NiTi files - RECENT ADVANCES

Dr. K. Palani Selvi MDS
Conservative Dentist & Endodontist

 Introduction
 NiTi metallurgy
 Advances in NiTi files
- Metallurgy
- File motion
 Conclusion

INTRODUCTIO
N
 Nickel titanium being super elastic, allows preparation of
curved canals with minimal transportation
 Nickel titanium (NiTi) rotary files decrease the procedural
errors especially in the apical area of the curved canal
 The disadvantages of NiTi files are their high cost and
unexpected fracture
 The recently introduced nickel-titanium (NiTi) files are
claims to be able to completely prepare and clean root
canals with only one instrument

Austenitic phase:
 Body centred cubic
 Higher temperature
 Lower stresses
Martensitic phase:
 Monoclinic
 Lower temperature
 Higher stress
R phase:
 Rhomboidal structure
 Intermediate between transition
NiTi Metallurgy

ADVANCES IN NITI FILES
Broadly grouped as
 Advances in Metallurgy
 Advances in file Motion

ADVANCES IN NITI METALLURGY
1. Austenite NiTi – One shape
2. Electrochemical surface treatment - BT-RaCe
3. M-wire - WaveOne and Reciproc
4. Martensitic NiTi alloy - Hyflex CM
5. Electrical discharge machining - Hyflex EDM
6. Gold and Blue heat-treated instruments
7. MaxWire - XP-endo Shaper and XP-endo Finisher
8. Other newer files

ADVANCES IN FILE MOTION
1. Centric rotation - Vortex Blue; ProTaper Gold
2. Reciprocation - Reciproc Blue; WaveOne Gold
3. Combined - Genius system
4. Eccentric rotation - XP-endo Shaper
5. Transaxial - Self-Adjusting File

 Austenite transformed to martensite by stress
(e.g. insertion of the instrument into a curved root
canal)
 This effect is called stress-induced martensite
(SIM) transformation
 Complete recovery of the deformation up to 8%
strain (Thompson)
 Stress-induced martensitic state is not stable
 Unloading of the endodontic instrument (e.g.
withdrawal of an instrument out of a curved root
canal) leads to retransformation to the austenite
phase
 Spring-back of the endodontic instrument to its
original shape

ONE SHAPE
 Conventional austenite 55-NiTi alloy
 Single- file instrumentation
 Used in a full clockwise rotation
 Tip size of 25 and a constant taper of 0.06, 400 rpm
 Characterised by different cross sectional designs
over the entire length of the working part & non-
cutting safety tip
Apical part - three symmetrical cutting edges
Middle part - two asymmetrical cutting edges
Coronal part - two S shaped cutting edges

ADVANTAGES:
 Root canal shaping with one single instrument
 Root canal treatment is done approximately 4 times faster than a
conventional treatment
 Minimal fatigue along the length of the file virtually eliminates the risk of
separation
 The variable pitch of One Shape reduces instrument screwing effects
 ABC (Anti Breakage Control): The instrument will unwind to avoid
separation
 Its non-working (safety) tip ensures an effective apical progression
avoiding obstructions which are often preceded by instrument separation

 Remove surface irregularities, cracks and residual
stress that are caused by the previous grinding process
 Improve fracture resistance, cutting efficiency and
resistance to corrosion
 Lopes et al 2016 the cracks of nonpolished instruments
run along the machining grooves, whilst electropolished
instruments exhibited a fine irregular zigzag crack
pattern

 Characteristic uniform triangular cross section and a blunt tip design called the booster tip
 The non cutting booster tip is claimed to reduce the occurrence of deviation and
transportation
 This specialized tip is the unique feature of the BT-RaCe system that allows it to track canal
curvatures with less stress and increased safety
 They undergo a surface electrochemical treatment that increases the resistance to cyclic
fatigue

 Simplified sequence with three instruments: BT-1
(10/.06), BT-2 (35/.00), and BT-3 (35/.04)
 (BT-2) should be used in a delicate, smooth pecking
motion,
 Because it is less resistant to buckling than an
instrument of the same diameter and greater taper,
 Due to its cylindrical design, which also makes
progression of this instrument more time-
consuming

