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Orthodontic archwires /certified fixed orthodontic courses by Indian dental academy


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Orthodontic archwires /certified fixed orthodontic courses by Indian dental academy

  2. 2. Contents Introduction  Physical Properties of archwires  Evolution of archwires  Gold  Stainless steel  Cobalt chromium  Nickel Titanium  Alpha & Beta titanium  Esthetic archwires  Conclusion 
  3. 3. Orthodontic wires which generate the biomechanical forces communicated through brackets for tooth movement ,are central to the practice of profession. In the rational selection of wires for a particular treatment ,the orthodontist should consider a variety of factors ,including the amount of force delivery that is desired ,the elastic range or springback ,formability and the need for soldering and welding to assemble the appliance
  4. 4.  With the need to maintain a relatively large inventory ,orthodontists must be concerned with the costs of wires ,which can vary considerably among wire alloys as well as among companies
  5. 5. PROPERTIES OF ORTHODONTIC WIRES Physical properties of materials can be considered as the ways that Materials respond to changes in their environment Physical properties : Descriptive of size, shape and appearance. Material properties : Subdivided into . •Characteristics that are independent of external influences simply termed “Material” properties. •Those that are associated in someway with the conditions of use or the use environment. e.g : Mechanical, Chemical, Thermal and Magnetic
  6. 6.
  7. 7. 1. Elastic or reversible deformation Proportional limit, Resilience, Modulus of Elasticity. 2. Plastic or irreversible deformation e.g :- Percent elongation. 3. Combination of Elastics Plastic deformation e.g :- Toughness and Yield strength
  8. 8. STRESS :When a force acts on a body tending to produce deformation a resistance is developed to this external force application. The INTERNAL reaction is equal in intensity and opposite in direction to the applied external force and is called stress. Stress( ) = Force/Area Commonly expressed as Pascal 1Pa = 1N/m2. It is common to report stress in units of Megapascals (MPa) where 1 MPa = 106 Pa. TYPES OF STRESS :- tensile ,compressive & shear
  9. 9. STRAIN :Whenever a force is applied to a body it undergoes deformation. Strain is described as the change in length (Δ L = L – LO) per unit length of the body when it is subjected to a stress. Change in length L – Lo ΔL Strain ( ) = = = Original length Lo Lo  Strain has no units of measurement.  It is a Dimensionless quantity.  Reported as an absolute value or as a percentage.
  10. 10. Strain Elastic Plastic Each type of stress is capable of producing a corresponding deformation in a body.  Tensile stress produces tensile strain.  Compressive stress produces compressive strain.  Shear stress produces shear strain.
  11. 11. STRESS STRAIN CURVE: Represents energy storage capacity of the wire so determines amount of work expected from a particular spring in moving a tooth.  Engineering Stress-Strain Curve  In the calculation of stress it is assumed that the cross sectional area of the specimen remains constant during the test. Stresses are calculated based on original cross sectional area.  
  12. 12.  True Stress Strain Curve :A stress strain curve based on stresses calculated from a Non Constant Cross sectional area is called a true stress strain Curve. A true-stress strain curve may be quite different from an engineering stress-strain curve at high loads because significant changes in the area of specimen may occur.
  13. 13.
  14. 14.  Poisson‟s ratio – When a tensile force is applied to an object ,the object becomes longer & thinner ,the ratio of accompanying strain in direction perpendicular to force application to the strain in the force direction is poisson‟s ratio
  15. 15. Important mechanical properties based on Elastic or reversible deformation are : ELASTIC MODULUS  FLEXIBILITY.  RESILIENCE Other properties that are determined from stresses at the end of elastic region of stress -strain plot and at beginning of plastic deformation region.  PROPORTIONAL LIMIT.  ELASTIC LIMIT.  YIELD STRENGTH
  16. 16. ELASTIC MODULUS (Young‟s Modulus or Modulus of Elasticity)  The term elastic modules describes the relative STIFFNESS or rigidity of a material which is measured by the elastic region of stress – strain diagram.  It is denoted by letter E  determined from stress stain curve by calculating ratio of stress to strain or slope of linear portion of curve. Stress Elastic Modulus = = Strain 
  17. 17.  Modulus of elasticity is independent of the ductility of a material and it is not a measure of its strength.  it is an inherent property of a material and cannot be altered appreciably by heat treatment, work hardening or any other kind of conditioning. This property is called STRUCTURAL INSENSITIVITY.
  18. 18. FLEXIBILITY :The maximum flexibility is defined as the strain that occurs when the material is stressed to its proportional limit. RESILIENCE :Popularly the term Resilience is associated with “springiness”.  It is defined as the amount of energy absorbed by a structure when it is stressed to its proportional limit. Area bounded by the elastic region is measure of Resilience
  19. 19. SPRINGINESS :Proportional to slope of elastic portion stress-strain curve. More Horizontal the slope Springier the wire having low stiffness TOUGHNESS Higher the strength and higher the ductility (total plastic strain) greater the toughness. The total area under the entire stress-strain curve is a measure of the energy required to fracture the material A tough material is generally strong although a strong material is not necessarily tough
  20. 20. BRITTLENESS :It is the relative inability of a material to sustain plastic deformation before fracture of a material occurs. ULTIMATE STRENGTH :Ultimate tensile strength or stress is defined as the maximum stress that a material can withstand before failure in tension. YIELD STRENGTH ( Yield Stress, Proof Stress) It is defined as the stress at which a material exhibits a specified limiting deviation from proportionality of stress to strain. Amount of permanent strain is arbitrarily selected for material being examined and may be indicated as 0.1%, 0.2% or 0.5% (0.001, 0.002, 0.005) permanent strain Amount of permanent strain may be referred to as PERCENT OFFSET. Many specifications use 0.2% as convention.
