Acrylic resin .pdf

Acrylic

1. DENTAL RESIN

3. INTRODUCTION -Denture
base resin
Choice of material for denture base fabrication
since 1940s
AVAILABLE in Powder and liquid system
Composition:
The liquid
The powder

4. Powder:Polymethylmethacrylate
colorlesstransparentsolid
Thepolymercanbetintedtoprovidealmostanycolor,
shade,anddegreeoftranslucency.
Itscolor,opticalcharacteristics,anddimensional
propertiesremainstableundernormalintraoral
conditions,anditsphysicalpropertieshaveprovento
beadequatefordentalapplications.
Easyprocessing
Liquid–Methylmethacrylate

5. Classification of Denture base resin
Type of polymerization
Type I –Heat-polymerizablepolymers
Type 2 –Auto-polymerizablepolymers
Type 3-Thermoplastic
Type 4-Light activated
Type 5-Microwave cured materials

6. Classification
Type of method of fabrication:
1.Compression molding technique ( heat activated)
2.Injection molding technique ( heat activated)
3.Fluid resin technique ( chemically activated resin)
4.Visible light curing technique

7. Heat activated denture base
resin
COMPOSITION:
-POWDERANDLIQUID
-GEL
-SHEETS
-CAKES
Commercialnames:Stellon(DPI),Trevelon(Dentsply),Lucitone
(Bayer)

8. Heat activated denture base
resin
ThePowder:Thepowdermaybetransparentor
toothcoloredorpinkcolored
PolymethylMethacrylate-Majorcomponent
TheInitiator-BenzoylPeroxide
Opacifiers-Zincortitaniumoxide
Plasticizer-Dibutylphthalate(plasticity-softer,flexible)
Dyes-Compoundsofmercuricsulfide,cadmiumsulfide,etc
Others-Inorganicfillers-improvesphysicalpropertiesandacrylic
fibers-tosimulatesmallcapillaries

9. Heat activated denture base
resin
Theliquid:Theliquidissuppliedintightlysealed
ambercoloredbottlestopreventprematurepolymerization
bylightorultravioletradiationonstorage
Methylmethacrylate
Plasticizer-Dibutylphthalate
Cross-linkingagent:Glycoldimethacrylate
Inhibitor:HydroquinonePreventsundesirablepolymerization
or“setting”oftheliquidduringstorageandretardthecuring
processandtherebyincreaseworkingtime

10. Mechanism of crosslinking
agent
Methylmethacrylatepossessesonecarbon-carbon
doublebondpermoleculeandglycoldimethacrylate
possessestwodoublebondspermolecule.
Asaresult,anindividualmoleculeofglycol
dimethacrylatecanparticipateinthepolymerizationof
twoseparatepolymerchainsthatunitesthetwo
polymerchains.
Ifsufficientglycoldimethacrylateisincludedinthe
mixture,severalinterconnectionscanbeformedand
solventswellingmayoccur.
Theseinterconnectionsyieldanetlikestructurethat
providesincreasedresistancetodeformation.

11. Polymerization reaction
Powder + Liquid + Heat= Polymer + Heat ( reaction)

12. 1. Compression molding
technique
Most commonly used technique in denture fabrication

13. Compression molding
technique
Steps
1. Preparation of the waxed denture pattern.
2. Preparation of the split mold.
3. Application of separating medium.
4. Mixing of powder and liquid.
5. Packing.
6. Curing.
7. Cooling.
8. Divesting, finishing and polishing

14. 1. Preparation of waxed
denture pattern
Wax pattern is constructed
Wax will be replaced by acrylic

15. 2. Preparation of the split
mold
Waxed denture is invested in dental flask with dental
stone or plaster called flasking
Mastercastiscoatedwiththinlayerofseparatorto
preventadherenceofthedentalstonetothemaster
castduringtheflaskingprocedure.
Flasking is done using 3 pour technique

16. 3 pour technique
The lower portion of a denture flask is filled with
freshly mixed dental stone, and the master cast is
placed into this mixture.
Dental stone is contoured to facilitate wax elimination,
packing and deflasking procedures.
After initial set, the stone is coated with a separator
Upper portion of the flask is positioned above the lower
portion. Surface tension reducing agent is applied to
exposed wax surfaces

17. Second mix of dental stone is prepared and poured in
the denture flask.
Dental stone is added until it covers all surfaces of
denture and arranged tooth
Incisal and occlusal surfaces are minimally exposed to
facilitate deflasking procedures.
After it has set another coat of separator is placed.
Remainder of the flask is then poured with the stone
and covered with the lid.

