Conventional Glass Ionomer

Question 1

What are the different types of glass ionomer

Answer 1

Conventional

Resin modified

Question 2

What are the different types of conventional glass ionomer

Answer 2

Anhydrous

Original

Question 3

What are the uses of glass ionomer

Answer 3

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

Question 4

What two materials are present in original glass ionomer

Answer 4

Zinc Polycarboxylate Cement

Silicate Cement

Question 5

What are the components of conventional glass ionomer

Answer 5

Acid - liquid

Base - glass powder

Question 6

What acids are used in conventional glass ionomer

Answer 6

Polyacrylic acid

Tartaric acid

Question 7

What does tartaric acid do in conventional glass ionomer

Answer 7

Allows the setting characteristics to be controlled

Question 8

What powders are found in conventional glass ionomer

Answer 8

Silica
Alumina
Calcium fluoride
Aluminium phosphate
Sodium fluoride

Question 9

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

Answer 9

Strontium and lithium salts

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

Question 10

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

Answer 10

Alters the translucency

More silica, more translucent

Question 11

Describe the use of anhydrous materials in conventional glass ionomer

Answer 11

The acid if freeze dried and added to the powder

The liquid is distilled water

Question 12

Why are anhydrous materials used in conventional glass ionomer

Answer 12

It allows easier handling of the material, particularly mixing

Question 13

Why are encapsulated materials used in conventional glass ionomer

Answer 13

Consistency of the powder/liquid ratio

Easier to use

Question 14

Describe how powder particle size can affect conventional glass ionomer

Answer 14

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

Question 15

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

Answer 15

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

Question 16

Describe the setting reaction of conventional glass ionomer

Answer 16

Acid base reaction

Glass and acid react to give salt and silica gel

Question 17

What are the phases of the conventional glass ionomer setting reaction

Answer 17

Dissolution
Gelation
Hardening

Question 18

Describe dissolution

Answer 18

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

Question 19

What is gelation

Answer 19

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

Question 20

How long does gelation take

Answer 20

Several minutes depending on the material

Question 21

Describe hardening

Answer 21

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

Question 22

How long does hardening take

Answer 22

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

Question 23

What can happen if contamination occurs in conventional glass ionomer

Answer 23

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

Question 24

When is conventional glass ionomer most susceptible to contamination

Answer 24

Following gelation and before setting

Question 25

What can be used to protect conventional glass ionomer

Answer 25

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

Question 26

What provides better protection for conventional glass ionomer and why

Answer 26

Varnishes and gels

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

Question 27

Describe handling within conventional glass ionomer

Answer 27

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

Question 28

Describe the adhesion of conventional glass ionomer

Answer 28

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

Question 29

Describe the bonding mechanism of conventional glass ionomer

Answer 29

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

Question 30

What is required for a good bond

Answer 30

A clean surface

A conditioned surface

Question 31

What is used as a conditioner and why

Answer 31

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

Question 32

Describe the aesthetics of conventional glass ionomer

Answer 32

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

Question 33

Compare the mechanical properties of conventional glass ionomer with composite

Answer 33

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

Question 34

Describe the mechanical properties of conventional glass ionomer

Answer 34

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

Question 35

Describe the fluoride release of conventional glass ionomer

Answer 35

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

Question 36

Describe how conventional glass ionomer can uptake flouride from its environment

Answer 36

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

Question 37

What are the uses of conventional glass ionomer

Answer 37

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

Question 38

What are the advantages of using conventional glass ionomer

Answer 38

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

Question 39

What are the disadvantages of using conventional glass ionomer

Answer 39

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

Question 40

What is cermets and is it useful

Answer 40

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