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Journal of Applied Oral Science

Print version ISSN 1678-7757On-line version ISSN 1678-7765

J. Appl. Oral Sci. vol.21 no.1 Bauru Jan./Feb. 2013

http://dx.doi.org/10.1590/1678-7757201302280 

Original Articles

Water fluoridation in 40 Brazilian cities: 7 year analysis

Suzely Adas Saliba MOIMAZ1 

Nemre Adas SALIBA1 

Orlando SALIBA1 

Doris Hissako SUMIDA2 

Neila Paula de SOUZA3 

Fernando Yamamoto CHIBA4 

Cléa Adas Saliba GARBIN5 

1DDS, MsC, PhD, Full Professor, Preventive and Social Dentistry Post-Graduation Program, Univ. Estadual Paulista - UNESP, Araçatuba, SP, Brazil

2DDS, MsC, PhD, Associate Professor, Preventive and Social Dentistry Post-Graduation Program, Univ. Estadual Paulista - UNESP, Araçatuba, SP, Brazil

3Master Degree candidate, Preventive and Social Dentistry Post-graduation Program, Univ. Estadual Paulista - UNESP, Araçatuba, SP, Brazil

4Doctor Degree candidate, Preventive and Social Dentistry Post-Graduation Program, Univ. Estadual Paulista - UNESP, Araçatuba, SP, Brazil

5DDS, MsC, PhD, Associate Professor and Coordinator of Preventive and Social Dentistry Post-Graduation Program, Univ. Estadual Paulista - UNESP, Araçatuba, SP, Brazil

ABSTRACT

Objectives

Fluoride levels in the public water supplies of 40 Brazilian cities were analyzed and classified on the basis of risk/benefit balance.

Material and Methods

Samples were collected monthly over a seven-year period from three sites for each water supply source. The samples were analyzed in duplicate in the laboratory of the Center for Research in Public Health - UNESP using an ion analyzer coupled to a fluoride-specific electrode.

Results

A total of 19,533 samples were analyzed, of which 18,847 were artificially fluoridated and 686 were not artificially fluoridated. In samples from cities performing water fluoridation, 51.57% (n=9,720) had fluoride levels in the range of 0.55 to 0.84 mg F/L; 30.53% (n=5,754) were below 0.55 mg F/L and 17.90% (n=3,373) were above 0.84 mg F/L (maximum concentration=6.96 mg F/L). Most of the cities performing fluoridation that had a majority of samples with fluoride levels above the recommended parameter had deep wells and more than one source of water supply. There was some variability in the fluoride levels of samples from the same site and between collection sites in the same city.

Conclusions

The majority of samples from cities performing fluoridation had fluoride levels within the range that provides the best combination of risks and benefits, minimizing the risk of dental fluorosis while preventing dental caries. The conduction of studies about water distribution systems is suggested in cities with high natural fluoride concentrations in order to optimize the use of natural fluoride for fluoridation costs and avoid the risk of dental fluorosis.

Key words: Fluorine; Fluoridation; Water supply; Oral health; Public health

INTRODUCTION

Water is required to sustain life on the planet24, and access to clean water is one of the fundamental rights described in Article 3 of the Universal Declaration of Human Rights23. In Brazil, a portion of the population has been denied this right, since 17% of Brazilian cities do not have municipal water systems11.

An inverse relationship between the fluoride levels in drinking water and the incidence of dental caries was first observed in the United States at the beginning of the last century14. This observation, in association with later studies, resulted in the addition of fluoride to public water supplies to prevent dental caries, a strategy that is now recommended for all citizens22.

The first implementation of a water fluoridation system occurred in Grand Rapids, Michigan, USA, in 1942. Widespread adoption of fluoridation potentially reduces the incidence of caries by 50%, and for this reason fluoridation has been used in several countries17.

