Analysis of water sorption, water solubility and monomer elution of bulk-fill composites

Objectives: Introduction: The interaction with water as it diffuses into the resin matrix results in composite shrinkage and swelling. Water sorption would result in elution of unreacted monomers, which in turn will result in loss of weight and shrinkage. The aim of this study was to compare the water sorption and solubility of two conventional viscosity bulk-fill and two low viscosity bulk-fill flowable composites and to determine monomer elution.
Methods: Specimes (n=120) were light cured in teflon moulds (ISO 4049). Specimens were placed in an oven (37 degrees C) to stabilize their weights and recorded as m₁. Specimens were immersed in glass containers containing 10 ml distilled water for 24 hours, 7, and 14 days and weighed (m₂). The specimens were then desiccated for two hours at 58 degrees C and weighted to obtain m₃. Water sorption and solubility was calculated as follows:
Water sorption (SP) = m₂ -m₃ / v.
Water solubility (SI) = m₁ -m₃ / v.
For monomer leakage high performance liquid chromatography (HPLC) was used to identify monomers: Bis-GMA, TEGDMA, UDMA and Bis-EMA.
Results: Over all three time intervals (24 hrs, 7 days and 14 days) SDR showed significantly lowest (p<0.05, ANOVA) mean water sorption values (10.191) followed by Filtek (11.135), Tetric (16.419); Surefil (21.515). The overall means of water solubility for the two bulk-fill flowables i.e. Filtek and SDR were smaller than bulk-fill conventional Surefil and Tetric N-Ceram but statistically not significant (p > 0.05 two way ANOVA test). The amounts of eluted monomers from bulk-fill conventional viscosity materials (Surefil and Tetric N-Ceram) were higher than bulk-fill flowable materials (SDR and Filtek) with UDMA>Bis-GMA>TEGDMA.
Conclusions: The bulk-fill flowables showed lower water sorption than the conventional viscosity bulk-fills. SDR was significantly lower than the other materials followed Filtek, Tetric N-Ceram and the highest overall means were recorded for Surefil. For water solubility the overall means of Filtek and SDR were smaller than Surefil and Tetric N-Ceram.