Dental amalgam controversy

In 1855, Dr. J. Foster Flagg, a professor of dental pathology in Philadelphia, experimented with new mixtures of amalgam. In 1861, he presented his findings to the Pennsylvania Association of Dental Surgeons and, in 1881, he published his book, Plastic and Plastic Fillings. (Amalgam fillings were often called "plastic fillings" at the time.) The inevitable result of this affair was that silver amalgam was proven to be "an excellent filling material", and expanded dentistry's "ability to save teeth". Around the same time, John and Charles Tomes in England conducted research on the expansion and contraction of the various amalgam products. During the American Civil War, the debate on the merits of amalgam continued. In dental meetings, with now decades of use and dental research came the recognition of the importance of good technique and proper mixture on long-term success. It was argued, "the fault was not in the material but in the manipulation.... Some men's amalgam is good universally, and some men's gold is bad universally; the difference lies in the preparation of the tooth and in the plug (filling)."[40]

More controversy came in 1872, when an amalgam filling was reported as the cause of death of a Nebraska middle-aged man, resulting in a public outcry against the use of amalgam.[41] His physicians reported that the filling caused swelling of his mouth, throat and windpipe, completely hindering respiration. Given that the involved tooth was a lower second molar, it was later considered very likely that the patient died from Ludwig's Angina, which is a type of cellulitis, rather than mercury poisoning. Another alleged case of "pytalism" causing headache, fever, rapid pulse, metallic taste, loss of appetite, and generalized malaise was reported in 1872 in a female patient following the insertion of eight amalgam fillings.[42] Later, however, another dentist examined the fillings and noted they had, in a short period of time, washed away, and that upon gentle pressure the metal crumbled away. He removed all the fillings with an explorer in three minutes; and concluded poor workmanship alone could have explained the patient's symptoms.

Alfred Stock was a German chemist who reported becoming very ill in the 1920s and traced his illness to his amalgam fillings and resulting mercury intoxication. He described his recovery after the fillings were removed and believed that amalgam fillings would come to be seen as a "sin against humanity".[43] Stock had also previously been exposed to toxic levels of mercury vapor during the course of his work, due to his use of liquid mercury in some novel laboratory apparatus he invented.[44]

In the 1990s, several governments evaluated the effects of dental amalgam and concluded that the most likely health effects would be due to hypersensitivity or allergy. Germany, Austria, and Canada recommended against placing amalgam in certain individuals such as pregnant women, children, those with renal dysfunction, and those with an allergy to metals. In 2004, the Life Sciences Research Office analyzed studies related to dental amalgam published after 1996 and concluded that mean urinary mercury concentration (μg of Hg/L in urine, HgU) was the most reliable estimate of mercury exposure.[45] It found that those with dental amalgam were unlikely to reach the levels where adverse effects are seen from occupational exposure (35 μg HgU). Some 95% of study participants had μg HgU below 4–5. Chewing gum, particularly for nicotine, along with more amalgam, seemed to pose the greatest risk of increasing exposure. One gum-chewer had 24.8 μg HgU. Studies have shown that the amount of mercury released during normal chewing is extremely low. It concluded that there was not enough evidence to support or refute many of the other claims such as increased risk of autoimmune disorders, but stated that the broad and nonspecific illness attributed to dental amalgam is not supported by the data.[45] Mutter in Germany, however, concludes, "removal of dental amalgam leads to permanent improvement of various chronic complaints in a relevant number of patients in various trials."[46]

Hal Huggins, a Colorado dentist (previous to having his license revoked), was a notable critic of dental amalgams and other dental therapies he believed to be harmful.[47] His views on amalgam toxicity were featured on 60 Minutes[48] and he was later criticized as a dentist, "prospecting for disease" and having only an "aura of science" by Consumer Reports.[7] In 1996, a Colorado state judge recommended that Huggins's dental license be revoked, for tricking chronically ill patients into thinking that the true cause of their illness was mercury. Time reported the judge's conclusion that Huggins, "diagnosed 'mercury toxicity' in all his patients, including some without amalgam fillings."[49] Huggins's license was subsequently revoked by the Colorado State Board of Dental Examiners for gross negligence and the use of unnecessary and unproven procedures.[50][51][52]

