Introduction

The development of the Original Glass Ionomer cement by Wilson

and Kent 1969 was significant in that it made available for the first time a

restorative dental material that had long-term adhesion to the tooth

structure, along with cariostatic potentials.

Recent development in the chemistry and clinical application of

Glass-Ionomer cements offer great promise in the treatment of early

carious lesion.

History

The GIC were invented by Wilson and Kent in 1969s and developed

by Mclean and Wilson during 1970s (Q.I. vol. 25 No. 9, 1994).

This cement was invented particularly to overcome the deficiencies

and limitations of silicate cements i.e. high solubility mechanical adhesion

to tooth and severe pulp irritant which was the principal restorative

material until than.

Invention

The invention of GIC resulted directly from basic studies on dental

silicate cements (Wilson et al 1972) and studies where in the phosphoric

acid in silicate cement was replaced by organic chelating acids (Wilson

1968).

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A significant contribution was also made by D.C. Smith in 1968

who used polyacrylic acid in his zinc polycarboxylate cement.

Thus, GIC – (Termed by B.E. Kent) has been described as a hybrid

of dental silicate cements and zinc polycarboxylate cements.

But the reaction between the Glasses and polyacrylic acid was

uncontrollable which was later controlled by addition of tartaric acid.

EARLY DEVELOPMENT

Scientific development of GIC has occurred in two steps:

a. Firstly, effort was devoted to improving properties to make it a fully

practical material for anterior restoration.

b. Secondly, properties were modified in order to extend its range of

applications.

In 1960 and 1966, in their early research A.D. Wilson examined

cements prepared by mixing silicate glass powder with aqueous solutions

of various organic acids, including polyacrylic acid.

The disadvantages of these polyacrylates cements were:

a. Cements were almost unworkable.

b. Set slowly and sluggishly.

c. Not hydrolytically stable i.e. dissolved in water.

Later in 1968 and 1969 Wilson, Kent and Lewis found that by

employing novel glasses formulation hydrolytically stable cements could

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be produced as the setting of these cement was controlled by Al2O3 / SiO2

ratio in the glass.

This discovery enabled more reactive glasses to be prepared suitable

to forming rapid setting cements with polyacrylic acid.

The first GIC lacked workability and hardened slowly.

Eventually Kent et al, (1973, 1979) found a glass that was high in

fluorides (G-200) which was termed as ASPA-I (Aluminosilicates

polyacrylates).

This cement also had:

a. Slow set.

b. Minimum working time.

c. Post set hardening was slow.

In 1972 Wilson and Crisp discovered that tartaric acid modified the

cement forming reaction thus:

i. Improving manipulation.

ii. Extended working time.

iii. Increased setting rate.

This refinement of ASPA-I was termed as ASPA II which was the

first practically used GIC and was used mainly for Class III restorations.

3

Disadvantages of ASPA II

a. Hardened very slowly and during this stage was vulnerable to

moisture contamination.

b. Poor aesthetic properties because of use of G-200 glass with a

very high fluoride content.

c. Liquid tended to gel : This last problem was solved by the

development of a copolymer of acrylic and itaconic acid that did

not gel at high concentrations (50%) in aqueous solution.

This was termed as ASPA IV. The ASPA IV was inferior to ASPA

II in other properties.

In 1974 Mclean and Wilson used GIC as a fissure sealants.

ASPA IVa – For luting purposes developed in 1977 by Wilson et al.

ASPA X – Was developed by Crisp et al in 1979 with excellent

translucency.

In 1977 – Mclean and Wilson introduced sandwich technique /

laminate technique.

Definition:

A. GIC is an acid-base reaction cement as defined by Wilson

(1978) and Wygant (1958), the product of reaction being a

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hydrogel salt which acts as a binding matrix (Alan D. Wilson,

GIC).

B. According to Skinners – Glass ionomer is the generic

name of a group of materials that use silicate glass powder and

an aqueous solution of polyacrylic acid. Also known as

“Polyalkenoate cement”.

C. A cement that consists of a basic glass and an acidic

polymer which sets by an acid base reaction between these

components as described by Wilson and Nicholson (QI vol. 25

No. 9, 1994).

CLASSIFICATION: By SkinnersA. Type I – Luting cements.

Type II – Restorative materials.

Type III – Liners and base.

Type IV – Metal reinforced - Miracle mix

- Cermet

Type IX – For geriatric and pediatric patients.

