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Journal of Endodontics


Introduction: The purpose of this in vitro study was to determine whether para-chloroaniline (PCA) is formed through the reaction of mixing sodium hypochlorite (NaOCl) and chlorhexidine (CHX).

Methods: Initially, commercially available samples of chlorhexidine acetate (CHXa) and PCA were analyzed with 1H nuclear magnetic resonance (NMR) spectroscopy. Two solutions, NaOCl and CHXa, were warmed to 37ºC, and when mixed they produced a brown precipitate. This precipitate was separated in half, and pure PCA was added to 1 of the samples for comparison before they were each analyzed with 1H NMR spectroscopy.

Results: The peaks in the 1H NMR spectra of CHXa and PCA were assigned to specific protons of the molecules, and the location of the aromatic peaks in the PCA spectrum defined the PCA doublet region. Although the spectrum of the precipitate alone resulted in a complex combination of peaks, on magnification there were no peaks in the PCA doublet region that were intense enough to be quantified. In the spectrum of the precipitate to which PCA was added, 2 peaks do appear in the PCA doublet region. Comparing this spectrum with that of precipitate alone, the peaks in the PCA doublet region are not visible before the addition of PCA.

Conclusions: On the basis of this in vitro study, the reaction mixture of NaOCl and CHXa does not produce PCA at any measurable quantity, and further investigation is needed to determine the chemical composition of the brown precipitate.


Post-print. Journal of Endodontics, Volume 36, No. 2 (February 2011), DOI: 10.1016/j.joen.2009.10.028. Used with permission.

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