denture base Resins

it has good history and photographs, values are reliable

1. DENTURE BASE RESINS

Dipal mawani
pOST GRaDUaTE STUDEnT

2. Contents
Introduction
History
Definitions
Classification
Ideal requirements
Stages of polymerization
Manipulation
Properties of Denture Base Resins
Recent advancement
Review of literature
Conclusion
References

3. Introduction
Dentistry as a speciality is believed to have begun about
3000 BC.
The first dental prostheses was believed to have been
constructed in Egypt around 2500 BC.
Skillfully designed dentures were made as early as 700BC.

4. Brief History
Of Evolution Of Denture Base Materials
Hesi-Re Egyptian dentist of about
3000 BC

6. Year Material Advantages disadvantages
700 BCIvory Comparitively durable,
esthetic
Legal issues and
Nonavailability makes it
inexpensive

7. Gold
In 1794 AD John Greenwood began to
swage gold bases for dentures.
Made George Washington's dentures.

8. Year Material Advantages Disadvantages
1800 ADPorcelain
Nicholas Dubulous
de Chemant
Easy to shape
Stable
Minimal water
absorption
Smooth surfaces
Less porosity
Low solubility
Can be tinted to
required shape
Brittle
Bulky
Difficult to repair

9. Year Material Advantages Disadvantages
1840 ADVulcanized Rubber
(vulcanite)
Charles Goodyear

Well adapted
Good retention
Easy to process
Quite stable
Lack of translucency
Color modification
difficult
Poor aesthetics
Porous
Unhygienic

10. Year Material Advantages Disadvantages
1868 AD Celluloid
John Smith Hyatt
Translucent
Ability to mimic
gingival color
Distortion
Discoloration
Camphor taste
1907 AD Stainless Steel and
Base Metal Alloys
E Haynes
low density
low material cost
higher resistance
to tarnish and
corrosion
high modulus of
elasticity.

11. Year Material Advantages Disadvantages
1909 ADPhenol formaldehyde
resin
Dr. Leo Bakeland
Ease of
availability
Good initial
aesthetics
Brittle
Poor color
Poor shelf life
1930 ADPoly Vinyl ChlorideFlexibility
Indicated for
mouth guards and
denture liners
Distortion
Discoloration

1937 ADPolymethylmethacrylate
Dr Walter Wright and
Vernon brothers,
Philidelphia USA
Transparent
Adequate strength
and stability
Biocompatible
Low solubility
Tasteless
odorless
Easy to repair and
process
Pigmentable
Brittle
Poor flexural
strength
Polymerization
shrinkage
High
coefficient of
thermal
expansion
Radiolucent
Allergic

12. Definitions
Denture base: A denture base may be defined as the
part of denture that rests on the foundation tissue
and to which teeth are attached. (GPT-8)
Denture base material is any substance of which a
denture base may be made.

13. Classification

14. ISO classification
Type Name Features
1 Heat cure polymers >65 degree Celsius
2 Self cure polymers <65 degree Celsius
3 Thermoplastic materialsMoldable polymers
4 Light cure materialsVisible or ultraviolet radiation
5 Microwave materialsMicrowave heat polymerization

16. Ideal properties of denture base
materials
1.Biological: tasteless, odorless, non toxic,
nonirritating, impermeable to oral fluids and discourage
bacterial growth.
2.Physical: adequate strength and resilience, good
dimensional stability and resistance to thermal changes
3.Esthetics: exhibit sufficient translucency, accede
pigmentation and show no color change over time.

17. 4. Handling: Should not produce toxic fumes, easy to
mix, shape and cure, easy to polish and repair.
5. Economic: cost of the material and processing
should be practical and feasible.

18. Mechanical properties
Applied forces produce stresses within polymers that
cause materials to deform via
Plastic strain - irreversible
Elastic strain - reversible
Viscoelastic strain – combination, recovers over time
Where as the amount of deformation that is not
recovered is plastic deformation.

