Cents and sensibility

X-ray taken by Dr. HB Johnson circa 1939 (courtesy Dr. Tom McDonald, Atlanta GA)

X-ray taken by Dr. HB Johnson circa 1939 (courtesy Dr. Tom McDonald, Atlanta GA)

When preparing a root canal, there seems to be nothing that can’t be achieved by a skilled endodontist. In the right hands, virtually any root canal can be prepared with virtually any file or number of files. The very small curvature radius and large curvature angle in the featured x-ray illustrates the extraordinary skill for using carbon steel files in 1939 by Dr. H.B. Johnson, the individual that gave us the term “endodontics.”

Curiously, it is rare that a file is promoted today without an accompanying x-ray depicting an extraordinarily difficult case. Should we conclude then that all files will enable you to achieve ideal root canal preparations? We can eliminate almost all restrictions except for one, our inability to freeze time. Ahh… there’s the rub. Time is our most valuable commodity.

Many years ago, a clever sales rep showed me a time saving formula demonstrating the annual money savings that a very expensive digital x-ray device would provide before convincing me to buy what turned out to be the very first digital x-ray device sold in the US. Ever since, that formula has continuously convinced me that penny-pinching at the expense of saving time isn’t really saving money at all. It’s no different with endodontic files. Consider that by saving 10 minutes/patient with each of 6 cases/day for 200 days results in 5 weeks of chair time saved annually. That’s more than a month of additional production, vacation or whatever you like!

A file’s ability is not the issue. Rather, a file’s efficiency during performance is THE most important issues and our guiding objectives when designing NanoEndo files. Our results are extremely successful in this regard and our customers agree that NanoEndo’s highly efficient designs save them time and reduce risks during root canal preparations. See for yourself and review our comparisons with the files you are using now or give us a call (844.ONE.FILE) to learn more. Remember lost time can never found.

If a picture is worth a thousand words, then what’s that worth?

X-ray taken by Dr. HB Johnson circa 1939 (courtesy Dr. Tom McDonald, Atlanta GA)

Most of the time x-rays of tortuous canals are used to demonstrate the capabilities of a file. This begs the question: exactly how much information do we get from an x-ray. Dr. HB Johnson, one of the pioneers of endodontics and the man who coined the term endodontics, is the person that performed the RCT of the featured x-ray taken around 1939. If we use this x-ray (courtesy of Dr. Tom McDonald, Atlanta GA) illustrating a successful end result as a benchmark, then we shouldn’t be so impressed with x-rays portrayed today as an indication of how good a file is. The files he used were carbon steel, worse than any file than most of us have ever seen. I’m including two x-rays of cases I completed soon after the introduction of NiTi rotary files. I cannot even remember which files were used, but probably not the ones I would recommend today.  The point is: virtually any file can prepare virtually any canal. More difficult to illustrate is the ease, predictability, and productive capability of a file. This is why our research focuses on determining endo file limitations and efficiencies rather than endo file abilities, given the time and skill of the operator.

What difference does unwinding an endodontic file make if it doesn’t break?

extrusion segI was recently asked why would it matter if an endodontic file unwound as long as it didn’t break. First, let us think of a file as not only an instrument that enlarges a canal but one that acts as an auger as well; it conveys debris. When a file unwinds to the extent that its helix augers apically rather than in a coronal direction (as in segment 1), then debris is extruded through the apical foramen. Note that part of the file becomes denuded. Post operative pain will most likely be the consequence. The unwound segment 2 continues to auger debris in a coronal direction while the unwound segment 3 augers in an apical direction. The result is compression of debris, additional torsional stress and a greater propensity for breakage. Keep in mind most files will not even unwind 2 revolutions without fracturing. If the file is rotating 500rpm, 2 revolutions require less than 1/4 second before failure.

The short answer to the question is: it probably matters. Luck is not nearly as predictable as cause and effect.

