Basics of nickel titanium instruments in Endodontics

1. NICKEL-TITANIUM
Instruments
In ENDODONTICS
Presenter:
Dr. Ashok Ayer
Department of Conservative Dentistry & Endodontics
College of Dental Surgery
BPKIHS, Dharan, Nepal

2. Contents:
1. Brief History of Canal Instrumentation
2. Manufacture of Instruments
3. Nickel Titanium in Endodontics
4. Basic Properties of metals
5. Atomic structure of Ni-Ti
6. Shape memory
7. Superelasticity
8. Effects of Heat Sterilization on Properties of Nickel-Titanium
Instruments
9. Failure of Nickel-Titanium Instruments and Failure Mechanisms
10. Strategies for Improved Nickel- Titanium Instruments
11. Comparative studies
12. Endodontic Instrument Standardization
13. Sotokawa classified Instrument damage
14. Nickel- Titanium Precautions and Prevention
15. Handpieces for engine driven instruments
16. Controlled Memory / M / R phase Nickel-Titanium Wires
17. Conclusion

3. Brief History of Canal Instrumentation
Historically the earliest instruments were crude
made initially out of watch springs.
The first recorded was in 1838 manufactured by
Edwin Maynard (Castellucci).
In 1864 a thin rubber leaf retained by a clamp
was used to isolate the tooth (Castellucci) and
protect the patient while preparing the tooth

4. Early files were ground into a barbed
shape out of circular wire and were used
to remove vital or non-vital pulp
remnants.
Reamers and files are most commonly
made out of round wire that has been
ground to a tapered square or triangular
section and twisted to form the reamer
or file.

5. Manufacture of
Instruments
Files can be manufactured by either twisting
or by machining. Some files are ground out of
a circular blank of stainless steel, for example
Hedstrom files, rather than twisted
The most common method of manufacture is
to grind the blank metal shape and then twist
it.

6. The nickel- titanium alloy is difficult to
machine as the properties of the alloy can be
changed during the manufacturing process.
Variables such as feed rate, lubrication, and
heat treating during the fabrication process
can influence the final product
New manufacturing methods that employ
casting of the alloy or stamping wire blanks.

7. Different properties can be afforded to the
file if the wire is ground to a different
shape before twisting.
K Flex. files, for example, are twisted out
of a rhomboid metal blank rather than the
square blank used to create the file
resulting in greater flexibility

8. The design of the blank affects how
efficiently the file cuts dentine.
The efficiency is dictated by the rake
angle of the files.
A positive rake: are efficient and remove
dentine, but can more easily get stuck
as they will lock into the canal wall if
screwed in.

9. A neutral rake angle exists where the flutes are at
90 degrees to the tooth surface and cut as they are
scratched over the dentine.
A negative rake is where the cutting blade is angled
away from the direction of cutting
With the ability to machine flutes, many new
designs such as radial lands have become
available.
Radial lands allow nickel- titanium files to be used
as reamers in a 360˚ motion as opposed to the
traditional reamers with more acute rake angles.

11. Most instruments have a non-cutting tip
that is not active.
The non-cutting tip is designed so that it
will follow the root canal rather than cut
and so reduces the incidence of ledges

12. Nickel Titanium in
Endodontics
A new generation of endodontic instruments,
made from nickel- titanium, has added a new
dimension to the practice of endodontics.
The superelasticity of nickel- titanium, the
property that allows it to return to its original
shape following significant deformation,
differentiates it from other metals, such as
stainless steel, that sustain deformation and
retain permanent shape change.

13. Stainless steel is the main metal used
for hand instruments in root canal
therapy.
Its advantage over carbon steel is that it
is not prone to corrosion caused by the
chemicals used in root canals or by
steam sterilisation
NiTi:(rotary instruments): shape
memory, flexibility characteristics, and
resistance to torsional fracture.

