Dual functions of methacryloyloxydecyl dihydrogen phosphate monomer with de- and re- mineralizing ability

Background: Methacryloyloxydecyl dihydrogen phosphate (MDP) is one of the most commonly used acidic functional monomers in dentin adhesives. MDP has been speculated to induce mineralization, but there has been no convincing evidence of its ability to induce intrafibrillar mineralization. Polymers play a critical role in biomimetic mineralization as the stabilizers/inducers of amorphous precursors. Hence, MDP-induced biomimetic mineralization without the addition of polymers has not been fully verified or elucidated. Results MDP-collagen fibrils were heavily mineralized after 48 h. Amphiphilic MDP can not only demineralize dentin (0.5-1 µm) but also induce remineralization of demineralized dentin at 28 days without polymer additives. By combining three-dimensional stochastic optical reconstruction microscopy (3D-STORM), surface zeta potentials, contact angle measurements, inductively coupled plasma-optical emission spectroscopy, transmission electron microscopy, atomic force microscopy, and Fourier transform infrared spectroscopy with circular dichroism, we show that amphiphilic MDP can not only demineralize dentin by releasing protons but also infiltrate collagen fibrils, including dentin collagen, break hydrogen bonds between polypeptides, unwind the triple helical structure and finally immobilize collagen by the formation of chemical bonds. MDP-bound collagen functions as huge collagenous phosphoprotein (HCPP) unlike chemical phosphorylation modifications. HCPP can induce biomimetic mineralization itself without polymer additives by alternatively attracting calcium and phosphate through electrostatic attraction. Conclusions We herein propose the dual functions of amphiphilic MDP monomer with de- and re-mineralizing ability. MDP in the free state can demineralize dentin substrates by releasing protons, whereas MDP in the collagen-bound state as HCPP can induce intrafibrillar mineralization. The dual functions of MDP monomer with de- and re-mineralization properties might create new epochs in adhesive dentistry and preventive dentistry.