Glass Ionomer Cements

Question 1

what are the different types of GIC?

Answer 1

• conventional GI

- resin modified GI

Question 2

what are some uses of GIC?

Answer 2

• restorative
• core build up (prior to crown restoration)
• lining
• luring

Question 3

what are the two main components of conventional GI?

Answer 3

• acid (liquid)

- base (glass powder)

Question 4

what acids are found within conventional GI?

Answer 4

• polyacrylic acid

- tartaric acid

Question 5

why is tartaric acid added to glass ionomer?

Answer 5

added to control the setting characteristics of the material

Question 6

what is the powder aspect of convential GI composed of?

Answer 6

• silica
• alumina
• calcium fluoride
• aluminium fluoride
• aluminium phosphate
• sodium fluoride

Question 7

what additional molecules may be added to the powder of GI and why?

Answer 7

• strontium and lithium salts

- increase radiopacity

Question 8

what determines the translucency of GIC?

Answer 8

ratio of alumina to silica

Question 9

a GIC containing high levels of silica will be…

Answer 9

more translucent

Question 10

what are the variations of chemical compositions of conventional glass ionomer?

Answer 10

• anhydrous materials

- encapsulated materials

Question 11

what is meant by an anhydrous GI material?

Answer 11

• acid is freeze dried and added to the powder
• liquid is distilled water
• makes for easy handling of material (mixing)

Question 12

why are encapsulated GI materials superior to anhydrous materials?

Answer 12

• consistent powder/liquid ratio
• easier to use
• more consistent properties of the mixed material

Question 13

how does powder particle size in GIC determine the setting reaction of the material?

Answer 13

smaller particle size = quicker setting reaction (more opaque cement)

Question 14

how does the molecular weight of the acid found in GIC relate to the mechanical properties of the material?

Answer 14

higher molecular weight (of acid) = better the mechanical properties

Question 15

what are some contraindications of high molecular weight acids used in GIC?

Answer 15

• very viscous

- hard to mix

Question 16

what are the three phases of the (conventional) glass ionomer setting reaction?

Answer 16

• dissolution
• gelation
• hardening

Question 17

what is the acid base reaction for GIC?

Answer 17

glass + acid —> salt + silica gel

Question 18

what occurs during the dissolution phase of the glass ionomer setting reaction?

Answer 18

• acid into solution
• H+ ions attack the glass surface
• Ca, Al, Na and F ions are released
• leaves silica gel around unreacted glass

Question 19

what is meant by gelation (in reference to the GIC setting reaction)?

Answer 19

the phase that initially makes the material hard

Question 20

what occurs during the gelation phase of the glass ionomer setting reaction?

Answer 20

• 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

Question 21

why is crosslinking during gelation of GIC not ideal?

Answer 21

Ca can chelate with two carboxyl groups on the same molecule

Question 22

how long does the gelation phase of GIC setting reaction take?

Answer 22

several minutes

Question 23

what occurs during the hardening phase of the glass ionomer setting reaction?

Answer 23

• trivalent aluminium ions ensure good cross linking with an increase in strength
• aluminium polyacrylate is formed

Question 24

how long does the hardening phase of the glass ionomer setting reaction take?

Answer 24

• does not start for at least 30 mins

- can take a week/longer to be complete

Question 25

what must GIC be protected from during its setting phase?

Answer 25

moisture and desiccation (following gelation)

Question 26

what occurs if GIC is contaminated during the setting reaction?

Answer 26

- 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

Question 27

what are the different methods of protection used following glass ionomer placement?

Answer 27

- varnishes - resins - greases/gels

Question 28

what protect the GIC better, varnishes, resins or gels?

Answer 28

- varnish & resins provide better protection | - petroleum gel is quickly removed from mouth

Question 29

what is different between GIC and composite in terms of bonding to teeth surfaces?

Answer 29

- GIC can bond to enamel and dentine without the need for use of an intermediate material - GIC bond is weaker than composite bond

Question 30

what is the bond strength of GIC compared to composite?

Answer 30

``` GIC = 5MPa Composite = 20MPa ```

Question 31

what is the bonding mechanism of GIC?

Answer 31

- chelation between carboxyl groups in the cement and Ca on the tooth surface - hydrogen bonding or metallic ion bridging to collagen

Question 32

before placing GIC, what must be done to the tooth surface?

Answer 32

surface must be CONDITIONED to produce clean, smooth surface

Question 33

what is used to condition a tooth before placement of GIC?

Answer 33

polyacrylic acid

Question 34

what are disadvantages of GIC when compared to composite?

Answer 34

- lower bond strength | - poorer aesthetics

Question 35

what are some poor mechanical properties of GIC?

Answer 35

- poor tensile strength - subject to abrasion (poorer wear resistance than comp) - lower hardness than comp - high solubility

Question 36

what are some good mechanical properties of conventional GIC?

Answer 36

- good thermal expansion (similar to dentine) - no contraction on setting - fluoride release - lower modulus can be a good thing

Question 37

what are some advantages of conventional GIC to composite?

Answer 37

- stable chemical bond to enamel and dentine - low micro leakage - fluoride release - good thermal properties - no contraction on setting