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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
what does comonomer such as TEGMA control?
controls viscosity : - facilitates manufacturers filler addition - clinical handling
26
why are inhibitors in the resin composites?
to stop early setting accidentally
27
In terms of resin matrix, discuss viscosity of matrix polymer.
• 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.
28
what 3 fillers can you get?
- quartz - silica - glasses
29
what is the coupling agent in resin composites?
δ – methacryloxypropyltrimethoxysilane
30
what are the functions of methacryloxypropyltrimethoxysilane?
* Methacrylate charcteristics | * Silane interacts and bonds with glass
31
How does the coupling agent spread?
good wetting
32
What happens to surface hardness as %filler content by volume increases?
increases
33
what happens to % volume setting reaction as %filler content by volume increases?
decreases
34
what happens to coefficient of thermal expansion as %filler content by volume increases?
decreases
35
what are the two ways to activate resin composites?
- chemical | - light
36
How can you chemically activate of resin composites?
* Powder Liquid * Paste Liquid * Encapsulated
37
How can you activate resin composites by light?
• Early ones U V (health risks) • Today Camphorquinone – Protect eyes – Will set under operating light to a certain extent
38
what does Camphorquinone do?
Yieldsthenecessary free radicals to start the polymerisation
39
At what wavelength does camphorquione become excited?
460-480nm | visible blue light
40
what is camphorquinone blue light most readily generated by?
quartz halogen lights
41
what do all types of resin composites contain?
- resin - filler - coupling agent
42
what is resin susceptible to upon polymerisation?
shrinkage
43
how can resin be modified?
-methacrylate/acrylate -OR a chemical that upon setting expands due to a ring opening mechanism eg Oxirane
44
what effect does expansion of resin have?
-This expansion in resin volumes offsets to a degree the polymerisation shrinkage » Still however a net shrinkage
45
what filler properties control resin composite properties?
- type - concentration - particle size - particle size distribution
46
what role does the coupling agent have?
The coupling agent transfers the stresses generated under loading from the rigid and brittle filler to the more flexible and ductile polymer matrix
47
what is the filler regarded as?
shock absorber
48
how is resin composites classified?
- method of activation (chemical/light) - filler particle size and distribution - handling characteristics - intended clinical application
49
what are the 4 types of resin composites?
- conventional - microfilled - hybrid (conventional + microfilled) - nanocomposites
50
What is conventional resin composite?
- 1-50 micrometers | - 60-80% by weight
51
What is microfilled resin composite?
- 0.01-0.1 micrometers | - 30-60% by weight
52
What is hybrid resin composite?
- blend of conventional and microfilled | - 83-90% by weight
53
What is nanocomposite resin composite?
uses particle less than 1 micrometer diameter
54
what are the different handling characteristics?
``` • Packable – Highly viscous – Presents packaging challenges to manufacturers • Flowable – More fluid – Less filler ```
55
what are different types for clinical application (ISO 4049)?
– Type 1 – restoration of cavities involving occlusal surfaces – Type 2 – All other polymer based filling and restorative materials
56
what does resin composite need to be on the market?
conform with ISO 4049
57
are resin composites biocompatible?
• Less scrutiny than amalgam – Cytotoxicity of components – Oestrogenicity of commonly used resin precurrsors – Tumour producing aerosols of fine glass particles
58
what happens to viscosity of resin composite when leaving the tube?
Viscosity increases on leaving tube - filler particles become bunched up in the mix as its pushed out
59
Describe the setting of resin.
- exothermic set | - contract not towards light source
60
what are the thermal properties of resin?
– Mismatch tooth for thermal expansion • Risks marginal percolation – Thermal diffusivity matches dentine
61
what is the difference in working time between chemically and light activated?
* Limited working time if chemically activated | * Extended working time if light activated
62
how does the resin set?
gradual set from outer surface within
63
When are physical properties reduced?
with porosity
64
what strength is considered more important?
Tensile and flexural now considered more important than compressive
65
what is tribology?
changes with function and loss of resin rich outer layer
66
why is thermal properties important to filler content?
As filler increases coefficient of thermal expansion | decreases
67
why is thermal properties important mechanically?
• Dependent upon – Filler content and type – Efficiency of coupling – Degree of porosity
68
what happens to strength with increased porosity?
decrease
69
what happens to strength with decreased coupling?
decrease (by 30%)
70
what happens to fatigue with increased porosity?
decrease
71
what happens to fatigue with decreased coupling?
decrease (by 30%)
72
Describe the staining properties.
– 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
Does cavity shape influence overall success of restoration?
Yes
74
what is the C factor?
ratio of number of nodes surfaces to number of un-bonded surfaces
75
why does C factor matter?
composite shrinks
76
what should clinical application be based upon?
– Awareness of shortcomings | – Understanding of properties

Applied Dental materials (5 decks)

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