Novel Silicone-Epoxy Composites for Dental Restorations
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Novel Silicone-Epoxy Composites for Dental Restorations Liyun Ren1, Vaibhav Pandit2, Amanda Mixon2, Crivello James3, Shiva P. Kotha 2 1
Materials Science and Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180, U.S.A. 2 Biomedical Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180, U.S.A. 3 Chemistry and Chemical Biology, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180, U.S.A. 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. INTRODUCTION Most composites used in the clinic to repair cavities consist of a mixture of bisphenolacrylate resin mixed predominantly with silane coated silica based particulate, along with other additives. In the short term, one of the main drawbacks of using these bisphenol-acrylate based resin composites are the stresses associated with volumetric shrinkage 1-3. This stress, termed the polymerization stress or shrinkage stress, can directly or indirectly lead to failure of the restoration 4,5. Over the long-term, there are concerns related to hydrolytic, oxidative, and enzymatic degradation of the polymer and release of the unreacted monomer or its by-products 610 . Furthermore, since the FDA has banned the use of bisphenol containing materials in some
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plastics based on concerns rel
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