All about Glass Ionomer Cements

by dr.anoop.v.nair

• Introduction

• Definitions & terminologies

• Scientific & clinical development

• Classification

• Composition

• Setting reaction

• Water balance

• Adhesion

• Properties

• Clinical implications

• Instructions to dental assistants

• Review of literature

• References

• Summary & conclusion

DEFINITIONS & TERMINOLOGIES

• The word “ionomer” was coined by Dupont company

• Describe its range of polymers containing a small proportion of ionized or ionizable groups generally of the order of 5% to 10%.

• Does not properly apply to components of GI dental cement

• Therefore the term Glass polyalkenoate cement was devised.

• Systematic name in Chemical Abstracts ; Official ISO terminology

• Does not apply to recently developed poly(vinyl phosphonic acid) cements ---- Glass Polyphosphonates.

• Therefore the term “Glass - ionomer cement” is a generic one for all glass polyacid cements.

• Glass : Acid-decomposable glass

• Acidic polymer : Typically poly(acrylic acid)

• Successful acids are – water soluble & polyelectrolytes.

Acid-base reaction : The cement forming reaction is defined as the conversion of initially viscous paste to a hard solid, & in a true glass-ionomer cement this reaction takes place within a clinically acceptable time i.e, a few minutes.

Definition of glass ionomer cement

A cement that consists of a basic glass & an acidic polymer

which sets by an acid-base reaction between these

components. (Mclean & Wilson 1994)

The essential elements of a true glass ionomer :

• Acid-base setting reaction

• Ion-exchange adhesion with underlying tooth structure

• Continuing ion activity, with mobility of fluoride, calcium and phosphate ions

• Definition (Akinmade & nicholson, 1993) water based cement where-in following mixing, the glass powder & polyalkenoic acid undergo an acid/base setting reaction. The acid attacks the surface of powder particles, releasing calcium & aluminium ions, thus developing a diffusion-based adhesion between powder & liquid

Types of glass ionomer cements

1. Based on chemical composition 2 types of glass ionomer :

• Glass-ionomer cement • Glass polyalkenoates• Glass polyphosphonates

• Glass-ionomer hybrid materials • Resin modified glass-ionomer

2. Based on types of cure :

• Autocure : Chemical cure – acid-base reaction• Dualcure : Light initiation followed by acid-base reaction• Tricure : Autocure resin reaction in remaining uncured resin

Glass-ionomer hybrid materials

• The term “Resin-modified glass-ionomer” originally used by Antonucci et al, is the trivial name.

• Systematic name, for precise chemical nomenclature as in ISO standards is “Resin-modified glass-polyalkenoate”

• Consists of components of glass ionomer, modified by inclusion of a small quantity of additional resin, mostly HEMA.

• They set partly by acid-base reaction & partly by photochemical polymerization.

Other polymerizable restorative materials :Polyacid modified composite resins (Compomers)

• Donot belong to glass-ionomer category.

• The correct ingredients are present (acid decomposable glass & possibly some polymeric acid) but in an insufficient amount to promote acid-base cure in dark

• Donot set without light activation.

• Donot bond to tooth structure through ion-exchange mechanism.

• Fluoride reservoir effect of glass ionomer is not available.

Diagram showing theoritical composition of various resin-modified materials &

the potentialeffect of modifying the relative percentage of the contents

As resin component increases – acid-base reaction reduces ; benefits of

glass ionomer are lost & the material becomes light activated only

Compomers would belong in one of the middle 2 bars (acid-base component

is negated & therefore belong to composite resin end of table)

Compomer -

– anhydrous resin-based material

– not possible to have ion

transport within it.

Fluoride release is minimal

At 20 min ; compomer does not

show signs of set if not light

activated

Resin modified glass ionomers

-By 7-10min show signs of

chemical set

-Over the next 15020min becomes

quite hard

Mix under a light proof cover

SCIENTIFIC & CLINICAL DEVELOPMENT

• INVENTION :

• Resulted directly from basic studies on dental silicate cements & studies where the phosphoric acid in dental silicate cements were replaced by organic chelating acids.

EARLY DEVELOPMENT

• 1966 : A.D.Wilson – examined cements prepared by mixing dental silicate glass powder with aqueous solutions of various organic acids (including poly(acrylic acid)

- unworkable, set slowly, sluggish, not hydrolytically stable.Silica glass :

Highly cross linked

network of connected

silicon & oxygen

atoms; does not carry

an electric charge

Impervious to acid

attack

Ionomer glass :

ionic polymer ;

contains negative

sites which are

vulnerable to attack

by positive hydrogen

ions of acid

• 1968,1969 : A.D.Wilson + Kent & Lewis – found that hydrolytically stable cements could be produced by employing novel glass formulations.

• 1968 : Kent – found that setting of these cements was controlled by Al2O3/ SiO2 ratio in the glass.

• 1973,1979 : Kent et al – found a glass that was high in fluoride that gave a usable cement ASPA 1 (aluminosilicate polycrylates).

• 1972 (reported in 1976): Wilson & Crisp – key discovery –tartaric acid – modified the cement-forming reaction, thus improving manipulation, extending working time & greatly sharpening setting rate.

• This refinement of ASPA I was termed ASPA II & constituted the first practical GIC.

• 1975 : Crisp et al – the disadvantage for general practice was that its liquid tended to gel.

• 1975,1977 : Crisp & Wilson – developed copolymer of acrylic & itaconic acid that did not gel at high (50%) concentration in aqueous solution

• ASPA IV. But this was inferior in other properties to ASPA II

• 1974 : McLean & Wilson – used it for fissure sealing & filling

• 1977c : McLean & Wilson – ideal for restoration of class V erosion lesions.

• 1979 : Crisp et al – ASPA X – with excellent translucency.

• 1977 : Wilson et al – ASPA IVa – fine grained version for luting.

• With less viscous polyacid, lacked the mobility of traditional zinc phosphate cement.

• 1977 : Mclean & Wilson – in a review article suggested use in pediatric dentistry & as a liner in composite – resin / ionomer laminate.

LATER DEVELOPMENT

• 1973 : Wilson & Kent – reported use of poly(acrylic acid) in dry powder form blended with glass powder.

• The cement was formed by mixing this powder with water or tartaric acid solutions.

• 1984 : Prosser et al – re-examined the above & resulted in development of ASPA V

• ASPA Va – a water-hardening luting agent – proved to have the mixing qualities & mobility of zinc phosphate cement.

• 1985 : McLean et al – the original 1977 idea of using composite resin / ionomer laminate was revived in a modified form.

• GIC & enamel was etched – double etch technique (composite resin was attached micromechanically to enamel & GIC bonded indirectly to dentin).

• 1984 : Hunt & Knight – tunnel preparation for Class II

• The reasoning behind the technique – GIC core bonds enamel shell together, preventing fracture (described by Hunt 1984, & Mclean 1987)

• 1980 : Sced & Wilson & 1983 : Simmons – incorporated metallic oxides & metal alloy fillers, to improve strength of GIC.

• 1985 : McLean & Gasser – fused silver particles onto ionomer glass, giving cement radioopacity, burnishability, smoother surface, increased wear resistance (reported by Moore et al 1985)

• 1986 : McLean – Developed new Cermet cements for clinical use.

