In Vitro Evaluation The Antibacterial Effect Of 2.5% Sodium Hypochlorite Adjust To PH12, 9, 7.5 And 6 On Enterococcus Faecalis

Background: Antibacterial property is one of the important indicators to evaluate the effectiveness of irrigating solutions. Sodium hypochlorite is the irrigating solution most widely used. It has been used for more than 70 years. Sodium hypochlorite is an efficient broad-spectrum antimicrobial agent. It can rapidly kill various pathogenic microorganisms such as bacteria, protozoa, fungi, spores and viruses. The antibacterial effect of sodium hypochlorite is based on the chlorination and strong oxidation of hypochlorous acid. The most important factor affecting hypochlorous acid content in the sodium hypochlorite solution is pH, given that a decrease in pH increases the concentration of dissociated hypochlorous acid and thus its antimicrobial effectiveness. The purpose of the present study is to compare the antimicrobial efficacy of sodium hypochlorite adjust to different pH in vitro.Objective:1. To set up the model of E. faecalis within root canals in vitro.2. To compare the antimicrobial efficacy of 2.5% sodium hypochlorite adjusted to pH 12, 9, 7.5 and 6 in human root canals infected by E. faecalis.3. To compare the direct inhibitory effect of 2.5% sodium hypochlorite adjusted to pH12, 9, 7.5 and 6 on E. faecalis.Methods:1. Forty extracted human anterior teeth with a single root canal, were selected for this study. Conventional access preparations were made and the root canals were instrumented with K-type files up to size 30, under irrigation with 17% EDTA and 2.5% sodium hypochlorite. After root canal preparation, the enlarged apical foramen was sealed by epoxy resin. The smear layer was removed by treatment with 17% EDTA and 2.5% sodium hypochlorite. The effectiveness of this treatment was confirmed in the scanning electron microscope. Other thirty-six root canals were sterilized and each of them was filled with the E. faecalis suspension. Bacteriology characterization approaches were used to make sure that there were no living contaminants. The development of tubule infection up to 21 days was evaluated in the scanning electron microscope.Thirty-two root canals were divided into four experimental groups accordingly to the sodium hypochlorite solution used in irrigation. Each of them was irrigated by 2.5% sodium hypochlorite adjusted to pH 12, 9, 7.5 or 6. Canals were sampled using three paper points. After 10-fold serial dilutions in saline, aliquots were plated onto agar plates and incubated at 37°C for 48 hours. The colony-forming units grown were counted and a log transformation was performed.2. Inhibitory effects of 2.5% sodium hypochlorite adjusted to pH 12, 9, 7.5 and 6 on E.faecalis were evaluated by means of the agar diffusion test. Sterile saline solution was used as the control group. The diameters of the zones of bacterial inhibition were measured and recorded for each solution tested.Results:1. After irrigation with 17% EDTA and 2.5% sodium hypochlorite, the smear layer was removed and the dentinal tubules were opened.2. After incubated aerobically at 37°C for 24h, the liquid medium was still clear. All samples were sterilized successfully.3. By means of sorts of bacteriology characterization approaches, the infection of root canal by E. faecalis could be sure and results showed that there were no living contaminants.4. Biofilm was formed. Cells of E. faecalis were in dentinal tubules and the pulp canal wall after a 21-day infection period in the scanning electron microscope. The infection model could be sure successfully established.5. Comparison between the samples taken before and after irrigation showed that all test solutions significantly in reducing the number of bacterial cells inside the root canal (p < 0.05). Comparisons between groups failed to find a significant difference between group A1, group B1 and group C1 (p > 0.05). Group D1 was significantly more effective than A1, group B1 and group C1(p < 0.05).6. The four pH sodium hypochlorite showed large zones of inhibition against E. faecalis in the agar diffusion test. Saline showed no antibacterial activity. The diameters of the inhibition zone were ranked from the smallest to the biggest solutions as follows: group E2, group A2, group B2, group C2 and group D2. All sodium hypochlorite solution groups were significantly bigger than saline solution (p < 0.05). There were no statistically significant among group A2, group B2 and group C2 (P>0.05). Group D2 was significantly bigger than A2, group B2 and group C2(p < 0.05).Conclusion:1. The model for root canal in vitro invaded by E.facealis can be established successfully.2. 2.5% sodium hypochlorite was effective on E.facealis in the agar diffusion test and in vitro infected root canal.3. The antibacterial effect on E.facealis was different between 2.5% sodium hypochlorite at different pH.4. Bactericidal activity of sodium hypochlorite solution was enhanced by weak acidification of 2.5% sodium hypochlorite. In the study, 2.5% sodium hypochlorite at pH6 was most effective on E.facealis.