GLASS IONOMER CEMENTBYDR V.VASUNDHARAFIRST YEAR PG

DEFINITIONINTRODUCTIONHISTORY AND EVOLUTIONCLASSIFICATIONCOMPOSITIONCHEMISTRY OF SETTINGFLUORIDE RELEASEPROPERTIES MECHANISM OF ADHESION

CONTENTS

INDICATIONSCONTRAINDICATIONSADVANTAGESDISADVANTAGESUSES OF GICMANIPULATIONRECENT ADVANCESNEWER ADAVANCEMENTCONCLUSION

DEFINITION Glass-ionomer is the generic name of a group of materials that use silicate glass powder and aqueous solution of polyacrylic acid

-Kenneth J Anusavice Glass ionomer cement is a basic glass and an acidic polymer which sets by an acid- base reaction between these components

JW McLean, LW Nicholson. AD Wilson (1994)

Glass ionomer is a water- based material that hardens following an acid-base reaction between fluroaluminosilicate glass particles and an aqueous solution of polyacid. (Davidson and Mjor)A non metallic material used for luting, filling permanent or temporary restorative purposes, made by mixing components into a plastic mass that sets or as an adherent sealer in attaching various dental restorations in or on the tooth ( Acc to CRAIG)

Glass ionomer cement was developed by Wilson and Kent in the British Laboratory of the Government Chemist, England in the early 1970sINTRODUCTIONThe design of the original glass-ionomer cements was a hybrid formulation of silicate and polycarboxylate cements. Glass ionomers used the aluminosilicate powder from silicates and the polyacrylic acid liquid of polycarboxylates. The earliest commercial product was named using the acronym for this hybrid formulation and was called aluminosilicate polyacrylic acid (ASPA).Alumino-Silicate Polyacrylic Acid (ASPA); Glass Ionomer Cements (GIC); Polyalkeonate cement; Glass polyalkeonate cement. Glass Ionomer Cements or GIC is the popular name for this cement. Because of the extensive use of this cement as a dentin replacement material it has also been referred to as Manmade Dentin or Dentin Substitute.

Originally, the cement was intended for aesthetic restoration of anterior teeth and it was recommended for use in restroring teeth with class III and class V cavity preparation. Because of its adhesive bond to tooth structure and its caries prevention potential, the types of glass ionomers have expanded to include their use as luting agent, orthodontic bracket adhesives, pit and fissure sealants, liners and bases, core buildups, and intermediate restorations. The original polyacrylic acid in the liquid component was modified by copolymerization with different amounts of maleic acid, itaconic acid, and/or tartaric acid to increase the stability of the liquid and modify its reactivity. Powder particles were reduced in size and modified by incorporating additional types of powder particles for reinforcement.

Ag-Sn particles (amalgam alloy particles) were admixed in some formulations to produce an amalgam substitute. This combination became known as the "miracle mixture"

History And EvolutionThe development of amalgam, gold, and porcelain restorative materials in the mid-1800s stimulated the creation of dental cements.

In 1855, Sorel introduced zinc oxychloride cement, the first popular dental cement. In 1871- T. Fletcher introduced the first tooth colored filling material, silicate cement. It lost its popularity due to its high degree of acidity and solubilityThe work of Ames and Fleck established the modern-day zinc phosphate cement.In 1870, Pierce introduced zinc oxidephosphoric acid cement, which replaced oxychloride and oxysulfate cements, because it caused less irritation to the pulp and had greater durability.

In 1951 swiss chemist DR OSCAR HAGGER was the first to demonstrate adhesionIn 1955 BUONCORE defined the principles of acid etch technique for micro mechanical adhesionIn 1956 BOWEN defined conventional composite resinIn 1966, D.C. Smith introduced yet another class of cement, in which the liquid of the zinc phosphate cement was replaced by aqueous polyacrylic acid. This so-called carboxylate cement opened up new prospects for self-adhesive dental materials.

In 1972 Wilson and Kent developed a new translucent cement- Aluminium Silicate Poly Acrylate (ASPA), which later became popular as Glass Ionomer Cement (GIC).

It was B E KENT who coined the term GLASS IONOMER1972 Wilson & Crisp found that tartaric acid improves manipulative properties 1974 Mc. Lean & Wilson proposed clinical use of GIC In 1974 they discovered ASPA 3 which had methyl alcohol added to poly acrylic acid but used to get stained

In1975 they discovered ASPA 4 which contained co polymers of acrylic acid and itaconic acid

FORSTEN studied the pattern of fluoride release from GIC

CRISP ABEL AND WILSON in 1979 discovered ASPA-X which had excellent translucency

AD WILSON AND SIMMONS [1983]developed Miracle Mix cement by incorporating metal oxide metal alloy filler in gic for improving strengthProsser et al in 1984 developed ASPA 5 which contained poly acrylic acid in dry powder form blended with glass powder mixed with water /tartaric acid

The tunnel preparation for class 2 was suggested for GIC by HUNT AND KNIGHT in 1984 In 1985 MCLEAN et al developed lamination sandwich technique now called as bilayer techniqueIn 1985 MCLEAN and GASSER developed cermet ionomer cement by fusing silver particlesANTONUCCI AND MCKINNEY IN 1986 added polymerizable free radically active methacrylate monomers and pre polymers and coined the term resin modified gic

MC LEAN et al in 1994 termed the word Polyacid Modified Composite Resin

Atraumatic Restorative Therapy was presented for first time by WHO

In 2002 SHAFER company developed giomers

In 1989 Mitra developed Resin Modified GIC

ClassificationAccording to clinical use as:

Type I- Luting TYPE II- Restorative Type III-Fast setting Liner/ Base Type IV- Pit & Fissure Sealant Type V- Luting for Orthodontic Purpose Type VI- Core build up material Type VII- High fluoride releasing command set GIC Type VIII-GIC for ART Type IX- Geriatric & Paediatric GIC

According to characteristics specified by the manufactures :

1. Type I - Luting Cement Eg: Fuji 1, Ketac cement

2. Type II - Restorative material Eg: Ketac Fil, Fuji II, Fuji IX

3. Type III: a. Bases and Liners - Weak with low acidity Eg: AC lining cement, Shofu liner b. Bases and Liners - strong but more acidic Eg: Ketac Bond, Shofu base, GC Dental Cement c. Bases and Liners - strong even in thin layer light Eg: Vitrebond

