Effect of ultrasonic irrigant activation and negative apical pressure in removing mature biofilm from the isthmus of curved root canal: A 3D-printed model study

Introduction Although the iVac® system has shown promising cleaning performance, its effectiveness in biofilm removal from anatomically complex areas remains untested in standardized 3D models, highlighting the relevance of the present study to evidence-based irrigation strategies. Methods A standardized 3D mandibular molar model with curvature and an isthmus was created, incorporating dentin blocks and a 21-day E. faecalis biofilm. Samples ( n = 48) were randomized into four groups: syringe-needle irrigation, iVac System, ultrasonic irrigant activation (UIA), and control. All groups received NaOCl, EDTA, PBS, and sodium thiosulfate. Biofilm removal was assessed by CFU counting and SEM. Results ANOVA of CFUs showed that UIA and iVac significantly reduced bacterial counts compared to the control ( p < 0.001), with no difference between them ( p = 0.342). Syringe and needle irrigation showed results similar to the control ( p = 0.124) and iVac ( p = 0.087), but had higher CFUs than UIA ( p = 0.017). These reductions corresponded to substantial decreases in bacterial load. SEM revealed that iVac and UIA groups exhibited exposed dentinal tubules with few scattered bacteria, while syringe and needle irrigation showed a dense amorphous matrix with E. faecalis -like cells covering most of the dentin, with limited exposed areas. Conclusions Active irrigant agitation with UIA or iVac was more effective in reducing mature biofilm and promoting its disruption in the isthmus of curved root canals than syringe and needle irrigation.