4. COMPOSITION OF MONOMER
Methyl methacrylate
Main chemical which will polymerize
Hydroquinone (o.Oo3-o.1%)
Inhibitor while storage
Dibutyl phthalate
Plastisizer
Glycol dimethacrylate (1-2%)
Cross linking agent
Styrene vinyl acetate or ethyl methacrylate
As copolymers
5. Typical smell of its own
Clear, transparent liquid
Boiling point 100.3*c
Good organic solvent
Can get evaporated
Inflammable
Stored in dark colored bottle
Light weight
Volumetric shrinkage of 21%
It is a known allergen
6. LIQUID
Methyl methacrylate monomer
Cross linking agent Ethylene glycol
dimethacrylate(5-15%).they are added to
avoid crack or craze produced by stresses
during drying.
Inhibitor Hydroquinone (trace) to avoid
premature polymerization and enhance
shelf life.
When MMA polymerizes it shrinks 21% by
volume.
Using a 3:1 powder liquid ratio it could be
minimized to 6%.
A correctly heat processed denture base
could have as little as 0.3% to 2% residual
monomer.
8. Mercuric sulfide or iron oxide or titanium oxide
- pigments and dyes
Glass fibres or beads or zirconium sulfate
- to increase stiffness
Nylon or acrylic fibres
- in veined type
- capillaries of gum
9. Normal pink
-which resembles the normal pink
color of gum
Clear polymer
- no coloring agents are added
- indicated in palatal area
Translucent
Veined or deep veined
10. Stable at room temperature
- has long shelf life
Softening temperature
- 125 * c
- 125*-200*c
depolymerization occurs
- 450 *c
converted back to monomer
Absorbs water and soluble in chloroform
11. Tensile strength
- 600 kg/sq cm
Appearance
- shiny
- transparent
Produced in two shapes
- spherical
- granular
12. Control of particle size
- no.52 sieve mesh
- 300 micrometer
If particle size is smaller
- softening will be quicker
- granular shape softens faster
13. Spherical particles
By suspension polymerization
- monomer and water are mixed with an emulsifier i.e,
powder talc.
- then the mixture is heated and stirred
- at the end talc is washed off to
get polymerized polymer particles
Granular particles
- solid block
- then it is grinded or milled
14. CURING CYLES EMPLOYED
A Recommended curing cycles
overnight water-bath cures:
1) 7hr at 70 C
2) 14hr at 70 C
3) 7hr at 70 C +1hr at 100C
4) 14hr at 70C + 1hr at 100C
Dry heat cure:
5)temp in excess of 100C using dry heat system
15. B Short curing cycles
6) 7hr at 60C
7) 7hr at 60C +1 hr at 90C
16. (II)PHYSICAL PROPERTIES
Should possess adequate strength and resiliency and resistance
to biting and chewing forces impact forces and excessive wear
in oral cavity.
Should be dimensionally stable under all conditions of service
including thermal changes and variations in loading.
I) Specific gravity: It should have low value of specific gravity in
order that dentures should be as light as possible.
II) Thermal conductivity: It is defined as the number of calories per
second flowing through an area of 1cm2 in which the
temperature drop along the length of the specimen is 1°C/cm.
It should have high value of thermal conductivity
Radiopacity: It is the inhibition of passage of radiant energy.
It should be ideally radiopaque
17. Glass transition temperature:
It is the temperature at which molecular motions become
such that whole chains are able to move. It is close to
softening temperature. At this temperature sudden change in
elastic modulus occurs.
Amorphous polymer below Tg behave as rigid solids while
above Tg they behave as viscous liquids, flexible solids or
rubbers.
Increased chain branching Decreased Tg.
Increased number of cross links Increased Tg
Effect of molecular weight on properties
In many polymers the chains are held together by secondary, or
Vander Waals forces and molecular entanglement. Materials of high
molecular weight have a greater degree of molecular entanglement,
and have greater rigidity and strength and higher values of Tg and
melting temperature than low molecular weight polymers.
18. Effect of plasticizers
Plasticizers penetrate between the randomly oriented chains
of polymer as a result of which molecules are further apart
and forces between them are less. They soften the material
and make it more flexible by lowering its Tg. They lubricate
the movements of polymer chains and are sometimes added
to help molding characteristics. This principle is used in
producing acrylic soft lining materials.
