composite material Flashcards
name 5 different restorative materials
- composite resins
- amalgam
- glass ionomers
- compomers
- ceramics
when do you use direct filling materials
- new dental caries
- abrasion / erosion
- failed restoration / secondary caries
- trauma
what are the ideal properties of composite
- mechanical
- bonding to tooth / compatible with bonding systems
- thermal properties
- aesthetics
- radiopaque
- handling / viscosity
- anticariogenic
- smooth surface finish / polishing
- low setting shrinkage
- biocompatible
what traits are included in mechanical properties
- strength
- rigidity
- hardness
want it to be strong enough to withstand forces and be long lasting
what are the 2 main components of composite
- glass ionomer particles
> hard - resin material
> soft
> holds the particles together
what are the components of composite resin
- filler particles
- resin
- camphorquinone
- low weight dimethacrylates
- silane coupling agent
what is camphorquinone
the photo initiator
why is low weight dimethacrylates added
to improve the product
name filler particles in glass
- microfine silica
- quartz
- borosilicate glass
- lithium aluminium silicate
- barium aluminium silicate
- others
compare the particle size and % volume of different types of composite
conventional:
> Particle Size = 10-40um
> % volume = 50
microfine
> Particle Size = 0.04-0.2 um
> % volume = 25
fine
> Particle Size = 0.5-3um
> % volume = 60-70
hybrid
> Particle Size = range
> % volume = 70
what is meant by hybrid composite?
a mix of large particles and smaller sizes
what does more filler particles do to the material
increases the hardness of the material
what monomers are used in resins
> BIS-GMA
[reaction product of bisphenol-A and glycidyl methacrylate]
> urethane dimethacrylates§
what are the key characteristics of monomer
> difunctional molecule
- C = C bonds
- facilitate crosslinking (needed for polymerisation reaction)
> undergoes free radical addition polymerisation
[need composite to be cured to be a rigid, strong material with a hard surface]
what is camphorquinone activated by
blue light (curing light)
what does camphorquinone produce
radical molecules (electrical charge) these initiate free radial addition polymerisation of BIS-GMA [goes from the paste like material to undergo polymerisation and from the cross links so they end up a much stronger material]
what changes does the the camphorquinone product / reaction lead to in resin properties
> increased molecular weight
increased viscosity
increased strength
causes a degree of conversion of resin (35-80% unreacted monomer)
give an example of a low weight dimethacrylates
TEGDMA
why is low weight dimethacrylates added
to adjust viscosity and reactivity
to improve the material
[material would set too quickly without this being added so you would have no time to work in the patient’s mouth - allows more time as it slows it down a little]
why is silane coupling agent added
use to preferentially bond to glass and also bond to resin
a good bond between filler particles and resin is essential so this helps with that
what effect does water have on the bond between filler particles and resin
normally water will adhere to the glass filler particles and this prevents resin from bonding to the glass surface
name resin-filler particle coupling materials (unsure if this is even a q im not sure what i meant in my notes lol typical x)
> silane
eg methacryloxypropyltrimethoxysilane
> methoxy groups hydrolyse to hydroxyl groups react with absorbed water or -OH groups in filler
what are the uses of composite
> aesthetic importance
class III, IV and V permanent restorations
class II - limited occlusal wear
labial veneers
inlays, onlays indirect technique)
cores
modified forms as luting cements (some dual cured)
what are the classifications of composite
> filler type
curing method
area of use
handling characteristics
what are the types of curing methods
> light cured
> self cured
what are the different areas of use for composite
> anterior
- microfilled
- submicron
- hybrid
> posterior
- heavily filled
> universal
- submicron hybrid
what are the different classifications of the handling characteristics of composite
> condensable
- amalgam feeling
- pack into cavity
- greater porosity
> syringeable
- good adaptation
- less porosities
- easy to apply
> flowable
- lower filler content
- more shrinkage
- difficult to apply
- less viscous
what is involved in composite development
> filler particles
curing (activation)
particle / resin bonding
what are the effects of adding filler particles
> improved mechanical properties
- strength
- hardness
- rigidity
> improved aesthetics
- gives a real tooth like appearance
> increased abrasion resistance
> lower thermal expansion
- still not perfect
> lower polymerisation shrinkage
> less heat of polymerisation
> some radiopaque
explain the composite curing developments
