Evaluation of the interaction of chlorhexidine and MDP and its effects on the durability of dentin bonding

Objective This study aimed to evaluate the potential interaction of chlorhexidine (CHX) and 10-methacryloyloxydecyl dihydrogen phosphate (MDP) and its effects on the durability of dentin bonding. Methods Two commercial adhesives were tested: a MDP-free adhesive (Single Bond 2, SB2) and a MDP-containing adhesive (Single Bond Universal, SBU). Teeth were randomly assigned to six groups and tested for micro-tensile bond strength (μTBS): Ctr, direct bonding with SB2; CHX, CHX conditioning and SB2; MDP, MDP conditioning and SB2; CHX   +   MDP, combined CHX and MDP conditioning and SB2; SBU, direct bonding with SBU; CHX   +   SBU, CHX conditioning and SBU. The potential interaction of CHX and MDP was assessed by measuring nanoleakage, in situ zymography, and chemoanalytic characterization via Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR). Specimens for μTBS and nanoleakage tests were first subjected to water storage for 24   h or 6 months. Results The initial μTBS values of the Ctr and CHX groups were significantly lower than those of the other four groups (P   <   0.05). Water storage for 6 months significantly weakened all groups (P   <   0.05), with the Ctr group showing the lowest μTBS. This group also showed more obvious nanoleakage than the other five groups. In situ zymography revealed that the Ctr group showed the strongest fluorescence and that the CHX   +   MDP group showed greater fluorescence than either CHX or MDP group. FTIR, XPS, and NMR indicated that MDP can interact with hydroxyapatite. NMR detected no Ca 2+ salt peak for MDP when it was combined with CHX. Significance The application of either CHX or MDP alone can improve dentin bond durability. However, CHX may interfere with the formation of MDP–Ca salts.