composite Flashcards
composition of comp
1 glass filler particles
2 resin
3 camphorquinon
4 low weight dimetharcylate
5 silane coupling agent
sizes of filler particles
conventional 10-40um
fine
microfine extremely small about 0.04um
hybrid most common
common resin
BIS GMA = bisphenol and glycidyl methacrylate
urethane dimethacrylate
chemical structure of resins
c=c
difunctional molecules
what sort of reaction does comp undergo
resin facilitate crosslinking when double bonds are activated by light
free radical addition polymerisation
blue light wavelength
430-490nm
do all resin monomers react?
only 30-80%
what happens when resin is light cured and undergoes additon polymerisation
resin increases in molecular weight and viscosity and strength
function of Low weight dimethacrylate
adjust viscosity and reactivity
adjust rate of polymerisation
function of Silane coupling agent
allow intimate contact between filler and resin
normally water adheres to glass filler particle preventing resin from boding to surface
is glass filler or resin stronger and harder
glass filler
which filler type has the highest filler load
hybrid
Effect of adding filler particles
o improved mechanical properties
o improves strength
o rigidity
o hardness
o abrasion resistance
o lower thermal expansion
o lower polymerisation shrinkage because less resin as a % of volume
o less exothermic
o improved aesthetics
types of Curing method of comp
self cure 2 paste
light cure 1 paste
posterior restoration use what type of filler particle comp
heavly filled
anterior restoration use what type of filler particle comp
microfine or submicron hybrid
Advantages of light curing
- extended working time
- short setting time
- higher filler levels than 2 paste
- less porosity than 2 paste
- less bubbles, voids which makes the material weaker
Disadvantages of light curing
- premature polymerisation
- overly optimistic depth of cure
- retinal damage
- exothermic rxn might damage pulp and soft tissues
- polymerisation shrinkage -> debond -> microleakage
- If you use increments that is >2mm, soggy bottom, underpolymerised base, wont bond to underlying tooth fully
recommended setting time
> 30s
Differing definitions of DoC
Old ISO4049 definition:
Height of the residual fully cured composite divided by 2
New definition:
DoC is defined as the depth at which the material hardness is about 80%-90% that of the cured surface
DoC definition
Which is defined as the layer thickness you can apply while ensuring the composite is cured adequately
DoC values
- 2mm for hybrid comp
- up to 6mm for bulk fill comp but usually 4mm
What is bulk fill?
- can place larger increments in bulk
what light source for bulk
polywave
what photo initiator in bulkfill
- Lucerin initiator + camphorquinone
thermal properties of CR
- high thermal expansion (bad)
- low thermal diffusivity (good)
- low thermal conductivity (good)
MECHANICAL properties of CR
- stronger than enamel and dentine
- hard
- rigid
- bonds to tooth
does enamel or dentine have higher frature stress and rigidity
- enamel has higher fracture stress and rigidity ie more brittle
PL vs EL
PL= beyond PL, stress and strain not linear
EL=when elastic limit stress is released, material will still return to the original dimension. beyond EL, permanent deformation
Conventional vs microfine vs hybrid in terms of strength
hybrid > conventional > microfine (lower EL and YM)
aesthetics
microfine (smooth) > hybrid > conventional (staining)
which thermal property should ideally be the same as tooth structure
thermal expansion
what about composite affets plaque retention?
surface ruhgness
what determines the surface roughness of the composite
size of the particles.
larger particles ie conventional will have more roughness because more resin removed first
higher filler load = less or more wear?
less wear
what clinical factors affect the wear of composite
clinical factors:
size of cavity
location ie post or ante
technique of placement
cure time
occlusion
How does comp bond to tooth?
- acid etch for enamel
- dentine bonding system for dentine
Advantages of GOOD composite bonding
- reduces microleakage
- counteracts polymerisation shrinkage
- no need for undercuts like amalgam so less tooth structure removed
- stress transfer to bone and tooth
- good bond spreads load evenly
what happens when there is a poor bond between comp and tooth?
- poor bond concentrates stress as certain points leading to fracture or failure
How to decide between RMGIC, compomer, composite?
- RMGIC for high caries risk
- compomer for medium caries risk
- comp for low caries risk
what initiates free radical additoin poly
camphorquinone
material factors affecting wear of composite
material factors:
glass filler type, some glass harder
particle size distribution
filler loading ie % of volume filled by particles
resin formula
coupling agent strength
