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Polymeric Denture Base - Prof.Dr Manal A.

Elebiary 1

Prof. Dr. Manal A. El Ebiary

Dental Bio- Materials Department

Faculty of Dentistry

Tanta & MUST Universities


Elebiary 2

Metallic Non Metallic

Gold alloy type IV

Base Metal alloys

Acrylic Resin

Combination

of Metallic and Non

Metallic


Elebiary 4

Before After

Polymeric Denture Base - Prof.Dr

Manal A. Elebiary 6

Denture base is that the

part of denture which

rests on the soft tissues

and carries the artificial

teeth


Elebiary 7


Elebiary 8

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.


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


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.


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.


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.


Elebiary 13

Low value of specific gravity

A high value of thermal conductivity

Radiopaque.


Elebiary 14

A denture base material should be chemically

inert.

It should be insoluble in oral fluids and should

not absorb water or saliva


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.


Elebiary 16


Elebiary 17

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


Elebiary 18


Elebiary 19

Liquid

Monomer

Powder

Polymer


Elebiary 20

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


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



Elebiary 23

The same composition as heat cure except

presence of chemical accelerator tertiary

amine e.g. ethyl p-toluidine

Uses :-

Denture repair & special tray




Elebiary 25

free radical addition polymerization involving

the normal sequence of

activation & initiation

propagation

termination.


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


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


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.


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.


Elebiary 31

1- Sandy stage. 2- Sticky stage.



• 3- Dough stage • 4- Rubber stage


Elebiary 33

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.


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.


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.


Elebiary 36

• The mixture should packing in the dough stage.


Elebiary 37

Packing before dough stage;-

- easily flow.

- Denture porosity.

Packing after dough stage;-

- Too viscous.

- Movement or teeth fracture.


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.


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


Elebiary 40


Elebiary 41

• to control the polymerization reaction of

acrylic resin to transform MMA to PMMA.

There are two curing cycles.


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


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.


Elebiary 44


Elebiary 45


Elebiary 46

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.


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


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

•


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.


Elebiary 50

1- Tensile & compressive strength;-

adequate tensile and compressive

strength.

2- Elastic modulus;-

Quite low in comparison with metals and

alloys.



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.



4-Fatigue strength;-

Dentures are subjected to repeated small

cyclic load during mastication. Heat cure

PMMA has adequate fatigue strength.


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


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.



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.



I- Porosity

II- Crazing


Elebiary 57

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


Gaseous

porosity

Contraction

porosity


Elebiary 59

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


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.




Elebiary 62


Elebiary 63

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


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



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


Elebiary 66

• Presence of cross-linking agent in the resin

reduces crazing.


Elebiary 67


Elebiary 68

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.



• They are poured in an agar mold.

• They give excellent reproduction of surface

details.

• Injection moulding technique can be used.

• Good flow

• Easy manipulation




Elebiary 71

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


Elebiary 72

Chemical initiator

polymerized rapidly

Heat initiator

polymerized in

boiling water for 20

minutes


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.


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


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


Elebiary 76


Elebiary 77

The main composition is polyamide nylon

thermoplastic material.


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


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


Elebiary 80


Elebiary 81

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