Endodontic Instrumentation Options
Choosing proven devices that provide clinicians with predictable results
Endodontics has witnessed many changes within the past 20 years. Principal among these has been the method in which we shape and instrument a root canal. Canal preparation has been facilitated by better materials, improved file design, and more user-friendly techniques. Consequently, we now have many more options than ever to achieve the shaping portion of the cleaning, shaping, and obturation triad (Figure 1).
However, it should be emphasized at the outset that the most important goal of treatment remains the disinfection and removal of the pathogens1 from the root canal rather than shaping the canal for obturation. Studies have demonstrated that mechanical instrumentation alone, whether with nickel-titanium (NiTi) or hand files, is inadequate in fully disinfecting the root canal system.2,3 Therefore, an efficiently prepared root canal using the latest file will fail clinically if microorganisms are not thoroughly removed through proper irrigation and disinfection.
Although NiTi and rotary instrumentation alone have not been shown unequivocally to improve clinical outcomes,4 efficient shaping of the root canal system in combination with effective disinfection and aseptic protocol remains the best available method to achieve clinical success at the present time. Multiple instrumentation systems are available to the clinician today. How do these systems differ, and is one better than the others? How can the clinician decide which system is best for him/her? To fully evaluate these questions, some historical perspective is required.
Evolution of File Design
The first change in the way of instrumenting a root canal came with the conversion of carbide steel hand files to stainless steel hand files. This was significant in terms of repeated use and sterilization aspects. Stainless steel hand files became very popular, and although they were initially of a K-file and reamer design, hedstroms soon became accepted as well. Reamers were used with a circumferential technique, whereas K-files employed a quarter turn twist and pull method. Due to their greater cutting efficiency, hedstrom files were used with a push and pull motion.
The next major change (and a seminal event in endodontics) was the introduction of NiTi rotary files in the early 1990s. For those using hand instrumentation, the shift to a rotary technique was significant for a number of reasons. Initially, clinicians realized that a rotary technique was less fatiguing to the practitioner and, more importantly, produced a predictability of shaping not seen with hand instrumentation. A further benefit of this new technology was a dramatic decrease in instrumentation time and a reduction in procedural errors such as ledging and transportation. On the other hand, if a technique or design increased torque and cyclic fatigue on a given file, NiTi file breakage occurred.5 As more dentists began utilizing rotary instrumentation and techniques and designs became more refined, however, the incidence of file separation dropped significantly and the benefits of NiTi rotary instrumentation became firmly established.6 At this point, the addition of a high-torque rotary engine that could operate between 300 and 1,000 rpm became a staple of endodontic armamentarium and a requirement for those practitioners adding rotary instrumentation to their practice.
The first rotary file introduced was LightSpeed. This file shaped canals by cutting at its very tip. This design shaped canals effectively but required a very large assortment of files to do so, thus prolonging the shaping process. As a result, longer cutting shank instruments were developed by other manufacturers that extended the cutting surface to the traditional 16 mm seen in hand instruments.
Products such as the ProFile® (DENTSPLY International, www.dentsply.com); Quantec™, K3™, and Twisted Files™ (Sybron Dental Specialties Inc., www.sybronendo.com); GT®, ProTaper® Universal, ProTaper NEXT™, GT® Series X, and Vortex® (DENTSPLY Tulsa Dental Specialties, www.tulsadentalspecialties.com); HERO Shaper® (Micro-Mega www.micro-mega.com); RaCe™, BioRaCe™, and EndoSequence® (Brasseler USA, www.brasselerusa.com); Liberator™ (Integra Miltex, www.miltex.com); V-Taper™ (Guidance Endodontics, www.guidanceendo.com); HyFlex® (Coltene Group, www.coltene.com); and others evolved during this rotary NiTi instrumentation period, which spans to today. These files differed from each other by variations in their design, cross sectional shape, cutting edges, pitch and helical angles, metallurgy, surface polishing method, speed, and other unique characteristics.6 More rotary files are being designed at the time of writing this article, and clinicians are nearly guaranteed to see additional files released to the market soon.
If the number and complexity of the rotary file systems were not confusing enough, another camp began to claim that rotary instrumentation’s shortcomings can be overcome by a whole other method of file motion in the canal that involves instrument reciprocation along its own axis. SafeSiders® (Essential Dental Systems, www.edsdental.com), WaveOne® (DENTSPLY Tulsa Dental Specialities), and Reciproc® (VDW, www.vdw-dental.com) are some examples of this alternative method of canal instrumentation. Each system has its own specific and somewhat proprietary reciprocal motion during instrumentation. Although reciprocation is marketed as a safer method of canal instrumentation than rotation, clinical or scientific evidence does not yet exist to support this claim.
