Comparison of curved canal shape using filing and rotational instrumentation techniques.

Summary. The shaping of curved canals produced by rotational and filing instrumentation techniques was compared in 40 human molar root canals which were prepared in vitro. The tech niques used for filing were the stepback and the serial, and for rotational instrumentation were the ‘balanced force’ and an experimental technique, similar to the balanced force concept, but featuring only clockwise rotated instruments. The results were collected from pre- and postoperative radiographs as well as from scanning electron microscope analysis of longitudinally ground half-sections of the roots. Each preparation was qualitatively rated for its centering, flow, taper, apical design and wall surface appearance. The stepback shapings consistently presented the best taper and apical stop design along with scratch-free surfaces. The serial technique produced the best centered flow and apically deigned preparations. The rotational techniques produced less consistent results. With the exception of some straightened specimens, the balanced force concept proved to be effective at least for the shaping of moderately curved canals. The lack of taper as well as the absence of apical stop in the balanced force shapings have been found to be more inherent in the concept of shaping than in the technique of the preparation itself. The experimental rotational preparations showed almost exactly the same shaping patterns as the balanced force ones, apart from better taper and apical design but poorer flow and visible instrument scratches. The latter two observations were related to the use of non-tip-smoothed instruments.