Focal infection theory
Focal infection theory (FIT) describes a localized site of infection that disseminates microorganisms or their toxins to distal locations, which thereupon host secondary infections that initiate, sustain, or worsen systemic diseases, usually chronic, such as atherosclerosis or arthritis or cancer. (The criterion of spread to distant sites distinguishes focal infection from infectious spread by progressively expanding invasion of local tissues.) Such idea is ancient, yet took modern form around 1900, and was widely accepted in Anglosphere medicine by the 1920s.
In the theory, the focus of infection is often unrecognized, while secondary infections might occur at sites particularly susceptible to such microbial species or toxin. Several locations were commonly claimed as foci—appendix, bladder, gall bladder, kidney, liver, prostate, and sinuses—but most commonly oral tissues. Not only dental decay, but also sites of dental restoration and root canal therapy were indicted as the 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 chronic diseases.
Drawing severe criticism in the 1930s, focal infection theory, whose popularity far outstripped evidence, was generally discarded in the 1940s amid overwhelming evidence of its general falsity, whereupon dental restorations and root canal therapy became again favored. Untreated endodontic disease retained recognition as fostering systemic disease, but only alternative medicine and later biological dentistry continued highlighting sites of dental treatment—root canal therapy, dental implant, and, as newly claimed, tooth extraction, too—as foci of infection promoting systemic diseases. The primary recognition of focal infection is endocarditis if oral bacteria enter blood and infect the heart, perhaps its valves.
Entering the 20th century, scientific evidence supporting general relevance of focal infection theory remained slim, yet evolved understanding of disease had granted the theory a third possible mechanism—altogether, metastasis of infection, metastatic toxic injury, and, recently revealed, metastatic immunologic injury—that might occur simultaneously, even interacting. Meanwhile, focal infection theory has resurged, as dental infections apparently are widespread and significant contributors to systemic diseases, but mainstream attention is on ordinary periodontal disease, not hypotheses of stealth infections at sites of dental treatment. Despite some doubts renewed from dentistry's fringe since the 1990s, dentistry scholars maintain that endodontic therapy can be performed without creating focal infections.
- 1 Rise and popularity (1890s–1930s)
- 2 Criticism and decline (1930s–1950s)
- 3 Revival and evolution (1980s–2010s)
- 4 Footnotes
Rise and popularity (1890s–1930s)
Roots and dawn
In ancient Greece, Hippocrates reported cure of an arthritis case by tooth extraction. Yet modern focal infection theory awaited Robert Koch's establishment of medical bacteriology in the late 1870s to early 1880s. At 1890, Willoughby Miller attributed a set of oral diseases to infections, and a set of general diseases—as of lung, stomach, brain abscesses, and other conditions—to those. In 1894, Miller became the first to reveal existence of bacteria in samples of dental pulp. Miller advised root canal therapy. Yet focal infection theory met a cultural climate where ancient and folk ideas, long entrenched via Galenic humoral medicine, found new outlet through bacteriology—a pillar of the new "scientific medicine".
At 1886, emigrating from Russia, international scientific celebrity Elie Metchnikoff—discoverer of phagocytes, mediating innate immunity—was embraced in Paris by Louis Pasteur, who granted him an entire floor for research once Pasteur Institute, the globe's first biomedical institute, opened in 1888. Later the Institute's director and 1908 Nobelist, Metchnikoff believed, as did his rival Paul Ehrlich—theorist on antibody, mediating acquired immunity—and as did Pasteur, that nutrition influenced immunity. Sharing Pasteur's view of science as a means to suppress the problems plaguing humankind, Metchnikoff brought into France its first cultures of yogurt for probiotic microorganisms to foster health and longevity by suppressing the colon's putrefactive microorganisms alleged that foster the colon's toxic seepage, autointoxication.
Opening the 20th century, British surgeons, still knife-happy, called for "surgical bacteriology". Sir Arbuthnot Lane, famed for his appendectomy saving England's monarch, issued dire warnings about "chronic intestinal stasis"—that is, constipation—"flooding of the circulation with filthy material" and causing autointoxication, thereupon treated with colon bypass and colectomy. In America, degeneration and disease via bowel sepsis had been attacked since 1875 by John Harvey Kellogg in Michigan at his huge Battle Creek Sanitarium—he coined the term sanitarium—yearly receiving several thousand patients, including US Presidents and celebrities, and advertising itself as "University of Health". Yet admonishing alleged "health faddists" like Kellogg and Graham, American physicians embracing focal infection theory cast themselves in the academic tradition of German "scientific medicine".
In 1900, British surgeon William Hunter identified oral sepsis as a cause of systemic diseases. Lecturing in 1910 at McGill University's medical school in Montreal, Canada, he claimed, "The worst cases of anemia, gastritis, colitis, obscure fevers, nervous disturbances of all kinds from mental depression 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 produced by these gold traps of sepsis". Hunter apparently indicted dental restorations. His American critics incriminated their execution, a view lobbied to impose stricter dental licensing requirements. Still, Hunter's lecture—as later recalled—"ignited the fires of focal infection". Ten years later, Hunter proudly accepted such credit. And yet, read carefully, his lecture lists only one cause of dental sepsis: dentists who instruct patients to never, under any circumstance, remove partial dentures from their mouths.
