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BDS2 Clinical > Glass Ionomer Cements > Flashcards

Glass Ionomer Cements Flashcards

1
Q

what are the 2 types of glass ionomer cements?

A

conventional GIC

resin modified GIC

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2
Q

what are the 2 types of conventional GIC?

A

anhydrous Vs original

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3
Q

when were conventional GIC first made?

A

1970s, still used today

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4
Q

what are the 2 types of RMGIC?

A

self cure and light cure

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5
Q

why was RMGIC created

A

changes in GIC to make it more handling friendly

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6
Q

4 categories of GIC use

A

restorative

core build up

lining

luting

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7
Q

what is the main use of glass ionomer cements?

A

as a filling materials
- in children’s teeth
certain areas in adult teeth (cervical, temporary fillings but not load bearing areas)

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8
Q

what are core build ups with GIC used for?

A

placed prior to restoration with a crown

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9
Q

restorative GICs

A

riva

vitremer

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10
Q

core build up GICs

A

vitremer

crown core

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11
Q

lining GICs

A

vitrebond

ionoseal

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12
Q

luting GICs

A

fuji luting
vitremer luting cement
aquachem

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13
Q

when are GICs used as linings?

A

underneath permanent fillings to prevent thermal conductivity

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14
Q

when are GICs used as luting agents?

A

cementing indirect restorations e.g. cementing in crowns

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15
Q

what are conventional GICs made from?

A

The original cement came from two different materials

  • Zinc Polycarboxylate Cement
  • Silicate cement. An anterior filling material based on fluoro-alumino-slicate glass combined with phosphoric acid.
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16
Q

what does the combination of zinc polucarboxylate and silicate cement allow?

A

combination fo the 2 materials led to the best properties of both materials
- fluoride releasing filling material which had the ability to bond to tooth structure.

glass from the aluminum silicate was dissolved in the polyacrylic acid from the zinc cement

it was the only ‘white’ filling 50 years ago

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17
Q

what are the main advantages of GICs?

A

fluoride releasing filling material which had the ability to bond to tooth structure.

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18
Q

what is the acid component of GICs?

A

liquid

polyacrylic acid and tartaric acid

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19
Q

what is the base component of GICs?

A

powder

alumina silica glass

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20
Q

acids in GICs

A

polyacrylic acid (with a few copolymers of acrylic and itaconic acid or acrylic and maleic acid)

tartaric acid

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21
Q

why is tartaric acid added to GICs?

A

Added to control the setting characteristics of the material (makes quicker)

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22
Q

what is in the base powder component of GICs?

A
  • Silica, SiO2 (Silicone dioxide, quartz) 30% - 40%
  • Alumina, Al2O3 (Aluminium dioxide) 15% - 30%
  • Calcium Fluoride, CaF2 15% - 35%
  • Aluminium Fluoride 2% - 10%
  • Aluminium phosphate 4% - 20%
  • Sodium fluoride 4% - 10%
  • Adding Strontium and lithium salts can increase the radiopacity but these play no part in the reaction chemistry.
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23
Q

why are heavy metal powders added to the base component of GICs sometimes?

A

Adding Strontium and lithium salts can increase the radiopacity but these play no part in the reaction chemistry.

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24
Q

what does the ration of alumina/silica alter in GICs?

A

translucency

  • more silica more translucent
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25
Q

anhydrous GICs

A

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
- Add water to the 2 powders to reconstitute and mix together

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26
Q

encapsulated GICs

A

Consistent powder/liquid ratio
- Easier to use
Push capsule together, place in amalgamator, shakes the materials together

Should be more consistent properties of the mixed material
- Can be advantage or disadvantage (may want to alter viscosity depending on patient compliancy)

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27
Q

which is more consistent - encapsulated or anhydrous GICs?

A

Encapsulated should be more consistent properties of the mixed material

  • Can be advantage or disadvantage (may want to alter viscosity depending on patient compliancy)
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28
Q

what can vary between GICs? (2)

A

powder particle size

molecular weight of acid

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29
Q

how does powder particle size effect GICs?

A

smaller the particle size the quicker the setting reaction and the more opaque the cement

larger particle size = more aesthetic the material

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30
Q

what particle size is needed for luting GICs?

A

<20um required for luting cement to give a low film thickness.

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31
Q

how does the acid molecular weight effect GIC properties?

A

the higher the weight the better the mechanical properties of the set material. (larger chain)

However the higher molecular weight acids are viscous and difficult to mix.
- Need balance

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32
Q

what are the 3 phases of the setting reaction?

A

dissolution

gelation

hardening

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33
Q

what type of reaction is the setting reaction?

