Properties of orthodontic wires /certified fixed orthodontic courses by Indian dental academy


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  • Lattice- arrangements of points in a regular periodic pattern2D or 3D manner
  • Grain boundaries interfere with the movement of atoms found on slip planes, thereby increasing the strength
  • Monoclinic and closed hexagonal lattice
  • Secondary electron images of as-received wires. Excessively porous surfaces with a high susceptibility to pitting corrosion attributed to manufacturing defects.
  • Thurow emphasized on the need to understand the phy and mech behaviour of various wires in orthodontics-he has described the manufacturing process as follows:
  • Compare
  • Writing system using picture symbols used in ancient egyt
  • They do not follow the regular order according to their temper in an expected manner but they are scattered hapazardly
  • Properties of orthodontic wires /certified fixed orthodontic courses by Indian dental academy

    1. 1. Properties of Orthodontic Wires Part I INDIAN DENTAL ACADEMY Leader in continuing dental education
    2. 2. Introduction Moving teeth and craniofacial harmony Forces and moments Wires Light continuous forces
    3. 3. History 1. Material Scarcity, Abundance of Ideas (1750-1930) noble metals Gold, platinum, iridium and silver alloys good corrosion resistance acceptable esthetics lacked the flexibility and tensile strength
    4. 4. History Angle (1887)  German silver (a type of brass) Opposition Farrar – discolored Neusilber brass (Cu 65%, Ni 14%, Zn 21%) various degrees of cold work (diff prop)    jack screws, expansion arches, Bands
    5. 5. History Wood, rubber, vulcanite, piano wire and silk thread No restrictions.
    6. 6. History Stainless steel (entered dentistry -1920) Stahl and Eisen – Benno Strauss & Eduard Maurer in 1914 By 1920 – Dr. F Hauptmeyer. Simon, schwarz, Korkhous, De Costerorthodontic material Replaced Opposition  Emil Herbst  gold wire was stronger than stainless steel. (1934) Steel as ligature wire
    7. 7. History 2. Abundance of materials, Refinement of Procedures (1930 – 1975)  Improvement in metallurgy and organic chemistry – mass production(1960)  Farrar’s dream(1878) Cobalt chrome (1950s)-Elgin watch co Rocky Mountain Orthodontics- Elgiloy Nitinol (1970s)- Buehler, into orthodontics- Andreasen. Unitek
    8. 8. History 3. The beginning of Selectivity (1975 to the present) Orthodontic manufacturers Beta titanium (1980) CAD/CAM – larger production runs Composites and Ceramics Iatrogenic damage  Nickel and bis-GMA New products- control of govt agencies, pri organization
    9. 9. Basic Properties of Materials Elements –all particles identical  Atoms-smallest Electrons – orbits around nucleus Floating in shells of diff energy levels Electrons form the basis of bonds Atoms interact via electrons In metals, the energy levels are very closely spaced and the electrons tend to belong to the entire assembly rather than a single atom.
    10. 10. Basic Properties of Materials Array of positive ions in a “sea of electrons” Electrons free to move electrical and thermal conductivity Ductility and malleability electrons adjust to deformation
    11. 11. Basic Properties of Materials Molecules – 2 or more atoms Amorphous – similar properties in all directions – isotropy  Glass atoms organize themselves into specific lattices  geometry CRYSTAL  anisotropy
    12. 12. Basic Properties of Materials CRYSTALS Perfect crystals: anion – cation –anion – cation extremely strong Thin wiskers reinforce If like ions are forced together, breakage results. Unlike metals, crystals cannot deform.
    13. 13. Basic Properties of Materials alloy crystals grow anion – cation –anion – cation Perfect crystals seldom exist Crystals penetrate each other such that the crystal shapes get deformed and cannot be discerned grains
    14. 14. Basic Properties of Materials Grains  microns to centimeters Grain boundaries Atoms are irregularly arranged, and this leads to a weaker amorphous type structure. Alloy  combination of crystalline (grains) and amorphous (grain boundaries) Decreased mechanical strength and reduced corrosion resistance
    15. 15. Basic Properties of Materials Stages in the formation of metallic grains during the solidification of a molten metal Polycrystalline- each crystal - grain
    16. 16. Basic Properties of Materials Vacancies – These are empty atom sites
    17. 17. Interstitials – Smaller atoms that penetrate the lattice Eg – Carbon, Hydrogen, Oxygen, Boron. Often distort the metal structure
    18. 18. Basic Properties of Materials Substitutial Element – another metal atom can substitute one of the same or similar size. E.g. Nickel or Chromium substituting iron in stainless steel.
    19. 19. Imperfections- although they lower the cleavage strength of the metal , increase its resistance to deformation
    20. 20. LATTICE The three dimensional arrangement of lines that can be visualized as connecting the atoms in undisrupted crystals, is called a lattice. Unit cell Crystal  combination of unit cells, in which each cell shares faces, edges or corners with the neighboring cells 14 crystal lattices
    21. 21. Basic Properties of Materials
    22. 22. Basic Properties of Materials The atoms, which are represented as points, are not static. Instead, they oscillate about that point and are in dynamic equilibrium.