The era really began with physician Frank Billings, based in Chicago, Illinois, and his case reports of tonsillectomies and dental extractions claimed to have cured infections of distant organs. Replacing Hunter's term oral sepsis with focal infection, Billings on 15 November 1911 lectured at Chicago Medical Society, and published it in 1912 as an article for the American medical community. In 1916, Billings lectured in California at Stanford University Medical School, this time printed in book format. Billings thus popularized intervention by tonsillectomy and dental extraction. A pupil of Billings, Edward Rosenow held that extraction alone was often insufficient, and urged teamwork by dentistry and medicine. Rosenow developed the principle elective localization, whereby microorganisms have affinities for particular organs, and also espoused extreme pleomorphism.
Since 1889, in Rochester, Minnesota, brothers William Mayo and Charles Mayo had built an international reputation for surgical skill at their Mayo Clinic, by 1906 performing some 5,000 surgeries a year, over 50% intra-abdominal, a tremendous number at the time, with unusually low mortality and morbidity. Though originally distancing themselves from routine medicine and skeptical of laboratory data, they later recruited Rosenow from Chicago to help improve Mayo Clinic's diagnosis and care and to enter basic research via experimental bacteriology. Rosenow influenced Charles Mayo, who by 1914 published to support focal infection theory alongside Billings and Rosenow.
At Johns Hopkins University's medical school, launched in 1894 as America's first teaching "scientific medicine", the eminent Sir William Osler was succeeded as professor of medicine by Llewellys Barker, who became a prominent proponent of focal infection theory. Although many of Hopkins' medical faculty remained skeptics, his colleague William Thayer cast support. As Hopkins' chief physician, Barker was a pivotal convert propelling the theory to the center of American routine medical practice. Russell Cecil, famed author of Cecil's Essentials of Medicine, too, lent support. In 1921, Hunter in Britain announced that oral sepsis was "coming of age".
Although physicians had already interpreted pus within a bodily compartment as a systemic threat, pus from infected tooth roots often drained into the mouth and was thought systemically inconsequential. Amid focal infection theory, it was concluded that that was often the case—while immune response prevented dissemination from the focus—but that immunity could fail to contain it, could thus permit dissemination from the focus, and result in systemic disease, often neurological. By 1930, excision of focal infections was considered a "rational form of therapy" undoubtedly resolving many cases of chronic diseases. Its inconsistent effectiveness was attributed to unrecognized foci—perhaps inside internal organs—that had been missed by clinicians.
Reception by dentistry
In 1923, upon some 25 years of researches, dentist Weston Price of Cleveland, Ohio, published a landmark book, then a related article in Journal of the American Medical Association in 1925. Price concluded that after root canal therapy, teeth routinely host bacteria producing potent toxins. Transplanting the teeth into healthy rabbits, Price and his researchers duplicated heart and arthritic diseases. Although Price noted often 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", his 1925 debate with John P Buckley was decided in favor of Price's position: "practically all infected pulpless teeth should be extracted". As chairman of American Dental Association's research section, Price was recognized even in Britain as the individual who, perhaps beyond any other, shaped opinion in the dentistry profession. His 1923 treatise was relied on by textbook authors into the late 1930s.
Unsuspected periapical disease was first revealed by dental X-ray in 1911, the year that Frank Billings lectured on focal infection to the Chicago Medical Society. Introduced by C Edmund Kells, the technology became used to feed the "mania of extracting devitalized teeth". Even Price was cited as an authoritative source espousing conservative intervention at focal infections. Kells, too, advocated conservative dentistry. Many dentists were "100 percenters", extracting every tooth exhibiting either necrotic pulp or endodontic treatment, and extracted apparently healthy teeth, too, as suspected foci, leaving many persons toothless. A 1926 report published by several authors in Dental Cosmos—a dentistry journal where Willoughby Miller had published in the 1890s—advocated extraction of known healthy teeth to prevent focal infection. Endodontics nearly vanished from American dental education. Some dentists held that root canal therapy should be criminalized and penalized with six months of hard labor.
in American state New Jersey at psychiatric asylum Trenton State Hospital, its director since 1907 was Henry Cotton. Drawing influence from the medical popularity of focal infection theory, Cotton identified focal infections as the main causes of dementia praecox (now schizophrenia) and manic depression (now bipolar disorder). Cotton routinely prescribed surgery to clean the nasal sinuses and to extract the tonsils and dentition. Yet, seeking to clean the entire body of focal infections, Cotton frequently prescribed surgical removal of appendix, gall bladder, spleen, stomach, colon, cervix, ovaries, testicles, and thereby claimed up to 85% cure rate.
Despite the death rate of some 30%, Cotton's fame rapidly spread through America and Europe, and the asylum drew influx of paying patients. New York Times praised his accomplishments and heralded "high hope". Cotton made a European lecture tour, and Princeton University Press and Oxford University Press simultaneously published his book in 1922. Despite skepticism within his profession, psychiatrists were under pressure to match Cotton's treatments, as patients would ask why they were being denied successful intervention. Cotton had his two sons' teeth extracted as prophylactic measure—although each later committed suicide.
