Written by Dr Aaron Nicholas, DDS
As the saying goes “It’s a pretty sorry carpenter that blames his tools for a failed result”.But the opposite is also true. If we have a great result, it’s not because of the “tools” that were used. Sure, great tools make getting that great result easier, but great tools in the hands of an unskilled operator will not turn him or her into a savant.
So, since we’re going to be talking about endodontics, let’s stop talking about tools and start talking about instruments. If you read and believe too much of the marketing in the dental literature, you might start to entertain the idea that all you need to be a great endodontist is the latest great file or irrigation system.
Or you might talk to a colleague who has discovered THE file system that will solve all of the challenges they have been having with instrumentation. “No, really. Its amazing. I haven’t separated an instrument this year.”
Or maybe you were trained on a particular system and are hesitant to switch because it’s what you know and you’re afraid of having even more issues with an unknown. Not an unreasonable fear.
Just as we don’t want to blame our instruments for our “failures”, we also don’t want to give them too much credit for our “successes”. I became a doctor in the 80’s before NiTi and rotary instrumentation even existed. Back then the success rates were comparable to the success rates that we are seeing today with endodontic therapy. So, it’s not the instrumentation.
What the current generations of instruments has done for us, is make it easier and less fatiguing to perform endodontic therapy. They have made obtaining the desired shaping much more technology driven as opposed to being operator driven. Less “art” more “system” thus allowing doctors with much less experience to create better and more consistent outcomes.
All wonderful achievements.
But they aren’t magic.
Let’s start at the top
Almost universally, when I talk to doctors during our 1 Hour Molar RCT, Buildup and Crown course (shameless plug) the three issues that have finally convinced them to refer out all their endodontic cases come down to three things:
1. I can’t find all the canals consistently and in a timely manner.
2. When I’m instrumenting everything Is going fine till the last few millimeters and then I get blocked out or ledge. After that, I can’t get through the blockage or past the ledge, so I must refer the case out anyway. Or it takes so long that it wrecks my schedule.
3. I’ve separated enough instruments and had that conversation with enough patients enough times that I don’t ever want to go through that again. So, it’s easier to just send it out and I’ll do the crown when the case comes back.
I think we can agree that challenge number one is not one that we expect that a better file system is going to cure. There is some technology and training that can make this easier and more streamlined but we’re not trying to cover that here.
Challenges numbers two and three are commonly blamed on or have cures attempted by the selection of our file system. In truth, both challenges are merely symptoms that a greater problem that has already occurred “upstream”. The blockage or file separation is merely the symptom of this. It’s not the real issue.
To consistently not have these issues requires a greater degree of knowledge, training, and practice. However, the file system selected with these challenges can give the operator a bit more “grace” and latitude to solve the upstream issues before they become catastrophic.
Before nickel titanium, there was still root canal therapy. Canals still had to be instrumented. Debris still had to be removed. And healing still had to take place. It was just done a little differently. Typically, the coronal end of the canal was opened with a series of Peeso Reamers or Gates Glidden instruments. It could also be done with a combination of K and H files, but usually some assortment of rotary instruments were used to speed up the process. In using these, the dentin triangles were removed, and this set the operator up to negotiate the canal system to the apex.
I remember sitting in lecture and the endodontist talking about the “beautiful wine bottle shapes” that could be seen on the radiograph after successful instrumentation and obturation. This shape was created by orifice opening with Peezo reamers and then hand instrumentation. If we saw an obturation with that shape today, we would all be critical of the undue amount of dentin that had been removed. So truly our technology drives what we deem to be acceptable treatment.
So, let’s talk about what you came here for, the files.
There are two major considerations in choosing hand files. Size (diameter) and stiffness (flexibility).
Most of us were given a size 10 (purple) file as our smallest file when we were in our initial years of training. While that might be sufficient for anterior teeth or less calcified canals it is not sufficient for the challenges that prompt most GPs to start referring their endodontic cases. In our office, we keep and regularly use both #6 (pink) and #8 (gray) files. If it’s a highly calcified case, I don’t even attempt the #10, I go straight to the #6. Using too large of a file in a canal too soon is one of the surest ways to create ledging. While it might take a couple more minutes to run through the #6 and #8 before introducing the #10, it will take FAR longer to diagnose and correct a ledge or blockage created by an incorrect file sequencing.
As far as file stiffness goes, C hand files were a game changer for me. A C file is the same diameter as its counterpart but it’s a stiffer file. Additionally, the #6 C file is end cutting. In my practice we use C files to cut through blockages that have been created by dentinal “sludge” being packed apically during instrumentation. Just like the smaller K files we keep these in sizes 6,8, and 10. When needed, it is not unusual to go through a box of #6 C files to restore patency. Those tiny blades (flutes) get dull quickly. A small price to pay to keep the procedure in house and moving forward to completion.
As file systems have progressed there have been numerous improvements that are mixed and matched to achieve better results. None can be completely separated from the others.
At present there seem to be four major variables.
1. Structural design - The first popular rotary systems were introduced in 1992. Changes in structural design have been ongoing since day one. Structural design refers to all the tapers, variable tapers, flute designs and file cross sections.
