Oral cavity is a very suitable habitat for a wide range of bacteria of which a significant proportion is facultative or strict anaerobes. In healthy individuals, specific sites of the oral cavity are colonized by specific microbial communities, and a balance of the species within the community, known as “microbial homeostasis”, is maintained. When this balance is disrupted by ecological perturbations, the biofilm composition changes leading to the initiation of local infections that may ultimately lead to tooth loss. At the onset of the infections, Gram-positive bacteria dominate the biofilm composition, but if left undisturbed, a more complex biofilm builds up where Gram-negative anaerobic and proteolytic rods become dominant.