Introduction. Root canal irrigation aims to clean and disinfect root canal system by removing organic tissue, smear layer and microorganisms. The most commonly used irrigants are: NaOCl 0,5-5,25%, EDTA 17%, MTAD, CHX (0.2%, 1%, and 2%), citric acid (10%).   Aim of the study. To monitor over the time the effectiveness of endodontic treatment using different irrigants in combination with sonic and ultrasonic activation systems.  Materials and methods. The study was based on the treatment of 15 patients with pulpitis and periapical processes who were subjected to endodontic treatment of 9 single rooted teeth and 10 multiple rooted teeth. The irrigation protocol of pulpitis treatment entailed: 2,5%NaOCl; 17%EDTA;5,25%NaOCl; final irrigation: 5,25%NaOCl+ultrasonic activation;17%EDTA+sonic activation; distilled water; drying and filling. In the treatment of patients with periapical processes, the root canals were irrigated as follows: 5,25%NaOCl ;17% EDTA ;2%CHX, temporary filling with calcium hydroxide for 10 days. The second visit entailed removal of the temporary filling, irrigation with 17%EDTA; distilled water; 2%CHX drying and filling, X-ray.  Results. The patients were examined at 3, 6 and 12 moths. The study showed that treatment by using different irrigants in combination with sonic and ultrasonic activation had a high rate of success (95-97%).  This protocol of irrigation was selected in treatment of pulpitis and periapical lesions due to the properties of each irrigant: NaOCl has bactericidal cytotoxicity, dissolves organic material, it has no effect on the smear layer. EDTA effectively removes the smear layer by chelating the inorganic components of the dentine. It does not have any antibacterial activity and does not dissolve the organic tissues. CHX has a wide antimicrobial spectrum and is effective against Gram-positive and Gram- negative bacteria, especially against E.faecalis.   Conclusions. Successful endodontic treatment depends on the correct use of the irrigants, respecting the consecutivity, concentration and application time of each irrigant and also a tridimensional filling of root canal.