الفهرس 
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Abstract
This study was done to compare the antibacterial effect of various disinfecting procedures in root canals infected with Enterococcus faecalis.
Forty-six single-canaled lower premolars were used in this study. Teeth were instrumented, autoclaved and then three specimens were randomly chosen to serve as negative control. The remaining specimens were inoculated with Enterococcus faecalis suspension for two weeks and then another three specimens were randomly selected to serve as positive control.
The remaining 40 specimens were randomly divided into four equal experimental groups of ten specimens each, according the disinfecting procedure carried out. group I: Dry laser irradiation with Er,Cr:YSGG laser. group II: Laser activated irrigation using Er,Cr:YSGG laser. group III: Passive ultrasonic irrigation. group IV: Conventional syringe irrigation with 2.5% NaOCl.
Following each disinfecting procedure, bacterial sampling from inside the root canals was collected by both paper points and dentin chips from the treated root canals and analyzed for the presence of Enterococcus faecalis using culture method. The CFU% reduction of each group was determined in relation to the positive control.
The results were collected, tabulated and statistically analyzed. Results showed that by the paper points method of sampling, group III had the highest the CFU % reduction followed by group II and group IV with no statistical differences among them. A statistical significant difference was found only between group III and group I (P=0.006). While by the dentine chips method of sampling, group II had the highest
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CFU % reduction followed by group III and group IV with no statistical differences among them. A statistical significant difference was found between group II and group I (P=0.02) and between group III and group I (P=0.035). Also, a statistical significant difference in group IV between the two sampling methods was found (P=0.011). Results showed that the wet techniques tested (using NaOCl) were statistically superior to the dry one (without using NaOCl) (P=0.004).