An amalgam filling is a silver-colored dental restoration made from a mixture of metals, used to repair teeth damaged by cavities. It’s one of the oldest and most durable filling materials in dentistry, with a track record stretching back more than 150 years. About half of an amalgam filling by weight is liquid mercury, and the other half is a powdered alloy of silver, tin, and copper. That mercury content is what makes amalgam both effective and controversial.
What’s Inside an Amalgam Filling
The filling starts as two separate components: liquid elemental mercury and a fine metal powder. When mixed together, the mercury binds with the silver, tin, and copper particles to form a putty-like substance that a dentist can pack into a prepared cavity. Within minutes, the mixture begins to harden into a solid, corrosion-resistant mass.
Mercury makes up roughly 50% of the final filling. Silver is the largest component of the powder, giving the filling its characteristic metallic color, while tin and copper round out the alloy. Once the metals fully react with the mercury, the result is a stable compound that holds up well under the heavy chewing forces in your back teeth.
How Long Amalgam Fillings Last
Durability is the main reason dentists still use amalgam. On average, an amalgam filling lasts about 15 years before it needs to be replaced, though the actual range is wide. Some fillings fail in under a decade, while others hold up for 30 or even 40 years. A 2008 analysis of fillings placed in private dental practices found survival times ranging from roughly 7 to 45 years, depending on the size of the filling, its location, and the patient’s oral habits.
Amalgam handles compressive force well, which is why it’s most commonly placed in molars. These are the teeth that bear the brunt of chewing, and amalgam can withstand that pressure without cracking or wearing down the way some other materials might. It also tolerates moisture during placement better than tooth-colored alternatives, which makes it easier to work with in areas that are hard to keep dry.
How Amalgam Compares to Composite Fillings
The main alternative to amalgam is composite resin, a tooth-colored material made of plastic and fine glass particles. For most patients choosing between the two, the tradeoffs come down to appearance, longevity, and cost.
- Appearance: Composite fillings match the color of your natural teeth, making them nearly invisible. Amalgam fillings are silver when new and darken over time, which makes them noticeable when you open your mouth wide.
- Longevity: Amalgam generally outlasts composite. Composite fillings typically need replacement sooner, especially in large cavities on back teeth where chewing forces are highest.
- Tooth preservation: Composite bonds directly to the tooth surface, so the dentist can often remove less healthy tooth structure during preparation. Amalgam doesn’t bond to teeth. Instead, the dentist has to shape the cavity with slight undercuts so the filling locks into place mechanically, which sometimes means removing a bit more tooth material.
- Cost: Amalgam fillings are generally less expensive than composite, though the gap has narrowed as composite techniques have improved.
The Mercury Safety Question
The presence of mercury is the single biggest concern patients have about amalgam. Once hardened, amalgam fillings do release tiny amounts of mercury vapor, particularly during chewing, tooth grinding, and drinking hot liquids. Studies measuring the vapor released inside the mouth estimate the average daily dose absorbed through the lungs at about 1.3 micrograms per day, with a range of 0.3 to 2.2 micrograms depending on the number and size of fillings. A small additional amount, roughly 1 microgram per day, is absorbed through the digestive tract from mercury-containing saliva that gets swallowed.
To put those numbers in perspective, the average person absorbs more mercury from food (especially fish) and environmental exposure than from a few amalgam fillings. The FDA considers amalgam safe for the general adult population but has flagged specific groups that may face higher risk from even low-level mercury exposure. Those groups include:
- Pregnant women and women planning to become pregnant
- Nursing mothers
- Children under six years old
- People with neurological conditions like multiple sclerosis, Alzheimer’s disease, or Parkinson’s disease
- People with impaired kidney function
- Anyone with a known allergy to mercury or other amalgam components
For these groups, the FDA recommends considering alternative filling materials when possible.
Sensitivity After Placement
One common complaint with new amalgam fillings is heightened sensitivity to hot and cold. Metal conducts temperature far more efficiently than your natural tooth enamel, so when you sip something ice-cold or eat something hot, the sensation reaches the inner nerve of the tooth faster than it otherwise would. Cold temperatures also cause the metal to contract slightly, creating a pulling force on the surrounding tooth. Heat does the opposite, causing expansion.
Over time, these repeated cycles of expansion and contraction can create microscopic cracks in the tooth around the filling. These tiny fractures can let temperature changes penetrate even deeper, which is why some people with older amalgam fillings notice increasing sensitivity years after placement. For most people, the sensitivity right after getting a new filling settles down within a few weeks as the tooth adjusts.
What Happens When You Have One Removed
If you’re having an amalgam filling replaced, whether because it has failed or because you prefer a mercury-free option, the removal process itself generates mercury vapor and fine amalgam particles. Standard removal involves drilling the filling out with a high-speed handpiece and water spray, which breaks the amalgam into small pieces.
Some dentists follow a specialized protocol designed to minimize mercury exposure during removal. These precautions typically include placing a rubber barrier (dental dam) over the tooth to isolate it, using high-volume suction near the mouth to capture vapor, cutting the filling into large chunks rather than grinding it into dust, and running air filtration systems in the treatment room. The patient may also rinse with an absorbent solution like activated charcoal before and after the procedure. An amalgam separator captures waste so mercury doesn’t enter the water supply.
Not every dental office offers these additional precautions, so if minimizing vapor exposure during removal is important to you, it’s worth asking your dentist about their specific approach before scheduling the procedure.
The Global Phase-Out
Amalgam’s days are numbered on a global scale. In November 2024, the sixth meeting of the Minamata Convention on Mercury adopted an amendment to phase out dental amalgam worldwide by 2034. The decision was described by delegates as a historic milestone, marking the first firm deadline for eliminating mercury use in dentistry entirely. Several European countries have already banned or severely restricted amalgam, and the global agreement will push the remaining holdouts to follow.
This phase-out is driven more by environmental concerns than by patient safety worries. Mercury from dental offices enters wastewater systems and eventually accumulates in the environment, where it converts to a more toxic form that builds up in fish and wildlife. As composite resins and other mercury-free materials continue to improve, the practical case for sticking with amalgam has weakened considerably, even in the back teeth where it once had the clearest advantage.