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Wires in orthodontics


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Wires in orthodontics

  1. 1.  INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. Introduction Evolution of materials Physical & Elastic properties Requirements of an ideal arch wire Composition, Heat treatment, manufacture of 1.Gold Alloy wires 2.Stainless Steel wires 3.Chrome Cobalt wires 4.Nickel Titanium wires 5.Copper Nickel Titanium wires 6.Alpha-Titanium wires
  3. 3. 7.Beta-Titanium wires 8.Tooth colored wires  Clinical importance of various wires  Choice of wires in the clinical situation  References
  4. 4.  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  Inappropriate for complex machining and joining.
  5. 5.  Angle (1887)  German silver (a type of brass)  -To obtained desired properties --varied the proportion of Cu, Ni & Zn and applied cold working operation a.  Neusilber brass (Cu 65%, Ni 14%, Zn 21%)  jack screws (rigid)  expansion arches (elastic)  Bands (malleable)  Opposition by Farrar – discolored
  6. 6.  Stainless steel (introduced in dentistry -1919).  Angle used steel ligature wires (1930).
  7. 7.  Opposition By,  Emil Herbst -Gold wire was stronger than stainless steel (1934).  Begg (1940s) with Wilcock-produced resilient arch wires-Australian SS.
  8. 8.  Cobalt chrome (1950s)-Elgin watch company developed a complex alloy- Cobalt(40%),Chromium(20%),iron(16%)&nickel(15%).  Rocky Mountain Orthodontics first introduced Co-Cr wires by name ElgiloyTM  1958-1961 various tempers Red – hard & resilient green – semi-resilient Yellow – slightly less formable but ductile Blue – soft & formable
  9. 9.  1962 - Buehler discovered nickel-titanium named NITINOL (Nickel Titanium Naval Ordnance Laboratory) . Developed for space program.  1970-Dr.George Andreason (Unitek) introduced NiTi to orthodontics.  Late 1980s –NiTi with active austenitic grain structure.  β titanium –Burstone and Goldberg-1980
  10. 10.  Chinese NiTi (1985) –by Burstone et al  Japanese NiTi (1986) – by Miura et al  Cu NiTi – (1994) -by Rohit Sachdeva.
  11. 11.  Stress  Strain  Modulus of elasticity  Proportional limit  Elastic limit  Yield strength  Ductility Richman G.Y. Practical metallurgy for Orthodontist, AJO 1957;vol.42,573-576
  12. 12.  Malleability  Elongation  Formability  Resilience  Flexibility  Spring back Kohl R.w. Metallurgy in orthosontics,A.O.1964,Vol 34,37-52
  13. 13. Stress-  It is the internal distribution of the load measured as force per unit area i.e., Force/Original area.  For simple compression or tension the stress is given by the expression, Stress =F/A Where, F= force applied A= cross-sectional area
  14. 14.  Stress is measured in common units of psi or MPa (Mega Pascal).  1 Pascal – stress resulting from a force of 1 Newton (N) acting upon 1 sq. meter of surface and is equal to 0.145 x 10–3 psi, (1000 psi = 6.894 MPa).
  15. 15.  By means of their directions ,stress can be classified under three types  TENSION OR TENSILE STRESS  COMPRESSION OR COMPRESSIVE STRESS  SHEAR STRESS Sunil Kapila Sachdeva R.:Mechanical properties and clinical applications of orthodontic wires.AJO 1989,Vol.96,100-109
  16. 16. TENSION OR TENSILE STRESS  Any induced force that resists a deformation caused by a load that tends to stretch or elongate a body
  17. 17.  COMPRESSION OR COMPRESSIVE STRESS If a body is placed under load that tends to compress or shorten it , the internal forces that resist such a load are called compressive stress.
  18. 18.  SHEAR STRESS  A Stress that tends to resist a twisting motion ,or a sliding of one portion of a body over another ,is a shear or shearing stress
  19. 19.  Complex Stresses
  20. 20.  Poisson’s ratio (ν) ν = - εx/ εz = -εy / εz  Axial tensile stress (z axis) produces elastic tensile strain and accompanying elastic contractions in x in y axis.  The ratio of x,y or x,z gives the Poissons ratio of the material  It is the ratio of the strain along the length and along the diameter of the wire.
  21. 21. Strain- It is the internal distortion produced by load or a stress, i.e., change in length per unit length when stress is applied.  Strain = L’ = change in length  L original length  • The common units of strain are inch per inch or centimeter per centimeter.
  22. 22.  Strain may be either elastic or plastic or a combination of two.  Elastic strain is reversible ,it disappears after the stress is removed.  Plastic strain is permanent displacement of atoms inside the material.
  23. 23.  Types of strains 1) Compressive strain-Contraction /original length 2) Tensile strain =Elongation/Original length 3) Shear strain =Shear angle
  24. 24.
