Ashok Sir Arch Wire

Evolution Of Archwire In Fixed Appliance Orthodontics1 Introduction Wire is one of the important components of all most all orthodontic appliances. Practically all orthodontic forces for which appliances are used exert forces by means of wires – not just any wire, but a wire properly selected in size, shape, material, properties and properly bent to exert the desired force. An understanding of the well balanced relationship that exists between the applied techniques and the basic principles, leads to a broader application of skills to serve the need of orthodontics. An orthodontist spends much of his professional career handling wires and the success or failure of many forms of treatment depends upon the correct selection of wires, possessing adequate properties combined with careful manipulation beside bracket and auxillaries. The search for correct materials has continued from the beginning of dental art to the present time. Through the ages, dentistry has been dependent to a great degree on the advances made by the contemporary art and sciences for improvements in materials. 1 Evolution Of Archwire In Fixed Appliance Orthodontics The materials used by orthodontists have changed rapidly in recent years and will continue to do so in the future. As esthetic composite arch wires are introduced, metallic arch wires are likely to be replaced for most orthodontic applications in the same way as metals have been replaced by composites in aerospace industry. Arch wires are reviewed in the order of their development, with emphasis on specific properties and characteristics, such as strength, stiffness, range, formability and weldability. Because an ideal material has not yet been found, arch wires should be selected within the context of their intended use during treatment. Over the last century, material science has made rapid progress. This has been evident in our day to day life also. Orthodontics, particularly, has benefited largely from this. In this branch of dentistry, not only have the materials been improved, but also the philosophies have changed. Orthodontics has come a long way since the days of the E-arch and various removable appliances used in the early 20th century. With the introduction of the Edgewise appliance, newer materials have introduced in order to make the most of these appliances. Wires which had good formability, increased resilience and low cost were obviously favoured. This was probably the reason why stainless steel (and Elgiloy) prevailed over the noble metal alloys. The need of the Begg appliance was quite different from that of the traditional edgewise appliance. This led Begg and Wilcock to produce a variety of stainless steel that would provide low continuous forces over a long period of time. The NickelTitanium(Ni-Ti) alloys  introduced  in  the  1970’s  showed  some  remarkable  properties   of superelasticity and shape memory, although these could not be exploited clinically at that time. The wires had limited formability, but could still be used in the 2 Evolution Of Archwire In Fixed Appliance Orthodontics traditional edgewise appliance. The next generation of NiTi wires benefited a lot by the pre adjusted edgewise appliance. This appliance required lesser amount of bends incorporated into the wire, and the A-NiTi’s  perfectly  suited  this. However, introduction of the TMA wires bridged the gap between stainless steel and Nickel Titanium alloys wires, with properties that were intermediate to the two of these alloys. Thus, one can see how the appliance philosophies and material science progress is closely interrelated. All these wire alloys that were introduced and the newer ones have individualistic and unique properties associated with them. In order to use the newer wires, it is important to know as to why they have specific properties. 3 PIERRE FAUCHARD. and a thread passing partially forms a loop and by the pressure and support given the inclined  teeth  will  be  made  upright”. This appliance was very heavy and unwieldy. The width of band should be less than the height of the teeth to which it is applied. The urge for better performance has resulted in the development of newer orthodontic wires with promising physical properties. particularly the anterior teeth. The teeth were ligated towards their positions. It was also designed to expand the arch.2 4 . The band should neither be too stiff or too flexible. Two holes are made at each end.Review of Literature 2 Review of Literature Rapid strides have been made in the field of arch wire materials. the father of modern dentistry in 1723 developed what is probably the first orthodontic appliance in evolution of fixed orthodontic appliance. It was called as Bandolet or Bow. it is necessary to use a band of silver or gold. It was flat piece of metal scalloped out for the ideal position of the teeth. FAUCHARD said “If the teeth are much out of line and cannot be corrected by means of thread. He was also the first one to classify malocclusion. Fitch MD.  until  the   teeth have resumed their proper position – that is to say. advertised that “He supplies ligatures  to  teeth  of  an  irregular  position”. His treatment consists of “Application of an instrument adapted to arch of the mouth. He wrote in his  book  that  “The  strings  should  be  removed  and  retightened  twice  a  week. so as to prevent them  from  completely  closing”. until the teeth of upper Jaw are drawn forward so that no part of them is hidden behind  those  of  the  lower  jaw”.2 Leonard Koecker (1728 to 1850) in 1826. practicing in Philadelphia.2 William Lintott in 1841 described a bite opening appliance.2 5 .Review of Literature In 1757. which consisted of a labial arch of a light bar of gold or silver passed around front surfaces of teeth by means of ligatures (known as Indian twist) and the necks of irregular teeth with pressure applied for movement. whose book entitled A system of dental surgery. advocated the Fauchard method but went a step further by recommending only gold strips on the labial surface of upper arch and lingual surface of lower arch.2 Samuel S. the dentist to the king of France.2 Shearjashub Spooner (1809 to 1859) in 1838 found various types of treatments. published in 1829. devoted a significant amount of information on irregularities of the teeth. Etienne Bourdet (1722 to 1789). fastening a ligature on the irregular tooth and removing the resistance of the lower teeth by placing some intervening substances between the teeth of upper and lower jaw. such as use of gold and silver plates to exert a gentle and continued pressure to correct irregularities of teeth. Angle introduced the round labial arch wire which was supported by clamp bands on molar teeth. the E arch gave way to flat wire 0.022″ x 0. As demand increased for more and better control of the teeth. Like this the pin and tube appliance was developed.Review of Literature As early as in 1871 William E. the arch wires in each succeeding mechanism was thinner than the immediately preceding mechanism. Thus the edgewise appliance was introduced.R. Dr. It has excellent rotating ability but lacked the power to tip the teeth. Magill (1825 to 1896). It could be observed that in Angle’s orthodontic appliance. In 1916 with the advent of ribbon arch. This flat flexible wire was molded to fit the malocclusion and was held in close approximation to the teeth by a bracket that opened occlusally. In 1929 Dr.036″ placed against the teeth.028″ dimension.2 In 1887. The appliance is commonly referred to as E (expansion) arch. Begg designed an appliance for moving roots of teeth. bands were added to anterior teeth with vertical tubes placed over them. Dr. so that the amount of forces delivered for tooth movement became less in each later 6 . In 1908. was first to use cemented bands on the teeth by oxychloride of zinc cement. Angle introduced an appliance that engages the teeth edge wise by way of new bracket that opened bucally and used flat wires of 0. P. It was on the foundation of this cemented tooth band and circumferential arch wires that modern orthodontic appliance have developed. If molar expansion was desired the arch wire was expanded. It also was an expansion arch and teeth were ligated towards their preplanned arch. Review of Literature mechanism. He used two different forms of labial wire. s universal appliance.J. good resistance to corrosion and low cost. F.s and 40. Becket of USA. In 1937. Atkinson introduced Atkinson. A significant advancement in orthodontic materials was made in late 30. This indicates that Angle was aware that the tooth moving forces delivered by his earlier forms of orthodontic appliance were too great. A. This reduction of tooth moving forces in each new orthodontic mechanism permitted greater control of tooth movement. Up to 1930. The cobalt alloys were simultaneously developed in the mid century and this has physical properties very similar to that of stainless steel. The procedure increases its strength significantly. In 1952 Dr.s when stainless steel wires became widely available. Beune Strauss and Edward Maurer of Germany shared the honor for the development of the materials. It was in between 1903 and 1921 that Harry Brearley of Sheffield.M. one rectangular and one round and was designed to bring about every tooth movement possible. In 1929 Lucien de Costa a Belgian and editor of Archives of orthodontics introduced austenitic stainless steel orthodontic wire with greater strength. They had an advantage that they could be supplied in softer and more formable state and then could be hardened by heat treatment. high modulus of elasticity. Begg in collaboration with Mr.s the only orthodontic wire available was made of gold. It made possible to move the teeth rapidly and reduced the pain that patient had to bear during treatment.Willcock sought to develop tensile wire materials that were thin enough to distribute forces at an optimum level 7 . The name Nitinol is an acronym derived from elements which comprises the alloy. The wire was thick enough to resist masticatory stress. such as high elastic limit and low modules of elasticity.014″ arch wire.9 8 . over a long distance and with minimal loss of force intensity.018″ to 0. Later developments related to Niti alloy came from China in Beijing in General research institute for Non-ferrous metal in 1978.s by William F. Hau-Chang Tien and his colleagues with Niti a new super elastic orthodontic wire with high spring back and low stiffness properties.4 Then came the most talked Niti wire which was invented in 60. Niti was introduced to orthodontics by Andreasen and his associates. Ni from nickel. a research metallurgist at the Naval Ordinance Laboratory in Silver Spring. He did extensive research and published his findings on the properties and uses of his new alloy. The diameter of wire initially produced was progressively decreased from the thicker diameter to 0.Review of Literature for tooth movement over a considerable period of time. Buchler. It has an excellent spring back property but does not possess shape memory or super elasticity because it has been manufactured by a work hardening process. In 1971. Ti from titanium and nol from Naval Ordinance Laboratory. by DR. They were attracted to unique properties of Niti alloy. Maryland (now called as Naval Surface Weapons Center). they reported the results of their investigation for clinical use and subsequently Unitek Corporation started producing this wire for clinical use under the trade name of Nitinol. The wire was initially in the0. He was the first person to suggest the use of shape changes in Nitinol wires to apply forces to the teeth in order to move them orthodontically.J. A. of Australia developed a much harder. 9 . supreme grade as per the request of Dr. It has a unique balance of low stiffness.Mollenhauer of Melbourne. Willcock Jr.Review of Literature In the same year Furukawa electric company Ltd of Japan produced a new type of Japanese Niti alloy possessing properties of excellent spring back. good formability and weldability which indicates its use in a wide range of clinical applications. Charles J.009″. Dr. Jon Goldberg. At around the same time in 1980. Andreasen tested thermodynamic nitinol wires and introduced them to clinical orthodontics. Dr. These wires can return to previously set shape when heated to their transition temperature range (TTR). Burstone and A.29 In 1980.010″ diameter and was further reduced to 0. Burstone reported the development of Chinese Niti alloy and in 1986 Miura Fetal reported Japanese Niti alloy.8 In 1985. near alpha-phase titanium alloy comprising of 6% Aluminum and 4% Vanadium for orthodontic purposes. shape memory and super elasticity.4 He also started the production of ultra high tensile stainless steel fine round wire. introduced new Beta-titanium alloy (Titanium-molybdenum alloy) in clinical use of orthodontics. C.J. These two alloys have a basic austenitic grain structure and have the advantage of a transition in the internal structure without requiring a significant temperature change to do this. high spring back. In 1988 Mr. Hudgins.8 10 . It is made up of clean optical fiber and has unique mechanical properties. Richhold and Etal investigated the Nickel titanium alloy to determine the effect of clinical recycling on load deflection characteristics and surface topography of Nickel-titanium alloy. Studies have shown that Nickel titanium and TMA have higher coefficient of friction than stainless steel. Glenn R.17 In 1991 Sunil Kapila. The various procedure included disinfection alone and in conjugation with steam autoclave. dry heat and cold solution sterilization. J.26 In 1992.Review of Literature In 1990 John J. Smith. Von Fraunhofer. A low coefficient of friction is usually desirable in orthodontic arch wire. Michael D. was introduced to orthodontics by Tallas. Erickson studied the effect of long term deflection on permanent deformation of Nickel. Bagby and Leslie C. Gary D.Casey studied the effect of clinical use and various sterilization procedures on three types of Nickeltitanium and one type of Beta-titanium and stainless steel arch wire. Burstone demonstrated Titanium molybdenum alloy (TMA) with ion implantation. In case of TMA.Titanium. OPTIFLEX an aesthetic arch wire. Ion implantation increases its hardness and reduces coefficient of friction of TMA wire. In 1992 Glen A. the friction is probably high due to its relative softness compared to harder stainless steel bracket. the same year.36 In 1995 Charles J.A. nickel. Dead Soft Security Arch wires has been introduced by Binder and Scott.5 11 . Recently in 2001. It’s an alloy of copper. These arches are bend to lie passively in all attachments. the same year Rohit Sachdeva and Suchio Miyasaki introduced copper-Niti alloy in family of Niti.Review of Literature In 1995. titanium and chromium. Classification 3 Classification Arch wires can be broadly classified according to chemical composition. microstructure and mechanical properties. 1) According to Materials used GOLD ARCHWIRES STAINLESS STEEL ARCHWIRES AUSTRALIAN ARCHWIRES CHROME COBALT NICKEL ALLOY ARCHWIRES JAPANESE NITI ARCHWIRES CHINESE NITI ARCHWIRES ALPHA-TITANIUM ALLOY ARCHWIRES COPPER-NITI ALLOY ARCHWIRES NICKEL SILVER ALLOY ARCHWIRES FORSTADENT TITANOL ARCHWIRES 12 . Classification OPTIFLEX ARCHWIRES DEAD SOFT SECURITY ARCHWIRES NICKEL TITANIUM ARCHWIRES  CONVENTIONAL  PSEUDOELASTIC  THERMODYNAMIC 2) According to Cross.008″ to 0.60″ FOR EXTRA ORAL APPLIANCES 13 .045″ FOR INTRA ORAL APPLIANCES 0.045″ to 0.section ROUND RECTANGULAR ROUNDED RECTANGULAR SQUARE BRAIDED MULTISTRANDED 3) According to Diameter 0. NEWTON. S SECOND LAW OF MOTION If the particle is subjected to an unbalanced system of forces. S FIRST LAW OF MOTION A particle subjected to a balanced system of concentrated forces will remain at rest. subjected to forces. which is concerned with the state of rest or motion of bodies. 14 . or will with constant speed in a straight line if originally in motion. FORCE Force is defined as an act upon a body that changes or tends to change the state of rest or motion of that particular body.Terminology / Definitions 4 Terminology / Definitions MECHANICS 34 Is an area of study of physical science. the particle will be accelerated in the direction of net force exerted. if originally at rest. NEWTON. Although strain is dimensionless quantity. the paired active and reactive forces are equal in magnitude but are directly opposite to one another and are exerted on adjacent particles. it disappears after the strain is removed. It is measured in terms of pounds/ square inch or psi. When an external force acts upon a solid body. Plastic strain is permanent displacement of the atoms inside the material. The external force will be called the load on the body. STRAIN Change in dimension is called as strain. Strain may be Elastic Plastic Combination of two Elastic strain is reversible. The internal forces divided by the area over which it acts within the body is the resultant stress. STRESS Stress is the force per unit area acting on millions of atoms in a given plane of a material OR Displacing forces measured across a given area. S THIRD LAW OF MOTION States that. a reaction force results within the body that is equal in magnitude but opposite in direction to the external force. units such as m/m or cm/cm are often used to remind one of system of units employed in actual measurements. 15 .Terminology / Definitions NEWTON. the forces are applied at right angles to the area over which they act.Terminology / Definitions TYPES OF STRESSES AND STRAINS TENSILE STRESS A tensile stress is caused by a load that tends to stretch or elongate a body. the internal resistance to such a load is called compressive stress. when a wire is stretched. For example. but the shearing stresses and strain will also be present. the experimentally observed stress will be predominantly tensile. COMPLEX STRESSES It is extremely difficult to induce a stress of a single type in body. COMPRESSIVE STRESS If a body is placed under a load that tends to compress or shorten it. A shear stress is always accompanied by shear strain. With both tensile and compressive stress. Furthermore during 16 . SHEAR STRESS A stress that tends to resist a twisting motion or sliding of one portion of a body over another is a shear on shearing stress. A tensile stress is always accompanied by a tensile strain. A compressive stress is always accompanied by a compressive strain. compressive. As can be seen. a stress value finally will be found at which the wire does not return to its original length after it is unloaded. PROPORTIONAL LIMIT If the wire discussed above is loaded in tension in small increments until the wire ruptures without removal of load each time. In such a case the wire is said to have been stressed beyond its elastic limit. tensile and shear stresses are present in various parts of structure. such that it will return to its original dimensions when the forces are released. An example of complex stresses as shown in figure is produced by bending a beam in three point loading. the atoms will move into their regular positions) when the load is removed. and if each stress is plotted on a vertical coordinate and corresponding strain is plotted on a horizontal coordinate. the resulting strain may be such that the wire will return to its original length (i. a curve is obtained. If the load is increased progressively in small increments. a condition that obviously indicates the presence of compressive stresses.e. The elastic limit of a material is the greatest stress to which a material can be subjected.Terminology / Definitions the deformation. ELASTIC LIMIT If a small tensile stress is induced in a wire. since the volume of wire remains constant. 