B. By Wilson and Mclean 1988a; Mount 1989a (Based on

application) (Opt. Dents, 1994).

Type I – Luting crowns, bridges and orthodontic brackets.

Type II – Restorative cements.

Type II 1 – Esthetic restoration cements.

Type II 2 – Reinforced restoration cements.

Type III

- Lining cements with powder / liquid ratio 1.5 : 1.

5

- Dentine substitute or base with powder / liquid ratio 3:1.

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COMPOSITIONThe composition of glass ionomer cement is complex and varied.

[Dispensing medium] mode of supply- GIC is dispensed in1. Powder and liquid form

2. Capsulated form.

3. Powder and water (powder contains dried acid too)

4. Light-cure system

The basic composition of powder and liquid formulation is as

follows:

Powder : is an acid soluble calcium fluoroalumino silicate glass

Composition of 2 GIC powders

Species Weight %A B

SiO2 41.9 35.2

Al2O3 28.6 20.1

AlF3 1.6 2.4

CaF2 15.7 20.1

NaF 9.3 3.6

AlPO4 3.8 12.0

Function of each component:

a. Silica (SiO2), Alumina (Al2O3), Flourite (CaF2) take part in reaction

with acid to form a soluble gel.

b. Fluoride

i. Lowers the fusion temperature.

ii. Improves the working characteristics of paste.

iii. Increases the strength of set cement.

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iv. In moderate amounts enhances translucency.

v. Contributes to anticariogenic property of cement by

releasing fluoride over a prolonged period.

c. Alumina

- Increased content increases compressive strength.

- Decreases translucency.

d. Crylite (Na3AlF6)

- Lowers the fusion temperature (acts as a flux).

- Increases the translucency of set cement.

e. Aluminium phosphate

- Improves translucency of set cement.

- Gives strength to the cement.

Notes :

The ratio of Al2O3 / SiO2 is crucial and is required to be 1:2.

The increase in ratio gives rise to:

1. Glasses which are more basic and reactive.

2. Reduction in setting time of cement.

LIQUID

Originally the liquid was an aqueous solution of polyacrylic acid

50%.

Disadvantages:a. Liquid was too viscous.

b. Tended to gel with time.

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c. Current cements contain the acid in the form of copolymer of

itaconic, maleic or tricarboxylic acid.

Functions of acids:a. Tend to increase the reactivity of liquid.

b. Decreases the viscosity.

c. Reduces the tendency for gelation.

Explanation:

The copolymeric acids are irregularly arranged as compared to

uniform arrangement of acrylic acids in liquid. This configuration reduces

hydrogen bonding between acid molecules and thus reduces the degree of

gelling.

Preparation of glasses

The raw material are fused to a uniform glass by heating them to

temperature of 1100°C to 1500°C.

- Lanthanum, strontium, barium or zinc oxide

additions provide radioopacity.

- The glass is ground into a powder having

particles in the range of 20-50µm.

CHEMISTRY OF SETTING- The reaction is an acid-base reaction.

- Also known as auto-cure cements because of this reaction.

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STAGES ARE:Stage I : Release and migration of glass ions after acid attack.

Stage II : Ion binding of cations to polyacrylic and precipitation of salts.

i) Gelation.

ii) Hardening.

Stage III : Hydration of salts (Strength of material is achieved).

Stage I:

- When the powder and liquid are mixed to form a

paste, the surface of the glass particles is attacked by the acid.

- Calcium, fluoride, aluminium and sodium ions

are leached into the aqueous medium.

Stage II:

- The polyacrylic acid chains are cross-linked by

the calcium ions and form a solid mass.

- Within next 24 hours, a new phase forms in

which aluminium ions become bound within the cement mix.

This leads to a more rigid set cement.

- Sodium and fluorine ions do not participate in the

cross-linking of the cement.

- Instead some of the sodium ions replace

hydrogen ions of carboxylic group and remaining combine with

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fluorine to form sodium fluoride uniformly dispersed in the set

cement.

- During the maturing process the cross-linked

phase is also hydrated by the same water used as the medium.

Stage III:

- Hydration of salts (Role of water in setting

process).

- When fully hardened GIC is fully impervious to

oral fluids.

- The cement is most vulnerable to contamination

by moisture at stage II.

- This vulnerability occurs while cement forming

ions (Ca+ Al+) from the glass are being transferred to the

polyacid, where ultimately they are locked in a resistant gel. If

water comes in contact with this surface before it hardens (Stage

III) the calcium and aluminium ions-will be washed out and lost

for cement formation.

