Q: I heard that dental fillings contain mercury. Are these fillings safe? Do I need to worry about mine?

Do you have silver-colored fillings in your teeth? This type of dental filling, called amalgam, contains 50% mercury. If you have one or more, you aren’t alone. Amalgam is the most common type of dental filling and is used by dentists around the world.

This may seem strange and even scary because we’ve all heard the dangers of mercury. If too much of this toxic heavy metal gets into your system, you become tired, disoriented, have behavior changes, and lose control over your body and senses¹ Mercury. November, 2009, from https://www.cdc.gov/biomonitoring/pdf/Mercury_FactSheet.pdf . Ever hear of the term “Mad Hatter” or “mad as a hatter”? Long ago, English hat makers used mercury to treat animal fur when making felt hats. After years of exposure to mercury, they showed these symptoms. Their rapid mood changes and quick tempers, in particular, led others to refer to the condition as mad hatter’s disease² Mad hatter’s disease https://dictionary.webmd.com/mad-hatter’s-disease.

If mercury is so dangerous, why in the world do we use it in dental fillings?

Concerns about safety aside, mercury is a great element to use in fillings. Besides mercury, amalgam contains primarily silver, tin, and copper³About Dental Amalgam Fillings. (2017, December 5). https://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/DentalProducts/DentalAmalgam/ucm171094.htm. These metals provide strength and durability to the filling, but dentists need a way to combine them. Mercury is a liquid metal and so serves as an excellent mixing agent. It also lets the material remain pliable long enough for a dentist to fill in a cavity before hardening. Compared to other types of fillings that don’t contain mercury, amalgam is cheaper and lasts longer through all the chewing, talking, and jaw clenching that happen on a daily basis⁴Bernardo, M., Luis, H., Martin, M. D., Leroux, B. G., Rue, T., Leitão, J., & Derouen, T. A. (2007). Survival and reasons for failure of amalgam versus composite posterior restorations placed in a randomized clinical trial. The Journal of the American Dental Association,138(6), 775-783. doi:10.14219/jada.archive.2007.0265 https://www.ncbi.nlm.nih.gov/pubmed/17545266⁵Soncini, J. A., Maserejian, N. N., Trachtenberg, F., Tavares, M., & Hayes, C. (2007). The longevity of amalgam versus compomer/composite restorations in posterior primary and permanent teeth. The Journal of the American Dental Association,138(6), 763-772. doi:10.14219/jada.archive.2007.0264 https://www.ncbi.nlm.nih.gov/pubmed/17545265⁶Alcaraz, M. G., Veitz-Keenan, A., Sahrmann, P., Schmidlin, P. R., Davis, D., & Iheozor-Ejiofor, Z. (2014). Direct composite resin fillings versus amalgam fillings for permanent or adult posterior teeth. Cochrane Database of Systematic Reviews. doi:10.1002/14651858.cd005620.pub2 https://www.ncbi.nlm.nih.gov/pubmed/24683067. Mercury fillings also take the least amount of time to complete, which kids (and adults) who dread sitting in the dental chair appreciate. For all of these reasons, amalgam became and remains popular over the 100+ years we’ve used it.

Ok, sounds logical, but it contains mercury! Mercury! I don’t want to become a mad hatter! Is it safe to have or get these fillings?

