composite and acid etching
TRANSCRIPT
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Composite ResinsComposite Resins
Dr.Shahbaz Ahmed
BDS, MSc (UK), FCPS (Pak)
Assistant Professor
Department of Operative Dentistry
DIKIOHS
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Overview
• Direct restoratives– Composition– Classification– Performance factors
• Forms
- Flowable
- Packables
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Composite• Material with two or more distinct substances
– metals, ceramics, or polymers
• Dental resin composite– soft organic-resin matrix
• polymer
– hard, inorganic-filler particles• glass particles
• Most frequently used– esthetic-restorative material
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History
• 1871 – silicate cements – alumina-silica glass &
phosphoric acid– very soluble– poor mechanical properties
• 1948 – acrylic resins – polymethylmethacrylate– high polymerization shrinkage– Known as ‘Unfilled acrylics’
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History(cont.)
• 1962 – Bis-GMA– stronger resin
• 1969 – filled composite resin– improved mechanical properties
– less shrinkage
– paste/paste system
• 1970’s – acid etching and microfills• 1980’s – light curing and hybrids• 1990’s – flowables and packables• 2000’s – nanofills
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Indications
• Anterior restorations
• Posterior restorations– preventive resin– conservative class 1 or 2– cuspal coverage– core Build up- materials
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Contraindications
• Large posterior restorations
• Bruxism
• Poor isolation
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Advantages
• Esthetics
• Conservation of tooth structure
• Adhesion to tooth structure
• Low thermal conductivity
• Alternative to amalgam
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Disadvantages
• Technique sensitivity
• Polymerization shrinkage – marginal leakage– secondary caries– postoperative sensitivity
• Decreased wear resistance
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Composition• Resin matrix
– Monomer – initiator– inhibitors– pigments
• Inorganic filler– glass– quartz– colloidal silica
• Coupling Agent - Silane agent
OCH2CHCH2O-C-C=CH2CH2=C-C-O-CH2CH-CH2O -C-
CH3 CH3
CH3
CH3OH OH
O O
Bis-GMA
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Monomers• Binds filler particles together• Provides “workability”• Typical monomers
– Bisphenol A glycidyl methacrylate (Bis-GMA)
– Urethane dimethacrylate (UEDMA)
– Triethylene glycol dimethacrylate (TEGMA) Lower viscosity Diluent
CH2=C-C-O-CH2CH2-O-C-NHCH2CH2CHCH2-C-CH2-NH-C-
CH3
CH3
OCH2CH2O-C-C=CH2
CH3
O OOO
CH3
CH3
OCH2CHCH2O-C-C=CH2CH2=C-C-O-CH2CH-CH2O -C-
CH3 CH3
CH3
CH3OH OH
O O
CH2=C-C-O-CH2CH2-OCH2CH2
CH3
OCH2CH2O-C-C=CH2
CH3
O O
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Monomers• Bis-GMA
– extremely viscous– lowered by adding TEGDMA
• freely movable
• increases polymer conversion• increases crosslinking• increases shrinkage
CH2=C-C-O-CH2CH-CH2O -C- OCH2CHCH2O-C-C=CH2
CH3 CH3
CH3
CH3OH OH
O O
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Monomers
• Shrinkage– 2 – 7 %– marginal gap
formation
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Filler Particles
• Crystalline quartz– larger particles– not polishable
• Silica glass– barium
– strontium– Lithium
- Polishable
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Filler Particles
• Increase fillers, increase mechanical properties– strength
– abrasion resistance
– esthetics
– handling
0
0.5
1
1.5
2
Fra
ctur
e T
ough
ness
0 28 37 48 53 62
% Filler Volume
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Coupling Agent
• Chemical bond– filler particle - resin matrix
• Organosilane (bifunctional molecule)– siloxane end bonds to hydroxyl groups on filler– methacrylate end polymerizes with resin
CH3-C-C-O-CH2-CH2-CH2-Si-OH
CH2
O OH
OH
Bonds with filler
Silane
Bis-GMABonds with resin
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Inhibitors
• Prevents spontaneous polymer formation
• Extends shelf life
• Butylated Hydroxytoluene
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Pigments and UV Absorbers
• Pigments– metal oxides
• provide shading and opacity
• titanium and aluminum oxides
• UV absorbers– prevent discoloration– acts like a “sunscreen”
• Benzophenone
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Visible-Light Activation• Camphorquinone