A

acid base reaction

MO.SiO2 + H2A –> MA + SiO2 + H2O
(M = metal, A = polyacid)

glass + acid –> salt + silica gel

water absorbed into the surface of silica

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34
Q

dissolution phase of setting reaction

A

Acid into solution

H+ ions attack the glass surface – dissolves the surface of the glass

Ca, Al, Na & F ions are released into solution

Leaves silica gel around large unreacted glass

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35
Q

gelation phase of setting reaction

A

This GELATION equates to the initial set of the material and takes several minutes depending on the particular material.
- caused by formation of Calcium polyacrylate

calcium ion crosslinking with the polyacid by chelation with the carboxyl groups.

Polyacrylic acid molecules are long chain molecules with many bonding sites
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
- not cross linking, just bends the molecule, increasing molecule strength

Following this reaction the material will appear hard in the mouth

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36
Q

hardening phase of setting reaction

A

Trivalent Aluminium ions ensure good crosslinking with an increase in strength.
- Bonds to 3 at the same time

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.

The Aluminium reaction ensures a much higher degree of crosslinking
- greatly improves the mechanical properties of the material.

This is when it is ‘set hard’ in the mouth but before maturation has begun

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37
Q

what does GIC nee to be protected from following Gelation?

A

moisture and desiccation

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38
Q

why does GIC need to be protected from moisture and desiccation following the setting reaction?

A

First week relatively soluble, feels hard but isn’t,
Al ions can dissolve out.
Can lose water from crack

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39
Q

what does contamination of GIC lead to? (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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40
Q

what are the properties of a contaminated GIC?

A

weak material which will be rough, break up and have poorer aesthetics

41
Q

what 3 types of material can protect GIC after placement?

A

varnish

resin

greases/gels

42
Q

2 examples of varnishes that can protect GICs

A

copal ether

acetate

43
Q

2 examples of resins which can protect GICs

A

dentine/enamel bonding agents

unfilled Bis-GMA resins

44
Q

example of grease/gel which can protect GICs

A

vaseline

45
Q

what provides the better protection for GICs?

A

varnishes and resins

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

46
Q

when may you need to place protection on a GIC? (2)

A

following placement (soluble for first week after setting reaction)

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.

47
Q

issue with hardening in early GICs

A

Working and setting times were too long.

48
Q

why was tartaric acid added to GICs?

A

Working and setting times were too long

Working time is largely unchanged but setting time is shortened

49
Q

tartaric effect on handling properties of GICs

A

Working time is largely unchanged but setting time is shortened

50
Q

adhesion properties of GICs

A

Can chemically bond to enamel and dentine without the need for use of an intermediate material
- No need to etch

Good sealing ability with little leakage around margins

51
Q

bond strength of GICs

A

Bond strength not high compared with composite to acid etched enamel
- About 5MPa vs 20MPa

Probably not measuring the bond itself as GIC tends to fail cohesively

52
Q

do you need to etch prior to GIC placement?

A

no - can chemically bond to enamel and dentine

53
Q

bonding mechanism of GIC

A

Chelation between carboxyl groups in the cement and Ca on the tooth surface.
- Acid base reaction to Ca ions in tooth

  • 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
54
Q

2 things a good GIC bond requires

A

clean surface

conditioned surface

55
Q

what is a conditioned surface?

A

not etched
little or no tissue is removed (keeps Ca ions)

purpose is to create a smooth surface

56
Q

example of a surface conditioner

A

polyacrylic acid

  • mild solution of polyacrylic acid and some HEMA
57
Q

when should you surface condition in GIC application?

A

if the manufacturer’s guideline suggests

58
Q

aesthetics of GICs

A

colour is OK but lack translucency
- not as good as composite

not suitable for placement on anterior teeth

59
Q

what can be done to improve GIC aesthetics?

A

higher silica content

bigger particle size

60
Q

effect of time on translucency of GICs

A

improves over 24 hours when X-linking occurs

61
Q

tensile strength of GIC

A

poor

62
Q

compressive strength of GIC

A

poor

lower than composite
- less than half (80-100MPa Vs 300+MPa)

63
Q

wear resistance of GIC

A

poorer than composite

- subject to abrasion

64
Q

hardness of GIC

A

poorer than composite

65
Q

solubility of GIC

A

higher than composite

  • dissolution of unprotected material during gelation phase
  • long term acid erosion
66
Q

thermal properties and expansion of GICs

A

good, unlike composite

  • similar to dentine
  • not stressing bond
67
Q

polymerisation contraction of GIC

A

none

  • not pulling away from margins when light cured
  • doesn’t need a high bond strength as less polymerisation contraction
68
Q

staining of GIC

A

once set less susceptible to staining and colour changes than composite

69
Q

modulus of GIC

A

lower than composite

Cervical restorations - tooth moves from side to side/flexes
- GIC moves with tooth - less bond stressing and likelihood to fall out compared to higher modulus material

70
Q

main physical property advantage of GIC

A

fluoride release without compromising GIC structure

71
Q

how is fluoride released from GIC?

