The Full Story
Do dental fillings containing amalgam ("silver fillings") cause mercury poisoning?
Most research finds no relationship between fillings and symptoms of mercury poisoning.
Dental caries (tooth decay) are pervasive. The U.S. Centers for Disease Control and Prevention (CDC) reported that 41 percent of children had dental caries in their primary (baby) teeth and 90 percent of adults had caries in their permanent teeth. 
Tooth decay begins when bacteria in saliva and plaque, a sticky substance found on gums and teeth, interact with sugars and starches in the diet. The result is acid which can erode dental enamel. Untreated tooth decay leads to holes in the teeth (cavities), infections (abscesses), pain, and tooth loss. 
Dental cavities are treated by drilling out the decayed material and replacing it with a filling, either an amalgam filling or one of the newer types of tooth-colored composite fillings. The choice of filling materials depends on the location of surface(s) to be repaired, how cooperative the patient is, and several other factors.
Dental amalgam fillings contain mercury and other metals. Because mercury has long been recognized as poisonous to humans, concerns about the potential of mercury poisoning from dental amalgams have been addressed by abundant research. Most scientific studies find no relationship between amalgam fillings and symptoms of mercury poisoning in any age group, although a small number of people have allergic reactions to these fillings. Research continues in order to expand knowledge about any potential effects of amalgam fillings on certain populations, particularly fetuses, breast-fed infants, and very young children.[a]
Facts about Fillings
Dental amalgam fillings contain powdered silver, tin, and copper combined with metallic mercury (liquid mercury, quicksilver).[b] The components, mixed together in the dentist's office immediately before use, form a hard, stable material. These "silver" fillings have been used since the nineteenth century and are still used millions of times every year in the United States. The U.S. Food and Drug Administration (FDA) estimated that more than one billion dental amalgam fillings were placed between 1988 and 2008. 
Amalgam fillings are widely used because they are strong and so provide durable chewing surfaces. They can be inserted more quickly than some other types of fillings, making them useful when treating children. They are less expensive to place than other types of fillings and they usually last longer. 
In recent decades, composite filling materials have become available; these contain quartz or glass in resin (plastic). Composite fillings have cosmetic advantages over amalgam fillings because they mimic the color of natural teeth. They are often the choice for fillings in or near the front of the mouth because they are less visible than amalgam fillings. They are suitable for tooth surfaces which don't experience a lot of pressure or friction, for example, along the sides of teeth or below the gum line. Some dental practitioners offer these fillings to their patients because they do not contain mercury.
Eventually, any filling can fail. Continued pressure from chewing may cause filling materials or the teeth around fillings to crack. The edges of the fillings may become detached from the teeth that they fill. In either case, bacteria can enter around the filling and cause further tooth decay, even in the absence of visible cracks or pain. If not detected and treated, this tooth decay can lead to pain, infection, and even tooth loss. (This is one important reason why regular dental care is important.) Removing the old filling, removing the new decay, and replacing the filling may be indicated.[c]
Facts about Metallic Mercury 
Mercury is a naturally occurring substance found in earth, water, and air. Most people have measurable but small amounts of mercury in their bodies. Eating fish and shellfish is associated with higher mercury levels, as is working with or handling mercury in an unprotected environment, for example, amateur smelting of gold ore. Another source of mercury in humans is vapor from the metallic mercury in dental amalgam fillings.
Metallic mercury, like other forms of mercury, occurs naturally. Also referred to as "silver mercury" and "quicksilver", metallic mercury has a long history of use in commercial and medical applications. Until recently, it was found in most fever thermometers used by consumers along with blood pressure monitors and other medical equipment.
Unlike other types of mercury, metallic mercury is essentially non-toxic if swallowed; it passes through a healthy gastrointestinal tract without being absorbed into the body or causing harm. Even swallowing metallic mercury from a broken thermometer, a dental amalgam preparation, or pieces of an amalgam filling would not cause mercury poisoning.
In contrast, breathing in large amounts of metallic mercury vapor can cause poisoning. Once breathed into the lungs, metallic mercury vapors are quickly absorbed into the bloodstream. The mercury is carried to all body organs, but is especially dangerous to the brain and the kidneys. It can pass through the placenta into fetal circulation and passes into the milk of breast-feeding women.
