Click here to enlarge imageRotary endodontic procedures are now an established part of dental treatment. Between the two of us, we have performed over ten thousand rotary cases, and, at times, we learned proper technique the hard way. While there is no difference in separation between stainless steel hand files and NiTi rotaries, there is a significant difference in rotary technique. It is extremely important to understand what causes breakage with rotary files. The key to minimizing separation is prevention. If you know what causes separation, you can prevent it. We can separate these "gems" into five areas: access, the file itself, concepts, technique, and operatory management. In Part One of this article, we will discuss various "gems" we have learned concerning the first three. Techniques and operatory management will be discussed in a subsequent article.
The file
Our first "gem" involves the condition of the file. Always monitor the condition of your rotaries; when you see evidence of unwinding (shiny mark on the file), discard the file. Rotary files, when stressed, actually elongate. Unwinding is a prime indicator. Rotaries by design are meant to unwind before they break. Your assistant should have alcohol gauze pads to wipe off the file after every use in a canal.
Another "gem" concerns the length of the file. We now have the option of 17, 21, 25, and 30 mm. files. However, the two most common sizes are 21 and 25. We believe there is a significant difference between a 21 mm and a 25 mm rotary file. Most endodontists use 21 mm. files and for good reason: They offer more tactile awareness and are seemingly more resistant to breakage. We seriously believe that you will have fewer breakage problems if you use 21 mm length files.
Whatever file system you use, make some notation how you can mentally extend the length of the file onto the handle. This will help you as you treat more molar cases. The most difficult cases for rotary instrumentation usually involve mandibular molars with MB roots that are 25 mm plus. If you start with a 25 mm file, you can feel it grinding and working along the entire length of the file. The best way to handle this is to start with a 21 mm file. A 21 mm file can be used to a length of 23 mm if you know where the 2 mm mark is on the handle. Most rotary files have a "shoulder" that is 2 mm from the beginning of the handle. Instrument the canal to 23 mm, making certain that you maintain patency. After it has been instrumented to the proper size at 23 mm, it only requires one or two 25 mm files. Take the 25 mm files to full length. However, these files are now only engaged in the apical 2-3 mm. This takes a lot of stress off the file.
Here is another tip for file usage: Never run a file dry. Keep it in a moist environment (NaOCl or EDTA). At the beginning of your crown-down procedure, use a lubricant such as RC Prep or ProLube. Simply coat the file with the lubricant. The lubricant will help the file function in a smooth manner, and it will emulsify the tissue in the coronal half of the canal.
The creation of a glide path with a hand file will also help a rotary file to perform at maximum capability. We recommend creating a glide path when you establish your working length. This is after the coronal half of the canal has been opened by the crown-down technique. The path will be created with a No. 15 or No. 20 hand file. Do not attempt to create a glide path at the start of treatment, as this is when the clinician is most prone to ledging and transportation errors.
The last tip concerns the amount of time you will be in the canal with a rotary file. Most rotary techniques require being in the canal for only 3-10 seconds. Many clinicians spend too much time working the rotary file in the canal. After 10 seconds, most rotaries are no longer working properly. This is because either their flutes are full or the file is loose in the canal. Leaning on the rotary file and forcing it to "work" will only result in fracture. This is a big problem. Many clinicians are accustomed to using a hand file for a period of two to three minutes in a canal. Do not use a rotary for this period of time. Use it in the correct manner; be in the canal for no more than 10 seconds. This will further reduce the chance of separation.
For a torque control engine to work properly, the file must engage the canal wall. If a canal has been over-instrumented, we no longer have the "circumferential grab" necessary for the engine to reverse itself. This is why we can separate a file even with torque control. It is always about proper technique and, if we slip up and lean on the file, torque control is there as a safety measure.
Concepts
The clinician needs to visualize an image of what the final preparation will look like. This conceptualization of the canal shape will help determine what size file to initially use. You also should have an idea regarding the final size, which is very important if using the Pro GT files — often called the shaping objective and the shaping objective file. With this technique, the shaping objective file is the last rotary file that goes to length with resistance. This is very similar to how we determine when we are finished with any rotary technique. Generally, the first rotary file that goes to length with resistance indicates completion of the preparation.
Another critical concept is resistance. We only take rotary files to resistance. What is resistance? We now understand that resistance is when the file no longer progresses apically in an easy manner. We do not lean-on or "muscle" files. If you lean on nickel titanium, it will break. Torque control motors, if used properly, can help in this area. If you push on a file too much and exceed the torque setting, the engine will reverse itself. Torque-control engines are an asset, but as previously mentioned, correct technique is most important.
Patency is also an important concept and can be one of two types: apical or coronal. Establishing coronal patency is critical to a successful crown-down procedure. The idea is that if we have coronal patency, it generally implies the remainder of the canal is "open" and can be instrumented. We can confirm coronal patency by using a No. 10 stainless-steel file and taking it half way down the canal.
We do this prior to the placement of any rotary file into the canal. The only exception to this notion of coronal patency can be in some periodontally involved teeth. These teeth may have calcification coming from both apical and coronal directions.
The other patency, and the one more commonly understood, is that of apical patency. Apical patency is the concept of using a small hand file to keep the apical constriction open. Think how many times you have blocked yourself out when doing an RCT. By maintaining patency, we can avoid this problem. We recommend using a No. 8 or a No.10 stainless-steel hand file. Take it to length and extend it .25 — 5 mm past the constriction. Doing this after every working file will prevent blockage. This is particularly helpful on vital teeth because these teeth are most susceptible to blockage.
By using small files and extending a minimal distance past the constriction, you will not create postoperative problems. This concept applies to both hand-filing and to the use of rotary instruments; however, when using rotaries, you can use a patency hand file after every other rotary.
Our final "gem" concerning concepts is that of recapitulation. Recapitulation means repeating earlier steps in a crown-down procedure. For example, you are using multiple tapers in a crown-down fashion — .10, .08, .06, .04 — but are still considerably short. Instead of pushing on the file, you can repeat part of the sequence — .06 to resistance, .04 to resistance, .06 to resistance, .04 to resistance, etc. The concept behind recapitulation is that it offers an alternative to forcing files. As previously mentioned, if you lean on nickel titanium, you will break nickel titanium. Of course, another alternative is to size down to another taper such as .03 or .02.
In our next article, we will have more gems that will assist dentists with proper techniques and operatory management when meeting the myriad challenges endodontists face utilizing rotary files.
