Glass ionomer cement

Question 1

what are the two types of glass ionomer cements?

Answer 1

• conventional GI
• resin modified GI

Question 2

what are the uses of glass ionomer cements?

Answer 2

• dressing (temp material)
• fissure sealant
• endodontic access cavity temporary filling
• luting (e.g. for crowns)
• orthodontic cement
• restoration of deciduous teeth
• restoration of permanent teeth
• base or lining under permanent restoration

Question 3

what are the components of GICs?

Answer 3

• acid - polyacrylic acid and tartaric acid
• base - silica, alumina, calcium fluoride, aluminium fluoride, aluminium phosphate, sodium fluoride

Question 4

what does adding strotium and lithium salts to GICs do?

Answer 4

increase the radiopacitiy of the material so it is more visible in radiographs

Question 5

how does the silica to alumina ratio affect GICs?

Answer 5

the more silica, the more translucent the material and the better the aesthetics

Question 6

what are the two different variations that GICs can come in?

Answer 6

• anhydrous materials - acid is freeze dried and added to the powder, the liquid added is distilled water
• encapsulated materials - consistent power to liquid ratio and more consistent properties

Question 7

what size of powder particle is required for luting cement to give a low film thickness?

Answer 7

<20um

Question 8

how does a smaller powder particle size affect the properties of GIC?

Answer 8

• quicker setting reaction
• more opaque cement

Question 9

how does the molecular weight of the acid affect the GIC?

Answer 9

• the higher the molecular weight, the better the mechanical properties of the set material
• the higher the molecular weight, the more viscous and diffucult to mix the GIC is

Question 10

what is the setting reaction for GIC?

Answer 10

M = metal
A = polyacid

Question 11

what are the three phases of the setting reaction of GICs?

Answer 11

1. dissolution
2. gelation
3. hardening

Question 12

what happens in the dissolution phase of the setting reaction of GICs?

Answer 12

• acid is in solution
• H+ ions from acid attach to the glass surface
• Ca, Al, Na and F ions are released
• silica gel is left around the unreacted glass

Question 13

what happens in the gelation phase of the setting reaction of GICs?

Answer 13

• bivalent calcium ion crosslinking with the polyacid by chelation with carboxyl groups cause the initial set of the material (2 crosslinks)
• takes several minutes to initial set
• formation of calcium polyacrylate
• the material will appear hard in the mouth but is not fully set

Question 14

what happens in the hardening phase of the setting reaction of GICs?

Answer 14

• trivalent aluminium ions ensure good crosslinking and increases the strength (3 crosslinks)
• aluminium polyacrylate forms after a long time - does not start for 30 mins and can take over a week to complete
• greatly improves the mechanical properties of the set material

Question 15

what can happen when the GIC is contaminated?

Answer 15

• aluminium ions diffuse out of material and becomes less hard - mechanical properties are reduced
• excessive drying means water will be lost
• saliva contamination can cause absorption of water
• leads to a weak material which will be rough, break up and have poor aesthetics

Question 16

how can GIC be protected after placement?

Answer 16

• varnishes e.g. copal ether, acetate
• resins e.g. dentine/enamel bonding agents, unfilled Bis-GMA resins
• greases or gels e.g. vaseline (can be removed quickly by lips or tongue)

Question 17

what component of GIC improves the handling?

Answer 17

Tartaric acid improves ease of use with a long working time and a short setting time

Question 18

describe is the adhesion properties of GIC?

3

Answer 18

• can bond to enamel and dentine without the need of an intermediate material
• bond strength is not high compared to composite on etched enamel
• good sealing ability with little leakage around margins

Question 19

how does GIC bond to the teeth?

Answer 19

chelation reaction between carboxyl groups in the cement and Ca on the tooth surface

Question 20

what does a good bond of GICs require?

Answer 20

• a clean surface
• a conditioned surface (little/no tissue removes to get a clean smooth surface)

Question 21

what are some of the disadvantageous properties of GIC compared to composite?

Answer 21

• poor tensile strength - brittle
• lower compressive strength than composite
• poorer wear resistance than composite - susceptible to abrasion
• lower hardness than composite
• higher solubility than composite - long term erosion by acids
• moisture susceptible when first placed
• poor aesthetics
• susceptible to acid attacks and drying out over itme
• possible problems bonding to composite

Question 22

what are some of the advantageous properties of GIC?

Answer 22

• good thermal properties - expansion similar to dentine
• no contraction on setting unlike composite
• less susceptible to staining and colour change after setting than composite
• good chemical bond to enamel and dentine
• low microleakage
• releases fluoride
• lower modulus

Question 23

describe the fluoride releasing property of GICs

Answer 23

• releases fluoride without damaging their structure
• has a high initial fluoride release but diminishes very quickly over the first week
• GICs can take up fluoride when the F concentration around them is higher (toothpaste)
• they can release fluoride again when the ambient concentration falls

Question 24

what is the difference between resin modified GIC and conventional GIC?

Answer 24

RMGIC is light cured, has improved physical properties and better aesthetics - composites properties added to GIC

Question 25

what component of RMGICs provide radiopacity?

Answer 25

**barium glass** in the powder

Question 26

what component of RMGIC is a REDOX catalyst?

Answer 26

**potassium persulfate** in the powderb to provide resin cure in the dark

Question 27

what component in RMGICs speed up setting reactions?

Answer 27

**tartaric acid** in the liquid

Question 28

what component of RMGICs enablelight curing?

Answer 28

**photo-initiators** in the liquid

Question 29

describe the dual curing setting reaction in RMGICs

Answer 29

* **acid-base reaction** begins the same way as GIC - several hours * **light reaction** - free radical methacrylate reaction occurs - need to place in layers - 20 seconds

Question 30

describe the tri curing setting reaction in RMGICs

Answer 30

* **acid-base reaction** begins the same way as GIC - several hours * **light reaction** - free radical methacrylate reaction occurs - can be placed in bulk - 20 seconds * **REDOX** (reduction-oxidisation) reaction occurs - 5 mins

Question 31

what are some of the disadvantageous properties of RMGICs?

Answer 31

* **polymerisation contraction** * **exothermic setting reaction** - can burn pulp * **swelling** due to uptake of water - HEMA (resin) is hydrophilic * **monomer leaching** - HEMA is toxic to pulp - needs to be polymerised completely * **reduced strength** if not light cured * **light curing slows down the acid-base setting reaction** * **benzoyl iodides and bromides** can be released which are **cytotoxic** * **fluoride release no better than GIC**

Question 31

what are some of the advantageous properties of RMGICs?

Answer 31

* good bond to enamel and dentine * better physical properties * lower solubility * fluoride release * better translucency and aesthetics * better handling

Question 32

what are the difference in properties between RMGIC and GIC?

Answer 32

RMGIC has: * **better aesthetics** * **easier to use** * **stronger**

Question 33

what are the differences in properties between RMGIC and composite?

Answer 33

RMGIC is: * **easier to use** * **fluoride releasing**