polymers in dentistry

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2. Presented By
Dr. Abbasi Begum M
Pg.Department Prosthodontics
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3. contents INTRODUCTION
 CLASSIFICATION
 REQUISITES FOR DENTAL RESINS
 FUNDAMENTAL NATURE OF POLYMERS
 Physical Properties of Polymers
 Chemistry of Polymerization
 Copolymerization
 Acrylic Dental Resins
 Applications of Resins in Dentistry
 RECENT ADVANCES
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4. INTRODUCTION
Polymers are finding increased application in almost every
sphere of life. In almost every field of dentistry these are
being used successfully.
However as the field is dynamic & new types of resins are
being developed on regular basis, it is important for us to
know the basic chemistry of polymers so that new
developments can be critically evaluated.
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5. g
Polymers& polymerisation
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6. DEFINITION
 MONOMER
A chemical that can undergo polymerization; any molecule that can bound to a similar
molecule to form a polymer. (GPT-8)
 POLYMER
A chemical compound consisting of large organic molecules built by repetition of smaller
monomeric units. (GPT-8)
 DENTURE BASE :
A denture base may be defined as the part of the denture that rests on the foundation and
to which teeth are attached.
Gpt-8 (2005)
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7.  POLYMERIZATION :
The forming of a compound by the joining together of molecules of small
molecular weights into a compound of large molecular weight. (GPT-8).
polymerization
 Monomer + Monomer + Monomer + Monomer Mcr - Mcr - Mcr
–Mcr
 Polymers have had an enormous impact on dentistry
 used as sealants, bonding materials, restorative materials,
Veneering materials,
 denture bases, denture teeth, and impression materials.
polymers
sealants
Impression
materials
Bonding
material
veneering
Denture
bases
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8. BASIC NATURE OF POLYMERS
 Poly – Many
Mer – Parts
Derived from the Greek language
It consist of large no. of repeating units known as monomers
The no. of repeating units in a chain of polymer is known as degree of polymerization
 Naturally occurring polymers are agar ,cellulose
D.N.A proteins , natural rubber, collagen & silk.
 Synthetic polymers are rubber & nylon. 5/1/2015
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9. Structure of a polymer
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10. classification
 Based on their
1) thermal behavior, they can be divided into
a. Thermoplastic
b. Thermosetting
 Based on
2) Classification based on polymerization
a)Additionpolymers
formed by the repeated addition of monomer molecules possessing double or triple bonds
b)Condensationpolymers
formed by repeated condensation reaction between two different bi-functional or tri-functional
monomeric units.
3) Source[origin]
Natural
Synthetic
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11. 4) TechnologicalUse
Adhesives
Fibers
Plastics
Elastomers
Paint & Coatings
5) Architecture
Linear
Branched
Cross-linked 5/1/2015
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12. 6) Microstructure
Crystalline –chains align themselves to form highly ordered ,or crystalline structure
Amorphous-chains are randomly coiled & entangled in a very distorted pattern
7) Chemistryof Composition
Homopolymer Copolymer
AAAAAAAAAAA
Block Graft Alternating
Homopolymer
Consist of only one type of constitutional repeating unit (A)
AAAAAAAAAAAAAAA
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13. copolymerization
 Two or more chemically different monomers, each with a desirable property can be combined
to yield specific physical properties ,such a polymer is called as copolymer
 The process of formation is called as copolymerization
 RANDOM CO-POLYMER
 BLOCK CO-POLYMER
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14.  RANDOM CO-POLYMER
 If a monomer A is mixed with monomer B prior to polymerization they will co-polymerize
to form polymer chains containing both A & B monomer units.
 The sequence of the original monomer s in the polymer may be random producing a ‘
RANDOM CO-POLYMER’
 A-B-A-B-A-B-B-A-B-B-A-A-B-B-A
 BLOCK CO-POLYMER
If the monomers self polymerize more readily then they
copolymerize that they will result in a “block copolymer”
where segments' of each homo polymer are linked.