While reciprocation and rotation camps were busy fighting regarding the merits of instrumentation motion, a novel concept of instrumentation and file design was introduced. This was the self-adjusting file (SAF). The SAF was a departure from traditional instrumentation technique. This file consists of a hollow, collapsible cylinder made up of a very thin NiTi lattice that adapts to the canal walls and sandpapers the dentin instead of cutting it. Some studies showed this file to be effective at adapting to canal walls but its efficiency was questionable compared with the traditional rotary instrumentation. Furthermore, final shapes created by the SAFs were nontraditional and canal obturation was a challenge. Both reciprocation and SAF systems require additional investment on the part of clinicians, as a new mechanical engine is required to utilize each file system. Therefore, because neither system has proved superior in a definitive way to the traditional rotary instrumentation, their appeal appears limited to those entering NiTi instrumentation for the first time and those who do not already own a high-torque, low-speed rotary engine.
Given the limited scope of this article, only three of the numerous file systems mentioned earlier are briefly discussed here. For more detailed information, the reader is encouraged to study the technique card associated with each system. The instrumentation systems discussed here are some of the more popular files in the North American market at the present time and no endorsement is implied in their inclusion. The ProTaper Universal, EndoSequence, and WaveOne instrumentation systems will be briefly described here.
The ProTaper is a modified reamer with a variable taper blank. This system uses six files to instrument most canals. The first file, SX, is an orifice shaper with a size 19 tip. Additional files S1 and S2 have size 17 and 20 tips, respectively, with variable tapers up the cutting shank. After preparation of the canal with SX, S1, and S2, the three finishing files (F1, F2, and F3) subsequently finish the preparation depending on the desired apical diameter and the complexity of the case. These files at the tip are sizes 20/.07, 25/.08, and 30/.09 respectively. The later addition of ProTaper Universal file system added two additional finishing files (F4 and F5, with size 40 and 50 tips, respectively) for finishing larger diameter canals.
All ProTaper finishing files are variable taper and have diminishing taper along the cutting shank. The recommendation is to take the ProTaper file to resistance without forcing the instrument. It is also recommended by the manufacturer to use the file in a brushing action on the withdrawal stroke in order to create straight-line access and to passively progress to the apical area. Additionally, the ProTaper guidelines recommend using a SX file to relocate the coronal aspect of the canals away from the furcation area (a type of an anti-curvature filing motion.) Finally, this file operates at 300 rpm and the directions for use recommend taking the ProTaper finishing instrument to length only once and for no more than one second, or one may risk transportation.7
If these techniques are followed closely, a predictable instrumentation system is possible for a large portion of clinical cases. (Note: at the writing of this article, ProTaper NEXT was not yet released to the market. This system was therefore not included in this discussion.)
The EndoSequence File is a true reamer. This electro-polished, triangular-shaped file with constant taper is very sharp and highly efficient in cutting dentin. Unlike many other file systems on the market that limit the clinician to a specific sequence of files for use, the EndoSequence come in nearly all ISO file sizes. Files with tip sizes 15 to 80 are available in .04 tapers and sizes 15 to 50 are available in .06 tapers. This provides the clinician with a very large repertoire of files that allows for customization of a preferred sequence for use. Furthermore, a great variability of cases with diverse apical diameters can be handled within the system. The file operates at 500 to 600 rpm.
The procedural EndoSequence technique is based on three procedural packs: sizes small, medium, and large for corresponding canals. Each package contains four files. An expeditor file screens the canals and the corresponding procedural pack is opened for that given canal. A pure crown down approach is used from the larger to the smaller of the four files in the package until the desired apical file reaches the apex. Because reamers are very efficient at removing dentin, debris will accumulate on the file fairly rapidly. Therefore, each EndoSequence file is engaged in the canal only one or two seconds at a time. This action allows sharing of the cutting burden between four files. This technique efficiently prepares the root canal.8 The author uses this system in standard clinical cases (Figure 2 through Figure 4).
For more complicated cases, hybridizing the EndoSequence files with BioRaCe files allows handling of more sophisticated canal anatomy (Figure 5 through Figure 7). This specific technique sequence has been developed by the author and requires a total of 6 files (2 BioRaCe and 4 EndoSequence Files), but this hybridization reduces the torque on each file dramatically and allows the management of more complicated anatomy by sharing the burden of cutting dentin among several files rather than only one or two files. Although a larger number of files are used in this hybridized technique, in the author’s opinion, the overall outcome is more efficient because the rate of procedural errors such as file separation and ledging is reduced as a result of sharing the cutting burden. When multiple files are used, each file does some of the work and gets stressed less compared with systems where a single file is doing all of the work.
