Denture base resins /orthodontics website

DENTURE BASE RESINSDENTURE BASE RESINS
INDIAN DENTAL ACADEMYINDIAN DENTAL ACADEMY
Leader in continuing dental educationLeader in continuing dental education
www.indiandentalacademy.comwww.indiandentalacademy.com

CONTENTSCONTENTS
• IntroductionIntroduction
• HistoryHistory
• ClassificationClassification
• RequirementsRequirements
• Application of resins in DentistryApplication of resins in Dentistry
• Chemistry of polymersChemistry of polymers
• Denture base acrylic resins
• Properties of denture base resins
• Repair resins
• Reling and rebasing denture resins
• Short term and long term soft
denture

• Resin impression trays and tray materialsResin impression trays and tray materials
• Resin teeth for prosthetic applicationResin teeth for prosthetic application
• Resin as Maxillofacial materialResin as Maxillofacial material
• Temporary crown and bridge resinsTemporary crown and bridge resins
• Occlusal splintsOcclusal splints
• Inlay patternsInlay patterns
• Resins used as implantsResins used as implants
• Resin cementsResin cements
• Resin sealantsResin sealants
• Athletic mouth protectorAthletic mouth protector
• ReviewReview
• ConclusionConclusion

IntroductionIntroduction
Synthetic polymers often termed as plastics are usedSynthetic polymers often termed as plastics are used
extensively in prosthetic dentistry. Before the introductionextensively in prosthetic dentistry. Before the introduction
of acrylic polymers to dentistry in 1937, the principalof acrylic polymers to dentistry in 1937, the principal
polymer used was vulcanized rubber for denture bases.polymer used was vulcanized rubber for denture bases.
Polymers introduce since then have included vinyl acrylics,Polymers introduce since then have included vinyl acrylics,
polystyrene, epoxies, polycarbonates, polyvinyl acetatepolystyrene, epoxies, polycarbonates, polyvinyl acetate
polyethylene, cis and trans-poly isoprene, polysulfides,polyethylene, cis and trans-poly isoprene, polysulfides,
silicones, polyethers, and poly acrylic acids.silicones, polyethers, and poly acrylic acids.

• Resins today occupy a prominent place in the spectrum ofResins today occupy a prominent place in the spectrum of
materials used in dental profession. They have earned thismaterials used in dental profession. They have earned this
place on the basis of performance, plus the apparentlyplace on the basis of performance, plus the apparently
unlimited ability of dental researchers, educators andunlimited ability of dental researchers, educators and
clinicians to develop new techniques and materials to meetclinicians to develop new techniques and materials to meet
specific needsspecific needs

HistoryHistory
• Before 1880 AD dentures were fabricated from hard wood;Before 1880 AD dentures were fabricated from hard wood;
ivory and bone with natural teeth held by screws or otherivory and bone with natural teeth held by screws or other
means.means.
• In about 1855 vulcanite rubber was introduced as denture baseIn about 1855 vulcanite rubber was introduced as denture base
material with porcelain mounted on them the vulcanite basematerial with porcelain mounted on them the vulcanite base
material ruled the field of prosthetics for denture base materialmaterial ruled the field of prosthetics for denture base material
nearly about 75yers.nearly about 75yers.
• In 1868 Werley Hyatt prepared 1st organic plastic moldingIn 1868 Werley Hyatt prepared 1st organic plastic molding
compound which was cellulose nitrate and popularly known ascompound which was cellulose nitrate and popularly known as
“Celluloid”.“Celluloid”.

• In 1909 Dr Leo Bakland discovered Phenol formaldehydeIn 1909 Dr Leo Bakland discovered Phenol formaldehyde
resin known as “Bakelite”resin known as “Bakelite”
• In 1924 Dr Stryker used Phenol formaldehyde for the purposeIn 1924 Dr Stryker used Phenol formaldehyde for the purpose
of dentures.of dentures.
• After 1932 mixtures of polymerized vinyl chloride and vinylAfter 1932 mixtures of polymerized vinyl chloride and vinyl
acetate were also used as denture base.acetate were also used as denture base.
• In 1937 Dr. Walter Wright introduce more satisfactory plasticIn 1937 Dr. Walter Wright introduce more satisfactory plastic
denture base materials called methyl methacrylate resins.denture base materials called methyl methacrylate resins.
• By 1965-1970 polymers of vinyl styrenes, polycarbonates,By 1965-1970 polymers of vinyl styrenes, polycarbonates,
nylons, polyurethane and other have been investigated butnylons, polyurethane and other have been investigated but
found suitable only for limited applicationfound suitable only for limited application

Classification of resinsClassification of resins
• Based on thermal behavior:Based on thermal behavior:
– Thermoplastic:Thermoplastic: Polymers that may be softened byPolymers that may be softened by
heating and solidified by cooling, the process beingheating and solidified by cooling, the process being
repeatable.repeatable.
– Thermosetting:Thermosetting: refers to plastics that solidify duringrefers to plastics that solidify during
fabrication but cannot be softened by reheating.fabrication but cannot be softened by reheating.
• Based on spatial structureBased on spatial structure::
– LinearLinear
• Linear homopolymerLinear homopolymer  has mer units of same typehas mer units of same type
• Random copolymer of linear typeRandom copolymer of linear type  has two merhas two mer
units randomly distributed along the chainunits randomly distributed along the chain
• Linear block copolymerLinear block copolymer  has segments or blockshas segments or blocks
align the chain where the mer units are the samealign the chain where the mer units are the same

– BranchedBranched
• Branched homopolymerBranched homopolymer  consist of same mer unitsconsist of same mer units
• Graft branched copolymerGraft branched copolymer  has one type mer unitshas one type mer units
on the main chain and another mer for brancheson the main chain and another mer for branches
– Cross linkedCross linked
• Is made up of homopolymer cross-linked with aIs made up of homopolymer cross-linked with a
single cross linking agent.single cross linking agent.
• The spatial structure of polymers affects their flowThe spatial structure of polymers affects their flow
propertiesproperties
• In general cross-linked polymers flow at a higherIn general cross-linked polymers flow at a higher
temperature than linear (or) branched polymers.temperature than linear (or) branched polymers.
Another distinguishing feature of some cross-linkedAnother distinguishing feature of some cross-linked
polymers is that they do not absorb liquids as readilypolymers is that they do not absorb liquids as readily
as linear (or) branched.as linear (or) branched.

Spatial structure:Spatial structure:
There are 3 basic types of structures – linear, branched, and cross-linked.There are 3 basic types of structures – linear, branched, and cross-linked.

The linearThe linear homopolymer has mer units of the same type.homopolymer has mer units of the same type.
And theAnd the random polymerrandom polymer of the linear type has the two mer units randomlyof the linear type has the two mer units randomly
distributed along the chain.distributed along the chain.
TheThe linear block copolymerlinear block copolymer has segments or blocks along the chain where thehas segments or blocks along the chain where the
mer units are the same.mer units are the same.

• TheThe branched homopolymerbranched homopolymer consists of the same mer units,consists of the same mer units,
• whereas thewhereas the graft branched copolymergraft branched copolymer consists of one type of mer unit onconsists of one type of mer unit on
the main chain and another mer for the branches.the main chain and another mer for the branches.

Chemistry of polymersChemistry of polymers
• Polymers are prepared by a process called polymerization,Polymers are prepared by a process called polymerization,
which consist of momeric units becoming chemically linkedwhich consist of momeric units becoming chemically linked
together to form high molecular weight molecules.together to form high molecular weight molecules.
• Most polymerization reactions fall in two basic typesMost polymerization reactions fall in two basic types
– Addition polymerizationAddition polymerization
– Condensation polymerization (step growth polymerization)Condensation polymerization (step growth polymerization)

Addition polymerizationAddition polymerization
• Most dental resins are polymerized by a mechanism in whichMost dental resins are polymerized by a mechanism in which
monomers are added sequentially to end of growing chain.monomers are added sequentially to end of growing chain.
Addition polymerization starts from as active center addingAddition polymerization starts from as active center adding
one monomer at a time to rapidly form a chain.one monomer at a time to rapidly form a chain.

