Introduction: This randomized clinical study compared the antibacterial effectiveness of treatment protocols using either a triple antibiotic solution (1 mg/mL) or calcium hydroxide/chlorhexidine paste as interappointment medication in infected canals of teeth with primary apical periodontitis. Methods: The root canals of single-rooted teeth with apical periodontitis were prepared by using a reciprocating single-instrument technique with 2.5% sodium hypochlorite irrigation and then medicated for 1 week with either a triple antibiotic solution (minocycline, metronidazole, and ciprofloxacin) at 1 mg/mL (n = 24) or a calcium hydroxide paste in 2% chlorhexidine gluconate (n = 23). Samples were taken from the canal at the baseline (S1), after chemomechanical preparation (S2), and after intracanal medication (S3). DNA extracts from clinical samples were evaluated for total bacterial reduction using a 16S ribosomal RNA gene-based quantitative polymerase chain reaction assay. Results: All S1 samples were positive for the presence of bacteria, and counts were substantially reduced after treatment procedures (P <.01). Bacterial levels in S2 and S3 samples did not significantly differ between groups (P >.05). S2 to S3 reduction was 97% in the antibiotic group and 39% in the calcium hydroxide/chlorhexidine group; only the former reached statistical significance (P <.01). There were significantly more quantitative polymerase chain reaction–negative S3 samples in the antibiotic group than in the calcium hydroxide group (P <.05). Conclusions: Interappointment medication with a triple antibiotic solution at the concentration of 1 mg/mL significantly improved root canal disinfection, and its effects were at least comparable with the calcium hydroxide/chlorhexidine paste. Effectiveness and easy delivery of the antibiotic solution make it an appropriate medicament as part of a disinfecting protocol for conventional nonsurgical endodontic treatment and possibly regenerative endodontic procedures.
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