Archwires ORTHO / orthodontic courses by Indian dental academy

INDIAN DENTAL ACADEMYLeader in continuing dental education

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ARCH WIRES

CONTENTS• Introduction• Properties of wires• Phases of Archwire Development• The Early archwires• Gold alloy wires • Stainless steel wires• Australian orthodontic wires• Braided wires

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• Chrome cobalt Alloy wires• Nickel Titanium wires• Alpha Titanium• B-Titanium• Esthetic archwires• Cross section v/s Modulus v/s Transition

temperature• Applying archwires• In search of an Ideal archwire• Conclusion.


INTRODUCTION

• Over the last century, material science has made rapid progress. This has been evident in our day to day lives also. And Orthodontics, particularly, has benefited largely from this. In this branch of dentistry, not only have the materials been improved, but also the philosophies have changed. Orthodontics has come a long way since the days of the E-arch and various removable appliances used in the early 20th century.


• With the introduction of the Edgewise appliance newer materials needed to be introduced in order to make the most of these appliances. This was the first time that precise positioning of the crown and root was possible. Wires which had good formability, increased resilience and low cost were obviously favoured. This was probably the reason why stainless steel (and Elgiloy) prevailed over the noble metal alloys. The needs of the Begg appliance were quite different from that of the traditional edgewise appliance. This led Begg and Wilcock to produce a variety of stainless steel that would provide low continuous forces over a long period of time.


• The nickel-titanium alloys introduced in the 1970’s showed some remarkable properties of superelasticity and shape memory, although these could not be exploited clinically at that time. The wires had limited formability, but could still be used in the traditional edgewise appliance. The next generation of NiTi wires benefited a lot by the pre adjusted edgewise appliances popularity. This appliance required lesser amount of bends incorporated into the wire, and the A-NiTi’s perfectly suited this. However, the TMA wires introduction filled the gap between stainless steel and Nickel Titanium alloys wires, with properties that were intermediate to the two of these alloys.


• Thus, we can see how the appliance philosophies and material science progress is closely interrelated. All these wire alloys that were introduced and the newer ones have some very individualistic and unique properties associated with them. So in order to use the newer wires, it is important to know as to why they behave this way i.e., their properties.


PROPERTIES OF WIRES

• Stiffness:It can be defined as the ratio of force to deflection of a member.


Strength:Strength is the maximal stress required to fracture a structure.


Range/FlexibilityRange is defined as the distance the wire will bend

elastically before deformation occurs, and is measured in millimeters.


Resilience:It represents the energy storage capacity of the wire

and is a combination of strength and springiness.It is the area in the stress stain curve out to the

proportional limit.


• Formability:• Formability is the

amount of permanent deformation a wire can withstand before failing. It represents total amount of permanent bending a wire will tolerate before it breaks.

• It is represented by the area under the curve between yield stress and tensile strength.


• Evans (BJO 1990) divided the phases of archwire development into five phases on the basis of (a) Method of force delivery, (b) Force/Deflection characteristics and (c) Material.

• PHASE I• Method of force delivery: Variation in archwire

dimension• Force/Deflection characteristics: Linear force/deflection

ratio• Material: Stainless steel, Gold

PHASES OF ARCHWIRE DEVELOPMENT


• PHASE II• Method of force delivery: Variation in archwire material

but same dimension• Force/Deflection characteristics: Linear force/deflection

characteristics• Material: Beta Titanium, Nickel titanium, Stainless steel,

Cobalt chromium

• PHASE III• Method of force delivery: Variation in archwire diameter• Force/Deflection characteristics: Non-linear force

deflection characteristic due to stress induced structural change

• Material: Superelastic Nickel Titanium


• PHASE IV• Method of force delivery: Variation in structural composition

of archwire material• Force/Deflection characteristics: Non-linear force/deflection

characteristic dictated by thermally induced structural change • Material: Thermally activated Nickel titanium

• PHASE V• Method of force delivery: Variation in archwire

composition/structure• Force/Deflection characteristics: Non-linear force/deflection

characteristics dictated by different thermally induced structural changes in the sections of the archwire

• Material: Graded, thermally activated nickel titanium


THE EARLY ARCHWIRES• The scarcity of adequate dental materials at the end of the

nineteenth century launched E.H. Angle on his quest for new sources

• Angle listed only a few materials as appropriate work. These included strips or wires of precious metal, wood, rubber, vulcanite, piano wire, and silk thread.

