Click here to enlarge imageWe have standardized and nonstandardized cones. Standardized cones are the cones most dentists have in their cabinets. For example, 20, 25, 30, 35, etc. are ISO-sized in apical diameter, as well as ISO-sized in taper (.02). Nonstandardized cones come in sizes fine-fine, medium-fine, fine, fine-medium, medium, and coarse. As previously mentioned, the sizes you will employ 98 percent of the time are fine-medium (F-M) and medium (M). Nonstandardized cones have a more pronounced taper and can be fit to either an .04 or .06 tapered preparation. As an alternative, you can use a tapered cone such as a .06 (SybronEndo).
There are other cones available from Charles Schwed and DiaDent that are ISO-sized, (25,30, etc.) that come in different tapers such as .04 and .06. Also, some manufacturers have cones that match specific file tapers such as the Autofit cones by Analytic Endodontics and the GTs by Dentsply Tulsa Dental.
What is most important is to know how to properly fit or size a nonstandardized cone. Here is an easy way : Let's say, for example, the last instrument was a size 25. You take the F-M cone and place it into the canal, going a bit past the apical constriction. This is not a problem because it is only a gutta-percha cone.
Instead of guessing at the apex, like we often do with standardized cones, we advance the cone until it is snug at the apex. An example would be if you make a small circle with your left thumb and forefinger and then place your right forefinger through the circle until it binds. Of course, at this point your cone fit will be slightly overextended, but not underfilled at the constriction.
The great part of this technique is that when we remove the cone and examine it, the section of the cone that is over-extended is generally bent and crinkled. All we now do is trim the cone at the level of the crinkles. This corresponds to the level of the apical constriction. Of course, you can verify the adjusted cone with an X-ray to confirm that it matches the final working length. We can't make it any more simple! This is a sweet way to achieve a good cone fit.
The frequent criticism, "How do we know where the cone is binding?" does not apply here because we have created a fully tapered, .06 preparation, not a .02 parallel shape as with hand files. We can confidently state that whatever obturation method you use — lateral condensation, vertical condensation, System B, etc. — all work better with a .06 preparation. Even the solid-core obturator systems such as Thermafil work better with a .06 preparation because you do not have to "verify" the size. This is related to the taper of the plastic carrier. If you finish with a No. 25 .06 taper, you simply fill with a No. 25 Thermafil.
When we do live demonstrations at our Real World Endo courses, the participants are always stunned at the ease of the cone fit. It is all a result of the .06 preparation. The rotary files that we prefer to use when performing a fully tapered, .06 preparation are the Series 29 .06 Profile (Dentsply Tulsa Dental) and the new .06 taper K3 file by SybronEndo. These are both excellent files and we recommend that you try both of these files on extracted teeth or blocks before using them on patients.
There is even more good news concerning this "endodontic genie." Because it is faster and more effective, the .06 preparation allows you to perform more single-visit endodontics. This is not only very profitable, it is a huge practice builder. The timesavings, of course, translate into greater production and net profit. We also want to stress that there is a tremendous savings in consumables, such as patient set-up supplies (napkins, anesthetic solution, suction tips, etc.).
The continuously tapered .06 preparation will increase your ability to ideally prepare most root canals and to create a preparation that is well-suited for all obturation techniques.
Will this Genie ever go back into its bottle? That's hard to say. But what we can say is this — it is clear, as our motto states, that with "Just the Facts, Nothing But the Facts," you will be able to make endodontics a profit center for your practice.
Drs. Brave and Koch together are Real World Endo, an endodontic education company. They can be reached at (866) RWE-ENDO, or visit their Web site at www.realworlden do.com.