Metal tooth fillings are most commonly made of dental amalgam, a mixture of roughly 50% liquid mercury and 50% a powdered alloy of silver, tin, copper, and zinc. When these components are blended together, they react chemically to form a hard, durable solid that can last 16 years or more. Gold alloys and base metal alloys are also used in dental restorations, each with a different mix of metals and a different price tag.
What’s Inside a Silver Amalgam Filling
The silver-colored fillings that have been used in dentistry for over 150 years are called dental amalgam. The alloy powder that gets mixed with mercury typically contains 67% to 74% silver, 25% to 28% tin, up to 6% copper, up to 2% zinc, and a small amount of mercury (up to 3%). That powder is then combined in roughly equal proportion with liquid elemental mercury. The mercury binds with the other metals in a process called amalgamation, creating a soft, workable paste that your dentist packs into the prepared cavity. Within minutes it begins to harden, and over the next 24 hours it sets into a rigid, corrosion-resistant mass.
Amalgam’s strength is its main advantage. A systematic review of long-term studies found that amalgam restorations have a median survival time exceeding 16 years, compared to about 11 years for tooth-colored composite resin fillings. That durability makes amalgam particularly suited for large cavities in back teeth, where chewing forces are highest. It’s also the least expensive metal option, typically running $50 to $150 for one to two teeth.
What Gold Dental Alloys Contain
Gold fillings, inlays, and onlays aren’t pure gold. They’re alloys designed to be hard enough to withstand years of biting and chewing. The composition varies by type. Softer gold alloys used for small inlays average about 86% gold, 9% silver, and 4% copper, with trace amounts of palladium, platinum, and zinc. Harder alloys meant for larger restorations and crowns contain less gold (around 69%) and more copper (about 12%), along with higher levels of palladium and platinum (each around 3%).
These additions aren’t random. Copper increases hardness. Platinum and palladium improve strength and resistance to corrosion. The result is a filling material that’s extremely long-lasting and biocompatible, meaning it rarely causes allergic reactions or irritation. The tradeoff is cost: gold restorations range from $250 to $4,500 for one to two teeth, reflecting both the price of the precious metals and the lab work required to custom-cast each piece.
Base Metal Alloys for Crowns and Bridges
Not all metal dental work uses precious metals. Base metal alloys made from nickel, chromium, and cobalt are widely used for crowns, bridges, and post-core constructions. A common nickel-chromium alloy contains about 61% nickel, 26% chromium, and 11% molybdenum, with small amounts of silicon and other elements. Cobalt-chromium alloys run about 64% cobalt, 21% chromium, and 6% each of molybdenum and tungsten.
These alloys are stiffer and harder than gold, which means they can be made thinner while still holding up. They resist tarnish and corrosion reasonably well. The main concern is nickel sensitivity. A small percentage of people are allergic to nickel, which can cause inflammation in the gums or surrounding tissue. If you know you react to nickel jewelry, mention it to your dentist before any metal restoration.
The Mercury Question
The fact that amalgam is half mercury understandably raises safety concerns. Mercury in its liquid elemental form is toxic, and amalgam fillings do release tiny amounts of mercury vapor, especially during chewing and brushing. However, the measured release from a single amalgam filling is approximately 0.03 micrograms per day, a fraction of the 82.29 micrograms per day considered the threshold for dangerous occupational exposure in the United States.
The FDA’s position is that available evidence does not show amalgam causes adverse health effects in the general population. But the agency does flag several groups as potentially more susceptible to mercury exposure: pregnant women, nursing mothers, children under six, people with kidney impairment, those with neurological disease, and anyone with a known allergy to mercury, silver, copper, or tin. For these groups, the FDA strongly encourages non-amalgam alternatives like composite resin or glass ionomer cement when appropriate for the tooth in question.
Why Mixing Metals Can Cause Problems
Your mouth is a warm, wet environment full of saliva, which happens to be an excellent conductor of small electrical currents. When two different metals sit close together in that environment, they can create what’s known as oral galvanism, essentially a tiny battery effect. This most commonly happens when a new gold crown is placed next to an existing amalgam filling, or when different metal alloys contact each other during chewing.
The main symptom is a sharp, momentary jolt of pain, sometimes described as a metallic taste or a zing. In some cases, ongoing galvanic currents can contribute to oral discomfort, gum inflammation, or corrosion of the metal surface. This is one reason dentists generally try to avoid placing dissimilar metals directly adjacent to each other. If you already have amalgam fillings and are getting new metal work, it’s worth discussing material compatibility.
Environmental Rules for Amalgam Waste
Mercury doesn’t just raise health questions for patients. It’s also an environmental concern. When dentists place or remove amalgam fillings, waste particles can wash into the sewer system and eventually reach waterways. Since 2017, the EPA has required dental offices that place or remove amalgam to install and maintain amalgam separators, devices that capture mercury and other metals before they enter the drain. Captured mercury can then be recycled rather than released into the environment. Dental offices are also prohibited from flushing scrap amalgam down the drain or using certain line-cleaning chemicals that could dissolve captured amalgam.