    23. 23. Lattice deformations: various defects  slip planes-along which dislocation occurs
    24. 24. Basic Properties of Materials shear stress  atoms of the crystals can glide along these planes more the slip planes easier is it to deform Slip planes intercepted at grain boundaries-increases the resistance to further deformation
    25. 25. Basic Properties of Materials If the shearing force is:Small - atoms slip, and return back to their original position (elastic deformation) Beyond the elastic limit crystal suffers a slight deformation permanent (plastic deformation) Greater stress - fracture
    26. 26. Basic Properties of Materials During deformation - atomic bonds within the crystal get stressed  resistance to more deformation Number of atoms that get stressed also increases  resistance to more deformation Strain or work hardening or cold work
    27. 27. Work hardening Forced interlocking of grains and atoms of metal. Locked in and under pressure/tension Carried at room temperature.
    28. 28. Basic Properties of Materials Strain hardening- principle  Hard and strong, tensile strength Brittle. Annealing – heat below melting point.    More the cold work, more rapid the annealing Higher melting point – higher annealing temp. ½ the melting temperature (oK)
    29. 29. Basic Properties of Materials ANNEALING: Recovery Recrystallization Grain Growth
    30. 30. Basic Properties of Materials
    31. 31. Before Annealing Recovery – Relief of stresses Recrystallization – New grains from severely cold worked areas -original soft and ductile condition Grain Growth – large crystal “eat up” small ones-ultimate coarse grain structure is produced
    32. 32. Annealing Smaller grains – harder and stronger Larger grain boundaries to oppose the slip planes.
    33. 33. Basic Properties of Materials Various methods of obtaining smaller grain size 1. Enhancing crystal nucleation by adding fine particles with a higher melting point, around which the atoms gather. 2. Preventing enlargement of existing grains. Abrupt cooling (quenching) of the metal. Dissolve specific elements at elevated temperatures. Metal is cooled Solute element precipitates barriers to the slip planes.
    34. 34. Solution heat treatment Heat below the solidus temp Held for sometime, - random solid soln Cool rapidly to room temp. retained. Soft and ductile AGE HARDENING Below : ordered structure Time period Stronger, harder but less ductile.
    35. 35. Basic Properties of Materials Twinning Closed packed hexagonal type of crystals Two symmetric halves Fixed angle NiTi - multiple Subjected to a higher temperature, de - twinning occurs (shape memory)
    36. 36. Basic Properties of Materials
    37. 37. Basic Properties of Materials Polymorphism Metals and alloys exist as more than one type of structure Transition from one to the other Allotropy - reversible At higher temperature, iron FCC structure (austenite) lower temperatures,  BCC structure (ferrite)
    38. 38. Transition of Iron Iron  FCC stable (austenite), 912*c1394*c Lattice spaces greater, Carbon atom can easily be incorporated into the unit cell
    39. 39. Transition of Iron On Cooling <912*c FCC  BCC Carbon diffuses out as FeC FeC adds strength to ferrite and austenite TIME
    40. 40. Transition of Iron Rapidly cooled (quenched)  Carbon cannot escape Highly strained, distorted body centered tetragonal lattice called martensite
    41. 41. Basic Properties of Materials Grain boundaries are more in number Alloy is stronger and more brittlemartensitic change – various types of steel Interstitials are intentionally incorporated into the alloy to make it hard when it is quenched.
    42. 42. Basic Properties of Materials Cooled slowly Other crystal structures are formed at intermediate temperatures Softer Some are stable at room temperature Ultimately, the final structure is softer and more workable
    43. 43. Basic Properties of Materials Tempering – Reheat the alloy to intermediate temperature(1000*F/525*c) Partial transformation into softer alloys Remedy brittle martensite more workable
    44. 44. Basic Properties of Materials Some alloys FCC to BCC by rearrangement of atoms  Diagonal plane of the BCC unit becomes the face of the FCC unit
    45. 45. Shape memory alloys – Easy switching from one type of structure to another. Bain distortion Over a range of temperature {hysteresis} unlike iron
    46. 46. Elastic Properties Stress and strain Stress- internal distribution of load. F/A Strain- internal distortion produced by load deflection/unit length
    47. 47. Elastic Properties Force applied to wire Deflection Internal force---- (equal and opposite) Internal force = Stress Area of action Deflection change in length = Strain Original length
    48. 48. Elastic Properties Types of stress/strain Tensile –stretch/pull Compressive – compress/towards each other Shear – 2 forces opp direction, not in same line. sliding of one part over another Complex force systems
    49. 49. Elastic Properties Stress Wire returns back to original dimension when stress is removed Elastic Portion Strain
    50. 50. Elastic Properties Hooke’s law Spring stretch in proportion to applied force (proportional limit) Modulus of elasticity – constant for a given material
    51. 51. Elastic Properties Stress Yield strength 0.1% Proportional Limit Elastic Limit Strain
    52. 52. Stress Elastic Properties Ultimate Tensile Strength Fracture Point Strain
    53. 53. Elastic Properties ultimate tensile strength is higher than the yield strength important clinically  maximum force that the wire can deliver Ultimate tensile strength higher than the stress at the point of fracture  reduction in the diameter of the wire
    54. 54. Stress Elastic Properties Slope α Stiffness Stiffness α 1 . Springiness Strain
    55. 55. Elastic Properties Stress Point of arbitrary clinical loading Yield point Range Springback Strain
    56. 56. Elastic Properties Clinically, ortho wires are deformed beyond their elastic limit. Springback properties are important Strength = Stiffness x Range
    57. 57. Elastic Properties Resiliency When a wire is stretched, the space between the atoms increases. Within the elastic limit, there is an attractive force between the atoms. Energy stored within the wire. Strength + springiness
    58. 58. Stress Elastic Properties Yield strength Proportional limit Resilience Formability Strain
    59. 59. Elastic Properties Formability - amount of permanent deformation that the wire can withstand without breaking Indication of the ability of the wire to take the shape Also an indication of the amount of cold work that they can withstand
    60. 60. Elastic Properties Flexibility large deformation (or large strain) with minimal force, within its elastic limit. Maximal flexibility is the strain that occurs when a wire is stressed to its elastic limit. Max. flexibility = Proportional limit Modulus of elasticity.