  21. 21. Proportional Limit :- (PL) It is defined as the greatest stress that a material will sustain without a deviation from the linear proportionality of stress to strain. Hooke‟s Law :- States that stress – strain ratio is constant upto the proportional limit, the constant in this linear stressstrain relationship is Modulus of Elasticity. Below PL no permanent deformation occurs in a structure. Region of stress stain Curve. Below PL – ELASTIC REGION Above Pl – PLASTIC REGION
  22. 22. ELASTIC LIMIT :- (EL) It is defined as maximum stress that a material can withstand before it undergoes permanent deformation.  For all practical purposes PL and EL represent same stress. But they differ in fundamental concept : PL deals with proportionality of strain to stress in structure.  EL describes elastic behavior of the material. EL & PL limits are usually assumed to be identical although their experimental values may differ slightly.
  23. 23. DUCTILITY AND MALLEABILITY :Ductility represents the ability of a material to sustain a large permanent deformation under tensile load without rupture. A material that may be drawn readily into a wire is said to be DUCTILE. Malleability :Ability of a material to sustain considerable permanent deformation without rupture under compression as in hammering or rolling into a sheet. - Gold is most ductile and malleable pure metal - Silver is second. - Platinum ranks 3rd in ductility. Copper ranks 3rd in malleability
  24. 24. Formability :It is defined as the amount of permanent deformation that a wire can withstand before failing. Represents the amount of permanent bending the wire will tolerate before it breaks. Can be interpreted as area under plastic region of stress – strain curve.
  25. 25.
  26. 26. SPRING BACK It represents the elastic strain recovered on unloading from permanent deformation range. Given by Expression :- YS/E. ( Yield strength / elastic modulus). In many clinical situations, orthodontic wires are deformed beyond their Elastic limit. Their spring back properties in portion of load deflection curve between elastic limit and ultimate strength are important in determining clinical performance. Unloading curve from the permanent deformation range for well behaved orthodontic wire alloys (i.e., other than NiTi wires) is parallel to the elastic loading curve the value of YS/E represents the approximately amount of elastic strain released by archwire on unloading
  27. 27.
  28. 28. . THREE BASIC ELASTIC PROPERTIES Three basic properties of elastic materials and devices follow :STIFFNESS STENGTH RANGE STIFFNESS :- It is a force / distance ratio that is a measure of resistance to deformation. It is a measure of the force required to bend or otherwise deform the material a definite distance.
  29. 29. STRENGTH : - It is a force value that is a measure of the maximum possible load, the greatest force the wire or arch arrangement can sustain or deliver if it is loaded to the limit to the material. RANGE :- (WORKING RANGE) It is defined as the distance that the wire will bend elastically before permanent deformation. Relationship b/w three elastic properties :Strength = Stiffness x Range. Factors that influence Strength Stiffness and Range :  Mechanical arrangement by which force is applied to teeth e.g :- bracket width, length of archwire, span and loops.  Form of wire itself – size and shape of cross section. Material including the alloy formula, its hardness etc
  30. 30.  BEHAVIOUR OF ARCHWIRE IN BENDING :- When an archwire is bent the metal is stretched along the outside curvature and compressed along the inside curvature.  This combination of tension and compression that resists bending and actually accomplishes energy storage in the spring action of wire 
  31. 31. Bending Moment :A measure of bending effort at any specified point in a beam, measured in units of force times distance (Ounce inches, grams-centimeters etc.) critical (dangerous) section :Maximum bending moment in a cantilever is at the supported end. In beam terminology the location of this maximum bending moment is called CRITICAL or DANGEROUS section
  32. 32.
  33. 33.  NEUTRAL AXIS: The part of a beam that is neither elongated nor compressed in bending. The neutral axis is like a flat ribbon through the center of the wire, midway between outer and inner curved sides.
  34. 34. . EFFECTS OF LENGTH AND CROSS SECTION ON ELASTIC PROPERTIES: EFFECTS OF LENGTH :IN BENDING :- 1 Stiffness Strength Range (Length)3 1 (Length) (Length)2
  35. 35.
  36. 36. BEHAVIOUR OF ARCHWIRE IN TORSION TORSION :Torsion is the actual twisting (strain) that takes place in the material as s result of the torque Torque is the force (Stress) that causes twist. In case of rectangular wire ”C” is the distance from center of wire to an outer corner instead of to one of the sides.
  37. 37. IN TORSION :There are no exponential effects of length in torsion. 1. Strength :- Length has absolutely no effect on strength. 2. Range :- Range in torsion is directly proportional to length 3. Stiffness :- Stiffness in torsion is inversely proportional to length.
  38. 38. EFFECTS OF CROSS SECTION - Most potent single factor available for control of orthodontic force application. IN BENDING Round Wires 1. Range „C‟ It is the distance b/w extreme fiber and neutral axis. „Index of working range of a bending wire 1 Range  C Therefore range is inversely proportional to diameter.
