Dental caries, periodontitis, and the tooth loss and other sequelae that follow are secondary to the microbial build up on teeth called plaque. The prevention and/or halting of the progression of these diseases relies on the elimination of dental plaque from the tooth surfaces. In addition to causing caries and chronic periodontitis, the bacteria of dental plaque play a role in more aggressive forms of periodontitis and necrotizing periodontal diseases.
Dental plaque is an adherent dental deposit that forms on the tooth surface composed almost entirely of bacteria derived from the resident flora of the mouth. From a microbial pathogenesis standpoint, dental plaque is the most prevalent and densest of human biofilms (Figure 41–1). The biofilm first forms in relation to the dental pellicle, which is a physiologic thin organic film covering the mineralized tooth surface composed of proteins and glycoproteins derived from saliva and other oral secretions. As the plaque biofilm evolves, it does so in relation to the pellicle, not the mineralized tooth itself. The formation of plaque takes place in stages and layers at two levels. The first is the anatomic location of the plaque in relation to the gingival line. The earliest plaque is supragingival, which may then extend to subgingival plaque. The second level is the layering within the plaque, the bacterial species involved, and the bacteria/pellicle and bacteria/bacteria binding mechanisms required.
Dental plaque biofilm. The stages of formation of the bacterial biofilm called dental plaque are shown. Early colonizers bind to the enamel pellicle and late colonizers bind to the other bacteria. (Reproduced with permission from Willey JM: Prescott, Harley, & Klein's Microbiology, 7th edition. McGraw-Hill, 2008.)
Dental plaque is a bacterial biofilm
Plaque forms in stages
The initial supragingival plaque primarily involves Gram-positive bacteria using specific ionic and hydrophobic interactions as well as lectin-like (carbohydrate binding) surface structures to adhere to the pellicle and to each other. The prototype early colonizer is Streptococcus sanguis, but other streptococci (S mutans, S mitis, S salivarius, S oralis, S gordonii), lactobacilli, and Actinomyces species are usually present. If the early colonizers are undisturbed, the late colonizers appear in the biofilm in as little as 2 to 4 days. These are primarily Gram-negative anaerobes including anaerobic spirochetes. These include Fusobacterium, Porphyromonas, Prevotella, Veillonella, Treponema denticola, and more Actinomyces species. These bacteria use similar mechanisms to bind to the early colonizers and to each other. This sets up a highly complex biofilm in which coaggregation involves structures that the bacteria brought with them (lectins), quorum sensing, and new metabolic activity. An example of the latter is the formation of extracellular glucan polymers, which act like a cement binding the plaque biofilm together. The biofilm also fastens nutrient and growth regulatory relationships ...