Microbiological analysis of endodontically treated teeth with apical periodontitis before and after endodontic retreatment.

To characterize the microbiota of teeth with endodontic treatment failure by 16S ribosomal RNA genetic sequencing (GS) and PCR at the different phases of the endodontic retreatment and to associate the presence of specific bacteria with clinical and radiographic features in teeth with apical periodontitis. Twenty infected root canals of single-rooted teeth were selected. Samples were collected with sterile paper points before chemo-mechanical preparation (CMP) (S1), after CMP (S2) and after 30 days of intracanal medication (ICM) (S3). Microbial identification was performed using GS and PCR. Tukey-Kramer post hoc test and post hoc ANOVA were used for intergroup analysis. Paired t test and repeated-measures ANOVA were applied for intragroup analysis, at a significance level of 5%. A total of 89 strains were identified using GS. Sixty-five strains were recovered in S1 and 15 strains in S2, and 9 strains remained in S3. Enterococcus faecalis was the most predominant bacteria. Gram-positive cocci bacteria predominated. Gram-negative species were also detected. Using species-specific PCR primers to detect seven species, the most prevalent ones at all the phases of the endodontic retreatment were E. faecalis and Porphyromonas gingivalis. However, Parvimonas micra and P. gingivalis were associated with previous pain, P. gingivalis was associated with tenderness to percussion and E. faecalis, Fusobacterium nucleatum and P. gingivalis were associated with periapical lesion > 3 mm. In conclusion, the microbiota of persistent infection is polymicrobial with predominance of E. faecalis and P. gingivalis in all phases of the endodontic retreatment, regardless of the method used for microbial identification. Associations were found between specific bacteria and clinical/radiographic features. The characterization of the bacteria present at all phases of the endodontic retreatment is important for the monitoring of the effectiveness of the techniques used and to better understand the susceptibility of these species to the disinfection agent used during the procedures.