18. 3 pour technique

19. Dewaxing:Aftertheplasterhasset,thedentureflaskis
immersedinboilingwaterfor5min.Theflaskisthen
removedfromthewaterandtheappropriatesegments
areseparated.
Therecordbaseandsoftenedwaxremaininthelower
portionofthedentureflaskwhiletheprostheticteeth
remainfirmlyembeddedintheinvestingstoneofthe
remainingsegment
Therecordbaseandsoftenedwaxarecarefully
removedfromthesurfaceofthemold.Residualwaxis
removedfromthemoldcavityusingwaxsolvent.The
moldcavityissubsequentlycleanedwithamild
detergentsolutionandrinsedwithboilingwater

20. 3. SELECTION AND APPLICATION
OF A SEPARATING MEDIUM
Applicationofseparatingmediumontothesurfacesof
themoldcavity.
Function:
1.Preventswaterfromthemoldenteringintoacrylicresin
2.Preventmonomerpenetratingintomoldmaterial
3.Helpsineasyretrievalofthedenturefromthemold

21. Failuretoplaceseparating
mediumcanleadtotwomajor
difficulties:
1.Ifwaterispermittedtodiffusefromthemoldsurface
intothedenturebaseresin,itcanaffectthe
polymerizationrateaswellastheopticalandphysical
propertiesoftheresultantdenturebase.
2.Ifdissolvedpolymerorfreemonomerispermittedto
soakintothemoldsurface,portionsoftheinvesting
mediumcanbecomefusedtothedenturebase.
Thesedifficultiesoftenproducecompromisesinthe
physicalandestheticpropertiesofprocesseddenture

22. Types of separating media
Tinfoil
Cellulose lacquers
Solution of alginate compounds
Calcium oleate
Soft soaps
Sodium silicate
starches

23. Tin foil
It was the material used earlier
Very effective
-However, its manipulation is time consuming and
difficult
-Replaced by other separating media called tin foil
substitutes

24. Sodium Alginate solutions
Itismostpopular
Itiswatersoluble
Theyproducethininsolublecalciumalginatefilms
Composition:
2%sodiumalginateinwater,glycerine,alcohol,sodium
phosphateandpreservatives

25. Precautions
Waxes remaining on the mold surface will interfere with
the action of separating medium
Mold should be warm not hot as it might not form
continuous film if hot
Avoid coating the teeth as it will prevent bonding of
teeth with the denture base.

26. Mode of application
Afinebrushisusedtospreadtheseparatingmedium
ontotheexposedsurfacesofawarm,cleanstonemold.
Separatorshouldnotbepermittedtocontactexposed
portionsofacrylicresinteeth,sinceitspresence
interfereswithchemicalbondingbetweenacrylicresin
teethanddenturebaseresins.
Thereshouldnotbe“pooling”ofseparator,andthe
solutionispermittedtodry.
Oneortwocoatsmaybeapplied

27. 4. Mixing of powder and
liquid
POLYMER-TO-MONOMERRATIO
3:1byvolumeor2:1byweight
Themeasuredliquidispouredintoacleandrymixing
jar
Powderisslowlyaddedforbetterwetting
Mixtureisstirredandleftforsometimeinclosed
container

28. If excess monomer
-greater polymerization shrinkage
-more time is needed to reach packing consistency
-Porosity can occur
If less monomer
-Not all polymer is wetted thus granular
-Dough will be difficult to manage

29. Physical stages
After mixing the material goes through various physical
phases.
No polymerization reaction takes place during these
stages
A plastic dough is formed

30. Physical Stages
Stage I: Wet sand stage
Stage II: Sticky (sticky:cob-weblike) stage
Stage III: Dough (gel) stage
Stage IV: Rubbery stage
Stage V: Stiff stage
Wet sand –sticky –dough -rubbery -stiff

