Glass Ionomer

Question 1

what is the liquid composed of in GIC

Answer 1

polyacrylic acid and tartaric acid

Question 2

what is the powder composed of in GIC

Answer 2

silica dioxide, almunia dioxide, alumium fluoride, calcium fluoride

Question 3

what is the difference between anhydrous and encapsulated GIC

Answer 3

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

Question 4

what difference does particle size have on material

Answer 4

smaller - sets faster, better for cementing crowns etc

bigger - slower set

Question 5

what difference does composition of acid have on material

Answer 5

more acid - thicker, more viscous, increased mechanical properties

Question 6

what are the 3 phases of setting reaction

Answer 6

dissolution, gelation, hardening

Question 7

describe the events in the dissolution phase

Answer 7

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

Question 8

describe the events in the gelation phase

Answer 8

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

Question 9

describe the events in the hardening phase

Answer 9

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

Question 10

why does the GIC have to protected after placement

Answer 10

as it can take days to completely harden, needs to be conditioned to prevent any moisture entering the restoration

Question 11

how can moisture contaminate the GIC and what affect does this have

Answer 11

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

Question 12

what is the role of tartaric acid

Answer 12

it reduces the setting time to make it easier to handle

Question 13

how is the GIC bonded to tooth

Answer 13

calcium ions on enamel surface can bond to the polyacryclic acid to aid cross linking

Question 14

what are some advantages of GIC

Answer 14

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

Question 15

describe how fluoride is released from GIC

Answer 15

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

Question 16

what are the disadvantages of GIC

Answer 16

poor mechanical strength - 100MPa compared to 300MPa of composite, poor aesthetics

Question 17

what is added in RMGI to alter the properties

Answer 17

HEMA - resin 
polyacrylic acid contains methacrylate monomers
photo initiators
barium glass - radiopacity
potassium persulphate - REDOX iniator

Question 18

what is dual setting in RMGI

Answer 18

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

Question 19

what is the consequence of not fully curing the resin

Answer 19

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

Question 20

what is tri setting in RMGI

Answer 20

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

Question 21

what advantages does RMGI have over GIC

Answer 21

initially better bond strength and properties. Resin increases mechanical strength. better aesthetics,

Question 22

what disadvantages does RMGI have over GIC

Answer 22

light curing slows down acid base reaction, polymerisation contraction shrinkage, unpolymerised HEMA is toxic to pulp

Question 23

how can RMGI be anti-cariogenic

Answer 23

contains benzyl iodides and bromides which are cytotoxic to bacteria, however, can also be toxic to pulp

Question 24

give examples of when RMGI might be used

Answer 24

as a lining under a restoration, luting cement for crowns, orthodontic cement, temporary restoration over access cavity for endodontics