Abstract
Photocure bonding resins to smear layer retained dentin were studied.The most effective photocure bonding resin among those studied was composed of 0.5% camphorquinone, 0.5% N-phenylglycine, 5.0% 2-methacryloyloxyethyl phenyl hydrogen phosphate(Phenyl-P)in triethyleneglycol dimethacrylate.Tensile bond strength after immersion in 37℃ water for 1 day was 6MPa, but that after water immersion for 1 year, decreased to 3MPa, because a sufficient amount of monomers could not diffuse into the intact dentin through the smear layer.Suitable pretreatments were considered to improve permeability of smear layer retained dentin.Experimental pretreatments were composed of aqueous mixtures of phosphoric acid or phosphoric methacrylates in 30% 2-hydroxyethyl methacrylate(HEMA).Phosphoric methacrylates were 2-methacryloyloxyethyl dihydrogen phosphate(Phosmer-M), 10-methacryloyloxydecyl dihydrogen phosphate(MDP)and Phenyl-P.Bovine dentin samples were ground with 600 grid Carbimet paper discs(Buehler, USA)and subjected to one of the experimental pretreatments.Pretreated with an aqueous mixture of 5 or 10% Phenyl-P in 30% HEMA, hybrid layer was demonstrated, but bond strength did not increase.Because the hybrid layer was thinner than 1μm and monomers could not diffuse into intact dentin.On the other hand, the bond strength was increased to 10MPa and hybrid layer was demonstrated on SEM and TEM by an aqueous mixture of 20, 30 or 40% Phenyl-P in 30% HEMA pretreatment.The hybrid layer improving tensile bond strength was thicker than 2μm from the adhesive interface.These findings indicate that 1μm hybrid layer was created with a smear layer and the 2μm was created with both smear layer and intact dentin.The smear layer hybrid is not so strong as the intact dentin one at the same resin concentration.
