orthodontic wires

All about wires and their properties, usage, selection, advantages

1. Dr. DHANASEKARAN.R FIRST YEAR MDS Dept. of Orthodontics & Dentofacial Orthopaedics WIRES IN ORTHODONTICS

2. Contents:- Introduction History Properties Ideal requirements Stainless steel High tensile Australian wires Multistranded wires Cobalt Chromium Nickel Titanium Chinese NiTi alloy Copper NiTi alloy β- Titanium α- Titanium Tooth colored wire (Opti Flex) Conclusion References 2

3. INTRODUCTION Active components of fixed appliances. Bring about various tooth movements through the medium of brackets and buccal tubes. The main components of an orthodontic appliance Brackets and Wires

4. History Before Angle’s era. Noble metals and their alloys. - Gold (at least 75%), platinum, iridium and silver alloys. Good corrosion resistance. Acceptable esthetics. Lacked flexibility and tensile strength. 4

5. Angle introduced German silver into orthodontics. (1887) Use prevailed up to 2nd half of the 20th century. Some of the other materials Angle used were wood, rubber, vulcanite, piano wire and silk thread. In late 1930, stainless steel was introduced for appliance fabrication. Angle used stainless steel in his last year, as ligature wire. By 1950s stainless steel alloy was used by most of the orthodontist.

6. Cobalt chrome alloys used as a spring in the watches. In 1950s cobalt chromium alloys drawn into wires available for use in orthodontic appliances Marketed as Elgiloy. In 1970s, introduction of titanium alloys as orthodontic wire materials. Beta titanium alloys were developed around 1980 by Charles J. Burstone, marketed as TMA (titanium-molybdenum alloy). 6

7. In 1985, Dr. C.J. Burstone reported the development of Chinese Niti alloy and in 1986 Miura Fetal reported Japanese Niti alloy. In 1992, the OPTIFLEX an aesthetic arch wire, was introduced to orthodontics by Tallas. Recently in 2001, Dead Soft Security Arch wires has been introduced by Binder and Scott. These arches are bend to lie passively in all attachments. 7

8. Mechanical properties Stress & strain Elastic properties Young’s modulus (modulus of elasticity) Range Springback Formability Resiliency Flexibility 8

9. Strength properties Proportional limit (elastic limit) Yield strength Plastic deformation stiffness/load deflection rate 9

10. Stress and strain The elastic behavior of any material is defined in terms of its stress–strain response to an external load. Stress - internal distribution of the load Stress = force/area Strain - internal distortion produced by the load Strain = deflection/unit length. 10

11. Types of stress/strain:- Tensile –stretch/pull Compressive – compress towards each other Shear – 2 non linear forces in opposite direction which causes sliding of one part of a body over another. 11

12. Orthodontic archwires and springs can be considered as beams, supported either only on one end (e.g., a spring projecting from a removable appliance) or on both ends (the segment of an archwire spanning between attachments on adjacent teeth) 12

13. Three major properties of beam materials are critical in defining their clinical usefulness: Strength, Stiffness, Range. 13

14. Three different points on a stress–strain diagram can be taken as representative of the STRENGTH Proportional limit Yield strength Ultimate tensile strength 14

15. Proportional limit The point at which first deformation is seen. Highest point where stress and strain still have a linear relationship (Hooke’s law). At this point if the stress is removed the wire returns back to its original form. 15

16. Yield strength The stress at which a material exhibits a specified limiting deviation from proportionality of stress to strain. It is more practical indicator True elastic limit lies between these two points. 16

17. 17 Ultimate tensile strength Maximum load the wire can sustain Reached after some permanent deformation and is greater than the yield strength. Clinical implication: Determines the maximum force the wire can deliver.

