(29a) Hybrid Polymer Networks to Address Dental Adhesive Failure

Cellulose nanomaterials, including cellulose nanocrystals (CNCs) are of growing interest in materials applications because of their high abundance in nature and biocompatibility. Furthermore, these nanomaterials have unique properties due to their crystalline nature and rod-like shape, including an associated high modulus (strength) and low permeability. This is advantageous for many materials applications, as the incorporation of CNCs can reduce the permeability of an organic matrix or material to a number of gases (O₂, CO₂) and moisture. This enhanced performance associated with CNCs has been leveraged to improve composites and barrier films. However, limited studies explore the use of CNCs in dental material applications. This is particularly relevant, as dental adhesives, which serve as a bridge between native dentin tissue and bulk composites, are susceptible to hydrolytic degradation. Specifically, dental adhesives are heterogeneous in nature, often having macroscopic domains that are more hydrophilic which form during in situ polymerization and readily take up water present in the oral environment. Therefore, identifying strategies that tailor moisture sensitivity and sorption, even for a hydrophilic dental adhesive network, could significantly improve performance.

In this work, we investigate the influence of CNC integration on dental adhesives performance, particularly adhesive strength and moisture sensitivity. Model adhesive formulations were developed using methacrylate comonomers (hydroxy-ethyl methacrylate – HEMA, urethane dimethacrylate – UDMA, bisphenol-A glycidyl methacrylate – BisGMA, etc.) and solvents (ethanol / water) commonly found in commercial formulations. CNCs were incorporated at 0.5 wt% loading level. A combination of in situ and post polymerization characterizations were conducted. Our results highlight that when CNCs are uniformly dispersed within the adhesive network, there is an enhancement to network strength and modulus, while water sorption is reduced. However, this dispersion was not achieved for all adhesive formulations tested. This provides a starting point from which biosourced additives can be explored for dental materials, which have typically relied on inorganic nanoparticles to tailor material properties. Utilizing biosourced compounds, such as cellulose nanocrystals, may provide a sustainable approach to improve the longevity of these biomaterials.