THE ROLE OF SUPRAGINGIVAL DENTAL PLAQUE IN THE INITIATION OF GINGIVITIS
Many types of materials accumulate on teeth. By far the most widespread and important deposit is dental plaque. Plaque consists primarily of microorganisms in an organ-ized matrix of organic and inorganic components. Bacteria account for at least 70% of the mass of plaque. In fact, one cubic millimeter of dental plaque contains more than 100 million bacteria consisting of more than 400 species. The organic matrix of plaque consists of polysaccharide, pro-tein, and lipid components, while the inorganic matrix is composed primarily of calcium and phosphorous ions.
The dental plaque above the gingival margin of the tooth is designated as supragingival, and the dental plaque below the gingival margin (i.e., in the gingival sulcus or pocket) is called subgingival. Gingivitis can be experimentally induced in an uninflamed periodontium by allowing the unimpeded accumulation of supragingi-val plaque and is reversed completely by the thorough and complete removal of supragingival plaque.
Gingivitis is due principally to the accumulation and retention of plaque at or near the gingival margin. The accumulation of supragingival plaque is also a prime in-fluence in the development of subgingival plaque. As undisturbed plaque matures, it changes in composition and becomes more complex. A bacterial succession oc-curs whereby microorganisms associated with gingival health, that is, gram-positive rods and cocci, are re-placed by microorganisms associated with gingivitis, that is, gram-negative rods and cocci, as well as spiral or-ganisms and spirochetes. As a consequence of the change in microflora, the inflammation-induced changes in the gingiva cause an increase in epithelial cell turnover and connective tissue degradation, resulting in anatomical changes that tend to deepen the gingival sulcus, causing a gingival pocket to form. This change in gingival architecture and the subgingival environment provides a new and better protected niche for bacteria to grow. Here they are continually bathed by exudate from the gingival crevice and end products from the supragingival plaque. Hence, control of supragingival plaque will also have a profound influence on the de-veloping composition of periodontitis-associated sub-gingival plaque.