An endodontist is a dentist who, in addition to traditional dental education, has completed formal graduate training in this specialized field of dentistry.  Endodontics, or root canal therapy, is the branch of dentistry dedicated to saving teeth that have become diseased -- teeth that otherwise would have to be removed.  The goal of the endodontist is to allow patients to maintain their natural teeth, and the course of treatment proceeds with this purpose in mind.
When performed by an endodontist, root canal therapy enjoys a clinical success rate well over 90%.  Although root canal therapy has a high degree of success, it cannot be guaranteed.  Occasionally a tooth which has had root canal therapy may require retreatment, surgery or even extraction.

Conventional root canal therapy is preferably completed in one visit, but it may require multiple appointments depending on the circumstances.