he ability to practice mini-mally invasive dentistry relies on techniques and materials that maximize the preserva-tion of tooth structure. Glass ionomer cements, which were first introduced more than three decades ago, have contributed to this practice. Since then, glass ionomers have been developed that offer improved physical strength and esthetics. This has led to their use for non-stress-bearing posterior restorations and for anterior and Class V restorations. Currently, these materials are used for anterior and posterior restorations, sand-wich technique restorations, build-ups, sealants, lining cements and cement bases under restorations, T long-term temporary restorations, luting of indirect restorations and for bonding orthodontic brackets and bands. (Table 1) STRUCTURE OF GLASS IONOMERS Glass ionomers start as ultrafine particles of aluminofluorosilicate glass powder and an aqueous solu-tion of polymeric organic acid (polyalkenoic acid) with distilled water, and resin-modified glass ionomers (RMGI) also contain acrylic resins and other components that result in increased strength. The coef-ficient of thermal expansion of glass ionomers is similar to that of dentin, making the expansion and contrac-tion of the glass ionomer and dentin similar when exposed to thermal stimuli thereby reducing the risk of failure associated with stress created by differing amounts of expansion at the dentin-material interface. Resin-modified glass ionomers (RMGI) have demonstrated low failure rates following thermocycling. 1 On the other hand, a lower cohe-sive bond is found with glass ionomers than with composite resins which increases the risk of cohesive bond fail-ure. This is the rationale for reinforcing glass ionomers for use in indications where cohesive strength is important, such as for restorations. Non-resin modified glass ionomers are currently typically used for sealants and cements – (e.g., in situations where bond strength plays less of a role in success). Resin-modified results in higher Table 1 Glass Ionomer Uses Class I/II restorations, deciduous teeth Crown and Bridge (metal, PFM, high strength ceramic) Class I/II Class V, root semi-permanent Class III surface caries, restorations in restorations cervical permanent (pre)molars erosions Inlays Onlays Liner under amalgam or composite restorations Base under amalgam, composites or porcelain inlays and onlays Glass Ionomer Restoratives Glass Ionomer Cements Core build-up 24 January/February 2013 JAOS
Journal of the American Orthodontic Society January-February 2013: Page 24