In 1953, Baixo Gandu City in the state of Espírito Santo became the first Brazilian city to employ water supply fluoridation19. Some years later, Federal Law number 6050 (May 24th, 1974) required the addition of fluoride to public water supplies in cities with water treatment systems1. This measure is considered one of the 10 most important public health advances in the 20th century5 because it established a comprehensive, economical, and effective means of continuously providing a health benefit to a large population at minimal risk.

Periodic analyses of fluoride levels in water supplies originated with the goal of providing uniform fluoride levels independent of natural concentrations or water supply companies. The external control consists in the principle that if any service offers risk or represents a protection factor for public health, the control regarding producer, production process, distribution and consumption, should be controlled by State Institutions. It has evolved into a way of improving the quality and consistency of fluoridation, and has been instituted in many different regions of Brazil12,16,18.

The existence of mechanisms that enable the control of naturally-occurring and supplemental fluoride levels in water maximizes the benefits of preventing dental caries while minimizing the risk of dental fluorosis6,8,13.

Previous studies20,21 have measured the fluoride levels in public water supplies and classified samples into “appropriate” and “inappropriate” categories. However, this dichotomous classification limits the interpretation of the water analysis results.

We classified fluoride levels in samples from public water supplies in 40 cities, according to the recently proposed risk/benefit criteria6, and investigated the consistency of fluoride concentrations in the samples over a 7-year period.

MATERIAL AND METHODS

Type and period of study

A longitudinal study was conducted using sampling sites in 40 cities located in São Paulo State, Brazil. To conduct the study, formal and personal contacts were made with the secretaries of health, oral health coordinators and those responsible for the public water supply of each municipality. The trial included all cities (n=40) belonging to the Regional Health Department II (RHDII). Samples were collected monthly from public water distribution systems from November 2004 to October 2011, yielding 84 months of analysis.

Identification of collection sites

Sample collection sites were selected according to the number of water sources or treatment plants in each city. Each source was assigned three collection sites21. Maps of the distribution system were obtained from the water treatment authority and used to randomize the collection sites, including all sources of treated water.

Collection of water samples

Polyethylene bottles (50 mL) were rinsed with deionized water and identified with the city name, collection site, and date. At the collection site, the bottles were rinsed three times with the water comprised of the sample. Samples were collected on the same day during the first week of each month and analyzed in the laboratory of NEPESCO (Center for Research in Public Health) at the Universidade Estadual Paulista - UNESP.

Analysis of fluoride levels

The fluoride content of the samples was determined potentiometrically using an ion analyzer (Orion EA940) equipped with a fluoride ion-specific electrode (Orion 9609BN). A calibration curve was constructed over the expected concentration range of the samples using standards containing 0.1, 0.2, 0.4, 0.8, and 1.6 mg F/L and prepared using NaF. The standards were prepared in triplicate to minimize the effect of measurement errors. To avoid interference from other ions, an equal volume (1 mL) of TISAB II® solution was added to each sample (Orion, USA). Duplicate measurements of each sample were recorded using the Excel software (Microsoft Office 2010), and values of mV were converted to mg F/L using a standard curve [correlation coefficient (r) 0.999]. When the difference between the duplicate readings was larger than 1 mV, a third reading was obtained for confirmation of the data.

Sample classification

Considering that the average maximum annual temperatures in the cities participating in this study were between 26.3°C and 32.5°C, the fluoride level offering the best risk-benefit combination was 0.55-0.84 mg F/L (Table 1)6.

Table 1 Distribution of samples from public water supplies from 40 Brazilian cities, according to fluoride concentration (mgF/L), from November 2004 to October 2011 

