Light-propelled dental adhesives with enhanced bonding capability

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Project Summary/Abstract: The growing preference for aesthetically pleasing composite restorations is reflected in the over 122 million dental restorations placed annually in the U.S. However, the replacement of failed restorations accounts for greater than 50% of all restorative dental work. The relatively short duration composite restorations last in comparison to traditional restorations (e.g., amalgam) is attributed to a weak hybrid layer, which is the layer that bonds the adhesive to the tooth structure. Bonding to dentin in the tooth in a consistent and stable manner is challenging. While applying the adhesive resin on etched dentin, relying on simple diffusion to homogenously infiltrate the dentinal tubules up to the etch depth in the presence of pulpal pressure makes adhering to dentin less predictable and more technique sensitive. Leaving exposed collagen within the hybrid layer compromises its mechanical strength and long-term stability by leaving it vulnerable to proteolytic degradation. We propose a solution to this problem by introducing light-responsive, methacrylated nanoadditives that swell and disperse within conventional adhesives and are designed to move away from a visible light source. By using light-induced resin mobility, we propose to drive the controlled, light-activated, homogenous diffusion of hydrophobic and hydrophilic adhesive resin components within dentinal tubules up to the depth of etching. This will ensure that the demineralized surfaces and exposed collagen networks are now evenly and homogenously enveloped by resin within the hybrid layer to form a mechanically robust anchor with the tooth. Subsequently, pendant functionality on the surface of the nanoadditives will further enhance the strength of the resin-dentin interface and the stability of the collagen by introducing crosslinking via primary and secondary bonds. The presence of labile functional groups that can induce intermolecular and intermicrofibrillar collagen crosslinks, along with hydrophobic interactions can enhance the mechanical properties and biostability of the adhesive layer. Increased crosslinking will also decrease the susceptibility of the hybrid layer to bacterial collagenase and MMPs. Therefore, we will specifically aim to 1) synthesize 4 to 6 light-responsive nanoadditives that can be incorporated within conventional adhesive resins and study adhesive resin propulsion as a function of 430-480 nm light exposure, polymerization kinetics, degree of conversion, and mechanical properties under simulated pulpal pressure. Toward this end, light-responsive nanoadditives will be synthesized using a solution polymerization protocol and the adhesive resin-nanoadditive networks will be characterized based on the type and concentration of light-responsive moieties within the networks. Pendant functionality introduced via nanoadditives to enhance bioadhesion and collagen crosslinking will also be evaluated. In Aim 2, we will establish the conditions by which the nanoadditives can enhance bioadhesion within the hybrid layer via additional crosslinking and characterize the µTBS, interfacial gap formation, and stability of the resin-tooth interface in the oral physiochemical environment.