www.indiandentalacademy.com
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com
seminar byseminar by
Dr. DavidDr. David
Done under the guidance ofDone under the guidance of
Prof. Ashima ValiathanProf. A...
INTRODUCTIONINTRODUCTION
 Metals are very remarkable materials.Metals are very remarkable materials.
 Their ability to b...
 Metals resist wear and corrosion; they conductMetals resist wear and corrosion; they conduct
heat and electricity, they ...
Atomic arrangements forAtomic arrangements for
metallic materialsmetallic materials
 In general, materials can be subdivi...
 There are seven crystal systems, with latticeThere are seven crystal systems, with lattice
parameters. (The three dimens...
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Crystal System Space Lattice
Cubic Simple cubic
Body-centered cubic
Face-centered cubic
Tetragonal Simple tetragonal
Body-...
Triclinic Simple triclinic
It is most convenient to visualize the crystal structuresIt is most convenient to visualize the...
 The hexagonal close-packed (hcp) structures can beThe hexagonal close-packed (hcp) structures can be
considered as forme...
 GrainsGrains  microns to centimetersmicrons to centimeters
 Grain boundariesGrain boundaries
 Atoms are irregularly ...
Stages in the
formation of metallic
grains during the
solidification of a
molten metal
Polycrystalline- each
crystal - gra...
Structure of metallic materialsStructure of metallic materials
 Crystals or grains of metals and alloys are composedCryst...
 various defectsvarious defects  slipslip planesplanes --alongalong
which dislocation occurswhich dislocation occurs
ww...
 To prevent breakage, a softening stepTo prevent breakage, a softening step
(annealing) must be added to render the(annea...
ANNEALING:ANNEALING:
RecoveryRecovery
RecrystallizationRecrystallization
Grain GrowthGrain Growth www.indiandentalacademy....
Before Annealing
Recovery – Relief of stresses
Recrystallization – New grains from
severely cold worked areas
-original so...
 AusteniteAustenite::
This form presents as the face-centeredThis form presents as the face-centered
cubic crystalline st...
 MartensiticMartensitic::
This form presents as a body-centeredThis form presents as a body-centered
cubic phase in stain...
Physical propertiesPhysical properties
PhysicalPhysical
propertiesproperties
Mechanical
properties
Electrical and
Electroc...
Basic properties of elastic materialsBasic properties of elastic materials
 The elastic behavior of any material is defin...
 Complex stressesComplex stresses: It is very difficult to: It is very difficult to
induce a single type of stress in the...
 StrainStrain: when a material is subjected to a force: when a material is subjected to a force
or load, there is a equiv...
Elastic PropertiesElastic Properties
Strain
Stress
Elastic Portion
Wire returns back to
original dimension when
stress is ...
 Hooke’s lawHooke’s law: states that in an elastic: states that in an elastic
deformation, the stress is directly proport...
 Proportional limitProportional limit: It is defined as the greatest: It is defined as the greatest
stress, the material ...
 Yield strengthYield strength: It is the point of stress at: It is the point of stress at
which the material undergoes a ...
Elastic PropertiesElastic Properties
Strain
Stress
Elastic Limit
Proportional Limit
Yield strength
0.1%
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 Ultimate tensile strengthUltimate tensile strength : If a material: If a material
continues to have more and more weight...
 ToughnessToughness: this is the entire area under the: this is the entire area under the
stress – strain curve is a meas...
Elastic PropertiesElastic Properties
Strain
Stress
Ultimate Tensile
Strength Fracture Point
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 FormabilityFormability - amount of permanent- amount of permanent
deformation that the wire can withstanddeformation tha...
Elastic PropertiesElastic Properties
Strain
Stress
Resilience Formability
Proportional limit
Yield strength
www.indiandent...
 FlexibilityFlexibility
 large deformation (or large strain) withlarge deformation (or large strain) with
minimal force,...
 BrittlenessBrittleness ––opposite of toughness. A brittleopposite of toughness. A brittle
material, is elastic, butmater...
Stiffness / Load deflection RateStiffness / Load deflection Rate
 Magnitude of the force delivered by the applianceMagnit...
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StrengthStrength
 Yield strength, proportional limit and ultimateYield strength, proportional limit and ultimate
tensile/...
 TheThe shapeshape andand cross sectioncross section of a wire have anof a wire have an
effect on the strength of the wir...
RangeRange
 Distance that the wire bends elastically, beforeDistance that the wire bends elastically, before
permanent de...
SpringbackSpringback
 KusyKusy -- The extent to which a wire recovers its-- The extent to which a wire recovers its
shape...
 Large springbackLarge springback
 Activated to a large extent.Activated to a large extent.
 Hence it will mean fewer a...
Elastic PropertiesElastic Properties
Strain
Stress
Range Springback
Point of arbitrary clinical loading
Yield point
www.in...
Physical properties ofPhysical properties of
orthodontic wiresorthodontic wires
 The force required for the tooth movemen...
 Moreover, the surface roughness of the wire,Moreover, the surface roughness of the wire,
which has a clinically signific...
 In general, an orthodontist should consider theIn general, an orthodontist should consider the
following aspects in the ...
Requirements of an ideal archwireRequirements of an ideal archwire
(Kusy )(Kusy )
1.1. EstheticsEsthetics
2.2. StiffnessSt...
Orthodontic archwiresOrthodontic archwires
 Orthodontic wires, which generate theOrthodontic wires, which generate the
bi...
 The gold alloy wire compositions wereThe gold alloy wire compositions were
generally similar to those of the type IV gol...
Stainless steelStainless steel
 Since 1950s stainless steel were used for mostSince 1950s stainless steel were used for m...
 The modulus of elasticity in tension for stainlessThe modulus of elasticity in tension for stainless
steel orthodontic w...
 The use of heat treatment to eliminate residualThe use of heat treatment to eliminate residual
stresses that might cause...
 The stainless steel alloys used for orthodonticThe stainless steel alloys used for orthodontic
wires are of “18-8” auste...
 The chromium in the stainless steel forms aThe chromium in the stainless steel forms a
thin, adherent passivating oxide ...
 Nickel ion release from the alloy surface causesNickel ion release from the alloy surface causes
implications for the bi...
 Formation of the martensitic phase resulted inFormation of the martensitic phase resulted in
substantial reduction in th...
 The modulus of resilience, represents the totalThe modulus of resilience, represents the total
elastic biomechanical ene...
 For clinical purpose, heat treatment stainlessFor clinical purpose, heat treatment stainless
steel orthodontic appliance...
Cobalt-chromium-nickel wiresCobalt-chromium-nickel wires
 A cobalt-chromium-nickel orthodontic wireA cobalt-chromium-nick...
 As with the stainless steel alloys, the corrosionAs with the stainless steel alloys, the corrosion
resistance of Elgiloy...
 The maximum yield strength for straight, 0.41The maximum yield strength for straight, 0.41
mm diameter, wire segments is...
 Because of its “soft feel” (due to relatively lowBecause of its “soft feel” (due to relatively low
YS) during manipulati...
Wire alloy Composition Modulus of elasticity YS Springback
Austenitic 17-20% Cr, 8-12% Ni, 160-180 1100-1500 0.0060-0.0094...
 Another clinical use of Elgiloy blue wires isAnother clinical use of Elgiloy blue wires is
fabrication of the fixed ling...
Beta-Titanium WiresBeta-Titanium Wires
 A Beta-titanium wire for orthodontics is marketedA Beta-titanium wire for orthodo...
 The elastic modulus for the beta-titaniumThe elastic modulus for the beta-titanium
wires is approximately 40% that of th...
 Another clinical advantage of the beta-Another clinical advantage of the beta-
titanium wires is excellent formability, ...
 The x-ray diffraction pattern for a beta-The x-ray diffraction pattern for a beta-
titanium (TMA) orthodontic wire shows...
 TheThe ZirconiumZirconium andand zinczinc in the alloyin the alloy
composition contribute increased strength andcomposit...
 Heat treatment by the orthodontist is notHeat treatment by the orthodontist is not
recommended for the beta-titanium wir...
 The next clinical advantage of beta-titanium isThe next clinical advantage of beta-titanium is
that it is the only ortho...
 The beta-titanium wires are generally the mostThe beta-titanium wires are generally the most
expensive of the orthodonti...
Nickel titanium wiresNickel titanium wires
 The pioneer for the development of nickel-titaniumThe pioneer for the develop...
 The Nitinol orthodontic wire offered aThe Nitinol orthodontic wire offered a
modulus of elasticity about 20% that of the...
 Heat treatment of the Japanese NiTi wires atHeat treatment of the Japanese NiTi wires at
500500°c was found to significa...
 In the early 1990s a NiTi orthodontic wireIn the early 1990s a NiTi orthodontic wire
alloy (Neo Sentalloy) with true sha...
 There are two major NiTi phases in the nickel-There are two major NiTi phases in the nickel-
titanium wires. Austenitic ...
 In some cases an intermediate R-phase havingIn some cases an intermediate R-phase having
a rhombohedral crystal structur...
 In 1994 Ormco Cooperation introduced a newIn 1994 Ormco Cooperation introduced a new
orthodontic wire alloy, copper NiTi...
 In the recent studies 27In the recent studies 27°°c copper NiTi wirec copper NiTi wire
alloy contain a single peak on bo...
 Element analysis using SEM have indicatedElement analysis using SEM have indicated
that the three Copper NiTi variants h...
Nickel-titanium open and closed coilNickel-titanium open and closed coil
springssprings
 Super elastic nickel titanium al...
 Advantages of the compression and tensileAdvantages of the compression and tensile
springs made of nickel-titanium are: ...
 Miura et alMiura et al (AJODO 1988) subjected Japanese(AJODO 1988) subjected Japanese
nickel-titanium closed and open co...
 When the diameter remained constant, the loadWhen the diameter remained constant, the load
value of super elastic activi...
 RyanRyan (BJO 1995), compared the force(BJO 1995), compared the force
characteristics of different commerciallycharacter...
 BarwartBarwart ( AJODO 1996) in a study examined( AJODO 1996) in a study examined
the effect of temperature change on th...
 Angolkar et alAngolkar et al (AJODO 1992) conducted an(AJODO 1992) conducted an
in-vitro study on closed coiled springs ...
 Effect of lumen size on force characteristicsEffect of lumen size on force characteristics::
Jebby Jacob, Divakar Karant...
 Effect of wire diameter on force characteristicsEffect of wire diameter on force characteristics::
 In springs with a c...
 When the closed coil springs of differentWhen the closed coil springs of different
diameters were compared, it was found...
 Effect of spring length on force characteristicsEffect of spring length on force characteristics::
The length of the spr...
 Effect of static, simulated oral environmentEffect of static, simulated oral environment::
The load deflection rate of o...
 Summary and conclusion: the forceSummary and conclusion: the force
characteristic of the open and closed coilcharacteris...
As the length of open coil springs was increased, theAs the length of open coil springs was increased, the
range of super ...
Property Stainless steel Cobalt-chromium- Beta-titanium (TMA) Nickel-titanium
Nickel (Elgiloy Blue)
Cost Low Low High High...
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Orthodontic bracketsOrthodontic brackets
 The original treatment approach utilized a slotThe original treatment approach ...
 The next stage of bracket evolution includedThe next stage of bracket evolution included
modification of the base design...
 Early commercially available aesthetic productEarly commercially available aesthetic product
included both plastic brack...
 In describing bracket evolution, it is important toIn describing bracket evolution, it is important to
include the intro...
Metallic bracketsMetallic brackets
 The morphology of the base of the stainless steelThe morphology of the base of the st...
Advance in metallic bracketsAdvance in metallic brackets
 Despite the clinically sufficient bond strengthDespite the clin...
 For metal brackets, the non-mesh, plasma-sprayedFor metal brackets, the non-mesh, plasma-sprayed
bases had tensile adhes...
 Although the 316L stainless steel bracket alloyAlthough the 316L stainless steel bracket alloy
has performed well clinic...
Aesthetic bracketsAesthetic brackets
 Appliances fabricated from alumina and zirconiaAppliances fabricated from alumina a...
 MatasaMatasa measured the microhardness values ofmeasured the microhardness values of
the metallic brackets to obtain in...
Plastic bracketsPlastic brackets
 The first plastic brackets were manufacturedThe first plastic brackets were manufacture...
 Plastic brackets are generally made fromPlastic brackets are generally made from
polycarbonate, but were subsequently fo...
