Dental amalgam: composition, properties, and clinical applications

Dental Amalgam

The use of amalgam for dental fillings is nothing new. However, the use is also relatively controversial in some circles. While there are many companies and organizations that discuss the safety of amalgam fillings, there are many more that say these kinds of fillings are dangerous and should not be used. Which option is correct and whether it varies from person to person has to be considered. That is the main reason behind this paper - there is controversy, and until there has been information provided and examined it is hard to come to a conclusion about the use of amalgam in dental fillings. People outside of the dental profession may not be familiar with amalgam, and they may refer to their fillings as "silver" fillings because of their color. Despite the coloration, however, these fillings are not silver and contain many other types of chemicals, including mercury.

In an effort to clearly understand the issues and controversy surrounding amalgam fillings, it is necessary to look at the background information on the issue. From that point, a discussion can be engaged in and conclusions can be drawn that will allow the researcher to better understand why amalgam is used, what the concerns are regarding it, and how others have determined that it is safe to continue to use. Only then can suggestions and recommendations be made that will allow for further research and discussion to take place. With that in mind, the researcher can provide insight and helpful information to others who will study the use of amalgam in dental fillings in the future. Whether amalgam is deemed safe or whether it should no longer be used for fillings, the only way to decide the issue is through proper research and understanding.

Background Information

One of the best ways to begin a study is by writing down some of the prior assumptions on dental amalgams. Many people know that they are commonly used in dentistry and supported by established dentists. They also know that the American Dental Association (ADA) supports the use of dental amalgams, and deems them safe. However, one of the reasons why it is important to study the topic of dental amalgams is because they are controversial. Many patients believe that dental amalgams are toxic. A quick, simple online search reveals a large number of websites that talk about the dangers of dental amalgams. Taking a day and reviewing many of these websites is very enlightening. In addition to using the standard search engine, it is also valuable to use Google Scholar to collect information. That site leads a researcher to a number of publications, websites, books, and journals. Each had something different and interesting to say on dental amalgams.

The United States Food and Drug Administration defines dental amalgams broadly and generally. An amalgam is simply defined as "a dental filling material that is used to fill cavities caused by tooth decay," (FDA, 2012). The FDA (2012) has evaluated dental amalgams for safety because amalgams are classified as medical devices, which fall under the FDA's jurisdiction. Therefore, one of the things the researcher learned early on in the search was the process by which any medical device is evaluated. A company cannot simply market a medical product without first receiving approval from government bodies like the Food and Drug Administration. The researcher also learned that the U.S. FDA works together with other organizations such as the American Dental Association when it comes to products like amalgams. Another organization that has some jurisdiction over the use of mercury in amalgams is the United States Environmental Protection Agency (EPA, 2012).

In the course of the search, the researcher learned a little of the history of dental amalgams. They are not new. They have been used since the early 19th century (Scenihr & Scher, 2008). However, this fact alone would not deem amalgams safe. One of the causes of concern about amalgams is that they contain mercury, which is a known toxin when introduced into the human body. "As a single element, mercury is a poisonous metal to which we are all exposed through air, water, soil and food," (Canadian Dental Association, 2012). Mercury is classified as a heavy metal. It is unique in that mercury is liquid at room temperature, unlike other metals such as gold. It even turns into a vapor, which is one of the presumed problems with using mercury as a filling. Even in the 19th century, dental amalgams contained mercury as well as other metals. The other metals contained in amalgam alloys include silver, copper, and tin. These other metals are combined with mercury in an alloy amalgam.

Amalgams are used when there is a significant enough amount of tooth decay to warrant a filling. The dentist takes the material (the amalgam) and repairs the surface or structure of the tooth. At this point in the search, it was easy to wonder why mercury was used in dental amalgams and whether there were properties of mercury that made it attractive for that particular usage. After all, dental amalgams can be made with a number of materials that do not include mercury. Patients frequently request fillings that are made with alternative materials for two main reasons: one is concern over the safety of mercury in their mouths, and the other is aesthetics. Some new composite materials can be the color of the surrounding tooth. Acrylic is one of the materials that is used in amalgams. According to the EPA (2012), materials such as resin composite, glass ionomer, resin ionomer, porcelain, and gold alloys may also be used in tooth fillings. A tooth-colored filling is appealing because the filling blends in with the surrounding tooth, and does not stand out as a silver-filled tooth would.