• 1988 : Wilson & McLean – Highly viscous glass ionomer cements

• Late 1980’s : Resin-modified glass ionomer cements

COMPOSITION

Glass ionomer cement is defined as an acid-base

reaction cement (Wilson 1978, Wygant 1958)

Basic component Acid component

Calcium aluminosilicate

glass containing fluoride

Polyelectrolyte which is a

homopolymer or copolymer of

unsaturated carboxylic acids

known scientifically as

alkenoic acids.

Types of Calcium fluoroaluminosilicate glass:

SiO2 - Al2O3 - CaF2 (Simple 3-component system)

SiO2 - Al2O3 - CaF2 - AlPO4

SiO2 - Al2O3 - CaF2 - AlPO4 – Na3AlF6

Components are fused between 1100°C - 1500°C

Melt poured onto metal plate / into water

Glass then ground to fine powder

(Maximum particle size: 50µm for restorative & 20µm for luting)

Chemical composition of original ionomer glass (G-200)

(Modified from Barry et al 1979)

SiO2 30.1%

Al2O3 19.9%

AlF3 2.6%

CaF2 34.5%

NaF 3.7%

AlPO4 10.0%

Fluoride – Lowers temperature of fusion

Improves working characteristics of cement paste

Increases markedly strength of set cement

Enhances translucency

Contributes to cements therapeutic value

Cryolite (Na3AlF6) - Supplements fluxing action of CaF2

Reduces temperature at which glass will fuse

Increases translucency of set cement

AlPO4 - Increases translucency

Adds body to set cement

Visual appearance of glass – clear /

opal / opaque

Glasses high in SiO2 (>40%) -

transparent

Glasses high in Al2O3 -

opaque

Al2O3 / SiO2 ratio :

Crucial , required to be 1:2

Increase in ratio

• Decreases setting time

• Clear to opaque

• Compressive strength increases

• Determines the rate at which

breakdown of glass matrix occurs Negative sites are vulnerable to acid

attack ; if enough Al atoms, all the

connecting links in network will be

completely decomposed ; such a glass

has cement forming potential

VARIATION ON BASIC GLASS COMPOSITION

1. Calcium may be replaced by strontium / barium / lanthanum

2. Disperse phase glasses

Flexural strength

3. Fibre re-inforcement (eg. Alumina fibres ) Flexural strength

4. Metallic inclusions

Radioopaque glass

POLYELECTROLYTES • Are both electrolytes and polymers

• includes copolymers of unsaturated mono-, di-, and tri-carboxylic acids, particularly those of acrylic acids.

• The more important carboxylic acids in ionomer include acrylic acid, maleic acid and itaconic acid.

• The polyacids may be

• in the form of concentrated aqueous solution (40-50% by mass)

• Blended dry with glass powder

COMPOSITION OF ASPA CEMENTS

• ASPA I – G-200 + 50% polyacrylic acid

• ASPA II – G-200 + 47.5% polyacrylic acid + 5% tartaric acid

• ASPA III – G-200 + 45% polyacrylic acid + 5% tartaric acid + 5% methyl alcohol

• ASPA IV – G-200 + 47.5% copolymer of acrylic & itaconic acid 2:1 ratio + 5% tartaric acid

Different configurations affect adhesion ??

• Polyacrylic acid cements – bond more strongly to enamel &dentin (Aboush & Jenkins, 1986)

• Copolymer cements – less resistant to acid attack thanPolyacrylic acid cements (Setchell et al, 1985)

• Copolymer cements – harder than polyacrylic acid aids earlyfinishing (Mount & Makinson 1982, Matis & Philips 1986)

Effect of molecular weight and concentration of polyacrylic acid

• Increase in molecular weight and concentration

• Shortens setting time

• Increases strength

• Increased viscosity of mix

Water

• Reaction medium

• Plays role in hydrating reaction products i.e metal polyalkenoate salts and silica gel

Tartaric acid

• The principal obstacle in developing practical GIC was

• Sluggish nature of set

• Working time was minimal

• Slow hardening

• In 1976 Wilson et al reported addition of tartaric acid made glass ionomer cement a practical one

• It enabled reduction of fluoride

• Delayed onset of viscosity

Other additives

Working time Setting time

Polyphosphates

Metals

Stannous

fluoride

SETTING REACTION

Cement forming reaction of glass ionomer cement

Showing extraction of ions from the glass, migration into aqueous

phase, & subsequent precipitation as polyanion hydrogels

There are 4 overlapping

stages that can be identified

but not clearly separated out

Unattacked

glass

particles

dispersed

in polyacid

liquid

Outer layer of glass

particles is depleted

of metal ions &

degraded to silica gel.

Metal ions migrate to

liquid, where they

remian in soluble form

(red dots)

Initial gelation

Soluble metal

ions remain ..

The cement is

still vulnerable

to moisture

Fully hardened glass

ionomer in an

insoluble form

Cement is no longer

vulnerable to attack

by moisture

Decomposition

Migration

Gelation

Further slow maturation

Post-set hardening

Glass structure

unattacked

(electrically charged

network)

H ions attack

network dwelling

ions, Ca 2+ & Na+

H ions attack the

charged aluminosilicate

network, destroying the

glass network &

liberating Al ions

1st

s

t

a

g

e

2n

d

s

t

a

g

e

3r

d

s

t

a

g

e

Silicic acid formed condenses

to form silica gel

Setting reaction of auto cure cements

Only the surface of each particle is

atacked by the acid

Releasing Ca & Al ions, & F ions which

remain free & are not part of the matrix

The calcium polyacrylate chains form

first then the aluminium polyacrylate

chains follow immediately

By stage 3, there is a degree of maturity,

with more calcium & aluminium chains

Also a halo of siliceous hydrogel

surrounding each glass particle, which

increases resistance to acid attack

Note : these chains can break & reform

throughout the life of the restoration

Stage 1 : Decomposition of glass & migration of metal ions (Dissolution)

• 20-30% of glass is attacked by polyacid

• Surface of the glass particles decompose

• Releasing metal ions (Al 3+ , Ca 2+ )

• Glass network breaks down into silicic acid which polymerises at surface of the glass powder

• As pH of aqueous phase increases, polyacrylic acid will ionize & create electrostatic field that will aid the migration of liberated cations into the aqueous phase

• The ions thus migrate into the aqueous phase

• As the negative charge increases, polymer chains unwind, viscosity increases

Stage 2 : Precipitation of salts; gelation & hardening

• At a critical pH & ionic concentration, precipitation of insoluble polyacrylates begins

• Ca 2+ &Al 3+ bind to polyanions via carboxylate groups

• The initial set is achieved by the cross-linking of the more readily available Ca 2+ (forming clinically hard surface within 4minutes of start of mix)

• Maturation occurs over the next 24hours when the less mobile Al 3+

become bound within the cement matrix, leading to more rigid cross-linking between poly (alkenoic acid) chains

• Aluminium polyacrylate ultimately predominates in the matrix

Few points to remember ….

1. Why not sodium ions ???

2. What happens to fluoride & phosphate ions??

3. Do all COOH convert to COO-

4. Period of vulnerability ??

5. Causes of gelation

1. Why not sodium ions ???

• They cannot displace the hydrogen sphere

• They are not site bound, because of their low ionic charge

• They do not precipitate as polyacrylates

What happens to them ??