31. Stage I : Wet sand stage
The polymer gradually settles into the monomer forming a
fluid, incoherent mass

32. Stage II –Sticky stage
The monomer attacks the polymer by penetrating into
the polymer.
The mass is sticky and stringy ( cobweb like) when
touched a pulled apart

33. Stage III –Dough or gel stage
The monomer diffuses into the polymer, it becomes
smooth and dough like.
It does not adhere to the walls of the jar
It contains undissolved polymer particles suspended in a
plastic matrix of monomer and dissolved polymer.
The mass is plastic and homogenous and can be packed
into the mold at this stage

34. Stage IV-Rubbery stage
The monomer disappears by further penetration into
the polymer or evaporation
The mass is rubberlike, non plastic
It cannot be molded

35. Stage V-Stiff stage
The mass is totally unworkable and is discarded

36. Working time
The working time is the time from Stage II and the
beginning of Stage IV.
The ideal packing phase is the dough stage
Working time is affected by temperature.
In warm condition the working time is less thus the jar
is chilled to prolong the working time

37. 5.Packing
The mixture is packed into the flask in dough stage
-If it is packed at the sandy or stringy stages, too much
of monomer will be present between the polymer
particles, and the material will be of too low viscocity
and will flow out of the flask too easily. It may also
cause porosity in the final denture base.
-If packed at the rubbery to stiff stage, the material
will be too viscous to flow and metal to metal contact
of the flask halves will not be obtained. It may result in
movement or fracture of the teeth, Loss of detail,
Increase in the vertical height of the denture

38. Trial closure
Theacrylicdoughispackedintotheflaskinslightexcess
Theexcessisremovedduringthetrialclosurepackingwith
adampcellophanefilmusedasaseparatorfortheupper
halfoftheflask
Ahydraulicormechanicalpressmaybeusedtoapply
pressure
Theclosingforceisappliedslowlyduringthetrialpackingto
allowexcessdoughcalledflashtoflowoutoftheflask.
Theflaskisopenedflashistrimmedaway.
Theseparatingfilmisremoved.
Thefinalclosureoftheflaskormetaltometalcontactofthe
flaskhalvesisthencompletedinthepress.
Theflasksarethentransferredtoaholdingclampwhich
maintainsthepressurethroughoutthecuringprocess

39. Curing ( polymerization)
After final closure the flasks are kept in room
temperature for 30-60 minutes called bench curing
Purpose of bench curing:
1.Equalizes the pressures throughout the mold
2.Uniform dispersion of monomer throughout the mass of
dough
3.Longer exposure of resin teeth to the monomer
producing better bond of the teeth and base.

40. Curing cycle
Curing cycle or polymerization cycle is the process of
heating used to initiate and control the complete
polymerization of the resin in the mold
The time depends on the thickness of the resin in the mold
THICKER-long curing cycle to avoid porosity
1.Long curing cycle
2.Short curing cycle

41. Long Curing Cycle:
a.74 cfor 8 hours
b.74 cfor 8 hours then boil for 1 hour
Short Curing Cycle
a. 74 cfor 2 hours, then boil for 1 hour

42. Cooling
The flask should be cooled slowly called as bench
cooling.
Fast cooling can result is warpage of the denture due to
differential thermal contraction of the resin and gypsum
mold.
Cooling overnight is ideal
However, bench cooling for 30 minutes and then placing
in cold tap water for 15 minutes is satisfactory.

43. Deflasking
The cured acrylic is retrieved from the flask called
deflasking
Flask is opened and mold is retrieved
Deflasking should be done with great care to avoid flexing
and breaking of the denture.

