Dental composite is a tooth-colored filling material made from a blend of plastic resin and fine glass particles. It’s the most widely used alternative to traditional silver (amalgam) fillings, and its main appeal is simple: it can be color-matched to your natural teeth so the repair is virtually invisible. Composite is used for fillings, bonding chipped teeth, reshaping teeth, and building up veneers directly in the dental chair.
What Composite Is Made Of
At its core, dental composite has three components: a resin base, filler particles, and a coupling agent that binds them together. The resin is a type of plastic, most commonly one called Bis-GMA, that starts as a paste and hardens when exposed to a special curing light. Mixed into that resin are microscopic particles of glass, silica, or ceramic materials like zirconia. These filler particles give the composite its strength and determine how well it polishes to a natural-looking sheen.
The ratio matters. More filler generally means a stronger, more wear-resistant filling, while less filler makes the material easier to polish to a smooth, glossy finish. Manufacturers balance these trade-offs differently depending on where the filling is intended to go in your mouth.
Types of Composite
Not all composites are identical. They’re categorized mainly by the size of their filler particles, and each type suits different situations.
- Microhybrid composites contain particles averaging 0.4 to 1.0 micrometers, blended with very fine silica. They offer a good balance of strength and polishability, making them a reliable choice for both front and back teeth.
- Nanofill composites use particles as small as 1 to 100 nanometers. Because the particles are so tiny, these composites can be polished to an exceptionally smooth surface while still holding up well under chewing forces. They’re recommended for both anterior and posterior restorations.
- Microfill composites contain ultra-fine silica particles (around 40 nanometers) that polish beautifully but have lower strength due to reduced filler content. They’re typically reserved for front teeth, where appearance matters most and biting forces are lighter.
Your dentist chooses the type based on location, size of the cavity, and how much stress the filling will bear.
How It’s Placed
Getting a composite filling takes a few more steps than an amalgam one, which is part of why appointments can run slightly longer. After removing decay and shaping the cavity, your dentist treats the tooth surface with a mild acid (usually phosphoric acid) for about 15 to 30 seconds. This etching step creates microscopic pores in the enamel that give the bonding agent something to grip.
Next, a liquid bonding agent is painted onto the etched surface. Then the composite itself is placed in thin layers, each one hardened with a blue LED curing light before the next layer goes on. Building up the filling in layers is important because the resin shrinks slightly as it hardens. Placing it all at once would create too much shrinkage stress, potentially pulling away from the tooth walls and leaving tiny gaps. The layering technique minimizes that risk. Once the final layer is cured, the dentist shapes and polishes the filling to match your bite and the contours of the tooth.
How Dentists Match the Color
One of composite’s biggest advantages is that it blends in. Dentists typically select the shade by holding a standardized color guide, most commonly the Vita Classical Shade Guide, next to your tooth and comparing under good lighting. This is a visual, somewhat subjective process, but experienced clinicians get very close matches.
For more visible teeth, especially front ones, dentists often use a layering technique that mimics the way a natural tooth is built. A natural tooth has a more translucent enamel layer on the outside and a more opaque, yellowish dentin layer underneath. By placing a dentin-shade composite first and then covering it with an enamel-shade layer of specific thickness, the restoration picks up light the same way a real tooth does. The amount of filler in each composite shade directly affects translucency and brightness, so the layering choices matter for a lifelike result.
How Long Composite Fillings Last
Composite fillings in back teeth have a median survival time of about 11 years. That’s shorter than amalgam, which typically lasts 16 years or more. In one large study, composite restorations had an 85.5% survival rate compared to 94.4% for amalgam. However, other research looking at five-year outcomes found the two materials performed nearly identically, with about 78% of both types rated satisfactory.
The gap in longevity tends to widen in larger fillings and in patients who grind their teeth or have a high rate of new cavities. Smaller composite fillings in people with good oral hygiene routinely last well beyond the 11-year median. Placement technique also plays a significant role. Because composite is more technique-sensitive than amalgam, the skill and care taken during placement directly affects how long the filling holds up.
Post-Filling Sensitivity
Some people experience sensitivity to hot or cold for a few days to weeks after getting a composite filling. This is usually caused by polymerization shrinkage. As the composite hardens, it contracts slightly. If that contraction creates a microscopic gap between the filling and the tooth, dentinal fluid seeps in within the first 24 to 36 hours. When you drink something hot or cold, that trapped fluid expands or contracts, triggering movement in the tiny tubes inside your tooth and causing a brief jolt of sensitivity.
This typically resolves on its own as the area settles. Dentists can reduce the risk by using incremental layering and adjusting the intensity of the curing light, starting at a lower power and ramping up (a technique called “soft start” curing) to give the composite more time to flow before it locks into place.
Staining and Maintenance
Composite doesn’t stain as easily as some people fear, but it isn’t stain-proof either. Coffee is the biggest culprit, producing noticeably more discoloration than soft drinks or water in lab studies. Cola, despite containing acid, doesn’t appear to cause significant color change in most composites.
The good news is that staining tends to sit on the surface rather than penetrating deeply into the material. A professional repolishing with fine aluminum oxide discs can bring coffee-stained composites back to clinically acceptable color levels. How quickly your fillings discolor depends largely on your habits: frequent coffee or tea drinking, smoking, and inconsistent brushing all accelerate the process. Regular dental cleanings help keep composite restorations looking fresh.
Safety and BPA Concerns
Because the main resin in most composites is derived from a chemical related to bisphenol A (BPA), there have been questions about whether composite fillings expose you to meaningful amounts of it. The concern gained attention in the late 1990s when one study found unexpectedly high BPA levels in saliva shortly after sealant placement. Since then, the science has become much clearer.
BPA levels in saliva do rise temporarily right after a composite is placed, but they return to baseline within 24 hours. After that initial period, long-term release is extremely low. A meta-analysis of resin-based composites found average 24-hour BPA release of about 0.55 nanograms per cubic millimeter of material. Over months, the cumulative release remains minimal. The current scientific consensus is that BPA exposure from dental composites falls far below the estimated daily exposure people get from food packaging, receipts, and other common sources.
Proper curing is the most important factor in minimizing any chemical release. When the composite is thoroughly hardened by the curing light, fewer unreacted components remain to leach out over time.
Composite vs. Amalgam
The choice between composite and amalgam comes down to a few practical trade-offs. Composite wins on aesthetics, since it can be matched to your tooth color, while amalgam’s silver appearance is immediately visible. Composite also bonds directly to tooth structure, which means your dentist can often preserve more of the healthy tooth when preparing the cavity. Amalgam requires a more aggressive preparation because it’s held in place mechanically rather than chemically.
Amalgam wins on durability in large, stress-bearing restorations and costs less in most dental offices. It’s also less technique-sensitive, meaning the result is more forgiving of small variations during placement. For small to medium cavities in back teeth, composite performs comparably. For front teeth, composite is the standard choice since appearance matters most and biting forces are lower.
Many dental insurance plans cover composite fillings for front teeth at the same rate as amalgam. For back teeth, some plans still reimburse only the amalgam rate and require you to pay the difference, though this practice is becoming less common as composite use has grown.