Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy


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Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy

  3. 3. INTRODUCTION   Metals are very remarkable materials. Their ability to be rolled into sheets as thick as the hulls of ships or as thin as gold and aluminum foil, to be drawn into wire cables supporting bridges or into fine strands, onehalf the thickness of a human hair, for delicate electronic instruments, to be softened with heat and hardened by cold working.
  4. 4.  Metals resist wear and corrosion; they conduct heat and electricity, they are generally inexpensive.
  5. 5. Atomic arrangements for metallic materials  In general, materials can be subdivided into two categories according to their atomic arrangements. In crystalline material there is a three dimensional periodic pattern of the atoms, whereas no such long-periodicity is present in noncrystalline materials, which possess only short-range atomic order.
  6. 6.  There are seven crystal systems, with lattice parameters. (The three dimensional arrangement of lines that can be visualized as connecting the atoms in undisrupted crystals, is called a lattice.)  Inherently, a space lattice is a geometric construct wherein each point has identical surroundings. Crystal structures of real material are based upon space lattices, where there is a single atom or a group of atoms at each space lattice point. 
  7. 7.
  8. 8. Crystal System Cubic Tetragonal Orthorhombic Rhombohedral (Trigonal) Hexagonal Monoclinic Space Lattice Simple cubic Body-centered cubic Face-centered cubic Simple tetragonal Body-centered tetragonal Simple orthorhombic Body centered orthorhombic Face-centered orthorhombic Base-centered orthorhombic Simple rhombohedral Simple hexagonal simple monoclinic Base-centered monoclinic
  9. 9. Triclinic Simple triclinic It is most convenient to visualize the crystal structures of metals in terms of their unit cells, where a unit cell is the smallest portion that can be repeated in three dimensions to produce the crystal structure. Crystal  combination of unit cells, in which each cell shares faces, edges or corners with the neighboring cells Unit cells for the simple cubic are a) Body-centered cubic, b) Facecentered cubic, and c) Hexagonal close-packed.
  10. 10.   The hexagonal close-packed (hcp) structures can be considered as formed from two interpenetrating simple hexagonal structures. It can be seen that, while nickel and chromium have body centered cubic and face centered cubic structures, respectively, all temperatures below their melting points, iron and titanium have crystal structures that depend upon temperature.
  11. 11.  Grains  microns to centimeters  Grain boundaries Atoms are irregularly arranged, and this leads to a weaker amorphous type structure. Alloy  combination of crystalline (grains) and amorphous (grain boundaries) Decreased mechanical strength and reduced corrosion resistance   
  12. 12. Stages in the formation of metallic grains during the solidification of a molten metal Polycrystalline- each crystal - grain
  13. 13. Structure of metallic materials    Crystals or grains of metals and alloys are composed of billion upon billion of atoms regularly arranged in a space lattice. When stress is first applied, the space lattice is slightly distorted out of shape, but returns to its original position upon release of the stress. This deformation is called elastic strain. Whenever a crystal deforms, its lattice is distorted. As the deformation increases, so does the distortion. Simultaneously, the number of atomic dislocation increases, disrupting the path of the sliding or twinning planes produced by stress.
  14. 14.  various defects  slip planes -along which dislocation occurs
  15. 15.   To prevent breakage, a softening step (annealing) must be added to render the distorted, cold material, strain free. Each alloy has a specific recrystallization and annealing temperature at which the grains, forcibly reduced by cold work, can enlarge to allow further processing. Thus annealing causes a sharp drop in tensile strength. Metals made of large grains are weak, the smaller the grains, the more the intergranular boundaries that oppose the planes slip.
  16. 16. ANNEALING: Recovery Recrystallization Grain Growth
  17. 17. Before Annealing Recovery – Relief of stresses Recrystallization – New grains from severely cold worked areas -original soft and ductile condition Grain Growth – large crystal “eat up” small ones-ultimate coarse grain structure is produced
  18. 18. Austenite: This form presents as the face-centered cubic crystalline structure in iron and steel, or the body-centered cubic structure in nickel-titanium alloys, at higher temperatures. Appropriate cooling of nickel-titanium alloys can induce a transformation to a close-packed hexagonal martensitic phase. The transformation from austenitic to martensitic and vise versa is what gives alloys such as Ni-Ti the characteristic properties of shape memory and superelasticity. 
  19. 19.  Martensitic: This form presents as a body-centered cubic phase in stainless steels, or a monoclinic, triclinic or hexagonal crystalline structure in Ni-Ti alloys. The martensitic phase of nickel titanium exists at lower temperatures and is characterized by high ductility. It is formed as a result of quenching or cold work austenitic phase.
  20. 20. Physical properties Mechanical properties Physical properties Tensile Strength Compressive Shear Elasticity Elastic modulus Resilience Ductility Percentage Plasticity elongation Electrical and Yield Electrode strength Electrochemical potential properties Electrical Thermal resistivity properties
  21. 21. Basic properties of elastic materials The elastic behavior of any material is defined in terms of its stress-strain response to an external load. Both stress and strain refer to the internal state of the material being studied.  Stress: When an external force or load is applied to a solid body, an internal force equal in magnitude and opposite in direction is set up in the body. This internal force divided by the area over which it acts is called stress.  The basic types of stresses produced in dental structures under force are tensile, compressive, and shear. 
  22. 22.   Complex stresses: It is very difficult to induce a single type of stress in the body. For example, when a wire is stretched, it becomes longer suggesting that there is a tensile stress. But a wire, which becomes longer, will also becomes thinner. This means that there is a compressive stress also in it. This is called complex stresses and is an engineering principle called Poisson’s ratio. A material fractures in the area of maximum stress concentration.
  23. 23.  Strain: when a material is subjected to a force or load, there is a equivalent stress induced in the material. This internal stress brings about change in dimension and shape of the material. This change in dimension is usually measured by change in length. Change in length Strain = Original length
  24. 24. Elastic Properties Stress Wire returns back to original dimension when stress is removed Elastic Portion Strain
  25. 25. Hooke’s law: states that in an elastic deformation, the stress is directly proportional to strain.  Elastic limit: It is the greatest limit upto which an object can be stressed so that it will recover or return to its original dimension, when the load is withdrawn. Only upto a point of stress or limit the elastic can undergo Elastic Deformation. Beyond this point, it undergoes a plastic or permanent deformation. 
  26. 26.  Proportional limit: It is defined as the greatest stress, the material will sustain without a deviation from the Hooke’s law or proportionality of stress to strain. Upto this point, the stress and strain are proportional. This is the proportional limit. Beyond this point, the strain will not be proportional to stress.
  27. 27.  Yield strength: It is the point of stress at which the material undergoes a SLIGHT but permanent deformation or offset. Yield strength is slightly more than the proportional limit and for practical purposes the same as proportional limit. It is sensitive to work hardening.  Young’s Modulus or Modulus of Elasticity: is an inherent property of the material and cannot be altered appreciably by heat treatment, work hardening, or any other kind of conditioning. This property is called structure insensitivity.
  28. 28. Elastic Properties Stress Yield strength 0.1% Proportional Limit Elastic Limit Strain
  29. 29.
  30. 30.   Ultimate tensile strength : If a material continues to have more and more weight applied to it, it will eventually break. If the material is being stretched, the stress at breakage is called the ultimate tensile strength. When many metals are stressed above their proportional limits, they undergo a process called work hardening, and actually become stronger and harder.
  31. 31.   Toughness: this is the entire area under the stress – strain curve is a measure of the energy required to fracture the material. Resilience: The area under only the elastic region of the stress-strain curve is a measure of the ability of the material to store elastic energy.