- Water will be absorbed, cement will lose its

translucency and weakened surface will erode.

According to Skinners, water is most important consituent of

cement liquid.

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- During the initial reaction, this water can readily

be removed by dessication and is known as “loosely bound

water”.

- As the reaction continues, the same water

hydrates the matrix and cannot be removed by dessication and is

known as “Tightly bound water”.

Effect of water on cement:

1) Dehydration of cement causes fissuring and

cracking as the water of hydration is lost.

2) Exposure of cement to saliva causes the

surface to soften as the vital cement forming ions are lost.

Exposure of cement to water can be prevented by:

a. Use of cotton rolls, gingival retraction cord, rubber dam (Rubber

dam can create conditions which may dehydrate the cement,

resulting in loss of water required for cement formation).

b. A coat of light-curing bonding agent should be applied to cement

immediately after removal of the matrix.

c. Use of proprietary varnishes.

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Thus, a critical water balance at the interface, between water needed

for cement formation and water absorbed from saliva which will weaken

the cement must be maintained.

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Set structure of cement

The set cement consists of an agglomeration of unreacted powder

particles surrounded by a silica gel (that develop during the removal of

cations from the surface of the particles), in an amorphous matrix of

hydrated calcium and aluminium polysalts.

Factors affecting setting reaction:a. Chemical factors.

b. Physical factors.

Chemical factorsa. Fluoride delays gelation and prolongs the working time.

b. Tartaric acid increases working time.

Proportion of glass and water

Decreased water content, faster the set and shorter the working time.

Physical factors

a. Alumina/silica ratio i.e. glass composition – Higher the ratio, faster

the set and shorter the working time.

b. Particle size of glass powder: Finer the powder, faster the set and

shorter the working time.

c. Temperature of mixing: Higher the temperature, faster the set and

shorter the working time.

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CHARACTERISTICS OF GIC (Quis Int. 1994)a. Hard substance on setting.

b. Low-reaction exotherm.

c. No polymerization shrinkage.

d. No free monomer present.

e. Dimensional stability at high humidity.

f. Filler-matrix interaction.

g. Adhesion to enamel and dentine.

h. Fluoride release.

i. Early moisture sensitivity requiring protection (e.g., with varnish)

immediately after placement.

PROPERTIES

The GIC possess a number of very useful properties, some of which

are unique in a restorative material.

Properties of GIC can be divided into two group:

a. Physical properties.

b. Biological properties.

PHYSICAL PROPERTIES

1. STRENGTH

a. Compressive strength - 150 mPa / 22,000Psi after 24 hrs.

- becomes double in a year

b. Weak flexural strength - 6.6mPa or 960 psi after 24 hours.

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2. FRACTURE TOUGHNESS

A measure of energy required to produce fracture.

Type II GIC are much inferior to composites in this respect.

3. SETTING TIME 3-8 MINUTES

4. TRANSLUCENT

The set cement has a translucency that matches with the tooth

enamel.

5. GIC cements are the most resistant to erosion in the acidic

stagnation regions of mouth (Wilson et al 1986).

6. Resistant to staining and maintain their colour match better

than composite resins.

7. Hardens – 48 kHN

8. Solubility – 0.4 which is less than that of silicate cements

(0.7).

9. Poor wear resistance.

10. If conditions of moisture control are followed there is no

change in dimensions of GIC.

11. ADHESION

- The precise mechanism of adhesion of GIC is

based on both diffusion and adsorption phenomena.

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- The nature of adhesion is physico-chemical.

Mechanism of adhesion (OP. Dents 1999)

The polyalkenoic acid of the glass-ionomer will penetrate the tooth

structure releasing phosphate ions each of which will take with it a calcium

ion from the tooth surface to maintain electrical neutrality.

These ions will combine with surface layer of new material which is

firmly attached to the tooth surface (Geigger and Weiner 1993). This has

been described as a “Diffusion based adhesion”. (Achinmade and

Nicholson in 1993).

There is also a degree of adhesion available to the collagen of

dentine through either hydrogen bonding or metallic ion bridging between

the carboxyl groups on the polyacid and the collagen molecules

(Akinmade, 1994).

The bond to enamel is always higher than that to dentine probably

because the greater inorganic content of enamel and its greater

homogenicity in morphology.

This ion-exchange system is unique in dentistry and is of

considerable significance.

