Wires in othodontics

UNDER THE GUIDANCE OF :
DEPARTMENT OF ORTHODONTICS AND
DENTOFACIAL ORTHOPEDICS
N.B.D.C &H

Orthodontic Arch wires are one of the active
components of fixed appliances.
They can bring about various tooth movements
through the medium of brackets and buccal-
tubes, which act as handles on the teeth.

Stress : internal force per unit cross-section area (F/A)
Strain : change in dimension per unit length (∆L/L)
Typical orthodontic appliance is not usually loaded
in simple manner. Tension, compression, torsion,
bending are combined to a complicated pattern of
loading pattern referred to as Compound loading

 Hook’s law
Stress ∞ Strain (upto elastic limit)
Stress/Strain = E (modulus of elasticity), represented by slope of elastic
portion of the force-deflection curve
Stiffness ∞ modulus of elasticity
Springiness ∞ 1/ stiffness
Strength
Strength is required for an orthodontic appliance
 to resist distortion or displacement of the force giving component
 how much activation or clinical loading of the spring is possible before it
fails

 Yield strength: The point at which a deformation of 0.1% is
measured
 Ultimate tensile strength: The maximum load the wire can
sustain and beyond which it will behave as plastic. UTS
determines the maximum force the wire can deliver if used
as a spring.
 Factors that can influence elastic limit, yield strength
 cold working
cold working --------------------------- elastic limit/
strength
too much cold working ------------------- wire becomes too
brittle to use
 Heat treatment
Elgiloy and gold can be heat treated to raise the EL
stress relief heat treatment of 18-8 stainless steel can be
done after completion of all clinical bendings (850⁰F, 3mins)

Resilience and Formability
 Formability is the amount of permanent
deformation that a wire can withstand before
failing. It represents the amount of permanent
bending the wire will tolerate before it breaks
 Resilience is the amount of energy absorbed by
a structure when it is stressed not to exceed its
proportional limit

Load Deflection Rate: Force produced per
unit activation of the system
Low Deflection Rate
Eg. 10gm/mm
Desirable
High Deflection Rate
Eg. 100gm/mm
Undesirable
easier control on activation difficult control
of force system

 Factors influencing load-deflection rate
1) length & cross-section of wire
2) manner of loading
3) mechanical properties of the metal
Deflection(X) ∞
of a cantilever spring
Force(F) x L3
D4

 Spring Back-It is the measure of how far a wire
can be deflected without causing permanent
deformation. It is also called elastic deflection.
The arch wire should ideally possess high spring
back, which results in an increase in its range of
action.
 Stiffness-The presence of a low stiffness
provides the ability to apply lower forces and a
more constant force over time
 Formability-The orthodontic archwire material
should exhibit high formability so as to bend the
arch wire into desired configuration such as
coils,loops etc ,without fracturing the wire

 Resilience-Resilience is the amount of force the wire
can withstand before permanent deforation.Archwire
should exhibit high resilience so as to increase the
working range of the appliance
 Biocompatibility-Orthodontic archwires should exhibit
resistance to tarnish and corrosion and should be non -
toxic.The material should maintain its desirable
properties for extended periods of time after
manufacture
 Joinability-The orthodontic wire should be easily
joined by soldering & welding
 Friction-Orthodontic wire should provide least friction
at wire bracket interface to avoid undue strain on
anchorage and limitation of tooth movement

 Based on material used –
1- Gold and gold alloys
2- Stainless steel
3- Nickel Titanium alloys
4-Beta Titanium
5-Cobalt chromium nickel alloys
6- Optiflex archwires

 Based on cross section-
1- Round
2- Square
3- Rectangular
4- Multi stranded

Phase l : Gold and Stainless steel ( 1900-1960’s)
Phase ll: Stabilized NiTi “ Stabilized Martensitic” (
1970’s)
Phase lll : Superelastic NiTi “ Active Austenitic” (
1980’s)
Phase lV : Thermodynamic NiTi “Active Martensitic”
( Early 1990’s)
Phase V : Graded thermodynamic ( Late 1990’s)

 Popular till 1940’s
 Noble metal
 Type IV commonly used
 COMPOSITION-
Gold: 55-65%
Platinum: 5-10%
Palladium: 5-10%
Copper: 11-18%
Nickel: 1-2%

 Advantages :
Inert metal
High corrosion resistance
Good formability
 Disadvantages :
Low yield strength
Limited springback
High cost

 Accidentally discovered a few year before first world
wire
 Entered in dentistry in 1919
 Used as orthodontic wire in 1929
 Classification
1-Austenitic stainless steel/ 18:8 SS wire(300
series)
Type 302 austenite is the basic alloy,
containing
Chromium: 17-20%
Nickel: 8-12%
And maximum of 0.15% carbon

Type 304 also has similar composition but the carbon
content is 0.08%
Type 316L (low carbon) contains 16-18% chromium,10-
14% nickel,0.03% carbon & mainly used for making
implants
2- Ferritic stainless steel (400 series)-
Cr- 11.5-27% ,Ni- 0% ,C- 0.2% max
Can not be hardened by heat treatment
Not readily work hardenable
3-Martensitic stainless steel (400 series)
Cr- 11.5-17% ,Ni- 0-0.25% ,C- 0.15-1.2%
Less corrosion resistant
Used for surgical and cutting instruments

