On Communication and Collaboration for Advancing Endodontic File Design

While the overwhelming majority of comments we receive regarding our research and innovations is very positive and complementary, publishing our independent research while marketing our own endodontic file designs and claiming unbiased objectivity opens us up to criticism and scrutiny. We expect and welcome such skepticism as it inspires discussion and informs further investigations. Our hope is that our openness to criticism and our transparency in operations will ultimately serve to balance biases and provide an open dialogue wherein all perspectives may be granted equal consideration. To that end, please consider the following comments we’ve received regarding our most recent series of endo file evaluations alongside our responses to them:

Alex’s Comment: (background unknown)

Great job Dr. McSapdden! Your experiment’s design proved that your file is the best! Well done!! Now it’s time to put together an experiment to prove that your children are the cutest!! Come on man! Is this a joke? How can you sell a file and test competitor files? Well. Thanks for wasting my time reading this commercial.

Dr. McSpadden’s Response:

The instant formula for failure may be to try to please everyone but we try. We try by using equipment that can give results that can be consistently replicated independent of the operator. We try with a commitment to publishing the results without knowing in advance what the results will be. We try by inviting any change in the parameters we use for testing as well as inviting anyone to observe the results as they occur. We try by including 35 years of our past testing experience to provide the most useful information we know how. We try by using the information we have accumulated to design instruments that might help in providing solutions for clinical needs. We try by having our quest for solutions to be a continuing endeavor. We try by convincing ourselves that trying is better than doing nothing when success is unknown but that even failure might be at least some benefit. And, we will try to help you find solutions if you should ask and hope that you might try to do the same for us. And, yes my grandchildren are the cutest and, as a 75 year old grandfather who doesn’t need to sell files, I will admit that particular claim might be biased.


David Clement’s Comment: (UTHSC Grad Endo)

This is a great project you are sharing with the Endo Community.  I look forward to seeing further results which you say will be distributed regularly. Just one comment, and perhaps a description criteria you could consider adding to the Descriptive Characteristics. The Circular core dimension as a percentage of the circumferential size (diameter) would be a very interesting characteristic to see.  The bulk of metal in the core (Not including the exposed cutting edges) could give fundamental information/understanding on torsional strength and and Cyclic fatigue characteristics of these rotary files.  It would also give information is the core area changes in the length of the blade, theoretically increasing the Flute space ( debris removing area). Again, Many thanks for sharing the project information with us. 

Dr. McSpadden’s Response:

…I think your idea is excellent. It might be good to carry it a step further and have the core as a percent of the total x-sectional area. If we cannot change the program easily I can include it in the discussion. I really appreciate your interest and comments.

If you have any questions or comments of your own, please feel free to share them with us however you like. Post them here, send us an email or give us call (844) ONE-FILE [663-3453]. We value your input and perspective and hope you will help us in collaborating for the advancement of endodontics.

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

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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 differences do endo file design differences make?

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What differences do design differences make? We intend to find out. We are embarking on a very ambitious research program to test each part of every major file in production, from tip to handle. We have completely up-dated the computer controlled Endo File Evaluator to improve resolution of its sensors and motors and to expand its capability for performing new testing protocols. As such, we have created what I believe is not only the most objective means for evaluating endodontic files, but also the best method for testing file functions in a manner that is truly relevant within a clinical setting. We do this while letting the data determine the results for objective comparisons independent of operator skill or marketing bias.

What difference does this endeavor make? Our first objective is to finally determine how to minimize risk and maximize efficiency, how file designs relate to function, how function relates to canal anatomy, and how anatomy relates to technique. Our second objective is to present the Endo File Evaluator results using the numerous different parameters for testing, and to use high resolution images and SEMs in a manner that allows clinicians to save and apply the information to enhance their skill and treatment.

How will this process take place? About every ten days we will share test results and observations of only one segment of each file beginning with the file tips. Through this blog, we invite you to participate in discussions and critiques to create group research dynamics as this project progresses. Once all segments of the files have been covered, a composite of each whole file will be available as an endodontic reference along  with any contributing assessments gathered from our readers. We will continue providing results as we find them through this comprehensive series of evaluations and add to them in the future as needed. We are excited to embark on this endeavor and hope you will follow along and contribute your own thoughts and impressions.

