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The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.

Indian dental academy provides dental crown & Bridge,rotary endodontics,fixed orthodontics,
Dental implants courses.for details pls visit www.indiandentalacademy.com ,or call
0091-9248678078

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Properties of orthodontic wire /certified fixed orthodontic courses by Indian dental academy Properties of orthodontic wire /certified fixed orthodontic courses by Indian dental academy Presentation Transcript

  • Properties of Orthodontic Wires Part I INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  • Introduction Moving teeth and craniofacial harmony Forces and moments Wires Light continuous forces www.indiandentalacademy.com
  • History 1. Material Scarcity, Abundance of Ideas (1750-1930) noble metals Gold, platinum, iridium and silver alloys good corrosion resistance acceptable esthetics lacked the flexibility and tensile strength www.indiandentalacademy.com
  • History Angle (1887)  German silver (a type of brass) Opposition Farrar Neusilber brass (Cu 65%, Ni 14%, Zn 21%) various degrees of cold work – jack screws, – expansion arches, – Bands www.indiandentalacademy.com
  • History Wood, rubber, vulcanite, piano wire and silk thread Steel - as ligature wire. www.indiandentalacademy.com
  • History Stainless steel (entered dentistry -1919) Opposition  Emil Herbst  gold wire was stronger than stainless steel. (1934) www.indiandentalacademy.com
  • History 2. Abundance of materials, Refinement of Procedures (1930 – 1975)  Improvement in metallurgy and organic chemistry Cobalt chrome (1950s) Nitinol (1970s) www.indiandentalacademy.com
  • History 3. The beginning of Selectivity (1975 to the present) Beta titanium (1980) CAD/CAM Composites and Ceramics Iatrogenic damage  Nickel and bis-GMA www.indiandentalacademy.com
  • Basic Properties of Materials Elements – no simpler form  Atoms Electrons – orbits around nucleus Electron shells Electrons form the basis of bonds In metals, the energy levels are very closely spaced and the electrons tend to belong to the entire assembly rather than a single atom. www.indiandentalacademy.com
  • Basic Properties of Materials Molecules – 2 or more atoms Amorphous – similar properties in all directions – isotropy  Glass atoms organize themselves into specific lattices  geometry CRYSTAL  anisotropy www.indiandentalacademy.com
  • Basic Properties of Materials anion – cation –anion – cation extremely strong Wiskers reinforce If like ions are forced together, breakage results. Unlike metals, crystals cannot deform. www.indiandentalacademy.com
  • Basic Properties of Materials alloy crystals grow anion – cation –anion – cation Order is the dream of man, and chaos the rule of nature www.indiandentalacademy.com
  • Basic Properties of Materials Crystals penetrate each other such that the crystal shapes get deformed Grains  microns to centimeters Grain boundaries Atoms are irregularly arranged, and this leads to a weaker amorphous type structure. Alloy  combination of crystalline (grains) and amorphous (grain boundaries) www.indiandentalacademy.com
  • Basic Properties of Materials www.indiandentalacademy.com
  • Basic Properties of Materials Vacancies – These are empty atom sites www.indiandentalacademy.com
  • Interstitials – Smaller atoms that penetrate the lattice Eg – Carbon, Hydrogen, Oxygen, Boron. www.indiandentalacademy.com
  • Basic Properties of Materials Substitutial Element – another metal atom can substitute one of the same or similar size. E.g. Nickel or Chromium substituting iron in stainless steel. www.indiandentalacademy.com
  • Basic Properties of Materials The three dimensional arrangement of lines that can be visualized as connecting the atoms in undisrupted crystals, is called a lattice. Unit cell Crystal  combination of unit cells, in which each shell shares faces, edges or corners with the neighboring cells 14 crystal lattices www.indiandentalacademy.com
  • Basic Properties of Materials www.indiandentalacademy.com
  • Basic Properties of Materials The atoms, which are represented as points, are not static. Instead, they oscillate about that point and are in dynamic equilibrium. www.indiandentalacademy.com
  • Basic Properties of Materials various defects  slip planes www.indiandentalacademy.com
  • Basic Properties of Materials shear stress  atoms of the crystals can glide more the slip planes easier is it to deform Slip planes intercepted at grain boundaries www.indiandentalacademy.com
  • Basic Properties of Materials If the shearing force is:- Small - atoms slip, and return back to their original position (elastic deformation) Beyond the elastic limit - crystal suffers a slight deformation permanent (plastic deformation) Greater stress - fracture www.indiandentalacademy.com
  • Basic Properties of Materials During deformation - atomic bonds within the crystal get stressed  resistance to more deformation Number of atoms that get stressed also increases  resistance to more deformation Strain or work hardening or cold work www.indiandentalacademy.com
  • Basic Properties of Materials Strain hardening  Hard and strong Brittle. Annealing – heat below melting point. – More the cold work, more rapid the annealing – Higher melting point – higher annealing temp. – ½ the melting temperature (oK) www.indiandentalacademy.com
  • Basic Properties of Materials Recovery Recrystallization Grain Growth www.indiandentalacademy.com
  • Basic Properties of Materials www.indiandentalacademy.com
  • Before Annealing Recovery – Relief of stresses Recrystallization – New grains from severely cold worked areas Grain Growth – large crystal “eat up” small ones www.indiandentalacademy.com
  • Basic Properties of Materials Recovery Heat Treatment – Relief of internal stresses – Heating to low temperatures (370 – 480oC) for 11 mins – Increase in measured elastic properties – Residual stresses + External stresses www.indiandentalacademy.com