Maximizing Efficiency – for what it’s worth


Time is the one commodity shared equally with all. No matter who we are or where we are we each get 60 minutes with every hour, 24 hours each and every day and then it is gone forever. One cannot keep time from passing, yet, profoundly, one can save time.

Early in my career, I had the good fortune to enroll in a course on ergonomics. The curriculum was about efficiency and how best to streamline all the individual movements and methods used to complete a procedure. This concept resonated with me and guided my thinking and methods throughout the rest of my career. In fact, my endless pursuit of efficiency within my own practice is what ultimately inspired me to design and modify my own instruments and techniques.

Even very small gains in efficiency will compound over time and can have a profound impact on a practice over the course of a career. Suppose you could save 10 minutes with each patient. If you see only 6 patients in a day, that would equal an extra hour each day; 5 hours each week; 260 hours each year. That’s the same as 32.5 eight hour working days a year! Can you imagine that a simple 10 minute gain in efficiency might result in gaining an entire month’s worth of time over a year? What is the value of such a proposition? Keep in mind that there is a big difference in saving time and wasting time.

In my practice, I bought and tried every new gadget that came to market, always searching for new ways to save time and effort. Mine was one of the first practices to use digital x-rays, electric handpieces and a microscope. Later, I introduced a NiTi rotary file simply because I knew it would make me more efficient. Ultimately, I became so efficient that I had even more time to seek out even greater efficiencies and now that I’m retired from practice, the fascination remains.

The One Endo file’s design was born from my unending pursuit of maximizing efficiency in instrumentation and my research continues to validate that combining two or more dissimilar tapers side-by-side within the same instrument, significantly enhances virtually any endodontic file design. Recently I was asked to describe why an established practice should consider switching file systems to incorporate the One Endo file in terms of a return on investment. Addressing any ROI demands that benefits are quantified, so I turned to data from our research for insight.

What I found when taking a very broad view for comparison was striking: the One Endo file is 33% more efficient on average than every other file we’ve tested to date. This number is a comparison of the average maximum torque and pressure values from all files and sizes tested with our Endo File Evaluator against the same parameters for all sizes of the One Endo. More importantly, it should be noted that half of our competitors’ files failed their respective evaluations resulting in broken/distorted tips or screwing into or transporting the canal.

While this finding does not mean that switching to the One Endo will save you 33% more time or money, it does mean that it is very likely to allow you to complete the same amount of work with less effort. Depending on how you adapt your technique to incorporate such a gain in efficiency, this could result in time/money savings, but most importantly, it is likely to improve your results. This poses a new question: If you can become more effective by using a new file, why wouldn’t you try it? Remember that 10 minutes I saved way back when? Consider this – at the end of my 31 years of practice, those 10 minutes managed to free up over 2.5 years of extra time! Granted, I can’t tell you where that time went, but it wasn’t wasted and I loved every minute of it.

Stacking the Deck : A response to questions about our selection of testing protocols


Recently, we received feedback regarding our methodology for creating protocols for evaluating endo file performance on our Endo File Evaluator, a computer controlled clinical simulator. As always, we encourage your participation in our discussions and we felt others might benefit from including these comments in our public forum. The comment submitted through our website contact form is as follows:

“I’ve been looking over some of your data comparison in regards to your Evaluator V2 and am borderline appalled at how misleading it is and how you’ve set your file system up to succeed in that scenario and make sure that others do not perform. You have all 11 file systems in that Evaluator V2 running at 550rpm [sic] knowing good and well that for several of the file systems on there 550rpm is much higher than the recommended speeds Many of those systems run at 300rpm. Not to mention the torque you are using in the settings is also much higher than normal for many of the files. I find it to be quite a coincidence that the speed you choose to do the Evaluator V2 test comparisons at is the exact optimal speed of your own file. It seems to me that without testing each of these systems at their optimal speed torque technique your are doing nothing more than publishing skewed results that have been made to lean in your direction.”

