11. GIC + Resin Modified Glass Ionomer Flashcards
LOs
GIC
What are GICs and what do they exhibit ?
- they are versatile materials that exhibit?
(HINT - good properties they exhibit???)
GIC
- have ability to self adhere to tooth so used in range of applications
What applications are they used for?
GIC origin - need to know??? Or delete
Why is isolation from moisture not really required for GIC compared to dental composites?
- as GIC is a water based cement
GIC
1
Composition?
2
EGs of these components (HINT what acid or glass powder may be used?)
3
From these components, what are the 3 essential ingredients?
3
- polyalkenoic acid
- glass powder
- water
GIC composition
- why is water an important/ main component?
- as water based cement
- water is essential for the setting of these cements
THE BASE: ION LEACHABLE GAS
1
What does the glass included in GIC formulation function as?
2
Why is this important?
3
What type of glass do commercially available GIC contain?
1
- a base
2
This allows the acid-base reaction to occur
3
Fluoro/ alumino/ silicate (FAS)
EXTRA
- the role of glass was first used by Wilson + Kent + recognised the importance of alumina: silicate ratio
THE BASE: ION LEACHABLE GAS
1
What does the basicity of the glass depend on?
2
What would happen if we just used silicate glasses on their own without alumina?
3
Why?
1
alumina : silicate ratio
2
- silicate glasses on their own lack the basicity
3
- BECAUSEs it contains sillica tetrahedra that are linked together hence carry no charge
- the inclusion of alumina into the sillica network makes it adopt a tetrahedral geometry similar to sillica to form an alumina tetrahedra
EXTRA Explanation
- alumina is trivalent + carries a 3+ charge HENCE it does not counteract the negatively charged Oxygens as effectively as sillicone with a 4+ charge
- hence additives such as sodium, calcium + strontium are included which makes it not only basic but also enhances the ability of these ions to be leached out - which can then take part in the acid-base reaction
- the substitution of calcium with strontium in these glasses can be achieved using strontium oxide and strontium fluoride in places calcium oxide and calcium fluoride with the glass forming mixed
- strontium also enhances the radioopacity of these cements
THE BASE: ION LEACHABLE GAS
1
Why are additives such as sodium, calcium + strontium added? Why is this useful?
2
How can the substitution of calcium with strontium in these glasses be achieved?
3
Why is strontium useful?
1
- alumina is trivalent + carries a 3+ charge HENCE it does not counteract the negatively charged Oxygens as effectively as sillicone with a 4+ charge
- hence additives such as sodium, calcium + strontium are included which makes it not only basic but also enhances the ability of these ions to be leached out - which can then take part in the acid-base reaction
2
- by using strontium oxide and strontium fluoride in places calcium oxide and calcium fluoride with the glass forming mixed
3
- strontium also enhances the radioopacity of these cements
- enhances the ability of these ions to be leached out - which can then take part in acid-baser reaction
THE ACID: POLY(ALKENOIC ACID)
1
What acids are used in GIC formulations?
2
Examples of these acids and copolymers (IMAGE)
3
How does the nature of the polymer affect the set cement?
1
Polyalkenoic acids
- these are water soluble polymers that behave as acids
3
- the nature of the polymer influences the properties of the set cement
- use of high molecular weight polymer
= usu better mechanical properties of cement
= BUT there is also an increase in viscosity so harder to mix powder phase with it
- hence a balance is needed for optimum properties
TARTARIC ACID
- present in nearly all GIC formulations
1
Advantages of GIC containing tartaric acid?/ main func? (IMAGE)
2
How does Tartaric acid extend setting time / how does it work on a molecular level?
3
How do you use GIC/ mix the components in clinic? (DIAGRAM on image)
2
- interacts with glass particles + liberates aluminium ions which interact with polymeric acid
- hence aluminium ions aren’t immediately available for reaction with the polymeric acid so working time of cement is maintained
furthermore
- also inhibits dissociation of polymeric acid hence delaying the onset of the initial setting
3
- have powder + liquid
- one level scoop of powder on polymer paper mixing pad
- add 2 drops of liquid (hold bottle vertically)
- (ensure good drops with no air bubbles)
- mix and use
GIC SETTING REACTION
1
Type of reaction
2
What is produced?
3
Approx setting time?