  • Basic Properties of Materials Various methods of obtaining smaller grain size 1. Enhancing crystal nucleation by adding fine particles with a higher melting point, around which the atoms gather. 2. Preventing enlargement of existing grains. Abrupt cooling (quenching) of the metal. Dissolve specific elements at elevated temperatures. Metal is cooled Solute element precipitates barriers to the slip planes. www.indiandentalacademy.com
  • Basic Properties of Materials Twinning Closed packed hexagonal type of crystals Two symmetric halves Fixed angle NiTi Subjected to a higher temperature, de - twinning occurs www.indiandentalacademy.com
  • Basic Properties of Materials www.indiandentalacademy.com
  • Basic Properties of Materials Polymorphism Metals and alloys exist as more than one type of structure Transition from one to the other Allotropy At higher temperature, ironFCC structure (austenite) lower temperatures,  BCC structure (ferrite) www.indiandentalacademy.com
  • Basic Properties of Materials Iron  FCC form (austenite), Lattice spaces greater, Carbon atom can easily be incorporated into the unit cell www.indiandentalacademy.com
  • Basic Properties of Materials On Cooling FCC  BCC Carbon diffuses out as FeC FeC adds strength to ferrite and austenite TIME www.indiandentalacademy.com
  • Basic Properties of Materials Rapidly cooled (quenched) – Carbon cannot escape Distorted body centered tetragonal lattice called martensite www.indiandentalacademy.com
  • Basic Properties of Materials Grain boundaries are more in number Alloy is stronger and more brittle Interstitials are intentionally incorporated into the alloy to make it hard when it is quenched. www.indiandentalacademy.com
  • Basic Properties of Materials Cooled slowly Other crystal structures are formed at intermediate temperatures Softer Some are stable at room temperature Ultimately, the final structure is softer and more workable www.indiandentalacademy.com
  • Basic Properties of Materials Tempering – Reheat the alloy to intermediate temperature Partial formation of the softer alloys More workable www.indiandentalacademy.com
  • Basic Properties of Materials Some alloys FCC to BCC by rearrangement of atoms Diagonal plane of the BCC unit becomes the face of the FCC unit Shape memory alloys – Easy switching from one type of structure to another. Bain distortion Over a range of temperature {hysteresis} www.indiandentalacademy.com
  • Elastic Properties Force applied to wire Deflection External force Internal force (equal and opposite) Internal force = Stress Area of action Deflection change in length = Strain Original length www.indiandentalacademy.com
  • Elastic Properties Types of stress/strain Tensile Compressive Shear Complex force systems www.indiandentalacademy.com
  • Elastic Properties www.indiandentalacademy.com
  • Stress Elastic Properties Elastic Portion www.indiandentalacademy.com Strain
  • Elastic Properties When the stress is removed, the wire returns back to its original dimension. Hooke’s law www.indiandentalacademy.com
  • Elastic Properties Stress Yield strength Proportional Limit Elastic Limit 0.1% www.indiandentalacademy.com Strain
  • Stress Elastic Properties Ultimate Tensile Strength www.indiandentalacademy.com Fracture Point Strain
  • Elastic Properties ultimate tensile strength is higher than the yield strength important clinically  maximum force that the wire can deliver Ultimate tensile strength higher than the stress at the point of fracture – reduction in the diameter of the wire www.indiandentalacademy.com
  • Stress Elastic Properties Slope α Stiffness Stiffness α 1 . Springiness www.indiandentalacademy.com Strain
  • Stress Elastic Properties Range Springback www.indiandentalacademy.com Strain
  • Elastic Properties Strength = Stiffness x Range www.indiandentalacademy.com
  • Elastic Properties Resiliency When a wire is stretched, the space between the atoms increases. Within the elastic limit, there is an attractive force between the atoms. Energy stored within the wire. www.indiandentalacademy.com
  • Elastic Properties Formability - amount of permanent deformation that the wire can withstand without breaking Indication of the ability of the wire to take the shape Also an indication of the amount of cold work that they can withstand www.indiandentalacademy.com
  • Stress Elastic Properties Resilience Formability www.indiandentalacademy.com Strain
  • Elastic Properties Flexibility large deformation (or large strain) with minimal force, within its elastic limit. Maximal flexibility is the strain that occurs when a wire is stressed to its elastic limit. Max. flexibility = Proportional limit Modulus of elasticity. www.indiandentalacademy.com
  • Elastic Properties Toughness –force required to fracture a material. Total area under the stress – strain graph. Brittleness –opposite of toughness. A brittle material, is elastic, but cannot undergo plastic deformation. Fatigue – Repeated cyclic stress of a magnitude below the fracture point of a wire can result in fracture. This is called fatigue. www.indiandentalacademy.com
  • Requirements of an ideal archwire (Kusy 1. Esthetics 7. Resiliency 2. Stiffness 8. Coefficient of friction 3. Strength 9. Biohostability 4. Range 10. Biocompatibility 5. Springback 11. Weldability 6. Formability www.indiandentalacademy.com
  • 1. Esthetics Desirable No compromise on mechanical properties White coloured wires discolour Destroyed by oral enzymes Deformed by masticatory loads Except the composite wires www.indiandentalacademy.com
  • 2. Stiffness / Load deflection Rate Thurow - force:distance ratio, measure of resistance to deformation. Burstone – Stiffness is related to – wire property & appliance design Wire property is related to – Material & cross section. Wilcock – Stiffness α Load Deflection www.indiandentalacademy.com
  • Stiffness / Load deflection Rate Magnitude of the force delivered by the appliance for a particular amount of deflection. Low stiffness or load deflection rate implies that:1) Low forces will be applied 2) The force will be more constant as the appliance deactivates 3) Greater ease and accuracy in applying a given force. www.indiandentalacademy.com