  32. 32. Stress Elastic Properties Ultimate Tensile Strength Fracture Point Strain
  33. 33.  Formability - amount of permanent deformation that the wire can withstand without breaking  Indication of the ability of the wire to take the shape  Also an indication of the amount of cold work that they can withstand
  34. 34. Stress Elastic Properties Yield strength Proportional limit Resilience Formability Strain
  35. 35.    Flexibility large deformation (or large strain) with minimal force, within its elastic limit. Maximal flexibility is the strain that occurs when a wire is stressed to its elastic limit. Max. flexibility = Proportional limit Modulus of elasticity.
  36. 36.  Brittleness –opposite of toughness. A brittle material, is elastic, but cannot undergo plastic deformation. eg: Glass  Fatigue – Repeated cyclic stress of a magnitude below the fracture point of a wire can result in fracture. This is called fatigue.
  37. 37. Stiffness / Load deflection Rate  Magnitude of the force delivered by the appliance for a particular amount of deflection. Low stiffness or Low LDR implies that:1) Low forces will be applied 2) The force will be more constant as the appliance deactivates 3) Greater ease and accuracy in applying a given force.
  38. 38.
  39. 39. Strength  Yield strength, proportional limit and ultimate tensile/compressive strength  Kusy - force required to activate an archwire to a specific distance.  Proffit - Strength = stiffness x range.  Range limits the amount the wire can be bent, Stiffness is the indication of the force required to reach that limit.
  40. 40.  The shape and cross section of a wire have an effect on the strength of the wire.
  41. 41. Range  Distance that the wire bends elastically, before permanent deformation occurs (Proffit).  Kusy – Distance to which an archwire can be activated- working range.  Thurow – A linear measure of how far a wire or material can be deformed without exceeding the limits of the material.
  42. 42. Springback  Kusy -- The extent to which a wire recovers its shape after deactivation  Ingram et al – a measure of how far a wire can be deflected without causing permanent deformation. (Contrast to Proffit yield point).
  43. 43.  Large springback  Activated to a large extent.  Hence it will mean fewer archwire changes.  Ratio – yield strength Modulus of elasticity
  44. 44. Elastic Properties Stress Point of arbitrary clinical loading Yield point Range Springback Strain
  45. 45. Physical properties of orthodontic wires    The force required for the tooth movement has always highlighted the importance of “Light continous force.” (JIOS 2002; 76-88) Metallic orthodontic wires are manufactured by series of proprietary steps, typically involving more than one company. Initially the wire is cast in the form of an ingot, which must be subjected to successive deformation stages, until the cross section becomes sufficiently small for wire drawing.
  46. 46.  Moreover, the surface roughness of the wire, which has a clinically significant effect on the arch wire bracket sliding friction, varies considerably among the various products and is generally greater for the beta-titanium and nickel titanium wires.
  47. 47.  In general, an orthodontist should consider the following aspects in the selection of wires: force delivery characteristics, elastic working range, ease of joining individual segments to fabricate more complex appliances, corrosion resistance and biocompatibility in the oral environment and cost.
  48. 48. Requirements of an ideal archwire (Kusy ) 1. Esthetics 7. Resiliency 2. Stiffness 8. Coefficient of 3. Strength 4. Range 9. Biohostability 5. Springback 10. Biocompatibility 6. Formability 11. Weldability friction
  49. 49. Orthodontic archwires   Orthodontic wires, which generate the biomechanical forces, communicate through brackets for tooth movement, are central to the practice of the profession. Historically, gold alloy wires were first used in orthodontic practice, although these noble metal wires have minimal use currently because of their much greater cost compared to the popular base metal wires.
  50. 50.  The gold alloy wire compositions were generally similar to those of the type IV gold casting alloys, and their modulus of elasticity was approximately 100Gpa. Thus the gold alloy wires had elastic force less than that for stainless steel wires with the same crosssectional dimensions and segment lengths.
  51. 51. Stainless steel    Since 1950s stainless steel were used for most orthodontic wires. This continues to be the most popular wire alloy for clinical orthodontics because of an outstanding combination of mechanical properties, corrosion resistance in the oral environment, and cost. The wires used in orthodontics are generally American iron and steel institute (AISI) types 302 and 304 austenitic stainless steels. These contained 17-25% chromium and 8-25% nickel and the remaining were iron.
  52. 52.    The modulus of elasticity in tension for stainless steel orthodontic wires, ranges from about 160 to 180 GPa. The yield strength for the stainless steel archwires shows a much wider variation than the elastic modulus and to range from 1,100 to 1,500 MPa. Heat treatment of these wires also causes significant decrease in residual stress and modest increase in resilience.
  53. 53.    The use of heat treatment to eliminate residual stresses that might cause fracture during manipulation of stainless steel appliances can be important under clinical conditions. Austenitic stainless steel can be rendered susceptible to intergranular corrosion when heated to temperatures between 400°c and 900°c, due to the formation of the chromium carbides at the grain boundaries. Since the stainless steel alloys must be heated within this temperature range for soldering, clinicians are cautioned to minimize the time required for this process.
  54. 54.  The stainless steel alloys used for orthodontic wires are of “18-8” austenitic type. whereas 17-7 precipitation-hardenable stainless steel alloy had higher yield strength in bending than the commonly used stainless steel wire alloys.
  55. 55.  The chromium in the stainless steel forms a thin, adherent passivating oxide layer that provides corrosion resistance by blocking the diffusion of oxygen to the underlying bulk alloy. About 12-13 wt% chromium is required to impart the necessary corrosion resistance to these alloys.
  56. 56.    Nickel ion release from the alloy surface causes implications for the biocompatibility of these alloy. X-ray diffraction has shown that austenitic stainless steel orthodontic wires may not always possess the single-phase austenitic structure that is based upon a face-centered-cubic (fcc) arrangement of the iron atoms. In a two phase structure the austenitic was accompanied by a body-centered cubic (bcc) martensitic phase.
  57. 57.   Formation of the martensitic phase resulted in substantial reduction in the modulus of elasticity, from about 200Gpa to about 150Gpa for heavily cold worked alloys. Extensive cold working can increase the yield strength of austenitic stainless steels from about 275 to 1100Mpa.
  58. 58.  The modulus of resilience, represents the total elastic biomechanical energy or spring energy in the wire, is given approximately by (YS)²/2E. This expression can be used to estimate the changes in elastic spring energy resulting from the heat treatment.
  59. 59.   For clinical purpose, heat treatment stainless steel orthodontic appliances is to minimize breakage rather than achieve significant increase in resilience. Heat treatment of stainless steel wires at temperatures above 650°c must be avoided because rapid recrystallization of the wrought structure takes place, with deleterious effects on the wire properties.
  60. 60. Cobalt-chromium-nickel wires   A cobalt-chromium-nickel orthodontic wire alloy (Elgiloy) was developed during the 1950s by the Elgiloy cooperation (Elgin, IL, USA). This was originally used for watch springs, is available in four tempers (levels of resilience) that are colour-coded by the manufactures: blue (soft), yellow (ductile), green (semiresilient), and red (resilient).
  61. 61.   As with the stainless steel alloys, the corrosion resistance of Elgiloy arises from a thin passivating chromium oxide layer on the wire surface. Elgiloy blue alloy is very popular with many orthodontists because the as-received wire can easily be manipulated into the desired shapes and then heat treated to achieve considerable increases in strength and resilience.
