Stainless steel final /certified fixed orthodontic courses by Indian dental academy


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Stainless steel final /certified fixed orthodontic courses by Indian dental academy

  1. 1. STAINLESS STEEL INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. STAINLESS STEEL Introduction Carbon steel History Structure Composition Classification Properties Hyper & Hypo Eutectoid steels Duplex stainless steel Manufacture of stainless steel Corrosion Sensitization Functions of alloying elements Heat Treatment Types of stainless steel arch wires Merits of stainless steel wire alloys A.J. Wilcock Wire
  3. 3. Stainless Steel Introduction Orthodontic wires, which generate the biomechanical forces communicated through brackets for tooth movement are central to the practice of the profession.
  4. 4. CARBON STEEL  The American Iron and Steel Institute (AISI) defines carbon steel as follows:  Steel is considered to be carbon steel when no minimum content is specified or required for chromium, cobalt, columbium [niobium], molybdenum, nickel, titanium, tungsten, vanadium or zirconium, or any other element to be added to obtain a desired alloying effect.
  5. 5.    Carbon steel can be classified, according to various deoxidation practices, as rimmed, capped, semi-killed, or killed steel. Deoxidation practice and the steelmaking process will have an effect on the properties of the steel. However, variations in carbon have the greatest effect on mechanical properties, with increasing carbon content leading to increased hardness and strength. As such, carbon steels are generally categorized according to their carbon content. Generally speaking, carbon steels contain up to 2% total alloying elements and can be subdivided into low-carbon steels, medium-carbon steels, high-carbon steels, and ultrahigh-carbon steels
  6. 6. Low-carbon steels contain up to 0.30% C. The largest category of this class of steel is flat-rolled products (sheet or strip), usually in the coldrolled and annealed condition. The carbon content for these highformability steels is very low, less than 0.10% C, with up to 0.4% Mn. Typical uses are in automobile body panels, tin plate, and wire products.
  7. 7.  Medium-carbon steels are similar to lowcarbon steels except that the carbon ranges from 0.30 to 0.60% and the manganese from 0.60 to 1.65%. Increasing the carbon content to approximately 0.5% with an accompanying increase in manganese allows medium carbon steels to be used in the quenched and tempered condition.
  8. 8.   High-carbon steels contain from 0.60 to 1.00% C with manganese contents ranging from 0.30 to 0.90%. Highcarbon steels are used for spring materials and highstrength wires. Ultrahigh-carbon steels are experimental alloys containing 1.25 to 2.0% C. These steels are thermo mechanically processed to produce microstructures that consist of ultra fine grains of spherical, discontinuous proeutectoid carbide particles.
  9. 9.   Carbon steels are steels whose alloying elements do not exceed the following limits: Element Max weight Element Max weight % C 1.00 Cu 0.60 Mn 1.65 P 0.40 Si S 0.60 0.05
  10. 10. Disadvantages of carbon steel.      The hardenability is low. The physical properties (Loss of strength and brittle) are decreased by both high and low temps Subject to corrosion in most environments Toughness and formability are quite low. Not recommended for welding  These properties of carbon steel lead to the development of stainless steel by alloying with chromium and less than 1-2 % carbon.
  11. 11. STAINLESS STEEL  Extensively used in dentistry. Used for almost all components of fixed appliance and removable appliance  HISTORY  Discovered in England by Sheffield metallurgist during early first world war. Introduced for the construction of orthodontic appliances in Ireland by Friel (1933) By 1950, Stainless Steel alloys were used for most orthodontic wires.   
  12. 12. STRUCTURE    Steel are iron based alloys, that contain less than 1-2% carbon. The different classes of steel evolve from possible lattice arrangement of Iron (Fe) Pure Iron at room temperature has a body-centered cubic. (BCC) Structure and is referred to as “FERRITE” This phase is stable up to 912oC (1674F). The spaces between atoms in the BCC structure are small and oblate, hence “C” has a very low solubility in ferrite.
  13. 13. At temperature between 912oC & 1394oC stable form of iron is a Facecentered cubic (FCC) structure called Austenite. The interstices in the FCC lattice are larger than those in the BCC. However the size of the “C” atom is such that the lattice strain still limits the maximum carbon solubility to 2.11 wt%.
  14. 14. When austenite is cooled slowly from high temperature, the excess “C” not soluble in ferrite form FeC3. This hard brittle phase adds strength to the relatively soft and ductile ferritic and austenitic forms of Fe. However this transformation requires, Diffusion and a defined period of time. If the austenite is cooled very rapidly (Quenched) it transformation to a Tetragonal structure called martensite. This lattice is highly distorted and strained resulting in a very hard, strong, brittle alloy.
