Glass Ionomers Flashcards
Name the different types of GIC’s (2)
- Conventional GI
- Resin Modified GI
- Self cure
- Light cured
State the uses of GIC’s (4)
- Restorative
- filling material e.g. RIVA, vitremer - Core build up
- Prior to restoration with crown e.g. vitremer crown core - Lining
- Underneath permanent fillings
e. g. Vitrebond - Luting
- Cementing indirect restorations
What are the components of a GIC? (2)
- Acid
- Liquid - Base
- Glass powder
What makes up the acid component of a GIC? (2)
- Polyacrylic acid
(Ionic monomers) - Tartaric acid
(added to control setting characteristics of the material)
What makes up the base component of a GIC?
- Silica
- Alumina
- CaF
- AlF
- Aluminium Phosphate
- NaF
Advantage of adding more silicone to a GICl?
More translucent
Define the term radiopaque
White area seen in an X-ray
Advantage of adding Strontium and Lithium salts to a GIC?
Can increase radiopacity (but play no part in chemistry reaction)
What affects the translucency of a GIC?
Ratio of alumina/silica
More silica = more translucent
Compare:
Anhydrous materials
Encapsulated materials
Anhydrous materials:
- The acid is freeze dried and added to the powder
- Liquid is distilled water (easier handling of material, particularly mixing)
Encapsulated materials:
- Consistent powder/liquid ratio
- Easier to use
- More consistent properties of mixed material
What are some of the variations that can exist in GIC composition? (2)
- Powder particle size can vary
<20um required for luting cement to give a low film thickness - Molecular weight of acid changes
- The higher the weight the better the mechanical properties of the set material
Advantage of small particle size?
> Smaller the particle size, the quicker the setting reaction and the more opaque the set cement
What are the 3 phases of the setting reaction?
- Dissolution
- Gelation
- Hardening
What happens during dissolution? (4)
- Acid into solution
- H+ ions attack the glass surface
- Ca, Al, Na and F ions are released
- Leaves silica gel around unreacted glass
What happens during gelation? (3)
- Initial set of material caused by formation of calcium polyacrylate, can take several mins
- Material will appear hard in mouth
What is the initial set of material due to?
- Ca ion cross linking with the polyacid by chelation with the carboxyl groups
- Ca ions = bivalent so can react with 2 molecules joining them
Why is crosslinking of Ca ions not ideal
The Ca can chelate with 2 carboxyl groups on the same molecule
What happens during the setting reaction? (4)
- Trivalent Al ions ensure good cross linking with an increase in strength
- Al polyacrylate formation takes a long time, doesn’t start for at least 30mins and can take a week/longer to be complete
- Al reaction ensures a higher degree of cross linking
- This improves mechanical properties of material
How does contamination affect the setting reaction?
- Al ions diffuse out material
- Excessive drying means water will be lost
- Saliva contamination causes absorption of water
- Leading to a weak material which will be rough, break up and have poorer aesthetics
How is conventional GIC protected during placement?
- Varnishes
- Resins
- Dentine/enamel bonding agents
- Unfilled Bis-GMS resins - Greases/gels
- Vaseline in paeds
Compare the GIC protection efficacy of varnishes to resins
Varnishes + resins provide better protection
Petroleum gel is quickly removed by lips/tongue so offers little protection
State properties of GIC (2)
- Handling
- Adhesion
- Good sealing ability with little leakage around margins
Can bond to enamel and dentine without need of intermediate material (i.e. acid etch)
How does tartaric acid favour the GIC?
Setting time shorted, working time unchanged
Bond strength of GIC
5MPa
Describe the bonding mechanism
- Chelation between carboxyl groups in the cement and Ca on tooth surface
- Re-precipitation of complex mixture of Calcium phosphate and calcium salts form the polyacid onto and into the tooth surface
- Hydrogen bonding or metallic ion bridging to collagen
Requirements of a good bond?
- Clean surface
- Conditioned surface (NOT etched)
- Little or no tissue removed
Whats the best conditioner to use?
