Glass ionomer cement – Building upon the polycarboxylates, researchers developed the glass ionomers in the mid-1970s. The glass ionomer cement liberate large amounts of fluoride ions, which have been demonstrated to increase resistance to recurrent decay.
Use of glass ionomer cement as Luting Cement
Because of their cariostatic property, glass ionomer cement have become highly desirable as luting cements for fixed restorations.
• The powder-to-liquid ratio is very critical when measuring and mixing. Altering that ratio will affect the physical characteristics as well as the bond strength.
• Glass ionomers are extremely hydrophilic (having a strong attraction to water) in nature and will absorb moisture freely.
• Glass ionomers are very soluble in water when setting. The area being treated must be kept dry while the cement is setting.
• Overfilling of the crown with glass ionomer mix will lead to excessive hydraulic pressures upon seating.
These problems compound one another, but they can be avoided by carefully following the manufacturer’s instructions. Precapsulated versions ensure that proper measurement of powder and liquid are maintained. glass ionomer cement is among the most popular luting cements today.
Use of glass ionomer cement as Filling Material
These self-curing glass ionomer cements undergo a two-stage set. The first stage occurs within the initial 5 minutes. The second occurs over about 24 hours. Although the material appears hard and set after 5 minutes, the final hardness is not achieved for 24 hours. Self-cure glass ionomers, when used as restorative materials, therefore require an external coating of varnish or bonding agent to protect the material during that 24 hour cure to final set.
They are generally used in restorations not involved with stress. They are particularly useful for Class V cervical erosions and dental decay on root surfaces. Because of the significant release of fluoride (which helps to protect against caries), glass ionomer cement are also very suitable for use in children who are Cariogenic (prone to having caries). Available in various shades, they are moderately esthetic. Self-cure glass ionomer cements are available as precapsulated or powder/liquid products. They are also available as light cured formation.
GLASS-IONOMER-SILVER ALLOY CEMENT
Recently another popular versions of glass ionomer cement filling materials that incorporate silver into the cement base, has been introduced in the field of restorative dentistry. These products can be used for crown and bridge core buildups or as a temporary or semi-permanent posterior restorative material, especially in cariogenically prone patients.
They are available in precapsulated and powder/liquid formulations. Mixing Technique for Powder/Liquid glass ionomer cement: Follow these steps while mixing powder and liquid product:
1. Fluff the powder and measure with the supplied scoop onto the mixing pad.
2. Dispense the liquid drops by inverting the bottle to the vertical position.
3. Mix to the desired consistency in 15 to 20 seconds.
If using precapsulated products, do the following steps:
1. Tap the capsule to make sure that the powder is not clumped.
2. Activate the capsule by twisting it until it is tight or by using the manufacturer’s supplied applicator.
3. Triturate in an amalgamator (triturator) at high speed for approximately 10 seconds.
4, Place the material into the cavity preparation with the applicator or a placement instrument, filling the entire preparation.
5. Once set (approximately 10 minutes), carefully finish (shape and make smooth) the glass ionomer cement with diamonds, finishing burs, or disks.
6. Apply a protective coating of a glass ionomer varnish over the completed restoration. This coating is necessary to protect the glass ionomer from moisture until the final set is achieved.
Use of glass ionomer cement as a Cavity Liner or Base.
The combination of excellent cariostatic and themial insulative properties and bonding to tooth structure makes glass ionomer cement ideal for use as a base or liner under all types of restorative materials.