Orthodontic wires 1 /certified fixed orthodontic courses by Indian dental academy

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The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.

Indian dental academy provides dental crown & Bridge,rotary endodontics,fixed orthodontics,
Dental implants courses.for details pls visit www.indiandentalacademy.com ,or call
0091-9248678078

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Orthodontic wires 1 /certified fixed orthodontic courses by Indian dental academy

  1. 1. Orthodontic wires-I INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com 1
  2. 2. Contents  Introduction  Evolution of materials  Basic properties of materials  Mechanical & Elastic properties  Physical properties  Requirements of an ideal arch wire  Properties of wires  Orthodontic arch wire materials www.indiandentalacademy.com 2
  3. 3. Introduction “All you can do is push, pull or turn a tooth. I have given you an appliance and now for God’s sake use it” Edward.H.Angle  The main components of an orthodontic appliance -brackets and wires.  Active and reactive elements (Burstone)  Wires Brackets Bonding www.indiandentalacademy.com 3
  4. 4. Introduction  Orthodontics involves correction of the position of teeth –requiring moving teeth.  Forces and Moments  Optimum orthodontic tooth movement- light continuous force. www.indiandentalacademy.com 4
  5. 5. Introduction  The challenge – Appliance which produces forces that are neither too great nor variable.  Different materials and type of wires introduced to provide forces. www.indiandentalacademy.com 5
  6. 6. Evolution of Materials 1.       Material Scarcity, Abundance of Ideas (1750-1930) Before Angle’s search; 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. www.indiandentalacademy.com 6
  7. 7. Evolution of Materials  Angle listed few materials appropriate for work:  Strips of wire of precious metals.  Wood  Rubber  Vulcanite  Piano wire  Silk thread www.indiandentalacademy.com 7
  8. 8. Evolution of Materials  Angle (1887)  German silver (a type of brass)  “according to the use for which it was intended”-varying the proportion of Cu, Ni & Zn and various degrees of cold work.  Neusilber brass (Cu 65%, Ni 14%, Zn 21%)  jack screws (rigid)  expansion arches (elastic)  Bands (malleable)  Opposition by Farrar – discolored www.indiandentalacademy.com 8
  9. 9. Evolution of Materials  Stainless steel (entered dentistry -1919).  Dumas ,Guillet and Portevin-(France), qualities reported in Germany –Monnartz (1900-1910).  Discovered by chance before W W I.  1919 – Dr. F Hauptmeyer –Wipla (wie platin).  Simon, Schwarz, Korkhous, De Coster- orthodontic material.  Angle used steel as ligature wire (1930). www.indiandentalacademy.com 9
  10. 10. Evolution of Materials     Opposition Emil Herbst -Gold wire was stronger than stainless steel (1934). “The Edgewater" tradition-1950-2 papers presented back to back-competition between SS & gold. - B/w Dr.Brusse (The management of stainless steel) and Drs.Crozat & Gore (Precious metal removable appliances). Begg (1940s) with Wilcock-ultimately resilient arch www.indiandentalacademy.com wires-Australian SS. 10
  11. 11. Evolution of Materials 2.  Abundance of materials, Refinement of Procedures (1930 – 1975). Kusy-after 1960s-proliferation abounds.  Improvement in metallurgy and organic chemistry – mass production(1960).  Farrar’s dream(1878)-mass production of orthodontic devices. www.indiandentalacademy.com 11
  12. 12. Evolution of Materials  Cobalt chrome (1950s)-Elgin watch company developed a complex alloyCobalt(40%),Chromium(20%),iron(16%)&nickel(15%).  Rocky Mountain Orthodontics- ElgiloyTM  1958-1961 various tempers Red – hard & resilient green – semi-resilient Yellow – slightly less formable but ductile Blue – soft & formable www.indiandentalacademy.com 12
  13. 13. Evolution of Materials Variable cross-section orthodonticsBurstone  To produce changes in load-deflection rate- wires of various cross sections were used.  Load deflection rate varies with 4th power of the wire diameter. www.indiandentalacademy.com 13
  14. 14. Evolution of Materials  1962 - Buehler discovers nickel-titanium dubbed NITINOL (Nickel Titanium Naval Ordnance Laboratory)  1970-Dr.George Andreason (Unitek) introduced NiTi to orthodontics.  50:50 composition –excellent springback, no superelasticity or shape memory (M-NiTi).  Late 1980s –NiTi with active austenitic grain structure. www.indiandentalacademy.com 14
  15. 15. Evolution of Materials     Exhibited Superelasticity (pseudoelasticity in engineering). New NiTi by Dr.Tien Hua Cheng and associates at the General Research Institute for non Ferrous Metals, in Beijing, China. Burstone et al–Chinese NiTi (1985). In 1978 Furukawa electric co.ltd of Japan produced a new type of alloy 1. High spring back. 2. Shape memory. 3. Super elasticity. www.indiandentalacademy.com Miura et al – Japanese NiTi (1986) 15
  16. 16. Evolution of Materials Variable – modulus orthodontics-Burstone  (1981) Wire size was kept constant and material of the wire is selected on the basis of clinical requirements.  Fewer wire changes.  Different materials-maintaining same cross-section. www.indiandentalacademy.com 16
  17. 17. Evolution of Materials  Cu NiTi – (thermoelasticity) - Rohit Sachdeva. •Quaternary metal – Nickel, Titanium, Copper, Chromium. •Copper enhances thermal reactive properties and creates a consistent unloading force. Variable transformation temperature orthodontics www.indiandentalacademy.com 17
  18. 18. Evolution of Materials The beginning of Selectivity (1975 to the present)  Orthodontic manufacturers  CAD/CAM – larger production runs  Composites and Ceramics  Iatrogenic damage  Nickel and en-masse detachments New productscontrol of government agencies, private organizations 3. www.indiandentalacademy.com 18
  19. 19. Evolution of Materials      β titanium –Burstone and Goldberg-1980 β phase –stabilized at room temperature. Early 1980s Composition  Ti – 80%  Molybdenum – 11.5%  Zirconium – 6%  Tin – 4.5% Burstone’s objective  deactivation characteristics 1/3rd of SS or twice of conventional NiTi TMA – Titanium Molybdenum alloy - ORMCO www.indiandentalacademy.com 19
  20. 20. Evolution of Materials   Titanium-Niobium- M. Dalstra et al. Nickel free Titanium alloy.  Finishing wire.  Ti-74%,Nb-13%,Zr-13%.  TiMolium wires (TP Lab)-Deva Devanathan (late 90s)  Ti - 82% ,Mo - 15% , Nb-3% www.indiandentalacademy.com 20
  21. 21. Evolution of Materials  β III- Ravindra Nanda (2000-2001) • Bendable,inc. force-low deflection • Ni free • Versatility of steel with memory of NiTi. www.indiandentalacademy.com 21
  22. 22. Evolution of Materials Fiber reinforced polymeric composites:   Next generation of esthetic archwires Many orthodontic materials adapted-Aerospace industry  Pultrusion – round + rectangular  ADV – tooth colored  enhanced esthetics - reduced friction  22 DISADV – difficult towww.indiandentalacademy.com once manufactured change its shape
  23. 23. Basic Properties of Materials To gain understanding of orthodontic wires – basic knowledge of their atomic or molecular structure and their behavior during handling and use in the oral environment . www.indiandentalacademy.com 23
  24. 24. Basic Properties of Materials  Atom - smallest piece of an element that keeps its chemical properties.  Element - substance that cannot be broken down by chemical reactions. www.indiandentalacademy.com 24
