STAINLESS STEEL IN ORTHODONTICS & DO.pptx

Dr.ZANAB FARHEEN FAYAZ,MDS(ORTHODONTICS AND DENTOFACIAL ORTHOPEDICS).

1. stainless steel as an orthodontic alloy Under The Guidance Of: (Prof) Dr. Muhammed Mushtaq. Head Of The Department Department Of Orthodontics and Dentofacial orthopedics. Presented by: Dr. Zanab Farheen Fayaz PG 2 nd Year

2. Contents introduction history composition classification properties types sensitization stabilization uses conclusion

3. Introduction Steel is one of the foremost discoveries in the world. S teel is a widely used quality product for both domestic and industrial applications like manufacturing of aircrafts, vehicles, construction purposes, production of surgical equipments etc. Different types of steels are available in a variety of compositions, with each having very specific properties that are carefully tailored to suit their particular applications.

4. Steel is an alloy of iron and carbon. When 12-30 percent chromium is added, the alloy so formed is called as Stainless steel. The most commonly used steel in the field of Orthodontics is the 18-8 Austenitic stainless steel containing 18% chromium and 8% nickel which belongs to the group of corrosion resistant alloys . Contemporary Orthodontics By William R Proffit

5. Stainless Steel Historical Overview The discovery of stainless steel occurred in the 1900-1915 time period. It was discovered accidentally in 1913 by the Sheffield Metallurgist Harry Brearly , of the Brown Firth Research Lab. who noticed that a discarded steel sample was not rusting. Two months later stainless steel was cast for first time 0n August 13, 1913.

6. Between 1903 and 1921, Harry Brearley of Sheffield, F.M Becket of the USA, Benno Strauss and Edward Maura of Germany shared the honor for the development of the material. Stainless steel entered dentistry in 1919,it was introduced at Krupp’s Dental Polyclinic in Germany by F. Hauptmeyer , who called it Wipla (Wie Platin; in German, like Platinum). By 1930 in America and 1932 in England , it was introduced in wire and ribbon form for orthodontic use and has dominated till recent times as a chief material of use in orthodontics.

7. Application of stainless steel for the fabrication of appliances was credited to a Belgian metalurgist Lucien de Coster . Research study related to metallurgy with particular references to orthodontic applications was done by a Metallurgis t named R.M.Williams . Angle used stainless steel in the last year of his life (1930) in the form of ligature wires. By 1937, the value of stainless steel as an orthodontic material had been confirmed.

8. Stainless Steel Composition: Steel is an alloy of iron and carbon . When 12-30 percent chromium is added, the alloy so formed is called as Stainless steel. Carbon content should not exceed 1.2%. Elements other than iron, carbon and chromium may also be present, resulting in a wide variation of composition and properties of stainless steel. Contemporary Orthodontics By William R Proffit

9. Chromium  Minimum amount required is 12%. I ncreases T arnish and corrosion resistance. I ncreases hardness, tensile strength and proportional limit. Nickel  Minimum requirement is 8%, it strengthens the alloy, increases the ductility & toughness. Modifying Elements And Their Function Anusavice ,Phillips’-Science Of Dental Materials

10. Cobalt  Increases hardness at higher temperatures. Manganese  acts a scavenger and increases the hardness during quenching. Silicon  Acts as a deoxidizer. Carbon : Should be less than 1.2%. It substantially increases the mechanical strength. Carbon reduces resistance to intergranular corrosion.

11. Titanium  Inhibits the precipitation of chromium carbide. Copper : used to increase the strength. Molybdenum: It increases the mechanical Strength. 2% Mb increases resistance to pitting corrosion. Sulphur: A 0.015% sulphur content increases the machinability. Phosphorous : Allows the use of a lower temperature for sintering .

12. Properties Of Stainless Steel Stress; Defined as the internal resistance within a structure subjected to an external force or pressure. Stress=force/cross-sectional area Tensile stress; Tensile stress is a stress caused by a load that tends to elongate a body. Calculated as the ratio of tensile force to the original cross-sectional area perpendicular to direction of applied force. Anusavice , Phillips’- Science of Dental Materials.

