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Contemporary Archwires

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

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  1. Contemporary Archwires Dr. Firas Elayyan University of Manchester

  2. 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.

  3. Factors affects the force wire exerts: Thickness Length Material

  4. 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

  5. W h3 Effect of thicknessRectangular wires Stiffness is proportional to w x h3

  6. 19x25 18x25 Stiffness of 19x25 > 18x25

  7. 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

  8. Materials -Stainless steel -Cobalt Chromium -Beta-Titanium -Nickel Titanium alloys -Glass Optiflex -Fibre reinforced composite

  9. Range

  10. Stiffness and Range

  11. S.S. Stress NiTi Strain Stiffness

  12. 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)

  13. 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.

  14. 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.

  15. Shape memory effect (SME) !!

  16. 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.

  17. Properties of different phases

  18. 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.

  19. Transitional Transformation Range (TTR) 100 % Austenite 0 % Temperature

  20. 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)

  21. 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

  22. 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

  23. 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.

  24. 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

  25. Advantages of Superelastic NiTi archwires -Excellent springback (4-5 of SS) -Constant forces over large wire deflection Activation Deactivation

  26. 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

  27. Effect of heat treatment on SE NiTi deformation Muira et al. AJODO 1986

  28. 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.

  29. 60°C 37°C 23°C Deflection Thermal Wires ( Af=37°) Stress Iijima et al. Dental Material 18 ( 2002) 88-93

  30. 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.

  31. -Allow more severely displaced brackets to be engaged by chilling the wire locally.

  32. 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.

  33. Effect of temperature changes on thermal archwires during activation T.Melling and J.Odegaard AJODO 2001; 119: 263-73

  34. Effect of temperature changes on thermal archwires during deactivation T.Melling and J.Odegard AJODO 2001; 119: 263-73

  35. 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

  36. Stress 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°.

  37. CuNiTi 27˚ -Af at 27˚. -Superelastic wire • In patients : -with average or high pain threshold. -Normal periodontal health. -where rapid tooth movement is required

  38. 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

  39. CuNiTi 40˚ -Af at 40˚. -Thermoelastic wire • In patients : -who are sensitive to pain . -with compromised periodontal conditions. • Good as initial rectangular wire.

  40. 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.

  41. 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

  42. Archwire application More Stiffness Less Range -Aligning arches -Working arches -Finishing arches

  43. Springback and stiffness ratios of different materials* *Evans (1996), Profit (2000)

  44. Aligning wires need: -Low stiffness:low forces on activation -High strength:prevent permanent deformation -Long working range : maximize activation

  45. First aligning wireWhich 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 !?

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