A 2006 Zogby International poll of 2,590 US adults found that 72% of respondents were not aware that mercury was the main component of dental amalgam, and 92% of respondents would prefer to be told about mercury in dental amalgam before receiving it as a filling. A 1993 study published in FDA Consumer found that 50% of Americans believed mercury filings caused health problems. Some dentists, including one member of the FDA's Dental Products Panel, have suggested that the factors obligate dentists to apply the doctrine of informed consent by notifying their patients that amalgam contains mercury.
Dentists who advocate the use of amalgam point out that it is durable, cheap, and easy to use. On average, resin composites last only half as long as mercury amalgam, although more recent studies find them comparable to amalgam in durability, and dental porcelain is much more expensive. However, the gap between amalgam and composites may be closing. Further, concerns have been raised about the endocrine disrupting (in particular, estrogen-mimicking) effects of plastic chemicals such as Bisphenol A used in composite resins.
In addition to health and ethics issues, opponents to mercury amalgam fillings point to the negative externalities of water contamination and environmental damage of mercury, especially since its use by dentists goes largely unregulated in many places, including the United States. The WHO reports that mercury from amalgam and laboratory devices accounts for 53% of total mercury emissions. Separators may dramatically decrease the release of mercury into the public sewer system, where dental amalgams contribute one-third of the mercury waste, but they are not required in the United States.
A Swedish study of autopsies examined the mercury levels in brains and kidneys and found a strong correlation with the number of amalgam fillings. A German study found that mercury urinary excretion was significantly higher in those with mercury amalgam fillings.
Research on monkeys has shown that mercury released from dental amalgam restorations is absorbed and accumulates in various organs such as the kidney, brain, lung, liver, gastro-intestinal tract, the exocrine glands. It was also found to have crossed the placental barrier in pregnant rats and proven to cross the gastrointestinal mucosa when amalgam particles are swallowed after amalgam insertion or after removal of old amalgam fillings.
Various diagnostic methods exist to detect the level of mercury in the body, including blood tests, urine tests, stool tests, saliva tests, DMPS or DMSA chelation urine tests, hair analysis and others. Opinions differ on which of these tests, if any, is the most accurate, 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.
The degree of accuracy which can be expected from urine based mercury tests given the observations cited above (outlining the drop in mercury excretion levels, after two years, in children with amalgam fillings despite a constant or increased magnitude in the level of mercury exposure) indicates the possibility of clear limitations in the efficacy of urine based mercury tests as an accurate statistic for the purposes of dental studies.
Further, none of these tests can link mercury levels to dental amalgams for methodological reasons, except (a) on an epidemiological scale; or (b) through measuring levels before and after dental work. Studies have investigated both angles and results have differed, fueling the controversy since the scientific data remains inconclusive and has not yet proven either safety or danger.
Potential amalgam-induced health risks which have been studied by researchers include those related to allergy as well as toxicity. In 2002, the Food and Drug Administration issued a statement on dental amalgam which asserted that "no valid scientific evidence has shown that amalgams cause harm to patients with dental restorations, except in the rare case of allergy". A 1991-1997 study of 3162 patients in Sweden and Germany found that 719 of those with mercury fillings, or 23 percent, tested positive for systemic allergic sensitivity to inorganic mercury on the MELISA lymphocyte proliferation test. In a smaller group of 85 patients who suffered from symptoms resembling Chronic Fatigue Syndrome and had their amalgams replaced with composites and metal-free ceramics, "over 78 percent reported improvement in health status as compared to the period prior to metal removal." A paper published as part of a 1991 National Institutes of Health conference on side-effects of dental restorative materials reported a 22.53% incidence of allergy in subjects who had amalgam fillings for more than five years. Despite these findings, the ADA claimed as recently as 2004 that there had been less than 100 reported cases of allergic reactions to amalgam filings.
The Fédération Dentaire Internationale performed a meta-analysis of the literature on mercury toxicity and concluded that there is no documented scientific evidence to show adverse effects from mercury in amalgam restorations except in extremely rare cases of mercury hypersensitivity.
