When nerve tissue or pulp is damaged, it breaks down, and bacteria begin to multiply within the pulp chamber. The bacteria and other decayed debris can cause an infection or abscessed tooth. An abscess is a pus-filled pocket that forms at the end of a tooth's root. In addition to an abscess, an infection in the root canal of a tooth can cause:

► Swelling that may spread to other areas of the face, neck, or head

► Bone loss around the tip of the root

► Drainage problems extending outward from the root. A hole can occur through the side of the tooth, with drainage into the gums or through the cheek into the skin.