Root canal treatment is where the nerve of the tooth is removed. The canal where the nerve of the tooth lives is disinfected and filled. The tooth is then sealed. The seal used is commonly a crown.
Once the nerve of the tooth has been infected, root canal treatment is performed to remove the infection and keep the tooth from being extracted. The tooth will usually require a crown after the root canal treatment.
If infected teeth are left in the mouth, they may become very painful and the infection can spread and cause facial swelling. The infection can spread to the bone and other teeth. If there is infection associated with a bad tooth, removing the tooth or performing a root canal treatment treats the infection and allows the area to heal.