Composites

Question 1

what are the 2 main components of composite resins

Answer 1

glass filler particles (hard) and resin (soft)

Question 2

what is added to composites to give it better mechanical properties

Answer 2

dimethacrylates

eg Bis-GMA

Question 3

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

Answer 3

camphorquinone - a photo initiator

Question 4

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

Answer 4

silane coupling agent

hydrophilic end - bond to hydroxyl group of glass
hydrophobic - resin

Question 5

conventional composite

Answer 5

large particles that take up about half of the material volume

Question 6

microfine composite

Answer 6

tiny particles that take up a small portion of material

Question 7

fine composite

Answer 7

small particles that take up a large portion of material

Question 8

hybrid composite

Answer 8

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

Question 9

what monomer is commonly used in resins

Answer 9

BIS - GMA

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

Question 10

how does camphorquinone influence composite resins

Answer 10

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

Question 11

what does a greater number of filler particles result in

Answer 11

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

Question 12

hardness ratio test

Answer 12

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

Question 13

depth of cure

Answer 13

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

Question 14

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

Answer 14

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

Question 15

what do bulk fill composites claim

Answer 15

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

Question 16

is polymerisation an exothermic or endothermic reaction

Answer 16

exothermic meaning there is the potential for pulpal damage

Question 17

hybrid layer

Answer 17

resin material penetrating into dentinal tubules

Question 18

what dentine is most favourable for bonding

Answer 18

primary as open tubules allowing a good hybrid layer

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

Question 19

configuration factor

Answer 19

ratio of bonded to unbonded surfaces

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

Question 20

polymerisation contraction shrinkage

Answer 20

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

Question 21

why do dentine bonding agents contain a solvent

Answer 21

to dry off any moisture

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

Question 22

pros and cons of conventional composite

Answer 22

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

Question 23

pros and cons of microfine composite

Answer 23

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

Question 24

pros and cons of hybrid composite

Answer 24

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

Question 25

hardness

Answer 25

measure of how resistant a material is to indentation

Question 26

discuss composites thermal properties

Answer 26

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

Question 27

discuss biocompatility of composite resins

Answer 27

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