  25. 25. Proportional limit  It may be defined as the greatest stress which may be produced in a material such that the stress is directly proportional to the strain
  26. 26. Proportional limit Hook’s law- The stress is directly proportional to strain in elastic deformation  Proportional limit for Tooth enamel - 225 MPa Tooth dentin - 147 MPa Acrylics - 27.5 MPa Stainless steel - 1630 MPa
  27. 27. Yield Strength  It is defined as the stress at which a material exhibits a specified limiting deviation from proportionality of stress to strain.  It is a more practical indicator , at which a plastic deformation of 0.1% is seen
  28. 28.
  29. 29.  Bauschinger Effect If the wires are straightened by the process of reverse straining, meaning flexing in a direction opposite to that of original bend ,the yield point of the wire reduces. This phenomenon is known as work softening due to reverse staining or the Bauschinger effect.
  30. 30. Elastic Limit The elastic limit of a material is the greatest stress to which a material can be subjected ,such that it will return to its original dimensions when the forces are released
  31. 31.
  32. 32.  Although the three terms, elastic limit, proportional limit and yield strength are defined differently, their magnitudes are so nearly the same that for all practical purposes the terms can often be used interchangeably.
  33. 33. MODULUS OF ELASTICITY (E) If any stress value equal to or less than proportional limit is divided by its corresponding strain value ,a constant of proportionality will result, which is known as the modulus of elasticity
  34. 34. Types of MODULUS OF ELASTICITY  Young’s modulus (E)  Bulk modulus  Modulus of rigidity/stiffness (shear modulus-G)
  35. 35.  Usually expressed as force per unit area (MPa/psi) It is an index of stiffness or flexibility of a material within the elastic range.
  36. 36. Stress Fl E = ---------- = ------ Strain eA E-Young’s modulus F-Applied force or load A-Cross section of material under stress e-Increased in length l-Original length
  37. 37. FLEXIBILITY  It is defined as the strain which occurs when material is stressed to its proportional limit or  It is the measure of the strain that a wire can withstand without undergoing plastic deformation
  38. 38. The relation between the proportional limit, flexibility & modulus of elasticity εm = P/E Where, E=Modulus of elasticity P=Proportional limit ε m =Maximal Flexibility
  39. 39. RESILIENCE ( stored or spring energy)  It can be defined as the amount of energy absorbed by a structure when it is stressed not to exceed its proportional limit.  The energy stored is released when the wire springs back to its original shape after removal of an applied stress.
  40. 40.
  41. 41. Toughness -It is defined as the energy required to fracture a material -Toughness is more dependent upon the ductility or malleability of the material than upon its flexibility -Tough material is generally strong
  42. 42.  It is the ability of a material to be plastically strained in tension i.e., ability of a material to withstand permanent deformation under a tensile load without rupture  Ductility decreases with increase in temperature
  43. 43.  The ability of a material to withstand permanent deformation without rupture under compression ,as in hammering or rolling into sheet is termed as malleability  Malleability increases with increase in temperature
  44. 44.  Creep (Visco-Elasticity)  If a metal is held at a temperature near its melting point and subjected to a constant applied force ,the resulting strain will be found to increase as a function of time. This time dependent plastic deformation is referred to as creep
  45. 45.  Static creep- It is the time dependent deformation produced in a completely set solid subjected to a constant stress.  Dynamic creep- It refers to this phenomenon when applied stress is fluctuating.
  46. 46.  It is the deformtion as a result of tensile force application  It is usually expressed as percentage elongation & is equal to Increase in length x 100/Original length
  47. 47. • Formability is the amount of permanent deformation that a wire will withstand before failing i.e. before breaking or fracture.
  48. 48.
  49. 49.  It is expressed as YS/E i.e., the ratio of yield strength to modulus of elasticity which represents the approximate amount of strain released by the wire on unloading.
  50. 50. ELASTIC PROPERTIES  Strength  Stiffness  Range
  51. 51. Strength  It is a force value, that is a measure of the maximum possible load i.e. the greatest force that a wire can sustain or deliver, if it is loaded to the limit of the material.  It is equivalent to the proportional limit (PL) or approximately the yield strength (YS) of the wire segment.
  52. 52.  Considering the graphic representation of the stress – strain curve three points can be taken as representative of the strength of a material - elastic limit - yield point -ultimate tensile strength
  53. 53. 1. Esthetics 2. Stiffness 3. Strength 4. Range 5. Spring back 6. Formability 7. Resiliency 8. Coefficient of friction 9. Biocompatibility 10. Weldability
  54. 54.  It is the rate of force delivery required for a unit activation .  It is the measure of the force required to bend or otherwise deform the material to a definite distance.
  55. 55.  Stiffness is proportional to the modulus of elasticity and cross-section of a given wire and is not appreciably influenced by any hardening treatment.  Stiffness and springiness are reciprocal properties. Springiness = 1 / stiffness.
