Antibacterial Efficacy and Discoloration Potential of Endodontic Topical Antibiotics

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The optimal concentration for the use of endodontic topical antibiotics is not known. The aims of this study were to determine the minimum bactericidal concentrations (MBCs) and minimum inhibitory concentrations (MICs) of metronidazole, ciprofloxacin, minocycline, Augmentin (GlaxoSmithKline, Research Triangle Park, NC), and tigecycline against common endodontic pathogens and to evaluate ex vivo the antibacterial efficacy and discoloration effect of triple antibiotic paste (TAP), Augmentin, and tigecycline at different concentrations using a slow-release hydrogel scaffold.


Using the Epsilometer test method (Etest; bioMérieux USA, St Louis, MO), MICs and MBCs of selected antibiotics were determined against Fusobacterium nucleatum, Porphyromonas gingivalis, Streptococcus intermedius, and Enterococcus faecalis. Biofilms of these bacterial species were then grown in extracted single-rooted teeth anaerobically for 3 weeks. Root canals were filled with TAP, Augmentin, and tigecycline at concentrations of 1 or 0.1 mg/mL in a degradable hydrogel scaffold or pure TAP at 1 g/mL for 7 days. Coronal discoloration was evaluated spectrophotometrically at 1, 2, and 3 weeks after dressing.


MIC/MBC data showed significant efficacy of tigecycline, Augmentin, and minocycline compared with the other antibiotics (P < .05). Significant differences were found when comparing the log10 colony-forming units of all experimental groups (P < .05). TAP at 1 g/mL had no bacterial growth but caused the greatest discoloration. Hydrogel mixtures with TAP, Augmentin, or tigecycline at 1 mg/mL significantly reduced bacterial growth and the number of positive samples compared with those at 0.1 mg/mL (P < .05) with minimal discoloration.


TAP, Augmentin, and tigecycline in a hydrogel at 1 mg/mL reduced bacterial growth significantly with minimal color change.

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