Denture Base Resin

14-05-2008

DEPARTME�T OF PROSTHETICS @ Chettinad Hospital & Research Institute

Dental material lecture

DENTURE BASE RESIN

DR.VINAMRA DHARIWAL

Dr. Vinamra Dhariwal

DEFI�ITIO�:

• According to GPT - VI, Denture Base is

defined as the part of Denture that rests on

the foundation tissue and to which teeth are

DR.VINAMRA DHARIWAL



the foundation tissue and to which teeth are

attached.

• Denture Base Material is any substance of

which denture base may be made

HISTORY


Dental material lectureDR.VINAMRA DHARIWAL

WOODEN DENTURES



BONE, IVORY AND

NATURAL TEETH



• In 1794 John Greenwood began to swage gold bases for dentures. Made George

Washington's dentures.

George washington’s last dental prosthesis. The palate was swaged from a sheet of gold and ivory teeth riveted

To it.The lower denture consists of a single carved block of ivory. The two dentures were held togther by steel

Springs.

DR.VINAMRA DHARIWAL Dental material lecture

CERAMIC

• ADVANTAGES over wood, bone , ivory were

-Could be shaped using additive technique rather than subtractive (carving).

-Additive technique facilitated correction of denture base surface.

-this permitted more intimate contact with



-this permitted more intimate contact with underlying soft tissues.

-Could be tinted to simulate the colors of teeth and oral soft tissues.

-stable in oral environment.

-Minimal water sorption, porosity, and solubility.

-Smooth surface provided hygienic properties.

Among the drawbacks

BRITTLENESS was most

significant, fractures were common,

often irreparable.

DR.VINAMRA DHARIWAL

�ELSO� GOODYEAR

vulcanite dentures in 1864.

Vulcanized hard rubber was discovered and introduced as denture base material



denture base material (Ebonite). It ruled dentistry until about 1940(during which Vulcanite, Metal and Porcelain became the standard combination.

DR.VINAMRA DHARIWAL

Disadvantages

• It absorbs Saliva and becomes unhygienic

due to bacterial proliferation.



due to bacterial proliferation.

• Esthetics were poor.

• Dimensionally unstable.

• Objectionable taste and odor

DR.VINAMRA DHARIWAL

CELLULOID

DENTURES

• In 1868 John Hyatt, A

US Printer, discovered

the first plastic

molding compound,



molding compound,

called celluloid. He

made it by dissolving

nitrocellulose under

pressure

DR.VINAMRA DHARIWAL

Other cellulose compounds were cellulose

acetate, acetate butyrate, ethyl cellulose.



• Substitute for vulcanite was unsuccessful as

It absorbs stains and odors in the mouth,

Gradually turns black and was flammable.

DR.VINAMRA DHARIWAL

• In 1909, another promising organic compound was found. This was phenol formaldehyde resin discovered by Dr. Leo Bakeland . “BAKELITE”.

Disadvantages

• Variable strength , Lack of uniform quality



• Variable strength , Lack of uniform quality

• Variable color , Dimensional instability.

• Vinyl chloride and vinyl acetate dentures were available from 1932.

DR.VINAMRA DHARIWAL

METALLIC

DENTURE BASES

ADV:

1.Good thermal conductive property.

2.Can be as thin as possible, hence indicated in decreased interocclusal clearance cases.

3.Weight of the denture is comparatively less which helps in retention (esp. upper denture)



3.Weight of the denture is comparatively less which helps in retention (esp. upper denture)

4.Breakage is minimal.

5.Fit of the denture is improved when compared with acrylic denture.

6.These are kind to the underlying tissues because of excellent tolerance of the tissues.

7.Increased patient comfort.

DR.VINAMRA DHARIWAL

• DISADV:

1.Poor esthetics.

2.Increased chances of discoloration if poorly maintained.



maintained.

3.Casting shrinkage had to be taken in consideration.

4.Relining and rebasing is difficult.

