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Dental Material Science > Glass Ionomer > Flashcards

Flashcards in Glass Ionomer Deck (24)
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1
Q

what is the liquid composed of in GIC

A

polyacrylic acid and tartaric acid

2
Q

what is the powder composed of in GIC

A

silica dioxide, almunia dioxide, alumium fluoride, calcium fluoride

3
Q

what is the difference between anhydrous and encapsulated GIC

A

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

4
Q

what difference does particle size have on material

A

smaller - sets faster, better for cementing crowns etc

bigger - slower set

5
Q

what difference does composition of acid have on material

A

more acid - thicker, more viscous, increased mechanical properties

6
Q

what are the 3 phases of setting reaction

A

dissolution, gelation, hardening

7
Q

describe the events in the dissolution phase

A

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

8
Q

describe the events in the gelation phase

A

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

9
Q

describe the events in the hardening phase

A

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

10
Q

why does the GIC have to protected after placement

A

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

11
Q

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

A

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

12
Q

what is the role of tartaric acid

A

it reduces the setting time to make it easier to handle

13
Q

how is the GIC bonded to tooth

A

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

14
Q

what are some advantages of GIC

A

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

15
Q

describe how fluoride is released from GIC

A

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

16
Q

what are the disadvantages of GIC

A

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

17
Q

what is added in RMGI to alter the properties

A
HEMA - resin 
polyacrylic acid contains methacrylate monomers
photo initiators
barium glass - radiopacity
potassium persulphate - REDOX iniator
18
Q

what is dual setting in RMGI

A

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

19
Q

what is the consequence of not fully curing the resin

A

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

20
Q

what is tri setting in RMGI

A

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

21
Q

what advantages does RMGI have over GIC

A

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

22
Q

what disadvantages does RMGI have over GIC

A

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

23
Q

how can RMGI be anti-cariogenic

A

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

24
Q

give examples of when RMGI might be used

A

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