 While the metal slot-reinforced polycarbonateWhile the metal slot-reinforced polycarbonate
brackets appear to be capable...
 A beneficial consequence of the relatively lowA beneficial consequence of the relatively low
elastic modulus of polycarb...
 Attempts have been made to combine the bestAttempts have been made to combine the best
properties of plastic and ceramic...
Ceramic bracketsCeramic brackets
 Most of the ceramic brackets are made of high-Most of the ceramic brackets are made of ...
 Heat treatment must be carefully controlled toHeat treatment must be carefully controlled to
prevent grain growth that w...
 The single crystal alumina bracket contain lessThe single crystal alumina bracket contain less
impurities than are found...
 Zirconia brackets have the possibility ofZirconia brackets have the possibility of
achieving much higher values of fract...
Self ligating bracketsSelf ligating brackets
 Self-ligating brackets result in greater patientSelf-ligating brackets resu...
 Self-ligating brackets has been reported toSelf-ligating brackets has been reported to
reduce the risk of percutaneous i...
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 Frictional Resistance of the Damon SL Bracket
RUPALI KAPUR et al (JCO 1998)
 Twenty Damon SL self-ligating brackets and...
 Results
 The Damon SL bracket showed significantly lower
kinetic frictional forces (p < .0001) than the Mini -Twin
brac...
Comparison of self- ligated and ligatedComparison of self- ligated and ligated
brackets:brackets:
Ligation stability
Ligat...
 Comparison behavior of 2205 duplex stainlessComparison behavior of 2205 duplex stainless
steelsteel: (: (Jeffrey A. Plat...
 Electrochemical testing indicates that 2205 hasElectrochemical testing indicates that 2205 has
a longer passivation rang...
 Considering corrosion resistance, 2205 duplexConsidering corrosion resistance, 2205 duplex
stainless steel is an improve...
 Shear, torsional, and tensile bond strengths ofShear, torsional, and tensile bond strengths of
ceramic brackets using th...
 No significance was found in the shear, torsional, orNo significance was found in the shear, torsional, or
tensile bond ...
 Corrosion of orthodontic bracket basesCorrosion of orthodontic bracket bases:: R. MaijerR. Maijer
and D.C. Smithand D.C....
 Multiple voids were observed at the resin-bracketMultiple voids were observed at the resin-bracket
interface, especially...
 Alternatives to ceramic brackets: the tensile bondAlternatives to ceramic brackets: the tensile bond
strengths of two Ae...
 Failure of the ceramic-reinforcedFailure of the ceramic-reinforced
polycarbonate brackets occurredpolycarbonate brackets...
 The fracture strength of ceramic bracketsThe fracture strength of ceramic brackets::
Daniel A. Flores et al; (AO 1989).D...
 Non-scratched single-crystal brackets had higherNon-scratched single-crystal brackets had higher
fracture strengths and ...
Elastomeric ligatures and chainsElastomeric ligatures and chains
 Elastomeric products are used in orthodontics asElastom...
 Elastomeric ligatures and chains are poly urethanes,Elastomeric ligatures and chains are poly urethanes,
which are therm...
 The highest values of tensile strength andThe highest values of tensile strength and
stiffness are obtained after full s...
 Riley et alRiley et al (1979) determined that steel(1979) determined that steel
ligatures generated more friction than e...
 Schumacher and BourauelSchumacher and Bourauel (1990) conducted a(1990) conducted a
series of experiments to find the fr...
 Conventional ligaturesConventional ligatures::
clinician prefer to use these materials over theclinician prefer to use t...
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy
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Physical properties of orthodontic materials /certified fixed orthodontic courses by Indian dental academy

  1. 1. www.indiandentalacademy.com INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com
  2. 2. seminar byseminar by Dr. DavidDr. David Done under the guidance ofDone under the guidance of Prof. Ashima ValiathanProf. Ashima Valiathan B.D.S. (pb), DDS, MS (USA)B.D.S. (pb), DDS, MS (USA) Director of Post Graduate StudiesDirector of Post Graduate Studies Professor and headProfessor and head Department of orthodonticsDepartment of orthodontics & Dentofacial& Dentofacial OrthopedicsOrthopedics Manipal college of dental sciences ManipalManipal college of dental sciences Manipal.. PHYSICAL PROPERTIES OFPHYSICAL PROPERTIES OF ORTHODONTIC MATERIALSORTHODONTIC MATERIALS www.indiandentalacademy.com
  3. 3. INTRODUCTIONINTRODUCTION  Metals are very remarkable materials.Metals are very remarkable materials.  Their ability to be rolled into sheets as thick asTheir ability to be rolled into sheets as thick as the hulls of ships or as thin as gold andthe hulls of ships or as thin as gold and aluminum foil, to be drawn into wire cablesaluminum foil, to be drawn into wire cables supporting bridges or into fine strands, one-supporting bridges or into fine strands, one- half the thickness of a human hair, for delicatehalf the thickness of a human hair, for delicate electronic instruments, to be softened withelectronic instruments, to be softened with heat and hardened by cold working.heat and hardened by cold working. www.indiandentalacademy.com
  4. 4.  Metals resist wear and corrosion; they conductMetals resist wear and corrosion; they conduct heat and electricity, they are generallyheat and electricity, they are generally inexpensive.inexpensive. www.indiandentalacademy.com
  5. 5. Atomic arrangements forAtomic arrangements for metallic materialsmetallic materials  In general, materials can be subdivided intoIn general, materials can be subdivided into two categories according to their atomictwo categories according to their atomic arrangements. In crystalline material there is aarrangements. In crystalline material there is a three dimensional periodic pattern of thethree dimensional periodic pattern of the atoms, whereas no such long-periodicity isatoms, whereas no such long-periodicity is present in noncrystalline materials, whichpresent in noncrystalline materials, which possess only short-range atomic order.possess only short-range atomic order. www.indiandentalacademy.com
  6. 6.  There are seven crystal systems, with latticeThere are seven crystal systems, with lattice parameters. (The three dimensional arrangement ofparameters. (The three dimensional arrangement of lines that can be visualized as connecting the atomslines that can be visualized as connecting the atoms in undisrupted crystals, is called a lattice.)in undisrupted crystals, is called a lattice.)  Inherently, a space lattice is a geometric constructInherently, a space lattice is a geometric construct wherein each point has identical surroundings.wherein each point has identical surroundings.  Crystal structures of real material are based uponCrystal structures of real material are based upon space lattices, where there is a single atom or aspace lattices, where there is a single atom or a group of atoms at each space lattice point.group of atoms at each space lattice point. www.indiandentalacademy.com
  7. 7. www.indiandentalacademy.com
  8. 8. Crystal System Space Lattice Cubic Simple cubic Body-centered cubic Face-centered cubic Tetragonal Simple tetragonal Body-centered tetragonal Orthorhombic Simple orthorhombic Body centered orthorhombic Face-centered orthorhombic Base-centered orthorhombic Rhombohedral Simple rhombohedral (Trigonal) Hexagonal Simple hexagonal Monoclinic simple monoclinic Base-centered monoclinic www.indiandentalacademy.com
  9. 9. Triclinic Simple triclinic It is most convenient to visualize the crystal structuresIt is most convenient to visualize the crystal structures of metals in terms of their unit cells, where a unit cellof metals in terms of their unit cells, where a unit cell is the smallest portion that can be repeated in threeis the smallest portion that can be repeated in three dimensions to produce the crystal structure.dimensions to produce the crystal structure. CrystalCrystal  combination of unit cells, in which eachcombination of unit cells, in which each cell shares faces, edges or corners with thecell shares faces, edges or corners with the neighboring cellsneighboring cells Unit cells for the simple cubic are -Unit cells for the simple cubic are - a) Body-centered cubic, b) Face-a) Body-centered cubic, b) Face- centered cubic, and c) Hexagonal close-packed.centered cubic, and c) Hexagonal close-packed. www.indiandentalacademy.com
  10. 10.  The hexagonal close-packed (hcp) structures can beThe hexagonal close-packed (hcp) structures can be considered as formed from two interpenetratingconsidered as formed from two interpenetrating simple hexagonal structures.simple hexagonal structures.  It can be seen that, while nickel and chromium haveIt can be seen that, while nickel and chromium have body centered cubic and face centered cubicbody centered cubic and face centered cubic structures, respectively, all temperatures below theirstructures, respectively, all temperatures below their melting points, iron and titanium have crystalmelting points, iron and titanium have crystal structures that depend upon temperature.structures that depend upon temperature. www.indiandentalacademy.com
  11. 11.  GrainsGrains  microns to centimetersmicrons to centimeters  Grain boundariesGrain boundaries  Atoms are irregularly arranged, and this leadsAtoms are irregularly arranged, and this leads to a weaker amorphous type structure.to a weaker amorphous type structure.  AlloyAlloy  combination of crystalline (grains)combination of crystalline (grains) and amorphous (grain boundaries)and amorphous (grain boundaries)  Decreased mechanical strength and reducedDecreased mechanical strength and reduced corrosion resistancecorrosion resistance www.indiandentalacademy.com
  12. 12. Stages in the formation of metallic grains during the solidification of a molten metal Polycrystalline- each crystal - grain www.indiandentalacademy.com
  13. 13. Structure of metallic materialsStructure of metallic materials  Crystals or grains of metals and alloys are composedCrystals or grains of metals and alloys are composed of billion upon billion of atoms regularly arranged inof billion upon billion of atoms regularly arranged in a space lattice.a space lattice.  When stress is first applied, the space lattice isWhen stress is first applied, the space lattice is slightly distorted out of shape, but returns to itsslightly distorted out of shape, but returns to its original position upon release of the stress. Thisoriginal position upon release of the stress. This deformation is called elastic strain.deformation is called elastic strain.  Whenever a crystal deforms, its lattice is distorted.Whenever a crystal deforms, its lattice is distorted. As the deformation increases, so does the distortion.As the deformation increases, so does the distortion. Simultaneously, the number of atomic dislocationSimultaneously, the number of atomic dislocation increases, disrupting the path of the sliding orincreases, disrupting the path of the sliding or twinning planes produced by stress.twinning planes produced by stress.www.indiandentalacademy.com
  14. 14.  various defectsvarious defects  slipslip planesplanes --alongalong which dislocation occurswhich dislocation occurs www.indiandentalacademy.com
  15. 15.  To prevent breakage, a softening stepTo prevent breakage, a softening step (annealing) must be added to render the(annealing) must be added to render the distorted, cold material, strain free. Each alloydistorted, cold material, strain free. Each alloy has a specific recrystallization and annealinghas a specific recrystallization and annealing temperature at which the grains, forciblytemperature at which the grains, forcibly reduced by cold work, can enlarge to allowreduced by cold work, can enlarge to allow further processing. Thus annealing causes afurther processing. Thus annealing causes a sharp drop in tensile strength.sharp drop in tensile strength.  Metals made of large grains are weak, theMetals made of large grains are weak, the smaller the grains, the more the intergranularsmaller the grains, the more the intergranular boundaries that oppose the planes slip.boundaries that oppose the planes slip. www.indiandentalacademy.com
  16. 16. ANNEALING:ANNEALING: RecoveryRecovery RecrystallizationRecrystallization Grain GrowthGrain Growth www.indiandentalacademy.com
  17. 17. Before Annealing Recovery – Relief of stresses Recrystallization – New grains from severely cold worked areas -original soft and ductile condition Grain Growth – large crystal “eat up” small ones-ultimate coarse grain structure is produced www.indiandentalacademy.com
  18. 18.  AusteniteAustenite:: This form presents as the face-centeredThis form presents as the face-centered cubic crystalline structure in iron and steel, or thecubic crystalline structure in iron and steel, or the body-centered cubic structure in nickel-titaniumbody-centered cubic structure in nickel-titanium alloys, at higher temperatures.alloys, at higher temperatures. Appropriate cooling of nickel-titanium alloys canAppropriate cooling of nickel-titanium alloys can induce a transformation to a close-packed hexagonalinduce a transformation to a close-packed hexagonal martensitic phase. The transformation frommartensitic phase. The transformation from austenitic to martensitic and vise versa is what givesaustenitic to martensitic and vise versa is what gives alloys such as Ni-Ti the characteristic properties ofalloys such as Ni-Ti the characteristic properties of shape memory and superelasticity.shape memory and superelasticity. www.indiandentalacademy.com
  19. 19.  MartensiticMartensitic:: This form presents as a body-centeredThis form presents as a body-centered cubic phase in stainless steels, or a monoclinic,cubic phase in stainless steels, or a monoclinic, triclinic or hexagonal crystalline structure in Ni-Titriclinic or hexagonal crystalline structure in Ni-Ti alloys. The martensitic phase of nickel titaniumalloys. The martensitic phase of nickel titanium exists at lower temperatures and is characterized byexists at lower temperatures and is characterized by high ductility. It is formed as a resulthigh ductility. It is formed as a result of quenchingof quenching or cold work austenitic phase.or cold work austenitic phase. www.indiandentalacademy.com