• Before Angle began his search for new materials, orthodontists made attachments from noble metals and their alloys Gold (at least 75%, to avoid discoloration), platinum, iridium, and silver alloys were esthetically pleasing and corrosion resistant, but they lacked flexibility and tensile strength


• In 1887 Angle tried replacing noble metals with German silver, a brass. His contemporary, J.N. Farrar, condemned the use of the new alloy, showing that it discolored in the mouth Farrar’s opinion was shared by many

• To obtain the desired properties, Angle acted, as stated in 1888, “by varying the proportion of Cu, Ni and Zn” around the average composition of the Neusilber brass (German silver, 65%Cu, 14%Ni,21%Zn), as well as by applying cold working operations at various degrees of plastic deformation.

• Besides its “unsightliness” and obvious lack of reproducibility (variations in composition and processing), the mechanical and chemical properties of German silver were well below modern demands. However, because it could be readily soldered, this brass allowed Angle to design more complex appliances.


• The material that was to truly displace noble metals was stainless steel. As with German silver, it had its opponents. As late as 1934 Emil Herbst held that gold was stronger than stainless steel without exfoliation. If forced to choose, he even preferred German silver to stainless steel. Eventually, better manufacturing procedures and quality control made stainless steel the material of choice.


GOLD ALLOYS

• Their composition is very similar to the Type IV gold casting alloys. The typical composition of the alloy is as follows-

• Gold – 15 – 65% (55-65% more typical)• Copper – 11 – 18%• Silver – 10 – 25%• Nickel – 5 – 10%


• The alloys contain quite a high amount about (20 – 25%) of palladium. Platinum is also present and in presence of palladium, it raises the melting point of the alloys, and makes it corrosion resistant.

• Copper incorporates strength to the wire. They acquire additional strengthening through cold working, which is incorporated during the wire drawing process


• This combination of properties makes gold very formable and capable of delivering lower forces than stainless steel. These wires are easily joined by soldering and the joints are very corrosion resistant.

• The gold wires are not used anymore in orthodontics mainly because of their low yield strength and increasing cost has made its use prohibitive.


HEAT TREATMENT OF GOLD WIRE

• The changes that are produced in the strength and ductility of a wrought gold alloy by heat treatment are due to the alterations in the gold-copper compound present in the alloy.

• In order to uniformly soften most wrought gold wire it is heated to 1300° F. for approximately 10 minutes and then quenched


• The wire is very soft and ductile and may be easily manipulated

• If left standing at room temperature for several days, will become much harder. This phenomenon is known as “age-hardening” or “precipitation-hardening”.


• Other method: If, after quenching from 1300° F. The wire is reheated to approximately 840° F. and allowed to cool slowly from this temperature, the gold-copper compound tends to come out of solution.

• By not using heat treatment procedures the orthodontist is not obtaining the maximum properties from his alloys.


• Besides precipitation hardening there are two other ways by which the strength of wrought gold wire may be increased. One of these methods is cold working. The other method is to vary the composition of the alloy constituents.


STAINLESS STEEL

• CARBON STEEL: Steels are iron-based alloys that contain less than 1.2% carbon.


CHROMIUM STEEL

• When chromium (generally 12-30%) is added to the steel, the alloy is called stainless steel.

• Chromium & Nickel are also called “Austenitic fillers”

• Chromium has a “passivating effect” on steel


Types of stainless steels

• FERRITIC STAINLESS STEEL (AISI series 400)

• MARTENSITIC STAINLESS STEEL: (AISI series 400)

• AUSTENITIC STAINLESS STEELS (AISI series 302 & 304)


SENSITIZATION

• The 18-8 stainless steels may lose its corrosion to resistance if it is heated between 400-9000 C

• Due to precipitation of chromium carbide at the grain boundaries


Overcoming Sensitization

• Reduce the carbon content• Cold working• STABILIZATION: Addition of Titanium


HEAT TREATMENT OF STAINLESS STEEL

Done to • Overcome decrease in yield stress

(Bauschinger effect)• Stability: Arch form & Wire bending



• Kemler: 700-8000F for 5-15 minutes• Backofen and Gales: 750-8200F for 10

minutes• Funk: 8500F for 3 minutes


• Properties:• The modulus of elasticity ranges from 23 X

106 to 24X106 psi. The wires have a very high yield strength of 50,000-280,000 psi.

• This wire is strong, has excellent formability, adequate springback, offers low frictional resistance, can be soldered, has good corrosion resistance & moderate cost.


