EndoSequence: Melding Endodontics With Restorative Dentistry, Part 2

In part 1, we discussed the differences in shape and reproducibility between constant taper preparations versus variable taper. We also addressed how to achieve endodontic synchronicity and why this will lead eventually to an endo-restorative continuum. The key to achieving this endodontic synchronicity, which ultimately results in the conservation of radicular den-tin, is the file. Let’s begin by examining the design features of the EndoSequence file and see why it’s unique.

RATIONALE FOR DEVELOPMENT 

The rationale behind the development of the EndoSequence file was straightforward. The goal was to create a file that would work equally as well for the general practitioner doing 100 endodontic cases a year, as it would for the specialist performing 1,000 cases annually. Secondly, the instrument had to be a constant taper because such a shape would act as the foundation for creating endodontic synchronicity. Thirdly, an instrument was needed that would conserve radicular dentin. To satisfy this requirement, the EndoSequence .06 taper series of files ends at size 50. Anything larger than this size (in a .06 taper) is generally too large at the top of the canal. (The .04 taper series goes all the way to size 80.) Finally, the instrument had to be efficient. Endodontics can be performed well and it can be done in an expeditious manner. But, the key to having success with speed (in endodontics) is consistent, reproducible results. An efficient instrument is critical if we want to achieve these goals.1

Figures 1. The alternating contact points (ACPs) minimize engagement and promote disengagement of the instrument.

The EndoSequence file is designed in such a way that there are alternate contact points (ACPs) along the cutting surface of the instrument. This design not only keeps the file centered in the canal, but the alternate contact points limit its contact with the dentinal walls (thereby reducing torque) and simultaneously promotes disengagement. Consequently, as a result of its reamer blank design and alternating contact points, the file is never fully engaged (loaded) along its entire length.2 Please rethink what was just described: the reduced torque and the disengagement of the file (created by the ACPs) give you the exact benefits of a variable taper system, but it occurs on a constant taper blank! So, what you have, in fact, is the best of both worlds––reduced engagement and predictable, reproducible shaping (Figure 1).

Cutting Efficiency 

The EndoSequence file has superb cutting efficiency. This is a result of its reamer design (lack of radial lands) combined with electropolishing that results in its extremely sharp edges. Additionally, it possesses a large chip space that allows for excellent debris removal. The efficiency of this instrument is such that the clinician should be aware to clean or change it after every 3 engagements. Each file should work in the canal for no more than 2 to 3 seconds before cleaning or moving to the next sequential instrument. If the instrument is left in the canal longer than 3 seconds, the flutes will become clogged with debris and the file will no longer work as efficiently. In fact, in a recent study on cutting efficiency, Shafer and Oitzinger5 noted that instruments with a triangular cutting section are associated with an enhanced cutting efficiency.

Speed and Ergonomics 

This file has been shown repeatedly through test cases (both clinically and bench top) to work best in a range of 500 to 600 rpm. The ideal speed may vary a little according to personal preference and the engine used: 500 rpm for desktop models and 600 rpm for true portable handpieces. Furthermore, every engine seems to have an optimal rpm for specific files. But why run the EndoSequence file at a higher rate of rpm, when we know that a higher rate of speed will decrease the cycles to failure? Precision is the answer.
Some clinicians, in fact, may be hesitant to run these files at 500 to 600 rpm. In this case, the following formula may be helpful: E = T x S. This means that the energy required to remove dentin (E) is a function of both torque (T) and speed (S). Consequently, if the torque requirements are reduced, the file can be run at a higher rpm. The rationale to go to a higher rpm is that the increased rate of speed allows for greater tactile awareness (increased proprioceptive ability) and more precision.6 The net result is that we will have a better sense of how the instrument is working in the canal (something lacking with landed files).

Figure 3. New digital, portable EndoSequence handpiece.

The EndoSequence technique has also been designed with ergonomics in mind. Therefore, the 2 handpieces we recommend are both rheostat-free. Subsequently, the clinician and the assistant can work with multiple handpieces which will enhance the efficiency of the procedure. The first handpiece (EndoSequence) is a true portable, battery powered handpiece that will work for months before any batteries are replaced. A change in battery technology has made this handpiece the choice of many clinicians. As a result of this improved technology, we no longer have to completely drain the battery before recharging. At any time, simply place the handpiece back into the charging pod and it will recharge.
A further enhancement has been made to this handpiece making it totally digital. A fully digital unit makes it easier for the clinician to change speeds and work in different modes. Also, the charging pod has been streamlined making it even more user-friendly (Figure 3). The second handpiece option associated with EndoSequence is the EndoMate DT. This engine (a desktop model) is also rheostat-free but it does have a corded titanium handpiece. The difference between this and the regular EndoSequence handpiece is the amount of available torque. The DT has a significantly greater amount of torque, which some clinicians prefer.

