Objective: In this study, we aimed to investigate the occurrence of several microbial species in cases of failed endodontic therapy by means of the polymerase chain reaction (PCR). Study design Root canal samples were taken from 22 root-filled teeth with persistent periradicular lesions selected for re-treatment. DNA was extracted from the samples and analyzed for the presence of 19 microbial taxa by using the polymerase chain reaction.
Results: All samples were positive for at least 1 of the target microbial species. Enterococcus faecalis was the most prevalent species-detected in 77% of the cases. The other most prevalent species were Pseudoramibacter alactolyticus (52%), Propionibacterium propionicum (52%), Dialister pneumosintes (48%), and Filifactor alocis (48%). Candida albicans was found in 9% of the samples. The mean number of species in samples filled up to 2 mm short of the radiographic apex was 3 (range, 1-5), whereas cases in which the filling was greater than 2 mm from the apex yielded a mean of 5 species (range, 2-11). This difference was statistically significant (P <.05).
Conclusions: Microorganisms occurred in all cases of root-filled teeth associated with periradicular lesions, which lends strong support to the assertion that treatment failures are rather of infectious etiology, caused by persistent or secondary intraradicular infections. E faecalis was the most prevalent species, followed by 4 other anaerobic species: P. alactolyticus, P. propionicum, D. pneumosintes, and F. alocis. All examined samples harbored at least 1 of the following gram-positive bacterial species: E. faecalis, P. alactolyticus, or P. propionicum.