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Dentistry year 2 > Clinical aspects of GIC > Flashcards

Clinical aspects of GIC Flashcards

1
Q

what are the key components of glass ionomer cement

A
  1. a glass powder: ‘calcium-alumina-fluori-silicate glass’

2. a liquid poly-acrylic acid, also called a ‘poly-carboxylic acid chain’

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2
Q

GIC directly binds to teeth. how is this possible? and how is it improved?

A

some of the H+ ions which are released from the poly-acid chain will bind to the ca2+/phosphate ions in enamel (similar to etching)

we can improve adhesion via dentine conditioner (a 10% polyacrylic acid).

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3
Q

GICs can help prevent secondary caries and are cariostatic due to fl. release when there is HAP dissolution.

explain the concept of fluoride re-charging?

A

this is when, if the pt. uses a fl. mouthwash/ toothpaste, the GIC will soak the fl up from it and release it over time in bursts.

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4
Q

after placing a GIC restoration, why do we apply varnish?

A
  1. allows the maturation stage to occur
  2. prevents the ca/al which didn’t form cross-links being lost into saliva/GI tract.

…therefore STRENGTHENS the restoration and prevents cracks from forming

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5
Q

what is the clinical name for a GIC/ glass ionomer cement?

A

glass poly-alkenoate cement

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6
Q

name 2 tooth coloured filling materials which are hydrophilic and 2 which are hydrophobic?

A

hydrophilic: GIC and RMGIC
hydrophobic: compomer and composite

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7
Q

what is the key reaction which underpins the chemistry of GICs

A

acid- base reaction –>poly-salt and water

here the acid is the poly-acid chain and the base is the powder glass

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8
Q

what are the advantages and disadvantages of GIC?

A

BAD:

technique sensitive
moisture sensitive
cannot be placed in stress bearing areas
low tensile strength 
low fracture toughness
poor wear resistance
only has average aesthetics- not as good as composite
lower survival times than composite and amalgam

GOOD:
cario-static- release of fl. (but is it even good because main reason for replacing GIC is due to secondary caries forming?)
directly bonds to tooth
tooth coloured

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9
Q

the setting reaction in GIC has 3 main stages. describe these.

A
  1. DISSOLUTION: H+ ions are released from the poly-acid chain so the FG is now COO-. The al/ca ions are released from the glass and bond to the poly-acid chain (acid-base reaction). Each ion can interact with 2 poly-acid chains at the same time= crosslinking.

As the ions are released from the glass they form an ion depleted layer.

  1. GELATION/HARDENING: more cross-links form to make the material harder. as the ion depleted layer interacts with water it forms a gel. Fl- ions are released into solution also.
  2. MATURATION: once the GIC is placed, it continues to undergo further reactions:
    - further precripitation of Al3+ salts for 24hrs after
    - continued formation of poly-salts including the hydration of poly-salts
    - more crosslinks form

this makes the GIC stronger.

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10
Q

why is water/ hydration of crosslinks important in GIC?

A

increases strength
improves translucency
increases resistance to desiccation (extreme dryness)

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11
Q

although we want hydration of GIC, we do not want excess, or too less water. why?

A

too much h20:

  • increased opacity, reduced strength and hardness

too little h20:

  • desiccation which causes cracking
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12
Q

why is GIC ‘biocompatible’?

A
  1. plaque does not thrive on GIC surface
  2. strep mutans growth is inhibited by GIC restorations
  3. the soft tissue response to GIC is favourable as shown by gingival tissue response to class V restorations
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13
Q

RMGIC is a modified GIC that has resin (HEMA) added to it which replaces some of the COOH groups on the poly-acid chain.
this means there is a polymerisation AND acid-base reaction at the same time when setting occurs.

what are the +ves/-ves of RMGIC?

A
  • command set- light cure.
  • longer working time
  • easier to use
  • improved aesthetics
  • medium fl. release
  • fewer steps than composite
  • will stop acting like a GIC once light cured. lower fl. release than normal GIC
  • no longer directly bonds to teeth
    -polymerisation shrinkage since resin added.
    once we add the resin it acts like composite so might as well use composite?
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14
Q

what is HEMA?

A

a hydrophilic resin monomer (rare)
polymerises when light cured
contact allergen which irritates eye.

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15
Q

what are clinical indications of using RMGIC?

A
  • abfraction lesions
  • cervical and root caries
  • base for bonded amalgam
  • non-loading bearing restorations
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16
Q

what are clinical indications of using GIC?

A
  • sub-gingival cavities (where getting good moisture control for composite would be hard)
  • temporary restorations (gic doesnt exactly match tooth therefore easier to remove, especially if use contrast white or fuji triage)
  • deeper cavities where you can leave some infected caries behind and place GIC to release fl, then seal the cavity chemically. This helps to arrest caries and preserve tooth
  • as fissure sealants since GIC can directly bond to tooth
  • cervical cavities. this is the main use of GIC.

in other words: on subgingival restorations, temporary restorations, and in step-wise excavation.

17
Q

what is zinc reinforced GIC (also called chemfil rock)?

what are its advantages?

A

here the ca2+ in the glass powder is replaced by zinc which is also 2+ charged therefore the same chemical reactions but zinc is stronger.

better wear resistance, doesnt need condition/ varnishing, stronger.
on top of this will also release fl, undergo maturation/ crosslinking to improve their physical properties.

18
Q

what is a compomer?

give an example of a compomer.

A

dyract is a popular compomer used in paediatric dentistry.

  1. similar to composites in chemistry/ composition but has TWO resins which have both acidic AND acrylate groups!
  2. it undergoes polymerisation AND acid-base reaction.

it is neither a composite or a GIC. best to think of it as a composite that requires a bonding agent.

19
Q

what are the +Ves/ -ves of compomers?

A

GOOD:

  • excellent handling
  • command set
  • good strength

BAD:

  • poor adhesion
  • low fl. release
  • needs a bonding agent

Dentistry year 2 (15 decks)

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