  39. 39. 2. Stiffness :Stiffness of wires depends on value called the Moment of Inertia (I). Moment of Inertia Property of the cross section of a beam that is proportional to the effect of the cross section on resistance to bending or twisting (Stiffness). Stiffness  (diameter)4
  40. 40. 3. Strength : Engineering term that defines strength in terms of wire‟s cross section is SECTION MODULUS – Denoted by letter Z. Z = I/C. Strength  (Diameter)3
  41. 41. Rectangular wires: In round wires  width and thickness are always same . Both are called Diameter and treated as single dimension. Width & Thickness  Vary independently of one another in rectangular wires. Width: Used to describe dimension perpendicular to direction of bending in plane of neutral axis. Thickness:  dimension in plane of bend
  42. 42.  Effect of width & thickness on range: Width has no effect on bending range of wire. Range is inversely related to thickness. 2. Effect of width on stiffness and strength: Width is directly proportional to strength and stiffness in rectangular wires. 1. 3. Effect of thickness on stiffness and strength: Stiffness  (Thickness)3 Strength  (Thickness)2
  43. 43.
  44. 44.
  45. 45. LABORATORY TESTS In 1977, ADA specification No. 32 was published. This ADA specification No. 32 for orthodontic wires not containing precious metals contains directive on testing, packaging and marketing of orthodontic arch wires. Properties of orthodontic arch wires are commonly determined by means of various laboratory tests. Mechanical properties of orthodontic wires are determined from:- Tension test - Bending test - Torsion test.
  46. 46. Bending test: Considered more representative of clinical conditions than the tension test. Provides information on behaviour of wires when subjected to 1st and 2nd order bends. Torsion tests: Reflect wire characteristics in third order direction Graphic descriptions: - Stress against strain in tension - Bending moment against angular deflection. Torsional moment against torque angle.
  47. 47. Elastic Bending test: Bending couple is applied at one end of specimen where only rotation is permitted ; at the other end of test span wire is held against fixed knife edge stop. Angular deformation measured is rotation of the shaft ( ). A typical plot of applied couple versus angular deformation is done. - Specified offset (2.9 according to ADA Sp. No. 32) is used to determine yield strength.
  48. 48. MANUFACTURING OF ORTHODONTIC WIRES Metallic orthodontic wires are manufactured by a series of proprietary steps, typically involving more than one company. Sources:- Stainless steel orthodontic wires are procured by suppliers from commercial sources of stainless steel. Ingot:- Initially the wire alloy is cast in the form of an ingot which must be subjected to successive deformation stages until cross section becomes sufficiently small for wire drawing. Rolling: The first mechanical step is rolling the ingot into a long bar. This is done by series of rollers that gradually reduce the ingot to a relatively small diameter.
  49. 49. Considerable work hardening of the alloy occurs during rolling.  It may fracture if rolling is continued beyond this point.  TO PREVENT THIS: Rolling process is interrupted Metal is ANNEALED by heating to a suitably high temperature
  50. 50. . Drawing: After ingot has been reduced to a fairly small diameter by rolling, it is further reduced to its final size by drawing. It is a forming process that is used to fabricate metal wire and tubing. Deformation is accomplished by pulling the material through a die by means of tensile force applied to the exit side of a die. Before it is reduced to orthodontic size, a wire is drawn through many series of dies and annealed several times along the way to relieve work hardening.
  51. 51.  Important proprietary details include: v Rate of drawing. v Amount of cross section reduction per pass. v Nature of intermediate heat treatments. v Die material. v Ambient atmosphere
  52. 52. RECTANGULAR WIRES: v Rectangular cross section wires are fabricated from round wires by a rolling process using TURK‟S HEAD which contains series of rolls. v Rectangular or square cross section wires – have some degree of rounding at corners (EDGE BEVEL).
  53. 53. SPRING PROPERTIES OF WIRES: Hardness and spring properties of most orthodontic wires depend almost entirely on effects of work hardening during manufacture. v If metal is almost in need of another annealing at its final size – it will have maximum work hardening and spring properties. v If drawing is carried too far enough after last annealing – wire will be brittle. If drawing is not carried far enough after last annealing – too much residual softness and very low working range and strength
  54. 54. STRUCTURE OF METALS AND ALLOYS ALLOY: A solid mixture of a metal with one or more other metals or with one or more non metals which are mutually soluble in molten state is called an alloy. e.g., Steel – Alloy of iron and carbon Stainless steel alloy of iron, carbon and chromium. PHASE: A phase is any physically distinct, homogenous and mechanically separable portion of a system. SOLID SOLUTION: An alloy phase in which one alloying elements enters space lattice of the other.
  55. 55. GRAIN:- Metal is made up of thousands of tiny crystals. Such a metal is said to be polycrystalline and each crystal in a structure is called GRAIN. UNIT CELL:- The smallest division of the crystalline metal that defines the unique packing is called unit cell.