  56. 56.  Stiffness = Ed/L, higher the elastic modulus, stiffer the wire.
  57. 57.  Range is defined as the maximum amount of elastic activation before the onset of a permanent or plastic deformation.  Range is usually determined from the 0.1% offset point on the force – deflection diagram.
  58. 58.  Strength, Stiffness and Range have an important relationship, i.e., Strength = Stiffness x Range
  59. 59.  The mechanical arrangement by which force is applied to the teeth, e.g. length of archwire.  The second factor is the form of the wire itself – the size and shape of cross section.  The material, including the alloy composition, its hardness.
  60. 60.  The first wire introduced for orthodontic purpose was made of gold.  Gold arch wires were the ideal choice of arch wires with good bio-compatibility.
  61. 61.  Composition of many gold alloy wires corresponds to the type IV gold casting alloys  They are also subjected to softening and hardening heat treatments.
  62. 62.  Their composition is very similar to the Type IV gold casting alloys. The typical composition of the alloy is as follows-  Gold – 15 – 65% (55-65% more typical)  Copper – 11 – 18%  Silver – 10 – 25%  Nickel – 5 – 10%
  63. 63.  Many wires appear to contain less than 60% gold with some containing less than 25 to 30% or even less.  The palladium content of the alloy is relatively high, which gives a composition closely resembling white gold casting alloys.
  64. 64.  Palladium and platinum cause rise in the melting point, improve corrosion resistance and increase hardness and strength during heat treatment.  The copper content of most wires is well above 9%.
  65. 65.  Gold alloys used, can be called to a large extent as binary alloys, as only gold and copper are major metals used.  These binary alloys to a large extent exhibit severe grain growth on heating and have poor ductility in the hardened state.
  66. 66.  The changes that are produced in the strength and ductility of a wrought gold alloy by heat treatment are due to the alterations in the gold copper compound present in the alloy.  Softening heat treatment is undertaken initially by heating the wire to 1300° F, for approximately ten minutes and then quenching it.
  67. 67.  Softening of the alloys is produced as the gold copper alloy enters into solid solution at 1300° F.  All of the hardening elements are completely dissolved in each other in solid solution, the space lattice is free to move on the slip planes without interference.
  68. 68.  Increased number of slip planes, causes increased ductility of the wire.  This wire left at room temperature for several days becomes harder.  Alternatively, after the wire is heated to 1300°F, it is reheated to 840°F and allowed to cool slowly. This allows the gold copper compound to come out of the solution.
  69. 69.  This causes the formation of segregated molecules which produce a locking effect on the space lattice and causes resistance to slip.  The space lattice itself is also distorted to some degree, thus decreasing the number of planes on which slip can occur. In this way, the material becomes stronger and more resilient.
  70. 70.  Besides (age) precipitation hardening, cold working of gold alloys increases strength of the wrought gold wires. The alloy hardens as the grain structure becomes broken up and the space lattice is distorted during cold working.
  71. 71.  This type of hardening is easily relieved by heating the wire to recrystallization temperatures, recrystallization will take place and allow the atoms to return to normal position in the space lattice.
  72. 72.  Yield strength of the gold wires range from 50,000 to 1,60,000 psi, depending on the alloy.  Modulus of elasticity of gold copper alloys is approximately 15,00,000 psi.  The combination of these properties makes gold very formable and capable of delivering lower forces than stainless steel
  73. 73.  Stainless steel (SS) entered dentistry in 1919  Introduced by R.Hauptmeyer in Garmany  First it was known as Wipla-Like platinum  Discovered by chance a few years before World war I  Angle used it in his last year (1930) as ligature wire
  74. 74.  Stainless steel wires began to replace gold wires in the 1930’s .  Steels are iron – based alloys that usually contain less than 1.2% carbon.  When 12-30% chromium is added to steel the alloy is commonly called STAINLESS STEEL.
  75. 75.  Silicon ,phosphorous ,sulphur, manganese, tantalum, and niobium may also be present in small amounts. The balance is iron.  A variety of SS have been developed ,and at least 10 are or were used to manufacture orthodontic instruments & attachments.
  76. 76.  Steels are classified according to the American Iron and Steel Institute ( AISI) System  This classification parallels the United Number System (UNS) & German Standards (DIN)  Steel that have AISI numbers beginning with the number 3 , for austenitic  The higher this number ,the less ferrous the alloy are  The letter L signifies lower carbon content
  77. 77.  Scan page 358 vanarsdall
  78. 78.  The name derives from the fact that microstructure of these steels is same as that of iron at room temperature(bcc)  These alloys are often designated as American Iron and Steel Institute(AISI) Series 400 stainless steels.  The ferritic alloys provide good corrosion resistance at a low cost , provided that high strength is not required
  79. 79.  Because temperature change induces no phase change in the solid state , the alloy is not hardenable by heat treatment.  The modern “super ferritics”in which chromium is substituted for some of the iron atoms in the unit cells ,contain 19% to 30%chromium are used in several nickel free brackets
  80. 80.  Ferrictic steels are highly resistant to chlorides these alloys contain small amounts of aluminum and molybdenum and very little carbon  This series of alloys finds little application in dentistry.
