Influence of Root Canal Size and Curvature on Insertion Depth of Three Different Endodontic Irrigation Needles

The aim of this study was to evaluate the influence of root canal size and curvature on the insertion depth of three different endodontic irrigation needles. Four root canals with curvatures ranging from 0° to 69.72° were first enlarged to size .04/25. The insertion depths of a standard open-ended irrigation needle (SI), a single side-vented needle (SV), and a TruNatomy irrigation needle (TN) were then measured repeatedly in the chosen root canals and recorded as distances short of the working length. In curved canals, the SI and SV were tested with and without pre-bending. After enlargement to a greater taper (.06/25), these measurements were repeated. For a descriptive analysis, means and standard deviations were computed, and comparison was performed using the Wilcoxon test and formulated using a Monte-Carlo approximation with the level of significance set to 5%. Due to its flexible material, the best overall results in terms of insertion depth close to the working length were observed for the TN. The SI and SV could be inserted deeper in straight root canals and after enlargement to a greater taper (p < 0.05). In curved root canals, pre-bending of the SI and SV resulted in statistically significantly higher insertion depths (p < 0.05). In conclusion, cannula material properties, preparation size, and insertion depth mainly depend on each other. In curved root canals, a more flexible cannula like the TN should be favored to achieve better insertion depths. If using stainless-steel cannulas, they should be pre-bent to facilitate an insertion closer to the working length.