44. Finishing and polishing
The denture is smoothened using progressive grades of
sandpaper
Finely ground pumice in water

45. Injection molding technique
A special thermoplastic resin is used (Thermoplastic
resins arematerials that soften to a liquid in high heat
and then harden again when cooled)
Special bath is required for curing

46. Injection molding technique
A spruehole and a vent hole are formed in the gypsum
mold with the help of sprueformers
The soft resin is contained in the injector and is forced
into the mold space as needed
It is kept under pressure until it is hardened
Continuous feeding of the material under pressure
compensates for shrinkage

47. Advantages
1.Dimensional accuracy
2.No increase in vertical dimension
3.Homogeneous denture base
4.Low free monomer content
5.Good impact strength

48. Disadvantages
1.Higher cost of equipment
2.Mold design problems
3.Less craze resistance (surface defect)
4.Special flask is required

49. 2. Chemically activated
denture base resin
does not require the application of thermal energy
Polymerization can be completed at room temperature
Chemically activated resins often are referred to as
cold-curing, self-curing, or autopolymerizingresins

50. composition
Powder :
1.Polymethylmethacrylate
2.Benzoyl peroxide –Initiator
3.Compounds of mercuric sulfide, cadmium sulfide-dyes
4.Zinc or titanium oxide-opacifier
5.Dibutyl phthalate-Plasticizer
6.Dyed organic fillers-esthetics

51. Composition
Liquid :
1.Methyl methcrylatemonomer
2.Dimethyl p toluidine-activator
3.Dibutylphthalate-Plasticizer
4.Glycol dimethacrylate-cross linking agent
5.Hydroquinone-inhibitor

52. Uses
1.For making temporary crowns and bridge
2.Construction of special trays
3.Denture repair, relining and rebasing
4.For making removable orthodontic appliances
5.For adding a post dam
6.For making temporary and permanent denture bases
7.For making inlay and post core patterns

53. Polymerization reaction
Polymer + Monomer === Polymer + Heat

54. Mechanism of reaction
Activator-Tertiaryaminesuchasdimethylp-toluidineto
theliquid
Causesdecompositionofbenzoylperoxideproducing
freeradicalsandpolymerizationisinitiated
Polymerizationprogressesinamannersimilartothat
describedforheat-activatedsystems

55. Thedegreeofpolymerizationislessinchemically
activatedthaninheat-activatedsystems
Thereisagreateramountofunreactedmonomerwhich
causes
-First,itactsasaplasticizer,resultingindecreased
transversestrengthofthedentureresin.
-Second,theresidualmonomerservesasapotential
tissueirritant,thereby compromising the
biocompatibilityofthedenturebase.

56. COLORSTABILITY:
Colorstabilityofchemicallyactivatedresinsgenerallyis
inferiorduetothepresenceoftertiaryamineswithin
thechemicallyactivatedresins.
Suchaminesaresusceptibletooxidationand
accompanyingcolorchangesthataffecttheappearance
oftheresin.Discolorationcanbeminimizedby
stabilizingagentsthatpreventsuchoxidation.
WORKINGTIME:
Theworkingtimeforchemicallyactivatedresinsisshorter
thanforheat-activatedmaterials.

57. Advantages
Better initial fit as curing occurs in room temperature
so less thermal contraction
Easy to use for repairing as heat cure causes warpage
(change in shape or fit)

58. Disadvantages
Color stability is inferior to heat cure resin due to
oxidation of the tertiary amine.
Properties are inferior to heat cure as degree of
polymerization in self cure

59. Manipulation of self cure
1.Sprinkle on technique
2.Finger adapting technique
3.Fluid resin technique

60. 1. Sprinkle on technique
-Also known as salt and pepper technique
-Powder and liquid is applied alternatively from droppers
-Powder is sprinkled on the cast and then wet with
monomer

61. The appliance is constructed section by section until
completion
To improve the strength it is placed in pressure pot at
20 psi for around 20 minutes

62. 2. Finger adapted method
•Powder and liquid is proportioned and mixed in a
porcelain jar
•When it reaches dough stage it is removed and adapted
on to the cast and manually molded to the desired
shape
•Curing is completed in a pressure pot

63. 3. Fluid resin technique
A special resin is available for this technique
Pour type of denture resin have high molecular weight
powder particles that are much smaller and when they
are mixed with the monomer, the resulting mix is very
fluid.
Thus they are referred to as fluid resin
They have low powder liquid ratio 2:1 or 2.5:1 makes it
easier to mix and pour
Polymerization is done under pressure at 20 psi at 45 c
for 25 minutes

