Solvent-Dependent Monomer Leaching From Two Commercial Dental Resin Composites: A Time-Dependent Elution Behaviour

Resin-based composites remain incompletely polymerised after light-curing, leaving unreacted monomers that can leach into oral fluids. Data on the temporal patterns of this release - especially contrasting flowable and packable composites under varying solvent conditions - remain limited.

This in vitro study evaluated the identity and time-dependent elution of residual monomers from a packable composite (Charisma Smart) and a flowable composite (Fusion Flo). Specimens (n = 10 per composite × medium combination; 40 total) were immersed continuously in either deionised water or a 1:1 water-ethanol mixture. The extraction medium was fully replenished on Days 1, 2, 7, and 14, tracking the same specimens longitudinally (160 eluates total). High-resolution mass spectrometry (HRMS) qualitatively identified leached species. Ultraviolet-visible (UV-Vis) spectrophotometry tracked relative monomer quantities calibrated against a triethylene glycol dimethacrylate (TEGDMA) standard; for co-eluting species, values are reported as approximate methacrylate equivalents. Data were analysed using a split-plot three-way analysis of variance (ANOVA) with Tukey's HSD post-hoc tests. Qualitative scanning electron microscopy (SEM) surveyed surface topography before and after 30-day immersion.

Monomer leaching differed significantly by composite, medium, interval, and all interactions (p < 0.001). Water-ethanol produced substantially greater leaching than water for both composites (p < 0.05), with the packable composite releasing the largest absolute quantities (1,086.1 µg at Day 1). HRMS also detected urethane dimethacrylate (UDMA) exclusively in the flowable composite's water-ethanol eluate. Only the flowable composite in water exhibited a simple monotonic decline across intervals. The other three conditions showed a sharp initial drop from Day 1 to Day 2, followed by a significant secondary rise at Day 7. SEM confirmed structural surface cracking and flaking in both media, alongside filler-scale pitting on water-ethanol-immersed surfaces.

Both composites released statistically distinguishable amounts of monomer, heavily accelerated by the water-ethanol medium. The non-monotonic temporal pattern reveals a complex secondary release phase not captured by standard single-decay models, highlighting the critical relevance of observation duration and solvent dynamics in biocompatibility screenings.