When a tooth loses its blood supply, the tooth is rendered nonvital. This occurs due to tooth decay that has either approached or penetrated the pulp cavity of the tooth. A tooth may also become devitalized by trauma to the tooth or by preparation of the tooth (preparing a tooth for a crown for example.

When the blood supply is lost, the pulp tissue becomes necrotic. The dead pulp tissue becomes infected with bacteria and bacterial toxins begin to leak out through the tip of the root.  This leads to abscess formation which is evidenced by bone loss around the root of the tooth, pain, or drainage of pus in the area of the tooth.

Granted that there is enough tooth structure remaining to support a restoration, a root canal must be performed on a nonvital tooth. The goal of root canal therapy is to remove all the dead pulp tissue from the root canals of the tooth and to fill the root canals with an inert filler material (gutta-percha).

The structure of the root canals themselves can be complex. For instance multiple canals can exist in a single root. Microchannels or microcanals can branch off from the main canal through the sides or the tip of the root. More commonly, these microcanals occur at the tip of the root.

Because the internal structure of root canals can be complex, conventional root canal therapy is not 100% successful. This is because standard root canal therapy may not remove all the necrotic pulp within a root canal. 

Failure of primary root canal treatment is evidenced by the persistence of infection. The evidence of this may not be apparent for weeks to months following initial root canal treatment. If the tooth fails initial root canal treatment, a repeat root canal can be attempted (retreatment).

If a tooth cannot be retreated, fails retreatment, or if a patient simply does not want to attempt retreatment, an apicoctomy/retrofill can be performed.

The goal of an apicoectomy/retrofill is to surgically remove the tip of the root where microcanals usually exist, and to seal the root tip itself. This is performed by surgically exposing the root tip and removing any infected material (granulation tissue and dead bone). The root tip is then shaved down using a drill and the root canal opening is prepared using an ultrasonic device. The opening is then sealed with an inert material.

This procedure can be performed under local anesthesia; however, most patients prefer general anesthesia.

This procedure is considered a last resort to saving a tooth. If the tooth fails this treatment then it will have to be removed. Sometimes in the process of exposing a root in preparation for an apicoectomy, the surgeon may find a situation that warrants removal of the tooth. Such situations include extensive bone loss and a fracture through the root of the tooth.