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Contemporary Archwires. Dr. Firas Elayyan University of Manchester. Orthodontic Archwires Key considerations. 2-Springback ( range of action): Will it deflect that far?. 1-Stiffness ( Spring rate): magnitude of force at a given deflection?.

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Contemporary archwires

Contemporary Archwires

Dr. Firas Elayyan

University of Manchester


Orthodontic archwires key considerations

Orthodontic ArchwiresKey considerations

2-Springback ( range of action): Will it deflect that far?

1-Stiffness ( Spring rate): magnitude of force at a given deflection?

3-Strength: The highest amount of force delivered by the wire.


Factors affects the force wire exerts

Factors affects the force wire exerts:

Thickness

Length

Material


1 effect of thickness round wires

14

20

1-Effect of thicknessround wires

Stiffness is proportional to (diameter)4

DiameterStiffness

14 1.00

16 1.71

18 2.73

20 4.16

Small increment in size= big increment in force


Effect of thickness rectangular wires

W

h3

Effect of thicknessRectangular wires

Stiffness is proportional to w x h3


19x25

18x25

Stiffness of 19x25 > 18x25


2 effect of length stiffness is inversely proportional to l 3

2-Effect of LengthStiffness is inversely proportional to L3

SpanStiffness

6 mm 1.00

5 mm 1.73

4 mm 3.38

3 mm 8.00

2 mm 27.00

Critical areas: smallest interbracket span


Materials

Materials

-Stainless steel

-Cobalt Chromium

-Beta-Titanium

-Nickel Titanium alloys

-Glass Optiflex

-Fibre reinforced composite




Stiffness

S.S.

Stress

NiTi

Strain

Stiffness


The chronological development of archwires evans 1996
The Chronological Development of Archwires ( Evans,1996)

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)


Stainless steel archwires
Stainless steel archwires

  • SS was developed in World War l, only in the 1940’s was introduced to orthodontics.

  • Very rigid wire, good for space closure but not for alignment .

  • This was solved by: Wire bending and loops, the use of multistrand SS.

  • Multistrand SS has 20% of the stiffness and twice as range as SS.


Development of the high technology alloys
Development of the High Technology Alloys

-NiTi alloys were developed in early1960’s for space programs by W.Buehler in USA.

-This metal was called “ The Memory Metal”

-Very complex structure and mechanical behavior.

-Mechanical properties and thermal behavior are highly affected by composition, machining characteristics and heat treatment during manufacturing.



Niti transformation
NiTi Transformation

Austenite

High Temperature

TTR

Martensite

Low Temperature

In response to temp variation, the crystal structure undergoes deformations in which the molecular arrangement is modified without a change of atomic composition.



Niti alloys
NiTi Alloys

-Martensitic NiTi is responsible for the lowering of the delivery force.

-Austenitic NiTi is responsible for elasticity.

-Modulus of elasticity of Austenitic NiTi is 3-4 times than Martensitic NiTi.


Transitional transformation range ttr
Transitional Transformation Range (TTR)

100 %

Austenite

0 %

Temperature


Niti alloys development
NiTi Alloys Development

Stage l : Nitinol “Stabilized Martensetic”

(1970’s)

Stage ll : Superelastic NiTi “ Active Austenite”

( Mid 1980’s)

Stage lll: Thermal Wires “ Active Martensite”

(Early 1990’s)

Stage lV: Development of Copper NiTi “CuNiTi”

(Late 1990’s)


Stage l stabilized martensetic nitinol
Stage l: Stabilized Martensetic “ Nitinol”

-Composed of 55 Ni:45 Ti

-Introduced to Orthodontic by Dr.Andreasen mid 1970’s.

-No shape memory or superelasticity.

-Deformation occurring during processing

( work hardening) suppress SME

-It is passive “ Stabilized” alloy


Cont stabilized martensitic wires nitinol
Cont. Stabilized Martensitic wires( Nitinol)

Advantages:

-Low stiffness

( 20% of SS)

-Springy

( range 2.5 as SS)

-Light, continuous and linear force delivery.