 Mechanical properties of SS wire:
1- High yield strength and high modulus of elasticity
2-High load-deflection rate
3-Low springback
4-High stiffnes increases resistance to deformation
5-Cold working increases resistance strength but reduces ductility
6-Annealing can cause re-crystallization
Stainless steel
soft, high formability (e.g ligature wire)
high yield strength, poor formability,
cannot withstand sharp bends (e.g AZW
wire)

 Advantages:
Greater springback than gold
Excellent formability
Higher yield strength
Moderate cost
Low levels of bracket/wire friction
 Disadvantages:
Springback lesser than Ti based alloys
Not as resillient as β- Ti or Nitinol
High force are produced that dissipates over longer
periods of time

 Cobalt based alloy
 Elgin watch company(1950’s) – Elgiloy
 Composition:
Co- 40% , Cr- 20%, Ni- 15% , Fe- 15.8% ,Mo- 7%,
Mn- 2% ,C- 0.15% , Be- 0.04%
 TYPES-
1- Blue Elgiloy (Soft)
2- Yellow Elgiloy (Ductile)
3- Green Elgiloy (Semi-resillient)
4- Red Elgiloy (Resillient)

Advantages-
1-Greater resistance to fatigue & distortion
2-Longer function as a resilient spring
3-Better corrosion resistance
4-High modulus of elasticity delivers twice the force of
β- Ti and 4 times the force of Nitinol
5- Exhibits good formability before heat treatment and
better springback properties after heat treatment
Disadvantages-
Loss in yield strength and tensile strength if annealed.
So weld and solder with caution.

 Introduced by Jon Goldberg & C.J.Burstone
 Available by the trade-name of T.M.A wires
 Composition: Ti- 77.8%, Mo- 11.3%, Zr- 6.6%, Sn- 4.3%
 Exhibit high range of action and springback
 Permit making of loops and helices due to their high
formability
 They can be welded
Uses
This makes it an excellent choice for
auxiliary springs
intermediate and finishing arch wires at late stages of edgewise
treatment

 It is a new type of arch wire developed by M.F.Talass
in 1992
 These are made of clear optical fibre and are therefore
highly esthetic
 In addition they exhibit high resilience
 The drawback of this wire is that it cannot accept a
sharp bend.

 Developed by William R Buchler at the Naval
Ordinance Laboratory
 Also called Nitinol : Nickel Titanium Naval Ordinance
Laboratory
 1971- introduced to orthodontics by George
Andreasen and marketed by Unitek Corporation as
Nitinol
 Composition: Ni- 55%, Ti- 45%

 Key Properties
1-Large forces that can be generated due to the shape
memory effect
2-Super elasticity
3-Excellent corrosion resistance
4-Nonmagnetic
5-High fatigue strength
6-Moderate impact resistance
7-Moderate heat resistance
8-Biocompatible

Stabilized NiTi/Nitinol (Martensitic NiTi)
 Introduced to orthodontics by Dr George Andreasen in
1971 who realized its shape memory potential
 However the shape memory effect could not be exploited
because it was suppressed during cold working
 Low temp phase
 Body centered tetragonal crystal structure
 Low stiffness compared to austenitic NiTi
 Low force per unit deactivation delivering light continuous
forces
 Elastic properties due to inherently stable structure
 Springy wire
 Poor formability

Austenitic NiTi
 Introduced in 1980’s
 Active austenitic alloys Form SIM or Stress
Induced Martensite
 High temp phase
 Rigid and stiffer
 Symmetrical
 Simple cubic structure
 Uniform structures-allows sound waves to pass
through it easily
 Less dense
 Super elasticty

Active NiTi
Fixed composition
Capable of undergoing changes in its crystal
structure when stress/temp is applied
Active Austenitic
Austenitic Martensitic Austenitic
Active Martensitic
Austenitic Martensitic Austenitic
stress stress
cold hot

 Shape Memory
Andreasen & Morrow have explained it as the
capability of the NiTi wire to return to a previously
manufactured shape when it is heated through its
Transition Temp Range

 Super Elasticity-
Ability to withstand elastic deformation to very
high degree when compared to other alloys and
return to its original shape without undergoing
plastic deformation
 Thermodynamic Property-
Refers to the ability of an archwire to return to its
itended shape once heated through its transition
temperature
 Transition Temp Range-
It is the temp at which martensitic NiTi is converted
to Austenitic wire
To be of clinical value thermodynamic archwires
should have a transition temp close to mouth temp

REFERENCES
 CONTEMPORARY ORTHODONTICS
FIFTH EDITION
WILLIAM R. PROFFIT, HENRY W. FIELDS,
DAVID M. SARVER
 ORTHODONTICS THE ART AND SCIENCE
SIXTH EDITION
S I BHALAJHI

Wires in othodontics

More Related Content

What's hot

Viewers also liked

Similar to Wires in othodontics

More from Sk Aziz Ikbal

Recently uploaded

Wires in othodontics