A cavity filling is a dental restoration that replaces tooth structure lost to decay. Your dentist removes the damaged portion of the tooth, cleans the area, and fills the resulting space with a durable material that seals the tooth against further bacterial damage. Fillings also repair minor chips and cracks, restore your ability to chew normally, and preserve what remains of the natural tooth.
How the Procedure Works
Getting a filling is one of the most common dental procedures, and the process is straightforward. Your dentist starts by numbing the area around the affected tooth with a local anesthetic so you won’t feel pain during the work. Once the area is numb, they use a small drill or laser to remove the decayed portion of the tooth. An acid gel cleans away any remaining bacteria and debris.
What happens next depends on the type of filling material. For composite (tooth-colored) fillings, the dentist first isolates the tooth from moisture, then applies adhesive layers before packing the composite material into the cavity. A special curing light hardens each layer of composite in seconds. For amalgam (silver) fillings, the material is packed directly into the prepared space and left to harden on its own. Either way, the dentist finishes by shaping and polishing the filling so your bite feels natural.
Most fillings take 20 to 60 minutes from start to finish, depending on the size and location of the cavity.
Types of Filling Materials
The two most widely used filling materials are composite resin and silver amalgam, and each has real trade-offs worth understanding.
Composite Resin
Composite fillings match the color of your teeth, making them the go-to choice for visible areas. They bond directly to the tooth surface, which can help preserve more of the remaining structure. The downside is durability: composite fillings typically last 5 to 10 years, and a Cochrane review found they have roughly double the failure rate of amalgam fillings. They’re also more prone to developing new decay around the edges of the restoration. A Canadian cost analysis estimated that the lifetime cost of composite fillings is about twice that of amalgam because they need replacing sooner.
Silver Amalgam
Amalgam is a metallic alloy that has been used in dentistry for over a century. It’s exceptionally durable, lasting 10 to 15 years on average, and costs less upfront than composite. The obvious drawback is appearance: amalgam is silver-gray, which makes it conspicuous. Some patients also have concerns about mercury content, though major dental organizations consider the levels in set amalgam fillings safe for most adults. Environmental concerns around mercury disposal have led several countries to phase down its use.
Glass Ionomer
Glass ionomer fillings have a unique advantage: they release fluoride continuously after placement, at levels sufficient to inhibit bacterial growth and promote remineralization of surrounding tooth structure. Unlike composite, glass ionomer can also reabsorb fluoride from toothpaste and rinses, essentially recharging its protective effect over time. These fillings are commonly used for small cavities near the gum line, in baby teeth, or as temporary restorations. They aren’t as strong or long-lasting as composite or amalgam for large cavities in back teeth.
Inlays and Onlays for Larger Cavities
When a cavity is too large for a standard filling but doesn’t require a full crown, your dentist may recommend an inlay or onlay. These are custom-made restorations, typically crafted from porcelain or a similar material in a dental lab. An inlay fits within the grooves of a tooth, between the raised points (cusps) on the chewing surface. An onlay covers one or more of those cusps, providing more structural support. Both resist shrinkage better than direct fillings, making them a more stable option for larger areas of damage.
What Recovery Feels Like
Some sensitivity after a filling is normal. You may notice mild discomfort when biting down or when your tooth encounters hot, cold, or sweet foods. This typically resolves within a few days to two weeks. During that window, brushing gently with a soft-bristled toothbrush and chewing on the opposite side of your mouth can help. Avoiding very hot or cold drinks for the first few days also reduces the chance of triggering sensitivity.
If the sensitivity gets progressively better, you’re on track. But if pain lingers beyond two weeks, intensifies, or you notice swelling around the filled tooth, your dentist may need to adjust the bite height, reseal the filling, or investigate whether the nerve is inflamed enough to require further treatment.
How Fillings Fail Over Time
No filling lasts forever. Understanding what wears them down can help you get more years out of yours.
Size matters: larger fillings have more surface area exposed to the bacteria and forces in your mouth, so they tend to break down faster. Grinding or clenching your teeth puts enormous stress on fillings that they weren’t designed to absorb repeatedly, and this is one of the most common causes of cracking. Smoking and regular alcohol consumption have also been shown to shorten filling lifespan. Poor oral hygiene allows new decay to creep in around the edges of a filling, eventually undermining the seal.
The warning signs of a failing filling are often subtle at first. You might notice dental floss catching or shredding on a rough edge that wasn’t there before. Increasing sensitivity to hot and cold can mean the seal between filling and tooth has broken, exposing the softer interior layer of the tooth (dentin) to temperature changes. Pain when biting down, or a dull ache that develops gradually, can signal decay forming beneath the old filling. Your dentist can catch early signs of failure on X-rays before symptoms appear, which is one reason routine checkups matter even when nothing hurts.
When a filling does fail, the fix depends on how much damage has occurred. Sometimes the old filling is simply replaced with a new one. If enough tooth structure has been lost, your dentist may recommend an onlay or crown instead. In cases where decay has reached the nerve, a root canal becomes necessary before the tooth can be restored.