Exposure to large amounts of metallic mercury vapor, as opposed to the small amounts released from amalgam fillings, has occurred as a result of unprotected occupational exposure, school children handling and bringing home quantities of liquid mercury, broken medical devices, folk remedies, and use during religious or magical ceremonies.  Symptoms of such large exposures may include cough, fever, skin rashes, tremor, difficulty with muscle coordination and walking, kidney abnormalities, and memory loss. 
With mercury, as with other toxic substances, the amount of the substance that reaches target organs determines whether or not someone will be poisoned. To determine how much mercury is in someone's body, blood levels are measured in cases of short-term, large exposures to mercury vapor. In chronic exposures, urine levels are measured to assess the likelihood of mercury poisoning. The fact that a substance can be measured in a person's body fluids does not necessarily indicate poisoning.
Individuals with dental amalgam fillings ("restorations") have measurable amounts of mercury in their blood and urine. [8, 9, 10] This is because the mercury from the filling evaporates, is inhaled, and then absorbed into the blood stream. Increased, but still small, amounts of mercury are released when people grind their teeth or chew. Scientific evidence (discussed below) is overwhelmingly in agreement that the very small amounts of mercury released and absorbed in this way are not a risk to human health.
Scientific Consensus about Amalgams and Mercury
National and international bodies have determined that the use of mercury-containing dental amalgams is safe.
- The World Health Organization stated that "dental amalgam restorations are considered safe…", though the document goes on to note that there are instances of local allergic reactions or side effects. 
- The U.S. Food and Drug Administration (FDA) reviewed 200 scientific articles and an additional 70 relevant abstracts. FDA stated that "dental amalgam is a commonly used device with a low risk of adverse events reported to the agency". 
- The American Dental Association Council on Scientific Affairs wrote that "the scientific evidence supports the position that amalgam is a valuable, viable and safe choice for dental patients". This assessment was supported by a literature review which stated that "studies continue to support the position that dental amalgam is a safe restorative option for both children and adults". The paragraph continues with a statement about the important "distinction between known and hypothetical risks". 
These reports, and a number of review articles with similar conclusions, are based on research which is abundant for children over the age of six and for adults. There are subsets of the population for which the research is less abundant; however, available summary research still supports the safety of dental amalgam use. Details and continuing research needs for special population groups are found below, in the section titled "The Evidence".
In the 1970's, a Colorado dentist named Hal A. Huggins began advocating for removal of mercury-containing dental amalgams, linking them to a variety of health conditions: multiple sclerosis, depression, heart disease, cancer, arthritis, Crohn's Disease, and many other illnesses. (There was, and is, no scientific evidence identifying mercury toxicity as causes of these conditions.) He established a business to promote amalgam removal according to his protocol, removal of teeth which had had root canals, and studies of blood chemistry in order to recommend dietary changes based on individualized "ancestral diets".
On May 1, 1996, the Colorado Board of Dentistry revoked Huggins' license to practice dentistry.  On November 7, 2008 a "cease and desist" order was issued because Huggins was practicing dentistry in Colorado without a license. 
Consumer concern spiked after the television show 60 Minutes aired a story on December 23, 1990 called "Is There Poison in Your Mouth?" "Poison" referred to mercury in dental amalgam fillings. Several dentists in private practice talked about why they choose not to use dental amalgam fillings, citing anecdotal evidence as factors in that decision. For example, one dentist described a patient with severe arthritis. She began seeing a rheumatologist, who prescribed anti-inflammatory drugs. She also had her amalgam fillings removed. The dentist attributed her clinical improvement to removal of fillings.
A number of patients who had had their amalgam fillings removed also appeared on the segment. A woman with diagnosed multiple sclerosis had her fillings removed. She stated that her symptoms abated literally overnight. It is unlikely that this could be an effect of removing dental amalgams, as there is actually a short-term increase in mercury levels after amalgam removal.  Another woman diagnosed with multiple sclerosis improved over a six-month period after having her amalgam fillings removed. Her physician attributed her improvement to the normal waxing and waning of symptoms associated with multiple sclerosis, but the patient was convinced that removing her fillings caused her clinical improvement.