DR.VINAMRA DHARIWAL

Listing requirements

DR.VINAMRA DHARIWAL

REQUIREMENTS

Requirements of a denture base material can

be listed under the following headings:

�Physical properties



�Physical properties

�Mechanical properties

�Chemical properties

�Biological properties

�Miscellaneous

DR.VINAMRA DHARIWAL

PHYSICAL

PROPERTIES:

1.Appearance—An ideal denture base should be capable matching the appearance of the oral soft tissues-depending on whether the base will be visible when the mouth is opened. 2. Glass transition temperature:

Should be high enough to prevent softening and distortion during use.



Should be high enough to prevent softening and distortion during use.

3. Dimensional stability:

Should have good dimensional stability in order that the shape of the denture does not change over a period of time.

Factors influencing dimensional instability are temperature, internal stresses, continued polymerization &water sorption.

DR.VINAMRA DHARIWAL

4.Specific Gravity:

Should have a low value of specific gravity in order that dentures should be as light as possible. This reduces the gravitational displacing forces



This reduces the gravitational displacing forces which may act on an upper denture.

5. Thermal Conductivity:

A high value would enable the denture wearer to maintain a healthy oral mucosa and to retain a normal reaction to hot and cold stimuli.

DR.VINAMRA DHARIWAL

Radio-opacity:

The denture base should ideally be RADIOPAQUE. It should be capable of detection using normal diagnostic



RADIOPAQUE. It should be capable of detection using normal diagnostic radiographic techniques. This might be helpful in detection of denture if accidentally swallowed.

DR.VINAMRA DHARIWAL

MECHANICAL

PROPERTIES

1. The denture base should be rigid therefore a high value of modulus of elasticity is advantageous.

2. A high value of elastic limit is required to ensure that stresses encountered during biting and mastication do not cause



encountered during biting and mastication do not cause permanent deformation. A combination of high modulus and high elastic limit would allow the denture base to be fabricated in thin sections.

3. The denture base should have sufficient flexural strength to resist fracture. Fractures of upper dentures occurring through the midline of the denture are due to flexing.

DR.VINAMRA DHARIWAL

4. The base material should have an adequate fatigue

life and a high value of fatigue limit.

5. The denture base should have a good impact

strength. Impact strength is the ability of the denture



strength. Impact strength is the ability of the denture

base to resist fracture.

6. The denture base material should have sufficient

abrasion resistance to prevent excessive wear of

material by abrasive denture cleansers or food stuffs.

DR.VINAMRA DHARIWAL

CHEMICAL

PROPERTIES:

1. Base material should be chemically inert

.

2. It should, naturally, be insoluble in oral



2. It should, naturally, be insoluble in oral

fluids and should not absorb water or

saliva since this may alter the mechanical

properties of the material and cause the

denture to become unhygienic.

DR.VINAMRA DHARIWAL

BIOLOGICAL

PROPERTIES:

• The denture base materials should not beharmful to the technician involved in itshandling in the unmixed or uncured states.

• The set denture base should be non toxic and non



• The set denture base should be non toxic and nonirritant to the patient.

• The base ideally should be impermeable to oralfluids. If a degree of absorption occurs however,the base should not be able to sustain the growthof bacteria or fungi.

DR.VINAMRA DHARIWAL

MISCELLANEOUS

PROPERTIES:

• An ideal denture base should be relatively inexpensive.

• It should have a long shelf life.

• Material should be easy to manipulate and fabricate

without having to resort to using expensive processing



without having to resort to using expensive processing

equipments.

• It should be easy to repair, if fractures do occur.

In addition the denture base should have color stability,

absence of taste and odor, adhesion to plastics, metals and

porcelains.

DR.VINAMRA DHARIWAL

All through the history

of the making of

dentures, we find a



dentures, we find a

constant struggle of

packing all the

properties in a single

material

DR.VINAMRA DHARIWAL



• In 1937 Dr. Walter

Wright gave dentistry

its very useful resin.



• It was polymethyl

methacrylate which

proved to be much

satisfactory material

tested until now.DR.VINAMRA DHARIWAL

Requisites for a

dental resin:

1.Biological considerations: 1.Biological considerations:

• The resin should be tasteless, odorless, non-toxic and non-irritating to the oral tissues.

• Should be insoluble in saliva or any other fluids taken into the mouth.

• Should be impermeable to oral fluids.

