I had my first tooth cavity in my late teens. The dentist used a silver-mercury amalgam as the filling material. Amalgams contain silver and approximately 50% elemental mercury along with small amounts of tin and copper, all mixed before filling a tooth. Amalgam has been a dental standard for almost 150 years. It forms a barrier to further tooth decay with the mix keeping the mercury bound so that it never becomes a health risk. Or so we thought.

It turns out that mercury overexposure can lead to neurological, lung, muscle and kidney damage. It can affect cognition, memory and cause behavioural and anxiety issues. It causes skin rashes.

The recommendation regarding mercury is to limit exposure. So, why has mercury been a staple in treating cavities? And other than dental fillings, how else can we be exposed to elemental mercury?

In Canada, mercury poisoning has made headlines. The notoriety of a Dryden, Ontario pulp and paper mill causing mercury pollution to the Wabigoon River in the 1960s is a story without an end. It has been a public health disaster. Two First Nations communities, Grassy Narrows and the Wabaseemoong Independent Nation, have been exposed to elevated mercury levels from fish caught in the Wabigoon. This has led to Minamata disease, a neurological disorder caused by mercury poisoning. Despite the plant's discharge of 10 tons of mercury from 1962 to 1970, and subsequent attempts at cleanup, the river continues to be a source of mercury pollution affecting more than half of the inhabitants of these two communities.

Another source of mercury comes from old glass thermometers that contained a column of mercury. These thermometers tended to break with the contents spilling out and forming tiny silver spherules. When I was young, my brothers and I would scoop up the liquid mercury and use it to coat coins. When the mercury dried, it turned into a red powdery residue.

Another mercury source dates back to my childhood. Back then, a commonly used topical antiseptic was called Mercurochrome. As you might guess, Mercurochrome contained elemental mercury. When I had a cut or scrape, my mom would apply Mercurochrome. It was an alternative to iodine, which stung. When Mercurochrome disappeared from drugstore shelves in North America in 1998, I didn't think about the potential health hazard.

By far, however, the most common source of mercury exposure comes from ingesting it in food. Large game fish like tuna, swordfish, marlin, mackerel, grouper, and tilefish are apex predators, at the top of the food chain and accumulate mercury in their tissue over a lifetime. The mercury at Grassy Narrows came from eating Walleye, a freshwater fish considered to be a riverine apex predator.

For fish eaters, it should be noted that smaller saltwater and freshwater species, such as cod, tilapia, and sardines, don't pose a mercury health threat with concentrations at safer levels.

When a press release I received on November 4, 2025, talked about dental amalgams and elemental mercury as a threat, I decided it was worth investigating. The release came from the International Academy of Oral Medicine and Toxicology (IAOMT). It was entitled "Dental Amalgams and Blood Mercury Concentrations in American Adults" and presented data from a CDC study stating that approximately 104 million Americans with mercury amalgam dental fillings were at risk of elevated blood mercury levels to dangerous thresholds. The study revealed that adults between the ages of 18 and 70 with amalgam fillings had significantly higher blood inorganic mercury levels than those without. The number of filled cavities where amalgam was used strongly correlated with increased mercury levels in blood. The CDC study estimated that 16 million adults were being exposed to mercury vapour doses exceeding U.S. EPA safety limits. Mercury in the blood was the key to delivering the toxin in tissues and cells throughout the body, leading to increased risk of asthma, arthritis, hearing loss, neurological disorders, and perinatal death.

In this week's IAOMT press release, Dr. Douglas Green, the organization's president, states, "The evidence is irrefutable. Mercury amalgam fillings are a public health crisis, poisoning millions of Americans with unsafe levels of mercury. We urgently call on the FDA to ban these harmful fillings in order to safeguard public health."

Interestingly, these conclusions had been stated before. A 2020 research report commissioned by the U.S. Food and Drug Administration (FDA) led to a recommendation back then that silver-mercury amalgams were a risk to pregnant women and their fetuses, nursing mothers, children under six, individuals with mercury allergies, and those with neurological or kidney impairments.

What about dentists, hygienists and assistants who were handling the materials in amalgams? I thought of my wife, who in the past had worked for several dental practices as a chairside assistant. Among her responsibilities was mixing amalgams, which exposed her to mercury. Could this continuous exposure have put her at risk?

In a 2018 study appearing in Environmental Research, symptoms reported by dental personnel noted "deleterious health effects from occupational exposure to metallic mercury." Despite these effects, that study noted that amalgam continued to be used as the most common dental restorative material even though the World Health Organization (WHO) had recommended phasing it out and exchanging it for alternatives. Why hadn't this happened? The reason given for the continuing use of amalgams was that alternative materials were considered too expensive for middle and low-income countries. Meanwhile studies continued to report that dentists and staff exposed to excessive amounts of mercury had increased risk of neurological and cognitive problems, and elevated reports of fibromyalgia and chronic fatigue syndrome.

For patients, the IAOMT is recommending that they talk to their dentists and doctors about the option to safely remove amalgam fillings where old fillings are breaking down and in need of replacement. The IAOMT offers a training program called the Safe Mercury Amalgam Removal Technique (SMART) that can protect both patients and dental staff from exposure to mercury vapour.

With what we know about mercury poisoning and the hundreds of millions of people with amalgams, wouldn't you think that we would be monitoring mercury levels through normal blood screening? No! Currently, a dedicated mercury blood level test is required if there is suspicion of mercury exposure or poisoning. Why? Because the occurrence within the general population is still considered uncommon.