Expeditor 

Another innovation with the EndoSequence system is the introduction of a new file and concept. This is the “Expeditor.” The “Expeditor” is a 21 mm, size 27, .04 taper NiTi rotary file. The EndoSequence technique is based upon the concept of using an “Expeditor” file that helps the clinician choose the correct canal size and select the appropriate package of files (small, medium, large, or extra large) to properly prepare the canal (Figure 4). Canal preparation generally will require only 3 files, but there is a fourth file in each assortment pack for more challenging cases.
Having discussed some of the design features and innovations of EndoSequence, let’s now examine the clinical techniques.

ENDOSEQUENCE FILE TECHNIQUE (BASIC) 

The EndoSequence instruments come in packages of 4 files each. The selection of EndoSequence files is as follows: an “Expeditor File” (4 to a pack), .04 taper rotary files in sizes XS/S, M, L, XL and .06 taper rotary files in sizes XS/S, M, and L. Naturally, EndoSequence files are also available in individual size packages (Figure 5).

Figure 4. The Expeditor acts as a gauging tool to select the proper package of files.

Figure 5. EndoSequence files are available in both .04 and .06 taper.

Coronal Patency 

Use a No. 10 hand file (possibly a No. 15) to establish coronal patency. This will facilitate the use of the first rotary file. The hand file employed only needs to go to approximately one half the projected working length or until patency is confirmed. This is because if a canal is patent in the coronal half, it generally will be open all the way to the apex. Following the confirmation of coronal patency, we begin our rotary technique.

Figure 6. The ideal package of files is opened depending upon the depth of penetration of the Expeditor.

After coronal patency has been confirmed, we choose an “Expeditor File” as the first rotary file to be placed into the canal. The purpose of the “Expeditor” is to determine the approximate size of the canal and thereafter which package of files should be opened.7 So, in a way, the Expeditor is a gauging tool.
Upon entering the canal with the “Expeditor,” we take this file into the canal only until initial engagement is encountered. Engagement occurs when the file first contacts and cuts dentin. Having gone to initial engagement with the “Expeditor,” we now remove this file from the canal, and subsequently choose the correct package of files to open. This decision is based upon information obtained from the pre-op x-ray, the resistance of the No. 10 hand file, and the depth of penetration of the “Expeditor.” If the “Expeditor” meets engagement at approximately half its length (or less), this signifies a small canal. But, if the “Expeditor” goes down more than halfway, this means the canal is medium sized. A totally loose “Expeditor” signifies a large canal. Once the canal size is determined, you simply pick the appropriate package of files (Figure 6).

Begin the crown down process with the largest file from the selected package as determined by your x-ray, hand file, and the Expeditor. After the second largest rotary file from the package has been used in the canal, determine the final working length with a No. 10 or No. 15 hand file and apex locator. We generally determine working length after the second rotary file to take advantage of the multiple benefits associated with a crown down technique. The first benefit is less binding of the file in the canal. The second benefit and one that is more profound is the following. After having used 2 rotary files, we have generally opened up the coronal half of the root canal system. But while we have opened up the coronal half of the system, we have actually removed 70% to 80% of the contents from the root canal system. This is due to the way most root canals are shaped. Taking a hand file to length, after the coronal half has been cleared, has the additional benefit of making it less likely to carry diseased tissue into the apical area. Net result: less postoperative sensitivity.
Once the working length has been determined, complete the preparation in a straight crown down fashion, taking each rotary file to engagement. The first EndoSequence file to reach working length with resistance completes the preparation. An alternative rule is: first rotary file to reach working length, and then one size larger. Either way works fine. At this point, to confirm sufficient apical sizing, the clinician may choose to use a regular hand file (.02 K file) one size larger than the last rotary file. While maintaining apical pressure, take the hand file a one fourth turn to the left, and then a three fourths turn to the right and remove. In this manner, the hand file will act as an apical verifier.
It also should be noted that if you must crown down all the way to a No. 15 rotary file, we recommend that you loop back with No. 20 and No. 25 EndoSequence files, also taking these to length. We do not advocate finishing the preparation (if possible) with a size smaller than a No. 25. This applies to both .04 and .06 fully tapered preparations.

