Glass ionomer cement

INTRODUCTION

Glass ionomer cement is a tooth coloured material, introduced by Wilson & Kent in 1972.

-a.k.a glass polyalkenoate

Silicate Glass Powder

Polyacrylic acid

GIC

CLASSIFICATION

Type I. For lutingType II. For restoration

Type II.1 Restorative esthetic Type II.2 Restorative reinforced

Type III. For liner & basesType IV. Fissure & sealentType V. As Orthodontic cementType VI. For core build up

COMPOSITION

Powder:Acid soluble calcium fluroalumino

silicate glass.Silica - 41.9%Alumina - 28.6%Aluminum fluoride - 1.6%Calcium fluoride - 15.7%Sodium fluoride - 9.3%Aluminum phosphate - 3.8%Fluoride portion act as ceramic flux.Strontium, barium or zinc oxide

provide radio opacity.

Liquid:1.Polyacrylic acid in the form co-

polymer with itaconic acid & maleic acid .

2.Tartaric acid: improves handling characteristic

& increase working time.3.Water : Medium of reaction &

hydrates the reaction products

SETTING REACTION

When the powder & liquid are mixed, surface of glass particles are attacked by acid. Then Ca, Al, sodium, & fluoride ions are leached into aqueous medium.

Calcium poly salts are formed first, then followed by aluminum poly salts which cross link with poly anion chain.

Set cement consist of unreacted powder particle surrounded by silica gel in amorphous matrix of hydrated calcium & aluminum poly salts.

Calcium poly salts are responsible for initial set.

Aluminum poly salts form the dominant phase.

Water plays an important role in structure of cement.

After hardening, fresh cement is extremely prone to the cracking & crazing, due to drying of loosely bound water .

Hence these cements must be protected by application of varnish.

SETTING TIME

Type I 4 - 5 minutes

Type II 7 minutes

PROPERTIES

Handling characteristics: Previous versions of GIC had problems

with inappropriate working and setting time. Tartaric acid inclusion resulted in: ▪ Tartaric acid reacting with calcium as it was

released which extends working time to reasonable values

▪ Enhances rate of formation of aluminum polyacrylate crosslinks which speeds up setting.

Solubility and disintegration:

Initial solubility is high due to leaching of

intermediate products.

The complete setting reaction takes

place in 24 hrs, cement should be

protected from saliva during this period.

Adhesion: Glass ionomer cement bonds chemically

to the tooth structure. Bonding is due to reaction occur

between carboxyl group of poly acid & calcium of hydroxyl apatite.

Bonding with enamel is higher than that of dentin, due to greater inorganic content.

Esthetics: GIC is tooth coloured material &

available in different shades. Inferior to composites. They lack translucency & rough

surface texture. Potential for discolouration &

staining.

Biocompatibility: Pulpal response to glass ionomer cement is favorable.

Pulpal response is mild due to ▪ High buffering capacity of hydroxy apatite.

▪ Large molecular weight of the polyacrylic acid , which prevents entry into dentinal tubules

Anticariogenic effect: Fluoride is released from glass

ionomer at the time of mixing & lies with in matrix. Fluoride can be released out without affecting the physical properties of cement.

Initial release is high. But declines after 3 months.After this, fluoride release continuous for a long period.

Fluoride can also be taken up into the cement during topical fluoride treatment and released again ,thus GIC act as fluoride reservoir.

Strength: Compressive strength - 150 mpa Tensile strength - 6.6 mpa. Hardness - 49 KHN.

ADVANTAGES:

♣ Inherent adhesion to the tooth surface.

♣ Good marginal seal.

♣ Anticariogenic property.

♣ Biocompatibilty♣ Minimal cavity

preparation required.

DISADVANTAGES:

♦ Low fracture resistance.

♦ Low wear resistance.

♦ Water sensitive during setting phase .

♦ Less esthetic compared to composite.

USES

1. Anterior esthetic restoration material for class III & V restorations.

2. For luting.3. For core build up.4. For eroded area .5. For atraumatic restorative

treatment.6. As an orthodontic bracket adhesive.7. As restoration for deciduous teeth.8. Used in lamination/ Sandwich

technique.

