الفهرس 
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Abstract
This study aimed to compare the bactericidal effect of diode laser radiation to both passive ultrasonic irrigation and conventional irrigation with NaOCl after single file canal preparation. Methods: Thirty-six anterior teeth with straight roots and single canals were selected, cleaned, prepared manually with K files up to file # 25 to facilitate bacterial inoculation and sterilized. Microbial strain Enterococcus faecalis American type culture collection ”ATCC 29212” was maintained on brain heart infusion (BHI) agar and subcultured monthly. All procedures were done in strict aseptic conditions. A biofilm of E. faecalis was prepared by inoculating a loopful of E.facalis into BHI broth. 20 microns were measured by automatic pipette and incubated in Brain Heart Blood Agar plate for 24 hours at 37°C as a confirmatory step for susceptibility of bacterial strain to form biofilm. Biofilm formation was checked by formation of black strains.Afterwards, the bacterial suspension was adjusted to reach a final concentration of about 3xl08 cells/ mL, and adjusted to No. 0.5 McFarland turbidity standard. Each root canal was completely filled with E. faecalis suspension by using sterile 1 ml insulin syringe. The roots were incubated for one week. During this period, refreshing broth was added every 48 hours. Three specimens were longitudinally sectioned and scanned by scanning electron microscope (SEM) to confirm the adherence of biofilm on canal wall. Specimens were mechanically prepared by F2 ProTaper file as a single file canal preparation technique. Three specimens were inoculated with bacteria and were not mechanically prepared. These specimens served as positive control group. Another three specimens wee only sterilized without inoculation and served as negative control group.
The rest of specimens were divided into 3 groups each containing 10 teeth according to the irrigant used:• Group I: Specimens were irrigated with conventional syringe loaded with 1% sodium hypochlorite as a final flush irrigant for one min.
• Group II: Specimens were irrigated with passive ultrasonic irrigation (PUT) with l% sodium hypochlorite as a final flush irrigant for one min.•Group HI: Specimens were irradiated with diode laser as a final flush irrigant.
Teeth of each group were used for antibacterial effectiveness evaluation by Agar Diffusion Method and incubated at 37°C for 24 hours. After 24 hours, Plates were examined for bacterial growth and colonies were counted .Results: The results were calculated as colony firming unit (cfu)/ml. The results revealed that bacterial biofilm was almost completely removed in both Group I and Group II with higher effectiveness of group 2 but with no significant difference. There was a considerable amount of bacterial reduction in Group III but it could not completely eradicate bacteria from root canals.CONCLUSION Under the limitations of this study, the following can be concluded:1.Irrigation is important for cleaning the root canal and for eradication of bacteria.2.Conventional irrigation with 1% NaOCl is as effective as passive ultrasonic irrigation in complete removal of bacterial biofilm.3.Laser radiation can significant Liecrease the amount of bacteria in root canal but cannot completely eradicate.