Dr Abhishek

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By- Abhishek SharmaM.D.S(1st year) Deptt. Of Orthodontics and Dentofacial Orthopaedics

Definition History Uses Structure

of matter Basic properties of metal Mechanical properties of metal Clinical implications Toxicity Futuristic views

Metal an opaque lustrous chemical substance that is a good conductor of heat and electricity and, when polished ,is a good reflector of light.(metal handbook 1992) Alloy A crystalline substance with metallic properties that is composed of two or more chemical elements, at least one of which is metal. Wrought alloys Alloys which are hammered or drawn or bent into shape at temp. well below recrystallization temp. of the metal, often a room temp.

Gold Stainless Steel Cobalt-Chromium ( Elgiloy) Titanium AlloysNickel-Titanium. Beta-Titanium. (TMA)

1.

2.

Brief history of orthodontics

As early as 400 BC Hippocrats referred in his writings the correction of tooth irregularities. Meanwhile Etruscans were burying their dead with appliance in their mouth. Then in a Roman tomb in Egypt the dead were found with teeth bound with gold wire by Breccia. Later at the time of Christ, Aurelius Cornlius Celsus first records teeth by finger pressure.

Inherent malocclusion and use of corrective forces are recognized, the virtue of maintaining space is appreciated and the first orthodontic material is documented a gold ligature wire.

In the latter half of the 19th century Henry Clifton Sorby(1863-1887) and Edward Hartley Angle(1886-1930) professionally become the pioneers of modern metallography and modern orthodontics. In 1887 (German silver or Neusilber) were introduced by Angle which was alloy of copper, nickel and zinc alloys.

During this period, Gold, Platinum, brass, Silver, Steel, Gum rubber, Vulcanite were used in the form of loops, hooks, spurs and ligatures.

14-18 karat gold was routinely used for- wires, bands, clasps, ligatures and spurs as well as iridium- platinum bands and archwires and platinized gold for brackets.

From 1930s-1960s, the proliferation of materials did not occur.

During this stagnation period, Gold alloys were found to have deficiencies. Dumas, Guillet and Portevin 1st made Stainless Steel in France and its qualities 1st reported in Germany by Monnartz during 1900 1910. During World War 1, the Germans, British, and Americans developed an austenitic, martensitic and ferritic Stainless Steel. In 1930- Stainless steel was generally available.

In 1940s, Begg partnered with Wilcox and formed Australian Stainless Steel which is the back bone of light arch wire technique. 1n 1950, Stainless Steel was gaining prominence as ligature wire over soft brass wire. In 1960s, Gold was officially abandoned for Stainless Steel ever since most of the practitioners have relied on it. In 1960 Cobalt Chromium was introduced. In 1962, Buehler discovered Nitinol at the Naval Ordinance Lab. 1978 Andreasen introduced Nitinol to orthodontics.

1n 1981 Burstone introduced Beta titanium (TMA) to the orthodontic profession. In 1986, two superelastic alloy are offered- a Japanese by Dr. Tien Hua Cheung and a Chinese NiTi by Miura F. In the early 1990s Neo Sentalloy is introduced. In 1994, three Copper NiTi products are introduced by Rohit Sachdev and Suchio Miya Saki.

Esthetic wires were introduced such as Optiflex wires by Dr Talan and also composite and teflon coated wires.

(Robert P.Kusy Angle Orthodontist vol 72, no 6, 2002 Orthodontics Biomaterials : From the past to the present.)

Space Lattice - Any atom arrangement of atoms in space in which every atom is situated similarly to every other atom.

Unit Cell - It is the smallest box containing one or more atoms in a spatial arrangement of atoms.

14 possible lattice types, but many of the metals used in dentistry belong to the cubic system.

Pure iron at room temperature has body centered cubic (BCC) structure and is referred to as ferrite.

This phase is stable upto 9120C.

The spaces between atoms in BCC structure are small and oblate, hence carbon has very low solubility in ferrite (0.02 wt%).

