Denture base resins

2
 Introduction
 History
 Requirements of an ideal denture base material
 Introduction to PMMA
 Polymerisation reaction
 Types of denture base resin
 Heat activated resins
 Chemically activated resin
 Light activated resin
 Physical properties of resins
 Recent advancements
 Summary
 Bibliography

3
 Dentures – mode of replacement of
natural teeth since 700 BC
 Increased patient awareness lead to
increased expectations
 Significant advances in development of
new materials for replacement of lost
teeth
 Acrylic resin is the most widely accepted
and used Denture base material.

4
 First Dental prosthesis – Egypt in 2500 BC
TORTOI
SE
SHELL
PORCE
-LAIN
CELLUL
OID
WOOD
CHEOP
LASTIC
ALUMI
NIUM
BONE
GUTTA
PERCH
A
BAKELI
TE
PVC
SS &
alloys
GOLDIVORY
VULCA
NITE
PMMA

5
 WOOD:
 Readily available and inexpensive
 Easily carvable
X Cracked in moisture
X Lacked aesthetics
X Degraded in oral environment

6
 BONE
 Available at reasonable costs
 Carvable
 Better dimensional stability
X Aesthetic and hygiene concerns
 IVORY
 Stable in oral environment
 Aesthetic and hygienic
X Not readily available
X expensive
First
fabricated
by
FAUCHARD

7
 PORCELAIN
 Shaped easily
 Ensured intimate contact with
underlying tissue
 Stable
 Minimal water sorption
 Smooth surface
 Less porosity
 Low solubility
X Brittle
X Difficult in grinding and polishing
ALEXIS
DUCHATEAU
in 1774 - first
to fabricate
porcelain
denture

8
18 – 20 karat gold alloyed with silver and teeth riveted to it

9
 TORTOISE SHELL
• It was the first thermoplastic denture base
material
• Formed by CF HARRINGTON in1850
 GUTTA PERCHA
• Unstable
• First formed by EDWIN TRUMAN in 1851

10
 CHEOPLASTIC
• It is a low fusing alloy of silver, bismuth and
antimony
• First formed by ALFRED A BLANDY in 1856

11
 VULCANITE
• First self retaining dentures
• Functional
• Affordable
• Durable
• Dark red colour
• Unhygienic
NELSON
GOODYEAR
in 1864

12
 ALUMINIUM
• By Dr Bean in 1867 ( he also invented the
casting machine
 CELLULOID
• Discolours easily
• Has a residual camphor taste
• Difficult to repair
• Obtained by plasticizing cellulose nitrate
with camphor
J. SMITH
HYATT in
1869

13
 BAKELKITE
• Stains easily
• Residual phenol taste
• Brittle
• Difficult to repair
• Short shelf life
 POLY VINYL CHLORIDE
• Pleasing colour but difficult processing
methods
Dr. LEO
BAKELAND in
1909

14
 STAINLESS STEEL and BASE METAL ALLOYS
• Low density
• Low metal cost
• Higher resistance to tarnishing and
corrosion
• High modulus of elasticity
• Allergy to nickel
 POLYMETHYL METHACRYLATE
• Most satisfactory material
tested till date.
Dr. WALTER
WRIGHT
(1937)

17
 PMMA/Acrylic resin is the material of
choice for full denture bases
 Chemical model for many other
material developments – restorative
materials
 The most satisfactory denture base
material used till date
REFERENCE : Material science for dentistry, B. W. Darwell, 9th Ed

18
Acrylic resins are prepared by a free
radical addition polymerisation chain
reaction

19
 INITIATION RECTION
• Vinyl group susceptible to attack by free
radical
• Opening of π bond, and formation of σ
bond
• Shift of electron takes place
Initiation reaction

20
 PROPAGATION REACTION
• Process of repeated reaction of the same
type - chain propagation
• Steric hindrance effects – increased effects
on attack on next double bond
• Polymer chains with free radical – growing
or live chains

21
 TERMINATION REACTION
• Not a function of the chain length already
created
• Depends on the concentration of free
radicals in the system
• Self limitation of the reaction – mutual
annihilation of free radicals

22
 CHAIN TRANSFER
• Hydrogen abstraction - simple transfer of
an H2 atom to attacking radical
• Leaves a free radical residing on attacked
species

23
 Based on the mode of activation
• Heat activated PMMA
 High impact resin
 Rapid heat polymerising resin
 Microwave – activated PMMA
• Chemical activated PMMA
• Light activated PMMA

