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2 - Dental Material Science > Glass Ionomer > Flashcards

Glass Ionomer Flashcards

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1
Q

What are the uses of GI? and what are examples of each use?

A

Restorative - filling materials (riva, vitremer)

Core build up - prior to restoration with crown (vitremer crown core)

Lining - underneath permanent fillings (vitrebond, ionoseal)

Luting - cementing indirect restorations (fuji luting, vitremer luting cement, aquachem)

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2
Q

What are the liquid acid components of GI and what is their role?

A

Polyacrylic acid (ionic monomers) - usually copolymers of acrylic and itaconic acid or acrylic and maleic acid

Tartaric acid - added to control the setting times

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3
Q

What are the biggest glass base powder components of GI?

A

— Silica, SiO2 (Silicone dioxide) 30% - 40%
— Alumina, Al2O3 (Aluminium dioxide) 15% - 30%
— Calcium Fluoride, CaF2 15% - 35%

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4
Q

What does adding strontium and lithium salts do?

A

can increase the radiopacity but these play no part in the reaction chemistry.

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5
Q

What does the ratio of alumina/ silica do?

A

The ratio of alumina/silica alters the translucency.

More silica more translucent.

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6
Q

What are the two variations of the acid being mixed with the base?

A

anhydrous materials (no water)
— 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

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7
Q

What does the powder particle size dictate?

what size gives a luting cement a low film thickness?

A

The smaller the particle size the quicker the setting reaction and the more opaque the set cement.

<20 micrometres

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8
Q

What are the 3 phases of the setting reaction?

A

— Dissolution
— Gelation
— Hardening

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9
Q

What occurs during dissolution phase?

A

Acid (H+ ions) attacks the glass powder, releasing metal ions (Ca, Al, Na & F). Leaves silica gel around unreacted glass

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10
Q

What occurs during the gelation phase?

how long does it take?

A

initial set due to calcium ion crosslinking with polyacrylic acid forming calcium polyacrylate

several minutes

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11
Q

What occurs during hardening phase?

how long does this take?

A

Continued crosslinking with aluminum ions for increased strength over time forming aluminium polyacrylate

increased strength

process does not start until 30 minutes and takes a week

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12
Q

What is important following gleation and why?

A

— It is important that GIC is protected from moisture and dessication following gelation.
— This is when it is ‘set hard’ in the mouth but before maturation has begun

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13
Q

What can contamination cause?

A

— 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

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14
Q

What materals offer better protection after placement?

A

varnish (acetate)
resins (DBA, unfilled Bis-GMA)

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15
Q

Why is petroleum gel not as effective?

A

removed by action of lips and tongue

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16
Q

What was used in newer formulations to improve their ease of use?

A

Tartaric acid, this greatly improved their ease of use
— Working time is largely unchanged but setting time is shortened

17
Q

What are the properties of adhesion of GIC?

What is bond strength to enamel?

A

— Can bond to enamel and dentine without the need for
use of an intermediate material
— Bond strength not high compared with composite, about 5MPa
— Good sealing ability with little leakage around margins

18
Q

What is chemical bonding mechanism of GIC?

A

— Chelation between carboxyl groups in the cement and Ca on the tooth surface.
— Re-precipitation of complex mixture of calcium phosphate (from apatite) and calcium salts from the polyacid onto and into the tooth surface
— Hydrogen bonding or metallic ion bridging to collagen

19
Q

What does a good bond require?

What conditioner is best?

A

— 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

20
Q

What does higher silica content improve?

A

higher translucency = better aesthetics

21
Q

What are the mechanical properties of GIC compared to composite?

A

Lower compressive strength than composite. Less than
half. 80 – 110MPA

Poorer wear resistance than composite, subject to abrasion

Lower hardness than composite

Higher solubility than composite (dissolution of unprotected material during gelation phase, and long term erosion by acids)

Good thermal properties expansion similar to dentine

No contraction on setting

Once set less susceptible to staining and colour
change than composites

Fluoride release (recharge)

Brittle

Low aesthetics

22
Q

How is fluroide released for GIC?

A

Initial fluoride release but this diminishes very quickly, over the first week.
then
recharges from environment

23
Q

What were cermets developed for and why were they not useful?

A

Developed to overcome Glass Ionomer brittleness

Silver was added to the glass (equal volumes) to
increase toughness and wear resistance.

No evidence that this was the case, only ended up making a silver coloured GIC. Looks like dull amalgam

24
Q

What are the power and liquid components of RMGIC?

A

Powder: Fluoro-alumino-silicate glass, barium glass, polyacrylic acid, initiators

Liquid: HEMA (resin), polyacrylic acid with methacrylate groups, water, initiators

25
Q

Why does a redox reaction happen in some RMGIC after the conventional acid-base reaction?

What is it called?

A
  • Free Radicals and Polymerization: The redox reaction generates free radicals. These free radicals act similarly to those produced during light-cure activation. They attack the methacrylate molecules (present in the resin component) and initiate the polymerization process, which hardens the material.

backup mechanism to ensure cure of full thickness of material

The REDOX reaction continues for about 5 minutes after initial mixing

26
Q

What varies between manufacturers?

A

about conditioning of the tooth surface prior to cement placement.

27
Q

What are the advantages of RMGIC?

A

— Better physical properties
— Lower solubility
— Fluoride release
— Better translucency and aesthetics
— Better handling
— Good bond to enamel and dentine
Set in cure

28
Q

What are the disadvantages of RMGIC?

A

Polymerisation Contraction

Exothermic setting reaction

Swelling due to uptake of water (HEMA is extremely) hydrophilic

HEMA is toxic to the pulp it must be polymerised completely

Benzoyl iodides and bromides can be released which are cytotoxic

29
Q

How is RMGIC compared to GIC?

A

— Better aesthetics
— Easier to use
— Stronger

30
Q

How is RMGIC compared to composite resin?

A

— Easier to use
— Fluoride release

31
Q

What are the uses of RMGIC?

A

— Dressing
— Fissure sealant
— Endodontic access cavity temporary filling
— Luting
— Orthodontic cement
— Restoration of deciduous teeth
— Restoration of permanent teeth
— Base or Lining

32
Q

What is the most likely reason for placing a resin modified glass ionomer lining under an amalgam restoration?

A

Thermal protection of the pulp

2 - Dental Material Science (17 decks)

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