• By The 50’s Rocky Mountain Orthodontics offered two tempers of cold worked stainless steels: Standard and extra hard grade

• Today American Orthodontics advertises three grades of stainless steel wires: Standard, Gold Tone, Super Gold Tone


AUSTRALIAN ORTHODONTIC WIRES

• Developed by Mr. A. J. Wilcock & Dr. P. R. Begg

• Acquaintance goes back to the war years at the University of Melbourne.

• Dr. Begg demanded a wire that remained active in the mouth for long periods.

• High Tensile wires were developed


• Difficulties faced with high tensile wires(1970s):

• Impossible to straighten.

• Work softening

• Breakage of wire


OVERCOMING THE DIFFICULTIES

• Old method - Spinner straightening: Yield stress decreases due to Bauschinger effect

• New method - Pulse straightening(1980s) : No plastic deformation whatsoever.


Advantages of Pulse straightening

• Permits the highest tensile wire to be straightened, previously not possible.

• The material tensile yield stress is not suppressed in any way.

• The wire has a much smoother appearance and hence less bracket friction.


Mr. Wilcock, Jr.’s recommendations to decrease breakage:

• Use the flat beak• Round the edges of the pliers

• Warm the wire


Two philosophy approach to Flexibility- Resiliency

(I). Flexibility (Fl) strain(II). Elastic modulus (E) = yield stress

Strain Multiplying (I) and (II), we get (Fl) x (E) = (Strain) x Yield stress

Strain

(Fl) x (E) = yield stress Flexibility = yield stress E



Elastic modulus (E) = yield stress

Strain

` Strain = yield stress

Elastic modulation (A)

In an right angled triangle ,Area = ½ x base x height

Resilience = area under the graph

Resilience = ½ x height x base

= ½ x (yield stress) x (strain)

Replacing the value of strain from equation (A), we get

Resilience= ½ x (yield stress) x (yield stress)

E

Resilience = ½ x (yield stress) 2

E

Resilience (yield stress) 2

E


RESILIENCY (Yield stress) 2

Elastic modulus

FLEXIBILITY Yield stressElastic modulus




Grades of wire availableRegular with white label

Regular plus with green label Special grade with black label Special plus with orange label Extra special plus (ESP) with blue labelPremium with blue label Premium plus Supreme with blue labelRegular grade is the least and premium grade is the most

resilient of all the wireswww.indiandentalacademy.com

Properties• The ultimate tensile strength for pulse-

straightened wires is 8-12% higher than stainless steel wires.

• The load-deflection rate is higher

• The pulse-straightened wires have a significantly higher working range and recovery patterns.

• Frictional resistance of the pulse-straightened wires is lesser


Zero Stress Relaxation

• This is the ability of a wire to deliver a constant light elastic force when subjected to an external force or forces of occlusion.

• This indicates that the wire should have a very high and sharp yield point with low elongation.

• This is probably in the region of ‘special plus’ and above


• The stiffness of an archwire can be varied in three ways.

• The first and traditional approach has been to vary the dimensions of the wire. Small changes in dimensions can result in large variations in stiffness.The difference between .016” and .014” diameter is approximately 40%.

• The second approach to vary the elastic modulus E. That is, use various archwire materials such as Nitinol , Beta-Titanium, Gold alloys and stainless steel.

BRAIDED WIRES


• A third approach, which is really an extension of the second, is to build up a strand of stainless steel wire, for example, a core wire of .0065” and six .0055” wrap, wires will produce an overall diameter approximately .0165 inches. The reason why the strand has a more flexible feel is due to the contact slip between adjacent wrap wires and the core wire of the stand.

• When the strand is deflected the wrap wires, which are both under tension, and torsion will slip with respect to the core wire and each other. Providing there is only elastic deformation each wire should return to its original position.


• Kusy and Dilley noted that the stiffness of a triple stranded 0175” ( 3 X 008”) stainless steel arch wire was similar to that of 0.010” single stranded stainless steel arch wire. The multistranded archwire was also 25% stronger than the .010” stainless steel wire.

• The .0175” triple stranded wire and .016” Nitinol demonstrated a similar stiffness. However nitinol tolerated 50% greater activation than the multistranded wire.

• The triple stranded wire was also half as stiff as .016” beta-titanium.

• Multistranded wire can be used as a substitute to the newer alloy wire considering the cost of nickel titanium wire.


