“…During the 1950's and 1960's, indigenous micro-organisms were finally implicated as the primary etiologic agents of dental caries and periodontal diseases (Orland et al, 1954(Orland et al, , 1955Jordan et al, 1959;Fitzgerald and Keyes, I960;Fitzgerald, 1963a,b;Jordan and Keyes, 1964;Fitzgerald et al, 1966). A small cadre of microbial ecologists revealed, through germ-free (gnotobiotic) and conventional animal models, that certain indigenous oral bacteria were more "virulent" than others and were able to cause gross disease in teeth, e.g., S. mutans and, in the periodontal supporting structures, Actinomyces species (Keyes, 1958(Keyes, , 1959Fitzgerald, 1963b;Fitzgerald and Keyes, 1963).…”