14. Harmeet Walia thought that nickel
titanium alloy might have enormous
potential for endodontic files.
The NiTi alloy used in orthodontics and
endodontics was developed by Wiliam E
Buehler and associates
"Nitinol" from nickel, titanium, (and in
1960s) -- nickel titanium alloy by the U.S.
Naval Ordinance Laboratory

15. Using special large-diameter orthodontic
wires contributed by the,
Unitek Corporation, Quality Dental
Products (Johnson City, TN)
Fabricated the first prototype NiTi hand files
by machining rather than the conventional
manner of twisting the tapered stainless
steel wire blanks

16. Both Ni and Ti have several valences
-- NiTi, Ti2Ni3 , and Ti2Ni,
Original alloy-- 55% Nickel and 45% titanium
Nickel 52%
Titanium 45%
Cobalt 3% modify transition temperature
and mechanical properties

17. Types of Nickel Titanium alloy
1.Conventional or elastic
2.Newer or superelastic
A. Pseudoelastic
B. Thermoelastic

18. 1. Crystals
• Specific geometry
• Atoms are arranged in unit cells, repeated
again to form lattice
cation- anion
arrangement resist
deformation
Increases the
strength of crystals

20. 2. Grain
• A microscopic single crystal in the
microstructure of a metallic material.
Crystal
growth
Crystal
penetrate
each other
Grain
Boundary:
Weaker,
noncrystalline
structure

21. 3. Lattices
The three-dimensional network of lines
connecting the atoms in undisturbed crystals
Body centred
cubic (BCC)
Face centred
cubic (FCC)

22. Monoclinical
Martensite (low-temperature phase, with a
monoclinic B19 structure

23. 4. Lattice defects:
• Weaken the material
• Substituent metals: Nickel or chromium for iron
in stainless steel

24. 5. Lattice deformation
Metals with BCC or FCC cells are densely
packed,
Slip planes - plastic deformation (e.g.pressing,
spinning, rolling, drawing, extruding) yet maintain
the integrity of the crystal.
Small stress - atoms return back- nonpermanent
or elastic deformation

25. • Stress exceeding the elastic limit- permanent
or plastic deformation results.
• Greater stress causes the material to fracture.
Crystal deform Lattice deform
Stresses atomic
bond
Increases resistance to
further deformation
Strain, work
hardening or cold
work

26. 6. Polymorphism
Crystallize into more than one structure
(FCC) Low temperature (BCC)

27. 7. Twinning
Deformation that divides lattice into two
symmetric parts at an angle
• High temperature- detwinning occurs- shape
memory

28. 8. Transition
Iron--- higher temperature--- austenite
(912C to 1394C)
Ni substituted for some Fe atoms, it can be
stable even at room temperature.

29. Ni-Ti alloy is present in-
Austenitic phase: Body centred cubic
Higher temperature
Lower stresses
Martensitic phase: Monoclinic
Lower temperature
Higher stress
R phase: Rhomboidal structure
Intermediate between transition

30. Formation of R-phase is favoured by the
presence of dislocations and
precipitates in the NiTi alloy.

31. Bradley et al. used DSC (Differential Scanning
Calorimetry) to compare superelastic, nonsuperelastic,
and shape memory NiTi orthodontic wires.
This later transformation is completed at an Af
temperature of approximately 25°C, so the as-received
instrument will be in the superelastic condition at
37˚C.
(Bradley et al. Am J Orthod dentofacial Orthop 1996)

32. The optimum microstructure for
superelastic NiTi rotary instruments would
have the maximum amount of austenite
that could reversibly transform to
martensite, with a large enthalpy change.
Transformation temperatures were
decreased after clinical use of the
instruments.

33. Springback
Chinese NiTi Nitinol
Stainless
> > steel
1.6 times 4.4 times

34. SHAPE MEMORY
A phenomenon that can recover
permanent strains when they are heated
above a certain temperature.
(specific thermodynamic property)
Transformation between austenite and
martensite occurs by a twinning process
at the atomic level, and the reversibility
of this twinning is the origin of shape
memory.

