Dennis Brave and Ken Koch
As readers of our Real World Endo column know, we are strong proponents of a fully tapered .06 preparation. This preparation offers multiple benefits. But the question we often get is, "How am I going to place a .06 taper file into a space that is problematic with a .02 taper? Isn't a .06 taper file just three times the width of a .02 taper?
Actually, the answer this question is "no." A .06 taper, in fact, is not just three times the width of a .02 taper. The proof is in the arithmetic. Let's take the following example.
A number 20, .02 taper file (20/.02) is .20 mm at D-1, and at D-10, the diameter is actually .40 mm. We have calculated this number by multiplying the taper (.02) times the length (10 mm). We then add the apical tip size at D-1 (.20) to the previously calculated number and we get .40 mm. Let's now increase the taper from .02 to .04. Do the math, and we now determine the width at D-10 (for the new file) is .60 mm. Well, isn't this interesting? We have increased the taper 100 percent from .02 to .04, but the width at D-10 increased only 50 percent (.40 to .60 mm).
Now, let's do one more thing. Let's increase the apical size of the file at D-1 to a size 40 (.40 mm). We can now calculate the diameter at D-10 for this file and, in fact, we determine it is .60 mm. Again, let's increase the taper from .02 to .04. We do the math and we find the diameter at D-10 for the 40/.04 is .80 mm. So, while we have increased the taper 100 percent (.02 to .04), the width at D-10 has, in fact, only increased 33 1/3 percent.
But what does this really mean? It means that the effect of taper is inversely proportional to the apical tip size. In other words, as the size of the file increases, the effect of taper decreases. This is very significant because it explains why we can use a .06 taper rotary file with minimal problems. Additionally, this is why we can actually perform a fully tapered .06 preparation and still consider it a conservative one.
A knowledge of taper also helps us comprehend that there are two ways to perform a root canal. We can use a sequence of files that employ a common tip size but have varying tapers. For example, a 20/.10 file followed successively by a 20/.08, 20/.06, and, eventually, a 20/.04 file. The ProSystem GT employs a variable taper sequence as do a number of other file systems, such as the Quantec and RACE.
A second option is to use a constant taper file with variable tip sizes, such as a 35/.04 followed by a 30/.04, 25/.04, and finally a 20/.04. Two file systems that employ a constant taper are the Profile and the K3.
We agree that the biggest obstacle to endodontic success is the step-back preparation. For the past two years, Real World Endo has been trying to get this point across both at lectures and in print. However, we would like to take this one step further.
We strongly believe in using a constant taper file such as a .04 or .06 taper to shape the root canal preparation. A variable taper concept, in our opinion, does not work nearly as well clinically as it does on paper. Think about it: A variable taper sequence is nothing more than a step-back preparation from the opposite end of the tooth. As a result of better manufacturing, we now have the ability — with constant taper files — to create predictable, reproducible shapes. The variable taper sequence results in a different shape each time you do a root canal. The result? A lack of reproducibility that makes obturation more challenging.
It's crucial to understand the effect of taper if you want to increase the quality of your endodontics. We hope this discussion helps you in your practice. And, as usual, we will continue to give you, "Just the Facts, Nothing but the Facts."
Dr. Dennis Brave is a diplomate of the American Board of Endodontics and was the senior managing partner of a group specialty practice for 27 years. Dr. Kenneth Koch is the founder and past director of the new program in postdoctoral endodontics at the Harvard School of Dental Medicine. Drs. Koch and Brave together are Real World Endo, an endodontic education company. They can be reached at (866) RWE-ENDO, or visit their Web site at RealWorldEndo.com.