  15. 15. Composition When chromium (12-30%) is added to steel the alloy is called stainless steel. Other Constituents of stainless steel are.  Chromium  Nickel  Carbon  Silicon  Phosphorus  Sulphur  Manganese  Tantalum  Niobium
  16. 16. COMPOSITION. IRON 73-74% CHROMIUM 18% NICKEL 8% CARBON 0-0.2%
  17. 17. Classification The classification is based on the previously described crystal structure.  Ferritic  Martensitic  Austenitic
  18. 18. Composition in % Type of lattice cr ni c Ferritic(bcc) 11.5-27 0 0.2max Austentic(fcc) 16-26 7-22 0.25max Matensitic(bct) 11.5-17 0-2.5 0.15-1.20
  19. 19. FERRITIC STAINLESS STEEL       AISI series No 400 (American Iron & Steel Institute) Good corrosion resistance Higher strength cannot be applied Not readily work hardenable Lower cost Not hardenable by heat treatment as temperature changes induce no phase change in solid state.
  20. 20. MARTENSITIC STAINLESS STEEL         AISI series 400 Can be heat treated High Strength and hardness Corrosion resistance is less than other 2 types Ductility is less Yield strength may range from 492 mpa in the annealed condition up to 1696 mpa in the hardened (quenched & tempered) state. BHN range – 230 to 600 Used for surgical and cutting instruments
  21. 21. AUSTENITIC STAINLESS STEEL        Most Corrosion resistant 2 types - AISI 302  AISI 304 AISI 302 is the basic type, containing 18%, Chromium, 8% Nickel and 0.15% Carbon. AISI 304 has “C” content limited to 0.08% Both may be designated as 18-8 stainless steel Used by orthodontist to form bands & wires Type 316L (0.03%C) is used for implants.
  22. 22. PROPERTIES Greater ductility and ability to undergo more cold work without breaking Greater ease of welding substantial strengthening during cold working Readily overcomes sensitization less critical grain growth Comparative ease in forming reasonable cost.
  23. 23. MECHANICAL PROPERTIES ADA (American Dental Association) Specification No 32, for orthodontic wires not containing precious metals. Type I (Low resiliency) Type II (High resiliency) Tensile strength of 2100 mpa Yield strength of 1400 mpa KHN 600
  24. 24.
  25. 25. TYPES OF STAINLESS STEEL ARCH WIRES 1. Rectangular arch wire 2. 0.16x0.22 inches 0.17x0.25 inches 0.19x0.25 inches 3. 4. 2.Round wires 3.Square Wires 0.16x0.16inches
  26. 26. 2. CO-AXIAL WIRES Consist of varying no. of wires wrapped around a single core wire which is stronger and resilient Excellent initial arch wire.
  27. 27. 3. BRAIDED & TWISTED WIRES Small separate strands interwined to form round or rectangular shaped wires . Can sustain large elastic deflections in bending Better resilience They apply a low force for a given deflection compared to solid stainless steel wires Server as a transitional wire from round to rectangular
  28. 28. EFFECTS OF COOLING AUSTENITE Slow Cooling Pearlite Ferrite + Cementilte Fast Cooling Tempering Martensite
  29. 29.  At a “C” concentration of 0.08% the alloy shows a transformation from the single phase austenite to a two structure consisting of “Ferrite” & “Cementite”. This solid transformation is defined as a eutectoid.  Steels with a “C” content of greater that 0.08% are hypereutectoid steels.  If “C” content of lesser that 0.08% then it is hypo eutectoid steels.
  30. 30. DUPLEX STAINLESS STEEL Refers to steel having a 2 phase structure of almost equal properties of austenite & ferrite. High resistance to stress corrosion cracking Higher tensile strength than austenite or ferrite Weldable Increased resistance to chloride ion attack.
  31. 31. MANUFACTURING OF STAINLESS STEEL WIRES An ingot of appropriate composition is cast. Ingot is then subjected to a series of mechanical reduction, operations till the cross sections is enough for wire drawing. Drawing is performed in a series of steps as work hardening occurs in each step . Square and rectangular wires are made from round wires using “Turks head apparatus” having 2 pairs of rollers at right angle. This results in some inevitable rounding of corners.
  32. 32. CORROSION RESISTANCE Stainless Steel resist tarnish and corrosion primarily because of the passivating effect of chromium. A very thin, transparent but tough & impervious oxide layer forms on the surface of the alloy when it is subjected to an oxidizing atmosphere as mild as clean air. This protective oxide layer prevents further tarnish and corrosion.
  33. 33. SENSITIZATION The 18-8 Stainless Steel may lose its resistance to corrosion if heated between 400o & 900oC, the exact temperature depending on its “C” content. The reason is the precipitation of chromium carbon at the grain at high temperature. The small rapidly diffusing “C” atom migrate to the grain boundaries from all parts of the crystal to combine with the large, slowly diffusing chromium atoms at the periphery of the grain, where the energy is highest the formation of Cr3C is most rapid at 650oC; Below it, the diffusion rate is less, whereas above it a composition of Cr3C begins.
  34. 34. When chromium combines with “C” in this manner, its passivating qualities are lost. This condition can be minimized by reducing the “C” content of steel to such an extend that such carbide precipitations cannot occur.
  35. 35. FUNCTIONS OF ALLOYING ELEMENTS Chromium - Passivating Effect Molybdenum - Increase resistance to pitting corrosion Nickel - Helps reduce corrosion & Increases strength Cobalt - Decreases hardness Manganese - Acts as scavenger and increases hardness during quenching Silicon - Acts as deoxidizer Titanium - Inhibits precipitation of chromium carbide
  36. 36. STABILIZATION It is a process of protecting the chromium – carbide precipitate at the grain boundaries, when steel is subjected to high temperature in case of soldering & welding Titanium is added.