36. Temperature-induced phase transformation without
mechanical loading.

37. Transition temperature:
Pure substance -- definite melting point
In NiTi alloys, martensitic transformation occur within
the temperature range (TTR).
Varies –
Eg: Thermal NiTi: 25 C- 82 C
the cooling and heating curves do not overlap.
This difference (40- 60C) is called hysteresis

39. Composition and metallurgical treatments
have dramatic impacts on these transition
temperatures.
NiTi can have 3 different forms: martensite,
stress-induced martensite (SE), and austenite.
When the material is in its martensite form, it is
soft and ductile and can easily be deformed.
SE NiTi is highly elastic.
Whereas austenitic NiTi is quite strong and
hard

40. Superelasticity
Superelasticity is a phenomenon wherein the stress
remained nearly constant despite the strain change within
a specific range.
Alloys such as nickel- titanium, that show superelasticity,
undergo a stress-induced martensitic transformation from
a parent structure, which is austenite.
On release of the stress, the structure reverts back to
austenite, recovering its original shape in the process.
Deformations involving as much as a 10% strain can be
completely recovered in these materials, as compared
with a maximum of 1% in conventional alloys.

41. NiTi particularly exhibits superelastic
behavior between 10oC – 125oC
Other alloys with superelastic properties
are the alloys of copper-zinc, copper-aluminum,
or titanium-niobium
Ideal temperature range in endodontics is
23oC to 36oC, the temperatures found in
the composition of 50% Ni and 50% Ti

42. Stoeckel and Yu.
Stress of 2,500 MPa was required to stretch a
piano wire to 3% strain, as compared with only
500 MPa for a nickel-titanium wire.
At 3% strain, the music wire breaks.
Minimum residual deformation occurs at
approximately room temperature.
(Stoeckel D, Yu W. Wire J Int 1991 march: 45-50)

43. The First Use of NiTi in Endodontic Rotary Files
1991 NiTi Co. had two rotary file designs
to make up their file line
These two file designs were developed
uniquely for continuous 360o rotation

44. The first file design, U-File design, which
continues to be offered today as the
Profile, GT and LightSpeed, for sizes #15
through #35
The second file design, the Sensor File,
was used in sizes #40 to #60 and
incorporated two sets of flutes having
different helical angles

45.  Oregon Health Sciences University compared
four instrumentation techniques
1) Step-back preparation with K-files
2) Crown-down preparation with K-files
3) Sonic instrumentation with Shaper-Sonic files
4) NiTiMatic preparation system with NiTi rotary
files

46. Incidence of zipping, ledging, and elbow
formation was found to be the lowest with the
use of the NiTiMatic preparation system with
NiTi rotary files

47. In 1993 the University of Tennessee
Amount of material removed at the
working length:
Rotary 0.017 mm
Hand NiTi 0.023 mm
Hand stainless steel 0.139 mm
The canal width of the inner wall to be
closer to the original width and more
centered with the rotary group

48. This illustrates the increase in canal width on
the inside of the curve at the point of
curvature

49. Nickel-titanium instruments are as effective
as or better than comparable stainless steel
instruments in machining dentin.
Nickel- titanium instruments are more wear
resistant
Nickel- titanium files are biocompatible and
appear to have excellent anticorrosive
properties

50. Kuhn and Jordan:
Heat treatments below 600°C caused increased
bending flexibility.
Flexibility was decreased by heat treatments
above 600°C
Heat treatment at 400°C, corresponding to
the recovery annealing stage before
recrystallization,
Be utilized by manufacturers prior to machining
the NiTi instruments to decrease the work
hardening of the alloy.
(Kuhn G, Jordan L. J Endod 2002;28:716-20)

51. Effects of Heat Sterilization on Properties
of Nickel-Titanium Instruments
Repeated sterilization has been found by
Silvaggio and Hicks and Canalda-Sahli et
al. to cause changes in torsion and
bending properties, and to affect cutting
efficiency.
Hilt et al. found no effects on the torsional
properties, hardness, and microstructure of
NiTi files from the number of sterilization
cycles and the type of autoclave
sterilization.
(Hilt BR et al. J Endod 2000)
(Silvaggio J, Hicks ML. J Endod 1997) (Canalda-Sahli et al. Int Endod J 1998)

52. Whether sterilization caused relief of the
residual stresses present in the as-received
instruments from the
manufacturing process.
Such residual stresses may contribute to
the clinical failure of the NiTi
instruments.

