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Dental Materials Science BDS2 > Composite Resin > Flashcards

Composite Resin Flashcards

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1
Q

what are the applications of direct filling materials?

A

new dental caries, abrasion/erosion, failed restoration/secondary caries, trauma

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2
Q

what are the ideal properties of direct filling materials?

A

strength, rigidity, hardness, bonding to tooth, thermal properties, aesthetics, handling/viscosity, smooth surface finish, low setting shrinkage, radiopaque, anticariogenic, biocompatible

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3
Q

what is composite resin composed of?

A

filler particles, resin, camphorquinone, low weight dimethacrylates, silane coupling agent

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4
Q

what are the different types of filler particles?

A

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

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5
Q

what are the monomers used in the resin?

A

BIS-GMA or urethane dimethacrylates

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6
Q

what are the key characteristics of a monomer?

A

difunctional molecule, undergoes free radical addition polymerisation

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7
Q

what is camphorquinone

A

photoinitiator

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8
Q

how is camphorquinone activated?

A

blue light

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9
Q

what does cahmphorquinone do?

A

produces free radical molecules which initiate free radical addition polymerisation of bis-GMA leading to changes in resin properties. This causes a degree of conversion of resin

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10
Q

what do low weight dimethacrylates do?

A

adjust viscosity and reactivity

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11
Q

what is a silane coupling agent used for?

A

to preferentially bond to glass and also bond to resin

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12
Q

where does the silane coupling agent sit?

A

around the perimeter of the filler particles

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13
Q

when is composite used?

A

where aesthetics are important, class 3,4,5 restorations, labial veneers, inlays and onlays, luting cements

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14
Q

how are composite resins classified?

A

filler type, curing method, area of use (anterior/posterior/universal), handling characteristics (syringable, flowable)

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15
Q

what is the effect of adding filler particles?

A

improved mechanical properties, lower thermal expansion, lower polymerisation shrinkage, less heat of polymerisation, improved aesthetics, some radiopaque

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16
Q

what are the different types of composite curing?

A

self curing, UV activation, light curing (blue light)

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17
Q

how is self curing composite activated?

A

benzoyl peroxide and aromatic tertiary amine come together which causes free radicals to break C=C bonds causing polymerisation

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18
Q

how is light curing composite activated?

A

camphorquinone is activated by blue light which causes free radicals to break resin C=C bonds causing polymerisation

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19
Q

what are the advantages of light curing systems?

A

extended working time, less finishing, immediate finishing, less waste, higher filler levels, less porosity

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20
Q

what is the consequence of most of the blue light being absorbed close to the surface of the composite resin?

A

composite resin nearest the surface sets the most readily and becomes hard

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21
Q

what is the ISO 4049

A

the cure test where you cure a cylinder of composite resin then scrape away the unpolymerisation layer at the bottom and measure the length of it - depth of cure defined as half of this length

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22
Q

what is the hardness ratio?

A

another way of assessing depth of cure where hardness is assessed at various depths of the resin and each value is compared to the surface

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23
Q

what is depth of cure defined as?

A

depth at which material hardness is about 80% that of the cured surface

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24
Q

what is the typical depth of cure?

A

2mm

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25
Q

what does depth of cure indicate?

A

increment thickness to use when building a restoration

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26
Q

what does using increments greater than 2mm result in?

A

under-polymerised base so poor bonding to teeth and early failure

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27
Q

what is the depth of cure of hybrid composites?

A

2mm

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28
Q

what is the depth of cure for bulk-fill composites?

A

supposedly 6mm

29
Q

what initiator do bulk fill composites also have apart from camphorquinone?

A

lucerin initiator

30
Q

why do bulk fill composites have an extra photo initiator?

A

as it has different optical absorption spectrum and so UV and blue light are needed to polymerise material fully

31
Q

what are the potential problems with light curing?

A

light/material mismatch (overexpose), premature polymerisation from dental lights, optimistic depth of cure values, recommended setting times too short, polymerisation shrinkage

32
Q

how do you overcome recommended setting times being too short for light curing composites?

A

use a light curing time >30s

33
Q

what does polymerisation shrinkage affect?

A

affects bond to tooth

34
Q

how do you overcome the polymerisation shrinkage problems with light cured composites?

A

use small increments and light from different angles

35
Q

what are the safety concerns for the patient with light cured composites?

A

exothermic reaction (heat released exceeds that of heat needed for pulpal damage), divergent light beam, modern devices are brighter/more intense and may cause thermal trauma to patients soft tissues

36
Q

what are the safety concerns of light cured composite for the clinical staff?

A

occular damage from looking at the light

37
Q

how do you overcome the risk of occular damage from curing lights?

A

use safety shields or safety glasses

38
Q

what is the compressive strength of composite?

A

300MPa

39
Q

what is the rigidity of composite?

A

15GPa so it is rigid with high Young’s modulus

40
Q

what are the mechanical requirements for a posterior composite?

A

high strength, high YM, high abrasion resistance

41
Q

what are the mechanical requirements for a deciduous composite?

A

strong in thin section, wear = wear of tooth, bonding and microleakage

42
Q

describe the properties of conventional composite

A

strong but problems with finishing and staining due to soft resins and hard particles

43
Q

describe the properties of microfine composites

A

smaller particles for smoother surface and better aesthetics for longer period but inferior mechanical properties

44
Q

describe the properties of hybrid composites

A

improved filler loading and coupling agents which have improvements in mechanical properties

45
Q

what is hardness?

A

material surface’s resistance to scratching and resistance to indentation

46
Q

what is abrasion

A

removal of surface layers when two surfaces make frictional contact

47
Q

what does surface roughness affect?

A

appearance, plaque retention, sensation when in contact with tongue

48
Q

what factors of the material affect wear?

A

filler material, particle size distribution, filler loading, resin formulation, coupling agent

49
Q

what are the clinical factors affecting wear?

A

cavity size and design, tooth position, occlusion, placement technique, cure efficiency, finishing methods

50
Q

what is the typical bond strength of composite to enamel and dentine?

A

40MPa

51
Q

what is bond strength dependent on?

A

surface preparation of tissue, composite brand and test method

52
Q

what are the aims of bonding to the tooth?

A

reduce microleakage, counteract polymerisation shrinkage, minimise cavity design, stress transfer to tooth

53
Q

what is the compressive strength of enamel?

A

262MPa

54
Q

what is the compressive strength of dentine?

A

235MPa

55
Q

what is the thermal conductivity for composite?

A

low

56
Q

what is the thermal diffusivity for composite?

A

low

57
Q

what is the thermal expansion coefficient for composite?

A

high which is poor

58
Q

why should thermal conductivity of composite be low?

A

to avoid pulpal damage from hot and cold foods/fluids

59
Q

what is thermal diffusivity?

A

how readily a material transmits heat when exposed to a short transient stimulus

60
Q

why should thermal expansion coefficient be equal to the tooth?

A

to reduce microleakage

61
Q

what is the thermal expansion coefficient for enamel?

A

11

62
Q

what is the thermal expansion coefficient of dentine?

A

8

63
Q

what is the thermal expansion coefficient for amalgam?

A

22-28

64
Q

what is the thermal expansion coefficient for composite?

A

25-68

65
Q

what are the properties of aesthetics?

A

shade range, translucency, maintenance of properties over lifetime, resistance to staining, surface finish

66
Q

which type of restorative material is used for high caries risk and frequent attenders?

A

RMGI

67
Q

what type of restorative material is used for medium caries risk regular attenders?

A

compomer

68
Q

what type of restorative material is used for low caries risk patients?

A

composite resin

Dental Materials Science BDS2 (15 decks)

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