• Should inhibit growth of micro-organisms.

DR.VINAMRA DHARIWAL

2. Physical properties:

• Adequate strength and

resilience to resist biting|

chewing forces, impact forces

and excessive wear.

• Should be dimensionally • Should be dimensionally

stable.

• Specific gravity should be

low.

DR.VINAMRA DHARIWAL

3. Aesthetic properties:

• Should exhibit

sufficient translucency

or transparency to

match the appearance

of the oral tissues.

• Should be capable of • Should be capable of

being tinted or

pigmented.

• Color stability.


4. Handling properties:

• The material should not produce toxic

fumes or dust during handling.

• Ease of manipulation.

• Oxygen inhibition, saliva contamination

and blood contamination should have and blood contamination should have

little or no effect on the final outcome.

• Should be easy to polish.

• Should be capable of being easily and

efficiently repaired if fracture occur.


5. Economic

considerations:

• Cost and processing

method should of the method should of the

resin should be low.

• Processing equipment

should be simple and

inexpensive.

“�o resin has yet met all of these ideal criteria”. Methacrylate

polymers fulfill the aforementioned requirement reasonably well.

DR.VINAMRA DHARIWAL

POLYMER RESINS

DEFI�ITIO�: A polymer is a long chain organic molecule. It is produced by the reaction of many smaller molecules called monomers, or mers.



• If reaction occurs between two different but compatible monomers the polymeric product is called a COPOLYMER.

• Resin : A broad term used to describe natural or synthetic substances that form plastic materials after polymerization (GPT-7th edition).

DR.VINAMRA DHARIWAL

METHYL METHACRYLATE

The acrylic resins are derivative of ethylene and contains a vinyl group

(-c=c-)

Polyacids tends to imbibe water, due to polarity related to carboxyl group.

Water tends to separate the chain and cause softening and loss of strength.

Methyl methacrylate is a transparent liquid at room temp.Methyl methacrylate is a transparent liquid at room temp.

Physical properties

-Molecular wt=100

-Melting point=-48 C

-Boiling point=100 C

-Density=0.945g/ml at 20 C

-Heat of polymerization=12.9 Kcal/mol



POLYMETHYL

METHACRYLATE

• Transparent resin, transmits light in UV range to a wavelength of 250 nm.

it has got remarkable clarity.

• Hard resin, knoop hardness no of 18 to 20.

• Tensile strength is 60 MPa

• Density is 1.19 g/cm cube.



• Modulus of elasticity 2.4 GPa(2400 MPa)

• It is chemically stable and softens at 1250C

• It can be molded as a thermoplastic material between 125 and 200 C

• Depolarization takes place at approx 450 C .

• Absorbs water by imbibition

• Non crystalline structure possess high internal energy.

• Polar carboxyl group can form hydrogen bridge to a limited extent with water.

DR.VINAMRA DHARIWAL

Polymerization MechanismsPolymerization Mechanisms :

Basically of 2 types-------

1.Step-growth or condensation type.

2.Addition polymerization



STAGES OF

POLYMERIZATION

• INDUCTION



• PROPAGATION

• TERMINATION

• CHAIN TRANSFER

DR.VINAMRA DHARIWAL

COPOLYMERIZATION:

• When 2 or more

chemically different

monomers combine to

form macromolecules



form macromolecules

or COPOLYMERS,

the reaction is said to

be

COPOLYMERIZATI

ON.

DR.VINAMRA DHARIWAL

CROSS-LINKING:

• Cross-linking is formation of molecular networks

through joining or bridging linear polymers

through certain reactive side chains.

• Cross-linkage provides a sufficient no., of bridges



• Cross-linkage provides a sufficient no., of bridges

between the linear macromolecules to form a

three-dimensional network that alters the strength,

solubility, and water sorption of the resin.

DR.VINAMRA DHARIWAL

TYPES OF DE�TURE

BASE POLYMERS

1)CO�VE�TIO�AL HEAT CURED POLYMETHYL METHACRYLATE

• Supplied as powder and liquid

POWDER



• Polymer of PMMA in the form of spheres or beads.

