Positive Pressure and Negative Pressure Irrigation Dynamics with Different Needle Designs Using Computational Fluid Dynamics

This study aimed to investigate the irrigation dynamics of the positive pressure side-vented (SV) needle, EndoVac (micropores) needle and modified apical negative pressure (mANP) open-ended needle using computational fluid dynamics (CFD). A simulation of a prepared root canal (conical frustum) of 15 mm length with an apical diameter of 0.40 mm following Protaper F4 apical preparation was created using three-dimensional (3D) CAD software. 3D simulated needle of SV 30G needle, EndoVac with micropores needle and mANP, 30G flat open-ended needle were also created. The irrigation dynamics were evaluated through transient CFD simulations. In addition, the irrigation dynamics of mANP at 0.2 mm, 0.5 mm, and 1.0 mm short from the working length (WL) were also assessed. The EndoVac and mANP showed negative apical static pressure and streamline patterns able to reach the apical region, thus indicating negligible extrusion. Meanwhile, SV showed positive apical static pressure and almost nonexistence streamlines beyond the needle tip. The SV showed the highest wall shear stress magnitude of 1030Pa whereas Endovac (161 Pa) and mANP1 (258 Pa). However, SV revealed lower average wall shear stress (10 Pa) compared to mANP1 (13 Pa) and mANP2 (11 Pa). This is due to SV developed a localised maximum WSS opposite the open vent area only therefore, uneven distribution of WSS. The EndoVac system developed a localised maximum WSS in the pair of micropores furthest away from the apical. CFD analysis of the EndoVac, mANP and SV showed different technique approach, needle design and needle depths insertion affect the irrigation dynamics pattern and magnitude.