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BDS2 CLINICAL Dental Materials > Glass Ionomer Cements > Flashcards

Glass Ionomer Cements Flashcards

1
Q

what are the 2 types of glass ionomer

A

conventional

resin modified glass ionomer

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2
Q

what are the 2 types of conventional glass ionomer

A

anhydrous

original

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3
Q

what are the 2 types of RMGI

A

self cure

light cure

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4
Q

what is GI used in

A

restorative
core build up
lining
luting for cementing indirect restorations

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5
Q

when is GI used as a filling material

A

often in children’s teeth

sometimes in adults if in a non-load bearing area e.g cervical

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6
Q

what are names of GI used as filling materials

A

riva

vitremer

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7
Q

when is GI used for a core build up

A

prior to a restoration with a crown

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8
Q

what is the name of the GI used for core build up

A

vitremer crown core

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9
Q

what are examples of GI used for linings

A

vitrebond, ionoseal

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10
Q

what are examples of GI used for luting

A

Fuji Luting
Vitremer luting cement
Aquachem

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11
Q

what two materials did GI originate from

A

zinc polycarboxylate cement

silicate cement

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12
Q

what is silicate cement

A

n anterior filling material based on fluoro-alumino-silicate glass combined with phosphoric acid

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13
Q

what properties did mixing silicate cement and zinc polycarboxylate cement result in

A

resulted in a fluoride releasing filling material (from the silicate material) which had the ability to bond to tooth structure (from the carboxylic acid material

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14
Q

what are the two components of GI cements

A

acid (liquid)

base (glass powder)

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15
Q

what are the two acids present in GI cement

A

poly acrylic acid

tartaric acid

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16
Q

what is polyacrylic acid

A

ionic monomer

usually copolymers of acrylic and itaconic acid or acrylic and malice acid

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17
Q

what is tartaric acid used for

A

added to control the setting characteristics of the material

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18
Q

what does the base consist of

A 
silica, SiO2 (silicone dioxide) 
alumina, Al2O3 (aluminum dioxide) 
calcium fluoride
aluminium fluoride
aluminium phosphate
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19
Q

what does adding strontium and lithium salts to the powder do

A

increase the radiopacity but these play no part in the reaction chemistry

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20
Q

what does the ratio of alumina/silica affect

A

translucency

more silica = more translucent

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21
Q

what are the variations in the composition

A

material may be anhydrous or encapsulated
there can be significant variations in the composition of the powder
the molecular weight of the acid can change

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22
Q

what are anhydrous material GI

A

the acid is freeze dried and added to the powder and the liquid is distilled water.

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23
Q

what is the advantage of having anhydrous GI

A

This makes for easier handling of the material, particularly mixing as polyacrylic acid is not an easy material to mix with so now we have an anhydrous material.

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24
Q

what is the advantage of encapsulated materials

A

consistent powder/liquid ratio. The proportions are set and controlled by the manufacturer and mixing is a quick and clean process as it goes in an amalgamator. It is therefore easier to use. It should therefore have more consistent properties of the mixed material.

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25
Q

what are the variations in the composition of the powders

A

Powder particle size can vary

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26
Q

what does a bigger particle size lead to

A

The bigger the particle, the better the aesthetic especially if it is larger silica particle

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27
Q

if the material is a luting agent what should the particles be

A

particle size has to be smaller than 20 micrometres to give a low film thickness and to not interfere with the restoration you are cementing.

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28
Q

how does particle size effect the setting reaction

A

The smaller the particle size the quicker the setting reaction and the opaquer the set cement.

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29
Q

what does a higher molecular weight acid have an effect on

A

Generally, the higher the weight (the longer the acid chain) the better the mechanical properties of the set material.
However the higher molecular weight acids are viscous and difficult to mix (liquid is less liquid) so need to find a balance.

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30
Q

what type of reaction is the setting reaction of GIC

A

acid/base

31
Q

what is the reaction of GIC

A

glass + acid –> salt + silica gel

32
Q

what are the 3 phases of the setting reaction

A

dissolution
gelation
hardening

33
Q

what happens in the dissolution phase

A

When the proprietary solution or the water is mixed with the powder, the acid goes into solution and reacts with the outer layer of the glass. This layer becomes depleted in aluminum, calcium, sodium and fluorine ions, so that only a silica gel remains.
The hydrogen ions that are released from the carboxyl groups on the polyacid chain diffuse to the glass and make up for the loss of the other ions.

