Even if root canal treatment is performed in an outstanding manner, it will not be successful if the coronal restoration that is placed leaks. This is why there must be synergy between the restorative and endodontic treatments. With such synergy, and proper home care that maintains a health periodontium, endodontically treated teeth can be retained in function and without symptoms for many years at a 90% success level or higher. Studies suggest that persistent intraradicular or secondary infections, and extraradicular infections in some cases, are the major causes of endodontic treatment failure, even in well-treated teeth. Even with meticulous treatment some patients may not heal, for unknown reasons. In such cases treatment options such as nonsurgical retreatment, surgical intervention, intentional replantation or autotransplantation should be considered. When periradicular radiolucencies and clinical signs and/or symptoms are present, the literature supports retreatment; subsequent survival rates are higher than 90%.
(Source: Endodontics: Colleagues for Excellence, Fall/Winter 2003)