1. Aberrant anatomy
2conventionally blocked apices
3. iatrogenic
4.persistent cyst/ radicular lesions/sinus tract
5.acute pain
6.perforated apex
7. when biopsy and surgical exploration of the area is necessary
8.when there is a post present or seperated instrument and non surgical approach is inevitable and access to apex is not accessible thru any other approach
9. marked overfilling with extrusion of fillinf in periradicular area