Advanced ESX® instrumentation: segmental crown down and hybridization of tapers

Dr. Allen Ali Nasseh discusses a clinical case to demonstrate the application of Advanced ESX instrumentation

Introduction
All root canals are not created equal. The root canal shapes we face on a daily basis are as unique as the individual patients who present them. Preparing such a variety of shapes and canal morphologies efficiently with a minimum number of files has been a consistent goal in endodontic therapy.

However, a magic file or formula that would make root canal shaping a universal sequence for all canal shapes and types has proven elusive. Even the single NiTi file techniques are mere finishing files, and in many cases, considerable instrumentation is required with other files prior to finishing the shape with them.

The ESX® Rotary NiTi Instrumentation System (Brasseler USA) comes as close to the goal as is currently possible. Its goal is to minimize the number of files needed for each root canal procedure while at the same time respecting that all canals are unique. This is accomplished with two specific instrumentation protocols: the Basic and Advanced ESX Techniques that address the varying degrees of case difficulty. Each protocol has its own specific sequence of use for both hand and rotary files based on the level of complexity of the case. This results in the general use of two to five rotary and/or hand files per case based on a given canal morphology.1
The clinical case discussed in this article demonstrates the application of the Advanced ESX theory for managing molars. However, a brief review of the Basic Technique is required first.

Basic ESX Technique
The Basic ESX Technique can be summarized as the instrumentation of a canal to a minimum size 15/.02 hand file to full working length (WL), followed by instrumentation to that length with the ESX Expeditor™ File (15/.05), and thereafter, a single ESX Finishing File (either sizes 25/.04, 35/.04, 45/.04, or 55/.04). A key point here is that both the Expeditor and the ESX Finishing Files are used with a Single Stroke and Clean (SSC)™ operator motion, a motion that helps reduce the torque on the files. The ESX finishing files have a patented file tip called a “Booster Tip,” which makes reducing the number of files possible when combined with the SSC motion. In summary, the Basic ESX technique (for most anteriors and premolars) is a two-file technique (Expeditor + one Finishing File.)  The Choice of which Finishing File to use is determined by the level of engagement experienced by the Expeditor on its journey down to the apex. If significant engagement occurs (~more than 5 strokes to apex), then a 25 Finishing file is used. If moderate engagement is experienced with the Expeditor, then a size 35/.04 is used, and if minimal engagement, then the 45/.04 is used. If additional enlargement is needed after the 45 reaches the apex (remaining tissue in file flutes), then a 55/.04 can be used to finish the preparation.3 Therefore, the Basic Technique algorithm can be shown in Figure 1.

Advanced ESX Technique
The Advanced ESX Technique is used in most all molars and difficult premolars and anteriors. These are generally cases that are narrower or curved. For ESX Purposes, we define Advanced cases as follows:
“Advanced canals are defined as those canals where working a number 15/.02 hand file straight to the apex (to working length) is not possible or easily accomplished.” In other words, if the No. 15 hand file does not go straight to the apex easily after access opening and minimal orifice shaping, you’re facing an Advanced Case that requires the use of the Advanced ESX Technique (Figure 2).

Generally, at least one canal in a multi-rooted tooth is either narrow, calcified, or curved. Therefore, we can make a general statement that multi-rooted teeth are for the most part advanced cases and require the Advanced ESX Technique. Remember that the technique (Basic or Advanced) is set by the lowest common denominator of a case, meaning the toughest canal in a multi-rooted tooth. Therefore, most molars are advanced.
Since the difficulty in Advanced cases is working the apex to a size 15/.02, the purpose of the Advanced Technique is to safely and efficiently prepare the apex to the 15/.02 size, thus allowing the Basic Sequence to follow and complete the preparation.   

Advanced Technique —> 15/.02 to working length —> Basic Technique
The Advanced Technique utilizes three additional files before the Basic Sequence is employed. They are the ESX Scout Files (sizes 15/.02 and 15/.04) in conjunction with the help of the ESX Orifice Opener (20/.08). They work together and take advantage of increasing taper while maintaining an ISO 15 tip to enlarge the canal (Figure 3). This creates a phenomenon of “Hybridization of Tapers,” where files with the same tip sizes but varying constant tapers slowly remove dentin laterally and incrementally in a crown-down fashion (Figure 4).