Criticism and decline (1930s–1950s)
Addressing the Eastern Medical Society in December 1918, New York City physician Robert Morris had explained that focal infection theory is drawing much interest but that the knowledge was complete, and the theory was earning disrepute in some fields through overzealousness of advocates. Morris called for facts and explanation from "philosophers"—that is, scientists—before physicians continue investing so steeply in it, already triggering vigorous combats and division among clinicians and uncertainty among patients.
In New Orleans at the 1919 annual meeting of National Dental Association, forerunner of American Dental Association, dental X-ray originator and pioneer C Edmund Kells delivered a lecture, published in 1920 in the Association's journal, largely discussing focal infection theory, which Kells condemned as a "crime". Kells stressed that X-ray technology is to improve dentistry, not to enhance the "mania of extracting devitalized teeth". Kells urged dentists to reject physicians' prescriptions.
Focal infection theory's elegance suggested simple application, but this met meager "cure" rate, occasional disease worsening, and inconsistent experimental results, although the lack of controlled clinical trials, among present criticism, was standard at the time—except in New York City. Around 1920, at Henry Cotton's claims of up to 85% success treating schizophrenia and manic depression, Cotton's major critic was George Kirby, director of New York State Psychiatric Institute, from which bacteriologist Nicolas Kopeloff and psychiatrist Clarence Cheney ventured to New Jersey to investigate Cotton's practice.
In two controlled clinical trials, using alternate allocation of patients, Kopeloff with Cheney and with Kirby found no treatment effect of Cotton's psychiatric surgeries, as patients who improved had already had that prognosis and others did so even without surgeries. They presented the findings at American Psychiatric Association's 1922 and 1923 annual meetings, and published two papers. At Johns Hopkins University, Phyllis Greenacre, a later leader in New York's psychoanalytic movement, questioned most of Cotton's data. During psychoanalytic ascendance, colectomy for psychosis vanished except at the Trenton asylum until Cotton—who used publicity and word of mouth, kept the 30% death rate unpublicized, and somehow passed a 1925 investigation by New Jersey Senate—died by heart attack in 1933.
As early as 1927, Weston Price's researches were criticized for "faulty bacterial technique". In the 1930s and 1940s, researchers and editors dismissed the studies of Rosenow and of Price as flawed by use of insufficient controls, massive bacterial doses, and contamination of endontically treated teeth during extraction. In 1938, Cecil and Angevine reported 200 cases of rheumatoid arthritis, finding no curative effect of tonsillectomies or tooth extractions. They noted 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 became a harsh critic, commenting that the foci were "anything readily accessible to surgery".
In 1939, E W Fish implanted bacteria into guinea pigs' jaws and reported that four zones develop. The first being the zone of infection, the other three zones, surrounding the zone of infection, revealed immune cells or other host cells but no bacteria. Fish theorized that removing the infectious nidus would permit recovery from infection—and this became the basis for successful root canal treatment. Still, endodontic therapy of the era indeed posed substantial risk of failure, and fear of focal infection crucially motivated endontologists to develop new, improved technology and techniques.
End of the focal era
The review and "critical appraisal" by Hobart A Reimann and W Paul Havens, published in January 1940, was perhaps the most influential criticism of focal infection theory. Recasting Hunter's views of 30 years earlier as widely misinterpreted, they summarized that "the removal of infectious dental focal infections in the hope of influencing remote or general symptoms of disease must still be regarded as an experimental procedure not devoid of hazard". By 1940, Louis I Grossman's textbook Root Canal Therapy flatly rejected the methods and conclusions made earlier by Price and especially by Rosenow. Amid improvements in endodontics and medicine, including release of sulfa drugs and antibiotics, a backlash to the "orgy" of tooth extractions and tonsillectomies ensued.
Easlick's 1951 review in Journal of the American Dental Association notes, "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". A 1952 editorial in Journal of the American Medical Association tolled the era's end by stating that "many patients with diseases presumably caused by foci of infection have not been relieved of their symptoms by removal of the foci, many patients with these same systemic diseases have no evidence focus of infection, foci of infection are as common in apparently healthy persons as in those with disease". Some support extended into the late 1950s, yet waning as the primary explanation of chronic, systemic diseases, it was generally abandoned in the 1950s.
Revival and evolution (1980s–2010s)
Via continuing case reports claiming cures of chronic diseases like arthritis after extraction of infected or root-filled teeth, and despite lack of scientific evidence, "dental focal infection theory never died". Otherwise, it is embedded in understanding of tuberculosis, gonorrhea, syphilis, pneumonia, typhoid fever, and mumps complications. It formally remained with idiopathic scrotal gangrene and angioneurotic edema. And severe endodontic disease resembles classic focal infection theory. In 1986, it was noted that, "in spite of a decline in recognition of the focal-infection theory, the association of decayed teeth with systemic disease is taken very seriously".
Reported during the 1960s and 1970s were cryptic, pleomorphic bacteria—bacterial L forms as well as bacterial genus Mycoplasma—in fluid samples from both healthy and rheumatoid arthritic humans, but far more numerous in the latter, and in any event difficult to culture. By the 1980s, microbiologists accepted that over 99% of microorganisms in most natural environments elude culturing. By 2010, the Human Microbiome Project helped provide crucial, mounting evidence that within human bodies, unculturable microroganisms and pleomorphic bacteria, long studied but controversial, contribute to diverse diseases. Meanwhile, researchers sought reevaluation of focal infection theory. Apparently, infection of dental structures, including with uncultured or cryptic microorganisms, can contribute to systemic diseases. Conversely, attribution of endocarditis to dentistry has entered doubt via case-control study and realization that the species usually involved is present throughout the human body.
