Information on Retreatment is at AAE website:

Frequently Asked Questions about Endodontics Retreatment
(or above address: http://www.aae.org/patients/faqs/cracksum.htm)

Select Back from your brower menu to return to this page.

Or visit the American Association of Endodontists website, and select Patients, then Frequently Asked Questions from the menu:
American Association of Endodontists
(or above address: http://www.aae.org)