Sample Selection: How we select files for evaluation on the Endo File Evaluator

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In any scientific study that intends to make inferences about an entire production of endodontic files its primary objective, the sample size is a very important feature for having sufficient statistical power. In estimating unknown parameters, larger sample sizes generally result in greater statistical confidence. Unfortunately the clinician rarely has that opportunity. If he uses 10 out of 100,000 files, that’s only a 0.001% chance that all of the others are the same. He relies on the manufacturing regulatory procedures for confidence in using every single instrument as 1 in 100,000 or the production number. In other words, the clinician relies on the one that comes out of the box. In our evaluations and in our imaging we make the same sample selection as does the clinician, the one that comes out of the box. With that selection we make the ethical commitment that every image we show and every test we conduct is unaltered and as independent as possible from operator influence.

Recently we received a complaint from Komet that the SEM we received from NOVA University and featured in a previous blog was not representative of their files. Their claim may be entirely valid. One out of the box may not be a representative selection but it is the selection upon which the clinician relies. If Komet would like to provide us with us with a statistical analysis and standard deviation of what is representative, we would welcome the opportunity to post their analyses and images.

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

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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.

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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.

The Emperor’s Clothes; Making the Invisible Visible

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The ability to provide unparalleled critical information about teeth and their surrounding tissues has been transformed with the development of 3-D imaging systems such as Cone Beam Computed Tomography. Our knowledge is no longer limited to conventional intra-oral radiographs that represent a two-dimensional view of three-dimensional anatomic structures. Our two-dimensional interpretations can now be replaced with a vast array of three-dimensional data that are more apparent and more applicable for statistical analyses.

We might say that the testing of endodontic files is undergoing a comparable transformation. We are no longer limited to two image representations of a file, (1) the image resulting from scientific research encompassing only one feature of a file and (2) the image resulting from claims of marketing, the emperor’s clothes. The clinical simulator used by NanoEndo to compare files has the ability to precisely determine and record the extent of a file’s capabilities under various circumstances and simultaneously assess its efficacy compared to that of other files. This development is an important step towards being able to distinguish between hype and useful information and may radically change the dentist’s ability to evaluate files. NanoEndo aspires to be the one that points out, “But he isn’t wearing anything at all!” and to make a file’s proficiencies apparent and assessable to all. Is it marketing or is a file carrying a $19 price tag that valuable? Is a $4 price tag cheap? We can provide unbiased computerized testing; you can make the judgement.

 

The file is a Sequence EXS 25/04 before testing. The claim: allows for stress free apical progression and clearing of debris while respecting even the most challenging canal anatomy. The patented BT Tip™ features 6 cutting edges, for increased cutting efficiency. This revolutionary design allows for the use of fewer instruments per treatment. Retail price: $19.33 per file.

The file is a Sequence EXS 25/04 before testing. The claim: allows for stress free apical progression and clearing of debris while respecting even the most challenging canal anatomy. The patented BT Tip™ features 6 cutting edges, for increased cutting efficiency. This revolutionary design allows for the use of fewer instruments per treatment. Retail price: $19.33 per file.

 

This is the same Sequence EXS 25/04 shown above after testing (refer to: https://nanoendo.com/evaluator-v2.php). Reason for failure: The claim features 6 cutting edges at its tip but close inspection shows smooth edges until the greatest tip diameter, 0.25mm, is reached. This causes the tip to have to burnish its way into a canal that has a diameter smaller than 0.25mm. The stress causes the tip to unwind. As the tip unwinds debris in the flutes becomes trapped and causes greater stress from abrasion.

This is the same Sequence EXS 25/04 shown above after testing (refer to: Endo File Evaluator). Reason for failure: The claim features 6 cutting edges at its tip but close inspection shows smooth edges until the greatest tip diameter, 0.25mm, is reached. This causes the tip to have to burnish its way into a canal that has a diameter smaller than 0.25mm. The stress causes the tip to unwind. As the tip unwinds debris in the flutes becomes trapped and causes greater stress from abrasion.

The file is a One Endo file after testing (refer to: Endo File Evaluator). Reason for success: Sharp cutting edges extend very close to the actual tip end, yet opposite the cutting edge the tip is smooth enabling it to follow the canal. Retail price: $11.25 per file with frequent discounts.

