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Applied Dental materials > L4- Composite structures > Flashcards

L4- Composite structures Flashcards

1
Q

what was the earliest direct tooth coloured restorative material? (1950-1960s)

A

silicates

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2
Q

how is silicate formed?

A

Reaction product of an acid base reaction (giving a salt

plus water) between – Aluminosilicate glass and Phosphoric acid

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3
Q

what are properties of silicate?

A
  • Releases Fluoride
  • Moisture sensitive
  • Erosion prone
  • Brittle
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4
Q

what restorative material was used between 1960 -1980s?

A

acrylics

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5
Q

what was acrylics derived from?

A

products used to fabricate dentures

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6
Q

how is acrylics presented?

A

powder and mixer in which it is mixed to a precise ratio for correct properties

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7
Q

why is working time limited?

A

chemical set

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8
Q

what is included in the powder of acrylics?

A

– Pmma beads of no greater than 50 μm
– Chemical Initiator (commonly a peroxide)
– Pigment

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9
Q

what is included in the liquid of acrylics?

A

– Mma monomer

– Chemical activator (tertiary Amine)

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10
Q

what type of reaction is the setting reaction in acrylics?

A

free radical addition polymerisation

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11
Q

what are the stages of free radical addition polymerisation of methyl methacrylate?

A
  • activation
  • initiation
  • propagation
  • termination
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12
Q

what occurs in activation?

A

free radical breaks double bond and joins together

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13
Q

what occurs in propagation?

A

linking one by one like building blocks

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14
Q

what is termination?

A

when chain attaches to impurity / free radical or further growing chain

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15
Q

why is this free radical reaction important for the clinician?

A 
• Material contracts on polymerisation 
• Reaction is exothermic
• Tertiary amine is not all used up
– Poor colour stability (clear – brown) 
• Must use correct P:L
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16
Q

what are acrylics compared to silicates?

A 
acrylics are less :
-prone to erosion
-soluble
-acidic
-brittle
Exhibit lower thermal diffusivity
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17
Q

Describe the properties of acrylics.

A
  • Match tooth shade (but not in long term if have amine)
  • Are exothermic when setting
  • Irritant to pulp due to residual mma
  • Interact with Eugenol
  • Contract (6% by volume)
  • Have low hardness
  • Poor abrasion resistance
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18
Q

what was introduced to acrylics in 1951 ?

A

Introduced inert filler particles to reduce shrinkage

– Though successful in this regard they weakened the material

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19
Q

what is in the 1963 composite ?

A
  • BIS GMA resin matrix
  • Coupling Agent
  • Filler particles
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20
Q

what is a resin composite?

A

A combination of two chemically different materials with a distinct interface separating the components and having properties which could not be achieved by any of the components acting alone

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21
Q

how are resin composites retained?

A

acrylics free radical addition polymerisation

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22
Q

Describe early products in resin composites.

A

two pastes were mixed together :
– Limited working time
– Incorporation of porosity

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23
Q

Describe later products in resin composites.

A

light curing technology was developed to give command curing

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24
Q

what is included In resin matrix?

A 
– Generally based upon
methacrylate or dimethacrylate monomers.
• E.g. BIS GMA, Urethane dimethacrylate
– Include comonomers such as TEGMA
– Inhibitors
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25
Q

what does comonomer such as TEGMA control?

A

controls viscosity :

  • facilitates manufacturers filler addition
  • clinical handling
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26
Q

why are inhibitors in the resin composites?

A

to stop early setting accidentally

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27
Q

In terms of resin matrix, discuss viscosity of matrix polymer.

A

• Reduces mobility of unreacted monomers
• A consequence that in any composite of this type there
are unreacted monomers offering scope for chairside
repair.
• C=C take part in free radical polymerisation
• In new products, based on Siloranes, ring opening
occurs (not free radical), producing expansion that offsets shrinkage. Still however an overall contraction.

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28
Q

what 3 fillers can you get?

A
  • quartz
  • silica
  • glasses
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29
Q

what is the coupling agent in resin composites?

A

δ – methacryloxypropyltrimethoxysilane

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30
Q

what are the functions of methacryloxypropyltrimethoxysilane?

A
  • Methacrylate charcteristics

* Silane interacts and bonds with glass

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31
Q

How does the coupling agent spread?

A

good wetting

32
Q

What happens to surface hardness as %filler content by volume increases?

A

increases

33
Q

what happens to % volume setting reaction as %filler content by volume increases?

A

decreases

34
Q

what happens to coefficient of thermal expansion as %filler content by volume increases?

A

decreases

35
Q

what are the two ways to activate resin composites?

A
  • chemical

- light

36
Q

How can you chemically activate of resin composites?

