Different types of bacteria cause cavities as opposed to those causing periodontal disease. The former are caused by obligate aerobes, the latter by facultative

Different types of bacteria cause cavities as opposed to those causing periodontal disease. The former are caused by obligate aerobes, the latter by facultative anaerobes and are far more dangerous. The purpose of flossing is to get at the plaque (which forms tartar within 1-3 days) that exists interdentally and below the gum-line.