S.S.

Stress

NiTi

Strain


Stage ll superelastic niti japanese or chinese wires
Stage ll: Superelastic NiTi (Japanese or Chinese Wires)

-Developed by Dr.Burstone and Muira mid 1980’s

-TTR below room temperature ( Cr, Nb additions)

-Active Austenitic at room temperature

-Af is lower than oral temperature so no thermoelastic properties.


Superelasticity
Superelasticity

-Occurs above TTR

-Wire initially austenitic

-Only stressed ares transform to martensite Stress Induced Martensitic Transformation ( SIMT).

-Superelasticity only exists when both phases of metal are present.

-Delivery of forces will be lowered in the needed areas only.

Muira et al. AJODO 90: 1-10; 1986


Advantages of superelastic niti archwires
Advantages of Superelastic NiTi archwires

-Excellent springback (4-5 of SS)

-Constant forces over large wire deflection

Activation

Deactivation


Se niti wires
SE NiTi wires ??

-The slope of the graph starts with a slope three times that of Nitinol .

-2 mm deflection is necessary for the formation of SIM in austenitic wires

- Austenitic alloys only behave superelastically in very severe crowding cases.

Muira et al. AJODO 90: 1-10; 1986



Stage lll thermal wires martensitic active
Stage lll: Thermal Wires(Martensitic Active)

-For the memory property to be clinically detectable, Af has to be slightly below oral temperature.

-For every 150 ppm variation in composition, a 1°C change in TTR occurs.

-Mainly Martensitic at room temperature-softish, ductile with shape memory

Mouth Temp

A

U

S

T

E

N

I

T

E

Room Temp

-Austenitic with SIMT at 37˚ C

-Deliver 25-30% of the force of SE NiTi and greater range of action.


Thermal wires a f 37

60°C

37°C

23°C

Deflection

Thermal Wires ( Af=37°)

Stress

Iijima et al. Dental Material 18 ( 2002) 88-93


Thermal niti
Thermal NiTi

-The main benefit is that these wires generate lower forces at mouth temperature than the corresponding size of non-thermal wire.

-Allow earlier progression to large dimension wirese.g. 18x25,20x20.

-Allow control amount of force delivered to posterior and anterior teeth.



But thermal wires
But Thermal wires: chilling the wire locally.

-More expensive.

-Very sensitive to manufacturing process.

-Offer little advantages in small diameters.

-May give almost no force in the unloading curve if they are not formulated correctly, so may be inefficient.

-Very sensitive to temperature changes in the oral cavity.


Effect of temperature changes on thermal archwires during activation
Effect of temperature changes on thermal archwires during activation

T.Melling and J.Odegaard AJODO 2001; 119: 263-73


Effect of temperature changes on thermal archwires during deactivation
Effect of temperature changes on thermal archwires during deactivation

T.Melling and J.Odegard AJODO 2001; 119: 263-73


Effect of repeated short term exposure to ice cream on torsional stiffness of thermal archwires
Effect of repeated short-term exposure to ice cream on torsional stiffness of thermal archwires

T.Melling and J.Odegaard Angle Orthod 1998; 68: 369-376


Stage lv development of copper niti cuniti

Stress torsional stiffness of thermal archwires

CuNiTi 27°

CuNiTi 35 °

CuNiTi 40 °

Deflection

Stage lV: Development of Copper NiTi “’ CuNiTi”

-5% Copper, 0.2-0.5% Chromium

-The addition of Cu:

Increase strength, reduce energy loss and allows greater control of TTR.

-Long force plateau

-Better manufacturing consistency

-Tolerate repeated loading better

-3 Types 27°, 35°, 40°.


Cuniti 27
CuNiTi 27˚ torsional stiffness of thermal archwires

-Af at 27˚.