At temperature between 9120C and 13940C the stable form of iron is face centered cubic structure called austenite.

The interstices in (FCC) are larger than BCC structure.

Maximum carbon solubility is 2.11 wt %.

When austenite form is cooled very rapidly (quenched) it undergoes a spontaneous, diffusion less transformation to body centered tetragonal (BCT) structure called Martensite.

This lattice is highly distorted and strained, resulting in very strong hard and brittle alloy.

Grain- a microscopic single crystal in the microstructure of a metallic material. Nucleus- stable cluster of atoms of a new phase that forms within a parent phase, such as during solidification of a metal. Dendritic microstructure- a cast alloy microstructure consisting of highly elongated crystals a branched morphology.

Stress Strain Youngs modulus Resilience Toughness Hardness Strain hardening Strength

Stress- it is the force per unit area acting on millions of atom or molecule in a given plane of a material. Stress = Force/Area tensile stress. shear stress. compressive stress.

Strain . Whenever a force is applied to a body it undergoes deformation. Strain is described as the change in length ( L = L LO) per unit length of the body when it is subjected to a stress. Change in length Strain ( ) = ___________________ Original length

Youngs modulus It describe the relative stiffness or rigidity of a material, which is measured by the slope of the elastic region of the stress-strain graph. Stress Elastic Modulus =_________ Strain

Resilience Amount of energy absorbed within a unit volume of a structure when it is stressed to its proportional limit. Toughness - It is defined as the amount of elastic and plastic deformation energy required to fracture a material.

Hardness The ability to resist scratching.Cold working( strain or work hardening) When a metal is stressed beyond its proportional limit, the hardness and the strength of the metal but the ductility of the metal decreases Strength- it is the stress necessary to cause either fracture (ultimate strength) or a specified amount of plastic deformation (yield strength).

Orthodontic wires manufactured by series of steps-

Initially, the wire is drawn in form of ingot, which must be subjected to deformation stages, until the crossection becomes small for wire drawing.

Round wires manufactured by drawing through the dies.

Rectangular wires are fabricated by rolling round wires, using Turks head apparatus that consists of pairs of rollers.

The surface roughness of the wire has a clinically effect on archwire-bracket sliding friction.

Generally greater in beta-titanium and nickel-titanium wires.

At stress below proportional limit, atoms in crystal lattice displaced elastically and when stress is relieved they can return to their original position.

Once proportional limit exceeded both plastic and elastic deformation occurred and when stress relieved structure does not return to original position.

Lattice Imperfections Crystallization from nucleus does not occur in a regular fashion.

Instead growth is more random with some lattice positions vacant and other overcrowded with atoms, these are classified as POINT DEFECTS

Dislocations The simplest type of dislocation known as Edge Dislocation The plane along which a dislocation moves Slip planes

Springback- This is also referred to as maximum elastic deflection, maximum flexibility, range of activation, range of deflection, or working range.1.

Springback is related to the ratio of yield strength to the modulus of elasticity of the material (Y S / E).Springback is also a measure of how far a wire can be deflected without causing permanent deformation

Stiffness or load deflection rate -This is the force magnitude delivered by an appliance and is proportional to the modulus of elasticity (E).2.

Low stiffness or load deflection rates provide (1) the ability to apply lower forces. (2) a more constant force over time as the appliance experiences deactivation, and (3) greater ease and accuracy in applying a given force

Formability - High formability provides the ability to bend a wire into desired configurations such as loops, coils, and stops without fracturing the wire.3.

Modulus of resilience or stored energy (MR). This property represents the work available to move teeth. It is reflected by the area under the line describing elastic deformation of the wire4.

Biocompatibility and environmental stability Biocompatibility includes resistance to corrosion and tissue tolerance to elements in the wire. Environmental stability ensures the maintenance of desirable properties of the wire for extended periods of time after manufacture.5.

joinability - The ability to attach auxiliaries to orthodontic wires by welding or soldering provides an additional advantage when incorporating modifications to the appliance.6.