CLINICAL USE

For luting: Advantages:

▪ Fluoride release▪ Low film thickness▪ Kind to pulp▪ Bond to tooth structure

Their use decreased after hybrid ionomers and resin cements were introduced since they are stronger

As restorative material: used in non-stress bearing areas:

▪ Root caries▪ Occlusal lesions in primary teeth▪ Temporary restorations▪ Cervical cavities (abrasion and erosion

lesions)▪ Anterior class III when color matching

is not an issue

As liners and bases: used to protect the pulp from:

▪ Temperature changes▪ Chemicals from other restorative materials▪ Acid etchants

Liners have lower powder: liquid ratio and weak.

GIC bases are used to rebuild missing tooth structure, stronger than liners and have a higher powder: liquid ratio

As pits and fissure sealants: The use of GICs as sealants have been

suggested due to:▪ Fluoride release.▪ Adhesion to moist tooth structure

Disadvantages:▪ Inability to fully penetrate fissures▪ Brittleness▪ Low wear resistance

Core build up materials: cermet GICs are usually used for

this purpose. They are used:▪ In locations were esthetics are not

important▪ To replace missing tooth structure

where the permanent restoration is crown.

SANDWICH TECHNIQUE

Devolped by Mclean,To combine the beneficial properties

of GIC & composite.

An effective technique for both anterior and posterior resin based restorations.

For pulpal protection from the acid-etch technique.

And as a mechanism for sealing the cavity in the absence of good dentin adhesion available with the materials of the time.

Clinical steps: After cavity preparation, condition the cavity

to develop good adhesion with GIC. Place Type III GIC into prepared cavity. After setting, etch the enamel & GIC with

orthophosphoric acid for 15 seconds. This will improve micromechanical bond to composite resin.

Apply a thin layer of low viscosity enamel bonding agent & finally place the composite resin over GIC & light cure it.

Advantages: Polymerisation shrinkage is less,due to

reduced bulk of composite. Favorable pulpal response. Chemical bond to the tooth and

composite increasing retention form. Provides better seal when used at

nonenamel margins.

Advantages: Anticariogenic property Potential for recurrent caries low. Decreased microleakage and gap

formation. Better strength, finishing, esthetics of

overlying composite resin.

Advantages for the flowable composite:

(as a liner under a composite) Acts as a shock absorber, distributing

stresses applied to the more rigid composite.

Reduce some of the negative effects of polymerization shrinkage.

TWO TECHNIQUES:1. Closed Technique- The traditional technique.-Involves the placement of GIC at the base of the proximal box so as it falls just short of the external cavo surface. After setting, the GIC is etched with phosphoric acid and dentin bonding agent is applied before placing composite resin into the proximal box and occlusal surface.

2. Open Technique- Involves the placement of GIC into the base of a proximal cavity and filling the preparation with glass ionomer upto the DEJ. The last portion of the restoration is placed with composite resin to provide wear resistance and esthetics on the occlusal surface.- For clinical situations where a portion of the restoration would have a dentin only margin (as in a deep class II or a class V on a root surface).

- Advantage of Open Technique:a. The large area of GIC available for buffering any changes in acidic pH.

-Disadvantage of Open Technique:b. Over time the GIC succumbs to acid breakdown over the surface resulting in food packing and recurrent caries within glass ionomer.

Factors necessary for successful tooth restoration: Removal of infected dentin and enamel

completely Treating the enamel and dentin

appropriately with bonding materials. Manipulating properly the to-be-bonded

restorative material. Contouring the restoration to provide

proper form and function.

Advantages: Polymerisation shrinkage is less,due to

reduced bulk of composite. Favorable pulpal response. Chemical bond to the tooth. Anticariogenic property Better strength, finishing, esthetics of

overlying composite resin.

GIC MODIFICATIONS

1. Water settable glass ionomer cement:

Liquid is delivered in a freeze dried form, which is incorporated into the powder.

Liquid used is clean water.

Advantages: low viscosity in the early mixing stages improved shelf Improved strength

2. Resin modified glass ionomer cement:

Resin composite + conventional GIC Powder component consist of ion

leachable fluroalumino silicate glass particles & initator for light curing.

Liquid component consist of water & poly acrylic acid with methacrylate & hydroxyl ethyl methacrylate monomer.

