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
RESIN MODIFIED GLASS IONOMER CEMENTS (RMGIC)
- Similar to GICs
1
Set by what reaction?
2
Release fluoride?
3
Composition?
4
What is HEMA?
RMGIC
Setting reaction
1
Why does setting primarily occur?
2
Rapid set is due to?
3
What happens after polymerisation occurs?
2
EXTRA
- shine light you’re initiating photo polymerisation reaction
- HEMA polymerises + material solidifies
RMGIC’s PROPERTIES
1
(Similar to GIC??)(Tensile strength, shear bond strength?)
Advantages compared to GIC?
2
Disadvantage of RMGIC compared to GIC
RMGICs + GICs
Clinical considerations
(Make Q’s???)
Although GIC exhibit low solubility after maturation, excessive consumption of acidic or soft drinks can put conventional GIC restorations at some risk
1
Typical pH of common drinks:
- orange juice
- coffee
- Coca Cola
- apple juice
- wine
2
Do RMGICs and GIC exhibit different rates of erosion when subjected to acidic/ soft drinks/ low ph?
2
- RMGICs usu exhibit less erosion than GICs when subjected to low pH
STUDY
- Cariostatic effect of using restorative materials in conjunction with dentrifices that are fluoridated and non-fluoridated
- old study
- shows comparison
- just by using visual examination, the scores of the cariostatic effect of using restorative materials in conjunction with dentrifices that are fluoridated and non-fluoridated
- clear from graph that without fluoridated dentrifices, can get much more formation of caries compared to restorative materials that have been used in conjunction with fluoridated dentrifices
What are giomers?
EG of giomer material names
SUMMARY
1
Use GIC for?
2
2 main advantages?
