This document discusses denture base materials and focuses on acrylic resin denture bases. It defines key terms related to polymers and polymerization. It describes the three types of acrylic resin activation: heat, chemical, and light. For heat-activated acrylic resin, it details the components, mixing, stages of polymer-monomer interaction, packing, and polymerization cycle. It also briefly discusses rapid heat polymerization, microwave activation, chemical activation, and fluid resin techniques.

1. DENTURE BASE MATERIALs PART 2
▪ GUIDED BY –
▪ DR AJIT JANKAR
▪ DR BHUSHAN BANGAR
▪ DR SUSHEEN GAJARE
▪ DR SANDEEP FERE
▪ DR SHASHI PATIL
PRESENTED BY –
DR NITIN KALE
1st MDS
1

2. CONTENT
▪ TERMINOLOGIES
▪ POLYMERIZATION
▪ NON METLLIC DENTURE BASE MATERIAL
▪ ACRYLIC RESIN
– Heat Activated
– ChemicallyActivated
– LightActivated
▪ PROPERTIES OF DENTURE BASE RESINS.
▪ RECENT ADVANCES IN DENTURE BASE MATERIALS.
2

3. TERMINOLOGIES
▪ Mer – repeating unit or units in polymer chain – “links”
▪ Monomer – chemical compound that is capable of reacting to form
polymer.
▪ Polymer – chemical compound i.e. consist of large organic molecule
formed by union of many smaller repeating units.
▪ Free radical – atom or group of atoms with unpaired electrons.
3

4. ▪ Activator – source of energy used to activate an initiator and produce free
radicals –
▪ a)Heat – thermal energy
▪ b) an electron donating chemical – tertiary amine
▪ c) visible light – supplies energy for photoinitiation.
▪ Initiator – a free radical forming chemical used to start the polymerization
▪ Inhibitor – a component that prevents or inhibits undesirable
polymerization of the monomeric liquid during storage – for prolonged
shelf life
4

5. Polymerization
▪ Definition – chemical reaction in which monomers of low molecular
weight are converted into chains of polymer with high molecular
weight .
▪ Chemical Stages of Polymerization -
▪ Induction – activation of free radicals – initiates growing polymer
chain
▪ Propagation – stage of polymerization - polymer continue to grow to
high molecular weight
▪ Termination – stage of polymerization during which polymer chain
no longer grow .
5

6. INDUCTION
▪ It includes Activation and Initiation .
▪ ACTIVATION
6

7. INITIATION
7

8. PROPAGATION
8

9. CHAIN TRANSFER
9

10. TERMINATION
10

11. 11

12. RESIN DENTURE BASE MATERIALS
Majority of dentures are fabricated using Polymethyl-methacrylate.
PMMA – Pure is colorless transparent solid.
It is tinted to provide any color.
Its color, optical properties remain stable under normal intraoral
condition.
Advantage – ease in processing.
Supplied as – Powder – Liquid System.
12

13. Heat Activated
Chemically Activated
Light Activated
13

14. Heat Activated Denture Base Resins
COMPONENTS
▪ Liquid
▪ (non polymerized ) Methyl methacrylate - Plasticizes the polymer
(97%)
▪ Dibutyl phthalate - Plasticizer
▪ Glycol dimethacrylate (1-2%) - Cross-linking agent (reduces crazing)
▪ Hydroquinone (0.006%) Inhibitor- Prevents premature
polymerization
14

15. ▪ Powder
▪ Poly (methyl methacrylate) Major component
▪ Ethyl or butyl methacrylate (5%) Copolymers - improves properties
▪ Benzoyl peroxide - Initiator
▪ Compounds of mercuric sulfide, cadmium sulfide - Dyes
▪ Zinc or titanium oxide - Opacifiers
▪ Dibutyl phthalate - Plasticizer
▪ Inorganic fillers like glass fibers - Improves physical properties like
stiffness.
▪ Dyed synthetic nylon or acrylic fibers -To simulate small capillaries 15

16. Techniques of processing
Compression MoldingTechnique
Injection MoldingTechnique
Modifications – a) Rapid heat-polymerized resin
b) Microwave-activated PMMA
16

17. Compression Moulding Technique
▪ Preparation of the mold.
▪ Selection and application of a Separating medium
▪ Polymer – Monomer Interaction
▪ Packing
17