A Cautionary Note
In an editorial in the Journal of the American Medical Association (Needleman), Needleman comments on two studies of children treated with dental amalgam. There was no evident neurological or renal impairment in these children, despite their having higher urinary levels of mercury than children without amalgams. Needleman cautions that subtle effects may be possible but not yet recognized; he cites the example of lead, now known to be toxic at much lower levels than once thought.
In a broader context, the United Nations has identified the "precautionary principle" as a means of dealing with uncertainty in scientific issues, a way of potentially preventing harm to people or the environment before all necessary facts are known.  Some European countries have acted In accordance with the precautionary principle in regard to dental amalgams. Hujoel cites Austria, Germany, Finland, Norway, the United Kingdom, and Switzerland as countries which have recommended that dentists not use amalgam fillings in pregnant women.  Bose-O'Reilly cites Germany as one of several countries in which amalgam fillings are no longer permitted. 
Hundreds of published research studies have examined the relationship between dental amalgam fillings and mercury levels in human tissue; the presence or absence of symptoms of mercury poisoning in people with dental amalgam fillings; and any established link between the presence of dental amalgams and systemic illness. Following are illustrative examples of studies associated with children over the age of six, adults, vulnerable populations such as infants, pregnant and breast-feeding women and their infants, those sensitive to dental amalgam, and selected neurological conditions.
Age-Based Research about Mercury in Amalgam Fillings and Human Health
Children under age six: The U.S. Food and Drug Administration (FDA) reviewed hundreds of articles about dental amalgam and found none that studied clinical effects in children under the age of six. As part of the same study, FDA determined that there was no evidence of clinical harm to adults from mercury in amalgam. FDA further determined that children younger than 6 years who had dental amalgams in place were not at risk of mercury toxicity, because these children have smaller and fewer teeth than adults, and also because they inhale smaller volumes of air than adults, making their estimated daily intake less than that of adults.  Confirming this would require clinical research.
To address concerns about mercury exposure and the development of autism and autism spectrum disorders, Hertz-Picciotto and colleagues evaluated mercury levels and sources of mercury exposure in 452 children from the ages of 24 to 60 months: 249 diagnosed with autism or an autism spectrum disorder, 143 typically developing children, and 60 children who had developmental delays, but not autism or an autism spectrum disorder.
A number of factors were studied:
- how much and what type of fish the mothers and children ate;
- how many and what type of vaccinations the children had had;
- whether the children had amalgam fillings and, if so, how many and when they were placed;
- whether the children chewed a lot of gum or ground their teeth;
- whether the children were given over-the-counter products, such as nasal sprays and earwax removers, which sometimes contain mercury preservatives.
The researchers found no differences in the mercury levels of children who were typically developing and the children with autism and autism spectrum disorders. This held true after accounting for fish intake, the biggest source of mercury exposure in the U.S., and continued to hold for children who did not eat fish. In addition, they found that the mercury levels in children with autism or autism spectrum disorders were similar to a nationally representative sample of U.S. children aged 1-5 years. The researchers do note that this study could not account for possible effects of maternal mercury exposure while pregnant or immediately after pregnancy. 
Children age six and older: Recent studies have evaluated whether children with dental amalgams developed evidence of neurological or renal effects.
- In a study of 507 children from the ages of eight to ten with dental caries, approximately half were treated with amalgam fillings and half with composite fillings. They were evaluated for the presence or absence of neurological and behavioral findings. At the end of the study, there were no statistical differences between the groups. The authors noted, though, that the group who received composite fillings needed to have more fillings replaced than the children who received amalgam fillings. 
- In a follow-up study of these children, the authors state that "current evidence is that potential neurobehavioral or neurological effects from dental amalgam mercury exposure in children are inconsequential". 
- In a study of 534 children from six to ten years old with dental caries, half were treated with amalgam fillings and half with composite fillings. After five years, there were tested for changes in IQ, memory, other neurological findings, and kidney function. The authors report that there were no statistically significant differences between the two groups at the end of the study period. They note that this study could not eliminate the possibility of very small effects on IQ. 
Adults: An evidence-based review of articles concerning amalgam safety concluded that "the evidence supporting the safety of amalgam restorations is compelling". 