    61. 61. Elastic Properties Toughness –force required to fracture a material. Total area under the stress – strain graph. Brittleness –opposite of toughness. A brittle material, is elastic, but cannot undergo plastic deformation. eg: Glass Fatigue – Repeated cyclic stress of a magnitude below the fracture point of a wire can result in fracture. This is called fatigue.
    62. 62.
    63. 63. Properties of Orthodontic Wires Part I Dr. Vijaya Lakshmi
    64. 64. Elastic Properties
    65. 65. Elastic Properties
    66. 66. Stress Elastic Properties Yield strength Proportional limit Resilience Formability Strain
    67. 67. Requirements of an ideal archwire (Kusy ) 1. Esthetics 7. Resiliency 2. Stiffness 8. Coefficient of friction 3. Strength 9. Biohostability 4. Range 10. Biocompatibility 5. Springback 11. Weldability 6. Formability
    68. 68. 1. Esthetics Desirable No compromise on mechanical properties White coloured wires discolour Destroyed by oral enzymes Deformed by masticatory loads Except the composite wires
    69. 69. 2. Stiffness / Load deflection Rate Proffit: - slope of stress-strain curve Thurow - force:distance ratio, measure of resistance to deformation. Burstone – Stiffness is related to – wire property & appliance design Wire property is related to – Material & cross section. Wilcock – Stiffness α Load
    70. 70. Stiffness / Load deflection Rate Magnitude of the force delivered by the appliance for a particular amount of deflection. Low stiffness or Low LDR implies that:1) Low forces will be applied 2) The force will be more constant as the appliance deactivates 3) Greater ease and accuracy in applying a given force.
    71. 71. 3 point bending test
    72. 72. 3. Strength Yield strength, proportional limit and ultimate tensile/compressive strength Kusy - force required to activate an archwire to a specific distance. Proffit - Strength = stiffness x range. Range limits the amount the wire can be bent, Stiffness is the indication of the force required to reach that limit.
    73. 73. Strength The shape and cross section of a wire have an effect on the strength of the wire. The effects of these will be considered subsequently.
    74. 74. 4. Range Distance that the wire bends elastically, before permanent deformation occurs (Proffit). Kusy – Distance to which an archwire can be activated- working range. Thurow – A linear measure of how far a wire or material can be deformed without exceeding the limits of the material.
    75. 75. 5. Springback Kusy -- The extent to which a wire recovers its shape after deactivation Ingram et al – a measure of how far a wire can be deflected without causing permanent deformation. (Contrast to Proffit yield point).
    76. 76. 5. Springback Large springback Activated to a large extent. Hence it will mean fewer archwire changes. Ratio – yield strength Modulus of elasticity
    77. 77. 6. Formability Kusy – the ease in which a material may be permanently deformed. Ease of forming a spring or archwire Proffit: amount of permanent deformation a wire can withstand without breaking
    78. 78. 7. Resiliency Store/absorb more strain energy /unit volume before they get permanently deformed Greater resistance to permanent deformation Release of greater amount of energy on deactivation High work availability to move the teeth
    79. 79. 8. Coefficient of friction Brackets (and teeth) must be able to slide along the wire High amounts of friction  anchor loss.
    80. 80. 9. Biohostability:- site for accumulation of bacteria, spores or viruses. An ideal archwire must have poor biohostability. 10.Biocompatibility:- Resistance of corrosion, and tissue tolerance to the wire. 11. Weldability:- the ease by which the wire can be joined to other metals, by actually melting the 2 metals in the area of the bond. (A filler metal may or may not be used.)
    81. 81. Properties of Wires Before the titanium alloys were introduced into orthodontics, the practitioners used only steel wires. So the way to control the stiffness of the wire was:1. Change the cross section of the wire 2. Increase the length of the wire (  inter bracket distance, incorporate loops.)
    82. 82. Effects of Wire Cross Section Wires of various dimensions and cross sections. Does the wire need to be move teeth over large distances, or does it need to correct the torque of the tooth? Is it primarily going to be used to correct first order irregularities, or second order?