At the 1990s emergence of epidemiological associations between dental infections and systemic diseases, American dentistry scholars have been cautious, some seeking successful intervention to confirm causality. Some have emphasized epidemiology's inability to determine causality, categorized the phenomena as progressive invasion of local tissues, and distinguished that from focal infection theory—which they assert was evaluated and disproved by the 1940s. Others have found focal infection theory's scientific evidence still slim, but conceded that evolving science might establish it.
European sources find it more certain that dental infections drive systemic diseases at least by driving systemic inflammation, and probably, among other immunologic mechanisms, by molecular mimicry resulting in antigenic crossreaction with host biomolecules, while some seemingly find progressive invasion of local tissues compatible with focal infection theory. Acknowledging that beyond epidemiological associations, successful intervention is needed to establish causality, they emphasize that biological explanation is needed atop both, and the biological aspect is thoroughly established already, such that general healthcare, as for cardiovascular disease, must address prevalent periodontal disease, a stance matched in Indian literature. Thus, there has emerged the concept periodontal medicine.
Amid continuing research interest focus, Indian textbooks find focal infection theory established, if in more modest form than originally. Akshata et al have attacked the stigma and posed focal infection theory as a correct theory earlier misapplied and thereby discredited yet later refined as knowledge grew over time. In a paper winning an Indian prize, they clarify "that the oral cavity can act as the site of origin for dissemination of pathogenic organisms to distant body sites, especially in immunocompromised hosts", especially those "suffering from malignancies, diabetes, rheumatoid arthritis", or "undergoing other immunosuppressive treatment", and that "uncontrolled advanced periodontitis" "presents a substantial infectious burden for the entire body by releasing bacteria, bacterial toxins, and other inflammatory mediators into the bloodstream that then affect the other parts of the body", this altogether "a paradigm shift in thinking about the directionality of oral and systemic associations".
During the 1980s, controversial dentist Hal Huggins spawned biological dentistry, so called, which claims that conventional tooth extraction routinely leaves within the tooth socket the periodontal ligament that often becomes gangrenous, then, forming a jawbone cavitation seeping infectious and toxic material. Sometimes forming elsewhere in bones after injury or ischemia, cavitations are recognized as dental foci of infection also in osteopathy and in alternative medicine, but are generally found nonexistent in conventional dentistry. Huggins and many biological dentists also espouse Weston Price's findings on endodontically treated teeth routinely being foci of infection, although these dentists have been accused of quackery. Conventional belief is that microorganisms within inaccessible regions of a tooth's roots are rendered harmless once entombed by the endodontist's filling material, although little evidence supports this.
Rogers in 1976 and Ehermann in 1977 had dismissed any relation between endodontics and focal infection. Dentist George Meinig's 1994 book Root Canal Cover-Up Exposed, discussing researches of Rosenow and of Price, provoked some dentistry scholars' fears that patients would lend new credence to these works deemed already evaluated and disproved by the 1940s. Suggesting that even Price would have disapproved of Meinig's presentation of Price's work, Hasselgren asserted existence of debate, not coverup. Still, Hasselgren noted that many endodontists seem enraptured by endodontic technology but neglect biological principles underlying their work, as "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 cannot be underestimated".
A European source places Meinig among three authors who, in the early 1990s, independently renewed concern about endodontic therapy promoting disease systemically. Yet there remained a lack of carefully controlled studies, and no investigations had definitely established adverse systemic effects. The possibility appears especially likely amid compromised immunity, as in individuals cirrhotic, asplenic, elderly, rheumatoid arthritic, or using steroid drugs. Conversely, some if few studies have investigated effects of systemic disease on root canal therapy's outcomes, which apparently tend to worsen with poor glycemic control, perhaps via impaired immune response, a factor largely ignored until recently but now being recognized as important. Still, even by 2010, "the potential association between systemic health and root canal therapy has been strongly disputed by dental governing bodies and there remains little evidence to substantiate the claims".
Although researchers have noted L forms or Mycoplasma present but routinely overlooked in normally healthy humans' blood, molecular methods have, even nearing 2010, brought no generally accepted reports of bacteremia traced to asymptomatic endodontic infection. Even some biological dentists respecting Meinig's indications as to conventional filling material have concluded that innovative filling material and especial care during clinical application minimize risk of focal infection. Although endodontic therapy can fail and eventually often does, dentistry scholars maintain that it can be performed without fostering systemic disease. The predominant view is that shunning endodonthic therapy or routinely extracting endodontically treated teeth to treat or prevent systemic diseases remains unscientific and misguided.
Chronic infections are established to contribute to cancers by driving chronic inflammation, although there are other possible mechanisms, including biochemical. Yet microorganisms recovered from tumor samples might often have arrived after tumor development, as varying species have affinities for particular tissues, and can promote a tumor's either growth or regression. Apparently, the microbiome's diversity of microorganisms associating with diverse diseases and conditions, even obesity, often exist normally in symbiosis with human hosts. Like head and neck malignant tumors found to harbor bacteria deep within, human internal organs previously presumed sterile might not be sterile. Thus, in such recent findings as saliva's bacterial profile associating with chronic pancreatitis and with pancreatic cancer, the direction of possible causality is unclear. Infectious but "unculturable" factors of chronic prostatitis, for instance, seem frequent but overall ambiguous.