The type of failure of adhesion leading to loss of restoration is

cohesive i.e. within the cement itself and not adhesive between cement and

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tooth structure. There, even after loss of cement from tooth surface a layer

is left intact thus sealing the surface and preventing microleakage.

SURFACE CONDITIONING – As a mechanism of bonding.

The question of conditioning the tooth surface in preparation for

adhesion is widely debated.

Retreatment of surface was first introduced by Mclean and Wilson

in 1977 and they termed it as surface conditioning.

Different acids used are:

a. 50% citric acid.

b. Surface active microbicidal solutions such as

- Tublicid contains – 0.1% chlorhexidine gluconate.

- 0.08% dodicin

- 3% NaF – strengthens bond to enamel and dentine.

c. Tannic acid 25% (for dentine).

d. Ferric chloride (by Powis et al) 2% aqueous alcholic solutions.

- Provides metal linkages between GIC and collagen.

- Gets incorporated into GIC and apatite.

e. Mineralizing solutions – Developed by Causton and Johnson in

(1979, 1982).

Examples : Levine et al solution – ITS Solution

f. EDTA

g. 10% aqueous solution of polyacrylic acid (Powis et al 1982).

Advantages of Polyacrylic acid:

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i) Part of cement forming system.

ii) Cleans the surface with in 10 seconds.

iii) Alters the surface energy of tooth thus encouraging

adaptation of cement to the cavity walls.

BIOLOGIC PROPERTIESThe two main biologic properties of GIC are:

1. Anticariogenic potential due to release of fluoride.

2. Biocompatibility.

I] Fluoride Release

- One of the important properties GIC shares with

silicate cement is the release of fluoride ions throughout the life

of the restoration (Forsten 1994).

- This fluoride release provides for the cariostatic

effect of GIC.

- The influence of fluoride is found in a zone of

resistance to demineralization which is at least 3mm thick

around a GIC restoration (Kidd et al 1978).

- The spread of caries is arrested at the restoration

or cavity wall margins.

- The glass powder of both the silicate and GIC is

prepared in a Fluoride Flux. Fluoride ions are released from the

set material and taken up by the surrounding tooth structure.

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- Enamel solubility is reduced by this process of

fluoride release and uptake.

- Consequently, the incidence and severity of

recurrent caries are reduced.

Fluoride contributes to caries inhibition by two processes:

1) Physico-chemical F ions released from

restorative material become incorporated in hydroxyapatite crystals of

adjacent tooth structure to form fluorapatite which is more resistant to

acid decalcification.

- Also the formation of this acid resistant phase

enhances remineralization of demineralized enamel.

- Carious enamel is more porous than sound

enamel, this porosity allows increased penetration of

fluoride which contributes to formation of acid-resistant

crystals and reduces caries risk.

2) Biologic Mechanism

- Fluoride inhibits carbohydrate metabolism by the

acidogenic plaque microflora.

- Fluoride enters microorganism against a

concentration gradient and accumulation intracellularly as the

extracellular pH reduces.

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- This intracellular HF breaks into H+ and F- ions

which causes enzyme inhibition and leads to slower rate of acid

production.

- GIC also acts as a fluoride reservoir within the

oral environment GIC uptakes fluoride ions on application of

topical fluorides and increased the rate of release for a short

period.

II] BIOCOMPATIBILITY

Biocompatibility is defined as the ability of a material to perform

with an appropriate host response in a specific application.

GIC are generally biocompatible with oral tissues and as restorative

materials, result in only mild pulpal irritation at a level similar to that

produced by zinc polycarboxylate or zinc phosphate cements.

This can be attributed to polyalkenoic acid which is a weak acid and

also has high molecular weight of liquid and larger molecule size of acid,

thus it is not able to penetrate the dentinal tubules.

Their adhesion to tooth structure ensures that they provide an

excellent marginal seal and prevent microleakage.

GIC is well-tolerated even by the healthy exposed pulp tissue.

When lesion is close to pulp, it is better to place Ca(OH)2 as a sub-

base, avoided if pulpitis is apparent / suspected.

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Though glass ionomers have become increasingly popular as a

luting agent, post-operative sensitivity has been reported with these cement

at times.

22

Theories / Reasons:

a) First relates to powder-liquid ratio.

b) Another cause for post-operative sensitivity may be

related to the manner in which the prepared surface of the

dentine is dried before the cementation process. Overdessication

of dentine may result in aspiration of the odontoblastic processes

which then causes necrosis.

c) Overfilling of crown before the seating process

which may lead to excessive hydraulic pressure.