Polyacrylic acid
Function of conditioner
To produce a clean smooth surface
Disadvantages of GIC’s in terms of aesthetics (2)
> Colour is ok but lacks translucency (improves a bit over time)
> Opaque in colour, if they dry out can become chalky
Disadvantages of GIC’s, in terms of mechanical properties
- Poor tensile strength
- Lower compressive strength than composite (less than half)
- Poorer wear resistance than composite
- Subject to abrasion - Lower hardness than composite
- Higher solubility than composite
- Dissolution of unprotected material during gelation phase
- Long term erosion by acids
Mechanical properties of GIC
- Good thermal properties expansion similar to dentine
- No contraction on setting
- Once set less susceptible to staining and colour change than composites
- Fluoride release
Function of fluoride release in GIC’s (3)
> GIC’s can release fluoride without damage to their structure
In vitro this has been shown to be beneficial against secondary caries
FLUORIDE RELEASE INHIBITS BACTERIAL GROWTH
GIC can take up fluoride from the environment
When do GIC’s recharge their fluoride (2)
> They can recharge their fluoride when the FI concentration around them is higher than that in the cement
> They then release FI again when the ambient concentration falls
Uses of GIC’s (7)
- Dressing
- Fissure sealant
- Endodontic access cavity temporary filing
- Luting
- Ortho cement
- Restoration of deciduous teeth
- Restoration of permanent teeth
- Base or lining
GIC advantages (5)
- Stable chemical bond to enamel and dentine
- Low microleakage
- Fluoride release
- Good thermal properties
- No contraction on setting
GIC disadvantages (7)
- Brittle
- Poor wear resistance
- Moisture susceptible when first placed
- Poor aesthetics
- Poor handling characteristics
- Susceptible to acid attack and drying out over time
- Possible problems bonding to composite
- Etching damages the surface
Why were cermets developed?
To overcome the GIC brittleness
But theres no advantages and theres worse aesthetics (they look like dull amalgam fillings)
Why were RMGIC’s developed?
To add advantages of composite technology:
> Light curing (command set)
Improved physical properties
Better aesthetics
What makes up a RMGIC? (2)
- Powder
2. Liquid
Name constituents of RMGIC powder (4)
- Barium glass
- Provides radiopacity - Potassium Persulphate
- Redox catalyst to provide resin cure in the dark - Ascorbic acid
- Pigments
- Varies shade
Name constituents of RMGIC liquid (5)
- HEMA
- Water miscible resin - Polyacrylic acid with methacrylate groups
- This can undergo both acid base and polymerisation reactions - Tartaric acid
- Speeds up the setting reaction - Water
- Allows reaction between polyacid + glass - Photo-initiators
- Enable light curing
What happens during the setting reaction of RMGIC’s
DUAL CURING
> Begins same as conventional GIC
> On light activation leads to free radical methacrylate reaction which makes a resin matrix
> Light activation complete in 20 seconds
> Acid base reaction continues within the resin matrix for several hours
Why should RMGIC be placed in layers?
How is this problem counteracted?
Material quite opaque, so light does not penetrate deeply into the material
REDOX reaction to counteract this
How does light affect the properties of RMGIC’s?
Physical properties of the set material are reduced by 25%
State the 2 types of curing for RMGIC’s
- Dual curing
2. Tri curing
Does Vitrebond require pre-conditioning of the tooth surface?
NO
Does vitremer require pre-conditioning of the tooth surface?
YES
State RMGIC’s properties (6)
- Good bond to enamel and dentine
- Better physical properties
- Lower solubility
- Fluoride release
- Better translucency and aesthetics
- Better handling
State RMGIC’s disadvantages (4)
- Polymerisation contraction
- Exothermic setting reaction
- Swelling due to uptake of water
- HEMA is extremely hydrophilic - Monomer leaching
- Hema is toxic to the pulp, it must be polymerised completely - Benzoyl iodides and bromides can be released, which are cytotoxic
Compare RMGIC to conventional GIC (3)
- Better aesthetics
- Easier to use
- Stronger
Compare RMGIC to composite resin (2)
- Easier to use
2. Fluoride release
RMGIC uses (7)
- Dressing
- Fissure sealant
- Endodontic access cavity temporary filling
- Luting
- Orthodontic cement
- Restoration of deciduous/permanent teeth
- Base or lining
