Controversy Over Mercury in Amalgam Fillings
Amalgam Dental Fillings
Figure 1: A mercury amalgam filling on the first molar.
For years, people have suffered from dental caries (or cavities) and have needed dental restoration procedures, especially fillings. The most common filling material, and the one at the center of a hot debate, is amalgam. Commonly known as silver fillings, amalgams are 50% metal alloy powder and 50% liquid mercury. The mercury binds the metal components (including silver, tin, and copper) to form a pliable substance that hardens after being placed into the tooth (Allen). However, since mercury can be toxic at certain levels, the use of mercury in the dental amalgam has been very controversial. Elemental mercury in fillings releases minute quantities of mercury vapor, which at high levels is known to be toxic to organs such as the brain and kidneys, causing severe neurological and behavioral problems. Vapor levels have been found to be highest immediately after fillings have been placed into the tooth and when they are replaced or removed. The concentration of mercury in the blood of unexposed individuals is usually less than 2 ug/100 ml. Early effects of mercury toxicity have been observed in individuals with blood mercury concentrations of 3 ug/100 ml and greater. In 2009, the Food and Drug Administration (FDA) ruled that amalgam fillings do not contain harmful levels of mercury. However, due to reports from dental professionals and the public, the FDA advisory committee suggested in December 2010 that the administration should look at data from more recent studies and that more studies should be done on the effects of mercury in amalgam fillings especially on children.
Figure 2: Ceramic dental porcelain that resembles true tooth enamel but is more costly than amalgam filling.
Dentists have used amalgam fillings since the mid-1800s to fill teeth after caries are drilled out. Their use has continued due to the amalgams' durability and ability to withstand pressures of biting. Since they are non-porous, amalgams do not harbor bacteria. Many patients have preferred this inexpensive material to newer, more costly technologies such as gold, ceramic, and resin-ionomer cements even though these new materials resemble natural tooth enamel more closely (Willingham). However, while more expensive composite materials bind to the tooth chemically, amalgams bind to the tooth mechanically, which increases the underlying inner tooth tissue's risk of being exposed. Over time, this exposure can increase the chance of continued tooth decay and the incidence of root canals in patients. Nevertheless, new technologies are not a panacea. While mercury is on California's list of chemicals known to cause birth defects and cancer, some alternative composite resins contain crystalline silica, which is also listed as carcinogenic chemical in Proposition 65 (The Safe Drinking Water and Toxic Enforcement Act of 1986).
Reports of the Toxicities of Mercury Amalgam Fillings
Studies have shown that mercury in amalgam fillings can be detrimental to health. Dr. Anne Summers, a microbiologist at the University of Georgia, found that animal subjects with amalgam fillings have higher levels of mercury in their GI tract, feces, and throughout their bodies than subjects that had consumed mercury-rich fish on a daily basis. Furthermore, when children are exposed to high levels of mercury, the electrical signals between neurons travel slower than their normal speed, leading to varying degrees of mental impairment and a weakened heartbeat (Weise). Some people with amalgam fillings have reported psychological disturbances, short-term memory loss, and shaking that culminated in seizures (LaPook).
Researchers have found that when pregnant women have high exposure to mercury, their children have an increased rate of birth defects. Dr. Mark Geier, president of Genetics Center of America and founder of Autism Spectrum Disorders Research Centers, examined the effect of the number of mercury fillings in mothers' mouths on the incidence of their children being born with autism. Children of mothers who had less than six amalgam fillings had no significantly increased chance of autism, while those of mothers who had more than six fillings had higher chances and severity of autism (Willingham). This implies that multiple amalgam fillings leads to an increased amount of mercury vapors that can cause toxicities in the body and ultimately cause damage to the embryo. Professor Grandjean and his colleagues at Harvard University reported in the Journal of Pediatrics that when pregnant women have high exposure to mercury, this exposure can halt or impair the children's brain development during growth in the womb. During fetal development, mercury affects migration of brain cells, preventing certain signal transmission pathways from forming the proper connections. Looking at such data, many dentists, such as Dr. Stacey Cole, believe that mercury is undoubtedly poisonous and have stopped using amalgam fillings in their practice.
Legal arguments against the use of amalgams are also prevalent. Dr. Richard F. Edlich, Professor of Plastic Surgery and Biomedical Engineering at the University of Virginia, urges the FDA to provide patients with information and informed consent agreements before their dentists insert amalgam fillings. Similarly, James S. Turner, a Washington attorney and chairman of Citizens for Health group, accuses the FDA of hiding the mercury content of the fillings from the public by using a misleading, yet FDA-approved, marketing term, "silver fillings" to deceive patients when they get fillings installed at the dentist's office (Allen).
Some patients with amalgam fillings have complained of health problems and have had their fillings removed and replaced with newer composite materials. One man had his ten amalgams replaced with composite substitutes since he claimed that the fillings had made him sick, causing him to vomit everyday for months. Another woman reported that her son, who has had amalgams for several years, continues to suffer from upwards of fifty seizures a day.
Because of such testimony from patients and family and from dental professionals, the FDA advisory panel has recommended that the FDA reevaluate its past ruling in favor of amalgams. The panel reported that more research needs to be done on the long-term health consequences of the fillings (LaPook). The results from such future studies will be particularly important for patients who are considering to have their fillings replaced despite the high financial cost.
Some dental professionals are not alarmed by amalgam fillings and do not consider them to be toxic. Jennifer Jablow is a dentist in New York City who asserts that mercury fillings be replaced with newer technologies not because of safety concerns regarding mercury toxicity but rather because there are newer, better technologies that prevent tissue exposure (ABC News/Health). Dr. Ada Cooper, DDS, a representative of the American Dental Association (ADA), explained in an interview with NBC that amalgam fillings are a safe and important option for patients, citing several organizations that support this claim, including the World Health Organization, the Centers for Disease Control, and the American Association of Pediatrics (Allen). Moreover, the ADA declared that studies of the dental amalgam have been reviewed with great care and have shown the amalgam to be a safe, cost-effective, and stable material that has been successfully used in more than 100 million dental restorations. However, these positive reviews fail to address the toxicities and symptoms that patients are reporting and that studies are uncovering.
The Future of Amalgam Fillings
In light of the struggle to understand the amalgam fillings' possible dangers to health, ongoing studies are attempting to reveal new insights about the long-term behavior of mercury fillings. A recent study in the Chemical Research in Toxicology journal suggests that mercury fillings lose their toxic properties over time (George et al). Using x-ray spectroscopy to compare new amalgams to twenty-year-old amalgams, the scientists found that 95% of the mercury on the older fillings' surfaces had undergone chemical transformations into beta-mercury sulfide. Since mercury sulfide is not absorbed by the body's tissues, it does not pose as much danger to the body as does elemental mercury. However, the study does not provide proof against potentially harmful effects of new mercury fillings. Furthermore, studies need to be done to determine if mercury build-up from new fillings can lead to toxicities in the future. Reports from patients and past findings of the harmful effects of amalgam fillings have prompted researchers to continue to study the effect of mercury in dental fillings on patients' health.