  20. 20. Physical propertiesPhysical properties PhysicalPhysical propertiesproperties Mechanical properties Electrical and Electrochemical properties Thermal properties Strength Tensile Compressive Shear Elasticity Elastic modulus Resilience Plasticity Ductility Percentage elongation Yield strengthElectrode potential Electrical resistivity www.indiandentalacademy.com
  21. 21. Basic properties of elastic materialsBasic properties of elastic materials  The elastic behavior of any material is defined inThe elastic behavior of any material is defined in terms of its stress-strain response to an externalterms of its stress-strain response to an external load. Both stress and strain refer to the internalload. Both stress and strain refer to the internal state of the material being studied.state of the material being studied.  StressStress:: When an external force or load is appliedWhen an external force or load is applied to a solid body, an internal force equal into a solid body, an internal force equal in magnitude and opposite in direction is set up inmagnitude and opposite in direction is set up in the body. This internal force divided by the areathe body. This internal force divided by the area over which it acts is called stress.over which it acts is called stress.  The basic types of stresses produced in dentalThe basic types of stresses produced in dental structures under force arestructures under force are tensile, compressive,tensile, compressive, and shearand shear.. www.indiandentalacademy.com
  22. 22.  Complex stressesComplex stresses: It is very difficult to: It is very difficult to induce a single type of stress in the body. Forinduce a single type of stress in the body. For example, when a wire is stretched, it becomesexample, when a wire is stretched, it becomes longer suggesting that there is a tensile stress.longer suggesting that there is a tensile stress. But a wire, which becomes longer, will alsoBut a wire, which becomes longer, will also becomes thinner. This means that there is abecomes thinner. This means that there is a compressive stress also in it. This is calledcompressive stress also in it. This is called complex stresses and is an engineeringcomplex stresses and is an engineering principle called Poisson’s ratio.principle called Poisson’s ratio.  A material fractures in the area of maximumA material fractures in the area of maximum stress concentration.stress concentration.www.indiandentalacademy.com
  23. 23.  StrainStrain: when a material is subjected to a force: when a material is subjected to a force or load, there is a equivalent stress induced inor load, there is a equivalent stress induced in the material. This internal stress brings aboutthe material. This internal stress brings about change in dimension and shape of the material.change in dimension and shape of the material. This change in dimension is usually measuredThis change in dimension is usually measured by change in length.by change in length. Change in lengthChange in length Strain =Strain = Original lengthOriginal length www.indiandentalacademy.com
  24. 24. Elastic PropertiesElastic Properties Strain Stress Elastic Portion Wire returns back to original dimension when stress is removed www.indiandentalacademy.com
  25. 25.  Hooke’s lawHooke’s law: states that in an elastic: states that in an elastic deformation, the stress is directly proportionaldeformation, the stress is directly proportional to strain.to strain.  Elastic limitElastic limit: It is the greatest limit upto: It is the greatest limit upto which an object can be stressed so that it willwhich an object can be stressed so that it will recover or return to its original dimension,recover or return to its original dimension, when the load is withdrawn.when the load is withdrawn. Only upto a point of stress or limit the elasticOnly upto a point of stress or limit the elastic can undergo Elastic Deformation. Beyond thiscan undergo Elastic Deformation. Beyond this point, it undergoes a plasticpoint, it undergoes a plastic or permanentor permanent deformation.deformation. www.indiandentalacademy.com
  26. 26.  Proportional limitProportional limit: It is defined as the greatest: It is defined as the greatest stress, the material will sustain without astress, the material will sustain without a deviation from the Hooke’s law ordeviation from the Hooke’s law or proportionality of stress to strain. Upto thisproportionality of stress to strain. Upto this point, the stress and strain are proportional.point, the stress and strain are proportional. This is the proportional limit.This is the proportional limit. Beyond this point, the strain will not beBeyond this point, the strain will not be proportional to stress.proportional to stress. www.indiandentalacademy.com
  27. 27.  Yield strengthYield strength: It is the point of stress at: It is the point of stress at which the material undergoes a SLIGHT butwhich the material undergoes a SLIGHT but permanent deformation or offset. Yieldpermanent deformation or offset. Yield strength is slightly more than the proportionalstrength is slightly more than the proportional limit and for practical purposes the same aslimit and for practical purposes the same as proportional limit. It is sensitive to workproportional limit. It is sensitive to work hardening.hardening.  Young’s Modulus or Modulus ofYoung’s Modulus or Modulus of ElasticityElasticity: is an inherent property of the: is an inherent property of the material and cannot be altered appreciably bymaterial and cannot be altered appreciably by heat treatment, work hardening, or any otherheat treatment, work hardening, or any other kind of conditioning. This property is calledkind of conditioning. This property is called structure insensitivity.structure insensitivity.www.indiandentalacademy.com
  28. 28. Elastic PropertiesElastic Properties Strain Stress Elastic Limit Proportional Limit Yield strength 0.1% www.indiandentalacademy.com
  29. 29. www.indiandentalacademy.com
  30. 30.  Ultimate tensile strengthUltimate tensile strength : If a material: If a material continues to have more and more weightcontinues to have more and more weight applied to it, it will eventually break. If theapplied to it, it will eventually break. If the material is being stretched, the stress atmaterial is being stretched, the stress at breakage is called the ultimate tensile strength.breakage is called the ultimate tensile strength.  When many metals are stressed above theirWhen many metals are stressed above their proportional limits, they undergo a processproportional limits, they undergo a process called work hardening, and actually becomecalled work hardening, and actually become stronger and harder.stronger and harder. www.indiandentalacademy.com
  31. 31.  ToughnessToughness: this is the entire area under the: this is the entire area under the stress – strain curve is a measure of the energystress – strain curve is a measure of the energy required to fracture the material.required to fracture the material.  ResilienceResilience: The area under only the elastic: The area under only the elastic region of the stress-strain curve is a measure ofregion of the stress-strain curve is a measure of the ability of the material to store elasticthe ability of the material to store elastic energy.energy. www.indiandentalacademy.com
  32. 32. Elastic PropertiesElastic Properties Strain Stress Ultimate Tensile Strength Fracture Point www.indiandentalacademy.com
  33. 33.  FormabilityFormability - amount of permanent- amount of permanent deformation that the wire can withstanddeformation that the wire can withstand without breakingwithout breaking  Indication of the ability of the wire to take theIndication of the ability of the wire to take the shapeshape  Also an indication of the amount of cold workAlso an indication of the amount of cold work that they can withstandthat they can withstand www.indiandentalacademy.com
  34. 34. Elastic PropertiesElastic Properties Strain Stress Resilience Formability Proportional limit Yield strength www.indiandentalacademy.com
  35. 35.  FlexibilityFlexibility  large deformation (or large strain) withlarge deformation (or large strain) with minimal force, within its elastic limit.minimal force, within its elastic limit.  Maximal flexibility is the strain that occursMaximal flexibility is the strain that occurs when a wire is stressed to its elastic limit.when a wire is stressed to its elastic limit. Max. flexibility =Max. flexibility = Proportional limitProportional limit Modulus of elasticity.Modulus of elasticity. www.indiandentalacademy.com
  36. 36.  BrittlenessBrittleness ––opposite of toughness. A brittleopposite of toughness. A brittle material, is elastic, butmaterial, is elastic, but cannot undergo plasticcannot undergo plastic deformationdeformation. eg: Glass. eg: Glass  FatigueFatigue –– Repeated cyclic stress of aRepeated cyclic stress of a magnitude below the fracture point of a wiremagnitude below the fracture point of a wire can result in fracture. This is called fatigue.can result in fracture. This is called fatigue. www.indiandentalacademy.com
  37. 37. Stiffness / Load deflection RateStiffness / Load deflection Rate  Magnitude of the force delivered by the applianceMagnitude of the force delivered by the appliance for a particular amount of deflection.for a particular amount of deflection. Low stiffness or Low LDR implies thatLow stiffness or Low LDR implies that:-:- 1) Low forces will be applied1) Low forces will be applied 2) The force will be more constant as the appliance2) The force will be more constant as the appliance deactivatesdeactivates 3) Greater ease and accuracy in applying a given3) Greater ease and accuracy in applying a given force.force. www.indiandentalacademy.com
  38. 38. www.indiandentalacademy.com
  39. 39. StrengthStrength  Yield strength, proportional limit and ultimateYield strength, proportional limit and ultimate tensile/compressive strengthtensile/compressive strength  KusyKusy - force required to activate an archwire to a- force required to activate an archwire to a specific distance.specific distance.  ProffitProffit - Strength = stiffness x range.- Strength = stiffness x range.  Range limits the amount the wire can be bent,Range limits the amount the wire can be bent, Stiffness is the indication of the force required toStiffness is the indication of the force required to reach that limit.reach that limit. www.indiandentalacademy.com
  40. 40.  TheThe shapeshape andand cross sectioncross section of a wire have anof a wire have an effect on the strength of the wire.effect on the strength of the wire. www.indiandentalacademy.com
  41. 41. RangeRange  Distance that the wire bends elastically, beforeDistance that the wire bends elastically, before permanent deformation occurs (permanent deformation occurs (ProffitProffit).).  KusyKusy – Distance to which an archwire can be– Distance to which an archwire can be activated- working range.activated- working range.  ThurowThurow – A linear measure of how far a wire or– A linear measure of how far a wire or material can be deformed without exceeding thematerial can be deformed without exceeding the limits of the material.limits of the material. www.indiandentalacademy.com
  42. 42. SpringbackSpringback  KusyKusy -- The extent to which a wire recovers its-- The extent to which a wire recovers its shape after deactivationshape after deactivation  Ingram et alIngram et al – a measure of how far a wire can– a measure of how far a wire can be deflected without causing permanentbe deflected without causing permanent deformation. (Contrast to Proffitdeformation. (Contrast to Proffit yield pointyield point).). www.indiandentalacademy.com
  43. 43.  Large springbackLarge springback  Activated to a large extent.Activated to a large extent.  Hence it will mean fewer archwire changes.Hence it will mean fewer archwire changes.  Ratio –Ratio – yield strengthyield strength Modulus of elasticityModulus of elasticity www.indiandentalacademy.com
  44. 44. Elastic PropertiesElastic Properties Strain Stress Range Springback Point of arbitrary clinical loading Yield point www.indiandentalacademy.com
  45. 45. Physical properties ofPhysical properties of orthodontic wiresorthodontic wires  The force required for the tooth movement hasThe force required for the tooth movement has always highlighted the importance of “Lightalways highlighted the importance of “Light continous force.” (continous force.” (JIOS 2002; 76-88JIOS 2002; 76-88))  Metallic orthodontic wires are manufactured byMetallic orthodontic wires are manufactured by series of proprietary steps, typically involvingseries of proprietary steps, typically involving more than one company.more than one company.  Initially the wire is cast in the form of an ingot,Initially the wire is cast in the form of an ingot, which must be subjected to successivewhich must be subjected to successive deformation stages, until the cross sectiondeformation stages, until the cross section becomes sufficiently small for wire drawing.becomes sufficiently small for wire drawing.www.indiandentalacademy.com
  46. 46.  Moreover, the surface roughness of the wire,Moreover, the surface roughness of the wire, which has a clinically significant effect on thewhich has a clinically significant effect on the arch wire bracket sliding friction, variesarch wire bracket sliding friction, varies considerably among the various products andconsiderably among the various products and is generally greater for the beta-titanium andis generally greater for the beta-titanium and nickel titanium wires.nickel titanium wires. www.indiandentalacademy.com
  47. 47.  In general, an orthodontist should consider theIn general, an orthodontist should consider the following aspects in the selection of wires:following aspects in the selection of wires: force delivery characteristicsforce delivery characteristics,, elastic workingelastic working rangerange,, ease of joining individual segments toease of joining individual segments to fabricate more complex appliancesfabricate more complex appliances,, corrosioncorrosion resistance and biocompatibility in the oralresistance and biocompatibility in the oral environment and cost.environment and cost. www.indiandentalacademy.com