• They contribute to formation of orthosilicic acid on the

surface of particles

• As pH rises, this converts to silica gel which assists in

binding the powder to matrix

2. What happens to fluoride & phosphate ions??

• They form insoluble salts and complexes

3. Do all COOH convert to COO-?? …. No

1. When most of the carboxylic acid groups have ionized

• Negative charge on polymer chain increases

• Positively charged H ions now become very strongly bound to remaining un-ionized carboxylic acid group & not easily replaced by metal ions

2. As density of cross-links increase

• Hinders movement of metal ions towards carboxyl sites

4. Period of vulnerability ??

• Till soluble ions insoluble matrix

• After material is set, but not fully hardened; a proportion of ions (Ca 2+ ,Al 3+

polyacrylate ions ) are in soluble form

• Can be dissolved out by aqueous fluids

• Weakened cement

• Softened surface

• Opaque restoration

[In a freshly set cement, calcium polyacrylate predominate, they are more vulnerable to water than aluminium polyacrylates]

5. Causes of gelation

• Multivalent Ca 2+ ,Al 3+ ions displace various hydration spheres that interpose themselves between cation-anion pairs

• Cation-polyacrylate ion pairs are formed

• Desolvation of hydration spheres renders ionic pairs more hydrophobic and precipitation occurs

Chain entanglement

Ionic cross-linking

Hydrogen bonds

Involved in matrix formation

Ca 2+ bridge 2 chains ; so do Al 3+ bridge 3??

Stearically unlikely because of presence of negatively charged

ligands

Coordination number of Al is 6 in water, therefore it should be

attached to 6 ligands

In glass ionomer cement, ligands are COO-, F-, OH-, water

molecules

Possible molecular structure of the set glass ionomer cement

A- represents F- / OH-

Fig 3-4

Stage 3 : Hydration of salts ; Hardening & Slow maturation• Progressive hydration of matrix salts, leading to sharp

improvement in physical properties

• Continues for about 24hours

• Slight expansion under high humidity

• Further changes occur for >= 1 year

What are the underlying chemical changes ?

What are the indicators of these slow changes ?

What are the underlying chemical changes ?

• Increase in bound water (Wilson et al)

• Slow increase in cross-linking (Hill,1986)

• Slow replacement of residue carboxyl hydrogen ions by ,metal ions, increasing cross-linking

• Increasing predominance of Al over Ca in the matrix

What are the indicators of these slow changes ?

• Translucency improves

• Becomes more resistant to dessication

• Strength continues to increase for atleast 1 year

• Ability to absorb / loose water decreases with age

• Initially the cement is plastic, then as it ages rigidity increases,

approaching that of phosphate bonded cements

Cement structure Hydrogel matrix :

Ca & Al polyacrylates + fluorine

as fluoroaluminium polyacrylate

Water – in bound & free form

Glass core pitted by

selective etching

Siliceous

hydrogel

(with fluorite

crystallites)

Smaller filler

particles; contain

only siliceous

hydrogel

Cohesive forces binding matrix together :

mixture of ionic cross-links, hydrogen

bridges, chain entanglement

This framework is porous ; ions with

small dimensions (Eg. OH- & F-) are

free to move through the material

Role of water

Glass ionomer cements are water based cements- they contain water

- make water during setting reaction Role of water / Significance

Water plays an important role in

Setting reaction Final structure

-Reaction medium

-Coordinating species

-Hydrating species

-plasticizer

In the set cement

24% is water

Loosely bound Tightly bound

As it ages tightly bound : loosely bound increases

Early contamination

Loss of calcium polyacrylate chains

Absorption of water

Loss of translucency

Loss of physical properties

Leaves cement susceptible to erosion

Dehydration

Cracking & fissuring of cement

Softening of surface

Loss of matrix-forming ions

Factors affecting setting characteristics

• Role of fluoride

• Role of tartaric acid

Role of fluoride

Fluoride forms metal complexes

They retard the binding of cation to

anion sites on polyacrylate chain

Delays gelation & prolongs working

time

Release of H+

Acidity of paste increases

Delays pH dependant gelation

Role of tartaric acid

• Tartaric acid is stronger than polyacrylic acid

Forms stronger complex with Al

Therefore increases extraction of Al from glass

• Initially tartaric acid alone complexes cations

As neutalisation proceeds & pH ~ 3

Polyacrylic acid becomes neutralised by metal ions until cement sets at pH ~ 5-5.5

• Also ionization of polyacrylic acid is suppressed & unwinding of the

chain is retarded, resulting in decrease in viscosity & delaying gelation

• Once gelation occurs, tartaric acid accelerates hardening

• Tartaric acid & calcium react preferentially therefore initial set may be due to

formation of calcium tartarate

• Tartaric acid controls initial setting of cement

• Improves

manipulation

• Increases working

time

• Sharpens set by

accelerating

precipitation

• Increases strength

Factors affecting rate of setting

1. Glass composition : increase in Al/Si ratio – faster set

2. Particle size : finer – faster set

3. Tartaric acid – sharpens set without shortening working time

4. Relative proportion of constituents – Powder : Liquid

5. Temperature of mixing – increase – faster set

Among these the factors within the province of the clinician are

Temperature of mixing

Powder : Liquid

Factors within the province of the clinician

1. Temperature of mixing

• Chilling powder & mixing pad – increases working time up to 25% (Mc Lean 1970)

• Increase in working time occurs without loss of physical properties (Makinson 1978)

• Word of warning –

• Chilling of liquid will cause gelation

• Increase in humidity & temperature below dew point – weakens the cement

2. Powder : Liquid

• Increase in powder – faster set

• But insufficient liquid – decrease in translucency of the set cement

Setting reaction of resin-modified light cured materials

• 2 distinct mechanisms :

• The original acid – base setting reaction

• Vinyl polymerisation of acrylate groups that can be activated through the presence of photo initiators such as camphorquinone

When mixed, original acid base reaction appears to continue without interruption

Resin component provides as umbrella effect

Some degree of cross linking may be present between 2 matrices ;

both reactions may proceed without interference

Over time, any remaining resin not affected by light - activation may

undergo further chemical setting reaction

A “Dark – cure reaction”

Lead to the term “Tricure” or “Triple-cure”

Light activation

Is depth of cure an important factor??? … Yes…

1. Lack of water inhibition of acid-base reaction

2. Residual HEMA in lower levels, closest to pulp

3. Fully light activated restoration is notably superior in physical properties

Therefore, depth of cure is important ; incremental build up recommended

Unless, a mechanism for chemical curing of methacrylate

groups is incorporated

“Redox” catalyst

Allows for continuing polymerisation in absence of light activation,

thus ensuring activation of any remaining HEMA

Micro – encapsulated potassium persulphate & ascorbic acid

The red chains represent fully

activated resins to the depth of

penetration of activator light

Showing influence of resins

incorporated into the glass

ionomer

Note : there is already a degree

of cross-linking between the

polyalkenoic acid chains and

the polymer chains

Showing progress of setting reaction

of resin component of RMGIC

Autocure redox reaction continues

until entire mass is set

Red chains represent completion of

auto cure setting

Note complete cross linking between

polyalkenoic acid chains & polymer chains

To summarise..

