Heat-activated acrylic resins are the most commonly used denture base materials. They undergo polymerization when heated above the glass transition temperature, resulting in a permanent hardening. Some key advantages are good physical properties, color stability, and easy repair ability. However, the polymerization requires specialized laboratory equipment and produces heat, which can damage oral tissues if not cured properly.
2) Chemically activated
3) Microwave activated
7. A denture base may be defined as that part of
denture that rests on the foundation and to
which teeth are attached.1 (Gpt-9 ).
Denture base material: any substance of which
A denture base may be made.1 (Gpt-9)
7
1. Glossary of prosthodontics terms. J Pros Dent. 2005;94:10-85
8. HISTORY2
8
2. Tandon R. Gupta S. Agarwal SK. Denture base materials: From past to future. Indian Journal of Dental Sciences. 2010 March;
2(2): 33-39
9. Dentistry as a speciality is believed to have begun about
3000 BC. The first dental prosthesis was believed to
have been constructed in Egypt about 2500 BC. Skilfully
designed dentures were made as early as 700BC.
9
2. Tandon R. Gupta S. Agarwal SK. Denture base materials: From past to
future. Indian Journal of Dental Sciences. 2010 March; 2(2): 33-39
10. WOOD: For years, dentures were designed from wood
because it was readily available, relatively inexpensive
and could be carved to desired shape. However, it
warped and cracked in moisture, lacked aesthetics and
got degraded in the oral environment.
10
11. BONE: Dentures made from bone became very popular
due to its availability, reasonable cost and carvability. It
had better dimensional stability than wood, however,
esthetic and hygienic concerns remained.
11
12. IVORY: Ivory denture bases and prosthetic teeth were
fashioned by carving this material to desired shape.
These were relatively stable in the oral environment,
offered esthetic and hygienic advantages compared to
wood or bone. However, ivory was not readily available
and was relatively expensive.
12
13. PORCELAIN: Alexis Duchateau (1774) was the first to
fabricate porcelain dentures. The advantages were that it
could be shaped easily, ensured intimate contact with
the underlying tissues, was stable, smooth surfaces after
glazing, less porosity, low solubility and could be tinted
but its drawbacks were brittleness and difficulty in
grinding and polishing
13
14. GOLD: In 1794 AD, john greenwood began to swage
gold bases for dentures. Usually 18 to 20 carat gold was
alloyed with silver and teeth were riveted to it.
14
15. VULCANITE DENTURES: Charles Goodyear, in 1839,
discovered the process of dry-heat vulcanization of
rubber.
In 1851, Goodyear used this technique to produce a
highly cross-linked hard rubber named vulcanite.
15
16. TORTOISE SHELL: Harrington
(1850) introduced the first
thermoplastic denture material, the
tortoise shell base.
GUTTA PERCHA: Edwin Truman
(1851) used Gutta percha as a
denture base but it was unstable.
CHEOPLASTIC: Alfred A Blandy
(1856) made dentures from a low
fusing alloy of silver, bismuth and
antimony but it was never
accepted.
16
17. ALUMINIUM: Dr. Bean (1867) invented the casting machine and
did the first casting of a denture base in aluminium.
CELLULOID: J. Smith Hyatt (1869) introduced celluloid that was
later used as a denture base material because of its translucency
and pink colour. However, this material did not gain much
popularity because of distortion and discolouration.
17
BAKELITE: Dr. Leo Bakeland (1909) introduced this phenol
formaldehyde resin which was easily available but lacked colour
quality.
18. STAINLESS STEEL and BASE METAL ALLOYS: Ni-Cr
and Co-Cr were obtained by E. Haynes (1907) but they
gained popularity after 1937 because of their low density,
low material cost, higher resistance to tarnish and
corrosion and high modulus of elasticity. Allergy to Nickel
and difficulty in adjustment, posed a practical problem.
18
19. VINYL RESIN: Mixtures of polymerized vinyl chloride and
vinyl acetate were under experimentation during 1930 due
to their pleasing colour but had difficult processing methods.
19
20. POLYMETHYL METHACRYLATE: Rohm and Hass (1936)
introduced PMMA in sheet form and Nemours (1937) in
powder form. Dr. Walter Wright (1937) introduced
Polymethyl methacrylate as a denture base material which
became the major polymer to be used in years.
20
21. 213. O’Brien J W. Dental materials & their selection. 3rd ed. Hanover Park,(IL): Quintessence; 2002.
22. 22
3. O’Brien J W. Dental materials & their selection. 3rd ed. Hanover Park,(IL): Quintessence; 2002.
23. 23
Type I – Heat-polymerizable polymers
Class 1 – Powder and liquid
Class 2 – Plastic cake
Type 2 – Autopolymerizable polymers
Class 1 – Powder and liquid
Class 2 – Powder and liquid for pour-type resins
Type 3 – Thermoplastic blank or powder
Type 4 – Light-activated materials
Type 5 – Microwave cured materials
4. Available from: URL:https://www.sis.se/api/document/preview/915928//
25. Chemical stability in the
mouth
Ease of manipulation
Mechanical and physical
properties
Biological compatibility
Aesthetic qualities
Relatively low cost
25
29. Clinical complications, such as salivary and
blood contamination, should have little or no
effect on the outcome of handling procedure.
The final product should be easy to polish,
and in case of unavoidable breakage, it
should be possible to repair the resin easily
and efficiently.
29
30. AESTHETIC PROPERTIES
The material should exhibit sufficient
translucency or transparency so that it
can be made to match the
appearance of the oral tissues it
replaces.
The resin should be capable of being
tinted or pigmented, but there should
be no change in colour or appearance
of the material subsequent to its
fabrication
30
31. ECONOMIC CONSIDERATIONS
The cost of the resin and its processing method
should be relatively low, and processing should not
require complex and expensive equipment.
31
32. CHEMICAL STABILITY
The conditions in the mouth are highly
demanding, and only the most chemically stable
and inert materials can withstand such
conditions without deterioration.
32
33. 33
6. Anusavice KJ. Phillip’s science of dental materials: denture base resins. 11th ed. Philadelphia: Saunders; 2003. 143-
34. FUNDAMENTAL NATURE OF
POLYMERS
34
• The two most significant features of polymers are that
they consist of very large macromolecules and that
their chainlike molecular structure is capable of
virtually limitless configurations and conformations.
• Chain length, the extent of chain branching and
crosslinking, and the organization of the chains
among themselves, determine the properties of
35. CHAIN LENGTH AND MOLECULAR WEIGHT
35
• The longer the polymer chain, the greater are the numbers of
entanglements (temporary connections) that can form along it.
Therefore, the longer the chain, the more difficult it is to distort the
polymeric material.
• The number average molecular weight for various commercially
available dental denture polymers typically varies from 8,000 to
39,000, but molecular weights as high as 600,000 have been
reported. Denture teeth with cross-linked resins may have even
36. CHAIN BRANCHING AND CROSSLINKING37
• In addition to linear macromolecules,
polymer chains are often connected together
to form a nonlinear, branched, or cross-
linked polymer.
• Branching is analogous to extra arms
growing out of a polymer chain; thus, the
probability of entangled, physical
37. 38
• In cross-linked polymers, some of the structural units
must have at least two sites where reactions can
occur. For Example , during curing of polysulfide
impression material, linear polymers are joined, or
bridged, through reactive side chains to form cross-
linked molecular networks.
• Crosslinking forms bridges between chains and
dramatically increases molecular weight.
38. • The three-dimensional network of cross-linked
polymers increases rigidity and resistance to solvents.
39
39. COPOLYMERIZATION6
40 Polymer have two or more type of MER (repeating) units are known as
Copolymer and process of formation is known as copolymerization.
3 different type of copolymers-
Random copolymer-
ABBABABAAABAAAABABBBBABAAAABABABB
BLOCK copolymer-
AAAAABBBBBBBBAAAAAAABBBBBBBBBAAAABBB…..
Graft or Branch copolymer-……AAAAAAAAAAAAAAAAAAAAAAA……….
| |
B B
B B
B B
40. Molecular organization41
In some polymers the chains are randomly coiled and entangled
in a very disordered or random pattern known as an
amorphous structure. In others, the chains align themselves to
form a highly ordered, or crystalline, Structure. Most polymeric
materials combine these two forms of organization in greater or
41. 42
Schematic diagram of polymers that contain only amorphous intermolecular and intramolecular
organization (left) and combinations of both amorphous and crystalline regions
42. Factors that reduce or prevent crystallinity include
the following:
• Copolymer formation, which inhibits polymer chain alignment
•Polymer-chain branching, which also interferes with chain
alignment
• Random arrangement of substituent groups, particularly large
side groups that keep polymer chains separated
• Plasticizers, which tend to separate the chains
43
43. 44
Anusavice KJ. Phillip’s science of dental materials: denture base resins. 11th ed. Philadelphia: Saunders; 2003. 143-
170.
