Novel Silicone-Epoxy Composites for Dental Restorations

Abstract

A novel silicone-epoxy oligomer was synthesized and evaluated for its use as the polymer in photopolymerizable dental composites. This synthesized oligomer contained rigid and non-rigid groups with 1–8 epoxy functionalities as characterized using ¹H NMR and ²⁹Si NMR and MALDI-TOF analysis. In comparison to the traditional BisGMA/TEGDMA monomer system, the photo-polymerized silicone-epoxy demonstrated significantly improved material properties (148% greater elastic modulus, 12% greater ultimate strength, 48% greater fracture toughness), as well as 61% lower polymerization shrinkage and 58% lower polymerization stresses. Furthermore, the silicone-epoxy system demonstrated enhanced resistance to degradation of its material properties after accelerated (24hr) aging, i.e. exposure to severe hydrolytic (boiling in ethanol at 100 □C), oxidative (exposed to 5% H₂O₂), and low pH (0.05M acetic acid) stress. Under these conditions, the properties of conventional BisGMA/TEGDMA systems deteriorated by 22–47%, while the properties of the silicone-epoxy composites decreased by 2–10%. Bisphosphonate additives enhanced the precipitation of mineral in a dose-dependent manner, but inhibited polymerization due to interactions with epoxy groups. Bisphosphonate additives also dose-dependently demonstrated anti-bacterial efficacy as demonstrated using live-dead, MTT and crystral violet assays. The silicone-epoxy polymer was demonstrated to be biocompatible when compared to tissue culture plastic. When calcium fluoride was incorporated into this system, fluoride was found to be released quantities significant enough to engender anti-bacterial effects. In summary, the designed multifunctional dental resin exhibits higher stability as demonstrated by lower chemical, mechanical and enzymatic degradation.