Dental Plaque

Dental Plaque

Define dental plaque and give its Classification and composition, describe in detail the role of dental plaque in initiation and progression of periodontal disease.
Or
Define dental plaque. Discuss its role in etiology of periodontal disease.
Or
Define and classify plaque. Write its role in periodontal disease.
Answer. Dental plaque: Dental plaque is Defined as an adherent intercellular matrix consisting primarily of proliferating microorganisms along with a scattring of epithelial cells, leucocytes and macrophages.

Plaque

It is Defined as the sof deposit which forms the biofim adhering to the tooth surface or other hard surfaces in oral cavity including removable and fied restorations.

Classification of Dental Plaque

Based on the relationship to gingival margin

• Supragingival:
  • Coronal plaque: Plaque in contact with only tooth surface
  • Marginal plaque: Associated with the tooth surface at gingival margin
• Subgingival:
  • Attached plaque: It can be tooth, epithelium and/or connective tissue associated.
  • Unattached subgingival plaque

Composition of Dental Plaque

• Bacteria along with the intercellular matrix are microbial plaque.
• 1 mg of dental plaque contains up to 250 million bacteria.
• Non-bacterial microorganisms such as yeast, mycoplasma, protozoa as well as some viruses are seen in small amount.
• Various host cells, i.e. epithelial cells, macrophages and leucocytes are also present.
• Intercellular matrix accounts for 25% of plaque volume and have organic and inorganic materials.
• Organic matter has polysaccharide protein complex produced by microorganisms.
• Protein such as albumin present in plaque is derived from gingival crevicular fluid.
• Various carbohydrates are also present, i.e. levans, glucans, galactose and methylpentose. Carbohydrates in form of levans provide mainly energy while glucans not only provide energy but also work as organic skeleton of plaque.
• Lipids are also present in plaque and are derived from disrupted cell wall of gram-negative bacteria.
• Various inorganic material of plaque are calcium, phosphorus with small amount of magnesium, potassium and sodium.

Role of Dental Plaque in Periodontal Disease

• Gingival sulcus and periodontal pocket consists of plenty of gingival crevicular fluid, which flows outward from the base of the pocket. So, to colonize themselves, bacteria must attach to available surfaces for preventing the displacement by fluid flow. So adherence represents a virulence factor. Surfaces which are available for attachment are as follows:
  • Tooth or root, e.g. A. viscosus binds to proline-rich proteins which are found on saliva-coated tooth surfaces.
  • Tissues, i.e. P. gingivalis bind to connective tissue components i.e. firinogen and fironectin.
  • Pre-existing plaque, e.g. A. viscosus bind to polysaccharide receptor present on cells of Streptococcus sanguinis.
• Bacteria present in plaque can lead to periodontal disease directly by injuring the host tissues through toxins, enzymes and toxic metabolic end products or indirectly by stimulating host-mediated responses which leads to tissue injury.
• Process of tissue destruction results from elaboration of bacterial substances that directly or indirectly cause degradation of the periodontal tissues.
• Many of the periodontal pathogens invade the periodontal tissues and evade the host defenses which cause them to infect and as well as damage the periodontal tissues.
• Bacteria may enter host tissues by following:
  • Bacteria penetrate directly by widening and rupturing intercellular spaces of stratum spinosum and perforation found in basal lamina.
  • Bacteria can also penetrate through the ulcerations in epithelium of sulcus or pocket.
  • Bacteria can invade throughout the microholes present in the surface created by transmigrating leucocytes.
• Pathogens such as A. actinomycetemcomitans and P. gingivalis suppress the host defense cells. A. actinomycetemcomitans secrete an exotoxin, i.e. leukotoxin which inhibit the function of polymorphoneutrophils and is also capable of killing mature T and B cells.
• IgA, IgG proteases, firolysin catalase and superoxide dismutase leads to evasion of host defenses.
• Various enzymes are released by these pathogens such as collagenases, aminopeptidases, gelatinase, acid phosphatase, alkaline phosphatase and hyaluronidase causes tissue destruction and periodontal disease manifestations.
• Lipopolysaccharides of gram-negative bacterial cell wall has complex lipid, i.e. lipid A which is attached to a polysaccharide. This lipopolysaccharide is known as endotoxin as it is fimly bound to tooth surface and is released when the cells are lysed.
• As there are many gram-negative bacteria present in periodontal pocket which leads to release of endotoxin which interact with the receptors present on macrophages and monocytes which causes release of cytokines, i.e. Interleukin 1 and tumor necrosis factor. Complements are also activated through alternative pathway. This causes intravascular coagulation and tissue necrosis and also has cytotoxic effects on fibroblasts and various other cells.
  • Endotoxins also cause leucopenia and play an important role in pathogenesis of periodontal diseases.
  • Peptidoglycan found in many bacteria causes stimulating bone resorption and inducing macrophages to produce prostaglandin and collagenases.
• Capsular substances also lead to tissue destruction. These capsular substances are seen on outermost surface of many bacterial cells.