Denture Base Resin

1. Denture Base Resin
-Dr. Soham Prajapati
1st Year Post Graduate,
Dept. of Prosthodontics
& Maxillofacial Prosthesis
Including Oral Implantology.
7/12/2013 & 9/12/2013
1

2. • Definition
• History
• Classification
• Dental polymers
• Ideal requirements of Denture Base Resin
• Principal ingredients of Denture Base Resin
• Different Types Denture Base Resins
• Properties of PMMA
• Cytotoxicity of Denture Base Acrylic Resins
• Recent Advances
• Conclusion
• References
2

3. Definition
• DENTURE BASE: The part of a denture that
rests on the foundation tissues and to which
teeth are attached.
• RESIN: A broad term used to describe natural
or synthetic substances that form plastic
materials after polymerization.
- GPT 8 3

4. Key Points of DENTAL RESINS
• ADA/ANSI Specification no 12 - Denture base
resins.
• ISO 1567
4

5. History
• Skillfully designed dentures were made as
early as 700 BC using ivory and bone.
• Till 1800s, dentures were hand carved and
tied in place with silk threads.
• Queen Elizabeth I and George Washington
suffered from tooth loss and unfit dentures.
5

6. History
• In 1774, Duchateaus and Dubois de Chemant
designed a full set of dentures that would not
rot.(made of porcelain.)
6

7. History
• Giuseppangelo Fonzi created a single
porcelain tooth held in place by a steel pin in
1808.
• Claudius Ash made an improved porcelain
tooth in 1837.
• Porcelain dentures moved to US in 1800s and
marketed on a large scale. Fit was eventually
improved as well.
7

8. History
• In 1700s, plaster of paris was introduced. It
was used to make a mold of the patient’s
mouth. This helped to make the dentures
precise.
• Swaged Gold was used as denture base for
those who could afford it.
8

9. • Real breakthrough when vulcanized rubber
was discovered by Charles Goodyear in 1840.
– Cheap
– Easy to work
– Hold the denture
• Vulcanite dentures were available in India
under British rule by British and other
European Dentists.
History
9

10. Vulcanite
• Contains 32 % sulphur and metallic oxides for
color.
Advantages Disadvantages
Nontoxic
Non-irritant
Excellent Mechanical Properties
Quiet hard to polish
Absorbs Saliva
Becomes unhygienic.
Unpleasant odor(when
processed)
Poor esthetics (opacity of rubber)
Dimensional changes.
10

11. Nitrocellulose
• Dimensionally stable
• Excessive Warpage
• High water absorption
• Poor color stability
• Contains unpleasant tasting plasticizer
• Highly flammable
11

12. Other
• Celluloid
– Was tried in place of rubber but didn’t prove best
of the material.
• Porcelain
– It was tolerate by denture bearing mucosa, but
difficult to fabricate and easily broken.
• Phenol Formaldehyde
– Becomes dicolored and unesthetic and being
thermosetting, it is difficult to repair
12

13. History
• In 1937 Dr. Walter Wright gave dentistry its
very useful resin.
• It was polymethyl methacrylate which proved
to be much satisfactory material tested until
now.
• By 1946, 98% of all denture bases were
fabricated from PMMA.
13

14. Classification
• According to ISO 1567
– Type 1
• Class 1 Heat processing polymers, powder and liquid
• Class 2 Heat processed (plastic cake)
– Type 2
• Class 1 Autopolymerized polymers, powder and liquid
• Class 2 Autopolymerized polymers (powder and liquid pour
type resins)
– Type 3 Thermoplastic blank or powder
– Type 4 Light Activated Materials
– Type 5 Microwave-Cured Material
14
Applied Dental Materials, 8th edition,
John F McCabe & Angus W. G. Walls

15. Classification
• Based on the usage:-
– Temporary Denture Base Resin
• E.g. Self Cure Acrylics
• Shellac base plate
• Base plate wax
• Injection Molded resins
• Metallic Bases
– Permanent Denture Base Resin
• E.g. Heat Cure Denture Base
• Light Cures Resins
• Pour Type Resins
15

16. Classification
• Based on the METHOD USED FOR ITS
ACTIVATION:-
– Chemically activated
– Heat activated
– Light activated
16

17. DENTAL POLYMERS
• Polymer is chemical compound consisting of
large organic molecules formed by the union
of many repeating smaller monomer units.
17

18. • Polymerization occurs through a series of chemical reactions
by which the macromolecule, or the polymer, is formed from
large numbers of molecules known as monomers.
• TYPES:-
– CONDENSATION POLYMERIZATION
– ADDITION POLYMERIZATION
18

19. CONDENSATION POLYMERIZATION
• TWO GROUPS
– Those in which polymerization is accompanied by
repeated elimination of small molecules. The
process repeat itself and form macromolecules.
E.g. water, halogen acids, ammonia, etc.
19

20. – Those in which functional groups are repeated in
the polymer chains. The polymers are joined by
functional groups. Formation of a by-product is
not necessary. E.g. polyurethane.
Not widely used in DENTISTRY
20

