I clinical report _ shaping system Endodontically speaking, the proof is in the pudding Author_Dr Barry Musikant, USA _Having lived through the traditional (hand instrumentation) and rotary NiTi periods of endodontics, the main drawback of both periods, in my estimation, has been in not applying what our clinical experience and our wealth of research has told us. Today, we essentially use K-files as if they were reamers. By this, I mean that we use them predominantly in a watch-winding motion, a reaming action by another name. Does it matter if a K-file is used in a reaming motion? What are the differences between a K-file and a K-reamer that call for differences in their usage? A K-file has twice as many flutes along the 16 mm working length that a K-file and K-reamer have in common. Twice as many flutes means twice as much engagement along length and at least twice the resistance encountered during apical negotiation. Increased resistance to gaining apical length does not sound like a desirable trait. Are there any other differences? The flutes on a reamer are twice more vertically oriented than those on a file. Does this have implications for using the recommended watch-winding motion? The more the cutting edges of the flutes approach a right angle to the plane of motion (which is mainly horizontal), the greater the cutting efficiency of the flutes. An easy way to visualise this concept is to consider the use of a file in carpentry. The carpenter is able to cut wood with a file because he/she is applying a vertical motion to an instrument that has horizontal flutes. If the flutes were vertical, in the same plane Fig. 1 Fig. 2 12 I roots 4_ 2009