“…It is generally accepted that mutans streptococci and lac tobacilli are associated with dental caries [Loesche, 1986], The presence o f these bacteria in human dental plaque is indicative of an increased cariogenic activity [Krasse,1984;Loesche, 1986;Aaltonen et al" 1987;de Soet et al, 1990b;Takei et al, 1992;Batoni et al, 1992]. The bacterial flora of open carious lesions is complex, with lactobacilli, mutans streptococci, and many other oral microorganisms being isolated from the dentine [Going et al, 1978], We reported recently that the bacterial composition o f HCL is less com plex [Weerheijm et al, 1990], Bacteria other than mutans streptococci and lactobacilli are found only rarely, even when using non-selective blood agar; Actinomyces spp.…”