Conventional Glass Ionomer Flashcards by David Jack

What are the different types of glass ionomer

Conventional

Resin modified

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What are the different types of conventional glass ionomer

Anhydrous

Original

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What are the uses of glass ionomer

Restorative - filling material
Core build up - prior to restoration with crown
Lining - underneath permanent fillings
Luting - cementing indirect restorations

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What two materials are present in original glass ionomer

Zinc Polycarboxylate Cement

Silicate Cement

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What are the components of conventional glass ionomer

Acid - liquid

Base - glass powder

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What acids are used in conventional glass ionomer

Polyacrylic acid

Tartaric acid

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What does tartaric acid do in conventional glass ionomer

Allows the setting characteristics to be controlled

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What powders are found in conventional glass ionomer

Silica
Alumina
Calcium fluoride
Aluminium phosphate
Sodium fluoride

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What salts can be found in conventional glass ionomer and what is their purpose

Strontium and lithium salts

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

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How does the ratio of silica to alumina affect conventional glass ionomer

Alters the translucency

More silica, more translucent

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Describe the use of anhydrous materials in conventional glass ionomer

The acid if freeze dried and added to the powder

The liquid is distilled water

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Why are anhydrous materials used in conventional glass ionomer

It allows easier handling of the material, particularly mixing

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Why are encapsulated materials used in conventional glass ionomer

Consistency of the powder/liquid ratio

Easier to use

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Describe how powder particle size can affect conventional glass ionomer

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

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Describe how the molecular weight of the acid can affect conventional glass ionomer

The higher the weight the better the mechanical properties of the set material
However, higher molecular weight acids are viscous and difficult to mix

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Describe the setting reaction of conventional glass ionomer

Acid base reaction

Glass and acid react to give salt and silica gel

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What are the phases of the conventional glass ionomer setting reaction

Dissolution
Gelation
Hardening

Describe dissolution

H+ ions attack the glass surface so that Ca, Al, Na and F ions are released
This leaves silica gel around the unreacted glass

What is gelation

The initial set of the material caused by the formation of calcium polyacrylate
Bivalent calcium ions crosslink with the poly acid by chelation with the carboxyl groups

How long does gelation take

Several minutes depending on the material

Describe hardening

Trivalent aluminium ions crosslink with the polyacrylate ensuring an increase in strength

How long does hardening take

Does not start for at least 30 minutes and can take a week or longer to be complete

What can happen if contamination occurs in conventional glass ionomer

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

When is conventional glass ionomer most susceptible to contamination

Following gelation and before setting

What can be used to protect conventional glass ionomer

Varnishes - copal ether, acetate Resins - dentine/enamel bonding agents or unfilled Bis-GMS resins Greases or gels - Vaseline

What provides better protection for conventional glass ionomer and why

Varnishes and gels | Petroleum gel is quickly removed by the action of the lips and tongue

Describe handling within conventional glass ionomer

Major problems with early materials as working and setting times were too long Newer formulations incorporated tartaric acid to improve the setting time Working time was largely unchanged

Describe the adhesion of conventional glass ionomer

Can bond to enamel and dentine without the need for an intermediate material Bond strength not high compared with composite to acid etched enamel - about 5MPa vs 20MPa Good sealing ability with little leakage

Describe the bonding mechanism of conventional glass ionomer

Chelation between carboxyl groups in the cement and Ca on the tooth surface Hydrogen bonding or metallic ion bridging to collagen in dentine surface

What is required for a good bond

A clean surface | A conditioned surface

What is used as a conditioner and why

Polyacrylic acid as it cleans the surface but doesn’t etch the tooth which takes away the calcium needed to bond

Describe the aesthetics of conventional glass ionomer

Main problem Colour is okay but lacks translucency Materials with higher silica content are better Translucency improves when the cross linking occurs

Compare the mechanical properties of conventional glass ionomer with composite

Poor tensile strength Lower compressive strength than composite - 80-110MPa vs 300 MPa Subject to abrasion Lower hardness than composite Higher solubility than composite Once set less susceptible to staining and colour change than composite

Describe the mechanical properties of conventional glass ionomer

Good thermal properties with expansion similar to dentine No contraction on setting Flouride release Lower modulus - good thing as it moves as the tooth does so there is less stress in the bond between the tooth and glass ionomer

Describe the fluoride release of conventional glass ionomer

GICs can release flouride without damage to their structure In vitro this has been shown to be beneficial against secondary caries as fluoride release inhibits bacterial growth There is still debate about the clinical benefits

Describe how conventional glass ionomer can uptake flouride from its environment

They can recharge their flouride when the Fl- concentration around them is higher than that in the cement They then release Fl- again when the ambient concentration falls May have anti-caries effect but it is not certain

What are the uses of conventional glass ionomer

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

What are the advantages of using conventional glass ionomer

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

What are the disadvantages of using conventional glass ionomer

Brittle Poor wear resistance Susceptible to moisture when first placed Poor aesthetics Poor handling characteristics Susceptible to acid attack and drying out over time Possible problems bonding to composite as etch damages the surface

What is cermets and is it useful

The addition of silver to the glass to increase toughness and wear resistance No evidence that this was the case, only made it silver coloured, giving worse aesthetics