    83. 83. Effects of Wire Cross Section primary factor  load deflection rate or stiffness play of the wire in the second order – 0.016” wire in 0.022” slot is only 1.15 times the play of a 0.018” wire. The play in the second order becomes significant if the wire dimensions are drastically different (0.010” and 0.020”)
    84. 84. Effects of Wire Cross Section Based on stiffness/load deflection rate Force delivered by a wire with high load deflection rate
    85. 85. Effects of Wire Cross Section Force delivered by a wire with low load deflection rate Force delivered by a wire with low load deflection rate
    86. 86. Load deflection rate Shape Moment Ratio to stiffness of of Inertia round wire Пd4 64 s4 12 b3h 12 1 1.7 1.7 b3h:d4
    87. 87. Effects of Wire Cross Section Dimension of wire increases- LDR increases Round and square wire of same dimension-LDR of square wire is more. Rectangular wire – maximum stiffness
    88. 88. Effects of Wire Cross Section Stiffness of different dimensions of wires can be related to each other. Relative stiffness Stiffness number (Burstone) 3500 3000 2500 2000 1500 1000 500 0 14 16 18 20 22 16x16 18x18 21x21 16x22 22x16 18x25 25x18 21x25 25x21 215x28 28x215 Wire dimension
    89. 89. Effects of Wire Cross Section Rectangular wires  bending perpendicular to the larger dimension (ribbon mode) easier than bending perpendicular to the smaller dimension (edgewise). Relative stiffness 3000 (Burstone ) Stiffne ss numbe r 3500 2500 2000 1500 1000 500 0 14 16 18 20 22 16x16 18x18 21x21 16x22 22x16 Wire dime nsion 18x25 25x18 21x25 25x21 215x28 28x215
    90. 90. Effects of Wire Cross Section The larger dimension  correction is needed. The smaller dimension  the plane in which more stiffness is needed. > first order, < second order – RIBBON > Second order, < first order - EDGEWISE
    91. 91. Effects of Wire Cross Section > 1st order correction in anterior segment > 2nd order in the posterior segment, wire can be twisted 90o If both, 1st & 2nd order corrections are required to the same extent, then square or round wires. The square wires - advantage - simultaneously control torque better orientation into a rectangular slot.
    92. 92. Effects of Wire Cross Section Cross-sectional shape:  On range and strength  Diameter increases-strength third power of diameter  Range increases proportional to diameter
    93. 93. Effects of Wire Cross Section In torsion - absolute values of strength, stiffness and range are different, but the overall effect of changing the diameter of the wire is the same. 1. Strength – Increases with increase in diameter 2. Stiffness – increases 3. Range – decreases.
    94. 94. Effects of Length Loops,  the inter-bracket distance 1. 2. 3. For bending Strength – decreases proportionately Stiffness – decreases as a cubic function Range – increases as a square.
    95. 95. Effects of Length In the case of torsion, the picture is slightly different. Increase in length: – 1. Stiffness decreases proportionately 2. Range increases proportionately 3. Strength remains unchanged.
    96. 96. Effects of Length Way the beam is attached also affects the values cantilever, the stiffness of a wire is obviously less wire is supported from both sides (as an archwire in brackets), again, the stiffness is affected
    97. 97. Effects of Length Cantilever Beam supported on both ends Fixed at both ends
    98. 98. Effects of Length Stiffness is also affected by the method of ligation of the wire into the brackets. Loosely ligated, so that it can slide through the brackets, it has ¼th the stiffness of a wire that is tightly ligated.
    99. 99. Clinical Implications LIGHT CONTINUOUS FORCES Stiff wires should be taboo to the orthodontist? Springier wire, can be easily distorted in the harsh oral environment. Aim at balance.
    100. 100. Clinical Implications Removable appliance cantilever spring The material of choice is usually steel. (Stiff material) Sufficiently thick steel wire Good strength to resist masticatory and other oral forces. Increase the length of the wire   Proportionate decrease in strength, but the stiffness will decrease as a cubic function  Length is increased by either bending the wire over itself, or by winding helicals or loops into the spring
    101. 101. Clinical Implications In archwires of stiffer materials the same principle can be used. The length of wire between brackets can be increased  loops, or smaller brackets, or special bracket designs. Also, the use of flexible wires Multistranded wires
    102. 102. Variable cross-section orthodontics. Variable modulus orthodontics.
    103. 103. Clinical Implications NiTi – high springback Initial stages – NiTi instead of steel Towards the end- stiff steel wire TMA - intermediate properties- transition wire
    104. 104. Clinical Implications variable modulus orthodontics – Advantage  relatively constant dimension important for the third order control variable stiffness approach,   compromise control for getting a wire with adequate stiffness, had to spend clinical time bending loops into stiffer archwires, which would offer less play.
    105. 105. Clinical Implications Requirements of arch wires in different stages of treatment
    106. 106. Appropriate wire Take into account the amount of force that wire can deliver. For example, a NiTi wire  efficient in tipping teeth to get them into alignment, but may not be able to achieve third order corrections. After using rectangular NiTi wires for alignment, rectangular steel wire must always be used to achieve the correct torque of the tooth.
    107. 107. Nomograms
    108. 108. Nomograms
    109. 109. A rough idea can be obtained clinically as well Forming an arch wire with the thumb gives an indication of the stiffness of the wire. Flexing the wires between the fingers, without deforming it, is a measure of flexibility Deflecting the ends of an archwire between the thumb and finger gives a measure of resiliency.
    110. 110. Corrosion Nickel 1. Carcinogenic, 2. mutagenic, 3. cytotoxic and 4. allergenic.  Stainless steels, Co-Cr-Ni alloys and NiTi are all rich in Ni
    111. 111. Corrosion Placement in the oral cavity  Greater peril than implanting  Implanted material gets surrounded by a connective tissue capsule  In the oral cavity, the alloy is free to react with the environment.