Obturation 

After the preparation has been completed and fully dried, obturate the canal using the matching (laser verified) EndoSequence master cone and the technique of your choice. An excellent master cone fit will work well with either a room temperature lateral condensation technique, or a warm vertical compaction method. There are other noteworthy changes associated with EndoSequence obturaton.
Obturation has also been enhanced with this technique and the changes begin with the gutta-percha cone itself. Gutta-percha cones vary significantly from one manufacturer to the next. They not only differ in pro-prietary composition, they also differ in true size. This variation can be a serious impediment when fitting master cones to a machined, constant taper preparation. Another limitation has been the historical lack of stiffness in gutta-percha cones. Too often, gutta-percha either collapsed at the end (especially in small sizes) or doubled back on itself. EndoSequence addressed these challenges by making the cones stiffer. In fact, these cones can be pre curved by the clinician.
An additional challenge was to have cones that would precisely fit constant tapered, machined preparations. This was important because, as previously mentioned, endodontic therapy should be precision based. Again, history has shown that there has been significant variation among manufacturers in ISO sized, tapered cones. However, the problem of variable cones has now been solved because the EndoSequence cones are laser verified to confirm their size and taper. The laser verification process is, in fact, applied to every gutta-percha cone at D1, D3, and D16, not merely a random sample. The net result is the creation of endodontic synchronicity between the gutta-percha cone and the canal shape.

ENDOSEQUENCE FILE TECHNIQUES (ADVANCED)

Prior to a discussion of advanced techniques, the differentiation between resistance and engagement must be understood. Historically, when using radial landed files to perform endodontic procedures, they were used (taken) to resistance. This meant that apical pressure was exerted on the file until it no longer advanced apically in the canal despite the moderately applied force. However, engagement is a very different tactile feel from resistance. Engagement is a cutting position in the canal that is short of the resistance point—it occurs before resistance is met. This position can vary from a fraction of a millimeter to several millimeters short of the point of resistance.
In order to understand the concept of engagement you must consider the following fact. If a rotary file is operating at the speed of 500 to 600 rpm (as recommended for EndoSequence files), a cutting blade is making 8 to 10 circumferential rounds of cutting for every second that it is in the canal and is in contact with the canal wall. As previously mentioned, once the file flutes are full of debris, the file is no longer doing any significant cutting and it’s only accumulating more torque. Therefore, the contact time between the rotating file and the canal walls should be minimized and frequent attempts at wiping and removing the debris should be made to allow for minimum loading of each file.
The point of engagement occurs when the file is in contact with the canal wall for no more than a second and the flutes are loaded. At this point, the file should be removed from the canal and wiped clean prior to further cutting. This light, gentle wiping action produces the feeling of delaminating the dentin one layer at a time. Therefore, engagement can be considered to have occurred when enough debris has filled the flutes of the file such that it needs to be wiped clean. This means no more than one second of contact in the canal when you are dealing with an efficient reamer at a higher rpm. Consequently, if an overly ambitious attempt is made to bite off more than the file can chew, the file may overload. This is a universal rule of safety and applies to any instrumentation system on the market today.8

