Nanoscale Characterisation of Salivary Pellicle
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Nanoscale Characterisation of Salivary Pellicle Michelle E. Dickinson and Adrian B. Mann Department of Ceramics & Materials Engineering and Department of Biomedical Engineering, Rutgers University, Piscataway, NJ 08854, USA ABSTRACT Salivary pellicle is an organic biofilm formed by the physisorption of proteins and carbohydrates onto the surface of dental enamel exposed to the oral environment. The pellicle has several key roles in oral physiology including lubrication and reduction of friction between teeth during mastication, as well as chemical protection of the enamel against acidic solutions. However, pellicle proteins are known to react with dietary compounds to cause extrinsic staining on the tooth surface. In this study, nanoindentation and AFM have been used in vitro to examine the acquired salivary pellicle formed in vivo on dental enamel. The mechanical properties, growth, structure and morphology of pellicle grown in vivo on human enamel surfaces have been analysed. In addition, the effects of dietary agents such as polyphenols on the pellicle’s morphology and properties have been studied. It was found that initial adsorption of proteins on the enamel surface occurred within 30 seconds of exposure to the oral cavity, with full growth achieved within 2 hours. Differences in the properties of the pellicles such as surface adhesion, and time dependent effects due to polyphenol interaction were measured using nanoindentation. It was seen that the polyphenol interaction has a significant effect on these properties. These results suggest that the stained pellicle is mechanically stiffer, but also less viscous and more fluid like. This could explain why traditional tooth brushing techniques do not efficiently remove this layer. INTRODUCTION Saliva is the body's natural protective mechanism against tooth decay. It contains salivary proteins which adsorb strongly onto the teeth, offering the enamel some protection against acid dissolution. This adsorbed protective layer is referred to as salivary pellicle, which adsorbs onto all solid materials exposed to the oral cavity and provides both chemical protection and lubrication. The initial stages of pellicle formation on enamel are still largely unknown; however, current research shows that a complete pellicle layer forms within 2.5 minutes [1], and the full thickness of ≈1 µm is reached within 2 hours [2,3]. The morphology of the pellicle layer has been visualised using scanning and transmission electron microscopy [4,5] which revealed a globular and granular structure. However, the preparation of these samples involves fixing and dehydrating, which may affect the morphology when compared to pellicle in its normally hydrated state. To overcome this problem, atomic force microscopy has been utilised to allow three-dimensional imaging of the pellicle without prior treatment. Similar experiments have previously been done using atomically flat samples such as silicon wafers as substrates for the pellicle to grow on to. However, it has been seen that the
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