Traditionally, rotary Ni-Ti (RNT) choices for canal enlargement were either “safe” or “efficient” and rarely, if ever, both simultaneously in all anatomies. Safe files were fracture-resistant but may not have cut as effectively as their efficient counterparts. Efficient files cut well and yet broke more often and had a greater risk of canal transportation. This inherent lack of both safety and efficiency is now a thing of the past. The introduction of the Twisted File (TF [Sybron-Endo]) represents a huge step forward for endodontic canal preparation. It is truly safe and efficient. TF is very difficult to fracture if used as directed and has excellent cutting efficiency without undue risk of transportation.
Inherent to the challenges manufacturers face is that grinding nickel titanium has always had to be performed against the grain structure of the metal. Grinding has the potential to create microcracks that can later be the focal point for failure due to ex-cess torsion and cyclic fatigue. Some brands of files have been electro-polished to reduce the effects of these microcracks (in theory); yet such electro-polishing may reduce the sharpness of the cutting edge and removes some amount of the surface layer of the metal
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