4. Type IV- Admixtures Eg: Ketac Silver, Miracle mix.

According to Philips

Type I Luting

Type II - Restorative

Type III - Liner & base

According to Davidson and Mjor:

1. Conventional/ Traditional Glass Ionomer for direct restorations Metal reinforced GIC High viscosity GIC Low viscosity GIC Base/Liner Luting

2. Resin modified GIC

RestorativeBase/LinerPit & fissure sealantLuting Orthodontic cementation material

3. Polyacid modified resin Composites/Compomers

According to GJ Mount:

1. Glass ionomer cements:

a. (i) Glass Polyalkeonates (ii) Glass polyphosphonates

b.Rein modified GIC c.Polyacid modified composite resin

2. a. Auto-cureb. Dual Curec. Tri cure

3. a. Type I Luting b. Type II Restorative Type II.1. Restorative aesthetic Type II.2. Restorative reinforced

c. Type III Lining or Base

According to Sturdvent:

1. Traditional or conventional

Metal modified GIC

a.Ceremets b.Miracle Mix

3. Light cured GIC4. Hybrid (Resin modified GIC)5. Polyacid modified resin composites or Compomer

According to Wilson & McLean (1998)

1.Type I Luting2.Type II

a.Aesthetic filling material b.Bis-reinforced filling material (includes ceremets)

3. Type III Lining, base and fissure sealant

According to McLean, Nicholson & Wilson (1994):

1.Glass Ionomer cement

a.Glass polyalkeonates b.Glass Polyphosphonates

2.Resin modified GIC3.Polyacid modified GIC

NEWER CLASSIFICATION

1.TRADITIONAL GLASS IONOMER

A.TYPE I LUTING CEMENT B. TYPE II RESTORATIVE CEMENTS C. TYPE III LINERS AND BASES

2. METAL MODIFIED GLASS IONOMER

A. MIRACLE MIX B. CERMET CEMENT

3. LIGHT CURE GLASS IONOMER HEMA ADDED TO LIQUID

4. HYBRID GLASS IONOMER

A. COMPOSITE RESIN IN WHICH FILLER SUBSTITUTED WITH GLASS IONOMER PARTICLES.

B. PRE-CURED GLASSES BLENDED INTO COMPOSITES

Powder Is basically an acid soluble calcium aluminosilicate glass containing fluoride. It is formed by fusing silica + alumina + calcium fluorite, metal oxides and metal phosphates at 11000-15000 C and then pouring the melt onto a metal plate / into water. The glass formed is crushed, milled and ground to a form powder of 20 50 m size depending on what its going to be used for. They get decomposed by acids due to the presence Al +3 ions which can easily enter the silica network. It this property that enables cement formation.

POWDER

SILICA (SIO2) 35.2--41.9%

ALUMINA (AL2O3) 20.1--28.6%

ALUMINIUM FLOURIDE (ALF3) 1.6 2.4 %

CALCIUM FLUORIDE (CAF2) 15-20 %

SODIUM FLUORIDE (NAF) 3.6--9.3 %

ALUMINIUM PHOSPHATE (ALPO4) 3.8 12 %

LANTHANUM, STRONTIUM, BARIUM IN TRACES ( FLUORIDES ACT AS CERAMIC FLUX )

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Alumina : It forms the skeletal structure of the glass. It also increases the opacity of the glass.

Silica :It forms the skeletal structure of the glass and increases the transparency of the glass

Aluminium Fluoride :It partially replaces silicon in the glass network providing negative sites, which are vulnerable to acid attack by H+ leading to decomposition of glass and providing cement potential. FUNCTIONS OF COMPONENTS :

Fluoride :It contributes to therapeutic value by releasing fluoride over a prolonged period of time. It helps to lower the fusion temperature. It enhances translucency and improves the working characteristics. It also helps to increase the strength of set cement

Calcium Fluoride :It acts as a flux and provides opacity to the set cement

Phosphate :It lowers the melting temperature and modifies the setting characteristics of the cement.

Lanthanum, Strontium, Barium : It provides radio - opacity to the cement

Na+ Ca+2, Sr+2 Works as modifying ions and induce high reactivity of glass with polyacid.

Cryolite (Na3 AIF6)It acts as a flux and increases the translucency of the cement Aluminum phosphate :It helps to add body to cement and improve the translucency of the cement.

Liquid: Originally, the liquid for GIC was an aqueous solution of PAA in a concentration of about 50%. This was quite viscous and tended to gel over time. Thus, PAA was co- polymerized with other acids such as itaconic, maleic and tricarboxylic acids. This polyelectrolytic liquid of GIC is, thus, also called as polyalkenoic acids. Recently polyvinyl phosphoric acid has also been introduced to this system.A typical liquid of GIC contains 40-55% of 2:1 polyacrylic : itaconic acid co- polymer and water.

The basic functions of these copolymers include: the co- polymeric acids are more irregularly arranged than the homo polymer. This reduces H- bonding between acid molecules and reduces degree of gelling decrease the viscosity reduce tendency for gelation,hence, improves storage. Increase the reactivity of liquid

LIQUID

POLYACRYLIC ACID 45%

ITACONIC ACID 5%

MALEIC ACID 5%

TRICARBOXYLYLIC ACID 5%

TARTARIC ACID TRACES

WATER 50% (HYDRATES REACTION PRODUCT)

Additives: 1.Tartaric acid - Increases working time- Increases translucency - Improves manipubality - Increases strength 2.Polyphosphates: extends working time 3.Metal oxides: accelerates setting time

Modifications in liquid

- Only water and tartaric acid[anhydrous cement] -Hema [light cure components]

Recently polyvinyl phosphonic acid has been addedModifications in Powder * Dried Poly Acrylic Acid (anhydrous GIC). * Silver-Tin alloy (Miracle Mix). * Silver-Palladium/Titanium (Cermet cement). * BiSGMA, TEGDMA and HEMA (Light/Dual cure GIC).

Bulk of powder and liquid for hand mix version. Pre-proportioned capsules form for mixing in mechanical mixers.

Anhydrous glass ionomer cements are supplied as powder that may be mixed with water or water with tartaric acid.

