Glass Ionomer Cements Flashcards
what are the 2 types of glass ionomer
conventional
resin modified glass ionomer
what are the 2 types of conventional glass ionomer
anhydrous
original
what are the 2 types of RMGI
self cure
light cure
what is GI used in
restorative
core build up
lining
luting for cementing indirect restorations
when is GI used as a filling material
often in children’s teeth
sometimes in adults if in a non-load bearing area e.g cervical
what are names of GI used as filling materials
riva
vitremer
when is GI used for a core build up
prior to a restoration with a crown
what is the name of the GI used for core build up
vitremer crown core
what are examples of GI used for linings
vitrebond, ionoseal
what are examples of GI used for luting
Fuji Luting
Vitremer luting cement
Aquachem
what two materials did GI originate from
zinc polycarboxylate cement
silicate cement
what is silicate cement
n anterior filling material based on fluoro-alumino-silicate glass combined with phosphoric acid
what properties did mixing silicate cement and zinc polycarboxylate cement result in
resulted in a fluoride releasing filling material (from the silicate material) which had the ability to bond to tooth structure (from the carboxylic acid material
what are the two components of GI cements
acid (liquid)
base (glass powder)
what are the two acids present in GI cement
poly acrylic acid
tartaric acid
what is polyacrylic acid
ionic monomer
usually copolymers of acrylic and itaconic acid or acrylic and malice acid
what is tartaric acid used for
added to control the setting characteristics of the material
what does the base consist of
silica, SiO2 (silicone dioxide) alumina, Al2O3 (aluminum dioxide) calcium fluoride aluminium fluoride aluminium phosphate
what does adding strontium and lithium salts to the powder do
increase the radiopacity but these play no part in the reaction chemistry
what does the ratio of alumina/silica affect
translucency
more silica = more translucent
what are the variations in the composition
material may be anhydrous or encapsulated
there can be significant variations in the composition of the powder
the molecular weight of the acid can change
what are anhydrous material GI
the acid is freeze dried and added to the powder and the liquid is distilled water.
what is the advantage of having anhydrous GI
This makes for easier handling of the material, particularly mixing as polyacrylic acid is not an easy material to mix with so now we have an anhydrous material.
what is the advantage of encapsulated materials
consistent powder/liquid ratio. The proportions are set and controlled by the manufacturer and mixing is a quick and clean process as it goes in an amalgamator. It is therefore easier to use. It should therefore have more consistent properties of the mixed material.
what are the variations in the composition of the powders
Powder particle size can vary
what does a bigger particle size lead to
The bigger the particle, the better the aesthetic especially if it is larger silica particle
if the material is a luting agent what should the particles be
particle size has to be smaller than 20 micrometres to give a low film thickness and to not interfere with the restoration you are cementing.
how does particle size effect the setting reaction
The smaller the particle size the quicker the setting reaction and the opaquer the set cement.
what does a higher molecular weight acid have an effect on
Generally, the higher the weight (the longer the acid chain) the better the mechanical properties of the set material.
However the higher molecular weight acids are viscous and difficult to mix (liquid is less liquid) so need to find a balance.
what type of reaction is the setting reaction of GIC
acid/base
what is the reaction of GIC
glass + acid –> salt + silica gel
what are the 3 phases of the setting reaction
dissolution
gelation
hardening
what happens in the dissolution phase
When the proprietary solution or the water is mixed with the powder, the acid goes into solution and reacts with the outer layer of the glass. This layer becomes depleted in aluminum, calcium, sodium and fluorine ions, so that only a silica gel remains.
The hydrogen ions that are released from the carboxyl groups on the polyacid chain diffuse to the glass and make up for the loss of the other ions.
what happens in the gelation phase
The initial set is due to the rapid action of the calcium ions, which being divalent and more abundant initially, react more readily with the carboxyl groups of the acid than do the trivalent aluminum ions. The efficiency with which the calcium ions cross link the polyacid molecules is not as good as it might be because they are also able to link carboxyl groups on the same molecule.
This gelation equates to the initial set of the material and takes several minutes depending on the particular material. this initial set is caused by the formation of calcium polyacrylate. Following this reaction the material will appear hard in the mouth.
what happens in the hardening phase
After the gelation phase, there is a hardening phase that can last as long as 7 days. It takes some 30 minutes for the uptake of aluminum ions to become significant, yet it is the aluminum ions that provide the final strength to the cement, as they are responsible for the introduction of the cross links. In contrast to the calcium ions, the trivalent nature of the aluminum ions ensures that a a high degree of cross linking of the polymer molecules takes place.
what is the final structure
There is a continuation of the formation of aluminum salt bridges, and water becomes bound to the silica gel, which now surrounds the residual core of each of the glass particles. Once the cement has fully reacted, the solubility is quite low, the final structure consists of glass particles, each which is surrounded byy a silica gel in a matrix of cross linked poly-acrylic acid.
why is it important that GIC is protected from moisture and desiccation following gelation
it is hard in the mouth but maturation has not begun.
what could happen if GIC is not protected after gelation
- Aluminum ions may diffuse out of the material and be lost to the cement, thereby being unable to cross link the polyacrylic acid chains.
