Microbial cells (predominantly bacteria) in an extracellular polymer substratum are called biofilms . Complex physical, chemical, and biological processes govern bacterial attachment, biofilm formation, and persistence . The following fundamental processes comprise the development of a bacterial biofilm: (1) Substratum pre-conditioning by circumstantial or pre-meditated adsorption of fluid phase organic molecules; (2) bacterial cell transport to the surface; (3) cell desorption from the substratum; (4) permanent cell adhesion to the substratum; (5) bacterial metabolism (cell substrate conversion; cell growth and replication; extracellular exopolymer production; cell starvation, death, lysis); and (6) biofilm removal (cell and biofilm detachment; biofilm sloughing). Naturally, the relative influence of each process is dependent upon the specific system, the prevailing environmental conditions, and biological changes throughout the lifetime of the biofilm.
A diverse community of bacteria comprises tooth plaque biofilm. Early tooth colonizers (e.g., Streptococcus, Hemophilus, Neisseria, and Veillonella) adhere to enamel pellicle protein layers via specific and non-specific adhesion mechanisms. Subsequently, other species adhere to the developing biofilm. Once established, the biofilm flora remain relatively stable, despite periodic perturbations in the environment. Oral microbial disease is associated with major shifts in the biofilm ecology. Dental caries is associated with an increased frequency of consumption of fermentable sugars in the diet, which results in an increase in the acidogenic and aciduric species (e.g., S. mutans, Lactobaccilli). Factors affecting dental plaque include fermentable sugars, low pH, redox potential, and ambient nutrients.