-A-A-A-B-B-B-A-A-A-B-B-B-
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16. Several classes of copolymer are possible
 Statistical copolymer (Random)
ABAABABBBAABAABB
two or more different repeating unit are distributed randomly
 Alternating copolymer
ABABABABABABABAB
are made of alternating sequences
of the different monomers
 Block copolymer
AAAAAAAAABBBBBBBBB
long sequences of a monomer are followed by long sequences of another monomer
 Graft copolymer
AAAAAAAAAAAAAAAAAA
B B B
B B B 5/1/2015
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17. REQUISITES FOR DENTAL RESINS
 Methacrylate polymers are capable of providing
 an excellent balance of performance features and characteristics needed for
use in the oral cavity.
 Ideally, these characteristics include
 (1) biological compatibility
 (2) physical properties
 (3) ease of manipulation
 (4) aesthetic qualities
 (5) relatively low cost
 (6) chemical stability in the mouth
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18. 1)Biological Compatibility
Biological
Compatibility
tasteles
odorless
nontoxic
Non-
irritating
Set fairly
rapidly to
prevent
bacterial
ingrowth at
tooth-
restoration
interface
Insoluble in
saliva
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19. 2)Physical Properties 3)Aesthetic
Properties
adequate
strength
resilience
resistance to
biting chewing
forces, impact
forces
Dimentional
stability
Should be
Sufficient
translucency or
transparency
capable of being
tinted or pigmented
no change in color
No change appearance of
the material subsequent to
its fabrication.
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20.  4)Economic Considerations
should not require complex and expensive equipment.
 5)Chemical Stability
 PHYSICAL PROPERTIES OF POLYMERS
1. Deformation and Recovery
Applied forces produce stresses within polyrners that can cause elastic strain, plastic
 strain, or combination of elastic plus plastic strain.
 plastic deformation is irreversible and results in a new permanent shape.
 Elastic deformation is reversible and will be completely recovered when the stress is
eliminated.
 Viscoelastic deformation is a combination of elastic and plastic strain, but recovery of only
elastic strain occurs as the stress is decreased. '
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21. 2.Rheometric Properties
Flow behavior of solid polymers involves combination of elastic & plastic deformation & the elastic
recovery when the stresses are eliminated
 This combination of elastic and plastic changes is termed viscoelasticity
 Actual dental polymeric materials are deformed by a combination of elastic plus plastic strain
processes.
 chain length, no. of cross links, temperature , & rate of force application determines which type of
behavior dominates
 elastomers do not always recover fully and retain a small degree of plastic deformation ,
 Where as plastics exhibits high level of plastic deformation ,but they also have at least some
small degree of elastic recovery .
 This phenomenon is called as viscoelastic recovery
Stretching only No additional stretching Full recovery 5/1/2015
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22. .
3.Solvation Properties
 The longer the chains (the higher the molecular weight), the more slowly a polymer
dissolves.
 Polymers tend to absorb a solvent, swell, and soften, rather than dissolve.
 Cross-linking prevents complete chain separation and retards dissolution.
 highly cross-linked polymers cannot be dissolved.
 Elastomers swell more than plastics.
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Stretching only
Loading
continued
Unloaded
Partial recovery with
permanent deformation
loaded
Slipping occurred
(Quantity of slippage
depends
on the duration of loading)

23.  A small amount of swelling of dental polymeric devices can have undesirable
results on the fit of prostheses.
 Absorbed molecules (e.g., water-) spread polymer chains apart and facilitate
slip between chains. This lubricating effect is called plasticization.
4.Thermal Properties
The physical properties of , polymer are influenced by changes in
 temperature and environment
 by the composition, structure, and molecular weight of the polymer.
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24. CHAIN CONFIGURATIONS
 POLYMER CHAINS ARE HELD TOGETHER BY
1) weak secondary bonds( Vander wall bonds)
2) entanglement of chains if they are sufficient long.
 The higher the molecular weight ,the more entanglements there will be , giving a stiffer &
stronger polymer.
 GLASS TRANSITON TEMPERATURE
 In a polymer ,such as polyethylene which has a linear chain configuration ,the weak
bonds between chains can be easily be broken by increasing the temperature of the
polymer.
 When this happens the chain can flow past one another so that the polymer softens
and readily deforms. 5/1/2015
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25.  On cooling the bonds are re-established and the polymer becomes hard again and
retains the shape it was in at the higher temperature.