Stages in addition polymerizationStages in addition polymerization::
• InductionInduction:: For an addition polymerization process to begin aFor an addition polymerization process to begin a
source of free radical is required. Free radicals can be generatedsource of free radical is required. Free radicals can be generated
by activation of radical producing molecules using a secondby activation of radical producing molecules using a second
chemical, heat, visible light, U.V light or energy transfer fromchemical, heat, visible light, U.V light or energy transfer from
another compound that acts like a free radical.another compound that acts like a free radical.
• The most commonly employed initiator (for methyl methacrylateThe most commonly employed initiator (for methyl methacrylate
resin) is benzoyl peroxide, which is activated rapidly between 50resin) is benzoyl peroxide, which is activated rapidly between 50
to 1000 C.to 1000 C.
• Induction is the period during which initiator molecule becomesInduction is the period during which initiator molecule becomes
energized and breaks down into free radicals followed by theseenergized and breaks down into free radicals followed by these
radicals reacting with monomer molecule to initiate chain growth.radicals reacting with monomer molecule to initiate chain growth.
This period is greatly influenced by purity of monomer molecule.This period is greatly influenced by purity of monomer molecule.
Any impurity increases the length of the period by consuming theAny impurity increases the length of the period by consuming the
activated initiator molecules higher the temperature, the moreactivated initiator molecules higher the temperature, the more
rapid the formation of free radicals and consequently shorter therapid the formation of free radicals and consequently shorter the
induction period.induction period.

• The polymerization process for dental resins is activated byThe polymerization process for dental resins is activated by
one of the three energy sources.one of the three energy sources.
• HeatHeat
• ChemicalsChemicals
• LightLight
• Heat activationHeat activation:: the free radicals liberated by heating benzylthe free radicals liberated by heating benzyl
peroxide will initiate polymerization of methyl methacrylateperoxide will initiate polymerization of methyl methacrylate
monomer.monomer.
• Chemical ActivationChemical Activation:: system consists of two reactants.system consists of two reactants.
• That when mixed together undergo a chemical reaction thatThat when mixed together undergo a chemical reaction that
generates free radicals.generates free radicals.
• Eg. Tertiary amine activator and benzyl peroxide initiator,Eg. Tertiary amine activator and benzyl peroxide initiator,
which are mixed together to initiate polymerization of sowhich are mixed together to initiate polymerization of so
called self, cured resins.called self, cured resins.

• Light activatedLight activated:: In this system photons from a light sourceIn this system photons from a light source
activate the initiator to generate free radicals that in turn canactivate the initiator to generate free radicals that in turn can
initiate polymerization process. When this system wasinitiate polymerization process. When this system was
introduced in dentistry U.V light was used. However becauseintroduced in dentistry U.V light was used. However because
of concerns about the effect of U.V light on retina andof concerns about the effect of U.V light on retina and
unpigmented oral tissues, its limited penetration depth, andunpigmented oral tissues, its limited penetration depth, and
loss of intensity of U.V light source over time, initiatorloss of intensity of U.V light source over time, initiator
systems where subsequently developed that are activated bysystems where subsequently developed that are activated by
visible light.visible light.
• PropagationPropagation: The resultant free radical-monomer complex: The resultant free radical-monomer complex
than acts as a new free radical center when it approachesthan acts as a new free radical center when it approaches
another monomer to form a dimer, which also becomes a freeanother monomer to form a dimer, which also becomes a free
radical.radical.
Theoretically the propagation reaction should continue withTheoretically the propagation reaction should continue with
evolution of heat until all monomer has been changed toevolution of heat until all monomer has been changed to
polymer. Actually the polymerization is never completepolymer. Actually the polymerization is never complete

• Chain transferChain transfer:: In this process, the active free radical ofIn this process, the active free radical of
growing chain is transferred to another molecule (Eg: Agrowing chain is transferred to another molecule (Eg: A
monomer or inactive polymer chain) and a new free radical formonomer or inactive polymer chain) and a new free radical for
further growth is created.further growth is created.
• TerminationTermination: Addition polymerization reactions are most: Addition polymerization reactions are most
often terminated by direct coupling of two free radical chainoften terminated by direct coupling of two free radical chain
ends or by exchange of hydrogen atom from one growingends or by exchange of hydrogen atom from one growing
chain to another. Chain termination can also result from chainchain to another. Chain termination can also result from chain
transfer .transfer .

Inhibition of addition polymerizationInhibition of addition polymerization
• The polymerization reactions are not likely to result in aThe polymerization reactions are not likely to result in a
complete exhaustion of the monomer, nor do they always formcomplete exhaustion of the monomer, nor do they always form
polymer of high molecular weight. Such reactions arepolymer of high molecular weight. Such reactions are
inhibited by:inhibited by:
ImpuritiesImpurities: - an impurity can react with the activated initiator: - an impurity can react with the activated initiator
or with an activated growing chain to prevent furtheror with an activated growing chain to prevent further
growth.growth.
• For example: the addition of small amount of commonFor example: the addition of small amount of common
inhibitor such as hydroquinone to monomer inhibitsinhibitor such as hydroquinone to monomer inhibits
spontaneous polymerization if no initiator is present, andspontaneous polymerization if no initiator is present, and
retards the polymerization in the presence of an initiator.retards the polymerization in the presence of an initiator.
– Oxygen: reacts rapidly with free radicals, and its presenceOxygen: reacts rapidly with free radicals, and its presence
retards the polymerization reaction.retards the polymerization reaction.

Step growth polymerizationStep growth polymerization
- It is a process in which polymerization is accompanied by- It is a process in which polymerization is accompanied by
repeated elimination of small molecules. The primaryrepeated elimination of small molecules. The primary
compounds react often with the formation of by products suchcompounds react often with the formation of by products such
as water, alcohols, halogen acids and ammonia. The formationas water, alcohols, halogen acids and ammonia. The formation
of these by products is the reason step growth polymerizationof these by products is the reason step growth polymerization
is called condensation polymerization.is called condensation polymerization.
- In step growth polymerization, a linear chain- In step growth polymerization, a linear chain
of repeated mer units is obtained by the step wise interof repeated mer units is obtained by the step wise inter
molecular condensation or addition of reactive groups inmolecular condensation or addition of reactive groups in
which bi functional or tri functional monomers are allwhich bi functional or tri functional monomers are all
simultaneously activated, as opposed the activation of onesimultaneously activated, as opposed the activation of one
monomer at a time in chain growth addition polymerization.monomer at a time in chain growth addition polymerization.

CopolymersCopolymers
• Polymer chains, which contain two or more different type ofPolymer chains, which contain two or more different type of
monomeric units, are called copolymers. In order to improvemonomeric units, are called copolymers. In order to improve
physical properties it is often advantageous to use two or morephysical properties it is often advantageous to use two or more
chemically different monomers as starting materials. Thus thechemically different monomers as starting materials. Thus the
polymer found may contain units of all the monomerspolymer found may contain units of all the monomers
originally present.originally present.
Types:-Types:-
• Alternating copolymers:Alternating copolymers: In alternating copolymers differentIn alternating copolymers different
mers are alternatively distributed along the polymer chain.mers are alternatively distributed along the polymer chain.
• Random:Random: type of copolymer the different mers are randomlytype of copolymer the different mers are randomly
distributed along the chain such as.distributed along the chain such as.
• Block typeBlock type: Here identical monomeric units occur in relatively: Here identical monomeric units occur in relatively
long sequences along main polymer chain.long sequences along main polymer chain.
• Graft typeGraft type: Here sequences of one of the monomers area: Here sequences of one of the monomers area
grafted onto the backbone of second monomer species.grafted onto the backbone of second monomer species.

Heat Activated Denture base resins:Heat Activated Denture base resins:
CompositionComposition
PowderPowder
Polymethyl methacrylatePolymethyl methacrylate
Benzyl peroxide (initiator)Benzyl peroxide (initiator)
Zinc or titanium oxide (opacifier)Zinc or titanium oxide (opacifier)
Dibutyl phthalate (plasticizer)Dibutyl phthalate (plasticizer)
Compounds of mercury sulfide, cadmium sulfide (Dyes)Compounds of mercury sulfide, cadmium sulfide (Dyes)
LiquidLiquid
Non-polymerized methyl methacrylateNon-polymerized methyl methacrylate
Hydroquinone (inhibitor)Hydroquinone (inhibitor)
Glycol dimethacrylate (Cross linking agent)Glycol dimethacrylate (Cross linking agent)
Dibutyl phthalate (plasticizer)Dibutyl phthalate (plasticizer)
The accepted polymer – monomer ratio is 3:1 by volume (or) 2:1 byThe accepted polymer – monomer ratio is 3:1 by volume (or) 2:1 by
weight.weight.

