Influence of the quantity of extraction solvent on monomer leachability from dental composites

Objectives: To determine whether the volume of extraction solvent influences monomer leachability from dental composites.
Methods: Composite disks of two commercial dental composites (Filtek Supreme XTE, 3M ESPE, Seefeld, Germany and Gaenial Universal Flow, GC, Tokyo, Japan) were prepared using teflon molds (h=2mm; d=5,75mm). After application, the unpolymerized composite was covered with a glass plate, in order to prevent formation of an oxygen inhibition layer and polymerized for 40s using a light curing lamp with an output >1100 mW cm^-2. Next, the disks (n=10) were placed in a glass vial with either 1ml, 2ml or 3ml of extraction solvent (100% ethanol with deuterated diethylphalate as internal standard). Either after 7 or 30 days at 37°C, the supernatant was collected and the amount of released monomers (BisEMA, BisGMA, UDMA, TEGDMA) and Bisphenol A was measured with liquid chromatography mass spectroscopy (LC-MS/MS, Acquity Systems, Waters, USA).
Results: For both tested composites, the highest amount of released monomers was measured after sample incubation in 3ml, while the lowest amount was measured in 1ml of extraction solvent. Furthermore, there was no significant difference noted in quantity of released monomers in the same volume after 7 and 30 days of incubation.
Conclusions: The amount of solvent certainly plays an important role in the monomer release from dental composites, which must be attributed to a saturation effect and the development of an equilibrium, which slows down further monomer release. This also explains why longer incubation times do not lead to more monomer release.