• Benzoyl peroxide is attached to it (initiator) 0.5%

• Plasticizer is incorporated (methacrylate or acrylate monomer).

• Coloring pigments cadmium/ organic dyes/ iron are added for esthetics.

DR.VINAMRA DHARIWAL

LIQUID

• Methyl methacrylate monomer

• Cross linking agent Ethylene glycol dimethacrylate(5-15%).they are added to

avoid crack or craze produced by stresses during drying.



• Inhibitor Hydroquinone (trace) to avoid premature polymerization and enhance

shelf life.

• As a rule,heat activated denture base are

shaped via compression molding technique.DR.VINAMRA DHARIWAL






HEAT ACTIVATED DENTURE BASE RESINS

Composition:

Powder: 1. prepolymerized spheres of poly(methyl-

metha-acrylate).

2 . Initiator – benzoyl peroxide

Liquid: 1 . Unpolymerized methyl metha

acrylate.

2 . Inhibitor – hydroquinone to prevent

undesirable polymerization or setting of the liquid

during storage.

3 . Cross linking agent – glycol di

methacrylate.


Activator: heat.

Thermal energy required for polymerization

may be provided using

a. water bath

b. micro wave oven.

Polymer : monomer ratio – 3 : 1. This ratio

will reduce volumetric shrinkage from 21%

to 6%


Processing techniques :

• Commonly employed technique to shape

a heat activated resin - compression

molding technique.

• The other technique is injection molding

technique, For which specially designed

flask is used. Commonly used resin is flask is used. Commonly used resin is

polystyrene resin.

After shaping denture base resin is

polymerized.


Polymer monomer interaction

When polymer and monomer are mixed it passes through following stages

SandySandy

Stringy

Dough like

Rubbery or elastic

Stiff



Dough forming time

• According to ANSI/ADA specification no 12 for denture base resins requires that this consistency be reached in less than 40 min from start of mixing time.



be reached in less than 40 min from start of mixing time.

• In clinical use it is achieved in less than 10 min.

Working time

• Time that a denture base remains in a dough like stage.ANSI/ADA specification no 12 requires the dough to remain moldable for 5 min.

DR.VINAMRA DHARIWAL

2)AUTOPOLYMERIZI�G/COLD CURE POLYMETHYL METHACRYLATE (POUR RESI�)

• Composition same as the heat cure version with following differences



1)The powder contains beads of polymer that have a lower molecular wt. and benzoyl proxide (initiator)

2) The liquid contains a chemical activator ,tertiary amine such as dimethyl-para-toluidine.

• Upon mixing tertiary amine causes decomposition of benzoyl peroxide.

DR.VINAMRA DHARIWAL

• Dentures processed have more residual monomer (1-4%),but lower dimensional change.

• Decreased transverse strength (residual monomer act as plastisizer).



act as plastisizer).

• Compromised biocompatibility (residual monomer)

• Color stability inferior (teriaty amine susceptible to oxidation), stabilizing agents should be added

DR.VINAMRA DHARIWAL

• Fluid resin and

compression molding

technique can be

employed for the



employed for the

fabrication of denture.

• Also used as repair

material

DR.VINAMRA DHARIWAL

CHEMICALLY ACTIVATED DENTURE BASE

RESINS:

Activator: addition of tertiary amine(di methyl-

para-toluidine) to the liquid component.

Advantage:

greater dimensional accuracy because of less

complete polymerization there by less complete polymerization there by less

shrinkage.

Processing shrinkage:

chemical cure = 0.26%

heat cure = 0.53%


DIS ADVANTAGES:

1. Degree of polymerization – not as complete as

heat cured ones – more of free monomer which

leads to

a. tissue irritation.

b. acts as a plasticizer resulting in decreased

transverse strength and dimensional instability.transverse strength and dimensional instability.

Free monomer – chemical cure = 3 – 5%.

heat cure = 0.2 – 0.5%

Can be over come by ensuring complete

polymerization- holding the flask under

pressure for minimum of 3 hrs though initial

hardening occurs in 30 min.


2.Color stability is inferior to that of heat cured one – presence of tertiary amine which oxidises easily.

Discoloration can be minimized by addition of stabilizing agents to prevent oxidation.

