A root canal treatment is needed when the pulp inside the tooth becomes infected due to bacteria entering through cracks, decay, or failing restorations. This causes inflammation and can lead to an abscess, pain, and swelling. Eventually the tooth may die. When a tooth dies, the root canal system is infected. To remove the infection, the tooth can either be extracted or undergo a root canal treatment. During a root canal treatment, the infected pulp is removed and the inside of the tooth is cleaned and sealed to prevent reinfection and allow the tooth to be saved and function normally.