    112. 112. Corrosion Stainless steel- Ni austenite stabilizer. Not strongly bonded- slow release Passivating film  traces of Fe ,Ni and Mo. Aqueous environment   inner oxide layer outer hydroxide layer. CrO is not as efficient as TiO in resisting corrosion some Ni release Improper handling  sensitization
    113. 113. Corrosion 1. Uniform attack – the entire wire reacts with the environment, hydroxides or organometallic compounds detectable after a large amount of metal is dissolved. 2. Pitting Corrosion – manufacturing defects sites of easy attack
    114. 114. Corrosion Pitting corrosion Stainless Steel NiTi
    115. 115. Corrosion 3. Crevice corrosion or gasket corrosion Parts of the wire exposed to corrosive environment Sites of tying to the brackets Plaque build up  disturbs the regeneration of the passivating layer Reach upto 2-5 mm High amount of metals can be dissolved in the mouth.
    116. 116. Corrosion 4. Galvanic /Electrochemical Corrosion two metals are joined or even the same metal after different type of treatment (soldering etc) difference in the reactivity  Galvanic cell.  Less Reactive (Cathodic)  More Reactive (Anodic) less noble metal
    117. 117. Corrosion Anodic  Looses Electrons  Soluble ions  Leach out Cathodic (nobel)  Accepts electrons  Even less reactive S.Steel- active and passive areas : depletion & regeneration of passivating film
    118. 118. Corrosion 5. Intergranular corrosion Sensitization - ppt of CrC 6. Fretting corrosion Wire and brackets contact Friction  surface destruction Pressure  rupture of the oxide layer Debris get deposited at grain boundaries, grain structure is disturbed.
    119. 119. Corrosion 7. Microbiologically influenced corrosion Adhesive Craters at the base of brackets Or wires directly bonded on to teeth shown by Matasa. Certain bacteria dissolve metals directly form the wires. Others affect surface structure.
    120. 120. Micro-0rganisms on various dental materials
    121. 121. Corrosion 8. Stress corrosion Similar to galvanic corrosion Bending of wires  different degress of tension and compression. Alter the electrochemical behavior   anode cathode
    122. 122. Corrosion 9. Corrosion Fatigue: Cyclic stressing of a wire Resistance to fracture decreases Accelerated in a corrosive medium such as saliva
    123. 123. Corrosion Analysis of used wires also indicated that a biofilm was formed on the wire. Eliades et al Calcification  Shielding the wire  Protecting the patient from the alloy Stainless steel: Fe, Ni, Cr. Allergic potential
    124. 124. OrthOdOntic Arch Wire MAteriAls
    125. 125. Precious Metals Upto about the 1950s Gold alloys Only wire which would tolerate the oral environment Crozat appliance – according to original design
    126. 126. Stainless Steel 1919 – Germany  used to make prostheses. Extremely chemically stable High resistance to corrosion. Chromium content. The chromium gets oxidized,  Impermeable, corrosion resistant layer.
    127. 127. Stainless Steel Variety of stainless steels Varying the degree of cold work and annealing during manufacture Fully annealed stainless steel  extremely soft, and highly formable Ligature wire “Dead soft”
    128. 128. Stainless Steel stainless steel arch wires are cold worked to varying extents,  yield strength increases, at the cost of their formability The steel with the highest yield strength, the Supreme grade steels, are also very brittle, and break easily when bent sharply.
    129. 129. Stainless Steel Structure and composition Chromium (11-26%)–improves the corrosion resistance Stabilizes BCC phase Nickel(0-22%) – austenitic stabilizer copper, manganese and nitrogen - similar  amount of nickel added to the alloy  adversely affect the corrosion resistance.
    130. 130. Stainless Steel Carbon (0.08-1.2%)– provides strength Reduces the corrosion resistance Sensitization. During soldering or welding, 425-815 oc Chromium diffuses towards the carbon rich areas (usually the grain boundaries)
    131. 131. Stainless Steel Chromium carbides Amount of chromium decreases Chromium carbide is soluble,  intergranular corrosion. Stabilization
    132. 132. Stainless Steel Stabilization –      Element which precipitates carbide more easily than Chromium. Usu. Titanium. Ti 6x> Carbon No sensitization during soldering. Most steels used in orthodontics are not stabilized.
    133. 133. 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.
    134. 134. MANUFACTURE Manufacture: AISI ,specially for orthodontic purposes Various steps – 1. Melting 2. Ingot Formation 3. Rolling 4. Drawing
    135. 135. steps Melting   Various metals of the alloy are melted Proportion influences the properties Ingot formation     Molten alloy into mold. Non uniform chunk of metal Porosities and slag. Grains seen in the ingot – control of mechanical properties
    136. 136. Ingot formation  Porosities due to dissolved gases (produced / trapped)  Vacuum voids due to shrinking of late cooling interior.  Important to control microstructure at this stage – basis of its phy properties and mechanical performance
    137. 137. steps Rolling –  First mechanical process.  Ingot reduced to thinner bars  Finally form a wire  Different wires from the same batch, differ in properties
    138. 138. Rolling  Retain their property even after rolling  Shape & arrangement altered  Grains get elongated, defects get rearranged  Work hardening – structure locked up.  Wires start to crack if rolling continued  Annealing is done- mobile  Cooling – structure resembles original ingot, uniform
    139. 139. steps Drawing  More precise  Ingot  final size.  Wire pulled through small hole in a die  Progressively smaller diameter-uniform squeezing.  Same pressure all around, instead of from 2 opposite sides.