A
  • Powder Liquid
  • Paste Liquid
  • Encapsulated
37
Q

How can you activate resin composites by light?

A

• Early ones U V (health risks)
• Today Camphorquinone
– Protect eyes
– Will set under operating light to a certain extent

38
Q

what does Camphorquinone do?

A

Yieldsthenecessary free radicals to start the polymerisation

39
Q

At what wavelength does camphorquione become excited?

A

460-480nm

visible blue light

40
Q

what is camphorquinone blue light most readily generated by?

A

quartz halogen lights

41
Q

what do all types of resin composites contain?

A
  • resin
  • filler
  • coupling agent
42
Q

what is resin susceptible to upon polymerisation?

A

shrinkage

43
Q

how can resin be modified?

A

-methacrylate/acrylate
-OR a chemical that upon setting expands due to a ring
opening mechanism eg Oxirane

44
Q

what effect does expansion of resin have?

A

-This expansion in resin volumes offsets to a degree the
polymerisation shrinkage
» Still however a net shrinkage

45
Q

what filler properties control resin composite properties?

A
  • type
  • concentration
  • particle size
  • particle size distribution
46
Q

what role does the coupling agent have?

A

The coupling agent transfers the stresses generated under loading from the rigid and brittle filler to the more flexible and ductile polymer matrix

47
Q

what is the filler regarded as?

A

shock absorber

48
Q

how is resin composites classified?

A
  • method of activation (chemical/light)
  • filler particle size and distribution
  • handling characteristics
  • intended clinical application
49
Q

what are the 4 types of resin composites?

A
  • conventional
  • microfilled
  • hybrid (conventional + microfilled)
  • nanocomposites
50
Q

What is conventional resin composite?

A
  • 1-50 micrometers

- 60-80% by weight

51
Q

What is microfilled resin composite?

A
  • 0.01-0.1 micrometers

- 30-60% by weight

52
Q

What is hybrid resin composite?

A
  • blend of conventional and microfilled

- 83-90% by weight

53
Q

What is nanocomposite resin composite?

A

uses particle less than 1 micrometer diameter

54
Q

what are the different handling characteristics?

A 
• Packable
– Highly viscous
– Presents packaging challenges to manufacturers 
• Flowable
– More fluid 
– Less filler
55
Q

what are different types for clinical application (ISO 4049)?

A

– Type 1 – restoration of cavities involving occlusal surfaces
– Type 2 – All other polymer based filling and restorative
materials

56
Q

what does resin composite need to be on the market?

A

conform with ISO 4049

57
Q

are resin composites biocompatible?

A

• Less scrutiny than amalgam
– Cytotoxicity of components
– Oestrogenicity of commonly used resin precurrsors
– Tumour producing aerosols of fine glass particles

58
Q

what happens to viscosity of resin composite when leaving the tube?

A

Viscosity increases on leaving tube - filler particles become bunched up in the mix as its pushed out

59
Q

Describe the setting of resin.

A
  • exothermic set

- contract not towards light source

60
Q

what are the thermal properties of resin?

A

– Mismatch tooth for thermal
expansion
• Risks marginal percolation
– Thermal diffusivity matches dentine

61
Q

what is the difference in working time between chemically and light activated?

A
  • Limited working time if chemically activated

* Extended working time if light activated

62
Q

how does the resin set?

A

gradual set from outer surface within

63
Q

When are physical properties reduced?

A

with porosity

64
Q

what strength is considered more important?

A

Tensile and flexural now considered more important than compressive

65
Q

what is tribology?

A

changes with function and loss of resin rich outer layer

66
Q

why is thermal properties important to filler content?

A

As filler increases coefficient of thermal expansion

decreases

67
Q

why is thermal properties important mechanically?

A

• Dependent upon
– Filler content and type
– Efficiency of coupling
– Degree of porosity

68
Q

what happens to strength with increased porosity?

A

decrease

69
Q

what happens to strength with decreased coupling?

A

decrease (by 30%)

70
Q

what happens to fatigue with increased porosity?

A

decrease

71
Q

what happens to fatigue with decreased coupling?

A

decrease (by 30%)

72
Q

Describe the staining properties.

A

– Initially good appearance but may stain
• Microfine best at maintaining – In general:
» Resin matrix can take up fluids eg wine
» Picture Frame stain if marginal deterioration eg wine/smoking.

73
Q

Does cavity shape influence overall success of restoration?

A

Yes

74
Q

what is the C factor?

A

ratio of number of nodes surfaces to number of un-bonded surfaces

75
Q

why does C factor matter?

A

composite shrinks

76
Q

what should clinical application be based upon?

A

– Awareness of shortcomings

– Understanding of properties

Applied Dental materials (5 decks)

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