Once the decision has been made to retain the tooth there are two ways for ttt:

•     Non surgical retreatment :

            -  guided access to apex via coronal access
            - Inadequate previous root canal obturation

•     Surgical retreatment like :

- reach apex via flap and bone removal
-Periradicular curettage m apical root resection ( with or without root filing ), root amputation or hemisection,and intentional replantation

-American association of endodontists has published guidelines that may help the clinician with clinical decision making .

-If the suspected etiology is persistent or reintroduced mircroorganisms several choices are available (surgical or nonsurgical retreatment)
-If the cause is persistent extraradicular infection , foreign body reaction , or the presence of a true cyst, nonsurgical root canal therapy has little healing to occur , and surgical methods should be employed.