Indian Dental Academy Guide to Biomaterials in Orthodontics

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INDIAN DENTAL ACADEMYINDIAN DENTAL ACADEMY
 Leader in continuing dental educationLeader in continuing dental education
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BiomaterialsBiomaterials
inin
OrthodonticsOrthodontics

ContentsContents
 IntroductionIntroduction
 Structures and properties of materialsStructures and properties of materials
 Orthodontic wiresOrthodontic wires
 Orthodontic bracketsOrthodontic brackets
 Etching agents, Adhesive resins & CementsEtching agents, Adhesive resins & Cements
 Elastomeric ligatures & ChainsElastomeric ligatures & Chains
 Impression materialsImpression materials
 Prophylactic agentsProphylactic agents
 & Miscellaneous& Miscellaneouswww.indiandentalacademy.comwww.indiandentalacademy.com

IntroductionIntroduction
 Knowledge of fundamental principlesKnowledge of fundamental principles
governing the relationship betweengoverning the relationship between
composition, structure and properties is centralcomposition, structure and properties is central
to an understanding of orthodontic materials.to an understanding of orthodontic materials.
Because wide array of metallic, ceramic andBecause wide array of metallic, ceramic and
polymeric materials are used in thepolymeric materials are used in the
profession, and new materials are continuouslyprofession, and new materials are continuously
being introduced. It is essential that thebeing introduced. It is essential that the
scientific basis for selection and proper use ofscientific basis for selection and proper use of
materials for clinical practice be thoroughlymaterials for clinical practice be thoroughly
understoodunderstood www.indiandentalacademy.comwww.indiandentalacademy.com

StructureStructure
andand
properties of materialsproperties of materials

MetalsMetals
Stainless steel:Stainless steel:
 F. Huaptmeyer in 1919F. Huaptmeyer in 1919
 These family of steels contain more than 12% ofThese family of steels contain more than 12% of
chromium which owes for its successchromium which owes for its success
 Relatively high Chromium content in SSRelatively high Chromium content in SS→→ favors thefavors the
stability of BCC unit cells of ferritestability of BCC unit cells of ferrite
 Ni, Cu, Mn, NNi, Cu, Mn, N→→ favors an FCC structure of austenitefavors an FCC structure of austenite
 Other additives areOther additives are
- carbon, Silica, Sulfur, Phosphorus, Manganese- carbon, Silica, Sulfur, Phosphorus, Manganese
 Heat treatment of these stainless, which promotes theHeat treatment of these stainless, which promotes the
precipitation of some elements addedprecipitation of some elements added..

Stainless steels are classifiedStainless steels are classified
according to the American Iron andaccording to the American Iron and
Steel InstituteSteel Institute
Various steels are:Various steels are:
 Austenitic steels (300 series)Austenitic steels (300 series)
 Martensitic steels (400 series)Martensitic steels (400 series)
 Ferritic steelsFerritic steels
 Duplex steelsDuplex steels
 Precipitation-hardenable (PH) steelsPrecipitation-hardenable (PH) steels
 Cobalt containing alloysCobalt containing alloys

Manganese containing steelsManganese containing steels

BCC FCCBCC FCC

MARTENSITIC STEELS (400 SERIES)MARTENSITIC STEELS (400 SERIES)
 In Microstructure of these steels is the same as that of iron atIn Microstructure of these steels is the same as that of iron at
room temperature (BCC).room temperature (BCC).
 These steels are stronger but less corrosion resistant alloysThese steels are stronger but less corrosion resistant alloys
 Such stainless steels should be used only for a short contactSuch stainless steels should be used only for a short contact
with oral environmentwith oral environment
 It is used for sharp instruments and resistant edgesIt is used for sharp instruments and resistant edges
 Austenitic FCC structure is unstable at lower temperature.Austenitic FCC structure is unstable at lower temperature.
 Austenizing elements (Ni, Mn and N) are added, the highlyAustenizing elements (Ni, Mn and N) are added, the highly
corrosion resistant solid solution phase can be preserved evencorrosion resistant solid solution phase can be preserved even
at room temperature.at room temperature.
 The 300 series steels are used for most attachments because ofThe 300 series steels are used for most attachments because of
there corrosion resistance.there corrosion resistance.
AUSTENITIC STEELS (300 SERIES )AUSTENITIC STEELS (300 SERIES )

Ferritic steelsFerritic steels
 Chromium is substituted for some of the iron atoms in the BCCChromium is substituted for some of the iron atoms in the BCC
unit cellsunit cells
 Modern “Super ferritics” contain 19% to 30 % chromium and areModern “Super ferritics” contain 19% to 30 % chromium and are
used in several nickel free brackets. These are highly resistant toused in several nickel free brackets. These are highly resistant to
chlorides and alloys contain small amounts of aluminum andchlorides and alloys contain small amounts of aluminum and
molybdenum and very little carbon.molybdenum and very little carbon.
 It consists of an assembly of both austenite and ferrite grains.It consists of an assembly of both austenite and ferrite grains.
They also contain molybdenum and chromium and lower nickelThey also contain molybdenum and chromium and lower nickel
contentcontent
The duplex structure results in improvedThe duplex structure results in improved
toughness and ductility.. These steels have been used for thetoughness and ductility.. These steels have been used for the
manufacture of one-piece brackets (Eg: Bioline “low nickel”manufacture of one-piece brackets (Eg: Bioline “low nickel”
brackets).brackets).
Duplex steelDuplex steel

PRECIPITATION-HARDENABLEPRECIPITATION-HARDENABLE
STEELSSTEELS
 These steels can be hardened by heatThese steels can be hardened by heat
treatment, which promotes the precipitation oftreatment, which promotes the precipitation of
some elements added.some elements added.
 PH 17-4 stainless steel is widely used forPH 17-4 stainless steel is widely used for
“mini” brackets.“mini” brackets.
 PH 17-7 stainless steel is used to manufacturePH 17-7 stainless steel is used to manufacture
Edgelock brackets (Ormco)Edgelock brackets (Ormco)

TitaniumTitanium
 The unparalleled tissue tolerance and biocompatibility of titaniumThe unparalleled tissue tolerance and biocompatibility of titanium
have made it the leading metal for dental implants. .have made it the leading metal for dental implants. .
 Most alloys used in orthodontics contain potentially toxic nickel,Most alloys used in orthodontics contain potentially toxic nickel,
chromium, and cobalt. .chromium, and cobalt. .
 Titanium alloy are highly corrosion resistantTitanium alloy are highly corrosion resistant
 They are strong but not as stiff as stain less steel, hence needed toThey are strong but not as stiff as stain less steel, hence needed to
be compensated by over sizebe compensated by over size
 It exists in alpha and beta forms; beta form is stable above 1620It exists in alpha and beta forms; beta form is stable above 1620
deg c . But can be stabilized at lower temperaturedeg c . But can be stabilized at lower temperature
 Titanium oxide film has high affinity which may be the cause forTitanium oxide film has high affinity which may be the cause for
its high frictional resistance.its high frictional resistance.
 It is used to make intermediate arch wires and can beIt is used to make intermediate arch wires and can be welded .welded .

Beta –titaniumBeta –titanium
 Introduced BY BURSTONE AND GOLDBERGIntroduced BY BURSTONE AND GOLDBERG
 Commercial name – TMA (Titanium MolybdenumCommercial name – TMA (Titanium Molybdenum
Alloy)Alloy)
 beta-stabilized titaniumbeta-stabilized titanium
 CompositionComposition
Titanium – 77.8 %Titanium – 77.8 %
Molybdenum – 11.3 %Molybdenum – 11.3 %
Zirconium – 6.6 %Zirconium – 6.6 %
Tin – 4.3 %Tin – 4.3 %
 A clinical advantage ofA clinical advantage of ββ - titanium is its excellent- titanium is its excellent
formability which is due to the BCC structure of betaformability which is due to the BCC structure of beta
stabilized titaniumstabilized titanium
 Zirconium and zinc - contribute to increased strengthZirconium and zinc - contribute to increased strength
and hardness.and hardness. www.indiandentalacademy.comwww.indiandentalacademy.com

CeramicsCeramics
 The first ceramic used was aluminum oxide or alumina,The first ceramic used was aluminum oxide or alumina,
followed by zirconiafollowed by zirconia
 alumina and zirconia can be found as tridimensionalalumina and zirconia can be found as tridimensional
inorganic macromolecules & are esthetically pleasinginorganic macromolecules & are esthetically pleasing
 The ionic crystalline structure accounts for its hardness andThe ionic crystalline structure accounts for its hardness and
compressive strength which exceeds that of the metals, butcompressive strength which exceeds that of the metals, but
they have poor flexure strengththey have poor flexure strength
 Alumina is quite stable at normal conditions but zirconiaAlumina is quite stable at normal conditions but zirconia
under goes phase transformation from the tetragonalunder goes phase transformation from the tetragonal
structure to monoclinic structure when cooled through 1100structure to monoclinic structure when cooled through 1100
-1200 range. with a volume change of approximately 3-1200 range. with a volume change of approximately 3
%that can cause fracture of ceramics%that can cause fracture of ceramicswww.indiandentalacademy.comwww.indiandentalacademy.com

 Small addition of yttrium oxide and hot isostaticSmall addition of yttrium oxide and hot isostatic
pressing can be employed to achieve very small grainpressing can be employed to achieve very small grain
size yttrium oxide partially stabilized zirconiasize yttrium oxide partially stabilized zirconia
 This transformation toughness results in high factureThis transformation toughness results in high facture
toughness 9- 10mpa.m1/toughness 9- 10mpa.m1/
A l 3 +
A l 3 +
A l 3 +
A l 3 +
A l 3 + A l 3 +
O 2 -
O 2 -
O 2 -
O 2 -
O 2 -
O 2 -
b 2 "
b 1
b '
b "
3
2
1

