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Resin composites containing reinforcing inert glass fillers combined with bioactive glass (BG) can aid in the prevention of secondary caries, which is a major cause of failure of contemporary composite restorations. A series of previous studies on experimental resin composites filled with BG 45S5 has demonstrated that methacrylate resin polymerization can be impaired by the addition of unsilanized BG, leading to lower degrees of conversion (DC). In order to distinguish whether the polymerization inhibition is caused by a direct (temperature-independent) effect of BG or an indirect (temperature-dependent) effect of restricted mobility of reactive species, this study used Raman spectroscopy to evaluate the DC values of experimental composites post-cured at 37 °C and 150 °C. The potential of BG to adversely affect DC was highly dependent on the resin system. The highest DC reduction was observed in the resin system based on ethoxylated bisphenol A dimethacrylate (Bis-EMA), followed by bisphenol A glycidyl methacrylate (Bis-GMA). In contrast, the DC for urethane dimethacrylate (UDMA) was not compromised by BG. Increasing the mobility of reactive species by heating at 150 °C showed limited potential for increasing the DC in the Bis-EMA and Bis-GMA resin systems, indicating a direct inhibitory effect of BG on polymerization.

Some of the bulk-fill composites may need longer times than the commonly accepted 24 h to reach the final conversion. This may be attributed to their compositional modifications that are mostly undisclosed by manufacturers. Our findings imply that investigations commonly performed 24 h post-cure may underestimate some of the bulk-fill composite properties, if these are affected by the slowly-developing DC. Reactive species may also be available for leaching out of the restoration during an extended time period, with possible implications on biocompatibility.

OBJECTIVES To evaluate the degree of conversion, light transmittance, and depth of cure of two experimental light-curable bioactive glass (BG)-containing composite series based on different resin systems. METHODS Experimental composite series based on either Bis-EMA or UDMA resin were prepared. Each series contained 0, 5, 10, 20, and 40wt% of BG 45S5. Reinforcing fillers were added up to a total filler load of 70wt%. The degree of conversion was evaluated using Raman spectroscopy, while light transmittance was measured using visible light spectroscopy. The depth of cure was estimated from the degree of conversion data and using the ISO 4049 scraping test. RESULTS Replacement of reinforcing fillers with BG can diminish the degree of conversion, light transmittance, and depth of cure. The effect of BG on the aforementioned properties was highly variable between the experimental series. While in the Bis-EMA series, the degree of conversion was significantly impaired by BG, all of the composites in the UDMA series attained clinically acceptable degree of conversion values. The reduction of the degree of conversion in the Bis-EMA series occurred independently of the changes in light transmittance. The UDMA series showed better light transmittance and consequently higher depth of cure than the Bis-EMA series. The depth of cure for all composites in the UDMA series was above 2mm. SIGNIFICANCE While the Bis-EMA series demonstrated clinically acceptable curing potential only for 0-10wt% of BG loading, an excellent curing potential in the UDMA series was observed for a wide range (0-40wt%) of BG loadings.

The aim of this study was to evaluate water sorption and solubility of two series of experimental composites containing amorphous calcium phosphate (ACP) or bioactive glass (BG). Water sorption and solubility were measured for up to 287 days. The surface precipitation of calcium phosphates was evaluated by scanning electron microscopy. The ACP-series showed higher water sorption (223-568 µg/mm 3) than the BG-series (40-232 µg/mm 3). In contrast, the ACP-series had generally lower solubility (37-106 µg/mm 3) than the BG-series (1-506 µg/mm 3). The constant specimen mass for the ACP-series was attained after 14 days of water immersion, while the mass decrease due to long-term solubility in the BG-series lasted beyond 287 days. Calcium phosphates precipitated in composites with the BG filler loading of 10 wt% or more, as well as in all of the ACP-containing composites. The experimental composite series showed water sorption and solubility considerably higher than commercial materials.

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ObjectiveTo investigate the real-time temperature rise during light-curing of experimental composite materials containing bioactive glass 45S5 (BG) and compare it to the temperature rise in three commercial composites.Materials and methodsFive light-curable composite materials containing 0-40 wt% of BG and a total filler load of 70 wt% were prepared. Cylindrical composite specimens 6 mm in diameter and 2 mm thick were cured using Bluephase G2 (Ivoclar Vivadent) at 1200 mW/cm2 for 30 s. The rise in temperature during light-curing was measured at the bottom of the specimens using a T-type thermocouple at the data collection rate of 20 s -1. An additional illumination for 30 s was performed after the specimen temperature returned to the baseline in order to record the temperature rise due to the heating from the curing unit. Statistical analysis was performed using the one-way ANOVA and Pearson correlation analysis with α=0.05.ResultsTemperature rise during light-curing of experimental composites amounted to 12.2-14.0 °C and was comparable to that of the flowable commercial composite (12.5 °C) but higher than that of nano- and micro-hybrid commercial composites (9.6-10.3 °C). The temperature rise during the second illumination was similar for all composites (7.8-9.1 °C). In experimental composites, the temperature rise which was attributable to the polymerization exotherm amounted to 3.1-5.8 °C and was negatively correlated to the BG fraction (R2=0.94). Times at which temperature reached maximum values were in the range of 6.5-19.8 s and were positively correlated to the BG fraction (R2=0.98).ConclusionsTemperature rise during light-curing of experimental composites was comparable to that of commercial composites, suggesting that the amount of heat released is tolerable by dental pulp.