19. Rheometric properties
Rheometry or flow behaviour of solid polymers, which
involves a combination of elastic and plastic
deformation.
The chain length, number of crosslinks, temperature,
and rate of force application determines which type of
behaviour dominates.

20. Solvation and dissolution properties
The longer the chains the more slowly a polymer
dissolves.
Polymer tend to absorb a solvent, swell, and soften
rather than dissolve.
Crosslinking prevents complete chain seperation and
retards dissolution; thus highly crosslinked polymers
cannot be dissolved.

21. Thermal properties
Polymers can be formed into many desired shapes
depending on which the polymeric material is
thermoset or a thermoplastic type.

22. Chemistry of polymerization
Monomers are joined together by means of either
Addition polymerization
Monomers are activated one at time and added together
in sequence.
Condensation polymerization
The components are difunctional,
Byproduct is formed.

23. Four distinct stages includes
Induction
Propagation
Chain transfer
Termination
Stages in Addition polymerization

24. Induction
Two processes controls induction stage – activation
and initiation.
A source of free radical R is required.
Free radicals are generated by activation of radical
producing molecule such as,
chemical, heat, visible light, ultraviolet light or energy
transfer from another compound.

25. Requisites of an addition-polymerizable compound are
•presence of unsaturated group(=)
• source of free radicals.
When the free radical and its unpaired electron
approach a monomer with its high-electron-density
double bond, an electron is extracted and pairs with R
electron to form a bond between the radical and the
monomer molecule, leaving the other electron of the
double bond unpaired.
Thus the original free radical bonds to one side of the
monomer molecule and forms a new free radical site at
the other end.

27. Substances capable of generating free radicals are
potent intiators.
The most commonly employed initiator is benzoyl
peroxide which is activated rapidly between 50
0
C and
100
o
C. (2 per molecule)

28. Polymerization process useful for dental resins are
1)Heat activated
2)Chemically activated
Tertiary amine and the benzyl peroxide
3)Light activated
Photons from a light source
Visible light – camphorquinone and an organic amine
(e.g., dimethylaminoethylmethacrylate).
generate free radicals

29. Propagation
The resulting free radical monomer complex acts as a
new free radical center which is approached by another
monomer to form a dimer, which also becomes a free
radical.

30. Chain Transfer
When a free radical approaches methyl methacrylate
molecule and donates a hydrogen atom to the
methylmethacrylate molecule.
This causes free radical rearrangement to form a double
bond and unreactive.

31. Termination
Can result 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.

32. Heat-Activated Denture Base Resins
Composition
Powder:
Beads or granules of PMMA
Initiator: benzoyl peroxide
Pigments: mercuric sulphide, cadmium sulphide,
Opacifier: zinc oxide, titanium oxide
Plasticizer: dibutyl phthalate
Synthetic fibers: nylon/acrylic
Liquid:
Methyl methacrylate monomer
Crosslinking agent: Ethylene glycol dimethacrylate (1-2 % 14%).
Inhibitors: Hydroquinone (0.003-0.1%)

33. COMPRESSION MOLDING
TECHNIQUE

34. Preparation of the mold

37. Selection and application of separating
medium
Failure to place an separating medium
1. Water from mold surface may diffuse in to
denture resin, it may affect the polymerization rate as
well as optical and physical properties.
2. Free monomer may soak into mold surface
portions of investing medium may become fused to the
denture base.

38. Separating medium
Currently the most popular separating agents are water
soluble alginate solutions.
When applied to the dental stone surfaces, these
solution produce thin, relatively insoluble calcium
alginate films.

39. Polymer – monomer interaction
When mixed in proper proportions, the resultant mass
passes through five distinct stages:
1.Sandy
2.Stringy
3.Dough-like
4.Rubbery or Elastic and
5.Stiff

41. Wet/Sandy stage
Little or no interaction occurs at molecular level.
Polymers remains unaltered.
consistency of the mixture – “coarse” or “grainy.”

