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"A 'positive attitude' is definitely "A 'positive attitude' is definitely one of the keys to success. one of the keys to success. My definition of a positive attitude My definition of a positive attitude is a simple one: is a simple one: Looking for the good in all Looking for the good in all circumstancescircumstances
INTRODUCTION
BASIC PROPERTIES OF WIRES
CRITERIA FOR IDEAL ARCHWIRES
CLASSIFICATION OF WIRES GOLD WIRES STAINLESS STEEL WIRES MULTISTRANDED WIRES ELGILOY WIRES TITANIUM BASED WIRE NEWER WIRES
FRICTION & WIRES
STERILIZATION & ITS EFFECTS
CLINICAL APPLICATIONS
CONCLUSION 3
INTRODUCTION
Basically an orthodontist moves the teeth to an desired predetermined position by means of biomechanics.
For optimum tooth movement to be produced one should be able to design an appliance that provides light continuous force.
The force produced should neither be too great nor too variable over time.
It should not decrease rapidly or decay away because of the material involved .
In order to provide the efficient appliance the knowledge about wires is essential because wires are the fundamental device that produces the said force. 4
Orthodontic wires, are central to the practice of our profession.
They generate the biomechanical forces communicated through brackets for tooth movement
Forces vary with property of the wire used,malocclusion and tooth movement.
5
Selection of appropriate wire size and alloy type in turn provide the benefit of optimum and predictable treatment results.
The clinician must therefore be thorough with the mechanical properties and the relevant clinical applications of these properties
6
Orthodontists must also be concerned with the costs of wires, which can vary considerably among wire alloys as well as among companies
7
EVOLUTION OF ORTHODONTIC
ARCHWIRES GOLD :-
Until 1930’s the only orthodontic wires available were made of Gold and their alloys.
Gold alloys- Esthetically pleasing
Excellent Corrosion resistanceLow proportional limit.
1940’s :-With the substantial rise in the cost of gold, Austenitic stainless steel began to displace gold.
8
In early 1940 s Begg partnered with Wilcock to make resilient orthodontic wires – AUSTRALIAN STAINLESS STEEL. By 1960s gold was universally abandoned in favour of stainless steel.
In 1960s :-Cobalt –Chromium alloys were introduced.
Their physical properties were very similar to stainless steel along with superior formability.
Advantages- supplied in softer and more formable state that could be hardened by heat treatment
9
In 1962 :-Buehler discovered Nitinol at Naval Ordinance laboratory.
In 1970 :- Andreasen brought this intermetallic composition of 50% Ni and 50% Ti to orthodontics through University of Iowa.
Unitek company licensed the patent (1974) and offered a stabilized martensitic alloy under the name NITINOL.
10
In 1977 :Beta titanium was introduced to orthodontic profession by C.J. Burstone and John Goldberg.
This alloy had a modulus of elasticity closest to that of
traditional gold along with good springback, formability and weldability.
11
In 1984 :
A.J Wilcock Jr. as per request of Dr. Mallenhauer of Melbourne Australia, innovated in production of Ultra high tensile stainless steel round wires – The SUPREME GRADE.
In 1985 :- Burstone reported of an alloy, Chinese NiTi, developed by
Dr. Tien Hua Cheng and associates at the General Research Institute for nonferrous metals in Beijing china.
12
In 1986 :Miura et al reported on Japanese NiTi, an alloy developed at Furukawa Electric Company Limited Japan in 1978.
Both Chinese NiTi and Japanese NiTi are active austenitic alloys that form Stress Induced Martensite (SIM)
13
In 1988 :A.J Wilcock Jr. developed much harder Alpha Titanium
archwires.
In 1990 :Neo-Sentalloy is introduced as a true active martensitic alloy.
In 1992 :Optiflex a new Orthodontic archwire – developed by M.F Talass. Combined unique mechanical properties with a highly esthetic appearance.
14
In 1994 :-Copper NiTi, a new quaternary alloy containing Ni, Ti, Cu and Cr was invented by Dr. Rohit Sachdeva. Display phase transition at 27 C, 35 C, 40C.
In 2000 :- Titanium Niobium – an innovative new arch
wire designed for precision finishing, reported by Dalstra et al.
15
PROPERTIES OF ORTHODONTIC WIRESPhysical properties of materials can be considered as the ways that Materials respond to changes in their environment
Physical properties : Descriptive of size, shape and appearance.
Material properties :Those associated directly with the material .
16
Subdivided into Characteristics that are independent of external
influences simply termed “Material” properties.
Those that are associated in someway with the conditions of use or the use environment. e.g : Mechanical, Chemical, Thermal and Magnetic
17
Basic properties of wires
Knowledge of fundamental principles governing the relationships between compositions, structures & properties is central to an understanding of orthodontic materials.
Since new wires are continuously being introduced it is essential that the scientific basis for the selection & proper use of wires for clinical practice be thoroughly understood.
18
STRESS :- internal distribution of applied load It is defined as force applied per unit area to a body.
When a force acts on a body tending to produce deformation ,a resistance is developed to this external force application.
The INTERNAL reaction is equal in intensity and opposite in direction to the applied external force and is called stress.