Organic polymersOrganic polymers
 Are natural allies of medicine because they enter theAre natural allies of medicine because they enter the
composition of living tissues.composition of living tissues.
 To be used in the oral cavity these materials must be non-To be used in the oral cavity these materials must be non-
degradable, stable and should not be mutagenic ordegradable, stable and should not be mutagenic or
carcinogeniccarcinogenic
 The first organic polymer to be used in orthodontics wereThe first organic polymer to be used in orthodontics were
rubber and its sulfur cross linked derivatives like vulcaniterubber and its sulfur cross linked derivatives like vulcanite
 Polymers truly adequate for dental purpose were onlyPolymers truly adequate for dental purpose were only
discovered in late 1930 s’discovered in late 1930 s’
 Polymethy-methacrylates and polyurethanes by Obeyer inPolymethy-methacrylates and polyurethanes by Obeyer in
19371937
 Polycarbonates and polysulfones has made possiblePolycarbonates and polysulfones has made possible
manufacturing esthetic attachment.manufacturing esthetic attachment.
 The discovery of epoxies and cyanoacrylates led to theThe discovery of epoxies and cyanoacrylates led to the
convenient use of adhesivesconvenient use of adhesiveswww.indiandentalacademy.comwww.indiandentalacademy.com

Structure and compositionStructure and composition
 Even though the chemical composition is theEven though the chemical composition is the
same the materials exhibit different propertiessame the materials exhibit different properties
this is basically determined by the polymerthis is basically determined by the polymer
chain length. small chains and residualchain length. small chains and residual
monomer can be detrimental to their propertiesmonomer can be detrimental to their properties
 The polymeric chains may be linear branchedThe polymeric chains may be linear branched
or three dimensionalor three dimensional
 with the increase in the side chains thewith the increase in the side chains the
polymer becomes stiffpolymer becomes stiff
 Polymer shrinkage occurs due to excessPolymer shrinkage occurs due to excess
monomermonomer

HandlingHandling
 The chemical degradation of the polymer and theirThe chemical degradation of the polymer and their
precursor often takes place well in advance of theirprecursor often takes place well in advance of their
deliverydelivery
 Among the most sensitive products are polyurethaneAmong the most sensitive products are polyurethane
elastomers.when these materials are subjected to lightelastomers.when these materials are subjected to light
high temperature, ph variations, solvents, or even airhigh temperature, ph variations, solvents, or even air
polyurethanes degrade and become brownish.polyurethanes degrade and become brownish.
 To control these undesirable effects various additivesTo control these undesirable effects various additives
are need, like the initiators, accelerators ,polymerizationare need, like the initiators, accelerators ,polymerization
inhibitors, plasticizers and uv –stablizers.inhibitors, plasticizers and uv –stablizers.

 Poly urethanes are further hydrophilic. waterPoly urethanes are further hydrophilic. water
and especially saliva hydrolyses themand especially saliva hydrolyses them
 The polymer surface may develop crazes anThe polymer surface may develop crazes an
lodge micro-organism , and becomelodge micro-organism , and become
unpleasantunpleasant
 BiocompatibilityBiocompatibility
 Adhesives, sealants and restorations containAdhesives, sealants and restorations contain
various additives, aromatic amines , peroxide,various additives, aromatic amines , peroxide,
inhibitors and uv –stabilizersinhibitors and uv –stabilizers
 Some of them are potentially toxic,Some of them are potentially toxic,
carcinogeniccarcinogenic www.indiandentalacademy.comwww.indiandentalacademy.com

ImplantsImplants

Implants materialsImplants materials
The materials commonly used for implants canThe materials commonly used for implants can
be divided into 3 categories:be divided into 3 categories:
 Biotolerant - stainless steel, chromium-cobaltBiotolerant - stainless steel, chromium-cobalt
alloy.alloy.
 Bioinert - titanium, carbon andBioinert - titanium, carbon and
 Bioactive - vetroceramic apatite hydroxide,Bioactive - vetroceramic apatite hydroxide,
ceramic oxidized aluminum.ceramic oxidized aluminum.

Titanium ImplantsTitanium Implants
Advantages of titaniumAdvantages of titanium
 Commercially pure titanium is the materialCommercially pure titanium is the material
most often used in implant logy.most often used in implant logy.
 It consists of 99.5% titanium, and theIt consists of 99.5% titanium, and the
remaining 0.5% is other elements, such asremaining 0.5% is other elements, such as
carbon, oxygen, nitrogen, and hydrogen.carbon, oxygen, nitrogen, and hydrogen.
 Osseo integrationOsseo integration
 no allergic or immunological reactionsno allergic or immunological reactions
 Mechanical characteristics -very light weight,Mechanical characteristics -very light weight,
excellent resistance to traction and breakingexcellent resistance to traction and breaking..

Orthodontic wiresOrthodontic wires

Orthodontic wires , which generateOrthodontic wires , which generate
the bio-mechanical forcesthe bio-mechanical forces
communicate through brackets forcommunicate through brackets for
tooth movement , are central to thetooth movement , are central to the
orthodontic practice. In the rationalorthodontic practice. In the rational
selection of wires forselection of wires for
particularparticular
treatment, the orthodontist shouldtreatment, the orthodontist should
consider a variety of factors.consider a variety of factors.

 Low stiffness, good spring back andLow stiffness, good spring back and
produce light forcesproduce light forces
 highly formable and Ability and ease ofhighly formable and Ability and ease of
joining.joining.
 Low coefficient of frictionLow coefficient of friction
 Corrosion resistanceCorrosion resistance
 Cost and biocompatibilityCost and biocompatibility

Stainless steel wires –Stainless steel wires –
Austenitic stainless steelAustenitic stainless steel
 excellent formability & corrosion resistanceexcellent formability & corrosion resistance
 Stainless steel alloy used for orthodontic wires areStainless steel alloy used for orthodontic wires are
18-8 austenitic type, containing approximately 1818-8 austenitic type, containing approximately 18
% chromium and 8 % nickel and less than 0.20% chromium and 8 % nickel and less than 0.20
percent carbon.Nickel,percent carbon.Nickel,
 Heat treatment of 400 – 500 degree c ……residualHeat treatment of 400 – 500 degree c ……residual
stress, heat treatments above 650 degrees cstress, heat treatments above 650 degrees c
……..precipitation of chromium carbide at the……..precipitation of chromium carbide at the
grain boundariesgrain boundaries
 The free hand soldering should be done rapidlyThe free hand soldering should be done rapidly
with a well controlled torch and use of flux .with a well controlled torch and use of flux .
 spot welding often causes localized loss of wroughtspot welding often causes localized loss of wrought
microstructuremicrostructure

Cobalt chromium nickel wiresCobalt chromium nickel wires
 Elgiloy 1950 .Elgiloy 1950 .
 It is available in four tempers that are color coded –It is available in four tempers that are color coded –
blue (soft) , yellow (ductile) , green (semi resilient)blue (soft) , yellow (ductile) , green (semi resilient)
and red (resilent)and red (resilent)
 Composition is 40 % Co, 20% Cr, 15 % Ni, 7 % Mo,Composition is 40 % Co, 20% Cr, 15 % Ni, 7 % Mo,
and 16% Fe.and 16% Fe.
 Corrosion resistance & lower elastic force deliveryCorrosion resistance & lower elastic force delivery
 The eigiloy blue as received wire can easilyThe eigiloy blue as received wire can easily
manipulated into desired shapes and then heatmanipulated into desired shapes and then heat
treated to achieve considerable strength andtreated to achieve considerable strength and
resilience.resilience.
 Elgiloy has been used for making fixed lingual quadElgiloy has been used for making fixed lingual quad
helix appliancehelix appliance

 Has excellent formability.Has excellent formability.
 Spring characteristics are similar to thoseSpring characteristics are similar to those
of stainless steel.of stainless steel.
 Can be soldered, but technique isCan be soldered, but technique is
demanding.demanding.
 Corrosion resistance of the wire isCorrosion resistance of the wire is
excellent.excellent.

Beta titaniumBeta titanium
 TMA by Burstone and GoldbergTMA by Burstone and Goldberg
 highest friction owing to substantial coldhighest friction owing to substantial cold
welding or mechanical abrasion.welding or mechanical abrasion.
 Ion-implantation - causes surface hardeningIon-implantation - causes surface hardening
and can decrease frictional force by as muchand can decrease frictional force by as much
as 70% and improve compressive strength,as 70% and improve compressive strength,
fatigue resistance and ductility of the wiresfatigue resistance and ductility of the wires
 Katherine Kula and proffit in AJO 1998Katherine Kula and proffit in AJO 1998
concluded that there was no significantconcluded that there was no significant
difference when ion implanted TMA wiredifference when ion implanted TMA wire
when compared to unimplanted TMA wire inwhen compared to unimplanted TMA wire in
sliding mechanics clinicallysliding mechanics clinically..

PropertiesProperties
 Corrosion resistant and biocompatibleCorrosion resistant and biocompatible
 Deflection 2 ( S.S) = TMADeflection 2 ( S.S) = TMA
 Beta titanium is ductileBeta titanium is ductile
 Allows direct welding of auxiliaries to anAllows direct welding of auxiliaries to an
arch wire without reinforcement byarch wire without reinforcement by
soldering.soldering.
 Beta titanium wires are the most expensiveBeta titanium wires are the most expensive
of all the orthodontic wire alloys but theof all the orthodontic wire alloys but the
increased cost is offset by its combinedincreased cost is offset by its combined
advantageous properties.advantageous properties.www.indiandentalacademy.comwww.indiandentalacademy.com

Nickel titanium wiresNickel titanium wires
IntroductionIntroduction
 Andreasen and Hillman in 1971.Andreasen and Hillman in 1971.
 Nitinol- Buehler.Nitinol- Buehler.
 Naval Ordinance Laboratory, its place ofNaval Ordinance Laboratory, its place of
origin.origin.
 NiTi, Nitinol, Orthonol, Sentinol andNiTi, Nitinol, Orthonol, Sentinol and
TitanalTitanal
 Good spring back and flexibilityGood spring back and flexibility
 large deflections but low forceslarge deflections but low forces

CompositionComposition
 Nitinol is approximately 52 percent nickel,Nitinol is approximately 52 percent nickel,
45 percent titanium, and 3 percent cobalt.45 percent titanium, and 3 percent cobalt.
 With proper heat treatment, the alloyWith proper heat treatment, the alloy
demonstrates significant changes indemonstrates significant changes in
mechanical properties and crystallographicmechanical properties and crystallographic
arrangement.arrangement.
 Have a stabilized martensitic phase formedHave a stabilized martensitic phase formed
by cold welding, were the shape memoryby cold welding, were the shape memory
effect has been suppressed.effect has been suppressed.

