文摘
The effects of torsional preloading in various conditions on the torsional resistance of nickel-titanium (NiTi) endodontic instruments were investigated. Two NiTi instrument systems, WaveOne Primary made from M-wire from a reciprocating system and ProTaper Universal F3 made from conventional NiTi from a continuous rotation system, were used in this study. All preloaded groups showed significantly higher ultimate strength than the unpreloaded groups. There was no significant difference among all groups for distortion angle and toughness. Scanning electron microscopic examinations of the fractured surface showed typical features of torsional fracture. The total energy until fracture was maintained constantly, regardless of the alloy type.