Written by Richard Mounce, DDS Friday, 01 September 2006 00:00
Some endodontic manufacturers have sold their products as "plug-and-play" systems. Via a technique card of some kind, the clinician is instructed to take a given file to a certain depth in the canal, do so in a given file sequence, and then, once the canal is prepared to some minimal diameter, place either a pre-fit matching master cone or other device into the canal to the same depth as the last shaping file. In theory this might mechanically place a white line to the apex (or somewhere close). In reality, however, it has nothing to do with the tooth being properly cleansed, shaped, and obturated in 3 dimensions and/or the biologic objectives of root canal therapy being achieved. Filling material or sealer to the apex is not evidence of adequate debris removal, canal preparation, or canal cleanliness.
The procedure known as a root canal is far more complex than simply pushing sealer and gutta-percha to the end of the root. Such a white line mentality is akin to painting by numbers versus what was done on the ceiling of the Sistine Chapel in Rome. While probably none of us is a Michelangelo, it is possible to take a healthy dose of art and blend it with hard science to create results that can give patients the success they deserve (Figures 1 and 2). Simply put, following cookbook menus for root canal treatment is fraught with obstacles. In this article, one such difficulty is described along with its solution.
Figures 1 and 2. Challenging clinical cases that appear to be half completed. Did the clinician get in the middle of the process and not know where to go to bring it to a proper end?
The problem with plug-and-play systems is that the process can easily break down when the tooth does not respond as expected. Most often the clinician is instructed to use a certain set of instruments in a given order, but the next file in the suggested sequence won't advance to the desired length. Unless one is experienced and has significant practice with the system and/or the given anatomy present, it can be difficult at times to know what to do next. For example, in a significant mid-root curvature, a clinician might be trying to get a rotary Ni-Ti (RNT) file past the canal level (in this case the middle third), and the file is not advancing as expected, even if the coronal third was easily negotiated. Pushing on the given RNT at that moment to achieve an arbitrary length in order to follow the menu on a technique card is usually the least productive move possible. Forcing a RNT where it doesn't want to go will lead either to transportation of the canal or instrument fracture (or both) very quickly.
Solutions to this challenge are both philosophical and technical. The clinician will profit from a mindset that each tooth and patient is different, despite the similarities that might exist between cases. The clinician needs to assess, among many factors, the following issues before ever beginning treatment, with an eye toward how such issues will be managed once treatment commences:
•Is there physical access to a specific tooth given the patient's level of cooperativeness, his or her ability to open, etc?
•Through which material is access being achieved (crowns, alloy, natural tooth structure, porcelain, etc)? What is the root curvature, root length, calcification, etc?
•Is the clinician using a rubber dam (they should be used always and without exception) and a surgical operating microscope (it is the ideal means for visualizing the canals and tooth during treatment)?
•Does the clinician have an intimate knowledge of the materials to be employed? Does he or she have experience with these materials on extracted teeth and in live practice?
Once the above issues are addressed and solutions to challenges that might arise are considered (at a minimum), the cognition could and should arise that the tooth and patient are unique and that a given, rigid formula for instrumenting a tooth might not be applicable to that tooth. In other words, not all teeth can or obviously should be treated from a cookbook. While patterns certainly can be used and repeated in instrumentation of root canal systems, and such patterns have value, doing it the same way every time or attempting to do a root canal the same way every time is the harbinger of an iatrogenic event. In the authorÌs empirical opinion, such menus arise because they are a simple way to teach, but often they lose their value in translation as they move toward utilization in live patients.
The strategies that provide excellent clinical results include optimal irrigation, achievement and maintenance of apical patency, crown-down instrumentation utilizing RNT files from larger tip sizes to smaller and larger tapers to smaller (ie, the coronal third is instrumented first, the middle third second, and the apical third last), excellent length control, and optimal visualization (most often through the surgical operating microscope), among other key concepts.
So where to go once the cookbook breaks down and isn't working in the particular case?
REDIRECT TO A POSITIVE OUTCOME
The answer is simpler than one might imagine. First off, if the clinician has kept the canal path open and avoided iatrogenic events, the case can virtually always be redirected to a positive and productive outcome. In other words, if the recipe breaks down and the clinician is confused about what to do next and the given file won't advance to where one would like, then it is important to do the following:
1) keep the canal path open, patent, and debris-free so that working length can be established and adjustments made to the given prepared canal shape thus far, and
2) if no significant iatrogenic events have been created up to this point, then simply treat the present situation as a starting point for the next canal third to be treated, rather than being lost within the context of a larger procedure.
For example, if the clinician is not able to advance a RNT file beyond mid root but there are no existing iatrogenic events or blockages, it has value to make sure first that the coronal third shaping is ideal and to double-check patency in the middle third. If the canal is patent in the middle third, the next step is to make sure there is a glide path present. Once this middle third glide path is created, the clinician can then begin using RNT files in a crown-down fashion from larger tapers to smaller and from larger tip sizes to smaller. Use of such files implies that they will be used with the correct touch and pressure. Such a touch will be gentle, passive, deliberate, file turning upon entry into the canal, slow, and with finger pressure (not from the forearm). It is common for clinicians new to RNT instrumentation to use the files far too rapidly and forcefully in their insertion, and as such to push the files from their forearms, risking fracture. Ideally, the files will be cutting only 1 to 2 mm of canal at any given time rather than a larger length of the canal. Such limited cutting of the canal wall at any given insertion can go far toward reducing breakage and creating effective preparation of the canal wall by virtue of the reduced transportation that will ensue. This sequence can and should allow the middle third to be shaped efficiently and safely.
It may be necessary to use various tapers to shape the canal as one moves apically. For example, if a .06-tapered RNT won't advance beyond mid root, a .04-tapered file used with diminishing tip sizes can be employed. If a .04-tapered RNT won't advance, one can consider a .02-tapered file used always with diminishing tip sizes so as to provide a crown-down approach to canal preparation.
Figures 3 and 4. Challenging clinical cases completed with the K3 rotary Ni-Ti system.
As an aside, the author rotates the K3 RNT system (SybronEndo) at 900 rpm. The K3 system has .06-, .04-, and .02-tapered RNT files and can be used as described in the above sequence. Using the K3 files at 900 rpm creates efficiency, because at the higher speeds the files cut even more effectively than they do at lower speeds (usually 350 rpm). Also, higher rotational speeds and resulting cutting efficiency reduce the frictional resistance of the K3 as it rotates. Minimizing engagement to 1 to 2 mm of the canal wall on each insertion asks the file to carry less debris and reduces fracture potential as well. The K3 has an excellent tactile feel, cutting ability, and flexibility (Figures 3 and 4). While it works very well at 350 rpm, its design characteristics allow it to be used with ease at the higher speed mentioned above.
In summary, when the cookbook breaks down, it is valuable to step back and assess the given clinical situation in the canal. When the clinician is unsure where to go next in a procedure because he or she is following a menu-driven cookbook, arbitrarily inserting RNT files into the canal without a clear understanding of what the file is attempting to do is unproductive. It not only wastes time, but it risks iatrogenic events, further transports the canal, and most often takes the clinician away from the desired result. In the absence of an iatrogenic event and with patency, simply ensuring patency, irrigating copiously, creating a glide path, and utilizing RNT files from larger tapers to smaller and larger tip sizes to smaller with a gentle touch can all go far toward instrumenting the canal in a crown-down manner. This has desirable benefits with regard to efficiency, preventing possible iatrogenic events, and placing more irrigant farther down the canal system.
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