Two major NiTi phases are:Two major NiTi phases are:
 1. Austenitic Niti - a ordered BCC structure1. Austenitic Niti - a ordered BCC structure
occurs at high temperatures / low stress.occurs at high temperatures / low stress.
 2.Martensitic NiTi- distorted monoclinic,2.Martensitic NiTi- distorted monoclinic,
triclinic or hexagonal structure and forms at lowtriclinic or hexagonal structure and forms at low
temperatures / high stress.temperatures / high stress.
 shape memory effect is associated with ashape memory effect is associated with a
reversible martensite to austenite transformation,reversible martensite to austenite transformation,
which occurs rapidly by crystallographic twinningwhich occurs rapidly by crystallographic twinning
 When these alloys are subjected to highWhen these alloys are subjected to high
temperatures, detwinning occurs, and the alloytemperatures, detwinning occurs, and the alloy
reverts to the original shape or size - shapereverts to the original shape or size - shape
memory effect.memory effect.

Kusy has classified nickel titanium wires asKusy has classified nickel titanium wires as
 Martensite stabilised alloys- Nitinol.Martensite stabilised alloys- Nitinol.
 Martensite active alloys- employ theMartensite active alloys- employ the
thermoelastic effect for shape memory. alloysthermoelastic effect for shape memory. alloys
such as Neo-Sentalloy and Copper Ni-Tisuch as Neo-Sentalloy and Copper Ni-Ti
 Austenitic active alloys (SIM) These alloysAustenitic active alloys (SIM) These alloys
are the super elastic wires that do not possessare the super elastic wires that do not possess
thermoelastic shape memory at thethermoelastic shape memory at the
temperature of the oral environment such astemperature of the oral environment such as
Nitinol SENitinol SE

Shape memory effectShape memory effect
Hurst and Nanda in AJO 1990 -specific TTRHurst and Nanda in AJO 1990 -specific TTR
depends on the chemical composition of the alloy anddepends on the chemical composition of the alloy and
its processing historyits processing history..
 Memory is set in the material by holding it in theMemory is set in the material by holding it in the
desired shape while annealing it at 450° F to 500° Fdesired shape while annealing it at 450° F to 500° F
for 10 minutesfor 10 minutes
 Once a certain shape is set, the alloy can then beOnce a certain shape is set, the alloy can then be
plastically deformed at temperatures below its TTR.plastically deformed at temperatures below its TTR.
On heating through the TTR, the original shape ofOn heating through the TTR, the original shape of
the alloy is restored.the alloy is restored.
 To obtain maximum shape recovery, the deformationTo obtain maximum shape recovery, the deformation
should be limited to 7% or 8% , below TTR .should be limited to 7% or 8% , below TTR .
 Buehler and Cross- shape-memory phenomenon wasBuehler and Cross- shape-memory phenomenon was
related to the inherent capability of a nickel-titaniumrelated to the inherent capability of a nickel-titanium
alloy to alter its atomic bonding as a function ofalloy to alter its atomic bonding as a function of
temperaturetemperature www.indiandentalacademy.comwww.indiandentalacademy.com

Superelasticity / PseudoelasticitySuperelasticity / Pseudoelasticity
 In response to temperature variations, the crystal structureIn response to temperature variations, the crystal structure
undergoes deformationsundergoes deformations
 On activation, the wire undergoes a transformation fromOn activation, the wire undergoes a transformation from
austenitic to martensitic form due to stressaustenitic to martensitic form due to stress
 The different loading and unloading curves produce theThe different loading and unloading curves produce the
remarkable effect the force delivered by the austenitic NiTiremarkable effect the force delivered by the austenitic NiTi
wire can be changed during clinical use by merely releasingwire can be changed during clinical use by merely releasing
the wire and retying it.the wire and retying it.
 Deflection generates a local martensitic transformation andDeflection generates a local martensitic transformation and
produces stress-induced martensite (SIM).produces stress-induced martensite (SIM).
 In orthodontic clinical applications, SIM forms where theIn orthodontic clinical applications, SIM forms where the
wire is tied to brackets on malaligned teeth so that the wirewire is tied to brackets on malaligned teeth so that the wire
becomes noticeably pliable in the deflected areas, withbecomes noticeably pliable in the deflected areas, with
seemingly permanent deformationseemingly permanent deformation

Clinical usageClinical usage
 The high springback of nitinol is useful in circumstances thatThe high springback of nitinol is useful in circumstances that
require large deflections but low forcesrequire large deflections but low forces
 This results in increased clinical efficiency of nitinol wiresThis results in increased clinical efficiency of nitinol wires
since fewer arch wire changes or activations are required.since fewer arch wire changes or activations are required.
 for a given amount of activation, wires made of titanium alloysfor a given amount of activation, wires made of titanium alloys
produce more constant forces on teeth than stainless steelproduce more constant forces on teeth than stainless steel
wires. A distinct advantage of nitinol is realized when awires. A distinct advantage of nitinol is realized when a
rectangular wire is inserted early in treatment. Thisrectangular wire is inserted early in treatment. This
accomplishes simultaneous leveling, torquing, and correctionaccomplishes simultaneous leveling, torquing, and correction
of rotations.of rotations.
 Andreasen and Morrow - fewer arch wire changes, lessAndreasen and Morrow - fewer arch wire changes, less
chairside time, reduction in time required to accomplishchairside time, reduction in time required to accomplish
rotations and leveling, and less patient discomfort.rotations and leveling, and less patient discomfort.
 Since hooks cannot be bent or attached to nitinol, crimpableSince hooks cannot be bent or attached to nitinol, crimpable
hooks and stops are recommended for use.hooks and stops are recommended for use.
 Cinch-backs distal to molar buccal tubes can be achievedCinch-backs distal to molar buccal tubes can be achieved

Chinese Ni Ti wireChinese Ni Ti wire
 Chinese NiTi wire is applicable in situationsChinese NiTi wire is applicable in situations
where large deflections are requiredwhere large deflections are required
 Used in conditions were teeth are badlyUsed in conditions were teeth are badly
malaligned and in appliances designed tomalaligned and in appliances designed to
deliver constant forces.deliver constant forces.
 There is a force difference if the appliance isThere is a force difference if the appliance is
left in place throughout the deactivation or ifleft in place throughout the deactivation or if
it is removed and retied. If the force levelsit is removed and retied. If the force levels
have dropped too low for a given type of toothhave dropped too low for a given type of tooth
movement, then the simple act of untying andmovement, then the simple act of untying and
retying can increase the magnitude of theretying can increase the magnitude of the
force.force. www.indiandentalacademy.comwww.indiandentalacademy.com

Copper Ni – Ti wiresCopper Ni – Ti wires
 In 1994 copper Ni –Ti wires were introduced by theIn 1994 copper Ni –Ti wires were introduced by the
ormco corporation.ormco corporation.
 It is available in three temperature variants: 270 C,It is available in three temperature variants: 270 C,
350 C and 400 C corresponding to the austenite350 C and 400 C corresponding to the austenite
finish temperaturesfinish temperatures
 Shape memory behaviors is reported to occur forShape memory behaviors is reported to occur for
each variant at temperatures exceeding the specifiedeach variant at temperatures exceeding the specified
temperature.temperature.
 The addition of copper to nickel titanium enhancesThe addition of copper to nickel titanium enhances
the thermal- reactive properties of the wire, therebythe thermal- reactive properties of the wire, thereby
enabling the clinician to provide optimal forces forenabling the clinician to provide optimal forces for
consistent toothconsistent tooth movement.movement.

 They are composed ofThey are composed of
 Nickel – 44%Nickel – 44%
 Titanium – 51%Titanium – 51%
 Copper – less than 5%Copper – less than 5%
 Chromium – 0.2 – 0.3%Chromium – 0.2 – 0.3%
 Kusy - wire contains nominally 5-6 wt% of copperKusy - wire contains nominally 5-6 wt% of copper
and 0.2-0.3 % of chromium.and 0.2-0.3 % of chromium.
 The 27deg C variant contains 0.5% of chromium toThe 27deg C variant contains 0.5% of chromium to
compensate for the effect of copper in raising the Afcompensate for the effect of copper in raising the Af
above that of the oral environment.above that of the oral environment.
 The addition of copper to Ni-Ti not only modifies theThe addition of copper to Ni-Ti not only modifies the
shape memory , but also increases the stability ofshape memory , but also increases the stability of
transformation and also helped to control hysteresistransformation and also helped to control hysteresis
width and improved corrosion resistance.width and improved corrosion resistance.www.indiandentalacademy.comwww.indiandentalacademy.com

Uses of copper Ni - Ti wiresUses of copper Ni - Ti wires
 27°C Copper Ni-Ti generates forces in the high range of27°C Copper Ni-Ti generates forces in the high range of
physiological force limits and produces constant unloading forcesphysiological force limits and produces constant unloading forces
that can result in rapid tooth movement. Engagement force isthat can result in rapid tooth movement. Engagement force is
lower than with other superelastic wires. This variant would belower than with other superelastic wires. This variant would be
useful in mouth breathers.useful in mouth breathers.
 35°C Copper Ni-Ti generates mid-range constant force levels35°C Copper Ni-Ti generates mid-range constant force levels
when the wire reaches mouth temperature. Early ligation is easierwhen the wire reaches mouth temperature. Early ligation is easier
with full-size archwires due to the lower loading forces. Whenwith full-size archwires due to the lower loading forces. When
earlier engagement of full-size wires and sustained unloadingearlier engagement of full-size wires and sustained unloading
forces at body temperature are desired, 35°C Copper Ni-Ti is theforces at body temperature are desired, 35°C Copper Ni-Ti is the
ideal wire. This variant is activated at normal body temperature.ideal wire. This variant is activated at normal body temperature.
 40°C Copper Ni-Ti provides intermittent forces that are activated40°C Copper Ni-Ti provides intermittent forces that are activated
when the mouth temperature exceeds 40°C. It is useful as anwhen the mouth temperature exceeds 40°C. It is useful as an
initial wire and can be used to engage severely malaligned teethinitial wire and can be used to engage severely malaligned teeth
(such as high cuspids) without creating damaging or painful levels(such as high cuspids) without creating damaging or painful levels
of force or unwanted side effects. It is also the wire of choice forof force or unwanted side effects. It is also the wire of choice for
patients scheduled for long intervals between visits when controlpatients scheduled for long intervals between visits when control
of tooth movement is a concern. This variant would provideof tooth movement is a concern. This variant would provide
activation only after consuming hot food and beverages.activation only after consuming hot food and beverages.