Another report by Chey and Buchanan notes that "there currently is no scientific evidence that supports the association between amalgam mercury exposure and adverse health effects in adults or children". 
Bates and colleagues studied records of 20,000 members of the New Zealand Defense Forces and found nothing to indicate that dental amalgams are unsafe. They did report seven cases of multiple sclerosis among the 20,000 patients, a slight increased risk which they state should be studied further. 
Fung and Molvar found no evidence for mercury-related health effects in dental patients, though they noted that a small number of people have true allergies to amalgam components. 
Pregnant women: Counter and Buchanan reviewed literature about the sources and effects of all types of mercury on children. They cite many studies which show a correlation between maternal dental amalgam and the presence of mercury in fetuses, neonates, and infants and they note the possibility of neurological effects on these children. They go on to state that there is little evidence of such harm. 
Daniels and colleagues studied 7,375 children whose mothers had professional dental care while they were pregnant. Even in the pregnant women who had had amalgam fillings placed, the researchers found no negative effects on the infants' birth weights. Also, they found no negative effects on language development of these children at the age of 15 months. 
Breast-fed infants: There is conflicting research about whether the amount of mercury in human breast milk is correlated with maternal amalgam fillings. Questions remain about how much of this inorganic mercury is bound to proteins in the milk, how much is passed along to the infant, and how much an infant's immature gastrointestinal system will absorb. Clifton, in an extensive review of mercury exposure, summarizes approximately 500 references , yet notes that additional research is indicated in this area. There is no evidence that women with amalgam fillings should not breast feed their children.
Disease-based research about mercury in amalgam fillings and human health: The symptoms of mercury poisoning can mimic the symptoms of some neurological diseases, for example multiple sclerosis and Alzheimer's disease. Currently, there is no evidence that dental amalgam causes these diseases. Also, there is no evidence that dental amalgams cause a poorly-defined, inconsistent cluster of symptoms which some have termed "dental amalgam disease".
Multiple sclerosis (MS):
- Some speculation about a possible association between MS and dental amalgam has been based on a 1978 study reporting that the incidence of MS correlated geographically with a high incidence of dental caries.  Suggestions were made that perhaps the association was due to the use of amalgams in areas with high population levels of dental decay. 
- Bangsi and colleagues studied two groups of patients who had dental amalgams: dental patients with MS and a matched group of patients without MS. Researchers found no statistically significant relationship between the groups. 
- Bates and colleagues reported on 20,000 members of the New Zealand Defense Force, all of whom had "regular and consistent" dental care.  They found no relationship between dental amalgam fillings and renal disease, Parkinson's disease, or chronic fatigue syndrome. They reported a slightly increased risk of multiple sclerosis (MS): seven cases of MS out of a study group of 20,000 individuals.
- In an attempt to determine if there is a relationship between amalgam fillings and MS, Aminzadeh and Etminan reviewed studies published over a 40-year period. They determined that there is a non-statistically significant, but slightly elevated, risk of MS associated with amalgam use. They call for further studies that would examine not simply the presence of amalgam fillings, but the number, size, location, and time in place of amalgam fillings to "definitively rule out any link between amalgam and MS". 
- Noting that there is no scientific evidence that MS is caused by mercury or other heavy metals, the National Multiple Sclerosis Society cautions that there is no proven benefit to removing or replacing dental fillings. 
Alzheimer's disease: Alzheimer's disease is a neurological illness which results in dementia. The cause is unknown and there are no treatments known to prevent or reverse memory loss. Currently, the only way to definitively diagnose Alzheimer's disease is by conducting an autopsy of the brain after death.
In an attempt to determine if mercury and dental amalgams play a role in the development of Alzheimer's disease, Saxe and colleagues conducted autopsies on the brains of 68 patients with Alzheimer's disease and 33 people without Alzheimer's. People in the study came from two different states, Kentucky and Wisconsin. Each person's dental history was known so that their exposure to dental amalgam fillings could be detailed. Mercury levels in several areas of the brains were determined.
The researchers determined that there was no relationship between brain mercury levels or Alzheimer's disease and the presence of dental amalgam fillings, regardless of their number, size, or length of time present in a person's mouth. 
"Dental amalgam disease": There have been reports of individuals who attributed a variety of health effects to their dental amalgams. Research does not indicate a correlation between amalgams and generalized health symptoms.
