What difference does unwinding an endodontic file make if it doesn’t break?

extrusion segI was recently asked why would it matter if an endodontic file unwound as long as it didn’t break. First, let us think of a file as not only an instrument that enlarges a canal but one that acts as an auger as well; it conveys debris. When a file unwinds to the extent that its helix augers apically rather than in a coronal direction (as in segment 1), then debris is extruded through the apical foramen. Note that part of the file becomes denuded. Post operative pain will most likely be the consequence. The unwound segment 2 continues to auger debris in a coronal direction while the unwound segment 3 augers in an apical direction. The result is compression of debris, additional torsional stress and a greater propensity for breakage. Keep in mind most files will not even unwind 2 revolutions without fracturing. If the file is rotating 500rpm, 2 revolutions require less than 1/4 second before failure.

The short answer to the question is: it probably matters. Luck is not nearly as predictable as cause and effect.

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