Root canal treatment removes the nerve of the tooth If a tooth is hurting, is at high risk of hurting, or has a past history of infection or injury that disrupts pulp or surrounding bone of a tooth - known as an abscess - root canal or endodontic treatment is used to remove the infected tissue in the pulp chamber and canal system of the tooth, so it can be restored.
My tooth used to hurt, now it doesn't. Do I still need a root canal? Your dentist can asses whether your tooth would benefit from root canal treatment.
What happens after a root canal? Some teeth that have root canal treatment can be restored with fillings, but most benefit from full coverage restorations, like crowns.

When a tooth is hurting, the doctor will create an opening in the tooth to access and clean out the decay and the infected pulpal tissue. Small files are used to reach all the way to the end of the root, to ensure no infected tissue remains.
Once the tooth is free of disease, the root canal and tooth are filled. Because the tooth may be weaker than it was before the infection, the doctor may recommend a crown. Crowns offer full coverage of the tooth, to help avoid fracture.

Pulp/Nerve Tissue can become infected if you have:

• A deep cavity
• Trauma to the face or mouth
• Repeated dental procedures that disturb this tissue
• A cracked or fractured tooth
• Injury to the tooth (even if there’s not a visible crack or chip)