The effect of heating to intracanal temperature on the stability of sodium hypochlorite admixed with etidronate or EDTA for continuous chelation

Tetrasodium etidronate (Na etidronate) and tetrasodium EDTA (Na EDTA) are chelators that can combine with sodium hypochlorite (NaOCl) as a 1-mix endodontic irrigant in a process called continuous chelation. The therapeutic window of these mixtures is determined by the chemical reaction between NaOCl and the chelator. At room temperature, this window is 60\ua0minutes for Na etidronate and 30\ua0minutes for Na EDTA. Because reaction kinetics are influenced by heat, this study assesses the influence of heating to an intracanal temperature of 35°C on the therapeutic window in continuous chelation.The loss of free available chlorine (FAC) in NaOCl mixtures with Na etidronate or NaEDTA was determined by iodometric titration at 23°C\ua0±\ua00.7°C (23°C) and 34.6°C\ua0±\ua00.3°C (35°C) at 1, 20, 40, and 60\ua0minutes after mixing. The pH and temperature of the mixtures were measured.At 23°C, 18% Na etidronate/5% NaOCl solutions at 20, 40, and 60\ua0minutes lost 4%, 9% and 18% FAC, and at 35°C, they lost 20%, 68% and 92% FAC; 5% Na EDTA/2.5% NaOCl solutions at 20, 40, and 60\ua0minutes at 23°C lost 88%, 94%, and 97% FAC, and at 35°C, they lost 96%, 99%, and 100%. Decreases in FAC were accompanied by pH declines.The effect of heating to 35°C from a room temperature of 23°C on 18% Na etidronate/5% NaOCl solutions reduces its therapeutic window to 20\ua0minutes. Solutions of 5% Na EDTA/2.5% NaOCl are not useful in the continuous chelation technique. Tracking pH changes could be used to estimate NaOCl degradation