A

It has been established that GICs can take up fluoride from the environment

They can recharge their fluoride when the Fl concentration around them is higher than that in the cement
- From mouthwash, toothpaste

release Fl again when the ambient concentration falls
- act as a fluoride reservoir or fluoride sink

May have anti-caries effect. Not certain
F release will have a longer duration

72
Q

8 uses of GICs and RMGICs

A

Dressing

Fissure sealant e.g. if child won’t let you etch

Endodontic access cavity temporary filling

Luting

Orthodontic cement (not strong enough to stick bracket on)

Restoration of deciduous teeth often

Restoration of permanent teeth on non-load bearing areas

Base or Lining

73
Q

5 advantages of GICs

A

Stable chemical bond to enamel and dentine

Low microleakage

Fluoride release

Good thermal properties

No contraction on setting

74
Q

7 disadvantages of GICs

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 (e.g. if used as a lining, requires a retentive surface)

Etching damages surface
- RMGI: the resin will bond to the resin – no need to etch

75
Q

cermets where developed to…

A

overcome glass ionomer brittleness

76
Q

what are cermets?

A

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

No advantages and worse aesthetics. They looked like dull amalgam fillings
- Looks like silver amalgam but functions like glass ionomer

77
Q

why were resin modified GICs developed?

A

to overcome shortcomings of conventional GICs

78
Q

what 2 advantages of GICs did RMGICs want?

A

bonding to tooth

fluoride release

79
Q

what 3 advantages of composites did RMGICs want?

A
  • light curing (command set)
  • improved physical properties
  • better aesthetics
80
Q

powder component of RMGICs

A

Fluro-alumino-silicate Glass

Barium Glass
- Provides Radiopacity

Vacuum dried Polyacrylic acid

Potassium persulphate
- Redox catalyst to provide resin cure in the dark

Ascorbic acid

Pigments
- Varies shade

81
Q

liquid component of RMGICs

A

HEMA
- Water miscible resin only resin that works in water

Polyacrylic acid with pendant methacrylate groups
- This can undergo both acid base and polymerisation reactions.

Tartaric acid
- Speeds up the setting reaction

Water
- Allows the reaction between polyacid and glass

Photo-initiators
- Enables light curing

82
Q

3 main differences in constituents of GIC and RMGIC

A
  • redox catalyst (potassium persulphate)
  • HEMA
  • photo initiator
83
Q

2 types of setting reaction for RMGICs

A

dual and tri curing
- majority tri curing

glass ionomer part sets in same way as conventional

84
Q

dual curing setting reaction for RMGICs

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

85
Q

why should RMGICs be placed in layers?

A

quite opaque so light does not penetrate deeply into the material
- layers so it sets

86
Q

why does a redox reaction occur in RMGICs

A

to ensure setting as light may not penetrate to allow sufficient setting
- important in methacrylate polymerisation reaction

in the absence of light the physical properties of the set material are reduced by 25%

87
Q

tri curing setting reaction of RMGICs

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

88
Q

parts of tri curing RMGICs setting reaction

A

acid-base reaction + light activation + dark redox

89
Q

bond strength of RMGICs compared to GICs

A

good bond to enamel and dentine - higher than GICs

- better initial strength

90
Q

physical properties of RMGICs compared to GICs

A

better

  • lower solubility
  • better translucency and aesthetics (due to resin)
  • better handling
91
Q

6 disadvantages of RMGICs

A

Polymerisation Contraction (due to resin)

Exothermic setting reaction
- both polymerisation and dark cure

Swelling due to uptake of water
- HEMA is extremely hydrophilic, Take up water from mouth

Monomer leaching
- HEMA and Benzoyl iodides and bromides are cytotoxic to the pulp - it must be polymerised completely

Reduced strength if not light cured

Light curing slows down the acid base setting reaction and may not occur as successfully
- Resin makes it easier to use but may interfere with best aspect of glass ionomer reaction

92
Q

what are the effect of Benzoyl iodides and bromides?

A

can be released from RMGICs
kill bacteria
but also harmful to pulp

need to ensure fully cured to prevent cytotoxic damage

93
Q

fluoride release comparison of RMGICs and GICs

A

similar (no better)

94
Q

RMGIC benefits of GICs

A
  • easier to use (main)
  • better aesthetics
  • stronger
95
Q

RMGIC benefits compared with composite resin

A
  • easier to use
  • fluoride release
  • aesthetically not as good (still cannot be used on anterior teeth)
96
Q

material to use on lower 8

A

conventional GIC

- moisture control and light cure issues

97
Q

material to use if able to light cure

A

RMGIC

- better aesthetics than GIC

98
Q

redox reaction

A

reduction-oxidation reaction

atoms have their oxidation state changed

BDS2 Clinical (6 decks)

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