2023 Volume 3 Issue 1 Pages 59-72
Purpose: The purpose of this study was to investigate the influence of additional insertion of the master apical file (MAF) after the file has reached its working length on root canal transportation and extrusion of the trial gutta-percha point out of the root apical foramen using five Ni-Ti rotary file systems with different bending properties.
Methods: The cantilever bending test was used to measure the bending load of the MAF. The untreated J-shaped curved root canal model blocks were obtained, and the root canals were negotiated with a #10 stainless steel K-file. Root canal preparation was performed in five groups: ProTaper Gold (PTG), TruNatomy (TN), HyFlex EDM (HEDM), WaveOne Gold (WOG), and RECIPROC Blue (RCB) to around size 25 using X-smart IQ (n＝10). The post-preparation images were then obtained and superimposed on the pre-preparation images using image processing software. Additional insertions of MAF up to the working length were repeated ten, twenty, and thirty times for the post-preparation block, and the images were obtained and superimposed to measure the increase in the width diameter of the inner side and outer side. Gutta-percha points of the same size as the MAF of each group were inserted to the position of resistance of the root canal wall for each block. The length to the tip of the gutta-percha point was then measured using a digital microscope. The obtained values were statistically analyzed by the Kruskal-Wallis test with a significance level of 5%.
Results: In all files, the bending load values increased linearly and then leveled off. After unloading, the values decreased, and except for TN, the bending load became zero during unloading. At 0-1.0 mm from the apex, transportation tended to occur on the outer side of the root canal, but at 2.0 mm and above, transportation tended to occur on the inner side. In the WOG and RCB groups, transportation to the inner side of the canal was observed at 2.0 mm. No gutta-percha point extrusion was observed in the final enlarged model, but the length of extrusion increased as the number of insertions increased.
Conclusion: Additional insertion of the file caused root canal transportation inward above the root canal curvature and outward below the curvature, extending the apical reach of the gutta-percha point.
