DENTURE BASE

MATERIALS

CLASSIFICATION

BASED ON CHEMISTRY• Metals – Co Cr, Type IV Gold etc

• Non metals – Acrylics, Shellac etc

CLASSIFICATION

BASED ON DURABILITY

• Temporary – Self cure acrylic, Shellac etc.

• Permanent - Heat cure acrylic, metals etc

DENTURE

A removable dental prosthesis with artificial teeth attached to the base that replaces the masticatory surfaces and associated structures of maxillary or mandibular dental arch.

DENTURE BASE RESINS

• Acrylics• Vulcanite• Phenol

formaldehyde• Vinyl etc

REQUIREMENTS

• Color same as mucosa

• Translucent

• Less water sorption

• Non toxic and non irritant

• Tasteless, odorless

• Low sp gravity, i.e. low weight

• Dimensional stability if temp is changed

REQUIREMENTS

• Softening temp above oral temp

• Good thermal conductivity

• Easily available

• Easy to manipulate

REQUIREMENTS

• Fabrication and repair easy

• Radio opaque

• Strong

• Resilient

• Abrasion resistant

ACRYLIC RESINS

Derivatives of ethylene

Contain vinyl group (-C==C-)

TypesFrom acrylic acid CH2==CH-COOH

From methacrylic acid CH2==C(CH3)-COOH

COMPOSITION - Powder

PMMA -

Ethacrylate 5%- Copolymer

Dibutyl pthalate 10% - Plasticizer

Benzoil peroxide 0.5% - Initiator

COMPOSITION - Powder

Mercuric sulfide Red pigment

Cd sulfide Yellow

Ferric oxide Brown

Dyed Nylon fibers

Glass, Zr silicate Inorganic particles

10-15% Uranyl salts Opacifier

35% Zr di methacrylate Opacifier

USE OF INGREDIENTS

Copolymer – Increase solubility of PMMA

Polymer less brittle

Plasticizer – Soft resilient workable polymer

Pigments – for color

Initiator – Initiate free radical production

USE OF INGREDIENTS

Fibers – To duplicate BV & capillaries

Inorganic particles – Improve mech properties

Opacifier – To make resin radio opaque

Adv- Identified in X ray

Disadv - More water sorption

Less handling properties

More deflection

COMPOSITION - Liquid

• Methyl methacrylate – Monomer

• 0.6% Hydroquinone – Inhibitor

• 10% Dibutyl pthalate – Plasticizer

• Glycol di methacrylate – Cross linking agent

USE OF INGREDIENTS

• Monomer• Inhibitor – Retard polymerization

• Plasticizer – Increase workability

• Cross linking agent – Improve mech prop

PROPERTIES PMMA & CURED RESIN

• Odorless

• Tasteless

• Translucent

• Can be pigmented

• Density 11.9 gm/cm3• Mole wt – 50000-1000000 PMMA

1200000 Cured resin

PROPERTIES PMMA & CURED RESIN

• TS 55 MN/M2• CS 76 ,,

Strength affected bydesign of denturemole wt of polymerresidual monomerporosity & crazingforeign materialwater sorption

PROPERTIES PMMA & CURED RESIN

Elongation – 2%

Coe of thermal expn – 81units

Water solubility – 0.02 mg/cm2

Dimensional stability - water

sorption(rln)

PROPERTIES PMMA & CURED RESIN

Distortion temp – 95 degree

24 hr water sorption – 0.6 – 0.7 mg/cm2Less in ht cure type

Comp for poly shrinkage

Can act as plasticizer

PROPERTIES Monomer

MP – -48 degree

BP – 100.8 degree

HT OF POLYMERIZATION – 12.9Cal/Mol

POLY SHRINKAGE - 21%

CRAZING

Formation of macro/microscopic surface cracks in the denture.

Formed perpendicular to tensile stresses

Clinical appearance…

• HAZY

• FOGGY

Disadvantages…..

• Un-esthetic

• Weakening

Causes……….

• TS causing poly chain separation

• Release of internal stresses

• Solvents like alcohol

Contd…..

Causes……….