Stealth or cryptic dissemination of bacteria from foci, including internal organs like spleen as well as dental structures, is evidenced for bacterial L forms, which can adhere to and travel via red blood cells. Perhaps some of Weston Andrew Price's identified "toxins" in endodontically treated teeth were L forms, thought nonexistent by bacteriologists of his time and widely overlooked into the 21st century. Despite mention of L forms in medical education, some activists for conventional medicine incidentally deride their existence. Since the 1920s, basic research has amassed evidence that pleomorphic bacteria, including L forms and Mycoplasma, can have intimate yet stealthy casual roles in cancerous tumors, although progress to clinical application for corroboration by intervention trials in humans has been stymied by rival interests via ideological, cultural, and socioeconomic factors. Evidence is strong for their causal roles in diverse diseases of cryptic etiology and especially autoimmune diseases where recent results of clinical application for intervention have been encouraging.
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- Shanon Patel & Justin J Barnes, "Introduction: How has endodontics developed?", in Shanon Patel & Justin J Barnes, eds, The Principles of Endodontics, 2nd edn (Oxford: Oxford University Press, 2013), pp 4–5.
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- As later elucidated, antibody molecules, which are secreted by activated B cells, mediate but one arm of acquired immunity, whose other arm is mediated by killer T cells. As acquired immunity's two principal mediators, B cells and T cells are subsets of lymphocytes—themselves a subset of white blood cells, aka leukocytes—as their base of residence is peripheral lymphoid tissues. On the other hand, innate immunity is mediated not only by phagocytes but also by a third subset of lymphocytes: natural killer cells. Further, innate immunity also includes soluble components—complement proteins and, more recently identified, innate antibody secreted by B cells—while still other lymphocytes, specifically helper T cells, bridge innate immunity to adaptive immunity, and vice versa. Thus, the seeming division between innate immunity and acquired immunity is more practical than natural. Immunology's early feuds over whether immunity is innate or is acquired reflected limited perspectives.
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- Baumgartner et al, Ingle's Endodontics, 6th edn (Hamilton: BC Decker, 2006), p 286, not giving that precise summary, cite Weston A Price & John P Buckley, "Buckley–Price debate on the subject 'Resolved: that practically all infected pulpless teeth should be extracted'", Journal of the American Dental Association, 1925;12:1468–524.
- British Journal of Dental Science, 1928;72:101.
- Examples: Louis V Hayes, Clinical Diagnosis of Diseases of the Mouth: A Guide for Students and Practitioners of Dentistry and Medicine (Brooklyn NY: Dental Items of Interest Publishing, 1935), p 389; William H O McGehee, A Text-book of Operative Dentistry, 2nd edn (Philadelphia: Blackiston's Son & Co, 1936), pp 39, 110.
- Kracher, CM (2000). "C. Edmund Kells (1856-1928)". Journal of the history of dentistry 48 (2): 65–9. PMID 11794365.
- ADA: "C Edmund Kells was a dental pioneer who championed the use of X-rays in dentistry during the late 19th century and early 20th century. 'The X-ray in dental practice' is a paper read by Dr Kells at a 1919 Association meeting in New Orleans. Much of the paper discusses focal infection theory, which Dr Kells argued was leading to the unnecessary extraction of teeth. He also made it clear that dental X-rays should be used to enhance dentistry, and not to encourage the 'mania for extracting devitalized teeth' " ["JADA Centennial: From the February 2013 issue of JADA", American Dental Association, Website access: 21 Sep 2013].
- Journal of the Canadian Dental Association, 1935;1:451.
- C Murray, ch 48 "Endontology and general systemic health", §§ "The 'focal infection' era" & "Effects of general systemic health on endodontics", in Michael Baumann & Rudolf Beer, eds, Endodontology, 2nd edn (New York: Thieme, 2010).
- Wessely, S (2009). "Surgery for the treatment of psychiatric illness: The need to test untested theories". Journal of the Royal Society of Medicine 102 (10): 445–51. doi:10.1258/jrsm.2009.09k038. PMC 2755332. PMID 19797603.
- Henry A Cotton, The Defective, Delinquent, and Insane: The Relation of Focal Infections to their Causation, Treatment and Prevention (Princeton/London: Princeton University Press/Oxford University Press, 1922).
- Robert T Morris: "The matter of focal infections is one of the very new subjects of the day which men are taking up with a great deal of interest but are going ahead perhaps with incomplete knowledge and not comprehending the range and scope of the entire subject; consequently this subject is falling into disrepute in certain fields because of the over-enthusiasm of some of the advocates of focal infection theory in relation to distant demonstration—endocarditis, rheumatism, gastric ulcer, cholecystitis, various forms of neuritis, etc. The philosopher, taking all evidence judicially, will eventually give the medical profession the basic facts and what is valuable in the subject. Right now one might utter a warning to the general medical profession against taking too active an interest in the subject" ["Address on medicine and surgery", American Medicine, 1919 Jan;25(1):17–23, pp 18–19].