Indications

I] As a Restorative Materiala. Restoration of erosion / abrasion lesion – Class V lesion.

b. Anterior restorations.

c. Sealing and filling of occlusal pits and fissures.

d. Restoration of Class III carious lesions, preferably using a lingual

approach.

e. Restoration of deciduous teeth Class I and Class II.

f. Repair of defective margins in restoration or temporary coverage of

fractured teeth.

g. Minimal cavity preparation – approximal lesions, buccal and

occlusal approach (Tunnel preparation).

h. Core build-up.

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i. Provision restorations where future veneer crowns are contemplated.

j. Sealing of root surfaces for overdentures.

II] Fast Setting lining cements and base

a. Lining of all types of cavities where a biological seal and cariostatic

action are required.

b. Dentine substitute in laminate techniques.

c. Sealing and filling of occlusal fissures showing early signs of caries.

III] Luting Cements (Fine grain version of GIC)

a. Useful in patients with rampant caries and as well as multiple

carious lesions.

b. In exposed porcelain margins used for cosmetic reasons, because of

its increased translucency.

c. Crown and prosthesis cementation. Because:

i) Its ability to release F ions into underlying dentine. This is

of great value as secondary caries is a common cause of

failure for cementation prosthesis.

ii) Chemical bonding.

Contraindications

1. Class IV carious lesions or fractured incisors.

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2. Lesions involved large areas of labial enamel where

esthetics is of major importance.

3. Class II carious lesions where conventional cavities

are prepared; replacement of existing amalgam.

4. Lost cusp area.

Advantages: (QI 1988)

1. Anticariogenic – Because of fluoride ions they can alleviate

sensitivity and reduces recurrent caries.

2. Biocompatible – Least irritant to pulp.

3. Chemical bond to enamel / dentine – thus provide good

marginal seal.

4. Minimal setting shrinkage.

5. Coefficient of thermal expansion similar to tooth structure

(i.e. dentine) thus it prevents microleakage because as the

coefficient of thermal expansion increases, microleakage

increases (JADA vol. 124, Sept. 1993).

6. Relatively resistant to acid and wear.

Disadvantages:1. Brittle material.

2. Low tensile strength thus used in bulk and low stress –

bearing area.

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3. Esthetically less pleasing than composite restorations.

4. Relatively opaque and lack polishability thus poor surface

finish.

5. Technique sensitive (But lesser than composite).

6. Lack of toughness.

7. Because of powder liquid, formulations alterations.

- Post operative sensitivity.

- Reduced physical and mechanical properties.

- Decreased bond strength.

- Prone to porosity a further cause of weakness.

Water contamination during early stages of setting reaction (15

seconds to 1 minute) can cause porosity, gazing and later staining and

solubility. Thus, GIC should be covered with varnish / DBA.

8. Poor edge strength, GIC do not perform well in saucer

shaped lesions (QI vol. 19, No. 12; 1988).

MANIPULATION

The P: L ratio recommended by the manufacturer should be

followed because any reduction in the ratio of set cement adversely affects

the properties of set cement.

- For mixing, a paper pad or a cool-dry glass slab

is required. As stated earlier, high temperature may alter the

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working time. Also temperature should not be below the dew

point as it may alter acid water balance.

- The powder and liquid should not be dispensed

onto the slab until just before the mixing procedure is started.

Exposure to air may alter the acid water ratio. The powder

should be incorporated rapidly into the liquid using a stiff plastic

spatula using folding technique. Plastic spatula is used because

cement sticks to stainless steel instruments.

- Mixing time should not exceed 45 seconds.

- The mix should have a glossy surface that

indicates the presence of unreacted polyacid which ensures

adhesive bonding to the tooth.

- If mixing is prolonged a dull surface will develop

and adhesion will not be achieved.

- Type II GICs are also supplied in capsules

containing proportioned powder and liquid.

- The mixing is accomplished in an amalgamation

after the seal that separates the powder and liquid is broken.

Advantages of capsules:a. Convenient.

b. Consistent control of P:L ratio.

c. Elimination of variation associated with hand spatulation.

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RECENT ADVANCES

The GIC has come a long way since it was first introduced its

properties have improved and there are now many versions for various

applications.