• Frequent repairs

• Frequent removal & insertion of prosthesis in mouth

• Around ceramic teeth

PREVENTION OF CRAZING

• Reinforced acrylic teeth

• Cross linked acrylic

• Place denture in water when not in use

Polymerization shrinkage

•Conventional heat cure – 0.43%•Conventional cold cure – 0.26%•Pour type – 0.48%•Rapid cure resin – 0.90%•High impact – 0.12%

POROSITY

Inclusion of surface and sub-surface voids in the denture that has undesirable effects on physical, esthetic & hygienic properties of the denture

Classification……

•External / Shrinkage•Internal / Gaseous

Clinical features – External porosity

•Occur anywhere•Uniform distribution•Cant be removed by trimming

•Resin appear pale

Causes of external porosity..

•Inadequate mixing•Excess monomer•Packing in wrong stage•Insufficient material in flask•Inadequate pressure of packing

Prevention of external porosity..

• Proper proportioning of P & L• Proper mixing• Adequate pressure• Pack in dough stage

C/F of internal porosity

•Non-uniform distribution•Seen in thick areas•Not present on surface

Causes of internal porosity

• Water in dough• Air incorporation• Impurity• No separating media• No bench cooling• Sudden temp raise

Prevention of internal porosity

•Long and low temp for curing

•Temp not above 100.8 degree

•No impurities

Disadvantages of porosity

• Poor color properties

• Less translucent• Low strength• More water sorption• Food accumulation• Bacterial growth• Less cleansable

Technical considerations

•Compression molding technique

• Injection molding technique

•Light technique•Fluid resin

method

COMPRESSION MOULDING

I. Finishing waxed denturesII. Mounting & investing

Remove master cast from articulatorApply separator on the castMount the cast in the lid of flask with

stone/plasterContour to facilitate wax elimination

• Upon reaching initial set coat a separator

• Place body of flask, apply ST reducing agent on wax & pour second mix of plaster

• Teeth can be splinted in stone• Place lid in position and close

III. Dewaxing & preparation of split mould

• Place the flask in boiling water for less than 5 mts.

• Pour hot water onto the split mould carefully to eliminate wax completely

• Pack when the flask is still warm

IV. Selection & application of separating medium

Uses

Prevent physical contact between resin & plaster

Water in plaster affect polymerization & optical properties of resin

If resin penetrate into plaster, cleaning & finishing of denture is difficult

Retrieval of denture is easy

Examples…

• Tin foil ( First material, Time consuming)

• Cellulose lacquers

• Soluble alginates (Cold mold seal)

• Soaps

• Sodium silicate

• Starches

• Calcium oleate

Cold mold seal

• Composition

Na/K Alginate

Glycerin

Alcohol

Na phosphate

Preservatives

Cold mold seal contd…

• PrecautionsNo residual waxWarm but not hot moldDon't apply over teethOne/two layer is enoughAvoid pooling of separating medium

Cold mold seal contd…

• MechanismNa/K alginate react with Ca in

gypsum forming calcium alginate. It forms a film over the mould wall.

V. Proportioning & mixing

• 3:1 by volume 2:1 by weight

• Dry glass or porcelain tumbler is used

• Dispense monomer and then sift polymer

• Cover the glass after mixing to prevent evaporation of monomer

Proportioning & mixing

• Less monomer

Less strength

Poor color

Porosity

• More monomer

Porosity

Polymerization shrinkage

VI. Identifying dough stage

5 distinct phases in mixed acrylic mass

Wet sandy

Stringy / Sticky

Dough / Plastic

Rubbery / Elastic

Stiff

1. Sandy

• Little / no molecular level interaction

• Mix coarse or grainy

• Fluid incoherent mass

2. Stringy

• Monomer penetrate polymer

• Uncoil polymer chains

• Viscosity increases

• Mass is stringy when touched with spatula

3.Dough

• More polymer enter the solution.

• Sea of monomer & dissolved polymer is formed

• Behaves like a pliable dough

• Not sticky and wont adhere to vessels and spatula

• Ideal for compression molding

Dough contd…

Dough forming time – The time required for the resin mixture to reach the dough like stage is called so.

ADA / ANSI Specification 12 --- <40 mts

10 mts

Dough contd…

Working time – The time that a denture base material remains in the dough like stage.

