There is no doubt that many different approaches to endodontic shaping and obturation can produce successful results. Even before the advent of greater tapered shaping and thermoplastic obturation, excellent results were often attained by those skilled in the art of the day. With different techniques, all producing to one degree or another successful results, is there some way of evaluating which (if any) system is best? And is the superiority of a particular system, if it in fact exists, enough to differentiate it consistently from all the others?
Figure 1. A radiograph that clearly demonstrates the technique’s ability to shape, debride, and obturate all main and lateral canals.
Figures 2 and 3. Radiographs that demonstrate undistorted shaping apically, while removing minimal dentin coronally.
Figure 4. Further proof that the recommended shaping and obturation techniques provides for distortion-free shaping, while creating 3-dimensional fills.
Figures 5 and 6. Canals with extraordinary curves are routinely shaped to a minimum apical diameter of 35—a space compatible to effective irrigation.
|Figures 7 and 8. The same principle of minimum shaping to at least a 35 is demonstrated in these S-shaped canals. For a shaping system to effective, it must have the ability to widen the canal to a minimum of 35 providing for adequate space for effective irrigation.|
ESTABLISHING CRITERIA FOR EVALUATION
I would suppose that one way to evaluate the value of a system is to use a list of criteria that would outline what it is that we would ideally like to achieve. These criteria might include the following:
- Instruments that stay intact independent of the shape of the canal being instrumented.
- Instruments that do not distort the apical third of the canal.
- Instruments that can be used many times, keeping costs down.
- Instruments which are efficient in their use. (“Efficiency” being defined as the ability to negotiate to the apex with minimal resistance.)
- Instruments that can differentiate between a solid wall and a tight canal.
- Instruments that can differentiate between a round and oval canal.
- Instruments that can be engine-driven to avoid hand fatigue.
- Instruments that can do all the above while shaping canals to a sufficiently wide apical preparation and taper.
- A system that is relatively easy to learn and master.
EVALUATING SYSTEMS AGAINST THE CRITERIA
Interestingly, a number of systems that have been introduced do not include all the above outlined criteria. In my opinion, some new systems have become popular because enough criteria have been met to convince the dentist that they are at least a definite improvement over what was previously used. For example, rotary Ni-Ti has issues regarding breakage and must be used with caution to reduce these incidences. They are recommended for single usage and therefore quite expensive. Often, they cannot be used to widen canals to an apical dimension and taper that we would like to see. They cannot differentiate between a round and oval canal and can never be used in a way that attempts to differentiate a solid wall from a tight canal. However, within their parameters, they will efficiently shape canals distortion-free, with the aid of an engine-driven handpiece taking away a good deal of the hand fatigue that dentists formally had.
Again, while all the criteria for a superior system have not been met, it is likely that the new system is fulfilling more of the criteria than what the dentist was using before. If the doctor had been using K-files to shape the entire canal system, the main criteria met would be that they are low cost. However, thin K-files offer so little tactile perception to the dentist that, in thin sizes, it is difficult to tell when the instrument is binding in the apical third. Without clearly knowing when it is binding, it is quite easy to keep rotating the instrument coronally thinking that the apical end is rotating too when, in fact, it is locked into position. It only takes a few rotations coronally with a K-file locked apically to cause separation.
Poor tactile perception also leads to canal distortions such as ledging, perforations, and transportations. They cannot differentiate between a round or oval canal and cannot differentiate between a solid wall and a tight canal. In short, they have fewer favorable criteria of use than the rotary Ni-Ti systems developed to augment this poorly functioning approach. Please note that I said augment, not replace. Most dentists who use rotary Ni-Ti know that the initial glide path is created with the K-files. Rotary Ni-Ti simply reduces the amount of work that the K-files must do, while not eliminating them altogether.
So when it comes to comparing rotary Ni-Ti systems to K-files, it appears that the difficulty in using K-files is an important reason that rotary Ni-Ti has caught on, even as the K-files must still be used to do the initial canal shaping required before the rotary Ni-Ti instruments are employed with at least a modicum of safety.
A different approach that substitutes K-reamers relieved and unrelieved for K-files, and also substitutes both a tight watch winding motion, as well as a 30º-reciprocating handpiece for full rotations, is a superior system if we use the criteria set up for evaluation of the different systems.
First, where rotary Ni-Ti is recommended for single usage, the instruments in a reciprocating system can be used 6 to 7 times with no downside of separation. In fact, if they are used many more times the downside to the doctor is a dull instrument not a separated one. Next, separation is not an issue because 30º-reciprocation virtually eliminates the torsional stress and cyclic fatigue associated with rotary Ni-Ti. In addition, because they can be used many times before replacement and they cost less than rotary Ni-Ti to start with, the financial burden to the dentist is at least 90% less.
For many reasons, K-reamers relieved and unrelieved produce a superior tactile perception that goes a long way in preventing apical distortions such as perforation, ledging, and transportation. They are also able to differentiate between a tight canal and hitting a solid wall of dentin. In addition, their asymmetric configuration along the length of the canal also gives these instruments the ability to differentiate between a round and oval canal.