  48. 48. Requirements of an ideal archwireRequirements of an ideal archwire (Kusy )(Kusy ) 1.1. EstheticsEsthetics 2.2. StiffnessStiffness 3.3. StrengthStrength 4.4. RangeRange 5.5. SpringbackSpringback 6.6. FormabilityFormability 7.7. ResiliencyResiliency 8.8. Coefficient ofCoefficient of frictionfriction 9.9. BiohostabilityBiohostability 10.10. BiocompatibilityBiocompatibility 11.11. WeldabilityWeldability www.indiandentalacademy.com
  49. 49. Orthodontic archwiresOrthodontic archwires  Orthodontic wires, which generate theOrthodontic wires, which generate the biomechanical forces, communicate throughbiomechanical forces, communicate through brackets for tooth movement, are central to thebrackets for tooth movement, are central to the practice of the profession.practice of the profession.  Historically, gold alloy wires were first used inHistorically, gold alloy wires were first used in orthodontic practice, although these nobleorthodontic practice, although these noble metal wires have minimal use currentlymetal wires have minimal use currently because of their much greater cost comparedbecause of their much greater cost compared to the popular base metal wires.to the popular base metal wires. www.indiandentalacademy.com
  50. 50.  The gold alloy wire compositions wereThe gold alloy wire compositions were generally similar to those of the type IV goldgenerally similar to those of the type IV gold casting alloys, and their modulus of elasticitycasting alloys, and their modulus of elasticity was approximately 100Gpa. Thus the goldwas approximately 100Gpa. Thus the gold alloy wires had elastic force less than that foralloy wires had elastic force less than that for stainless steel wires with the same cross-stainless steel wires with the same cross- sectional dimensions and segment lengths.sectional dimensions and segment lengths. www.indiandentalacademy.com
  51. 51. Stainless steelStainless steel  Since 1950s stainless steel were used for mostSince 1950s stainless steel were used for most orthodontic wires.orthodontic wires.  This continues to be the most popular wireThis continues to be the most popular wire alloy for clinical orthodontics because of analloy for clinical orthodontics because of an outstanding combination of mechanicaloutstanding combination of mechanical properties, corrosion resistance in the oralproperties, corrosion resistance in the oral environment, and cost.environment, and cost.  The wires used in orthodontics are generallyThe wires used in orthodontics are generally American iron and steel institute (AISI) typesAmerican iron and steel institute (AISI) types 302 and 304 austenitic stainless steels. These302 and 304 austenitic stainless steels. These contained 17-25% chromium and 8-25%contained 17-25% chromium and 8-25% nickel and the remaining were iron.nickel and the remaining were iron.www.indiandentalacademy.com
  52. 52.  The modulus of elasticity in tension for stainlessThe modulus of elasticity in tension for stainless steel orthodontic wires, ranges from about 160 tosteel orthodontic wires, ranges from about 160 to 180 GPa.180 GPa.  The yield strength for the stainless steel archwiresThe yield strength for the stainless steel archwires shows a much wider variation than the elasticshows a much wider variation than the elastic modulus and to range from 1,100 to 1,500 MPa.modulus and to range from 1,100 to 1,500 MPa.  Heat treatment of these wires also causesHeat treatment of these wires also causes significant decrease in residual stress and modestsignificant decrease in residual stress and modest increase in resilience.increase in resilience. www.indiandentalacademy.com
  53. 53.  The use of heat treatment to eliminate residualThe use of heat treatment to eliminate residual stresses that might cause fracture duringstresses that might cause fracture during manipulation of stainless steel appliances canmanipulation of stainless steel appliances can be important under clinical conditions.be important under clinical conditions.  Austenitic stainless steel can be renderedAustenitic stainless steel can be rendered susceptible to intergranular corrosion whensusceptible to intergranular corrosion when heated to temperatures between 400heated to temperatures between 400°c and°c and 900°c, due to the formation of the chromium900°c, due to the formation of the chromium carbides at the grain boundaries.carbides at the grain boundaries.  Since the stainless steel alloys must be heatedSince the stainless steel alloys must be heated within this temperature range for soldering,within this temperature range for soldering, clinicians are cautioned to minimize the timeclinicians are cautioned to minimize the time required for this process.required for this process. www.indiandentalacademy.com
  54. 54.  The stainless steel alloys used for orthodonticThe stainless steel alloys used for orthodontic wires are of “18-8” austenitic type. whereaswires are of “18-8” austenitic type. whereas 17-7 precipitation-hardenable stainless steel17-7 precipitation-hardenable stainless steel alloy had higher yield strength in bending thanalloy had higher yield strength in bending than the commonly used stainless steel wire alloys.the commonly used stainless steel wire alloys. www.indiandentalacademy.com
  55. 55.  The chromium in the stainless steel forms aThe chromium in the stainless steel forms a thin, adherent passivating oxide layer thatthin, adherent passivating oxide layer that provides corrosion resistance by blocking theprovides corrosion resistance by blocking the diffusion of oxygen to the underlying bulkdiffusion of oxygen to the underlying bulk alloy. About 12-13 wt% chromium is requiredalloy. About 12-13 wt% chromium is required to impart the necessary corrosion resistance toto impart the necessary corrosion resistance to these alloysthese alloys.. www.indiandentalacademy.com
  56. 56.  Nickel ion release from the alloy surface causesNickel ion release from the alloy surface causes implications for the biocompatibility of these alloy.implications for the biocompatibility of these alloy.  X-ray diffraction has shown that austenitic stainlessX-ray diffraction has shown that austenitic stainless steel orthodontic wires may not always possess thesteel orthodontic wires may not always possess the single-phase austenitic structure that is based upon asingle-phase austenitic structure that is based upon a face-centered-cubic (fcc) arrangement of the ironface-centered-cubic (fcc) arrangement of the iron atoms.atoms.  In a two phase structure the austenitic wasIn a two phase structure the austenitic was accompanied by a body-centered cubic (bcc)accompanied by a body-centered cubic (bcc) martensitic phase.martensitic phase. www.indiandentalacademy.com
  57. 57.  Formation of the martensitic phase resulted inFormation of the martensitic phase resulted in substantial reduction in the modulus ofsubstantial reduction in the modulus of elasticity, from about 200Gpa to about 150Gpaelasticity, from about 200Gpa to about 150Gpa for heavily cold worked alloys.for heavily cold worked alloys.  Extensive cold working can increase the yieldExtensive cold working can increase the yield strength of austenitic stainless steels fromstrength of austenitic stainless steels from about 275 to 1100Mpa.about 275 to 1100Mpa. www.indiandentalacademy.com
  58. 58.  The modulus of resilience, represents the totalThe modulus of resilience, represents the total elastic biomechanical energy or spring energyelastic biomechanical energy or spring energy in the wire, is given approximately byin the wire, is given approximately by (YS)(YS)²/2E. This expression can be used to²/2E. This expression can be used to estimate the changes in elastic spring energyestimate the changes in elastic spring energy resulting from the heat treatment.resulting from the heat treatment. www.indiandentalacademy.com
  59. 59.  For clinical purpose, heat treatment stainlessFor clinical purpose, heat treatment stainless steel orthodontic appliances is to minimizesteel orthodontic appliances is to minimize breakage rather than achieve significantbreakage rather than achieve significant increase in resilience.increase in resilience.  Heat treatment of stainless steel wires atHeat treatment of stainless steel wires at temperatures above 650temperatures above 650°c must be avoided°c must be avoided because rapid recrystallization of the wroughtbecause rapid recrystallization of the wrought structure takes place, with deleterious effectsstructure takes place, with deleterious effects on the wire properties.on the wire properties. www.indiandentalacademy.com
  60. 60. Cobalt-chromium-nickel wiresCobalt-chromium-nickel wires  A cobalt-chromium-nickel orthodontic wireA cobalt-chromium-nickel orthodontic wire alloy (Elgiloy) was developed during thealloy (Elgiloy) was developed during the 1950s by the Elgiloy cooperation (Elgin, IL,1950s by the Elgiloy cooperation (Elgin, IL, USA).USA).  This was originally used for watch springs, isThis was originally used for watch springs, is available in four tempers (levels of resilience)available in four tempers (levels of resilience) that are colour-coded by the manufactures:that are colour-coded by the manufactures: blue (soft), yellow (ductile), green (semi-blue (soft), yellow (ductile), green (semi- resilient), and red (resilient).resilient), and red (resilient). www.indiandentalacademy.com
  61. 61.  As with the stainless steel alloys, the corrosionAs with the stainless steel alloys, the corrosion resistance of Elgiloy arises from a thinresistance of Elgiloy arises from a thin passivating chromium oxide layer on the wirepassivating chromium oxide layer on the wire surface.surface.  Elgiloy blue alloy is very popular with manyElgiloy blue alloy is very popular with many orthodontists because the as-received wire canorthodontists because the as-received wire can easily be manipulated into the desired shapeseasily be manipulated into the desired shapes and then heat treated to achieve considerableand then heat treated to achieve considerable increases in strength and resilience.increases in strength and resilience. www.indiandentalacademy.com
  62. 62.  The maximum yield strength for straight, 0.41The maximum yield strength for straight, 0.41 mm diameter, wire segments is obtained with amm diameter, wire segments is obtained with a heat-treatment temperature of about 500heat-treatment temperature of about 500°c.°c. This heat treatment causes complexThis heat treatment causes complex precipitation processes that substantiallyprecipitation processes that substantially increase the yield strength of the alloy.increase the yield strength of the alloy.  Heat treatment of straight segment of ElgiloyHeat treatment of straight segment of Elgiloy blue wire causes an increase of about 10% inblue wire causes an increase of about 10% in modulus of elasticity and about 20-30% inmodulus of elasticity and about 20-30% in yield strength.yield strength. www.indiandentalacademy.com
  63. 63.  Because of its “soft feel” (due to relatively lowBecause of its “soft feel” (due to relatively low YS) during manipulation, orthodontists canYS) during manipulation, orthodontists can mistakenly believe that as-received Elgiloymistakenly believe that as-received Elgiloy blue wires have substantially lower elasticblue wires have substantially lower elastic force delivery than stainless steel wires. Inforce delivery than stainless steel wires. In reality, the values of modulus of elasticity forreality, the values of modulus of elasticity for Elgiloy blue and stainless steel orthodonticElgiloy blue and stainless steel orthodontic wires are similar.wires are similar. www.indiandentalacademy.com
  64. 64. Wire alloy Composition Modulus of elasticity YS Springback Austenitic 17-20% Cr, 8-12% Ni, 160-180 1100-1500 0.0060-0.0094 (AR) Stainless steel 0.5% C. balance Fe 0.065-0.0099 (HT) Cobalt- 40% Co, 20% Cr, 160-190 830-1000 0.0045-0.0065 (AR) chromium- 15%Ni, 1.8% Fe, 0.0054-0.0074 (HT) Nickel (Elgiloy) 7%Mo, 2%Mn, 0.15% C, 0.04% Be. Beta-titanium 77.8% Ti, 11.3% Mo, 62-69 690-970 0.0094-0.011 (TMA) 6.6% Zr, 4.3% Sn. Nickel-titanium 55% Ni, 45% Ti 34 210-410 0.0058-0.016 (approx. and may contain small amounts of Cu or other elements) www.indiandentalacademy.com
  65. 65.  Another clinical use of Elgiloy blue wires isAnother clinical use of Elgiloy blue wires is fabrication of the fixed lingual quad-helixfabrication of the fixed lingual quad-helix appliance, which produces slow maxillaryappliance, which produces slow maxillary expansion for the treatment maxillaryexpansion for the treatment maxillary constriction or cross bite in the primary andconstriction or cross bite in the primary and mixed dentitions.mixed dentitions. www.indiandentalacademy.com
  66. 66. Beta-Titanium WiresBeta-Titanium Wires  A Beta-titanium wire for orthodontics is marketedA Beta-titanium wire for orthodontics is marketed by the Ormco Corporation (Glendora, CA, USA).by the Ormco Corporation (Glendora, CA, USA). The commercial name for this wire is TMA, whichThe commercial name for this wire is TMA, which represents “titanium-molybdenum alloy”.represents “titanium-molybdenum alloy”.  The Beta-titanium wire was conceived forThe Beta-titanium wire was conceived for orthodontic use about two decades ago by Burstoneorthodontic use about two decades ago by Burstone and Goldberg, who recognized its potential forand Goldberg, who recognized its potential for delivering lower biomechanical forces compared todelivering lower biomechanical forces compared to the stainless steel and cobalt-chromium-nickelthe stainless steel and cobalt-chromium-nickel alloys.alloys. www.indiandentalacademy.com
  67. 67.  The elastic modulus for the beta-titaniumThe elastic modulus for the beta-titanium wires is approximately 40% that of thewires is approximately 40% that of the stainless steel and Elgiloy blue wires. Becausestainless steel and Elgiloy blue wires. Because of the much lower value of elastic modulus,of the much lower value of elastic modulus, despite lower values for yield strength, thedespite lower values for yield strength, the beta titanium wires have significantlybeta titanium wires have significantly improved values of spring back (YS/E), whichimproved values of spring back (YS/E), which increases their working range for toothincreases their working range for tooth movement.movement. www.indiandentalacademy.com
