Syringe Irrigation in Minimally Shaped Root Canals Using 3 Endodontic Needles: A Computational Fluid Dynamics Study

Introduction: The aim of this study was to compare the irrigant flow in curved root canals prepared to various apical sizes by constant-taper or variable-taper instruments during syringe irrigation with 3 endodontic needles at 2 different flow rates. Methods: Two matched curved mesial root canals of human mandibular molars were imaged by micro-computed tomographic imaging after preparation to apical size 20, 25, and 30/.06 taper either by constant taper or variable-taper instruments. A Computational Fluid Dynamics model was used to simulate the irrigant flow in the 2 root canals prepared to each apical size during syringe irrigation with a 30-G open-ended needle and 30-G and 31-G closed-ended needles at 0.05 and 0.15 mL/s. Results: The irrigant could not penetrate up to the working length in root canals prepared to apical size 20 or 25/.06 taper. The 30-G open-ended needle combined with the low flow rate allowed the irrigant to reach the working length in size 30/.06 taper root canals while maintaining a relatively low apical pressure, but the wall shear stress was very low. The 31-G closed-ended needle combined with the high flow rate also delivered the irrigant to the working length in size 30 root canals and developed higher wall shear stress, but the apical pressure was also higher. Conclusions: Syringe irrigation using 30-G and 31-G needles was compromised in minimally shaped root canals. (J Endod 2021;47:1487-1495.)

Automated summary

The study compared the effects of using constant or variable taper instruments to prepare curved root canals during syringe irrigation with different apical sizes, showing that irrigant could not reach the working length in small apical sizes, while using a 30-G open-ended needle with low flow rate achieved the working length with low wall shear stress, and using a 31-G closed-ended needle with high flow rate reached the working length with higher wall shear stress and apical pressure.