  • Stiffness / Load deflection Rate The shape and cross section of a wire have an effect on the strength of the wire. The effects of these will be considered subsequently. www.indiandentalacademy.com
  • 3. Strength Yield strength, proportional limit and ultimate tensile/compressive strength Kusy - force required to activate an archwire to a specific distance. Proffit - Strength = stiffness x range. Range limits the amount the wire can be bent, Stiffness is the indication of the force required to reach that limit. www.indiandentalacademy.com
  • 4. Range Distance that the wire bends elastically, before permanent deformation occurs (Proffit). Kusy – Distance to which an archwire can be activated Thurow – A linear measure of how far a wire or material can be deformed without exceeding the limits of the material. www.indiandentalacademy.com
  • 5. Springback Large springback Activated to a large extent. Hence it will mean fewer archwire changes. Ratio – yield strength Modulus of elasticity www.indiandentalacademy.com
  • 5. Springback Kusy -- The extent to which a wire recovers its shape after deactivation Ingram et al – a measure of how far a wire can be deflected without causing permanent deformation. (Contrast to Proffit). www.indiandentalacademy.com
  • 6. Formability Kusy – the ease in which a material may be permanently deformed. www.indiandentalacademy.com
  • 7. Resiliency Amount of energy stored in a body. www.indiandentalacademy.com
  • 8. Coefficient of friction Brackets (and teeth) must be able to slide along the wire High amounts of friction  anchor loss. www.indiandentalacademy.com
  • 9. Biohostability:- site for accumulation of bacteria, spores or viruses. An ideal archwire must have poor biohostability. 10. Biocompatibility:- Resistance of corrosion, and tissue tolerance to the wire. 11. Weldability:- the ease by which the wire can be joined to other metals, by actually melting the 2 metals in the area of the bond. (A filler metal may or may not be used.) www.indiandentalacademy.com
  • Properties of Wires Before the titanium alloys were introduced into orthodontics, the practitioners used only steel wires. So the way to control the stiffness of the wire was:1. Change the cross section of the wire 2. Increase the length of the wire ( inter bracket distance, incorporate loops.) www.indiandentalacademy.com
  • Effects of Wire Cross Section Wires of various dimensions and cross sections. Does the wire need to be move teeth over large distances, or does it need to correct the torque of the tooth? Is it primarily going to be used to correct first order irregularities, or second order? www.indiandentalacademy.com
  • Effects of Wire Cross Section primary factor  load deflection rate or stiffness play of the wire not very significant ligature ties minimizes the play in the first order www.indiandentalacademy.com
  • Effects of Wire Cross Section Play in the second order – 0.016” wire in 0.022” slot is only 1.15 times the play of a 0.018” wire. The play in the second order becomes significant if the wire dimensions are drastically different (0.010” and 0.020”) www.indiandentalacademy.com
  • Effects of Wire Cross Section www.indiandentalacademy.com
  • Effects of Wire Cross Section www.indiandentalacademy.com
  • Effects of Wire Cross Section Shape Moment of Inertia Ratio to stiffness of round wire Пd4 64 1 s4 12 1.7 b3h 12 1.7 b3h:d4 www.indiandentalacademy.com
  • Effects of Wire Cross Section Stiffness of different dimensions of wires can be related to each other. Relative stiffness Stiffness number (Burstone) 3500 3000 2500 2000 1500 1000 500 0 14 16 18 20 22 16x16 18x18 21x21 16x22 22x16 18x25 25x18 21x25 25x21 215x28 28x215 Wire dimension www.indiandentalacademy.com
  • Effects of Wire Cross Section www.indiandentalacademy.com
  • Effects of Wire Cross Section www.indiandentalacademy.com
  • A rough idea can be obtained clinically as well Forming an arch wire with the thumb gives an indication of the stiffness of the wire. Flexing the wires between the fingers, without deforming it, is a measure of flexibility Deflecting the ends of an archwire between the thumb and finger gives a measure of resiliency. www.indiandentalacademy.com
  • Effects of Wire Cross Section Rectangular wires  bending perpendicular to the larger dimension (ribbon mode) easier than bending perpendicular to the smaller dimension (edgewise). Relative stiffness Stiffness number (Burstone) 3500 3000 2500 2000 1500 1000 500 0 14 16 18 20 22 16x16 18x18 21x21 16x22 22x16 18x25 Wire dimension www.indiandentalacademy.com 25x18 21x25 25x21 215x28 28x215
  • Effects of Wire Cross Section The larger dimension  correction is needed. The smaller dimension  the plane in which more stiffness is needed. > first order, < second order – RIBBON > Second order, < first order - EDGEWISE www.indiandentalacademy.com
  • Effects of Wire Cross Section > 1st order correction in anterior segment > 2nd order in the posterior segment, wire can be twisted 90o ribbon mode in anterior region and edgewise in posterior region. www.indiandentalacademy.com
  • Effects of Wire Cross Section If both, 1st & 2nd order corrections are required to the same extent, then square or round wires. The square wires - advantage simultaneously control torque better orientation into a rectangular slot. (do not turn and no unwanted forces are created). www.indiandentalacademy.com
  • Effects of Wire Cross Section In torsion - absolute values of strength, stiffness and range are different, but the overall effect of changing the diameter of the wire is the same. 1. Strength – Increases with increase in diameter 2. Stiffness – increases 3. Range – decreases. www.indiandentalacademy.com
  • Effects of Length Loops,  the inter-bracket distance For bending 1. Strength – decreases proportionately 2. Stiffness – decreases as a cubic function 3. Range – increases as a square. www.indiandentalacademy.com
  • Effects of Length In the case of torsion, the picture is slightly different. Increase in length – 1. Stiffness decreases proportionately 2. Range increases proportionately 3. Strength remains unchanged. www.indiandentalacademy.com
  • Effects of Length Way the beam is attached also affects the values cantilever, the stiffness of a wire is obviously less wire is supported from both sides (as an archwire in brackets), again, the stiffness is affected www.indiandentalacademy.com
  • Effects of Length www.indiandentalacademy.com
  • Effects of Length Stiffness is also affected by the method of ligation of the wire into the brackets. Loosely ligated, so that it can slide through the brackets, it has ¼th the stiffness of a wire that is tightly ligated. www.indiandentalacademy.com
  • Clinical Implications LIGHT CONTINUOUS FORCES Stiff wires should be taboo to the orthodontist? Springier wire, can be easily distorted in the harsh oral environment. Aim at balance. www.indiandentalacademy.com
  • Clinical Implications Removable appliance cantilever spring The material of choice is usually steel. (Stiff material) Sufficiently thick steel wire Good strength to resist masticatory and other oral forces. Increase the length of the wire  – Proportionate decrease in strength, but the stiffness will decrease as a cubic function – Length is increase by either bending the wire over itself, or by winding helicals or loops into the spring www.indiandentalacademy.com
  • Clinical Implications In archwires of stiffer materials the same principle can be used. The length of wire between brackets can be increased – loops, or smaller brackets, or special bracket designs. Also, the use of flexible wires www.indiandentalacademy.com
  • Clinical Implications Multi-stranded wires Twisting of the two wires causes the strength to increase, so that the wire can withstand masticatory forces. The properties of multistranded wires depend on the individual wires that are coiled, and on how tightly they are coiled together. www.indiandentalacademy.com
  • Clinical Implications Variable cross-section orthodontics. Variable modulus orthodontics. www.indiandentalacademy.com
  • Clinical Implications www.indiandentalacademy.com
  • Clinical Implications variable modulus orthodontics – Advantage– relatively constant dimension – important for the third order control variable stiffness approach, – compromise control for getting a wire with adequate stiffness, – had to spend clinical time bending loops into stiffer archwires, which would offer less play. www.indiandentalacademy.com
  • Clinical Implications Take into account the amount of force that wire can deliver. For example, a NiTi wire  efficient in tipping teeth to get them into alignment, but may not be able to achieve third order corrections. After using rectangular NiTi wires for alignment, rectangular steel wire must always be used to achieve the correct torque of the tooth. www.indiandentalacademy.com
  • Corrosion Nickel 1. Carcinogenic, 2. mutagenic, 3. cytotoxic and 4. allergenic. Stainless steels, Co-Cr-Ni alloys and NiTi are all rich in Ni www.indiandentalacademy.com
  • Corrosion Placement in the oral cavity  Greater peril than implanting  Implanted material gets surrounded by a connective tissue capsule  In the oral cavity, the alloy is free to react with the environment. www.indiandentalacademy.com
  • Corrosion Passivating film  traces of Fe Ni and Mo. Aqueous environment – inner oxide layer – outer hydroxide layer. CrO is not as efficient as TiO in resisting corrosion some Ni release Improper handling  sensitization www.indiandentalacademy.com
  • Corrosion 1. Uniform attack – the entire wire reacts with the environment, hydroxides or organometallic compounds detectable after a large amount of metal is dissolved. 2. Pitting Corrosion – manufacturing defects sites of easy attack www.indiandentalacademy.com
  • Corrosion Steel NiTi www.indiandentalacademy.com
  • Corrosion 3. Crevice corrosion or gasket corrosion - Parts of the wire exposed to corrosive environment Sites of tying to the brackets Plaque build up  disturbs the regeneration of the passivating layer Reach upto 2-5 mm High amount of metals can be dissolved in the mouth. www.indiandentalacademy.com
  • Corrosion 4. Galvanic corrosion two metals are joined or even the same metal after different type of treatment (soldering etc) difference in the reactivity  Galvanic cell.  Less Reactive (Cathodic)  More Reactive (Anodic) www.indiandentalacademy.com
  • Corrosion Anodic  Looses Electrons  Soluble ions  Leach out Cathodic  Accepts electrons  Even less reactive www.indiandentalacademy.com
  • Corrosion 5. Intergranular corrosion Sensitization 6. Fretting corrosion Wire and brackets contact Friction  surface destruction Pressure  rupture of the oxide layer Debris get deposited at grain boundaries, grain structure is disturbed. www.indiandentalacademy.com
  • Corrosion 7. Microbiologically influenced corrosion Adhersive Craters at the base of brackets Or wires directly bonded on to teeth shown by matasa. Certain bacteria dissolve metals directly form the wires. Others affect surface structure. www.indiandentalacademy.com
  • Corrosion www.indiandentalacademy.com
  • Corrosion 8. Stress corrosion Similar to galvanic corrosion Bending of wires  different degress of tension and compression. Alter the electrochemical behavior   anode cathode www.indiandentalacademy.com
  • Corrosion 9. Fatigue corrosion – Cyclic stressing of a wire Accelerated in a corrosive medium such as saliva www.indiandentalacademy.com
  • Corrosion Analysis of used wires also indicated that a biofilm was formed on the wire. Eliades et al Calcification – Shielding the wire – Protecting the patient form the alloy www.indiandentalacademy.com
  • Corrosion Ni and Cr – impair phagocytosis of neutrophils and – impair chemotaxis of WBCs. Ni at conc. Released from dental alloys – activating monocytes and endothelial cells, – promote intracellular adhesion. – This promotes inflammatory response in soft tissues. Arsenides and sulfides of Ni - carcinogens and mutagens. Ni at non toxic levels - DNA damage. www.indiandentalacademy.com
  • Orthodontic Arch Wire Materials www.indiandentalacademy.com
