(a)
(b)
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Figure 2: Scanning electron microscopy photographs of the fractured surface of NiTi files after the torsional fatigue resistance test. Fractured surfaces of the One Shape (a), ProTaper NEXT (b), NRT file (c), and V taper 2H (d) (original magnification, x200) showed circular abrasion marks and skewed dimples at the center of the rotation region. (e) Magnified view of upper box of (d) showing a crack line from the boundary to the central region (x500). (f) Magnified view of lower box of (d) showing circular abrasion marks at the periphery of the fractured surface (x1,000).