  56. 56. Crystal System Space Lattice Cubic Simple cubic Body-centered cubic Face-centered cubic Tetragonal Simple tetragonal Body-centered tetragonal Orthorhombic Simple orthorhombic Body-centered orthorhombic Face-centered orthorhombic Base-centered orthorhombic Rhombohedral (Trigonal) Simple rhombohedral Hexagonal Simple hexagonal Monoclinic Simple monoclinic Base-centered monoclinic Triclinic Simple triclinic
  57. 57. DEFORMATION IN METALS – ATOMIC LEVEL VIEW: 1. Elastic strain: v Atoms are shifted from their equilibrium positions by fraction of their atomic spacing. v When stress is removed atoms return to equilibrium atomic spacing. 2. Plastic Deformation: This mode of deformation requires that atoms be shifted to new atomic sites on lattice. Mechanism of plastic deformation is called “DISLOCATION MOTION”.
  58. 58.
  59. 59. LINE DEFECTS (DISLOCAITONS): e.g., Edge dislocation: Dislocation line:- The lattice is regular except for one plane of atoms which is discontinuous forming a dislocation line. The plane along which dislocation moves is known as SLIP PLANE.
  60. 60.  POINT DEFECTS
  61. 61. STRAIN HARDENING / WORK HARDENING:Process resulting from cold working (i.e., deformation at room temperature) as a result of which greater stress is required to produce further slip and the metal becomes stronger, harder and less ductile. Ultimate result of strain hardening with further increase in cold working is FRACTURE. RESULTS OF STRAIN HARDENING:v Increased surface hardness, strength and PL. v Decreased ductility and resistance to corrosion.
  62. 62. CAUSES OF STRAIN HARDENING:If dislocation during translation meets some other type of lattice discontinuity, its gliding movement under stress might be inhibited. Such discontinuities are: POINT DEFECTS.  Collision of one dislocation with different type  Foreign atom or group of atoms of different lattice characteristics.  GRAIN BOUNDARIES
  63. 63. . HEAT TREATMENT: A process characterized by the transfer of energy in the form of heat to a metallic material to alter its mechanical and / or thermal properties. Carried out in 3 Steps:1. System temperature is elevated by placing it in a high temperature environment. (e.g., furnance or a hot salt bath or by electric resistance/ induction heating). 2.Upon reaching desired temperature the system is maintained there for a specific period of time. 3.System is returned to its initial state temperature.
  64. 64.
  65. 65. TYPES OF HEAT TREATMENT: 1.Stress relief heat treatment. 2.Annealing heat treatment. 3.Hardening heat treatment.
  66. 66. 1. Stress relief heat treatment:Releases the stresses incorporated in metal due to cold working procedures. Mechanism: Internal stresses are relieved by minute slippages and readjustments in intergranular relations without loss of hardening. e.g., - Recommended temperature for stress relieving stainless steel is 750F (399C) for 11min.
  67. 67. 2.Annealing heat treatment: A heat treatment process employing a relatively high temperature that results in recrystallisation of microstructure and produces marked changes in mechanical properties. Stages of annealing:  Recovery Recrystallisation Grain growth. Temperature are substantially above that of stress relief – Annealing of stainless steel requires few minutes at 1800-2000F.
  68. 68. 3. Hardening heat treatment (precipitation hardening): Process by which a metal alloy is hardened and strengthened by extremely small and uniformly dispersed particles that precipitate from a supersaturated solid solution. - Also called Age hardening. - Long term process (of several hours). Carried out at temperature somewhat below that necessary to anneal followed by rapid quenching. e.g., heat treatment of Co-Cr alloy to increase their strength and resilience.
  69. 69.      CHEMICAL INFLUENCES: Oral cavity environment is inherently corrosive. The oral fluids are strong, potential reactants toward oxidation of metals. CORROSION: A chemical or electrochemical process through which a metal is attacked by natural agents such as air and water, resulting in partial or complete dissolution, deterioration or weakening of any solid substance. TARNISH: A process by which a metal surface is dulled in brightness or discolored through formation of chemical film such as sulfide and an oxide. Tarnish is often forerunner of corrosion
  70. 70. 1. Galvanic corrosion: An accelerated attack occurring on a less noble metal when electrochemically dissimilar metals are in electrical contact in presence of liquid corrosive environment. - Also known as Dissimilar metals corrosion. 2. Stress corrosion: Cold working of an alloy by bending, burnishing etc localizes stresses in some parts of the structure.  A couple composed of stressed metal, saliva and unstressed metal is formed.  Stressed area is more readily dissolved by the electrolyte
  71. 71. 3. Concentration cell corrosion: e.g., crevice corrosion. Accelerated corrosion in narrow spaces caused by localized electrochemical processes and chemistry changes such as acidification and depletion of O2 content. OTHER TYPES OF CORROSION: Pitting corrosion. Microbiologically induced corrosion. Fretting corrosion
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  74. 74.
  75. 75. EVOLUTION OF ORTHODONTIC ARCHWIRES GOLD :Up until 1930‟s the only orthodontic wires available were made of Gold and their alloys. 1887 – Angle tried replacing noble metals with German silver (Neusilber) a Brass (65% Cu, 14% Ni, 21% Zn). Gold alloys Esthetically pleasing Excellent Corrosion resistance Low proportional limit. The material that was to truly displace noble metals was stainless steel. 1940‟s :With the substantial rise in the cost of gold Austenitic stainless steel began to displace gold. 
  76. 76. In early 1940 s Begg partner with Wilcock to make what they envisioned to the ultimate in resilient orthodontic wires – AUSTRALIAN STAINLESS STEELS. By 1960s gold was universally abandoned in favour of stainless steel. In 1960s :Cobalt –Chromium alloys were introduced. Their physical properties were very similar to stainless steel. However they had the advantage that they could be supplied in softer and more formable state that could be hardened by heat treatment . In 1962 :Buehler discovers Nitinol at Naval Ordinance laboratory.
