Supervisor : Salma El Ashry, Ahmed Mostafa Ghobashy.Hussein, Dina Nashaat Hassan,2022-01-182022-03-272022-01-182022-03-272017.EG-CaMIUThs250https://iorep.miuegypt.edu.eg/handle/20.500.13071/83DISSERTATION NOTE-Degree type M.Sc.DISSERTATION NOTE-Name of granting institution Misr International University, Faculty of Oral and Dental MedicineIncludes bibliographic references (p. 97-104)`Includes summary in Arabic.The definitive goal of root canal treatment is to obtain a root canal system free of irritants, as any remaining microorganisms can cause persistent inflammation in the periradicular tissues. Success of endodontic therapy depends on complete elimination of pathogenic micro flora from the root canal system. Enterococcus faecalis is the most common bacteria associated with persistent endodontic infections. It is a facultative gram-positive anaerobic coccus that has the ability to exist in root canals without the support of other microorganisms. It has the ability to infect the whole length of dentinal tubules within a few days, and is considered difficult to eradicate. It can also survive harsh environmental factors, and form biofilms that are difficult to detach. Biofilm disruption and root canal disinfection are the most important steps during root canal treatment. Sodium hypochlorite is one of the most commonly used irrigating solutions in endodontics. The antibacterial efficiency of sodium hypochlorite solution against E. faecalis is well known to be affected by its concentration and contact time. Adjunctive techniques of root canal disinfection have been proposed, and the introduction of lasers in endodontics is one. Lasers have dramatically improved the effectiveness and success rate of root canal treatment. According to several studies, the use of laser systems for endodontic disinfection provides an opportunity to reduce the problems concerning the difficult access of instruments and irrigants to certain areas of root canals, mainly at the apical ramifications. It has been recognized that near-infrared lasers (810 nm to 1340 nm) have greater depth of penetration when compared to the penetration power of chemical disinfectants, which allows for better bactericidal effect in deeper dentin layers. The use of photosensitizing agents has been proposed in endodontics used with methods such as ‘photodynamic therapy’ (PDT) or “photoactivated disinfection” (PAD). Photosensitizing solutions have better wetting capabilities as they have lower surface tension than sodium hypochlorite. Photosensitizer concentration, light intensity and time of application have to be precise in order to achieve optimal results. Laser thermal effect can generate damage to the dentin walls. Several studies investigated the laser-induced morphological effects on root canal walls. When they are used on dry tissue, near-infrared lasers produce characteristic thermal effects. Morphological alterations of the dentinal wall occur, and the smear layer is only partially removed. Dentinal tubules are primarily closed as a result of melting of the inorganic dentinal structures. Employing the correct parameters and treatment protocol for laser use in root canal disinfection and bacterial elimination can help replace the conventional syringe irrigation methods of disinfection, reduce the morphological alteration of root canal dentin, and improve the treatment outcome.110 pages : illustrations ; 30 cmtextapplication/pdfengEndodonticstext