  81. 81.  Martensitic stainless steel alloys share the AISI 400 designation with the ferritic alloys.  Starting in 1970 ,in addition to carbon other elements were added to SS to increase their tensile strength  Martensitic stainless steel have good tensile strength but less corrosion resistance. Such SS could only be used in oral environment for short contact.
  82. 82.  They can be heat treated in the same manner as plain carbon steels , with similar results.  Because of their higher strength and hardness, martensitic stainless steels are used for surgical and cutting instruments.
  83. 83.  The austenitic stainless steel alloys are the most corrosion resistant of the stainless steels.  AISI 302 is the basic type , containing 18% chromium , 8% nickel , and 0.15% carbon. Type 304 has a similar composition , but the chief difference is its reduced carbon content (0.08%).
  84. 84.  Both 302 and 304 stainless steel may be designated as 18-8 stainless steel ; they are the types most commonly used by the orthodontist in the form of band and wires .  Type 316L (0.03% maximum carbon) is the type ordinarily employed for implants.
  85. 85.  The alloying elements Chromium, Nickel ,Mn (austenizing elements) maintains austenite at room temperature and prevents conversion of face centered cubic lattice structure of austenite to a martensitic cubic lattice structure.
  86. 86.  By nature austenite is malleable and ductile whereas martensite is hard and brittle. By maintaining austenite at room temperature, several uses of austenitic stainless steel are made use of in orthodontics, such as wires, bands, instruments etc.
  87. 87. Passivating effect-Chromium when exposed to atmosphere, immediately gets oxidised to form a very thin atomic layer of chromium oxide which is firmly bonded to the substrate.This film prevents further oxidation by penetration of oxygen and thus protects the material from corrosion  Tarnish and corrosion are resisted by stainless steel due to the passivating effect of chromium
  88. 88.  This protective oxide layer prevents tarnish and corrosion, but can be ruptured by mechanical or chemical means resulting in corrosion.  However ,the passivating oxide layer eventually forms again in an oxidizing environment.
  89. 89.  Sensitization-Loss of corrosion resistance(due to loss of chromium) When SS is heated between 400 c to 900 c  These temperatures are within the range of soldering & welding temperatures. Corrosion taking place at the soldered joints & weld nuggets is due to loss of passivation & localised stress in the welded or soldered interface .These lead to failures known as weld decay
  90. 90.  stabilization. A procedure to introduce some element that precipitates carbide in preference to chromium.  Titanium is often used for this purpose
  91. 91.  Titanium introduced in amount approximately six times the carbon content, the precipitation of chromium carbide can be inhibited for a short time at the temperature ordinarily encountered in soldering .  SS that have been treated in this manner are said to be stabilized
  92. 92.  The physical properties of orthodontic stainless steel wires improve by heat treatment at low temperatures between 750° C to 820° C for ten minutes and at a lower temperature of 250° C for twenty minutes.  By heat treatment residual stresses are removed.
  93. 93.  Biocompatibility  High corrosion resistance  Chemically Stable in oral & implant environment  Superior mechanical properties Yield strength-11oo-1759 MPa Ultimate tensile strength upto 2200 MPa Modulus of elasticity about 170,000-200,000 MPa Density -8.5 gm/cc
  94. 94.  Arthur. J. Wilcock of Victoria, Australia, produced the orthodontic archwire to meet Dr. Begg’s needs for use in Begg technique.  The wire produced has certain unique characteristics different from usual stainless steel wires .
  95. 95.  REGULAR GRADE : White label. Lowest grade and easiest to bend. Used for practice bending or forming auxillaries. It can be used for archwires when distortion and bite opening are not a problem.
  96. 96.  REGULAR PLUS GRADE : Green Label Relatively easy to form, yet more resilient than regular grade. Used for auxillaires and archwires when more pressure and resistance to deformation is required.
  97. 97. SPECIAL GRADE : Black Label. Highly resilient, yet can be formed into intricate shapes with little danger of breakage. SPECIAL PLUS GRADE : Orange Label Hardness and resiliency of the wire are excellent for supporting anchorage and reducing deep overbites.
  98. 98.  EXTRA SPECIAL PLUS GRADE :Blue Label. Highly resilient and hard, difficult to bend and subjects to fracture.  Supreme Grade : Blue Label. Primarily used in early treatment for correction of rotations, alignment and levelling. Its yield strength exceeds that of E.S.P.
