composite resins

Question 1

classification

Answer 1

filler particles - conventional, microfine or hybrid
setting - light or self-cure
area of use - anterior/posterior
handling - condensable/syringeable/flowable

Question 2

composition

Answer 2

filler particles - glass
resin
camphorquinone
low weight dimethacrylates
silane coupling agent

Question 3

ideal properties

Answer 3

mechanical - strength, rigidity, hardness
bonding to tooth/compatible with bonding systems
thermal
aesthetics
radiopaque
handling/viscosity
anticariogenic
polishable
low setting shrinkage
biocompatible

Question 4

filler particles

Answer 4

control aesthetics
not involved in polymerisation
polymerisation shrinkage inversely proportional to filler loading

Question 5

hybrid

Answer 5

range of filler particle sizes so can have higher %

• better mechanical properties
• less polymerisation shrinkage
• less heat of polymerisation

Question 6

camphorquinone

Answer 6

photoinitiator
activated by blue light
produces radical molecules
initiates free radical addition polymerisation of Bis-GMA
leads to changes in resin properties
- increased molecular weight so increased viscosity and strength
can add inhibitor (hydroquinone) to prevent premature polymerisation - shelf-life (0.1%)

Question 7

resin - monomers used

Answer 7

Bis-GMA

urethane dimethacrylates

Question 8

resin - monomer characteristics

Answer 8

difunctional molecule
C=C bonds facilitate X-linking
undergoes free radical addition polymerisation

Question 9

unreacted monomer

Answer 9

potential to cause an allergic reaction

Question 10

low weight dimethacrylates

Answer 10

e.g. TEGDMA
added to adjust viscosity and reactivity
because the resin monomers are highly viscous, adding any filler would make it too stiff

Question 11

why is a silane coupling agent necessary?

Answer 11

good bond between filler particle and resin is essential

- but normally water adheres to glass filler particles, prevents resin from bonding to the glass surface

Question 12

silane coupling agent

Answer 12

preferentially bonds to glass and also to resin
bonds hydrophobic resins to hydrophillic glasses
hydroxyl group bonds to glass
methacrylate group bonds to resin via C=C

Question 13

flowable

Answer 13

lower filler content

• more shrinkage
• poorer mechanical properties

Question 14

effect of adding filler particles

Answer 14

improved mechanical properties
improved aesthetics
increased abrasion resistance
lower thermal expansion
reduced polymerisation shrinkage
reduced heat of polymerisation
some radiopaque

Question 15

curing development

Answer 15

self (2 pastes)
UV activation (obsolete, 1 paste)
light curing (blue light, 440nm, 1 paste)
direct curing
indirect/post curing (in lab)

Question 16

advantages of light curing

Answer 16

extended working time
less finishing
immediate finishing
less waste
higher filler levels - not mixing 2 pastes
less porosity - not mixing 2 pastes

Question 17

light cure sources

Answer 17

halogen or LED

LED much more efficient - light source spectra matches camphorquinone absorption much better

Question 18

activation self-curing 2 pastes

Answer 18

benzoyl peroxide initiator

aromatic tertiary amine activator

Question 19

light-curing 1 paste

Answer 19

camphorquinone
blue light (430-490nm)

Question 20

activation

Answer 20

free radicals break resin C=C bonds

Question 21

hardness

Answer 21

most of blue light absorbed close to surface - where it sets most readily and becomes hard

Question 22

depth of cure

Answer 22

depth to which it polymerises sufficiently such that its hardness is about half that of the cured surface
2mm
increment thickness

Question 23

> 2mm

Answer 23

underpolymerised base

• ‘soggy bottom’
• poor bonding to tooth - early failure

Question 24

what do manufacturers do re depth of cure?

Answer 24

exaggerate it

Question 25

bulk fill e.g. tetric ceram

Answer 25

different optical absorption spectrum - UV and blue light needed to polymerise (cure) fully
lucerin initiator as well as camphorquinone

Question 26

safety

Answer 26

exothermic reaction
divergent light beam
thermal trauma to STs
staff - ocular damage

Question 27

light curing potential problems

Answer 27

light/material mismatch - overexposure
premature polymerisation from dental lights
optimistic DOC values
recommended setting times
polymerisation shrinkage - micro leakage - use small increments

Question 28

properties

Answer 28

biocompatible (but unreacted monomer)
quite hard but some concerns for posterior
strong 
rigid - high YM
bonding good but technique dependent 
hybrid best mechanical properties
thermal conductivity low - good as avoids pulpal damage
TEC high - poor (micro leakage)
good aesthetics - translucency
some radiopaque
not anticariogenic
on demand set and polishable
polymerisation shrinkage

Question 29

conventional

Answer 29

strong
but problems with finishing and staining
soft resins and hard particles

Question 30

microfine

Answer 30

smoother surface - better aesthetics for longer period
reduce shrinkage stress
inferior mechanical properties

Question 31

wear

Answer 31

resin soft relative to hard filler particles - more wear

conventional - bigger filler particles so rougher surface

Question 32

factors affecting wear - material

Answer 32

filler material
particle size distribution
filler loading
resin formulation
coupling agent

Question 33

factors affecting wear - clinical

Answer 33

cavity size and design
tooth position
occlusion
placement technique
cure efficiency
finishing methods

Question 34

bonding to tooth surface

Answer 34

reduce microleakage
counteract polymerisation shrinkage
shear bond strength
minimise cavity design
stress transfer to tooth and bone
 - good bonding = no stress concentration areas

Question 35

amalgam vs composite failure rate

Answer 35

amalgam much lower failure rate

Question 36

Filtek silorane posterior composite

Answer 36

not methacrylate based - lower polymerisation shrinkage

no grey/white high stress areas in stress concentration map