Written by L. Emery Karst, DDS Saturday, 31 May 2003 19:00
In the last few years, root canal therapy (RCT) has undergone such drastic changes in methods of treatment that practice management gurus have had to change their recommendations of “referring root canals to the specialists” to “it’s the most lucrative procedure that you can do in your office”. The specific reason for this change is NiTi files and their adaptation for use in a rotary contra-angle handpiece. There were, and still are, some grave concerns over file separations, especially when the tactile sense is lost to a handpiece. However, there are some improvements in design and techniques that significantly reduce this danger. Various endodontic lecturers have systems that improve the odds so the prudent dentist can stay out of trouble and make a good living performing RCT.
There are many endodontic courses making the circuit now. Each lecturer promotes his method as being the best approach. While almost all progress comes as a result of these lecturers’ expertise, very few are willing to readily acknowledge that there might be a superior way of doing things in regard to some aspect of their technique. I have developed a method that incorporates the best of several lecturers’ techniques. It reduces the armamentarium and time to the point where it is by far the most lucrative procedure that is done in my dental office. It is also the most accurate and produces the best seal. The total procedure for an anterior tooth should take no more than 10 minutes, and for a molar with easy access, 20 minutes.
Difficulty in locating the canal(s) and gaining access is the only variable in this procedure that can disrupt your schedule. (Send those to the endodontist!) Once this is accomplished, the rest is simple. An apex locator is essential to determine working length. Once you have confidence in this device, you won’t need to take pre-op films very often. To obtain readings accurately, rinse and dry the chamber, add a few drops of tap water, then vacuum the excess water from the chamber. The tap water provides an electric conducting medium.
|Figure 1. Package of EndoMagic No. 8 files with a 0.06 taper and a No. 25 size tip.|
I use the EndoMagic NiTi rotary file system (Figure 1) developed by Dr. Arthur (Kit) Weathers (Practical Endodontics). However, I don’t use the whole system. I use only 2 out of the series of 10 files (Nos. 8 and 10). I prefer these files because of their flexibility. There may be other manufacturers of NiTi files that work as well as the EndoMagic workhorse, a No. 8 0.06T file, but they have to be a 0.06 taper with the same amount of flexibility. A file with a 0.04 taper will separate more easily under the same circumstances. A file with a taper greater than 0.06 will be too stiff to negotiate a curved canal adequately.
Understanding the taper is simple. The diameter of a file increases by the taper number in millimeters (mm) for each mm of progression up the file. A No. 20 file with a 0.02 taper has a 0.2-mm diameter tip, 0.22 mm in diameter at 1 mm from the tip, and is 0.30 mm in diameter at 5 mm from the tip. At 10 mm from the tip, it has a diameter of 0.40 mm.
|Figure 2. The No. 8 file can successfully negotiate extreme canal curvature.|
Before beginning the reaming process, mark the working length with the rubber stopper supplied on the No. 8 file. It is presumed that the canal has been located and opened to at least a No. 20 0.02T file at the working length. When using the No. 8 file, you will notice that the distance from first resistance to the working length is somewhere around 6 or 7 mm. That is no problem since the area of contact is small, and it will be part way up the flutes where the strength precludes any separation. The area of contact is small because of the smaller taper canal (0.02T) created by the hand files that are used first, versus the larger taper (0.06T) of the No. 8 rotary NiTi file. As you progress toward the apex with the No. 8 file, a larger and larger area of the file will be contacting the interior of the canal. Hundreds of canals have been done with only a No. 8 (after the canal has been opened and negotiated to the apex with a No. 20 0.02T file) without unwinding or separation of the file. In addition, there is a lot of flexibility in the apical one quarter of this file, so most curved canals can be negotiated and cleaned with this file. See Figure 2 for the amount of curvature that can be negotiated with this file.
Work hardening is not a problem, provided you use the No. 8 file on only one tooth (if it is a molar) and then discard it. File separation is not a problem unless extra pressure is applied to save a few seconds of reaming. It is advisable to practice on an extracted tooth and apply enough pressure to separate the file. It is difficult to apply enough pressure to do this, but at least you will know how much pressure it takes. Separation usually occurs for 2 reasons: too much pressure, or work hardening from using the file too many times. The file will be less sharp each time it is used, which then requires more pressure to cut the dentin, thus placing more torque on the file, (with the possibility of separation because of 1 or both of the above reasons). Discard each No. 8 file after one use unless it is a straight single canal tooth, but 3 canals (not teeth) is maximum recommended usage. In fact, if there are extremely curved canals, it is recommended to use a new file for each canal.
The No. 10 file is a 0.02 taper with a No. 40 tip. It completes the reaming except in cases with large canals, such as adolescent anterior teeth. In these cases, use successively larger files with a 0.02 taper until dentin is finally engaged adequately.
|Figure 3. Package of size 40 and 45 SimpliFill apical plugs.||Figure 4. Size 40, 45, and 50 SimpliFill apical plugs. The gutta-percha is 5 mm long. One mm needs to be cut off before use.|
Obturating the canal is done in 2 stages. The apical 4 mm is sealed first with an apical plug of gutta-percha (SimpliFill, LightSpeed Technology, Figures 3 and 4) in a size No. 45 with a 0.02 taper. The company has other sizes (up to No. 130 for larger canals), but the one I use most is the No. 45 and sometimes the No. 50, except in larger anterior canals.