21. ADDITION POLYMERIZATION
• All resins employed extensively in dental
procedure are produced by addition
polymerization.
• No change in chemical composition and no by-
products are formed.
21

22. How??
• Starting from an active centre, one molecule
at a time is added and a chain rapidly builds
up, which can grow almost indefinitely as long
as the supply of building blocks are available.
22

23. Chemical Stages of Polymerization
4 Stages:-
• Induction
• Propagation
• Chain Transfer
• Termination
23

24. INDUCTION
• Induction or initiation period is the time
during which the molecules of the initiator
becomes energized or activated and start to
transfer the energy to the monomer.
24

25. • Three induction systems:-
– Heat Activation
– Chemical Activation
– Light Activation
• Heat Activated:- The free radical liberated by
heating benzoyl peroxide will initiate the
polymerization of methyl methacrylate
monomer. e.g. Denture base Resins
25

26. • Light Activated:-
– Photons of light energy activate the initiator to
generate free radicals. e.g. composite resin.
Chemical Activated:-
– System consists of at least two reactants, when
mixed they undergo chemical reaction and
liberate free radicals, e.g. Self Cured Resin
26

27. INDUCTION
27

28. INDUCTION
28

29. 29

30. PROPAGATION
• Once the growth has started, the process
continues with considerable velocity.
• Theoretically, the chain reactions should
continue with evolution of heat until all the
monomer has been changed to polymer.
• Actually, the polymerization is never
complete.
30

31. PROPAGATION
31

32. 32

33. CHAIN TRANSFER
• The chain termination can also result from
chain transfer. Here, the activated state is
transferred from an activated radical to an
inactive molecule, and a nucleus of growth is
created.
33

34. CHAIN TRANSFER
34

35. CHAIN TRANSFER
35

36. TERMINATION
• The chain reaction can be terminated either
by direct coupling or by exchange of hydrogen
atom from one growing chain to another.
36

37. Termination
37

38. Termination
38

39. 39

40. COPOLYMERIZATION
• The macromolecule may be formed by
polymerization of a single type of structural
unit.
• In order to improve the physical properties, it
is often advantageous to use two or more
chemically different monomers as starting
materials.
40

41. • The polymer thus formed may contain units of
these monomers. Such a polymer is called a
copolymer and its process of formation is
known as copolymerization.
41

42. Types of COPOLYMER
• There are three different types:-
• RANDOM TYPE
• GRAFT TYPE
• BLOCK TYPE
42

43. RANDOM TYPE
• In random type of copolymer the different
monomers are randomly distributed along the
chain.
……ABBABABAAAAAABBABABABBBBBABBABBAB….
43

44. GRAFT TYPE
• Sequence of one of the monomers are grafted
onto the ‘backbone’ of the second monomer
species.
44

45. • Identical monomer units occur in relatively
long sequences along the main polymer chain.
…..AAAAABBBBBAAAAABBBBBAAAAABBBBBAAAAA…..
BLOCK TYPE
45

46. IMPORTANCE OF COPOLYMERIZATION
• It is to better the physical properties of resins.
• Many useful resins are manufactured by
copolymerization.
46

47. CROSS-LINKING
• The formation of chemical bonds or bridges
between the linear polymer is referred to as
CROSS-LINKING.
• It forms a three-dimensional (3D) network.
47

48. Application Of Cross-Linking
• The more recent acrylic resins are of cross-
linked variety. It improves the strength, and
decreases the solubility and water sorption.
• Acrylic teeth are highly cross-linked to
improve its resistance to solvents, crazing and
surface stresses.
48

49. Requirements Of Denture Base
Materials
49

50. ADA Specification General
Requirements of the non-processed
Materials
Liquid
Clear as Water
Free of Extraneous
Material
50

51. Specification General Requirements of
the non-processed Materials
POWDER, PLASTIC CAKE
OR PRECURED BLANK
FREE OF IMPURITIES
SUCH AS DIRT AND LINT
51

52. GENERAL REQURIMENTSREQUIREMENTS
WITHIN FIVE MINUTES , AFTER REACHING THE PROPER
CONSISTENCY, INDICATED BY CLEAN SEPERATION FROM
THE WALLS OF GLASS MIXING JAR & THE MATERIAL
SHOULD HAVE ADEQUATE FLOW PROPERTY
WATER SORPTION SHALL NOT BE MORE THAN 0.8
mg/cm2 AFTER IMMERSION FOR 7 DAYS AT 37° C
SOLUTIBILITY SHALL NOT BE MORE THAN 0.04 mg/cm2
AFTER THE WATER SORPTION SPECIFIC IS DRIED TO
CONSTANT WEIGHT
52

53. GENERAL REQURIMENTSREQUIREMENTS
THE PLASTIC SHALL SHOW NO MORE THAN A SLIGHT
COLOUR CHANGE WHEN EXPOSED 24 HOURS TO A
SPECIFIED ULTRAVIOLET LAMP TEST.
THE TRANSVERSE DEFLECTION SHALL BE WITHIN THE
LIMITS LISTED IN THE DISCUSSION.
53