  62. 62.   The maximum yield strength for straight, 0.41 mm diameter, wire segments is obtained with a heat-treatment temperature of about 500 °c. This heat treatment causes complex precipitation processes that substantially increase the yield strength of the alloy. Heat treatment of straight segment of Elgiloy blue wire causes an increase of about 10% in modulus of elasticity and about 20-30% in yield strength.
  63. 63.  Because of its “soft feel” (due to relatively low YS) during manipulation, orthodontists can mistakenly believe that as-received Elgiloy blue wires have substantially lower elastic force delivery than stainless steel wires. In reality, the values of modulus of elasticity for Elgiloy blue and stainless steel orthodontic wires are similar.
  64. 64. Wire alloy Austenitic Stainless steel CobaltchromiumNickel (Elgiloy) Beta-titanium (TMA) Composition Modulus of elasticity YS Springback 17-20% Cr, 8-12% Ni, 0.5% C. balance Fe 160-180 1100-1500 0.0060-0.0094 (AR) 0.065-0.0099 (HT) 40% Co, 20% Cr, 15%Ni, 1.8% Fe, 7%Mo, 2%Mn, 0.15% C, 0.04% Be. 160-190 830-1000 0.0045-0.0065 (AR) 0.0054-0.0074 (HT) 62-69 690-970 0.0094-0.011 34 210-410 77.8% Ti, 11.3% Mo, 6.6% Zr, 4.3% Sn. Nickel-titanium 55% Ni, 45% Ti (approx. and may contain small amounts of Cu or other elements) 0.0058-0.016
  65. 65.  Another clinical use of Elgiloy blue wires is fabrication of the fixed lingual quad-helix appliance, which produces slow maxillary expansion for the treatment maxillary constriction or cross bite in the primary and mixed dentitions.
  66. 66. Beta-Titanium Wires   A Beta-titanium wire for orthodontics is marketed by the Ormco Corporation (Glendora, CA, USA). The commercial name for this wire is TMA, which represents “titanium-molybdenum alloy”. The Beta-titanium wire was conceived for orthodontic use about two decades ago by Burstone and Goldberg, who recognized its potential for delivering lower biomechanical forces compared to the stainless steel and cobalt-chromium-nickel alloys.
  67. 67.  The elastic modulus for the beta-titanium wires is approximately 40% that of the stainless steel and Elgiloy blue wires. Because of the much lower value of elastic modulus, despite lower values for yield strength, the beta titanium wires have significantly improved values of spring back (YS/E), which increases their working range for tooth movement.
  68. 68.   Another clinical advantage of the betatitanium wires is excellent formability, which is due to their body – centered cubic structure. (bcc) The addition of molybdenum to the alloy composition stabilizes the high-temperature bcc beta-phase polymorphic form of titanium at room temperature, rather than the hexagonal closed-packed alpha-phase.
  69. 69.   The x-ray diffraction pattern for a betatitanium (TMA) orthodontic wire shows a single phase bcc structure, with the broadened peaks and preferred crystallographic orientation expected for a heavily cold-worked alloy. The slip-systems for dislocation movement for the bcc crystal structure account for the high ductility of the beta-titanium wires.
  70. 70.  The Zirconium and zinc in the alloy composition contribute increased strength and hardness, and their presence avoids the formation of an embrittling omega-phase during wire processing at elevated temperatures. This wire processing is problematic because of the reactivity of titanium, and there have been reports of TMA archwires are susceptible to fracture during clinical manipulation, despite the excellent formability of the beta-titanium alloy.
  71. 71.   Heat treatment by the orthodontist is not recommended for the beta-titanium wires, heat treatment of the alloy by the manufacturer approximately 700-730°c followed by water quenching. Subsequent aging at approximately 480°c results in precipitation of alpha phase and a maximum of spring back for the TMA wires.
  72. 72.   The next clinical advantage of beta-titanium is that it is the only orthodontic wire alloy possessing true weldability. Another important feature of the beta-titanium wires is their absence of nickel that is present in the other three types of alloy types.
  73. 73.  The beta-titanium wires are generally the most expensive of the orthodontic wire alloys, but the greater cost is considered by orthodontist by the combined advantages of intermediate force delivery and the excellent formability and weldability when fabrication of more complex appliances is required.
  74. 74. Nickel titanium wires    The pioneer for the development of nickel-titanium wires for orthodontics was Anderson, who published articles with colleagues advocating in the early 1970s. The first nickel-titanium orthodontic wire alloy (Nitinol) was marketed in the Unitek Cooperation. The generic name nitinol that is applicable to group of nickel-titanium alloys originates from nickel, titanium and the Naval Ordinance Laboratory where the alloys were developed by Buehler and associates.
  75. 75.   The Nitinol orthodontic wire offered a modulus of elasticity about 20% that of the stainless steel wires, along with a very wide elastic working range. This was evident when the wire was tested in cantilever bending. Two new superelastic nickel-titanium wires, Chinese NiTi and Japanese NiTi were introduced during the mid 1980s.
  76. 76.   Heat treatment of the Japanese NiTi wires at 500°c was found to significantly alter the super elastic force plateau that occurred during unloading of three point bending test specimens. It was also observed that heat treatment at 600°c eliminated the superelastic behavior. The bending properties of nonsuperelastic nickel-titanium wires are not affected by heat treatments at 500°c and 600°c temperature range.
  77. 77.   In the early 1990s a NiTi orthodontic wire alloy (Neo Sentalloy) with true shape memory at the temperature of the oral environment was introduced by GAC International, which had an optimum combination of light force delivery and springback under clinical conditions. X-ray energy-dispersive spectroscopic analysis with the SEM suggests that commercial orthodontic wires are generally titanium rich.
  78. 78.   There are two major NiTi phases in the nickeltitanium wires. Austenitic NiTi has an ordered bcc structure that occurs at high temperatures and low stresses. Martensitic NiTi has been reported to have a distorted monoclinic, triclinic, or hexagonal structures, and forms at low temperatures and high stresses. The shape memory effect is associated with a reversible martensite austenite transformation.
  79. 79.  In some cases an intermediate R-phase having a rhombohedral crystal structure may form during this transformation process.  For the superelastic nickel-titanium alloy, complete transformation to austenite occurs only slightly above the temperature of the oral environment
  80. 80.   In 1994 Ormco Cooperation introduced a new orthodontic wire alloy, copper NiTi which is available in three temperature variants of 27 °c, 35°c, and 40°c. The shape memory behavior is reported by the manufacturer to occur for each variant at temperatures exceeding the specified temperature. For example, the 27°c variant would be useful at for mouth breathers; the 35°c variant is activated at normal body temperature; and the 40°c variant would provide activation only after consuming hot food and beverages.
  81. 81.  In the recent studies 27°c copper NiTi wire alloy contain a single peak on both the heating and cooling curves, indicating direct transformation from martensitic to austenite on heating and form austenite to martensite on cooling, without an intermediate R-phase. In contrast, the 35°c copper NiTi and 40°c copper NiTi wire alloys exhibited two overlapping peaks on heating, corresponding to transformation from martensite to R-phase followed by transformation from R-phase to austenite.
  82. 82.   Element analysis using SEM have indicated that the three Copper NiTi variants have very similar compositions of approximately 44% nickel, 51% titanium, and slightly less than 5% copper, and 0.2-0.3% chromium. Kusy, has reported that copper Ni-Ti contains nominally 5-6 wt% copper and 0.2 – 0.5 wt% chromium. The 27°c C variant contain 0.5% chromium to compensate for the effect of copper in raising the Af temperature above that of the oral temperature, and the 40°c C variant contains 0.2% chromium.