17 . and then released after each addition of stress. it must decrease slightly in cross-sectional area. and if the straight line is extended in a dotted line. is known as the proportional limit. Since the proportional limit is the greatest stress possible in accordance with this law. 18 . the straight line portion of the graph in figure is confirmation of this law. The yield strength will always be greater than the elastic limit or proportional limit and will vary with the offset chosen. If a ruler is laid on a straight line portion of the curve ( from O to P). at which the curve digresses from a straight line. Since direct proportionality between two quantities is graphically a straight line. HOOKE. it may be defined as the greatest stress that may be produced in a material such that the stress is directly proportional to strain. S LAW It states that the stress is directly proportional to the strain in elastic deformation.Terminology / Definitions It can be noted that the curve starts as a straight line but gradually curves after a certain stress value is exceeded. the stress at the point P. YIELD STRENGTH The yield strength is the stress required to produce the particular offset chosen. Since the modules of elasticity is the ratio of stress to the strain. the less the strain for the given stress. a constant proportionality will result. The formula for modules of elasticity in tension is derived as follows. proportional limit and yield strength are defined differently but their magnitude are so nearly the same that for all practical purpose the terms can often be used interchangeably.section of material under stress e= Increase in length l= Original length Stress = F/A =s Strain = e/l = ε Then E = Stress = s Strain = F/A = Fl e/l eA 19 . it follows that. the greater will be the value of the modulus. For example. considerable stress must be induced before a notable strain or deformation results. MODULUS OF ELASTICITY If any stress value equal to or less than the proportional limit is divided by its corresponding strain value.Terminology / Definitions The three terms elastic limit. Let E = Modules of elasticity F = Applied force on load A = Cross. Such a material would posses a comparatively high modulus of elasticity. if a wire is difficult to bend. This constant of proportionality is known as modulus of elasticity or Young’s Modules (E). The relation between the maximum flexibility.Terminology / Definitions The unit for modules of elasticity is forces per unit area (Mpa or Psi). the resulting deformations or strain cannot be measured. not to exceed its proportional limit. 20 . the proportional limit and modules of elasticity may be expressed as follows: Let E = Modulus of elasticity P = Proportional limit Εm = Maximum Flexibility From last equation E = P Εm Or Em = P/E STATIC AND DYNAMIC FORCES Forces that are applied constantly for an arbitrarily long time are called as static forces / static stresses. This property is indirectly related to other mechanical properties. MAXIMAL FLEXIBILITY It is defined as the strain that occurs when the material is stressed to its proportional limit. Since dynamic forces exits for only very short time. They are known as dynamic forces. The stresses in the teeth during mastication are not of this type. These stresses usually exist for only an instant. RESILIENCE It is defined as amount of energy absorbed by a structure when it is stressed. Properties of Alloys 5 Properties of Alloys The properties of orthodontic wires are the consequence of two principal origins. 2) The particular nature of the drawing process including the heat treatment by the manufacturers and clinician will have further significant effects on the specific properties.18.24 The elastic behavior of any material is defined in terms of its stress – strain response to an external load.22.19. defined as force 21 . 1) Basic composition will determine the broad range of inherent general properties of each wire type. Both stress and strain refer to the internal state of the material being studied: stress is the interval distribution of the load. BASIC PROPERTIES OF ELASTIC MATERIALS3. whereas strain is the internal distortion produced by the load. If a force is applied to such a beam.A UPPORTED BEAMS-B 22 . Orthodontic arch wires and springs can be considered as beams. its response can be measured as the deflection produced by the force. supported either only on one end (e.g. CRITERIA OF AN IDEAL ARCHWIRE CANTILEVER. a spring projecting from a removable appliance) or from both ends (a segment of an arch wire spanning between attachments on adjacent teeth). defined as deflection per unit area.Properties of Alloys per unit area. Force and deflection are external measurements. especially since yield strength and ultimate strength differ much for titanium alloys. strength. For Orthodontic purposes. three major properties of beam materials are critical in defining their clinical usefulness i.1% is measured. internal stress and strain can be calculated from force and deflection by considering the area and length of the beam. the point at which any permanent deformation is first observed. the maximal load that the material can resist. in a somewhat different way. Each represents.Properties of Alloys STRESS STRAIN DIAGRAM In tension. Springiness = 1/stiffness 23 .the ultimate tensile strength is reached after some permanent deformation and is greater than the yield strength. Three different points on a stress-Strain diagram can be taken as representative of the strength of a material. stiffness and range. The maximum load that the wire can sustain. Since this ultimate strength determines the maximum force the wire can deliver if used as a spring. The most conservative measurement is the proportional limit. Each can be defined by appropriate reference to a force deflection or stress strain diagram. this is defined as the yield strength. Strength is measured in stress units (gm/cm square) Stiffness and springiness are reciprocal properties.e. it is important clinically. A more practical indication is the point at which a deformation of 0. This spring back is measured along the horizontal axis as shown in figure. Their spring back properties in the portion of the load-deflection curve 24 . it will not return to its original shape. the springier the wire. orthodontic wires are deformed beyond their elastic limit. the stiffer the wire. Range is defined as the distance that the wire will bend elastically before permanent deformation occurs. In many clinical situations.Properties of Alloys FORCE DEFLECTION CURVE STRESS STRAIN DIAGRAM Each is proportional to the slope of the elastic portion of force deflection curve. but clinically useful spring back will occur unless the failure point is reached. This distance is measured in mm. If the wire is deflected beyond its yield strength. The more horizontal the slope. the more vertical the slope. Formability is the amount of permanent deformation that a wire can withstand before failing. 25 . It should also be reasonable in cost.strain curve out to the proportional limit. In addition. These three major properties have an important relationship.Properties of Alloys are between the elastic limit and the ultimate strength. therefore. It represents the energy stored capacity of the wire. In contemporary practice . Strength = Stiffness X Range. and the best results are obtained by using specific arch wire materials for specific purposes. which is a combination of strength and springiness. the material should be weldable or solderable so that hooks or stops can be attached to the wire. are important in determining clinical performance. resilience and formability. Two other characteristics of some clinical importance can also be illustrated with a stress strain diagram. It represents the amount of permanent bending the wire will tolerate before it breaks. no one arch wire material meets all these requirements . The properties of an ideal wire material from orthodontic purposes can be described largely in terms of these criteria: High Strength Low stiffness High range High formability. Resilience is the area under the stress. (Ys/E). high stored energy. environment stability. Higher spring back values provide the ability to apply large activation with a resultant increase in working time of the appliance. a more constant force overtime as the appliance experiences deactivation and greater ease and accuracy in applying a given force. These include a large spring back. high formability. Spring back is related to the ratio of yield strength to the modules of elasticity of the material. 2) STIFFNESS OR LOAD DEFLECTION RATE This is the force magnitude delivered by an appliance and is proportional to the modulus of elasticity. low surface friction and the capability to be welded or soldered to auxiliaries and attachments. maximum flexibility and range of activation or working range. A brief description of each of these desirable wire characteristics is provided. 1) SPRING BACK This is also referred to as maximum elastic deflection. Spring back is also a measure of how far a wire can be deflected without causing permanent deformation or exceeding the limits of the material. low stiffness. This in turn implies that fewer arch wire changes or adjustments will be required.Properties of Alloys WIRE CHARACTERSTICS OF CLINICAL RELEVANCE Several characteristics of orthodontic wires are considered desirable for optimum performance during treatment. biocompatibility. Low stiffness provides the ability to apply lower forces. 26 . coils and stops without fracturing the wire. The preferred wire material for moving a tooth relative to the wire would be one that produces the least amount of friction at the bracket / wire interface. This in turn ensures a predictable behavior of the wire when in use. Environmental stability ensures the maintenance of desirable properties of the wire for extended periods of time after manufacture. 5) BIOCOMPATIBILITY AND ENVIRONMENTAL STABILITY Biocompatibility includes resistance to corrosion and tissue tolerance to elements in the wire. 6) JOINABILITY The ability to attach auxiliaries to orthodontic wires by welding or soldering provides an additional advantage when incorporating modifications to the appliance. 7) FRICTION Space closure and canine retraction in continuous arch wire techniques involve a relative motion of bracket over wire.Properties of Alloys 3) FORMABILITY High formability provides the ability to bend a wire into desired configurations such as loops. 4) MODULUS OF RESILIENCE OR STORED ENERGY This property represents the work available to move the teeth. Excessive amount of bracket / wire friction may result in loss of anchorage or binding accompanied by little or no tooth movement. It is reflected by the area under the line describing elastic deformation of the wire. 27 . INGOT Dentists are so used to forget that an orthodontic wire is actually a modified cast.Manufacturing 6 Manufacturing All stainless steel orthodontic wires are produced with the help of standard formulas based on specifications of the American Iron and steel Institute. beginning with the selection and melting of alloying metals. Like any casting it will have varying degree of porosity and inclusions of slag in different part. The physical properties of metals are influenced at every step in production. This Ingot is far from being a uniform chunk of metal. In metallurgical terminology these crystals are usually called 28 . A magnified view of inside of Ingot would show it. to be made up of crystals of component metals. One of the critical steps in wire making is pouring the molten alloy into a mold to produce an Ingot. Manufacturing grains, and it is this granular structure which controls many of the mechanical properties. Grains in a crystal are found in definite patterns typical of individual metals, but they are far from perfect because of conditions under which they must form. When the Ingot is cooling and solidifying, many different grains are forming at once. These growing crystals crowd and surround one another, so that the ingot becomes a mesh work of many irregularly shaped grains of different materials. The size and distribution of these grains are very dependent on the rate of cooling and the size of the ingot. The cooling and pouring processes affect the porosity as well as grain structure. Porosity in the ingot comes from either of two sources, gases that are either dissolved in the metal or produced by chemical reactions within the molten mass from bubbles which are trapped in metal. As the ingot cools and shrinks, the late cooling interior section shrinks inside an already hardened shell. This shell does not permit the volume to adjust enough to the shrinkage, so additional voids of the vacuum results. So, before further processing begins the ingot is trimmed to remove the undesirable parts. The microstructure of a metal is the very basic of its physical properties and mechanical performance and every step in production is directed at getting the most out of the original grain structure of the ingot. ROLLING The first mechanical step in processing is rolling the ingot into a long bar. This is done by a series of rollers which gradually reduce the ingot to a relatively smaller 29 Manufacturing diameter. Through all this rolling and later processing into the final wire, the different parts of original ingot never lose their identity. The metal that was on the outside of the ingot forms the finest wire. Wire is actually a grossly distorted ingot, thus it is easy to see that different pieces of wires from the same batch can differ depending upon which part of ingot they came from. The individual grains of the ingot also keep their identity through the rolling process until certain heat treatment is applied. Each grain is elongated in the same proportion as the Ingot. The squeezing, massaging action of rolling the Ingot has a very important effect on the grain structure, actually increasing the strength of the metal. Where the original crystal fitted together rather indifferently with gaps and voids scattered among them, the mechanical action of rolling, forces them into long, finger like shapes that are closely meshed together. This causes an increase in the hardness or brittleness of the metal, as the grains are forced to interlock even more highly with one another. This is a form of work hardening. Even the atoms which make up the crystal structure are forced into new positions, filling in gaps and irregularities that may have been left in original crystals. Each pass through the rollers, increases this work hardening and finally the structure becomes so locked up that it can no longer adjust enough to adapt to the squeezing of the rollers. If rolling is continued beyond this point the surface will start to show many small cracks and begin to crumble. Before this happens the rolling process is stopped and the metal is annealed by heating to a suitable high temperature. At annealing temperature the atoms become mobile enough to move about within the 30 Manufacturing mass, breaking up the tight crystalline structure. When the metal is cooled again, the annealed structure resembles that of the original casting but in more uniform form. Grains size can be controlled in annealing by adjustment of the time and temperature of annealing and rate of cooling. DRAWING After the ingot has been reduced to a fairly small diameter by rolling, it is reduced to its final size by drawing. This a more precise process in which the wire is pulled through a small hole in a die. This hole is slightly smaller than the original diameter of the wire so that the walls of the die squeeze the wire uniformly from all sides, as it passes through. This reduces the wire to the diameter of the die. Drawing the wire subjects the entire surface of the wire to the same pressure instead of squeezing from only two sides as in rolling. Drawing is much precise process than rolling, but the effect on grain structure is much the same. Before it is reduced to orthodontic wire/size, the wire must be drawn through many series of dies and annealed several times along the way to relieve work hardening. These intermediate annealing is very important for strength and especially to resistance to breakage. The purpose of heating and cooling a large coil of wire so that all parts are treated alike is not as easy as it may seem. It must be done slowly to prevent the outer coils from being heated more than those on the inside and temperature must be carefully controlled. 31 Hardness and spring properties of orthodontic wires depend almost entirely on the effect of work hardening during manufacture. This effect is usually rather small and because of different drawing schedules that are used. there will be too much residual softness. it will have maximum work hardening and spring properties. Gold work hardness slowly.Manufacturing Even with the most careful procedures. Gold is extremely ductile and can be reduced considerably with each draft. Variations such as these can create many problems in sampling for quality control. When wire is annealed in processing at one size and different parts of the batch are then drawn to different final sizes. If drawing is not carried out for enough time after the last annealing. The actual no of drafts through the dies as well as frequency of annealing depends on the alloy being drawn. which is desirable as long as brittleness does not become excessive. Ordinary carbon steel requires many more steps than gold and stainless steel requires many more than carbon steel. so that it also needs less frequent annealing than the more rapidly work hardening steel. Wires can be reduced through much of the range of orthodontic size without an intermediate annealing. it is not consistent. situations can arise in which one side of the coil or the inner or outer part will be affected differently. This means that the entire drawing and annealing schedule must be carefully planned with the final size in mind. the smaller of these wires will be subjected to more hardening. Differences in these cases make the smaller wire proportionally harder. 32 . If the metal is almost in need of another annealing at its final size. Manufacturing RECTANGULAR WIRES Rectangular wire can be made by drawing the materials through a rectangular die or by rolling round wires to a rectangular shape. There appears to be no significant difference in the wires formed by the two processes but is difficult to evaluate. Round wires made by drawing, vary as much in physical properties as most of rectangular wires. Therefore it would be unrealistic to attribute specific differences to rolling and drawing process. Drawing can however produce a sharper corner on a rectangular wire and this can be an advantage in the application of torque. 