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

www.indiandentalacademy.com
INDIAN DENTAL ACADEMY
Leader in continuing dental education

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

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.

 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.

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.

 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.

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

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.

 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.

 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

Stages in the
formation of metallic
grains during the
solidification of a
molten metal
Polycrystalline- each
crystal - grain

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

 various defectsvarious defects  slipslip planesplanes --alongalong
which dislocation occurswhich dislocation occurs

 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.

ANNEALING:ANNEALING:
RecoveryRecovery
RecrystallizationRecrystallization
Grain GrowthGrain Growth www.indiandentalacademy.com

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

 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.

 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.

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

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

 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

 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

Elastic PropertiesElastic Properties
Strain
Stress
Elastic Portion
Wire returns back to
original dimension when
stress is removed

 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

 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.

 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

Strain
Stress
Elastic Limit
Proportional Limit
Yield strength
0.1%

 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.

 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.

Strain
Stress
Ultimate Tensile
Strength Fracture Point

 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

Strain
Stress
Resilience Formability
Proportional limit
Yield strength

 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.

 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.

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

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.

 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.

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.

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).).

 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

Strain
Stress
Range Springback
Point of arbitrary clinical loading
Yield point

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

 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.

 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.

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

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.

 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.

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

 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.

 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.

 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.

 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..

 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.

 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.

 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.

 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.

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).

 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.

 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.

 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.

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)

 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.

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.

 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.

 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.

 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.

 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.

 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.

 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.

 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.

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

 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.

 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.

 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.

 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.

 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

 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

 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.

 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

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.

 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.

 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.

 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.

 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.

 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

 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.

 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.

 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

 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.

 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.

 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.

 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

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

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

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.

 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.

 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.

 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

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.

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.

 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.

 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.

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.

 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.

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.

 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))

 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.

 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))

 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

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

 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.

 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.

 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.

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.

 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

 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.

 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.

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

 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

 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

 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.

 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.

 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

 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.

 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

 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

 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.

 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.

 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.

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.

 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.

 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

 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

 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

 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

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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