Resin Based Composite Materials - disadvantages

Question 1

What is the most important shortcoming of resin based composites?

Answer 1

polymerisation shrinkage, lead to microshrinkage

Question 2

What is microleakage?

Answer 2

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

Question 3

What are the effects of polymerisation shrinkage?

Answer 3

debonding

inflammation of the pulp

secondary caries

microleakage

marginal staining

Question 4

What is more significant, shrinkage or shrinkage stress?

Answer 4

shrinkage stress

microfracture of the tooth tissue

Question 5

How can you overcome polymerisation shrinkage stress?

Answer 5

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

Question 6

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

Answer 6

they exhibit the greatest shrinkage on polymerisation

Question 7

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

Answer 7

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

Question 8

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

Answer 8

hydrophobic

Question 9

What is the configuration factor?

Answer 9

C factor - ratio of bonded to unbonded surfaces

Question 10

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

Answer 10

more stress potential

Question 11

How would you build up a cavity?

Answer 11

incremental build up

Question 12

Why build up a cavity in increments?

Answer 12

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

Question 13

Do you want to increase or decrease the C factor?

Answer 13

decrease

Question 14

What is the compliance of the tooth?

Answer 14

ability of the tooth to withstand flexure

Question 15

What does compliance of the tooth depend upon?

Answer 15

amount of the remaining tooth tissue

quality of the remaining tooth tissue

position of the remaining tooth tissue

Question 16

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

Answer 16

photophilic, light loving

Question 17

What is command cure?

Answer 17

up to us to determine when the material sets

Question 18

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

Answer 18

quicker it will set

Question 19

What is the oxygen inhibition layer?

Answer 19

material only partially cured in air

surface of the restoration remains tacky

has inferior mechanical properties

Question 20

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

Answer 20

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)

Question 21

Are resin-based composites hydrophobic or hydrophilic?

Answer 21

hydrophobic

Question 22

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

Answer 22

yes

resin is sensitive to water contaomination

Question 23

What happens if resin is contaminated with water?

Answer 23

water sorption

causes irreversible degradation of properties of resin composite

affects wear resistance and colour stability (staining)

Question 24

What is hydroscopic expansion?

Answer 24

material swells with water sorption

Question 25

When can hydroscopic expansion occur?

Answer 25

start 15 mins after initial polymerisation and continues for up to 10 weeks

Question 26

What is coefficient of thermal expansion?

Answer 26

resin has a COTE similar to that of the tooth

Question 27

What is the effect of bisphenol A? (biocompatibility)

Answer 27

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

Question 28

What is the problem with HEMA? (in many resin and bonding agents)

Answer 28

POWERFUL DERMATOLOGICAL SENSITISER CAUSING CHEMICAL DERMITITIS

Question 29

Is HEMA cytotoxic after curing?

Answer 29

no, only before

Question 30

When are Bis-GMA, TEGDMA and UDMA cytotoxic?

Answer 30

in vitro in their pure form

Question 31

What is the drawback of composites?

Answer 31

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

Question 32

When would you use a dual-cured composite?

Answer 32

for crowns etc

Question 33

What are the advantages of dual-cured resin composites?

Answer 33

if you cant get all the light to the area you can use a chemical