A tooth that has had a root canal in the past may still develop problems at its apex, leading to re-infection that may be painful. The apex of a tooth is the very tip of its root, where blood vessels and nerves enter a tooth. The dentist will assess the tooth clinically and with X-rays, and may need to perform an apicoectomy to remove all of the infection. This is done by making a small cut into the gum and underlying bone to access the root tip, removing the infection along with a few millimeters of the apex. The area will then be completely cleaned and the end of the root will be sealed off.