Purpose: In this study, the protective effects of restorative materials with fluoride content, resin-modified glass-ionomer cement (RMGIC), giomer, and glass carbomer against artificial initial caries lesions in a simulated highly cariogenic oral environment were evaluated. Considering the reported recharging abilities of these restorative materials, fluoridated toothpaste was applied to some groups, in which the anti-demineralising effect was also evaluated. Materials and Methods: Two enamel blocks were produced from each of 60 sound permanent molars. Sixty specimens were used for microhardness analysis, and the rest were used for SEM-EDX analysis. Enamel specimens were randomly assigned to three groups according to the restorative material: A = resin-modified glass-ionomer cement; B = giomer; C = glass carbomer. Artificial initial caries lesions were created using demineralising solutions, after which specimens were exposed to in vitro pH cycling simulating a highly cariogenic oral environment. Microhardness and mineral analyses were performed on the enamel surrounding the restorative materials at three different times during the experiment: at the beginning of the experiment, then after the creation of the artificial early caries lesions, and finally after pH cycling. Results: Microhardness and SEM-EDX results mostly confirmed each other. RMGIC and glass carbomer groups with added fluoride toothpaste showed statitsically significantly better anti-demineralising effects in comparison to other groups. Neither of the giomer groups performed as well as RMGIC or glass carbomer. Conclusion: Because of the similarity between the demineralisation inhibitory activity of glass carbomer and RMGIC, glass carbomer may be preferred as a restorative material in paediatric dentistry. Keywords: fluoride, giomer, glass carbomer, resin-modified glass ionomer, SEM-EDX