Both those opposed and those not opposed to dental amalgam recognize that amalgam has been found to be a rare contributor to localized and temporary tissue irritation known as oral lichenoid lesions.[14][62][63][66] These mild, lichenoid reactions have also been reported in composite resin fillings.[67] Those opposed to amalgam believe that amalgam fillings are also associated with increased risk of other autoimmune conditions such as multiple sclerosis (MS), lupus, thyroiditis, and eczema.[68]

Consumer Reports considered these alleged associations between amalgam and chronic disease made by some health practitioners as "prospecting for diseases".[7] The National Multiple Sclerosis Society (USA) similarly has stated, "There is no scientific evidence to connect the development or worsening of MS with dental fillings containing mercury, and therefore no reason to have those fillings removed. Although poisoning with heavy metals-such as mercury, lead, or manganese can damage the nervous system and produce symptoms such as tremor and weakness, the damage is inflicted in a different way than occurs in MS and the process is also different."[27] The Lupus Foundation of America also states on their website, "At the present time, we do not have any scientific data that indicates that dental fillings may act as a trigger of lupus. In fact, it is highly unlikely that dental fillings aggravate or cause SLE."[33]

In 2006, a literature review was undertaken to evaluate the research on amalgam and its potential health effects on dentists and dental staff.[69] It was reported that there is currently no conclusive epidemiological evidence regarding risks for adverse reproductive outcomes associated with mercury and dental professionals. It is mentioned that evidence to date fails to account for all confounding variables (such as alcohol consumption) and recommends more comprehensive and rigorous studies to adequately assess the hazards faced by dental personnel.[69]

The American College of Medical Toxicology and the American Academy of Clinical Toxicology still claim that mercury from amalgams does not cause illness because "the amount of mercury that they release is not enough to cause a health problem".[34] In response to some people wanting their existing amalgam removed for fear of mercury poisoning, these societies advise that the removal of fillings is likely to cause a greater exposure to mercury than leaving the fillings in place.[34] These societies also claim that removal of amalgam fillings, in addition to being unnecessary health care and likely to cause more mercury exposure than leaving them in place, is also expensive.[34]

Dentists who advocate removal of amalgam fillings often recommend wearing breathing apparatus, using high-volume aspiration, and performing the procedure as quickly as possible. Sources of mercury from the diet, and the potential harm of the composite resins to replace the purportedly harmful amalgam fillings, may also need to be considered.[70]

Alternative materials which may be suitable in some situations include composite resins, glass ionomer cements, porcelain and gold alloys.[71] Most of these materials, with the notable exception of gold, have not been used as long as amalgam, and some are known to contain other potentially hazardous compounds. Teaching of amalgam techniques to dental students is declining in some schools in favor of composite resin,[72] and at least one school, University of Nijmegen in the Netherlands, eliminated dental amalgam from the curriculum entirely in 2001.[73] This is largely a response to consumer pressure for white fillings for cosmetic reasons, and also because of the increasing longevity of modern resin composites. These alternative dental restorative materials are not free of potential health risks, such as allergenicity, inhalation of resin dust, cytotoxicity, and retinal damage from blue curing light.[74]

Anti-amalgam sources typically promote removal of amalgam fillings and substitution with other materials. Detoxification may also be advised, including fasting, restricted dieting to avoid mercury containing foods, and quasi-chelation therapies, allegedly to remove accumulated mercury from the body.[75] The American College of Medical Toxicology and the American Academy of Clinical Toxicology recommend against chelation therapy and say that chelation therapy can artificially and temporarily elevate the levels of heavy metals in the urine (a practice referred to as "provoked" urine testing).[34] They also mention that the chelating drugs may have significant side effects, including dehydration, hypocalcemia, kidney injury, liver enzyme elevations, hypotension, allergic reactions, and mineral deficiencies.[34]

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 use[76] 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 used for many years to come.[77][78] Over a lifetime, dietary sources of mercury are far higher than would ever be received from the presence of amalgam fillings in the mouth. For example, due to pollution of the world's oceans with heavy metals, products such as cod liver oil may contain significant levels of mercury.