Physical stagesPhysical stages;;
1.1.Sandy stageSandy stage: Little or no interaction occurs on a molecular: Little or no interaction occurs on a molecular
level. Consistency of mixture may be described as “course” orlevel. Consistency of mixture may be described as “course” or
“grainy”.“grainy”.
2.2.Stringy stageStringy stage: During this stage monomer attacks the surface: During this stage monomer attacks the surface
of individual polymer beads.of individual polymer beads.
This stage is characterized by stringiness or stickiness when theThis stage is characterized by stringiness or stickiness when the
material is touched or drawn apart.material is touched or drawn apart.
3.3.Dough like stageDough like stage: At molecular level increased no. of polymer: At molecular level increased no. of polymer
chains enter solution. Hence a sea of monomer and dissolvedchains enter solution. Hence a sea of monomer and dissolved
polymer. Clinically the mass behaves as pliable dough. It is nopolymer. Clinically the mass behaves as pliable dough. It is no
longer tacky and does not adhere to surface of mixing vessellonger tacky and does not adhere to surface of mixing vessel
or spatula. The mass is packed into mold at their stage.or spatula. The mass is packed into mold at their stage.
4.4.Rubbery stageRubbery stage: The monomer disappears by further: The monomer disappears by further
penetration into the polymer and evaporation. The mass ispenetration into the polymer and evaporation. The mass is
cohesive rubber like non-plastic and cannot be molded.cohesive rubber like non-plastic and cannot be molded.
5.5. Stiff stageStiff stage: upon standing for an extended period, the mixture: upon standing for an extended period, the mixture
becomes stiff. This may be attributed to the evaporation ofbecomes stiff. This may be attributed to the evaporation of
monomer.monomer. www.indiandentalacademy.comwww.indiandentalacademy.com

Technical considerationsTechnical considerations
Compression molding techniquesCompression molding techniques
Injection molding techniquesInjection molding techniques

Polymerization cyclesPolymerization cycles
• The recommended curing cycles are: -The recommended curing cycles are: -
– One technique involves processing the denture bone resinOne technique involves processing the denture bone resin
in a constant temperature water bath at 740C for 8 hrs orin a constant temperature water bath at 740C for 8 hrs or
longer with not terminal boiling temperature.longer with not terminal boiling temperature.
– A second technique consists of processing in a 740C waterA second technique consists of processing in a 740C water
bath for 8 hrs and then increasing the temperature to 1000Cbath for 8 hrs and then increasing the temperature to 1000C
for 1 hr.for 1 hr.
– A third technique involves processing the resin at 740C forA third technique involves processing the resin at 740C for
2 hrs and then increasing temperature of water bath to2 hrs and then increasing temperature of water bath to
1000C and processing for 1 hr.1000C and processing for 1 hr.

Polymerization Via microwave energy:-Polymerization Via microwave energy:-
Poly methyl methacrylate resin can also be polymerizedPoly methyl methacrylate resin can also be polymerized
using microwave energy. This technique employs a speciallyusing microwave energy. This technique employs a specially
formulated resin and a non metallic flask. A conventionalformulated resin and a non metallic flask. A conventional
microwave oven is used to supply the thermal energy requiredmicrowave oven is used to supply the thermal energy required
for polymerization.for polymerization.
Major advantage of this technique is speed with whichMajor advantage of this technique is speed with which
polymerization is accomplished.polymerization is accomplished.
The physical properties and fit of microwave resins areThe physical properties and fit of microwave resins are
comparable to conventional resins.comparable to conventional resins.

Chemically activated denture base resinsChemically activated denture base resins
compositioncomposition
LIQUIDLIQUID
• Methyl metha acrylateMethyl metha acrylate
• Dimethyl-p-toulidineDimethyl-p-toulidine
• Dibutyl phthalateDibutyl phthalate
• Glycol dimethaacrylateGlycol dimethaacrylate
• hydroquinonehydroquinone
POWDERPOWDER
• Poly methyl metha acrylatePoly methyl metha acrylate
• Other co polymersOther co polymers
• Benzoyl peroxideBenzoyl peroxide
• Mercury sulfateMercury sulfate
• Cadmium sulfateCadmium sulfate
• Dyed organic fillers andDyed organic fillers and
inorganic particles.inorganic particles.

• The degree of polymerization achieved using chemicallyThe degree of polymerization achieved using chemically
activated resins is not as complete as that achieved using heatactivated resins is not as complete as that achieved using heat
activated systems. This indicates that there is great amount ofactivated systems. This indicates that there is great amount of
unreacted monomer in denture bases fabricated via chemicalunreacted monomer in denture bases fabricated via chemical
activation. This unreacted monomer creates two majoractivation. This unreacted monomer creates two major
difficulties. First it acts as a plasticizer those results indifficulties. First it acts as a plasticizer those results in
decreased transverse strength of denture resin. Second thedecreased transverse strength of denture resin. Second the
residual monomer serves as a potential tissue irritant therebyresidual monomer serves as a potential tissue irritant thereby
compromising biocompatibility of denture bases. Fromcompromising biocompatibility of denture bases. From
physical standpoint, chemically activated resins displayphysical standpoint, chemically activated resins display
slightly less shrinkage than heat activated counter parts. Thisslightly less shrinkage than heat activated counter parts. This
imparts greater dimensional accuracy to chemically activatedimparts greater dimensional accuracy to chemically activated
resins. The color stability of chemically activated resinsresins. The color stability of chemically activated resins
generally is inferior to the color stability of heat-activatedgenerally is inferior to the color stability of heat-activated
resins. This property is related to presence of tertiary aminesresins. This property is related to presence of tertiary amines
within the chemically activated resins.within the chemically activated resins.

Technical considerations:Technical considerations:
• Chemically activated denture base resins are most often moldedChemically activated denture base resins are most often molded
using compression techniques. Therefore the mold preparation andusing compression techniques. Therefore the mold preparation and
resin packing are essentially the same as for heat activated dentureresin packing are essentially the same as for heat activated denture
resins.resins.
• Polymer and monomer are mixed according to manufacturesPolymer and monomer are mixed according to manufactures
directions and permitted to attain dough like consistency. Thedirections and permitted to attain dough like consistency. The
working time for chemically activated resins is shorter than forworking time for chemically activated resins is shorter than for
heat-activated materials. Therefore special attention must be paidheat-activated materials. Therefore special attention must be paid
for consistency of material and rate of polymerization.for consistency of material and rate of polymerization.
• A lengthy initiation period is desirable, since this providesA lengthy initiation period is desirable, since this provides
adequate time for trial closure. One method form prolongingadequate time for trial closure. One method form prolonging
initiation period is to decreases the temperature of resin mass.initiation period is to decreases the temperature of resin mass.
This may be accomplished by refrigerating the liquid componentThis may be accomplished by refrigerating the liquid component
and/ or mixing vessel before the mixing process. When theand/ or mixing vessel before the mixing process. When the
powder and liquid are mixed the rate of polymerization processpowder and liquid are mixed the rate of polymerization process
decreases. As a result the resin mass remains in dough stage for adecreases. As a result the resin mass remains in dough stage for a
extended period and the working tune is increased.extended period and the working tune is increased.
• Mold preparation and resin packing are accomplished in the sameMold preparation and resin packing are accomplished in the same
manner as described for heat-activated resins.manner as described for heat-activated resins.

Processing considerationsProcessing considerations
• Following final closure of the denture flask, pressure must beFollowing final closure of the denture flask, pressure must be
maintained throughout the polymerization process. Initialmaintained throughout the polymerization process. Initial
hardening of resin will occur within 30 min of final flaskhardening of resin will occur within 30 min of final flask
closure. However it is doubtful that polymerization isclosure. However it is doubtful that polymerization is
complete at this point. To ensure complete polymerization thecomplete at this point. To ensure complete polymerization the
flask should be held under pressure for a min of 3 hrs.flask should be held under pressure for a min of 3 hrs.
• Resins polymerized via chemically activation generallyResins polymerized via chemically activation generally
display 3% to 5% free monomer, whereas heat activated resinsdisplay 3% to 5% free monomer, whereas heat activated resins
exhibit 0.2% to 0.5% free monomer.exhibit 0.2% to 0.5% free monomer.

Fluid resin techniques:-Fluid resin techniques:-
• These technique employees a pourable, chemically activatedThese technique employees a pourable, chemically activated
resin for the fabrication of denture bases. The chemicalresin for the fabrication of denture bases. The chemical
composition is similar to auto polymerized resins. Thecomposition is similar to auto polymerized resins. The
principal difference is that the pour type of denture base resinsprincipal difference is that the pour type of denture base resins
has higher molecular weight powder particles that are muchhas higher molecular weight powder particles that are much
smaller and when they are mixed with monomer the resultantsmaller and when they are mixed with monomer the resultant
mix is very fluid. Therefore referred to as fluid resins. Theymix is very fluid. Therefore referred to as fluid resins. They
are used with a significantly lower powder-liquid ratio, whichare used with a significantly lower powder-liquid ratio, which
ranges from 2:1 to 2:5:1.ranges from 2:1 to 2:5:1.