25
 COMPOSITION:
• Polymer:
 pre-polymerised spheres of PMMA
 Benzoyl peroxide – initiator
• Monomer:
 Hydroquinone – Inhibitor
 Glycol dimethacrylate – cross linking agent (1%
- 2% by vol)
REFERENCE : Phillips' Science of dental materials, Anusavice,
11th Ed

26
BENZOYL PEROXIDE
is not a catalyst!!!

27
 STORAGE
• Specific time and limits for storage
• May undergo changes
• Causes changes in working properties
• Change in Chemical and physical
properties of processed denture
11th Ed

28
MANIPULATION
COMPRESSION
MOLD TECHNIQUE
INJECTION MOLD
TECHNIQUE
11th Ed

29
• Preparation of the mold
• Selection of separating medium
• Polymer -to-monomer ratio
• Polymer –monomer interaction
• Dough forming time
• Working time
• Packing
• Polymerization procedure
• Temperature rise
• Internal porosity
• Polymerisation cycle
11th Ed

32
 Proper finishing
 Periphery should be sealed
 Apply petroleum jelly on the inner surface of
the flask and on the casts
 Adjustment of the plaster model
 Plaster models are wetted - soaked with slurry
water
11th Ed

33
 Flask is filled with freshly mixed stone
 Place cast on to the mixture
 Contour the stone
 coated with separating media (after
initial set)
 Another mix of stone is poured into the
flask
11th Ed

34
 Incisal and occlusal surfaces of teeth
should be slightly exposed
 Allow to set and coat with separating
media
 Additional increment of stone filled
 Lid is gently tapped in place
 Apply pressure with pressure clamp
11th Ed

35
11th Ed

37
 Place the flask in boiling water for 4 mins
 Remove and separate segments
 Baseplate and softened wax are
removed
 Prosthetic teeth remain firmly
 Cleaned with mild detergent and rinsed
in boiling water
Dewaxing
11th Ed

38
 Prevent direct contact between
denture base resin and the mold
Failure
Water may affect
polymerisation rate and
alter optical and physical
properties
Presence of Monomer or
free polymer may fuse the
investment to denture base
11th Ed

39
 Water soluble alginate solution – most
popular separating agents
 Produce thin film of calcium alginate
Water soluble
alginate solution
+
Calcium sulphate
dihydrate
Calcium alginate
11th Ed

40
 Application
• Applied on the exposed surfaces of a
warm, clean stone mold
• Carefully applied in the interdental surfaces
• Should not contact exposed tooth surfaces
11th Ed

41
 Polymerisation results in volumetric and
linear shrinkage (21% decrease)
 Manufactures pre-polymerize – pre
shrinking
 Powder + liquid = dough like mass
 3:1 is accepted monomer : polymer
ratio (0.5% linear shrinkage)
11th Ed

42
 A workable mass is produced, which
passes through 5 stages
Sandy Stringy
Dough-
like
Rubbery Stiff
11th Ed

43
 SANDY
• Coarse or grainy
• Polymer beads remain unaltered
 STRINGY
• Increased viscosity
• Monomer attacks polymer beads
 DOUGH-LIKE (ideal for compression molding)
• Pliable dough
• Increased number of polymer chains
11th Ed

44
 RUBBERY OR ELASTIC
• Mass rebounds when compressed or
stretched
• Excess monomer is dissipated by
evaporation
 STIFF
• Due to complete evaporation of free
monomer
11th Ed

45
 Time required to reach a dough like
stage
 According to ADA spec.no.12 , required
consistency should be reached in
<40mins (clinically - <10min)
11th Ed

46
 Defined as the time that a denture base
material remains in the dough like stage
 According to ADA spec. 12, material
should remain in dough like stage for
atleast 5 min
 Refrigerating increases working time
 Presence of moisture degrades physical
and aesthetic properties
11th Ed

47
 Placement and adaptation of denture
base resin within the mold cavity
Denture with
excessive thickness
and resultant mal-
positioning
Noticeable denture
porosities
OVERPACKING
UNDERPACKING
11th Ed

48
 Resin should be in dough-like state
 Bent into an horse-shoe shape and
placed in position
 Polyethylene sheet placed over resin –
incremental pressure applied
11th Ed

49
 Excess material – flash
 Trial closures are repeated till no flash
remains
 No polyethylene sheet to be placed for
final closure
 Flask is transferred to a flask carrier –
maintains pressure
11th Ed

50
Cross sectional representation of the flask and its contents
11th Ed

51
 When heated above 60⁰C, benzoyl
peroxide decomposes
 Yields free radicals
 Acts rapidly with monomer – chain
growth polymerisation
11th Ed

