basic on denture base resins

2. All through the history of the making of dentures,we find a
constant struggle of the dentist to find a suitable denture
base material

3. COMPLETE DENTURE:
“ A Removable Dental Prosthesis That Replaces the Entire Dentition and
Associated Structures of the Maxilla or Mandible ”
Composed of
Artificial teeth
Denture base
Support
Contact with with underlying oral tissues
Teeth
Implants

4. Denture base materials
Metallic
Alloys
Denture base resins
Advantages of denture base resins
Denture should be
Comfort esthetics
FUNCTION
RETENTION
Efficiency

6. GENERAL TECHNIQUE
Clinical steps laboratory steps

7. TEETH ARRANGEMENT
PROCESSING
( acrylization )

9.  Definition : According to GPT - VI, Denture
Base is defined as the part of Denture that
rests on the foundation tissue and to which
teeth are attached. Denture Base Material is
any substance of which denture base may
be made

10.  Skillfully designed dentures
were made as early as 700
BC.and
 Talmud a collection of books
of hebrews in 352-407 AD
mentioned that teeth were
made of gold ,silver,and wood.
 Egypt was the medical center
of ancient world, the first
dental prosthesis is believed to
have been constructed in egypt
about 2500 BC.
Hesi-Re Egyptian dentist of about
3000 BC

11. Front and back views of mandibular fixed bridge, four natural incisor teeth
and two carved ivory teeth
Bound With gold wire found in Sidon-ancient Phoenicia about fifth and
fourth century BC.

12.  During medieval times dentures were seldom considered
,when installed they were hand carved and and tied in place
with silk threads.
 Those wearing full denture had to remove them before
eating.
 Upper and lower teeth fit poorly and were held together by
steel springs.
 Earlier pictures of dental prosthesis are delivered to us by
ABUL-CASIM an Arab born in Cordova Spain.
Persian dentist of late eighteen Indian surgeon of mid
century nineteenth century

13. WOOD
 For years, dentures were fashioned from wood .
 Wood was chosen
-readily available
-relatively inexpensive
-can be carved to desired shape
 Disadvantages
-warped and cracked in moisture
-esthetic and hygienic challenges
-degradation in oral environment

14. Wooden denture believed to be carved out of box wood in 1538 by Nakoka
Tei a Buddist priestess
Wooden dentures

15. Bone
 Bone was chosen due to its availability, reasonable cost and
carvability .
 It is reported that Fauchard fabricated dentures by measuring
individual arches with a compass and cutting bone to fit the
arches .
 It had better dimensional stability than wood, esthetic and
hygienic concerns remained.

16. IVORY
 Denture bases and prosthetic teeth were fashioned by carving this
material to desired shape
 Ivory was not available readily and was relatively expensive.
 Denture bases fashioned from ivory were relatively stable in the oral
environment
 They offered esthetic and hygienic advantage in comparison with
denture bases carved from wood or bone.
Carved ivory upper denture retained in the mouth by springs with natural human teeth
cut off at the
Neck and riveted at the base.

17.  Since ancient times the most
common material for false
teeth were animal bone or
ivory,especially from elephants
or hippopotomus.
 Human teeth were also
used,pulled from the deceased
or sold by poor people from
their own mouths.
 Waterloo dentures
G.Fonzi an italian dentist in Paris invented the
Porcelain teeth that revolutionized the
 1788 A.D. Improvement and construction
development of porcelain dentures by Of dentures.Picture shows partial denture of
DeChemant. about
1830,porcelain teeth of fonzi’s design have
been
Soldered to a gold backing.

18. CERAMICS
 Porcelain denture bases were relatively expensive
 During subsequent years secrets of porcelain denture became
known and it became common and inexpensive.
 ADVANTAGES over wood, bone , ivory were
-Could be shaped using additive technique rather than
subtractive (carving).
-Additive technique facilitated correction of denture base
surface.
-this permitted more intimate contact with underlying
soft tissues.
-Could be tinted to simulate the colors of teeth and oral
soft tissues.
-stable in oral environment.
-Minimal water sorption, porosity, and solubility.
-Smooth surface provided hygienic properties.
 Among the drawbacks BRITTLENESS was most significant,
fractures were common, often irreparable.

19. One piece porcelain upper denture crafted by Dr John
Scarborough,Lambertville,New Jersey 1868.

20.  In 1794 John Greenwood began to swage gold bases for dentures.
Made George Washington's dentures.
George washington’s last dental prosthesis. The palate was swaged from a sheet of
gold and ivory teeth riveted
To it.The lower denture consists of a single carved block of ivory. The two
dentures were held togther by steel
Springs.