44. Involves a combination of elastic and plastic
deformation (viscous flow) and elastic recovery
when stresses are eliminated.
This combination of elastic and plastic changes
is termed viscoelasticity.
45
47. 4. SOLVATION PROPERTIES
General nature of polymers:
The longer the chains , the more slowly a polymer
dissolves.
Polymers tend to absorb a solvent, swell, and soften,
rather than dissolve.
Cross-linking prevents complete chain separation and
retards dissolution.
48
48. Highly cross-linked polymers cannot be dissolved.
Elastomers swell more than plastics.
A small amount of swelling can have undesirable results on
the fit of prostheses.
Absorbed molecules spread polymer chains apart and
facilitate slip between chains. This lubricating effect is called
plasticization.
49
49. 5. PLASTICIZER
Plasticizer are added to reduce the softening and fusion
temperature of resin.
Plasticizer acts to partially neutralize secondary bonds
or intermolecular forces that normally prevent the resin
molecules from slipping past one another when the
material is stressed.
50
50. Plasticizers usually reduce the strength, hardness,
and the softening point of the resin.
Plasticizer are two types
1. External plasticizer
2. Internal plasticizer
51
51. 6. THERMAL PROPERTIES
Polymers are of two types
Thermoplastic :
Made of linear and branched chain.
They soften when heated , at this time, resin can be shaped and
molded.
Upon cooling, it will harden in this form.
Thermoplastic resins are fusible i.e. They melt.
52
52. Thermosetting :
Undergo a chemical change and become permanently
harden when heated above the glass transition
temperature at which they begin to polymerize.
They have superior abrasive resistance and dimensional
stability.
53
54. 55
Anusavice KJ. Phillip’s science of dental materials: denture base resins. 11th ed. Philadelphia: Saunders; 2003. 143-
170.
55. Polymerization is the forming of a compound by the joining
together of molecules of small molecular weights into a
compound of large molecular weight (GPT9)
Its of two Types:
Addition polymerization
Condensation polymerization
56
62. Inhibition of addition polymerization63
• Impurities in the monomer often inhibit such reactions.
• Any impurity in the monomer that can react with free radicals
inhibits or retards the polymerization reaction.
• An impurity can react with the activated initiator or with an
activated growing chain to prevent further growth.
• The presence of such inhibitors markedly influences the length
of the induction period as well as the degree of polymerization.
63. • Inhibitors affect both the storage stability and the working time of
a dental resin.
• For this reason, commercial dental resins commonly contain a
small amount (approximately 0.006% or less) of an inhibitor such
as the methyl ether of hydroquinone to aid in the prevention of
polymerization during storage and in the case of two-part (self-
cure) systems, to provide adequate time for mixing and
placement.
64
64. Condensation polymerization665
The reactions that produce step-growth polymerization can progress by
any of the chemical reaction mechanisms that join two or more
molecules in producing a simple, non-macromolecular structure.
The primary compounds react, often with the formation of by-products
such as water; alcohols, halogen acids, and ammonia.
The formation of these by-products is the reason step-growth
polymerization often is called as condensation polymerization.
65. ACRYLIC RESINS666
• The acrylic resins are derivatives of ethylene and
contain a vinyl group in their structural formula.
• There are two acrylic resin series that are of dental
interest.
• One series is derived from acrylic acid, and the
other from methacrylic acid.
66. METHYL METHACRYLATE67
• Methyl methacrylate is a transparent liquid at room temperature with
the following physical properties.
• Molecular weight = 100 g/mol
• Melting point = -480 C
• Boiling point = 100.80 C
• Density = 0.945 g/ml, at 200 C
• Heat of polymerization = 12. 9 kcal/mol
• Methyl methacrylate exhibits a high vapour pressure and is an
excellent organic solvent.
67. POLY(METHYL METHACRYLATE)
• Its a transparent resin of remarkable clarity; it transmits light
in the ultraviolet range to a wavelength of 250 nm .
• Knoop hardness number of 18 to 20.
• Tensile strength approximately 60 Mpa
• Density of 1.19 g/cm3
• Modulus of elasticity of approximately 2.4 GPa (2400 MPa).
• It is chemically stable to heat and softens at 1250 C,
• Between 1250 and 2000 C, depolymerization takes place.
71. Acrylic plastics have been
supplied in a variety of forms,
such as powder liquid, gels, and
sheets or blanks.
Currently the powder-liquid type is
the most popular
72
73. POWDER
• Pre-polymerized spheres of poly(methyl methacrylate) which are
modified with small amounts of ethyl, butyl or alkyl methacrylates
to produce polymer more resistant to fracture.
• Benzoyl peroxide as Initiator to initiate polymerization after
monomer is added. It is present in amounts from 0.5% to 1.5%.
• Mercuric sulfide, cadmium sulfide, cadmium selenide, ferric oxide
are used as Pigments although the use of cadmium salts is
suspect because of demonstrated toxicity.
74
74. • Zinc or titanium oxide as Opacifier with titanium oxide being more
effective.
• Dibutyl phthalate as Plasticizer
• Dyed synthetic fibers made from nylon as organic fibers
• Inorganic particles such as glass fibres and beads or zirconium
silicates have been added to plastics. Addition of glass fibres
increases stiffness and decreases the thermal coefficient of
expansion.
• Few denture materials consists of barium to improve radiopacity.75
75. LIQUID
• Non polymerized methyl methacrylate
• Hydroquinone as Inhibitor present in quantities of 0.003% to
0.1%.
• Glycol dimethacrylate as Cross-linking agent at a concentration
of 1% to 2% by volume.
76
76. COMPRESSION MOLDING TECHNIQUE5
Heat-activated denture base resins are shaped via compression
molding.
Steps include:
Dearticulation of cast
Flasking
Selection ,application of separating media and pouring.
Dewaxing
Anusavice KJ. Phillip’s science of dental materials: denture base resins. 11th ed. Philadelphia: Saunders; 2003. 721-
758
77. Application of separating media
Mixing of polymer and monomer
Packing
Curing
Cooling, Deflasking, Finishing And Polishing
78
78. DE-ARTICULATION OF CAST
79
The casts are detached from the
articulator.
The master cast is coated with a thin
layer of separator.
80. FLASKING8
81
A FLASK is defined as a metal case or tube
used in investing procedure(GPT- 9)
FLASKING : It is defined as the process of
investing the cast and a wax replica of desired
form in a flask preparatory to mold the
restoration into a desired product.
Murrow R, Rudd D, Rhoads E. Total laboratory procedures of complete denture. 2nd ed. USA: Mosby; 1986.
82. HANAU FLASK 9– It is an ejector type flask.
The parts of the flask are usually referred to as :
• The drag
• Cope and
• The cap
83
Zarb GA. Bolender CL. Prosthodontic treatment for edentulous patients. 12th ed. Missouri(USA): Mosby; 2004.
83. For Microwave Polymerization84
Special polycarbonate or fibre-
reinforced plastic flasks are used
instead of metallic flasks as
microwaves will reflect from the
surface.
86. • The denture with master cast is placed in the flask to establish its
height in relation to the height of the drag of the flask .
• The cope of the flask is placed in position to ensure that the teeth
do not project beyond the top of the flask.
• Ideally, approximately 1/8 to ¼ inch (3 to 6 mm) of space should be
available between the occlusal surface of the teeth and the top of
the flask.
• If the teeth are too high, the cast must be reduced in thickness.
87
Zarb GA. Bolender CL. Prosthodontic treatment for edentulous patients. 12th ed. Missouri(USA): Mosby; 2004.
87. 88
• The land area of the cast should be flush with the drag of the flask
to prevent possible breakage of the cast in later separation of the
two halves of the flask.
89. TWO POUR TECHNIQUE : The drag of the denture flask is filled with freshly
mixed dental plaster, and the master cast is placed into this mixture. Then
middle portion of the flask is placed on the bottom and the flask is filled with
plaster.
