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Dental Materials > Resin Composites > Flashcards

Resin Composites Flashcards

1
Q

in the 1950’s/1960’s what were used?

A

silicates

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2
Q

silicates were the earliest what?

A

tooth coloured material

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3
Q

silicates are the product of?

A

an acid base reaction of aluminasilicate glass, phosphoric acid

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4
Q

properties of silicates?

A

release F
moisture sensitive
erosion prone
brittle

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5
Q

what were used in the 1960’s/1980’s?

A

acrylics

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6
Q

where were acrylics derived from?

A

denture making products

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7
Q

what form did acrylics come in?

what type of set were they?

A

powder to liquid

chem set = limited working time

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8
Q

what were acrylics powder component?

A

polymethylmethacrylate pmma beads under 50nanometres

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9
Q

liquid portion of acrylics?

what was the chem activator?

A

methyl methacrylate monomer

chem activator = tertirary amine

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10
Q

acrylic setting reaction is?

A

free radical addition polymerisation

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11
Q

stages of a free radical addition polymerization of methyl methacrylate?

A

activation
initiation
propogation
termination

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12
Q

what happens at the termination stage?

A

chain attaches to impurity/free radical or further growing chain

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13
Q

what is the mechanism of polymerization?

A

free radical addition

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14
Q

material contracts on?
reaction is?
what gives poor colour stability?
must use correct?

A

polymerization
exothermic
tertiary amine not all used up
powder:liquid

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15
Q

compared to silicates, acrylics are less? exhibit?

A

less prone to erosion, soluble, acidic, britlle

exhibit lower thermal diffusivity

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16
Q

acrylics match?
do not use long term if?
setting reaction is?
residual mma causes?

A

tooth shade
if amine present
exothermic
pulp irritancy

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17
Q

acrylics interact with?
contract what % by volume?
low?
poor?

A

eugenol
6%
low hardness
poor abrasion resistance

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18
Q

in 1951 Knock and Glenn?

A

introduced inert filler particles to reduce shrinkage = also weakened the material

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19
Q

in 1963 Bowens composite had?

A

BISGMA resin matrix

coupling agent and filler particles

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20
Q

what is a resin composite?

A

a combination of 2 different chemical materials with distinct interface separating the components and properties which could not have been achieved alone.

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21
Q

early composites retained?

later became?

A

acrylics free radical addition polymerization - 2 pastes mixed together = reduced working time and incorporated porosities
later = light cured

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22
Q

resin matrix includes?

A

methacrylate/dimethycrylate monomers e.g BISGMA
includes monomers e.g TEGMA
inhibitors

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23
Q

what does TEGMA allow?

A

controls viscosity
facilitates manufacturers filler addition
easier clinical handling

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24
Q

what does the viscosity of the matrix polymer do?

A

reduces mobility of unreacted monomers

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25
Q

what do unreacted monomers allow?

A

space for chairside repair

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26
Q

what does the C to C double bond take part in?

A

take part in free radical polymerisation

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27
Q

in new products based on silaranes, ring opening occurs, producing what?

A

expansion that offsets shrinkage

still an overall contraction

28
Q

types of silaranes?

A

siloxanes - hydrophobicity

oxiranes - ring opening polymerisation

29
Q

how are they cationic cured?

A 
camphorquinone - photosensitiser 
iodium salt
electron donor - decomposes iodium salt to an acidic cation
ring opening polymerisation
less shrinkage
30
Q

what kind of fillers can be used?

A

quartz
silica
glasses - aluminasilicate, borosilicate, barium oxide

31
Q

what kinds of coupling agents?

A

6-methacryloxypropylthimethaxyslane = gamma silane
difunctional - methacrylate characteristics - silane interacts and bonds with glass
good wetting = 1g->412m2

32
Q

if you increase the % of filler what happens to surface hardness?

A

increased surface hardness

33
Q

if you increase the % of filler what happens to the setting contraction?

A

decrease in % volume setting contraction

34
Q

if you increase the % of filler what happens to the thermal expansion?

A

decreased thermal expansion

35
Q

In what forms composites be activated chemically?

A

powder/liquid mixed
paste/liquid mixed
encapsulated

36
Q

early light set composite was?

composite light set today was?

A

early - UV

today - camphorquinone - protects eyes, sets a little under operating light

37
Q

how does camphorquinone cause setting?

A

yields the necessary free radicals to start polymerisation
becomes excited at 460-480nm (visible blue light)
most readily generated by quartz halogen lights

38
Q

how does shrinkage occur?

A

resins are susceptible to shrinkage on polymerisation
may be modified methacrylate or a chemical that on setting expands due to ring opening mechanism - e.g oxirane = expansion in resin volumes offsets to a degree the shrinkage

39
Q

what aspect of the filler controls the properties?

A

type
concentration
particle size/distribution

40
Q

resin and filler are useless without a?

A

coupling agent

41
Q

what does a coupling agent do?

A

transfers stresses generated under loading from rigid/brtille filler to more flexible and ductile polymer matrix

42
Q

what does the filler act as?

A

a shock absorber

43
Q

how are composites classified?

A

by mode of activation

filler particle size/distribution

44
Q

conventional composite particle size? by weight?

A

1-50micrometre

60-80% by weight

45
Q

microfilled composite?

A

0.01-0.1um

30-60% by weight

46
Q

hybrid?

A 
mean = 0.04um 
hybrid
75% 1 
8% 2
total = 83-90 by weight
47
Q

nanocomposites?

A

particles less than 1um

48
Q

handling classifications?

A

packable - highly viscous, packaging = challenge

flowable - more fluid less filler

49
Q

intended clinical application

ISO 4049 type 1? type 2?

A

1 - cavities including occlusal surfaces

2 - all other polymer based filling and restorative material

50
Q

for a material to be on the market what must it conform with?

A

ISO 4049

51
Q

what happens to the viscosity of composite on leaving the tube?

A

increases

52
Q

what kind of set does composite have?

A

exothermic

53
Q

where does the setting contraction go towards?

A

not towards light source

54
Q

thermal properties of composite?

A

mismatch tooth for thermal expansion
= risks marginal prelocation
thermal diffusivity matches dentine

55
Q

if chemically activated what is the working time like?

A

less working time

56
Q

extended working time if activated how?

A

light activated
gradual set from outer to inner
distance light from surface and use incremental curing

57
Q

physical properties of composite are reduced with what?

A

porosities

58
Q

what is considered to be more important than compressive strength?

A

tensile and flexural strength

59
Q

what is tribology?

A

composite changes with function/loss of resin rich outer layer

60
Q

thermal properties of composite are proportional to what?

A

filler content

61
Q

if filler is increased what happens to the coefficient of heat expansion?

A

increase

62
Q

mechanical properties of composite are dependent on?

A

filler content and type
efficiency of coulping
degree of porosity

63
Q

increased porosity and reduced coupling, what happens to the strength?

A

reduced strength with porosity

reduced strength with coupling by 30%

64
Q

increased porosity and reduced coupling, what happens to the amount of fatigue composite can take?

A

reduced fatigue with porosity

reduced fatigue with coupling by 30%

65
Q

why may composite stain?

A

resin matrix can take up fluids e.g wine

66
Q

what creates a picture frame stain?

A

marginal deterioration

Dental Materials (13 decks)

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