All through the history of the making of dentures,we find a

constant struggle of the dentist to find a suitable denture base material

INTRODUCTION

COMPLETE DENTURE:

“ A Removable Dental Prosthesis That Replaces the Entire Dentition and Associated Structures of the Maxilla or Mandible ”

Composed of

Artificial teeth

Denture base

Support

Contact with with underlying oral tissues

Teeth

Implants

Denture base materials

Metallic

Alloys

Denture base resins

FUNCTION

estheticsComfort

RETENTIONEfficiency

Advantages of denture base resins

Denture should be

GENERAL TECHNIQUE

Clinical steps laboratory steps

PROCESSING

( acrylization )

TEETH ARRANGEMENT

Processed denture

Definition : According to GPT - VI, Denture Base is defined as the part of Denture that rests on the foundation tissue and to which teeth are attached. Denture Base Material is any substance of which denture base may be made

HISTORY

Skillfully designed dentures were made as early as 700 BC.and

Talmud a collection of books of hebrews in 352-407 AD mentioned that teeth were made of gold ,silver,and wood.

Egypt was the medical center of ancient world, the first dental prosthesis is believed to have been constructed in egypt about 2500 BC. Hesi-Re Egyptian dentist of about

3000 BC

Front and back views of mandibular fixed bridge, four natural incisor teeth and two carved ivory teeth

Bound With gold wire found in Sidon-ancient Phoenicia about fifth and fourth century BC.

During medieval times dentures were seldom considered ,when installed they were hand carved and and tied in place with silk threads.

Those wearing full denture had to remove them before eating.

Upper and lower teeth fit poorly and were held together by steel springs.

Earlier pictures of dental prosthesis are delivered to us by ABUL-CASIM an Arab born in Cordova Spain.

Persian dentist of late eighteencentury

Indian surgeon of mid nineteenth century

WOOD

For years, dentures were fashioned from wood .

Wood was chosen -readily available -relatively inexpensive -can be carved to desired shape

Disadvantages -warped and cracked in moisture -esthetic and hygienic challenges -degradation in oral environment

Wooden denture believed to be carved out of box wood in 1538 by Nakoka Tei a Buddist priestess

Wooden dentures

Bone

Bone was chosen due to its availability, reasonable cost and carvability .

It is reported that Fauchard fabricated dentures by measuring individual arches with a compass and cutting bone to fit the arches .

It had better dimensional stability than wood, esthetic and hygienic concerns remained.

IVORY Denture bases and prosthetic teeth were fashioned by carving this

material to desired shape Ivory was not available readily and was relatively expensive. Denture bases fashioned from ivory were relatively stable in the

oral environment They offered esthetic and hygienic advantage in comparison with

denture bases carved from wood or bone.

Carved ivory upper denture retained in the mouth by springs with natural human teeth cut off at the

Neck and riveted at the base.

Since ancient times the most common material for false teeth were animal bone or ivory,especially from elephants or hippopotomus.

Human teeth were also used,pulled from the deceased or sold by poor people from their own mouths.

Waterloo dentures

1788 A.D. Improvement and development of porcelain dentures by DeChemant.

G.Fonzi an italian dentist in Paris invented the

Porcelain teeth that revolutionized the construction

Of dentures.Picture shows partial denture of about

1830,porcelain teeth of fonzi’s design have been

Soldered to a gold backing.

CERAMICS Porcelain denture bases were relatively expensive During subsequent years secrets of porcelain denture

became known and it became common and inexpensive. 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 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.

One piece porcelain upper denture crafted by Dr John Scarborough,Lambertville,New Jersey 1868.

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.

In 1839 an important development took place CHARLES GOODYEAR

discovered VULCANIZATION of natural rubber with sulphur(30%) and was patented by Hancock in england in 1843.

NELSON GOODYEAR (brother of charles goodyear) got the patent for vulcanite dentures in 1864.

. They proceeded to license dentists who used their material, and charged a royalty for all dentures made. Dentists who would not comply were sued.

The Goodyear patents expired in 1881, and the company did not again seek to license dentists or dental products.

Vulcanite dentures were very popular until the 1940s, when acrylic denture bases replaced them.

A set of vulcanite dentures worn by Gen. John J. (Blackjack) Pershing, commander of the American Expeditionary Forces in France during the First World War

Set of complete dentures having palate of swaged

Gold and porcelain teeth set in vulcanite.

