It has been shown that teeth with inadequate root canal treatment and available coronal access are good candidates for retreatment. Surgery may be the best option in the following circumstances: teeth with well-treated canals where retreatment offers no better prognosis; retreatment is not feasible because coronal access to the apical canal is impossible or with high risk of accidents (extensive restorations, fractured instruments, perforations, ledges, etc); teeth that have already been subjected to retreatment; and cases where there is a need for biopsy.