Friction.-Space closure and canine retraction in continuous arch wire techniques involve a relative motion of bracket over wire. Excessive amounts of bracket/wire friction may result in loss of anchorage or binding accompanied by little or no tooth movement.7.

The preferred wire material for moving a tooth relative to the wire would be one that produces the least amount of friction at the bracket/wire interface.

(Mechanical properties and clinical applications of orthodontic wires by Sunil kapila and Rohit sachdeva, Ajo 1989;96:100-109)

2 types of gold wires are recognized in A.D.A specification no. 7 : type 1 and type 2Composition : Gold Platinum Palladium Silver Copper Nickel Type 1 54-63 7-18 0-8 9-12 10-15 0-2 Type 2 60-67% 0-7 0-10 8-21 10-20 0-6

Gold - Provides malleability and ductility Copper Contributes to age hardening Silver To balance the colour Nickel Acts as a strengthener Palladium Most effective element for raising melting point.

The increased palladium, platinum content ensures that wire will not melt or recrystallize during soldering procedure. Ensure fine grain structure. Platinum Imparts strength, toughness and resistance to tarnish and corrosion Zinc As a scavenger to obtain oxide free ingot.

Gold content of a dental alloy has been specified on the basis of karat or fineness.

Karat system specifies the gold content of an alloy based on parts of gold per 24 parts of alloy.

Eg 24-karat gold is pure (100%), whereas 22-karat gold (91.67%) is an alloy containing 22 parts pure gold and 2 parts other metals

Fineness is the unit that describes the gold content in noble metal alloys by the number of parts of gold per 1000 parts of alloy. E.g. Pure (100%)gold has fineness of 1000, and a 650 fine alloy has a gold content of 65%. Fineness rating is 10 times the gold % in an alloy. 18-karat alloy that is 75% pure gold is 750 fine.

Extremely formable Strength can be increased by heat treatment as well as cold working

The yield strength of wrought-gold wires can range from 50,000 to 160,000 p.s.i.,Percentage elongation is 16%

Good environmental stabilityGood joinability

Excellent biocompatibility

Gold alloy can be hardened by heating it to 2500 450 0C for 15-20 minute and quenching it.

This changes the crystal structure from FCC to FCT thus improving strength and hardness.

Heating the alloy just below the solidus temperature i.e. approximately 700oC for 10 minute.This changes alloy composition to random solution. Thus alloy becomes softer and ductile. This is often done after cold working to reduce stresses induced by cold working.

Now a days use of Gold is greatly reduced because 1.It is too soft to use as an orthodontic appliance 2.High cost 3.Lacked flexibility and tensile strength. 4.These alloys were inappropriate for complex machining and joining when used in the traction bars.

5. Stainless steel had excellent corrosion resistence, work hardening capabilities. 6. Being smaller in size stainless steel appeared more esthetic..

When approx 12-30% chromium is added to iron, the alloy is commonly called Stainless Steel. The resistance of stainless steel to tarnish and corrosion is associated with the passivating effect of chromium. Thin, transparent adherent layer of cr2o3 forms on the surface of SS when it is exposed to oxidizing atmosphere and this layer provide a barrier to 02 diffusion and prevents further corrosion of the underlying alloy.

Stainless Steel classified 3 types on the basis of crystal structureFerritic Stainless Steel Martensitic Stainless Steel Austenitic Stainless Steel Duplex steels, consisting of mixture of ferrite and austenite

Chromium - It is by far the most important alloying element in stainless steel production.

A minimum of 10.5% chromium is required for the formation of a protective layer of chromium oxide on the steel surface. The strength of this protective (passive) layer increases with increasing chromium content.

Nickel- It improves general corrosion resistance and prompts the formation of austenite (i.e. it is an austenite stabiliser). Stainless steels with 8-9% nickel have a fully austenitic structure and exhibit superior welding and working characteristics to ferritic stainless steels. Increasing nickel content beyond 8-9% further improves both corrosion resistance (especially in acid environments) and workability

Molybdenum -It increases resistance to both local and general corrosion. Molybdenum is added to martensitic stainless steels to improve high temperature strength. Nitrogen It increases strength and enhances resistance to localised corrosion.