21.  In 1839 an important development took place CHARLES GOODYEAR
discovered VULCANIZATION of natural rubber with sulphur(30%)
and was patented by Hancock in england in 1843.
 NELSON GOODYEAR (brother of charles goodyear) got the patent for
vulcanite dentures in 1864.
 . They proceeded to license dentists who used their material, and charged a
royalty for all dentures made. Dentists who would not comply were sued.
 The Goodyear patents expired in 1881, and the company did not again
seek to license dentists or dental products.
 Vulcanite dentures were very popular until the 1940s, when acrylic denture
bases replaced them.

22. A set of vulcanite dentures worn by
Gen. John J. (Blackjack) Pershing,
commander of the American
Expeditionary Forces in France during
the First World War
Set of complete dentures having palate
of swaged
Gold and porcelain teeth set in
vulcanite.

23.  In 1868 John Hyatt, A US
Printer, discovered the first
plastic molding compound,
called celluloid. He made it by
dissolving nitrocellulose under
pressure
 In 1909, another promising
organic compound was found.
This was phenol formaldehyde
resin discovered by Dr. Leo
Backeland .
Celluloid upper denture 1880,celluloid as a
Substitute for vulcanite was unsuccessful as
It absorbs stains and odors in the mouth,
Gradually turns black and was flammable.

24.  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.
Dentures made of polymethyl methacrylate

25.  1. Vulcanite :
In 1839 Vulcanized rubber was discovered and
introduced as a Vulcanite and Ebonite.
For the next 75 years Vulcanite rubber was the
principal Denture base Material. But failed because
of following reasons :
Disadvantages
 It absorbs Saliva and becomes unhygienic due to
bacterial proliferation.
 Esthetics were poor.
 Dimensionally unstable.
 Objectionable taste and odor

26. 2. Celluloid
Although it was having tissue like color
but having principal disadvantages like
Disadvantages
 Lack of stability
 Unpleasant taste
 Unpleasant odor
 Stainability
 Flammable

27. 3. Bakelite
It was formed by heating and compressing a
mixture of phenol and formaldehyde.
Disadvantages
 Lack of uniform quality
 Variable strength
 Variable color
 Dimensional unstability.

28. Chronology of events
 Charles Goodyear discovery of vulcanized rubber in 1839.
 John hyatt discovered celluloid in 1868
 Dr Leo Bakeland discovered phenol-formaldehyde resin (Bakelite).
 In the 1930’s Dr Walter Wright and the Vernon brothers working at
the Rohn and Haas company in Philadelphia developed
Polymethylmethacrylate (PMMA), a hard plastic.
 Although other materials were used for dental prosthesis, none
could come close to PMMA and by the 1940;s 95% of all dentures
were made from this acrylic polymer.

29.  Natural polymers include:
 Proteins (polyamides or polypeptides) containing the chemical
group (-Co-NH-); this is known as an amide or peptide link.
 Polyesoprenes such as rubber and gutta percha.
 Polysaccharides, such as starch, cellulose, agar and alginates.
 Polynucleic acids, such as deoxyribonuclei acids (DNA) and
ribonucleic acids (RNA).
 Synthetic polymers are produced industrially or in the
laboratory, by chemical reaction.
Synthetic polymer : Defined as a non metallic compound
synthetically produced (usually from organic compounds) which
can be molded into various useful forms and then hardened for
use.

32. METHYL METHACRYLATE
H CH3
C C
H C O
O
CH3

35. POLY(METHYL METHACRYLATE)
H CH3 H CH3 H CH3
C C C C C C
H C O H C O H C O
O O O
CH3 CH3 CH3

37.  Dimer - Polymer from two different
mers
 Terpolymer - Polymer from three
different mers

38. CH3 CH3
CH2 C CH2 C
C O C O
O O
CH3 C2H5
m
Methyl Ethyl

39. METHYL-, ETHYL-, BUTYL-
METHACRYLATE
COPOLYMER (TERPOLYMER)
CH3 CH3 CH3
CH2 C CH2 C CH2 C
C O C O C O
O O O
CH3 C2H5 C4H9
m
Methyl Ethyl Butyl

40.  Linear
 Branched
 Cross-linked

42. Homopolymer
Copolymer (random)
Copolymer (block)

44. Homopolymer
Copolymer (random)

48. PLASTICIZER
(dibutyl phthalate)
O
C O C4H9
C O C4H9
O

49. DEFINITION: A polymer is a long chain organic molecule .It is
produced by the reaction of many smaller molecules called
monomers,or mers.
 If reaction occurs between two different but compatible monomers
the polymeric product is called a COPOLYMER.
 Resin : A broad term used to describe natural or synthetic
substances that form plastic materials after polymerization (GPT-7th
edition).
USES IN DENTISTRY
 Denture bases and artificial teeth.
 Denture liners and tissue conditioners.
 composite restorative and pit and fissure sealent.
 Impression materials
 Custom trays for impression
 Temporary restoratives.
 Mouth-guards.
 Maxillofacial prosthesis.
 Space maintainers.
 Veneers.
 Cements and adhesives.