2 distinct types of setting reaction occur :

Acid-base neutralisation reaction

Free-radical metharylate cure

Relationship between the 2 reactions may take one of 2 forms

Formation of 2 separate matrices

Ionomer salt hydrogel

Poly-HEMA matrix

Multiple cross-linking pendant methacrylate groups may replace a small fraction of carboxylate groups of polyacrylic acid, thus preventing separation of 2 potential matrices

Cross – linking of polymer chains may take place through 1/more of the following reactions

Acid – base reaction

Light – cure mechanism

Oxidation – reduction reaction

Full physical properties are not achieved till acid – base reaction continues for some days

Structure of set cement• RMGIC is presumed to have either

• A multiple cross – linked matrix or

• Matrix containing 2 separate phases

Depth of cure

3-4mm

Criticisms against RMGI

1. HEMA – monomer – toxic – relative lack of biocompatibility, potential for allergic response

2. HEMA – hydrophilic – set material takes up water –expansion + less resistance to wear & erosion

3. Potential for color change over time (Doray 1994)

4. HEMA – low molecular weight monomer – more polymerisation shrinkage + substantial exotherm that can last for sometime

Setting reaction of resin – modified auto cure material

• Mixing of powder + liquid

• Usual acid base reaction initiated

• Catalyst in powder will initiate polymeristaion of HEMA & cross-linkable monomers

• Ultimately, there will be cross-linking between 2 systems & the entire mass will set hard with uniform physical properties

Setting reaction of light initiated auto cure material

• Involves enhancing speed of acid-base reaction by utilizing a simple physical principle

• No resin is added

• The glass ionomer is colored (Eg. red) ; on irradiation with a blue halogen activator light , acid-base reaction will take place more rapidly

• Setting time is reduced dramatically

• No heat generation

• Physical properties not downgraded

• Highly bactericidal

• Flows easily

• Easily identified Uses :

Fissure sealant

Uncooperative patient

Root surface protection

Lining/ base in very deep cavities

Transitional restoration during stabilization phase

Temporary seal for endodontics

ADHESION

• Glass ionomer cements are the only restorative materials that depend primarily on chemical bond to tooth structure.

• They form an ionic bond to the hydroxyapatite at the dentin surface and also obtain mechanical retention from microporosities in the hydroxyapatite.

Bond strength to dentin : (Richard S. Schwartz et al JOE,vol.31,no.3,March2005,156)

• Lower initial bond strength compared to resins (around 8MPa)

• Despite this they succeed clinically because of the following factors:

• They form “dynamic” bond. As the interface is stressed, bonds are broken, but new bonds are formed.

• Low polymerization shrinkage

• Coefficient of thermal expansion similar to tooth structure

Barriers to adhesion :

1. Water – aqueous fluids in dentin & enamel

• Hydrophilic, highly ionic GIC competes successfully with water because of its multiplicity of carboxyl groups that form H bonds with the substrate

2. Dynamic nature of tooth material

• Enamel : ion exchange

• Dentin : living material subject to change

• The adhesive bond must have dynamic character

• Polymeric nature of glass ionomer ensures multiplicity of bonds between GIC and substrate. Scission of single bond does not lead to failure because the bond can reform.

Bonding to these is

like trying to bond to

shifting sand

Mechanism of adhesion to enamel & dentin

• Smith (1968): Chelation of calcium contained in apatite – involved in adhesion

• Beech (1973): Suggested interaction of polyacrylic acid & apatite.

• Bonding only to apatite, therefore weaker adhesion of GIC to dentine and non existence of adhesion to decalcified dentine.

• Wilson (1974): Considered possibility of polyacrylates bonding to collagen.

• Initially, when paste is fluid, adhesion is by H-bonding provided by free carboxyl groups present in fresh mix.

• As cement ages, H bonds are progressively replaced by ionic bonds, the cations coming from cement or hydroxyapatite.

• McLean & Wilson (1977): Hypothesized presence of an intermediate later between cement 7 tooth surface.

• Wilson, Prosser & Powis (1983): Postulated the adsorption phenomenon of bond to mineralized tissue.

Adhesion

Bond to mineralized tissue

• Diffusion

• Adsorption phenomenon

Bond to collagen

• H bonding

• Metallic ion bridging

Bond to mineralized tissue

Phosphate ions are displaced from apatite by carboxyl groups.

To retain electrical neutrality, phosphate takes with it calcium.

Setting of the material + dissolution of enamel & dentin surface results in

buffering of polyacid.

Rise in local pH & reprecipitation of minerals at cement-tooth interface

occurs.

Therefore chemical bond is achieved by a calcium phosphate polyalkenoate

crystalline structure acting as an interface between enamel or dentin & the

set material.

Bond to collagen

May occur by H bonding or metallic ion bridging between carboxyl groups on

polyacid & collagen molecules of dentine.

Chain length may also be an important factor in adhesion.

The GIC is based on a polymer chain that is capable of bridging gaps between

the cement body and the substrate.

The poly (alkenoic acid ) chains actually

penetrate the surface of both enamle &

dentine & displace phosphate ions,

releasing them into the cement

Each phosphate ion takes with it

a calcium ion to maintain

electrolytic balance, leading to an

ion-enriched layer at the interface

As the acid is buffered by the release of ions the pH will rise & the interface will set

as a new ion-enriched material between the tooth & the restoration.

Bond strength & nature of polyacid

• Cements based on polyacrylic acid appear to bond more strongly than those based on copolymers of acrylic acid with itaconic & maleic acids (Aboush & Jenkins, 1986)

• Adhesion of cermet cements is inferior to conventional GIC (Thorton et al, 1986)

• Pretreatment of enamel & dentin with polyacrylic acid, which is not washed off, so that intermediary bonding is formed. (Powis, 1986)

Improving adhesion – surface conditioning :

• Surface conditioning – McLean & Wilson (1977) first used the term, to differentiate from acid etching.

• Powis et al (1982); Aboush & Jenkins (1986) – smoother the surface stronger the bond.

• Surface irregularity --- air entrapment + stress concentration

• Ideal requirement of surface conditioners (Mount, 1984)• Isotonic (to decrease osmotic effect)

• The Ph = 5.5 – 8 (neutral)

• Nontoxic

• Compatible with chemistry of cement

• Water soluble, be easily removed

• Not deplete enamel & dentine chemically

• Enhance surface chemically in preparation for bonding.

Agents Proposed

by

Conc

entr

ation

D

u

r

at

io

n

Advantage Disadvantage

Polyacrylic acid Powis et

al (1982)

25% Enamel –

etches slightly & removes

polishing marks.

Dentin - Removes debris,

smoothes irregularities &

opens up tubules

May cause sensitivity with

luting agents

Mount

(1984)

1

0

se

c

Long et al

(1986)

30-

35%

Tannic acid Powis et

al

3

0

se

c

Enamel –

smooth featureless

surface without etching/

decalcification

Dentine –

Tubules not opened

Mineralizing

solutions (Eg.

