Enzymatic degradation of dentin adhesives containing new urethane-linked trimethacrylate monomer

Human saliva contains a variety of enzymes which may participated in the degradation of the adhesive as well as the composites. The extent of hydrolysis for the methacrylate materials appeared to be largely dependent on chemical structures of the monomer. Objective: The goal of this study was to synthesize and characterize the urethane-linked trimethacrylate monomer and to evaluate the enzymatic degradation of dentin adhesives. Methods: A new monomer, 1,1,1-tri-[4-(methacryloxyethylaminocarbonyloxy)-phenyl]ethane (MPE), was synthesized by the reaction of 1,1,1-tris(4-hydroxyphenyl)ethane and 2-isocyantoethyl methacrylate. MPE structure was identified by FTIR and 1H-NMR spectroscopies. New adhesives, containing hydroxyethyl methacrylate and BisGMA (bisphenol A dimethacrylate) in addition to MPE were formulated with H2O at 0 (2A0T), 8 (2A8T) and 16 wt % water (2A16T) and compared with control adhesives [HEMA /BisGMA, 45/55 w/w, at 0 (2A0), 8 (2A8) and 16 wt% water (2A16)]. Following the pre-wash for three days, adhesive discs were incubated in buffer solution with/without porcine liver esterase(PLE) at 37oC. Supernatants were collected daily and analyzed for methacrylic acid (MAA) by HPLC. Results: Spectral data of MPE are as follows: 1H-NMR (CDCl3):7.1-6.9 (phenyl), 6.2 and 5.6 ppm (CH2=C(CH3)COO-), 5.4 (-NH), 4.25 (-NHCH2CH2O-), 3.5 -NHCH2CH2O-), 2.1 (CH3C-), 1.9 ((CH2=C(CH3)COO-); FTIR (neat): 3270 cm-1 (-NH), 1710 cm-1 (C=O), 1637.9 cm-1 (C=C, stretching), 1158.4 cm-1 (C-O, stretching). Exposure of photopolymerized discs to PLE showed that the net cumulative MAA release in adhesives formulated with the new monomer and 8% water (2A8T: 306 ug/mL) was dramatically (P < 0.05) decreased in comparison to the control (2A8: 1352 ug/mL). Conclusions: This enhanced esterase resistance afforded by adhesives containing the synthesized urethane-linked trimethacrylate monomer is greater when this material is photopolymerized in the presence of water, suggesting better performance in the moist environment of the mouth. Supported NIH/NIDCR R01 DE014392.