In 2001, the United States National Health and Nutrition Examination Survey of 31,000 adult Americans, NHANES III covering 1988-94, which cost $120 Million, is owned by the Centers for Disease Control (CDC) and published by the National Center for Health Statistics (NCHS) and is statistically valid for all 180,000,000 adult Americans found that the number of dental fillings was significantly correlated to incidence of cancer, thyroid conditions, mental conditions, diseases of the nervous system including MS, diseases of the respiratory and genito-urinary systems, and disorders of the eye, circulatory and respiratory systems. At the time of the survey (1988-94), the vast majority of dental fillings placed were silver amalgam. However, the United States FDA, various supreme court judges and others have determined that correlation does not sufficiently demonstrate causation.
Ten years earlier, unrelated to NHANES III and before the NHANES/Dental Filling correlations, in 1991 the United States Food and Drug Administration concluded that “none of the data presented show a direct hazard to humans from dental amalgams.”. The Food and Drug Administration in 2008 subsequently issued an advisory warning pregnant women and children about dental amalgam containing mercury, and posted this warning on their website. Again unrelated to NHANES III, on February 18, 2003, the New York Supreme Court dismissed two amalgam-related lawsuits against organized dentistry, stating the plaintiffs had “failed to show a 'cognizable cause of action'.” The plaintiffs blamed the ADA, the New York Dental Association and the Fifth District Dental Society for deceiving the “public about health risks allegedly associated with dental amalgam. A 2003 monograph on mercury toxicity from the World Health Organization concluded that:
Other lesser findings were reported, including a cross-sectional study in which cognitive function was not related to the number or surface area of occlusal dental amalgams, a case-control study in which patients with numerous amalgam fillings exhibited higher levels of neurological symptoms than the controls, and a study of self-referred patients who believed they were suffering ill-effects from dental amalgams which found no correlation between number of dental fillings and symptomatology, but higher mean neuroticism than two comparison groups (the authors concluded that self-referred patients with health complaints attributed to dental amalgam are a heterogeneous group of patients who suffer multiple symptoms and frequently have mental disorders).
Two recent randomized clinical trials in children discovered no statistically significant differences in adverse neuropsychological or renal effects observed over the five-year period in children whose caries were restored using dental amalgam or composite materials, although one study could not rule out the possibility of a small adverse effect on IQ in children with amalgam. In contrast, one study showed a trend of higher dental treatment need later in children with composite dental fillings, and thus, claimed that amalgam fillings are more durable. However, a subsequent study published in JAMA cites increased mercury blood levels in children with amalgam fillings. The study states, "during follow-up [blood mercury levels were] 1.0 to 1.5 μg higher in the amalgam group than in the composite group." EPA considers high blood mercury levels to be harmful to fetus, and also states that "exposure at high levels can harm the brain, heart, kidneys, lungs, and immune system of people of all ages." Currently, EPA has set the "safe" mercury exposure level to be at 5.8 micrograms of mercury per one liter of blood. While mercury fillings themselves do not increase mercury levels above "safe" levels, they been shown to contribute to such increase. However, such studies were unable to find any negative neurobehavioral effects.