- C Edmund Kells, "X-ray in dental practice", Journal of the National Dental Association, 1920 Mar;7(3):241–72 [JADA provides the article free in two parts (1 & 2)].
- Jacobsohn, PH; Kantor, ML; Pihlstrom, BL (2013). "The X-ray in dentistry, and the legacy of C. Edmund Kells: A commentary on Kells CE. The X-ray in dental practice. J Natl Dent Assoc 1920;7(3):241-272". Journal of the American Dental Association 144 (2): 138–42. PMID 23372129.
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- Nicolas Kopeloff & Clarence O Cheney, "Studies in focal infection: Its presence and elimination in the functional psychoses", American Journal of Psychiatry, 1922 Oct 1;79(2):139–56.
Nicolas Kopeloff & George H Kirby, "Focal infection and mental disease", American Journal of Psychiatry, 1923 Oct 1;80(2):149–91.
- Henry W Crowe & Herbert G Franking, "Aetiology continued: Dental infections and degenerative diseases—a review and commentary", pp 23–32, Bacteriology and Surgery of Chronic Arthritis and Rheumatism with End-Results of Treatment (New York/London: Humphrey Milford/Oxford University Press, 1927), p 32.
- "Clinical and Experimental Observations on Focal Infection, with an Analysis of 200 Cases of Rheumatoid Arthritis". Annals of Internal Medicine 12 (5): 577. 1938. doi:10.7326/0003-4819-12-5-577.
- E Wilfred Fish, "Bone infection", Journal of the American Dental Association, 1939;26(5):691–712.
- Louis I Grossman, Root Canal Therapy (Philadelphia: Lea & Febiger, 1940), ch 2, reprinted in Journal of Endodontics, 1982 Jan;8(Suppl):S18-S24, available at Robert Kaufmann's EndoExperience.com under "The endo file cabinet: Textbook excerpts: Grossman's Endodontics: Chapter on focal infection", Accessed online 17 Feb 2014.
- Easlick, KA (1951). "An evaluation of the effect of dental foci of infection on health". Journal of the American Dental Association 42 (6): 615–97. PMID 14831976.
- Philip M Preshaw & John J Taylor, ch 21 "Periodontal pathogenesis", in Michael G Newman, Henry Takei, Perry R Klokkevold & Fermin A Carranza, Carranza's Clinical Periodontology, 11th edn (St Louis: Saunders/Elsevier, 2012).
- "Focal Infection". JAMA: the Journal of the American Medical Association 150 (5): 490. 1952. doi:10.1001/jama.1952.03680050056016.
- Joseph M Dougherty & Anthony J Lamberti, Textbook of Bacteriology, 3rd edn (St Louis: Mosby, 1954), p 231
- Galloway, Thomas C. (1957). "Relation of Tonsillectomy and Adenoidectomy to Poliomyelitis". Journal of the American Medical Association 163 (7): 519–21. doi:10.1001/jama.1957.02970420001001. PMID 13398294.
- Nikos Donos & Francesco D'Aiuto, ch 3 "Periodontitis: A modern clinical perspective", in Brian Henderson, Michael Curtis, Robert Seymour & Nikolaos Donos, eds, Periodontal Medicine and Systems Biology (West Sussex: Wiley-Blackwell, 2009), pp 33–34.
- Southern California State Dental Association Journal, 1952, p 27.
- Ronald T Lewis, ch 25 "Soft tissue infection and loss of abdominal wall substance", in Robert Bendavid, ed, Abdominal Wall Hernias: Principles and Management (New York, Berlin, Heidelberg: Springer, 2001), p 192.
- Technical Manual #8-225: Dental Specialist (Washington DC: Department of the Army Headquarters, 20 Sep 1971), pp Glossary-7 & 5-14.
- James M Dunning, Principles of Dental Public Health, 4th edn (Cambridge MA: Harvard University Press, 1986), ch 13 "Dental needs and resources", § "Systemic infection of dental origin", p 272–73.
- Bisset, KA (1979). "Origin of the diphtheroid bacteria, mycoplasmas, etc., reported in association with autoimmune condition". Annals of the Rheumatic Diseases 38 (2): 199. PMC 1000356. PMID 443890.
- Amy D Proal, Paul J Albert & Trevor G Marshall, ch 12 "Autoimmune disease and the human metagenome", in Karen E Nelson, ed, Metagenomics of the Human Body (New York, Dordrecht, Heidelberg, London: Springer, 2011).
- Siqueira Jr, JF; Rôças, IN (2013). "As-yet-uncultivated oral bacteria: Breadth and association with oral and extra-oral diseases". Journal of Oral Microbiology 5: 10.3402/jom.v5i0.21077. doi:10.3402/jom.v5i0.21077. PMC 3664057. PMID 23717756.
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- Peter Mullany, Philip Warburton & Elaine Allan, ch 9 "The human oral metagenome", Karen E Nelson, ed, Metagenomics of the Human Body (New York, Dordrecht, Heidelberg, London: Springer, 2011), p 166.
- Akshata, KR; Ranganath, Ashishs; Nichani, V (2012). "Thesis, antithesis, and synthesis in periodontal and systemic interlink". Journal of Indian Society of Periodontology 16 (2): 168–73. doi:10.4103/0972-124X.99257. PMC 3459494. PMID 23055580.
