Improved Dental Adhesive Formulations Based on Reactive Nanogel Additives

Abstract

Current challenges in adhesive dentistry include over-hydrophilic bonding formulations, which facilitate water percolation through the hybrid layer and result in unreliable bonded interfaces. This study introduces nanogel-modified adhesives as a way to control the material's hydrophobic character without changing the basic monomer formulation (keeping water-chasing capacity and operatory techniques unaltered). Nanogel additives of varied hydrophobicity were synthesized in solution, rendering 10-to 100-nm-sized particles. A model BisGMA/HEMA solvated adhesive was prepared (control), to which reactive nanogels were added. The increase in adhesive viscosity did not impair solvent removal by air-thinning. The degree of conversion in the adhesive was similar between control and nanogel-modified materials, while the bulk dry and, particularly, the wet mechanical properties were significantly improved through nanogel-based network reinforcement and reduced water solubility. As preliminary validation of this approach, short-term micro-tensile bond strengths to acid-etched and primed dentin were significantly enhanced by nanogel inclusion in the adhesive resins.

Photopolymerizable nanogels as macromolecular precursors to covalently crosslinked water-based networks

“…Solution free radical polymerization produced particles with molecular weight in the 30–150 kDa range and radius <10 nm while avoiding macrogelation. The MH-α values are significantly reduced compared to typical values for a linear polymer and correspond well to previous reports on the GPC analysis of nanogels and hyperbranched polymers 25,31,32 .…”

Solvent content and dentin bond strengths using water-wet, ethanol-wet and deproteinization bonding techniques

“…Regarding the solvent types in terms of viscosity, acetone solutions showed significantly lower viscosity than ethanol solutions; this is in line with findings from a recent study [25]. The results also showed no changes in viscosity between the medium and high acetone contents, which indicates that lower acetone content could be used in commercial bonding agents.…”

Construction of Monomer-free, Highly Crosslinked, Water-compatible Polymers

“…We have demonstrated previously that ~10-to 20-nm reactive nanogels that are dispersed in and swollen by monomer can be used to significantly modify properties of the resultant hybrid polymer networks as applied to monomer reactivity (Liu et al, 2012(Liu et al, , 2014, shrinkage and stress in resinbased composites (Moraes et al, 2011), and mechanical strength in model dental adhesives (Moraes et al, 2012). Here, we focus on nanogels that are water-compatible or near-water-compatible for potential application in dental adhesives; however, for better appreciation of the relationship between nanogel structure and network properties conveyed by the nanogel component rather than nanogel entwined in a resin matrix, this work emphasizes nanogelderived networks created in inert dispersion media.…”