| Pulp and periapical diseases are of microbial origin, and root canal therapy are the best choice for the diseases, which conclude three parts: root canal preparation, root canal disinfection and root canal filling. Root canal preparation is the key to the success of the treatment, it provide a thorough cleaning of root canal. However, the process also produce smear layer, which prevents penetration of intracanal medication into the irregularities of the root canal system and the dentinal tubules and also prevents complete adaptation of obturation materials to the prepared root canal surfaces. Therefore the smear layer should be removed.In this study, we investigate self-made root canal lubricants combined with different concentrations of sodium hypochlorite during the root canal preparation on the Enterococcus faecalis-contaminated root canals of extracted human teeth. The antimicrobial effect, the ability to remove smear layer, the cytotoxicity and the effect on the dentinal micro-hardness were observed. 1. The antimicrobial effect of the self-made root canal lubricants combined with different concentrations of sodium hypochlorite on Enterococcus faecalis contaminated root canals of extracted human teeth150 extracted human teeth were contaminated with Enterococcus faecalis for 4 weeks. We use self-made root canal lubricants (including three formulations) and the GlydeTM File Prep combined with different concentrations of sodium hypochlorite (0.5%, 2.5%, and 5.25%) during the root canal preparation. We collect the bacteria samples with sterile paper points before, during and after the instrumentation. Statistical analysis of the data using Kruskal-Wallis H test and Nemeny test showed that the combination of the root canal lubricants and 5.25% NaOCl was significantly more effective against Enterococcus faecalis than the other regimens(P<0.05). There are no significant differences between the three formulations of the self-made root canal lubricants and the GlydeTM File Prep(P>0.05). It showed that the combination of the root canal lubricants and 5.25% NaOCl was significantly more effective against Enterococcus faecalis than the other regimens, and as effective as the combination of GlydeTM File Prep and 5.25% NaOCl.2. The effect of the self-made root canal lubricants combined with different concentrations of sodium hypochlorite on removal of smear layer150 extracted human teeth were contaminated with Enterococcus faecalis for 4 weeks. We use self-made root canal lubricants (including three formulations) and the GlydeTM File Prep combined with different concentrations of sodium hypochlorite (0.5%, 2.5%, and 5.25%) during the root canal preparation. We examined the root canal surfaces under the scanning electron microscope and scored for debris and smear layer removal. Statistical analysis showed that self-made root canal lubricants (including three formulations) combined with different concentrations of sodium hypochlorite (0.5%, 2.5%, and 5.25%) can remove the smear layer, the effect of debris removal increased with increased concentration of sodium hypochlorite. The debris removal effect of the combination of the root canal lubricants and 5.25% NaOCl was significantly more effective than the other regimens (P<0.05). There are no significant differences between the three formulations of the self-made root canal lubricants and the GlydeTM File Prep(P>0.05). It showed that the combination of the root canal lubricants and 5.25% NaOCl was significantly more effective on smear layer removal than the other regimens, and as effective as the combination of GlydeTM File Prep and 5.25% NaOCl.3. The cytotoxic effects of the self-made root canal lubricants and three different concentrations of sodium hypochlorite solutionsWe evaluated the cytotoxicity of the self-made root canal lubricants, the GlydeTM File Prep and three different concentrations of sodium hypochlorite solutions on L929 fibroblasts by MTT test. It showed that the three self-made root canal lubricants and the GlydeTM File Prep were significantly cytotoxic than the negative control group while diluted to 1:10(P<0.05), and there were no differences between the experimental groups (P>0.05). 0.5%, 2.5%, 5.25% sodium hypochlorite and 3% hydrogen peroxide showed cytotoxicity while diluted to 1:10, and were significantly cytotoxic than the negative control group (P<0.05), of which 5.25% sodium hypochlorite was the most cytotoxic. In addition, 5.25% sodium hypochlorite was still cytotoxic while diluted 1000 times, significantly different with the negative control group (P<0.05). The rest of the experimental groups had no significant cytotoxicity, and there were no differences between these experimental groups and the negative control group (P>0.05). 4. The effects of the combination of the self-made root canal lubricants and three different concentrations of sodium hypochlorite solutions on the dentin micro-hardness of human teethSeventy root canals were treated with the combination of self-made root canal lubricants and three different concentrations of sodium hypochlorite solutions during the root canal preparation. Then the dentin micro-hardness was examined after ProTaper instrument F1 and F3 prepared. It showed that the dentin micro-hardness decreased after the treatment, and the decrease after prepared with F3 was more significant than F1 (P<0.05). There were significant differences between these experimental groups and the negative control group (P<0.05). After prepared with ProTaper instrument F3, there were significant differences between the group contain 5.25% sodium hypochlorite and the group contain 0.5% or 2.5% sodium hypochlorite (P<0.05). The results showed that the self-made root canal lubricants combined with three different concentrations of sodium hypochlorite solutions decrease the dentin micro-hardness of human teeth, and the effect id similar to GlydeTM File Prep.
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