42. Stringy stage
Monomer attacks the surfaces of individual polymer
beads and is absorbed into beads.
Polymer chains uncoils,
Increase in viscosity of the mix.
Characterized by “stringiness” or “stickiness.”

43. Dough stage
An increased number of polymer chains enter the
solution.
Thus, monomer & dissolved polymer are formed.
Clinically the mass behaves like a pliable dough.
It is no longer tacky and does not adhere to surface.
As a result, material should be packed into the mold
cavity in this stage.

44. Rubbery or Elastic stage
Monomer is dissipated by evaporation and by further
penetration into remaining polymer beads.
The mass rebounds when compressed or stretched.
Stiff stage
Clinically mixture appears very dry and
Resistant to mechanical deformation.

45. Dough-forming time
The time required for the resin mixture to reach a dough
like stage is termed as dough-forming-time.
ANSI/ADA specification No.12
for denture base resins requires that this consistency be
attained in less than 40 min from the start of mixing
process.
The majority of denture base products reach a dough like
consistency in less than 10 min.

46. Working time
Working time is defined as the time a denture base
materials remains in the doughlike stage.
ANSI/ADA Sp. No.12 requires the dough to remain
moldable for at least 5 min.
Ambient temperature affects the working time.
Hence, can be extended via refrigeration
Drawback – moisture, degrade the physical and esthetic
properties

47. Packing
The placement and adaptation of denture base resin
within the mold cavity are termed packing.
Over packing leads to excessive thickness and
malpositioning of prosthetic teeth.
Under packing leads to noticeable denture base
porosity
After the closure the flasks should remain at room
temperature for 30- 60 min it is called bench curing

48. pressure is
applied
incrementally

50. Curing cycle
The following curing cycle have been quite successful
1.Processing in a constant temperature water bath at 74
o
C
for 8 hrs. or longer with no terminal boil.
2.Processing in a 74
0
C water bath for 8 hrs. and then
increasing the temperature to 100
o
C for 1 hr.
3.Processing resin at 74
o
C for approx. 2hrs and increasing
the temperature of to 100
o
C for 1 hr.

51. Following the completion of curing, the denture flasks
should be cooled slowly to room temperature.
Rapid cooling may result in warping of denture base
because of difference in thermal contraction of resin and
investing stone.
Hence flasks should be removed from the water bath and
bench cooled for 30 min.

52. Injection molding technique
Sprues or ingates are attached to
the wax denture base, which
lead to an inlet or pressure port

55. Available data and clinical information indicate
denture bases fabricated from injection molding
result in fewer dimensional inaccuracies and
polymerization shrinkage than conventional
processing.

56. Chemically activated denture base resins
Often referred to as cold curing, self-curing or auto-
polymerizing resins.
Composition: Identical to heat cure resin except
polymerization is initiated by tertiary amine (e.g.
sulfinic acid or dimethyl-para-toluidine).

57. ADVANTAGE
 Exhibit less shrinkage, so greater dimensional accuracy.
 Easy manipulation
 Used as repair material
DISADVANTAGE
Increased porosity
Tissue irritation from residual monomer.
 Colour stability-inferior due to tertiary amine (oxidation)
Decreased flexural strength.

58. Fluid resin technique

59. Laboratory steps

62. Advantages
•Improved adaptation
•Decreased possibility of damage to prosthetic teeth
and denture bases during deflasking
•Reduced material cost
•Simplification of flasking, deflasking, and finishing
procedures.

63. Disadvantages
•Air entrapment
•Poor bonding between the denture base material and
acrylic resin.
•Technique sensitive procedure

64. Light activated denture base resins
These material have been described as resin-based having a
matrix of:
urethane dimethacrylate,
light when irradiated at 400-500nm-activator
Camphoroquinone, organic amine-initiator
Supplied in sheet & rope forms & packed in light proof
pouches to prevent inadvertent polymerization.