13. Compressive stress; Stress caused by a load that tends to compress or shorten a body. Calculated as the ratio of compressive force to the cross-sectional area perpendicular to axis of applied force Shear stress; Shear stress tends to resist the sliding or twisting of one portion of body over another. Shear stress can also be produced by twisting or torsional action on a material.

14. Strain; Defined as change in dimension per unit original dimension.It is calculated as: Strain=change in dimension/original dimension Strain may be either elastic or plastic. Elastic strain; is reversible. The object returns to its original shape fully when the force is removed. Plastic strain ; represents a permanent deformation of the material that does not decrease when the force is removed.

15. Stress-strain diagram; A convenient means of comparing the mechanical properties of materials is to apply various forces to a material and to determine the corresponding values of stress and strain. A plot of corresponding values of stress and strain is reffered to as a stress-strain curve.

16. Proportional Limit; It is the highest point where stress and strain still have a linear relationship. It is measured in units of PSI or Mpa or gm/cm2. Clinical Significance; The value for Stainless steel is 205 Mpa The proportional limit of stainless steel is less than that of NiTi and hence it can be deformed easily than NiTi . This means that stainless steel wires need frequent changes when compared to NiTi wires.

17. Yield Strength ; The maximum stress that a body can withstand without plastic deformation. or The stress beyond which a body starts to deform plastically. or It is the Intersection of stress strain curve with a parallel line offset at 0.1% strain.

18. Clinical Significance; It determines the practical limit of elastic working range of material. Practically yield strength should be higher as there are lesser chances of deformation of appliance by extra and intra oral forces. It is measured in units of psi or Mpa or gm/cm 2 . For stainless steel yield strength is 1.6 Gpa which is more than Ni- Ti , Beta- Ti and Co-Cr-Ni alloys. Ni- Ti has lowest.

19. Modulus Of Elasticity This describes the relative stiffness or rigidity of a material which is measured by the slope of the elastic region of the stress strain diagram. If any stress value equal or less than the proportional limit is divided by its corresponding strain value, a constant of proportionality will result, this constant is as called Modulus of elasticity.

20. Modulus of Elasticity = Stress/Strain till pl. Unit for modulus of elasticity is force per unit area ( Mpa or psi). Modulus of elasticity of stainless steel is 28x10 6 psi or 179 Gpa which is more than Ni- Ti and Beta- Ti and less than Co-Cr-Ni alloy. Co-Cr-Ni alloy has highest.

21. The very high elastic modulus of stainless steel results in very high forces being delivered as compared to other alloys. Large modulus of elasticity/high stiffness, advantages in resisting deformation by extra and intra-oral forces. Wires with high MOE are difficult to bend. Particularly wires with low MOE should be used because, it permits force application within physiological limits. Clinical Significance;

22. The force magnitude delivered by an appliance is proportional to the modulus of elasticity. The mechanical property that determines the load deflection rate is the modulus of Elasticity.

23. Load Deflection Rate; LDR gives the force produced per unit activation of the system. It is the clinical analogue to modulus of elasticity of a wire. LDR = LOAD/DEFLECTION. The slope of the curve below the maximum elastic load in the stress-strain graph represents the LDR. For the amount of load applied, the deflection produced varies depending upon the length of the wire and the diameter of the wire.

24. Ideally for an orthodontic spring we prefer a low load-deflection rate i -e, for a lesser load the deflection should be greater such a spring applies a lesser force and a longer range of action. LDR is directly proportional to MOE. According to Burstone , load deflection rate depends on the cross section and length of the wire as follows:- DEFLECTION ∞ FORCE(F) × L 3 D 4 Factors Influencing Load Deflection Rate;

25. Comparison Of Load Deflection Rates Of Various Orthodontic Wires; Note that after initial force level has been reached, NiTi wires have a considerably flatter load deflection curve than stainless steelwires ,which has high LDR. Brantley WA: Orthodontics wires.