Amongst the recent development are:

1. Metal reinforced ionomer cements.

2. New fast setting lining cements.

3. Water hardening luting agents.

4. Dual cure system which include:

- Resin modified GIC.

- Poly acid modified resin / compomer.

5. Packable GIC.

6. Self hardening resin GIC.

7. Smart materials / fluoride charged materials.

8. Bioactive GIC.

1) Metal Modified GIC

The metal modified GIC were introduced in an attempt to improve

the strength, fracture toughness and resistance to wear and yet maintain the

potential for adhesion and anticariogenic property.

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Two methods were employed:

a. Miracle mix : Spherical silver alloy. Powder is mixed with type II

GIC powder (in the ratio of 7:1 GIC and silver alloy).Developed by

SIMMONS in 1983(BDJ 1988)

b. Cement : Fusion of glass particles to silver elemental particles

through high temperature sintering of a mixture of two powders.

- Developed by Mclean and Gasser in 1985.

Properties of Metal Modified GIC

a) Mechanical properties:

i) The strength of miracle mix GIC is higher than that of

conventional GIC.

ii) Increased flexural strength.

iii) Increased resistance to abrasion.

iv) Increased fracture resistance.

v) Low thermal conductivity.

vi) Coefficient of thermal expansion same as dentine.

vii) Passes anticariogenic property due to decrease of

fluorides.

viii) Chemical adhesion to tooth surface.

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Uses:

1. As an alternative to amalgam in conservative Class

II cavities, mainly in primary teeth.

2. Core build up material.

3. Lining of Class II SAF restoration / composite

restoration.

4. Root caps for teeth used under overdenture.

5. Material used in conjunction with ortho traumatized

or mobile posterior teeth (Dental Update Nov. 1991).

Contraindication:

1. Anterior teeth because of esthetics and where strong axial wall

support is needed.

Disadvantages:

1. Fluoride release is less than conventional GIC because the portion

of original Glass particles is metal coated.

2. Esthetically poor.

3. Rough surface.

4. Reduced setting time.

Advantages:

1. Ease of preparation and placement.

2. Adhesion to tooth structure.

3. Crown cutting can be done immediately.

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2) Fast Setting Lining Cements (BDJ 1988) – These faster setting GIC were discovered by Wilson and Crisp in 1972.

They found that optically active d-tactaric acid modified the cement

forming reaction thus improving.

i) Handling characteristics.

ii) Increases the working time.

iii) Shortens the setting time.

iv) Enabled the fluoride contents of glasses to be reduced.

v) Increases cement strength.

3) Water Hardening Cements / Anhydrous Cements

(BDJ 1988)

To solve the problems associated with the instability of polyacrylic

acid, copolymer of acids were introduced which although stable in water

might not yield the best cements.

Thus in 1973 Wilson and Kent described the use of polyacrylic acid

in dry form blended with Glass powder. Liquid consisted of water or an

aqueous solution of tartaric acid.

This was termed as ASPA V by Prosser et al 1984.

Advantages:

1. Developed very low viscosity in early mixing stages.

2. Rapid set at minimal temperature.

3. Easy manipulation.

4. Excellent shelf life.

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4) Dual Cure / Photocured GIC

A) Resin Modified GIC

Moisture sensitivity and low early strength of GIC are the results of

slow acid base setting reaction. Hence to overcome these two inherent

drawbacks, some polymerizable resin functional groups have been added to

GIC to impart additional curing process and allow the bulk of material to

mature through acid base reaction.

1. According to Nicholson (QI 1977)

Resin modified GIC are those Glass ionomer materials that

are modified by the inclusion of resin, generally to make them partly

photo curable.

2. According to WM Tay (Dental Update Sept. 95)

These are hybrid materials that certain significant acid base

reaction as a part of their overall curing process.

3. According to Mount (Op. Dent. 1994)

The term “dual cure” has been suggested because these

cements undergo the original acid base setting reaction

superimposed over that.

4. According to Christensen (JADA 1997)

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These materials are termed as Tricure as the RMGIC sets by

3 phenomena.

a. Acid base reaction between the components of conventional

GIC.

b. Light cure reaction stimulated by light application activates

the initiated catalyst resin cure system.

c. Auto cure reaction when the powder and the liquid

components are mixed together the initiation catalyst system

for resin gets activated and ensures that over time these will

be a complete cure throughout the entire restoration with no

free resin remaining.

A feature of these material is that they will set in the dark.

Dark setting although the process is slower than the conventional

GIC and produce a material that is inferior to the product obtained

by light curing.