The American Dental Association (ADA) has asserted that dental amalgam is safe since its foundation in 1859. In its advisory opinion to Rule 5.A. of the ADA Code of Ethics, it has also held that, "the removal of amalgam restorations from the non-allergic patient for the alleged purpose of removing toxic substances from the body, when such treatment is performed solely at the recommendation of suggestion of the dentist, is improper and unethical". According to the Boston College Law School study, "A dentist who is found guilty of violating the ADA Code of Ethics can be sentenced, censured, suspended, or expelled from the ADA" and the "ADA forbids its dentists from suggesting mercury removal under threat of license suspension". The same study pointed out that state dental associations and disciplinary boards have "not only adopted the ADA's position as a matter of routine" in proceedings which have sanctioned anti-amalgam dentists or stripped them of their licenses in California, Maryland, Arizona, Colorado, and Minnesota, but in many cases "the board members themselves often belonged to the ADA as well". A 2002 article in the Atlanta Journal and Constitution reported allegations by anti-amalgamists that the ADA had effectively imposed gag rules which forbade them from discussing their positions with patients. The Boston College Law School study also cites proceedings in which an Arizona dentist, "is facing sanctions for advocating alternative materials", a California dentist lost his license, "for running an advertisement entitled: "Mercury Emission from Silver Filings Unsafe by Government Standards", and a Maryland dentist, "was sanctioned for writing an article on mercury amalgam removal". More recently, the ADA has entered into litigation "aimed at defending its reputation and discouraging further lawsuits by patient-plaintiffs against mercury amalgam".
In response to studies which assert amalgam safety, anti-amalgam groups, such as the International Academy of Oral Medicine and Toxicology (IAOMT), state that these studies are poorly designed and raise ethical questions. An analysis of the data collected during the studies showed that the authors of the studies ignored the drop in mercury excretion, after two years, in the urine in the children with amalgam fillings, even though the mercury exposure from amalgam remained the same or increased. This is explained in a response by Dr. Boyd Haley, to the 2006 publication, in JAMA, of the NIDCR-funded children's amalgam study. According to Haley, this is evidence that these children are losing the ability to excrete mercury with increased exposure. This observation points to a strong limitation in the use of mercury concentrations within urine as an indicator of mercury exposure from amalgam (and, potentially, as an indicator of mercury concentration within the bloodstream).
Better dental health overall coupled with increased demand for more modern alternatives such as resin composite fillings (which match the tooth color), as well as public concern about the mercury content of dental amalgam, have resulted in a steady decline in dental amalgam in developed countries, though overall amalgam use continues to rise worldwide. Given its superior strength, durability and long life relative to the more expensive composite fillings, it will likely be around for many more years to come.
Some practitioners may also recommend that patients with amalgam fillings have them removed and replaced, particularly if the patient is experiencing the symptoms that they attribute to the use of amalgam. These professionals recommend that unprotected amalgam removal should be avoided even in routine dental procedures to avoid exposure to mercury vapor and amalgam particulate matter.
Organizations opposed to amalgam use, such as Consumers for Dental Choice, claim to have over 65,000 studies on file implicating amalgam fillings as the cause of a diversity of health disorders. These studies have been used in various lawsuits, and were the main contributing factor to the passage of Californian legislation concerning the issuing of warnings to patients about mercury, and to the federal bill introduced in 2002 proposing that amalgam fillings be made illegal after 2006. That has not happened.
Consumer Reports magazine, among others, claims that the connection between many of these diseases and amalgam fillings is solely revenue generating propaganda. Consumer Reports told its readers on several occasions that “if a dentist wants to remove your fillings because they contain mercury, watch your wallet.”
A study examining the health effects of mercury on dentists in the UK published in the Occupational and Environmental Medicine Journal concluded that 180 dentists had on average 4 times the urinary mercury excretion levels of 180 people in a control group. Dentists were significantly more likely than control subjects to have had disorders of the kidney or memory disturbance. No direct correlation between urinary mercury levels and the disability, however, was found. Urine testing is unreliable for showing lifetime mercury accumulation rather than recent exposure.
In the 2005 lawsuit Barnes vs. Kerr, the dentist David Barnes brought action against the Kerr Corporation, a major manufacturer of dental amalgams. This suit was originally decided in the Circuit Court for Bedford County and reviewed by Sixth Circuit of the United States Court of Appeals. Barnes argued that his alleged mercury poisoning was caused by exposure to toxic mercury vapors, and that Kerr Corporation's amalgams were the major source of this poisoning.
