The dental amalgam controversy refers to the conflicting views over the use of amalgam as a filling material mainly because it contains the element mercury. The concern centers on the health effects of toxicity or allergy which may be associated with constant mercury exposure, particularly as a potential cause of chronic illnesses, autoimmune disorders, neurodegenerative diseases, birth defects, oral lesions, and mental disorders. Scientists agree that dental amalgam fillings leach mercury into the mouth, but different studies have concluded that this exposure may be as low as 1-3 µg/day (FDA), or as high as 27 µg/day (Patterson). The effects of this exposure is disputed, and currently dental amalgam is approved for use in most countries, although Norway and Sweden are notable exceptions.
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. A 1993 study published in FDA Consumer found that 50% of Americans believed fillings containing mercury caused health problems. 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.
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 dental 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 dental 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 1993 study published in FDA Consumer found that 50% of Americans believed mercury filings caused health problems. The broad lack of knowledge among the public was 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.
The World Health Organization (WHO) notes that exposure can be greatly increased by personal habits such as bruxism or gum-chewing, and cites a report which found a 5.3 fold increase in mercury levels after chewing, eating, or toothbrushing. They report that amalgam is estimated to contribute 50% of mercury exposure in adults. In the studies the WHO reviews, daily mercury exposure estimates range from 3 μg/day to 9 μg/day. Separately the World Health Organization reports that "there may be no level of mercury at which some adverse effects do not occur". A study conducted by measuring the intraoral vapor levels over a 24-hour period in patients with at least nine amalgam restorations showed the average daily dose of inhaled mercury vapor was 1.7 µg (range from 0.4 to 4.4 µg), which is approximately only 1% of the threshold limit value of 300 to 500 µg/day established by the World Health Organization, based on a maximum allowable environmental level of 50 µg/day in the workplace.
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 dental 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.
Peer-reviewed scientific studies have come to opposite conclusions on whether the mercury exposure from amalgam fillings causes health problems. A 2004 systematic review conducted by the Life Sciences Research Office, whose clients include the FDA and NIH, concluded that "the current data are insufficient to support an association between mercury release from dental amalgam and the various complaints that have been attributed to this restoration material". Another review published in 2005 by the Freiburg University Institute for Environmental Medicine found that "mercury from dental amalgam may lead to nephrotoxicity, neurobehavioural changes, autoimmunity, oxidative stress, autism, skin and mucosa alterations or non-specific symptoms and complaints", that "Alzheimer's disease or multiple sclerosis has also been linked to low-dose mercury exposure", and that "removal of dental amalgam leads to permanent improvement of various chronic complaints in a relevant number of patients in various trials.
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.
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