90
90. THREE POUR TECHNIQUE10
• The three-pour flasking technique consisted of placing the center
portion of the flask in position and mixing and vibrating dental stone
into the flask to a level just covering the incisal and occlusal edges of
the teeth.
• Before the stone completely set, stone is scooped out to barely
expose the incisal and occlusal surfaces of the teeth and to form a
depression in the palatal area.
• The stone is allowed to set and coated with a light film of petroleum
jelly. The third pour of stone slightly overfills the flask, and the top of
the flask is placed in positionOlivia RA. Lowe JA. Denture flasking: A comparative study of three techniques. J Pros Dent. 1982 Dec; 48(6): 736-9.
91. When teeth are exposed and an additional thin pour of 2 to 3
mm is used, then third pour will easily be separated during the
divesting procedure , and the technician will be aware of the
position of the teeth when using any mechanical devices to
break away the stone mold.
It is also useful when easily breakable porcelain teeth are
used on the denture.9
Zarb GA. Bolender CL. Prosthodontic treatment for edentulous patients. 12th ed. Missouri(USA): Mosby; 2004
94. Reverse flasking11
95
1. Complete the wax-up of the interim partial denture.
2. Soak the cast in water for 5 minutes.
3. Coat cast with petroleum jelly.
4. Separate the upper and lower sections of a maxillary denture flask.
Lightly coat the inside of the flask with petroleum jelly.
5. upper section of the flask to be filled with dental stone
6. Then stone to be placed on the outside of the cast to cover all
surfaces including the denture teeth but not the wax.
Green AJ, Nimmo A. A two-pour technique for investing interim partial dentures. J Pros Dent. 1985 Jul;54(1):151-2.
95. 96
7. The cast is seated in the upper section of the flask and remove
the excess stone .
8. After the stone sets, coat it with petroleum jelly.
9. Mix the stone and place it in the lower half of the flask. Set the
upper half into the lower half to extrude the excess stone.
10. Allow the stone to set; boil out and pack with conventional
procedures.
98. 99
• Application of separating medium prevent direct contact between the denture
base resin and the mold surface.
• Currently, 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.
99. 100
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 .
Separator should not be permitted to contact exposed portions of acrylic
resin teeth, since its presence interferes with chemical bonding between
acrylic resin teeth and denture base resins.
Subsequently, the mold sections are oriented to prevent “pooling” of
separator, and the solution is permitted to dry.
100. TYPES OF SEPERATING MEDIA
101
COLD MOULD SEAL
Composition :
Distilled Water 95.0 %
Salt of Alginate Acid 2.0%
Surfactant 1.0 %
Paraformaldehyde Less than 1.0%
Pigment Less than 1.0%
101. Various separating media used are:
Tin foil substitutes :
Tin foil,
Cellulose lacquers,
Solution of alginate compounds,
Soft soaps,
Sodium silicate,
Starches.
102
106. 107
• After the stone is dry, but while still hot, the inside of the
mold and the cast are painted with tinfoil substitute . The
tinfoil substitute must not come in contact with the teeth
or pool in the mold around the teeth.
• It is allowed to dry, and a second coat is painted on the
inside of the mold. The flask is allowed to cool to room
temperature.
107. • When acrylic resin teeth are used, the exposed
surfaces of the teeth must be free of wax and tinfoil
substitute and any other debris. Residue on the teeth
is the main cause for adhesive failure.
• Later these would result into minute spaces leading to
seepage of saliva and food debris which over the time
causes staining at the cervical lines.
108
108. • Only one coat is required on tissue surface of the
edentulous cast whereas two to three coats is strongly
recommended on opposite of open flask over those
surfaces which becomes oral or polished side of
denture.
• This extra coat will cause acrylic resin to pull away
from these regions and thus shrink towards and hug
the cast for optimal tissue contact.
109
109. MIXING OF POWDER AND LIQUID5
110
POLYMER MONOMER RATIO:
The accepted polymer to monomer ratio is 3:1 by volume.
This ratio provides sufficient monomer to thoroughly wet the
polymer particles, but this ratio does not contribute excess
monomer that would lead to increased polymerization shrinkage.
Using a 3:1 ratio, the volumetric shrinkage may be limited.
Anusavice KJ. Phillip’s science of dental materials: denture base resins. 11th ed. Philadelphia: Saunders; 2003.
721-758.
110. The measured liquid is poured into a clean, dry mixing
jar. Powder is slowly added allowing each particle to
become wetted by monomer. The mixture is then
stirred and allowed to stand in a closed container.
111. Arora et al. (2017) Conducted a study to evaluate the mechanical
properties of high impact denture base resins with different polymer to
monomer ratio.
The result showed that the flexural strength values and Vicker’s
hardness number values showed a similar trend. The values decreased
significantly as the ratio was increased or decreased from the normal
ratio i.e. 3:1
The result also showed that there was no significant difference between
the impact strength values as the polymer monomer ratio was increased
or decreased.
112. Polymer Monomer Interaction5
When monomer and polymer are mixed in the proper ratio
,a workable mass is produced.
Upon standing, the resultant mass passes through five
distinct stages
These may be described as (1) sandy,(2) stringy, (3)
dough like, (4) Rubbery or elastic, and (5) stiff.
113
113. 1) Sandy
• Little or no interaction at molecular
level.
• Polymers remains unaltered.
• Mixture is coarse or grainy
2) Stringy
• Polymer chains uncoil
• Increase in viscosity of the mix.
• Characterized by stringiness or stickiness.
3) Dough like
• Increase in no. of polymer chains.
• Does not adhere to surface.
114
114. DOUGH FORMING TIME5
115
The time required for the resin mixture to reach a dough like stage is
termed the dough forming time.
ANSI /ADA sp. No. 12 - <40min. from the start of mixing process
Clinically- < 10min.
Working time- 5min
115. 4) Rubbery or Elastic
• Monomer is dissipated by evaporation &
by further penetration into remaining polymer
• Mass rebounds when compressed or stretched.
5) Stiff
• Due to evaporation of free monomer.
• Mixture appears very dry
• Resistant to mechanical deformation
116. PACKING5
117
• The placement and adaptation of denture base resin within
the mold cavity is termed as packing.
• The resin is removed from its mixing container and rolled into
a ropelike form.
• The resin is now bent into a horse shoe shape and placed into
the portion of the flask that houses the prosthetic teeth.
118. • A polyethylene sheet is placed over the
resin and the flask is reassembled
• Pressure is applied incrementally until the
flask is firmly closed and excess material is
displaced eccentrically.
• The flask portions are subsequently
separated, and the polyethylene packing
sheet is removed from the surfaces of the
resin with a rapid, continuous tug.
119
119. Therefore, Excess resin will be found on the relatively flat areas
surrounding the mold cavity. This excess resin is called flash. Using a
gently rounded instrument, the flash is carefully teased away from the
body of resin that ocupies the mold cavity.
120. • A fresh polyethylene sheet is placed between the major portions of the flask,
and the assembly is once again placed in the press, another trial closure is
made.
• Care should be taken not to apply excessive force to effect closure.
• Trial closures are repeated until no flash is observed.
• Definitive closure of the flask may now be accomplished.
121
121. • Now mold sections are placed in the flask press and pressure is applied
incrementally.
• The flask is then transferred to a bench press, which maintains pressure
on the flask assembly during processing of the denture base.
• This is done to avoid warpage of the denture.
122
123. Bench-curing heat-processed acrylic resins before processing is
suggested for the purpose of equalizing pressure in the mold, releasing
internal stress, dispersing monomer uniformly, and exposing resin teeth
to the monomer. Opinion varies on the exact amount of time a packed
flask should bench-cure before being placed in a processing unit. Two
hours is the most commonly quoted length of time.
Firtell DN, Larry L. Bench curing acrylic resins. J Pros Dent. 1984 Jul;51(3):431-33.
124. 125
CURING CYCLES5
Anusavice KJ. Phillip’s science of dental materials: denture base resins. 11th ed. Philadelphia: Saunders; 2003. 721-
125. LONG CURING CYCLE
126
Processing the denture base in a constant temperature water
bath at 740 C for 8 hrs or longer with no terminal boiling.
Processing at 740 C in a water bath for 8 hrs and increasing
the temp to 1000 C for 1 hr.
126. SHORT CYCLE
127
According to CRAIG- 740C (165F) water bath for 1.5 hours
and then increasing the temperature to 1000C for 1 hour
According to Winkler- 740C (165F) water bath for 1.5 hours
and then increasing the temperature to 1000C for 30 Min.