City Artificial Fluoride Classification of fluoride levels
0.00 - 0.44 0.45 - 0.54 0.55 - 0.84 0.85 - 1.14 1.15 - 1.44 ≥1.45 Total
n % n % n % n % n % n % n %
Alto Alegre 9 3.6 17 6.8 221 88.8 2 0.8 0 0 0 0 249 100
Araçatuba 29 4.2 91 13 455 65.2 119 17 0 0 4 0.6 698 100
Auriflama 16 6.6 6 2.5 219 90.9 0 0 0 0 0 0 241 100
Avanhandava 21 14.9 11 7.8 94 66.7 12 8.5 0 0 3 2.1 141 100
Barbosa 24 3.7 35 5.4 493 76.4 77 11.9 6 0.9 10 1.6 645 100
Bento de Abreu 13 5.2 44 17.7 176 70.7 15 6 1 0.4 0 0 249 100
Bilac 40 29.6 9 6.7 47 34.8 28 20.7 6 4.4 5 3.7 135 100
Birigui 254 11.7 82 3.8 832 38.4 866 40 108 5 25 1.2 2,167 100
Braúna 255 36.6 51 7.3 262 37.6 109 15.6 12 1.7 8 1.1 697 100
Brejo Alegre 6 2.6 27 11.7 185 80.1 10 4.3 0 0 3 1.3 231 100
Buritama 576 39.3 113 7.7 623 42.5 122 8.3 26 1.8 6 0.4 1,466 100
Castilho 140 11.8 167 14.1 663 55.9 159 13.4 24 2 33 2.8 1,186 100
Clementina 651 50.6 53 4.1 406 31.5 117 9.1 21 1.6 39 3 1,287 100
Coroados 0 0 9 3.6 233 93.6 7 2.8 0 0 0 0 249 100
Gabriel Monteiro 12 4.8 7 2.8 215 86.3 14 5.6 1 0.4 0 0 249 100
Glicério 381 54 31 4.4 250 35.5 29 4.1 13 1.8 1 0.1 705 100
Guaraçaí 295 33.9 67 7.7 339 38.9 140 16.1 14 1.6 16 1.8 871 100
Guararapes 8 3.3 15 6.1 192 78 31 12.6 0 0 0 0 246 100
Guzolândia 6 2.4 10 4 224 90 9 3.6 0 0 0 0 249 100
Ilha Solteira 13 5.3 14 5.8 213 87.7 0 0 0 0 3 1.2 243 100
Itapura 348 50.4 69 10 161 23.3 82 11.9 20 2.9 11 1.6 691 100
Lavínia 276 30.9 120 13.5 299 33.5 147 16.5 41 4.6 9 1 892 100
Lourdes 3 1.2 30 12 213 84.9 5 2 0 0 0 0 251 100
Mirandópolis 74 16 83 18 218 47.2 63 13.6 17 3.7 7 1.5 462 100
Muruntinga do Sul 164 67.5 34 14 39 16 6 2.5 0 0 0 0 243 100
Nova Castilho 31 14 42 19 74 33.5 44 19.9 13 5.9 17 7.7 221 100
Nova Independência 126 28 38 8.4 219 48.7 48 10.7 13 2.9 6 1.3 450 100
Nova Luzitânia 2 2.4 31 37.8 49 59.8 0 0 0 0 0 0 82 100
Penáplis 1 0.4 19 7.9 203 84.6 17 7.1 0 0 0 0 240 100
Piacatú 8 3.2 14 5.6 214 84.9 13 5.2 0 0 3 1.2 252 100
Rubiácea 20 4.3 58 12.5 354 76.3 27 5.8 2 0.4 3 0.6 464 100
Santópolis do Aguapeí 4 1.8 2 0.9 219 96.1 3 1.3 0 0 0 0 228 100
Santo Antônio do Aracanguá 171 37.5 55 12.1 169 37.1 50 11 6 1.3 5 1.1 456 100
Sud Mennucci 2 0.8 51 20.5 196 78.7 0 0 0 0 0 0 249 100
Suzanápolis 162 29 37 6.6 149 26.7 109 19.5 59 10.6 43 7.7 559 100
Turiúba 6 2.5 17 7.1 211 87.9 6 2.5 0 0 0 0 240 100
Valparaíso 34 5.1 14 2.1 391 59 220 33.2 4 0.6 0 0 663 100
Subtotal 4,181 22.2 1,573 8.3 9,720 51.6 2,706 14.4 407 2.2 260 1.4 18,847 100
Natural Fluoride
Andradina 114 50.7 7 3.1 38 16.9 38 16.9 18 8 10 4.4 225 100
Luiziânia 4 1.8 6 2.6 216 95.2 0 0 1 0.4 0 0 227 100
Pereira Barreto 0 0 0 0 58 24.8 175 74.8 1 0.4 0 0 234 100
Subtotal 118 17.2 13 1.9 312 45.5 213 31 20 2.9 10 1.5 686 100
Total 4,299 22 1,586 8.1 10,032 51.4 2,919 14.9 427 2.2 270 1.4 19,533 100