53. Failure of Nickel-Titanium Instruments
and Failure Mechanisms
The manufacturing process of machining
the NiTi rotary instruments from starting
wire blanks results in rollover at the edges
of the flutes and a variety of surface
defects.
Machining grooves, microcracks, and
surface debris are evident when as-received
instruments are examined with a
scanning electron microscope, and
instrument fracture generally occurs at
surface defects.

54. Clinical studies by Knowles et al. for
LightSpeed instruments and by Di Fiore et
al. for ProFile, ProTaper, ProFile GT, and K3
Endo instruments reported separation
(fracture) rates of less than 1.5% and much
less than 1% respectively.
One contributing mechanism for clinical
failure of NiTi instruments, reported by
Alapati et al, may be the widening of surface
machining grooves by tenacious dentin
debris deposits.
(Alapati et al. J Endod 2005;31:40-3)
(Knowles et al. J Endod 2006;32:14-16) (Di Fiore et al. Int Endod J 2006;39:700-8)

55. Instruments generally appeared to
exhibit ductile fracture, rather than brittle
fracture
NiTi alloys for rotary instruments can
possess significant ductility in bending
and torsion, without experiencing
separation in certain clinical cases,
where the canals have substantial
curvature or where rotation of the tip is
hindered.

56. Fracture initiation often appears to occur
at machining grooves, with a possible
role from retained dentin debris in these
grooves.
Retrieved instruments, which failed
during clinical use, may fracture from
cyclic fatigue after longer periods of use
or from single overload events after
relatively brief periods of use.

57. Tepel et al. Bending and Torsional properties of 24
different types of nickel- titanium, titanium-aluminum,
and stainless steel instruments.
They found the nickel-titanium K-files to be the
most flexible, followed in descending order by
titanium-aluminum, flexible stainless steel, and
conventional stainless steel.
When testing for resistance to fracture they found
that No. 25 stainless steel files had a higher
resistance to fracture than their nickel- titanium
counterpart.
(Tepel et al. J Endod 1997;23:141-5)

58. While studying cyclic fatigue using nickel-titanium
instruments: canal curvature and
the number of rotations determined file
breakage.
Separation occurred at the point of
maximum curvature of the shaft.

59. A series of studies considered rpm as a
primary factor.
Two studies concluded that higher rpm
resulted in more separation and distortion.
Another concluded that lower rpm resulted
in more file distortion.
Zelada et al. stated that rpm was not a
significant factor but that a canal curvature
of greater than 30˚ was significant.
(Zelada et al. J Endod 2002;28:540-2)

60. In general, instruments used in rotary
motion break in two distinct modes,
torsional and flexural.
Torsional fracture occurs when an
instrument tip is locked in a canal while
the shank continues to rotate, thereby
exerting enough torque to fracture the
tip.
Cohen’s Pathways of the Pulp: 10th ed.

61. Cohen’s Pathways of the Pulp: 10th ed.
Diagram comparing fracture loads at D3 (upper section of graph) to torques
occurring during preparation of root canals (lower section of graph). Filled
columns represent the largest file in each set, and open columns show the scores of
the most fragile file.

62. A crown-down approach is
recommended to reduce torsional loads
(and thus the risk of fracture) by
preventing a large portion of the tapered
rotating instrument from engaging root
dentin (known as taper lock)
The clinician can further modify torque
by varying axial pressure, because
these two factors are related.
Cohen’s Pathways of the Pulp: 10th ed.

63. Flexural fracture occurs when the cyclic
loading leads to metal fatigue.
This problem precludes the manufacture of
continuously rotating stainless steel
endodontic instruments, because steel
develops fatal fatigue after only a few
cycles.
NiTi instruments can withstand several
hundred flexural cycles before they fracture
Cohen’s Pathways of the Pulp: 10th ed.