Japanese Ni-Ti wiresJapanese Ni-Ti wires
Classic NiTi alloy wire used in clinicalClassic NiTi alloy wire used in clinical
orthodontics is the work-hardened type wireorthodontics is the work-hardened type wire
called Nitinol.called Nitinol.
 The Japanese NiTi alloy wire possessesThe Japanese NiTi alloy wire possesses
excellent springback property, shape memory,excellent springback property, shape memory,
and super-elasticity.and super-elasticity.
 Super-elasticity is especially desirable becauseSuper-elasticity is especially desirable because
it delivers a relatively constant force for a longit delivers a relatively constant force for a long
period of time, which is considered aperiod of time, which is considered a
physiologically desirable force for toothphysiologically desirable force for tooth
movementmovement www.indiandentalacademy.comwww.indiandentalacademy.com

Orthodontic bracketsOrthodontic brackets

Orthodontic brackets bonded toOrthodontic brackets bonded to
enamel provide the means toenamel provide the means to
transfer the force applied by thetransfer the force applied by the
activated arch wire to the tooth.activated arch wire to the tooth.

TYPES OF BRACKETSTYPES OF BRACKETS
A) METAL BRACKETSA) METAL BRACKETS
1) Stainless steel brackets1) Stainless steel brackets
2) Gold-coated brackets2) Gold-coated brackets
3) Platinum-coated brackets3) Platinum-coated brackets
4) Titanium brackets4) Titanium brackets
B) PLASTIC BRACKETSB) PLASTIC BRACKETS
1) Polycarbonate brackets1) Polycarbonate brackets
2) Polyurethane-composite brackets2) Polyurethane-composite brackets
3) Thermoplastic-polyurethane brackets3) Thermoplastic-polyurethane brackets
C) CERAMIC BRACKETSC) CERAMIC BRACKETS
1) Monocrystalline alumina (Sapphire)1) Monocrystalline alumina (Sapphire)
2) Polycrystalline alumina2) Polycrystalline alumina
3) Polycrystalline Zirconia (YPSZ)3) Polycrystalline Zirconia (YPSZ)

Stainless steel bracketsStainless steel brackets
 The bracket material used for metal brackets is of Aisi typeThe bracket material used for metal brackets is of Aisi type
316L austentic stainless steel ,to stabilize the austentic316L austentic stainless steel ,to stabilize the austentic
structure at room temperature nickel is addedstructure at room temperature nickel is added
 This Ni leaches out in the oral environment leading toThis Ni leaches out in the oral environment leading to
biocompatibility problems.biocompatibility problems.
 These brackets have 16 -18 Cr ,10-14 Ni ,2-3 Mo and aThese brackets have 16 -18 Cr ,10-14 Ni ,2-3 Mo and a
maximum of 0.03 C. The content of Cr is comparative less andmaximum of 0.03 C. The content of Cr is comparative less and
Cro does not form that effective film compared to Tio .Cro does not form that effective film compared to Tio .
 A 2205 stainless steel alloy than contains half the amount ofA 2205 stainless steel alloy than contains half the amount of
nickel found in 316L alloy has recently been proposed bynickel found in 316L alloy has recently been proposed by
Oshida and colleagues. The 2205 stainless steel alloy has aOshida and colleagues. The 2205 stainless steel alloy has a
duplex microstructure consisting of martensitic and delta-duplex microstructure consisting of martensitic and delta-
ferrectic phases, and is harder then the 316L alloy. Moreover,ferrectic phases, and is harder then the 316L alloy. Moreover,
the 2205 alloy demonstrates substantially less corrosion thenthe 2205 alloy demonstrates substantially less corrosion then
316L alloy316L alloy

Titanium bracketsTitanium brackets
Pure titanium bracket (Rematitan-DENTAURUM) is aPure titanium bracket (Rematitan-DENTAURUM) is a
one-piece construction requires no brazing layer, andone-piece construction requires no brazing layer, and
thus it is a solder- and nickel-free bracket.thus it is a solder- and nickel-free bracket.
 These brackets appear grey and have greaterThese brackets appear grey and have greater
coefficient of friction then stainless steelcoefficient of friction then stainless steel
 According to Hamula et al in JCO 1996, theAccording to Hamula et al in JCO 1996, the
problems of nickel sensitivity, corrosion, andproblems of nickel sensitivity, corrosion, and
inadequate retention of SS brackets has been solvedinadequate retention of SS brackets has been solved
with the introduction of new, pure titanium bracketwith the introduction of new, pure titanium bracket
(Rematitan).(Rematitan).

 A computer-aided laser (CAL) cuttingA computer-aided laser (CAL) cutting
process generates micro- and macro-process generates micro- and macro-
undercuts, making it possible to design anundercuts, making it possible to design an
“ideal” adhesive pattern for each tooth.“ideal” adhesive pattern for each tooth.
 Single-piece construction allows the lowestSingle-piece construction allows the lowest
possible bracket height, This makes thepossible bracket height, This makes the
miniaturized appliance even less conspicuousminiaturized appliance even less conspicuous
 A low bracket profile can be helpful inA low bracket profile can be helpful in
assessing lip balance during treatment,assessing lip balance during treatment,
especially in cases of lip insufficiency andespecially in cases of lip insufficiency and
protrusion.protrusion.

..
 Titanium also has low thermal conductivity,Titanium also has low thermal conductivity,
and thus alleviates the sensitivity to extremeand thus alleviates the sensitivity to extreme
temperature changes often experienced bytemperature changes often experienced by
patients wearing metal appliances.patients wearing metal appliances.
 It imparts none of the metallic taste ofIt imparts none of the metallic taste of
stainless steel brackets.stainless steel brackets.
 Such brackets may provide an alternativeSuch brackets may provide an alternative
to SS brackets for those who are concernedto SS brackets for those who are concerned
with nickel toxicitywith nickel toxicity

 A commercially pure (cp) medical grade 4 TiA commercially pure (cp) medical grade 4 Ti
(designation DIN 17851-German standards) is(designation DIN 17851-German standards) is
used as the basis for the manufacture of titaniumused as the basis for the manufacture of titanium
brackets.brackets.
 Composition isComposition is
Titanium - over 99%Titanium - over 99%
Iron - < 0.30%Iron - < 0.30%
Oxygen - < 0.35%Oxygen - < 0.35%
Nitrogen - < 0.35%Nitrogen - < 0.35%
Carbon - 0.05%Carbon - 0.05%
Hydrogen - 0.06%Hydrogen - 0.06%

Surface characteristicsSurface characteristics
 The surface texture of the Ti brackets is muchThe surface texture of the Ti brackets is much
rougher than that of the SS brackets.rougher than that of the SS brackets.
 These are the reasons for significantly moreThese are the reasons for significantly more
plaque accumulation and a more marked changeplaque accumulation and a more marked change
of color with titanium brackets.of color with titanium brackets.
 Titanium brackets are a suitable alternative toTitanium brackets are a suitable alternative to
conventional metal brackets in many aspects.conventional metal brackets in many aspects.
Their biocompatibility, absence of nickel, goodTheir biocompatibility, absence of nickel, good
corrosion resistance, superior dimensionalcorrosion resistance, superior dimensional
stability, comparable frictional characteristics andstability, comparable frictional characteristics and
decreased conspicuousness along with low thermaldecreased conspicuousness along with low thermal
conductivity make these brackets a suitableconductivity make these brackets a suitable
alternative to conventional S.S brackets speciallyalternative to conventional S.S brackets specially
in nickel sensitive patients.in nickel sensitive patients.

Gold coated bracketsGold coated brackets
 Recently gold-coated steel brackets have beenRecently gold-coated steel brackets have been
introduced and rapidly gained considerableintroduced and rapidly gained considerable
popularity.popularity.
 Brackets are now available with 24 karat goldBrackets are now available with 24 karat gold
plating, plated with 300 micro inches of gold.plating, plated with 300 micro inches of gold.
 Gold-coated brackets may be regarded as an estheticGold-coated brackets may be regarded as an esthetic
improvement over stainless steel attachments, andimprovement over stainless steel attachments, and
they are clean and thus more hygienic than ceramic.they are clean and thus more hygienic than ceramic.
 Patient acceptance of gold-coated attachments isPatient acceptance of gold-coated attachments is
generally positive. Significant side effects in the formgenerally positive. Significant side effects in the form
of corrosion or allergic reactions have not beenof corrosion or allergic reactions have not been
observed clinically.observed clinically.www.indiandentalacademy.comwww.indiandentalacademy.com

Platinum coated bracketsPlatinum coated brackets
 The result is a bracket with greater abrasionThe result is a bracket with greater abrasion
resistance than gold.resistance than gold.
 A smoother, harder surface than stainless steelA smoother, harder surface than stainless steel
for reduced friction and improved slidingfor reduced friction and improved sliding
mechanics is achieved.mechanics is achieved.
 By combining platinum metal and an exclusiveBy combining platinum metal and an exclusive
implantation process, a barrier has been createdimplantation process, a barrier has been created
against the diffusion of nickel, cobalt, andagainst the diffusion of nickel, cobalt, and
chromium.chromium.
 Platinum has been found to be superior to allPlatinum has been found to be superior to all
other known metalsother known metalswww.indiandentalacademy.comwww.indiandentalacademy.com

Nickel free bracketsNickel free brackets
 Made of Cobalt chromium (CoCr) dentalMade of Cobalt chromium (CoCr) dental
alloyalloy
 One-piece construction (without solder) byOne-piece construction (without solder) by
metal injection molding techniquemetal injection molding technique
 Laser structured bracket base for retentionLaser structured bracket base for retention

Plastic bracketsPlastic brackets
 Unfilled polycarbonate 1970 s.Unfilled polycarbonate 1970 s.
 creep deformation, discolorationcreep deformation, discoloration
 ceramic reinforced, fiberglass and metal slot-ceramic reinforced, fiberglass and metal slot-
reinforced polycarbonate brackets were introduced.reinforced polycarbonate brackets were introduced.
while metal slot reinforcedwhile metal slot reinforced
 polycarbonate brackets reported problems with thepolycarbonate brackets reported problems with the
integrity of the slot periphery.integrity of the slot periphery.
 The beneficial effect of these brackets due to theirThe beneficial effect of these brackets due to their
low modulus of elasticity they tend to peel of duringlow modulus of elasticity they tend to peel of during
debonding like the metal brackets.debonding like the metal brackets.