The file is a One Endo file after testing (refer to: Endo File Evaluator). Reason for success: Sharp cutting edges extend very close to the actual tip end, yet opposite the cutting edge the tip is smooth enabling it to follow the canal. Retail price: $11.25 per file with frequent discounts.

NiTi Endo 101: understanding terminology of nickel titanium endodontic files

Contributed by Matthew Brock DDS - Southeastern Endodontics

Image contributed by Matthew Brock DDS – Southeastern Endodontics

The success of using instruments while preventing failure depends on how the material, design and technique relate to the forces exerted on the instruments. To fully understand how the file reacts to applied forces, terms have been defined to quantify the actions and reactions to these forces. Common terms related to forces exerted on files have the following definitions:

  1. Stress — the deforming force measured across a given area.
  2. Stress concentration point — an abrupt change in the geometric shape of a file, such as a notch, will result in a higher stress at that point than along the surface of the file where the shape is more continuous
  3. Strain — the amount of deformation a file undergoes
  4. Elastic limit — a set quantity which represents the maximal strain that, when applied to a file, allows the file to return to its original dimensions; the residual internal forces that remain after strain is removed and return to zero.
  5. Elastic deformation — the reversible deformation that does not exceed the elastic limit
  6. Shape memory — the elastic limit is substantially higher than is typical of conventional metals
  7. Plastic deformation — permanent bond displacement caused by exceeding the elastic limit
  8. Plastic limit — the point at which the plastic deformed file breaks

These terms are especially useful in understanding the properties of nickel titanium. The significant advantage of a file made of a nickel titanium alloy is its unique ability to negotiate curvatures during continuous rotation without undergoing  permanent plastic deformation or failure. Simply restated, nickel titanium alloys were the first, and are currently the only readily available economically feasible materials that have the flexibility and toughness necessary for routine use as effective rotary endodontic files in curved canals.

In 1991, the first commercial nickel titanium manual and rotary files were introduced by Dr. John T. McSpadden. In 1993, Dr. McSpadden also introduced the first series of nickel titanium rotary files having multiple non-conventional tapers (McXIM Series) that had six graduating tapers ranging from the conventional 0.02 taper to a 0.05 taper file.  The progressive tapers served to reduce stress by limiting the file’s engagement during the serial enlargement of rotary instrumentation. Nickel titanium is termed an exotic metal because it does not conform to the normal rules of metallurgy. As a super-elastic metal, the application of stress does not result in the usual proportional strain other metals undergo. When stress is initially applied to nickel titanium the result is proportional strain. However, the strain remains essentially the same as the application of additional stress reaches a specific level forming what is termed a loading plateau, during which the strain remains essentially constant as the stress is applied. Eventually, of course, excessive stress causes the file to fail.

This unusual property of changing from an anticipated response to an unanticipated response is the result of undergoing a molecular crystalline phase transformation. NiTi can have three different forms: martensite, stress-induced martensite (superelastic), and austenite. When the material is in its martensite form, it is relatively soft and can be easily deformed. Superelastic NiTi is highly elastic, while austenite NiTi is non-elastic and hard. External stresses transform the austenitic crystalline form of nickel titanium into the stress induced martensitic crystalline structure that can accommodate greater stress without increasing the strain. Due to its unique crystalline structure, a nickel titanium file has shape memory or the ability to return to its original shape after being deformed.

Why different endo files have a different “feel”

The One Endo file's cutting edge extends through its tip.

The One Endo file’s cutting edge extends through its tip allowing it to cut very efficiently. This efficiency, however, may be perceived as having an “aggressive feel”.

Endodontic files basically have three functions: forming a dentinal chip, dislodging the chip, and transporting the chip from an area of file engagement to an area of file disengagement.

A file may have a smooth feel when the blade is burnishing more than cutting, or when the flutes are compacted with debris. Using a “smooth” file usually requires a heavier touch or more pressure for advancement into the canal. Often this feel is confused as an attribute of a more effective file. In fact, the greater pressure required for advancement into the canal causes greater torsion stress that results in a greater propensity for failure compared to more efficient files.

