Hydrophobic monomer systems for dental composites: development and physicochemical evaluation of UDMA/IBOMA formulations

The objective of this study was to evaluate UDMA/IBOMA formulations at varying ratios as hydrophobic alternatives to conventional Bis-GMA/TEGDMA dental resin composites, assessing hydrophobic properties, polymerization efficiency, mechanical performance, water sorption behavior, and color stability. A total of 120 disc specimens (15 mm × 1 mm) were prepared in four groups (n = 40): Group 1 (control) containing Bis-GMA: TEGDMA (70:30 wt%), and Groups 2–4 containing UDMA: IBOMA at 50:50, 60:40, and 70:30 wt%, respectively. The photoinitiators of 0.5 wt% Camphorquinone and 0.5 wt% Ethyl 4-dimethylaminobenzoate were added to each group. Specimens were evaluated for contact angle, surface free energy, degree of conversion (FTIR), Vickers microhardness, water sorption, and color stability (ΔE after 28-day immersion in coffee and turmeric). Data were analyzed using one-way and two-way ANOVA with Tukey’s HSD post-hoc test (α = 0.05). All UDMA/IBOMA formulations exhibited significantly higher water contact angles (> 90°) and lower surface free energy than the control (p < 0.05). The degree of conversion showed no significant differences. Microhardness was comparable in Groups 2 and 3 but reduced in Group 4 (p < 0.05). Water sorption decreased progressively with increasing IBOMA content, with Group 4 demonstrating 71% reduction versus control (p < 0.05). UDMA/IBOMA formulations showed higher apparent staining for both solutions, primarily due to lighter baseline colors. The 70:30 UDMA/IBOMA formulation demonstrated superior water uptake resistance, representing significant advancement toward durable, BPA-free restorative materials with greatest potential for long-term clinical performance.