  99. 99.  Each grade of wire is available in diameters of 0.010″, 0.012″, 0.014″, 0.016″, 0.018″, 0.020″, 0.022″. They are supplied in the form of spools or cut lengths of the wire.  With the demand for harder wires , even higher grades , premium and premium plus wires were developed .
  100. 100.  The new grades and sizes of wire made available are: Sizes Available Premium : .020″ Premium Plus : .010″,.O12″,.014″,.016″, Supreme : .008″, .009″, .010″, .011″.
  101. 101.  The low and medium grade wires exhibit better formability as they are subjected to less work hardening and hence are more ductile.  The wires were straightened by spinner straightening. The wire is pulled through high speed rotating bronze rollers which twist the wire into a straightened condition.
  102. 102.  Presently the premium and supreme wires are straightened by a process called pulse straightening .Though the exact procedure remains a trade secret , it enables to straighten these high yield strength wires , without structural deformation and altering the physical properties.
  103. 103.  These are ultra high tensile austenitic stainless steel arch wires.  The wires are resilient, certain bends when incorporated into the arch form and pinned to the teeth become activated by which stresses are produced within the wires which generates forces.
  104. 104.  The wires must be sufficiently resilient to resist permanent deformation and maintain their activation, for maximum control of anchorage.  All these properties make these wires very hard and brittle.
  105. 105.  The properties of the wire are affected by the way the wire is straightened before bending it to form any component of the appliance .  If the wires are straightened by the process of reverse straining, meaning flexing in a direction opposite to that of the original bend, the yield point of the wire reduces.
  106. 106.  The phenomenon is known as work softening due to reverse straining or the ‘Bauschinger Effect’ , named after the person who described it for the first time .
  107. 107.  1)The ultimate tensile strength for Premium Plus wire is 8-12% higher than SS wire indicating greater resistance to fracture in oral cavity  2)The pulse straightened wires have significantly higher working range and show good recovery patterns.
  108. 108.  3) Frictional resistance of the P.S. wires is lesser by a factor of 50% than SS wire  4)There is no significant difference in stress relaxation properties
  109. 109.  A cobalt-chromium-nickel orthodontic wire alloy was developed during the 1950’s by the Elgiloy Corporation (Elgin, IL,USA).  Initially it was manufactured for watch springs by Elgin watch company, hence the name Elgiloy.  Rocky Mountain Orthodontics first introduced Co- Cr wires by name ElgiloyTM
  110. 110.  Chrome cobalt alloy is a cobalt base alloy containing  40% cobalt,  20% chromium,  15% nickel,  7% Molybdenum,  2% manganese,  0.16% carbon,  0.04% beryllium ,  15.8% iron.
  111. 111.  Elgiloy is manufactured in four tempers Red – hard & resilient green – semi-resilient Yellow – slightly less formable but ductile Blue – soft & resilient
  112. 112.  Blue(soft) elgiloy : Can be bent easily with finger pressure and pliers. Heat treatment of blue elgiloy increases its resistance to deformation.
  113. 113.  Yellow elgiloy : Relatively ductile and more resilient than blue elgiloy. Further increase in its resilience and spring performance can be achieved by heat treatment.
  114. 114.  Green elgiloy : More resilient than yellow elgiloy and can be shaped with pliers before heat treatment.
  115. 115.  Red elgiloy : Most resilient of elgiloy wires, with high spring qualities. Heat treatment makes it extremely resilient
  116. 116.  William F. Buehler in 1960’s invented Nitinol Ni – Nickel ti-titanium Nol-Naval Ordinance Laboratory,U.S.A.
  117. 117. Andreasen G.F. and co-workers introduced the use of nickel-titanium alloys for orthodontic use in the 1970’s.
  118. 118.  55% nickel, 45% titanium resulting in a stoichiometric ratio of these elements.  1.6% cobalt is added to obtain desirable properties.
  119. 119.  Like stainless steel ,NiTi can exist in more than one form or crystal structure  The martensite form exist at lower temperatures, the austenite form at higher temperatures
  120. 120.  Transition Temperature Range : TTR  Shape Memory  Super elasticity
  121. 121.  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.
  122. 122.  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.
  123. 123.  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.
  124. 124.  Shape memory refers to the ability of the material to "remember” its original shape after being plastically deform while in martesitic form
  125. 125.  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
  126. 126.
  127. 127.  This property can be produced by stress and not temperature difference. Therefore it is called as stress induced martensitic transformation.
  128. 128.  Japanese Niti wire introduced by Fujio Miura in 1986 & is manufactured by a different process and demonstrates super elasticity.  Fujio Miura et al:The super elastic property of Nickel titanium wire for use in orthodontics AJO 1986,Vol 90,1-10
  129. 129.  A new type of heat treatment was reported by Fujio Miura and associates which is known as Direct Electric Resistance Heat Treatment (DERHT).  An electric current is directly passed through the wire, thus generating enough heat to make it possible to bend it as well as impart change in the super elastic property of the wire.
