Contemporary Archwires
Dr. Firas Elayyan
University of Manchester
Orthodontic Archwires
Key considerations
1-Stiffness ( Spring rate):
magnitude of force at a
given deflection?
2-Springback ( range of
action): Will it deflect
that far?
3-Strength: The highest
amount of force delivered
by the wire.
Factors affects the force
wire exerts:
Thickness
Length
Material
1-Effect of thickness
round wires
Stiffness is proportional to
Diameter
14
16
18
20
(diameter)4
Stiffness
1.00
1.71
2.73
4.16
Small increment in size= big increment in force
14
20
Effect of thickness
Rectangular wires
Stiffness is proportional to w x h3
W
h3
Stiffness of 19x25 > 18x25
19x25
18x25
2-Effect of Length
Stiffness is inversely proportional to L3
Span
Stiffness
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
-Stainless steel
-Cobalt Chromium
-Beta-Titanium
-Nickel Titanium alloys
-Glass Optiflex
-Fibre reinforced composite
Range
160
140
120
100
80
Range
60
40
20
0
SS
CoCr
TMA
NiTi
Stiffness and Range
180
160
140
120
100
Stiffness
Range
80
60
40
20
0
SS
CrCO
TMA
NiTi
Stiffness
Stress
S.S.
NiTi
Strain
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
-
-
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
-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.
Shape memory effect (SME) !!
NiTi Transformation
High Temperature
Austenite
TTR
Low Temperature
Martensite
In response to temp variation, the crystal structure
undergoes deformations in which the molecular
arrangement is modified without a change of atomic
composition.
Properties of different phases
Austenite NiTi
Martensite NiTi
Crystalline structure
Cubic
Hexagonal
Elastic Modulus
98 GPa
31 GPa
379 MPa
138 MPa
Yield Strength
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)
100 %
Austenite
0%
Temperature
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”
-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)
Advantages:
-Low stiffness
( 20% of SS)
-Springy
( range 2.5 as SS)
-Light, continuous and
linear force delivery.
Stress
S.S.
NiTi
Strain
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
-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
-Excellent springback (4-5 of SS)
-Constant forces over large wire deflection
4
Standard force in N
3
Activation
2
1
Deactivation
0
0
1
2
Strain in mm
3
4
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
Effect of heat treatment on SE NiTi
deformation
Muira et al. AJODO 1986
Stage lll: Thermal Wires
(Martensitic Active)
-For the memory property to
be clinically detectable, Af
Mouth Temp
has to be slightly below oral
A
U
temperature.
S
T
E
-For every 150 ppm variation N
I
in composition, a 1°C
T
E
change in TTR occurs.
Room Temp
-Mainly Martensitic at room
temperature-softish, ductile
with shape memory
-Austenitic with SIMT at 37˚ C
-Deliver 25-30% of the force of SE NiTi and greater range
of action.
Thermal Wires ( Af=37°)
Stress
60°C
37°C
23°C
Deflection
Iijima et al. Dental Material 18 ( 2002) 88-93
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
wires e.g. 18x25,20x20.
-Allow control amount of force delivered to
posterior and anterior teeth.
-Allow more severely displaced brackets to
be engaged by chilling the wire locally.
But Thermal wires:
-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
T.Melling and J.Odegaard AJODO 2001; 119: 263-73
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
T.Melling and J.Odegaard Angle Orthod 1998; 68: 369-376
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°.
Stress
CuNiTi 27°
CuNiTi 35 °
CuNiTi 40 °
Deflection
CuNiTi 27˚
-Af at 27˚.
-Superelastic wire
- In patients :
-with average or high pain threshold.
-Normal periodontal health.
-where rapid tooth movement is required
CuNiTi 35˚
-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˚
-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
-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)
-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
Stiffness ( Young's Modulus) GPa
180
SS
CoCr
TMA
NiTi
160
140
120
100
80
60
40
20
0
0
1
2
3
Stiffness
4
5
6
Archwire application
-Aligning arches
-Working arches
-Finishing arches
More Stiffness
Less Range
Springback and stiffness ratios of
different materials*
Springback
Stiffness
Stainless steel
1
1
Multistrand SS
1.5-2
.13
B-Titanium
1.75
.36
Nitinol
2.5
.17
SE NiTi
4-5
.41
*Evans (1996), Profit (2000)
Aligning wires need:
-Low stiffness: low forces on activation
-High strength: prevent permanent deformation
-Long working range : maximize activation
First aligning wire
Which 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
16x22 Nitinol
307 gm
16x22 NiTi SE
193 gm
16x22 Thermal
143 gm
16x22 CuNiTi 27 ˚
137 gm
16x22 CuNiTi 35˚
100 gm
18 thermal
87 gm
16 NiTi SE
73 gm
16 Thermal
60 gm
17.5 Multistrand
43.1gm
Advantages of NiTi as aligning
archwires compare to Multistrand SS:
-Long working range
-Damage resistance
-Sustained forces!
-Low Forces!
Aligning Archwires
-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
Multiple round & rectangular wires
e.g. 12-14-16-18-16x22-18x25
Evidence based archwire
selection
“Clinical trials”
-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
-
-
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
-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
-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
Archwire
sequence
Time ( Months)
No of visits
A Lower
Upper
6.8 ( 2.5)
6.7 ( 3.5)
5.7 ( 2.1)
5.4 ( 2.1)
B Lower
Upper
9.3 ( 4.4)
7.9 ( 3.5)
7.5 ( 1.9)
7.1 ( 2.6)
C Lower
Upper
8.3 ( 4.2)
7.1 ( 3.4)
6.4 ( 2.2)
5.9 ( 2.8)
Can Thermal Rectangular wires be
used as first aligning archwires?
First aligning 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 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
-18x25 NiTi
-20x20 CuNiTi
Possible uses of 20x20 CuNiTi
-Final alignment wire
after round NiTi wire
-Sole aligning wire for
mild irregularities
( few cases)
-Realignment after
bracket repairs or
repositioning.
Working archwires
Photo 
Working arch usage
0.022 slot
Rec SS ( 18x25+)
Rec SS (<18x25)
Round SS
Rec NiTi
Percentage of Force loss due to
Friction
90
80
70
60
50
%
40
30
20
10
0
SS
NiTi
TMA
16x22 archwires, Slot size 18, bracket width 3.3mm ( D.Tidy)
Stainless steel working arches
-High stiffness-good control
-Easily adjusted
-Low friction
-Can be welded or soldered
-Cheap
NiTi working arches
-Flexible- poorer control
-Difficult to adjust
-Higher friction
-Cannot weld or solder
-More expensive
Finishing archwires (22 slots)
Loose fitting SS
Close fitting SS
Multistrand SS
Others
Finishing wires
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- 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
Damon
4 Solid
Walls
19x25
Conventional
Wire Out
Of Slot
Self-Ligating Brackets
-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!!
4
3.5
Frictional
Resistance N/m
3
2.5
2
1.5
1
0.5
0
016 x 022
DAMON
017 x 025
SPEED
018 x 025
SWA 'O'
019 x 025
SWA '8'
Sims, Birnie and Waters (1993)
self-ligating brackets
Elastomeric ligature
Forces ( gram)
300
200
100
0
0
1
2
3
4
Deflection (mm)
F.Elayyan et al. Angle Ortho ( 2006) , in press
Archwires in Self-Ligating brackets
-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
Fiber-reinforced composite Archwires
Future