Ultrastructure of the Dentin Pellicle and the Impact of Erosion

While the ultrastructure of the enamel pellicle and its erosion protective properties are well studied, the dentin pellicle is still neglected in dental research. Therefore, the ultrastructure and erosion protective properties of a pellicle formed on bovine dentin specimens were investigated in the present study. The dentin pellicle was formed in situ for 3, 30, 120, and 360 min at buccal or palatal oral sites of 3 subjects and analyzed by transmission electron microscopy. In order to clarify the impact of an erosive challenge to the ultrastructure of the pellicle and the underlying dentin, specimens were exposed to the oral cavity and eroded in vivo with 0.1% or 1% citric acid either immediately or after 30 min of pellicle formation. Specimens that were eroded without exposure to the oral cavity served as control. In another trial, specimens with a 30-min pellicle were exposed to the oral cavity for a further 60 min after the erosive challenge to investigate the effect of saliva on the impaired pellicle and dentin. Transmission electron micrographs reveal a globular and granular structured pellicle layer, which was thicker when the pellicle was formed buccally or with longer formation times. Erosion with citric acid reduced the thickness of the pellicle and interrupted its continuity. The dentin was also affected by erosion, which was represented by a lower electron density and formation of demineralized lacunae. These were infiltrated by a granular structured material when specimens were exposed to the oral cavity. After further intraoral exposure, the infiltration was more pronounced, indicating a significant impact of saliva on the demineralized dentin. A reformation of the dentin pellicle on the other hand did not occur. In conclusion, the dentin pellicle is neither acid-resistant nor able to effectively protect dentin from erosion.