18. Preparation of the Mold
▪ Completed tooth arrangement is sealed to the master cast.
▪ The master cast is coated with a thin layer of separator to prevent
adherence of dental stone to the master cast during the flasking
process.
▪ The lower portion of a denture flask is filled with freshly mixed dental
stone, and the master cast is placed into this mixture.
18

19. ▪ The upper portion of the selected denture flask is then positioned
atop the lower portion of the flask.
▪ Care is taken to ensure that the investing stone achieves intimate
contact with all external surfaces of the mounted teeth.
▪ The investing stone is added until all surfaces of the tooth
arrangement and denture base are completely covered.
▪ Incisal and occlusal surfaces are minimally exposed to
facilitate subsequent deflasking procedures.
19

20. ▪ The stone is permitted to set and is coated with separator.
▪ At this point an additional increment of dental stone is mixed and the
remainder of the flask is filled.
▪ The lid of the flask is gently seated and the stone is allowed to
harden.
▪ After the stone has hardened, the record base and wax must be
removed from the mold.
20

21. ▪ The record base and softened wax remain in the lower portion of the
denture flask.
▪ The prosthetic teeth remain firmly embedded in the investing stone
of the remaining segment.
21

22. Selection and application of a
Separating medium
▪ This medium must prevent direct contact between the denture base
resin and the mold surface.
▪ Failure of which leads to two major difficulties:
▪ (1) If water is permitted to diffuse from the mold surface into the
denture base resin, it can affect the polymerization rate as well as the
optical and physical properties of the resultant denture base.
▪ (2) If dissolved polymer or free monomer is permitted to soak into
the mold surface, portions of the investing medium can become
fused to the denture base.
22

23. ▪ The most popular separating agents are water soluble alginate
solutions.
▪ When applied to dental stone surfaces, these solutions produce thin,
relatively insoluble calcium alginate films.
▪ These films prevent direct contact of denture base resins and the
surrounding dental stone, thereby eliminating undesirable
interactions.
23

24. ▪ Placement of an alginate-based separating medium is relatively
uncomplicated.
▪ A small amount of separator is dispensed into a disposable
container.
▪ Then a fine brush is used to spread the separating medium onto the
exposed surfaces of a warm, clean stone mold.
24

25. Mixing of Powder and Liquid
▪ Polymer : monomer proportion = 3:1 by volume .
▪ The measured liquid is poured into a clean, dry mixing jar.
▪ Powder is slowly added allowing each powder particle to become wetted by monomer.
▪ The mixture is then stirred and allowed to stand in a closed container.
▪ If too much monomer is used (Lower polymer/monomer ratio) - there will be greater
curing or polymerization shrinkage. More time is needed to reach the packing
consistency. Porosity can occur in the denture.
▪ If too little monomer is used (Higher polymer/monomer ratio) .Not all the polymer
beads will be wetted by monomer and the cured acrylic will be granular.
▪ Dough will be difficult to manage and it may not fuse into a continuous unit of plastic
during processing. 25

26. Physical Stages of polymer-monomer
Interaction
▪ When monomer and polymer are mixed in proper proportion a
workable mass is produced.
▪ Resultant mass passes through five distinct stages –
▪ Sandy
▪ Stringy
▪ Dough like
▪ Rubbery or elastic
▪ Stiff
26

27. ▪ Sandy Stage – little or no interaction occur on a molecular level.
▪ Polymer beads remain unaltered.
▪ Consistency – “Coarse or grainy”
▪ Stringy Stage – monomer attacks the surfaces of individual
polymer beads and is absorbed into beads.
▪ Some polymer chains are dispersed in the liquid monomer.
▪ These polymer chains uncoil , thereby increasing the viscosity of the
mix .
▪ Characterized by “stringiness or stickiness” when the material is
touched or drawn apart.
27

28. ▪ Dough like stage – increased number of polymer chains enter the
solution.
▪ Monomer and dissolved polymer formed
▪ Does not adhere to mixing vessel or spatula.
▪ Rubbery or elastic stage – monomer is dissipated by
evaporation and by further penetration into remaining polymer
beads
▪ Mass rebound when compressed or stretched.
28

29. ▪ Stiff stage – by continue evaporation of monomer
▪ Mixture appears very dry.
▪ Resistant to mechanical deformation.
29

