Mechanism of action of sodium hypochlorite and its effects on dentin

The complex internal anatomy, host defences and the virulence of micro-organisms are important factors to consider in choosing a root canal treatment. The choice of an irrigation solution for use in infected root canals requires an exact knowledge of the micro-organisms responsible for the infective process, as well as the properties of different irrigation solutions in the treatment of teeth with asymptomatic apical periodontitis. Irrigation solutions must have a targeted antimicrobial action and the ability to dissolve organic tissues. Sodium hypochlorite (NaOCl) is the most used irrigation solution in endodontics and, because of its mechanism of action, it causes a biosynthetic alteration in cellular metabolism and a phospholipid destruction, a formation of chloramines which interferes in cellular metabolism, an oxidative action with irreversible enzymatic inactivation in bacteria, and a lipid and fatty acid degradation. However, it must be said that its use is able to remove collagen fibres and thereby to prevent the hybrid layer formation, which is considered by many authors as the fundamental qualification for a correct and adequate adhesion to dentin. The aim of this paper is to examine the mechanisms of action of sodium hypochlorite based on its antimicrobial and physical-chemical properties and to see how its action could interfere in the resistance of dentin adhesion. Scientific research has shown the now attested validity of sodium hypochlorite as an antibacterial agent with a proteolytic action, while other studies made on the adhesion strength on dentin surface have given conflicting results.