There is little evidence to suggest that amalgam fillings have any negative direct effects on pregnancy outcomes or on an infant post-pregnancy. A study, consisting of 72 pregnant women, was conducted to determine the effects of dental amalgam on babies in utero. Results indicated that although the amount of amalgam the mother had was directly related to the amount of mercury in the amniotic fluid, no negative effects on the fetus were found. A larger study, consisting of 5,585 women who had recently given birth, was used to determine if amalgam restorations during pregnancy had any effects on infant birthweight. Among the study group, 1,117 women had infants with low birth weights and 4,468 women had infants with normal birth weights. Approximately five percent of the women had one or more amalgam filling restorations during their pregnancy term. These women had little to no difference in infant birth weight compared to the women whom did not undergo amalgam restoration during pregnancy.[2]

A 2006 Zogby International poll of 2,590 US adults found that 72% of respondents were not aware that mercury was a 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.[79] A 1993 study published in FDA Consumer found that 50% of Americans believed fillings containing mercury caused health problems.[80] Some dentists (including a member of the FDA's Dental Products Panel) suggest that there is an obligation to inform patients that amalgam contains mercury.[81][82]

A prominent debate occurred in the late 20th century, with consumer and regulatory pressure to eliminate amalgam being "at an all-time high".[82] In a 2006 nationwide poll, 76% of Americans were unaware that mercury is the primary component in amalgam fillings,[79] and this lack of informed consent was the most consistent issue raised in a recent U.S. Food and Drug Administration (FDA) panel on the issue by panel members.[82]

The broad lack of knowledge that existed among the public was also displayed when a December 1990 episode of the CBS news program 60 Minutes covered mercury in amalgam. This resulted in a nationwide amalgam scare and additional research into mercury release from amalgam. The following month Consumer Reports published an article criticizing the content of the broadcast, stating that it contained a great deal of false information and that the ADA spokesperson on the program was ill-prepared to defend the claims.[7] For example, 60 Minutes reported that Germany was planning to pass legislation within the year to ban amalgam, but the institute of German Dentists said one month later that there was no such law pending. Also, one physiologist interviewed by Consumer Reports noted that the testimonials are mostly anecdotal, and both the reported symptoms and the rapid recovery time after the fillings are removed are physiologically inconsistent with that of mercury poisoning. Consumer Reports goes on to criticize how 60 Minutes failed to interview the many patients who had fillings or teeth removed only to have the symptoms stay the same or get worse.[7]

In 1991, the United States Food and Drug Administration concluded, "none of the data presented show a direct hazard to humans from dental amalgams."[83] In 2002, a class action lawsuit was initiated by patients who felt their amalgam fillings caused them harm. The lawsuit named 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." On 18 February 2003, the New York Supreme Court dismissed the two amalgam-related lawsuits against organized dentistry, stating the plaintiffs had "failed to show a 'cognizable cause of action'".[84]

The proper interpretation of the data is considered controversial only by those opposed to amalgam. The vast majority of past studies have concluded that amalgams are safe. However, although the vast majority of patients with amalgam fillings are exposed to levels too low to pose a risk to health, many patients (i.e. those in top 0.1%) exhibit urine test results which are comparable to the maximum allowable legal limits for long-term work place (occupational) safety.[58][59] Two recent randomized clinical trials in children[85] discovered no statistically significant differences in adverse neuropsychological or renal effects observed over a five-year period in children whose caries were restored using dental amalgam or composite materials. 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, the other 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 the fetus and also states, "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 μg of mercury per one liter of blood.[86] While mercury fillings themselves do not increase mercury levels above "safe" levels, they have been shown to contribute to such increase. However, such studies were unable to find any negative neurobehavioral effects.[87][86][88]

The American Dental Association (ADA) has asserted that dental amalgam is safe and has held, "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 or suggestion of the dentist, is improper and unethical".[102] Under the comments of the American Dental Association before the FDA's Dental Products Panel[103] of the Medical Devices Advisory Committee,[104] the ADA supports the 2009 FDA ruling on dental amalgam.[14][105] ADA states, "dental amalgam has an established record of safety and effectiveness, which the scientific community has extensively reviewed and affirmed."[106][107][108] The ADA also supports the 2017 EPA wastewater regulation and is providing information and assistance to its members in implementation of amalgam separators.[109] The ADA asserts the best scientific evidence supports the safety of dental amalgam.[110] Clinical studies have not established an occasional connection between dental amalgam and adverse health effects in the general population.[111]

In 2002, Dr. Maths Berlin of The Dental Material Commission published an overview and assessment of the scientific literature published between November 1997 and 2002 for the Swedish Government on amalgam and its possible environmental and health risks.[112] A final report was submitted to the Swedish Government in 2003 and included his report as an annex to the full report. In the final report from 2003, Berlin states that the 1997 summary had found "... no known epidemiological population study has demonstrated any adverse health effects in amalgam". He reports that researchers have been able to show effects of mercury at lower concentrations than before and states, "... the safety margin that it was thought existed with respect to mercury exposure from amalgam has been erased." He recommends eliminating amalgam in dentistry for medical and environmental reasons as soon as possible.[112]