64. Composition
Polymer:
Polymethylmethacrylate copolymer
Barbiturate acid derivatives
Color pigments
Monomer:
Methyl methacrylate
Quaternary Ammonia
Stabilizers
Catalyst
vulcaniser

65. Method of flasking and curing
Agarhydrocolloidorsiliconeisusedforthemold
preparationinsteadofgypsum
Aspecialflaskandresinisusedisused
Involvespreparingthemoldwithsilicone,creation
ofchannelsforpouringandventing
Fluidresinispouredthroughonechannelinathin
streamtillexcessisseenthroughthevent
Polymerizationisdoneunderpressureat0.14Mpa
(20psi)atatemperatureof45cfor25minutes

66. Advantages
1.Better tissue fit
2.Fewer open bites
3.Less fracture of porcelain teeth during deflasking
4.Reduced material cost
5.Simple laboratory procedure for flasking, deflasking and
finishing of the dentures

67. Disadvantages
1.Air inclusion
2.Shifting of teeth during processing
3.Infraocclusion
4.Occlusal imbalance due to shifting of teeth
5.Incomplete flow of denture base material over neck of
anterior teeth
6.Formation of films of denture material over cervical
portions of plastic teeth that had not been previously
covered with wax
7.Poor bonding to plastic teeth
8.Technique sensitivity
9.Low mechanical properties than conventional heat cure

68. LIGHT-ACTIVATED DENTURE
BASE RESINS
Single-componentdenturebaseresinsare
suppliedinsheetandropeformsandare
packedinlightproofpouchestoprevent
inadvertentpolymerization.
COMPOSITION:
Urethanedimethacrylatemicrofinesilica,
andhigh-molecular-weightacrylicresin
monomers.
Fillers-Acrylicresinbeads
Activator-Visiblelight
Initiator-Photosensitizingagentsuchas
Camphorquinone

69. Light activated denture base
-Suppliedinpremixedsheetsofhavingaclaylike
consistency
-Suppliedinvariouscolorslikepink,transparent
-obtainedinlighttightpackagestoavoidpremature
polymerization

70. Themostrecentgenerationoflight-activateddenture
baseresinsconsistsofthreeresins.
3forms
1.base-formingresin
2.tooth-settingresin
3.contouringresin

71. Thebase-formingresinisadaptedtothedentalcast.The
castanddenturebaseareplacedintoahigh-intensitylight
chambertoinducepolymerization.
Thetooth-settingresinisusedtoattachtheprosthetic
teethtothepolymerizedbase.Ahigh-intensitylightsource
isusedtopolymerizethetooth-settingresin,thereby
maintainingprostheticteethinthedesiredpositions.
Thecontouringresinisusedtogeneratethedesiredfinal
surfaceform.Theresultantprosthesisisplacedintothe
lightchambertocompletethedenturebasefabrication
process.Thedentureisthenremovedfromthecast,
finished,andpolishedinaconventionalmanner.

73. Manipulation
-Denturebasematerialisadaptedtothecastwhileitis
inaplasticstate.
-Thedenturebasecanbepolymerizedwithoutteethand
usedasbaseplate
-Theteethareaddedtothebasewithadditional
materialandtheanatomyissculptedwhilethematerial
isstillsoft
-Itispolymerizedinalightchamberwithbluelightof
400-500nmfromhighintensityquartzhalogenbulbs
-Thedentureisrotatedcontinuouslyinthechamberto
provideuniformexposuretothelightsource

74. Chemical stages of
polymerization
Four stages
1.Induction-activation and Initiation
2.Propagation
3.Chain transfer
4.Termination

75. Chemical stages of
polymerization
1.Induction:
Induction is the time during which the molecules of
the initiator becomes activated to form free radical
which reacts with monomer and start to transfer the
energy to other monomer
Impurities can increase the length of this period
Higher the temperature, shorter the length of the
induction period
Initiation energy for activation of each monomer unit is
16000-29000 calories per molin the liquid phase

77. Heat activation:
-Free radicals liberated by heating benzoyl peroxide will
initiate the polymerization of methyl methacrylate
monomer
Chemical activation:
-Consists of two reactants, when mixed they undergo
chemical reaction and liberate free radicals. E.g. use of
benzoyl peroxide and dimethyl p-toluidine in self cured
dental resins
Light activation:
-Photons of light energy activate the initiator to generate
free radicals, e.g. Camphorquinone and an amine react to
form free radicals, when they are irradiated with visible light.