30. DOUGH-FORMING TIME
▪ The time required for the resin mixture to reach a dough like stage.
▪ American National Standards Institute/American Dental Association
(ANSI/ ADA) Specification No. 12 (ISO 20795-1:2008: Dentistry—
Base polymers—Part 1: Denture base polymers) for denture base
resins requires that this consistency be attained in less than 40 min
from the start of the mixing process.
▪ In clinical use, the majority of denture base products reach a dough
like consistency in less than 10 min.
30

31. WORKING TIME
▪ The time a denture base material remains in the dough like stage.
▪ This period is critical to the compression molding process.
▪ ANSI/ADA Specification No. 12 requires the dough to remain
moldable for at least 5 min.
31

32. PACKING
▪ The powder liquid mixture should be packed into the flask at the
dough consistency.
▪ If packed in Sandy or Stringy stages – too much monomer will be
present between the polymer particles .
▪ Material – too low viscosity to pack well – it will flow out of the flask
easily
▪ May lead to porosity in the final denture base.
32

33. ▪ If packed at Rubbery to Stiff stage – Material will be too viscous to
flow .
▪ Metal to Metal contact of the flask halves will not be obtained.
▪ Delayed Packing – movement or fracture of the teeth
▪ Loss of detail
▪ Increase inVertical height of the denture.
33

34. ▪ The placement and adaptation of denture base resin within the mold
cavity are termed packing.
▪ The placement of too much material yields a denture base that
exhibits excessive thickness and resultant malpositioning of
prosthetic teeth.
▪ Conversely, the use of too little material leads to noticeable denture
base voids or porosity.
34

35. ▪ While in a dough like state, the resin is removed from its mixing
container and rolled into a ropelike form.
▪ Monomer is painted over the necks of the denture teeth to promote
bonding to the denture base.
▪ Subsequently, the resin form is bent into a horseshoe shape and
placed into the portion of the flask that houses the prosthetic teeth.
35

36. ▪ A thin polyethylene separator sheet is placed over the master cast,
and the flask is reassembled.
▪ The flask assembly is placed into a specially designed press and
pressure is applied incrementally.
▪ Excess material (flash) is displaced eccentrically.
▪ The application of pressure is continued until the denture flask is fully
closed.
36

37. ▪ Next the flask is opened and the polyethylene packing sheet is
removed from the surface of the resin with a rapid, continuous tug.
37

38. ▪ When flash is no longer apparent, the mold
is closed for the last time with no
polyethylene sheet interposed.
▪ Again, pressure is incrementally applied.
Following definitive closure, the flask is
transferred to a flask carrier.
38

39. Injection Molding Technique
▪ Using specially designed flasks.
▪ One half of the flask is filled with freshly mixed dental stone, and the
master cast is settled into this mixture.
▪ The dental stone is appropriately contoured and permitted to set.
▪ Subsequently, sprues or ingates are attached to the wax denture
base, which lead to an inlet or pressure port.
39

40. ▪ The remaining half of the flask is positioned, and the investment
process is completed.
▪ Wax elimination is performed
▪ The flask is reassembled.
40

41. ▪ Subsequently, the flask is placed into a carrier that maintains
pressure on the assembly during resin introduction and processing.
▪ Upon completion of the foregoing steps, resin is mixed and injected
into the mold cavity.
▪ The flask is then placed into a water bath for polymerization of the
denture base resin if a heat-curing resin is used.
▪ The denture is recovered, adjusted, finished, and polished
41

42. POLYMERIZATION CYCLE
▪ 1) Constant-temperature water bath at 74 °C (165 °F) for 8 h or
longer, with no terminal boiling treatment.
▪ 2)Processing in a 74 °C water bath for 8 h and then increasing the
temperature to 100 °C for 1 h.
▪ 3) Processing the resin at 74 °C for approximately 2 h and increasing
the temperature of the water bath to 100 °C and processing for 1 h.
42

43. Modification
Rapid heat-polymerized resin
Hybrid acrylics, with both chemical and heat-activated initiators.
Polymerized in boiling water for 20 minutes immediately after being
packed into a denture flask.
After bench cooling to room temperature, the denture is deflasked,
trimmed and polished in the conventional manner.
43

44. Microwave-activated PMMA
▪ This technique employs a specially formulated resin and a
nonmetallic flask
▪ A conventional microwave oven is used to supply the thermal energy
required for polymerization.
▪ The major advantage of this technique is the speed with which
polymerization can be accomplished,
▪ Disadvantage - overheating can occur in thick sections, causing the
monomer to boil and produce porosity.
44