  68. 68.  Another clinical advantage of the beta-Another clinical advantage of the beta- titanium wires is excellent formability, whichtitanium wires is excellent formability, which is due to their body – centered cubic structure.is due to their body – centered cubic structure. (bcc)(bcc)  The addition ofThe addition of molybdenummolybdenum to the alloyto the alloy composition stabilizes the high-temperaturecomposition stabilizes the high-temperature bcc beta-phase polymorphic form of titaniumbcc beta-phase polymorphic form of titanium at room temperature, rather than the hexagonalat room temperature, rather than the hexagonal closed-packed alpha-phase.closed-packed alpha-phase. www.indiandentalacademy.com
  69. 69.  The x-ray diffraction pattern for a beta-The x-ray diffraction pattern for a beta- titanium (TMA) orthodontic wire shows atitanium (TMA) orthodontic wire shows a single phase bcc structure, with the broadenedsingle phase bcc structure, with the broadened peaks and preferred crystallographicpeaks and preferred crystallographic orientation expected for a heavily cold-workedorientation expected for a heavily cold-worked alloy.alloy.  The slip-systems for dislocation movement forThe slip-systems for dislocation movement for the bcc crystal structure account for the highthe bcc crystal structure account for the high ductility of the beta-titaniumductility of the beta-titanium wires.wires. www.indiandentalacademy.com
  70. 70.  TheThe ZirconiumZirconium andand zinczinc in the alloyin the alloy composition contribute increased strength andcomposition contribute increased strength and hardness, and their presence avoids thehardness, and their presence avoids the formation of an embrittling omega-phaseformation of an embrittling omega-phase during wire processing at elevatedduring wire processing at elevated temperatures. This wire processing istemperatures. This wire processing is problematic because of the reactivity ofproblematic because of the reactivity of titanium, and there have been reports of TMAtitanium, and there have been reports of TMA archwires are susceptible to fracture duringarchwires are susceptible to fracture during clinical manipulation, despite the excellentclinical manipulation, despite the excellent formability of the beta-titanium alloy.formability of the beta-titanium alloy. www.indiandentalacademy.com
  71. 71.  Heat treatment by the orthodontist is notHeat treatment by the orthodontist is not recommended for the beta-titanium wires, heatrecommended for the beta-titanium wires, heat treatment of the alloy by the manufacturertreatment of the alloy by the manufacturer approximately 700-730approximately 700-730°c followed by water°c followed by water quenching.quenching.  Subsequent aging at approximately 480°cSubsequent aging at approximately 480°c results in precipitation of alpha phase and aresults in precipitation of alpha phase and a maximum of spring back for the TMA wires.maximum of spring back for the TMA wires. www.indiandentalacademy.com
  72. 72.  The next clinical advantage of beta-titanium isThe next clinical advantage of beta-titanium is that it is the only orthodontic wire alloythat it is the only orthodontic wire alloy possessing true weldability.possessing true weldability.  Another important feature of the beta-titaniumAnother important feature of the beta-titanium wires is their absence of nickel that is presentwires is their absence of nickel that is present in the other three types of alloy types.in the other three types of alloy types. www.indiandentalacademy.com
  73. 73.  The beta-titanium wires are generally the mostThe beta-titanium wires are generally the most expensive of the orthodontic wire alloys, butexpensive of the orthodontic wire alloys, but the greater cost is considered by orthodontistthe greater cost is considered by orthodontist by the combined advantages of intermediateby the combined advantages of intermediate force delivery and the excellent formability andforce delivery and the excellent formability and weldability when fabrication of more complexweldability when fabrication of more complex appliances is required.appliances is required. www.indiandentalacademy.com
  74. 74. Nickel titanium wiresNickel titanium wires  The pioneer for the development of nickel-titaniumThe pioneer for the development of nickel-titanium wires for orthodontics waswires for orthodontics was AndersonAnderson, who, who published articles with colleagues advocating in thepublished articles with colleagues advocating in the early 1970s.early 1970s.  The first nickel-titanium orthodontic wire alloyThe first nickel-titanium orthodontic wire alloy (Nitinol) was marketed in the Unitek Cooperation.(Nitinol) was marketed in the Unitek Cooperation.  The generic name nitinol that is applicable to groupThe generic name nitinol that is applicable to group of nickel-titanium alloys originates from nickel,of nickel-titanium alloys originates from nickel, titanium and the Naval Ordinance Laboratory wheretitanium and the Naval Ordinance Laboratory where the alloys were developed bythe alloys were developed by Buehler andBuehler and associatesassociates.. www.indiandentalacademy.com
  75. 75.  The Nitinol orthodontic wire offered aThe Nitinol orthodontic wire offered a modulus of elasticity about 20% that of themodulus of elasticity about 20% that of the stainless steel wires, along with a very widestainless steel wires, along with a very wide elastic working range. This was evident whenelastic working range. This was evident when the wire was tested in cantilever bending.the wire was tested in cantilever bending.  Two new superelastic nickel-titanium wires,Two new superelastic nickel-titanium wires, Chinese NiTi and Japanese NiTi wereChinese NiTi and Japanese NiTi were introduced during the mid 1980s.introduced during the mid 1980s. www.indiandentalacademy.com
  76. 76.  Heat treatment of the Japanese NiTi wires atHeat treatment of the Japanese NiTi wires at 500500°c was found to significantly alter the°c was found to significantly alter the super elastic force plateau that occurred duringsuper elastic force plateau that occurred during unloading of three point bending testunloading of three point bending test specimens. It was also observed that heatspecimens. It was also observed that heat treatment at 600°c eliminated the superelastictreatment at 600°c eliminated the superelastic behavior.behavior.  The bending properties of nonsuperelasticThe bending properties of nonsuperelastic nickel-titanium wires are not affected by heatnickel-titanium wires are not affected by heat treatments at 500treatments at 500°c and 600°c temperature°c and 600°c temperature range.range. www.indiandentalacademy.com
  77. 77.  In the early 1990s a NiTi orthodontic wireIn the early 1990s a NiTi orthodontic wire alloy (Neo Sentalloy) with true shape memoryalloy (Neo Sentalloy) with true shape memory at the temperature of the oral environment wasat the temperature of the oral environment was introduced by GAC International, which hadintroduced by GAC International, which had an optimum combination of light forcean optimum combination of light force delivery and springback under clinicaldelivery and springback under clinical conditions.conditions.  X-ray energy-dispersive spectroscopic analysisX-ray energy-dispersive spectroscopic analysis with the SEM suggests that commercialwith the SEM suggests that commercial orthodontic wires are generally titanium rich.orthodontic wires are generally titanium rich. www.indiandentalacademy.com
  78. 78.  There are two major NiTi phases in the nickel-There are two major NiTi phases in the nickel- titanium wires. Austenitic NiTi has an orderedtitanium wires. Austenitic NiTi has an ordered bcc structure that occurs at high temperaturesbcc structure that occurs at high temperatures and low stresses. Martensitic NiTi has beenand low stresses. Martensitic NiTi has been reported to have a distorted monoclinic,reported to have a distorted monoclinic, triclinic, or hexagonal structures, and forms attriclinic, or hexagonal structures, and forms at low temperatures and high stresses.low temperatures and high stresses.  The shape memory effect is associated with aThe shape memory effect is associated with a reversible martensite austenitereversible martensite austenite transformation.transformation. www.indiandentalacademy.com
  79. 79.  In some cases an intermediate R-phase havingIn some cases an intermediate R-phase having a rhombohedral crystal structure may forma rhombohedral crystal structure may form during this transformation process.during this transformation process.  For the superelastic nickel-titanium alloy,For the superelastic nickel-titanium alloy, complete transformation to austenite occurscomplete transformation to austenite occurs only slightly above the temperature of the oralonly slightly above the temperature of the oral environmentenvironment www.indiandentalacademy.com
  80. 80.  In 1994 Ormco Cooperation introduced a newIn 1994 Ormco Cooperation introduced a new orthodontic wire alloy, copper NiTi which isorthodontic wire alloy, copper NiTi which is available in three temperature variants of 27available in three temperature variants of 27°°c,c, 3535°°c, and 40c, and 40°°c. The shape memory behavior isc. The shape memory behavior is reported by the manufacturer to occur for eachreported by the manufacturer to occur for each variant at temperatures exceeding the specifiedvariant at temperatures exceeding the specified temperature.temperature.  For example, the 27For example, the 27°°c variant would be usefulc variant would be useful at for mouth breathers; the 35at for mouth breathers; the 35°°c variant isc variant is activated at normal body temperature; and theactivated at normal body temperature; and the 4040°°c variant would provide activation onlyc variant would provide activation only after consuming hot food and beverages.after consuming hot food and beverages.www.indiandentalacademy.com
  81. 81.  In the recent studies 27In the recent studies 27°°c copper NiTi wirec copper NiTi wire alloy contain a single peak on both the heatingalloy contain a single peak on both the heating and cooling curves, indicating directand cooling curves, indicating direct transformation from martensitic to austenite ontransformation from martensitic to austenite on heating and form austenite to martensite onheating and form austenite to martensite on cooling, without an intermediate R-phase. Incooling, without an intermediate R-phase. In contrast, the 35contrast, the 35°°c copper NiTi and 40c copper NiTi and 40°°c copperc copper NiTi wire alloys exhibited two overlappingNiTi wire alloys exhibited two overlapping peaks on heating, corresponding topeaks on heating, corresponding to transformation from martensite to R-phasetransformation from martensite to R-phase followed by transformation from R-phase tofollowed by transformation from R-phase to austenite.austenite. www.indiandentalacademy.com
  82. 82.  Element analysis using SEM have indicatedElement analysis using SEM have indicated that the three Copper NiTi variants have verythat the three Copper NiTi variants have very similar compositions of approximately 44%similar compositions of approximately 44% nickel, 51% titanium, and slightly less than 5%nickel, 51% titanium, and slightly less than 5% copper, and 0.2-0.3% chromium.copper, and 0.2-0.3% chromium.  KusyKusy, has reported that copper Ni-Ti contains, has reported that copper Ni-Ti contains nominally 5-6 wt% copper and 0.2 – 0.5 wt%nominally 5-6 wt% copper and 0.2 – 0.5 wt% chromium. The 27chromium. The 27°c C variant contain 0.5%°c C variant contain 0.5% chromium to compensate for the effect ofchromium to compensate for the effect of copper in raising the Af temperature abovecopper in raising the Af temperature above that of the oral temperature, and the 40°c Cthat of the oral temperature, and the 40°c C variant contains 0.2% chromium.variant contains 0.2% chromium.www.indiandentalacademy.com
  83. 83. Nickel-titanium open and closed coilNickel-titanium open and closed coil springssprings  Super elastic nickel titanium alloy wires and springsSuper elastic nickel titanium alloy wires and springs introduced the concept of applying a super-elasticintroduced the concept of applying a super-elastic unloading curve that could potentially deliver aunloading curve that could potentially deliver a more constant force.more constant force.  Springs differ from archwires in that; springs areSprings differ from archwires in that; springs are necessarily subjected to an additional manufacturingnecessarily subjected to an additional manufacturing procedure of winding, which might effect theirprocedure of winding, which might effect their mechanical properties. Another difference is that,mechanical properties. Another difference is that, the forces applied to springs include torsional andthe forces applied to springs include torsional and tensional components in addition to bending force.tensional components in addition to bending force. www.indiandentalacademy.com
  84. 84.  Advantages of the compression and tensileAdvantages of the compression and tensile springs made of nickel-titanium are: asprings made of nickel-titanium are: a minimum of permanent deformation andminimum of permanent deformation and possibility of a more constant force duringpossibility of a more constant force during unloading.unloading.  The closed coil nickel titanium springs areThe closed coil nickel titanium springs are used for space closure; open coil nickelused for space closure; open coil nickel titanium springs are mainly used for openingtitanium springs are mainly used for opening space to unravel the teeth for molarspace to unravel the teeth for molar distalization.distalization. www.indiandentalacademy.com
  85. 85.  Miura et alMiura et al (AJODO 1988) subjected Japanese(AJODO 1988) subjected Japanese nickel-titanium closed and open coil springs tonickel-titanium closed and open coil springs to tensile and compression tests respectively. Springstensile and compression tests respectively. Springs of various lumen sizes, wire size, and different pitchof various lumen sizes, wire size, and different pitch was used in the study. It was observed that thewas used in the study. It was observed that the lumen of coil springs remained constant, the loadlumen of coil springs remained constant, the load value of the super elasticity increased as wirevalue of the super elasticity increased as wire diameter increases.diameter increases. www.indiandentalacademy.com
