Stainless steel and it’s application in orthodontics /certified fixed orthodontic courses by Indian dental academy

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  • 2. SYNOPSIS  Introduction.  History of stainless steel.  Composition and functions of each ingredient.  Types and grade of stainless steel.  Metallurgy.  Nature of metallic bonding.
  • 3. SYNOPSIS  Structure on solidification and grain structure.  Types of crystal lattice.  Crystal imperfections.  Physical properties.  Tensile strength  Proportional limit and Hooke’s law.  Mechanical properties.  Elasticity and Elastic limit.  Modulus of elasticity .  Ductility and malleability.  Yeild strength and ultimate strength
  • 4. SYNOPSIS  General properties of stainless steel.  Sensitisation.  Stabilisation.  Ductility and malleability.  Soldering and welding.  Strain hardening.  Cold working.  Heat treatment.  Annealing.  Hardening heat treatment
  • 5. SYNOPSIS  Characteristics of Clinical relevance.  Spring back.  Modulus of resilience.  Stiffness.  Load deflection rate.  Working range and flexibility.  Formability.
  • 6. SYNOPSIS  Stress relaxation.  Strength.  Biohostability.  Application in Orthodontic wires.  Ideal requirements of Orthodontic wires.  Wire characteristics and clinical relevance.  Variation in diameter and length it’s relation with strength stiffness and range.
  • 7. SYNOPSIS  Australian orthodontic arch wire.  Unique characteristics.  Manufacture, grading and color coding.  Advantages of stainless steel.  Disadvantages of stainless steel.  Conclusion.
  • 8. INTRODUCTION  Steel is an alloy of Iron and Carbon. Carbon content should not exceed 0.2% max.  When it contains 12 to 13% chromium it is called stainless steel.  Steel exists in three Ferritic, austenitic and martensitic forms.
  • 9. HISTORY  First developed by accident by Harry Brearley in Sheffield, England.  Stainless steel entered dentistry in 1919, introduced at Krupp’s dental poly clinic in Germany by F. Haupt Meyer.  In 1930 Angle used it to make ligature wires.  By 1937 the value of stainless steel as an orthodontic wire had been confirmed.  Stainless steel today is used to make arch wires,ligature wires, band material, brackets and buccal tubes.
  • 10. COMPOSITION TYPES CHROMIUM NICKEL CARBON FERRITIC 11.5-27% 0 0.2% MAX AUSTENITIC 16-26% 7-22% 0.25% MARTENSITIC 11.5-27% 0-2.5% 0.15-1.2% Minor quantities of Silicon, phosphurous, sulphur, Manganese, Tantalum. BALANCE COMPOSED OF IRON
  • 11. FUNCTIONS  Chromium:  Increases tarnish and corrosion resistance. A thin transparent, tough, impervious oxide layer of Chromium oxide forms on the surface of the alloy when subjected to room air.- “passivating film effect”.  Increases hardness, tensile strength and proportional limit.  Nickel:  Increases strength.  Increases tarnish and corrosion resistance.  Cobalt:  Decreases hardness.  Manganese:  Scavenger for sulphur.  Increases hardness during quenching.
  • 12. FUNCTIONS  Silicon:  Deoxidiser and scavenger.  Titanium:  Inhibits the precipitation of Chromium carbide.
  • 15. Types of crystal lattice – (FCC) Austenitic *  Most corrosion resistant of all types of stainless steel.  Formed between 912 – 1394C  AISI 302,304 – 18% Chromium, 8% Nickel and 0.15%(302) 0r 0.08%(304) Carbon – 18-8 stainless steel.  Austenite is pefered to Ferritic because of greater ductility, ability to undergo more cold work without fracture. Increased strength during cold working, ease of welding, readily overcomes sensitisation, less critical grain growth and ease of forming.  When austenite is allowed to cool slowly to room temperature it forms Fe3C and ferrite. The iron carbide compound is called cementite and the solid solution of ferrite along with cementite is called pearlite.
  • 16. Types of crystal lattice – (BCC) Ferritic  Stable between room temperature and 912 C.  Carbon has low solubility in this structure.  Interstices in BCC are very small.  ASI 400  Good corrosion resistance at low cost provided increased strength is not required.  Temperature change does not nduce phase change in solid state.  The alloy is not hardenable by heat treatment.  Not readily work hardenable.  Little application in Dentistry.
  • 17. Types of crystal lattice – (BCT) Martensitic.  If austenite is cooled rapidly (Quenched) it will undergo spontaneous diffisionless transformation to a Body Centered Tetragonal.  The lattice is highly distorted, strained resulting in a hard strong brittle alloy.  Martensite decomposes into ferrite and carbide.  Decomposition is accelerated by appropriate heat treatment to reduce hardness but this is counter balanced by increased toughness – “Tempering”  AISI 400
  • 18. Types of crystal lattice – (BCT) Martensitic.  Increased strength and hardness – used for surgical and cutting instruments.  Yeild strength of 492 MPa (annealed). Hardened – 1898 MPa  Brinell’s hardness range- 230 – 600.  Elongation – less than 2%.  Reduced ductility.  Corrosion rsistance is the least. Reduced further with Hardening heat treatment.