  • Precious Metals Upto about the 1950s Gold alloys Only wire which would tolerate the oral environment Crozat appliance – according to original design www.indiandentalacademy.com
  • Stainless Steel 1919 – Germany  used to make prostheses. Extremely chemically stable High resistance to corrosion. Chromium content. The chromium gets oxidized,  Impermeable, corrosion resistant layer. www.indiandentalacademy.com
  • Stainless Steel Variety of stainless steels Varying the degree of cold work and annealing during manufacture Fully annealed stainless steel  extremely soft, and highly formable Ligature wire “Dead soft” www.indiandentalacademy.com
  • Stainless Steel stainless steel arch wires are cold worked to varying extents,  yield strength increases, at the cost of their formability The steel with the highest yield strength, the Supreme grade steels, are also very brittle, and break easily when bent sharply. www.indiandentalacademy.com
  • Stainless Steel Structure and composition Chromium (11-26%)–improves the corrosion resistance Nickel(0-22%) – austenitic stabilizer copper, manganese and nitrogen - similar – amount of nickel added to the alloy – adversely affect the corrosion resistance. www.indiandentalacademy.com
  • Stainless Steel Carbon (0.08-1.2%)– provides strength Reduces the corrosion resistance Sensitization. Improper cooling after heat treatment – During soldering or welding – 400-900oc Chromium diffuses towards the carbon rich areas (usually the grain boundaries) www.indiandentalacademy.com
  • Stainless Steel Chromium carbides Amount of chromium decreases Chromium carbide is soluble,  intergranular corrosion. Stabilization www.indiandentalacademy.com
  • Stainless Steel Stabilization – – Element which precipitates carbide more easily than Chromium. – Usu. Titanium. – Ti 6x> Carbon – No sensitization during soldering. – Most steels used in orthodontics are not stabilized. www.indiandentalacademy.com
  • Stainless Steel Silicon – (low concentrations) improves the resistance to oxidation and carburization at high temperatures. Sulfur (0.015%) increases ease of machining Phosphorous – allows sintering at lower temperatures. But both sulfur and phosphorous reduce the corrosion resistance. www.indiandentalacademy.com
  • Stainless Steel Manufacture Various steps – 1. Melting 2. Ingot Formation 3. Rolling 4. Drawing www.indiandentalacademy.com
  • Stainless Steel Melting – Various metals of the alloy are melted – Proportion influences the properties Ingot formation – Molten alloy into mold. – Non uniform in compositon – Porosities and slag. – Grains seen in the ingot – control of grain size. www.indiandentalacademy.com
  • Stainless Steel – Porosities due to dissolved gasses (produced / trapped) – Vacuum voids due to shrinking of late cooling interior. – Important to control microstructure at this stage. www.indiandentalacademy.com
  • Stainless Steel Rolling – – First mechanical process. – Ingot reduced to thinner bars – Finally form a wire – Different wires, slightly different composition. www.indiandentalacademy.com
  • Stainless Steel – Altering of the shape of grains during rolling – Grains get elongated, defects get rearranged – Work hardening. – Wires starts to crack if rolling continues – Annealing is done – Rolling continued www.indiandentalacademy.com
  • Stainless Steel Drawing – More precise – Ingot  final size. – Wire pulled through small hole in a die – Progressively smaller diameter. – Same pressure all around, instead of from 2 opposite sides. www.indiandentalacademy.com
  • Stainless Steel – Annealing at regular intervals. – Exact number of drafts and annealing cycles depends on the alloy. www.indiandentalacademy.com
  • Stainless Steel Classification American Iron and Steel Institute (AISI) Unified Number System (UNS) German Standards (DIN). www.indiandentalacademy.com
  • Stainless Steel The AISI numbers used for stainless steel range from 300 to 502 Numbers beginning with 3 are all austenitic Higher the number  – More the iron content – More expensive the alloy – Numbers having a letter L signify a low carbon content www.indiandentalacademy.com
  • Stainless Steel www.indiandentalacademy.com
  • Stainless Steel Austenitic steels (the 300 series) Corrosion resistance FCC structure,  non ferromagnetic Not stable at room temperature, Austenite stabalizers Ni, Mn and N Known as the 18-8 stainless steels. www.indiandentalacademy.com
  • Stainless Steel Martensitic steel FCC  BCC BCC structure is highly stressed. More grain boundaries, – Stronger – Less corrosion resistant Making instrument edges which need to be sharp and wear resistant. www.indiandentalacademy.com
  • Stainless Steel Ferritic steels – (the 400 series) Good corrosion resistance Low strength. Not hardenable by heat treatment. Not readily cold worked. www.indiandentalacademy.com
  • Stainless Steel Austenitic steels more preferable :- Greater ductility and ability to undergo more cold work without breaking. Substantial strengthening during cold work. (Cannot be strengthened by heat treatment). Strengthening effect is due partial conversion to martensite. Easy to weld Easily overcome sensitization Ease in forming. www.indiandentalacademy.com
  • Stainless Steel Duplex steels Both austenite and ferrite grains Increased toughness and ductility than Ferritic steels Twice the yield strength of austenitic steels Lower nickel content Manufacturing low nickel attachments www.indiandentalacademy.com
  • Stainless Steel Precipitation hardened steels Certain elements added to them  precipitate and increase the hardness on heat treatment. The strength is very high Resistance to corrosion is low. Used to make mini-brackets. www.indiandentalacademy.com
  • Stainless Steel General properties of steel Relatively stiff material www.indiandentalacademy.com
  • Stainless Steel www.indiandentalacademy.com
  • Stainless Steel Yield strength and stiffness can be varied – Altering the carbon content and – Cold working and – Annealing High forces - dissipate over a very short amount of deactivation (high load deflection rate). www.indiandentalacademy.com
