Effect of Canal Size on Isthmus Cleaning Efficiency and Safety of High-Frequency Sonic Agitation: An In Vitro Study

<ns3:p> Objective This study aimed to evaluate the effect of root canal preparation size on isthmus cleaning efficiency and periapical extrusion using high-frequency sonic agitation with the EDDY irrigation system. Materials and Methods Thirty custom-made epoxy split models were used to simulate a root canal system with two curved canals merging at the apical 1 mm and an isthmus extending along their length. A periapical lesion was simulated to assess the extrusion tendency. Canals were prepared using the WaveOne Gold system in small, primary, and medium sizes. The isthmuses were filled with bovine dentin debris, while dyed gelatin was used in the periapical lesion to quantify extruded irrigant volume. EDDY irrigation efficiency was evaluated based on the total cleared surface area (mm <ns3:sup>2</ns3:sup> ) using ImageJ software. Statistical analysis was performed using one-way ANOVA and post hoc multiple comparisons, with a significance level of P ≤ 0.05. Results Isthmus cleaning efficiency remained consistent across all canal sizes, with no significant differences among groups (P &gt; 0.05). However, periapical extrusion increased significantly with larger canal preparation sizes, with medium-sized preparations showing significantly higher extrusion than small (P = 0.001) and primary (P = 0.026) sizes. Conclusion EDDY irrigation was effective in achieving isthmus cleanliness regardless of canal preparation size. However, larger instrumentation increased the risk of apical extrusion, underscoring the need for careful irrigation management in clinical applications. </ns3:p>