In 1868 John Hyatt, A US Printer, discovered the first plastic molding compound, called celluloid. He made it by dissolving nitrocellulose under pressure

In 1909, another promising organic compound was found. This was phenol formaldehyde resin discovered by Dr. Leo Backeland .

Celluloid upper denture 1880,celluloid as aSubstitute for vulcanite was unsuccessful asIt absorbs stains and odors in the mouth,Gradually turns black and was flammable.

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.

Dentures made of polymethyl methacrylate

1. Vulcanite : In 1839 Vulcanized rubber was discovered and

introduced as a Vulcanite and Ebonite. For the next 75 years Vulcanite rubber was the

principal Denture base Material. But failed because of following reasons :

Disadvantages It absorbs Saliva and becomes unhygienic due to

bacterial proliferation. Esthetics were poor. Dimensionally unstable. Objectionable taste and odor

Disadvantages of different denture base

2. Celluloid Although it was having tissue like color

but having principal disadvantages like Disadvantages Lack of stability Unpleasant taste Unpleasant odor Stainability Flammable

3. Bakelite It was formed by heating and compressing

a mixture of phenol and formaldehyde.

Disadvantages Lack of uniform quality Variable strength Variable color Dimensional unstability.

Chronology of events

Charles Goodyear discovery of vulcanized rubber in 1839. John hyatt discovered celluloid in 1868 Dr Leo Bakeland discovered phenol-formaldehyde resin (Bakelite).

In the 1930’s Dr Walter Wright and the Vernon brothers working at the Rohn and Haas company in Philadelphia developed Polymethylmethacrylate (PMMA), a hard plastic.

Although other materials were used for dental prosthesis, none could come close to PMMA and by the 1940;s 95% of all dentures were made from this acrylic polymer.

POLYMERS

Natural polymers include:

Proteins (polyamides or polypeptides) containing the chemical group (-Co-NH-); this is known as an amide or peptide link.

Polyesoprenes such as rubber and gutta percha.

Polysaccharides, such as starch, cellulose, agar and alginates.

Polynucleic acids, such as deoxyribonuclei acids (DNA) and ribonucleic acids (RNA).

Synthetic polymers are produced industrially or in the laboratory, by chemical reaction.Synthetic polymer : Defined as a non metallic compound

synthetically produced (usually from organic compounds) which can be molded into various useful forms and then hardened for use.

MER or MONOMER Single organic molecule capable of uniting

MER or MONOMER Single organic molecule capable of uniting

METHYL METHACRYLATE (MMA) MONOMER

synthetic resins commonly used in dentistry

METHYL METHACRYLATE (MMA) MONOMER

synthetic resins commonly used in dentistry

METHYL METHACRYLATEMETHYL METHACRYLATE

CH3CH3

CC

CC

CH3CH3

OO

OO

HH

CC

HH

POLYMER Macromolecule formed by small repeating units called mers

POLYMER Macromolecule formed by small repeating units called mers

POLY(METHYL METHACRYLATE) (PMMA)

Large number of MMA units linked together

POLY(METHYL METHACRYLATE) (PMMA)

Large number of MMA units linked together

POLY(METHYL METHACRYLATE)POLY(METHYL METHACRYLATE)

HH CH3CH3

CC

CC

CC

CH3CH3

HH OO

OO

HH CH3CH3

CC

CC

CC

CH3CH3

HH OO

OO

HH CH3CH3

CC

CC

CC

CH3CH3

HH OO

OO

COPOLYMERIZATIONPolymerization of two or more different monomers at the same time

COPOLYMERIZATIONPolymerization of two or more different monomers at the same time

Dimer - Polymer from two different mers Terpolymer - Polymer from three

different mers

Dimer - Polymer from two different mers Terpolymer - Polymer from three

different mers

COPOLYMERSCOPOLYMERS

METHYL ETHYL METHACRYLATECOPOLYMER (DIMER)METHYL ETHYL METHACRYLATECOPOLYMER (DIMER)

