Comparison of nickel-titanium and stainless-steel spreader penetration andaccessory cone fit in curved canals

The purpose of this study was to compare nickel-titanium and stainless-stee l spreader penetration in curved canals. Twenty prepared plastic blocks wit h a 30 degrees curvature were used for each part of the study. In part 1, t he force required to insert each spreader to within 1 mm of working length in an empty canal was measured. In part 2, the force required to insert eac h spreader to within 3 mm of working length was measured in a canal contain ing a master cone. In part 3, the depth of penetration of each spreader wit h a master cone in place using a 1.5 kg force was measured. Additionally, i n part 3, the depth of penetration of the first accessory cone was measured . The results from part 1 showed that a nickel-titanium spreader required s ignificantly less force than a stainless-steel spreader (0.30 kg vs. 0.59 k g). In part 2, a nickel-titanium spreader required significantly less force than a stainless-steel spreader (1.56 kg vs. 2.42 kg). In part 3, a nickel -titanium spreader penetrated significantly deeper than a stainless-steel s preader (15.0 mm vs. 14.0 mm). There was no significant difference in the d epth of penetration of the first accessory cone used after either spreader (0.8 mm vs. 0.7 mm). Therefore, the potential for vertical root fracture in curved canals during lateral condensation may be minimized by using nickel -titanium spreaders.