Upload
others
View
3
Download
0
Embed Size (px)
Citation preview
Prof. Dr. Manal A. El Ebiary
Dental Bio- Materials Department
Faculty of Dentistry
Tanta & MUST Universities
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 2
Metallic Non Metallic
Gold alloy type IV
Base Metal alloys
Acrylic Resin
Combination
of Metallic and Non
Metallic
Denture base is that the
part of denture which
rests on the soft tissues
and carries the artificial
teeth
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 7
the denture base material should not be harmful
to the technician
The denture base material should be nontoxic
and non-irritant to the patient.
Should not be able to sustain the growth of
bacteria or fungi.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 9
A high modulus of elasticity and elastic modulus to
insure that the stress during biting and mastication do
not cause permanent deformation. This allows the base
can be fabricated in a relatively thin section.
High proportional limit to avoid permanent deformation
High resilience to absorb energy without permanent
deformation
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 10
• The upper denture should have high value of
transverse to resist fracture especially in the
upper denture, because fracture occurs though the
midline of upper denture due to flexing.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 11
Adequate fatigue strength to resist fracture under force
of mastication.
Adequate impact strength to resist fracture if the
denture is accidentally dropped onto hard surface.
Sufficient abrasion resistance & hardness to prevent
excessive wear of material by abrasive denture cleaners
or foodstuffs.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 12
Matching the appearance of the natural oral
soft tissues.
High Glass transition temperature (Tg) to prevent
softening and distortion during use
Good dimensional stability.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 13
Low value of specific gravity
A high value of thermal conductivity
Radiopaque.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 14
A denture base material should be chemically
inert.
It should be insoluble in oral fluids and should
not absorb water or saliva
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 15
The denture material should be relatively inexpensive
Long shelf life is required.
The material should be easy to manipulate and
fabricate.
Should be easy repair.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 16
1. Heat cured acrylic resin
2. Self-cured acrylic resin
3. Rapid heat polymerized acrylic resin
4. Visible light cure acrylic resin
5. Microwave cured materials
6. Pour type denture base
7. High impact strength acrylic resin
8. Gel types
9. Flexible denture base
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 18
Composition
Its role
Polymethyl methacrylate
( PMMA)
The reactive ingredient
Initiator as ( benzoil
peroxide)
To initiate the polymerization reaction
Plasticizer as bulty
phathalate
Added to soften the material and to make it more
flexible and resilient
ferric oxide Act as a pigment to give the natural color of the soft
tissue
Nylon fibres To simulate the minute blood vessels
Pacifier
To improve the radiopacity of the denture base
Alumina, carbon fiber Increase stiffness and decrease coefficient of
thermal expansion
Polymeric Denture Base - Prof.Dr
Manal A. Elebiary 21
Composition Its role
Methyl methacrylate
(MMA)
The reactive ingredient
0.006%
hydroquinone
Inhibitor to prevent polymerization during
storage
Glycol dimethacrylate
Act as a cross-linking agent.
Plasticizer as bulty
phathalate
It may sometimes added to either the
powder or the liquid Polymeric Denture Base - Prof.Dr
Manal A. Elebiary 22
The same composition as heat cure except
presence of chemical accelerator tertiary
amine e.g. ethyl p-toluidine
Uses :-
Denture repair & special tray
Polymeric Denture Base - Prof.Dr
Manal A. Elebiary 24
free radical addition polymerization involving
the normal sequence of
activation & initiation
propagation
termination.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 26
• The polymerization reaction is exothermic
reaction
• Accompanied by polymerization shrinkage
• There is residual monomer which depend
on degree of polymerization
• The amount of residual monomer is
greater in self cured resin
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 27
1- Proportion:-
Polymer : monomer 3 : 1 by volume 2.5 : 1 by weight it control the workability of the mix the dimensional change on setting. Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 28
Polymerization shrinkage of 21% on conversion
to polymer this shrinkage is considerably reduced
by using a mix accurate proportion.
