| ObjectiveTo evaluate the bactericidal effect of Nd:YAG laser for Enterococcus faecalis in infectious root canal, and to provide theoretical basis for clinical generalization and application of Nd:YAG laser.Materials and methodsModel of infection of Enterococcus faecalis in root canal was established,1 day,3 days,5 days,1 week,2 weeks and 3 weeks after infection,2 samples were randomly selected for scanning electron microscopy to observe the situation of infected root canals and the formation of biofilms of Enterococcus faecalis.40 anterior teeth specimens in 3 weeks(21 days) after infection were randomly divided into 5 groups, each with 8 teeth.Group A applied 1.5W laser dose in root canals, and the reaction time was 30s. Group B applied 2.1W laser dose, and the reaction time was 30s. Group C applied 2.1 W laser dose repeated 3 times, each reaction time was 30s, and the interval was 15s. Group D, after being washed with 2.5% sodium hypochlorite,2.1 W laser repeated 3 times. Group E was washed with 2.5% sodium hypochlorite, as a control group. Six samples were randomly selected from each group for bacterial culture immediately before and after the irradiation and washing the root canals, and the colony-forming units (CFU) were counted after 48h; 2 specimens for scanning electron microscopy to observe the bactericidal effect of Enterococcus faecalis in root canalsResults1) Colony counting results:Bacteria in root canal after irradiation and irrigation were both significantly decreased. There are significant difference among the reduction of bacteria in canals of each group before and after irradiation and irrigation. Pairwise comparison of the reduction of bacteria in canals of each group before and after irradiation and irrigation:Group A had significant differences compared with group C, group D and the control group (P<0.05);but no significant differences with group B(p> 0.05); Group B had significant differences compared with group C, group D and the control group (P<0.05); Group C had no significant differences compared with group D and the control group (P >0.05); Group D had no significant differences compared with the control group (P>0.05).2) SEM Results:Enterococcus faecalis biofilm got colonization on root canal dentin walls and invade dentinal tubules. With the time of infection increasing, the form of biofilms was changed, and bacteria invaded the dentinal tubules deeper. The formation of mature biofilm was observed after 21 days. Samples of group A and group B after irradiation can be observed that biofilm structure was destroyed, bacteria amount decreased obviously, but more sporadic bacteria still remained in root canals lumen, while dentinal tubules retained a small amount of bacteria. Samples of group C and group D were observed that no bacteria existed basically in root canals lumen, and almost no bacteria existed in dentinal tubules. Samples of group D were also observed that part of dentinal tubules orifice were opened, root canal walls were clean. Most bacteria in root canals lumen of samples of group E was sterilized, but still more bacteria was found in the depth of dentinal tubules.Conclusions1. Single strain of Enterococcus faecalis in vitro root canals can form biofilms.2. Nd:YAG laser has the ability to kill Enterococcus faecalis quickly and effectively. Disinfection of Enterococcus faecalis was better when irradiation was repeated in root canal, especially bacteria in the depth of the dentinal tubules.3.2.5% sodium hypochlorite has strong bactericidal effect for Enterococcus faecalis in root canal lumen, but the bactericidal effect for the bacteria inside the dentinal tubule was ineffective.4. A combined application of Nd:YAG laser and 2.5% sodium hypochlorite can produce cooperative and the best antibacterial effect, and the root canal walls were more clean. |
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