After FDA's deliberations and review of hundreds of scientific studies relating to the safety of dental amalgam, the FDA concluded, "clinical studies have not established a causal link between dental amalgam and adverse health effects in adults and children age six and older."[113] The FDA concluded that individuals age six and older are not at risk of mercury-associated health effects from mercury vapor exposure that come from dental amalgam.[105]

In 2009, the FDA issued a final rule which classified dental amalgam as a "Class II" (moderate risk) device, placing it in the same category as composite resins and gold fillings.[14] In a press release announcing the reclassification, the agency again stated, "the levels [of mercury] released by dental amalgam fillings are not high enough to cause harm in patients."[114]

Also, in the FDA final regulation on dental amalgam in 2009, the FDA recommended the product labeling of dental amalgam. The suggested labeling included: a warning against the use of dental amalgam in patients with mercury allergy, a warning that dental professionals use appropriate ventilation when handling dental amalgam, and a statement discussion of scientific evidence on dental amalgam's risks and benefits in order to make informed decisions amongst patient and professional dentists.[105][115]

In 2020, the FDA updated their guidelines to recommend against amalgam for certain high-risk groups, including children, pregnant and nursing women, people with neurological disease, impaired kidney function, and known sensitivity to mercury, due to potential harmful health effects of mercury vapor.[39] They acknowledge that breathing in mercury vapor may be harmful to certain populations, but recommend against removal of amalgam fillings unless medically necessary.[116]

FDI World Dental Federation recognizes the safety and effectiveness of amalgam restorations. FDI is a federation of approximately 200 national dental associations and dental specialist groups representing over 1.5 million dentists. In collaboration with the WHO, they have produced an FDI position statement and WHO consensus statement on dental amalgam.[13] Their position regarding the safety of dental amalgam is that, aside from rare allergic reactions and local side effects, "the small amount of mercury released from amalgam restorations, especially during placement and removal, has not been shown to cause any other adverse health effects." The paper goes on to say that there have been "no controlled studies published that show adverse systemic effects" from amalgam restorations and there is no evidence that removing amalgam restorations relieves any general symptoms. More recently, FDI has published a resolution confirming that their position on the safety and effectiveness of amalgam has not changed despite the phasing-down in some countries.[120]

In the United States, numerous respected professional and non-profit organizations consider amalgam use to be safe and effective and have publicly declared such.[5] In addition to the American Dental Association,[14][121] other American organizations, including the Mayo Clinic,[21] the U.S. Food and Drug Administration (FDA),[38] Alzheimer's Association,[23] American Academy of Pediatrics,[24] Autism Society of America,[25] U.S. Environmental Protection Agency,[26] National Multiple Sclerosis Society,[27] New England Journal of Medicine,[28] International Journal of Dentistry,[29] National Council Against Health Fraud,[30] The National Institute of Dental and Craniofacial Research NIDCR,[31] American Cancer Society,[32] Lupus Foundation of America,[33] Consumer Reports[7] and WebMD[36] have all given formal, public statements declaring that amalgam fillings are safe based on the best scientific evidence.

On 28 July 2009, the U.S. Food and Drug Administration (FDA) recategorized amalgam as a class II medical device, which critics claim indicates a change in their perception of safety. The ADA has indicated that this new regulation actually places encapsulated amalgam in the same class of devices as most other restorative materials, including composite and gold fillings.[14]

Despite the research regarding the safety of amalgam fillings, the state of California requires warning information given to patients for legal reasons (informed consent) as part of Proposition 65. This warning also applied to resin fillings for a time, since they contain bisphenol A (BPA) a chemical known to cause reproductive toxicity at high doses.[122]

In Canada, amalgam use is considered safe and effective by some groups. A 2005 position statement from the Canadian Dental Association (CDA) states "current scientific evidence on the use of dental amalgam supports that amalgam is an effective and safe filling material that provides a long-lasting solution for a broad range of clinical situations. The CDA has established its position based on the current consensus of scientific and clinical experts and on recent extensive reviews of strong evidence by major North American and international organizations, which have satisfactorily countered any safety concerns."[15] Amalgam use is regulated by Health Canada as are all medical treatments[123] and Health Canada has also stated that dental amalgam is not causing illness in the general population.[22]

