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The role of dental plaque biofilm in oral health

Access, Sept-Oct, 2007 by JoAnn R. Gurenlian

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Initial Adherence and Lag Phase

The first phase of supragingival biofilm formation is the deposition of salivary components, known as acquired pellicle, on tooth surfaces. This pellicle makes the surface receptive to colonization by specific bacteria. Salivary glands produce a variety of proteins and peptides that further contribute to biofilm formation. For example, salivary mucins, such as [MUC.sub.5]B and [MUC.sub.7], contribute to the formation of acquired pellicle, (16,17) and statherin, a salivary acidic phosphoprotein, and proline-rich proteins promote bacterial adhesion to tooth surfaces. (18) Acquired pellicle formation begins within minutes of a professional prophylaxis; within 1 hour, microorganisms attach to the pellicle. Usually, gram-positive cocci are the first microorganisms to colonize the teeth. As bacteria shift from plank-tonic to sessile life, a phenotypic change in the bacteria occurs requiring significant genetic up-regulation (gene signaling that promotes this shift). As genetic expression shifts, there is a lag in bacterial growth.

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Rapid Growth

During the rapid growth stage, adherent bacteria secrete large amounts of water-insoluble extracellular polysaccharides to form the biofilm matrix. The growth of microcolonies within the matrix occurs. With time, additional varieties of bacteria adhere to the early colonizers--a process known as coaggregation--and the bacterial complexity of the biofilm increases. These processes involve unique, selective molecular interactions leading to structural stratification within the biofilm. Coaggregation and subsequent cell division also increase the thickness of biofilm. (19-21)

Steady State/Detachment

During the steady state phase, bacteria in the interior of biofilms slow their growth or become static. Bacteria deep within the biofilm show signs of death with disrupted bacterial cells and other cells devoid of cytoplasm; bacteria near the surface remain intact. During this phase, crystals can be observed in the interbacterial matrix that may represent initial calculus mineralization. (22) As noted above, during the steady state stage, surface detachment and sloughing also occur, with some bacteria traveling to form new biofilm colonies.

Biofilm and Oral Disease

Biofilms can cover surfaces throughout the oral cavity. Microcolonies exist on oral mucosa, the tongue, biomaterials used for restorations and dental appliances, and tooth surfaces above and below the gingival margin (Figure 3). It is important for oral health professionals to communicate to their patients that both dental caries and periodontal disease are infectious diseases resulting from dental plaque biofilm accumulation. Each of these diseases requires specific strategies for prevention and treatment.

With respect to periodontal disease, dental plaque biofilm demonstrates a succession of microbial colonization with changes in bacterial flora observed from health to disease. Researchers studied over 13,000 plaque samples from 185 patients with conditions ranging from oral health to periodontal disease. (4,23) As noted above, based on their findings, a number of microbial complexes were identified that were associated with various stages of disease initiation and progression. Bacterial species contained in the yellow, green, and purple complexes appear to colonize the subgingival sulcus first and predominate in gingival health. In contrast, orange complex bacteria are associated with gingivitis and gingival bleeding. Interestingly, bacteria of the orange complex may also be associated with red complex microorganisms including Porphyromonas gingivalis, Tannerella forsythensis, and Treponema denticola, organisms found in greater numbers in diseased sites and in more advanced periodontal disease. (10,24)

Health Care Industry

The role of dental plaque biofilm in oral health

Access, Sept-Oct, 2007 by JoAnn R. Gurenlian

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