54. 54

55. Ideal Requirements Of Denture Base
Materials
Final report of the workshop on clinical requirements of
ideal denture base material
1. Physiologic compatability
• Nontoxic
• Noncarcinogenic
• Nonallergenic
• Compatible with physiologic requirements of mucous
membranes Optimum consistency to maintain or
promote tissue health
• Not deleterious to adjacent and underlying tissues
• Conducive to normal salivary flow
55ATWOOD:JPD 1968 (20) 101-105

56. 2. Acceptability to patients' senses
• Acceptable to all five senses-sight, sound, smell, taste,
and touch
• Able to duplicate and simulate oral tissues as nearly as
possible
• Possessing wide selection of color
• Possible for esthetics to be easily modified
• Color stable
• Odorless
• Tasteless
• Possessing instantaneous temperature conductivity
• Light weight
• Possessing sensation of natural texture
56

57. 3. Functional usefulness
• Rigid enough so that teeth penetrate the bolus
• No interference with oral functions of chewing,
swallowing, self cleansing, singing, speech, sneezing,
breathing, laughing, coughing, etc.
57

58. 4. Hygienic factors
• Sterilizable
• Resistant to stain, calculus, and adherent substances
• Nonporous to microorganisms
• Low fluid absorption
• Wettable (low surface tension)
• Easily cleaned
58

59. 5. Durability
• Not affected by oral environment-bacteria, food,
medicines, etc. Unbreakable (not brittle)
• Not crazing
• Dimensionally stable and statically stable
• Minimal internal strain
• Good bond between different base materials
• Good bond between base and teeth
• Not flammable
• Resistant to weak acids and alkalis
• Resistant to abrasion and wear
• Resistant to strain
• Long lasting
59

60. 6. Adaptability to clinical problems
• Adjustable
• Easily polished
• Easily repaired
• Easily relined
• May need more than one type of material
• May use combinations of materials (soft for
tissues, hard for teeth) Choice of hardness or
softness (various materials for different
situations
60

61. 7. Cost factors
• Simple to manipulate
• Simple to process
• Inexpensive equipment for processing Average
skill required for processing No separation
medium required Easily separated from cast
• Moderate cost of fabrication
• Good shelf life
• Predictable properties
61

62. PRINCIPAL INGRIDIENTS OF DENTURE
BASE RESIN
62

63. PRINCIPAL INGREDIENTS OF ACRYLIC
DENTURE BASE RESIN
POWDER LIQUID
Acrylic polymer (or Copolymer) beads
Initiator
Pigments
Dyes
Opacifiers Plasticizer
Dyed organic fibers
Inorganic particles
Monomer
Inhibitor
Accelerator
Plasticizer
Cross-linking agent
63CRAIG RESTORATIVE DENTAL MATERIAL

64. Acrylic Resins used In Dentistry
• Derivatives of Ethylene and contains a vinyl
group in their structural formula.
• Acrylic resin used in dentistry are the esters of
:-
– Acrylic acid, CH2 = CHCOOH
– Methacrylic acid, CH2 = C(CH3)COOH
64

65. DENTURE BASE RESINS
HEAT ACTIVATED DENTURE BASE RESINS
• Most widely used resins for the fabrication of complete
dentures.
• Available as:-
– Powder and liquid
• Powder may be transparent or tooth colored or pink colored
(to stimulate the gum, some even contain red fibers to
duplicate blood vessels).
• Monomer is supplied in tightly sealed amber colored bottles
(to prevent premature polymerization by light or ultraviolet
radiation on storage).
65

66. • Commercial Names:-
– Stellon (DPI)
– Lucitone (Bayer)
– Travellon (Dentsply)
66

67. Composition
67
POWDER
Poly (methyl methacrylate)
Ethyl or butyl Methacylate (5 %)
Benzoyl Peroxide
Compounds of Mercuric sulfide, cadmium
sulfide, etc.
Zinc or titanium oxide
Dibutyl phthalate
Inorganic fillers like glass fibers, zirconium
silicate, alumina, etc.
Dyes synthetic nylon or acrylic fibers
Major component
Copolymers – improved properties
Initiator
Dyes
Opacifiers
Plasticizer
Improves physical properties like stiffness,
etc.
To simulate small capillaries

68. Composition
68
LIQUID
Methyl methacrylate
Dibutyl phthalate
Glycol Dimethacrylate
Hydroquinone (0.006%)
Plasticizes the polymer
Plasticizer
Cross-Linking agent (reduces Crazing)
Inhibitor – prevents premature
polymerization

69. 69
Chemical Basis

70. 70
POLYMER POWDER OF ACRYLIC DENTURE BASE MATERIAL

71. TECHNIQUE
• Primary impressions
• Secondary impressions
• Jaw relations
• Try in stage
• Acrylization
– Flasking
– Dewaxing
– Packing- under pressure
– Curing
71

72. Flasking
• The Art of Investing in a Flask ”
- GPT
• Flask
“ a metal case or tube used in investing
procedure”
- metal
- brass
- 3 or 4 parts
72

