OBJECTIVETo analyze the flow of four irrigations in a root canal with different needle-insertion depth by using a computational fluid dynamics (CFD) model in order to provide a reference to the needle placement in clinical practice.

METHODSThe density and viscosity of 5.25% sodium hypochlorite (A), 3% sodium hypochlorite (B), 17% ethylenediaminetetraacetic acid (EDTA, C), 2% chlorhexidine (D) were measured. A CFD model by ICEM software was used to simulate irrigant flow from an open-ended flat needle positioned at the depth of 1, 3, 5 mm to the physiological apical within the root canal. Velocity, wall shear stress and pressure in the root canal were evaluated after setting the computing conditions with FLUENT14.0 software.

RESULTSAll the wall shear stress generated by four fluids was at peak when the needle was positioned 1 mm to the physiological apical, which were 6.72 × 10³ Pa(A), 6.35 × 10³ Pa(B), 7.47 × 10³ Pa(C), 5.26 × 10³ Pa(D), respectively. With the distance increasing, wall shear stress gradually decreased. The wall shear stress of A, B, C, D was 2.31 × 10³, 2.05 × 10³, 2.59 × 10³ and 1.81 × 10³ Pa, respectively in 3 mm group. The wall shear stress of A, B, C, D was 2.16 × 10³, 1.91 × 10³, 2.42 × 10³, 1.71 × 10³ Pa, respectively in 5 mm group.

CONCLUSIONSIt was recommended that the distance between the needle and physiological apical is 1-3 mm when flushing the root canal. The injection speed of 17% EDTA should be slower than that of the other three solutions.