Levine et al

solution & ITS

solution)

2-

3

m

in

Smear layer will be

included in ion-exchange

layer & will not interfere

with adhesion

Forms calcium & phosphate

rich layer between GIC &

tooth - ineffective

CLASSIFICATION

1. By Wilson & McLean (1988)

2. By McLean et al (1994)

3. By Smith / Wright (1994)

Classification by Wilson & Mclean (1988)

• Type I : Luting & bonding materials

• Type II : Restorative

• Type II.1 : Restorative aesthetic (autocure & resin-modified)

• Type II.2 : Restorative reinforced / Bis-reinforced filling materials

• Type III : Lining or Base

Classification by Mclean et al (1994)

• Glass ionomer cement

• Resin modified glass ionomer cement

• Polyacid modified composite resin

Classification by Smith / Wright (1994)

• Type I – Luting cement

• Type II – a) aesthetic filling material

b) reinforced resin filling material

• Type III – Fast setting lining cement

• Type IV – Fissure sealing cements

• Type V – Orthodontic cements

• Type VI – Core build up material

Type I : Luting & Bonding

Factors in favor of glass ionomer lute

1. Tensile strength – as high as zinc phosphate

2. Solubility – lower

3. Thixotropic flow properties – allow easier placement ; without need to vent

casting / retain pressure during setting

4. Fine film thickness

5. Fluoride release

6. Potential for postinsertion sensitivity – same as for other cements

4. Fine film thickness2. Solubility – lower

Significant factors

• Powder particle size - 4-15 µm

• Film thickness – 10-20 µm

• P/L ratio – 1.5:1

• pH – newly mixed cement – 1.8 ; within 30min – 4.5

• Dispensing & mixing – P/L system & 2 paste system

• Time to mature – less time desirable; break away excess when cement is crisp

& firm

• Adhesion to enamel & dentin – cementation of crown – hydraulic pressure –

penetartion of polyacrylic acid into tubules – post-insertion sensitivity – therefore

seal surface of dentin ; do not remove smear layer

•Adhesion to noble metals – by electroplating the fitting surface with 2-5µm tin

oxide immediately prior to placement

•Cementation on vital teeth - 25% tannic acid (for 2min) or dentin bonding

agent containing polalkenoic acid applied just before cementation

Remove temporary

cement

Washed only ; not

conditioned / seal

Mixing time – 25 seconds

String up 2-3 cmApply to inside,

especially margins

Seat crown with positive

pressure ; no need to

maintain pressure

Paint small quantity

on tooth

Remove excess when

cannot be indented with

sharp instrument

Remove debris from

gingival crevice

Cemented crown

•Cementation on non vital teeth – 10% polyacrylic acid conditioning (for 10-15sec) to

remove smear layer

Preparation cleaned Root surface & post

hole conditioned

Washed & dried with

alcohol

Cement painted on

post

Canal filled to top

with cementPost seated Inside of crown

painted with cementSeat crown with positive

pressure ; no need to

maintain pressure

Cemented crown

Bonding with glass ionomer - Bonding composite resin

Glass ionomer used as

bonding agent in small shallow

cavities (Yamada et al 1996)

• Prepare cavity

• Condition for 10sec ; wash &

dry

• Paint thin layer of Glass

ionomer bonding agent over

entire cavty including walls

• Blow off excess

• Light activate for 20sec

• Place composite

incrementally ; finish, contour

& polish

Advantage :acid-base reaction

of glass ionomer will continue

& compensate for shrinkage of

glass ionomer

Prepare cavity

Condition

Glass ionomer

bonding agent

Light activate

Place composite

finish, contour & polishSEM showing interaction

layer / ion-exchange layer

Low viscosity, low P/L ratio, resin-

modified glass ionomer used

Bonding with glass ionomer - Bonding amalgam

Long term results – not available

Short term results suggest – reduced

post-insertion sensitivity to

temperature changes in newly placed

restoration

Greatest hazard – potential for

incorporation of fragments of glass

ionomer into amalgam during

condensation – reducing the physical

properties ; unlikely to be sufficient to

prevent cusp loss

Similar clinical technique

Type II.1 : Restorative

aesthetic materials

Factors in favor :

Adequate aesthetics & translucency

Sufficient physical properties in fully supported restoration

Adhesion achieved

Fluoride reservoir

Significant factors

P/L ratio – 2.9:1 to 3.6:1 (if polyacrylic acid is liquid)

6.8:1 (in anhydrous cements)

Time to mature :

Autocure - Initial snap set - 4min from start of mix

Resin modified Require atleast 1 week to mature

Light activation - 20-40sec

Resin glaze : to paint over finished restoration ;

no effect on continuing maturation ;

will seal voids / porosities on surface

Matrix checked for

accuracy of fit

Pumice slurry - 5

seconds ; flushed

& dried

10% polyacrylic

acid - 10-15 sec

Cement placed

excess removed

after 4 min

After matrix

removed ; bonding

resin applied

Bonding resin light

activated

Erosion lesion

Finished

restoration

Type II.2 : Restorative

reinforced materials

Reasons for use :

When fast setting material is desirable

With increased physical property

But where color match not important

Significant factors:

• Resistant to uptake of water in 5min

• But first 2 weeks water loss is a problem

Following material earlier marketed as reinforced ; now considered a misnomer

• Because physical properties not significantly improved

• Adhesion & fluoride release reduced

• Need another material to cover for esthetics

1. Silver cermet

2. Amalgam alloy admix

3. Silver alloy admix

Newer generation high strength glass ionomers

Silver cermet

• Manufactured by incorporating 40% by weight of microfine silver particles <

3.5µm in diameter in which powdered glass particles

• The 2 were then sintered under pressure

• Unreacted silver was washed out

• 5% titanium dioxide added to modify color

Advantages :

Surface could be burnished

High density & low porosity restoration

High abrasion resistance

High compressive strength & fracture resistance

Disadvantage :

Earlier used for “core build-up“ but their

physical properties cannot be relied on

Less adhesion (mechanical retention required)

Uses : In repairing chipped &

faulty margins of existing

restorations ; alternative to

replacement

Color : closer to tooth

Radioopacity : same as amalgam

Amalgam alloy admix

Spherical amalgam alloy particles incorporated with a fast-setting glass

ionomer powder (Simmons 1983)

Amalgam alloy was incorporated in proportion of 8 parts cement powder

: 1 part alloy by volume

This was then mixed with polyacrylic acid (3:2 by weight)

• black restoration

•Physical properties slightly improved

•Early resistance to water uptake

•Set rapidly

•Adhesion & fluoride release less than unfilled

•Difficult to mix to required consistency by hand ; capsules were later

available

Silver alloy admix

Include silver containing alloy in flat brokenpieces rather than

spheres ; flakes would offer larger surface area for reaction with

polyacrylis acid

Higher abrasion resistance because when subjected to wear, the

preparation developed a Beilby – type smear layer on its surface

Physical properties, color, fluoride release, adhesion – better

than above 2

But material has had limited market

New generation High strength / Condensable glass

ionomers

Fast setting Auto cure

10-15% better physical properties than resin modified glass ionomer

Available as “normal set” or “fast-set”

Particularly useful as transitional restoration

Changes : powder particle size

particle size distribution

heat history of glass (improvement in surface reactivity of powder )

Significant factors :

• P/L ratio : 3:1 to 4:1

• Time to mature : resistant to water uptake / loss as soon as set

• Adhesion : stronger because cement is stronger

• Release of ions : similar to other types of autocure, therefore useful for root

surface caries, tunnels

Physical properties :

• Tensile strength & fracture resistance substantially better than autocure,

marginally better than resin modified glass ionomer

• Abrasion resistance – as they mature they match that of amalgam, composite

resin

• Radioopacity – adequate

Main application :

1. Minimal lesions

2. Transitional restoration

Type III :Lining & Base

cements

Definition :

Lining – thin layer of a neutral material placed on the floor of a cavity, prior

to final restoration, to make good a deficiency in the cavity design or to

provide thermal protection to the pulp

Base – is identified as a dentine substitute that is placed to make up for

major area of dentine loss prior to lamination of an enamel substitute over

the top

Significant factors :

Lining cements :

• Low P/L 1.5 :1 (do not act as bonding agent ; should not be

left exposed ; low physical properties)

• used in thin sections to fill voids in cavity design ; act as

thermal insulator

Base / dentin substitute :

