essay 22 - Glass ionomer cements - classification, types, composition, properties, indications, working techniques

what is a glass ionomer cement (GICs)?

• ion cross linked polymer matrixes surrounding glass-reinforcing filler particles. They are hydrophilic, fluoride releasing materials used in restorative dentistry

classifications of glass ionomer cements according to Sturdevant

• Type I = Luting cements

• Types II = Restorative cements

• Type III - Liners/bases

Types of glass ionomer cements

1. Conventional glass ionomer (GIC)

• found in the form of powder and liquid systems and must be hand mixed with a spatula

• May also be found in a encapsulated form that is mixed by trituration

• self cured

• most inferior

2. Resin modified glass ionomer (RMGIC or RMGI)

• glass ionomers to which resin has been added

• can be light or auto cured

• easier to use, stronger, more aesthetic and better wear resistance than conventional GIC

• most appropriate for liners, bases and luting agents

3. Compomers (polyacid modified composites)

• composites to which some glass ionomer components have been added

• primarily light cured and very easy to use

• Have a superior properties to GIC and RMGI, but inferior to composites

Composition of Conventional Glass Ionomer (GIC)

• powder (calcium alumino-fluorosilicate glass) and liquid (polyacrylic acid)

• Setting: acid-base reaction → forms a salt matrix (calcium and aluminium polycarboxylate)

Composition of resin modified glass ionomers (RMGIC or RMGI)

• calcium alumino-fluorosilicate glass and polyacrylic acid + water soluble resin monomers (e.g HEMA)

• acid base reaction (like GIC) and light activated free radical polymerisation (from the resin component)

Composition of compomers (polyacid modified composites)

• resin matrix (like composites) with a single component paste + acidic monomers + alumino-fluorosilicate glass

• purely light cured polymerisation

properties of glass ionomer cements

• fluoride release (initial burst, then slows)

• chemical adhesion to tooth structure via chelation

• Biocompatibility improves as pH rises from -1 to -7 over time

• modest mechanical strength (lower than composites)

• hydrophilic nature, water sensitive during early setting

• recharging possible with fluoride exposure

• low wear resistance (especially conventional types

indications for glass ionomer cements

• class V restorations, especially in high caries risk patients

• restoration of root surface caries, or low stress areas

• paediatric use (class I/II in primary teeth)

• liners, bases and luting agents

• slot restorations in non-aesthetic class II/III cervical areas

working technique of glass ionomer cements

1. Tooth prep

• use mild cavity preparation (butt joint, no bevel)

• apply calcium hydroxide liner if RDT (remaining dentin thickness) <0.5mm

2. Surface conditioning

• optional mild etch with 10% polyacrylic acid for 20 sec

• rinse and leave surface moist (not wet)

3. Mixing and insertion

• GIC: hand mix powder and liquid (30s) or use encapsulated systems. Place in slight excess, shape quickly and apply bonding resin to prevent dehydration and cracking

• RMGI: encapsulated systems. Place into cavity and shape, light cure for minimum 40 seconds

• Compomers: always used a bonding agent, place single component paste and sculpt as you would composite, light cure

4. Finishing

• conventional GIC: wait 24 hrs

• RMGI and compomers: finish immediately

• Used hand instruments, fine diamonds with lubricant or polishing paste