Dental fillings are made from one of several materials, with composite resin (tooth-colored plastic) and amalgam (a metal mixture containing mercury and silver) being the two most common. Gold alloys, ceramic, and glass ionomer cement round out the options. Each material has a different composition, lifespan, and set of trade-offs worth understanding before you sit down in the chair.
Composite Resin: The Tooth-Colored Standard
Composite resin is now the most widely placed filling material in most countries. It consists of two main parts: a plastic resin matrix and tiny filler particles made of glass or silica. The resin portion is built from specialized molecules that link together into a hard, durable network when exposed to light. The filler particles, which can make up more than half the filling’s weight, give it strength and help it expand and contract at a rate closer to natural tooth structure. Fillings with a higher percentage of filler particles tend to last longer and seal more tightly against the tooth.
Your dentist hardens composite resin with a curing light that emits blue light at a wavelength of about 470 nanometers. A light-sensitive compound in the resin absorbs that blue light and triggers a chemical chain reaction that sets the material in roughly 20 to 40 seconds per layer. Because the filling is built up in thin layers and cured one at a time, the appointment takes longer than it would for amalgam, but the result matches the color of your tooth closely enough that most people can’t spot it.
Composite fillings generally last 5 to 15 years depending on the size and location. One large longitudinal study found a median survival time of about 7.8 years for composites compared to 12.8 years for amalgam, though more recent data from the 1990s onward shows the gap narrowing, with composites reaching a 10-year survival rate above 80%.
BPA Concerns
Composite resins are sometimes flagged for containing traces of BPA, a chemical linked to hormonal effects. Pure BPA is not actually an ingredient in dental composites, but it can appear in tiny amounts as an impurity or breakdown product of the resin. Studies measuring BPA released from composite fillings into saliva and blood found that even the highest detected levels (under 0.52 ng/mL in saliva and 1.66 ng/mL in blood) were well below toxic thresholds and did not alter hormone levels in the weeks following placement.
Amalgam: The Metal Filling
Dental amalgam is the silver-colored filling that has been used for over 150 years. A conventional amalgam alloy contains 67% to 74% silver, 25% to 28% tin, and smaller amounts of copper (up to 6%), zinc (up to 2%), and mercury (up to 3% in the alloy powder itself). That powder is then mixed with roughly equal weight liquid mercury at the dental office, so the final placed filling is about 50% mercury by weight. The mercury binds the other metals into a solid, stable mass.
Amalgam is exceptionally durable. Median survival times range from about 9 to 22 years across different studies, and it handles the heavy chewing forces on back teeth better than most alternatives. It’s also less technique-sensitive, meaning it performs well even if placement conditions aren’t perfect.
The mercury content is the primary concern. Small amounts of mercury vapor release from amalgam fillings over time, particularly during chewing and tooth grinding. For most adults, the exposure level is considered safe by major health agencies. However, the FDA has recommended that certain groups avoid amalgam whenever possible: pregnant women, nursing mothers, children under six, and people with neurological conditions like multiple sclerosis, Alzheimer’s, or Parkinson’s disease, as well as anyone with impaired kidney function or a known mercury sensitivity. For these groups, the FDA suggests non-mercury options like composite resin or glass ionomer. 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.
Glass Ionomer Cement
Glass ionomer fillings are made from a powdered fluoride-containing glass mixed with an acid liquid. When combined, the acid dissolves the surface of the glass particles, releasing calcium, sodium, silica, and fluoride ions that react to form a hard cement. The interesting property of this material is that fluoride ions aren’t locked into the final structure. They sit in an unbound form within the set cement and slowly diffuse out into the surrounding tooth and saliva, providing a sustained low-level fluoride release that helps protect against further decay.
This fluoride release happens in two phases: a short burst from the outer surface in the first days, followed by a gradual, continuous diffusion that can last months to years. That makes glass ionomer a popular choice for fillings in baby teeth, areas near the gum line, and patients at high risk for cavities. The trade-off is that glass ionomer is weaker than composite resin or amalgam and wears down faster, so it’s not ideal for large fillings on chewing surfaces.
Gold Alloy Fillings
Gold fillings (technically inlays or onlays, since they’re made in a lab and cemented in) use alloys rather than pure gold. High-noble gold alloys typically contain 50% to 78% gold by weight, with silver, copper, palladium, and platinum making up the rest. A common formulation is about 75% gold with roughly 10% each of silver and copper and 2% to 3% palladium.
Gold is extremely durable, resists corrosion in the mouth, and can last 20 years or more. It’s also biocompatible, meaning allergic reactions are rare. The obvious drawback is appearance: gold fillings are visible. They also cost significantly more than other options because the material is expensive and the filling requires at least two dental visits, one to prepare the tooth and take an impression, and a second to bond the custom-made piece in place.
Ceramic Fillings
Ceramic fillings and inlays are made from materials like lithium disilicate or zirconia, both of which are strong, tooth-colored, and highly resistant to staining. Like gold, ceramic restorations are fabricated in a lab or milled by an in-office machine from a solid block, then bonded to the tooth. They match natural tooth color better than composite resin and are more resistant to wear, but they’re also more brittle and more expensive. Ceramic restorations are commonly used for larger cavities where a standard composite filling might not hold up, and for teeth that are visible when you smile.
How Materials Compare in Practice
The choice of filling material depends on the tooth’s location, the size of the cavity, your budget, and any health considerations. Here’s how the main options stack up:
- Composite resin: Tooth-colored, bonds directly to the tooth, moderate durability (5 to 15 years), placed in a single visit, mid-range cost.
- Amalgam: Silver-colored, extremely strong, longest track record (10 to 20+ years), single visit, lowest cost. Not recommended for certain populations due to mercury content.
- Glass ionomer: Tooth-colored, releases fluoride, weaker than other options, best for small or low-stress fillings and children’s teeth.
- Gold: Highly durable (20+ years), excellent biocompatibility, visible metallic color, highest cost, requires two visits.
- Ceramic: Tooth-colored, stain-resistant, strong but brittle, high cost, requires lab fabrication or in-office milling.
For most small to mid-sized cavities on any tooth, composite resin is the default choice today. Amalgam remains a solid option for large cavities on back teeth in adults who aren’t in a high-risk group for mercury exposure. Gold and ceramic are reserved for situations where maximum durability or aesthetics justify the higher cost and extra appointments. Glass ionomer fills a niche for pediatric teeth and root-surface cavities where fluoride release offers a real protective advantage.