112 © 2006 The Authors Journal compilation © 2006 Australian Society of Endodontology Aust Endod J 2006; 32: 112–115 Blackwell Publishing IncMalden, USAAEJAustralian Endodontic Journal1329-19472006 Australian Society of Endodontology2006323112115Original Research Antibacterial Action of Intra-canal AgentsA. ali Khademi et al. ORIGINAL RESEARCH Evaluation of the antibacterial substantivity of several intra-canal agents Abbas ali Khademi, DMD, MS 1 ; Zahed Mohammadi, DMD, MS 2 ; and Asgar Havaee, PhD 3 1 Department of Endodontics, Isfahan University of Medical Sciences, Isfahan, Iran 2 Department of Endodontics, Shahid Sadoughi University of Medical Sciences, Yazd, Iran 3 Department of Microbiology, Isfahan University of Medical Sciences, Isfahan, Iran Abstract The aim of this in vitro study was to compare the antimicrobial substantivity of 2% chlorhexidine gluconate (CHX), 100 mg ml -1 doxycycline and 2.6% sodium hypochlorite (NaOCl) in bovine root dentine. Eighty dentine tubes prepared from bovine incisors were infected in vitro for 14 days with Enterococcus faecalis. The specimens were divided into five groups as follows: doxycycline HCl; CHX; NaOCl; infected dentine tubes (positive control); and sterile dentine tubes (neg- ative control). Dentine chips were collected with round burs into tryptic soy broth. After culturing, the number of colony-forming units (CFU) was counted. In all experimental groups, the number of CFU was minimum in the first cul- tures, and the results obtained were significantly different from each other at any time period (P < 0.05). In the first culture, the NaOCl group and doxycy- cline HCl group showed the lowest and highest number of CFU, respectively. In each group, the number of CFU increased significantly by time-lapse ( P < 0.05). In conclusion, the substantivity of CHX was significantly greater than NaOCl and doxycycline. Introduction Viable microorganisms remaining after root canal prepa- ration and disinfection contribute significantly to failure in endodontic therapy (1). Numerous measures have been described to reduce the numbers of root canal micro- organisms, including the use of various instrumentation techniques, irrigation regimens and intra-canal medica- ments (1). In cases with necrotic pulps as well as in retreat- ment cases, treatment should be performed in two visits, which is more time-consuming than one-visit treatment (2). Furthermore, some studies have suggested that cal- cium hydroxide is ineffective against Enterococcus faecalis (3). To overcome the aforementioned problems, an alter- native protocol is to use antimicrobial agents that exhibit substantivity, that is, agents that can have a therapeutic effect for a prolonged period. Sodium hypochlorite (NaOCl) is the most commonly used root canal irrigant. It has both antimicrobial and tissue-dissolving properties (4,5). Chlorhexidine glucon- ate (CHX) seems to act by adsorbing onto the cell wall of microorganisms and causing the leakage of intracellular components (6). The antimicrobial substantivity of CHX in the root canal system has been reported to last from 48 h to 21 days (7–9). However, Rosenthal et al. indicated that the substantivity of CHX could last up to 12 weeks (1). Tetracyclines are effective against a wide range of micro- organisms (10). Tetracyclines readily attach to dentine and are subsequently released without losing their antibacte- rial activity (11). In endodontics, tetracyclines have been used to remove the smear layer from the instrumented canals (12,13), irrigation of root–end cavities (14) and as an intra-canal medicament (15). The aim of this study was to compare the antimicrobial substantivity of CHX, doxy- cycline HCl and NaOCl against E. faecalis in bovine root dentine in vitro. Materials and methods The method used in this study was a modification of one previously described by Haapasalo and Ørstavik (3). Thirty intact bovine central incisors were selected for this study. Keywords chlorhexidine, doxycycline HCl, Enterococcus faecalis, substantivity. Correspondence Dr Zahed Mohammadi, Department of Endodontics, Shahid Sadoughi University of Medical Sciences, Yazd, Iran. Email: mohammadi_zahed@yahoo.com doi: 10.1111/j.1747-4477.2006.00033.x