26. Stiffness Is the measure of resistance to deformation. It is measure of force required to bend or otherwise deform the material over a definite distance. Stiffness is proportional to the slope of the elastic portion of the force-deflection curve. The more vertical the slope the stiffer the wire, the more horizontal the slope, the more flexible the wire.

27. STIFFNESS=FORCE/DISTANCE Stiffness is dependent on MOE and is not affected by any hardening heat treatment.  All wires of same alloy whatever may be the temper i.e., soft or hard will be equally stiff and behave similarly below the point where the plastic deformation of the soft wire begins.

28. Material Stiffness Numbers ( M s ) Of Orthodontic Alloys ALLOY MATERIAL- STIFFNESS NUMBER (M S ) STAINLESS STEEL 1.00 TMA 0.42 NITINOL 0.26 ELGILOY 1.19 Wire stiffness(W s ) = Material stiffness(M s ) x Cross-sectional stiffness(C s )

29. Clinical Significance; Low stiffness provides: Ability to apply lower forces. More constant force over time as the appliance experiences deactivation. Greater ease and accuracy in applying a given force. Stainless steel has high stiffness while Ni- Ti has low stiffness.

30. 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. Kusy Defines It As The Force Required To Activate An Arch Wire To A Specific Distance.

31. It can also be defined as the maximum stress required to fracture a structure (can be tensile, compressive or shear, depending upon the predominant type of stress present). Three different points on a stress strain diagram can be taken as the representative of the strength of a material which are : Proportional limit Yield strength Ultimate tensile strength. Each represents, in a somewhat different way, the maximum load that the material can resist .

32. Ultimate Tensile Strength; It is the maximum load a wire can sustain before breaking. It determines the maximum force the wire can deliver if used as a spring so it is important clinically, especially because yield strength and ultimate tensile strength differ much more for the newer titanium alloys than for steel wires. It is measured in units of psi or Mpa or gm/cm 2 . It is 2.1 Gpa for stainless steel which is highest among arch wires. Beta- Ti has lowest.

33. Clinically it determines the maximum amount of force a wire can deliver before fracture. Knowing the value of Ultimate Tensile Strength, a clinician can determine the amount of force a particular wire can deliver and decide accordingly that which type of wire is clinically relevant in a particular situation. Conditions where higher force application is required e.g ; orthopedic cases; require usage of materials having higher ultimate tensile strength . Clinical Significance;

34. Formability; Kusy defines it as the ease with which a material maybe permanently deformed as measured by the magnitude of the difference between the elastic range (which occurs as the proportional limit) and the range failure. It can be related to the percentage elongation a wire can undergo before fracture. Wires with high and sharp yield points possess low elongation values. The property relates to the area under the graph between the yield point and the failure point.

35. Clinical Significance; High formability provides the ability to bend a wire into desired configuration such a loop, coils etc without fracturing the wire. Formability is excellent for stainless steel alloys and poor for Ni- Ti alloys.

36. Toughness; It is defined as the amount of elastic and plastic deformation energy required to fracture a material and it is a measure of the resistance to fracture. Can be defined as energy required to fracture a material. It is dependent on the ductility of the material, also the tough materials are generally strong. Is related to the total area within the elastic and plastic regions.

37. Brittleness; Brittleness is opposite of toughness. Brittle materials are apt to fracture at or near its proportional limit. Brittle materials not necessarily lack in strength. Can be defined as the relative inability of a material to sustain plastic deformation before fracture of a material takes place. No. of 90 cold bends without fracture for SS is 5. Where as it is 8 for Co-Cr-Ni alloy, 2 for Ni- Ti and 4 for Beta- Ti .

