Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Dental Materials Y2 > Composite Properties And Principles > Flashcards

Composite Properties And Principles Flashcards

1
Q

What are the 3 phases in composite resin

A

Organic phase, dispersed phase, interfacial phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What key monomer does all composites have

A

Bis-GMA (bisphenol glycidyl methacrylate)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is TEGDMA added for (2)

A

Reduce viscosity of resin matrix ie viscosity controller

Diluent to attain high filler levels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Does BISGMA have high degree of conversion

A

No! BISGMA has lowest degree of conversion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is camphorquinone

A

Photochemical initiator

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Max excitation of camphorquinone at what wavelength

A

468nm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the role of benzoyl peroxide

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is function of uv light absorber

A

Reduce risk of composite discoloration when irradiated with strong uv

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What makes up interfacial phase

A

Silane coupling agent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How much of composite is made up of fillers by weight

A

More than 50%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How does filler content affect polymerisation shrinkage

A

Increased VOLUME = decreased matrix= contract less

Fillers do not contract

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Name some advantages of quartz fillers

A

Strong and hard

Highly aesthetic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Disadvantages of quartz fillers

A

Difficult to polish

Abrasive to opposing teeth/restorations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Advantages of glass fillers with heavy metals

A

Adequate refractive index

Provide radioopacity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Disadvantages of glass fillers

A

Lease inert

Leaches and weakens in acidic juices

More susceptible to wear

Shorter functional lifetime

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the filler loading of icrofillers

A

30-50%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Contraindications of microfileld cr

A

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

Cusps in posterior teeth

Because deforms early under stress and lower fracture resistance

25
Q

Hybrid fillers proeprties

A

High strength and fracture resistance

Good polishability

High filler loading
Good wear resistance

26
Q

Indications of hybrid filler composite

A

High stress area

Larger restorations

27
Q

Why does bisgma have low polymerisation shrinkage

A

Big monomer

28
Q

Thermal property of composite resin

A

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
Q

Is composite resin radio opaque

A

Yes

30
Q

Discuss cytotoxicity of composite resin

A

Biocompatible

Increased curing time means less cytotoxicity because less residual monomer (leakage of bisphenol A from bisgma)

31
Q

What is the polymerisation shrinkage of composite

A

1.2-2%

32
Q

What is the polymerisation shrinkage of methyl methacrylate

A

20%

33
Q

What is the polymerisation shrinkage of bisgma

A

2.6-7.1%

34
Q

In what direction does shrinkage occur in composite resin

A

CR pulls away from least retentive surface towards most retentive wall

35
Q

What is the c factor

A

Ratio of number bonded surfaces to number of unbonded surfaces

36
Q

How does c factor affect adhesive bond

A

Higher c factor = higher contraction stress of adhesive bond

37
Q

Effects of water on CR

A

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
Q

Abrasion vs attrition

A

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
Q

Microfills vs hybrid fillers in the way they respond to attrition and abrasion

A

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
Q

Composite resin modulus of elasticity vs that of amalgam

A

Low. CR elastic deformation 6x more than amalgam

Low modulus = less rigid, deform more under masticatory forces

Low resistance to occlusal loading

41
Q

How to calculate elastic modulus

A

Tension (N)/ deformation (mm)

42
Q

What can increase in filler fraction achieve

A

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
Q

For amalgam, gic, cr, ceramic, rank flexure strength, fracture toughness, tensile strength

A

Ceramic most

Cr more or equal to amalgam

More than gic

44
Q

Point of GIC liner

A

Protect pulp

Less polymerisation stress and shrinkage

Fluoride release

Improve marginal integrity

45
Q

How does CLT of CR compare with that of tooth structure

A

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
Q

What is the effect of adding low viscosity small monomers like TEGDMA and MMA

A

Improve handling properties by reducing viscosity (bisgma too viscous)

Increase polymerisation shrinkage

47
Q

Advantages of using smaller particles for filler loading

A

Better optical properties ie more aesthetic. Excellent polishability. Higher refractive index results in most realistic translucency

48
Q

How big are microfillers

A

0.01-1um, 0.04um

49
Q

How large are midi filliers

A

1-10um

50
Q

How big are minifillers

A

0.1-1um

51
Q

How big are nanofillers

A

0.005-0.01um

52
Q

Properties of microfillers

A

Make resin viscous, improve handling

Low filler loading

Excellent polishability

Poor mechanical properties, low fracture resistance

Good wear resistance

53
Q

Difference between filler loading of flowable and packable composite

A

Flowable less viscous = lower filler content

Which leads to higher polymerisation shrinkage, lower mechanical properties, less hardness, less radioopacity

54
Q

What is the filler loading by weight and volume fo hybrid minifills

A

85% by weight 70% by volume

55
Q

Microhybrid vs microfiller

A

Microhybrid is less polishable, difficult to marginate, wears faster than microfiller

Increased strength due to larger particle size (0.4-0.6um)

56
Q

What does filler volume fraction affect

A

Elastic modulus (rigidity)

Fracture strength

Fracture toughness

57
Q

How large are particles in agglomerated microfiller heterogenous complexes

A

0.3-50um

Filler particles artificially agglomerated via hydrolysis or precipitation

58
Q

Hybrid vs agglomeration

A

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
Q

How do fillers increase mechanical properties

A

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)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions