Resin composites

Question 1

acrylics are made up of a powder containing what? 3

Answer 1

Pmma beads
chemical initiator
pigment

Question 2

acrylics are made up of a liquid containing what? 2

Answer 2

Mma monomer
chemical activator - tertiary amine

Question 3

what is the type of setting reaction for acrylics?

Answer 3

free radical addition polymerisation

Question 4

what are the 4 stages for the free radical addition polymerisation of methyl methacrylate in the setting reaction of acrylic?

Answer 4

activation - peroxide exposed to tertiary amine creating 2 reactive units
initiation - methyl methacrylate cleaves double bond to single bond
propagation - units keep joining
termination - chain attaches to impurity/free radical or further growing chain

Question 5

what does a clinician have to consider when using acrylics? 8

Answer 5

material contracts on polymerisation
exothermic
potential discolour as any tertiary amine left over denatures turning clear-brown
correct powder to liquid ratio
irritate pulp -> methyl methacrylate
interact with eugenol - liner
low hardness
poor abrasion resistance

Question 6

compare the properties of acrylics to silicates 5

Answer 6

acrylics are less
- prone to erosion
- soluble
- brittle
- acidic
exhibit less thermal diffusivity

Question 7

what was added to acrylics to reduce shrinkage? what was the disadvantage?

Answer 7

inert filler
weakened the material

Question 8

definition of a resin composite

Answer 8

combination of 2 chemically different materials with an interface separating them. the properties could not be achieved by any of the components acting alone.

Question 9

resin composites are composed of a resin matrix containing what?

Answer 9

methacrylate/dimethacrylate monomers e.g. BIS GMA (big molecules with c=c to facilitate polymerisation

comonomers e.g. TEGMA

inhibitors

Question 10

what is the function of comonomers in the resin matrix of resin composites?

Answer 10

controls viscosity for manufacturers addition of filler and clinical handling

Question 11

what is the function of inhibitors in the resin matrix of resin composites?

Answer 11

stops the polymerisation occurring in storage

Question 12

the viscosity of the resin matrix reduces the mobility of unreacted monomers, what does this allow?

Answer 12

chair-side repair if restoration breaks as the C=C that have not been used can take part in further polymerisation with the repair

Question 13

resin composite is composed of what?

Answer 13

resin matrix
fillers
coupling agent

Question 14

resin composites have fillers (glass) which contain heavy metal in them, why is this useful?

Answer 14

for distinguishing restorations on radiographs due to radiopacity

Question 15

the coupling agent dimethacryloxypropyltrimethoxysilane (vinylsilane) is difunctional, explain this

Answer 15

the methacrylate interacts with the resin itself

the silane interacts and bonds with glass

Question 16

what is a property of the coupling agent dimethacryloxypropyltrimethoxysilane (vinylsilane)

Answer 16

good wetting - spreadability and coverage

Question 17

as the filler content increases in resin composite what happens to the surface hardness

Answer 17

increases

Question 18

as the filler content increases in the resin composite what happens to the % volume setting contraction

Answer 18

decreases

Question 19

as the filler content increases in the resin composite what happens to the coefficient of thermal expansion

Answer 19

decreases

Question 20

how do resin composites set?

Answer 20

chemically
or light

Question 21

what is camphorquinone?

Answer 21

its a component of resin
it gets excited at the wavelength of blue light and contains the necessary free radicals to start the polymerisation (curing)

Question 22

what are the 2 classifications of handling characteristics for resin composite?

Answer 22

packable -> highly viscous, packaging challenges for manufacturer

flowable -> more fluid, less filler

Question 23

what are the two classification of resin composites based on the ISO 4049?

Answer 23

type 1: restoration of cavities involving occlusal surfaces
type 2: all other polymer based filling and restorative materials

Question 24

to be on the market a resin composite must conform with what?

Answer 24

ISO 4049

Question 25

resin composites are under scrutiny for what? 3

Answer 25

cytotoxic components oestrogenicity of precursors tumour producing aerosols of fine glass particles

Question 26

what happens to the viscosity of resin composite when you squeeze it out of a tube?

Answer 26

increases so don't hang around

Question 27

what happens to the volume or resin composite when it sets?

Answer 27

contraction

Question 28

what are the 2 thermal properties of resin composite?

Answer 28

different thermal expansion than tooth which risks marginal percolation (separation from tooth at margin) thermal diffusivity matches dentine (conduction of heat)

Question 29

if the shade of resin composite is dark the incremental cure depth should be ?

Answer 29

reduced

Question 30

what is tribology?

Answer 30

as the material wears the amount of resin on the outer layer will change and that will affect the wear characteristics of the produce

Question 31

does resin composite have self adhesive mechanisms to bond to tooth substance?

Answer 31

no

Question 32

with increased porosity of resin composite strength?

Answer 32

decreases

Question 33

with increased porosity of resin composite the ability of the material to withstand fatigue forces?

Answer 33

decreases

Question 34

with increased coupling of resin composites strength

Answer 34

increases

Question 35

with increased coupling of resin composite the ability of the material to withstand fatigue forces

Answer 35

increases

Question 36

resin composite initially has a good appearance but it is susceptible to ? why?

Answer 36

staining resin matrix can take up fluids e.g. wine marginal deterioration - picture fram staining from wine/smoking etc.

Question 37

what is C-factor? (configuration factor)

Answer 37

the way the composite shrinks is based on the C-factor. the higher the C-factor the worse the possible outcome (marginal gaps caused by shrinkage)

Question 38

how is C-factor calculated?

Answer 38

number of bonded surfaces / number of un-bonded surfaces

Question 39

what is the photosensitiser that resin composite contains making it light sensitive?

Answer 39

camphorquinone

Question 40

what is the wavelength range that camphorquinone is sensitive to?

Answer 40

460-480nm -> visible blue light

Question 41

what should u do when light curing to avoid damage to the tissues?

Answer 41

wait for at least 30s between cycles to avoid heat build up

Question 42

what causes resin matrix softening? 2

Answer 42

air pockets cause inhibition of polymerisation chemical softening from foods and plaque acids

Question 43

how are cracks in resin restorations at the resin/filler interface propagated?

Answer 43

stress corrosion of filler causes hydrolytic filler degradation (filler breaks up) means lots of molecules at the interface increasing osmotic pressure