NMR ANALYSIS OF BONDING INTERACTIONS OF DENTIN ADHESIVES

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During the past decade advances in dental science have led to the introduction of many improved restorative materials which offer long-term stability in the oral cavity. In the area of dental adhesives much interest has focused upon the development of agents capable of chemically bonding with tooth structure. There is an extensive body of knowledge available on the physical characteristics of the interface between these adhesive materials and the tooth surface. However, very little is presently known about the chemical nature of this interface, in particular, what occurs on a molecular level between the organic adhesive agents and the mineralized tooth substrata. The purpose of this study is to utilize solid-state carbon-13 nuclear magnetic resonance (13C-NMR) to elucidate the chemical nature of the bonding interactions of the two adhesive agents N-phenyl glycine (NPG) and its gylcidyl methyl methacrylate analogue (NPG-GMA) with human dentin. Carbon-13 iostope-enriched NPG and NPG-GMA will be synthesized and interacted with prepared human dentin and dentinal collagen. The treated dentinal components will be subjected to high resolution 13C-NMR using a cross-polarization-magic angle spinning method. The nature of chemical bonding interactions between these agents and the dentin support will be determined from the resonance shifts seen in the 13C-NMR. We hypothesize that increased chemical bonding interactions between the bonding agent and the dentin will result in observable downfield anisotropic shifts of the carbon-13 labeled agent which will be seen in the 13C-NMR. The successful application of solid-state NMR technology to study the chemical interactions of dental adhesives will serve as the basis for a larger proposal to investigate bonding interactions among other families of bonding agents and to study the stability of these bonding materials under a variety of biological environments. The long-term goal of this proposal is to develop the application of "state of the art" NMR technology to reliably predict microleakage potential and the adhesive characteristics of a dental materials. Solid-state NMR offers the potential to quantitatively measure traditional parameters of adhesion with refined technologies. These carbon-13 enriched probes in conjunction with this advanced NMR analytical technology will allow the study of the molecular chemistry of the bonding interface at the restorative-tooth junction.