Formulating Mechanically Robust Composite Restorative Materials for High Performance

Although dental resin composite restoratives offer a widely used direct-placement treatment option aimed at replacing the form and function of a natural tooth, there are several clinically relevant performance aspects of these materials that can be improved. The formulation of the resin matrix phase of dental composites for high-efficiency photopolymerization leading to polymers with excellent mechanical properties has always been a challenge that is addressed here through the use of structurally new and more reactive monomers as well as the formation of polymer networks that incorporate non-covalent reinforcing interactions. The purpose of this study was to validate that a set of tetraurethane diacrylates (TUDAs) with a novel configuration of their urethane linkages in coordination with acidic comonomers could be devised to obtain highly robust new composite materials. Due to the novel molecular design, this exploratory approach was conducted using reaction kinetics and three-point bend testing to assess the performance. Conversion and mechanical properties were measured to refine these formulations prior to the addition of filler. The initial formulations demonstrated outstanding dry mechanical test results that subsequently showed a major intolerance to water storage, which led to a model study using urethane diacrylate (UDA) followed by the addition of hydrophobic TUDA monomers. Once the resin formulations were optimized, silane-treated particulate filler was added to determine the effectiveness as composite materials. The final formulation used a hydrophobic, aromatic TUDA along with 4-methacryloxyethyl trimellitic anhydride (4-META) as a latent acidic comonomer and a mixture of acrylic acid (AA) and methacrylic acid (MAA). This formulation achieves a very high level of both reactivity and mechanical properties relative to current dental composite restoratives.