  86. 86.  When the diameter remained constant, the loadWhen the diameter remained constant, the load value of super elastic activity increased, as thevalue of super elastic activity increased, as the lumen of the coil became smaller. It was alsolumen of the coil became smaller. It was also shown that the open coil springs showed ashown that the open coil springs showed a more constant load value of super elasticitymore constant load value of super elasticity when compared to closed coil springs.when compared to closed coil springs. www.indiandentalacademy.com
  87. 87.  RyanRyan (BJO 1995), compared the force(BJO 1995), compared the force characteristics of different commerciallycharacteristics of different commercially available open and closed coiled nickelavailable open and closed coiled nickel titanium springs. He stated that the supertitanium springs. He stated that the super elastic nickel titanium coil springs possesselastic nickel titanium coil springs possess superior properties than other springs.superior properties than other springs. www.indiandentalacademy.com
  88. 88.  BarwartBarwart ( AJODO 1996) in a study examined( AJODO 1996) in a study examined the effect of temperature change on the forcethe effect of temperature change on the force delivery of nickel titanium closed coil springs.delivery of nickel titanium closed coil springs. The springs were heated and cooled betweenThe springs were heated and cooled between 2020°°c and 50c and 50°°c, while held in constantc, while held in constant extension.extension.  Load values were found to increase with risingLoad values were found to increase with rising temperature. The force measured at 37temperature. The force measured at 37°°c wasc was about twice as high as at 20about twice as high as at 20°°c. Immediatelyc. Immediately after the temperature started to drop, a rapidafter the temperature started to drop, a rapid decrease in the force occurred to levels belowdecrease in the force occurred to levels below those found at raising temperatures.those found at raising temperatures.www.indiandentalacademy.com
  89. 89.  Angolkar et alAngolkar et al (AJODO 1992) conducted an(AJODO 1992) conducted an in-vitro study on closed coiled springs ofin-vitro study on closed coiled springs of different length, and lumen in stainless steel,different length, and lumen in stainless steel, cobalt chromium nickel and nickel-titaniumcobalt chromium nickel and nickel-titanium alloys. They showed that all the springsalloys. They showed that all the springs demonstrated loss of force over a time period.demonstrated loss of force over a time period. Most spring showed a major force reduction inMost spring showed a major force reduction in first 24 hours to 3 days. Nickel-titaniumfirst 24 hours to 3 days. Nickel-titanium springs showed least force decay and it wassprings showed least force decay and it was observed that increase in lumen size reducedobserved that increase in lumen size reduced the force delivery, and an increase in the wirethe force delivery, and an increase in the wire size, increased the force delivery.size, increased the force delivery. www.indiandentalacademy.com
  90. 90.  Effect of lumen size on force characteristicsEffect of lumen size on force characteristics:: Jebby Jacob, Divakar Karanth, K. SadashivaJebby Jacob, Divakar Karanth, K. Sadashiva shetty. (JIOS 2002)shetty. (JIOS 2002)  Findings of this study on open coil springsFindings of this study on open coil springs revealed that, as the size of lumen increased,revealed that, as the size of lumen increased, the force delivered decreased for a giventhe force delivered decreased for a given diameter. In case of large size lumen adiameter. In case of large size lumen a decrease in force value and increased range ofdecrease in force value and increased range of super elastic activity is seen. These findingssuper elastic activity is seen. These findings confirm the findings of Miura et al.confirm the findings of Miura et al. www.indiandentalacademy.com
  91. 91.  Effect of wire diameter on force characteristicsEffect of wire diameter on force characteristics::  In springs with a constant lumen size, as theIn springs with a constant lumen size, as the diameter of the wire increased, the forcediameter of the wire increased, the force delivered increased minimally. The super elasticdelivered increased minimally. The super elastic activity range was almost the same. Theseactivity range was almost the same. These findings slightly differed from the studies offindings slightly differed from the studies of Chaconas et al (1984) who observed that, with aChaconas et al (1984) who observed that, with a constant lumen size, an increase in wire diameterconstant lumen size, an increase in wire diameter produced an increase in force at a givenproduced an increase in force at a given activation.activation. www.indiandentalacademy.com
  92. 92.  When the closed coil springs of differentWhen the closed coil springs of different diameters were compared, it was found thatdiameters were compared, it was found that larger diameter spring produced significantlylarger diameter spring produced significantly higher force levels. It was also found that ashigher force levels. It was also found that as the wire increased, force levels also increasedthe wire increased, force levels also increased drastically.drastically.  Studies on Japanese nickel titanium springs byStudies on Japanese nickel titanium springs by Miura et al (1988) showed that, the load valueMiura et al (1988) showed that, the load value of super elastic activity increased in proportionof super elastic activity increased in proportion to increase in diameter of wire.to increase in diameter of wire. www.indiandentalacademy.com
  93. 93.  Effect of spring length on force characteristicsEffect of spring length on force characteristics:: The length of the spring has a great effect on theThe length of the spring has a great effect on the load deflection rate. A shorter spring stifferload deflection rate. A shorter spring stiffer than a larger spring of same dimensions. Asthan a larger spring of same dimensions. As the length of the open coil spring increased,the length of the open coil spring increased, initial force delivered was high, but the rangeinitial force delivered was high, but the range of super elastic activity increased significantly.of super elastic activity increased significantly. Shorter springs delivered more force than longerShorter springs delivered more force than longer springs.springs. www.indiandentalacademy.com
  94. 94.  Effect of static, simulated oral environmentEffect of static, simulated oral environment:: The load deflection rate of open coil springsThe load deflection rate of open coil springs showed minor changes over 4 weeks in staticshowed minor changes over 4 weeks in static simulated oral environment.simulated oral environment. It was noticed that for an open coil spring ofIt was noticed that for an open coil spring of 9mm length at given activation the force level9mm length at given activation the force level decreased from week 0 to week 2, butdecreased from week 0 to week 2, but surprisingly the force level regained at week 4surprisingly the force level regained at week 4 to that of week 0.to that of week 0. www.indiandentalacademy.com
  95. 95.  Summary and conclusion: the forceSummary and conclusion: the force characteristic of the open and closed coilcharacteristic of the open and closed coil springs were concluded as :springs were concluded as : As the size of lumen increased, the forceAs the size of lumen increased, the force delivered by the open spring decreased.delivered by the open spring decreased. Increase in the wire diameter increased the forceIncrease in the wire diameter increased the force level in both open and closed coil spring.level in both open and closed coil spring. Closed coil spring of smaller diameter fromClosed coil spring of smaller diameter from “Ultimate Arch Forms” showed good range of“Ultimate Arch Forms” showed good range of super elastic activity.super elastic activity.www.indiandentalacademy.com
  96. 96. As the length of open coil springs was increased, theAs the length of open coil springs was increased, the range of super elastic activity increasedrange of super elastic activity increased significantly. In case of closed coil springs, shortersignificantly. In case of closed coil springs, shorter springs exhibited wide super elastic range.springs exhibited wide super elastic range. Closed coil springs of similar dimension fromClosed coil springs of similar dimension from different manufactures showed the variation in theirdifferent manufactures showed the variation in their properties.properties. The ideal spring for clinical situation should be theThe ideal spring for clinical situation should be the one with optimum force level and with greater rangeone with optimum force level and with greater range of super elastic activity.of super elastic activity. Open coil springs with largeOpen coil springs with large lumen size and length and smaller diameter wouldlumen size and length and smaller diameter would meet these criteria. Closed coil spring with shortermeet these criteria. Closed coil spring with shorter length and the smaller diameter showed good superlength and the smaller diameter showed good super elastic range.elastic range. www.indiandentalacademy.com
  97. 97. Property Stainless steel Cobalt-chromium- Beta-titanium (TMA) Nickel-titanium Nickel (Elgiloy Blue) Cost Low Low High High Force High High Intermediate Light delivery Elastic Low Low Intermediate High Range (springback) Formability Excellent Excellent Excellent Poor Ease of Can be soldered. Can be soldered Only wire alloy that cannot be Joining Welded joints Welded joints must has true weldability. Soldered or must be be reinforced with welded. reinforced with solder solder Archwire- Lower Lower Higher Higher Bracket www.indiandentalacademy.com
  98. 98. www.indiandentalacademy.com
  99. 99. Orthodontic bracketsOrthodontic brackets  The original treatment approach utilized a slotThe original treatment approach utilized a slot attached to a stainless steel band that wasattached to a stainless steel band that was cemented to the tooth, and early attempts tocemented to the tooth, and early attempts to modify this attachment resulted in wide basemodify this attachment resulted in wide base surfaces on to which a slot was soldered. Thissurfaces on to which a slot was soldered. This appliance was then bonded to the tooth withappliance was then bonded to the tooth with epoxy resin. In the late 1970s the directepoxy resin. In the late 1970s the direct bonding to the enamel was widely accepted asbonding to the enamel was widely accepted as a standard procedure to replace banding.a standard procedure to replace banding. www.indiandentalacademy.com
  100. 100.  The next stage of bracket evolution includedThe next stage of bracket evolution included modification of the base design to providemodification of the base design to provide higher bond strength with adhesives, whilehigher bond strength with adhesives, while concurrent efforts focused on decreasing theconcurrent efforts focused on decreasing the bracket surface.bracket surface.  The bracket manufacturing process employedThe bracket manufacturing process employed mechanical deformation or wrought processingmechanical deformation or wrought processing technique to fabricate these appliances.technique to fabricate these appliances. www.indiandentalacademy.com
  101. 101.  Early commercially available aesthetic productEarly commercially available aesthetic product included both plastic brackets fabricated from eitherincluded both plastic brackets fabricated from either poly crystalline or single crystal alumina.poly crystalline or single crystal alumina.  The thicker profile of the initial ceramic bracketsThe thicker profile of the initial ceramic brackets caused slight discomfort for some patients.caused slight discomfort for some patients. www.indiandentalacademy.com
  102. 102.  In describing bracket evolution, it is important toIn describing bracket evolution, it is important to include the introduction of the self ligating bracket.include the introduction of the self ligating bracket.  This was the result of an effort to develop a reliableThis was the result of an effort to develop a reliable appliance that would maintain steady force levelsappliance that would maintain steady force levels during activation while providing decreasedduring activation while providing decreased frictional resistance and optimum three dimensionalfrictional resistance and optimum three dimensional control of the tooth movement.control of the tooth movement.  Important characteristic of these appliancesImportant characteristic of these appliances documented through both in vitro and vivo studies isdocumented through both in vitro and vivo studies is the potential elimination of cross-contaminationthe potential elimination of cross-contamination through the avoidance of elastomeric ligature.through the avoidance of elastomeric ligature.www.indiandentalacademy.com
  103. 103. Metallic bracketsMetallic brackets  The morphology of the base of the stainless steelThe morphology of the base of the stainless steel brackets, which is composed of metal mesh, yieldsbrackets, which is composed of metal mesh, yields adequate adhesive bond strength values to enamel.adequate adhesive bond strength values to enamel.  GwinnettGwinnett and his colleagues, determined theand his colleagues, determined the optimum mesh size for increased bond strength.optimum mesh size for increased bond strength.  Recent investigations were not able to identify anyRecent investigations were not able to identify any differences in the bond strength betweendifferences in the bond strength between conventional bracket bases with more condensedconventional bracket bases with more condensed mesh configurations.mesh configurations. www.indiandentalacademy.com