50. CHEMISTRY OF POLYMERIZATION
 Monomers react to form polymer by a chemical reaction called
polymerization.
 The most common polymerization reaction for polymers used in
dentistry is addition polymerization.
ADDITION POLYMERIZATION
 INDUCTION
 PROPOGATION
 CHAIN TRANSFER
 TERMINATION
INDUCTION
1)ACTIVATION
2)INITIATION

51. ACTIVATION Free radicals can be generated by activation of radical producing
molecule using.
 Second chemical
 Heat
 Visible light
 Ultraviolet light
 Energy transfer from another compound that acts as a free radical.

52.  Commonly employed initiator is Benzoyl peroxide which is
activated rapidly between 50 degree and 100 degree C to release
two free radicals per benzoyl peroxide molecule.
 Second type is chemically activated ,consists of two reactants when
mixed undergo reaction eg tertiary amine (the activator) and benzoyl
peroxide (the initiator). Amine forms a complex with benzoyl
peroxide which reduces the thermal energy (and thus the
temperature) needed to split it into free radicals.
 Third type is light activated .The visible light light cured dental
restoratives,camphorquinone and an organic amine
(dimethylaminoethylmethacrylate) generate free radicals when
irradiated by light in the blue to violet region.
 Light with a wavelength of about 470nm is needed to trigger this
reaction.

59. PROPOGATION

60. CHAIN TRANSFER
 The active free radical of a growing chain is transferred to another
molecule (eg monomer or inactivated polymer chain) and a new free
radical for further growth is created termination occurs in the latter.

61. Reaction terminates when
insufficient free radicals exist.
Reaction also may be stopped by
any material that will react with
free radical, decreasing the rate
of initiation, or increasing rate of
termination.

63. TERMINATION
 Can occur from chain transfer.
 Addition polymerization reaction is terminated by
-Direct coupling of two free radical chains ends
-Exchange of hydrogen atom from one growing chain to another.

64. INHIBITION OF ADDITION REACTION
 Addition of small amount of Hydroquinone to the monomer inhibits
spontaneous polymerization if no initiator is present and retards the
polymerization in the presence of an initiator.
 Amount added is 0.006% or less
 Methyl ether of hydroquinone is generally present.
COPOLYMERIZATION
 When two or more chemically different monomers each with
desirable properties can be combined to yield specific physical
property of a polymer .eg small amount of ethyl acrylate may be co-
polymerized with methyl methacrylate to alter the flexibility and
fracture resistance of a denture.

65. METHYL METHACRYLATE
 The acrylic resins are derivative of ethylene and contains a vinyl
group
(-c=c-)
 Polyacids tends to imbibe water, due to polarity related to carboxyl
group.
 Water tends to separate the chain and cause softening and loss of
strength.
 Methyl methacrylate is a transparent liquid at room temp.
 Physical properties
-Molecular wt=100
-Melting point=-48 C
-Boiling point=100 C
-Density=0.945g/ml at 20 C
-Heat of polymerization=12.9 Kcal/mol
Methyl methacrylate
molecule

66. POLYMETHYL METHACRYLATE
 Transparent resin, transmits light in uv range to a wavelength
of 250 nm.
it has got remarkable clarity.
 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)
 It is chemically stable and softens at 1250C
 It can be molded as a thermoplastic material between 125
and 200 C
 Depolarization takes place at approx 450 C .
 Absorbs water by imbibition
 Non crystalline structure possess high internal energy.
 Polar carboxyl group can form hydrogen bridge to a limited
extent with water.

68.  Conventional heat cure acrylic resins
 Conventional cold cure acrylic resins
 High impact resistant acrylic resin
 Injection moulding resin
 Rapid heat polymerizing resin
 Light activated resin

70. 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

71.  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

72. 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.

