Denise Ramos Silveira Alves et al 340 ABSTRACT Objective: The aim of this study was to evaluate the effect of irrigation methods on antibacterial potential of 2.5% NaOCl on Enterococcus faecalis bioilm. Materials and methods: Enterococcus faecalis bioilms were prepared during 60 days on 48 human root canals and rand- omized into control and experimental groups using positive and negative pressure irrigation. Bacterial growth was analyzed using turbidity of culture medium followed by UV spectropho- tometry, and scanning electron microscopy (SEM) analyses were performed. Mean and standard deviations were used for evaluate the mean optical densities associated to the number of bacteria present culture, and Scheirer-Ray-Hare (an extension of the Kruskal-Wallis test) and Tamhane test to analyze the SEM images in the groups and thirds. Signiicance was set at 5%. Results: Enterococcus faecalis was still present after root canal cleaning regardless of irrigation methods or bacterial identiication methods. Conclusion: Positive and negative pressure irrigation protocols using 2.5% NaOCl show a similar capacity to reduce E. faecalis in infected root canals. Keywords: Sodium hypochlorite, Bioilm, Irrigating solution, Root canal infection, Negative pressure system. Antibacterial Potential of 2.5% Sodium Hypochlorite in Distinct Irrigation Protocols on Enterococcus faecalis Bioilm 1 Denise Ramos Silveira Alves, 2 Rodrigo Sanches Cunha, 3 Carlos Eduardo da Silveira Bueno 4 Ana Helena Gonçalves de Alencar, 5 Cyntia Rodrigues de Araújo Estrela 6 Tatiane Oliveira dos Santos, 7 Carlos Estrela 1,4,5,7 Department of Stomatologic Sciences, Federal University of Goiás, Goiânia, State of Goiás, Brazil 2 Department of Conservative Dentistry, University of Manitoba Canada 3 Department of Conservative Dentistry, Sao Leopoldo Mandic School of Dentistry, Campinas, São Paulo, Brazil 6 Department of Physics, Federal University of Goiás, Goiânia State of Goiás, Brazil Corresponding Author: Denise Ramos Silveira Alves Professor, Department of Stomatologic Sciences, Federal University of Goiás, Praça Universitária s/n, Sector Universitário CEP: 74605-220, Goiânia, State of Goiás, Brazil, e-mail: denisealves1@brturbo.com.br How to cite this article: Alves DRS, Cunha RS, da Silveira Bueno CE, de Alencar AHG, de Araújo Estrela CR, dos Santos TO, Estrela C. Antibacterial Potential of 2.5% Sodium Hypochlorite in Distinct Irrigation Protocols on Enterococcus faecalis Bioilm. J Contemp Dent Pract 2015;16(5):340-346. Source of support: Nil Conlict of interest: None INTRODUCTION The treatment of endodontic infection has better chances of success when an adequate cleaning and shaping protocol is adopted. The root canal microenvironment favors the adhesion of several bacterial species to the dentin surface, as well as the formation of a dense bioilm resistant to antimicrobial treatment, often inaccessible to endodontic instruments and irrigants. 1 Areas that remain untouched canal preparation 2 may lead to root canal and dentinal tubule infection. 3,4 Of the different root canal irrigants suggested for infection control, 5,6 sodium hypochlorite is the most common. 5-9 Sodium hypochlorite leads to biosynthetic changes in cell metabolism, phospholipid destruction and chloramine formation, which affects cell metabo- lism and oxidation and results in irreversible enzymatic inactivation in bacteria and lipid and fatty acid degrada- tion. 9 However, its irrigant eficacy depends on its direct contact with microorganisms. Irrigation volume, as well as exposure time and irrigation protocol, is important. 5,7,10 In the conventional irrigation technique, a syringe is used, and the pressure on the plunger is regulated by the operator. 11 The needle tip is placed 2 to 3 mm from the apex, and the irrigant is passively released. The solution does not reach farther than 1 mm beyond the needle tip and seems ineffective in cleaning the apical third of the root canal. 12 When the needle is locked in the apical ORIGINAL RESEARCH 10.5005/jp-journals-10024-1687