Composite resins Flashcards
direct filling materials - ideal properties
mechanical properties;
- strength, rigidity, hardness
bonds to tooth/compatible with bonding systems
good aesthetics
suitable handling and viscosity
good thermal properties
smooth surface finish/polishable
radiopaque
anticariogenic
biocompatible
composite r
esin constituents
filler particles
resin
camphorquinone
low weight dimethacrylates
silane coupling agent
direct filling materials; applications
new dental caries
abrasion/erosion
failed restorations/secondary caries
trauma
types of composite resin filler particles
microfine silica
quartz
borosilicate glass
lithium aluminium silicate
barium aluminium silicate
monomers used in the resin of composite
BIS-GMA
urethane dimethacrylates
key characteristics of the monomer in composite resin
C=C bonds
- facilitate cross linking
undergoes free radical addition polymerisation
Camphorquinone - features and purpose in composite resin
activated by blue light
produces radical molecules
- these initiate free radical addition polymerisation of BIS-GMA
- leads to changes in resin properties
low weight dimethacrylates - why are these added to composite?
to adjust viscosity and reactivity
function of a silane coupling agent in composite resin?
normally water will adhere to glass filler particles, preventing resin from bonding
- a coupling agent is used to preferentially bond to glass and also bond to resin
uses of composite resin
where aesthetics important
inlays, inlays
cores
modified forms as luting cements
- some dual cured
classifications of compose resin
filler type
curing method
- light cured
- self cured
- dual cured
area of use
handling characteristics
- condensable - greater porosity
- syringe able - good adaptation - less porosities
- flowable - lower filler content, more shrinkage
effects of adding filer particles to composite
improved mechanical properties
- strength, rigidity, hardness etc
lower thermal expansion
lower polymerisation shrinkage
less heat of polymerisation
improved aesthetics
some radiopaque
advantages of light curing system
extended working time
- on demand set
less finishing
immediate finishing
less waste
higher filler levels
less porosity
- not mixing 2 pastes
define ‘depth of cure’
the depth to which the composite resin polymerises sufficiently
- hardness is about 80% of the cured surface
typically 2mm
6mm for bulk fill
indicates increment thickness to use when building a restoration
consequences of using increments larger than 2mm
under-polymerised base
- ‘soggy bottom’
- poor bonding to tooth = early failure
potential problems with light curing
premature polymerisation from dental lights
- avoid exposure
optimistic ‘depth of cure’ values
- dependent on product, shade and light intensity
polymerisation shrinkage
- affects bond to tooth
- potential for cuspal fracture and microleakage
light curing - safety
use safety shields or safety glasses
material factors affecting wear of composite
filler material
particle size distribution
resin formulation
filler loading
coupling agent
clinical factors affecting wear of composite
cavity size and design
tooth position
occlusion
placement technique
cure efficiency
finishing methods
Acid etch technique for composite
30% phosphoric acid for 20 seconds
bonding to tooth surface - benefits
reduce micro leakage
counteract polymerisation shrinkage
- good bond reduces likelihood of gap between restoration and tooth
minimise cavity design
- no need for retention undercuts as bond holds restoration in place
stress transfer
- restoration does not have to withstand full stress - transferred to tooth and bone
composite resin thermal properties
low thermal conductivity - good
low thermal diffusivity - similar to dentine
high thermal expansion coefficient = poor
composite resin biocompatibility
generally considered ok
- increasing concern about resins in general - not all monomer polymerised
