Most old fillings are dental amalgam, a mixture that is roughly 50% liquid mercury by weight, with the other half being a powdered alloy of silver, tin, and copper. If you have dark, silver-colored fillings that have been in your mouth for years or even decades, that’s almost certainly what they’re made of. But amalgam isn’t the only material dentists used over the years. Depending on when and where your filling was placed, it could also be gold, an early plastic resin, or one of several tooth-colored cements.
Amalgam: The Classic Silver Filling
Amalgam was the workhorse of dentistry for over 150 years. The process is straightforward: a dentist mixes liquid elemental mercury with a fine powder of silver, tin, and copper. The mercury binds the metals together into a durable, solid mass that hardens inside the cavity. The result is that distinctive metallic, silver-gray appearance that darkens and tarnishes over time.
Amalgam fillings release small amounts of mercury vapor, particularly during chewing. This has understandably raised questions about safety. The FDA’s position is that amalgam is generally safe for most adults but recommends that certain groups avoid it whenever possible. Those groups include pregnant or nursing women, children under six, and people with neurological conditions like multiple sclerosis, Alzheimer’s, or Parkinson’s disease. People with impaired kidney function or a known sensitivity to mercury are also on that list.
If you already have amalgam fillings that are in good condition, the FDA does not recommend removing them. Drilling out an intact filling temporarily increases your exposure to mercury vapor and can destroy healthy tooth structure, potentially creating more risk than it prevents.
Gold Fillings and Inlays
Gold fillings are easy to spot: they’re the ones that gleam. These aren’t pure gold but a gold alloy mixed with metals like silver, tin, copper, or palladium to improve strength. Gold was considered a premium material, and for good reason. It’s extremely durable, resists corrosion, and wears at a rate similar to natural enamel. Gold fillings placed in the 1970s or 1980s can still be functioning perfectly today. The main downsides were always cost and appearance, which is why they fell out of favor as tooth-colored options improved.
Silicate Cement: An Early Tooth-Colored Option
Before modern composites existed, dentists who wanted a tooth-colored filling for front teeth had limited choices. One of the earliest was silicate cement, made by mixing a powder of ground glass (specifically an alumino-silicate glass containing about 15% fluoride) with phosphoric acid. The fluoride content was actually a bonus, since it helped protect surrounding tooth structure from further decay.
The other early option was an acrylic resin, essentially ground-up plastic mixed with a liquid monomer. Neither material held up especially well. Silicate cements dissolved over time in the mouth, and the acrylic resins wore down and discolored. If you have very old tooth-colored fillings from the 1960s or early 1970s, they may have been one of these materials, though most have long since been replaced.
Composite Resin Fillings
Composite resin is the tooth-colored filling material that largely replaced amalgam in modern dentistry. It consists of a plastic resin base packed with tiny filler particles. The earliest composites used relatively large quartz or glass particles as reinforcement. Later generations introduced heavier glass fillers containing barium, strontium, or zirconium, which made the fillings show up on X-rays (a useful diagnostic feature amalgam had always offered). The biggest leap came with the development of extremely fine silica particles, roughly 40 to 50 nanometers in size, which allowed for smoother, more polished, and more natural-looking results.
If you have tooth-colored fillings from the 1980s or 1990s, they likely contain those older, coarser filler particles. They may look slightly rougher or more opaque than a modern composite, and they tend to pick up staining over time. A large-scale study tracking filling outcomes over eight years found composite restorations had a failure rate of about 12%, compared to roughly 17% for amalgam over the same period. That gap was most noticeable in fillings covering one to three tooth surfaces. For very large fillings spanning four or five surfaces, both materials failed at similar rates.
Glass Ionomer Cement
Glass ionomer is another tooth-colored material you might encounter, particularly in fillings placed near the gum line or in baby teeth. It’s made from a specialized glass powder (containing silica, alumina, calcium fluoride, and other mineral components) mixed with an acidic liquid. Like silicate cement before it, glass ionomer releases fluoride over time, which helps protect the tooth around the filling from new decay. That fluoride release happens in two phases: an initial burst shortly after placement, followed by a slower, sustained release through a process where fluoride ions swap out for other ions from saliva.
Glass ionomer isn’t as strong as composite resin or amalgam, so it’s typically used in low-stress areas or as a base layer under other materials. A modified version, called resin-modified glass ionomer, adds a plastic component to improve strength and handling while keeping the fluoride-releasing benefit.
How to Tell What Your Fillings Are Made Of
You can often identify your filling material just by looking in the mirror. Amalgam appears silver or dark gray and may have tarnished to near-black over the years. Gold is unmistakable. Composite resin, glass ionomer, and porcelain all aim to match your tooth color, making them harder to distinguish from each other visually. Porcelain fillings (made from minerals like feldspar, quartz, and kaolin) tend to have a slightly translucent, glass-like quality and are typically used for inlays or onlays fabricated in a lab rather than packed directly into the tooth.
If you’re unsure, your dentist can tell you exactly what’s in your mouth. Your dental records should note the material used, and even without records, an experienced dentist can identify the material by its appearance, texture, and how it shows up on an X-ray.
Signs an Old Filling Needs Attention
No filling lasts forever. The most common warning signs that an old filling is failing include sharp pain when you bite down that disappears when you stop chewing, and new sensitivity to hot, cold, sweet, or acidic foods. You might feel something hard and loose in your tooth, or your tongue might catch on a rough edge, crack, or dent in the filling’s surface that wasn’t there before.
A cracked or broken filling opens a gap between the filling and the tooth, letting bacteria and food debris reach the vulnerable inner layers. That can lead to new decay underneath the old restoration. In some cases, it also causes persistent bad breath, because bacteria trapped inside the tooth produce sulfur compounds. If any of these signs sound familiar, it’s worth having the filling evaluated sooner rather than later, since catching a failing filling early usually means a simpler repair.