-Superelastic wire

  • In patients :

    -with average or high pain threshold.

    -Normal periodontal health.

    -where rapid tooth movement is required


Cuniti 35
CuNiTi 35˚ torsional stiffness of thermal archwires

-Af at 35˚.

-Thermoelastic wire

  • In patients :

    -with low to normal pain threshold.

    -Normal to compromised periodontal health.

    -where relative low forces are required


Cuniti 40
CuNiTi 40˚ torsional stiffness of thermal archwires

-Af at 40˚.

-Thermoelastic wire

  • In patients :

    -who are sensitive to pain .

    -with compromised periodontal conditions.

  • Good as initial rectangular wire.


Stage v graded thermodynamic niti archwires
Stage V: Graded Thermodynamic NiTi archwires torsional stiffness of thermal archwires

-Deliver different amount of force at different areas of the dentition according to the surface area of periodontium.

- Controlled by specifying different TTR.

-80 gm of force anteriorly and 300 gm posteriorly.


Beta titanium alloy tma
Beta-Titanium Alloy ( TMA) torsional stiffness of thermal archwires

-Contains 80% Ti, 11% Mo, 7% Zr and 4% Sn.

-Medium stiffness ( 1/3 of SS and twice of (Nitinol)

-Produce gentler linear forces than SS

-Has more range and greater springback

-Has rough surface


Archwire application

Archwire application torsional stiffness of thermal archwires

More Stiffness

Less Range

-Aligning arches

-Working arches

-Finishing arches


Springback and stiffness ratios of different materials
Springback and stiffness ratios of different materials* torsional stiffness of thermal archwires

*Evans (1996), Profit (2000)


Aligning wires need

Aligning wires need: torsional stiffness of thermal archwires

-Low stiffness:low forces on activation

-High strength:prevent permanent deformation

-Long working range : maximize activation


First aligning wire which is the best
First aligning wire torsional stiffness of thermal archwiresWhich is the best?

-15 Multistrand SS

-12 SE NiTi

-14 SE NiTi

-16 SE NiTi

-16 Thermal

-18 Thermal

-16x22 Thermal

-14x25 Thermal

-20x20 Thermal

Physiological Force !?


Amount of force delivered by wires
Amount of force delivered by wires torsional stiffness of thermal archwires


Advantages of niti as aligning archwires compare to multistrand ss
Advantages of NiTi as aligning archwires compare to Multistrand SS:

-Long working range

-Damage resistance

-Sustained forces!

-Low Forces!


Aligning archwires
Aligning Archwires Multistrand SS:

-The smallest diameter archwire to be avoided at this stage :

-Small amount of force

-Play between bracket and wires limits the accuracy of alignment produced


Inefficient archwire progression
Inefficient archwire progression Multistrand SS:

Multiple round & rectangular wires

e.g. 12-14-16-18-16x22-18x25



Clinical trials
“Clinical trials” Multistrand SS:

-Superelastic NiTi vs Stabilized NiTi

O’Brien et al , EJO 12 ( 1990) 380-384

-Superelastic NiTi vs multistrand steel

West. Jones & Newcombe , AJODO 108 (1995) 464-471

-Thermal NiTi vs graded force NiTi vs multistrand steel

Evans, jones & Newcombe, AJODO 114 ( 1998) 32-39

-Superelastic NiTi vs ion implanted NiTi vs multistrand steel

Cobb et al, clin orth Res 1 ( 1998 ) 12-19

-Does the transition temperature of CuNiTi archwires affect the amount of tooth movement during alignment?

Dalstra & Melsen Orthd. Craniof. Res. 7 (2004) 21-25


Results of clinical trials
Results of clinical trials Multistrand SS:

  • Rates of tooth movement hardly affected by type of wire, any difference no clinically significant.

  • Pain experience not affected.

  • Results are related to the individual variations in metabolic response within the periodontal ligaments and bone.


