Antagonistic interactions between sodium hypochlorite, chlorhexidine, EDTA, and citric acid

By Rossi-Fedele G, Doğramaci EJ, Guastalli AR, Steier L, de Figueiredo JA

Date: 01/2012
Journal: JOE


  • Purpose: to review the undesired effects after interactions between NaOCl, CHX, and chelating agents EDTA and Citric Acid (CA). 
  • Interactions between NaOCl and Chelating Agents:
  • Chelating agents reduces pH of NaOCl to (8 with EDTA, 1.8-4.3 with CA). which results in the release of chlorine gas (significantly more with CA) which has potentially hazardous effects on humans. 
  • Both CA and EDTA reduces the free available chlorine which affects the tissue dissolving capacity.
  • Antimicrobial activity of NaOCl is affected only when initial concentration is low.
  • NaOCl does not reduce the calcium chelating or smear layer ability of EDTA and CA. 
  • Interactions between NaOCl and CHX:
  • Mixing CHX and NaOCl results in the formation of dark-brown precipitate (parachloroaniline).
  • This precipitate act as a chemical smear layer which reduces dentine permeability in the apical 3rd, it also stained the dentine and adhere to its wall.
  • Interactions between CHX and Chelating Agents: Mixing CHX and CA had not effect on the CA demineralization activity. Produced no precipitate, only milky solution was produced which could be removed with further irrigation with CHX. When mixing CHX and EDTA, it is difficult to obtain a homogenous solution, and a precipitate composed mainly of those substances is formed. 

Clinical significance:

  • Mixing EDTA, NaOCl: do copious irrigation with NaOCl after EDTA.
  • NaOCl and CHX: use intermediate Irrigant