Were this in fact the case, we also would be appalled. Distinguishing hype from fact was precisely the reason Dr. McSpadden developed his Endo File Evaluator. The protocol mentioned and its use of 500 rpm and unlimited torque setting is actually arbitrary and was intended to establish a baseline for future comparisons. Our goal with protocols is primarily to find the limitations that dictate optimum performance. The first series of protocols takes various file sizes to a canal’s apex with a particular speed and rate of insertion with no regard for the file’s size relative to the canal opening. This is not a technique we, or I dare say anyone else, would ever recommend using in their practice.

Rather, our methodology allows for direct comparison of torque and pressure readings that may be viewed in a graphic format and ensures a level playing field for interpreting the data. Previous testing performed on the V1 Evaluator used several various protocols with multiple rotation speeds and insertion rates. This data informed Dr. McSpadden as he wrote Mastering Endodontic Instrumentation and ultimately inspired his design of the One Endo file. It has always been our intent to continue our testing and comparative analyses of endo files using an ever broadening scope of protocols. To that point, we  are currently completing a full evaluation of most endodontic file designs in an ongoing series that we will share as a new blog scheduled to launch next week.

Furthermore, from our beginning, we have invited anyone to Request-A-Test on our Endo File Evaluator. Through this online form, anyone may submit ideas for additional protocols they wish to see performed on our Endo File Evaluator and we will be happy to perform them and publish the results, even if they prove unfavorable to our own designs. Our mission is to empower endodontic practitioners and advance their potential by offering the most effective products while providing open access to unbiased informational resources for instrumentation and design. What we seek is knowledge and what we hope for is your participation.

What is the fewest number of endodontic files required for canal instrumentation?


After 35 years of research for endo file efficiency vs. file stress, I continue to be puzzled for how to best answer the frequent question: “How few of your instruments are necessary to prepare a canal?” Just as perplexing are the marketing claims asserting that only 3-5 of their particular files are necessary for instrumentation.

How few files?  – How few wrenches are required to work on a car? How few stitches are required for sewing a garment? How little study is required to learn the Krebs Cycle? The endodontist, the mechanic, the tailor and the biochemist have to be careful not to sound too glib in answering that sincere question, the importance of which has been instilled by marketing. “Whatever is necessary” should be the common answer.

In considering the question for fewer files, the following questions encompass greater significance: Does fewer mean less file stress or chance of file failure? Does fewer mean more effective files? Does fewer mean better results? Does fewer mean a better canal shape? Does fewer mean greater biomechanical cleaning? Does fewer mean less time? If that answer is yes then these are the attributes marketing should claim.

Perhaps we should ask what was the rationale for having multiple file sizes and having multiple tapers. Why don’t we just start with the final file? Intermediate steps in the progression of sizes and tapers reduces the stress introduced into the file, maintains the central axis of the canal more effectively and provides the greatest flexibility relative to its function.

Probably the greatest perceived advantage of fewer files is the idea that less time is required. However, it has been my observation that the end result with fewer files requires a greater amount of time than multiple files. An occasional exception might be when the clinician spends so much time in changing instruments. This time can be virtually eliminated by using 2 handpieces  and having an assistant to have the next file in the sequence ready while the operator is instrumenting. Two wireless handpieces easily accomplish this function but the solution I preferred was 1 control unit and foot switch but 2 handpieces wired through an A-B switch so only 1 was on at a time.


All of my research has been focused on how to maximize efficiency while minimizing stress during instrumentation and the results have consistently evidenced the following:

  • Advance the file into the canal with no more than 1mm increments with insert/withdraw motions.
  • Advancement into the canal should be able to occur at a rate of approximately 1/2mm per second with each insertion without increasing the force of insertion.
  • Engage no more than 6mm of a file if engaged in a curvature.

When one can no longer comply with these parameters, changing to a different file is recommended. Reaching the desired result may require 2 files of 9 files or “Whatever is necessary”, but efficiency (time reduction) is maximized and stress is minimized.