38. Hardness; It is defined as resistance to indentation. Resistance of metal to plastic deformation. Factors influencing the hardness of a material are its : Proportional limit Ductility Malleability Resistance to abrasion

39. PROPERTY STAINLESS STEEL Co-Cr-Ni TMA Ni- Ti COST LOW LOW HIGH HIGH FORCE DELIVERY HIGH HIGH INTERMEDIATE LOW ELASTIC RANGE LOW LOW INTERMEDIATE HIGH FORMABILITY EXCELLENT EXCELLENT EXCELLENT POOR EASE OF JOINING CAN BE SOLDERED AND WELDED CAN BE SOLDERED AND WELDED TRIED WELDABILITY CANNOT BE SOLDERED OR WELDED ARCHWIRE BRACKET FRICTION LOWER LOWER HIGHER HIGHER Comparision Of Properties Of Various Arch Wire Materials

40. Resilience; Can be defined as amount of energy absorbed by a structure when it is stressed not to exceed its proportional limit. It can also be defined as maximum amount of energy a material can absorb without undergoing permanent deformation .

41. It is the property of the material itself and is not related to the size or form of the wire. It is the area under the stress-strain curve at the given maximum stress required to fracture a structure. Clinical Signifance ; Stainless steel has low resilence but is high in Ni- Ti . A highly resilient wire will be able to exert force for a larger range and sustain the activation for longer period of time. Hence resilient wires give better control and need fewer wire changes.

42. Flexibility; It is the property of elastic deformation under loading. Maximum flexibility may be defined as the strain that occurs when the material is stressed to its proportional limit. Clinical Significance; It is a non significant term denoting the ease of bending. It may indicate low stiffness, low strength, high working range or low brittleness, either singly or in a combination.

43. Springback Defined as the amount of elastic strain that a metal can recover when loaded to and unloaded from its yield strength. Clinically springback refers to maximum elastic deflection i.e .the extent to which a wire recovers its shape after deactivation. Mathematically, Springback =yield strength/elastic modulus

44. Wires should have a larger springback which means that wire will regain its original shape even after being greatly deformed and hence fewer wire changes. The YS/E ratio indicates low springback of stainless steel.The stored energy of steel is less than NiTi that dissipates over shorter periods of time,thus requiring more frequent activations or arch wire changes.

45. Range; Proffit defines range as the distance that the wire will bend elastically before permanent deformation occurs. In orthodontics this distance is measured in mm. If the wire is deflected beyond this point, it will not return to its original shape but clinically useful spring back will still occur unless the failure point is reached.

46. The elastic range for STAINLESS STEEL is LOW as compared to TMA and Ni-Ti which have INTERMEDIATE and HIGH range respectively. Range of SS is more than Elgiloy . Higher the spring back, greater the working range and lesser are the requirements of frequent activations. These three major properties have an important relationship: Strength=Stiffness x Range Clinical Significance

47. Relationship Between Stiffness, Strength, Range And Other Variables Of Wire Component. STIFFNESS STRENGTH RANGE α Modulus of Elasticity α Resilence α Elastic Limit α (1/Length) 3 α (1/Length) α (Length) 2 α (Diameter if wire) 4 α (Diameter of wire) 3 α (1/Diameter of wire) α (1/No. of coils) - α (No. of coils) α (1/coil diameter) 3 α (1/Coil diameter) α (Coil diameter) 2

48. Variation Of Properties Of Stainless Steel Wires Variation in Diameter: The force that can be developed in a given length of wire increases 16 times per unit of deflection when diameter is doubled. If the diameter of the given length of wire is doubled total load will increase by 8 times. Range decreases as the diameter is doubled.

49. Variation In Length; The force that can be developed decreases 1/8 th when the length of the wire is doubled. Increase in length will proportionately decrease the maximum load on a one for one ratio. If the amount of length of wire is doubled the amount of deflection increases 4 times.

50. More precisely, the strength of the wire changes as the third power of ratio of the larger to the smaller wire. The springiness changes as the fourth power of the ratio of the smaller to the larger and range changes directly as the ratio of the smaller to larger wire.

