Composite Flashcards
What are the ideal properties of direct filling materials
mechanical – strength, rigidity, hardness
bonding to tooth / compatible with bonding systems
thermal properties
aesthetics
handling / viscosity
smooth surface finish/ polishable
low setting shrinkage
radiopaque
anticariogenic
biocompatible
What types of glass filler particles are in composite resin
microfine silica
quartz
borosilicate glass
lithium aluminium silicate
barium aluminium silicate
What is BIS-GMA a reaction product of
bisphenol-A and glycidyl methacrylate
What are the key characteristics needed to be monomers in resin
- difunctional molecule
(C=C bonds – facilitate crosslinking)
undergoes free radical addition polymerisation
How is composite resin able to be cured by light
Camphorquinone
What process occurs under blue light to cause the composite to cure
Camphorquinone –
-activated by blue light
-produces radical molecules
-these initiate free radical addition polymerisation of BIS-GMA
-leading to changes in resin properties (ie increased molecular weight, so increased viscosity, and strength)
causes degree of conversion of resin:
35-80%
Why do composite resins contain low weight dimethacrylates (eg TEGDMA)
added to adjust viscosity & reactivity
Why does composite contain silane coupling agent
good bond between filler particle and resin is essential
normally water will adhere to glass filler particles, preventing resin from bonding to the glass surface
a coupling agent is used to preferentially bond to glass and also bond to resin
How does a coupling agent act with the fillers and resin
Surrounds the glass fillers allowing better bonding between them and the resin
What handling characteristics are desirable
condensable - “amalgam feeling” - greater porosity
syringeable - good adaptation, less porosities, easy to apply
flowable - lower filler content, more shrinkage, difficult to apply, place for them -with fibre ribbons
What effect does adding filler particles have on composite resins
improved mechanical properties
-strength, rigidity, hardness, abrasion resistance etc
lower thermal expansion (still not perfect)
lower polymerisation shrinkage (still a problem)
less heat of polymerisation (BUT not negligible)
improved aesthetics
some radiopaque
What types of composite curing are there
self curing (two pastes)
UV activation (obsolete, one paste)
Light curing
-blue light 440nm(one paste)
direct curing (in mouth)
indirect curing / post curing(in laboratory)
How does a composite self cure
Free radicals from the reaction break the resin c=c bonds
polymerisation (formation of chain)
What reactants are present in self cure composite
benzoyl peroxide + aromatic tertiary amine
What are the advantages of light curing systems
extended working time
-on-demand set, triggered when light activated
less finishing
immediate finishing
less waste
higher filler levels (not mixing two pastes)
less porosity (not mixing two pastes)
What part of composite sets quickest
Most of blue light absorbed close to surface which sets readily and becomes hard
How is depth of cure value calculated according to ISO 4049
Column of composite light cured, soft comp scraped off, measured distance of hard comp is then divided by 2 giving the depth of cure
How is depth of cure defined
DoC is defined as depth at which material HARDNESS is about 80% that of the cured surface
the depth to which the composite resin polymerises sufficiently
At what depth does the composite resin usually polymerise sufficiently
typically 2mm
What composite increment thickness is best to use in restorations
2mm as greater than this wikk result in under-polymerised bases
-soggy bottom and poor bonding to tooth
What is an example of a bulk fill comp
Tetric evoceram
How is a bulk fill composite different to hybrid composites
Lucerin initiator as well as camphorquinone
Has different optical absorption spectrum
hence UV and blue light needed to polymerise (cure) material fully
What are some potential problems of light curing
light / material mismatch - overexpose
premature polymerisation from dental lights - avoid exposure
optimistic “depth of cure” values
-product, shade, light exposure & intensity
-use small increments - 2 mm max
recommended setting times too short
-product, light used, light/ material distance,
-contamination or damage to light guide,
-timer accuracy,
-variations in light output (eg over repeated use, between different units)
use > 30 s
polymerisation shrinkage
-affects bond to tooth,
-potential for cuspal fracture, microleakage
- use small increments - light from different angles
What dangers occur with light curing
Exothermic reaction so adjacent enamel and dentine can conduct heat up to 16 degree rise
Divergent light beam - unless optical rod is ALWAYS close to the composite resin surface
SOME blue light MAY illuminate patient’s soft tissues and may cause thermal trauma
two clinical incidents in 2017
