Systematic review of cold vs warm sodium hypochlorite irrigation for postoperative pain in root canal therapy

This systematic review thoroughly evaluates the impact of various temperatures of sodium hypochlorite (NaOCl) used during root canal therapy (RCT) on postoperative pain (POP). After registering with PROSPERO (CRD420251235909, https://www.crd.york.ac.uk/PROSPERO/view/CRD420251235909), a search was carried out by using PubMed, Scopus, Web of Science, Cochrane library published in the years 2015 January 1 to 2025 November 16. Randomized clinical trials comparing NaOCl irrigant temperatures and reporting POP outcomes were included. Three randomised Control Trial (total N ≈ 183 patients) assessed NaOCl temperature (cold ≈ 2–2.5 °C, room ≈ 22–25 °C, warm ≈ 40–66 °C). Two trials reported lower postoperative pain with cold NaOCl compared with warmer solutions at early timepoints (notably 6 h or day-1). Another trial (various concentrations and temperatures) found no statistically significant difference across temperatures or concentrations at the timepoints measured. Heterogeneity in diagnosis (vital vs. non-vital teeth), irrigant concentration, scale used for pain measurement (0–10 vs. 0–100), and timepoints limited performing meta-analysis. Evidence from recent RCTs suggests a short-term reduction in early postoperative pain with cold NaOCl vs. warm NaOCl or room temperature in some settings, while other trials show no difference. Temperature modulation is promising but not conclusively proven; further standardized RCTs (harmonized pain scales, same timepoints, same diagnoses) or pooled analyses with harmonized data are needed. https://www.crd.york.ac.uk/PROSPERO/view/CRD420251235909, PROSPERO CRD420251235909.