- Lida H Mattman, Cell Wall Deficient Forms: Stealth Pathogens, 3rd edn (Boca Raton FL: CRC Press, 2000), pp 286 & 289, while p 291 lists for p 289 a citation of B Haley, "Root canal teeth contain toxins according to new and old research", Dent Amalgam Merc Synd, 1996;6(4):1–4.
- John I Ingle, PDQ Endodontics, 2nd edn (Shelton CT: People's Medical Publishing House, 2009), p xv.
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- Sanjay Saraf, Textbook of Oral Pathology (New Delhi: Jaypee Brothers Medical Publishers, 2006), ch 9 "Spread of oral infections".
- Leon Chaitow, Cranial Manipulation: Theory and Practice, 2nd edn (Edinburgh, London, New York, elsewhere: Elsevier, 2005), p 348–49.
- Examples: Ellen Hodgson Brown, Healing Joint Pain Naturally: Safe and Effective Ways to Treat Arthritis, Fibromyalgia, and Other Joint Diseases (New York: Broadway Books, 2001); Shirley MacLaine, Sage-ing While Age-ing (New York: Atria Books, 2007).
- Stephen Barrett, "Stay away from 'holistic' and 'biological' dentists", Quackwatch, accessed online: 17 Sep 2013.
- J Craig Baumgartner, José F Siqueira Jr, Christine M Sedgley & Anil Kishen: "Microorganisms found in failed endodontically treated teeth have either remained in the root canal from previous treatment or have entered since treatment via leakage. ... Those remaining from the original microbiota would need to have maintained viability throughout treatment procedures, including exposure to disinfectants, and thereafter adapted to a root canal environment in which the availability of a variety of nutrients is more limited because of lack of pulp tissue. This might occur as a result of an inability of chemomechanical instrumentation procedures to completely debride the root canal system in a single visit and because of the inaccessible locations of bacteria in isthmuses, accessory canals, and apical regions of canals. While it is considered that many such remaining bacteria will be unable to cause harm once entombed by the obturation material, there is little evidence for this" [ch 7 "Microbiology of endodontic disease", in John I Ingle, Leif K Bakland & J Craig Baumgartner, eds, Ingle's Endodontics, 6th edn (Hamilton Ontario: BC Decker, 2008), p 257].
- J Craig Baumgartner, Leif K Bakland & Eugene I Sugita, ch 3 "Microbiology of endodontics and asepsis in endodontic practice", in John Ide Ingle & Leif K Bakland, eds, Endodontics, 5th edn (Hamilton Ontario: BC Decker, 2002), p 64.
- Pallasch, Thomas J.; Wahl, Michael J. (2003). "Focal infection: New age or ancient history?". Endodontic Topics 4: 32. doi:10.1034/j.1601-1546.2003.00002.x.
- Gunnar Hasselgren: "I wonder how the serious researcher Weston Price would have reacted to the way his work has been presented. ... The 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" [Annals of Dentistry, 1994;53–54:42].
- Gunnar Hasselgren: "[M]any 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 cannot be underestimated" [Annals of Dentistry, 1994;53–54:42].
- McLaughlin, RW; Vali, H; Lau, PC; Palfree, RG; De Ciccio, A; Sirois, M; Ahmad, D; Villemur, R; Desrosiers, M; Chan, EC (2002). "Are there naturally occurring pleomorphic bacteria in the blood of healthy humans?". Journal of Clinical Microbiology 40 (12): 4771–5. doi:10.1128/JCM.40.12.4771-4775.2002. PMC 154583. PMID 12454193.
- Mark A Breiner, Whole-Body Dentistry: A Complete Guide to Understanding the Impact of Dentistry on Total Health (Fairfield CT: Quantum Health Press, 2011), pp 162–63, 168–69, 174.
- Y L Ng, V Mann, S Rahbaran, J Lewsey & K Gulabivala, "Outcome of primary root canal treatment: Systematic review of the literature—part 1. Effects of study characteristics on probability of success", International Endodontology Journal, 2007 Dec;40(12):921–39.
- Coussens, LM; Werb, Z (2002). "Inflammation and cancer". Nature 420 (6917): 860–7. doi:10.1038/nature01322. PMC 2803035. PMID 12490959.
- Shacter, E; Weitzman, SA (2002). "Chronic inflammation and cancer". Oncology 16 (2): 217–26,229. PMID 11866137.
- Lax, AJ; Thomas, W (2002). "How bacteria could cause cancer: One step at a time". Trends in microbiology 10 (6): 293–9. doi:10.1016/S0966-842X(02)02360-0. PMID 12088666.
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- Cummins, J; Tangney, M (2013). "Bacteria and tumours: Causative agents or opportunistic inhabitants?". Infectious agents and cancer 8 (1): 11. doi:10.1186/1750-9378-8-11. PMC 3668256. PMID 23537317.
- Mager, DL (2006). "Bacteria and cancer: Cause, coincidence or cure? A review". Journal of translational medicine 4: 14. doi:10.1186/1479-5876-4-14. PMC 1479838. PMID 16566840.
