ORIGINAL RESEARCH Antimicrobial efficacy of clindamycin and triple antibiotic paste as root canal medicaments on tubular infection: An in vitro study Nazanin Zargar, DDS, MS 1 ; Motahare Rayat Hosein Abadi, DDS 2 ; Mohammad Sabeti, DDS, MS 3 ; Zahra Yadegari, PhD 4 ; Alireza Akbarzadeh Baghban, PhD 5 ; and Omid Dianat, DDS, MS 6,7 1 Department of Endodontics, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran 2 Private Practice, Tehran, Iran 3 Department of Endodontics, School of Dentistry, University of California, San Francisco, California, USA 4 Oral Molecular and Cellular Biology Laboratory, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran 5 Proteomics Research Center, Department of Basic Sciences, School of Rehabilitation, Shahid Beheshti University of Medical Sciences,Tehran, Iran 6 Endodontic Division, School of Dentistry, University of Maryland, Baltimore, Maryland, USA 7 Iranian Center For Endodontic Research, Research Institute of Dental Sciences, Dental School, Shahid Beheshti University of Medical Sciences, Tehran, Iran Keywords calcium hydroxide, clindamycin, Enterococcus faecalis, triple antibiotic. Correspondence Omid Dianat, Endodontic Division, School of Dentistry, University of Maryland, 650 West Baltimore St., Baltimore, Maryland 21201, USA. Email: omiddianat@umaryland.edu doi: 10.1111/aej.12288 (Accepted for publication 26 May 2018.) Abstract This study compared the antibacterial effect of 2% clindamycin and 2% and 100% concentration of triple antibiotic paste (TAP) on an Enterococcus faecalis biofilm. Dentinal tubules of 100 root specimens were infected and randomly assigned to five groups. A total of 1000 mg mL À1 of TAP, 20 mg mL À1 of TAP and clindamycin, calcium hydroxide or methylcellulose (control) were placed in the root canal for 1 week. After treatment, dentine shavings were collected from 200 and 400 lm dentine depth and the number of colony-forming units (CFU) per mg was determined. Reduction in viable bacteria in first three groups was significantly better than calcium hydroxide and control groups. However, the antimicrobial effectiveness among these three groups was not significantly different from each other. There was no significant difference between data at 200 and 400 lm in all groups except the Ca(OH) 2 group. The antibiofilm effect of clindamycin was comparable with TAP, so it may be used instead of TAP. Introduction One of the main goals of root canal treatment is to elimi- nate bacteria and their by-products from the root canal system. The success rate of endodontic treatment could be at least 26% higher if there were not any bacteria in root canal system (1). Chemomechanical instrumenta- tion can eliminate the majority of infecting bacteria but complete disinfection is not achieved by this way because of root canals anatomical complexity and bacterial vari- ety, so the use of intracanal medicaments to disinfect the root canal system has been suggested for achieving long term successful outcome of treatment (2). Calcium hydroxide has been widely used in endodon- tic treatments. The main benefit of calcium hydroxide as an intracanal medicament is the bactericidal effect related to its high pH (3). However, recent studies showed its low antibacterial effect on Enterococcus faecalis, a resistant microorganism observed in primary and secondary infections (4–6). The antimicrobial efficacy of Ca(OH) 2 on microorganisms in the dentinal tubules is also questionable (7). The triple antibiotic paste (TAP), mixture of metronida- zole, ciprofloxacine and minocycline has been suggested as an intracanal medicament for disinfection of infected root canal dentine (8); but there is some concerns with using TAP. Discoloration is a real concern in teeth treated with TAP (9). The use of TAP also significantly reduced dentine flexural strength, microhardness and root resis- tance to fracture (10). High concentrations of TAP were found to be toxic to dental papillae stem cells and it affects negatively on their attachment and proliferation. Therefore, recent studies recommended low concentra- tions of TAP to reduce its toxicity (11). © 2018 Australian Society of Endodontology Inc 1 Aust Endod J 2018