Aside from some allergic reactions, abundant scientific research, carried out over decades and around the world, shows no link between amalgam fillings and negative health effects.⁷Ahlqwist, M., Bengtsson, C., & Lapidus, L. (1993). Number of amalgam fillings in relation to cardiovascular disease, diabetes, cancer and early death in Swedish women. Community Dentistry and Oral Epidemiology,21(1), 40-44. doi:10.1111/j.1600-0528.1993.tb00717.x https://www.ncbi.nlm.nih.gov/pubmed/8432105⁸Ahlqwist, M., Bengtsson, C., Lapidus, L., Gergdahl, I. A., & Schütz, A. (1999). Serum mercury concentration in relation to survival, symptoms, and diseases: Results from the prospective population study of women in Gothenburg, Sweden. Acta Odontologica Scandinavica, 168-174. https://www.ncbi.nlm.nih.gov/pubmed/10480284⁹Bates, M. N. (2004). Health effects of dental amalgam exposure: A retrospective cohort study. International Journal of Epidemiology,33(4), 894-902. doi:10.1093/ije/dyh164 https://www.ncbi.nlm.nih.gov/pubmed/15155698¹⁰Herrström, P., Schütz, A., Raihle, G., Holthuis, N., Högstedt, B., & Råstam, L. (1995). Dental Amalgam, Low-Dose Exposure to Mercury, and Urinary Proteins in Young Swedish Men. Archives of Environmental Health: An International Journal,50(2), 103-107. doi:10.1080/00039896.1995.9940886 https://www.ncbi.nlm.nih.gov/pubmed/7786045¹¹Pang, B. K., & Freeman, S. (1995). Oral lichenoid lesions caused by allergy to mercury in amalgam fillings. Contact Dermatitis,33(6), 423-427. doi:10.1111/j.1600-0536.1995.tb02079.x https://www.ncbi.nlm.nih.gov/pubmed/8706402¹²Kingman, A., Albers, J. W., Arezzo, J. C., Garabrant, D. H., & Michalek, J. E. (2005). Amalgam Exposure And Neurological Function. NeuroToxicology,26(2), 241-255. doi:10.1016/j.neuro.2004.09.008 https://www.ncbi.nlm.nih.gov/pubmed/15713345¹³Factor-Litvak, P., Hasselgren, G., Jacobs, D., Begg, M., Kline, J., Geier, J., . . . Graziano, J. (2002). Mercury Derived from Dental Amalgams and Neuropsychologic Function. Environmental Health Perspectives,111(5), 719-723. doi:10.1289/ehp.5879 https://www.ncbi.nlm.nih.gov/pubmed/12727600¹⁴Bjorkman, L., Pedersen, N. L., & Lichtenstein, P. (1996). Physical and mental health related to dental amalgam fillings in Swedish twins. Community Dentistry and Oral Epidemiology,24(4), 260-267. doi:10.1111/j.1600-0528.1996.tb00856.x https://www.ncbi.nlm.nih.gov/pubmed/8871034¹⁵Saxe, S. R., Snowdon, D. A., Wekstein, M. W., Henry, R. G., Grant, F. T., Donegan, S. J., & Wekstein, D. R. (1995). Dental Amalgam and Cognitive Function in Older Women: Findings From the Nun Study. The Journal of the American Dental Association,126(11), 1495-1501. doi:10.14219/jada.archive.1995.0078 https://www.ncbi.nlm.nih.gov/pubmed/7499646¹⁶Saxe, S. R., Weksein, M. W., Kryscio, R. J., Henry, R. G., Comett, C. R., Snowdon, D. A., . . . Markesbery, W. R. (1999). Alzheimer’s disease, dental amalgam and mercury. The Journal of the American Dental Association, 191-199. https://www.ncbi.nlm.nih.gov/pubmed/10036842¹⁷Bailer, J., Rist, F., Rudolf, A., Staehle, H. J., Eickholz, P., Triebig, G., . . . Pfeifer, U. (2001). Adverse health effects related to mercury exposure from dental amalgam fillings: Toxicological or psychological causes? Psychological Medicine,31(2), 255-263. doi:10.1017/s0033291701003233 https://www.ncbi.nlm.nih.gov/pubmed/11232913¹⁸Mercury Study Report to Congress. (1997, December). https://www.epa.gov/sites/production/files/2015-09/documents/volume5.pdf How is this possible, you ask?

We tend to look at elements and think we know the whole story. Iron is iron, mercury is mercury, right? Well, you may be surprised to know that there are different types of mercury, each with unique properties¹ Mercury. November, 2009, from https://www.cdc.gov/biomonitoring/pdf/Mercury_FactSheet.pdf :

• Elemental mercury is the most familiar to us. This is the silver liquid you see in old thermometers, electronics, and some blood pressure monitors. This is also the type used in dental fillings.
• Inorganic mercury compounds are formed when elemental mercury combines with other elements. Some industries use these in chemical reactions to make other products. In some countries (but not the United States), companies use these compounds in lotions to lighten skin tones. These lotions are not safe to use!
• Organic mercury compounds comprise another solid form of mercury and are created when elemental or inorganic mercury combine with carbon. Methyl mercury is an organic mercury compound that people have probably warned you about. Has anyone ever told you to stop eating so much fish? Methyl mercury accumulates in fish, and in us if we eat too much fish. That’s right—slow down on the tuna fish crackers. 

