Getting a cavity filled is one of the most common dental procedures, and the whole process typically takes about 20 minutes to an hour from start to finish. If you’ve never had one before, or you’re just curious about what happens in the chair, here’s what each step actually looks like.
What a Cavity Looks Like Before Treatment
A cavity doesn’t always look like a dramatic hole in your tooth. In its earliest stage, it appears as a white spot on the enamel surface, a chalky, matte patch where minerals have started to dissolve. At this point, the surface is still intact, just weakened underneath.
If it keeps progressing, the white spot turns rough and eventually breaks down into a tiny pit or crack in the enamel. A more advanced cavity becomes a visible hole, sometimes brown or dark in color. Older, inactive spots tend to look brownish and shiny, while active decay is whiter, rougher, and often surrounded by plaque buildup. Many cavities between teeth aren’t visible at all and only show up on X-rays as dark shadows.
Numbing the Area
The first thing you’ll notice is your dentist applying a small amount of topical gel to your gum near the affected tooth. This pre-numbs the tissue so you feel less of what comes next: a local anesthetic injection. The syringe looks different from a medical one. It’s a metal, pen-like device with a very thin, short needle, and it delivers the anesthetic right into the gum tissue surrounding the tooth.
Within a few minutes, the area goes numb. Your lip, cheek, or tongue on that side of your mouth will feel thick and tingly. This numbness typically lasts one to three hours after the procedure, well beyond the actual appointment.
Removing the Decay
This is the part most people picture when they think of a filling. Your dentist uses a dental handpiece, the high-pitched drill, fitted with a small rotating bur to open the tooth surface and access the decay underneath. For smaller cavities, a low-speed handpiece with a round bur may be enough.
What’s happening inside the tooth is interesting. Decay often spreads horizontally once it passes through the hard outer enamel, so the cavity in the softer inner layer (dentin) is frequently wider than the small opening on the surface. The decayed dentin is soft and offers noticeably less resistance to the drill. Your dentist removes this compromised material until only solid, healthy tooth structure remains. The result is a clean, hollowed-out space inside the tooth, shaped with smooth walls and defined edges so the filling material can bond properly.
During this step, a small suction tube rests inside your mouth to pull away water, debris, and saliva. You’ll also see your dentist periodically rinsing the area with a water spray.
Placing the Filling
What happens next depends on the type of filling material. The two most common are composite resin (tooth-colored) and amalgam (silver-colored), and they look and behave quite differently.
Composite Resin (Tooth-Colored)
Composite is a mixture of plastic and fine glass particles that can be shade-matched to your natural tooth color. Your dentist selects a shade using a small color guide held against your teeth. The material starts as a soft, putty-like paste and is applied in layers directly into the prepared cavity.
After each layer, your dentist aims a small wand-shaped device at the tooth. This is a curing light, and it emits a bright blue light at a wavelength of about 470 nanometers. The blue light triggers a chemical reaction inside the composite that causes it to harden from a soft paste into a rigid solid within seconds. You’ll notice the dental team using an orange shield or asking you to look away, since the blue light is extremely bright.
The layering process is what makes composite fillings take a bit longer than amalgam. Each layer needs to be individually cured before the next one goes on. Once the cavity is fully built up, the dentist shapes and polishes the surface with fine burs and polishing instruments until it’s smooth and blends with the surrounding tooth. The finished result is nearly invisible.
Amalgam (Silver)
Amalgam is a metallic mixture of roughly half mercury by weight, combined with silver, tin, and copper. It arrives as a soft, silvery material that your dentist packs firmly into the cavity in one step. No curing light is needed because amalgam hardens through a self-setting chemical reaction over several hours. It’s shaped while still slightly soft, then left to fully set.
The finished filling is distinctly silver and metallic-looking, which is why it’s less commonly used on front teeth. Amalgam remains durable and effective, but the FDA recommends that certain groups, including pregnant women, children under six, nursing mothers, and people with neurological conditions or kidney problems, use non-amalgam alternatives when possible.
Checking and Adjusting the Bite
Before you leave the chair, your dentist places a thin strip of colored marking paper (called articulating paper) between your upper and lower teeth and asks you to bite down and grind gently side to side. The paper leaves small colored marks on any spots where the new filling sits too high. These “high spots” create uneven pressure when you chew, so your dentist shaves them down with a fine bur until the bite feels balanced and natural.
This step is quick but important. A filling that’s even slightly too tall can cause soreness, jaw pain, or sensitivity in the days that follow. If your bite still feels off after the numbness wears off, that’s worth a follow-up call, as a simple adjustment can fix it.
What the Finished Filling Looks Like
A polished composite filling is designed to be undetectable. It matches the color, translucency, and sheen of natural enamel so closely that even you may have trouble spotting it in a mirror. On back teeth, it fills the grooves and contours of the chewing surface seamlessly.
An amalgam filling, by contrast, is immediately visible as a silver patch on the tooth surface. Over time, amalgam can tarnish and darken to a grayish-black color, and it may also cause slight staining of the surrounding tooth structure. This discoloration is cosmetic, not a sign of new decay.
If you already have amalgam fillings in good condition with no decay underneath, the FDA advises against removing them. The removal process strips away healthy tooth structure and briefly increases your exposure to mercury vapor, so replacement only makes sense if the filling is failing or medically necessary.
What to Expect Afterward
Composite fillings are fully hardened by the time you leave the office, so you can eat and drink as soon as the numbness fades. Amalgam fillings need several hours to fully set, so your dentist will likely tell you to avoid chewing on that side for the rest of the day.
Mild sensitivity to hot, cold, or pressure around the filled tooth is common for a few days to a couple of weeks. This gradually fades as the tooth settles. The filled tooth should otherwise look and function like any other tooth in your mouth, with no visible seam or rough edge if the polishing was done well.