 The temperature at which a plastic softens such that the molecules can begin to
flow is defined as glass transition temperature.
 They are similar to those of glasses except that the temperatures involved are
much lower in case of plastics.
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26.  Thermoplastic polymers made of linear & or branched chains
 They may be softened by heating & solidify on cooling …….the process being repetable
 E.g. –poly (methyl methacrylate) , polystyrene etc.
when heated above the glass (transition temperature (Ig), at which molecular
motion begins to force the chains apart
 The resin can then be shaped and molded, upon cooling, they soften
again and can be reshaped if required before hardening as the temperature decreases- this cycle
can be carried out repeatedly
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27.  Thermosetting polymers
 undergo a chemical change and become permanently hard when heated above the
temperature at which they begin to polymerize, and do not soften again on reheating .
 Thermosetting plastics have superior abrasion resistance and dimensional stability
compared to thermoplastic which have better flexural & impact properties.
 Eg. cross linked poly methyl methacrylate.silicones
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28.  Thus heat plays an important role in affecting the physical properties of resins
 When temp.↑ it results In thermal expansion, break polar bonds & facilitate
disentanglement of chains
 This causes slippage of chains & results in thermoplastic behavior
 When crosslinking is present it is difficult to soften resin ,as slippage cannot
occur……….
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29. CHEMISTRY OF POLYMERIZATION
 The process of polymerization were divided by Flory (1953) and
Carothers (Mark 1940) into two groups,
 two types of reaction:
addition polymerization……. monomers are activated one at a time and add together in
sequence to form a growing chain.
 and step-growth or condensation polymerization…………….
POLYMERIZATION IS ACCOMPLISHED BY repeated elimination of small molecules
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30.  Addition polymerization
 Monomers are activated one at time
and together in a sequence to form
growing or smaller chains
 Types
 Free Radical
 Ring opening
 Ionic polymerization
Eg.heat cured or autopolymerizing
poly methyl methacrylate etc.
 Fast process
 Step Growth polymerization /
Condensation Polymerization
 Chemical reaction takes place
with the release of by-product
or smaller units and there is
change in the final composition.
Ex. Proteins, carbohydrates
 Slow process
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31. Addition Polymerization
Addition polymerization occurs among the molecules containing double or triple bonds
No small molecules are liberated and reaction is rapid chain type reaction.
 Monomers add sequentially to the end of a growing chain
 Is very fast and exothermic
 Produces high molecular weight polymers
 The macromolecules are formed from smaller units, or monomers, without change in compositio
because the monomer and the polymer have the same empirical formulas.
 In other words the structure of the monomer is repeated many times in the polymer
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32. Types of addition polymerizations
 Free-radical polymerization
Active center is a radical (contains unpaired electron) and the propagating site
of reactivity is a carbon radical.
 Cationic polymerization
The active center is an acid, and the propagating site of reactivity is positively
charged
 Anionic polymerization
The active center is a nucleophile, and the propagating site of reactivity is
negatively charged
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33. Few common polymers prepared via addition
polymerization
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Name(s) Formula Monomer Properties
Polyethylene
low density (LDPE)
–(CH2-CH2)n– ethylene
CH2=CH2
soft, waxy solid
Polyethylene
high density (HDPE)
–(CH2-CH2)n– ethylene
CH2=CH2
rigid, translucent solid
Polypropylene
(PP) different grades
–[CH2-CH(CH3)]n– propylene soft, elastic solid
isotactic: hard, strong
solid
Poly(vinyl chloride)
(PVC)
–(CH2-CHCl)n– vinyl chloride
CH2=CHCl
strong rigid solid
Polytetrafluoroethylene
(PTFE, CF2=CF2
–(CF2-CF2)n– Teflontetrafluoroethylene resistant, smooth solid
Poly(methyl
methacrylate)
(PMMA, Lucite, Plexiglas)
–[CH2-
C(CH3)CO2CH3]n–
methyl methacrylate
CH2=C(CH3)CO2CH3
hard, transparent solid

34. STAGES
 The process of free radial additional polymerization to produce the polymers
involves 4 stages
Activation
1. Induction
Initiation
2. Propagation
3. Chain Transfer
4. Termination
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35.  Two process control the Induction stage. They are
a)Activation
b)Initiation
 To begin additional polymerization process. A source of free radicals “R”
is required.