AdvantagesAdvantages
• Improved adaptation to underlying soft tissuesImproved adaptation to underlying soft tissues
• Decreased probability of damage to prosthetic teeth andDecreased probability of damage to prosthetic teeth and
denture bases during deflaskingdenture bases during deflasking
• Reduced material costReduced material cost
• Simplification of flasking, deflasking and finishing proceduresSimplification of flasking, deflasking and finishing procedures
• DisadvantagesDisadvantages
• Noticeable shift of prosthetic teeth during processingNoticeable shift of prosthetic teeth during processing
• Air entrapment within the denture base materialAir entrapment within the denture base material
• Poor bonding between denture base material and acrylic resinPoor bonding between denture base material and acrylic resin
teethteeth
• Technique sensitiveTechnique sensitive

Light activated denture base resins:Light activated denture base resins:
• This denture base materials consists of urethane dimethacrylateThis denture base materials consists of urethane dimethacrylate
matrix, microfine silica, and higher molecular weight acrylicmatrix, microfine silica, and higher molecular weight acrylic
monomers. Acrylic resin beads are included as organic fillers.monomers. Acrylic resin beads are included as organic fillers.
Visible light is activator whereas camphoroquinone serves as theVisible light is activator whereas camphoroquinone serves as the
initiator of polymerization.initiator of polymerization.
• The single component denture base resin is supplied in sheet andThe single component denture base resin is supplied in sheet and
rope forms and is packed in lightproof pouches to preventrope forms and is packed in lightproof pouches to prevent
inadvertent polymerization. Denture base fabrication using a lightinadvertent polymerization. Denture base fabrication using a light
activated resin in significantly different opaque investing mediaactivated resin in significantly different opaque investing media
prevent the passage of light; therefore light activated resins cannotprevent the passage of light; therefore light activated resins cannot
be fabricated in conventional manner. Instead teeth are arranged,be fabricated in conventional manner. Instead teeth are arranged,
and the denture base is molded on an accurate cast. Subsequently,and the denture base is molded on an accurate cast. Subsequently,
the denture base is exposed to high intensity visible light source forthe denture base is exposed to high intensity visible light source for
an appropriate period. Following polymerization the denture base isan appropriate period. Following polymerization the denture base is
removed from cast, finished and polished in conventional manner.removed from cast, finished and polished in conventional manner.

Properties of denture resins:Properties of denture resins:
A.A. Methyl Methacrylate monomer:Methyl Methacrylate monomer:
It is clear, transparent, volatile liquid at roomIt is clear, transparent, volatile liquid at room
temperature. It has a characteristic sweetish odor: -temperature. It has a characteristic sweetish odor: -
The physical properties of monomer areThe physical properties of monomer are
• Melting pointMelting point  480C480C
• Boiling pointBoiling point  100.80C100.80C
• DensityDensity  0.945gm/ ml at 200C0.945gm/ ml at 200C
• Heat of polymerizationHeat of polymerization  12.9 K cal / mol12.9 K cal / mol
• Volume shrinkage during polymerizationVolume shrinkage during polymerization  21%21%

B.B. Poly (methyl methacrylate)Poly (methyl methacrylate)
1.1. Taste and odorTaste and odor::
Completely polymerized acrylic resin is tasteless and odorlessCompletely polymerized acrylic resin is tasteless and odorless
2.2. EstheticsEsthetics::
It is a clear transparent resin, which can be pigmented easily toIt is a clear transparent resin, which can be pigmented easily to
duplicate oral tissues. It is also compatible with dyed synthetic fillers.duplicate oral tissues. It is also compatible with dyed synthetic fillers.
3.3. DensityDensity::
Polymer has a density of 1.19 gm/cm3.Polymer has a density of 1.19 gm/cm3.
2.2. Compressive and tensile strengthCompressive and tensile strength::
These materials are typically low in strength. However they haveThese materials are typically low in strength. However they have
adequate compressive and tensile strength for complete or partialadequate compressive and tensile strength for complete or partial
denture application.denture application.
3.3. Transverse strengthTransverse strength::
Measurements are used to a greater extent than either tensile (or)Measurements are used to a greater extent than either tensile (or)
compressive strength, because the test more closely represents thecompressive strength, because the test more closely represents the
type of loading in vivo. Under clinical conditions, heat curetype of loading in vivo. Under clinical conditions, heat cure
polymethyl methacrylate is stiff enough not to flex unduly duringpolymethyl methacrylate is stiff enough not to flex unduly during
function and recovers well from this degree of bending.function and recovers well from this degree of bending.www.indiandentalacademy.comwww.indiandentalacademy.com

4)4) Impact strength:Impact strength:
The impact strength of polyvinyl acrylic is about twice that ofThe impact strength of polyvinyl acrylic is about twice that of
poly (methyl methacrylate). Addition of plasticizers may increase thepoly (methyl methacrylate). Addition of plasticizers may increase the
impact of plastics.impact of plastics.
5)5) Hardness and abrasion resistance:Hardness and abrasion resistance:
Heat cured acrylic resin: 18-20 KHNHeat cured acrylic resin: 18-20 KHN
Self cured resin: 16-18 KHNSelf cured resin: 16-18 KHN
Cross-linked poly (methyl methacrylate) is only slightly harderCross-linked poly (methyl methacrylate) is only slightly harder
than regular poly (methyl methacrylate). The incorporation of fillersthan regular poly (methyl methacrylate). The incorporation of fillers
may alter resistance to abrasion but the hardness of plastic matrixmay alter resistance to abrasion but the hardness of plastic matrix
remains unchanged.remains unchanged.
6)6) Fatigue strength and fracture toughness:Fatigue strength and fracture toughness:
Acrylic polymers show sensitivity. Over stressing of dentures onAcrylic polymers show sensitivity. Over stressing of dentures on
deflasking must be avoided. Otherwise a small crack may be produceddeflasking must be avoided. Otherwise a small crack may be produced
which will later propagate through the material. Similarly surface of awhich will later propagate through the material. Similarly surface of a
denture must be smoothly polished. In an upper denture stressdenture must be smoothly polished. In an upper denture stress
accumulation during chewing may occur at a point between centralaccumulation during chewing may occur at a point between central
incisors. Here a notch to accommodate labial frenum frequentlyincisors. Here a notch to accommodate labial frenum frequently
weakens the facial flange. Fatigue or midline fracture may occur if theweakens the facial flange. Fatigue or midline fracture may occur if the
masticatory forces are relatively large. Fatigue strength increases withmasticatory forces are relatively large. Fatigue strength increases with
a higher molecular weight and an increase in the plasticizer content.a higher molecular weight and an increase in the plasticizer content.www.indiandentalacademy.comwww.indiandentalacademy.com

7) Modulus of elasticity:7) Modulus of elasticity:
Acrylic resins have sufficient stiffness (modulus of elasticityAcrylic resins have sufficient stiffness (modulus of elasticity
2400 MPa) for use in complete and partial dentures. However when2400 MPa) for use in complete and partial dentures. However when
compared with metal denture bases it is low.compared with metal denture bases it is low.
8) Polymerization shrinkage:8) Polymerization shrinkage:
When methyl methacrylate monomer is polymerized to formWhen methyl methacrylate monomer is polymerized to form
polymethyl methacrylate the density of the mass changes from 0.94 topolymethyl methacrylate the density of the mass changes from 0.94 to
1.19g/cm3. This change in density results in volumetric shrinkage of1.19g/cm3. This change in density results in volumetric shrinkage of
21% when a conventional heat activates resin is mixed at a suggested21% when a conventional heat activates resin is mixed at a suggested
powder: liquid ratio about 1/3rd of resultant mass is liquid.powder: liquid ratio about 1/3rd of resultant mass is liquid.
Consequently the volumetric shrinkage exhibited by polymerizedConsequently the volumetric shrinkage exhibited by polymerized
mass should be approximately 7%.mass should be approximately 7%.
In addition to volumetric shrinkage, linear shrinkage occurs.In addition to volumetric shrinkage, linear shrinkage occurs.
Greater the linear shrinkage greater is the discrepancy observed in theGreater the linear shrinkage greater is the discrepancy observed in the
initial set of dentures. Based on a projected volumetric shrinkage ofinitial set of dentures. Based on a projected volumetric shrinkage of
7% the linear shrinkage exhibited should be 2%. But the observed7% the linear shrinkage exhibited should be 2%. But the observed
linear shrinkage is less then 1%linear shrinkage is less then 1%
Processing shrinkage has been measured as 0.26% for aProcessing shrinkage has been measured as 0.26% for a
representative chemically activated resin, compared with 0.53% for arepresentative chemically activated resin, compared with 0.53% for a
representative heat activated resins.representative heat activated resins.www.indiandentalacademy.comwww.indiandentalacademy.com