Advantages: greater working time command set on application of visible

light good adaptation and adhesion acceptable fluoride release aesthetics similar to those of composites superior strength characteristics

Disadvantages: setting shrinkage limited depth of cure especially with

more opaque lining cements.

3. Metal modified glass ionomer cement: Glass ionomer have been modified by addition

of filler particles to improve strength , fracture toughness & resistance to wear.

Silver alloy mix / miracle mix:- This is made by mixing of spherical silver

amalgam alloy powder with glass ionomer powder.

Cermet: Bonding of silver particles to glass ionomer

particles by fusion through high temperature sintering.

Cermets Grey in color Greater value of compressive strength

and fatigue limit than conventional glass ionomers

Flexural strength and resistance to abrasive wear appear no better than values recorded for conventional GIC

Rapid setting improved erosion resistance

Lower Fl release

4. GiomerIt is basically a modified Glass

Ionomer. It is a hybrid of Glass Ionomer and

Composite.The GIOMER concept is based on the

novel PRG (Pre-Reacted Glass Ionomer) technology, where special PRG fillers are included in the resin matrix which differs it from Compomer making it possess both properties of Composite and Glass Ionomer.

PRG technology is used in production of two types of fillers. S-PRG(Surface Pre-reacted GI) eg.

Beautiful by Shofu F-PRG(Full Pre-reacted GI) eg. Reactimer

by shofu

Properties Fluoride release Esthetics (shade conformity) Ease in Polishing Strength (resistance to wear) High radiopacity Anti-Plaque Effect Biocompatibility Long term clinical stability

Composition Bisphenol A Glycidyl Dimethacrylate TEGDMA Inorganic Glass Filler Aluminuoxide Silica PRG filler DL-camphorquinone

Indications Diastema Closure Discoloration Non-Carious Defect(attrition/ abrasion/

surface defects Carious Defect Fracture Malformation Faulty and Old Restoration

Diastema closure

Discoloration

Non-Carious Defect(attrition/ abrasion/ surface defects

Carious defect

Fracture

Malformation

Faulty and old restoration

Compomer These are recently introduced products

marketed as a new class of dental materials.

These materials are said to provide the combined benefits of composites (the “comp” in their name) and glass ionomers (“omer”).

These materials have two main constituents: dimethacrylate monomer(s) with two

carboxylic groups present in their structure and

filler that is similar to the ion-leachable glass present in GICs.

The ratio of carboxylic groups to backbone carbon atoms is approximately 1:8.

There is no water in the composition of these materials, and the ion-leachable glass is partially silanized to ensure some bonding with the matrix. These materials set via a free radical polymerization reaction, do not have the ability to bond to hard tooth tissues, and have significantly lower levels of fluoride release than GICs.

Although low, the level of fluoride release has been reported to last at least 300 days.

They do not set via an acid-base reaction and do not bond to hard-tooth tissues, they cannot and should not be classified with GICs.

Properties Fluoride release, Radiopaque, Quick cure time and Good handling characteristics (no slumping, easy

to shape/polish, no sticking) Can be light-cure or self-cure Packaging can be unit dose (capsule) or multi-

dose (syringe) Curing time: 10-20 secs (depending on brand) Esthetics

Indications Deciduous teeth Cervical defects

Disadvantages Lower flexural modulus of elasticity, Compressive strength, Flexural strength, Fracture toughness and hardness, Higher wear rates

References

Davidson, C. (2009) Advances in glass-ionomer cements. Journal of Minimum Intervention Dentistry.

Forsten L. Fluoride release of glass ionomers. J Esthet Dent 1994; 6:216-22.

Forsten L. Resin-modified glass ionomer cements: fluoride release and uptake. Acta Odontol Scand 1995; 53:222-5.

McCabe, J. and Walls, A. Applied Dental Materials 9th edition Chap.24 pp.245-256

Millar BJ, Abiden F, Nicholson JW. In vitro caries inhibition by polyacid-modified composite resins (‘compomers’). J Dent 1998; 26:133-6.

Nagaraja Upadhya P and Kishore G. (2005) Glass Ionomer Cement – The Different Generations. Trends Biomater. Artif. Organs, Vol 18 (2)

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