Aim Secondary caries is one of the main reasons for the failure of contemporary composite restorations. Bioactive composite materials based on bioactive glass (BG) offer the potential to prevent secondary caries via the release of remineralizing ions and precipitation of the hydroxyapatite layer at their surface. The aim of this study was to prepare a series of experimental composite materials containing variable filler ratios of BG and test some of their basic properties which are important for clinical applicability. The following properties of experimental BG-containing composites were tested: the potential to precipitate hydroxyapatite when immersed in a phosphate buffered saline (PBS) solution, degree of conversion, depth of cure, light transmittance, temperature rise during light curing, water sorption and solubility. Materials and methods Five experimental composite materials were prepared with 0 – 40 wt% of BG 45S5 in a resinous matrix of Bis-GMA/TEGDMA in a ratio of 60:40. The experimental composites also contained reinforcing fillers comprising silanized barium glass and silica, up to a total filler load of 70 wt%. To assess the hydroxyapatite precipitation, composite specimens were immersed in PBS for 7 days and examined using Fourier-transform infrared spectroscopy, FT-Raman spectroscopy, scanning electron microscopy and energy dispersive spectroscopy. The degree of conversion was examined as a function of curing time (20 and 40 s) and composite layer thickness (0 – 4 mm) using FT-Raman spectroscopy. The depth of cure was assessed according to the ISO 4049 method and alternatively by determining the depth at which the degree of conversion declined to 80% of the maximum attainable value. Light transmittance was evaluated by real-time measurements of the light transmitted through 2 mm thick composite specimens during light-curing by means of a uv-vis spectrometer. Temperature rise during light curing was assessed at the bottom of 2 mm thick composite layers using a T-type thermocouple. Water sorption and solubility were measured according to a modified ISO 4049 protocol. Statistical analysis was performed using one-way and mixed model analysis of variance (ANOVA), Welch ANOVA with Tukey, Bonferroni and Games-Howell post-hoc adjustments, as appropriate. Correlations were tested using the Pearson correlation analysis. The global level of statistical significance for all tests was set at 0.05. Results Cured specimens of BG-composites formed a surface hydroxyapatite precipitate which was confirmed using infrared spectroscopy and visualized by a scanning electron microscope. Energy dispersive spectroscopy indicated that the precipitate was calcium-deficient hydroxyapatite. The thickness and morphology of the precipitate depended on the ratio of BG fillers in experimental composites. The BG-composites showed a clinically acceptable degree of conversion values which were in the range of commercial composites. For the curing time of 20 s, all of the BG-composites attained the depth of cure higher than 2 mm, as stipulated by the ISO 4049 requirements for conventional composites. The presence of BG fillers in experimental composites decreased the maximum attainable degree of conversion and caused a steeper decline of the degree of conversion values through increasing layer thicknesses. This effect was unrelated to the influence of the BG ratio on light transmittance and could be attributed to a hypothesized direct inhibitory effect of BG fillers on the free radical-mediated polymerization reaction. The addition of 5 wt% of BG fillers caused a significant decline in light transmittance in comparison with the experimental composite containing only reinforcing fillers, whereas a further increase in the BG load of up to 40 wt% showed a minor effect on light transmittance. Temperature rise during light curing of BG-composites was comparable or higher to that measured in commercial control materials. However, the temperature rise produced by BG-composites was within the range of commercial composites reported in the literature. Higher amounts of BG fillers in experimental composites resulted in lower temperature rise and later times at which temperature peak was attained, suggesting a possible effect of BG fillers on polymerization kinetics. Water sorption and solubility in experimental composites were significantly higher than the maximum values stipulated by the ISO 4049. Water sorption and solubility values increased with the increasing amount of BG fillers in the experimental composite series. A continuous decline in specimen mass during 287 days of water immersion, which was observed in experimental composites with a BG load of 10 wt% or more, indicates a long-term remineralizing potential. Conclusions The tested properties of experimental BG-containing composite materials indicate their potential for clinical applicability. Further studies should address mechanical properties and the remineralizing effect on dental hard tissues.