Denture base resins/ dental crown & bridge courses

DENTURE BASE RESINS
Part I
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.com

TABLE OF CONTENTS
• INTRODUCTION
• HISTORY
• REVIEW OF LITREATURE
• IDEAL REQUIREMENTS OF DENTURE
BASE RESINS
• COMPOSITION

• ANSI/ADA SPECIFICATIONS
• CLASSIFICATION OF DENTURE BASE
RESINS.
• PROPERTIES OF DENTURE BASE RESINS
• TECHNICAL CONSIDERATIONS &
MANIPULATION OF DENTURE BASE
RESINS.
•

• STRENGHTNING OF DENTURE BASE
RESINS.
• CHARECTARISATION OF DENTURE BASE
MATERIALS
• ALLERGIC REACTIONS OF DENTURE BASE
RESINS.
• SUMMARY
• CONCLUSION
• REFERENCES

INTRODUCTION
A denture prosthesis is composed of artificial teeth
which are attached to the denture base.In turn the
denture base derives its support from the
underlying tissues or implants.
Although individual denture bases may be formed
from metal or metal alloys,majority of the
dentures bases are fabricated using common
polymers.
Such polymers are chosen based on
availability,dimensional stability,handling
characteristics,color &compatibility with tissues

HISTORY OF DENTURE BASE
RESINS
1800 : Was 200th
anniversary of united states
and by this time dentistry depended to a
large degree of naturally available materials
such as hard wood ,ivory or natural bone
with teeth held by screws.
1839 :Dr Charles Goodyear discovered
vulcanisation.

1853: first vulcanite denture was fabricated
1891: vulcanite was considered as the
universal material for fabrication of
dentures.
1901:Dr Otto Rohm ,as a part of his Phd
thesis, produced

Solid , transperent polymers of acryl
acid
1927:Acryloid and Plexigum, both polymers
of methyl methacrylate were produced by
Rohm and Hass as molding powders.
1932:mixtures of PVC and vinyl acetate both
polymers were used as denture base
materials .
1936:Veronite : a poly methyl methacrylate ,
heat processed was used as denture base
materials.

1943:self cure resins were introduced.
1945:plastic teeth were made from resins.
1960:Dr Rafeal Bowen discovered high
molecular weight monomer
1970:Light cure resins were developed.

REVIEW OF LITREATURE
Alexander A.Fisher(1956):-Four patients
were studied who had allergic type of
dermatitis of hands and were clinically proved
by patch test as allergic sensitivity to
monomer.They concluded that methyl
methacrylate liquid is the sensitizer and
caused allergic type of reaction on skin & oral
mucosa.

• DH.Anthony, FA. Peyton(1962):-
evaluated the fit of dentures made from
different materials& processed by different
techniques.they concluded that :
A) dentures processed using self cure had
better fit as there were fewer processing
strains.
b)injection molded group of dentures
showed overall accuracy of dentures

Walter H.Swartz(1966) tested the retention
exerted by various dentures.The materials
tested were heat cure acrylic resins
processed 12hrs at 1700
F, cold cure
acrylic,porcelain,aluminium.
They concluded that the cast aluminium
alloys were most resistant to vertical
dislodgement in all tests.

Jerome C. Strain (1967):-did a clinical study
of 321 denture patients with sore mouth.He
concluded that
a)the reaction to colored denture base
materials did not differ from the reaction to
pure ,clear,methyl methacrylate resin when
it was implanted in laboratory animals.
b)Trauma is probably one of the important
causative factors in neoplastic changes
associtated with denture base materials.
c)the prolonged &continuous combined action
of the dissolved polymer &illfitting
dentures may lead to tumour formation in
man www.indiandentalacademy.com

Theodore Berg et al (1967):-observed and
defined the relationships between pressures
involved in denture compressibility,
vascular bed embarassement, comfort
threshold,adaption of denture impression
materials & the physiological qualities of
complete dentures.
They concluded that the retention & denture
seal should be retention by extention rather
than excessive destructive adaption to soft
tissue’

Ellesworthy Kelly(1969):-observed the flexibility of
the dentures which leads to breakage of dentures.
The concluded that the flexibility can be reduced by
incorporating nylon, rayon or acrylic fibers.
William M.Harisson BruceE.Stansbury(1970)
investigated and evaluated three of more commonly
used surface dentures used for repair of
dentures.The experimental data found that the
rounded joint is clearly superior to the rabetted joint
&the butt joint.

AA. Grant , H. F. Atikson(1971) compared the
dimensional accuracy of dentures produced with
pour type of acrylic resin & heat processed
materials.
They found that the heat cure resins showed
uniform vertical dimension in tooth height that can
be compensated by grinding the teeth but the tooth
movement in fluid resin technique were un
predictable.

I.Eystein Ruyter, Svend A.Svendson(1980):-
investigated the flexural properties of heat polymerised,
self cure,&pour type of resins.
They found that heat polymerised resins with the
cross linking agent 1,4-BDMA have similar flexural
properties but better than self cure resins.The self cure
resins crosslinked with 1,4-BDMA has flexure
properties intermediate to heat cure resins.

• Xia chun Ming, DMD, Shi Changxi, DMD, and He
Weizhou (1996)
• This study introduces a new rapid-processing
procedure for curing polymethyl methacrylate
denture base resin in an automatically controlled
pressure cooker. The cooker filled with water was
inflated with 6 kgf/cm2
air pressure and heated to 120
C (248 F) and maintained for 10 minutes. No
significant differences were found between the new
pressure cooker method and the conventional method
for surface hardness and porosity (p>0.05). The
pressure cooker significantly shortened
polymerization time, and the polymerization is
controlled automatically.