Copper It increases general corrosion resistance to acids and reduces the rate of work hardening (e.g. it is used in cold-headed products such as nails and screws). It is an austenite stabiliser.

Carbon - It enhances strength (especially, in hardenable martensitic stainless steels), but may have an adverse affect on corrosion resistance by the formation of chromium carbides.

Titanium (Niobium & Zirconium) - Where it is not desirable or, indeed, not possible to control carbon at a low level, titanium or niobium may be used to stabilise stainless steel against intergranular corrosion.

Sulphur - It is added to improve the machineability of stainless steels. As a consequence, sulphur-bearing stainless steels exhibit reduced corrosion resistance.

Cerium - a rare earth metal, improves the strength and adhesion of the oxide film at high temperatures.Manganese- It increases the solubility of nitrogen in the steel and may be used to replace nickel in nitrogenbearing grades. Silicon- It improves resistance to oxidation and is also used in special stainless steels exposed to highly concentrated sulphuric and nitric acids

These alloys are designed as American Iron and Steel Institute(AISI) Series 400 Stainless Steel.

This series number is shared with the Martensitic Stainless Steels.

This Steel provide good corrosion resistance at low cost, provided that high strength is not required.

These steels are not hardenable by heat treatment also ferritic steels are not readily work-hardenable.

These steels have numerous Industrial uses, they have little application in dentistry.

They share the AISI Series 400 designation with the ferritic stainless steel.

Due to high strength and hardness, they are used for surgical and cutting instruments.

Corrosion resistance of this is less than that of the other types and is further reduced following heat treatment.

These are most corrosion-resistant alloy. The Austenitic structure for the AISI Series 300 Steels is achieved by the addition of nickel to the iron-chromiumcarbon composition Type 302 SS is basic alloy, containing 17-19% chromium,8-10% nickel, and a maximum of 0.15% carbon. Type 304 SS has similar composition 18-20% chromium and 8-12% nickel, along with maximum carbon content 0.08%.

Both 302 and 304 SS are given the designation 18-8 Stainless Steel, based on the % of chromium and nickel in composition.

These types most commonly used in Orthodontic Stainless Steel wires and bands.

Type 316L(low carbon) contains 10-14% nickel, 23%molybdenum,16-18%chromium and 0.03% carbon and the SS ordinarily employed for implants.

Greater ductility and ability to undergo more cold work without fracturing. Greater ease of welding. Ability to overcome sensitization Less critical grain growth Comparitive ease in forming.

These consist of chromium (18-26%) nickel(4-7%), molybdenum (0-4%), copper and iron. These stainless steels have a microstructure consisting of austenite and ferrite, which provides a combination of the corrosion resistance of austenitic stainless steels with greater strength. Formability is reasonable, but higher forces than those used for austenitic stainless steels are required.

The 18-8 steel may lose its resistance to corrosion if heated 400-900 c.

Due to precipitation of chromium carbide at grain boundaries.

Small rapidly diffusing carbon migrate to grain boundaries and combine with chromium at the periphery of grain forming chromium carbide

Sensitization can be minimized by stablilization.

Introduction of one or two elements that form carbide precipitates in preference to chromium such as niobium or titanium.

But this not be used for SS orthodontic wires because of the additional cost.

Modulus of elasticity- 179(Gpa) Yield strength- 1.6 (Gpa) Ultimate tensile strength- 2.1 (Gpa) No. of 90 degree cold bends without fracture- 5 (ADA Specification no. 32 for orthodontic wires)

Stainless steel alloys derive most of their strength from cold working and carbon interstitial hardening. - leads to high yield strength and high modulus of elasticity. Residual stress present in the wire because of bending (loops,springs) can affect the elastic properties of the wire.