Processing techniques:

1 .compression molding technique.

2 .fluid resin technique – employs a pour able, 2 .fluid resin technique – employs a pour able, chemical cured resin. Supplied as powder and liquid, which when mixed in proper ratio yield a low viscosity resin.

resin is poured into the mold cavity subjected to increased atmospheric pressure and allowed to polymerize.


Advantages:

• Improved adaptation to the underlying soft tissues.

• Decreased damage to prosthetic teeth and denture bases during deflasking.

• Reduced material cost.

• Simplification of flasking, deflasking and finishing procedures.

Disadvantages:

• Shifting of teeth during processing.

• Air entrapment within the resin.

• Poor bonding between the denture base and the teeth.

• Technique sensitive.


3)HIGH IMPACT RESISTA�T ACRYLIC

• Similar to heat cured material but less likely to be broken if dropped.

• Produced by substituting the PMMA in the powder with a copolymer.

• Copolymer of butadiene with styrene or methyl methacrylate are incorporated into

the beads.

• Phase inversion resulting in dispersion throughout the beads of tiny islands of

rubber containing small inclusions of rubber/PMMA graft polymer.

Electron micrograph of high impact denture

Base showing size and shape of polystyrene-butadiene

Rubber inversion phase. DR.VINAMRA DHARIWAL

4) Injection molded polymers

• These are made of Nylon or

Polycarbonate.

• The material is supplied as a gel in the

form of a putty .

• It has to be heated and injected into a

mold

• Equipment is expensive.

• Craze resistance is low .

The SR-Ivocap system uses specialized flasks and clamping presses

to keep the molds under a constant pressure of 3000 lbs

DR.VINAMRA DHARIWAL

5) RAPID HEAT POLYMERIZED POLYMER

• Same as conventional material except that they contain altered

initiation system.

• These initiator allow them to be processed in boiling water for 20 min.

• A problem with these is that areas of the base thicker than approx.6mm

have a high level of porosity.

• Short duration of heating also leaves a higher level of residual

monomer,3-7 times greater than conventional heat cured denture base.


6) MICROWAVE

POLYMERIZED

POLYMERS

• Resins are the same as used

with conventional material and

are processed in a microwave.

• Denture base cures well in

Special polycarbonate flask

(instead of metal).(instead of metal).

• The properties and the accuracy

of these materials have been

shown to be as good or better

than those of the conventional

heat cured material.

• Processing time is much shorter

(4-5 min).

Microwave resin and non metallic microwave flask


POLYMERIZATION VIA MICRO WAVE ENERGY:

• Technique employs a specially formulated resin and a nonmetallic flask.

• A conventional microwave oven is used to supply the thermal energy required for polymerization.

• Advantage is the speed, with which polymerization is accomplished.

• Micro wave polymerization is an effective way of processing acrylic resins. Resultant denture bases appear extremely dense Significant porosity was reduced when conventional resins were polymerized using microwave.

• Micro wave processed dentures provide best fit to be compared with auto polymerizing resin.


7)Light activated denture base

resins

• This material is a composite having a

matrix of urethane dimethacrylate,

microfine silica and high molecular wt

acrylic resin monomers

• Acrylic resin beads are included as

organic fillers.

• Visible light is the activator, whereas • Visible light is the activator, whereas

camphorquinone serves as the initiator

for polymerization.

• Can be used as repair material and as

custom tray material.

• Single component denture base is

supplied as sheet and rope form in

light proof pouches. Light curing unit for polymerizing Dimethacrylate


Light activated denture base resins:

• Composition: composite having a matrix of

a. urethane-di-methacrylate.

b. micro fine silica.

c. high molecular weight

acrylic resin monomers.acrylic resin monomers.

d. fillers-acrylic resin beads.

e. initiator-camphoro

quinone

Activator – visible light.


• Single component denture base resin is supplied in sheet and rope forms and packed in light proof pouches to prevent inadvertent polymerization.

• It cannot be flasked in a conventional manner as the normal investing medium is an opaque material.

• Hence teeth are arranged and the denture base is molded on an accurate cast.molded on an accurate cast.

