Figure 1.

Three hypothetical sufficient causes of disease are pictured representing 3 different mechanisms in the etiology of periodontitis. In these models Porphyromonas gingivalis (Pg), Aggregatibacter actinomycetemcomitans (Aa), Tanerella forsythia (Tf), Filifactor alocis (Fa), Treponema denticola (Td), smoking, diabetes, and gene mutations 1, 2, 3, and 4 represent causal components for periodontitis; whereas Pg is pictured as a necessary cause for periodontitis. Modified from Kenneth Rothman's model of causation⁹¹ with approval from Oxford University Press and the author.