Interactions between the Tetrasodium Salts of EDTA and 1-Hydroxyethane 1,1-Diphosphonic Acid with Sodium Hypochlorite Irrigants

A clinically useful all-in-one endodontic irrigant with combined proteolytic and decalcifying properties is still elusive. In this study, the chemical effects of dissolving the tetrasodium salts of 1-hydroxyethane 1,1-diphosphonic acid (Na₄HEDP) or Na₄EDTA directly in sodium hypochlorite (NaOCl) irrigants in polypropylene syringes were assessed during the course of 1 hour.

The solubility of the salts in water was determined. Their compatibility with 1% and 5% NaOCl was measured by iodometric titration and in a calcium complexation experiment by using a Ca²⁺-selective electrode.

The salts dissolved within 1 minute. The dissolution maximum of Na₄HEDP in water (wt/total wt) was 44.6% ± 1.6%. The corresponding dissolution maximum of Na₄EDTA was 38.2% ± 0.8%. Na₄HEDP at 18% in 5% NaOCl caused a mere loss of 16% of the initially available chlorine during 1 hour. In contrast, a corresponding mixture between NaOCl and the Na₄EDTA salt caused 95% reduction in available chlorine after 1 minute. Mixtures of 3% Na₄EDTA with 1% NaOCl were more stable, but only for 30 minutes. Na₄HEDP lost 24% of its calcium complexation capacity after 60 minutes. The corresponding loss for Na₄EDTA was 34%.

The compatibility and solubility of particulate Na₄HEDP with/in NaOCl solutions are such that these components can be mixed and used for up to 1 hour. In contrast, short-term compatibility of the Na₄EDTA salt with NaOCl solutions was considerably lower, decreasing at higher concentrations of either compound. Especially for Na₄HEDP but also for Na₄EDTA, the NaOCl had little effect on calcium complexation.