Barry Musikant

-REAMERS, particularly those relieved with a flat along their length, encounter far less resistance along length than what we are used to from our experience with K-files. This reduction in resistance is a result of the fewer flutes along the length of the K-reamer shaft and their more vertical orientation. This article is essentially a short tutorial on how to use reamers—both unrelieved and relieved—to negotiate through calcified canals. They are generally used in a watch-winding motion, but that does not tell the whole story. There are variables that you can control, such as the degree of rotation when using watch-winding and the amount of apical force that you apply. The one variable that you cannot control is the amount of resistance that the canal produces as you attempt to negotiate apically. The three factors are all interrelated in the following ways: the less the resistance to apical negotiation, the more you can rotate the instrument. This is beneficial in these circumstances because the vertically oriented flutes along the length of the reamers will shave more dentin away as the arc of motion increases. In these situations there is no need to apply much apical pressure since so little resistance is being encountered. As canals become more curved, the resistance to apical negotiation increases. With this increasing resistance it becomes mandatory that the arc of motion decreases as the amount of apical force applied to the instrument must necessarily increase.
    The right amount to decrease the arc of rotation and to increase the apical force is determined by the ability to make further apical progress and—of even more importance—by the observation that we are not distorting the reamer. The configuration of the flutes should remain intact. If this is not the case, then we are either applying too much apical force, are still rotating the instrument too much, or doing some combination of the two. In fact, this is the beauty of the 30-degree reciprocating handpiece: 30 degrees is such a short arc of motion that it will virtually never lead to instrument distortion even if excessive apical force is applied.
    Once you know the parameters of the reamers when initially used manually, you have a tool that you can adapt to all situations. There are occasions when the instrument is indeed in the canal but will not advance under watch-winding motion no matter how much apical force is applied. In these cases, we use a twist-and-pull motion. We don’t initiate the twist-and-pull unless we are sure that we are in a canal, albeit a tight one, the tightness of which is determined by its having immediate tugback. Without immediate and continuous tugback, we must assume that the tip of the instrument is hitting a solid obstacle that would call for removing the instrument, prebending it, and finding the patent pathway to the apex. After the pathway has been discovered, we would reinstitute the watch-winding motion.
    The important thing is to understand the interrelationship between the apical resistance encountered—which will vary widely with curvature and state of calcification—and the application of the correct amount of instrument rotation and the appropriate amount of apical force. Once you learn to adapt to increased resistance by varying the degree of rotation and apical force, you will be able to safely negotiate just about any canal no matter how curved or calcified as long as there is the smallest degree of patency.
    To see a video that illustrates this discussion, please go to DDSCHAT.Com and read the thread “How to negotiate thru calcified canals.”
    Please note in the video that watch-winding is also associated with an up-and-down motion. The purpose of the up-and-down motion is to carry the debris coronally, freeing up the apical portion of the instrument that is doing the initial penetration. In a really tight canal, it doesn’t hurt to remove the instrument to wipe off the debris that has accumulated in the flutes. If you try this procedure with reamers both unrelieved and relieved, you will be quite surprised at the ease of penetration even in challenging cases as compared to your experience using K-files. Once patency is well established, say after shaping to a 20 either with a manual or engine-driven reciprocating approach, you can generally continue to complete shaping of the canal using the same system of relieved reamers, noting and adapting to the relationship between apical resistance and apical pressure.
    When using the 30-degree reciprocating handpiece, we are necessarily limiting ourselves to a short arc of motion, but that is compensated for by the high frequency of 3000–4000 oscillations per minute that from the dentists’ point of view allows for rapid and accurate penetration of the canal to the apex.

January - March 2012