Comparison of first accessory cone penetration after using stainless-steel and Ni-Ti spreaders in curved resin blocks

The purpose of this study was to compare first accessory gutta-percha penetration after the use of nickel-titanium (Ni-Ti) or stainless-steel spreaders in curved resin blocks. Forty resin blocks with 30º and 45º curvatures (20 blocks for each) were prepared and #30 master cones were placed in canals. In part one, under 20 Newton pressure, Ni-Ti or stainless-steel spreaders were placed alongside the master cone and their penetration was measured with a millimeter ruler. In part two, after removing the spreader, one of the accessory cones (#15, #20 or MF) was substituted in the canal and its penetration was measured. The Mann-U Whitney test was used for the final evaluation. In both curvatures, the penetration of Ni-Ti spreaders were significantly more than stainless-steel spreaders(p≤0.005).Penetration of the first accessory cones (#15 and MF) in Ni-Ti spreader group were also significantly more than stainless-steel group (p≤0.05) (in both curvature groups). This study showed that Ni-Ti spreaders and #15 accessory cones penetrated deeper in curved canals than stainless spreaders and #15 accessory cones. Therefore, the use of NiTi spreader in lateral condensation technique is suggested for better results.