When you have a cavity, the dentist removes the decayed part of your tooth and fills the hole with a durable material to restore its shape and function. The whole process typically takes an hour or less, and a simple, small cavity can be done in as few as 20 minutes. Here’s what actually happens at each stage.
How the Dentist Finds the Cavity
Before any treatment starts, the dentist needs to confirm the cavity exists and figure out how deep it goes. This usually happens during a routine exam or when you come in with tooth pain. The two main tools are a visual inspection and X-rays. The dentist looks at the color and texture of your tooth surfaces, checking for dark spots, chalky white patches, or soft areas. X-rays reveal decay hidden between teeth or beneath the surface that isn’t visible to the naked eye.
Dentists also use a thin metal instrument called an explorer to gently probe suspicious spots on the tooth. Decayed enamel feels softer and stickier than healthy tooth structure. Some offices use newer technology like laser fluorescence devices, which shine a light on the tooth and measure how much decay is present based on how the light bounces back. These tools help the dentist decide whether the cavity is shallow enough for a standard filling or deep enough to need more involved treatment.
Numbing the Tooth
The first step of the actual procedure is numbing. The dentist applies a topical gel to your gum tissue, which starts working within about 30 seconds and reaches full effect in two to three minutes. This takes the sting out of the injection that follows. The injection delivers a local anesthetic into the tissue around the affected tooth, blocking pain signals from that area.
The numbness typically lasts three to five hours for the most commonly used anesthetic, though some longer-acting options can keep you numb for four to nine hours. The tooth itself goes numb quickly, but your lip, cheek, and tongue on that side will stay numb well after you leave the office. For very small, shallow cavities, some patients don’t need anesthesia at all, especially if the dentist is using a laser instead of a traditional drill.
Removing the Decay
Once you’re numb, the dentist uses a high-speed drill to remove the decayed portion of your tooth. The drill cuts away softened, damaged enamel and the layer beneath it (called dentin), leaving only healthy tooth structure behind. You’ll hear the sound of the drill and feel vibration and pressure, but no pain. The dentist may switch to slower, more precise instruments as they get closer to the inner part of the tooth.
Some dental offices now use lasers instead of drills for cavity removal. These lasers vaporize decay with pulses of light energy. Clinical studies have shown laser preparation to be equal to or better than the drill for removing decay, with the added benefit that many patients can be treated without anesthesia. Lasers also don’t create the microfractures in tooth structure that drills sometimes cause. However, lasers aren’t suitable for every type of cavity, particularly very large or deep ones, so drill-based removal remains the standard in most practices.
Filling the Tooth
After all the decay is removed, the dentist cleans the cavity to remove bacteria and debris, then fills it with a restorative material. The two most common options are composite resin and amalgam, and they differ in several ways.
- Composite resin (tooth-colored fillings) are made of a plastic and glass mixture that can be color-matched to your natural tooth. They’re placed in layers, and each layer is hardened with a special blue curing light. These are the most popular choice for visible teeth because they blend in. Newer formulations have improved their ability to withstand chewing forces, though they still don’t last quite as long as amalgam on average.
- Amalgam (silver fillings) are a mix of metals including silver, tin, copper, and mercury. They’re extremely durable and cost less than composite. Because of their silver color, they’re typically used on back teeth where appearance matters less. Amalgam restorations last longer on average than composite ones, particularly on chewing surfaces that take heavy force.
Your dentist may recommend one type over the other based on the cavity’s location, its size, and your preference. Front teeth almost always get composite. For back teeth, either option works, though many patients now choose composite for cosmetic reasons despite the slight trade-off in longevity.
Shaping and Checking Your Bite
Once the filling material is in place and hardened, the dentist shapes it to match the natural contours of your tooth. They smooth and polish the surface so it doesn’t catch on your tongue or feel rough. The final step is checking your bite: you’ll be asked to bite down on a thin piece of colored paper that marks any high spots. If the filling sits even slightly too high, it can cause discomfort every time you chew, so the dentist will shave it down until your bite feels normal.
What Happens If the Cavity Is Too Deep
A standard filling works for minor to moderate decay that hasn’t reached the innermost part of the tooth. When a cavity grows deep enough to reach the pulp, which contains the tooth’s nerve and blood supply, a filling alone won’t solve the problem. At that point, the dentist will recommend a root canal instead.
Signs that decay has gone too far for a filling include persistent or severe tooth pain, swelling around the tooth, and prolonged sensitivity to hot or cold that lingers for minutes rather than seconds. During a root canal, the infected pulp tissue is removed, the inside of the tooth is cleaned and sealed, and the tooth is typically covered with a crown afterward. If the tooth is too badly damaged even for a root canal, extraction becomes the remaining option.
For certain patients, particularly young children, people with medical conditions that make dental procedures risky, or those who can’t tolerate traditional treatment, dentists sometimes use a liquid called silver diamine fluoride. This is painted directly onto the cavity to stop decay from progressing without any drilling. It’s not a permanent fix and it stains the treated area dark, but it can buy time or serve as a practical alternative when conventional treatment isn’t feasible. It’s not appropriate for teeth where decay has already reached the nerve.
What to Expect After the Filling
Some sensitivity after a filling is completely normal. You may feel a brief shock of discomfort when eating hot, cold, or sweet foods, or when biting down with pressure. This sensitivity typically improves within a few days to a couple of weeks as the tooth adjusts to the new material.
While your mouth is still numb, be careful not to bite your cheek, lip, or tongue. Most dentists suggest waiting to eat until the numbness wears off, especially if the filling is on a chewing surface. If your bite still feels “off” after the numbness fades, call your dentist. A high filling is an easy fix: they just smooth it down, usually without needing to numb you again. If sensitivity gets worse over time rather than better, or if you develop a sharp, throbbing pain, that could indicate the decay was close to the nerve and further treatment may be needed.