2 archwires sequence
2-Archwires Sequence Multistrand SS:

-A recent RCT in Manchester by Mandall N. et al. EJO in press

-Three randomly allocated archwire sequence in terms of : efficiency, patient discomfort, root resorption.

-A=16 NiTi, 18x25 NiTi ( n=41)

-B=16 NiTi, 16 SS, 20 SS ( n= 44)

-C=16x22 CuNiTi, 19x25 CuNiTi ( n=44)

The endpoint was the passive placement of 19x25 SS for at least 4 weeks


Results
Results Multistrand SS:

-No statistical difference for patient discomfort at hours 4 hrs, 24 hrs, 3 days and 1 week.

-Root resorption was not statistically significant with average root resorpion between .96-1.39 mm


Time required to reach the working archwire
Time required to reach the Multistrand SS:working archwire



First aligning archwires
First aligning archwires archwires?

-Mild crowding:15 Multistrand SS

14 Nitinol

18 Thermal

(20x20 CuNiTi)

-Moderate crowding:16 Thermal

14 SE NiTi

-Severe crowding:14 Thermal

12 SE NiTi


When to move to the next wire
When to move to the next wire? archwires?

-When the next wire can be engaged in all the slots

-Look at the worst tooth to decide

-Watch for rotation particularly

-Give enough time for the wire to work especially the new high technology wires


Second aligning archwire
Second aligning archwire archwires?

-18x25 NiTi

-20x20 CuNiTi


Possible uses of 20x20 cuniti
Possible uses of 20x20 CuNiTi archwires?

-Final alignment wire after round NiTi wire

-Sole aligning wire for mild irregularities

( few cases)

-Realignment after bracket repairs or repositioning.


Working archwires
Working archwires archwires?

  • Photo


Working arch usage 0 022 slot
Working arch usage archwires?0.022 slot


Percentage of force loss due to friction
Percentage of Force loss due to Friction archwires?

16x22 archwires, Slot size 18, bracket width 3.3mm ( D.Tidy)


Stainless steel working arches
Stainless steel working arches archwires?

-High stiffness-good control

-Easily adjusted

-Low friction

-Can be welded or soldered

-Cheap


Niti working arches
NiTi working arches archwires?

-Flexible- poorer control

-Difficult to adjust

-Higher friction

-Cannot weld or solder

-More expensive



Finishing wires
Finishing wires archwires?

Options for close-fitting archwires (21x25):

-Steel : Too stiff

-NiTi: Not adjustable

Poor torqueing

-B-Titanium: Ideal stiffness

used to provide root paralleling


Self ligating brackets
Self-Ligating Brackets? archwires?

Self- Ligation

Low Force, Low Friction

Active Ligation High Force, High Friction


What Are The Limitations Of Conventional or Active Ligation?

Poor Control – Less Effective Torque

Elastic Ligature or Metal Clip

19x25

19x25

Damon 4 Solid Walls

Conventional Wire Out Of Slot


Self-Ligating Brackets Conventional or Active Ligation?

  • -Friction is increased 500% over Damon, if using a conventional bracket with steel ligatures

  • -Friction is increased 1500% over Damon, if using an elastic ligature

  • There are 70 grams of frictional force, per tooth, when using an elastic ligature

  • EJO 2004 Khandy


Friction!! Conventional or Active Ligation?

Frictional Resistance N/m

Sims, Birnie and Waters (1993)


F.Elayyan et al. Angle Ortho ( 2006) , in press Conventional or Active Ligation?


Archwires in self ligating brackets
Archwires in Self-Ligating brackets Conventional or Active Ligation?

-High Technology Wires should be used

( e.g. CuNiTi).

-Smaller dimensions ( Start with 14)

-Give 10 weeks appointment interval.

-Use 14x25 CuNiTi as second aligning archwires to correct rotations.

- Then 18x25 CuNiTi to express additional torque.


Future

Future Conventional or Active Ligation?

Future

Fiber-reinforced composite Archwires


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