Hybridization of Tapers
In this article, the use of files with the same tip size but varying tapers is referred to as Hybridization of Tapers. As previously mentioned, Advanced cases are those where a size 15/.02 file does not easily reach the apex. In these cases, smaller hand files (sizes 6/.02, 8/.02, or 10/.02) are used to explore the initial Available Length (AL). This available canal length is noted. Available length is the space that a size 10 hand file can achieve by simply placing the file in the canal and advancing it lightly until it stops. 

Once the AL is noted, the ESX orifice opener (20/.08) is used to open up the coronal third of the root, making sure that the file does not pass beyond the AL. Hybridization of Tapers is then initiated using the Expeditor and the two ESX Scout Files (15/.04 and 15/.02) in descending taper (from 15/.05 to 15/.04 to 15/.02) until the AL is reached. In most cases, this sequence will instrument anywhere between one-half to two-thirds of the root even in complex anatomies. After the AL is reached, an apex locator and a radiograph is used to determine the actual working length (WL) by negotiating beyond the AL and to the WL using appropriate small hand files.

Once the working length has been noted and confirmed with a file radiograph, this Hybridization of Taper sequence (15/.05 —> 15/.04 —> 15/.02) is used in a crown-down fashion until the WL is achieved with the Expeditor (15/.05). It’s important to note that each file is used with a Single Stroke and Clean Motion to engagement (not resistance) followed by switching to the next smaller taper file all the way to the WL. This motion is the safest way to use instruments and will dramatically reduce torque on each file. Once the Expeditor has reached the WL, the case is completed following the Basic Protocol by using the appropriate ESX Finishing File. Most Advanced cases are completed with either a size 25/.04 or a 35/.04 ESX Finishing File (Figure 5).

Segmental Crown Down
Excessively difficult cases require even more diligence than typical advanced cases (Figure 5). In such cases, referred to as Advanced2 (Advanced squared!), the canal is broken down into several segments (either thirds or fourths), and each segment is instrumented sequentially in a crown-down fashion. On that basis, small size instruments (sizes 6, 8, and 10 Stainless Steel Hand Files) are used to explore and determine the AL followed by the use of Hybridization of Tapers to that AL. Once the first AL is reached by the 15/.05, a hand file is used again to determine the next AL followed by the same sequence of Hybridization of Tapers. This process of exploration followed by Hybridization of Tapers helps crown down the canal in several segments in a safe and effective manner. The use of stainless steel hand files to first explore the canal is important, as it allows for these stronger metal files to do the more difficult part of discovery followed by the more efficient rotary files to enlarge the discovered space laterally.

Conclusion
The ESX instrumentation system is a versatile instrumentation system that addresses Basic, Advanced, and Super Advanced canal anatomies to be instrumented with the minimum number of NiTi files required for that specific anatomy. This robust algorithm respects the complexity of some clinical cases more advanced users run into while reducing the use of un-necessary files in more basic cases. In addition, the utilization of an advanced bonded bioceramic obturation technique such as EndoSequence® BC Sealer™ (Brasseler USA) can further help maximize the efficiency between the instrumentation and obturation phases of root canal therapy.4

References
1.    Nasseh AA. Clinical Use of the ESX file system. Inside Dentistry. 2014;10(7):74-77.
2.    Nasseh AA. Real World Endo’s Single Stroke and Clean™ (SCC) Motion!  Real World Endo. 2014. Available at https://realworldendo.com/videos/realworldendo-s-single-stroke-and-clean-ssc-motion. Accessed August 25, 2014.
3.    Nasseh AA. The ESX Rotary NiTi Instrumentation System (6 part tutorial). Real World Endo. 2014. Available at https://realworldendo.com/videos/the-esx-rotary-niti-instrumentation-system-6-part-tutorial. Accessed August 25, 2014.
4.    Koch KA, Brave DG, Nasseh AA. Bioceramic Technology: closing the endo-restorative circle, Part 2, Dent Today. 2010:29(3):98, 100, 102-105.