Introduction: This randomized clinical study compared the in vivo antibacterial efficacy of Reciproc Blue (RB), XP-endo Shaper (XP-S),XP-endo Shaper associated with XP-endo Finisher (XP-F) systems in infected oval-shaped root canals with primary apical periodontitis.Methods: In this study, 28 human teeth with a single root and a single canal were randomly assigned to two groups according to the instrumentation technique: group-1, RB (n = 14) and group-2, XP-endo (XP-S and XP-F, n = 14). The single-rooted teeth were prepared by reciprocating and rotary nickel-titanium (NiTi) instruments with 5.25% sodium hypochlorite irrigation. Samples were collected from the canal at the baseline (S1), after chemomechanical preparation (S2), and after XP-F instrumentation (S3). The DNA extracts were subjected to quantitative analysis for total bacterial counts by quantitative real-time polymerase chain reaction. The data were analyzed using the analysis of variance test (ANOVA), and the level of significance was set at 5%. Results:All samples tested positive for the presence of bacteria at baseline, and the bacterial counts substantially reduced after treatment procedures (P < 0.01). The results showed no statistical difference between RB and XP-S instrumentation with respect to the bacterial reduction (P ˃ 0.05). A marked bacterial reduction was observed after the use of the XP-F instrument (P < 0.01). Conclusion:The XP-S and RB systems sharply reduced the bacterial load in oval-shaped root canals with primary apical periodontitis. XP-F, used as a supplementary instrument to chemomechanical preparation, promoted a significantly higher bacterial reduction.

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