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Dental Materials > Composite 3 > Flashcards

Composite 3 Flashcards

1
Q

What does a one paste system?

A

no mixing required

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2
Q

2 one paste systems for composites

A
  • syringe and bottle systems
  • capsules
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3
Q

Explain syringe and bottle systems

A
  • transfer to cavity using spatula
  • dispense onto mixing pad
  • don’t take straight from bottle - cross infection risk
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4
Q

Advantages and disadvantages of capsules

A
  • pre-measured dose size and easy to transfer
  • more waste
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5
Q

4 steps of free radical addition polymerisation

A
  • activation
  • initiation
  • propagation
  • termination
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6
Q

Explain propagation

A
  • monomer converts to polymer, chains crosslink
  • mechanical/physical properties related to molecular weight
  • proceeds for as long as possible
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7
Q

3 steps of termination

A
  • viscosity increases too high to allow radicals and monomers to meet
  • two radicals meeting - cancel each other out
  • impurity atoms react with radicals (oxygen can react easily but oxygen radicals much less reactive)
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8
Q

What is the oxygen inhibition layer?

A
  • often called air inhibition
  • prematurely terminated polymer
  • weak, soft layer - easily damaged
  • potentially leads to composite restoration failing
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9
Q

Explain matrix strip

A
  • typically a thin polymer film
  • provides barrier between composite and atmosphere during polymerisation
  • reduces oxygen inhibition must be used carefully
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10
Q

A freshly polymerised surface is … and …

A

smooth and glossy

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11
Q

How does polishing and finishing happen?

A
  • polished to adapt margins
  • use a range of products with different particle sizes and abrasive types
  • glaze applied
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12
Q

Traditional vs modern glaze technique

A
  • trad is not filled, like acrylic resin so had poor abrasion resistance
  • modern some are filled for better abrasion resistance
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13
Q

Process of choosing aesthetics of composite

A
  • initial shade matching by shade and polish/gloss
  • time constraints - accurate matching is time constraining
  • requirements for location (posterior vs anterior)
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14
Q

How does staining affect aesthetics?

A
  • dietary considerations
  • solvents like alcohol, mouthwashes
  • dietary factors like coffee, wine, turmeric
  • whitening agents
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15
Q

How do CQ influence long term colour?

A

yellowing over time

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16
Q

How does roughening affect long term stability?

A
  • abrasion from food and oral hygeine
  • matrix removed
  • lose gloss
17
Q

How does marginal staining affect aesthetics over time?

A
  • polymerisation shrinkage pulls away from margin
  • microleakage
  • amount of shrinkage related to adhesion strength
18
Q

Chemical activation patterns

A
  • shrinkage is uniform within filling
19
Q

Light activation patterns of shrinkage

A
  • non-uniform within filling
  • shrinkage tends to be towards light
  • relevant to adhesion - different stress depending on cavity
20
Q

Magnitude of shrinkage depends on …

A
  • degree of conversion
  • monomer molecular weight
  • filler concentration
  • strength of adhesion to tooth tissue
  • configuration factor termed C-factor
21
Q

How does degree of conversion affect polymerisation shrinkage?

A
  • monomers take up more volume than polymer
  • greater conversion the greater the contraction
22
Q

How does monomer molecular weight affect polymerisation shrinkage?

A
  • greater monomer mass lower shrinkage
23
Q

How does filler concentration affect polymerisation shrinkage?

A
  • more filler leads to lower shrinkage
24
Q

How does strength of adhesion to tooth tissue affect polymerisation shrinkage?

A
  • composites don’t bond to enamel or dentine
  • need an adhesive
25
Q

The more surfaces composite bonded to, …

A
  • shrinkage will have more effect
  • shrinkage affects different cavities classes differently
26
Q

C factor =

A

ratio of bonded surfaces to free surfaces

27
Q

High C factor indicates …

A

shrinkage is a problem

28
Q

What is meant by
- C factor 0
- C factor 0.2
- C factor 0.5

A
  • no bonded surfaces
  • one bonded surface
  • two bonded surfaces
29
Q

Failure composite restorations is due to …

A
  • posterior restorations
    (secondary caries, wear, fracture)
  • 1-5% anterior restorations
30
Q

Failure depends on what factors?

A
  • number of restored walls (C factor)
  • composite volume (size of cavity)
  • endodontic treatment
  • correct use of composite by clinician
31
Q

Properties of light activated composites depend on degree of conversion. How?

A
  • requires good illumination
  • make sure light guides are clean from contamination
  • greater conversion near surface - use matrix strip to reduce air inhibition
  • limited depth of cure
32
Q

Polymerisation is a exo/endothermic reaction
Explain

A
  • exothermic
  • temp rise is proportional to volume
  • larger cavities = larger temp rise
  • light unit will contribute to heat
33
Q

Light activated composites are available in what varieties?

A
  • microfilled
  • hybrid
  • universal
  • bulk fill
  • packable
34
Q

Composites vs amalgam in appearance

A
  • composites tooth coloured
  • patients prefer ‘invisible’ restorations
  • tooth matching only at time of placement
35
Q

Compare biocompatibility of composite and amalgam

A
  • mercury in amalgam is public health issue
  • no evidence it poses a health risk to people
  • composites contain BisGMA with BPA, concerns of estrogenicity
  • all monomers and amines are cytotoxic
  • polishing comp leads to aerosols of silica - can cause pneumo-silicosis
36
Q

Cavity design of composite vs amalgam

A
  • undercuts required for amalgam
  • amalgam weak in thin sections - angle at interface with enamel important
  • composite adhesively attached to enamel and dentine - can be conservative
37
Q

Composite vs amalgam for cavity sealing

A
  • bonding of composite to enamel and dentine reduces marginal leakage
  • depends on successful bonding and magnitude of polymerisation shrinkage
  • amalgams not normally bonded - corrosion products
38
Q

Compare durability of composite and amalgam

A
  • hardness, stregnth and toughness are similar as composite is improving
  • amalgam slightly more so as thick sections

Dental Materials (17 decks)

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