Statistical analysis

Descriptive analyses were based on absolute and relative frequencies.

RESULTS

Fluoride was not added to public water supplies in 7.5% (n=3) of the cities, and in other cities, ion aggregation occurred in at least one water source (Table 2).

Table 2 Number of collection sites, utilization of natural or artificially added fluoride in the public water supply, and the type of water supply source for the 40 Brazilian cities in this study from November 2004 to October 2011 

Cities Collection sites Fluoride Water sources
Artificial Natural Shallow well Deep well River, stream or dam
Alto Alegre 3 X X
Andradina 3 X X
Araçatuba 9 X X X
Auriflama 3 X X X
Avanhandava 3 X X
Barbosa 9 X X
Bento de Abreu 3 X X
Bilac 12 X X
Birigui 42 X X X
Braúna 9 X X
Brejo Alegre 3 X X
Buritama 24 X X
Castilho 15 X X
Clementina 18 X X
Coroados 3 X X
Gabriel Monteiro 3 X X
Glicério 9 X X
Guaraçai 12 X X
Guararapes 3 X X X
Guzolândia 3 X X
Ilha Solteira 3 X X
Itapura 12 X X
Lavínia 12 X X
Lourdes 3 X X
Luiziânia 3 X X
Mirandópolis 6 X X X
Murutinga do Sul 3 X X
Nova Castilho 3 X X
Nova Independ 6 X X
Nova Luzitânia 3 X X
Penápolis 3 X X
Pereira Barreto 3 X X
Piacatu 3 X X X
Rubiácea 6 X X
Santo Antônio do Aracanguá 6 X X
Santópolis do Aguapeí 3 X X X
Sud Mennucci 3 X X
Suzanápolis 9 X X
Turiúba 3 X
Valparaíso 9 X X

A variety of water sources are used in the composition of the water supply system of the cities, among which can be observed 67.5% (n=27) from shallow wells, 25% (n=10) from deep wells, and 22.5% (n=9) from rivers, streams, or dams. Some cities had more than one source of water supply (Table 2). Between November 2004 and October 2011, 19,533 samples of water were analyzed in duplicate from 291 collection sites in 40 cities, totaling 39,066 analyses (Table 3). In some months, the collect of samples was not performed due to difficulties in accessing the location.

Table 3 Classification of fluoride levels in water for locations where the mean of maximum annual temperatures are between 26.3°C and 32.5°C 

Fluoride level (mgF/L) Benefit Risk
0.00 to 0.44 insignificant insignificant
0.45 to 0.54 minimum low
0.55 to 0.84 maximum low
0.85 to 1.14 maximum moderate
1.15 to 1.44 questionable high
1.45 or more harm very high

In 62% (n=24) of the cities, most of the samples were classified into the category that offer the best combination of risk-benefit (0.55 to 0.84 mg F/L). It was observed that 51.57% of the samples from cities with fluoridated water and 45.48% of the samples from cities with non-fluoridated water were included in this category.

Fluoride levels below 0.55 mg F/L were found in 30.13% of the water samples. Of this total, 30.53% were in cities providing fluoridated water. Among the non-fluoridated water samples, 35.42% had fluoride levels above 0.84 mg F/L.

Table 4 shows the variation of fluoride average concentrations (mgF/L) of the water samples, and the standard variation, according to the cities, during 7 years of analysis.