Porosity may be:Porosity may be:
• Internal porosityInternal porosity
• External porosityExternal porosity
Internal porosity:Internal porosity: is in the form of void or bubbles within the massis in the form of void or bubbles within the mass
of polymerized acrylic. It is confined to thicker portion of theof polymerized acrylic. It is confined to thicker portion of the
denture. Such porosity results from vaporization of unreacteddenture. Such porosity results from vaporization of unreacted
monomers and low molecular wt polymers, when the temperature ofmonomers and low molecular wt polymers, when the temperature of
a resin surpasses the boiling point of these species. In the center ofa resin surpasses the boiling point of these species. In the center of
the thick portion the heat cannot be conducted away therefore thethe thick portion the heat cannot be conducted away therefore the
temperature on the thicker portions may rise above the boiling pointtemperature on the thicker portions may rise above the boiling point
of monomer.of monomer.
Internal porosity can be avoided by using long and low temperatureInternal porosity can be avoided by using long and low temperature
occurring cycles.occurring cycles.
External porosity:External porosity: can occur due to two reasons:can occur due to two reasons:
• Lack of homogeneityLack of homogeneity
• Lack of adequate pressureLack of adequate pressure
It can be avoided by using proper powder liquid ratio and mixingIt can be avoided by using proper powder liquid ratio and mixing
it well. The mix is more homogenous in dough stage so packingit well. The mix is more homogenous in dough stage so packing
should be done in dough stage.should be done in dough stage.

SolubilitySolubility
The denture base resins are soluble in a variety of solvents.The denture base resins are soluble in a variety of solvents.
They are soluble in ketones, esters and aromatic chlorinatedThey are soluble in ketones, esters and aromatic chlorinated
hydrocarbons. Alcohol causes crazing in some resins. A smallhydrocarbons. Alcohol causes crazing in some resins. A small
amount of monomer may be leached out when stored in water.amount of monomer may be leached out when stored in water.
The acrylic resins are virtually insoluble in fluids commonlyThe acrylic resins are virtually insoluble in fluids commonly
encountered in oral cavity. The solubility of resins is low. Theencountered in oral cavity. The solubility of resins is low. The
degree of solubility did not seem to affect the clinicaldegree of solubility did not seem to affect the clinical
performance of dentures.performance of dentures.

Crazing:Crazing:
Crazing is formation of surface cracks on the denture baseCrazing is formation of surface cracks on the denture base
resins. These cracks may be microscopic or macroscopic inresins. These cracks may be microscopic or macroscopic in
size. In some cases it has a hazy (or) foggy appearance rathersize. In some cases it has a hazy (or) foggy appearance rather
than cracks. In tinted resin, crazing imparts a whitishthan cracks. In tinted resin, crazing imparts a whitish
appearance. In addition surface cracks predispose a dentureappearance. In addition surface cracks predispose a denture
resin to fracture.resin to fracture.
From physical standpoint, crazing may result from stressFrom physical standpoint, crazing may result from stress
application or partial dissolution of a resin, for example attackapplication or partial dissolution of a resin, for example attack
by a solvent. Tensile stresses are most often responsible forby a solvent. Tensile stresses are most often responsible for
crazing in denture application. It is believed that crazing iscrazing in denture application. It is believed that crazing is
produced by mechanical separation of individual polymerproduced by mechanical separation of individual polymer
chains that occur on application of tensile stresses. Crazingchains that occur on application of tensile stresses. Crazing
generally begins on the surface of a resin and is oriented atgenerally begins on the surface of a resin and is oriented at
right angles to tensile forces. Micro cracks formed in thisright angles to tensile forces. Micro cracks formed in this
manner subsequently progress internally.manner subsequently progress internally.
Micro cracks or grazing produced as a result of solventMicro cracks or grazing produced as a result of solvent
action are oriented randomly. Solvent induced crazingaction are oriented randomly. Solvent induced crazing
generally results from prolonged contact with liquids such asgenerally results from prolonged contact with liquids such as
ethyl alcohol.ethyl alcohol.

Creep:Creep:
Denture resins display viscoelastic behavior. In otherDenture resins display viscoelastic behavior. In other
words, these materials act as rubbery solids that recover elasticwords, these materials act as rubbery solids that recover elastic
deformation over time once the stresses induced in the resindeformation over time once the stresses induced in the resin
have been eliminated. When a denture base resin is subjectedhave been eliminated. When a denture base resin is subjected
to a sustained load the material exhibits an initial deflection orto a sustained load the material exhibits an initial deflection or
deformation. If this load is not removed, additional plasticdeformation. If this load is not removed, additional plastic
deformation may occur over time. This additional deformationdeformation may occur over time. This additional deformation
is termed creep. The rate at which this progressiveis termed creep. The rate at which this progressive
deformation occurs is termed creep rate. This rate may bedeformation occurs is termed creep rate. This rate may be
elevated by increasing in temperature, applied load, residualelevated by increasing in temperature, applied load, residual
monomer, and presence of plasticizer. Although creep rates formonomer, and presence of plasticizer. Although creep rates for
heat activated and chemically activated resins are similar atheat activated and chemically activated resins are similar at
low stresses, creep rates for chemically activated resinslow stresses, creep rates for chemically activated resins
increases more rapidly as stress are raised.increases more rapidly as stress are raised.

Repair resins:Repair resins:
Repair materials are usually acrylic plastics of powder liquidRepair materials are usually acrylic plastics of powder liquid
types similar to those used for denture base, and are usually eithertypes similar to those used for denture base, and are usually either
heat cured (or) chemically cured. Light activated acrylic has alsoheat cured (or) chemically cured. Light activated acrylic has also
been shown to be fast and effected repair materials.been shown to be fast and effected repair materials.
One technique for making a repair requires holding orOne technique for making a repair requires holding or
luting the broken pieces together with sticky wax, pouring theluting the broken pieces together with sticky wax, pouring the
stone model on inside of the denture and investing the model andstone model on inside of the denture and investing the model and
denture in flask.denture in flask.
If a heat activated acrylic is used, the denture should beIf a heat activated acrylic is used, the denture should be
completely flasked and curing should be carried out at acompletely flasked and curing should be carried out at a
temperature no greater then 740c to 770c for 8hrs or longer.temperature no greater then 740c to 770c for 8hrs or longer.
The use of chemically activated and light activated resinsThe use of chemically activated and light activated resins
for repair does not require flasking. The procedure is rapid. Thefor repair does not require flasking. The procedure is rapid. The
dimensional accuracy is maintained because not enough heat isdimensional accuracy is maintained because not enough heat is
present during polymerization to cause warpage from release ofpresent during polymerization to cause warpage from release of
stresses. The chemically activated resins however have astresses. The chemically activated resins however have a
disadvantage of having a lower transverse strength.disadvantage of having a lower transverse strength.www.indiandentalacademy.comwww.indiandentalacademy.com

RELININGRELINING
For relining a low polymerization temperature is desirable toFor relining a low polymerization temperature is desirable to
minimize distortion of the remaining denture base. Hence, aminimize distortion of the remaining denture base. Hence, a
chemically activated resin is usually chosen. The selected material ischemically activated resin is usually chosen. The selected material is
mixed according to manufacturer’s recommendation, placed in themixed according to manufacturer’s recommendation, placed in the
mould, compressed, and permitted to polymerize. In turn, the denturemould, compressed, and permitted to polymerize. In turn, the denture
is recovered, finished and polished.is recovered, finished and polished.
Relining also may be accomplished using resins that areRelining also may be accomplished using resins that are
activated by heat, light and microwave energy. In all these instancesactivated by heat, light and microwave energy. In all these instances
significant heat may be generated, and distortions of existing denturesignificant heat may be generated, and distortions of existing denture
base is more likely.base is more likely.
Some relining materials are marketed for home use.Some relining materials are marketed for home use.
Unfortunately majority of patients do not posses adequate knowledgeUnfortunately majority of patients do not posses adequate knowledge
to manipulate these materials adequately and correctly. As a result theto manipulate these materials adequately and correctly. As a result the
use of such products may result in irreparable damage to oral tissues.use of such products may result in irreparable damage to oral tissues.
The purchase and use of such products should be discouraged.The purchase and use of such products should be discouraged.