  130. 130.  Heat treating equipment consists of an electric power supply, a pair of electric pliers, an electric arch holder.  The amount of heat can be controlled by amperage and the heating time.  The DERHT method utilizes the electric resistance of the wire to generate heat.
  131. 131.  In spite of resulting molecular re-arrangement, the mechanical properties of the wire are unchanged.  On testing it was found that the heat treated segments demonstrated better super elastic properties in relation to time.
  132. 132.  Hence it is possible to heat treat any desired section of the archwire by DERHT method and utilize optimally the super elastic property of the wire.  For smaller diameter wires lesser current is required. For eg : 0.022” wire requires 8.0A for 2.0 seconds, 0.014” wire requires 3.5A for 2.0 seconds.
  133. 133.  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 Burstone al:Chinese NiTi wore,a new orthodontic alloy AJO 1985 Vol 87 ,445- 452
  134. 134.  At 80° of activation the average stiffness of Chinese NiTi wire is 73% that of stainless steel wire and 36% that of nitinol wire.
  135. 135.  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.
  136. 136.  Orthodontic archwires fabricated from this alloy have been developed for specific clinical situations and are classified as follows: Type I Af 15 0C Type II Af 27 0C Type III Af 35 0C Type IV Af 40 0C
  137. 137.  These variants would be useful for different types of orthodontic patients.  For example, the 27oC variant would be useful for mouth breathers; the 35oC variant is activated at normal body temperature; and the 40 o C variant would provide activation only after consuming hot food and beverages.
  138. 138.  With the exception of red temper non heat treated Co-Cr wires have a smaller spring back than SS of comparable sizes. This property can be removed by adequate heat treatment .  The ideal temperature for heat treatment is 900 F for 7-12 minutes . This causes precipitation hardening of the alloy, increasing the resistance of the wire to deformation  This type of wire shows properties similar to SS
  139. 139.
  140. 140.  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 (B.C.C.), referred to as ‘Beta’ phase. Charles J.Burstone & A.J. Goldberg,Beta Titanium:A new Orthodontic alloy AJO-DO Feb 1980(121-132)
  141. 141.  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.  Such alloys are referred as beta stabilized titaniums.
  142. 142.  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.
  143. 143. Alloy Modulus of Elasticity (10³ MPa) 0.2% Offset Yield Strength(MP a) Ultimate Tensile Strength (MPa) Number 90-degree Cold Ben without fracture β- Titanium 71.7 931 1276 4 Alloy Modulus of Elasticity (10³ MPa) 0.2% Offset Yield Strength(MP a) Ultimate Tensile Strength (MPa) Number 90-degree Cold Ben without fracture β- Titanium 71.7 931 1276 4 AlloyAlloy Modulus of Elasticity (10³ MPa) Modulus of Elasticity (10³ MPa) 0.2% Offset Yield Strength(MP a) 0.2% Offset Yield Strength(MP a) Ultimate Tensile Strength (MPa) Ultimate Tensile Strength (MPa) Number 90-degree Cold Ben without fracture Number 90-degree Cold Ben without fracture β- Titanium β- Titanium 71.771.7 931931 12761276 44
  144. 144.  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 ( Kenneth Nelson,Charles Burstone ,Optimal welding of beta titanium orthodontic wire.AJO-DO 1987;213-219)
  145. 145.  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.
  146. 146.  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.
  147. 147.  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.
  148. 148.  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  Vinod Krishnan,Weld charactristics of Orthodontic Archwire Material,AO2004,Vol 84,No 4
  149. 149.  Optiflex is a new orthodontic archwire that is designed to combine unique mechanical properties with a highly esthetic appearance  M.F. Talass,Optiflex Archwire Treatment of a Skeletal Class III Open Bite,JCO 1992,April,245- 252)
  150. 150.  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
  151. 151.  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.
  152. 152.  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.  Sharp bends must be avoided ,since they could fracture the core.  Highly resilient wire that is especially effective in the alignment of crowded teeth
  153. 153.  Flexibility of stainless steel wire can be increased by building up a strand of stainless steel wire around a core of 0.0065” wire along with 0.0055” wires used as wrap wires.  This produces an overall diameter of approximately 0.165”.
  154. 154.  The strand of stainless steel wire is more flexible due to the contact slip between adjacent wrap wires and the core wire of the strand.  When the strand is deflected the wrap wires will slip with respect to the core wire and each other. If there is no elastic deformation each wire returns to its normal position, giving elasticity to the strand of the wire.