    140. 140. Drawing  Series of dies  Annealing at regular intervals.  Exact number of drafts and annealing cycles depends on the alloy (gold <carbon steel<stainless steel)
    141. 141. Stress relief During manufacture, wire highly stressed. Adverse effects on mechanical properties Annealing heat treatment By minute slippages & readjustments in intergranular relations without the loss of hardening higher temp of annealing Alternate sequence of cold working & heat treatment—improve strength
    142. 142. Clinical implications Soldering attachments to arch wire:     Raise in temp----wire dead Quick and well controlled. Cinch back, heat Wire #
    143. 143. Stainless Steel Classification American Iron and Steel Institute (AISI) Unified Number System (UNS) German Standards (DIN).
    144. 144. Stainless Steel The AISI numbers used for stainless steel range from 300 to 502 Numbers beginning with 3 are all austenitic Higher the number   More the iron content  More expensive the alloy  Numbers having a letter L signify a low carbon content
    145. 145. Stainless Steel Austenitic steels (the 300 series) Better corrosion resistance -attachments FCC structure  non ferromagnetic Not stable at room temperature, Austenite stabilizers Ni, Mn and N Known as the 18-8 stainless steels .
    146. 146. Stainless Steel Martensitic steel FCC  BCC BCC structure is highly stressed. More grain boundaries,   Stronger Less corrosion resistant Making instrument edges which need to be sharp and wear resistant.
    147. 147. Stainless Steel Ferritic steels – (the 400 series) Good corrosion resistance Low strength. Not hardenable by heat treatment. Not readily cold worked.
    148. 148. Stainless Steel Austenitic steels more preferable :Greater ductility and ability to undergo more cold work without breaking. Substantial strengthening during cold work. (Cannot be strengthened by heat treatment). Strengthening effect is due partial conversion to martensite. Easy to weld Easily overcome sensitization Ease in forming.
    149. 149. Stainless Steel Duplex steels Both austenite and ferrite grains Increased toughness and ductility than Ferritic steels Twice the yield strength of austenitic steels Lower nickel content Manufacturing low nickel attachments
    150. 150. Stainless steel Precipitation hardened steels Certain elements added to them  precipitate and increase the hardness on heat treatment. The strength is very high Resistance to corrosion is low. Used to make mini-brackets.
    151. 151. General properties of Stainless Steel Relatively stiff material Yield strength and stiffness can be varied  Altering the carbon content and  Cold working and  Annealing High forces - dissipate over a very short amount of deactivation (high load deflection rate).
    152. 152. Stainless Steel Clinical terms:Loop - activated to a very small extent so as to achieve optimal force Deactivated by only a small amount (0.1 mm) Force level will drop tremendously Not physiologic More activations
    153. 153. Stainless Steel Force required to engage a steel wire into a severely mal-aligned tooth.  Either cause the bracket to pop out,  Or the patient to experience pain. Overcome by using thinner wires, which have a lower stiffness. Fit poorly loss of control on the teeth.
    154. 154. Stainless Steel High stiffness  Maintain the positions of teeth Hold the corrections achieved Begg treatment, stiff archwire, to dissipate the adverse effects of third stage auxiliaries
    155. 155. Stainless Steel Lowest frictional resistance Ideal choice of wire during space closure with sliding mechanics Teeth be held in their corrected relation Minimum resistance to sliding
    156. 156. 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.
    157. 157. High Tensile Australian Wires Beginners found it difficult to use the highest tensile wires Grading system Late 1950s, the grades available were –  Regular  Regular plus  Special  Special plus
    158. 158. High Tensile Australian Wires Newer grades were introduced after the 70s. Premium, premium +, supreme Raw materials directly from the suppliers from out of Australia More specific ordering and obtaining better raw materials Premium grade-high tensile strength Brittle. Softening , loss of high tensile properties
    159. 159. 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.
    160. 160. High Tensile Australian Wires
    161. 161. High Tensile Australian Wires 1. Plastic prestrain increases the elastic limit of deformation in the same direction as the prestrain. 2. Decreases in opposite If the magnitude of the prestrain is increased, the elastic limit in the reverse direction can reduce to zero.
    162. 162. High Tensile Australian Wires Straightening a wire  pulling through a series of rollers Prestrain in a particular direction. Yield strength for bending in the opposite direction will decrease. Premium wire  special plus or special wire
    163. 163. Spinner straightening It is mechanical process of straightening resistant materials in the cold drawn condition. The wire is pulled through rotating bronze rollers that torsionally twist it into straight condition. Disadv: Decreases yield strength Creates rougher surface
    164. 164. Pulse straightening Special method Placed in special machines that permits high tensile wires to be straightened. Advantages: 1. 2. 3. Permits the straightening of high tensile wires Does not reduce the yield strength of the wire Results in a smoother wire, hence less wire – bracket friction.
