Complete chemomechanical debridement of the root canal system is fundamental for achieving long-term endodontic success. Mechanical instrumentation creates an amorphous irregular smear layer covering the instrumented dentinal walls and occluding dentinal tubules in the apical third [1,2]. Because conventional syringe irrigation rarely penetrates beyond 1 mm from the needle tip in narrow or curved apical anatomy, adjunctive irrigation activation systems have been developed to enhance hydrodynamic shear stress and acoustic streaming [3].

Sixty extracted human single-rooted mandibular premolars with curvatures between 15° and 25° were selected under institutional ethical approval. Root canals were instrumented up to ProTaper Gold F3 (30/.09) and randomly allocated into three experimental activation groups (n = 20): Group I (Conventional Side-Vented Syringe Irrigation), Group II (Sonic Activation / EndoActivator), and Group III (Passive Ultrasonic Irrigation / PUI using a #20 IrriSafe tip) with 2.5% NaOCl followed by 17% EDTA. High-resolution Micro-CT scans (isotropic voxel size 9.0 µm) were acquired before and after final irrigation activation.

Quantitative 3D volumetric Micro-CT reconstruction demonstrated statistically significant reductions in accumulated hard-tissue debris and apical smear layer scores in the Passive Ultrasonic Irrigation (PUI) group compared to sonic and syringe irrigation (p < 0.05) (Table 1). Acoustic cavitation in Group III achieved 91.4% tubule patency in the apical 3 mm segment (Figure 1).

The superior debridement efficacy of PUI in the apical third is attributed to high-frequency (28–32 kHz) acoustic microstreaming and transient cavitation, which effectively disrupt vapor locks and propel chelating solutions into lateral fins and isthmuses [3,4].

Passive Ultrasonic Irrigation (PUI) demonstrated superior smear layer and debris clearance in the apical third of curved root canals compared to sonic activation and conventional needle irrigation.