Residual Active Chlorine in Sodium Hypochlorite Solutions after Tissue Dissolution

Objectives: In previous studies, surfactant-containing brands of sodium hypochlorite solutions (Hypochlor: Dentalife Pty Ltd, Victoria, Australia) showed better tissue solubilizing abilities than a commonly used endodontic irrigating solution (Milton: Milton Australia Pty Ltd, Queensland, Australia); differences were not explained by original active chlorine content or presence of surfactant. It was postulated that exhaustion of active chlorine content could explain these differences. This project aimed to assess whether exhaustion of active chlorine content explained difference in tissue dissolving abilities of some sodium hypochlorite solutions. Parallel experiments assessed the influence of titration methods, and the presence of chlorates, on active chlorine measurements.

Methods: Time required to dissolve one or groups of ten samples of porcine incisor pulp samples in Milton was determined. Residual active chlorine was assessed by thermometric titration. Iodometric and thermometric titration was carried out. Chlorate content was also measured.

Results: Dissolution of single and ten pulp samples caused a mean loss of 1 and 3% respectively of active chlorine, not being proportional to tissue dissolved. Thermometric ammonium ion titration resulted in 10% lower values than iodometric titration. Chlorate accounted for much of this difference.

Conclusions: Depletion of active chlorine is not the reason for differences in tissue dissolving capabilities of sodium hypochlorite solutions. Thermometric ammonium ion titration gives more accurate measurement of active chlorine content than iodometric titration.

This abstract is based on research that was funded entirely or partially by an outside source: Australian Dental Research Fund project number 35/2008