34
Q

what happens in the gelation phase

A

The initial set is due to the rapid action of the calcium ions, which being divalent and more abundant initially, react more readily with the carboxyl groups of the acid than do the trivalent aluminum ions. The efficiency with which the calcium ions cross link the polyacid molecules is not as good as it might be because they are also able to link carboxyl groups on the same molecule.

This gelation equates to the initial set of the material and takes several minutes depending on the particular material. this initial set is caused by the formation of calcium polyacrylate. Following this reaction the material will appear hard in the mouth.

35
Q

what happens in the hardening phase

A

After the gelation phase, there is a hardening phase that can last as long as 7 days. It takes some 30 minutes for the uptake of aluminum ions to become significant, yet it is the aluminum ions that provide the final strength to the cement, as they are responsible for the introduction of the cross links. In contrast to the calcium ions, the trivalent nature of the aluminum ions ensures that a a high degree of cross linking of the polymer molecules takes place.

36
Q

what is the final structure

A

There is a continuation of the formation of aluminum salt bridges, and water becomes bound to the silica gel, which now surrounds the residual core of each of the glass particles. Once the cement has fully reacted, the solubility is quite low, the final structure consists of glass particles, each which is surrounded byy a silica gel in a matrix of cross linked poly-acrylic acid.

37
Q

why is it important that GIC is protected from moisture and desiccation following gelation

A

it is hard in the mouth but maturation has not begun.

38
Q

what could happen if GIC is not protected after gelation

A
  • Aluminum ions may diffuse out of the material and be lost to the cement, thereby being unable to cross link the polyacrylic acid chains.
  • Excessive drying may mean that the water is lost meaning the reaction cannot go to completion
  • Additional moisture may be absorbed, which may be contaminated with blood or saliva, leading to compromised aesthetics, with the restoration looking exceptionally dull and white. The contaminating moisture will also weaken the material and may cause it to crumble
39
Q

how can GIC be protected

A 
•	Varnishes 
o	Copal ether
o	Acetate 
•	Resins 
o	Dentine/enamel bonding agents 
o	Unfilled bis-GMS resins 
•	Greases or gels 
o	Vaseline
40
Q

what provide better protection to GIC

A

varnishes and resin

41
Q

why is petroleum gel not that good for GIC protection

A

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

42
Q

why is protection also required at a later date

A

f 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.

43
Q

describe the handling properties of GIC

A

there were major problems with early materials as working and setting times were too long. Newer formulations incorporated tartaric acid, this greatly improved their ease of use. The working time is largely unchanged but setting time is shortened

44
Q

describe adhesive properties of GIC

A

can bond to enamel and dentine without the use of an intermediate material. The bond strength is not high compared with composite to acid etched enamel. It is about 5MPa vs 20Mpa. It is however probably not measuring the bond itself as GIC tends to fail cohesively – the bond created is strong enough that when a GIC is bonded, the fracture will generally run through the GIC (cohesive failure) and not along the interface (adhesive failure). It has good sealing ability with little leakage around the margin.

45
Q

describe the bonding mechanism of GIC

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.

46
Q

what does a good bond require for GIC

A
  • Clean surface

* Conditioned surface

47
Q

what is the best conditioner to use for GIC

A

poly acrylic acid

48
Q

what is the purpose of conditioning the surface

A

produce a clean smooth surface

49
Q

why do we not etch

A

we do not want to take calcium out so we do not etch

50
Q

describe the aesthetics of GIC

A

Colour is okay but they lack translucency
New materials are better
Materials with a higher silica content are better
Translucency improves over 24+ hours when the extra cross linking occurs
Not suitable where aesthetics are of prime importance

51
Q

what are the disadvantages of the mechanical properties of GIC

A

Poor tensile strength
Lower compressive strength than composite. Less than half. 80-110 MPa vs 300+ MPa
Poorer wear resistance than composite – subject to abrasion
Lower hardness than composite
Higher solubility than composite – dissolution of unprotected material during gelation phase but also long term erosion by acids.