Too high polymer the mix becomes dry and lead
to granular cured acrylic
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 29
• Insufficient monomer in a dry mix to bind all the
polymer beads together. This produces a granular
effect on the denture surface, which is normally
referred to as granular porosity.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 30
The powder and liquid are mixed with stainless –
steel spatula and kept in a sealed glass jar to
avoid loss of the monomer by evaporation.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 31
During these stages no polymerization
reaction occurs while partial solutions of the
polymer in the monomer occur.
The desirable consistency for packing the
plastic in to the denture flask are the dough
stage.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 34
1- P / M the time is indirect proportionally to
monomer ratio.
2- The high temp. the shorter the time.
To reduce this time we can elevate the
temperature by putting the sealed glass jar,
which contain the plastic mixture in a hot water
bath.
Avoid direct heating of this mixture to avoid
boiling and evaporation of the monomer.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 35
3- The high molecular weight the longer the
time.
4- Copolymerization with Ethylacrylate
decrease the time.
5- The smaller particle size the higher
surface area the rapid dissolution the shorter
the time.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 36
• The mixture should packing in the dough stage.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 37
Packing before dough stage;-
- easily flow.
- Denture porosity.
Packing after dough stage;-
- Too viscous.
- Movement or teeth fracture.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 38
• The flask is opened at
interval to trim the
excess.
• Metal to metal contact
of the flask halves
completed in the press
assuring adequate and
effective pressure.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 39
A- Decrease in curing time produce under cured
denture and high residual monomer
B- Increase in the temp. rate ( rapid curing )lead to
accumulated temp .due to low thermal conductivity of
gypsum product plus exothermic reaction during
polymerization. This might reach the boiling temp. of the
monomer = 100.3 C . This lead to formation of gaseous
porosity
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 40
• to control the polymerization reaction of
acrylic resin to transform MMA to PMMA.
There are two curing cycles.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 42
B- Short cycle (2½h)
Keep at 74 C for 1½ h
100 C for 1 hour
A- Long cycle ( 8 h)
Keep at 74 C for 8 h
Used in bulky denture
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 43
• Allows cooling slowly to room temperature.
• Avoid rapid cooling because it increases the
internal stress within the denture, which is
released at a later time.
• the excess material is trimmed and removes
the adherent stone.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 44
The polymerization shrinkage of the monomer
about 21%.
While in heat cure acrylic resin mixing polymer
and monomer with a proper ratio results in
shrinkage about 6 %. This reduction in
polymerization shrinkage results from the
polymer beads was already polymerized.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 47
• About 0.2: 0.5 of the monomer remains un-polymerized
• Excess free monomer lead to :
irritation of soft tissue
Act as plasticizer
Make the denture weak and flexible
Decrease mechanical properties
Increase porosity
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 48
Clinically this water sorption =2 % it compensate polymerization shrinkage
Drying of denture base is associated with shrinkage . For this reason the denture should kept wet when not in service
•
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 49
Water sorption leads to forcing molecules away
from each other and induces stress within the
denture base, relaxation of this stress leads to
warpage (distoration) of denture base.
The absorbed water acts as a plasticizer which
decrease its mechanical properties.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 50
1- Tensile & compressive strength;-
adequate tensile and compressive
strength.
2- Elastic modulus;-
Quite low in comparison with metals and
alloys.
Polymeric Denture Base - Prof.Dr
Manal A. Elebiary 51
3- Transverse strength;-
It represents the type of loading applied to a
denture in the mouth it is a combination
between the tensile and compressive strength.
Polymeric Denture Base - Prof.Dr
Manal A. Elebiary 52
4-Fatigue strength;-
Dentures are subjected to repeated small
cyclic load during mastication. Heat cure
PMMA has adequate fatigue strength.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 53
5-Impact strength;-
It measures the energy absorbed by a denture
when it is subjected to sudden blow.
The impact strength of Poly vinyl acrylate
is twice than PMMA.
In high impact strength resin presence of
Butadien-styrene rubber will stop crack
then increase impact strength
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 54
A- Thermal conductivity
Very low thermal conductivity which may cause the following effects;
Heat can’t escape during processing that causes porosity and warpage
No stimulation to the underlying soft tissue which cause ischemia of the oral mucosa .