78. 2. Propagation:
After the growth has started only 5000-8000 calories per
mole are required
Process continues rapidly with evolution of heat
The chain reactions should continue with the evolution of
heat until all the monomer has been changed to polymer.
Theresultingfreeradical-monomercomplexthenactsasa
newfreeradicalcenterwhenitapproachesanother
monomertoformadimer,whichalsobecomesafree
radical.
Thisreactivespecies,inturn,canaddsuccessivelytoa
largenumberofethylenemoleculessothatthe
polymerizationprocesscontinuesthroughthepropagation
ofthereactivecenter.

80. 3. Chain transfer:
The chain termination can result from chain transfer. The
active state is transferred from an activated radical to an
inactive molecule and a new nucleus of growth is created.
An already terminated chain can be reactivated by chain
transfer resulting in continued growth

81. 4. Termination:
The chain reaction can be terminated either by direct
coupling of two chain ends or by exchange of a hydrogen
atom from one growing chain to another

82. Inhibition of Polymerization
Inhibitors:
These react with the activated initiator or any activated
nucleus, or with an activated growing chain to prevent
further growth, e.g. hydroquinone (0.006%) is added to
prevent polymerization of monomer during storage.
Oxygen
Presence of oxygen also inhibit polymerization

83. Co-polymerization
Inordertoimprovethephysicalpropertiesitis
advantageoustousetwoormorechemicallydifferent
monomersasstartingmaterials
Thepolymersthusformedmaycontainunitsofthese
monomers.Suchapolymeriscalledcopolymerandits
processofformationisknownascopolymerization

84. Importance of
copolymerization
Toimprovethephysicalpropertiesofresin
-Smallamountsofethylacrylatewithmethylmethacrylateto
altertheflexibility
-Blockandgraftpolymersshowimprovedimpactstrength.They
modifytheadhesivepropertiesofresinsandtheirsurface
characteristics.

85. Cross linking
The formation of chemical bonds or bridges between
the polymer chains is called cross linking
Application:
1.Increases rigidity and decreases solubility and water
absorption
2.Improve resistance to solvents, crazing and surface
stresses

86. Plasticizers
Function:
1.Increases solubility of the polymer in the monomer
2.Decreases the brittleness of the polymer
3.But excess decreases strength, hardness and softening
point

87. PHYSICAL PROPERTIES
POLYMERIZATION SHRINKAGE
POROSITY
WATER ABSORPTION
SOLUBILITY
PROCESSING STRESS
CRAZING

88. Methyl methacrylate monomer
It is a clear, transparent, volatile liquid at room
temperature.
It has a characteristic sweetish odor
Physical properties:
Melting point = -48 c
Boiling point = 100 c
Density 0.945 gm/ml at 20 c
Heat of polymerization = 12.9 Kcal/mol
Volume shrinkage during polymerization= 21%

89. Polymethylmethacrylate
1.Taste and odor:
They are tasteless and odorless
Poorly made dentures with porosity absorb food and
bacteria, resulting in an unpleasant taste and odor
2. Esthetics:
It can be pigmented easily to duplicate oral tissues
It is compatible with dyed synthetic fibers
3. Density:
Polymer has a density of 1.19 gm/cm3

90. 4. Strength:
Adequate compressive and tensile strength for complete or
partial denture applications
Compressive strength-75 Mpa
Tensile strength-48-62 Mpa
Self cure resin have low strength, it is affected by:
1.Composition
2.Technique of processing
3.Degree of polymerization
4.Water sorption
5.Subsequent environment of the denture

91. Impact strength:
It is a measure of energy absorbed by a material when it is
broken by a sudden blow. It can be increased by
modification with rubber.
Chemically activated-13 (J/m)
Conventional heat cured acrylic resin-15 (J/m)
Rubber modified-31 (J/m)
Polyvinyl resins-30 (J/m)
Fatiquestrength:
Ability of the denture to withstand large number of small
cyclic loading such as mastication.