33 Ideal Orthodontic Alloy 7 Ideal Orthodontic Alloy The ideal orthodontic wire for an active member is one that gives a high maximal elastic load and low load deflection rate. The mechanical properties that determine these characteristics are elastic limit and modules of elasticity. The ratio between the elastic limit and modules of elasticity (EL/E) determines the desirability of the alloy. The higher the ratio, the better will be the spring properties of wire. The orthodontist should look for alloys that have high EL,s and low E,s . For an alloy to be superior in spring properties, it must possess a significantly higher ratio.12 By contrast, in the reactive member of an appliance not only is a sufficiently high elastic limit required but a high modulus of elasticity is also desirable. Since it is common practice to use the same size of slot or tube opening throughout the treatment, it is possible to use different alloys combined in the same appliance so that the needs of both the active and reactive members can be served. 34 Ideal Orthodontic Alloy Four other properties of wire should be mentioned in evaluating an orthodontic wire. 1) The alloy must have a reasonable resistance to corrosion caused by the fluids of the mouth. 2) It should have sufficient ductility so that it will not fracture under accidental loading in the mouth or during fabrication of an appliance. 3) It is desirable to have a wire that can be fabricated in a soft state and later heat treated to a hard temper. 4) A desirable alloy is one to which attachments can easily be soldered. A thorough knowledge of the mechanical and physical properties of an alloy is important in the design of an orthodontic appliance. WIRE CROSS SECTION TYPE (ROUND, FLAT, SQUARE, RECTANGULAR) A most critical factor in the design of an orthodontic appliance/wire is the cross–section of the wire to be used. Small changes in cross-section can dramatically influence both the maximal elastic load and the load deflection rate. The maximal elastic load varies directly as the third power of the diameter of round wire, and the load deflection rate varies directly as the fourth power of the diameter. It may seem that the most obvious method of reducing the load deflection rate of an active member is to cut down the size of the wire. The problem in reducing the size of cross-section is that the maximal elastic load is also reduced at an high rate (d3). In the design of the active member it is good policy to use as small as cross –section as possible consistent 35 so that a sufficiently high load deflection rate exists.018″ wire is not interchangeable with 0. any attempt to reduce the size of cross. Factors influencing load deflection LOAD DEFILATION RATE MAXIMUM INCREASE MAXIMUM DEFLECTION Activation of wire without changing length decreased No change Increase Activation in direction of original bending - Increase Increase Alteration of cross section to rectangular form If rate is maintained as constant Increase as 1/h Increase as 1/h MECHANICAL PROPERTIES OF WIRE MODULUS OF ELASTICITY PROPORTIONAL LIMIT SP/E Cross section(round) L d 1/d Cross section(rectangle) h h 1/h 1/L 1/L L DESIGN FACTOR Length/cantilever 36 .020″ wire. load deflection rate rather than maximal elastic load is the prime consideration.20″ wire will deliver almost twice as much force.section. A piece of 0. for with a similar activation. the 0.Ideal Orthodontic Alloy with a safety factor. The fact that the load deflection rate varies as the fourth power of the diameter in round wire suggest the critical nature of selection of proper cross-section. Beyond this. so that undue permanent deformation will not occur. In the selection of proper cross-section for the rigid reactive members of an appliance.section to improve spring properties may well lead to undesirable permanent deformation. Under normal circumstances it is necessary to select a large enough wire cross. beyond the needed maximal elastic load to have sufficient rigidity. Moreover. In cases of unidirectional activations.Ideal Orthodontic Alloy A): Optimal Cross section for flexible member Generally for multi directional activations in which the structural axis is bent in more than one plane. a circular cross-section is the choice. these can roll into either the gingival or the check. while limited tooth movement in other plane. round wire may rotate in the bracket and if certain loops are incorporated in wire. a square or rectangular wire would appear superior to a round one because of the ease of orientation and greater multi directional rigidity. Flat wire can also be used in certain situations when considerable tooth movement is required in one plane. This leads to more definite control of anchorage units also. Another advantage of flat wire is that the problems of orientation of the wire can be more simply solved than with a round cross-section. B): Optimal Cross section for reactive member With respect to reactive member. 37 . unless it is properly oriented. flat wire is the cross-section of choice as more energy can be absorbed into a spring made of flat wire than of any other crosssection. Flat or ribbon wire can deliver lower load-deflection rates without permanent deformation than can any other type of cross-section. activations may not rotate in the intended plane. Flat wire can be definitely anchored into a tube or a bracket so that it will not spin during the deactivation of given spring. One of the problems of round wire is that. The mechanical properties of the round wire and cross-section tolerances are far superior to those of other cross-sections. Secondarily. The major reason why the orthodontist should select a particular wire size is the stiffness of the wire or its load deflection rate. the ligature wire minimizes a great amount of play in a first order direction. for instance. In an edgewise appliance.Ideal Orthodontic Alloy SELECTION OF PROPER WIRE (CROSS SECTION SIZE & ALLOY USED) The selection of proper wire is based primarily on the load deflection rate required in the appliance.014″ wire that deflected over 2 mm would give the desired force. In a replacement technique.18″ wire over 0.018″ which would give almost the same force with 1 mm of activation. After the tooth had moved 1 mm. Sometimes 2 other factors can be used in selecting wire cross section size. the orthodontist might begin with a 0. in other words the smaller the wire the greater it will get deflected without permanent deformations.016″ wire primarily because of the difference in play. it is dependent on the magnitude of the forces & moments required. Therefore the clinician does not select a 0. 1) It may be believed that increasingly heavier wires are needed in a replacement technique to eliminate the play in a first order direction between wire and the bracket. but maximum elastic deflection varies inversely with the diameter of wire. since it can fully seat in the brackets. the wire could be replaced with a 0. 38 . 2) A wire may also be selected because it is believed that the smaller the wire the greater will be the amount of maximum elastic deflection possible. 004 0.762 3164.406 256.018 0.00 39 .014 0.00 0.06 0.006″ wire has a Cs of 5.06 0.020 0.102 1.036 0.Ideal Orthodontic Alloy Small differences in cross-section produces large changes in load deflection rates. Therefore a simple numbering stuff has been developed.1 mm (0.004″) round wire as a base of a 0. CROSS SECTIONAL STIFFNESS NUMBER OF ROUND WIRE Cross section Cs (m) (mm) 0. since in round wires load deflection rate varies as the fourth power of diameter. which means that for the same activation five times as much form is delivered.016 0. based on engineering theory that gives the relative stiffness of wires of different cross-sections if the material composition of wire is the same. Manufacturing variations in wires or mislabeling of wires obviously can significantly alter the actual Cs number.994 6561. The cross-sectional stiffness no (Cs) uses .356 150.010 0.254 39.00 0.00 0.457 410.022 0.559 915.06 0. Clinicians are interested in the relative stiffness of the wire that they use.06 0. but they have neither the time nor the inclination to use engineering formulas to determine their stiffness.06 0.030 0.508 625. 035 0.531 FIRST ORDER 130.004″ round wire. The overall stiffness of an appliance (S) is determined by two factors. Appliance stiffness = Wire stiffness x Design stiffness 40 .79 1805.010 X 0.457X0. In the past.535X0.025 0. one relates to the wire itself (Ws).018X0.254X0. which means that for an identical activation it will deliver 256 times as much force as a 0.406X0.035 0.57 966.Ideal Orthodontic Alloy CROSS SECTIONAL STIFFNESS NUMBER OF RECTANGULAR AND SQUARE WIRE Cross section Shape RECTANGULAR RECTANGULAR RECTANGULAR RECTANGULAR RECTANGULAR Shape SQUARE SQUARE SQUARE M CS mm 0.87 1535.022 0.14 1289.95 3129.457 0. For purposes of comparison both the wire configuration and the alloy are identical and only the cross-section varies.021 0.10 2173.0215X0.406X0.016X0.69 Wires with a cross-section of 0.531X0.52 1129.021X0.37 CS 434 646.025 0.018 0.020 0.016″has a Cs of 256.546X0.35 1845.018X0.406 0.021X0.028 0.016 0.63 297.016X0.550 0.711 Cross section M mm 0.508 0. wire cross-section has been varied to produce different stiff nesses. and one is the design of an appliance (As): S = Ws x As Where S = Appliance load deflection rate Ws = The wire stiffness As = Design stiffness factor In general terms.457X0.83 SECOND ORDER 132. Ws = Ms x Cs Where Ws is wire stiffness number Ms is material stiffness number Cs is cross sectional stiffness number. With the availability of new materials. The material stiffness number (Ms) is based on the modulus of elasticity of the material. only the size of the wire was varied and no concern was given to the material property. since most orthodontists used only stainless steel with identical modulus of elasticity.Ideal Orthodontic Alloy As the appliance design is changed by increasing wire between the brackets or adding loops. However. the orthodontist is not concerned only with ways by which wire stiffness can be altered.the cross-section and material of the wires. which determines wire stiffness. it is now possible to maintain the same cross-section of wire but use different materials with different stiff nesses to produce a wide range of forces and load deflection rates required for comprehensive orthodontics. Wire stiffness is determined by two factors. 41 . A numbering system can be used to compare relative stiff nesses based on the material. the stiffness can be reduced as the design stiffness factor changes. In general terms Wire stiffness = Material stiffness x Cross sectional stiffness Previously. 08 Respond 0.18-0. the history of the wire (drawing process) may have some influence on the modulus.19 Elgiloy blue(Heat treated) 1.07-0. In addition to new alloys.08 The load deflection rate can be changed by maintaining wire size and varying the load deflection rate as significantly as by altering the cross-section. Typical stiffness numbers for other alloys are given in table.26 Elgiloy blue 1. For practical clinical purposes. Braids take advantage of smaller cross-sections. which have higher maximum elastic deflections. The material stiffness numbers of representative braided wires is given in table.04-0. Using the principle of variable cross-section orthodontics.S 1. steel is currently the most commonly used alloy in orthodontics. the amount of play between the 42 . MATERIAL STIFFNESS NUMBER OF ORTHODONTIC ALLOYS & BRADED STEEL MS ALLOYS S.16 D-rect 0. however. braided wires have been used in orthodontics. and in process produce wires that have relatively low stiffness.00 TMA 0.22 Braids Twist-hex 0. its Ms Number has been arbitrarily set at 1.14-0. the material stiffness number (Ms) can be used to determine the relative amount of force that a wire will give per unit activation.Ideal Orthodontic Alloy Since. Although the modulus of elasticity is considered a constant.20 Force -9 0.42 Nitinol 0. In this way the play between the wire and the attachment is not dictated by the stiffness required but is under the full control of the operator. the stiffness of wire can be produced by using a material with a proper material stiffness. 43 . WIRE LENGTH The length of a member may influence the maximum elastic load and the load deflection in a number of ways depending upon the configuration and loading of the spring. depending on the stiffness required. On the other hand if the principle of variable modulus orthodontics is employed. In some instances more play is needed to allow freedom of movements of brackets along the arch wire. Once the desired amount of play has been established. More important.Ideal Orthodontic Alloy attachments and the wire can be varied. excessive play may lead to lack of control over tooth movement. The cantilever has been chosen to demonstrate the effect of length. A rectangular wire orients in the bracket and hence offers greater control in delivering the desired force system. when placed in the brackets. the clinician determines the amount of play required before selecting the wire. the wire will not turn or twist to allow the forces to be dissipated in improper directions. since the cantilever principle is widely used in orthodontic mechanisms. as well as heavy force applications and stabilizations. The variable modulus principle allows the orthodontist to use oriented rectangular wires or square wires in light force. With small low-stiffness wires. In other situations little play is required to allow good orientation and effective third-order movements. Vertical segments in the wire are limited by occlusion and the extension of the muco-buccal fold. The distance L represents the length of the cantilever measured parallel to its structural axis. since it varies linearly with the length. 44 . the longer the cantilever the lower the load deflection rate. only minimally altering their maximal elastic loads. However there are limitations in how much the length can be increased. Increasing the length of the cantilever markedly reduces the load deflection rate. In this type of loading the load deflection rate will very inversely as the third power of the length.Ideal Orthodontic Alloy The figure shows a cantilever attached at B with vertical force applied at A. Once again. in other words. the longer the cantilever the lower the maximal elastic load. The distance between brackets in a continuous arch is predetermined by tooth and bracket width. The maximal elastic load varies inversely as the length of the cantilever. Adding length within the practical confines of the oral cavity is an excellent way of improving spring properties. Increasing the length of a wire with vertical loops is one of the more effective means of reducing load deflection rates for flexible members and at the same time. Increasing the length of cantilever is a better way to reduce the load deflection rate than is reducing the cross-section. yet the maximal elastic load is not radically altered. This tends to lower the load deflection rate and increases the range of action of the flexible member. Helical coils can be used to reduce the load deflection rate. If location and formation are properly done. The load deflection rate is maximally lowered for the given amount of wire used if the helix is placed at the point of support rather than anywhere else along the length of wire.Ideal Orthodontic Alloy AMOUNT OF WIRE Additional length of wire may be incorporated in the form of loops and helices or some other configuration. In the case of cantilever the position for additional wire would be at the point of support. When a member is designed that incorporates additional wire. The figure illustrates the proper positioning of helical coil for this purpose. almost 1000 gm. it should be possible to lower the load deflection rate without altering the maximal elastic load merely by adding the least amount of wire that will achieve these ends. since here the bending moment is the greatest. The optimal place for additional wire is at cross-sections where bending moment is largest. it is necessary to locate properly the parts of the configuration where additional wire should be placed and to determine the form that the additional wire should take. 45 . The maximal elastic load may or may not be affected. In short it is not the amount of wire used that is important in achieving a desirably flexible member. To achieve this objective with the minimal amount of wire. A practical way of deciding where these parts of a wire might be. This should not be surprising since the maximal elastic load is a function of this length of the configuration rather than the amount of wire incorporated in it. it should be avoided in the reactive or rigid members. but rather it is the placement of additional wire and its form. These are the sections where the bending moments or torsion moments are the greatest: the cross-sections of wire that have the greatest stress. method of lowering the load deflections rate without subsequently reducing the maximal elastic load has been discussed. this is important because for the first time.Ideal Orthodontic Alloy The placement of additional coils at the point of support in a cantilever does not alter the maximal elastic load. Loops 46 . Although additional wire is quite helpful in the design of flexible members of an orthodontic appliance. the optimal placement of additional wire is at cross-sections where the bending moment is the greatest. From the point of view of design. provided they have the same lengths measured from the force to the point of support. It is also true for many other configurations: load deflection rate can be lowered without altering the maximal elastic load if additional wire is properly incorporated. is to activate a configuration and see where most of the bending or torsion occurs. A straight wire of a given length and a wire with numerous coils at the point of support have identical maximal elastic loads. 