• Subsequently the material is exposed to a high intensity visible light source far an appropriate period.

various methods were used to adapt these resin sheets to cast but vacuum forming produce the best adaptation.


8) FIBER –REI�FORCED POLYMER

• Glass, carbon/graphite, aramid and ultrahigh molecular wt

polyethylene have been used as fiber reinforcing agents.

• Metal wires like graphite has minimal esthetic qualities.

• Fibers are stronger than matrix polymer thus their inclusion • Fibers are stronger than matrix polymer thus their inclusion

strengthens the composite structure.

• The reinforcing agent can be in the form of unidirectional,

straight fiber or multidirectional weaves.


Physical properties of denture base resins:

1. Polymerization shrinkage:

when pure monomer is polymerized there

is a volumetric shrinkage of 21% but when

mixed with polymer in 3:1 ratio it reduces to mixed with polymer in 3:1 ratio it reduces to

7% and this is distributed uniformly to all

surfaces , hence produce clinically satisfactory

results.

DR.VINAMRA DHARIWAL

• Whereas linear shrinkage exerts significant

effects on denture base adaptation. Based

on the above value-7%, this should be 2%.

Thermal shrinkage is the primary cause for Thermal shrinkage is the primary cause for

the linear shrinkage.


2.POROSITY:

Presence of surface and subsurface voids compromise the physical, aesthetic, and hygienic properties of a processed denture base. Could be due to:base. Could be due to:

a. inadequate mixing of polymer and monomer---large voids resulting from localized polymerization shrinkage. Can be minimized by ensuring the greatest possible homogeneity of the resin.(proper polymer-monomer ratio).


b. rapid heating of the resin--- causes localized

subsurface porosity near the center of the

investment mass.

c. inadequate pressure or insufficient material

in the mold during polymerization ------

irregular large voids, make the denture more

opaque.


3. WATER SORPTION:

PMMA absorbs relatively small amounts of

water when placed in aqueous environment.

Ingress of water is by diffusion.

this causes a slight expansion of the

polymerized mass and also water interfere with polymerized mass and also water interfere with

entanglement of polymer chain , thereby act as

plasticizer.

Water sorption=0.69mg\cm2.


4. SOLUBILITY:

Though soluble in some solvents ,

virtually insoluble in oral fluids.

5. CRAZING:

Stress relaxation may sometimes

produce small surface flaws or micro produce small surface flaws or micro

cracks ----CRAZING. Adversely affect

aesthetic and physical properties. Imparts a

“hazy” appearance, also predisposes to

fracture. Generally begins at the surface of

a resin, oriented at right angles to tensile

stress. Dental material lectureDR.VINAMRA DHARIWAL

6. STRENGTH:

Depends on composition, processing technique and oral environment.

7. CREEP:

Denture resins when subjected to sustained load, the material exhibits an sustained load, the material exhibits an initial deflection. If the load is not removed,additional deformation may occur over time----CREEP.Creep rate increase with in temperature, applied load, residual monomer and presence of plasticizer.


ADVA�TAGES OF DENTURE BASE

RESINS:

• Ease of manipulation and processing.

• Good esthetic quality.

• Rebasing and relining possible.

• Cost effective.• Cost effective.

Disadvantages:

• Poor thermal conductivity

• Polymerization shrinkage.

• Bulk.

• Color instability.DR.VINAMRA DHARIWAL

RECE�T ADVA�CEME�T

• Modifications of acrylic resin materials designed to improve specific properties

included.

1 plasticization,

2 copolymerization,

3.cross linking and reinforcement.

• Internal plasticization by co-polymerization may improve strength properties.

• Cross-linking is a special case of co-polymerization. In general cross-linking lowers

strength and flexibility but increases solvent resistance, softening point and hardness

DR.VINAMRA DHARIWAL

• One disadvantage of cross-linking is the reduction of bonding between acrylic

resin teeth and the base which may occur particularly with a cold curing base

material

• Reinforcement by glass fibers is easily accomplished. This is done by mixing

discrete fibers with dough or by combination with glass cloth.

• Specially primed glass is necessary to bring out good adhesion to the resin

and to maintain it particularly in wet conditions.