45. Chemically Activated
Thermal energy – decomposition of benzoyl peroxide.
Production of free radical.
Chemical activation does not need thermal energy – so that it can be
completed at room temperature
 Cold curing
 Self curing
 Auto polymerizing resins.
Addition of tertiary amine in – dimethyl-para-toludiene ( to Liquid)
Causes decomposition of Benzoyl Peroxide – release of free radicals –
initiation of polymerization
45

46. Monomer Dimethyl-para-toluidine
(tertiary amine)
Benzoyl peroxide
Free radicals
Polymerization
Decomposes
46

47. Advantages
Less shrinkage – Greater
dimensional accuracy.
Disadvantages
Polymerization achieved is not
complete as that of Heat
activated.
Greater amount of unreacted
monomer.2 difficulties –
 1. Plasticizer- it decreases transverse
strength.
 2.Tissue irritant- Compromises
biocompatibility.
Color stability is inferior
47

48. Fluid resin technique
▪ When mixed in the proper proportions, these components yield a
low-viscosity resin.
▪ This resin is poured into a mold cavity, subjected to increased
atmospheric pressure, and allowed to polymerize at ambient
temperature.
▪ Tooth arrangement is accomplished using accepted prosthodontic
principles.
▪ The completed tooth arrangement is then sealed to the underlying
cast and placed in a specially designed flask.
▪ The flask is filled with a reversible hydrocolloid investment medium.
48

49. ▪ Following gelation of the hydrocolloid, the cast with the attached
tooth arrangement is removed from the flask
▪ At this stage, sprues and vents are cut from the external surface of
the flask to the mold cavity.
A, Completed tooth arrangement
positioned in a fluid
resin flask.
B, Removal of tooth arrangement
from reversible hydrocolloid
investment.
C, Preparation of sprues and
vents
for the introduction of resin
49

50. ▪ Wax is eliminated from the cast with hot water.
▪ The prosthetic teeth are retrieved and carefully seated in their
respective positions within the hydrocolloid investing medium.
▪ Subsequently, the cast is returned to its position within the mold
D, Repositioning of the
prosthetic teeth and master
E, Introduction of pour-type resin.
50

51. ▪ The resin is mixed according to the manufacturer’s directions and
poured into the mold via the sprue channels
▪ The flask is then placed in a pressurized chamber (i.e., a pressure pot)
at room temperature and the resin is permitted to polymerize.
▪ According to available information, only 30 to 45 minutes are
required for polymerization.
F, Recovery of the completed
prosthesis.
51

52. Advantages
▪ (1) improved adaptation to underlying soft tissues,
▪ (2) decreased probability of damage to prosthetic teeth and denture
bases during deflasking,
▪ (3) reduced material costs,
▪ (4) and simplification of the flasking, deflasking, and finishing
procedures.
52

53. Disadvantages
▪ (1)noticeable shifting of prosthetic teeth during processing,
▪ (2)air entrapment within the denture base material,
▪ (3)poor bonding between the denture base material and acrylic resin
teeth,
▪ (4)technique sensitivity
53

54. Light-Activated
Described as resin based composites having matrices of
 Urethane dimeth acrylate,
 Microfine silica and
 High molecular weight acrylic resin monomers.
Acrylic resin beads are included as organic fillers
Activator –Visible Light
Initiator - Photosensitizing agent – Camphorquinone.
54

55. ▪ Supplied as -
Sheet and rope form
Packed in lightproof pouches ( to prevent inadvertent
polymerization).
It cannot be flasked in conventional manner.
Opaque investing media prevent penetration of light.
55

56. The denture base is placed into a light
chamber and polymerized according to the
manufacturer’s recommendations.
Teeth are arranged and the denture
base sculpted using light-activated resin.
56

57. Recent generation Light activated resin
A base forming resin – it is adapted to the dental cast.
The cast and base forming resin – placed into high intensity light chamber –
to induce polymerization
Tooth setting resin – to attach prosthetic teeth to polymerized base. (high
intensity light chamber – to induce polymerization)
Contouring resin – to generate the desired final surface form.
Placed into light chamber
complete denture base fabrication process.
57

