Determination of Molecular Species of Calcium Salts of MDP Produced in Demineralization of Tooth Apatite

<p> Purpose: One-step self-etch adhesives (G-Bond Plus) based on 10-methacryloyloxydecyl dihydrogen phosphate (MDP) have become widely utilized due to their simplicity of application. The aim of this study was to determine the type of molecular species of calcium salts of MDP (MDP-Ca salts) that form to understand the layering mechanism of MDP-Ca salts.</p><p> Methods: Bovine crown enamel particles or bovine crown dentin particles of 0.200 g were suspended in 1.000 g of G-Bond Plus, and the suspensions were vibrated for 1, 30, or 60 minutes. After centrifuging these suspensions, solid-state ³¹P NMR spectra of the supernatant solution of adhesives were observed using an EX-270 spectrometer. The enamel and dentin reactants of G-Bond Plus (MDP-based) were analyzed using phosphorous-31 nuclear magnetic resonance (³¹P NMR) and X-ray diffraction (XRD) techniques. Curve-fitting analyses of the corresponding ³¹P NMR spectra were performed by assuming that DCPD with an amorphous phase was also produced along with several types of MDP-Ca salts synthesized previously.</p><p> Results: The curve-fitting analyses of each ³¹P NMR spectrum of enamel and dentin reactants of G-Bond Plus were performed. The curve-fitting analyses demonstrated that enamel and dentin developed several types of MDP-Ca salts and amorphous DCPD during decalcification. The peak intensity of MDP that had been consumed yielding several types of MDP-Ca salts was determined by totaling the relative intensity ratios of the simulated peaks for each MDP-Ca salt in each group. The amounts of MDP-Ca salts and DCPD produced by the enamel or dentin differed with reaction time. MDP was utilized in all of the all-in-one adhesives. The curve-fitting analyses demonstrated that enamel and dentin developed four types of MDP-Ca salts and amorphous DCPD during decalcification.</p><p> Conclusion: The molecular species of MDP-Ca salts produced by enamel and dentin were mono-calcium salts of MDP-monomer and MDP-dimer, and di-calcium salts of MDP-monomer and MDP-dimer.</p>