Glass Ionomer Cements Flashcards
what are the 2 types of glass ionomer cements?
conventional GIC
resin modified GIC
what are the 2 types of conventional GIC?
anhydrous Vs original
when were conventional GIC first made?
1970s, still used today
what are the 2 types of RMGIC?
self cure and light cure
why was RMGIC created
changes in GIC to make it more handling friendly
4 categories of GIC use
restorative
core build up
lining
luting
what is the main use of glass ionomer cements?
as a filling materials
- in children’s teeth
certain areas in adult teeth (cervical, temporary fillings but not load bearing areas)
what are core build ups with GIC used for?
placed prior to restoration with a crown
restorative GICs
riva
vitremer
core build up GICs
vitremer
crown core
lining GICs
vitrebond
ionoseal
luting GICs
fuji luting
vitremer luting cement
aquachem
when are GICs used as linings?
underneath permanent fillings to prevent thermal conductivity
when are GICs used as luting agents?
cementing indirect restorations e.g. cementing in crowns
what are conventional GICs made from?
The original cement came from two different materials
- Zinc Polycarboxylate Cement
- Silicate cement. An anterior filling material based on fluoro-alumino-slicate glass combined with phosphoric acid.
what does the combination of zinc polucarboxylate and silicate cement allow?
combination fo the 2 materials led to the best properties of both materials
- fluoride releasing filling material which had the ability to bond to tooth structure.
glass from the aluminum silicate was dissolved in the polyacrylic acid from the zinc cement
it was the only ‘white’ filling 50 years ago
what are the main advantages of GICs?
fluoride releasing filling material which had the ability to bond to tooth structure.
what is the acid component of GICs?
liquid
polyacrylic acid and tartaric acid
what is the base component of GICs?
powder
alumina silica glass
acids in GICs
polyacrylic acid (with a few copolymers of acrylic and itaconic acid or acrylic and maleic acid)
tartaric acid
why is tartaric acid added to GICs?
Added to control the setting characteristics of the material (makes quicker)
what is in the base powder component of GICs?
- Silica, SiO2 (Silicone dioxide, quartz) 30% - 40%
- Alumina, Al2O3 (Aluminium dioxide) 15% - 30%
- Calcium Fluoride, CaF2 15% - 35%
- Aluminium Fluoride 2% - 10%
- Aluminium phosphate 4% - 20%
- Sodium fluoride 4% - 10%
- Adding Strontium and lithium salts can increase the radiopacity but these play no part in the reaction chemistry.
why are heavy metal powders added to the base component of GICs sometimes?
Adding Strontium and lithium salts can increase the radiopacity but these play no part in the reaction chemistry.
what does the ration of alumina/silica alter in GICs?
translucency
- more silica more translucent
anhydrous GICs
The acid is freeze dried and added to the powder
The liquid is distilled water
This makes for easier handling of the material, particularly mixing
- Add water to the 2 powders to reconstitute and mix together
encapsulated GICs
Consistent powder/liquid ratio
- Easier to use
Push capsule together, place in amalgamator, shakes the materials together
Should be more consistent properties of the mixed material
- Can be advantage or disadvantage (may want to alter viscosity depending on patient compliancy)
which is more consistent - encapsulated or anhydrous GICs?
Encapsulated should be more consistent properties of the mixed material
- Can be advantage or disadvantage (may want to alter viscosity depending on patient compliancy)
what can vary between GICs? (2)
powder particle size
molecular weight of acid
how does powder particle size effect GICs?
smaller the particle size the quicker the setting reaction and the more opaque the cement
larger particle size = more aesthetic the material
what particle size is needed for luting GICs?
<20um required for luting cement to give a low film thickness.
how does the acid molecular weight effect GIC properties?
the higher the weight the better the mechanical properties of the set material. (larger chain)
However the higher molecular weight acids are viscous and difficult to mix.
- Need balance
what are the 3 phases of the setting reaction?
dissolution
gelation
hardening
what type of reaction is the setting reaction?
acid base reaction
MO.SiO2 + H2A –> MA + SiO2 + H2O
(M = metal, A = polyacid)
glass + acid –> salt + silica gel
water absorbed into the surface of silica
dissolution phase of setting reaction
Acid into solution
H+ ions attack the glass surface – dissolves the surface of the glass
Ca, Al, Na & F ions are released into solution
Leaves silica gel around large unreacted glass
gelation phase of setting reaction
This GELATION equates to the initial set of the material and takes several minutes depending on the particular material.
- caused by formation of Calcium polyacrylate
calcium ion crosslinking with the polyacid by chelation with the carboxyl groups.
