Composite Flashcards
name three advantageous properties of composite
aesthetic
strong
wear resistant
what three phases do composites exist as
resin matrix
dispersed inorganic filler particles
silane coupling agents
what size of composite filler particles are considered to be fine
0.5 -3 micrometres
what size of composite filler particles are considered to be microfine
0.04 micrometres - 0.2 micrometres
what size of composite particles are considered to be nanofilled
1-10 micrometres
name three clinical uses of composite
direct filling material for caries
abrasion/ erosion restoration
trauma
what are the five components of composite filling material
filler particles
resin
camphorquinone
low weight dimethacrylates
silane coupling agents
what is the purpose of camphorquinone
it is a photoinitiator
what is the function of low weight dimethacrylates in composite
allow mechanical properties to be varied
what is the function of silane coupling agents in composite
allows intimate contact between filler and resin
what monomers are used in the resin for composite material
Bis-GMA
urethane dimethacrylates
what is a key characteristic of a monomer for composite resins
has a difunctional molecule
- carbon-carbon double bonds that facilitate crosslinking that generate the growth of the monomer via free radical addition polymerisation
what does camphorquinone require to be activated
blue light
what does camphorquinone produce when activated by blue light
radical (electrically changed) molecules which initiate polymerisation of Bis-GMA
what are the two changes that occur to composite resin properties after activation of camphorquinone
increases molecular weight of resin
increases viscosity and strength
what is the action of silane coupling agents in composite
prevents moisture that might develop on the glass (filler) surface - which would prevent a good bond
where should microfilled or submicron hybrid composites be used
anteriorly
where should heavily filled composites be used
posterior
what type of composite resin can be used anywhere in the mouth
submicron filled
which type of composite material has the highest filler loading capacity which is wanted for a stronger material
hybrid composite resin
name four effects of adding more filler particles to composite
improved mechanical properties
lower thermal expansion
lower polymerisation shrinkage
improved aesthetics
how does light-cure composite become activated
blue light (430-490 nm) activates camphorquinone which forms free radicals, breaking double bonds which establishes polymerisation reaction
how do self cured composites become activated
when the 2 pastes are mixed together they produce free radicals, breaking double bonds and allowing polymerisation reaction
name three advantages of using a light-cure composite
extended working times
less finishing and polishing
higher filler particles
why do light cure composites have higher filler composition that self cure composites
self cure composite requires 2 pastes to be mixed and must be low enough viscosity to allow this to happen
what is the standard way of testing a composite’s depth of cure
cure composite in a cylinder - scrape soft uncured composite from bottom, half the volume of hard composite that remains and this value is considered depth of cure
what is the hardness profile of a composite
the depth of cure is the depth at which the hardness is 80% of the top surface
which layer of thickness should you use for hybrid composites
2mm increments
name three potential problems of light curing composite
premature polymerisation from dental lights
optimistic depth of cure values
light/ material mismatch leading to overexposure
name four factors that depth of cure depends on
product
shade
duration of light exposure
intensity of blue light source
name two patient considerations when using light cure composite
it is an exothermic reaction - can be damaging to the pulp if not sufficient hard tissue left
diverging blue light beam
name two of the main concerns of polymerisation shrinkage
poor bonding to tooth/ microleakage
potential for cuspal fracture
how does the fracture strength of composite resin compare to enamel
it is better than enamel (350 MPa for composite)
what characteristics would a composite being placed in large posterior cavity require
high strength
high young’s modulus (rigidity)
high abrasion resistance
what is one advantage and one disadvantage of conventional filler composite
strong
problems with finishing due to soft resins and hard particles
name one advantage and one disadvantage of microfine filler composites
smooth surface for longer due to smaller particles
lower fracture strength and easily abraded
what three factors of composite affect its wear resistance
filler particle size distribution
resin type
effectiveness of coupling agent
what is used to etch enamel when preparing the tooth for composite application
37% phosphoric acid for 20 seconds
what is the purpose of acid etch technique
removing the top layer of enamel, revealing a notched sub-structure
what are the aims of bonding to tooth structure
reduce microleakage
counteract polymerisation shrinkage
what two characteristics does composite fall short on when compared to enamel and dentine
hardness
elastic modulus
what is composite’s thermal conductivity
low - good as it avoids pulpal damage
which materials match enamel and dentine the best for thermal expansion
glass ionomer cements
when may composite filling materials be considered not biocompatible
if they are not fully cured which can lead to unpolymerised resin leaking out
what does caries left at the ADJ result in
unsupported enamel and early breakdown of the restoration margin
what is the smear layer and how is it removed
layer of organic material which is produced whenever a highspeed or slow speed handpiece is used on dentine
this is removed by etch
when finishing a composite restoration, what is used for gross reduction
diamonds, carbide finishing burs
finish disks
strips of alumina
what is used for final finishing of composite
abrasive impregnated rubber rotary instruments
disks
rubber cup with polishing paste
why is a smooth finish of composite desired
to prevent retention of plaque
when might flowable composites be indicated
cervical erosion
abfraction