64. Strategies for Improved Nickel- Titanium
Instruments
Electropolishing the machined surfaces.
Ion implantation to create harder surfaces, and use
of special surface coatings.
Boron-ion implantation more than doubled the
surface hardness of Nitinol at the nano-indentation
depth of 0.05 μm, yielding a hardness
value greater than that of stainless steel
(Lee DH et al. J Endod 1996;22:543-6)

65. Schafer used a physical vapor
deposition (PVD) process to create a
TiN surface coating on NiTi instruments.
Surface-coated instruments had greater
cutting efficiency (penetration into plastic
samples with cylindrical canals)
compared with control instruments.
Their cutting efficiency was not altered
by repeated autoclave or sodium
hypochlorite sterilization.
(Schafer E. Et al. Int Endod J 2002;35:867-72)

66. COMPARATIVE
STUDIES
Himel et al. compared hand nickel- titanium filing of plastic
blocks with curved canals to stainless steel filing.
Working length was maintained significantly more often (p<
.05) in the nickel- titanium group than in the stainless steel
group.
There was no ledging of canals using the more flexible
nickeltitanium files compared with 30.4% ledging when
stainless steel files were used.
Apical zipping occurred 31.7% less often with the Nitinol files.
Stripping of the canal walls was less with NiTi
(Himel et al. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1995;79:232-7)

67. Gambill et al.
Using computed tomography
Reamed extracted teeth with either stainless
steel or NiTi files.
Nickel- titanium files caused less canal
transportation, removed less dentin, were more
efficient, and produced more centered canals.
(Gambill et al. J Endod 1996;22:369-75)

68. Elliot et al.
 Compared Stainless steel (Flexofiles) and NiTi
(NiTi flex) files
 It is preferable to use nickel- titanium
instruments in a balanced force technique and
stainless steel in a filing technique because
stainless steel files can be precurved.
 Considering these results, nickel-titanium
instruments should be used as reamers, not
files.
(Elliot LM et al. Endod Dent Traumatol 1998;14:10-15)

69. Blum et al.
The crown-down technique with ProFile instruments
produced less force than the stepback technique
The more a file was in contact with the canal wall, the
higher the forces on the instrument and the canal wall.
Another study compared the use of a sequence
of 0.04 tapered instruments with a sequence
using 0.04 and 0.06 instruments.
The sequence using the two different tapers produced
less force.
(Blum et al. Int Endod J 1999;32:32-46) (Schrader et al. J Endod 2005;31:120-3)

70. When more flutes per unit length are
engaged, higher forces are the result.
Lubrication also influences the forces
that can be generated during canal
instrumentation.
In particular, the use of an EDTA
chelation solution significantly reduced
maximum torque values for ProFile
instruments.

71. Nickel-titanium instruments showed
superior resistance to angular deflection;
they fractured after,
2½ full revolutions (900 degrees)
Compared to 540 degrees for stainless steel
instruments.
Cohen’s Pathways of the Pulp: 10th ed.

72. IRRIGANTS AND
STERILIZATION
Haikel showed that even lengthy
exposure to sodium hypochlorite did not
cause nickel-titanium fiIes to fail at lower
torsional moment values
In a study that compared nickel- titanium
files with stainless steel files, it was
shown that even 40 sterilization cycles
had no effect on the torsional moment at
failure for either file type.
(Haikel et al. J Endod 1998;24:731-5) (Hilt B et al. J Endod 2000;26:76-80)

73. Endodontic Instrument Standardization
International Standards Organization (ISO)
(based on use)
Group I: hand use only:
 K-type files
 H type file
 R-Type rasps
 Barbed broaches
 spreaders
 condenser
Group II: engine driven latch type
Same design as in group I but made to attach to hand piece.
Niti Rotary instruments like Profile, Lightspeed.

74. Group III: engine driven latch type
Endodontic engine driven instruments fabricated from a
single metal latch and shaft and operative head.
Gates Glidden drills and Peeso reamers.
Group IV: root canal points.
Gutta percha, silver points and paper points.