  155. 155.  According to studies conducted by Kusy ,a multi- stranded wires have elastic properties similar to nickel-titanium arch wires. Hence they can be used as a substitute to the newer alloy wires considering the cost of the nickel titanium wires .  The 0.0175” triple stranded wire and 0.016” Nitinol demonstrated a similar stiffness  Robert Kusy, A review of contemporary Archwire,AO 1997,No.3,(197-207)
  156. 156.  The strand of stainless steel wire is more flexible due to the contact slip between adjacent wrap wires and the core wire of the strand.  When the strand is deflected the wrap wires will slip with respect to the core wire and each other. If there is no elastic deformation each wire returns to its normal position, giving elasticity to the strand of the wire.
  157. 157.  CV(tm) Niti wires are introduced by Masel  It is used as an alternative to the copper NiTi wires in many orthodontic procedures  When cold ,CV NiTi is very soft & workable  When it warms up in patient’s mouth ,it returns to its perfect arch shape,moving the teeth along the way
  158. 158.  CV NiTi comes in three types -27 c CV NiTi for maximum force activation -35 c CV NiTi for moderate force activation -40 c CV NiTi for the most gentle activation Each type of CV NiTi gives consistent, predictable force which the clinician can use to affect tooth movement
  159. 159.  REQUIREMENTS OF AN IDEAL ARCH WIRE  A Review of Contemporary Arch Wires Robert P.Kusy Angle Orthod 1997;67(3);197-208
  160. 160.  No ideal arch wire exists.  The demands of the treatment plan require different characteristic stiffness and ranges.  Nonetheless, several desirable characteristics would be appropriate to list.
  161. 161.  Wires should be esthetic.  Although esthetics are important to the orthodontist, function is paramount
  162. 162.  Wires should have poor biohostability. This characteristic goes beyond biocompatibility.  As a poor biohost, the ideal archwire should neither actively nurture nor passively act as a substrate for micro-organisms that will smell foul, cause color changes that detract from esthetics, or remove and/or build up material that compromise mechanical properties.
  163. 163.  Wires should possess low coefficients of friction.  Finally, wires should have formability, weldability, resilience, and springback so that they may be deformed into loops or bends, fused onto a clasp, employed to maximize their stored elastic energy, and ultimately return to their initial shape.
  164. 164. Robert P.Kusy Angle Orthod 1997;67(3);197-208
  166. 166.  Stainless steel wires began to replace gold wires from 1930. Stainless steel is the most widely used alloy in orthodontics. It finds its application as arch wires, auxiliaries, orthodontic appliances, bands, etc.  These wires are available both in round as well as rectangular cross-sections
  167. 167.  The Australian stainless steel wires described previously are used in the Begg’s technique as well as in the preadjusted edgewise technique.  These wires are available both in round as well as rectangular cross-sections
  168. 168.  NiTi is the ideal wire for initial aligning &levelling due its superior spring back, superelasticity, shape memory  Rectangular NiTi allows full engagement of the bracket slot and give better torque control in the initial phase of treatment.
  169. 169.  NiTi is also available in the form of coil springs. These NiTi coil springs greatly enhance efficiency in both - space closure and space opening.  NiTi coil springs are also used for distalization of molars.
  170. 170.  The advantage of elgiloy over SS wires include greater resistance to fatigue and distortion & longer function as a resilient spring  The blue elgiloy is very popular because it can be easily manipulated into desired shapes and then heat treated to achieve considerable increases in strength and resilience
  171. 171.  This heat treatment can be performed easily with the aid of an electrical resistance welding apparatus.  The other three tempers of Elgiloy have mechanical properties that are similar to tempers that are available with the less expensive stainless steel wire alloys.
  172. 172.  Orthodontic archwires fabricated from this alloy have been developed for specific clinical situations and are classified as follows: Type I Af 15 0C Type II Af 27 0C Type III Af 35 0C Type IV Af 40 0C
  173. 173.  Type I wire – Af 15 0C Dr. Sachdeva does not recommend the frequent use of this alloy because it generates very heavy forces and clinical indications are few.
  174. 174. Type II wire Af 270C  In patients where rapid tooth movement is required ; the force system generated by this orthodontic arch wire is constant.
  175. 175.  Type III wire – Af 350C This wire generates force in the midrange and is best used : 1. In patients who have a low to normal pain threshold. 2. In patients whose periodontium is normal to slightly compromised. 3. When relatively low forces are desired.
  176. 176.  Type IV wire – Af 40 0C These wires generate forces when the mouth temperature exceeds 400C. These forces are intermittent in nature. Used in :-  Patients who are sensitive to pain.  Patients who have compromised periodontal conditions.
  177. 177.  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  Optiflex can be used in presurgical stage in cases which require orthognathic intervention as part of the treatment s  .
