The effect of apical preparation size on irrigant flow in root canals evaluated using an unsteady Computational Fluid Dynamics model

Aim  To evaluate the effect of apical preparation size on irrigant flow inside a root canal during final irrigation with a syringe and two different needles types, using a Computational Fluid Dynamics (CFD) model.
Methodology  A validated CFD model was used to simulate the irrigant flow from either a side-vented or a flat 30G needle positioned inside root canals having sizes of 25, 35, 45 and 55, all with a .06 taper, at 3 mm short of working length (WL). Velocity, pressure and shear stress in the root canal were evaluated.
Results  Different preparation sizes resulted in minor differences in the flow pattern in the apical root canal. Major differences were observed between the two needle types. The side-vented needle could not achieve irrigant replacement to the WL even in a size 55, .06 taper root canal. Significant irrigant replacement was evident almost to the WL in size 35, 45 and 55, .06 taper root canals with the flat needle. The maximum shear stress decreased as the preparation size increased. The flat needle developed higher mean pressure at the apical foramen. Both needles led to a similar gradual decrease in apical pressure as the preparation size increased.
Conclusions  Apical preparation size affected irrigant replacement, the shear stress on the canal wall and the pressure at the apical foramen. Root canal enlargement to sizes larger than 25 appeared to improve the performance of syringe irrigation. Adequate space between the needle and the canal wall should be ensured to allow for an effective reverse flow of the irrigant towards the canal orifice