73. 73
3 PART FLASK

74. 4 PART FLASK
74

75. PRESSURE CLAMP
75

76. FLASKING
76
3 POUR
TECHNIQUE
4 POUR
TECHNIQUE

77. COMPRESSION MOLDING TECHNIQUE
 Periphery of flask should be in
level with the rim of the flask
 Occlusal plane – parallel to the
base of the flask
77

78. • Tilting of the casts
• Retromolar pads and tuberosity
should be protected
• Checking the seating of flask
members
• Distance from top lid – 6 mm
78

79. • Paint on separating
media like cellulose
lacquers, solution
containing alginate
compounds, calcium
oleate ,soaps, sodium
silicate, starches were
introduced….. Tin foil
substitutes.
• Most popular… water
soluble alginate solution
• Produce thin, relatively
insoluble calcium
alginate films…..
79

80. Sodium Alginate Solution
• Water soluble.
• Reacts with the calcium of plaster or stone to
form a film of insoluble calcium alginate.
• Composition
– 2 % sodium alginate in water
– Glycerine
– Alcohol
– Sodium phosphate
– Preservatives
80

81. Sodium Alginate Solution
• Application
– Applied using brush, coating only the plaster
surfaces.
– One or two coats are applied.
81

82. Sodium Alginate Solution
• Precautions to be taken
– Waxes or oils remaining on the mold surface will
interfere with the action of the separating
medium.
– Mold should not be warm, not hot. Continuity of
the film will break if the mold is steaming hot.
– Avoid coating on teeth.
82

83. • Second mix is mixed
• Lid is closed
• Flask is clamped
83

84. Polymer – Monomer Interaction
• Sandy, stringy, dough like, rubbery or elastic,
stiff
• During sandy stage, little or no interaction
occurs on a molecular level. Polymer beads
remain unaltered.
• Later, mixture enters stringy stage. Monomer
attacks the surfaces of individual polymer
beads. Stage characterized by stringiness.
84

85. Polymer – Monomer Interaction
• Subsequently the mass enters a dough like
stage. On molecular level increased number of
polymer chains are formed. Clinically the mass
becomes as a pliable dough. It is no longer
tacky
• This stage is ideal for compression molding.
• Hence material is inserted into mold cavity
during dough like stage.
85

86. • Following dough like stage, the mixture enters
rubbery or elastic stage. Monomer is
dissipated by evaporation and by further
penetration into remaining polymer beads. In
clinical use the mass rebounds when
compressed or stretched.
• Upon standing for an extended period, the
mixture becomes stiff. This may be attributed
to the evaporation of free monomer. From
clinical point, the mixture appears very dry
and resistant to mechanical deformation
86

87. DOUGH FORMING TIME
• The time required for the resin mixture to
reach a dough like stage is termed the dough
forming time.
• In clinical use, the majority of resin reach a
dough like consistency in less than 10 min.
87

88. PACKING
• Placement and adaptation of denture
base material within the mold cavity is
termed packing.
Over packing- leads to excessive
thickness and malposition of prosthetic
teeth
Under packing- leads to noticeable
denture base porosity
• Trial packing is done to ensure proper
packing of resin mass in the mold.
• After the final closure of the flasks,
they should remain at room
temperature for 30- 60 min. it is called
bench curing
88

89. Bench curing
• It permits equalization of
pressure throughout the mold
• Allows more time for uniform
dispersion of monomer
throughout the mass of dough
• If resin teeth are used, it
provides a longer exposure of
resin teeth to the monomer
producing a better bond of the
teeth with the base material
89

90. POLYMERIZATION PROCEDURE / CURING
• When heated above 60 °C, molecules of benzoyl
peroxide decompose to yield free radicals.
• Each free radicals, rapidly reacts with an available
monomer molecule to initiate polymerization.
• Heat is required to cause decomposition of
benzoyl peroxide. Therefore heat is termed as
activator.
• Decomposition of benzoyl peroxide molecule
yields free radicals that are responsible for
initiation of chain growth. Hence it is termed as
initiator
90

91. Temperature rise
• Because resin and dental stone are relatively
poor thermal conductors, the heat of reaction
cannot be dissipated. Therefore the
temperature of resin rises well above the
temperature of investing stone and
surrounding water.
• It should be noted that temperature of resin
not allowed to exceed the boiling point of the
monomer (100.8oC) – which produces
significant effects on the physical
characteristics of the processed resin.
91

92. Curing cycle
• Following curing cycle have been quite
successful
– Processing in a constant temperature water bath
at 74oC for 8 hours or longer with no terminal
boil.
– Processing in a 74 0C water bath for 8 hours and
then increasing the temperature to 100oC for 1
hour.
– Processing resin at 74oC for approximately 2
hours and increasing the temperature of water
bath to 100oC for 1 hour.
92

93. Polymer – Monomer Ratio
• Polymerization of MMA to PMMA yields 21%
decrease in the volume of material, which would
create difficulties in denture base fabrication and
clinical use.
• To minimize dimensional changes, Resin
manufacturers prepolymerize a significant
fraction of the denture base resin.
• The accepted polymer to monomer ratio is 3:1 by
volume.
• Using this ratio the volumetric shrinkage is
limited to 6% and 0.5% linear shrinkage.
93

