Denture base resins are typically made of polymethyl methacrylate (PMMA) and are fabricated using heat- or chemically- activated resins. PMMA denture bases are hard, transparent, and resistant to discoloration. The resins undergo polymerization shrinkage of around 21% as the monomer methyl methacrylate forms chains and evaporates slightly during processing. Proper mixing and compression molding can minimize porosity and achieve adequate polymerization for optimal denture fit and function.

1. Denture Base ResinsDenture Base Resins
By: Dr Neha JainBy: Dr Neha Jain

2. IntroductionIntroduction

3.  Denture baseDenture base – that part of denture which rests– that part of denture which rests
on the soft tissues and to which artificial teethon the soft tissues and to which artificial teeth
are attachedare attached
 Denture base materialDenture base material – any material from– any material from
which denture base can be fabricatedwhich denture base can be fabricated

4. General Classification of MaterialsGeneral Classification of Materials
 Based on material:Based on material:
 Metallic – gold alloys, cr-ni alloys, ti alloys &Metallic – gold alloys, cr-ni alloys, ti alloys &
18-8 st st18-8 st st
 Non metallic – includes resinsNon metallic – includes resins
vulcanite, polycarbonates,vulcanite, polycarbonates,
PMMA (PMMA ( modified & unmodifiedmodified & unmodified ))

5. Metallic denture base
Non metallic denture base

6. Basic chemistryBasic chemistry
 PolymerPolymer is a macromolecule made up ofis a macromolecule made up of
recurring simple structural unitsrecurring simple structural units
 PolymerisationPolymerisation is a process that occursis a process that occurs
through a series of chemical reaction by athrough a series of chemical reaction by a
large number of single molecules “ monomer”large number of single molecules “ monomer”
form a polymerform a polymer

7.  The utility of resins is derived from theirThe utility of resins is derived from their
ability to be formed into complex shapes,ability to be formed into complex shapes,
often by application of heat and pressureoften by application of heat and pressure
 Based on their thermal behavior:Based on their thermal behavior:
1.1. ThermoplasticThermoplastic
2.2. ThermosettingThermosetting

8. PolymerisationPolymerisation
 2 types:2 types:
 AdditionAddition – activated one at a time– activated one at a time
 Condensation or Step growthCondensation or Step growth – components– components
are difunctional, become reactiveare difunctional, become reactive
simultaneously, often but not always produce asimultaneously, often but not always produce a
low molecular weight byproductlow molecular weight byproduct

9. Addition polymerisationAddition polymerisation
 Starts from one active center, adding oneStarts from one active center, adding one
monomer at a time to rapidly form a chainmonomer at a time to rapidly form a chain
 4 stages:4 stages:
1.1. InductionInduction
2.2. PropagationPropagation
3.3. Chain transferChain transfer
4.4. TerminationTermination

10. InductionInduction
It is the period during which initiatorIt is the period during which initiator
molecule becomes energized and breaksmolecule becomes energized and breaks
down into free radical, followed bydown into free radical, followed by
these radicals reacting with monomerthese radicals reacting with monomer
molecules to initiate chain growthmolecules to initiate chain growth

11. Induction: controlled by activationInduction: controlled by activation
initiationinitiation
ActivationActivation InitiationInitiation
Heat benzoyl peroxideHeat benzoyl peroxide
Chemical tertiary amine + BPChemical tertiary amine + BP
Light camphorquinone +Light camphorquinone +
organic amineorganic amine

12. PropagationPropagation
 The resulting free radical monomer complexThe resulting free radical monomer complex
then acts as a new free radical center – addthen acts as a new free radical center – add
successivelysuccessively
 Little energy required – large polmer moleculeLittle energy required – large polmer molecule
is formed within seconds with evolution ofis formed within seconds with evolution of
heatheat

13. Chain transferChain transfer
 Active free radical of a growing chain isActive free radical of a growing chain is
transferred to another molecule or chaintransferred to another molecule or chain
-can result in formation of new growth-can result in formation of new growth
centercenter

14. TerminationTermination
 By either direct coupling of two freeBy either direct coupling of two free
radicals or by exchange of a hydrogenradicals or by exchange of a hydrogen
atom from one growing chain to anotheratom from one growing chain to another