|Figure 5. Package of Westdent T-40 gutta-percha points having a 0.06 taper.||Figure 6. Two Westdent T-40 gutta-percha points and one having 4 mm cut off the tip making it ready for use.|
The second stage seals the rest of the canal. WestDent makes a gutta-percha point called a T-40 (Figures 5 and 6). It has a 0.06 taper that fits very intimately with the walls of the canal, since the canal was filed with a 0.06 taper file. This forces the sealer laterally, and often accessory canals can be seen filled at right angles to the main canal. The T-40 was made to be used alone to obturate the canal in one step. However, there are several reasons I don’t use the T-40 alone. The apical plug method is much more accurate and produces a better seal. The T-40 bends so easily that you can never be sure that the tip reaches the apex. Occasionally, the extreme end folds over and wedges before the apex is reached. Because of the bulk of the T-40, it is easy to push sealer past the apex unless the apical plug is in place first. Because the very tip of the T-40 does not have a consistent taper (it is greater that 0.06), there in no way a tight seal can be achieved at the apex. There is, however, a consistent taper when the tip is cut off approximately 4 mm, and this is what is used to seal the rest of the canal. You will have to experiment with how much to cut off to fit the walls snugly yet reach to the coronal end of the apical plug.
Step 1. Open the tooth and gain access to the canals.
Step 2. Open the canals to the working length with whatever files you are comfortable with. They will have a 0.02 taper. Use up to a No. 20 at the working length.
Step 3. Now use the No. 8 rotary file. It is has a 0.06 taper with the tip size of No. 25 ISO. You must have a 300-rpm handpiece when using this or other rotary files.
Use plenty of water or other irrigant when using rotary files. Use medium pressure on the handpiece when reaming. One might think that this would screw the file into the tooth. It won’t happen because of the greater taper (0.06) and the irregular distances between the flutes. In addition, because the pressure is applied along the long axis of the tooth, the flexible nature of these NiTi files keeps them relatively within the center of the roots. These files are only working when pressure is applied apically. Whether you are applying light or heavy pressure determines whether dentin is removed on the inside or the outside of the curve. Hand files will always remove more dentin on the inside of the curve. However, there is very little danger of perforating the side of a root as can happen with hand files in the larger sizes.
Apply medium pressure for approximately 5 seconds (maximum) before retracting to clear the flutes of dentin chips. Reinsert the rotary file and apply pressure for another 5 seconds and retract to clear the flutes again. Repeat this process until the working length is reached. This may take 15 or more repetitions, but that will only take from 1 to 2 minutes for each canal. It may not look like you are progressing toward the apex, but after a few times it should be noticeable that you are making progress. It could be as little as one-quarter mm for each insertion. You will see progress unless the file is dull from overuse.
Step 4. The No. 10 rotary file is next. It has a 0.02 taper with a No. 40 size tip. Set the rubber stopper to working length. Use a pecking motion with light pressure, still rotating at 300 rpm with lots of irrigant. This is accomplished in just a few motions, approximately 10 to 15 seconds per canal. The removal of dentin with the No. 10 file will extend approximately 4 mm up the canal from the apex. Therefore, the apical 4 mm of the canal will have a 0.02 taper and end in a No. 40 size apex. The rest of the canal will have taper of 0.06.
Step 5. Flush the canal with a needle and syringe filled with your favorite liquid. After drying the pulp chamber as much as possible with air and vacuum, take the needle off the syringe and insert it into the canal. Put a surgical tip into the vacuum hose and place the tip into the open end of the needle, and presto! The majority of the liquid has been removed, requiring only 1 or 2 paper points to dry the canal completely.
Step 6. The next step is apical sealing. After cleaning and drying each canal, place sealer into the pulp chamber with a CR syringe applicator tip and tease it into each canal with a No. 20 hand file set to 1 mm short of working length.
In preparation for using the No. 45 apical plug, cut 1 mm off the tip, leaving 4 mm of gutta-percha attached to the carrier (Figure 4). Adjust the rubber stopper on the shaft of the apical plug to the working length and insert into the canal. You will feel some resistance approximately 2 mm before reaching working length. This is good. Push the applicator to working length. This will compress the plug intimately into the apical 4 mm of the canal. The tip of the plug will always be at the anatomical apex. The obvious reason for such accuracy is because the metal carrier, which is 0.35 mm in diameter, has no taper and will easily follow the canal, pushing the apical plug to the working length. In addition, the seal is superior to any other method because the tip of the apical plug is a size No. 45 with a 0.02 taper, and it is being forced into a No. 40-sized apex also with a 0.02 taper. Therefore, if the rotary files have been used to the exact length of the canal, you will always have a perfect result. If the rotary file has gone past the tip of the canal, you will need to use a No. 50 apical plug to obtain the tight seal and to preclude an overfill.
Now rotate the handle of the apical plug counterclockwise several times and re-move. There are 2 metal parts to the apical plug, and both parts may not come out at the same time. If one of the parts remains, remove it with cotton pliers. It is not attached to the gutta-percha so it will not pull out the apical plug.
Step 7. Filling the rest of the canal is simple. Whatever you have available will work. Just fill the space. I have a method that works fast for me. I use a gutta-percha point called a T-40. The method and reasons for its use are explained in the “Armamentarium” section above.
Step 8. Use a hot endo plugger to clip off the excess gutta-percha, and you are ready for a crown or buildup with nothing but gutta-percha to remove if you need to do a post and core.
The technique described is so fast that you can throw away the No. 8 file after one use and feel good about it. Do not use for more than one molar endo! The No. 10 file can be used for more canals than the No. 8 file, but be cautious about file separation if used too many times. The cost of materials for a molar endo is less than $20. Compare that with the cost of providing a full crown restoration!
Dr. Karst maintains a private practice in Salem, Ore. He served as an associate clinical instructor at the Oregon Health Sciences University, and as a product innovator, he has developed such products as the Stainbuster air polishing device and the Bite-Tray Plus impression tray for his company, Emery Dental. He can be reached at (503) 378-0523 or (800) 637-6611.
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