According to PHILLIPS’- 740C (165F) water bath for 2 hours
and then increasing the temperature to 1000C for 1 hour.
128. COOLING
129
To minimize potential difficulties, the flask should be removed
from the water and bench cooled for 30 min.
Afterwards, the flask should be immersed in cool tap water for 15
min.
Rapid cooling may result in warping of the denture base because
of differences in thermal contraction of resin and investing stone.
The denture base can then be deflasked and prepared for
delivery. To decrease the probability of unfavorable dimensional
129. DEFLASKING
130
Remove the lid from the flask containing the bench
cooled denture.
Use care in separating the stone cap from dentures with
porcelain teeth.
With a saw and spiral blade, cut through the stone that
encloses the denture opposite the central incisor teeth.
Place more saw cuts at the distobuccal corners of the
flasked denture, so the stone enclosing the denture has
130. Make more cuts lingual to the heel area of the mandibular
dentures if necessary.
Remove the denture from the investing stone except where it
encloses the cast.
Protect the teeth with the hand, Carefully tap away the stone
enclosing the cast. .
After cured acrylic denture is retrieved from the stone taking
care not to allow flexing and warpage of denture.
131.
132. FINISHING AND POLISHING
133
Cured denture is smoothened using different grades of sand paper
progressively.
For the purpose of final polishing, finely ground pumice slurry is
used.
133. Adverse reactions to PMMA13
134
• 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
Dermatitis
Fisher AA. Allergic sensitization of the skin and oral mucosa to acrylic resin denture
materials. J Pros Dent. 1956 Sep; 6(5): 593-602.
134. Allergic stomatitis
Usually associated with release of
• Residual monomer
• Benzoic acid
Contact Dermatitis
• Most common in dental laboratories
• Associated with regular contact with monomer when
handling the dough
• Must avoid direct contact
135
135. • Possible toxic or allergic reactions to poly(methyl
methacrylate) have long been postulated.
• Theoretically, such reactions could occur following contact
with
PMMA
Residual monomer
Benzoyl peroxide
Hydroquinone
Pigments or a reaction product between some components of
the denture base and its environment.
136
136. • Clinical experience indicates that true allergic reactions
to acrylic resins seldom occur in the oral cavity.
• Residual monomer is the component most often cited
as an irritant.
• It should be recognized that the residual monomer
content of a properly processed denture is less than
1%.
137
138. • Polymerization shrinkage encountered in conventionally cured
PMMA led to the development of a special injection moulding
technique.
• Initially developed as a fluoropolymer (1962), acetyl 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.
139
139. TECHNIQUE
140
• One half of the flask is filled with freshly mixed dental stone,
and the master cast is settled into the stone.
• The dental stone is appropriately contoured and permitted
to set.
• Subsequently, sprues are attached to the wax denture base.
• The remaining portion of the flask is positioned, and the
investment process is completed.
143. • Flask is placed into a carrier that maintains pressure on the
assembly during resin introduction and processing
• When a powder liquid mixture is used, resin is mixed and
introduced into mold while at room temp.
• The flask is then placed into water bath for polymerization of
denture base resin.
• As the material polymerizes, additional resin is introduced into
the mold cavity.
144
144. DEWAXING
145
It is done by placing flasks
in boiling water for 5
minutes to soften the wax.
Open the flask and flush
with clean boiling water to
remove all the wax residue.
Application of separating
medium
145. FINISHING AND POLISHING
146
• Sprue formers are cut with special type of knife or disc.
• Finishing is done with vulcanite burs.
146. 147
• It was concluded that significantly less shrinkage was found in
injection processed resin because of continuous application of
pressure to the system and subsequent layering of base
material.
• Also that samples of injection processed showed less
variance in comparison to conventional method because of
more consistent mix of the monomer and polymer.Anderson GC, Schulte JK, Arnold TG.Dimensional stability of injection and conventional processing of denture base
resins.J Prosthet Dent 1988 Sep; 60(3): 394-8.
147. Strohaver et al conducted a study on changes in vertical
dimension between compression and injection molded complete
dentures15
15 were processed with conventional method and 15 with
injection system.
Complete dentures were made for 30 patients.
Changes in vertical dimension between waxed and
processed dentures were measured at incisal guide pin.
The injection method produced a negligible change in
vertical dimension, whereas the conventional
148
Strohaver RA .Comparison of changes in vertical dimension between compression and injection molded complete
149. CHEMICALLY ACTIVATED DENTURE
BASE RESINS5
150
Anusavice KJ. Phillip’s science of dental materials: denture base resins. 11th ed. Philadelphia: Saunders; 2003. 721-758.
150. 151
Chemical activators can also be used to induce denture base
polymerization.
Chemical activation does not require the application of thermal
energy. Therefore, it can be completed at room temperature.
As a result, chemically activated resins often are referred to as
cold-curing, self-curing, or autopolymerizing resins.
151. • It should be noted that the fundamental difference between heat-
activated resins and chemically activated resins is the method by which
benzoyl peroxide is divided to yield free radicals. All other factors in this
process (e.g., initiator and reactants) remain the same.
• There is a greater amount of unreacted monomer in denture bases
fabricated via chemical activation. This unreacted monomer creates two
major difficulties.
First, it acts as a plasticizer, resulting in decreased transverse strength
of the denture resin.
Second, the residual monomer serves as a potential tissue irritant,
153. Chemically activated resins display slightly less
shrinkage than their heat-activated
counterparts.
This imparts greater dimensional accuracy to
chemically activated resins.
The color stability of chemically activated resins
generally is inferior to the color stability of heat-
activated resins.
Discoloration of these resins may be minimized
via the addition of stabilizing agents that
prevent such oxidation.
154
155. COMPRESSION MOULDING TECHNIQUE
To ensure sufficient polymerization, the flask should be
held under pressure for a minimum of 3 hours
Initial hardening of the resin occurs within 30 minutes of
flask closure
Mold preparation and packing are done in the same
manner as for the heat activated resins.
The powder and liquid are mixed and permitted to attain a
dough like consistency.
156
156. FLUID RESIN
TECHNIQUE5
It employs a pourable, chemically activated resin for
fabrication of denture bases.
When powder and liquid are mixed a low viscosity resin is
yielded.
The resin is mixed according to manufacturer’s directions
& poured into the mold cavity via sprue openings.
157
157. The flask is then placed in a pressurized
chamber at room temperature, & the resin is
permitted to polymerize.
158
164. ADVANTAGES
165
Improved adaptation to underlying soft tissues.
Decreased probability of damage to prosthetic teeth & denture base
during deflasking.
Reduced material costs
Simplification of flasking, deflasking& finishing procedures.
165. DISADVANTAGES
166
Noticeable shifting of prosthetic teeth during processing.
Air entrapment within the denture base material.
Poor bonding between the denture base material & acrylic resin
teeth.
Technique sensitive.
166. 167
Tandon R. Gupta S. Agarwal SK. Denture base materials: From past to future. Indian J Dent Sci. 2010 March; 2(2):
33-9
167. Microwave-activated PMMA2
168
Poly(methyl methacrylate) resin also may be polymerized
using microwave energy.
Nishii (1968) first used microwave energy to polymerize
denture base resin in a 400 watt microwave oven for 2.5
minutes. This technique employs a specially formulated resin
and a non metallic flask
169. Types:
a) Compression moulding technique
b) Injection moulding technique
Supplied in Powder liquid system. Special polycarbonate or fibre-
reinforced plastic flasks (1985) are used instead of metallic flasks as
microwaves will reflect from the surface.
COMPOSITION-
Methyl methacrylate, ethylacrylate copolymer,
benzoyl peroxide, N-dimethyl p-toludine, hydroquinone
170
171. Technique
Microwaves are a form of electromagnetic radiation produced by a
generator called a magnetron, which can be used to generate heat
inside the resin. Methylmethacrylate molecules are able to orient
themselves in the electromagnetic field and at a frequency of
2450MHz, their direction changes nearly 5 billion times a second.
Consequently, numerous intermolecular collisions occur causing
rapid heating.
172
172. As the heat required to break the benzoyl peroxide molecule into
free radicals is created inside the resin, the temperature outside the
flask remains cool. The polymerization heat is dispersed more
efficiently and the polymerization is rapid with less risk of porosity. In
addition, this technique eliminates the time needed to transfer the
heat of the oven or the hot water, through the various structures,
such as the flask, investment and stone cast to the resin itself.
