Microscopic Features of Fractured Fragment of Nickel-Titanium Endodontic Instruments by Two Different Modes of Torsional Loading

Figure 2

Longitudinal and lateral aspects of representative fractured fragments from the RTL method (left two columns) and STL method (right two columns). Specimens from the RTL method show rare unwinding near the fracture area, while the specimens from UTL method show typical features of unwinding (white arrow). The specimens from the RTL method show irregular and catastrophic aspects with some cracks without unwinding. RTL: repetitive torsional loading; STL: single continuous torsional loading.