Barnes' suit alleged that his exposure came from three sources. The first was "mercury vapor and mercury contained in amalgam particulate inhaled when removing existing amalgam from the teeth of patients". The second was "contaminated office air due to a variety of sources, including mercury released during trituration of capsules, opening of triturated capsules, free mercury that may have leaked during transport, and particulate released into the office air during amalgam removal". The third source was "was mercury vapor and mercury particulate generated during the placement of new amalgams".
Barnes' office was found to be contaminated with mercury by the Tennessee Occupational Health and Safety Administration (TOHSA) , even after it had been thoroughly cleaned, and mercury droplets were found in the machine he had used to mix amalgam capsules. An industrial hygienist found that "89% of the surfaces in Barnes’s office still showed traces of mercury", even after two intensive cleanings.
Kerr Corporation argued that they had not manufactured a majority of the amalgams Barnes had removed, that the contamination of Barnes' office, "could have come from sources other than leaking capsules", and that Barnes could not have been exposed to mercury during the placement of amalgams because of the methods he used.
Kerr Corporation's amalgam capsules bore prominent warning labels in capital letters stating that they "CONTAIN[ED] METALLIC MERCURY" and featured a skull and crossbones next to the word "POISON". A detailed warning enclosed with the amalgam capsule described mercury as a "hazardous ingredient" and listed potential health hazards associated with exposure including nervous irritability, weakness, tremors, gingivitis, erethism, greying of the lens of the eye, nephrotoxic effects, and aggravation of kidney disorders. This full text of the warning read, "WARNING ... Alloy amalgam capsule products contain mercury. Since mercury is a potentially hazardous substance, proper care should be taken to prevent exposure to mercury. These preventative measures include the wearing of gloves, good ventilation, the use of an enclosed amalgamator, proper disposal of capsules once they have been activated and used, and the use of HGX or similar-type mercury absorbing chemicals in the event of spillage. Infrequently capsules may leak mercury and, as a consequence, the above precautionary measures should always be utilized".
The district court held that the testimony of Barnes' expert witnesses in support of "a strong minority view that dental amalgam containing mercury is both unreasonably dangerous and hazardous to human health" was admissible. The district court decided in favor of Kerr Corporation because Barnes had "not demonstrated that his injuries would have occurred ‘but for’ exposure to Kerr’s dental amalgam product". They also ruled that the numerous warnings provided by Kerr "more than adequate [because] ...[r]easonable minds could not differ as to their sufficiency". Barnes' suit against Kerr Corporation was dismissed because he had been warned that amalgam was poisonous and that its use could result in the contamination of his office, and because he could not prove that the majority of the amalgam which had contaminated his office had been manufactured by the Kerr Corporation.
Environmental risks are mitigated provided that amalgams are disposed of properly. ISO has issued standards regarding the proper handling and disposal of amalgam waste, and legislation to enforce these standards is being adopted in some US states.
The Association of Metropolitan Sewerage Agencies (AMSA)studied seven major waste-water treatment plants and found that dental uses were "by far" the greatest contributors of mercury load, on average contributing 40%, over 3 times the next greatest contributor. The EPA recognizes mercury amalgam as a major source of the mercury in the water. The Western Lake Superior Sanitary District that dentists emit .1 grams of mercury per day per dentist. Based on this, mercury amalgam contributes 14% of the mercury in Seattle and 12% of the mercury in San Francisco. 4% of the mercury in Lake Superior is believed to originate from amalgam. The National Association of Clean Water Agencies noted in a report that purification of mercury from waste water will impose a significant financial burden upon municipal treatment plants. Several other groups have analyzed mercury in waste water and concluded that it is a serious problem. Other studies have shown this to be a gross exaggeration. With respect to pollution in the United States, a study done in 1992 showed that batteries “accounted for 86 percent of discarded mercury and dental amalgam a mere 0.56 percent”.
In 1859, the American Dental Association (ADA) was founded by twenty-six delegates representing various dental societies in the United States at a meeting in Niagara Falls, New York. The ADA did not forbid use of amalgams. The ADA position on the safety of amalgam has remained consistent since its foundation. As of 2006, the ADA has over 152,000 members and is the largest and longest-standing professional association of dentists in the world.
