GIC Flashcards
what are the different types of GIC?
- conventional GI
- resin modified GI
what are some uses of GIC?
- restorative
- core build up (prior to crown restoration)
- lining
- luring
what are the two main components of conventional GI?
- acid (liquid)
- base (glass powder)
what acids are found within conventional GI?
- polyacrylic acid
- tartaric acid
why is tartaric acid added to glass ionomer?
added to control the setting characteristics of the material
what is the powder aspect of convential GI composed of?
- silica
- alumina
- calcium fluoride
- aluminium fluoride
- aluminium phosphate
- sodium fluoride
what additional molecules may be added to the powder of GI and why?
- strontium and lithium salts
- increase radiopacity
what determines the translucency of GIC?
ratio of alumina to silica
a GIC containing high levels of silica will be…
more translucent
what are the variations of chemical compositions of conventional glass ionomer?
- anhydrous materials
- encapsulated materials
what is meant by an anhydrous GI material?
- acid is freeze dried and added to the powder
- liquid is distilled water
- makes for easy handling of material (mixing)
why are encapsulated GI materials superior to anhydrous materials?
- consistent powder/liquid ratio
- easier to use
- more consistent properties of the mixed material
how does powder particle size in GIC determine the setting reaction of the material?
smaller particle size = quicker setting reaction (more opaque cement)
how does the molecular weight of the acid found in GIC relate to the mechanical properties of the material?
higher molecular weight (of acid) = better the mechanical properties
what are some contraindications of high molecular weight acids used in GIC?
- very viscous
- hard to mix
what are the three phases of the (conventional) glass ionomer setting reaction?
- dissolution
- gelation
- hardening
what is the acid base reaction for GIC?
glass + acid —> salt + silica gel
what occurs during the dissolution phase of the glass ionomer setting reaction?
- acid into solution
- H+ ions attack the glass surface
- Ca, Al, Na and F ions are released
- leaves silica gel around unreacted glass
what is meant by gelation (in reference to the GIC setting reaction)?
the phase that initially makes the material hard
what occurs during the gelation phase of the glass ionomer setting reaction?
- initial set due to calcium ion crosslinking with the poly acid by chelation with the carboxyl groups
- calcium ions are bivalent so they can react with 2 molecules joining them
- formation of calcium polyacrylate
why is crosslinking during gelation of GIC not ideal?
Ca can chelate with two carboxyl groups on the same molecule
how long does the gelation phase of GIC setting reaction take?
several minutes
what occurs during the hardening phase of the glass ionomer setting reaction?
- trivalent aluminium ions ensure good cross linking with an increase in strength
- aluminium polyacrylate is formed
how long does the hardening phase of the glass ionomer setting reaction take?
- does not start for at least 30 mins
- can take a week/longer to be complete
what must GIC be protected from during its setting phase?
moisture and desiccation (following gelation)
what occurs if GIC is contaminated during the setting reaction?
- 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
what are the different methods of protection used following glass ionomer placement?
- varnishes
- resins
- greases/gels
what protect the GIC better, varnishes, resins or gels?
- varnish & resins provide better protection
- petroleum gel is quickly removed from mouth
what is different between GIC and composite in terms of bonding to teeth surfaces?
- GIC can bond to enamel and dentine without the need for use of an intermediate material
- GIC bond is weaker than composite bond
what is the bond strength of GIC compared to composite?
GIC = 5MPa Composite = 20MPa
what is the bonding mechanism of GIC?
- chelation between carboxyl groups in the cement and Ca on the tooth surface
- hydrogen bonding or metallic ion bridging to collagen
before placing GIC, what must be done to the tooth surface?
surface must be CONDITIONED to produce clean, smooth surface
what is used to condition a tooth before placement of GIC?
polyacrylic acid
what are disadvantages of GIC when compared to composite?
- lower bond strength
- poorer aesthetics
what are some poor mechanical properties of GIC?
- poor tensile strength
- subject to abrasion (poorer wear resistance than comp)
- lower hardness than comp
- high solubility
what are some good mechanical properties of conventional GIC?
- good thermal expansion (similar to dentine)
- no contraction on setting
- fluoride release
- lower modulus can be a good thing
what are some advantages of conventional GIC to composite?
- stable chemical bond to enamel and dentine
- low micro leakage
- fluoride release
- good thermal properties
- no contraction on setting