Effect of fillers
Modulus of elasticity and strength are generally increased.
A degree of anisotropy exist, that is the strength depends on
the orientation of fibres in the polymers.
Viscoelasticity : Polymers show viscoelastic behavior. Elastic
behavior is caused by uncoiling of polymer molecules. Plastic
behavior is caused by breaking of intermolecular Vander
Waals forces
19. (III) MANIPULATION
Should not produce toxic fumes or dust
Easy to mix, insert, shape and cure and short setting time
Oxygen inhibition, saliva and blood contamination should have little
or no effect.
Final product should be easy to polish and easy to repair in case of
breakage.
(IV)AESTHETIC PROPERTIES
Should be translucent to match oral tissues
Capable of pigmentation
No change in color after fabrication.
(v)ECONOMIC CONSIDERATION
Cost should be low
Processing should not require complex and expensive instruments.
20. (VI) CHEMICAL STABILITY
Conditions in mouth are demanding and only the most chemically
stable and inert materials can withstand such conditions without
deterioration.
“No resin has yet met all of these ideal criteria”. Methacrylate
polymers fulfill the aforementioned requirement reasonably
well.
21. 2)AUTOPOLYMERIZING/COLD CURE
POLYMETHYL METHACRYLATE (POUR RESIN)
Composition same as the heat cure version
with following differences
1)The powder contains beads of polymer that
have a lower molecular wt. and benzoyl
proxide (initiator)
2) The liquid contains a chemical activator
,tertiary amine such as dimethyl-para-
toluidine.
22. Upon mixing tertiary amine causes
decomposition of benzoyl peroxide.
Dentures processed have more residual
monomer (1-4%),but lower dimensional
change.
Decreased transverse strength (residual
monomer act as plastisizer).
Compromised biocompatibility (residual
monomer)
Color stability inferior (teriaty amine
susceptible to oxidation), stabilizing agents
should be added
23. Fluid resin and compression molding technique can be employed for
the fabrication of denture.
Also used as repair material
24. 3)HIGH IMPACT RESISTANT ACRYLIC
Similar to heat cured material but less likely to be broken if
dropped.
Produced by substituting the PMMA in the powder with a copolymer.
Copolymer of butadiene with styrene or methyl methacrylate are
incorporated into the beads.
Phase inversion resulting in dispersion throughout the beads of tiny
islands of rubber containing small inclusions of rubber/PMMA graft
polymer.
Electron micrograph of high impact denture
Base showing size and shape of polystyrene-butadiene
Rubber inversion phase.
25. 4) Injection molded polymers
These are made of Nylon or Polycarbonate.
The material is supplied as a gel in the form of a putty .
It has to be heated and injected into a mold
Equipment is expensive.
Craze resistance is low .
The SR-Ivocap system uses specialized flasks and clamping
presses to keep the molds under a constant pressure of 3000
lbs
26. 5) RAPID HEAT POLYMERIZED POLYMER
Same as conventional material except that they contain
altered initiation system.
These initiator allow them to be processed in boiling water
for 20 min.
A problem with these is that areas of the base thicker than
approx.6mm have a high level of porosity.
Short duration of heating also leaves a higher level of residual
monomer,3-7 times greater than conventional heat cured
denture base.
27. 6) MICROWAVE POLYMERIZED POLYMERS
Resins are the same as used with conventional material and are
processed in a microwave.
Denture base cures well in Special polycarbonate flask (instead of
metal).
The properties and the accuracy of these materials have been shown
to be as good or better than those of the conventional heat cured
material.
Processing time is much shorter (4-5 min).
Microwave resin and non metallic microwave flask
28. 7)Light activated denture base resins
This material is a composite having a matrix of urethane
dimethacrylate, microfine silica and high molecular wt acrylic resin
monomers
Acrylic resin beads are included as organic fillers.
Visible light is the activator, whereas camphorquinone serves as the
initiator for polymerization.
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.
Light curing unit for polymerizing
Dimethacrylate
29. 8) FIBER –REINFORCED POLYMER
Glass, carbon/graphite, aramid and ultrahigh molecular wt
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.