Reciprocating files are a relatively new option available to clinicians. The WaveOne system uses a single-file technique with a reciprocating file and a proprietary engine for instrumentation. Although reciprocating file systems have not yet passed the test of time, the WaveOne is worth mentioning here as a popular representative of this type of instrumentation. The technique is as follows.
Select the appropriate WaveOne file (one of the three files, most often the Primary WaveOne, which is a 25/.08 file) and initiate the shaping procedure in the presence of an irrigant/lubricant. Use a gentle, inward pecking motion with short 2- to 3-mm amplitude strokes to passively advance the WaveOne down the canal. Continue with this motion until the instrument no longer easily (and in a passive manner) progresses apically. Withdraw the instrument from the canal, remove the debris from the flutes on the file, and repeat the procedure until the coronal two thirds of the canal space has been shaped. After the apical third has been negotiated with a hand file (and working length established), take the WaveOne file all the way to the final working length. The final shape is confirmed if the apical flutes of the file are loaded with debris. The manufacturer additionally notes that re-use of the WaveOne files can increase the risk of cross-contamination and breakage.9
A potential disadvantage of single file systems is the inability to accurately gauge the apical diameter prior to instrumenting that space. If a single file has to be chosen before instrumenting the apex with an appropriately sized file, either over-instrumentation or under-instrumentation of the apex is a potential occurrence. If additional files are needed for instrumenting that space for proper fit, the promise of a single file technique has then been violated.
After examining all the various file options available, one comes to the conclusion that, in fact, they all work. Indeed, excellent results can be achieved with all of these instruments if used properly. The author recommends employing a file technique that works well in each clinician’s hands and is compatible with his or her personal philosophy, such as being conservative in the coronal two thirds of the root. This is critical. Also, it is paramount for the long-term success of the tooth to have a technique that allows you to fill the canal space without having to remove further coronal tooth structure. Think endodontic synchronicity. This is so important because endodontics is not just about debridement and disinfection. It is about connecting a bridge between endodontics and the ultimate restoration of the tooth. In essence, one can think of it as an endo-restorative continuum.10
Other instrumentation options will surely be introduced in the near future that may improve the efficacy of care as well as its efficiency. When such instrumentation systems arrive, it will be very important for practitioners to decipher between manufacturer claims and scientifically tested evidence substantiating such claims. Disruptive technologies using lasers, sonics, and ultrasonics to achieve endodontic success have long been the promise of the “next” breakthrough technology for the past 30 years. These methodologies have yet to show clear science to merit the paradigm shift in thinking they would require from the practitioner, however.
Furthermore, a worrying current trend involving reducing the number of files needed to perform root canal therapy appears to be underway. The competition among manufacturers and pressure to introduce the next competitive file to the market has resulted in several manufacturers claiming that fewer files are now needed in their techniques to perform root canal therapy. Whether such claims are substantiated by science or are just marketing claims is presently unclear. If these claims prove to be marketing ploys to sell endodontic armamentarium, we can be certain that our patients have the most to lose in this transaction. What is intuitive to all clinicians is that the apical diameter can not be determined with accuracy preoperatively. Therefore, assigning a single file for any given root in advance of properly gauging the apical diameter is counterintuitive to any experienced practitioner. What appears intuitive is that safe manipulation and enlargement of most root canal systems requires more than a single file. Clinicians must be prudent in following manufacturers’ advice in the absence of clear scientific evidence supporting such claims.
The high success rate of endodontic therapy using older, conventional methods should serve as a reminder that the current state of clinical treatment is already highly predictable.11,12 If performed under the current standards of care, we can improve our success rate an additional 5% to 10% from the baseline. But we can do so only if we embrace a clinical methodology that is shown to work scientifically rather than adopt one that is marketed more proficiently. Technology can improve the efficiency, comfort, and cost of procedures even if dentists maintain the current success rates. Improving efficiency, comfort, and cost of each endodontic procedure through lowering overhead cost of instrumentation is a win-win for both the patient and the practitioner, provided that we do no overreach in this process and affect clinical case outcomes.
There is no best instrumentation system/method that has been shown unequivocally to improve case outcome during endodontic therapy. In fact, there appear to be as many instrumentation techniques as there are operators using files.
Each practitioner must experiment with as many file systems as possible to make an informed choice about which system works best in his or her hands. This also can be achieved through continuing education courses and obtaining further training for various available systems. Practitioners should be cautious in deciphering facts from marketing. Systems that appear to oversimplify should be rigorously researched.
The author received material support from BrasselerUSA for this manuscript.
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Allen Ali Nasseh, DDS, MMSc
Department of Restorative Dentistry and Biomaterial Sciences
Harvard University School of Dental Medicine