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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Dr. Firas Elayyan
University of Manchester
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.
Stiffness is proportional to (diameter)4
Small increment in size= big increment in force
Stiffness is proportional to w x h3
Stiffness of 19x25 > 18x25
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
-Nickel Titanium alloys
-Fibre reinforced composite
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)
-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.
In response to temp variation, the crystal structure undergoes deformations in which the molecular arrangement is modified without a change of atomic composition.
-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.
Stage l : Nitinol “Stabilized Martensetic”
Stage ll : Superelastic NiTi “ Active Austenite”
( Mid 1980’s)
Stage lll: Thermal Wires “ Active Martensite”
Stage lV: Development of Copper NiTi “CuNiTi”
-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
( 20% of SS)
( range 2.5 as SS)
-Light, continuous and linear force delivery.
-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.
-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
-Excellent springback (4-5 of SS)
-Constant forces over large wire deflection
-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
Muira et al. AJODO 1986
-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
-Austenitic with SIMT at 37˚ C
-Deliver 25-30% of the force of SE NiTi and greater range of action.
DeflectionThermal Wires ( Af=37°)
Iijima et al. Dental Material 18 ( 2002) 88-93
-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.
-Allow more severely displaced brackets to be engaged by chilling the wire locally.
-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.
T.Melling and J.Odegaard AJODO 2001; 119: 263-73
T.Melling and J.Odegard AJODO 2001; 119: 263-73
T.Melling and J.Odegaard Angle Orthod 1998; 68: 369-376
Stress torsional stiffness of thermal archwires
CuNiTi 35 °
CuNiTi 40 °
DeflectionStage 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°.
-Af at 27˚.
-with average or high pain threshold.
-Normal periodontal health.
-where rapid tooth movement is required
-Af at 35˚.
-with low to normal pain threshold.
-Normal to compromised periodontal health.
-where relative low forces are required
-Af at 40˚.
-who are sensitive to pain .
-with compromised periodontal conditions.
-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.
-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
*Evans (1996), Profit (2000)
-Low stiffness:low forces on activation
-High strength:prevent permanent deformation
-Long working range : maximize activation
-15 Multistrand SS
-12 SE NiTi
-14 SE NiTi
-16 SE NiTi
Physiological Force !?
-Long working range
-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
Multiple round & rectangular wires
-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
-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
-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
-Mild crowding:15 Multistrand SS
-Moderate crowding:16 Thermal
14 SE NiTi
-Severe crowding:14 Thermal
12 SE NiTi
-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
-Final alignment wire after round NiTi wire
-Sole aligning wire for mild irregularities
( few cases)
-Realignment after bracket repairs or repositioning.
16x22 archwires, Slot size 18, bracket width 3.3mm ( D.Tidy)
-High stiffness-good control
-Can be welded or soldered
-Flexible- poorer control
-Difficult to adjust
-Cannot weld or solder
Options for close-fitting archwires (21x25):
-Steel : Too stiff
-NiTi: Not adjustable
-B-Titanium: Ideal stiffness
used to provide root paralleling
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
Damon 4 Solid Walls
Conventional Wire Out Of Slot
Self-Ligating Brackets Conventional or Active Ligation?
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?
-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 Conventional or Active Ligation?Future
Fiber-reinforced composite Archwires