Summary:
Problems difficult or impossible to solve without surgery:
•Inadequate RCT with altered morphology:
•In a study by Gorni & Gagliani (2004), the success rate of retreatment in this group was 47%
•Infection in inaccessible areas:
1.According to Rubinstein & Kim (1999), 81% of molars and 16% of premolars had isthmuses at the level 3mm short of the apex.
2.Findings from recent studies have shown that infection in inaccessible areas in the apical portion of roots cannot be removed using non-surgically treatment modalities
•Extra-radicular infection, true cyst, foreign body reaction

Problems that may be solved non-surgically: -inadequate RCT without altered root canal morphology
Successful outcomes with surgical endodontics •The success rate of current apical surgery was reported to be 97% at 1 year (Rubinstein and Kim, 1999).
Timely management of persistent apical periodontitis surgically or nonsurgically:
•In the study by
-rstavik (1996), 95 roots (99%) with pre-operative apical radiolucency, ‘completely healed’ during a 4-year period following the RCT, of which (85%) ‘completely healed’ already at 2 years.
•Therefore, the chance for late healing is lowà It seems that presence of post-treatment apical periodontitis can be diagnosed within 2 years after the previous treatment