• Kenneth B. May, Jeffery R. Shotwell, Andrew
Koran III, Rui-Feng Wang,(1996)
• Several quick heat-cured denture base resin
systems and microwave provessing resins have
been introduced to provide easier and faster
processing. The microwave processing method is
the fastest of the heat-cured processing methods.
Conventional acrylic resins processed with the
microwave method seem to possess adequate
physical properties, and one study indicated that a
microwave acrylic resin was reasonably color
stable under conditions of accelerated aging,
although manufactures do not recommend using
them for microwave processing

• The purpose of this study was to evaluate the color
stability of seven conventional and one microwave
heat-cured denture base materials processed with
the microwave method. The results of this study
revealed that color changes occurred after
accelerated aging in heat-cured denture base resins
and Acron GC microwave acrylic resins processed
with the microwave method. Hy-pro and TruTone
materials exhibited the least color change; Hy-pro
material was the most color stable material.

• Van Ramos, Dennis A. Runyan, Loren C.
Christensen(1996)
•
• The effect of a plasma-treated polyethylene fiber on the
fracture strength of polymethyl methacrylate was
evaluated in this study. Under the conditions of this
experiment the treated bars showed a mean fracture
strength of 12.56 MPa compared with 9.81 MPa for the
untreated samples. In addition to the increased fracture
strength, the treated bars also demonstrated resistance to
crack propagation. The bars remained in one piece, held
together throughout the compression loading by the
polyethylene fiber.
•

Nur Hersek, Senay Canay, Gulay Uzun, Fatih Yildiz.(1999)
•
• The color stability of 5 commercially available denture base
acrylic resins (QC-20, Meliodent, Trevalon, Trevalon High,
and Lucitone) was studied in vitro. In this study, Lucitone
QC-20 acrylic resin specimens exhibited noticeable color
change or staining in compliance with the NBS unit system.
Staining in Meliodent, Trevalon, and Trevalon High acrylic
resins were at Slight or trace levels. As the frequency of
ingestion and contact of the erythosine, tartrazine, and
sunset yellow food colorants with dentures was limited to
only a few minutes a day, it is unlikely the colorants can
stain clean acrylic resin surfaces.

• Eiichi Nagai, Kenji Otani, Yoshinori Satoh,
shiro Suzuki.((2001)
• This study evaluated the strength and modalus
elasticity of repaired acrylic specimens reinforced
with various processes. The results of this study
indicate that the mechanical strength of a repaired
acrylic denture base can be improved by
pretreatment of the surface with methylene
chloride. Woven glass fiber reinforcement with
methylene chloride may most effectively minimize
the recurrent fracture of repaired denture bases.

• Rafael Leonardo Xediek Consani, Saide
Sarckis Domitti, simonides Consani.(2002)
• Investigated differences between the dimensional
stability of standardized simulated denture bases
processed by traditional moist heat-
polymerization and those processed by use of a
new tension system

The maxillary denture bases; however, the
dimensional changes were probably not
clinically significant processed with the new
tension packing system were statistically
more dimensionally stable than those
processed with the conventional acrylic resin
packing method.

• Rodrigo Nunes Rached, John M. Powers, Altair
Antoninha Del Bel Curry.(2004)
• This study evaluated the transverse repair strength of a
conventional heat-polymerized (Lucitone 199, “L”) and
a microwave-polymerized (Acron MC, “A”) acrylic
resin that were repaired with these same resins and with
an autopolymerizing acrylic resin (Acron MC/R,
“AR”). In this in vitro study, the autopolymerizing
acrylic resin material exhibited repair strengths equal to
the conventional heat-polymerized acrylic resins tested.
Specimens made of microwave-polymerized acrylic
resins exhibited the highest strength of all materials
tested. www.indiandentalacademy.com

• Macro Antonio Compagnoni, Debora Barros Barbosa,
Raphael Freitas De Souza, Ana Carolina Pero.(2004)
• This study evaluated the effect of different microwave
polymerization cycles on the porosity of a denture base
resin designed for microwave polymerization. The results
of this in vitro study suggest that microwave
polymerization can produce denture base resin with
similar levels of porosity to conventional water bath
polymerized resin, thus saving processing time.

Y.Sinasi Sarac , Duguya Sarac(2005)
studied the shear bond strenght of 4 acrylic resins
following the use of 3 chemical solvents & to
examine treated acrylic surfaces under a field
emmision scanning electron microscope.they
concluded that chemical treatment prior to denture
base repair showed significant improvement on
the bond strenght of the base materials.

• The following are the requirements of clinically
acceptable denture base materials:-
1. Adequate strength and durability.
2. Satisfactory thermal properties.
3. Processing ability and dimensional stability.
4 . Good chemical stability.
5. Insolubility in and low sorption of oral fluids.
6 Absence of taste and odour

• 7. Biocompatibility.
• 8. Natural appearance
• 9. Color stability.
• 10. Adhesion to plastics, metals and porcelain.
• 11. Easy to fabricate and repair.
• 12. Moderate cost.

PHYSICAL FORM AND
COMPOSITION.
Denture base resins are commonly
supplied in two forms:-
• 1. Powder and liquid form.
• 2. Gel form.

• Composition of powder and liquid form of
acrylics.
• POWDER:-
Acrylic polymer (copolymer) beads
Initiator –benzoyl peroxide
Opacifiers
Pigments
Dyes

• Dyed organic fillers
• Inorganic particles
• LIQUID:-
.Monomer
• Inhibitor
• Accelator
• Plasticisers
• Cross linking agent

ANSI/ADA SPECIFICATIONS
FOR DENTURE BASE RESINS
• The ANSI/ADA specification No 12 lists
the scope requirements , procedures for
evaluating denture base plastics.This
specification includes acrylic, vinyl, styrene
polymers and mixture of any of these
polymers.

• The specifications are :-
• 1.The liquid should be clear as water and free
from extraneous materials.
• 2.the powder, plastic cake, precured blanks
should be free of impurities such as dust or
lint

• 3.A statisfactory denture will result when
manufacturers instructions are followed.
• 4.The denture base should be non porous
and free fromsurface defects.
• 5.The cured plastic should teke high gloss
when polished.
• 6The processed denture should be non toxic
to healthy,normal individuals

• 7.The colour should be as specified.
• 8.The plastic should be translucent.
• 9.The cured plastic should not show any
bubbles or voids.