  104. 104. Advance in metallic bracketsAdvance in metallic brackets  Despite the clinically sufficient bond strengthDespite the clinically sufficient bond strength provided by conventional metal brackets, someprovided by conventional metal brackets, some attempts have focused on increasing theattempts have focused on increasing the strength of the bracket-adhesive interface.strength of the bracket-adhesive interface.  DroeseDroese andand DiedrichDiedrich have introduced thehave introduced the plasma-coated metal bracket bases having aplasma-coated metal bracket bases having a variety of mesh design as well as ceramicvariety of mesh design as well as ceramic bracket bases. They reported that thebracket bases. They reported that the enormously increased active surface area ofenormously increased active surface area of the base resulted in much greater interlocking.the base resulted in much greater interlocking. www.indiandentalacademy.com
  105. 105.  For metal brackets, the non-mesh, plasma-sprayedFor metal brackets, the non-mesh, plasma-sprayed bases had tensile adhesives bond strengths similar tobases had tensile adhesives bond strengths similar to those of unsprayed bases.those of unsprayed bases.  There was alarming reports on the corrosionThere was alarming reports on the corrosion potential of the AISI type 316L austenitic stainlesspotential of the AISI type 316L austenitic stainless steel alloy. This alloy contains – 16-18% Cr, 10-steel alloy. This alloy contains – 16-18% Cr, 10- 14% Ni, 2-3% Mo and maximum of 0.03% C, the14% Ni, 2-3% Mo and maximum of 0.03% C, the “L” designation refers to the lower carbon content“L” designation refers to the lower carbon content compared to type 316 stainless steel.compared to type 316 stainless steel. www.indiandentalacademy.com
  106. 106.  Although the 316L stainless steel bracket alloyAlthough the 316L stainless steel bracket alloy has performed well clinically, some corrosionhas performed well clinically, some corrosion of this material may be identified in the formof this material may be identified in the form of discoloration of the underlying adhesiveof discoloration of the underlying adhesive layer.layer.  MaijerMaijer andand SmithSmith have attributed this effect tohave attributed this effect to the diffusion of corrosion products from thethe diffusion of corrosion products from the bracket base to the adhesive, noting also thebracket base to the adhesive, noting also the potential for enamel discoloration.potential for enamel discoloration. www.indiandentalacademy.com
  107. 107. Aesthetic bracketsAesthetic brackets  Appliances fabricated from alumina and zirconiaAppliances fabricated from alumina and zirconia ceramics, as well as a variety of plastic brackets.ceramics, as well as a variety of plastic brackets.  A 2205 stainless steel alloy that contains half theA 2205 stainless steel alloy that contains half the amount of nickel found in the 316L, alloy has beenamount of nickel found in the 316L, alloy has been recently proposed byrecently proposed by OshidaOshida,, MooreMoore and theirand their colleagues.colleagues.  The 2205 stainless steel alloy has a duplexThe 2205 stainless steel alloy has a duplex microstructure consisting of austenitic and delta-microstructure consisting of austenitic and delta- ferritic phases, and is harder than the 316L alloyferritic phases, and is harder than the 316L alloy when coupled with NiTi, beta-titanium, or stainlesswhen coupled with NiTi, beta-titanium, or stainless steel archwires.steel archwires. www.indiandentalacademy.com
  108. 108.  MatasaMatasa measured the microhardness values ofmeasured the microhardness values of the metallic brackets to obtain informationthe metallic brackets to obtain information about the relative strengths of the bracketabout the relative strengths of the bracket alloys, it was found that the 316L alloy hadalloys, it was found that the 316L alloy had much lower hardness compared to themuch lower hardness compared to the precipitation hardening 17-4 stainless steelprecipitation hardening 17-4 stainless steel bracket alloy, although the former hadbracket alloy, although the former had significantly higher corrosion resistance.significantly higher corrosion resistance. www.indiandentalacademy.com
  109. 109. Plastic bracketsPlastic brackets  The first plastic brackets were manufacturedThe first plastic brackets were manufactured from unfilled polycarbonate and introducedfrom unfilled polycarbonate and introduced during the early 1970s. But, unfortunatelyduring the early 1970s. But, unfortunately these brackets had a tendency to undergo creepthese brackets had a tendency to undergo creep deformation when transferring torque loadsdeformation when transferring torque loads generated by archwires. To alleviate thisgenerated by archwires. To alleviate this problem ceramic reinforced, fiberglass-problem ceramic reinforced, fiberglass- reinforced, and metal slot-reinforcedreinforced, and metal slot-reinforced polycarbonate brackets were introduced.polycarbonate brackets were introduced. www.indiandentalacademy.com
  110. 110.  Plastic brackets are generally made fromPlastic brackets are generally made from polycarbonate, but were subsequently found topolycarbonate, but were subsequently found to suffer from several problems. These includedsuffer from several problems. These included distortion following water absorption, fracture,distortion following water absorption, fracture, wear, discolouration and an inability towear, discolouration and an inability to withstand the torquing forces generated bywithstand the torquing forces generated by rectangular wires. (rectangular wires. (Reynolds, 1975Reynolds, 1975)) www.indiandentalacademy.com
  111. 111.  While the metal slot-reinforced polycarbonateWhile the metal slot-reinforced polycarbonate brackets appear to be capable of generating thebrackets appear to be capable of generating the desired torque on teeth under clinicaldesired torque on teeth under clinical conditions, problems have been reported withconditions, problems have been reported with the integrity of the slot periphery. Some of thethe integrity of the slot periphery. Some of the metal slots have a level of surface roughnessmetal slots have a level of surface roughness that may significantly effect archwire slidingthat may significantly effect archwire sliding friction.friction. www.indiandentalacademy.com
  112. 112.  A beneficial consequence of the relatively lowA beneficial consequence of the relatively low elastic modulus of polycarbonate is that theelastic modulus of polycarbonate is that the load applied during debonding of the plasticload applied during debonding of the plastic brackets results in abrackets results in a peel-offpeel-off effect.effect.  Ceramic brackets have the advantages ofCeramic brackets have the advantages of permanent translucency and greater strength.permanent translucency and greater strength. Unfortunately they have the disadvantage ofUnfortunately they have the disadvantage of brittleness and excessive bond strength.(brittleness and excessive bond strength.( Scott,Scott, 19881988) and enamel damage on debonding) and enamel damage on debonding ((Joseph and Russouw, 1990Joseph and Russouw, 1990)) www.indiandentalacademy.com
  113. 113.  Attempts have been made to combine the bestAttempts have been made to combine the best properties of plastic and ceramic materials in aproperties of plastic and ceramic materials in a single bracket. One approach has been thesingle bracket. One approach has been the ceramicceramic filled plastic bracketfilled plastic bracket. Although these brackets are. Although these brackets are easier to remove from enamel than the ceramiceasier to remove from enamel than the ceramic brackets, this is due to their significantly lower bondbrackets, this is due to their significantly lower bond strength.strength.  A different approach has been taken by combining aA different approach has been taken by combining a ceramic bracket with a polycarbonate laminate asceramic bracket with a polycarbonate laminate as the bracket base. (Ceramaflex* brackets. TPthe bracket base. (Ceramaflex* brackets. TP Orthodontics, Indiana).Orthodontics, Indiana).www.indiandentalacademy.com
  114. 114. Ceramic bracketsCeramic brackets  Most of the ceramic brackets are made of high-Most of the ceramic brackets are made of high- purity aluminum oxide, and the brackets arepurity aluminum oxide, and the brackets are available in both polycrystalline and single-crystalavailable in both polycrystalline and single-crystal forms.forms.  Ceramic brackets fabricated from the polycrystallineCeramic brackets fabricated from the polycrystalline zirconium oxide were subsequently manufactured inzirconium oxide were subsequently manufactured in Australia and Japan.Australia and Japan.  Optical properties and strength are inversely relatedOptical properties and strength are inversely related to the polycrystalline alumina ceramics: the largerto the polycrystalline alumina ceramics: the larger the individual grains in the microstructure, thethe individual grains in the microstructure, the greater is the ceramics translucency.greater is the ceramics translucency.www.indiandentalacademy.com
  115. 115.  Heat treatment must be carefully controlled toHeat treatment must be carefully controlled to prevent grain growth that would degrade theprevent grain growth that would degrade the physical properties.physical properties.  While the manufacturing process readilyWhile the manufacturing process readily allows alumina brackets to be molded to theallows alumina brackets to be molded to the desired geometry, structural imperfections atdesired geometry, structural imperfections at the grain boundaries or trace amounts ofthe grain boundaries or trace amounts of sintering aids can servesintering aids can serve as sites of crackas sites of crack initiation under stress.initiation under stress. www.indiandentalacademy.com
  116. 116.  The single crystal alumina bracket contain lessThe single crystal alumina bracket contain less impurities than are found in the polycrystallineimpurities than are found in the polycrystalline alumina brackets, which require the presencealumina brackets, which require the presence of sintering aids during manufacturing. Singleof sintering aids during manufacturing. Single crystal alumina has lower resistance to crackcrystal alumina has lower resistance to crack propagation than does polycrystalline alumina.propagation than does polycrystalline alumina. www.indiandentalacademy.com
  117. 117.  Zirconia brackets have the possibility ofZirconia brackets have the possibility of achieving much higher values of fractureachieving much higher values of fracture toughness than are possible for polycrystallinetoughness than are possible for polycrystalline alumina brackets.alumina brackets.  Smooth bracket base surfaces should betterSmooth bracket base surfaces should better distribute the shear stresses over the entiredistribute the shear stresses over the entire adhesive, while minimizing localized areas ofadhesive, while minimizing localized areas of stress concentration.stress concentration. www.indiandentalacademy.com
  118. 118. Self ligating bracketsSelf ligating brackets  Self-ligating brackets result in greater patientSelf-ligating brackets result in greater patient comfort, shorter treatment time, reduced chaircomfort, shorter treatment time, reduced chair time, and greater precision and control of toothtime, and greater precision and control of tooth translation.translation.  Self-ligating bracket design permit the use ofSelf-ligating bracket design permit the use of lighter force levels and impart lower frictionallighter force levels and impart lower frictional forces compared with ligated brackets.forces compared with ligated brackets.  Friction during tooth translation is reducedFriction during tooth translation is reduced significantly, due to elimination of steel orsignificantly, due to elimination of steel or elastic ligatures.elastic ligatures. www.indiandentalacademy.com
  119. 119.  Self-ligating brackets has been reported toSelf-ligating brackets has been reported to reduce the risk of percutaneous injury and thereduce the risk of percutaneous injury and the potential for transmission of hepatitis B virus,potential for transmission of hepatitis B virus, hepatitis c virus, or human immunodeficiencyhepatitis c virus, or human immunodeficiency virus for the orthodontist and the support staff,virus for the orthodontist and the support staff, self-ligation decreases the possibility of softself-ligation decreases the possibility of soft tissue laceration and infection from the cut endtissue laceration and infection from the cut end of ligature ties.of ligature ties.  The elimination of tie – wings and other typeThe elimination of tie – wings and other type of food traps on some self-ligating bracketof food traps on some self-ligating bracket designs significantly elevates the hygiene leveldesigns significantly elevates the hygiene level of all patents.of all patents. www.indiandentalacademy.com
  120. 120. www.indiandentalacademy.com
  121. 121.  Frictional Resistance of the Damon SL Bracket RUPALI KAPUR et al (JCO 1998)  Twenty Damon SL self-ligating brackets and 20 Mini-Twin brackets were tested.  All samples were .0225" X .030" maxillary first premolar brackets with standard Andrews prescriptions.  Wires used were 55mm lengths of .018" X .025" nickel titanium and .019" X .025" stainless steel. www.indiandentalacademy.com
  122. 122.  Results  The Damon SL bracket showed significantly lower kinetic frictional forces (p < .0001) than the Mini -Twin bracket with both wires. With the nickel titanium wires, the Damon SL brackets had a mean friction of 15.0g, compared to 41.2g for the Mini-Twin brackets. With the stainless steel wires, the Damon SL brackets produced a mean friction of only 3.6g, compared to 61.2g for the Mini-Twin brackets. www.indiandentalacademy.com
  123. 123. Comparison of self- ligated and ligatedComparison of self- ligated and ligated brackets:brackets: Ligation stability Ligation Force level FrictionSliding mechanism Office visits Treatment time Esthetics Patient comfort Oral hygiene Infection control Instruments Staff www.indiandentalacademy.com
