Abstract: ［Abstract］ ObjectiveTo compare the effects of nickel titanium Reciproc, K3, ProTaper system and stainless steel system KFile in the preparation of the root canal forming of the severe bending molar. MethodsForty first molar with severe bending of the mandibular canal were randomly divided into four groups. Reciproc, K3, ProTaper system and manual stainless steel system KFile were used for root canal preparation. The position of the tip of the instruments in the 4 groups before and after the root canal preparation were recorded. The changes of root canal curvature, the change of working length in root canal and the operation time were compared between the 4 groups. ResultsAmong 4 groups, the operation time of Reciproc group was the shortest, and the stainless steel manual KFile time was the longest. There was no significant difference in the changes of the working length of the root canal after Reciproc, K3 and ProTaper in each group. Before the root canal preparation, there was no significant difference in root canal curvature between the 4 groups. After root canal preparation, the changes in Reciproc, K3, root canal curvature ProTaper groups are less than KFile group.  ConclusionThe applications of Reciproc, K3, after ProTaper nickeltitanium instruments prepared for molar curved root tube forming were with high efficiency and strong ability.

Key words: periodontics, root canal therapy, root canal preparation