Brainscape's Knowledge GenomeTM

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


See full index

Dental Materials > Composite 2 > Flashcards

Composite 2 Flashcards

1
Q

Acrylic resin filling materials based on …

A

methyl methacrylate/MMA

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

Features of MMA

A
  • 100.1g/mol molar mass so small
  • large polymer shrinkage around 21%
  • low viscosity (0.6mPa at 20 degrees)
  • monofunctional - linear polymer making
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What does the low viscosity of MMA mean?

A
  • easy to mix
  • difficult to transfer to cavity
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How to fix the shrinkage of MMA?

A
  • add PMMA powder
  • reduces shrinkage to 5-6%
  • still a clinical problem
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Acrylic resin fillings have good/poor durability
Explain

A
  • poor
  • marginal leakage and staining
  • poor colour stability
  • low strength, stiffness, hardness
  • high coeffiicent of thermal expansion
  • no adhesion to enamel/dentine
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is Bowen’s resin made in 1962?

A
  • bisphenol A-glycidyl methacrylate or BisGMA
  • matrix phase
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Features of BisGMA

A
  • big monomer (513g/mol)
  • lower polymerisation shrinkage (2-3%)
  • high viscosity (1200Pas)
  • difunctional -crosslinked polymers
  • more rigid monomer
  • good potential but too viscous
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Explain the high viscosity of BisGMA

A
  • 1 million times more than water
  • hard to mix
  • increased with filler addition makes it even harder to mix
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Why is it good that BisGMA is rigid?

A
  • steric hinderance of aromatic groups
  • creates stiffer and stronger polymers
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why do we make copolymers of BisGMA?

A
  • to reduce viscosity
  • dilute the BisGMA
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Most common diluent monomer used with BisGMA

A

triethylene glycol dimethacrylate
- TEGDMA

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

Properties of TEGDMA

A

-286 g/mol molar mass
- 0.01Pas viscosity - closer to water
- difunctional - crosslinked polymers
- flexible monomer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

TEGDMA can be mixed with BisGMA from … to …

A

1 to 100%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

With more TEGDMA, BisGMA is …
Even more …
And even more …

A
  • easier to mix, lower viscosity
  • weaker copolymer
  • more shrinkage/lower molar mass
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

List problems that cause shrinkage

A
  • debonding
  • marginal staining
  • microleakage
  • secondary caries
  • enamel micro-cracks
  • post-operative sensitivity
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Link of high molar mass to shrinkage

A
  • low polymerisation shrinkage
  • high viscosity
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Link of low molar mass to shrinkage

A
  • low viscosity
  • but high polymerisation shrinkage
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How to compromise between high and low molar mass to balance shrinkage and viscosity

A
  • balance mixing and placing with shrinkage
  • leads to different products
  • different types like packable, flowable or universal composites
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Universal composite is good for …

A

general work

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

Properties of flowable composite

A
  • lower viscosity (low filler conc or increased diluent)
  • weaker
  • less wear resistant
  • more shrinkage than universal
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Uses of flowable composite

A
  • non-carious tooth surface loss repair
  • fissure sealant
  • cavity lining
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Properties of packable composite

A
  • higher viscosity (higher filler conc)
  • similar feel to amalgam
  • increased risk of porosity
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Packable composite is used for …

A

posterior restorations

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

2 reasons we’re looking for alternative monomers than BisGMA

A
  • reduce and remove bisphenol A (BPA) use
  • better clinical properties
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Why are we trying to reduce BPA use?

A
  • health issues related to BPA
  • anti-BPA public campaigns
26
Q

Why are we looking for better clinical outcomes than BisGMA?

A
  • better handling, mixing, placement
  • lower polymerisation shrinkage
  • better mechanical properties
27
Q

Lots of papers are produced each year about alternatives. What’s the problem?

A
  • hard to translate lab reasearch to clinic
28
Q

3 recently developed monomers

A
  • urethane dimetacrylate (UDMA)
  • ethoxylated BisGMA (BisEMA)
  • silorane
29
Q

Explain features of UDMA

A
  • high molecular weight
  • low viscosity
  • no BPA
30
Q

Features of BisEMA

A
  • high molecular weight
  • low viscosity
  • low BPA
31
Q

Features of silorane
Is it available now?

A
  • polymerised by different route (ring-opening), claimed to be low shrinkage
  • clinical results didn’t match lab results so withdrawn from market
32
Q

Why are coupling agents needed?