• The specific requirements are :-
1.Within 5 minutes after reaching the proper
consistency, indicated by a clean seperation from
the walls of a glass mixing jar, the material shall
hava adequate flow properties so it will intrude to
a depth of atleast 0.5 mm into a 0.75mm diameter
hole when a load of 500gm is placed on a plate
5mm thick and 50mmin area.

2.The water solubility shall not be more than
0.8mg/cm.after immersion in water for 7 days at
370
c.
3.The solubility shall not be more than 0.04mg/cm2
after the water sorption specimen is dried to
constant weight.
4.The resin shall show no more than slight color
change when exposed to a specified ultraviolet
lamp test.

CLASSIFICATION
• Heat cured acrylic resins
• Self cure acrylic resins
• Light cure acrylic resins

Modified types of denture materials
Pour type of resins :They contain smaller acrylic
beads& when mixed with monomer the mix is
fluid. They are also called as “fluid resins”
or”hydrophillic resins”.
High impact resins :they are reinforced with
butadiene-styrene rubber.

Rapid heat polymerised resins: the initiator is
formulated with both chemical and heat
activated initiators with out the porosities
that one might expect.

Properties of denture base resins

DENTURE BASE RESINS
(PART II)

Chemistry of denture base resins
Monomers may be joined via one of two
types of reactions:
1)Addition polymerization.
2)Condensation polymerization.

Addition polymerization: is used to describe
formation of chains of linked molecules,
monomer molecules join to form polymer
chains that can be linear or cross-linked
macromolecules. If different monomers
(Comonomers) are joined, copolymer are
formed. Acrylic polymers set by this
mechanisms.

• Addition polymerization occurs in
three main stages
• Initiation
• Propagation
• Chain transfer
• Termination

• Initiation
This first step requires input of heat,
light or chemical energy in order to
form free radicals [chemical groups
with unshared electrons] by opening
unsaturated (double or triple) bonds in
the monomer molecules.

• The free radicals join other free
radicals in adjacent monomer
molecules and linkage occurs .
• In heat activated resins heat is the
activator. heat decomposes
benzoylperoxide to two free radicals
which react with the monomer
nolecules to initiate chain growth.

If any initiators are present they react
with the free radicals which increase
the length of induction period.

In self cure resins the amine reduces the
temperature required to break the
initiator into free radicals at mouth
temperature.
The amine complex with benzyol
peroxide reduces the thermal energy
required to split into free radicals.

In light cure resins the photons from
light activate the initiator to produce
free radicals.

Propagation:
The resulting free radical monomer
complex then acts as new radical center
when it approches another monomer to
form dimer, which also become free
radical.this inturn add to large number of
ethylene molecules so that
polymerisation continues.

Chain transfer:in this process ,the free
radical of a growing chain is
transferred to another molecule and a
free radical further is created.

• III. Termination
Propagation continues until no free
radicals are available either because all
have been joined or because there are
no adjacent linkages available.

• Step-Growth Polymerization
• 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,
nonmacromolecular structure

• In step-growth polymerization, a linear
chain of repeating mer units is obtained
by the stepwise intermolecular
condensation or addition of the reactive
groups in which bifunctional or
trifunctional monomers are all
simultaneously activated, as opposed
to the activation of one monomer at a
time in chain-growth addition
polymerization

Heat polymerising denture base
resins.
• Compression molding technique:
• Preparation of the Mold
• At this stage, the master cast and completed tooth
arrangement are removed from the dental articulator.
• The master cast is coated with a thin layer of
separator to prevent adherence of dental stone during
the flasking process.www.indiandentalacademy.com

• The lower portion of a denture flask is
filled with freshly mixed dental stone,
and the master cast is placed into the
mixture of the dental stone is
contoured to facilitate wax elimination,
packing and deflasking procedures.
Upon reaching its initial set, the stone
is coated with an appropriate separator.

• The lower portion of a denture flask is filled
with freshly mixed dental stone, and the
master cast is placed into the mixture..
• The dental stone is contoured to facilitate
wax elimination, packing and deflasking
procedures. Upon reaching its initial set, the
stone is coated with an appropriate separator.

• The upper portion of the selected denture
flask is then positioned atop the lower
portion of the flask.
• The dental stone is poured into the denture
flask.
• Care is taken to ensure that the investing
stone achieves intimate contact with all
external surfaces.
• The investing stone is added until all
surfaces of the denture flask.

• Care is taken to ensure that the investing
stone achieves intiamate the tooth
arrangement and denture base are
completely covered.
• Incisal and occlusal surfaces are
minimally exposed to facilitate
subsequent deflasking procedures.
• The stone is permitted to set and is
coated with separator.

• At this point, an additional increment
of dental stone is mixed, and the
reminder of the flask is filled.
• The lid of the flask is gentally taped
into place, and the stone is allowed to
set.

• Upon completion of the setting process, the
record base and wax must be removed from
the mold.
• To accomplish this, the denture flask is
immersed in boiling water for 4 min. the
flask is then removed from the water, and
the appropriate segments are separated.

• The record base and softened wax
remain in the lower portion of the
denture flask, while the prosthetic teeth
remain firmly embedded in the
investing stone of the remaining
segment.
• The record base and softened wax are
carefully removed from the surface of
the mold

• The record base and softened wax are
carefully removed from the surface of the
mold
• . Residual wax is removed from the mold
cavity using wax solvent.
• The mold cavity subsequently is cleaned
with a mild detergent solution and rinsed
with boiling water.

• Selection and Application of a Separating
Medium:
• The next step in denture base fabrication
involves the application of an appropriate
separating medium onto the walls of the
mold cavity. This medium must prevent
direct contact between the denture base resin
and the mold surface. Failure to place an
appropriate separating medium may lead to
two major difficulties:www.indiandentalacademy.com

• 1) If water is permitted to diffuse from the mold
surface into the denture base resin, it may affect the
polymerization rate as well as the optical and
physical properties of the resultant denture base
• (2) If dissolved polymer of free monomer is
permitted to soak into the mold surface, portions of
the investing medium may become fused to the
denture base. These difficulties often produce
compromises in the physical and aesthetic properties
of processed denture bases.

