Assessment of Ion Leachable Resin Composites: Time-Dependent Water Sorption, Solubility and Hygroscopic Expansion

This study aimed to assess the time-dependent water sorption, solubility and hygroscopic expansion of experimental resin composites modified with three different types of ion-leachable glasses (ILGs): 45S5 Bioglass (BG), Fluoride-containing glass (F9) and Experimental fluoride-phosphate glass (F9X), incorporated in varying weight percentages (5%, 10% and 15%).

A 50:50 Bis-GMA/TEGDMA-based resin matrix was loaded with each ILG type in 5, 10 and 15 wt% and compared against a control without filler. Disc-shaped specimens (n = 3 per group; total = 39) were fabricated using a stainless-steel mould and cured using an LED light-curing unit (1200 mW/cm², 20 s per side). The water sorption and solubility were evaluated using a modified ISO 4049 protocol over a 12-week immersion period in distilled water at 37°C, followed by an 8-week desorption phase. Hygroscopic expansion was evaluated through volume change using a digital micrometre. Data were statistically analysed using one-way ANOVA and Tukey's post-hoc test.

All ILG-containing composites showed significantly increased water sorption compared to the control, with the BG-15 group demonstrating the highest sorption (3.37% ± 0.09) and expansion. Solubility increased with ILG concentration, especially in the BG and F9X groups. Hygroscopic expansion correlated positively with water uptake. No significant changes were observed in specimen mass after desorption in low filler groups.

The incorporation of ILGs into resin composites significantly altered their water uptake and dimensional stability. While these effects could compromise long-term mechanical properties, the resulting hygroscopic expansion may aid in reducing microgaps and secondary caries at restoration margins. Veneering ILG-containing composites with conventional materials is recommended to limit degradation. These findings contribute novel insights into time-dependent dimensional behaviour of bioactive composites.