(C) Peter Meiers - http://www.fluoride-history.de


Dental Fluorosis (Mottled Teeth)

"When a large percentage of the children in a community have mottled enamel, they do not notice this condition; they have grown up with it. Let them move to a community that is free from this defect, where they are the only ones with mottled enamel, and at once they are ashamed of their teeth and appearance ... Mottled enamel handicaps a child for life ... It is a disgrace to humanity to continue to make dental cripples of children."

J. Scott Walker, D.D.S., J. Am. Dent. Assn. 20 (1933) 1867


The early research on "mottled teeth" is usually associated with a dentist, Frederick Sumner McKay, who moved to Colorado Springs in 1901, and found strange marks on the teeth of native people in that city. There were earlier occasional reports on the strange tooth discolorations in humans, but, apparently, no serious research efforts were undertaken until about 1902.

In 1888, a German dentist Kuehns reported at a meeting of his association his observations on strangely discolored teeth among some members of a family which had moved to his location from Durango (Mexico) (1). All family members grown up in Durango had black stains on their teeth, "similar to the polished areas in caries nigra", the intensity depending on how long they had been living there. Kuehns thought that their local water, originating from a hot spring and formerly used by the family for household purposes, contains rather high amounts of iron compounds. Along with this iron, he speculated, manganese compounds might find their way into the dental tissue. As the discoloration occurred on the front teeth, he supposed that under the action of light these manganese compounds form manganese oxides (colored dark brown to almost black), not just at the surface of the teeth but deep within the dental tissue. Bleaching was held ineffective as these supposed "oxides" would only be removed by some acid (1). The water of Durango was later found to have 7.5 ppm fluoride (1a).

Another early report on this defect was written in 1901 by Passed Assistant Surgeon J. M. Eager (2) who was stationed in Naples, Italy, where emigrants were embarking for the United States: the inhabitants of Pozzuoli, a suburb of Naples, Italy, are distingushed from people of the neighbouring places by their black teeth ("denti neri") or teeth with black markings (teeth appear as if written upon, thus called "denti scritti"). Here too the defect was thought to be caused by the water consumed during infancy. "The environs of Pozzuoli are everywhere volcanic". It was a common belief among the locals that the noisome volcanic gases and dusts are inhaled or ingested with food and water contaminated by them and thereby lead to the dental disfigurement in exposed people.

Among the many regions in the USA, which attracted tourists and emigrants from all over the world, was Colorado Springs, Colorado. The city had its beginnings about 1870 and profited greatly from the Cripple Creek goldfields and other mining developments. Because of gold and silver mining fortunes,  Colorado Springs soon laid claim to being the most wealthy city per capita in the United States (3). And, the more money there is to be possibly spent for health care, the higher the ratio of dentists and physicians (4). - "Long before the turn of the century it was evident that Colorado Springs was to be one of the largest cities in the state. It was publicized as the state´s outstanding health and recreation center, and its quickly established international reputation added luster to its rapidly developing cosmopolitan nature. Dentists and physicians naturally migrated to this health center in large numbers, and it was not surprising that the dentists of the city formed a local dental organization quite early" (5).

On May 15, 1902, a group of  Colorado Springs dentists formed the "El Paso County Odontological Society" (which in 1912 was renamed the Colorado Springs Dental Society, CSDS). At the first regular meeting, two weeks later, a young dentist, Frederick Sumner McKay, a 1900 graduate of the University of Pennsylvania School of Dentistry, presented the Society´s first paper: "A plea for the less frequent use of arsenic for devitalization of the dental pulp" (6). Yet, famous he would become for addressing quite a different problem. McKay had moved to Colorado Springs in 1901. New to the region, he noticed on the teeth of most of the natives strange discolorations, "Colorado Brown Stain" as the local people used to call it after the most prominent and disturbing feature of the condition:


"Mottled enamel is characterized by minute white flecks, or yellow or brown spots or areas, scattered irregularly or streaked over the surface of a tooth, or it may be a condition, where the entire tooth surface is of a dead paper-white, like the color of a china dish. In many cases the surface of the tooth is dotted with irregular, shallow pits, which are usually darkly discolored because of the lodgement therein of débris. Such are spoken of as the ´pitted´ variety. ..."