– most common photoinitiator• absorbs blue light
– 400 – 500 nm range
• Initiator reacts with amine activator
• Forms free radicals
• Initiates addition polymerization
OCH2CHCH2O-C-C=CH2CH2=C-C-O-CH2CH-CH2O -C-
CH3 CH3
CH3
CH3OH OH
O O
Bis-GMA
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Polymerization
• Initiation– production of reactive free radicals
• typically with light for restorative materials
• Propagation– hundreds of monomer units– polymer network
• Termination
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Classification System
• Matrix composition
• Method of cure
• Filler content
• Filler particle size– traditional ( macrofilled)– microfilled– small particle – hybrid
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Newer Classification System
• Based on particle size– megafill
• 0.5–2 millimeters– macrofill
• 10–100 microns– midifill
• 1–10 microns– minifill
• 0.1–1 microns– microfill
• 0.01–0.1 microns– nanofill
• 0.005–0.01 microns
• Most new systems– minifillers
• Newest trend – nanofillers
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Nanofilled Composite
• Filtek Supreme (3M ESPE)
• Filler particles– filled: 78% wgt– nanomers
• 0.02 – 0.07 microns
– nanocluster• act as single unit
– 0.6 – 1.4 microns
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Performance Factors
• Material factors– biocompatibility– polymerization shrinkage– wear resistance– polish mechanisms– placement types – mechanical & physical properties
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Biocompatibility
• Tolerated by pulp– with good seal
• Rare allergic reactions– HEMA
• Cytotoxicity– short lived
• Degree of cure important– decrease free monomer
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Systemic• Estrogenic effects seen in cell cultures
– impurities in Bis-GMA-based resins• Bis-phenol A in sealants
– Olea, EHP 1996
– however, insignificant short-term risk
• literature review– Soderholm, JADA 1999
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Polymerization Shrinkage• Significant role in restoration failure
– gap formation• secondary caries formation
• marginal leakage
• post-operative sensitivity
• Counteract– lower shrinkage composites– incremental placement
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Composite Wear• Less wear
– small particle size• less abrasion
– heavier filled• less attrition
– non-contact areas• 3 - 5 times less
– less surface area– anterior location
• premolars vs. molars
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Polish Mechanisms
• Acquired polish– clinician induced
• Inherent polish– ultimate surface
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Composite Selection
• Anterior/stress (Class 4)– hybrid
• mini- or midi-fill
– hybrid/microfill
• Anterior/non-stress (Class 3 or 5)– hybrid
• mini-fill
– microfill
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Composite Selection
• Posterior composites– hybrid
• mini- or midi-fill
– reinforced microfill
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Composite Variants
• Packable
• Flowable
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Packable Composites
• Marketed for posterior use– increase in viscosity
• better proximal contacts • handle like amalgam?
• Subtle alteration of filler– shape– size– particle distribution
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Flowable Composites
• Marketed – class 1, 3, 5– liner
• Particle size similar to hybrid composites• Reduced filler content
– reduces viscosity
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Flowable Composites
• Clinical applications– preventive resin restorations– small Class 5– provisional repair– composite repair– Liners ??
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Future Composites
• Low-shrinking monomers
• Self-adhesive ?
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Composite Curing
• Original composites (Chemical cured)
• UV- Light curing
• Visible light curing
- “ Dual curing”
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Light curing
• Quartz- Tungsten Halogen (QTH)
• Light- emitting diode (LED)
• Plasma Arc
• Laser
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Light Curing variables
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Curing equipment factors
• Bulb degradation
• Light reflector degradation
• Optical filter degradation
• Light guide fracture
• Tip contamination
• Sterilization problems ?