  37. 37. STRESS RELIEF HEAT TREATMENT  Heat treatment of stainless steel wire (b/w 370 – 480C) is recommended to eliminate residual stress from wire manufacture  Prevents breakage of complex appliances during assembly  Stabilize shape of appliances. 18/8 stainless steel after heat treatment effects are :Slight increase in modulus of elasticity Greater increase in yield strength Considerable increase in modulus of resistance Resistance in failure due to corrosion . Increase of stabilized austenitic stainless steel, stress relief treatment is done at 370C. Heat treatment above 650 C results in :Recrystallization of microstructure Compositional changes Formation of chromium carbide
  38. 38. RELATIVE MERITS OF STAINLESS STEEL WIRE ALLOYS High force delivery Low spring back Excellent formability Orthodontist can fabricate arch wire or segments with complicated loop configuration High stiffness Good resilience Adequate ductility Low cost Can be soldered and welded easily.
  39. 39. A.J. WILCOCK WIRES  Late A.J. Wilcock founded A.J. Wilcock Scientific & Engineering Pvt. Ltd in 1946  Initially involved in manufacture of metallurgical research eg. Lagter led to the dev. Of high tensile stainless steel wires.
  40. 40.  Today A.J. Wilcock Australian wire is an international house hold name in orthodontics & sets the standard against all other stainless steel wires.  Strain aged processing ensures extra ordinary St. Steel wire products.  A.J. Wilcock St. Steel rectangular wires are manufactured using a unique ageing process giving the wire unmatched resistency and energy storage.  Wilcock wires are well known for their ability to withstand masticatory forces as well as being able to maintain their shape even when auxiliaries and elastics are used.  There is no other wire which opens the bite as effectively as wilcock wires
  41. 41. WIRE GRADES  Regular Grade  Regular Plus Grade  Special Grade  Special Plus Grade  Premium Grade  Premium Plus Grade  Supreme Grade. TYPES  Hard drawn S.S. Wires  Pulse Straightened  Rectangular Wire  Australian Wire up righting springs
  42. 42. AVAILABLE IN 8 GRADES: REGULAR GRADE White label lowest grade and easiest to bend. Used for practice bending or forming auxiliaries. It can be used as arch wire when distortion and bite opening is not a problem.  REGULAR PLUS GRADE: Green label relatively easy to form yet more resilient than regular grade. Used for auxiliaries when more pressure and resistance to deformation is required.
  43. 43.  SPECIAL GRADE: Black label highly resilient yet can be formed into intricate shapes with little danger of breakage  SPECIAL PLUS GRADE: Orange label - hardness and resiliency of the wire are excellent for Supporting anchorage and reducing deep overbite. PREMIUM GRADE More difficult to bend—occasional breakage to be expected PREMIUM PLUS GRADE Extremely resilient, not suitable for sharp bends SUPREME GRADE Highest degree of resiliency, not suitable for sharp bends.   
  44. 44.  Till 1980wires were straightened by what is called as spinner straightening process. Spinner straightening is a mechanical process of straightening, usually in the cold hard drawn conditions.  The wire is pulled through high speed rotating bronze rollers which torsionally twist the wire into a straightened condition. This can result in permanent deformation.
  45. 45. The Mollenhauer bending pliers is strongly recommended for bending Wilcock wire as it helps to minimize breakage. The tips are tungsten carbide for durability with rounded & highly polished edges. BENDING RECOMMENDATIONS Sharp bends not recommended in grades above special carbide tip pliers will cause wire fracture in all grades Always grasp wire lightly with instruments to avoid nicking wire surface Grip the wire with thumb & forefinger 1- 1.5” from pliers contact point. While holding the pliers steady, slowly rotate the wire around the instrument using thumb pressure.
  46. 46. PULSE STRAIGHTENED WIRES One of the most popular products especially when time is a factor. Convenient to use Easy to store Unmatched resiliency & smoothness Available only in Special Plus, Premium, Premium plus & Supreme Available 30 pieces / tube Stiffness of the wire by 300% Improved martensitic response & smooth surface characteristic for reduced frictions Larger diameter are ideal for application Small diameter best used for forming auxiliaries and early treatment alignment.
  47. 47. REFERENCES 1. Phillips Science of Dental Materials 2. William R. Profit Contemporary Orthodontics 3. William A. Brantley Orthodontic Materials 4. Craig RG Dental Materials 10th ed. St. Louis 5. www. ADA Specifications. com Orthodontic wires not containing precious metals 6. WWW. A j Wilcock. com
  48. 48.  7. Am j orthod 1981; 80: 1-16  8. www.AISI. Com  9. Angle orthod 1981; 51: 319-24  10.Am j orthod 1984; 86: 396-402  11. Angle orthod 1997; 67: 197-208  12. Am j orthod 1998; 113: 91-5  13.Am j orthod 1990; 98: 300-312
  49. 49.  THANK YOU