INTERACTIONS BETWEEN CHLORHEXIDINE AND SODIUM HYPOCHLORITE: CHEMICAL ANALYSIS

Endodontic failure may occur in cases of persistent bacteria in the root canal system (RCS). Mechanical instrumentation alone is not able to obtain a complete cleaning of the RCS, so a commonly used method of disinfection in endodontic treatments consists in the use of sodium hypochlorite (NaOCl) followed by the use of chlorhexidine gluconate (CHX). After each irrigating solution, distilled water should be used to prevent possible reaction among the components. In fact, if NaOCl is present when CHX is added, a brown precipitate is formed with a possible negative effect on the outcome of the treatment. Some literature works reported the presence of 4-chloroaniline (PCA) in brown precipitate, other, on the contrary, didn’t observed its formation; in our study, we have tried to explain the reason of this discrepancy using HPLC-UV technique. To 1.0 mL of 2% CHX were added different volumes of 6.0% NaOCl (from 0.01 to 0.12 mL). Also the reaction mixtures between 6.0% NaOCl and PCA (5 mg /mL in methanol) were prepared. The specimens were centrifuged (13400 x g 5 min) and both supernatants (SNs) and precipitates (PTs) (re-suspended in 1 mL of methanol) were analyzed. The column used was a Discovery HS C18 (250mm × 4.6mm, 5 µm) (SUPELCO, PA, USA), flow rate 0.7 mL/min, detection 214 nm. Water (A) and acetonitrile (B) were used for the elution: from 50% (B) to 70% (B) in 10 min and to 85 % (B) in 5 min. The chromatograms of CHX showed a signal with a Retention Time (RT) 3.0 min. When NaOCl was added, many other signals appeared with RT between 20 and 25 min. Similar results were obtained in the PTs. The presence of PCA signal was not observed neither in PTs nor in SNs. The HPLC analysis of mixture between NaOCl and PCA showed the presence of signal with RT 9.1 min (PCA), its intensity decreases when NaOCl was added, and completely disappeared with 0.12 mL of NaOCl. Simultaneously signals with RT between 20 and 25 minutes are produced, similarly to what was observed for the CHX. In PTs are present many peaks with RT around 2-3 min and at 25-30 min. The obtained results showed that PCA is transformed in presence of NaOCl. Thus, the discrepancy of literature data could be due to the reaction conditions: the newly-formed PCA reacts with NaOCl and is transformed.