18. Stiffness Stiffness is proportional to the slope of the elastic portion of the force–deflection curve. The more vertical the slope, the stiffer the wire, the more horizontal the slope, the more flexible the wire. 18

19. Range The distance that the wire will bend elastically before permanent deformation occurs. If the wire is deflected beyond this point, it will not return to its original shape, but clinically useful springback will still occur unless the failure point is reached. Strength = × Stiffness Range 19

20. Resilience and Formability Two other important characteristics also can be illustrated with a stress–strain graph Resilience is the area under the stress–strain curve out to the proportional limit. Represents the energy storage capacity of the wire. Strength and springiness. 20

21. Formability The amount of permanent deformation that a wire can withstand before failing. It represents the amount of permanent bending the wire will tolerate before it breaks. 21

22. Ideal Requirements 22

23. Stainless steel 23

24. Stainless Steel 3 major types are present Ferretic SS Martensitic SS Austenitic SS 400 series Good corrosion resistance , < strength Share 400 series Have high strength & hardness 300 series Most corrosion resistant Not hardenable by heat treatment or cold work Can be heat treated Contain approx 18 – 20 % Cr 8 – 12% Ni 18-8 steel Industrial purposes Surgical and cutting instruments Type 302 & 304 Orthodontic wires and bands 24

25. Stainless Steel Other elements Nickel – stabilizes the crystal into a homogenous austenitic phase adversely affect the corrosion resistance. Other elements like Mb, Mn , Cu are added to in steels used for implants 25

26. Stainless Steel Silicon – (low concentrations) improves the resistance to oxidation and carburization at high temperatures. Sulfur (0.015%) increases ease of machining Phosphorous – allows sintering at lower temperatures. But both sulfur and phosphorous reduce the corrosion resistance. 26

27. Austenitic steels more preferable :- Greater ductility and ability to undergo more cold work without breaking. Substantial strengthening during cold work. Easy to weld Easily overcome sensitization Ease in forming. 27

28. Duplex steels Both austenite and ferrite grains Increased toughness and ductility than Ferritic steels Twice the yield strength of austenitic steels Lower nickel content Manufacture of one piece brackets ( eg Bioline ‘low nickel’ brackets) 28

29. Properties of Stainless Steel 1. Relatively stiff material Yield strength and stiffness can be varied Altering diameter/cross section Altering the carbon content and Cold working and Annealing High forces - dissipate over a very short amount of deactivation (high load deflection rate). 29

30. Properties of Stainless Steel Clinically:- Loop - activated to a very small extent so as to achieve optimal force Once deactivated by only a small amount (0.1 mm) Force level will drop tremendously Not physiologic More activations 30

31. Properties of Stainless Steel Difficult to engage a steel wire into a severely mal-aligned tooth bracket to pops out, pain. Overcome by using thinner wires, which have a lower stiffness. Fit poorly  loss of control on the teeth. 31

32. Properties of Stainless Steel High stiffness can be advantageous  Maintain the positions of teeth & hold the corrections achieved Begg treatment, stiff archwire, to dissipate the adverse effects of third stage auxiliaries 32

33. Properties of Stainless Steel 2. Lowest frictional resistance Ideal choice of wire during space closure with sliding mechanics Teeth will be held in their corrected relation Minimum resistance to sliding 33

34. Properties of Stainless Steel Sensitization During soldering or welding, 400 - 900 o c Reduces the corrosion resistance -Sensitization. Diffusion of Chromium carbide towards the carbon rich areas (usually the grain boundaries) 34

35. Properties of Stainless Steel Stabilization – methods to overcome sensitiztion One or two elements that form carbide precipitates more easily than Chromium are added Eg titanium, tantalum or niobium Expensive – not used for orthodontic wires 35

36. High Tensile Australian Wires History Early part of Dr. Begg’s career Arthur Wilcock Sr. Lock pins, brackets, bands, wires, etc Wires which would remain active for long No frequent visits This lead Wilcock to develop steel wires of high tensile strength. 36

37. High Tensile Australian Wires Beginners found it difficult to use the highest tensile wires H D Kesling – US - Grading system Late 1950s, the grades available were – Regular Regular plus Special Special plus 37

