ITS ALL ABOUT G.I.C (GLASS IONOMER CEMENT)

Glass Ionomer cements: a hybrid of dental silicate and polycarboxylate cements. use aluminosilicate powder from silicates and polyacrylic acid liquid of polycarboxylates.Invention reported by Wilson and Kent, 1971

Fluorides act as ceramic fluxes: Lower the fusion temperature Improves the working characteristics Increases strength of the cement Enhances translucency in moderate amounts Contributes to the therapeutic valueThe powder is calcium-fluoro-alumino-silicate glass (SiO2 -Al2O3 -CaF2 -AlPO4 Na3 Al F6) referred to as ion leachable glass.

strength increases with alumina content but at the expense of translucency. Al2O3 / SiO2 ratio should to be 1:2 or more by mass for cement formation. AlPO4: improves translucency adds bulk to the cement

Finer the particle size faster the setting reaction

Itaconic acid: Promotes reactivity between glass and liquid Prevents gelation of liquid, which can result from hydrogen bonding between 2 polyacrylic acid chains.Poly Maleic acid: Stronger acid than polyacrylic acid Causes the cement to harden and lose its moisture sensitivity faster This is because it contains more carboxyl groups, which leads to more rapid polycarboxylate cross-linking. Water: Reaction medium Hydrates the reaction products (metal polyalkenoate salts and silica gel)

Tartaric acid: A reaction controlling additive Extends the working time and promotes a snap set strengthens and hardens the cement Improves the handling characteristics of the cement Called as the fourth component

STAGES IN SETTING REACTION (Based on the work of Crisp and Wilson 1972-1974) 1. Decomposition: of glass and release of cement forming metal ions (A13+ and Ca2+)2. Migration: of these metal ions into the aqueous phase of the cement. 3. Gelation: of the polyacid by metal ions leading to set. 4. Post set hardening: when metal ions become increasingly bound to the polyacid chain. (continues for 24 hrs) 5. Further Slow Maturation: takes place even after 24 hrs. Translucency develops further as does resistance of desiccation and acid attack.

GELATION AND VULNERABILITY TO WATER

Precipitation of Calcium polyacrylate initially predominates in the mixture but the hardening process is derived from the slower formation of aluminium polyacrylate. Not All the carboxyl groups of poly (acrylic acid) are converted to carboxylate groups Chain entanglement, weak ionic cross-linking and hydrogen bonds are involved in matrix formation

HARDENING AND SLOW MATURATION continues for about 24 hours, accompanied by a slight expansion under conditions of high humidityFurther changes continue to take place for atleast a year or more. Translucency improves and the cement becomes resistant to desiccation. Strength increases for atleast a year becomes rigid as it ages and the ability to absorb lost water decreases Increase in cross-linking result from the slow replacement of residual carboxyl hydrogen ions by metal ions of aluminium over calcium in the matrix.

CEMENT STRUCTURE cored filler is bound together by a hydrogel of calcium and aluminium polyacrylates that contains fluorine as fluoroaluminium polyacrylate. Filler particles contain a glassy core pitted by a siliceous hydrogel.

ROLE OF WATER reaction medium into which the cement forming cations are leached and transported to react with poly acid to form a matrix hydrates siliceous hydrogel and metal polyacrylate salts formed. Water can be of two forms: 1. Loosely bound water Readily removed by Dessication 2.Tightly bound water- cannot be removed and is associated with the hydration shell of the cation- polyacryate bond, particularly that of aluminium and some silica gel water.

With aging, tightly bound water increases, increasing the strength, modulus of elasticity and decreasing the plasticity

Cement is stable in an atmosphere of 80% relative humidity High humidityabsorbs waterhygroscopic expansion Dry conditionsloses watershrinking and crazing Loss of water also retards cement formation.

Factors affecting the rate or setting 1. Glass composition:Higher Alumina Silica ratio, faster set and shorter working time.

