The buccal cavity presents microorganismes whose the number and composition vary with oral hygiene and medical context (pathologies and associated drug therapies) of the patient. More than 1200 bacterial species have been identified, and among them, 400 are inhabitants of the sub-gingival biofilm. Among all these microorganismes, only 20 species participate to the etiopathogenesis of periodontal diseases.Some are recognised as major periodontopathogens other play unclear role in this pathology. They belong respectively to the red and orange complex of Socransky et al. (1998).