How root canal treatment is done, step by step

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Root canal treatment (endodontics) removes the tooth's inflamed or infected pulp, cleans and disinfects the inside of the roots, and seals that space so bacteria can't move back in. The goal is to save the tooth — a root canal exists precisely to avoid an extraction.

Much of the fear around the procedure comes from not knowing what happens inside. Once the steps are clear, a root canal stops seeming like a painful mystery and becomes what it really is: a precision procedure done under local anesthesia.

In this article, Dr. Cléo Salustiano (CRO-SP 170844) describes the process step by step, from diagnosis to the final restoration, and explains why the last step is just as important as the first ones.

This article comes from Dr. Cléo Salustiano's dental office in Mooca, São Paulo (care in English, Portuguese and Spanish). See the root canal treatment page to learn how the treatment is done here and book your assessment.

Step by step

1. Diagnosis. Clinical exam, sensitivity tests and X-rays confirm whether the pulp is irreversibly damaged and reveal the canal anatomy.
2. Local anesthesia. The area becomes completely numb. With very inflamed teeth, extra anesthesia may be needed — which is normal.
3. Rubber dam isolation. A rubber sheet isolates the tooth from the rest of the mouth, keeping the area dry and preventing saliva and bacteria from entering the canal.
4. Access and locating the canals. Access through the crown to the pulp chamber, followed by locating the canals — there can be one to four, each with its own curves.
5. Cleaning, shaping and irrigation. Fine instruments remove the contents and shape the walls, while irrigating solutions disinfect and dissolve what the instruments can't reach.
6. Measuring the working length. With an apex locator and X-ray confirmation, to work to the end of the canal without going past it.
7. Medication between sessions, when indicated. In some cases, medication is left inside the canal to control infection — which is why treatment may take more than one session.
8. Sealing the canal. The clean, dry space is filled with a material that occupies its whole volume, preventing bacteria from returning. A final X-ray confirms it.
9. Permanent filling or crown. A non-optional step: it restores strength to the weakened tooth and reduces the risk of fracture, the main reason a treated tooth is lost.

What happens at each stage of a root canal?

It starts with diagnosis. Besides the clinical exam, sensitivity tests and X-rays are used to confirm whether the pulp is irreversibly damaged, whether there's infection at the root tip and what the canal anatomy of that tooth looks like. Not every toothache means a root canal, and this exam tells the difference.

Next comes local anesthesia, which leaves the area completely numb. That's why you don't feel pain during the procedure — at most pressure or movement. When the tooth is very inflamed, extra anesthesia may be needed, and that's normal.

Rubber dam isolation is the step almost nobody knows about, and it makes a big difference. A rubber sheet is placed to isolate the tooth from the rest of the mouth, keeping the area dry and preventing saliva and bacteria from getting into the canal during the work. It's a technical requirement, not a whim.

Then the tooth is opened: an access is made through the crown down to the chamber where the pulp sits. Through it, the root canals are located — and this is where anatomy matters, because a tooth can have one to four canals, each with its own curves and branches.

Next come cleaning and shaping. With fine hand or rotary instruments, the contents of the canal are removed and the walls are shaped. At the same time, irrigating solutions disinfect and dissolve debris the instruments can't reach — chemical disinfection is as important as mechanical cleaning.

The working length is measured so the instrument goes all the way to the end of the canal without going past it. This is done with an apex locator and checked by X-ray. Stopping short leaves contaminated tissue; going too far irritates the area beyond the root.

In some cases, medication is placed inside the canal between sessions to control infection. That's why treatment may take more than one session — it's not unnecessary delay, it's a disinfection strategy.

With the canal clean, dry and disinfected, it's sealed: the space is filled with a material that occupies its whole volume, preventing bacteria from settling back in. A final X-ray confirms the fill.

Finally, the restoration. The tooth leaves root canal treatment with a temporary seal and needs a permanent filling or a crown. This step isn't optional: a treated tooth is more fragile and, without proper protection, the risk of fracture is real.

What to expect afterward, and why is the restoration so important?

In the first few days, mild to moderate sensitivity is common, especially when biting. This reflects inflammation around the root resolving, and it tends to ease gradually. Intense or worsening pain isn't expected and is worth a call.

While the anesthesia wears off, avoid chewing on the treated side. For the first few days, choose soft foods and chew on the other side, especially while the tooth has a temporary filling — it protects, but it isn't as strong as the permanent one.

If the temporary filling breaks or falls out, contact the dentist to have it replaced soon. With the seal compromised, bacteria can recontaminate the freshly treated canal, which is exactly what we want to avoid.

Keep up your normal hygiene, including the treated tooth. And it's worth knowing: a tooth that's had a root canal can still get cavities in its remaining structure, because the crown is still exposed to the mouth. Having no nerve doesn't protect against decay.

The permanent restoration shouldn't be postponed. Without the pulp, the tooth loses some internal hydration and its ability to sense overload, and it was opened for access. A proper crown or filling restores strength and reduces the risk of fracture — the main reason a treated tooth is lost.

Once restored, the tooth goes back to chewing normally, with the same common sense as the others: don't use it as a tool, don't bite hard objects and, if you grind your teeth, consider a night guard.

Keep up with your checkups. At these visits, healing at the root tip and the condition of the restoration are monitored with X-rays. A well-done, well-restored root canal can last many years, and follow-up is what catches any issue early.

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