    165. 165. High Tensile Australian Wires Methods of increasing yield strength of Australian wires. 1. Work hardening 2. Dislocation locking 3. Solid solution strengthening 4. Grain refinement and orientation
    166. 166. By alternate sequence of cold working and heat treatment the yield point of wire can be increased to as much as 200tons/sq inch as shown in this graph.
    167. 167. High Tensile Australian Wires Higher yield strength  more flexible. Supreme grade flexibility = βtitanium. Higher resiliency  nearly three times. NiTi  higher flexibility but it lacks formability
    168. 168. High Tensile Australian Wires Mollenhauer  Supreme grade wire  faster and gentler alignment of teeth. Intrusion  simultaneously with the base wires Gingival health seemed better Originally in lingual orthodontics Equally good for labial orthodontics as well.
    169. 169. High Tensile Australian Wires Clinical significance of high yield strength 1. Increased working range: Yield strength modulus of elasticity 2. Increased resiliency: ( yield strength)2 elastic modulus Stiffness remains the same
    170. 170. High Tensile Australian Wires 3. Zero Stress Relaxation If a wire is deformed and held in a fixed position, the stress in the wire may diminish with time, but the strain remains constant. Engineering terms, implies that a form of slip by dislocation movement takes place at the atomic level Property of a wire to give constant light force, when subjected to external forces (like occlusal forces).
    171. 171. High Tensile Australian Wires external forces  particles slip over each other  activation of the wire is lost Overcome   Internal friction Between particles  yield strength
    172. 172. High Tensile Australian Wires Zero stress relaxation in springs. To avoid relaxation in the wire’s working stress Diameter of coil : Diameter of wire = 4 smaller diameter of wires  smaller diameter springs (like the mini springs) Midi springs
    173. 173. High Tensile Australian Wires Twelftree, Cocks and Sims (AJO 1977) Premium plus, Premium and Special plus wires showed minimal stress relaxation. Special, Remanit, Yellow Elgiloy, Unisil.
    174. 174. High Tensile Australian Wires Hazel, Rohan & West (1984)  Stress relaxation of Special plus wires after 28 days was less than Dentaurum SS and Elgiloy wires. Barrowes (1982) & Jyothindra Kumar (1989)  Higher working range among steel wires.
    175. 175. High Tensile Australian Wires Pulse straightened wires – Spinner straightened wires (Skaria 1991)  Strength, stiffness and Range higher  Coeff. of friction higher  Similar surface topography, stress relaxation and Elemental makeup.
    176. 176. High Tensile Australian Wires A study of the metallurgical properties of newly introduced high tensile wires in comparison to the high tensile Australian wires for various applications in orthodontic treatment Dr. Anuradha Acharya (2000)  Super Plus (Ortho Organizers) – between Special plus and Premium  Premier (TP) – Comparable to Special  Premier Plus – Special Plus  Bowflex – Premium
    177. 177. High Tensile Australian Wires Highest yield strength and ultimate tensile strength as compared to the corresponding wires. Higher range Lesser coefficient of friction  Surface area seems to be rougher than that of the other manufacturers’ wires. Lowest stress relaxation.
    178. 178. Clinical implications Stage I: 1. Wilcock (P) / S+ base wire(.014”) 2. Ortho organizers (super +)  Wilcock (P) & S+; T.P. Bowflex .016”  Ortho organizers ( super +) T.P P+  Latter part of Stage I and most of Stage II 1. T.P (Premier), Wilcock P ,S+ .018” dia 2. Ortho Organizers (super +) T.P Bowflex  Base wires in Stage III , torquing auxiliaries, uprighting springs 1. Wilcock S+ / P .020” base wire  Wilcock P and Supreme in .012”, .010” dia respectively
    179. 179. High Tensile Australian Wires Dislocation locking  High tensile wires have high density of dislocations and crystal defects  Pile up, and form a minute crack  Stress concentration
    180. 180. High Tensile Australian Wires Small stress applied with the plier beaks  Crack propagation  Elastic energy is released  Propagation accelerates to the nearest grain boundary
    181. 181. High Tensile Australian Wires Ways of preventing fracture 1. 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.
    182. 182. High Tensile Australian Wires
    183. 183. High Tensile Australian Wires 2. 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.
    184. 184. High Tensile Australian Wires
    185. 185. High Tensile Australian Wires 3. The edges rounded  reduce the stress concentration in the wire. 4. Ductile – brittle transition temperature slightly above room temperature. Wire should be warmed. Spools kept in oven at about 40o, so that the wire remains slightly warm.