> self curing
- 2 pastes
> UV activation
- obsolete
- 1 paste
> light curing
- blue light 440nm
- 1 paste
> direct curing
- in mouth
> indirect curing / post curing
- in lab
how does self curing composite activation work
benzoyl peroxide and aromatic tertiary amine
results in free radicals (break resin C=C bonds)
how does light curing composite activation activation
camphorquinone and blue light (430-490nm)
results in free radicals (break resin C=C bonds)
the blue light activates the material which breaks the carbon bonds
what are the light sources for curing composite resin
> halogen
[old style - have ordinary white light and a filter which allows the blue light to pass through]
> LED
This is most efficient
what are the advantages of light curing systems
> extended working time
- on demand set
- can pack / place the material the way you want to before you activate it
> less finishing
> immediate finishing
> less waste
> higher filler levels
> less porosity
what is the depth of cure for composite
the depth is which the composite resin polymerises sufficiently such that is hardness is about half of that cured surface
typically 2mm
indicates increment thickness to use when building a restoration
can you cure increments greater than 2mm
no
by definition you wont have polymerised that material accurately
soggy bottom
what are the different problems with light curing
> light / material mismatch
- overexposure
- dont match up to the composite resin absorption spectrum (need to use correct blue light for the material)
> premature polymerisation from dental lights
- avoid exposure
- careful with operating light as it contains blue light in lower intensities
> optimistic depth of cure values
- small increments = 2mm max
> recommended setting times too short
- timer accuracy
- depends on light used
- distance of light from material
- use longer than 30 seconds (dont want to undercook)
> polymerisation shrinkage
- affects bond to tooth
- potential for cuspal fracture
- microleakge
- use small increments
- light from different angles
what needs to be considered with regards to the curing light and the patient
consider the patient’s safety
> exothermic reaction
- release of heat in resin material
- heat conducts to adjacent enamel and dentine
- there can be a 16 degrees rise in temperature (a 5.5 change is accepted as potentially irreversible traumatising dental pulp)
> modern devices are brighter / more intense
- idea is that more intensity accelerates curing, reducing exposure duration needed
- optical rod must always be close to the composite resin surface or some blue light might escape and may cause thermal trauma to the patient’s soft tissues
what needs to be considered with regards to the curing light and the clinical staff
> ocular damage
- dont look directly at the light on a regular basis
> use safety shields and glasses to protect eyes
what are the clinical requirements of a large posterior cavity filled with composite
- high strength
- high young’s modulus
- high abrasion resistance
- can withstand biting forces
what are the clinical requirements of filling a deciduous tooth with a large pulp with composite
- strong in thin section
- wear of tooth
- other properties more important like bonding and microleakge
what are the advantages and disadvantages of conventional composite
- strong
- problems with finishing and staining due to soft resins and hard particles
what are the advantages and disadvantages of microfine composite
smaller particles = smoother surface, better aesthetics for longer
but
inferior mechanical properties (elastic limit and young’s modulus)
what are the advantages and disadvantages of hybrid composite
originally compromise between conventional and microfine
improved filler loading and coupling agents have led to improvements in mechanical properties
can hardness be derived from a stress strain curve
no
hardness is no strength
what does hardness as a property include
- material surface
- resistance to scratching
- indentation resistance
if you dont have a hard material it will experience abrasion or wear
define abrasion
removal of surface layers when two surfaces make frictional contact
how does abrasion happen to a restored tooth
Tooth grinds / slides along the opposing tooth surface (or restorative material at its surface)
Tooth surface is abraded - loss of material surface layers, roughened surface
how affects does abrasion have on the tooth
> appearance - can be visible to the eye
plaque retention
sensation when in contact with tongue - unpleasant feeling
explain the wear removal process with regards to composite
resin is initially removed
then when the glass filler particles are exposed then they are removed
different depths of roughness for the different particle sizes
> conventional = 80microns
> microfine = 10 microns
what are the factors affecting wear of a material?