Table 4 Annual mean of fluoride levels (mg F/L), standard deviation (SD), observed in analyzed water samples, according to the cities in this study, from November 2004 to October 2011 (ND= not determined) 

City 2004 2005 2006 2007 2008 2009 2010 2011
Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD
Araçatuba 0.64 0.12 0.53 0.14 0.66 0.1 0.79 0.1 0.76 0.13 0.81 0.38 0.73 0.14 0.82 0.08
Auriflama 0.61 0.13 0.42 0.32 0.58 0.14 0.7 0.03 0.65 0.05 0.67 0.03 0.67 0.02 0.68 0.02
Barbosa 0.39 0.2 0.6 0.3 0.75 0.24 0.78 0.3 0.75 0.17 0.85 0.14 0.71 0.17 0.6 0.11
Bento de Abreu 0.53 0.17 0.6 0.1 0.65 0.13 0.66 0.18 0.57 0.08 0.58 0.12 0.72 0.13 0.77 0.09
Bilac 0.12 0.07 0.66 0.47 0.76 0.43 ND ND ND ND ND
Braúna 0.06 0.01 0.05 0.02 0.07 0.02 0.57 0.26 0.69 0.2 0.74 0.26 0.71 0.36 0.83 0.19
Buritama 0.1 0.01 0.08 0.04 0.54 0.36 0.5 0.44 0.33 0.29 0.53 0.32 0.58 0.26 0.63 0.3
Gabriel Monteiro 0.76 0.02 0.67 0.08 0.69 0.06 0.71 0.05 0.72 0.09 0.71 0.06 0.66 0.24 0.67 0.18
Glicério 0.41 0.12 0.33 0.18 0.42 0.19 0.39 0.19 0.4 0.19 0.43 0.25 0.69 0.17 0.76 0.37
Lourdes 0.54 0.05 0.56 0.08 0.65 0.08 0.67 0.05 0.66 0.06 0.71 0.07 0.62 0.07 0.62 0.11
Luiziânia 0.55 0.12 0.63 0.15 0.59 0.13 0.66 0.02 0.66 0.03 0.66 0.02 0.66 0.02 0.7 0.03
Muruntinga do Sul 0.62 0.18 0.37 0.12 0.49 0.19 0.49 0.2 0.33 0.11 0.38 0.19 0.32 0.21 0.23 0.08
Pereira Barreto 0.88 0.1 0.79 0.07 0.88 0.05 0.91 0.07 0.9 0.04 0.88 0.04 0.88 0.02 0.86 0.06
Rubiácea 0.78 0.05 0.64 0.21 0.7 0.14 0.63 0.1 0.6 0.1 0.58 0.12 0.74 0.21 0.73 0.12
Santópolis do Aguapeí 0.69 0.02 0.66 0.13 0.69 0.08 0.68 0.06 0.67 0.07 0.7 0.05 0.66 0.05 0.68 0.13
Suzanápolis 1.05 0.02 0.91 0.13 0.61 0.3 0.82 0.36 0.81 0.35 2.93 6.06 0.93 2.23 0.59 0.24
Turiúba 0.64 0.04 0.59 0.07 0.58 0.05 0.66 0.08 0.64 0.05 0.65 0.06 0.68 0.07 0.7 0.17
Alto Alegre 0.54 0.14 0.67 0.08 0.66 0.06 0.61 0.07 0.64 0.06 0.66 0.07 0.6 0.1 0.63 0.09