• P/L : 3:1

Properties

• Physical Properties

• Erosion & Longevity

• Aesthetic properties

• Biologic properties

Cement

type

Settin

g time

(min)

Film

thickness

(µm)

24hr

compressive

strength

(MPa)

24 hr

Diametral

tensile

strength

(MPa)

Elastic

modulus

(GPa)

Solubility

in water

(wt%)

Pulp

response

Glass

ionome

r luting

7.0 24 86 6.2 7.3 1.25 Mild to

moderat

e

Properties of glass ionomer luting cement

Compressive strength is comparable to zinc phosphate

Diametral strength is slightly higher

Modulus of elasticity is ½ of zinc phosphate

Thus, it is less stiff & more susceptible to elastic deformation

It is thus not as desirable as zinc phophate to support an all ceramic crown,

because greater tensile stress would develop in the crown under occlusal loading

Properties of restorative glass ionomers

Compressive

strength

(MPA)

Diametral

tensile

strength

(MPa)

Knoop

hardness

(KHN)

Solubility

(ANSI/ADA

test)

Anticariogenic/

Pulp response

Glass

ionomer

type II

150 6.6 48 0.4 YES/MILD

Cermet 150 6.7 39 - YES/MILD

Hybrid

Ionomer

105 20 40 - YES/MILD

Material Fracture

toughness

(MPa.m1/2)

Admixed

amalgam

1.29

Light cured glass

ionomer

1.37

Hybrid composite 1.17

Glass ionomer

lining cement

0.88

Cermet 0.51

Metal-reinforced

glass ionomer

0.30

Fracture toughness – a measure

of energy required to cause crack

propagation that leads to fracture

Restorative glass ionomers

are much inferior to

composites

Also more

vulnerable to wear

Erosion & Longevity

1. Dissolution & erosion

2. Durability & longevity

Dissolution & erosion

2 aspects

Leaching of soluble

constituents from cement

Actual erosion

Because of chemical &

mechanical wearDisintegration only if they

are matrix formers

Short term aspects Long term aspects

Because of acids from plaque,

food & beverages

Damage in

technique

Moisture

contamina

tion before

cement

hardened

Desiccation

before cement

fully matured

In glass ionomer cement,

anion is a polymer where the

active carboxylic groups are

connected by covalent

linkages impervious to acid

attack.

Only cross-links are ionic, and

many of these have to be

broken before the matrix would

decompose

Fig 7.4 wilson &

mclean

Acid erosion :

Glass ionomer < silicates < zinc phosphate < zinc polycarboxylate

Durability & longevity

• Depends on

• Adequate preparation of cement

• Adequate protection

• Conditions of mouth

Aesthetic properties

• Translucency

• Glass ionomer cements has a degree of translucency

• Because its filler is a glass (not opaque)

• Because of slow hydration reactions, glass ionomer cements take at least 24hrs to fully mature & develop translucency

• Early contamination with water reduces translucency

• Dark shades are less translucent

• Glass ionomer remain unaffected by oral fluids

• Opacity

• Opacity is also termed as contrast ratio (Cr)

• If Cr=1 – material is opaque

• If Cr = 0 – perfectly translucent

• To match enamel Cr < 0.55

• Glass ionomers Cr < 0.9

• Scattering power & reflectance

• Opacity also depends on the scattering coefficient

• Light reflectance

• Thickness of specimen

Biologic properties

Biocompatibility

• They elicit greater pulp reaction than ZOE (Plant et al 1984)

• But less than zinc phosphate (Tobias 1978)

• With any glass ionomer cement, it is wise to place a thin layer of protective liner, such as Ca(OH)2 , within 0.5mm of pulp chamber (Anusavice)

• Inflammatory response of pulpal tissues resolves within 30 days & there is no enhancement of reparative or secondary dentine formation (G J Mount)

• Response of gingival tissues is minimal (Garcia et al 1981)

Effect on pulp & cells

Reasons for blandness of polyacrylic acid (McLean & Wilson, 1974)

• Polyacrylic acid – weak acid • Dissociated H+ ions remain in neighbourhood of polyanion

chain because of electrostatic attraction from multiple negative charges.

• When partly neutralized, the negative charge on the chain increase, tendency of polyacylic acid to dissociate into H+ ions & polyacrylate ion decreases.

• Diffusion of polyacrylic acid into dentinal tubules is unlikely because of its high molecular weight & chain entanglement.

• Polyacrylic acid is readily precipitated by Ca+2 in tubules.• Therefore sensitivity under luting GIC may be due to faulty

technique than chemistry of cement.

Fluoride release

Biological potential of glass ionomer cements

• Significance of water in glass ionomer cements

• Glass ionomer – water based material

• Water plays important part in

• Setting reaction

• Final structure

• Water is the reaction medium

• Hydrates siliceous hydrogel

Once GI sets, Loosely bound – easily lost shrinkage& cracking & undue

stress on ion exchange

adhesion

Tightly bound - cannot be removed ; associated with hydration shell of

cation-polyacrylate bond

Increase in strength & modulus & decrease in plasticity

One important factor in these materials being water based lies in the

chemical principle that it is only possible to have ion mobility in presence of

water

Which is essential for demineralization-remineralisation of tooth

(anhydrous material can play no part )

Water is in

the form of

As material ages, ratio of tightly bound water : loosely bound water increases

• Ionic components of GIC

• Calcium

• Strontium

• Aluminium

• Silica

• Fluoride

• All ions are available for transfer from matrix into surrounding because of presence of water.

• Lower the pH, greater the release of ions.

• Note: (i) Calcium & strontium have similar polarity & atomic size, therefore they can replace each other in cement & hydroxyapatite.

• (ii) Strontium imparts radioopacity

• (iii) Strontium has anticariogenic properties.

• Therefore strontium can participate effectively in remineralisation.

Mineral phase of enamel & dentin

Enamel & Dentin are porous to migrating ions especially dentin

Enamel :

Each crystal of hydroxyapatite is surrounded by a

layer of tightly bound water – hydration shell –

which shows that the crystal is electrically charged

& can attract ions that are able to play a part in

remineralization

Remaining water fills spaces between rods – main

diffusion pathway into & thru enamel

Dentin :

23% water by volume

Water filled pores + inter-tubular lateral

microtubules + dentinal tubules

Increased potential for ion transfer

By weight By volume

By weight By volume

• Enamel rods are tightly packed

• Pores are not large enough to allow bacteria

• Only when sufficient disintergration has occurred, process becomes irreversible

• Outer apatite crystals dissolve from surface

• Increase porosity

• Facilitating acid transport & demineralisation

• Also, ions can return along the same pathway

Carious lesion

• 1960’s – Massler, Fusayama & Brannstrom wrote detailed reports on science of demineralisation & remineralisation ; & theoritical value of ion exchange

Carious dentin

1st decalcified layer 2nd decalcified layer Fusayama et al 1966

Massler 1967 Infected layer Affected layer

Pitts 1983,

Mertz – Fairhurst et al

1992

Actively carious Pre-carious

• This concept was reinforced by a clinical study

• Heavily carious 1st molars taken

• Minimal caries removal

• Restored using strontium based high strength glass ionomer cement

• Harvested

• Fl & Sr penetrated both layers of dentin & became part of normal apatite crystals beyond

• 2 distinct zones identified

Outer layer of non-

remineralised dentine with

minimal Fl & Sr uptake

Deeper zone of well

re-mineralised dentine

Postulated that

Collagen network in outer zone is totally devoid of mineral

Lack of seeding sites

Preventing uptake of mineral ions

Remineralisable dentine contained atleast 20% by weight of mineral onto

which incoming ions were able to absorb

External ion exchange

• Glass ionomer acts as fluoride reservoir

• Movement of fluoride out of glass ionomer

• Electrolytic imbalance on surface of restoration

• Cations from plaque & salive are taken up by the restoration

• Balanced state

• Increase in maturation & strengthening of restoration

(Nicholson et al, 1999)

• Also, plaque on surface of glass ionomer will have reduced count of S.mutans, therefore tissue tolerance of glass ionomer is more & less inflammation is

seen.