  83. 83. Nickel-titanium open and closed coil springs   Super elastic nickel titanium alloy wires and springs introduced the concept of applying a super-elastic unloading curve that could potentially deliver a more constant force. Springs differ from archwires in that; springs are necessarily subjected to an additional manufacturing procedure of winding, which might effect their mechanical properties. Another difference is that, the forces applied to springs include torsional and tensional components in addition to bending force.
  84. 84.   Advantages of the compression and tensile springs made of nickel-titanium are: a minimum of permanent deformation and possibility of a more constant force during unloading. The closed coil nickel titanium springs are used for space closure; open coil nickel titanium springs are mainly used for opening space to unravel the teeth for molar distalization.
  85. 85.  Miura et al (AJODO 1988) subjected Japanese nickel-titanium closed and open coil springs to tensile and compression tests respectively. Springs of various lumen sizes, wire size, and different pitch was used in the study. It was observed that the lumen of coil springs remained constant, the load value of the super elasticity increased as wire diameter increases.
  86. 86.  When the diameter remained constant, the load value of super elastic activity increased, as the lumen of the coil became smaller. It was also shown that the open coil springs showed a more constant load value of super elasticity when compared to closed coil springs.
  87. 87.  Ryan (BJO 1995), compared the force characteristics of different commercially available open and closed coiled nickel titanium springs. He stated that the super elastic nickel titanium coil springs possess superior properties than other springs.
  88. 88.   Barwart ( AJODO 1996) in a study examined the effect of temperature change on the force delivery of nickel titanium closed coil springs. The springs were heated and cooled between 20°c and 50°c, while held in constant extension. Load values were found to increase with rising temperature. The force measured at 37°c was about twice as high as at 20°c. Immediately after the temperature started to drop, a rapid decrease in the force occurred to levels below those found at raising temperatures.
  89. 89.  Angolkar et al (AJODO 1992) conducted an in-vitro study on closed coiled springs of different length, and lumen in stainless steel, cobalt chromium nickel and nickel-titanium alloys. They showed that all the springs demonstrated loss of force over a time period. Most spring showed a major force reduction in first 24 hours to 3 days. Nickel-titanium springs showed least force decay and it was observed that increase in lumen size reduced the force delivery, and an increase in the wire size, increased the force delivery.
  90. 90.   Effect of lumen size on force characteristics : Jebby Jacob, Divakar Karanth, K. Sadashiva shetty. (JIOS 2002) Findings of this study on open coil springs revealed that, as the size of lumen increased, the force delivered decreased for a given diameter. In case of large size lumen a decrease in force value and increased range of super elastic activity is seen. These findings confirm the findings of Miura et al.
  91. 91.   Effect of wire diameter on force characteristics : In springs with a constant lumen size, as the diameter of the wire increased, the force delivered increased minimally. The super elastic activity range was almost the same. These findings slightly differed from the studies of Chaconas et al (1984) who observed that, with a constant lumen size, an increase in wire diameter produced an increase in force at a given activation.
  92. 92.   When the closed coil springs of different diameters were compared, it was found that larger diameter spring produced significantly higher force levels. It was also found that as the wire increased, force levels also increased drastically. Studies on Japanese nickel titanium springs by Miura et al (1988) showed that, the load value of super elastic activity increased in proportion to increase in diameter of wire.
  93. 93. Effect of spring length on force characteristics : The length of the spring has a great effect on the load deflection rate. A shorter spring stiffer than a larger spring of same dimensions. As the length of the open coil spring increased, initial force delivered was high, but the range of super elastic activity increased significantly. Shorter springs delivered more force than longer springs. 
  94. 94. Effect of static, simulated oral environment : The load deflection rate of open coil springs showed minor changes over 4 weeks in static simulated oral environment. It was noticed that for an open coil spring of 9mm length at given activation the force level decreased from week 0 to week 2, but surprisingly the force level regained at week 4 to that of week 0. 
  95. 95. Summary and conclusion: the force characteristic of the open and closed coil springs were concluded as : As the size of lumen increased, the force delivered by the open spring decreased. Increase in the wire diameter increased the force level in both open and closed coil spring. Closed coil spring of smaller diameter from “Ultimate Arch Forms” showed good range of super elastic activity. 
  96. 96. As the length of open coil springs was increased, the range of super elastic activity increased significantly. In case of closed coil springs, shorter springs exhibited wide super elastic range. Closed coil springs of similar dimension from different manufactures showed the variation in their properties. The ideal spring for clinical situation should be the one with optimum force level and with greater range of super elastic activity. Open coil springs with large lumen size and length and smaller diameter would meet these criteria. Closed coil spring with shorter length and the smaller diameter showed good super elastic range.
  97. 97. Property Stainless steel Cobalt-chromium- Beta-titanium (TMA) Nickel-titanium Nickel (Elgiloy Blue) Cost Low Low High High Force High High Intermediate Light Low Low Intermediate High Formability Excellent Excellent Excellent Poor Ease of Can be soldered. Can be soldered Only wire alloy that cannot be Joining Welded joints Welded joints must has true weldability. Soldered or delivery Elastic Range (springback) must be reinforced with be reinforced with welded. solder solder ArchwireBracket Lower Lower Higher Higher
  98. 98.
  99. 99. Orthodontic brackets  The original treatment approach utilized a slot attached to a stainless steel band that was cemented to the tooth, and early attempts to modify this attachment resulted in wide base surfaces on to which a slot was soldered. This appliance was then bonded to the tooth with epoxy resin. In the late 1970s the direct bonding to the enamel was widely accepted as a standard procedure to replace banding.
  100. 100.   The next stage of bracket evolution included modification of the base design to provide higher bond strength with adhesives, while concurrent efforts focused on decreasing the bracket surface. The bracket manufacturing process employed mechanical deformation or wrought processing technique to fabricate these appliances.
  101. 101.   Early commercially available aesthetic product included both plastic brackets fabricated from either poly crystalline or single crystal alumina. The thicker profile of the initial ceramic brackets caused slight discomfort for some patients.
  102. 102.    In describing bracket evolution, it is important to include the introduction of the self ligating bracket. This was the result of an effort to develop a reliable appliance that would maintain steady force levels during activation while providing decreased frictional resistance and optimum three dimensional control of the tooth movement. Important characteristic of these appliances documented through both in vitro and vivo studies is the potential elimination of cross-contamination through the avoidance of elastomeric ligature.
  103. 103. Metallic brackets    The morphology of the base of the stainless steel brackets, which is composed of metal mesh, yields adequate adhesive bond strength values to enamel. Gwinnett and his colleagues, determined the optimum mesh size for increased bond strength. Recent investigations were not able to identify any differences in the bond strength between conventional bracket bases with more condensed mesh configurations.
  104. 104. Advance in metallic brackets   Despite the clinically sufficient bond strength provided by conventional metal brackets, some attempts have focused on increasing the strength of the bracket-adhesive interface. Droese and Diedrich have introduced the plasma-coated metal bracket bases having a variety of mesh design as well as ceramic bracket bases. They reported that the enormously increased active surface area of the base resulted in much greater interlocking.
  105. 105.   For metal brackets, the non-mesh, plasma-sprayed bases had tensile adhesives bond strengths similar to those of unsprayed bases. There was alarming reports on the corrosion potential of the AISI type 316L austenitic stainless steel alloy. This alloy contains – 16-18% Cr, 1014% Ni, 2-3% Mo and maximum of 0.03% C, the “L” designation refers to the lower carbon content compared to type 316 stainless steel.
