Aim: This study was carried out to assess the recovery rate of Enterococcus faecalis count after disinfection of the root canals with Er,Cr:YSGG laser. Methodology: Freshly extracted 40 human teeth of single straight root canals were prepared to a size 50; these specimens were sterilized and then inoculated with E.faecalis suspension and incubated for 48 hrs. They were randomly allocated to three treatments and one control negative group. The infected root canals underwent laser treatment. Then samples were collected immediately (after irradiation of root canal) and after 7 days of irradiation, after that surviving of bacteria were checked by counting the colony-forming units (CFU). Results: The results indicated that the Er,Cr:YSGG laser was capable of significant reduction of E.faecalis in the infected root canal at all selected output powers 0.75W, 1W and 1.5W as well as there was significant antibacterial differences among these powers. In addition the results showed increased in the number of bacterial colonies in the second microbiological sampling compared with the first microbiological sampling, The bacterial recovery decreased when laser irradiation power increased. The best result for the laser that showing less number of E.faecalis after 7 days of irradiation at 1.5W. Conclusions: This study recognized the disinfection ability of Er,Cr:YSGG laser against the most resistant bacteria that is associated with endodontic infection.

Er, Cr:YSGG laser, E. faecalis, recovery of bacteria, endodontics, bacteriology