38. High Tensile Australian Wires Newer grades were introduced after the 70s. Premium, premium +, supreme Disadvantages: Brittle. Softening , loss of high tensile properties 38

39. High Tensile Australian Wires BAUSCHINGER EFFECT Described by Dr. Bauschinger in 1886. Material strained beyond its yield point in one direction & then strained in the reverse direction, its yield strength in the reverse direction is reduced. 39

40. High Tensile Australian Wires Imp during manufacturing processes. Wire is subjected to plastic deformation during Straightening processes. Prestrain in a particular direction. Yield strength for bending in the opposite direction will decrease. Premium wire  special plus or special wire. 40

41. Fracture of wires & Crack propagation High tensile wires have high density of dislocations and crystal defects  Pile up, and form a minute crack  Stress concentration  sensitization 41

42. High Tensile Australian Wires Small stress applied with the plier beaks  Crack propagation  Fracture of wire 42

43. High Tensile Australian Wires Ways of preventing fracture Bending the wire around the flat beak of the pliers. Introduces a moment about the thumb and wire gripping point, which reduces the applied stress on the wire. 43

44. High Tensile Australian Wires 44

45. High Tensile Australian Wires The wire should not be held tightly in the beaks of the pliers. Area of permanent deformation to be slightly enlarged, Nicking and scarring avoided. The tips of the pliers should not be of tungsten carbide. 45

46. High Tensile Australian Wires The edges rounded  reduce the stress concentration in the wire. Ductile – brittle transition temperature slightly above room temperature. Wire should be warmed. Spools kept in oven at about 40 o , so that the wire remains slightly warm. 46

47. Multi stranded Wires Two or more wires of smaller diameter are twisted together/coiled around a core wire. Individual diameter - 0.0165 or 0.0178 final diameter – 0.016" – 0.025", rectangular or round On bending  individual strands slip over each other and the core wire, making bending easy. (elastic limit) 47

48. Multi stranded wires 48 Co-axial Twisted wire Multi braided

49. Multistranded Wires – general considerations 49 Implies that the wire delivers lighter forces per unit activation over a greater distance strength – distortion + fracture Twisting of wires Result - high elastic modulus wire behaving like a low stiffness wire

50. Multistranded Wires Elastic properties of multistranded archwires depend on – Material parameters – Modulus of elasticity Geometric factors – wire dimension Constants: Number of strands coiled The distance from the neutral axis to the outer most fiber of a strand Plane of bending Poisson’s ratio 50

51. Cobalt Chromium 51

52. Cobalt Chromium 1950s the Elgin Watch “The heart that never breaks” Rocky Mountain Orthodontics - Elgiloy CoCr alloys - stellite alloys Superior resistance to corrosion, comparable to that of gold alloys. 52

53. Cobalt Chromium Cobalt – 40-45% Chromium – 15-22% Nickel – for strength and ductility Iron, molybdenum, tungsten and titanium to form stable carbides and enhance hardenability. 53

54. Cobalt Chromium properties Strength and formability modified by heat treatment. Before heat treatment - highly formable and can be easily shaped. Heat treated. Strength  Formability  54

55. Cobalt Chromium Heat treated at 482 o c for 7 to 12 mins -Precipitation hardening  ultimate tensile strength of the alloy, without hampering the resiliency. After heat treatment, elgiloy has elastic properties similar to steel. 55

56. Cobalt Chromium 56

57. Cobalt Chromium 57 various tempers Red – hard & resilient green – semi-resilient Yellow – slightly less formable but ductile Blue – soft & formable

58. Cobalt Chromium Blue  considerable bending, soldering or welding Red  most resilient and best used for springs difficult to form, (brittle) After heat treatment , no adjustments can be made to the wire, and it becomes extremely resilient. After heat treatment  Blue and yellow ≡ normal steel wire Green and red tempers ≡ higher grade steel 58

59. Cobalt Chromium Heating above 650 o C partial annealing, and softening of the wire Optimum heat treatment  dark straw color of the wire Advantage of Co-Cr over SS Greater resistance to fatigue and distortion longer function as a resilient spring 59

