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.

Exo Endo : Tip Evaluation (1st 3mm)

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DETAILS:

FILE NAME: Exo Endo
COMPANY: NanoEndo, LLC
MANUFACTURER: D&S Dental
MADE IN: USA
WEBSITE: NanoEndo.com

 

CHARACTERISTICS:

SIZE: 25/04
FLUTES: 3; changes to 4
SPIRALS PER 16MM: 2.3
HELIX ANGLE: 9º (25º at handle end) [fig. 2]
CUTTING ANGLE: (-)33º [fig. 1]
DEBRIS REMOVING AREA: 52% [fig. 1]
ROTATION TO FAILURE: 535º
PEAK TORQUE AT FAILURE: 5.06 gf/cm
60 ̊ DEFLECTION: 7.4 g
PLASTIC DEFORMATION: 0º
FILE CORE AREA RELATIVE TO CIRCUMFERENCE AREA: 24%
FILE CORE AREA RELATIVE TO FILE X-SECTION AREA: 66%

 

DISCUSSION:

  • The EXO ends file is comparatively favorable for rotation to failure and peak torque at failure.

    Tip SEM

    Tip SEM

    Fig. 1

    Fig. 1

    Fig. 2

    Fig. 2

     

     

     

     

     

     

     

    SEMs are provided by Dr. Franklin Garcia-Godoy, Professor and Senior Executive Associate Dean for Research Director, Bioscience Research Center University of Tennessee Health Science Center

     

ProTaper Universal : Tip Evaluation (1st 3mm)

DETAILS:

FILE NAME: ProTaper Universal
COMPANY: Dentsply Tulsa Dental
MANUFACTURER: Dentsply Tulsa Dental
MADE IN: USA
WEBSITE: tulsadentalspecialties.com

 

CHARACTERISTICS:

SIZE: X2
FLUTES: 3 (convex)
SPIRALS PER 16MM: 3
HELIX ANGLE: 20º [fig. 2]
CUTTING ANGLE: (-)31º [fig. 1]
DEBRIS REMOVING AREA: 35.8% [fig. 1]
ROTATION TO FAILURE: 358º
PEAK TORQUE AT FAILURE: 11 gf/cm
60 ̊ DEFLECTION: 1.42 g
PLASTIC DEFORMATION: 0º
FILE CORE AREA RELATIVE TO CIRCUMFERENCE AREA: 54%
FILE CORE AREA RELATIVE TO FILE X-SECTION AREA: 83%

 

DISCUSSION:

  • The resistance to torsional failure was relatively high compared to triangular x-sections. This is due to the greater x-sectional area of convex flutes. The cutting angle is less aggressive and requires greater torsion during performance.

    Tip SEM

    Fig. 1

    Fig. 2

     

     

     

     

     

     

     

    SEMs are provided by Dr. Franklin Garcia-Godoy, Professor and Senior Executive Associate Dean for Research Director, Bioscience Research Center University of Tennessee Health Science Center

     

Direct comparisons of a singular NiTi file design with and without heat treatment

TreatmentVsNone

The physical properties of nickel titanium endodontic files that are heat treated for enhancing flexibility differ so widely that definite correlations are difficult to determine. This is particularly true when there are no controls for heat treated files having the same design dimensions. D&S Dental, LLC provided identical files having different degrees of heat treatment for testing and determining correlations. One group of files had no heat treatment (Group A), one group had medium heat treatment (Group B) and one group had greatest heat treatment (Group C). Each group was tested for rotation until failure (suspended at 3mm from tip), peak torque at failure, and force required for 5mm deflection on a 60 degree inclined plane to measure tip flexibility. Group A, no treatment, values were used as base lines for comparisons.The results are as follows:

 

Group B Group C
Degrees Rotation to Failure (+)61% (+)33%
Peak Torque at Failure (-)7.6% (-)69%
Force on 60 Degree Incline (-)12.5% (-)26.6%

 

Although there is an approximate direct correlation for peak torque at failure and force for 60 degree incline flexibility, the degree of rotation to failure appears to be an aberration of expectation. Within the scope of this limited research, we can conclude that heat treatment applied to enhance flexibility will accompany a decrease in resistance in torsional stress.

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

TimeManagement1

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

CardCheat

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?

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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.

handpiece

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

emporer

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.