2. Manufacturing treatment – Soon thereafter (1999) companies started looking for ways to manufacture stronger more consistent quality files. Variables here would be twisting wire, milling, electropolishing, etc.
3. Metallurgical developments – Still looking improve strength and flexibility (2007), file manufacturers started incorporating heating and cooling the metals to achieve stronger files with increased flexibility and resistance to fatigue. Enter the gold and blue files to which we have become accustomed.
4. Movements – Improvements to the motions that the files make came next and are still ongoing. This includes things like off-center rotation of the file as well as reciprocating and pure rotary filing. Also included are motors that measure torque on the file and unwind to reduce forces before a separation might occur.
Hand files do a great job, but they take a longer and make fingers sore and tired.
Enter handpiece driven filling.
This basically breaks down into three types of systems. Sonic and ultrasonic, rotary or reciprocating systems.
I remember trying various sonic and ultrasonic filing systems years ago. It seemed like the files always separated at the tip or became embedded in the canal wall. Both situations would necessitate stopping the procedure, correcting the problem, and then starting again. Frequently, only to be challenged by the same issue all over again. As I was doing research for this article, I couldn’t find a single sonic/ultrasonic system that recommended using the instruments for enlarging the canal. Most were recommending using it for agitating the irrigants used during the procedure.
So, we’re left with reciprocating and rotary filling.
Reciprocation systems are ones in which the file isn’t just going round and round. Sometimes the motion is 180 degrees clockwise and 180 degrees counter-clockwise. Other systems, cut 150 degrees counterclockwise and then 30 degrees clockwise to disengage the file. There are many other systems out there with many different reciprocation patterns. Most claim a proprietary pattern to make their files work effectively. Intuitively, reciprocating filing seems a little safer since the file isn’t moving in an unending circle. This probably played heavily into the decision most dental schools made to provide one of these systems for their students to learn on. The other might be that a lot of these systems are “one file” systems. So cost is presumably less, and the process is less complicated. Some systems even claim that a reciprocating motion reduces apical transportation of the canal terminus compared to full rotary files. This, however, is controversial and at least one study has created doubt in regard to the claim.
Using a reciprocating file compared to a rotating file can take longer to instrument the canal (the file is not cutting all the time it’s in the canal space) and it is more likely to push debris into the periapical tissues. But these, for the most part, seem to be minor issues. It is still far superior to hand filing an entire case and yields more consistent results in less experienced hands. Which is not to say it’s a “beginner’s file system”. It just has a much easier learning curve.
Final outcomes are stellar.
Now we come to “true” rotary files. Files that rotate in one direction, pretty much continuously. Rotary files have numerous strategies for achieving final canal shape. Some are more “crown down” while others finish different areas of the canal in sequence. Some have a variable taper in the same file while other use a consistent taper within the file but a different taper between files. Almost universally though, manufacturers recommend hand filing to a #10 or #15 before introducing rotary files into a canal system. This usually does not include using the rotary orifice opener that comes with many systems. Rotary systems will tend to push less debris apically and typically allow the operator to finish instrumentation more quickly than with a reciprocating system, even if multiple files are being used in the purely rotary system.
To add to our confusion, different handpiece manufacturers claim superiority based on sensing of torque on the file and having automatic settings to stop rotation or to stop and temporarily reverse the motion until stress is relieved. If the motor is paired with an apex locator, most such systems will allow the operator to set a distance from the apex where they would like to stop filing. Sensing this measurement, the handpiece will auto reverse the file at the pre-appointed measurement.
And finally, we come to metallurgy of the files, both rotary and reciprocating. Originally, NiTi files were not heat treated and not very flexible by today’s standards. Almost all rotatory files at present are heat treated. Not to go into a lot of manufacturing science but there are basically two types of heat treatments currently. Both achieve a tougher file that is less likely to break under load. Looking at a file that appears gold in color is the original commercially popular heat treatment. It created a file that was tougher, more flexible and had some memory. This treatment dramatically reduced the number of file separations that doctors experienced. It gave them a bit more grace and latitude in over torquing a file and possible separation. While a lot of doctors were working well with the original NiTi files, this extra breathing room greatly reduced the number of separations of files and the stress on the doctors performing treatment.
A slightly different heat treatment leaves the file with a bluish or purplish hue. Files with this treatment tend to be even more flexible and with a bit less memory. All while not giving up the toughness that helped reduce the incidence of separations. In the hand, both feel comparable. More experienced operators might be able to feel that the bluish/purplish heat-treated files are a little “softer”, but it doesn’t seem to affect cutting efficiency or reduce strength. Additionally, a more flexible file in a more tortuous canal seems like it would be a big advantage. If you are looking for a definitive answer to “What is the best file” or “Which system should I buy” I don’t think it’s a straight-forward evaluation and decision. A lot depends on your previous experience and what challenges you are encountering.
I encourage you to ask around, look at the claims and research regarding different systems and see what seems to make sense. Insist that the rep allow a reasonable demo period so that you can try it out on some extracted teeth. (Acrylic blocks don’t give any insight on how the file will perform under clinical conditions). Use what seems right and feels good when you are actually performing the procedure. Don’t be impressed by “proprietary” anything. We all think our stuff is best. As they say “The proof is in the pudding”
And remember, it’s not the files doc.
You’re the magic in your treatment.