  124. 124.  Comparison behavior of 2205 duplex stainlessComparison behavior of 2205 duplex stainless steelsteel: (: (Jeffrey A. PlattJeffrey A. Platt) AJODO 1997-) AJODO 1997- The 2205 stainless steel is a potential orthodonticThe 2205 stainless steel is a potential orthodontic bracket material with low nickel content (4-6wtbracket material with low nickel content (4-6wt %) whereas the 316L stainless steel with a nickel%) whereas the 316L stainless steel with a nickel content (10-14wt%) is a currently used bracketcontent (10-14wt%) is a currently used bracket material.material. Both were subjected to electrochemical andBoth were subjected to electrochemical and immersion corrosion tests in 37immersion corrosion tests in 37°c, 0.9wt%°c, 0.9wt% sodium chloride solution.sodium chloride solution.www.indiandentalacademy.com
  125. 125.  Electrochemical testing indicates that 2205 hasElectrochemical testing indicates that 2205 has a longer passivation range than 316L.a longer passivation range than 316L.  When 316L is coupled with NiTi, TMA, orWhen 316L is coupled with NiTi, TMA, or stainless steel arch wire and was subjected tostainless steel arch wire and was subjected to the immersion corrosion test, it was found thatthe immersion corrosion test, it was found that 316L suffered from cervical corrosion. On the316L suffered from cervical corrosion. On the other hand, 2205 stainless steel did not showother hand, 2205 stainless steel did not show any localized cervical corrosion, although theany localized cervical corrosion, although the surface of 2205 was covered with corrosionsurface of 2205 was covered with corrosion products, formed when coupled to NiTi andproducts, formed when coupled to NiTi and stainless steel wires.stainless steel wires.www.indiandentalacademy.com
  126. 126.  Considering corrosion resistance, 2205 duplexConsidering corrosion resistance, 2205 duplex stainless steel is an improved alternative tostainless steel is an improved alternative to 316L for orthodontic bracket fabrication, when316L for orthodontic bracket fabrication, when used in conjunction with titanium, its alloys, orused in conjunction with titanium, its alloys, or stainless steel wires.stainless steel wires. www.indiandentalacademy.com
  127. 127.  Shear, torsional, and tensile bond strengths ofShear, torsional, and tensile bond strengths of ceramic brackets using three adhesive fillerceramic brackets using three adhesive filler concentrationsconcentrations:: Alan J.Ostertag et alAlan J.Ostertag et al (AJODO 1991)(AJODO 1991)  210 bovine teeth were bonded with one of three210 bovine teeth were bonded with one of three ceramic brackets using a 30%, 55%, or 80% filledceramic brackets using a 30%, 55%, or 80% filled adhesives.adhesives.  The brackets were debonded with a shear, torsional,The brackets were debonded with a shear, torsional, or tensile force to test the bond strength and the siteor tensile force to test the bond strength and the site of bond failure.of bond failure. www.indiandentalacademy.com
  128. 128.  No significance was found in the shear, torsional, orNo significance was found in the shear, torsional, or tensile bond strength of each ceramic bracket type intensile bond strength of each ceramic bracket type in relation to changes in the adhesive fillerrelation to changes in the adhesive filler concentration. However, there was a trend towardconcentration. However, there was a trend toward increased bond strength with increasing fillerincreased bond strength with increasing filler concentration.concentration.  The mechanically retained ceramic bracket showedThe mechanically retained ceramic bracket showed greater shear bond strength and maximum sheargreater shear bond strength and maximum shear bond strength in torsion than the chemical orbond strength in torsion than the chemical or chemical/mechanically retained ceramic bracket.chemical/mechanically retained ceramic bracket.  The failure site was at the bracket-adhesiveThe failure site was at the bracket-adhesive interface.interface. www.indiandentalacademy.com
  129. 129.  Corrosion of orthodontic bracket basesCorrosion of orthodontic bracket bases:: R. MaijerR. Maijer and D.C. Smithand D.C. Smith.: AJO January 1982..: AJO January 1982.  Recently attention was focused on the developmentRecently attention was focused on the development of black and green stains in association with directlyof black and green stains in association with directly bonded stainless steel brackets. 12 clinical cases ofbonded stainless steel brackets. 12 clinical cases of staining were studied. After intraoral photography ofstaining were studied. After intraoral photography of the stains, the brackets were removed forthe stains, the brackets were removed for examination.examination. www.indiandentalacademy.com
  130. 130.  Multiple voids were observed at the resin-bracketMultiple voids were observed at the resin-bracket interface, especially at the periphery. Considerableinterface, especially at the periphery. Considerable deterioration of the alloy base and mesh structuredeterioration of the alloy base and mesh structure was observed in the void areas.was observed in the void areas.  Findings suggested that the presence of voids,Findings suggested that the presence of voids, together with poor oral-hygiene, led to corrosion oftogether with poor oral-hygiene, led to corrosion of the type 304 stainless steel and formation of coloredthe type 304 stainless steel and formation of colored corrosion products which can result in enamelcorrosion products which can result in enamel stains. Thus use of improved corrosion resistantstains. Thus use of improved corrosion resistant stainless steel is recommended.stainless steel is recommended.www.indiandentalacademy.com
  131. 131.  Alternatives to ceramic brackets: the tensile bondAlternatives to ceramic brackets: the tensile bond strengths of two Aesthetic brackets compared Exstrengths of two Aesthetic brackets compared Ex vivo with stainless steel foil-mesh bracket basesvivo with stainless steel foil-mesh bracket bases:: S. Arici and D. ReganS. Arici and D. Regan. BJO 1997.. BJO 1997. The mean tensile/peel bond strength were evaluatedThe mean tensile/peel bond strength were evaluated for three types aesthetic brackets (a ceramic-for three types aesthetic brackets (a ceramic- reinforced bracket and two generations of areinforced bracket and two generations of a ceramic/polycarbonate combination bracket). Theseceramic/polycarbonate combination bracket). These were found to be significantly lower than the meanwere found to be significantly lower than the mean tensile/peel bond strength of a conventional foil-tensile/peel bond strength of a conventional foil- mesh stainless steel bracket base.mesh stainless steel bracket base.www.indiandentalacademy.com
  132. 132.  Failure of the ceramic-reinforcedFailure of the ceramic-reinforced polycarbonate brackets occurredpolycarbonate brackets occurred predominantly by fracture of the tie wingspredominantly by fracture of the tie wings during testing.during testing.  With the ceramic/polycarbonate combinationWith the ceramic/polycarbonate combination brackets, the majority of the specimens failedbrackets, the majority of the specimens failed due to separation of the ceramic anddue to separation of the ceramic and polycarbonate parts of the bracket.polycarbonate parts of the bracket. www.indiandentalacademy.com
  133. 133.  The fracture strength of ceramic bracketsThe fracture strength of ceramic brackets:: Daniel A. Flores et al; (AO 1989).Daniel A. Flores et al; (AO 1989). The fracture strength of different ceramicThe fracture strength of different ceramic bracket under different surface conditions andbracket under different surface conditions and ligation methods using a torsional wireligation methods using a torsional wire bending force were compared.bending force were compared. Five different bracket types (two polycrystalline,Five different bracket types (two polycrystalline, two single-crystal, and one metal) were testedtwo single-crystal, and one metal) were tested using elastic and wire ligation.using elastic and wire ligation. Results showed a significant difference betweenResults showed a significant difference between bracket types and surface conditions.bracket types and surface conditions. www.indiandentalacademy.com
  134. 134.  Non-scratched single-crystal brackets had higherNon-scratched single-crystal brackets had higher fracture strengths and slightly higher fracturefracture strengths and slightly higher fracture loads than polycrystalline brackets. However,loads than polycrystalline brackets. However, single crystal brackets were significantlysingle crystal brackets were significantly adversely affected by surface damage, whileadversely affected by surface damage, while polycrystalline brackets were not significantlypolycrystalline brackets were not significantly affected by surface damage.affected by surface damage. www.indiandentalacademy.com
  135. 135. Elastomeric ligatures and chainsElastomeric ligatures and chains  Elastomeric products are used in orthodontics asElastomeric products are used in orthodontics as ligatures and as continous modules (chains) for theligatures and as continous modules (chains) for the engagement and retraction of teeth.engagement and retraction of teeth.  The elastomeric modules were first introduced toThe elastomeric modules were first introduced to orthodontics three decades ago and have gainedorthodontics three decades ago and have gained almost universal acceptance by the profession.almost universal acceptance by the profession.  Due to the force degradation exhibited by theDue to the force degradation exhibited by the elastomeric chains, over the past decade there haselastomeric chains, over the past decade there has been increasing interest in self-ligating brackets.been increasing interest in self-ligating brackets. www.indiandentalacademy.com
  136. 136.  Elastomeric ligatures and chains are poly urethanes,Elastomeric ligatures and chains are poly urethanes, which are thermosetting polymers possessing awhich are thermosetting polymers possessing a structural unit formed by step-reactionstructural unit formed by step-reaction polymerization.polymerization. General properties of electrometers: byGeneral properties of electrometers: by BillmeyerBillmeyer,,  when stretched rapidly, elongations greatly inwhen stretched rapidly, elongations greatly in excess of 100% can be achieved, with no major lossexcess of 100% can be achieved, with no major loss of energy.of energy. www.indiandentalacademy.com
  137. 137.  The highest values of tensile strength andThe highest values of tensile strength and stiffness are obtained after full stretching.stiffness are obtained after full stretching.  Upon removal of the tensile force, a rapidUpon removal of the tensile force, a rapid contraction occurs, since the polymer structurecontraction occurs, since the polymer structure has a strong tendency to return to its originalhas a strong tendency to return to its original condition.condition.  Full recovery takes place as long as the tensileFull recovery takes place as long as the tensile force does not exceed the elastic limit,force does not exceed the elastic limit, demonstrating the high resilience of thesedemonstrating the high resilience of these materials.materials. www.indiandentalacademy.com
  138. 138.  Riley et alRiley et al (1979) determined that steel(1979) determined that steel ligatures generated more friction than elasticligatures generated more friction than elastic ligatures, particularly when plastic bracketsligatures, particularly when plastic brackets were used.were used.  Kusy et alKusy et al (1988) used laser spectroscopy to(1988) used laser spectroscopy to study surface roughness of orthodontic wires.study surface roughness of orthodontic wires. Among the 4 wire-alloys that are commonlyAmong the 4 wire-alloys that are commonly used in orthodontic practice, stainless steelused in orthodontic practice, stainless steel appeared the smoothest, followed by cobalt-appeared the smoothest, followed by cobalt- chromium, beta-titanium and Nickel-titanium.chromium, beta-titanium and Nickel-titanium. Kusy cautioned that surface roughness andKusy cautioned that surface roughness and friction in orthodontic appliance systems havefriction in orthodontic appliance systems have yet to be correlated.yet to be correlated.www.indiandentalacademy.com
  139. 139.  Schumacher and BourauelSchumacher and Bourauel (1990) conducted a(1990) conducted a series of experiments to find the friction forcesseries of experiments to find the friction forces affected by the ligation technique. Theyaffected by the ligation technique. They inferred that friction is determined by the sortinferred that friction is determined by the sort of ligature and the way of ligation and not byof ligature and the way of ligation and not by the dimensions of different archwires.the dimensions of different archwires.  Sims and WatersSims and Waters (1993) compared self –(1993) compared self – ligating and two other type of ligations. Theligating and two other type of ligations. The placing of figure of “8” tie increased frictionplacing of figure of “8” tie increased friction than self ligating brackets, because the selfthan self ligating brackets, because the self ligating brackets apply less frictional contactligating brackets apply less frictional contact to the arch wire than conventional ties Siameseto the arch wire than conventional ties Siamese brackets.brackets. www.indiandentalacademy.com
  140. 140.  Conventional ligaturesConventional ligatures:: clinician prefer to use these materials over theclinician prefer to use these materials over the 0.20mm to 0.36mm stainless steel ligature wires for0.20mm to 0.36mm stainless steel ligature wires for several reasons, including the ease of application,several reasons, including the ease of application, potential for fluoride release, patient-friendly nature,potential for fluoride release, patient-friendly nature, aesthetic appearance and decreased force delivery.aesthetic appearance and decreased force delivery. This force been found to reach the levels achievedThis force been found to reach the levels achieved with stainless steel ligatures in twin brackets werewith stainless steel ligatures in twin brackets were the extension of the elastomer is maximized becausethe extension of the elastomer is maximized because of the large size of the bracket.of the large size of the bracket.www.indiandentalacademy.com

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