• Polymer-monomer ratio.
• The powder consists of prepolymerized poly
(methyl methacrylate) beads, commonly referred
to as polymer. The liquid contains non
polymerized methyl methacrylate and therefore is
termed the monomer.
• When the powder and liquid components are
mixed in the proper proportions, a doughlike mass
results.

• The accepted polymer-to-monomer ration is
3:1 by volume. This provides sufficient
monomer to thoroughly wet the polymer
particles, but this ratio does not contribute
excess monomer that would led to increased
polymerization shrinkage
• Using a 3:1 ratio, the volumetric shrinkage
may be limited to approximately 6% (0.5%)
linear shrinkage).

• Polymer- Monomer Interaction
• When monomer and polymer are mixed in
the proper proportions, a workable mass is
produced. Upon standing, the resultant
mass passes through five district stages
• . These stages may be described as (1)
sandy, (2) stringy, (3) doughlike, (4)
rubbery or elastic, and (5) stiff

• During the sandy stage, little or no
interaction occurs on a molecular level.
Polymer beads remain unaltered, and
the consistency of the mixture may be
described as “coarse” or “grainy”.
• Later, the mixture enters a stringy
stage. During this stage, the monomer
attacks the surfaces of individual
polymer beads. Some polymer chains
are dispersed in the liquid monomer.

• Subsequently, the mass enters a
doughlike stage. Clinically, the mass
behaves as a pliable dough.
• It is no longer tacky and does not
adhere to the surfaces of the mixing
vessel or spatula.
• The physical and chemical
characteristics exhibited during the
latter phases of this the mold cavity
during the latter phases of the
doughlike stage.

• These polymer chains uncoil, thereby
increasing the viscosity of the mix.
This stage is characterized by
“stringiness” or “stickiness” when the
material is touched or drawn apart

• Following the doughlike stage, the mixture
enters a rubbery or elastic stage.
• Monomer is dissipated by evaporation and
by further penetration into remaining
polymer beads.
• In clinical use, the mass rebounds when
compressed or stretched. Because the mass
no longer flows freely to assume the shape
of its container, it cannot be molded by
conventional compression techniques.

• Dough-Forming Time
• The time required for the resin mixture to reach a
doughlike stage is termed the dough-terming time.
• American National Standards Institute/American
Dental Association (ANSI/ADA) Specification
NO.12 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 resins reach a doughlike consistency in
less than 10 min.

• Working Time
• Working may be defined as the time that
a denture base material remains in the
doughlike 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.

• Packing
• The placement and adaptation of denture
base resin within the mold cavity is termed
packing. This process represents one of the
most critical steps in denture base
fabrication. It is essential that the mold
cavity be properly filled at the time of
polymerization.

• The placement of too much material, that is,
“overpacking,” leads to a denture base that
exhibits excessive thickness and resultant
malpositioning of prosthetic teeth. Conversely,
the use of too little material, that is,
“underpacking,” leads no noticeable denture
base porosity. To minimize the likelihood of
overpacking or underpacking, the mold cavity
is packed in several steps

• A fresh polyethylene sheet is placed between
the major portions of the flask, and the flask
assembly is once again placed in the press.
Another trial closure is made. In most
instances, the flask can be closed entirely
during the second trial closure. Care should be
taken not to apply excessive force to effect
closure. Trial closures are repeated until no
flash is observed.

• A fresh polyethylene sheet is placed
between the major portions of the.
• When flash is no longer apparent, definitive
closure of the mold may be accomplished.
• During the final closure process, no
polyethylene sheet is interposed between the
major mold sections.
• The mold sections are properly oriented and
placed in a flask press.the flask is transferred
to the flask carreir which maintains pressure
on the flask during processing.www.indiandentalacademy.com

Injection molding technique.
In this technique one half of the flask is
filled with the dental stone & the
master cast is settled into the stone.
The sprues are attached to the denture
base.
The remaining portion of the flask is
seated & the investment is completed.

The flask is placed into the carrier that maintains
the pressure on the assembly during resin
introduction & processing.
Upon completion of these steps the resin is
injected into the mold cavity.
The resin is mixed & introduced into the mold
cavity at room temperature.

The flask is then placed in the water bath
for polymerisation .
As the material polymerises ,additional
resin is introduced into the mold
cavity.
This process ofsets the effects the
polymerisation shrinkage.

Upon completion the denture is
recovered & finished.
Available data & clinical information
indicate dentures processed by thi s
method may provide slightly improved
clinical accuracy.

Polymerisation procedure.
Benzyol peroxide when heated around
600
c decompose to yeild neutral
unpaired electrons.
These are free radiclals.
Each free radical react with the monomer
molecule to initiate chain growth
polymerisation.

Since the reaction also posseses unpaired
electrons, the additional monomer molecule
become attached to individual polymer chains.
This process is terminated by
1)Coupling of two chains.
2)Transfer of hydrogen ions from one chain to
other.
Hence heat is the activator that decomposes
benzoyl peroxide &benzyol peroxide is the
initiator.

Temperature rise:
The polymerisation of denture base resin
is exothermic, the amount of heat
effects the properties of denture base
resins.
The temperature of the resin lags during
initial stages of polymerisation because
resin occupies the central portion of the
flask.

The dental stone & resin is poor thermal
conductors the heat of reaction cannot
be dissipated.

Internal porosity.
The polymerization is exothermic, if the
the temperature of resin exceeds the
boiling temperature the unreacted
monomer may boil which leads to
internal porosities usually not seen on
the surface of the dentures.

As resin is poor thermal conductor heat
generated in the thick portions cannot
be dissipated leading to internal
porosities of denture.

Polymerisation cycle
The heating process used to control is
termed as polymerisation cycle.
Research has lead to the development of
guidelines for polymerisation that
would decrease the internal porosities.

1) This technique involves processing
dentures in constant temperature in a
water bath at 740
c for 8hrs with no
terminal boiling treatment.
2) Processing the dentures at 740
c for
8hrs & increasing the temperature to
1000
c for 1hr.

