Orthodontic Wires Part 1

1. 1 Orthodontic wires Orthodontic wires Part 1 Part 1 Prepared by Prepared by Dr: Mohammed Alruby Dr: Mohammed Alruby كل اهميلعتب رخا صخش موقيس هوسقلا لاا كدرفمب ءىش لك ملعتتس هايحلا هذه يف O Orthodontic rthodontic wires Part 1 wires Part 1 Dr Mohammed Alruby Dr Mohammed Alruby

2. 2 Orthodontic wires Evolution: = in early days, noble metals like gold, platinum and silver were used in manufacture of wires because of their biological safety and inertness in the oral environments = in late 1800 the typical arch bow was drawn in nickel –silver or platinum gold alloy of diameter 0.032 - 0.036 inches = Angle 1887 introduced neu-silver or nickel silver alloys called German silver in (USA) = in 1929 st st alloys were used in orthodontic appliances construction = in 1930 type IV gold alloy comprised the most widely used material for wire manufacture = 1950 Elgin watch company of USA = 1950 Elgin watch company of USA developed Elgiloy (Co,Cr, Ni) which had a very attractive properties = 1970 G Andresen and William F Buchler introduce Nickel titanium alloy in orthodontics, this alloy regains its original shape on heating =1979 Burston and Goldbery introduce a new alloy TMA that had B-titanium structure = 1990 thermodynamic nickel titanium was introduced = 1990 copper nickel titanium become available = in 2000 to improve esthetics a new material was introduce like optiflex and Teflon coated wires Properties of orthodontic wires It is necessary for the arch wire to remain active for many months, So the wire must be sufficiently resilient to resist permanent deformation and maintain its activation 1-Load: The external force acting or applied to an orthodontic wire 2-Stress: Internal distribution of load applied to the material Stress = internal force / area of action (force /unit) Tensile stress: is caused by load that tend to stretch the body Compressive stress: is caused by load that compress the body Shear stress: is caused by load that slide one part of body over another 3-Strain: Change in length / unit length dimension compared to the original dimension Strain: = change in length / original length Thus with increasing load there is corresponding deformation in the wire 4-Strain, work hardening, cold working: It is process of plastic deforming a metal at temperature which is usually one third to one – half of its absolute melting point Cold working disrupts the normal atomic arrangement and incorporates strain across the grain boundaries 5-Elastic limit: It describes the greatest load that wire can be subjected and return to its original form After this point, when load on wire is removed it does not return back to its original length 6-Modulus of elasticity: young modulus E Stress and strain are directly proportional within elastic limit It represents the magnitude of force delivered by an arch wire at a given deflection 7-Stiffness: = Refers to the resistance of the wire to deformation O Orthodontic rthodontic wires Part 1 wires Part 1 Dr Mohammed Alruby Dr Mohammed Alruby

3. 3 = Low stiffness means that wire will apply low forces = Burston believes that the stiffness of wire related to both material and cross section = Stiff wire will not be easily deformed and hence and hence used in situation where teeth need to be maintained in their positions = Low stiffness is desirable as it provides: -The ability to apply lower force -More constant force over time -Greater ease and accuracy in applying a given force 8-Strength: = Force required to activate an arch wire to a specific distance = strength = stiffness X range = various measures of strength: yield strength, proportional limit, ultimate tensile strength 9-Yield strength: Stress required to produce permanent deformation, the deformation most used is 0.2% and strain corresponding to yield strength called yield strain 10-Ultimate tensile strength: The maximum force that wire can withstand before fracture It is usually indicator of the maximum force that wire can deliver 11-Proportional limit: It is the point at which first deformation is seen Below the proportional limit no permanent deformation occurs in structure Proportional limit and elastic limit represent the same point OR: it is the greatest stress that may produce in a body which is directly proportional to strain 12-Range: The distance that wire bends elastically, before permanent deformation occurs Range limit: the amount of wire can be bent Stiffness: force required to reach that limit Strength: combination of both range and stiffness 13-Spring back: How much far wire can be deflected without causing permanent deformation The wire should ideally possess high spring back which result in an increase in its range of action Spring back=maximum elastic deflection=range of deflection=working range=range of activation 14-Flexibility: Large deformation (large strain) with minimal force within its elastic limit Max. flexibility = proportional limit / modulus of elasticity E = P / Em Em = P / E Whereas: E: modulus of elasticity P: proportional limit Em: maximum flexibility 15-Resilience: maximum energy The wire which is more resistant to deformation in the mouth will be the one which has high value for maximum stored energy. 16- Formability: The ability to change the shape of material into a required configuration as loops, coils, stops without fracture of the wire The wire which can be give high number of bends without fracture can be termed most formable This property is opposite to spring back or flexibility wire can be given least number of bends O Orthodontic rthodontic wires Part 1 wires Part 1 Dr Mohammed Alruby Dr Mohammed Alruby

