Dental fillings are made from one of several materials, with the two most common being silver-colored amalgam (a mix of mercury, silver, tin, and copper) and tooth-colored composite resin (a plastic matrix packed with glass or ceramic particles). Your dentist chooses between them based on the tooth’s location, the size of the cavity, and your preference for appearance versus durability. Beyond these two, gold alloys, ceramics, and glass ionomer cements round out the options.
Silver Amalgam Fillings
Amalgam is roughly 50% liquid mercury by weight, mixed with a powdered alloy of silver, tin, and copper. The alloy powder itself typically contains 67% to 74% silver, 25% to 28% tin, and up to 6% copper, with small amounts of zinc. When the liquid mercury and powder are combined in a 1-to-1 ratio, they react chemically to form a hard, stable solid within minutes.
A newer variation called high-copper amalgam contains up to 30% copper in the alloy. These formulations corrode less over time and tend to hold up better than traditional amalgam. On average, amalgam fillings last about 15 years, and some survive decades in the mouth.
The mercury content understandably raises questions. Amalgam does release low levels of mercury vapor that you inhale and absorb through your lungs. For most adults, the FDA considers this exposure too small to cause harm. However, the FDA strongly encourages alternatives for pregnant women, nursing mothers, children under six, and people with kidney disease or neurological conditions, since developing brains and compromised organs may be more sensitive to mercury’s effects. If you already have amalgam fillings in good condition, removing them isn’t recommended. The removal process itself temporarily increases mercury vapor exposure and sacrifices healthy tooth structure.
Composite Resin Fillings
Composite fillings are the tooth-colored option most people receive today. They consist of two main components: a plastic resin matrix and inorganic filler particles. The resin is built from monomers, the most common being a compound called Bis-GMA, which forms the structural backbone of the filling. Other monomers are blended in to adjust how the material flows, how thick it is, and how well it cross-links into a solid network.
The filler particles are what give composite its strength and wear resistance. These are tiny pieces of silica, quartz, zirconia, or specialty glasses like barium or strontium glass. The ratio of resin to filler varies by product, but more filler generally means a harder, more durable result. Some composites also include hydroxyapatite, a mineral that mimics natural tooth structure.
Composite starts as a soft paste that your dentist sculpts directly onto the tooth, then hardens with a blue LED curing light. The light activates a yellow-tinted chemical called camphorquinone embedded in the resin. When camphorquinone absorbs blue light (around 470 nanometers), it enters a high-energy state and reacts with a partner chemical to kick off a chain reaction that locks the resin monomers together into a rigid polymer. As the camphorquinone gets used up in the reaction, it loses its yellow color, which is why a freshly cured filling doesn’t look yellowish.
Composite fillings average about 7 years of lifespan, roughly half that of amalgam, though many last longer with good oral hygiene and smaller cavity sizes.
BPA in Composite Fillings
The base monomer Bis-GMA is derived from bisphenol A (BPA), which has raised concerns about hormone-disrupting effects. BPA isn’t deliberately added to fillings, but trace amounts exist as impurities in BPA-based monomers. A small fraction of these monomers can also break down into BPA through contact with saliva and oral bacteria. Research shows the highest BPA release happens in the first 24 hours after placement, then tapers off. The amounts are very small, and BPA-free composites made with alternative monomers like urethane dimethacrylate are available if this is a concern for you.
Glass Ionomer Cement
Glass ionomer fillings are made from a powder-liquid combination. The powder is a fluoride-containing glass (fluoroaluminosilicate) composed of 25% to 50% silica, 20% to 40% aluminum oxide, and 1% to 20% fluoride, along with other metal oxides and phosphates. The liquid is a water-based solution of polyacrylic acid, typically making up 45% to 60% of the liquid component.
When mixed, the acid reacts with the glass powder in a setting reaction that bonds chemically to tooth structure, something composite resin cannot do on its own. Glass ionomers also release fluoride over time, which helps protect the surrounding tooth from further decay. The trade-off is that they’re weaker and more prone to wear than composite, so they’re most often used in low-stress areas: small cavities near the gum line, baby teeth, or as a temporary filling. They’re also a common choice in settings where the blue curing light needed for composite isn’t available, since glass ionomers set through a chemical reaction rather than light activation.
Gold Alloy Fillings
Gold fillings are actually made from a gold alloy, not pure gold. The alloy blends gold with other metals like copper, palladium, and platinum to improve strength and wear resistance. These are fabricated in a dental lab based on an impression of your tooth, then cemented into place at a second appointment.
Gold is the longest-lasting filling material, averaging 20 years or more according to the American Dental Association, with many lasting 30 years. Gold also wears at a rate similar to natural enamel, so it doesn’t grind down opposing teeth the way harder materials can. The downsides are obvious: gold is expensive, requires at least two visits, and its metallic appearance makes it a poor cosmetic choice for visible teeth.
Ceramic Fillings
Ceramic fillings are most commonly made from porcelain. Like gold restorations, they’re fabricated outside the mouth, either in a dental lab or milled on-site using digital scanning and a milling machine. Porcelain resists staining better than composite resin and holds its color over time, making it a strong cosmetic option for visible teeth.
Ceramic fillings last about 15 years on average, comparable to amalgam. They’re harder than composite and more resistant to wear, but that hardness can work against opposing teeth if the bite isn’t adjusted carefully. They also cost significantly more than composite or amalgam, putting them closer to gold in price.
Bioactive Fillings
A newer category of filling material incorporates bioactive glass particles into a composite resin base. Bioactive glass was originally developed for bone repair. In the mouth, it reacts with saliva to form a layer of hydroxyapatite, the same mineral that makes up natural tooth enamel, on the filling’s surface. This layer can seal the microscopic gaps that inevitably form between a filling and the surrounding tooth, which is where recurrent decay typically starts.
Bioactive fillings are already available commercially, though they haven’t yet replaced standard composite as the default choice. Their ability to essentially “grow” a mineral seal makes them particularly promising for reducing the secondary cavities that are the main reason fillings eventually need replacement.