Internal remineralization

• Dental pulp demonstrates very high level of tolerance to glass ionomer.

• Very mild inflammatory response to freshly mixed GIC seen, with rapid recovery.

• Snuggs et al, 1993 – dentin bridging in mechanical exposure of pulp sealed with GIC

• Brannstrom, 1982 – Pulpal irritation is direct result of bacterial activity. Therefore, if no irritation, no inflammation will occur.

• Glass ionomer demonstrates ion-exchange adhesion, which could be an ideal sealant, thus preventing ingress of bacterial nutrients.

• Therefore GIC can be placed in very close proximity to pulp without risk of irreversible pulp inflammation & CaOH sub-lining is not justified.

Entire margin of

cavity cleaned down

to sound dentine

Axial wall still in softened

demineralised affected

dentine is retained

10% polyacrylic acid 10

second conditioning

Light initiated autocure

glass ionomer over axial

wall (sublining)

High strength autocure glass

ionomer then placed

Cut back to expose

enamel walls

Entire cavity covered with thin

layer of Resin modified

adhesive glass ionomer

composite

Suggested clinical technique

Glass ionomer as bone substitute

• Rober Purrmann – originated the work

• Owing to its properties of bioactivity & biocompatibility, glass ionomer has been tried as bone cement & bone replacement material.

• Through ion-exchange mechanism, it can cause stable integration with bone & can affect both its growth & development adjacent to surface of material.

• Note : unset GI is strictly contraindicated to be contacted with neural tissues (because of controversy over Al release)

Glass ionomer as bone cement

• Prof. Charnley’s, 1960’s – Use of PMMA to provide stable mechanical anchor for metallic prosthesis.

• Morphologic fixation / cement fixation

• Owing to disadvantages of PMMA, glass ionomers replaced them

• Advantage :

• - No exotherm setting reaction

• Chemically bond to bone & some metals & less shrinkage

• Osteoconductive property of material

• In oral surgery,

• Applied to prevention of bone loss following extraction

• Used as filler for bone donor sites & cyst cavities.

Clinical applications of glass ionomer cements

Uses Conservative

• Luting & bonding

• Restorative

• Lining & base

• Minimal intervention – the place of glassionomer

• Transitional restoration

Endodontics

• Root canal sealing

• Orthograde root canal sealing

• Root-end filling material

• Repair of perforations and root resorption defects

• Perforation repair

• Repair of root resorption cavities

• Treatment of vertically fractured teeth

• Coronal seal

Use of glass ionomer in conventional & surgical endodontics

• Pitt Ford (1979) - Use in root canal first introduced

• Stewart (1990) - made modifications

• to increase working time

• added barium sulphate : increase radioopacity

• Ray & Seltzer (1991) – usable experimental formulation

• Adequate working time

• Adequate radioopacity

• Adequate adhesion to root canal wall

These modifications led to commercialization of Ketac –

Endo (ESPE, Germany) in 1991

RMGIC – Vitrebond (RM)

More recent developments : KT- 308 (GC)

ZUT

Minimal intervention cavity designs – The place of glass ionomers

Site 1 Size 0 lesions

Site 1 : pit & fissure on occlusal surface of posterior teeth

Size 0 : initial lesion ; not yet resulted in cavitation

Concept of fissure seal – 1st discussed by Simonsen (1989)

The anatomy of enamel within a fissure is covered with a

layer of enamel rods that appear to run parallel with the

surface rather than at right angles. When etched, it will not

develop the usual pattern of porous enamel that allows

penetration of unfilled resin

Wilson & McLean (1988) show that a glass ionomer will

successfully occlude fissure

This is now termed “fissure protection” to differentiate it

from a “resin seal”

Neither resin nor glass ionomer will flow into a fissure beyond the point where

fissure narrows to 200µm

Retention thus mainly depends on adhesion to enamel at the entrance to fissure

rather than mechanical interlocking into complexities of fissure

Even though enamel rods lie in different

orientation, glass ionomer will develop ion

exchange adhesion & show acceptable longevity

(Mount & Hume, 1998)

8 years

12 years

Technique involvedIn young patient fast set autocure

like light initiated autocure glass

ionomer used

Site 1 Size 1 lesions

Size 1 : smallest minimal lesion

requiring operative intervention

Fissures are explored using small tapered

diamond bur #8107 at intermediate high speed

under air water spray then lightly polished with

#3107

Technique

involved

Satisfactory

adaptation of

entire fissure

Site 1 Size 2 lesions

Size 2 : Moderate size cavities

Technique

involved Why glass ionomer used as base ?

If resin composite used, might

require removal of more dentin

which would otherwise remineralize

Site 2 Size 0 lesions

Site 2 – contact areas between anteriors / posteriors

Size 0 : initial lesion ; not yet resulted in cavitation

Site 2 Size 1 lesions

If lesion 3 mm below the crest of marginal

ridge – “Tunnel” cavity design

If lesion < 2mm from the crest of marginal

ridge – “ Slot ” cavity design

If proximal surface accessible – “Proximal

approach”

Site 2 – contact areas between anteriors / posteriors

Size 1 : smallest minimal lesion requiring operative intervention

Access through

occlusal surface

Triangular

access cavity

Clean enamel

margins

“Tunnel” cavity design

Glass ionomer syringed

mylar strip in place

Completed

restoration

Note : internal

dimension of cavity

Glass ionomer will flow readily into a

small cavity & has the ability to

remineralise

“ Slot ” cavity design

Glass ionomer is a sound

option because occlusal

load will not be great

“Proximal approach”Fast set, high strength auto

cure used because

radioopaque & will not be

under occlusal load

Site 2 Size 2 lesions

Site 2 – Contact areas between anteriors / posteriors

Size 2 : Moderate size cavities

Laminate technique / bilayered restoration with glass ionomer as the base

If resin modified is used; no

need to etch after placement

because enough resin content

to provide adhsion with

composite

Substantial layer of glass ionomer

across the entire floor is exposed to

oral environment at gingival

proximal box

Site 3 lesions

Cervical areas related to gingival tissues including exposed root surface

Glass ionomer ideal : Because can withstand flexure

Root surface not under occlusal load

INSTRUCTIONS FOR DENTAL ASSISTANTS

Storage

Powder & liquid by different manufacturers should

not be interchanged

Both bottles firmly closed (water based)

Polyacrylic acid liquid thickens over time, within 12 months

viscosity increases. It can be thinned down by : immerse bottle

with lid on in water at 75°C for 15minutes, place in rubber

bowl, let water from hot tap run over it. Test at 15minutes for

viscosity. Let it cool before use.

Liquid should never be refrigerated.

Mixing slab should cool, but never below

dew point.

Full spoon, no excess

Tip liquid bottle to side,

then invert completely

If water / tartaric acid, only

1 drop used.