4. 4 17-Bio-compatibility and environmental stability: Biocompatibility: the wire should resist any corrosion and not give any allergic response Environmental stability: maintain the wire in the oral environment for long period without any changes in the properties of it (not harmful when used in the mouth) 18-Bi-hostability: Ability of wire to allow accumulate bacteria, virus, spores Ideal wire should be poor bio-host 19-Joinability: Ability to attach auxiliaries on arch wire by welding or soldering 20-Friction: Presence of friction at wire bracket interface result in limitation in tooth movement The wire should provide least friction at wire bracket interface Definition: it is resistance of one material with another which is closely approximated 21-Annealing: Simply heating the metal until it appears red hot 22-Brittles: Material which cannot undergo plastic deformation 23-Cyclic fatigue: Repeat cyclic stress of magnitude below the fracture point of wire, then fracture will occur 24-Heat treatment: Using thermal energy to change the characteristic of metallic alloys Wire is considered heat treated when it appears straw colored 25-Hysteresis: The difference between the energy required to activate the wire by deflection and energy released during deactivation 26-Sensitization: When st st heated between 400-900 degree it may lose its corrosive resistance due to precipitation of chromium carbide that lose the passivating qualities Reducing the carbon content minimize this condition 27-Stabilization: Process to reduce the carbon content of the material for sensitization, steel that heated to reduce the available carbon is called stabilized steel 28-Toughness: The force required for fracturing a material Clinically: this property is seen when giving bends in a wire and when giving deflection 29-Zero stress relaxation: Property of wire to give content light force when subjected to external forces, this property is desirable if a wire provide constant forces for longer period of time especially in springs N: B: Wire characteristics with clinical relevance: -Spring back -Stiffness -Formability -Joinability -Modulus of elasticity O Orthodontic rthodontic wires Part 1 wires Part 1 Dr Mohammed Alruby Dr Mohammed Alruby

5. 5 -Biocompatibility -Friction Classification of orthodontic wires According to materials: 1-Precious metal gold alloy 2-Stainless steel 3-Cobalt chromium 4-Nickel titanium 5-B- titanium 6-Alpha titanium 7-Copper niti According to cross section: 1-Round arch wire: The arch wire is light, does not fit in all bracket slot and so the tooth is free to tip in all direction and to rotate in one plane so the torque movement cannot be achieved Can used for: uprighting, levelling, alignment, de-rotation Round wire available in dimension of 0.010, 0.012, 0.014, 0.016, 0.018, 0.020 2-Square arch wire: Available in 0.016 X 0.016 inch 3-Rectangular arch wire: Heavy wire fit into the bracket so the tooth is locked on the arch wire in all planes and available in: 0.016 X 0.022 0.017 X 0.025 0.018 X 0.025 0.019 X 0.025 0.021 X 0.027 Standard bracket size: 0.022 x 0.018 OR, 0.018 X 0.028 Wire thickness: is smaller and fit the height of slot of bracket Wire width: larger dimension and always fit the depth of slot of bracket Example: 0.017 X 0.025 inch (0.017: thickness, and 0.025: is width) 4-Ribbon arch wires: Is rectangular one but thickness is greater than width as: 0.017 X 0.025 (0.017: is width, and 0.025 is thickness) 5-Multistrand arch wires: These wires are manufacturing by braiding together 3 fine high tensile st st wires More flexible than single strand of the same over all diameter Full engagement of the arch wire in the bracket can be obtained at early stage According to shape: 1-Full arch: Plain smooth arch wire 2-Segmented arch wire: May be used for leveling and depend on establishing stabilized posterior segment and controlling the point of force application against an anterior segment May use sectional short arch wire extended from molar tube to canine and help for canine retraction O Orthodontic rthodontic wires Part 1 wires Part 1 Dr Mohammed Alruby Dr Mohammed Alruby

