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BDS2 - DMS > Glass Ionomers > Flashcards

Glass Ionomers Flashcards

1
Q

What are the 2 types of glass ionomer cement?

A
  • Conventional GI

- Resin modified GI

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2
Q

What is the restorative use of GIC’s and give 2 examples of these?

A
  • Used as filling material

- Riva, Vitremer

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3
Q

What is the ‘core build up’ use of GIC’s and what is an example of this?

A
  • Prior to restoration with crown

- Vitremer Crown Core

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4
Q

What is the ‘lining’ use of GIC’s and give 2 examples of these?

A
  • Underneath permanent fillings

- Vitrebond, Ionoseal

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5
Q

What is the ‘luting’ use of GIC’s and what are 3 examples of these?

A
  • Cementing indirect restorations

- Fuji luting, Vitremer luting cement, Aquachem

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6
Q

What 2 different materials were conventional GIC’s made from?

A
  • Zinc Polycarboxylate Cement

- Silicate cement

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7
Q

What are the 2 components of conventional GIC’s?

A

Acid - liquid

Base - Glass powder

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8
Q

Which 2 acids are found in Conventional GIC’s?

A
  • Polyacrylic acid (ionic monomers) - usually copolymers of acrylic and itaconic acid or acrylic and maleic acid
  • Tartaric acid - added to control the setting characteristics of the material
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9
Q

What is the powder (base) of conventional GIC’s made from? (6 points)

A
  • Silica, SiO2 (30-40%)
  • Alumina, Al2O3 (15-30%)
  • Calcium Fluoride, CaF2 (15-35%)
  • Aluminium fluoride (2-10%)
  • Aluminium phosphate (4-20%)
  • Sodium fluoride (4-10%)
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10
Q

What can adding strontium and lithium salts to the powder of conventional GIC’s do?

A
  • Can increase the radiopacity but plays no part in the reaction chemistry
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11
Q

The ration of alumina to silica in the powder of conventional GIC’s can alter the translucency. What does adding more silica do ?

A
  • Makes the GIC more translucent
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12
Q

What is the benefit of an anhydrous conventional GIC?

A
  • The acid is freeze dried and added tot he powder (the liquid is distilled water)
  • This make for easier handling of the material, particularly mixing
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13
Q

What are the benefits of using encapsulated conventional GIC’s? (3 points)

A
  • Consistent powder/liquid ratio
  • Easier to use
  • Should be more consistent properties of the mixed material
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14
Q

What does varying the particle size of conventional GIC’s do? (3 points)

A
  • <20um required for luting cement to give a low film thickness
  • The smaller the particle size the quicker the setting reaction and the more opaque the set cement
  • The bigger the particle size the better the aesthetic
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15
Q

What does varying the molecular weight of conventional GIC’s do? (2 points)

A
  • Generally, the higher the weight the better mechanical properties of the set material
  • However, the higher molecular weight acids are viscous and difficult to mix
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16
Q

What are the 3 phases of the setting reaction of conventional GIC’s?

A
  • Dissolution
  • Gelation
  • Hardening
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17
Q

What is meant by dissolution?

A
  • Acid dissolves the surface of the glass particles
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18
Q

What is the process of dissolution in conventional GIC’s? (4 points)

A
  • Acid into solution
  • H+ ions attack the glass surface
  • Ca, Al, Na & F ions are released
  • Leaves silica gel around unreacted glass
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19
Q

What causes the initial set of conventional GIC’s? (3 points)

A
  • Initial set is due to calcium ions that begin to dissolve, crosslinking with the polyacid by chelation with the carboxyl groups
  • Calcium ions are bivalent so they can react with two molecules joining them
  • Crosslinking is not ideal as the Ca can chelate with two carboxyl groups on the same molecule
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20
Q

The GELATION of conventional GIC’s equates to the initial set of the material. How long does this take?

A
  • Takes several minutes depending on the particular material
  • This initial set is caused by formation of calcium polyacrylate
  • Following this reaction the material will appear hard in the mouth
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21
Q

What ions are present in the hardening reaction of conventional GIC’s?

A
  • Trivalent aluminium ions ensure good crosslinking with an increase in strength
  • the aluminium reaction ensures a much higher degree of crosslinking
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22
Q

Why does the hardening reaction of conventional GIC’s not happen quickly? (2 points)

A
  • Aluminium Polyacrylate formation takes a long time

- This process does not start for at least 30 minutes and can take a week or longer to be complete

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23
Q

What does the process of hardening of conventional GIC’s improve?