92. 5. Hardness and wear resistance:
-Acrylic resin have low hardness
-Easily scratched and abraded
Heat cured acrylic resin-18 KHN
Self cured acrylic resin-16KHN
Rubber modified acrylic resin-14KHN
Light cured resin-18KHN

93. 6. Modulus of elasticity:
Sufficient stiffness for use in complete and partial dentures
Self cure have slightly lower values
7. Creep:
When load is applied an initial deflection is observed
If the load is sustained additional deformation is observed
over time. The additional deformation is called creep
Self cure resin have higher creep rates

94. 8. Dimensional stability:
Well process acrylic resin denture has good dimensional
stability
9. Water sorption:
Acrylic resin absorb water 0.7mg/cm2 and expand
This partially compensates for the shrinkage
10. Solubility
-Insoluble in water and oral fluids
-Soluble in ketones,esters
-Alcohol causes crazing in some resins
-ISO stipulates solubility should not exceed
Heat cure-1.6ug/mm2
Self cure-8 ug/mm2

95. 11. Thermal properties:
Polymethylemethacrylate:
125 c = softens
125 –200 c= depolymerize
450 c = polymer will depolymerize to monomer
Thermal conductivity:
They are poor conductors of heat and electricity. Patient
wearing acrylic dentures do not feel any temperature of
food thus reducing the pleasure.
Heat distortion temperature for PMMA= 71-91 c
It is of concern during repairing or polishing of dentures

96. 12. Color stability:
Self cure have lower color stability then heat cure. Self
cure slightly gets yellow.
13. Biocompatibility:
Completely polymerized resins are biocompatible
14. Adhesion:
Adhesion of acrylic to metal and porcelain is poor and
mechanical adhesion is required.
Adhesion to plastic denture teeth is good (chemical
adhesion)
Adhesion to metal or ceramic can be improved by treating
with silanecoupling agent

97. 15. Radiopacity:
Radiopacityis desirable property to enable easy location of
fragments.
Inclusion of heavy metals like bismuth or uranyl10-15%
16. Shelf life:
Acrylic in powder and liquid form have best shelf life than
in compare to that obtained in gel form.

98. 17. Residual monomer:
-During polymerization process the amount of residual
monomer decreases rapidly initially and then later more
slowly
The highest residual monomer level is observed with self
cure resin at 1-4% shortly after processing
long cure cycle used then residual monomer is 0.4%.
Short cure cycle-1-3%
To reduce residual monomer in heat cured resin, it should
be processed for longer time.
Gradual temperature raise, temperature should be raised
to boiling only after most of the polymerization is
completed or else porosity may result.

99. 18.POLYMERIZATION
SHRINKAGE
Methyl methacrylate monomer is polymerized to form
Polymethylmethacrylate
The density of the mass changes from 0.94 to 1.19
g/cm3 .
This change in density results in a volumetric shrinkage
of 21%.
In addition to volumetric shrinkage, one also must
consider the effects of linear shrinkage.
Linear shrinkage exerts significant effects upon
denture base adaptation and cuspalinterdigitation.

100. POLYMERIZATION SHRINKAGE
Processingshrinkagehasbeenmeasuredas0.26%fora
representativechemicallyactivatedresin,compared
with0.53%forarepresentativeheat-activatedresin.
However,thereareseveralotherfactorsthataffectthe
overalldimensionalcharacteristicsofprocesseddenture
basesincludingthe
typeofinvestingmedium,
methodofresinintroduction,and
temperatureusedtoactivatethepolymerization
process

101. Processing errors
1.Porosity
2.Crazing
3.Denture warpage

102. Porosity
Porosity results in:
1.Makes the appearance of denture unsightly
2.Proper cleaning is difficult thus hygiene compromised
3.Weakens the denture base. There is stress
concentration in the porosity area causing denture
warps
Types
1.Internal porosity
2.External porosity