- Malt and colleagues studied 99 patients complaining of symptoms they attributed to amalgams and compared them to three other groups of patients, one with chronic medical problems seen in a family medicine practice, a similar group seen in an alternative medical practice, and another group of patients with amalgams seen in a dental practice. The researchers concluded that the dental amalgam group complaining of symptoms reported a wide variety of symptoms that were not seen in the other groups; the control group with dental amalgams had almost no symptoms. They caution, though, that there could be some patients with sensitivity to metals in amalgams. 
- Melchart and colleagues measured mercury levels in patients with amalgams who believed that their fillings were causing a variety of health problems. They compared the levels with those found in symptom-free patients with amalgam fillings. There was no difference. 
- Gottwald and colleagues likewise found no differences in mercury levels between patients who attributed health complaints to amalgam fillings compared with a control group. 
Removal of Dental Amalgams: The World Health Organization states that "there is no scientific evidence showing that general symptoms are relieved by the removal of amalgam restorations".  In the absence of a compelling reason, such as an allergic reaction, it is NOT recommended that amalgam fillings be removed. In fact, the drilling required to remove amalgam fillings can expose the individual to a minor increased amount of mercury in blood plasma. 
Patients allergic to the mercury in dental amalgams may have systemic allergic responses, including itching and hives, and such local effects as soreness, burning, and dryness in the throat and mouth. If symptoms do not resolve spontaneously or do not respond to antihistamines, amalgam removal is indicated. 
- In a study of 206 patients with amalgam fillings, 28 had positive patch test reactions to the metals in dental amalgams. Fourteen had symptoms of a contact allergy. One of these patients improved within two weeks of having her amalgam filling removed. 
- A patient with a severe local reaction to an amalgam filling developed burning, itching, and trouble breathing within two hours of treatment. Her symptoms were treated, the filling was removed within two hours, and her symptoms subsided by the next day. 
- A lesion known as oral lichen planus has been associated with the presence of dental amalgams in some patients. Patients with oral lichen planus who have a positive patch test reaction to amalgam components may benefit from amalgam removal. 
Summary: Mercury is a naturally occurring substance, found in air, water, and soil. Among other sources of human exposure, it also is found in dental amalgam fillings. In sufficient quantity, mercury is known to be toxic to humans.
A review of scientific evidence, accumulated over decades, supports the view that there is no clinical evidence of mercury poisoning in people who have amalgam fillings in their mouths. (Allergy to mercury is an exception which affects a small number of people.) Studies do not support any statistically significant association between the presence of dental amalgam and disease.
The public health benefits of breast feeding and controlling tooth decay in children are established. Studies do not associate mercury poisoning with the use of amalgams in pregnant women, fetuses, infants, or young children. Because children are more sensitive to the effects of mercury than adults, research continues into the possibility of as-yet undiscovered effects of low-level mercury exposure from dental amalgams in fetuses, breast-fed infants, and young children. Alternatives to amalgam fillings are available for people who choose to avoid them.
Some countries have limited the use of dental amalgam fillings, for environmental and occupational reasons and for adherence to the "precautionary principle", i.e. preventing potential harm though that harm has not been established. In other countries, including the United States, dental amalgam fillings continue to be used because they are a durable, efficient, cost-effective means of addressing the problem of pervasive tooth decay in children and adults.
There are no current recommendations on the part of U.S. federal agencies to prevent dentists from placing amalgam fillings where indicated because studies consistently have failed to document mercury toxicity associated with amalgam fillings. Except for the unusual cases of allergic reaction, there are no data supporting any recommendations to remove fillings.
Rose Ann Gould Soloway, RN, BSN, MSEd, DABAT emerita
[a] This paper discusses mercury in dental amalgam as it concerns consumers/dental patients. The body of literature which addresses dental professionals and their occupational exposure to mercury is not specifically considered here.
[b] Note that metallic mercury is a different form of mercury from methyl mercury, correctly associated with eating contaminated fish and shellfish, and ethyl mercury, incorrectly associated with toxicity from vaccines.
[c] If the tooth cannot sustain this type of repair, a more extensive repair, e.g. a cap or crown, may be needed. These are often made of porcelain or gold.
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