Development of new diacrylate monomers as substitutes for Bis-GMA and UDMA

Bisphenol A-glycidyl methacrylate (Bis-GMA) and urethane dimethacrylate (UDMA) are widely used as the primary components of (meth)acrylic monomers. However, the use of Bis-GMA, which is a bisphenol A derivative, in dentistry is being questioned after bisphenol A was found to exhibit estrogenic activity. Although UDMA is being considered as a substitute for bis-GMA, the mechanical properties of cured resin composites containing UDMA are less than desirable. Therefore, in this study, we developed new alternative (meth)acrylic monomers to enhance the mechanical strength of cured composite resins.

Five urethane acrylic monomers were synthesized in this study as (meth)acrylic monomer substituents to replace Bis-GMA and UDMA. The elastic modulus, strength, and breaking energy values of cured resins consisting of mixtures of the urethane acrylates and diluting monomers were determined using the three-point flexural test. The data obtained were analyzed using one-way ANOVA and the post-hoc Tukey HSD tests (p < 0.05). Viscosities of the urethane acrylic monomers were measured with a cone-plate viscometer. Refractive indices of the urethane acrylic monomers were determined with an Abbe refractometer.

The results of the three-point flexural tests revealed that the cured urethane acrylic monomer-based resin exhibited higher elastic modulus (up to 40%) and strength (up to 21%) compared to the cured UDMA-based resin. Viscosity and refractive index of the urethane acrylic monomers were between those of UDMA and Bis-GMA.

The developed urethane diacrylates prepared from diisocyanates which have an aromatic or aliphatic ring, 1,3-bis(1-isocyanato-1-methylethyl)benzene (TMXDI), 1,3-bis(isocyanatomethyl)benzene (XDI), or norbornane diisocyanate (NBDI) are worth considering as alternative options of Bis-GMA and UDMA for restorative resin composites.