Influence of pH changes on chlorine-containing endodontic irrigating solutions

Abstract

Chlorine-containing solutions are used for broad disinfection purposes. Water disinfection literature suggests that their disinfectant action depends on pH values as this will influence the available free chlorine forms. Hypochlorous acid (HOCl) has been suggested to have an antimicrobial effect around 80-100 times stronger than the hypochlorite ion. The aim of this paper was to review the influence of pH changes on the efficacy of chlorine-containing endodontic irrigating solutions. An electronic and hand search (articles published through to 2010, including 'in press' articles; English language; search terms 'root canal irrigants AND sodium hypochlorite or hypochlorous acid or superoxidized water or electrochemically activated solution'; 'antimicrobial action AND sodium hypochlorite or hypochlorous acid or superoxidized water or electrochemically activated solution'; 'tissue dissolution AND sodium hypochlorite or hypochlorous acid or superoxidized water or electrochemically activated solution'; 'smear layer AND sodium hypochlorite or hypochlorous acid or superoxidized water or electrochemically activated solution') was performed to identify publications that compared chlorine water solutions with different pH. Of 1304 publications identified, 20 were considered for inclusion in the review. The search resulted in the retrieval of articles studying sodium hypochlorite (NaOCl), superoxidized waters (SOW) and sodium dichloroisocyanurate (NaDCC). Regarding antimicrobial efficacy, the literature suggested that reducing the pH value of NaOCl to between 6 and 7.5 would lead to improved action; SOW was described as having a lower antimicrobial effect. The tissue dissolution activity NaOCl decreased when the pH reached values between 6 and 7.5; NaDCC and SOW had no clinically relevant tissue dissolution capability. Chlorine solutions of different characteristics appeared to have some cleaning efficacy although they should to be used in conjunction with chelating and/or detergent agents.

Antagonistic Interactions between Sodium Hypochlorite, Chlorhexidine, EDTA, and Citric Acid

“…A reduction of the pH to values around 6.0 to 7.5 has been found to improve the antimicrobial efficacy (11-13) but hinders tissuedissolution action (11,(13)(14)(15). If the pH is lowered to values below 4, then the amount of chlorine gas in the solution will increase (16).…”

“…It has been suggested that variations of NaOCl pH will modify the antimicrobial and tissue-dissolution activities (11). A reduction of the pH to values around 6.0 to 7.5 has been found to improve the antimicrobial efficacy (11-13) but hinders tissuedissolution action (11,(13)(14)(15).…”

Bactericidal and Fungicidal Activity in the Gas Phase of Sodium Dichloroisocyanurate (NaDCC)

“…NaDCC is largely employed as antimicrobial agent for its efficacy against both bacteria and fungi; however, it has been adopted as disinfectant only as aqueous solution, at direct contact with microorganisms [20].…”

Effect of an Alcohol-Based Caries Detector on the Surface Tension of Sodium Hypochlorite Preparations

“…Accoding to the manufacturer, the Kurakay Caries Detector contains a mixture of dyes and propane-1,2-diol, with the latter component being an alcohol, and known to be incompatible with oxidizing agents. Chlorine-containing solutions such as NaOCl are oxidizing agents (15), and the addition of a different alcohol, ethanol, as a surface tension depressant increases the penetration of NaOCl containing mixtures in vitro (16). Therefore, a better understanding of the behaviour of NaOCl and Kurakay mixtures is necessary.…”