6. 6 Rectangular wire is the most suitable material for construction of sectional arch wire because: a-Rigid, so permit the bucco-palatal position of canine and allow apical movement b-Fit into the bracket so decrease tipping movement 3-Multilooped arch wires: Round multilooped arch wire particularly useful for producing alignment of the teeth Full engagement of arch wire in bracket, and teeth move with the arch wire rather than sliding along the arch wire Multiloop allow an arch wire to be rigid to resist unwanted movement in one area and flexible enough to produce tooth movement in another area == vertical loop: Increase flexibility of arch wire Allow movement in bucco-lingual direction Length 8mm U, and 6mm L to prevent injury to gingiva == horizontal loop: Offer flexibility in inciso-gingivally N: B: wire diameter: = the diameter of the wire has major influences on elastic properties = small diameter of wire when maximum flexibility is required = small diameter arch wire may be used to produce initial alignment Large diameter is used when rigidity is needed N: B: wire length: Increase the length of wire by incorporation of loops lead to increase resilience and decrease force N: B: types of wire bends: 1-1st order bend: = introduced in horizontal plane of arch wire to compensate the differences in bucco-lingual thickness of teeth (offset & inset) In maxilla: offset at canine and 1st molar, -----inset: at lateral incisors In mandible: offset at canines and 1st molars 2-2nd order bends: Introduced in the vertical plane of arch wire: tip back bends Vertical adjustment in the arch wire also 2nd order bend: omega loop, vertical loop, V bend, artistic bend for positioning maxillary incisors 3-3rd order bend: torque Twist the wire along the horizontal plane of the arch to control the labio-lingual or bucco-lingual position to control the crowns and roots of single tooth or group of teeth Arch form and preformed arch wires The following is as guide to prepare arches: 1-Bonwill- Hawly arch form: 1905: = the six anterior teeth can arrange on the arc of circle, radius of which determined by mesio- distal widths of maxillary central, lateral, canines. = Bonwill- Hawly chart is prepared for each individual case of malocclusion and as used as a templet guide to prepare and coordinate arches 2-Brader arches: 1972: O Orthodontic rthodontic wires Part 1 wires Part 1 Dr Mohammed Alruby Dr Mohammed Alruby

