[Comparative study of hand-held nickel-titanium dental instruments based on the shape of the prepared root canal].

The aim of this study was to compare the shaping characteristics of two hand instruments: the NiTi K-files and the NiTi S-files. A total of 60 extracted human roots were embedded in resin blocks. The roots were divided into three groups according to their shape: straight, apically curved and entirely curved. Each of the three groups was divided into two subgroups for the NiTi K-file and the NiTi S-file instrumentation. The files were used with a step-back technique and enlarged so that the master apical file was size 30, and the canals were stepped back to size 40. The performance of the files was assessed by the superimposition of projected radiographs taken in bucco-lingual and mesio-distal views before and after preparation. The results were analyzed statistically using of analysis of covariance and Duncan's multiple range test. Although canal preparation using NiTi K-files was quicker, there were no statistically significant differences between file types. The NiTi S-file removed significantly more dentine at the most coronal level (p < 0.05). There were minor differences between instruments at the apical level. Only in the proximal view of apically curved canals prepared with NiTi S-files was significantly more dentine removed from the convex side of the wall (p < 0.05). At the middle level the NiTi S-files removed more dentine from the concave wall in apically curved canals. Under the conditions of this study, preparation with NiTi K-files produced more appropriate shapes in roots with apically curved canals than NiTi S-files.