CH3CH3

CC

CC

CH3CH3

OO

OO

CH2CH2

CH3CH3

CC

CC

C2H5C2H5

OO

OO

CH2CH2

mm

Methyl Ethyl

CH3CH3

CC

CC

CH3CH3

OO

OO

CH2CH2

CH3CH3

CC

CC

C2H5C2H5

OO

OO

CH2CH2

mm

CH3CH3

CC

CC

C4H9C4H9

OO

OO

CH2CH2

METHYL-, ETHYL-, BUTYL- METHACRYLATE

COPOLYMER (TERPOLYMER)

EthylMethyl Butyl

Linear Branched Cross-linked

Linear Branched Cross-linked

SPATIAL CONFIGURATION OF POLYMER MOLECULESSPATIAL CONFIGURATION OF POLYMER MOLECULES

LINEAR POLYMER linear chain of mers attached by primary bonds; may be either homo- or copolymer

LINEAR POLYMER linear chain of mers attached by primary bonds; may be either homo- or copolymer

LINEAR POLYMERSLINEAR POLYMERS

HomopolymerHomopolymer

Copolymer (random)Copolymer (random)

Copolymer (block)Copolymer (block)

BRANCHED POLYMER

Linear chains of mers with pendant linear chains; forces between intertwined chains and pendants are secondary

BRANCHED POLYMERSBRANCHED POLYMERS

HomopolymerHomopolymer

Copolymer (random)Copolymer (random)

CROSS-LINKED POLYMERFormation of primary bonds between linear chains resulting in a three-dimensional molecule

CROSS-LINKED POLYMERFormation of primary bonds between linear chains resulting in a three-dimensional molecule

CROSS-LINKED POLYMERCROSS-LINKED POLYMER

PLASTICIZERS

Used to reduce the brittleness of cross-linked polymers. Generally do not enter reaction, serve as interference for the cross-linking, or lubricant between chains

PLASTICIZERS

Used to reduce the brittleness of cross-linked polymers. Generally do not enter reaction, serve as interference for the cross-linking, or lubricant between chains

CC OO

OO

C4H9

OO

CC OO C4H9

PLASTICIZERPLASTICIZER(dibutyl phthalate)(dibutyl phthalate)

DEFINITION: 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).

USES IN DENTISTRY Denture bases and artificial teeth. Denture liners and tissue conditioners. composite restorative and pit and fissure sealent. Impression materials Custom trays for impression Temporary restoratives. Mouth-guards. Maxillofacial prosthesis. Space maintainers. Veneers. Cements and adhesives.

CHEMISTRY OF POLYMERIZATION Monomers react to form polymer by a chemical reaction called

polymerization. The most common polymerization reaction for polymers used in

dentistry is addition polymerization.

ADDITION POLYMERIZATION INDUCTION PROPOGATION CHAIN TRANSFER TERMINATION

INDUCTION 1)ACTIVATION 2)INITIATION

ACTIVATION Free radicals can be generated by activation of radical producing molecule using.

Second chemical Heat Visible light Ultraviolet light Energy transfer from another compound that acts as a free radical.

Commonly employed initiator is Benzoyl peroxide which is activated rapidly between 50 degree and 100 degree C to release two free radicals per benzoyl peroxide molecule.

Second type is chemically activated ,consists of two reactants when mixed undergo reaction eg tertiary amine (the activator) and benzoyl peroxide (the initiator). Amine forms a complex with benzoyl peroxide which reduces the thermal energy (and thus the temperature) needed to split it into free radicals.

Third type is light activated .The visible light light cured dental restoratives,camphorquinone and an organic amine (dimethylaminoethylmethacrylate) generate free radicals when irradiated by light in the blue to violet region.

Light with a wavelength of about 470nm is needed to trigger this reaction.

INITIATION STAGE Energy source forms free radicals which open double or triple carbon bonds in the monomer

INITIATION STAGE Energy source forms free radicals which open double or triple carbon bonds in the monomer

MONOMERethylene C2H4

INITIATIONOpening of double bond

INITIATION

PROPAGATION STAGE

Rapid addition of monomer molecules to free radical - free electrons shifted to end of chain

PROPAGATION STAGE

Rapid addition of monomer molecules to free radical - free electrons shifted to end of chain

PROPAGATION Realigning of molecules leading to addition of monomer molecules

The resulting free radical monomer complex acts as a new free radical center which is approached by another monomer to form a dimer, which also becomes a free radical.