52
Q

what are the advantages of the good mechanical properties of GIC

A

Good thermal properties – expansion is similar to dentine meaning that the bond is not stressed when hot/cold foods eaten as it contracts/expands at the same rate.
There is no contraction on setting – no polymerization stress
Once set less susceptible to staining and colour change than composites
Fluoride release
Lower modulus can be a good thing particularly in cervical restorations where the restoration flexes with the tooth preventing it from being stressed

53
Q

describe fluoride release in GIC

A

Initial fluoride release is high but this diminishes very quickly over the first week however it has been established that these materials can take up fluoride from the environment.
They can recharge their fluoride when the fluoride concentration around them is higher than that in the cement.
They can release fluoride again when the ambient concentration falls. They can act as a fluoride reservoir or fluoride sink.

54
Q

what are uses for conventional GIC

A
  • Dressing
  • Fissure sealant
  • Endodontic access cavity remporary filling
  • Luting
  • Orthodontic cement
  • Restoration of deciduous teeth
  • Restoration of permanent teeth
  • Base/lining
55
Q

what are avdnagtaes of conventional GIC

A 
Stable chemical bond to enamel and dentine 
Low microleakage 
Fluoride release
Good thermal properties
No contraction on setting
56
Q

what are disadvantages of conventional GIC

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 binding to composite – etching damages surface.

57
Q

what are cermet

A

Developed to overcome glass ionomer brittleness
Silver was added to glass (equal volumes) to increase toughness and wear resistance
No evidence that this was the case
Only ended up making silver GIC
No advantages and worse aesthetics. They looked like dull amalgam fillings

58
Q

what is the advantage of composite technology to GIC

A
  • Light curing (command set)
  • Improved physical properties
  • Better aesthetics
59
Q

what does the powder of RMGI cement consist of

A 
fluoro-alumino-silicate glass
barium glass
vacuum dried poly acrylic acid
potassium persulphate 
ascorbic acid
pigments
60
Q

what does barium glass do

A

provides radiopacity

61
Q

what does potassium persulphate do

A

o Redox catalyst to provide resin cure in the dark

62
Q

what do pigments do

A

vary shade

63
Q

what does the liquid of RMGIC consist of

A 
HEMA
poly acrylic acid
tartaric acid
water
photoinitiators
64
Q

what happens in dual curing

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 (20 seconds)
  • Acid base reaction continues with the resin matrix for several hours
65
Q

why does light not penetrate deeply into these materials

A

opaque

may have to bet placed in layers

66
Q

how is the problem of depth of cure counteracted

A 
a REDOX (reduction oxidation) reaction also occurs in some of these materials. 
This is only important in the methacrylate polymerisation reaction 
This gives confidence that the material will set even if insufficient light penetration occurs
67
Q

describe tricking

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
68
Q

what brands say that conditioning of the tooth surface prior to cement placement for RMGI should occur

A

fuji cement LC
fuji II LC
vitremer

69
Q

what is the advantages of RMGI in terms of properties

A
  • Good bond to enamel and dentine
  • Bond is superior to conventional GIC – difficult to know what is being measured but definitely better initially
  • Better physical properties
  • Lower solubility – because of the resin
  • Fluoride release
  • Better translucency and aesthetics – because of the resin
  • Better handling – most important thing
70
Q

what is the disadvantages of RMGI in terms of properties

A

• Polymerization contraction
• Exothermic setting reaction
o Both polymerization and dark cure
• Swelling due to uptake of water
o Hema is extremely hydrophilic
• Monomer leaching
o Hema is toxic to the pulp so it must be polymerized completely but there is risk of unreacted HEMA in the depth of the cavity
• Reduced strength if not light cured
• Light curing slows down the acid base setting reaction
• Benzoyl iodides and bromides can be released which are cytotoxic
• Fluoride release no better than conventional

71
Q

how is RMGIC compared with conventional

A
  • better aesthetics
  • easier to use
  • stronger
72
Q

how is RMGI compared to composite

A
  • easier to use – no etching, or drying

* fluoride release

73
Q

what are the uses of RMGIC

A
  • dressing
  • fissure sealant
  • endodontic access cavity temporary filling
  • luting
  • orthodontic cement
  • restoration of deciduous teeth
  • restoration of permanent teeth
  • base or lining
74
Q

is RMGIC best or GIC

A

Depends on the clinical situation
Sometimes there will be times where only one of these is correct
More often though either would be appropriate and ease of use is often the deciding factor

BDS2 CLINICAL Dental Materials (15 decks)

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