Root canal-treated teeth with AP were randomly distributed in two groups according to the irrigant used. After removal of the previous filling material, bacteriological samples were taken from the canals before (S1) and after chemomechanical preparation using either NaOCl or CHX (S2), and after calcium hydroxide medication for 2-3 weeks (S3). 16S rRNA gene-based real-time qPCR was performed to detect and quantify total bacteria, Streptococcus species and Enterococcus faecalis.