Page 28 - The Beauty and Sorrow in Endodontics (WL and C/S)

irrigating solution inside the canal.

3. The points with the highest cutting force on a pre-curved file are at the tip of the file
and the curve. Once these two points are place in the canal and activated, their contact
points on the canal wall will vary with each stroke as the depth of file placement and
the rotation speed will be different each time. After multiple cycles, the irregularities
on the wall will gradually be smoothened and removed while maintaining its original

canal flow.
4. The envelope of motion (Fig B6) allows precurved files to remove all the restrictive
and irregular dentin each time it is translated back coronally in the canal.

Rotational Speed +/- Translational Speed = Various Combinations of Cutting
A. If we want to enlarge the canal quickly, we need more rotary and less translation
movement of the instrument. This is used when the canal is straight and has adequate
dentinal thickness (less risk of perforation) and no resistance.

B. More rapid translation and less rotation of the instrument will slowly produce the best
shape for individual canals. This is used when either the dentinal wall is thin or the
canals are curved.

ISO Traditional Stainless-Steel Files

Traditional stainless-steel files have 0.02 taper, meaning the diameter of the cross-
section of the file increases by 0.02mm each 1mm increment coronally. Similarly, if a file

has a 0.04 taper, its diameter increases by 0.04mm every 1mm of coronal advancement.
Presently, the ISO stainless-steel system is still widely accepted around the world and its
design recommendation is to use 0.02 taper as the standard. If a larger taper was used, the

rigid stainless-steel file will not be able to enter and shape a curved canal. Of course,
most canals don’t have an even 0.02 taper, and with the advancement of materials and
technology, many files with varying tapers can still maintain its flexibility. The logic
behind this development is to reduce the number of files required to shape the canal to the
targeted taper, which will ultimately reduce the amount of time required to complete

cleaning and shaping. In addition, many manufacturers have designed files with specific
cross-sections, cutting angle, sharp transition angle, etc. Many of these designs aim to
reduce the risk of perforation and damage to the walls while simultaneously increasing

the efficiency at shaping.
During cleaning and shaping, the first file to enter the canal is often a stainless-steel

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