Abstract: Objective: To observe the development of dentinal microcracks after root canal preparation with there kinds of reciprocating nickel-titaninm instruments using an in situ cadaver model by means of micro-computed tomography (Micro CT),and to provide the reference for their clinical application. Methods: A total of 15 mandible bone specimens having at least the anterior teeth (n=60)with single root were selected and there was no dentina microcrack, then they were randomly divided into 4 groups (n=15) according to the preparation protocol:Wave One,Reciproc,One File and ProTaper Universal groups,and ProTaper Universal was used as control group.The root canals were prepared up to 25# instruments in Wave One,Reciproc and One File groups and F2 instruments in ProTaper Universal groups. After the preparation procedures, the specimens were scanned by Micro CT again,and the number of dentinal microcracks were investigated and analyzed statistically. Results: Compared with ProTaper Universal group,the incidence rates in Wave One, Reciproc and One File groups were significantly reduced(P<0.05).There were no statistical differences in the incidence rates of dentinal microcracks between Wave One, Reciproc and One File groups(P>0.05). Conclusion: Root canal preparation can cause the dentinal microcracks,so it is important to choose the types of instruments.Root canals prepared with Reciproc,Wave One and One File produce less dentinal microcracks,which can decrease the risk of vertical root fracture.

Key words: mandibular specimen, dentinal microcrack, single files, Micro CT