47 . with a continuous arch wire. It is therefore desirable to mark wires by other means than a file. the force or stress required to permanently deform a given wire can be calculated. Flexible member should be designed with gradual bends so that they will be more free from permanent deformations than comparable ones with sharp or sudden bends.Ideal Orthodontic Alloy and other types of configurations decrease the rigidity of wire and hence may be responsible for some loss of control over the anchor units. Two common stress raisers are sudden changes in cross-sections and sharp bends. however. A: Any nick in a wire will tend to raise the stress at that cross-section and hence may be responsible for permanent deformation or fracture at this point. the orthodontist is somewhat limited in space between brackets and many times is required to make sharp bends because of this limitation. in many instances the wire will deform at values much lower than predicted ones because the presence of certain local stress raisers increases the stress values in a wire far beyond what might be predictable by commonly used engineering formulas. Unfortunately. particularly the wires of smaller cross-sections used in the flexible member of an appliance. B: A sharp bend in a wire also may result in higher stress than those might be predicted for a given cross-section of wire. A sudden sharp bend will far more easily deform than a more rounded or gradual bend. STRESS RAISERS From a theoretical point of view. The configuration with the most gradual bending is the loop with a helical coil C. areas of high stress exist. for instance. but might will lead to 48 . since the bending is more gradual. Not only would the helical coil enhance the flexible properties of the spring because of its additional wire. A number of precautions should be observed at critical sections.Ideal Orthodontic Alloy For example. a plain one and one with a helical coil. three vertical loops might be compared: a squashed one. In terms of permanent deformation. A nick in a wire. There are certain sections along a wire where stresses are maximal. These may be called as critical sections. might not be so disastrous where the stresses are low. First stress raisers should be avoided in these sections at all costs. It has already been seen that in sections where the bending moments are the largest. but the each of gradual bend would further increase its range of action without permanent deformation. for it is here that permanent deformation is most likely to occur. The plain vertical loop B would be slightly superior. These critical sections are important from the point of view of design. the poorest design would be loop A. Nevertheless a fairly sharp bend occurs at its apex. which because of its squashed state has a very sharp bend at its apex. If a straight piece of wire is bent so that permanent deformation occurs and an attempt is made to increase the magnitude of the bend. the elastic limit of the wire should be carefully watched at a critical section. Second.Ideal Orthodontic Alloy deformation or fracture where the stress level is high. The wire is more resistant to permanent deformation because certain residual stresses remain in it after the placement of the first bend. 1) All stress raisers should be eliminated as completely as possible. It will be greatest in the direction that is identical to original 49 . DIRECTION OF LOADING Not only is the manner of loading important. lowering the elastic limit at another place in the wire where the stresses are low. 3) The appliance may be so designed that it will elastically rather than permanently deform under normal loading. bending in the same direction as had originally been done. might not be too undesirable but could be responsible for failure at a critical section. If a bend is made in an orthodontic appliance. There are three rules to be kept in mind as far as designs of critical sections. Therefore in high stress areas it is desirable to use other means of attaching an auxiliary than soldering or if soldering is to be used as a method of attachment. 2) A large cross-section can be used to strengthen this part of the appliance. it should be done with considerable care. but the direction in which a member is loaded can markedly influence its elastic properties. the wire is more resistant to permanent deformation than if an attempt had been made to bend in the opposite direction. the maximal elastic load will not be the same in all directions. reducing the no of coils and lengthening the spring. increasing the no of turns in the helix and shortening the length. The figure demonstrates a vertical loop with the coil at the apex and a number of turns in the coil under different directions of loading. The type of loading seen in B tends to unwind the helix. The loading in A tends to activate the spring in the same direction as it was originally wound and hence is the correct method of activation.Ideal Orthodontic Alloy direction of bending or twisting. The phenomenon responsible for this difference is referred to as BAUSCHINGER EFFECT. ACTIVATION OF HELICAL COIL A.CORRECT B-INCORRECT PLACING A REVERSE CURVE OF SPEE 50 . The loading in A tends to wind the coil. If there is a defect in the material. PREVENTION OF FATIGUE FAILURE Broken wire can add time to treatment. Metals that work hardens rapidly may fatigue more easily. The operator should be sure that the last bend made in an arch wire is in the same direction as the bending produced during its activation. Below a certain stress level. gradually bring about additional work hardening until the metal finally fails in a brittle fracture. Hard wires are more brittle than soft wires of the same materials. But fatigue of metal is hastened tremendously by flaws of any kind. below that which would normally cause failure. So. if a reverse curve of spee is to be placed in an arch wire.Ideal Orthodontic Alloy The same principles can be applied to less complicated configurations such as in a continuous arch wire. Only then will the activation of the arch wire be in the same direction as the last bend. usually in the low plastic deformation range. For example. a material can be subjected to repeated stresses without fracture. the curve should be first over bent and than partly removed. it is important that all possible preventive measures be taken. These stresses. even minute scratch. FATIGUE OF METALS Fatigue is the result of repeated stresses at a level. Hardness level should be selected 51 . the metal remaining around the defect will have to carry an added load and may lead to failure. such as a scratch or an internal flaw. Care should be taken in wire selection. even though most suppliers offer wires in which every effort has been made to keep breakage low. This can be minimized by careful soldering but additional protection will be provided by careful cleaning and electro polishing after the procedure. Experience with specific materials is often the only criteria in this regard. During arch designing careful handling should be done.Ideal Orthodontic Alloy on the basis of individual demands. as a larger stiffer and seemingly stronger wire. Repeated bending at the same spot should be avoided. All adjustments should be made away from high stress areas and previous bends at soldered joints should be avoided. Good surface finish eliminates many of the small stress raiser that can initiate the process of failure. as wire adjacent to solder joints may be subjected to intergranular corrosion initiated by heat soldering. Smooth beaked pliers should be used to avoid unnecessary damage to the surface. and pliers should be selected and manipulated so as to avoid marking the wire with the sharp edge of the beaks. For this reason change to smaller diameter wire may be the only answer in some cases of recurrent breakage. A wire should never be marked or notched with a file or other sharp instrument. Smaller diameter wire have a broader working range and may not be so easily stressed to the proportional limit. 52 . as shown by its ability to be hammered to a thickness of 0. It is the most ductile of all metals.s Gold and other precious 53 . Before 1950. about one third of thinnest gold foil used in dentistry. Although its ductility decreases after cold working. and it is not affected by air. but after cold working.Gold Wires 8 Gold Wires Pure Gold is the noblest of all dental metals.34. its hardness approaches that of Type II Gold alloy (90 VHN). its hardness ( 52 to 75 Vickers hardness no [VHH]) is equivalent to and may exceed that of conventional Type I gold alloy (50 VHN) in its softened state. and after work hardening.39 Pure gold is extremely soft. rarely tarnishing and corroding in the oral cavity. It is the most malleable of all metals.00013 mm. It is inactive chemically. wire is the principal form in which wrought gold dental alloy is used. as demonstrated by its ability for a 1oz cylinder to be drawn into a wire 100 km long in length. heat. moisture and most solvents. Gold Wires metal alloys were used routinely for orthodontic purpose because nothing else was able to tolerate oral conditions. Palladium-Gold-Platinum (P-G-P) Because of their high fusion temperature and therefore high crystallization temperature.s two other types of wires were also used with high content of Gold in at least one of them. The corrosion resistance of palladium-silver dental alloy. Palladium-Silver-Copper (P-S-C) These wires are neither Type I nor Type II gold wires. copper. silver. Type I: They must contain at least 75% gold and platinum group metals. year 1984. nickel and zinc. both in cast and wrought forms. In addition to Type I and II Gold wires used in orthodontics before 1950. Type II: They must contain at least 65% gold and platinum group metals. The basic composition of alloys consists of Gold. platinum. COMPOSITION There are two types of Gold wires recognized in American Dental Association (ADA) specification no 7. but their mechanical properties would meet the requirements for an ADA Type I or Type II alloy. they are especially useful as wires to be cast against and meet the composition requirements for an ADA type I wire. is generally satisfactory. [Detail in Table] 54 . palladium. The presence of large quantity of nickel tends to decrease the tarnish resistance and change its response to age hardening. 3) Palladium: It is the most effective element known for raising. 2) Platinum: It is used to convey greater strength and toughness to assist in obtaining controllable hardness in the finished wire and contributes substantially to the resistance of the alloy to tarnish and corrosion by oral fluids. silver may be added to balance the colour. 4) Copper: Copper contributes to the ability of the alloy to age harden.Gold Wires WIRE TYPE GOLD PLATINUM PALLIDUM SILVER COPPER NICKEL ZINC ADA-I 54-66 7-18 0-8 9-12 10-15 0-2 0-0. When Copper is present. The increased palladium and platinum content ensures that the wire does not melt or recrystallize during soldering process.6 ADA-II 60-67 0-7 0-10 8-21 10-20 0-6 0-1. 6) Zinc: Zinc acts as a scavenger agent to obtain oxide free ingots. 55 . Also these two metals ensure a fine grain structure. from which the wires are drawn. 5) Nickel: Nickel is sometimes included in small amounts as a strengthener of the alloy.7 P-G-P 25-30 40-50 25-30 - 16-17 - - P-S-C - 0-1 42-44 38-41 16-18 0 - GENERAL EFFECTS OF THE CONSTITUENTS 1) Gold: Provides Malleability and Ductility. although it tends to reduce the ductility. without widening the melting range of gold alloys. the small pores and surface projections may be collapsed. 56 . Fusion temperature of wrought wires must be known to ensure that the wires do not melt or lose their wrought structure during normal soldering procedures.Gold Wires FUSION TEMPERATURE The minimum fusion temperature of an alloy is usually taken as a temperature halfway between the liquidus and solidus temperature. When the cast ingot is drawn into a wire. this temperature is 9550 C (17510 F) or higher. for a type I wire. MECHANICHAL PROPERTIES Yield Strength Tensile Strength Elongation Fusion Temperature TYPE MPa 1000psi MPa 1000PSI % % C F ADA TYPE I 582 125 991 117 13 4 995 1750 ADA TYPE II 690 100 862 125 15 2 971 1400 Strength Yield Strength Tensile Strength Elongation Fusion Temperature P-G-P 5921034 80-150 4621241 125-180 11-15 - 1300-1530 27307750 P-B-C 640-793 100-115 9651170 140-155 16-24 8-15 1050-1080 17101970 A wire of a given composition is generally superior in mechanical properties to a casting of same composition. for the type II wire the minimum fusion temperature should be 8710 C (16000 F). Any defects of this type that are not eliminated will weaken the wire. The casting contains unavoidable porosity which has a weakening effect. According to ADA specification no 7. and welding may occur so that such defects disappear. 000 to 117. Type I and II alloys usually do not harden. The hardening heat treatment is termed as age hardening SOFTENING HEAT TREATMENT Gold alloy is placed in an electric furnance for 10 min at a temperature of 7000 C or 12920 F. Although the precise mechanism may be in doubt.000 Psi) which is slightly higher than that for gold casting alloys. This is called as annealing.000.Gold Wires PHYSICAL PROPERTIES ARE LISTED IN TABLE The modulus of elasticity of wrought gold wires is in the range of 97.000.000 Mpa (14. or they harden to a lesser degree than do the type III and IV alloys. 57 . the criteria for successful hardening are time and temperature. can of course.000 to 17. Alloys that can be hardened. During this period all intermediate phases are presumably changed to a disordered solid solution. The actual mechanism of hardening is probably the result of several different solid state transformations. also be softened. Then it is quenched in water. It increases by approximately 5% after a hardening heat treatment. HEAT TREATEMENT OF GOLD ALLOY All gold alloy wires that contain copper are heat treatable as the Gold casting alloys. In metallurgic terminology the softening heat treatment is referred to as solution heat treatment. and the rapid quenching prevents ordering from occurring during cooling. because the increase in strength. Otherwise. Although 7000 C is an adequate average softening temperature.Gold Wires The tensile strength. hardness. or otherwise cold worked.  One  of  the  must  practical  hardening  treatments  in  by  “   soaking  “  or ageing the alloy at a specific temperature for definite time. shaped. Ideally. and to start the hardening treatment with the alloy as a disordered solid solution. there would not be a proper control on the hardening process. each alloy has its optimum temperature and manufacturer should specify the most favorable temperature and time. The softening heat treatment is indicated for structures that are to be ground. usually 15-30 minutes. either in or out of the mouth. The transformations in turn. before it is water quenched. and the reduction in ductility are controlled by the amount of solid-state transformations. proportional limit. it should be subjected to a softening heat treatment to relieve all strain hardening. proportional limit and hardness are reduced by such a treatment but the ductility is increased. The ageing temperature depends upon the alloy composition but is generally between 2000 C (4000 F) to 4500 C (8400 F). The proper time and temperature are specified by the manufacture. if it is present. before the alloy is given an age-hardening treatment. HARDENING HEAT TREATMENT The age hardening or hardening heat treatment of dental alloys can be accomplished  in  several  ways. are controlled by the temperature and time of age-hardening treatment. COLD WORKING OR WORK HARDENING 58 . Gold Wires Cold working is also the usual method of hardening gold alloy. This is to adjust the drawing and annealing schedule to compensate.e. it means that these metals are less brittle and will need much more manipulation before they have hardened excessively. The slow cooling permits optimum grain growth for the production of a hard material. cold rolling or bending. usually by heating to about 8000 F to 10000 F and cooling slowly. Some special alloys such as those that are high in platinum. 59 . this low work hardening means that drawing is much easier. any plastic deformation of metal by hammering. Much more cold working is required for Gold alloys than Steel to harden it. can be harden materially by temperature manipulation. cold forging. To the manufacturer. drawing. Gold alloy work hardens much more slowly and to lesser degree than Steel. with fewer intermediate anneals required to orthodontist. Cold working is defined as deforming a metal at temperature that are low compared with its melting temperatures i. There is a tendency for wrought alloys to recrystallize during heating operations. The extent of crystallization is related directly to the duration of heating. its high cost. 60 . Therefore of all those wires. Because there is concomitant decrease in the mechanical properties of alloys as recrystallization increases. so sufficient platinum and palladium should be present to increase the fusion temperature of the wrought gold alloy wire. It results from the deformation of the grains during the drawing operation to form the wire.Gold Wires MICROSTUCTURE The micro-structural appearance of cold-worked on wrought alloys is fibrous with extremely elongated crystals. the P-G-P wires are the most resistant to recrystallization. and the cold work or strain energy imparted to the alloy when the wire was drawn. recent advances in the wire materials. the temperature employed. mechanical properties of the same and due to their low yield strength. Such a structure generally exhibits enhanced mechanical properties as compared with corresponding cast structure. Recrystallization is inversely related to the fusion temperature of the wire when heating temperature and time are constant. Now a days the use of Gold alloys is markedly reduced because it is too soft to use as an orthodontic appliance. that HARRY BREALY OF SHEFFIELD. It is the major alloy system used in orthodontics. F. In the mid century stainless steel was applied to dentistry and orthodontics.A.M.Stainless Steel Arch Wires 9 Stainless Steel Arch Wires CARBON STEELS Stainless steel is the most widely used and accepted material in orthodontics.S. 61 .BECKET OF U. Although it was around 1920. and BENNO STRAUSS EDWARD MAURS of Germany shared the honor for the development of materials. If the AUSTENITE is cooled rapidly (Quenched).02 Wt %). At temperatures between 9120 C and 13940 C.1 Wt%. brittle alloy. The spaces between atoms in the BCC structure are small and oblate.carbon alloy system and to carbon steel alloys.39 Steels are iron based alloys that usually contain less than 1. brittle phase adds strength to the relatively soft and ductile ferritic and austenitic forms of iron. carbon has a very low solubility in ferrite (maximum of 0. The interstices in the FCC lattice are larger than those in the BCC structure.10. 