51. The chromium in the stainless steel forms an impervious oxide layer on the surface of the alloy when it is subjected to an oxidizing atmosphere as mild as clean air. This prevents further tarnish and corrosion by blocking the diffusion of oxygen to the underlying bulk alloy. This is called 'passivating effect’. For this effect to take place, a minimum of 12% of chromium is required. If the oxide layer is ruptured by mechanical or chemical means, a loss of protection against corrosion results . Passivation

52. Sensitization; At temperature in excess of 500  c (exact temperature depends upon its carbon content) [ Range 400  c -900  C according to skinner’s] chromium and carbon react to form chromium carbide (Cr 3 c), which precipitate at the grain boundaries causing brittle behaviour. Also the corrosion resistance decreases due to depletion of the central regions of the crystals of chromium, which has migrated to the boundaries to form the carbides. This process in known as sensitization or weld decay . Orthodontis , Diagnosis and Management of Malocclusion and Dentofacial Deformities by Om Prakash Kharbanda.

53. The formation of chromium carbide is most rapid at 650 c (skinner’s) below this diffusion rate is less whereas above it a decomposition of (Cr 3 C) begins. There are several methods by which this condition can minimized. Ways to over come sensitization: 1.Reduce the carbon content of steel ; Uneconomical 2.If the stainless steel is severely cold worked: If stainless steel is severely cold worked , carbides precipitate in the bulk of the grain rather than the grain boundaries. 3.Stabilization

54. Sensitization can also be overcome by adding titanium plus tantalum or niobium to the alloy. The effect is that carbon preferentially reacts with the dispersed titanium such that the chromium remains where it is most effective. This process is called Stabilization and the stainless steel so treated is known as stabilized stainless steel. Stabilization

55. If titanium is introduced in amount approximately 6 times the carbon content, precipitation of CrC 3 can be inhibited for a short time at temperature ordinarily encountered in soldering procedures, this gives what is known as stabilised austentic stainless steel. weld decay can also be avoided by adding columbium E.C Coombe

56. Classification 1) Based on crystal structure formed by iron atoms Crystal structure Chromium Nickel Carbon Ferritic B.C.C. 11.5-27 0.20 Austenitic F.C.C. 16-26 7-22 0.25 Martensitic BCC 11.5-17 0-3.6 0.15-1.20 Duplex BCC/FCC 18-28 4.8-8% Journal of British Orthodontic Society vol:30,2003.

57. 2) According to American Iron and Steel Institute (AISI) Classification 200 Series  Chromium, Nitrogen, Manganese (Austenitic) 300 Series  Chromium, Nickel (Austenitic) 400 Series  Ferritic/ Martensitic 4 .600 Series  Precipitatiion hardenable .

58. The old AISI three digit stainless steel numbering system (e.g. 304 and 316) is still commonly used. New grades are defined under the SAE and ASTM system that uses a 1-letter + 5-digit UNS number. An example of this is the new term for 304, which is S30400 Standard Classifications of Stainless Steel

59. Grades Of Stainless Steel Fully Annealed :Have high formability and are very soft(ligature wire) . Partially Annealed : They have increased strength but less formability(Arch Wires). Regular Grade  Can be bent to any desired shape without breaking. Super grade:- Impressive yield strength Almost brittle Will break if bent sharply

60. Ferritic Stainless Steels (400series); Microstructure of these steels is similar to iron at room temperature (BCC). The difference being that in ferritic steel chromium is substituted for some iron atoms in the unit cells. The degree of substitution can go as high as 30% in the presence of small amounts of other elements ( eg : Carbon, Nitrogen, Nickel) Types Of Stainless Steel

61. Modern super ferrites contain 19-30% chromium and are used in several nickel free brackets. Highly resistant to chlorides these alloys contain small amounts of aluminium , molybdenum and very little carbon. Ferritic alloys provide good corrosion resistance at lower cost, provided high strength is not required. Since temperature change induces no phase change in the solid state, the alloy is not hardenable by heat treatment. Ferritic stainless steels are not readily work hardenable . This series of alloys find little application in dentistry Variable-modulus orthodontics American Journal Of Orthodontics 80(1),1-16, 1981.