Stress= Force/Area. Denoted by S or TYPES OF STRESS :- tensile ,compressive & shear
PHILLIPS SCIENCE OF DENTAL MATERIALS 11TH- EDITION Anusavice
19
Strain- internal distortion produced by applied load
Strain is described as the change in length per unit length of the body when it is subjected to a stress.
Strain has no units of measurement. It is a Dimensionless quantity. Reported as an absolute value or as a
percentage denoted by denoted by (Epsilon(Epsilon
denoted by denoted by (Epsilon(Epsilon
20PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION - EDITION
AnusaviceAnusavice
Strain Elastic
PlasticTypes of stress/strain
Tensile –stretch/pull
Compressive – compress/towards each other
Shear – 2 forces opp direction, not in same line. sliding
of one part over another
21
STRESS STRAIN CURVE:-A graph showing the relationship of stress and
strain as a material is subjected to increasing loads
The curve produced in this diagram may also be called Elastic Curve
Represents energy storage capacity of the wire, so determines amount of work expected from a particular spring in moving a tooth.
22PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION Anusavice - EDITION Anusavice
Mechanical properties based on Elastic or reversible deformation are :-
ELASTIC MODULUS FLEXIBILITY. RESILIENCE
23
Other properties that are determined from stresses at the end of elastic region of stress -strain plot and at beginning of plastic deformation region.
PROPORTIONAL LIMIT YIELD STRENGTH
24
THREE BASIC ELASTIC PROPERTIES
STIFFNESS :- It is a force / distance ratio that is a measure of resistance to deformation.
It is a measure of the force required to bend or otherwise deform the material to a definite distance.
25PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION Anusavice - EDITION Anusavice
STRENGTH : - measure of the maximum possible load,
the greatest force the wire can sustain ,if it is loaded to
the limit of the material.
Kusy - force required to activate an archwire to a
specific distance.
Proffit - Strength = stiffness x range.
26PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION Anusavice - EDITION Anusavice
RANGE :- (WORKING RANGE) Distance that the wire bends elastically, before
permanent deformation occurs (Proffit).
Kusy – Distance to which an archwire can be activated
Thurow – A linear measure of how far a wire or material can be deformed without exceeding the limits of the material.
27PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION Anusavice - EDITION Anusavice
Factors that influence Strength, Stiffness and Range :
Mechanical arrangement by which force is applied to teeth e.g :- bracket width, length of archwire, span and loops.
Form of wire itself – size and shape of cross section.
Material including the alloy formula, its hardness etc
28
STRENGTH PROPERTIES Strength is the stress that is necessary to cause
fracture or a specified amount of plastic deformation.
Both types of deformational behaviour can be described by strength properties, but we must use proper strength terms to differentiate between maximum stress to produce permanent deformation and that required to produce fracture.
29
Strength of a material can be described by one or more of the following properties
Proportional Limit Elastic Limit Yield Strength. Ultimate Tensile Strength, Shear strength and
compressive strength.
30
Proportional Limit :- (PL)
It is defined as the greatest stress that a material will sustain without a deviation from the linear proportionality of stress to strain.
Hooke’s Law :- States that stress – strain ratio is constant upto the proportional limit, the constant in this linear stress-strain relationship is Modulus of Elasticity.
Proportional limitProportional limit
31PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION Anusavice - EDITION Anusavice
Below PL no permanent deformation occurs in a structure.
Below PL – ELASTIC REGION
Above PL – PLASTIC REGION
32
MODULUS OF ELASTICITY (E ) ~ MODULUS OF ELASTICITY (E ) ~ It represents relative stiffness or rigidity of the wire within elastic range. Also called YOUNG ‘ S MODULUS . So less the strain for the given stress greater will be the stiffness. Stress E = --------- Strain
An ideal arch wire should have sufficient stiffness so as to withstand masticatory forces.But it also be low enough so as to provide 1. The ability to apply lower forces 2. A more constant force over time as the appliance experiences deactivation. 3. Greater ease & accuracy in applying a given force.
33PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION Anusavice - EDITION Anusavice
It is an inherent property of a material and cannot be altered appreciably by heat treatment, work hardening or any other kind of conditioning. This property is called STRUCTURAL INSENSITIVITY.
35
ELASTIC LIMIT :-
It is defined as maximum stress that a material can withstand before it undergoes permanent deformation.
For all practical purposes PL and EL represent same stress. But they differ in fundamental concept :-
PL deals with proportionality of strain to stress in structure.
EL describes elastic behavior of the material.
36PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION Anusavice - EDITION Anusavice
BRITTLENESS :-It is the relative inability of a material to sustain plastic deformation before fracture of a material occurs.
ULTIMATE STRENGTH :-Ultimate tensile strength or stress is defined as the maximum stress that a material can withstand before failure in tension.
37PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION Anusavice - EDITION Anusavice
StrainStrain
Str
ess
Str
essUltimate TensileUltimate TensileStrengthStrength
Fracture PointFracture Point
38
FLEXIBILITY :The maximum flexibility is defined as the strain that occurs when the material is stressed to its proportional limit.