15.  Inhibition of add polymerisation:Inhibition of add polymerisation:
 hydroquinonehydroquinone
 oxygenoxygen
 Control working time and storage stabilityControl working time and storage stability
 0.006% HQ added commercially available0.006% HQ added commercially available
resinsresins

16. Condensation polymerisationCondensation polymerisation
A linear chain of repeating mer units isA linear chain of repeating mer units is
obtained by the step wise intermolecularobtained by the step wise intermolecular
condensation or addition of the reacrivecondensation or addition of the reacrive
groups in whichgroups in which bifunctionalbifunctional oror trifunctionaltrifunctional
monomers are all simultaneously activated asmonomers are all simultaneously activated as
opposed to the activation of one monomer atopposed to the activation of one monomer at
atime in chain growth additionatime in chain growth addition typetype

17. CopolymerisationCopolymerisation
 Polymerisation of two or more chemicallyPolymerisation of two or more chemically
different monomersdifferent monomers
 Each type of monomer with some desirableEach type of monomer with some desirable
property polymerizes to yield a copolymerproperty polymerizes to yield a copolymer
with specific physical propertieswith specific physical properties

18.  In dentistry most resins are based onIn dentistry most resins are based on
methacrylatemethacrylate
1.1. Easy processing, simple techniqueEasy processing, simple technique
2.2. AestheticAesthetic
3.3. EconomicalEconomical

19. Acrylic resinsAcrylic resins
 Derivatives of ethylene and contain a vinylDerivatives of ethylene and contain a vinyl
groupgroup
 Two important acrylic resin series are : acrylicTwo important acrylic resin series are : acrylic
acid & methacrylic acidacid & methacrylic acid
 TheThe estersesters of theseof these polyacidspolyacids are of dentalare of dental
interestinterest

20. Methyl methacrylateMethyl methacrylate
 PMMA by itself is not usedPMMA by itself is not used
 Liquid monomer methyl methacrylate is mixedLiquid monomer methyl methacrylate is mixed
with the powder polymer.with the powder polymer.
 Monomer partially dissolves polymer to formMonomer partially dissolves polymer to form
a plastic dough.a plastic dough.
 Monomer present in dough is polymerized byMonomer present in dough is polymerized by
methods described earlier.methods described earlier.

21.  MMA is a transparent liquid at room temp.MMA is a transparent liquid at room temp.
 Molecular wt. – 100Molecular wt. – 100
 Melting point - -48degreeMelting point - -48degree
 Boiling point – 100.8 degreeBoiling point – 100.8 degree
 Density – 0.945 g/mL at 20 degreeDensity – 0.945 g/mL at 20 degree
 Heat of polymerisation – 12.9 kcal/molHeat of polymerisation – 12.9 kcal/mol
 High vapor pressureHigh vapor pressure

22. PMMAPMMA
 Transparent resinTransparent resin
 Hard – KHN 18-20Hard – KHN 18-20
 Tensile Strength- 60 MPaTensile Strength- 60 MPa
 Density – 1.19 g/sq. cmDensity – 1.19 g/sq. cm
 MOE – 2.4 GPaMOE – 2.4 GPa
 Does not discolorDoes not discolor
 Softens at 125 degreeSoftens at 125 degree
 Absorbs water by imbibitionAbsorbs water by imbibition

23. Composition of Heat activatedComposition of Heat activated
denture base resindenture base resin
Liquid:Liquid:
 Monomer – MMAMonomer – MMA
 Plasticizer – dibutyl phthalatePlasticizer – dibutyl phthalate
 Cross linking agent – ethylene glycolCross linking agent – ethylene glycol
dimethacrylatedimethacrylate
 Inhibitor – hydroquinone (0.006%)Inhibitor – hydroquinone (0.006%)

24. Powder:Powder:
 Polymer – prepolymerised beads of PMMA &Polymer – prepolymerised beads of PMMA &
its copolymers (5%)its copolymers (5%)
 Initiator – benzoyl peroxide (0.5%)Initiator – benzoyl peroxide (0.5%)
 Dyes – mercuric sulphide, cadmium sulphidesDyes – mercuric sulphide, cadmium sulphides
 Opacifiers – zinc or titanium oxideOpacifiers – zinc or titanium oxide
 Organic fillers & inorganic fibersOrganic fillers & inorganic fibers