62. They can be heat treated in the same manner as plain carbon steels with similar results. Because of their high strength and hardness martensitic stainless steels are used for surgical & cutting instruments. Martensitic Stainless Steels (400series)

63. Corrosion resistance of martensitic stainless steel is less than that of other types and is reduced following hardening heat treatment. As usual, when the strength and hardness increase ductility decreases. It may go as low as 2% elongation for a high carbon martensitic stainless steel .

64. Austenite, also known as gamma phase iron ( γ -Fe), is a metallic, non-magnetic alloy of iron or a solid solution of iron with an alloying element. Most commonly used stainless steel in Orthodontics & Dentofacial Orthopaedics . Has FCC crystal structure & is named after UK Metallurgist Sir William Chandler Robert-Austen (1843-1902) Austenitic Stainless Steels (300series)

65. These are most corrosion resistant of stainless steels. AISI 302 is the basic type containing 18% Cr, 8% Ni and .15% carbon. Type 304 has similar composition, chief difference being that the carbon content is limited to .08%. Both 302 and 304 may be designated as 18/8 stainless steel and are most commonly used in orthodontics in form of bands and wires.

66. Type 316 L (.03% max. carbon) is the type ordinarily employed for implants. The 316 & 316 L types have been recently introduced and 316 differs in that it contains 2% more Nickel in addition to about 2% Mb, thus improving its corrosion resistance. FCC crystal structure renders these steel “ non ferromagnetic” i.e not strongly attracted to a magnet.

67. Austenitic FCC structure is unstable at lower temperature where it tends to turn into BCC ( ferrite). If austenizing elements ( nickel, manganese and nitrogen) are added highly corrosion resistant solid solution phase can be preserved even at room temperature.

68. Generally, austenitic stainless steel is preferable to the ferritic alloy because of : Greater ductility & ability to undergo more cold work without breakage. Substantial strengthening during cold working. Greater ease of welding. Ability to readily overcome senstization . Less critical grain growth. Comparative ease in formation.

69. Duplex Steels Consist of an assembly of both austenite and ferrite grains. Along with Fe these steels have Mb and Cr and low amounts of Ni. As opposed to austenitic ones these steels are attracted to magnets. Duplex structure ( γ +α') results in improvement in ductility and toughness compared to ferritic ones, while the yield strength is more than twice that of similar austenitic steels.

70. High corrosion resistance. When improperly heat treated, these steels have a tendency to form a brittle phase that diminishes their corrosion resistance. Combining a lower Ni content with superior mechanical properties it is used for manufacture of one piece brackets ( eg. Bioline “low nickel” by CEOSA, madrid )

71. PH steels can be hardened by heat treatment the process being an aging treatment which promotes the precipitation of some elements like Cu ,Mb ,Al , Ti which are added either singly or in combination. High tensile strength PH17-7 stainless steel is widely used for “mini” brackets Ormco uses PH to make its edgelock brackets. The added metals lower the corossion resistance. Precipitation- hardenable (PH) Steels

72. Cobalt Containing Alloys Commonly used in orthodontics e.g. Elgiloy and Flexiloy Some contain large amounts of Ni others however are Ni free Ni free steels are used to make arch wires Generally corrosion resistant To manufacture attachments such as Prestige (pyramid orthodontics), NU Edge LN ( TP orthodontics) and Elite – optimim (ortho organisers).

73. Manganese Containing Steels One of the austenizing element. Manganese acts by interstitially solubilizing the really “austenitizing” element, nitrogen thus replacing Ni. Unfortunately high proportions of Mn increases the alloys susceptibility to corrosion.

