Which of the following is the most common organism found in retreatment cases of periapical abscess?
E. faecalis
Trepenoma denticola
S. mutans
Actinomyces
PERSISTENT APICAL PERIODONTITIS

It is post-treatment apical periodontitis in an endodontically treated tooth (re-treatment case).
Enterococcus faecalis is found the most consistently reported organism in persistent apical periodontitis.