39
PlPl
PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION Anusavice - EDITION Anusavice
RESILIENCE :- is associated with “springiness”.
It is defined as the amount of energy absorbed by a structure when it is stressed to its proportional limit.
Area bounded by the elastic region is measure of Resilience
40PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION Anusavice - EDITION Anusavice
Importance :- Represents energy storage capacity of the wire,
so determines amount of work expected from a particular spring or wire in moving a tooth.
High resilience- light forces for longer duration
Low resilience- high forces for shorter duration- frequent wire changes
41
SPRINGINESS :- Kusy - The extent to which a wire recovers its shape
after deactivation
Ingram et al – a measure of how far a wire can be deflected without causing permanent deformation. (
Springiness 1 Stiffness
42PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION Anusavice - EDITION Anusavice
TOUGHNESS The total area under the entire stress-strain curve is a
measure of the energy required to fracture the material
Higher the strength and higher the ductility (total plastic strain) greater the toughness.
43PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION Anusavice - EDITION Anusavice
SPRING BACK
It represents the elastic strain recovered on unloading from permanent deformation range.
Spring back is portion of load deflection curve between elastic limit and ultimate strength
Given by Expression :- YS/E. ( Yield strength / elastic modulus)
44PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION Anusavice - EDITION Anusavice
FF
FORMABILITY ~FORMABILITY ~ It is the amount of permanent deformation that a wire can withstand before it breaks.
An arch wire should have high formability that provides the ability to bend the wire into desired configurations such as loops coils & stops.
45PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION Anusavice - EDITION Anusavice
JOINABILITY ~ JOINABILITY ~ It’s the ability to attach auxiliaries to wires by welding or soldering provides an additional advantage when incorporating modifications to the appliance.
FRICTION ~FRICTION ~ Ability of wire to bind to a surface produces friction. An ideal arch wire should produce least friction because space closure & canine retraction in continuous arch wire technique 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.
46PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION Anusavice - EDITION Anusavice
BIOCOMPATABILITY ` BIOCOMPATABILITY ` It includes resistance to corrosion & tissue tolerance to elements in the wire .
ENVIRONMENTAL STABILITY ~ ENVIRONMENTAL STABILITY ~ It ensures the maintenance of desirable properties of the wire for extended periods of time after manufacture. This in turn ensures predictable behavior of the wire when in use.
47PHILLIPS SCIENCE OF DENTAL MATERIALS 11PHILLIPS SCIENCE OF DENTAL MATERIALS 11THTH- EDITION Anusavice - EDITION Anusavice
FACTORS AFFECTING WIRE PROPERTIESFACTORS AFFECTING WIRE PROPERTIES
1.Cross section of the wire:1.Cross section of the wire: Changing the diameter of the wire no Changing the diameter of the wire no matter how it is supported greatly affects its matter how it is supported greatly affects its properties but vary in their magnitude.properties but vary in their magnitude.
In doubling the cross section affects In doubling the cross section affects • Strength - 8 times stronger( ie – increases Strength - 8 times stronger( ie – increases by cubic function)by cubic function)• Springiness – Decreases by a factor of 16 (ie- Springiness – Decreases by a factor of 16 (ie- Decreases by 4Decreases by 4thth power function) power function)• Range – Decreases by factor of 2 (ie – it Range – Decreases by factor of 2 (ie – it decreases proportionately) -decreases proportionately) - Pascal Garrec et Pascal Garrec et al ANGLE 2004 Octal ANGLE 2004 Oct
49
2. Length of the wire:2. Length of the wire: Changing the length of the wire Changing the length of the wire dramatically affects its propertiesdramatically affects its properties
In doubling the length of the wireIn doubling the length of the wire
• Strength – Decreases in halfStrength – Decreases in half
• Springiness – Increases by a factor of 8Springiness – Increases by a factor of 8
• Range – Increases by a factor of 4.Range – Increases by a factor of 4.
50
3. 3. Type of attachment:Type of attachment:
The elastic properties of the wire is The elastic properties of the wire is affected by whether the wire is tied tightly affected by whether the wire is tied tightly or held loosely in a bracket.or held loosely in a bracket.
Supporting the wire in both endsSupporting the wire in both ends
• Strength – Increases twiceStrength – Increases twice
• Springiness - decreases by a factor of 4Springiness - decreases by a factor of 4
• Range - Decreases in halfRange - Decreases in half
51
TYPES OF WIRE:
ClassificationGold wireStainless steel wireCobalt chromiumBeta titaniumNickel titanium
52
CLASSIFICATION OF ORTHODONTIC WIRES
In 4 ways :
1. By design or cross sectional form ( Round , Rectangle , Square )
2. By no of wires ( single , multistranded )
3. By diameter ( 0.016 inch ,0.018 inch ,etc )
4. By composition a) Gold wires b) Stainless steel wires c) Co – Cr wires d) Titanium based wires e) Composite wires
53
GOLD WIRESGOLD WIRES COMPOSITION :
1. Gold - 55 % to 65 %2. Copper – 11% to 18% 3. Palladium – 5% to 10%4. Platinum – 5 % to 10 %5. Nickel – 1 % to 2%.
Additional strengthening by cold working during wire drawing process & by proper heat treatment.