Microwaves act only on the monomer, which decreases in the same
proportion as the polymerization degree increases.
173
173. Therefore, the same amount of energy is absorbed by less and
less monomer, making the molecules increasingly active. This
self regulatory curing program leads to complete polymerization
of the resin.
TECHNICAL SPECIFICATION
• TIME -3 mins
• TEMPERATURE - 450° C
• ENERGY – 2450 MHz 174
174. The latest microwave-polymerized polymer with the
injection moulding system for denture construction claims
to have the advantages of both the injection –processing
and microwave-curing methods. The one-component paste
form resin is packaged in a disposable plastic cartridge that
eliminates mixing and direct handling. It is a polyurethane-
based polymer and is biologically compatible.
175
181. DISADVANTAGES
Less bond strength to the denture teeth.
Increased porosity
The plastic flasks and polycarbon bolts are relatively
expensive and have a tendency to break down on
exceeding packing pressure (1200psi) and after
processing several dentures.
182
182. LAI et al (2004) conducted a study on properties of denture acrylic
resin cured by microwave energy and conventional water bath.
The study showed that microwave can efficiently polymerize the
denture base. However the amount of porosity increased with an
increase in microwave energy level.
Thus water bathed specimen showed better flexural strength and
flexural modulus than microwave energy.
183
Lai CP, Tsai MH, Chen M, Chang HS, Tay HH. Morphology and properties of denture acrylic resins cured by microwave
energy and conventional water bath. Dental Materials 2004; 20: 133–141.
183. There were no significant differences in surface
hardness.
Choice of a suitable microwave power and
polymerization time is important in order to reduce
porosity.
184
185. COMPOSITION 2
Matrix - Urethrane dimethacrylate
Filler - Acrylic resin beads microfine silica
Initiator– Camphorquinone - amine(e.g. Dimethylaminoethyl
methacrylate)
Activator - Visible lightPhotons from a light source activate the
initiator to generate free radicals that, in turn, initiates the
polymerization process
Photons from a light source activate the initiator to generate free
186
186. TECHNIQUE 2,3
After the try-in of the waxed-up trial denture is
completed, a roll of light-activated acrylic is placed over
the occlusal surfaces of the teeth to form a template
having three reference areas on the master cast
187
187. The template is cured in the light chamber for 10
minutes, then the teeth are removed from the
trial denture.
The teeth, the attached template, and the cast
are placed in boiling water to remove all traces of
wax
188. After coating the master cast
with a release agent, a sheet
of the light-activated denture
base material is adapted to
the cast and trimmed to the
boxing edge.
The base is then
polymerized in the
light chamber.
189
189. A strip of the light-activated acrylic is
placed on the underside of the teeth after
they have been coated with a bonding
agent
190
190. The teeth are then
repositioned in the original
position on the denture
base using the template .
The teeth are held in
position by polymerization
in the light chamber.
191
191. The anatomical portion of the denture is completed using
more of the base material to sculpt the surface and
develop the final shape of the denture.
192
192. After contouring, final
polymerization is
accomplished in the light
chamber and the denture
is removed from the cast
and finished in a
conventional manner.
In the visible light-cured
material,
camphoroquinone and an
organic amine generate
free radicals when
irradiated by light in the
blue to violet region.
193
193. ADVANTAGES2
Less porosity than chemically activated denture
base resins.
Facilitate fabrication and final adjustment in
mouth.
25% lighter than conventional denture base
resins.
Free of methylmethacrylate.
194
194. DISADVANTAGES2
They cannot be flasked in a conventional manner.
Depth of cure, shrinkage and appearance of long life free
radicals are areas of concern.
Factors such as light intensity, angle of illumination, and
distance of resin from the light source can significantly affect the
number of free radicals that are formed, thereby making this
system technique sensitive.
195
196. INDICATIONS 2
Full dentures
Partial dentures
Bases and relines
In cases with bilateral inoperable undercuts
when preprosthetic surgery is contraindicated.
197
197. ADVANTAGES16
Flexible dentures are translucent which picks up underlying tissue
tones, making it almost impossible to detect in mouth.
No clasping is visible on tooth surfaces, improving esthetics.
The material is exceptionally flexible and strong.
Excellent biocompatibility.
198
198. DISADVANTAGES
Not used for long term restorations and is intended only for
temporary applications.
Tend to absorb water and will discolor often.
Technique sensitive
199
200. VALPLAST16
Valplast is a flexible
denture base resin that is
ideal for partial dentures
and unilateral restorations.
201
16. Shamnur SN, Jagadeesh KN, Kalavathi SD, Kashinath KR. journal of dental sciences &
201. PROFLEX16
Used for full & partial flexible
denture
It is hypo-allergenic
recommended for patients
with known acrylic 0r metal
sensitivities.
202
202. SUNFLEX16
Made of nylon thermoplastic
virtually invisible, unbreakable
metal-free, lightweight and
incredibly comfortable.
Exclusively used in partially
edentulous arches
203
204. To improve the physical and mechanical properties of
acrylic resin, it was reinforced with EMBEDDED METAL
FORMS
FIBRES – fibres have been used in three forms, namely,
continuous parallel, chopped and woven.
205
205. Carbon fibres. Carbon fibres have been shown to
improve flexural and impact strength, prevent fatigue
fracture and increased fatigue resistance on treating with
silane coupling agent (yazdanie-1985). However, carbon
fibres have an undesirable dark colour.
206
206. Kevlar fibres (synthetic aramid fibres) :aramid is a generic
term for wholly aromatic fibres. These fibres are resistant to
chemicals, are thermally stable, and have a high mechanical
stability, melting point, and glass transitional temperature.
They also have pleated structure that makes aramid weak as
far as flexural, compression, and abrasion behaviour are
concerned.
207
207. Glass fibres :glass is an inorganic substance that has been
cooled to a rigid condition without crystallization. Different types of
glass fibres are produced commercially; these include e-glass, s-
glass, r-glass, v-glass, and cemfil. Of these, e-glass fibre, which
has high alumina and low alkali and borosilicate, is claimed to be
superior in flexural strength. Because the modulus of elasticity of
glass fibres is very high, most of the stresses are received by
them without deformation.
208
208. Polyethylene fibres have also been observed to increase the impact
strength. Polyethylene fibres increase modulus of elasticity and flexural
strength and they are almost invisible in denture base acrylic resins.
Polyethylene fibres in woven form are more effective than carbon fibres
in enhancing impact strength and flexural strength.
Polyester fiber, methacrylated polyhedral silsesquioxanes, silica-
glass fiber reinforced polymeric materials and nylon fibres are
polyamide fibres and are based primarily on aliphatic chains.
209
209. The chief advantage of nylon lies in its resistance to shock and
repeated stressing. However, water absorption affects the
mechanical properties of nylon. Nylon-reinforced bases display
higher fracture resistance than PMMA.
Compared with conventional polymer materials, fibre- reinforced
polymers are successful in their application primarily because of
their high specific modulus and specific strength.
210
210. 211
Alla et al concluded that Reinforcement of dentures with various fibres
have shown a significant improvement in flexural strength, impact
strength and fatigue resistance of the materials. Significant difference
in reinforcing characteristics of different fibres was evident from the
literature. Further, processing of fibre reinforced denture bases seems
to be technique sensitive and difficult to fabricate in the dental
laboratory.
Alla RK, Sajjan S, Alluri VR, Ginjupalli K, Upadhya N. Influence on fibre reinforcement on properties of denture base
resins. JBNB. 2013;4:91-97
211. PHYSICAL PROPERTIES OF DENTURE BASE
RESINS5
The physical properties of denture base resins are
critical to the fit and function of removable dental
prostheses. Characteristics of interest include
polymerization shrinkage, porosity, water absorption,
solubility, processing stresses and crazing.
212
212. POLYMERIZATION SHRINKAGE5
When methyl methacrylate monomer is polymerized to form
polymethyl methacrylate, the density of the mass changes from 0.94
g/cm3 to 1.19 g/cm3.
This change in density results in a volumetric shrinkage of 7% in case
of heat activated systems.
Also, the linear shrinkage of 2% is exhibited.
213
213. POROSITY 5
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.
214
214. 215
Heat-activated denture base resin exhibiting different types and degrees of porosity.
A, Properly polymerized; no porosity. B and C, Rapid heating, relatively small subsurface voids. D, Insufficient
mixing of monomer and polymer; large voids resulting from localized polymerization shrinkage.
