Mercury fillings, formally called dental amalgam, are a mixture of roughly 50% liquid mercury and 50% metal alloy powder used to fill cavities. They’ve been a standard dental material for over 150 years, recognizable by their silver-gray metallic appearance. Despite their long track record, growing concerns about mercury exposure have led to significant regulatory shifts worldwide, and many dentists now default to newer alternatives.
What’s Actually in a Mercury Filling
The name “silver filling” is a bit misleading. While silver is the largest component of the alloy powder, mercury makes up about half the filling by weight. The liquid mercury is mixed with the alloy in a 1-to-1 ratio, creating a putty-like material that hardens inside the tooth.
The alloy powder in a conventional amalgam contains 67% to 74% silver, 25% to 28% tin, and smaller amounts of copper (up to 6%), zinc (up to 2%), and trace mercury. Some newer formulations, called high-copper amalgams, bump the copper content up to 30%, which improves strength and corrosion resistance. Once mixed and placed in a cavity, the mercury binds with these metals to form a solid, durable restoration.
Why Mercury Is the Controversial Part
Mercury doesn’t just sit inert in the filling. Small amounts of mercury vapor are continuously released, especially when you chew, grind your teeth, or drink hot liquids. This vapor is inhaled and absorbed into the bloodstream. For most adults, the levels are extremely low. But those low levels have raised questions about long-term effects on two organ systems in particular: the kidneys and the nervous system.
A study on children with amalgam fillings found measurable effects on kidney tubular function, with a dose-dependent relationship between urinary mercury levels and markers of kidney stress. The lowest observable effect appeared at mercury concentrations below previously reported thresholds, suggesting that even small exposures may not be entirely benign for developing bodies. Researchers also found that mercury from amalgam may disrupt the body’s ability to repair DNA damage and can interfere with porphyrin metabolism, a process essential for making hemoglobin and other critical molecules.
None of this means a single filling will poison you. The debate is about cumulative, lifelong exposure, particularly for people who have many fillings or who belong to sensitive populations. The dose matters, and so does individual vulnerability.
Who Should Avoid Them
The FDA updated its recommendations to identify specific groups who should avoid amalgam fillings when possible:
- Children under six
- Pregnant women or women planning to become pregnant
- Nursing mothers
- People with existing kidney dysfunction
- People with neurological conditions
- Anyone with a known sensitivity to mercury, silver, copper, tin, or zinc
For everyone else, the FDA considers amalgam an acceptable material but acknowledges the need for continued evaluation. The practical takeaway: if you fall into one of these groups and need a filling, ask your dentist about alternatives.
How They Compare to Modern Alternatives
Composite resin fillings (tooth-colored fillings) have become the dominant alternative. They’re made from a blend of plastic resin and fine glass particles, bonded directly to the tooth. Beyond the obvious cosmetic advantage of matching your natural tooth color, the performance data is surprisingly favorable.
A large-scale study analyzing over 668,000 restorations found that composite fillings actually had a lower failure rate than amalgam: 11.87% versus 17.38% over the study period. The mean annual failure rate was 3.06% for composites compared to 3.55% for amalgam. This challenges the long-held assumption that amalgam lasts significantly longer. Composites do have limitations in very large cavities or areas under extreme chewing force, but for most fillings, they perform at least as well.
Other options include glass ionomer fillings, which release fluoride and are sometimes used in children, and ceramic or gold restorations for situations requiring maximum durability. Your dentist can help match the material to the size and location of the cavity.
Global Phase-Down Efforts
The Minamata Convention on Mercury, an international treaty, requires participating countries to phase down the use of dental amalgam. The treaty specifically restricts amalgam use in children and pregnant women and has been amended over time to tighten these provisions. The European Union has gone further, banning amalgam use in children under 15 and in pregnant or nursing women since 2018, with broader restrictions continuing to expand.
In the United States, the EPA passed regulations in 2017 requiring all dental offices that place or remove amalgam to install and maintain amalgam separators. These devices capture mercury waste before it enters the public sewer system. Dental offices must also avoid discharging scrap amalgam and submit compliance reports to local authorities. Mercury from dental offices had been one of the largest sources of mercury entering wastewater treatment plants, so these rules addressed a significant environmental pathway.
What Happens If You Want Existing Fillings Removed
If you already have mercury fillings, the general consensus is that removing them solely to reduce mercury exposure isn’t always necessary, especially if the fillings are intact and you’re not in a high-risk group. Removal itself temporarily spikes your mercury exposure because drilling through amalgam generates vapor and fine particles.
When removal is warranted (because a filling is damaged, decayed, or a patient’s health situation calls for it), some dentists follow a protocol called SMART, developed by the International Academy of Oral Medicine and Toxicology. The key protective measures include:
- External air or oxygen delivered through a nasal mask so you don’t inhale vapor during the procedure
- A non-latex nitrile dental dam sealed around the tooth, with a saliva ejector underneath to catch debris
- High-volume air filtration capable of removing mercury vapor from the room
- Full-body impermeable barriers covering the patient’s skin, head, face, and neck
- A pre-procedure rinse with charcoal or a similar substance to help absorb any particles that reach the throat
- Mercury-rated respiratory masks for the dentist and all staff in the room
Not every dental office offers this level of protection. If safe removal matters to you, look for a dentist who specifically follows these protocols and has the equipment to do it properly. The filling is then replaced with composite resin or another mercury-free material.
The Bottom Line on Safety
Mercury fillings are not acutely dangerous for most adults. Millions of people have them without obvious health effects. But the evidence for subtle biological effects, particularly on kidney function and at lower exposure thresholds than previously assumed, has been strong enough to shift both regulatory policy and clinical practice. Most dentists in North America and Europe now place composite fillings by default, and amalgam use continues to decline year over year. If you’re getting a new filling, composite resin is the standard choice. If you have old amalgam fillings that are still intact, there’s no urgent need to rush into removal unless you’re in a high-risk group or the filling itself needs replacing.