Urethane Tetramethacrylate Monomers and Nano-Fillers Enhance Dentin Bond Strength of a One-Step Universal Adhesive

This study evaluated the effects of incorporating urethane tetramethacrylate (UTMA) monomers and inorganic nano-fillers on the bonding performance and mechanical properties of a next-generation one-step universal adhesive, Clearfil Universal Bond Quick 2 (UBQ2), with a focus on clarifying its improvements over the previous formulation.

Five adhesive systems were investigated: UBQ2, two experimental variants lacking either UTMA (UBQ2-U) or nano-fillers (UBQ2-F), the predecessor adhesive (Clearfil Universal Bond Quick, UBQ), and a gold-standard two-step self-etch adhesive (Clearfil SE Bond 2, SE2). Microtensile bond strength (μTBS), bond layer thickness (L), ultimate tensile strength (UTS), and water sorption (Wsp) were evaluated.

UBQ2 demonstrated significantly higher UTS and lower Wsp than UBQ2-U (P 0.001 and P = 0.03, respectively), indicating enhanced mechanical resilience and hydrolytic stability due to the presence of UTMA. Compared to UBQ, UBQ2 showed improved mechanical properties while maintaining comparable μTBS. The absence of nano-fillers (UBQ2-F) significantly reduced μTBS (P 0.05), confirming their critical role in bonding performance. Despite forming a thinner adhesive layer, UBQ2 achieved dentin bond strength comparable to SE2.

By combining UTMA and nano-fillers, UBQ2 has improved wettability compared to conventional products, while also providing high bonding performance and mechanical properties with a one-step application. These findings support the development of universal adhesives through simplified clinical protocols and improved material properties.

This study demonstrates that incorporating nano-fillers and UTMA into a one-step universal adhesive (UBQ2) enhances mechanical strength, reduces water sorption, and maintains high dentin bond strength. Clinically, UBQ2 offers a simplified yet reliable bonding performance comparable to SE2.