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Dental Materials Y2 > Composite Properties And Principles > Flashcards

Composite Properties And Principles Flashcards

(59 cards)

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1
Q

What are the 3 phases in composite resin

A

Organic phase, dispersed phase, interfacial phase

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2
Q

What key monomer does all composites have

A

Bis-GMA (bisphenol glycidyl methacrylate)

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3
Q

Some features of Bis GMA

A 
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
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4
Q

What is TEGDMA added for (2)

A

Reduce viscosity of resin matrix ie viscosity controller

Diluent to attain high filler levels

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5
Q

Does BISGMA have high degree of conversion

A

No! BISGMA has lowest degree of conversion

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6
Q

How does degree of conversion affect water sorption of material

A

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

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7
Q

What is camphorquinone

A

Photochemical initiator

Very yellow, absorbs blue light (491-424nm) then start polymerisation

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8
Q

Max excitation of camphorquinone at what wavelength

A

468nm

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9
Q

What is the role of benzoyl peroxide

A

Catalyst for thermochemical initiators, which result in free radicals to initiate polymerisation

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10
Q

How is premature polymerisation prevented

A

Inhibitors eg hydroquinone

Black syringe, less light transmitted to composite

Keep in fridge, less polymerisation at lower temperature

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11
Q

What is function of uv light absorber

A

Reduce risk of composite discoloration when irradiated with strong uv

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12
Q

What makes up interfacial phase

A

Silane coupling agent

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13
Q

Function of coupling agent

A

Bond filler to matrix

Promote wettability and dispersion of filler particles

Decrease viscosity

Improve physical and mechanical properties by bonding fillers

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14
Q

Effect of dispersed phase on composite

A

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

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15
Q

How much of composite is made up of fillers by weight

A

More than 50%

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16
Q

How does filler content affect polymerisation shrinkage

A

Increased VOLUME = decreased matrix= contract less

Fillers do not contract

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17
Q

Name some advantages of quartz fillers

A

Strong and hard

Highly aesthetic

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18
Q

Disadvantages of quartz fillers

A

Difficult to polish

Abrasive to opposing teeth/restorations

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19
Q

Advantages of glass fillers with heavy metals

A

Adequate refractive index

Provide radioopacity

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20
Q

Disadvantages of glass fillers

A

Lease inert

Leaches and weakens in acidic juices

More susceptible to wear

Shorter functional lifetime

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21
Q

What is the filler loading of icrofillers

A

30-50%

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22
Q

Some properties of microfillers

A

Makes resin very viscous, good handling properties

Lower filler loading

Excellent polishability and aesthetics

Low fracture resistance ie poor mechanical properties

Good wear resistance

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23
Q

Problems with loading microfillers directly to resin

A

Low percentage loading

Tend to agglomerate to form bigger particles

Increase internal friction of mixture

Mixture unmanageably viscous

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24
Q

Contraindications of microfileld cr

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A

High stress bearing areas, eg class 4 (incisal edge)

Cusps in posterior teeth

Because deforms early under stress and lower fracture resistance

25
Hybrid fillers proeprties
High strength and fracture resistance Good polishability High filler loading Good wear resistance
26
Indications of hybrid filler composite
High stress area Larger restorations
27
Why does bisgma have low polymerisation shrinkage
Big monomer
28
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
29
Is composite resin radio opaque
Yes
30
Discuss cytotoxicity of composite resin
Biocompatible Increased curing time means less cytotoxicity because less residual monomer (leakage of bisphenol A from bisgma)
31
What is the polymerisation shrinkage of composite
1.2-2%
32
What is the polymerisation shrinkage of methyl methacrylate
20%
33
What is the polymerisation shrinkage of bisgma
2.6-7.1%
34
In what direction does shrinkage occur in composite resin
CR pulls away from least retentive surface towards most retentive wall
35
What is the c factor
Ratio of number bonded surfaces to number of unbonded surfaces
36
How does c factor affect adhesive bond
Higher c factor = higher contraction stress of adhesive bond
37
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
38
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
39
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.
40
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
41
How to calculate elastic modulus
Tension (N)/ deformation (mm)
42
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
43
For amalgam, gic, cr, ceramic, rank flexure strength, fracture toughness, tensile strength
Ceramic most Cr more or equal to amalgam More than gic
44
Point of GIC liner
Protect pulp Less polymerisation stress and shrinkage Fluoride release Improve marginal integrity
45
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
46
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
47
Advantages of using smaller particles for filler loading
Better optical properties ie more aesthetic. Excellent polishability. Higher refractive index results in most realistic translucency
48
How big are microfillers
0.01-1um, 0.04um
49
How large are midi filliers
1-10um
50
How big are minifillers
0.1-1um
51
How big are nanofillers
0.005-0.01um
52
Properties of microfillers
Make resin viscous, improve handling Low filler loading Excellent polishability Poor mechanical properties, low fracture resistance Good wear resistance
53
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
54
What is the filler loading by weight and volume fo hybrid minifills
85% by weight 70% by volume
55
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)
56
What does filler volume fraction affect
Elastic modulus (rigidity) Fracture strength Fracture toughness
57
How large are particles in agglomerated microfiller heterogenous complexes
0.3-50um Filler particles artificially agglomerated via hydrolysis or precipitation
58
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
59
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

Dental Materials Y2 (11 decks)

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