"It is a curious fact that the earlier thought was directed toward, or confined to that phase of the lesion which was spoken of as the brown stain; and this is easily accounted for by its conspicuousness, being located as it is, almost without exception, upon the labial surfaces of the upper incisors (*). The white spotted or opaque appearance of the enamel of the entire denture seemed hardly to have been noticed, or at least it was rarely spoken of in discussions."

McKay F.S.: Dental Cosmos 58 (1916) 479 

* - "... It is curious that when the stain does occur on the lowers, it is never so pronounced as upon the uppers." (p. 483)


At one of the early CSDS meetings, he urged the odontological Society to send out letters asking dentists for information about the distribution of the phenomenon in their respective communities. Yet, the answers revealed nothing except that many dentists had not even noticed the stain. The Society dropped the project. And so did McKay. After an interval of study, in 1903, at the Angle School of Orthodontia, St. Louis, Mo., he moved to St. Louis in 1905 to practice orthodontics and to serve as superintendent of a private school of orthodontics (7,8).

Even in the absence of McKay interest in the mottled-teeth problem continued among at least a few local dentists. At a meeting of the El Paso County Odontological Society in 1906, dentist Walter A. Brown read a paper on the "Colorado Stain", which is the first written record containing this word combination (9). Around the same time, "several dentists resident in the Rocky Mountain region" (George Y. Wilson and Isaac Burton) contacted Greene Vardiman Black, a famous dental researcher and dean of the Northwestern University Dental School of Chicago. As Black recalled in an article published in 1916, they "told me of a peculiar condition of the teeth in certain areas in their neighborhood, which they said was not found elsewhere, and which had not been described in the literature. This condition they called mottled enamel or mottled teeth. These men claimed that a very large proportion of those born and reared in these areas had teeth of this character. I requested that some of the teeth be sent to me for examination, and after a time (1908) I received the crowns of a number of incisors with the astonishing report that the teeth of a very large proportion of the children in the areas mentioned were of the same character. All of the crowns I received were of incisors that had been cut away for the purpose of putting on artificial crowns to improve the appearance of the persons" (10).

Also in 1907 appeared the first indication that "mottled teeth" did not only affect humans. Cattle, occasionally also horses and sheep, in the vicinity of the great Butte copper district in the Dear Lodge Valley, Montana, were reported to exhibit so-called "copper teeth". An analysis of such teeth by a chemist of the Anaconda Copper Mining Company revealed, however, no copper but chiefly calcium phosphate with some organic material making up the stain. "An interesting fact in this connection is that boiling seems to bring out the lustre, and many jaws which normally have a blackish or brownish color, on boiling assume the copper or gold lustre. It is worthy of note in this connection that these deposits occur in a region whose waters are strongly alkaline to cochineal solution, and further, because of the arid climate, there are large quantities of soluble soil constituents present, with a consequent high ash percentage in the plants grown upon it" (11).

F. S. McKay returned from St. Louis to Colorado Springs in 1908 (because of "ill health") and again opened a dental practice. He also resumed his investigations on mottled teeth. At the meeting of the local society, he led a discussion on the Brown Stain problem and secured the society´s support to present a patient afflicted with the stain at the State Dental Association Meeting in Boulder. Representing the El Paso County Odontological Society he thus attended, on June 19, the annual meeting of the Colorado State Dental Association, where he exhibited a patient with mottled teeth. "Relatively little interest was manifested by those at the meeting", he summarized the result, except that he was told of a few more localities where people with mottled teeth have been seen (12). What more could he expect?

Late in 1908, the Colorado State Dental Association called a special meeting of the officers to extend to Greene Vardiman Black an urgent and formal appeal to attend its next convention in 1909 (13).

While Black examined the samples of mottled teeth finally sent to him in 1908, McKay prepared for Black´s visit to Colorado Springs and made plans for a study on the prevalence of the problem among the school children of the city. On December 11, 1908, a committee consisting of Frederick McKay, Isaac Burton and A. Fleming was formed to examine the teeth of the public school children for evidence of the brown stain (14). In January 1909, the School Board granted permission for the examination and shortly thereafter, McKay and Burton went from desk to desk noting the condition of the teeth and indicating the degree of stain or mottling. Of 2,945 children examined, 87.5 percent were afflicted. All were native to Colorado Springs and vicinity (15).

Black arrived early in July, and on July 12, 1909, gave an "exceptionally well-attended lecture", a lantern-slide illustrated talk describing his own recent observations. Outlining the scope of the problem rather than attempting to offer a solution, the presentation of such a famous person "raised the problem to a level of scientific importance which created increasing interest in the dental profession".

Possible causes were discussed at the convention on July 13, 1909, by another speaker, H. A. Fynn, a "Professor of Regional Anatomy" and one of the private owners of the Colorado College of Dental Surgery. Fynn ruled out faulty metabolism and malnutrition, the local water (which he called "exceptionally pure and differing in no essential degree from the water of Denver"), meats of all kinds and different grains which are no local products. Of the remaining possibilities, vegetables and milk, he assumed that "the cause of this trouble lies in the lack of calcium constituents in the grasses and vegetables grown in the vicinity of this city, because cow´s milk is simply a by- or secondary product of grass, herbage and vegetables". The discoloration he ascribed to a deposit of more than the normal proportion of iron, somehow derived from the blood (16).  

Relative to later allegations that Colorado Springs children with mottled teeth have a lower incidence of tooth decay, the following excerpts from William Alan Douglas´ "History of dentistry in Colorado, 1859-1959" (17,18) are of special interest as they outline another activity of McKay´s:


"As the ´Brown Stain´ studies progressed in the Colorado Springs area, the local dentists became more aware of the exceptional number of children who had never had dental care and were, in fact, wholly ignorant of any understanding of dental health. As a result, late in 1910 the Colorado Springs Dental Society began a free clinic for indigent children intended to spur a general interest in the subject of dental health. The Fort Collins´ dentists had also introduced a similar program of dental education about this time and also were offering free treatment to indigent children. The culmination of these efforts came in 1911 when the CSDA [Colorado State Dental Association], under the direction of President F. S. McKay, created an Oral Hygiene Committee whose mission was to acqaint the general public with the importance of dental hygiene through lectures and lantern slides. ... Partly as result of the Colorado Springs Dental Society´s interest in oral hygiene, partly because of the  program begun by the CSDA, and partly through the inspiration received from the 1910 National Dental Association meeting held in Denver, the Denver Dental Association undertook an examination of Denver school children late in 1911. This survey developed into one of the most extensive educational and clinical dental programs attempted in Colorado until the official state dental health program was initiated in 1937. Since 1910, practically every local dental society in Colorado has actively engaged in some form of dental educational or clinical work; and in the many areas without organized dental societies individual dentists have conducted personal programs ...." (3)


On pages 75-77 of his book Douglas explains:      


"During the first year´s study of the ´Brown Stain´, a committee of the Society energetically engaged in collecting information, making examinations of school children and preparing case studies for one of the nation´s outstanding dental researchers, Dr. G. V. Black. At the same time, however, the local dentists became increasingly aware of the extremely large segment of the local citizenry who were ignorant of even the basic fundamentals of dental health. By the fall of 1909 the local pressure of the "Brown Stain" investigations had eased, and many dentists diverted their interest to the problem of oral hygiene. The subject was first formally introduced to the CSDS [Colorado Springs Dental Society] by Dr. McKay on October 8, 1909, when he commented, following the examinations, on the deplorable conditions of the teeth of the public school children and suggested that the Society offer its services to the School Board immediately for general examination of the children´s teeth. This program was discussed the following month at a meeting attended by members of the School Board, teachers, parents, and officials from the CSDA as well as local dentists. In December the CSDS submitted three proposals to the School Board: 1) the local dentists would provide free examinations and reports on the condition of the mouth and teeth of all the public school children; 2) the dentists would cooperate in the establishment of a dental clinic for the indigent; and, 3) they would conduct dental hygiene classes for parents, teachers, and children. Within the next two years all three proposals were placed in operation. ... As the city grew the school dental health program expanded; in 1917 Dr. Isaac Burton reported at a joint meeting of the Denver Dental Association and the Colorado Springs Dental Society that over 3500 children had been examined during the previous year. Unfortunately, however, the educational program up to that time had not been completely successful, since at least eighty per cent of those examined needed dental care. For the next two decades the Oral Hygiene Program continued uninterrupted, with the Colorado Springs Health Department continuing to underwrite the expense and the members of the Society continuing to donate their services ... At the present time [1959] this pioneering program of dental health and education continues with undiminished effort to maintain a high standard of oral health in the Colorado Springs area." (18)


In 1910 and 1911 McKay also served as a professor of orthodontia at Denver Dental College (19). Early in 1910 he conducted a study among the students at the Colorado College and found that students native to Colorado Springs had mottled and stained teeth while those from other areas were free from the affliction. "Now that he possessed information that could be detrimental to the tourist visitors to Colorado Springs, McKay hoped that he would be able to receive financial assistance (he estimated that $ 2,000 would be needed) to accomplish an exhaustive study. A local citizens´ committee agreed to submit such a request to the city and county officials. Because of the possibility of adverse publicity, the local newspapers agreed to ignore the discussions. In March 1910, the city and county agreed to give $500 each to the proposed investigation. Only the city government actually appropriated the money; and since only $125 of it had been used by the end of the fiscal year in July, the remainder of the appropriation reverted to the city. Despite a letter of protest from McKay, the city never again made funds available to continue the investigation of mottled teeth" (20). 

The election of McKay to the presidency of the Colorado State Dental Association for 1910-1911 gave him the opportunity to devote his Presidential Address to his favorite subject. He also was able to convince the Association to appoint a committee of one to carry on an investigation as to the cause of mottled teeth and brown stain in Colorado, and that an appropriation of $150 be made. The committee of one consisted, of course, of Frederick S. McKay (20). This backing would enable him to extend his studies on the distribution of the stain beyond the city´s boundaries and thoughout the state.

Shortly before Black died on August 31, 1915, at the age of 79,  from an attack of pernicious anemia (21), "McKay realized the necessity for publishing his and Black´s studies before the volume of the material became unmanageable" (22). Their joint papers were published in the Dental Cosmos, starting with the February issue of 1916 (23, 24). Black´s contribution detailed his histological studies on mottled teeth, while McKay outlined geographic boundaries of the endemic areas and determined the percentage of affliction. Much of his evidence pointed to the water supply as a cause of the endemic occurrence of the lesion. As an official response, Surgeon F.C. Smith, of the U. S. Public Health Service, summarized the available evidence in a paper (25), that was later sent to state officials upon request.

In the series of papers published in 1916, McKay never mentioned any names of localities examined by him (*), as he feared that doing so would bring great blame upon him, for Colorado Springs was a health resort. This fact is outlined in a letter from G. V. Black to McKay, dated March 3, 1915 (and in earlier letters from McKay to Black):

At the annual meeting of the American Dental Association at Denver, Colorado, McKay met another dental researcher, James Leon Williams, and called his attention to the phenomenon (26). But it would take some years until Williams published his related histological studies (in 1923). Williams´ results essentially agreed with Black´s early description. He also found that, in contrast to normal enamel (even of the same tooth), mottled enamel -because of its defective structure- can easily be penetrated by stains. The opaque white areas of mottled teeth are not fully calcified, as is the case with early stages of caries, which he examined. Williams found it highly probable that "we shall sooner or later discover that mottled enamel and other similar conditions of this tissue are due to a disturbance of balance in the functioning of the endocrine glands" (27).

In several of the afflicted districts examined by McKay (24), the water used for household purposes had been in contact with shale rock, associated with the large coal mines owned by the Colorado Fuel & Iron Company (CF&I), a Rockefeller undertaking. After the terrible Ludlow massacre of April 20, 1914, the Rockefellers decided that a new approach was needed between the workers and the management and, in 1916, extended the medical welfare program to include a comprehensive dental program. CF&I thus became the first industrial organization to add dental care to the benefits it provided for its workers. In the 28 mining camps run by the company, CF&I paid the entire cost of the program (28). CF&I was also cooperative with regard to McKay´s "mottled teeth" studies: Cambier, the chemist whose water analyses are cited in several of McKay´s papers (e.g. Ref. 24), was with the Colorado Fuel & Iron Company at Pueblo (29).