Sharper more efficient files may have a rougher, scratchier feel than that of less efficient files. This is due to the formation of greater dentinal chips. These files require a lighter touch or less pressure for advancement to achieve the same results as less efficient files.

Often when one transitions from using a less efficient file to a more efficient file they have the tendency to use the same force as was required for the less efficient. Greater pressure can result in the formation a larger dentinal chips than can be easily removed and result in unnecessary excessive torsion stress.

Our extensive testing has consistently indicated that applying the following considerations will maximize efficiency and minimize risks:

  • Advance into the canal using no more pressure than was required to advance the first 1mm.
  • 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).
  • 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.

What does progressive flexibility for the One Endo file mean?

Heat treated One Endo files are distinguished by a golden coloration.

In short, progressive flexibility means the flexibility increases as the need for flexibility increases. This is in contrast to the all or nothing approach of other brands. Flexibility of a file can be increased by the following means:

  1. Increase the depth of grooves. However, increasing the depth of flutes can make the instrument more vulnerable to torsional failure, particularly if applied to all file sizes.
  2. Increase the number of spirals. Yet, increasing the number of spirals has two consequences: the file has a greater tendency to screw-in, and debris has a greater distance to travel causing more abrasion and torsional stress.
  3. Apply heat treatment. However, heat treatment usually means decreasing the file’s resistance to torsional stress. Some manufacturers claim that their heat treatment  process actually enhances or has no effect on the file’s resistance to torsion stress. These claims are usually justified by measuring only the number of turns of rotation a file can be twisted before failure without consideration for peak torsion (greatest amount) the file can resist.

For virtually all cases, increasing flexibility decreases a file’s resistance to torsional failure. On the other hand, once the file has adequate resistance to torsional failure due to size, greater cross-sectional mass or flute design, the file’s flexibility can be increased by any or all of the means listed above progressively to enhance the file’s performance. The objective of the One Endo file series is to balance the need for flexibility with the need for torsional resistance. You will notice that One Endo files size 35 and larger are heat treated. The exception is size 35 .04/.06 in which its flexibility is increased by increasing flute depth. File size 55 .04/06 is heat treated to a greater degree to provide the needed flexibility for this large size.

Resistance to Change: What keeps you from leaping ahead?

Are dentists really, as the cliche goes, the most resistant to change? I contend that they change when change is worthwhile. So, what does it take for you to embrace changing endodontic files? Math can affirm that saving just 5 minutes a case can amount to 10-25 days a year of additional income or days off, not to mention the other benefits of efficiency. Even if these savings are validated, resistance to change could be influenced by many factors. Let’s consider some of the usual suspects:

  • You resist change because you feel you will not be able to make the transition easily.
    • Changing the instruments you use on a daily basis is a daunting prospect, especially when it means having to change your technique. While there are basic considerations to address within any technique to maximize its effectiveness, the One Endo File can be used with ANY technique to achieve better results. Also, It can even be used with a reciprocating handpeice as long as its clockwise angle of rotation is greater than that of its counterclockwise rotation. Objection over-ruled?
  • You resist change because you feel you have insufficient information.
    • NanoEndo provides you the opportunity to view side-by-side testing to measure the efficacy, efficiency and stresses of the file you are using with a comparable One Endo file. This is accomplished by using a computerized clinical simulator with precise prescribed movements. Objection over-ruled?
  • You resist change because you feel you believe the current way of doing things works well.
    • I have always identified with a quote from Henry Ford who said, “If I’d asked people what they wanted, they would have told me – faster horses.” Subscribing to the idea that well enough is good enough guarantees that your development and attitude will stagnate. Only with change can you enjoy the benefits of expertise while realizing your full potential. Objection over-ruled?
  • You resist change because you are too invested in inventory.
    • Can you justify investing in new inventory when you already have old inventory? Progress always pays off. We are providing the opportunity to buy what is arguably the best endo file available at half price with no limits on quantity. This price-benefit of the One Endo file is without equal in the market place. But the clock is ticking, and at the end of this year we will end what we think is the best deal around: every time you order a pack, we’ll ship you another for free – plus free shipping on all orders! Objection over-ruled

Remember the quote from Churchill, “To improve is to change; to be perfect is to change often.” Our goal is perfection; the next step is yours. We look forward to serving you. Visit the NanoEndo Store.