Nickel–titanium: a super-elastic alloyNi–Ti endodontic instruments

NiTi

Triveni institute of dental sciences, hospital and research centre

Guided by-Dr. Vinod Agarwal

Submitted by- Vivek Upadhyay Final year BDS

Date of submission- 28-01-2013

Department of Conservative & Endodontics.

Introduction-NiTi was developed by Buchler 40 years ago.

NiTi is also known as the NiTinol (NiTi Navol Ordinance Laboratory)

Two types of NiTi alloy used in endodontics- -55 NiTinol (55%Ni-45%Ti)

-60 NiTinol (60%Ni-40%Ti)

First use of NiTi in endodontics was reported in 1988, by Walia when a

15 No. NiTi file was made from orthodontic wire.

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Manufacturing-

Nickel–titanium “shape memory metal alloy” can exist in two different

temperature-dependent crystal structures called

-martensite(lower temperature or daughter phase) and

-austenite (higher temperature or parent phase)

Ni–Ti can have three different forms:

-martensite,

-stress-induced martensite (super-elastic) and

-austenite.

When thematerial is in its martensite form, it is soft and ductile, and it can be easily

deformed. Super-elastic Ni–Ti is highly elastic (rubber-like),

while austenitic Ni–Ti is quite strong and hard.

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Phase transformation of NiTi alloy

• Austenite: (BCC) high temperature and low stress

• Martensite: (Mono-Triclinic) low temperature and high stress

• R-phase: intermediate phase

A

M

R

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Design & Structure- NiTif-files are manufactured from nickel-titan wire that is ground to give the

typical profile of a K-file. The angle between the long-axis and the cutting blade is

bigger than in reamers, and therefore preparation by NiTi-file is effective both in

rotating motion and in filing motion (up and down movement).

NiTi The tip of the instrument is non-cutting ('bat-tip') which makes the NiTi-file well suited

for the preparation of curved canals without the risk of ledge formation.

Sizes & Codes- NiTi-files come in sizes 15 - 60, all with a taper of 0.02. K-file design is identified by

the square symbol on the handle.

NiTi-files can be best distinguished from normal K-files by the code that in NiTi-files

is printed with two colors.

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Advantage of NiTi alloy-1. Shape memory

2. Super elasticity

3. Low modulus of elasticity

4. Good resiliency

5. Corrosion resistance

6. Softer than stainless steel.

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Disadvantages of NiTi Files-1. Poor cutting efficiency.

2. NiTi files do not show sings of fatigue before they fracture.

3. Poor resistance to fracture as compare to stainless steal.

4. Break after 720 degree of rotation

Safety tips-NiTi-files can be rotated only using moderate pressure.

Use of force may result in fracture also with bigger sized instruments.

NiTi-files are super-elastic and always return to their original shape (= elastic

memory), which makes it difficult or impossible to detect weakened structure by

visual observation.

Fracture risk is best controlled by correct use and by using the instrument no

more than ten times

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A. Torsional fracture occurs when a rotary is forced into a small canal area,

engaging the tip,which then becomes overloaded. Consequences

are plastic deformation and a particular breakage

pattern (arrowhead).

B. Fatigue fracture occurs when a rotary is

overused and accumulates too much stress in

curved canals over time. There are usually no

warning signs and no particular patterns visible

on the fracture surface.

Instrument deformation and breakage

Scanning electron micrographs illustrateNiTi rotary fracture mechanisms. Fractures wereproduced in experiments; note the grinding markson both of the instruments.NiTi

Nickel–titanium rotary systemsThese Ni–Ti rotary files are mainly manufactured for use in

a torque-controlled handpiece at constant speed (rpm).

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A. Pro Taper

B. Great Taper

C. ProFile

D. Quantec

E. RACE

F. K3

G. EndoSequence

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The “Golden Rules” for NiTi Rotary PreparationUse only tourque controlled handpiece.

Proper glide path must be stablished before using file.

Examin the file & bend the file at least 80 degree angle, every time before placing into

canal.

Use crown down method.

Do not force apically against resistance.

Remove the possible pulp tissue by broach.

Canal should be well lubricated and irrigated.

Dentine mud should be cleared off by frequent irrigation.

Discard the file if it is bend, streched or has a shiny spot.

Do not use rotary instrument to true working length specially in teeth with “S-shaped

canal”.

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A. Pro Taper-

Design and Structure -ProTaper instruments are prepared from round nickel-titan wire by grinding.

Cross-section of the instruments shows a triangular structure with three cutting

points and no radial lands.

ProTaper instruments have a non-cutting tip that guides the instrument in the canal

and reduces the risk for ledge formation.

The convex triangular cross-section which reduces the contact area between the file

and dentine.

ProTaper is used in a rotating constant speed of 150 - 350 rpm.

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This greater cutting efficiency has been safely incorporated through balancing the

pitch and helical angles.

A progressively tapered file engages a smaller zone of dentine which reduces

torsional loads, file fatigue and the potential for breakage.

It clinically serves to improve flexibility, cutting efficiency and typically reduces the

number of recapitulations needed to achieve length, especially, in tight or more curved

canals.

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Sizes & Codes :

six sizes: Three shapers and three finishing files.SX file (no color ring)- 19 mm long -tapers of 3.5% (D1)

19% (D9), and 2.0% (D14).

The tip is 0.19 mm in diameter.

S1 (violet)- taper from 2% (D1) to 11% (D14).

