Stability of antibacterial activity of Chlorhexidine and Doxycycline in bovine root dentine

OBJECTIVE: The aim of this study was to compare the substantivity of chlorhexidine (CHX) and doxycycline bond to the dentin in diffusion disk method. METHODS: A total of 92 dentin disks were prepared from Bovine's teeth root. After removing cementum and standardizing disks in weight and outer diameter, they were irrigated with sodium hypochlorite 2.5%, ethylenediaminetetraacetic acid 17% and sterile saline and sterilled in autoclave. Then, the first group (n = 36) were irrigated with chlrohexine 2% and the second group (n = 36) with doxycycline 100 mg/mL, each for a period of 10 min. The third group (n = 20) was considered as the control group. Samples were divided into four subgroups, which after 1 day, 3, 6, and 12 weeks were incubated in plates containing Muller Hinton agar broth and Enterococcus faecalis for a period of 48 h at 37°C temperature; then the diameter of the zone of inhibition was measured. The antimicrobial effect of irrigating solutions without binding to the dentin was also studied using the plate well method. One-way and univariate variance tests as well as Post-hoc Tukey were used for data analyses. FINDINGS: The diameter of the zone of inhibition of doxycycline group was significantly more than the CHX group from the beginning to the 3(rd) week (P < 0.005). After 3(rd) week, mean diameter in doxycycline group declined as compared with the CHX group up to 12(th) week (P < 0.005). The difference between means in two groups was not significant in the 3(rd) week (P = 0.87). CONCLUSION: The results of this study show that CHX and doxycycline show antibacterial activity for 12 weeks; although after 3(rd) week, the substantivity of CHX was significantly greater than doxycycline. Both of these irrigants can be used in other pharmacological and medical fields whenever a long-lasting antibacterial action is needed.