Antibacterial effects of pulsed Er:YAG laser radiation at different energy settings in molars with root canal isthmuses

Er:YAG lasers have been demonstrated the usefulness for disinfection of anterior teeth with single root canal. However there has been few articles about the antibacterial effects in molars with root canal isthmuses (RCIs). 160 roots containing RCIs were selected, prepared up to file #40, and sterilized. They were divided evenly into two groups using randomization method, and inoculated with either E. faecalis or E. coli. The canals were either rinsed by 2% Chloramine T and 2% H2O2 (hydrogen peroxide) alternately for 30 s or irradiated with an Er:YAG laser for 30 s. The output power of Er:YAG laser was set as: 1.5 W, 2 W, 2.5 W, 3 W, 3.5 W, and 4 W respectively. The bacteria remaining after irradiation were counted using colony counting method. The results show that Er:YAG laser has better antibacterial effects than 2% Chloramine T and 2% H2O2 irrigation. Moreover, we confirm 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. Additionally, the E. coli is more sensitive to Er:YAG laser than E. faecalis at low power setting (≤2 W).