Dentists fix cavities by removing the decayed portion of your tooth and replacing it with a filling material that restores the tooth’s shape and function. The entire process typically takes 20 to 60 minutes per tooth, depending on the size and location of the cavity. Here’s what actually happens at each stage, from diagnosis through recovery.
How Your Dentist Finds a Cavity
Before any drilling starts, the dentist needs to confirm the cavity exists and decide whether it actually needs a filling. The primary method is a careful visual examination of the tooth surface. Your dentist may use a ball-ended probe, a blunt instrument that gently checks for soft spots or tiny holes in the enamel. The older sharp-tipped explorer that “sticks” into grooves has fallen out of favor because it can get caught in healthy fissures and lead to overdiagnosis, with a specificity of only about 40%.
Bitewing X-rays are the standard imaging tool, especially useful for catching decay between teeth where the dentist can’t see directly. For surfaces on top of the tooth, X-rays are less helpful unless the decay has already progressed significantly. Some offices also use newer light-based tools that detect decay by measuring how light scatters through or fluoresces within the tooth structure.
Not every cavity needs a filling. Very early-stage decay that hasn’t broken through the enamel surface can sometimes be reversed with fluoride treatments, which help the tooth rebuild its mineral content. Once the decay creates an actual hole or reaches the softer layer beneath the enamel, a filling becomes necessary.
Numbing the Tooth
Your dentist injects a local anesthetic, most commonly lidocaine, into the gum tissue near the affected tooth. The drug works by blocking nerve signals in that area so you don’t feel pain during the procedure. You’ll typically feel a brief pinch from the needle, then gradual numbness that spreads across the tooth, gum, and sometimes your lip or tongue. The numbness usually lasts one to three hours after the appointment, depending on the dose.
For very small, shallow cavities, some dentists may skip anesthesia entirely, since the decay hasn’t reached deep enough to cause pain during removal. Laser-equipped offices can sometimes treat cavities without numbing at all, because the laser doesn’t create the same pressure and vibration as a drill.
Removing the Decay
This is the part most people picture when they think of cavity treatment. The traditional method uses a high-speed dental handpiece, the familiar drill with a small rotating tip called a burr. It spins at extremely high speeds to cut away the softened, decayed tooth structure while leaving healthy material intact. The sound and vibration are what most patients find unpleasant.
Some practices now offer laser decay removal as an alternative. Instead of a rotating burr, a laser uses a focused beam of light energy to vaporize decayed tissue. It works without direct contact, produces no vibration, and sterilizes the area as it goes, which may reduce bacteria left behind. The tradeoff is that lasers aren’t suitable for every type of cavity, particularly very large or deep ones, and they’re not yet available in most dental offices.
Regardless of the tool, the goal is the same: remove every bit of decay while preserving as much healthy tooth as possible. Once the decay is gone, the dentist shapes the remaining space so the filling material can bond securely.
Placing the Filling
With the cavity cleaned out, the dentist prepares the tooth surface for bonding. For tooth-colored composite fillings, this involves applying a mild acid solution to the enamel, which creates microscopic rough textures that the filling material grips onto. A bonding agent is then painted on and the composite resin is placed in layers. Each layer is hardened with a blue curing light, a UV-like beam that triggers the resin to set solid in seconds. The dentist builds up the filling to match the original contour of your tooth.
Silver amalgam fillings use a different approach. The material is a mixture of metals that packs directly into the prepared cavity and hardens through a chemical reaction over the next 24 hours. No curing light or bonding agent is needed.
After the filling is placed, the dentist polishes the surface smooth, trims any excess, and has you bite down on a thin piece of marking paper to check your bite alignment. Even a filling that sits slightly too high can cause discomfort when chewing, so this step matters. Adjustments are quick and painless.
Filling Materials Compared
The two most common filling materials are composite resin (tooth-colored) and silver amalgam, and your choice affects cost, appearance, and longevity.
- Composite resin matches your tooth color and bonds directly to the tooth structure. It costs between $173 and $439 per tooth. In general dental practice settings, studies report a median survival time of around 16 years for composites in back teeth, though failure rates climb noticeably after the 15-year mark. Composite is the standard choice for front teeth and is increasingly used everywhere.
- Silver amalgam is extremely durable and costs less, ranging from $108 to $256 per tooth. Studies in private practices report median survival times between 7 and 45 years, with considerable variation depending on cavity size and location. Its silver-black appearance makes it a less popular choice for visible teeth.
Annual failure rates for both materials are actually quite similar in controlled studies, around 1.7% for composites and 2.0% for amalgam. The practical difference in durability is smaller than many people assume.
Amalgam and Mercury Safety
Silver amalgam contains about 50% mercury, which has raised safety questions for decades. The FDA classifies amalgam as safe for most adults and children over six, but explicitly recommends non-mercury alternatives for certain groups: pregnant or nursing women, children under six, people with kidney disease, those with neurological conditions, and anyone with a known sensitivity to mercury or other metals in amalgam.
If you already have amalgam fillings that are intact and free of decay underneath, the FDA does not recommend removing them. The removal process itself can temporarily increase mercury exposure, so replacing functional amalgam fillings purely as a precaution isn’t advised.
When a Standard Filling Isn’t Enough
Standard fillings work well for small to moderately sized cavities. When the damage is more extensive but doesn’t warrant a full crown, your dentist may recommend an inlay or onlay instead. An inlay fits within the grooves of the tooth, while an onlay extends over one or more of the raised edges (cusps) on the biting surface. Both are custom-fabricated outside the mouth, usually from ceramic or composite, and cemented into place at a second appointment. They’re stronger than direct fillings for large restorations but cost more and require two visits.
If the cavity has reached the nerve inside the tooth, a filling alone won’t solve the problem. At that point, root canal treatment is typically needed before the tooth can be restored.
What Recovery Feels Like
Some sensitivity after a filling is normal. The tooth’s inner pulp gets mildly inflamed from the vibration, pressure, and temperature changes during the procedure. You might notice sharp twinges when eating hot or cold foods, or a dull ache when biting down. This typically resolves within two to four weeks as the tooth settles.
Sensitivity that persists beyond four weeks is not normal. It could mean the filling sits too high and needs adjustment, the cavity was deep enough to irritate the nerve more seriously, or there’s a gap forming between the filling and tooth. Persistent or worsening pain, swelling, or redness around the filled tooth suggests possible infection that needs attention.
Signs a Filling Needs Replacing
Fillings don’t last forever. The most common reason for failure is new decay forming around or beneath the existing filling, sometimes called secondary caries. Microscopic gaps between the filling and tooth allow bacteria to sneak in and start the process over again. Here’s what to watch for:
- Visible damage: Cracks, chips, missing pieces, or rough surfaces you can feel with your tongue.
- Dark edges: Gray shadows, brown or black staining at the margins of the filling, which often indicate leakage or decay underneath.
- Food trapping: Food constantly getting stuck around the filling, or floss shredding in that area, suggests the seal has broken down.
- Looseness: A filling that shifts or moves when you chew means the bond has failed. This is considered urgent because bacteria can reach deep into the tooth quickly.
- Lingering pain: Sensitivity that appears in a tooth that previously felt fine after filling, especially pain that worsens rather than improves.
Even without symptoms, your dentist checks existing fillings during routine exams using visual inspection and X-rays. Catching a failing filling early means a simpler, smaller replacement rather than a crown or root canal down the line.