Tip diameter of 0.185 mm.

S2 (white)- a taper from 4% (D1) to 11.5% (D14).

Tip diameter of 0.20 mm.

The diameter of all three Shaper files at D14 is the same.

F1 file (yellow)

F2 (red)

F3 (blue).

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B. Great Taper- Design and StructureGT instruments are prepared from round nickel-titan wire by grinding.

Cross-section of the instruments shows a U-file structure with radial lands that inhibit

screwing effect in dentin.

GT instruments have a bat-tip (= inactive tip) that guides the instrument in the canal

and reduces the risk for ledge formation.

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Sizes & Codes :-

GT instruments are produced in three sizes (iso tip sizes), 20, 30, and 40, and each

size comes in four tapers: 12, 10, 08, 06 and 04.

In addition, three bigger instruments are included in the GT family; sizes 35, 50 and

70, all with a taper 12, for preparation of very large canals and for coronal flare in other

canals.

Negative rake angle makes them too scrape the dentine rather than cutting.

Recommended use-

GT instruments are used in a rotating contra-angle with a high torque and a

constant speed of 350 rpm.

Each instrument is used for 5 to 10 seconds in a pecking motion: push forward -

draw back - push forward etc.

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C. ProFile -Design and Structure

Profile instruments are prepared from round nickel-titan wire by grinding.

Cross-section of the instruments shows a U-file structure with radial lands that

inhibit screwing effect in dentin.

Profile instruments have a bat-tip (= inactive tip) that guides the instrument in the

canal and reduces the risk of ledge formation.

Profile is used in high torque and a constant speed of 250-300 rpm.

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Sizes & Codes- Profile comes in three series that have different tapers.

04-series (taper 0.04) includes sizes 15-45, 60 and 90, all in lengths 21 and 25

mm.

06-series (taper 0.06) includes sizes 15-40 in lengths 21 and 25 mm.

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D.Quantec -Design and Structure Quantec are prepared from round nickel-titan wire by grinding.

Cross-section of the instruments shows a special structure of two cutting points and

radial lands that inhibit screwing effect in dentin.

Quantec is used in a rotating contra-angle with a high torque and a constant speed of

250 rpm

Quantec instruments are manufactured in two types;-

SC series has a cutting tip that has limited ability

to penetrate into dentin, and the LX-series with a non-cutting tip.

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Sizes & Codes

Quantec comes in a series of sixteen

instruments with its own color code.

1: #25/06

2: #15/02

3: #20/06

4: #25/02

5: #25/03

6: #25/04

7: #25/05

8: #25/06

9: #40/02

10#45/02

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E.RaCe- Design and Structure

RaCe is an acronym standing for Reamer with Alternating Cutting Edges.

The cross-section of the RaCe instruments is a convex triangle, with the exception of

the two smallest instruments, #15/02 and #20/02 (taper 02), which both have a square

cross-section.

In the manufacturing process, special attention has been focused on achieving a

smooth metal (NiTi) surface of the instruments.

Each RaCe instruments has a constant taper throughout the working area, ranging

from 02 taper to 10 taper, depending on the instrument.

The instruments have a rounded tip and three sharp cutting edges.

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Sizes & Codes The RaCe instruments are produced as "Pre-RaCe"

instruments with a short working area for preparation

of the coronal canal.

"RaCe" instruments for the preparation of the

middle and apical portions of the canal.

Twenty different basic designs of RaCe instruments

are available, different lengths (21 and 25 mm)

The sizes from #15 to #60 are available in the 02

taper series, while RaCe instruments in the 04 and 06

series have only three sizes (#25 - #35 and #20 - #30).

The RaCe used with low torque at a speed of 300 -

600 rpm.

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G.K3 The cross section of a K3 instrument reveals three cutting blades with slightly

positive rake angles, followed by radial lands.

Two of the radial lands have been partly reduced (Radial Land Relief) in order to

improve the cutting efficiency of the file.

The safe-ended non-cutting tip of the K3 instrument follows the root canal and

reduces risk of transportation.

K3 instruments have a "Variable Core Diameter", or variable flute depth.

The instruments also have a variable helical flute angle to reduce screwing effect.

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H.EndoSequence-

Design and Structure

Triangular cross section with sharp reamer-type cutting edges.

Instruments has a constant taper throughout the working area, tapers 04 and 06 are

available.

The instruments have a self-centering and rounded tip.

The instrument design includes "alternate contact points" (ACP’s) along the shank of

the instrument.

Despite of constant taper, ACP should result in reduced contact area during

preparation. which according to the manufacturer helps keeping the file centered in the

canal and reduces the torque requirements of the file.

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Sizes & Codes EndoSequence files are manufactured in tapers 06 and 04.

The smaller 04 files have a golden shank. sizes 15 - 40

The 06 files have a silver color. sizes of 45 and 50.

For initial canal preparation, an intermediate file with a size 27 and 04 taper is

available (Expeditor file).

Recommended use-

The recommended speed is 500 - 600 rpm.

After inspection of the canal with a #10 manual

instrument (K-file), the recommended

technique is crown-down preparation

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Conclusions- Root canal preparation with NiTi rotaries is a very effective

and safe procedure. However, it demands understanding

of root canal anatomy and the usage principles of the selected rotary system.

Every canal needs to be evaluated on its own merit regarding length, width

and curvature. It is only then that an educated decision about the strategy for

the preparation of that particular canal can be made.

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