Your tooth consists of two main parts: the crown, which is the part of the tooth above the gumline and visible in your mouth; and the root or roots, which is the part that lies beneath the gumline and is surrounded by bone. Inside each root is a channel that runs the length of the tooth. This channel is the root canal and contains the pulp (nerve, blood vessels and soft tissue), which is often referred to as the nerve of the tooth. The pulp may be irreversibly damaged by bacteria, very deep restoration, fractures, trauma or periodontal "gum" disease.

Endodontic therapy removes only the injured pulp from the root canal system. The tooth functions normally because supporting tissues remain intact. It is advisable to remove the injured pulp because it may become infected or act as an irritant to the tissue surrounding the tooth.