• In the dough fiber method, the percentage of glass which can be incorporated is • In the dough fiber method, the percentage of glass which can be incorporated is

limited to about 20% by weight because of reduction of flow of the dough.

DR.VINAMRA DHARIWAL

Alternatives to methacrylate materials

• Most alternatives to polymethacrylate are vinyl acrylic, polysterene,

acrylic styrene, acrylonetrile copolymers .

�EW PLASTIC MATERIAL

• High impact methacrylates (IM): These are basically similar to standard

methacrylate but have a higher impact and fatigue strength.

• Epoxy resins (E): The general properties of these materials are

strength, hardness, toughness, low curing shrinkage and good adhesion

to metals. The disadvantages for dental use are the toxicity, the yellow

colour which darkens further, high water absorption, poor adhesion to

vinyl polymers

DR.VINAMRA DHARIWAL

• �ylon materials: They were found to be unsatisfactory for denture base because of high molding shrinkage which led to warpage, high water absorption and yellowing.

•

• High impact polystyrene (IS): This is an elastomer graft copolymer with styrene. It is basically similar to polysterene and injection molded in a similar way.

• High density polythene (DE): This is stiffer stronger variety of polyether.

• Polypropylene (PP): this is a hydrocarbon polymer similar to polyethylene but stiffer and • Polypropylene (PP): this is a hydrocarbon polymer similar to polyethylene but stiffer and stronger.

• Polyacetal (A): Also called polyformaldehyde. It has lower water absorption with good resilience and toughness, and resistance to fatigue

DR.VINAMRA DHARIWAL

• Polycarbonate (PE): It is thermoplastic material with low water absorption and

very high impact strength and toughness.

• Chlorinated polyether: It has very low water absorption and low mold shrinkage

with excellent resistance to staining and chemical agents

• Eclipse prosthetic resin system is a new method of fabricating dentures from

Dentsply International. It is being marketed as an indirect build-up method for

fabricating dentures that is monomer-free and flask-free. Eclipse is a light-cured fabricating dentures that is monomer-free and flask-free. Eclipse is a light-cured

system that does not contain any ethyl-, methyl-, butyl-, or propyl-methacrylate

monomers.

• System uses three resins to form the denture: Baseplate Resin, Set-up Resin and

Contour Resin. The resins were developed to handle like wax, yet be cured into a

denture base material – without investing and flasking.


• VALPLAST -

Valplast is a flexible denture base resin that is ideal for partial

dentures and unilateral restorations.

• The resin is a biocompatible nylon thermoplastic ,it eliminates the

concern about acrylic allergies.


MISCELLA�EOUS RESI�S A�D TECH�IQUES :

1. REPAIR RESINS:

May be light or chemical or heat activated. Chemical resins are more activated. Chemical resins are more preferred because they polymerize at room temperature.

Heat and light activated should be kept in water- bath and light chambers respectively.


2. RELINING RESIN DENTURE BASES:

Relining involves replacement of tissue

surface of an tissue surface of an existing

denture .

Rebasing is replacement of the entire

denture base.denture base.

May be heat, light, microwave energy

activated resins


Introduction

• Dentures are rigid pieces of acrylic resin

which are shaped to fit the soft tissue

covering of the jaw and to be compatible covering of the jaw and to be compatible

with the functioning and ever-changing oral

environment.

-Heartwell


Dentures need to be “serviced” to keep pace with changing foundation

The clinical effort that aim at prolonging the useful life of complete dentures involve a refitting of the impression surface of the refitting of the impression surface of the denture by means of a reline or a rebase procedure

-Boucher


Definitions

• Relining – the procedure used to resurface

the tissue side of a denture with a new base

material, thus producing an accurate material, thus producing an accurate

adaptation to the denture foundation area.

- G.P.T-7


• Relining – it is the process of adding some

material to the tissue side of a denture to fill

the space between the tissue and denture

base

-Winkler


• Rebasing –the laboratory process of

replacing the entire denture base material on

an existing prosthesis.

-G.P.T-7

• Rebasing is a process of replacing all the

base material of a denture.

