One-step self-etch adhesives containing different amounts of MDP are designed. Amounts of MDP-Ca salts produced by enamel and dentin depend on the MDP concentration. Dentin develops a greater amount of MDP-Ca salts than enamel by 1.5 times. Type of the molecular species of MDP-Ca salts differs between enamel and dentin. Species of MDP-Ca salts forming a layered structure differs between enamel and dentin.