CHROME COBALT ALLOY• Initially it was manufactured for watch springs by Elgin

Watch Company, hence the name Elgiloy.CONTENTS

• 40% Cobalt• 20% Chromium• 15% Nickel• 7% Molybdenum • 2% Manganese• 0.15% Carbon• 0.4% Beryllium• 15% Iron.


Types of Elgiloy

• Blue Elgiloy – can be bent easily with fingers and pliers.

• Yellow Elgiloy – Relatively ductile and more resilient than blue Elgiloy.

• Green Elgiloy – More resilient than yellow Elgiloy

• Red Elgiloy -Most resilient of Elgiloy wires


HEAT TREATMENT

• The ideal temperature for heat treatment is 900°F or 482°C for 7-12 min in a dental furnace.

• This causes precipitation hardening of the alloy increasing the resistance of the wire to deformation.



Disadvantages• Greater degree of work hardening • High temperatures (above 1200°F) cause

annealing

Advantages• Greater resistance to fatigue and distortion• Longer function as a resilient spring• High moduli of elasticity


NICKEL TITANIUM ALLOYSNickel titanium alloys have certain characteristic properties

associated with them. These properties are primarily exhibited due to its crystal structure. At higher temperatures the crystal structure is that of a body centered cubic (BCC) and is called AUSTENITE. At lower temperatures the crystal structure is that of a hexagonal closed packed structure called MARTENSITE.

The two most important properties of nickel titanium alloys are1. SHAPE MEMORY2. SUPER ELASTICITY



SHAPE MEMORY

• Shape memory refers to the ability of the material to “remember” its original shape after being plastically deformed while in the martensitic form.

• Also called THERMOELASTICITY


SUPERELASTICITY• This is a mechanical equivalent of the

change, which is observed due to cooling of austenite

• This is possible because the TTR for these alloys is very close to room temperature.

• Kusy has also called it Pseudoelasticity.www.indiandentalacademy.com

• Whether, it is thermo or pseudo - elasticity, the transition from martensite to austenite occurs with ease.


Hysteresis

• When the austenitic nickel-titanium wire is stressed, it can be observed that the loading curve differs from its unloading curve.

• This reversibility has an energy loss associated with it, this is known as hysteresis


Loading-Unloading for S.S.


Loading-Unloading for Niti


Effect of temperature on the bending characteristics


CONVENTIONAL/STABILIZED NICKEL-TITANIUM ALLOYS

• ‘Nitinol’ was developed in the early 1960’s by William F.Buehler, a research metallurgist at the Naval Ordnance Laboratory, Silver Springs, Maryland.

• Clinical use of nickel-titanium was started by Andreasen in May, 1972

• The shape memory effect (SME) had been suppressed by cold working

• Proffit refers to these alloys as M-NiTi’s.



Advantages• Low stiffness• Outstanding range• High springback(Comparable to braided S.S. wires - Barrowers,

Kusy and Stevens)

Disadvantages• Lack of formability • No shape memory, super elasticity, and hysteresis


SUPERELASTIC NICKEL TITANIUM ALLOYS (Active Austentic)

• Chinese Niti-developed by Dr.Tien Hua Cheng reported by Burstone (1985)

• Japanese Niti produced by the Furukawa Electric Co, which was first reported by Miura (1986)


• These wires, in their ‘as received’ condition were in the austenitic phase, and they showed the property of superelasticity.

• Super elasticity results from stress induction, as in archwire ligation.

• ‘Hysteresis’ is seen in these wires.

Disadvantage• Wire bending is all bit impossible with these

alloys



DERHT• Miura et al (1988)• Direct Electric Resistance Heat treatment


• Wire bending done with two pliers that are connected to electrode

• Also, changes the force exerted by that segment of the wire through which current is passed

• However not found to be practically feasible at that time

• Now this method is used (eg.Archmate)


New Application of Superelastic NiTi Rectangular Wire

• (Miura 1990) In heat treatment, the superelastic NiTi alloy not only changes its force level, but memorizes form. The latter characteristic makes it possible to condition an archwire so that it memorizes a particular archform, including torque, angulation, and buccolingual movements. The archwire can therefore be formed in the laboratory ahead of time, rather than using precious chairtime. The archform will also be more accurate than if it were bent at chairside.




THERMODYNAMIC NICKEL TITANIUM ALLOYS

• After experimentation, it was observed that the transition temperature range (TTR) of the nickel titanium alloys could be altered and infact carefully controlled using certain procedures and additions.

