Abstract: Abstract Objective To evaluate the apical canal transportation and centralizing ability of NiTi instruments WaveOne after root canal preparation by Micro-CT．Methods Forty extracted premolar teeth were randomly divided into four groups: Root canals were respectively prepared using WaveOne(group A),motor ProTaper(group B),hand ProTaper(group C) nickel-titanium instruments with crown-down technique and using the stainless steel hand K-files with standardized technique ( group D) .A series of preoperative and postoperative images were taken by Micro-CT.Canal transportation and centralizing ability were measured with reference to the distance between the noninstrumented portion of the root canals and the mesial and distal periphery of the root.（Double root canals only recorded the buccal one.）Results Canal transportation after preparation:the Group A was less than the other three group(P＜0.05). The centring ratio values:Group A was more than the other three group(P＜0.05).Conclusion Within the limitation of this present study,WaveOne can well maintain the original root canal path and center in the preparation of root canal.Therefore,it has practical value for clinical use.

Key words: Micro-CT, canal transportation, nickel－titanium instrument , root canal preparation