  106. 106.   Although the 316L stainless steel bracket alloy has performed well clinically, some corrosion of this material may be identified in the form of discoloration of the underlying adhesive layer. Maijer and Smith have attributed this effect to the diffusion of corrosion products from the bracket base to the adhesive, noting also the potential for enamel discoloration.
  107. 107. Aesthetic brackets    Appliances fabricated from alumina and zirconia ceramics, as well as a variety of plastic brackets. A 2205 stainless steel alloy that contains half the amount of nickel found in the 316L, alloy has been recently proposed by Oshida, Moore and their colleagues. The 2205 stainless steel alloy has a duplex microstructure consisting of austenitic and deltaferritic phases, and is harder than the 316L alloy when coupled with NiTi, beta-titanium, or stainless steel archwires.
  108. 108.  Matasa measured the microhardness values of the metallic brackets to obtain information about the relative strengths of the bracket alloys, it was found that the 316L alloy had much lower hardness compared to the precipitation hardening 17-4 stainless steel bracket alloy, although the former had significantly higher corrosion resistance.
  109. 109. Plastic brackets  The first plastic brackets were manufactured from unfilled polycarbonate and introduced during the early 1970s. But, unfortunately these brackets had a tendency to undergo creep deformation when transferring torque loads generated by archwires. To alleviate this problem ceramic reinforced, fiberglassreinforced, and metal slot-reinforced polycarbonate brackets were introduced.
  110. 110.  Plastic brackets are generally made from polycarbonate, but were subsequently found to suffer from several problems. These included distortion following water absorption, fracture, wear, discolouration and an inability to withstand the torquing forces generated by rectangular wires. (Reynolds, 1975)
  111. 111.  While the metal slot-reinforced polycarbonate brackets appear to be capable of generating the desired torque on teeth under clinical conditions, problems have been reported with the integrity of the slot periphery. Some of the metal slots have a level of surface roughness that may significantly effect archwire sliding friction.
  112. 112.   A beneficial consequence of the relatively low elastic modulus of polycarbonate is that the load applied during debonding of the plastic brackets results in a peel-off effect. Ceramic brackets have the advantages of permanent translucency and greater strength. Unfortunately they have the disadvantage of brittleness and excessive bond strength.( Scott, 1988) and enamel damage on debonding (Joseph and Russouw, 1990)
  113. 113.   Attempts have been made to combine the best properties of plastic and ceramic materials in a single bracket. One approach has been the ceramic filled plastic bracket. Although these brackets are easier to remove from enamel than the ceramic brackets, this is due to their significantly lower bond strength. A different approach has been taken by combining a ceramic bracket with a polycarbonate laminate as the bracket base. (Ceramaflex* brackets. TP Orthodontics, Indiana).
  114. 114. Ceramic brackets    Most of the ceramic brackets are made of highpurity aluminum oxide, and the brackets are available in both polycrystalline and single-crystal forms. Ceramic brackets fabricated from the polycrystalline zirconium oxide were subsequently manufactured in Australia and Japan. Optical properties and strength are inversely related to the polycrystalline alumina ceramics: the larger the individual grains in the microstructure, the greater is the ceramics translucency.
  115. 115.   Heat treatment must be carefully controlled to prevent grain growth that would degrade the physical properties. While the manufacturing process readily allows alumina brackets to be molded to the desired geometry, structural imperfections at the grain boundaries or trace amounts of sintering aids can serve as sites of crack initiation under stress.
  116. 116.  The single crystal alumina bracket contain less impurities than are found in the polycrystalline alumina brackets, which require the presence of sintering aids during manufacturing. Single crystal alumina has lower resistance to crack propagation than does polycrystalline alumina.
  117. 117.   Zirconia brackets have the possibility of achieving much higher values of fracture toughness than are possible for polycrystalline alumina brackets. Smooth bracket base surfaces should better distribute the shear stresses over the entire adhesive, while minimizing localized areas of stress concentration.
  118. 118. Self ligating brackets    Self-ligating brackets result in greater patient comfort, shorter treatment time, reduced chair time, and greater precision and control of tooth translation. Self-ligating bracket design permit the use of lighter force levels and impart lower frictional forces compared with ligated brackets. Friction during tooth translation is reduced significantly, due to elimination of steel or elastic ligatures.
  119. 119.   Self-ligating brackets has been reported to reduce the risk of percutaneous injury and the potential for transmission of hepatitis B virus, hepatitis c virus, or human immunodeficiency virus for the orthodontist and the support staff, self-ligation decreases the possibility of soft tissue laceration and infection from the cut end of ligature ties. The elimination of tie – wings and other type of food traps on some self-ligating bracket designs significantly elevates the hygiene level of all patents.
  120. 120.
  121. 121. Frictional Resistance of the Damon SL Bracket RUPALI KAPUR et al (JCO 1998)  Twenty Damon SL self-ligating brackets and 20 Mini-Twin brackets were tested.  All samples were .0225" X .030" maxillary first premolar brackets with standard Andrews prescriptions.  Wires used were 55mm lengths of .018" X .025" nickel titanium and .019" X .025" stainless steel. 
  122. 122.   Results The Damon SL bracket showed significantly lower kinetic frictional forces (p < .0001) than the Mini -Twin bracket with both wires. With the nickel titanium wires, the Damon SL brackets had a mean friction of 15.0g, compared to 41.2g for the Mini-Twin brackets. With the stainless steel wires, the Damon SL brackets produced a mean friction of only 3.6g, compared to 61.2g for the Mini-Twin brackets.
  123. 123. Comparison of self- ligated and ligated brackets: Ligation stability Ligation Force level Friction Sliding mechanism Office visits Treatment time Esthetics Patient comfort Oral hygiene Infection control Instruments Staff
  124. 124. Comparison behavior of 2205 duplex stainless steel: (Jeffrey A. Platt) AJODO 1997The 2205 stainless steel is a potential orthodontic bracket material with low nickel content (4-6wt %) whereas the 316L stainless steel with a nickel content (10-14wt%) is a currently used bracket material. Both were subjected to electrochemical and immersion corrosion tests in 37°c, 0.9wt% sodium chloride solution. 
  125. 125.   Electrochemical testing indicates that 2205 has a longer passivation range than 316L. When 316L is coupled with NiTi, TMA, or stainless steel arch wire and was subjected to the immersion corrosion test, it was found that 316L suffered from cervical corrosion. On the other hand, 2205 stainless steel did not show any localized cervical corrosion, although the surface of 2205 was covered with corrosion products, formed when coupled to NiTi and stainless steel wires.
  126. 126.  Considering corrosion resistance, 2205 duplex stainless steel is an improved alternative to 316L for orthodontic bracket fabrication, when used in conjunction with titanium, its alloys, or stainless steel wires.
  127. 127.    Shear, torsional, and tensile bond strengths of ceramic brackets using three adhesive filler concentrations: Alan J.Ostertag et al (AJODO 1991) 210 bovine teeth were bonded with one of three ceramic brackets using a 30%, 55%, or 80% filled adhesives. The brackets were debonded with a shear, torsional, or tensile force to test the bond strength and the site of bond failure.
  128. 128.    No significance was found in the shear, torsional, or tensile bond strength of each ceramic bracket type in relation to changes in the adhesive filler concentration. However, there was a trend toward increased bond strength with increasing filler concentration. The mechanically retained ceramic bracket showed greater shear bond strength and maximum shear bond strength in torsion than the chemical or chemical/mechanically retained ceramic bracket. The failure site was at the bracket-adhesive interface.
  129. 129.   Corrosion of orthodontic bracket bases : R. Maijer and D.C. Smith.: AJO January 1982. Recently attention was focused on the development of black and green stains in association with directly bonded stainless steel brackets. 12 clinical cases of staining were studied. After intraoral photography of the stains, the brackets were removed for examination.