  77. 77. In 1970 :- Andreasen brought this intermetallic composition of 50% Ni and 50% Ti to orthodontics through University of Iowa. Unitek company licensed the patent (!974) and offered a stabilized martensitic alloy that doesn‟t exhibit shape memory effect under the name NITINOL. In 1977 : Beta titanium was introduced to orthodontic profession by C.J Burstone and Jon Goldberg. This beta titanium alloy had a modulus closest to that of traditional gold along with good springback, formability and weldability.
  78. 78. In 1984 : Mr. A.J Wilcock Jr. as per request of Dr. Mallenhauer of Melbourne Australia resulted in production of Ultra high tensile stainless steel round wires – The SUPREME GRADE. In 1985 :Burstone reported of an alloy, Chinese NiTi developed by Dr. Tien Hua Cheng and associates at the General Research Institute for nonferrous metals in Beijing china. In 1986 : Miura et al reported on Japanese NiTi, an alloy developed at Furukawa Electric Company Limited Japan in 1978. Both of these alloys i.e Chinese NiTi and Japanese NiTi are active austenitic alloys that form Stress Induced Martensite (SIM)
  79. 79. In 1988 : Mr. A.J Wilcock Jr. develops much harder. Alpha Titanium archwires. In 1990 : Neo-Sentalloy is introduced as a true active martensitic alloy. In 1992 : Optiflex a new Orthodontic archwire – developed by M.F Talass. Combined unique mechanical properties with a highly esthetic appearance. In 1994 :Copper NiTi, a new quaternary alloy containing Ni, Ti, Cu and Cr was invented by Dr. Rohit Sachdeva. Display phase transition at 27 C, 35 C, 40C.
  80. 80. In 2000 :Titanium Niobium – an innovative new arch wire designed for precision tooth to tooth finishing reported by Dalstra et al. Additional progress in orthodontic arch wire materials including composite “plastic” wires is being made.
  81. 81. GOLD ALLOYS I .
  82. 82. . COMPOSITION :Similar to type IV gold casting alloys. Two types of gold wires are recognized in ADA Sp. No. 7 Type I wire (75% gold) High noble or Type II wire (65% gold) Noble Metal alloys
  83. 83. Wire type Gold Platinu m Palladiu m Silve r Coppe r Nicke l Zin c ADA Type I 54-63 7-18 0-8 9-12 10-15 0-2 00.6 ADA Type II 60-67 0-7 0-10 8-21 10-20 0-6 01.7 P-G-P 25-30 40-50 25-30 0-1 42-44 P-S-C 16-17 3841
  84. 84. General effects of Constituents Pt and Pd   the fusion temperature. Copper  Contributes to ability of alloy to AGE HARDEN Nickel Strengthens the alloy. Zinc  Scavenger agent.
  85. 85. . MECHANICAL PROPERTIES : Yield strength 50 x 103 – 160 x 103 p.s.i Elongation 3 – 16%. Modulus of Elasticity 15 x 106 p.s.I . HEAT TREATMENT:Strengthened to variable stiffnesses with proper heat treatment, although they are typically used in the as – drawn condition. Accomplished by :Heating at 450 C (842 F) for 2 min. Cooling to 250 C (482 F) over a period of 30 min . Quenching to room temp.
  86. 86. ADVANTAGES : Good formability.  Capable of delivering lower forces than stainless steel.  Easily joined by soldering.  Excellent corrosion resistance. DISADVANTAGES : High Cost.  Low proportional limit / yield strength. USES :Only the Crozat appliance is still occasionally made from gold following original design of early 1900s.
  88. 88. . HISTORICAL BACKGROUND : The corrosion resisting steel was reported by Berno Strauss and Edward Maurer of Germany in Journal Stahl Undeisen in 1914.  Stainless steel (SS) entered dentistry in 1919 Introduced at Krupp‟s Dental Polyclinic in Germany by the company‟s dentist Dr. F. Hauptmeyer. He first used it to make a prosthesis and called it Wipla (Wieplatin ; In German like platinum). By 1937 – value of SS as an orthodontic material had been confirmed.
  89. 89. . METALLURGICAL ASPECTS :Steels – Iron based alloys that usually contain less that 1.2% carbon. Lattice arrangements of Iron Ferrite Austentite Martensite Ferrite :- ( - iron)  Pure iron has BCC structure at room temp  Stable upto 912 C.  Carbon has a very low solubility in ferrite (0.02 wt %) – because spaces between atoms in BCC structure are small and oblate. Austenite :- ( - Iron )  Face centred Cubic (FCC) structure.  Exists between 912 C - 1394C. Maximum carbon solubility of 2.1 weight %.
  90. 90. Martensite :  It Austenite is cooled rapidly (quenched).  Undergoes a spontaneous DIFFUSIONLESS transformation to Body Centered tetragonal (BCT) structure.  Highly distorted and strained lattice.  Hard, strong, brittle.