Claims of strength for endo files: Hype or Fact

Creating the most useful file requires balancing properties of flexibility, resistance to torsion stresses, cutting ability, and debris removal.

Creating the most useful file requires careful balancing of properties.

Is there a Relationship between Cyclic Fatigue and Strength?

The short answer is no. Metal fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic or regular repetitious loadings such as a file rotating around a curvature during which each side of the file is alternately undergoing tension and compression forces. Strength, on the other hand, can best be explained as a file’s ability to resist or withstand an applied load without being deformed from its original shape. If a file is heat treated to increase its ability to resist fatigue yet it unwinds more easily, its strength is actually reduced and the claim for having more strength is erroneous. Further defined, the yield strength of a file is the stress at which the file begins to show plastic deformation. The ultimate strength of a file is the maximum stress and deformation a file can endure without breaking.

A more useful term for an endodontic file might be the measure of its toughness.  In order to be tough, a material must be both strong and ductile. For example, brittle materials (like ceramics) that are strong but with limited ductility are not tough. Conversely, very ductile materials with low strengths are also not tough. To be tough, a material should withstand both high stresses and high strains. Generally speaking, strength indicates how much force the material can support, while toughness indicates how much energy a material can absorb before breaking. The key consideration for designing the most useful endodontic file is balance.

The objective of NanoEndo is to maximize efficiency and minimize risks. That requires balancing properties of flexibility, resistance to torsion stresses, cutting ability and debris removal. You might think of these properties as members of a team; not one can stand alone, no matter how superior, without the support of the others and expect to be effective.

Does the quality of manufacturing make much difference for endo files?

SEM courtesy Nova Southeastern University College of Dental Medicine

Before different types of files are studied, it should be stressed that the quality of manufacturing is the most basic consideration for determining the success or failure of endodontic files independent of their composition or design. Less than ideal manufacturing quality controls result in the formation of micro-cracks and defects along the surface of a file. Cracks can propagate to failure at a stress level lower than the stress ordinarily encountered during instrumentation and other defects can cause stress concentration points that lead to file failure and jeopardize endodontic success. It should be noted; considerably less force is required to propagate a crack than is required to form it. If the defects are in a position of high stress, failure can occur quickly. The area of highest stress is along the blade or leading edge. The formation of micro-cracks shown on the file’s cutting edge indicated by the arrow is an area for potential failure.

How to Interpret Graphs from NanoEndo’s Endo File Evaluator

View the test at http://nanoendo.com/evaluator-v2.php

View the test at http://nanoendo.com/evaluator-v2.php

What do the graphs we display provide to us as beneficial information that can be used to enhance our instrumentation expertise? Generally speaking, as long as the plotted coordinates remain within the grid boundaries, the file is suitable to be used with the parameters specified in a canal with identical dimensions and properties if the file did not distort, break or excessively screw- in. That may sound like too many limitations to consider, but the trial run in practice blocks offer surprisingly relevant information clinically.

As an example, let’s take a look at the graph above for the Edge file 20/06. First we note that the tip distorted, although positive coordinates (points above base line zero) do not seem alarmingly high. We only have to consider positive measurements for torque because this is this is the only stress for torsion that will cause distortion. Negative pressure, on the other hand, indicates the screwing-in factor. Negative readings exceeding -2lbs should be a matter of concern (note the reading at 11:46:06 where the measurement is more negative than -2). Remember in this situation the device automatically reverses after 1mm of advancement. Manual reflexes might not be as quick since screwing-in forces are more insidious. Note also, the spike in negative pressure was accompanied with a spike in torsion and both occurred early in the cycle. It is at this point that the tip probably distorted.

What does this information tell us if we are to use this file? It means that we should be careful to limit the progress of advancement into the canal with very short pecking motions and to exercise caution with each insertion to counteract any sudden screwing-in forces. In addition, we should check for distortion frequently.

