Effect of inflow temperature on root canal irrigation: A computational fluid dynamics study

Root canal therapy is one of the main treatment options for endodontic diseases in which an effective irrigation is key to a successful therapy. In the present paper, the irrigation flow inside an instrumented root canal is numerically investigated, and then the effect of inflow temperature on the irrigation is analyzed based on the computational fluid dynamics results. The magnitude of the shear stress and its corresponding coverage of the irrigation flow on the wall is adopted to characterize the clean efficiency. The axial velocity is used to represent the replacement of local flow field, which stands for the capability to carry away the cleaning residue. Results show that the effective area that the shear stress covers on the root canal wall behind the needle outlet is usually larger than that in front of the outlet, and both the effective coverage of the shear stress and the replacement of the irrigant are improved when the velocity increases. It is convinced that the critical shear stress, namely, the lowest shear stress required to peel off the smear layer on the root canal wall, decreases with the increase in the temperature. Although no apparent variation of the shear stress on the wall can be observed while improving the inflow temperature, the effective surface to be cleaned is improved to some extent because of the decrease in the critical shear stress. Meanwhile, the power consumption is reduced obviously. If the input power remains constant when the temperature increases, both the shear stress on the wall and the replacement are significantly improved besides the decrease in the critical shear stress. This means both the clean efficiency on the wall and the clearing capability (namely replacement) in local flow field are significantly promoted.