A
  • Improves the mechanical properties of the material
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24
Q

It is important that GIC is protected from moisture and dessica tion following gelation. This is when it is ‘set hard’ in the mouth but before maturation has begun. What are the consequences if this does not happen? (4 points)

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 poor aesthetics
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25
Q

Conventional GIC’s must be protected following placement. What can be used to do this? (5 points)

A

Varnishes

  • Copal ether
  • Acetate

Resins

  • Dentine/enamel bonding agents
  • Unfilled Bis-GMA resins

Greases or gels

  • Vaseline
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26
Q

Out of varnishes, resins and greases or gels, what provides better protection for conventional GIC’s? (2 points)

A
  • Varnishes and resins

- Petroleum gel is quickly removed b the action of the lips and the tongue and offers little protection

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27
Q

When may protection of a conventional GIC be required at a later date then when being placed?

A
  • If desiccation of a GIC restoration is possible during work on other areas in the mouth
  • A thin layer of varnish or resin should be applied at this time to prevent surface damage due to excess drying
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28
Q

There used to be major handling problems with Conventional GIC’s as the working and setting times were too long. What was added to the to improve this and what did it do?

A
  • Tartaric acid was incorporated
  • This greatly improved their ease of use:
  • The working time is largely unchanged but setting time is shortened
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29
Q

Can conventional GIC’s bond to enamel and dentine without the need for an intermediate material?

A
  • Yes
30
Q

Compared to composite and etched enamel, what is the bond strength of conventional GIC’s like?

A
  • Not high in comparison

- About 5MPa vs 20MPa

31
Q

Do conventional GIC’s have a good sealing ability?

A
  • Yes, with little microleakage around the margins
32
Q

What is involved in the bonding mechanism of conventional GIC’s to tooth? (3 points)

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
33
Q

Good bonding of conventional GIC’s to enamel requires a clean surface but at the same time you don’t want to take Ca ions out of the enamel surface so what should you NOT do?

A
  • DO NOT etch before trying to bond to calcium
34
Q

A good bond of conventional GIC’s to enamel require a conditioned surface. What is the best conditioner for this and what is its purpose?

A
  • Best conditioner appears to be polyacrylic acid

- Purpose is to produce a clean, smooth surface

35
Q

What is one of the main problems with conventional GIC’s?

A
  • Aesthetics

- Colour is okay but they lack translucency

36
Q

When is the use of conventional GIC’s not suitable?

A
  • Where aesthetics are of prime importance
37
Q

Which conventional GIC’s have better aesthetics?

A
  • Ones with a higher silica content

- Translucency improves over 24+ hours when the extra cross-linking occurs

38
Q

What is the tensile strength of conventional GIC’s li ke?

A
  • Poor
39
Q

What is the compressive strength of conventional GIC’s like compared to composite?

A
  • Lower compressive strength than composite

- Less than half: 80-110MPa vs 300+MPa

40
Q

What is the wear resistance of conventional GIC’s like compared to composite?

A
  • Poorer wear resistance than composite (subject to abrasion)
41
Q

What is the hardness of conventional GIC’s like compared to composite?

A

Lower than composite

42
Q

What is the solubility of conventional GIC’s like compared to composite? (3 points)

A
  • Higher solubility:
  • Dissolution of unprotected material during gelation phase
  • Long term erosion by acids
43
Q

Do conventional GIC’s have good thermal properties?

A
  • Yes, thermal expansion is similar to dentine
44
Q

Do conventional GIC’s have contraction on setting?

A

No

45
Q

Once set, which material is more susceptible to staining and colour change: conventional GIC’s or composite?

A
  • Composite
46
Q

Do conventional GIC’s release fluoride?

A
  • Yes
47
Q

Why are conventional GIC’s better for cervical res torations than composite?

A
  • They have a lower modulus of elasticity

- They will bend more than a high modulus material

48
Q

There is an initial fluoride release from conventional GIC’s but this diminishes quickly (over the first week). However, what can they do to replenish fluoride? (4 points)

A
  • These materials can take up fluoride from the environment
  • They can recharge their fluoride when the Fl conc. around them is higher than that in the cement
  • They then release Fl again when the ambient concentration falls
  • They can act as a Fl reservoir or fluoride sink
49
Q

What are the possible uses of a conventional GIC? (8 points)

A
  • Dressing
  • Fissure sealant
  • Endodontic access cavity temporary filling
  • Luting
  • Orthodontic cement
  • Restoration of deciduous teeth
  • Restoration of permanent teeth
  • Base or lining
50
Q

What are the advantages of using conventional GIC’s? (5 points)

A
  • Stable chemical bond to enamel and dentine
  • Low microleakage
  • Fluoride release
  • Good thermal properties
  • No contraction on setting
51
Q

What are the disadvantages of using a conventional GIC? (7 points)

A
  • Brittle
  • Poor wear resistance
  • Moisture susceptible when first placed
  • Poor aesthetics
  • Poor handling characteristics
  • Susceptible to acid attack and drying out over time
  • Possible problems bonding to composite (etching damages surface)
52
Q

What are Cermets and do they have any advantages over conventional GIC’s?

