An amalgam filling is a silver-colored dental restoration made from a mixture of roughly 50% liquid mercury and 50% metal alloy powder, primarily silver and tin. Dentists have used this material to fill cavities in back teeth for over 150 years, and it remains one of the most durable filling options available, though its use is declining worldwide due to environmental and health concerns about mercury.
What’s Inside an Amalgam Filling
The metal alloy powder in a typical amalgam filling contains 67% to 74% silver, 25% to 28% tin, and smaller amounts of copper (up to 6%), zinc (up to 2%), and trace mercury (up to 3%). This powder is mixed with an equal weight of liquid elemental mercury right before the filling is placed. When the mercury contacts the alloy, it dissolves the silver and tin, and new crystalline structures begin forming almost immediately. These crystals grow and interlock over several hours, turning the soft paste into a hard, solid mass that can withstand years of chewing pressure.
Some modern formulations use higher copper content, up to 30%, which improves strength and corrosion resistance. These “high-copper” amalgams have largely replaced older formulations in practices that still offer the material.
How a Dentist Places One
After removing the decayed portion of tooth, the dentist mixes the alloy powder and mercury together in a small vibrating machine called an amalgamator. The freshly mixed amalgam has a soft, putty-like consistency that needs to be packed into the tooth quickly before it begins to harden.
The dentist loads small amounts into the cavity using a carrier tool, then firmly presses each layer down with a condenser. This compacting step is critical: it pushes the amalgam into every corner of the preparation and forces excess mercury to the surface, where it can be removed. The dentist overfills the cavity by about a millimeter, then immediately begins carving the extra material away with sharp instruments, sculpting the natural grooves and ridges of the tooth’s biting surface. The whole condensing phase takes roughly two and a half to three and a half minutes. The filling continues to harden over the next 24 hours, during which you’re typically told to avoid chewing hard foods on that side.
How Long They Last
Amalgam fillings are remarkably durable. A systematic review comparing amalgam to tooth-colored composite resin found that amalgam restorations had median survival times exceeding 16 years, compared to about 11 years for composites. One study tracked both materials and reported a 94.4% survival rate for amalgam versus 85.5% for composite fillings. That said, the gap has narrowed with newer composite materials. Some studies looking at five-year outcomes found no significant difference between the two, with both types surviving at rates around 77% to 79%.
The advantage of amalgam shows up most clearly in large fillings on back teeth, where the chewing forces are strongest. Amalgam’s self-sealing property also helps: as it corrodes slightly over time, the corrosion products fill microscopic gaps at the edges, reducing the chance of new decay forming underneath.
The Mercury Safety Question
Mercury is the part of amalgam that makes people uneasy, and reasonably so. Elemental mercury is a neurotoxin at high doses. Amalgam fillings do release tiny amounts of mercury vapor continuously, particularly during chewing, teeth grinding, and drinking hot liquids. Measurements of mercury vapor inside the mouths of people with amalgam fillings show an average daily dose of about 1.3 micrograms, with a range of 0.3 to 2.2 micrograms per day.
To put that in context, the World Health Organization estimates that most people absorb 2.4 micrograms of mercury daily from food alone, primarily from fish. The amount released by fillings is well below thresholds associated with health effects in the general population. However, the FDA has acknowledged uncertainty about cumulative exposure in certain groups and recommends that the following people avoid amalgam fillings when possible: pregnant women, women planning to become pregnant, nursing mothers, children under six, people with neurological conditions like multiple sclerosis, Alzheimer’s, or Parkinson’s disease, people with impaired kidney function, and anyone with a known allergy to mercury or other amalgam components.
Importantly, the FDA does not recommend removing existing amalgam fillings that are in good condition. The removal process itself temporarily increases mercury vapor exposure and can require drilling away healthy tooth structure, which may create more risk than leaving the filling in place.
Safe Removal If Needed
When amalgam fillings do need to come out, whether because they’re failing or a patient and dentist decide replacement is appropriate, some dentists follow specialized safety protocols to minimize mercury exposure during the procedure. These typically involve placing a rubber dam around the tooth to isolate it from the rest of the mouth, positioning activated charcoal or similar absorbents under the dam to catch any particles, supplying the patient with oxygen through a nasal mask so they aren’t breathing in vapor, and using high-volume suction along with continuous water spray during drilling. The dentist sections the filling into chunks and scoops them out rather than grinding the entire restoration into fine particles, which would release more vapor. Specialized air filtration systems may also be used in the treatment room.
Cost Compared to Tooth-Colored Fillings
Amalgam and composite resin fillings are priced similarly in many markets. Fee schedules from 2025 show identical reimbursement rates for both materials on back teeth, ranging from roughly $62 for a single-surface filling to $130 for a large four-surface filling. In private practice, composite fillings sometimes cost slightly more because the placement technique is more sensitive and time-consuming, but the difference is often modest. Insurance coverage for both types is generally comparable for back teeth.
The Global Phase-Down
Amalgam use is declining around the world, driven largely by the Minamata Convention on Mercury. This international treaty, adopted in 2013 and legally binding since 2017, calls for a phase-down of dental amalgam as part of broader efforts to reduce mercury in the environment. Over 128 countries signed on, and most are working toward implementation timelines between 2020 and 2030.
The European Union has gone further than most. Starting in January 2025, EU member states prohibited the export of dental amalgam and restricted its clinical use to situations where a dentist determines it is strictly necessary based on a patient’s specific medical needs. Manufacturing and importing dental amalgam within the EU will be banned entirely from July 2026. Many individual countries outside Europe have also moved toward elimination or significant restriction, though progress varies widely.
In the United States, amalgam remains available and legal, but its use has dropped substantially as composite materials have improved. Many dental schools now teach composite placement as the default technique, and a growing number of practices no longer stock amalgam at all.