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Dental Materials Y2 > Glass Ionomer Cements > Flashcards

Glass Ionomer Cements Flashcards

1
Q

What is the main component of GIC powder

A

Ionomer (ion leachable) glass

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2
Q

What are the 3 major basic components of GIC powder

A

SiO2
Al2O3
CaF2/SrF2

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3
Q

What governs the speed of reactivity of GICs

A

SiO2 : Al2O3 ratio

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4
Q

What ions can be used to add radiopacity

A

Sr2+
Ba2+
La3+

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5
Q

What can be used to boost fluoride release in GICs

A

Na3AlF6
AlF3
NaF

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6
Q

What can be used to provide phosphates in the GICs powder

A

P2O5

AlPO4

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7
Q

What temperatures do the GICs melt at to allow them to form

A

1150-1450C

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8
Q

After melting how is the GIC obtained

A
  • Rapidly cooled in ice water
  • Grind into a powder
  • Acid wash to control reactivity
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9
Q

What is the major component of the liquid component of GICs

A

Polyacrylic acid (PAA) - aqueous solution - usually about 50% conc.

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10
Q

What other acids can be used in the liquid component of GICs alongside PAA or in the place of PAA

A

Copolymers - itaconic acid

Polycarboxylic acids - Polymaleic acid

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11
Q

What other acids are usually in the liquid component of GICs

A

Tartaric acid - 10%

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12
Q

How are the acids in the liquid component of GICs converted into powder

A

Acids are freeze dried and the usually mixed with the GIC powder

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13
Q

What is the main difference between Acrylic acid and the Itaconic and Maleic carboxylic acids

A

The number of Carboxyl groups for each C=C bond in the acid, Acrylic acid has one and Itaconic and Maleic have 2 per double bond

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14
Q

What kind of reaction allows the setting of GICs

A

Acid base chemical reaction

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15
Q

What is the first stage of the acid base setting reaction for GICs and describe it

A

Dissolution stage - H+ ions from polyacid attack the glass, liberating Ca2+, Na+ and Al3+

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16
Q

Where are the protons lost from in the polyacrylic acid molecule that are used to attack the glass

A

Lost from the COOH group when they are dissociated and put into solution

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17
Q

What form are the Ca2+ and Al3+ ions released in, in the dissolution stage

A

Released in the form of complexes with F- or tartaric acid

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18
Q

What form is silicon released in

A

Si(OH)4

19
Q

How does tartaric acid increase working time for GICs

A

They hold the cement forming ions until the acid is partially neutralised then the insane released and give a sharp set

20
Q

What is the second stage of the GIC setting reaction

A

Gelation and Hardening stage

21
Q

How does the setting in the gelation and hardening stage occur

A

Occurs by polymer chain entanglement and cross linking of the chains by: Ca2+ (initial set) and Al3+ (final set)

22
Q

Describe the features of Calcium polyacrylates

A

As Ca2+ is a mobile ion its gives weak bonding and a water soluble polyacrylate

23
Q

Describe the features of Aluminium polyacrylates

A

As Al3+ is a less mobile ion it gives a strong bond and insoluble polyacrylate

24
Q

How does Gelation occur

A

Calcium ions link 2 carboxyl groups between 2 PAA molecules via an ionic bond - gives gel like consistency

25
Q

Describe how hardening happens

A

Aluminimum ions are trivalent so can cross link 3 carboxyl groups and that eventually leads to the hardening of the cement

26
Q

What is the 3rd stage of the GIC setting reaction

A

Final Maturation - Ratio of bound to unbound water increases - Strength increases and this can take 24 hours

27
Q

AY BAWS CAN I HABE DE NOTE PLZ

A

The cement needs to be protected immediately after placement

28
Q

What can be found in the structure of a GIC

A
  • Cross linked polyacrylic acid matrix
  • Unreacted glass that acts as a filler
  • The border between the glass and matrix = silica gel–
29
Q

What can early water exposure cause to GICs

A

Early water exposure will result in dissolution of the reactive components (cross linking ions)

30
Q

What can dehydration of GICs cause

A

Leads to loss of water that is critical for the continuation of the setting reaction

31
Q

What is done before the GICs are placed to prepare the tooth surface

A

Tooth surface is conditioned before GIC placement with PAA solution of 10-30% to remove smear layer and make surface chemically active

32
Q

What bond forms between the GICs and tooth

A

Chelation of Ca2+ from hydroxyapatite with the COO- from the PAA = strong ionic bond

33
Q

What other bonds can occur

A

Hydrogen bonding with amino groups e.g. in collagen

34
Q

Describe the levels of fluoride release from GICs

A

Initially is high from the exposed glass particles

Decreases over time but happens for a long time from the unreacted glass

35
Q

What does fluoride do in the oral cavity

A

Inhibits deminerlisation

Uptakes by dentin and enamel to become more acid resistant

36
Q

What other ion exchanges from GICs helps to inhibit caries

A

Sr2+ and Ca2+

37
Q

How are GICs low irritant despite their low pH

A

H+ movement is restricted as the high molecular weight polymeric anion

38
Q

What are some of the advantages of used GICs

A
  • Chemical bond to tooth (as opposed to mechanical)
  • Long term fluoride release and uptake
  • No shrinkage, No exotherm and no free monomers
  • Self healing and can be repaired, uptake of Ca2+ and PO4,3- from saliva onto the surface
  • Potential to remineralise
  • Thermal expansion coefficient similar to tooth
  • Aesthetics
39
Q

What are the some of the disadvantages of using GICs

A
  • Weaker than composites and amalgam but strength increases with age
  • Poor wear resistance at the early stage, improves with age
40
Q

What are the uses of GICs

A
  • Restoration of anterior teeth
  • Tunnel restorations
  • Cavity lining, base under amalgam and composites
  • Repair of erosion lesions and fissure sealants
  • With composites in the sandwich technique
  • Luting/cementing and repair materials for crown and bridge prostheses
41
Q

Describe the delivery of Powder and liquid GICs

A
  • Read instructions
  • Shake the bottle, scoop the powder, remove the excess
  • Dispense the liquid drops, no squeezing the liquid bottle
  • 2 increments of powder
  • Mix quickly, typically 20 secs
42
Q

Describe the delivery of encapsulated GICs

A
  • Read instructions
  • Shake the capsule
  • Activate the capsule by pushing the plunger inside the capsule
  • Spin (mixing) it in the amalgamator, typically 10-15secs
  • Dispense via the delivery gun
43
Q

How are high viscosity GICs different to conventional GICS

A
  • Designed for Atraumatic restorative treatment
  • Improved compressive strengths
  • High molecular weight acids - boost compressive strengthes
  • Higher fluoride release
  • Finer particle size powder accelerates initial setting reaction
44
Q

What cause the higher viscosity

A

Higher powder to liquid ratio

Dental Materials Y2 (13 decks)

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