54
PROPERTIES :
Yield strength - 50,000 – 1,6 0,000 psi
Modulus of elasticity – 15,000,000 psi ( 100 GPa )
ADVANTAGES :
Gold wires has less force delivery than stainless steel wires with the same cross section.
Very formable
Good joinability
High corrosion resistance
DISADVANTAGES
High cost
Decrease spring back55
STAINLESS STEEL WIRESSTAINLESS STEEL WIRES
With the advent of stainless steels in World War I and the refinement of drawing processes to form wires in the late 1930s, gold archwires gradually lost favor to the smaller cross-sectional areas that stainless steel archwires could provide.
In the 1940's, austenitic stainless steel began to displace gold as the primary alloy for orthodontic wires.
The most commonly used types are AISI ( American Iron & Steel Industry ) 302 and 304 stainless steels
56
When at least 10 to 13% chromium was present in the alloy, a coherent oxide layer formed that passivated the surface, thereby rendering the alloy “stainless.”
When at least 8% nickel was present, the single phase structure of austenite was stabilized, and the overall corrosion resistance was enhanced.
Carbon content was purposely maintained below 0.20%to reduce the formation of chromium carbides structures that can ultimately foster the corrosion of austenitic steels
58
The microstructure demonstrates the typical ‘face centered cubic arrangement (fcc).
This microstructure can be altered by short exposures to high temperatures, which is why soldering procedures have to be undertaken carefully.
The only heat treatments used with this wire are for stress relieving, which is typically done at 850° F. (454° C.) for less than 10 minutes.
59
ADVANTAGES :
High spring back due to high YS.
Good formability
Good joinability
Least friction
Decreased cost
DISADVANTAGES
High Modulus of Elasticity causes high forces.
So smaller diameter wires are used to decrease force levels .But this results in Lack of control & Poorer fit in brackets
Needs soldering to reinforce
61
COBALT CHROMIUM WIRESCOBALT CHROMIUM WIRES
Also in the 1950s, the Elgin Watch Company was developing a complex alloy whose primary ingredients were cobalt , chromium , iron & and nickel .This cobalt-chromium alloy was marketed as Elgiloy by Rocky Mountain Orthodontics.
62
PROPERTIES:
YS - 830 to 1000 MPa E - 160 to 190 GPa
ADVANTAGES :
Spring back similar to SS
High formability
Can be soldered but technique demanding
Excellent corrosion resistance
64
These are available commercially as Elgiloy , Azura & Multiphase.Elgiloy is manufactured in 4 tempers- soft ( blue) ductile ( yellow ) semi resilient ( green )resilient ( red ) in increasing order of resilience.
The blue elgiloy can be bent easily with fingers or pliers & recommended for use when considerable bending, soldering or welding is required.
Heat treatment increases its resistance to deformation.
65
Yellow wire is relatively ductile ,but more resilient than blue wire.
It also can be bent with relative ease. Further increase in resilience & spring back can be achieved
by heat treatment.
Green wire is more resilient & can be shaped with pliers before heat treatment.
The most resilient Elgiloy is red & provides high spring qualities.
66
Heat treatment of 900 ° F ( 400° C ) for 7 to 12 mins in a dental furnace causes precipitation – hardening of the alloy , increasing the resistance of the wire to deformation & results in properties similar to that of SS . Heat treatment at temp above 1200 ° f ( 749 ° c ) results in a rapid decline in resistance to deformation because of partial annealing. Caution should be exercised when soldering attachments to these wires since high temp causes annealing with resultant loss of yield & tensile strength.
67
The advantage of Co Cr wires over SS include a) greater resistance to fatigue & distortion b) longer function as resilient spring.
Both Co-Cr & SS wires has same high modulus of elasticity E = 160 to 190 GPa which suggest that these wires deliver twice the force of β- Titanium & four times the force of NiTi wires for equal amount of activation.
Clinically this may translate into faster rates of mesial movements of posterior teeth, thus placing greater demand on intra & extra oral anchorage..
68
TITANIUM BASED WIRESTITANIUM BASED WIRES
MANY TYPES:
1. Ni Ti wires
2. B- Titanium wires or TMA wires ( Titanium Molybdenum Alloy)
3. Alpha Titanium wires
4. Japanese NiTi wires
5. Chinese NiTi wires
6. Copper NiTi wires
7. Timolium wires
69
BETA TITANIUM WIRESBETA TITANIUM WIRES
It was popularized by Burstone & Goldberg( AJO 1980 Feb ) which is commertailly called TMA Titanium Molybdenum Alloy
Burstone & Goldberg recognized its potential for delivering low biomechanical forces compared to SS and CO-CR
It is commercially marketed by Ormco corporation, USA.
To compete with SS , a wire should possess at least comparable formability.
70
COMPOSITION : COMPOSITION :
Titanium – 77.8 % Molybdenum – 11.3% Zirconium – 6.6% Tin - 4.3 At temperatures above 1,625 °F pure titanium rearranges into a body- centered cubic ( BCC) lattice, referred as “ beta” phase.
With addition of elements like molybdenum or columbium ,the Ti based alloy can maintain its beta structure even when cooled to room temperature.So it is referred as Beta- stabilized titaniums.
