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UBC Theses and Dissertations

The effectiveness of heated sodium hypochlorite on Enterococcus faecalis in infected dentinal tubules Nio, Stefanie


Introduction: The goal of chemical irrigation in endodontics is to maximize the reduction of microbes and necrotic tissue remnants in the root canal system. Enterococcus faecalis is most frequently associated with persistent endodontic infections. Sodium hypochlorite (NaOCl) is the most commonly used root canal irrigant. Heating NaOCl has a positive effect on the tissue dissolving abilities of the solution. Objective: The aim of this study was to compare the killing effectiveness of two different sodium hypochlorite concentrations (2 % vs. 5.25 %) at two different temperatures (20 °C vs. 60 °C) against two strains of E. faecalis biofilm at different ages of maturation (3 days vs. 3 weeks), in a previously described dentin block model. Hypotheses: Temperature, concentration, the exposure time, the age of the biofilm nor the strain of E. faecalis have no effect on the killing efficacy of NaOCl on E. faecalis. Methods: Dentin blocks were prepared from human root dentin. Two E. faecalis strains were introduced into dentinal tubules by centrifugation and incubated to form biofilms. After 3 days and 3 weeks of growth, the E. faecalis dentin biofilm samples were exposed to sterile water, 2 %, and 5.25 % NaOCl for 3 and 10 minutes at room temperature (20 °C) and at 60 °C. After the exposure, the proportions of killed bacteria in dentin canals were assessed by viability staining and confocal laser scanning microscopy. Results: The killing efficacy of E. faecalis in dentin tubules was affected by an increase in temperature of the NaOCl solution. The concentration of the NaOCl solution and exposure time to the irrigant played a role in the killing efficacy of NaOCl. Overall, 5.25 % NaOCl demonstrated a greater effect on the killing efficacy on E. faecalis, except when NaOCl is used at 60 °C with an exposure time of 10 minutes. There was no significant difference (p>0.5) between the two different strains of E. faecalis or between the 3-day and 3-week old biofilms in their sensitivity to the bactericidal effect of NaOCl. Conclusion: Bacterial killing by NaOCl is enhanced by an increase in temperature and concentration.

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