Composites

Question 1

What is a resin composite?

Answer 1

an organic resin matrix bonded with an inorganic filler

Question 2

What are the different types of filler sizes? why are they spherical?

Answer 2

macro, micro, hybrid, modern hybrid, nanocomposites

shape = spherical - less shrinkage

Question 3

Why is Composite Easy to Use (3)

Answer 3

flowable
osmotic
bulk-fill

Question 4

PROS (5)

Answer 4

aesthetics
conserve tooth structure
high compressive and tensile strength
high coefficient of thermal expansion
low thermal conductivity

Question 5

CONS

Answer 5

Technique sensitivity
polymerisation shrinkage

Question 6

why is polymerisation shrinkage bad? (6)

Answer 6

causes secondary caries, sensitivity, lowers wear resistance, marginal leakage, poor retention, staining

Question 7

in activation, how do you chemically set composites?

Answer 7

organic amine + organic peroxide

Question 8

How is composite set?

Answer 8

free radical addition polymerisation

Question 9

in activation, how do you light cure composite?

Answer 9

camphorquinone + blue light (450-490nm)

or

lucirin photo-initiator, absorb light at 410nm

Question 10

what is the gel point when light curing?

Answer 10

the composite is yielding, stress is transferred to tooth

Question 11

what is the maximum depth to light cure

Answer 11

2mm

Question 12

what are the steps of free radical polymerisation

Answer 12

activation
initiation
propagation
termination

Question 13

what is the resin matrix made of?

Answer 13

Bis-GMA, UDMA or TEGMA

Question 14

Bis-GMA, UDMA and TEGMA are dimethacrylates, what does this mean?

Answer 14

C=C bonds on both ends

Question 15

BIS-GMA is very viscous, how is this lowered?

Answer 15

adding TEGMA

Question 16

properties of Bis-GMA

Answer 16

movable
increases polymer conversion
more crosslinking
less shrinkage

Question 17

How is a resin composite made?

Answer 17

add resin matrix
add filler
coupling phase

Question 18

properties of inorganic fillers (6)

Answer 18

reduce:
- shrinkage
- water absorption
- thermal expansion

increase:
- compressive and tensile strength
- modulus of elasticity
- abrasion resistance

Question 19

What is the coupling phase?

Answer 19

chemical bond transferring stress between filler particle and resin

Question 20

what coupling agent is usually used

Answer 20

organosilane
- hydroxyl group on filler - siloxane end
- resin - methacrylate end

Question 20

what coupling agent is usually used

Answer 20

organosilane
- hydroxyl group on filler - siloxane end
- resin - methacrylate end

Question 21

Pros of coupling agent

Answer 21

increase strength

Question 22

cons of coupling agent

Answer 22

silane ages quickly
sensitive to water

Question 23

are composites hydrophilic or hydrophobic

Answer 23

hydrophobic

Question 24

what pH is etching

Answer 24

0.2

Question 25

what does etching do

Answer 25

decalcifies portions of enamel rods in 5-8 seconds dissolving calcium salts exposing interprismatic areas

Question 26

what bond strength does etching make the composite to the tooth

Answer 26

20MPa

Question 27

is etching true adhesion?

Answer 27

no, it is mechanical bonding

Question 28

why shouldn't the smear layer be kept?

Answer 28

impairs the bond to dentine can harbour bacteria

Question 29

how is the smear layer created

Answer 29

mechanical cutting of dentine

Question 30

why was the smear layer thought to be good?

Answer 30

it would block tubules to prevent bacterial penetration ITS WRONG THO.

Question 31

What is the hybrid layer

Answer 31

infiltration of resin monomers into the collagen fibre matrix of demineralised dentine

Question 32

steps to setting composite (5)

Answer 32

etch primer bonding adhesive apply composite resin cure

Question 33

what is the purpose of etching?

Answer 33

improve retention more surface area remove surface layer allows penetration of bonding agent into dentin

Question 34

what acid is etching?

Answer 34

35-37% phosphoric acid

Question 35

how long should you wait for etching

Answer 35

5 seconds

Question 36

why dont we leave etching on for a long time

Answer 36

exposed collagen fibres in the dentine collapse

Question 37

how do you remove etching

Answer 37

rinse and blot

Question 38

what does a primer do?

Answer 38

improves wettability and penetrates etched dentin tubules

Question 39

what is the primer?

Answer 39

a amphiphilic resin monomer with low viscosity

Question 40

what the the types of primer

Answer 40

acetone, water or ethanol based

Question 41

what is the bonding adhesive?

Answer 41

unfilled/lightly filled resin

Question 42

what does the bonding adhesive do?

Answer 42

bonds to collagen fibres in dentin, forming hybrid layer

Question 43

what is self etch?

Answer 43

acidic monomers that etch and prime dentine don't need to rinse and so it reduces application time and technique sensitivity

Question 44

what does self etch have to do?

Answer 44

dissolve smear layer decalcify intertubular dentine penetrate to embed superficial collagen = produce effective hybrid layer

Question 45

what is the smear layer?

Answer 45

created when tissue is cut with hand or rotary instruments