Novel self-strengthening hybrid dentin adhesive via a facile visible-light irradiation triple polymerization

Abstract

Event Abstract Back to Event Novel self-strengthening hybrid dentin adhesive via a facile visible-light irradiation triple polymerization Qiang Ye1, Linyong Song1, Xueping Ge1, Anil Misra1, 2 and Paulette Spencer1, 3 1 University of Kansas, Bioengineering Research Center, United States 2 University of Kansas, Department of Civil Engineering, United States 3 University of Kansas, Department of Mechanical Engineering, United States Introduction: In vivo biodegradation of the bond between the composite and tooth, i.e. the composite restoration’s adhesive bond layer, is considered a major contributor to premature failure of composite restorations[1]. The structure of methacrylate-based dentin adhesives suggests a general mechanism for their chemical and enzymatic degradation in oral fluids. In our previous study[2], the crosslink density of dentin adhesives can be improved with the addition of epoxide monomers. The objective of this work was to further develop a self-strengthening methacrylate-based dentin adhesive system by introducing an epoxy cyclohexyl trimethoxysilane (TS) containing both epoxy and methoxysilyl functional groups and cured by visible-light photopolymerization. Materials and Methods: Neat methacrylate monomer mixture (Scheme 1) of HEMA/BisGMA at 45/55 wt% was used as the control (C0). Experimental formulation with HEMA/BisGMA/TS (22.5/27.5/50, wt%) was used to investigate the free radical polymerization of methacrylate, ring-opening cationic polymerization of epoxy, and photoacid-induced sol-gel reaction. The polymerization behavior was monitored in-situ using real-time Fourier transform infrared spectroscopy (FTIR). The properties of copolymers at TS concentration from 5 to 35 wt% were determined using dynamic mechanical analysis (DMA). The leachables from polymer discs were determined by HPLC using a reverse phase C18 column and UV/diode array detectors. Results and Discussion: In this triple polymIn this triple polymerization system, free radical polymerization rate was the highest and the hydrolysis-condensation reaction was the slowest. In acidic environments, the fast hydrolysis reaction and the limited condensation gave rise to the self-strengthening process, which significantly improved the mechanical properties. When the TS concentration was 10-20 wt%, the copolymers became more homogeneous and the storage modulus at 70 0C reached maximum. The cumulative amounts of leached monomers were reduced significantly (Figure 1). Conclusion: With the introduction of both epoxy and trimethoxysilyl functional groups, a self-strengthening hybrid system has been developed for application as a dentin adhesive. During visible-light irradiation, a triple polymerization mechanism was involved (Figure 2). Supported by grant NIH/NIDCR R01 DE022054. Scheme 1. Chemical structures of monomers used in the formulations. Figure 1. Cumulative release of HEMA from the dentin adhesive copolymers as a function of incubation time in ethanol at 23±2 0C Figure 2. Proposed polymethacrylate-based matrix network structure and the autonomic self-strengthening process with different TS concentrations. (A1 and A2) Polymethacrylate-based network formed by free radical polymerization, cationic ring-opening polymerization, and limited photoacid-induced sol-gel reaction in dry conditions after 40 s irradiation; (B1 and B2) photoacid-induced ring-opening polymerization and sol-gel reaction after 24 h; (C1 and C2) self-strengthening process via sol-gel reaction and ring-opening polymerization in wet environment. Supported by grant R01DE022054 (PS, JSL), from the National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892.