Composites Flashcards

1
Q

what are the 2 main components of composite resins

A

glass filler particles (hard) and resin (soft)

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2
Q

what is added to composites to give it better mechanical properties

A

dimethacrylates

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3
Q

what is added to composite to give it its light curing ability

A

camphorquinone - a photo initiator

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4
Q

what is added to composites to allow its intimate contact between glass filler particles and resin

A

silane coupling agent

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5
Q

conventional composite

A

large particles that take up about half of the material volume

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6
Q

microfine composite

A

tiny particles that take up a small portion of material

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7
Q

fine composite

A

small particles that take up a large portion of material

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8
Q

hybrid composite

A

mixture of tiny and large particles that take up a veyr large portion of the material

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9
Q

what monomer is commonly used in resins

A

BIS - GMA

has difunctional unit (c=c) that facilitates cross linking via free radical addition polymerisation

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10
Q

how does camphorquinone influence composite resins

A

requires blue light to be activated
once activated produces free radical molecules (electrically charges) which initiate polymerisation of monomer in resin e.g BIS-GMA
not all monomer molecules are converted

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11
Q

what does a greater number of filler particles result in

A

improved mechanical properties - increased strength, hardness, rigidity etc..
lower thermal expansion
lower polymerisation shrinkage

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12
Q

hardness ratio test

A

method of measuring depth of cure
cylinder of composite is cured
surface of column hardness determined and compared to other points. at 80% of surface value = depth of cure

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13
Q

depth of cure

A

depth at which composite resins polymerise sufficiently e.g where they are hard enough
standard depth usually = 2mm

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14
Q

what can happen if increments are more than 2mm in depth

A

under polymerised base resulting in decreased mechanical properties, poor bonding and subsequent early failure

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15
Q

what do bulk fill composites claim

A

they can have a depth of cure up to 6mm
use 2 photo initiators rather than one that have different absorption spectrums
controversy over whether claims can be replicated in mouth

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16
Q

is polymerisation an exothermic or endothermic reaction

A

exothermic meaning there is the potential for pulpal damage

17
Q

hybrid layer

A

resin material penetrating into dentinal tubules

18
Q

what dentine is most favourable for bonding

A

primary as open tubules allowing a good hybrid layer

tertiary dentine has an irregular structure so is harder to bond to

19
Q

configuration factor

A

ratio of bonded to unbonded surfaces

a high configuration factor increases polymerisation contraction stress that can lead to restoration failure

20
Q

polymerisation contraction shrinkage

A

monomers join together to form polymers during curing process (polymerisation) , as these short molecules join to form longer ones there is a decrease in volume - polymerisation contraction shrinkage
etch/bond is stronger than enamel interstitial strength so if a high configuration factor there is a risk of enamel fracture that can lead to early breakdown of restoration margins if microleakage occurs and possible secondary caries

21
Q

why do dentine bonding agents contain a solvent

A

to dry off any moisture

dont want to over dry dentine before placement as this can cause post - operative sensitivity

22
Q

pros and cons of conventional composite

A

strong but problems with finishing and staining as soft resin often at surface

23
Q

pros and cons of microfine composite

A

smaller particles give good aesthetics however has lower fracture stress, rigidity and increased abrasion

24
Q

pros and cons of hybrid composite

A

best all rounder out of composites on offer - mixture of particle sizes gives good mechanical and aesthetic properties

25
Q

hardness

A

measure of how resistant a material is to indentation

26
Q

discuss composites thermal properties

A

both thermal conductivity and diffusivity is low which is good
however thermal expansion coefficient is markedly higher than that of enamel or dentine so there is a risk of gaps forming

27
Q

discuss biocompatility of composite resins

A

generally okay unless material is not fully cured e.g due to poor technique, too deep an increment, inadequate light exposure etc
risk of unpolymerised resins irritating soft tissues