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.