3.HEAT
TREATMENTS
Four different reactions in the solid state
 Change in chemical composition (precipitation)
 Reorganization of defects (recovery)
 Reduction of defects (recrystallization)
 Structural phase transformation
Heat treatment of the cold-worked NiTi alloy in a temperature range around 450–550
°C is able to release the internal stresses and reduces the defects of the crystal
lattice by giving the atoms enough thermal energy to rearrange themselves (Zinelis
et al)

HEAT TREATMENTS

 Contains both the deformed and microtwinned
martensitic, premartensitic R-phase, and are
austenite whilst maintaining a pseudoelastic
state
 The austenite-finish temperature (Af) of M-
Wire is around (45°C–50°C)
 Martensitic phase at room temperature
 M-Wire instruments include WaveOne and
Reciproc
 It has greater flexibility and an increased
resistance to cyclic fatigue when compared to
traditional NiTi alloys
HEAT TREATMENTS

• M-Wire possesses a lower
initial elastic modulus
compared with
conventional NiTi which
can be seen by an initial
lower inclination of the
loading curve
HEAT TREATMENTS

HEAT TREATMENTS
WAVEONE FILES

4.Martensitic NiTi alloy
 Martensite NiTi alloy is softer and more ductile than austenite
 Stress occurring during cubic (B2) to monoclinic (B19) lattice transformation
 Released by twinning of the developed martensite (twinned martensite) without
macroscopic form changes of the endodontic instrument
 Twinned martensite can be plastically deformed under stress, leading to detwinning of
the lattice structure (deformed martensite)
 Transformation from twinned to deformed martensite is called martensite reorientation

Enhanced resistance to fatigue-crack initiation because of the better
reorientation capability of the martensitic variants

 Enables deformation up to 8% strain
without significant increase of stress
 By heating the deformed instrument
beyond the austenite finish temperature
(e.g. autoclaving), it will regain its
original shape by returning to the
primary austenitic state
 Martensitic instruments are pseudoplastic
and exhibit the shape memory effect
upon heating
 Hyflex CM

HYFLEX CM

5.ELECTRICAL DISCHARGE MACHINING
 Evolution of the Hyflex CM
 Hyflex EDM is produced
with CM alloy and uses the
EDM technology
 Noncontact machining
procedure
HYFLEX EDM

 Allows precise material removal via pulsed electrical discharge
 Both the machining tool (electrode) and the workpiece have to be electrically
conductive
 Embedded in a dielectric liquid
 Machining tool is moved towards the workpiece until the gap is small enough
 Applied voltage is able to ionize the dielectric liquid
 The resulting spark vaporizes small particles from the workpiece, which resolidify in
the dielectric liquid and are subsequently flushed away
 EDM does not require direct contact with the workpiece, which eliminates the chance
of mechanical stress as in the traditional grinding process
HYFLEX EDM

 The absence of austenite in Hyflex EDM files could
be explained by its increased austenite start
temperature (As 42 °C) compared with Hyflex CM
(As 21 °C) preventing the formation of austenite at
either room or body temperature
 Three instruments used in a sequence: One for
coronal (size 25,12 taper) enlargement, One for glide
path (size 10,.05 taper) and Last one for canal
shaping
 The file for canal shaping has a variable taper, 0.25
mm tip with a taper 0.08 for the initial 4 mm, which
decreases to 0.04 toward the midpoint
 A speed of 500 rpm with a torque of 2.5 N/ cm is
recommended
HYFLEX EDM

 Near the handle, the cross-section is triangular to
provide better cutting efficiency;
 In the middle portion, it is trapezoidal, providing greater
resistance and greater debris clearance; and
 The tip is quadrangular, facilitating penetration of the
instrument and reducing the risk of fracture
 Extremely flexible
 700% more resistant to cyclic fatigue in comparison
with traditional NiTi files
 Files preserve the original anatomy of the canal
 Reduces the risk of ledging, Canal Transportation and
perforation
HYFLEX EDM

6.GOLD AND BLUE HEAT-TREATED INSTRUMENTS
Two Gold and Two Blue heat treated NiTi systems available
 Rotary ( Vortex Blue; ProTaper Gold )
 Reciprocating motion (Reciproc Blue; WaveOne Gold )

Vortex Blue FILES
 Titanium oxide layer is responsible for the distinctive blue
colour that remains on the surface as a result of the post-
machining heat treatment
 The austenite finish temperature for Vortex Blue was found
to be around body temperature (38.5 °C), whilst the
martensite start temperature is approximately 31 °C
 These systems contain a greater amount of stable
martensite than M-wire, thus increasing the softness and
ductility of the alloy
GOLD AND BLUE HEAT-TREATED INSTRUMENTS