Compomers that are polyacid modified resins are supplied as single pastes in bulk as tubes or compules (cavifils) for single use. DISPENSING

SETTING REACTION OF CONVENTIONAL GLASS IONOMERThe material are supplied in two part powder-liquid systems that require mixing.Following are the essential components

Polycarboxylic acidFluoroaluminosilicate (FAS) glassWaterTartaric acid

The polymeric matrix of most glass ionomers is a copolymer of acrylic acid and itaconic acid or maleicacid. Tartaric acid is added to control the working and setting characteristics of the material. The powder consists of an acid-reactive comminuted FAS glass and has ions such as calcium, strontium, and lanthanum.

When heavy metal ions are used, the set material is radiopaque to x-rays.When the powder and liquid are mixed, an acid base setting reaction begins between tha FAS glass and polyacrylic acid. The acid etches the surface of the glass particles and calcium, aluminium, sodium and fluorine ions are leached into the aqueous medium.

An initial set is achieved within 3 to 4 minutes, but the ionic reaction continues for atleast 24 hours or more so that maturation is achieved much later

Maturation time has been improved in newer formulations to allow finishing after 15 minutes of placement of mix.Polyacid liquid

Stage 2- The hydrated proton attacks the surface of the glass particles releasing calcium and aluminium ions. The carboxylate ions from the polymer react with these metallic ions to form a salt bridge, resulting in gelation and setting

Stage 3- During the initial setting, calcium ions are more rapidly bound to polyacrylate chains; binding to the aluminium ions occurs at later stage. The strength of the cement builds with time

Stage 4- silicic acid is initially formed when the glass breaks down, but rapidly polymerizes to form silica hydrogelStage 1 - In an acid base reaction, all carboxylic acids have common organic functional group denoted COOH. In the presence of water, the COOH group undergoes partial ionization to yield a carboxylate anion COO and a hydrated proton, H3O.

The set cement is constituted by hydrogel of calcium, aluminium, and fluoroaluminum polyacrylates involving the unreacted glass particles sheathed by weakly bonded siliceous hydrogel layer.

About 20% to 30% of the glass is dissolved in the reaction. Smaller glass particle may be entirely dissolved and replaced by siliceous hydrogel particles containing fluorite crystallites.

The stability of matrix is given by an association of chain entanglement, weak ionic cross-linking and hydrogen bonding

WORKING TIME AND SETTING TIME OF GIC Fuji I : Mixing time = 30 sec. Working time = 60-90 sec. Fuji II : Mixing time 45 60 sec or 30 sec. (first half 15 sec. & other half 15 sec)Working time = 60-90 sec. Setting time = 2min 40 sec. RMGIC:Mixing time = 10 sec (in a capsule form, 20-25 sec manually) Working time = 3 min.

Fuji III : Mixing time = 10 sec Working time = 1 min 40 sec. Setting time = 2min 45 sec. Miracle mix :Mixing time = 10 sec (in a capsule form, 20-25 sec manually) Setting time = 4 min Fuji VII : Setting time = 1 min Mixing time = 20-25 sec.

Fuji IX : Working time = 2 min Setting time = 2.5min, 4.5 min from the start of mix. Fuji IX GP fast: Mixing time = Less than 30 sec.Setting time = initial set is 3 min 35 sec. Final finishing after 6 min

Factors Affecting setting:Glass composition : If the Al2O3 / SiO2 and fluoride content are higher in ratio faster the set and shorter the working timeParticle size of the glass powder: Finer the powder, faster the set and shorter the working time.Addition of tartaric acid: Sharpens the set without shortening the working time.

FLUORIDE RELEASE

The fluoride ions from the glass matrix is sustained and occurs a long period of time. The fluoride release is result of setting reactions and the ion exchange process in the cement

In this process the fluoride from the glass is being replaced by carboxylates and water

*

Importance of water

It provides ion transport needed for the acid base setting reaction and fluoride release.It is chemicaly bound in the set complex and provides stability to the restorative materialProvides plasticity during manipulative stage

Water present in the set cement can be arbitrarily classified as: - loosely bound water which can get readily removed by dessication. This is associated with Ca+2 during the initial reaction - tightly bound water is the one which hydrates the matrix as setting continuous and cannot be removed by dessication. This is associated with Al+3 and is critical in yielding a stable gel structure and building the strength of the cement.

Although the clinical set is completed within a few minutes, a continuing maturation phase occurs over subsequent months.

This is predominantly due to the slow reaction of the aluminium ions, and is the cause of the set materials sensitivity to water balance.

The set material needs to be protected from salivary contamination for several hours, otherwise the surface becomes weak and opaque.

From water loss for several months, otherwise the material shrinks and cracks and may debond.

SURFACE PROTECTION Certain materials are applied on the GIC restoration surface immediately after removal of matrix in order to prevent excessive imbibition or desiccation of the cement, these arePetroleum jellyCocoa ButterDentin Bonding agentsDental Varnish.

PROPERTIESProperties of GIC can be divided into two group: Physical properties. Biological properties.Physical properties:

Physical properties of glass ionomer cement Traditional GIC Glass cermet Light cure GIC Compomer Compressive strength 16000-22000 psi 150mpa27500 psi 23200 psi 29000 psi Tensile strength 900-960 psi 6.6 mpa950-1000 psi 2000-3000 psi 2000-3000 psi Modulus of elasticity 2900000 psi - 906175 psi 1217900 psi Coefficient of Thermal expansion/0C lO x lO-6 15 X 10-6 18 X lO-6 18 X lO-6 Solubility 0.3-0.5% 0.1% 0.08% 0.08% Opacity 90% 95% 85% 80% Hardness (KHN) 48 39 40 38 Film thickness (m)22-25 - 30-40 30-40

COMPRESSIVE STRENGTH :

TENSILE STRENGTH

HARDNESS

Solubility and disintegration

The surface of gic can be damaged in presence of low ph, like application of topical fluoride in cases of people having xerostomia due to lack of buffering the glass ionomer may disintegrate in faster time resin modified glass ionomers are more resistant to solubility

Physical properties Dimensional changes

Gic which have been manipulated correctly and protected from early exposure to moisture show a volumetric contraction of 3% at humidities.