 Free radical is an atom or group of atoms possessing an unpaired
electron.
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36.  The process of producing free radicals -Activation.
 Free radicals can be generated by activation of radical producing molecule
using
a)Chemical agents
b)Heat
c)Visible light
d)Ultra Violet Light
e)Energy transferred from another compound which acts as a free radical.
 Of these : Chemical agents, Heat & Visible light
are most often used in dentistry.
 Benzoyl peroxide-Peroxide commonly used in dentistry.
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Induction by heat or chemical

37.  The Activation is done by the decomposition of the benzoyl peroxide , due to the
use of an activator such as
A. Heat :
 When heated above 50 -100oC , benzoyl peroxide decomposes to form a free radical.
 Heat cure acrylic resins
B. Chemical Compounds :
 Benzoyl peroxide can also be activated when brought into contact with a tertiary amine.
 This method is employed in cold cure acrylic resins, also used in chemically cured
composite restorative materials , which consists of a base paste ( tertiary amine activator) &
a catalyst paste (containing benzoyl peroxide initiator)
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38. C)Light :
 Other forms of free radical production include the use of
1) ultra violet light in conjunction with a benzoic methyl ether.
2) visible light with an alpha- diketone and an amine.
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39. INITIATION
 The free radicals will react with a monomer such as ethylene
and initiate the polymerization process.
 When this occurs ,the remaining unpaired electron makes the
new molecule & a free radical
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H H H H
R* + c = c - R- c - c*
H H H H

40. PROPAGATION:
 The free radicals are transferred to the monomer which in turn reacts with other monomer
 Repeating this process again and again generates the polymer chain until the growing chains collide or
all the free radicals have reacted.
 As the initiated molecule approaches other methyl methacrylate molecule,the free electron interacts with
the double bond of the methymethacylate molecule, & a new, longer free radical is formed…….
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41.  CHAIN TRANSFER:
 In this process, the active free radical of a growing chain is transferred to another
molecule and a new free radical for further growth is created.
 Chain transfer occurs when a free radical approaches a methyl methacrylate molecule
and donates a hydrogen atom to methyl methacrylate molecule.
 This causes the free radical to rearrange to form a double bond & become unreactive,
& the MMA monomer to form a free radical that can participate in the chain
propagation reaction…………..
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42. TERMINATION
The chain reactions can be terminated by :
Direct coupling .of two free radical chain ends or by
Exchange of a hydrogen atom from one growing chain to another.
Collision of a growing chain with an initiation radical.
Collision of a growing chain with inhibitor.
Inhibition
 Any impurity if it is present ,it reacts with the monomer and inhibit polymerization .
eg. Hydroquinone 0.006%
Eugenol , Oxygen.
Main functions:
a) aids in prevention of polymerization during storage
b) in case of two parts(self cure) system….provides adequate time for mixing & placement
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43. STEP-GROWTH POLYMERIZATION
When two molecules react to form a large molecule with the elimination of a smaller molecule-
such as water, alcohol, halogen acids & ammonia…..
 Polymers are formed more slowly than by addition polymerization because
 the reaction proceeds in a stepwise fashion from monomer to dimer to trimer …….until
large polymer molecule containing many monomer molecule are eventually formed
 Polymers are generally of lower molecular weight
 E.g used in biological tissues to produce proteins, carbohydrate, DNA etc…
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44. prepolymers
 A monomer or system of monomers that have been reacted to an intermediate molecular mass
state or a substance which represents an intermediate stage in polymerization, & can be usefully
manipulated before polymerization is completed
 This material is capable of further polymerization by reactive groups to a fully cured high
molecular weight state
 As, such mixture of reactive polymers with unreacted monomers may also be referred to as pre-
polymers
 They are also called as polymer precursor
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45. Typical applications of polymers in
dentistry
 Dentures (bases, artificial teeth, relining materials)
 Filling materials (composites, cements, adhesives)
 Impression materials
 Obturation materials
 Equipment (spatulas)
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46. RESINS USED IN
DENTISTRY
Vinyl acrylics-
relining material
Epoxy resins- die
material
Polystyrene,
Polyethylene, Poly
vinyl acetate
Polyacrylic acid-
denture base
material
Polyether,Polysulphide
Silicone impression
material
Principal polymers-
Vulcanized rubber for
denture bases
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47. Acrylic resins
 Mostly used in fabrication of all complete dentures.
