4B Clinical Opinion ENDO TRIBUNE | February 2010 An endodontic absurdity By Barry Musikant, DMD Over time, it has become increasingly clear that teaching K-files is devoid of common sense and makes endodontics more difficult and fraught with procedural mishaps. Such a statement might be met with outrage by those who teach the use of K-files, but I would ask them to ask themselves (if no one else) what has been the greatest impedus for the introduction of rotary NiTi. Rotary NiTi did not appear out of the blue. It is an answer to a problem that is created by the ineffective use of K-files. If that were not the case, why would there be a need for rotary AD Fig. 1 NiTi in the first place? I don’t believe there is too much wiggle room here. We use K-files. They present prob- Fig. 2 lems that are recognized by the dentists using them, and there is a logical quest to find solutions. What is unique in the implementation of rotary NiTi is its continuing dependence on the very instruments they are at least partially replacing. K-files often do their damage at the beginning of instrumentation with the first few files used mostly through a No. 20. By this time, canals may be transported, blocked or ledged (figure 1). Yet these are the instruments recommended for glide path creation. It is important to emphasize K-file difficulties don’t start with a 25. Depending upon the canal they are negotiating blockage, ledging or transportation occurs before the canal is instrumented to a 20. Given this situation, the continued use of K-files to shape the canal prior to the use of rotary NiTi is an endodontic absurdity. A statement as strong as that requires rock solid logic to support it. The rest of this article will provide that logic. Let’s start with the fact that K-files have a working length of 16 mm with approximately 30 flutes along its working length. The compact array of these flutes forces them to align in a fairly horizontal orientation. Dentists generally employ these instruments with a back-andforth watch-winding motion with the occasional upstroke to remove the instrument to debride the shank. The predominant motion remains horizontal. This is the basic stroke we use in endodontics to negotiate to the apices of canals. Combining a horizontal stroke with flutes that are also horizontally inclined leads to a screwing in and a screwing out of the K-file. It does not lead to cutting the dentin along the length of the canal. That only occurs after the instrument engages the canal walls and is pulled up. Or it occurs when the K-file is screwed in clockwise and apical pressure applied as it is then rotated counterclockwise cleaving off the dentin that was initially engaged in the clockwise motion. Neither one truly represents watch-winding that is the motion most often employed when using these instruments. However, let’s consider the modification of their use as described above. If used with a twist-and-pull motion, dentin will only be cut on the pull stroke with the cutting action occurring selectively to the outer wall in curved canals. This leads to the transportation we wish to avoid. If used with balanced force, the second method described above, the instrument will stay centered, but please realize that it takes three motions to produce a cutting action. A clockwise motion must first be employed. Then apical pressure must be applied to the instrument and finally the instrument is rotated counterclockwise. Three motions employed for one cutting action, the height of inefficiency and one that cannot effec-