60. Cobalt Chromium Kusy et al (AJO 2001) Evaluated round , rectangular ,square Cs wires of sizes ranging from 14 mils to 21 x 25 mils of the 4 tempers available They evaluated the yield strength, ultimate tensile strength , ductility and elastic modulus 60

61. Cobalt Chromium The elastic modulus did not vary appreciably  edgewise or ribbon-wise configurations. Round wire had significantly higher ductility than square or rectangular wires The modulus of elasticity was independent of the temper of the wire The yield strength . ultimate tensile strength & ductilty - differed from diff cross sectional areas and tempers Diff tempers – diff mechanical properties – care during manufacturing 61

62. Nickel titanium alloy  William F. Buehler in 1960’s invented Nitinol Ni – Nickel ti-titanium Nol-Naval Ordinance Laboratory,U.S.A. Andreasen G.F. and co-workers introduced the use of nickel-titanium alloys for orthodontic use in the 1970’s. 62

63.  55% nickel, 45% titanium resulting in a stoichiometric ratio of these elements. 1.6% cobalt is added to obtain desirable properties. 63

64. Properties Transition Temperature Range (TTR) Shape Memory Super elasticity 64

65. Transition Temperature Range (TTR) Transition temperature range is a specific temperature range when the alloy nickel titanium on cooling undergoes martensitic transformation from cubic crystallographic lattice.( Austenitic phase of the alloy.) In martensitic phase, the alloy cannot be plastically deformed. 65

66.  At higher temperatures the alloy is found to be in cubic crystallographic lattice consisting of body centered cubic crystallographic structures. It is also known as Austenitic phase of the alloy. Plastic deformation can be induced, in austenitic phase of the alloy. 66

67. The same plastic deformation induced at the higher temperature returns back when the alloy is heated through a temperature range known as reverse transformation (transition) temperature range, RTTR. Any plastic deformation below or in the TTR is recoverable when the wire is heated through RTTR. 67

68. Shape memory Shape memory refers to the ability of the material to "remember” its original shape after being plastically deform while in martesitic form. 68

69. Super elasticity It is the property of the wire explained as even when the strain is added, the rate of stress increase levels off, due to the progressive deformation produced by the stress induced martinsitic transformation. 69

70. Chinese Niti Alloy Another nickel titanium alloy introduced by Burstone and developed by Dr Tien Hua Cheng is called as Chinese Niti alloy in1985 It has a springback that is 4.4 times that of comparable stainless steel wire and 1.6 times that of nitinol wire At 80° of activation the average stiffness of Chinese NiTi wire is 73% that of stainless steel wire and 36% that of nitinol wire. 70

71. Copper Niti alloy  In 1994 Ormco Corporation introduced a new orthodontic wire alloy, Copper NiTi. Copper Ni Ti is a new quaternary ( nickel, Titanium copper and chromium ) alloy. 71

72. 72 Orthodontic archwires fabricated from this alloy have been developed for specific clinical situations and are classified as follows: Type I A f 15℃ Type II A f 27℃ Type III A f 35℃ Type IV A f 40℃

73. These variants would be useful for different types of orthodontic patients. For example, The 27℃ variant would be useful for mouth breathers; The 35℃ variant is activated at normal body temperature; and the 40℃ variant would provide activation only after consuming hot food and beverages. 73

74. β – Titanium (Titanium Molybdenum Alloy)  In the 1960’s an entirely different “high temperature” form of titanium alloy became available. At temperature above 1625°F pure titanium rearranges into a body centered cubic lattice(BCC), referred to as ‘Beta’ phase. With the addition of such elements as molybdenum or columbium, a titanium based alloy can maintain its beta structure even when cooled to room temperature. 74

75. Such alloys are referred as beta stabilized titaniums. Goldberg and Burstone demonstrated that with proper processing of an 11% molybdenum, 6% Zirconium and 4% tin in beta titanium alloy, it is possible to develop an orthodontic wire with a modulus of elasticity of 9.4 x 10 6 psi and yield strength of 17 x 10 4 psi. The resulting YS/E ratio (springback) of 1.8 x 10 -2 is superior to 1.1 x 10 -2 for stainless steel. 75