ADA / ANSI Specification 12 --- 5 mts (Minimum)

DFT & WT influenced by temparature

4. Rubbery

• Monomer disappear by evaporation & penetration

• More elastic

• Rebound on compression

• Highly viscous and poor flow

5. Stiff

• Reaches this stage if mix is allowed to remain for a long period

• Due to evaporation of monomer

VII. Packing

Placement and adaptation of denture base resin within the mold cavity is termed packing.

Mould should be packed properly

Under packing – Porosity

Over packing – Thick base

Do packing in several steps

•Do packing in dough stage

• Place resin in flask

• Wet polyethylene sheet is kept over the resin

• Reassemble the flask

• Apply force incrementally to ensure uniform flow of resin

• Close flask till it is fully closed

• Open flask remove excess (flash) wit knife

• This is called trial closure

• Repeat trial closure till no flash comes out

• No polyethylene sheet is necessary in the final closure

VIII. Injection molding

• Special flask is necessary

• Place sprue before second pour of plaster

• Do dewaxing , apply separating medium

• Clamp flask & inject resin

• During polymerization resin shrink. Add additional resin

IX. Bench cooling

Keep the flask 30-60 mts @ room temperature before curing. This is done for

• Pressure equalization in the mould

• Uniform dispersion of monomer

• Attachment of DBR to resin teeth

X. Polymerization procedure

• Resin contain Benzoil peroxide (initiator)• @ 60 degrees it release free radical (Ht activator)

• Heating process used to control the polymerization is termed curing / polymerization cycle

Polymerization procedure Contd…

• @ 70 degree, temperature of resin increase rapidly because of decomposition of Benzoil peroxide

• Resin & stone are poor thermal conductors

• Exothermic heat accumulate in resin

• Porosity appear if temperature go above 100.8 degree

Polymerization cycles

• 65 deg for 90 mts (thick), 100 deg for 1 hr (thin)

• 60-70 deg for 9 hr or more

• 74 deg for 8 hr (one step low heat tech)

• 74 deg for 8 hr, increase to 100 deg in 1 hr

• 74 deg for 2 hr, increase to 100 deg in 1 hr

• After acrylization cool slowly to room temp to avoid warpage

• Remove from bath and cool for 30 mts

• Keep in tap water for 15 mts

• Do deflasking, finishing, polishing and delivery.

Other sources of heating………

• Steam• Dry heat ( oven, electric plates)• Induction heating• Infra red heating• Microwave heating

Special resin and nonmetallic flasks are neededQuick polymerizationPhysical properties same as conventional resinFit of denture- same as conventional resin

CHEMICAL CURE ACRYLIC

Self cure acrylic

Auto polymerizing resin

Cold cure acrylic

Dimethyl p toluidine - Activator in monomer

Main difference - Mode activation of initiator

• Polymerization not as complete in heat cure resin

• Less shrinkage / more dimensionally stable

• Less color stability as amines get oxidized. Add stabilizing agents

• WT less

Uses……

• To make RPD / CD

• Special tray fabrication

• Repair

• Relining and rebasing

• To make orthodontic appliances

Technical considerations

• Compression molding technique

Same as heat cure

Only 2 trial closure possible as WT is less

Time for polymerization 30 mts

Maintain pressure for 3 hrs

• Salt pepper

• Hand adapted dough

Heat cure resin Vs Self cure resin

• Heat activated• Complete polymerization• High mole wt• Resi monomer .2 - .5%• Water sorption 0.21%• Less porous• Solubility 0.2 mg/cm2• More warpage• Low mucosa irritation

• Chemically activated• Incomplete• Low mole wt• 3 – 5 %• 3%• More porous• 0.05 mg / cm2• Less warpage• More irritation

