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.