E, Insufficient pressure during polymerization; relatively large, irregular voids.
215. Specimens were flasked in such a manner that
the section displaying porosity was nearer the
center of the investment mass, whereas the
nonporous section was nearer the surface of
the metal flask. As might be expected, the metal
of the flask conducts heat away from the
periphery with sufficient rapidity to prevent a
substantial temperature rise.
216. Porosity can also result from inadequate mixing of
powder and liquid components. If this occurs,
some regions of the resin mass will contain more
monomer than others. During polymerization,
these regions shrink more than adjacent regions,
and the localized shrinkage tends to produce
voids.
217
217. Another type of porosity can be caused by
inadequate pressure or insufficient material
in the mold during polymerization. Voids
resulting from these inadequacies are not
spherical; they assume irregular shapes.
These voids may be so abundant that the
resultant resin appears significantly lighter
and more opaque than its intended color.
218
218. 3) Water Absorption5
Poly (methyl methacrylate) absorbs relatively small
amounts of water when placed in an aqueous
environment.
Although absorption is facilitated by the polarity of
poly(methy1 methacrylate) molecules, a diffusion
mechanism is primarily responsible for the ingress of
water.
219
219. In this instance, water molecules penetrate the
poly(methy1 methacrylate) mass, and occupy positions
between polymer chains.
The introduction of water molecules within the
polymerized mass produces two important effects.
First, it causes a slight expansion of the polymerized
mass.
220
220. Second, water molecules interfere with the entanglement of
polymer chains, and thereby act as plasticizers.
Poly(methyl methacrylate) exhibits a water sorption value of 0.69
mg/cm2.
According to ansi/ada specification no. 12, the weight gain
following immersion must not be greater than 0.8 mg/cm2
221
221. Solubility5
Although denture base resins are soluble in a variety of
solvents, they are virtually insoluble in the fluids commonly
encountered in the oral cavity.
222
222. PROCESSING STRESSES5
Whenever a natural dimensional change is inhibited, the
affected material contains stresses.
If stresses are relaxed, a resultant distortion of the material may
occur.
During denture base polymerization a moderate amount of
shrinkage occurs as individual monomers are linked to form
polymer chains.
223
223. During this process, it is possible that friction between the
mold walls and soft resin may inhibit normal shrinkage of
these chains.
As a result, the polymer chains are stretched, and the resin
sustains tensile stresses. Stresses also are produced as the
result of thermal shrinkage. As a polymerized resin is cooled
below its glass transition temperature, the resin becomes
relatively rigid. Further cooling yields thermal shrinkage.
224
224. CRAZING5
Stress relaxation may produce small surface flaws that can
adversely affect the aesthetic and physical properties of a denture
termed as crazing.
Crazing is evidenced by small linear cracks that appear to originate
at a denture's surface. Crazing in a transparent resin imparts a
"hazy" or "foggy" appearance. In a tinted resin, crazing imparts a
whitish appearance.
225
225. It is believed that crazing is produced by mechanical separation
of individual polymer chains that occurs on application of tensile
stresses.
Crazing generally begins at the surface of a resin and is
oriented at right angles to tensile forces.
Crazing also may be produced as a result of solvent action.
226
226. STRENGTH 5,7
Depends on
Composition of the resin.
Processing technique.
Conditions presented by oral environment.
Resin is strength determined by degree of
polymerization of material.
Increased degree of polymerization increases strength .
227
227. • Addition of plasticizers increases the impact strength of plastics,
but decreases in hardness, proportional limit, elastic modulus
and compressive strength.
Flexural strength 78 to 92 mpa
Flexural modulus 1.1 to 2.1 gpa
Values of the fatigue strength at a stress of 17.2 mpa for,
Pmma 1.5 106 cycles
Polyvinyl acrylic 1 106 cycles
228
228. Hazarika et al19. conducted a study to determine the effect on surface
roughness and hardness of commercially available denture base resins
on immersion at different pH.
140 samples of conventional and high impact denture base resins
were used in the study. Each group of samples were immersed in
the solution of pH 4,7 and 10 for 15 and 60 mins.
The study should that for pH 4 and 7 the mean surface roughness
of high impact denture base was significantly higher than that of
conventional. While for pH 10 the mean surface roughness of
conventional denture base was higher than that of high impact.
229
229. Creep5
Denture resins display viscoelastic behaviour.
These materials act as rubbery solids that recover elastic
deformation over time once the stresses induced in the
resin have been eliminated.
When a denture base resin is subjected to a sustained
load, the material exhibits an initial deflection or
deformation.
230
230. If this load is not removed, additional plastic
deformation may occur over time. This additional
deformation is termed creep.
The rate at which this progressive deformation occurs
is termed the creep rate.
This rate may be elevated by increases in
temperature, applied load, residual monomer, and the
presence of plasticizers .
231
231. Although creep rates for heat activated and chemically
activated resins are very similar at low stresses, (e g , 9
mpa) creep rates for chemically activated resins increase
more rapidly as stresses are raised.
232
233. Repair resins
Relining & rebasing
Short term & long term soft denture liners
Resin impression tray (custom made)
Resin teeth
235
234. REPAIR RESINS 5
Repair resins may be light, heat, or chemically
activated.
Chemically activated resins are preferred
because they may be polymerized at room
temperature.
The minimum requirements for chemically
activated resins used in repair application are
identified in ansi/ada specification no. 13.
236
236. Relining and Rebasing
Relining involves replacement of the tissue surface of an existing denture whereas
rebasing involves replacement of the entire denture base.
For relining, a low polymerization temperature is desirable to minimize distortion of
remaining denture base. Hence, chemically activated resin is chosen.
Material must comply with ansi/ada specification no. 17, which places limits on the
rate of temperature rise and maximum acceptable temperature
Peak temperature reached during processing should not be more than 750C.
Time for hardening should be between 6 and 15 minutes.
238
237. Short-Term and Long-Term Soft Denture Liners 5
The purpose of a soft denture liner is to absorb some of the energy
produced by masticatory impact. Hence a soft liner serves as a "shock
absorber" between the occlusal surfaces of a denture and the underlynig
oral tissues.
The most commonly used liners are plasticized acrylic resins. These
resins may be heat-activated or chemically activated.
239
238. • Chemically activated soft liners generally employ poly(methyl
methacrylate) or poly(ethyl methacrylate) and a plasticizer with
aromatic ester-ethyl alcohol (up to 30%) mixture as principal
structural components.
• The plasticizer usually is a large molecular species such as dibutyl
phthalate
• The slipping motion of individual chains permits rapid changes in the
shape of the soft liner and provides a cushioning effect for the
240
239. Unlike chemically activated soft liners, heat-activated materials generally are
more durable and may be considered long-term soft liners.
A number of heat-activated soft liners are supplied as powder-liquid systems.
The powder is composed of acrylic resin polymers and copolymers, whereas
the liquids consist of appropriate acrylic monomers and plasticizers. When
mixed, these materials form pliable resins exhibiting glass transition
temperatures below mouth temperature.
Soft liners become progressively more rigid due to leaching of plasticizers.
241
240. TISSUE CONDITIONERS20
Denture reliners find several uses in the specialty of prosthodontics.
They are used to
Improve fit of ill-fitting dentures,
To prevent traumatic damage to the mucosa,
As a cushion between denture bearing mucosa and denture,
To retain over denture bar attachments,
To retain extra oral prosthesis,
242
Prasad A. Prasad B. Shetty V. Shastry CS. Prasad D. Tissue conditioners : a review. NUJHS Vol. 4, No.2, June 2014.
241. To distribute occlusal forces,
To increase serviceable life of prosthesis,
To replace the fitting surface of conventional hard dentures,
To relieve mucosal pain under hard dentures,
Improves the rhythm of chewing strokes,
It also compensates for the volumetric shrinkage of acrylic
resin
243
242. Classification:
I. Based on curing :
• Self cure- eg.,soften,viscogel
• Heat cure-eg.,supersoft,molloplast B
• Light cure resins-eg.,clearfit LC
II . Based on composition :
• Silicone elastomers
• Soft acrylic compounds
• Pthalate ester free compounds
• Polyolefin liners
• Fluoride containing liners(fluoroalkyl methacrylate)-eg.,
III. Based on durability
• Temporary/short term liners-e.g.,
Soft comfort
• Definitive/long term liners
243. 245
iv. Based on consistency
• Hard denture liners-e.g.,Ufigel hard C
• Soft denture liners-e.g.,Silastic 390
• Soft denture liners are further classified as a) silicone based and resin based
b)auto cured and heat cured
v. Based on the availability
• Home reliners
• Tissue conditioners
vi. Based on water sorption property
• Hydrophilic- e.g.,Kooliner (polymethyl/ethyl methacrylate polymer)
• Hydrophobic- e.g.,Elite soft(silicone polymer)
244. RESIN TEETH5
Polymethyl methacrylate resins used in the fabrication of prosthetic teeth are
very similar to those used in denture base construction. The degree of cross-
linking at the occlusal and incisal surfaces of prosthetic teeth is much greater
that that exhibited by polymerized denture base materials.
