Dental Plaque and Biofilms

Biofilms are composed of microbial cells encased within a matrix of extracellular polymeric substances, such as polysaccharides, proteins, and nucleic acids.
Dental plaque is a type of biofilm that is composed primarily of microorganisms encased within an extracellular matrix.
One gram of plaque (wet weight) contains approximately 10^11 bacteria.

Organic constituents of the matrix include polysaccharides, proteins, glycoproteins, lipid material, and DNA.
Inorganic components of plaque are predominantly calcium and phosphorus, with trace amounts of other minerals, such as sodium, potassium, and fluorine.

Dental plaque is classified as supragingival or subgingival on the basis of its position on the tooth surface toward the gingival margin.
Supragingival plaque is found at or above the gingival margin; when in direct contact with the gingival margin, it is referred to as marginal plaque.
Subgingival plaque is found below the gingival margin, between the tooth and the gingival pocket epithelium.

The process of plaque formation can be divided into several phases: formation of the pellicle on the tooth surface, initial adhesion/attachment of bacteria, and colonization/plaque maturation.
The acquired pellicle is a layer of organic material that coats all surfaces in the oral cavity, including the hard and soft tissues.
The bacteria that adhere to tooth surfaces do not contact the enamel directly but interact with the acquired enamel pellicle.

The specific interactions between microbial cell surface “adhesin” molecules and receptors in the salivary pellicle determine whether a bacterial cell will remain associated with the surface.
Primary colonizers provide new binding sites for adhesion by other oral bacteria through coadhesion.
The metabolic activity of the primary colonizers modifies the local microenvironment in ways that can influence the ability of other bacteria to survive in the dental plaque biofilm.

Coaggregation is the ability of bacteria to adhere to different species and genera of microorganisms.
Well-characterized interactions of secondary colonizers with early colonizers include the coaggregation of F. nucleatum with S. sanguinis, Prevotella loescheii with A. oris, and Capnocytophaga ochracea with A. oris.
Secondary colonizers such as P. intermedia, P. loescheii, Capnocytophaga spp., F. nucleatum, and P. gingivalis do not initially colonize clean tooth surfaces but rather adhere to bacteria that are already in the plaque mass.

The nonspecific plaque hypothesis states that it is the total bulk of plaque, which determines the pathogenicity rather than the individual species within it.
The specific plaque hypothesis states that not all plaque is pathogenic and its pathogenicity depends on the presence of certain specific microbial pathogens in plaque.
The ecological plaque hypothesis states that both the total amount of dental plaque and the specific microbial composition of plaque may contribute to the transition from health to disease.

In a biofilm, bacteria have the capacity to communicate with each other through quorum sensing, in which bacteria secrete a signaling molecule that accumulates in the local environment and triggers a response such as a change in the expression of specific genes.
Organisms in a biofilm are 1000-1500 times more resistant to antibiotics as compared to their planktonic state.

Dental plaque biofilm cannot be eliminated permanently, but its pathogenic nature can be reduced by reducing the bioburden and maintaining a normal flora with appropriate oral hygiene methods.
This can result in the prevention or management of the associated sequelae, including the development of periodontal diseases.

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