Composite Properties And Principles Flashcards
What are the 3 phases in composite resin
Organic phase, dispersed phase, interfacial phase
What key monomer does all composites have
Bis-GMA (bisphenol glycidyl methacrylate)
Some features of Bis GMA
Colourless Undergoes high cross linkage Viscous Polymerisation strongly inhibited by air Lower polymerisation shrinkage (5-6%) Radiolucent Rapidly hardens and polymerises under oral conditions Hydrophobic
What is TEGDMA added for (2)
Reduce viscosity of resin matrix ie viscosity controller
Diluent to attain high filler levels
Does BISGMA have high degree of conversion
No! BISGMA has lowest degree of conversion
How does degree of conversion affect water sorption of material
Lower degree of conversion, increased residual monomer. There are more spaces between greater number of monomers, hence prone to contraction and degradation by water —> increased water sorption
What is camphorquinone
Photochemical initiator
Very yellow, absorbs blue light (491-424nm) then start polymerisation
Max excitation of camphorquinone at what wavelength
468nm
What is the role of benzoyl peroxide
Catalyst for thermochemical initiators, which result in free radicals to initiate polymerisation
How is premature polymerisation prevented
Inhibitors eg hydroquinone
Black syringe, less light transmitted to composite
Keep in fridge, less polymerisation at lower temperature
What is function of uv light absorber
Reduce risk of composite discoloration when irradiated with strong uv
What makes up interfacial phase
Silane coupling agent
Function of coupling agent
Bond filler to matrix
Promote wettability and dispersion of filler particles
Decrease viscosity
Improve physical and mechanical properties by bonding fillers
Effect of dispersed phase on composite
Dispersed phase is filler particles
Make composite harder, denser, more resistant to wear and fracture
Reduce polymerisation shrinkage (since fillers don’t shrink)
Reduce water sorption
Improve translucency and handling
Increase viscosity
How much of composite is made up of fillers by weight
More than 50%
How does filler content affect polymerisation shrinkage
Increased VOLUME = decreased matrix= contract less
Fillers do not contract
Name some advantages of quartz fillers
Strong and hard
Highly aesthetic
Disadvantages of quartz fillers
Difficult to polish
Abrasive to opposing teeth/restorations
Advantages of glass fillers with heavy metals
Adequate refractive index
Provide radioopacity
Disadvantages of glass fillers
Lease inert
Leaches and weakens in acidic juices
More susceptible to wear
Shorter functional lifetime
What is the filler loading of icrofillers
30-50%
Some properties of microfillers
Makes resin very viscous, good handling properties
Lower filler loading
Excellent polishability and aesthetics
Low fracture resistance ie poor mechanical properties
Good wear resistance
Problems with loading microfillers directly to resin
Low percentage loading
Tend to agglomerate to form bigger particles
Increase internal friction of mixture
Mixture unmanageably viscous
Contraindications of microfileld cr
High stress bearing areas, eg class 4 (incisal edge)
Cusps in posterior teeth
Because deforms early under stress and lower fracture resistance
Hybrid fillers proeprties
High strength and fracture resistance
Good polishability
High filler loading
Good wear resistance
Indications of hybrid filler composite
High stress area
Larger restorations
Why does bisgma have low polymerisation shrinkage
Big monomer
Thermal property of composite resin
Poor conductor of heat
Hardly transmit thermal change to pulp hence less pulp sensitivity
Less cyclic dimensional change vs amalgam, decreased tooth structure fatigue and cusp fracture
Is composite resin radio opaque
Yes
Discuss cytotoxicity of composite resin
Biocompatible
Increased curing time means less cytotoxicity because less residual monomer (leakage of bisphenol A from bisgma)
What is the polymerisation shrinkage of composite
1.2-2%
What is the polymerisation shrinkage of methyl methacrylate
20%
What is the polymerisation shrinkage of bisgma
2.6-7.1%
In what direction does shrinkage occur in composite resin
CR pulls away from least retentive surface towards most retentive wall
What is the c factor
Ratio of number bonded surfaces to number of unbonded surfaces
How does c factor affect adhesive bond
Higher c factor = higher contraction stress of adhesive bond
Effects of water on CR
Water is preferentially absorbed into resin component of CR
It swells the resin matrix, weaking the resin-filler bond. Water sorption causes polymers to be arranged more linearly, weaker, loss of mechanical properties. Resulting debond = hydrolytic degradation
Swelling can compensate for polymerisation shrinkage to some degree (close adaptation without adhesion
Water also act as plasticiser, lowering viscosity
Abrasion vs attrition
Abrasion is generalised wear across entire occlusal surface due to abrasive action during mastication
Attrition is loss of material due to direct contact with opposing tooth surfaces at occlusal contacts of restoration
Microfills vs hybrid fillers in the way they respond to attrition and abrasion
Microfills are subject to attrition. More resistant to abrasion due to smoother surface —> less interparticulate space —> less friction
Hybrids more resistant to attrition. Larger particle size result in higher abrasion wear.
Composite resin modulus of elasticity vs that of amalgam
Low. CR elastic deformation 6x more than amalgam
Low modulus = less rigid, deform more under masticatory forces
Low resistance to occlusal loading
How to calculate elastic modulus
Tension (N)/ deformation (mm)
What can increase in filler fraction achieve
Greater wear resistance
Decrease setting contraction because less monomer
Greater compressive and tensile strength, ie greater modulus of elasticity
Less thermal expansion
Increased fracture resistance
Decreased CLT, decreasing mismatch
For amalgam, gic, cr, ceramic, rank flexure strength, fracture toughness, tensile strength
Ceramic most
Cr more or equal to amalgam
More than gic
Point of GIC liner
Protect pulp
Less polymerisation stress and shrinkage
Fluoride release
Improve marginal integrity
How does CLT of CR compare with that of tooth structure
CLT of CR is greater, leading to marginal gap formation, fracture of enamel or CR due to expansion. Increase in filler loading will increase mismatch
What is the effect of adding low viscosity small monomers like TEGDMA and MMA
Improve handling properties by reducing viscosity (bisgma too viscous)
Increase polymerisation shrinkage
Advantages of using smaller particles for filler loading
Better optical properties ie more aesthetic. Excellent polishability. Higher refractive index results in most realistic translucency
How big are microfillers
0.01-1um, 0.04um
How large are midi filliers
1-10um
How big are minifillers
0.1-1um
How big are nanofillers
0.005-0.01um
Properties of microfillers
Make resin viscous, improve handling
Low filler loading
Excellent polishability
Poor mechanical properties, low fracture resistance
Good wear resistance
Difference between filler loading of flowable and packable composite
Flowable less viscous = lower filler content
Which leads to higher polymerisation shrinkage, lower mechanical properties, less hardness, less radioopacity
What is the filler loading by weight and volume fo hybrid minifills
85% by weight 70% by volume
Microhybrid vs microfiller
Microhybrid is less polishable, difficult to marginate, wears faster than microfiller
Increased strength due to larger particle size (0.4-0.6um)
What does filler volume fraction affect
Elastic modulus (rigidity)
Fracture strength
Fracture toughness
How large are particles in agglomerated microfiller heterogenous complexes
0.3-50um
Filler particles artificially agglomerated via hydrolysis or precipitation
Hybrid vs agglomeration
Both have large and small particles
But in agglomeration, large and small particles are of same material milled into different sizes
In hybrid, different types of inorganic fillers are used eg. Large ground glass and small silicon dioxide in midifill
How do fillers increase mechanical properties
When force is applied, crack will go around filler particle as silane is path of least resistance
Larger filler —> crack take more time to go around
