[6][19] In 1884, William Henry Welch, tasked to design the medical department at the newly forming Johns Hopkins University, imported the German model, "scientific medince", to America.
[32] Abdominal surgery's pioneer, Sir Arbuthnot Lane, based in London, drew from Metchnikoff and clinical observation to identify "chronic intestinal stasis"—in lay terms, intractable constipation—presumably, "flooding of the circulation with filthy material".
[27][31] Since 1875, in the American state Michigan, physician John Harvey Kellogg had targeted "bowel sepsis"—an allegedly prime cause of degeneration and disease—at his health resort, Battle Creek Sanitarium.
[27] Having, in fact, coined the term sanitarium, Kellogg yearly received several thousand patients, including US Presidents and celebrities, at his huge resort, advertised as the "University of Health".
[6][34][35] In 1910, lecturing in Montreal at McGill University, Hunter declared, "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.
[22] Rosenow developed the principle elective localization, whereby microorganisms have affinities for particular organs, and also espoused extreme pleomorphism, whereby a bacterium can drastically change form and perhaps evade conventional detection methods.
[27][42] Though originally distancing themselves from routine medicine and skeptical of laboratory data, they later recruited Edward Rosenow from Chicago to help improve Mayo Clinic's diagnosis and care and to enter basic research via experimental bacteriology.
[5] In 1923, upon some 25 years of researches, dentist Weston Andrew Price of Cleveland, Ohio, published a landmark book,[3][50] then a related article in the Journal of the American Medical Association in 1925.
[55] In 1911, the year that Frank Billings lectured on focal infection to the Chicago Medical Society, unsuspected periapical disease was first revealed by dental X-ray.
[64] Morris called for facts and explanation from scientists before physicians continued investing so steeply in it, already triggering vigorous disputes and embittering divisions among clinicians as well as uncertainty among patients.
[66] Focal infection theory's elegance suggested simple application, but the surgical removals brought meager "cure" rate, occasional disease worsening, and inconsistent experimental results.
[61] Antipsychotic colectomy vanished except in Trenton until Cotton—who used publicity and word of mouth, kept the 30% death rate unpublicized, and passed a 1925 investigation by New Jersey Senate—died by heart attack in 1933.
[70] In the 1930s and 1940s, researchers and editors dismissed the studies of Price and of Edward Rosenow as flawed by insufficient controls, by massive doses of bacteria, and by contamination of endontically treated teeth during extraction.
[3][71] They commented, "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.
[3] Still, endodontic therapy of the era indeed posed substantial risk of failure, and fear of focal infection crucially motivated endontologists to develop new and improved technology and techniques.
[6] Recasting British surgeon William Hunter's landmark pronouncements 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".
[59] By 1940, Louis I Grossman's textbook Root Canal Therapy flatly rejected the methods and conclusions made earlier by Weston Price and especially by Edward Rosenow.
[73] Amid improvements in endodontics and medicine, including release of sulfa drugs and antibiotics, a backlash to the "orgy" of tooth extractions and tonsillectomies ensued.
[6] K A Easlick's 1951 review in the Journal of the American Dental Association notes, "Many authorities who formerly 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".
[75][76] Although some support extended into the late 1950s,[77][78] focal infection vanished as the primary explanation of chronic, systemic diseases,[15] and the theory was generally abandoned in the 1950s.
[83] Despite the limited funding, research established that L forms can adhere to red blood cells and thereby disseminate from foci within internal organs such as the spleen,[85] or from oral tissues and the intestines, especially during dysbiosis.
[86][87] Perhaps some of Weston Price's identified "toxins" in endodontically treated teeth were L forms,[88] thought nonexistent by bacteriologists of his time and widely overlooked into the 21st century.
[90][91][92][93][88][87] At the 1990s' emergence of epidemiological associations between dental infections and systemic diseases, American dentistry scholars have been cautious,[79] some seeking successful intervention to confirm causality.
[3][94] Some American sources 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.
[12] Sometimes forming elsewhere in bones after injury or ischemia,[17] jawbone cavitations are recognized as foci also in osteopathy[17] and in alternative medicine,[101] but conventional dentists generally conclude them nonexistent.
[17] Although the International Academy of Oral Medicine & Toxicology claims that the scientific evidence establishing existence of jawbone cavitations is overwhelming and even published in textbooks, the diagnosis and related treatment remain controversial,[102] and allegations of quackery persist.
[59] At dentist George Meinig's 1994 book, Root Canal Cover-Up, discussing researches of Rosenow and of Price, some dentistry scholars reasserted that the claims were evaluated and disproved by the 1940s.
[110][88] Although such possibility appears especially likely amid compromised immunity—as in individuals cirrhotic, asplenic, elderly, rheumatoid arthritic, or using steroid drugs—there remained a lack of carefully controlled studies definitely establishing adverse systemic effects.
[59] Conversely, some if few studies have investigated effects of systemic disease on root-canal therapy's outcomes, which tend to worsen with poor glycemic control, perhaps via impaired immune response, a factor largely ignored until recently, but now recognized as important.
[59] 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".