Resin Based Composite Materials - disadvantages Flashcards

1
Q

What is the most important shortcoming of resin based composites?

A

polymerisation shrinkage, lead to microshrinkage

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2
Q

What is microleakage?

A

leakage of minute amounts of fluids, debris and microorganisms through the microscopic space between a dental restoration or its cement and the adjacent surface of the prepared tooth

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3
Q

What are the effects of polymerisation shrinkage?

A

debonding

inflammation of the pulp

secondary caries

microleakage

marginal staining

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4
Q

What is more significant, shrinkage or shrinkage stress?

A

shrinkage stress

microfracture of the tooth tissue

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5
Q

How can you overcome polymerisation shrinkage stress?

A

can be minimised by;

material selection

method of material placement into the cavity
- amount
- position

use of the correct matrix system when constructing the approximal wall

employing various curing techniques

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6
Q

What is the problem with adding the lowering molecular weight monomers to make the material more manipulatable?

A

they exhibit the greatest shrinkage on polymerisation

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7
Q

What do you mix bis-GMA with to minimise shrinking?

A

bisphenol A polyethylene glycol diether dimethacrylate (bis-GMA) and UDMA as their resin component

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8
Q

In bis-GMA, bis-EMA and IDMA, is the resin hydrophobic or hydrophilic?

A

hydrophobic

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9
Q

What is the configuration factor?

A

C factor - ratio of bonded to unbonded surfaces

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10
Q

What is the effect of a high ratio of bonded to unbonded surfaces?

A

more stress potential

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11
Q

How would you build up a cavity?

A

incremental build up

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12
Q

Why build up a cavity in increments?

A

with each cured increment shrinkage is minimised and compensated for to some extent

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13
Q

Do you want to increase or decrease the C factor?

A

decrease

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14
Q

What is the compliance of the tooth?

A

ability of the tooth to withstand flexure

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15
Q

What does compliance of the tooth depend upon?

A

amount of the remaining tooth tissue

quality of the remaining tooth tissue

position of the remaining tooth tissue

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16
Q

Is resin composite materials photophilic or photophobic and what does this mean?

A

photophilic, light loving

17
Q

What is command cure?

A

up to us to determine when the material sets

18
Q

What is the effect of increased tertiary amine in the paste?

A

quicker it will set

19
Q

What is the oxygen inhibition layer?

A

material only partially cured in air

surface of the restoration remains tacky

has inferior mechanical properties

20
Q

What do you do with the oxygen inhibition layer? (2 options)

A

remove and restorative trimmed back to fully set material

create anaerobic environment such as using a matrix strip or cover with glycerine or dentine binding agent (probs easier)

21
Q

Are resin-based composites hydrophobic or hydrophilic?

A

hydrophobic

22
Q

Do you need good moisture control for placing resin based composites?

A

yes

resin is sensitive to water contaomination

23
Q

What happens if resin is contaminated with water?

A

water sorption

causes irreversible degradation of properties of resin composite

affects wear resistance and colour stability (staining)

24
Q

What is hydroscopic expansion?

A

material swells with water sorption

25
When can hydroscopic expansion occur?
start 15 mins after initial polymerisation and continues for up to 10 weeks
26
What is coefficient of thermal expansion?
resin has a COTE similar to that of the tooth
27
What is the effect of bisphenol A? (biocompatibility)
known to mimic the hormone oestrogen in vitro in the monomeric form linkage with male infertility and prostatic and breast carcinomas after polymerisation the risks are reduced
28
What is the problem with HEMA? (in many resin and bonding agents)
POWERFUL DERMATOLOGICAL SENSITISER CAUSING CHEMICAL DERMITITIS
29
Is HEMA cytotoxic after curing?
no, only before
30
When are Bis-GMA, TEGDMA and UDMA cytotoxic?
in vitro in their pure form
31
What is the drawback of composites?
the resin is relatively much weaker than the filler moisture control hard in the mouth, so results more variable undergo slow but steady degradation after placement
32
When would you use a dual-cured composite?
for crowns etc
33
What are the advantages of dual-cured resin composites?
if you cant get all the light to the area you can use a chemical