Reduction in the cultivable bacterial populations in infected root canals by a chlorhexidine-based antimicrobial protocol

The present clinical study was conducted to assess the bacterial reduction after chemomechanical preparation using 0.12% chlorhexidine digluconate solution as an irrigant and the additive antibacterial effect of intracanal dressing with calcium hydroxide (Ca(OH)(2)) associated with 0.12% chlorhexidine digluconate gel. According to stringent inclusion/exclusion criteria, 13 teeth with primary intraradicular infections and chronic apical periodontitis were selected and followed in the study. Bacterial samples were taken at the baseline (before treatment) (S1), after chemomechanical preparation using chlorhexidine (CHX) as an irrigant (S2), and after a 7-day dressing with Ca(OH)(2)/CHX paste (S3). Cultivable bacteria recovered from infected root canals at the three stages were counted and identified by means of 16S ribosomal RNA gene sequencing analysis. At S1, all canals were positive for bacteria, with the mean number of 3.5 taxa per canal (range, 2-9). At S2, 7 cases (53.8%) still harbored cultivable bacteria, with a mean number of 1.7 taxon per canal (range, 1-4). At S3, only one case (7.7%) was positive for the presence of bacteria. The great majority of taxa found in posttreatment samples were gram-positive bacteria. A significantly high reduction in bacterial counts was observed between S1 and S2 and S1 and S3 (p<0.001). Also, significant differences were observed for comparisons involving S2 and S3 samples with regard to both quantitative bacterial reduction (p=0.014) and number of cases yielding negative cultures (p=0.01). It was concluded that chemomechanical preparation with 0.12% CHX solution as an irrigant significantly reduced the number of intracanal bacteria but failed to render the canal free of cultivable bacteria in about one half of the cases. Application of a 7-day intracanal dressing with Ca(OH)(2)/CHX paste further increased significantly the number of cases yielding negative cultures.