Denture base isolates the oral mucosa from hot or cold sensation.
Polymeric Denture Base - Prof.Dr
Manal A. Elebiary 55
High coefficient of thermal expansion
which leads to loosening of porcelain teeth
and crazing .
Addition of carbon fiber will reduce this
coefficient of thermal expansion.
Polymeric Denture Base - Prof.Dr
Manal A. Elebiary 56
It is a small void that may present internally or externally
on the surface of denture
Drawbacks of porosity;-
Poor aesthetic .
Rough surface
Difficulty in finishing and polishing.
Accumulation of dental plaque and food.
Foul odors.
Stress concentration
Bacterial growth & soft tissue irritation. Polymeric Denture Base - Prof.Dr
Manal A. Elebiary 58
appear as irregular voids
on the surface due to :-
Excessive monomer ratio.
Decrease resin mass.
Packing at sandy or
sticky stage.
under packing Polymeric Denture Base - Prof.Dr
Manal A. Elebiary 60
Appear as a fine uniform bubbles in the
thicker section of the denture
It is occur due to boiling of monomer
excessive curing time
Curing at high temperature.
Rapid increase of the temperature.
Polymeric Denture Base - Prof.Dr
Manal A. Elebiary 61
Accurate P / M ratio
i. 3:1 by volume
ii. 2:1 by weight
Good mixing
Close the mixing jar to avoid evaporation
of monomer
Paking in the dough stage only
Curing at the proper curing cycle
Curing at proper time
Curing under pressure
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 64
It is actual separation of the polymer chains under tensile stress. At first it appears at the superficial surface but after time it propagates to involve the whole thickness of the denture
Polymeric Denture Base - Prof.Dr
Manal A. Elebiary 65
Repeated drying and wetting during
Attack of solvent during repair of denture
Around porcelain teeth due to difference in
coefficient of thermal expansion
Cleaning the denture by bleaching agent or
alcohol
allowing of passing of water before curing
from gypsum product due to absence of
separating medium
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 66
• Presence of cross-linking agent in the resin
reduces crazing.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 67
Their chemical composition is similar to
self cure PMMA. The basic difference is
the particle size of polymer beads is very
fine and after mixing with the monomer
the mix is very fluid.
Polymeric Denture Base - Prof.Dr
Manal A. Elebiary 69
• They are poured in an agar mold.
• They give excellent reproduction of surface
details.
• Injection moulding technique can be used.
• Good flow
• Easy manipulation
Polymeric Denture Base - Prof.Dr
Manal A. Elebiary 70
Their composition is similar to heat cure PMMA with addition of Addition of butadiene styrene rubber to increase impact strength.
The rubber inclusion stop the crack growth
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 72
Chemical initiator
polymerized rapidly
Heat initiator
polymerized in
boiling water for 20
minutes
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 73
UDMA + micro fine silica filler + Photo initiator system .
It is supplied in the from of premixed sheet.
Polymerized by visible light 400: 500 nm.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 74
The same composition of heat cure
acrylic resin
It is supplied in the form of thick sheet
Stored in the refrigerator for about 2
years
Accurate proportion
Homogenous mix
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 75
polymerized by microwave energy using non- metallic flask and conventional microwave oven
This type characterized by; -
Faster penetration of microwaves
Homogenous curing
Physical properties comparable to heat cure Polymethyl methacrylate
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 76
The main composition is polyamide nylon
thermoplastic material.
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 78
It is soft, flexible, unbreakable
ability to engage undercut
no gingival inflammation
more comfortable
lighter in its weight
better aesthetic
short time during fabrication
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 79
De-bonding with acrylic artificial teeth
Tend to absorb water
Gradual fading of denture base color
High surface roughness which lead to
bacterial and fungal colonization.
Low hardness
Cannot reline or repair
Polymeric Denture Base - Prof.Dr Manal A.
Elebiary 80