 Thermal energy – required for polymerization- water bath or microwave.
 Dr. Walter Wright (1937) introduced Polymethyl methacrylate as a denture base
material ….
 COMPOSITION :HEAT CURE ACRYLIC DENTURES
POWDER LIQUID
Polymethyl meth acrylate
(Prepolymerized
spheres)
Benzoyl Peroxide( Initiator)
Pigment ( 1%)
Methyl meth acrylate
Hydroquinone ( <1% Inhibitor)
Glycol methacrylate
( Crosslinking agent 1-2%) 5/1/2015
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48. COMPOSITION – SELF CURE ACRYLIN
RESIN
Inhibitor- prevents undesirable polymerization during storage 5/1/2015
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49.  Glycol methacrylate – Crosslinking agent.
 Chemically and structurally similar to Methyl meth acrylate.
 Cross linking agents are added into liquid component in concentration of 1- 2% by
volume.
 The interconnections – netlike structure- increased resistance to deformation.
 POLYMER –TO- MONOMER RATIO
 The polymer to monomer ratio is 3:1 by volume.
Using this ratio the volumetric shrinkage can be limited to 7%
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50. Polymer – monomer interaction
 When mixed in proper proportions, the resultant mass passes through five distinct
stages
 1.Sandy
 2. stringy
 3. Dough like
 4. rubbery
 5. Stiff
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51. SANDY STAGE:
- Little or no interaction at molecular level.
- polymer beads remain unaltered
(Corse or grainy)
STRINGY STAGE:
- Monomer attacks the individual polymer beads and is absorbed into the beads.
- Some polymer chains are dispersed into monomer.
- characterized by Stringiness or Stickiness- touched
 DOUGH STAGE:
- At the molecular level, an increased number of polymer chains enter the solution, thus monomer and
dissolved polymer- formed.
- It is no longer tacky or and will no adhere to the mixing vessel or spatula .
-The later phase of this stage are ideal for compression molding. 5/1/2015
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52. RUBBERY STAGE:
- Because the monomer is dissipated by evaporation and by
further penetration into remaining polymer beads.
- Mass rebounds when compressed or stretched.
STIFF STAGE:
- Continued evaporation of unreacted monomer.
- Material looks dry and resistant to mechanical deformation
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53. DOUGH FORMING TIME
 The time required for the resin mixture to reach a dough like stage.
 In clinical use, majority of the denture base products reach dough stage
consistency in less than 10 min.
WORKING TIME
 Defined as the time a denture base material remains in the dough like stage.
 This period is critical to the compressive molding process.
 Ambient temperature affects the working time.
 Working time 5minutes.
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54. Residual Monomer
 Despite of various polymeriszation techniques used to initiate
polymerization reaction ,the conversion of monomer to polymer is not
complete………….some unreacted monomer persists---------
residual monomer
 During polymerization it decreases first rapidly & later more slowly after
most polymerization is over
 Residual monomer content in heat cure resins is around 0.3-0.5%
 Where as in self cure it is around 3-5%
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55. EFFECT:
 This residual monomer might leach out & contact oral mucosa
,specially denture bearing mucosa
 Irritant or allergic reaction by MMA monomer
 The amount of MMA released was related with the processing
condition & composition of material
 Light cure resins released comparatively less residual monomer
than heat or self cured
 For minimizing monomer released heat cure & chemical cured
dental resins must be immersed for 1 day in water before wearing
Huang.F.M , Chin Hu.C , Chang.Y.C , Chou.M.Y: Residual monomer releasing from
acrylic denture base in water , Chin Dent J 19(1) 17-22 March 2000 5/1/2015
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56. Polymerization shrinkage
It is the volumetric shrinkage that occurs during the polymerization of MMA to
PMMA polymer
Density of the mass changes from 0.94 to 1.19gm/cm3
Volumetric shrinkage of 21%
Along with volumetric shrinkage linear shrinkage occurs during the cooling
process
It can be minimized by
a) a correct proportioning of the monomer & the polymer
b) Packing in the dough stage
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57. Water Sorption & Solubility
 The dimensions of acrylics vary with water absorption
 This is reversible & denture contracts when dried
 Heat cure dentures immersed in water exhibits a linear expansion of 0.1%to
0.2%
 This compensates partially for polymerization shrinkage of 0.3% -0.5%
 Reason : water absorption results in a slight expansion of denture due to 2
reasons
1. Water enters the mass & occupies the space in between the polymeric
chains & causes a slight expansion of polymeric mass
2. Water also interferes with entanglement of polymeric chains there by acts
as plasticizers.
