tooth coloured resto materials 1: resin and bonding materials Flashcards
what are the properties were looking for in a material for a chipped tooth
strong durable aesthetic non toxic-safe needs to resist forces( for posterior) depending on the location in the mouth
what is a composite
a product with at least two distinct phases
what is the purpose of composite
to combine two or more materials to produce one with superior properties
what does composite contain
dental filler, resin matrix and an organic binder
can composites bind by themselves
no they need a binding agent which helps them bind to the tooth
what are advantages of composite
aesthetics conservation of tooth structure adhesion to tooth-by binding system low thermal conductivity alt to amalgam
what is the MINAMATA convention
the UK has signed up to get rid of mercury worldwide- not only in dentistry mostly about environmental conditions
when did the UK sign the MINAMATA convention
2016
disadvantages of composite
technique sensitivity
polymerisation shrinkage
decreased wear resistance
what is the disadvantage of polymerisation shrinkage
this can lead to gaps forming in the composite filling
bacteria can fill this
produce acid
and lead to the carious process all over again
what acid is used to etch the tooth
phosphoric acid
what % of phosphoric acid is in the etch
37%
how much % of bacteria spreading reduces with rubber dam isolation
98.5%
what are the two types of polymerisation
addition
condensation
how do composite fillings set
by free radical addition polymerisation
what are the stages of free radical addition polymerisation
activation
initiation
propagation
termination
what is the activation stage
chemical activation which requires organic amine and organic peroxide
or light activation camphorquinone and blue light
what is the wavelength of the blue light
450-490nm
how do we measure composite polymerisation
FTIR spectroscopy and see the different carbon carbon double bonds
how much do dental composites polymerise
50-60%
what does poor bonding to teeth lead to
poor retention
staining
sensitivity
secondary caries
what are the three materials which bind the filler particles together
bis-GMA
UDMA
TEGMA
what is the importance of binding the filler particles together
provides workablilty
characteristics of bis-GMA
extremely viscous
why is bis-gma viscous
due to large benzene rings
how is the viscosity in bis-GMA lowered
by adding TEGMA w
what happens when TEGMA is added to bis-GMA
FREELY MOVABLE
increases polymer conversion
increases crosslinkage
increases shrinkage
what happens when we light cure
stress set up at bonding interface
how do we reduce the shrinkage and stress
by adding filler- this doesn’t reduce the volume
most common filler materials
fine glass fibres of barium or strontium as they add radiopacity
how much shrinkage are most materials
2% linear shrinkage
how are fillers classified
type of material
size
shape
what shape are fillers
irregular or spherical
why are spherical particles easier
easier to incorporate into resin mix leaving less resin mix
why do we add different size spherical fillers
to fill in all the gaps possible therefore reduce polymer shrinkage
what are the typical percentages of resin and filler
20% resin
80% filler
why do we use fillers
we want to reduce
shrinkage
water sorption
thermal expansion
what do we want to increase when using fillers
tensile strength
modulus of elasticity
abrasion resistance
what do you need to add to bind the filler to the polymer
coupling agent
what are the adv of the coupling agent
transfers stresses
what do we use as the coupling agent
organosilane
what end does the siloxane bind to
hydroxyl groups on filler
what end binds to the resin
methacrylate
what does the OH groups on the filler bind to
siloxane on organosilane
what are the disadvantages of organosilane
age quickly in the bottle
sensitive to water so breaks down in contact with water
what are common silane agents
vinyl triethoxysilane
methacryloxypropyltrimethyloxysilane
what is the strength of composite
170-260 MPA
what is the tensile strength
30-55mpa
what are the three types of composite
universal
packable
flowable
what is the difference in the three types of composite
change is viscosity or filler type
what are flowables
slightly less filler- lower viscosity
disadvantages with flowables
less filler therefore more shrinkage and reduced wear
what is the ph of phosphoric acid
0.2
what does etching do
decalcifies part of the enamel rods
how long does it take for decalcification to occur
5-8 seconds
what type of bonding is etching
mechanical with only a strength of 20mpa
what is the point of etching
removing surface debris
produce 10-20 infold of SA
increase wetting
what is the issue with bonding to dentine
hard to keep dry-23% water
moist living tissue
what is the smear layer
created by the mechanical cutting of dentine- essentially dentine debris of variable thickness
in addition smear plugs block dentinal tubules
what are the benefits of the smear layer
can protect dentine and pulp from bacteria
eliminated diffusion of dentinal fluid
how do we achieve optimum bonding
leave the smear layer
remove the smear layer
the smear layer is modified
the smear layer is partially removed or partially replaced
how does enamel bond to dentine
it is essentially an exchange process involving replacement of minerals (removed by hard dental tissues) by resin monomers which when they set micro mechanically into the porosities
what is hybridisation
the infiltration of resin monomers into the collagen matrix of demineralised dentine followed by polymerisation
what are the steps for bonding to dentine
acid etching
primer
bonding adhesive
why do we acid etch
improves the retention of the restoration
increases the SA
removes smear layer from prep
allows penetration of bonding agent into dentine
what do we need to be careful of with acid etch
protecting the pulp
why do we use a primer
improves the wettability of the prep
penetrates etched dentine tubules
applied in a thin layer and air dry but don’t dry too much
why is the bonding agent important
unfilled or lightly filled resin
adhesive bonds to collagen fibrils in dentine mechanically locks in- hybrid layer
applied in a thin layer
how long do we light cure the bond
40 seconds- 2x 20 second timing
what are the characteristics of primer
it is amphiphilic and low viscosity
what is added to primer
solvents to improve viscosity
what are the three types of etch and rinse primers
acetone based
ethanol based
water based
example of acetone based primer
all bond 2
one step
example of ethanol based primer
optibond
example of water based primer
scotch bond MP
scotchbond 1
what are the advantages of 2 step process of bonding
application time is lower
technique sensitivity is lower