73.  Cyanide method
Acetone and hydrocynic acid
 Phosgene method
Petroleum propylene and phosgene

74. Polymethyl methacrylate
main ingredient
Benzoil peroxide
0.5-1.5%, initiator
Dibutyl phthalate
8-10%, plasticizer
Zinc or tetanium oxide
opacifier

75. 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

76. POLYMER POWDER OF ACRYLIC DENTURE BASE MATERIAL

77. 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

78. 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

79. Tensile strength
- 600 kg/sq cm
Appearance
- shiny
- transparent
- slippery
Produced in two shapes
- spherical
- granular

80. Control of particle size
- no.52 sieve mesh
- 300 micrometer
If particle size is smaller
- softening will be quicker
- granular shape softens faster

81. 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

82. CURING CYLES EMPLOYED IN THE STUDY
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
Short and reverse cures:
5) Boil water,insert flask , remove heat for 20 min return to boil for 10
min.
6) Boil water ,insert flask ,return to boil, boil for 10 min.
Dry heat cure:
7)temp in excess of 100C using dry heat system
B Short curing cycles
8) 7hr at 60C
9) 7hr at 60C +1 hr at 90C
10) Boil water, insert flask remove heat for 20 min return to 90 C hold at
90C for 5 min
11) Boil water insert flask return to 90C hold at 90C for 5min.

83. (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

84.  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.

85. 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

86. (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.

87. (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.

88. 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.
 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

89.  Fluid resin and compression molding technique can be employed for
the fabrication of denture.
 Also used as repair material

90. 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.

91. 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

92. 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.

93. 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

94. 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

95. 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.

97. COMPRESSION MOLD TECHNIQUE
INJECTION MOULD TECHNIQUE
FLUID RESIN TECHNIQUE
MICROWAVE PROCESSING
LIGHT ACTIVATED DENTURE BASE RESINS

98. Primary impressions
Secondary impressions
Jaw relations
Try in stage
acrylization
flasking
dewaxing
packing- under pressure
curing

99.  Acceptance before demounting
 Proper finishing
 Periphery is sealed
 Petroleum jelly
 inner surface of the flask
 Casts
 Adjustment of the plaster model
 Plaster molels are wetted
 Wax dentures with casts are soaked with
slurry water

100. “ The Art of Investing in a Flask ”
- GPT 99
“ The Process of Investing the Cast With the
Waxed Denture in a Flask to Make a Sectional
Mold Used to Form the Acrylic Resin Denture Base ”
- HEARTWELL
“ The process of investing the cast and a wax replica
of the desired form in a flask preparatory to molding
the restorative material into the desired product ”

101. Flask
surround or invest
“ a metal case or tube used in investing
procedure”
- metal
- brass
-3 or 4 parts

105. FLASKING
TWO POUR TECHNIQUE THREE POUR TECHNIQUE

106.  Selection of flask
 Petroleum jelly lubrication
 Demounting done
 Preparation of the waxed denture with the
stone cast
 Soaking of the cast – slurry water
 Artificial stone is mixed
 Stone mix is placed in flask and wax
denture and casts are settled in to the mix

108.  Periphery of
flask should be
in level with
the rim of the
flask
 Occlusal plane
– parallel to
the base of the
flask

109. Tilting of the casts
Retromolar pads and
tuberosity- should be
protected
Devoid of undercut
Shaping of the stone –
blade or knife

110.  Providing taper
 Undercuts – removed
or corrected
 Distance from top lid
– 6 mm
 Stone is smoothened

111. Checking the seating of flask
members
Investedflask & cast is
washed in clear slurry water
Surface tension reducing
agent is applied to the exposed
wax
Separating medium is applied

112.  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

113.  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

114.  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

115. Lid is closed
Flask is clamped

116. A. Flasks cannot be separated after dewaxing
Cause
Undercuts in flasking and casts
Improper application of separating medium
Solution
Examining the casts
Remove undercuts
Proper application of separating medium
B. Heel broken on mandibular cast
Cause
Undercut not blocked out
Solution
Blocking and protecting the heel area

117. C. Denture with acrylic blubs
Cause
-Investing stone not painted
Properly on waxed denture
During flasking
- Improper investing stone mix
Solution
- Paint investing stone on teeth
With brush
- Use of mechanical spatulator

118.  The denture is taken out from the flask.
 It is then trimed
 Finally wet and dry polishing is done.

119.  Porosity
 Crazing
 Warpage
 Fracture

120.  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.

122.  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.

123.  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

125.  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.

126. Denture warpage

127.  Improper deflasking
 Denture base excessively thin
 Accidental dropping at time of polishing

128.  Care to taken at time of dewaxing procedure
 Rearticulation to be done after processing the
denture to check of occllusal discrepancy.