7. 7 = mathematically the shape of maxillary arch best described by trifocal ellipse, this arch form show constriction in the 2nd molar region 3-Ricketts and Engle: 1979: They developed the pentamorphic arch form using dental records from Rocky Mountain data system Five distinct type of arches were stored: normal, tapering, ovoid, narrow tapered, narrow ovoid In clinical use: three type of arch form according to arch shape found commonly in general population: narrow or V shape -- square or U shape, --- ovoid shape. 4-James currier: 1969: 1st used computerized poly-normal least square program, he found that: a-Ellips filled well in maxillary arch b-Parabola showed bit in best fit in mandibular arch = Begole 1980: Individualized arch form like cubic inter-platory spline, that used to represent natural human arch forms This method initially used to evaluate the changes in arch form before and after treatment and now used to develop preformed arch wires for a particular population = Baun 1998: Developed a computerized curve filling program to represent the natural human arch form (B- function) He found that beta function is much more accurate than the previous methods of outlining the arch form ((Ideal arch form)) The conventional arch form may cause: 1-Expansion of intercanine widths particularly in mandibular arch 2-Round of anterior teeth has been reported Study by RMDS found to have closer fit over the natural arches in American population = Bonwill-Hawly and Brader arches show poor fits = using beta function ( Braun et al) 1999: found some expansion at mandibular inter-canine region by: 5.9mm and at maxillary intercanine region by 8.2mm when compared to the natural human arches Stainless steel arch wire = Entered dentistry in 1919 which first use for prosthetic purpose, and introduced for orthodontic wires in 1929. Angle used it as ligature wire in 1930 = it considered as the most popular wire alloy for clinical orthodontic because of their favorable combination of low cost and excellent formability Composition: 74% iron, -- 18% chromium – 8% nickel and trace amount of carbon 0.2% Stst used in orthodontic is 18-8 stst which is austenitic type that contain 18% chromium and 8% nickel = chromium: form thin passive layer provides corrosion resistance by prevent diffusion of oxygen through alloy = iron and carbon for interstitial solid solution of wire = nickel: give ductility and increase strength = other elements as: titanium, silicon, manganese as stabilizing element to prevent formation of carbide between the carbon present in the alloy O Orthodontic rthodontic wires Part 1 wires Part 1 Dr Mohammed Alruby Dr Mohammed Alruby

8. 8 Properties: clinical relevance: 1-Low spring back due to high modulus of elasticity 2-Low friction so there is low resistance to tooth movement 3-High stiffness due to high modulus of elasticity Advantage: high resistance to deformation Disadvantage: used in small size in moderate or severe displaced teeth alignment 4-Stored energy is less than niti and B ti so stst wire exert high force that dissipate over short periods than niti and B ti so need frequent activation 5-It can be soldered or welded 6-Biocompatible (corrosion resistance) due to chromium but solder joint corrode in the oral cavity 7-Good formability Advantages: 1-Corrosion resistance 2-High strength 3-High formability 4-Low cost 5-High compatibility 6-Can soldered and welded Disadvantages: 1-High force delivery 2-Low spring back in bending 3-Susceptible to inter-granular corrosion after heating to temperature required for soldering 4-Undergo plastic deformation 5-Disintegrate after using for long period so require frequent change Classification: 1-Austenitic steel: Are the most common corrosion resistance of stst alloys which called 18 -8 which is commonly used because: a-Greater ductability and can undergo more cold working without breaking b-Ease in forming and shaping c-Ease for welding d-Substantial strengthen during cold working e-High corrosion resistance N: B: Annealing: soften wire: ligature wire Cold working: hard wire: Wilcox regular Sensitization: heat 18 -8 stst between 400 -900 degree to lose its corrosion resistance due to precipitation of chromium carbide. The range degree of temperature for soldering and welding is between these degrees 2-Martensitic steel: Starting in 1970 in addition to carbon and other elements: -Less corrosion resistance -High tensile strength -Used for instrument and require sharp or wear resistance edges as: surgical and cutting instrument O Orthodontic rthodontic wires Part 1 wires Part 1 Dr Mohammed Alruby Dr Mohammed Alruby