A
  • acrylics don’t bond to silicates
  • heat and stress cause pores to form and these pores cause clinical failure
33
Q

How do coupling agents work?

A
  • silanes have carbon carbon double bonds and SiO groups
  • that bond acrylics to silicates (matrix to filler)
  • increases mechanical properties of composites
34
Q

Which coupling agent is most commonly used?

A

lambda-methacryloxypropyltrimethoxysilane

35
Q

Issue with silanes

A
  • they hydrolyse
  • and eventually break down
  • effects durability
36
Q

Conventional composites have a … system

A
  • two pastes
  • base and catalyst
37
Q

Explain hand mixed two paste system

A
  • inexpensive - spatula and pad in pack
  • technique sensitive
  • mixing can cause porosity
  • short working time, long setting time
38
Q

Issues with a short working time, long setting time

A
  • increases problems with technique sensitivity
  • patient comfort decreases over long setting time
39
Q

How does chemically activated polymerisation work with composite?

A
  • benzyl peroxide used as initiator
  • tertiary amine used as activator
  • uniform degree of polymerisation - but low levels, high residual monomer
40
Q

Do you still need 2 pastes with light activation?

A

no
- no mixing

41
Q

Advantages of light activation rather than hand mixing

A
  • no mixing so reduced porosity
  • unlimited working time ajnd command setting/only when light applied
  • higher degree of polymerisation - better mechanical properties
42
Q

Disadvantages of light activation of composite rather than hand mixing

A
  • require specialist light-activation unit - more expensive for purchase and maintenance
  • more expensive
  • limited depth of care
  • higher marginal stress in curing - faster rate leads to faster development of stress
43
Q

Explain process of UV light activation

A
  • light supplied by hand unit
  • light in UV range
  • used benzoin methyl ether as initiator
  • 2mm max depth of cure with 100% illumination (not often achieved)
44
Q

Disads of UV light curing
Consequence

A
  • health risks
  • corneal burns/melanoma
  • stopped in UK - no UV light used at all in UK dentistry
45
Q

Explain visible light activation

A
  • light units similar to UV - visible spectrum range (400-700nm)
  • camphoroquinone initiator - diff to UV
  • needs tertiary amine for activation
  • very yellow - colour stablility issues
46
Q

Compare visible light activation to UV

A
  • visible light has
  • improved depth of cure
  • improved degree of polymerisation
  • reduced health concerns
47
Q

Different designs of light activation units

A
  • originally fibre-optic cable
  • had low light intensity and optical fibres broke easily and needed replacing
  • so gun type - had a solid ‘light guide’ and was less prone to breaking
48
Q

List light source types

A
  • quartz, tungsten, halogen
  • plasma
  • LED
49
Q

Features of quartz, tungsten, halogen/QTH light

A
  • normal light bulb - broad spectrum light
  • needs filters to remove red light
50
Q

Is plasma lighting used?

A
  • proved unsuccessful
  • phased out
51
Q

Features of LED light

A
  • tuned to the initiator wavelength
  • more powerful LEDs being developed
52
Q

What is radiant energy?

A
  • light intensity x time
  • links the 2 and sees how much light exposure is needed for successful polymerisation
53
Q

Whats the optimum curing?

A
  • 16J/cm2
  • 10-20s of illumination
54
Q

Might curing time shorten?

A
  • as more intense LEDs are made hopefully
  • but no link found in dental composites
  • increased intensity did not allow shorter curing times
55
Q

Light intensity relates to …

A
  • LED power output
  • distance of light from surface (intensity dissipates over distance)
  • correct alignment of light (full coverage of restoration)
56
Q

Chemically activated composites and setting

A
  • uniform degree of conversion
  • placed in one procedure - bulk fill procedure
57
Q

Light activated composites and curing

A
  • light reduces over distance
  • non-uniform degree of conversion
  • requires placement in increments - depending on depth of cure, time consuming and technique sensitiven
58
Q

Bulk-fill materials and depth of cure

A
  • larger increments possible with recent developments
  • matchrefractive index of filler and matrix
  • increments max 4mm
  • products with higher TEGDMA concentration
  • weak clinical evidence
59
Q

Alternative initiators intend to improve …

A
  • curing time
  • depth of cure
  • colour stability
60
Q

Alternatives to CQ at the minute

A
  • PPD
  • TPO
  • BAPO
61
Q

Differences of alternative initiators to CQ

A
  • different excitation wavelengths
  • specialised light curing units required
  • very few products - limited clinical evidence

Dental Materials (17 decks)

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