Because these forms of mercury have different properties and chemical make-ups, our bodies treat them differently. Inorganic and organic mercury compounds are toxic if you eat or drink too much of them, but because they are solids, it’s rare to get sick from inhaling them¹ Mercury. November, 2009, from https://www.cdc.gov/biomonitoring/pdf/Mercury_FactSheet.pdf .

On the other hand, your gastrointestinal tract is terrible at absorbing elemental mercury—the kind in our fillings. According to studies analyzed by the EPA, you will only ingest 0.01% of the elemental mercury you swallow, making it essentially non-toxic¹⁸Mercury Study Report to Congress. (1997, December). https://www.epa.gov/sites/production/files/2015-09/documents/volume5.pdf . That means you absorb 1 mercury atom for every 10,000 that you swallow. However, elemental mercury can be quite toxic if you inhale it as a vapor, which is how happy hatters became mad hatters. It’s estimated that you absorb 80% of the mercury that you inhale¹⁹ Health Effects. https://www.atsdr.cdc.gov/toxprofiles/tp46-c2.pdf.

That said, you can begin to understand why elemental mercury in fillings doesn’t pose the health threat you might expect. If you swallow trace amounts (or even a small piece) of mercury from your fillings when you eat or drink, for example, it will pass harmlessly through your gut.

So…mercury dental fillings are safe? It’s ok to have a few?

The short answer based on current research is yes, but it would be irresponsible to not finish the story, which gets a little more complicated when you consider the other route of exposure: inhalation of mercury vapors. Studies show that mercury-based fillings do release small amounts of mercury vapor, which you inhale²⁰Berglund, A. (1992). Release of mercury vapor from dental amalgam. Sweedish Dental Journal Supplement, 1-52. https://www.ncbi.nlm.nih.gov/pubmed/1475757. This vapor is released naturally over time when you grind your teeth or chew. When scientists measured mercury levels in people’s exhaled air, blood, and urine, they found that those with fillings have higher levels of mercury than those without. Even so, these levels were 30x lower than the lowest concentration known to cause mercury poisoning symptoms²¹Taut, C. (2013). Dental amalgam: Is this the end? Journal of Irish Dental Association. https://www.ncbi.nlm.nih.gov/pubmed/24575616.

The World Health Organization (WHO), the Food and Drug Administration (FDA), and many other organizations have separately reviewed the scientific literature on the health risks of dental amalgam and declared it safe³ About Dental Amalgam Fillings. (2017, December 5). https://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/DentalProducts/DentalAmalgam/ucm171094.htm²²Mjör, I. A., & Pakhomov, G. N. (Eds.). (1997). Dental Amalgam and Alternative Direct Restorative Materials. http://apps.who.int/iris/bitstream/handle/10665/63711/WHO_ORH_AMAL_97.2.pdf?sequence=1&isAllowed=y. Comparatively little research has been done on children under six and pregnant women, so they aren’t given amalgam fillings as a safety precaution.

They say the dose makes the poison, and the dose of mercury that you get from fillings, even if you have many, isn’t high enough to make you sick.

Hold on! If amalgam fillings are safe, why are some countries talking about banning them or phasing them out?

Right now, many governments and health-related organizations share an opinion that healthcare products containing mercury should be phased out. This includes amalgam fillings, and several groups already put plans in motion to achieve this. Most notably, WHO is phasing out dental amalgam in several developing countries and pushing mercury-free fillings instead.

This movement stems from concerns over the environmental impact of mercury waste, not health concerns from dental fillings. For example, when human remains are cremated, the dental fillings will melt and release that mercury as vapor, which flows into the atmosphere and is breathed in by people everywhere. Additionally, mercury waste that seeps into the ground can combine with other elements to form mercury compounds that can easily enter the food chain. The full environmental impact of mercury waste isn’t fully understood, but many organizations and governments want to start taking safety measures.

So what’s your conclusion?

Researchers around the world have conducted numerous scientific studies on this topic and have not found proof that amalgam fillings lead to adverse health effects. Major health and safety organizations have analyzed the available research and declared dental amalgam safe because elemental mercury is poorly absorbed in your digestive tract and fillings generate too little mercury vapor to make you sick by inhalation.