26. PropertiesProperties
 Polymerization shrinkagePolymerization shrinkage
 density change volumetric shrinkagedensity change volumetric shrinkage
approx. 21%approx. 21%
 monomer forms 1/3 of mix vol.monomer forms 1/3 of mix vol.
shrinkage approx. 7%shrinkage approx. 7%
 distributed uniformly to all surfacesdistributed uniformly to all surfaces
 linear shrinkage less than 1%linear shrinkage less than 1%

27.  Heat activated or chemically activated resinsHeat activated or chemically activated resins
in conjunction with compression molding tech.in conjunction with compression molding tech.
usually displaysusually displays increase in overall verticalincrease in overall vertical
dimension.dimension. Minimal increase in verticalMinimal increase in vertical
dimension are considered desirable, since theydimension are considered desirable, since they
permit a return to the proposed occlusalpermit a return to the proposed occlusal
vertical dimension through occlusal grindingvertical dimension through occlusal grinding
procedures.procedures.

28.  Porosity:Porosity:
 develop indevelop in thickthick
portionsportions as a result ofas a result of
monomer vaporisationmonomer vaporisation
when temp. increaseswhen temp. increases
above boiling point.above boiling point.
 thick lingual posteriorthick lingual posterior
area of lower denturearea of lower denture
base are more likely tobase are more likely to
exhibit porosity than theexhibit porosity than the
buccal portionbuccal portion

29.  Lack of homogenityLack of homogenity in dough or gel –in dough or gel –
minimized by ensuring that the greatestminimized by ensuring that the greatest
possible homogenity of resin is attainedpossible homogenity of resin is attained
this can be achieved by use of proper P/L ratiothis can be achieved by use of proper P/L ratio
and favorable mixing procedures & packing inand favorable mixing procedures & packing in
dough stagedough stage
 Lack of adequate pressureLack of adequate pressure during packingduring packing

30.  Water sorptionWater sorption::
 Absorbs small amount of water when placedAbsorbs small amount of water when placed
in aqueous environmentin aqueous environment
 Water molecules penetrate the PMMA massWater molecules penetrate the PMMA mass
and force apart the polymer chains resulting inand force apart the polymer chains resulting in
slight expansion & interfere with entanglementslight expansion & interfere with entanglement
of polymer chain thereby act as plasticizerof polymer chain thereby act as plasticizer

31.  Linear expansion caused by water sorption isLinear expansion caused by water sorption is
approx. equal to the thermal shrinkage as aapprox. equal to the thermal shrinkage as a
result of polymerization process. Hence, theseresult of polymerization process. Hence, these
processes very nearly offset one another.processes very nearly offset one another.

32.  Solubility:Solubility:
 They are virtually insoluble in the fluidsThey are virtually insoluble in the fluids
commonly encountered in oral cavitycommonly encountered in oral cavity
 Processing stresses:Processing stresses:
 Range in 0.1 to 0.2 mm as measured fromRange in 0.1 to 0.2 mm as measured from
second molar to second molar – doubtful ifsecond molar to second molar – doubtful if
such changes would be noticed by the patientsuch changes would be noticed by the patient

33.  Crazing:Crazing:
 Stress relaxation produce small surface flawsStress relaxation produce small surface flaws
or micro cracks – effect esthetics & physicalor micro cracks – effect esthetics & physical
propertiesproperties
 Predispose denture to fracturePredispose denture to fracture
 Craze lines are oriented at right angle to tensileCraze lines are oriented at right angle to tensile
forcesforces

34.  Strength:Strength:
For heat cure acrylics-For heat cure acrylics-
 Density – 1.19 g/ ccDensity – 1.19 g/ cc
 Proportional limit – 27-45 MPaProportional limit – 27-45 MPa
 Compressive strength – 75 MPaCompressive strength – 75 MPa
 Tensile strength– 65 MPaTensile strength– 65 MPa
 Shear strength– 122 MPaShear strength– 122 MPa
 Transverse strength– 85 MPaTransverse strength– 85 MPa
 MOE – 2500 MPaMOE – 2500 MPa
 Fatigue strength– 17 MPaFatigue strength– 17 MPa

35.  Creep:Creep:
 Exhibit visco-elastic natureExhibit visco-elastic nature
 Although creep rates for heat and chemicallyAlthough creep rates for heat and chemically
activated resins are similar at low stresses,activated resins are similar at low stresses,
creep rates for chemically actiuvated resinscreep rates for chemically actiuvated resins
increases more rapidly as stresses are raised.increases more rapidly as stresses are raised.