Protection can be given by applying varnish the Resin modified glass ionomer restorative materials contain less than 5% of additional resin and show very small initial shrinkage in contrast light cured composite resins show immediate shrinkage with development of considerable stress at tooth interface

Resistance to fracture

The disadvantage of gic is its susceptibility to brittle fracture they should be avoided in areas of heavy occlusal loadingAbrasion resistance

Immediately after placement are less resistant to abrasion than composite resins but improves with maturationIn cermet the presence of silver particles improves abrasion resistanceRadio-opacity

These cements can be made radio opaque by addition of radio opacifiers like barium sulfate or metals like silver

the Glass ionomer cement is an aesthetic filling material because it has glass as its filler material

A degree of translucency exists for GIC due to the glass fillers. Its translucency depends on its formation.

It should be noted that because of slow hydration reaction glass ionomers take 24 hrs to fully mature and develop full translucency

Early contamination of cement surface with moisture adversely affects translucency

Resistance to stain is largely dependent on obtaining a good surface finish

Aesthetics

ADHESION 1. Chelation (Smith) 2. Hydrogen bonding followed by ionic bond (Wilson) 3. Hydroxyapatite & polyacrylic acid interaction (Beech) 4. Hydrogen bonding with dentin collagen (Akinmade)Mechanism of adhesion

Polyacid co- polymer liquids are thought to bond by an ionic interaction between the negatively charged polyacid chain of the ionomer matrix and the positively charged calcium on tooth surface.

Polyacid also form hydrogen bonds and undergo ion exchange in the collagen and in organic components of the tooth structure, particularly to calcium carboxylate and phosphate

They chemically bond to the restorative material and tooth structure.

The bond strength to enamel is always higher than that to dentin because of the greater inorganic content of enamel and its greater homogenicity from a morphological standpoint

Adhesion of conventional GIC to enamel and dentine only produces bond strength in the range of 6-12 Mpa

Polymerization of the Poly acid

Most GICs are aqueous systems that wet tooth structure very well because they are Hydrophilic.However GIC tends to have high viscosity and therefore do not flow and adapt to micro-mechanical spaces very readily

Adhesion can be improved by usage of surface conditioners which helps to eliminate the wide variation found after cutting better, wetting and inter facial contact will occur, if a smooth surface is attained

Bond strength

Enamel- 2.6 to 9.6 MpaDentin 1.1 to 4.5 Mpa

CONDITIONER helps toRemove the smear layerIncrease surface energy of toothincrease wettability and therefore decrease contact angle

Mechanical Properties STRENGTH:Mechanical mixing using capsules containing pre proportioned amounts of the components will statistically improve the performance of any Glass Ionomer Cement major limitaions of GIC: susceptibility to brittle fracture as compared to composite and amalgamweak lack rigidityweakness appears to be in the matrix, which is prone to crack propagation

Since glass ionomer cement is a hybrid of silicate cement and zinc poly carboxylate cement, it has mechanical properties that are in between these cements. silicate cement is a hard (70 KHN) but brittle material the glass ionomer cement is less hard (48 KHN) and less brittle than the silicate cement

The strength of GIC is increased as the filler contents is increasedthe water content is reduced using phase separated glassincreasing the molecular weight of the polyacid

increased strength is accompanied by an acceleration of setting and loss of workability.Increasing in molecular weight also increases fracture toughness and resistance to erosion but at the same time reduces the workability of the cement due to high viscosity of the liquid. phase separated glasses appeared to yield stronger cement than clear glasses. Reinforced fillers such as Alumina and Lathe cut silver tin alloy has been used successfully to increase the flexure strength GIC. However these strengths are still less than those for posterior filling material.

Different Conditioners used are :PAA : Is the conditioner of choice as it is a part of the cement forming acid. It alters the surface energy, exposing highly mineralized tooth surface to diffusion of acid and ion exchange. This enhances adaptation of cement (10%, 10sec)50% citric acid, 5 sec25% tannic acid, 30 s2% Ferric chloride NaFEDTAMineralising solution ITS solution, Levine solution

Compressive Strength :compressive strength is 150-200 MPa .Compressive strength is increased by increasing alumina content. The finer the particles the more will be the compressive strength.

Tensile Strength :It has a higher tensile strength when compared with silicates tensile strength 6.5 MPa - 17.4 MPa.

Flexure Strength :GIC are relatively brittle having a flexure strength of only 15-20 MPa and cannot be considered suitable as general purpose filling material for permanent teeth.

Hardness :

It is less than that of silicates the value is 48 KHN.

Fracture Toughness :

Glass ionomer cements are much inferior to composites

Thermal Properties :The thermal diffusivity value for glass ionomer cement ions is close to that dentin. Hence the material has an adequate thermal insulating effect on the pulp and helps to protect it from thermal trauma.

The co efficient of thermal expansion values of glass ionomer is 10.8x10 -6/degree centigrade and that of the tooth structure is 11.4x 10 -6/ degree centigrade thus the values of GIC and tooth structure are similar which means that the tooth structure and glass ionomer cemnts will expand and contrct at similar rates

The two main biologic properties of GIC are:Anticariogenic potential due to release of fluoride.Biocompatibility.BIOLOGIC PROPERTIESFluoride ReleaseOne 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).

Fluoride ions released from the restorative material becomes incorporated in hydroxyapatite crytals of adjacent tooth structure to form in a structure such as fluroapatite that is more resistant to acid mediated decalcification.

The fluoride originates from that used in preparing the alumina silicate glass which can contain upto 23% fluoride

Before it was found that the fluoride is released as sodium fluoride but recent studies have shown that some calcium too is released with fluoride

Large amount of fluorides are released during the first few days after placement after which it gradually declines during the first week and stabilizes after 2-3 months and continues for a long time that is 8 years after placement

BIOCOMPATIBILITYBio compatibility is defined as the ability of a material to perfom with an appropriate host response in a specific application GIC are generally biocompatible with oral tissues and as restorative materials results in only mild pulpal irritation at a level similar to that produced by zinc polycarboxylate or zinc phosphate cementsThis can be attributed to polykenoic acid which is a weak acid and also has high molecular weight (30,000-50,000) of liquid and larger molecular size of acid thus it is not able to penetrate the dentinal tubulesSetting reaction is min exothermic, rapidly neutralizes after mixing, slow release of ion which are biologically beneficialIt gets readily precipitated by the calcium ions in the tubulesDissociated H+ remains near the chains due to electrostatic attractionsTheir adhesion to tooth structure ensures that they provide an excellent marginal seal and prevent microleakage the traditional GICs are very acidic at times of initial mixing and have potential to produce post-operative sentivity and pulp irritation.