30. When mixed in proper proportions, the resultant
mass passes through five distinct stages
1.Sandy
2. stringy
3. Dough like
4. rubbery
5. Stiff
1.Sandy
During sandy stage, little or no interaction occurs
on a molecular level. Polymer beads remain
unaltered.
This stage is ideal for compression molding.
Hence material is inserted into mold cavity during
dough like stage.
31. 2. Stringy stage
Later, mixture enters stringy stage.
Monomer attacks the surfaces of
individual polymer beads.
Stage charcterized by stringiness,…
3. dough like stage
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 (
sticky)
32. 4.Rubbery or elastic stage
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
5. Stiff Stage
Upon standing for an extended period, the
mixture becomes stiff.
This may be due to the evaporation of free
monomer. From clinical point, the mixture
appears very dry and resistant to
mechanical deformation
41. Checking the seating of flask
members
Invested flask & cast is
washed in clear slurry water
Surface tension reducing
agent is applied to the exposed
wax
Separating medium is applied
42. Second mix is mixed
Hand spatulation
Mechanical spatulation
-Under reduced atmospheric pressure
-Minimum air inclusion
-Reduces finishing time
Stone is coated in occlusal & inter-
Proximal areas with stiff brush
43. Stone is poured in flask
Vibrator can be used
In absence of vibrator
Flask is filled till approximately ¼ of the flask
Stone is removed in incisal & occlusal surfaces
Stone is allowed to set
44. After the stone is set separating medium
is coated
Occlusal & incisal surfaces shouldn’t be
coated with the separating medium
Clear slurry is poured till the stone is
mixed
Slurry is poured off, flask is filled with
the stone
48. Presence of voids within structure of resin
Porosity can be of two types
◦ Internal
◦ External
Internal porosity is due to voids within the
structure usually at thicker portion
Cause – due to vaporization of the monomer
(100.8C)
Solution- long low temperature curing cycle
is recommended.
49. External porosity is due porosities which
occur near the surface of denture.
Cause
◦ Lack of homogeneity of dough.
◦ Lack of adequate pressure.
Prevention – use proper monomer – powder
ratio, packing in dough stage.
50. Crazing is formation of surface cracks on
denture base resin.
Causes –
◦ Incorportion of stress
◦ Attack by solvent (alcohol)
◦ Incorporation of water during processing.
Prevention
◦ Avoidance of solvent
◦ Proper use of separating media
◦ Metal moulds
◦ Use of cross linked acrylic
51.
52. Denture warpage is change in shape or fit of
denture.
Cause is incorporation of stress in deture
◦ Packing in late dough or rubbery stage.
◦ Stress induced during curing
◦ Improper deflasking
◦ Rise in temp while polishing
◦ Immersion of processed denture in hot water.
54. Improper deflasking
Denture base excessively thin
Accidental dropping at time of polishing
55. Care to taken at time of dewaxing procedure
Rearticulation to be done after processing the
denture to check of occllusal discrepancy.
56. The cured polymer should be stiff enough to
hold the teeth in occlusion during mastication
and to minimize uneven loading of the
mucosa, underlying the denture should not
creep under masticatory loads should not
deteriorate in the aqueous oral environment
and crazes should not form The cured
polymer should be biologically inert and slow
to foul
57. For an allergic patient, low free-monomer
content may be thought more important than
stiffness.
For a patient requiring a soft lining, stiffness
is very important if the reduced cross
sectional area of the denture, may lead to
stability or loading problems.
58. Curing the dough before the monomer has
diffused to the core of the beads may result in
reduced flexural strength and a tendency for
cracks to propagate.
The curing cycle is designed to raise the
temperature to a point at which
(1) sufficient benzoylperoxy radicals are
produced to overcome the scavenging effect of
oxygen,
(2) polymer chains form by free-radical addition
polymerization.
59. Too rapid a rise
in temperature produces large numbers of
radicals or radical avalanche, as a result,
many growing polymer chains. These chains
collide either with other radicals or with
polymer chains, producing an increase in
branching and cross-linking of the interstitial
polymer. This in turn reduces toughness.