2. Particle Size: finer the powder, faster the set. 3. Addition of Tartaric Acid:Sharpens set without shortening the working time. 4. Relative proportions of the constituents: Greater the proportion of glass and lower the proportion of water, the faster the set. 5. Temperature of mixing: Higher the temperature faster the set. Setting time: Type I: 7 minutes Type II: 4-5 minutes

MODIFICATIONS Modifications in the powder: Dried Poly Acrylic Acid (Anhydrous GIC) Silver-Tin Alloy (Miracle Mix) Silver-Palladium/ Titanium (Cermet cement) BisGMA, TEGDMA, HEMA (Light cure/Dual cure GIC) Modifications in the liquid: Only water and tartaric acid (Anhydrous GIC) HEMA (Light cure components)

Water-Mixed GICs: incorporation of freeze-dried or vacuum-dried polyacids into the powder. These cements are called "water mixed" or "water hardened." to maximize shelf life (because there is then no possibility of gelation occurring) to reduce viscosity (which makes the cement easier to handle). The liquid component of the water-mixed cements is distilled water or an aqueous solution of tartaric acid. E.g. Chelon-Fil (3M ESPE) nonencapsulated forms of Ketac-Cem (3M ESPE) Ketac-Bond (3M ESPE).

METAL MODIFIED GLASS IONOMERSMiracle Mix: Introduced by Simmons in 1983 Prepared by incorporation of silver-tin alloy into the GI cement powder Glass is brittle and addition of silver was expected to improve the toughness of the cement by silver acting as stress absorber. Most properties remained without improvement Gave a gray or blackish color to the cement

Glass Cermets

Introduced by McLean and Gasser in 1985 Glass and metal powders were sintered at high temperature. This could be made to react with polyacrylic acids to form improved GIC

Improved wear resistance and flexural strength at the same time maintained esthetics Titanium was also added (5%) as whitening agent.

Less fluoride is released from the cermet cement than for type II GIC, since a portion of original glass particle is metal coated. The admixed cement release more fluoride than type II GIC since metal filler particles are not bonded to the cement matrix and thus, create pathways for fluid exchange, increasing the surface area available for leaching of fluoride. Metal-reinforced GIC should not be used whenever the cement constitutes greater than 40% of the total core build up.

Easily mixable glass ionomer cements:Capsules Paste Paste dispensing system powder liquid system

RESIN MODIFIED GLASS IONOMER CEMENT

Designed to produce favorable physical properties similar to those of resin composites while retaining the basic features of conventional GIC.

Can be defined as a material that undergoes both polymerization reaction and acid-base reaction.

The light-curing resin-modified glass ionomer (dual cure) systems have been developed by adding polymerizable functional methacrylate groups with a photoinitiator to the formulation. Such materials undergo both an acid- base ionomer reaction curing by photo-initiation of methacrylate carbon double bonds. Some systems have also incorporated a chemical curing tertiary amine-peroxide reaction to polymerize the methacrylate double bonds along with the photoinitiation and acid-base ionic reaction. These materials are known as tri-cure glass ionomer cements.

Composition: cement liquid is polycarboxylic acid, water, and HEMA (up to 18-20%) may also contain a small amount of cross- linking material. E.g. Fuji II LC (GC America) Vitremer (3M ESPE) Photac-Fil (3M ESPE) The fluoride-release pattern is same as for conventional GIC; the majority of fluoride is released in the first few days to weeks and then drops to a low level that is released for a long time wear resistance is significantly less than that of traditional GICs, probably because of differences in their matrix formation.

Water sensitivity is reduced by incorporating photo polymerization, which promotes faster setting, into the setting reaction. The chemical setting reaction continues even though the

setting reaction initiated by light has been completed.

POLYACID MODIFIED COMPOSITE RESINS (COMPOMERS) Combination of composites (comp) and glass ionomers (omers). Compomer is a one-paste material consisting of fillers and a matrix that is similar to that of composite resin.

contains fluoroaluminosilicate glass powder as filler to release fluoride. Contains dimethacrylate monomer and carboxylic groups along with ion leachable glass. There is no water in the composition

Glass particles are partially silanated to ensure some bonding with the matrix. contains strontium or some other metal to make the material radiopaque E.g. Dyract AD Compoglass F

GIOMERS A recent addition to the continuum of hybrid materials is a class of anhydrous resin-based restoratives that utilizes prereacted glass ionomer technology (PRG). E.g. Beautiful (Shofu); Reactmer paste (Shofu). Known as giomers in Japanese market, these materials incorporate fillers that are produced from the complete or partial reaction of ion-leachable glasses with polyalkenoic acid.

giomers may contiain either fully prereacted (F-PRG) or surface prereacted (S-PRG) fillers as part of the total filler composition.

Unlike compomers, immediate fluoride release may occur from the PRG fillers without the need for in-situ acid-base reaction via water sorption.

