Antibacterial effect of Sodium hypochlorite is mainly due to:
Sodium Hypochlorite (NaOCl):
Sodium hypochlorite is the most commonly used endodontic irrigant known as "universal irrigant". It has a better bactericidal effect, tissue lytic effect and also acts as a canal lubricant. It gained its significance during world war - I where 0.5% sodium hypochlorite along with boric acid was used as Dakin's solution to clean the contaminated wounds of the soldiers by a chemist named Henry Drysdale Dakin and the surgeon Alexis Carrel. Due to its excellent broad-spectrum killing efficacy on microbes along with sporicidal effect and necrotic tissue dissolving effect which prompted the use of the aqueous solution of sodium hypochlorite in endodontics in the early 1920s.
In the root canal, it is effective against most difficult to eradicate microorganisms like enterococcus, actinomyces, and candida. As a canal irrigant, it is a reducing agent, which is clear, a straw-colored solution with 5% of available chlorine giving a strong odor of chlorine. Added to this sodium hypochlorite is an economical and easily available root canal irrigant.
Antimicrobial effect of sodium hypochlorite:
Ionization of NaOCl produces, hypochlorite ions and hypochlorous acid. Both are responsible for the antimicrobial effect but, the main effect is due to hypochlorous acid. Estrela et al. studied the biological effects of sodium hypochlorite on anaerobic organisms and proposed the following stages:
Stage 1: Saponification reaction
Sodium hypochlorite reacts with the cell wall by degrading the fatty acids and transforming them into fatty acid salts known as soap and then into glycerol i.e., alcohol. This reaction is known as saponification. The formation of this reaction products reduces the surface tension of the remaining solution.
Stage 2: Amino acid neutralization / Neutralization reaction
Sodium hypochlorite which is a base, neutralizes the cellular amino acids forming water and salt. During this reaction, there will be a release of hydroxyl ions resulting in a reduction of pH.
Stage 3: Chloramination
Hypochlorous acid, a substance that is present in the sodium hypochlorite solution, when it comes in contact with organic tissue releases the chlorine which, combined with the protein amino group, forms chloramines. These chloramines interfere with cell metabolism. Further chlorine inhibits the bacterial enzymes leading to irreversible oxidation of the sulphydryl group of essential bacterial enzymes.
Thus, sodium hypochlorite causes biosynthetic alteration in bacterial cellular metabolism and phospholipid destruction, also the formation of chloramines which interferes in cellular metabolism, and its oxidative action causing irreversible enzymatic inactivation in bacteria, with lipid and fatty acid degradation.