74. Uses Of Stainless Steel In Orthodontics Stainless steel finds a very important place in Orthodontics & Dentofacial Orthopaedics in the form of; Orthodontic wires . Bands . Brackets . Buccal tubes . Ligature wires . Springs . Pliers. Screws

75. Orthodontic Wires Stainless steel wires find their application in Orthodontics & Dentofacial Orthopaedics in the form of; Removable appliances (Clasps, springs, bows) Functional appliances(Clasps, springs, bows) Fixed appliances (arch wires) Orthopaedic appliances (head gear, facemask). Orthodontic wires are usually made from 304,302,316 AISI type of stainless steel

76. 304 type of stainless steel is most commonly used because of:- Forming and welding properties. Corrosion/ oxidation resistance. Deep drawing quality. Excellent toughness. Hardening by cold working. Ease of cleaning, ease of fabrication, beauty of appearance. Has two grades, Grade 304L and Grade 304H

77. Very small diameter stainless steel wires can be braided or twisted together to form wires for clinical orthodontics. The separate strands may be as small as .178 mm (.007”) but the final intertwined wires may be either round or rectangular in shape and between .406 mm (.016”) and .635 mm (.025”) in overall cross section. These wires have low stiffness & larger spring back than solid stainless steel wires. Multistrand wires

78. Multistranded wires are mostly made from 302 AISI type of stainless steel. They are able to sustain large elastic deflections. These wires apply low forces for a given deflection when compared to SSS wires Types of Multistranded wires include:- Twisted (3-stranded) Coax or coaxial (6-Strand) wires.

79. During initial orthodontic leveling arch wires require great working range to accommodate the usual malalignment of bracket slots in the untreated malocclusion. Co-axial/Braided wires offer a good choice for initial alignment and leveling. Uses;

80. Australian Archwires In 1952, Dr. Begg in collaboration with an Australian metallurgist A.J Wilcock, developed a high tensile stainless steel wire that is heat treated and cold drawn. These wires were made thin enough to distribute force at an optimal level for tooth movement over a considerable period of time with minimal loss of force intensity while doing so. The diameter of the wires initially produced was progressively decreased from .018” to .014”.

81. There are 6 types of Australian arch wires : Regular grade (white label ) lowest grade easiest to bend used for practice bending and forming auxillaries . Regular plus (green label) Relatively easy to form, yet more resilient than regular grade. Used for auxillaries and arch wires when more pressure and resistance to deformation are desired . Brantley WA: Orthodontics wires.

82. Special grade (black label) highly resilient yet can be formed into shape with little danger of breakage Special plus grade (orange label) Hardness and resiliency of .016” wire is excellent for supporting anchorage and reducing deep overbites. Must be bent with care. Routinely used by experienced operators.

83. Extra special plus grade (blue label); Also referred to as premium plus in Australia. This grade is unequalled in resiliency and hardness. More difficult to bend and more subjected to fracture. ESP’s ability to move teeth, open bites and resist deformation are excellent.

84. Supreme grade (blue label); Further develop by A. J Wilcock Jr. in 1982 on request of Dr. Mullenhauer of Australia. Is ultra light tensile fine round stainless steel wire. Was initially introduced in the .010” diameter and was further reduced to .009” diameter. Is primarily used in early treatment for rotation ,alignment and leveling. Although, supreme exceeds the yield strength of ESP, it is intended for use in either short section or full arches where sharp bends are not required .

85. Newer Wilcock Arch Wires Recently, A.J. Wilcock scientific and engineering company , have introduced a new series of wire grades and sizes with superior properties by use of new manufacturing process called pulse straightening. The new grades available now are : premium .020” premium plus .010”, .011”, .012”, .014”, .016” .018” supreme .008”, .009”, .010”, .011”

86. In 1940s with the rise in cost of gold and stainless steel being approved for use in the oral cavity the use of gold brackets was replaced by stainless steel brackets. Though stainless steel was developed as early as 1920s it was not until the mid century that it was applied widely in orthodontics. Stainless Steel Brackets Kusy RP, and Greenberg AR:Angle Orthodontic Journal 51:325,1981

87. SS brackets Are essential components of modern fixed appliances. Mostly made from 304L AISI type of stainless steel, has low carbon content typically less than 0.03%. Can also be made from Super stainless steel or duplex steel .