The alloying and body-centered cubic structure impart a unique set of properties.
71
The BCC structure provides excellent formability to ß -titanium The addition of zirconium & tin contributes to increased strength &hardness.
ADVANTAGES: 1. Elastic modulus for ß -titanium is approximately 40% that of SS & Elgiloy wires.
Thus they have improved values of Springback which markedly increases its working range.
72
2. Excellent formability The high formability of titanium allows the fabrication of closing loops with or without helices.
The low stiffness of the material and its high springback improve a loop of any given design or allow for the maintenance of a given force system with simpler designs, as in the elimination of helices or loops.
73
3. It is the only wire with true weldability. It allows direct welding of auxiliaries to an arch
wire without reinforcement by soldering. Using a light-capacitance weld, a smaller cross section
of titanium can be welded directly to the main arch-on-arch segment .
Finger springs and other auxiliaries of an active nature can also be welded directly to an arch wire.
The welding has not appreciably altered the mechanical properties of the spring, and it can be activated a full 90 degrees without any permanent deformation..
74
Welding should be performed with care.
Unlike steel, where too much heat will produce softness in the wire, overheating of titanium could lead to brittleness.
4. Absence of nickel makes the wire more biocompatible & can be used in nickel sensitive patients.
75
5. Has excellent corrosion resistance & biocompatibility which is due to the presence of a thin , adherent passivating surface layer of titanium oxide.
DISADVANTAGES;
1. According to SEM studies , this wire has a relatively rough surface due to adherence or cold welding of the Ti during wire processing.
This causes high friction.
2. Highest cost.
76
Ni Ti WiresNi Ti Wires
NiTi alloy was originally engineered by NASA to automatically activate antennae or solar panels of space craft orbiting into the sun ‘ s rays
Conventional Nitinol In the late ’60s, the Office of the Navy was actively studying new types of alloys that exhibited a shape memory effect (SME). One of these, a nickel-titanium alloy, showed great promise and was dubbed nitinol, an acronym for nickel-titanium Naval Ordnance Laboratory.
77
This alloy was capable of being deformed, clamped, heated, and cooled into a specified shape, so that when it was later deformed into a new shape and subsequently heated, the material would remember its previous post-heat treatment shape.
Around 1970, Dr. George Andreasen recognized the potential of this alloy, the first nitinol alloy was marketed to orthodontists as Nitinol
COMPOSITION :nickel – titanium wires contain
1. Ni – 52%
2. Ti – 45%
3. Co – 3%
78
PHASE TRANSFORMATION :There are 2 major NiTi phases in nickel titanium wires 1. Austenitic NiTi 2. Martensitic NiTi Austenitic NiTi has a ordered FCC structure that occurs at High temperature & Low stresses.
It is relatively rigid & unyielding.
79
80
Martensitic NiTi has a distorted monoclinic , triclinic or hexagonal structure that forms at High stresses & Low temperatures.
In this phase the wire is said to be ductile & readily capable of plastic deformation.
81
The Shape memory effect is associated with a reversible martensite to austenite transformation, which occurs by Crystallographic twinning at the atomic level.
In some cases an intermediate R – Phase having a rhomboidal crystal structure may form during this transformation process
TEMPERATURE TRANSITION RANGE ( TTR ): The phase transformations do not occur at a particular temperature but rather within in a range known as temperature transition range.It refers to the temperature range for the start & completion for that particular structure. On Cooling : Ms ( martensite start ) – The start of martensite formation Mf ( martensite finish ) - The end of martensite formation
82
83
On Heating:
As ( austenite start ) – Here the martensite begins to decline & austenite begins to form.
Af ( Austenite finish ) Till here the whole structure is austenite
Md ( martensite deformation ) – For stress induced martensite SIM formation an additional Md temp, is defined as the highest temp at which it is possible to have martensite
84
This graph illustrates a stress-strain curve illustrating the changes observed in nickel-titanium alloys15.
Section A-B represents purely elastic deformation of the austenitic phase. The stress corresponding to point B is the minimum stress at which the transformation occurs.
This is known as the Martensitic start or Ms phase.
85
At point C, the transformation to martensite is finished; this is known as the Martensitic finish or Mf phase.
The difference between the slopes of A-B and B-C indicates the ease with which transformation occurs..
SHAPE MEMORY EFFECTSHAPE MEMORY EFFECT Hurst & Nanda in AJO 1990. According to them the specific TTR depends on the
chemical composition of the alloy & its processing history.
Shape memory refers to the ability of the material to “remember” its original shape after being plastically deformed while in the martensitic form.
86
In a typical situation, a certain shape is set while the alloy is maintained at an elevated temperature i.e., it is in an austenitic form.
When the alloy is cooled below the transition temperature, it changes to a martensitic form. Now, it can be plastically deformed.
When this deformed metal is heated again, the reverse transition occurs is from martensite to austenitic form. Thus, the original shape is restored.
This property is also called THERMOELASTICITY.
87
The TTR can be changed by altering the proportion of Ni to Ti or by substituting Co for Ni.