  25. 25. Basic Properties of Materials Electrons – orbit around nucleus. Floating in shells of diff energy levels Electrons form the basis of bonds www.indiandentalacademy.com 25
  26. 26. Basic Properties of Materials   Pure substances are rare-eg. Iron always contains carbon, gold though occurs as a pure metal can be used only as an alloy. An ore contains the compound of the metal and an unwanted earthly material.  Compound - substance that can be broken into elements by chemical reactions.  Molecule - smallest piece of a compound that keeps its chemical properties (made of two or more atoms). www.indiandentalacademy.com 26
  27. 27. Basic Properties of Materials  Cohesive forces-atoms held together. Interatomic bonds Primary Ionic Covalent Metallic Secondary Hydrogen Van der Waals forces www.indiandentalacademy.com 27
  28. 28. Basic Properties of Materials  Ionic-mutual attraction between positive and negative ions-gypsum, phosphate based cements.  Covalent-2 valence electrons are shared by adjacent atoms-dental resins. www.indiandentalacademy.com 28
  29. 29. Basic Properties of Materials    Metallic –increased spatial extension of valence-electron wave functions. The energy levels are very closely spaced and the electrons tend to belong to the entire assembly rather than a single atom. Array of positive ions in a “sea of electrons” www.indiandentalacademy.com 29
  30. 30. Basic Properties of Materials    Electrons free to move Electrical and thermal conductivity Ductility and malleability -electrons adjust to deformation www.indiandentalacademy.com 30
  31. 31. Basic Properties of Materials METALLIC BOND IONIC BOND Metallic bond Ionic bond www.indiandentalacademy.com 31
  32. 32. Basic Properties of Materials  Materials broadly subdivided into 2 categories Atomic arrangement Crystalline structure Regularly spaced config-space lattice. Non-crystalline structure Possess short range atomic order. Anisotropic –diff in mechanical prop due directional arrangement of atoms. Isotropic-prop of material remains same in all directions. Amorphous www.indiandentalacademy.com 32
  33. 33. Characteristic properties of metals  An opaque lustrous chemical substance that is a good conductor of heat and electricity & when polished is a good reflector of light – Handbook of metals.  Metals are• Hard • Lustrous • Dense (lattice structure) • Good conductors of heat & electricity • Opaque (free e- absorb electromagnetic energy of light) • Ductile & Malleable www.indiandentalacademy.com 33
  34. 34. Basic Properties of Materials Crystals and Lattices 1665-Robert Hooke simulated crystal shapes –musket ball. 250 years later-exact model of a crystal with each ball=atom. Atoms combine-minimal internal energy. Space lattice- Any arrangement of atoms in space in which every atom is situated similarly to every other atom. May be the result of primary or secondary bonds. www.indiandentalacademy.com 34
  35. 35. Basic Properties of Materials  Crystal  combination of unit cells, in which each shell shares faces, edges or corners with the neighboring cells There are 8 crystal systems: Cubic system –Important as many metals belong to it. www.indiandentalacademy.com 35
  36. 36. Basic Properties of Materials There are 14 possible lattice forms.( Bravais lattices) The unit cells of 3 kinds of space lattices of practical importance – 1.Face-centered cubic: Fe above 910°C & Ni. www.indiandentalacademy.com 36
  37. 37. Basic Properties of Materials 2.Body centered cubic: Fe-below 910°C &above 1400°C. Cr &Ti above 880°C. www.indiandentalacademy.com 37
  38. 38. Basic Properties of Materials 3.Hexagonal close packed: Co & Ti below 880°C www.indiandentalacademy.com 38
  39. 39. Basic Properties of Materials      Perfect crystals - rare - atoms occupy well-defined positions. Cation-anion-cation-anionDistortion strongly opposed -similarly charged atoms come together. Single crystals- strong Used as reinforcements –whiskers (single crystals- 10 times longer, than wide) www.indiandentalacademy.com 39
  40. 40. Basic Properties of Materials     Crystal growth-atoms attach themselves in certain directions. Perfect crystals-atoms-correct direction. In common metals the crystals penetrate each other such that the crystal shapes get deformed. Microscopic analysis of alloys-grains (microns to centimeters). www.indiandentalacademy.com 40
  41. 41. Basic Properties of Materials www.indiandentalacademy.com 41
  42. 42. Basic Properties of Materials     Grain boundaries-area-crystals meet. Atoms-irregular Decrease mechanical strength Increase corrosion  imperfections beneficial-interfere with movement along slip planes  Dislocations cannot cross boundary- deformation requires greater stress. www.indiandentalacademy.com 42
  43. 43. Basic Properties of Materials Usually crystals have imperfections- Lattice defects. 1.Point defects: a. Impurities  •Interstitials – Smaller atoms that penetrate the lattice Eg – Carbon, Hydrogen, Oxygen, Boron. •Substitutial Element – Another metal atom of approx same size can substitute . E.g. - Nickel or Chromium substituting iron in www.indiandentalacademy.com 43 stainless steel.
  44. 44. Basic Properties of Materials b.Vacancies: These are empty atom sites. 2.Line defects: Dislocations along a line. Plastic deformations of metals occurs –motion of dislocations. www.indiandentalacademy.com 44
  45. 45. Basic Properties of Materials  Edge dislocation Sufficiently large forcebonds broken and new bonds formed.     Slip plane + Slip direction = Slip system www.indiandentalacademy.com 45
  46. 46. Basic Properties of Materials  Significance of slip planesShear stress  atoms of the crystal can glide. More the slip planes easier is it to deform. Slip planes intercepted at grain boundaries. www.indiandentalacademy.com 46
  47. 47. Basic Properties of Materials Elastic deformation Plastic deformation Greater stress - fracture www.indiandentalacademy.com 47
  48. 48. Basic Properties of Materials    Twinning – alt. mode of permanent deformation. Seen in metals-few slip planes (NiTi & α-titanium) Small atomic movements on either side of a twinning plane results in atoms with mirror relationship www.indiandentalacademy.com 48
  49. 49. Basic Properties of Materials  Also the mechanism for reversible transformationaustenite to martensite. • A movement that divides the lattice into 2 planes at a certain angle. •NiTi – multiple twinning •Subjected to a higher temperature, stress de - twinning occurs (shape memory) www.indiandentalacademy.com 49
  50. 50. Basic Properties of Materials  Cold working ( strain hardening or work hardening) • During deformation - atomic bonds within the crystal get stressed  resistance to more deformation • Dislocations pile up along the grain boundaries. • Hardness & strength • Plastic deformation-difficult. ductility www.indiandentalacademy.com 50
  51. 51. Basic Properties of Materials  An interesting effect of cold work-crystallographic orientation in the distorted grain structure.  Anisotropic (direction dependant) mechanical properties.  Slip planes align with shear planes.  Wires – mechanical properties different when measured parallel and perpendicular to wire axis. www.indiandentalacademy.com 51
  52. 52. Basic Properties of Materials   Implications: Fine grained metals with large no. of grains - stronger •Enhancing crystal nucleation by adding fine particles with a higher melting point, around which the atoms gather. •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 www.indiandentalacademy.com 52 slip planes.
