Aim To evaluate the effect of root canal taper on irrigant flow inside a prepared root canal during final irrigation with
a syringe and two types of needles, using a Computational Fluid Dynamics (CFD) model.
Methodology A validated CFD model
was used to simulate irrigant flow from either a side-vented or a flat 30G needle positioned inside size 30, .02 taper, 30,
.04, 30, .06, ProTaper F3 or size 60, .02 taper root canals, at 3 mm short of working length (WL). Velocity, pressure and
shear stress in the root canal were evaluated.
Results The side-vented needle could not achieve irrigant replacement
to the WL in any of the cases. Significant irrigant replacement was evident further than 2 mm apically to the tip of the flat
needle in the size 30, .06 taper, F3 and size 60, .02 taper canal. A wider distribution of wall shear stress was noted as
the canal taper increased but the maximum shear stress decreased. The flat needle led to higher mean pressure at the apical
foramen. Both needles showed a similar gradual decrease in apical pressure as the taper increased, but the least pressure
was calculated in the size 60, .02 taper canal.
Conclusions An increase in root canal taper improved irrigant replacement
and wall shear stress whilst reducing the risk for irrigant extrusion. Irrigant flow in a minimally tapered root canal with
a large apical preparation size also improved irrigant replacement and wall shear stress and reduced the risk for irrigant
extrusion, compared to the tapered root canals with a smaller apical preparation size.