Getting a cavity filled is one of the most common dental procedures, and the whole process typically takes 20 to 60 minutes depending on the size and location of the decay. Your dentist numbs the area, removes the damaged portion of your tooth, and fills the hole with a material that restores the tooth’s shape and function. Here’s what actually happens at each stage.
Numbing the Tooth
The procedure starts with a local anesthetic, most commonly lidocaine, injected near the tooth being treated. Lidocaine kicks in within two to four minutes, which is why your dentist pauses briefly after the injection before picking up any tools. The numbness in your lip, cheek, and gums typically lasts three to five hours, well beyond the procedure itself. For people anxious about the needle, many offices apply a topical numbing gel to the gum first so you barely feel the injection.
Removing the Decay
Once you’re numb, the dentist uses a high-speed handpiece (the classic “dental drill”) to cut through enamel and remove the decayed portion of the tooth. The high-speed rotation makes quick work of hard tooth structure. For softer, deeper decay closer to the nerve, the dentist often switches to a low-speed handpiece that offers more control and gentler removal. The goal is to take out every bit of damaged tissue while preserving as much healthy tooth as possible.
You’ll hear the drill and feel pressure or vibration, but the anesthetic blocks pain signals. A small suction tube keeps the area dry and clears debris as the dentist works. By the end of this step, you’re left with a clean, hollowed-out preparation ready for filling material.
Bonding the Filling to Your Tooth
If you’re getting a tooth-colored composite filling, there’s an important intermediate step before the material goes in: bonding. The dentist applies a mild acid solution (phosphoric acid) to the prepared surface for a few seconds, then rinses it off. This etching creates microscopic pores in the enamel and exposes a scaffold of tiny collagen fibers in the deeper layer of the tooth. A liquid bonding agent is then painted on, which seeps into all those micro-pores by capillary action.
When the bonding agent hardens, it forms what’s called a hybrid layer, essentially a zone where tooth structure and resin interlock at a microscopic level. Small resin “tags” extend into the tooth’s tiny tubules, locking the filling in place mechanically rather than relying on adhesive alone. This is why modern composite fillings bond directly to the tooth and can actually strengthen what’s left of the structure.
Placing and Hardening the Filling
With the bonding layer set, the dentist packs the filling material into the prepared cavity. For composite fillings, the material goes in as a soft, putty-like resin and is shaped to match the tooth’s natural contours. The dentist then aims a blue LED curing light at the filling for about 20 to 60 seconds. This light, at a wavelength around 440 to 480 nanometers, triggers a chemical reaction that hardens the resin almost instantly. For deeper cavities, the material is placed in layers, with each layer cured individually to ensure the filling hardens completely from bottom to top.
Amalgam (silver) fillings work differently. The dentist mixes a metal alloy powder with liquid mercury right before placing it. The mixture is packed into the cavity while still pliable, then carved to shape. Amalgam doesn’t need a curing light. It self-hardens through a chemical reaction over the next 24 hours.
Shaping and Checking Your Bite
Once the material is in place, the dentist smooths and polishes the surface, trimming away any rough edges or excess material with fine-grit tools and the low-speed handpiece. You’ll then be asked to bite down on a thin piece of colored paper called articulating paper, which marks the high spots where your teeth make contact. If the filling sits even slightly too high, it can cause discomfort when you chew or lead to cracking over time. The dentist shaves down any high points until your bite feels natural.
Common Filling Materials Compared
The two most widely used filling materials are composite resin and amalgam, though gold and ceramic are also options. Each has trade-offs in durability, appearance, and cost.
- Composite resin: Tooth-colored and bonded directly to the tooth. The resin matrix is roughly 80 to 84 percent mineral filler by weight, which gives it strength. In general dental practice, composites last a median of about 16 years in back teeth, with over 80% still intact after five years. Cost runs $200 to $400 per surface without insurance.
- Amalgam (silver): Made of 40 to 70% silver, 12 to 30% tin, and 12 to 24% copper, mixed with mercury. Extremely durable, with median survival times of 7 to 45 years in private practice settings and over 85% still functional after five years. Cost is lower at $150 to $300 per surface. The silver color makes them visible, so they’re mainly used on back teeth.
- Gold: Cast in a lab and cemented in place, gold fillings are the most durable option but cost $400 to $650 per surface and require multiple appointments.
- Ceramic: Usually porcelain, these are tooth-colored, highly stain-resistant, and the most expensive option at $500 to $2,800 per surface. Like gold, they’re typically fabricated outside the mouth and bonded in.
What to Expect After the Procedure
Composite fillings harden completely under the curing light, so they’re ready to use immediately. The main reason to wait before eating is the lingering numbness. Most dentists recommend holding off one to three hours so you don’t accidentally bite your cheek or tongue while you can’t feel them. Amalgam fillings take about 24 hours to reach full strength, so you should avoid chewing on that side for a full day.
Some sensitivity to hot, cold, or pressure is normal for a few days to a couple of weeks after a filling, especially if the cavity was deep. This usually resolves on its own as the tooth settles. Sharp pain when biting down that doesn’t fade, though, can signal a filling that’s too high and needs a quick adjustment.
How Fillings Wear Over Time
No filling lasts forever. Years of chewing, grinding, and clenching gradually wear the material down and can cause it to chip or crack. The more critical failure point is at the edges where the filling meets the tooth. If that seal breaks down, bacteria and food particles can slip underneath, leading to new decay forming beneath the old filling. You often can’t feel this happening. Your dentist checks for these early signs of breakdown during routine exams, which is one of the practical reasons regular checkups matter even when nothing hurts.
When a filling does fail, the fix is straightforward: the old material is drilled out, any new decay is removed, and a fresh filling is placed. If too much tooth structure has been lost by that point, a crown may be needed instead.