  53. 53. Basic Properties of Materials  The effects of cold working can be reversed-heating the metal to appropriate temperature- Annealing • Relative process-heat below the melting temperature •More the cold work, more rapid the annealing •Higher melting point – higher annealing temp •Rule of thumb-½ the melting temperature (°K) www.indiandentalacademy.com 53
  54. 54. Basic Properties of Materials  Recovery-cold work disappears. • Ortho appliances heat treated (recovery temperature)• stabilizes the configuration of the appliance and • reduces-fracture.  Recrystallization –severely cold worked-after recoveryradical change in microstructure. • New stress free grains • Consume original cold worked structure. • Inc. ductility ,dec. resiliency www.indiandentalacademy.com 54
  55. 55. Basic Properties of Materials  Grain growth - minimizes the grain boundary area. •Coarse grains www.indiandentalacademy.com 55
  56. 56. Basic Properties of Materials  Before Annealing  Recovery – Relief of stresses  Recrystallization – New grains from severely cold worked areas  Grain Growth – large crystal “eat up” small ones www.indiandentalacademy.com 56
  57. 57. Basic Properties of Materials Polymorphism  Metals and alloys exist as more than one type of structure  Transition from one to the other-reversible- Allotropy Steel and NiTi www.indiandentalacademy.com 57
  58. 58. Basic Properties of Materials   Steel -alloy of iron and carbon Iron – 2 forms• FCC-above 910°c • BCC-below-Carbon practically insoluble.(0.02%) •Iron  FCC form (austenite) •Lattice spaces greater •Carbon atom can easily be incorporated into the www.indiandentalacademy.com unit cell 58
  59. 59. Basic Properties of Materials  On Cooling  FCC  BCC  Carbon diffuses out as Fe3C  Cementite adds strength to ferrite and austenite Rapidly cooled (quenched) Carbon cannot escape Distorted body centered tetragonal lattice called martensite Too brittle-tempered-heat b/w 200-450°C –held at a given temp for known length of time-cooled rapidly. www.indiandentalacademy.com 59
  60. 60. Basic Properties of Materials www.indiandentalacademy.com 60
  61. 61. Basic Properties of Materials Austenite (FCC) slow cooling Mixture of: Ferrite(BCC) & Cementite(Fe3C) rapid cooling Tempering Pearlite www.indiandentalacademy.com Martensite (BCT) distorted latticehard & brittle 61
  62. 62. Basic Properties of Materials  NiTi• • • Transformations –temperature & stress. Austenite (BCC) Martensitic (Distorted monoclinic, triclinic, hexagonal structure. Austenite- high temperature & low stress. Martensite –low temperature & high stress. Twinning-Reversible below elastic limit Transformations and reverse-not same temperaturewww.indiandentalacademy.com 62 hysteresis
  63. 63. Basic Properties of Materials  Bain distortion • Transformations occur without chemical change or diffusion • Result-crystallographic reln b/w parent and new phase • Rearrangement of atoms-minor movements www.indiandentalacademy.com 63
  64. 64. Evolution of Materials           Gold 1887-Neusilber brass (Cu,Ni,Zn) 1919-Stainless steel 1950s-Cobalt chromium 1962-NiTiNOL-1970-Orthodontia Early 1980s-β-titanium 1985,86-superelastic NiTi 1989-α-Titanium 1990s- Cu NiTi, Ti Nb and Timolium 2000-β-III www.indiandentalacademy.com 64
  65. 65. Basic Properties of Materials  Metallic bond-properties  Crystals & lattices  Imperfections  Edge dislocations, Twinning  Cold working  Annealing  Polymorphism  Bain distortion www.indiandentalacademy.com 65
  66. 66. Making an orthodontic wire     Sources Stainless steel- based on standard formulas of AISI.  After manufacture –further selection to surpass the basic commercial standard  Orthodontists –small yet demanding customers Chrome – cobalt and titanium alloys- fixed formulas Gold –supplier’s own specification. www.indiandentalacademy.com 66
  67. 67. Making an orthodontic wire  4 steps in wire production 1. Melting 2.The Ingot 3.Rolling 4.Drawimg www.indiandentalacademy.com 67
  68. 68. Making an orthodontic wire  Melting -Selection and melting of alloy materials-important -Physical properties influenced -Fixes the general properties of the metal  The Ingot -Critical step- pouring the molten alloy into mold - Non –uniform chunk of metal - Varying degrees of porosities and inclusions of slag. www.indiandentalacademy.com 68
  69. 69. Making an orthodontic wire -Microscopy –grains –influence mechanical properties. -Size and distribution of grains –rate of cooling and the size of ingot. -Porosity -2 sources o Gases dissolved or produced o Cooling and shrinking –interior cools late -Ingot – trimmed Important to control microstructure at this stage – basis of its physical properties and mechanical performance www.indiandentalacademy.com 69
  70. 70. Making an orthodontic wire  Rolling - 1st mechanical step-rolling ingot –long bars -Series of rollers – reduced to small diameter -Different parts of ingot never completely lose identity -Metal on outside of ingot-outside the finest wire, likewise ends - Different pieces of wire same ingot differ depending on the part they came from -Individual grains also retain identity www.indiandentalacademy.com 70
  71. 71. Making an orthodontic wire -Each grain elongated in the same proportion as the ingot -Mechanical rolling-forces crystals into long finger-like shapes –meshed into one another -Work hardening-increases the hardness and brittleness -if excess rolling-small cracks -Annealing –atoms become mobile-internal stresses relieved -More uniform than original casting -Grain size controlled www.indiandentalacademy.com 71
  72. 72. Making an orthodontic wire  Drawing -Further reduced to final size -Precise process –wire pulled through a small hole in a die - Hole slightly smaller than the starting diameter of the wire – uniformly squeezed -Wire reduced to the size of die www.indiandentalacademy.com 72
  73. 73. Making an orthodontic wire - Many series of dies - Annealed several times at regular intervals - Exact number of drafts and annealing cycles depends on the alloy (gold <carbon steel<stainless steel) www.indiandentalacademy.com 73
  74. 74. Making an orthodontic wire  Rectangular wires -Draw through rectangular die or roll round wires to rectangular shape -Little difference in the wires formed by the 2 processes -Drawing –produces sharper corners –advantageous in application of torque www.indiandentalacademy.com 74
  75. 75. Making an orthodontic wire  Hardness and spring properties depend–entirely on the effects of work hardening during manufacture  Drawing –Annealing schedule –planned carefully with final properties & size in mind  Metal almost in need of annealing at final size-maximum spring prop.  Drawing carried too far-brittle, not enough-residual softness. www.indiandentalacademy.com 75
  76. 76. www.indiandentalacademy.com 76
  77. 77. Mechanical properties  Strength-ability to resist stress without fracture or strain (permanent deformation).  Stress & strain-internal state of the material. Stress-internal distribution of load – force/ unit area (Internal force intensity resisting the applied load)   Strain- internal distortion produced by the loaddeflection/unit length (change in length/original length) www.indiandentalacademy.com 77
  78. 78. Mechanical properties  Material can be stressed in 4 ways• Compression • Tensile • Shear • Complex force systems www.indiandentalacademy.com 78
  79. 79. Mechanical properties  Evaluation of mechanical properties – • Bending tests • Tension tests • Torsional tests  • • • Bending tests : 3 types A cantilever bending test-Oslen stiffness tester (ADA32) 3 point 4 point www.indiandentalacademy.com 79
  80. 80. Mechanical properties www.indiandentalacademy.com Universal testing machine 80
  81. 81. Mechanical properties www.indiandentalacademy.com 81
  82. 82. Mechanical properties  The modulus of elasticity calculated from the force-deflection plot, using equations from solid mechanics.  Cantilever bending test-incompatible with flexible wires-(NiTi and multistranded).  Disadvantage of 3 point-bending moment-maximum at loading point to zero at the 2 supports.  4 point –uniform bending momentspecimen fails at the weakest point. www.indiandentalacademy.com 82
  83. 83. Mechanical properties  Nikolai et al proposed a 5 point bending test: -2 loading points at each end-simulate a couple. -simulates engagement of arch wire in bracket.  Tensile testing-strain - rate mechanical testing machine is used. www.indiandentalacademy.com 83
  84. 84. Elastic properties  Stress-Strain relationship (ductile material) www.indiandentalacademy.com 84
  85. 85. Elastic properties STRESS Wire returns back to original dimension when stress is removed Elastic portion (Hooke’s law) www.indiandentalacademy.com STRAIN 85
  86. 86. Elastic properties Proportional limit Yield point stress Elastic limit 0.1% www.indiandentalacademy.com strain 86
  87. 87. Elastic properties  Elastic /Proportional limit-used interchangeably  Proportional limit –determined by placing a straight edge on the stress-strain plot. Elastic limit -determined with aid of precise strain measurement apparatus in the lab. Yield strength (Proof stress) -PL-subjective ,YS used to for designating onset of permanent deformation.0.1% is reported. Determined by intersection of curved portion with 0.1% strain on horizontal axis.    www.indiandentalacademy.com 87
  88. 88. Elastic properties stress Ultimate tensile strength Fracture point Plastic deformation www.indiandentalacademy.com strain 88
