When a cavity reaches the center of the tooth, known as the pulp, the tissue becomes inflamed and results in a toothache. Besides being very painful, this dental infection can spread to other areas of the body including the heart and brain. In order to save the tooth and prevent the infection from spreading, the infected pulp must be removed and the center of the tooth must be sterilized. This process is known as a root canal.
Sometimes a tooth will hurt for a while and then the pain will stop. It is still important to visit the dentist because this could be a sign the tooth is now dead. A dead tooth may or may not hurt, the infection can still spread to other areas of your body.