The Effects of Torsional Preloading on the Torsional Resistance of Nickel-titanium Instruments

Rotary science and its impact on instrument separation: A focused review

“…A rotary file is often subjected to a combination of torsional and cyclic stresses in the canal. In vitro studies have shown that torsional preloads increase the fatigue,[ 60 ] but improve torsional strength,[ 61 ] where as cyclic preloads add to tosional failure. [ 62 ]…”

Past, Present, and Future Trends of Nickel Titanium Rotary Instrumentation

“…Cyclic fatigue occurs when an instrument rotates in a curved canal, leading to motion-induced repeated compressive and tensile stress. 24,25 It is a product of hardening and metal fatigue, resulting in failure. Torsional fracture occurs when the instrument tip is locked within the canal while the shaft continues to rotate.…”

“…However, cyclic fatigue tends to occur more frequently within curved canals. 24 A previous study evaluated defects in rotary NiTi files after clinical use and found that fractures occurred due to torsional failure with smaller files (55.7%), while larger files were prone to fracture from cyclic fatigue (44.3%). 23…”

Torsional Resistance of Two New Heat Treated Nickel Titanium Rotary Instruments: An in Vitro Evaluation

“…The separation due to torsional stress occurs when the tip or part of the instrument binds into the canal, and the remaining part of the instrument continues to rotate and the torsional resistance of the instrument is overloaded [11]. Nevertheless, doubtful information is available on torsional resistance.…”