Amalgam formulations and properties were gradually improved, notably by Dr. G.V. Black in 1895. Despite these changes, debate over the use of amalgams persisted in the dental profession. The ADA maintained until 1984 that mercury was bound in amalgam and did not release mercury vapor. In the 1970s studies demonstrated that a small amount of mercury vapor was constantly being released from amalgam, corroborating the first such study published in 1882 in the Ohio State Journal of Dental Science by Dr. Eugene S. Talbot.
Sewers from Norwegian dental clinics older than 1994 (or if there is other reason to believe amalgam have ended up in the sewers instead of the patients mouth) shall be cleaned by experienced personnel to properly remove any residual mercury. The detailed procedure to do so is available from SFT free of charge
As a result of this classification, amalgams have not been subject to official government testing in the United States such as is required for medicines. However, the FDA maintains a web page on the use of amalgam, last updated in December 2002, on which it states, "no valid scientific evidence has shown that amalgams cause harm to patients with dental restorations, except in the rare case of allergy. The FDA's assertion that there is no scientific evidence of health risks associated with amalgam is based on periodic reviews of scientific literature it has published in so-called "white papers". But in September 2006, a joint meeting of three FDA committees voted that the most recent FDA white paper was limited in scope, had gaps in knowledge regarding exposure limits, included contradictory evidence, did not include data from other countries, and did not provide a rationale for excluding some studies. According to the meeting summary posted on the FDA's web site, "To the question of whether the white paper 'objectively and clearly presented the current state of knowledge about the exposure and health effects related to dental amalgam,' the panel voted 'no' by a 13-7 margin." Prior to the joint meeting, some scientists and consumer advocates had raised questions about the fairness of this process, as planned by the FDA.
In 2001 in a lawsuit involving California Proposition 65 and amalgams, a California Superior Court judge ruled that all dental offices with more than nine employees must provide notices on the contents of dental fillings. The mandated notice reads:
In 2002, eight members of the U.S. House of Representatives introduced the Mercury in Dental Filling Disclosure and Prohibition Act (H.R. 4163, 107th Congress, 2nd Session, April 10th 2002), which would have prohibited any mercury in dental fillings starting in 2007. In an interim period between July 1, 2002 and 2007, the bill would have required labeling of amalgam with a warning. The bill was referred to a subcommittee, which tabled it. It has since been re-introduced as bill HR-4011 by congresswoman Diane Watson, who issued a public statement after the September 2006 decision of the FDA Review panel on dental amalgam.
Following the meeting of the joint committees on 6-7 September 2006, when the panel of outside advisers that the FDA had asked to assess the conclusions of its report on amalgam safety rejected the FDA report in a 13-7 vote, they stated the report's conclusions were "unreasonable", given the quantity and quality of information currently available. Panelists said remaining uncertainties about the risk of so-called silver fillings demanded further research, in particular, on the effects of mercury-laden fillings on children and the fetuses of pregnant women with fillings and the release of mercury vapor on insertion and removal of mercury fillings. Michael Aschner, a professor of pediatrics and pharmacology at Vanderbilt University and a panel consultant said "There are too many things we don't know, too many things that were excluded.
Shortly after the decision of the joint advisory panel, the president of the International Academy of Oral Medicine and Toxicology (IAOMT) wrote to the FDA to ask for an expanded review of current science on dental mercury amalgams, a definitive date for such a hearing, and a format that will assure that the full breadth of health effects is assessed. In a press release the ADA wrote that it " welcomes the call by a U.S. Food and Drug Administration (FDA) panel for additional review of scientific studies on the safety of dental amalgam fillings." and reiterated that "the overwhelming weight of scientific evidence supports the safety and efficacy of dental amalgam, and it should continue to be made available to dentists and their patients " and " dental amalgam contains elemental mercury combined with other metals such as silver, copper, tin and zinc to form a safe, stable alloy.