In vitro spectroscopic analysis of the chemical interaction between calcium hypochlorite and chlorhexidine

This study aimed to identify the chemical composition resulting from the chemical interaction between calcium hypochlorite [Ca(OCl)₂] and chlorhexidine (CHX) using different ¹H and ¹³C nuclear magnetic resonance spectrometry (NMR), correlated two-dimensional spectroscopy (2D COSY), heteronuclear single quantum coherence (HSQC), and Fourier Transform Infrared Spectroscopy (FTIR) experiments. The 5.25% Ca(OCl)₂ was mixed with 2% CHX in a 1:1 ratio, obtaining an orange-brown precipitate that was filtered, washed in ultrapure water, dried and characterized by ¹H and ¹³C NMR, 2D COSY, HSQC and FTIR. One-dimensional and two-dimensional NMR spectra demonstrated the chemical changes around the protons and carbon atoms of the initial CHX and after reacted with Ca(OCl)₂. These techniques and FTIR show that the interaction generated two by-products from the degradation of CHX, none of which were parachloroaniline (PCA) despite both products obtained being substituted benzene compounds. Using NMR and FTIR data together with a previously proposed catalytic cleavage degradation mechanism for CHX, the products appear to be parachlorophenylurea (PCU) and parachlorophenylguanidyl-1,6-diguanidyl-hexane (PCGH). Therefore, this in vitro study demonstrated that the precipitate formed from the chemical interaction between Ca(OCl)₂ and CHX results in two by-products, PCU and PCGH, neither of which is PCA. Due to the absence of cytotoxicity studies on the products generated from the combination of Ca(OCl)₂ and CHX, an intermediate rinse with an inert solution is recommended to remove these compounds from the root canals.