  • 19. PHYSICAL PROPERTIES.  stress:  Force per unit area.  Tensile, compressive or shear stress.  Strain:  Proportion of change in dimension to the applied stress.  Elastic strain: Original shape is regained.  Plastic strain: Original shape is not regained.  Elasticity:  Ability of the stressed material to return to it’s original form.  Elastic limit:  The greatest stress to which a material can be subjected so that it will return to it’s original dimension when the forces are released.  Hookes law:  Stress is proportional to strain within the proportional limit.  Proportional limit:  Greatest possible stress that can be induced in a material such that stress is directly proportional to strain.
  • 20. MECHANICAL PROPERTIES. • Modulus of Elasticity: This is a measure of stiffness of the material. Gives the flexibility of the wire component. 179 GPa • Strength: Capacity of a material to resist a deforming load without exceeding the limits of plastic deformation. Strength is proportional to the resiliency of the material. • Yield strength: The stress at which increase in strain is disproportionate to stress. 1579 MPa 0.2% plastic deformation. •Ultimate strength: The strength at which the material fractures. 2117 MPa •Tensile strength – 200 MPa •Resilience: Total energy storage capacity. The amount of energy absorbed by a structure when it is stressed within it’s proportional limit. •Knoop hardness: 600 • Stiffness: Force/ distance. It is the measure of resistance to
  • 21. GENERAL PROPERTIES  SENSITISATION:  When heated between 400 and 900 C 18-8 stainless steel loses it’s resistance to tarnish and corrosion.  Carbon atoms migrate to grain boundaries and combine with chromium to form chromium carbide where the energy is the highest.  If the stainless steel is severely cold worked the carbide precipitate along slip planes, as a result the areas deficient in chromium are less localized and carbides are more uniformly distributed.
  • 22. GENERAL PROPERTIES  Stabilization:  Introduction of any element which precipitates as carbide instead of chromium.  Titanium approximately six times the carbon content.
  • 23. GENERAL PROPERTIES  Ductility:  Ability of a material to be drawn into wires.  Ability of a material to withstand permanent deformation under tensile load without fracture.  Malleability:  Ability of a metal to withstand permanent deformation under compressive forces without fracturing.
  • 24. SOLDERING  It is a process of joining two metals by the use of a intermediate alloy which has a lower melting point.  Soldering temperature – 620 – 665 C.  Ideally silver solders are used- alloy of silver, copper, zinc to which tin and indium are added to lower the fusion temperature and improve solderability.  Technical considerations:  Needle like non luminous gas air flame is used.  Thinner the diameter of the flame, less the metal surrounding the joint is annealed.  The work is held 3mm beyond the tip of the blue cone in the reducing zone of the flame.  Soldering should be observed in shadow against a black background so the temperature can be judged by the color of the work. The color should not exceed dull red.  If possible the parts should be tag welded to hold the parts together.
  • 25. SOLDERING  The flux is applied and the heavier gauge is heated first.  Flux should cover all the area and the metal should be allowed to flow around the joint. The work should be immediately quenched in water.  Other methods of soldering:  Electric resistance heating.  Indirect heating using brass wire intermediary.
  • 26. SOLDERING  Flux:  Aids in removing the oxide coating so as to increase the flow.  Dissolves any surface impurities.  Reduces the melting point of the solder.  Composition:  Borax glass – 55%  Boric acid – 35%  Silica – 10%  Potassium flouride is added to dissolve the passivating effect of Chromium.  Potassium flouride and Boric acid should be in 1:1 concentration
  • 27. Welding  Joining of two or more metal pieces directly under pressure without introduction of an intermediary or a filler material.  Spot welding is used to join various components in orthodontics. A large current is allowed to pass through a limited area on the overlapping metals to be welded.  The resistance of the material to the flow of current produces intense localized heating and fusion of metals.  The welded area becomes susceptible to corrosion due Chromium carbide precipitation and loss of passivation.  The grain structure is not affected.  Increased weld area increases the strength.
  • 28. Factors to be taken into account during soldering and welding  As the annealing temperature of stainless steel falls within the soldering and welding temperature ranges, these procedure can lead to loss of working range and elasticity of the metal.  Precautions:  By using low fusing solders.  Using low diameter needle like flame.  Reducing the number of welding procedures and duration.
  • 29. Cold Working  The process of plastically deforming a metal at a temperature below that at which it recrystallises new grains, which is usually one-third to one half times is absolute melting point temperature.  The deformation of space lattices of stainless steel by mechanical manipulation at room temperature.
