RESUMO
Background: The permanence of microorganisms in the root canal system represents the main cause of endodontic failure. Considering the impossibility of effective action of the endodontic files in ramifications of the main canal and mainly inside the dentinal tubules, a better understanding of the irrigation dynamics to enhance endodontic prognosis is essential. Objective: To evaluate the depth of intratubular penetration values of sodium hypochlorite (NaOCl) (dependent variable) by comparing different concentrations, methods of irrigation, and root canal thirds (independent variables) and to investigate the existence of interactions among them, capable of influencing the dependent variable. Material and Methods: 40 roots from extracted human maxillary central incisors were stained and instrumented according to four irrigation protocols (n. 10): conventional irrigation (CI) at each use or change of instrument, and final irrigation with 5ml of 2.5% or 5.25% NaOCl, with or without passive ultrasonic irrigation (PUI), respectivelly. Measurements based on stereomicroscopic images were obtained, and the data were subjected to statistical analysis (p< 0.05). Results: The highest depth values of intratubular penetration of NaOCl were observed in the cervical third, at 5.25%, and by PUI. When only two independent variables were analyzed in association, the highest penetration depth values of NaOCl were obtained at 5.25%, regardless of irrigation method, at 5,25%, in the cervical third, and; in the cervical third, despite of irrigation method. Considering the three independent variables simultaneously, the highest depth values of intratubular penetration of NaOCl were observed in the cervical third, at 5.25%, no matter the irrigation method. The interaction between the independent variables on the penetration depth values of NaOCl was only confirmed considering the irrigation method and root canal third. Conclusions: Intratubular penetration of NaOCl was influenced by the three independent variables individually and when the irrigation method and root canal third were considered simultaneously. Key words:Dentinal tubules, Depth, Disinfection, Irrigation, Root canal system, Sodium hypochlorite.