The Smear Layer, a coating of debris adhered to the dentinal tubules of the root canal walls, has, in its composition, organic matter including microorganisms, but mostly inorganic tissue, can conditionate the success of Non-Surgical Endodontic Treatment as it acts as barrier precluding an efficient disinfection. Its removal is still a topic that remains controversial, which is achieved through the application of irrigants, a chelating agent followed by sodium hypochlorite, with or without agitation techniques. It is intended to compare the cleaning capacity of conventional passive manual irrigation with sonic and ultrasonic techniques (“Passive Ultrasonic Irrigation”, “EndoActivator ®” and “Eddy ®”), through selected studies that used the Scanning Electron Microscopy methodology. It is also proposed that this work could be a useful clinical guide for Dentists.