nickel titanium in endodontics

NICKEL-TITANIUM Instruments

In ENDODONTICS

Presenter:

Dr. Ashok AyerDepartment of Conservative Dentistry & EndodonticsCollege of Dental SurgeryBPKIHS, Dharan, Nepal

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

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

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.

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.

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.

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

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.

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.

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

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.

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.

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

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

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

Types of Nickel Titanium alloy

1.Conventional or elastic

2.Newer or superelastic

A. Pseudoelastic

B. Thermoelastic

Basic properties of metals1. Crystals

• Specific geometry

• Atoms are arranged in unit cells, repeated again to form lattice

cation- anion arrangement resist

deformation

Increases the strength of crystals

2. Grain

• A microscopic single crystal in the microstructure of a metallic material.

Crystal growth

Crystal penetrate each other

Grain Boundary:Weaker, noncrystalline structure

3. Lattices

The three-dimensional network of lines connecting the atoms in undisturbed crystals

Body centred cubic (BCC)

Face centred cubic (FCC)

Monoclinical

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

4. Lattice defects:

• Weaken the material

• Substituent metals: Nickel or chromium for iron in stainless steel

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

• 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

6. Polymorphism

Crystallize into more than one structure

(FCC) (BCC)Low temperature

7. Twinning

Deformation that divides lattice into two symmetric parts at an angle

• High temperature- detwinning occurs- shape memory

8. Transition

Iron--- higher temperature--- austenite (912C to 1394C)

Ni substituted for some Fe atoms, it can be stable even at room temperature.

ATOMIC STRUCTURE OF NI-TI

Ni-Ti alloy is present in-

Austenitic phase: Body centred cubicHigher temperatureLower stresses

Martensitic phase: MonoclinicLower temperatureHigher stress

R phase: Rhomboidal structureIntermediate between transition

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

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)

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.

Springback

Chinese NiTi NitinolStainless steel> >

4.4 times1.6 times

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.

Temperature-induced phase transformation without mechanical loading.

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- 60C) is called hysteresis

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

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.

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

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)

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

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

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

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

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

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

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

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)

Effects of Heat Sterilization on Propertiesof 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.

(Silvaggio J, Hicks ML. J Endod 1997) (Canalda-Sahli et al. Int Endod J 1998)

(Hilt BR et al. J Endod 2000)

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.

Failure of Nickel-Titanium Instrumentsand 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.

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.

(Knowles et al. J Endod 2006;32:14-16) (Di Fiore et al. Int Endod J 2006;39:700-8)

(Alapati et al. J Endod 2005;31:40-3)

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.

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.

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)

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.

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)

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.

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.

Cohen’s Pathways of the Pulp: 10th ed.

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.

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.

Strategies for Improved Nickel- TitaniumInstruments

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)

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)

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)

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)

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)

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)

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.

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.

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)

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.

Endodontic Instrument Standardization

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.

According to stockTwisted Machined

K-files H file

K- reamer Flex R

K-flex file Canal master

Flexo Heliapical

Zipperer flexicut Flexogates

Mc spadden engine file

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

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.

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.

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

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

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

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.

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.

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.

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.

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.

ROTARY CONTRA-ANGLE HANDPIECEINSTRUMENTS

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

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

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

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

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.

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)

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)

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)

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.

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)

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.

To be Continued……..

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

SR-71 Blackbird: titanium-molybdenum alloy

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