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BDS2 CDS DMS > 8. Glass Ionomer Cements > Flashcards

8. Glass Ionomer Cements Flashcards

1
Q

Types of GICs (2)

A

Conventional GI

RMGI

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2
Q

Uses for GI (4)

A

Restorations
Core build-up
Lining
Luting

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3
Q

Chemical components of GIs (2)

A

Acid (liquid)

Base (glass powder)

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4
Q

Components of acid (2)

A 
Polyacrylic acid (ionic monomers)
Tartaric acid
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5
Q

Function of polyacrylic acid

A

Usually copolymers of acrylic and itaconic acid or acrylic and maleic acid

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6
Q

Function of tartaric acid

A

Added to control the setting characteristics of the material

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7
Q

Components of base/powder (6)

A 
Silica (silicon dioxide) – 30-40%
Alumina (aluminium dioxide) – 15-30%
Calcium fluoride – 15-35%
Aluminium fluoride – 2-10%
Aluminium phosphate – 4-20%
Sodium fluoride – 4-10%
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8
Q

Effect of adding strontium and lithium salts to the base (2)

A

Can increase the radiopacity

Play no part in the reaction chemistry

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9
Q

Effect of alumina/silica ratio (2)

A

Ratio of alumina/silica alters the translucency

More silica, more translucent

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10
Q

GI setting reaction (2)

A

MO.SiO2 + H2A –> MA + SiO2 + H2O
Glass + acid –> salt + silica gel
M – metal; A – polyacid

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11
Q

GI setting reaction phases (3)

A

Dissolution
Gelation
Maturation/hardening

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12
Q

Process of dissolution (4)

A 
The acid is added into the solution
The H+ ions interact and attack the glass surface
Glass ions (Ca, Al, Na, F) are released/leach out
This leaves silica gel around unreacted glass
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13
Q

Process of gelation (4)

A

The initial part of the setting reaction is due to Ca2+ ions crosslinking with the polyacid by chelation with the carboxyl groups (quite quick), forming calcium polyacrylate (causing the material to appear quite hard in the mouth)
Ca ions are bivalent, so can react with two molecules and join them

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14
Q

Issue with crosslinking

A

Crosslinking is not ideal as calcium can chelate with two carboxyl groups on the same molecule

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15
Q

Process of maturation/hardening (2)

A

Trivalent Al3+ ions ensure good crosslinking with an increase in strength
Aluminium polyacrylate formation takes a while – it does not start for at least 30 mins and can take around a week to complete

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16
Q

Effect of aluminium reaction

A

The aluminium reaction ensures a much higher degree of crosslinking, greatly improving the mechanical, physical and aesthetic properties of the material

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17
Q

Effects of contamination, by moisture and desiccation (4)

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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18
Q

Materials used to protect GIC following placement (3)

A

Varnishes (copper ether, acetate)
Resins (DBAs, unfilled Bis-GMA)
Greases/gels (vaseline)
Varnishes and resins provide better protection; petroleum gel is quickly removed by the action of the lips and tongue and offers little protection
Protection is also required at a later date 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 excessive drying

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19
Q

Bond strength of conventional GIC to enamel/dentine

A

5MPa

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20
Q

Features of GIC

A

Good sealing ability with little leakage around margins

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21
Q

Conventional GIC bonding mechanism (3)

A

Chelation between carboxyl groups in the cement and calcium 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

22
Q

Requirements of a good bond (2)

A

Clean surface
Conditioned (not etched) surface (to produce a clean, smooth surface, removal of little/no tissue, best conditioner appears to be polyacrylic acid)

23
Q

GIC aesthetics (4)

A

Colour is acceptable
Lack translucency
Material with a higher silica content are better
Translucency improves over 24+ hours when extra crosslinking occurs. GICs are not suitable when aesthetics is of prime importance

24
Q

Mechanical properties of GIC (10)

A 
Poor tensile strength
Lower compressive strength than composite
Poorer wear resistance than composite
Lower hardness than composite
Higher solubility than composite
Good thermal properties
No contraction on setting
Once set, less susceptible to staining and colour changes than composite
Fluoride release
Lower modulus can be a good thing
25
Q

Compressive strength of GIC

A

80-110MPa

26
Q

Features of high GIC solubility (2)