PROPOGATION

CHAIN TRANSFER The active free radical of a growing chain is transferred to another

molecule (eg monomer or inactivated polymer chain) and a new free radical for further growth is created termination occurs in the latter.

TERMINATION STAGETERMINATION STAGE

Reaction terminates when insufficient free radicals exist. Reaction also may be stopped by any material that will react

with free radical, decreasing the rate of initiation, or increasing

rate of termination.

TERMINATIONdepletion of free radicals - formation of polyethylene (C2H4)n

TERMINATION Can occur from chain transfer. Addition polymerization reaction is terminated by -Direct coupling of two free radical chains ends -Exchange of hydrogen atom from one growing chain to

another.

INHIBITION OF ADDITION REACTION

Addition of small amount of Hydroquinone to the monomer inhibits spontaneous polymerization if no initiator is present and retards the polymerization in the presence of an initiator.

Amount added is 0.006% or less

Methyl ether of hydroquinone is generally present.

COPOLYMERIZATION When two or more chemically different monomers each with

desirable properties can be combined to yield specific physical property of a polymer .eg small amount of ethyl acrylate may be co-polymerized with methyl methacrylate to alter the flexibility and fracture resistance of a denture.

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. 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

Methyl methacrylatemolecule

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.

Conventional heat cure acrylic resins

Conventional cold cure acrylic resins

High impact resistant acrylic resin

Injection moulding resin

Rapid heat polymerizing resin

Light activated resin

COMPOSITION OF MONOMER

Methyl methacrylate

Main chemical which will polymerize

Hydroquinone (o.Oo3-o.1%)

Inhibitor while storage

Dibutyl phthalate

Plastisizer

Glycol dimethacrylate (1-2%)

Cross linking agent

Styrene vinyl acetate or ethyl methacrylate

As copolymers

PROPERTIES OF MONOMER

Typical smell of its own Clear, transparent liquid Boiling point 100.3*c Good organic solvent Can get evaporated Inflammable Stored in dark colored bottle Light weight Volumetric shrinkage of 21% It is a known allergen

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.

When MMA polymerizes it shrinks 21% by volume. Using a 3:1 powder liquid ratio it could be minimized to 6%. A correctly heat processed denture base could have as little as

0.3% to 2% residual monomer.

Manufacturing of monomer

Cyanide methodAcetone and hydrocynic acid

Phosgene methodPetroleum propylene and phosgene

Composition of polymer

Polymethyl methacrylate

main ingredient

Benzoil peroxide

0.5-1.5%, initiator

Dibutyl phthalate

8-10%, plasticizer

Zinc or tetanium oxide

opacifier

Composition of polymer

Mercuric sulfide or iron oxide or titanium oxide

- pigments and dyes

Glass fibres or beads or zirconium sulfate

- to increase stiffness

Nylon or acrylic fibres

- in veined type

- capillaries of gum

POLYMER POWDER OF ACRYLIC DENTURE BASE MATERIAL

Different types of polymer powder

Normal pink

-which resembles the normal pink

color of gum

Clear polymer

- no coloring agents are added

- indicated in palatal area

Translucent

Veined or deep veined

Properties of polymer powder

Stable at room temperature

- has long shelf life

Softening temperature

- 125 * c

- 125*-200*c

depolymerization occurs

- 450 *c

converted back to monomer

Absorbs water and soluble in chloroform

Properties of polymer powder

Tensile strength

- 600 kg/sq cm

Appearance

- shiny

- transparent

- slippery

Produced in two shapes

- spherical

- granular

Properties of polymer powder

Control of particle size

- no.52 sieve mesh

- 300 micrometer

If particle size is smaller

- softening will be quicker

- granular shape softens faster

Manufacturing of polymer powder

Spherical particles

By suspension polymerization

- monomer and water are mixed with an emulsifier i.e, powder talc.

