Ding! The wretched sound of a nickeltitanium
(NiTi) file breaking in a patient’s
tooth. Ding! That was the sound of the
cash register when it came to pay for NiTi
files. For many years that was the duality
of nickel titanium instruments. You had
these wonderfully efficient files that far
surpassed the shaping instruments before
them, but that still had two major flaws—
breakage and cost.
In 1988, Dr. Harmeet Walia presented
the modern use of NiTI rotary instruments
in endodontic therapy and the path
of future treatment changed forever. The
benefits of NiTi, such as the ability to
negotiate curved canals and reduce transportation
made the shaping of root canals
significantly more efficient and predictable.
Early NiTi rotary instruments
were fairly rigid and lacked
the advances in metal chemistry that exist today. Because most root canal systems are dynamic
and not straight, early NiTi files had the propensity to fracture
during use. This tragic event is called cyclic fatigue and
is thought to be brought on from crack initiation on a surface
irregularity during manufacturing.2,3 When the material
has reached its elastic limit, it breaks. This is not dissimilar
to a paper clip being broken after repeated movement.
Many studies have shown that as the angle of the curve
increases, the time to fail decreases.4 Therefore, as the number
of rotations or the amount of curvature increase, the
chance of fracture increases and the time for the instrument
to reach its elastic limit greatly decreases. Thus the goal of
any advances in NiTi rotary design would address the
amount of stiffness and flexibility of the instrument as well
as the mean seconds to fracture.
In the past two years a new advance in endodontic NiTi
instrumentation has taken place. Addressing many of the
negatives of previous systems, the EdgeEndo files have made
a monstrous jump in our ability to clean and shape curved
canals quickly, efficiently and in a cost effective manner. The
files utilize heat treatment as well as advanced metallurgy to
significantly alter the ability of the files to shape curved
canals, and do so with almost zero risk of separation.
Edgefiles have a high fatigue threshold (655.6 seconds). This
extra time gives the operator a safety cushion when shaping
cases. They also have flexibility–.0047nm according to an
ISO stiffness test, which tests ductility or flexure.
So what does all this mean, and how does this translate
to clinical endodontics? Well, when I first started using these
files after over 10 years of GT files, I was awestruck at just
how efficient these files were. After treating one of my
patient’s first lower molars with two files, I went and used
the same files on six more extracted teeth without the
instrument showing any signs of cyclic fatigue. And after
almost a year and a half of use I haven’t seen one separation,
and as an endodontist practicing in the state of Florida, I
live in calcified canals all day. It is only one in 50 cases that
is truly “open.” The Edge files have really changed the way
I perform my shaping procedures and are so efficient that I
find I have to have patients sit for additional time to allow
the sodium hypochlorite to have enough exposure time to
be fully effective.
A further benefit of the Edgefile system is that it allows
conservation of dentin. Older systems required very large initial
tapers used in a crown down manner. The GT file system
for example required the use of a .12, .10, .08, and then a .06
taper instrument. The use of such large initially tapered instruments
places the tooth at risk for fracture and loss of retention.
The Edgefiles allow a single .06 taper to fully shape the canal
while not removing excess dentin. While there aren’t any current
studies that can quantify just how much dentin removal
causes a certain proclivity to fracture, all studies point to the
conservation of dentin being paramount to tooth retention
and prevention of vertical root fractures.
Clinically the Edgefiles couldn’t be easier for a general
dentist or endodontist to integrate into the current technique.
I have tried all current file systems and have come up
with an extremely simple system which can be used in the
majority of cases.
After access is made (preferably under a microscope),
length is obtained using an electronic apex locator with a 10-
C file followed by a 15 Hedstrom file. Now the case is ready
for the Edgefiles. While keeping the chamber flooded with
8% NaOCL (for organic tissue removal and lubrication) a 30
.04 Edgefile X5 is taken to length. Next a 30 .06 Edgefile X5
is taken to length. If the 30 .06 file won’t go to length after
two passes, a 25 Hedstrom file can be used to open up a large
glide path. If the canal is wide enough to warrant further apical
enlargement (such as palatal roots and distal canals of
lower molars) a 40 .06 can be used as a final shape. This technique is almost foolproof and fully reproducible in most of
the cases I see. My goal is to fully instrument to the anatomic
apex (0.0 on the apex locator), although the literature shows
this might be past the actual foramen. By instrumenting in
this manner it allows the custom fit .06 gutta percha to
exhibit a very strong tugback without false binding coronal to
the apical 2-3mm. After using sonics and ultrasonics to activate
8% NaOCL, 17% EDTA and 2% CHX, the case is ready
to be filled. Here are six cases that exhibit the benefit of flexibility
and resistance to fracture.
One of the dings of nickel titanium is breakage, but let’s
spend a moment discussing the elephant in the room: cost. For
years, nickel-titanium patents were controlled by one company
and prices were on an ever-lasting slope. The ding of the cash register!
This was the other main disadvantage of utilizing rotary
instruments. A busy endodontic practice might be spending
upwards of $20,000 per year on rotary instruments. With the
Edgefiles being priced at a third of the cost of competitors’ files,
the practitioner will be saving a tremendous amount of money.
It’s a win-win for the practitioner. Ding!
- Walia H, BrantleyWA,GersteinH.Aninitialinvestigationofthebendingandtorsional properties of nitinol
root canal files. J Endod 1988;14:346
- Haikel Y, Serfaty R, Bateman G, Senger B, Allenmann C. Dynamic and cyclic fatigue of enginedriven
rotary nickel-titanium endodontic instruments. J Endod 1999;25:434 – 40. –51.
- SattapanB,NervoG,PalamaraJ,MesserH.Defectsinrotarynickeltitaniumfileafter clinical use. J Endod
- LiU,LeeB,ShihC,LanW,LinC.Cyclicfatigueofendodonticnickel-titaniumrotary instruments: static
and dynamic tests. J Endod 2002;28:448 –51.