36.  Impact strength:Impact strength:
 The value for high impact acyrlic such asThe value for high impact acyrlic such as
Lucitone 199 is twice as high as that forLucitone 199 is twice as high as that for
conventional PMMA resinsconventional PMMA resins
 Color stability:Color stability: GoodGood

37. Polymer – monomer interactionPolymer – monomer interaction
 When polymer and monomer are mixed it
goes through 5 distinct stages:
 SandySandy
 StringyStringy
 Dough likeDough like
 Rubbery or elastic StiffRubbery or elastic Stiff

38.  Dough forming time:: time required to reach a dough liketime required to reach a dough like
stagestage
 Acc to ADA specification no. 12: less than 40 minAcc to ADA specification no. 12: less than 40 min
 In clinical use, majority of resins reach a dough like stageIn clinical use, majority of resins reach a dough like stage
in less than 10 minin less than 10 min
 Working time: the time that a denture base material remainsthe time that a denture base material remains
in the dough like stagein the dough like stage
 critical to compression molding timecritical to compression molding time
 Acc. To ADA specification no. 12: dough stage for at leastAcc. To ADA specification no. 12: dough stage for at least
5 min5 min
 Working time can be extended by refrigeration in air tightWorking time can be extended by refrigeration in air tight
containerscontainers

39. Polymerization cyclePolymerization cycle
 Heating process used to controlHeating process used to control
polymerizationpolymerization
 Should be well controlled to avoid boiling ofShould be well controlled to avoid boiling of
unreacted monomerunreacted monomer
 Constant temp. water bath at 74 deg for 8 hrsConstant temp. water bath at 74 deg for 8 hrs
 74 deg for 2 hrs followed by 100 deg for 1 hr74 deg for 2 hrs followed by 100 deg for 1 hr
Following completion of polymerization cycleFollowing completion of polymerization cycle
flasks should be cooled to room temp.flasks should be cooled to room temp.

40. Chemically activatedChemically activated
 Cold curing, self curing or autopolymerizingCold curing, self curing or autopolymerizing
 Addition of tertiary amineAddition of tertiary amine dimethyl – para –dimethyl – para –
toluidinetoluidine to monomerto monomer
 This amine causes activation ofThis amine causes activation of benzoylbenzoyl
peroxideperoxide
 Degree of polymerization achieved inDegree of polymerization achieved in
chemically cured resins is not as complete aschemically cured resins is not as complete as
heat curedheat cured

41.  This leaves unreacted monomer which posesThis leaves unreacted monomer which poses
2 major problems2 major problems::
1.1. Acts as plasticizer – decreased transverseActs as plasticizer – decreased transverse
strengthstrength
2.2. Potential tissue irritantPotential tissue irritant
But they have less shrinkage than heat cured –But they have less shrinkage than heat cured –
greater dimensional accuracygreater dimensional accuracy

42.  Molded generally by compression moldingMolded generally by compression molding
tech.tech.
 Shorter working time - can be increased byShorter working time - can be increased by
refrigeration of monomerrefrigeration of monomer
 Initial hardening occurs within 30 minInitial hardening occurs within 30 min
 To complete polymerization flask should heldTo complete polymerization flask should held
under pressure for 3 hrsunder pressure for 3 hrs

43. Light activatedLight activated
 Matrix of urethane dimethacrylate, micro fineMatrix of urethane dimethacrylate, micro fine
silica, and high molecule wt. acrylic resinsilica, and high molecule wt. acrylic resin
monomermonomer
 Acrylic resin beads are included as organicAcrylic resin beads are included as organic
fillerfiller
 Activator – visible lightActivator – visible light
 Initiator -Initiator - camphorquinonecamphorquinone

44.  Supplied in premixedSupplied in premixed
sheets having clay likesheets having clay like
consistencyconsistency
 Special light curing unitSpecial light curing unit
 Curing time approx. 10Curing time approx. 10
min for one sheetmin for one sheet
 Whole processing can beWhole processing can be
done within an hourdone within an hour
 Can be used for dentureCan be used for denture
repair as wellrepair as well

