# How root canal treatment works > What happens inside a tooth when the pulp is inflamed or infected, how root canal treatment usually proceeds step by step, the alternatives and the risks. General information with sources. Source: https://www.nazemalioussef.com/en/patient-guides/root-canal-treatment/ Updated: 2026-09-28 Patient guide Root canal treatment removes inflamed or infected pulp from inside a tooth, cleans the canals and seals them. It is a way to keep a tooth that would otherwise have to be taken out. From the professional website of Dr Nazem Al Ioussef Published 27 September 2026 Last reviewed 27 September 2026 ## Inside a tooth Under the hard enamel of the crown lies dentine, and at the centre of the tooth is the pulp: soft tissue with nerves and blood vessels. The pulp fills a chamber in the crown and runs down a narrow canal inside each root to its tip, where it joins the tissues of the jaw. Front teeth usually have one canal; molars have three or more. ## Why the pulp becomes inflamed or infected The pulp can be damaged by: - deep decay that reaches it; - a crack or a broken tooth; - a knock to the tooth, sometimes years earlier; - a leaking or very deep filling, or repeated work on the same tooth. Signs include pain that lingers after hot or cold, pain on biting, swelling of the gum, a small spot on the gum that discharges, or a tooth that darkens. Sometimes there are no symptoms, and the problem shows up on an X-ray. If an infected pulp is left, the infection can spread to the bone at the tip of the root and form an abscess. ## How treatment usually proceeds ### Root canal treatment in four stages 1. **Infected pulp.** Bacteria reach the pulp; an abscess can form at the root tip. 2. **Access and cleaning.** A small opening is made through the crown, and fine instruments and disinfecting solutions clean and shape each canal. 3. **Filling.** The cleaned canals are filled and sealed, usually with a rubber‑like material called gutta-percha. 4. **Restoration.** The tooth is closed with a filling and, for back teeth, often protected with a crown. Simplified drawing, not to scale. 1. **Diagnosis.** An examination, tests of how the tooth responds, and X-rays. 2. **Anaesthesia and isolation.** A local anaesthetic, and a thin rubber sheet (a dental dam) around the tooth to keep it clean and dry. 3. **Cleaning and shaping.** The pulp is removed and the canals are cleaned and shaped. A medicine may be left inside between visits. 4. **Filling and sealing.** The canals are filled and the tooth is sealed. 5. **Restoring the tooth.** A final filling or a crown restores the tooth so that it can be used for chewing. ## Risks and alternatives Tenderness after treatment is common. Less often: - a very narrow or curved canal cannot be fully cleaned, or an extra canal is missed; - a fine instrument breaks inside a canal, or a small hole is made through the side of the root; - the tooth cracks, particularly if it is not protected with a crown; - the infection persists or returns, and the tooth needs further treatment or removal. The alternative to root canal treatment is to remove the tooth. The space can then be left, or filled with a bridge, a denture or an [implant](https://www.nazemalioussef.com/en/clinical-interests/dental-implants/). ## Protecting the pulp Most pulp problems start with decay. Brushing twice a day with a fluoride toothpaste, cutting down on sugary food and drinks, wearing a mouthguard for contact sports and having regular check‑ups, so that decay is found while it is small, all help to protect the pulp. ## Questions patients ask **Does root canal treatment hurt?** It is carried out under local anaesthetic, so the tooth is numb during treatment. The tooth and gum are often tender for a while afterwards, especially when biting, and this usually eases as the area settles. The dentist advises on pain relief. **Is the tooth dead afterwards?** The pulp is removed, so the tooth no longer has a nerve supply inside it. It stays held in the jaw by its ligament and keeps working for chewing. Because it can become more brittle, a back tooth is often protected with a crown. **How many visits does it take?** It can be done in one visit or over two or more, depending on the tooth, the number and shape of its canals and whether there is an active infection. **What if the infection comes back?** Sometimes a treated tooth becomes infected again, for example if a canal was very narrow or curved, if the seal breaks down or if the tooth cracks. The options then include treating the canals again, a small operation at the root tip (apicectomy), or removing the tooth. **Would it be simpler to take the tooth out?** Removing the tooth is an alternative. Keeping a natural tooth that can be restored is generally preferred, because a gap may later need a bridge, a denture or an implant. The choice depends on the tooth and is discussed at the examination. ## What this page rests on This page rests on published patient guidance from national health bodies and professional associations, listed below. It is general information: whether a tooth needs root canal treatment, and whether it can be kept, is decided after an examination and X-rays. General health information, not a diagnosis or a treatment recommendation for any individual. ### Sources 1. NHS — [Root canal treatment](https://www.nhs.uk/tests-and-treatments/root-canal-treatment/) 2. Oral Health Foundation — [Root canal treatment](https://www.dentalhealth.org/root-canal-treatment) 3. American Dental Association, MouthHealthy — [Root canals](https://www.mouthhealthy.org/all-topics-a-z/root-canals) 4. NHS — [Dental abscess](https://www.nhs.uk/conditions/dental-abscess/) ## Related pages - [Crowns and bridgesHow a weakened tooth is covered with a crown, and how a bridge fills the gap left by a missing tooth.](https://www.nazemalioussef.com/en/patient-guides/crowns-and-bridges/) - [Dental emergenciesWhat to do if a tooth is knocked out or broken, or the face swells, and when to call 998.](https://www.nazemalioussef.com/en/patient-guides/dental-emergencies/) - [Dental abscessWhat a dental abscess is, why it needs prompt treatment, and when swelling is urgent.](https://www.nazemalioussef.com/en/patient-guides/dental-abscess/)