> filler material > particle size distribution > filler load > resin formulation (if it is very soft it will wear easily but if it is hard then it will resist) > coupling agent (affects bonding)
what are the factors affecting wear clinically?
> cavity size and design > tooth position > occlusion > placement technique > cure efficiency (need to cure properly to get the properties you expect) > finishing methods
how do you bond composite to enamel?
acid etch technique
how do you bond composite to dentine?
dentine / universal bonding systems
what is the acid etch technique?
apply 37% phosphoric acid to the enamel surface for 20 seconds then wash off
this creates etches / gaps in the enamel that is then filled with unfilled resin
what is the typical bond strength of enamel and dentine to composite
40MPa
dependent of surface preparation of tissue, composite brand and test method
what does bonding to tooth substance do
> reduce microleakage
- good bond will reduce the likelihood of gap between restoration and tooth
- microorganisms can exist in these gaps and cause the restoration to fail
> counteract polymerisation shrinkage
> shear bond strength
> minimise cavity
- no need for retention undercuts
- bond holds restoration in place
> stress transfer
- restoration does not have to withstand full stress
- stress is transferred to tooth and bone
what are the composite mechanical properties
there was a table w lots of numbers but i dunno how important it was to know ALL of them lol this is a reminder to have a littlee nosey at it but i personally dont think i’ll know it xoxo gossip girl
what are the thermal properties of composite?
> thermal conductivity is low (this is good)
> thermal expansion coefficient is high (this is poor)
explain thermal conductivity with composite
it is low
avoids pulpal damage from hot and cold foods and drinks
heat is transferred poorly so composite acts as a protector
explain thermal expansion with composite
we want thermal expansion to be the same as the tooth to reduce microleakage
thermal contraction causes an ingress of saliva and bacteria
thermal expansion of dentine and enamel is roughly half of that of composite
this means composite tries to expand at twice the rate of the tooth which puts more stress on the bond making it more likely to fracture
explain the aesthetic property of composite
good range of shades to match tooth colour important in the anterior more than the posterior translucency maintenance of properties over life time resistance to staining surface finish
explain radiopaque as a property of composite
some are radiopaque not all
helps to diagnose secondary caries
ideal for looking for fragments that have come off or fracturered
explain the handling / viscosity properties of composite
gives a choice on what material suits you / what you prefer to use
> light curing
- demand setting
- more time to work with material
- problems w safety
> mixing / working times
> viscosity
- variations
- some materials flow
- others need to be packed / condensed
- advantage / disadvantage depends on cavity
is composite anticariogenic
generally no
few products claim to release fluoride
does composite give a smooth surface finish / is it polishable
- can be good
- technique / product sensitive
- part of aesthetics
what does low setting shrinkage have to do with composite
polymerisation shrinkage is still a problem as stresses develop at hard tissue surfaces (make debonding more likely)
bond agents and clinical techniques help minimise the impact of this
what is the biocompatibility of composite
- ok
- increasing concern about resins in general
- not all monomer is polymerised
- over time the monomer can be released and irritate surrounding tissues
list the properties of composite that affect choice of material
mechanical bonding thermal aesthetic handling surface finishing polymerisation shrinkage anticariogenic biocompatible radiopacity
when would you use RMGI
high caries risk patients who are frequent attenders
when would you use compomer
medium caries risk patients
caries under control
regular attenders
when would you use composite resin
low caries risk patients
