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2 - Dental Material Science > Composite 1 > Flashcards

Composite 1 Flashcards

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1
Q

What clinical cases can direct filling materials be applied in?

A
  • new dental caries
  • abrasion / erosion
  • failed restoration/secondary caries
  • trauma
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2
Q

What are the components of composite resin?

A
  1. Filler particles
  2. Resin
  3. Camphorquinone
  4. Low weight dimethacrylates
  5. Silane coupling agent
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3
Q

What are the types of filler particles?

A

types of glass

– microfine silica
– quartz
– borosilicate glass
– lithium aluminium silicate
– barium aluminium silicate

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4
Q

What are the types of resin?

A

Monomers used:-
– BIS-GMA - reaction product of bisphenol-A and glycidyl methacrylate
– urethane dimethacrylates

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5
Q

What are the key characteristics of resin monomers?

A
  • bifunctional molecule
    (C=C bonds – facilitate crosslinking)
    – undergoes free radical addition polymerisation
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6
Q

What are properties of camphorquinone and why is it added?

A

– activated by blue light
– produces radical molecules
– these initiate free radical addition polymerisation of BIS-GMA
– leading to changes in resin properties
(ie increased molecular weight, so increased viscosity, and strength)

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7
Q

Why are low weight dimethacrylates (e.g TEDGDMA) added?

A

added to adjust viscosity & reactivity

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8
Q

Why is a silane coupling agent added?

A

– normally water will adhere to glass filler particles, preventing resin from bonding to the glass surface
– a coupling agent is used to preferentially bond to glass and also bond to resin

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9
Q

What are the classifications of composite?

A
  • Curing method
    – light cured
  • self cured
  • Filler type:
    – microfilled
  • submicron hybrid
  • heavily filled
  • Handling characteristics
    – condensable
    – syringeable
    – flowable
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10
Q

What are the 3 steps of composite development?

A
  • filler particles
  • curing (activation)
  • particle /resin bonding
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11
Q

What is the advantageous effect of adding filler particles?

A
  • improved mechanical properties
    – strength, rigidity, hardness, abrasion resistance etc
  • lower thermal expansion (still not perfect)
  • lower polymerisation shrinkage (still a problem)
  • less heat of polymerisation (BUT not negligible)
  • improved aesthetics
  • some radiopaque
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12
Q

What are the ways composite can be cured?

A
  • self curing (two pastes)
  • Light curing (blue light 440nm, one paste)
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13
Q

How is composite actived in the curing process of self curing and light curing?

A

self curing = benzoyl peroxide + aromatic tertiary amine

light curing = camphorquinone + blue light

=

free radicals are formed (polymerisation)

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14
Q

What are the two lights used for light curing?

A

halogen
LED

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15
Q

What are the advantages of a light curing system?

A
  • extended working time
    – on-demand set, triggered when light activated
  • less finishing
  • immediate finishing
  • less waste
  • higher filler levels (not mixing two pastes)
  • less porosity (not mixing two pastes)
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16
Q

What layer of composite sets best/first in light curing?

A

Most of blue light is absorbed close to the surface.

Composite resin nearest the surface sets the most readily and becomes hard.

17
Q

What is used to signify the depth of cure? (system)

A
  • Surface hardness profile is accepted as more realistic
  • Instrumentation used to create indentations on surface, that are quantified
  • And then sub-surface measurements related to this
  • DoC is defined as depth at which material HARDNESS is about 80% that of the cured surface
18
Q

What is the depth of cure and what is it used to assess?

A

Depth of cure
– the depth to which the composite resin polymerises sufficiently

it’s HARDNESS is about 80% (to 90%) of the cured surface (D = 0mm)

typically 2mm

indicates increment thickness to use when building a restoration

using increment > 2mm results in UNDER-POLYMERISED base “soggy bottom” poor bonding to tooth….early failure !

19
Q

What layer thickness should be used for hybrid composites?

A

2mm

20
Q

What are bulk fill composites?

why are they used

A

Has lucerin initiator as well as camphorquinone

UV and blue light needed to polymerise (cure) material fully

produce a deeper DOC resulting in less time wasted

21
Q

What layer thickness is recommended for bulk fill composites?

A

4-6mm

22
Q

What are the problems that can occur with light curing?

A
  • light / material mismatch - overexpose
  • premature polymerisation from dental lights - avoid exposure
  • optimistic “depth of cure” values (small increments)
  • recommended setting times too short
  • polymerisation shrinkage
23
Q

What are the safety concerns for light curing?

A

thermal trauma from heat generation (exothermic reaction)
ocular damage from intense light sources,

2 - Dental Material Science (17 decks)

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