Investigation of flow field regulation in narrow root canal irrigation cavity based on swirling jet impingement

A novel needle design integrating a swirling jet structure is proposed in this work to enhance the circumferential uniformity and safety of root canal irrigation. The design combines the principle of passive self-excitation with a swirling jet device. Computational fluid dynamics simulations are used to investigate the effects of key geometric parameters, including swirl channel ratio, installation angle, twisting unit number, and swirl channel height/thickness, on irrigation performance and the underlying mechanism of jet coupling. The results show that an optimal coupling of swirling and oblique jets is achieved by maintaining the oblique jet as the main flow, while using the swirling jet to strengthen the main flow and enhancing the cleaning effectiveness. The recommended optimal parameters are a swirl channel ratio of 0.25, an installation angle of 0°, and a minimum of three twisting units. Compared to the prototype 30 G needle used commonly in clinical applications, the optimal designs increase the effective cleaning area by up to 26.12% and the extending depth by up to 54.76%, while reducing the mean apical pressure by up to 22.85%. Through computational fluid dynamics studies of flow field in narrow cavity, a potential solution is provided for the bottleneck problem of root canal irrigation in oral medicine.