  91. 91. TEMPERING :Heat Martensite Ferrite + Carbide Treatment (525 C) This process results in -  The hardness  toughness
  92. 92. COMPOSITION AND TYPES OF STAINLESS STEEL :Steel + 12-30% Chromium  STAINLESS STEEL  When at least 10-12% Chromium is present.   A Coherent oxide layer formed that passivated the surface rendering the alloy „STAINLESS‟ CLASSIFICATION : Steels are classified according to the American Iron and Steel Institute (AISI) system. Ferritic Three types of stainless steel Austenitic Martensitic
  93. 93. TYPE (Space lattice) CHROMIUM NICKEL CARBON 11.5 – 27 0 0.20 max. Austenitic (FCC) 16 –26 7 – 22 0.25 max. Martensitic (BCT) 11.5 – 17 0 – 2.5 0.15 – 1.20 Ferritic (BCC) BALANCE is Iron
  94. 94. Ferritic Stainless steels – AISI 400 series  Provide good corrosion resistance at a low cost provided that high strength is not required.  Not readily work hardenable.  Finds little application in dentistry. Martensitic Stainless steels – AISI 400 Series  High strength and hardness.  Less corrosion resistant and less ductile. Used for surgical and cutting instruments
  95. 95. Austenitic Stainless Steel – AISI 300 series Most commonly used for orthodontic materials. Most corrosion resistant of the stainless steels. AISI 302 Three Types AISI 304 AISI 316 L 18% Chromium. AISI 302 8% Nickel. 0.15% Carbon. Balance iron
  96. 96. Function of Nickel - Stabilizes Austenite phase at room temp so it is an “AUSTENIZING ELEMENT”. Other e.g :- Mn and N. Mechanism : Makes diffusion of carbon so low that Austenite cannot decompose to pearlite and temperature is too low to allow formation of Martensite. AISI 304 :- Similar Composition Chief difference  Carbon content (0.08%) Both 302 and 304 stainless steel are designated as 18-8 stainless steel Type 316 L – „L‟  Low Carbon Content Carbon content  0.03% max. carbon Used for implants.
  97. 97. Austenitic stainless steel is preferable to Ferritic SS b‟coz  Greater ductility and ability to undergo more cold work without fracturing.  Substantial strengthening during cold working  Greater ease of welding.  Ability to fairly readily overcome sensitization. 
  98. 98. 1. STIFFNESS :- High stiffness demonstrated by large values of Modulus of Elasticity.  Necessitate use of smaller wires for alignment of moderately or severely displaced teeth.  Advantageous in resisting deformation caused by extra and intraoral tractional forces. 160-180 GPa 2. SPRING BACK :SS has lower spring back than those of newer titanium based alloys.- .0060-.0094
  99. 99. 3. RESILIENCE OR STORED ENERGY :Represents work available to move teeth. Resilience of activated SS wires is substantially less than that of Beta titanium and Nitinol wires. Clinical Relevance : Implies that stainless steel wires produce higher forces that dissipate over shorter periods of time than either beta titanium or nitinol wires, thus requiring more frequent activation or archwire changes. 4. FORMABILITY :Excellent formability,yield strength- 1100-1500MPa 5. JOINABILITY :SS wires can be soldered and welded. Stainless steel wires can be fused together by welding but this generally requires reinforcement with solder.
  100. 100. Important Considerations in Soldering SS : SS wire should not be heated to too high temp  To minimize Carbide precipitation.  To Prevent excessive softening of wire.  Use of low fusing sliver solders (620 C - 665 C). Silver solders corrode in use because they are anodic to stainless steel.  Fluoride containing fluxes should be used because they dissolve the passivating film formed by chromium. Solder does not wet the metal when such a film is present. Welding : Needs reinforcement by solder Bands and Brackets are usually welded.
  101. 101. BIOCOMPATIBILITY AND ENVIRONMENTAL STABILITY :CORROSION RESISTANCE :SS owes it corrosion resistance to Chromium – a highly reactive base metal . A thin transparent but tough and impervious oxide layer ( Cr2 O3 forms [PASSIVATION] on surface of alloy when it is subjected to oxidizing atmosphere such as room air. O2 is necessary to form and maintain the film. Causes of Corrosion of Stainless Steel : Any surface roughness or unevenness.  Incorporation of bits of Carbon steel or similar metal in its surface.
  102. 102.  Stress Corrosion. Severe strain hardening may produce localized electric couples in presence of an electrolyte such as saliva.  Soldered joints. Attack by solutions containing chlorine 
  103. 103. Classification Example Acetic acid Vinegar Copper chloride Certain appliance cleansers Fatty acids By - products of the micro-organism, Streptococcus mutans General foods Beet juice Hydrogen sulfide Effluent of mouth air Lactic acid Spoiled milk Phosphoric acid Colas Salt water Saliva Sodium hypochlorite Certain appliance cleansers Sulfite solution Wine Zinc chloride Certain mouth washes and certain appliance cleansers
  104. 104. SENSITIZATION OF 18-8 SS :18–8 stainless steel may loose its resistance to corrosion if it is heated b/w 400 C-900C. The reason for decrease in corrosion resistance is :  Precipitation of Chromium Carbide (Cr3 C) at the grain boundaries.  Formation of Cr3-C is most rapid at 650C. Chromium is depleted adjacent to grain boundaries. When chromium combines with carbon its passivating qualities are lost  Chromium is depleted adjacent to grain boundaries.  Alloy becomes susceptible to INTERGRANULAR CORROSION.