65. Following polymerization , the denture is removed from the
cast, finished and polished in a conventional manner

66. MICROWAVE POLYMERIZED PMMA (Nishii in 1968)
Resins are the same as used with conventional material
and are processed in a microwave-400 watt oven in 2.5
minutes.
Special polycarbonate flask used 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 (2.5 min).
Microwave resin and non metallic microwave flask

67. Properties of denture base resins

Methyl methacrylate
Methyl methacrylate is a transparent liquid at room temp.
Physical properties
 Melting point= -48
o
C
 Boiling point=100.8
o
C
 Density=0.945g/mL at 20
o
C
 Heat of polymerization=12.9 Kcal/mol
 Volumetric shrinkage= 21%

68. Polymethyl methacrylate
Transparent resin, transmits light in UV range to a
wavelength of 250 nm.
Hard resin, knoop hardness number of 18 to 20.
Tensile strength is 55 Mpa
Compressive strength is 76 MPa
Density is 1.19 g/cm cube.
Modulus of elasticity 3800 Mpa
Proportional limit is 26MPa

69. Polymer – monomer ratio
Research indicates that,
 methylmethacrylate polymethylmethacrylate
Yields a decrease in volume of material.
This would create a significant difficulty in denture base
fabrication.
Hence, to minimize the dimensional changes resin
manufacturers prepolymerize a significant fraction of the
denture base material.
This can be thought of as “preshrinking” the selected resin
fraction.
21%

70. In practice the prepolymerized fraction is encountered
as a powder, and is commonly referred to as
polymer.
The non polymerized fraction is supplied as supplied as
liquid, and is termed as monomer.
The accepted polymer to monomer ratio is 3:1 by
volume.
Using a 3:1 ratio, the volumetric shrinkage can be
approximately limited to
7%

71. It appears the shrinkage exihibited by these materials is
distributed uniformly to all the surfaces.
Hence the adaptation of denture bases to underlying
soft tissue is not significantly affected, provided the
materials are manipulated properly.

72. Porosity
The presence of surface and subsurface voids can compromise
physical, esthetic and hygienic properties of processed dentures base.
4 types- a) gaseous porosity
 b) granular porosity
 c) air inclusion porosity
 d) contraction porosity


73. Reasons for porosity:
1)Inadequate mixing of powder and liquid components.
2)Inhomogeneity of resin mass
3)Inadequate pressure or insufficient material
4)Air inclusions incorporated during mixing and pouring
procedures.

74. Water Absorption
PMMA absorbs small amount of water has significant
effect on mechanical & dimensional properties of the
processed polymer.
1)Slight expansion of polymerized mass(water occupy
positions between polymer chains)
2)water molecules interferes with the entanglement of
polymer chains (thereby act as plasticizer)
PMM exhibits a water sorption value of 0.69mg/cm
2
.
For each 1% increase in weight due to absorption, acrylic
resin exhibits a linear expansion of 0.23% .

75. Solubility
Denture base resins are virtually insoluble in the fluids of
oral cavity.
 ANSI/ADA sp. No. 12  weight loss not greater than
0.04 mg/cm
2
(negligible to clinical standpoint) 

76. Crazing
Stress relaxation produce small surface flaws
that affect esthetic & physical properties.
Production of such flaws, or microcracks, is termed crazing.
Crazing in a transparent resin imparts a “hazy” or “foggy”
appearance.
Caused by
Internal strains in flask,
Heat (due to polishing),
Differential contraction around porcelain teeth,
Attack by solvents such as ethyl alcohol.

77. Strength
Resins are typically low in strength, however they have
adequate compressive and tensile strength for complete or
partial denture applications.
Heat cured have greater strength.
Strength is affected by
Composition of the resin,
Technique of processing,
Degree of polymerization,
Water sorption,
Subsequent environment of the denture.

78. Creep
Denture resins display viscoelastic behaviour(rubbery
solids)
When subjected to sustained load, material exhibits
both elastic and plastic components
Additional plastic deformation which occurs is termed
creep. And the rate is termed creep rate.