75. According to stock
Twisted Machined
K-files H file
K- reamer Flex R
K-flex file Canal master
Flexo Heliapical
Zipperer flexicut Flexogates
Mc spadden engine file

76. According to Cohen
• Hand instruments: those specific to endodontics
• Instruments for pulp space preparation
• Group I
• Group II
• Group III
• Devices for root canal length measurements
• Instruments for root canal obturation
• Devices for removal of root canal obstructions

77. STANDARDIZATION (Ingle and Levine)
(1959)
Instrument are numbered from 10 to 100, the numbers
advance by 5 units to size 60 & then by 10 units till size
100.
Each number shall describe the diameter of instrument
in 100th of a mm at the tip
Ex: No.20 is 0.20 mm (20/100) at the tip.
The working blade (flutes) shall begin at the tip
designated as D1 & the flutes extend to the length of
16mm designated as D2.

79. The diameter of D2 shall be 32/100 or 0.32mm
greater than that of D1.
This sizing ensures a constant increase in taper of
0.02mm per mm for every instrument regardless of
the size.
Other specifications were added later. These includes:–
• The tip angle = 75±150
• Addition of D3
 3mm from D1.
• Instrument sizes should increase by 0.05mm at D1
between Number 10 – 60.
From Number 60- they should increase by 0.1mm.

81. ADA Specification revised in March 1981 stated
 Instrument sizes No. 6,8,10 were added to original
standardization.
 Also 110 to 150 were added for increased selection.
 D1 and D2 changed to D0 and D16
Newer changes includes:
 Addition of tapers greater than ISO 0.02 taper

82. Colour coding :
The instrument handles have been color coded for easier
recognition.
White 15 45 90
150
Yellow 20 50 100
Red 25 55 110
Blue 30 60 120
Green 35 70 130
Black 40 80 140
Pink 06
Grey 08
Purple 10

83. ADA/ANSI AND ISO/FDI NUMBERING
SYSTEMS
ANSI GENERAL DESCRIPTION ISO / FDI
28
58
63
71
78
Root Canal Files (K-type)
Hedstroem Files (H-type)
Barbed Broaches and Rasps
Root canal Enlargers
Condensers, Pluggers, Spreaders
Obturating Points
3630/1
3630/1
3630/1
3630/2
3630/3
6877

84. Sotokawa classified Instrument damage :
Type I : Bent instrument.
Type II : Stretching / straightening of twist contour.
Type III : Peeling off metal at blade edges.
Type IV : Partial clockwise turn.
Type V : Cracking along axis.
Type VI : Full fracture.

85. Nickel- Titanium Precautions
and Prevention
Avoid too much pressure is applied to the file.
Never force a file! These instruments require
a passive technique.
If resistance is encountered, stop
immediately, and before continuing, increase
the coronal taper and negotiate additional
length, using a smaller, 0.02 taper stainless
steel hand tile.

86. Canals that join abruptly at sharp angles are
often found in roots such as the mesiobuccal
root of maxillary molars, all premolars, and
mandibular incisors and the mesial roots of
mandibular molars.
The straighter of the two canals should first be
enlarged to working length and then the other
canal, only to where they join.
If not, a nickel-titanium file may reverse its
direction at this juncture, bending back on itself
and damaging the instrument.

87. Curved canals that have a high degree and
small radius of curvature are dangerous.
Such curvatures (over 60˚ and found 3 to 4
mm from working length)
A nickel-titanium instrument should not be
used to bypass ledges.
Teeth with "S"-type curves should be
approached wlith caution! Adequate flaring
of the coronal third to half of the canal.

88. When the file feels tight throughout the length
of blade, it is an indication that the orifice and
coronal one-third to two-thirds of the canal
need increased taper
The file should be straight. If any bend is
present, the instrument is fatigued and should
be replaced.