  89. 89. Elastic properties  Ultimate tensile strength -the maximum load the wire can sustain (or) maximum force that the wire can deliver.  Permanent (plastic) deformation -before fractureremoval of load-stress-zero, strain = zero.  Fracture -Ultimate tensile strength higher than the stress at the point of fracture  reduction in the diameter of the wire (necking) www.indiandentalacademy.com 89
  90. 90. stress Elastic properties Slope α Stiffness Stiffness α 1 Springiness www.indiandentalacademy.com strain 90
  91. 91. Elastic properties  Slope of initial linear region- modulus of elasticity (E). (Young’s modulus) • Corresponds to the elastic stiffness or rigidity of the material • Amount of stress required for unit strain • E = σ/ε where σ does not exceed PL (Hookean elasticity) • The more horizontal the slope-springier the wire; vertical-stiffer www.indiandentalacademy.com 91
  92. 92. Elastic properties www.indiandentalacademy.com 92
  93. 93. Elastic properties YP force Point of arbitrary clinical loading Range www.indiandentalacademy.com Springback deflection 93
  94. 94. Elastic properties of metals  Range- • Proffit-Distance that the wire bends elastically, before permanent deformation occurs • Kusy – Distance to which an archwire can be activated- • Thurow – A linear measure of how far a wire or material can be deformed without exceeding the limits of the material. www.indiandentalacademy.com 94
  95. 95. Springback• Proffit- Portion of the loading curve b/w elastic limit and ultimate tensile strength.  •Kusy -- The extent to which the range recovers upon deactivation •Ingram et al – a measure of how far a wire can be deflected without causing permanent deformation. •Kapila & Sachdeva- YS/E www.indiandentalacademy.com 95
  96. 96. Elastic properties YP formability resiliency stress PL www.indiandentalacademy.com strain 96
  97. 97. Elastic properties  Resiliency-Area under stress-strain curve till proportional limit. -Maximum amount of energy a material can absorb without undergoing permanent deformation. 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 www.indiandentalacademy.com 97
  98. 98. Elastic properties  Work = f x d • When work is done on a body-energy imparted to it. • If the stress not greater than the PL elastic energy is stored in the structure. • Unloading occurs-energy stored is given out www.indiandentalacademy.com 98
  99. 99. Elastic properties  It depends on – Stiffness and Working Range  Independent of – Nature of the material Size (or) Form www.indiandentalacademy.com 99
  100. 100. Elastic properties  Formability – • Amount of permanent deformation that the wire can withstand before failing. • Indication of the ability of the wire to take the shape • Also an indication of the amount of cold work that it can withstand www.indiandentalacademy.com 100
  101. 101. Elastic properties  • Flexibility – Amount a wire can be strained without undergoing plastic deformation. • 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. www.indiandentalacademy.com 101
  102. 102. stress Elastic properties Toughness www.indiandentalacademy.com strain 102
  103. 103. Elastic properties  Toughness –Amount of elastic & plastic deformation required to fracture a material. Total area under the stress – strain graph.  Brittleness –Inability to sustain plastic deformation before fracture occurs.  Fatigue – Repeated cyclic stress of a magnitude below the fracture point of a wire can result in fracture. Fatigue behavior determined by the number of cycles required to produce fracture. www.indiandentalacademy.com 103
  104. 104. Elastic properties  Poisson’s ratio (ν) ν = - εx/ εy = -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. www.indiandentalacademy.com 104
  105. 105. Elastic properties  Ductility –ability to sustain large permanent deformation under tensile load before fracturing. Wires can be drawn  Malleability –sustain deformation under compressionhammered into sheets. www.indiandentalacademy.com 105
  106. 106. Requirements of an ideal arch wire  Robert P.Kusy- 1997 (AO) 1. Esthetics 2. Stiffness 3. Strength 4. Range 5. Springback 6. Formability 7.Resiliency 8.Coefficient of friction 9.Biohostability 10.Biocompatibility 11.Weldability www.indiandentalacademy.com 106
  107. 107. Requirements of an ideal arch wire  Esthetic •Desirable •Manufacturers tried-coating -White coloured wires • Deformed by masticatory loads •Destroyed by oral enzymes •Uncoated-transparent wires-poor mechanical properties •Function>Esthetics •Except the composite wires www.indiandentalacademy.com 107
  108. 108. Requirements of an ideal arch wire  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 Deflection www.indiandentalacademy.com 108
  109. 109. Requirements of an ideal arch wire  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. www.indiandentalacademy.com 109
  110. 110. Requirements of an ideal arch wire  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. www.indiandentalacademy.com 110
  111. 111. Requirements of an ideal arch wire  Range •Distance to which an archwire can be activated • Distance wire bends elastically before permanent deformation. •Measured in millimeters. www.indiandentalacademy.com 111
  112. 112. Requirements of an ideal arch wire  Springback • The extent to which the range recovers upon deactivation •Clinically useful-many wires deformed -wire performance-EL & Ultimate strength www.indiandentalacademy.com 112
  113. 113. Requirements of an ideal arch wire  Formability • Kusy – The ease in which a material may be permanently deformed. • Clinically- Ease of forming a spring or archwire www.indiandentalacademy.com 113
  114. 114. Requirements of an ideal arch wire  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 www.indiandentalacademy.com 114
  115. 115. Requirements of an ideal arch wire  Coefficient of Friction • Brackets (and teeth) must be able to slide along the wire • Independent of saliva-hydrodynamic boundary layer • High amounts of friction  anchor loss. • Titanium wires inferior to SS www.indiandentalacademy.com 115
  116. 116. Requirements of an ideal arch wire  Biohostability- •Site for accumulation of bacteria, spores or viruses. • An ideal archwire must have poor biohostability. •Should not-actively nurture nor passively act as a substrate for micro-organisms/spores/viruses •Foul smell, discolouration, build up of material-compromise mechanical properties. www.indiandentalacademy.com 116
  117. 117. Requirements of an ideal arch wire  Biocompatability • Ability of a material to elicit an appropriate biological response in a given application in the body • Wires-resist corrosion –products – harmful • Allergies • Tissue tolerance www.indiandentalacademy.com 117
  118. 118. Requirements of an ideal arch wire  Weldability – • Process of fusing 2 or more metal parts though application of heat, pressure or both with/out a filler metal to produce a localized union across an interface. • Wires –should be easily weldable with other metals www.indiandentalacademy.com 118
  119. 119. Elastic properties  Thurow - 3 characteristics of utmost importance - Important for the orthodontist –selection of the material and design-any change in 1 will require compensatory change in others. Strength = Stiffness x Range www.indiandentalacademy.com 119
  120. 120. Elastic properties  • Clinical implications: The properties can be expressed in absolute terms -in orthodontics-simple comparison. • Main concern-change in response – if there is change in material, wire size or bracket arrangement. • Knowledge- force and movement can be increased or decreased in certain circumstances Comparing the 3 properties www.indiandentalacademy.com 120
  121. 121. Elastic properties  Stiffness indicates rate of force delivery how much force how much distance can be covered  Strength –measures the load or force that carried at its maximum capacity  Range-amount of displacement under maximum load www.indiandentalacademy.com 121
  122. 122. Elastic properties  Factors effecting the 3 components - Mechanical arrangement-includes bracket width, length of arch wire. -Form of wire-size, shape & cross-section - Alloy formula, hardness, state of heat treatment www.indiandentalacademy.com 122
  123. 123. Optimal Forces & Wire Stiffness Varying force levels produced during deactivation of a wire: excessive, optimal, suboptimal, & subthreshold. During treatment by a wire with high load deflection rate the optimal zone is present only over a small range www.indiandentalacademy.com 123
  124. 124. Optimal Forces & Wire Stiffness Overbent wire with low load-deflection rate (Burstone) Tooth will reach desired position before subthreshold force zone is reached. Replacement of wires is not required www.indiandentalacademy.com 124
  125. 125. Effects of wire cross-section  Variable-cross section orthodontics How does change in size and shape of wire effect stiffness, strength & springiness? Considering a cantilever beam; www.indiandentalacademy.com 125
  126. 126. Effects of wire cross-section       Doubling diameter makes beam 8 times stronger But only 1/16 times springy ½ the range. Strength changes as a cubic fn of the ratio of the 2 cross sections. Springiness-4th power Range-direct proportion www.indiandentalacademy.com 126
  127. 127. Effects of wire cross-section   Rectangular wire The principle is same In torsion more shear stress rather than bending stress in encountered However the principle is same  Increase in diameter – increase in stiffness & strength rapidly– too stiff for orthodontic use & vice-versa Ideally wire should be in b/w these two extremes www.indiandentalacademy.com 127