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 silver coloured GIC
  • No advantages and worse aesthetics. They looked like dull amalgam fillings
53
Q

Why were RMGIC’s developed?

A
  • To take the advantages of GIC technology (bonding to tooth, fluoride release) and add the advantages of composite technology (light cure, improved physical properties and better aesthetics)
54
Q

What is included in the powder of RMGIC’s? (6 points)

A
  • Fluro-alumino-silicate glass
  • Barium glass (provi des radiopacity)
  • Vacuum dried polyacrylic acid
  • Potassium persulphate (redox catalyst to provide resin cure in the dark)
  • Ascorbic acid
  • Pigments
55
Q

What is included in the liquid of RMGIC’s? (5 points)

A
  • HEMA (water miscible resin)
  • Polyacrylic acid with pendant metharylate groups
  • Tartaric acid (speeds up setting reaction)
  • Water (allows the reaction between polyacid and glss)
  • Photo-initiators (enables light curing)
56
Q

What is involved in the dual curing setting reaction of RMGIC’s? (4 points)

A
  • Initially on mixing the acid base reaction begins in the same was as conventional GIC
  • On light activation a free radical methacrylate reaction occurs resulting in a resin matrix being formed
  • Quickly light activation is complete (20s)
  • Acid base reaction continues within the resin matrix for several hours
57
Q

RMGIC’s are quite opaque so light does not penetrate deeply into the material. It should consequently be placed in layers or it may not set. What can be done to counteract this problem ?

A
  • A REDOX reaction also occurs in some of these materials
  • This is important in the methacrylate polymerisation reaction
  • This gives confidence that the material will set even if insufficient light penetration occurs
58
Q

In the absence of light, by how much are the physical properties of RMGIC’s reduced?

A
  • By 25%
59
Q

What is involved in the tri cure setting reaction of RMGIC’s? (7 points)

A
  • Initially on mixing acid base reaction begins in the same way as GIC
  • The REDOX reaction begins
  • On light activation a free radical methacrylate reaction occurs resulting in a resin matrix being formed
  • Quickly light activation is complete (20s)
  • The REDOX reaction continues for about 5 minutes after initial mixing
  • Acid base reaction continues within the resin matrix for several hours
  • Final hardening of the acid/base phase with aluminium polyacrylate formation can take days
60
Q

What is advised to be placed prior to RMGIC placement? (3 points)

A
  • Fuji Cement LC (optional)
  • Fuji II LC (yes)
  • Vitremer (yes)
61
Q

Do RMGIC’s have a good bond to enamel and dentine?

A

Yes

62
Q

Do RMGIC’s have better physical properties than conventional?

A

Yes

63
Q

What has a lower solubility RMGIC or conventional?

A

RMGIC

64
Q

Do RMGIC’s release fluoride?

A
  • Yes
65
Q

What has better translucency and aesthetics: RMGIC’s or conventional?

A

RMGIC

66
Q

What has better handling: RMGIC’s or conventional?

A

RMGIC

67
Q

What are the disadvantages of RMGIC’s? (5 points)

A
  • Polymerisation contraction
  • Exothermic setting reaction
  • Swelling due to uptake of water
  • Monomer leaching
  • Reduced strength if not light cured
68
Q

What can be released from RMGIC’s which can be cytotoxic? (2 points)

A
  • Benzoyl iodides and bromides
69
Q

What are the advantages of RMGIC’s in comparison to conventional? (3 points)

A
  • Better aesthetics
  • Easier to use
  • Stronger
70
Q

What are the advantages of RMGIC’s in comparison to composites? (2 points)

A
  • Easier to use

- Fluoride release

71
Q

What are the uses of RMGIC’s? (8 points)

A

(same as conventional)

  • Dressing
  • Fissure sealant
  • Endodontic access cavity temporary filling
  • Luting
  • Orthodontic cement
  • Restoration of deciduous teeth
  • Restoration of permanent teeth
  • Base or lining
72
Q

Which GI is best: RMGIC or conventional? (2 points)

A
  • Clinically there will be times when only one of these materials is the correct choice
  • More often though either would be appropriate and ease of use is often the deciding factor

BDS2 - DMS (14 decks)

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