60. Slow cures result in much tougher denture bases,
producing fewer cross-links and branches, and
having a higher overall molecular weight between
cross-links because
Free-monomer content is often lower
also, because the steadier rise in internal
viscosity of the curing polymer allows the
monomer easier access to the growing free
radicals. The cross-linker is more completely
polymerized in heat-cured systems; this results
in significantly lower creep values due to removal
of the plasticizing effect of unreacted pendant
crosslinker groups.
61. Heat-cured systems have one great
advantage over autopolymerized and
injection molding methods: an increased rate
of monomer diffusion at the higher
temperature.
Conversely, an increased temperature of cure
can also result in the annealing of stresses
that build up in the structure due to
polymerization shrinkage. If this stress is not
released, it can act as the foci for crazes or
distortions
62. The pour technique for dentures, originally
developed during the 1960s, reversible
hydrocolloid. The fitting surface of the mold
consists of the plaster model itself; the acrylic
teeth occupy their positions in the agar mold
in the same way they do in a conventional
plaster mold. In general, the creep of these
products is greater than that of heat-cured
acrylics.
63.
64.
65. acrylics that have a natural glass-transition
temperature at least 25°C less than that of
the mouth. The plasticizer used to soften the
acrylic can either be unbound to the acrylic
and hence free to diffuse out during use,
resulting in a loss of resilience,
66. The silicones used as soft liners can be
divided into two types:
room-temperature vulcanizing (RTV)
and heat curing.
The RTV silicones' greatest drawback is their
lack of adhesion, which is especially a
problem around the edges of the attachment
between acrylic and silicone
67. it is their viscoelastic properties that are
important,
specifically their ability to flow under
masticatory and linguistic forces, spreading
the load on the mucosa evenly.
68.
69.
70.
71.
72. 1) In heat cure denture base resins the
monomer is
a) methacrylate
b) ethylmethacrylate
c) metyl ethyl methacrylate
d) polymethylmethacrylate
73. 2)If curing occurs at temperature more than
100 degree celsius porosity results in which
are of denture
a)hard thick central area
b) thin palatal area
c)thin area of flanges
d) porosity is uniformly distributed
74. 3)What is the shrinkage if 3:1 powder:liquid
ratio is used
a) 6%
b) 8%
c) 10%
d) 21%
75. 4) Hydroquinone is added to methyl
methacrylate monomer
a) to prevent polymerization during storage
b)to initiate release of free radicles
c) to enable polymerisation reaction at room
temperature
d)all of the above
76. 5) cross linking of denture base is
contributed by
a)gylcol dimethacrylate
b) benzoyl peroxide
c) N para toluidine
d) methyl methacrylate
77. 6) use of dimethyl P toluidine is indicated for
a) thermal polymerization of acrylic
b) chemical polymerization
c) retarding the polymerizing reaction
d) to inhibit the action of benzoyl peroxide
78. 7)Porosity present in acrylic denture is usually
the result of
a) prolonged curing cycle
b) lack of sufficient pressure applied to flask
c) insufficient acrylic resin monomer
d) prolonged bench cooling after curing
79. 8)The most important disadvantage of acrylic
denture base is
a) porosity
b)shrinkage
c)tooth breakage
d)water absorption
80. 9)In self cure acrylic resin the activator is
a) toluidine
b) quaternary ammonium compound
c) benzoyl peroxide
d) tertiary amine
81. 10) Which of the following may result if an
excessive amount of monomer is
incorporated into an acrylic resin mixture
a) excessive expansion
b) low impact strength
c) excessive shrinkage
d) excessive brittleness
82. 11) Porosity of denture base is due to
a) packing at dough stage
b) curing at 160 degree Celsius
c) inadequate pressure
d) all of the above
83. 12) Subsurface porosity is due to
a) thermal changes
b) thickness of resin
c) lack of temperature
d) packing past the dough stage
84. 13) To prevent porosity in self cure acrylic
resin curing should be carried in
a) cold water
b) hot water
c) under tap water
d) under vaccum pressure
85. 14) Acrylic resins are used for
a) anterior restorations
b) temporary brigdes
c) denture bases
d) all
86. 15) Packing of heat cure acrylic resin should be
done in which stage
a) Sandy stage
b)Stringy stage
c)Dough stage
d)Rubbery stage