76. The low elastic modulus yields large deflections for low forces. The high ratio of yield strength to elastic modulus produces orthodontic appliances that can sustain large elastic activations when compared with stainless steel devices of the same geometry. 76

77. β- titanium can be highly cold worked . The wrought wire can be bent into various orthodontic configurations and has formability comparable to that of austenitic stainless steel . Clinically satisfactory joints can be made by electrical resistance welding of β- titanium (light-capacitance weld). Such joints need not be reinforced with solder. 77

78.  Beta titanium wire possesses a unique balance of high spring back & formability with low stiffness ,making it particularly suitable for a number of treatment modalities. 78

79. Alpha Titanium Alloy The alpha titanium alloy is attained by adding 6% aluminium and 4% vanadium to titanium Because of its hexagonal lattice, it possesses fewer slip planes making it less ductile from β- titanium. The hexagonal closed packed structures of Alpha-Titanium has only one active slip plane along its base rendering it less ductile.  79

80. Composotion Alpha-Beta alloy with titanium, aluminum, vadadium A smooth surface structure Less friction at the archwire bracket inter Better strength than existing titanium based alloy Poor in its weld characteristics 80

81. Tooth Colored Wire (OPTIFLEX) Optiflex is a new orthodontic archwire that is designed to combine unique mechanical properties with a highly esthetic appearance. 81

82. Made of three clear optical fiber A silicon dioxide core that provides the force for moving teeth A silicon resin middle layer that protect the core from moisture & adds strength A strain resistant nylon layer that prevent the damage to the wire 82

83. It is used in adult patients with high aesthetic requirements. It can be used as an initial wire in cases with moderate amounts of crowding in one or both arches. The wire can be round or rectangular & is manufactured in various sizes.  Mechanical properties includes a wide range of action & ability to apply light continuous force. 83

84. Sharp bends must be avoided ,since they could fracture the core. Highly resilient wire that is especially effective in the alignment of crowded teeth. 84

85. Applying archwires Stage Wires Reason I aligning Multistranded SS, NiTi Great range and light forces are reqd II stage Β - Ti , larger size NiTi , SS – if sliding mechanics is needed Increased formability, springback , range and modest forces per unit activation are needed III stage SS , preferably rectangular More stability & less tooth movement reqd 85

86. Conclusion It is important to know the properties of the arch wires as it is widely used in orthodontics. Proper handling of the material gives the best result. Material with excellent aesthetics and strength expected to replace metals in orthodontics in the near future. 86

87. References Proffit – Contemporary orthodontics Graber vanarsdall – orthodontics – current principles and techniques Kusy & Greenberg. Effects of composition and cress section on the elastic properties of orthodontic wires. Angle Orthod 1981;51:325-341 Kapila & Sachdeva. Mechanical properties and clinical applications of orthodontic wires. AJO 89;96:100-109. Burstone. Variable modulus orthodontics. AJO 81; 80:1-16 Kusy. A review of contemporary archwires: Their properties and characteristics. Angle orthodontist 97;67:197-208 87

88. Ingram, Gipe, Smith. Comparative range of orthodontic wires AJO 1986;90:296-307 Tidy. Frictional forces in fixed appliances. AJO 89; 96:249-54 Twelftree, Cocks, Sims. Tensile properties of Orthodontic wires. AJO 89;72:682-687 Kusy and Dilley. Elastic property ratios of a triple stranded stainless steel archwire. AJO 84;86:177-188 Arthur J Wilcock. JCO interviews. JCO 1988;22:484-489 Frank and Nikolai. A comparative study of frictional resistance between orthodontic brackets and archwires. AJO 80;78:593-609 Arthur Wilcock. Applied materials engineering for orthodontic wires. Aust. Orthod J. 1989;11:22-29. 88

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