Inhibition of matrix metalloproteinase-9 by 10-MDP and its calcium salt contributes to improved dentin-bonding durability

The activation of matrix metalloproteinases (MMPs) is responsible for degradation of the hybrid layer. The effect of 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) on biodegradation of the hybrid layer remains unknown. This study aimed to evaluate the effects of 10-MDP and its Ca salt on MMP-9 activity and dentin-bonding durability. 10-MDP-Ca salt was synthesized and characterized by X-ray diffraction (XRD) and nuclear magnetic resonance (NMR). The effects of chlorhexidine (CHX), 10-MDP, and 10-MDP-Ca salt on MMP activity were evaluated by in-situ zymography, MMP-9 inhibition assay, and hydroxyproline (HYP) assay. Dentin-resin bonded specimens were fabricated with using CHX or 10-MDP, including Single Bond 2 (Ctr), CHX + Single Bond 2 (CHX), 10-MDP + Single Bond 2 (10-MDP), and SBU (SBU). Micro-tensile bond strength (μTBS) and nanoleakage tests were performed after 24-h or two-years water storage. XRD and NMR confirmed the presence of 10-MDP-Ca salt. The relative inhibition percentages of recombinant MMP-9 for 10-MDP and 10-MDP-Ca salt were 8.04 ± 0.83% and 55.96 ± 1.82% respectively. HYP assay showed that 10-MDP, CHX, and 10-MDP-Ca salt conditioning decreased collagen degradation. Water storage weakened μTBS of all the groups, with the Ctr and CHX groups showing more significant decreases (P < 0.05). After aging, the Ctr and CHX groups also presented more nanoleakage, and the CHX group showed more in-situ zymography fluorescence than the 10-MDP and SBU groups. The capacity to inhibit MMP-9 activity, decrease HYP release, and reduce nanoleakage of 10-MDP and its salt contribute to improvement of dentin-bonding durability.