During dentin bonding with etch-and-rinse
adhesive systems, phosphoric acid etching of mineralized dentin solubilizes the mineral crystallites and replaces them with bound and unbound water. During the infiltration phase of dentin bonding, solvated
adhesive resin comonomers are supposed to replace all of the unbound collagen water and polymerize into copolymers. A recently published review suggested that dental monomers are too large to enter and displace water from tightly-packed collagen
molecules. Conversely, recent work from the authors’ laboratory demonstrated that HEMA and TEGDMA freely equilibrate with water-saturated dentin matrices. However, because
adhesive blends are solvated in organic solvents, those solvents may remove enough free water to allow collagen
molecules to come close enough to exclude
adhesive monomer permeation. The present study analyzed the size-exclusion characteristics of dentin collagen, using a gel permeation-like column chromatography technique, filled with dentin powder instead of Sephadex beads as the stationary phase. The elution volumes of different sized test
molecules, including
adhesive resin monomers, studied in both water-saturated dentin, and again in ethanol-dehydrated dentin powder, showed that
adhesive resin monomers can freely diffuse into both hydrated and dehydrated collagen
molecules. Under these
in vitro conditions, all free and some of the loosely-bound water seems to have been removed by ethanol. These results validate the concept that
adhesive resin monomers can permeate tightly-bound water in ethanol-saturated collagen
molecules during infiltration by etch-and-rinse
adhesives.
Statement of Significance
It has been reported that collagen molecules in dentin matrices are packed too close together to allow permeation of adhesive monomers between them. Resin infiltration, in this view, would be limited to extrafibrillar spaces. Our work suggests that monomers equilibrate with collagen water in both water and ethanol-saturated dentin matrices.