  • Stainless Steel Clinical terms:- Loop - activated to a very small extent so as to achieve optimal force Deactivated by only a small amount (0.1 mm) Force level will drop tremendously Not physiologic More activations www.indiandentalacademy.com
  • Stainless Steel Force required to engage a steel wire into a severely mal-aligned tooth. – Either cause the bracket to pop out, – Or the patient to experience pain. Overcome by using thinner wires, which have a lower stiffness. Fit poorly loss of control on the teeth. www.indiandentalacademy.com
  • Stainless Steel High stiffness  Maintain the positions of teeth Hold the corrections achieved Begg treatment, stiff archwire, to dissipate the adverse effects of third stage auxiliaries www.indiandentalacademy.com
  • Stainless Steel Lowest frictional resistance Ideal choice of wire during space closure with sliding mechanics Teeth be held in their corrected relation Minimum resistance to sliding www.indiandentalacademy.com
  • Stainless Steel Ni is used as an austenite stabilizer. Not strongly bonded to produce a chemical compound. d likelihood of slow release of Ni www.indiandentalacademy.com
  • Stainless Steel Nickel and chromium content in the steel wires Cause patients to be sensitized Cause reactions in already sensitized patients www.indiandentalacademy.com
  • Stainless Steel Passivating layer dissolved in areas of plaque accumulation – Crevice corrosion. Different degrees of cold work – Galvanic corrosion Different stages of regeneration of passivating layer – Galvanic corrosion Sensitization – Inter-granular corrosion www.indiandentalacademy.com
  • High Tensile Australian Wires History Early part of Dr. Begg’s career Arthur Wilcock Sr. – Lock pins, brackets, bands, wires, etc Wires which would remain active for long No frequent visits This lead wilcock to develop steel wires of high tensile strength. www.indiandentalacademy.com
  • High Tensile Australian Wires Beginners found it difficult to use the highest tensile wires Grading system Late 1950s, the grades available were – – Regular – Regular plus – Special – Special plus www.indiandentalacademy.com
  • High Tensile Australian Wires Newer grades were introduced after the 70s. Raw materials directly from the suppliers from out of Australia More specific ordering and obtaining better raw materials Higher tensile strength wires – premium www.indiandentalacademy.com
  • High Tensile Australian Wires Highly brittle, and broke easily Straightening the wire  softening and loss of high tensile properties. www.indiandentalacademy.com
  • High Tensile Australian Wires Bauschinger effect. Described by dr. Bauschinger in 1886. Material strained beyond its yield point in one direction, then strained in the reverse direction, its yield strength in the reverse direction is reduced. www.indiandentalacademy.com
  • High Tensile Australian Wires www.indiandentalacademy.com
  • High Tensile Australian Wires Plastic prestrain increases the elastic limit of deformation in the same direction as the prestrain. Plastic prestrain decreases the elastic limit of deformation in the direction opposite to the prestrain. If the magnitude of the prestrain is increased, the elastic limit in the reverse direction can reduce to zero. www.indiandentalacademy.com
  • High Tensile Australian Wires Straightening a wire  pulling through a series of rollers Prestrain in a particular direction. Yield strength for bending in the opposite direction will decrease. Premium wire  special plus or special wire www.indiandentalacademy.com
  • High Tensile Australian Wires Special pulsing process. This method : 1. Permits the straightening of high tensile wires 2. Does not reduce the yield strength of the wire 3. Results in a smoother wire, hence less wire – bracket friction. www.indiandentalacademy.com
  • High Tensile Australian Wires Higher yield strength  more flexible. Supreme grade flexibility = β-titanium. Higher resiliency  nearly three times. NiTi  higher flexibility but it lacks formability www.indiandentalacademy.com
  • High Tensile Australian Wires Mollenhauer  Supreme grade wire  faster and gentler alignment of teeth. Intrusion  simultaneously with the base wires Gingival health seemed better Originally in lingual orthodontics Equally good for labial orthodontics as well. www.indiandentalacademy.com
  • High Tensile Australian Wires Methods of increasing yield strength of Australian wires. 1. Work hardening 2. Dislocation locking 3. Solid solution strengthening 4. Grain refinement and orientation www.indiandentalacademy.com
  • High Tensile Australian Wires Clinical significance of high yield strength. Flexibility – Yield strength Elastic Modulus Resilience - (Yield strength)2 Elastic Modulus Plastic portion of the stress-strain graph is smaller  wires are more brittle. www.indiandentalacademy.com
  • High Tensile Australian Wires Zero Stress Relaxation If a wire is deformed and held in a fixed position, the stress in the wire may diminish with time, but the strain remains constant. Property of a wire to give constant light force, when subjected to external forces (like occlusal forces). www.indiandentalacademy.com
  • High Tensile Australian Wires external forces  particles slip over each other  activation of the wire is lost Overcome  Internal friction Between particles   yield strength www.indiandentalacademy.com
  • High Tensile Australian Wires Zero stress relaxation in springs. To avoid relaxation in the wire’s working stress Diameter of coil : Diameter of wire = 4 smaller diameter of wires  smaller diameter springs (like the mini springs) Higher grade wires, ratio can be 2 www.indiandentalacademy.com
  • High Tensile Australian Wires Twelftree, Cocks and Sims (AJO 1977) Premium plus, Premium and Special plus wires showed minimal stress relaxation. Special, Remanit, Yellow Elgiloy, Unisil. www.indiandentalacademy.com
  • High Tensile Australian Wires Hazel, Rohan & West (1984) – Stress relaxation of Special plus wires after 28 days was less than Dentaurum SS and Elgiloy wires. Barrowes (82) & Jyothindra Kumar (89) – Higher working range among steel wires. www.indiandentalacademy.com