The increased cross-linking of prosthetic teeth in conjunction with the
addition of inorganic filler yields enhanced stability, increased wear
resistance, and improved clinical properties.
246
245. Resin teeth are capable of chemical bonding with commonly used denture
base resins.
Porcelain teeth, however, do not form chemical bonds with denture resins
and must be retained by bonded pins or mechanical undercuts. Leakage at
the tooth-denture base junction can be seen as a dark line when food and
microbes penetrate the interface.
247
246. 24
8
PLASTIC TEETH POECELAIN TEETH
High resilience Very brittle
Tough Friable
Soft-low abrasive resistance Hard-high abrasive resistance
Insoluble in mouth fluid-some dimensional change Inert in mouth fluid- no dimensional change
Low heat-distortion temperature, High- heat distortion temperature,
Bond to denture base plastic Poor bond to denture base plastic
Natural appearance Natural appearance
Natural feel- silent Possible clicking sound use
Easy to grind and polish Grinding removes surface glaze
Crazing and blanching- if non cross linked Occasional cracking
249. DENTURE LABELLING21
Denture labelling is used as a method of
identifying persons in geriatric institutions or
post-mortem during war, natural disasters and
crimes.
Denture labelling methods:
Surface marking method
Inclusion method
251
Gujjalapudi M, Anam C, Mamidi P, Saxena A, Kumar G, Rathinam J. The new id proof: A case report of denture
250. Methods of marking in complete dentures:
The materials that can be used for this purpose are
Lenticular cards,
Lead foils
Laser etched discs
Bar codes
Matrix codes
Microchips for radiofrequency tagging
Patient photographs
Metal strips of stainless steel
Matrix band, aluminium foil
Mixing paper pad and
Wax separating paper.
251. Appropriate areas for denture marking include:
In maxillary denture, the posterolateral region in
the palate or buccal to tuberosity.
Polished surface is given preference.
Distolingual flange of mandibular denture
253
252. METHODS OF DENTURE IDENTIFICATION
Barcode system can contain large amount of data.
However scanning of barcodes may be difficult due to
opacity of acrylic resin.
Furthermore the curvature of the denture may case
distortion of barcode, making it unreadable.
254
253. Another method, radiofrequency identification (RFID) is
used to reduce the errors of patient identification,
particularly during blood transfusion and drug
administration in hospitals
RFID is a method of identifying by using radio waves.
The RFID system consists of a data carrier, generally
referred to as tag or transponder, and an
interrogator/reader with an antenna.
255
254. Richmond et al (2009) studied on the use of radio-
frequency identification tags for labeling dentures
scanning properties22
The inclusion of radio-frequency identification (rfid)-tags
within dental prostheses has been suggested as means
of effectively labeling such devices and permitting rapid
and reliable identification of the wearer.
The results demonstrate that the rfid chips can only be
read when the interrogator is in close proximity to the
denture and thus should alleviate any concerns over
256
255. However, evidence obtained from both the literature and
experiments suggests that authorities must agree upon
a unified standard for chip and reader specifications and
protocols in order to avoid cases in which rfid-tags may
fail to be read by an incompatible reader.
257
258. 260
1. Glossary of prosthodontics terms. J Prosthet Dent. 2005;94:10-85
2. Tandon R. Gupta S. Agarwal SK. Denture base materials: From past to
future. Indian J Dent Sci. 2010 March; 2(2): 33-9
3. O’Brien J W. Dental materials & their selection. 3rd ed. Hanover
Park,(IL): Quintessence; 2002.
4. Available from: URL:https://www.sis.se/api/document/preview/915928//
259. 261
5. Anusavice KJ. Phillip’s science of dental materials: denture base resins.
11th ed. Philadelphia: Saunders; 2003. 721-758.
6. Anusavice KJ. Phillip’s science of dental materials: denture base resins.
11th ed. Philadelphia: Saunders; 2003. 143-170.
7. Craig GR, Powers MJ. Restorative dental materials. 10th ed. Missouri:
Mosby ;2002. 500-551.
8. Murrow R, Rudd D, Rhoads E. Total laboratory procedures of complete
denture. 2nd ed. USA: Mosby; 1986.
260. 262
9. Zarb GA. Bolender CL. Prosthodontic treatment for edentulous patients.
12th ed. Missouri(USA): Mosby; 2004.
10.Olivia RA. Lowe JA. Denture flasking: A comparative study of three
techniques. J Pros Dent. 1982 Dec; 48(6): 736-9.
11.Green AJ, Nimmo A. A two-pour technique for investing interim partial
dentures. J Pros Dent. 1985 Jul;54(1):151-2.
12.Firtell DN, Larry L. Bench curing acrylic resins. J Pros Dent. 1984
Jul;51(3):431-33.
13.Fisher AA. Allergic sensitization of the skin and oral mucosa to acrylic resin
denture materials. J Pros Dent. 1956 Sep; 6(5): 593-602.
261. 26314. Anderson GC, Schulte JK, Arnold TG.Dimensional stability of injection
and conventional processing of denture base resins.J Prosthet Dent 1988
Sep; 60(3): 394-8.
15. Strohaver RA.Comparison of changes in vertical dimension between
compression and injection molded complete dentures. J Prosthet Dent
1989;62:716-18.
16. Laia CP, Tsai MH, Chen M, Chang HS, Tay HH. Morphology and
properties of denture acrylic resins cured by microwave energy and
conventional water bath. Dental Materials 2004; 20: 133–141.
17. Shamnur SN, Jagadeesh KN, Kalavathi SD, Kashinath KR. journal of
dental sciences & research 1:1: pages 74 – 79.
262. 26418. Alla RK, Sajjan S, Alluri VR, Ginjupalli K, Upadhya N. Influence
on fibre reinforcement on properties of denture base resins. JBNB.
2013;4: 91-97.
19. Hazarika P. To determine the effect of surface roughness and
hardness of commercially available denture base resins on
immersion at different pH :in vitro study[M.D.S. thesis]. Moradabad,
M.J.P. Rohilkhand University, Barielly; 2019.
20. Prasad A. Prasad B. Shetty V. Shastry CS. Prasad D. Tissue
conditioners : a review. NUJHS Vol. 4, No.2, June 2014.
263. 265
21. Gujjalapudi M, Anam C, Mamidi P, Saxena A, Kumar G, Rathinam J. The
new id proof: A case report of denture labelling. Jorofac Res. 2013;3(1):63-65
22. Richmond R, Pretty LA. The Use of Radio-Frequency IdentificationTags
For Labeling Dentures Scanning Properties. j.forensic sci 2009
may;54(3):664-8.
Editor's Notes
A complete denture may be defined as a removable dental prosthesis intended to replace the masticatory surfaces and associated structures of a maxillary or mandibular dental arch. Such a prosthesis is composed of artificial teeth attached to a denture base.
So, The denture base derives its support through intimate contact with the underlying oral tissues.
A Denture base material is any substance of which denture base may be made.
During medieval times, dentures were seldom
considered as a treatment option. They were hand
carved and tied in place with silk threads and had to be
removed before eating
During medieval times, dentures were seldom
considered as a treatment option. They were hand
carved and tied in place with silk threads and had to be
removed before eating
Which
By 1940, 95% dentures made from them.
Poly(methylmethacrylate) is still the most predominantly used denture base material because of its excellent esthetics, ease of processing & repair and being economical.
Methacrylate polymers r capable of providing an excellent balance of performance features and characteristics needed for use in the oral cavity. This characteristics include
To fullfill these reqirements resin should be insoluble in saliva and any other oral fluids.it should be impermeable to oral fluids to the extent that it does not become unhygenic or disagreeble in taste or odor.
