A tooth with a failed root canal treatment requires retreatment. What is the correct sequence of treatment steps?

The correct sequence for retreating a failed root canal and restoring the tooth is: first, re-endodontic treatment (retreatment of the canal system to eliminate infection); second, crown lengthening if needed to expose adequate tooth structure for the ferrule; third, post and core placement to provide coronal retention; and finally, the definitive crown. Re-endodontic treatment must be completed first because subsequent crown lengthening or post placement should not be performed until the root canal is clean and sealed. Performing crown lengthening or post placement before retreatment would risk bacterial recontamination of the canal.