Figure 1.

Representative photos of the separated surfaces of ProTaper Next X1 files: (a) axial view of the separated surface from the rotation group; (b) axial view of the separated surface from the OTR group; (c) lateral view of the separated area from the rotation group; (d) lateral view of the separated area from the OTR group. The dimpling areas visible on the whole instrument’s axial view surfaces and the absence of plastic deformations on the tips indicate features consistent with cyclic fatigue failure.