Composition:

- Polyacrylic acid / modified polyacrylic acid with a light

activated polymerizable side chain app. 5%.

- Photo polymerizable monomer – HEMA app. 5wt%.

- Ionizable glasses app. 70wt%.

- Water app. 8%, examples : Fuji II LC (GC), Photac Fil

(ESPE), Vitremer 3M.

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Properties:

1. Strength

Die material values are higher than conventional GIC

Type II GIC RM GIC

Composite strength 24 hours 150mPa 105mPa

Hardness strength 24 hours 48 40

Diamaterial strength 24 hours 6.6mPa 20mPa

2. Translucency:

There is a decrease of translucency as a significant difference

between the refraction index of the GI powder and set resin matrix

is present.

3. Fluoride release : According to Skinners – There is increased

fluoride release as compared to GIC.

Conventional GIC 440µgF in 14 days.

650µgF in 30 days

L-C GIC 1200 in 14 days.

1600 in 30 days.

4. Adhesion to tooth structure:

- Bond strength is higher than conventional GIC to tooth

structure and also to other restorative material such as

composites.

5. Marginal adaptation:

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- RM GIC exhibit a greater degree of shrinkage on setting as a

result of polymerization thus exhibit greater microlekage.

6. Water sensitivity : Resins are added to GIC’s to reduce the water

sensitivity of GIC. Studies show that GIC liners are still susceptible

to dehydration and that this material can also absorb water which

can result in dimensional change.

7. Biocompatibility : Biocompatibility of RMGIC’s is controversial

certain studies suggests that precaution such as Ca(OH)2 for deep

preparation are recommended as there is a transient rise in

temperature associated with polymerization process.

Advantages: (DM Sept. 1995).

1. Sufficiently long working time controlled in command to a snap set

by photo-curing.

2. Improved setting characteristics.

3. Protects the acid base reaction from problem of water balance.

4. Rapid deviation of early strength.

5. Can be finished and polished immediately after set.

6. Repairs can be easily carried out as the bond between old and new

material is strong.

7. Exhibits increased adhesion to composite when as a base.

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8. Fluoride release is present which is greater conventional GIC.

9. Increased tensile strength (20mPa).

Disadvantages (DM 1995)

1. Biocompatibility is controversial.

2. Setting shrinkage is higher – microleakage is more, poor marginal

adaptation (about 1%).

3. Low wear resistance compared to composite (JADA 97).

4. Depth of cure can be a problem : Incremental placement technique

necessary. Depth of cure – 3-4mm.

Uses: (DM Feb 1996)

a. Liners and bases.

b. Class V, III restorations.

c. Cervical abrasion / Erosion lesion, root

caries.

d. Core build ups where sufficient tooth

structure remains.

e. Class I and II restorations in deciduous

teeth.

f. Microcavity / Tunnel preparation.

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g. Temporary repairs of # teeth.

h. Temporary repairs of deflection crown

margins.

B) Polyacid Modified Resin Composite

Definition : According to Mclean and Nicholson – Materials that may

contain either or both of the essential components of GIC but at levels

insufficient to promote the acid base curing reaction in the “dark”.

This material is essentially a resin composite in which the filler is

Glass and variable quantity of dehydrated polyalkenoic acid which reacts

only if water is available.

- Here there is a limited degrees of acid base reaction. The

adhesion system is based on the resin to dentine method

because ion-exchange method cannot arise at any stage.

Hence photoactivation is necessary for type of materials.

Indications:

1. Pit and fissure sealants.

2. Restoration of deciduous teeth.

3. Minimal cavity preparation / tunnel preparation.

4. Lining of all types of cavities where a biological seal and cariostatic

action is required.

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5. Core build up.

6. Dentine substitutes as in sandwich techniques.

7. Repair of defective restoration margins.

8. Class III and IV lesions.

9. Abrasion / Erosion.

10. Sealing of root surfaces for overdentures.

11. Potential root canal sealers.

12. Retrograde filling materials in endo emergencies.

13. Luting agents.

Advantages :

1. Superior working characteristics to RMGIC.

2. Ease of use.

3. Easily adapts to tooth.

4. Good esthetics.

5. Fluoride release, which is less than that of RMGIC.

Contraindications:

1. Class IV carious lesion.

2. Lesions involving large areas of labial surface where esthetics is of

prime concern.

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3. Class II carious lesions where conventional cavities are prepared,

replacement of old amalgam restoration.

