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BDS2; Dental materials > DML3: Glass ionomer cements > Flashcards

DML3: Glass ionomer cements Flashcards

1
Q

What is the composition of GICs

A
  1. Ion leachable ionomer glass

2. SiO2-Al2O3-CaF2/SrF2 basic components

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2
Q

Why is the ratio between SiO2 and Al2O3 important

A

Because it governs reactivity and how fast the cement will form

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3
Q

What components are added to GICs for radiopacity

A

Sr2+
Ba2+
La3+

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4
Q

What components are added to GICs to boost fluoride release

A

Na3AlF6, AlF3, NaF

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5
Q

What components in GICs provide phosphate and why are they needed

A

P2O5, AlPO4 ; governs reactivity

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6
Q

How is the ion leachable ionomer glass prepared for GICs

A
  1. Melted at high temperature (1150-1450)
  2. Rapidly cooled
  3. Ground into powder
  4. Acid washed to control reactivity
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7
Q

Why is ion leachable ionomer glass acid washed

A

Because it controls the reactivity making it easier to mix the cement at the chair side

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8
Q

What is the liquid composition of GIC

A
  1. Polyacrylic acid = PAA, 50% aqueous solution
    - or a copolymer of acrylic and itaconic acid
    - or other polycarboxylic acids e.g. polymaleic acid
  2. Tartaric acid, 10% aqueous solution
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9
Q

How is the liquid composition of GIC treated

A

Both acids are freeze dried and mixed with the ionomer glass powered, this means that the liquid composition is the water added

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10
Q

How do alkenoic acids modify the strength of GICs

A

These are aliphatic carboxylic acids - the strength of the cement can be increased by having more than 2 COOH groups

This is because there will be increased cross-linking which enabled higher strengths of the final set

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11
Q

What are the stages involved in the GIC setting reaction

A

Sets by an acid-base chemical reaction

  1. Dissolution stage
  2. Gelation and hardening stage
  3. Final maturation
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12
Q

What happens in the dissolution stage of GIC setting reaction

A

Protons dissociate in the presence of water

H+ ions from the poly acid attack the glass to liberate Ca2+ and Al3+ (as well as Na+ and F- and released silicon forms Si(OH)4)

These start forming complexes with tartaric acid and fluoride which are stable up to a set pH

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13
Q

What is the action of tartaric acid in GIC during the setting reaction

A

Tartaric acid complexes with the liberated ions from the ionised glass and this holds the cement forming ions to increase the working time until the acid is partially neutralised. The ions will then be released from the tartaric acid to five a sharp set

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14
Q

Why does tartaric acid bind cations rather than poly acrylic acid

A

Because it is stronger

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15
Q

What happens in the gelation and hardening stage of GIC setting reaction

A

Polymer chain entanglement and cross-linking occurs by Ca2+ initial set and Al3+ final set which will cross link the COOH groups in the polymer chains

This forms hydrated Ca- and Al- polyacrylates

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16
Q

What is the difference in properties produced by Ca2+ and Al3+

A

Ca2+ = mobile ion, weak bonding, water soluble polyacrylate

Al3+ = less mobile, strong bond, insoluble polyacrylate

17
Q

What is gelation

A

It is the formation of cross links via ionic bonds to give a gel like consistency

  • Ca2+ gives divalent bonds
  • Al3+ gives trivalent bonds causing the cement to harden
18
Q

What happens in the final maturation stage of the GIC setting reaction

A

The ratio of bound to unbound water increases which increases strength

19
Q

Why must the GIC be protected immediately after placement

A

Because it can take unto 24hours for the final maturation stage where the water is bound to increase strength of the cement

20
Q

What does early water exposure to GIC result in

A

Dissolution of reactive components leading to poor properties

21
Q

What does dehydration of GICs result in

A

Leads to loss of water which is critical for the continuation of the setting reaction leading to poor properties

22
Q

Why does the tooth surface have to be conditioned before placement of GIC and how is this done

A

It removes the smear layer to make the surface chemically active and ready to receive the GIC, this is done by application of PAA solution (10-30%)

23
Q

How does the GIC adhere and chemically bond to the tooth (3)

A

Once the smear layer has been removed by PAA, there is chelation of Ca2+ from HAP with COO- from the PAA within the GIC forming a strong ionic bond

There is hydrogen bonding with the amino groups

There is ion exchange between the tooth structure and the cement to form an ion rich interfacial layer

24
Q

Describe the patters of fluoride release from GICs

A
  • initially high level release from exposed glass particles
  • long term lower level release from deeper areas (diffusion controlled)
  • uptake of fluoride by enamel and dentine leads to HAF production which inhibits demineralisation

The main source of F- is the unreacted glass particles within GIC

25
Q

Describe the biocompatibility of GICs

A
  • bioactive as release F-
  • low irritant despite the low pH ~4
  • H+ movement contained by high molecular weight polymeric anion
  • restricts diffusion down dentinal tubules
26
Q

What are the advantages of GICs (6)

A
  1. Chemically bonded to tooth
  2. Long-term fluoride release and uptake
  3. No shrinkage, no exotherm, no free monomer
  4. Self healing and can be repaired as Ca2+ and PO43- is taken up from the saliva
  5. Potential to remineralise
  6. Thermal expansion coefficient is similar to tooth
27
Q

What are the disadvantages of GICs

A
  1. Weaker than composites and amalgam but strength increases with age
  2. Poor wear resistance at the early stage
28
Q

When are GICs used

A
  • anterior teeth
  • along with composite in sandwich technique
  • tunnel restorations
  • luting and repair of materials for crowns and bridges
  • cavity lining, base under amalgam and composties
  • repair of erosion lesions and fissure sealants
29
Q

How is GIC delivered/dispensed

A
  1. Powder liquid = fluff powder, scoop, remove excess - dispense liquid drops without squeezing - 2 powder increments - quick mixing time = 20seconds
  2. Encapsulated = shake capsule - activate by pressing in plunger - spin in amalgamator = 10-15seconds - dispense via delivery gun
30
Q

What are high viscosity GICs and why were they developed

A

These have higher powder:liquid ratios as the particle size is finer and so have improved compressive strength;

  • designed for atraumatic restorative treatment
  • have a higher fluoride release
  • they have a faster strength build up

BDS2; Dental materials (11 decks)

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