94. Polymer – Monomer Ratio
94
If too much monomer is use:- If too little monomer is use:-
Greater curing or polymerization shrinkage
More time is needed to reach the packing
consistency
Porosity may occur in denture
Not all the polymer bead will be wetted by
monomer and the cured acrylic will be
granular.
Dough will be difficult to manage and it
may not fuse into a continuous unit of
plastic during processing

95. • First reported by Kimura et. al
• This technique employs a
specially formulated resin and
a non metallic flasks. FRP Flask
[ Fiber Reinforced Plastic flasks]
95
POLYMERIZATION VIA MICROWAVE
ENERGY

96. Advantages:
• Cleaner and faster polymerization.
3 minutes
• Minimal color changes
• Less fracture of artificial teeth and
resin bases
• Superior denture base adaptability
96

97. • No noticeable difference
• Trade name
– Keystone Diamond D
• Disadvantages
Flasks are expensive and have tendency to
break down after processing several dentures.
The polycarbon bolts tend to break if
tightened too firmly.
97
Bernard Levin et al [ JPD 1989;61: 381-383]

98. Injection molded
polymers
• In mid 1970’s, Ivoclar introduced
this system.
• These are made of Nylon or
Polycarbonate.
• It has to be heated and injected
into a mold
98
The SR-Ivocap system uses specialized flasks and
clamping presses to keep the molds under a
constant pressure of 3000 lbs

99. Injection molded polymers
• Flask is then placed into water bath
for polymerization as the material
polymerizes addition resin is
introduced into the mold cavity. This
process offsets the effects of
polymerization shrinkage.
• Equipment is expensive.
99
The SR-Ivocap system uses specialized flasks and
clamping presses to keep the molds under a
constant pressure of 3000 lbs

100. Injection molded polymers
• Advantages
– Dimensional Accuracy
– No increase in vertical dimension.
– Homogenous denture base
– Low free monomer content
– Good impact strength
• Disadvantages
– High cost of equipment
– Difficult mold design
– Less craze resistant
– Special flask is required.
100

101. 101

102. Technique
102

103. Technique
103

104. Chemically Activated Denture Base
Resins
• Does not require thermal energy.
• Hence often referred to as cold curing, self
curing or autopolymerizing resins.
104

105. Chemically Activated Denture Base
Resins
• Chemical activation is accomplished through
the addition of a tertiary amine such as
dimethyl- Para- toluidine to the liquid.
• Upon mixing, the tertiary amine causes
decomposition of benzoyl peroxide.
Consequently, free radicals are produced and
polymerization is initiated.
105

106. Composition
106
POWDER
Poly (methyl methacrylate) and
other co-polymer(5 %)
Benzoyl Peroxide
Compounds of Mercuric sulfide,
cadmium sulfide, etc.
Zinc or titanium oxide
Dibutyl phthalate
Dyes organic fillers and inorganic
particles like glass bead fibers or
beads.
Dissolves the monomer to form
dough
Initiator
Dyes
Opacifiers
Plasticizer
Esthetics

107. Composition
107
LIQUID
Methyl methacrylate
Dimethyl-p-toluidine
Dibutyl phthalate
Glycol Dimethacrylate 1 to 2%
Hydroquinone (0.006%)
Dissolves/Plasticizes the polymer
Activator
Plasticizer
Cross-Linking agent (reduces Crazing)
Inhibitor – prevents premature
polymerization

108. MANIPULATION OF
AUTOPOLYMERIZATION RESINS
• Sprinkle on technique
• Adapting technique
• Fluid resin technique
• Compression molding technique
108

109. • There is greater amount of
unreacted monomer which
creates two major difficulties.
1. It acts as plasticizer that results
in decreased transverse
strength of denture resin.
2. Residual monomer serves as a
potential tissue irritant,
thereby compromising the
biocompatibility of the
denture base.
109

110. Technical considerations
• Most often molded using compression
technique.
• Mold preparation and resin packing are
essentially same.
• Working time for self cure resin is shorter
than heat cured resins.
• Refrigerating the liquid component or mixing
vessel before mixing process can prolong the
working time.
110

111. Processing considerations
• Following final closure of the denture flask,
pressure must be maintained throughout
polymerization process.
• Initial hardening of resin occurs within 30
minutes of final closure.
• To ensure sufficient polymerization, the flask
should be held under pressure for minimum 3
hours
• Resins polymerized via chemical activation
generally display 3-5% free monomer where as
heat activated resins 0.2-0.5% free monomer.
111

112. Uses
• Temporary crowns and FPDs.
• Construction of special tray.
• For denture repair, relining and rebasing.
• Making removable orthodontic appliances.
• For adding a post dam to an adjusted upper
denture.
• For making temporary and permanent
denture bases.
112

113. FLUID RESIN TECHNIQUE
• Special resin is available.
• Chemical composition is similar to polymethyl
methacrylate materials.
• Principal difference is they have high
molecular weight powder particles that are
much smaller and when they are mixed with
monomer, the resulting mix is very fluid.
• Significantly lower power: liquid ratio ranges
from 2:1 to 2.5:1.
113

