Focal infection
Focal infection theory is the idea that a local infection affecting a small area of the body can lead to subsequent infections or symptoms in other parts of the body due either to the spread of the infectious agent itself or toxins produced from it.

Early proponents of FIT variously listed infection in the tonsils, oral cavity, sinuses, prostate, appendix, bladder, gall bladder, and kidney as possible causes of systemic disease. Many of these areas were targets of operations in an attempt to heal the entire body. Opponents at the time criticized FIT as blaming systemic problems on "anything that is readily accessible to surgery."

The theory became popular in the late 19th and early 20th century, especially in the field of oral medicine. Connecting disease to dental infections resulted in an extremely high number of pulled teeth during the 1920s. Studies in the 1930s showed that previous evidence in support of this application were flawed, and more rigorous research did not find evidence for dental infections as a major source of systemic disease.

FIT was greatly refined over the 20th century to explain specific diseases such as tuberculosis, gonorrhea, syphilis, pneumonia, typhoid fever, and mumps, all of which do follow its general principle albeit in much narrower pathways than was originally suggested by the theory's early proponents.

In the dental community, current consensus is that FIT is not a valid reason to remove teeth or to avoid root canals—as ways to cure systemic infections or prevent bacteria from spreading from the tooth to the body. More recent studies have shown a relationship between dental health and heart disease, but these are only correlation
In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....

al and do not support conclusions about the root cause. At the same time the academic community has cautiously reinvestigated FIT, the natural health and holistic dentist
Holistic dentistry
Holistic dentistry also called alternative dentistry, unconventional dentistry, biologic dentistry, or biocompatible dentistry emphasizes approaches to dental care which consider the patient's dental health in the context of their entire physical as well as emotional or spiritual health in some...

 communities have enthusiastically revived early research into FIT as the basis for a broad criticism of mainstream dental practices. The academic community considers these critiques unsupported by both the early and more recent research into FIT.

Primary cause of systemic disease era (1890s—1950s)

The notion of removing the focus of infection to cure a systemic disease may go back as far as Hippocrates
Hippocrates of Cos or Hippokrates of Kos was an ancient Greek physician of the Age of Pericles , and is considered one of the most outstanding figures in the history of medicine...

, but the modern theory of focal infection can be traced back to the late 19th century amidst a growing interest in bacteriology
Bacteriology is the study of bacteria. This subdivision of microbiology involves the identification, classification, and characterization of bacterial species...

 and the work of Robert Koch
Robert Koch
Heinrich Hermann Robert Koch was a German physician. He became famous for isolating Bacillus anthracis , the Tuberculosis bacillus and the Vibrio cholerae and for his development of Koch's postulates....

. In the 1890s, Willoughby D. Miller
Willoughby D. Miller
Willoughby D. Miller was an American dentist and the first oral microbiologist.-Biography:Born in AlexandriaHe later returned, though, for further training at the Pennsylvania Dental College. He was later appointed dean of the dental school, but he died prior to assuming the position.While in...

, who worked in Koch's laboratory, proposed that oral microorganisms found in cavities
Dental caries
Dental caries, also known as tooth decay or a cavity, is an irreversible infection usually bacterial in origin that causes demineralization of the hard tissues and destruction of the organic matter of the tooth, usually by production of acid by hydrolysis of the food debris accumulated on the...

 played a role in the etiology
Etiology is the study of causation, or origination. The word is derived from the Greek , aitiologia, "giving a reason for" ....

 of pulmonary diseases, gastric problems, and brain abscesses among other medical conditions. He published his findings as "The Micro-Organisms of the Human Mouth: The Local and General Diseases Which Are Caused by Them" in Germany in 1890, and then in Dental Cosmos in 1891, in an article titled, "The Human Mouth as a Focus of Infection." However, Miller did not recommend extracting infected teeth and was a proponent of root canal
Root canal
A root canal is the space within the root of a tooth. It is part of a naturally occurring space within a tooth that consists of the pulp chamber , the main canal, and more intricate anatomical branches that may connect the root canals to each other or to the surface of the root.-Root canal anatomy:...


In 1900, William Hunter, a British physician, also claimed that poor dental health could cause several systemic diseases, In 1911 he gained wide attention to these theories by presenting them in a speech to the medical students of McGill University. Hunter claimed that, "[t]he worst cases of anemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...

, gastritis
Gastritis is an inflammation of the lining of the stomach, and has many possible causes. The main acute causes are excessive alcohol consumption or prolonged use of nonsteroidal anti-inflammatory drugs such as aspirin or ibuprofen. Sometimes gastritis develops after major surgery, traumatic...

, colitis
In medicine, colitis refers to an inflammation of the colon and is often used to describe an inflammation of the large intestine .Colitides may be acute and self-limited or chronic, i.e...