Various plastic brackets were:Various plastic brackets were:
 Polycarbonate brackets (E.g.Elation)Polycarbonate brackets (E.g.Elation)
 Reinforced polycarbonate brackets ( D BReinforced polycarbonate brackets ( D B
fibre )fibre )
 Polyurethane-composite bracketsPolyurethane-composite brackets
(E.g.Envision)(E.g.Envision)
 Thermoplastic-polyurethane bracketsThermoplastic-polyurethane brackets
(E.g.Value line)(E.g.Value line)

Polycarbonate bracketsPolycarbonate brackets
 Various reinforced polycarbonate brackets:Various reinforced polycarbonate brackets:
 Polymer fiber reinforced polycarbonate bracketsPolymer fiber reinforced polycarbonate brackets
 Fiberglass reinforced polycarbonate bracketsFiberglass reinforced polycarbonate brackets
 Ceramic reinforced polycarbonate bracketsCeramic reinforced polycarbonate brackets
 Metal slot reinforced polycarbonate bracketsMetal slot reinforced polycarbonate brackets
 Metal slot and ceramic reinforced polycarbonateMetal slot and ceramic reinforced polycarbonate
bracketsbrackets

 Bonding mechanism of plastic brackets is mainlyBonding mechanism of plastic brackets is mainly
mechanical retentionmechanical retention
 DisadvantagesDisadvantages
 Polycarbonate brackets undergo creepPolycarbonate brackets undergo creep
deformation when transferring torque loadsdeformation when transferring torque loads
generated by arch wires to the teethgenerated by arch wires to the teeth
 Discoloration of first generation unfilledDiscoloration of first generation unfilled
polycarbonate brackets during clinical aging.polycarbonate brackets during clinical aging.
 They absorb water to a slight extent and tend toThey absorb water to a slight extent and tend to
weaken in the course of about one year (Newmanweaken in the course of about one year (Newman
1973).1973). www.indiandentalacademy.comwww.indiandentalacademy.com

Ceramic bracketsCeramic brackets
 Ceramics used for the manufacturing of ceramicCeramics used for the manufacturing of ceramic
brackets were Alumina and Zirconia. Both can bebrackets were Alumina and Zirconia. Both can be
found as tridimensional inorganic macromolecules.found as tridimensional inorganic macromolecules.
 Types of ceramic bracketsTypes of ceramic brackets
 Monocrystalline (Sapphire)-Inspire ,Starfire TMBMonocrystalline (Sapphire)-Inspire ,Starfire TMB
 Polycrystalline Alumina-Allure, Mxi, ClarityPolycrystalline Alumina-Allure, Mxi, Clarity
 Polycrystalline Zirconia (YPSZ) ) Hi-BracePolycrystalline Zirconia (YPSZ) ) Hi-Brace

Bonding mechanisms :Bonding mechanisms :
 Mechanical retention employing largeMechanical retention employing large
recesses.recesses.
 Chemical adhesion facilitated by the use of aChemical adhesion facilitated by the use of a
silane layer.silane layer.
 Micromechanical retention through theMicromechanical retention through the
utilization of a number of configurations,utilization of a number of configurations,
including protruding crystals, grooves, aincluding protruding crystals, grooves, a
porous surface, and spherical glass particlesporous surface, and spherical glass particles

 Strength of the brackets can be increasedStrength of the brackets can be increased
by eliminating the surface flaws that canby eliminating the surface flaws that can
serve as the sites of stress concentration andserve as the sites of stress concentration and
fracture initiation. Decreasing the grain sizefracture initiation. Decreasing the grain size
also increases the strength of polycrystallinealso increases the strength of polycrystalline
brackets. The polycrystalline zirconiabrackets. The polycrystalline zirconia
brackets manufactured by injectionbrackets manufactured by injection
molding technique followed by isostaticmolding technique followed by isostatic
pressing in partially stabilized zirconia 5pressing in partially stabilized zirconia 5
%wt yttrium oxide%wt yttrium oxide

RECYCLING OF ORTHODONTICRECYCLING OF ORTHODONTIC
BRACKETS AND ITS EFFECTSBRACKETS AND ITS EFFECTS
 Several in-office bracket-reconditioning methodsSeveral in-office bracket-reconditioning methods
have been introduced since 1980,have been introduced since 1980,
 Grinding - Wright and Powers (1985)Grinding - Wright and Powers (1985)
 Sandblasting - Millet et al (1993), Sonis (1996)Sandblasting - Millet et al (1993), Sonis (1996)
 Direct flamingDirect flaming
 Buchman method - Buchman (1980)Buchman method - Buchman (1980)
 BigJane machine method - Buchman (1980BigJane machine method - Buchman (1980))

 Buchman (1980) concluded that asBuchman (1980) concluded that as
temperatures are increased in thermaltemperatures are increased in thermal
treatment, the hardness and tensile strengthtreatment, the hardness and tensile strength
are decreased and the microstructuresare decreased and the microstructures
illustrate corresponding susceptibility toillustrate corresponding susceptibility to
metallic intergranular corrosion.metallic intergranular corrosion.
 Matasa et al (1989) described that heatingMatasa et al (1989) described that heating
method used for reconditioning metal bracketsmethod used for reconditioning metal brackets
causes intergranular corrosion. He alsocauses intergranular corrosion. He also
enumerated the effects of heat on bracketsenumerated the effects of heat on brackets
like, structural metal weakening, vertical slotlike, structural metal weakening, vertical slot
obstruction, steel corrosion and base cloggingobstruction, steel corrosion and base cloggingwww.indiandentalacademy.comwww.indiandentalacademy.com

Enamel Etching

 Traditionally slots were welded to the bands andTraditionally slots were welded to the bands and
cemented to the crowns, before the introduction ofcemented to the crowns, before the introduction of
etching agents and adhesive resins, whichetching agents and adhesive resins, which
demanded extra arch width ,time of the clinician,demanded extra arch width ,time of the clinician,
compromised oral hygiene and estheticscompromised oral hygiene and esthetics
 With the introduction of acid etching (Bonocore)With the introduction of acid etching (Bonocore)
opened new vents for bonding brackets to theopened new vents for bonding brackets to the
teeth. Etching of enamel creates microporositiesteeth. Etching of enamel creates microporosities
with in the enamel and reduces the surface tensionwith in the enamel and reduces the surface tension
that allows resins to penetrate and polymerizethat allows resins to penetrate and polymerize
with in the etched enamel rods (mechanicalwith in the etched enamel rods (mechanical
bonding)bonding)

Enamel etching with acidsEnamel etching with acids
 Type and concentration of acidType and concentration of acid
 Orthodontic bonding of brackets to teeth does not require high bondOrthodontic bonding of brackets to teeth does not require high bond
strength (6-8 mpa), as need in restorative dentistry. Various studies havestrength (6-8 mpa), as need in restorative dentistry. Various studies have
shown that etching with 10%-37% phosphoric acid has providedshown that etching with 10%-37% phosphoric acid has provided
adequate bond strength.adequate bond strength.
 Some studies have also shown that even treating the enamel with 2%Some studies have also shown that even treating the enamel with 2%
phosphoric acid have been able to provide adequate bond strength.phosphoric acid have been able to provide adequate bond strength.
 The use of 10% maleic acid for etching results in lower bond strength.The use of 10% maleic acid for etching results in lower bond strength.
 Duration of etchingDuration of etching
 No difference in bond strength was detected between 15 second and 60No difference in bond strength was detected between 15 second and 60
second etching with 37% phosphoric acidsecond etching with 37% phosphoric acid
 However shorter etching time results in decreased bond strength (0 – 5However shorter etching time results in decreased bond strength (0 – 5
seconds)seconds)
 Scanning electron microscopy showed that etching with 37% phosphoricScanning electron microscopy showed that etching with 37% phosphoric
acid for atleast 30 seconds produces more optimal etchin pattern thanacid for atleast 30 seconds produces more optimal etchin pattern than
etching for 15 seconds.etching for 15 seconds.

 Resin composite does not bond well to unResin composite does not bond well to un
etched enamel; however, hybrid inomeretched enamel; however, hybrid inomer
orthodontic cements have a bond strengthorthodontic cements have a bond strength
ranging from 8 to 25 mpa .ranging from 8 to 25 mpa .
 Hybrid inomer cements have better bondHybrid inomer cements have better bond
strength to enamel than sand blasted metalstrength to enamel than sand blasted metal
bracket base.bracket base.
 And these cements lack cohesive strengthAnd these cements lack cohesive strength
 Use of pumice before etching to clean theUse of pumice before etching to clean the
enamel of surface deposits has shown noenamel of surface deposits has shown no
alteration in bond strengthalteration in bond strength

Iatrogenic effect of etchingIatrogenic effect of etching
 Fracture or cracking of the enamel duringFracture or cracking of the enamel during
debondingdebonding
 Porosities caused by etching may causePorosities caused by etching may cause
staining of toothstaining of tooth
 Loss of enamel. (10- 20 um)Loss of enamel. (10- 20 um)
 Resin tags retained in the enamel afterResin tags retained in the enamel after
debonding may get discolored.debonding may get discolored.
 Alternate methods for etching enamelAlternate methods for etching enamel

Acidic primerAcidic primer
 Acid(phenyl-p)Acid(phenyl-p)
 HEMAHEMA
 And dimethacrylateAnd dimethacrylate
 Although they are expensive ,comparableAlthough they are expensive ,comparable
bond strength can be attainedbond strength can be attained
 It also reduces the chair timeIt also reduces the chair time

Air abrasionAir abrasion
 Also known as micro etching is a tecniqueAlso known as micro etching is a tecnique
in which particles of aluminum oxide arein which particles of aluminum oxide are
propelled against the surface of enamelpropelled against the surface of enamel
causes abrasion of the enamel surfacecauses abrasion of the enamel surface
 Micro etching metals is an effective way ofMicro etching metals is an effective way of
increasing bond strength of bracketsincreasing bond strength of brackets
 Microetching of enamel produces only 50 %Microetching of enamel produces only 50 %
of the bond strength to that of acid etchingof the bond strength to that of acid etching

