Glass Ionomer Flashcards
what is the liquid composed of in GIC
polyacrylic acid and tartaric acid
what is the powder composed of in GIC
silica dioxide, almunia dioxide, alumium fluoride, calcium fluoride
what is the difference between anhydrous and encapsulated GIC
anhydrous - mix liquid and powder, can change ratio to have different properties, liquid is distilled water, freeze dried acid is added to powder
encapsulated - same mix all the time, stable, easier to use
what difference does particle size have on material
smaller - sets faster, better for cementing crowns etc
bigger - slower set
what difference does composition of acid have on material
more acid - thicker, more viscous, increased mechanical properties
what are the 3 phases of setting reaction
dissolution, gelation, hardening
describe the events in the dissolution phase
acid and base mix, hydrogen ions attack the silica, causes it to release calcium, sodium, aluminium and fluoride ions. The unreacted silica becomes covered in a silica gel as silica mixes with water
describe the events in the gelation phase
calcium ions are bivalent, can bond to two molecules. Allows for cross linking within the polyacrylic acid, results in calcium polyacrylate forming. Cross linking increases mechanical properties, this will appear hard in the mouth although hardening is not finished
describe the events in the hardening phase
aluminium ion is trivalent, can bond to 3 molecules. Can bond to polyacrylic acid to form aluminium acrylate, however, this can take hours, days or a week for it to be complete. this further increases the strength
why does the GIC have to protected after placement
as it can take days to completely harden, needs to be conditioned to prevent any moisture entering the restoration
how can moisture contaminate the GIC and what affect does this have
water from saliva being absorbed, aluminium ions diffuse out of material, excess drying
result in a weak restoration, will be rough, break up and have poor aesthetics
what is the role of tartaric acid
it reduces the setting time to make it easier to handle
how is the GIC bonded to tooth
calcium ions on enamel surface can bond to the polyacryclic acid to aid cross linking
what are some advantages of GIC
good bond to the tooth - good marginal seal although the bond strength is much lower compared to composite
low thermal conduction, good thermal expansion - expands at same rate as enamel and dentine, prevent microleakage, no contraction on setting, fluoride release
describe how fluoride is released from GIC
fluoride release peaks initially and then reduces over time so little is released. however, thought it can act as a reservoir, when fluoride levels are high, it will absorb it and then when they dip it can release
what are the disadvantages of GIC
poor mechanical strength - 100MPa compared to 300MPa of composite, poor aesthetics
what is added in RMGI to alter the properties
HEMA - resin polyacrylic acid contains methacrylate monomers photo initiators barium glass - radiopacity potassium persulphate - REDOX iniator
what is dual setting in RMGI
same steps as conventional but has the resin to set. Mixing of acid and base as before, then light cure causes polymerisation of resin and the methacrylate groups in polyacrylic acid. After, REDOX reaction for further polymerisation. Acid base reaction continues
what is the consequence of not fully curing the resin
the REDOX reaction should ensure all resin polymerisations even in dark, however, mechanical properties are reduced by 25% and unpolymerised HEMA is toxic to pulp
what is tri setting in RMGI
same steps as conventional, mixing of acid and base. REDOX reaction begins also at this stage, some polymerisation of resin. then light cure, more polymerisation. After, REDOX and acid base reactions continue
what advantages does RMGI have over GIC
initially better bond strength and properties. Resin increases mechanical strength. better aesthetics,
what disadvantages does RMGI have over GIC
light curing slows down acid base reaction, polymerisation contraction shrinkage, unpolymerised HEMA is toxic to pulp
how can RMGI be anti-cariogenic
contains benzyl iodides and bromides which are cytotoxic to bacteria, however, can also be toxic to pulp
give examples of when RMGI might be used
as a lining under a restoration, luting cement for crowns, orthodontic cement, temporary restoration over access cavity for endodontics