, obscure fevers, nervous disturbances of all kinds from mental depression
Depression (mood)
Depression is a state of low mood and aversion to activity that can affect a person's thoughts, behaviour, feelings and physical well-being. Depressed people may feel sad, anxious, empty, hopeless, helpless, worthless, guilty, irritable, or restless...

 to actual lesions of the cord, chronic rheumatic infections, kidney diseases, are those which owe their origin to, or are gravely complicated by the oral sepsis
Sepsis is a potentially deadly medical condition that is characterized by a whole-body inflammatory state and the presence of a known or suspected infection. The body may develop this inflammatory response by the immune system to microbes in the blood, urine, lungs, skin, or other tissues...

 produced by these gold traps of sepsis." In other words, according to Hunter, dental restorations were to blame. Hunter's American critics, however, pointed to the poor state of dental health in the United Kingdom and shifted the blame from the dental procedures themselves to their poor execution, an argument that eventually led to the removal of untrained dental practitioners by improving licensing requirements.

Frank Billings formally introduced the focal infection theory to American physicians in 1912 with his lectures at Stanford University Medical School being published in 1916. Living at a time when sanitation was at its infancy and human contact diseases were prevalent, he believed that most infections were "filth diseases" and therefore preventable. Billings went a step further than Hunter, and promoted tonsillectomies and dental extractions as remedies for focal infections. Billiings' theories lived on in his pupil, E.C. Rosenow who emphasized cooperation between dentists and physicians in curing these infections, and postulated that tooth extraction was often not enough on its own. When prominent doctors like Charles Mayo
Charles Mayo
Charles Mayo is the name of:*Charles Horace Mayo , American physician*Charles Herbert Mayo , English antiquarian*Charles William Mayo , American surgeon*Charles Mayo , Canadian-born English cricketer...

 and Russell Cecil joined ranks in promoting the theory and the surgical remedy, "millions of tonsils and teeth were removed in what was later described as an 'orgy of extractions.'"

Criticism, research, detraction, and decline

Despite gaining mainstream support the focal infection theory had it detractors.

Robert T Morris in a December 13, 1918 address to the Eastern Medical Society stated focal infection theory was already falling into disrepute in certain fields due to the other-enthusiasm of some of its advocates and stated that more evidence was needed before the medical profession continued taking active interest in the matter.

In the October 20–24, 1919 National Dental Association annual session C. Edmund Kells presented a paper that was highly critical of the mass extractions and recommended that dentists refuse the instructions of physicians who recommend them. When the presentation was printed in the 1920 Journal of the National Dental Association a dentist named Titeston praised Kells for his stance and went further saying the tooth extraction craze resulting from focal infection theory qualified as a fad.

However in 1923 Weston Price
Weston Price
Weston Andrew Valleau Price was a prominent dentist known primarily for his theories on the relationship between nutrition, dental health, and physical health...

, chairman of the Research Section of the American Dental Association, published the two volume set Dental Infections, Oral and Systemic in full support of FIT. Regarding how FIT was being applied Price also noted that he was continually seeing patients "suffering more from the inconvenience and difficulties of mastication and nourishment than they did from the lesions from which their physician or dentist had sought to give them relief" a view that a 1935 Journal of the Canadian Dental Association article author would cite as an example of 'the authorities that emphasize my contentions for conservatism' (even as he called Price "radical") Despite this and Price's later 1925 "Dental Infections and related Degenerative Diseases" work being criticized for "faulty bacterial technique" Dental Infections, Oral and Systemic fit so well into the existing thought of the day that it would be used as a reference in textbooks and diagnosis guides clear into the early to mid 1930s.

In 1938 a former proponent of the theory, Russell Cecil stated that "focal infection is a splendid example of a plausible medical theory which is in danger of being converted by its enthusiastic supporters into the status of an accepted fact." Cecil published the findings from a study of 200 cases of rheumatoid arthritis
Rheumatoid arthritis
Rheumatoid arthritis is a chronic, systemic inflammatory disorder that may affect many tissues and organs, but principally attacks synovial joints. The process produces an inflammatory response of the synovium secondary to hyperplasia of synovial cells, excess synovial fluid, and the development...

 documenting no curative benefit of tonsillectomies or dental extractions.

In 1940, H.A. Reimann and W.P. Havens, published what was perhaps "the most influential critique of the focal infection theory", showing that it was completely unproven.

By 1950 focal infection theory had fallen from its status as the primary cause of systemic disease and a special 1951 issue of the Journal of the American Dental Association stated: "Many Authorities who formally felt that focal infection was an important etiologic factor in systemic disease have become skeptical and now recommend less radical procedures in the treatment of such disorders."

