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3. Dental Materials > Resin composites > Flashcards

Resin composites Flashcards

1
Q

acrylics are made up of a powder containing what? 3

A

Pmma beads
chemical initiator
pigment

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2
Q

acrylics are made up of a liquid containing what? 2

A

Mma monomer
chemical activator - tertiary amine

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3
Q

what is the type of setting reaction for acrylics?

A

free radical addition polymerisation

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4
Q

what are the 4 stages for the free radical addition polymerisation of methyl methacrylate in the setting reaction of acrylic?

A

activation - peroxide exposed to tertiary amine creating 2 reactive units
initiation - methyl methacrylate cleaves double bond to single bond
propagation - units keep joining
termination - chain attaches to impurity/free radical or further growing chain

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5
Q

what does a clinician have to consider when using acrylics? 8

A

material contracts on polymerisation
exothermic
potential discolour as any tertiary amine left over denatures turning clear-brown
correct powder to liquid ratio
irritate pulp -> methyl methacrylate
interact with eugenol - liner
low hardness
poor abrasion resistance

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6
Q

compare the properties of acrylics to silicates 5

A

acrylics are less
- prone to erosion
- soluble
- brittle
- acidic
exhibit less thermal diffusivity

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7
Q

what was added to acrylics to reduce shrinkage? what was the disadvantage?

A

inert filler
weakened the material

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8
Q

definition of a resin composite

A

combination of 2 chemically different materials with an interface separating them. the properties could not be achieved by any of the components acting alone.

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9
Q

resin composites are composed of a resin matrix containing what?

A

methacrylate/dimethacrylate monomers e.g. BIS GMA (big molecules with c=c to facilitate polymerisation

comonomers e.g. TEGMA

inhibitors

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10
Q

what is the function of comonomers in the resin matrix of resin composites?

A

controls viscosity for manufacturers addition of filler and clinical handling

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11
Q

what is the function of inhibitors in the resin matrix of resin composites?

A

stops the polymerisation occurring in storage

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12
Q

the viscosity of the resin matrix reduces the mobility of unreacted monomers, what does this allow?

A

chair-side repair if restoration breaks as the C=C that have not been used can take part in further polymerisation with the repair

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13
Q

resin composite is composed of what?

A

resin matrix
fillers
coupling agent

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14
Q

resin composites have fillers (glass) which contain heavy metal in them, why is this useful?

A

for distinguishing restorations on radiographs due to radiopacity

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15
Q

the coupling agent dimethacryloxypropyltrimethoxysilane (vinylsilane) is difunctional, explain this

A

the methacrylate interacts with the resin itself

the silane interacts and bonds with glass

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16
Q

what is a property of the coupling agent dimethacryloxypropyltrimethoxysilane (vinylsilane)

A

good wetting - spreadability and coverage

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17
Q

as the filler content increases in resin composite what happens to the surface hardness

A

increases

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18
Q

as the filler content increases in the resin composite what happens to the % volume setting contraction

A

decreases

19
Q

as the filler content increases in the resin composite what happens to the coefficient of thermal expansion

A

decreases

20
Q

how do resin composites set?

A

chemically
or light

21
Q

what is camphorquinone?

A

its a component of resin
it gets excited at the wavelength of blue light and contains the necessary free radicals to start the polymerisation (curing)

22
Q

what are the 2 classifications of handling characteristics for resin composite?

A

packable -> highly viscous, packaging challenges for manufacturer

flowable -> more fluid, less filler

23
Q

what are the two classification of resin composites based on the ISO 4049?

A

type 1: restoration of cavities involving occlusal surfaces
type 2: all other polymer based filling and restorative materials

24
Q

to be on the market a resin composite must conform with what?

A

ISO 4049

25
Q

resin composites are under scrutiny for what? 3

A

cytotoxic components
oestrogenicity of precursors
tumour producing aerosols of fine glass particles

26
Q

what happens to the viscosity of resin composite when you squeeze it out of a tube?

A

increases so don’t hang around

27
Q

what happens to the volume or resin composite when it sets?

A

contraction

28
Q

what are the 2 thermal properties of resin composite?

A

different thermal expansion than tooth which risks marginal percolation (separation from tooth at margin)

thermal diffusivity matches dentine (conduction of heat)

29
Q

if the shade of resin composite is dark the incremental cure depth should be ?

A

reduced

30
Q

what is tribology?

A

as the material wears the amount of resin on the outer layer will change and that will affect the wear characteristics of the produce

31
Q

does resin composite have self adhesive mechanisms to bond to tooth substance?

A

no

32
Q

with increased porosity of resin composite strength?

A

decreases

33
Q

with increased porosity of resin composite the ability of the material to withstand fatigue forces?

A

decreases

34
Q

with increased coupling of resin composites strength

A

increases

35
Q

with increased coupling of resin composite the ability of the material to withstand fatigue forces

A

increases

36
Q

resin composite initially has a good appearance but it is susceptible to ? why?

A

staining
resin matrix can take up fluids e.g. wine

marginal deterioration - picture fram staining from wine/smoking etc.

37
Q

what is C-factor? (configuration factor)

A

the way the composite shrinks is based on the C-factor. the higher the C-factor the worse the possible outcome (marginal gaps caused by shrinkage)

38
Q

how is C-factor calculated?

A

number of bonded surfaces / number of un-bonded surfaces

39
Q

what is the photosensitiser that resin composite contains making it light sensitive?

A

camphorquinone

40
Q

what is the wavelength range that camphorquinone is sensitive to?

A

460-480nm -> visible blue light

41
Q

what should u do when light curing to avoid damage to the tissues?

A

wait for at least 30s between cycles to avoid heat build up

42
Q

what causes resin matrix softening? 2

A

air pockets cause inhibition of polymerisation

chemical softening from foods and plaque acids

43
Q

how are cracks in resin restorations at the resin/filler interface propagated?

A

stress corrosion of filler causes hydrolytic filler degradation (filler breaks up) means lots of molecules at the interface increasing osmotic pressure

44
Q
A

3. Dental Materials (7 decks)

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