114. Method of Flasking and Curing
• Agar hydrocolloid is used for the mold
preparation in place of the usual gypsum.
• Fluid mix is quickly poured into the mold and
allowed to polymerize under pressure at 0.14
MPa .
114

115. Fluid Resin Technique
• Employs a pourable chemically activated
resin
Advantages
• Improved adaptation to underlying soft
tissues.
• Decreased damage to prosthetic teeth and
denture base during deflasking.
• Reduced material costs.
• Simplification of flasking, deflasking, finishing
procedure
115
Walter Shepard [ JPD 1968;19: 562-564]

116. Fluid Resin Technique
Disadvantages
• Noticeable shifting of prosthetic teeth
during processing
• Air entrapment
• Poor bonding between denture base and
acrylic teeth
• Technique sensitivity
116
Walter Shepard [ JPD 1968;19: 562-564]

117. • Fluid denture resin processing in a rigid mold
• Koblitz FF et al described a fluid resin processing
technique using rigid, modified gypsum
investment as replacement for hydrocolloid
investment.
• Advantages
• Method requires no specialized equipment such
as metal flasks or hydrocolloid conditioning
apparatus
• The technique eliminates the time consuming
step of sorting and replacing artificial teeth in as
hydrocolloid mold.
117[ JPD 1973; 30; 339-345 ]

118. 118

119. 119

120. Self Cured Heat Cured
Heat is not necessary for polymerization
Porosity is greater
Has lower average molecular weight (not
Strong)
Higher residual monomer content
Rheological properties
- Shows greater distortion
- More initial deformation
- Increased creep and slow recovery
Poor color stability
Easy to flask
Heat is necessary
Porosity is less
Higher molecular weight
Lower residual monomer content
- Shows less distortion
- Less initial deformation
- Less creep and quicker recovery
Color stability is good
Difficult to deflask
Increased rate of monomer diffusion at
higher temperature.
120

121. Light Activated Denture Base Resins
• This material has been
described as a composite
having a matrix of urethane
dimethacrylate and microfine
silica
• Visible light is the activator
• Camphoroquinone serves as
the initiator for
polymerization
• Supplied in sheets and rope
forms and is packed in light
proof pouches.
121

122. Light Activated Denture Base Resins
• Can be used as repair material and as custom
tray material.
• Single component denture base is supplied as
sheet and rope form in light proof pouches.
122

123. • Technique
– Teeth are arranged, and the denture base is molded on an
accurate cast.
– Subsequently the denture base is exposed to high intensity
visible light source for an appropriate period
– Following polymerization, the denture is removed from the
cast, finished and polished in a conventional manner.
123

124. Properties Of Denture Base Resins
• METHYL METHACRYLATE
 Methyl methacrylate is a transparent liquid at room
temp.
 Physical properties
-Molecular weight = 100
-Melting point = - 48 C
-Boiling point = 100.8 C
-Density = 0.945g/ml at 20 C
-Heat of polymerization=12.9 Kcal/mol
124

125. POLYMETHYL METHACRYLATE
• Transparent resin, transmits light in UV range
to a wavelength of 250 nm.
• Hard resin knoop hardness no of 18 to 20.
• Tensile strength is 60 MPa
• Density is 1.19 g/cm cube.
• Modulus of elasticity 2.4 GPa(2400 MPa)
125

126. POLYMETHYL METHACRYLATE
• It is chemically stable and softens at 1250C
• It can be molded as a thermoplastic material
between 125oC and 200oC.
• Depolarization takes place at approx. 450oC .
• Absorbs water by imbibition
• Non crystalline structure possess high internal
energy.
126

127. Strength
• Resins are typically low in strength, however they
have adequate compressive and tensile strength
for complete or partial denture applications.
• Compressive strength- 75 Mpa
• Tensile strength- 52 Mpa
Affected by:-
• Composition of the resin
• Technique of processing
• Degree of polymerization
• Water sorption
• Subsequent environment of the denture
127

128. Hardness
• Resins have low hardness. They can be easily
scratched and abraded.
• Heat cured resin- 18-20 KHN
• Self cured resin- 16-18 KHN
128

129. Modulus of elasticity
• Resins have sufficient stiffness [ 2400MPa] for
use in complete and partial dentures.
Impact Strength
• It is the measure of energy absorbed by a
material when it is broken by a sudden blow.
• Addition of plasticizers increase the impact
strength.
129

130. 130

131. Polymerization shrinkage
• When MMA monomer is polymerized to form PMMA..
Results in 21% volumetric shrinkage.
• To reduce this high % of shrinkage… polymer powder is
supplied in prepolymerized beads form which accounts
for only 7% of volumetric shrinkage.
• Distributed uniformly to all surfaces, hence the
adaptation of denture bases to underlying soft tissues
is not significantly affected.
Processing shrinkage
Due to stresses induced during processing
• 0.26% for self cure resin
• 0.53% for heat activated resin
131

132. 132

133. Denture Warpage
• It is the deformity or change of shape of the
denture which affect the fit of the denture.
• Stresses incorporated during processing.
133

