The purpose of this systematic review was to quantitatively find out whether resin-modified glass-ionomers (RM-GIC), in comparison to fluoride-containing composite resin and composite resin without fluoride, are associated with a more effective reduction of demineralization in hard tooth tissues under caries challenge. Five databases were systematically searched on clinical trials up to 6 April 2009. Article inclusion criteria: titles/abstracts relevant in answering the review question, published in English, two-arm (prospective) longitudinal trial; Exclusion criteria: not all included subjects accounted for at the end of the trial; subjects of both groups not followed up the same way; no randomized, quasi-randomized controlled study design for in situ and clinical trials; contains no computable continuous data. Quality assessment of the accepted in situ and clinical trials was performed. Data were extracted in the form of datasets, containing numbers of evaluated samples and mean result with standard deviation for both groups. Fifteen articles were selected for review. Two lacked computable data and were excluded; nine laboratory trials, three randomized in situ trials and one randomized control trial were accepted. From these, 97 continuous datasets were extracted. The evidence suggests that RM-GIC is associated with a higher reduction of demineralization in adjacent hard tooth tissue than composite resin without fluoride. No difference was found when RM-GIC was compared with fluoride-containing composite resin. RM-GIC showed efficacy in reducing demineralization. However, the internal validity of the current evidence is limited and further high-quality trials are needed. (J Oral Sci 52, 347-357, 2010)