A Novel Oxirane/Acrylate Restorative System With Multifunctional Acrylate

Objectives: To develop a novel hydrophobic, degradation-resistant restorative resin based on a multifunctional acrylate combined with a difunctional oxirane, with the ultimate goal of doubling the clinical lifetime of restorative composites.
Methods: Five different acrylate/oxirane blends were prepared using dipenta erythritol hexaacrylate (Dipenta, Sigma-Aldrich), plus p-cycloaliphatic diepoxide (EPALLOY 5000, CVC Thermoset Specialties). A 2-component camphorquinone (CQ)/iodonium ion photoinitiator ([4-(octyloxy) phenyl] phenyl iodonium hexafluoroantimonate; OPPI) was optimized together with an oligomeric diol (polytetrahydrofuran; THF-250, BASF Corp.), to increase degree of polymerization. The control was 70:30 BisGMA/TEGDMA resin. Samples were light-cured and tested for degree of cure (Durometer-D hardness), mechanical properties (3-point bend test), hydrophobicity (contact angle), near-IR FTIR degree-of-conversion, index of refraction, polymerization shrinkage (Accuvol), and shrinkage stress (ProTest).
Results: At 24hr all 5 blends achieved acceptable hardness and 3 blends had comparable or higher hardness than the control. Most blends were significantly more hydrophobic than the control. The modulus and ultimate transverse strength (UTS) increased with increasing oxirane content. All experimental groups had comparable or slightly higher index of refraction as compared to the control. Acrylate degree of conversion was similar across all experimental groups, and oxirane conversion increased substantially after 24 hours. Volumetric shrinkage averaged 7% for all blends. Shrinkage stress showed dramatic decreases with increased oxirane content.
Conclusions: The five optimized blends demonstrated the benefits of a restorative system based on a multifunctional acrylate combined with a difunctional oxirane, as well as the challenges when the oxirane content becomes too high. Currently water sorption and degradation in acidic, basic and esterase environments are being evaluated. With the demonstrated beneficial physical and mechanical properties this blended resin system shows promise in producing a hydrophobic, degradation-resistant resin with low polymerization stress that could achieve a doubling of the clinical lifetime of restorative composites.