Influence of passive ultrasonic irrigation cycles on the penetration depth of sodium hypochlorite into root dentin

This study explores innovative passive ultrasonic irrigation (PUI) parameters by investigating a novel, shorter, and more repetitive agitation cycle to enhance the penetration depth of sodium hypochlorite (NaOCl) within dentinal tubules. Forty extracted human mandibular premolars were prepared (size 40, 0.06 taper) and stained with 0.5% crystal violet. Samples were divided into four irrigation groups: (I) Conventional Needle Irrigation (CNI), (II) PUI with 2 cycles of 30 s each, (III) PUI with 3 cycles of 20 s each, and (IV) PUI with 6 cycles of 10 s each. Coronal, middle, and apical sections were analyzed by light microscopy, and NaOCl penetration depth was measured at four sites (mesial, distal, buccal, lingual) using ImageJ. Data were analyzed using Kruskal-Wallis/Dunn's test (α < 0.05). The CNI group demonstrated significantly lower NaOCl penetration compared to all PUI groups (P < 0.001). The 6 × 10 s protocol achieved significantly greater penetration in all regions (P < 0.001). While no significant differences were observed between the 2 × 30 s and 3 × 20 s protocols in the coronal and middle thirds, the 3 × 20 s group showed significantly greater penetration in the apical third (P < 0.001). The findings of this study suggest that optimizing PUI agitation parameters can lead to more effective, efficient, and predictable endodontic treatment, enhancing irrigation efficacy. Shorter and more frequent cycles (6 × 10 s) proved to be the most effective, providing valuable information for clinical practice.