52
 Additional monomer molecules attach
to individual polymers – rapid
 Heat required - activator
 Benzoyl peroxide - initiator
Coupling of 2 grouping chains Transfer of H2 ion from one
chain to another
11th Ed

53
Temperature - time heating curves for the water
Bath, investing plaster and acrylic resin during polymerisation
ofa thick denture base

54
 Initially heating is slow - resin occupies I
the centre of the mold
 Temperature >70C – begin to increase
rapidly
 Decomposition rate of benzoyl peroxide
is significantly increased
 Resin and dental stone are poor
conductors – heat not dissipated
Temperature rises from that of the boiling point of monomer
(100.8 C)
11th Ed

56
 Porosities are formed when the
temperature of the resin exceeds that of
the unreacted monomer
 resin is poor thermal conductor - heat
generated cannot be dissipated
11th Ed

57
 Heating process used to control
polymerization – curing cycle
Constant temp – 74C
For 8 hrsor longer with no
Terminal boiling treatment
Processing at - 74 C for 8hrs
and then increasing to 100
At 74 C for 2 hrs and then
Increasing to 100 C for 1 hr
11th Ed

58
Temperature changes in acrylic resin when
subjected to various curing schedules

59
 Denture flask should be bench cooled
for 30mins before retrieval
 Rapid cooling – warpage – differences
in thermal contraction of resin and
investing material
 Immersed in cool tap water for 15 mins
 Deflasked
 Stored in water until delivery
11th Ed

60
 Half of the flask is filled with stone
 Contoured and permitted to set
 Sprues are attached to the wax denture
base
11th Ed

61
 Investment process is completed.
 Wax elimination is performed
 Flask is placed under pressure
 Resin mix is introduced into the mold
 polymerised
11th Ed

62
 High-impact strength resin
• Reinforced with butadiene-styrene rubber.
• Rubber particles are grafted to methyl
methacrylate to bond to the acrylic matrix
• Supplied in powder-liquid form
• Conventionally processed

63
 Rapid heat-polymerized resin
• Hybrid acrylics, with both chemical and
heat-activated initiators - allow rapid
polymerization
• No porosity expected
• polymerized in boiling water for 20 minutes

64
 Microwave-activated PMMA:
• Nishii (1968) first used microwave energy to
polymerize denture base resin in a 400 watt
microwave oven for 2.5 minutes. This
research was later carried on by Kimura et
al (1983) and De Clerk.

66
 Chemical activators used to induce
polymerisation
 Cold curing / self curing/ auto-
polymerising resin
 Chemical used – dimethyl –para-
toluidine (to monomer)
Initiates breakdown of benzoyl
peroxide to produce free radicals and
Hence polymerisation
11th Ed

67
 Degree of polymerisation is not
complete – greater amount of
unreacted monomer
 Less colour stability due to the presence
of the amine – susceptible to oxidation
Plasticizer -
Results in decreased
transverse strength
Potential tissue irritant
11th Ed

68
 Less shrinkage and greater dimensional
accuracy compared to heat activated
PMMA
11th Ed

69
 Supplied in monomer – polymer form
 Mixed according to manufacturer’s
instructions to attain dough like
consistency
 Working time is shorter
 Refrigerating monomer increases
working time – rate of polymerization
decreases
11th Ed

70
 Pressure must be maintained throughout
 Initial hardening – 30 min
 Flask should be held under pressure for
min. 3 hrs
 Low degree of polymerisation –
dimensional instability – soft tissue
irritation
11th Ed

71
 Employs a pourable, chemically
activated resin
 When mixed – low viscosity resin
 Completed tooth arrangement is sealed
to the underlying cast
 Flask is filled with reversible hydrocolloid
– allowed to cool
11th Ed

72
 After gelation – cast is removed and
sprues and vents are cut on the external
surface
 Wax is eliminated using hot water
 Teeth are carefully retrieved and placed
in position
 Resin is mixed and poured via sprue
channels
11th Ed

73
 Placed in pressurised chamber at room
temperature
 Allowed to polymerize for30 – 45minutes
 Denture is retrieved, sprues are removed
 Returned to articulator for correction of
processing changes
11th Ed

75
 Advantages
• Improved adaptation
• Decreased probability to damage to the
teeth
• Reduced cost
• Simplification of procedure
11th Ed

76
 Disadvantages
• Noticeable shift of teeth
• Air entrapment
• Poor bonding
• Technique sensitive
11th Ed

78
 COMPOSITION:
• Matrix : Urethane dimethacrylate, microfine
silica
• Filler : acrylic resin beads
• Activator : visible light
• Initiator : camphorquinone
11th Ed

