Efficacy of high-frequency sonic irrigation on removing debris from root canal isthmus: an in vitro study based on simulated root canals.

Background: Infection control is important in root canal treatment. Effective cleaning and shaping are challenging due to complex anatomy, particularly in the isthmus-narrow connections between canals that can harbor bacteria. Conventional needle irrigation (CNI) is inadequate in this region, prompting the use of passive ultrasonic irrigation (PUI) and high-frequency acoustic instruments like EDDY. This study evaluates the cleaning effects of four irrigation protocols using 3D-printed isthmus models.

Methods: Sixty digital root canal models with isthmuses in the coronal, middle, and apical thirds were designed using Ansys 19.0 and 3D printer (20 specimens per isthmus location). Specimens were prepared to 30#, 0.04 without irrigation. Debris accumulation in the isthmus was photographed and analyzed using Image J to calculate the initial debris area (S1). Specimens were then irrigated using CNI, low-frequency sonic irrigation (EndoActivator, EA; Dentsply, Charlotte, NC, USA), PUI, or high-frequency sonic irrigation (EDDY), followed by re-imaging to calculate remaining debris area (S2). Debris reduction percentage was determined using the formula: (S1-S2)/S1 × 100%.

Results: Debris reduction varied with isthmus position. In the coronal third, EDDY achieved the highest debris reduction (86.18 ± 2.25%), followed by PUI, EA, and CNI, with significant differences among groups (P < 0.05). The same trend was observed in the middle third, with EDDY showing the highest efficacy (73.96 ± 6.75%). In the apical third, debris reduction was lower overall, with no significant difference between EDDY and PUI, but both outperformed EA and CNI.

Discussion: Our results showed that EDDY demonstrated superior debris removal in the coronal and middle thirds, but all irrigation protocols showed limited efficacy in the apical third.