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The purpose of this study was to evaluate dental erosion in 0.1 and 1.0% citric acid in vitro by several different methods and to assess the protective potential of experimentally formed salivary pellicle (24 h in vitro). Bovine enamel slabs were embedded in epoxy resin and polished. Erosion was performed in citric acid for 1, 5 or 10 min and recorded as microhardness loss, as changes of surface roughness (R_a, R_t and R_zDIN) and as calcium release. Additionally, erosive alterations were observed with scanning electron microscopy. Significant microhardness loss on non-pellicle-covered specimens was measured after 1-min exposure to 0.1% citric acid. Microhardness loss was time- and concentration-dependent. Salivary pellicle significantly inhibited both microhardness loss, except after 10-min immersion in 1.0% citric acid, and significantly reduced the increase of surface roughness. There were, however, no significant differences in calcium release between pellicle-covered and non-covered enamel. The results support the general conclusion that salivary pellicle effectively protects enamel surface against short-term erosion in organic acids.

Immunological and biochemical analyses have shown that alpha-amylase is an essential component of the acquired pellicle. After adsorption, this enzyme might act as a receptor for bacterial adherence. However, data indicating that amylase is bound to the pellicle surface in vivo and thus available for adhering bacteria are rare. Therefore, the present study focused on alpha-amylase within the pellicle formed in situ, using gold-immunolabeling electron microscopic techniques. Pellicles were formed by intra-oral exposure of enamel specimens for 30 and 120 min in six subjects. The results obtained by transmission electron microscopy indicate that amylase was randomly distributed in the pellicle layer without any preferential localization within the pellicle. Thus, salivary alpha-amylase might be considered as an important structural component that is even involved in the early stages of pellicle formation. The findings of field emission in-lens scanning electron microscopy provided evidence that the enzyme is located on the pellicle surface. It could be concluded that alpha-amylase might act as a receptor for bacterial adherence to the pellicle in vivo.

Saliva contacting with solid surfaces in the oral cavity forms a coat termed the pellicle. However, its formation is not fully understood. Although indications for the existence of supramolecular pellicle precursors have been reported, the possible relationship between them and pellicle formation is unclear. This study investigates the ability of supramolecular precursors to form the pellicle via interaction with a solid surface. Fixed and unfixed salivary globes were spread onto a microscopic grid and examined by transmission electron microscopy. Biochemical pretreatment of saliva revealed that neither disulphide links nor transglutaminase-mediated crosslinking are responsible for maintaining the salivary globes, i.e. supramolecular pellicle precursors. However, the detergent, sodium dodecyl sulphate, caused dissociation of the salivary globes, indicating their micellar nature. Saliva contacting a formvar film for 10 s did not form a complete surface coating, but single supramolecular pellicle precursors were observed attached to the surface. After extension of the contact time to 60 s, a surface layer was formed by clustering and fusion of the supramolecular pellicle precursors. The supramolecular pellicle precursors are unstable and attain a thermodynamically more favourable state by adhesion to a solid surface. As a result, a layer of fused precursors covering the solid surface is formed -- the salivary pellicle.

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