Antibacterial And Cleaning Effects Of Pulsed Er:YAG Laser Radiation In Roots With Root Canal Isthmuses

PURPOSE 1.To evaluate the antibacterial effects of pulsed Er:YAG（erbium-doped yttrium aluminium garnet）laser radiation at different energy settings in roots with root canal isthmuses.2.To evaluate the efficacy of sodium hypochlorite（NaClO）and in combination with Er:YAGlaser irradiation at different outputting power in cleaning root canals as well as canal isthmuses in roots of premolars.METHODS 1.160 roots containing RCIs were selected,prepared up to file #40,and sterilized.They were divided evenly into two groups and inoculated with either E.faecalis or E.coli.The canals were either rinsed by 2% Chloramine T and 2% H₂O₂ alternately for 30 s or irradiated with an Er:YAG laser for 30 s.The output power of Er:YAG laser was set as: 1.5W,2W,2.5W,3W,3.5W,and 4W respectively.The bacteria remaining after irradiation were counted using colony counting method.2.After scanned by CBCT（cone-beam computed tomography）,50 well-prepared premolars with root canal isthmuses were randomly assigned into five groups.Each group consisted of 5 roots.They were subsequently subjected to different regimens as followed: group A-irrigated with 1%NaClO for 1 minute,group B-irradiated by Er:YAG laser at 0.5W combined with 1% NaClO irrigation for 1 minute,group C-irradiated by Er:YAG laser at 1.0W combined with 1% NaClO irrigation for 1 minute,group D-irradiated by Er:YAG laser at 2.0W combined with 1% NaClO irrigation for 1 minute,group E-negative control.After histological preparation and staining,thecross-sections were evaluated for percentage of tissue removal.RESULTS 1.The results show that Er:YAG laser has better antibacterial effects than 2% Chloramine T and 2%H₂O₂ irrigation.2.5 W is the optimal output power of the Er:YAG laser to effectively kill both E.faecalis and E.coli in molars with root canal isthmuses.Additionally,the E.coli is more sensitive to Er:YAG laser than E.faecalis at low power setting（≤2 W）.2.The mean percentage of root canal and isthmus cleanliness values were significantly higher in group B,C and D（P<0.05）.There was no significant differences of root canal and isthmus cleanliness among group B,C and D.CONCLUSIONS1.2.5 W is the optimal output power of the Er:YAG laser to effectively kill both E.faecalis and E.coli in molars with RCIs 2.Er:YAG laser combined with 1%NaClO irrigation may be used effectively in root canal and root canal isthmus cleanliness as a new method.