Antibacterial Efficacy and Discoloration Potential of Endodontic Topical Antibiotics Turky AlSaeed, BDS, MS,* Ali Nosrat, DDS, MS, MDS, † Mary Anne Melo, DDS, MSc, PhD, † Ping Wang, DDS, PhD, ‡ Elaine Romberg, PhD, † Huakun Xu, PhD, † and Ashraf F. Fouad, DDS, MS § Abstract Introduction: 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 concen- trations (MICs) of metronidazole, ciprofloxacin, minocy- cline, Augmentin (GlaxoSmithKline, Research Triangle Park, NC), and tigecycline against common endodontic pathogens and to evaluate ex vivo the antibacterial ef- ficacy and discoloration effect of triple antibiotic paste (TAP), Augmentin, and tigecycline at different concen- trations using a slow-release hydrogel scaffold. Methods: Using the Epsilometer test method (Etest; bioM erieux USA, St Louis, MO), MICs and MBCs of selected antibiotics were determined against Fusobac- terium nucleatum, Porphyromonas gingivalis, Streptococcus intermedius, and Enterococcus faecalis. Biofilms of these bacterial species were then grown in extracted single-rooted teeth anaerobi- cally for 3 weeks. Root canals were filled with TAP, Aug- mentin, 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 dres- sing. Results: MIC/MBC data showed significant effi- cacy of tigecycline, Augmentin, and minocycline compared with the other antibiotics (P < .05). Signifi- cant 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 signifi- cantly reduced bacterial growth and the number of pos- itive samples compared with those at 0.1 mg/mL (P < .05) with minimal discoloration. Conclusions: TAP, Augmentin, and tigecycline in a hydrogel at 1 mg/mL reduced bacterial growth significantly with minimal color change. (J Endod 2018;-:1–5) Key Words Augmentin, bacteria, crown discoloration, regenerative endodontics, tigecycline, triple antibiotic paste D isinfection of the pulp space has been shown to play a critical role in the success of regenerative endodontic procedures (1–3). One commonly accepted disinfection pro- tocol for regenerative endodontic procedures is irrigation of the root canal space with sodium hypochlorite in the first visit and then dressing the root canal with triple antibiotic paste (TAP) (4–6), which includes equal proportions of ciprofloxacin, metronidazole, and minocycline (7). Crown discoloration was reported in 40% of the studies on regenerative endodon- tic treatments (8). Such a complication in anterior teeth can affect patients’ quality of life (9). Minocycline in TAP causes tooth discoloration (10). High concentrations of anti- biotics were shown to be toxic to the stem cells of apical papilla (11, 12). Although generic, broad-spectrum, hypoallergenic antibiotics are recommended for these pro- cedures, the efficacy of reduced concentrations of these antibiotics and their discolor- ation potential have not been adequately investigated. Moreover, the possibility of incorporating these antibacterial agents within scaffolds used in tissue development, which also need to be biocompatible and color neutral, has not been sufficiently explored. These scaffolds can also serve as a carrier for low-dose antibiotics to maintain them in the root canal system and allow the disinfection process to take place. Therefore, the aims of this study were: 1. To determine in vitro the minimum bactericidal concentration (MBC) and mini- mum inhibitory concentration (MIC) of Augmentin, tigecycline, metronidazole, cip- rofloxacin, and minocycline against selected common endodontic pathogens 2. To evaluate the antibacterial efficacy of TAP, Augmentin, and tigecycline at different concentrations in a slow-release hydrogel scaffold 3. To evaluate the discoloration potential of TAP, Augmentin, and tigecycline in a hy- drogel scaffold ex vivo From the *Dental Department, National Guard Health Affairs, Riyadh, Saudi Arabia; † Department of Advanced Oral Sciences and Therapeutics, School of Dentistry, University of Maryland, Baltimore, Baltimore, Maryland; ‡ School of Dentistry, Temple University, Philadelphia, Pennsylvania; and § Department of Endodontics, School of Dentistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina. Address requests for reprints to Dr Ashraf F. Fouad, Department of Endodontics, School of Dentistry, University of North Carolina at Chapel Hill, 1098 First Dental Building, CB# 7450, Chapel Hill, NC 27599-7450. E-mail address: afouad@unc.edu 0099-2399/$ - see front matter Copyright ª 2018 American Association of Endodontists. https://doi.org/10.1016/j.joen.2018.03.001 Significance This ex vivo study investigated the antimicrobial ef- ficacy and color differences for several concentra- tions of antibiotic/hydrogel mixtures with potential use as medicaments in regenerative endodontic therapy. The findings would guide the provider in selecting the most efficacious and least discoloring agent. Basic Research—Biology JOE — Volume -, Number -, - 2018 Endodontic Topical Antibiotics 1