As the reaction proceeds the PH increases from initial value to 1 to the range of 4 to 5. As the setting reaction nears completion the final PH value reaches 6.7 to 7

In deep cavities pulp protection is needed either by placing ca(OH)2.Post-operative sensitivity Post-operative sensitivity is usually associated with poor manipulation and/or poor powder/liquid ratio. This is also related with moisture contamination during setting of the cement leading to hydraulic effect on dentinal fluid. However, the menace of post-operative sensitivity is less affected with light cure glass ionomers and compomers.

INDICATIONSI] As a Restorative MaterialRestoration of erosion / abrasion lesion Class V lesion.Anterior restorations.Sealing and filling of occlusal pits and fissures.Restoration of Class III carious lesions, preferably using a lingual approach.Restoration of deciduous teeth Class I and Class II.Repair of defective margins in restoration or temporary coverage of fractured teeth

Core build-up.Provision restorations where future veneer crowns are contemplated.Sealing of root surfaces for overdentures.II] Fast Setting lining cements and baseLining of all types of cavities where a biological seal and cariostatic action are required.Dentine substitute in laminate techniques.Sealing and filling of occlusal fissures showing early signs of caries.

Luting Cements (Fine grain version of GIC)Useful in patients with rampant caries and as well as multiple carious lesions.In exposed porcelain margins used for cosmetic reasons, because of its increased translucency.Crown and prosthesis cementation. Because: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.Chemical bonding.

CONTRAINDICATIONSClass IV carious lesions or fractured incisors.Lesions involved large areas of labial enamel where esthetics is of major importance.Class II carious lesions where conventional cavities are prepared; replacement of existing amalgam.Lost cusp area.

ADVANTAGESAnticariogenic Because of fluoride ions they can alleviate sensitivity and reduces recurrent caries.Biocompatible Least irritant to pulp.Chemical bond to enamel / dentine thus provide good marginal seal.Minimal setting shrinkage.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).Relatively resistant to acid and wear.

DISADVANTAGESBrittle material.Low tensile strength thus used in bulk and low stress bearing area.Esthetically less pleasing than composite restorations.Relatively opaque and lack polishability thus poor surface finish.Technique sensitive (But lesser than composite).Lack of toughness.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. Poor edge strength, GIC do not perform well in saucer shaped lesions (QI vol. 19, No. 12; 1988).

Restoration of permanent teeth : Class V and Class III cavities Abrasion / Erosion lesion Root caries

2) Restoration of deciduous teeth Class I Class VI cavities Rampant caries, nursing bottle caries

3) Luting or cementing Metal restorations viz. inlays, onlays, crowns Non-metal restorations viz composite inlays and onlays Veneers Pins and posts Orthodontic bands and brackets

Uses of GIC

Preventive restorations Tunnel preparation Pit and fissure sealant

5) Protective liner under composite and amalgam 6) Core build up 7) Splinting of periodontally weak teeth 8) Glazing (Fuji Coat LC ) Glazing of traditional GIC filling Improving aesthetics of old GIC filling Protection of new GIC filling

9) Other restorative technique Sandwich technique / Layered restorations/ Laminated restorations / Bilayered restorations Atraumatic restorative treatment (Fuji VIII and Fuji IX). Co-cure technique Bonded restorations

10) Endodontics Repair of external root resorption Repair of perforation Retrograde filling

MANIPULATIONIsolation Tooth preparation/ Conditioning of the tooth surfaceCement placementFinishing & polishingSurace protection

ISOLATIONSaliva control is an essential step in the restoration of glass ionomer cement.

The cement is very sensitive for water loss as well as contamination.

Saliva, sulcular fluid and gingival haemorrhage, have to be controlled during the restoration procedure.

Rubber dam, retraction cords and cotton rolls with saliva ejectors are generally used and are rather mandatory in the restoration of lesions close to the gingival margins of the tooth.

TOOTH PREPARATIONTo achieve long lasting restorations, the following conditions must be satisfied:Surface of the tooth must be clean & dry

Consistency of the cement must allow complete coating of the surfaces irregularities

Surface must be finished without excessive drying

Surface protection must be done properly.

Tooth surface cleaned With pumice slurry

Conditioning With (34% to 37%) phosphoric acid or an organic acid like polyacrylic acid (10 to 20%) for 10 to 20 seconds, followed by a 20 to 30 sec of water rinsing.

Drying by gentle air blow

Excessive air blow causing desiccation should be avoided.

Any further contamination with saliva or blood impairs bonding.

SURFACE PREPARATION

POSTCONDITIONING SURFACE PRECONDITIONING SURFACE

P/L ratio recommended by the manufacturer should be followed ( usually 4 :1)PREPARATION OF THE MATERIAL Mixing is usually done on plastic crafted paper pad.

277.bin

Plastic spatula is most commonly used.Powder incorporated rapidly in the liquid.Mixing done for 45 to 60 Seconds

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Mix should be glossy at this time which indicates unreacted polyacid on the surface. This residual acid on the surface is critical for bonding to the tooth.

A dull appearance indicates inadequacy of free acid for bonding.Preproportioned capsule of GIC are also available.

They are used with amalgamators or specialy designed triturators.The preproportioned capsules have nozzles so that the mixed material can directly be injected in the prepared cavity.

Advantages of mechanical mixing are

ConvenienceConsistent control over P/L ratio Elimination of variation associated with hand spatulation.

Cement is placed using a plastic instrument or injected into cavity Cavities are slightly overfilled & surface immediately covered by using plastic matrix at least for 5 minutes.

Excess is trimmed off.

Surface protection is done immediately.

Further finishing procedure if needed should be delayed for at least 24 hrs.PLACEMENT OF RESTORATION & REMOVAL OF EXCESS

FINISHING & POLISHING

PREOPERATIVE VIEW POSTOPERATIVE VIEW

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:Metal reinforced ionomer cements.New fast setting lining cements.Water hardening luting agents.Dual cure system which include:Resin modified GIC.Poly acid modified resin / compomer.Packable GIC.

