If you have a tooth that develops a crack, has a large amount of dental decay, or has received trauma, bacteria can enter the tooth and travel to the pulp, where the nerve of the tooth lies. If this infection is left untreated, it may lead to an abscess in the jawbone which can cause severe pain and swelling. Treatment includes removing the infected pulp and thoroughly cleaning the canal inside the root of the tooth. The root canal is then sealed to protect it from further infection. Many teeth need a crown placed in order to strengthen the remaining tooth structure. The alternative treatment is extraction of the problematic tooth.