The memory configuration of the alloy must be first set in the material by holding it in desired shape while annealing it at 450 °F to 500 °F for 10 mins.
88
Through deflection & repeated temp cycles the wire in the austenite phase is able to “ memorize ‘’ the preformed shape including specific orthodontic archforms.
Once a certain shape is set , the alloy can then be plastically deformed at temperatures less than it TTR.
On heating through the TTR , the original shape of the alloy is restored.
To obtain maximum shape recovery the amount of plastic deformation should be limited to 7% to 8% of the original linear
length.
89
When an external force is applied , the deformation is induced with formation of martensite.
This phase can be reversed by heating the alloy so it is gradually transformed by reversing back to the energy stable condition – the austenite phase.
The shape memory wire alloys have Af temperatures that are below the temperature of oral environment, so that the wire have essentially the completely austenitic structure in vivo
90
SUPERELASTICITY It is determined by the typical crystallographic
characteristic of NiTi .
In response to temp variations , the crystal structure undergoes deformations in which the molecular arrangement is modified without a change in the atomic composition so that the transformation is diffusion less.
The alloy essentially undergo a reorganization to meet the new environmental conditions & so called as Smart materials.
91
The transformation from the austenitic to martensite is reversible ( thermoelastic martensite transformation) is reversible & called pseudoshearing.
On activation the wire undergoes a transformation from austenite to martensite form when stress level reaches a certain level.
On deactivation a reverse phase transformation occurs when the stress is decreased to an appropriate level.
92
Hence it is necessary to manufacture wire in the austenitic phase for it to possess Superelastic behavior. These wires are called A – NiTi wires.
The non super elastic NiTi wires contain substantial quantities of heavily cold – worked & stable martensite.
As temp of these alloys are much higher than room temp & the temp of oral environment .They are now commercially available & are referred to as M – NiTi wires. A clinical useful consequence of superelastic behavior is that variations in heat treatment by manufacturer can result in differing stress levels to initiate the phase transformations..
93
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.
94
CLASSIFICATION OF NI -TI WIRESKusy has classified nickel – titanium wires as
1. Martensite stabilized alloys ( M – NiTi ) These do not possess shape memory or
superelasticity,because the processing creates a stable martensite structure.( ex- Nitinol )
95
2. Martensite active alloy. These alloys employ thermoelastic shape
memory effect.
The oral environment raises the temp of the deformed archwire in martensite phase to transform into stable austenite form.
This can be observed by the clinician if a deformed archwire segment is warmed in the hands.( ex – Neo- Sentalloy & Copper NiTi)
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3. Austenitic- active wires.( A – NiTi ) These under a Stress Induced Martensite ( SIM ) formation when activated.
These alloys have both superelastic & shapememory effect.
They do not exibit thermoelastic behavior when deformed wire segment is warmed in the hands.( ex – Chinese NiTi & Japanese NiTi ).
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In A NiTi wires over a considerable range of deflection the force produced hardly varies.
This means the wire exerts about the same force whether it was deflected a relatively small or a large distance.
This is a unique & extremely desirable property.(ex – Chinese & Japanese NiTi.) Burstone CJ et al AJO 1985 June
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The unique force deflection curve for A –NiTi wire occurs because of a phase transformation in grain structure from austenite to martensite ,in response not to a temperature change but to applied force.
The transformation is a mechanical analogue to the thermally induced super elasticity.
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The unique force deflection curve for A –NiTi wire is that its unloading curve differs from loading curve – ie reversibility has an energy loss associated with it termed HYSTERESIS . This means the force delivered is not the same as the force applied to activate. The different loading & unloading curves produce the remarkable effect that the force delivered can be changed by merely releasing the wire & retying it.
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In clinical applications SIM forms where the wire is tied to the brackets on malaligned teeth, so the wire becomes noticeably pliable in deflected areas , with seemingly permanent transformation .
Therefore force delivery will be lowered in the needed areas only. In those areas the wire will be superelastic .
After tooth movement ,a self controlled reduction of the deflection will restore the stiffer austensitic phase.
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On conclusion ,the formation of SIM partially compensates for the lack of thermally induced martensite & contributes to the superelastic behavior of A –NiTi alloys.
This property is termed PSEUDOELASTICITY. & can be considered a localized stress related super elastic phenomenon.
Only in cases of very severe crowding will an austenitic alloy behave superelastically.
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PROPERTIES :
1. Good spring back2. Excellent flexibility3. Low stiffness4. High range
ADVANTAGES:1. Large elastic deflections is capable in these wires
because of their flexibility & spring back effect.2. Because of their low stiffness these wires produce
low forces.Also for a given amount activation they produce more constant force than that produced by SS wires.
.
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3. Andreasen & morrow In AJO 1980 Nov indicate that these wires are associated with fewer arch wire changes , less chair side time , reduction in time required to accomplish rotations & leveling & less patient discomfort.
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DISADVANTAGES:
1. Poor formability allows the wire best suitable only for preadjusted systems & so cannot be used in Begg or similar techniques which require formation of loops & coils etc.
2. The low stiffness provides inadequate stability at the completion of treatment
3. Some patient are sensitive to Nickel.
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4. NiTi also fractures readiliy when bent over a sharp edge. In addition bending also adversely affects the spring back property, & so loops & stops or not recommended in these wire.
