A root canal may be needed if the nerve in the centre of the tooth becomes infected due to a large cavity or through trauma. An infected tooth can become quite painful. Root canals are used as a method to save damaged teeth. The dentist removes the infected nerve tissue inside the tooth and then places a soft filling material inside the root, helping any infection to heal. The tooth is then sealed with a filling and typically a crown is placed over the weakened tooth to protect it and to restore the tooth back to function.