GIC SETTING REACTION
Stages? (IMAGE)
EXTRA INFO SAID IN LECTURE FOR STAGE 2 - help with understanding
- on ionisation, polymeric acid molecules adopt a more linear form which makes the carboxylic acid groups more accessible
- hence ions released on interaction of polymeric acid with glass then interact with poly acid molecules to form ionic cross links that causes the gelation
- set cement contains glass particles cores embedded in a poly acid salt matrix
- water is also present both as loose and bound
- loose water can be removed via desiccation
- bound water is chemically trapped within the matrix
GIC SETTING REACTION
SUMMARY OF 3 STAGES
GIC
- ratio of powder:liquid is V important
1
Usually supplied as?
2
Potential problems when hand mixing?
3
How is this hand mixing variation being overcome?
4
Why is this useful?
5
2
EXTRA
- EG if powder left in bottle for long time, settles at bottom and becomes more compact + dense , so if scoop, would be too much
- hence recommended to turn bottle upside down to loosen powder before dispensing
5
EXTRA
- need to secure mixing devices do not incorporate air bubbles
GIC
1
Forms it is dispensed?
2
Other types of cements
+ what type of glass do they contain?
GIC - AQUEOUS SYSTEMS
- are aqueous systems
- water is essential for reaction to take place
1
Water allows what to occur?
2
How does water cause acid-base reaction to occur + how does it cause F- to be released?
WATER BALANCE IN GICs
- Water is essential ingredient in setting of GICs
1
What happens if water is absent?
2
How long is the setting reactions
3
the balance of water in the first 24-48 hrs is also V important
Why?
4
What happens if you have excess hydration or a lot of moisture around restoration
5
What happens if dehydration occurs or if Material not given correct amount of moisture?
6
Why may this dehydration occur?
1
GIC cannot set + reaction cannot occur
6
- patient is a mouth breather
- patient has dry mouth
ADHESION BETWEEN GIC + TOOTH STRUCTURE
- GIC can adhere to tooth tissue
- huge clinical advantage
- exact mechanism of adhesion is not clear
But what are the suggested 2 theories for mechanism of adhesion?
Make more Q’s??
EXTRA DETAIL STATED
THEORY 1
- poly acid molecules curate?? with calcium available on the enamel + dentine surface (shown in diagram)
- the formation of the calcium polyalkenoic salts is similar to the setting reaction of GIC
- has been observed that bond strength is greater between enamel + GIC than dentine + GIC - this could be due to Ca ions in tooth
THEORY 2
- application of a fresh GIC paste, enables a good wetting of the surface of it’s tooth, due to it’s hydrophilicity
- adhesion then occurs as a result of hydrogen bonding between the free carboxylic acid groups of the cement + the bound water on the surface of the tooth
- H bonds are then replaced by ionic bonds that are formed between cations in the tooth (Ca) and anionic functional groups in the cement
- this causes a slow formation of ion exchange layer
- 2 theories are similar except for stages that have been used to explain
- during application of GIC - tooth us usually conditioned, this allows the removal of smear layer and partial demineralisation of the tooth surface, thereby increasing the surface area, which allows for micro mechanical attachment
- BOTH micro mechanical attachment + true ionic bonding contribute to adhesion
GENERAL PROPERTIES
1
what are they?
2a
- GIC have inferior aesthics compared to dental composites
Why?
2b
- how can this be overcome?
3
Why is fluoride release a useful property?
- powder : liquid is important factor that determines physical properties
- hand mixing usu ends in dry, crumbly mix
- adding water to smooth paste + ease application of GIC adversely affects properties of cement
- although GIC rapid initial setting, the hardening of cement takes a while
- important during this phase, the GIC is protected from environment (early contamination of water can adversely affect properties of cement)
- hence suggested that cements be covered with varnish or resin during first 24hr of setting
- low solubility - only first 24 hours that protection is needed, once set has very little interaction with environmental moisture
GIC - PROPERTIES
1
What important factor determines physical properties?
2
- hand mixing usu ends in dry, crumbly mix
What would happen if you added water to this mix?
3
- although GIC rapid initial setting, the hardening of cement takes a while
3a
- what is important to do during this hardening phase?
3b
WHY?
3c
How may we do this?
1
powder : liquid ratio
2
- makes smooth paste + eases application of GIC
BUT
- adversely affects properties of cement
3a
- protect the GIC from environment
3b
- early contamination of water can adversely affect properties of cement
3c
- suggested that cements be covered with varnish or resin during first 24hr of setting
MINIMUM REQUIREMENTS OF GIC (set by ISO)
1
Luting cement
2
Restorative cement
A - setting time / min
B - compressive strength / MPa
C - opacity, C0.70
GIC advantages + disadvantages summary