Protaper Gold
 Same geometries as ProTaper Universal with a convex
triangular cross section and progressive taper
 Post heat treatment is applied after the flutes of a file have been
manufactured
 The temperature used is in a range of 370-510°C for a variable
period of time
 Files exhibit two stage specific transformation behavior and
high Af temperature around 50°C similar to CM wire
 Increases flexibility and resistance to cyclic fatigue, helping
ensure a more centered preparation of curved canals
 The connecting handle is shorter than that of ProTaper
Universal files (11mm), which facilitates clinical access to the
root canal system

Protaper Gold

WaveOne Gold File

7.MaxWire (Martensite-Austenite Electropolishing-Flex
 First endodontic NiTi alloy that combines both shape
memory effect and superelasticity in clinical application
 Two instruments available that are made of MaxWire; the
XP-endo Shaper and XP-endo Finisher.

 XP-endo Shaper expands at temperatures equal to or greater than 35°C
 At room temperature, it is in the martensitic phase
 When introduced into the canal, it changes its shape due to the molecular memory of
the austenitic phase
 Booster tip – unique property
 ISO 15 initial diameter, which increases gradually to a diameter of ISO 30 and 0.01
taper
 Final canal preparation corresponding to #30/.04
 Exhibit a shape memory effect when inserted into the root canal (M-phase to A-phase)
and possess superelasticity during preparation
 Azim et al. ,demonstrated that XP-S had the ability to expand beyond the size of its
core to conform to the anatomy of the root canal space by preparing and touching more
walls in oval canals than the Vortex Blue system
MaxWire (Martensite-Austenite Electropolishing-)
XP-endo shaper &
Finisher

 At temperatures equal to or greater than 35°C, it shifts from the martensitic to
the austenitic phase, giving the instrument a semi-circular shape that allows it
to project against the walls of the root canal when rotating, performing
eccentric rotary motion
 Able to adapt to the morphology of the root canal system, expanding or
contracting as they advance along the working length
 Provide supplementary cleaning of the canal at the end of chemical and
mechanical preparation by touching hard-to-reach areas of the root canal
walls, preserving dentin and the internal anatomy of the canal
 The XP-endo Finisher has an ISO 25 diameter and zero taper (25/.00)
MaxWire (Martensite-Austenite Electropolishing-)
XP-endo shaper &
Finisher

 Incorporate two or more different tapers into the same instrument - “Delta-type
design”
 Superior flexibility, reduced torque loading, and an improved ability to remove
debris
 Larger tapered cutting edge engages the canal wall, its opposing smaller tapered
edge provides additional space for breaking down and removing debris
 This reduces excess friction caused by debris build up and optimizes pressure on
the file’s cutting edge as it engages the canal wall
8. Other newer files

 Flute that extends through its tip creating a “cut-flip” tip
 Resembling a thick spoon with a sharpened edge, the tip’s blade effectively forms
dentinal chips while its opposite side’s curved surface acts as a self-guiding pilot
 The result is a flexible tip that manages torsion, reduces canal transportation, quickly
pulls debris away
 Significantly reduces apical extrusion while enlarging a canal that is smaller than the
file size
 This design also preserves the dental structure during preparation of the cervical
portion of the canal, while simultaneously providing enlargement of the apical region
 EXO Endo SIZE: 25/04
 The ONE Endo instrument must be used for initial enlargement, followed by the EXO
Endo for final shaping
8.Other newer files

2Shape File System
(MicroMega)
 An inactive tip to guide the instrument
avoiding any risk of perforation
 The asymmetrical cross section reduces the
risk of instrument fracture
 A progressively increasing pitch to avoid the
screwing and to further improve flexibility
 Heat treated using the T. Wire method, which
improves the instrument flexibility
8.Other newer files

One Curve (MicroMega)
 One Curve is a smart, efficient, and
conservative instrument
Clinical performance:
 Shaping ability
 Debris removal and cutting
efficiency
 Respect of canal anatomy
 Geometry adapted to irrigation
 Maintain of the apical foramen in its
original position
8.Other newer files

