The Biofilm Community: Rebels with a Cause

Oral biofilms are some of the most complex and diverse ecosystems developed by successive colonization of more than 600 bacterial taxa. Development starts with the attachment of early colonizers such as Actinomyces species and oral streptococci on the acquired pellicle and tooth enamel. These bacteria not only adhere to the tooth’s surface, but also interact with each other and lay foundation for attachment of bridging colonizers such as Fusobacterium nucleatum followed by late colonizers including the red complex species Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola, the founders of periodontal disease. As the biofilm progresses from supragingival sites to subgingival sites, the environment changes from aerobic to anaerobic, thus favoring the growth of mainly Gram-negative obligate anaerobes while restricting the growth of the early Gram-positive facultative aerobes. Microbes present at the supragingival level are mainly related to gingivitis and root caries, whereas subgingival species advance the destruction of teeth supporting tissues, and thus cause periodontitis. This review summarizes our present understanding and recent developments on the characteristic features of supra- and subgingival biofilms, interaction between different genera and species of bacteria constituting these biofilms, and draws our attention to the role of some of the recently discovered members of the oral community.