Competitive interaction of 10-MDP and 4-MET with hydroxyapatite

Objectives: The functional monomer 10-methacryloxydecyl dihydrogen phosphate (10-MDP) bonds more strongly to hydroxyapatite (HAp) than 4-MET (Yoshida et al., JDR 2004). Although several adhesives contain both 10-MDP and 4-MET as functional monomers, no data is available if these functional monomers may hinder each other in their chemical interaction with HAp. We hereby aimed to study the competitive interaction of 10-MDP and 4-MET with HAp. Methods: The chemical interaction with HAp of 4 experimental adhesive solutions, containing 15 wt% 4-MET dissolved in 40 wt% H2O with 10-MDP and EtOH, respectively, varying following the weight ratios 0:45 (Exp-1), 5:40 (Exp-2), 10:35 (Exp-3), and 15:30 (Exp-4), and 1 control, containing 15 wt% 10-MDP, 40 wt% H2O, and 45 wt% EtOH (Control), was examined by means of XRD and solid-state NMR (1H MAS NMR, 31P CP-MAS NMR and 13C CPMAS NMR). TEM interfacial characterization at dentin was conducted to confirm the chemical analytic data. Results: XRD revealed nano-layering of 10-MDP-Ca salts for Exp-3 and -4 and Control, but not for Exp-1 and -2. The nano-layering intensity corresponded to the concentration of 10-MDP. 1H NMR disclosed a weak peak at 1.59 ppm for Exp-1, -2 and -3 that can be assigned to 4-MET. For the same experimental adhesive formulations, 13C CP-MAS NMR also disclosed a weak peak at 62.4 ppm that can be assigned to 4-MET. For Exp-3, -4 and -5, strong peaks were detected that represent 10-MDP and 10-MDP-Ca salts. XRD and NMR data of Exp-4 (equal amount of 4-MET and 10-MDP) and Control (no 4-MET) revealed equally intense peaks representing 10-MDP and 10-MDP-Ca salts irrespective of presence of 4-MET or not. TEM observation confirmed the chemical analytic data. Conclusions: This experiment showed that 4-MET can adsorb onto HAp, but 10-MDP’s interaction with HAp is more intensive, even when 4-MET is present as well.status: submitte