LAUSR

Introduction Tetrasodium etidronate (Na4 etidronate) and tetrasodium EDTA (Na4 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 minutes for Na4 etidronate and 30 minutes for Na4 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. Methods The loss of free available chlorine (FAC) in NaOCl mixtures with Na4 etidronate or Na4EDTA was determined by iodometric titration at 23°C ± 0.7°C (23°C) and 34.6°C ± 0.3°C (35°C) at 1, 20, 40, and 60 minutes after mixing. The pH and temperature of the mixtures were measured. Results At 23°C, 18% Na4 etidronate/5% NaOCl solutions at 20, 40, and 60 minutes lost 4%, 9% and 18% FAC, and at 35°C, they lost 20%, 68% and 92% FAC; 5% Na4 EDTA/2.5% NaOCl solutions at 20, 40, and 60 minutes 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. Conclusions The effect of heating to 35°C from a room temperature of 23°C on 18% Na4 etidronate/5% NaOCl solutions reduces its therapeutic window to 20 minutes. Solutions of 5% Na4 EDTA/2.5% NaOCl are not useful in the continuous chelation technique. Tracking pH changes could be used to estimate NaOCl degradation. HighlightsHeat accelerates the fall in free available chlorine in continuous chelation.Heat reduces the therapeutic window in continuos chelaton.Tetrasodium EDTA mixtures are unsuitable for continuous chelation.Decreases in free available chlorine parallel declines in pH.pH measurements can estimate the use life of continuous chelation mixtures.