Laser etchingLaser etching
 The application of laser energy on the enamelThe application of laser energy on the enamel
surface causes localized melting and ablation.surface causes localized melting and ablation.
 Removal of enamel results primarily by microRemoval of enamel results primarily by micro
explosion of entrapped water in the enamelexplosion of entrapped water in the enamel
 Laser etching is done by neodymium-yttrium-Laser etching is done by neodymium-yttrium-
aluminum garnetaluminum garnet
 Laser typically produces low bond strengthLaser typically produces low bond strength
compared to acid etchingcompared to acid etching

Crystal growing solutionCrystal growing solution
 A proposed alternative to etching for retention ofA proposed alternative to etching for retention of
adhesive is to grow crystals on the enamel surfaceadhesive is to grow crystals on the enamel surface
 This technique is called crystal bondingThis technique is called crystal bonding
 The potential advantages of crystal bondingThe potential advantages of crystal bonding
include easy debonding, less residual adhesive leftinclude easy debonding, less residual adhesive left
on the tooth, and less enamel damage.on the tooth, and less enamel damage.
 It includes application of poly(acrylic acid)It includes application of poly(acrylic acid)
solution containing sulfate ions,which causesolution containing sulfate ions,which cause
growth of calcium sulfate dehydrate crystals ongrowth of calcium sulfate dehydrate crystals on
the enamelthe enamel
 It produces 60-80 %0f bond strength compared toIt produces 60-80 %0f bond strength compared to
acid etching Acidic primersacid etching Acidic primers

Bonding agentsBonding agents

Based on the polymerization initiationBased on the polymerization initiation
mechanism:mechanism:
 Chemically activated (self cured ) :two pasteChemically activated (self cured ) :two paste
or one pasteor one paste
 Light cured ( photo cured )Light cured ( photo cured )
 Dual cured (chemically activated and lightDual cured (chemically activated and light
curedcured
 Thermo curedThermo cured

Chemically activated orthodonticChemically activated orthodontic
adhesive systemsadhesive systems
 These adhesives employ benzoyl as an initiator and tertiaryThese adhesives employ benzoyl as an initiator and tertiary
aromatic amine such as dimethy-p-toluidene as activatoraromatic amine such as dimethy-p-toluidene as activator
 Initiation occurs from the mixing of the paste and liquidInitiation occurs from the mixing of the paste and liquid
components of these systems and free radicals are formed bycomponents of these systems and free radicals are formed by
multi step processesmulti step processes
 Chemically cured two phase systems:Chemically cured two phase systems:
 Polymerization is initiated by mixing of liquid and pastePolymerization is initiated by mixing of liquid and paste
 Clinical handling is laborious; time consumingClinical handling is laborious; time consuming
 PropertiesProperties
 Increased exposure of the components to the air inducesIncreased exposure of the components to the air induces
oxygen inhibitionoxygen inhibition
 Mixing introduces defects due to trapping of air andMixing introduces defects due to trapping of air and
formation of voidsformation of voids
 Concise (3M)Concise (3M) www.indiandentalacademy.comwww.indiandentalacademy.com

Chemically cured one phase systemChemically cured one phase system
 Application of the liquid component on the enamel and on theApplication of the liquid component on the enamel and on the
bracket base.bracket base.
 No mixing is involvedNo mixing is involved
 Clinical handling: - efficient application ;limitation in timeClinical handling: - efficient application ;limitation in time
requirementsrequirements
 PropertiesProperties
 Limited data is available on the bond strength and degree ofLimited data is available on the bond strength and degree of
curingcuring
 Inhomogeneous Patten of curing due to the sandwich involvedInhomogeneous Patten of curing due to the sandwich involved
 Enamel bracket sides of the polymer is more polymerized thanEnamel bracket sides of the polymer is more polymerized than
the middle of the bracketthe middle of the bracket
 System 1(ormco)System 1(ormco)
 Unite (3M)Unite (3M) www.indiandentalacademy.comwww.indiandentalacademy.com

Visible light curedVisible light cured
 The photo initiator in these systems isThe photo initiator in these systems is
camphoroquinone and a reducing aminecamphoroquinone and a reducing amine
 Polymerization is initated by exposure to lightPolymerization is initated by exposure to light
curing sourcecuring source
Clinical handlingClinical handling
 Provides increased working time and bracketProvides increased working time and bracket
placement time.placement time.
 Curing should be done from the incisal and cervicalCuring should be done from the incisal and cervical
marginsmargins
 The degree of cure of a stain less steel bracketsThe degree of cure of a stain less steel brackets
bonded with light cured adhesive is comparable tobonded with light cured adhesive is comparable to
that of a transparent aesthetic bracketthat of a transparent aesthetic bracket

Dual cureDual cure
 Polymerization is initiation is achieved by throughPolymerization is initiation is achieved by through
exposure to light and the reaction progress followingexposure to light and the reaction progress following
a chemically cured patterna chemically cured pattern
 Combines the disadvantages of handling both lightCombines the disadvantages of handling both light
cured and chemical cured materials.cured and chemical cured materials.
 Most time consuming applicationMost time consuming application
 Increased degree of cure and bond strength ,but ofIncreased degree of cure and bond strength ,but of
questionable clinical significancequestionable clinical significance
 Ideal for bonding molar tubesIdeal for bonding molar tubes

Moisture activeMoisture active
 Polymerization – cyanoacrylate, no liquidPolymerization – cyanoacrylate, no liquid
component is involved. Polymerization iscomponent is involved. Polymerization is
initiated on exposure to waterinitiated on exposure to water
 One step procedure-intentionally the surfaceOne step procedure-intentionally the surface
of the tooth must be wettedof the tooth must be wetted
 One of the study has shown acceptable bondOne of the study has shown acceptable bond
strengthstrength
 Smart bond (Gestenco)Smart bond (Gestenco)www.indiandentalacademy.comwww.indiandentalacademy.com

Moisture resistantMoisture resistant
 Primer compatible with the use of thePrimer compatible with the use of the
adhesiveadhesive
 Clinical handlingClinical handling
 Application of primer on wet enamelApplication of primer on wet enamel
surfacesurface
 Trans bond MIP(3M)Trans bond MIP(3M)

Microbial alteration and cariesMicrobial alteration and caries
prophylaxisprophylaxis

 Individuals with malocclution have manyIndividuals with malocclution have many
retion site owing to the irregularities ofretion site owing to the irregularities of
teeth .more retion sites are introduced whenteeth .more retion sites are introduced when
orthodontic appliances are bonded andorthodontic appliances are bonded and
banded to teeth. Oral hygine is thusbanded to teeth. Oral hygine is thus
markedly more difficult to maintain formarkedly more difficult to maintain for
orthodontic patientsorthodontic patients

 Table 6.1Table 6.1

Caries prophylaxis aspect of orthodontic treatmentCaries prophylaxis aspect of orthodontic treatment
 Fluoride is the most caristatic agent knowFluoride is the most caristatic agent know
 The mechanism of action of fluoride is generallyThe mechanism of action of fluoride is generally
believed to be due to its effect in plaque filmbelieved to be due to its effect in plaque film
around the mineral crystallites, by inhibitingaround the mineral crystallites, by inhibiting
demineralizing and increasing remineralizing ofdemineralizing and increasing remineralizing of
mineral lost during the caries processesmineral lost during the caries processes
 Rationale caries prophylactic measures forRationale caries prophylactic measures for
orthodontic patient is prevention of caries lesionorthodontic patient is prevention of caries lesion
developed during orthodontic treatmentdeveloped during orthodontic treatment

Fluoride tooth pastesFluoride tooth pastes
Fluoride toothpaste is the basis for all cariesFluoride toothpaste is the basis for all caries
prevention. Most tooth pastes contain sodiumprevention. Most tooth pastes contain sodium
fluoride, monofluorophosphate, stannous fluoridefluoride, monofluorophosphate, stannous fluoride
 The fluoride concentration may vary, but theThe fluoride concentration may vary, but the
maximum concentration allowed is 0.15 %.fluoridemaximum concentration allowed is 0.15 %.fluoride
concentration less than 0.1 % should not beconcentration less than 0.1 % should not be
recommended for orthodontic patientsrecommended for orthodontic patients
 The cariostatic effect of fluoride will improvedThe cariostatic effect of fluoride will improved
significantly if oral hygiene is improvedsignificantly if oral hygiene is improved
 The anionic agent sodium lauryl sulphate is aThe anionic agent sodium lauryl sulphate is a
popular detergentpopular detergent
 It increases the permeability of the oral mucosa andIt increases the permeability of the oral mucosa and
increases the nickel sensitivity and has been reportedincreases the nickel sensitivity and has been reported
for helping in development of ulcersfor helping in development of ulcers

 Stannous fluoride has a plaque inhibiting effect inStannous fluoride has a plaque inhibiting effect in
addition to the anticaries action. the stannous ionaddition to the anticaries action. the stannous ion
is responsible for the plaque inhibiting effect.is responsible for the plaque inhibiting effect.
Stannous inhibit the adsorption of plaque bacteriaStannous inhibit the adsorption of plaque bacteria
to the enamel by bonding to the phosphateto the enamel by bonding to the phosphate
polymer lipoteichoic acid present on the surface ofpolymer lipoteichoic acid present on the surface of
gram positive bacteria. Stannous fluoride alsogram positive bacteria. Stannous fluoride also
interferes with the acidogenicity of the plaque. It isinterferes with the acidogenicity of the plaque. It is
possible that tin atoms bound to the surface of thepossible that tin atoms bound to the surface of the
bacteria also block the sucrose from entering thebacteria also block the sucrose from entering the
cell and there by preventing acid formationcell and there by preventing acid formation
 Detergents and surface active agents areDetergents and surface active agents are
incorporated in to the tooth paste and mouthincorporated in to the tooth paste and mouth
rinses to lower the surface tension and loosen andrinses to lower the surface tension and loosen and
penetrate the deposits and emulsify and suspendpenetrate the deposits and emulsify and suspend
the debristhe debris

