Zandi H, et al. - The physicians used the pyrosequencing method to examine the root canal microbiota in root-filled teeth with post-treatment apical periodontitis before and after chemomechanical instrumentation and irrigation with either 1% sodium hypochlorite (NaOCl) or 2% chlorhexidine digluconate. They observed a high interindividual diversity in both samples, with no difference between the 2 irrigation groups. During retreatment of root-filled teeth with infection, the most prevalent species in pre-preparation and post-preparation samples were F. nucleatum ss. vincentii and some Streptococcus species.