Polyacrylic acid molecules are long chain molecules with many bonding sites
Calcium ions are bivalent so they can react with two molecules joining them
Crosslinking is not ideal as the Ca can chelate with two carboxyl groups on the same molecule
- not cross linking, just bends the molecule, increasing molecule strength
Following this reaction the material will appear hard in the mouth
hardening phase of setting reaction
Trivalent Aluminium ions ensure good crosslinking with an increase in strength.
- Bonds to 3 at the same time
Aluminium Polyacrylate formation takes a long time
- This process does not start for at least 30 minutes and can take a week or longer to be complete.
The Aluminium reaction ensures a much higher degree of crosslinking
- greatly improves the mechanical properties of the material.
This is when it is ‘set hard’ in the mouth but before maturation has begun
what does GIC nee to be protected from following Gelation?
moisture and desiccation
why does GIC need to be protected from moisture and desiccation following the setting reaction?
First week relatively soluble, feels hard but isn’t,
Al ions can dissolve out.
Can lose water from crack
what does contamination of GIC lead to? (4)
Aluminium ions diffuse out of the material
Excessive drying means water will be lost
Saliva contamination causes absorption of water
All lead to a weak material which will be rough, break up and have poorer aesthetics
what are the properties of a contaminated GIC?
weak material which will be rough, break up and have poorer aesthetics
what 3 types of material can protect GIC after placement?
varnish
resin
greases/gels
2 examples of varnishes that can protect GICs
copal ether
acetate
2 examples of resins which can protect GICs
dentine/enamel bonding agents
unfilled Bis-GMA resins
example of grease/gel which can protect GICs
vaseline
what provides the better protection for GICs?
varnishes and resins
Petroleum gel is quickly removed by the action of the lips and tongue and offers little protection
when may you need to place protection on a GIC? (2)
following placement (soluble for first week after setting reaction)
desiccation of a GIC restoration is possible during work on other areas in the mouth.
- A thin layer of varnish or resin should be applied at this time to prevent surface damage due to excessive drying.
issue with hardening in early GICs
Working and setting times were too long.
why was tartaric acid added to GICs?
Working and setting times were too long
Working time is largely unchanged but setting time is shortened
tartaric effect on handling properties of GICs
Working time is largely unchanged but setting time is shortened
adhesion properties of GICs
Can chemically bond to enamel and dentine without the need for use of an intermediate material
- No need to etch
Good sealing ability with little leakage around margins
bond strength of GICs
Bond strength not high compared with composite to acid etched enamel
- About 5MPa vs 20MPa
Probably not measuring the bond itself as GIC tends to fail cohesively
do you need to etch prior to GIC placement?
no - can chemically bond to enamel and dentine
bonding mechanism of GIC
Chelation between carboxyl groups in the cement and Ca on the tooth surface.
- Acid base reaction to Ca ions in tooth
- Re-precipitation of complex mixture of calcium phosphate (from apatite) and calcium salts from the polyacid onto and into the tooth surface
- Hydrogen bonding or metallic ion bridging to collagen
2 things a good GIC bond requires
clean surface
conditioned surface
what is a conditioned surface?
not etched
little or no tissue is removed (keeps Ca ions)
purpose is to create a smooth surface
example of a surface conditioner
polyacrylic acid
- mild solution of polyacrylic acid and some HEMA
when should you surface condition in GIC application?
if the manufacturer’s guideline suggests
aesthetics of GICs
colour is OK but lack translucency
- not as good as composite
not suitable for placement on anterior teeth
what can be done to improve GIC aesthetics?
higher silica content
bigger particle size
effect of time on translucency of GICs
improves over 24 hours when X-linking occurs
tensile strength of GIC
poor
compressive strength of GIC
poor
lower than composite
- less than half (80-100MPa Vs 300+MPa)
wear resistance of GIC
poorer than composite
- subject to abrasion
hardness of GIC
poorer than composite
solubility of GIC
higher than composite
- dissolution of unprotected material during gelation phase
- long term acid erosion
thermal properties and expansion of GICs
good, unlike composite
- similar to dentine
- not stressing bond
polymerisation contraction of GIC
none
- not pulling away from margins when light cured
- doesn’t need a high bond strength as less polymerisation contraction
staining of GIC
once set less susceptible to staining and colour changes than composite
modulus of GIC
lower than composite
Cervical restorations - tooth moves from side to side/flexes
- GIC moves with tooth - less bond stressing and likelihood to fall out compared to higher modulus material
main physical property advantage of GIC
fluoride release without compromising GIC structure
how is fluoride released from GIC?
