The effectiveness of newly developed photocurable bonding agents in creating adhesion between composite resin and polished dentin without any pretreatment was investigated. Methacryloyl tyrosine amide (MTYA) and glyceryl methacrylate (GM) were used as an adhesive monomer and a water soluble methacrylate monomer, respectively. A water soluble photoinitiator, 2-hydroxy-3-(3, 4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-N, N, N-trimethyl-1-propanaminium chloride (QTX) was used in combination with 2-(N, N-dimethylamino)ethyl methacrylate (DMAEMA) and benzene sulfinic acid sodium salt (BSNa).
Fresh bovine dentin was prepared by wet grinding with #1000 stones. The two parts of photocurable bonding agents were mixed well before application. After application of photocurable bonding agents to the polished surface, polymerization was performed for one min irradiation. Then Protect Liner (Kuraray Co.) was applied and polymerized by one min irradiation. The tensile bond strengths were measured after one day of immersion in 37℃ water.
The one min application of photocurable bonding agent (A1: 6% MTYA+70% GM+4% DMAEMA+1% BSNa aqueous solution, BSu3: 3% succinic acid+5% glutaraldehyde+2% QTX aqueous solution) gave a mean bond strength of 6 MPa, while 5 min application gave 11 MPa. The incorporation of acidic monomers, such as acrylamido glycolic acid or phenyl-p, was not very effective in increasing bond strengths. SEM observation showed the formation of a hybrid layer 2 μm thick by applying mixtures of A1 and BSu3 for 5 min.