58. Physical properties of Denture base Resins
Polymerization Shrinkage
Porosity
Water absorption
Solubility
Strength
Creep
58

59. Polymerization Shrinkage
▪ When methyl methacrylate monomer is polymerized to form
polymethyl methacrylate, the density of the mass changes from 0.94
to 1.19 g/cm3 .
▪ This change in density results in a volumetric shrinkage of 21%.
▪ When a conventional heat activated resin is mixed at the suggested
powder-to-liquid ratio (3:1) - the volumetric shrinkage exhibited by
the polymerized mass should be approximately 7%.
▪ The shrinkage exhibited by these materials is distributed uniformly
to all surfaces.
▪ Hence the adaptation of denture bases to underlying soft tissues is
not significantly affected
59

60. Porosity
▪ The presence of surface and subsurface voids can compromise the
physical, esthetic, and hygienic properties of a processed denture
base.
▪ It has been noted that porosity is likely to develop in thicker portions
of a denture base.
▪ Such porosity results from the vaporization of unreacted monomer
and low-molecular-weight polymers when the temperature of a resin
reaches or surpasses the boiling points of these species
60

61. 61

62. Water absorption
▪ Polymethyl methacrylate absorbs small amounts of water when
placed in an aqueous environment.
▪ This water exerts significant effects on the mechanical and
dimensional properties of the processed polymer.
▪ Water molecules penetrate the polymethyl methacrylate mass, they
occupy positions between polymer chains.
▪ Consequently, the affected polymer chains are forced apart.
62

63. Solubility
▪ Denture base resins are soluble in a variety of liquids, they are
virtually insoluble in the fluids commonly encountered in the oral
cavity.
63

64. ▪ The introduction of water molecules produces two important effects.
▪ First, it causes a slight expansion of the polymerized mass.
▪ Second, water molecules interfere with the entanglement of polymer
chains and thereby act as plasticizers.
64

65. Strength
▪ The strength of an individual denture base resin is dependent on
many factors.
▪ These factors include composition of the resin, processing technique,
and conditions presented by the oral environment.
▪ The most important determinant of resin strength is the degree of
polymerization exhibited by the material.
▪ As the degree of polymerization increases, the strength of the resin
also increases.
65

66. ▪ In comparison with heat-activated resins, the chemically activated
resins generally display lower degrees of polymerization.
▪ As a result, chemically-activated resins exhibit increased levels of
residual monomer as well as decreased strength and decreased
stiffness.
66

67. Creep
▪ Denture resins display viscoelastic behavior.
▪ In other words, these materials act as rubbery solids.
▪ When a denture base resin is subjected to a sustained load, the
material may exhibit deformation with both elastic (recoverable) and
plastic (irrecoverable) components.
▪ If this load is not removed, additional plastic deformation can occur
over time.
▪ This additional deformation is termed creep.
▪ The rate at which this progressive deformation occurs is termed the
creep rate
67

68. RECENT ADVANCES IN DENTURE
BASE MATERIALS
68

69. Vinyl acrylic copolymer and Polystyrene
In 1942, vinyl acrylic copolymer (Luxene 44) and in 1948 polystyrene
(Jectron), a styrene polymer developed by Charles Dimmer, were
introduced as denture base materials.
Denture base plastics such as vinyl acrylic copolymer (1942) were
supplied in gel form.
These gels have the same components as the powder-liquid type,
except that the liquid and powder have been mixed to form a gel and
have been shaped into a thick sheet. 69

70. Chemical accelerators cannot be used in a gel because the initiator,
accelerator and monomer would be in intimate contact.
Accuracy of proportioning and thoroughness of mixing are the
advantages claimed for the gel types.
70

71. Nylon
Nylon was introduced in London in the 1950’s as a denture base
material, proving to be entirely unsatisfactory owing to its poor
ability to resist oral conditions, thus resulting in swelling of the
denture base due to absorption of moisture.
71

72. POLYCARBONATE
Polycarbonate, polyethers and others have been investigated but
found suitable only for limited applications.
72

73. Nylon and polycarbonate are injection molded
polymers
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 .
73
SR-Ivocap system

74. Commercially Pure Titanium
This metal offers the advantage of light weight, strength and above
all biocompatibility.
Some difficulties have been encountered in the titanium casting
procedure such as necessity for an inert casting environment and the
presence of voids and gas inclusion in the finished casting.
74