According to a 2000 Journal of the California Dental Association article by Pallasch, the general application of focal infection theory fell out of scientific favor due to improved dental care, advent of antibiotics, the small percent of "cures" and occasional exacerbation of the disease after the removal of the foci, a backlash to the "orgy" of dental extractions and tonsillectomies, an inability to replicate experiments, and a lack of controlled clinical studies.

Evolution and revival of FIT

However, the fall of focal infection theory as primary cause of systemic disease did not mean the theory itself did not continue to find enough supporters to appear in textbooks such as Dougherty's 1954 Textbook of bacteriology regarding teeth and peer reviewed papers such as Galloway's 1957 JAMA article on tonsillectomies and as late as 1986 it was stated "(t)oday, in spite of a decline in the recognition of the focal infeciton theory the association of decayed teeth with systemic disease is taken very seriously."

Furthermore the mechanism of focal infection theory survived in general medicine with regards to specific diseases such as tuberculosis, gonorrhea, syphilis, pneumonia, typhoid fever, and mumps as well as conditions such as idiopathic scrotal gangrene and angioneurotic edema.

Finally a continual influx of new cases demonstrating its possible validity kept the concept alive in the dental community

All these factors have resulted in a disagreement not only about when focal infection theory fell out of favor but also the degree to which it did. For example in 2002 Ingle's Endodontics 5th edition stated "(i)n the 1930s, editorials and research refuted the theory of focal infection". while 2006 Carranza's clinical periodontology stated "(t)he focal infection theory fell into disrepute in the 1940s and 1950s", and the 2009 Textbook of Endodontology stated that while it had lost its influence "dental focal infection theory never died"

In 1989 a respected study showed a significant correlation between poor dental health and myocardial infarction, which was followed by other studies showing similar results, prompting the dental community to do a cautious reevaluation of focal infection theory. By 2006 the idea that some aspects of focal infection might be valid was finding greater validity especially in immunocompromised people.

In 1994 George E. Meinig published Root Canal Cover-up Exposed which resurrected the old studies by Rosenow and Price, raising the concern among dentists that patients hearing about these studies might view them as new and reliable. Hasselgren stated in New York Academy of Dentistry's Annals of dentistry that Meinig's book was in major need of professional editing, used Price's 1923 Dental Infections, Oral and Systemic (but not his other works), made unsubstantiated claims, confused the meaning of terms (such as infection and inflammation), and expanded into areas unrelated to the main topic to the point Hasselgren ends the review with the comment "I wonder how the serious researcher Weston Price would have reacted to the way his work has been presented." Hasselgren observed, "[t]he focal infection theory, supported by many including Dr. Price, has been attacked, debated, accepted, criticized, agreed upon, etc. but it has not been covered up." Of modern dentistry he noted, "many clinicians appear today to have lost sight of the fact that endodontical treatment shall be based on biology and not on the use of various gadgets to sweep canals. Also, one-visit treatment of necrotic, infected teeth is being advocated and practiced even if no long-term study has been performed to investigate this kind of treatment. The work of Dr. Weston Price is therefore still to a great extent valid and important and the role of infection can not be underestimated."

In a 2000 issue of the Journal of the California Dental Association Pallasch stated "The focal infection theory was (is) elegant in its simplicity and offered quick and easy (as well as lucrative) solutions to a myriad of problems for which medicine had no answers. It also afforded medicine the chance to deflect the blame from its ignorance to relative defenseless and unwitting victims: dentists and patients. All of its proponents were infected with the concept that "after it, because of it" for which even today there is no vaccine. Bearing the above in mind, it is useful to now examine the resurgence of the focal infection theory of disease in its newer guises." In a 2003 issue of Endodontic Topic Pallasch expressed concern that these studies would be greeted with the same over enthusiasm that Weston Price's and Edward C Rosenow's rabbit experiments had been back in the 1920s and that said dentists advising dental treatment to reduce patient's risk for myocardial infarction or stroke were giving advice no more scientific then the ‘100 percenters’, ‘therapeutic edentulism’ and ‘clean sweep’ advice given in the hayday of focal infection theory.

In the introduction to a supplement of the Journal of the American Dental Association
Journal of the American Dental Association
The Journal of the American Dental Association is a monthly peer-reviewed medical journal on dentistry published by the American Dental Association. It is freely available to the public after a one-year embargo....

dedicated to this renewed interest, Micheal L. Barnett states that "[t]he investigation into oral-systemic disease connections is a rapidly advancing area of research." Barnett cautions his readers that it is important to distinguish between data that merely suggest correlations between oral infection and systemic disease and data that show a causal relationship. With that in mind, the articles in the supplement investigate "the connection between dental plaque and periodontal disease and adverse pregnancy outcomes, cardiovascular disease, bacterial pneumonia and diabetes."
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