[Mixed infection: specific canal aspects]

The fundamental feature of the bacteriologic flora that causes endodontic lesions is its mixed nature. It has been demonstrated that a mixed flora can more easily give rise to both acute and chronic inflammatory reactions. The coexistence of different families of bacteria within the same environment is based upon a very delicate balance given by the interplay of the various mechanisms of bacterial relationships: mutualism (symbiosis and commensalism), antagonism and synergism. The metabolic needs (nutritive and respiratory) of the different types of bacteria which cause endodontic infections are so specific that these organisms are strictly dependent on each other for their own survival in the radicular canal system and for their pathogenicity.