Fluoride supplementsFluoride supplements
High and long lasting cariogenic challengeHigh and long lasting cariogenic challenge
 For average orthodontic patient it was found that tooth pastesFor average orthodontic patient it was found that tooth pastes
alone were inadequate to stop caries and there forealone were inadequate to stop caries and there fore
recommended the use of fluoride mouth rinses (0.05 % NaF )recommended the use of fluoride mouth rinses (0.05 % NaF )
dailydaily
 An improved cariostatic effect can be achieved by use ofAn improved cariostatic effect can be achieved by use of
fluoride in combination with antibacterial agents likefluoride in combination with antibacterial agents like
chlorhexidine, triclosan and zincchlorhexidine, triclosan and zinc
 Topical fluoride in the form of varnishes or gels may beTopical fluoride in the form of varnishes or gels may be
recommendedrecommended
 Solution of titanium tetra fluoride inhibits the development ofSolution of titanium tetra fluoride inhibits the development of
lesions associated with fixed appliances more efficiently thanlesions associated with fixed appliances more efficiently than
other conventional preparation ,its mechanism of action isother conventional preparation ,its mechanism of action is
probably due to retentive, titanium rich. Glaze like coatingprobably due to retentive, titanium rich. Glaze like coating
formed on the treated enamelformed on the treated enamel

Fluoride releasing bonding agentsFluoride releasing bonding agents
 Fluoride reservoir that does not depend on patient co operationFluoride reservoir that does not depend on patient co operation
.and fluoride is deposited in an area immediately adjacent to the.and fluoride is deposited in an area immediately adjacent to the
caries susceptible areas.caries susceptible areas.
 Gass inomer cements, and resin modified glass inomer cementsGass inomer cements, and resin modified glass inomer cements
 In studies simulating oral environment, it was found that theIn studies simulating oral environment, it was found that the
fluoride availability from glass inomer cements is PH-controlled.fluoride availability from glass inomer cements is PH-controlled.
 glass inomer cements take up fluoride from the oral environmentglass inomer cements take up fluoride from the oral environment
and released .and released .
 It is seen that much fluoride is released during the first few daysIt is seen that much fluoride is released during the first few days
to weeks. Short term studies have shown that here is reduction into weeks. Short term studies have shown that here is reduction in
incidence of caries but long term effect shows there was aincidence of caries but long term effect shows there was a
significant reduction in the release of fluoridesignificant reduction in the release of fluoride
 Fluoride releasing sealants are also available sFluoride releasing sealants are also available s

Elastomeric ligatures and chainsElastomeric ligatures and chains

 Elastomeric products are used inElastomeric products are used in
orthodontics as ligatures and as continuousorthodontics as ligatures and as continuous
modules for the engagement and themodules for the engagement and the
retraction.retraction.
 Despite the popularity, there has been someDespite the popularity, there has been some
concern about the force degradationconcern about the force degradation
exhibited by the elastomeric chainsexhibited by the elastomeric chains
 Efforts have also been directed to minimizeEfforts have also been directed to minimize
plaque retention capacity of elastomericplaque retention capacity of elastomeric
chains. Fluoride releasing elastomericchains. Fluoride releasing elastomeric
ligatures has been introduced to minimizeligatures has been introduced to minimize
the risk of demineralization of enamelthe risk of demineralization of enamel
marginsmargins

Composition and structureComposition and structure
 The elastomeric ligature and chains areThe elastomeric ligature and chains are
polyurethanes, which are thermosetting polymerspolyurethanes, which are thermosetting polymers
possessing a –(NH)-(C=O)-O-stural unit formed bypossessing a –(NH)-(C=O)-O-stural unit formed by
condensation polymerization.condensation polymerization.
 The cross linking between the chains must beThe cross linking between the chains must be
relatively few to facilate large extension with therelatively few to facilate large extension with the
failure of primary bonds.failure of primary bonds.
 The glass transition temperature of biomedicalThe glass transition temperature of biomedical
polyurethanes range from -50 to -80 deg. Cpolyurethanes range from -50 to -80 deg. C
 The difference in energy between the rigid andThe difference in energy between the rigid and
rubber states corresponds to increase in the amountrubber states corresponds to increase in the amount
of molecular motion experienced by the polymerof molecular motion experienced by the polymer
after undergoing the glass transition temperatureafter undergoing the glass transition temperature

 Greater the glass transition temperature more rigidGreater the glass transition temperature more rigid
is the polymer and generates more force.is the polymer and generates more force.
 The two main methods of processing the modulesThe two main methods of processing the modules
are injection molding technique and die stamping.are injection molding technique and die stamping.
The die stamping polymers are found to be moreThe die stamping polymers are found to be more
consistent in physical properties.consistent in physical properties.
 It is said that pigments added to the elastomers alsoIt is said that pigments added to the elastomers also
effect the physical properties of polymer, howevereffect the physical properties of polymer, however
the general studies has shown that there is nothe general studies has shown that there is no
difference between the conventional and the coloreddifference between the conventional and the colored
elastomeric materials.elastomeric materials.

Fluoride releasing polyurethanesFluoride releasing polyurethanes
 Advances in the field of elastomerics include theAdvances in the field of elastomerics include the
introduction of products withintroduction of products with
 fluoride releasing featuresfluoride releasing features
 It was thought a reliable means of long termIt was thought a reliable means of long term
fluoride releasing areas adjacent to the bracketfluoride releasing areas adjacent to the bracket
margins would be paramount significance.margins would be paramount significance.
 Though it was thought such fluoride release isThough it was thought such fluoride release is
beneficial it is said to hamper the properties ofbeneficial it is said to hamper the properties of
elastomers and early degrading of elastomerelastomers and early degrading of elastomer

Elastomeric chainsElastomeric chains
 Significant differences in their force decaySignificant differences in their force decay
characteristics have been reported. Thesecharacteristics have been reported. These
differences may be attributed to several factors ,differences may be attributed to several factors ,
variation in manufacturing techniques, variationsvariation in manufacturing techniques, variations
in additives incorporated in the basicin additives incorporated in the basic
polyurethane polymer, variation in morphology orpolyurethane polymer, variation in morphology or
dimensional characteristics .dimensional characteristics .
 Many in vitro studies that have measures theMany in vitro studies that have measures the
force degradation rate of he elastomerics modulesforce degradation rate of he elastomerics modules
……the census of these studies is that elastomerics……the census of these studies is that elastomerics
modules experience a steeps decline in force ,modules experience a steeps decline in force ,
ranging from 40 to 50 % during the first 24 hrsranging from 40 to 50 % during the first 24 hrs
which continues at a lower rate for nest 2 to 3which continues at a lower rate for nest 2 to 3
weeks.weeks.

 Traditionally these modules have been used forTraditionally these modules have been used for
retraction of anterior teeth to close extraction spacesretraction of anterior teeth to close extraction spaces
as well as midline diastemasas well as midline diastemas
 with the advent of Super elastic ni ti coil springswith the advent of Super elastic ni ti coil springs
which can deliver low constant forces , use ofwhich can deliver low constant forces , use of
elastomerics has diminished significantlyelastomerics has diminished significantly
 Then there has been a criticism related to lack ofThen there has been a criticism related to lack of
mechanical control of teeth Engaged withmechanical control of teeth Engaged with
elastomerics chains , because loss of directionalelastomerics chains , because loss of directional
control of moments leads occasionally to undesirablecontrol of moments leads occasionally to undesirable
mesio-distal or bucco-lingual rotations as describesmesio-distal or bucco-lingual rotations as describes
previously that the elastometic chains loose almostpreviously that the elastometic chains loose almost
half the applied forcehalf the applied force

 very early , some investigators have proposed thatvery early , some investigators have proposed that
this deficiency can be counteracted by application ofthis deficiency can be counteracted by application of
higher initial force of 3 to 4 times the desired forcehigher initial force of 3 to 4 times the desired force
level .Some other investigators felt that thelevel .Some other investigators felt that the
application of orthodontic force up to 4 times theapplication of orthodontic force up to 4 times the
optimal level for tooth moment may haveoptimal level for tooth moment may have
unpredictable outcomes on biological processesunpredictable outcomes on biological processes
 Several studies have also dealt with the use ofSeveral studies have also dealt with the use of
prestreaching to eliminate the force loss byprestreaching to eliminate the force loss by
elastomerics modules . 2 methods have beenelastomerics modules . 2 methods have been
suggested , one is instantaneous pre stretchingsuggested , one is instantaneous pre stretching
technique by young and et el other is the extendedtechnique by young and et el other is the extended
time technique by Brantley et al but evidence hastime technique by Brantley et al but evidence has
also shown that it only eliminates about 10 % ofalso shown that it only eliminates about 10 % of
force decayforce decay

Cements in orthodonticsCements in orthodontics

 In orthodontics application of cements isIn orthodontics application of cements is
limited to luting of appliances,limited to luting of appliances,
 for acceptable performance the luting agentfor acceptable performance the luting agent
should have a variety of properties :should have a variety of properties :
 Adequate working time and setting time.Adequate working time and setting time.
 high tensilehigh tensile
 CompressiveCompressive
 Shear strengthShear strength
 Resistance to dissolutionResistance to dissolution
 Clinically acceptable bond strength lowClinically acceptable bond strength low
adhesive remnant index score on debonding,adhesive remnant index score on debonding,
and anti carigenic potentialand anti carigenic potentialwww.indiandentalacademy.comwww.indiandentalacademy.com

Zinc phosphate cementZinc phosphate cement
 Once zinc phosphate cements were widelyOnce zinc phosphate cements were widely
used for cementation of orthodontic bands.used for cementation of orthodontic bands.
 These cements are available as hand mixedThese cements are available as hand mixed
powder and liquid system although somepowder and liquid system although some
encapsulated products are marketedencapsulated products are marketed