  130. 130.   Multiple voids were observed at the resin-bracket interface, especially at the periphery. Considerable deterioration of the alloy base and mesh structure was observed in the void areas. Findings suggested that the presence of voids, together with poor oral-hygiene, led to corrosion of the type 304 stainless steel and formation of colored corrosion products which can result in enamel stains. Thus use of improved corrosion resistant stainless steel is recommended.
  131. 131. Alternatives to ceramic brackets: the tensile bond strengths of two Aesthetic brackets compared Ex vivo with stainless steel foil-mesh bracket bases : S. Arici and D. Regan. BJO 1997. The mean tensile/peel bond strength were evaluated for three types aesthetic brackets (a ceramicreinforced bracket and two generations of a ceramic/polycarbonate combination bracket). These were found to be significantly lower than the mean tensile/peel bond strength of a conventional foilmesh stainless steel bracket base. 
  132. 132.   Failure of the ceramic-reinforced polycarbonate brackets occurred predominantly by fracture of the tie wings during testing. With the ceramic/polycarbonate combination brackets, the majority of the specimens failed due to separation of the ceramic and polycarbonate parts of the bracket.
  133. 133. The fracture strength of ceramic brackets : Daniel A. Flores et al; (AO 1989). The fracture strength of different ceramic bracket under different surface conditions and ligation methods using a torsional wire bending force were compared. Five different bracket types (two polycrystalline, two single-crystal, and one metal) were tested using elastic and wire ligation. Results showed a significant difference between bracket types and surface conditions. 
  134. 134.  Non-scratched single-crystal brackets had higher fracture strengths and slightly higher fracture loads than polycrystalline brackets. However, single crystal brackets were significantly adversely affected by surface damage, while polycrystalline brackets were not significantly affected by surface damage.
  135. 135. Elastomeric ligatures and chains    Elastomeric products are used in orthodontics as ligatures and as continous modules (chains) for the engagement and retraction of teeth. The elastomeric modules were first introduced to orthodontics three decades ago and have gained almost universal acceptance by the profession. Due to the force degradation exhibited by the elastomeric chains, over the past decade there has been increasing interest in self-ligating brackets.
  136. 136. Elastomeric ligatures and chains are poly urethanes, which are thermosetting polymers possessing a structural unit formed by step-reaction polymerization. General properties of electrometers: by Billmeyer,  when stretched rapidly, elongations greatly in excess of 100% can be achieved, with no major loss of energy. 
  137. 137.    The highest values of tensile strength and stiffness are obtained after full stretching. Upon removal of the tensile force, a rapid contraction occurs, since the polymer structure has a strong tendency to return to its original condition. Full recovery takes place as long as the tensile force does not exceed the elastic limit, demonstrating the high resilience of these materials.
  138. 138.   Riley et al (1979) determined that steel ligatures generated more friction than elastic ligatures, particularly when plastic brackets were used. Kusy et al (1988) used laser spectroscopy to study surface roughness of orthodontic wires. Among the 4 wire-alloys that are commonly used in orthodontic practice, stainless steel appeared the smoothest, followed by cobaltchromium, beta-titanium and Nickel-titanium. Kusy cautioned that surface roughness and friction in orthodontic appliance systems have yet to be correlated.
  139. 139.   Schumacher and Bourauel (1990) conducted a series of experiments to find the friction forces affected by the ligation technique. They inferred that friction is determined by the sort of ligature and the way of ligation and not by the dimensions of different archwires. Sims and Waters (1993) compared self – ligating and two other type of ligations. The placing of figure of “8” tie increased friction than self ligating brackets, because the self ligating brackets apply less frictional contact to the arch wire than conventional ties Siamese brackets.
  140. 140. Conventional ligatures: clinician prefer to use these materials over the 0.20mm to 0.36mm stainless steel ligature wires for several reasons, including the ease of application, potential for fluoride release, patient-friendly nature, aesthetic appearance and decreased force delivery. This force been found to reach the levels achieved with stainless steel ligatures in twin brackets were the extension of the elastomer is maximized because of the large size of the bracket. 
  141. 141.  Taloumis et al have reported the force decay of variety of elastomeric ligatures in a simulated oral environment. There was an initial force loss of about 50-60% during the first 24-hour interval. The force decrease continued at a significantly slower rate for 7-10 days, and signs of permanent deformation and alteration of the shape of the elastomers were evident following their recovery from the medium.
  142. 142.    When overall diameter of the module is decreased for a given mass of elastomer, the force delivery increases because of the greater wall thickness; this anticipated relationship was observed by Taloumis et al. Huget et al observed that water acts as a plasticizer by weakening intermolecular forces in the polyurethanes, leading to chemical degradation. Chromatographic analysis has shown increased leaching from elastomeric modules immersed in water and subjected to 7 days of stretching.
  143. 143.   Elastomeric ligatures may be ineffective for the treatment applications involving large rotational moments, where the exertion of an substantially decreased force would fail to completely engage the archwire in the bracket slot for the full term of activation. The PH and temperature variations in the oral environment, along with accumulation of plaque and formation of microbial colonies on the surface of the elastomerics, may effect the structure, surface properties, and conformation of the polyurethanes.
  144. 144. Elastomeric chains: Difference in the force decay between the ligature and the chain are:  Variations in the additives incorporated in the basic polyurethane polymer to obtain the final product.  Variations in manufacturing techniques, where die stamping or injection moulding is used to fabricate the modules.  Variations in morphological or dimensional characteristics of the chains. 
  145. 145.   Ash and Nikolai showed that the force degradation is greater in vivo compared to in vitro conditions. More recently, Stevenson and Kusy employed a Maxwell-Weichert model. The model assumes that the force degradation arises from two processes: a rapid mechanism that is responsible for the large initial force loss, and a second mechanism that accounts for the relatively slow rate of force loss at longer period of time.
  146. 146.   Traditionally these modules have been used for the retraction of the anterior teeth to close the extraction spaces as well as for the closure of the diastemas. With the advent of rare-earth magnets and superelastic NiTi coil springs that are capable of producing constant low force over a extended period of time, the use of elastomerics has diminished significantly.
  147. 147.  Several studies have also dealt with the use of prestretching to eliminate the force loss by elastomeric modules. Two modes of pre stretching have been proposed; the instantaneous prestretching technique used by young and Sandrik and by Chang would be much more convenient for the orthodontist than the extended time technique of prestretching described by Brantley et al.
  148. 148. Evaluation of frictional forces of different archwires materials against preadjusted edgewise stainless steel bracket, using two modes of ligation: Friction has always been one of the main factors in orthodontic movement that has occupied the clinician’s mind. In this study five different alloys were used to find the least amount of friction: Stainless steel, Nickel titanium, Chrome-cobalt, Copper-NiTi and Beta-Titanium. 
  149. 149.     The bracket chosen for the experiment is stainless steel preadjusted edgewise with a 0.022 x 0.025 inch slot size. The two modes of ligation are: Elastic modules and Stainless Steel ligature wires. The test was done using an instrument called “the cool flow factor controller apparatus”. The results obtained from this study demonstrate that the least frictional forces generated is that of Stainless steel wires, using elastomeric modules.
  150. 150.  Also the most values were recorded using the beta-titanium alloy archwire, which in addition to high surface roughness, the form of microwelds with the brackets in dry conditions with process of ion implantation implemented on TMA alloys, there is a favourable 54% reduction of kinetic friction presenting a viable method of reducing the amount of friction.