Steps of Endodontic Instrumentation Technique

Many endodontists have spent a great deal of time deciding on the file sequence that serves them best and would prefer not to have to learn a new technique. For those, we would recommend no technique change since the One Endo file was designed to give better results with any technique simply by using One Endo files approximating the sizes of the files of your technique.

On the other hand, we have had requests for specific technique recommendations of how we would recommend the One Endo file should be used. Practitioners should keep in mind the purpose of any recommendation is to provide a means for maximizing efficiency for enlarging the canal space while minimizing instrument failure—not to advocate a particular canal size or taper.The final canal dimensions should be adjusted to conform to the judgment of the operator and the requirements of the obturation technique used.

1 – No Change:

The One Endo file was designed to be used without changing the operator’s preferred technique. The fact is, if the One Endo file performs better than other files of the same approximate size, they can be used exactly in the same way  and achieve better results.

2 – Same Technique with added Parameters:

This step requires no technique change but does make the following recommendations during the procedure:

•Advance into the canal using no more pressure than was required to advance the first 1mm. If more pressure is required, change files.
•Engage no more than 6mm of a file if it is engaged in a curvature (the exception would be a size 20-.02 or smaller). If engagement is greater than 6mm, change files.
•Advance a file into the canal with no more than 1mm increments with insertion/withdrawal motions.
•Advancement into the canal should be able to occur at a rate of approximately 0.5mm/s without increasing the pressure of insertion.
•Withdrawing at a rate greater than the rate of insertion improves debris removal.
•Follow the use of one file with a file having a different taper.

Even though more files may be used in following these parameters, the total cumulative time can be less when compared to other techniques. Each step of instrumentation can occur quickly without repetitive non-productive attempts.

3 – Technique Change:

We recommend a technique change to incorporate the findings of our research to maximize efficiency while avoiding probable risks. We refer to this technique as the zone technique in which we divide the canal into two zones, the coronal zone or the portion of the canal coronal to a curvature, and the apical zone or the portion of the canal apical to a curvature.The zone technique was designed with two objectives for minimizing file stress: One, the canal diameter should be large enough coronal to a curvature to prevent any stress due to engagement in that portion of the canal when any file is being used apical to the curvature. Two, the file diameter is not too large to rotate safely in a curvature; the file diameter is sufficiently small in a curvature to avoid excessive cyclic stress.


The first step is to determine if there is a curvature of any significance and how far the curvature is from the apex. Withdrawing the file used to establish the working length, and passively re-inserting will indicate a curvature if it meets any resistance short of the working length since the canal is now larger than the file. The canal portion short of the resistance defines the coronal zone and the portion beyond the resistance defines the apical zone. The length of the canal to the curvature, the coronal zone, is measured and recorded with the same importance as determining the working length. The working length minus the coronal zone length provides the distance the curvature is from the apex, the apical zone length.

The second step is to determine the distance each of the files having different sizes and tapers can safely be advanced around the curvatures and which size file will need to be used in the coronal zone to prevent any subsequent file from binding in the apical zone. At the point of curvature in the, the file diameter should be no greater than .60mm for a .02 taper, .55mm for .04 taper, .50mm for .06 taper, and .35mm for a .08 taper. (This consideration is the result of testing for 45-degree curvatures having 8 mm radii and applies only to these dimensions for rotary NiTi files. File diameters should be smaller for more severe curvatures and can be adjusted larger for less severe ones.) By using the parameters suggested above for diameter limitations, we can calculate if the diameter of a selected file would exceed our limitations.

Example: If the point of curvature is 6mm from the working length and we are considering using a .25/.06 file. The parameters above state that a .06 tapered file should not have a diameter greater than .50mm at the point of curvature and that diameter for a .25/.06 file is at 4mm from its tip. Therefore, in this situation the .25/.06 should only be advanced 4mm into the apical zone and if it is carried to that point, the terminus of the coronal zone should previously be prepared to a size .50mm. Following this procedure at first may seem complicated but it can be learned quickly. The result is a very expeditious and relatively worry free of threat of breakage.