79
 Supplied in sheet and rope form
 Packed in light proof pouches
 Opaque investing material is required –
no conventional method
11th Ed

80
 Denture is moulded on an accurate cast
 Exposed to a high intensity visible light
for a period
 Removed from the mold
 Finished and polished
11th Ed

82
The physical properties will be discussed
under the following headings:
 Polymerisation shrinkage
 Porosity
 Water absorption
 Solubility
 Processing stresses
 Crazing
11th Ed

83
 During polymerization the density of the
mass changes from 0.94 g/cm3 to 1.19
g/cm3. thus a volumetric shrinkage of
21%
 Linear shrinkage – denture base
adaptation and cuspal interdigitation
11th Ed

84
 Volumetric shrinkage – 7%, hence linear
shrinkage 2%
 Initial cooling – resin is soft – contraction
occurs at the same rate as that of
dental stone
 At glass transition temperature –
contraction occurs at a faster rate than
the surrounding stone.
11th Ed

86
Decreases
in vertical
dimension
Increase in
overall
vertical
dimension
Fluid
Resin
technique
Heat/chemically
activated
11th Ed

87
 Surface or subsurface voids compromise
physical and aesthetic properties
 More likely to develop in thicker portions
 Due to vapourization of unreacted
monomer and low molecular weight
polymers
 Does not occur equally
11th Ed

88
 Can also be due to inadequate mixing
of powder and liquid
 Regions with more monomer, shrink
more – resulting in voids
 Using proper monomer – polymer ratio is
essential
11th Ed

89
 Also due to insufficient pressure or less
material during polymerisation
 Assume irregular shape
 Resultant resin appears lighter
11th Ed

90
 Final type is associated with fluid resins
 Caused due to air inclusions during
mixing and pouring
11th Ed

91
 Absorbs relatively small amounts when
placed in water
 Water molecules penetrate the PMMA
and occupy positions between polymer
chains – forces them apart
Slight expansion
In polymerised mass
Water acts as
plasticizers
11th Ed

92
Water absorption value – 0.69 mg/cm2
Interferes with the polymer chain
Making them more mobile by releasing
stresses
Changes in shape
(insignificant)
11th Ed

93
 Insoluble in fluids in the oral cavity
 Negligible loss
11th Ed

94
 Natural dimensional change is inhibited -
contains stresses
 Stresses relaxed - distortion occurs
 During polymerization tensile stresses are
sustained
 Stress is produced during thermal
shrinkage also (cooling < glass transition
temperature)
11th Ed

95
 Additional factors include
• improper mixing and handling of the resin
• Poorly controlled heating and cooling of
flask assembly
 Dimensional changes due to small
stresses - 0.1 to 0.2mm
11th Ed

96
 Stress relaxation may produce flaws -
CRAZING
 Hazy or foggy appearance
 Tensile stresses most often responsible
and may result the denture to crack.
11th Ed

97
 Produced due to mechanical
separation of individual polymer chains –
tensile stresses
 Also due to solvent action
 Begins at surface of the resin and
oriented to right angles to the tensile
forces.
11th Ed

98
 Load application produces stresses
within the resin – change in shape
 Strength of the resin is directly
proportional to the degree of
polymerisation shrinkage
 Heat activated resins display lower
degree of polymerisation

99
 Act as rubbery solids that recover from
elastic deformation once stresses are
eliminated – viscoelastic behaviour
 If load is not removed additional plastic
deformation occurs – creep
 Rate at which this deformation occurs –
creep rate
11th Ed

101
 The radiolucent nature of PMMA is one of
its disadvantages as a denture base
material.
 Denture wearers can endure serious
complications if their dentures fractures
and a portion is inhaled or ingested.
 Use of sophisticated ultrasound techniques
also prove to be difficult for detection.

102
 The most promising material - Silanated
barium fluoride impregnated powdered
glass. (kasim 1998)
 Barium sulphate (BaSO4) has also been
added to denture base resins to
improve radiopacity.
 Lang et al. (2000) investigated the
potential for triphenylbismuth
incorporated into injection moulded
heat cure resins to improve radiopacity.

