Numerical and analytical investigation of irrigant penetration into dentinal microtubules

Irrigation is one of the most important steps in root canal therapy. Sodium hypochlorite is inserted into the root canal to eliminate bacteria and dissolve necrotic tissue. Dentinal tubules are micrometer sized channels along the dentin thickness. An irrigant should have the ability to penetrate into these tubules to remove bacteria residing in them. The difference between the concentrations of the inserted irrigant and the dentinal tubule fluid is the main factor of penetration. This study attempts to model dentinal tubules with precise dimensions and to study the time dependent irrigant penetration into them by using Computational Fluid Dynamics (CFD). The effects of needle type and position in the dentinal tubule were also considered. The results showed that concentration distribution would be different when the tubule was modeled as a frustum compared to the cylindrical shape tubule. Dentinal tubule curvature, however, did not have a noticeable effect in irrigant penetration. It was also concluded that when the needle working length is 3 mm, concentration can be considered constant at the tubule's entrance for tubules located at more than 1 mm from the apex. Moreover, by irrigating the root canal with a side-vented needle instead of an open-ended one, the concentration would be less for the tubules located in the apex region. Analytical solutions for different cases were also obtained, and their predictions were found to be in good agreement with the numerical results. Therefore, the presented analytical solutions can be directly used to obtain irrigant concentration in tubules with no need for additional computer simulations.