Cutting pattern of nickel-titanium files using two preparation techniques

The aim of this study was to examine the cutting patterns of recently introduced nickel-titanium endodontic files and compare them with similarly shaped stainless steel files using both balanced-force and stepback techniques. Simulated canals were constructed in resin blocks with 40 degrees curvature. Fifty blocks were prepared by a balanced-force technique: 25 with Nitiflex (Maillefer) and 25 with Flexofiles (Maillefer) to master apical file size 40. Fifty blocks were prepared by a stepback technique: 25 with Nitiflex and 25 with Flexofiles to a master apical file size 30. Composite prints were made of pre- and post-instrumentation canals using a computerized imaging system. The amount of material removed from the inner and outer canal curvatures was measured at eight levels in the apical 11 mm of the canal. The results were analysed by Kruskal-Wallis ANOVA. Using the balanced-force technique, Nitiflex files removed less material on the outer curve apically and less on the inner curve mid-canal (P < 0.05), while Flexofiles caused more apical transportation. In the stepback technique, the Nitiflex files removed more material from the outer curve apically (P < 0.05); the Flexofiles removed more material along the entire inner curve (P < 0.05), and maintained canal curvature better than Nitiflex files. It appeared preferable to use Nitiflex files in a balanced-force technique, and Flexofiles in a filing technique as stainless steel files can be precurved.