Composite has largely replaced amalgam in modern practices, but each material still has a clinical role. Here is what separates them - and which one is right for your tooth.
The materials, in brief
Composite resin is a tooth-colored mixture of plastic resin and glass particles. It is bonded chemically to the tooth and cured with a blue light. Comes in dozens of shades and is sculpted directly in the mouth.
Amalgam (silver fillings) is a metal alloy of mercury (~50%), silver, tin, copper, and trace zinc. The dentist mixes the alloy chairside; it sets via metallic crystallization and is held in place mechanically - by undercuts in the cavity preparation - rather than by a chemical bond.
Aesthetics - visible vs. invisible
Composite is virtually invisible. We match the shade to your existing tooth, sculpt the surface to mimic enamel translucency, and polish to a natural luster. Most patients cannot find their composite fillings in a mirror.
Amalgam is silver-gray. On a back molar this matters less, but on any tooth visible when you smile or talk, it is noticeable. Over years, amalgam can also corrode and stain the surrounding tooth gray - a phenomenon called amalgam tattoo. For our office, this is the single largest reason almost every patient chooses composite, even on back teeth.
Tooth conservation - how much enamel is removed
A major clinical advantage of composite: it bonds chemically to enamel and dentin, so it does NOT require mechanical undercuts. The dentist can remove only the decayed tooth structure, then bond the composite to what remains.
Amalgam holds in place by mechanical retention, which means the cavity preparation must be wider and deeper than the decay itself, with undercuts and "retention grooves." Net result: amalgam preparations remove 20-40% more healthy tooth structure than composite preparations for the same decay. That extra removal weakens the tooth and increases the long-term risk of fracture and the eventual need for a crown.
Durability and lifespan
Both materials are long-lasting in the right application:
- Composite: 7-10+ years on small-to-medium fillings; 15+ years possible. Less durable on very large molar restorations under heavy clenching loads.
- Amalgam: 10-15+ years on average; 25+ years not unusual. Highly wear-resistant.
For very large back-molar restorations in a heavy grinder, the case can sometimes be made for amalgam - or, more commonly today, for an onlay or crown as the more durable solution. For most fillings, composite is fully adequate.
Mercury, safety, and removal of old amalgams
Amalgam contains elemental mercury bound chemically into the alloy. Concerns about mercury vapor have been studied extensively; the FDA, ADA, WHO, and EU agencies all conclude that placed and intact amalgam fillings do not pose a meaningful health risk to most patients. Pregnant women, nursing mothers, children under 6, and patients with kidney disease are the only groups for whom the FDA suggests caution.
At our office, we do not place new amalgam fillings. For patients with intact amalgam fillings: we typically recommend leaving them in place unless they are leaking, fractured, or causing symptoms - replacing a healthy amalgam exposes the patient to MORE mercury vapor than leaving it alone. When removal is clinically indicated, we use rubber-dam isolation and high-volume suction to minimize exposure.
Cost and insurance coverage
Per filling:
- Amalgam: $100-$200 in most California offices.
- Composite (1-2 surfaces): $200-$300.
- Composite (3+ surfaces): $300-$450.
Most insurance plans cover composite at 70-80% - same as amalgam - for any tooth that shows when you smile or talk. Some plans pay only the amalgam fee on back teeth, with patient responsibility for the difference. We verify coverage before treatment so there are no surprises.
Frequently asked questions
- Should I replace all my old amalgam fillings?
- Generally, no - replacing an intact, sealed amalgam exposes you to more mercury vapor than leaving it. We replace amalgams that are fractured, leaking, contributing to a cracked tooth, or causing aesthetic concerns the patient wants resolved.
- Will my new composite filling stain?
- Modern composites resist staining well. Heavy coffee, tea, red wine, and tobacco use can cause some surface stain over years; a quick polish at your cleaning usually restores it.
- Is composite weaker than amalgam?
- Slightly less wear-resistant on very heavy chewing surfaces, but for the size of fillings most adults need, the difference is clinically irrelevant. The tooth conservation advantage usually outweighs the wear difference.
- Can I have composite on a back molar?
- Absolutely - most modern back-molar fillings are composite. We modify the technique slightly (incremental layering, careful contouring) to handle the heavier bite forces. The outcome is excellent in well-placed cases.