LIGHT ACTIVATED RESIN

• Contain urethane di methacrylate

micro filled silica

high mole wt acrylic monomer

acrylic beads as filler

• Single component sheet & rope forms

• Special flask and investment needed

• Light is used to cure resin

FLUID / POUR TYPE RESINS

• Pourable chemically activated resin for denture bases

• Mount cast with waxed denture on the lid of flask

• Pour with agar

• Open flask remove cast with denture

• Attach sprues

• Dewax trial denture

• Replace cast in flask

• Place teeth in indentations in agar

• Pour resin through sprue

• Polymerization complete in 30-45mts

Advantages

• Good denture adaptation

• Less damage to cast during deflasking

• Cheaper than heat cure material

• Simple & less time consuming

• Trial closure not needed

Disadvantages

• Teeth position may change due to pressure

• Bond between DBR and teeth poor

• Technique sensitive

• Air entrapment in base

• Incomplete flow of resin

Radio opaque resins

• Acrylic is radio lucent

• Difficult to retrieve if ingested

• 10-15% uranyl salts or 35% zirconyl di methacrylate is added

• Disadvantages

More water sorption

Less handling properties

More transverse deflection

High impact / rubber reinforced resin Butadiene styrene rubber is grafted with

methacrylate which is dispersed in a PMMA matrix

AdvantagesHigh impact strengthLow stiffnessLess water sorption

DisadvantageTissue fit less

GEL TYPE RESIN

In gel form like vinyl resins

Components blended together, so can never be auto polymerization type

Only heat activated type available in market

Stiffer than conventional type

Rapid heat polymerized resin

• Hybrid resin

• Modified initiator

• 20 mt curing in hot water

Repair resin

• Auto poly acrylic

• Heat cure acrylic

• Light cure acrylic

• Vulcanite

a. Auto poly resins…• No warpage

• Room temperature curing

• Low TS

• High residual monomer

• More porosity

• More creep

• Poor color stability

b. Heat activated resins

• More TS

• Low porosity

• Low residual monomer

• Good color stability

• Warpage as heat needed

• More time consuming

c. Vulcanite

• Non toxic

• Non irritant

• Opaque so unaesthetic

• Dimensional shrinkage 2-4%

d. Light activated resin

• Supplied in sheets

• Should be adapted and contoured

• More TS

• Costly instruments needed

RELINE RESINS

The procedures used to resurface the tissue side of a removable dental prosthesis with new base material, thus producing an accurate adaptation to the denture foundation area.

Classification

• TemporaryHeat cure siliconAuto polymerization siliconPlasticized acrylic

• Permanent Heat cure acrylicSelf cure acrylicLight cure acrylic

• Direct

Chemical & light cure resins

• Indirect

Heat cure acrylic

• Chair side

Chemical & light cure resins

• Lab

Heat cure acrylic

• Hard

• Soft

Material pliable for 1- 2 years

Less chance for sore spots

• Therapeutic / temporary

In red, swollen tissue casesPoor bonding with base

More than 40% dimensional change

Can loose plasticizer

Candida growth

Resin teeth Vs ceramic teeth

• High fracture resistance• Significant wear • Grinding & polishing easy• No clicking• Chemical bond• Loss of VD• Minimum wear of natural

teeth• Less esthetic• Less color stable

• Low• Less• Difficult• Present• Mechanical • VD stable• Max wear

• More esthetic• More

TISSUE CONDITIONERSApplied to the fitting surface of a denture to provide cushion and prevent the masticatory load from being transferred to the underlying

bone

They are short term soft liners.

They are chemically activated polymeric materials that tend to degrade more rapidly than heat

activated resins.

Indications…

• To promote recovery of tissues

• Post surgical care

• Immediate denture base

• Final impression to register tissues

Examples…

• Auto polymerized silicon (Best)

• Heat activated silicon (Best)

• Acrylic with butane instead of methane

• Plasticized acrylic

• PVC

Plasticized acrylic…

• PowderPMMA / Poly ethyl methacrylate

• Liquid60-80% plasticizer (Dibutyl

pthalate)

Cause slip in polymer

Change in linear pattern

Cushioning effect

• Heat cure type lasts long

• Self cure type lasts short and called tissue conditioner

• When plasticizer leaches out, liner become rigid

• PEMA is more durable

Denture cleaners

• Don’t use hot water to clean dentures as it causes warpage

• Light brushing help to clean dentures

• Clean daily

Requirements…

• Non toxic

• Non allergic

• Non irritant

• Dissolve deposits

• Microcidal

Types…

• Abrasive powder & paste

Eg- Calcium carbonate ( But abrade resin & teeth)

• Sodium per borate (May not dissolve had deposits, harmful to resin)

• Hypochlorite solutions (Dissolve mucoprotiens, May cause bleaching)

• Enzyme cleaners ( Proteolytic enzymes break organic compounds of deposits)