  128. 128. Effects of wire cross-section      Wire selection-based on load -deflection rate requirement -magnitude of forces and moments required Is play a factor? Wire ligature minimizes the play in I order direction as wires can seat fully. Narrow edgewise brackets-ligature tie tends to minimize No point-0.018” over 0.016-diffrence in play. www.indiandentalacademy.com 128
  129. 129. Effects of wire cross-section Should a smaller wire be chosen to obtain greater elastic deflection?  Elastic deflection varies inversely with diameter of wire but differences are negligible 0.016 has 1.15 times maximum elastic deflection as 0.018 wire. Major reason- load deflection rate  Small changes in the wire produce large changes in L-D rate  Determined by moment of inertia. www.indiandentalacademy.com 129
  130. 130. Effects of wire cross-section Shape Moment of Inertia Ratio to stiffness of round wire Пd4 64 1 s4 12 1.7 b3h 12 1.7 b3hd4 www.indiandentalacademy.com 130
  131. 131. Effects of wire cross-section  The clinician needs a simplified system to determine the stiffness of the wire he uses. Cross-sectional stiffness number (CS)-relative stiffness  0.1mm(0.004in) round wire-base of 1.  www.indiandentalacademy.com 131
  132. 132. Effects of wire cross-section www.indiandentalacademy.com 132
  133. 133. Effects of wire cross-section 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 www.indiandentalacademy.com 133
  134. 134. Effects of wire cross-section  • • Rectangular wires Bending perpendicular to the larger dimension (ribbon mode) Easier than bending perpendicular to the smaller dimension (edgewise). •The larger dimension  correction is needed. •The smaller dimension  the plane in which more stiffness is needed. www.indiandentalacademy.com 134
  135. 135. Effects of wire cross-section  > first order, < second order – RIBBON  > Second order, < first order - EDGEWISE •> 1st order correction in anterior segment •> 2nd order in the posterior segment, wire can be twisted 90° •Ribbon mode in anterior region and edgewise in posterior region. www.indiandentalacademy.com 135
  136. 136. Effects of wire cross-section  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. (do not turn and no unwanted forces are created). www.indiandentalacademy.com 136
  137. 137. Orthodontic wires         Mechanical & Elastic properties Ideal requirements of an arch wires Strength, stiffness & range Optimal forces and wire stiffness Effects of cross-section Strength changes as a cubic fn of the ratio of the 2 cross sections. Springiness-4th power Range-direct proportion www.indiandentalacademy.com 137
  138. 138. Effects of length   Changing the length-dramatically affects properties Considering a cantilever ; www.indiandentalacademy.com 138
  139. 139. Effects of length If length is doubled• Strength – cut by half-(decreases proportionately) • Springiness – inc. 8 times ( as a cubic function) • Range – inc 4 times (increases as a square.) In the case of torsion, the picture is slightly different. Increase in length – •Stiffness decreases proportionately •Range increases proportionately •Strength remains unchanged. www.indiandentalacademy.com 139
  140. 140. 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 • 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. www.indiandentalacademy.com 140
  141. 141. Effects of material    Modulus of elasticity varied by changing the material Material stiffness number-relative stiffness of the material Steel -1.0(Ms) www.indiandentalacademy.com 141
  142. 142. Effects of material www.indiandentalacademy.com 142
  143. 143. Nomograms  Developed by Kusy  Graphic representation-comparing wire materials and sizes  Fixed charts that display mathematical relationshipsscales  Nomograms of each set drawn to same base, any wire on 1 of 3 can be compared to any other. www.indiandentalacademy.com 143
  144. 144. Nomograms A reference wire is chosen (0.012”SS) and given a value of 1 . The strength , stiffness and range of other wires are calculated to this reference www.indiandentalacademy.com 144
  145. 145. Nomograms www.indiandentalacademy.com 145
  146. 146. Nomograms www.indiandentalacademy.com 146
  147. 147. Clinical implications  Balance between stiffness, strength & range  Vary - material ,cross-section or length as the situation demands. www.indiandentalacademy.com 147
  148. 148. Clinical implications  Variation in Cross-Section Wires with less cross-section-low stiffness (changes by 4th power)   Used initial part of treatment Thicker-stiffer wires used later www.indiandentalacademy.com 148
  149. 149. Clinical implications   Multi-stranded wires 2 or more wires of smaller diameter are twisted together/coiled around a core wire  Twisting of the two wires causes the strength to increase, so that the wire can withstand masticatory forces.  The properties of multistranded wires depend on the individual wires that are coiled, and on how tightly they are coiled together. www.indiandentalacademy.com 149
  150. 150. Clinical implications  Variation in length •Removable appliance -cantilever spring •The material of choice is usually steel. (Stiff material) •Good strength to resist masticatory and other oral forces. www.indiandentalacademy.com 150
  151. 151. Clinical implications  Increase the length of the wire-  Proportionate decrease in strength, but the stiffness will decrease as a cubic function  Length is increase by either bending the wire over itself, or by winding helices or loops into the spring www.indiandentalacademy.com 151
  152. 152. Clinical implications  Fixed appliance  The length of wire between brackets can be increased  Loops, or Smaller brackets, or Special bracket designs –Mini-unitwin bracket,Delta www.indiandentalacademy.com 152
  153. 153. Clinical implications  Variation in the material  Relatively constant dimension important for the third order control  Titanium wires-low stiffness-used initial part of treatment  Steel-when rigidity-control and torque expression required www.indiandentalacademy.com 153
  154. 154. Clinical implications www.indiandentalacademy.com 154
  155. 155. Clinical implications Stage Wires Reason Aligning Multistranded SS, NiTi Great range and light forces are reqd Space closure Β-Ti (frictionless), SS – if sliding mechanics is needed Increased formability, springback , range and modest forces per unit activation are needed Finishing SS , preferably rectangular More stability & less tooth movement reqd www.indiandentalacademy.com 155
  156. 156. Clinical implications Stage Wires Reason Aligning Multistranded SS, Low LDR-SS Great range and light forces are reqd Space closure SS(high resilience aust.wire) – sliding mechanics Increased formability, springback , range and modest forces per unit activation are needed Finishing SS , α-titanium More stability & less tooth movement reqd www.indiandentalacademy.com 156
  157. 157. Clinical implications A rough idea can be obtained clinically  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. www.indiandentalacademy.com 157
  158. 158. Physical properties  Corrosion Chemical or electrochemical process in which a solid, usually a metal, is attacked by an environmental agent, resulting in partial or complete dissolution.    Not merely a surface deposit –deterioration of metal Localized corrosion-mechanical failure Biological effects-corrosion products www.indiandentalacademy.com 158
  159. 159. Physical properties Nickel 1. Carcinogenic, 2. Mutagenic, 3. Cytotoxic and 4. Allergenic.   Stainless steels, Co-Cr-Ni alloys and NiTi are all rich in Ni Co & Cr can also cause allergies. www.indiandentalacademy.com 159
  160. 160. Physical properties  Studies-Ni alloy implanted in the tissue  Although-more invasive –reactivity of the implanted material is decreased –connective tissue capsule  Intraoral placement-continuous reaction with environment Corrosion resistance of steel SS- passivating layer-Cr-also contains Fe, Ni, Mo www.indiandentalacademy.com 160
  161. 161. Physical properties  Passivating film-inner oxide layer-mainly-Cr oxide outer- hydroxide layer Elgiloy-similar mechanism of corrosion resistance  Titanium oxides-more stable  Corrosion resistance of SS inferior to Ti alloys  www.indiandentalacademy.com 161
  162. 162. Physical properties -Forms of corrosion 1.     2.   Uniform attack – Commonest type The entire wire reacts with the environment Hydroxides or organometallic compounds Detectable after a large amount of metal is dissolved. Pitting Corrosion – Manufacturing defects Sites of easy attack www.indiandentalacademy.com 162
  163. 163. Physical properties  Excessive porous surface-as received wires Steel NiTi www.indiandentalacademy.com 163
  164. 164. Physical properties 3. Crevice corrosion or gasket corrosion  Parts of the wire exposed to corrosive environment  Non-metallic parts to metal (sites of tying)  Difference in metal ion or oxygen concentration  Plaque build up  disturbs the regeneration of the passivating layer  Depth of crevice-reach upto 2-5 mm  High amount of metals can be dissolved in the mouth. www.indiandentalacademy.com 164
  165. 165. Physical properties www.indiandentalacademy.com 165
  166. 166. Physical properties 4.Galvanic /Electrochemical Corrosion  Two metals are joined  Or even the same metal after different type of treatment are joined  Difference in the reactivity  Galvanic cell.  Less Reactive (Cathodic)  More Reactive (Anodic) less noble metal www.indiandentalacademy.com 166
