265 RESEARCHrestorative dentistry limited the scope of conventional GICs in clinical application. More recently-introduced resin ionomers have less water sensitivity, and improved aesthetic and mechanical properties. 11 However, there are great differences between various materials in the levels of fluoride released, 12 and there is also less fluoride released when artificial 13 and human saliva 14 are used, rather than deionised water. Some materials claimed by their manufacturers to release fluoride hardly do so in measurable quantities. 15 In fact, a variety of such fluoride-releasing materials are primarily resin-composite systems with some form of fluoride incorporated into the resin matrix. 16 Most of these materials have a lower level of fluoride release than GICs, and their clinical effectiveness is also unknown.Therefore, the objectives of this study were to investigate the long-term levels of fluoride released from selected GICs and resin ionomers, and the effects of acidulated phosphate fluoride (APF) gel on the levels of fluoride released and on the physical structure of the glass ionomer cements, by monitoring their weights and surface changes. Materials and methods Restorative materialsThe details of the materials investigated in the present study are listed in Table 1. ChemFil Superior was the positive control and Z100 was the negative control. Specimen preparation and immersionFive specimens of each material were prepared according to the manufacturers' instructions and placed into disposable, cylindrical Teflon moulds (3.0 mm diameter × 2.7 mm height), 17 and then pressed between two Mylar-covered glass slides. The resin ionomer cements were light cured from both ends of the moulds for 40 seconds using a VCL 200 visible light unit (Demetron Research Corporation, Danbury, CT, USA). They were allowed to set for about an hour. After setting, each specimen was removed from its mould, weighed by an electronic balance, then placed in a polypropylene vial with 2 mL of artificial saliva (0.05 M acetate buffer with 2.2 mM CaHPO 4 adjusted with glacial acetic acid to pH 5.0) and stored at 37°C. The solution was replaced at 6 hours, 1 day and 2 days, then weekly for 12 weeks. The amount of fluoride released was also measured at these same times for the first 5 weeks, then at 8 weeks and 12 weeks. Each specimen was dabbed dry before weighing at the times of solution replacement. Determination of fluorideOne mL of the solution was mixed with 0.1 mL of TISAB III solution and the fluoride concentration was measured with a specific fluoride electrode (Orion 9609BN electrode: Orion Research Incorporated, Boston, MA, USA) and read in millivolts. Calibration of the fluoride electrode was done before each measurement session Objective In this investigation, the in vitro sustained fluoride release, weight loss and erosive wear of three conventional glass ionomer cements (Fuji IX, ChemFil Superior, Ketac-Silver), three resin-modified glass ionomer cements (Fuji II LC, Vitremer, Photac-Fil), a polyacid-modified resin ...