Abstract:

Objective　To study the changes of root canal curvatures and apical transportation index when the curved root ca- nals were prepared by hand-use ProTaper, stainless steel K-files or nickel-titanium K-files.Methods　Forty-five extracted mo- lars, with the degree of root canal curvature from twenty to forty, were divided into fifteen sections in curvature sequence. After that, three canals of each section were randomly distributed to three different instrumentation groups. One group of themwas pre- pared by hand-use ProTaperwith crown-down technique. The othertwo groupswere instrumented by stainless steel or nickel titani- um K-files with modified step-back technique to working length. The standard digital radiographs were taken to record the profiles of root canals and the positions of the tips of the instruments. The change of curvature degree between pre- and post-instrumenta- tion and the apical transportation indexes (ATI) among three groups were analyzed respectively using SAS statistical software.Re- sults　The change of curvature degree between pre- and post-instrumentation for stainless steel K-files groupwas largest, and the ATI of stainless steel K-files group was significantly greater than that for nickel titanium K-files group (P<0.05). The canals prepared by hand-use ProTaper was smallest in the change of curvature and ATI among the three groups(P<0.01).Conclusion 　When preparing curved molar canals, hand-use ProTaperwith crown down technique can obtain better shaping effect and higher efficiency.

Key words: curved root canal, root canal preparation, modified step-back technique, crown-down technique, apical