• Sachdeva has stated that the factors affecting the TTR of these alloys include:

• .Amount of Nickel content.• .Annealing temperature• .Amount of cold working• .Amount of third element, which is copper (Cu).


Amount Of Nickel Content


Annealing Temperature


Copper - The Third Element

• Copper additions increase the strength and reduce the energy lost

• However,increases its phase transformation temperature above that of the ambient oral cavity.

• 0.5% chromium is added to return the transformation temperature to 27°C


• Thus, by making use of these variables, the manufacturers have been able to make archwires that have different TTR’s. It means that the austenitic finish (Af) phase is reached at different temperatures. This temperature is called Austenitic finish temperature or Af temp.

• Also, the surrounding temperature affects the force that these wires exert on the tooth


Types of thermodynamic nickel titanium

• TYPE I: Af temperature – 10-15 °C• TYPE II: Af temperature – 27 °C• Type III: Af temperature – 35°C• Type IV: Af temperature – 40°C.


GRADED THERMODYNAMIC NICKEL TITANIUM ARCHWIRES

• The response of a tooth to force application and the rate of tooth movement is dependent upon the surface area of the periodonitum

• Variable forces within the archwires would be better

• Bioforce archwire: Differential force anteriorly and posteriorly


• Variety of stress versus strain relationships are exhibited by current NiTi alloys, which are available in the market (Proffit, Sachdeva)

• Trials have failed to demonstrate any significant differences in the alignment capabilities of superelastic versus ‘Nitinol’ archwires, (O’Brien et al., 1990; West et al., 1995).


ALPHA TITANIUM

Pure titanium: • Below 885° C - hexagonal closed packed or

alpha lattice is stable• At higher temperature the metal rearranges

into body centered cubic or beta crystal.

• HCP- possesses fewer slip planes


• Gets hardened by absorbing intraoral free hydrogen ions, which turn it into titanium hydride, at the oral temperature of 37°C and 100% humidity.

• Any modifications if required should be done within six weeks (Mollenhauer)


BETA TITANIUM (TITANIUM MOLYBDENUM ALLOY OR

T.M.A.)• Introduced by Dr. Burstone (1980)

Composition80% Titanium11.5% Molybdenum6% Zirconium4.5% Tin


Advantages of TMA v/s Nitinol• Smoother• Can be welded• Good formability

Advantages of TMA v/s S.S.• Gentler forces• More range• Higher springback

• Drawback: High coefficient of friction


Low friction TMA:• Introduced by Ormco• Done by ion implantation beam mechanism

TMA Colours:• Also developed by Ormco• Implantation of oxygen and nitrogen ions • Ensures colour fastness


ESTHETIC ARCHWIRES

• Composites: can be composed of ceramic fibers that are embedded in a linear or cross-linked polymeric matrix.

• Developed by a process known as pultrusion


A prototype (reported by Kusy) shows the following characteristics:

• Tooth coloured• Adequate strength• Variable stiffness• Resilience and springback comparable to Niti

• Low friction (beta staging)• Enhanced biocompatibility (beta staging)

(Formability, weldability are unknown)www.indiandentalacademy.com

OPTIFLEXMade of clear optical fibre; comprises of three layers:1. A silicon dioxide core 2. A silicon resin middle layer3. A stain resistant nylon outer layer

Silicon Dioxide Core Nylon Outer Layer

Silicon resin Middle Layer


Properties

• The most esthetic orthodontic arch wire to date.

• Completely stain resistant• Exerts light continuous forces• Very flexible


Precautions to be taken with Optiflex

• Use elastomeric ligatures. • No Sharp bends• Avoid using instruments with sharp edges, like the

scalers etc., to force the wire into the bracket slot. • Use the (501) mini distal end cutter (AEZ)• No rough diet • Do not “cinch Back”


Other esthetic archwires

• E.T.E. coated Nickel Titanium: E.T.E. is an abbreviation for ELASTOMERIC POLY TETRA FLORETHYLENE EMULSION

• Stainless steel or Nickel titanium arch wire bonded to a tooth coloured EPOXY coating


Cross-section 1970s: Only S.S.;

varying the cross-sectional diameter)

v/s Modulus

(1980s: S.S., Niti, B-Ti; varying the elastic modulus)

v/s Transition temperature (1990s: Cu Niti; Varying TTR/Af)


APPLYING ARCHWIRES


IN SEARCH OF THE IDEAL ARCHWIRE


CONCLUSION• It can be seen that there is not archwire meets all the

requirements of the orthodontist. We still have a long way to go, in terms of finding the ‘ideal’ archwire. But, with such rapid progress being made in science and technology, I am sure that we will see significant improvements in archwires in the near future.