Since hooks cannot be bent or attached to NiTi , CRIMPABLE HOOKS & stops are recommended.
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CINCH BACKS distal to molar buccal tubes can be obtained by resistance or by flame annealing the end of the wire.
This makes the wire dead soft & it can be bent into any preferred configuration.
A dark blue color indicates the attainment of desired a annaeling temp. Care should be taken not to over heat the wire because this makes it brittle.
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Contents Alpha titanium Chinese NiTi Japanese NiTi Copper NiTi Australian wire Multi strained wire Newer arch wire Clinical application Reference Conclusion
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COPPER NI – TI WIRESCOPPER NI – TI WIRES
Introduced in 1994 by Dr. Rohit Sachdeva
The addition copper to nickel titanium enhances the thermal – reactive properties of the wires thereby enabling the clinician to provide optimal forces for consistent tooth movement.
It is available in four temperatures variants: 15°C , 27°C , 35 °C & 40° C corresponding to the austenite finish temperature (Af ) for the completion of martensite to austenite transformation. Shape memory behavior is reported by the manufacturer to occur for each variant at temperatures exceeding the specified temperature.
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COMPOSITION:COMPOSITION:
All four Copper NiTi wires on elamental analysis indicate that they have very similar compositions.
1. Nickel – 44% 2. Titanium – 51% 3. Copper - < 5% 4. Chromium – 0.2% to 0.3%
Kusy has reported that Copper NiTi contains nominally 5to6 wt % cu & 0.2 to 0.5 wt% Cr. The 27°C variant contains 0.5% Cr to compensate for the effect of copper in raising the Af temp above that of the oral environment. The 35°C & 40°C variant contains 0.2% Cr..
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IMPORTANCE OF COPPER
It not only modifies the shape memory , but also increases the stability of transformation .
It also helps to control hysteresis width & improves corrosion resistance.
The superelastic wire contains Cu of 5 to 6 wt % to increase strength & to reduce energy loss.
Unfortunately these benefits are associated with an increase in phase transformation temp above that of the ambient value in mouth.
Thus necessitates addition of 0.55 Cr. 112
2727°C Copper NiTi :°C Copper NiTi :
11. Differential Scanning Calorimetry ( DSE ) demonstrates that this wire contains a single peak both on heating & cooling.
This indicates a direct transformation from martensite to austenite on heating & reverse transformation on cooling without an intermediate R phase.
2. It generates forces in the high range of physiological force limits & produces constant unloading forces that can result in rapid tooth movement.
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Engagement force is lower than that of other superelastic wires because of the lower loading forces built into the Cu alloy.
At the same time unloading force levels are comparable.
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This varient would be useful in mouth breathers In patients who have an average or higher pain
threshold. In patients who have normal periodontal health. In patients where rapid tooth movement is required
and the force system generated by the orthodontic archwire is constant.
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3535° C Copper NiTi :° C Copper NiTi :
1. DSC on this alloy shows two overlapping peaks on heating ,corresponding to transformation from martensite to R phase followed by transformation from R phase to austenite.
2. They generate mid- range constant force levels when the wire reaches oral temp. Early engagement is easier with full size arch wire due to lower loading forces.
Unloading forces are higher & more sustained than other shape memory wires when it reaches body temp.
3. This variant is activated at normal body temp.
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In patients who have a low to normal pain threshold.
In patients whose periodontium is compromised.
When relatively low forces are desired.
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4040°C Copper NiTi :°C Copper NiTi :
11. . DSC is similar to 35 °C Copper NiTi with two peaks. 2. It provides intermittent forces that are activated when oral temp exceeds 40°C.
It is useful as an initial arch wire & can be used to engage severely malaligned teeth like highly placed canine,without creating damaging or painful levels of force or unwanted side effects.
It is also the wire of choice for patients scheduled for long intervals bt visits when control of tooth movement is a concern.
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3. This variant would be activated only after consuming hot food or beverages.
Patients who are sensitive to pain.
Patients who have compromised periodontal conditions.
Where tooth movement is deliberately slowed down; i.e., when the patient may not be able to visit the orthodontist regularly or his/her cooperation is very poor and orthodontist does not want things to get out of hand.
This wire is very beneficial as an initial rectangular wire.
ADVANTAGES OVER TRADITIONAL NI-TI ALLOYS:ADVANTAGES OVER TRADITIONAL NI-TI ALLOYS:
1. Copper NiTi is more resistant to permanent deformation & exhibits better springback.
2. It demonstrates a smaller loading force for the same degree of deformation, making it possible to engage the wire to severely malposed tooth with less patient discomfort & potential for root resorption.
3. The decreased hysteresis & flatter unloading curve result in more consistent forces that are active longer within the optimal range for tooth movement.
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4. It exhibits a more constant force/ deformation relationship, providing superior consistency from archwire to archwire.
5. As copper is an efficient conductor of heat, these wire demonstrates consistent transformation temperatures that ensure consistency of force. This equates to effectiveness in moving teeth.