– Infection control barriers
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Procedural factors
• Light tip direction - adjacent to the surface
• Access to restoration – light transmitting wedges
• Distance from surface – 1-2mm ideally
• Size of tip
• Tip movement• Time of exposure – minimum of 20 secs
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Restoration factors
• Restoration thickness – 1.5 to 2mm incrementally
• Cavity design – C Factor
• Filler amount – scatter light
• Restoration shade – darker shades decrease depth of cure – 1mm increment, Increase curing time
__ “ Post Curing”
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Curing methods
• Stepped or Soft start
- Start at low intensity 2-10 seconds
and later increase intensity
- Decreases stress, marginal leakage
and fewer gaps
- Increases mechanical properties
- Controversial ?
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• Pulse delay technique
• Used with final increment
• Waiting period between exposures – shape occlusal surface
• Improved physical properties?
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C- Factor – Cavity Configuration
C=C=BONDED WALLSBONDED WALLS
C-FACTORC-FACTOR
UNBONDED WALLS
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Smooth surface restoration
C=C= 1155
C-FACTORC-FACTOR 0.20.2
BondedBonded
UnbondedUnbonded
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Two walled cavity
C=C= 2244
C-FACTORC-FACTOR 0.50.5
CAVITY CLASSCAVITY CLASS IVIV
BondedBonded
UnbondedUnbonded
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Three walled cavity
C=C= 3333
C-FACTORC-FACTOR 11
CAVITY CLASSCAVITY CLASS IIIIII
BondedBonded
UnbondedUnbonded
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Four walled cavity
C=C= 4422
C-FACTORC-FACTOR 22
CAVITY CLASSCAVITY CLASS IIII
BondedBonded
UnbondedUnbonded
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Five walled cavity
C=C= 5511
C-FACTORC-FACTOR 55
CAVITY CLASSCAVITY CLASS V & I V & I
BondedBonded
UnbondedUnbonded
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C-Factor
• Increasing C-Factor increases the shrinkage stress loading on the tooth-resin interface leading to de-bonding
• Once failure occurs, post insertion sensitivity and recurrent caries can become a problem
• C-Factor problem is a consequence of resin chemistry
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Possible solutions
• Don’t cut G.V.Black style cavity preps
• Bonded base or Sandwich techniqueBonded base or Sandwich technique
• Incremental placementIncremental placement
• Restoration sectioningRestoration sectioning
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Acid Etching / ConditioningAcid Etching / Conditioning
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History
Buonocore 1955, applied acid to teeth
‘ Render the tooth surface more
receptive to adhesion’
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Theories of Adhesion
• Mechanical
• micromechanical interlocking
• Adsorption - chemical bonds
• Primary - ionic and covalent
• Secondary - hydrogen, van der Waals
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Acid Etchants / Conditioners
• Citric acid
• lactic acid
• Maleic acid
• EDTA• Phosphoric acid - a strong inorganic acid
(30% - 50%) most commonly used for etching
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Conditioning Enamel
• Removes 10 microns of surface and creates microporous layer
• Three etching patterns
- Type I – Core etching
- Type II – Periphery etching
- Type III – Mixed patterns
• Resin tags
- Macrotags
- Microtags
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Etched Enamel
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Important considerations
• Type of acid• Acid Concentration• Etching time• Form of etchant• Enamel instrumented prior• Condition of enamel• Primary or permanent enamel• Prism or prismless enamel
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Conditioning Dentine
• Chemical alteration of dentine
• Objective is to remove the smear layer
• Demineralizing the dentine to expose a microporous scaffold of collagen fibrils
(Hybrid layer)
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Conditioned Dentine
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Important considerations
• Kind of acid
• Application time
• Acid concentration and pH
• Distance between tubules
• Type of dentine
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Acid Etching
• Enamel• Selective Demineralization• Increases surface area• Increases life of composite• Decreases marginal staining• Decreases secondary caries• Decreases post-operative
sensitivity• Permits efficient wetting by
hydrophobic resin• Tag formation in
microporosities
• Dentine• Demineralizes dentine
surface• Opens dentinal tubules• Exposes collagen
• Conditions dentine for better wetting of the primer
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Thank You