Effect of irrigant type, activation method, and contact time on dentin diffusion and ultrastructure

This study aimed to evaluate the effects of different endodontic irrigation protocols on irrigant diffusion, dentin microhardness, and dentinal collagen organization. Bovine dentin specimens were irrigated with 2.5% sodium hypochlorite (NaOCl), 2% chlorhexidine (CHX), or 0.9% saline solution (SS) and subdivided according to the irrigation protocol as follows: conventional irrigation (CI), passive ultrasonic irrigation (PUI), Easy Clean activation (EC), and prolonged contact without activation. Irrigant diffusion within dentin was evaluated by optical coherence tomography (OCT), and dentin microhardness was measured using Knoop microhardness testing before and after the irrigation protocols. Dentinal collagen organization was assessed by Picrosirius Red staining under polarized light microscopy. Data were analyzed using nonparametric tests with a significance level of 5%. OCT analysis showed no significant differences in irrigant diffusion among NaOCl and CHX across the irrigation protocols tested (p>0.05). Dentin microhardness values did not differ significantly before and after irrigation for any solution or protocol tested (p > 0.05). Picrosirius Red analysis showed no significant differences in total birefringent area among groups (p>0.05). However, prolonged exposure to chlorhexidine resulted in significant differences in the distribution of collagen fiber birefringence for yellow, red, and green fibers compared with other irrigation protocols (p < 0.05). The irrigation protocols evaluated did not affect dentin microhardness or irrigant diffusion, but influenced dentinal collagen organization and surface morphology in an irrigant- and exposure time-dependent manner.