Synthesis and Characterization of New Methacrylate Monomers for Dentin Adhesives

Water is a major interfering factor in bonding of composite materials thus, it is critical to understand the effect of water on dentin adhesives. Various methacrylate-monomers have been used to formulate dentin adhesives and properties e.g. polymerization reactivity in water, enzymatic degradation vary with monomeric structure. Objective: The aim of this study was to synthesize and characterize branched or urethane-based methacrylate monomers, to use the new monomers in dentin adhesives, and to evaluate their properties. Methods: New monomers, trimethylolpropane mono allyl ether dimethacrylate (TMPEDMA) and 1,1,1-tri-[4-(methacryloxyethylaminocarbonyloxy)-phenyl]ethane (MPE) were synthesized by the condensation and addition reaction, respectively. The synthesized monomers were identified by FTIR and 1H-NMR spectroscopies. New adhesives, containing hydroxyethyl methacrylate (HEMA) and BisGMA (bisphenol A dimethacrylate) in addition to TMPEDMA or MPE were light polymerized in the presence of 0, 8, or 16 wt% H2O and compared to control adhesives [HEMA /BisGMA, 45/55 w/w, at 0, 8, 16 wt% H2O]. The degree of conversion (DC), tensile strength and thermal properties were determined. Following a 3-day pre-wash, adhesive discs were incubated in phosphate buffer with/without porcine liver esterase (PLE) for 8days; supernatants were collected daily and analyzed for methacrylic acid (MAA). Results: DC, tensile and thermal properties were comparable for the control and experimental adhesives. Exposure to PLE showed that the net cumulative MAA release for adhesive discs formulated with the new monomers and polymerized in water was dramatically decreased (p < 0.05) in comparison to the control. Conclusion: Adhesives are formulated in the presence of water to simulate the behavior of these materials within the wet demineralized dentin matrix. When polymerized in the presence of water, dentin adhesives that include urethane or branched linkage within the polymer matrix show greater resistance to esterase degradation, suggesting improved performance in the wet, oral environment. Supported NIH/NIDCR R01 DE014392.