75. Flexible denture base material
Polymerization shrinkage encountered in conventionally cured PMMA led
to the development of a special injection moulding technique.
Initially developed as a fluoropolymer (1962), acetal began to be used in
1971.
The material used nowadays is nylon based plastic (Polyamide).
Elastomeric resins can be added to resin polymer formulas to create greater
flexibility and can be strengthened with glass fibres.
75

76. Advantages
Nearly unbreakable
Pink coloured like the gums.
No metallic taste
Non allergic.
“A built in stress breaker”
Can be built quite thin, and can form both the denture base and the clasps as
well. 76

77. Disadvantages:
 Flexibility is not an advantage in complete dentures as the retentive
peripheral seal can be broken in function.
It is difficult to use where inter-ridge space is less as bulk of tooth is
needed for mechanical retention.
77

78. Indications:
Full dentures, Partial dentures, Bases and relines, in cases with
bilateral inoperable undercuts when preprosthetic surgery is
contraindicated.
In combination with Cast Partial framework-The clasps and the
saddle are flexible and the rest of the components are in metal.
78

79. Modified and novel denture base materials
1. Reinforced resins
a) High impact resins
b) Fiber-reinforced
c) Particulate reinforced
2. Hypoallergenic resins
3. Resins with modified chemical structure
4. Enigma gum toning in denture bases
79

80. Reinforced resins
a)High Impact Resins
Rubber reinforced (butadiene-styrene polymethyl methacrylate)
Rubber particles grafted to MMA for better bond with PMMA
Indicated for patients who drop their dentures repeatedly e.g.
parkinsonism, senility.
Powder-liquid system
Processed as heat cure resins
80

81. 81

82. b)Fibre reinforced:
Primary problem with PMMA is low impact strength & low fatigue
resistance
Fiber reinforcement result in a 1000% strength increase over non-
reinforced (if there is proper bonding)
Fibers can be used in three different forms, namely continuous
parallel, chopped and woven.
82

83. Metal fibre reinforced
Not widely used because unesthetic, expensive, poor adhesion
between wire & acrylic resin & metal being prone to corrosion.
Using full lengths of metal fibers offers the best reinforcement
83

84. Carbon/graphite fibre reinforced
Carbon fibers (65-70 mm length, 5 % by weight & treated with silane
coupling agent) are placed during packing.
Anisotropic & provide greatest reinforcement of denture base resins
in terms of flexural strength & bending properties when placed
longitudinally ( perpendicular to applied forces).
Tubes of braided fibres provide a more even distribution of
reinforcement, high filler loading & easy handling
84

85. ADVANTAGES
Increases flexural strength, impact strength, prevents fatigue and
strengthens the resin.
DISADVANTAGES
Unesthetic
The polishing is difficult & also weakens the finished prosthesis.
Lateral spreading of fibers during pressing.
85

86. Kevlar (Synthetic Aramid Fiber)
The advantages are increase in modulus of elasticity, increase in
fracture resistance.
Pleated structure that makes aramid weak as far as flexural,
compression, and abrasion behaviour are concerned
Poor esthetics because of yellow color, difficulty in polishing
86

87. Polyethylene fibre reinforced
Multifibered polyethylene strands cut to 65
mm length & surface treated with epoxy-
resin are placed in resin during packing
They develop an isotropic properties to the
composite
87
Polyethylene reinforcement fibres

88. ADVANTAGES
Exhibit highest impact strength & modulus of elasticity.
Highly esthetic, almost invisible
DISADVANTAGES
Slight decrease in transverse strength
Placement & finishing is difficult
Does not bond even with plasma
88

89. Woven polyethylene fiber reinforcement can significantly increase
the elastic modulus and toughness of PMMA. However, the
procedures of woven fiber etching, preparing, and positioning were
found impractical.
89

90. Highly drawn linear polyethylene fibres (HDLPF)
Patterns of continuous parallel fibers provide maximum reinforcement to
both maxillary & mandibular bases
Maxilla- horizontally positioned fibers in anterior part of labial flange and
laterally oriented in palate
Mandible- fibres at right angle to ridge located close to polished & fitting
surface.
Between the two outer layers lies the main component of reinforcement i.e
fibers in horizontal plane along dental arch
90

91. ADVANTAGES
 DLPF have high tensile stiffness & strength, notch insensitivity &
cracks do not propagate through array of fibres.
The coherence is maintained even after a large number of testing
cycles.
91