In fact, the European Union released a report noting that fillings that use tooth-colored materials not only look better; they are also easier to maintain because they require less intervention or maintenance (Scenihr & Scher, 2008). Therefore, many people prefer to use materials other than mercury in their fillings. The researcher concluded, based on the research conducted, that mercury is a preferred material in dental fillings precisely for its unique chemical properties. It is liquid at room temperature, suggesting that the dentist can work easily with the material used in the amalgam. Yet the researcher could not help but wonder why there were no other materials with similar qualities that could be used, and which clearly posed no danger. The researcher also wondered if there were financial reasons why mercury has been supported by so many dental associations. Perhaps there are contracts that need to be fulfilled between amalgam manufacturers and mercury harvesters and distributors? Or perhaps the mercury-containing amalgams are significantly cheaper than their other composite components.

Scenihr & Scher (2008) point out that, in addition to silver, copper, and tin, zinc may also be used in the creation of amalgam. According to Scenihr & Scher (2008), the general proportion, or ratio, for an amalgam filling is one part mercury to one part alloy (any combination of silver, copper, tin, or zinc). The researcher was correct in assuming that the malleability of the mercury is the main reason why it is a favored amalgam material. The dentist will form a paste from the metal mixture, and apply this paste to the cavity. Then, the filling is pressed while it is still malleable. During the installation process, some mercury vapor may escape into the patient's mouth (Scenihr & Scher, 2008). The filling will also gradually release some vapor into the person's mouth over time, something that cannot be avoided. All of the major research organizations that the researcher came across in the search, including the American Dental Association, the Canadian Dental Association, the European Union, the United States Environmental Protection Agency, and the United States Food and Drug Administration, stated that the mercury content contained in dental amalgam is at levels that are safe for most adults and children over the age of six years.

However, there were some clear warnings of using mercury fillings provided by the FDA (2012). According to its research, "there is limited clinical information about the potential effects of dental amalgam fillings on pregnant women and their developing fetuses, and on children under the age of 6, including breastfed infants," (FDA, 2012). In addition to the lack of research on this potentially sensitive population, there may be individuals with an allergy to heavy metals (FDA, 2012). Concerns over the safety of mercury in general have led to a heavy reduction in the use of the metal. The EPA (2012) states, "the amount of mercury used in consumer products dropped 83% between 1980 and 1997, largely as a result of federal legislation and state regulatory limits on mercury usage." This could suggest that mercury is more dangerous than many dentists believe. Dentists, the researcher learned, are actually more at risk than their patients. "Dental workers are considerably more exposed to mercury than the general population. Their main sources of exposure are vapours released when placing or removing fillings and the exhaust air from dental vacuum systems," (Scenihr & Scher, 2008).

Therefore, the researcher learned that all dentists should be aware that their patients may not be entirely comfortable using dental amalgams containing mercury. Dentists should be open to discussing other filling options with their patients, and pointing out the pros and cons of each. The more the researcher studied the topic of dental amalgams, the more interested in them the researcher became. That led to a narrowing of the topic, as the researcher decided to focus on possible financial differences between mercury-containing amalgams and other types of amalgams. Perhaps the mercury supply companies are interested in recouping their losses due to the stricter regulations of mercury in products like paint and batteries (EPA, 2012). It would be an interesting research report, to discover whether there were financial motives to the continued use of mercury in dental fillings. The organization DAMS (2012) takes a more cynical approach. "Perhaps the ADA feels that, since it has defended and promoted the use of mercury amalgam fillings throughout its entire history, it could not survive if it were to admit that it has been wrong over the last century and a half."

As the researcher did the search, the researcher also became interested in knowing what dentist's general attitudes are toward the use of mercury fillings. After all, having mercury in the office can be a potential hazard. If there is a natural disaster of sorts that upsets the office storage unit containing mercury, the poisonous vapors can be released into the environment. There is a non-profit organization called Dental Amalgam Mercury Solutions that has been formed in response to concerns about mercury in dental amalgams. The researcher went to their website to learn about the opposition movement against this heavy metal in amalgam. The DAMS (2012) website claims, "We believe there a cover-up of the health hazards of dental mercury and a failure by regulators who are responsible for protecting the public health."

