Demineralization Mechanism of Enamel and Dentin Cut With a Diamond Bur by MDP-based One-step Self-etch Adhesive

Objectives: The 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-based one-step self-etch adhesives have become widely utilized due to their simplified application procedures. The aim of this study was to clarify the mechanism that MDP demineralizes the enamel and dentin cut with a diamond bur.
Methods: The enamel and dentin particles were prepared by cutting the bovine teeth using a diamond bur. Three types of experimental MDP-based one-step self-etch adhesives (EX adhesives) were prepared using acetone aqueous solutions containing different amounts of water. The quantities of water in the EX adhesive were 46.6, 93.2 and 208.1 mg/g, however, the quantity of MDP was kept a constant at 49.9 mg/g. Enamel and dentin reactant residues of EX adhesives were prepared after the reaction with enamel or dentin particles for 30 sec. Enamel and dentin reactants were repeatedly rinsed with 30 ml of ethanol after the reaction. Each reactant was dried at 20°C for 3 h and then analyzed using phosphorous-31 nuclear magnetic resonance (³¹P NMR) and X-ray diffraction (XRD) techniques. The curve-fitting analyses of ³¹P NMR spectrum of each enamel and dentin reactant were then performed.
Results: The amount of MDP-Ca salts produced by the demineralization of enamel and dentin increased with increasing the amount of water added (p< 0.05). The enamel and dentin samples showed a knee-point on the production rate of MDP-Ca salts at the water concentration of 93.2 mg/g. The dentin sample produced di-calcium salts of the MDP monomer and dimer along with mono-calcium salts of the MDP monomer and dimer in contrast to the enamel sample.
Conclusions: These results suggest a change in the calcium site of enamel and dentin samples that MDP demineralizes from the smear layer to the underlying enamel and dentin.