Funk recommends the use of color index he suggests that straw colored wire indicates optimum heat treatment has been achieved.

the high modulus of elasticity and high stiffness necessitates the use of smaller wires for alignment of moderately or severely displaced teeth but smaller wire dimensions can lead to poorer fit in bracket and loss of control during tooth movement. However high stiffness is advantageous in resisting deformation caused by intra oral and extraoral tractional forces.

yield strength to high modulus ratio (YS/E) indicates a lower springback. The stored energy of activated stainless steel is less than other available alloys thus it produces higher forces that dissipates over shorter periods of time , requiring more frequent activations or arch wire changes. low levels of bracket/ wire friction has been noted using stainless steel . Thus it signifies that stainless steel wires offer lower resistance to tooth movement than other orthodontic alloys.

Park and Shearer demonstrated release of nickel and chromium from SS. (Ajo 1983;84:156-9) The amount of nickel and chromium release are below the average dietry intake.

(Mechanical properties and clinical applications of orthodontic wires, by Sunil kapila and Rohit Sachdeva in AJO 1989;96:100-9)

Increase in elastic properties of SS wire by heating to temp. approx 400 and 500 degree c after it has been cold worked.

This stress-relief heat treatment promote the recovery annealing stage, which remove residual stress introduced during manipulation of wire.

Effects associated with cold working such as strain hardening. Low ductility, distorted grains can be reversed by simple heating the metal. Benefits of annealing dependent upon the melting range of the alloy and the annealing temp. StagesRecovery Recrystallization Grain growth

Recovery- it is the stage at which the cold worked properties begin to disappear. Slight increase in tensile strength and no change in the ductility. Orthodontic appliances fabricated by bending wrought wires are often subjected to a stress relief anneal before placement.

Recrystallization- involve radical change in microstructure. The old grains disappear and are replaced by a new set of strain free grains. These grains nucleate in the most severly cold worked regions in the metal usually grain boundaries. On completion, the material essentially attain its original soft and ductile condition.

Grain growth- recrystallized structure has average grain size depending on the number of nuclei.

More severe the cold working the more no. of nuclei.

Excess annealing can lead to larger grains.

Silver solders are alloy of silver, copper and zinc to which elements such as tin and indium may be added.

Soldering temperature for orthodontic silver solders are typically between 620-665 degree c. For better flow of the solder Fluxes are used like boric acid.

Electric spot welding.

Flat structures like bands and brackets are usually joined by welding.

The spot welding apparatus produces a large current that is forced by the electrode to flow through a limited area ( spot) on the overlapped material to be welded

The interfacial resistance of the material to the current flow produce intense localized heating and fusion of the overlapped metals.

The welded joint is susceptible to corrosion, because of the loss of passivation resulting from chromium-iron carbide precipitation at the elevated temp. associated with welding.

To improve the strength and at the same time to maintain the desirable stiffness and range properties many small wires are twisted together and even swaged or spot welded.

The result is an inherently high elastic modulus material having low stiffness because of its co-axial spring like nature

Multistranded wires are available in round, rectangular, square cross sections. Subclassification based on the number of constituent strands - 3 strands - 6 strand

Subclassification based on the mode of joining the constituent strandsBraided Twisted

Core of 0.0065" strand of stainless steel wire along with 0.0055" wire used as wrap wires. This produces an overall diameter of approximately 0.0165".

These wires can be used as a substitute to the newer alloy wire considering the cost of nickel-titanium wire.

Kusy and Dilley noted that the stiffness of a triple stranded 0.0175 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 triple stranded wire was also half as stiff as .016" Btitanium.

(Ref: Kusy R. P. and Dilley G. J. Elastic property ratios of a triplestranded stainless steel arch wire. Am. J. Orthod. 1984;86:177188)

Ingram, Gipe, and Smith noted that titanium alloy wires and multistranded stainless steel wires have low stiffness when compared with solid stainless steel wires.

The investigators also found that most multistranded wires had a springback similar to that of nitinol, but a larger springback when compared with solid stainlesssteel or beta-titanium wires.