  167. 167. Physical properties  Less noble metal-oxidizes-anodic-soluble  Nobler metal-cathodic-corrosion resistant  “Galvanic series”  SS-can be passive or active depending on the nobility of the brazing material www.indiandentalacademy.com 167
  168. 168. Physical properties 5.Intergranular corrosion  Sensitization - Precipitation of CrC-grain boundaries -Solubility of chromium carbide 6.Fretting corrosion  Material under load  Wire and brackets contact –slot – archwire interface Friction  surface destruction Cold welding -pressure  rupture at contact pointswww.indiandentalacademy.com wear oxidation pattern  168
  169. 169. Physical properties 7.Microbiologically influenced corrosion (MIC)   Sulfate reducing-Bacteroides corrodens Matasa – Ist to show attack on adhesives in orthodontics  Craters in the bracket  Certain bacteria dissolve metals directly form the wires.  Or by products alter the microenvironment-accelerating corrosion www.indiandentalacademy.com 169
  170. 170. Physical properties www.indiandentalacademy.com 170
  171. 171. Physical properties 8.Stress corrosion  Similar to galvanic corrosion-electrochemical potential difference-specific sites  Bending of wires - different degrees of tension and compression develops locally  Sites-act as anodes and cathodes. www.indiandentalacademy.com 171
  172. 172. Physical properties  9.Corrosion Fatigue: Cyclic stressing of a wire-aging  Resistance to fracture decreases  Accelerated in a corrosive medium such as saliva  Wires left intraorally-extended periods of time under load  www.indiandentalacademy.com 172
  173. 173. Physical properties  Corrosion – Studies  In vitro Vs In vivo  Never simulate the oral environment  Retrieval studies  Biofilm-masks alloy topography  Organic and inorganic components  Mineralized –protective esp. low pH www.indiandentalacademy.com 173
  174. 174. Physical properties  Ni hypersensitivity-case reports-very scarce  Insertion of NiTi wires –  rashes  swelling  Erythymatous lesions  Ni and Cr  impair phagocytosis of neutrophils and  impair chemotaxis of WBCs. www.indiandentalacademy.com 174
  175. 175. Physical properties  Ni at conc. released from dental alloys  Activating monocytes and endothelial cells,  Promote intercellular adhesion(molecule 1)  Promotes inflammatory response in soft tissues.  Arsenides and sulfides of Ni - carcinogens and mutagens.  Ni at non toxic levels - DNA damage. www.indiandentalacademy.com 175
  176. 176. www.indiandentalacademy.com 176
  177. 177. Stainless steel  Gold  1960s-Abandoned in favour of stainless steel  Crozat appliance –original design  1919 – Dr. F Hauptmeyer –Wipla (wie platin). •Extremely chemically stable •Better strength and springiness • High resistance to corrosion-Chromium content. www.indiandentalacademy.com 177
  178. 178. Stainless steel  Properties of SS controlled-varying the degree of cold work and annealing during manufacture  Steel wires-offered in a range of partially annealed states –yield strength progressively enhanced at the cost of formability compromised  Fully annealed stainless steel  extremely soft, and highly formable  Ligature wire-“Dead soft” www.indiandentalacademy.com 178
  179. 179. Stainless steel  Steel wires with high yield strength- “Super” grade wiresbrittle-used when sharp bends are not needed  High formability- “regular” wires-bent into desired shapes www.indiandentalacademy.com 179
  180. 180. Stainless steel  Structure and composition  Iron –always contains carbon-(2.1%)  When aprrox 12%-30% Cr added- stainless  Cr2O3-thin transparent, adherent layer when exposed to oxidizing atm.  Passivating layer-ruptured by chemical/mechanical means-protective layer reforms  Favours the stability of ferrite (BCC) www.indiandentalacademy.com 180
  181. 181. Stainless steel  Nickel(0-22%) – Austenitic stabilizer (FCC)  Loosly bound  Copper, manganese and nitrogen – similar function  Mn-dec corrosion resistance  Carbon (0.08-1.2%)– provides strength  Reduces the corrosion resistance www.indiandentalacademy.com 181
  182. 182. Stainless steel  Sensitization.     400-900oC-looses corrosion resistance During soldering or welding Chromium diffuses towards the carbon rich areas (usually the grain boundaries)-chromium carbide-most rapid 650°C Chromium carbide is soluble- intergranular corrosion. www.indiandentalacademy.com 182
  183. 183. Stainless steel  3 methods to prevent sensitization- 1. Reduce carbon content-precipitation cannot occur-not economically feasible 2. Severely cold work the alloy-Cr carbide ppts at dislocations-more uniform  Stabilization Addition of an element which precipitates carbide more easily than Chromium. Niobium, tantalum & titanium   www.indiandentalacademy.com 183
  184. 184. Stainless steel  Usually- Titanium.  Ti 6x> Carbon  No sensitization during soldering.  Most steels used in orthodontics are not stabilizedadditional cost www.indiandentalacademy.com 184
  185. 185. Stainless steel  Other additions and impurities-  Silicon – (low concentrations) improves the resistance to oxidation and carburization at high temperatures and corrosion resistance  Sulfur (0.015%) increases ease of machining  Phosphorous – allows sintering at lower temperatures.  But both sulfur and phosphorous reduce the corrosion resistance. www.indiandentalacademy.com 185
  186. 186. Stainless steel  Classification  American Iron and Steel Institute (AISI)  Unified Number System (UNS)  German Standards (DIN). www.indiandentalacademy.com 186
  187. 187. Stainless steel  The AISI numbers used for stainless steel range from 300 to 502  Numbers beginning with 3 are all austenitic  Higher the number   Less the non-ferrous content  More expensive the alloy  Numbers having a letter L signify a low carbon content www.indiandentalacademy.com 187
  188. 188. Basic Properties of Materials Austenite (FCC) slow cooling Mixture of: Ferrite(BCC) & Cementite(Fe3C) rapid cooling Tempering Pearlite www.indiandentalacademy.com Martensite (BCT) distorted latticehard & brittle 188
  189. 189. Stainless steel www.indiandentalacademy.com 189
  190. 190. Stainless steel Austenitic steels (the 300 series)  Most corrosion resistance  FCC structure,  non ferromagnetic  Not stable at room temperature,  Austenite stabalizers Ni, Mn and N www.indiandentalacademy.com 190
  191. 191. Stainless steel  Type 302-basic alloy -17-19% Cr,8-10% Ni,0.15%-C  304- 18-20%-Cr, 8-12%Ni,0.08%-C  Known as the 18-8 stainless steels- most common in orthodontics  316L-10-14%-Ni,2-3%Mo,16-18%-Cr,O.03%-Cimplants www.indiandentalacademy.com 191
  192. 192. Stainless steel  The following properties Greater ductility and malleability  More cold work-strengthened  Ease –welding  Dec. sensitization  Less critical grain growth  Ease in forming  X-ray diffraction-not always single phase-Bcc martensitic phase present www.indiandentalacademy.com 192
  193. 193. Stainless steel Khier,Brantly,Fournelle(AJO-1998) Austenitic structuremetastable Decomposes to martensitecold work & heat treatment Manufacturing process www.indiandentalacademy.com 193
  194. 194. Stainless steel Martensitic steel (400)  FCC  BCC  BCC structure is highly stressed. (BCT) More grain boundaries,  Stronger  Dec. ductulity-2%  Less corrosion resistant   Making instrument edges which need to be sharp and wear resistant. www.indiandentalacademy.com 194
  195. 195. Stainless steel www.indiandentalacademy.com 195
  196. 196. Stainless steel Ferritic steels – (the 400 series)  Name derived from the fact-microstr (BCC) same as iron  Difference-Cr  “super ferritics”-19-30% Cr-used Ni free brackets  Good corrosion resistance, low strength.  Not hardenable by heat treatment-no phase change  Not readily cold worked. www.indiandentalacademy.com 196
  197. 197. Stainless steel Duplex steels  Both austenite and ferrite grains  Fe,Mo,Cr, lower nickel content  Increased toughness and ductility than ferritic steels  Twice the yield strength of austenitic steels  High corrosion resistant-heat treated –sigma-dec corrosion resistance  Manufacturing low nickel attachments-one piece brackets www.indiandentalacademy.com 197
  198. 198. 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. www.indiandentalacademy.com 198
  199. 199. Stainless steel -General properties 1. Relatively stiff material  Yield strength and stiffness can be varied   Altering the carbon content and  Cold working and   Altering diameter/cross section Annealing High forces - dissipate over a very short amount of deactivation (high load deflection rate). www.indiandentalacademy.com 199
  200. 200. Stainless steel  In clinical terms•Loop - activated to a very small extent so as to achieve optimal force but •Deactivated by only a small amount (0.1 mm) force level will drop tremendously •Type of force-Not physiologic •More activations www.indiandentalacademy.com 200
  201. 201. Stainless steel  Force required to engage a steel wire into a severely malaligned tooth.    Either cause the bracket to pop out, Or the patient to experience pain. Overcome by using thinner wires, which have a lower stiffness.  Not much control. www.indiandentalacademy.com 201
  202. 202. Stainless steel High stiffness can be advantageous  Maintain the positions of teeth & hold the corrections achieved  Begg treatment, stiff archwire, to dissipate the adverse effects of third stage auxiliaries www.indiandentalacademy.com 202
