الفهرس 
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Abstract
Objective: to assess antibacterial effect of Photodynamic Therapy using Nano Silver Particles (AgNps) or Toluidine blue O (TBO) with Hydrogen Peroxide (H2O2) and 635 nm diode laser with output power 100 mw against E. faecalis biofilms compared to calcium hydroxide paste Ca(OH)2 as intracanal medicament. Materials and Methods: One hundred and fifty-four extracted single rooted human teeth with a single canal were decoronated with high-speed diamond wheel stone under water-cooling to facilitate access to the root. Final length was 15mm ± 1. Then instrumented by Protaper universal system up to F3 then until size 50# taper 4٪ to the working length. The files were used in outward brushing mode at 300rpm/2.6nm torque . With the use of each file , the canal was irrigated with 5.25 ٪ NaOCL. E. faecalis Biofilms were generated based on a previously established protocol. four teeth were used to check the biofilm formation by Confocal laser scanning microscopy ”CLSM” and act as a control (no treatment) .Then the remaining teeth were randomly divided into three main lines of treatments ; Line1, PDT using TBO as photosensitizer , line 2, PDT using AgNPs as photosensitizer and line 3,Ca(OH)2 . The antibacterial efficacy of the three lines of treatment was evaluated by colony forming units, and relative intensity of live/dead bacteria, using Confocal Laser Scanning Microscopy. Data of the study were analyzed by statistical analysis with P= 0.05. Results: E. faecalis reduction was significantly better in all the experimental groups than in the control group (p value < 0.001). However, the highest bacterial reduction was obtained with the combined effect of PDT and H2O2 and Ca(OH)2 . Conclusion: the combination of PDT (TBO and AgNps activated by 635 nm diode laser with output power 100 mw ) with H2O2 and Ca(OH)2 exert highest percentage of E.Faecalis reduction in infected root canals.