Influence of Continuous Chelation on Root Dentin: A Laboratory Study

Background/Objectives: Continuous chelation has emerged as an alternative to conventional sequential irrigation by combining sodium hypochlorite (NaOCl) with weak chelators in a single irrigant solution. This study evaluated and compared the effects of different final irrigation protocols on root dentin microhardness, chemical composition, and irrigant surface tension. Methods: Sixty extracted human canines were standardized for root length and canal lumen. Root dentin discs obtained from the middle third were randomly assigned to five groups according to the irrigation protocol: 3% NaOCl (total exposure time, 24 min), 17% EDTA (3 min), 3% NaOCl-DR HEDP (total exposure time, 24 min), 3% NaOCl/17% EDTA (NaOCl total exposure time, 24 min; EDTA 3 min), and 3% NaOCl/17% EDTA/3% NaOCl (NaOCl total exposure time, 24 min; EDTA 3 min). Dentin microhardness was assessed before and after treatment using the Vickers hardness test. Chemical composition was analyzed by energy-dispersive X-ray spectroscopy, and surface tension was measured using the pendant drop method. Data were analyzed using one-way ANOVA and Tamhane’s T2 post hoc test (α = 0.05). Results: Dentin microhardness decreased by approximately 4.0% with NaOCl-DR HEDP, 4.1% with EDTA alone, 14.3% with NaOCl, 16.9% with NaOCl/EDTA/NaOCl, and 39.7% with NaOCl/EDTA. Post hoc analysis showed that NaOCl/EDTA resulted in significantly greater reductions in dentin microhardness than EDTA alone, continuous chelation with NaOCl-DR HEDP, and the NaOCl/EDTA/NaOCl protocol (p < 0.05). EDTA and NaOCl-DR HEDP exhibited the smallest reductions in microhardness and did not differ significantly from each other. Regarding chemical composition, NaOCl-DR HEDP induced intermediate changes in organic and inorganic components. NaOCl alone yielded the lowest carbon content, while EDTA and NaOCl/EDTA sequence showed the lowest calcium and phosphorus levels. Surface tension was highest for the H2O-HEDP solution, followed by 3% NaOCl-DR HEDP and 17% EDTA, and lowest for 3% NaOCl. Conclusions: Despite its higher surface tension, the continuous chelation protocol with NaOCl-DR HEDP preserved dentin microhardness to a similar extent as EDTA alone and promoted more moderate changes in dentin chemical composition than the conventional final irrigation protocols, particularly NaOCl/EDTA, suggesting a conservative effect on root dentin.