Effects of Contemporary Irrigant Activation Schemes and Subsequent Placement of an Interim Dressing on Bacterial Presence and Activity in Root Canals Associated with Asymptomatic Apical Periodontitis.

New tools for activating endodontic irrigants have evolved, yet their impact on root canal disinfection, in comparison to the passive placing of an inter-visit medication, have not yet been fully elucidated. The use of DNA- and rRNA-based methods may cast some new light on this issue, as they allow a comparison to be made between microbial presence and activity. Therefore, the aim of this single-arm intervention trial is to evaluate the antibacterial effect of endodontic procedures using both molecular methods. Root canal samples were obtained from 20 patients with asymptomatic apical periodontitis after each treatment step: access cavity, chemo-mechanical preparation, adjunctive procedures (XP-endo Finisher file and passive ultrasonic irrigation), calcium hydroxide medication, and 2nd-visit root canal preparation. DNA and cDNA from the samples were subjected to quantitative polymerase chain reaction with universal primers for the bacterial 16S rRNA gene. Chemo-mechanical preparation promoted a drastic reduction in bacterial levels and activity, whereas the adjunctive procedures did not make a significant contribution to further disinfection. At the 2nd visit, bacteria were active after the use of calcium hydroxide medication; however, they were significantly reduced after a 2nd-visit preparation. Consequently, the lowest bacterial levels were found at the end of the treatment. This clinical trial, which used an rRNA and rDNA combined approach, confirmed previous studies showing that root canal preparation represents the main strategy for root canal disinfection.

Analysis of Active Bacteria Persisting after Chemomechanical Procedures: An RNA- and DNA-based Molecular Study.

INTRODUCTION: Because active cells present higher abundance of ribosomal RNA (rRNA) than rDNA (rRNA genes), data obtained with rDNA-based quantitative polymerase chain reaction (qPCR) and rRNA-based qPCR (RT-qPCR) were correlated to search for active bacteria after chemomechanical procedures (CMP). In addition, the ability of both assays to detect bacteria in endodontic samples was evaluated. METHODS: Samples were taken from 40 teeth with primary endodontic infections before (S1) and after CMP (S2). DNA and cDNA (synthetized from RNA) were used as templates for qPCR using universal primers for bacteria and species-specific primers for Bacteroidaceae sp. HOT-272, Cutibacterium acnes, Selenomonas spp., and Enterococcus faecalis. RESULTS: After CMP, there was a drastic reduction in the number of total bacteria, Selenomonas spp., and E. faecalis, whereas no significant difference was observed for the levels of Bacteroidaceae sp. HOT-272 and C. acnes. The concentration of rRNA copies in S2 samples was significantly higher than the corresponding levels of rDNA for assays targeting total bacteria, Bacteroidaceae sp. HOT-272, and C. acnes (P < .05), indicating persistence of active bacteria. The rDNA-based qPCR presented low sensitivity and high specificity when compared with RT-qPCR. For most assays, samples positive for rDNA were also positive for rRNA (positive predictive value = 100%). CONCLUSIONS: CMP was effective in reducing levels but not the metabolic activity of total bacteria. Bacteroidaceae sp. HOT-272 and C. acnes were active members of the persistent community. Although less sensitive than RT-qPCR, most rDNA-based qPCR assays had a low risk of providing false-positive results in postinstrumentation samples.