92. Polypropylene fibre
Polypropylene fiber increased the impact strength of PMMA, and surface
treatment of the fiber resulted in a further increase in its impact strength.
The highest impact strength- polypropylene fibers treated with plasma,
used to strengthen acrylic resin and reduce fracturing.
Ismaeel IJ et al. (2015) found that incorporating silanized polypropylene
fiber in heat-cured PMMA resin significantly improved its transverse,
tensile, and impact strengths, but its wear resistance was highly decreased.
92

93. Glass fibres
Glass is an inorganic substance that has been cooled to a rigid
condition without crystallization
Continuous parallel fibers provide high strength & stiffness in one
direction (anisotropic) while randomly oriented fibers provide similar
properties in all directions (isotropic properties)
Chopped fibres mixed with denture base acrylic resin enhance
isotropic mechanical properties.
93

94. 6 mm chopped glass fibres with 5% fiber in combination with
injection moulding technique result in increase in transverse
strength, elastic modulus & impact strength
ADVANTAGES
Improvement in flexural properties and fatigue resistance, best
aesthetics, excellent polishing characteristics
In addition, they resist extreme temperature.
94
Glass fibers

95. E-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 has high alumina and low alkali and borosilicate, is
superior in flexural strength
Each strand of this E-glass is computer impregnated with a PMMA
(porous polymer) and silane coupler that allows dissoloution bonding
to acrylic. (e.g. Preat Perma Fiber )
95

96. ADVANTAGES
Available in two forms (mesh & fiber) & are transluscent providing
esthetics
Because of glass fiber bonding, they also have more strength
96

97. Natural fibers
Natural fibers were suggested to reinforce denture base resins, among
which are, oil palm empty fruit bunch (OPEFB) and vegetable fiber (ramie
fiber).
OPEFB significantly increased the flexural strength and flexural modulus of
acrylic resin.
Short ramie fiber also increased the flexural modulus of acrylic resin
compared with conventional PMMA, but its flexural strength decreased as a
result of weak interfacial bonding.
97

98. COMPARISON OF IMPACT STRENGTH OF RESINS REINFORCED WITH
DIFFERENT FIBERS:
Polyethylene > glass > thick Kevlar >carbon >thin Kevlar > unreinforced
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99. Position and placement of fibres
99
Fiber placed in weakest area Fiber at 90° to fracture

100. 100
Unidirectional fibers are stronger Mesh placed on exterior of prosthesis

101. Particulate reinforced resins/Fillers
a)Alumina(Al2O3)
Abdul kareem and Hatim (2015) reported that addition of alumina
(Al2O3) nanoparticles (NPs) to microwave treated and untreated
PMMA powder has a good level of biocompatibility.
The addition of Al2O3 to PMMA significantly increased thermal
conductivity, but the flexural strength of PMMA did not change
significantly (Kul et al., 2016).
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102. Also, the addition of silane-treated aluminum particles to PMMA
powder significantly increased the compressive, tensile, and flexural
strength and the wear resistance of denture base resin
(Chaijareenont et al., 2012).
Surface roughness and water sorption of aluminum-reinforced
PMMA were not significantly changed (Vojdani et al., 2012).
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103. Zirconia (ZrO2)
Incorporating ZrO2 NPs in PMMA increased its thermal conductivity,
impact strength, and flexural strength
The adhesion between the resin matrix and filler particles is very
important to enhance the composite’s properties.
Therefore a silane coupling agent could be useful to improve the
bond strength between zirconia NPs and PMMA.
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104. The flexural strength and impact strength of acrylic resin increased,
but its tensile strength was not improved.
In addition, zirconia nanotubes showed a better reinforcing effect
than zirconia NPs but, in contrast to zirconia NPs, surface treatment
would decrease the reinforcing effect of zirconia nanotubes
In addition, it may have an antifungal effect and may play a
preventive role in patients susceptible to fungal infections
104

105. Different results were obtained regarding the effect of ZrO2 on the
water sorption and solubility of PMMA.
Asar NV et al (2013) found that adding ZrO2 significantly decreased
the water sorption and solubility of PMMA, while an insignificant
difference in water solubility and an increase in water sorption within
the limit of ADA specifications were reported by Ayad NM et al (2008)
and AsopaV et al (2015)
105