  • High Tensile Australian Wires Pulse straightened wires – Spinner straightened (Skaria 1991) – Strength, stiffness and Range higher – Coeff. of friction higher – Similar surface topography, stress relaxation and Elemental makeup. www.indiandentalacademy.com
  • High Tensile Australian Wires Anuradha Acharya (2000) – Super Plus (Ortho Organizers) – between Special plus and Premium – Premier (TP) – Comparable to Special – Premier Plus – Special Plus – Bowflex – Premium www.indiandentalacademy.com
  • High Tensile Australian Wires Highest yield strength and ultimate tensile strength as compared to the corresponding wires. Higher range Lesser coefficient of friction – Surface area seems to be rougher than that of the other manufacturers’ wires. Lowest stress relaxation. www.indiandentalacademy.com
  • High Tensile Australian Wires Fracture of wires and crack propagation Dislocation locking  High tensile wires have high density of dislocations and crystal defects  Pile up, and form a minute crack  Stress concentration www.indiandentalacademy.com
  • High Tensile Australian Wires Small stress applied with the plier beaks  Crack propagation  Elastic energy is released  Propagation accelerates to the nearest grain boundary www.indiandentalacademy.com
  • High Tensile Australian Wires Ways of preventing fracture 1. Bending the wire around the flat beak of the pliers. Introduces a moment about the thumb and wire gripping point, which reduces the applied stress on the wire. www.indiandentalacademy.com
  • High Tensile Australian Wires www.indiandentalacademy.com
  • High Tensile Australian Wires 2. The wire should not be held tightly in the beaks of the pliers. Area of permanent deformation to be slightly enlarged, Nicking and scarring avoided. The tips of the pliers should not be of tungsten carbide. www.indiandentalacademy.com
  • High Tensile Australian Wires www.indiandentalacademy.com
  • High Tensile Australian Wires 3. The edges rounded  reduce the stress concentration in the wire. 4. Ductile – brittle transition temperature slightly above room temperature. Wire should be warmed. Spools kept in oven at about 40o, so that the wire remains slightly warm. www.indiandentalacademy.com
  • Multistranded Wires 2 or more wires of smaller diameter are twisted together/coiled around a core wire. Diameter - 0.0165 or 0.0175, but the stiffness is much less. On bending  individual strands slip over each other and the core wire, making bending easy. www.indiandentalacademy.com
  • Multistranded Wires As the diameter of a wire decreases – Stiffness – decreases as a function of the 4th power Range – increases proportionately Strength – decreases as a function of the 3rd power Multistranded wires  Small diameter wires, High strength www.indiandentalacademy.com
  • Multistranded Wires Elastic properties of multistranded archwires depend on – 1. Material parameters – Modulus of elasticity 2. Geometric factors – moment of inertia & wire dimension 3. Dimensionless constants – Number of strands coiled – Helical spring shape factor – Bending plane shape factor www.indiandentalacademy.com
  • Multistranded Wires Helical spring shape factor Coils resemble the shape of a helical spring. The helical spring shape factor is given as – 2sin α 2+ v cos α α - helix angle and v - Poisson’s ratio (lateral strain/axial strain) Angle α can be seen in the following diagram :www.indiandentalacademy.com
  • Multistranded Wires α = tan -1 l* . π (D-d) www.indiandentalacademy.com
  • Multistranded Wires Bending shape factor Complex property – number of strands – orientation of the strands – diameter of the strands and the entire wire – helix angle etc. Different for different types of multistranded wires www.indiandentalacademy.com
  • Multistranded Wires Kusy (AJO 1984) Triple stranded 0.0175” (3x0.008”) SS GAC’s Wildcat Compared the results to other wires commonly used by orthodontists. www.indiandentalacademy.com
  • Multistranded Wires www.indiandentalacademy.com
  • Multistranded Wires www.indiandentalacademy.com
  • Multistranded Wires Did not resemble the 0.018” SS wire except Size Wire-bracket relation. www.indiandentalacademy.com
  • Multistranded Wires Ingram, Gipe and Smith (AJO 86) Range independent of wire size Consistent for different configurations of wires. For round as well as rectangular multistranded wires. www.indiandentalacademy.com
  • Multistranded Wires Nanda et al (AO 97) Increase in No. of strands  stiffness Unlike single stranded wires – stiffness varied as deflection varied. www.indiandentalacademy.com
  • Multistranded Wires Kusy (AO 2002) Interaction between individual strands was negligible. Range and strength Triple stranded Ξ Coaxial (six stranded) Stiffness  Coaxial < Triple stranded Range of small dimension single stranded SS wire was similar. www.indiandentalacademy.com
  • Multistranded Wires www.indiandentalacademy.com
  • Friction Two bodies in contact, Relative motion 2 components :- Frictional force –contact force between the sliding surfaces and is opposite to it. Normal (perpendicular force) – forces that arise which are normal (perpendicular) to the two surfaces in contact www.indiandentalacademy.com
  • Friction Frictional force = Coefficient of friction x normal force. Coefficient of friction – static – kinetic www.indiandentalacademy.com
  • Friction Normal Force - www.indiandentalacademy.com
  • Friction Friction is determined by the relative roughness of the two materials in contact. This depends on :1. The material itself 2. manufacturing process (polishing, heat treatment etc.) 3. Shelf and/or use time.(due to corrosion, creep etc) www.indiandentalacademy.com
  • Friction Normal force – 1. Stiffness of the wire in bending. www.indiandentalacademy.com
  • Friction Friction is independent of the area of contact - Proffit Rough at molecular level – Asperities Real contact only at these spots. www.indiandentalacademy.com
  • Friction Light loads can cause plastic deformation. Shearing of asperities. “Stick-slip” phenomenon. Interlocking of asperities. Harder materials plow into softer materials. www.indiandentalacademy.com