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58. Recent Advances
 Flexible Thermoplastic Denture Base Materials - Removable Partial Denture
Framework.
 The resin is a biocompatible nylon thermoplastic
 unique physical and aesthetic properties that provides unlimited design versatility
 eliminates the concern about acrylic allergies.
 allows the restoration to adapt to the constant movement and is flexible in the mouth.
VALPLAST Flexible Dentures
Maxillary esthetic valplast denture
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59.  FLEXIBLE DENTURE BASE MATERIAL
 Free movement is allowed by the overall flexibility and can, therefore, be referred to
 as “a built in stress breaker”.
Sunitha N ,Shamnur, Jagadeesh KN, Kalavathi SD, Kashinath KR :“Flexible dentures” – An alternate for rigid
dentures. Journal of Dental Sciences & Research 1:1: Pages 74 - 79
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60.  FIBER-REINFORCED DENTURE BASE RESINS
• Reinforced denture base with glass fillers: (Ref: JOP1999, 18-26, vol-8,
no.1) Mona K.Marie has conducted a study to evaluate the effect of short
glass fibers on the transverse strength of a heat polymerized denture base
material.
• Optimal adhesion between the fibers and the polymer matrix can be
obtained by mixing with silane coupling agents
• Incorporation of glass fibers in a continuous roving form increases the
strength of dentures and enhances the fracture resistance
• disadvantage of this system is difficulty in handling the fibers and
inadequate degree of impregnation of fibers with the resin.
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61. CONCLUSION
 Polymers are very rarely used in their pure form
 Modifications are carried out to improve the properties of the polymers.
 Depending upon the use modifications are done in order to meet the requisites of the
material.
 Some of the fairly good properties of the polymers make, the use of the polymers,
in dentistry very wide . In almost every field of dentistry they can be used
successfully.
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62. REFERENCES
 PHILLIPS SCIENCE OF DENTAL MATERALS-ANUSAVICE.11th edition
 Craig’s restorative dental materials-powers.J.M, Sakaguchi.R.L-12th edition
 William J .O’Brien-Dental materials & selection-4t edition
 Singh.H, Aeran.H, Kumar ,Gupta.N ;Flexible Thermoplastic Denture Base Materials - Removable
Partial Denture Framework.
 Kutsch VK, Whitehouse J, Schermerhorn K, Bowers R. The evolution and advancement of dental
thermoplastic. Dental Town Magazine. 2003.
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63.  Negrutiu M, Sinescu C, Romanu M, Pop D, Lakatos S. Thermoplastic resin for removable
partial dentures. TMJ. 5 (3).
 Uzun.G ,Hersek.N, Teoman .T. Effect of five woven fiber reinforcements on the impact and
transverse strength of a denture base resin. J Prosthet Dent 1999;81:616-20
 Marie.M.K- FIBER-REINFORCED DENTURE BASE RESINS .JOP1999, 18-26, vol-8, no.
 Sunitha N ,Shamnur, Jagadeesh KN, Kalavathi SD, Kashinath KR :“Flexible dentures” – An
alternate for rigid dentures. Journal of Dental Sciences & Research 1:1: Pages 74 - 79
 Huang.F.M , Chin Hu.C , Chang.Y.C , Chou.M.Y: Residual monomer releasing from acrylic
denture base in water , Chin Dent J 19(1) 17-22 March 2000
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64. Next seminar
 Dr. NAVEEN REDDY
 TOPIC: IMPLANT FAILURES
 date:06/01/2015
5/1/2015
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65. 5/1/2015
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