62 . This lattice is highly distorted and strained. the size of the carbon atom limits the maximum carbon solubility to 2. strong. the stable form of iron is a Face Centered Cubic structure (FCC) called AUSTENITE. resulting in an extremely hard. diffusion less transformation to a Body-Centered Tetragonal (BCT) structure called MARTENSITE. This phase is stable at temperatures as high as 9120 C. When AUSTENITE is cooled slowly from high temperatures. The different classes of steel are based on three possible lattice arrangements of iron. This hard.Stainless Steel Arch Wires The metallurgy and terminology of these alloys are intimately connected to those of the simpler binary iron .26. the excess carbon that is not soluble in ferrite. Therefore this discussion begins with a brief outline of the metallurgy of the ironcarbon system. it will undergo a spontaneous. However.2% carbon. this transformation requires diffusion and a definite period of time. Pure iron at room temperature has a Body Centered Cubic (BCC) structure and is referred to as FERRITE. hence.34. However. forms iron carbide (Fe3C). Such a heat treatment process is called as tempering. If the oxide layer is ruptured by mechanical or chemical means. evolving from the possible lattice arrangement of iron previously described. There are essentially three types of stainless steels. a thin.0-26 7-22 0. These steels resist tarnish and corrosion primarily because of the passivating effect of the chromium. carbon and chromium may also be present. Martensite decomposes to form ferrite and carbide. resulting in a wide variation in composition and properties of stainless steels.5-27 0 0. TYPE (SPACE LATTICE) CHROMIUM NICKEL CARBON Ferratic(BCC) 11.20 max Austantic(FCC) 16. the passivating oxide layer. eventually forms again in an oxidizing environment.25 max Martenstic(BCT) 11.5-17 0-2. STAINLESS STEELS / CHROMIUM CONTAINING STEELS When 12 to 30% chromium is added to steel. The cutting edges of carbon steel instruments are ordinarily martensitic. but this is counter balanced by an increase in toughness.15-1.20 63 . This process can be accelerated by appropriate heat treatment to reduce the hardness. For passivation to occur. This protective oxide layer prevents further tarnish and corrosion. Elements other than iron.5 0. transparent but tough and impervious oxide layer of Cr2O3 forms on the surface of the alloy when it is subjected to an oxidizing atmosphere such as room temperature. because the extreme hardness allows for grinding a sharp edge that is retained in use.Stainless Steel Arch Wires The formation of martensite is an important strengthening mechanism for carbon steels. a temporary loss of protection against corrosion will occur. However. the alloy is commonly called stainless steel. .. The ferritic alloys provide good corrosion resistance at a low cost.15% 64 .. Because of their strength and hardness. 2. martensitic stainless steel alloys share the AISI 400 designation with the ferritic alloys. They can be heat treated in the same manner as plain carbon steels... This series no is shared with the martensitic alloys. with similar results.. MARTENSITIC STAINLESS STEELS As noted in above paragraph. Because temperature change induces no phase change in the solid state. 3..... It may decrease to as low as 2% elongation for a high carbon martensitic stainless steel. ferritic stainless steel is not readily work hardenable.. AUSTENITIC STAINLESS STEELS The austenitic stainless steel alloys are the most corrosion resistant of the stainless steels... when the strength and hardness increases. 18% Nickel .. As usual. 8% Carbon ... ... Corrosion resistance of martensitic stainless steel is less than that of the other types and is reduced further following a hardening heat treatment. ductility decreases. FERRITIC STAINLESS STEELS These alloys are often designated as American Iron and Steel institute (AISI) series 400 stainless steels.... AISI 302 is the basic type with composition: Chromium .Stainless Steel Arch Wires 1. martensitic stainless steels are used for surgical and cutting instruments.... provided that high strength is not required. Also. the alloy is not hardenable by heat treatment........ This series of alloys finds little application in dentistry. Less critical grain growth. Substantial strengthening during cold working. since the body centered lattice are ferromagnetic at room temperature. MECHANICAL PROPERTIES The property of readily strain hardened is a characteristic of austenitic stainless steel. it has lost much of the range of elasticity or working range. They are the types most commonly used by the orthodontist in the form of bands and wires. But a considerable amount is the result of phase change from a face centered to a body centered lattice. a stainless steel wire can become fully annealed in few seconds at a temperature of 7000 C to 8000 C. Ability to fairly and readily overcome sensitization. Both 302 and 304 stainless steel may be designated as 18-8 stainless steel.Stainless Steel Arch Wires Type 304 stainless steel has a similar composition. This phase change can be readily demonstrated. austenitic is non magnetic. Comparative ease in forming. Part of this increase in hardness is ordinary strain hardening.08%). Greater ease of welding. so necessary to a satisfactory orthodontic appliance. It is unfortunate that after strain hardening. Generally austenitic stainless steel is preferable to ferritic stainless steel because of the following characteristics: Greater ductility and ability to undergo cold work without fracturing. Because the annealing temperature involved in 65 . After such an annealing. but the chief difference is its reduced carbon content (0. 25 max Martenstic(BCT) 11. normally employee an unavoidable softening of the wire during normal heating.20 max Austantic(FCC) 16.5-17 0-2. This implies that stainless steel wire produces higher forces that dissipate over shorter periods than nitinol wires. A reduction in wire size results in poorer fit in the bracket and may cause loss of control during tooth movements. Low levels of bracket/wire friction have been reported with experiments using stainless steel wires. high stiffness is advantageous in resisting deformation caused by extra oral and intra oral tractional forces.Stainless Steel Arch Wires the soldering and welding temperature ranges. RARK and SHEARER have demonstrated the release of nickel and chromium from stainless steel appliances. it is a decided disadvantage. TYPE (SPACE LATTICE) CHROMIUM NICKEL CARBON Ferratic(BCC) 11. However.5 0. 66 . This signifies that stainless steel wire offer lower resistance to tooth movement than other orthodontic alloys. The stored energy of activated stainless steel is substantially less than that of beta titanium and Nitinol wires.5-27 0 0.0-26 7-22 0. The yield strength to elastic modulus ratio indicates a lower spring back of stainless steel than those of newer alloys.20 The large modulus of elasticity of stainless steel and its associated high stiffness necessitate the use of smaller wire for alignment of moderate and severely displaced teeth.15-1. thus requiring more frequent activation or arch wire changes. Work hardening also brings about some transformation of parts of the austenite into martensite which adds to the hardening effect. Cooling from the annealing temperature must be rapid. most workable state. Work hardening steel is hardened by the interlocking of grains and atoms are locked in situations in which. Austenite steel hardens rapidly by cold working with the usual realignment of the crystalline structure. At this temperature all of the effects of cold working are eliminated and the metal returns to its softest. but it is important for corrosion control. usually by quenching. Orthodontic bands and ligature wires are usually supplied fully annealed. they are under stress. 1. The only way by which these steels can be hardened is by cold working. This rapid cooling is not an essential part of the annealing process. STRESS RELIEF OF STAINLESS STEEL The most important heat treatment process for orthodontic stainless steel is the relatively low temperature process of stress relieving which is used both in manufacturing and in orthodontist’s office. 2.Stainless Steel Arch Wires HEAT TREATMENT OF AUSTENITIC STEEL Austenite cannot be hardened like carbon steel by quenching or similar heat treatment. even when the piece as a whole is not stressed. ANNEALING AUSTENITIC STEEL Stainless steel requires a higher temperature for annealing (18000 F to 20000 F) than does carbon steel. 67 . In general. most of the benefits of heat treatment can be produced in few minutes or less at temperature of 8000 F. When this treatment is applied to an arch.Stainless Steel Arch Wires When a wire with such internal stresses is bend to produce a spring action. low temperature treatment (4000 F to 7000 F) over a long period of time is most desirable. A stress relieving heat treatment accelerates this change in shape so that the wire will be more stable. the two actually augment each other. A wire that is bend to form an arch is full of residual stresses which tend to return it towards its original form. Stress relieving changes depend on both time and temperature. 68 . and they can be controlled by the adjustment of either of these factors. Fortunately. This goes on gradually at ordinary temperature causing a slow change in arch form (elastic memory). As internal stresses are relieved. Stress relief eliminates such areas of stress within the wire and puts it into the condition to work most effectively. a part of their reserve of strength has already been used up by their limit of strength. action of the wire is weakened by the internal stress. If the applied force must be resisted by the stressed regions. If the internal stress is in the same direction as the new load. This is especially true if the wires have been previously stress relieved in manufacturing to eliminate the stress in wire making process. This is the second reason for stress relieving in orthodontics. there previously stressed areas can not do their full share. there may also be some change in the shape of the wire. the arch formed for a patient in the chair cannot be treated for hours or even for too many minutes. But. the form should always be checked and arch reshaped if necessary after the heat treatment. In either case. Such temperatures are definitely within the range used by the orthodontist in brazing. above it. and forms chromium carbide (Cr3C). Because that portion of grain adjacent to grain boundary is generally depleted to produce chromium carbide. the exact temperature depending upon carbon content.Stainless Steel Arch Wires The oven is the most reliable method for heat treatment because of relatively uniform temperature. Below this temperature the diffusion rate is less. 69 . The formation of chromium carbide is called as sensitization. whereas. and a partial disintegration of the metal may result with a general weakening of the structure. The small rapidly diffusing carbon atoms migrate to the grain boundaries from all parts of the crystal to combine with the large. a decomposition of chromium carbide occurs. its passivating qualities are lost. The 18-8 stainless steel may lose its resistance to corrosion if it is heated between 4000 C to 9000C. When the chromium combines with carbon in this manner. soldering and welding. intergranular corrosion occurs. INTERGRANULAR CORROSION OF STAINLESS STEEL Carbon is an undesirable property in austenitic stainless steel. but it is difficult to remove it completely. where the energy is highest. The reason for decrease in corrosion resistance is the precipitation of chromium carbide at the grain boundaries at high temperatures. The formation of chromium carbide is highest at 6500C. slowly diffusing chromium atoms at the periphery of the grain. the corrosion resistance of steel is reduced. and as a consequence. as during soldering can be very effective means of minimizing sensitization. it must be quenched immediately after soldering. This is the most commonly used procedure in soldering stainless steel. This is also the reason for quenching after annealing.Stainless Steel Arch Wires PREVENTION OF INTERGRANULAR CORROSION There are several methods by which this condition can be minimized. Stainless steel should always be quenched immediately after soldering to bring it down to a safe temperature as soon as possible. solder. there will be a zone 70 . If only part of the steel is heated to this high soldering temperature. Both low temperature and high temperature solders can be used to control intergranular corrosion. If they are used properly with low temperature solder (silver solder that melts below 11000 F) the objective is to heat it to soldering temperature. but only if the entire piece of steel can be heated to this high temperature. and thus it is perfectly safe. Keeping out of the sensitizing temperature range. At annealing temperature the chromium carbide is broken up. High temperature solder (Gold solder that melts above 12000F ) also can be used. Two most commonly used methods are: 1. while it is being soldered. If a metal is cooled rapidly from annealing to room temperature there is no opportunity for chromium carbide to form. Of course. Speed in handling the metals in the sensitizing temperature range. and then quench as quickly as possible. The metal is then above the sensitizing range. Stabilized steel is less susceptible to intergranuler corrosion but it is still not 100% safe. the precipitation of chromium carbide can be inhibited for a short period at the temperatures ordinarily encountered in soldering procedures. In terms of performance. but the final intertwined wires may be either round or rectangular in shape. Proper handling by orthodontist can modify the advantage completely. 2. Titanium is often used for this purpose. and their cross-sectional dimension is in between . TWISTED OR MULTISTRANDED WIRES Very small diameter stainless steel wires can be braided or twisted together by the manufacturer to form larger wires for clinical orthodontics.406 mm and . 71 . If titanium is introduced in an amount approximately six times the carbon content. Stainless steel that have been treated in this manner are said to be stabilized.635 mm.Stainless Steel Arch Wires outside the soldering area which is in the sensitizing temperature range. Therefore this method is useful only for small pieces. Controlling the carbon content (stabilization) The second method for control of intergranular corrosion is introduction of some elements which tie up with chromium or by keeping the carbon content exceptionally low (below . The result is an inherently high elastic modulus material with low stiffness because of its co-axial spring like nature.178 mm. the wire is delivering higher forces per unit of activation over a greater distance and strength is also increased.08%). BRAIDED. The separate strands may be as small as 0. 0175″   (3   x   0.26 Ingram.0175″multi  stranded  wire  was  25%   stronger than 0.008″) stainless steel arch wire was similar to that of 0.0175″   multi   stranded   wire   and   0. 72 . However Nitinol tolerated 50% greater activation than the multi stranded wires.  The  0.016″   nitinol   showed   similar   stiff   nesses. Kusy and Dilley investigated the strength. stiffness and springback properties of multistranded wires in a bending mode of stress. The triple stranded wire was also half as stiff as a 0. these types of wires apply low forces for a given deflection when compared to solid stainless steel wires.010″  single  stranded  stainless  steel  wire.Stainless Steel Arch Wires Because   of   their   low   “apparent”   elastic   modulus   in bending. They noted that the stiffness of a triple stranded 0.016″  beta  titanium  wire.010″  stainless  steel  wire. Gipe and Smith noted that titanium alloy wires and multi stranded stainless steel wires have low stiffness when compared with solid stainless steel wires.   The 0. ADVANTAGES OF STAINLESS STEEL Lowest cost of the wire alloys. Can be soldered and welded. although welded joints may require solder reinforcement. Can be susceptible to intergranular corrosion after heating to temperatures required for joining.Stainless Steel Arch Wires The investigators also found that most multi stranded wires had a spring back similar to that of nitinol. Proven biocompatibility from extensive clinical use Excellent formability for fabrication into orthodontic appliances. 73 . DISADVANTAGES OF STAINLESS STEEL High force delivery Relatively low spring back in bending compared to beta-titanium and Nickel titanium alloys. but a larger spring back when compared with solid stainless steel or beta-titanium wires and they have spring back properties that are relatively independent of wire size. 74 . semi resilient and resilient. The wires are furnished to orthodontist in different gauges and cross-sectional shapes with differing physical properties.34.Nickel Alloy Archwire 111 Chrome-Cobalt -Nickel Alloy Archwire Cobalt – Chromium – Nickel Orthodontic wires are very similar in appearance. They can be subjected to same welding and soldering procedures as described for stainless steel orthodontic wires. ductile. Their resistance to tarnish and corrosion in the mouth is excellent. mechanical properties and joining characteristics to stainless steel wires.Chrome . but have a much different composition and considerably greater heat treatment response. The differences in mechanical properties arise from proprietary variations in the wire manufacturing process.Cobalt . but their properties are also excellent for orthodontic purpose.39 These alloys were originally developed for use as watch springs (ELGILOY). These wires are available in four tempers: soft. For the alloy Elgiloy the alloy should be held at 4820C for 5 hours. 