  • Friction Frank and Nikoli (AJO-1980) Friction depends on wire bracket angulation – At lower angulations surface – Higher angulations Normal force www.indiandentalacademy.com
  • Friction Rectangular wires > Round wires – Greater area of contact. At higher angulations  0.020” higher friction than some rectangular wires (17x25) www.indiandentalacademy.com
  • Friction Influence of wire material NiTi wires - rougher surface than steel or Elgiloy – more friction at low angulations at high angulations - normal force – NiTi  lower stiffness than steel or Elgiloy  lower frictional resistance. www.indiandentalacademy.com
  • Friction Stannard et al (AJO 1986) surface layer of oxides - harder than the material on the interior unpredictability of the exact area of contact Friction cannot be determined accurately every time. www.indiandentalacademy.com
  • Friction Before and after slidingSS had a smooth and polished structure before sliding & surface roughness and wear tracks were seen after sliding β titanium had a grainy surface before and a smoother surface after sliding. NiTi and cobalt chrome had a fibrous surface before and no change after sliding. www.indiandentalacademy.com
  • Friction Dry and wet conditions Wet condition  the coefficient of friction Except cobalt chromium Liquid  the adhesion b/w molecules of the wire and bracket Saliva does not act as a lubricant www.indiandentalacademy.com
  • Friction Stainless steel and β titanium - lowest friction. NiTi Cobalt Chrome. - Highest www.indiandentalacademy.com
  • Friction Tidy (AJO 1989) stainless steel - lowest friction NiTi second TMA TMA 5 times > stainless steel www.indiandentalacademy.com
  • Friction At high wire bracket angulations – normal force more important. – Initial stages – High friction of steel wires – NiTi and β titanium have lower friction. (lower stiffness) After alignment, surface characteristics more important – Steel has smoother surface. www.indiandentalacademy.com
  • Friction Round or Rectangular for sliding? – After alignment, difference is negligible. – Rect. Wire Better torque control Leave rect. Wire in place for final corrections Start sliding after 1 visit. www.indiandentalacademy.com
  • Welding of Steel 3 useful properties – 1. Comparatively low melting point, 2. High electrical resistance and 3. Low conductivity of heat. www.indiandentalacademy.com
  • Welding of Steel Important to – minimize the time of passing the current – minimize the area of heating Sensitization - between 400 and 900oC Chromium carbides need time for their formation. www.indiandentalacademy.com
  • Welding of Steel Join two thin sheets of metal Same thickness Joining tubes, wires and springs, soldering is generally recommended. Electrodes - small tips, not exceeding 1 mm in diameter. www.indiandentalacademy.com
  • Cobalt Chromium 1950s the Elgin Watch Rocky Mountain Orthodontics Elgiloy CoCr alloys - satellite alloys – superior resistance to corrosion, comparable to that of gold alloys. www.indiandentalacademy.com
  • Cobalt Chromium Cobalt – 40-45% Chromium – 15-22% Nickel – for strength and ductility Iron, molybdenum, tungsten and titanium to form stable carbides and enhance hardenability. www.indiandentalacademy.com
  • Cobalt Chromium Strength and formability modified by heat treatment. The alloy is highly formable, and can be easily shaped. Heat treated. – Strength  – Formability  www.indiandentalacademy.com
  • Cobalt Chromium www.indiandentalacademy.com
  • Cobalt Chromium Heat treated at 482oc for 7 to 12 mins Precipitation hardening –  ultimate tensile strength of the alloy, without hampering the resilience. After heat treatment, elgiloy had elastic properties similar to steel. www.indiandentalacademy.com
  • Cobalt Chromium www.indiandentalacademy.com
  • Cobalt Chromium Blue – soft Yellow – ductile Green – semiresilient Red – resilient www.indiandentalacademy.com
  • Cobalt Chromium Blue considerable bending, soldering or welding Red  most resilient and best used for springs – difficult to form, (brittle) – After heat treatment , no adjustments can be made to the wire, and it becomes extremely resilient. www.indiandentalacademy.com
  • Cobalt Chromium After heat treatment  Blue and yellow ≡ normal steel wire Green and red tempers ≡ higher grade steel www.indiandentalacademy.com
  • Cobalt Chromium Heating above 650oC – partial annealing, and softening of the wire Optimum heat treatment  dark straw color of the wire advantage of Co-Cr over SS is – – Greater resistance to fatigue and distortion – longer function as a resilient spring www.indiandentalacademy.com
  • Cobalt Chromium Properties of Co-Cr are very similar to that of stainless steel. Force – 2x of β titanium and – 1/4th of niti. www.indiandentalacademy.com
  • Cobalt Chromium Frank and Nikoli (1980) – Co-Cr alloys ≡ stainless steel. Stannard et al (AJO 1986) – Co-Cr highest frictional resistance in wet and dry conditions. www.indiandentalacademy.com
  • Cobalt Chromium Ingram Gipe and Smith (AJO 86) Non heat treated – Range < stainless steel of comparable sizes But after heat treatment, the range was considerably increased. www.indiandentalacademy.com
  • Cobalt Chromium Kusy et al (AJO 2001) The elastic modulus did not vary appreciably  edgewise or ribbonwise configurations. www.indiandentalacademy.com
  • Cobalt Chromium Round wires  higher ductility than square or rectangular wires. www.indiandentalacademy.com
  • Cobalt Chromium As expected, the modulus of elasticity was independent of temper of the wire. www.indiandentalacademy.com
  • Cobalt Chromium Elastic properties (yield strength and ultimate tensile strength and ductility) were quite similar for different cross sectional areas and tempers. This does not seem to agree with what is expected of the wires. www.indiandentalacademy.com
  • Cobalt Chromium www.indiandentalacademy.com
  • Cobalt Chromium Different tempers with different physical properties – attractive More care taken during the manufacture of the wires. www.indiandentalacademy.com
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