Aim: To assess whether Dual Rinse HEDP, an etidronate that can be combined with NaOCl to create an endodontic irrigating solution containing both hypochlorite and a chelator in the form of 1-hydroxyethane 1,1-diphosphonic acid (HEDP), alters the clinical efficacy of NaOCl or adds any untoward clinical effects. Methodology: In this randomized controlled double-blind single-centre trial, a pure NaOCl solution was compared to a HEDP-containing counterpart regarding antimicrobial efficacy, postoperative pain, and the host response by means of changes in MMP-9 levels in periapical fluid. Sixty patients presenting with asymptomatic apical periodontitis (one tooth each) were randomly divided into two groups (N = 30) based on irrigation regime. Pre- and post-treatment microbial aerobic and anaerobic cultures and MMP-9/total protein (TP) periapical fluid samples were collected. Postoperative pain levels were assessed 24 h after treatment. Categorical data were compared between groups using the Fisher's exact test, continuous data using the Wilcoxon signed-rank test, α = 0.05. Results: Irrigation with pure NaOCl rendered 40% canals free of culturable microorganisms, compared to 50% with the NaOCl/HEDP mixture (P = 0.60). As assessed by matrix-assisted laser desorption/ionization-time-of-flight analysis (MALDI-TOF), no apparent selection of aerobic or anaerobic taxa occurred in either group. One patient in the NaOCl group experienced moderate pain, whilst two patients in the NaOCl/HEDP group experienced mild postoperative pain. MMP-9/TP levels in periapical fluid declined significantly (P < 0.001) after 1 week with no medication in the root canal, without significant difference between treatment groups (P > 0.05). Conclusions: This trial found no influence of HEDP on clinical NaOCl effects.
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