  151. 151.  Conclusion: Admitting there is no such thing as the “ideal” archwire material that can satisfy all the criteria for an ideal treatment, and is devoid of any disadvantages. Therefore, the final say belongs to the clinician to use that knowledge, strike a compromise and improvise his objectives and treatment plan based on the choice of the material at hand, which in turn will differ.
  152. 152.    So far the stainless steel has been proven to allow the least amount of friction among the vast number of materials available to the clinician. The Beta-Titanium had the highest frictional values recorded. Therefore it is safe to say that the material of choice for maximum anchorage cases with least resistance in sliding of the wire is Stainless Steel. Also that the ligation using elastic modules produces less amount of friction as compared to stainless steel wire ligation.
  153. 153.
  154. 154. Orthodontic adhesive systems  The basis for the adhesion of brackets to enamel has been enamel etching with phosphoric acid, as first proposed by Buonocore in 1955.  Bonding of brackets to enamel has been the crucial issue in orthodontics research. The introduction of an acid-etching technique in the 1950s to bond dental restorations to tooth structure was the breakthrough point in the history of orthodontic bonding. 
  155. 155.  The chemically activated orthodontic adhesives employ benzoyl peroxide as an initiator, which is activated by a tertiary aromatic amine such as dimethyl-p-toluidine or dihydroxyethyl-p- toluidine.  Two-phase products were the first to be tried by orthodontist in the early days of bonding. The manipulative process is problematic, relatively time consuming, and these materials are gradually being eliminated from orthodontic practice. 
  156. 156.  Mixing of the two components causes surface porosities and air voids in bulk of the material, owing to the prolonged exposure to air and the inevitable entrapment of air bubbles.  Studies have shown that photo-cured composites, intentionally mixed as if they were chemically cured materials, also demonstrated severely porous surfaces and air voids in the bulk materials.
  157. 157.   One phase adhesive system: The principle of inhomogeneous polymerization was introduced in orthodontics with the development of the no-mix bonding resins, which were intended to minimize the mixinginduced defects of the material. Recent evidence suggest that the degree of cure for these adhesives is comparable to that of the two-phase systems for surfaces in contrast with the enamel.
  158. 158.  This might be attributed to the surface-tovolume ratio of the adhesive layer, which can depend on several factors. A study found that the thickness of adhesive layers prepared under simulated clinical conditions ranged from 120-250 µm, depending on the morphology and design of the bracket base.
  159. 159. D.N Kapoor, V.P Sharma, Pradeep Tandon, Kamlesh Pandey: Comparative evaluation of Tannic acid, Citric acid and phosphoric acid as etching agents for direct bonding (JIOS 2002) Concluded that: 1.Application of 37% phosphoric acid for 15 seconds produced comparable etching topography when 50% tannic acid was applied for 90 seconds. 2. Electrothermal debracketing technique produced bond failure at adhesive bracket interface with no iatrogenic damage to enamel. 
  160. 160. 3.Assessment of penetration depth revealed that 37% phosphoric acid dissolves more enamel than tannic acid or citric acid. 5. 50% Tannic acid when applied on enamel for 90 sec provided the tensile bond strength closer to 37% phosphoric acid. So 50% Tannic acid could be an alternative to phosphoric acid for etching as it dissolves lesser amount of enamel and at the same time provides similar tensile bond strength.
  161. 161. Ashima Valiathan, Ashil A.M. African Journal of Oral Health Sciences 2006 _ Invitro study (In press)  Found out the efficacy of Transbond Moisture insensitive primer , in the dry state and in the presence of saliva and compared it with conventional Transbond XT.  It was found that in the presence of salivary contamination, brackets bonded using Transbond MIP showed significantly higher bond strength (14.53 Mpa) as compared to brackets bonded with conventional primer (9.36 Mpa)
  162. 162.  Francesca, Cacciafesta, Andrea, Brinkmann AJO April 2006 assessed the effect of light tip distance on the shear bond strength and failure site of the bracket cured with 3 light curing units (halogen, LED, Plasma arc) At a light tip distance from bracket base of 0 mm they showed no significantly different shear bond strength, At light tip distance of 3mm no significant differences were found between the halogen and plasma arc lights but they showed higher bond strengths than the LED. At 6mm plasma arc cure showed significantly higher shear bond strengths than the other two.  Conclusion: In hard to reach areas plasma arc cure light is suggested for optimal efficiency
  163. 163. Moisture-resistant adhesive: Transbond MIP(3M).,Assure (Reliance)   It is available in a primer formulation (MIP) that replaces the conventional bonding agents applied to the enamel surface and is based on the hydrophilic attraction of its constituents.  The main reactive component of this product is a methacrylate-functionalized polyalkenoic acid copolymer originally used in the dentin bonding system marketed by the same manufacturer.
  164. 164.     Moisture-active adhesives: They require rather than tolerate the presence of moisture for proper polymerization. They require no bonding agent. However, the surface must be intentionally wetted prior to application. A recent product based on a cyanoacrylate formulation (Smartbond, Gestenco International AB,Sweden) has demonstrated superior properties, excellent in vitro performance and easy clinical application without the need for etching and liquid resin coating.
  165. 165.    Srivastava A; Gorantla S; Valiathan A. (TIBAO 2002) compared the bond strength of two indigenously developed cyanoacrylates (N-Butyl cyanoacrylate and Isoamyl-2cyanoacrylate) with a conventional self-cured composite (Right On). Results : N-Butyl cyanoacrylate had higher bond strength than the control composite, but it deteriorated when stored in physiologic saline for 48 hours.
  166. 166.  Isoamyl-2-cyanoacrylate had significantly lower bond strength when compared to the other samples in all the three groups under study.  So this study showed the need for further work to be done with cyanoacrylates to decrease their bio-degradability, so that they can be clinically useful in orthodontics.
  167. 167.      James Sunny P, Valiathan A. A comparative invitro study with new generation ethyl cyanoacrylate(smartbond) and a composite bonding agent (TIBAO 2003) Cyanoacrylate (Smart Bond) was compared with a conventional composite (Right-On) Shear bond strength was measured at 1 hour (dry), 24 hrs and 48 hrs (in artificial saliva). Results: Composite showed higher bond strength than cyanoacrylate at all time intervals. Smartbond achieved a maximum bond strength of 5.07 Mpa at 24 hours, which declined at 48 hours to 5.01Mpa. It was concluded that Smartbond might not be a better option for bonding compared to conventional composite.
  168. 168.  Ashima Valiathan, Gikku Philip, Sunil Sachdeva: Clinical evaluation of Chitra Composite - A comparative study  In 1992 The first and only BIS_GMA based, 2 component chemically cured composite was developed by Valiathan et al at the Sree Chitra Thirunal Institute of Medical Sciences and Technology (Trivandrum)  Aim: To evaluate clinically Chitra composite in comparison with Right-On ( commercially available imported composite).  Subjects and Methods: 50 patients that reported to the orthodontic department were selected.12-35 years.
  169. 169. Teeth on Left side bonded with Chitra composite (Test) 1 batch,25 patients with smaller filler size particle. 2 batch,25 patients with larger filler size particle. Right side with Right-On composite (Control) 42 cases were bonded with standard edgewise brackets, 7 Beggs and 1 straight wire. The duration of evaluation was 6months to 15 months. Results: The Overall Bond Failure for Chitra composite was on an average 17% 1st batch – 20% failure 2nd batch – 14% failure For Right- On group it was 14.3%
  170. 170. In 24 hours failure: For Chitra composite, it was 7.6% For Right- On group it was 4.7% The difference of 1.07 was statistically insignificant among the test and control groups Conclusion: 1.The bond failure of Chitra composite is comparable to Right-On group. 2. Chitra composite with larger filler size had greater bond strength at both 24 hrs and overall breakage. 3. There were no incidence of white spot decalcification.