134. Denture Warpage
• Caused by:-
• Stress causes by curing shrinkage or uneven or
rapid cooling.
• Packing of resin in rubbery stage.
• Improper flasking.
• During polishing, a rise in temperature occurs.
134

135. Denture Warpage
• Caused by:-
• Immersion of the denture in hot water.
• Recuring of the denture after addition of relining
material, etc.
135

136. Porosity
• May compromise physical, aesthetic and
hygienic properties of processed dentures.
136

137. Porosity
Internal Porosity:
• Is in form of voids or bubbles within the mass
of processed resin. It is confined to thick
portions of denture base.
• Results from vaporization of unreacted
monomer and low molecular wt. polymers,
137

138. Porosity
External Porosity:
• Inadequate mixing of powder liquid
components.
• Inhomogeneity of resin mass
• Inadequate pressure or insufficient material
• Air inclusions incorporated during mixing
procedures.
138

139. Water Sorption
• Absorption is primarily by diffusion
mechanism.
• Water molecules occupy positions between
polymer chains forcing the polymer chains
apart.
• The introduction of water molecules in the
polymerized mass produces two important
effects
• Acts as plasticizers
• It causes slight expansion of polymerized mass
139

140. Water Sorption
• PMMA exhibits a water sorption value of
0.69mg/cm2
• Fortunately these changes are relatively
minor and do not exert significant effects
on the fit or function of processed bases.
140

141. Crazing
• Is formation of surface cracks on
denture base resin.
• Due to
-Stress relaxation
-Solvent action e.g. Ethyl
alcohol
• Crazing in a transparent resin
imparts a hazy or foggy
appearance.
• These surface cracks predispose
a denture resin to fracture.
141

142. Plaque Adhesion
• An invitro study done on the adhesion and
penetration of C. Albicans proved that
adhesion of C. Albicans occur, but they cant
penetrate the Denture Base Resin.
142
A COMPARATIVE IN-VITRO STUDY ON THE ADHERENCE AND
PENETRATION OF C. ALBICANS TO THREE DIFFERENT RESIN DENTURE
BASE SURFACE -Dr. Divyang Patel

143. Other Microorganisms
• Streptococcus Oralis, Bacteroides gingivalis, B.
Intermedius And S. Sanguis.
• It was found, they adhere to rougher surface
than those that are highly polished.
143

144. Solution for Plaque Adhesion
• Chlorhexidine apparently can bind to acrylic
surfaces for atleast 2 weeks.
• Treating acrylic with Nystatin, followed by
drying, produced similar results.
144

145. Resistance to Acids, Bases And Organic
Solvents
• Weak acids or bases = Excellent
• Quiet resistant to Organic Solvents
• Soluble in aromatic hydrocarbons, ketones and
esters.
• Alcohol will cause crazing in Denture plastic.
• Incorporating ethylene glycol dimethacrylate as a
cross linking agents significantly improves solvent
resistance.
145

146. DENTURE CLEANSER
146
• Most immersion denture cleansers are
effective in the removal of mucin, stains, and
loosely attached food debris.
• A solution consisting of 1 tsp of a hypochlorite
such as Clorox, and 2 tsp of calgon in half glass
has been recommended for occassional
overnight immersion of plastic dentures.

147. DENTURE CLEANSER
147

148. Cytotoxicity of Denture Base Acrylic
Resins
[ JPD 2003: 90; 190-195 ]
• Residual monomer, resulting from incomplete conversion of
monomers into polymer, has the potential to cause
– irritation,
– inflammation,
– and an allergic responses of oral mucosa.
• Clinical signs and symptoms reported include
– erythema,
– erosion of oral mucosa,
– burning sensation of mucosa and tongue.
148

149. Cytotoxicity of Denture Base Acrylic
Resins
[ JPD 2003: 90; 190-195 ]
Effect of polymer : monomer ratio
• More monomer added to the mixture, the greater amount of
residual monomer and therefore more potential for cytotoxicity
.
Effect of storage time and water immersion
• Sheridan et al reported that cytotoxic effect of acrylic resins was
greater in first 24 hours after polymerization and decreased with
time.
• Therefore it is recommended that dentist soak the resin
prosthesis in water for atleast 24 hours before placing them in
the patients mouth.
149

150. • Effects of polymerization cycle
• Reduced amount of residual monomer when
polymerization time extended was observed.
• Auto polymerized resins exhibited higher
content of residual monomer than heat
polymerized resins.
150

151. • Lamb et al observed that levels of residual
monomer were higher for specimens
polymerized at 200C as compared with those
at 550C.
• Therefore it is suggested that the
Autopolymerized acrylic resins should be heat
treated to decrease cytotoxic effects.
151

152. Occupational Hazard
• Plastic dough should not be manipulated
excessively with bare hands.
• The monomer is a good solvent for body oils
and may pick up dirt from the hands,
resulting in a non esthetic denture.
• Monomer may also enter blood stream
through the skin.
152
Restorative Dental Materials, Robert G. Craig & John
M Powers, 11th edition