79. Recent Advances

80. Reinforced denture base resins
Attempts to improve the mechanical properties of
PMMA.
Inclusion of metals, hydroxyapatite, and rubber fillers
are used.
Fibers like non impregnated polyethylene fibres, light-
polymerized monomer impregnated fibres are also
used.

81. Metal and metal-reinforced denture bases
The common metals include
1)cast gold
2)aluminium and
3)chrome based alloys.
Advantages over resin bases, which include thermal
conductivity, minimal bulk, and more strength with
high dimensional stability.

82. Disadvantages are heavy, inability of being rebased,
poor esthetics and not economical.
To circumvent the disadvantages of metal dentures
bases, acrylic resins have been reinforced with wrought
or cast mesh framework or metal elements or nano
particles.

83. Glass flake-reinforced PMMA
Glass flakes are added to PMMA in the ratio of 5% -
20% w/w to polymer powder , which leads to 69%
increase in fracture toughness.

84. Rubber-reinforced PMMA
PMMA is blended with rubbery inclusions such as
butadiene-styrene incorporated with copolymers of
vinyl and hydroxyethyl monomers by the process
called rubber toughening; these are known as high
impact resins.
Advantage: enhanced fracture toughness
Disadvantage : reduced stiffness, creep, water sorption
as well as increased adhesion of microbial plaque.

85. Fiber-reinforced PMMA
Various fibers such as carbon, kelvar, glass, and nylon fibers
have been added to PMMA to improve their flexibility.
Carbon fibres have been used as denture base
strengtheners.
Advantage: improved flexural strength and impact strength
Disadvantage: they change the color of the resin and hence
are unesthetic.

86. Kelvar fibers are synthetic aromatic fibers.
These fibers are thermally and chemically resistant and
have high melting point
Because of the pleated structure they display lower
flexural strength
Unesthetic
Complicated etching process

87. Glass fibers
The most common method of reinforcement of PMMA
E-glass fibers - which as high alumina and low alkali
Borosilicate – superior in flexural strength.
Polyethylene fibers
They contribute to the impact strength, modulus of
elasticity, and flexural strength of the dentures.
Nylon fibers
They are polyamide fibers based on aliphatic chains
Fracture resistance and water absorption affects the
mechanical properties of nylon.

88. Rapid Heat Polymerized Polymer
These are hybrid acrylics which have had the
initiator formulated to allow for very rapid
polymerization without 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.

89. High impact resistant
acrylic
Butadiene- styrene rubber is incorporated with
copolymer of vinyl and hydroxyl ethyl monomer.
These materials are slightly stiffer, have twice the
impact strength, absorbs less water and lower linear
shrinkage. But are not entirely color stable.

90. Valplast
Nylon like material
It is a flexible denture base resin that is ideal for
partial dentures and unilateral restorations.
The resin is a biocompatible nylon thermoplastic, it
eliminates the concern about acrylic allergies.

91. High Tensile Strength
Abrasion Resistant
Highly Resilient
High Flexural Strength
Elastic Memory
Undercut Areas In R.P.D
Tori, tuberosity
Extremely Bulging Alveolar
Process
Obturators or Cleft Palates
Properties Indications

92. Review of Literature

93. Adverse reactions to PMMA
Methyl methacrylate and formaldehyde formed as oxidation
products of the residual monomer are allergic agents
responsible for mucosal injuries.
Monomer can lead to
 Allergic stomatitis
 Contact Dermatitis
Allergic sensitization of the skin and oral mucosa to acrylic resin denture
materials. J Prosthet Dent 1956

94. Irritant contact dermatitis
Most common in dental laboratories
Associated with regular contact with monomer
Must avoid direct contact
Rubber gloves may not provide sufficient protection.
Barrier creams can help

95. Allergic contact stomatitis
Usually associated with release of
residual monomer
Benzoic acid
Heat cured resin < chemical cured resin
May use an extra cycle of polymerisation (but denture may warp)
May need to consider alternative material.

