DM L1 Composites pt 2 Flashcards
what is a composite
2 or more material put together with each contributing to the overall properties
what are the 3 types of ways you can cure a composite + what system do they use
polymerisation/initiator system
- heat cured
- room temp cured
- light cured
how are light cured composites available to use + what does it contain
only 1 paste
DHPT (tertiary amine) + camphorquinone (light initiator)
both only react on presence of blue light
how do light curing composites set
polymerising (setting) = when light directed onto the paste
tertiary amine + light initiator react -> forms free radicals -> starts addition polymerisation reaction
what are the 6 advantages of light cured composites
- single component system
- less discolouration
- minimal porosity
- virtually command set (only set when light directed)
- rapid polymerisation
- thin inhibited layer
what are the disadvantages of light cured composites
- light sensitive during application (sunlight can set it)
- retina damage
- limited depth of cure
what does light cured composites have a limited depth of cure mean
cant pack whole restoration in at once, must do in small layers
OR ELSE
uncured resin at base of cavity -> soggy bottom
for curing composites , why do we need a high degree of conversion
high degree of conversion of C=C for optimum mechanical properties otherwise, restoration has poor foundation + will facture
what do the mechanical properties of composites depend on + percentages of how much is converted in monomers of light, self and heat cured
mech props depend on how much monomer is converted to polymer (via free radical polymerisation)
light cured: 65-80%
self cured: 60-75%
heat cured >90%
what must you ensure about the quality of the light source for curing composites + why
- VLA (visible light activated) between 450-500nm
- bc max light output of 460-480nm for camphorquinone absorption
how do you light cure a composite
- tip of light source close as possible to restoration surface - curing efficiency ↓ when light tip moved away
- light tip mustn’t be contaminated - curing efficiency ↓
- cure for recommended time + no less
- large restorations - no fanning, curing spots must overlap
what else affects depth of cure for composites
type + colour affects it
darker shades take longer to set than lighter
what current light sources are being used now for light curing units
VLA (visible light activated)
All light cured composites contain α-di-ketone (initiator)/Amine (activator)
E.g. Camphorquinone (activates 460-480nm) + DHPT
what are come examples of physical light curing units
- quartz-tungsten- halogen unit
- LED unit
- Plasma Arc (PAC) unit
- Argon laser unit
what are main advantages of using LED curing unit
- cordless (rechargeable battery)
- slimline
- ↓ lateral heat production (cf halogen)
- Long lasting light source
- Narrow emission spectrum (460-480 nm)
Peak 470 nm - Ultra energy efficient
- Near absorption of camphorquinone
1st gen cost >2nd gen
1 st gen low intensity radiation < 2 nd gen higher intensity radiation
what does PAC curing unit use + what are advants + disadvants
- Use xenon gas-ionised plasma
- High intensity white light filtered (↓heat) and allow emitting of blue light
- Claim to cure in 1-3secs -> used privately - expensive
what does Argon laser curing unit use + what are advants + disadvants
- Not used - high energy, intensity.
- expensive - lots of caution required
- Emits light at a SINGLE wavelength (490nm)
what are the 3 advantages of using composites
excellent easthetic results
less tooth tissue removed
command set if light cured
what are the disadvantages of using composites
- Lining materials limited - Ca(OH)2 , GIs
- Setting inhibited with eugenol based materials
- Doesn’t adhere intrinsically to enamel + dentine
- Adhesion to tooth cavity possible with acid-etch and adhesives
- Incremental placement + light-cure (3x’s longer to place compared to amalgam)
- Caries tends to progress more rapidly (-> polymerisation shrinkage on setting)
- Stick to instruments – problems with marginal adaptation
why does polymerisation shrinkage occur in setting composites + why problems occur bc of it
shrinkage -> double bonds converting to single bonds
- marginal adaptation
- breakdown of bonds to tooth tissues
- results recurrent caries
why do problems caused by composition up-taking water by adsorption
- glass filler adsorbs water onto its surface
- amount of water depends on resin content + quality of bond between filler + resin
- hydrolytic breakdown of bond between filler + resin
why do problems caused by composition up-taking water by absorption
as water absorbed:
- unreacted monomer ( incomplete polymerisation) + high soluble fractions in composite are released –> leaves a space which fills up with water
- water fills pores/air voids in cured resin -> due to mixing/placement
absorbed water affects wear resistance + colour stability
how can composite staining occur
- marginal - gap between restoration + tooth tissue - debris penetrates -> staining
- surface roughness of composite - debris gets trapped in spaces
- bulk discolouration - 2 paste amine cured systems
how can composite wear occur (disadvant)
abrasive, fatigue + corrosive wear
with time, resin matrix wears + filler particles protrude through surface giving material a dull appearance
