Plastic restorations - resin modified glass Ionomer cements Flashcards
What type of reaction is the polymerisation component?
light activated free-radical methacrylate reaction
What is the maximum depth of the cement which can be light cured (polymerisation)?
0.5mm
Why is the max depth of light curing for the polymerisation reaction 0.5mm?
limited light transmission through these material
What is a tri-cured glass ionomer resin?
material can be light cured and chemically cured
a second chemical initiator system has been incorporated into some RMGIC products to compensate for the limited light-cure polymerisation reaction
to set the resin
What are the 2 types of reactions in order to set the resin part?
polymerisation reaction - free radical methacrylate reaction effected by light activation
- light
+ redox reaction
- chemical
How any stages are in the dual-cured RMGIC reaction?
4
What are the 4 clinical stages of the dual-cured RMGIC reaction?
- commences when powder and liquid mixed together
- light activation of polymerisation reaction
- light activation stopped
- restoration complete
What are the 4 sages of the dual-cured RMGIC setting reaction?
What are the stages of the tri-cured RMGIC setting reaction?
Do the acid-base and polymerisation setting reactions need to be initiated at the same time?
yes
Why do the acid-base and polymerisation setting reactions need to be initiated at the same time?
as the material wont fully set at the same time
Why is does the acid-base and polymerisation reactions rarely start at the same time?
as the addition of HEMA retards the setting rate of the acid-base reaction
Why does shrinkage occur?
polymerisation phase
What kind of setting reaction occurs when HEMA polymerises?
exothermic
What are the 2 mechanisms for bonding to the tooth?
calcium chelation
subsidiary collagen bonding
What are factors limiting the success of the adhesive bond?
What can cause excessive expansion?
affinity for polyHEMA for water can cause excess expansion if not mixed correctly (i.e too much monomer)
What happens as the polyEMA absorbs water?
mechanical properties begin to fall
What is the fluoride release like?
sustained release
When is the most fluoride released form the cement?
first 10-15 days
What allows fluoride release long-term?
slow setting of glass ionomer phase of the cement
polyHEMA matrix provides n easier pathway for the ionic species to migrate through the cement
HEMA is hydrophilic
What is occurring as fluoride is released?
the restoration is degrading
is R,GIC prone to staining?
yes, intrinsic staining
When should a tri-cure system be used?
where the material cannot be fully light cured
What can occur if the material is not fully cured?
unconverted monomer can easily leach out from incompletely cured RMGIC
Adverse reactions reported with HEMA
risk of damage to pulpal tissue if in contact
What are the advantages of RMGIC?
Fluoride ion release
early strength
adhesion - molecular bonding
long working time
limited moisture sensitivity
low solubility or erosion of cement margins
simple to use
command set
can be finished immediately after light curing (resin part might be cured but the acid -base reaction will be going on for some time)
seals dentinal tubules
What can be released as part of the setting reaction?
benzoyl iodides and benzoyl bromides
What are the benefits/disadvantages of releasing benzoyl iodides and benzoyl bromides during the setting reaction?
they are cytotoxic and can potentially mop up ay residual cavity bacteria
What are the disadvantages of RMGIC?
EXOTEERMIC REACTION ON CURNG
SHRINKAGE ON CURING
INCOMPLETE CURE PROCEDES WEAK MATERIAL
MONOMER LEACH
SWELLIG DUE TO MOISTURE UPTAKE
powder is moisture sensitive (storage problem)
releasing benzoyl iodides and benzoyl bromid
Why is there shrinkage on curing?
due to the polymer in it (resin)
Why is phase separation a disadvantage?
lead to expansion and potentially fracture of the teeth
where is the material weaker?
where redox setting of the resin phase is used
When would you use the RMGIC?
Small-sized class I cavities
class III and V cavities
non-carious tooth surface loss lesions
core build ups
Can be used as a lining material and composite on top
deciduous teeth
blocking undercuts
bonding dental amalgam
How much tissue do you need remaining to use RMGIC?
> 50%
Why ca you use RMGI on deciduous teeth?
How are RMGICs predominantly used?
lining material
What does increasing the powder in the RMGIC do?
increase strength of the material and decrease its retention to tooth tissue and vice versa
What 3 forms can the RMGIC come in?
powder/liquid
encapsulated (best)
paste/paste systems
What does the paste/paste system claim to enhance?
the polishability and wear resistance
by utilising nanotechnology
Why can the paste/paste presentations lead to non-uniform mix?
may become separated during storage
Do some RMGIC requirre a primer?
yes
What is the role of a primer?
usually infiltrate the dentine and make alternative adhesive restorations less successful
modify smear layer, wet tooth surface and facilitate adhesion of the RMGIC