(Ajo,1986; 90: 296-307)

Unlike stainless steel wires, in which springback decreases with increasing thickness, the titanium and multistranded wires have springback properties that are relatively independent of wire size

Deactivation force deflection behaviour of multistranded stainless steel wires Parul Taneja , Manville.G, Sharokh S, Ram S Nanda AmJ orthd Dentofacial Orthop 2003:124: 61-8.

The first stage of orthodontic treatment requires leveling and aligning the teeth. To achieve this , an appliance that delivers forces that are light and decrease only moderately between appointments is required. The force to level and align is not the activation but the the deactivation force or the unloading force of the appliance. When a clinician engages the wire in the bracket slot energy is stored, work is done on the dentition during deactivation, evidence is the resulting tooth movement

multistranded wires are optimal choice for leveling and

aligning as they deliver light forces to the teeth over a significant range of deactivation.

the wire also serves as an alternative to expensive nickel titanium wireswires Parul Taneja , Manville.G, Sharokh S, Ram S Nanda Am J orthd Dentofacial Orthop 2003:124: 61-8.

Deactivation force deflection behaviour of multistranded stainless steel

Australian wire was developed by Begg, the father of the Begg technique, and Wilcock. Begg was seeking a light, flexible, stainless steel wire with high resiliency and toughness to use in his newly developed Begg technique. available in sizes ranging from 0.012 to 0.024 round wire

regular, regular+, special, special+, premium, premium+, and supreme grades.

The wires are graded according to their resiliency, with resiliency increasing from regular to supreme.Regular and regular+ Australian wire is often used in situations that require significant bending or loop forming of the arch wire

Special and special+ wires are stronger and are not suitable for bending. These wires are often used in the treatment of deep bites because of their increased resistance to permanent deformation.

The remaining grades are very resilient but are not appropriate for situations that require that sharps bends be placed in the archwire, because of their brittle nature. These high resiliency grades are often used as auxiliaries.The topography of the wires showed rough surfaces with characteristic striations derived from the drawing process, along with excessive porosity and irregularities.

A.J. Wilcock Australian wires were of the 18/8 stainless steel type but made no note of the carbon content. Therefore, it could be assumed that the carbon content was within the 0.20% range of traditional stainless steel wires to reduce formation of chromium carbides.

( Ref. structure, composition and mechanical properties of Australian orthodontic wires, Angle orthod. 2009;79:97-101)

Research has focussed on the release of metal ions from stainless steel brackets, mainly iron, chromium, and nickel. All these have adverse effect, nickel received the most attenuation because of its reported potential for hazardous effect. Effects of nickel are carcinogenic, mutagenic and cytotoxic.

The studies indicated no ionic release for the niti alloy, whereas measurable nickel and traces of chromium were found in stainless steel.

(characterization and cytotoxicity of ions released from stainless steel and niti orthodontic alloys, Ajo2004;125:24-9)

An esthetic archwire with excellent overall properties involves the use of composites. Which is composed of ceramic fibers that are embedded in linear polymeric matrix.

When compared with niti, resilience and springback are comparable.( A review of contemporary archwires: their properties and characterstics,

angle orthodontist vol 67 no. 3 1997)

These alloys were originally developed for use as watch springs (Elgiloy). CompositionCobalt-40% Chromium-20% Nickel-15% Iron-15.8% Molybdenum-7% Mangenese-2% Carbon-0.16% Beryllium-0.04%

Excellent resistance to tarnish and corrosion. Same welding and soldering procedures used for stainless steel.

4 tempers (soft, ductile, semiresilient and resilient) Colour coded for clinician convenience

Modulus of elasticity- 184 (Gpa)Yield strength- 1.4 (Gpa)

Ultimate tensile strength- 1.5 (Gpa)Number of 90 degree cold bends without fracture- 8

Comes in 4 temeprsSoft (blue) Ductile (yellow) Semiresilient (green) Resilient (red) Blue is the softest and can bent easily with fingers or pliers Advantage of co-cr wires over ss wires include greater resistance to fatique and distortion, longer function as a resilient spring.