Andradina 0.74 0.16 0.77 0.22 0.65 0.47 0.59 0.41 0.55 0.38 0.51 0.36 0.63 0.49 0.75 0.4
Avanhandava 0.89 0.17 0.66 0.22 0.48 0.01 5.66 3.24 0.76 0.09 0.65 0.11 0.49 0.3 0.64 0.22
Birigui 0.21 0.2 0.62 0.29 0.69 0.31 0.64 0.34 0.76 0.33 0.81 0.28 0.83 0.28 0.9 0.37
Brejo Alegre 0.54 0.06 0.59 0.09 0.65 0.14 0.71 0.05 0.69 0.13 0.73 0.33 0.63 0.05 0.79 0.04
Castilho 0.47 0.17 0.62 0.2 0.73 0.28 0.7 0.4 0.78 0.17 0.74 0.25 0.64 0.2 0.72 0.53
Clementina 0.1 0.02 0.07 0.03 0.1 0.11 0.58 1.2 0.53 0.58 0.41 0.67 0.94 3.25 0.74 0.16
Coroados 0.76 0.01 0.71 0.06 0.7 0.1 0.67 0.08 0.73 0.07 0.63 0.05 0.59 0.04 0.64 0.06
Guaraçaí 0.57 0.13 0.47 0.19 0.48 0.49 0.5 0.39 0.49 0.26 0.69 0.11 0.78 0.13 0.85 0.17
Guararapes 0.6 0.01 0.61 0.06 0.65 0.13 0.72 0.15 0.79 0.1 0.73 0.17 0.68 0.09 0.73 0.11
Guzolândia 0.71 0.01 0.66 0.06 0.75 0.07 0.73 0.08 0.63 0.14 0.66 0.07 0.62 0.09 0.75 0.08
Ilha Solteira 0.63 0.08 0.66 0.07 0.61 0.18 1.1 1.72 0.55 0.18 0.63 0.07 0.59 0.13 0.66 0.04
Itapura 0.08 0.01 0.39 0.24 0.18 0.25 0.67 0.34 0.45 0.27 0.31 0.21 0.62 0.46 0.58 0.37
Lavínia 0.12 0.1 0.3 0.26 0.47 0.32 0.67 0.31 0.7 0.33 0.69 0.3 0.68 0.33 0.64 0.34
Mirandópolis 0.48 0.12 0.69 0.17 0.73 0.26 0.7 0.31 0.79 0.45 0.62 0.23 0.57 0.15 0.49 0.22
Nova Castilho 0.53 0.1 0.52 0.09 0.78 0.32 0.63 0.54 0.75 0.5 0.94 0.36 0.83 0.28 0.87 0.48
Nova Independência 0.71 0.1 0.69 0.41 0.58 0.44 0.34 0.21 0.59 0.17 0.76 0.1 0.67 0.24 0.69 0.18
Nova Luzitânia 0.59 0.06 0.57 0.11 0.61 0.1 0.55 0.13 0.58 0.06 0.76 0.01 ND 0.67 0.08
Penápolis 0.83 0.07 0.66 0.06 0.73 0.11 0.76 0.1 0.64 0.06 0.61 0.06 0.6 0.07 0.62 0.07
Piacatú 0.7 0.06 0.61 0.1 0.67 0.09 0.8 0.45 0.64 0.1 0.75 0.07 0.74 0.05 0.72 0.17
Sant. Ant. do Aracanguá 0.07 0.01 0.4 0.36 0.72 0.15 0.51 0.24 0.52 0.18 0.37 0.29 0.79 0.38 0.65 0.14
Sud Mennucci 0.51 0.06 0.57 0.07 0.63 0.07 0.57 0.06 0.57 0.04 0.63 0.05 0.58 0.03 0.67 0.08
Valparaíso 0.8 0.08 0.72 0.2 0.79 0.25 0.79 0.21 0.73 0.13 0.73 0.13 0.8 0.13 0.81 0.06

