The effects of the water concentration in an experimental 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-based all-in-one (EX) adhesive were examined on the ability of MDP to remove the smear layer from the ground dentin surface and on the dentin bonding performance. Four types of EX adhesives were prepared by varying the amount of water (46.6, 93.2, 149.8 and 208.1 mg/g), but the MDP concentration was kept a constant at 49.9 mg/g. Scanning electron microscopy and bond strength measurements were performed on the dentin surface demineralized by each EX adhesive. Increased amount of water in the EX adhesive increased the ability of MDP to remove the smear layer. However, the solubilization of the smear layer into the EX adhesive decreased the dentin bond strength. The water concentration in the EX adhesive affected the efficacies of smear layer removal and dentin bonding performance more strongly than the pH value of the EX adhesive.
Keywords: All-in-one adhesive; Demineralization ability of MDP; MDP; Smear layer.