  178. 178.  27 c CV NiTi is a high activation force wire used to move a severely malpositioned tooth  27 c CV NiTi wire can be readily deformed when the wire is colder than about 10 c, but wire recovers its original shape after the wire has been in patients mouth for about two weeks
  179. 179.  350 c CV NiTi is a moderate force activation wire used to level ,align and rotate teeth  This type of wire can be readily deformed when the wire is colder than about 20 o c but the wire recovers original shape when the wires warms up in the patients mouth.  The wire is set at body temperature ,so the patient needs to drink warm fluids to activate the wire.  Rectangualr 350 c CV NiTi is ideal for a “settling in”arch
  180. 180.  400 c NiTi is used as an initial arch wire .It is designed to level & align malposed teeth with minimal gentle force .  400 c NiTi is body heat activated & is stimulated by hot liquids .Therefore ,the patient need to be told to drink hot liquids to activate the wire  To use 400c CV NiTi wire cool the wire by storing the wire in a freeze for an hour or more
  182. 182.  In nearly every patient with malaligned teeth, the root apices are closer to the normal position than the crowns.  This is so as malalignment almost always develops as the eruption paths of teeth are deflected.
  183. 183.  To bring teeth into alignment, a combination of labiolingual and mesiodistal tipping guided by an archwire is needed, but root movement is usually not.  Several important consequences for orthodontic mechanotherapy follow from this.
  184. 184.  Initial arch wires should provide light, continuous force of approximately 50 grams, to produce the most efficient tooth tipping.  Arch wire should be able to move freely within the brackets (2 mil clearance required).  In an 18-slot edgewise bracket, 16 mil can be used.
  185. 185.  Rectangular arch wires that tightly fit within the bracket should be avoided as the position of the root apex can be affected.  Although a highly resilient 0.017” X 0.025” NiTi could be used, it will create undesirable root movement at this stage.
  186. 186.
  187. 187.  The springier the arch wire, more important it is that the crowding should be at least reasonably symmetric.  Otherwise, there is a danger that archform will be lost as asymmetrically irregular teeth are brought into alignment.
  188. 188.  If only one tooth is crowded and out of line, a rigid wire is needed that maintains the arch form, and an auxillary wire should be used to correct the malaligned tooth.
  189. 189.  Arch wire materials appropriate for initial alignment stage are round cross-section wires as follows: 1. Nickel- titanium (preferably in its superelastic form) 2. Multistranded stainless steel 3. Australian premium and supreme grade wires.
  190. 190.  Where tooth displacements are marked , the first arch wire should be particularly low in stiffness and high in range .  ‘Superelastic’ nickel titanium wire of 0.014” to 0.016” diameter or six- strand multistranded stainless steel wire of 0.0175” diameter may be chosen.
  191. 191.  In most cases, initial alignment is complete within two months of commencing treatment.  Considering the poor control offered and the dangers of producing unwanted tooth movement , initial archwires should be exchanged for the archwires of mid-treatment as soon as possible.
  193. 193.  The highly flexible arch wires used for initial alignment are replaced by a series of arch wires of increasing stiffness, offering progressively greater control over tooth position.
  194. 194.  In the early stages of mid-treatment single strand , round, stainless steel arch wires of small diameter are appropriate .  Arch wires of 0.016” and then 0.018” diameter are used.
  195. 195.  Inter and intra-maxillary elastic forces can be used safely with stainless steel single strand round wires of 0.016” diameter and above.
  196. 196.  These wires are used for the purpose of canine retraction using sliding mechanics.  Australian ss arch wires are sufficiently stiff to enable the molars to resist unwanted movement, and they therefore play an important part both in molar control and in anchorage management.
  197. 197.  After canine retraction, 0.016” X 0.022” NiTi progressing to 0.017” X 0.025” NiTi or 0.017” X 0.025” NiTi is directly given for levelling and alignment.  Then 0.016” X 0.022” ss closing loop arch wire is given for anterior retraction.
  198. 198.  In case of enmass retraction, after the first stage, 0.016” X 0.022” NiTi progressing to 0.017” X 0.025” NiTi is given for completing the levelling and alignment.  Then 0.016” X 0.022” ss closing loop arch wire is given for anterior retraction.
  200. 200.  If preadjusted edgewise brackets have been used then theoretically the detailing stage will be unnecessary because of the activation programmed into the brackets.  However, minor errors in bracket positioning will become obvious in these final stages of treatment , and arch wire modification may still be required.
  201. 201.  The arch wire requirements at this stage are for high stiffness and low range.  When rectangular wire has been used at the end of mid-treatment stage the detailing arch wire should also be rectangular ,of increased stiffness
  202. 202.  With the 18-slot appliance, the finishing arch wire is either 0.017” X 0.022” or 0.017” X 0.025” ss.  They are flexible enough to engage brackets even if mild tipping has occurred.  These arch wires generate the necessary root paralleling moments
  203. 203.  If greater tipping has occurred, a more flexible full-dimension rectangular arch wire is required.  In such cases, a β-Ti or M-NiTi 0.017” X 0.025” wire may be needed initially.
  204. 204. For more details please visit