  105. 105. Methods to Minimize Sensitization :1. Keeping out of sensitizing temp range (425 - 650 C) 2. Controlling the Carbon. 1. Controlling temp to prevent intergranular corrosion :Speed in handling metal in sensitizing temp range – effective means of minimizing sensitization. e.g Quenching immediately after soldering.
  106. 106. 2. Stabilization of stainless steel :Objective  To make Carbon unavailable for sensitizing action Introduction of some element that precipitates as a carbide in preference to chromium. e.g :- Titanium and Columbium.  Titanium is introduced in an amount approx 6 times the carbon content. Steel that has been treated in any of the foregoing ways to reduce the available Carbon is called STABILIZED STEEL.  Stabilized steel is less susceptible to Intergranular corrosion, but it is still not 100% safe.
  107. 107.  FRICTION :- Low levels of bracket / wire friction have been reported with experiments using stainless steel wires. This signifies that stainless steel arch wires offer lower resistance to tooth movement than other orthodontic alloys
  108. 108. . HEAT TREAMENT :STRESS RELIEVING HEAT TREATMENT Only heat treatment used with stainless steel after bending wire into an arch, loops or coils. Purpose : Causes significant decrease in residual stress.  Enhances elastic properties of wire – slight  resilience. Temperature :- Recommended temperature time schedule is 750 F (399 C) for 11 min 
  109. 109. Funk (1951) :Recommends use of color Index to determine when adequate heat treatment is achieved. He suggests a straw colored wire indicates that optimum heat treatment has been attained.  METHODS OF HEATING :1. Oven is most reliable medium for heat Rx because of its relatively uniform temperature. 2. Heating the wire with Electric current from a welder or special heat treating power source. Disadvantage: Lack of uniform temperature. 
  110. 110. I. SOLID STAINLESS STEEL ARCH WIRES Are available in :1. Various sizes and cross sections Round  0.012, 0.014, 0.016, 0.018, 0.020 etc. Rectangular  0.016x 0.022, 0.017x 0.025, 0.018x 0.025, 0.019x 0.025 etc. Square  0.016 x 0.016 , 0.017 x 0.017 
  111. 111.
  112. 112. 2. Various Grades :American Orthodontics  Dentaurum Unitek RMO Available in Standard Gold tone Super Gold tone Super special spring hard Extra spring hard Spring hard Standard Resilient Resilient arch wire temper Retainer wire temper Clasp wire temper Ligature wire temper Spooled forms Straight lengths Preformed arches
  113. 113.       Preformed arches :Tru – Arch arch forms (A company) Natural arches (American Orthodontics) Preformed Anatomically Refined arches (Ormco) Pentamorphic arches (RMO) Standard and Proform (Ortho Organizers).
  114. 114. . MULTISTRANED STAINLESS STEEL WIRES : Composed of specified numbers of thin wire sections coiled around each other to provide round or rectangular cross section.  Idea behind Multistranded Wires : To improve strength and at the same time to maintain desirable stiffness and Range properties, many small wires are twisted together and even swaged or spot welded.  Result is an inherently high elastic modulus material behaving as a low stiffness member because of its Co-axial spring like nature. 
  115. 115. overall stiffness of the orthodontic appliance (S) is determined by the wire stiffness (Ws) and design stiffness (As) as represented by: S = Ws x As Design stiffness (As) is dependent on factors such as interbracket distance and the incorporation of loops and coils into the wire. Altering the cross-sectional stiffness (Cs) and/or the material stiffness (MS) as designated by the formula, on the other hand, can bring about changes in wire stiffness (Ws). Ws = Ms x Cs
  116. 116.
  117. 117. PROPERTIES : Kusy and Dilley (1984) :Investigated strength, stiffness and spring back properties of Multistranded SS wires in a bending mode of stress. They noted that  Stiffness of triple stranded 0.0175 inch (3 x 0.008 inch) SS arch wire was similar to that of 0.010 inch single stranded SS wire.  25 % stronger than 0.010 inch SS wire.  0.0175 inch triple stranded wire and 0.016 Nitinol demonstrated similar stiffness. Nitinol tolerated more than 50% greater activation than multistranded wire. Triple stranded wire – half as stiff as 0.016 inch Beta titanium wire.
  118. 118. Ingram, Gipe and Smith (1986)  Titanium alloy wires and multistranded SS wires have low stiffness when compared with solid SS wires.  Multistranded wires – spring back similar to Nitinol but greater as compared to solid SS or Beta titanium wires.  Multistranded and titanium wires have spring back properties that are relatively independent of wire size unlike solid stainless steel wires in which springback decreases with increasing thickness.
  119. 119. Clinical applications - Compare favourably with titanium wires. Provide a viable alternative to more expensive titanium wires for initial leveling. Braided rectangular steel wires are available in variety of stiffnesses and the stiffest of these is 0.021 x 0.025 – useful in 0.022 slot for finishing.