- Excessive drying may mean that the water is lost meaning the reaction cannot go to completion
- Additional moisture may be absorbed, which may be contaminated with blood or saliva, leading to compromised aesthetics, with the restoration looking exceptionally dull and white. The contaminating moisture will also weaken the material and may cause it to crumble
how can GIC be protected
• Varnishes o Copal ether o Acetate • Resins o Dentine/enamel bonding agents o Unfilled bis-GMS resins • Greases or gels o Vaseline
what provide better protection to GIC
varnishes and resin
why is petroleum gel not that good for GIC protection
quickly removed by the action of the lips and tongue and offers little protection
why is protection also required at a later date
f 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.
describe the handling properties of GIC
there were major problems with early materials as working and setting times were too long. Newer formulations incorporated tartaric acid, this greatly improved their ease of use. The working time is largely unchanged but setting time is shortened
describe adhesive properties of GIC
can bond to enamel and dentine without the use of an intermediate material. The bond strength is not high compared with composite to acid etched enamel. It is about 5MPa vs 20Mpa. It is however probably not measuring the bond itself as GIC tends to fail cohesively – the bond created is strong enough that when a GIC is bonded, the fracture will generally run through the GIC (cohesive failure) and not along the interface (adhesive failure). It has good sealing ability with little leakage around the margin.
describe the bonding mechanism of GIC
Chelation between carboxyl groups in the cement and Ca on the tooth surface.
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.
what does a good bond require for GIC
- Clean surface
* Conditioned surface
what is the best conditioner to use for GIC
poly acrylic acid
what is the purpose of conditioning the surface
produce a clean smooth surface
why do we not etch
we do not want to take calcium out so we do not etch
describe the aesthetics of GIC
Colour is okay but they lack translucency
New materials are better
Materials with a higher silica content are better
Translucency improves over 24+ hours when the extra cross linking occurs
Not suitable where aesthetics are of prime importance
what are the disadvantages of the mechanical properties of GIC
Poor tensile strength
Lower compressive strength than composite. Less than half. 80-110 MPa vs 300+ MPa
Poorer wear resistance than composite – subject to abrasion
Lower hardness than composite
Higher solubility than composite – dissolution of unprotected material during gelation phase but also long term erosion by acids.
what are the advantages of the good mechanical properties of GIC
Good thermal properties – expansion is similar to dentine meaning that the bond is not stressed when hot/cold foods eaten as it contracts/expands at the same rate.
There is no contraction on setting – no polymerization stress
Once set less susceptible to staining and colour change than composites
Fluoride release
Lower modulus can be a good thing particularly in cervical restorations where the restoration flexes with the tooth preventing it from being stressed
describe fluoride release in GIC
Initial fluoride release is high but this diminishes very quickly over the first week however it has been established that these materials can take up fluoride from the environment.
They can recharge their fluoride when the fluoride concentration around them is higher than that in the cement.
They can release fluoride again when the ambient concentration falls. They can act as a fluoride reservoir or fluoride sink.
what are uses for conventional GIC
- Dressing
- Fissure sealant
- Endodontic access cavity remporary filling
- Luting
- Orthodontic cement
- Restoration of deciduous teeth
- Restoration of permanent teeth
- Base/lining
what are avdnagtaes of conventional GIC
Stable chemical bond to enamel and dentine Low microleakage Fluoride release Good thermal properties No contraction on setting
what are disadvantages of conventional GIC
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 binding to composite – etching damages surface.
what are cermet
Developed to overcome glass ionomer brittleness
Silver was added to glass (equal volumes) to increase toughness and wear resistance
No evidence that this was the case
Only ended up making silver GIC
No advantages and worse aesthetics. They looked like dull amalgam fillings
what is the advantage of composite technology to GIC
- Light curing (command set)
- Improved physical properties
- Better aesthetics
what does the powder of RMGI cement consist of
fluoro-alumino-silicate glass barium glass vacuum dried poly acrylic acid potassium persulphate ascorbic acid pigments
what does barium glass do
provides radiopacity
what does potassium persulphate do
o Redox catalyst to provide resin cure in the dark
what do pigments do
vary shade
what does the liquid of RMGIC consist of
HEMA poly acrylic acid tartaric acid water photoinitiators
what happens in dual curing
- 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 (20 seconds)
- Acid base reaction continues with the resin matrix for several hours
why does light not penetrate deeply into these materials
opaque
may have to bet placed in layers
how is the problem of depth of cure counteracted
a REDOX (reduction oxidation) reaction also occurs in some of these materials. This is only important in the methacrylate polymerisation reaction This gives confidence that the material will set even if insufficient light penetration occurs
describe tricking
- 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
what brands say that conditioning of the tooth surface prior to cement placement for RMGI should occur
fuji cement LC
fuji II LC
vitremer
what is the advantages of RMGI in terms of properties
- Good bond to enamel and dentine
- Bond is superior to conventional GIC – difficult to know what is being measured but definitely better initially
- Better physical properties
- Lower solubility – because of the resin
- Fluoride release
- Better translucency and aesthetics – because of the resin
- Better handling – most important thing
what is the disadvantages of RMGI in terms of properties
• Polymerization contraction
• Exothermic setting reaction
o Both polymerization and dark cure
• Swelling due to uptake of water
o Hema is extremely hydrophilic
• Monomer leaching
o Hema is toxic to the pulp so it must be polymerized completely but there is risk of unreacted HEMA in the depth of the cavity
• Reduced strength if not light cured
• Light curing slows down the acid base setting reaction
• Benzoyl iodides and bromides can be released which are cytotoxic
• Fluoride release no better than conventional
how is RMGIC compared with conventional
- better aesthetics
- easier to use
- stronger
how is RMGI compared to composite
- easier to use – no etching, or drying
* fluoride release
what are the uses of RMGIC
- dressing
- fissure sealant
- endodontic access cavity temporary filling
- luting
- orthodontic cement
- restoration of deciduous teeth
- restoration of permanent teeth
- base or lining
is RMGIC best or GIC
Depends on the clinical situation
Sometimes there will be times where only one of these is correct
More often though either would be appropriate and ease of use is often the deciding factor
