• Perforations
• Separated instruments in root canals
• External root resorption
• Coexistent periodontal- periradicular lesion
• Developing apical cyst
• Silver points with peri-apical pathology
• Accessory canal unfilled
• Constant trauma

Mode of Retreatment

(A) Non-surgical - done by orthograde route and is for treating

• Missed canals
• Poor obturations
• Peri-apical Pathology
• Instrument fragmentation
• Root Perforations
• Posts removal

(B) Micro Surgical - done by retrograde approach to manage

• Calcified Canals
• Root resorptive defects
• Root resection
• Instrument fragmentation
• Irretrievable posts
• Non-negotiable ledging
• Root perforation
• Symptomatic overfilling