  120. 120. Examples :1. Ormco Corporation : Triple flex (Triple stranded twisted wire).  Respond (Coaxial – 6 stranded).  D-rect (Braided Rectangular stranded)  Force 9 (Braided Rectangular stranded). 2. TP Orthodontics :- Co-Ax wire ( 5 strands) 3. Unitek :- Twist flex (Triple stranded) 4. RMO :- Triflex (3 strands, twisted – 8 – 9
  121. 121. . AUSTRALIAN ARCH WIRES Historical Background :Wilcock archwires have been the mainstay of Begg technique. In 1940 S :Dr. Begg met Mr. Arthur J. Wilicok Sr. of Whittlesea, Victoria who was directing metallurgical research projects at University of Melbourne. After many years of research and development introducing high tensile wires Mr. Wilcock produced cold drawn heat treated wire that combined the balance between hardness and resiliency with unique property of zero stress relaxation. Different grades of Australian wires formerly used
  122. 122. Regular Grade :Lowest grade and easiest to bend. Used for practice bending. Regular plus : Used for auxiliaries and archwires when more pressure and resistance to deformation is required. Special Grade :0.016 is often used for starting archwires in many techniques. Special plus :Routinely used by experienced operators Hardness and resiliency of 0.016 is excellent for supporting anchorage and reducing deep overbites. Must be bent with care. Extra Special plus grade (ESP) :  This grade is unequalled in resiliency and hardness  Difficult to bend and brittle.
  123. 123. RECENT ADVANCES IN AUSTRALIAN WIRES A.J Wilcock scientific and Engineering Company. Announced new series of wire grades and sizes. The fundamental difference for the superior properties for these new wires is use of new manufacturing process called PULSE STRAIGHTENING. Wires are straightened by use of 2 processes :1. SPINNER STRAIGHTENING. 2. PULSE STRAIGHTENING.
  124. 124. 1. SPINNER STRAIGHTENING :Mechanical process of straightening materials usually in cold drawn condition. Wires are straightened by process of REVERSE STRAINING. Flexing in a direction opposite to that of original bend (This is what is done manually in clinical setting). In conventional manufacturing wire is pulled through high speed rotating Bronze rollers which torsionally twist the wire into straight condition. Disadvantage : Resultant deformation.  Decreased yield strength in tension and compression as compared to that of the “as drawn” material. 
  125. 125. 2. PLUSE STRAIGHTENING : This process was developed to overcome above mentioned difficulties. Has several advantages over other straightening methods : Permits higher tensile wires to be straightened.  Material yield strength is not diminished in any way. Wire has smoother surface and hence less bracket friction. 
  126. 126. NEWER GRADES OF WILCOCK WIRES :3 more grades have been introduced :  Premium  Premium plus  Supreme PROPERTIES :Higher yield strength of newer grade wires influences following properties :-
  127. 127. 1. SPRINGBACK - (YS/E) :– Newer grade wires have better springback than lower grade wires. 2. RESILIENCY – (YS2/2E) :For the same material (ie with same modulus of elasticity) higher yield strength results in greater resiliency. This means that higher grade wires store or absorb more energy per unit volume before they get permanently deformed. Higher YS results in greater resiliency. 3. ZERO STRESS RELAXATION :Ability of wire to deliver over long periods a constant force when subjected to an external load. Newer wires maintain their configuration over long periods against deforming forces (forces of occlusion). Forces generated by them remain practically unaffected over long periods.
  128. 128. 4. FORMABILITY :- For the same material greater resiliency lesser the formability. Theses wires are more brittle than lower grade wires and need to be bent in specific way.  Warm the wire by pulling through fingers before bending because these wires have a ductile brittle transition temp. slightly above room temp.  Bend the wire around square beak of pliers.
  129. 129. CLINICAL USAGE OF NEW GRADES OF AUSTRALIAN WIRES :Their specific applications are :1. When relatively high load deflection rate is required :a) For generating relatively lighter forces in stage I (for incisor intrusion and lateral contraction or expansion of post teeth).  0.016 or 0.018 Premium + or P wires are used. b) Large resistance to deformation is required e.g., :Maintaining arch from  0.018 P or P + or 0.020 P wires are indicated.  Similarly for overcoming undesired reactions of a torquing auxiliary or uprighting springs in IIIrd stage – 0.020 P wire is employed
  130. 130. 2. When a low load deflection rate is required. Supreme grade arch wires of sizes 0.008 – 0.011 are used for : Unravelling of crowded anterior teeth.  MAA (Mollenhauer aligning auxiliary)  Miniuprighting springs. 0.010 Supreme : Used to form Reciprocal torquing auxiliaries.  Best indicated for incisially activated mouse traps and Minisprings. 0.011 /0.012 supreme : Used for aligning second molars towards and of stage III. 0.012 Supreme – Torquing Auxiliary in Stage III because of its high resiliency and springback
  131. 131. IV. RECENT ADVANCES IN STAINLESS STEEL METALLURAGY :1. NICKEL FREE STAINLESS STEEL :The steel Din 1.4456 with its variations is one of them. COMPOSITION :15 – 18% Chromium. 3 – 4% Molybdenum 10 - 14% Manganese. 0.9 % Nitrogen – To compensate for Ni. Nickel is no more an alloying element (but only an impurity). Orthodontic wires  Menzamium (Scheu Dental)  Noninium (Dentaurum
  132. 132. Menzanium Wire : SS is fabricated in a patented high pressure melting process where Manganese and Nitrogen replace allergic components of Ni.  Ideal for Ni sensitive patient.  Corrosion resistant and durable. Availability :Supplied by Great lakes orthodontics. Grade :- Hard and spring Hard. Sizes :- 0.028, 0.032, 0.036.
  133. 133. Thank you For more details please visit