96. Cytotoxicity-
Autoploymerized resins are the most cytotoxic denture base
material.
Acrylic resins polymerized by microwave irradiation are less
cytotoxic.
Water storage may reduce the level of residual monomer,
resulting in decreased cytotoxicity.

97. FA PEYTON et al 1963, evaluated dentures
processed by different technique. Four self
cure type, seven heat cure type, three injection
products, two cr-co alloys were studied.
They concluded that,
The most accurate dentures were self cure type. And it offers
simplest method and involves least amount of equipment.
Second best was found to be heat cure type, but the total
processing time is long.
Injection molding technique required highly trained personnel
and equipment is more complicated and expensive.

98. ROBERT E OGLE et al 1999, compared incisal
pin opening, dimensional accuracy, and
laboratory working time for dentures
constructed by injection system with
conventional compression molding technique.
They concluded that
Injection molding method produced a significant smaller incisal
pin opening over standard compression molding technique.
Injection molding technique was more accurate method for
processing dentures.
There were no appreciable difference in laboratory working time
between the two.

99. FD MIRZA 1961, clinically evaluated the
dimensional stability of heat cure and self
cure type.
Heat cure dentures were processed with conventional
compression molding technique and self cure resin were processed
with fluid resin tech.
He concluded that, the clinical fit of auto polymerized dentures
was equally as good as that of heat cured dentures, even though
the magnitude of linear dimensional changes of auto polymerized
dentures after 3 months of use was greater than heat cured group.
This continuous shrinkage may be due to greater volume of
monomer employed in resin mix.
The difference was statistically significant when compared with
heat cured group.

100. WONG et al in 1999 did a study which investigated
linear dimensional changes and water sorption of
dentures processed by dry and wet heat with
different rates of cooling.
•Water uptake of dry and wet heat–processed acrylic resin dentures
after deflasking was in both cases were low, and the dentures did not
reveal significant differences in shrinkage at water saturation.
•Air oven–processed and water bath–processed acrylic resin dentures
show similar dimensional shrinkage at water.
Wong Debby. Effect of processing method on the dimensional accuracy and
water sorption of crylic resin dentures. J Prosthet Dent 1999;81:300-4.

101. BECKER, SMITH et al 1997, compared some of
the physical properties acrylic resin when
processed using
all gypsum pressure molding technique
silicone gypsum molding technique
fluid resin system
They Concluded that,
Increase in thickness of acrylic resin in the palate occurs for all
three processing technique.
Fluid resin showed greatest increase in palatal thickness which
may be attributed to lack of force used to hold the master cast
position against investment material.
Color stability of the resin for all three processing technique
passed ADA sp no.12 for acrylic resin.
All three processing technique demonstrated the ability of the
resin to reproduce minute detail.

102. Conclusion
A widely used polymer in dentistry is acrylic resin.
However, the choice of material should be based on the
purpose , properties, and the practicality of the clinical
situation in hand.
New materials and processes that help clinicians and
dental technicians provide quality care while
improving patient connivance and access will continue
to be successful.

103. Kenneth j. Anusavice ; Phillips Science of dental material
.Eleventh edition, Elsevier,2004.
William J. O’Brien; Dental materials and their selection. Third
edition, quintessence Publishing co. 2002.
Robert C. Craig John M. Powers, John C.Wataha ;Dental
materials properties and manipulation,. Eight edition,2004.
Robert L.Engelmeier; The dental clinics of North America-
complete dentures, W B Saunders company jan 1996 vol.40
no.1
Peyton F.A., Anthony D.H., 1963: “Evaluation of dentures
processed by different techniques”. J. Prosthet Dent.; March –
April 13(2): 269-282.
Braden M., 1964: “The absorption of water by acrylic resins
and other materials”. J Prosthet Dent.; March/April 14(2):
307-316
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nd
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th
edition
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