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One of the primary goals of endodontic therapy is the
complete debridement of pulp tissue from the canal, coupled
with shaping of the root canal system.
The ability to enlarge a canal without deviation from the
original canal curvature is a primary objective in endodontic
Standard Nickel Titanium rotary endodontic
files, because of their shape memory
property and larger tapers can often not serve
well for complicated cases such as those with
very fine and curved canals.
NiTi is a shape-memory alloy also commonly referred to by the
name Nitinol, derived from its place of discovery, the Nickel
Titanium Naval Ordinance Laboratory. William Buehler, along
with Frederick Wang, discovered its properties during research
The discovery of the shape-memory effect dates to 1932, when
Swedish researcher Arne Olander first observed the property in
gold-cadmium alloys. The material, if deformed while cool,
returns to its undeformed shape when warmed.
Nitinol shape-memory alloys undergo a phase transformation in
their crystal structure when cooled from the stronger, high
temperature form (austenite) to the weaker, low temperature form
How does Nitinol work?
*Austenite: it is quite strong and hard.
Martensite: it is soft and ductile, and it can be easily deformed.
Stress-induced martensite (superelastic): it is highly elastic (rubber-like).
This inherent phase transformation is the basis for the
unique properties of these alloys-in particular, shape
memory and super elasticity.
Eventually a concept emerged which revolutionized the
technology of rotary endodontic files, which was based
on ‘Controlled memory’ in contrast to the classical
‘Shape memory’ one.
A new Nitinol rotary instrument files with controlled
memory (HyFlex® CM, Coltene) was introduced by
Riacrdo Caiecedo & Stephen Clark in 2011, which was
machined from a wire termed (CM-wire) previously
subjected to a proprietary, novel, thermomechanical
processing procedure. Clinical and experimental studies
have indicated that these new HyFlex® CM rotary
instruments have outstanding clinical fatigue resistance.
HyFlex CM file
The Controlled memory effect helps the file to retain the
shape of the canal even when it is out of the canal. This
property is responsible for avoiding procedural errors
such as ledge formation, transportation, perforations
The extreme flexibility and lesser taper of these files
make them very advantageous in curved canal cases.
• ISO color coded on handle-indicates size of file, diameter [mm]
at the tip, assortment (19mm, 21mm, 25mm, 31mm lengths).
• Printed number indicates degree of taper.
• Accelerated flute design provides excellent flexibility, tip
strength and debris transportation.
• Positive rake angle* (except for
orifice opener neutral) for efficient
•rake angle is the angle between the leading edge of a cutting tool and perpendicular
to the surface being cut.
• Non-active tip of file.
• 2 cutting blades.
• Sizes of files have 3 tapers 0.04, 0.06, 0.08
• Cross section was double fluted Hedstroem design, 2 cutting
Features of File
1. Unique NiTi wire treatment that controls the material’s
memory makes the file extremely flexible without rebound
providing superior canal tracking thus virtually eliminates these
typical problems with other files such as:
Superior Flexibility + No Rebound = Superior Tracking
Standard NiTi File Material Hyflex CM NiTi file Material
2. Unique NiTi wire treatment controls the material’s memory
making the file Up to 339% higher fatigue resistance than
standard NiTi files
• Virtually eliminates
• File unwinds before it
separates, this provides
a clear visual warning
4. Controlled Memory (HyFlex CM) files , retain their
shape in curved canals and do not possess the ‘Spring
back action’, thereby avoiding any perforation.
3. Additional file features:
• Increasingly wider flutes provides efficient debris
transportation & prevents file from “screwing” into the canal.
•Absence of radial lands allows the instrument to be sharper and
consequently more efficient.
*Pitch is the distance between a point on the leading edge and the corresponding point
on the adjacent leading edge.
• Accelerated Flute Design (Variable pitch)*.
• The conventional NiTi files have another drawback of not
giving a ‘warning sign’ before breakage (unlike stainless steel
files, which show such signs in the form of unwinding of
flutes, or presence of a shiny spot on the file, indicating that
the file should be discarded). HyFlex files have overcome this
problem with the unique characteristic of rewinding of the file
• If the file does not
rewind, it indicates that it
needs to be discarded.
This is a very useful
criteria for the clinician
to decide when to discard
The following are general recommendations for
the instrumentation process:
• Sterilize files prior to use.
• Operate the handpiece at 500 rpm. Recommended torque setting
is up to 2.5 N.cm.
• Instruments need to be inspected before and after use.
• Recapitulate between each step with the patency file.
• Irrigate/lubricate the canal frequently when using the files.
• Clean file flutes after each insertion into the root canal.
• The number of times the instruments can be reused is
dependent on treatment and procedure.
An advantage of HyFlex® CM files is that they can be used with
multiple techniques (crown-down, step-back) or with the single-
length technique proposed by the manufacturer:
• HyFlex CM showed the highest resistance to fracture than
ProTaper Universal and ProTaper next.
Some of studies on HyFlex CM file
Apical Extrusion of Debris:
• Reciprocating files (WaveOne and RECIPROC) had more
extrusion than HyFlex CM.
• HyFlex CM had significantly less debris extrusion than the
• HyFlex CM had less dentinal crack than the ProTaper Universal
and ProTaper Next.