  203. 203. Stainless steel 2. Lowest frictional resistance  Ideal choice of wire during space closure with sliding mechanics   Teeth will be held in their corrected relation Minimum resistance to sliding www.indiandentalacademy.com 203
  204. 204. Stainless steel 3.High corrosion resistance Ni is used as an austenite stabilizer.  Not strongly bonded to produce a chemical compound.  Likelihood of slow release of Ni  Symptoms in sensitized patients www.indiandentalacademy.com 204
  205. 205. Stainless steel  Passivating layer dissolved in areas of plaque accumulation – Crevice corrosion.  Different degrees of cold work – Galvanic corrosion  Different stages of regeneration of passivating layer – Galvanic corrosion  Sensitization – Inter-granular corrosion www.indiandentalacademy.com 205
  206. 206. Stainless steel  1919-SS introduced  Structure and composition-stainless  Classifications  FCC-BCC  General properties www.indiandentalacademy.com 206
  207. 207. www.indiandentalacademy.com 207
  208. 208. High Tensile Australian Wires  Claude Arthur J. Wilcock started association with dental profession-1936-37  Around 1946-asssociation with Dr.Begg  Flux, silver solder, lock pins, brackets, bands, ligature wires, pliers & high tensile wire   Needed-wires that were active for long Dr Begg-progressively harder wires www.indiandentalacademy.com 208
  209. 209. 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 www.indiandentalacademy.com 209
  210. 210. High Tensile Australian Wires  Demand-very high-1970s  Raw materials overseas  Higher grades-Premium  Preformed appliances, torquing auxiliaries, springs  Problems-impossibility in straightening for appliances -work softening-straightening -breaking www.indiandentalacademy.com 210
  211. 211. High Tensile Australian Wires •Higher working range- E (same) But inc. YS Range=YS/E •Higher resiliency ResilαYS2/E •Zero stress relaxation •Reduced formability www.indiandentalacademy.com 211
  212. 212. High Tensile Australian Wires 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.  Property of a wire to deliver a constant light elastic force, when subjected to external forces (like occlusal forces).  Only wires with high yield strength-possess this desirable property www.indiandentalacademy.com 212
  213. 213. High Tensile Australian Wires  Relaxation in material- Slip dislocation  Materials with high YS-resist such dislocations-internal frictional force.  New wires-maintain their configuration-forces generated are unaffected www.indiandentalacademy.com 213
  214. 214. 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 (spring index)  smaller diameter of wires  smaller diameter springs (like the mini springs)  Higher grade wires (high YS), ratio can be =2, much lighter force  Bite opening anchor bendszero stress relaxation –infrequent reactivation www.indiandentalacademy.com 214
  215. 215. High Tensile Australian Wires  Spinner straightening  It is mechanical process of straightening resistant materials in the cold-hard drawn condition The wire is pulled through rotating bronze rollers that torsionally twist it into straight condition Wire subjected to tension-reverse straining. Disadv:  Decreases yield strength (strain softened)  Creates rougher surface    www.indiandentalacademy.com 215
  216. 216. 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. www.indiandentalacademy.com 216
  217. 217. 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. www.indiandentalacademy.com 217
  218. 218. High Tensile Australian Wires roundning www.indiandentalacademy.com 218
  219. 219. High Tensile Australian Wires  Plastic prestrain increases the elastic limit of deformation in the same direction as the prestrain.  Plastic prestrain decreases the elastic limit of deformation in the direction opposite to the prestrain.  If the magnitude of the prestrain is increased, the elastic limit in the reverse direction can reduce to zero. www.indiandentalacademy.com 219
  220. 220. High Tensile Australian Wires  JCO,1991 Jun(364 - 369): Clinical Considerations in the Use of Retraction Mechanics - Julie Ann Staggers, Nicholas Germane  The range of action will be greatest in the direction of the last bend  With open loop, activation unbends loop; but with closed loop, activation is in the direction of the last bend -increases range of activation.  Premium wire  special plus or special wire www.indiandentalacademy.com 220
  221. 221. www.indiandentalacademy.com 221
  222. 222. High Tensile Australian Wires  Pulse straightening Placed in special machines that permits high tensile wires to be straightened. This method : Permits the straightening of high tensile wires 1. Does not reduce the yield strength of the wire 2. Results in a smoother wire, hence less wire – bracket friction. www.indiandentalacademy.com 222
  223. 223. High Tensile Australian Wires  Dr.Mollenhauer requested –ultra high tensile SS round wire.  Supreme grade wire –lingual orthodontics-initial faster and gentler alignment of teeth-brackets close  Labial Begg brackets-reduces tenderness  Intrusion  simultaneously with the base wires  Gingival health seemed better www.indiandentalacademy.com 223
  224. 224. High Tensile Australian Wires  Higher yield strength  more flexible  Supreme grade flexibility = β-titanium.  Higher resiliency  nearly three times.  NiTi  higher flexibility but it lacks formability www.indiandentalacademy.com 224
  225. 225. 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 www.indiandentalacademy.com 225
  226. 226. High Tensile Australian Wires Twelftree, Cocks and Sims (AJO 1977)  Wires-0.016-7 wires  Premium plus, Premium and Special plus wires showed minimal stress relaxation-no relaxation -3 days  Special,  Remanit,  Yellow Elgiloy,  Unisil.  Special plus maintained original coil size, Unisil-inc. curvature www.indiandentalacademy.com 226
  227. 227. 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 (82)  Sp.plus greater working range than stnd. SS but NiTi,TMA & multistranded-greater  Jyothindra Kumar (89) -evluated working range  Australian wires-better recovery than Remanuim www.indiandentalacademy.com 227
  228. 228. High Tensile Australian Wires  Pulse straightened wires – Spinner straightened (Skaria 1991)  Strength, stiffness and Range higher than spinner staightened wires  Coeff. of friction higher-almost double  Similar- surface topography, stress relaxation and Elemental makeup. www.indiandentalacademy.com 228
  229. 229. High Tensile Australian Wires  Anuradha Acharya (2000)  Super Plus (Ortho Organizers) – between Special plus and Premium  Premier (TP) – Comparable to Special  Premier Plus (TP)– Special Plus  Bowflex (TP) – Premium www.indiandentalacademy.com 229
  230. 230. 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. www.indiandentalacademy.com 230
  231. 231. High Tensile Australian Wires      High and sharp yield points-freeing of dislocations and effective shear stress to move these dislocations. Flow stress dependent on Temperature  Density of dislocations in the material Resulting structure-hard-high flow stress Plastic deformation absence of dislocation locking-low YS Internal stress=applied stress x density of dislocations www.indiandentalacademy.com 231
  232. 232. High Tensile Australian Wires Fracture of wires and crack propagation Dislocation locking  High tensile wires have high density of dislocations and crystal defects  Pile up, and form a minute crack  Stress concentration www.indiandentalacademy.com 232
  233. 233. High Tensile Australian Wires Small stress applied with the plier beaks  Crack propagation  Elastic energy is released  Propagation accelerates to the nearest grain boundary www.indiandentalacademy.com 233
  234. 234. 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. www.indiandentalacademy.com 234
  235. 235. High Tensile Australian Wires www.indiandentalacademy.com 235
  236. 236. 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 3.Wilcock-Begg light wire pliers, preferably not tungsten carbide tipped www.indiandentalacademy.com 236
  237. 237. High Tensile Australian Wires www.indiandentalacademy.com 237
  238. 238. High Tensile Australian Wires 4. The edges rounded  reduce the stress concentration in the wire. –sandpaper & polish if sharp. 5.Ductile – brittle transition temperature slightly above room temperature. Wire should be warmed – pull though fingers Spools kept in oven at about 40o, so that the wire remains slightly warm. www.indiandentalacademy.com 238
  239. 239. Multistranded wires  They are composed of specified numbers of thin wire sections coiled around each other to provide round or rectangular cross section  The wires-twisted or braided  When twisted around a core wire-coaxial wire www.indiandentalacademy.com 239
  240. 240. Multistranded wires Co-axial Twisted wire www.indiandentalacademy.com 240
  241. 241. Multistranded wires  Individual diameter - 0.0165 or 0.0178 final diameter – 0.016" – 0.025“  On bending - individual strands slip over each other , making bending easy.  Strands of .007 inch twisted into .017 inch-(3 wires) stiffness comparable to a solid wire of .010 inch www.indiandentalacademy.com 241
  242. 242. Multistranded wires    Stiffness – decreases as a function of the 4th power Range – increases proportionately Strength – decreases as a function of the 3rd power Result - high elastic modulus wire behaving like a low stiffness wire www.indiandentalacademy.com 242