• Also, we must consider ourselves fortunate to have such a wide array of materials to choose from. Just imagine working with just a single type of Gold alloy wire, like they used to not so long ago. So we should appreciate this fact and try to make the most of what we have.


THANK YOU


LIST OF REFERENCES • Applied Dental Materials: John F. Mc Cabe 7th Edition 1990 Blackwell

Scientific Publication. Pg. 69.• The Clinical handling of Dental Materials: Bernard G.N. Smith, Paul S.

Wright, David Brown. WRIGHT Publications, 2nd Edition, 1994; Pg. 195-199.

• Howe G.L. Greener E.H., Crimmins D.S.: Mechanical properties and stress relief of stainless steel orthodontic wire. AO 1968; 38: 244-249.

• Andreasen G. Heilman H., Krell D.: Stiffness changes in thermodynamic NiTinol with increasing temperature AO 1985; 55:120-126.

• Edie J.W.: Andreasen G.F., Zaytoun M.P.: Surface corrosion of Nitinol and stainless steel under clinical conditions AO 1981; 51:319-324.

• Miura F, Mogi M. Yoshiaki O: Japanese NiTi alloy wire use of electric heat resistance treatment method EJO 198; 10; 187-191.

• Andreasen G.F., Murrow R.E. : Laboratory and clinical analyses of nitinol wire AJODO 1978; 73: 142-151.

• Evans T.J.W, Durning P: Orthodontic Product update – Aligning archwires, the shape of things to come? – A fourth and fifth phase of force delivery. BJO 1996; 23:269-275.

• Kusy R.P. : A review of contemporary archwires-Their properties and characteristics AO 1997; 67: 197-207.


• Wilcock A.J., Jr. : Applied materials engineering for orthodontic wires. Aust. Jor. Orthod. 1989; V:22-29.

• Burstone C.J. Bai Q., Morton J.Y. : Chinese NiTi Wire – A new orthodontic alloy AJODO 1985; 87; 445-452.

• Fillmore G.M., Tomlinson J.L.: Heat treatment of Cobalt chromium alloys of various tempers AO : 1979; 49: 126-130.

• Kohl R.W. : Metallurgy in orthodontics. AO 1964; 34: 37-42.• Waters N.E.: Orthodontic product update-Super elastic Nickel-

Titanium wires. BJO 1992; 19: 319-322.• Andreasen G.G., Hilleman T.B.: An evaluation of 55 Cobalt

substituted NiTinol wire for the use in orthodontics. JADA 1971; 82: 1373-1375.

• Beckoten W.A., Gales G.F.: Heat treated stainless steel for orthodontics. AJODO 1952; 38: 755-765.

• Wilcock A..J., Jr: JCO Interview, JCO 1988; 22: 484-489.• Burstone C.J., Goldberg A.J.: Beta Titanium. A new orthodontic alloy.

AJODO 1980; 77; 121 –132.• Kapilla S., Sachdeva R: Mechanical properties and clinical

applications of orthdontic wires.


• Miura F, Mogi M., Ohura Y and Humanaka H: The super-elastic property of Japanese NiTi alloy wire for use in orthodontics AJODO 1986; 90:1-10.

• Proffit W.R., Fields H.W Jr.: Contemporary orthodontics – Mosby 3rd Edition 2000 Pg 326-334.

• Thurow R.C.: Edgewise orthodontics. The C.V.Mosby Company 1982 4th Edition. Graber T.M., Vanarsdall R.L. Jr: Orthodontics – Current principles and Techniques. Mosby 1994 2nd Edition.

• Philips R.W.: Skinner’s Science of dental Materials Prism Books Pvt. Ltd. 1991 – 9th Edition.

• Craig R.G. : Restorative dental materials. The C.V. Mosby Co. 1989 8th Edition.

• Hudgine J.J.: The effect of long-term deflection on permanent deformation of Nickel titanium archwires AO 1990: 283-293.

• Kusy R.P., Sterens L.E: Triple Stranded stainless steel wires 1987: 18-32.

• Sachdeva R.C.L.: Orthdontics for the next millennium. ORMCO Publishing.


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