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Contemporary Archwires

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Presentation on theme: "Contemporary Archwires"— Presentation transcript:

1 Contemporary Archwires
Dr. Firas Elayyan University of Manchester


3 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.

4 Factors affects the force wire exerts:
Thickness Length Material

5 1-Effect of thickness round wires
14 20 Stiffness is proportional to (diameter)4 Diameter Stiffness Small increment in size= big increment in force

6 Effect of thickness Rectangular wires
Stiffness is proportional to w x h3 W h3

7 Stiffness of 19x25 > 18x25 19x25 18x25 KEY POINT – Full engagement is as important as low friction, regarding treatment efficiency Elastic ligature OR metal clip, fails to give FULL ENGAGEMENT → Poor Control and Less Effective Torque The ligature or clip becomes distorted, the Damon slide cannot be distorted, therefore “full engagement” is always possible

8 2-Effect of Length Stiffness is inversely proportional to L3
Span Stiffness 6 mm 5 mm 4 mm 3 mm 2 mm Critical areas: smallest interbracket span

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

10 Range

11 Stiffness and Range

12 Stiffness S.S. Stress Strain NiTi

13 The Chronological Development of Archwires ( Evans,1996)
Phase l : Gold and Stainless steel ( ’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)

14 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.

15 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.

16 Shape memory effect (SME) !!

17 NiTi Transformation Austenite Martensite
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.




21 Properties of different phases
Martensite NiTi Austenite NiTi Hexagonal Cubic Crystalline structure 31 GPa 98 GPa Elastic Modulus 138 MPa 379 MPa Yield Strength

22 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.

23 Transitional Transformation Range (TTR)
100 % Austenite 0 % Temperature

24 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)

25 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

26 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

27 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.

28 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

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

30 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

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

32 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 Room Temp -Austenitic with SIMT at 37˚ C -Deliver 25-30% of the force of SE NiTi and greater range of action.

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

34 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.

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


37 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.

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

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

40 Effect of repeated short-term exposure to ice cream on torsional stiffness of thermal archwires
T.Melling and J.Odegaard Angle Orthod 1998; 68:

41 Stage lV: Development of Copper NiTi “’ CuNiTi”
-5% Copper, % 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 40 ° CuNiTi 35 ° CuNiTi 27° Stress Deflection

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

43 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

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

45 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.

46 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

47 -Aligning arches -Working arches -Finishing arches
Archwire application -Aligning arches -Working arches -Finishing arches More Stiffness Less Range

48 Springback and stiffness ratios of different materials*
1 Stainless steel .13 1.5-2 Multistrand SS .36 1.75 B-Titanium .17 2.5 Nitinol .41 4-5 SE NiTi *Evans (1996), Profit (2000)

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

50 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 !?

51 Amount of force delivered by wires
307 gm 16x22 Nitinol 193 gm 16x22 NiTi SE 143 gm 16x22 Thermal 137 gm 16x22 CuNiTi 27 ˚ 100 gm 16x22 CuNiTi 35˚ 87 gm 18 thermal 73 gm 16 NiTi SE 60 gm 16 Thermal 43.1gm 17.5 Multistrand

52 Advantages of NiTi as aligning archwires compare to Multistrand SS:
-Long working range -Damage resistance -Sustained forces! -Low Forces!

53 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

54 Inefficient archwire progression
Multiple round & rectangular wires e.g x22-18x25

55 Evidence based archwire selection

56 “Clinical trials” -Superelastic NiTi vs Stabilized NiTi
O’Brien et al , EJO 12 ( 1990) -Superelastic NiTi vs multistrand steel West. Jones & Newcombe , AJODO 108 (1995) -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

57 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.

58 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

59 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 mm

60 Time required to reach the working archwire
No of visits Time ( Months) Archwire sequence 5.7 ( 2.1) 5.4 ( 2.1) 6.8 ( 2.5) 6.7 ( 3.5) A Lower Upper 7.5 ( 1.9) 7.1 ( 2.6) 9.3 ( 4.4) 7.9 ( 3.5) B Lower 6.4 ( 2.2) 5.9 ( 2.8) 8.3 ( 4.2) 7.1 ( 3.4) C Lower

61 Can Thermal Rectangular wires be used as first aligning archwires?

62 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

63 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

64 Second aligning archwire
-18x25 NiTi -20x20 CuNiTi

65 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.

66 Working archwires Photo

67 Working arch usage 0.022 slot

68 Percentage of Force loss due to Friction
16x22 archwires, Slot size 18, bracket width 3.3mm ( D.Tidy)

69 Stainless steel working arches
-High stiffness-good control -Easily adjusted -Low friction -Can be welded or soldered -Cheap

70 NiTi working arches -Flexible- poorer control -Difficult to adjust
-Higher friction -Cannot weld or solder -More expensive

71 Finishing archwires (22 slots)

72 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

73 Self-Ligating Brackets?
KEY POINT – The high friction and binding that exists with ACTIVE or CONVENTIONAL systems Sales Tools 15x D2/D3 model with ligature Competitor brackets on wire Self- Ligation Low Force, Low Friction Active Ligation High Force, High Friction

74 What Are The Limitations Of Conventional or Active Ligation?
Poor Control – Less Effective Torque Elastic Ligature or Metal Clip 19x25 19x25 KEY POINT – Full engagement is as important as low friction, regarding treatment efficiency Elastic ligature OR metal clip, fails to give FULL ENGAGEMENT → Poor Control and Less Effective Torque The ligature or clip becomes distorted, the Damon slide cannot be distorted, therefore “full engagement” is always possible Damon 4 Solid Walls Conventional Wire Out Of Slot

75 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 KEY POINT - High Force will produce More patient discomfort – Periodontal ligament becomes crushed Longer treatment times - Periodontal ligament becomes crushed – less blood flow – slower tooth movement More anchorage required (to be discussed later in presentation) High forces WILL NOT work with the patients biology. Teeth are pushed into their new position rather than utilizing the light forces which exist with the Damon System, allowing a more natural (biological) tooth position

76 Frictional Resistance N/m
Sims, Birnie and Waters (1993)

77 F.Elayyan et al. Angle Ortho ( 2006) , in press

78 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.

79 Future Fiber-reinforced composite Archwires Future

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