In 1917, McKay summarized his researches conducted under the auspices of the American Dental Association´s Research Institute, of which Weston A. Price was president and managing director (30). McKay expressed an urgent need for chemical, physical, and histological studies on mottled teeth, as well as for thorough analyses of the waters in afflicted areas. Particularly he desired the cooperation and assistance of dental researchers like William John Gies and Russell Welford Bunting. His efforts, since the early years, to have others involved in the problem were really remarkable.

McKay was convinced that the agent responsible for the "extremely disfiguring defect of the enamel" would have to be found in the water, not by routine analyses but by a search for a rather rare substance not detected by the usual methods of water analysis. It was now a job for water works engineers and, therefore, he summarized his evidence in a related journal (31), hoping for support. One of the responses was sent in as a letter to the editor by chemist Frank Hannan, of Toronto, Ontario, who suggested a lack of fluorine as the basic cause:


"The French chemist Gautier found fluorine practically universally present in water. That it cannot exist there in more than traces is fortunately secured to us by the low solubility product of calcium fluoride, fluorine in sizeable doses being rather powerful poison. How our other articles of diet stand in respect to fluorine content is a matter of which I must confess complete ignorance. ... Should the incriminated water prove to be all alike fluorine free, the case for fluorine deficiency will become strong; but even then it will have to be shown that the rest of the dietary was incapable of making good the fluorine shortage in the water. And Gautier´s work on the water of France will have to be repeated on those of America." (32)

McKay apparently ignored Hannan´s letter. Moreover, work allegedly done for him earlier had indicated otherwise. In a footnote to the "History of Dentistry in Colorado", William Alan Douglas claims (referring to an Interview with Dr. J. L. Carmen, Denver, Colorado, Jan. 7, 1958):  "In 1922, a Colorado Springs High School chemistry class under the direction of their teacher, Mr. Willet R. Willis, conducted a survey for McKay of the Colorado Springs watershed to determine the concentration of fluorspar, a natural fluoride compound". According to Douglas, the results seemed to indicate a higher fluoride content where the stain occurred, yet lack of money ended any further study (33). However, the water tests by Willet R. Willis, reported in 1934 (33a), were done using the Willard & Winter method (published in 1933), long after fluoride had already been found by Churchill, the Smiths and others in the water of afflicted districts. Thus, up to 1931 at least, McKay was not aware of fluoride as a possible cause.

On January 9, 1926, McKay wrote to the U.S. Public Health Service, summarizing the situation and requesting assistance in a chemical study of these waters with the view of determining what peculiarity of a chemical nature differentiates them from other waters, and what chemical ingredients or combinations exist as a common factor in these waters from the various afflicted districts (34). His letter was forwarded to the Hygienic Laboratory and returned by its director, George Walter McCoy, to the Surgeon General, with the remark: "Of course, the subject deserves a much fuller study but, without some special provision, this office does not  see how it can be undertaken."  This statement was forwarded together with a memorandum from Professor Carl Voegtlin and Professor Mansfield Clark of the Hygienic Laboratory. Clark in his memo again considered a lack of fluorine, while Voegtlin suggested that "these waters be examined for their content in heavy metals. It would also be of interest to secure some discolored teeth and to submit them to chemical analysis with a view of elucidating the chemical nature of the pigment, whether organic or inorganic" (35). On December 22, 1926, the editor of Water Works Engineering assured Taliaferro Clark, of the U.S.P.H.S., that "Water Works Engineering stands ready to cooperate most thoroughly with your department in any investigation that you may conduct as far as we are able to do so" (36). This time, McCoy agreed and added "Ways and means perhaps form a separate consideration" (37). And while the academic discussions of the problem continued, citizens of Oakley, Idaho, became active and changed the city´s water supply to avoid mottled teeth in future generations (Details).