RECENT ADVANCES

6. Self hardening resin GIC.7. Smart materials / fluoride charged materials.Bioactive GIC.giomers

HIGH VISCOSITY GICDeveloped as an alternative to amalgam.Packable / condensable glass ionomer cements

Composition: Powder: Ca,La,Al fluorosilicate glassLiquid: PA,TA,water and benzoic acid

INDICATIONS: Molar restoration of primary teethIntermediate restorationCore build up materialFor A R T

ADVANTAGES: Packable or condensableImproved wear resistanceEasy to useLow solubilityRapid finishing possibleDecrease moisture sensitivity

DISADVANTAGES: Limited lifeModerately polishableNot esthetic .

LOW VISCOSITY GICAlso called as Flowable GICLow P:L ratio thus increase flow.Use for lining, pit and fisure sealer, endodontic sealer and for sealing hyper sensitive cervical area.Eg fuji lining LC, Ketac endo etc.Fuji lining LCKetac-Endo

The main shortcoming of GIC that limits its use in stress bearing areas is its lack of fracture toughness. To improve upon it metal reinforced GICs were developed. They are mainly of two types:Miracle Mix Cermets METAL MODIFIED GICMiracle mixKetac Silver

Seed & Wilson (1980) invented miracle mix: Spherical silver amalgam alloy+Type II G I C in ratio 7:1Mc lean & Gasser (1985) invented ceremet: Glass powder sintered to metal fillers (

Indications:

Class I cavities in primary teethCore build up materialLining of class II amalgam restorationsRoot caps for teeth under over denturesAs a preventive restoration

Contraindications:

Anterior restorationIn areas of high occlusal loading

Advantages: Ease for placementAdhesion to tooth structure and anticariogenic potentialCrown cutting can be done immediatelyIncreased wear resistance

Disadvantages: Esthetically poorTooth discolorationRough surfaceReduced W.L and S.T

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RESIN MODIFIED GICTo overcome low early strength and moisture sensitivity

Defined as HYBRID CEMENT that sets partly by acid base reaction and partly by polymerisation reaction (Mc Lean)

Materials that are modified by the inclusion of resin, generally to make the them more photo curable (Nicholson)

Powder Ion leachable glass and initiators liquid water, Poly acrylic acid, HEMA (15-25%), methacrylate monomers.

Setting reaction:- Dual cure

- Tricure

PROPERTIES Esthetic Superior than conventional GICFluoride release:

Conventional 440gF after 14 days650 gF after 30 daysRMGIC-1200 gF after 14 days1600 gF after 30 days

Strength: Diametral strength

Conventional G I C: 6.6Mpa RMGIC: 20 Mpa

Compressive strength

Conventional G I C:150MpaRMGIC: 105MpaHardness:Conventional GIC:48KHNRMGIC:40KHNShear bond strength: lesser than conventional GIC (Acc to skinner)Marginal adaptation: poor compare to conventional GICBiocompatibility: Transient rise in Temperature

Advantages Long working time due to photo curingImproved setting characteristicsDecrease sensitivity to water (but not significantly, Journal of Conservative Dentistry, June 2005) Increase early strengthFinishing & polishing can be done immediatelyImproved tensile strength. Better adhesion to composite restoration Increase fluoride release.Repairable.

DisadvantageBiocompatibility is controversial More setting shrinkage leading increase microleakage and poor marginal adaptation

Uses As a luting cement (FUJI PLUS Ketac-cem 3M ESPE, Fuji Cem)

As a liner and bases (Fuji LC)

As a pit and fissure (Vitre Bond)

Core build up material (Fuji I LC)

Retrograde filling material

POLYACID MODIFIED COMPOSITE RESIN Also called as COMPOMERDefined as : material that contain both the essential components of GIC but in an amount insufficient to carry out acid base reaction in dark.They are developed to combine fluoride release of GIC and durability of composite

Composition: one paste system containing ion leach able glass, sodium fluoride, polyacid modified monomer but no water Recently 2 paste or powder liquid system is introduced.Powder: Strontium aluminium flurosilicate glass particles, metal oxides,and intiatorsLiquid:Polymerizable methacrylate/caboxylic acidic monomers multi functional acrylate monomers and water ;

Setting reaction Initially light curing forms resin network around the glass After 2 to 3 month there is water uptake which initiates slow acid base reaction and fluoride release.

Properties Adhesion Micromechanical, absence of water thus no self adhesionFluoride release minimal. Physical properties better than conventional GIC but less than composite.Optical properties superior to conventional GIC.

Uses Pit and fissure sealantRestoration of primary teethLiners and bases Core build up material For class III & V lesions Cervical erosion / abrasion Repair of defective margins in restorationsSealing of root surfaces for over denturesReterograde filling material.

ContraindicationsClass IV carious lesions Large areas of labial surfacesClass II cavities where conventional cavity is preparedLost cusp areasUnder full crown or PFM crowns.

Advantages Ease of use Easy adaptation to the tooth Good esthetics More working time than RM GIC

Commercial ProductsCompoglass FCompoglass FlowPrinciple

Bioactive glassIntroduce by Hench in 1973 Acid dissolution of glass forms calcium and phosphate rich layers The glass can form bioactive bonds with bone cells Better than hydroxyapatite Can grow calcium and phosphate rich layer in presence of calcium and phosphate saturated saliva.They are less abrasive than feldspathic porcelain to opposing teeth

UsesBone cement Retrograde filling material For perforation repairAugmentation of resorbed alveolar ridgeImplant cementationInfra bony pocket correctionBio glass ceramic crown.

Fiber-reinforced Glass Ionomer CementsAl and Sio2 fibers added to glass powder (PRIMM)Diameter of fiber is 2m.