75 . the wires are heat treated before supplied to the user and may be ordered in several degrees of hardness. The other tempers are less popular than the soft temper because wires made from them have lower formability and are somewhat higher in cost than stainless steel HEAT TREATMENT Cobalt-Chromium-Nickel alloy may be softened by heat soaking at 11000C to 12000C. In addition. then heat treated to provide substantially increased values of yield strength and resilience.04% IRON 15.Nickel Alloy Archwire COMPOSITION: COBALT 40% CHROMIUM 20% NICKEL 15% MOLYBDENUM 7% MANGANESE 2% CARBON . followed by a rapid quench. This heat treatment would increase the yield strength and decrease the ductility. A typical cycle would be 4820C for 7 to 12 minutes.15% BERYLLIUM .Cobalt . The age hardening temperature range is 2600C to 6500C.Chrome . the orthodontist can heat treat the wires by placing them in an oven or by passing an electric current through them with certain types of spot welders. Ordinarily.8% The soft temper wires are popular with clinicians because they are easily deformed and shaped into appliances. if only a portion of a wire is annealed.7 931 1276 4 Wires made from this alloy should not be annealed. The resulting softening effect cannot be reversed by subsequent heat treatment.2% Offset yield strength (MPa) Ultimate Tensile Strength Number of 90 degree cold bends without fracture S.Cobalt . The stress relief heat treatment removes residual stresses during recovery without pronounced alteration in mechanical properties. Hardness. PHYSICAL PROPERTIES Tarnish and corrosion resistance are excellent.Chrome .S 179 1579 2117 5 Co-Cr 184 1413 1682 8 NiTi 41. Such a treatment also stabilizes the shape of the appliance. Moreover. Cobalt-Chromium-Nickel wires are more responsive than the 18-8 stainless steel wires to the low temperature heat treatment.4 427 1489 2 B-TITANUM 71. A reduction in ductility 76 . RECOVERY HEAT TREATMENT An increase in the measured elastic properties of a wire can be affected by heating it to comparatively low temperatures (3700C to 4800C) after it has been cold worked.Nickel Alloy Archwire Alloys Modulus of Elasticity (103 MPa [GPa] 0. Typical mechanical properties of orthodontic wires are shown in table. severe embrittlement of adjacent sections may occur. Ductility in the softened condition is greater than that of 18-8 stainless steel alloys and less than the alloys in the hardened condition. yield strength and tensile strength are approximately the same as those of 18-8 stainless steel. This temperature is also below the lower limit (4250 C) of the sensitization temperature range. but this property can be improved by adequate heat treatment. Although the optimum temperature range for the stress relief heat treatment is most often reported at 3700C to 4800C. there appears to be no reason to exceed the low temperature limit of 3700C when the wire is in nonstabilized grade of austenitic stainless steel.Chrome . non heat treated co-cr wire have a smaller spring back than stainless steel wires of comparable size. Caution must be used to avoid excessive embrittlement. Eleven minutes at approximately 3700 C results in a maximum proportional limit for a severely cold worked appliance. To use Elgiloy properly the user must be thoroughly familiar with it. which may occur in areas of high localized stress. Optimum levels of heat treatment can be confirmed by a dark straw colored wire or by use of temperature indication paste. A phase change as well as stress relief is probably responsible. MECHANICAL PROPERTIES With the exception of red temper Elgiloy. The softest Elgiloy (Blue) cannot be heat treated to become as brittle or hard as the high spring temper.Cobalt . or hardest Elgiloy (Red) wire. 77 . A stress relief heat treatment not only improves the working elastic properties of a wire appliance but also can reduce failure caused by corrosion.Nickel Alloy Archwire accompanies the increase in yield strength. Excellent corrosion resistance in mouth. although greater than stainless steel Proven biocompatibility from extensive clinical use Outstanding formability in as-received condition. since high temperature can cause annealing with resultant loss in yield and tensile strength.The high modulus of elasticity of cocr wires suggest that these wire deliver twice the force of Beta-titanium wires and four times the force of Nitinol wires for equal amount of activation.Cobalt . DISADVANTAGES High elastic force delivery Lower spring back than stainless steel. the mechanical properties of co-cr wires are very similar to those of stainless steel wires. Can be soldered and welded. In most other respects.Chrome .Nickel Alloy Archwire The advantage of co-cr wire over stainless steel wires includes greater resistance to fatigue and distortion and longer function as a resilient spring. ADVANTAGES Relatively low cost. Co-cr wires have good formability and can be bent into many configurations relatively easily. Low fusing solder is recommended for this purpose. 78 . Therefore stainless steel wires may be used instead of co-cr wires of same size in clinical situations in which heat hardening capability and added torsional strength of co-cr wires are not required. Caution should be exercised when soldering attachments to these wires. 025″. A true arch form is available in sizes from 0. They are highly flexible and resistant to set.Cobalt .017″ x 0.016″ x 0. 2.016″ x 0. fatigue and corrosion.016″. colboloy.019″ x 0. 0. The wires are available in natural arch sizes of 0. 79 .016″   x 0. The wire also offers reduced bracket friction and greater spring efficiency than typical stainless steel wires.018″ round and 0. G and H WIRE COMPANY Combining ductility and strength.022″ to 0.Chrome .014″ to 0. nickel-cobalt wires can be heat treated in bend areas and easily soldered without annealing.025″ rectangular.022″ and 0. MASAL ORTHODONTICS INTERNATIONAL Heat treatable blue Masiloy chrome-cobalt arches can accept sharp bends without breakage. Heat treatment increases the resiliency by 20%.Nickel Alloy Archwire RECENT ADVANCES IN COBALT-CHROMIUM 1. 38 80 . It is also thick enough to resist weakening and distortion due to the wear and tear exerted on appliances within the mouth.Australian Archwires 11 Australian Archwires In collaboration with an Australian metallurgist. Begg sought to develop a wire material which met his paradoxical requirements. After several years of experimentation they produced a wire which is thus enough to distribute forces at an optimal level for tooth movement over a considerable distance for a long period of time and with a minimal loss of force and intensity while doing so.4. Special Black 4. Extra special plus Blue 6. Special plus Orange 5.018″ and 0. slight fluctuation in the speed at which the wire is drawn through the dies affects its physical properties. 0.012″. Regular plus Green 3. 0. 1. One of the outstanding property of Australian wire is its resilience or ability to spring back after having been deflected. yet contains flaws which cause breakage during arch fabrication.016″. Another problem is that the wire may seem satisfactory. This property can be checked by bending the wire with the fingers while holding it with the pliers. and this may combine to aggravate the variations introduced previously. Supreme Blue REGULAR GRADE Lowest grade and easiest to bend.020″ 81 . Used for forming auxiliaries and can be used for forming arch wires when distortion and bite opening is not a problem. Regular grade White 2. Available in sizes of 0.014″. 0. This quality control problem may result in a wire that is too soft or too brittle.Australian Archwires In addition to variables like wire drawing and heat treatment. Additional variations can be caused by fluctuations in the rate at which the wire passes the heat source. Australian wires are available in the following forms. 014″. This wire can be easily broken if not bent properly.Australian Archwires REGULAR PLUS GRADE Relatively easy to form. 0.016″. EXTRA SPECIAL PLUS This grade is unequated in resilience. yet can be formed into intricate shapes with little danger of breakage. Used for auxiliaries and arch wires when more pressure and resistance to deformation is desired. there is no margin for bending errors.020″. 0. Available in size of 0.016″. 0. 82 .016″ is often used for starting arches.014″.020″. Available in sizes 0. 0. 0. open deep overbites and resist deformation far outweighs the inconvenience caused by an occasional breakage while bending. an intermaxillary hook is bent in the wire and left as evidence that the wire is of proper quality. Each 25 foot spool is pretested. Available in sizes 0.018″. SPECIAL PLUS GRADE Special plus wire is routinely used by experienced operators. yet more resilient than regular grade. However many orthodontists feel that the ability of this wire to move teeth.014″.016″ wire is excellent for supporting anchorage and reducing deep over bites.016″. The 0.020″ and 0. 0.018″ and 0. Hardness and resiliency of 0.022″. It is more difficult to bend and more subject to fracture. SPECIAL GRADE Highly resilient.018″ and 0.016″only. 0. Available in sizes 0. Never pinch the wire with the pliers before or during bending. 2. It is intended for use in either short sections or full arches where sharp bends are not required. Pliers must have smooth beaks.012″ and 0. Due to extreme hardness of Australian wire. Australian wires become hard from bending (work hardening). Do not scratch the wire to locate bends. 83 .Australian Archwires SUPREME GRADE / PREMIUM PLUS Primarily used only in treatment of rotations. alignment and leveling. Do not squeeze or pull the wire. 5. Bend the wire very slowly pressing with the thumb or forefinger. carbide tips are not recommended. 3.016″.010″. Pre-warm the wire by sliding between the thumb and forefinger. Hence. 1. 4. Do not rotate the pliers while beading loops and circles should be formed against the square beak and beaks should be apart slightly. 0. Hold pliers very lightly when bending the wire. there is no need for heat treatment and no margin for back bending to correct mistakes. Do not attempt to straighten the wire by stripping between the plier beaks. special attention must be given to bend it successfully. Available in 0. s aligning auxiliary). WILCOCK ARCH WIRES SPINNER STRAIGHTENING It is a mechanical process of straightening resistant materials.008″. The material yield strength is not altered and surface has a smoother finish and therefore causes low friction. Udder arch etc.J. 84 .011″ are used for - Relieving crowding. - 0. the wire is pulsed in a special machine which permits high tensile wires to be straightened and into lower diameters than possible earlier with spinner straightening. usually in the cold drawn condition.0.011" wire can be used for aligning second molar towards the end of stage III. - For making mini uprighting springs. Spec auxiliary. The wire is pulled through rotating bronze rollers which torsionally twist the wire into straight condition. The disadvantage of this process is - Resultant deformation - Decrease yield stress value.-For making different auxiliaries like MAA (Mollenhauer. PULSE STRAIGHTENING In pulsed straightening.Australian Archwires USE OF NEWER AUSTRALIAN WIRES The supreme grade of sizes 0. MANUFACTURING OF A. Since that time there has been continuous evolutionary improvement in the strength and resiliency of wires used for orthodontic treatment.13.39 85 .16.17.Nickel Titanium Arch Wires 12 Nickel Titanium Arch Wires A significant advancement in orthodontic materials was made in the late 1930.37.11.14.1.33.s and 1940.7.35.20.10.s when stainless steel wire became widely available. The development of Nitinol wire was another improvement which emerged from the orthodontic search for lighter force and greater working range.6.15.34. s by WLLIAM F. Many minerals contain titanium. (Now called as Naval Surface Weapons Centre). high strength and corrosion resistance. He did extensive research and published his findings on the properties and uses of this new alloy. Ti from titanium and Nol from Naval ordinance laboratory. Nitinol was invented in early 1960. the main ones being Ilmenite and Rutile. has changed very rapidly from a rare metal to an important structural metal because of its high weight.H. the first Nitinol alloy was marketed to orthodontists as Nitinol.9 and occupies ninth place in abundance of metals in earth’s crust. 98% of all rocks examined contained titanium besides sand.Nickel Titanium Arch Wires Titanium. Rutile is titanium oxide and is richer in titanium content. i. a research metallurgist at the Naval Ordinance Laboratory in Silver Spring. Ilmenite is a non-titanium oxide ore or Iron titanate which contains 32% titanium. as the shape memory effect had been suppressed by cold working the wire during drawing. CONVENTIONAL NITINOL Niti was introduced to orthodontics by Dr. Ni from nickel. clay and other soils. Indeed this alloy was passive. its low 86 . BUEHLER. GEORGE ANDREASEN and his associates. Largely through his efforts and those of the Unitek Company. a metal discovered by M. It has an atomic number 22 and atomic weight 47.KLAPROTH in 1795.e. this first 50:50 composition of Nickel and titanium was a shape memory alloy in composition only. Maryland.. What was so attractive about this martensitic stabilized alloy was its low force per unit of deactivation. The name Nitinol is an acronym derived from the elements which comprises the alloy. Ironically. e. the austenitic active alloy produces some three times the force per activation of the conventional martensitic stabilized nitinol alloy. The lack of formability largely remains today. Fortunately this effect is short lived. both the martensitic and austenitic phases play an important role during its mechanical deformation. this wire was quite springy. one might presume that this wire was the ideal. but the initial brittleness that plagued the early nitinol product has long since been rectified. Martensitic active alloy In the austenitic active alloy. wherein the stiffness is comparable to that of martensitic 87 . but presenvence prevails. When this stiffness was combined with its outstanding range and high spring back. Two generic alloys are 1.Nickel Titanium Arch Wires stiffness. Compared with the competition of the day. especially when wires broke. delivering only 1/5th to 1/6th the force per unit of deactivation and better meeting the criteria of light. they undergo some form of shape memory effect (SME) and are super elastic. It did not take long. Martensite represents the low stiffness phase and austenite represents the high stiffness phase. continuous force. however. At first glance one would suspect that the mechanical properties are dismal. PSEUDOELASTIC NITINOL In addition to conventional Martensitic stabilized alloy. Thus on loading. before its lack of formidability was recognized as limitation. Austenitic active alloy 2. two other generic nitinol type alloys are available today that are active. i. In fact a stress induced phase transformation has occurred in which the austenitic phase has transformed to the martensitic phase. Most common of these is 270C super elastic copper niti described later. a 1oC change in transition temperature occurred. After a 20 years delay. THERMOELASTIC NITINOL The third Nitinol type alloy in the market today is a martensitic active alloy that ultimately exhibits a thermally induced Shape Memory Effect (SME). 88 . this series of clinical events is elastic despite the fact that the appearance is quite non linear. and yet it was known that for every 150 parts per million variations in composition. the appliance would be activated by the warmth of oral cavity and return to its predetermined shape. Because the spring back is nearly total.Nickel Titanium Arch Wires nitinol. represent the key attribute to this nonlinear but nonetheless elastic alloy and is called pseudo elasticity. This is the long awaited Nitinol alloy that Dr. MIURA showed that surgical cases could be treated by preparing a series of arches in which the desired shape was set by heat. By capitalizing on thermo elasticity. Today several alloys are being marketed that utilize pseudo elasticity.  Sentalloy light. Upon deactivation the reverse occurs and martensitic phase is gradually transformed to the austenitic phase. a series of final arch forms could be generated and thereby the practitioner could maintain control. Here the martensite reversibly transforms to austenite and thereby changes shape to maintain force. Upon distortion and insertion into patient’s mouth. Today the thermo elastic effect is demonstrated in  GAC  international’s  alloy. For many years the alloy compositions simply could not be controlled precisely enough to make a uniform wire product. Transition temperature from Martensitic to Austenitic had to occur in the region of ambient oral temperature. ANDREASEN hoped to someday employ in orthodontics. After the wire has cooled to room temperature.Nickel Titanium Arch Wires COMPOSITION AND PHYSICAL PROPERTIES The composition of Nickel-Titanium used in dentistry is as follows: NICKEL - 54% TITANIUM - 44% COBALT - 2% This composition results in a 1 to 1 atomic ratio of the major components. As with other systems.  Nitinol  has  the  characteristics of being able to return to a previously manufactured shape when it is heated through a transition temperature range.When heated to its unique transition temperature range. referred to as austenitic phase is stable. At high temperatures a body centered cubic lattice (BCC). it may be deformed within certain strain limits. it will remember its shape and return to the original configuration. Though the orthodontic wires available today do not fully utilize this characteristic.e. shape memory and super elasticity or pseudo elasticity. 89 . SHAPE MEMORY WIRE Most orthodontists are aware of Nitinol because of unique property of the alloy  called  “shape  memory”. To use this property.   research   into   orthodontic   application   for   the   “memory”   aspects of Nitinol wire are continuing at the University Of Iowa and at unitek. the wire must first be set into the desired shape and held while undergoing a high-temperature heat treatment. whereas appropriate cooling can induce transformation to a close packed hexagonal martensitic lattice. This characteristic transformation of austenitic to martensitic phase results in two unique features of potential clinical relevance i. this alloy can exist in various crystallographic forms. Subsequent heating through a lower transition temperature causes the wire to return to its original shape. The cobalt content is used to control the lower transition temperature which can be near mouth temperature 370C (98. The wire is then cooled and formed into a second shape.40 F). 90 .Nickel Titanium Arch Wires The  “memory” effect is achieved by first establishing a shape at temperature near 4820C (9000 F). there is sufficient increase in strain. a phenomenon which is employed with some Nickel – orthodontic wires. Care should be taken not to overheat the wire because this makes it brittle. it initially results in the strandard proportional stress-strain behavior. Findings on resistance to corrosion of nitinol wires have been inconsistent. This additional strain is due to the volume change that results from change in crystal structure. This makes the wire dead soft and can be bent into preferred configuration. However at a stress. since the alloy can neither be soldered nor welded. various authors have found nitinol to be more susceptible to corrosion than other 91 . sufficient to induce phase transformation. They are difficult to join and have to be joined by mechanical crimps. In general Nickel-titanium wire has relatively low modulus values and larger working range. referred to as super elasticity or pseudo elasticity. Although some investigators reports that nitinol is resistant to corrosion as stainless steel. therefore can be produced with either the austenitic or mastensitic structure having varying degree of cold work and variations in transition temperature. If alloy is stressed. OTHER PROPERTIES Clinch back distal to molar buccal tube can be obtained by resistance or flame annealing the end of the wire. Nickel titanium alloy.Nickel Titanium Arch Wires SUPER ELASTICITY Inducing the austenitic to martensitic transition by stress can produce super elasticity. A dark blue color indicates the desired annealing temperature. Cl. With small metallic prominences Nitinol wire frequently exhibits an undulating bubbling or mottled cake appearance. Nitinol has been reported to be more susceptible to electrolytic dissolution than stainless steel. 92 . P. leveling. In few instances the active case has been treated with just one arch wire. The examination of unused wires revealed large variation in surface texture of nitinol wire when compared to stainless steel. SARKAR and FOSTER have noted that corrosion does not affect flexibility properties of nitinol wires. S. Because of the variation of unused Nitinol surface and possible organic contamination. tipping and torquing can be achieved with a resilient rectangular wire such as nitinol. SCHWANINGER. Some reports indicates an increase in permanent deformation and decrease in elasticity caused by corrosion or the cumulative effects of cold working. The most important benefit from Nitinol wires are realized when a rectangular wire is inserted early in treatment. it is difficult to assess the degree of corrosion existing on surfaces by visual inspection. Used unclean wires are frequently covered with organic layer which possesses significant elements such as Na. The electrolytically corroded Nitinol wires have either obvious pits which occurs along the sharp edges of rectangular wires where the electric field would be greatest or have very irregular surfaces with loosely bound corrosion products.Nickel Titanium Arch Wires orthodontic alloys. Clinicians have been successful in beginning treatment of certain carefully selected cases with full size rectangular wires that nearly fills the bracket slot. Simultaneous rotation. K and Ca. These layers are not usually present on cleaned surfaces. 