Isfahan University of Medical SciencesDental Research Journal1735-33274120080120Antibacterial Substantivity of Three Concentrations of Doxycycline on Bovine Root Dentin Infections: an In Vitro Study4949Z.Mohammadi. mohammadi_zahed@yahoo.comA. R.FarhadF.Ezoddini Ardakani20101106Introduction The aim of this in vitro study was to compare the antimicrobial activity and substan-tivity of three concentrations of doxycycline on bovine root dentin infections. Methods and Materials Seventy dentin tubes prepared from intact bovine incisors were infected in vitro for 14 days with Enterococcus faecalis. The specimens were divided into five groups accord-ing to the used intracanal irrigation as follows: Group1: l00mg/ml of doxycycline hydrochloride so-lution (DHS) (n=20); Group 2: 50mg/ml of DHS (n=20); Group 3: 10mg/ml of DHS (n=20); Group 4: positive control (infected dentin tubes) (n=10); and Group 5: sterile saline (negative control) (n=10). Dentin chips were removed from the canals with sequential sterile low - speed round burs with increasing diameters of ISO sizes: 025, 027, 029, 031, and 033 at experi-mental times of 0, 7, 14, 21, and 28 days. After culturing, the numbers of colony-forming units (CFUs) were counted. Data were analyzed using analysis of variance and covariance with repeated measures (ANOVA) to indicate differences between the experimental groups and the positive control. One-way ANOVA (Tukey's method) was used to indicate differ-ences within each layer. Results The numbers of CFUs in all three experimental groups were minimum in first cultures, and the obtained results were significantly different from each other at any time period (P