Advantages: Increased wear resistance. Improved handling characteristicsIncreased depth of cureReduction of polymerization shrinkageImproved flexure strength(50Mpa)

GIOMERSTrue hybridization of GIC and composite Combine fluoride release and fluoride recharge of GIC with esthetic easy polishability and strength of compositeTwo typesG- PRG : (Fully pre reacted giomers)S-PRG: (Surface pre reacted giomers)INDICATIONSClass I, II, III, IV, and Class V cavitiesRestoration of cervical erosion and Root caries Laminates and core build upRestoration of primary teeth.Repair of fracture of porcelain and composites

BEAUTIFUL (SHOFU)

F-prg used as dentin bonding agents, pit and fissure sealants & restorative material for cervical abrasionS-prg used insituations like composites*

Advantages Increase wear resistanceIncrease Radiopacity (glass filler)Ideal shade match (improved light diffusion and fluorescence)High and sustained fluoride release and recharge Provide almost complete seal against bacterial microleakage Little mechanical and chemical pulp irritation Inhibit demineralization

Amino-acid modified GICs

- introduced to improve the strength of the glass ionomer so as to make it suitable for restoring high stress sites such as class I and II cavities. - Examples for amino acids used in GICs include:N- acryloyl - glutamic acid (AGA) N -acryloyl - 6- aminocaproic acid (AACA) N- Methacryloyl glutamic acid (MGA)

NEWER ADVANCEMENTS

Many modifications to the inorganic component of glass-ionomer cements have been attempted.

Metals, fibers and other nonreactive fillers have been evaluated in an attempt to improve the mechanical properties of GICs without compromising the handling or biological characteristics.

In most cases, the bonding between the reinforcing agent and the cement matrix has proven challenging.

Additionally, modifications to the chemistry of the basic glass have been attempted to strengthen the cement.

The first attempt to increase the strength of conventional glassionomer cements by addition of reinforcing fillers were reported by Simmons in 1983

he added amalgam alloy powder to GIC powder composition

One of the commercially available products resulting from this innovation was Miracle Mix (MM, GC Corporation, Japan)

due to metalcarboxylate matrix interface failure, the simple addition of amalgam powder did not exhibit promising results

McLean and Gasser fused and sintered amalgam powders to basic glass particles (cermet-ionomer cements)

The resulting cermet particles exhibited strong bonding between the metallic and glass particles.

Cermetionomer cements showed increased resistance to abrasion when compared with glassionomer cements and their flexural strength was also higher. However, their strength is still not enough to replace amalgam restoration for posterior teeth

Kerby et al. prepared stainless-steel glass-ionomer cements by combining atomized stainless-steel powder with an average particle size of 9 mm with a commercially available glass-ionomer powder one hour after curing

the mechanical strengths of stainless steel reinforced glass-ionomers were more than 40% greater than commercially available glass-ionomer cements more than 50% greater in compressive strength and more than 60% greater in diametral tensile strength These values continued to increased after 24 h, resulting in 50% and 100% increases in compressive and tensile strength respectively of stainless steel glass-ionomers compared to commercial controlsstainless steel cements provided the most desirable physical properties that include high compressive and tensile strength, favorable working and setting times and low acid solubilitydisadvantage of the stainless steel GIC is the grayish color which makes it not a suitable choice for anterior tooth restoration

STAINLESS-STEEL GLASS-IONOMER CEMENTS

REACTIVE GLASS FIBERS: FIBER REINFORCED GLASS-IONOMER CEMENTSLohbauer et al. reported that a reactive glass fiber (the composition of the glass fibers was SiO2: 33.3, Al2O3: 16.7, CaO: 14, NaF: 3.3, AlF3: 3.3, Na3AlF6: 16.2%) with 20 vol% of fiber loading (fiber length 254 nm)

had the ability to increase the fracture toughness of glass-ionomer cements

Yli-Urpo et al. added bioactive glass particles (particle size: less than 45 mm), with a composition of: SiO2 53%, Na2O 23%, CaO 20%, and P2O5 4%, into the composition of GIC powder

Bioactive glasses are known to promote healing and incorporate into hard tissue

decreased the compressive strength of the cement on average by 54%.

This phenomenon suggested that BAG particles might be only loosely attached to the glass-ionomer matrix

INCORPORATION OF HYDROXYAPATITE (HA) AND HA/ZrO2 IN GICSLucas et al. in their studies added 0.350 m spherical HA particles to the powder of a capsulated GIC (Fuji IX GP) with a particle size of 0.3200 m HA-ionomers are promising filling dental materials and the incorporation of HA particles into the powder of glass-ionomer cements increased the mechanical properties of the set cementaddition of HA did not impede sustained fluoride release and also maintained long-term bond strength to dentine.

However Gu et al. found that the substitution of GIC glass with crystalline HA did not affect compressive strength significantly. They also found that the substitution of the glassionomer glass with HA did not affect diametral tensile strength.In addition, they reported that the addition of HA in the glassionomer powder composition in higher amounts than had adverse effects on the mechanical properties of the glassionomers.

In a recent study, Moshaverinia et al. synthesized nanohydroxy- and fluoroapatite using an ethanol based solgel technique and incorporated the synthesized nanoparticles into commercial glass-ionomer powder (Fuji II GC).

Compressive, diametral tensile and biaxial flexural strengths of the modified glass-ionomer cements were evaluated. Results of their studies showed that after 24 h and one week of setting, the nanohydroxyapatite/ fluoroapatite added cements exhibited higher compressive strength (177179 MPa), higher diametral tensile strength (1920MPa) higher biaxial flexural strength (2628 MPa) as compared to the control group (160 MPa in CS, 14 Mpa in diametral tensile strength and 18 MPa in biaxial flexural strength).

Gu et al. in their studies added a mixture of HA/ZrO2 (440% by volume) to glassionomer powder (Fuji IX GP) and then measured the mechanical properties of the resulting cement

As a result, the mechanical properties of HA/ZrO2 were significantly improved compared to HA-GICs

The main disadvantage of incorporation of ZrO2/HA, as shown by high magnification SEM, is the propagation of the cracks around the glass and HA/ZrO2 particles rather than through the particles

GICS CONTAINING YBF3 (ytterbium) AND BASO4In the study carried out by Prentice et al., nanoparticles of YbF3(25 nm) and BaSO4 (less than 10 nm) were added to conventional glass-ionomer cement powderThe BaSO4 was incorporated to increase the radiopacity of the cement and the YbF3 was a fluoride source that can modify both setting and working timesaddition of BaSO4 and YbF3 nanoparticles reduced the working time and the initial setting time, However, the effect was reversed at higher concentrations.significantly reduced 24 h compressive and surface hardness of glass-ionomersFinally, they concluded that YbF3 accelerated the glass-ionomer curing reaction, as did low concentrations of BaSO4, but higher amounts of BaSO4 had opposite effects