Hand dispensing

Hand mixingLiquid should not stay on paper pad

longer than 1minute (some of it may

soak into it)

First half folded into liquid in 10-15seconds

Second half incorporated in 15 seconds

Small mixing area

Don’t mix beyond 30 seconds

The objective is – only wet the

particle – no dissolving it.

Mixing of capsules

• To activate capsule apply pressure 3-4 seconds before placing in machine

• Ultrahigh speed machine : 4000 cycles/minute

• (< 3000 cycles/minute – not desirable)

Loss of gloss test

This point is reached at 2minutes

after start of mix

10sec in 4000cycles/minute

Correct consistency for hand mixed

Type I : Luting : string up to 3-4cm from

slab

Type II : string 1cm + gloss

Type III : for lining amalgam : 1.5:1 P/L

ratio : 3-4cm string

For base for composite : 3:1 P/L ratio :

1-1.5cm string

Clean – up

Before it sets, immerse slab

& spatula in water

If set, chip off / place in

water then clean

Summary & Conclusion

Review of literature

REFERENCES

REFERENCES : (Text books)

1. Glass-ionomer cement : Alan D. Wilson / John W. Mclean2. An atlas of Glass Ionomer Cements – A Clinician’s guide (3rd

edition) : Graham J. Mount3. Preservation & restoration of tooth structure : Graham J.

Mount4. Phillip’s Science of Dental Materials (11th edition) : Kenneth

J. Anusavice5. Sturdevant’s Art & Sience of Operative Dentistry (4th

edition):Theodore M. Roberson et al6. Tylman’s theory & practices of fixed prosthodontics, chapter

21, page 394-406 : Franklin Garcia Godoy et al

REFERENCES : (Journals)

1. Proposed nomenclature for glass-ionomer dental cements & related materials. John W. Mclean et al. QI vol. 25, no. 9, 1994 ; 587-589.

2. GIC – Past, present & future. Graham J. Mount. Buonocore memorial lecture (Michael B.) Operative dentistry 1994, 19, 82-90.

3. Glass ionomer cements in restorative dentistry. John W. Nicholson et al. QI vol. 28, no.11, 1997, 705-714.

4. The need for caries preventive restorative materials. Gordon J. Christensen. JADA, vol. 131, sept. 2000, 1347-1349.

5. Composite resin & GIC : current status for use in cervical restorations –William W. Brackett et al. QI 1990; 21: 445-447.

6. Longevity in glass-ionomer restorations: review of successful technique. Graham J. Mount. QI 1997 ; 28: 643-650.

7. Viscous GIC : a new alternative to amalgam in primary dentition. Roland frankenberger et al. QI 1997 ; 28:667-676.

8. Adhesion of GIC in clinical environment. G.J.Mount. operative dentistry 1991;16:141-148.

9. Glass ionomer : a review of their current status. G.J.Mount. Operative dentistry 1999 ; 24 : 115-124.

10.The use of glass ionomer cements in both conventional & surgical endodontics. (review) M.A.A.De Bruyne et al. IEJ, 37; 2004: 91-104.

11.Pulpal consideration of adhesive materials. Harold R. Stanley. Operative dentistry, supplement 5, 1992, 151-164.

12. Glass ionomer cements used as fissure sealants with the atraumatic restorative treatment (ART) approach : review of literature. H.K.Yip et al. IDJ (2002)52, 67-70.

13. Demineralization & remineralization of dentine caries, and role of glass-ionomer cements. W. Gao et al. IDJ (2000) 50, 51-56.

14. Advances in restorative materials. Charles W. Wakefield et al. DCNA, Vol. 45, no. 1, January 2001, 7- 27.

15.Direct & indirect restorative materials. ADA council on scientific affairs. JADA, vol.134, April 2003, 463-471.

16. Minimal intervention dentistry : Rationale of cavity design. G.J.Mount. Operative dentistry, 2003, 28, 92-99.

17. The sealant restoration : indications, success and clinical technique. D.C.Hassall et al. BDJ, vol. 191, no.7, October 13, 2001, 358-362.

18. Minimally invasive dentistry. Carol Anne Murdoch-Kinch et al. JADA, vol.134, January 2003, 87-94.

19. The influence of various conditioning agents on the interdiffusion zone & microleakage of a glass ionomer cement with a high viscosity in primary teeth. Y. Yilmaz et al. Operative dentistry 2005, vol. 30, no.1, 105-113

20. Effect of prophylaxis regimens on surface roughness of glass ionomer cements. S.S. Wu et al. Operative dentistry 2005; 30-2; 180-184

21. Invitro evaluation of cariostatic action of esthetic restorative materials in bovine teeth under severe cariogenic challenge. MLG Pin et al. Operative Dentistry 2005, 30-2, 368-375

22. The microtensile bond strength of Fuji IX GIC to antibacterial conditioned dentin. M.G.Botello. Operative Dentistry 2005, 30-3 ; 311-317

23. Fluoride release & neutralising effect by resin-based materials. T.Itota et al. Operative Dentistry 2005, 30-4, 522-527

24. Effect of neutral citrate solution on the fluoride release of conventional restorative glass ionomer cements. Roeland J.C.De Moor et al. Dental Materials 2005, 21-4, 318-323

25. Effect of cavity configuration & ageing on the bonding effectiveness of 6 adhesives to dentin. Kenichi Shirai et al. Dental Materials 2005, 21-2, 110-124

26. Salivary contamination & bond strength of glass ionomers to dentin. S.K.Sidhu. Operative Dentistry 2005, 30-6, 676-684

27. Early & long-term wear of “Fast-set” convetional GIC. A.Werner et al Dental Material 2005, 21-8, 716-720

28. Dental materials 2005, 21, 498-504 Steven R. Armstrong

29. Dental materials 2005, 21, 695-703 H.K.Yip et al

30. Dental materials 2005, 21, 704-708 Martin J. Tyas

Materials 2005, Vol.21, No.3, 201-209

32. Restorative dentistry for pediatric teeth – state of the at 2001. Gordan J. Christensen, JADA, Vol. 132, March 2001, 379-381

33. Fluoride containing restorative materials. Edward J. Swift, Clinical Preventive Dentistry 1988, vol.10, no.6, 19-24

34. Root end filling materials- a review. Vasudev SK et al, Endodontology 2003, vol. 15, 12-18

35. Fluoride releasing restorative materials & secondary caries. John Hicks et al, DCNA 2002, 46, 247-276

36. Minimal intervention dentistry – a review, Martin J. Tyas, IDJ 2000, 50, 1-12

37. Minimally invasive dentistry . Carol Anne Murdoch-Kinch et al, JADA 2003, vol 134, 87-94

38. Glass ionomer cements used as fissure sealants with the ART approach : review of literature. H.K.Yip et al, IDJ 2002, 52, 67-70

39. The ART approach for primary teeth : review of literature. Roger J Smales et al, Pediatric Dentistry 2000, 22:4, 294-298

40. The ART approach for the management of dental caries. Roger J. Smales et al, QI 2002; 33: 427432

41. Direct & indirect restorative materials, JADA vol. 134, 2003, 463-471

42. The sealant restoration : indications, success and clinical technique. D.C.Hassall, BDJ 2001, VOL.191, NO.7, 358-362

43. Adhesive dentistry & endodontics : materials, clinical strategies and procedures for restoration of access cavities : a review. Richard S. Schwartz et al, JOE vol 31, no.3, march 2005, 151- 164