Glass Ionomers

Question 1

What are the types of GI

Answer 1

Conventional
Resin modified

Question 2

What are the uses of GI

Answer 2

Restorative
Core build up
Lining
Luting (cementing indirect restorations)

Question 3

What are the two components of GI

Answer 3

Acid (liquid)
Base (powder)

Question 4

What acids are used in GI

Answer 4

Polyacrylic acid
Tartaric acid

Question 5

What is the composition of the powder base

Answer 5

Silica, SiO2 (Silicone dioxide) 30% - 40%​

Alumina, Al2O3 (Aluminium dioxide) 15% - 30%​

Calcium Fluoride, CaF2 15% - 35%​

Aluminium Fluoride 2% - 10%​

Aluminium phosphate 4% - 20%​

Sodium fluoride 4% - 10%

Question 6

What ingredients alter the translucency of GI

Answer 6

The ratio of alumina/silica alters the translucency.​

More silica more translucent.

Question 7

How do anhydrous and encapsulated materials vary in composition

Answer 7

Anhydrous materials​
-The acid is freeze dried and added to the powder​
-The liquid is distilled water​
-This makes for easier handling of the material, particularly mixing

Encapsulated materials​
-Consistent powder/liquid ratio​
-Easier to use​
-Should be more consistent properties of the mixed material

Question 8

When is a smaller particle size needed

Answer 8

For luting cements for a low film thickness and quicker setting reaction

Question 9

What does a higher molecular weight mean

Answer 9

Better mechanical properties however too high can make the material difficult to mix

Question 10

What is the GI setting reaction

Answer 10

MO.SiO2 + H2A —> MA + SiO2 + H2O​

glass + acid —> salt + silica gel

Question 11

What are the phases to setting GI

Answer 11

Dissolution
Gelation
Hardening

Question 12

What occurs during dissolution

Answer 12

Acid into solution​
H+ ions attack the glass surface​
Ca, Al, Na & F ions are released​
Leaves silica gel around unreacted glass

Question 13

What occurs during gelation of GI setting

Answer 13

Initial set is due to calcium ion crosslinking with the polyacid by chelation with the carboxyl groups.​

Calcium ions are bivalent so they can react with two molecules joining them​

Crosslinking is not ideal as the Ca can chelate with two carboxyl groups on the same molecule

This GELATION equates to the initial set of the material and takes several minutes depending on the particular material.​

This initial set is caused by formation of Calcium polyacrylate​

Following this reaction the material will appear hard in the mouth.​

Question 14

What causes GI hardening

Answer 14

Trivalent Aluminium ions ensure good crosslinking with an increase in strength.​

Aluminium Polyacrylate formation takes a long time​

This process does not start for at least 30 minutes and can take a week or longer to be complete.​

The Aluminium reaction ensures a much higher degree of crosslinking​

This process greatly improves the mechanical properties of the material.​

Question 15

How long does hardening take in GI

Answer 15

Up to a week or longer

Question 16

When does hardening start

Answer 16

Not for atleast 30 mins

Question 17

What happens when GI is contaminated with water

Answer 17

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 which will be rough, break up and have poorer aesthetics​

Question 18

How is GI protected

Answer 18

Varnishes​
-Copal ether​
-Acetate

Resins​
-Dentine/Enamel bonding agents​
-Unfilled Bis-GMA resins

Greases or gels​
-Vaseline

Question 19

How does tartaraic acid affect GI property

Answer 19

Increases viscosity

Question 20

What are the adhesion properties of GI

Answer 20

Can bond to enamel and dentine without the need for use of an intermediate material​

Bond strength not high compared with composite to acid etched enamel​
-About 5MPa vs 20MPa​
-Probably not measuring the bond itself as GIC tends to fail cohesively​

Good sealing ability with little leakage around margins

Question 21

What groups within GI does the Ca in enamel bond to

Answer 21

COO-
Carboxyl groups

Question 22

How is the best bond acheived with GI

Answer 22

Clean surface​

Conditioned surface​
-Conditioned, not etched.​
-Little or no tissue is removed.​
-Best conditioner appears to be polyacrylic acid​
-Purpose is to produce clean smooth surface

Question 23

What are the issues with aesthetics in GI

Answer 23

Lack translucency
Not suitable where aesthetics are of prime improtance (anterior teeth)

Question 24

What are the sub-optimal mechanical properties of GI

Answer 24

Poor tensile strength​

Lower compressive strength than composite​
-Less than half. 80 – 110MPA vs 300+MPa​

Poorer wear resistance than composite​
-Subject to abrasion​

Lower hardness than composite​

Higher solubility than composite​
-Dissolution of unprotected material during gelation phase​
-Long term erosion by acids

Question 25

What are the mechanical advantages of GI

Answer 25

Good thermal properties ​ -Expansion similar to dentine​ No contraction on setting​ Once set less susceptible to staining and colour change than composites​ Fluoride release​ Lower modulus can be a good thing​

Question 26

What are the benefits of fluoride release

Answer 26

They can recharge their fluoride when the Fl concentration around them is higher than that in the cement​ They then release Fl again when the ambient concentration falls​ They can act as a fluoride reservoir or fluoride sink​ May have anti-caries effect. Not certain

Question 27

How is GI used

Answer 27

Dressing Fissure sealants Temp filling Luting Orthodontic cement Base/lining

Question 28

What are the general advantages of GI

Answer 28

Stable chemical bond to enamel and dentine​ Low microleakage​ Fluoride release​ Good thermal properties​ No contraction on setting

Question 29

What are the general disadvantages of GI

Answer 29

Brittle Poor wear resistance Moisture susceptible initially Poor aesthetics Susceptible to acid attack/drying out

Question 30

What are the ingredients in RMGIC powder

Answer 30

Fluoro-alumino-silicate Glass​ Barium Glass -Provides Radiopacity​ Vacuum dried Polyacrylic acid​ Potassium persulphate​ -Redox catalyst to provide resin cure in the dark​ Ascorbic acid​ Pigments​ -Varies shade

Question 31

Howis the liquid component modified in RMGIC

Answer 31

Contains HEMA, water, photo-initiators (light curing)

Question 32

What are the dual cure setting reactions og RMGIC

Answer 32

Acid base reaction initially Light - free radical methacrylate reaction forming a resin matrix

Question 33

What are the tri-curing steps

Answer 33

Initial acid base reaction Redox reaction Light activates free radical methacrylate reaction

Question 34

What are the properties of RMGIC

Answer 34

Good bond to enamel and dentine​ Superior to conventional GIC ??​ -Difficult to know what is being measured​ -Definitely better initially​ Better physical properties​ Lower solubility​ Fluoride release ​ Better translucency and aesthetics​ Better handling

Question 35

What are the poor properties of RMGIC

Answer 35

Polymerisation Contraction​ Exothermic setting reaction ​ -both polymerisation and dark cure​ Swelling due to uptake of water ​ -HEMA is extremely hydrophilic​ Monomer leaching​ -HEMA is toxic to the pulp it must be polymerised completely​ Reduced strength if not light cured

Question 36

What are the benefits of RMGIC compared to GI and composite

Answer 36

Compared with conventional GIC​ -Better aesthetics​ -Easier to use​ -Stronger ​ Compared with Composite Resin​ -Easier to use​ -Fluoride release