Page 31 - The Beauty and Sorrow in Endodontics (WL and C/S)

misinterpreted as material that is not in accordance with standard operating protocols.

As mentioned before, usually the determination of cleaning and shaping completion
is if the master GP cones can be placed smoothly to lWL. This is because in a curved
canal, even if a stiff stainless-steel master file can be pushed to reach the lWL, the soft
and flexible GP may not be able to do the same. Therefore, it is commonly thought that as
long as the GP cone can be place to lWL without obstacles, then shaping of the canals is

completed. However, whether or not the cleaning portion is completed depends on if the
contact time and amount of sodium hypochlorite solution in the canal space is adequate.
Additionally, it is recommended that the master GP cone is precurved to the same degree

as the last instrument to the terminus (master apical file) before cone fit to better
appreciate the fit and tug back sensation of the cone within the canal.

Cone Fit Try-In

How to we choose the correct size and taper for our master cone fit check then? Even
though we don’t know exact what the taper of the original canals are, they are most likely
greater than the standard 0.02, therefore, the standard 0.02 tapered gutta percha cones are

not suitable for obturation. Dr. Schilder recommended the use of conventional gutta
percha cones for master cone fit check. They come in three main tapers: fine (F), fine-
medium (FM), and medium (M). Depending on the manufacturer, their exact taper may
differ, but generally F is 0.04-0.06, FM 0.06-0.08, and M 0.08-0.10. The tip of these
cones resembles a pointed needle tip.

Typically, the last instrument used to clean and shape the apical third of the canal is
at least an ISO #25, meaning the apical diameter would be enlarged to at least 0.25mm or
more. Because of the apical diameter size, when a FM gutta percha cone (0.06 taper) has

been selected as the master cone, a portion of the pointed apical tip should be removed so
that the cross-sectional diameter of the tip on gutta percha cone matches the last
instrument used. Then, this trimmed cone can be pre-curved and gently placed into the
canal to see if it reaches the lWL. If the process is successful, and proper tug back is felt,
the cone can then be further modified based on the cone fit radiograph to the ideal length

(0.5-1mm short of lWL). This 0.5-1mm gap provides enough space for the subsequent
down-pack of warmed gutta percha with pluggers to the ideal obturation depth (fWL).
This master cone fit test is a crucial step to a root canal treatment. It tells the operator if

the canals have been shaped appropriately, and thus is the last step of cleaning and
shaping. It is also the first step to a perfect obturation (Fig B12).

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