Comparison Of The Formation Of Dentinal Microcracks After Root Canal Preparation With Four Kinds Of Mechanical Nickel-titanium Files

Objective: The aim of this study was to compare the difference of four kinds of mechanical Ni-Ti files(T-flex,Reciproc Blue,Pro Taper Gold and Pro Taper Universal)in dentinal microcracks generation after root canal preparation in vitro,using micro-computed tomography(micro-CT)analysis,so as to provide a reference for clinical selection of Ni-Ti instruments with high safety.Methods: Thirty-two freshly extracted double-root-canal premolars with an angle no more than 10° were selected and established as root canal preparation models in vitro.Then the specimens were randomly assigned to 4 experimental groups(n=8)according to the different Ni-Ti systems used for root canal preparation: Group T-flex,Group Reciproc Blue(RB),Group Pro Taper Gold(PTG)and Group Pro Taper Universal(PTU).The voxel size of micro-CT was set at 17.18μm.Pre-and post-operative cross-sectional images of roots(N = 56940)were scanned and analyzed to identify the presence of dentinal microcracks.The results of each group were expressed by both quantity and percentage of sectional images with microcracks.Mc Nemar test was used to compare whether there was a significant difference in the existence of dentinal microcracks before and after instrumentation.The level of significance was set at P < 0.05.Results: Overall,11.05% of the images presented dentinal defects(n = 6288).Dentinal microcracks were observed in 9.82%,12.09%,12.27% and 11.25% of the post-instrumentation images from T-flex,RB,PTG and PTU groups,respectively.However,all these dentinal microcracks were already present in the corresponding pre-operative images.No new microcrack of premolars were generated after the root canal preparation utilizing the aforementioned systems.Conclusions: Dentinal microcracks are already existed in advance in extracted teeth before root canal preparation.Root canal preparation with T-flex,RB,PTG and PTU systems did not induce the formation of new dentinal microcracks on the straight root canals of premolars.