Australia recognizes the safety and effectiveness of amalgam restorations. In 2012, the Australian Dental Association published a position paper on the safety of dental amalgam.[16] Their position is "Dental Amalgam has been used as a dental restorative material for more than 150 years. It has proved to be a durable, safe and effective material which has been the subject of extensive research over this time" and "amalgam should continue to be available as a dental restorative material".[124]

Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) is a scientific committee within the European Commission. In a 2008 document of 74 pages, its research on the subject of amalgam safety concluded "there is no scientific evidence for risks of adverse systemic effects exist [sic] and the current use of dental amalgam does not pose a risk of systemic disease."[125]

England and Scotland recognize the safety and effectiveness of amalgam restorations. A policy statement from the British Dental Health Foundation states that they do not consider amalgams containing mercury a significant health risk.[126]

Ireland recognizes the safety and effectiveness of amalgam restorations. The Irish Dental Association has published on their website: "Dental amalgam has been used on patients for over 150 years. All available world-wide research indicates that amalgam is not harmful to health.... No Government or reputable scientific, medical or dental body anywhere in the world accepts, on any published evidence, that dental amalgam is a hazard to health."[18] The Irish Dental Association provides additional detail in a published patient information letter.[19]

France has publicly recognized the safety and effectiveness of amalgam restorations. A position paper on the Association Dentaire Française website states that amalgam restorations have proven to have no biological or toxic effect.[20] They also mention that no serious pathological fact has ever been observed and no general toxic action has been scientifically proven to date.[20] The most exposed subjects remain dentists in whom it did not identify occupational diseases related to mercury and other rare that any allergies. These amalgam allergies are about 40 times less than that of resin fillings[20]

During the 1980s and 1990s in Norway, there was considerable and intense public debate on the use of dental amalgam.[127] The Norwegian Dental Patients Association (Forbundet Tenner og Helse), made up of people who believe they suffered health effects from amalgam fillings, was a driving force in this debate.[127] During this time, the media often featured interviews with people claiming that their health problems were caused by amalgam fillings, and who have regained their health after replacing their amalgam fillings with a different material. Some scientific studies also reported that patients have been restored to health after having had their amalgam fillings replaced. However, these studies were heavily disputed at the time and the Norwegian Board of Health still maintain there is no scientifically proven connection between dental amalgam and health problems.[127]

In 1991, organized through the ministry of the environment, Norway began phasing out the use of most mercury-containing products (not limited to amalgam fillings but also including mercury-based batteries, thermometers, sphygmomanometers, consumer electronics, vehicle components, etc.).[128] The ban on the import, export, and use of most mercury-based products began on 1 January 2008.[128] The Norwegian officials stressed that this is not a decision based on using an unsafe health product, but rather that the "overall, long term goal is to eliminate the use and release of mercury to the environment".[127] Despite the mercury ban, dental offices in Norway may apply for exemptions to use amalgam on a case-by-case basis.[127]

Similar to Norway, from 1995 to 2009 the Environment Ministry of the Government of Sweden gradually banned the import and use of all mercury-based products (not limited to amalgam fillings alone, but also including mercury-based batteries, thermometers, sphygmomanometers, consumer electronics, vehicle components, lightbulbs, analytical chemicals, cosmetics, etc.).[129][130] These mercury-based products were phased out for environmental reasons and precautionary health reasons.[131] Like Norway, there was considerable public pressure in the years leading up to the ban.[127] Since the ban, the Government of Sweden continued to investigate ways of reducing mercury pollution.[132] The Swedish Chemicals Agency state that they may grant exemptions on the use of amalgam on a case-by-case basis.[132]

Following the Minamata Convention on Mercury, from July 2018 onwards, the EU Mercury Regulation prohibits the use of dental amalgam in children under 15 years old and pregnant or breastfeeding woman. Additional requirements include the use of pre-encapsulated mercury and ethical disposal of waste amalgam.[133] The British Dental Association has worked with the Council of European Dentists to prevent an immediate ban of amalgam until further research into practicalities has been undertaken,[134] which is currently ongoing.[135][136] The European Commission will report to European Parliament by June 2020, and to the European Council by 2030 regarding the viability of ending dental amalgam use by 2030.[133]

In Japan, the use of amalgam began to decline around the 1990s; since 2016, fillings with amalgam alloys have been excluded from insurance coverage. Amalgam is still allowed as of 2023, but is rarely used because it is very expensive. Dental composite and palladium alloys are used instead.[137]