3)Processing the resin at 740
c for 2hrs &
at 1000
c for 1hr.
Following completion the flask is cooled
slowly to room temperature, if rapidly
cooled causes warpage of denture base
because of differences in the thermal
contraction of resin & investing
medium. www.indiandentalacademy.com

The flask should be bench cooled for
30mins, followed by cool tap water for
15mins.

Polymerisation via microwave
energy.
This technique involves specially
formulated resin & non metallic flask.
A conventional microwave oven is used
for this polymerisation.
The advantage of this technique is speed
of polymerisation &similar levels of
porosities.
(J Prosthet Dent2004;91:281-5)www.indiandentalacademy.com

Acron GC material cure by microwave
method exhibited good color stability
(J Prosthet Dent1996;76:581-9)

As the temperature rises above 700
c the
temperature of the resin increases
&decomposition of the benzyol
peroxide is increased.
This leads to increased rate of
polymerisation which inturn increases
in the exothermic heat.

Effect of auxillary materials on
denture resins.
Number of materials are used in
making the dentures which may
effect the final properties &
function of denture. They are:

Plaster & dental stone:
The thermal coefficient of expansion
or contraction of dental stone is
different of that of dental stone this
creates residual stresses in the acrylic
as it cools .These stresses are released
after the dentures are processed &
deformation or crazing may result.

Impression materials :
The presence of zinc oxide eugenol on the
cast from the impression will function as an
inhibitor in polymerisation of resins.
Waxes:
Baseplate wax that is not removed from the
crown portion of the teeth prevents the
adherance of the teeth to the resins.

Mold seperators:
Care should be taken to aviid coating
of mold seperators to teeth as they
interfere with bond between denture
base & the teeth.

Denture cleansers:
Denture cleansers have pronounced effect on
the plastic dentures as they cause scratches
& wear of the dentures,
The use of soap water produced little effect
on dentures.
A solution containing 1tsp of
hypochlorite(clorox) & 2tsp of glassy
phosphate(colgon) in half glass of water is
recommended for cleaning of dentures.

Chemically accelerated denture base
resins.
Compression molding technique:
The principle difference between the
heat cure acrylics & self cure acrylics
is that of chemical reaction is
accelerated chemical accelerator such
as amines rather than heat.

The amine accelerator reacts with the
peroxide reactor at room temperature
& sufficient free radicals are produced
to initiate the polymerisation
reaction.Except for initation all the
reactions are same as that heat cure
resins.The reaction is exothermic.

It is considered that the polymerisation is
not complete as is heat cure resins. The
residual monomer acts as a plasticiser
which decreases the strenght of the
denture &residual monomer acts as a
irritant.

Technical considerations: self cure resins
are usually molded with compression
techniques therefore mold preparation
& resin packing is same as those
described for heat cure resins.

Polymer & monomer are supplied in
powder & liquid form.
They are mixed according to the
manufacturers directions to attain a
doughy stage.
The working time is shorter than heat
cure resins so attention should be paid
to consistency of resins.

To increase the working time
refrigeration of the liquid mass /mixing
vessel is done.
Mold preparation& packing is same as
heat cure resin.
Due to minimal working time more than
two trial closures cannot be done.
Following final closure of the denture
flask,pressure should be maintained
throught the polymerising period.

Initial hardening occurs within 30min of
final flask closure. However to ensure
sufficient polymerisation,the flask is
held under pressure for 3hrs.
Resins polymerised via chemical
activation generally display 3% to 5%
of free monomer.

Fluid resin technique: this technique employs
a pourable , chemically activated resin for
fabrication of dentures.
The resin is supplied in powder & liquid
form, when mixed yeild a low viscosity
resin.
After tooth arrangement is accomplished, it is
sealed to the cast a & placed in a specially
designed flask.

The flask is filled with reversible hydrocolloid
investment material & rthe assembly is cooled.
Following gelation ,the cast with teeth arrangement is
removed from the flask.
At this stage the, sprues& vents are cut from external
surface of the flask to the mold cavity.
Wax is eliminated using hot water ,the teeth are
retrieved & placed in positions within the mold.

The resin is mixed as per as manufacturers
direction & poured into the mold via the sprue
channels.
The flask is placed under pressure for 30-
45mins.
Following completion the denture is retrieved
&polished.

Advantages:
1.Improved adaptation to underlying soft
tissue,
2.Decreased probability of damage to
teeth & denture during deflasking.
3.Reduced material costs.
4.Simple technique.

Disadvantages:
1.Shifting of teeth
2.Air entrapment within denture base.
3.Poor bonding between denture teeth
&denture base.
4.Technique sensitivity.

Light activated denture base resins.
The material used is described as a composite
having matrix of urethane dimethacrylate,
silica& high molecular weight acrylic
monomers.
Visible light is the activator &
camphorquinone is used as initiator.

The material is supplied as a single sheet or rope
forms & is packed in light-proof pouches.
Opaque investing media prevents passage of
light, so they cannot be flasked in
conventional manner.
After try in of dentures,a roll of light activated
acrylic is placed on the occlusal surfaces of the
teeth to form a template with three references.

The template is cured in light chambers for
10mins.
The teeth are removed from the trial dentures,
wax is eliminated using high intensity light
bulbs.
The teeth are arranged on the template.
Master cast is coated with the seperating
medium.

A sheet of light cure resin is adapted on the
cast and trimmed to the boxing edge.
The base is polymerised in the light curing
chamber.
A strip of resin is placed on the under side of
the teeth after they have been coated with a
bonding agent.

The teeth are repositioned on the denture
base using the template.
The teeth are fixed in position by
polymerisation in the light cure
chamber.
The anatomical portion is sculpted & the
final shape of the denture is developed.

Sterenghtning of denture base
materials.
As complex stresses act on the denture
bases in the oral cavity the denture
bases shuld have enough strength to
resist fracture.

