My father has often told me that we dentists are penny smart and dollar stupid. We tend to focus on saving a little on supplies and such to keep our overhead down, but we often miss the bigger picture and become inefficient. Efficiency in the operatory and around the office can really add up. If you do 10 procedures a day and find a way to efficiently shave five minutes from each procedure without losing quality of care, that would really help your bottom line. This would allow you to either add one more procedure per day or leave the office one hour earlier. I have found a few things that make me more efficient around the office: technology (such as digital radiographs) and office software for a virtually paperless office. But the most important variable in my efficiency is my NiTi rotary armamentarium.
I use files with different designs for cleaning and shaping different parts of the tooth. This concept is based on Dr. John McSpadden’s “Zone Technique,” which actually divides the tooth into two zones. The first zone is the “coronal zone” since it is coronal to the canal curvature. The second zone is the “apical zone” since it is apical to the curvature. Each file has various attributes that make its design better for working in different parts of the canal system. Understanding what each file can and cannot do allows you to maximize that file’s efficiency and more effectively clean and shape the entire canal system. The Zone Technique minimizes both the torsional stresses put on the files and the chance of torsional separation.
Canal anatomy, file design, and file dimension all come together to determine how a file will react in a given canal. Understanding the consequential relationships of file design and canal anatomy are important in understanding how files function most efficiently. No amount of research can establish with absolute certainty what a file will do in all cases, but research can give us a high level of predictability in those given situations. This knowledge then guides us in instrument and technique design.
Dr. John McSpadden has developed the following considerations and ramifications of designs that are important in formulating techniques for difficult endodontic cases:
①A file with a more efficient cutting design requires less torque, pressure, or time to accomplish root canal enlargement.
② In a straight canal, the ability of a file to withstand torque is related to the square of its diameter.
③In a curved canal, the ability of a file to resist fatigue has an inverse relationship with the square of its diameter.
④The torque required to rotate a file varies directly with the surface area of the file’s engagement in the canal.
⑤ Fatigue of a file increases with the number of rotations of the file in a curvature.
⑥ Fatigue of a file increases with the degree of curvature of the canal.
⑦ To improve efficiency, the smaller the surface area of a file engaged in the canal, the greater the rotation speed should be.
⑧ The more spirals a flute has per unit length around the shaft of a ground file, the less resistance to torsion deformation there is, but the more flexible the file is.
⑨The fewer spirals a flute has per unit length around the shaft of a ground file, the more it resists torsion deformation, but the more rigid it is.
nt-family: "Janson Text LT Std"; ">The sharper the cutting blade of a file, the fewer spirals per unit length the file should have.
⑩The greater the number of flutes with similar helix angles, the greater tendency a file has to screw into the canal and become bound.
⑰Maximum engagement of a file occurs when it progresses into the canal at a rate equal to its feed rate, the rate at which the file progresses into the canal without application of positive or negative pressure.
⑱Less canal transportation occurs when a file has greater flexibility, an asymmetrical cross-section design, and/or a land.
I begin my cases with a 25/.06 17mm Quantec file, which offers great strength combined with some flexibility for opening the orifice of the canals. Then, I like to change my taper and tip size dramatically. This usually takes me to a 15/.02 Quantec SC, which is one of my favorite instruments. This instrument is extremely efficient because of its safe cutting tip. The safe cutting tip also allows it to negotiate canals that traditional hand files or even other rotaries with noncutting tips cannot negotiate. I find these attributes particularly useful in negotiating MB2 canals of maxillary molars. These canals are notoriously difficult to find, and when found, are often difficult to negotiate. The 15/.02 Quantec SC makes this a much more efficient process. I am able to negotiate canals that I used to have great difficulty placing size .08 or .10 hand files into. Of course, the microscope helps with visibility in locating these MB2s also.
After I have negotiated to my estimated working length (WL), I use a 35/.08 instrument to work the coronal aspect of the canal a bit more. This is followed by a 25/.04 K3 to work a different part of the canal system. Alternating the tip size and taper with every instrument minimizes the torsional stresses placed on each instrument as well as the incidence of torsional fatique. This, in turn, reduces the likelihood of having a separated instrument. Each instrument is chosen to work a specific part of the canal, which creates a more efficient cleaning and shaping regimen. I can now find my working length with the SybronEndo Elements Diagnotic Unit and verify with digital radiographs if needed. An accurate electronic apex locator is indispensable in an office which performs endodontics regularly. It quite simply removes the guesswork from establishing a WL in each canal.
Now that the working length has been confirmed, I can use a 25/.02 Quantec SC to clean to the apex in most cases, instrument coronally, and then blend the coronal and apical portions together to create a canal with smooth constant flow. Every canal has a unique morphology. With this in mind, they should all be treated differently with a specific protocol for each canal. This might sound a bit complicated, but it is actually quite efficient in that it reduces wasted steps and motion that many others follow in their cookbook approach to cleaning and shaping the root canal system.
Dr. Herb Schilder’s “Five Mechanical Principles of Cleaning and Shaping” states the following:
①The well-shaped canal should have the shape of a continually shaped canal.
②The diameter of each cross-section becomes narrower apically.
③The concept of flow: make the preparation in multiple planes.
④Never transport the foramen.
⑤Always keep the foramen as small as is practical.
There are many ways to mechanically clean and shape the root canal system. However, when you let go of the dogma of the cookbook approach, which says this is followed by this, you are free to visualize what is actually happening in the canal itself. When you can visualize the canal three-dimensionally and understand where each file contacts the canal walls and why, you then are free to efficiently clean out the root canal system mechanically.
Dr. Matthew Brock is in private endodontic practice in Chattanooga, Tenn. He is also a part-time clinical instructor at UT Memphis College of Dentistry. He has conducted research on NiTi endodontic files since their development in 1991, and has lectured nationwide on this technology to promote NiTi rotary instrumentation expertise through understanding. For more information on this article or available courses, please contact Dr. Brock via e-mail at [email protected].
