sample presentation - denture base materials
TRANSCRIPT
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)