103. Internal porosity
Appears as voids or bubbles within the mass of acrylized
resin
Confined to the thicker portion of the denture base
May not occur uniformly
Causes:
Vaporization of monomer when the temperature of the resin
increase above the boiling point of monomer i.e 100.8 C
The center of the thick portion of acrylic cannot conduct
away the heat where temperature rises above the boiling
point causing porosity called localized subsurface porosity.
Dentures with excessive thickness should be cured using long
curing cycle

104. Localizedsubsurfaceporosity:
Seeninthecenteroftheflaskratherthannearthemetal
surface.Themetaloftheflaskconductsheatawayfromthe
peripherywithsufficientrapiditytopreventasubstantial
temperaturerise.Asaresult,thelow-molecularweightspecies
doesnotboilandporositydoesnotdevelop.Incontrast,resin
specimensoccupyingcentralpositionsinthemoldare
surroundedbylargeramountsofgypsum.Becausegypsumisa
poorthermalconductor,heatcannotreadilydissipated.
Consequentlylow-molecular-weightspeciesarevaporizedand
noticeableporosityisproduced.

105. External porosity
Surfaceporosityoccursdueto:
1.Lackofhomogeneity:
Ifthedoughisnothomogenousatthetimeof
polymerization,someregionsoftheresinmasswill
containmoremonomerthanothers.
Duringpolymerization,moremonomercontaining
regionsshrinkmorethanadjacentregions,andthe
localizedshrinkagetendstoproducevoids.Theresin
appearswhite.
Properpolymer-to-monomerratiosandwell-controlled
mixingproceduresanddoughlikestagehasmore
homogenousmixsoitiswisetodelay
1.Lack of homogeneity
2.Lack of adequate pressure
3.Air entrapment

106. 2. Lack of adequate pressure:
Lackofpressureduringpolymerizationorinadequate
amountofdoughinthemoldduringfinalclosurecauses
bubbles.Theyassumeirregularshapes.
Thesevoidsmaybesoabundantthattheresultantresin
appearssignificantlylighterandmoreopaquethanits
intendedcolor.
Remedy:Userequiredamountofdough.Checkforexcess
orflashduringtrailclosure.Flashindicatedadequate
material.

107. 3.Airentrapment:
Afinaltypeofporosityismostoftenassociatedwithfluid
resins.Suchporosityresultsfromairentrapmentduring
mixingandpouringprocedures.Ifairinclusionsarenot
removed,sizablevoidsmaybeproducedintheresultant
denturebases.Thereforecarefulmixing,spruing,and
ventingareessential.

108. Crazing
Formation of surface cracks on denture base resin
May be macroscopic or microscopic in size
Crazing weakens the resin and reduces the esthetic
qualities
Crack formed can cause fracture
Causes:
1.Mechanical stresses
2.Attack by solvent
3.Incorporation of water

109. Crazing is mechanical separation of the polymer chains
under tensile stress
Cracks are at right angles to the direction of tensile
stress
Crazing is visible around the porcelain teeth in the
denture and is due to contraction of the resin around
the porcelain teeth during cooling after processing
Water incorporation during processing will form stresses
due to evaporation of water after processing causing
crazing

110. Prevention of Crazing
1.Using cross linked acrylics
2.Tin foil separation medium
3.Metal molds

111. Denture warpage
-Deformity or change of shape of the denture which can
effect the fit of the denture.
-May occur during processing
Causes:
1.Release of stress incorporated during processing
2.Rise in temperature during polishing
3.Immersion of denture in hot water
4.Rapid cooling
5.Curing shrinkage
6.Packing during rubbery stage
7.Improper flasking
8.Re-curing of denture after relining

112. Repair of acrylic resin
Repair can be done using
-Heat cure
-Self cure
Heat cure resin-
Use of heat cure resin will tend to warp the denture during
processing
Self cure resin-
Insignificant warpage

113. Infection control
Ethylene oxide gas is suitable for disinfecting the
material
Phenol and gluteraldehydesolutions are avoided as
polymeric material can absorb such liquids

114. Care of Acrylic dentures
Proper care and maintenance of denture is essential
Methods:
1.Dentures should be stored in water when not in use.
Drying can cause dimensional changes
2.Avoid hot water for cleaning can cause distortion due to
release of stress
3.Abrasive dentrifices should not be used it will get
scratched and abraded.

115. THANK YOU