Around that time, feeding experiments with rats led a group of nutritionists close to a solution of the riddle, yet the generally prevailing view that fluoride is good for teeth and bones prevented them to draw the right conclusions. A team around Elmer Verner McCollum, of the Johns Hopkins University of Baltimore, in collaboration with Russell Welford Bunting, of the dental school of the University of Michigan, as their dental expert, described changes in teeth of rats fed a diet with added sodium fluoride (226 ppm) (38). Their aim was to see if fluoride would do any good to teeth as has been suggested in earlier European studies.  But instead of any benefits they found that the rats "developed incisors which were abnormal in color, the orange tint seen on the anterior surface of the incisors of normal rats being nearly absent. These teeth were also observed to grow into abnormal positions, the upper ones tending in nearly every case to grow backwards into a circle, finally penetrating the roof of the mouth."  Bunting´s description added that these teeth "are of a dull, opaque white color and lack the natural polish of well formed tooth substance. In certain areas they are corrugated transversely, suggesting intermitting transferences with development." However, neither McCollum´s group nor Bunting ("to his chagrin", as he wrote later) related these changes in rat teeth to mottled teeth as seen in humans. This failure they shared with many other researchers who repeated this experiment and found essentially the same results (39-41) but did not see a similarity to human mottled teeth.

Late in April, 1927, McKay met with Surgeon Grover A. Kempf and George Walter McCoy of the Public Health Service at McCoy´s house in Washington (42) to talk about details of a cooperation. The USPHS had been made aware of the occurrence of mottled teeth in Bauxite, a town where a subsidiary of ALCOA mined Bauxite ore. Kempf arranged to have McKay appointed special consultant. To possibly get a first hint, water from the former supply of Oakley, Idaho, was analyzed by the Hygienic Laboratory, again for usual constituents, but revealed nothing unusual (fluoride was not included in the analysis) (43). pH was toward the alkali end (around 8.0) (44). McKay was still not closer to a solution. However, his job as a consultant would soon lead him, together with Grover Kempf, to a survey in Bauxite, Arkansas ---



(*) The localities described in McKay's and Black's papers in 1916 are:

A- Brighton; B- Divide (town); C- Buttes; D- Alamosa; E- Chandler; F- Arvada; G- Castle Rock; H- Lafayette; I- Eastonville; J- Woodland Park; K- Cripple Creek district; L- Colorado Springs; M- Green Mountain Falls; N- Walsenburg; O- Denver; P- Raton; Q- Louisville; R- Monument; S- Palmer Lake; T- Pinon; U- La Junta; V- Pictou; W- Pueblo; X- Manitou; Y- Fountain; Z- Trinidad;