Rebasing resin dentures:Rebasing resin dentures:
The steps required in denture rebasing are very similar to thoseThe steps required in denture rebasing are very similar to those
described for relining. An accurate impression of soft tissue isdescribed for relining. An accurate impression of soft tissue is
obtained using existing dentures as custom tray. Subsequently aobtained using existing dentures as custom tray. Subsequently a
stone cast is fabricated in the impression. The cast and the denturesstone cast is fabricated in the impression. The cast and the dentures
are mounted in a device designed to maintain the correct verticalare mounted in a device designed to maintain the correct vertical
and horizontal relationship between stone cast and the surface ofand horizontal relationship between stone cast and the surface of
prosthetic teeth. The resultant assembly provides indices for theprosthetic teeth. The resultant assembly provides indices for the
occlusal surface of prosthetic teeth after the indices have beenocclusal surface of prosthetic teeth after the indices have been
established, the denture is removed and the teeth are separated formestablished, the denture is removed and the teeth are separated form
the existing denture base. The teeth are repositioned in theirthe existing denture base. The teeth are repositioned in their
respective indices and held in their original relationship to the castrespective indices and held in their original relationship to the cast
while they are waxed to the desired formed. The completed toothwhile they are waxed to the desired formed. The completed tooth
arrangement is sealed to the cast, and assembly is invested asarrangement is sealed to the cast, and assembly is invested as
previously described. . Following elimination of the wax andpreviously described. . Following elimination of the wax and
removal of the base plate resins is introduced into the mould cavity.removal of the base plate resins is introduced into the mould cavity.
The material is subsequently processed. Consequently theThe material is subsequently processed. Consequently the
prostheses consist of a new denture base in conjuncture with teethprostheses consist of a new denture base in conjuncture with teeth
from patient’s previous denture.from patient’s previous denture.www.indiandentalacademy.comwww.indiandentalacademy.com

Soft lining materials:Soft lining materials:
A soft (resilient) lining material may be defined as a softA soft (resilient) lining material may be defined as a soft
elastic and resilient material forming all or part of the fittingelastic and resilient material forming all or part of the fitting
(impression) surface of a denture. It usually acts as a cushion(impression) surface of a denture. It usually acts as a cushion
between the hard denture base and tissues to reduce the masticatorybetween the hard denture base and tissues to reduce the masticatory
forces transmitted by prosthesis to underlying tissues.forces transmitted by prosthesis to underlying tissues.
The earliest soft lining material recorded (soft rubber) wasThe earliest soft lining material recorded (soft rubber) was
used by Twitchell in 1869.No others are mentioned until 1940,whenused by Twitchell in 1869.No others are mentioned until 1940,when
a soft natural rubber known as “velum” was used with vulcanite.a soft natural rubber known as “velum” was used with vulcanite.
However this material had high water absorption, and it became foulHowever this material had high water absorption, and it became foul
and ill fitting after a period of time. One of the first synthetic resinsand ill fitting after a period of time. One of the first synthetic resins
used as soft lining material was poly (vinyl chloride), with which aused as soft lining material was poly (vinyl chloride), with which a
plasticizer was necessary. In 1945 Mathews used poly (vinylplasticizer was necessary. In 1945 Mathews used poly (vinyl
chloride), powder with a liquid di-n-butyl phthalate plasticizer as achloride), powder with a liquid di-n-butyl phthalate plasticizer as a
soft liner. This material hardened in a short period of time becausesoft liner. This material hardened in a short period of time because
the plasticizer leached out. Dioctyl phthalate was considered a betterthe plasticizer leached out. Dioctyl phthalate was considered a better
plasticizer for poly (vinyl chloride) because the lining remained softplasticizer for poly (vinyl chloride) because the lining remained soft
longer.Silicone rubber materials based on poly (dimethyl siloxane)longer.Silicone rubber materials based on poly (dimethyl siloxane)
have been used as soft liners since 1958.have been used as soft liners since 1958.

Resins as Maxillofacial materialsResins as Maxillofacial materials
Poly (methyl methacrylate) was once commonly used forPoly (methyl methacrylate) was once commonly used for
maxillofacial prostheses, and is still used occasionally to makemaxillofacial prostheses, and is still used occasionally to make
artificial facial parts. The main disadvantages are that the acrylic isartificial facial parts. The main disadvantages are that the acrylic is
hard and heavy and does not have the feel of skin.hard and heavy and does not have the feel of skin.
Vinyl plastisols (plasticized vinyl resins) sometimes are used inVinyl plastisols (plasticized vinyl resins) sometimes are used in
maxillofacial applications. Plastisols are thick liquids composed ofmaxillofacial applications. Plastisols are thick liquids composed of
small vinyl particles dispersed in plasticizers. Colorants are added tosmall vinyl particles dispersed in plasticizers. Colorants are added to
these materials to match individual skin tones. Major disadvantage ofthese materials to match individual skin tones. Major disadvantage of
these materials is that they harden with age as a resultant of plasticizerthese materials is that they harden with age as a resultant of plasticizer
migration U.V light also has as adverse effect on these materials. Formigration U.V light also has as adverse effect on these materials. For
these reasons use of vinyl plastisols is limited.these reasons use of vinyl plastisols is limited.
Polyurethane polymers are the most recent addition to materialsPolyurethane polymers are the most recent addition to materials
used in maxillofacial prosthesis. The material is placed in stone orused in maxillofacial prosthesis. The material is placed in stone or
metal mold and allowed to polymerize at room temperature althoughmetal mold and allowed to polymerize at room temperature although
polyurethane prosthesis has a natural feel and appearance it ispolyurethane prosthesis has a natural feel and appearance it is
susceptible to rapid deteriorationsusceptible to rapid deterioration

Temporary crown and bridge resins:-Temporary crown and bridge resins:-
Are used to provide temporary coverage following toothAre used to provide temporary coverage following tooth
preparation for crown and bridges. Chemically activated plastics havepreparation for crown and bridges. Chemically activated plastics have
become popular as temporary restorations. They have decreased thebecome popular as temporary restorations. They have decreased the
use of polycarbonate crowns and aluminum shell.use of polycarbonate crowns and aluminum shell.
Disadvantages of Resins used as temporary crown and bridgeDisadvantages of Resins used as temporary crown and bridge
material;material;
Heat generated during polymerization is harmful to the teethHeat generated during polymerization is harmful to the teeth
Marginal opening can be caused by polymerization shrinkageMarginal opening can be caused by polymerization shrinkage
Allergic reaction seen may be due to monomer componentAllergic reaction seen may be due to monomer component

Occlusal splintsOcclusal splints
Occlusal splints are used in the treatment of patients withOcclusal splints are used in the treatment of patients with
temporomandibular joint pain or excessive bruxism. Thesetemporomandibular joint pain or excessive bruxism. These
splints are made by the same technique used for dentures. Thesplints are made by the same technique used for dentures. The
splint is waxed on a model of the patient’s teeth, usually thesplint is waxed on a model of the patient’s teeth, usually the
maxilla. The model and wax pattern are invested in a denturemaxilla. The model and wax pattern are invested in a denture
flask and the wax is boiled out. After cooling separating mediaflask and the wax is boiled out. After cooling separating media
is painted on the mold and allowed to dry. A clear heatis painted on the mold and allowed to dry. A clear heat
accelerated (activated) acrylic resin is packed into the moldaccelerated (activated) acrylic resin is packed into the mold
and processed. Chemically activated acrylic resin is also usedand processed. Chemically activated acrylic resin is also used
but less often. The properties of acrylic splints are similar tobut less often. The properties of acrylic splints are similar to
those of heat activated acrylic materials .those of heat activated acrylic materials .

Inlay patternsInlay patterns
Chemically accelerated acrylic is used to fabricate inlayChemically accelerated acrylic is used to fabricate inlay
patterns are direct post and cores. Commercial products arepatterns are direct post and cores. Commercial products are
brightly pigmented and have good dimensional stability. Thebrightly pigmented and have good dimensional stability. The
pattern is made by painting the powder – liquid onto the die orpattern is made by painting the powder – liquid onto the die or
tooth in layers and allowing it to polymerized. Aftertooth in layers and allowing it to polymerized. After
polymerization the pattern can be modified with stones andpolymerization the pattern can be modified with stones and
burs. If necessary inlay wax may be added to complete theburs. If necessary inlay wax may be added to complete the
patterns. Considerably larger burnout times must be used withpatterns. Considerably larger burnout times must be used with
acrylic pattern.acrylic pattern.