It has been established that GICs can take up fluoride from the environment
They can recharge their fluoride when the Fl concentration around them is higher than that in the cement
- From mouthwash, toothpaste
release Fl again when the ambient concentration falls
- act as a fluoride reservoir or fluoride sink
May have anti-caries effect. Not certain
F release will have a longer duration
8 uses of GICs and RMGICs
Dressing
Fissure sealant e.g. if child won’t let you etch
Endodontic access cavity temporary filling
Luting
Orthodontic cement (not strong enough to stick bracket on)
Restoration of deciduous teeth often
Restoration of permanent teeth on non-load bearing areas
Base or Lining
5 advantages of GICs
Stable chemical bond to enamel and dentine
Low microleakage
Fluoride release
Good thermal properties
No contraction on setting
7 disadvantages of GICs
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 (e.g. if used as a lining, requires a retentive surface)
Etching damages surface
- RMGI: the resin will bond to the resin – no need to etch
cermets where developed to…
overcome glass ionomer brittleness
what are cermets?
Silver was added to the glass (equal volumes) to increase toughness and wear resistance.
No advantages and worse aesthetics. They looked like dull amalgam fillings
- Looks like silver amalgam but functions like glass ionomer
why were resin modified GICs developed?
to overcome shortcomings of conventional GICs
what 2 advantages of GICs did RMGICs want?
bonding to tooth
fluoride release
what 3 advantages of composites did RMGICs want?
- light curing (command set)
- improved physical properties
- better aesthetics
powder component of RMGICs
Fluro-alumino-silicate Glass
Barium Glass
- Provides Radiopacity
Vacuum dried Polyacrylic acid
Potassium persulphate
- Redox catalyst to provide resin cure in the dark
Ascorbic acid
Pigments
- Varies shade
liquid component of RMGICs
HEMA
- Water miscible resin only resin that works in water
Polyacrylic acid with pendant methacrylate groups
- This can undergo both acid base and polymerisation reactions.
Tartaric acid
- Speeds up the setting reaction
Water
- Allows the reaction between polyacid and glass
Photo-initiators
- Enables light curing
3 main differences in constituents of GIC and RMGIC
- redox catalyst (potassium persulphate)
- HEMA
- photo initiator
2 types of setting reaction for RMGICs
dual and tri curing
- majority tri curing
glass ionomer part sets in same way as conventional
dual curing setting reaction for RMGICs
Initially on mixing the acid base reaction begins in the same way as conventional GIC.
On light activation a free radical methacrylate reaction occurs resulting in a resin matrix being formed
- Quickly light activation is complete (20s)
Acid Base reaction continues within the resin matrix for several hours
why should RMGICs be placed in layers?
quite opaque so light does not penetrate deeply into the material
- layers so it sets
why does a redox reaction occur in RMGICs
to ensure setting as light may not penetrate to allow sufficient setting
- important in methacrylate polymerisation reaction
in the absence of light the physical properties of the set material are reduced by 25%
tri curing setting reaction of RMGICs
Initially on mixing the acid base reaction begins in the same way as conventional GIC.
The REDOX reaction begins
On light activation a free radical methacrylate reaction occurs resulting in a resin matrix being formed
- Quickly light activation is complete (20s)
The REDOX reaction continues for about 5 minutes after initial mixing
Acid Base reaction continues within the resin matrix for several hours
Final hardening of the acid/base phase with aluminium polyacrylate formation can take days
parts of tri curing RMGICs setting reaction
acid-base reaction + light activation + dark redox
bond strength of RMGICs compared to GICs
good bond to enamel and dentine - higher than GICs
- better initial strength
physical properties of RMGICs compared to GICs
better
- lower solubility
- better translucency and aesthetics (due to resin)
- better handling
6 disadvantages of RMGICs
Polymerisation Contraction (due to resin)
Exothermic setting reaction
- both polymerisation and dark cure
Swelling due to uptake of water
- HEMA is extremely hydrophilic, Take up water from mouth
Monomer leaching
- HEMA and Benzoyl iodides and bromides are cytotoxic to the pulp - it must be polymerised completely
Reduced strength if not light cured
Light curing slows down the acid base setting reaction and may not occur as successfully
- Resin makes it easier to use but may interfere with best aspect of glass ionomer reaction
what are the effect of Benzoyl iodides and bromides?
can be released from RMGICs
kill bacteria
but also harmful to pulp
need to ensure fully cured to prevent cytotoxic damage
fluoride release comparison of RMGICs and GICs
similar (no better)
RMGIC benefits of GICs
- easier to use (main)
- better aesthetics
- stronger
RMGIC benefits compared with composite resin
- easier to use
- fluoride release
- aesthetically not as good (still cannot be used on anterior teeth)
material to use on lower 8
conventional GIC
- moisture control and light cure issues
material to use if able to light cure
RMGIC
- better aesthetics than GIC
redox reaction
reduction-oxidation reaction
atoms have their oxidation state changed