YTTRIA STABILIZED ZrO2-GICSGu et al. added nano-sized yttrium stabilized ZrO2 (YSZ) powders and Y2O3 stabilized ZrO2 powders to the glass-ionomer cement powder

YSZ containing GICs are promising restorative materials only if the appropriate particle size distribution is used

NIOBIUM SILICATE GICSIn order to investigate the effect of addition of other glass compositions to conventional GIC glasses, Bertolini et al. used the following composition as the powder for glass-ionomer cements: 4.5 SiO2 : 3Al2O3 : xNb2O3 (niobium) 2CaO (0.1 < x < 2.0).

setting time of the cement pastes increased significantly for Nb containing GIC samples

micro hardness and DTS of the experimental glass-ionomer were decreased

ZINC BASED GLASS-IONOMER CEMENTSBoyd et al.84 investigated the effect of incorporation of Zn in the composition of glass-ionomer cements

Mechanical testing results demonstrated that Zn based GIC had approximately one quarter the strength of their aluminium silicate glass counterparts after 30 days of maturation

the flexural strength of these cements was comparable to the flexural strength of conventional GICs

BORIC ACID CONTAINING GLASS-IONOMER CEMENTSPrentice et al., incorporated boric acid (H3BO3) into the glass powder of a glass-ionomer cement in order to evaluate the effect of this acid on the mechanical properties of the glass-ionomer cements

indicated that the incorporation of boric acid was followed by a significant reduction in the compressive strength of the GIC

indicated that the incorporation of boric acid was followed by a significant reduction in the compressive strength of the GIC

SrO ADDED GLASS-IONOMER CEMENTSThe effect of strontium oxide on the mechanical properties of GICs was studied by Deb et al.

an increase in the amount of SrO led to increases in both working and setting times, indicating that SrO retarded the rate of reaction

The compressive strength of SrO modified cement was increased significantly by (05% m/m) SrO addition

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GLASS-IONOMERS CONTAINING SPHERICAL SILICA FILLER (SSF)Tjandrawinata et al. incorporated silica fillers into GIC compositions, and evaluated the various properties of the resulting material, such as 24 h compressive strength, modulus of elasticity, water uptake, and immediate setting shrinkage of conventional glass-ionomer (Fuji II GC).

The result of their study demonstrated that the addition of SSF increased the compressive strength value by 1.1 timesincrease of modulus of elasticity was 1.10 to 1.35 timesDecreased the 24 h water uptake to 8090% and reduced the immediate setting shrinkage to 7079% of the original material.

SIC ADDED GLASS-IONOMER CEMENTSIt has been reported that by adding silicone carbide whiskers containing a coating and followed by silanization, the polymeric matrix was bonded more tightly to the whiskers due to the coating on their surfaces

The results indicated the SiC added GIC exhibited improved transverse strength, enhanced fatigue resistance and improved the long term bond to enamel, while not inhibiting fluoride release and forming a thicker intermediate layer.

The main disadvantage of SiC added GIC is the risk of SiC particles migrating to vital organs since they do not bond to the matrix of GIC and therefore they can be potentially hazardous to human health

the current literature demonstrates that the mechanical properties of the glass-ionomer cements can not be enhanced by merely adding reinforcing particles and fillers such as bioactive glass fillers, spherical silica fillers and SiC. For instance, in the glass-ionomers modified with SiC there are no bonds between the added fillers and the organic/inorganic matrix of the glass-ionomer; therefore, there is a risk of filler migration to vital organs and so this modified GIC is contra-indicated. By incorporation of ceramic fillers such as ZrO2 into GIC powder composition, mechanical properties of conventional GIC can be increased. However, the optimum amount of filler should be added in order not to deteriorate other physical properties of the modified GIC.

For hydroxyapatite modified GICs, the main problem is the poor mechanical properties of the HA itself. However, it has the ability to react with PAA and bond to tooth structure. The addition of stainless steel particles to the composition of glassionomer cements causes an apparent increase in mechanical properties the main disadvantages of these kinds of materials are the grayish-like color of the set cement and also the probability of the toxicity of the released ions from the stainless steel particles. Adding niobium oxide could be a successful method, since they made the same structure as the aluminosilicate glasses. However, niobium oxide containing GICs showed decreased mechanical properties.

Addition of cations like Fe3+(ferrous) and Fe2+(ferric), which have the same charge and polarity as Al3+ and Ca2+, does not deteriorate the aesthetics of the glass-ionomer and is a good way of enhancing the mechanical properties of conventional GICs. These ions should not be toxic for the vital tissues and organs within the human body

By incorporation of reinforcing materials into glass-ionomer cement powders, such as hydroxyapatite and metallic nanofillers, it may be possible to use glass-ionomer cements as the primary material for tooth restoration and as a bone grafting material in stress bearing areas. In order to achieve these goals new powder combinations should be developed with the ability to improve the strength of the inorganic/organic matrix within the glassionomer cements.

CONCLUSIONFor the poor mechanical properties the GIC has good thermal, adhesive and biologic properties. With the current level of intensive research on glass ionomers, the deficiencies that exist seem certain to be eliminated, or at least reduced, resulting in an ever improving range of materials of this type. It is apparent that the whole family of glass ionomers is growing rapidly and areas of application are expanding along with further refinement.

Art And Science Of Operative Dentistry, Sturdevent..5th Edition

Phillips Science of Dental Materials, 11th edition, Anusavice KJ; WB Saunders Company

Nicholson JW, Croll TP. Glass Ionomer Cements in restorative dentistry. Quintessence Int. 1997, 28: 705- 714.

Mount GJ. An atlas of glass ionomer cements. Third edition

REFERENCESMoshaverinia A, Roohpour N A, Winston B, Cheea WL, Schricker SR:

A review of powder modifications in conventional glass-ionomer dentalCements, DOI: 10.1039,2010R.G. Craig Restorative Dental Materials.. 13 Edition

Advances In Glass Ionomer Cements , Davidson And Mjor

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*F-prg used as dentin bonding agents, pit and fissure sealants & restorative material for cervical abrasionS-prg used insituations like composites*

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