Glass Ionomer Cements
No description yet. This curated deck is ready for daily study.
Card preview (24)
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