  171. 171.   Upendra Kumar Gurjar, D.N. Kapoor, Amita Jain, V.P. Sharma and Pradeep: (JIOS 1998) A comparative evaluation of growth of microorganisms on the surface of various orthodontic bonding materials. This study was conducted to evaluate and compare the adherence and growth of alpha-haemolytic streptococci on the surface of commonly used nomix orthodontic bonding materials and further to scan the surfaces of these materials to find out a correlation between their surface roughness and adherence and growth of alpha-haemolytic streptococci.
  172. 172.   Microscope and alpha-hemolytic streptococci were grown on their surfaces. Weight gain due to microbial adhesion and growth was measured on the basis of measured weight of dried sample after microbial adhesion and growth of microorganisms minus weight of sample before adhesion and growth. It was found that the different no-mix orthodontic bonding materials have different surface roughness even when they were optimally prepared to be as smooth as possible, the adherence and growth of alpha-haemolytic streptococci on the surface of bonding materials was significantly different from each other and there was a definite correlation between the surface roughness and adherence and growth of alpha-haemolytic streptococci on the surface of bonding materials.
  173. 173. References 1. 2. 3. William R. Proffit, Henry W. Fields,Jr., and James L. Ackerman: Contemporary Orthodontics: Mosby: Third Edition: 2000. Page 326-398. William A. Brantly, Theodore Eliades: Orthodontic Materials. Scientific and clinical aspects: 2001; page 1-25, 77-104, 143-172, 173188. Robert P. Kusy: Morphology of polycrystalline alumina brackets and its relationship to fracture toughness and strength: Angle Orthodontist July 1988: Page 197-202.
  174. 174. R.J. Dobrin, I.L. Kamel, and D.R. Musich: Load-deflection characteristics of polycarbonate orthodontic brackets: AJO January 1975; vol67: Page 25-33. 5. Charles A. Frank, and Robert J. Nikolai: A comparative study of frictional resistance between orthodontic brackets and archwire: AJO December 1980; vol 78: Page593-609. 6. Alan J. Osttrertag, Virendra B. Dhuru, Donald J. Ferguson, and Ralph A. Meyer, Jr.: Shear, torsion, and tensile bond strengths of ceramic brackets using three adhesives filler concentrations: AJODO September 1991; vol 100: Page 25258. 4.
  175. 175. Jeffrey A. Platt, Andres Guzman, Arnaldo Zuccari, David W. Thonburg, Barbara E. Rhodes, YoshikiOshida, and B. Keith Moore: Corrosion behavior of 2205 duplex stainless steel: AJODO July 1997; vol 112: Page 69-79. 8. S. Aricl, and D. Regan: Alternatives to ceramic brackets: the tesile bond strengths of aesthetic brackets compared ex vivo with stainless steel foil-mesh bracket bases: BJO 1997: vol 24: Page 133-137. 9. Jan Odegaard and Dietmar Segner: shear bond strength of metal brackets compared with a new ceramic bracket: AJODO September 1988; vol94: Page 201-206. 7.
  176. 176. 10. Rodney K. Rhodes, Manville G. Duncunson, Jr., 11. 12. Ram S. Nanda, and Frans Currier: Fracture strengths of ceramic brackets subjected to mesial-distal archwire tipping forces: Angle Orthodontist 1992; vol62: Page 67-75. Sunil Kapila, Padmaraj V. Angolkar, Manville G. Ducanson, Jr., and Ram S. Nanda: Evaluation of friction between edgewise stainless steel brackets and orthodontic wire of four alloys: AJODO August 1990: vol 98: Page 117126. Daniel A. Flores, Joseph M. Caruso, Garland E. Scott, and M. Toufic Jeiroudi: The fracture strength of ceramic brackets: a comparative study: Angle Orthodontist May 1989; vol 60: Page 269-276.
  177. 177. 13. Mark H. Holt, Ram. S. Nanda, and Manville G. Duncanson: Fracture resistance of ceramic brackets during archwire torsion: AJODO April 1991; vol 99: Page 287-293. 14. Garland E. Scott, Jr.: Fracture toughness and surface cracks – The key to understand ceramic brackets: Angle Orthodiontist January 1988: Page 5-8. 15. Theodore Eliades, George Eliades, and William A. Brantley: Microbial attachment on orthodontic appliances: Wettability and early pellicle formation on bracket materials: AJODO 1995; vol 108: Page 351-60.
  178. 178. 16. Sandra Gunn, John M. Powers: Strength of ceramic brackets in shear and torsion tests: JCO 1991; vol 25: Page 355-358. 17. Thomas R. Katona: A comparison of the stress developed in tension, shear peel, and torsion strength testing of direct bonded orthodontic brackets: AJODO 1997; vol 112: Page 244-51: 18. Thomas R. Katona: Engineering and experimental analyses of the tensile loads applied during strength testing of direct bonded orthodontic brackets: AJODO August 1994; vol 106: Page 167-174.
  179. 179. 19. Upender Kumar Gurjar, D N Kapoor, Amita Jain, V P Sharma, and Pradeep Tandon: A comparative evaluation of growth of microorganisms on the surface of various orthodontic bonding materials: JIOS 1998; vol 31: Page 47-52. 20. Ashima Valiathan, Ashil A.M. Efficacy of moisture insensitive primer- An in vitro study. African Journal of Oral Health Sciences 2006 (In press) 21. K. Vijayalakshmi, M.S Rani: Comparison of shear bond strength Of GIC with composite resins- An Invitro Study JIOS 1995 Vol26 Num4 Page 144- 147 22. Denny J.Payyappilly, Ashima Valiathan, and Surendra Shetty: Wires in orthodontics: JIOS April 1993; vol 24: Page 60-65.
  180. 180. 23. Reddy BR, Vijayalakshmi K: Estimation of lactic acid around the brackets bonded with GIC and no mix adhesive. JIOS 1998 Vol 31 Num1 page 3-6 24. D.N Kapoor,V.P Sharma, Pradeep Tandon, Kamleash Pandey: Comparative evaluation of Tannic acid, Citric acid and phosphoric acid as etching agent for direct bonding. JIOS 2002 Vol35 Num 2 page 54-62. 25. Amit Srivastava, Suresh Gorantla and Ashima Valiathan. In Vitro evaluation of indigenously developed cyanoacrylates as bonding agents in comparison to a conventional bonding agent Trends Biomater. Artif. Organs 2002: 16:25-27.
  181. 181. 26. James Sunny and Ashima Valiathan “A comparative In vitro study with newer generation Ethyl Cyanoacrylate (Smartbond) and a Composite-bonding agent” Trends Biomater.Artif.Organs. 2003;16(2): page 83-89 27. Koyal Sarin and Ashima Valiathan. Comparison of bond failure of Fuji Ortho LC Transbond XT – A clinical study. Journal of Pierre Fauchard Academy 2003; 17:17-25 28. D. N. Kapoor, N. P. Sharma, Pradeep Tandon, Vipin Kumar Varshney: Bond strength as related to different guaze mesh size: JIOS 2001; vol 34: Page 2-7. 29. Nitin D. Gulve, T. M. Bhagtani: A comparison of shear bond strength and mean survival time treated and untreated mesh backed stainless steel brackets, an in-vitro assessment: JIOS 2002; vol 35: Page 124-128.
  182. 182. Thank you For more details please visit