89. ROTARY CONTRA-ANGLE HANDPIECE
INSTRUMENTS
Electric handpieces are available
wherein not only the speed can be
controlled but the torque as well.
The speed and torque can be set for a
certain size instrument and the
handpiece will "stall" and reverse if the
torque limit is exceeded

90. Tri Auto-ZX has three automatic functions:
The handpiece automatically starts when the file
enters the canal and stops when the file is
removed.
If too much pressure is applied, the handpiece
automatically stops and reverses rotation.
It also automatically stops and reverses rotation
when the file tip reaches the apical stop, as
determined by the built-in apex locator.
The Tri Auto-ZX works in a moist canal

91. RECIPROCATI NG HANDPIECE
Giromatic (Medidenta/Micro Mega).
Only latch-type instruments.
Quarter-turn motion is delivered 3,000 times per
minute.
The Endo-Gripper (Mayea/Union Broach) is
a handpiece, with a 10:1 gear ratio and a 45°
turning motion

92. M4 Safety Handpiece
(Sybron-Kerr, Orange,
CA).
30˚ reciprocating motion
and a chuck that locks
regular hand files in
place by their handles
Recommends their
Safety Hedstrom
Instrument

93. VERTICAL STROKE (HANDPIECE)
Driven either by air or electrically that delivers a vertical
stroke ranging from 0.3 to 1 mm.
The more freely the instrument moves in the canal, the
longer the stroke.
The handpiece also has a quarter-turn reciprocating motion
that "kicks in," along with the vertical stroke,
If it is too tight, the motion ceases, and the operator returns
to a smaller file.
The Canal Finder System (Marseille, France) uses the A-file,
a variation of the H- file.

94. Controlled Memory Nickel-Titanium Wires Used in the
Manufacture of Rotary Endodontic Instruments
CM wire, a kind of Ni-rich NiTi alloy that
possessed a relatively high As and Af
compared with regular Superelastic (SE) wire.
Maximum strain before fracture of the CM wires
was more than 3 times higher than it was for
the SE wires.
Greater flexibility of endodontic instruments
manufactured with CM wires than similar
instruments made of conventional SE wires.
HyFlex CM, TYPHOON Infinite Flex NiTi
(Hui-min Zhou, J Endod 2012;38:1535–1540)

95. M-Wire Nickel-Titanium Shape Memory Alloy
Used for Endodontic Rotary Instruments
Unique nano-crystalline martensitic
microstructure.
Higher strength and wear resistance
than similar instruments made
of conventional superelastic NiTi wires
ProFile GT Series X, ProFile Vortex, and
Vortex Blue
(Ya Shen et al. J Endod 2013;39:163–172)

96. CM Wire and M-Wire instruments have
increased austenite transformation
temperatures.
The Af of CM Wire, M-Wire, and
conventional SE NiTi wire are
approximately 55˚C, 50˚C, and 16- 31˚C
respectively.
(Ya Shen et al. J Endod 2013;39:163–172)

97. A hybrid (austenite-to-martensite)
microstructure with a certain proportion of
martensite is more likely to have favorable
fatigue resistance than a fully austenitic
microstructure
This is generally explained by the fatigue-crack
growth resistance of the martensite,
Which is found to be superior to that of
stable austenite, particularly near the
threshold, by comparing the fatigue behavior
of the various microstructures in nitinol.

98. R-Phase Alloy
The Twisted File is a NiTi rotary file
manufactured with R-phase alloy using a
twisting method. It has been reported to have
a higher fatigue fracture resistance than
ground files
The R-phase shows good superelasticity and
shape memory effects; its Young modulus is
typically lower than that of austenite.
(Ya Shen et al. J Endod 2013;39:163–172)

99. Conclusion:
The mechanical properties of the NiTi
alloy can be improved by altering the
microstructure via cold work and heat
treatment.
Therefore, new NiTi endodontic files with
superior properties can be developed
through special thermomechanical
processing.

100. To be
Continued……..

101. References:
1. John I Ingle ,Leif K Bakland ,J Craig
Baumgartner. Endodontics,6th edition .
2. Cohen and Hargreaves. Pathways of
pulp,10th edition
3. Franklin S Weine. Endodontic therapy. 6th
edition.
4. JAMES L.GUTMANN. Problem solving in
endodotics; 4th edition
5. Endodontics Principles and Practice. Fourth
edition by Mahmoud Torabinejad and Richard
E. Walton.
6. Journal of Endodontics
7. International Endodontic Journal

102. SR-71 Blackbird: titanium-molybdenum
alloy