- then the mixture is heated and stirred

- at the end talc is washed off to

get polymerized polymer particles

Granular particles

- solid block

- then it is grinded or milled

CURING CYLES EMPLOYED IN THE STUDYA Recommended curing cycles overnight water-bath cures: 1) 7hr at 70 C 2) 14hr at 70 C 3) 7hr at 70 C +1hr at 100C 4) 14hr at 70C + 1hr at 100CShort and reverse cures: 5) Boil water,insert flask , remove heat for 20 min return to boil for 10

min. 6) Boil water ,insert flask ,return to boil, boil for 10 min.Dry heat cure: 7)temp in excess of 100C using dry heat systemB Short curing cycles 8) 7hr at 60C 9) 7hr at 60C +1 hr at 90C 10) Boil water, insert flask remove heat for 20 min return to 90 C hold at

90C for 5 min 11) Boil water insert flask return to 90C hold at 90C for 5min.

(II)PHYSICAL PROPERTIES Should possess adequate strength and resiliency and

resistance to biting and chewing forces impact forces and excessive wear in oral cavity.

Should be dimensionally stable under all conditions of service including thermal changes and variations in loading.

I) Specific gravity: It should have low value of specific gravity in order that dentures should be as light as possible.

II) Thermal conductivity: It is defined as the number of calories per second flowing through an area of 1cm2 in which the temperature drop along the length of the specimen is 1°C/cm.

It should have high value of thermal conductivity

Radiopacity: It is the inhibition of passage of radiant energy. It should be ideally radiopaque

Glass transition temperature: It is the temperature at which molecular motions become

such that whole chains are able to move. It is close to softening temperature. At this temperature sudden change in elastic modulus occurs.

Amorphous polymer below Tg behave as rigid solids while above Tg they behave as viscous liquids, flexible solids or rubbers.

Increased chain branching Decreased Tg.Increased number of cross links Increased Tg

Effect of molecular weight on propertiesIn many polymers the chains are held together by secondary,

or Vander Waals forces and molecular entanglement. Materials of high molecular weight have a greater degree of molecular entanglement, and have greater rigidity and strength and higher values of Tg and melting temperature than low molecular weight polymers.

Effect of plasticizers Plasticizers penetrate between the randomly oriented

chains of polymer as a result of which molecules are further apart and forces between them are less. They soften the material and make it more flexible by lowering its Tg. They lubricate the movements of polymer chains and are sometimes added to help molding characteristics. This

principle is used in producing acrylic soft lining materials. Effect of fillers Modulus of elasticity and strength are generally increased. A degree of anisotropy exist, that is the strength depends

on the orientation of fibres in the polymers.

Viscoelasticity : Polymers show viscoelastic behavior. Elastic behavior is caused by uncoiling of polymer molecules. Plastic behavior is caused by breaking of intermolecular Vander Waals forces

(III) MANIPULATION Should not produce toxic fumes or dust Easy to mix, insert, shape and cure and short setting time Oxygen inhibition, saliva and blood contamination should have

little or no effect. Final product should be easy to polish and easy to repair in case of

breakage.

(IV) AESTHETIC PROPERTIES Should be translucent to match oral tissues Capable of pigmentation No change in color after fabrication.

(v)ECONOMIC CONSIDERATION Cost should be low Processing should not require complex and expensive instruments.

(VI) CHEMICAL STABILITY Conditions in mouth are demanding and only the most chemically

stable and inert materials can withstand such conditions without deterioration.

“No resin has yet met all of these ideal criteria”. Methacrylate polymers fulfill the aforementioned requirement reasonably well.

2)AUTOPOLYMERIZING/COLD CURE POLYMETHYL METHACRYLATE (POUR RESIN)

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.

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

Decreased transverse strength (residual monomer act as plastisizer).

Compromised biocompatibility (residual monomer) Color stability inferior (teriaty amine susceptible to

oxidation), stabilizing agents should be added

Fluid resin and compression molding technique can be employed for the fabrication of denture.

Also used as repair material

3)HIGH IMPACT RESISTANT 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 dentureBase showing size and shape of polystyrene-butadieneRubber inversion phase.

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

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). 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

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 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

8) FIBER –REINFORCED 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 strengthens the composite structure.

The reinforcing agent can be in the form of unidirectional, straight fiber or multidirectional weaves.

