Dimer Acid Derived Dimethacrylate for Ternary Dental Restorative Resins

Objectives: Incomplete polymerization, volumetric shrinkage and shrinkage stress are among the primary disadvantages of current resin based dental composites. By using dimer acid derived dimethacrylates (DADDMA), we aim to design dental resins that produce reaction-induced phase separation during polymerization to achieve increased final conversion with reduced shrinkage and shrinkage stress. Methods: Several high molecular weight (> 600 g/mol) DADDMA with different linking groups between the dimer acid core and the terminal methacrylate groups have been synthesized and investigated. These monomers were formulated with UDMA and/or BisEMA at various compositions to manipulate compatibility and mechanical properties. Real-time shrinkage stress and polymerization shrinkage were measured. Polymerization kinetics, dynamic mechanical analysis, and flexural strength were also characterized. The development of phase separation was monitored with an optical fiber spectrometer. Results: Controlled phase separation during polymerization can be achieved by varying the composition ratio between BisEMA, DADDMA, and UDMA in the ternary dimethacrylate systems. Reduced polymerization shrinkage was observed for DADDMA ternary systems (5.0 ~ 6.2%), compared with the Bis-GMA/TEGDMA control (7.3%). The reduced shrinkage is achieved not only by the elimination of low molecular weight diluent in the formulation (such as TEGDMA) but also by controlled phase separation during the photopolymerization process. Furthermore, certain ternary DADDMA systems demonstrated dramatically reduced polymerization shrinkage stress, while double bond conversion achieved is over 80% (compared with 64% for Bis-GMA/TEGDMA control). Modest stress relaxation behavior that accompanies the polymerization induced phase separation for certain ternary DADDMA systems have also been observed. Flexural strength and glass transition temperature values comparable to the control were obtained for some ternary DADDMA compositions. Conclusions: Certain dimer acid derived dimethacrylates possess very promising potential to replace TEGDMA as reactive diluents and can readily be applied to develop dental resins with a unique balance of favorable properties. Support: Confi-Dental Products Co.