Composite Resins Composite Resins Dr.Shahbaz Ahmed BDS, MSc (UK), FCPS (Pak) Assistant Professor Department of Operative Dentistry DIKIOHS
Composite ResinsComposite Resins
Dr.Shahbaz Ahmed
BDS, MSc (UK), FCPS (Pak)
Assistant Professor
Department of Operative Dentistry
DIKIOHS
Overview
• Direct restoratives– Composition– Classification– Performance factors
• Forms
- Flowable
- Packables
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
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’
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
Indications
• Anterior restorations
• Posterior restorations– preventive resin– conservative class 1 or 2– cuspal coverage– core Build up- materials
Contraindications
• Large posterior restorations
• Bruxism
• Poor isolation
Advantages
• Esthetics
• Conservation of tooth structure
• Adhesion to tooth structure
• Low thermal conductivity
• Alternative to amalgam
Disadvantages
• Technique sensitivity
• Polymerization shrinkage – marginal leakage– secondary caries– postoperative sensitivity
• Decreased wear resistance
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
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
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
Monomers
• Shrinkage– 2 – 7 %– marginal gap
formation
Filler Particles
• Crystalline quartz– larger particles– not polishable
• Silica glass– barium
– strontium– Lithium
- Polishable
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
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
Inhibitors
• Prevents spontaneous polymer formation
• Extends shelf life
• Butylated Hydroxytoluene
Pigments and UV Absorbers
• Pigments– metal oxides
• provide shading and opacity
• titanium and aluminum oxides
• UV absorbers– prevent discoloration– acts like a “sunscreen”
• Benzophenone
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
Polymerization
• Initiation– production of reactive free radicals
• typically with light for restorative materials
• Propagation– hundreds of monomer units– polymer network
• Termination
Classification System
• Matrix composition
• Method of cure
• Filler content
• Filler particle size– traditional ( macrofilled)– microfilled– small particle – hybrid
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
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
Performance Factors
• Material factors– biocompatibility– polymerization shrinkage– wear resistance– polish mechanisms– placement types – mechanical & physical properties
Biocompatibility
• Tolerated by pulp– with good seal
• Rare allergic reactions– HEMA
• Cytotoxicity– short lived
• Degree of cure important– decrease free monomer
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
Polymerization Shrinkage• Significant role in restoration failure
– gap formation• secondary caries formation
• marginal leakage
• post-operative sensitivity
• Counteract– lower shrinkage composites– incremental placement
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
Polish Mechanisms
• Acquired polish– clinician induced
• Inherent polish– ultimate surface
Composite Selection
• Anterior/stress (Class 4)– hybrid
• mini- or midi-fill
– hybrid/microfill
• Anterior/non-stress (Class 3 or 5)– hybrid
• mini-fill
– microfill
Composite Selection
• Posterior composites– hybrid
• mini- or midi-fill
– reinforced microfill
Composite Variants
• Packable
• Flowable
Packable Composites
• Marketed for posterior use– increase in viscosity
• better proximal contacts • handle like amalgam?
• Subtle alteration of filler– shape– size– particle distribution
Flowable Composites
• Marketed – class 1, 3, 5– liner
• Particle size similar to hybrid composites• Reduced filler content
– reduces viscosity
Flowable Composites
• Clinical applications– preventive resin restorations– small Class 5– provisional repair– composite repair– Liners ??
Future Composites
• Low-shrinking monomers
• Self-adhesive ?
Composite Curing
• Original composites (Chemical cured)
• UV- Light curing
• Visible light curing
- “ Dual curing”
Light curing
• Quartz- Tungsten Halogen (QTH)
• Light- emitting diode (LED)
• Plasma Arc
• Laser
Light Curing variables
Curing equipment factors
• Bulb degradation
• Light reflector degradation
• Optical filter degradation
• Light guide fracture
• Tip contamination
• Sterilization problems ?
– Infection control barriers
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
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”
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 ?
• Pulse delay technique
• Used with final increment
• Waiting period between exposures – shape occlusal surface
• Improved physical properties?
C- Factor – Cavity Configuration
C=C=BONDED WALLSBONDED WALLS
C-FACTORC-FACTOR
UNBONDED WALLS
Smooth surface restoration
C=C= 1155
C-FACTORC-FACTOR 0.20.2
BondedBonded
UnbondedUnbonded
Two walled cavity
C=C= 2244
C-FACTORC-FACTOR 0.50.5
CAVITY CLASSCAVITY CLASS IVIV
BondedBonded
UnbondedUnbonded
Three walled cavity
C=C= 3333
C-FACTORC-FACTOR 11
CAVITY CLASSCAVITY CLASS IIIIII
BondedBonded
UnbondedUnbonded
Four walled cavity
C=C= 4422
C-FACTORC-FACTOR 22
CAVITY CLASSCAVITY CLASS IIII
BondedBonded
UnbondedUnbonded
Five walled cavity
C=C= 5511
C-FACTORC-FACTOR 55
CAVITY CLASSCAVITY CLASS V & I V & I
BondedBonded
UnbondedUnbonded
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
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
Acid Etching / ConditioningAcid Etching / Conditioning
History
Buonocore 1955, applied acid to teeth
‘ Render the tooth surface more
receptive to adhesion’
Theories of Adhesion
• Mechanical
• micromechanical interlocking
• Adsorption - chemical bonds
• Primary - ionic and covalent
• Secondary - hydrogen, van der Waals
Acid Etchants / Conditioners
• Citric acid
• lactic acid
• Maleic acid
• EDTA• Phosphoric acid - a strong inorganic acid
(30% - 50%) most commonly used for etching
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
Etched Enamel
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
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)
Conditioned Dentine
Important considerations
• Kind of acid
• Application time
• Acid concentration and pH
• Distance between tubules
• Type of dentine
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
Thank You