 The principal constituent of cement powder is zincThe principal constituent of cement powder is zinc
oxide.oxide.
 A small quantity of Magnesium oxide whichA small quantity of Magnesium oxide which
improves mechanical properties and color stability.improves mechanical properties and color stability.
Small amounts of additives such as Silica or aluminaSmall amounts of additives such as Silica or alumina
which also improves mechanical properties.which also improves mechanical properties.
 Approximately 10% fluoride in the form of stannousApproximately 10% fluoride in the form of stannous
fluoride for anti cariogenic effect.fluoride for anti cariogenic effect.
 The liquid is an aqueous solution of phosphoric acidThe liquid is an aqueous solution of phosphoric acid
in concentrations from 45% to 64% buffered by 2 toin concentrations from 45% to 64% buffered by 2 to
3% of aluminum phosphate and 1 to 9% of zinc3% of aluminum phosphate and 1 to 9% of zinc
phosphate.phosphate.
 Buffered by a small quaintly of 2-3% of aluminumBuffered by a small quaintly of 2-3% of aluminum
phosphate .phosphate . www.indiandentalacademy.comwww.indiandentalacademy.com

Properties.Properties.
 The powder to liquid ratio for the cement stronglyThe powder to liquid ratio for the cement strongly
affects the working and setting times.affects the working and setting times.
 A thin consistency (low viscosity)is essential whenA thin consistency (low viscosity)is essential when
the cement is used as a luting agent, to ensurethe cement is used as a luting agent, to ensure
adequate flow during cementation of orthodonticadequate flow during cementation of orthodontic
bands.bands.
 A reasonable working time for zinc phosphateA reasonable working time for zinc phosphate
cements ranges between 3 and 6 minutes, and thecements ranges between 3 and 6 minutes, and the
setting time should be between 5 and 9 minutes.setting time should be between 5 and 9 minutes.
 For optimum results the powder should beFor optimum results the powder should be
incorporated into the liquid in small Proportionsincorporated into the liquid in small Proportions
and a relatively slow rate to achieve the desiredand a relatively slow rate to achieve the desired
consistency, the exothermic setting reaction isconsistency, the exothermic setting reaction is
retardedretarded www.indiandentalacademy.comwww.indiandentalacademy.com

 In contrast, rapid mixing of the cement powder andIn contrast, rapid mixing of the cement powder and
liquid causes substantial heat evolution, withliquid causes substantial heat evolution, with
considerable decrease in working and setting time.considerable decrease in working and setting time.
 Mixing over a large area of the glass slab also resultsMixing over a large area of the glass slab also results
in a lower temperature increase from the settingin a lower temperature increase from the setting
reactionreaction
 Cooled and dried mixing slab retards the reactionCooled and dried mixing slab retards the reaction
rate.rate.
 Care must be taken not to cool the slab below dewCare must be taken not to cool the slab below dew
point, since condensation from the air can causepoint, since condensation from the air can cause
contamination by water.contamination by water.
 The film thickness should be around 20 um SinceThe film thickness should be around 20 um Since
adhesion has not been documented to developadhesion has not been documented to develop
between zinc phosphate cements and orthodonticbetween zinc phosphate cements and orthodontic
bands, retention of the bands is attained bybands, retention of the bands is attained by
mechanical interlocking.mechanical interlocking.

 Initial setting takes place at 4-7 minutes it attains up to 50 %ofInitial setting takes place at 4-7 minutes it attains up to 50 %of
the final strength which is attained at 24 hours. Exhibitsthe final strength which is attained at 24 hours. Exhibits
compressive strength of 80 – 140 mpa tensile strength of lesscompressive strength of 80 – 140 mpa tensile strength of less
than 5 mpathan 5 mpa
 SolubilitySolubility
 During the first 24 hours of cementation significant solubilityDuring the first 24 hours of cementation significant solubility
of the cement has been reported as much as 0.04 -3.3 %byof the cement has been reported as much as 0.04 -3.3 %by
weight and decreases due time .weight and decreases due time .
 High powder liquid ratio decreases the solubility of the cementHigh powder liquid ratio decreases the solubility of the cement
Draw backsDraw backs
 Zinc phosphate is brittle.Zinc phosphate is brittle.
 It has a relatively high solubility in the mouth and it does notIt has a relatively high solubility in the mouth and it does not
adhere to tooth substance.adhere to tooth substance.
 Zinc phosphate relies on mechanical interlocking for itsZinc phosphate relies on mechanical interlocking for its
retentive effect.retentive effect.
 It does not provide any chemical bonding to tooth or metalIt does not provide any chemical bonding to tooth or metal
surfaces.surfaces.

Zinc polycarboxylate cements:Zinc polycarboxylate cements:
 These cement were introduced by smith inThese cement were introduced by smith in
1968 and these cements were the 1 st dental1968 and these cements were the 1 st dental
materials developed with an adhesivematerials developed with an adhesive
potential to enamel and dentin and it haspotential to enamel and dentin and it has
the desirable properties of zinc phosphatethe desirable properties of zinc phosphate
and zinc oxide eugenoland zinc oxide eugenol

 The zinc polycarboxylate is available in powder liquidThe zinc polycarboxylate is available in powder liquid
formations, the powder consists of zinc oxide with 10 % offormations, the powder consists of zinc oxide with 10 % of
magnesium oxide or tin oxide , silica , alumina , or bismuthmagnesium oxide or tin oxide , silica , alumina , or bismuth
salts and small quantities of stannous fluoride may besalts and small quantities of stannous fluoride may be
incorporated in some brandsincorporated in some brands
 The presence of fluoride in these cements also increases theThe presence of fluoride in these cements also increases the
strength while controlling the setting time,strength while controlling the setting time,
 The liquid is an aqueous solution of a homopolimer o acrylicThe liquid is an aqueous solution of a homopolimer o acrylic
acid or co polymers acrylic with other unsaturated carboxylicacid or co polymers acrylic with other unsaturated carboxylic
acids such as etaconic and maelic acid .acids such as etaconic and maelic acid .
 The acid concentration is 40 %by wt. it has a relatively highThe acid concentration is 40 %by wt. it has a relatively high
molecular wt which may increase the strength of the material .molecular wt which may increase the strength of the material .
 undesirable effects such as short shelf life and difficulties inundesirable effects such as short shelf life and difficulties in
manipulation occur because of high viscositymanipulation occur because of high viscosity

 Mixing of the polycarboxylate cements should beMixing of the polycarboxylate cements should be
completed rapidly within 30 to 40 seconds.completed rapidly within 30 to 40 seconds.
 The working time varies from 2 to 5 minutes atThe working time varies from 2 to 5 minutes at
room temperature and setting time ranges from 6room temperature and setting time ranges from 6
to 9 minutes at 37 degree centigrade.to 9 minutes at 37 degree centigrade.
 The powder should be rapidly incorporated intoThe powder should be rapidly incorporated into
the liquid in large quantities to optimise thethe liquid in large quantities to optimise the
working and setting time.working and setting time.
 The working time of polycarboxylate cement canThe working time of polycarboxylate cement can
be extended by lowering the temperature of thebe extended by lowering the temperature of the
mixing slab and storing the powder in amixing slab and storing the powder in a
refrigerator.refrigerator.

 Refrigeration of liquid is avoided because gelationRefrigeration of liquid is avoided because gelation
may occur from formation of hydrogen bonds.may occur from formation of hydrogen bonds.
 The cement mixture should be used while it stillThe cement mixture should be used while it still
has a glossy surface appearance.has a glossy surface appearance.
 Although the polycarboxylate cement mixture hasAlthough the polycarboxylate cement mixture has
a thicker consistency than that for zinc phosphatea thicker consistency than that for zinc phosphate
cement its flows readily when loaded, yielding ancement its flows readily when loaded, yielding an
appropriate film thickness of 20 μm.appropriate film thickness of 20 μm.
 The fully set cement at 24 hours after mixing hasThe fully set cement at 24 hours after mixing has
compressive strength ranging from 48 to 80 Mpa.compressive strength ranging from 48 to 80 Mpa.
 Tensile strength ranging from 8 to 12 MPa.Tensile strength ranging from 8 to 12 MPa.
Modulus of elasticity of zinc polycarboxylateModulus of elasticity of zinc polycarboxylate
cement is between 3 to 6 GPa.cement is between 3 to 6 GPa.

SolubilitySolubility
 The solubility of these cements in water is low ,The solubility of these cements in water is low ,
ranging between .1 % to .6%by wt.ranging between .1 % to .6%by wt.
 some products incorporating stannoussome products incorporating stannous
fluoride exhibit higher solubility because offluoride exhibit higher solubility because of
fluoride release .fluoride release .
 These cements have low resistance toThese cements have low resistance to
dissolution under acidic conditions such asdissolution under acidic conditions such as
lactic acid citric acid.depending upon the pHlactic acid citric acid.depending upon the pH
of the environment.of the environment.

BondingBonding
 These cements are capable of bonding withThese cements are capable of bonding with
surfaces of metallic restorations, prosthesessurfaces of metallic restorations, prostheses
and appliances particularly nickel-and appliances particularly nickel-
chromium, silver-palladium and stainlesschromium, silver-palladium and stainless
steel alloyssteel alloys
DisadvantagesDisadvantages
 High viscosity.High viscosity.
 High intraoral solubilityHigh intraoral solubility
 Short setting time.Short setting time.

Glass inomer cementGlass inomer cement
HistoryHistory
 Glass ionomer cements was firstGlass ionomer cements was first
introduced by Wilson and kent in 1972introduced by Wilson and kent in 1972
 It is referred to as polyalkenoate cementIt is referred to as polyalkenoate cement
,also known as ASPA(Alumino-silicate poly,also known as ASPA(Alumino-silicate poly
acrylate)acrylate)

Glass ionomer cements can be classified basedGlass ionomer cements can be classified based
on use as:on use as:
 Type I or luting cements.Glass particle sizeType I or luting cements.Glass particle size
is 13 to 19 microns.Powder to liquid ratio isis 13 to 19 microns.Powder to liquid ratio is
approximately 1.5:1.approximately 1.5:1.
 Type II or restorative cements.Particle sizeType II or restorative cements.Particle size
of upto 50 microns.Powder to liquid ratio isof upto 50 microns.Powder to liquid ratio is
approximately 3:1approximately 3:1
 Type III. Chemically set liners/bases or pitType III. Chemically set liners/bases or pit
and fissure forms.and fissure forms.
 Type IV.Visible light activated liners/basesType IV.Visible light activated liners/bases

Indian Dental Academy Guide to Biomaterials in Orthodontics

Indian Dental Academy Guide to Biomaterials in Orthodontics

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Indian Dental Academy Guide to Biomaterials in Orthodontics