Abstract
Our investigations have shown that the bond strength of adhesive resins to dentinal substrates can be altered by the rate of monomer diffusion into demineralized dentin after smear layer removal.The diffusion rate of monomers is a function of the diffusivity of dentinal substrates and diffusibility of the monomer itself.The effectiveness of treating dentin with 2-hydroxyethyl methacrylate(HEMA)prior to application of an adhesive resin was examined.The adhesive resin was 5% 4-methacryloxyethyl trimellitate anhydride(4-META)in methyl methacrylate(MMA)combined with a poly-MMA powder.Polymerization of this resin was initiated by tri-n-butyl borane(TBB).Bovine dentin samples were ground with 600 grid Carbimet paper discs(Buehler, USA), and demineralized with an aqueous solution of 65% phosphoric acid.Bond strength was improved by HEMA treatment of phosphoric etched dentin which could not be given high bond strength before.The adhesive resin impregnated the exposed collagen bundles and became entangled with them to create the"hybrid", essential in attaining high tensile bond strength. Specimens pretreated with phosphoric acid did not readily form"hybrid"layers.However, when the phosphoric acid pretreatment was followed by HEMA application, a"hybrid"was demonstrated on SEM and TEM, and bond strength increased to 16 MPa. This study indicates that HEMA applied to dentinal substrates enhances monomer diffusion and entanglement with demineralized dentin, and facilitates the formation of a"hybrid"layer.