The strength of the denture base can be
increased by:
Decreasing the free monomer content in
the final dentures. To accomplish this
the dentures should be boiled in water
for 3hrs

By using high impact denture base resins.
Reinforcing denture base resins using woven
metal &glass metal(JPD2001;85;496-500)
Curing in microwave increases the strength of
denture base resins(JPD2004;92:79-82)
Fine polymer beads contributes to the greater
fatigue strength &that even stronger results
may be obtained if the polymer beads are
fine but not if uniform size
(JPD1969;21(3):257-64)

The foreign particles act as stress
concentrators &results in fracture.Hence the
polymers should be free of impurities.
(JPD1969;21;257-264)
Heat polymerising resins with cross linking
agents increases the flexure strenght of resins
(JPD1980;43(1);95-104.

Addition of whiskers of alumina , silicon
carbide, boron nitride &corbon fibres
are added to improve the strenght of
denture base resins.

Tissue compatibily of denture base
resins.
Tissue compatibility or allergic reactions of
skin and oral mucosa are reported.
Allergy is cused due to free monomer content
of the denture base.
Allergic reactions to heat cure dentures occur
less frequently than in cold cure resins;

The effect ot methyl methacrylate monomer
vapours on respiration & circulation in rats
was studied. It showed that MMA resulted
in abnormal respiratory patterns,increased
systolic BP with increased RR &heart rate.
(JPD1982;48;344-37)

Four patients were studied who had allergic
type of dermatitis of hands and were
clinically proved by patch test as allergic
sensitivity to monomer.They concluded that
methyl methacrylate liquid is the sensitizer
and caused allergic type of reaction on skin
& oral mucosa.
(JPD1956;6:596-603)

Aclinical study of 321 denture patients
with sore mouth.He concluded that
a)the reaction to colored denture base
materials did not differ from the reaction to
pure ,clear,methyl methacrylate resin when
it was implanted in laboratory animals.

b)Trauma is probably one of the
important causative factors in
neoplastic changes associtated with
denture base materials.
c)the prolonged &continuous
combined action of the dissolved
polymer &illfitting dentures may
lead to tumour formation in man
(JPD1967;18:465-467

Characterization of denture base.

Visible soft tissues simulated by denture
bases should include the unattached
(marginal) gingiva, the attached gingiva,
the gingival papillae, the alveolar
mucosa, and the frenum attachments.

Papillae and the attached and unattached
gingiva are described as being coral
pink in the Caucasian, although there is
much variation in the shade.
Physiologic pigmentation caused by
melanin-containing cells is a common
finding in the gingival tissues of non-
Caucasians

Hence charectarisation & tinting of
the denture base is necessary for
the natural appearance of the
denture base.

Charecterization of denture base is
done by incorporating rugea
areas,gingival sulcus, interdental
papillae etc., & by incorporating
the colors & shades of the natural
oral tissues.

Several techniques are put forward
to achive charecterisation of
denture base to achieve more
natural appearance.

SIFT-IN technique :
This technique is proposed by Pound
in 1951.

PROCEDURE
Usually, five stains or tinting resins were
adequate to characterize dentures.
The stains used were Kayon denture
stains(Kay-see manufacturing co.)

H, basic color (light pink as in attached
gingival)
F, light red
A, medium red, use cautiously
E, purple, use sparingly in most dentures
B, brown, used for patients with heavy
gingival pigmentation

The resin used was Natural Coe-Lor
denture resin.(Coe
Labs,inc.,Chicago.)

1. When waxing the denture, use care in
carving appropriate contours on the
denture base. Skillful contouring is
probably more important for esthetics
than tinting. Application of stains is
related to carved contours
2. Flask and boil out of the denture, paint it
with tinfoil substitute and allow to dry.

3. Modify a glass
dropper by heating
and drawing to
create a smaller
orifice and better
monomer control.
Use heat-curing
monomer to wet
the resin.

4. Sift H resin over the facial aspect
of the flasking stone in the region
occupied by the attached gingival
and saturate it with monomer.
Tint half the denture, then tint the
other half.

5. Sift a light
coat of F over
the H, and
extend the F
higher on the
flange.

6.Sift E sparingly on the area of the
attached gingival/mucosa junction
and saturate it with monomer. Do
not overwet the resin, or it may
pool in the lower gingival areas.

7.Sift A higher on the flanges to
the borders of the denture. Use
care, since A is red.

8. After tinting one side of the
denture, complete the other side in
the same manner. Continually refer
to the tinted side for comparison to
avoid a pronounced difference
color and distribution of the tinting
resin

9. Place a plastic sheet over the tinted
flask, and allow it to set for 15 to 20
minutes before packing the denture
base. If the denture is packed too
soon, the tinting resin can be
squeezed out of the mold.
• 10. Cure the denture and finish and
polish it in the usual manner

The above technique describes the
tinting of the denture base without
pigmented oral tissues.

This method involves use of brown
& purple resins for those with
pigmented oral tissues.

• PROCUDURE
1. Sift F resin over necks of teeth
and saturate with monomer. This
should be a very thin layer.

2. Sift a layer of brown resin over
the F resin. Take care to
correlate the thickness of the
layer to obtain desired intensity
of the brown tint.

3. Place red fibers above the
mucogingival junction on attached
mucosal regions and sift A resin over
the fibers

4. Add E resin to mucosal areas to
create a mottled or scattered pattern.
A slight amount of yellow can be
used as a highlighter over the root
eminences. Saturate with monomer
5. Completed denture simulates color
and texture of natural tissue

• Disadvantage
• The principal problem with this
technique is related to poor results
because of improper application of
the tinting resin.

• It is important to note that the brown
gingival colors can be made more or
less intense with a variation of the
thickness of the application.
• The procedure must not be done
hastily or in a slipshod manner.

• It is important to overlay each
addition of tinting resin to produce a
gradual color change, rather than a
striped appearance.
• Experience is very important in
achieving an acceptable result

Characterization of dentures
using self cure resins

• Previous color characterization
techniques have generally involved
applying gingival stains to the gingival
surfaces in the flask after boil-out.

