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Previous reports have shown a release of fluoride from glass-ionomer cement (GIC) restorations into the oral fluids. Fluoride in the ambient fluids has a caries-preventive effect by enhancing remineralization and inhibiting demineralization of the dental hard tissues. Therefore, the current investigation was undertaken to determine whether GIC fillings could contribute to the remineralization of caries lesions in dentin. Small circular preparations were made in disks of dentin which had incipient caries-like lesions in the remaining tissue. The preparations were filled with amalgam or composite materials (as controls) or with GIC. The specimens thus contained a restoration close to a dentinal caries-like lesion. The specimens were placed contralaterally in the buccal surfaces of removable partial dentures and were worn intra-orally by volunteers for a 12-week experimental period, after which the specimens were sectioned and analyzed by microradiography. All specimens with GIC restorations exhibited hypermineralization in the tissue bordering the filling and in the wall of the preparation which had been in contact with the restoration. The (caries-like) lesions were remineralized, even under conditions of heavy plaque formation. In contrast, specimens with amalgam or composite restorations showed further extensive demineralization. This study demonstrates a significant remineralization potential exerted by the fluoride-releasing GIC restorative material. Consequently, the choice of the restorative material might be crucial for the occurrence or prevention of recurrent caries around restorations.

Various studies have shown that glass ionomers are susceptible to brittle fracture and acid conditions and that they undergo long-term changes in their mechanical properties. Little information is available on how brittleness, acid susceptibility, and long-term changes are reflected in the wear characteristics of glass ionomers. The purpose of this study was to evaluate long-term changes in conventional glass ionomers, metal-reinforced glass ionomers (including a cermet), and (light-curing) resinmodified glass ionomers by wear experiments simulating the wear process in occlusal contact-free areas. The wear tests were conducted periodically over a period of one year. In addition, wear was determined after one year at a pH of 5 or 6, for assessment of acid susceptibility, and at a condition as found in the occlusal contact areas. All materials showed high early-wear rates which decreased significantly during the one-year test period. This long-term process may be related to a slow progression of the acid-base reaction extending over several months. At each stage, the resinmodified glass ionomers wore significantly faster than the acid-base setting glass ionomers. Most of these materials were not affected at a pH of 6.0, while at a pH of 5.0 only the conventional and the metal-reinforced glass ionomers showed increased wear. Direct contacts with the antagonist led to a significant increase in wear in comparison with contact-free wear, probably as a result of sub-surface fatigue phenomena. In view of the unfavorable wear characteristics of the resin-modified glass ionomers and the high early wear of the conventional glass ionomers, including the metal-reinforced glass ionomers, it was concluded that none of these materials can yet be recommended for use in high-stress-bearing situations.

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