  • 30. Strain Hardening or Work Hardening.  If a metal is continuously stressed it becomes stiffer and harder.  Hardening of a metal by cold working is called strain hardening of work hardening.  During strain hardening dislocations tend to build up at grain boundaries. The barrier effect of grain boundaries will cause further slip to occur at intersecting slip planes. Point defects increase resulting in a distorted grain structure.  Consequences:  Increased surface hardness.  Greater yield and ultimate strength.  Less ductility.  Proportional limit is increased.  Reduced resistance to corrosion.  No change in elastic modulus.  Majority of these properties id due to a phase change from FCC to BCC lattice structure.
  • 31. Heat treatment  General process using thermal energy to change the characteristics of metallic alloys as in tempering, precipitation hardening or annealing. – Robert P Kusy 1997.  Annealing  Hardening
  • 32. Annealing  The effect associated with cold working such as strain hardening, low ductility and distorted grains can be reversed by simply heating the metal.  The greater the amount of cold working the more rapidly the effects can be reserved by annealing.  Stages of annealing:  Recovery.  Recrystallisation.  Grain growth.
  • 33. Annealing  Recovery:  Cold work properties begin to disappear.  Slight decrease in tensile strength and no change in ductility.  All the residual stress is relaxed.  Recrystallisation:  Old grains disappear totally and are replaced with strain free grains.  Occurs mostly in regions where defects have accumulated.  It attains it’s soft and ductile condition at the end of this stage.  Grain Growth  The Grain size and number of the recrystallised structure depends on the amount of prior cold working.  On repeated annealing larger grains consume smaller grains. At the end of annealing the number of grains decrease and size increases.
  • 34. Hardening heat treatment  There is no hardening heat treatment for austenitic steel due to it’s stability.  It can only be hardened by cold working.
  • 35. Characteristics of Clinical relevance  Spring back (maximum elastic deflection):  The extent to which the range recovers upon deactivation of an activated arch wire.  A measure of how far a wire can be deformed without causing permanent deformation or exceeding the limits of the material.  Higher the spring back, grater the working range and lesser are the requirements of frequent activations.  Stainless steel has a spring back lesser than Nickel-titanium or beta titanium.
  • 36. Characteristics of Clinical relevance  Resilience:  The capacity of a material to absorb energy when the material is elastically deformed.  It is measured by the area under the stress strain curve.
  • 37. Characteristics of Clinical relevance  Stiffness:  Amount of force required to produce a specific amount of deformation.  Stiffness d4
  • 38. Characteristics of Clinical relevance  Load deflection rate:  For a given load the deflection observed within the elastic limit.  The force magnitude delivered by an appliance and is proportional to the modulus of elasticity.  Low load deflection rate provides ability to apply low forces, a more constant force over time while deactivation, greater ease and accuracy in applying a given force.
  • 39. Working range and flexibilty  The distance a wire will bend elastically before permanent deformation occurs.  Measured in millimeter or other length units.  Flexibility is the measure of the amount at which the wire can be strained without undergoing plastic deformation.
  • 40. Formability  The ability to bend wires into desired configurations as loops, coils and stops without fracturing the wire.
  • 41. Stress relaxation  When a wire has been deformed and held in a fixed position the stress may diminish with time even though the total strain may remain constant.
  • 42. Biohostability  The ease with which a material will culture bacteria, spores or viruses.
  • 43. Ideal requirements of Orthodontic arch wires  Esthetic  Good range  Tough  Poor biohost  Good springback  Low friction  Weldable  Springy  Formable  Biocompatible  Resilient  Strong
  • 44. Variation in diameter and length of orthodontic wires STIFFNESS STRENGTH RANGE x MODULUS OF ELASTICITY X resiliency X elastic limit x 1/L3 X 1/length X L2 x d4 X d3 X 1/ d x1/ No of coils X no of coils X 1/coil dia3 X 1/ coil dia X coil dia 2
  • 45. Australian Orthodontic arch wires  Claude Arthur J Wilcock developed an orthodontic arch wire for use in the Beg technique.  Unique characteristics different from usual orthodontic arch wires.  They are ultra high tensile austenitic stainless steel arch wires.  The wires are highly resilient.  When arch wire bends are incorporated and pinned to the teeth the stress generated within the wire which generate a light force which is continuous in nature.  Wire is resistant to permanent deformation and maintains it’s activation for maximum control of anchorage.
  • 46. Australian Orthodontic arch wires  Manufacture:  Spinner straightening and pulse straightening.  Spinner straightening: The wire is passed through bronze rollers.  Pulse straightening: The wire is pulsed in a special machine which permits high tensile wires to be straightened.
  • 47. Australian Orthodontic arch wires  Types:  Regular  Regular plus  Special  Special plus  Extra special plus  Supreme  Premium plus
  • 48. Thank you For more details please visit