9. 9 3-Ferritic steel: = micro structure same as that of iron = contain small amount of aluminum, molybdenum, carbon = used in several nickel free bracket = chromium is substituted for some of the iron atoms 4-Duplex steel: Consists of austenitic and ferrite grains Contain iron, chromium, low nickel, and molybdenum High toughness and ductability compared to Ferritic steel High yield strength twice than austenitic steel High stress corrosion resistance Used in manufacture of one piece of bracket 5-Hardenable steel PH: Can be hardened by heat treatment because of its high tensile strength Low corrosion resistance Used for mini bracket 6-Manganese containing steel: Manganese increase alloy’s susceptibility to corrosion Nickel replaced by nitrogen N: B: Australian arch wires: = Heat treated stst wires: more resilient and higher tensile strength = Developed by Aj Wilcok mainly for use of light wire technique (Begg) = These wires are grading according to increasing order of tensile strength = Tensile wire are: brittle and break easily and relatively more expensive than stst wires = Grades are: regular, regular plus, special plus, premium, premium plus, supreme. N: B: Multistrand wires: 1-Coaxial wires: have central core wire for stability with other wire, are twisted around it for resistance 2-Twist flex: very small diameter wires can be braided / twisted together to form wire for clinical use in orthodontics = either round or rectangular in shape between 0.016 and 0.025 inch in overall cross section = types: 3-strand, 6-stranded, 8-stranded, 9-stranded wires = these wires able to large elastic deflection, and low force when compared with stst Cobalt –chromium nickel wires Elgiloy The Elgin watch company developed an alloy with excellent formability in 1950, this alloy later marked by Rocky Martin in orthodontics as: Elgiloy or multiphase Popular used by Ricketts in bioprogressive technique Composition: 40%: cobalt Co O Orthodontic rthodontic wires Part 1 wires Part 1 Dr Mohammed Alruby Dr Mohammed Alruby

10. 10 20%: chromium Cr 15%: nickel Ni 7%: molybdenum Mo 2%: manganese Mn 15%: iron 2%: carbon Advantages: 1-Low cost 2-Biocompatible 3-More ductile 4-Excellent corrosion resistance Disadvantages: 1-Larger frictional force than stst 2-Lowe spring back action 3-When soldering ------- loss in yield strength as annealing 4-High cost Types of Elgiloy: 1-Blue: Is the softest of 4 wires It can be easily bend with finger or plier Heat treatment increase its resistance to permanent deformation = contain comparable amount of nickel to that found in stst wires which is compatible to some orthodontist = used in clinical fabrication of fixed quad helix appliance which produce rapid maxillary expansion in mixed dentition in cases of collapsed arch 2-Yellow: Ductile and more resilient than blue It can be bent by finger By heat treatment increase resilience and increase spring performance 3-Green: More resilient than yellow It can be shaped with pliers before heat treatment 4-Red: Hardest More resilient High spring qualities Heat treatment: increase resilience but more brittle Heat treatment: Recommended temperature for heat treatment is 482 for 7-12 minutes in heat treatment furnace that lead to: -Improve spring back -Increase strength -Increase resistance to deformation -Increase resilience -Increase 10% of modulus -Increase 20% -30% of yield strength Heat treatment confirmed by: dark coloration of wires OR using temperature indicating past O Orthodontic rthodontic wires Part 1 wires Part 1 Dr Mohammed Alruby Dr Mohammed Alruby

11. 11 Properties and clinical relevance: 1-Non heat treatment Co - Cr wires have smaller spring back than stst wire except red type but this can be improved by heat treatment at 482 degree for 7 -12 minutes 2-High stiffness due to high modulus of elasticity so Co – Cr and stst deliver force twice of B-ti and 4 times of Niti with equal amount of activation 3-Good formability 4-Good compatibility 5-Can be soldered or welded but take care that high temperature may be annealing or low resistance to deformation 6-Higher friction than stst so lead to resistance to tooth movement 7-Stored energy: Blue: least resilience, used with considerable bend Yellow: more resilience than blue, can be bent easily Green: more resilience than yellow, can be bent with relative ease Red: more resilient, high spring qualities, fracture easily after heat treatment 8-Corrosion resistance outperform than stst by 17% 9-High cost O Orthodontic rthodontic wires Part 1 wires Part 1 Dr Mohammed Alruby Dr Mohammed Alruby