Chapter 13 Glass Ionomer Restoratives
Although glass ionomer restoratives are not highly esthetic, they are considered the material of choice for class V lesions in patients at high risk for caries and erosion lesions. They are also used in deciduous class I and II restorations. Glass ionomers in general are tooth colored but rather opaque in appearance. Esthetically they are inferior to conventional resin composites, but they offer the advantages of providing adhesion and fluoride release. The physical properties of glass ionomers tend to be inferior to those of resin composites, so they cannot be used for large restorations or cavities that will be subjected to occlusal forces.
Glass ionomers were developed in the 1970s by mixing silicate cement with polyacrylic acid. They set via an acid-base chemical reaction. They bond chemically to enamel and dentin. Glass ionomers are supplied as a liquid and powder system.
Because of the poor physical properties of glass ionomers, in the late 1980s resin-modified glass ionomers were introduced. They have an acid-base reaction in addition to free radical polymerization, either light or chemically activated. These refined materials (also called hybrid ionomer cements) offer better physical properties, are easier to finish, and set on demand.
In the early 1990s compomers were developed to mimic resins. These can be used with conventional dental adhesive systems. A liquid water-free polyacid monomer is used in place of the polyacrylic acid. Compomers bond and set like composite systems. Initially they release fluoride but that diminishes with time. Compomers are fairly popular in pediatric cases. In the late 1990s metal-reinforced glass ionomers were introduced for use as core buildups. These contain a silver alloy admix.
Although the caries-inhibiting effect of glass ionomers has been established, their clinical effectiveness has been questioned because of their relatively short clinical durability. Glass ionomers can recharge any lost fluoride (i.e., add fluoride back into the restorations for subsequent release) by exposing the surfaces to fluoride ion sources such as fluoride-containing toothpastes, fluoride mouthrinses, or topical fluorides. This temporarily boosts the fluoride concentration, but unfortunately the boosted levels are not high enough for even a short time to be considered clinically efficacious as an anti-caries therapy.
Glass ionomers are useful for posterior class II restorations, class II restorations prepared using the open sandwich technique (placed in the proximal box of a preparation at the cementum and dentin interface), and carious or noncarious class V restorations. They also serve as pit and fissure sealants and in atraumatic restorative technique (ART) restorations.
Conventional glass ionomers offer many biotherapeutic advantages (Table 13-1). They provide long term release of fluoride ions, ability to bond to tooth structure and are very biocompatible. Because they posses a coefficient of thermal expansion similar to tooth structure, they are able to provide excellent marginal seal around the preparation. They have adequate strength and release fluoride. These materials are not very expensive.