45. Polymerization via microwave
energy
 Specially formulated PMMA andSpecially formulated PMMA and non-metallicnon-metallic
flasksflasks eg Acron MCeg Acron MC
 Conventional microwave can be used forConventional microwave can be used for
polymerizationpolymerization
 Faster methodFaster method
 Physical properties comparable to conventionalPhysical properties comparable to conventional
PMMAPMMA

46. Polymerization via microwave
energy

47. Method of AcrylizationMethod of Acrylization
 There are 2 technique commonly used for finalThere are 2 technique commonly used for final
curing of denturecuring of denture
 Compression Moulding techniqueCompression Moulding technique
 Injection molding techniqueInjection molding technique

48. Compression MouldingCompression Moulding
Preparation of the mold
Application of separating media
P/L accepted rario is 3:1 by volume
Polymer – Monomer Interaction

49. Packing in dough stage
Pressure is applied incrementally
Trial closure - flash
Flasks should be closed entirely

53. Injection moldingInjection molding
 Specially designed flasksSpecially designed flasks
One half of flask is invested with dental stone inOne half of flask is invested with dental stone in
usual mannerusual manner
Sprues are attached to wax denture baseSprues are attached to wax denture base
Remaining part of flask is positioned andRemaining part of flask is positioned and
investment process is completedinvestment process is completed

54. Injection moldingInjection molding
wax eliminationwax elimination
Flask placed in special carrierFlask placed in special carrier
resin is mixed and introduced in mold atresin is mixed and introduced in mold at
room temp.room temp.
flask than placed in water bathflask than placed in water bath

56. Processed denture with sprues and vents attached

57. Recent advancesRecent advances

58. Acrylic – vinyl copolymerAcrylic – vinyl copolymer
 vinyl acetate & vinyl chloride copolymerizevinyl acetate & vinyl chloride copolymerize
with MMAwith MMA
 improved impact strengthimproved impact strength
 low MOElow MOE
 low water sorptionlow water sorption
 become slightly yellow after a period of timebecome slightly yellow after a period of time
 possible to injection mold thempossible to injection mold them
Eg. Luxene 44Eg. Luxene 44

59. Polystyrene copolymerPolystyrene copolymer
 High impact materialsHigh impact materials
 Show better mechanical propertiesShow better mechanical properties
 Injection moldedInjection molded
 Low water sorptionLow water sorption
 Low densityLow density
 Best fatigue resistanceBest fatigue resistance
Eg JectronEg Jectron

60. Polycarbonate resinsPolycarbonate resins
 Polyester resins or Epoxide resins
 New material include both thermoplastic &New material include both thermoplastic &
thermosetting typesthermosetting types
 High impact strength, low water sorption, inertHigh impact strength, low water sorption, inert
and good color stabilityand good color stability
 Injection molded at high temp.Injection molded at high temp.
 Addition of glass fiber improves strength stillAddition of glass fiber improves strength still
furtherfurther

61. High Impact Strength materialsHigh Impact Strength materials
 Reinforced withReinforced with
butadiene- styrenebutadiene- styrene
rubberrubber
 They act as shockThey act as shock
absorbersabsorbers
 Very expensiveVery expensive
High impact heat cure resin

62. Fiber reinforced polymersFiber reinforced polymers
 Glass fibers – irritatingGlass fibers – irritating
 Carbon or graphite fibersCarbon or graphite fibers
– improve strength but– improve strength but
difficult bonding, poordifficult bonding, poor
esthticsesthtics
 Kevlar fibers – betterKevlar fibers – better
mechanical propertiesmechanical properties
and good esthetics butand good esthetics but
difficult to packdifficult to pack

63. ReferencesReferences
 Phillip’s science of Dental materials 11 ednPhillip’s science of Dental materials 11 edn
 Recent Restorative materials by CraigRecent Restorative materials by Craig
 Dental material science by O’brienDental material science by O’brien
 Textbook of dental material by Shyama bhattTextbook of dental material by Shyama bhatt
 Comparison between dimensional accuracy ofComparison between dimensional accuracy of
dentures produced by pour type resin & withdentures produced by pour type resin & with
heat processed materials JPD 1971 vol 26;heat processed materials JPD 1971 vol 26;
296-301296-301