Once you understand the difference between engagement and resistance, we can proceed to advanced techniques. There are 2 advanced techniques primarily associated with EndoSequence. The first is relatively straightforward (a modified crown down) and the second is a technique based on the “cycling” of rotary instruments. Let’s first examine the modified crown down technique (Table).
As usual, we begin by confirming coronal patency with a No. 10 hand file. This is extremely important when treating narrow canals. We start the crown down preparation with a No.25/.04 taper EndoSequence file. We take this file only to engagement. Generally, this goes down the canal about 15 mm. We then follow this with the No. 30/.04 EndoSequence instrument. Likewise, we take this file also to engagement and it generally goes one to 2 mm less than the initial file. However, after only 2 files, we have successfully preflared the coronal half of the canal. We now determine our final working length with a No. 10 stainless steel file and an apex locator. At this point, a glide path to the final working length can be created with a No. 10 or No. 15 hand file. Following length determination or creation of a glide path, we return to our original No. 25/.04 file. As usual, we work this file in the canal to engagement. But instead of just going to 15 mm, the EndoSequence file now tracks down to about 18 mm. This is what is really sweet about this technique. Following this, we take the No.20/.04 to engagement. Quite often the No.20 file will reach the final working length. If not, continue the crown down with a No. 15/.04 and generally this will get you to your final working length. If in order to reach the final working length, you had to crown down all the way to the No. 15 file, we recommend that you loop back with a No. 20/.04 and then a No.25/.04 and also take these to length. We do not advocate (ideally) finishing a constant .04 taper preparation with an apical size less than a No. 25.
However, this technique is not limited only to narrow canals. It will work on all canals, if you just increase the size of the instruments. Once you understand what engagement is, and how it differs from resistance, this sequence will produce consistent, predictable results. We believe this is both a terrific and straightforward technique.
Another advanced technique for EndoSequence is one developed by Dr. Ali Nasseh, an endodontist in Boston. This is the concept of “cycling” instruments. Here is how Dr. Nasseh describes it (personal communication, July 10, 2008):
“The advanced EndoSequence technique is based on the concept of sharing the task of cutting dentin among several files, while emphasizing the fact that each file only removes a small amount of dentin in a crown down fashion. This minimal cutting and the usage of several files in a predetermined sequence, along with this file’s triangular cross section, imposes minimal torque on each file. The sequence of files used in this technique is referred to as a “cycle.” A series of files is laid out in sequence in this cycle and the first file is followed by the second, third, and so on until the last file is used at the end of the cycle. Once the end of the cycle is reached the file sequence is repeated from the beginning for a second cycle. Multiple cycles are used until the desired file reaches the apex. The final file is the Master Apical File which will be fitted with the corresponding EndoSequence or Active GP cone and obturated. The EndoSequence files in each cycle consist of sizes 40/.04 through 20/.04 in descending order of size. Therefore, each cycle consists of a total of 5, .04 constant taper EndoSequence files.”

Figure 7. The repetition of “cycles” significantly reduces stress on the instruments.

“After straight line access and identification of the canal orifice in a molar root canal and checking patency with size 10 hand file, a size 20 or 25/.06 EndoSequence file can be used lightly as orifice shaper. After the use of the orifice shaper file and the confirmation of a patent canal with hand files the cycle begins (Figure 7). A size 40/.04 taper file is introduced with a very light touch. Heavy engagement will be encountered very quickly due to this file’s large size. This means that the file is only used once with a single gentle motion (enough to engage the flutes and grab a chunk of dentin with its tip). The next file in the cycle, (35 /.04) is now introduced. It’s important that each file is used in a gentle, one- or 2-stroke motion with minimal engagement. Each file gently shaves off a thin layer of dentin from the canal walls and is not forced at any time. After each use, the next successive file (smaller tip) is used in this crown down fashion until either the end of the cycle is reached (size 20/.04) or a larger size file already reaches the apex. If a size 20/.04 is used and the apex is still not reached, a new cycle should begin (back to size 40/.04). If the apex is reached before the end of the first cycle (eg, size 25/.04 reaches apex before size 20/.04), and if that size is too small for a Master Apical File, then the cycle begins from the beginning, skipping smaller sizes (it would be redundant to take a smaller size file to the apex when a larger size has already reached the apex). It’s also better to start from the beginning of the cycle rather than moving back up the cycle one file. Often, larger size files may reach the apex if a crown down method is utilized. What size Master Apical File should be used for a given canal is a decision that cannot be made without considering the root shape, curvature, internal diameter of the canal vs. the external root diameter, root anatomy, and other related factors. No universal number is available for this decision. The only guiding principle is that the apical diameter should be the minimum size that allows for complete cleaning, disinfection, and obturation of the root canal space without compromising the structural integrity of the root.”

What is quite unique about Dr. Nasseh’s technique is that it also addresses the question of cyclic fatigue. By using the files in the manner described, he significantly reduces the cyclic fatigue of each instrument. This is critical because cyclic fatigue, unlike excessive torque forces, cannot be seen. Therefore, this is a technique that not only facilitates the treatment of difficult cases, it is also a method that will significantly reduce the potential for file separation (Figure 8).

CONCLUSION 

In part 3, we will complete the circle of endodontic synchronicity by discussing advanced obturation techniques (including the introduction of a new material), a new post system that requires no alteration of the root canal space prior to insertion, and retreatment. As always, the goal remains the same: to teach techniques that give the greatest percentage of dentists possible, the ability to produce stellar endodontic results.

References

Dr. Koch is the founder and past director of the New Program in postdoctoral endodontics at the Harvard School of Dental Medicine. In addition to having maintained a private practice limited to endodontics, he has written numerous articles on endodontics and lecturers world wide. He is a co-founder of Real World Endo and can be reached by visiting realworldendo.com.

Dr. Brave is a Diplomate of the American Board of Endodontics and is a member of the College of Diplomates. In endodontic practice for more than 25 years, he has lectured