The effect of needle-insertion depth on the irrigant flow in the root canal: evaluation using an unsteady computational fluid dynamics model.

Introduction: The aim of this study was to evaluate the effect of needle-insertion depth on the irrigant flow inside a prepared root canal during final irrigation with a syringe and two different needle types using a Computational Fluid Dynamics (CFD) model.

Methods: A validated CFD model was used to simulate irrigant flow from either a side-vented or an open-ended flat 30-G needle positioned inside a prepared root canal (45 .06) at 1, 2, 3, 4, or 5 mm short of the working length (WL). Velocity, pressure, and shear stress in the root canal were evaluated.

Results: The flow pattern in the apical part of the root canal was similar among different needle positions. Major differences were observed between the two needle types. The side-vented needle achieved irrigant replacement to the WL only at the 1-mm position, whereas the open-ended flat needle was able to achieve complete replacement even when positioned at 2 mm short of the WL. The maximum shear stress decreased as needles moved away from the WL. The flat needle led to higher mean pressure at the apical foramen. Both needles showed a similar gradual decrease in apical pressure as the distance from the WL increased.

Conclusions: Needle-insertion depth was found to affect the extent of irrigant replacement, the shear stress on the canal wall, and the pressure at the apical foramen for both needle types.