Fluoride, in drinking water

The presence of fluorine as a soluble fluoride in drinking water to the extent of 2 ppm may cause mottled enamel in teeth, when used by children acquiring permanent teeth in smaller amounts, however, fluorides are added to water supplies to prevent dental cavities. 

The concentration of fluoride in drinking water may be determined indirectly by its ability to form a complex with zirconium. In the presence of the dye SPADNS, solutions of zirconium form a reddish colored compound, called a lake, that absorbs at 570 nm. When fluoride is added, the formation of the stable ZrFe complex causes a portion of the lake to dissociate, decreasing the absorbance. A plot of absorbance versus the concentration of fluoride, therefore, has a negative slope. 

Frencken JE, Truin GJ, Van t Hof MA, Konig KG, Kahabuka FKA, Mulder J and Kalsbeek H (1991) Fluoride in drinking water and caries progression in a Tanzanian child population. Commun Dent Oral Epidemiol 19,180-181. 

As far as the addition of fluoride to drinking water is concerned, the key requirement is that the compound chosen should yield free fluoride ions readily on dissolution in water [123]. Sodium fluoride can be used as it is reasonably soluble and dissolves readily [124]. However, even by the 1950s it was proving relatively expensive, and so the use of alternative compounds was investigated [125]. This identified fluorosilicic acid and its disodium salt as possible alternatives (Table 4), and their use as the source of fluoride in drinking waters continues to this day. 

Due to ubiquitous exposure to fluoride sources other than drinking water, it is not possible to draw firm conclusions regarding the independent effects of fluoride in drinking water on dental caries and its prevention. It has been estimated that moderate dental fluorosis occurs in 1-2% of the population exposed to fluoride at 1 mg/L in drinking water and in about 10% of the population at 2 mg/L moderate/severe fluorosis occurs in variable percentages ranging up to 33% of the population exposed to fluoride at 2.4-4.1 mg/L [52]. 

Endemic crippling skeletal fluorosis is confined in temperate climates to individuals exposed continuously over many years to very high levels of fluoride these cases are associated with industrial situations, with unusually high levels of fluoride in drinking water (e.g., 10 mg/L) or the use of high fluoride coal for cooking and drying foodstuffs indoors [6,17,55]. 

Table 1. Effect of concentration of inorganic fluoride in drinking water on average concentrations of inorganic fluoride and organic fluorine in plasma [76]...

The natural concentration of fluoride in drinking water varies from trace amounts to toxic concentrations. Because of the low natural levels of fluoride in some water supplies and the high levels of dental caries, many authorities worldwide have permitted, or instigated, fluoridation of water supplies. The first artificial fluoridation trials started in 1945 in two towns in America - Newburgh and Grand Rapids [43], Commonly used compounds for water fluoridation are sodium or potassium fluoride or hexafluorosilicic acid (H2SiF6) and its sodium salt (Na2SiFe). 

According to WHO [6] recommendations, the absolute upper concentration for fluoride in drinking water is 1 mg/L. Yet even this concentration can be too high for many parts of the world due, not only to the greater consumption of water in hot climates, but also to the increasing levels of fluoride in, and increased consumption of, processed drinks and foods, the variety of dental practices and different lifestyles. WHO [6] therefore suggested that the level of 1.0 mg/L should be seen as an absolute upper limit, even in cold climates, while 0.5 mg/L may be appropriate lower limit. The history of water fluoridation and its value in the early years of the 21st century have recently been reviewed by Mullen [105]. 

Reference and comment on the concentration of fluoride in drinking water Age group Body weight [kg] Intake [mg/day] Intake [mg/day/kg body weight] Diet surveys... 

Reference and comment on the concentration of fluoride in drinking water... 

Fluoride supplements are recommended by medical societies in some countries for caries prevention, especially if the concentration of fluoride in drinking water is low. It is likely that past use of dietary fluoride supplements has been a prime factor in the increased prevalence of dental fluorosis, a relationship which may stem from the days when fluoride supplement schedules were higher than they are today [11]. Table 7 shows a fluoride supplement dosage schedule that was approved for U.S. and Canadian children by the American Dental Association and Canadian Paediatric Society [8] and a fluoride supplement dosage schedule approved by German Nutrition Society, Austrian Nutrition Society, Swiss Society for Nutrition Research and Swiss Nutrition Association [165]. 

A. Malhotra, A. Tewari, H.S. Chawla, K. Gauba, K. Dhall, Placental transfer of fluoride in pregnant women consuming optimum fluoride in drinking water, J. Indian Soc. Pedod. Prev. Dent. 11 (1993) 1-3. 

H.C. Hodge, The concentration of fluorides in drinking water to give the point of minimum caries with maximum safety, J. Am. Dent. Assoc. 40 (1950) 436-439. 

Fluorine in Plants and Animals, In 1802 Domenico Pini Morichini discovered the presence of fluorine in fossil ivory (157). He later detected it in the enamel of the teeth, and Berzelius soon confirmed the discovery and showed that fluorine is also a normal constituent of bone (158,159, 165). The presence of excessive amounts of fluoride in drinking water causes the well-known mottling of the enamel of children s teeth (160), but small amounts of fluoride protect the teeth from dental caries (161). 

Fluoride in drinking water appears to be most effective in preventing dental caries if consumed before the eruption of the permanent teeth. The optimum concentration in drinking water supplies is 0.5-1 ppm. Topical application is most effective if done just as the teeth erupt. There is little further benefit to giving fluoride after the permanent teeth are fully formed. Excess fluoride in drinking water leads to mottling of the enamel proportionate to the concentration above 1 ppm. 

Fluorine is used in the form of fluorides in drinking water and toothpaste because it reduces tooth decay by hardening the enamel on teeth. 

Fluoride in Drinking Water A Scientific Review of EPA s Standards (2006) State and Federal Standards for Mobile-Source Emissions (2006)... 

Y. Veressinina, M. Trapido, V. Ahelik, R. Munter, Fluoride in drinking water the problem and its possible solutions, Proc. Estonian Acad. Sci. Chem. 50 (2) (2001) 81-88. 

W. Czarnowski, K. Wrzesniowska, J. Krechniak, Fluoride in drinking water and human urine in Northern and Central Poland, Sci. Total Environ. 191 (1996) 177-184. 

S. Hillier, C. Cooper, S. Kellingray, G. Russell, H. Hughes, D. Coggon, Fluoride in drinking water and risk of hip fracture in the UK a case-control study, The Lancet 335 (2000) 265-269. 

A.K. Susheela, Sound planning and implementation of fluoride and fluorosis mitigation programme in an endemic village, International Workshop on Fluoride in Drinking Water, 2001. 

M.J. Rudolph, M. Molefe, U.M.E. Chikte, Dental fluorosis with varying levels of fluoride in drinking water. Fluoride and fluorosis, The Status of S. Afr. Res., North West Province, 5, 1995. 

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