These instruments can be used manually, or in an engine-driven handpiece, or both. There are times that an instrument may be negotiated to the apex (or close to it), and then attached to the reciprocating handpiece while it is still in the canal to the manually negotiated length. They can be prebent to take the shape of any canal as well as getting by a variety of blockages that might be present. Of clinical significance is the fact that they can shape a canal to a wider taper and tip size without any fear of breakage. This is important! When the dentist does not have confidence that the canals can be shaped to the desired dimensions because of the fear of breakage, the shaping will often be inadequate that can lead to subsequent inadequate irrigation with debris left in the canals that certainly cannot help the prognosis of the final case.
It is all well and good to speak about the benefits of one system over another, but nothing beats examples of their use to demonstrate their combination of safety and effectiveness.
In Figure 1 you can see a case completed by my partner, Dr. Steve Lipner. Because there is no concern over instrumentation separation, the canals were opened to a minimum of 35, 40 one-mm back and an overlayed 25/06 taper created. Shaping to this degree provides irrigation that is capable of digesting any tissue that may be present in lateral invaginations along the length of the canal. Steve employed a set of K-reamers, relieved and unrelieved, used with a combination of manual and reciprocating engine-driven instrumentation to create the entire shaping. As can be easily observed, a whole series of lateral canals were filled in the apical third. The obturation is a product of a single well-fitted and well-coated point placed into each canal that had been previously flooded with epoxy resin cement. Many advocates of the thermoplastic technique would say that this is impossible, but in reality the technique allows for results like this all the time.
A case that I did can be seen in Figures 2 and 3. This case is clearly an example of the smooth, continuous shaping that can be done with the relieved reamers, either manually, or in a reciprocating handpiece. Once again, and more importantly, the shaping is rarely done to less than a 35-apical preparation. This gives the ability to irrigate much more efficiently than if the preparation is limited to a 20/04 or a 25/06. Instrumenting to this degree may be good for the integrity of the rotary instrument used, but it is not necessarily good for the canal being instrumented.
Please note that in the distal root, 2 canals are coming together. These canal configurations are a concern when rotary Ni-Ti is used because it can lead to immediate separation. When reciprocating is used, these concerns do not exist. Each canal can be instrumented to length and to size, increasing the opportunity for complete debridement of the canal.
This case, seen in Figure 4, clearly demonstrates the correlation between adequately shaped central canals and the ability to obturate lateral canals done with single point systems. By flooding the canals with cement, and then placing a well-fitted and well-coated gutta-percha point, sufficient hydraulic forces are applied to the cement interface to drive it into all the nooks and crannies of the canal system.
The advantage of this room temperature obturation system is the subsequent expansion of the materials as they warm to body temperature. This is clearly an advantage that is just the opposite of any thermoplastic oburation system in which both the cement and gutta-percha shrink back as they cool to body temperature. Common sense tells us that a better seal will be created if the sealing materials expand after they have been placed, but before they set; compared to sealing materials that shrink after placement whether they have set or not.
CASES 4 and 5
In this case, seen in Figures 5 to 8, Dr. Bui shaped and obturated both mandibular molars. While the relieved reamers (used either manually or in the reciprocating handpiece) have the ability to shape severely curved or s-shaped teeth without distortion, there is a key to prevent clogging of the canals that is essential to maintaining these shapes as the canals are enlarged. It is crucial to extend the shaping 0.5 mm to 1.0 mm beyond the constriction thru a size 20 or 25 relieved reamer. By doing this, the buildup of impacted debris is avoided, patency is maintained, and loss of length does not occur. The prime reason for canal distortion—be it ledging, perforation, or transportation—is the deviation of the instrument caused by the impaction of debris. Eliminating impacted debris makes for smooth sailing since even highly curved canals are opened to at least a 30 with a 25/06 overlayed taper.
One can only appreciate the greater ease of apical negotiation and canal enlargement—first with relieved reamers rather than K-files, and then their use in a reciprocating engine rather than rotary Ni-Ti—if this alternative approach is tried. Without trying relieved reamers, a dentist might be content to know that rotary Ni-Ti has improved the technique compared to what he/she had been doing with K-files. However, most dentists who try this new approach are not only delighted by the safety and efficiency of the system, but also by the dramatic reduction in cost.
Dr. Musikant has lectured worldwide in more than 150 locations as well as co-authored more than 300 dental articles published in major dental journals. As a partner in a New York City endodontic practice, Dr. Musikant’s 35-plus years of clinical experience have crafted him into one of the top authorities in endodontics. He can be reached at (800) 223-5394, firstname.lastname@example.org, or essentialseminars.org. Essential Dental Systems offers a variety of workshops, some free and others tuition-based that give the dentist ample opportunity to test our approach to what he/she is presently using. For information regarding any of these courses, contact Ginger Pierro at (888) 542-6376.
Disclosure: Dr. Musikant holds 18 patents for coinventing endodontic products for Essential Dental Systems, a company that he co-founded.