A

Dissolution of unprotected material during gelation phase

Long-term erosion by acids

27
Q

Features of fluoride release (4)

A

Can release fluoride without damage to their structure
Beneficial against secondary caries (inhibits bacteria growth)
However, fluoride is released in negligible amounts
Initial fluoride release is high, but this diminishes very quickly, over the first week

28
Q

Features of GIC fluoride reservoir (4)

A

Can take up fluoride from the environment
Can recharge their fluoride when the F- concentration around them is higher than that in the cement.
Release F- again when the ambient concentration falls
Can act as a fluoride reservoir or fluoride sink

29
Q

Uses of GICs (8)

A 
Dressing
Fissure sealant
Endodontic access cavity temporary filling
Luting
Orthodontic cement
Restorations of deciduous teeth
Restorations of permanent teeth
Base or lining
30
Q

Advantages of GICs (5)

A 
Stable chemical bond to enamel and dentine
Low microleakage
Fluoride release
Good thermal properties
No contraction on setting
31
Q

Disadvantages of GICs (7)

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)

32
Q

Features of cermets (4)

A

Developed to overcome GI brittleness
Silver was added to glass to increase toughness and wear resistance - no evidence this worked.
No advantages
Worse aesthetics

33
Q

Development of RMGICs (3)

A

Developed to overcome the shortcomings of conventional GIC
Advantage of existing GIC technology (bonding to tooth, fluoride release)
Advantages of composite technology (light curing, improved physical properties, better aesthetics)

34
Q

Composition of RMGICs (2)

A

Powder (fluoro-alumino-silicate glass, barium glass, vacuum dried polyacrylic acid, potassium persulfate, ascorbic acid, pigments)
Liquid (HEMA, polyacrylic acid with pendant methacrylate groups, tartaric acid, water, photo-initiators)

35
Q

Function of barium glass in RMGIC powder

A

Provide radiopacity

36
Q

Function of potassium persulfate in RMGIC powder

A

Redox catalyst to provide resin cure in the dark

37
Q

Function of HEMA in RMGIC liquid

A

Water miscible resin

38
Q

Function of polyacrylic acid with pendant methacrylate groups in RMGIC liquid

A

Can undergo both acid base and polymerisation reactions

39
Q

Function of tartaric acid in RMGIC liquid

A

Speeds up setting reaction

40
Q

Function of water in RMGIC liquid

A

Allows reaction between polyacid and glass

41
Q

Function of photo-initiators in RMGIC liquid

A

Enables light curing

42
Q

Curing types of RMGICs (2)

A

Dual-curing

Tri-curing

43
Q

Curing process of dual-cure RMGIC materials (4)

A

Initially on mixing, the acid base reaction begins in the same way 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

44
Q

Features of dual-curing RMGIC materials (3)

A

Quite opaque so light does not penetrate deeply into the material
Should consequently be placed in layers or it may not set
To counteract the problem, a redox (reduction oxidation) reaction also occurs in some of these materials

45
Q

Curing process of tri-cure RMGIC materials (7)

A

Initially on mixing, the acid base reaction begins in the same way as conventional 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

46
Q

Advantages of RMGICs (7)

A 
Good bond to enamel and dentine
Potentially superior to conventional GIC
Better physical properties
Lower solubility
Fluoride release
Better translucency and aesthetics
Better handling
47
Q

Disadvantages of RMGICs (5)

A

Polymerisation contraction
Exothermic setting reaction (both polymerisation and dark cure)
Swelling due to uptake of water (HEMA is extremely hydrophilic)
Monomer leaching (HEMA is toxic to the pulp it must be polymerised completely)
Reduced strength if not light cured (redox cure is not as strong as light cure)

48
Q

Features of RMGICs (3)

A

Light curing slows down the acid base setting reaction
Benzoyl iodides and bromides can be released, which are cytotoxic
Fluoride release is no better than conventional GIC

49
Q

RMGIC benefits over conventional GICs (3)

A

Better aesthetics
Easier to use
Stronger

50
Q

RMGIC benefits over composite resins (2)

A

Easier to use

Fluoride release

51
Q

Uses of RMGICs (8)

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

BDS2 CDS DMS (15 decks)

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