PROPERTIES OF CONVENTIONAL GIC I Physical Properties moderately hard, brittle material with high compressive strength but low fracture toughness, flexure strength and wear resistance. Therefore should not be used in stress bearing areas.

II Sensitivity to Moisture

Very sensitive to moisture, especially during initial setting phase. Water absorption leads to weak cement and over drying leads to cracks in the cement.

solubility is 0.4%

III Biocompatibility GIC are relatively biocompatible. The pulpal response may be classified as mild, because polyacids are weak acids. The water settable cements show higher acidity.

As the reaction proceeds, the pH increases from initial values near 1 to a range of 4-5. Near completion, the final pH reaches 6.7 7

If RDT is less than 0.5 mm, protect dentin surfaces from direct contact with unset GIC materials by using calcium hydroxide.

If cement comes in direct contact with fluid-filled dentinal tubules: High ionic concentrations in unset GI caused dentinal fluid to rapidly diffuse outward into the cement, causing sensitivity/pain. Hydrogen ions may move into tubules towards the pulp causing irritation.

IV Adhesion A full 80% of ultimate bond strength develops within first 15 minutes following placement. Macroshear bond strength to enamel/dentin ranges from 6-12 Mpa. The bond density per unit area of retentive interface is higher for mechanical binding than for chemical bonding. Chemical bonding is due to the reaction between the carboxyl group of polyacids and calcium in the apatite of enamel and dentin. Bond to enamel is higher than that to dentin due to greater inorganic content of enamel and its greater homogeneity.

V Esthetics inferior to silicates and composites lack translucency have a rough surface texture.

VI Fluoride Release

ANTICARIOGENECITY

Due to F release Due to its adhesive effect, they have the ability to reduce infiltration of oral fluids at cement-tooth interface, thereby preventing secondary caries.

MANIPULATION

1. 2. 3. 4.

Conditioning of tooth surface. Proper manipulation Protection of cement during setting Finishing.

Preparation of the tooth surface:The smear layer present after cavity preparation tends to block off the tooth surface, and so should be removed to achieve adhesive bonding. This is achieved by: i) Pumice wash ii) Polyacrylic acid solution.

Apply 10% polyacrylic acid for 10 to 15 seconds. rinse with water for 30 seconds. Very deep areas of preparation should be protected by a dab of calcium hydroxide. After conditioning and rinsing, the surface is dried but not unduly desiccated. It should be kept free of contamination with saliva or blood, as these will interfere with bonding.

Proportioning and Mixing:

Powder/liquid ratio is 3:1 by weight

Hand Mixing:The powder is divided into two equal increments. The first increment is incorporated into the liquid rapidly to produce a homogenous milky consistency. The remainder of the powder is then added. The mixing is done with an agate or plastic spatula in a folding method. Mixing time: 45 seconds. The mixed cement is immediately packed into the cavity with a plastic instrument.

Mechanical Mixing: GIC supplied in capsule containing pre-proportioned powder and liquid is mixed in an amalgamator at a very high speed. The capsule contains a nozzle, and so the mix can be injected directly into the cavity.

Protection of Cement During Setting: immediately after placement of the material into the cavity, a preshaped matrix is applied to: Protect the cement from the environment during the initial set Provide maximum contour so that minimal finishing is required.The matrix is removed after five minutes. Immediately after removal the cement surface is again protected with: A special varnish supplied by manufacturer, OR An unfilled light cured resin bonding agent, OR Cocoa butter.

Finishing:Excess material is trimmed from the margins. Hand instruments are preferred to rotary tools to avoid ditching. Further finishing if required is done after 24 hours. Before dismissing the patient, the restoration is again coated with the protective agent, since the trimmed areas expose the cement. Failure to protect the cement surface, results in a chalky or crazed surface.

Precautions: 1. mix should have a glossy surface. This indicates presence of residual polyacid which ensures adhesive bonding to the tooth. The mix with the dull surface should be discarded as it indicates prolong mixing and reduces the adhesion. 2. If the liquid contains polyacids, it should not be placed in a refrigerator as it becomes very viscous. 3. The restorations must be protected from contact with air at all times, even when other dental procedures are to be carried out. The glass slab should not be cooled below dew point, as moisture may condense on the slab and change the acid-water balance.

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APPLICATIONS IN ENDODONTICS Glass-ionomer cements have been used in endodontics for: sealing root canals orthogradely and retrogradely sealing and restoring the pulp chamber repairing perforations rarely, for treating vertically fractured teeth.