Fig. 2.

A Description of the Driver-Passenger Model of the Oral Cavity. The gingiva of those who have periodontal disease are intrinsically colonized by pathogenic bacteria of the red complex or “drivers” of the disease process. These drivers can cause inflammation and increased cell proliferation. This leads to bleeding and rupturing of the tissue, which alters the microenvironment and the selective pressure on the local microbiota. These changes facilitate the gradual replacement of driver bacteria by “passengers,” consisting of opportunistic pathogens or other bacteria with a competitive advantage in the disease process. Progression of the disease may be either suppressed (by healthy passenger bacteria) or promoted (by pathogenic passenger bacteria) because of these microbial colonization changes.