Arizona: M- Mesa; F- Florence; T- Tempe; P- Phoenix

Virginia: F- Franklin; C- Courtland; I- Ivor

Texas: A- Amarillo



(1) Kuehns: Dtsch. Mschr. Zahnheilk. 6 (1888) 446; (1a) H.T. Dean to F. S. McKay, May 17, 1940; in the H. T. Dean papers, NLM, History of Medicine Division; (2) Eager J.M.: "Denti di Chiaie (Chiaie teeth)", Publ. Health Rep. 16 (Nov. 1, 1901) 2576-7; and abstr. in Dental Cosmos 44 (1902) 300; (3) McClure F.J.: "Water fluoridation. The search and the victory", NIDR, Bethesda 1970, p.7; (4) "Senate Hearings on Dental Research and Grants-in-aid bills", J. Am. Dent. Ass. 32 (1945) 1042  ; (5) Douglas W. A.: "History of dentistry in Colorado, 1859-1959", Johnson Publishing Co., Boulder 1959, p. 73; (6) Ref.3, p. 74; (7) McNeil D. R.: "The fight for fluoridation", Oxford University Press, 1957, p. 4; (8) Downs R.: "Orthodontic Profiles. Frederick Sumner McKay", Am. J. Orthodontics 46, No.9 (Sept. 1960) 695; (9) Douglas W.A. : "A history of dentistry in Colorado 1859-1959", p. 211; (10) Black G.V., McKay F.S.: "Mottled teeth. An endemic developmental imperfection of the enamel of the teeh heretofore unknown in the literature of dentistry", Dental Cosmos 58 (1916) 129; (11) "The so-called copper teeth of cattle", Brit. Dent. J. 28 (1907) 141; (12) Douglas W.A.: "A history of dentistry in Colorado", p. 188; (13) McNeil D.R.: "The fight for fluoridation", p. 5; (14) Douglas, p. 189; (15) Douglas W.A.: "A history of dentistry in Colorado", pp. 186-214; (16) Fynn H.A.: "Some remarks on the defects in enamel of the children of Colorado Springs", Items of Interest 32 (1910) 31; (17) Douglas, pp. 171-172; (18) Douglas, pp. 75-77; (19) Downs R.: "Orthodontic Profiles. Frederick Sumner McKay", Am. J. Orthodontics 46, No.9 (Sept. 1960) 695; (20) Douglas W.A.: "A history of dentistry in Colorado, 1859-1959", pp. 191-192; (21) "Obituary: Dr. Greene Vardiman Black", Dental Cosmos 57 (Oct. 1915) 1193; (22) Douglas W.A.: "A history of dentistry in Colorado", pp. 186-214; (23) Black G. V., in collaboration with F. S. McKay: "Mottled teeth", Dental Cosmos 58 (1916) 129; (24) McKay F.S., in collaboration with G. V. Black: "An investigation of mottled teeth", Dental Cosmos 58 (1916) 477, 627, 781, 894; (25) Smith F. C.: "Mottled enamel and brown stain", Public Health Reports 31 (1916) 2915;  (26) McKay F.S., Black G.V.: "An investigation of mottled teeth...", Dental Cosmos 58 (1916) 627; (27) Williams J. L.: "Mottled enamel, and other studies of normal and pathological conditions of this tissue", J. dent. Res. 5 (1923) 117; (28) Douglas, pp. 131, 221; (29) McKay F.S.: "Water supplies charged with disfiguring teeth", Int. J. Orthodontia oral Surg. Radiogr. 12 (1926) 211, as reprinted from Water Works Engineering, 79 (Jan. 1926); (30) McKay F.S.: "Investigation of Mottled Enamel and Brown Stain", J. Natl. Dent. Assoc. 4 (1917) 273; (31) McKay F.S.: "Water supplies charged with disfiguring teeth", Water Works Engineering 79 (Jan. 1926), reprinted in Int. J. Orthodontia and Oral Surgery and Radiography 12 (1926) 211; (32) Frank Hannan to Robert H. Lockwood, editor, February 3, 1926; in the H. T. Dean papers; (33) Interview with Dr. J. L. Carmen, Denver, Colorado, Jan. 7, 1958, cited in footnote 35, chapter IX, W. A. Douglas: "A history of dentistry in Colorado 1859 - 1959, p. 212; (33a) Willis W. R.: "The source of the flourine [sic!] in some water supplies", Bulletin of the Colorado State Dental Assoc. (1934) 39-44; (34) McKay to Surgeon General, Jan. 9, 1926, in the H. T. Dean papers; (35) McCoy to Surgeon General, Feb. 26, 1926, and Memorandum Manbsfield Clark and Carl Voegtlin, Feb. 25, 1926, in the H. T. Dean papers; (36) Robert H. Lockwood to Taliaferro Clark, Dec. 22, 1926, in the H. T. Dean papers; (37) McCoy to Surgeon General, Feb. 7, 1927, in the Ruth Roy Harris papers of the National Library of Medicine; (38)  McCollum E.V., Simminds N., Becker E., Bunting R. W.: "The effect of additions of fluorine to the diet of the reat on the quality of the teeth", J. Biol. Chem. 63 (1925) 553; (39) Pachaly W.: "Über Veränderungen der Zähne und Kieferknochen bei experimenteller chronischer Fluorvergiftung", Arch. Exp. Pathol. Pharmakol. 166 (1932) 1; (40) Dittrich W.: "Über Veränderungen der Knochen bei experimenteller chronischer Fluornatrium-vergiftung",  Naunyn-Schmidebergs Arch. exp. Pathol. 168 (1932) 319; (41) Genet G. (in the Department of H. Cristiani of Geneva): "Les altérations des dents dans l´intoxication fluorique chronique", Thesis, University of Geneva 1932; (42) McKay to Grover A. Kempf, April 18, 1927, in the Ruth Roy Harris Papers; Kempf to McKay, April 20, 1927, in the Ruth Roy Harris papers; Kempf to McKay, May 11, 1927, in the Ruth Roy Harris papers; (43) Mansfield Clark memorandum July 18, 1927  ; (44) R. Spencer to McCoy, July 18, 1927, in the Ruth Roy Harris papers;