comparison of first accessory cone penetration after using stainless-steel and ni-ti spreaders in curved resin blocks

introduction: 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. materials and methods: 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. results: 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). conclusion: 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.