A tooth composite is a tooth-colored filling material made from a blend of plastic resin and fine glass or ceramic particles. It’s the most widely used alternative to traditional silver (amalgam) fillings, designed to blend in with your natural teeth while restoring strength to a damaged or decayed tooth. Composites are used for everything from small cavity fillings to reshaping chipped or worn teeth.
What Composite Is Made Of
Dental composite has two main components: an organic resin matrix and inorganic filler particles. The resin portion is built on a chemistry that has been the industry standard since the early 2000s, using specialized plastic monomers that start as a paste and harden when exposed to a curing light. The filler particles, typically made of silica, glass, or zirconia, give the material its strength, wear resistance, and tooth-like appearance. Depending on the product, filler particles can range from extremely fine nanoparticles (10 to 99 nanometers) up to coarser micro-sized particles (20 to 100 micrometers).
The ratio and size of these fillers determine how the composite performs. Products with only nanoparticles can be polished to an incredibly smooth finish, with surface roughness as low as 2.5 nanometers. That makes them excellent for front teeth where appearance matters most. Composites that mix both nano and micro-sized particles tend to be stronger and more wear-resistant, making them better suited for back teeth that handle heavy chewing forces. Your dentist selects a specific type based on where in your mouth the filling will go and how much stress it needs to withstand.
How Composite Bonds to Your Tooth
Unlike amalgam fillings, which are essentially wedged into a cavity, composite chemically bonds to tooth structure. The process involves a few quick steps. First, your dentist applies a mild acid (usually phosphoric acid) to the prepared tooth surface for a few seconds. This etches tiny grooves into the enamel, creating a rough texture for the composite to grip. Then a liquid bonding agent is brushed on, which seeps into those grooves and acts as a glue layer between tooth and filling.
The composite paste is then placed in layers. Each layer is hardened with a blue LED curing light, which triggers a chemical reaction that transforms the soft paste into a solid in about 20 seconds per layer. Building the filling in thin layers helps manage one of composite’s known limitations: it shrinks slightly as it hardens, typically by about 1.9% to 2.9% in volume. Layering keeps that shrinkage small enough to maintain a tight seal against the tooth.
How Long Composite Fillings Last
A large systematic review pooling data from 12 clinical studies found that posterior composite fillings have an average annual failure rate of 1.8% over five years and 2.4% over ten years. In practical terms, that means the vast majority of composite fillings on back teeth are still functioning well after a decade. For people with low cavity risk, the annual failure rate drops to just 1.2% at five years. People with higher cavity risk see rates closer to 3% to 4% per year, mostly because new decay is more likely to develop around the edges of any filling.
One Canadian health technology assessment estimated the useful life of a composite restoration at around 8 years on average for a multi-surface filling on a back tooth, compared to about 11 years for amalgam in the same situation. That gap has been narrowing as composite formulations improve, and many single-surface composite fillings last well beyond that average.
Staining and Maintenance
Composite can pick up stains over time, particularly from coffee, tea, red wine, and tobacco. Front teeth fillings are more susceptible to noticeable discoloration because the margins where the filling meets the tooth tend to attract pigment. Minor surface staining can usually be managed with professional polishing and refinishing, which smooths the surface and removes the discolored outer layer without replacing the filling.
If staining has penetrated deeply into the material, refinishing alone won’t fix it, and a full replacement may be needed. In cases where the original shade was a poor match, your dentist can sometimes resurface just the visible portion with a better-matched composite rather than removing the entire filling. Keeping up with regular dental cleanings helps composites maintain their appearance longer.
Cost Compared to Amalgam
Composite fillings cost more than amalgam, both upfront and over a lifetime. For a two- or three-surface filling on a back tooth, the initial cost of composite runs roughly 25% to 30% higher than amalgam. Over a lifetime of replacements, that difference compounds. The same Canadian assessment estimated undiscounted lifetime costs of about $2,350 for composite versus $1,330 for amalgam on a single tooth, largely because composite fillings tend to need replacement somewhat sooner.
That said, amalgam use has been declining steadily. Many dental practices no longer offer it, and several countries have restricted or phased out mercury-containing amalgam for environmental reasons. For most patients today, composite is the default choice.
Safety and BPA Concerns
One concern that comes up with composite fillings involves BPA, an endocrine-disrupting chemical. Composite resins don’t contain pure BPA, but about 86% of products on the European market use chemical derivatives of BPA (most commonly a monomer called bis-GMA) in their formulation. Several studies have detected trace amounts of BPA or its derivatives in saliva and urine shortly after a composite filling is placed.
The amounts detected are very small, and a simple step like rinsing your mouth with warm water for 30 seconds after the filling is placed can significantly reduce salivary BPA levels. For patients who want to avoid BPA derivatives entirely, at least 18 commercial composite products have been identified as BPA derivative-free, typically using alternative resin chemistries. If this is a concern for you, particularly during pregnancy or for young children, BPA-free options exist and perform comparably.
Where Composite Works Best
Composite is versatile enough for both front and back teeth, but each location calls for a different formulation. For front teeth, dentists typically choose composites with finer filler particles that polish to a high gloss and mimic the translucency of natural enamel. For back teeth, composites with mixed particle sizes offer better resistance to the grinding forces of chewing, even if they sacrifice a small degree of surface smoothness.
Beyond cavity fillings, composite is used for cosmetic bonding to repair chips, close small gaps between teeth, or reshape uneven edges. It’s also used to build up worn teeth and protect exposed root surfaces. The material bonds directly to tooth structure, which means less healthy tooth needs to be removed during preparation compared to amalgam, where the dentist has to create a specific shape to lock the filling in place mechanically. That conservation of tooth structure is one of the strongest practical arguments in composite’s favor.