4. Cusp coverage.

5. Underneath metal /PFM crowns where light cannot penetrate. Ex:

Dyract (Dentsply), Compoglass (Ivoclar), Variglass (Caulk).

Packable (Condensable) GIC (Fuji IX GIC / Ketac Molar)

This is a new high viscosity GIC launched in early 1990’s. This

material was developed largely as a need for filling materials in the

automatic / atraumatic restoration therapy “ART”. ART refers to the

restoration of teeth under conditions of minimal instrumentation, especially

carried out in the third world nations.

Advantages:

1. Packable and condensable.

2. Easy placement.

3. Non-sticky.

4. Early moisture sensitivity is reduced.

5. Rapid finishing can be carried out.

6. Improved wear resistance.

7. Solubility in oral fluids is very low.

Indications:

1. Ideal material for molar restoration in deciduous teeth.

2. Intermediate treatment restoration for permanent teeth.

3. Core build up.

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Self Hardening Resin GIC

This is another recent development in resin modified GI luting

cements. These materials are not light activated but certain monomers with

initiators are added to allow self polymerization.

Composition :

- Benzoyl peroxide and amine accelerators are added to GIC.

Advantages:

1. Easily handled.

2. No significant post cementation sensitivity.

3. Significant fluoride release.

4. High compressive and fracture strength.

5. No length activation required.

Uses :

1. Used for luting stainless steel crowns, space maintainers,

orthodontic brackets, bands in pediatric cases.

Smart Mat / F Charged Materials (Dental Update 1998 Nov.)

The development of fluoride releasing material was made in order to

overcome the shortcomings faced by fluoride releasing materials.

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a. Increases the fluoride release more open

is the structure of the material. This is associated with low

strength.

b. In order to improve the strength of these

fluoride containing materials, if they are made more dense and

strong the efficiency of ion release is reduced only after

placement of restoration there is a sudden burst of fluoride

release followed by a rapid decline in ion release rate.

- Hence to overcome these shortcomings and improve the

therapeutic potential of these fluoride releasing materials two

approaches were developed.

a) Fluoride Charge Materials:

This is a modified GIC and has two parts material system :

Restoration part, Charge part.

The restorative part of the material is used in the usual way. When

the 1st burst of fluoride is expanded and the therapeutic potential of the

restoration is spent. The material is given a second. Fluoride change using

a gel material that replenishes the fluoride sites in the restoration by ion

exchange and recovers the fluoride release and therapeutic potential of the

restoration. This is achieved without replacing the material provided the

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restoration materials the normal standards of anatomical sufficiently. This

approach is still in the experimental stage.

b) Low pH smart materials

The second approach is to optimize the efficacy of fluoride

materials. This material is based on the fact that fluoride should be released

at a low pH i.e. when caries attack may be most threatening. Hence, these

materials are developed to release fluoride at a low oral pH. Hence termed

as smart materials. Hence in these fluorides is not released all the time the

episodic release prolongs the usefulness of the material.

Bioactive Glass

The idea of bioactive glasses were developed by Hench and Co-

workers in 1973. Studies show that on dissolution of the glass by acid there

is stimulation to formation of a layer rich in calcium and phosphate, around

the glass that can bond with intimate bioactive bonds with the bone cells

and hence the material gets fully integrated into the bone. These bioactive

glasses grow calcium phophate rich layers in the presence of calcium and

phosphate saturated saliva.

This is an excellent material for use in maxillofacial craniofacial

surgeries as it performs better than hydroxyapatite.

Uses:

1) Augmentation of alveolar ridges in edentulous patients.

2) Cementation of custom made present implants into place.

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Conclusion:- During the relatively short time in which GI have been

clinically – available they have undergone major

improvements.

- Consequently, their popularity and range of uses have been

extended considerably.

- Undoubtedly this class of restorative materials will be

important part of dental restorations for a long time to come.

GLASS IONOMER CEMENT

CONTENTS

1. INTRODUCTION

2. HISTORY

- Invention

- Early Development

3. DEFINITION

- Classification

4. COMPOSITION

5. CHARACTERISTICS OF GIC

6. CHEMISTRY OF SETTING

7. PROPERTIES

8. INDICATIONS

9. CONTRAINDICATIONS

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10. ADVANTAGES

11. DISADVANTAGES

12. MANIPULATION

13. RECENT ADVANCES

14. SUMMARY & CONCLUSION

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