The smear layer is created by an instrument touching the canal walls and is composed of organic and inorganic components. Sodium hypochlorite (NaOCl) is the most commonly used antibacterial irrigant, which is able to dissolve necrotic and vital pulp tissue, the organic components of dentin as well as biofilm. Any type of agitation (using temperature or ultrasound) of the NaOCl is a good way to increase the effectivness of this irrigating solution. Ethylenediaminetetraacetic acid (ethylenediaminetetraacetate or EDTA) was the first chelator used in dentistry as an agent capable of chemically softening the root canal dentin, dissolving the smear layer and decreasing dentin permeability. The citric acid demineralizes and softens dentin tissue and removes the smear layer on the radicular walls. Residual citric acid must be thoroughly flushed out to prevent continuing demineralization along the length of the tubules. Chlorhexidine digluconate has a broad spectrum of antibacterial action, sustained action and low toxicity. However, unlike NaOCl, it cannot dissolve organic substances and necrotic tissues present in the root canal system. Hydrogen peroxide (H2O2 ) is a clear, colorless, odorless liquid, which is active against viruses, bacteria, and yeasts. Although H2O2 has long been used in disinfection and canal irrigation in endodontics, the available literature does not support its use over that of other irrigating solutions. None of the presently available endodontic irrigants satisfy the requirements of ideal root canal irrigant. Newer root canal irrigants and techniques are studied for potential replacement of standard used. The purpose of this article is to present an overview on classical irrigating solutions in endodontics and some new concepts to improve the delivery of solution to the apical portion of the root canal system and the quality of removal of the smear layer.