103
 Inhibition of Candida albicans on
denture resins could play a significant
role in preventing the development of
denture stomatitis
 PMMA-silver nanoparticle discs were
formulated, with the commercial acrylic
resin

104
 The inner surface of the prosthesis is
rough, and in addition to local (eg, poor
hygiene, local trauma, tissue integrity
loss) and systemic factors (eg,
malnutrition, diabetes mellitus, human
immunodeficiency virus infection,
xerostomia), contributes to the
proliferation of C. albicans

105
 Spherical silver nanoparticles were
synthesized and added to a PMMA
formulation, resulting in successful
reduction of adherence of C. albicans

106
 Commercially pure (CP) titanium has
appropriate mechanical properties
 Lightweight (low density) compared with
conventional dental alloys
 Outstanding biocompatibility that
prevents metal allergic
reactions

107
 Flexible denture material is available in the
form of granules in cartridges of varying
sizes.
 It was first introduced by the name of
valplast and flexiplast to dentistry in 1956.
 These are superpolyamides which belong
to nylon family

108
 Advantages
• Soft inherent flexibility
• Will not warp
• Clinically unbreakable
• No porosity
• Less bulky
• Biocompatible
• Better esthetics
• Better chewing efficiency

109
 Disadvantages
• De-bonding of acrylic teeth
• Discolouration
• High surface roughness
• Cannot be relined
• Difficult to polish
• Technique sensitive
• Cannot be repaired

112
 Contraindications :
• Insufficient inter-arch space (< 4mm space
for placement of teeth)
• Prominent residual ridges
• Flat, flabby ridges

113
 Management of xerostomia patients - soft
and adapt well to the gums - comfortable
for wearing.
 retain moisture and give better lubrications
than acrylic dentures
 biocompatible - safe for patients with
carcinoma.
 lighter in weight, are not brittle, do not
warp
 suitable in conditions of inadequate
vertical dimension

114
 One modification of the Valplast partial
denture is called the Nesbit.
 The Nesbit is used to replace one to
three teeth on the same side of the
mouth and is much smaller than a
conventional partial denture.

115
 The procedure can be completed in
two short visits, requires no anesthesia or
drilling of teeth (in most cases), and the
cost is substantially less than either a
permanent bridge or dental implants.
 A Valplast Nesbit is generally easy to get
used to, and has a very realistic
appearance

116
 Incorporation of a rubber phase 
butadiene styrene
 Improved impact strength

117
 The transverse strength of high-impact
denture base resin can be increased
significantly by a factor of 29% and 76%
when reinforced with zirconia in a
concentration of 5% and 15%
respectively
 In this process, expansion of ZrO2 crystals
occurs and places the crack under a
state of compressive stress and crack
propagation is arrested

118
 To improve the physical and
mechanical properties of acrylic resin, it
was reinforced with fibres
1. Carbon fibres
2. Kevlar fibres
3. Glass fibres

119
 CARBON FIBRES:
• The use of Carbon fibres as denture base
strengtheners have been investigated by
Larson et al and Sonit(1991) .
• Carbon fibres have been shown to improve
flexural and impact strength, prevent
fatigue fracture and increased fatigue
resistance on treating with silane coupling
agent(Yazdanie-1985)

120
 KEVLAR FIBRES:
• These fibres are resistant to chemicals, are
thermally stable, and have a high
mechanical stability, melting point, and
glass transitional temperature
• Studies conducted by Berrong et al(1990)
have shown to significantly increase the
impact strength and the modulus of
elasticity of the resin but they are also
unesthetic

121
 GLASS FIBRES:
• Different types of glass fibres are produced
commercially; these include E-glass, S-glass,
R-glass, V-glass, and Cemfil.
• E-glass fibre - high alumina and low alkali
and borosilicate, is claimed to be superior in
flexural strength
• Because the modulus of elasticity of glass
fibres is very high, most of the stresses are
received by them without deformation

122
No denture base material has yet been
developed which completely fulfils all the
criteria for success and conversely does not
posses any of the above noted problems.
Since PMMA was introduced, most dental
material research has focused upon
developing materials with higher strength,
lower levels of residual methacrylate
monomer after processing, improved
dimensional stability, increased radiopacity
and improved resistance to candidal
infiltration

123
 Phillip’s Sciences of dental materials,
Anusavice, 11th Ed
 Material science for dentistry, B. W. Darwell,
9th Ed
 Young, Beth C. (2010) A comparison of
polymeric denture base materials.
 Cytotoxicity of denture base acrylic resins:
A literature review
http://www.iosrjournals.org/iosr-jdms/papers/Vol13-issue3/Version-2/C013320709.pdf.
 Denture base resins : From past to future
http://ijds.in/article-pdf-RENU_TANDON_SAURABH_GUPTA_SAMARTH_KUMAR_AGARWAL-63.pdf

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