Polymers used as ImplantsPolymers used as Implants
Polymeric implants in the form of poly methyl methacrylate andPolymeric implants in the form of poly methyl methacrylate and
polytetra fluoro ethylene were first used in 1930s. The lowpolytetra fluoro ethylene were first used in 1930s. The low
mechanical strength of the polymers has precluded their use asmechanical strength of the polymers has precluded their use as
implant materials because of their susceptibility for mechanicalimplant materials because of their susceptibility for mechanical
fracture during function. Also the physical properties of thefracture during function. Also the physical properties of the
polymers are greatly influenced by changes in temperature,polymers are greatly influenced by changes in temperature,
environment and composition and their sterilization can beenvironment and composition and their sterilization can be
accomplished only by gamma irradiation or exposure to ethyleneaccomplished only by gamma irradiation or exposure to ethylene
oxide gas. Contamination of these polymers is another disadvantage,oxide gas. Contamination of these polymers is another disadvantage,
because electrostatic charges often attract dust and other impuritiesbecause electrostatic charges often attract dust and other impurities
from the environment.from the environment.
During the mid 1940’s methyl methacrylate was used forDuring the mid 1940’s methyl methacrylate was used for
temporary acrylic implants to preserve the dissected space to receivetemporary acrylic implants to preserve the dissected space to receive
a co-cr implant at a later time.a co-cr implant at a later time.

The use of polymers for osseointegrated implants is nowThe use of polymers for osseointegrated implants is now
confined to components. The intra mobile zirconia (IMZ)confined to components. The intra mobile zirconia (IMZ)
implants are either titanium plasma sprayed or HA – coatedimplants are either titanium plasma sprayed or HA – coated
(hydroxyapatite) and incorporate a polyoxymethylene (POM)(hydroxyapatite) and incorporate a polyoxymethylene (POM)
intra mobile element. The IME is placed between prosthesisintra mobile element. The IME is placed between prosthesis
and implant body to initiate mobility, stress relief, and shockand implant body to initiate mobility, stress relief, and shock
absorption capability to mimic that of natural tooth. Whenabsorption capability to mimic that of natural tooth. When
incorporated into the IMZ implant, the IME initiates theincorporated into the IMZ implant, the IME initiates the
biomechanical function of the natural tooth unit, periodontalbiomechanical function of the natural tooth unit, periodontal
ligament and alveolar bone.ligament and alveolar bone.

Resin CementsResin Cements
The composition of most current resin cements is similar to that ofThe composition of most current resin cements is similar to that of
resin-based composite filling materials that is a resin matrix withresin-based composite filling materials that is a resin matrix with
silane treated inorganic fillers. The fillers are those used insilane treated inorganic fillers. The fillers are those used in
composites, that is silica or glass particles and / or colloidal silicacomposites, that is silica or glass particles and / or colloidal silica
used in micro filled resins.used in micro filled resins.
Resins cements have become attractive as a luting agent because ofResins cements have become attractive as a luting agent because of
the development of direct filling resins with improved properties.the development of direct filling resins with improved properties.
Chemically activated resin cements are supplied as two componentChemically activated resin cements are supplied as two component
systems, consisting of either powder and liquid or two paste systems..systems, consisting of either powder and liquid or two paste systems..
Light curable cements are single composition systems just as areLight curable cements are single composition systems just as are
the light curable resin based composites. They are indicated forthe light curable resin based composites. They are indicated for
cementation of thin ceramic prosthesis, resin based prosthesis, andcementation of thin ceramic prosthesis, resin based prosthesis, and
direct bonding of ceramic and plastic orthodontic brackets.direct bonding of ceramic and plastic orthodontic brackets.

The dual cure cements are two component systems andThe dual cure cements are two component systems and
require mixing in a manner similar to that used for chemicallyrequire mixing in a manner similar to that used for chemically
activated systems. Chemical activation is very slow andactivated systems. Chemical activation is very slow and
provides extended working time until the cement is exposed toprovides extended working time until the cement is exposed to
curing light, at which point the cement hardens rapidly. It thencuring light, at which point the cement hardens rapidly. It then
continues to gain strength over an extended period because ofcontinues to gain strength over an extended period because of
chemically activated polymerization process. These dual curechemically activated polymerization process. These dual cure
cements should not be used with light transmitting prosthesiscements should not be used with light transmitting prosthesis
thicker than 2.5mm; any thing thicker than 2.5 mm should bethicker than 2.5mm; any thing thicker than 2.5 mm should be
bonded with chemically curable cements.bonded with chemically curable cements.

Resin SealantsResin Sealants
The most common sealants are based on BIS-GMA resinThe most common sealants are based on BIS-GMA resin
and are mainly light cured although some self-cured productsand are mainly light cured although some self-cured products
are still available. The chemistry of BIS-GMA sealants isare still available. The chemistry of BIS-GMA sealants is
same as that of composites. The principle difference is that thesame as that of composites. The principle difference is that the
BIS-GMA sealants must be much more fluid to penetrate intoBIS-GMA sealants must be much more fluid to penetrate into
pits, fissures, and etched areas produced on enamel, whichpits, fissures, and etched areas produced on enamel, which
provide for retention of sealant. Three parts of viscous BIS-provide for retention of sealant. Three parts of viscous BIS-
GMA are mixed with one part of diluent such as methylGMA are mixed with one part of diluent such as methyl
methacrylate or triethylene glycol dimethacrylate to obtain amethacrylate or triethylene glycol dimethacrylate to obtain a
reasonable low viscosity sealant. To provide stiffness to thereasonable low viscosity sealant. To provide stiffness to the
material and improve wear resistance filler particles of fumedmaterial and improve wear resistance filler particles of fumed
silica or silinated inorganic glasses can be added to form lowsilica or silinated inorganic glasses can be added to form low
viscosity composites .viscosity composites .

Light cured sealants:Light cured sealants:
most sealants used today are light cured activated by amost sealants used today are light cured activated by a
diaketone and an aliphatic amine. The sealant is applied to thediaketone and an aliphatic amine. The sealant is applied to the
pit and fissure area with an appropriate applicator andpit and fissure area with an appropriate applicator and
polymerization is accomplished by holding the light source 1polymerization is accomplished by holding the light source 1
to 2 mm from the surface and the sealant is exposed to lightto 2 mm from the surface and the sealant is exposed to light
for 20 seconds. Sealants are applied in then sections such thatfor 20 seconds. Sealants are applied in then sections such that
depth of cure is adequate. The advantage of using light curvedepth of cure is adequate. The advantage of using light curve
sealant is that working time can be completely controlled bysealant is that working time can be completely controlled by
the operator.the operator.

Self cured sealantsSelf cured sealants
The material is supplied as two component system; oneThe material is supplied as two component system; one
component containing BIS-GMA resin and benzoyl peroxidecomponent containing BIS-GMA resin and benzoyl peroxide
initiator and other containing BISGMA resin with 5% organicinitiator and other containing BISGMA resin with 5% organic
amine accelerator. The two components are dispensed onto aamine accelerator. The two components are dispensed onto a
suitable mixing surface and after adequate mixing are appliedsuitable mixing surface and after adequate mixing are applied
directly to the tooth surface.directly to the tooth surface.
The reaction (i.e polymerization reaction) is exothermicThe reaction (i.e polymerization reaction) is exothermic
but the clinical effect is minimal because the material is placebut the clinical effect is minimal because the material is place
in limited bulk. Air inclusion during mixing and insertion canin limited bulk. Air inclusion during mixing and insertion can
be manifested clinically as surface voids, which can discolorbe manifested clinically as surface voids, which can discolor
and retain plaque. To ensure optimum penetration, apply selfand retain plaque. To ensure optimum penetration, apply self
cured sealant quickly after mixing.cured sealant quickly after mixing.

