When a tooth is badly decayed, has a large filling, or receives a blow in an accident, the soft tissues within it (the pulp) may die. The dead tissue must be removed to prevent infection and this is usually undertaken by your dentist by a procedure called root canal treatment.
Sometimes this root canal treatment is unsuccessful, and infection persists at the tip of the root. This may sometimes cause pain, but more often the infection will spread and cause a small spot or gumboil nest to the tooth.
An apicectomy is an operation designed to remove this infected part of the root tip.
Usually a small filling is also placed in the end of the root to seal it.