88. These are better than plastic and ceramic brackets in such a way that; The plastic brackets which are made of polycarbonate lack strength to resist distortion and breakage, wire slot wear (which leads to loss of tooth control), uptake of water, discolouration and the need for compatible bonding resins.

89. The ceramic brackets that are available at present are not optimal and show some significant drawbacks: The frictional resistance between orthodontic wire and ceramic brackets is greater and less predictable than it is with steel brackets. This makes determining optimal force levels and anchorage control difficult. Ceramic brackets are not as durable as steel brackets and are brittle by nature. These brackets break easily especially when full size stainless steel wires are used for torquing purposes.

90. Stainless Steel Orthodontic Bands Stainless steel Bands are made from 302,304 AISI type of stainless steel. Clean, polished surface, less prone to corrosion . Increased Stiffness, can be used in thinner gauges . Soldering & welding can be done.

91. Orthodontic Instruments Almost all the orthodontic instruments are made from stainless steel & these include:- Basic diagnostic instruments (Mouth mirror, Explorer, Probe) Instrument keeping trays (kidney tray, square tray). Impression trays. Wire forming Pliers:- a. Adams universal pliers b. Adams spring forming pliers

92. Pin & ligature cutters - Wire cutters - Heavy Duty wire cutter . Debonding instruments - Adhesive removing pliers - Bracket removing pliers. Banding instruments - Band removing pliers - Band contouring pliers . Surgical instruments . Measuring instruments - Gauges (Boley gauges, Vernier calipers) - Dividers

93. Nickel Allergy In Orthodontics “Nickel is with you and does things for you from the time you get up in the morning until you go to sleep at night.” ( The Romance of Nickel ) Most common metal to cause contact dermatitis in orthodontics. Elicits contact dermatitis, which is a type IV delayed hypersensitivity immune response that manifests within 24 -48 hours after contact. Has two interrelated, distinct phases, Sensitization phase & Elicitation phase. Indian Journal of Dental Research 2010,vol:21 issue:2.

94. Allergy due to nickel is more common in females (31 %) than in males (3%). Contrary to what rest of the orthodontic literature and texts say, Craig, O’ brien and Powers in their textbook- Restorative Dental Materials say that “Nickel allergy is more common in males (2o%) than in females(16%)”. Nickel sensitization is believed to be increased by mechanical irritation, skin maceration, or oral mucosal injury.

95. Signs & symptoms of the nickel allergy Intraoral symptoms:- - Stomatitis ,mild to severe erythema - Perioral rash - Loss of taste or metallic taste - Numbness - Burning sensation - Soreness at the side of tongue - Angular chielitis - Severe gingivitis in the absence of plaque

96. Extra oral symptoms; - Generalized urticaria - Widespread eczema - Flare-up of allergic dermatitis It has been found that the extra-oral reactions are more common than intra-oral reactions. Environmental temperatures and duration of exposure may also be factors.

97. Management of nickel allergic contact dermatitis; Diagnosis includes Proper history suggestive of nickel allergy. Lesions due to other causes should be eliminated. Preventive strategies; Avoidance of nickel using nickel free materials like Nickel lite or nickel free wires , Ceramic brackets, Polycarbonate brackets , Titanium brackets , Gold-plated brackets .

98. Therapeutic strategies; Therapy of nickel contact dermatitis can be very challenging and depends on clinical manifestations Symptomatic treatments Steroids - Topical steroids are very useful and represent the first-line treatment. - Oral steroids act as immunosuppressive agents and might be indicated for short-term treatment of severe dermatitis

99. Conclusion The progress of orthodontic treatment is dependant on the type of material used. The selection of the material should be based on physical/Mechanical properties, which produce physiologic forces ,better stability & flexibility. Stainless steel still holds a good position for its use not only in Orthodontics & Dentofacial Orthopaedics but in whole of Dentistry.