153. Recent Advances
HIGH IMPACT RESISTANT ACRYLIC
• Butadiene- styrene rubber is
incorporated with copolymer of vinyl
and hydroxyethyl monomer.
• These materials are
slightly stiffer
twice the impact strength
absorbs less water
lower linear shrinkage.
But are not entirely color stable.
153

154. Recent Advances
HIGH IMPACT RESISTANT
ACRYLIC
Phase inversion resulting in
dispersion throughout the beads of
tiny islands of rubber containing
small inclusions of rubber/PMMA
graft polymer.
154

155. Recent Advances
RAPID HEAT POLYMERIZED POLYMER
• These are hybrid acrylics which have had the
initiator formulated to allow for very rapid
polymerization without nearly as much porosity.
• The flasks are placed in boiling water immediately
after being packed. The water is then brought
back to a boil for 20 min to complete the curing
cycle.
• Fast, high temperature cure makes this material
stiffer than conventional acrylic processing.
• E.g. travelon
155

156. FIBER –REINFORCED POLYMER
• Glass, carbon/graphite, aramid and ultrahigh
molecular weight polyethylene have been used as
fiber reinforcing agents.
• Metal wires like graphite has minimal esthetic
qualities.
• Fibers are stronger than matrix polymer thus
their inclusion strengthens the composite
structure.
• The reinforcing agent can be in the form of
unidirectional, straight fiber or multidirectional
weaves.
156

157. Acrylic resins with improved thermal conductivity
• Thermal conductivity of PMMA is three times less
than metals.
• Thermal conductivity of denture base materials is
found to have an important effect on gustatory
sensitivity.
• Thermal conductivity of acrylic based materials
can be improved by introducing a more thermally
conducting phase within the insulating acrylic
resin matrix.
• E.g. Al2O3, porcelain whiskers
JPD 1998: 20; 278-
157

158. BPS (Biofunctional Prosthetic System)
• BPS is the system designed to work with the
body in a biologically harmonious way,
maximizing function, and giving comfort and
natural appearance to the patient.
158

159. 159
Resorbed ridges Occlussal centric tray loaded with impression
for recording initial vertical dimension
Biofunctional prosthetic system
impression trays

160. 160
Bite registration through Gnathometer M Secondary impression-making with zinc
oxide eugenol past
Wax-up trial for the patient

161. 161
Acrylized Denture

162. Flexible Denture
• First introduced in 1956.
• Trade name:-
– Flexiplast
– Valplast
• Superpolyamides, which belong to nylon
family, which inherent property of
flexibility.
• Flexibility depends on the thickness
• Good retention
162

163. Flexible Denture
Advantage
• Good retention
Disadvantage
• Acrylic teeth do not bond chemically
with flexible denture base.
163

164. VALPLAST
• Nylon like material
• Nearly unbreakable, pink colored
like gum
• Can be built quite thin, can form
not only denture base but the clasp
as well.
• Valplast is a flexible denture base
resin that is ideal for partial
dentures and unilateral
restorations.
164

165. VALPLAST –
• The resin is a biocompatible nylon thermoplastic
,it eliminates the concern about acrylic allergies.
• Quite hygienic. It is not possible for Valplast to
absorb the remnants of food or other stains. So
there will be no odor.
165

166. Conclusion
166

167. Conclusion
167

168. 168

169. 169

170. References
• Kenneth j. Anusavice ; Phillips Science of dental
material .Eleventh edition, Elsevier,2004.
• Robert C. Craig John M. Powers, John C.Wataha
;Dental materials properties and manipulation,.
Eleventh edition,2002.
• Applied Dental Materials, 8th edition, John F
McCabe & Angus W. G. Walls
• Rudd and morrow; dental laboratory procedures:
1986 2nd edition
• Vk subbarao ; notes on dental materials : 4th
edition
170

171. • Basic Dental Materials – John J. Manappallil,
3rd edition
• Walter Shepard : fluid resin technique; JPD
1968 (19) 561-
• Koblitz F.F et al: Fluid denture resin
processing in a rigid mold JPD1973 (30) 339-
• Dimensional accuracy of pour acrylic resin and
conventional processing of cold cure resin JPD
1970 (24) 662-
• Atwood et al: final report of the workshop on
clinical requirements of ideal denture base
material ; JPD 1968(20) 101-105
171

172. • EW Skinner; acrylic denture base material their
physical properties and manipulation. JPD 1951
(1) 161-
• Comparison of self curing and heat curing
denture base resins JPD 1953 (3) 332-
• FA Peyton; evaluation of dentures processed by
different technique JPD 1963 (13) 269-
• Cytotoxicity of denture base acrylic resin JPD
2003 (90) 190-
• Bernard Levin et al; use of microwave energy for
processing acrylic resins JPD 1989 (61) 381-
172

173. • Robert EO; Comparison of accuracy between
compression and injection molded complete
denture JPD 1999 (82) 291-
• Glossary of Prosthodontic Terms 8
• A comparative in-vitro study on the adherence
and penetration of c. ALBICANS TO THREE
DIFFERENT RESIN DENTURE BASE SURFACE -
Dr. Divyang patel
173

174. 174