[Performance simulation study of a modified root canal irrigation needle based on computational fluid dynamics]

Objective: To evaluate the irrigation performance of a modified flat-side open-ended needle (FS needle) in comparison with a traditional flat needle (F needle) and a side-vented needle (S needle), aiming to optimize clinical irrigation strategies. Methods: A 3% sodium hypochlorite solution was selected as the irrigant. Idealized root canal and three irrigation needle geometries were modeled using FreeCAD. Mesh generation and computational setup were performed using Fluent software to simulate the irrigation process with three needle types at working depths of 1, 3, and 5 mm (nine groups in total). Apical pressure, wall shear stress, and velocity data were extracted. Data were processed using Python, and flow field characteristics and irrigation efficacy were comparatively analyzed based on velocity and wall shear stress distributions, as well as four evaluation metrics: apical pressure, effective replacing depth, and effective shear stress depth and span. Results: The apical pressures of the FS needle were 14.22, 11.79, and 9.43 kPa at working depths of 1, 3, and 5 mm, respectively, which were lower than those of the F needle (35.09, 25.04, 17.78 kPa) and close to those of the S needle (9.49, 7.66, 5.92 kPa). The effective replacing depths of the FS needle were 1.25, 1.65, and 1.95 mm, slightly lower than those of the F needle (1.30 mm) but much higher than those of the S needle (0.15 mm) at 1 mm working depth, and comparable to the S needle (1.95 mm) at 5 mm working depth. The effective shear stress depths were 5.07, 3.36, and 1.56 mm, with spans of 3.18, 1.93, and 1.40 mm, respectively, slightly lower than those of the F needle in depth but close to or higher than the S needle in span. Conclusions: At working depths of 1-3 mm, the FS needle was associated with low apical pressure and superior fluid replacement capacity, indicating a favorable balance between pressure control and irrigation efficiency.