[17] Furthermore, it is difficult to simulate the environmental conditions required for cultivation of fastidious microorganisms. Polymerase chain reaction (PCR 16s rDNA) method selleck screening library is more specific, accurate, sensitive and rapid than the culture technique, allowing uncultivable and fastidious microorganisms to be detected.[17] Nevertheless, PCR cannot determine whether target DNA comes from live or dead bacteria.[18] This study revealed by culture technique, the presence of predominantly facultative anaerobes and Gram-positive species and how they relate with the different phases of the endodontic treatment (S1, S2, S3), showing a heterogeneous profile of polymicrobial infection. The use of PCR enabled us to detect some Gram-negative bacteria species that are difficult to grow, such as the genera Fusobacterium spp.

, Porphyromonas spp., Prevotella spp., Tannerella spp. and Treponema spp. Furthermore, their prevalence was much more pronounced with the use of PCR, differently from those studies using only culture techniques,[5,6,7,8,9] agreeing with the literature.[10,11] Obtaining a representative sample of root-filled canals is not an easy task because of the limitations imposed by the physical constraints of the root canal and the presence of the root-filling material itself.[10,17] In some cases, a negative culture result does not necessarily imply a bacteria-free root canal system, as microorganisms may be retained in complex areas of the system, embedded within a biofilm or exist in low numbers, thus being inaccessible to paper points used for sampling.

[18] Furthermore, microorganisms adhered to gutta-percha can be taken away after removal of the root canal-filling, and thus the CFU count may be underestimated. Even so, in this work, all teeth harbored microorganisms at S1, which were identified by culture techniques and detected by PCR. The main reason for a failure of the root canal therapy is the presence of persistent microorganisms after therapy or re-contamination of the canal system because of an inadequate seal. The clinical procedures require removal of the original root canal-filling, further instrumentation, disinfection and refilling.[4] Complete elimination and/or reduction of the microorganisms in teeth with persistent infection is the main objective of the root canal retreatment. Residual organisms are likely to play a role in treatment failures.

[5,6] Clinical follow-up studies have reported that chemomechanical procedures reduce Brefeldin_A microorganisms in the root canal system,[12,19] agreeing with the findings of the present study. After the first appointment, restoration was placed by using definitive composite in combination with an adhesive in order to prevent re-infection of the root canal. Our results showed that even using a crown-down technique with 2% CHX gel, apical patency and foramen enlargement, only 33.3% (5/15) of the canals were rendered bacteria-free after chemomechanical preparation.