COMPRESSION MOLD TECHNIQUE

INJECTION MOULD TECHNIQUE

FLUID RESIN TECHNIQUE

MICROWAVE PROCESSING

LIGHT ACTIVATED DENTURE BASE RESINS

Compression mold technique

Primary impressions

Secondary impressions

Jaw relations

Try in stage

acrylization

flasking

dewaxing

packing- under pressure

curing

Precautions before flasking

Acceptance before demounting Proper finishing Periphery is sealed Petroleum jelly inner surface of the flask Casts Adjustment of the plaster model Plaster molels are wetted Wax dentures with casts are soaked

with slurry water

Flasking

“ The Art of Investing in a Flask ”

- GPT 99

“ The Process of Investing the Cast With the

Waxed Denture in a Flask to Make a Sectional

Mold Used to Form the Acrylic Resin Denture Base ”

- HEARTWELL

“ The process of investing the cast and a wax replica

of the desired form in a flask preparatory to molding

the restorative material into the desired product ”

surround or invest

“ a metal case or tube used in investing procedure”

- metal

- brass

- 3 or 4 parts

Flask

FLASKING

TWO POUR TECHNIQUE

THREE POUR TECHNIQUE

THREE POUR TECHNIQUE

Selection of flask Petroleum jelly lubrication Demounting done Preparation of the waxed denture

with the stone cast Soaking of the cast – slurry water Artificial stone is mixed Stone mix is placed in flask and wax

denture and casts are settled in to the mix

Periphery of flask should be in level with the rim of the flask

Occlusal plane – parallel to the base of the flask

Tilting of the casts

Retromolar pads and tuberosity- should be protected

Devoid of undercut

Shaping of the stone – blade or knife

Providing taper

Undercuts – removed or corrected

Distance from top lid – 6 mm

Stone is smoothened

Checking the seating of flask members

Invested flask & cast is washed in clear slurry water

Surface tension reducing agent is applied to the exposed wax

Separating medium is applied

Second mix is mixed

Hand spatulation

Mechanical spatulation-Under reduced atmospheric

pressure-Minimum air inclusion-Reduces finishing time

Stone is coated in occlusal & inter- Proximal areas with stiff brush

Stone is poured in flask Vibrator can be used In absence of vibrator Flask is filled till approximately ¼ of the

flask Stone is removed in incisal & occlusal

surfaces Stone is allowed to set

After the stone is set separating medium is coated

Occlusal & incisal surfaces shouldn’t be coated with the separating medium

Clear slurry is poured till the stone is mixed

Slurry is poured off, flask is filled with the stone

Lid is closed

Flask is clamped

Problems & solutions is Flasking

A. Flasks cannot be separated after dewaxing

Cause

Undercuts in flasking and casts

Improper application of separating medium

Solution

Examining the casts

Remove undercuts

Proper application of separating medium

B. Heel broken on mandibular cast

Cause

Undercut not blocked out

Solution

Blocking and protecting the heel area

C. Denture with acrylic blubs

Cause

-Investing stone not painted

Properly on waxed denture

During flasking

- Improper investing stone mix

Solution

- Paint investing stone on teeth

With brush

- Use of mechanical spatulator

The denture is taken out from the flask. It is then trimed Finally wet and dry polishing is done.

Finishing and polishing

Porosity Crazing Warpage Fracture

Denture defects

Presence of voids within structure of resin Porosity can be of two types

◦ Internal◦ External

Internal porosity is due to voids within the structure usually at thicker portion

Cause – due to vaporization of the monomer (100.8C)

Solution- long low temperature curing cycle is recommended.

porosity

POROSITY

External porosity is due porosities which occur near the surface of denture.

Cause ◦ Lack of homogeneity of dough.◦ Lack of adequate pressure.

Prevention – use proper monomer – powder ratio, packing in dough stage.

Crazing is formation of surface cracks on denture base resin.

Causes –◦ Incorportion of stress◦ Attack by solvent (alcohol)◦ Incorporation of water during processing.

Prevention◦ Avoidance of solvent◦ Proper use of separating media◦ Metal moulds◦ Use of cross linked acrylic

Crazing

CRAZING

Denture warpage is change in shape or fit of denture.

Cause is incorporation of stress in deture◦ Packing in late dough or rubbery stage.◦ Stress induced during curing◦ Improper deflasking◦ Rise in temp while polishing◦ Immersion of processed denture in hot water.

Denture warpage

Denture warpage

Improper deflasking Denture base excessively thin Accidental dropping at time of polishing

Denture fracture

Care to taken at time of dewaxing procedure

Rearticulation to be done after processing the denture to check of occllusal discrepancy.

Change in tooth position

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