4 x 103 Mpa.Nickel Titanium Arch Wires It is ideally suited for use with most pretorque and preangulated appliances because tipping and up righting of the teeth can be initiated in the early stages of treatment. The alloy has limited formability. The low stiffness in combination with  moderately  high  strength  accounts  for  wire’s  large  elastic  deflection   or working range.S 179 1579 2117 5 Co-Cr 184 1413 1682 8 NiTi 41. once the spaces have been closed. These properties results in very low orthodontic forces when compared with similarly constructed and activated stainless steel.7 931 1276 4 93 . In the treatment of extraction cases with pretorqued and preangulated twin brackets and Nitinol. (6 x 106 psi). the yield strength is 427 Mpa (62. and the ultimate tensile strength is 1489 Mpa (216. Alloys Modulus of Elasticity (103 MPa [GPa] 0. Therefore time intervals between appointments cannot be extended. The use of nitinol with pretorqued and preangulated brackets. conventional auxiliary method of closing spaces may be used along with headgear when needed.2% Offset yield strength (MPa) Ultimate Tensile Strength Number of 90 degree cold bends without fracture S. require careful monitoring of tooth movements because of wires high elasticity and more continuous force. When the case is nearing completion with a nitinol arch wire.000 psi). MECHANICAL PROPERTIES The modulus of elasticity of nitinol is 41. there is very little to be done in the way of placing compensating bends to upright roots.4 427 1489 2 B-TITANUM 71.000 psi). GARHER. in both extraction on non extraction cases. shape memory and elasticity are important and advantageous properties for clinical application of Niti. Nitinol wires can be used in Class I. Niti can be successfully used in the treatment of Cross bite corrections Up righting impacted canines Opening the bites. the greater benefit nitinol wire has over stainless steel. The more the wire has to be deflected from the ideal arch form when ligated into the bracket. MOORE and KAPILA and associates have noted that bracket/wire frictional forces with nitinol wires are higher than those with stainless steel wire and lower than those with beta-titanium. low constant forces. the primary criteria is the amount of malalignment of the teeth from the ideal arch form. In selecting cases that benefit most from the use of nitinol wires. flexibility.Nickel Titanium Arch Wires CLINICAL APPLICATION OF NITI High spring back. Class II or class III malocclusions. That property is its extreme elasticity when it is drawn into high-strength wire. 94 . It’s   the nitinol extreme elasticity that offers the clinician an advancement in the application of orthodontic materials. This wire is much more difficult to deform during handling and seating in brackets slot than stainless steel. ALLAI. USE OF THERMOELASTIC NITINOL Nitinol has unique property which is of practical use to the orthodontist. The average temperature of the mouth is in this range and triggers the wire to assume the original shape bent into it. First. The two 95 . restoring the desired wire to its original shape. After the wire has cooled to room temperature. Nitinol wire after being deformed will spring back to its original shape by either of two methods.Nickel Titanium Arch Wires The wire can be used for a longer period of time without changing and it can shorter the treatment time needed in leveling the dentition. the wire must first be set into the desired shape while undergoing a high temperature heat treatment. when it is heated through a transition temperature range.   CLINICAL RECYCLING OF NICKEL TITANIUM Now a days two types of Nickel titanium alloy wires are commercially available. If we were to take advantage of this property. When heated to its unique TTR it will remember its shape and return to the original configuration. Second it will experience a complete spring back from the deformed shape by being placed in the TTR between 31 to 45oC. it may be deformed within certain strain limits. Nitinol has another remarkable property of returning to a previously manufactured shape. this thermal nitinol wire is alloyed so that the TTR corresponds to the approximate temperature in the mouth and therefore allows part of the  wire  “memory”  property  to  be  used  for  moving  teeth. First of them is Nitinol (Unitek Corporation) and the recent one marked as Niti Cormaco (Alif) and Sentalloy (GAC International) among others. The TTR of Nitinol can be adjusted by varying the Nickel and Cobalt content. For orthodontic purpose. it will experience a nearly complete spring back because of its modulus of elasticity without heat. BUCKTHAL and KUSY had studied the effects of cold disinfectants on the mechanical properties and surface topography for 0.infection. Three disinfections approved by the ADA were used at maximum antimicrobial concentration. especially those of newer pseudo elastic type. Whereas the original Nitinol wires are primarily in the martensitic phase at room temperature.025″ Nitinol wires.17″ x . the Niti wires are also 36% stiff at 80% of activations and are not time dependent with regard to stress relaxation. The desirable mechanical properties of Nickel Titanium alloy wires and their relatively high cost has prompted many clinicians to recycle these wires. undergoes phase changes as a result of heat treatment that substantially alter their properties.Nickel Titanium Arch Wires demonstrates several differences in properties. KAPILA. When compared with Nitinol. Bending and 96 . Nickel Titanium wires. the newer Niti wires have an austenitic grain structure and 1. STERELIZATION OF ORTHODONTIC ARCH WIRES The relatively high cost of nickel titanium wires and it ability to return to its original forms had raised concern about the treatment of the wire between patients for prevention of cross. Since various forms of heat treatment are often used for sterilization.6 times greater spring back. chlorine di oxide and iodophor were used. HAUGEN and WATANABE noted that temperatures greater than 600C increases the susceptibility of these newer austenitic Nickel Titanium wires to plastic deformation and decreases their spring back. further studies to determine the effects of recycling in conjuncture with heat sterilizations are indicated. 2% acidic glutaraldehyde. 1 and 5 cycles. Evaluation of sentalloy wire and dry heat sterilization demonstrated a significant increase in tensile strength when compared after 0. The sterilization methods investigated were Dry heat using the Dentronix DDS 5000 dry heat sterilizer (3750 F for 20 min). Autoclaving (2500F for 20 min) and ethylene oxide gas (4 hours). Autoclaving santalloy wire also produced a significant increase in the tensile strength of the wire after 1 and 5 cycles. particularly for newest products  Second highest arch wire-bracket friction after TMA  Difficult to place permanent bends and cannot bend wire over sharp edge or into complete loop 97 . STAGGERS and MARGESON studied the effects of various types of sterilization on tensile strength of orthodontic wires. PROBLEMS ENCOUNTERED IN NICKEL TITANIUM ARCHWIRE /DISADVANTAGES  Expensive. Ethylene oxide sterilization of sentalloy wires demonstrated no significant differences in tensile strength.Nickel Titanium Arch Wires tensile tests were conducted to determine weather the stiffness. Wires showed no additional surface pitting or corrosion. Further surface topography was also studied with laser spectroscopy to see surface changes from tarnish and corrosion. The result showed no significant changes in fundamental stiffness or inherent strength of the wires after multiple disinfectant cycles. The tested Niti wire was Sentalloy (GAC International). strength or range of the wires changes after disinfectant treatment. They provide the force needed to open the bite. in small.021″  x  0. The arch wires are available in 0.14″ to 0. particularly for super elastic and shape memory alloys. ALIGN NICKEL TITANIUM REVERSE CURVE OF SPEE ARCHWIRES These wires are made with the same highly elastic material as the regular align nickel titanium wires. ADVANTAGES  Lowest force delivery of orthodontic wire alloys.20″  round  and  0.016″ x 0.025″ rectangular sizes. 2.Nickel Titanium Arch Wires  Wires cannot be soldered and must be joined by mechanical crimping process. Align is engineered with high elasticity to easily engage brackets. It also exerts continuous low forces. sometimes causing them to stick out beyond the terminal molar. even on severely malposed teeth.  Excellent spring back in bending. medium and large arches. ALIGN TRUE These are the only wires preformed in the true arch shape.  Tendency of arch wire to slide from side to side. It features exceptional shape memory and smooth low frictional surfaces.  Lowest in vitro corrosion resistance of wire alloys  Not self limiting – frequent visits necessary.  Super elastic alloys can be heat treated by clinician to vary force delivery characteristics. PROPRIETARY ARCH WIRES A) A .016″  to  0. close spaces 98 .COMPANY 1. Force 1 (super elastic) from 0.016″ x 0.  Permanent centre line memory arches have a gable bend at the midline that acts as permanent reference point and a stop to prevent the wire from sliding through either central bracket during unscrambling.016″ and 0. Force 2 (high force) from 0.  Gold coated memory arches available only in 0.018″ round sizes.018″ round and 0.020″ round.025″ rectangular wires. B) AMERICAN ORTHODONTICS 1.022″ to 0. These wires are available in 0. TITANIUM MEMORY WIRE This is super elastic Nickel titanium wire available in several varieties.016″ and 0.016″ round.014″ to 0. Standard memory arches feature natural arch form and two force levels.021″ x 0.Nickel Titanium Arch Wires and align the curve of spee. are coated with 24 carat gold and are especially cosmetic with ceramic or plastic brackets. 99 .018″ round.016″ to 0. They come in 0. D) GAC INTERNATIONAL 1. can reduce treatment time and   improve   patient’s   comfort. NEO SENTALLOY This wire provides the capability of 3 – dimensional control with a full size. It offers outstanding shape memory and elasticity. 2.  reduced  chair  time  and  patient’s  comfort. The wire delivers gentle force. Its heat activated light continuous forces are designed to produce the ideal biological tooth movement. 100 .dimensional leveling of severely malposed teeth. The smooth surface virtually eliminates friction and midlines are marked for easy placement. It features low stiffness.   It   is   available   in   ideal   arch   form   compatible   with   preadjusted appliances. C) DENTAURUM INTERNATIONAL 1. single strand arch wire from the beginning of treatment. predictable  results. making it particularly suited to leveling phase. REMITAN  “LITE” It is a super elastic nickel titanium wire with high elasticity and nearly continuous force over a wide deflection range. SUPER BRAID It is eight stranded braided super elastic Nickel titanium wire designed for initial 3.Nickel Titanium Arch Wires  Reverse curve of spee memory arches feature built in leveling and light continuous force for less wire bending and better control. 3. 101 . They feature faster results. It comes in sizes of 0. discoloration. Elastic hooks.016″ to 0.016″ to 0.021″ x 0. BMA arch wires come in 0. BENDABLE MASAL ALLOY (BMA) BMA arches combine the continuous gentle force of titanium with the workability of steel.018″ round and 0.Nickel Titanium Arch Wires E) MASAL ORTHODONTICS INTERNATIONAL 1. 2. eliminating the need for auxiliaries.025″ rectangular sizes. 4.016″ x0. ORTHOCOSMETIC ELASTINOL These arches have an esthetic coating that blends well with ceramic or plastic brackets and resists staining.019″ x 0.025″ rectangular sizes. They come in 0.016″. 0.20″ round.018″ and 0. low bracket friction and relatively low cost. ELASTINOL NICKEL TITANIUM ARCH WIRES These wires retain their shape even when drastically deformed.016″ x 0.016″ and 0.020″ round and 0. reduced chair time. cracking and chipping. tear drop and bayonet bends can be bent into the wires. DRIFT FREE ELASTINOL Drift free elastinol features a permanent 1 mm midline stop that reduces arch wire drifting and acts as a reference point.012″ to 0. Toe in bends helps eliminate mesiolingual rotations and the extra wide form minimizes lingual drift of anterior teeth.018″ round and 0. 102 . consolidate the arch and eliminates the excess curve of spee. 6. making them useful in the initial leveling stages. NITINOL These arch wires are slightly stiffer than Elastinol.021″ x 0.014″ to 0. NICKEL TITANIUM WIRES Orec’s Nickel Titanium wire combines super elasticity with shape memory to provide optimum force distribution for leveling. F) OREC CORPORATION 1. RETROARCH Retro arch reverse curve super elastic nickel titanium arch wires have a rocking chair shape that can open or close the bite quickly.025″ rectangular sizes.016″ to 0. aligning and rotation control. The arch wires are available in sizes of 0.Nickel Titanium Arch Wires 5. The natural shape is designed to reduce the need for contouring.016″ x 0. 025″ arch wire sizes.020″  x 0. 103 .016″ x 0. The wires are designed to facilitate insertion into bracket and closure of speed bracket spring clips. Midlines are clearly marked and rounded edge is always directed towards the labial.022″ to  0.014″ to 0. Preformed upper and lower arches come in sizes from 0. 2. SPEED ARCH WIRES Nickel titanium and stainless steel speed arch wires have an arch form that reflects in-out effects of the speed appliance. The posterior toe-in counteracts undesirable mesiolingual rotation of the molars. It allows retraction without tipping of adjacent teeth into extraction sites or loss of incisor torque. 2.020″ round and 0.019″  x 0. REVERSE CURVE NITI Reverse curve Niti has a shape that counters the extrusive component of space closing forces while continuing the bite opening process. NITI WIRE Niti wire has an elastic range so great that it is virtually impossible to put a permanent set into the wire.025″ rectangular.Nickel Titanium Arch Wires It  enhances  patient’s  comfort  and  treatment  efficiency  while  reducing  bracket   friction.022″ to 0.017″ x0. Speed wires are available in upper and lower 0. Extra archwidth prevents lingual collapse in the extraction sites. G) ORMCO CORPORATION 1. The braiding process increases the super elastic properties of Niti. resistance to deformation.025″ rectangular. REFLEX Reflex super elastic Nickel Titanium arch wire is available in two arch forms. H) ORTHO ORGANIZERS INTERNATIONAL 1.Nickel Titanium Arch Wires 3.019″ x 0. NITANIUM ARCHES Nitanium arches are Nickel titanium wires available in sizes from 0.020″ round and 0.016″ x 0.  The   low stiffness of this wire makes it effective with ceramic as well as metallic brackets.014″ to 0. I) ROCKY MOUNTAIN ORTHODONTICS 1.   Its ultra smooth finish reduces bracket friction. J) TP ORTHODONTICS 1. ORTHONOL Orthonol Nickel Titanium wire features great working range for fewer wire changes and adjustments. so that a full size wire can be used in a very severe malocclusion without  patient’s  discomfort. Orthonol comes in 11 round and rectangular sizes of preformed arches and in 5 rectangular sizes of straight lengths. excellent shape memory and light continuous  forces  for  patient’s  comfort.022″ to 0. NEW TURBO WIRES This is a braided Nickel titanium arch wire that permits torque control from the first wire in treatment. 104 . 025″ rectangular. FLEXILOY Flexiloy is made of a cobalt base Nickel alloy.016″ to 0. K) UNITEK CORPORATION 1. it is especially useful for making complex bends and loops. yet with a slightly higher stiffness than most super elastic wires. Heat treatment approximately doubles its spring temper. In its initial work hardened temper. Blue and Yellow. continuous forces needed for efficient tooth movement throughout treatment.020″ round and 0. The added control allows it to hold bends longer than other Nickel titanium wires. 105 .014″ to0.021″ x0. Flexiloy is available in two initial tempers.Nickel Titanium Arch Wires  Curved memory arch (Reverse Curve of spee)  Straight arch (Natural) Reflex is available in sizes from 0.016″ x 0. 2. NITINOL ACTIVE Because of its unique formation it delivers the light. and its possible use in orthodontics has been suggested periodically.Beta Titanium Arch Wires 13 Beta Titanium Arch Wires Beta titanium is the newest alloy to be introduced to orthodontic profession.8. Titanium has been used as structural metal since 1952.27.23. which is proportional to the ratio of yield strength to modulus of elasticity (Ys/E).31 To compete with stainless steel. a wire must possess at least comparable formability and spring back. 106 . At temperatures above 16250 F pure titanium rearranges into a body  centered  cubic  (BCC)  lattice.  referred  to  as  “Beta  phase”. a titanium based alloy can maintain its beta structure even when cooled to room temperature. COMPOSITION Titanium 77.6% Tin 4.   107 . but still based on HCP structure.3% The alloy is marketed in the form of straight wire lengths or preformed arches under  the  trade  name  “TMA”  or  Titanium  molybdenum  alloy.6250 F this metal has a hexagonal closed packed (HCP) crystal form and an appliance constructed from pure titanium would have only 1/3rd the maximum elastic deflection of a comparable stainless steel appliance. In   the   1960. The  second  phase  of  titanium’s  chronology  saw  the  development   of  titanium   alloys.s   an   entirely   different   “high   temperature”   form   of   titanium   alloy   became available.  