¹³C NMR analysis of the etching efficacy of acidic monomers in self-etching primers

It is well understood that the application of a self-etching primer enhances the bonding of the resin to the tooth. In this study, the demineralisation aspects by the Mega Bond Primer (MB) or the UniFil Bond Primer (UB) on the tooth were investigated by using liquid-state and solid-state ¹³C NMR techniques. The addition of hydroxyapatite or dentine to MB and the addition of dentine to UB resulted in the decrease in the peak intensity of the ¹³C NMR peaks attributed to the methacryloxy decyl phosphoric acid, MDP in the MB or 4-methacryloyloxy ethoxy carbonylphthalic acid, 4-MET in the UB. This decrease was because the MDP or 4-MET demineralised the tooth and the calcium salts produced from the MDP or 4-MET were precipitated from the MB or UB solution. The NMR technique is very powerful in evaluating the demineralisation aspects of the tooth by a self-etching primer. However, the calcium salts produced by the MDP or 4-MET on the tooth surface would not facilitate retention in bonding, since these calcium salts were merely deposited on to the surface of the tooth.