Dental fillings are made from one of several materials, each with a different composition: metal alloy mixed with mercury, tooth-colored plastic resin, glass-based cement, porcelain ceramic, or gold. The material your dentist recommends depends on the size and location of the cavity, your budget, and your preferences about appearance. Here’s what actually goes into each type.
Amalgam (Silver Fillings)
Amalgam fillings are roughly 50% liquid mercury by weight. The other half is a powdered alloy of silver, tin, and copper. When mixed together, these metals form a durable, hardened material that has been used in dentistry for over 150 years. The mercury binds the metal particles into a solid mass that can withstand the heavy chewing forces on back teeth.
The mercury content raises understandable questions. The FDA considers amalgam safe for most adults and children over six 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 advised to choose alternatives. Importantly, the FDA does not recommend removing existing amalgam fillings that are in good condition, because the removal process itself temporarily increases mercury vapor exposure and can damage healthy tooth structure.
Amalgam is the least expensive option, averaging about $160 per tooth, and typically lasts 10 to 15 years or longer. Its main drawback is cosmetic: the silver-gray color is visible when you open your mouth.
Composite Resin (Tooth-Colored Fillings)
Composite resin is now the most popular filling material. It’s essentially a blend of plastic and glass. The plastic portion is built around a molecule called Bis-GMA, a resin developed in the early 1960s that forms the backbone of most modern composites. The glass portion consists of tiny filler particles, often made from silica, zirconia, or strontium and barium glasses, ground down to sizes measured in nanometers (billionths of a meter). These particles give the filling its strength and help it mimic the look of natural tooth enamel.
Different brands use different filler recipes. Some use clusters of silica and zirconia nanoparticles. Others incorporate barium-aluminum glass or titanium dioxide pigments for color matching. The filler can make up as much as 81% of the filling’s weight in some formulations. A higher filler content generally means a harder, more wear-resistant filling.
Before placing a composite, your dentist applies a bonding agent to glue the resin to your tooth. This adhesive is a mix of water-soluble monomers and solvents that seep into the microscopic pores of your enamel and dentin, then harden under a curing light. The bond is what keeps the filling locked in place, since composite doesn’t naturally grip tooth surfaces the way amalgam does mechanically.
One concern worth knowing about: Bis-GMA is manufactured using bisphenol A (BPA), and trace amounts of BPA can remain as an impurity. An estimated 86% of dental composites are based on BPA-derived ingredients. Small amounts of BPA may leach from the filling during the initial setting period or gradually over time as the material is exposed to chewing forces, bacteria, temperature changes, and saliva. The levels detected in studies are very low, but the presence of BPA derivatives is a tradeoff to be aware of.
Composite fillings average about $191 per tooth and last at least five years, though many last considerably longer with good oral hygiene. They’re the go-to choice for visible teeth because they can be closely matched to your natural tooth color.
Glass Ionomer Cement
Glass ionomer fillings are made from a mixture of acrylic acid and fine glass powder, typically containing strontium and calcium. What sets them apart is their ability to release fluoride directly into the surrounding tooth structure. This release is highest right after the filling is placed, then drops to a lower, steady level over the following weeks and months. The fluoride helps protect the tooth from further decay around the edges of the filling.
Glass ionomer also bonds chemically to tooth enamel and dentin without needing a separate adhesive layer. This makes placement simpler and faster. The tradeoff is durability: glass ionomer is weaker than composite resin and wears down more quickly, so it’s best suited for small fillings, areas that don’t bear heavy chewing forces, and temporary restorations. Dentists often use it for children’s teeth and for cavities near the gum line. A resin-modified version adds plastic to the mix, improving strength and extending fluoride release compared to the conventional formula.
Ceramic (Porcelain) Fillings
Ceramic fillings are made from materials like lithium disilicate or zirconia-reinforced glass ceramics. These are synthetic glass-ceramics, engineered to be both strong and translucent enough to look like natural tooth enamel. Unlike composite resin, which is placed soft and hardened in your mouth, ceramic fillings are fabricated outside the mouth (either in a dental lab or milled by an in-office machine) and then cemented into the prepared cavity.
Because of this fabrication process, ceramic fillings are technically “inlays” or “onlays” rather than direct fillings. They resist staining better than composite, last more than 15 years on average, and offer the best cosmetic result. They’re also the most expensive option, averaging around $1,150 per tooth, with costs ranging from $500 to $2,800 depending on the size and complexity of the restoration.
Gold Fillings
Gold fillings are made from a high-noble gold alloy, meaning gold is the primary metal, mixed with smaller amounts of other metals like palladium, silver, and copper for added strength. Like ceramic fillings, gold restorations are fabricated outside the mouth and cemented into place.
Gold is exceptionally durable, lasting 10 to 15 years at minimum and often much longer. It handles chewing forces well and doesn’t corrode. The obvious downside is appearance: gold fillings are highly visible. They average about $400 per tooth, placing them between composite and ceramic in cost. Gold fillings are uncommon today, largely because tooth-colored options have improved so much, but some patients and dentists still prefer them for molars where strength matters more than looks.
How the Materials Compare
- Amalgam: ~$160 per tooth, lasts 10-15+ years, silver-colored, contains mercury
- Composite resin: ~$191 per tooth, lasts 5+ years, tooth-colored, contains BPA-derived ingredients
- Glass ionomer: similar cost to composite, shorter lifespan, releases protective fluoride
- Gold: ~$400 per tooth, lasts 10-15+ years, gold-colored, requires two visits
- Ceramic: ~$1,150 per tooth, lasts 15+ years, tooth-colored, most stain-resistant
The “best” filling material depends on where the cavity is, how large it is, and what you prioritize. For a small cavity on a front tooth, composite resin is the standard choice. For a large cavity on a molar that needs to withstand years of heavy chewing, ceramic or gold offers superior longevity. Glass ionomer fills a niche role for patients at high risk of recurring decay, thanks to its fluoride release. Amalgam remains a functional, affordable option for back teeth in adults who aren’t in a high-risk group for mercury exposure.