Athletic Mouth protectorAthletic Mouth protector
The use of athletic mouth protector in contact sports hasThe use of athletic mouth protector in contact sports has
increased rapidly; they are routinely used in football, soccer, iceincreased rapidly; they are routinely used in football, soccer, ice
hockey, basketball, wrestling, field hockey, softball and other sports.hockey, basketball, wrestling, field hockey, softball and other sports.
This increase in use is justified by studies that showed that 38% ofThis increase in use is justified by studies that showed that 38% of
participants in sports sustained orofacial injuries and only 15% ofparticipants in sports sustained orofacial injuries and only 15% of
those injured were wearing a mouth protector at the time of injury.those injured were wearing a mouth protector at the time of injury.
Injuries to teeth from trauma caused by athletic activity have involvedInjuries to teeth from trauma caused by athletic activity have involved
pulpits, pulpal necrosis, replacement resorption, internal hemorrhage,pulpits, pulpal necrosis, replacement resorption, internal hemorrhage,
pulp canal obliteration and inflammatory resorption.pulp canal obliteration and inflammatory resorption.
Stock, mouth formed and custom mouth protector are three typesStock, mouth formed and custom mouth protector are three types
available. Custom made mouth protectors are usually vacuum formedavailable. Custom made mouth protectors are usually vacuum formed
from sheets of thermoplastic polymer (vinyl acetate – ethylenefrom sheets of thermoplastic polymer (vinyl acetate – ethylene
copolymers). The advantage of custom made mouth protectors arecopolymers). The advantage of custom made mouth protectors are
;Excellent fit, Comfortable, Ease of speaking, Durability.;Excellent fit, Comfortable, Ease of speaking, Durability.
These qualities are poor for stock protectors and poor to good forThese qualities are poor for stock protectors and poor to good for
mouth formed protector. Inspite of the advantages of custom mademouth formed protector. Inspite of the advantages of custom made
protectors they are not as common as stock or mouth formedprotectors they are not as common as stock or mouth formed
protectors because of high cost.protectors because of high cost.www.indiandentalacademy.comwww.indiandentalacademy.com

Review of literatureReview of literature
Re-enforcement of denturesRe-enforcement of dentures::
Journal of oral Rehabilitation 1999 (26)Journal of oral Rehabilitation 1999 (26)
The material most commonly used for fabrication of completeThe material most commonly used for fabrication of complete
dentures is poly (methylmethacrylate). Despite its popularity indentures is poly (methylmethacrylate). Despite its popularity in
meeting esthetic demands it is still far from ideal in fulfillingmeeting esthetic demands it is still far from ideal in fulfilling
mechanical requirements of prosthesis. The fracture of dentures maymechanical requirements of prosthesis. The fracture of dentures may
be due to mechanical properties of acrylic resin or may be due tobe due to mechanical properties of acrylic resin or may be due to
multiplicity of factors leading to failure of denture base material.multiplicity of factors leading to failure of denture base material.
Generally, there are three routes, which have been investigated toGenerally, there are three routes, which have been investigated to
improve the impact properties of PMMA.improve the impact properties of PMMA.
1. Development of alternative of an alternative material1. Development of alternative of an alternative material
Chemical modification of PMMA such as addition of a rubber graftChemical modification of PMMA such as addition of a rubber graft
copolymercopolymer
Reinforcement of PMMA with carbon fibers, glass fibers and ultraReinforcement of PMMA with carbon fibers, glass fibers and ultra
high modulus polyethylene.high modulus polyethylene.
The various alternatives developed where: polyamides, epoxyThe various alternatives developed where: polyamides, epoxy
reins, polystyrene, vinyl acrylic, rubber graft copolymers andreins, polystyrene, vinyl acrylic, rubber graft copolymers and
polycarbonates and nylon.polycarbonates and nylon.

Chemical modifications of PMMA: The addition of rubberChemical modifications of PMMA: The addition of rubber
produces a resin that consists of a matrix of PMMA within which isproduces a resin that consists of a matrix of PMMA within which is
dispersed interpenetrating network of rubber and PMMA. Adispersed interpenetrating network of rubber and PMMA. A
developed crack will propagate through the PMMA but willdeveloped crack will propagate through the PMMA but will
decelerate at rubber base interface. The objective of rubberdecelerate at rubber base interface. The objective of rubber
reinforced or high impact resin is that they absorb greater amountreinforced or high impact resin is that they absorb greater amount
of energy at a higher strain rate before fracture than the standardof energy at a higher strain rate before fracture than the standard
resins. A problem is that the impact strength is often improved atresins. A problem is that the impact strength is often improved at
the expense of the Young’s modulus producing a denture base withthe expense of the Young’s modulus producing a denture base with
increased impact strength but which is too flexible.increased impact strength but which is too flexible.
The addition of rubber to PMMA as a method of re-The addition of rubber to PMMA as a method of re-
enforcement is to date the most successful and widely accepted andenforcement is to date the most successful and widely accepted and
is alternative to the conventional PMMA resin. However, the highis alternative to the conventional PMMA resin. However, the high
cost of upto 20 times that of conventional resins, restricts by iscost of upto 20 times that of conventional resins, restricts by is
routine use.routine use.

Reinforcement of PMMA resins by carbon fibers increasesReinforcement of PMMA resins by carbon fibers increases
its transverse strength 50% compared to un-reinforced acrylicits transverse strength 50% compared to un-reinforced acrylic
resin specimen. But this method is rarely used due to difficultyresin specimen. But this method is rarely used due to difficulty
in handling characteristics of the fibers and their precisein handling characteristics of the fibers and their precise
placement in resin, problems in polishing, poor esthetics dueplacement in resin, problems in polishing, poor esthetics due
to black color the fibers impart on dentures, potential toxicityto black color the fibers impart on dentures, potential toxicity
of carbon and development of alternative methods ofof carbon and development of alternative methods of
reinforcement.reinforcement.
The incorporation of glass fibers produced an increase inThe incorporation of glass fibers produced an increase in
strength and decrease in fatigue weakening of PMMA resin. Itstrength and decrease in fatigue weakening of PMMA resin. It
decreases density and impact strength.decreases density and impact strength.
The reinforcement of PMMA resin with polyethylene in formThe reinforcement of PMMA resin with polyethylene in form
of woven mat is satisfactory however the fabrication ofof woven mat is satisfactory however the fabrication of
denture by this method is time consuming and prohibits isdenture by this method is time consuming and prohibits is
routine use in dental laboratory.routine use in dental laboratory.

Mechanical properties of new denture resins polymerizedMechanical properties of new denture resins polymerized
by visible light, heat and microwaveby visible light, heat and microwave::
The International Journal of Prosthodontics 1992The International Journal of Prosthodontics 1992
Properties of resins polymerized by visible light, microwaveProperties of resins polymerized by visible light, microwave
energy, using a water bathenergy, using a water bath
Were measured, the new resins were harder and less flexibleWere measured, the new resins were harder and less flexible
and had lower impact strength then did the heat –polymerizedand had lower impact strength then did the heat –polymerized
resin. The light activated urethane dimethacrylate resin wasresin. The light activated urethane dimethacrylate resin was
least flexible. Microwave polymerization improved theleast flexible. Microwave polymerization improved the
modulus of elasticity, decreases the impact strength. Themodulus of elasticity, decreases the impact strength. The
rubber modified resin luconite had the greatest impactrubber modified resin luconite had the greatest impact
strength.strength.

ConclusionConclusion
Resins have been used extensively asResins have been used extensively as
restorative materials in prosthodontics,restorative materials in prosthodontics,
especially the polymethyl methacrylate resinsespecially the polymethyl methacrylate resins
which is used in fabrication of completewhich is used in fabrication of complete
dentures. Though the material is far from idealdentures. Though the material is far from ideal
in fulfilling the mechanical requirements ofin fulfilling the mechanical requirements of
prosthesis, it is the combination of virtues ratherprosthesis, it is the combination of virtues rather
than single desirable property that accounts forthan single desirable property that accounts for
its popularity and usageits popularity and usage

ReferencesReferences
1.Science of dental materials-11th edition1.Science of dental materials-11th edition
2.Dental materials properties and manipulation-11th edition2.Dental materials properties and manipulation-11th edition
3.Anderson’s applied dental materials-John F.McCabe, 6th3.Anderson’s applied dental materials-John F.McCabe, 6th
editionedition
4.Notes on dental materials-E.C.Combe, 6th edition4.Notes on dental materials-E.C.Combe, 6th edition
5. The International Journal of Prosthodontics - Review-Soft5. The International Journal of Prosthodontics - Review-Soft
lining materials in prosthetic dentistrylining materials in prosthetic dentistry
6.Journal of oral rehabilitation- review- The reinforcement of6.Journal of oral rehabilitation- review- The reinforcement of
dentures.dentures.
7. The International Journal of Prosthodontics – Review-7. The International Journal of Prosthodontics – Review-
Mechanical properties of new denture resins polymerizedMechanical properties of new denture resins polymerized
by visible light, heat and microwaveby visible light, heat and microwave

Thank youThank you
For more details please visitFor more details please visit

Denture base resins /orthodontics website

Recomendados

Recomendados

Más contenido relacionado

La actualidad más candente

La actualidad más candente (20)

Destacado

Destacado (9)

Similar a Denture base resins /orthodontics website

Similar a Denture base resins /orthodontics website (20)

Más de Indian dental academy

Más de Indian dental academy (20)

Denture base resins /orthodontics website