ENDO TRIBUNE | February 2010 tively be employed with an engine driven system. With all those flutes engaging the walls of the canals, it is quite difficult to discern what the tip of the instrument is engaging; yet what the tip of the instrument is engaging is the single most important piece of information that must be transmitted to the dentist. If the tip of the instrument is hitting a wall and the dentist does not know it, his only guide is to maintain length. With enough twist-and-pull motions the length will be gained, but often this gain is through distortion of the original canal anatomy at times leading to frank perforations. As an aside, to bring the perspective of K-files into sharper focus, the flute design is quite similar to a screw. I don’t believe there are many dentists out there who would consider shaping canals with screws. They engage the walls of the canal, but serving the purpose of a screw they don’t cut dentin away. Rather, they cut into dentin maintaining the engagement. While this action is exactly what you want in a screw, it is exactly what you don’t want in an instrument that is shaping canals. Poor removal of dentin, distorted shaping of canals and inadequate tactile perception of the tip of the instrument are all features of K-files. Despite these inadequacies, the teachers continue to advocate their usage. The only way this can occur is a lack of thoughtful analysis for what they are advocating. Now let’s look at the problem of K-files from a different vantage point: its comparison to K-reamers both relieved and unrelieved. Many readers may not know there is really much of a difference between the two. In fact, there are major differences that lead to far more rational approaches to canal shaping. Perhaps the single most important difference between a K-file and a K-reamer are the number of flutes along their respective 16 mm of working length. K-reamers have about one half the number of flutes. As a result, the flutes have a more vertical orientation compared to those on a K-file. If K-reamers are used with the recommended watch winding motion, the primary movement will immediately cut dentin. There is nothing magical about this. Any carpenter knows if you plane a piece of wood, the cutting blade is at right angles to the plane of motion. In the same way, the vertically oriented flutes work productively with the horizontal motion of the instrument and the blades cut. K-files tend to screw in and out while K-reamers cut when the same motion is applied. Clinical opinion 5B One could not ask for a more basic difference. In addition, K-reamers provide the dentist with a superior tactile perception, a result of reduced engagement along length, more efficient cutting of dentin and greater flexibility of the shaft. The dentist can now make the all-important distinction between hitting a canal wall and being in a tight canal. The former will provide no immediate tugback while the latter produces tugback immediately. The ability to make the distinction tells the dentist when to remove the instrument, bend it at the tip and negotiate around the blockage, otherwise known as the solid wall. The vertical flutes along length make the instrument an effective cutting instrument along length when used with a watch winding motion, but a poor cutting instrument when used with the pull stroke and this is exactly what we want. Instruments that cut effectively with a pull stroke in curved canals will always tend to distort to the outer wall. For years K-files have been cutting dentin in ways that are detrimental to our final results and not cutting dentin well where it would be most effective. Less engagement, more flexibility, superior cutting ability, enhanced tactile perception, are all desirable qualities and every one of them is enhanced if we now modify the K-reamer, by placing a flat along its g ET page 6B AD AD