Antimicrobial Effect Of Nd:YAG Laser And Er:YAG Laser On Enterococcus Faecalis In Root Canals: An In Vitro Study

Objective: Root canal therapy is currently the most effective method for the treatment of pulpal and periapical diseases.Thorough removal of infected substances in root canals is the key to successful treatment.Enterococcus faecalis is the most commonly detected microorganism in root canal treatment failures and is difficult to completely remove by conventional sterilization methods.The purpose of this study was to observe the bactericidal effect of Nd:YAG laser,Er:YAG laser and their combination on enterococcus faecalis in root canals in order to provide reference for laser application in root canal disinfection.Methods: The standard strain of enterococcus faecalis(ATCC 29212)was recovered and cultured.The bacterial suspension was prepared and adjusted to an appropriate concentration.Crowns of one-root-canal extracted teeth were cut off to standardize the length of root canals to 10 mm.Each selected root was prepared to the size 30/0.06 and apical foramen was sealed with composite resin.After that,bacterial suspension was added to root canals.Teeth infected with enterococcus faecalis were randomly divided into five groups.Group A: normal saline(NS)irrigation;Group B: 1%Na Cl O irrigation;Group C: Nd:YAG laser;Group D: Er:YAG laser;Group E: Nd:YAG + Er:YAG laser.Half of the infected teeth from each group were randomly selected as controls without treatment.Samples on the surface of root canal walls were collected using sterile paper points and then spread onto BHI agar plates after dilution.After incubation,the CFUs were counted.Two teeth randomly selected from each treated samples,as well as two untreated ones,were split and then observed by SEM.Results: Bacteria counting results showed that the bactericidal rates in groups B,C,D and E were significantly higher than those in group A(P<0.05).Among them,group B had best antimicrobial effect,which was more than 99%,followed by group E.Except for the similar bactericidal rate between group C and group D(P>0.05),there was a significant difference among the groups(P<0.05).SEM showed that the laser groups and 1% Na Cl O solution group had good bactericidal effect in root canal.After Er:YAG laser irradiation,dentinal tubules were opened and root canal walls were smooth.Conclusion: Nd:YAG laser and Er:YAG laser have a certain degree of root canal bactericidal effect.Er:YAG laser can also remove smear layer.The combination of them can kill about two-thirds of enterococcus faecalis in root canal.Both of the lasers have unique advantages compared with traditional disinfection methods and can be seen as a supplement.However,laser disinfection methods cannot replace traditional disinfection methods.