Glass ionomer cement (GIC) is available as a powder and liquid which are mixed together on a waxed mixing pad, or as a capsule which is mixed in an amalgamator machine. The constituents of glass Ionomer are aluminosilicates (which is a glass like mixture) and polyacrylic or polymaleic acid (usually a liquid), which is sometimes dehydrated and added to the powder, allowing the powder to be mixed with water instead.
Once caries have been removed from a tooth a lining of calcium hydroxide may be placed to protect the pulp of the tooth, this is only necessary in deep cavities, otherwise glass ionomer is placed directly into the cavity using non-stick plastic instruments or by use of an injecting gun. The filling is shaped by using either a cellulose matrix strip or by using a specifically shaped buccal matrix, depending on the surface of the tooth involved. Glass ionomer takes several hours to set fully and to avoid water loss or dehydration, it is coated with a layer of waterproof varnish after it has been placed and trimmed to the correct shape and height. The most modern glass ionomer products are light cured which allows the material to be fully set in surgery and also reduces the risk of failure as moisture control is extremely important when using non light cured versions of this material.
Although glass Ionomer is available in a small variety of shades it is less aesthetically pleasing than composites are, as it is less translucent and doesn’t polish as well, but it is considerably better than amalgam in this respect.
Glass ionomer bonds to cairies free, dentine, enamel and cementum without the need for acid etching the tooth, and consequently requires very little cavity preparation, it also leaches fluoride over time and so prevents recurrence of decay in and around the cavity. Therefore there are two main uses for glass Ionomer as a filling material, and this is in class V cavities or in deciduous teeth.
Due to the unretentive nature of cervical cavities and the tooth surfaces which may be involved glass ionomer offers an ideal solution. As most people don’t show the cervical margins of anterior teeth when talking or smiling the appearance of the filling material is not priority this is also the case in posterior cervical restorations. Although glass ionomer is less strong than amalgam and is unlikely to withstand the forces of mastication over a long period of time it is usually strong enough to use in teeth which will be exfoliated in the future, and as it requires little cavity preparation is ideal for placement in deciduous carious teeth.
In comparison to many filling materials, glass ionomer is quick and fairly simple to use, enabling cairies to be treated well with little use of valuable surgery time.