- Robinson, CJ; Bohannan, BJ; Young, VB (2010). "From structure to function: The ecology of host-associated microbial communities". Microbiology and Molecular Biology Reviews 74 (3): 453–76. doi:10.1128/MMBR.00014-10. PMC 2937523. PMID 20805407.
- Gonzalez, A; Clemente, JC; Shade, A; Metcalf, JL; Song, S; Prithiviraj, B; Palmer, BE; Knight, R (2011). "Our microbial selves: What ecology can teach us". EMBO Reports 12 (8): 775–84. doi:10.1038/embor.2011.137. PMC 3147266. PMID 21720391.
- Costello, EK; Stagaman, K; Dethlefsen, L; Bohannan, BJ; Relman, DA (2012). "The application of ecological theory toward an understanding of the human microbiome". Science 336 (6086): 1255–62. doi:10.1126/science.1224203. PMID 22674335.
- Funchain, P; Charis, E (2012). "Hunting for cancer in the microbial jungle". Genome medicine 5 (5): 42. doi:10.1186/gm446. PMC 3707053. PMID 23731547.
- Jonathan M Zenilman, ch 64 "Prostatitis", in David Schlossberg, ed, Clinical Infectious Disease (New York: Cambridge University Press, 2008), p 444, recommends reading Domingue Gj, Sr; Hellstrom, WJ (1998). "Prostatitis". Clinical Microbiology Reviews 11 (4): 604–13. PMC 88899. PMID 9767058.
- Gerald J Domingue, Cell Wall-Deficient Bacteria: Basic Principles and Clinical Significance (Reading MA: Addison-Wesley Publishing, 1982), p 455.
- L H Mattman, Stealth Pathogens, 3rd edn (CRC Press, 2000), ch 1 "History".
- Amy Proal, "A history of cell wall deficient bacteria: A selection of researchers who have worked with the L-form", Bacteriality: Exploring Chronic Disease, 18 Aug 2007.
- Alvin Fox, Bacteriology, ch 1 "The bacterial cell", § "Bacterial structures", §§ "Wall-less forms of bacteria", Microbiology and Immunology On-line, University of South Carolina School of Medicine, 18 Nov 2008.
- Conflating bacterial pleomorphism with germ theory denialism, then mistaking mere infection for germ theory, Mark Crislip summarily attributes to famed germ-theory opponent Béchamp eight postulates, #4 being Microorganisms change their shapes and colours to reflect the medium, while Crislip answers, "Postulates 1, 2, 3, 4, and 6 are all flat out false. From 1950 to November 2nd 2008 at 9:50am PST, there were 909,599 citations on PubMed relating to infections. How many papers and experiments were done in the 100 years prior to 1950 I do not know, but it is a safe bet that germ theory is supported by over a million studies and experiments. A PubMed for terms to support pleomorphism finds zero references" ["'It's just a theory'", Science-Based Medicine, 7 Nov 2008].
A decade earlier, David J Hess explained that Béchamp's microzymian theory was doubtful, but pleomorphism was undoubted: "One needs only check Medline or another common index under CWD bacteria or L-forms (a plasmalike, fried-egg colony appearance) to see that there is continuing research on the topic in the major peer-reviewed journals. Nevertheless, there is still some stigma attached to the topic. In a conversation I had with Gerald Domingue, one of the foremost experts in the field, I learned that although the existence of L-forms and CWD is not controversial among microbiologists, the theory that they can persist in the host and play a role in pathology is still controversial" [Can Bacteria Cause Cancer? (New York & London: NYU Press, 1997), ch 4 "But is it good science?", subchs "Problems with Béchamp" pp 111–12 & "The consistency argument I: CWD bacteria research" pp 112–16].
Indeed, the pleomorphic variants of bacteria exist—established decades ago—and the controversy is merely over their roles in disease [M E Onwuamaegbu, R A Belcher & C Soare, "Cell wall-deficient bacteria as a cause of infections: A review of the clinical significance", J Int Med Res, 2005 Jan–Feb;33(1):1–20]. Yet even classical bacteria are pleomorphic, notably changing shape—sometimes reproductive mode, too—according to nutritional medium, while classical culturing methods might determine their classical morphology to begin with [Kevin D Young, "The selective value of bacterial shape", §§ "Morphological variation: True to form?" & "Differentition", Microbiol Mol Biol Rev, 2006 Sep;70(3):660–703].
- MacOmber, PB (1990). "Cancer and cell wall deficient bacteria". Medical hypotheses 32 (1): 1–9. doi:10.1016/0306-9877(90)90060-R. PMID 2190063.
- Robinson, Douglas H. (2005). "Pleomorphic mammalian tumor-derived bacteria self-organize as multicellular mammalian eukaryotic-like organisms: Morphogenetic properties in vitro, possible origins, and possible roles in mammalian 'tumor ecologies'". Medical Hypotheses 64 (1): 177–85. doi:10.1016/j.mehy.2004.04.023. PMID 15533638.
- David J Hess, Can Bacteria Cause Cancer?: Alternative Medicine Confronts Big Science (New York & London: New York University Press, 1997), pp 112–15, 134.
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- Proal, AD; Albert, PJ; Marshall, TG (2013). "The human microbiome and autoimmunity". Current opinion in rheumatology 25 (2): 234–40. doi:10.1097/BOR.0b013e32835cedbf. PMID 23370376.