Therefore, the search showed that even the simplest thing like dental amalgams can be hugely controversial. Whereas the American Dental Association (2012) clearly supports the use of dental amalgams, it fails to inform patients why mercury is actually necessary in those amalgams. Surely with the plethora of other materials on the market, there are substances that are non-toxic that can be used inside the mouth. Dentists should also be concerned about the way mercury is stored in their offices, because an earthquake or even just carelessness could lead to the release of toxic mercury vapors.

Discussion and Conclusion

The researcher used JSTOR to locate the article "The contribution of dental amalgam to urinary mercury excretion in children." (Woods, et al., 2007). Given the scientifically controversial nature of the topic, a peer-reviewed article containing recent data was fairly easy to locate. Simply typing in the words 'dental amalgam' yielded a current article from a peer-reviewed journal on a specific subtopic of interest to the researcher, namely the impact of amalgams on children's levels of mercury in their systems. The article was from Environmental Health Perspectives and was narrated primarily from a health-related perspective rather than from the perspective of the dental industry. The article compared urinary concentrations of mercury in 506 children, ages 8-10 over a period of seven years. Children were randomly assigned to a group of either amalgam or composite categories for treatment.

Higher urinary concentrations in the experimental amalgam group were noted. Girls seemed to show greater ability to excrete the mercury than boys, causing the researchers to hypothesize that "a specific urinary mercury concentration measured in girls represents a lesser risk of mercury toxicity than the same urinary concentration in boys. This issue speaks directly to the question of differential sensitivity" which warrants further explanation (Woods 2007: 1531). The article noted that it was building upon research that had studied different impacts of mercury upon different individuals -- not all persons are affected equally by exposure. Mercury exposure, according to Woods, et al. (2007), is associated with "impairment of the developing central nervous system, along with attendant personality, motor function, and behavioral disorders "(Woods 2007: 1527).

However, the New England Children's Amalgam Trial (NECAT), found no significant differences in "over a 5-year follow-up interval, between the neuropsychological scores of children for whom dental amalgam was used to repair caries and the scores of children for whom mercury-free composite materials were used" in a study of 534 6- to 10-year-old urban and rural children (Bellinger et al. 2007: 440). The discrepancy between the two studies is notable. Bellinger, et al. (2007) states that the results of the study support their contention that no alarm is warranted regarding the use of dental amalgams in children and that the amalgams are not associated with mercury toxicity. However, the authors do note "that the follow-up interval of 4-5 years might have been too short to allow for the expression of such deficits" and the Woods (2007) study was conducted over the course of ten years (Bellinger et al. 2007: 445). The authors also note that "the critical window of children's greatest vulnerability to elemental mercury might already have passed by the time the children were enrolled in the trial (6 years of age). Given the heightened sensitivity of the fetus to methylmercury, prenatal exposure to mercury vapor, which is known to cross the placenta, warrants increased attention" (Bellinger et al. 2007: 445).

After reading these two articles, the researcher first located an article in the journal of Pediatrics (a peer-reviewed journal available for public access on the World Wide Web) cited in the Woods (2007) piece discussing different levels of environmental sensitivity in different individuals. Although mercury at high levels is a toxin, the impact upon different persons on a case-by-case basis may vary. The researcher also reviewed two of the articles that had been consulted in a past piece of research, which the researcher retrieved from ProQuest, on the subject of levels of mercury in women who were breastfeeding or who had just given birth, and the notable effects on the mercury levels of infants.

According to Razagui & Haswell (2001), women and their infants who received amalgams during pregnancy have significantly higher concentrations of mercury in tests of their scalp hair. Norouzi, Bahramifar, & Ghasempouri (2012) found that women receiving amalgams who breast-fed had significantly higher concentrations of mercury in their breast milk than the safe levels set by the World Health Organization (WHO). The conclusion that emerges from this research is that more research needs to be done on different levels of sensitivity to mercury in children, especially young children, and that there is a pattern among a series of independent small studies indicating that mercury exposure to infants from maternal dental amalgams can be potentially harmful. While this is a serious issue, there is still no definitive conclusion as to the danger levels of dental amalgams. This is why more studies are clearly needed in order to study potential amalgam dangers.