  243. 243. Multistranded wires Elastic properties of multistranded archwires depend on – 1.Material parameters – Modulus of elasticity 2.Geometric factors – moment of inertia & wire dimension 3.Twisting or braiding or coaxial 4.Dimensionless constants  Number of strands coiled  Helical spring shape factor  Bending plane shape factor www.indiandentalacademy.com 243
  244. 244. 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 cos α α - helix angle and v - Poisson’s ratio (lateral strain/axial strain) Angle α can be seen in the following diagram :www.indiandentalacademy.com 244
  245. 245. Multistranded wires www.indiandentalacademy.com 245
  246. 246. Multistranded wires Schematic definition of the helix angle (a). If one revolution of a wire strand is unfurled and its base length [p(D-d)] and corresponding distance traversed along the original wire axis (S*) are determined, then a ratio of these two distances equals tan a. Everything else being equal, the greater p(D-d) or the less S* is, the more compliant a wire will be. www.indiandentalacademy.com 246
  247. 247. Multistranded wires    Bending shape factor Complex property  number of strands  orientation of the strands  diameter of the strands and the entire wire  helix angle etc . Different for different types of multistranded wires www.indiandentalacademy.com 247
  248. 248. 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  www.indiandentalacademy.com 248
  249. 249. Multistranded wires Kusy (AJO 1984)  Triple stranded 0.0175” (3x0.008”) SS  GAC’s Wildcat  Compared the results to other wires commonly used by orthodontists- SS,NiTi & β-Ti www.indiandentalacademy.com 249
  250. 250. Multistranded wires  The multistranded wire did not resemble the 0.018 wire in any way except for the size and & slot engagement Stiffness was comparable to 0.010 SS wire but strength was 20% higher  0.016 NiTi-equal in stiffness, considerably stronger and 50% more activation 0.016 β-Ti –twice as stiff, comparable to 0.012 SS www.indiandentalacademy.com 250
  251. 251. Multistranded wires www.indiandentalacademy.com 251
  252. 252. Multistranded wires www.indiandentalacademy.com 252
  253. 253. Multistranded wires Ingram, Gipe and Smith (AJO 86)  Range independent of wire size  Range seems to increase with increase in diameter  It varies only from 11.2-10.0largest size having slightly greater range than smallest wire. www.indiandentalacademy.com 253
  254. 254. Multistranded wires     Oltjen,Duncanson,Nanda,Currier (AO-1997) Wire stiffness can be altered by not only changing the Increase in but of strands size or alloy compositionNo. by varying the number of strands.  stiffness Unlike single stranded wires Increase in No. of strands  stiffness stiffness varied as deflection varied. Unlike single stranded wires  stiffness varied as deflection varied. www.indiandentalacademy.com 254
  255. 255. Multistranded wires Rucker & Kusy (AO 2002)  Interaction between individual strands was negligible.  Range and strength Triple stranded = Co-axial (six stranded)  Stiffness  Coaxial < Triple stranded  Range of small dimension single stranded SS wire was similar. www.indiandentalacademy.com 255
  256. 256. Multistranded wires www.indiandentalacademy.com 256
  257. 257. Cobalt chromium  1950s the Elgin Watch “The heart that never breaks”  Rocky Mountain Orthodontics - Elgiloy  CoCr alloys –belong to stellite alloys  superior resistance to corrosion (Cr oxide), comparable to that of gold alloys exceeding SS. www.indiandentalacademy.com 257
  258. 258. Cobalt chromium Composition  Co-40%  Cr-20%  Ni-15% - strength & ductility  Fe-16%,traces of Molybdenum, Tungsten, Titaniumstable carbides –enhance hardenability and set resistance. www.indiandentalacademy.com 258
  259. 259. Cobalt chromium Advantages over SS 1. Delivered in different degrees of hardening or tempers 2. High formability 3.Further hardened by heat treatment 4.Greater resistance to fatigue and distortion 5.Longer function as a resilient spring www.indiandentalacademy.com 259
  260. 260. Cobalt chromium   The alloy as received is highly formable, and can be easily shaped. Heat treatedConsiderable strength and resiliency  Strength   Formability  www.indiandentalacademy.com 260
  261. 261. Cobalt chromium  Ideal temperature- 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  . Heating above 650oC   partial annealing, and softening of the wire Optimum heat treatment  dark straw color of the wire or temperature indicating paste www.indiandentalacademy.com 261
  262. 262. Cobalt chromium 1958-1961-4 tempers Red – hard & resilient Green – semi-resilient Yellow – slightly less formable but ductile Blue – soft & formable www.indiandentalacademy.com 262
  263. 263. Cobalt chromium Blue-bent easily -fingers or pliers  Recommended –considerable bending, soldering or welding required  Yellow -bent with ease-more resilient -inc. in resiliency and spring performance-heat  Green –more resilient than yellow,can be shaped to some extent-pliers  Red- most resilient –high spring qualities,minimal working Heat treatment-inc. resilient but fractures easily.  www.indiandentalacademy.com 263
  264. 264. Cobalt chromium After heat treatment  Blue and yellow =normal steel wire  Green and red tempers =higher grade steel  E very similar –SS & blue elgiloy (10% inc in E)  Similar force delivery and joining characters www.indiandentalacademy.com 264
  265. 265. www.indiandentalacademy.com 265
  266. 266. Cobalt chromium  Comparable amount of Ni  Coefficient of friction higher than steel -recent studycomparable to steel-zero torque brackets are used.  The high modulus of elasticity of Co-Cr and SSDeliver twice the force of β-Ti and 4times NiTi for equal amounts of activation. www.indiandentalacademy.com 266
  267. 267. Cobalt chromium  Stannard et al (AJO 1986)  Co-Cr highest frictional resistance in wet and dry conditions. Ingram Gipe and Smith (AJO 86) •Non heat treated •Range < stainless steel of comparable sizes •But after heat treatment, the range was considerably increased. www.indiandentalacademy.com 267
  268. 268. Cobalt chromium    Kusy et al (AJO 2001) 16 mil (0.4mm or .016 inch) evaluated E values –identical -red –highest- YS & UTS -blue-most ductile www.indiandentalacademy.com 268
  269. 269. Cobalt chromium   The elastic modulus did not vary appreciably  edgewise or ribbon-wise configurations. Round wires higher ductility than square or rectangular wires www.indiandentalacademy.com 269
  270. 270. Cobalt chromium  The averages of E,YS,UTS and ductility plotted against specific cross-sec area.  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. www.indiandentalacademy.com 270
  271. 271. Cobalt chromium www.indiandentalacademy.com 271
  272. 272. Cobalt chromium  Conclusion- based on force-deactivation characteristics- interchangeably – SS  Can choose different tempers and amounts of formability  Inc the YS by heat treating  Fine in principle-but-lack of control of the processing variables in the as received state. www.indiandentalacademy.com 272
  273. 273. To strive, to seek to find ,and not to yield - Lord Tennyson ( Ulyssess) www.indiandentalacademy.com 273
  274. 274. References  Proffit – Contemporary orthodontics-3rd ed  Graber vanarsdall – orthodontics – current principles and techniques-3rd ed  Phillips’ science of dental materials-Anusavice -11th ed  Orthodontic materials-scientific and clinical aspectsBrantly and Eliades  Edgewise orthodontics-R.C. Thurow-4th ed  Notes on dental materials-E.C.Combe-6th ed www.indiandentalacademy.com 274
  275. 275. References  Frank and Nikolai. A comparative study of frictional resistance between orthodontic brackets and archwires. AJO 80;78:593-609  Burstone. Variable modulus orthodontics. AJO 81; 80:116  Kusy and Dilley. Elastic property ratios of a triple stranded stainless steel archwire. AJO 84;86:177-188  Stannard, Gau, Hanna. Comparative friction of orthodontic wires under dry and wet conditions. AJO 86;89:485-491Ingram, Gipe, Smith. Comparative range www.indiandentalacademy.com 275 of orthodontic wires AJO 1986;90:296-307
  276. 276. References  Ingram, Gipe, Smith. Comparative range of orthodontic wires AJO 1986;90:296-30  Arthur J Wilcock. JCO interviews. JCO 1988;22:484-489  Khier, Brantley, Fournelle,Structure and mechanical properties of as received and heat treated stainless steel orthodontic wires. AJO March 1988, 93, 3, 206-212  Twelftree, Cocks, Sims. Tensile properties of Orthodontic wires. AJO 89;72:682-687  Kapila & Sachdeva. Mechanical properties and clinical applications of orthodontic wires. AJO 89;96:100-109. www.indiandentalacademy.com 276
  277. 277. References  Arthur Wilcock. Applied materials engineering for orthodontic wires. Aust. Orthod J. 1989;11:22-29.  Julie Ann Staggers, Nicolas ,Clinical considerations in the use of retraction mechanics.. JCO June 1991  Klump, Duncanson, Nanda, Currier ,Elastic energy/ Stiffness ratios for selected orthodontic wires.. AJO 1994, 106, 6, 588-596  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. www.indiandentalacademy.com 277
  278. 278. References  Kusy, Mims, whitley ,Mechanical characteristics of various tempers of as received Co-Cr archwires.. AJO March 2001, 119, 3, 274-289  Eliades, Athanasios- In vivo aging of orthodontic alloys: implications for corrosion potential, nickel release, & biocompatibility –AO, 72,3,2002  Kusy.Orthodontic biomaterials: From the past to the present-AJO May 2002 www.indiandentalacademy.com 278
  279. 279. Thank you For more details please visit www.indiandentalacademy.com www.indiandentalacademy.com 279

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