• Applying stains to the gingival
surfaces in the flask before packing
has a major disadvantage. If any
reshaping of these surfaces is
required after processing, the stains
are lost in finishing and in
polishing

• Custom staining can be done
quickly and requires the following
armamentarium

• Denture tinting chart
• Soft tissue shade guide
• a #6 camel hair brush
• Acrylic resin stains or shade modifiers in
a variety of colors including red, brown
and black.
• Dappen dishes
• Pressure pot or a light curing unit for
curing the stains

Denture tinting chart
• A simple method of charting is
needed to record observations. The
denture tinting chart below may be
reproduced and used to provide
instructions for the dental
laboratory.

• AG = Attached Gingiva
Shade Light reddish pink
• AM = Alveolar Mucosa
Shade Reddish pink
B = Blanched areas over roots
Shade Pale pink
F = Frenum Attachments
Shade Red stain
• P = Papillae
Shade Light reddish pink

Soft tissue guide.
• A soft tissue shade guide may be
easily made by removing the teeth
from an old shade guide and
replacing them with processed
buttons of acrylic resin stain colors
and denture base colors

• The custom shade guide includes tabs of mild,
moderate and heavy Coe-Lor denture resin (GC
America Inc., Chicago, IL); and tabs of resin
shade modifiers in pale pink, tan, brown, purple,
red and black

• The soft tissue shade guide is used to
select a denture base material which is
most representative of each patient's
tissues. This is done at the appointment
when the artificial teeth are selected.
Using this same shade guide, other tissue
colors and unusual characteristics, i.e.,
blotches of melanin, are also recorded on
the denture tinting chart.

Stippling the denture base
• Stippling of the areas representing
the attached gingiva may be
accomplished in a variety of ways
but the blow-wax method is
preferred herein.

• A strip of masking tape is placed
over the artificial teeth and
marginal gingiva. Another strip of
masking tape is placed over the
alveolar mucosa, leaving the band
of attached gingiva exposed

• The result is natural looking,
positive stippling which seems to
collect less debris and calculus,
and is easier to clean than the
indentations made by negative
stippling techniques

• If the positive stippling is to be
preserved in the finished denture,
care must be taken in waxing the
denture to the proper thickness and
in finishing and polishing the
denture after processing

• Newer, autopolymerizing and light-cured
shade modifiers are cadmium-free and are
preferred. When the the denture has been
processed in the appropriate shade of
denture base material, it is contoured and
smoothed with an acrylic bur but not
polished.
• Custom tinting is done at this time. An
example of a typical procedure for a
Caucasian is as follows:www.indiandentalacademy.com

• Place monomer and colored powders in
different dappen dishes.
• Brush monomer on surfaces to be tinted.
• Wet brush and pick up increments of pale
pink powder (or gingival toner) and apply
to the blanched areas over root
prominences.

• Clean the brush and place red stain on the
alvoelar mucosa and frenum attachments.
• The unattached and attached gingiva and
the papillae remain as unstained denture
base material.
• Keep stains moist with the monomer
during this time to prevent crystallization.

• Cure the acrylic resin stains in the
pressure pot or light-curing unit
according to the manufacturers
instructions.

• The stains used are:Kayon Denture
Stains, Kay See Dental Mfg. Co.,
Kansas City, MO.
• The self cure resin used are :Palamed
Acrylic ShadeModifiers, Heraeus
Kulzer, Irvine, CA.

Characterization using photo cured
resins
• The light cured resins used
are:Dentacolor creactive
Photocuring Colorfluids, Heraeus
Kulzer, Irvine, CA .

• Previous color characterization
techniques rarely recommended
surface staining of finished dentures
with autopolymerizing acrylic resin
stains because of the lack of color
stability and the lack of abrasion
resistance of these stains

• In this technique, surface staining
of finished dentures is possible
because of clear, light-cured resin
coating.

• The clear coating provides a hard,
high gloss which makes the polishing
of dentures unnecessary.
• The coating seals the surface which
promotes the color stability of the
base and the stains.
• Abrasion resistance of the denture
base and custom staining should be
greatly improved .

• It is claimed that the coating render
the denture more wettable and
retentive, and that urethane
coatings may prevent allergic
responses to poly-methyl
methacrylate; but these claims
cannot be confirmed.

• The technique is as follows:
• Lightly sand or sandblast the unpolished
denture avoiding stained areas, then clean
with detergent solution and dry with oil-
free air.
• Using a soft clean brush, apply the
coating in a thin even film, painting in
one direction only to avoid air bubbles.
Do not brush a second time.

• Polymerize in
the
manufacturer's
laboratory light
curing unit
according to
instructions.

Technique for packing & staining
complete or partial dentures.
This technique was described by
Howard B.Jhosnon
(JPD1956:6(2):154-58)

The technique allows the operator to
observe his results while the staining
the resin, and it avoids the danger of
crazing acrylic resin teeth by the
monomer as the stains are applied.
Also it prevents the difficulty of
having the stone core adhere to the
acrylic resin teeth at the gingival
crevice if the monomer contacts the
teeth.

TECHNIQUE
The denture is waxed-up and contoured to
reproduce the buccal and labial anatomy
as accurately as possible.
The labial flange must not be waxed too
thick as it cannot be thinned down after
the denture is processed. (The stained
resin would be scraped or polished
away).

The wax pattern of the flange must have a
stippled effect over the buccal and labial
surfaces.
Stippling may be accomplished by tapping
the wax with a brush with stiff, short
bristles, or by crumpling tin foil into a
ball and pressing it against the softened
surface of the wax .The wax should be
flamed gently after stippling to round off
the sharp points.

• The first half of the flasking procedure is
carried out in the usual manner.
• Separating medium is applied and a core
of stone is painted over the labial and
buccal portions of the wax pattern and the
teeth to a depth of one-eighth inch.
• This stone will record every detail in the
pattern, including the stippling.

• A separating medium is applied to
the core and the investing is
completed in the usual manner.

• The wax in the flask is boiled out and
while the flask is still hot, the cast and
the stone core are pained with a tin-foil
substitute.
• After the flask has cooled to room
temperature, a quarter-inch groove is cut
around the labial portion of the land,
about 3 mm, from the pattern of the
flange .