    186. 186. Multistranded Wires 2 or more wires of smaller diameter are twisted together/coiled around a core wire. Diameter - 0.0165 or 0.0175, but the stiffness is much less. On bending  individual strands slip over each other and the core wire, making bending easy. (elastic limit)
    187. 187. Multi stranded wires Co-axial Twisted wire Multi braided
    188. 188. Multi stranded wires Strength – resist distortion Separate strands - .007” but final wire can be either round / rectangular Sustain large elastic deflection in bending Thurow: rough idea – multiply
    189. 189. Multistranded Wires As the diameter of a wire decreases – Stiffness – decreases as a function of the 4 th power Range – increases proportionately Strength – decreases as a function of the 3 rd power Multistranded wires  Small diameter wires, High strength Gentler force
    190. 190. Multistranded Wires Elastic properties of multistranded archwires depend on – 1. Material parameters – Modulus of elasticity 2. Geometric factors – wire dimension 3. 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
    191. 191. Multistranded Wires Deflection of multi stranded wire= KPL3 knEI K – load/support constant P – applied force L – length of the beam K – helical spring shape factor n- no of strands E – modulus of elasticity I – moment of inertia
    192. 192. Multistranded Wires Helical spring shape factor Coils resemble the shape of a helical spring. The helical spring shape factor is given as – 2sin α 2+ v cos2 α α - helix angle and v - Poisson’s ratio (lateral strain/axial strain) Angle α can be seen in the following diagram
    193. 193. Multistranded Wires
    194. 194. Multistranded Wires Kusy ( AJO-DO 1984) Compared the elastic properties of triple stranded S.Steel wire with S.Steel, NiTi & B-TMA
    195. 195. Results Results
    196. 196. Results
    197. 197. Results 0.0175” S.Steel wire had stiffness equal to 0.016”NiTi & 40% of 0.016”TMA Did not resemble the 0.018” SS wire except : Size Wire-bracket relation.
    198. 198. Multistranded Wires Ingram, Gipe and Smith (AJO 86) Range of 4 diff wires Results: NiTi>MS S.Steel>CoCr>Steel
    199. 199. Multistranded Wires Nanda et al (AO 97) …. stiffness Increase in No. of strands  stiffness
    200. 200. Multistranded Wires Kusy (AJO-DO 2002) Interaction between individual strands was negligible. Range and strength Triple stranded Ξ Coaxial (six stranded) Stiffness  Coaxial < Triple stranded Range of single stranded SS wire, triple stranded and co-axial were similar.
    201. 201. Multistranded Wires
    202. 202. Welding of Steel 3 useful properties – 1. Comparatively low melting point, 2. High electrical resistance and 3. Low conductivity of heat.
    203. 203. Welding of Steel Important to  minimize the time of passing the current  minimize the area of heating Sensitization - between 425 and 815 oC Chromium carbides need time for their formation.
    204. 204. Welding of Steel Join two thin sheets of metal Same thickness Joining tubes, wires and springs, soldering is generally recommended. Electrodes - small tips, not exceeding 1 mm in diameter.
    205. 205. Cobalt Chromium 1950s the Elgin Watch Rocky Mountain Orthodontics Elgiloy CoCr alloys - stellite alloys  superior resistance to corrosion, comparable to that of gold alloys.
    206. 206. 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.
    207. 207. Cobalt Chromium Strength and formability modified by heat treatment. The alloy is highly formable, and can be easily shaped. Heat treated.   Strength  Formability 
    208. 208. Cobalt Chromium
    209. 209. Cobalt Chromium Heat treated at 482oc for 7 to 12 mins Precipitation hardening   ultimate tensile strength of the alloy, without hampering the resilience. After heat treatment, elgiloy had elastic properties similar to steel.
    210. 210. Cobalt Chromium
    211. 211. Cobalt Chromium Blue – soft Yellow – ductile Green – semiresilient Red – resilient
    212. 212. 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.
    213. 213. Cobalt Chromium After heat treatment  Blue and yellow ≡ normal steel wire Green and red tempers ≡ higher grade steel
    214. 214. Cobalt Chromium Heating above 650oC  partial annealing, and softening of the wire Optimum heat treatment  dark straw color of the wire advantage of Co-Cr over SS is –  Greater resistance to fatigue and distortion  longer function as a resilient spring
    215. 215. Cobalt Chromium Properties of Co-Cr are very similar to that of stainless steel. Force  2x of β titanium and  4 times of NiTi.
    216. 216. Cobalt Chromium Frank and Nikolai (1980)  Co-Cr alloys ≡ stainless steel. Stannard et al (AJO 1986)  Co-Cr highest frictional resistance in wet and dry conditions.
    217. 217. Cobalt Chromium Ingram ,Gipe and Smith (AJO 86) Non heat treated Co-Cr  Range < stainless steel of comparable sizes But after heat treatment, the range was considerably increased.
    218. 218. Cobalt Chromium Kusy et al (AJO 2001) The elastic modulus did not vary appreciably  edgewise or ribbon-wise configurations.
    219. 219. Cobalt Chromium Round wires  higher ductility than square or rectangular wires.
    220. 220. Cobalt Chromium The modulus of elasticity 4 diff tempers of 0.016” elgiloy is almost similar
    221. 221. Cobalt Chromium Elastic properties (yield strength and ultimate tensile strength and ductility) were quite similar for different cross sectional areas and tempers. This does not seem to agree with what is expected of the wires.
    222. 222. Cobalt Chromium
    223. 223. Cobalt Chromium Different tempers with different physical properties – attractive More care taken during the manufacture of the wires.
    224. 224. References A study of the metallurgical properties of newly introduced high tensile wires in comparison to the high tensile Australian wires for various applications in orthodontic treatment. – Anuradha Acharya, MDS Dissertation September 2000. Kusy & Greenberg. Effects of composition and cress section on the elastic properties of orthodontic wires. Angle Orthod 1981;51:325341 Kapila & Sachdeva. Mechanical properties and clinical applications of orthodontic wires . AJO 89;96:100-109.
    225. 225. References Stannard, Gau, Hanna. Comparative friction of orthodontic wires under dry and wet conditions. AJO 86;89:485-491 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 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
    226. 226. References 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;11:2229.
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