DM L1 Composites pt 1

Question 1

what is a composite

Answer 1

2 or more materials put together with each contributing to overall properties

Question 2

name 5 uses of composites

Answer 2

restorative filling materials
fissure sealants
indirect restorations
endo post + cores
luting agents

Question 3

what are the 3 main phases/components of dental composites

Answer 3

organic matrix
inorganic filler
coupling agents

Question 4

what is the organic matrix phase of the dental composites

Answer 4

plastic monomer/resin material that polymerises (sets/cures) to form continuous phase
where binding the filler particles (via coupling agent)
hydrophobic

Question 5

what is the inorganic filler phase of the dental composites

Answer 5

enhances material’s mechanic properties

reinforcing particles and/or fibres dispersed in the matrix

Question 6

what is the coupling agent phase of the dental composites

Answer 6

bonding agent promotes adhesion between filler + resin matrix
hydrophilic end - chemically bonds to inorganic filler

Question 7

what is the organic matrix made of

Answer 7

monomers - chemically active components of composite - polymerises
-> glassy polymer in set state

Question 8

how do monomers form polymers in the organic matrix

Answer 8

monomer - viscous fluid, polymerises -> rigid polymeric material
free radical, addition polymerisation reaction

Question 9

what monomer does organic matrix contain

Answer 9

Bis-GMA = Bowens’ monomer
made from bisphenol A + glycidal methacrylate
2 metha
crylate groups , ends

Question 10

what is and why is another monomer used instead of Bis GMA in the organic matrix stage

Answer 10

Bis GMA = viscous monomer
so UDMA = urethane dimethacrylate used
UDMA less viscous than Bis GMA but still viscous

Question 11

except UDMA, what is alternate monomer can be used in the organic matrix

Answer 11

Ethoxylated Bisphenol A derivative

2 methacrylate undergo polymerisation - break C=C

Question 12

what does characteristics of monomers in organic matrix mean + how is it solved

Answer 12

Bis GMA - super viscous
UDMA - little less viscous
high viscous - monomers unworkable + add filler viscous increases more

diluent monomers (viscosity controllers added)
= gylcol dimethacrylates

Question 13

why dimethacrylates used in composites

Answer 13

low molecular weight of MMA (methyl methacrylate ) + low molar vol –> high vol shrinkage after polymerisation

high mole weight + low vol of Bis GMA –> lower vol shrinkage after polymerisation

Question 14

what happens to Bis GMA, UDMA + diluents when they polymerise

Answer 14

all have 2 sets of C=C double bonds

all polymerise + contribute to overall shrinkage of material when set

Question 15

what other 7 additives does organic matrix contain

Answer 15

1. hydroquinone = stabilises free radicals, prevents initiation inhibitor -> increases shelf life
2. Activator/initiator system for Room temp cure = DHPT/Benzoyl peroxide
3. Light cure = DHPT/Camphorquinone
   o Fillers
   o Pigments e.g. iron oxide
   o UV stabilisers
   o Optical brighteners

Question 16

what are 6 advantages of using fillers in composites

Answer 16

Advantages:
o Reduce setting shrinkage ∴ more filler-↓monomer/resin required
o Reduce coefficient of thermal expansion - closer to tooth tissue
o Enhance modulus and strength (compressive), hardness
o May provide radio-opacity e.g. quartz, fused silica, radio-opaque glass
o Control of aesthetics e.g. translucency, fluorescence, colour
o higher filler amounts, mech properties of composite increases

Question 17

what is important wheen choosing filler for composite

Answer 17

refractive index of filler + resin must closely match - avoid scattering light
–>otherwise full depth of cure not achieved on light curing the resin

end result = translucent material

Question 18

what must the filler be treated with and why is particle size of filler important

Answer 18

silane treated
o Single filler insufficient- many types used
o Avg particle size and particle size distribution = determines amt of incorporated filler
o Fillers have an effect on surface finish; i.e. smaller particles = smoother finish)

Question 19

what are 3 types of fillers

Answer 19

conventional/Macro
hybrid/blended or small particle hybrid
microfine/ microfillers

Question 20

what was 1st type of macro used in fillers and why is it not used much nowadays

Answer 20

>1µm
- 1 st used = ground quartz
- Good strength  BUT
Poor finish of composite - dull appearance ∵
protruding particles from resin surface

Question 21

what eg of microfillers used in fillers and why were they good + why bad

Answer 21

colloidal silica
increased viscosity to an already
viscous resin (more diluent had to be added)
- Can b e polished; v smooth surface finish
- V Large s.a. in contact with resin ∴ difficult to
obtain high filler loading ∴ mechanical props inferior
- CANNOT be used in post cavities

Question 22

what was the 2 stage process of microfillers

Answer 22

micro-filled composite polymerised - then ground into tiny particles
tiny particles put in another organic matrix to fill resin matrix
increases filler loading

Question 23

what are hybrid composites

Answer 23

contain large filler particles + small amount of colloidal silica

small particle hybrid comps -achieves high polished surfaces
packing density increases - as 2 diff sizes used as fillers

Question 24

what are 4 advantages of hybrid fillers + 1 disadvantage

Answer 24

• Favourable physical, mech and opt properties
• great wear resistance (compared to macrofilled)
• Surface morphology: superior to ; Conventional
• Radiopacity possible
  Disadvantages:
• ↑ surface roughness with time; resin wears

Question 25

what are characteristics of nano filled composites

Answer 25

Nano-filled composites:
Strength of a hybrid and polishing finish of a
microfilled material  to be researched

Question 26

when are micro-filled + hybrid composites used in teeth

Answer 26

micro-filled - anterior restorations –> low filler loading - so mech properties compromised
hybrid - posterior restoration - high filler loading

Question 27

what is coupling agent + how it works

Answer 27

silane

imp for filler + resin bonded -> so composite has acceptable mech properties
results in improved wear resistance of final result

Question 28

how is silane used with the filler particles

Answer 28

silane coated AROUND the filler particles (critical factor)

= silane treatment = γ-MPTS

Question 29

how does silane coupling agent bond to filler + organic matrix

Answer 29

silane coupling agent (hydrophilic) reacts with surface hydroxyl groups of filler - via condensation reaction

methacrylate group of silane (hydrophobic) bonds to (hydrophobic) organic resin - free radical polymerisation

Question 30

what is the other way for silane coupling agent to bind to filler + matrix

Answer 30

acid treating coupling agent

hydroxyl groups replaced with methoxy groups that carry out the reaction)

Question 31

why is stable adhesion bond needed between coupling agent + resin

Answer 31

o No bond; stress transfer between filler + resin insufficient -> creep/fracture/wear
o No bond; crack initiation sites -> fatigue failure
o Unstable bond = fracture -> disintegration

Question 32

what are advs of direct composites

Answer 32

excellent aesthetics
command set = light cure
conservative tooth tissue preparation

Question 33

what are disadvs of direct composites

Answer 33

polymerisation shrinkage
required bonding procedure
required incremental placement
residual monomer present
water uptake -> staining 
breakdown of bonding
wear of resin matrix