Focal infection theory and its acceptance and discreditation
- Focal infection theory is the historical concept that many chronic diseases are caused by localized 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.
Focal infection theory is the historical concept that many chronic diseases, including systemic and common ones, are caused by focal infections. In present medical consensus, a focal infection is a localized infection, often asymptomatic, that causes disease elsewhere in the host, but focal infections are fairly infrequent and limited to fairly uncommon diseases. (Distant injury is focal infection's key principle, whereas in ordinary infectious disease, the infection itself is systemic, as in measles, or the initially infected site is readily identifiable and invasion progresses contiguously, as in gangrene.) Focal infection theory, rather, so explained virtually all diseases, including arthritis, atherosclerosis, cancer, and mental illnesses.
An ancient concept that took modern form around 1900, focal infection theory was widely accepted in medicine by the 1920s. In the theory, the focus of infection might lead to secondary infections at sites particularly susceptible to such microbial species or toxin. Commonly alleged foci were diverse—appendix, urinary bladder, gall bladder, kidney, liver, prostate, and nasal sinuses—but most commonly were oral. Besides dental decay and infected tonsils, both dental restorations and especially endodontically treated teeth were blamed as foci. The putative oral sepsis was countered by tonsillectomies and tooth extractions, including of endodontically treated teeth and even of apparently healthy teeth, newly popular approaches—sometimes leaving individuals toothless—to treat or prevent diverse diseases.
Drawing severe criticism in the 1930s, focal infection theory—whose popularity zealously exceeded consensus evidence—was discredited in the 1940s by research attacks that drew overwhelming consensus of this sweeping theory's falsity. Thereupon, dental restorations and endodontic therapy became again favored. Untreated endodontic disease retained mainstream recognition as fostering systemic disease. But only alternative medicine and later biological dentistry continued highlighting sites of dental treatment—still endodontic therapy, but, more recently, also dental implant, and even tooth extraction, too—as foci of infection causing chronic and systemic diseases. In mainstream dentistry and medicine, the primary recognition of focal infection is endocarditis, if oral bacteria enter blood and infect the heart, perhaps its valves.
Entering the 21st century, scientific evidence supporting general relevance of focal infections remained slim, yet evolved understandings of disease mechanisms had established a third possible mechanism—altogether, metastasis of infection, metastatic toxic injury, and, as recently revealed, metastatic immunologic injury—that might occur simultaneously and even interact. Meanwhile, focal infection theory has gained renewed attention, as dental infections apparently are widespread and significant contributors to systemic diseases, although mainstream attention is on ordinary periodontal disease, not on hypotheses of stealth infections via dental treatment. Despite some doubts renewed in the 1990s by conventional dentistry's critics, dentistry scholars maintain that endodontic therapy can be performed without creating focal infections.