The notion of periodontal disease being the major cause of tooth loss among adults was rooted in the focal infection paradigm that dominated the first half of the 20th century. This paradigm was established largely by personal opinions, and it was not until the development of periodontal indices in the mid-1950s that periodontal epidemiology gained momentum. Unfortunately, the indices used suffered from a number of flaws, whereby the interpretation of the research results took the form of circular reasoning. It was under this paradigm that therapeutic and preventive intervention for periodontal diseases became entirely devoted to oral hygiene, as poor oral hygiene and older age were understood to explain nearly all the variation in disease occurrence. In the early 1980s, studies appeared that contradicted the concepts of poor oral hygiene as the inevitable trigger of periodontitis and of linear and ubiquitous periodontitis progression, whereby periodontal epidemiology was led into a relatively short-lived high-risk era. At this time, it became evident that old scourges continue to haunt periodontology: the inability to agree in operational clinical criteria for a periodontitis diagnosis and the inability to devise both a meaningful and a useful classification of periodontal diseases based on nominalist principles. The meager outcome of the high-risk era led researchers to resurrect the focal infection paradigm, which is now dressed up as periodontal medicine. Unfortunately, these developments have left the core of periodontology somewhat disheveled and deserted.