Clinical complications of manipulation…..
In addition,
Mer is a repeating unit, or is a part of a polymer whose repition would produce the complete polymer chain. In random type mers are randomly distributed along the chain. Block identical monomer units occur in long sequences along the main polymer chain. Graft- sequence of 1 monomer grafted onto 2nd monomer species.
The rheometry or flow behaviour, of solid polymers
spring like behaviour i.e. rapid n reversible. Chain uncoil, but they do not slip past one another bcz of crystalline (chain r highly ordered) region,entanglements, or cross linking.
Chain stretch n uncoil n also slip past one another, producing plastic,permanemt distortion n partial recovery when unloaded.
Actual dental polymeric materials r deformed by combination of plastic plus plastic strain process.
1. To increase the solubility of polymer in the monomer.
1. the plasticizing agent penetrating between the macromolecules and increasing the intermolecular spacing. this type of plasticizer is referred to as an external plasticizer because it is not a part of the polymer structure.
2.Plasticizing of a resin can also be accomplished by copolymerization with a suitable monomer. the plasticizing agent becomes part of the polymer
and thus acts as an internal plasticizer.
Tg-is a thermal range In which polymerized resin passes from soft, rubbery state to rigid, glassy state. It is 105 0C FOR P[LY.
In thermoplastics there is no cross linking between polymers chains so that’s y they can be reheated or reused
So there r permanently hardened n can nt be re used.
Induction is the first step in the chain rxn, where formation of free radical are formed which are unpaired species and r highly reactive in nature and these free radicals are required for the polymerization process.
In this process free radical can occur by two processes i.e activation and initiation .
these dot adjacent to the oxygen atom (O•) symbolizes the unpaired electron of the free radical.
Higher the temp, shorter is the length of the induction period.
3 induction systems heat, chemicals & light
a source of free radical is required. These free radicals are generated by activation of radical producing molecule using a second chemical heat, visible light and uv light.
As the unpaired electron of the free radical approaches the methyl methacrylate molecule, one of the electrons in the double bond is attracted to the free radical to form an electron pair. And a covalent bond between the free radical and the monomer molecule.
The resulting free radical monomer complex then act as anew free radical centre when it approaches another monomer molecule. Basically propogation of the reactive centre occurs.
.the active state is transferred from an activated radical to an inactive molecule and a new nucleus of growth is created. An already terminated chain can be reactivated by chain transfer resulting in continued growth.
either by direct coupling of two free radical chain ends. Or by. Donating a Hydrogen atom to MMA , so free radical rearrange n form double bond n become un reactive
It is also known as step growth polymerization.
Plasticizers are added to resin-
To increase the solubility of polymer to monomer
To decrease the brittleness of the polymer
But it also decreases strength, hardness and softening point.
(bottom),
(middle portion),
(thin top of the flask).
Third pour will be easily seperated during divesting procedure.
There will be an idea of the position of teeth when using any mechanical devices to break the stone mold.
1-4: the wax up is done and prepared for processing in conventional manner
5.
Calcium alginate film
Failure to place an appropriate separating medium can lead 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.
Failure to place an appropriate separating medium can lead 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.
Over boiling is not done.
This type of clean surface u will get….
Reason why extra coat is not painted ???
Reason why extra coat is not painted ???
Envision two methyl methacrylate molecules. Each molecule possesses an electrical field that repels nearby molecules.
Consequently, the distance between molecules is
significantly greater than the length of a representative
carbon-to-carbon bond. When the methyl methacrylate
molecules are chemically bonded, a new carbon-to-carbon
linkage is formed. This produces a net decrease in the space
occupied by the components
Envision two methyl methacrylate molecules. Each molecule possesses an electrical field that repels nearby molecules.
Consequently, the distance between molecules is
significantly greater than the length of a representative
carbon-to-carbon bond. When the methyl methacrylate
molecules are chemically bonded, a new carbon-to-carbon
linkage is formed. This produces a net decrease in the space
occupied by the components
The
physical and chemical characteristics exhibited during the
later phases of this stage are ideal for compression molding.
As a result, the material should be introduced into the mold
cavity during the latter phases of the doughlike stage.
During trial closure the pressure is 1500 psi and during final closure pressure is in range of 3400 – 3500 psi.
Bench curing for 30-60 mins
Sharry’ suggests a period of 1 to 4 hours without citing references, and Heartwell bench-curing of the denture 1 to more hrs . Boucher et al.9 suggest 30 to 60 minutes,
Bench curing is 30-60 mins
Materials used in injection molding technique :
1.Poly methylmethacrylate
2.Polycarbonate.
3.Nylon.
4.Polystrene.
Chemical activation is accomplished through the addition of a tertiary amine, such as dimethyl-para-toluidine, to the denture base liquid (i.e., monomer). Upon mixing of the powder and liquid components, the tertiary amine causes decomposition of benzoyl peroxide. As a result, free radicals are produced and polymerization is initiated. Polymerization progresses in a manner similar to that described for heat-activated systems.
. This property is related to the presence of tertiary amines within the chemically activated resins. Such amines are susceptible to oxidation and accompanying color changes that affect the appearance of the resin.
The flask is filled with reversible hydrocolloid investment medium, and the assembly is cooled.
1.Isolate the flask fully, e.g. with vaseline. Place the wax denture in the flask and fill with GC Advastone.
2. When the plaster has set, remove wax with boiling water and isolate the surface with GC Acro Sep, taking care not to contaminate the teeth.
3. First add the recommended quantity of liquid to the mixing jar, then the powder. Standard mixing proportions: 30 g powder /9 ml liquid. Do not mix.
Acron MC can be manipulated after standing at room temperature for 20 minutes.
4. Place the mixed dough in the die (use a thin polythene film and close the flask together).
5. Press the flask together slowly, open up, and remove excess material. Repeat the process until no excess remains.
6. Insert the bolts and tighten them under pressure. Place in the (500 W) microwave oven for 3 minutes to polymerise.
7. Leave the flask to stand for about 30 minutes at room temperature, then cool in water. Remove the plaster of Paris from the flask
8. Break the plaster of Paris and remove it from
the denture. Plaster residues can be removed
easily and safely with some plaster solvent
9. Trim and polish the denture, as usual
In addition, this technique eliminates the time needed to transfer the heat of the oven or the hot water, through the various structures, such as the flask, investment and stone cast to the resin itself.
increased porosity is due to heat entrapment in the nonmetallic flasks used for the purpose.
Opaque investing media prevents the passage of light, therefore light-activated resins cannot be flasked in a conventional manner
Removal is simple because the wax softens under the heat of the high-intensity light bulbs.
Initially, ultraviolet light was used, however, because of its effect on the retina and unpigmented oral tissues, limited penetration depth, and the loss in intensity of the ultraviolet light source over time, initiator systems activated by visible light were introduced
Contineous parallel fibres provide high strength n stiffness in one direction only(anisotropic)while randomly oriented provide similar effects in all directions (isotrophic properties) C0n II fibres difficult placement and formation of voids.
. This explains why aramid fibre-reinforced demonstrate a lower flexural strength than PMMA reinforced with glass fibre
volumetric shrinkage exhibited by the polymerized mass should be approximately 7%. There are several possible reasons why materials exhibiting such high volumetric shrinkages can be used to produce clinically satisfactory denture bases. It appears 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, provided the materials are manipulated properly.
This principle has important ramifications in the fabrication of denture bases, since stresses are always induced during processing.
In addition, surface cracks predispose a denture resin to fracture. From a physical standpoint, crazing may result from stress application or partial dissolution of a resin, for example, attack by a solvent.
Tensile stresses are most often responsible for crazing in denture base applications
Chemically cured display lower degree of polymerization.as a result they exhibit increased levels of residual monomer and decreased strength and stiffness.
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Inclusion methods :The inclusion methods are more permanent as opposed to the relatively simple surface marking methods; however, these techniques require certain skills and are time consuming. The marks are made by using metallic or non-metallic materials, microchips and micro labels which are enclosed in the denture at the packing stage. Sometimes, a dislocation, wrinkling or tear can occur proving to be a disadvantage as an identification method.
Without teeth, life can be a serious struggle. Tooth loss can make day-to-day tasks like speaking and chewing very difficult. As a result, people who suffer tooth loss often experience a lower quality of life. Dentures makes a foundation for a edentulous patient to smile again and for a prosthodontist a smiling patient with a well fitting denture is like a cherry on a cake.
