Dental pellicle is a protein film that forms on the surface enamel by selective binding of glycoproteins from saliva that prevents continuous deposition of salivary calcium phosphate. It forms in seconds after a tooth is cleaned or after chewing. It protects the tooth from the acids produced by oral microorganisms after consuming carbohydrates.
Pellicle and plaque formation
Plaque is a biofilm composed of several different kinds of bacteria and their products that develop over the enamel on a layer known as pellicle. The process of plaque formation takes several days to weeks and will cause the surrounding environment to become acidic if not removed. The surface of enamel attracts salivary glycoproteins and bacterial products creating the pellicle layer. This thin layer forms on the surface of the enamel within minutes of its exposure. These glycoproteins include proline rich proteins that allow bacterial adhesion.
The first bacteria to attach to these pellicle glycoproteins are gram positive aerobic cocci such as Streptococcus sanguinis. These bacteria are able to replicate in the oxygen rich environment of the oral cavity and form micro-colonies within minutes after attachment. Other bacteria including Streptococcus mutans are able to grow in these colonies. Streptococcus mutans is important because it is associated with dental caries. These bacteria produce an enzyme known as glucosyltransferase. Glucosyl transferase converts sucrose into exopolysaccharides. These exopolysacharides create a sticky environment that allows other bacteria to attach to the initial colonies and protect them from acidic environments. As the plaque begins to develop and expand, oxygen can no longer diffuse into the colonies.
After a few days anaerobic gram negative cocci, rods, and filaments begin to colonize the plaque. After several weeks the cocci, rods, and filaments grow together forming colonies known as corncobs. This anaerobic environment causes facultative anaerobes such as S. mutans and Lactobacilli to break down sucrose through fermentation pathways. These bacteria produce lactic acid as a metabolic byproduct. If the concentration of lactic acid becomes high enough it can cause the pH around the plaque to drop below 5.5 and demineralization will occur.
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