Formation of dentinal microcracks after root canal preparation with four kinds of mechanical nickel-titanium files
Objective This study aimed to compare the differences among four kinds of mechanical Ni-Ti files in-cluding T-Flex,Reciproc Blue(RB),ProTaper Gold(PTG),and ProTaper Universal(PTU)in dentinal microcrack genera-tion after root canal preparation in vitro by using micro-computed tomography(micro-CT)analysis.Methods A total of 32 freshly extracted double-root-canal premolars with an angle not exceeding 10° were selected and established as root canal preparation models in vitro.Then,the specimens were randomly assigned to four experimental groups(n=8)according to the different Ni-Ti systems used for root canal preparation:group T-Flex,group RB,group PTG,and group PTU.The voxel size of the micro-CT was set at 17.18 μm.Pre-and post-operative cross-sectional images of roots(n= 56 940)were scanned and analyzed to identify the presence of dentinal microcracks.The results of each group were ex-pressed by the quantity and percentage of sectional images with microcracks.McNemar test was used to determine whether a significant difference existed in the existence of dentinal microcracks before and after instrumentation.The level of significance was set at P<0.05.Results Overall,11.04%of the images presented dentinal defects(n=6 288).Dentinal microcracks were observed in 9.82%,10.79%,12.27%,and 11.25%of the post-instrumentation images from groups T-Flex,RB,PTG,and PTU,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 prepara-tion utilizing the aforementioned systems.Conclusion Denti-nal microcracks already existed in advance in extracted teeth before root canal preparation.Root canal preparation using the T-Flex,RB,PTG,and PTU systems did not induce the formation of new dentinal microcracks on the straight root canals of premolars.
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