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RECENT WIRESTimolium wiresTitanium niobium wiresSuper cableCombined wireComposite wireCoated wireClinical application Conclusion
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PROPERTY
SS ELGILOY TMA NiTi
Cost Low Low High High
Force Delivery
High High Intermediate
Light
Springback
Low Low Intermediate
High
Formability
Excellent Excellent Excellent Poor
Ease of joining
Must be reinforced with solder
Must be reinforced with solder
Weldable Cannot be soldered or welded
Friction Lower Lower Higher Higher
Biocompatibility
Concern Concern Excellent Concern
SUMMARY IN CHART FORM
Wire alloy
Composition (Wt%)
Modulus of elasticity (Gpa)
Yield strength (MPa)
Springback
Austenitic SS
17-20%Cr ,8-12%Ni0.15%C(max) Rest-Fe
160-180
1100-1500
0.0060-0.0094 Ar0.0065-0.0099 Ht
Co-Cr-Ni (Elgiloy -Blue)
40%Co, 20%Cr15%-Ni, 15.8%Fe, 7%Mo, 2%Mn 0.15%C, 0.04%Be
160-190
830-1000
0.0045-0.0065 Ar0.0054-0.0074 Ht
β-titanium (TMA)
77.8%Ti, 11.3%Mo, 6.6%Zr, 4.3%Sn
62-69 690-970 0.0094-0.011
NiTi 55%Ni, 45% Ti (Approx)-& may contain small amounts of Cu
34 210-410 0.0058-0.016
ALIGNMENTALIGNMENTPrinciples in the choice of alignment archwires;
1. Initial archwires should provide light continuous force of approximately 50 grams, to produce the most efficient tipping tooth movement.
2. The arch wire should be able to move freely within the brackets.
3. So cross section of the wire should be small & should be loosely tied to the bracket to minimize friction.
4. Rectangular archwires particularly those with tight fit within the bracket should be avoided.
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Springier the arch wire crowding of symmetric nature can be corrected without the danger of loosing the arch form.
If only one tooth is crowded out of line , a rigid arch wire is needed to maintain the arch & auxiliary wire
should be used to reach the malaligned tooth. So initial archwire should have • Excellent strength.• Good springiness• Long range of action• Small cross section
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Super elastic A NiTi with the cross section of 0.014 or 0.016 is ideal for this category.
If steel is used in this stage either multistranded wires or loops should be used to increase springiness. Beta titanium is rarely used.
Alignment with Begg technique: The narrow brackets used in Begg tech, provide the maximum possible interbracket distance .
Also the initial archwires bypass the premolars.
This long posterior span of wire makes it difficult to use the highly flexible Ti based wires.
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So SS wires with loops are used.
Latest combination technique uses combined wires with flexible anterior segment & stiff posterior segment like Dual- Flex.
.
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For levelling & space closure : It depends mainly on biomechanics involving either
intrusion of anteriors or extrusion of posteriors..
For space closure the wire should have least friction.
Usually round SS wires with a progressing increase in cross section
This method takes advantage of increasing wire size to increase the stiffness & to get constant force delivery
This method is termed as REPLACEMENT APPROACH or VARIABLE CROSS SECTION ORTHODONTICS
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There is another method proposed by Charles .J.Burstone (AJO 1981 July) as early as 1980”s called VARIABLE _ MODULUS ORTHODONTICS.
The author states that advances in orthodontic wire alloys have made it possible to control wire stiffness by varying material properties namely the Modulus of elasticity, hence the name.
Burstone formulates his concepts by stating that the over-all stiffness of our appliance (S) is determined by two factors; one factor relates to the wire itself, (Ws) and the other is the design of the appliance (As):
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In general terms,Appliance stiffness = Wire stiffness X Design
stiffness
Design stiffness is dependent on factors like interbracket distance brought by incorporating loops & coils.
Ws - Wire stiffness is determined by a cross-sectional property or by the material stiffness dependent on materials property such as the modulus of elasticity.
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Therefore an increase in appliance stiffness can brought about not only by change in appliance design or increase in cross section thickness of the wire but also by selecting material with higher modulus of elasticity while maintaining the same cross section.
Since steel was the most commonly used alloy at that
time in orthodontics, its (Ms) number has been arbitrarily set at 1.0.
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ADVANTAGES: 1. The amount of play bt bracket & wire is not dictated by
desired wire stiffness but is under the total control of the clinician.
Once the cross sectional size & shape have been established, the desired stiffness can be implemented by selecting the alloy with appropriate material stiffness.
2. The low Modulus of elasticity of the newer alloys allows the use of light , rectangular wire even during the early stages of treatment.
Rectangular wires are preferable over round wires because they can be better oriented in the bracket in such a way that forces work out in proper directions.
They further increase patient comfort by avoiding loops. 135
3. 3. The selection of an appropriate alloy type & wire size may reduce the no of archwires needed for alignment by reducing bracket / wire play early in treatment.
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Nickel Titanium palatl expanders. Wendell Arndt. JCO March 1993. Fujio Miura,Mogi,Ohura&Hamanaka;The super-elastic property of
the Japanese NiTi alloy wire for use in orthodontics;AMJ Orthod Dentofac Orthop,1986;90;1-10
Wikipedia
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