-Winkler


Material science

Denture liners

Hard liners Soft liners Tissue conditioners

AcrylicAcrylic

Silicone


Soft liners

Acrylic silicone

Heat activated

Chemically activated

Room temperature

vulcanizing (RTV)

Heat vulcanizing


3. SOFT LINERS:

Purpose ----to absorb some of the energy produced by masticatory impact. Commonly used are plasiticized acrylicresins. May be heat or chemical activated.

Can be a. Short term liners.

b. Long term liners.b. Long term liners.

Chemical soft liner-----poly(methyl\ethyl methacrylate), supplied in powder form and liquid contains 60% to 80% of plasticizer(dibutyl phthalate)----SHORT TERM SOFT LINERS. Do not contain acrylic monomers.

DR.VINAMRA DHARIWAL

• Heat- activated materials generally are durable and may be considered LONG TERM SOFT LINERS and not permanent liners.

Supplied as powder-liquid system. Powder—acrylic resin polymers and copolymers.copolymers.

Liquid----acrylic monomers and plasticizer

When mixed form pliable resins. Plasticizer are prone for leaching which can be minimized by decreasing its content. Leaching makes a material rigid.


When ethyl, n-butyl,and n-propyl are used,

less plasticizer is required. Now, the most

successful material is silicone rubber , can

be heat or chemical activated.

To promote adhesion between silicone and

resin denture base , rubber cements are resin denture base , rubber cements are

used.

Other polymers used are polyurethane and

polyphosphazine.


Relining technique

IMPRESSION

STATIC FUNCTIONAL

OPEN MOUTH

CLOSED MOUTH


4. RESI� IMPRESSIO� TRAYS A�D

TRAY MATERIALS:

Resin trays used to fit specific arches---

custom trays.

Most of the cases the material is

chemical cure poly(methyl methacrylate).chemical cure poly(methyl methacrylate).

Recently, light activated urethane

dimethacrylate resins have also been used

but these are brittle and release fine

powder particles during grinding.


DENTURE CLEANSERS :

1. Dentifrices

2. Proprietary denture cleansers

3. Mild detergents

4. Bleaches

5. Vinegar.

Both immersion and brushing

technique are used. Most common is

immersion type using cleansing powder

or tablets.


RESIN TEETH:

60% Of artificial teeth are made of acrylic or vinyl- acrylic resins with the a degree of cross- linking more than that in a denture base resin and thereby with increased stability and improved clinical properties. This increase is achieved by properties. This increase is achieved by elevating the monomer(cross- linking agent)in the liquid.

when compared with porcelain teeth, resin teeth are


When compared with porcelain teeth, resin

teeth :

1. Display more fracture toughness. Hence

less likely to chip or fracture when

denture is dropped.

2. Chemically bond with denture bases.2. Chemically bond with denture bases.

3. Easier to adjust and exhibit greater

resistance to thermal shock.


MAXILLO FACIAL MATERIALS:

1. Latexes :

Soft , inexpensive materials but are

weak, degenerate rapidly, exhibit color instability

and cause allergic reactions.

Recently developed synthetic latex ---

tripolymer of butyl acrylate, methyl methacrylate tripolymer of butyl acrylate, methyl methacrylate

and methyl methacrylamide—

transparent,colorants can be sprayed to improve

translucency and blending.

Lengthy processing, short life are

disadvantages.


2. Vinyl plastisols :

Plasticized vinyl resins---- colorants can be added to match skin tones .

Disadv---- harden with age, uv light has adverse effects on these materials.

3.Polyurethane polymers :

Most recent material to be used, requires accurate proportioning of three components. Has a natural feel and appearance.

Disadv----susceptible to deterioration rapidly


4. Silicone rubbers :

2 types are-----

1.Heat Vulcanizing

2.Room temperature vulcanizing.

Room temperature supplied as single paste system colored by addition of dyed rayon fibers, dry earth pigments and oil rayon fibers, dry earth pigments and oil paints. Not strong as heat vulcanizing.

Heat vulcanizing supplied as puttylike that requires milling, packing under pressure and 30 minute heat application at 180 c. Better strength and color stability. Lengthy procedure, not economical.



DR.VINAMRA DHARIWAL

Documents

Denture Base Resin