Root canal therapy may be necessary after tooth trauma/ injury, deep cavity, cracked tooth, or repeated dental procedures. The most common cause of infected pulp is a deep cavity that erodes the tooth to the point where bacteria are able to enter the root. Unfortunately, antibiotics cannot get to the site of infection so pain and swelling results. If root canal therapy is not used to save a diseased tooth, the infection can spread to other parts of the body. Symptoms indicating the need for a root canal include- sensitivity to hot or cold, swelling, pain when chewing, discolored or broken tooth.