Revo-S
Use the SC1, SC2 and SU instruments with a brushing motion (circumferential
filing) SC1 and SU should be used in a free progression and without pressure
8.Other newer files

• The AS instruments should be used without apical pressure, after using the SU
penetration depth corresponds to the working length
• This length is shortened in thin root canals or with a marked curvature
• Then used in a step back motion (AS at WL, AS35 at WL – 0.5 mm, AS40 at WL – 1
mm if necessary)
8.Other newer files
Revo-S

 The Advantages of Revo-S is it enables a better root canal penetration due to a
“snakelike” movement = better progression of the instrument toward the apical region of
the root canal
 This sequence has a cutting, debris elimination and cleaning cycle, which optimizes the
root canal cleaning by improving the upward removal of the generated dentine debris
 Reduces the stress on the instrument, no screwing effect, more flexibility, and better
ability to negotiate curves
 The instruments should be used with a rotation speed ranging between 250 and 400 rpm
with a low amplitude in-and-out movement inside the canal (3 to 4 downward
movements)
8.Other newer files
Revo-S

II.ADVANCES IN FILE
MOTION
 Electric motors and reduction contra-angle handpieces driving NiTi
files in full rotation (360°) within the root canal
 Reciprocating motion also uses electric motors and contra-angle
handpieces
 angles of rotation are asymmetrical, in the counterclockwise and
clockwise directions
 attempt to minimize the risk of fracture of endodontic instruments

Reciprocating movement
 Reciproc and WaveOne systems, both made from M-Wire alloy
 Rotating initially counterclockwise (Reciproc 150°, Wave One 170°) to cut
away dentin and
 Clockwise (Reciproc 30°, WaveOne 50°) to clear it, in order to avoid the
screw-in effect that occurs with some continuous rotary systems
 Reciprocating motion induces lower tensile and compressive stress in the
flexed region of the instrument providing greater fatigue resistance
II.ADVANCES IN FILE MOTION

Combined movements (centric rotary +
reciprocating)
 Genius system use in clockwise rotary and reciprocating (90° clockwise, 30°
counterclockwise) motion
 S-shaped cross-section
 Positive rake angles
 Reciprocating motion allows safer negotiation of the canal
 Symmetric rotary action is used to finish the preparation, guaranteeing
greater efficiency in dentin removal from the canal and less extrusion of
debris

 During the continuous rotation in clockwise, the torque is automatically
measured
 If Torque is greater than a certain threshold
 Instrument performs an oscillatory movement with 90o in counterclockwise
and clockwise
 This process will be repeated until that the torque present lower than the
threshold value
 Then continuous rotation is reestablished
 This kinematics may be used with any NiTi system that present active cut
angle in clockwise
Optimum Torque Reverse motion

Eccentric rotary motion
 Instruments rotate eccentrically or asymmetrically (i.e., the axis of
rotation is off-center)
 ProTaper Next system - asymmetrical rectangular cross-section
 XP-endo Shaper - expands beyond the size of its core at
temperatures equal to or greater than 35°C

Transaxial motion
• The SAF is operated with transline (in
and out) vibrating handpieces with
3,000 to 5,000 vibrations per minute
and an amplitude of 0.4 mm
• The vibrating movement combined
with intimate contact along the entire
circumference and length of the canal
removes a layer of dentin with a
grinding motion
Self-Adjusting File

 Shaping and cleaning system
 Hollow file - compressible, thin-walled, pointed
cylinder of 1.5 mm or 2.0 mm diameter and
composed of 120-μm-thick Ni-Ti lattice
 File adapts itself to the three-dimensional canal
morphology both longitudinally and
crosssectionally
 The surface of the lattice threads is lightly
abrasive, which allows it to remove dentin with
a back-and-forth grinding motion
 The hollow design allows for continuous
irrigation throughout the procedure
Transaxial motion- SAF

 A special irrigation device (VATEA, ReDent-Nova) is connected by a silicon tube to the
irrigation hub on the file and provides continuous flow of the irrigant of choice at a
low pressure and at flow rates of 1 to 10 mL/min
 SAF is inserted into the canal
 Reaches the predetermined working length
 Operated with inand-out manual motion and with continuous irrigation using two
cycles of 2 minutes each for a total of 4 minutes per canal
 Remove a uniform dentin layer 60- to 75-mm thick from the canal circumference
Transaxial motion- SAF

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