Determinants of the Durability of Resin-Dentin Bonds

DESCRIPTION: If resin composites are to provide a cost-effective alternative to silver fillings (dental amalgams), the adhesive bond between resins and dentin must be improved to increase its durability. To achieve adhesion of resins to dentin, the mineral phase is removed by acid etching. We posit that durable resin-dentin bonds require that stable resins fully replace the lost mineral volume. Such resin uptake requires extension of the collagen fibril matrix by water. Hydrophobic resins have been shown to be more stable when used as matrices for resin composites. Nevertheless, if hydrophobic monomers are applied to water-saturated dentin, they undergo phase changes and cannot penetrate the matrix. Hydrophilic monomers are more successful, but these bonds deteriorate over time by hydrolysis. Our recent work demonstrated that most of commercial adhesives cause a collapse of the water-saturated collagen matrix, that is largely due to their solvents having Hoy's solubility parameters for H-bonding forces (HHB) that are too low to prevent interpeptide H-bonding between collagen fibrils that occurs as the solvents replace water during monomer infiltration. We believe that the size of these interfibrillar spaces is critical because they serve both as diffusion channels for monomer infiltration and provide a protective resin coating for collagen fibrils. If the interfibrillar spaces collapse, there is little resin to protect the fibrils. We have ranked solvents and monomers for their HHB values. Ethanol has been shown to minimize matrix collapse, while acting as an excellent solvent for adhesive monomers. We have formulated a series of adhesive co-monomers that have a range of hydrophobicities/ hydrophilicities based on their HHB values, to test the hypothesis that hydrophobic resins provide more durable resin dentin bonds than current hydrophilic resins. The proposed studies provide a systematic sequence of experiments to select monomer/solvent combinations from a range of hydrophobic to hydrophilic resins, that minimize collapse of the matrix, maximize resin uptake between collagen fibrils, optimize resin dentin bond strength, while minimizing the permeability of resin-sealed dentin to water. We expect to minimize water sorption and maximize the long-term durability of resin-dentin bonds. This should provide important new insight into designing more durable resin-dentin bonds that can justify the placement of resin-based posterior composites.