Focal infection theory and its acceptance and discreditation - Focal infection theory is the historical concept that many chronic diseases are caused by localised infections. - Focal infections are often asymptomatic and cause disease elsewhere in the host. - The theory explained virtually all diseases, including arthritis, atherosclerosis, cancer, and mental illnesses. - Focal infection theory was widely accepted in medicine by the 1920s. - Focal infection theory was discredited in the 1940s due to research attacks that proved its falsity. - Dental restorations and endodontic therapy became favored again in mainstream dentistry and medicine.

Alleged foci of infection - Alleged foci of infection included the appendix, urinary bladder, gall bladder, kidney, liver, prostate, and nasal sinuses. - Dental decay, infected tonsils, dental restorations, and endodontically treated teeth were blamed as foci of infection. - Tonsillectomies and tooth extractions were popular approaches to treat or prevent diverse diseases.

Untreated endodontic disease and alternative perspectives - Untreated endodontic disease retained mainstream recognition as fostering systemic disease. - Alternative medicine and biological dentistry continued highlighting dental treatments as foci of infection causing chronic and systemic diseases. - Mainstream recognition of focal infection is endocarditis, if oral bacteria enter the blood and infect the heart. - Scientific evidence supporting general relevance of focal infections remained slim. - Evolved understandings of disease mechanisms established a third possible mechanism—metastasis of infection, metastatic toxic injury, and metastatic immunologic injury.

Renewed attention to dental infections - Dental infections are widespread and significant contributors to systemic diseases. - Mainstream attention is on ordinary periodontal disease, not on hypotheses of stealth infections via dental treatment. - Some doubts were renewed in the 1990s by conventional dentistry's critics. - Dentistry scholars maintain that endodontic therapy can be performed without creating focal infections. - Dental infections have gained renewed attention in recent years.

Rise and popularity (1890s–1930s) - Focal infection theory appeared in modern medicine in 1877. - The breakthrough by Robert Koch in 1882 premised the modern principle of focal infection. - In 1890, German dentist Willoughby D Miller attributed oral and extraoral diseases to infections. - Miller identified bacteria in tooth pulp samples in 1894 and advised root canal therapy. - Ancient and folk concepts found new outlet in medical bacteriology, a pillar of the new scientific medicine.