April 17, 2021

Pioneer in Dental Prevention Henry Trendley Dean (August 25, 1893 – May 13, 1962)

HT Dean has found the relationship between fluoride in water and caries prevention. He introduced the Drinking Water Fluoridation.
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Pioneer in Dental Prevention - H. Trendley Dean

H. Trendley Dean graduated as a dentist in 1916 from the St. Louis University and entered into private practice. During World War I he served with United States Army until 1919, when he returned to his practice. in 1921 he entered the United States Public Health Service, where he was first stationed in several US Marine Corps hospitals, before he became in charge of the dental research at the National Institure of Health. The made it his first task to follow up the concens of the dentist Dr. Frederik Mc Kay that the occurence of the so called mottling of enamel was correlated to the drinking water. Reports of three independant sources suspected that enamel mottling was caused by fluoride in the water, and the condition was therefore called fluorosis (Churchill 1931, Smith et al 1932 and Velu and Balozet 1931). Some years later HT Dean observed an association between mild florosis and unexpectedly low caries experience in in regions of the United States. From then on he devoted his scientific work to show the relationship of flouride in drinking water, fluorosis and caries. He came to the conclusion that approximately 1ppm (pat per million) Fluoride in drinking water was the best compromize between caries prevention and the occurrence of fluorosis.

Results of 9 out of the 21 city study showing the correlation between caries (number of DMFT = decayed, missed, filled teeth, red bars), % of individuals with fluorosis, yellow bars, and the fluoride concentration in ppm (part per million) of Fluoride in drinking water (numbers behind the city names). Data from Dean et al. 1941.

HT Dean analyzed the water of 21 US cities and correlated it to the occurrence of fluorosis and caries. He could see that 1 ppm Fluoride in water was the threshold value. Below this value the caries inhibition was high; occurrence of caries decreased as a function of the concentration, above this value the caries inhibition effect flattened out. On the contrary, the % of individuals with fluorosis increased mildly with the concentration of Fluoride in the drinking water, but values between 16 and 32 % of individuals with fluorosis were found, when the fluoride concentration in drinking water was higher than 1 ppm. HT Dean, based on this knowledge pushed for adding fluoride to the drinking waterfor the reason of caries prevention. This was the beginning of Drinking WaterFluoridation that started in 1945 in Grand Rapids , Michigen and was followed by very many cities in the USA and worldwide. In the 1980ies more than 30 nations worldwide had water fluoridation projects serving more than 250 million people. HT Dean created a fluorosis index, still used these days and is considered the Father of Drinking Water Fluoridation. 15 year-studies have shown remarkable success with caries reduction for 12-to 15 year old children between 48% and 70%. According to the WHO (World Health Organization) that has endorsed drinking water fluoridation, as the most cost-effective public health measure, the average annual cost per individual in the United States has been estimated to be 0.51$ per person. A workshop in Michigan in 1989 estimated that the drinking water fluoridation cost were at 3.35 $ per carious surface saved, which means much less disease for very little expenses, considering the price of restorations.

Initially it was thought that the ingested fluoride is the important part. Today we know, that the fluoride must be brought into contact with the enamel while the tooth is in the oral cavity and that fluoride brought into the enamel while it was formed is lost after the eruption of the tooth. Therefore, at least in industrialized nations where fluoridated toothpaste makes up the vast majority of all sold toothpaste, the toothpaste became the major sourceof fluoride for caries prevention.


Churchill HV (1938). Occurrence of fluoride in some waters of the United States. J Ind Eng Chem 23: 996-998

Smith MC, Lantz EM, Smith HV (1932). The cause of mottled enamel, a defect of human teeth. J Dent Res 12: 149-159.

Velu H and Balozet L (1931). Darmous (dystrophic dentaire) du mouton et solubilite du principe actif des phosphates naturels qui le provique. Bull Soc Path Exot 24: 848- 851

Dean HT, Jay P, Arnold FA, McClure FJ, Elvove E (1939). Domestic water and dental caries.  A study of 2832 white children aged 12-14 years of 8 suburban Chicago communities, including cerain epidemiological aspects of L. aciophilus. Public Heath Rep 54: 862-888

Dean HT, Jay P, Arnold FA, Elvove E (1939). Domestic water and dental caries II.  A study of 2832 white children aged 12-14 years of 8 suburban Chicago communities, including L. aciophilus studies of 1761 children. Public Health Rep 56: 761-792

Dean HT, Arnold FA, Elvove E (1942). Domestic water and dental caries V. Additional studies of the relation fluoride domestic waters to dental caries experience in 4425 white children age 12 - 14 years of 13 cities in 4 states. Public Heath Rep 57: 1155-1179

SUMMARY in Axelsson P. Preventive Materials, Methods, and Programs. Quintessence Chicago, 2004 p305-312

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