With  the  addition of elements such as molybdenum or columbium.8% Molybdenum 11.Beta Titanium Arch Wires The early industrial applications of titanium employed commercially pure material (99.2% titanium). At temperatures below 1. Such alloys are referred to as beta stabilized titanium.3% Zarconium 6. The alloying and body centered cubic structure import a unique set of properties. Wrought Beta – titanium orthodontic wire has an elastic modulus of 71. The high ratio of yield strength to elastic modulus produces orthodontic appliances that can sustain large elastic activations when compared with stainless steel devices of the same geometry. Its stiffness makes its ideal in applications where less force than steel is required but where lower modulus materials would be inadequate to develop required force magnitudes. However. The low elastic modulus yields large deflections for low forces. The wrought wire can be bent into various orthodontic configurations and has formability comparable to that of austenitic stainless steel.2% Offset yield strength (MPa) Ultimate Tensile Strength Number of 90 degree cold bends without fracture S.Beta Titanium Arch Wires MECHANICAL PROPERTIES The mechanical properties of many titanium alloys can be altered by heat treatments that use the transformation from the α to β lattice structure. heat treatment of the current orthodontic β  -titanium wire is not recommended.S 179 1579 2117 5 Co-Cr 184 1413 1682 8 NiTi 41. The modulus of elasticity of beta – titanium is approximately twice that of nitinol and less than one half that of stainless steel.7 931 1276 4 108 .Beta – titanium can be highly cold – worked.4 427 1489 2 B-TITANUM 71. These properties produce several clinically desirable characteristics. Alloys Modulus of Elasticity (103 MPa [GPa] 0.7 Gpa and a yield strength between 860 and 1170 Mpa. satisfactory joints can be made by electrical resistance welding of Beta titanium.Beta Titanium Arch Wires It has been shown that the formability of Beta titanium orthodontic wire. Foremost among these factors are the condition of the electrodes. A weld made with insufficient heat fails at the interface between the wires. Such joints need not be reinforced with solder. so that some care in the selection of pliers and bending procedure is required. as measured by the ADA cold bend test. The Beta titanium wire can be joined by welding alone and has good corrosion resistance. Beta titanium joints of adequate strength and ductility can be produced with the standard commercial welders available to the orthodontist. whereas overheating may cause a failure adjacent to weld joint. 109 . WELDING Clinically. Clinically a no of variables might cause joints of inconsistent strength with a given welder. This electrode arrangement further stabilizes the wires as suggested by Burstone. However the titanium alloy cannot be bent over as sharp a radius as stainless steel. and higher settings can be used with welders to obtain strong joints with less burning of metals. is similar to that of stainless steel. cleanliness of wire surfaces and proper positioning of the wires between the electrodes. Flat to flat electronic configuration generally produces joints with considerably less distortion than is found with point to point arrangement. The high ductility of Beta-titanium allows it to be formed into arches or segments with complicated loop configurations.020″ steel wire when activated in a second order direction. In many applications. They can be deflected approximately twice as far without permanent deformation. Ideal edge wise arches fabricated of titanium have significant superiority over stainless steel. which allows for placement of tie-back loops or complicated bends. as used in loop configuration.018″ x 0. than straight continuous wires. lies with loop incorporation in larger 110 . beta titanium wire can be used in a number of clinical applications. A continuous arch with  “T”. The high ductility and formability of titanium allowed the placement of a vertical loop tie-back mesial to first molar as well as finishing bends with the arch. it would have the advantage of full bracket engagement and third order or torque control if used in a 0. One of the advantages of beta-titanium. Furthermore.   helical  and  “L”  loops can be formed in small round wires.  vertical.Beta Titanium Arch Wires CLINCAL APPLICATION Because of its unique and balanced properties.025″ wire in beta-titanium delivers about the same force as an 0.018″ slot bracket.014″ x 0. for example an 0. producing a more gentle delivery of forces with an edge wise wire. Spring back properties are not lost during the bending operation and complicated configurations can be placed if needed. loop placement can better deliver the desired force system without side affects. The forces which are produced are approximately .4 that of steel. Beta titanium is ductile. which allows a greater range of action for either initial tooth alignment or finishing arches. Specialized springs or auxiliaries fabricated from beta-titanium allow for simplification in design in achieving identical force delivery. ION IMPLANTATION A low coefficient of friction is usually desirable in an orthodontic arch wire. Ion Implantation is a process by which various elements or compounds are ionized and then accelerated towards a target. where a vapour flux of ions is generated with an electron beam evaporator and deposited on the substrate. However studies have shown that TMA have a higher coefficient of friction than stainless steel. Ion implantation takes place in a vacuum chamber. as in elimination of helices or loops. The friction is probably due to its relative softness compared to the harder stainless steel bracket. The low load deflection rate produced by the low modulus of elasticity and the high spring back allow a 12 mm activation to produce 60 gm of force in the midline without the placement of helices posteriorly. The surface treatment can increase the hardness and reduce the coefficient of friction of TMA wire while maintaining its desirable mechanical properties. A high formability of titanium allows the fabrication of closing loops with or without helices. 111 . the orthodontic arch wire. there by simplifying the design.Beta Titanium Arch Wires cross-sections of edge wise wire which allows the loop to be positively oriented within the brackets. The low stiffness of the material and its high spring back improves a loop of any given design or allow for the maintenance of a given force system with simpler designs. At the same time it reduces high coefficient of friction to about the same level as that of stainless steel. The thickness of the implanted surface can be precisely controlled. Implantation produces no sharp interface between coating and wire which can lead to bond failure and it does not alter wire dimensions. Two varieties of TMA-low friction and colored wires were produced by varying the type and thickness of ions.The ions penetrate the surface of the wire on impact. building up a structure that consists of both the original wire and a layer of tin compounds on the surface and immediate subsurface. The superficial compressive forces also minimize any effects of surface flaws.Beta Titanium Arch Wires Gas ions (Nitrogen and oxygen) are simultaneously extracted from a plasma and accelerated in the growing physical vapour deposition film at energies of several hundred to thousand electrons volts. Studies have shown that surface treatment by ion implantation can maintain all the desirable properties of TMA and can improve its ductility and its resistance to fracture and fatigue. The compressive forces and increased surface hardness improves the fatigue resistance and ductility and reduce the coefficient of friction of the wire. Implantation can take place at relatively low temperatures from subzero to 7000C which allows improvement of surface characteristics without degradation of other mechanical properties. This layer is extremely hard and creates considerable amount of compressive forces in the material at the atomic level. 112 . It contains alloy additions of nominally 5 to 6 % copper and . This alloy has unique characteristics and offers significant potential in the design of orthodontic appliances. To compensate for this 113 . China.2 to . TIEN HUA CHENG and associates at the General Research institute for non ferrous metals in Beijing. Unfortunately this occurs at the expense of increasing its phase transformation temperature above that of the oral cavity.5 % chromium. which is austenite. Its history of little work hardening and a parent phase. According to its manufacturer.9 This wire is also called as 270 C super elastic copper NiTi. yield mechanical properties that differ significantly from nitinol wire.Chinese Ni-Ti Wire 14 Chinese Ni-Ti Wire A new nickel titanium alloy has been developed especially for orthodontic applications by Dr. In addition. this product is an austenitic active wire whose copper addition increases its strength. Chinese niti wire has a much lower transition temperature than nitinol wire. The load deformation rate at small activations is considerably higher than that at large activations. Because the transformation temperature of these latter two wires are higher than the before mentioned first wire. MECHANICAL PROPERTIES 1) The wire has a spring back that is 4. the average stiffness of Chinese Niti wire is 73% that of stainless steel wire and 36% that of nitinol wire. 3) Unlike wires of other orthodontic alloys.Chinese Ni-Ti Wire unwanted effect .6 times that of nitinol wire. the characteristic stiffness is determined by the amount of activation. The stiffness is approximately the same between room temperature at 220C and mouth temperature at 370C. 2) At 80% of activation. One that has a transformation temperature of 350C and other that contains .4 times that of comparable stainless steel wire and 1.5 % chromium is added to return the transformation temperature to 270C.2 % chromium and transforms at 400C. if spring back is measured at yield based on a 5 mm span cantilever test. Two other alloys are also available from this family of Nickel – Titanium – Copper – Chromium alloys. they will increasingly be influenced by temperature as they represent the thermoelastic Nitinol described before. 114 . Applications include straight wire procedures when teeth are badly malaligned and in appliances designed to deliver constant forces during major stages of tooth movements. for instance. Chinese niti wire is applicable in situations where large deflections are required. The amount of deformation without notable permanent set is remarkable – 4.Chinese Ni-Ti Wire 4) Chinese Niti wire deformation is not particularly time dependent and unlike Nitinol wire. This has been accomplished by configurational design. 5) Chinese Niti wire is highly suitable if low stiffness is required and large deflections are needed. Achievement of relatively constant forces has been obtained traditionally by lowering the load deflection rate of the orthodontic appliance. Its higher stiffness at small activations make it more effective than wires of traditional alloys whose force levels may be too low (as teeth approach the passive shape of the wire). 115 .6 times that of nitinol wire.4 times that of stainless steel wire and 1. CLINICAL SIGNIFICANCE Because of its high range of action or spring back. will not continue to deform a significant amount in the mouth between adjustments. placing helices or additional wire in the appliance. When the stretch exceeds 2 %. There was no permanent set when the stress reached zero. This property is called as super elasticity. Furukawa Electric company limited of Japan produced a new type of Japanese NiTi alloy possessing excellent spring back.Japanese Ni-Ti Alloy Arch Wires 15 Japanese Ni-Ti Alloy Arch Wires In 1978. In comparison when strain was reduced. Co-Cr-Ni and nitinol wires all exhibit almost straight stress strain curves. it produces stresses of 55 to 58 kg/mm2. the Japanese Niti alloy wire did not changes proportionally to the stress decrease from 8% to 2%. the stress value does not change appreciably. the stainless steel. When strain was reduced. the stress was increased further. 116 . When the wire specimen was then stretched for more than 8%. When the strain was induced at 8%. shape memory and super elasticity. MECHANICAL PROPERTIES The Japanese niti alloy wire has higher values of elastic modulus than the nitinol wire. setting arch wire have been fabricated to enhance the efficiency of multi bracketed technique. the force level indicating the super elastic property can be reduced.Japanese Ni-Ti Alloy Arch Wires Heat treatment of Japanese niti alloy does make a dramatic change in its mechanical property. in the preformed arch wire. Japanese niti possesses three good mechanical properties. 117 . the influence of various series of heat treatment was studied. When the heat application was raised to 5000C. To attain optimal use of super elastic property in clinical orthodontics. arch wires providing a different magnitude of force can be fabricated from the wires of same diameter. In addition. By evaluating clinical experience with the Japanese niti alloy wire.  excellent spring back  shape memory  super elasticity CLINICAL APPLICATION Since the metallurgical tests have determined that Japanese niti alloy wire is potentially useful and effective in clinical orthodontics. different magnitude of force can be produced by controlling the temperature and time in the desired section of arch wire. many possibilities exist with the use of its super elastic property. Thus. Slip planes are clusters of atoms in a crystal that glides past one another during deformation. Its composition is: Titanium 90% Aluminum 6% Vanadium 4% The alloy is different in that its molecular structure resembles a closely packed hexagonal lattice as against the BCC lattice of TMA. The hexagonal lattice possess fewer slip planes. 118 . More the slip planes. Thus the near alpha phase titanium alloy is less ductile than TMA. the easier it is to deform the material. BCC structures are defined as having two slip planes where hexagonal lattice has only one active slip plane along its base.Alpha Titanium Alloy Arch Wires 16 Alpha Titanium Alloy Arch Wires It is the recent alloy in the family of titanium alloys. The alloy is strictly near Alpha phase titanium alloy rather than a pure alpha titanium because there is a certain amount of Beta phase retained in them at room temperature. Copper niti is more resistant to permanent deformation compared with other Nickel-Titanium alloys. It exhibits a smaller drop in tooth driving force than other Nickel titanium alloys. This enables the clinician to select arch wires on a case specific basis. 119 . 350C and 400C. Copper and Chromium) with different advantages over the formerly available Nickel Titanium alloys. Titanium.Copper Ni-Ti Alloy Arch Wires 17 Copper Ni-Ti Alloy Arch Wires Copper Niti was introduced by Rohit Sachdeva and Suchio Mriyasaki in 1994. It exhibits better spring back characteristics. 270C . It’s   a   new   quaternary alloy (Nickel. Addition of copper combined with more sophisticated manufacturing and thermal processes make possible the fabrication of four different copper niti arch wires with precise and consistent transformation temperatures 150C. It generates a more constant force over long activation spans than other Nickel titanium alloys and does so on a consistent basis. Copper Ni-Ti Alloy Arch Wires COMPOSITION Titanium 43% Nickel 49.64% Copper niti delivers more constant forces especially for small activations compared to super elastic wires..5% Copper 5. It makes possible the insertion of larger size wires..86% Chromium . 270C Type III .. It resembles the surface of untreated TMA wire. 400C 120 . Depending upon transformation temperatures / austenitic finish temperature cu-niti can be classified into Type I austenitic finish 150C Type II . 350C Type IV . and better bracket slot engagement early in treatment without causing pain and discomfort. The surface of cu-niti is quite porous and rough. Copper Ni-Ti Alloy Arch Wires VARIABLE TRANSFORMATION TEMPERATURE The stability of the martensite and austenitc phase at a given temperature is based upon transformation temperature of the alloy. One of the most important markers is the materials austenitic finish temperature.(Af) It is the difference between Af temperature and mouth temperature that determines the force generated by Nickel Titanium alloys. Af temperature can be controlled over a wider range by affecting the composition, thermo mechanical treatment and manufacturing process of the alloy. This alloy has the advantage of generating more constant forces than any other super elastic Nickel Titanium alloy. It is more resistant to deformation as a result of thermo mechanical insults in the mouth. Type I is not used for clinical applications due to high force level. Type II produces the optimum force and is indicated in normal patients. Type III is indicated in patients with a low to normal threshold of pain and also in periodontically compromised patients. Type IV produces the lowest level of force and are good in patients who are highly sensitive to pain and periodontically compromised patients. Quick and simple trick is to apply ice to the section of arch wire and can be placed into the bracket easily. 121 Copper Ni-Ti Alloy Arch Wires Cu-Niti is supplied in various sizes. 270 C 0.014″, 0.016″, 0.018″,0.016″, 0.022″, 0.017″ x 0.025″, 0.017″ x 0.025″. 350 C  0.016″, 0.018″, 0.016″ x 0.022″, 0.017″ x 0.022″, 0.017″ x 0.025″. 400 C  0.016″ x 0.022″, 0.017″ x 0.025″, 0.019″ x 0.025″. 122 Optiflex Arch Wire 18 Optiflex Arch Wire Optiflex is a recently introduced arch wire by Tallas. It combines highly aesthetic appearance with unique mechanical properties. It is made of clean optical fiber and consisof 3 layers. Silicon-di-oxide core that provides the force for moving teeth. Silicon resin middle layer that protects the core from moisture and adds strength. Strain resistant nylon outer layer that prevents damage to the wire and further increases its strength. 123 It is highly resilient arch wire that is especially effective in the alignment of crowded teeth. It has got a wide range of action and apply light continuous force.Optiflex Arch Wire The wire is manufactured in various sizes. Sharp bends must be avoided. 124 . since they could fracture the core. and can be either round or rectangular. Lee white arch wire of Lee pharmaceuticals is tooth colored epoxy coated arch wire that has superior wear resistance. an arch wire is usually placed to initiate tooth movement immediately after bonding. This problem can be avoided by placing sectional arches made of dead soft brass wire or twisted double strands of 0. However. The same type of sectional arches can be used as final arch wires in one or both arches in conjugation with snake elastics to enhance intercuspation prior to appliance removal. In a non-extraction case.in an extraction case a proper arch wire might create undesired tooth movement before extractions are performed.010″ dead soft stainless steel ligature wires. These arches are bend to lie passively in all attachments.008″ or 0.Dead Soft Security Arch Wires 19 Dead Soft Security Arch Wires It has been introduced recently by Binder and Scott. 125 . instead. Success is not final. failure is not fatal: it is the courage to continue that counts.Conclusion 20 Conclusion Recent advances in orthodontic arch wires proves a clear commitment to high performance standard. lifelong learning and strict accreditation in search of an ideal wire. it playing with them and perhaps someday these wire benders will come up with long overdue research of an ideal wire and we wait that the dawn will come early. To obtain benefit of optimum and predictable treatment results one can depend on selection of appropriate wire size and alloy type. The eminent orthodontic campaigners have come so far in search of an ideal wire with which they can play with.” 126 . 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