

Among modern dentists who are exposed to the mercury and its vapor on a daily basis, no evidence of mercury poisoning has been demonstrably proven. However, some recent research is showing that mercury from amalgams may be affecting some dentists with mild toxicity. Dentists in several large-scale studies performed multiple cognitive and behavioural tests and, compared to a normal population, lagged behind in many areas. In one study this included 14% worse scores in memory, co-ordination, motor speed and concentration, and in others an increased rate of cancer, depression, irritability, chronic fatigue, headaches, tremors, arthritis, infertility and miscarriages.

A study examining the health effects of mercury on dentists was done in the UK and published in the Occupational and Environmental Medicine Journal. This study found that 180 dentists had on average 4 times the urinary mercury excretion levels of 180 people in a control group. Also, dentists were significantly more likely than control subjects to have had disorders of the kidney and memory disturbance. But a direct correlation between urinary mercury levels and the disability was not found. More research needs to be done before a solid conclusion can be reached. The unreliability of urine test in showing lifetime of mercury accumulation rather than recent exposure (and unreliability to measure recent exposure in autistics) has slowed down any kind of research on living humans, and the short life of animals in the classic lifetime exposure tests known as LD50 was not conductive of safety proofs in humans for chronic amalgam exposure.

Alternative dentists (variously known as biological or mercury-free, and in some cases also as holistic and/or homeopathic) sometimes advise patients to have some or all of their fillings removed and replaced with composites. While they may show no evidence that amalgam fillings cause health problems, which is difficult to prove, they sometimes suspect this is the case. More frequently, it may be the patient who requests the removal, as a consumer, whether or not they have received advice, particularly as many dentists may also be reticent to offer any advice when their private views do not coincide with the mainstream view.

Removing all of them at once can cause problems. For this reason, when biological dentists remove fillings, most follow set protocols which include sequential removal, usually of no more than two fillings at one time, or one quadrant.

Any time a filling is drilled out, there is always a risk that the drill will remove too much tooth material, requiring the tooth to be restored with a cap. Another risk is that the dentist may drill too far, hitting the pulp and causing an infection, subsequently requiring the tooth to be treated with a root canal. Removal can involve drilling into the amalgam so more vapors are released than in putting them in.

The alternatives to amalgam fillings usually selected are composites, although for larger fillings other materials may be used, such as porcelain. If the brand of composite is chosen carelessly, they do have drawbacks; they may have to be replaced more often, again causing risk of tooth damage or infection during replacement. However, there are now many different brands available, and the number continues to increase with new research. Those dentists who keep up to date with the latest developments may be aware of which composite materials may be comparable to, or even superior than, amalgams in terms of durability and strength. Usually less of the tooth material needs to be drilled out when placing a composite, as well. For these various reasons, there are proponents of non-amalgam dental procedures who now advocate them on the basis of professional preference rather than for any health reason relating to alleged amalgam toxicity.

The main contention of alternative dentists is that composites are now becoming safe, cheap alternatives to amalgams for normal dental practice, while in some countries, such as Japan, Sweden, Norway and Switzerland, these alternative materials are already the main option for the majority or all of the dentists. Most dentists in the USA and most other countries still maintain, however, that dental amalgam is the best choice of filling material in terms of many factors, such as strength, safety, durability and cost. Hence the dental amalgam controversy continues with strong advocates on both sides.

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