Composite Resin Material Science Flashcards
what are the IDEAL PROPERTIES of a restorative material?
- good mechanical properties
- bonds to tooth/compatible with bonding systems
- aesthetics
- easy to handle/viscosity
- thermal properties
- radiopaque
- anticariogenic
- biocompatible
what is composite resin composed of?
- filler particles
- resin
- camphorquinone
- low weight dimethacrylates
- silane coupling agent
what part of composite resin is hard?
the filler particles (glass)
what is the photo-initiator in composite called?
camphorquinone
what is the purpose of low weight dimethacrylates in composite resin?
allow varied mechanical properties
what is the purpose of silane coupling agent in composite resin?
allows intimate contact between filler and resin
what resin monomers are commonly used?
- BIS-GMA
* urethane dimethacrylates
what are the key characteristics of monomers?
- difunctional molecule (C=C bonds facilitate cross linking)
- undergoes free radical addition polymerisation
how is camphorquinone activated?
by blue light
what occurs when camphorquinone is activated?
- radical molecules produced
- these initiate free radical addition polymerisation of BIS-GMA
- leads to changes in resin properties
how can filler types in composite be classified?
- conventional
- microfilled
- hybrid
what are the handling characteristics of composite?
- condensable
- syringeable
- flowable
how can you make composite stronger?
adding more filler molecules
what occurs when more filler particles are added to composite?
- improved mechanical properties
- lower thermal expansion
- lower polymerisation shrinkage
- less heat of polymerisation
- improved aesthetics
what wavelength of light must be used when curing composite?
430nm-490nm
what are the advantages of light curing systems?
- extended working times
- less finishing
- immediate finishing
- less waste
- higher filler levels and less porosity
what is meant by depth of cure?
• the depth to which the composite resin polymerises sufficiently
what is the typical depth of cure for composite?
2mm
what can occur if you use increments larger than 2mm?
- underpolymerised base
* poor bonding to tooth
what problems can arise from light curing?
- recommended setting times too short
- polymerisation shrinkage
why is polymerisation shrinkage bad?
- affects bond to tooth
* potential for cuspal fracture & microleakage
how can polymerisation shrinkage be avoided?
use small increments
what type of composites are used most frequently now?
hybrids
what is meant by abrasion?
removal of surface layers when two surfaces make frictional contact
how can abrasion occur inside the mouth?
tooth grinds/slides along the opposing tooth surface
what acid is involved in the acid etch technique & how long must it sit on the tooth?
30% phosphoric acid & 20 secs
what is the thermal conductivity of composite?
low - which is good !
what is the thermal diffusivity of composite?
low - similar to dentine
what is the thermal expansion coefficient of composite?
high - which is bad !
what is meant by thermal diffusivity?
how readily a material transmits hear when exposed to a short/transient stimulus
