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YR 2 - Restorative Materials > Composites > Flashcards

Composites Flashcards

1
Q

What is a resin composite?

A

an organic resin matrix bonded with an inorganic filler

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2
Q

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

A

macro, micro, hybrid, modern hybrid, nanocomposites

shape = spherical - less shrinkage

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3
Q

Why is Composite Easy to Use (3)

A

flowable
osmotic
bulk-fill

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4
Q

PROS (5)

A

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

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5
Q

CONS

A

Technique sensitivity
polymerisation shrinkage

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6
Q

why is polymerisation shrinkage bad? (6)

A

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

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7
Q

in activation, how do you chemically set composites?

A

organic amine + organic peroxide

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8
Q

How is composite set?

A

free radical addition polymerisation

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9
Q

in activation, how do you light cure composite?

A

camphorquinone + blue light (450-490nm)

or

lucirin photo-initiator, absorb light at 410nm

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10
Q

what is the gel point when light curing?

A

the composite is yielding, stress is transferred to tooth

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11
Q

what is the maximum depth to light cure

A

2mm

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12
Q

what are the steps of free radical polymerisation

A

activation
initiation
propagation
termination

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13
Q

what is the resin matrix made of?

A

Bis-GMA, UDMA or TEGMA

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14
Q

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

A

C=C bonds on both ends

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15
Q

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

A

adding TEGMA

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16
Q

properties of Bis-GMA

A

movable
increases polymer conversion
more crosslinking
less shrinkage

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17
Q

How is a resin composite made?

A

add resin matrix
add filler
coupling phase

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18
Q

properties of inorganic fillers (6)

A

reduce:
- shrinkage
- water absorption
- thermal expansion

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

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19
Q

What is the coupling phase?

A

chemical bond transferring stress between filler particle and resin

20
Q

what coupling agent is usually used

A

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

20
Q

what coupling agent is usually used

A

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

21
Q

Pros of coupling agent

A

increase strength

22
Q

cons of coupling agent

A

silane ages quickly
sensitive to water

23
Q

are composites hydrophilic or hydrophobic

A

hydrophobic

24
Q

what pH is etching

A

0.2

25
Q

what does etching do

A

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

26
Q

what bond strength does etching make the composite to the tooth

A

20MPa

27
Q

is etching true adhesion?

A

no, it is mechanical bonding

28
Q

why shouldn’t the smear layer be kept?

A

impairs the bond to dentine
can harbour bacteria

29
Q

how is the smear layer created

A

mechanical cutting of dentine

30
Q

why was the smear layer thought to be good?

A

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

31
Q

What is the hybrid layer

A

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

32
Q

steps to setting composite (5)

A

etch
primer
bonding adhesive
apply composite resin
cure

33
Q

what is the purpose of etching?

A

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

34
Q

what acid is etching?

A

35-37% phosphoric acid

35
Q

how long should you wait for etching

A

5 seconds

36
Q

why dont we leave etching on for a long time

A

exposed collagen fibres in the dentine collapse

37
Q

how do you remove etching

A

rinse and blot

38
Q

what does a primer do?

A

improves wettability and penetrates etched dentin tubules

39
Q

what is the primer?

A

a amphiphilic resin monomer with low viscosity

40
Q

what the the types of primer

A

acetone, water or ethanol based

41
Q

what is the bonding adhesive?

A

unfilled/lightly filled resin

42
Q

what does the bonding adhesive do?

A

bonds to collagen fibres in dentin, forming hybrid layer

43
Q

what is self etch?

A

acidic monomers that etch and prime dentine

don’t need to rinse and so it reduces application time and technique sensitivity

44
Q

what does self etch have to do?

A

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

45
Q

what is the smear layer?

A

created when tissue is cut with hand or rotary instruments

YR 2 - Restorative Materials (7 decks)

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