Co-cr good formability and can be bent into many configuration but caution should be taken when soldering to these wires since high temp. cause annealing with loss in yield and tensile strength.

Larger frictional forces have been noticed between brackets and co-cr wires than between brackets and ss wires. (Frank CA,Nikolai RJ. Comparitive study of frictional resistances between orthodontic bracket and archwire. AJO 1980;78:593-609)

Nitinol a nickel-titanium alloy, represents the 1st product with significantly different properties than those of other base metal orthodontic alloys. CompositionNickel- 54% Titanium- 44% Cobalt- 2% or less

Modulus of elasticity- 41 (Gpa)Yield strength- 0.43 (Gpa)

Ultimate tensile strength- 1.5 (Gpa)Number of 90 degree cold bends without fracture- 2 Have a large working range Cannot be soldered or welded have to be joined by mechanical crimps.

This wire exist in various crystallographic form. At high temp. a stable BCC lattice (austenite phase) exists.

On cooling or application of stress, this BCC lattice transform intoa a close packed hexagonal martensitic phase.This BCC to HCP phase transformation results in 2 features called Shape Memory and Superelasticity

Shape memory effect is achieved by 1st establishing a shape temp. near 482 c.

The appliance (eg. Archwire) is then cooled and formed into a second shape.

Subsequent heating to a lower temp. (eg. 37 c mouth temp) cause the wire to return its original shape.

Superelasticity Inducing the austenite to martensite phase transition by stress can produce superelasticity.

Most advantageous properties of nitinol are the good springback and flexibility, which allow for large elastic deflection. Andreasen and Morrow described the shape memory phenomenon as the capability of the wire to return to a previously manufactured shape when heated through its transitional temp. range. (Andreasen GF, Morrow RE. lab. And clinical analyses of nitinol wire. AJO 1986;90:296-307)

Garner, Allai, and Moore and kapila hhace noted that bracket/wire frictional forces with nitinol wires are higher than those with ss and lower than beta-titanium wires. (AJO 1986;90:199-203).

Andreasen and Morrow indicates the nitinol wires are associated with advantages such as fewer arch wire changes, less chairside time, reduction in time required to accomplish rotation and levelling and less patient discomfort.

Limitations include poor formability of these wires . Fractures readily when bent over a sharp bent.

(Mechanical Properties and Clinical Applications of Orthodontic Wires by Sunil Kapila and Rohit Sachdeva in AJO 1989;96:100-9)

Like SS and nitinol, pure titanium has different crystallographic forms at high and low temp.

At temp. below 885 c, the hexagonal close packed or alpha lattice is stable. At higher temp. the metal re-arrange to a BCC lattice.

Alpha titanium is not used in orthodontic applications since they do not have improved springback properties. Beta titanium can be stabilised by the addition of molybdenum So beta-titanium used for orthodontic application Composition Titanium-11% Molybdenum- 6%

Modulus of elasticity- 72 (Gpa)Yield strength- 0.93 (Gpa)

Ultimate tensile strength- 1.3 (Gpa)Number of 90 degree cold bends without fracture- 4

Beta-titanium can be highly cold worked. Heat treatment of current beta-titanium orthodontic wire is not recommended.

Electric resistance weldingBoth alpha and beta titanium has excellent corrosion resistance and environmental stability.

Commercially available as TMA (titanium-molybdenum alloy) Modulus of elasticity is less than ss and twice that of nitinol. TMA also deliver about half the amountof force as do ss wires. TMA has a corrosion resistant comparable to ss and cocr alloys

Burstone and Goldberg recommend that these wires should not be bent over a sharp radius. (Burstone CJ, Goldberg AJO. Beta .titanium: a new orthodintic alloy. AJO 1980;77:121-32).

(Mechanical Properties and Clinical Applications of Orthodontic Wires by Sunil Kapila and Rohit Sachdeva in AJO 1989;96:100-9)