Clinical aspects of Composites

Question 1

what are the 4 key components of composite?

Answer 1

1. resin which forms the matrix
2. the filler particles
3. a coupling agent that must be bi-functional
4. optical modifiers/ pigments

Question 2

what is the role of the resin matrix?

Answer 2

absorb water, stain and prevent discolouration

Question 3

what is the resin matrix made of?

Answer 3

viscous MONOmers:

• bisGMA
• UDMA

these are highly viscous (aka thick and don’t move) due to their large benzene rings therefore TEGMA and HEMA are added to reduce viscosity.

Question 4

give examples of filler particles in composite

Answer 4

silica particles
quartz particles
glass particles like strontium, barium, zinc glass

Question 5

fillers are added because they REDUCE..

Answer 5

polymerisation shrinkage, water absorption, and thermal expansion

NB as more fillers are added, there is less resin matrix in the overall composite

Question 6

fillers are added because they INCREASE…

Answer 6

compressive/ tensile strength, modulus of elasticity, abrasion resistance, handling properties and aesthetics.

Question 7

what is name of the bifunctional molecule added to composite?
which FG’s does it have and what do they bind to?

Answer 7

organo-silane

silane= binds to OH group of filler particles
methacrylate= binds to resin matrix

Question 8

what is used as the optical modifier/ pigment?

Answer 8

a metal oxide like titanium oxide or aluminum oxide.

Question 9

what is used as the optical modifier/ pigment?

Answer 9

a metal oxide like titanium oxide or aluminum oxide.

Question 10

what is polymerisation shrinkage and why is it bad?

Answer 10

when monomers undergo chain reaction to join together, they will get smaller/ occupy a smaller space.

shrinkage causes MICROLEAKAGE (gap between the composite restoration and tooth) = secondary caries, staining and sensitivity.

Question 11

how do we prevent polymerisation shrinkage?

Answer 11

have large monomers

add more resin filler particles ( this will alter the handling too)

Question 12

for composite, excellent moisture control/ technique sensitivity is required.
When would it be hard to get moisture control?

Answer 12

when pt. has poor OHI- bleeding gum

on sub-gingival restorations

Question 13

etch, prime, bond…
what do we etch with?
what are the effects of etching on enamel?
what are the effects of etching on dentine?

Answer 13

37% phosphoric acid

etching ENAMEL: creates MICRO-PORES on surface, increase the SA therefore increases the surface energy

etching DENTINE: removes the smear layer (debris), unblocks and widens the dentinal tubules, exposes the network of collagen fibres

we etch for 15 s, wash for 15 s, gently dry. dont over dry= collapses the collagen network.

Question 14

composite restorations rely on INCREMENTAL build-up. what does this mean and why is it important?

Answer 14

the light wavelength can only penetrate 2mm max. of composite.

also reduces the Configuration- factor (RATIO of bonded tooth to un-bonded tooth) which reduces the stress on tooth.

incremental build up is able to occur due to the oxygen INHIBITION layer: the oxygen inhibits the top layer from setting fully therefore you can add more composite on top of it.

Question 15

composite sets by a FREE RADICAL ADDITION POLYMERISATION reaction. what are the stages of this?

Answer 15

1. ACTIVAION (via blue light at 450-490nm which activates the camphorquinone molecule in composite)
2. INITIATION - lucirin molecule
3. PROPOGATION
4. TERMINATION- hydroquinone

Question 16

why do we light cure composite for 30-50s for optimal light curing?

Answer 16

because only 50-50% of composite is converted from monomer to polymer during this time, by 50s everything that had to be converted from monomer to polyer has done, so shining the light for longer than this makes no difference.

Question 17

why does adding more fillers to composite reduce polymerisation shrinkage?

Answer 17

because if add large fillers, and then fill the spaces with smaller fillers, there is LESS RESIN therefore less polymerisation shrinkage upon light curing.

Question 18

organosilane is used as a bifunctional molecule to form a chemical bond between the filler particles and the resin matrix.
what are disadvantages of using a silane molecule?

Answer 18

age quickly in the bottle + become ineffective.

sensitive to water: break down in presence of moisture/ water.

Question 19

composites do NOT directly bond to teeth, therefore we need to bond them ourselves to teeth.

how do we bond composite to enamel?

Answer 19

we bond composite to enamel micro-mechanically via simply ETCHING with 37% phosphoric acid.

it de-calcifies the enamel rods –> exposes the prisms. this allows for MICRO-mechanical bonding to occur!

also etching is going to increase the SA therefore increase the surface energy.

Question 20

how do we bond composite to dentine?

Answer 20

harder to bond composite to dentine since dentine is wet/ hydrophilic whereas composite is hydrophobic.

1. ETCH: removes the smear layer, creates the HYBRID layer (where there is collagen AND resin) due to the infiltration of resin into the collagen matrix
2. add PRIMER: this will convert the hydrophilic dentine layer to hydrophobic
3. add DENTINE BONDING AGENT: this is basically unfilled/ lightly filled resin. this is light cured. there are new generations of DBA being developed such as the 2 in 1 systems or the self-etch primer.

Question 21

the etch, prime, bond technique is the gold standard for composite application.

what are the -ves/+Ves of this compared to the self-etch system?

Answer 21

etch, prime, bond= technique sensitive but self-etching systems are less technique sensitive

self-etch systems however use weaker acids= poorly etched enamel.