106. Titanium (TiO2)
A titanium coupling agent used to increase the adhesion between
resin matrix and filler particles
The incorporation of silanized TiO2 NPs in PMMA improved the
impact strength, transverse strength, and surface hardness of the
resin and decreased its water sorption and solubility.
Moreover, surface roughness increased with the addition of 3 wt.% of
silanizedTiO2 NPs to the acrylic resin
106

107. Addition of apatite-coated titanium dioxide and fluoridated apatite-
coated titanium dioxide after treatment with ultraviolet A irradiation
of PMMA inhibited Candida adhesion due to their antifungal effect,
and their use could be beneficial in obtaining appropriate denture
hygiene.
Addition of barium titanate (BaTiO3) as a radiopacifier to PMMA
showed a slight decrease in fracture toughness properties.
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108. Silver (Ag)
Antimicrobial effect and antifungal properties
Increased thermal conductivity, but the flexural strength values of
PMMA were not significantly changed
Addition of 10wt% and 20wt% silane-treated silver fillers enhanced
the tensile and flexural strength of PMMA
PMMA-silver NPs are not cytotoxic
108

109. `
Tensile strength did not change significantly after incorporating 0.2%
of Ag NPs in comparison with unmodified PMMA, but it decreased
significantly after incorporation of 2%.
Ag NPs improve viscoelastic properties
109

110. Nano-gold (Au), platinum (Pt), palladium (Pd)
Gold NPs improved the flexural strength and thermal conductivity to
almost double the value of pure PMMA
Pt NPs improve mechanical properties of PMMA and provide antimicrobial
effect, increased the bending deflection of PMMA
Pd improved the bending strength when compared to silver and gold,
which showed the lowest value of bending strength.
Addition of Au and Pd improved Vickers hardness of PMMA and was
decreased with the addition of Pt
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111. Hydroxyapatite fillers
Increased the flexural strength as well as the flexural modulus
3-methacryloxypropyl trimethoxysilane(γ-MPS) treatment enhances
interfacial interaction between HA filler and the PMMA matrix
A reduction in the flexural properties on water immersion was
attributed to water’s plasticizing effect, which weakens the bonding
between the HA filler and the PMMA matrix.
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112. Silicon dioxide (SiO2)
SiO2 NPs increase PMMA impact and transverse strength.
Improved hardness and fracture toughness were found with a low
concentration of SiO2 NPs.
Increasing its content resulted in agglomeration and crack propagation,
which reduces both hardness and fracture toughness
Cevik P (2016) found that silica NPs adversely affect the flexural strength of
PMMA
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113. Silica-based filler
Incorporation of mica in PMMA increased the hardness of acrylic
resin but its flexural strength was reduced because of the weak bond
between mica and acrylic resin (Mansour et al., 2013).
Fluoride glass fillers decreased microbial adhesion at the cost of
surface roughness (Al-Bakri et al., 2014;Tsutsumi et al., 2016)
Nanoclay particles improved the thermal conductivity, but negatively
affected the flexural strength (Ghaffari et al., 2016).
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114. Placing silicon carbide filler powders in the palatal region of dentures
can improve the thermal conductivity of PMMA without reducing
strength or increasing weight.
Halloysite nanotube (Abdallah in 2016) increased hardness of PMMA
when added in small percentages, while the flexural strength and
Young’s modulus did not show a significant increase.
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115. Hybrid reinforcements
Reinforcement of PMMA by more than one type of fiber was first
suggested by Vallittu in 1997.
The combination may be between different fibers, different metal
oxides and ceramics, and fibers with metal oxides, or ceramic
materials
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116. 116
Different hybrid reinforcement materials

117. Hypoallergenic resins
Diurethane dimethacrylate, Polyurethane, Polyethylenterephthalate
and Polybutylentereph-thalate.
Enterephthalate based (Promysan, thermoplastic) show low water
solubility than PMMA.
Light activated indirect composite containing methane
dimethacrylate (UDMA) is an alternative to PMMA for patients
hypersensitive to PMMA.
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118. Enigma gum toning
Custom shade matching of natural gingival tissue using ‘Enigma’
colour tones.
Gives extra confidence to patient in appearance of their dentures.
Available in Ivory, Light Pink, Natural Pink, Dark Pink & Light Brown.
Different colors are mixed to get the desired gum tone.
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