DISCUSSION

Discussions of optimal fluoride levels in public water supplies are ongoing among researchers worldwide. The United States Department of Health and Human Services (HHS) has proposed a new recommendation for fluoride content in drinking water of 0.7 mg F/L, replacing the current guideline that specifies a level between 0.7 and 1.2 mg F/L9. In Brazil, legislation establishing the procedures and responsibilities relating to the control and surveillance of water quality for human consumption2 has recently undergone public review6.

This study classified the water samples in accordance with recommendations published by the Collaboration Center for Oral Health Surveillance of the Health Ministry (CECOL/USP, 2011)6, taking into consideration both the benefits of fluoride in preventing dental caries and the risk of dental fluorosis. The document suggests three classifications based on the average maximum annual temperature of the locality, since the optimal fluoride concentration in drinking water is dependent on the level of water consumption. Higher levels are preferred in lower-temperature regions where water consumption is lower, whereas in higher temperature regions, the recommended fluoride levels are lower10. According to this classification, 51.36% of the 19,533 samples had fluoride levels within the optimum risk-benefit range.

Fluoride levels outside of the recommended parameters were observed during a previous research in the same region20,21. During a six-month analysis in 2005, Saliba, et al.21 (2006) reported that approximately 62% of the water samples were outside of the recommended fluoride concentration range. Another 36-month study found that approximately 43% of the samples from cities with only a single source of water were outside of the recommended parameters24. Deficiencies in fluoridation were also described in studies performed in other regions3,15.

Some cities undertaking water fluoridation had a majority of water samples outside the optimum range of fluoride levels. Most of these cities employed more than one water supply, promoting interconnection and mixing of water from different sources in the distribution system and making it difficult to maintain fluoride levels within the recommended range12. However, none of the deviations persisted for extended periods at any sampling site during the 7-year study, minimizing undesirable effects4.

Among the three cities that did not add fluoride, only one had a majority of samples within the recommended range. In that city, the source of supply already contained the recommended level of fluoride. In one of the remaining cities, 53.78% of the water samples contained less than 0.55 mg F/L, while in the third city approximately 75% of the samples contained fluoride levels above 0.84 mg F/L, increasing the risk of dental fluorosis.

Only 8% of the water samples from cities adding fluoride exhibited fluoride levels above 0.84 mg F/L, and fluoride levels were above 1.44 mg F/L in only 1.46% of the samples.

In two of the three cities performing water fluoridation in which most of the samples contained elevated fluoride levels, the water sources were deep wells that are known to naturally contain higher fluoride levels. This highlights the need to examine water distribution networks and to develop dilution and mixing procedures to optimize the use of the natural fluoride present in deep-water wells and achieve the desired fluoride concentrations7.

There was some variability among the samples from different sites in the same city, demonstrating the importance of selecting collection sites according to the number and location of the water supply. In addition to sample collection bottles, a document was sent each month to the cities requesting notification of any changes to the water distribution network caused by the opening or closing of any water supply. In order to assist the cities in achieving optimum fluoride levels, the results of the analyses were sent monthly to the secretaries of health, oral health coordinators, and those responsible for the water supply in each municipality.

The effect of fluctuations in fluoride concentration on the risk/benefit analysis is dependent on the duration of the fluctuations. It is essential that the addition of fluoride be maintained without large fluctuations, since reduced levels provide minimal health benefits while wasting public resources and excessive levels promote undesirable effects4.

The findings of this study demonstrate the importance of longitudinal studies to assist in maintaining optimum fluoride levels in public water supplies.

CONCLUSION

Most samples from cities providing fluoridated water were within the concentration range providing the best combination of risks and benefits, reaffirming the safety of the method. High fluoride levels were observed in samples from deep wells. We suggest further studies to optimize the use of natural fluoride to reduce fluoridation costs and the risk of dental fluorosis.

ACKNOWLEDGEMENT

The authors would like to thank the Coordination of the Improvement of Higher Education Personnel (CAPES) and the National Council for Scientific and Technological Development (CNPq) for providing financial support for this research.

REFERENCES

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Received: April 3, 2012; Revised: October 5, 2012; Accepted: November 30, 2012

Corresponding address: Suzely Adas Saliba Moimaz - Faculdade de Odontologia de Araçatuba - UNESP - Programa de Pós-graduação em Odontologia Preventiva e Social - NEPESCO - Núcleo de Pesquisa em Saúde Coletiva - Departamento de Odontologia Infantil e Social - Rua José Bonifácio, 1193 - P.O. Box - 341 - 16015-050 - Araçatuba - SP - Brasil - Phone: ++55 018 36363250 - e-mail: sasaliba@foa.unesp.br

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