• This moat is to allow any excess acrylic
resin to press into it, rater than to prevent
complete closure of the flask.
• A sheet of rubber dam is laid over the top
half of the flask covering the teeth and all
of the investing stone.
• The acrylic resin is placed in the top half
of the flask so that the rubber dam is
between the teeth and resin

• The trial closures are made.
• The flask is opened carefully and
usually the resin will remain attached
to the cast in the bottom half of the
flask. If it does not, the resin and the
rubber dam are removed from the top
half of the flask and placed in
position on the cast. Then the rubber
dam is removed.

• With the acrylic resin in place on
the cast in the bottom half of the
flask, the portion of the resin to
be stained is visible.
• The teeth remain in the top half
of the flask because they were
separated from the resin during
the trial packing by the sheet of
rubber dam.www.indiandentalacademy.com

• The stains used are the colors suggested
by Pound except that yellow is substituted
for white, as recommended by Hardy.
• The stains are dusted into the desired
positions from their special containers
• After the powder is placed (opposite four
teeth at a time) it is wetted with monomer
from an eye dropper with a 19 gauge
needle attached.

• The stain should be approximately
0.5 mm. in thickness. This small
addition will not cause the mold to
be overpacked.

• The stone in the top half of the flask is
painted with a second coat of a tin-foil
substitute. The flask is closed carefully in
such a way that the stained portion of the
resin does not scrape on the stone of the
top half of the mold.
• The resin is cured in the usual manner,
separated and a minimum of polishing is
done .

Esthetics & the denture base
Donald F. kemnitizer (JPD 1956;6(5):603-15)

Natural denture bases are obtained by
(1) an esthetic wax-up which re-
produces the contours of oral
anatomy lost with extraction of teeth
and alveolar resorption.
(2) staining these contours to give
them a vital appearance.
One is of little value without the other.

• The structures included in waxing the
maxillary are : the buccal and labial frenula,
the gingival margin (smooth surface), the
attached gingivae ( stippled surface), the
interdental papillae, the root surfaces.
• The incisive papilla, the rugae, the lingual
margin proximal to posterior teeth, and the
contour on approximation with the anterior
teeth are included on the lingual or palatal
surfaces.

• Rugae- the thickness of wax on the hard
palate is reduced until the color of the cast
just commences to become apparent
through it. The tin-foil rugae pattern made
earlier is placed in position and its edges
are sealed with a warm spatula. The
reduction of wax until the cast color is
visible through it creates minimal
impingement on the tongue space by the
vault surfaces

• Base-Anterior Teeth- A common
error in contouring palatal surfaces is
burying the cingula of anterior teeth
in the acrylic resin. The lingual
surfaces of the anterior teeth should
be given a natural cingulum form and
lingual anatomy by contouring the
wax adjacent to them .

• Base-Posterior Teeth- The maxillary bone
structure of skulls shows a moderate
thickness of alveolar process lingual to
the teeth (in fact, it is thicker than that on
the buccal side). This is recreated in the
denture by leaving 0.5 to 1 mm. of
buccolingual thickness of the wax
alveolar crest between the teeth and the
lateral alveolar processes during wax-up.

• Frenula: A small amount of wax
melted on the fine end of the spatula
is drawn from the fold toward the
marginal termination point. Wax bulk
will be greatest where the spatula is
first applied and minor carving to
give the frenula definition is all that
is done.

• Stippling- The surface of natural attached
gingiva appears rough when it is wiped
dry. This stippled effect is produced on
the denture by the use of a stiff-bristled
toothbrush, trimmed to one shortened
cross-row of bristles so that its application
can be will controlled. The stippling
terminates just posterior to the last tooth
in the arch

• The width of the stippled area is
optional but 1 cm. is the maximum
width ever necessary. Stippling
acts to blend the individual
anatomic components and causes
an uneven light refraction, which is
an important factor contributing to
naturalness.

• Gingival Sulcus-The sulcus is
produced by inserting a explorer
tip or similar sharp instrument
between the tooth and the wax at
the gingival margin and moving it
mesiodistally along this junction.

• All components of the form having
been completed the wax surfaces
are buffed with a silk cloth,
repeatedly dipped in cool water to
produce a hard, polished surface on
the wax.

Characterization of dentures
• Hobart H. proctor
• JPD1953;3(5):339-49

COE-LOR™ RTC
SELF-CURED DENTURE BASE RESIN

Summary

Conclusion

References
Restorative dental materials- Robert G. Craig
tenth edition.
Walter L Shepard ,Colonel :dentures
produced from fluid resins.J prosthet Dent
24:561,1968

Anthony DH, PeytonFA: Dimensional accuracy of
various denture base resins.J Prosthet
Dent12:67,1962.
Braden M,:The absorption of water by acrylic resins
& other materials,J Prosthet Dent14:307,1964.
Ellesworth K:Fatigue failure in denture base resins,J
Prosthet Dent.21:257,1969;

Firtell ,Harman:Porosity in boilable resins. J Prosthet
Dent.49:133,1983.
Grant, Atkinson:Comparission of denture bases processed
pour type & heat type of resins. J Prosthet
Dent.26:296,1971.
Harrision, Stanbury:the effect of joint contours on transverse
strenght of repaired acrylic dentures. J Prosthet
Dent.23:246,1970.

Ruyter, Svendson : Flexsural properties of denture
base resins. J Prosthet Dent43:95,1980.
Nur Hersek, Senay:Color stability of denture base
acrylic resin. J Prosthet Dent1999:81:375-9
Eiichi, Kenji: Repair of denture base resin using
woven metal & glass fiber. J Prosthet
Dent2001:85:496-95

Rafeal et al:Effect of a new tension system,
used in acrylic resin flasking. J Prosthet
Dent 2002 ;88:285-9
Macro Antonio,Deboro et al :The effect of
polymerisation cycles on the porosities if
microwave processed dentures. J Prosthet
Dent 2004;91:281-5.

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