Composites Flashcards
What is a resin composite?
an organic resin matrix bonded with an inorganic filler
What are the different types of filler sizes? why are they spherical?
macro, micro, hybrid, modern hybrid, nanocomposites
shape = spherical - less shrinkage
Why is Composite Easy to Use (3)
flowable
osmotic
bulk-fill
PROS (5)
aesthetics
conserve tooth structure
high compressive and tensile strength
high coefficient of thermal expansion
low thermal conductivity
CONS
Technique sensitivity
polymerisation shrinkage
why is polymerisation shrinkage bad? (6)
causes secondary caries, sensitivity, lowers wear resistance, marginal leakage, poor retention, staining
in activation, how do you chemically set composites?
organic amine + organic peroxide
How is composite set?
free radical addition polymerisation
in activation, how do you light cure composite?
camphorquinone + blue light (450-490nm)
or
lucirin photo-initiator, absorb light at 410nm
what is the gel point when light curing?
the composite is yielding, stress is transferred to tooth
what is the maximum depth to light cure
2mm
what are the steps of free radical polymerisation
activation
initiation
propagation
termination
what is the resin matrix made of?
Bis-GMA, UDMA or TEGMA
Bis-GMA, UDMA and TEGMA are dimethacrylates, what does this mean?
C=C bonds on both ends
BIS-GMA is very viscous, how is this lowered?
adding TEGMA
properties of Bis-GMA
movable
increases polymer conversion
more crosslinking
less shrinkage
How is a resin composite made?
add resin matrix
add filler
coupling phase
properties of inorganic fillers (6)
reduce:
- shrinkage
- water absorption
- thermal expansion
increase:
- compressive and tensile strength
- modulus of elasticity
- abrasion resistance
What is the coupling phase?
chemical bond transferring stress between filler particle and resin
what coupling agent is usually used
organosilane
- hydroxyl group on filler - siloxane end
- resin - methacrylate end
what coupling agent is usually used
organosilane
- hydroxyl group on filler - siloxane end
- resin - methacrylate end
Pros of coupling agent
increase strength
cons of coupling agent
silane ages quickly
sensitive to water
are composites hydrophilic or hydrophobic
hydrophobic
what pH is etching
0.2
what does etching do
decalcifies portions of enamel rods in 5-8 seconds
dissolving calcium salts
exposing interprismatic areas
what bond strength does etching make the composite to the tooth
20MPa
is etching true adhesion?
no, it is mechanical bonding
why shouldn’t the smear layer be kept?
impairs the bond to dentine
can harbour bacteria
how is the smear layer created
mechanical cutting of dentine
why was the smear layer thought to be good?
it would block tubules to prevent bacterial penetration ITS WRONG THO.
What is the hybrid layer
infiltration of resin monomers into the collagen fibre matrix of demineralised dentine
steps to setting composite (5)
etch
primer
bonding adhesive
apply composite resin
cure
what is the purpose of etching?
improve retention
more surface area
remove surface layer
allows penetration of bonding agent into dentin
what acid is etching?
35-37% phosphoric acid
how long should you wait for etching
5 seconds
why dont we leave etching on for a long time
exposed collagen fibres in the dentine collapse
how do you remove etching
rinse and blot
what does a primer do?
improves wettability and penetrates etched dentin tubules
what is the primer?
a amphiphilic resin monomer with low viscosity
what the the types of primer
acetone, water or ethanol based
what is the bonding adhesive?
unfilled/lightly filled resin
what does the bonding adhesive do?
bonds to collagen fibres in dentin, forming hybrid layer
what is self etch?
acidic monomers that etch and prime dentine
don’t need to rinse and so it reduces application time and technique sensitivity
what does self etch have to do?
dissolve smear layer
decalcify intertubular dentine
penetrate to embed superficial collagen = produce effective hybrid layer
what is the smear layer?
created when tissue is cut with hand or rotary instruments
