From 1995 to 1997, I had the distinct honor of studying endodontics under the late Dr. Herbert Schilder at Boston University. While Dr. Schilder is recognized as the founding father of “Vertical Compaction of Warm Gutta Percha”, his greatest contribution to endodontics was more likely in the realm of “Cleaning and Shaping”.
While a variety of NiTi Rotary systems were developing and evolving at that time, in our residency, we were wisely trained to clean and shape using hand reamers and files. Dr. Schilder’s reasoning was simple. While rotary instrument technology can be beneficial to the practice of endodontics, it certainly must not be viewed as a “magic bullet” but as a potentially valuable and efficient resource when logically applied under the appropriate circumstances.
So, practitioners need to be highly skilled in using hand instruments for canal cleaning and shaping. This mastery provides the clinician with a baseline for comparing different endodontic systems, hand or rotary. Another value of mastering hand instruments is the ability to treat RCS that are not good candidates for rotary instruments.
In my endodontic practice, the typical case that I see has a calcified RCS. I define a calcified canal as one that will accept an ISO size 10 or smaller file. Therefore, a certain amount of preliminary work with hand instruments is necessary to prepare the canal to accept a rotary instrument system. This process is what I call “standardizing the case”.
The process of standardizing requires initial utilization of hand reamers and files to open the body of the canal. Once the body of the canal is opened up enough so that an ISO #20 can be introduced to the apex without difficulty, it has been “standardized” and is ready for the introduction of rotary instruments. Obviously, if the canal is not calcified and an ISO size 20 or larger slides nicely to the apex, then the possibility of introducing a rotary handpiece, such as the NuTorque™ Electric by StarDental®, earlier in the case can be considered.
My clinical approach to treating endodontic cases nonsurgically utilizes the “Five Mechanical Objectives for Cleaning and Shaping”, as outlined by Dr. Schilder. Following the Five Mechanical Objectives ensures a preparation where the canal is cleaned and shaped to facilitate three dimensional canal obturation.
Briefly, the 5-Mechanical Objectives can be described as:
- Funnel-Form Shape.At the most basic, the shape must narrow from the orifice to the apical foramen.
- Cross-Sectional Diameters. To refine the concept of a tapering shape, the canal preparation should gradually and progressively get smaller as one advances apically. In other words, no matter how close together the cross-sections are, the next cross-section apically should be smaller. Consequently, areas of parallelism in the preparation are avoided.
- Concept of Flow. The canal preparation must follow the curvatures of the root not only along the plane of the film, but in and out of the plane of the film.
- Never Transport the Apical Foramen. There are two ways to transport the apical foramen, internally and externally. Internal transportation occurs when a blockage of debris is established. If this debris can not be disrupted, a false path or iatrogenic canal may occur.
External transportation occurs when the apical foramen is over-enlarged or the apical foramen is ripped. Both situations stem from aggressive use of instruments at the apex. Another way external transportation can occur is when the false path is pursued until a perforation occurs.
- Keep the Apical Foramen as Small as Practical. This has been misrepresented in the past by lecturers and authors who say “keep the apical foramen as small as possible”, this is wrong! The whole goal is to discover the natural size, diameter, or bore of the apical foramen and NOT manufacture it to a preconceived size. This technique requires delicacy!
To arrive at the design criteria outlined by the “Five Mechanical Objectives for Cleaning and Shaping,” I think of cleaning and shaping in four fundamental phases:
- Establishment of Canal Patency. This is accomplished by using appropriately fine hand instruments along with frequent irrigation using sodium hypochlorite. A chelating agent is also beneficial when dealing with tenacious and collagenous pulp tissue.
- Opening the Body of the Canal. In this phase, the coronal two-thirds of the canal is opened up using hand instruments in a reaming action and Gates-Glidden drills. At this point, I also can incorporate the NuTorque handpiece, as its smooth operation helps to blend the coronal two thirds into the apical third.
- Refinement of the Apical One-Third. Here, hand instruments are used in a filing action to advance the shape established in the middle one-third apically to the foramen. There are times when I will re-introduce rotary files with the NuTorque handpiece in order to help with final smoothing and refinement of the apical third prior to the cone fit. This will help avoid violation of Mechanical Objective #5 by iatrogenically altering the apical foramen.
- Cone Fit. If the cone buckles during the trial fit then the third phase must be revisited. An appropriate cone fit will have tug-back resistance, the tip of the cone will approximate the size of the tip of the final instrument that goes into the apex, and radiographically, the canal walls must not meet the sides of the cone at any place along the length of the cone except at the apex.
Because endodontic instrument separation is a counterproductive event, I am very cautious when it comes to the use of rotary instruments. When a handpiece does not incorporate a safety feature that warns the operator that instrument separation is imminent, the clinician must resort to an arbitrary means to control this variable.
The NuTorque Electric System by StarDental is equipped with several important features including customizable torque control and auto reverse, that drastically reduce the risk of instrument separation. Its flexibility, wide range of features, and smooth operation have established the NuTorque as a fully incorporated handpiece in my office and has greatly enhanced my process of smoothing and refining the apical third.
The NuTorque has a built-in torque limitation. By setting the torque limit as directed by the file manufacturer, the system has three reverse options for when the Newton-cm setting is met: one, the rotation stops; two, the rotation stops then reverses; and three, the rotation stops then reverses, and then proper rotational direction starts again.
TheNuTorque electric handpiece has a variety of attachment options; both high-speed and slow-speed, and all have fiber optic lighting. This is a feature that I really like, as proper lighting is critical when looking into an endodontic access. While using the high speed function, the handpiece is very quiet, a pleasant benefit to patients who are phobic of the whine of a pneumatic high-speed handpiece.
Moreover, the operation of the handpiece has a constant and reliable continuum – it remains smooth and maintains consistent power, regardless of the procedure or environment it is being used in. It does not matter whether the endodontic access is being made through a PFM crown, porcelain crown, cast crown, or a tooth restored with either composite or amalgam, I find the operation pleasantly consistent and smooth.
Much like a pneumatic handpiece, the rotational speed of the NuTorque can also be feathered with the rheostat. This gives the handpiece an operational feel very similar to a pneumatic handpiece, but with the consistent cutting power that electric systems are known for.
With 5 endodontic presets and 2 general presets, the NuTorque electric handpiece offers 29 possible reduction ratios and torque settings. For endodontics, the system can be set to accept a wide range of files. Like any new technology, there is a learning curve to master all of the options and features that the NuTorque offers. Many of us tend to quickly find our favorite settings and then not venture much beyond. But try to resist this temptation!
To go beyond the limitations of your favorite initial settings, take a day to yourself and explore the various functions and features of this multifaceted piece of technology. I found the NuTorque to encompass significant benefits – if you just take the time to explore its many features.